WY2015 C-BT East Slope North End Water Quality Report

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WY2000 – WY2015 C-BT East Slope North End Water Quality Report

March 17, 2017

Prepared by: Judith A. Billica, P.E., Ph.D.

Northern Colorado Water Conservancy District Berthoud, Colorado

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TABLE OF CONTENTS

TABLE OF CONTENTS ...... III

LIST OF TABLES ...... VII

LIST OF FIGURES ...... IX

ACRONYMS AND ABBREVIATIONS ...... XV

EXECUTIVE SUMMARY ...... XVII

1. INTRODUCTION ...... 1

1.1 COLORADO-BIG THOMPSON PROJECT & WINDY GAP PROJECT OVERVIEW ...... 1 1.2 BASELINE WATER QUALITY MONITORING PROGRAM OVERVIEW ...... 2 1.2.1 Purpose of Baseline Monitoring Program ...... 3 1.2.2 Scope of Baseline Monitoring Program ...... 4 1.2.3 Quality Assurance/Quality Control (QA/QC) ...... 6 1.3 BASELINE MONITORING PROGRAM: EAST SLOPE – NORTH END SITES ...... 6 1.3.1 Sampling Sites ...... 6 1.3.2 Parameters & Frequency ...... 14 1.3.3 Sample Collection and Laboratory Analysis ...... 16 1.4 COLLABORATIVE ROUTINE MONITORING ...... 20 1.4.1 Monitoring of the Big Thompson River: Big Thompson Watershed Forum ...... 20 1.4.2 City of Fort Collins Cooperative Monitoring of Horsetooth Reservoir ...... 20 1.5 REPORT OBJECTIVES AND SCOPE ...... 21 2. METHODS FOR DATA ANALYSIS ...... 23

2.1 HANDLING OF NON-DETECT DATA ...... 23 2.2 DATA REVIEW AND ANALYSIS TOOLS ...... 23 2.2.1 Graphical Analyses ...... 24 2.2.2 Statistical Analysis ...... 28 2.3 DATA LIMITATIONS AND EXCLUDED DATA ...... 31 3. WATERSHED DESCRIPTION, SIGNIFICANT EVENTS, WATER QUALITY CONCERNS & SPECIAL STUDIES ...... 33

3.1 OVERVIEW OF WATERSHEDS ...... 33 3.2 DESCRIPTION OF HORSETOOTH RESERVOIR ...... 36 3.3 SIGNIFICANT EVENTS ...... 38 3.3.1 Pine Beetle Epidemic ...... 38 3.3.2 Wildfires ...... 40 3.3.3 2013 Flood ...... 42 3.4 WATER QUALITY CONCERNS ...... 44 3.4.1 303(d) List of Impaired Waters ...... 44 3.4.2 Copper ...... 45 3.4.3 Drinking Water Treatment Concerns ...... 45

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3.4.4 Other Horsetooth Reservoir Issues ...... 46 3.5 OTHER RELATED WATER QUALITY STUDIES & REPORTS ...... 47 3.5.1 Emerging Contaminants Cooperative Monitoring Program ...... 47 3.5.2 Big Thompson Watershed Forum 2015 State of the Watershed Report ...... 48 3.5.3 City of Fort Collins 2013 Horsetooth Res Water Quality Monitoring Program Reports .... 49 3.5.4 2013 CE-QUAL-W2 Horsetooth Reservoir Modeling Report ...... 49 4. HYDROLOGY & OPERATIONS ...... 51

4.1 OVERVIEW OF WEST SLOPE COLLECTION & EAST SLOPE DISTRIBUTION SYSTEMS ...... 51 4.2 WY2000-WY2015 EAST SLOPE – NORTH END FLOWING SITES HYDROLOGY ...... 53 4.3 HORSETOOTH RESERVOIR HYDROLOGY & OPERATIONS ...... 55 5. FIELD PARAMETERS ...... 59

5.1 TEMPERATURE ...... 59 5.1.1 Flowing Sites ...... 60 5.1.2 Horsetooth Reservoir Profiles ...... 61 5.2 DISSOLVED OXYGEN (D.O.) ...... 66 5.2.1 Flowing Sites ...... 66 5.2.2 Horsetooth Reservoir Profiles ...... 67 5.3 SPECIFIC CONDUCTANCE ...... 70 5.3.1 Flowing Sites ...... 70 5.3.2 Horsetooth Reservoir Profiles ...... 71 5.4 PH ...... 72 5.4.1 Flowing Sites ...... 72 5.4.2 Horsetooth Reservoir Profiles ...... 73 5.5 HORSETOOTH RESERVOIR SECCHI DISK DATA...... 74 6. GENERAL CHEMISTRY ...... 77

6.1 MAJOR IONS AND ALKALINITY...... 77 6.2 FLOWING SITES TOTAL ORGANIC CARBON (TOC) ...... 81 6.3 HORSETOOTH RESERVOIR TOC, DOC, UVA & SUVA ...... 84 6.4 TOTAL SUSPENDED SOLIDS (TSS) ...... 88 6.5 TIME TREND ANALYSIS RESULTS FOR TOC & MAJOR IONS ...... 91 7. NUTRIENTS ...... 93

7.1 PHOSPHORUS ...... 94 7.2 NITROGEN ...... 98 7.3 HORSETOOTH RES NITROGEN TO PHOSPHORUS RATIOS ...... 102 7.4 TIME TREND ANALYSIS RESULTS FOR NUTRIENTS ...... 104 8. METALS ...... 107

8.1 ARSENIC (DISSOLVED & TOTAL RECOVERABLE) ...... 109 8.2 BORON (DISSOLVED) ...... 111 8.3 CADMIUM (DISSOLVED) ...... 111 8.4 CHROMIUM (DISSOLVED & TOTAL RECOVERABLE) ...... 112 8.5 COPPER (DISSOLVED) ...... 113

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8.6 IRON (DISSOLVED AND TOTAL RECOVERABLE) ...... 115 8.7 LEAD (DISSOLVED) ...... 117 8.8 MANGANESE (DISSOLVED) ...... 118 8.9 NICKEL (DISSOLVED) ...... 119 8.10 SELENIUM (DISSOLVED) ...... 120 8.11 SILVER (DISSOLVED) ...... 120 8.12 URANIUM (DISSOLVED) ...... 121 8.13 ZINC (DISSOLVED) ...... 121 8.14 TIME TREND ANALYSIS RESULTS FOR METALS ...... 122 9. HORSETOOTH RES PHYTOPLANKTON, CHLOROPHYLL & ZOOPLANKTON ...... 125

9.1 PHYTOPLANKTON ...... 125 9.2 CHLOROPHYLL-A ...... 128 9.2.1 Chlorophyll-a Data Review ...... 128 9.2.2 Comparison of Chlorophyll-a and Phytoplankton Biovolume ...... 129 9.2.3 Direct Use Water Supply Reservoirs and Chlorophyll-a ...... 130 9.3 TROPHIC STATE ...... 131 9.4 CITY OF FORT COLLINS GEOSMIN DATA ...... 133 9.5 ZOOPLANKTON ...... 139 9.5.1 Overview of Zooplankton Groups ...... 139 9.5.2 Summary of Horsetooth Reservoir Zooplankton Data ...... 141 9.6 FOOD WEB INTERACTIONS ...... 142 10. SUMMARY OF FINDINGS & RECOMMENDATIONS ...... 145

10.1 SUMMARY OF KEY FINDINGS ...... 145 10.1.1 Spatial & Seasonal Patterns ...... 145 10.1.2 Trend Analysis ...... 147 10.1.3 Horsetooth Reservoir Phytoplankton, Chlorophyll-a & Geosmin ...... 149 10.2 RECOMMENDATIONS FOR BASELINE MONITORING AND FUTURE SPECIAL STUDIES ...... 150 11. REFERENCES ...... 151

APPENDICES ...... 157

A - Summary Statistics B - Horsetooth Reservoir Profiles C - Time Series Plots D - Monthly Box Plots E - Annual Box Plots F - Box Plots of Spatial Variability G - Horsetooth Reservoir Phytoplankton Density & Biovolume Plots H - Horsetooth Reservoir Zooplankton Density Plots I – Seasonal Kendall Time Trend Analysis Results

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LIST OF TABLES

TABLE ES.1- SUMMARY OF SEASONAL KENDALL TIME TREND TEST RESULTS ...... XXIX

TABLE 1.1 - EAST SLOPE – NORTH END SAMPLING STATIONS...... 7 TABLE 1.2 - WATER QUALITY PARAMETERS AND PERIOD OF RECORD FOR EAST SLOPE-NORTH END SITES ...... 15 TABLE 1.3 - SAMPLING FREQUENCY ...... 16 TABLE 1.4 - LABORATORIES AND ANALYTICAL METHODS FOR WY2000 – WY2015 EAST SLOPE – NORTH END DATA ...... 18 TABLE 1.5 - LABORATORIES AND MDLS (METHOD DETECTION LIMITS) FOR WY2000 – WY2015 EAST SLOPE – NORTH END DATA ...... 19

TABLE 2.1 - DATA EXCLUDED FROM BOXPLOTS & SEASONAL KENDALL TREND ANALYSIS...... 27 TABLE 2.2 - SEASON DESIGNATIONS FOR SEASONAL KENDALL TREND ANALYSIS...... 29

TABLE 3.1 - LAND USE/LAND COVER TYPES FOR THE MAJOR WATERSHEDS ASSOCIATED WITH HORSETOOTH RESERVOIR...... 36 TABLE 3. 2 - HORSETOOTH RESERVOIR CHARACTERISTICS...... 37 TABLE 3.3 - SUMMARY OF 303(D) AND M&E LISTINGS ...... 44

TABLE 4.1 - HORSETOOTH RES ANNUAL INFLOWS, OUTFLOWS, AVG VOLUME AND HYDRAULIC RESIDENCE TIME (WY2006-WY2015)...... 57

TABLE 5.1- TEMPERATURE STANDARDS...... 59

TABLE 6.1 - SUMMARY OF SEASONAL KENDALL TREND TEST RESULTS FOR TOC AND MAJOR IONS ...... 92

TABLE 7.1 - FORMS OF NITROGEN AND PHOSPHORUS MEASURED FOR THE BASELINE MONITORING PROGRAM...... 93 TABLE 7.2 – TP:TN RATIOS (WEIGHT BASIS) REPORTED IN THE LITERATURE FOR PREDICTING NUTRIENT LIMITATIONS...... 102 TABLE 7.3 - SUMMARY OF SEASONAL KENDALL TREND TEST RESULTS FOR NUTRIENTS ...... 105

TABLE 8.1 - WATER QUALITY STANDARDS FOR BASELINE MONITORING PROGRAM METALS...... 108 TABLE 8.2 - SUMMARY OF SEASONAL KENDALL TREND TEST RESULTS FOR METALS ...... 122

TABLE 9.1 - TROPHIC CLASSIFICATION OF LAKES & RESERVOIRS BASED ON CHL-A, SECCHI DEPTH & TOTAL P (FROM CARLSON AND SIMPSON, 1996)...... 132

TABLE 10.1 - SUMMARY OF SEASONAL KENDALL TREND TEST RESULTS ...... 148

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LIST OF FIGURES FIGURE ES.1 - WEST SLOPE COLLECTION SYSTEM...... XVII FIGURE ES.2 - EAST SLOPE DISTRIBUTION SYSTEM...... XVIII FIGURE ES.3 - MAP OF BASELINE MONITORING PROGRAM EAST SLOPE – NORTH END SAMPLING SITES...... XIX FIGURE ES.4 - AERIAL PHOTO OF HORSETOOTH RESERVOIR, LOOKING NORTH...... XX FIGURE ES.5 - CONCEPTUAL CROSS-SECTION OF HORSETOOTH RESERVOIR SHOWING AUG 2014 TEMPERATURE PROFILES...... XXI FIGURE ES.6 - CONCEPTUAL DIAGRAM OF HANSEN FEEDER CANAL INTERFLOW IN HORSETOOTH RESERVOIR BASED ON SPECIFIC CONDUCTANCE PROFILES...... XXII FIGURE ES.7 - TYPICAL SUMMER DISSOLVED OXYGEN PROFILES IN HORSETOOTH RES...... XXII FIGURE ES.8 - PHOTO-MICROGRAPHS OF SOME COMMON CYANOBACTERIA FOUND IN HORSETOOTH RESERVOIR (TAKEN BY GRANT JONES, CITY OF FORT COLLINS)...... XXIII FIGURE ES.9 - WY2005-WY2015 MARCH - NOV CHLOROPHYLL-A DATA & AVERAGES FOR HORSETOOTH RES AT SOLDIER CANYON (HT-SOL)...... XXIV FIGURE ES.10 - CALCIUM SPATIAL BOXPLOT ...... XXV FIGURE ES.11 - TOTAL ORGANIC CARBON (TOC) SPATIAL BOXPLOT ...... XXV FIGURE ES.12 - ORTHOPHOSPHATE SPATIAL BOXPLOT ...... XXVI FIGURE ES.13 - TOTAL PHOSPHOROUS SPATIAL BOXPLOT ...... XXVI FIGURE ES.14 - NITRATE + NITRITE SPATIAL BOXPLOT ...... XXVII FIGURE ES.15 - COPPER SPATIAL BOXPLOT S: WY2002-WY2015 AND WY2012-WY2015 ...... XXVIII FIGURE ES.16 - MANGANESE (DISSOLVED) SPATIAL BOXPLOT ...... XXVIII FIGURE ES.17 - ANNUAL BOXPLOT FOR COPPER CONCENTRATIONS AT HFC-FRD...... XXX FIGURE ES.18 - ANNUAL BOXPLOT FOR COPPER CONCENTRATIONS AT THE ADAMS TUNNEL...... XXX

FIGURE 1.1- MAP OF C-BT & WINDY GAP PROJECTS ...... 2 FIGURE 1.2 - MAP OF EAST SLOPE WATER TREATMENT PLANTS WITH WATER SUPPLIES FROM C-BT & WINDY GAP PROJECTS ...... 3 FIGURE 1.3 - MAP OF WEST SLOPE BASELINE MONITORING LOCATIONS ...... 4 FIGURE 1.4 - MAP OF EAST SLOPE MONITORING SITES IN BASELINE PROGRAM ...... 5 FIGURE 1.5 - MAP OF EAST SLOPE – NORTH END SAMPLING SITES...... 8 FIGURE 1.6 - CONCEPTUAL ELEVATION PROFILE OF EAST SLOPE – NORTH END SAMPLING SITES...... 8 FIGURE 1.7 - LOOKING NORTH AT LAKE ESTES...... 9 FIGURE 1.8 - HANSEN FEEDER CANAL FLOWING NORTH OUT OF FLATIRON RESERVOIR...... 9 FIGURE 1.9 - HANSEN FEEDER CANAL UPSTREAM OF HORSETOOTH RESERVOIR, NEAR HFC-HT...... 10 FIGURE 1.10 - HANSEN SUPPLY CANAL FLOWING NORTH OUT OF HORSETOOTH RESERVOIR...... 10 FIGURE 1.11 - FLOW FROM THE HANSEN SUPPLY CANAL ENTERING THE POUDRE RIVER (MAY 2008) AT HSC-PR SAMPLING SITE...... 10 FIGURE 1.12 - LOOKING SOUTH AT HORSETOOTH RESERVOIR SAMPLING STATIONS...... 11 FIGURE 1.13 - SAMPLING STATIONS AT THE BIG THOMPSON RIVER ...... 12 FIGURE 1.14 - LOOKING WEST AT HFC-BTU SAMPLING SITE...... 12 FIGURE 1.15 - HANSEN SUPPLY CANAL AND POUDRE RIVER SAMPLING SITES...... 13 FIGURE 1.16 - LOOKING SOUTH AT HANSEN SUPPLY CANAL FLOW ENTERING THE POUDRE RIVER...... 13

FIGURE 2.1 - STACKED BAR GRAPH...... 24 FIGURE 2.2 - CONSTRUCTION OF BOXPLOTS ...... 25 FIGURE 2.3 - MONTHLY BOXPLOTS WITH DATA POINTS (OPEN CIRCLES)...... 26 FIGURE 2.4 - SPATIAL BOXPLOT...... 26

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FIGURE 3.1 - WATERSHEDS OF THE C-BT AND WINDY GAP PROJECTS...... 33 FIGURE 3.2 - NORTH END OF THE EAST SLOPE C-BT CONVEYANCE SYSTEM AND WATER TREATMENT PLANTS RECEIVING C-BT SOURCE WATER...... 34 FIGURE 3.3 - LAND USE/LAND COVER MAP FOR THE COMBINED WATERSHEDS OF THE C-BT AND WINDY GAP PROJECTS UPSTREAM OF HORSETOOTH RESERVOIR (2011 NATIONAL LAND COVER DATABASE FROM THE USDA NRCS)...... 35 FIGURE 3.4 - C-BT WATERSHED AREAS IMPACTED TO VARYING DEGREES BY MOUNTAIN PINE BEETLE & SPRUCE BEETLE THROUGH MAY 2015...... 39 FIGURE 3.5 - RECENT WILDFIRES IN AND NEAR C-BT PROJECT WATERSHEDS...... 41 FIGURE 3.6 - 2013 FLOOD DAMAGE TO HWY 34 ALONG THE BIG THOMPSON RIVER AT THE CANYON MOUTH...... 42 FIGURE 3. 7 - PRE- AND POST-FLOOD VIEWS ALONG THE BIG THOMPSON RIVER AT HFC-BTU AND HFC-BTD...... 43

FIGURE 4.1 - WEST SLOPE COLLECTION SYSTEM...... 51 FIGURE 4.2 - WEST SLOPE THREE LAKES ...... 51 FIGURE 4.3 - EAST PORTAL ADAMS TUNNEL & EAST PORTAL RESERVOIR...... 52 FIGURE 4.4 - EAST SLOPE DISTRIBUTION SYSTEM...... 52 FIGURE 4.5 - BIG THOMPSON RIVER JUST UPSTREAM OF LAKE ESTES (BTWF SITE M20), JULY 2008...... 53 FIGURE 4.6 - MAP OF AREA FROM EAST PORTAL TO OLYMPUS TUNNEL...... 53 FIGURE 4.7 - WY2005 – WY2015 DAILY FLOWS AT EAST PORTAL ADAMS TUNNEL & BIG THOMPSON RIVER ABOVE LAKE ESTES...... 54 FIGURE 4.8 - WY2005 – WY2015 PERCENT CONTRIBUTION OF EAST PORTAL ADAMS TUNNEL FLOWS & BIG THOMPSON RIVER FLOWS TO LAKE ESTES...... 54 FIGURE 4.9 - DILLE TUNNEL DIVERSIONS ENTERING THE HANSEN FEEDER CANAL...... 55 FIGURE 4.10 - WY2001 - WY2015 HORSETOOTH RESERVOIR VOLUMES AND WATER SURFACE ELEVATIONS...... 56 FIGURE 4.11 - WY2006 - WY2015 ANNUAL HORSETOOTH RESERVOIR INFLOWS & ANNUAL TOTAL DIVERSIONS AT DILLE TUNNEL...... 56 FIGURE 4.12 - WY2006 – WY2015 BAR GRAPH OF TOTAL ANNUAL INFLOWS AND OUTFLOWS, AVERAGE ANNUAL RESERVOIR VOLUME, AND ANNUAL HYDRAULIC RESIDENCE TIME FOR HORSETOOTH RESERVOIR...... 57

FIGURE 5.1 - SPATIAL BOXPLOT OF GRAB SAMPLE WATER TEMPERATURE DATA...... 60 FIGURE 5.2 - HANSEN SUPPLY CANAL & HORSETOOTH RES AT SOLDIER CANYON MONTHLY BOXPLOT OF GRAB SAMPLE WATER TEMPERATURES...... 61 FIGURE 5.3 - HANSEN SUPPLY CANAL & ASSOCIATED POUDRE RIVER SITES MONTHLY BOXPLOT OF GRAB SAMPLE WATER TEMPERATURES...... 61 FIGURE 5.4 - CONCEPTUAL CROSS-SECTION OF HORSETOOTH RESERVOIR SHOWING 8/11/14 TEMPERATURE PROFILES...... 62 FIGURE 5.5 - HORSETOOTH RESERVOIR TOP (1 METER) TEMPERATURES MINUS BOTTOM TEMPERATURES, PLOTTED TO INDICATE PERIODS OF MIXING (WHEN DIFFERENCE BETWEEN TOP AND BOTTOM TEMPERATURES ARE NEAR ZERO) AND THERMAL STRATIFICATION...... 63 FIGURE 5.6 - HORSETOOTH RESERVOIR TOP (1 METER) AND BOTTOM TEMPERATURES PLOTTED TO INDICATE PERIODS OF THERMAL STRATIFICATION (WHEN TOP & BOTTOM TEMPERATURES ARE SIGNIFICANTLY DIFFERENT) AND FALL TURNOVER (WHEN TOP & BOTTOM TEMPERATURES BECOME EQUAL)...... 63 FIGURE 5. 7 - CONCEPTUAL DIAGRAM OF HANSEN FEEDER CANAL INFLOW MOVING IN HORSETOOTH RESERVOIR AS AN INTERFLOW...... 65 FIGURE 5.8 - HANSEN FEEDER CANAL & HORSETOOTH RES AT SPRING CANYON MONTHLY BOXPLOT OF WATER TEMPERATURES...... 65

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FIGURE 5.9 - SPATIAL BOXPLOT OF DISSOLVED OXYGEN CONCENTRATIONS...... 66 FIGURE 5.10 - MONTHLY BOXPLOT OF D.O. AT OLYMPUS TUNNEL, BIG THOMPSON RIVER BELOW HFC, AND HFC AT HORSETOOTH...... 67 FIGURE 5.11 - DISSOLVED OXYGEN CONCENTRATIONS AT THE BOTTOM OF HORSETOOTH RESERVOIR...... 68 FIGURE 5.12 - HORSETOOTH RESERVOIR MONTHLY BOXPLOT OF D.O. CONCENTRATIONS AT SPRING CANYON TOP AND BOTTOM AND SOLDIER CANYON BOTTOM...... 68 FIGURE 5.13 - TYPICAL SUMMER D.O. PROFILES IN HORSETOOTH RESERVOIR...... 69 FIGURE 5.14 - HORSETOOTH RESERVOIR JUNE - SEPT MONTHLY BOXPLOT OF MINIMUM D.O. CONCENTRATIONS MEASURED IN THE METALIMNION...... 69 FIGURE 5.15 - SPECIFIC CONDUCTANCE SPATIAL BOXPLOT FOR FLOWING SITES...... 70 FIGURE 5.16 - SPECIFIC CONDUCTANCE MONTHLY BOXPLOTS FOR AT-EP, HFC-HT AND HSC-PR...... 71 FIGURE 5.17 - CONCEPTUAL DIAGRAM OF INTERFLOW IN HORSETOOTH RESERVOIR BASED ON SPECIFIC CONDUCTANCE PROFILES...... 72 FIGURE 5.18 - PH SPATIAL BOXPLOT FOR FLOWING SITES...... 73 FIGURE 5.19 - PH MONTHLY BOXPLOTS FOR AT-EP, HFC-HT AND HSC-PR...... 73 FIGURE 5.20 - COMPARISON OF D.O. AND PH PROFILES AT HORSETOOTH RESERVOIR (HT-SOL) ON 8/11/14...... 74 FIGURE 5.21 - SECCHI DISK ...... 74 FIGURE 5.22 - HORSETOOTH RESERVOIR SECCH DEPTH SPATIAL BOXPLOT...... 75 FIGURE 5.23 - HORSETOOTH RESERVOIR SECCHI DEPTH MONTHLY BOXPLOT...... 76

FIGURE 6.1 - CALCIUM SPATIAL BOXPLOT ...... 78 FIGURE 6.2 - ALKALINITY SPATIAL BOXPLOT ...... 78 FIGURE 6.3 - CALCIUM MONTHLY BOXPLOT FOR AT-EP, HFC-HT AND HSC-PR...... 79 FIGURE 6.4 - ALKALINITY MONTHLY BOXPLOT FOR AT-EP, HFC-HT AND HSC-PR...... 79 FIGURE 6.5 - MAJOR ION CONCENTRATIONS FOR DEC 2011 – JAN 2012 (WINTER) SAMPLES...... 80 FIGURE 6.6 - MAJOR ION CONCENTRATIONS FOR JUNE 2012 SAMPLES...... 80 FIGURE 6.7 - ION BALANCE DIAGRAMS FOR JUNE 2012 SAMPLES...... 81 FIGURE 6.8 - TOTAL ORGANIC CARBON (TOC) SPATIAL BOXPLOT...... 82 FIGURE 6.9 - MONTHLY BOXPLOT OF TOC CONCENTRATIONS SHOWING SEASONAL INFLUENCE OF TOC AT ADAMS TUNNEL & BIG THOMPSON RIVER (ABOVE LAKE ESTES) ON TOC AT HANSEN FEEDER CANAL AT HORSETOOTH...... 83 FIGURE 6.10 - MONTHLY BOXPLOT COMPARISON OF TOC CONCENTRATIONS IN HORSETOOTH RESERVOIR INFLOWS IN HANSEN FEEDER CANAL AND OUTFLOWS IN HANSEN SUPPLY CANAL...... 83 FIGURE 6.11 - TOC MONTHLY BOXPLOT FOR HORSETOOTH RESERVOIR...... 84 FIGURE 6.12 - TOC CONCENTRATIONS AT HORSETOOTH RESERVOIR, SOLDIER CANYON DAM SITE...... 85 FIGURE 6.13 - TIME SERIES PLOT OF DOC TO TOC RATIOS...... 85 FIGURE 6.14 - TIME SERIES PLOT OF UV254 DATA FOR HORSETOOTH RESERVOIR SITES & GRAND LAKE AT WEST PORTAL SITE...... 87 FIGURE 6.15 - TIME SERIES PLOT OF DOC DATA FOR HORSETOOTH RESERVOIR SITES & GRAND LAKE AT WEST PORTAL SITE...... 87 FIGURE 6.16 - TIME SERIES PLOT OF SUVA FOR HORSETOOTH RESERVOIR SITES & GRAND LAKE AT WEST PORTAL SITE...... 87 FIGURE 6.17 - MONTHLY BOXPLOT OF CALCULATED SUVA DATA FOR HORSETOOTH RESERVOIR AT SOLDIER CANYON SITES & GRAND LAKE AT WEST PORTAL SITE...... 88 FIGURE 6.18 (A) - TOTAL SUSPENDED SOLIDS SPATIAL BOXPLOT...... 89 FIGURE 6.18 (B) - TOTAL SUSPENDED SOLIDS SPATIAL BOXPLOT, RE-SCALED TO SHOW LOWER CONCENTRATIONS...... 89 FIGURE 6.19 - TSS TIME SERIES PLOT FOR BIG THOMPSON RIVER SITES ASSOCIATED WITH THE HFC...... 90 FIGURE 6.20 - TSS TIME SERIES PLOT FOR POUDRE RIVER SITES ASSOCIATED WITH THE HSC...... 91

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FIGURE 7.1 - SPATIAL BOXPLOT OF TOTAL PHOSPHOROUS...... 95 FIGURE 7.2 - SPATIAL BOXPLOT OF ORTHO-P...... 95 FIGURE 7.3 - MONTHLY BOXPLOTS OF ORTHO-P CONCENTRATIONS FOR HORSETOOTH RESERVOIR: SPRING, DIXON & SOLDIER CANYON SITES...... 97 FIGURE 7.4 - SIMPLIFIED NITROGEN CYCLE IN AQUATIC SYSTEMS ...... 98 FIGURE 7.5 - SPATIAL BOXPLOT OF NITRATE PLUS NITRITE...... 99 FIGURE 7.6 - MONTHLY BOXPLOTS OF NITRATE + NITRITE CONCENTRATIONS FOR HORSETOOTH RES (HT-SPR AND HT-SOL)...... 99 FIGURE 7.7 - MONTHLY BOXPLOT OF NITRATE+NITRITE CONCENTRATIONS AT HFC-HT, HT-SOL-1, HT-SOL-B, AND HSC-PR...... 100 FIGURE 7.8 - SPATIAL BOXPLOT OF AMMONIA...... 100 FIGURE 7.9 - SPATIAL BOXPLOT OF TOTAL KJELDAHL NITROGEN (TKN)...... 101 FIGURE 7.10 - SPATIAL BOXPLOT OF TOTAL NITROGEN...... 102 FIGURE 7.11 - TIME SERIES PLOT OF HORSETOOTH RESERVOIR CALCULATED TN:TP RATIOS ...... 103 FIGURE 7.12 - TIME SERIES PLOT OF HORSETOOTH RESERVOIR [TIN]:[ORTHO-P] RATIOS WITH NON-DETECTED ORTHO-P EVALUATED AT 1.0 X DL (ORTHO-P DL = 0.001 MG/L)...... 104

FIGURE 8.1 - HARDNESS SPATIAL BOXPLOT ...... 109 FIGURE 8.2 - DISSOLVED ARSENIC SPATIAL BOXPLOT...... 110 FIGURE 8.3 - TOTAL ARSENIC SPATIAL BOXPLOT ...... 110 FIGURE 8.4 - DISSOLVED BORON SPATIAL BOXPLOT ...... 111 FIGURE 8.5 - DISSOLVED CADMIUM SPATIAL BOXPLOT ...... 111 FIGURE 8.6 - DISSOLVED CHROMIUM SPATIAL BOXPLOT ...... 112 FIGURE 8.7 - TOTAL CHROMIUM SPATIAL BOXPLOT ...... 112 FIGURE 8.8 - DISSOLVED COPPER SPATIAL BOXPLOT FOR WY2002 – WY2015 PERIOD...... 113 FIGURE 8.9 - ANNUAL BOXPLOTS FOR COPPER: ADAMS TUNNEL, HANSEN FEEDER CANAL, HANSEN SUPPLY CANAL & HORSETOOTH RES SITES...... 114 FIGURE 8.10 - DISSOLVED COPPER SPATIAL BOXPLOT FOR WY2012 – WY2015 PERIOD...... 115 FIGURE 8.11 - DISSOLVED IRON SPATIAL BOXPLOT ...... 116 FIGURE 8.12 - TOTAL IRON SPATIAL BOXPLOT ...... 116 FIGURE 8.13 - TIME SERIES PLOT OF TSS AND TOTAL IRON CONCENTRATIONS IN THE BIG THOMPSON RIVER AT HFC-BTD...... 117 FIGURE 8.14 - TIME SERIES PLOT OF TSS AND TOTAL IRON CONCENTRATIONS IN THE POUDRE RIVER AT HSC- PRD...... 117 FIGURE 8.15 - DISSOLVED LEAD SPATIAL BOXPLOT...... 118 FIGURE 8.16 - DISSOLVED MANGANESE SPATIAL BOXPLOT...... 119 FIGURE 8.17 - DISSOLVED NICKEL SPATIAL BOXPLOT...... 119 FIGURE 8.18 - DISSOLVED SELENIUM SPATIAL BOXPLOT...... 120 FIGURE 8.19 - DISSOLVED SILVER SPATIAL BOXPLOT...... 120 FIGURE 8.20 - DISSOLVED URANIUM SPATIAL BOXPLOT...... 121 FIGURE 8.21 - DISSOLVED ZINC SPATIAL BOXPLOT...... 121

FIGURE 9.1 - DENSITIES OF DOMINANT CYANOBACTERIA AT HORSETOOTH RES AT SPRING CANYON (HT-SPR), 0-5 M DEPTH...... 127 FIGURE 9.2 - HORSETOOTH RES CORRECTED CHLOROPHYLL-A (0-5 M) MONTHLY BOXPLOT...... 128 FIGURE 9.3 - BOXPLOT OF HORSETOOTH RES SITES WY2005 – WY2015 MARCH-NOV 0-5 M CHLOROPHYLL-A DATA...... 129

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FIGURE 9.4 - COMPARISON OF TOTAL PHYTOPLANKTON BIOVOLUME & CHL-A DATA FOR HORSETOOTH RES (HT- SPR)...... 129 FIGURE 9.5 - WY2005-WY2015 MARCH - NOV CHLOROPHYLL-A DATA & AVERAGES FOR HORSETOOTH RES AT SPRING CANYON (HT-SPR)...... 130 FIGURE 9.6 - WY2005-WY2015 MARCH - NOV CHLOROPHYLL-A DATA & AVERAGES FOR HORSETOOTH RES AT SOLDIER CANYON (HT-SOL)...... 130 FIGURE 9.7 - HORSETOOTH RES WY2009 TO WY2015 TOC VERSUS CHLOROPHYLL-A CONCENTRATIONS...... 131 FIGURE 9.8 - HORSETOOTH AT SPRING CANYON: TROPHIC CLASSIFICATION BASED ON JULY-SEPT AVG CHLOROPHYLL-A...... 133 FIGURE 9.9 - HORSETOOTH AT SOLDIER CANYON: TROPHIC CLASSIFICATION BASED ON JULY-SEPT AVG CHLOROPHYLL-A...... 133 FIGURE 9.10 - 2008-2015 GEOSMIN TIME SERIES PLOT FOR HORSETOOOTH RESERVOIR SITES (DATA FROM CITY OF FORT COLLINS)...... 134 FIGURE 9.11 - 2009-2015 GEOSMIN TIME SERIES PLOT FOR ADAMS TUNNEL & HANSEN FEEDER CANAL SITES (DATA FROM CITY OF FORT COLLINS)...... 135 FIGURE 9.12 - ANNUAL BOXPLOT OF CITY OF FORT COLLINS GEOSMIN DATA FOR HORSETOOTH RESERVOIR SPRING CANYON & SOLDIER CANYON 1 METER AND BOTTOM SITES...... 135 FIGURE 9.13 - ANNUAL BOXPLOT OF CITY OF FORT COLLINS GEOSMIN DATA FOR ADAMS TUNNEL & HANSEN FEEDER CANAL SITES...... 136 FIGURE 9.17 - SIMPLIFIED AQUATIC FOOD CHAIN...... 139 FIGURE 9.18 - PHOTOGRAPHS OF REPRESENTATIVE ZOOPLANKTON FOUND IN THE LAKE/RESERVOIRS, (A) ROTIFER: KERATELLA, (B) CLADOCERAN: DAPHNIA, AND (C) COPEPOD: DICYCLOPS (PHOTOS TAKEN BY BSA ENVIRONMENTAL SERVICES INC, BEACHWOOD, OH; INCLUDED WITH PERMISSION)...... 140 FIGURE 9.19 - MONTHLY BOXPLOT OF TOTAL ZOOPLANKTON DENSITY AT HT-SPR...... 141 FIGURE 9.20 - MONTHLY BOXPLOT OF TOTAL CLADOCERAN DENSITY AT HT-SPR...... 141 FIGURE 9.21 - MONTHLY BOXPLOT OF TOTAL ROTIFER DENSITY AT HT-SPR...... 142 FIGURE 9.22 - MONTHLY BOXPLOT OF TOTAL COPEPOD DENSITY AT HT-SPR...... 142

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ACRONYMS AND ABBREVIATIONS

ac-ft acre-feet AF acre-feet BTWF Big Thompson Watershed Forum C-BT Colorado-Big Thompson CDPHE Colorado Department of Public Health and Environment cfs cubic feet per second chl-a chlorophyll-a CPW Colorado Parks and Wildlife DBPs Disinfection by-products D.O. Dissolved Oxygen DOC Dissolved Organic Carbon DOM Dissolved Organic Matter DUWS Direct Use Water Supply MCL Maximum Contaminant Level (health-based, primary drinking water standard) MDL Method Detection Limit mg/L milligrams per liter (parts per million) mL milliliter µg/L micrograms per liter (parts per billion) µm3/mL cubic micrometer/milliliter (used to express phytoplankton biovolume per mL of water sample) µS/cm microsiemens per centimeter N Nitrogen ng/L nanograms/liter (parts per trillion)

NH3 Ammonia

NO3 Nitrate

NO2 Nitrite NWFS Northern Water Field Services NWQL National Water Quality Laboratory (USGS laboratory) Ortho-P Ortho-phosphate PPCPs Pharmaceuticals and personal care products QA/QC Quality Assurance/Quality Control RL Reporting Limit SC Specific Conductance SCFP Soldier Canyon Filter Plant SMCL Secondary Maximum Contaminant Level (aesthetic-based, secondary drinking water standard)

-1 SUVA Specific UV absorbance [SUVA (L/mg-m) = (UV254 in cm )/(DOC in mg/L) x 100]

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TDS Total dissolved solids TKN Total Kjeldahl Nitrogen (TKN = ammonia + organic nitrogen) TN Total Nitrogen TOC Total Organic Carbon TP Total Phosphorus TSS Total Suspended Solids USBR United States Bureau of Reclamation USEPA United States Environmental Protection Agency USGS United States Geological Survey

UV254 Ultraviolet absorbance at a wavelength of 254 nanometers WQCC Colorado Water Quality Control Commission WQCD Colorado Water Quality Control Division WWTP Wastewater Treatment Plant WTF Water Treatment Facility WTP Water Treatment Plant WY Water Year (October 1 through September 30); identified by the year in which it ends (WY2011 ended on September 30, 2011)

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EXECUTIVE SUMMARY

Overview of Colorado-Big Thompson & Windy Gap Projects The Northern Colorado Water Conservancy District (Northern Water), a political subdivision of the State of Colorado created in 1937, provides water for agricultural, municipal, domestic and industrial uses to an eight-county service area with a population of about 925,000. Northern Water and the U.S. Bureau of Reclamation (USBR) operate the Colorado-Big Thompson (C-BT) Project, which collects water on the West Slope of the Rocky Mountains and delivers it to Northeastern Colorado through the 13-mile Adams Tunnel beneath Rocky Mountain National Park.

The C-BT Project delivers on average more than 200,000 acre-feet of water to northeastern Colorado each year. Water is provided to the Cities of Fort Collins, Greeley, Loveland, Longmont, Boulder, Louisville, Lafayette, and Broomfield, many smaller communities, rural and domestic water districts, and local industries. Water is also delivered to approximately 120 ditch, reservoir and irrigation companies serving about 640,000 irrigated acres of farm and ranch land between April and October, the primary growing season.

Runoff from the headwaters of the Colorado River is collected in the Three Lakes System (Granby Reservoir, Shadow Mountain Reservoir and Grand Lake; Figure ES.1). Granby Reservoir also receives water pumped from Willow Creek Reservoir and Windy Gap Reservoir. When direct runoff to Grand Lake is sufficient to meet East Slope delivery requirements, the rest of the flow moves naturally from Grand Lake to Shadow Mountain Reservoir, and then to Granby Reservoir. When East Slope delivery requirements are greater than the direct runoff to Grand Lake, water is pumped from Granby Reservoir to Shadow Mountain Reservoir via the Farr Pump Plant and the Granby Pump Canal, from where it is gravity fed to Grand Lake before reaching the West Portal of the Adams Tunnel.

FIGURE ES.1 - WEST SLOPE COLLECTION SYSTEM.

After exiting the Adams Tunnel, the water travels through a series of tunnels, pipelines and canals to eventually be stored in the East Slope terminal reservoirs (Figure ES.2): Horsetooth Reservoir, Carter Lake and Boulder Reservoir. Water is distributed to the end-users either directly from the canal system, the reservoirs, the Southern Water Supply Project Pipeline, or via deliveries to the South Platte tributaries (Cache La Poudre River, Big Thompson River, Little Thompson River, Saint Vrain Creek, Left Hand Creek and Boulder Creek) that are used as a conveyance system.

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Operated by Northern Water, the Windy Gap Project consists of a diversion dam on the Colorado River below the confluence with the Fraser River, the 445-acre-foot Windy Gap Reservoir, a pump plant and a six-mile pipeline to Granby Reservoir (Figure ES.1). The project came online in 1985 to serve municipal and industrial water needs, and utilizes C-BT infrastructure to move water to the East Slope. The Windy Gap Project was designed to annually divert and deliver an average of 48,000 acre feet of water, primarily between April and July. During the spring runoff, water is pumped from Windy Gap Reservoir to Granby Reservoir. The Windy Gap Project introduces water from the Fraser River watershed into the Three Lakes system. The Windy Gap Firming Project will provide dedicated storage for Windy Gap project water in a new East Slope reservoir (Chimney Hollow).

FIGURE ES.2 - EAST SLOPE DISTRIBUTION SYSTEM.

Steady population growth along the northern Colorado Front Range has resulted in a shift in ownership of C-BT Project water allotment contracts from agricultural users to municipal and industrial water users. This trend parallels an increased public awareness of water quality and environmental issues and a strengthening of the regulatory framework both at the Federal and State level. The C-BT and Windy Gap Projects are major drinking water supply sources for treatment plants on the East Slope and the monitoring, assessment, and protection of these waters is important to municipal users as they work to meet increasingly stringent drinking water treatment regulations.

In response to these developing needs, Northern Water has continuously expanded its water quality related activities over the past twenty years. The backbone of the Water Quality Program is the Baseline C-BT Monitoring Program. Purpose of East Slope – North End Water Quality Report

The purpose of this report is to characterize the water quality conditions of Horsetooth Reservoir and the flowing water (rivers and canals) monitoring sites (Figure ES.3) of the Baseline C-BT Monitoring Program, from the Adams Tunnel east to Flatiron Reservoir, and then north to Horsetooth Reservoir and the Poudre River, as revealed by data collected during the 16-year period WY2000 through WY2015. This characterization is an update of the data summaries and findings presented in two previous Northern Water Baseline C-BT Monitoring Program reports, the 2010 Flowing Sites Report (covering WY2000 – WY2009) and the 2013 Lake and Reservoirs Report (covering WY2005 – WY2011); http://www.northernwater.org/WaterQuality/WaterQualityReports1.aspx. However, the two previous reports summarized data collected at all (West Slope and East Slope) Baseline C-BT Monitoring Program sites, while this report has a focused geographical scope and provides for the evaluation of Horsetooth Reservoir together with its associated upstream and downstream flowing sites.

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Poudre River

Hansen Supply Canal

Horsetooth Reservoir

Hansen Feeder Canal

Big Thompson Lake River Estes Olympus Tunnel Flatiron Res Adams Tunnel Carter Lake Res

FIGURE ES.3 - MAP OF BASELINE C-BT MONITORING PROGRAM EAST SLOPE – NORTH END SAMPLING SITES.

Five categories of water quality parameters are routinely monitored at the Baseline C-BT Monitoring Program sites and are evaluated and summarized for this report:

• Field Parameters: Flowing sites - temperature, dissolved oxygen, specific conductance and pH; Horsetooth Reservoir - Secchi depth and depth profiles of temperature, dissolved oxygen, specific conductance and pH • General Chemistry: alkalinity, total organic carbon (TOC), total suspended solids (TSS), and major ions (calcium, magnesium, sodium, potassium, chloride, sulfate) • Nutrients: ammonia, nitrate plus nitrite, total Kjeldahl nitrogen (TKN), orthophosphate (ortho-P) and total phosphorus (TP) • Metals: arsenic (total and dissolved), boron (dissolved), cadmium (dissolved), chromium (total and dissolved), copper (dissolved), iron (total and dissolved), lead (dissolved), manganese (dissolved), nickel (dissolved), selenium (dissolved), silver (dissolved), uranium (dissolved), and zinc (dissolved) • Horsetooth Reservoir Biological Parameters: chlorophyll-a, phytoplankton, and zooplankton

The data analysis for these water quality parameters focused on characterizing general spatial and temporal patterns and not specific (outlier) data points or events. This Executive Summary synthesizes the main findings from the detailed analysis presented in the body of the report, including Horsetooth Reservoir profile data and biological parameters (chlorophyll-a and phytoplankton), spatial and seasonal patterns across all sites, and time trend analysis for selected parameters.

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East Slope - North End: Existing Water Quality Concerns Several aquatic life and/or drinking water treatment issues and concerns have been identified over the years in Horsetooth Reservoir and the flowing waters associated with the East Slope – North End monitoring sites, including:

• Copper: Dissolved copper present at very low concentrations can impact aquatic organisms including zooplankton and fish. Elevated concentrations of copper in waters associated with the C-BT Project have resulted in sections of the Big Thompson River, Poudre River and Horsetooth Reservoir being included on the State’s list of impaired waters. Copper sulfate was historically used in the C-BT Project canals to control periphyton (attached algae) and aquatic plants, but application of copper sulfate to the canals was discontinued in April 2008 by Northern Water and in 2012 by the USBR.

• Low Dissolved Oxygen (D.O.): Low dissolved oxygen levels occur at the bottom and middle depths of Horsetooth Reservoir (Figure ES.4). Low D.O. at the top and middle depths of a lake/reservoir can be an aquatic life concern, while low D.O. at the bottom can result in the release of nutrients and metals from bottom sediments.

• Manganese: Dissolved manganese in treated drinking water can change to a solid form and cause “brown water” episodes that stain plumbing fixtures and laundry, and result Dixon in customer complaints. Low Canyon Dam dissolved oxygen levels (< 2 mg/L) that occur at the bottom of Horsetooth Reservoir in the late summer and early fall favor Spring the release of dissolved Canyon Dam manganese from the bottom Horsetooth Reservoir sediments. FIGURE ES.4 - AERIAL PHOTO OF HORSETOOTH RESERVOIR, LOOKING NORTH.

• Total Organic Carbon (TOC): TOC occurs naturally from decomposing plant and animal matter and may originate within the water body (algae and other aquatic organisms) or be introduced through runoff from the surrounding watersheds. TOC is a concern for drinking water treatment plants because it reacts with disinfectants such as chlorine to form regulated (carcinogenic) disinfection by-products. Increasing concentrations of TOC have been noted in previous trend analyses conducted for Horsetooth Reservoir and sites along the C-BT convenience system.

• Geosmin: Geosmin is a compound produced by some species of cyanobacteria (blue-green algae). Although it is not a public health risk, geosmin imparts an earthy odor to water at extremely low concentrations (~5 parts per trillion). Geosmin is a concern for drinking water treatment plants because it is difficult to remove and its presence in treated drinking water results in customer complaints and questions about the quality and safety of the water. It has been detected in Horsetooth Reservoir and in water from the West Slope delivered through the Adams Tunnel.

• Nutrients & Chlorophyll: Nutrient (nitrogen and phosphorous) loading to water bodies is often the root cause of many water quality issues, including algal blooms, low dissolved oxygen, taste and odor issues,

WY2000-WY2015 East Slope - North End Water Quality Report 03/17/17

and algal toxins. The Colorado Water Quality Control Commission adopted interim numerical values for phosphorus, nitrogen and chlorophyll-a in 2012 to protect designated uses of Colorado waters. These values will be considered for adoption as standards in river/stream segments and in lakes/reservoirs within the boundaries of the C-BT and Windy Gap Projects.

• Mercury: Elevated levels of mercury have been detected in fish tissue collected from Horsetooth Reservoir and Carter Lake, resulting in these reservoirs being placed on the State’s list of impaired waters due to the public health risk associated with fish consumption.

In addition to these specific issues, there are also changes in water quality that may result from one or more large- scale environmental perturbations within the watersheds. Insect infestations such as the mountain pine beetle epidemic, floods, drought, climate change, changes in land use patterns, and catastrophic wildfires can all impact water quality. The extent of some of the potential water quality changes are unknown and occur slowly over time, while others are more abrupt and obvious including those caused by large wildfires (such as the June 2012 High Park Fire) and floods (such as the Sept 2013 Flood). Although it is beyond the scope of this report to provide a detailed analysis of the various specific and potential water quality issues, they are considered in relation to the baseline data. East Slope – North End Water Quality Findings & Highlights

HORSETOOTH RES: D.O., Temperature & Specific Conductivity Profiles

The density differences of water at various temperatures and depths in a lake/reservoir result in an annual cycle of thermal stratification and the associated differences in water quality that develop between the top and bottom of a lake/reservoir. The temperature profiles collected during the 2005-2015 time period for Horsetooth Reservoir continue to show the typical development of thermal stratification beginning in the spring, with the presence of the epilimnion, metalimnion, and hypolimnion clearly evident by late spring or early summer, and progressing through the summer and into the fall. The temperature profiles are similar for the three monitoring locations as shown, for example, in Figure ES.5 with August 2014 temperature profiles. Fall turnover occurs throughout Horsetooth Reservoir in October or November, when the reservoir is completely mixed from top to bottom and poorer quality water that may have existed in the hypolimnion is distributed throughout the entire reservoir.

Horsetooth Res Temperature Profiles - Aug 11, 2014 Conceptual cross-section of Horsetooth Res (thalweg)

5,440 HT-SPR HT-DIX HT-SOL

5,420 EPILIMNION

5,400 METALIMNION METALIMNION 5,380

5,360 HYPOLIMNION HYPOLIMNION 5,340

5,320

5,300 5,280

Thalweg Elevation (ft) Elevation Thalweg 5,260 5,240 0 4 8 12 16 20 24 0 4 8 12 16 20 24 0 4 8 12 16 20 24 Temperature ( C) 5,220 Temperature ( C) Temperature ( C)

5,200 Spring Dixon Soldier Canyon Canyon Canyon

FIGURE ES.5 - CONCEPTUAL CROSS-SECTION OF HORSETOOTH RESERVOIR SHOWING AUG 2014 TEMPERATURE PROFILES.

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The temperature and specific conductance profiles collected at Horsetooth Reservoir continue to show that inflows from the Hansen Feeder Canal occur as an interflow within the metalimnion during the summer and fall (Figure ES.6), with the inflow canal water plunging below the reservoir surface. The presence of this interflow represents a short-circuiting path through the reservoir.

Hansen Feeder Canal Horsetooth Reservoir Specific Conductance Profiles - Aug 11, 2014 Inflow (HFC-HT) Conceptual cross-section of Horsetooth Res (thalweg) Spec Cond = 31 uS/cm on 8/12/14 5,440 HT-SPR HT-DIX HT-SOL 5,420 EPILIMNION

5,400 METALIMNION Interflow METALIMNION 5,380 HYPOLIMNION 5,360 HYPOLIMNION 5,340 5,320 Soldier 5,300 Canyon Dam 5,280 outlet

Thalweg Elevation (ft) Elevation Thalweg 5,260 5,240 20 30 40 50 60 70 80 90 20 30 40 50 60 70 80 90 20 30 40 50 60 70 80 90 5,220 Spec Cond (uS/cm) Spec Cond (uS/cm) Spec Cond (uS/cm) 5,200 Spring Dixon Soldier Canyon Canyon Canyon

FIGURE ES.6 - CONCEPTUAL DIAGRAM OF HANSEN FEEDER CANAL INTERFLOW IN HORSETOOTH RESERVOIR BASED ON SPECIFIC CONDUCTANCE PROFILES. The dissolved oxygen (D.O.) profiles collected at Horsetooth Reservoir from 2005 through 2015 continue to show the same general patterns. D.O. concentrations at the bottom of the reservoir gradually decline during summer thermal stratification (Figure ES.7) due to microbial breakdown of settled organic matter. The pool at Spring Canyon generally experiences the lowest bottom D.O. concentrations, with annual minimum values before fall turnover generally below 2 mg/L and often below 1 mg/L. Organic matter that is brought in with the Hansen Feeder Canal inflows preferentially settles out in the upstream portions of the reservoir, resulting in lower D.O. levels in this area.

Horsetooth Reservoir Dissolved Oxygen (D.O.) Profiles - Aug 11, 2014 Conceptual cross-section of Horsetooth Res (thalweg) HT-SPR 5,440 HT-DIX HT-SOL 5,420 EPILIMNION

5,400 METALIMNION METALIMNION 5,380 5,360 HYPOLIMNION HYPOLIMNION 5,340 5,320 Soldier 5,300 Canyon Dam 5,280 outlet

Thalweg Elevation (ft) ElevationThalweg 5,260 5,240 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 5,220 Dissolved Oxygen Dissolved Oxygen Dissolved Oxygen (mg/L) (mg/L) (mg/L) 5,200 Spring Dixon Soldier Canyon Canyon Canyon D.O. depletion D.O. depletion at bottom in metalimnion FIGURE ES.7 - TYPICAL SUMMER DISSOLVED OXYGEN PROFILES IN HORSETOOTH RES.

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The Horsetooth Reservoir D.O. profiles also show oxygen depletion in the metalimnion beginning in June and progressing through the summer (Figure ES.7). Water quality modeling conducted on Horsetooth Reservoir indicates that low D.O. in the metalimnion is primarily controlled by the decay of inflowing organic matter (TOC in waters from the Hansen Feeder Canal that enter the reservoir as an interflow). D.O. concentrations in the Horsetooth Reservoir metalimnion fall below the 6 mg/L aquatic life standard every year, often falling within the range of 2 to 4 mg/L by September, but these situations are not considered to impact aquatic life if the chronic temperature standard and the D.O. standard are both being met in the top layer and providing adequate refuge.

HORSETOOTH RES: Phytoplankton, Chlorophyll-a & Geosmin

Phytoplankton. The Horsetooth Reservoir WY2006-WY2015 phytoplankton data show that the reservoir is generally dominated by diatoms, green algae and cryptomonads by density (cells/mL). Occasionally, cyanobacteria, or golden-brown algae may be a dominant algal group by density. Diatoms dominate the phytoplankton population by biovolume (µm3/mL). Cryptomonads and golden-brown algae may also be dominant by biovolume.

Although cyanobacteria “blooms” in Horsetooth Reservoir do not occur very often, the data indicate that when they do occur, they generally result from large densities (cell counts) of the small-celled Aphanocapsa (Figure ES.8), Aphanothece, Chroococcus, and Pannus. Two identified producers of geosmin, Anabaena circinalis and Aphanizomenon flos-aquae, have occasionally been found in Horsetooth Reservoir, but densities continue to be very low (≤ 60 cells/mL). Strains of some species of Anabaena and Aphanizomenon produce cyanotoxins, but the occurrence of cyanotoxin producers in Horsetooth Reservoir is unknown.

Aphanocapsa

Aphanothece

Anabaena

Aphanizomenon

FIGURE ES.8 - PHOTO-MICROGRAPHS OF SOME COMMON CYANOBACTERIA FOUND IN HORSETOOTH RESERVOIR (TAKEN BY GRANT JONES, CITY OF FORT COLLINS).

Chlorophyll-a. Median chlorophyll-a concentrations in Horsetooth Reservoir are 3.2, 3.2 and 3.1µg/L at Spring Canyon Dam (HT-SPR), Dixon Dam (HT-DIX), and Soldier Canyon Dam (HT-SOL), respectively, for all March – November data from the WY2005-WY2015 monitoring period. The seasonal peaks in chlorophyll-a in Horsetooth Reservoir are typically less than 10 µg/L and coincide with the summer (July) and fall peaks in biovolume that are often dominated by diatoms.

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The annual average hydraulic residence time of water in Horsetooth Reservoir was significantly higher in WY2014 and WY2015 (1.8 and 1.5 years, respectively) compared to the period WY2006 - WY2012 (range of 0.7 to 0.95 years). Longer hydraulic residence times can favor some phytoplankton, including cyanobacteria. However, the chlorophyll-a and phytoplankton data do not show any obvious increases coincident with these longer hydraulic residence times.

In 2012, the Colorado Water Quality Control Commission established a 5 µg/L chlorophyll-a interim value (March- November average, with a 1-in-5 year exceedance frequency) that applies to the epilimnion of Direct Use Water Supply (DUWS) lakes and reservoirs. Horsetooth Reservoir has been classified as a DUWS reservoir, but the 5 µg/L interim value has not been adopted for this reservoir. However, to evaluate how the existing conditions in the reservoir compare to the 5 µg/L chlorophyll-a value, the annual March-November averages were calculated using the 0-5 meter chlorophyll-a data as shown, for example, for the Soldier Canyon site in Figure ES.9. For the most recent 5 years of data, the 5 µg/L interim value was exceeded once at Spring Canyon (March- Nov average of 5.2 µg/L in 2012), with no exceedances at the Soldier Canyon and Dixon Canyon sampling sites.

The chlorophyll-a data indicate that Horsetooth Reservoir continues to be in the mesotrophic range (characterized by moderate algal productivity).

FIGURE ES.9 - WY2005-WY2015 MARCH - NOV CHLOROPHYLL-A DATA & AVERAGES FOR HORSETOOTH RES AT SOLDIER CANYON (HT-SOL).

Geosmin. The City of Fort Collins has monitored geosmin concentrations at Horsetooth Reservoir sites since 2008 and at the East Portal of the Adams Tunnel and Hansen Feeder Canal sites since 2009. Geosmin data collected by the City of Fort Collins were obtained by Northern Water and presented in this report since geosmin is an important taste and odor constituent of concern for drinking water treatment plants. Elevated geosmin concentrations were measured in Horsetooth Reservoir in 2008 and 2009 (nearly 53 nanograms/L (ng/L) at Spring Canyon 1-meter depth and 28 ng/L at the bottom of Solder Canyon Dam in 2008), but have been near or below the 5 ng/L odor threshold since 2010.

The conditions that allowed for the elevated geosmin concentrations within Horsetooth Reservoir in 2008 and 2009, but not in the 2010-2015 period, are unknown and difficult to determine due to the many contributing factors. Two identified producers of geosmin, Anabaena circinalis and Aphanizomenon flos-aquae, have occasionally been found in Horsetooth Reservoir, but densities have been very low, and at levels that would not be expected to result in taste and odor issues. Relatively high geosmin concentrations (greater than the odor threshold) are often detected at the East Portal Adams Tunnel (with sources assumed, but not confirmed, to be from cyanobacteria in the West Slope reservoirs) and in the Hansen Feeder Canal downstream of Flatiron Reservoir. The large geographical extent of the C-BT Project and the annual variations in operations, as well as the varying environmental conditions, all complicate the fate and transport of geosmin and its spatial variation. These factors together continue to prevent the establishment of cause and effect relationships for the occurrence of geosmin in Horsetooth Reservoir.

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SPATIAL & SEASONAL PATTERNS

The geographical scope of this report allows for visualization of the spatial patterns that include Horsetooth Reservoir together with its associated upstream and downstream flowing sites. Horsetooth Reservoir is directly influenced by the upstream water sources, but its water quality is different due to the detention time within the reservoir and the different biological, physical, and chemical processes that take place within a reservoir. Downstream of Horsetooth Reservoir, water in the Hansen Supply Canal takes on characteristics of the reservoir water and does not appear to have any detrimental impact on the Poudre River. Some key spatial and seasonal patterns are highlighted below.

Major Ions. The Baseline C-BT Monitoring Program shows that concentrations of the major ions are low at all the East Slope - North End sites. The highest median concentrations of calcium (Figure ES.10), magnesium, sulfate, alkalinity and hardness occur in Horsetooth Reservoir and downstream in the Hansen Supply Canal, with concentrations at these sites falling within narrow ranges. The flowing sites (river and canal sites, except for the Hansen Supply Canal) exhibit wider ranges of major ion concentrations than Horsetooth Reservoir due to the pronounced seasonal variability experienced by the flowing sites, with concentrations diluted during the spring runoff.

FIGURE ES.10 - CALCIUM SPATIAL BOXPLOT

TOC. The flowing sites (except for the Hansen Supply Canal) show a wider range in TOC concentrations (Figure ES.11) than Horsetooth Reservoir due to seasonal variability in the flowing sites, with increased concentrations during the spring snowmelt runoff period. The Horsetooth Reservoir bottom sites show the narrowest range in concentrations, and influence the narrow range also observed at the downstream Hansen Supply Canal site. TOC concentrations at the Horsetooth Reservoir 1-meter depth are generally the same as or higher than at the reservoir bottom since algal production near the surface contributes to the TOC pool.

FIGURE ES.11 - TOTAL ORGANIC CARBON (TOC) SPATIAL BOXPLOT

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Water from the Adams Tunnel mixes with Big Thompson River water at Lake Estes such that the water leaving Lake Estes in the Olympus Tunnel has a blend of characteristics from both sources. During the spring snowmelt runoff period (generally May through June), higher TOC concentrations in the Big Thompson River above Lake Estes result in TOC concentrations in the Olympus Tunnel and Hansen Feeder Canal that are generally higher than at the Adams Tunnel, depending on the relative flows from each source. Before and after the spring runoff (generally July through March), the TOC concentrations in the Hansen Feeder Canal are primarily influenced by the concentrations in the West Slope water as measured at the Adams Tunnel.

TOC concentrations in the Hansen Supply Canal are relatively constant from month to month, with median monthly concentrations of about 3.4 mg/L, and reflect the concentrations measured at the bottom of Horsetooth Reservoir at Soldier Canyon (HT-SOL-b).

Phosphorous. Ortho-phosphate (ortho-P) is a dissolved inorganic form of phosphorous and is the only form of phosphorus that is immediately available for uptake by algae. Ortho-P concentrations are generally highest at the Big Thompson River sites (since these sites are influenced by effluent from the wastewater treatment plants located upstream at Estes Park), and at the bottom of Horsetooth Reservoir at Spring Canyon due to organic matter degradation and release from bottom sediments during summer stratification (Figure ES.12). The lowest ortho-P concentrations are generally found at the Horsetooth Reservoir 1 meter depth due to algal uptake.

FIGURE ES.12 - ORTHOPHOSPHATE SPATIAL BOXPLOT

Total Phosphorous (Total P) includes dissolved and particulate forms of phosphorous, and includes phosphorous that is bound to sediments and phosphorus that is tied up within organic matter and phytoplankton. The Big Thompson and Poudre River sites experience the highest Total P concentrations (Figure ES.13) since Total P is associated with sediments that are mobilized during snowmelt runoff and significant rainfall events. Higher Total P concentrations at the Big Thompson River sites are associated with impacts of the 2013 flood and related construction work, while Total P concentrations at the Poudre River sites have been impacted by runoff from the 2012 High Park Fire burn areas.

FIGURE ES.13 - TOTAL PHOSPHOROUS SPATIAL BOXPLOT

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Nitrogen. Ammonia, nitrate and nitrite are the forms of nitrogen that are immediately available for uptake by algae. There are drinking water standards for nitrate and nitrite (10 mg/L and 1mg/L, respectively), but concentrations at the sites covered in this report are all significantly lower than these standards (Figure ES.14). The highest median nitrate+nitrite concentrations are found at the Big Thompson River sites (Figure ES.14), which are downstream of discharges from the wastewater treatment plants at Estes Park. The sites at the bottom of Horsetooth Reservoir have elevated nitrate+nitrite concentrations during the late summer and fall. At the bottoms of stratified water bodies such as Horsetooth Reservoir, nitrate concentrations increase as settled organic matter is decomposed in the presence of oxygen. The lowest median concentrations of nitrate+nitrite are found at the Horsetooth Reservoir 1 meter depth due to algal uptake.

FIGURE ES.14 - NITRATE + NITRITE SPATIAL BOXPLOT

Metals. The metals currently included in the Baseline C-BT Monitoring Program are arsenic (total and dissolved), boron (dissolved), cadmium (dissolved), chromium (total and dissolved), copper (dissolved), iron (total and dissolved), lead (dissolved), manganese (dissolved), nickel (dissolved), selenium (dissolved), silver (dissolved), uranium (dissolved), and zinc (dissolved). Sampling for total arsenic, boron, chromium (dissolved and total), and uranium began in WY2013 or WY2014, so it is premature to make conclusions about the spatial and seasonal patterns for these parameters. Cadmium and silver have rarely been detected, and most lab results have indicated that these trace metals are not present above their respective detection limits, which have varied over the years. Many of the other metals do not show strong spatial or seasonal variability. Some specific observations for dissolved arsenic, copper, total and dissolved iron, and manganese are presented below.

Arsenic. A primary maximum contaminant level (MCL) of 10 µg/L and an MCL goal of 0 µg/L have been set for arsenic by CDPHE for the protection of human health in treated drinking water. If a water body is both a drinking water supply and used by the public for fishing, the CDPHE has set a human health-based total recoverable arsenic standard of 0.02 µg/L (“water + fish ingestion” criteria) which applies to the sites in this report. Low levels of dissolved arsenic are detected at all sampling sites at concentrations that are higher than the total recoverable arsenic standard of 0.02 µg/L. The Horsetooth Reservoir sites and the Hansen Supply Canal sites generally have higher dissolved concentrations (median of about 0.3 µg/L) than the tunnel sites, Hansen Feeder Canal sites and Big Thompson River sites (median of about 0.2 µg/L). The highest dissolved concentrations (up to 1.6 µg/L) have been detected at the bottom of Horsetooth Reservoir at Spring Canyon Dam prior to fall turnover. Arsenic adsorbs onto iron oxide particulate material and, after settling to the bottom of a water body, this arsenic can be released into solution when iron oxides dissolve under anoxic/reducing conditions that can occur at the reservoir bottom prior to fall turnover.

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new pattern with only the WY2012 to WY2015 data (Figure ES.15). The highest median concentrations now occur at the Big Thompson River sites (median concentrations of 1.5 - 1.8 µg/L), followed by the Adams Tunnel and Olympus Tunnel sites (median concentrations of 1.4 µg/L).

FIGURE ES.15 - COPPER SPATIAL BOXPLOTS: WY2002-WY2015 AND WY2012-WY2015

Dissolved Iron. Dissolved iron concentrations at all sites are generally below the drinking water secondary MCL (300 µg/L) except for some occurrences above 300 µg/L at the Hansen Feeder Canal sites, Olympus Tunnel, Big Thompson River, and Poudre River. The highest dissolved iron concentrations include 1,170 µg/L at HFC-FRD, 1,090 µg/L at HFC-BT, and 1,110 µg/L at HFC-HT, and occurred in samples collected on Oct. 3, 2013 when these sites were impacted by floodwater that had entered Lake Estes and was then pumped through the Olympus Tunnel to Pinewood and Flatiron Reservoirs, and subsequently released to the Hansen Feeder Canal.

Total Iron. The highest total iron concentrations are generally associated with high total suspended solids (TSS) concentrations and have occurred at the Big Thompson River and Poudre River sites. The annual peaks in total iron are coincident with the annual peaks in TSS that generally occur during the spring runoff, but have been exacerbated by the High Park Fire in the Poudre Watershed and the September 2013 flood. The total iron concentration in the Big Thompson River reached a maximum value of 35,700 µg/L at HFC-BTD in April 2014, during the spring runoff after the river had been damaged by the September 2013 flood. Total iron concentrations are expected to remain elevated along with the TSS as restoration work continues in the Big Thompson Canyon.

Manganese. Elevated manganese concentrations (> 50 µg/L, the drinking water secondary MCL) occur at the bottom of Horsetooth Reservoir during periods of low dissolved oxygen, generally in September and October at the end of the summer stratification period (Figure ES.16). At the HFC-BTD Big Thompson River site, all concentrations above 50 µg/L occurred after the 2013 Flood. The highest dissolved manganese concentrations at the Poudre River sites occurred within 12 months after the 2012 High Park Fire.

FIGURE ES.16 - MANGANESE (DISSOLVED) SPATIAL BOXPLOT

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TREND ANALYSIS RESULTS

The analysis of water quality data conducted for this report included the determination of the statistical significance and magnitude of time trends to address the questions of whether and how much water quality has changed over the period of record. The Seasonal Kendall Test was used to provide a quantitative test for the statistical significance of trends in the concentration time series data. It is a test for monotonic changes in a data series (i.e., a change in only one direction, increasing or decreasing).

The results of the trend analysis conducted for this report are summarized in Table ES.1. The test was performed at a 90% confidence level (critical p-value = 0.10), which means that there is at most a 10% chance of concluding that a statistically significant trend exists when in fact there is no trend. If a computed p-value is less than 0.10, a statistically significant time trend is concluded to exist. For cases where a statistically significant trend is concluded to exist, the “Sen slope as a percent of the mean” is used to evaluate the magnitude of the trend in a relative manner. Cases where the absolute value of the Sen slope is greater than 4% of the mean are highlighted in Table ES.1 with an up or down arrow, where 4% was selected to allow for a focus on those parameters with the highest trend magnitudes (i.e., trends that are more likely to have significance from a practical standpoint). If the Sen Slope is equal to 4% of the mean value calculated over the study period, the annual average parameter concentration would change by 100% of that value in 25 years (or 4% of that value each year), assuming the trend continues over time.

TABLE ES.1- SUMMARY OF SEASONAL KENDALL TIME TREND TEST RESULTS TOC & Major Ions Nutrients Metals Other

Site ID System Feature TOC Alkalinity Calcium Magnesium Potassium Sodium Chloride Sulfate Ammonia N Nitrate + NitriteTotal N Kjeldahl NOrtho PhosphateTotal PhosphorusArsenic, dis Copper, dis Iron, dis Iron, total Manganese, disNickel, dis Selenium, dis Zinc, dis Chl-a (0-5 meter)Secchi Depth AT-EP Adams Tunnel ↓ ↑ ↑ ↓ OLY Olympus Tunnel ↑ ↑ ↓ HFC-FRD Hansen Feeder Canal, Flatiron ↓ HFC-BTU Big Thompson Riv, upstream HFC ↑ HFC-BT Hansen Feeder Canal, Big Thomp Riv ↓ ↓ HFC-BTD Big Thompson Riv, downstream HFC ↑ HFC-HT Hansen Feeder Canal, Horsetooth Res ↓ ↓ ↓

HT-SPR-1 Horsetooth Res, Spring Can, 1 meter ↑ ↓ ↓ ↓ ↓ ↓ HT-SPR-b Horsetooth Res, Spring Can, bottom ↑ ↓ ↓ HT-DIX-1 Horsetooth Res,Dixon Can, 1 meter ↑ ↓ ↓ ↓ ↓ ↓ HT-DIX-b Horsetooth Res, Dixon Can, bottom ↑ ↓ ↓ ↓ ↓ HT-SOL-1 Horsetooth Res, Soldier Can, 1 meter ↑ ↓ ↓ ↓ HT-SOL-b Horsetooth Res, Soldier Can, bottom ↑ ↓

HSC-PRU Poudre River, upstream HSC ↓ ↑ ↑ ↑ ↑ ↓ HSC-PR Hansen Supply Canal ↑ ↓ ↓ ↓ ↑ ↓ ↑ ↓ HSC-PRD Poudre River, downstream HSC ↓ ↑ ↑ ↑ ↓ ↑ ↑

Note: all trend tests are at the 90% confidence level (significant trend if p-value ≤ 0.10)

KEY: Statistically significant decreasing trend ↓ Statistically significant decreasing trend, Sen Slope ≥ 4% of mean Statistically significant increasing trend ↑ Statistically significant increasing trend, Sen Slope ≥ 4% of mean No statistically significant trend Not applicable; or not included in trend analysis if POR start > 2008 (≤ 7 years of data).

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Although the trend analysis was conducted for many parameters as indicated in Table ES.1 and a number of parameters showed statistically significant trends (increasing or decreasing), the results for copper, TOC, nutrients, and Horsetooth Reservoir chlorophyll-a concentrations and Secchi depth are the most noteworthy and of the most practical significance within the geographical scope of this report and are summarized below.

Copper. The trend analysis results in Table ES.1 show statistically and practically significant decreasing trends in copper concentrations in the canals and Horsetooth Reservoir. Copper concentrations in the canals and Horsetooth Reservoir have dropped since the use of copper sulfate was discontinued during the 2008 – 2011 period. This can be seen, for example, on the annual boxplot in Figure ES.17 for the Hansen Feeder Canal below Flatiron Reservoir. Copper concentrations in the Poudre River downstream of the Hansen Supply Canal (HSC-PRD) also show a statistically significant decreasing trend, coincident with the discontinued use of copper sulfate in the Hansen Supply Canal in 2008. At the Adams Tunnel and Olympus Tunnel sites, the analysis showed a statistically significant increasing trend in copper concentrations, consistent with the annual boxplots shown, for example, in Figure ES.18 for the Adams Tunnel. The cause of this increasing trend is not known.

FIGURE ES.17 - ANNUAL BOXPLOT FOR COPPER CONCENTRATIONS AT HFC-FRD.

FIGURE ES.18 - ANNUAL BOXPLOT FOR COPPER CONCENTRATIONS AT THE ADAMS TUNNEL.

TOC. Only two canal/tunnel sites, the Hansen Feeder Canal at the Horsetooth inlet and the Hansen Supply Canal, show statistically significant increasing trends in TOC concentrations although the magnitude of the trends are relatively small (and not considered significant from a practical standpoint). The TOC trend results shown in Table ES.1 differ from those reported previously by others for Horsetooth Reservoir and waters in the Hansen Feeder Canal, where previous studies have consistently indicated statistically significant increasing trends in TOC at many of the sites. For example, in the most recent BTWF report (Hydros Consulting, 2015), which included data for the period WY2000 – WY2014, TOC concentrations continued to show a statistically significant increasing trend at the east portal Adams Tunnel, Olympus Tunnel, and in the Hansen Feeder Canal sites HFC-FRD and HFC-BT, and HFC- HT was added to this list of sites with increasing TOC.

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Visual inspection of the time series plots and the annual boxplots in this report do not show any obvious trends in TOC concentrations over time, consistent with the statistical trend analysis results (from both a statistical and practical standpoint).

Nutrients. The time trend analysis for the ammonia data indicate statistically significant decreasing trends for many of the sites (Table ES.1), including Hansen Feeder Canal and Horsetooth Reservoir sites with relatively high trend magnitudes. However, the ammonia trend analysis is impacted by the changing detection limits (lowering over time) and the high number of non-detected values. At the Poudre River sites (HSC-PRU and HSC-PRD), increasing trends in nitrate, TKN, ortho-P and Total P are influenced by the increasing concentrations of these parameters that occurred after the 2012 High Park Fire.

Horsetooth Reservoir Secchi depth & Chlorophyll-a. The trend analysis did not show statistically significant trends in Secchi depth or chlorophyll-a concentrations at any of the three Horsetooth Reservoir sites. Summary & Recommendations Northern Water’s Baseline Water Quality Monitoring Program includes routine sampling of the East Portal Adams Tunnel, Olympus Tunnel, sites on the Hansen Feeder and Hansen Supply Canals, Big Thompson River and Poudre River sites associated with canal discharge locations, and three locations along the length of Horsetooth Reservoir. Water samples are collected for laboratory analysis of total organic carbon, total suspended solids, major ions, nutrients, metals, chlorophyll, phytoplankton, and zooplankton, and field measurements are made of Secchi depth and temperature, dissolved oxygen, pH and specific conductance.

At the most general level, the quality of water in the Hansen Feeder Canal is impacted by the West Slope water quality as well as the quality of the Big Thompson River. As this water enters and resides in Horsetooth Reservoir, it is further influenced by such factors as the hydraulic detention time, the annual cycle of thermal stratification over the summer and into the fall, with turnover (complete mixing) in the late fall, as well as the many biological and chemical processes that take place within a reservoir. The water quality in the Hansen Supply Canal generally reflects the water quality observed at the bottom of Horsetooth Reservoir at Soldier Canyon Dam.

The collected data have captured the seasonal and spatial patterns, and provide for the examination of site-specific water quality characteristics and trends. The data analyses conducted for this report have provided continued insight into the processes and factors that impact the various water quality parameters. The data analysis did not produce any unexpected results, and the findings are generally consistent with previous data summaries. The one exception to this is the finding that the trend analysis showed that only two sites (the Hansen Feeder Canal at the Horsetooth inlet and the Hansen Supply Canal) have statistically significant increasing trends in TOC concentrations, with the magnitude of the trends being relatively small and not considered significant from a practical standpoint. With these results, at least for now, increasing TOC concentrations is not viewed as a major concern, but given its importance to drinking water providers, it will continue to be closely monitored.

One of the goals of the Baseline Monitoring Program data assessment conducted for this report was to identify data/information gaps as well as possibilities to further optimize the monitoring program. Data/information gaps can be filled by changes to the Baseline Monitoring Program, by new special studies, or by more detailed analysis of existing data. Monitoring Program optimization consists of modifying the sampling sites, parameter list and/or sampling frequency to minimize costs while still providing for the collection of the data/information needed to address current and anticipated future issues. Some changes in parameters and sampling frequency have been made over the years to Northern Water’s Baseline C-BT Monitoring Program such that it is currently meeting the objectives of the program for the East Slope - North End sites. Changes to the program in the East Slope – North End geographical area are not recommended at this time.

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1. INTRODUCTION

1.1 COLORADO-BIG THOMPSON PROJECT & WINDY GAP PROJECT OVERVIEW Northern Water, a political subdivision of the State of Colorado created in 1937, provides water for agricultural, municipal, domestic and industrial uses to an eight-county service area with a population of about 925,000. Northern Water and the U.S. Bureau of Reclamation (USBR) operate the Colorado-Big Thompson (C-BT) Project, which collects water on the West Slope and delivers it to Northeastern Colorado through the 13-mile Adams Tunnel beneath Rocky Mountain National Park (Figure 1.1).

Runoff from the headwaters of the Colorado River is collected in the Three Lakes System (Granby Reservoir, Shadow Mountain Reservoir and Grand Lake). Granby Reservoir also receives water pumped from Willow Creek Reservoir and Windy Gap Reservoir in addition to the natural runoff from the Three Lakes watershed. When direct runoff to Grand Lake is sufficient to meet East Slope delivery requirements, the rest of the flow moves naturally from Grand Lake to Shadow Mountain, to the Colorado River and eventually Granby Reservoir. When East Slope delivery requirements are greater than the direct runoff to Grand Lake, Adams Tunnel deliveries are supplemented with water pumped from Granby Reservoir. Water is pumped from Granby Reservoir to Shadow Mountain Reservoir via the Granby Pump Canal, from where it is gravity fed to Grand Lake before reaching the West Portal of the Adams Tunnel.

After exiting the Adams Tunnel, the water travels through a series of tunnels, pipelines and canals to eventually be stored in the East Slope terminal reservoirs (Horsetooth Reservoir, Carter Lake and Boulder Reservoir). It is then distributed to the end-users either directly from the canals, the reservoirs, the Southern Water Supply Project Pipeline, or via deliveries to the South Platte tributaries (Cache La Poudre River, Big Thompson River, Little Thompson River, Saint Vrain Creek, Left Hand Creek and Boulder Creek) that are used as a conveyance system.

The Windy Gap Project is located just west of the town of Granby on Colorado's West Slope. The project consists of a diversion dam on the Colorado River below the confluence with the Fraser River, the 445-acre-foot Windy Gap Reservoir, a pump plant and a six-mile pipeline to Granby Reservoir. The project came online in 1985 to serve municipal and industrial water needs and utilizes C-BT infrastructure to move water to the East Slope. The Windy Gap Project was designed to annually divert and deliver an average of 48,000 acre feet of water, primarily between April and July. During the spring runoff, water from the Fraser and Colorado Rivers is pumped from Windy Gap Reservoir to Granby Reservoir where it is stored for delivery through the C-BT facilities to water users on the Front Range. The Windy Gap Project introduces water from the Fraser River watershed into the Three Lakes system. The Windy Gap Firming Project will provide dedicated storage for Windy Gap project water in a new East Slope reservoir (Chimney Hollow).

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FIGURE 1.1- MAP OF C-BT & WINDY GAP PROJECTS

1.2 BASELINE WATER QUALITY MONITORING PROGRAM OVERVIEW Steady population growth along the northern Colorado Front Range has resulted in a shift in ownership of C-BT Project water allotment contracts from agricultural users to municipal and industrial water users. This trend parallels an increased public awareness of water quality and environmental issues and a strengthening of the regulatory framework both at the Federal and State level. The C-BT and Windy Gap Projects are major drinking water supply sources for treatment plants on the East Slope (Figure 1.2) and the monitoring, assessment, and protection of these waters is important to municipal users as they work to meet increasingly stringent drinking water treatment regulations.

In response to these developing needs, Northern Water has continuously expanded its water quality related activities over the past twenty years. The backbone of the Water Quality Program is the Baseline Monitoring Program. As new water quality challenges surface, new monitoring programs and special studies are designed and implemented to target specific areas and issues of concern.

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The C-BT and Windy Gap Projects are Water water supply sources for drinking water Treatment Plant treatment plants operated by many East with water Slope entities, including: supplies from  YMCA of the Rockies C-BT and/or  Town of Estes Park Windy Gap  Tri-Districts (Fort Collins-Loveland Projects Water District, East Larimer County Water District & North Weld County Water District)  City of Fort Collins  City of Greeley  Eden Valley Institute  Sunrise Ranch  City of Loveland  Little Thompson Water District  Central Weld County Water District  Longs Peak Water District  Carter Lake Filter Plant  Town of Berthoud  City of Longmont  Left Hand Water District  City of Boulder  Town of Erie  City of Broomfield  City of Louisville  Town of Superior  City of Fort Morgan  City of Fort Lupton

FIGURE 1.2 - MAP OF EAST SLOPE WATER TREATMENT PLANTS WITH WATER SUPPLIES FROM C-BT & WINDY GAP PROJECTS

1.2.1 Purpose of Baseline Monitoring Program The objectives of the Baseline C-BT Monitoring Program are to provide data to:

• Understand current conditions and monitor trends/changes in water quality at lake/reservoir sites and flowing sites (streams, rivers and canals);

• Assess potential water quality changes in receiving streams where C-BT Project and Windy Gap Project water is released;

• Assess compliance with state water quality standards and potential inclusions on 303(d) List of Impaired Waters or Colorado’s Monitoring & Evaluation (M&E) List;

• Support development of total maximum daily loads (TMDLs), if required;

• Support water quality modeling efforts and special studies;

• Support current and future permitting requirements;

• Assess water quality impacts from adverse events such as floods, wildfires and spills.

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This report focuses on the first objective of the Baseline Monitoring Program as it applies to the East Slope – North End sites. State water quality standards related to the monitoring sites are discussed briefly throughout applicable sections of this report. A rigorous standards compliance assessment has not been conducted for this report since it is performed internally by Northern Water on an annual basis following the Water Quality Control Division’s (WQCD) 303d listing cycle that assesses impaired waters.

1.2.2 Scope of Baseline Monitoring Program The Baseline Monitoring Program covers 55 monitoring sites in eight watersheds on both sides of the Continental Divide in Northern Colorado. There are 41 flowing sites (canals and streams) and 14 lake and reservoir sites (Figures 1.3 and 1.4). The flowing sites are located upstream and downstream of the lake/reservoirs, in the canals at points of release to the streams, and in streams at locations upstream and downstream of these release points. This program monitors for nutrients, metals, general chemistry, and physical parameters, with the additional analyses for zooplankton, phytoplankton, and chlorophyll for the lake/reservoir sites. In order to optimize resources associated with the Baseline Program, not all parameters are analyzed during every sampling event. Funding for the Baseline Water Quality Monitoring Program comes from Northern Water, and in the past, has also been partially funded by the U.S. Bureau of Reclamation.

FIGURE 1.3 - MAP OF WEST SLOPE BASELINE MONITORING LOCATIONS

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FIGURE 1.4 - MAP OF EAST SLOPE MONITORING SITES IN BASELINE PROGRAM

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The data generated by the Baseline Water Quality Monitoring Program are internally analyzed, interpreted, assessed and reported on a periodic basis by Northern Water. In this process, the collected data are turned into information about current water quality conditions, seasonal and temporal patterns, and spatial and temporal trends in a system- wide context. The data can also be developed, as it permits, into information about potential causal relationships that may underlie the seasonal and spatial patterns and trends. The reported information can be subsequently used to support water quality management, planning, regulatory, and decision-making efforts.

The Baseline Monitoring Program produced the Flowing Sites Report in 2010 which included data collected at all (West Slope and East Slope) flowing sites through WY2009. The Lake/Reservoir Sites Report was produced in 2013 and included data collected at all of the lake/reservoir sites through WY2011 (both of these reports are available for review at http://www.northernwater.org/WaterQuality/WaterQualityReports1.aspx). This East Slope – North End Report focuses on a more narrow geographical scope and provides for evaluation of Horsetooth Reservoir together with its associated upstream and downstream flowing sites.

1.2.3 QUALITY ASSURANCE/QUALITY CONTROL (QA/QC) Quality assurance/quality control (QA/QC) measures form an important, integral component of Northern Water’s Baseline Water Quality Monitoring Program. QA/QC measures are applied to sample collection, laboratory analysis, and data processing and management. The purpose of Northern Water’s QA/QC program is to ensure high quality, high integrity data and to:

• Produce data that are comparable to the USGS and other water quality programs, • Minimize data bias (systematic error introduced by sampling or analytical methods), and • Produce data that are reproducible within acceptable limits of variability.

The QA/QC measures used by Northern Water are documented in the Water Quality Monitoring Program Standard Operating Procedures Document available for review at http://www.northernwater.org/WaterQuality/WaterQualityReports1.aspx.

1.3 BASELINE MONITORING PROGRAM: EAST SLOPE – NORTH END SITES

1.3.1 SAMPLING SITES Northern Water has 13 Baseline Monitoring Program sites in the East Slope-North End geographical area (Table 1.1 and Figures 1.5 and 1.6). There are two tunnel sites, the East Portal Adams Tunnel and Olympus Tunnel. Water samples collected at the Adams Tunnel site (Figure1.6) represent the water quality of the vast West Slope collection system that is transported to the East Slope. The Olympus Tunnel site is at the downstream end of Lake Estes (Figure 1.7) and represents the combined water quality of inflows to Lakes Estes from the West Slope and from the upper Big Thompson River watershed. Water in the Olympus Tunnel eventually reaches Flatiron Reservoir where it is then released to the Hansen Feeder Canal and flows north towards Horsetooth Reservoir (Figure 1.8).

There are three sampling sites along the Hansen Feeder Canal, including one downstream of the Flatiron Reservoir outlet, one downstream of where the Dille Tunnel flows enter the canal, and one just upstream of Horsetooth Reservoir (Figure 1.9). There is one sampling site on the Hansen Supply Canal (Figure 1.10), located just upstream of where it discharges into the Poudre River (Figure 1.11) and downstream of the location where Hansen Supply Canal water is diverted to the City of Greeley Bellvue Water Treatment Plant.

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TABLE 1.1 - EAST SLOPE – NORTH END SAMPLING STATIONS.

Station Description Latitude Longitude Rationale AT-EP East Portal Adams Tunnel 40.3278 -105.5782 Quality of water from the West Slope. Quality of water after blending West Slope OLY Olympus Tunnel at Lake Estes 40.3764 -105.4858 water with upper Big Thompson River water. Hansen Feeder Canal downstream of HFC-FRD 40.3748 -105.2306 Upstream end of the Hansen Feeder Canal. Flatiron Reservoir Hansen Feeder Canal downstream of Hansen Feeder Canal below inflow of Big HFC-BT 40.4234 -105.2265 trifurcation at USGS gage Thompson River water from the Dille Tunnel

Big Thompson River upstream of 40.422 -105.2269 Hansen Feeder Canal near canyon pre-Sept pre-Sept Big Thompson River, upstream of Hansen 2013 2013 mouth by USGS gaging station Feeder Canal releases; also represents water HFC-BTU quality of Dille Tunnel diversions to the 40.41489 -105.2510 Site was moved upstream of Dille Hansen Feeder Canal. Tunnel after Sept 2013 flood. Post-Sept Post-Sept 2013 2013

Big Thompson River downstream of Big Thompson River, downstream of Hansen HFC-BTD Hansen Feeder Canal and Trifurcation 40.4258 -105.2167 Feeder Canal releases. Plant Hansen Feeder Canal at Inlet to Hansen Feeder Canal inflow to Horsetooth HFC-HT 40.5056 -105.197 Horsetooth Reservoir Reservoir. Hansen Supply Canal Release to the Quality of Hansen Supply Canal water HSC-PR 40.659 -105.2098 Cache La Poudre River released to the Poudre River. Cache La Poudre River upstream of Poudre River, upstream of Hansen Supply HSC-PRU 40.6601 -105.2094 Hansen Feeder Canal Canal releases. Cache La Poudre River downstream of Poudre River, downstream of Hansen Supply HSC-PRD 40.6606 -105.2032 Hansen Feeder Canal Canal releases. Horsetooth Reservoir at Spring Canyon HT-SPR 40.5292 -105.1456 Horsetooth Reservoir, southern end. Dam Horsetooth Reservoir at Dixon Canyon HT-DIX 40.5543 -105.1506 Horsetooth Reservoir Dam Horsetooth Reservoir at Soldier Horsetooth Reservoir, north end, near water HT-SOL 40.5888 -105.1649 Canyon Dam treatment plant intake.

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Hansen Supply Canal

Horsetooth Reservoir

Hansen Feeder Canal

Lake Estes Olympus Tunnel

Carter Lake Res

FIGURE 1.5 - MAP OF EAST SLOPE – NORTH END SAMPLING SITES.

Approx Elevation (ft) 11,000 West East Slope Slope Continental Continental Divide Divide 10,000

9,000 Willow Granby Adams Creek Res Tunnel Res Shadow Mtn Res Marys Lake 8,000 Lake Olympus & Pole & Grand Estes Lake Big Thompson Hill Tunnels River

7,000 Hansen Feeder Canal Horsetooth Reservoir 6,000 Carter Lake Res Flatiron Res

5,000 Hansen Supply Poudre River Big Thompson River Canal FIGURE 1.6 - CONCEPTUAL ELEVATION PROFILE OF EAST SLOPE – NORTH END SAMPLING SITES.

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FIGURE 1.7 - LOOKING NORTH AT LAKE ESTES.

FIGURE 1.8 - HANSEN FEEDER CANAL FLOWING NORTH OUT OF FLATIRON RESERVOIR.

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FIGURE 1.9 - HANSEN FEEDER CANAL UPSTREAM OF HORSETOOTH RESERVOIR, NEAR HFC-HT.

FIGURE 1.10 - HANSEN SUPPLY CANAL FLOWING NORTH OUT OF HORSETOOTH RESERVOIR.

FIGURE 1.11 - FLOW FROM THE HANSEN SUPPLY CANAL ENTERING THE POUDRE RIVER (MAY 2008) AT HSC-PR SAMPLING SITE.

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There are three sampling sites within Horsetooth Reservoir, located at Spring Canyon Dam, Dixon Canyon Dam and Soldier Canyon Dam (Figure 1.12). Since Horsetooth Reservoir is a relatively long (approximately 6.7 miles in length), narrow reservoir, the three sampling sites allow for the evaluation of potential water quality changes as water enters from the Hansen Feeder Canal and then flows from the south end to the north end. The intake to the City of Fort Collins Water Treatment Facility and the Tri-Districts Soldier Canyon Filter Plant are located at the north end near the bottom of the reservoir, close to Soldier Canyon Dam as represented by the HT-SOL site.

Reservoir monitoring involves the collection of samples at specific depths. For the Baseline Monitoring Program, grab samples for laboratory analyses are collected at each reservoir site near the surface, at a depth of 1 meter. Grab samples are also collected at each site at the reservoir bottom (1 meter above bottom). Chlorophyll-a samples are collected as composite samples within the top 0-5 meter depth interval. Composite samples for phytoplankton analysis are collected from the 0-5 meter depth interval to correspond to the chlorophyll-a data, and prior to WY2014 were also collected from the 5-10 meter depth interval. Composite samples for zooplankton analysis have been collected from the 0-5 meter and 5-10 meter depth interval (prior to WY2014) and from the 0-10 meter depth interval (since WY2014). Finally, sampling at each reservoir site includes the field measurement of profiles for temperature, dissolved oxygen, specific conductance, and pH measured at 1-meter to 5-meter depth increments.

HT-SPR HT-DIX

HT-SOL City of Fort Collins Tri-Districts Water Soldier Treatment Canyon Facility Water Treatment Plant

Hansen Supply Canal

FIGURE 1.12 - LOOKING SOUTH AT HORSETOOTH RESERVOIR SAMPLING STATIONS.

River sampling sites are located upstream and downstream of canal release points. Flows in the Hansen Feeder Canal can be released to the Big Thompson River, so there are associated upstream and downstream sites located

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on the Big Thompson River (Figures 1.13 and 1.14). The Hansen Supply Canal discharges to the Poudre River and associated upstream and downstream sampling sites are located on the Poudre River (Figures 1.15 and 1.16).

Hansen Feeder Canal

Big Thompson River

Dille Tunnel

HFC-BTU Hansen (post-Sept 2013 flood) Feeder Canal

FIGURE 1.13 - SAMPLING STATIONS AT THE BIG THOMPSON RIVER (HFC-BTU site was moved upstream of the Dille Tunnel after the Sept 2013 flood)

Big Thompson River Canyon Hansen Feeder Canal

Hansen Feeder HFC-BTU (pre-Sept 2013 Canal flood) Big Thompson Siphon

FIGURE 1.14 - LOOKING WEST AT BIG THOMPSON RIVER CANYON MOUTH & PRE-FLOOD HFC-BTU SAMPLING SITE. (HFC-BTU site was moved upstream of the Dille Tunnel after the Sept 2013 flood)

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Poudre River

Hansen Supply Canal

FIGURE 1.15 - HANSEN SUPPLY CANAL AND POUDRE RIVER SAMPLING SITES.

HSC-PR

HSC-PRU

FIGURE 1.16 - LOOKING SOUTH AT HANSEN SUPPLY CANAL FLOW ENTERING THE POUDRE RIVER.

WY2000-WY2015 East Slope - North End Water Quality Report 03/17/17

1.3.2 PARAMETERS & FREQUENCY The Baseline Program monitors for nutrients, metals, general chemistry, and physical (field) parameters, with the additional analyses of zooplankton, phytoplankton, and chlorophyll for Horsetooth Reservoir. The parameters and period of record (beginning in WY2000) for the East Slope – North End sites are outlined on Table 1.2. There have been changes to the parameter list over the years to address specific issues.

The canal and river sampling historically conducted by Northern Water is in addition to sampling conducted by the USGS for the Big Thompson Watershed Forum (BTWF). The data evaluated in this report (WY2000 – WY2015) includes the data from the canal and river sampling conducted by Northern Water (and by Harlan & Associates for Northern Water) as well as the data from sampling conducted by the USGS for the BTWF. Sampling conducted by the USGS for the BTWF is reflected in the period of record listed for each parameter and site in Table 2.1.

In order to optimize resources associated with the Baseline Program, not all parameters are analyzed during every sampling event. The parameters listed in Table 1.2 constitute the “long list” for the Baseline Monitoring Program sites. The “short list” includes all the field parameters and the nutrients, but does not include metals analysis for the flowing sites and only includes copper, iron and manganese for the reservoir sites, and the general chemistry analyses include fewer parameters.

The sampling frequency at Horsetooth Reservoir has been in the range of 6 to 10 events per year over the WY2005 through WY2015 period, with the current sampling frequency of 9 events per year outlined in Table 1.3 along with either an “S” or “L” to indicate the long list of parameters or the short list. The sampling frequency for the flowing sites depends on the site and is designed to capture operational flows. For example, the Hansen Supply Canal is not in operation from November through March so no sampling of this canal (HSC-PR site) is scheduled for this period. The current sampling frequency for the flowing sites is shown in Table 1.3 and ranges from 3 to 10 events per year, depending on the site. The sampling frequency shown in Table 1.3 for the flowing sites has generally been the same since WY2011, with fewer sampling events/year prior to WY2011.

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TABLE 1.2 - WATER QUALITY PARAMETERS AND PERIOD OF RECORD FOR EAST SLOPE-NORTH END SITES (listed year indicates water year that sampling began) River Sites Tunnel Sites Canal Sites Big Thom. Poudre Horsetooth Res HFC- HFC- HFC- HSC- HFC- HFC- HSC- HSC- HT- HT- HT- AT-EP OLY FRD BT HT PR BTU BTD PRU PRD SPR DIX SOL FIELD PARAMETERS Temp, D.O., Spec. Cond., pH 2000 2000 2000 2000 2000 2000 2000 2000 2000 2005 2005 2005 2005 Secchi Depth (m) ------2005 2005 2005 GENERAL PARAMETERS Alkalinity, Total Dissolved (mg/L) 2002 2002 2002 2002 2002 2002 2002 2002 2009 2009 2008 2008 2008 Chlorophyll a (mg/m3) 2005 2005 2005 Dissolved Organic Carbon (mg/L) ------2011 2011 2011 Total Organic Carbon (mg/L) 2002 2002 2002 2000 2000 2000 2000 2004 2000 2009 2005 2005 2005 UV 254 (cm-1) ------2011 2011 2011 Total Suspended Solids (mg/L) 2006 2006 2005 2000 2000 2000 2000 2005 2000 2005 2005 2005 2005 Major Ions: Ca, K, Mg, Na, Cl, SO4 2000 2000 2002 2000 2000 2000 2000 2002 2000 2005 2008 2008 2008 (mg/L) NUTRIENTS Ammonia as N (mg/L) 2000 2000 2000 2000 2000 2000 2000 2000 2000 2006 2006 2006 2006 Kjeldahl Nitrogen as N, Total (mg/L) 2000 2000 2000 2000 2000 2000 2000 2000 2004 2006 2006 2006 2006 Nitrate plus Nitrite as N (mg/L) 2000 2000 2000 2000 2000 2000 2000 2000 2000 2006 2006 2006 2006 Ortho Phosphate as P (mg/L) 2000 2000 2000 2000 2000 2000 2000 2000 2000 2006 2006 2006 2006 Phosphorus, Total (mg/L) 2000 2000 2000 2000 2000 2000 2000 2000 2000 2006 2006 2006 2006 METALS Arsenic, Dis. (ug/L) 2002 2002 2002 2002 2002 2002 2002 2002 2005 2005 2008 2008 2008 Arsenic, Total Rec(ug/L) 2006 2006 2013 2013 2013 2013 2013 2013 2013 2013 2013 2013 2013 Boron, Dis. (ug/L) 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 Cadmium, Dis. (ug/L) 2006 2006 2005 2005 2005 2005 2005 2005 2005 2005 2008 2008 2008 Chromium, Dis. (ug/L) 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 Chromium, Total Rec. (ug/L) 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 Copper, Dis. (ug/L) 2000 2000 2002 2000 2000 2000 2000 2002 2000 2005 2008 2008 2008 Iron, Dis. (ug/L) 2000 2000 2002 2000 2000 2000 2000 2002 2000 2005 2005 2005 2005 Iron, Total Rec (ug/L) 2013 2013 2005 2000 2000 2000 2000 2005 2000 2005 2008 2008 2008 Lead, Dis. (ug/L) 2002 2002 2002 2002 2002 2002 2002 2002 2005 2005 2008 2008 2008 Manganese, Dis. (ug/L) 2000 2000 2002 2000 2000 2000 2000 2002 2000 2005 2005 2005 2005 Nickel, Dis. (ug/L) 2000 2000 2002 2002 2002 2002 2002 2002 2005 2005 2008 2008 2008 Selenium, Dis. (ug/L) 2005 2005 2005 2004 2004 2004 2004 2005 2004 2005 2008 2008 2008 Silver, Dis. (ug/L) 2002 2002 2002 2000 2000 2000 2000 2002 2000 2005 2008 2008 2008 Uranium, Dis. (ug/L) 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 2014 Zinc, Dis. (ug/L) 2000 2000 2005 2000 2000 2000 2000 2005 2000 2005 2008 2008 2008 BIOLOGICAL Phytoplankton, Density (cells/mL) & ------2005 2005 2005 Biovolume (um3/mL): 0-5 m & 5-10 m Zooplankton (#/L): 0-5 m & 5-10 m ------2005 2005 2005

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TABLE 1.3 - SAMPLING FREQUENCY (S = short list of parameters; L = long list of parameters) Total No Site Station Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep of Type Events/yr AT-EP Tunnel S S L S S L L S S L 10 OLY Tunnel S S L S S L L S S L 10 HFC-FRD Canal S S L S S L L S S L 10 HFC-BT Canal S S L S S L L S S L 10 HFC-BTU River L L L S S L 6 HFC-BTD River S S L S L L S S L 9 HFC-HT Canal S S L S S L L S S L 10 HSC-PR Canal S S L L S S L 7 HSC-PRU River L L L 3 HSC-PRD River S S L L S S L 7 HT-SPR Reservoir L S L S S L S S S 9 HT-DIX Reservoir L S L S S L S S S 9 HT-SOL Reservoir L S L S S L S S S 9

1.3.3 SAMPLE COLLECTION AND LABORATORY ANALYSIS The flowing sites water quality data evaluated in this report (WY2000 – WY2015) were collected by Northern Water Field Services (NWFS), the United States Geological Survey (USGS) and Harlan & Associates.

Six C-BT tunnel/canal sites (AT-EP, OLY, HFC-FRD, HFC-BT, HFC-HT, and HSC-PR) were originally all part of the Big Thompson Watershed Forum (BTWF) monitoring network. In 2009, the Hansen Supply Canal site (HSC-PR) was removed from the BTWF USGS monitoring program, while in 2011, the other five sites were removed from the BTWF USGS monitoring program to reduce financial burdens on the Forum. Since being removed from the BTWF USGS Program, sampling at four of these stations has been conducted by NWFS (HFC-FRD, HFC-BT, HFC- HT, and HSC-PR). Sampling at the two tunnel stations (AT-EP and OLY) has been continued by the USGS under a Joint Funding Agreement with Northern Water.

Harlan & Associates was contracted by Northern Water to collect samples at the canal and river sites from WY2000 through WY2006. Northern Water Field Services has been collecting samples at the canal and river sites since WY2007. The canal and river sampling conducted by Northern Water and Harlan & Associates is in addition to sampling conducted by the USGS for the BTWF. The data evaluated in this report (WY2000 – WY2015) includes the data from the canal and river sampling conducted by Northern Water and Harlan & Associates as well as the data from sampling conducted by the USGS for the BTWF.

Northern Water’s Baseline Monitoring Program for the lake/reservoir sites began in 2005, including Horsetooth Reservoir. The U.S. Bureau of Reclamation Technical Service Center (Denver) collected the lake/reservoir water samples for the Baseline Monitoring Program from WY2005 through WY2007 (Lieberman, 2008) with samples submitted to USBR laboratories. In WY2008, the USBR Technical Service Center shared the sampling of the lake/reservoirs sites with the USGS, with the USGS collecting the Jan-March 2008 samples. In WY2009, the

WY2000-WY2015 East Slope - North End Water Quality Report 03/17/17

lake/reservoir sampling was conducted by the USGS. From WY2010-WY2014, reservoir sampling for the Baseline Monitoring Program was split between NWFS and the USGS. The Horsetooth Reservoir sites were sampled by NWFS except for the winter events (December through April) which are sampled by the USGS or NWFS, depending on ice cover. Beginning in WY2015, all sampling of Horsetooth Reservoir is conducted by NWFS.

The sampling protocols used by NWFS for the flowing sites and the lake/reservoir sites are documented in Standard Operating Procedures (SOPs) for Northern Water’s Water Quality Monitoring Programs (Northern Water, 2016); http://www.northernwater.org/WaterQuality/WaterQualityReports1.aspx. The sample collection protocols are guided by the U.S. Geological Survey’s "National Field Manual for the Collection of Water-Quality-Data" (U.S. Geological Survey, variously dated), including the ‘clean hands, dirty hands’ technique. Implementation of Northern Water’s SOPs provide for consistency in sample collection and minimizes the chance of contamination during the sampling process, and are part of Northern Water’s overall quality assurance/quality control program.

Laboratory analysis has evolved over the years with changing labs, analytical methods and detection limits (Tables 1.4 and 1.5). Samples are currently sent to USGS-certified private laboratories for analysis, including High Sierra Water Lab for nutrients (since WY2008) and Huffman-Hazen Laboratories (since WY2009) for metals, major ions, and total organic carbon (Table 1.3). Analytical methods with low level detection limits are used at these labs for metals and nutrients. Samples collected by the USGS at the Big Thompson River sites for the BTWF Program are still analyzed by the USGS National Water Quality Lab (these samples are collected in addition to samples collected at HFC-BTU and HFC-BTD by Northern Water), while samples currently collected by the USGS at the tunnel sites are analyzed by Northern Water’s labs.

Nutrient analysis for samples collected by Harlan & Associates and Northern Water prior to WY2008 was conducted by Acculabs (WY2000-WY2001), Severn Trent Laboratories (WY2002-WY2004), USBR Denver (WY2004), USBR Boulder, NV (WY2005-WY2006), and USBR Boise (WY2006-WY2007). For samples collected by the USGS, the analysis period for nutrients by the USGS National Water Quality Lab has varied by site, including Adams Tunnel and Olympus Tunnel sites, WY2000 through WY2007; canal sites (samples collected for the BTWF Program) through WY2010; and Big Thompson River sites collected for the BTWF Program through WY2015.

Metals, major ions and TOC analyses for samples collected by Harlan & Associates and Northern Water prior to WY2009 were conducted by Acculabs (WY2000-WY2001), Severn Trent Laboratories (WY2002-WY2004), ACZ (WY2005-WY2008), and USBR Boise (WY2005-WY2007, iron and manganese in Horsetooth Reservoir only). For samples collected by the USGS, the analysis period for these parameters by the USGS National Water Quality Lab has varied by site, including Adams Tunnel and Olympus Tunnel sites, WY2000 through WY2011; canal sites (samples collected for the BTWF Program) through WY2010; Big Thompson River sites (collected for the BTWF Program) through WY2015; and Horsetooth Reservoir March, Oct, and Nov 2008 sampling only. TOC analysis for samples collected by the USGS for the BTWF Program has been conducted by the City of Fort Collins Water Quality Lab since WY2002.

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TABLE 1.4 - LABORATORIES AND ANALYTICAL METHODS FOR WY2000 – WY2015 EAST SLOPE – NORTH END DATA (see National Environmental Methods Index NEMI for analytical method descriptions at

https://www.nemi.gov/home/ )

WY2015 WY2015

SM 5310C SM

City of Fort Fort of City

CollinsWQL

SM 10200 H.2 10200 SM

TOC: WY2002- TOC:

chl-a: WY2015 WY2015 chl-a:

(IC)

WY2015

SM 5910 SM

(ICP-MS)

WY2009-

Huffman Huffman

(ICP-AES)

SM 5310C SM

SM 2320B SM

EPA 200.8 200.8 EPA

EPA 300.1 300.1 EPA

EPA 200.7 200.7 EPA

EPA 160.2 EPA

Hazen Lab Hazen

ACZ

WY2008

or 375.4 or

WY2005-

(ICP-AES)

EPA 200.7 200.7 EPA

SM 2540D SM

EPA 415.1 EPA

EPA 160.2/ 160.2/ EPA

(ICP) or EPA(ICP) or

Cl: EPA 325.2; 325.2; Cl:EPA

200.8 (ICP-MS) 200.8

SO4: EPA 375.3 375.3 EPA SO4:

Lab

High High

Sierra Sierra

Water Water

WY2015

WY2008-

modified

EPA 365.3 EPA

EPA 353.1 353.1 EPA

EPA 351.2 351.2 EPA

EPA 350.1 350.1 EPA

EPA 160.2 EPA

SM 4500-PE SM

only

WY2007

WY2005-

SM 3111B 3111B SM

SM 5310B SM

EPA 365.1 EPA

EPA 353.2 EPA

EPA 351.2 EPA

EPA 350.1 EPA

EPA 160.2 EPA

EPA 415.1/ 415.1/ EPA

manganese

USBR Boise USBR

(AA); iron&

USBR USBR

WY2006

WY2005-

Boulder, Boulder,

EPA 365.1 EPA

EPA 353.2 EPA

EPA 351.2 EPA

EPA 350.1 EPA

WY2014

WY2005 - WY2005

SM 10200 H.2 10200 SM

USBR Denver USBR

WY2004

EPA 365.1 EPA

EPA 353.2 EPA

EPA 351.2 EPA

EPA 350.1 EPA

AES)

WY2004

(ICP-MS)

WY2002-

EPA 365.3 EPA

EPA 300.0 EPA

EPA 353.2 EPA

EPA 350.1 EPA

EPA 160.2 EPA

EPA 415.1 EPA

or EPA 200.8 200.8 EPA or

Severn Trent Severn

EPA 300.0 (IC) 300.0 EPA

EPA 200.7 (ICP- 200.7 EPA

EPA 200.7 (ICP) 200.7 EPA

USGS USGS

WQ Lab WQ

National National

I-2522-90

I-2546-91

I-4515-91

I-2057-90

I-3765-85

I-2030-85

I-2522-90

EPA 365.1 EPA

I-2525-89; I-2525-89;

SM 5310B SM

I-4610-91; I-4610-91;

I-2525-89; I-2525-89;

O-3100-83; O-3100-83;

USGS Methods: USGS

WY2000 - WY2015 -WY2015 WY2000

I-2020-05 (cICP-MS) I-2020-05

I-2477-92 (ICP-MS); (ICP-MS); I-2477-92

I-1630-85 (AA K)for I-1630-85

I-1472-87 (ICP-AES); (ICP-AES); I-1472-87

I-1472-87 (ICP-AES); I-1472-87

I-2601-90; I-2606-89; I-2606-89; I-2601-90;

MS)

WY2001

WY2000-

Acculabs Acculabs

(ICP-AES)

EPA 200.7 200.7 EPA

EPA 365.2 EPA

EPA 353.2 EPA

EPA 350.3 EPA

300.1 (IC) 300.1

EPA 200.7 200.7 EPA

EPA 160.2 EPA

EPA 415.1 EPA

200.8 (ICP- 200.8

(ICP) EPA or

EPA 300.0 or or 300.0 EPA

Time Period: Period: Time

(approximate)

Laboratory:

AA = Atomic Absorption= AA

IC Ion = Chromatography

ICP-AES = InductivelyICP-AES = Coupled Plasma - Atomic Emission Spectrometry

ICP-MS Inductively = Coupled Plasma - Mass Spectrometry

See https://www.nemi.gov/home/ for descriptions https://www.nemi.gov/home/ See of methods

Metals

METALS

Phosphorus,(mg/L) Total

(mg/L)

Ortho PhosphateP Ortho as

(mg/L)

Nitrate + NitriteNitrate N+ as

(mg/L)

Total KjeldahlTotal N N. as

Ammonia as N (mg/L)AmmoniaN as

NUTRIENTS

(mg/L)

Major Anions: Cl, SO4 Major

Na, K (mg/L)KNa,

Major Cations: Ca, Mg, Mg, Cations:Ca, Major

Total Sus.SolidsTotal (mg/L)

UV 254 (cm-1) 254 UV

(mg/L)

Total Organic Carbon Carbon Organic Total

(mg/L)

Dis. Organic Carbon Carbon Dis. Organic

Chlorophyll(mg/m3) a Alkalinity(mg/L) GENERAL PARAMETERS GENERAL

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TABLE 1.5 - LABORATORIES AND MDLS (METHOD DETECTION LIMITS) FOR WY2000 – WY2015 EAST SLOPE – NORTH END DATA High City of USGS USBR Severn USBR Sierra Huffman Fort Laboratory Acculabs National USBR Denver Boulder, ACZ Trent Boise Water Hazen Lab Collins WQ Lab NV Lab WQ Lab TOC: WY2002- Time Period WY2000- WY2000 - WY2002- WY2005 - WY2005- WY2005- WY2008- WY2005- WY2009- WY2004 WY2015 (approximate) WY2001 WY2015 WY2004 WY2014 WY2006 WY2007 WY2015 WY2009 WY2015 chl-a: WY2015 RL = Reporting Limit MDL = Method Detection RL MDL MDL MDL MDL MDL MDL MDL MDL MDL RL Limit GENERAL PARAMETERS Alkalinity (mg/L) 1 - 5 1 Chlorophyll a (mg/m3) 0.1 0.5 Dis. Organic Carbon 0.2 0.02 (mg/L) Total Organic Carbon 1 0.2 - 0.3 0.3 - 0.5 0.2 1 0.02 0.5 (mg/L) UV 254 (cm-1) 0.001 Total Sus. Solids (mg/L) 5 10 - 15 0.9 - 1.8 1 0.3 (after 5 1 WY2012) Calcium (mg/L) 0.05 - 0.1 0.005 - 0.02 0.03 - 0.1 0.2 0.003 Magnesium (mg/L) 0.05 0.003 - 0.01 0.02 - 0.03 0.2 0.001 Sodium (mg/L) 0.1 - 0.5 0.03 - 0.1 1.1 0.3 0.01 Potassium (mg/L) 0.3 - 1.5 0.01 - 0.11 0.5 0.3 0.03 Chloride (mg/L) 0.5 0.03 - 0.17 0.1 - 0.2 1 0.03 Sulfate (mg/L) 1 0.05 - 0.15 0.1 - 0.2 1 - 10 0.03 NUTRIENTS

Ammonia as N (mg/L) 0.04 - 0.1 0.005-0.02 0.015 - 0.03 0.003 0.003 0.003 0.001

Total Kjeldahl N. as N 0.025 - 0.07 0.05 0.05 0.03 0.035 (mg/L) Nitrate + Nitrite as N 0.05 0.004 - 0.05 0.01 - 0.02 0.003 0.003 0.001 (mg/L) Ortho Phosphate as P 0.01 0.001 - 0.01 0.04 - 0.1 0.001 0.001 0.001 0.001 (mg/L) Phosphorus, Total (mg/L) 0.01 0.002 - 0.03 0.01 - 0.02 0.003 0.003 0.003 0.001 METALS Arsenic, Dis. (ug/L) 0.02 - 0.13 0.5 0.005, 0.03 Arsenic, Total Rec(ug/L) 0.06 - 0.3 0.1, 0.4 Boron, Dis. (ug/L) 7 0.01 Cadmium, Dis. (ug/L) 0.008 - 3 0.1 0.005, 0.01 Chromium, Dis. (ug/L) 7 0.03 Chromium, Total Rec. 0.2, 1 (ug/L) Copper, Dis. (ug/L) 1 0.12 - 10 0.095 - 0.25 0.5, 1, 10 0.02, 0.03 Iron, Dis. (ug/L) 10, 100 1.6 - 5 13, 19 20 10, 20 0.04, 0.06, 0.6 Iron, Total Rec (ug/L) 10, 100 3, 7 13, 19 10, 20 0.04, 1.8 Lead, Dis. (ug/L) 0.015 - 50 0.1 0.003, 0.004 Manganese, Dis. (ug/L) 3, 5 0.05 - 1.1 0.5 10 5 0.02 Nickel, Dis. (ug/L) 0.03 - 20 0.6, 10 0.02 Selenium, Dis. (ug/L) 0.02 - 0.2 0.004 0.1, 1 0.02 Silver, Dis. (ug/L) 0.1 0.004 - 3.5 0.016, 0.026 0.05 0.003, 0.005 Uranium, Dis. (ug/L) 0.003 Zinc, Dis. (ug/L) 3, 5 0.3 - 10 1.4, 2.4 10 0.1, 0.2

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1.4 COLLABORATIVE ROUTINE MONITORING

1.4.1 MONITORING OF THE BIG THOMPSON RIVER: BIG THOMPSON WATERSHED FORUM The Big Thompson Watershed Forum (BTWF) is a nonprofit stakeholder organization founded in 1997 and dedicated to protecting and improving water quality in the Big Thompson watershed (see http://btwatershed.org/). Northern Water is a major financial contributor to the BTWF and a Northern Water representative serves on the BTWF Board of Directors.

One of the BTWF’s key objectives is the collaborative monitoring and assessment of water quality in the Big Thompson River. The BTWF has historically had two monitoring programs: the U.S. Geological Survey (USGS) Cooperative (COOP) Program (August 2000 - present) and the U.S. Environmental Protection Agency (EPA) Volunteer Program (2001 - 2015).

The BTWF USGS COOP Program is a Joint Funding Agreement (JFA) with its major funders (City of Fort Collins, City of Greeley, City of Loveland, Northern Water and Tri-Districts Soldier Canyon Filter Plant) and the USGS. For this program, USGS personnel collect all samples and analyses have been split between three labs. The USGS National Water Quality Lab analyzes for metals, nutrients and physical parameters, the City of Fort Collins Water Quality Lab analyzes for total organic carbon and chlorophyll a, and the City of Loveland Water Quality Lab analyzes for E. Coli and total coliforms.

The BTWF USGS COOP Program includes 15 sites, with 12 mainstem Big Thompson River sites extending from Moraine Park in Rocky Mountain National Park to the confluence with the South Platte River, and three tributary sites, the North Fork, Buckhorn Creek, and Little Thompson River. Six C-BT Project tunnel/canal stations are also considered part of the COOP Program, and were originally sampled as part of the COOP Program. However, they were removed from the COOP Program to reduce financial burdens on the BTWF. Since that time, sampling at four of these stations (HFC-FRD or BTWF C30; HFC-BT or BTWF C40; HFC-HT or BTWF C50; HSC-PR or BTWF C120) has been conducted by Northern Water, while sampling at the other two stations (AT-EP or BTWF C10; and OLY or BTWF C20) was continued by the USGS under a Joint Funding Agreement with Northern Water.

River samples collected at BTWF USGS COOP Program monitoring sites that are upstream of the Dille Tunnel provide data that supplement the sites in Northern Water’s Baseline Program. USGS COOP sites above Lake Estes, below Lake Estes and above the Dille Tunnel are locations where changes in water quality can influence the water quality in the C-BT Project conveyances. The BTWF USGS COOP data is used to help evaluate influences on changing water quality conditions.

1.4.2 CITY OF FORT COLLINS COOPERATIVE MONITORING OF HORSETOOTH RESERVOIR City of Fort Collins staff began collecting water quality samples from Horsetooth Reservoir by boat at four sampling locations in 1996, with sampling conducted by others for them beginning in 1988. Three of the City’s routine sites are the same as those in Northern Water’s Baseline Program: HT-SPR (City of Fort Collins R-21), HR-DIX (City of Fort Collins R-30), and HT-SOL (City of Fort Collins R-40). The City of Fort Collins conducted a comparison of the 2005-2012 Horsetooth Reservoir water quality data collected by the two programs. The comparison showed consistent data sets within acceptable difference ranges that provide for similar conclusions about the quality of water in the reservoir. Northern Water and the City of Fort Collins both concluded that maintaining the two sampling efforts was redundant, inefficient, and not an optimal use of resources.

In 2015, a Memorandum of Agreement (MOA) was signed by the two entities for the joint monitoring of Horsetooth Reservoir water quality. The MOA specifies that the field sampling will be conducted by Northern Water staff, and laboratory analysis will be conducted at the laboratories used in Northern Water’s Baseline Program, except for

WY2000-WY2015 East Slope - North End Water Quality Report 03/17/17

chlorophyll-a. As part of the MOA, the City of Fort Collins conducts the chlorophyll-a analysis for the Horsetooth Reservoir samples as well as for all other samples in Northern Water’s Program that require chlorophyll-a analysis. This cooperative monitoring of Horsetooth Reservoir began in 2015.

1.5 REPORT OBJECTIVES AND SCOPE The purpose of this report is to characterize the water quality conditions in Horsetooth Reservoir and the flowing waters (rivers and canals) of the C-BT system from the Adams Tunnel east to Flatiron Reservoir, and then north to Horsetooth Reservoir and the Poudre River as revealed by data collected for the Baseline C-BT Monitoring Program during the 16-year period WY2000 through WY2015. This characterization is an update of the data summary and findings presented in two previous Northern Water reports, the 2010 Flowing Sites Report (covering WY2000 – WY2009) and the 2013 Lake and Reservoirs Report (covering WY2005 – WY2011); http://www.northernwater.org/WaterQuality/WaterQualityReports1.aspx.

Watershed features, significant events, water quality concerns and special studies associated with the East Slope – North End sites are discussed in Section 3 of this report to provide context for the observed data and to help focus the data analyses and interpretation. Hydrology and system operations related to the East Slope – North End are summarized in Section 4. The water quality parameters are generally classified into five categories (Table 1.2) and are discussed in Sections 5 through 9 of this report:

• Field Parameters (Section 5): Grab sample data for the flowing sites and Horsetooth Reservoir depth profiles of temperature, dissolved oxygen, specific conductance and pH, and Horsetooth Reservoir Secchi depth data.

• General Chemistry (Section 6): alkalinity, total organic carbon (TOC), total suspended solids (TSS), and major ions, plus dissolved organic carbon (DOC) and UV254 for the Horsetooth Reservoir sites.

• Nutrients (Section 7): ammonia, nitrate plus nitrite, total Kjeldahl nitrogen (TKN), ortho-phosphate and total phosphorus

• Metals (Section 8): all collected metals data is presented, including arsenic, boron, cadmium, chromium, copper, iron, lead, manganese, nickel, selenium, silver, uranium and zinc

• Horsetooth Reservoir Biological Parameters (Section 9): phytoplankton, chlorophyll-a and zooplankton

Graphical and statistical methods are used to characterize spatial and seasonal patterns and temporal trends in the water quality data. A comparison to water quality standards is made to provide a frame of reference and some context for the observed data, but a rigorous standards compliance assessment is not included here. From this data analysis, review, and reporting process, the primary goal is to turn the collected data into information that can be subsequently used to help support water quality management, regulatory, and decision-making efforts by Northern Water and its stakeholders.

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2. METHODS FOR DATA ANALYSIS

The field and laboratory data collected for the Baseline Water Quality Program are subject to a QA/QC review (as outlined in Section 7 of Northern Water’s Water Quality Monitoring SOP Document; http://www.northernwater.org/WaterQuality/WaterQualityReports1.aspx) and then housed in Northern Water’s SQL relational database. After extracting data from the database, it was analyzed for this report using the methods described in Section 2.0. Note that the data presented and summarized in this report can be accessed and retrieved by outside users at http://www.northernwater.org/DynData/WQDataMain.aspx.

2.1 HANDLING OF NON-DETECT DATA A method detection limit (MDL) is usually defined as the lowest concentration that can be reported that reliably measures the presence of a given constituent in a water sample. It is specific to the method and instrumentation used in analysis and can change over time. A reporting limit (RL) is slightly higher than the MDL and is the lowest concentration that can be reported with confidence, also specific to the method and instrumentation used in analysis. Concentrations between the MDL and RL are reported as estimated. Concentrations lower than the MDL are reported as non-detects or “less-thans” (for example, <1.0 µg/L).

There are various ways to handle non-detect data for use in data analysis. Two of the more common methods are substitution of the non-detect with either the MDL or half of the MDL. Setting the non-detect values equal to the MDL is generally a more conservative approach to water quality assessment. This method will artificially shift the data toward higher concentrations, especially when the MDL is significantly greater than the natural concentrations found in the water body. For this report, the non-detects were set equal to the MDL for data analysis, including construction of box-plots and the trend analysis.

When data are recorded as non-detects rather than a single numerical value, there is some impact on statistical and graphical analysis, depending on the fraction of non-detects in the record. If the fraction of non-detects is small, then the impact on summary and other statistics will be small as well. For low-level constituents (such as some trace metals), however, the fraction of non-detects may be greater than 50%, in which case the median will be a non- detect and will take on whatever numerical value is assigned to non-detects.

The effect of non-detects on data analysis is most problematic when the detection limit changes over time due to changes in laboratory or analytical methods. Most commonly the detection limit will decline over time due to improvements in laboratory analytical methods or a change in the laboratory doing the analysis. This can result in falsely apparent decreasing trends in water quality time series simply due to decreasing detection limits over time.

A list of the laboratories, methods, and method detection limits that apply to this report were presented in Tables 1.4 and 1.5. The implementation of low level metals analysis began in WY2009, resulting in a significant reduction in MDL’s for all metals.

2.2 DATA REVIEW AND ANALYSIS TOOLS The data analyses conducted for this report consist of basic graphical and statistical procedures to reveal spatial and temporal patterns and trends in the existing data. The methods include:

• Time series plots • Bar graphs • Box-and-whisker plots (monthly, annual and spatial) • Basic summary statistics • Seasonal Kendall Test for monotonic changes in concentration over time

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The statistical procedures used in the study are mostly nonparametric methods (not assuming a normal or other distribution shape) and are therefore “robust” or relatively uninfluenced by outliers. These procedures are, therefore, particularly appropriate for use with environmental data, which tend to contain outliers. The time series plots and boxplots were constructed using the Minitab® statistical analysis package, while the trend analysis was conducted using R.

2.2.1 GRAPHICAL ANALYSES

RESERVOIR DEPTH PROFILE PLOTS Field measurements of temperature, dissolved oxygen, specific conductivity, and pH are collected at 1- to 5-meter depth increments from the reservoir surface to near the reservoir bottom. The parameters are plotted for each reservoir as a function of depth (depth profiles) and allow for the examination of annual patterns of thermal stratification, mixing, interflows, and depletion of dissolved oxygen at the middle or bottom portions of the reservoir. Depth profiles from WY 2005 to WY 2015 are included in Appendix B, organized by parameter and site.

TIME SERIES PLOTS Time series plots of the water quality observations versus date are the starting point for water quality data analysis. These plots are effective for revealing random variability, seasonal patterns, longer-term trends, and outliers. Time series plots are also the best way to indicate when samples were collected, how sampling frequencies have changed over time, how detection limits have changed over time, and what data gaps exist. Connecting lines are used in the time series plots to highlight seasonal patterns and better indicate the order of the points. The lines are not meant to suggest that water quality can be interpolated between the observations or that there is a statistically significant trend. They are only intended to provide a visual aid in interpretation of the data. In this report, time series plots were prepared for data collected from WY 2000 to WY 2015, and are included in Appendix C. However, note that for many sampling sites and parameters, the period of record is shorter.

BAR GRAPHS Bar graphs are used for visual portrayal and comparison of concentrations of constituents across multiple locations or times without the indication of variability or spread in the data that is included in box-and-whisker plots. Stacked bar graphs are used to break down the contribution of individual components for a given bar. For example, the contribution of the various major ions to the total is concisely illustrated by a stacked bar graph as shown in Figure 2.1.

Major Ions (mg/L) June 2012 55 Cl (mg/L) 50

45 SO4 (mg/L) 40 HCO3 (mg/L) 35

30 K (mg/L) 25

20 Na (mg/L) Concentrationmg/Lin

15 Mg (mg/L) 10

5 Ca (mg/L)

0 1 1 b 1 b b ------EP BT PR HT - - - - OLY FRD BTD BTU PRD PRU - - - - - DIX DIX AT SPR SPR SOL SOL ------HFC HSC HFC HFC HFC HFC HSC HT HSC HT HT HT HT HT FIGURE 2.1 - STACKED BAR GRAPH.

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BOX-AND-WHISKER PLOTS Box-and-whisker plots (also called boxplots) contain a great deal of information about the distribution of the data within particular groups, such as sites or seasons. Boxplots are easy to use for comparing groups against one another, i.e. for revealing seasonality or trends over time or space. A crude test for significance of change between two groups can be performed by examining whether the Construction of Boxplots boxes for the two groups overlap.

Outliers In this type of plot, each box and set of whiskers corresponds to one group, such as a month, year or End of Upper Whisker site (Figure 2.2). The box corresponds to the middle Extends to highest data point that occurs within an upper limit given by: 50% of the data in that group. The bottom of the Q3 + 1.5(Q3 – Q1). box represents the 25th percentile, the horizontal line th 75th Percentile (Q3) within the box indicates the median or 50 percentile, and the top of the box represents the 75th middle percentile. The whiskers extend to representative 50% extreme values of the group, which can be the of the Median or 50th Percentile data minimum and maximum, the 5th and 95th percentiles, or other values. 25th Percentile (Q1)

End of Lower Whisker Extends to lowest data point that occurs within a lower limit given by: Q1 - 1.5(Q3 – Q1).

FIGURE 2.2 - CONSTRUCTION OF BOXPLOTS

Minitab extends the upper whisker to the highest value within an upper limit defined as:

Upper limit = Q3 + 1.5 (Q3 - Q1)

th th where Q3 is the third quartile or 75 percentile value, and Q1 is the first quartile or 25 percentile value. The lower whisker extends to the lowest value within a lower limit defined as:

Lower limit = Q1- 1.5 (Q3 - Q1)

Note that the distance (Q3-Q1) is equal to the length of the box. Individual values beyond the whiskers can be individually plotted or not as the user chooses. Because Minitab uses an actual data point rather than a percentile as the end of each whisker, in rare instances, a whisker may extend inward from the end of the box rather than outward. This problem is most likely to occur when sample sizes are small.

This report includes boxplots by month to reveal seasonal patterns (Appendix D). Figure 2.3 is an example of a monthly boxplot. Annual boxplots (Appendix E) have also been constructed for this report to help reveal patterns or trends that may have occurred over the period of record. The date range summarized in the monthly, annual and spatial boxplots depends on the parameter and site. For some sites and parameters, boxplots were constructed using a subset of the data, with some data and parameters excluded due to high detection limits that resulted in many non-detected values that skew the boxes. Data excluded from the boxplots are summarized on Table 2.1.

It should be noted that the number of individual data points that are summarized by each box in the boxplots is highly variable between sites, parameters, months and years. Each box on a graph will generally be constructed from a different number of data points than the other boxes on the graph. This is shown on Figure 2.3 which displays the boxes with the data points used to construct the boxes.

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FIGURE 2.3 - MONTHLY BOXPLOTS WITH DATA POINTS (open circles).

Boxplots by station (Appendix F) are included to reveal spatial patterns from sampling station to sampling station using data from the same time period ranges as the monthly and annual boxplots. The stations are organized in terms of direction of flow during operation of the C-BT and Windy Gap Projects, from the East Portal of the Adams Tunnel to the Hansen Supply Canal to Horsetooth Reservoir and, finally, the Hansen Supply Canal and Poudre River sites. Figure 2.4 shows an example of a spatial boxplot. In this figure, the medians of the boxes are connected by a line to help further reveal the spatial patterns.

FIGURE 2.4 - SPATIAL BOXPLOT.

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TABLE 2.1 - DATA EXCLUDED FROM BOXPLOTS & SEASONAL KENDALL TREND ANALYSIS. Group Parameter Description of excluded data Data excluded from trend analysis & all boxplots due to high detection limits with many/all non-detects: General Major Ions • Potassium data from Acculabs 5/2001 to 7/2001 (MDL = 1.5 mg/L) • Sulfate data from ACZ Lab 5/2005 through 4/2008 (MDL = 10 mg/L) TOC Trend analysis not conducted for HSC-PRD since period of record begins in 2009. Trend analysis not conducted for TSS due to changing detection limits & high values near end of TSS period due to flood; boxplots constructed with data later than 2008 only. Data excluded from trend analysis & all boxplots due to high detection limits with many/all non-detects: Nutrients • Acculabs 5/00 to 9/01 ( RL = 0.1 or 0.04 mg/L) Ammonia • USGS National Water Quality Lab 12/99 to 8/00 with MDL = 0.02 mg/L (NH3) • USGS National Water Quality Lab AT-EP 10/01 to 1/08 (MDL = 0.005, 0.008, 0.01 mg/L) • Severn Trent Lab 5/02 to 10/03 (MDL = 0.015 or 0.029 mg/L, RL = 0.04 mg/L) Data excluded from trend analysis & all boxplots due to high detection limits with many/all non-detects: Nitrate (NO3) • Acculabs 5/00 to 9/01 ( RL = 0.05 mg/L) • USGS National Water Quality Lab 12/99 to 8/00 with MDL = 0.05 mg/L Data excluded from trend analysis & all boxplots due to high detection limits with many/all non-detects: • Acculabs 5/00 to 9/01 ( RL = 0.01) Ortho-P • USGS National Water Quality Lab AT-EP & OLY 12/99 to 8/00 (MDL = 0.01 mg/L) • Severn Trent Lab 5/02 to 10/03 (MDL = 0.04 or 0.1 mg/L) Total P Data excluded from trend analysis & all boxplots due to high detection limits with all non-detects: • USGS National Water Quality Lab AT-EP & OLY 12/99 to 8/00 (MDL = 0.03 mg/L) Arsenic (tot), Arsenic (total), Boron, Chromium (dis & total) & Uranium data excluded from annual boxplots & Metals Boron, trend analysis due to short period of record (beginning in WY2013 or WY2014); early USGS NWQL Chromium, data for Boron & Chrom (dis) at AT-EP & OLY excluded due to high detection limits. Uranium Cadmium, Excluded from annual boxplots & trend analysis due to high number of non-detects & changing Lead, Silver detection limits. Data excluded from trend analysis & all boxplots due to high detection limits with all non-detects: Arsenic, dis • ACZ Lab 7/05 to 1/09 (MDL = 0.5 ug/L) Data excluded from trend analysis & all boxplots due to high detection limits with many/all non-detects: • USGS National Water Quality Lab AT-EP & OLY 12/99 to 8/00 (MDL = 10 ug/L) Copper, dis • ACZ Lab 5/16/06 and 6/10/08 (MDL = 10 ug/L) • Acculabs 5/00 to 9/01 ( RL = 1 ug/L) Iron, dis Data excluded from trend analysis & all boxplots due to high detection limits with many/all non-detects: • Acculabs 5/01 to 9/01 with RL = 100 ug/L Iron, total AT-EP and OLY excluded from trend analysis due to short period of record (10/2012 to 9/2015)

Data excluded from trend analysis & all boxplots due to high detection limits with many non-detects: • Acculabs 5/00 to 9/01 with RL = 3 - 5 ug/L Manganese, • ACZ Lab 5/05 to 1/09 with MDL = 5 ug/L dis • USGS National Water Quality Lab AT-EP 12/99 to 8/00 (MDL = 1.1 ug/L) • USBR Boise Lab - Horsetooth Res bottom sites 5/05 to 10/07 (MDL = 10 ug/L) Data excluded from trend analysis & all boxplots due to high detection limits with many non-detects: Nickel, dis • ACZ Lab 7/05 to 1/09 (MDL = 10 ug/L) • USGS National Water Quality Lab AT-EP & OLY 12/99 to 8/00 (MDL = 20 ug/L) Data excluded from trend analysis & all boxplots due to high detection limits with many non-detects: Selenium, dis • ACZ Lab 7/05 to 9/05 (MDL = 1 ug/L) & 4/06 to 1/09 (MDL = 0.1 ug/L) • USGS National Water Quality Lab 2/05 to 8/05 (MDL = 0.2 ug/L) Data excluded from trend analysis & all boxplots due to high detection limits with many non-detects: • Acculabs 5/00 to 9/01 (RL = 3 - 5 ug/L) Zinc, dis • ACZ Lab 7/05 to 1/09 (MDL = 10 ug/L) • USGS National Water Quality Lab AT-EP & OLY 12/99 to 8/00 (MDL = 10 ug/L) • USBR Boise Lab - Horsetooth Res bottom sites 5/05 (MDL = 5 ug/L)

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2.2.2 STATISTICAL ANALYSIS

BASIC SUMMARY STATISTICS Basic summary statistics are calculated for each water quality variable and site to provide quantitative measures of both central tendency and variability. These include:

• Mean (average) • Period of record • Min & max MDL • Median (50th percentile) • Number of Values • Min detected value • Number of non-detected • Standard Deviation • Max detected value values • Date of max detected value • Percent detected

Tables of summary statistics are provided in Appendix A.

TREND ANALYSIS Statistical analysis of water quality data includes the determination of the statistical significance and magnitude of time trends to address the questions of whether and how much water quality has changed over the period of record. The Seasonal Kendall Test for trend is used here to provide a quantitative test for the statistical significance of trends in the concentration time series data (Hirsch et al, 1982). The Seasonal Kendall slope estimator (a generalization of Sen’s estimator of slope) is used to estimate the trend magnitude over the period of record (Hirsch et al, 1982). These non-parametric procedures are commonly used for water quality data since they are not sensitive to outliers or non-detected values, not dependent on assumptions about the data distribution, and allow for the existence of missing data over the period of record.

The Seasonal Kendall Test is a test for monotonic changes in a data series (i.e., a change in only one direction, increasing or decreasing). The test accounts for seasonality by applying the Mann-Kendall test separately on each season, and then summing the Kendall’s S statistic computed for each season to arrive at a single S statistic to represent the entire period of record (Helsel and Hirsch, 2002; http://pubs.usgs.gov/twri/twri4a3/pdf/chapter12.pdf). The estimate of slope is taken as the median of all individual slopes computed between data pairs within the same season (and conducted for all seasons).

Hirsch et al (1982) originally developed the Seasonal Kendall Test for time series with monthly data, such that the seasons were set to 12 per year (monthly), although the test can be applied to any season designation. For Northern Water’s Baseline Program, the sampling frequency has varied over the period of record depending on the site and parameter. The sampling frequency at Horsetooth Reservoir has been in the range of 6 to 10 events per year over the WY2005 through WY2015 period. The sampling frequency for the flowing sites depends on the site and is designed to capture operational flows. For example, the Hansen Supply Canal is not in operation from November through March so no sampling of this canal takes place during this time period. The current sampling frequency for the flowing sites ranges from 3 to 10 events per year, depending on the site.

Because of the differences in sampling frequencies among Northern Water’s sites and parameters, seasons for the trend analysis were designated differently for each site and parameter group as outlined in Table 2.2. Individual months were designated as seasons in cases where one or more samples have been routinely collected in that month. Monthly seasons were used whenever possible since the different site types (rivers, canals, reservoir) have different patterns in the data, and selection of larger seasons (i.e., April – July, August – October, and November – March) may not best describe the patterns for the different site types. The exception is the winter months where only one sample is routinely collected during the Nov-Feb or Dec-March period so these periods have been designated as

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one season. For cases where limited sampling is conducted (such as HSC-PRU), multi-month seasons were designated to best capture the data. In all cases, the monthly boxplots were reviewed to confirm decisions about season designations.

The Seasonal Kendall Test was run using the seaKen routine in the R wq-package (Jassby and Cloern, 2016; Version 0.2-8). The test was performed at a 90% confidence level (critical p-value = 0.10), which means that there is at most a 10% chance of concluding that a statistically significant trend exists when in fact there is no trend. For the data sets read into the seaKen routine, each season in each analytical year must either have a concentration or, if there is no value for any particular season (missing data), “NA” is used. If there is more than one sampling event during any season, median concentrations were used such that there is one concentration value per season for each year. Non-detects were set equal to the detection limit.

TABLE 2.2 - SEASON DESIGNATIONS FOR SEASONAL KENDALL TREND ANALYSIS. Number & Description of Station Station Description Parameter Seasons AT-EP East Portal Adams Tunnel Nutrients, TOC, Alkalinity, 9 Seasons: Nov-Feb, Mar, Apr, OLY Olympus Tunnel at Lake Estes Major Ions, Arsenic (dis), May, Jun, July, Aug, Sept, Oct Copper, dis & total Iron, Hansen Feeder Canal downstream of HFC-FRD Manganese, Nickel Flatiron Reservoir

Hansen Feeder Canal downstream of HFC-BT Selenium & Zinc 3 Seasons: Nov-Mar, April-July, trifurcation at USGS gage Aug-Oct Big Thompson Riv upstream of Hansen HFC-BTU Feeder Canal at canyon mouth Big Thompson River downstream of HFC-BTD Hansen Feeder Canal & Trifurcation Plant Hansen Feeder Canal at Inlet to Horsetooth HFC-HT Reservoir 7 Seasons: Apr, May, Jun, July, Nutrients, TOC, Copper Aug, Sept, Oct Hansen Supply Canal Release to the Cache HSC-PR Alkalinity, Major Ions, La Poudre River Arsenic (dis), dis & total Iron, 3 Seasons: April-May, Jun-Aug, Manganese, Nickel, Sept-Oct Selenium, Zinc Nutrients, TOC, Major Ions, Cache La Poudre River upstream of Hansen 3 Seasons: April-May, June, HSC-PRU Copper, dis & total Iron, Feeder Canal July-Oct Manganese, Selenium, Zinc

7 Seasons: Apr, May, Jun, July, Nutrients Cache La Poudre River downstream of Aug, Sept, Oct HSC-PRD Hansen Feeder Canal Major Ions, Copper, dis & 3 Seasons: April-May, Jun-Aug, total Iron Sept-Oct Nutrients, TOC, Ca, Mg, Dis Iron, Dis Mn, Chl-a (0-5 9 Seasons: Dec-Mar, Apr, May, HT-SPR, meter composite), Secchi Jun, July, Aug, Sept, Oct, Nov Horsetooth Reservoir sites - HT-DIX, depth 1 meter & bottom samples HT-SOL Alkalinity, other major ions, 3 Seasons: Dec-Mar, Apr-Aug, Copper, Total Iron, Arsenic Sept - Nov, (dis), Nickel, Selenium, Zinc

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The Seasonal Kendall Test was applied here to a subset of the data, with some data and parameters excluded from the analysis due to high detection limits resulting in many non-detected values (Table 2.1), or a short period of record. The excluded data outlined in Table 2.1 are included in the time series plots (Appendix C), and visual inspection of the time series plots generally reveals why these data were excluded from the trend analysis. The trend analysis was limited to data sets where the period of record (after data were excluded as outlined in Table 2.1) began in 2008 or earlier (minimum of 7 years of data). The parameters included in the trend analysis for each site are indicated in Table 2.2.

Output from the R wq-package seaKen includes the Sen slope (change in concentration/year), Sen slope as a percent of the mean, and the computed p-value. If a computed p-value is less than the selected critical significance level (p- value < 0.10), a statistically significant trend is concluded to exist. However, the results of this statistical test must be paired with visual inspection of the time series plots to confirm that the statistical results make sense.

For cases where a statistically significant trend is concluded to exist, the “Sen slope as a percent of the mean” is used to evaluate the magnitude of the trend in a relative manner. In discussions of the trend analysis results, particular attention is given to cases where the absolute value of the Sen slope is greater than 4% of the mean. The selection of 4% allowed the analysis of trend test results to focus on those parameters with the highest trend magnitudes (i.e., those trends that are more likely to have significance from a practical standpoint). Note that if the Sen Slope is equal to 4% of the mean value calculated over the study period, the annual average parameter concentration would change by 100% of that value in 25 years (or 4% of that value each year), assuming the trend continues over time.

Output from the Seasonal Kendall Test are summarized in tables in Appendix I and discussed in the various sections of this report.

LIMITATIONS OF TREND ANALYSIS The trend analysis conducted here provides a yes/no answer to the question of whether an apparent trend is statistically significant as opposed to being the result of a chance arrangement of observations. However, this and other statistical approaches to trend analysis have limitations. It is important to keep in mind that statistical significance and practical significance are not the same thing. Trend analysis techniques are more likely to detect significant trends as the number of observations in the historical record increases. If the number of observations is very small, a practically significant trend may not be detected as statistically significant. Conversely, as the number of observations becomes very large, eventually even very small trends will be determined to be statistically significant. Therefore, the trend test should always be combined with a visual inspection of the time series plots or annual boxplots to determine whether there appears to be a trend that is large enough to be of interest or importance. Additionally, the computation of the trend magnitude should help determine if a trend is of practical importance.

Another limitation, particularly for longer records, is that significance tests and estimates of trend magnitude look only for a change in one direction and over the entire period of analysis. It is entirely possible that trends of shorter duration or that include a change of direction would be present and of interest. Also important is the effect of an unusual or extreme event (such as the 2012 High Park Fire, or the September 2013 flood) near the beginning or end of the period of analysis. When such events occur, an apparently significant long-term trend can result from a short- duration event. In all cases, visual inspection of the time series can help to avoid erroneous interpretations and to identify a need for more in-depth studies when appropriate.

Another important consideration in trend analysis of the type performed here is that a detected trend applies to the period of record only. Nothing can be inferred about the probability that an observed trend in the past will continue into the future.

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2.3 DATA LIMITATIONS AND EXCLUDED DATA Although this report covers data collected during the WY2000 through WY2015 time period, not all of the collected data have been included in the data analyses, data summaries, and graphs. Data have been excluded from the analyses in this report due to: (1) data quality issues (with data subsequently being flagged as “disqualified” or “suspect” in Northern Water’s database), or due to (2) significant changes in detection limits. Data excluded from the boxplots and/or the trend analysis in this report (but included in the time series plots) due to high detection limits (with many non-detects) were summarized in Table 2.1.

Data excluded from this report (including the time series plots) due to being flagged as “disqualified” or “suspect” in Northern Water’s database are summarized here. Note that data flagged as “suspect” in Northern Water’s database are returned during a data query and are available for use (but with caution) if desired. Data flagged as “disqualified” are not returned during a data query, are not used internally, and are not made available to outside users on the Northern website database interface. Since one of the goals of this report is to characterize the general recurring spatial and seasonal patterns, data flagged as “suspect” were also not reported or assessed in this document. Data excluded from the analyses in this report are discussed below.

Total Organic Carbon (TOC). TOC samples collected from 2005 through 2007 and analyzed at the USBR Boise Lab had reported TOC concentrations that were significantly lower compared to samples analyzed at other laboratories (including the City of Fort Collins Water Quality Lab) at the same sites during the period of record. TOC samples collected in 2005 through 2008 and analyzed at ACZ had concentrations significantly higher than expected. Because of this, all TOC samples analyzed at the USBR Boise Lab and ACZ Lab were flagged as “suspect” in the database and are not included in this report. TOC analysis was conducted during this time by the USGS National Water Quality Lab or by the City of Fort Collins Water Quality Laboratory for the Big Thompson Watershed Forum, and these data are included in this report for the applicable sites. However, for the Horsetooth Reservoir sites, exclusion of TOC data between 2005 to 2008 limits the data analysis in this report to TOC data collected from 2008 to WY2015.

Nutrients. Data quality issues were found with nutrient data that were collected from WY2005 through WY2007 as described in detail in Stephenson (2013b). All nitrate+nitrite, ammonia, TKN, ortho-P and Total P data collected from 4/2005 to 2/2006 and analyzed at the USBR Boulder (Nevada) Laboratory have been flagged as “disqualified” in the database and are not reported or assessed in this document. Northern Water’s data processing QA/QC also noted problems with some nitrate+nitrite and ammonia data collected in WY2006 and WY2007 and analyzed at the USBR Boise Lab. These cases could not be validated by typical patterns or concentrations at surrounding sites and were flagged as “suspect” in the database.

Metals. Dissolved zinc data collected by Northern Water in May, June, July and September 2014 were disqualified from Northern Water’s databases due to suspected contamination from the LDPE foam liners in the sample bottle caps as documented by Northern Water (2014). These data are not included in this report.

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3. WATERSHED DESCRIPTION, SIGNIFICANT EVENTS, WATER QUALITY CONCERNS & SPECIAL STUDIES

3.1 OVERVIEW OF WATERSHEDS The watersheds that make up the C-BT and Windy Gap Projects cover large areas on both sides of the continental divide (Figure 3.1). The West Slope watersheds include the Three Lakes (Granby Reservoir, Shadow Mountain Reservoir, and Grand Lake) Watershed, the Willow Creek Watershed, and the Windy Gap watershed (which includes the Fraser River watershed). On the East Slope, the quality of water within the canals and Horsetooth Reservoir reflects the influence of the West Slope watersheds as well as the Big Thompson watershed above Lake Estes, the middle Big Thompson watershed above the Dille Tunnel diversion, and the small, local Horsetooth Reservoir watershed.

Cache la Poudre River

² Roosevelt Larimer County 0 5 10 National Forest Miles July 2013 Horsetooth/Carter Horsetooth Watersheds Reservoir Jackson County Fort Collins Rocky Mountain National Park Big Thompson River

Middle Big Thompson Loveland Watershed Routt Lake National Forest Continental Divide Lake Estes Estes Watershed Three Lakes Watershed Carter Lake Arapaho Alva B. Adams Tunnel Reservoir Weld Willow CreekWillow Creek National Forest Grand County Watershed Lake East Slope Shadow Mtn Watersheds Reservoir (299,000 acres) St. Vrain Creek West Slope Longmont Watersheds (498,000 acres) Lake Granby Willow Creek Grand Reservoir County Boulder Boulder Colorado River County Reservoir Granby

Fraser River Blue River Windy Gap Boulder Reservoir Windy Gap Boulder Creek Watershed

S. Platte River Broomfield

Green Mountain Adams Winter Park County Reservoir Grand Jefferson County Summit County County

FIGURE 3.1 - WATERSHEDS OF THE C-BT AND WINDY GAP PROJECTS.

Water from the Big Thompson River enters the C-BT Project primarily at Lake Estes (and is diverted at the Olympus Tunnel), but there are also contributions downstream of Lake Estes at the Dille Tunnel diversion to the Hansen Feeder Canal (Figure 3.2). Native Big Thompson River water that enters Lake Estes has drained areas within Rocky

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Mountain National Park as well as the Town of Estes Park (2014 population of 6,165). Effluent from the Estes Park Sanitation District wastewater treatment plant discharges to the Big Thompson River just upstream of Lake Estes (Figure 3.2) and mixes with water that is diverted at the Olympus Tunnel. Downstream of Lake Estes, Big Thompson River water diverted at the Dille Tunnel is potentially further impacted by residents and businesses in the Big Thompson Canyon below Estes Park and by effluent from the Upper Thompson Sanitation District wastewater treatment plant that discharges to the Big Thompson River just downstream of Lake Estes.

Water Treatment Plant (WTP) City of Greeley - Bellvue WTP Wastewater Hansen Supply Treatment Plant Canal Tri-Districts (WWTP) Soldier Canyon Filter Plant (SCFP) C-BT Conveyance Fort Collins Water Treatment Facility Soldier System (FCWTF) Canyon Dam Outlet Conceptual; not to scale N HORSETOOTH RESERVOIR

Hansen Upper Thompson Feeder Sanitation District Canal Eden Valley Institute WTP WWTP Sunrise Ranch WTP City of Loveland WTP Estes Park Sanitation District WWTP Big Thompson Dille Tunnel Power Plant

Lake Estes Olympus & Pole Hill Flatiron East Portal Tunnels Pinewood Reservoir Adams Reservoir Tunnel Town of Estes Park Carter Lake Mary’s Lake WTP CARTER LAKE Filter Plant RESERVOIR

FIGURE 3.2 - NORTH END OF THE EAST SLOPE C-BT CONVEYANCE SYSTEM AND WATER TREATMENT PLANTS RECEIVING C-BT SOURCE WATER.

A land use/land cover map for the combined West and East Slope watersheds that that make up the C-BT and Windy Gap Projects and are associated with flows that enter Horsetooth Reservoir is shown on Figure 3.3 while the land cover areas for each watershed are summarized in Table 3.1 (prepared from 2011 National Land Cover Database from the USDA NRCS). The entire area encompasses over 1,100 square miles, with approximately 56% of this area consisting of forest cover and only 1.8% of the total area consisting of developed land.

On the West Slope, the Windy Gap Basin has the highest percent of developed land compared to the Three Lakes and Willow Creek watersheds. The Windy Gap Basin includes the towns of Winter Park, Fraser, Tabernash and Granby. The Fraser River upstream of Windy Gap Reservoir receives effluent from the three major municipal wastewater treatment plants (WWTP) that serve these towns. The Three Lakes Water & Sanitation District WWTP, which treats municipal wastewater from the Town of Grand Lake and developments in the Three Lakes

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area, discharges to the Willow Creek Watershed downstream of Willow Creek Reservoir but upstream of Windy Gap Reservoir.

FIGURE 3.3 - LAND USE/LAND COVER MAP FOR THE COMBINED WATERSHEDS OF THE C-BT AND WINDY GAP PROJECTS UPSTREAM OF HORSETOOTH RESERVOIR (2011 NATIONAL LAND COVER DATABASE FROM THE USDA NRCS).

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TABLE 3.1 - LAND USE/LAND COVER TYPES FOR THE MAJOR WATERSHEDS ASSOCIATED WITH HORSETOOTH RESERVOIR.

Big Thompson Local Windy Gap Combined Watershed: Willow Creek Three Lakes above Canyon Horsetooth Basin Watershed Area mouth Reservoir Land Cover sq sq sq sq sq sq % % % % % % Type: miles miles miles miles miles miles Open 0.5 0.4 % 0.5 0.1 % 13.9 4.2 % 0.7 0.2 % 1.6 0.6 % 17.2 1.6 % Water Perennial 1.3 0.9 % 15.4 4.7 % 42.1 13.5 % 12.9 4.1 % 0.0 0.0 % 71.7 6.5 % Snow/Ice

Developed 0.7 0.5 % 7.1 2.2 % 3.1 1.0 % 8.9 2.8 % 0.7 3.8 % 20.4 1.8 %

Barren 0.6 0.4 % 10.9 3.4 % 31.8 10.2 % 21.6 6.9 % 0.4 2.4 % 65.2 5.9 % Land Forest 74.7 52.8 % 185.4 57.2 % 156.3 50.0 % 195.2 62.7 % 4.6 26.5 % 616.2 55.7 % Grasses & 10.1 7.2% 35.2 10.9% 23.9 7.7% 38.3 12.3% 2.3 13.4% 109.8 9.9% Forbs Shrub/ 48.9 34.6 % 50.7 15.6 % 32.9 10.5 % 30.2 9.7 % 6.9 39.8 % 169.7 15.3 % Scrub Hay/ 2.2 1.5 % 5.4 1.7 % 1.3 0.4% 0.8 0.2 % 0.0 0.0 % 9.6 0.9 % Pasture Cultivated 0.0 0.0 % 0.0 0.0 % 0.0 0.0 % 0.0 0.0 % 0.0 0.2 % 0.0 0.0 % Crops Riparian/ 2.4 1.7 % 13.7 4.2 % 7.2 2.3 % 2.9 0.9 % 0.7 4.2 % 27.1 2.4 % Wetlands

Total Watershed 141.5 324.3 312.5 311.5 17.2 1,107 100% Area

3.2 DESCRIPTION OF HORSETOOTH RESERVOIR Horsetooth Reservoir is a long (approximately 6.7 miles), narrow reservoir formed by the construction of four dams: Spring Canyon, Dixon Canyon, Soldier Canyon, and Horsetooth. It has a total capacity of approximately 156,735 ac-ft and a maximum water depth of 188 feet. Some other characteristics of the reservoir are summarized in Table 3.2. The primary inflow to Horsetooth Reservoir is the Hansen Feeder Canal, which flows into the south end of the Reservoir at Inlet Bay. The Horsetooth Reservoir local watershed covers 17 square miles and includes several small, intermittent drainages that flow into the west side of the Reservoir (including Soldier Canyon, Well Gulch, Arthur’s Rock Gulch, Mill Creek, and Spring Creek) during the spring snowmelt period and after significant rainfall events. These drainages are ungauged and are considered insignificant (at least on an annual basis) compared to the Hansen Feeder Canal inflow.

There are two engineered outlets from Horsetooth Reservoir, both located at the north end of the reservoir: the Hansen Supply Canal at Horsetooth Dam, and the Soldier Canyon Dam Outlet (Figure 3.2). The Hansen Supply Canal operates during the irrigation season and conveys water to the City of Greeley Bellvue Water Treatment Plant (WTP) and to the Poudre River and farmers on the eastern Plains. The Soldier Canyon Dam Outlet, located near the bottom of the reservoir, provides water to the Fort Collins Water Treatment Facility (FCWTF), the Tri- Districts Soldier Canyon Filter Plant (SCFP), Colorado State University research facilities, Platte River Power Authority, and Dixon Reservoir (via the Dixon Feeder Canal). Water can also be sent from the Soldier Canyon

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Dam Outlet to the Bellvue WTP via the Pleasant Valley Pipeline in the winter and early spring (when the pipeline is not being used to convey Poudre River water).

TABLE 3. 2 - HORSETOOTH RESERVOIR CHARACTERISTICS. Characteristic Value Dam crest elevation 5,443 ft above sea level Water surface elevation at capacity 5,430 ft above sea level Reservoir volume at capacity 156,735 acre-ft Active reservoir volume (capacity minus dead storage) 149,732 acre-ft Reservoir surface area at capacity 1,900 acres Mean depth at capacity 82.5 ft Maximum water depth 188 ft (57.3 meters) Local watershed area 17.0 sq miles Shoreline length 25 miles Approximate hydraulic residence time ~ 0.7 to 1.8 years Reservoir bottom elevation at Soldier Canyon Dam (estimate) 5,255 ft above sea level Soldier Canyon Outlet elevation 5,270 ft above sea level

The Soldier Canyon Dam Outlet provides a continuous (year-round) supply of raw water to the FCWTF and the SCFP. Because of this direct connection between the reservoir and the two water treatment plants, Horsetooth Reservoir was classified as a Direct Use Water Supply (DUWS) reservoir in 2015. Regulation 31 includes a DUWS interim numeric value for chlorophyll-a of 5 µg/L to protect drinking water supplies from issues related to algae. This chlorophyll-a value could be applied to individual lake/reservoirs through the basin regulation rulemaking hearing process, but has not been adopted for Horsetooth Reservoir.

Although the primary purpose of Horsetooth Reservoir is to store and supply municipal and irrigation water, it also provides water and land-based recreational opportunities. Both Lory State Park and Larimer County Horsetooth Mountain Park are located in the foothills west of the reservoir, within the boundaries of the local Horsetooth Reservoir watershed. These parks are predominantly characterized by Ponderosa Pine (Pinus ponderosa) forests and shrub lands/grasslands. The occurrence of wildfires in the foothill areas has the greatest potential for the local watershed to impact the quality of water in Horsetooth Reservoir.

The recreational uses of the reservoir itself have been managed since 1954 by Larimer County. Campgrounds, trails, day use/picnic areas, boat ramps and associated facilities support boating, fishing, water skiing, camping, hiking, swimming, and other activities on and around the reservoir. Larimer County Park lands completely surround the reservoir. More than 500,000 people visit Horsetooth Reservoir each year for water and near-shore activities.

The potential sources of water quality pollutants associated with the recreational facilities and activities at Horsetooth Reservoir include:

• Runoff from construction areas, newly seeded areas, and other disturbed areas: sediments and nutrients (fertilizers) • Runoff from parking areas and roadways: hydrocarbons and other fluids leaked from vehicles • Boat fueling areas: hydrocarbons • Shoreline erosion: sediments • Swim beaches: microbiological contaminants

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Low density residential areas are present around the southern end of the reservoir. A sanitary sewer system for the subdivisions in this area was constructed by the Spring Canyon Water and Sanitation District in 1978 (http://www.springcanyonwsd.com/?p=28) and includes the pipelines and pump stations that convey wastewater to the South Fort Collins Sanitation District Fossil Creek Wastewater Treatment Plant for treatment. The Larimer County and Colorado Departments of Public Health and Environment had previously determined that the presence of failing septic systems required the installation of a sanitary sewer system with treatment at a wastewater treatment plant.

3.3 SIGNIFICANT EVENTS Large-scale environmental perturbations within the watersheds have the potential to cause changes in water quality. The mountain pine beetle epidemic, floods, drought, climate change, and catastrophic wildfires can all impact water quality. The extent of some of the potential water quality changes are unknown and occur slowly over time, while others are more abrupt and obvious such as those caused by large wildfires and floods. Although it is beyond the scope of this report to provide a detailed analysis of the various specific and potential water quality issues, they are discussed in this report in relation to the presented baseline data with some background information provided in this section.

3.3.1 PINE BEETLE EPIDEMIC Large areas of the West and East Slope C-BT source watersheds have been impacted to varying degrees by the mountain pine beetle epidemic that started in the late 1990’s as highlighted on Figure 3.4, which shows areas, shaded in red, that have been impacted to varying degrees by mountain pine beetle and spruce beetle (http://www.fs.usda.gov/detail/r2/forest-grasslandhealth/?cid=fsbdev3_041629 ). There has been continued concern over the past several years about the potential for runoff from drainages with large areas of dying and fallen trees to impact water quality in the C-BT watersheds. The Willow Creek watershed in particular has been significantly impacted with large areas of dead trees, resulting in a change in the land cover. Approximately 81% of the Willow Creek Watershed had previously been classified as forest (as reported in Billica and Oropeza, 2010). The Figure 3.3 land cover map, produced using the most recently available data (data from 2011, which could change again with the next update to the land cover database) indicates that much of this area in the Willow Creek Watershed has now been classified as “shrub/scrub”, with only 53 % of the total watershed classified as forest (Table 3.1).

Pine needles and twigs are relatively rich in nitrogen while branches and tree trunks are carbon rich (Clow et al, 2011). The death and decay of large areas of trees results in an increase in the release of organic matter to the litter and soil, with an increased opportunity for leaching and the transport of organic carbon to surface water, with expected increases in total organic carbon concentrations. This loss in the evergreen forest would also be expected to have an impact on nitrogen cycling within the watersheds with the decay of pine needles and twigs resulting in the accumulation of nitrogen in the litter and soil (Clow et al, 2011). Some portion of the released nitrogen would be expected to be transported as nitrate to surface water. Other potential impacts include increases in water yield, peak flows and sediment yield, and timing of snowmelt runoff.

Water quality impacts associated with the pine beetle epidemic in the West Slope C-BT Willow Creek watershed were investigated by Stednick et al (2010). Given the large beetle-kill area, they expected an increase in nutrient concentrations (including nitrate, TKN, ortho-P and Total P) but found no correlation between nutrient concentrations and beetle-kill watershed area. Studies reported by Rhoades et al (2013) and Clow et al (2011) also found that, contrary to expectations, the extensive tree mortality from the mountain pine beetle epidemic has not resulted in any large increases in streamwater nitrate concentrations. Rhoades et al (2013) hypothesized that the lack of a large streamwater nitrate response may be due to a combination of two factors: 1) heterogeneous (in space and time) tree mortality which would be expected to reduce the amount of nitrate loss at any given time (a damped response), and 2) uptake of dissolved inorganic nitrogen by the remaining live vegetation. Clow et al (2011)

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indicated that although streamwater nitrate concentrations did not increase, they observed an increase in Total N and Total P concentrations.

A study in Colorado conducted by Mikkelson et al. (2013) found higher TOC and disinfection byproducts (DBPs) concentrations at water treatment plants that treated raw water from watersheds with high levels of mountain pine beetle infestations. The TOC and DBP data used in this study came from CDPHE records or directly from the water treatment plants, and consisted of quarterly data required to be reported to the state. The data analysis was conducted for the period of 2004-2011 and included nine water treatment plants in Colorado, five associated with source watersheds that had high levels of beetle infestation (including Granby, Winter Park and Kremmling), and four (which were considered the “controls”) associated with watersheds that had low levels of infestations (including Aspen and Glenwood Springs). The TOC concentrations at the beetle-impacted water treatment plants showed a statistically significant increase since 2008, approximately 3-4 years after the beetle infestation began, while TOC concentrations at the control plants showed a decrease. After a tree becomes infested, it can take 3-5 years for the needles to drop, which Mikkelson et al. (2013) indicate could account for the shift in TOC concentrations in the beetle-impacted watersheds in 2008.

FIGURE 3.4 - C-BT WATERSHED AREAS IMPACTED TO VARYING DEGREES BY MOUNTAIN PINE BEETLE & SPRUCE BEETLE THROUGH MAY 2015. (Impacted areas shaded in red; http://www.fs.usda.gov/detail/r2/forest-grasslandhealth/?cid=fsbdev3_041629 ).

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3.3.2 WILDFIRES Water quality can be significantly impacted by wildfires depending on the size, severity, and location of the burn area within a watershed. The impacts of wildfires on water quality are summarized in literature reviews presented by others including Bitner et al (2001), Ranalli (2004), Neary et al (2005), and Sham et al (2013). Some of the main water quality impacts reported in these literature reviews include:

• Suspended Solids & Turbidity: High turbidity and high suspended solids concentrations in streamflow are the most obvious impacts of runoff from burn areas. Increased runoff and erosion rates across burn areas result in the transport of significant amounts of sediment and ash to receiving waters. Post-fire turbidity and suspended solids concentrations in streamflow are highly variable and can, at times, approach extreme values depending on the intensity of summer storm events, steepness of slopes, vegetation cover, fire severity (how much of the fuel is consumed), and the presence of a hydrophobic (water repellent) layer at the surface of burned soils.

• Major Ions: The inorganic component of ash produced by fire contains carbonates and oxides of calcium and magnesium, carbonates and chlorides of sodium and potassium, and polyphosphates of calcium and magnesium, with relative concentrations varying depending on plant species. Leaching of ash and partially burned forest floor litter results in the mobilization of calcium, magnesium, sodium, potassium, and chloride, resulting in increased concentrations of these constituents in water. Sulfate concentrations may increase due to the oxidation of sulfur present in soil organic matter. Post-fire increases in major ion concentrations are more apparent in streams that drain granitic bedrock basins, such as that of the headwaters of the Big Thompson River, since the pre-fire ion concentrations are normally very low.

• pH: The leaching of the alkaline compounds in ash (the carbonates and oxides of calcium and magnesium) generally results in an increase in pH in the waters draining from burn areas.

• Organic Carbon: The grey or black ash produced in most wildfires contains a significant amount of organic matter by weight (30 to 90 percent). Because of this, streamflow concentrations of particulate organic carbon and dissolved organic carbon can both exhibit post-fire increases.

• Metals: Increases in total iron, total manganese, and total mercury have been observed in runoff from some burn areas. These increases are generally associated with the increased sediment and ash loads.

• Nutrients: Increases in concentrations of one or more nutrients (nitrate, ammonia, organic nitrogen, orthophosphate (ortho-P), and total phosphorus (Total P)) in streams downstream of burn areas have been reported by many. Ammonia concentrations may increase during and immediately following a fire due to the release of ammonia during the combustion of organic matter. Nitrate concentrations can initially increase due to the nitrification of the ammonia released from the combustion of organic matter, with later increases in streamflow nitrate due to reduced uptake by plants in the burn area. Ortho-P concentrations can increase as a result of the leaching of ash, although it may be subsequently immobilized by adsorption onto soil iron and aluminum oxide surfaces. Increases in Total P, with or without significant increases in ortho-P, occur due to increased sediment loading to streams.

The major fires (≥ 750 acres) that have occurred since 2010 within the watersheds of the C-BT and Windy Gap Projects are shown on Figure 3.5. The 2012 High Park Fire and the 2012 Fern Lake Fire had the greatest potential to impact C-BT Project waters and are briefly discussed below.

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FIGURE 3.5 - RECENT WILDFIRES IN AND NEAR C-BT PROJECT WATERSHEDS.

High Park Fire. The High Park Fire (June 9 - July 2, 2012) burned over 87,000 acres and runoff from the burn area has significantly impacted Poudre River water quality, particularly during intense rainfall events during the summers of 2012 and 2013. Post-fire summer storm events in 2012 produced elevated levels of many parameters in the Poudre River including pH, conductivity, hardness, total dissolved solids, turbidity, TOC, ammonia, total Kjeldahl nitrogen (TKN), ortho-P, Total P, and dissolved aluminum (Oropeza and Heath, 2013). After storm events, concentrations generally returned to values within the range observed for the pre-fire data. Further data analysis conducted by the City of Fort Collins indicate that runoff from the burn area has continued to occasionally impact Poudre River water quality through 2015 (http://www.fcgov.com/utilities/what-we-do/water/water-quality/source-water- monitoring/water-quality-reports). Northern Water has two Baseline Monitoring sites on the Poudre River (HSC-PRU and HSC-PRD) that show water quality impacts from the High Park Fire.

Horsetooth Reservoir water quality did not experience significant impacts from the 2012 High Park Fire, with only about 400 acres burned within the local Horsetooth Reservoir watershed. However, Northern Water cooperated in several watershed projects with Lory State Park and the Natural Resources Conservation Service to minimize post-fire debris flows into Horsetooth Reservoir. Northern Water participated in the placement of debris booms in the drainages above Satanka Bay, Soldier Cove, and Eltuck Cove, upstream of Horsetooth Reservoir. Northern Water also participated in the construction of a temporary sediment basin debris catch dam in the Solider Canyon drainage upstream of Horsetooth Reservoir. Finally, Northern Water provided monetary contributions for mulching and reseeding of burn areas within Lory State Park.

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Fern Lake Fire. The Fern Lake Fire started on October 9, 2012 and burned approximately 3,500 acres in Rocky Mountain National Park (RMNP) before it was eventually extinguished by winter snows that began in early December, 2012. The fire occurred within the headwaters of the Big Thompson River in an area that had not burned in more than 800 years. The Fern Lake Fire was of concern because runoff from this area eventually flows into Lake Estes where it mixes with West Slope C-BT Project waters. A collaborative study with costs shared by Northern Water, the Town of Estes Park, the cities of Loveland, Fort Collins, Greeley, and Boulder, and the U.S. Geological Survey (USGS) was conducted to assess impacts of the Fern Lake Fire on downstream water quality during the first spring/summer after the fire (sample collection April – November, 2013). Water quality data collected in 2013 indicate that some water quality changes occurred in the Big Thompson River at the downstream end of the burn area in Moraine Park, particularly increases in the major ions and specific conductance. However, the measured impacts were generally short-lived, not significant enough to impact aquatic life and drinking water supplies, and/or occurred in parameters (major ions) that typically would not result in impacts to aquatic life or drinking water supplies (Billica, 2014). At the Big Thompson River monitoring site just upstream of Lake Estes (approximately 5.2 river-miles downstream of Moraine Park), the collected samples showed minimal water quality changes.

An evaluation of the second year of data collected after the Fern Lake Fire (data collected as part of the BTWF and USGS monitoring programs) was presented in Hydros (2015) and showed a dramatic increase in nitrate concentrations at the downstream end of Moraine Park just prior to the 2014 spring runoff. An increase in nitrate was not observed during the first year after the fire. The USGS also assessed water quality impacts from the Fern Lake Fire over the first two years after the fire (Mast et al, 2015) and reported similar findings.

3.3.3 2013 FLOOD A slow-moving rain event that took place over the period of Sept 9-15, 2013 resulted in historic flooding along Colorado’s Front Range and to the east. The flood caused widespread and significant damage to roads, bridges, homes, businesses, and the stream ecology of six major rivers/tributaries including the Big Thompson River. Highway 34 through the Big Thompson Canyon was severely damaged (Figure 3.6), and damaged sewer lines, roads, homes and businesses in Estes Park impacted Lake Estes and the Big Thompson River.

Estes Park received approximately 10 inches of rainfall over the Sept 9-15 event. COCORaHS data for station CO-LR- 767 just east of Mary’s Lake indicates that a total of 10.41 inches fell during the period of Sept 9 – 15; http://www.cocorahs.org/ViewData/ListDailyPrecipReports.aspx.

FIGURE 3.6 - 2013 FLOOD DAMAGE TO HWY 34 ALONG THE BIG THOMPSON RIVER AT THE CANYON MOUTH.

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Hydros (2015) summarized water quality impacts of the 2013 flood in the 2015 Big Thompson State of the Watershed Report prepared for the BTWF. The following summary of observed effects of the flood on water quality is from that report:

• C-BT Project canal locations downstream of Lake Estes exhibited short-lived increases in nutrients, TSS, TOC, sulfate, and possibly some metals, during and immediately following the flood. This largely reflected East Slope watershed floodwater that entered Lake Estes and was then pumped through the Olympus Tunnel (on Sept 12 and 13, before pumping was stopped on Sept 14) to Pinewood and Flatiron Reservoirs. Pumping from Lake Estes through the Olympus Tunnel was restarted in early November 2013. Pumping of West Slope water through the Adams Tunnel was stopped on Sept 11, 2013 and restarted in late Nov 2013.

• In the upper Big Thompson River (upstream of the Loveland WTP intake), where baseline concentrations tend to be low, increased TSS, turbidity, dissolved solids, and in some cases total phosphorus, total nitrogen, and nitrate were observed after the flood. These increases in the upper watershed reflect leaching from shallow soils and mobilization of solids available for transport following the high flood flows. BTWF data suggest that concentrations had largely returned to typical levels by the end of WY2014. However, periodic elevated turbidity has been reported into 2015, particularly during storm events and in response to post-flood recovery work in the river.

Northern Water’s two Baseline Monitoring sites on the Big Thompson River, HFC-BTU and HFC-BTD, are located in an area that has experienced significant impacts during and after the 2013 flood. The HFC-BTU site is located at the downstream end of the Big Thompson Pre-Flood View Canyon and water quality data collected HFC-BTD since the flood may reflect upstream restoration activities, depending on timing. The HFC-BTD site is located downstream of the Sylvan Dale Guest Ranch that experienced significant erosion of streambanks and adjacent HFC-BTU areas as can be seen by comparing the August 2012 Google Earth imagery with the June 2014 imagery, both shown in Figure 3.7. This area will be undergoing restoration activities to improve stream habitat.

Post-Flood View HFC-BTD

HFC-BTU site moved upstream after the flood

FIGURE 3. 7 - PRE- AND POST-FLOOD VIEWS ALONG THE BIG THOMPSON RIVER AT HFC-BTU AND HFC-BTD.

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3.4 WATER QUALITY CONCERNS This section summarizes ongoing water quality concerns related to the East Slope – North End Baseline Monitoring Program sites, including the State’s list of impaired waters, the use of copper sulfate for algae and aquatic weed control, concerns related to drinking water treatment, and Horsetooth Reservoir water quality issues.

3.4.1 303(d) LIST OF IMPAIRED WATERS Section 303(d) of the Clean Water Act requires states to identify waters that are in violation of state water quality standards. The most recent five years of data from all available sources are used by the Colorado Water Quality Control Division to make the assessments. If a water body is determined to be impaired, the Colorado Water Quality Control Commission (WQCC) places it on the state’s 303(d) List. Colorado’s 303(d) List includes waters where there are exceedances of water quality standards or non-attainment of uses, and includes waters impaired as a result of any combination of point source discharges, non-point sources, and natural sources. Colorado also has a Monitoring and Evaluation (M&E) List. When water quality exceedances are suspected, but uncertainty exists regarding one or more factors (such as the representative nature of the data used in the evaluation), a water body or segment is placed on the M&E List.

Colorado’s 303(d) and M&E Lists are normally updated every other year, and were updated and adopted in 2016 (WQCC, 2016a). The impairments identified on the 2016 list that are relevant to the sites in this report are shown on Table 3.3. The impairments identified on the 2012 lists are also included on Table 3.3 to show the dynamic nature of the lists (the 2014 listing cycle was canceled by the Colorado WQCC). The C-BT Project canals and tunnels are not included in the State’s assessments and 303(d) and M&E Lists.

TABLE 3.3 - SUMMARY OF 303(d) AND M&E LISTINGS NORTHERN WATER SEGMENT & PORTION 2012 IMPAIRMENTS 2016 IMPAIRMENTS MONITORING SITES COSPBT02 M&E: Sulfide M&E: none Big Thompson River and HFC-BTU, tributaries, RMNP to Home HFC-BTD 303(d): Copper, Cadmium, 303(d): Arsenic, Aquatic Supply Canal diversion Zinc, Temperature Life, Temperature

COSPBT16 M&E: none M&E: none none Lakes Estes 303(d): Copper, Lead 303(d): Copper, Lead

COSPCP10a Mainstem of the Cache La Poudre M&E: none HSC-PRU, M&E: none River from the Munroe Gravity 303(d): Arsenic, HSC-PRD 303(d): Copper, Temperature Canal Headgate to the Larimer Temperature County Ditch diversion

HT-SPR, M&E: none M&E: none COSPCP14 HT-DIX, Horsetooth Reservoir 303(d): Aquatic Life Use (Hg 303(d): Aquatic Life Use HT-SPR Fish Tissue), Copper, Arsenic (Hg Fish Tissue), Arsenic

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3.4.2 COPPER Dissolved copper present at very low concentrations can impact aquatic organisms including zooplankton and fish. Elevated concentrations of copper in waters associated with the C-BT Project have resulted in identified impairments and placements on the Colorado 303(d) List or the M&E List. These have included copper listings for the Big Thompson River, Poudre River and Horsetooth Reservoir on the 2012 303(d) List as indicated on Table 3.3.

Copper sulfate was historically used in the C-BT Project canals to control periphyton (attached algae) and aquatic plants, with Northern Water’s use dating back to around 1964. However, both Northern Water and the USBR have discontinued the use of copper sulfate in the C-BT canals. Northern Water discontinued its use in April 2008, while the USBR discontinued its use sometime before June 2012 when the Pole Hill canal was covered over (personal communication between J. Billica, Northern Water, and Tony Curtis, USBR, 5/8/15).

Copper concentrations in water samples have decreased since the use of copper sulfate was discontinued, resulting in copper de-listings from 2012 to 2016 as indicated in Table 3.3. The stream segments that are downstream of canals that Northern Water is responsible for algae and aquatic weed control, including the Big Thompson River, Horsetooth Reservoir, and the Poudre River, are no longer on the 303(d) List for copper. However, because of past copper impairments, the application of copper-containing products (including copper sulfate for algae control and copper carbonate Clearigate for aquatic weed control) is not considered to be a herbicide option by Northern Water at any time in the future within any portion of Northern Water’s canals. In any receiving water segment where there is a current 303(d) listing for copper, the use of copper-containing aquatic herbicides in C-BT canals is not allowed under the USBR’s EPA NPDES Pesticide General Permit or Northern Water’s Colorado Pesticide General Permit.

3.4.3 DRINKING WATER TREATMENT CONCERNS Waters of the C-BT Project are drinking water supply sources for many municipal drinking water treatment plants, including those shown on Figure 3.2 that are associated with the East Slope-North End monitoring sites. Some of the important water quality issues that have directly impacted these water treatment plants over the years have included increasing concentrations of total organic carbon; recurring episodes of geosmin, a taste and odor compound; and, for those treating water from Horsetooth Reservoir, low dissolved oxygen levels and associated high dissolved manganese concentrations at the bottom of the reservoir. These issues are briefly outlined below:

• Total Organic Carbon (TOC): TOC occurs naturally in water bodies but is a concern for drinking water treatment plants because it reacts with disinfectants such as chlorine to form regulated (carcinogenic) disinfection by-products. Previous reports and trend analyses have indicated increasing concentrations of TOC in Horsetooth Reservoir as well as sites along the Big Thompson River and C-BT canal system. Because of this, trends in TOC concentrations are being closely watched.

• Geosmin: Geosmin is a taste and odor compound produced by some species of cyanobacteria (blue-green algae). Although it is not a public health concern, geosmin imparts an earthy odor to water at extremely low concentrations (~5 nanograms/L (ng/L), or 5 parts per trillion). Geosmin is a concern for drinking water treatment plants because it is very difficult to remove and its presence in treated drinking water results in customer complaints and questions about the quality and safety of the water. It has been detected in samples collected from the Hansen Feeder Canal and Horsetooth Reservoir as well as in water from the West Slope delivered through the Adams Tunnel.

• Manganese: Dissolved manganese (Mn) in treated drinking water can change to a solid form and cause “brown water” episodes that stain plumbing fixtures and laundry, and result in customer complaints. Low dissolved oxygen conditions (< 2 mg/L) that occur at the bottom of Horsetooth Reservoir in the late

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summer and early fall favor the release of dissolved manganese from the bottom sediments. To minimize customer complaints, the Fort Collins WTF target for manganese in the treated water is 5 ug/L, while the Safe Drinking Water Act secondary (non-enforceable, aesthetic-based) maximum contaminant level for manganese is 50 ug/L.

3.4.4 OTHER HORSETOOTH RESERVOIR ISSUES In addition to water quality issues that have a direct impact on water treatment, there are also several other Horsetooth Reservoir water quality issues, including:

• Low Dissolved Oxygen (D.O.): Low D.O. levels occur at the middle (metalimnion) and bottom of Horsetooth Reservoir. Low D.O. at the top and middle depths of a reservoir can be an aquatic life concern, while low D.O. at reservoir bottoms can result in the release of nutrients and metals from bottom sediments.

• Nutrients: Nutrient loading to a lake/reservoir is potentially the root cause of many water quality issues, including algal blooms, clarity, low dissolved oxygen, taste and odor issues, and algal toxins. The Colorado Water Quality Control Commission adopted interim numerical values for phosphorus, nitrogen and chlorophyll-a in 2012 to protect designated uses of Colorado waters. These values include summer average concentrations in the top layer for cold water reservoirs of 25 µg/L for Total Phosphorus and 426 µg/L for Total Nitrogen, and a March-November average chlorophyll-a concentration in the top layer of 5 µg/L for reservoirs sub-classified as Direct Use Water Supply (DUWS). However, these values have not yet been adopted for Horsetooth Reservoir, although the WQCC adopted the DUWS sub-classification for Horsetooth Reservoir in 2015.

• Mercury: Elevated levels of mercury have been detected in fish tissue collected from Horsetooth Reservoir, resulting in the reservoir being placed on the 303(d) List of impaired waters due to the public health risk associated with fish consumption. This listing is not based on mercury concentrations in the water, which are very low.

• Zebra and quagga mussels (Dreissena spp) are considered to be among the worst aquatic nuisance species to be introduced to North America. In 2008, dreissenid mussel larvae (veligers) were found in West Slope C-BT lake/reservoirs (Willow Creek Reservoir, Granby Reservoir, Shadow Mountain Reservoir and Grand Lake) on several sampling dates and by multiple agencies, but no dreissenid mussel veligers have been found in these lake/reservoirs since 2008. No veligers have been found to date in Horsetooth Reservoir, and no adult dreissenid mussels have been found in any of the C-BT Project lake/reservoirs to date. Calcium concentration affects invasive mussel reproduction, growth, and survival and has been shown to be the key parameter for assessing risk of invasion. Calcium concentrations in C-BT reservoirs, including Horsetooth Reservoir, are generally below those likely to support veliger survival and possibly below levels required for long term survival of adults.

In 2009, Colorado Parks and Wildlife (CPW) initiated a boat inspection and decontamination program to control the introduction of invasive mussels into clean water bodies. In cooperation with CPW, Larimer County began mandatory inspections for all boats on Horsetooth Reservoir and Carter and Boyd Lakes in April 2009; inspections have been ongoing since.

• Daphnia lumholtzi is an invasive waterflea (a cladoceran zooplankton; see Section 9.5) that was first confirmed in Colorado in 2013 and is now known to be present in 24 Colorado water bodies including Horsetooth Reservoir (http://cpw.state.co.us/Documents/ANS/Fact-Sheet-Waterfleas.pdf). Daphnia lumholtzi has an elongated tail spine, abdominal barbs, and a large pointy “helmet”. They outcompete native

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juvenile fish for food and, because of their long tail spine and barbs, they are unpalatable to juvenile fish and thus avoid predation.

3.5 OTHER RELATED WATER QUALITY STUDIES & REPORTS There are several other water quality monitoring programs and/or special studies that have produced recent reports that summarize data related to the East Slope – North End sites. Four are briefly outlined below, including Northern Water’s Collaborative Emerging Contaminant Program, the Big Thompson Watershed Forum 2015 State of the Watershed Report, the City of Fort Collins Horsetooth Reservoir Water Quality Monitoring Program Reports, and the 2013 CE-QUAL-W2 Horsetooth Reservoir Modeling Report.

3.5.1 EMERGING CONTAMINANTS COOPERATIVE MONITORING PROGRAM Emerging contaminants are a growing concern to human health and the environment, particularly in drinking water supplies. The laboratory analyses can be costly and there is currently no clear standard list of constituents as analytical methods continue to develop. In 2008, Northern Water launched a collaborative emerging contaminants monitoring program, co-funded by the cities of Boulder, Broomfield, Fort Collins, Greeley, Longmont, and Loveland, and the Town of Estes Park. The program was designed to more cost effectively take a pro-active approach to determine the presence of pharmaceuticals and personal care products (PPCPs), hormones and hormone mimicking compounds (endocrine disruptors), and herbicides and pesticides in the C-BT Project and other nearby source waters associated with drinking water supplies. The program is developing a baseline of data for these compounds.

The program has been expanded and refined each year since 2008. Research scientists Imma Ferrer and Michael Thurman from the Center for Environmental Mass Spectrometry at the University of Colorado, Boulder provide the expertise and technical support to design and optimize the program, conduct the laboratory analysis, and help interpret the results. Three mass spectrometry methods are used: (1) a LC/TOF-MS method for the presence/absence screening of compounds, currently including 67 pesticides and 40 PPCPs, (2) a low-level method with LC/MS/MS triple quadrupole for 32 herbicides/pesticides and PPCPs (a subset of the LC/TOF-MS method suite), and (3) a LC/MS/MS triple quadrupole method for 8 hormone and hormone-mimicking compounds (endocrine disruptors). Detection of these compounds at the parts-per-trillion concentration level (trace level) is the lowest level that the most current methodology and laboratory instruments can detect.

In general, the drinking water sources in the study area have very clean water, free of most of the compounds included in the analysis. The detected compounds are ubiquitous in water resources throughout the country and are not unique to our system. Very low levels of the herbicide 2,4-D and compounds associated with recreational activities (DEET, caffeine and sucralose) are found at most of the sites, including Horsetooth Reservoir. The Big Thompson River sites just downstream of WWTP discharges have relatively high detections of PPCPs due to their proximity to WWTP discharges. Further downstream, Big Thompson River samples show many of the same compounds, but at lower concentrations due to dilution. Some of this WWTP-impacted water is diverted into the C-BT canals, but dilution is significant by water from other sources (including water from the Adams Tunnel and Upper Big Thompson River above Estes Park). The low concentration levels of the detected compounds do not present a known health hazard for drinking water and are well below any applicable drinking water standards.

Annual reports for the Emerging Contaminants Program that summarize the data collected since 2008 are available at http://www.northernwater.org/WaterQuality/WaterQualityReports1.aspx.

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3.5.2 BIG THOMPSON WATERSHED FORUM 2015 STATE OF THE WATERSHED REPORT The Big Thompson Watershed Forum contracted with Hydros Consulting in 2015 to prepare a State of the Watershed Report. The report (Hydros Consulting, 2015; http://btwatershed.org/reports-presentations/forum- water-quality-reports/) reviewed and evaluated the water quality data from rivers, streams and C-BT tunnel and canal sites in the Big Thompson watershed that were collected for the Forum’s monitoring programs from WY2000 through WY2014, and was an update of the 2010 State of the Watershed Report.

Note that five C-BT tunnel/canal sites (AT-EP, OLY, HFC-FRD, HFC-BT and HFC-HT), were originally all part of the BTWF monitoring network. In 2011, the five canal locations were removed from the BTWF USGS monitoring program to reduce financial burdens on the Forum. Since that time, sampling at three of these stations has been conducted by Northern Water (HFC-FRD, HFC-BT and HFC-HT), and sampling at the other two stations continued by the USGS under a Joint Funding Agreement with Northern Water, with laboratory analyses for all five canal sites conducted by laboratories used in Northern Water’s monitoring program. However, data at all five tunnel/canal sites were analyzed and included in the BTWF State of the Watershed Report.

The data assessment for the State of the Watershed Report focused on flow rates, select metals, general parameters, nutrients, and microbiological parameters. The significant findings related to the upper watershed and the tunnel/canal sites, taken directly from that report, include:

• Upper Watershed: The upper watershed is generally characterized by good water quality. This reflects the igneous and metamorphic rock of the subsurface geology, low populations, and natural runoff patterns (dominated by the annual snowmelt runoff hydrograph). Concentrations of dissolved solids (as represented by specific conductivity), metals, nutrients, chlorophyll a, total organic carbon (TOC), total suspended solids (TSS), and coliforms all tend to be low, especially relative to the lower watershed (i.e., downstream of the Loveland WTP intake).

• C-BT Canals: Water quality in the C-BT canals is good and reflects the conditions in Grand Lake on the west side of the Continental Divide. Average annual volumes of water delivered from the Adams Tunnel into the Big Thompson watershed are much greater than natural runoff volumes. These flows do not follow consistent seasonal patterns. Water quality in the canals is comparable to that of the upper-most Big Thompson watershed, with low nutrients, metals, and suspended solids. Differences include lower coliforms, orthophosphate and nitrate, and slightly higher chlorophyll a, TOC, and dissolved solids (specific conductivity, alkalinity, and hardness) in water from the Adams Tunnel.

• Below Wastewater Treatment Plants (WWTPs): WWTPs serve an important function in the watershed, treating wastewater and returning it to the river. For many rivers, including the Big Thompson River, WWTPs represent major point sources for loading of nutrients, organic matter, and sometimes metals. In the Big Thompson watershed, total nitrogen and total phosphorus concentrations increase at stations below each of the major WWTPs in the watershed: M30 (below the Estes Park Sanitation District effluent), M50 (below the Upper Thompson Sanitation District effluent), significantly at M140 (below the Loveland WWTP effluent), and at VT15 (below the Berthoud WWTP). These increases below WWTPs largely reflect loading of nitrate and orthophosphate, which are forms of nutrients that are readily available for algae and plant growth. Loadings for nitrogen and phosphorus are anticipated to decrease as WWTPs comply with Colorado Regulation 85 and 38 state standards.

• Increasing TOC in canals and the upper watershed: Statistically-significant trends of increasing TOC concentrations were found in the C-BT canal system (BTWF sites C10, C20, C30, C40 and C50, or Northern Water sites AT-EP, OLY, HFC-FRD, HFC-BT, and HFC-HT) as well as in much of the Big Thompson upper watershed mainstem (M20 to M130). This finding is in agreement with findings from previous State of the Watershed reports (Hydros Consulting, 2011), but it includes more stations. Further trend testing suggests that the increasing trend may have recently begun to plateau. The cause of this increasing trend in TOC concentrations in water from the west and

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east slopes is hypothesized to be the large-scale tree death from the ongoing mountain pine beetle epidemic. This finding agrees with recently published research from Colorado (Mikkelson et al., 2013).

• Decreasing nitrate in the upper watershed: In the upper-most portions of the watershed (monitoring sites upstream of Lake Estes, including M10, 794, M20, and M30), statistically-significant long-term trends of decreasing nitrate concentrations were found. Over the 15-year period, the trend corresponds to a decrease of 25 to 55% of the median concentration. This finding agrees with recently published findings of a long-term study in the Colorado Front Range (Mast et al., 2014). That study found that nitrate concentrations in streams in Rocky Mountain National Park increased in the 1990’s but have been decreasing since the early 2000s, coincident with a decline in atmospheric concentrations of nitrogen oxides.

3.5.3 CITY OF FORT COLLINS 2013 HORSETOOTH RES WATER QUALITY MONITORING PROGRAM REPORTS

The City of Fort Collins began collecting water quality samples from Horsetooth Reservoir by boat at four main sampling locations beginning in 1988. City of Fort Collins staff have evaluated and summarized these data in several reports that are available at http://www.fcgov.com/utilities/what-we-do/water/water-quality/source-water- monitoring/water-quality-reports. The data summaries presented in these reports are generally consistent with findings from data collected as part of Northern Water’s Baseline C-BT Monitoring Program. In 2015, the City of Fort Collins began participating with Northern Water to cooperatively collect one water quality data set for Horsetooth Reservoir (see Section 1.4.2).

3.5.4 2013 CE-QUAL-W2 HORSETOOTH RESERVOIR MODELING REPORT In 2010, a project to develop a hydrodynamic water quality model of Horsetooth Reservoir was begun with joint funding from Northern Water, the USBR, the City of Fort Collins, the City of Greeley, and the Tri-Districts Soldier Canyon Filter Plant. It was felt that a hydrodynamic water quality model would be an effective tool to better understand the D.O. levels in the reservoir and to evaluate a range of inter-related water quality issues (D.O., TOC, nutrients, and water quality fate and transport) under situations that include interflow from the Hansen Feeder Canal, seasonal thermal stratification and turnover within the reservoir, and variations in C-BT Project operations. Hydros Consulting Inc. was selected as the consultant for this project.

The U.S. Army Corps of Engineers (CE) numerical model, CE-QUAL-W2, was selected for the project. CE-QUAL- W2 is a two-dimensional (length and depth dimensions), laterally averaged (conditions averaged across the width dimension), hydrodynamic and water quality model for lakes, reservoirs, rivers and estuaries.

The project showed that Horsetooth Reservoir hydrodynamics, thermal stratification and water quality are well- simulated by CE-QUAL-W2. The model indicated that low D.O. in the metalimnion is primarily controlled by the decay of inflowing organic matter (TOC in waters from the Hansen Feeder Canal that enter the reservoir as an interflow) and secondarily by sediment oxygen demand (by sediments in contact with the metalimnion along the sides of the reservoir). Low D.O. at the reservoir bottom is strongly controlled by sediment oxygen demand and by the duration of thermal stratification. In addition, the model indicated that both inflow nitrogen and phosphorus are important in terms of their impact on the in-reservoir processes. Finally, reservoir operations can affect water quality. The model indicated that inflow rates affect mixing and dilution in the metalimnion; reservoir residence times affect TOC and D.O. concentrations within the reservoir; and bottom withdrawals may influence duration of thermal stratification at Soldier Canyon.

The project findings are presented in detail in the project report (Hawley and Boyer, 2013), available at http://www.northernwater.org/WaterQuality/WaterQualityReports1.aspx.

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4. HYDROLOGY & OPERATIONS

Hydrology and operations have an important impact on water quality because of their direct influence on the sources and volumes of water that flow through the tunnels and canals and enter the Big Thompson River, Horsetooth Reservoir, and the Poudre River. The hydrology and operations of the C-BT and Windy Gap Projects vary from year to year. General descriptions of the operations are presented here with a focus on the East Slope North End conveyances and Horsetooth Reservoir.

4.1 OVERVIEW OF WEST SLOPE COLLECTION & EAST SLOPE DISTRIBUTION SYSTEMS Runoff from the headwaters of the Colorado River is collected in the Three Lakes System (Granby Reservoir, Shadow Mountain Reservoir and Grand Lake; Figures 4.1 and 4.2). Granby Reservoir also receives water pumped from Willow Creek Reservoir and Windy Gap Reservoir. When direct runoff to Grand Lake is sufficient to meet East Slope delivery requirements, the rest of the flow moves naturally from Grand Lake to Shadow Mountain Reservoir, and then to Granby Reservoir. When East Slope delivery requirements are greater than the direct runoff to Grand Lake, water is pumped from Granby Reservoir to Shadow Mountain Reservoir via the Farr Pump Plant and the Granby Pump Canal, from where it is gravity fed to Grand Lake before reaching the Adams Tunnel.

FIGURE 4.1 - WEST SLOPE COLLECTION SYSTEM.

FIGURE 4.2 - WEST SLOPE THREE LAKES

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After exiting the Adams Tunnel (Figure 4.3), the water travels through a series of tunnels, pipelines and canals to eventually be stored in the East Slope terminal reservoirs (Figure 4.4): Horsetooth Reservoir, Carter Lake and Boulder Reservoir. Water is distributed to the end-users either directly from the canal system, the reservoirs, the Southern Water Supply Project Pipeline, or via deliveries to the South Platte tributaries (Cache La Poudre River, Big Thompson River, Little Thompson River, Saint Vrain Creek, Left Hand Creek and Boulder Creek) that are used as a conveyance system.

FIGURE 4.3 - EAST PORTAL ADAMS TUNNEL & EAST PORTAL RESERVOIR.

FIGURE 4.4 - EAST SLOPE DISTRIBUTION SYSTEM.

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4.2 WY2000-WY2015 EAST SLOPE – NORTH END FLOWING SITES HYDROLOGY Water within the East Slope North End conveyances is a mixture of native water from the Big Thompson River watershed and water from the West Slope Three Lakes System via the Adams Tunnel. Water from the Big Thompson River (Figure 4.5) enters the C-BT Project primarily at Lake Estes and is diverted at the Olympus Tunnel (Figure 4.6). There are also some Big Thompson River contributions to the C-BT Project that occur downstream

HT-SOL of Lake Estes at the Dille Tunnel diversion to the Hansen Feeder Canal. Fish Creek HT-DIX enters Lake Estes near its downstream end (Figure 4.6), but the flows are small compared to Adams Tunnel and Big Thompson River flows entering Lake Estes.

FIGURE 4.5 - BIG THOMPSON RIVER JUST UPSTREAM OF LAKE ESTES (BTWF SITE M20), JULY 2008.

Estes Park Sanitation District WWTP

Lake Estes

Upper Thompson Sanitation District WWTP

Mary’s Lake

Town of Estes Park Mary’s Lake WTP

East Portal Adams Tunnel

FIGURE 4.6 - MAP OF AREA FROM EAST PORTAL TO OLYMPUS TUNNEL.

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The West Slope (Adams Tunnel) water serves as the primary source (>90%) into Lake Estes during the winter months (Figures 4.7 and 4.8). During the spring runoff (May/June), native contributions from the Big Thompson River watershed increase and are generally the dominant inflow to Lake Estes. At other times of the year, native Big Thompson River inflows to Lake Estes may be dominant (even though total inflows are relatively small) if the Adams Tunnel is off for maintenance, or flows through the Adams Tunnel are minimized for other reasons. Over the past several years, different pumping scenarios have been applied to the Farr Pump Plant during the summer to investigate how different operations impact clarity in Grand Lake, including the 2-week August 2008, 2-week August 2009, and the 6-week Summer 2013 “stop pump” periods, and the pulse pumping operations of summer 2015. These differences in summer operation of the Farr Pump Plant impact the amount and pattern of water delivery through the Adams Tunnel. During and after the September 2013 flood, all Adams Tunnel diversions to the East Slope were stopped from September 11 through late November 2013.

Flow into Lake Estes: Contributions from East Portal Adams Tunnel & Big Thompson River above Lake Estes

2,200

2,000 East Portal Adams Tunnel

1,800 Big Thompson River above Lake Estes

1,600

1,400

1,200

1,000 Flow (cfs) 800

600

400

200

0 1-Oct-05 1-Oct-06 1-Oct-07 1-Apr-06 1-Apr-07 30-Sep-08 30-Sep-09 30-Sep-10 30-Sep-11 29-Sep-12 29-Sep-13 29-Sep-14 29-Sep-15 31-Mar-08 31-Mar-09 31-Mar-10 31-Mar-11 30-Mar-12 30-Mar-13 30-Mar-14 30-Mar-15

FIGURE 4.7 - WY2005 – WY2015 DAILY FLOWS AT EAST PORTAL ADAMS TUNNEL & BIG THOMPSON RIVER ABOVE LAKE ESTES. (data from http://www.dwr.state.co.us/SurfaceWater/data/detail_tabular.aspx?ID=ADATUNCO&MTYPE=DISCHRG and http://www.dwr.state.co.us/SurfaceWater/data/detail_tabular.aspx?ID=BTABESCO&MTYPE=DISCHRG)

Contribution of Inflows to Lake Estes: Percent from Adams Tunnel & Percent from Big Thompson River 100

0 Percent of flow to Lake Estes from Adams Tunnel Adams from Estes Lake to flow of Percent 1/1/2006 4/1/2006 7/1/2006 1/1/2007 4/1/2007 7/1/2007 1/1/2008 4/1/2008 7/1/2008 1/1/2009 4/1/2009 7/1/2009 1/1/2010 4/1/2010 7/1/2010 1/1/2011 4/1/2011 7/1/2011 1/1/2012 4/1/2012 7/1/2012 1/1/2013 4/1/2013 7/1/2013 1/1/2014 4/1/2014 7/1/2014 1/1/2015 4/1/2015 7/1/2015 10/1/2005 10/1/2006 10/1/2007 10/1/2008 10/1/2009 10/1/2010 10/1/2011 10/1/2012 10/1/2013 10/1/2014 10/1/2015 Flow from Adams Tunnel Flow from Big Thompson River FIGURE 4.8 - WY2005 – WY2015 PERCENT CONTRIBUTION OF EAST PORTAL ADAMS TUNNEL FLOWS & BIG THOMPSON RIVER FLOWS TO LAKE ESTES.

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Diversions out of the Big Thompson River occur during the spring runoff, and more particularly in wetter years, when water rights come into priority. Additionally, the USBR regularly diverts water from the Big Thompson River in order to generate power at the Big Thompson Power Plant located immediately downstream of the Hansen Feeder Canal (Figure 3.2). During this skim operation, water enters the Hansen Feeder Canal either through the Dille Tunnel (Figure 4.9) or through the Olympus Tunnel and is subsequently diverted to the power plant (and ultimately returned to the river) from the Hansen Feeder Canal. The City of Loveland Water Treatment Plant can also divert its decree water from the Big Thompson River through the Dille Tunnel to its intake on the Hansen Feeder Canal.

FIGURE 4.9 - DILLE TUNNEL DIVERSIONS ENTERING THE HANSEN FEEDER CANAL.

4.3 HORSETOOTH RESERVOIR HYDROLOGY & OPERATIONS Graphs of Horsetooth Reservoir volumes and water surface elevations presented in this section are plotted beginning with WY2001 in order to better observe the general patterns of operation and the influence of specific events such as the 2002 drought, the 2001-2003 Horsetooth Reservoir Dam Modernization Project, and the 2011 historic high snowmelt runoff.

Horsetooth Reservoir water surface elevations annually fluctuate 35 to 50 feet in response to water entering the reservoir from the Hansen Feeder Canal and water being released from the reservoir at the Soldier Canyon Dam Outlet and to the Hansen Supply Canal. Water levels and reservoir volumes are lowest in the late fall after the end of the irrigation season and rise over the winter during the reservoir filling period (Figure 4.10). Water levels and volumes are highest in the late spring or early summer before water is released to meet irrigation demands on the eastern Plains. The water surface elevation at full capacity is 5,430 feet.

The Horsetooth Reservoir Dam Modernization Project was conducted from February 2001 through October 2003 and consisted of work to modernize all four dams. Construction activities required that the reservoir volume be temporarily reduced during this time (Figure 4.10). Refilling of the reservoir commenced in late November 2003 and was brought back to full capacity in March 2004. A one-year study was conducted in 2003-2004 by the USBR to assess the physical, chemical and biological impacts of the drawdown and refilling of the reservoir (Lieberman, 2005). The study didn’t provide any significant conclusions due to its relatively short duration; however, it was noted that the reservoir may experience increased productivity in the upcoming years due to additional availability of nutrients and organic matter from inundated vegetation and soil.

Total annual inflows (from the Hansen Feeder Canal and precipitation) to Horsetooth Reservoir are plotted on Figure 4.11 for WY2006 through WY2015. The plot also includes the annual total Big Thompson River flows that

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are diverted at the Dille Tunnel and introduced into the Hansen Feeder Canal. Note that diversions to the Dille Tunnel that take place after the spring runoff period are made up predominantly of West Slope water that has been routed to the Big Thompson River downstream of Lake Estes. However, whether it is predominantly West Slope water or native Big Thompson River water, water that is diverted at the Dille Tunnel is potentially further impacted by residents and businesses in the Big Thompson Canyon and by effluent from the Upper Thompson Sanitation District wastewater treatment plant (that discharges to the Big Thompson River just downstream of Lake Estes).

WY2001 - WY2015 Horsetooth Res Volume & Water Surface Elevations Vol. (ac-ft) Elev. (ft) 200,000 5,450 Water surface elev at 180,000 capacity = 5,430 ft 5,430

160,000 Volume at 5,410 capacity = 156,735 ac-ft ft) - 140,000 5,390

120,000 5,370

100,000 5,350

80,000 5,330

60,000 5,310 Reservoir Volume (ac Volume Reservoir

Outlet invert elev to Hansen (ft) Elevation Surface Water 40,000 Supply Canal = 5,293 ft 5,290

20,000 Soldier Canyon outlet sill elev 5,270 = 5,270 ft 0 5,250 1-Oct-00 1-Oct-01 1-Oct-02 1-Oct-03 30-Sep-04 30-Sep-05 30-Sep-06 30-Sep-07 29-Sep-08 29-Sep-09 29-Sep-10 29-Sep-11 28-Sep-12 28-Sep-13 28-Sep-14 28-Sep-15 FIGURE 4.10 - WY2001 - WY2015 HORSETOOTH RESERVOIR VOLUMES AND WATER SURFACE ELEVATIONS.

WY2006 - WY2015 Annual Diversions at Dille Tunnel & Annual Horsetooth Res Total Inflows 180,000 Total Horsetooth Inflows 160,000 Diversions at Dille Tunnel 140,000

ft) 120,000 -

100,000

80,000 Flow (ac Flow

60,000

40,000

20,000

0 WY2006 WY2007 WY2008 WY2009 WY2010 WY2011 WY2012 WY2013 WY2014 WY2015

FIGURE 4.11 - WY2006 - WY2015 ANNUAL HORSETOOTH RESERVOIR INFLOWS & ANNUAL TOTAL DIVERSIONS AT DILLE TUNNEL.

Total annual inflows, total annual outflows, average annual reservoir volume, and annual hydraulic residence time for Horsetooth Reservoir are summarized on Figure 4.12 and Table 4.1 (from water balance prepared by Northern Water’s Water Resources Dept). The annual hydraulic residence time has ranged from 0.72 to 1.77 years (262 to

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645 days) and averaged 1.0 years during the ten-year period of WY2006 through WY2015. The hydraulic residence time is calculated based on the average annual volume of the entire reservoir and does not take into account the impact of thermal stratification and Hansen Feeder Canal interflows on short circuiting and flow times through the reservoir.

WY2006 - WY2015 Annual Horsetooth Inflow, Outflow, Avg Volume & Hydraulic Residence Time Avg Horsetooth Volume Total Inflows 180,000 Total Outflows Hydraulic Res Time 1.8 160,000 1.6 ft) - 140,000 1.4

120,000 1.2

100,000 1.0

80,000 0.8

60,000 0.6 Flow or Volume (ac Volume or Flow

40,000 0.4 (years) Time ResHydraulic

20,000 0.2

0 0.0 WY2006 WY2007 WY2008 WY2009 WY2010 WY2011 WY2012 WY2013 WY2014 WY2015 FIGURE 4.12 - WY2006 – WY2015 BAR GRAPH OF TOTAL ANNUAL INFLOWS AND OUTFLOWS, AVERAGE ANNUAL RESERVOIR VOLUME, AND ANNUAL HYDRAULIC RESIDENCE TIME FOR HORSETOOTH RESERVOIR.

TABLE 4.1 - HORSETOOTH RES ANNUAL INFLOWS, OUTFLOWS, AVG VOLUME AND HYDRAULIC RESIDENCE TIME (WY2006-WY2015). WY WY WY WY WY WY WY WY WY WY

2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

Hansen Inflows 114,625 124,023 121,251 111,781 136,391 138,785 99,090 115,479 106,890 53,914 (AF/yr) Feeder Canal

Precipitation 1,168 2,042 2,061 2,791 2,323 2,322 1,725 2,409 5,357 2,891

Total Inflows 115,793 126,065 123,312 114,573 138,714 141,106 100,815 117,888 112,246 56,805

Soldier Outflows Canyon 36,311 33,615 32,143 27,132 31,852 30,624 46,629 36,965 33,511 31,479 (AF/yr) Outlet Hansen 89,231 79,128 88,841 78,209 84,782 97,010 101,009 40,092 31,058 57,850 Supply Canal Evaporation 4,081 4,592 4,487 3,912 4,603 4,414 5,284 4,299 4,750 4,946 Seepage 400 170 146 -54 127 146 401 -31 127 -54 estimate Total 130,023 117,505 125,618 109,198 121,365 132,194 153,323 81,325 69,447 94,221 Outflows

Avg Annual Volume (AF) 93,180 98,539 103,926 103,646 106,741 107,785 113,999 95,946 122,796 138,519

Annual Hydraulic 0.72 0.84 0.83 0.95 0.88 0.82 0.74 1.18 1.77 1.47 Residence Time (yr)

(262 (306 (302 (346 (321 (298 (271 (431 (645 (537 = (Avg Annual Vol)/ days) days) days) days) days) days) days) days) days) days) (Total Ann. Outflows)

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The annual average hydraulic residence times for WY2013 - WY2015 range from 1.18 to 1.77 years and are greater than those calculated for WY2006 - WY2012 which range from 0.72 to 0.95 years. The higher annual hydraulic residence times for the WY2013 - WY2015 period are due to the lower total reservoir outflows, and for WY2014 and WY2015, a higher than normal annual average reservoir volume.

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5. FIELD PARAMETERS

Water temperature, dissolved oxygen (D.O.), specific conductance, and pH data reveal important characteristics of surface waters. This section includes an overview of the significance of each parameter followed by a discussion for the flowing sites and then Horsetooth Reservoir to summarize the important characteristics and general patterns revealed by the data. Instantaneous (grab sample) field data are collected at the flowing sites and time series plots are contained in Appendix C. Profiles in Horsetooth Reservoir are collected at one- to five-meter depth increments, starting at the water surface and generally ending at one meter above the reservoir bottom, with measurements taken using calibrated multi-parameter field probes. The Horsetooth Reservoir profiles collected for all sampling dates within the period of WY2005-WY2015 are included in Appendix B.

5.1 TEMPERATURE Water temperature is important because of its impact on aquatic life. For lakes and reservoirs, water temperature is also important because it has a direct impact on water density and whether or not a water body is thermally stratified or completely mixed from top to bottom. Temperature data for flowing waters combined with lake/reservoir temperature profiles also provide information to estimate the depth that inflow water will enter a lake/reservoir due to temperature-induced density differences between the inflow and the reservoir water temperature.

Colorado has numeric criteria for water temperature that are dependent on the aquatic life classification of the segment, time of year, size of the lake/reservoir, and the species of fish expected to be present. For rivers and streams, continuous temperature data are used to assess compliance with the temperature standards (not the grab sample data summarized in this report). Weekly average temperatures (WAT) are calculated to assess compliance with the chronic standard, maximum WAT (MWAT). Attainment with the acute standard is based on a daily maximum (DM), defined as the highest two-hour average water temperature during a 24-hr period (WQCD, 2015). The MWAT and DM water temperature standards for the stream segments associated with this report are shown AQUATIC in Table 5.1 (WQCC, 2013; MWAT DAILY MAXIMUM LIFE WQCC, 2016b). Continuous SEGMENT SITES (CHRONIC) (ACUTE) CLASSI- temperature data are not (°C) (°C) FICATION presented and evaluated in COSPBT02 this report; any comparisons Big Thompson River CS-II CS-II HFC-BTU, to the temperature standards & tribs, RMNP to Cold 1 Apr - Oct = 18.3 Apr - Oct = 23.9 HFC-BTD Home Supply Canal Nov-Mar = 9.0 Nov-Mar = 13.0 in Table 5.1 are only made to diversion provide some context for the COSPCP10a data. The stream standards Mainstem of Poudre CS-II CS-II do not apply to the tunnel River from Munroe HSC-PRU, Apr - Oct = 18.3 Apr - Oct = 23.9 Cold 1 and canal sites, but the Gravity Canal Hdgt to HSC-PRD Nov-Mar = 9.0 Nov-Mar = 13.0 Larimer Cty Ditch temperature of the water in div. these conveyances can Site Specific: impact the water HT-SPR, CLL COSPCP14 April – Dec = 22.8 temperature in receiving HT-DIX, Cold 1 April – Dec = 23.8 Horsetooth Reservoir CCL HT-SPR Jan-Mar = 13.0 waters. Jan-Mar = 9.0

TABLE 5.1- TEMPERATURE STANDARDS.

The temperature standards for Horsetooth Reservoir are shown in Table 5.1 and include a site-specific standard for the April-December MWAT. For lakes and reservoirs, the WAT is assumed to be equivalent to the average

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temperature of the upper portion (values collected between a depth of 0.5 to 2.0 meters) for each profile (WQCD, 2015). The WAT for each profile is compared to the MWAT (chronic) standard. During thermal stratification, the MWAT may be exceeded in the upper portion of the water body if an adequate refuge exists in water below the upper portion (adequate refuge implies concurrent attainment of both the applicable temperature and dissolved oxygen standards). Again, a standards assessment is not conducted in this report and comparisons to the temperature standards in Table 5.1 are only made to provide some context for the data.

5.1.1 FLOWING SITES The flowing sites temperature data is summarized here only to show the general patterns in the data. The grab sample data have limitations since temperatures can change significantly over the course of a day such that the time of day that a sample was taken has a significant influence on the recorded value for that date. For rivers and streams, continuous temperature data is required to assess compliance with the temperature standards.

A spatial boxplot of the grab sample temperature data is shown on Figure 5.1, with the number of data points used to construct the boxes ranging from about 170 for AT-EP and OLY to 60 to 80 for the river sites. This plot also includes the top and bottom temperatures for the Horsetooth Reservoir sites. The large range in temperatures at each site reflects the large annual variation in temperatures, with the Horsetooth Reservoir bottom sites showing the smallest range, as would be expected.

FIGURE 5.1 - SPATIAL BOXPLOT OF GRAB SAMPLE WATER TEMPERATURE DATA.

Several general observations can be made from Figure 5.1. As water flows from the East Portal Adams Tunnel to the Olympus Tunnel and then up the Hansen Feeder Canal, median water temperatures generally increase. Hansen Feeder Canal water entering Horsetooth Reservoir (HFC-HT) is generally warmer, with a wider range of temperatures, than outflow from the reservoir in the Hansen Supply Canal (HSC-PR). Water temperature in the Hansen Supply Canal is strongly influenced by the Horsetooth Reservoir bottom temperatures (HT-SOL-b; Figure 5.2). Hansen Supply Canal inflow to the Poudre River (HSC-PR) is generally cooler than the upstream Poudre River water (HSC-PRU), particularly during the July – September period, resulting in the canal water having a cooling effect on the river as suggested on Figures 5.1 and 5.3. This cooling effect generalization is not suggested by the data for the Hansen Feeder Canal (HFC-BT) and associated Big Thompson River sites (HFC-BTU and HFC-BTD).

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FIGURE 5.2 - HANSEN SUPPLY CANAL & HORSETOOTH RES AT SOLDIER CANYON MONTHLY BOXPLOT OF GRAB SAMPLE WATER TEMPERATURES.

FIGURE 5.3 - HANSEN SUPPLY CANAL & ASSOCIATED POUDRE RIVER SITES MONTHLY BOXPLOT OF GRAB SAMPLE WATER TEMPERATURES.

5.1.2 HORSETOOTH RESERVOIR PROFILES The density differences of water at various temperatures and depths in a lake/reservoir result in an annual cycle of thermal stratification and the associated differences in water quality that develop between the top and bottom of a lake/reservoir. Water is at its highest density (heaviest) at a temperature of 4°C. As the water warms above 4°C, it becomes progressively less dense (lighter); likewise, as the water temperature drops from 4°C to 0°C, it also becomes progressively less dense.

The literature contains many books that describe the thermal stratification cycle (e.g., Wetzel, 2001, pg 74; Martin and McCutcheon, 1999, pg 343; Chapra, 1997, pg. 577; Cole, 1975, pg 123). After ice-off in the spring, water

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temperatures within a reservoir are nearly uniform throughout the water column. The absorption of solar radiation by the water causes the water temperature at the surface to rise. The wind is initially able to mix and transfer the heated surface water down through the depth of the reservoir. However, as the surface continues to warm, the density difference between the warmer surface waters and the cooler waters of the bottom prevents the complete mixing of the reservoir from the surface to the bottom. A layer of warmer, lighter water forms at the surface that essentially floats on the cooler, denser water that makes up the bottom region of the reservoir. This upper warmer layer, the epilimnion, has a relatively uniform temperature because it is well mixed by the wind. The bottom layer, called the hypolimnion, is isolated from the top layer and develops its own set of water quality characteristics. The middle layer, called the metalimnion, is a transition between the epilimnion and the hypolimnion and contains the thermocline which is defined as the region where the water temperature drops by at least 1°C per meter of depth (e.g., Wetzel, 2001, pg. 75).

The temperature profiles collected during the 2005-2015 time period for Horsetooth Reservoir are included in Appendix B. The temperature profiles show the typical development of thermal stratification in Horsetooth Reservoir beginning in the spring, with the presence of the epilimnion, metalimnion, and hypolimnion clearly evident by late spring or early summer, and progressing through the summer and into the fall. The temperature profiles are similar for the three monitoring locations as shown, for example, in Figure 5.4 with August 2014 temperature profiles.

Horsetooth Res Temperature Profiles - Aug 11, 2014 Conceptual cross-section of Horsetooth Res (thalweg)

5,440 HT-SPR HT-DIX HT-SOL 5,420 EPILIMNION 5,400 METALIMNION METALIMNION 5,380 5,360 HYPOLIMNION HYPOLIMNION 5,340 5,320 5,300 5,280

Thalweg Elevation (ft) Elevation Thalweg 5,260 5,240 0 4 8 12 16 20 24 0 4 8 12 16 20 24 0 4 8 12 16 20 24 Temperature ( C) 5,220 Temperature ( C) Temperature ( C) 5,200 Spring Dixon Soldier Canyon Canyon Canyon

FIGURE 5.4 - CONCEPTUAL CROSS-SECTION OF HORSETOOTH RESERVOIR SHOWING 8/11/14 TEMPERATURE PROFILES.

Patterns of thermal stratification were evaluated for Horsetooth Reservoir by plotting the difference between the top temperature (at approximately 1 meter) and the bottom temperature (1 meter above bottom) versus time (Figure 5.5), where a zero value on the plot indicates isothermal, mixed conditions, while values that increasingly deviate from zero indicate increasingly stronger thermal stratification. Figure 5.5 shows that the reservoir is strongly stratified throughout the summer and into the fall as indicated by the relatively large (12 to 16°C) differences in temperatures between the top and bottom of the reservoir. The thermal stratification patterns are also seen on Figure 5.6 which is a time series plot of the temperatures at 1-meter and at the bottom.

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Horsetooth Res: [Temp near surface] minus [Temp near bottom] HT-SPR HT-DIX HT-SOL

18 16 14 12 10 8 6 degrees degreesC 4 2 0 -2 05 06 07 08 09 10 11 12 13 14 15 05 06 07 05 06 07 05 06 07 08 09 10 11 12 13 14 15 08 09 10 11 12 13 14 15 08 09 10 11 12 13 14 15 ------Jul Jul Jul - - - Jun Jun Jun Jun Jun Jun Jun Jun Apr Apr Apr Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Dec Dec Dec Dec Dec Dec Dec Dec Dec Dec Dec ------Mar Mar Mar Mar Mar Mar Mar Mar ------1 1 1 ------1 1 1 30 30 30 30 29 29 29 29 30 30 30 29 29 29 29 28 28 28 28 30 30 30 29 29 29 29 28 28 28 28 31 31 31 31 30 30 30 30

FIGURE 5.5 - HORSETOOTH RESERVOIR TOP (1 METER) TEMPERATURES MINUS BOTTOM TEMPERATURES, PLOTTED TO INDICATE PERIODS OF MIXING (WHEN DIFFERENCE BETWEEN TOP AND BOTTOM TEMPERATURES ARE NEAR ZERO) AND THERMAL STRATIFICATION.

Horsetooth Res: Top and Bottom Temperatures HT-SPR top HT-SPR bottom (approx 1 meter below surface & 1 meter above bottom) HT-DIX top HT-DIX bottom HT-SOL top HT-SOL bottom

24 Chronic Std = 22.8 °C

12 degrees degreesC

0 05 06 07 08 09 10 11 12 13 14 15 05 06 07 05 06 07 05 06 07 08 09 10 11 12 13 14 15 08 09 10 11 12 13 14 15 08 09 10 11 12 13 14 15 ------Jul Jul Jul - - - Jun Jun Jun Jun Jun Jun Jun Jun Apr Apr Apr Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Dec Dec Dec Dec Dec Dec Dec Dec Dec Dec Dec ------Mar Mar Mar Mar Mar Mar Mar Mar ------1 1 1 ------1 1 1 30 30 30 30 29 29 29 29 30 30 30 29 29 29 29 28 28 28 28 30 30 30 29 29 29 29 28 28 28 28 31 31 31 31 30 30 30 30

FIGURE 5.6 - HORSETOOTH RESERVOIR TOP (1 METER) AND BOTTOM TEMPERATURES PLOTTED TO INDICATE PERIODS OF THERMAL STRATIFICATION (WHEN TOP & BOTTOM TEMPERATURES ARE SIGNIFICANTLY DIFFERENT) AND FALL TURNOVER (WHEN TOP & BOTTOM TEMPERATURES BECOME EQUAL).

As the air temperatures cool in the fall and solar radiation decreases, the water near the surface begins to cool as it loses heat to the atmosphere. As it cools, the surface water becomes denser and mixes with deeper water. As cooling continues, winds mix the reservoir at progressively deeper depths and the metalimnion deepens. As the epilimnion and the hypolimnion approach the same temperature (near zero on Figure 5.5), complete mixing of the lake or reservoir takes place in a process referred to as fall turnover.

Figures 5.5 and 5.6 show that fall turnover often occurs first at Soldier Canyon (HT-SOL), and generally occurs throughout the reservoir by sometime in November. Turnover in the pool behind Soldier Canyon Dam is influenced

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by the withdrawal of hypolimnetic waters at the Soldier Canyon Outlet. Note that Figure 5.6 indicates turnover when the top temperature and the bottom temperature at a site meet each other on the plot. When turnover occurs, poorer quality water that may have existed in the hypolimnion (or one of the other stratums, depending on the case) is distributed throughout the entire reservoir.

After fall turnover, the reservoir continues to uniformly cool to about 4°C (Figure 5.6). Further cooling of water at the surface to temperatures below 4°C results in an inverse temperature stratification where colder, less dense water lies over the warmer, denser 4°C water. If there is no ice cover, wind can disrupt the inverse stratification because the density differences at these cold temperatures are very small and do not provide much resistance to mixing. The formation of an ice cover prevents wind mixing. The water near the ice remains at a temperature close to 0°C, while the bottom temperature remains close to 4°C. The period of ice cover for Horsetooth Reservoir begins later and is shorter than for the west slope reservoirs, and does not consistently cover the entire reservoir. Because of this, inverse thermal stratification does not appear to occur at Horsetooth Reservoir or, if it does, it does not persist for very long and is not captured during the sampling events. Temperature profiles collected in February and March indicate that the reservoir is well mixed over the winter. On Figure 5.5 (for the years when winter sampling was conducted), a zero (or close to zero) value on the plot during this period indicates isothermal, mixed conditions. As discussed later, dissolved oxygen levels remain high at the reservoir bottom over the winter, again indicating that the reservoir remains mixed over the winter.

Maximum surface water temperatures in Horsetooth Reservoir occur in July or August (Figure 5.6). Temperatures above the 22.8°C aquatic life chronic standard in the 0.5 to 2 meter depth interval have occurred in August 2005 (at HT-SPR, HT-DIX, HT-SOL), August 2007 (at HT-DIX, HT-SOL), July 2012 (at HT-SPR, HT-DIX, HT-SOL), and July 2013 (at HT-SOL only). Temperatures above 22.8°C appear to occur more frequently at HT-SOL. Note, again, that this is not a standards compliance assessment and the presence of adequate refuge is not addressed here.

In addition to providing information about whether or not a water body is completely mixed or stratified, temperature profiles also provide information to estimate the depth that inflows will enter a water body due to temperature-induced density differences. The temperature of the inflowing water compared to the temperatures within the profile of the reservoir will determine if the inflow waters become an overflow, underflow, or interflow within the lake/reservoir. If the inflow water is warmer (less dense) than the reservoir temperatures, the inflow will flow over the surface of the reservoir (overflow). If the inflow water is colder (more dense) than the reservoir temperatures, the inflow will plunge to the bottom of the reservoir (underflow). If the inflow water has a temperature that lies between the coldest and warmest temperatures present in the reservoir profile, the inflow will plunge below the reservoir surface until it reaches a level where the inflow and ambient reservoir water temperatures (densities) are the same (interflow). Because inflow water temperatures (densities) and reservoir water temperatures change throughout the year, a specific inflow to a reservoir may occur as an overflow, an interflow, or an underflow depending on the time of year.

The occurrence of an overflow, underflow, or interflow has implications for water quality. For example, overflows can directly add nutrients and other constituents to the more productive surface zones of the reservoir (Martin and McCutcheon, 1999). Underflows that are well oxygenated can improve the water quality of the hypolimnion, while underflows with low D.O. levels can degrade the quality of the bottom waters. Overflows, underflows, and interflows all provide short-circuiting paths through a reservoir and contribute to complicated flow paths and significant deviations from average hydraulic residence times.

When Horsetooth Reservoir is stratified over the summer, the temperature data indicate that the Hansen Feeder Canal inflow to Horsetooth Reservoir occurs as an interflow within the metalimnion as shown, for example, on Figure 5.7. The monthly boxplot of water temperatures (Figure 5.8) shows that during the period of strong thermal stratification (June – September), the Hansen Feeder Canal temperature is less than the top layer (epilimnion)

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temperature at Spring Canyon (represented by HT-SPR-1) and greater than the bottom layer (hypolimnion) temperature (represented by HT-SPR-b), indicating that canal temperatures are most similar to those occurring in the metalimnion.

Horsetooth Res Temperature Profiles - Aug 11, 2014 Hansen Feeder Canal Conceptual cross-section of Horsetooth Res (thalweg) Inflow (HFC-HT) Temp = 17.4 C on 8/12/14 5,440 HT-SPR HT-DIX HT-SOL 5,420 EPILIMNION 5,400 METALIMNION Interflow METALIMNION 5,380 5,360 HYPOLIMNION HYPOLIMNION 5,340 5,320 5,300 5,280

FIGURE 5. 7 - CONCEPTUAL DIAGRAM OF HANSEN FEEDER CANAL INFLOW MOVING IN HORSETOOTH RESERVOIR AS AN INTERFLOW.

FIGURE 5.8 - HANSEN FEEDER CANAL & HORSETOOTH RES AT SPRING CANYON MONTHLY BOXPLOT OF WATER TEMPERATURES.

The boxes in Figure 5.8 for the months of March and November are made up of a relatively small number of data points (4 to 5 for HFC-HT and 3 to 7 for HT-SPR). However, if they are representative of general conditions, the plot implies that flow from the Hansen Feeder Canal entering Horsetooth Reservoir during the November - March period occurs, during at least some times, as an underflow (note that water is most dense at 4°C). Underflows that occur during the winter allow for well-oxygenated canal water to enter the hypolimnion.

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5.2 DISSOLVED OXYGEN (D.O.) Dissolved oxygen (D.O.) is essential for fish and other aquatic life. Oxygen solubility depends on temperature, with higher D.O. concentrations occurring at lower water temperatures. Oxygen solubility also depends on the partial pressure of oxygen and varies with elevation of the water body. Sources of D.O. in a water body include oxygen transfer from the atmosphere by wind (re-aeration) and oxygen production by algae and aquatic plants. Oxygen in a water body is consumed during respiration by plants, animals, and microorganisms. Organic matter that settles to the bottom of a lake/reservoir (including dead algae, other plant matter, and organic wastes) is decomposed by microorganisms (bacteria) who, in the process, consume (and deplete) the D.O. at the reservoir bottom. Metals and nutrients are released from the bottom sediments when D.O. concentrations approach 0 mg/L.

Low levels of dissolved oxygen result in degraded habitat for fish and other aquatic organisms. Currently, Colorado has numeric standards for D.O. that are based on minimum allowable concentrations for the protection of aquatic life. The criterion for the sites in this report is 6.0 mg/L, except during spawning season when it is 7.0 mg/L (WQCC, 2013, Table 1; WQCC, 2016b). For Horsetooth Reservoir, D.O. is assessed in the top, mixed layer (epilimnion), between a depth of 0.5 and 2.0 meters below the surface, by comparing the average of the measurements made within this depth range to the standard. For the protection of aquatic life, the D.O. below this depth may be less than the standard unless the chronic temperature standard in the 0.5-2 meter depth range has been exceeded. In that case, adequate refuge for fish below the 0.5-2 meter depth range is assessed against both the chronic temperature standard and the D.O. standard.

5.2.1 FLOWING SITES A spatial boxplot of the flowing sites D.O. data is shown on Figure 5.9. This plot also includes the top and bottom D.O. for the Horsetooth Reservoir sites for comparison. Of the flowing sites, the East Portal Adams Tunnel has the lowest median D.O. concentration of 8.4 mg/L. The canal sites all have median D.O. concentrations that are higher than their associated river median concentrations, as can be seen by comparing HFC-BT with HFC-BTU and HFC-BTD, and HSC-PR with HSC-PRU and HSC-PRD. The D.O. in the Hansen Supply Canal does not appear to be impacted by low D.O. conditions in Horsetooth Reservoir, likely due to oxygenation that occurs as the canal water flows the five miles from Horsetooth Reservoir to the Poudre River. Seasonal patterns in D.O. concentrations at the flowing sites are influenced by several factors including water temperature, with the lowest D.O. concentrations occurring during the warm summer months as shown in Figure 5.10 for the sites at the Olympus Tunnel, Big Thompson River below the HFC, and Hansen Feeder Canal at Horsetooth.

FIGURE 5.9 - SPATIAL BOXPLOT OF DISSOLVED OXYGEN CONCENTRATIONS.

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FIGURE 5.10 - MONTHLY BOXPLOT OF D.O. AT OLYMPUS TUNNEL, BIG THOMPSON RIVER BELOW HFC, AND HFC AT HORSETOOTH.

5.2.2 HORSETOOTH RESERVOIR PROFILES When a lake/reservoir is stratified, the bottom layer is cut off from re-aeration by the wind. Decomposition of organic matter at the bottom results in a gradual, continuous depletion of D.O. until turnover occurs. As the D.O. concentration approaches zero at the reservoir bottom, nutrients and metals are released from the sediments. Increased concentrations of nutrients and metals, particularly orthophosphate, nitrate, and manganese, can be observed in the data at this time. In discussions of D.O. depletion, the term anoxic refers to complete depletion (absence) of D.O. (D.O. = 0 mg/L), while the term hypoxic is used to denote conditions where D.O. < 2 mg/L.

The Horsetooth Reservoir D.O. profiles collected during the 2005-2015 time period are included in Appendix B. A time series plot of the bottom D.O. concentrations from the 2005-2015 profiles are plotted on Figure 5.11. The D.O. concentrations at the bottom of the reservoir continue to decline through the summer and into the fall until fall turnover occurs (Figure 5.12). The data indicate that hypoxic conditions have occurred prior to fall turnover in 8 out of the 11 years at one or more of the Horsetooth Reservoir sites. Anoxic or nearly anoxic conditions often occur at the Spring Canyon Dam site in Horsetooth Reservoir prior to fall turnover, with annual minimum values generally below 2 mg/L and often below 1 mg/L (Figure 5.11). Organic matter that is brought in with the Hansen Feeder Canal inflows would generally be expected to settle out in the upstream portions of the reservoir, including the Spring Canyon Dam area, resulting in lower D.O. concentrations as oxygen is consumed during the degradation of the settled organic matter.

The Horsetooth Reservoir profile data collected to date indicate that D.O. concentrations at the bottom are not depleted, or even partially depleted, over the winter. Note that in C-BT Project lake/reservoirs on the West Slope (including Willow Creek Reservoir, Granby Reservoir and Grand Lake), D.O. concentrations at the bottom are depleted or partially depleted over the winter as well as over the summer prior to spring and fall turnover, respectively.

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Horsetooth Reservoir: Dissolved Oxygen at Reservoir Bottom HT-SPR HT-DIX HT-SOL 12 11 10 9 8 7 6 5 4 3 Dissolved OxygenDissolved(mg/L) 2 1 0 05 06 07 08 09 10 11 12 13 14 15 05 06 07 05 06 07 08 09 10 11 12 13 14 15 08 09 10 11 12 13 14 15 05 06 07 08 09 10 11 12 13 14 15 ------Jul Jul Jul - - - Jun Jun Jun Jun Jun Jun Jun Jun Apr Apr Apr Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Dec Dec Dec Dec Dec Dec Dec Dec Dec Dec Dec ------Mar Mar Mar Mar Mar Mar Mar Mar ------01 01 01 30 30 30 30 29 29 29 29 01 01 01 30 30 30 29 29 29 29 28 28 28 28 30 30 30 29 29 29 29 28 28 28 28 31 31 31 31 30 30 30 30 FIGURE 5.11 - DISSOLVED OXYGEN CONCENTRATIONS AT THE BOTTOM OF HORSETOOTH RESERVOIR.

FIGURE 5.12 - HORSETOOTH RESERVOIR MONTHLY BOXPLOT OF D.O. CONCENTRATIONS AT SPRING CANYON TOP AND BOTTOM AND SOLDIER CANYON BOTTOM.

The Horsetooth Reservoir D.O. profiles show oxygen depletion in both the metalimnion and the hypolimnion over the summer at all three monitoring sites as shown, for example, in Figure 5.13. A pronounced metalimnetic minimum in D.O. occurs every year in Horsetooth Reservoir, with D.O. depletion beginning in June and progressing through the summer (Figure 5.14). There are several possible causes for this phenomenon (e.g., Wetzel, 2001, pg. 159; Cole, 1975, pg. 172; Horne and Goldman, 1994, pg. 124), including oxygen consumption during the decomposition of organic matter that has slowed in its decent by the colder, denser water. Inflow waters with low D.O. concentrations could also be a source, but Hansen Feeder Canal water is generally well oxygenated (Figures 5.9 and 5.10). The Horsetooth Reservoir CE-QUAL-W2 modeling conducted by Hydros Consulting (Hawley and Boyer, 2013) indicates that the metalimnetic D.O. minima in Horsetooth Reservoir are primarily controlled by the decay of inflow organic matter (TOC that enters the reservoir from the Hansen Feeder Canal), and secondarily controlled by the sediment oxygen demand (by sediments in contact with the metalimnion). D.O. concentrations in

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the Horsetooth Reservoir metalimnion fall below the 6 mg/L aquatic life standard every year, often falling within the range of 2 to 4 mg/L by September (Figure 5.14), but these situations are not considered to impact aquatic life if the chronic temperature standard and the D.O. standard are both being met in the 0.5-2.0 meter depth range. The depth to the metalimnetic D.O. minimum increases into September as the metalimnion deepens.

Horsetooth Reservoir Dissolved Oxygen (D.O.) Profiles - Aug 11, 2014 Conceptual cross-section of Horsetooth Res (thalweg) HT-SPR 5,440 HT-DIX HT-SOL 5,420 EPILIMNION 5,400 METALIMNION METALIMNION 5,380 5,360 HYPOLIMNION HYPOLIMNION 5,340 5,320 5,300 5,280

FIGURE 5.13 - TYPICAL SUMMER D.O. PROFILES IN HORSETOOTH RESERVOIR.

FIGURE 5.14 - HORSETOOTH RESERVOIR JUNE - SEPT MONTHLY BOXPLOT OF MINIMUM D.O. CONCENTRATIONS MEASURED IN THE METALIMNION.

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5.3 SPECIFIC CONDUCTANCE Specific conductance (SC) is a measure of the ability of a water sample to conduct an electrical current. The most common units of SC are micro-Siemens per cm (µS/cm). SC increases as the number of ions, or dissolved charged particles, increase. Because of this, SC is often used as an estimate of the total dissolved solids concentration. The ratio of conductivity to total dissolved solids concentration varies with chemical composition and is specific to a given natural water system, frequently in the range from about 0.6 – 0.8 mg/L per µS/cm. Thus a conductivity of 100 µS/cm would often correspond roughly to about 70 mg/L total dissolved solids.

Specific conductance is largely controlled by geology. Waters that drain areas where the underlying geology is made up of igneous and metamorphic rocks, such as in the mountain headwater areas of the Colorado, Big Thompson and Poudre Rivers, are relatively dilute and typically have low specific conductance, particularly during the spring snowmelt period. In Colorado, high specific conductance is most commonly associated with marine shales deposited in the Cretaceous Seaway. Such shale formations are found along the Front Range, between the foothills and the South Platte River, and downstream of the sites summarized in this report. Human activity, such as agriculture, mining, and urbanization, which disturb and dissolve these shales, will increase salt concentrations in streams. Other anthropogenic sources include wastewater treatment plants and de-icing salts used on roads.

5.3.1 FLOWING SITES The spatial boxplot of specific conductance data for the flowing sites is shown on Figure 5.15 and indicates that specific conductance does not vary much from the Adams Tunnel (AT-EP) to the Hansen Feeder Canal upstream of Horsetooth Reservoir (HFC-HT) with median values of approximately 50 µS/cm. Specific conductance values at the tunnel/canal sites upstream of Horsetooth Reservoir vary seasonally, as shown on Figure 5.16 for the AT-EP and HFC-HT sites, with winter and early spring values in the 50 to 70 µS/cm range. The spring snowmelt runoff has a diluting effect, resulting in the June-July values dropping to the 30 to 40 µS/cm range before beginning to increase again. In the Hansen Supply Canal (HSC-PR), the higher specific conductance values reflect those in Horsetooth Reservoir, with a median value at HSC-PR of about 70 µS/cm and little variation in the median from month to month (Figures 5.15 and 5.16).

FIGURE 5.15 - SPECIFIC CONDUCTANCE SPATIAL BOXPLOT FOR FLOWING SITES.

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FIGURE 5.16 - SPECIFIC CONDUCTANCE MONTHLY BOXPLOTS FOR AT-EP, HFC-HT AND HSC-PR.

5.3.2 HORSETOOTH RESERVOIR PROFILES The specific conductance profiles collected during the 2005-2015 time period are included in Appendix B. Specific conductance has been noted by others as a valuable tracer of the interflow/overflow/underflow process in a lake/reservoir (e.g., Effler and O’Donnell, 2001) since significant seasonal differences commonly occur between the ambient lake/reservoir value and inflow values. The specific conductance of the Hansen Feeder Canal inflow waters are generally significantly less than that of the lake/reservoir water during the spring/early summer runoff period. Specific conductance is used as evidence that the Hansen Feeder Canal inflow to Horsetooth Reservoir occurs as an interflow within the metalimnion.

As an example of the use of specific conductance as a tracer, Figure 5.17 shows the specific conductance profiles collected for Horsetooth Reservoir on August 11, 2014. The profiles show a minima in specific conductance in the depth zone (the metalimnion) where the Hansen Feeder Canal inflow was predicted to occur as an interflow based on water temperature (Figure 5.7). The ambient specific conductance within Horsetooth at that time was 71 to 79 µS/cm, while the specific conductance of the Hansen Feeder Canal water was 31µS/cm on 8/12/14. Some amount of mixing and entrainment of ambient reservoir water into the canal water occurs when the canal water plunges below the surface of the reservoir. This causes the specific conductance of the interflow to be an intermediate value (50 to 60 µS/cm on August 11, 2014) between the reservoir and the canal water. A metalimnetic minimum in specific conductance occurs in all three profiles, indicating that the interflow occurs to some degree along the entire length of the reservoir. Recognizing the occurrence of an interflow is important since it represents the possibility for the inflowing waters to short-circuit through the reservoir.

The metalimnetic minimum in specific conductance is seen every year, clearly evident at the Spring Canyon and Dixon Canyon sites in June and becoming obvious at the Soldier Canyon site by July.

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5,400 METALIMNION Interflow METALIMNION 5,380 HYPOLIMNION 5,360 HYPOLIMNION 5,340 5,320 5,300 5,280

FIGURE 5.17 - CONCEPTUAL DIAGRAM OF INTERFLOW IN HORSETOOTH RESERVOIR BASED ON SPECIFIC CONDUCTANCE PROFILES.

5.4 PH pH is a measure of the hydrogen ion activity. The pH scale ranges from 0-14, acidic to basic, respectively, with 7 being neutral. pH is critically important in the control of overall water chemistry and suitability of water for aquatic habitat. The toxicity of many pollutants, particularly metals, is related to pH. pH is largely controlled locally by geology, but it is also influenced by algal activity. pH values can rise during the day when photosynthesis is at its peak and dominates respiration and decomposition processes. During the night, pH drops as carbon dioxide is released to the water during respiration and decomposition. The pH profiles for lakes and reservoirs often show higher pH in the top waters due to algal activity, and lower pH values in the bottom waters due to the decomposition of settled organic matter.

The alkalinity of a water body impacts the amount of change that will occur in pH. Waters that have a relatively high alkalinity will be buffered against significant pH changes. Low alkalinity waters, typical of the sites covered in this report, experience wider fluctuations in pH. During peak algal activity, low alkalinity lake/reservoir waters can experience significant diurnal fluctuations in pH near the surface as a result of diurnal patterns of photosynthesis.

Colorado has a numeric standard for pH whereby the pH must be within a minimum of 6.5 and a maximum of 9 (WQCC, 2013, Table 1). This range provides adequate protection for aquatic life; however rapid changes in pH within this range can have adverse effects on aquatic life and can increase the toxicity of pollutants (USEPA, 1976).

5.4.1 FLOWING SITES The spatial boxplot of pH data for the flowing sites is shown on Figure 5.18 and indicates that pH does not vary much across all sites. The monthly boxplots (Appendix D) do not show much seasonal variation, as also seen, for example, in Figure 5.19 for the Adams Tunnel, Hansen Feeder Canal above Horsetooth, and Hansen Supply Canal sites.

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FIGURE 5.18 - pH SPATIAL BOXPLOT FOR FLOWING SITES.

FIGURE 5.19 - pH MONTHLY BOXPLOTS FOR AT-EP, HFC-HT AND HSC-PR.

5.4.2 HORSETOOTH RESERVOIR PROFILES The pH profiles collected during the 2005-2015 time period are included in Appendix B. The pH profiles show that the pH within the reservoir is generally in the range of 6.5 to 8.3, with the higher values occurring near the surface during the summer and early fall, and the lower values occurring in the hypolimnion in the summer or fall.

During the summer and into the fall, the pH profiles show that the reservoir is stratified with respect to pH, with a nearly constant pH in the epilimnion and a rapid decrease in pH of approximately 0.5 to 1.5 pH units across the

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Horsetooth Res pH & D.O. Profiles at HT-SOL metalimnion. The profiles also sometimes show the presence of a Aug 11, 2014 slight pH minima in the metalimnion in August and/or September. 0 This pH minima is coincident with the D.O. minima as shown, for example, on Figure 5.20 for HT-SOL on 8/11/14. The decay of 10 organic carbon responsible for the low D.O. in the metalimnion is also the likely cause of the pH minima at that same depth (pH drops as carbon dioxide is released to the water during 20 decomposition of organic matter).

D.O. pH 40

Depth below water surface (meters) surface water below Depth

FIGURE 5.20 - COMPARISON OF D.O. AND pH PROFILES AT HORSETOOTH 60 RESERVOIR (HT-SOL) ON 8/11/14. 2 3 4 5 6 7 8 D.O (mg/L) or pH

5.5 HORSETOOTH RESERVOIR SECCHI DISK DATA The Secchi disk is used to determine the clarity or transparency of water. A Secchi disk is a 20 cm diameter disk painted with opposing black and white quarters (Figure 5.21). A calibrated line is attached to a ring at the center of the disk and a weight is attached to the line to hold the line vertical. The disk is lowered into the water until it is no longer visible; the depth at which the disc is no longer visible is the Secchi depth transparency, recorded as depth below the surface in meters. Higher Secchi depth measurements equate to greater water clarity.

Secchi depth data for Northern Water’s Monitoring Program include measurements with and without a view scope (sight tube). The use of a view scope tends to minimize the effects of reflected light, wave action and surface particles and generally results in greater, more reproducible values than without a view scope (Boyer and Hawley, 2011). At Horsetooth Reservoir, more Secchi depth measurements have been taken with a view scope so these are the data that are summarized here.

Clarity or transparency as measured by Secchi depth is a function of (Boyer and Hawley, 2011, pg 7):

• Algal (phytoplankton) biomass; • Non-algal organic particulates: fragments of dead organisms, including particles of decomposing aquatic weeds and terrestrial vascular plants; • Inorganic particulates: sand, silt and clay particles from inflowing waters, shoreline erosion and resuspension of bottom sediments;

FIGURE 5.21 - SECCHI DISK

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• Dissolved organic matter: washed in from the watersheds primarily during the spring runoff, and also produced within the water body via algal excretion.

An increase in the concentration of one or more of these parameters results in an increase in light attenuation and a decrease in Secchi depth. The concentrations of these parameters are influenced by hydrology, C-BT system operations, nutrient concentrations, and weather.

Time series plots of the Secchi depth data are contained in Appendix C. A spatial boxplot for the three Horsetooth Reservoir sites is shown in Figure 5.22 while a monthly boxplot is shown in Figure 5.23. The spatial boxplot indicates that clarity increases from the south end of Horsetooth Reservoir to the north end, with a median Secchi depth of 2.8 m at HT-SPR and a median Secchi depth of 3.2 at Soldier Canyon. The increase in Secchi depth from south to north is likely due to the settling of suspended material that has entered the south end of the reservoir from the Hansen Feeder Canal, combined with the slightly lower chlorophyll-a concentrations (algal biomass) generally present at the north end.

The highest Secchi depths generally occur in the spring while the lowest Secchi depths occur in July/August (Figure 5.23). Decreases in Secchi depth during July are sometimes (but not always) coincident with an increase in the 0-5 meter chlorophyll-a concentrations and an increase in algal biovolume. The Seasonal Kendall Test for time trends was applied to the Secchi depth data at each of the three sites and no statistically significant time trends were found in Secchi depth.

Since Secchi depth is influenced by algal biomass, it is often used as an indicator of the trophic state of a water body. The trophic state of a water body is defined as the total weight of living biological material (biomass) in a water body at a specific location and time (Carlson and Simpson, 1996). Under a trophic state classification system, low Secchi depths (<2 meters) would indicate the presence of a significant algal biomass under eutrophic conditions (see Table 9.1). However, this would not be the case for situations where high concentrations of inorganic total suspended solids were the cause of low Secchi depths.

FIGURE 5.22 - HORSETOOTH RESERVOIR SECCH DEPTH SPATIAL BOXPLOT.

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FIGURE 5.23 - HORSETOOTH RESERVOIR SECCHI DEPTH MONTHLY BOXPLOT.

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6. GENERAL CHEMISTRY

In this report, general chemistry parameters are those that require laboratory analysis and are not classified as nutrients or metals. The general chemistry parameters included in the Baseline Monitoring Program for the East Slope – North End sites are major ions, alkalinity, total organic carbon (TOC), and total suspended solids (TSS), plus, for Horsetooth Reservoir, dissolved organic carbon (DOC), ultraviolet absorbance at a 254-nanometer wavelength

(UV254), and chlorophyll. Chlorophyll data are presented in Section 9 with the phytoplankton data. Time series plots for all general chemistry parameters are found in Appendix C, monthly boxplots are in Appendix D, annual boxplots are in Appendix E, and spatial boxplots are contained in Appendix F.

6.1 MAJOR IONS AND ALKALINITY The major ions found in natural waters include the cations calcium (Ca2+), magnesium (Mg2+), sodium (Na+), and + - 2- - potassium (K ), and the anions chloride (Cl ), sulfate (SO4 ), and bicarbonate (HCO3 ). These ions together make up the majority of the total dissolved solids in a water body and determine the specific conductance. The Baseline Monitoring Program includes analysis for the major ions except for bicarbonate, which can be calculated from alkalinity by dividing the alkalinity values by 0.8202 (Hem, 1985, pg. 57).

Alkalinity is a measure of the ‘buffering capacity’ or the ability of water to neutralize acids and resist reductions in pH. Waters with low alkalinity (less than 20 mg/L as CaCO3) have a low buffering capacity and are susceptible to changes in pH. In most natural waters, alkalinity is primarily made up of bicarbonate (when pH is greater than about 6 and less than about 10) and/or carbonate (present when pH>8.5). Non-carbonate contributors to alkalinity may include silicate, borate, hydroxide, and organic anions, but in most natural waters their concentrations are very small (Drever, 1988, pg. 52).

The concentrations of the major ions and alkalinity are influenced primarily by the local geology, soils and hydrology. Major ion concentrations can also be impacted by urban and agricultural runoff, domestic and industrial wastewater, and salts from road de-icing. Waters that drain areas where the underlying geology is made up of igneous and metamorphic rocks, such as in the mountain headwater areas of the Colorado River, Big Thompson River and Poudre River, are relatively dilute and typically have bicarbonate as the major anion, and calcium and sodium as the major cations (Drever, 1988, pg. 205).

The Baseline Monitoring Program shows that concentrations of the major ions are low at the East Slope - North End sites. Spatial boxplots for calcium and alkalinity are shown, for example, in Figures 6.1 and 6.2, while spatial boxplots for the other major ions are included in Appendix F. The highest median concentrations of calcium, magnesium, sulfate, and alkalinity occur in Horsetooth Reservoir and downstream in the Hansen Supply Canal (HSC- PR), but median concentrations are not significantly higher than the median concentrations for the other sites and are within the range measured for the other sites. The range of major ion concentrations is greater for the flowing sites (except HSC-PR) than the reservoir since the flowing sites exhibit pronounced seasonal fluctuation with dilution during the spring runoff. The flowing sites alkalinity and major ion concentrations are generally lowest in June and July, as shown for example in Figure 6.3 for calcium and Figure 6.4 for alkalinity.

Calcium Concentrations and Invasive Mussels. Zebra and quagga mussels (Dreissena spp) are considered to be among the worst aquatic nuisance species to be introduced to North America. RNT Consultants (2009a; 2009b) conducted assessments of the potential impact of these mussels to water and power system facilities and structures associated with the C-BT Project. As part of that assessment, they conducted an evaluation of the suitability of C- BT project waters for sustaining dreissenid mussel populations. Calcium concentration affects invasive mussel reproduction, growth, and survival and has been shown to be the key parameter for assessing risk of invasion. RTN Consultants (2009b, page 7) used the following calcium criteria to assess risk:

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Calcium <8 to <10 mg/L: Adults do not survive long-term Calcium < 15 mg/L: Veliger survival unlikely Calcium 16-24 mg/L: Moderate infestation level Calcium ≥ 24 mg/L: High infestation level

RTN Consultants reviewed the available calcium data (through 2007 or 2008) for the C-BT Project reservoirs and found calcium levels in these water bodies to be below those likely to support veliger survival and possibly below levels required for long term survival of adults. Calcium concentrations for Horsetooth Reservoir were generally below 10 mg/L, and assessment of the Baseline C-BT Monitoring Program calcium data through WY2015 shows that this is still the case (Figure 6.1, where each box for the Horsetooth Reservoir sites summarizes 48 data points), with a maximum Horsetooth Reservoir concentration of 10.8 mg/L. However, a recent study conducted by Davis et al (2015) emphasized that even water bodies with low levels of calcium may be vulnerable to establishment of dreissenid mussel populations depending on the complexities of other site-specific variables and the adaptability of these mussels to a broad range of conditions.

FIGURE 6.1 - CALCIUM SPATIAL BOXPLOT

FIGURE 6.2 - ALKALINITY SPATIAL BOXPLOT

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FIGURE 6.3 - CALCIUM MONTHLY BOXPLOT FOR AT-EP, HFC-HT AND HSC-PR.

FIGURE 6.4 - ALKALINITY MONTHLY BOXPLOT FOR AT-EP, HFC-HT AND HSC-PR.

Proportions and Sums of the Major Cation & Anion Concentrations. Stacked bar graphs of the major ion concentrations were prepared using data from Dec 2011 - Jan 2012 (winter conditions) and June 2012 (representing spring runoff conditions) in order to better visualize the general observations about the proportions and sums of the major ion concentrations between the sites (Figures 6.5 and 6.6, respectively). Since concentrations of the major ions have not changed significantly over the period of record, data from other years would be expected to show similar patterns and distributions of the major ions. The sum of the major ion concentrations is very low, less than about 50 mg/L, with bicarbonate contributing the highest anion concentrations and calcium contributing the highest cation concentrations at all sites. The major ion concentrations at the flowing sites are higher over the winter (Figure 6.5) prior to being diluted during spring runoff (Figure6.6). Horsetooth Reservoir does not show seasonality

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in the major ions as again indicated by comparing Figures 6.5 and 6.6. Note that the Hansen Supply Canal and associated Poudre River sites do not appear in Figure 6.5 since the canal is off over the winter.

Major Ions (mg/L) Dec 2011 - Jan 2012 55 Cl (mg/L) 50

45 SO4 (mg/L) 40

35 HCO3 (mg/L)

30 K (mg/L) 25

20 Na (mg/L) Concentrationmg/Lin 15 Mg (mg/L) 10

5 Ca (mg/L)

0 1 b 1 1 b b ------BT EP HT - - - OLY FRD BTD BTU - - - DIX DIX AT SPR SPR SOL SOL ------HFC HFC HFC HFC HFC HT HT HT HT HT HT FIGURE 6.5 - MAJOR ION CONCENTRATIONS FOR DEC 2011 – JAN 2012 (WINTER) SAMPLES.

Major Ions (mg/L) June 2012 55 Cl (mg/L) 50

45 SO4 (mg/L) 40 HCO3 (mg/L) 35

30 K (mg/L) 25

20 Na (mg/L) Concentrationmg/Lin

15 Mg (mg/L) 10

5 Ca (mg/L)

0 1 1 b 1 b b ------EP BT PR HT - - - - OLY FRD BTD BTU PRD PRU - - - - - DIX DIX AT SPR SPR SOL SOL ------HFC HSC HFC HFC HFC HFC HSC HT HSC HT HT HT HT HT FIGURE 6.6 - MAJOR ION CONCENTRATIONS FOR JUNE 2012 SAMPLES.

Major Ion Balance. Units of mg/L express the concentration of a chemical constituent in terms of its weight per unit volume. However, different ions have different molecular weights and electrical charges. Units of milliequivalents per liter (meq/L) are used to express chemically equivalent concentrations of ions in terms of molecular weight and electrical charge. If all ions have been correctly determined in the laboratory and the results expressed in units of meq/L, an ion balance can be conducted and the sum of the cations in meq/L should equal the sum of the anions in meq/L (Hem, 1985; page 164). The predominant cations and anions expressed in meq/L allow for a general classification of water type. Note that the concentration of an ion in mg/L is converted to meq/L by dividing the mg/L value by the equivalent weight of the ion (equivalent weight = molecular weight of ion divided by the ion charge; for example, equivalent weight of calcium = 40.08/2 = 20.04). Major ion concentrations from

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samples collected in June 2012 were converted to meq/L as a general check on the ion balance and to visually assess the predominant ions present in the system (Figure 6.7). Data from other years would be expected to show similar patterns and distributions of the major ions (note that the Poudre River samples summarized in Figures 6.6 and 6.7 were collected prior to the start of the High Park Fire).

Ion Balance Diagram (meq/L): June 2012 samples

0.7 Ca (meq/L) K (meq/L) Na (meq/L) Mg (meq/L) HCO3 (meq/L) Cl (meq/L) SO4 (meq/L)

0.6

0.5

0.4

0.3

0.2 milliequivalentsperLiter 0.1

0.0 anions anions anions anions anions anions anions anions anions anions anions anions anions anions anions anions 1 cations 1 1 cations 1 b cations b b cations b cations 1 b cations b ------EP cations EP BT cations BT PR cations PR HT cations HT - - - - BTU cations BTU FRD cations FRD BTD cations BTD OLY cations OLY PRD cations PRD PRU cations PRU - - - - - DIX DIX SPR SPR SOL SOL AT ------HFC HSC HFC HFC HFC HFC HSC HT HSC HT HT HT HT HT FIGURE 6.7 - ION BALANCE DIAGRAMS FOR JUNE 2012 SAMPLES.

From Figure 6.7, it is clear that calcium is the predominant cation and bicarbonate is the predominant anion at all of the sites. Although concentrations may change seasonally, the distribution of the major ions does not significantly change. For the ion balances shown on Figure 6.7, the cations and anions for all samples are balanced within acceptable margins of error. The difference between the anions and cations relative to the sum of all ions in meq/L is less than 4% at all sites, and averages 1.1% across all sites, for the June 2012 ion balances shown in Figure 6.7.

6.2 FLOWING SITES TOTAL ORGANIC CARBON (TOC) Total organic carbon (TOC) is a measure of the amount of dissolved and particulate organic matter in a water sample. In most surface waters, dissolved organic carbon (DOC) comprises a significant fraction of the TOC (generally greater than 90% of the TOC is DOC). TOC is not directly toxic to aquatic life, but it can be a significant source of oxygen demand and high concentrations can deplete the system of dissolved oxygen due to the breakdown of TOC by microorganisms. TOC occurs naturally from decomposing plant and animal matter and may originate within the water body (algae and other aquatic organisms) or be introduced through runoff from the surrounding watersheds. The highest TOC concentrations in C-BT system headwater streams occur each year during the spring snowmelt runoff period. The flush from the spring snowmelt mobilizes naturally occurring dissolved organic matter (DOM; as measured in the laboratory by TOC) that is then transported from the surrounding watersheds to the streams, rivers, lakes and reservoirs.

Although TOC is not a direct human health hazard, the dissolved portion of the TOC can react with chemicals (chlorine and others) used for drinking water disinfection to form carcinogenic disinfection byproducts (DBPs), which are regulated in treated drinking water as part of the federal Safe Drinking Water Act. For this reason, TOC concentrations are closely monitored and reduced as necessary by water treatment plants. The state of Colorado does not have a standard for TOC. However, the Colorado Primary Drinking Water Regulations outline TOC removal requirements for drinking water treatment plants to minimize DBP formation. If water entering a treatment

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plant has a TOC concentration greater than 2.0 mg/L, the treatment plant must achieve 15 to 50 percent TOC removal (depending on the influent alkalinity and TOC concentration) or meet alternative compliance criteria.

A spatial boxplot of TOC data is shown in Figure 6.8, including the Horsetooth Reservoir sites. Note that a portion of the TOC data collected from 2005 through 2008 have been disqualified from the database (see Section 2.3) and are not included in the spatial boxplot, and some sites (such as the Horsetooth Reservoir sites) only include TOC data beginning in 2009. The flowing sites (except HSC-PR) show a wider range in TOC concentrations due to seasonal variability. The Horsetooth Reservoir bottom sites show the narrowest range in concentrations, and influence the narrow range also observed at the downstream Hansen Supply Canal site (HSC-PR).

FIGURE 6.8 - TOTAL ORGANIC CARBON (TOC) SPATIAL BOXPLOT.

Water from the Adams Tunnel mixes with Big Thompson River water at Lake Estes and the water leaving Lake Estes in the Olympus Tunnel has a blend of characteristics from both sources. During the spring snowmelt runoff period (generally May through June), higher TOC concentrations in the Big Thompson River above Lake Estes result in TOC concentrations in the Olympus Tunnel and Hansen Feeder Canal that are generally higher than at the Adams Tunnel, depending on the relative flows from each source. This can be seen on Figure 6.9 which includes BTWF USGS data for BT-LEU (Big Thompson River above Lake Estes, BTWF Site M-20) and the Hansen Supply Canal above Horsetooth (HFC-HT). High TOC water in the Big Thompson River can also be diverted to the Hansen Feeder Canal at the Dille Tunnel during the spring runoff, contributing to elevated TOC concentrations in the Hansen Feeder Canal at Horsetooth during this period.

Before and after the spring runoff (generally July through March), the TOC concentrations in the Hansen Feeder Canal are primarily influenced by the concentrations in the West Slope water as measured at the Adams Tunnel. This would be expected since flows in the Big Thompson River are low compared to the Adams Tunnel flows during this time. Figure 6.9 shows that TOC concentrations in the Hansen Feeder Canal at Horsetooth are similar to concentrations measured at the Adams Tunnel, and both are higher than the TOC concentrations in the Big Thompson River above Lake Estes after the spring runoff.

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FIGURE 6.9 - MONTHLY BOXPLOT OF TOC CONCENTRATIONS SHOWING SEASONAL INFLUENCE OF TOC AT ADAMS TUNNEL & BIG THOMPSON RIVER (ABOVE LAKE ESTES) ON TOC AT HANSEN FEEDER CANAL AT HORSETOOTH.

Figure 6.10 is a monthly boxplot that compares TOC concentrations in water entering Horsetooth Reservoir in the Hansen Feeder Canal (HFC-HT) with outflow concentrations as measured at the Hansen Supply Canal site (HSC- PR). TOC concentrations in HFC-HT are highest during the spring runoff period, May – June, and are significantly higher than the outflow concentrations during this time as measured at HSC-PR. TOC concentrations at HSC-PR are relatively constant from month to month (Figure 6.10), with median monthly concentrations of about 3.4 mg/L, and reflect the concentrations measured at the bottom of Horsetooth Reservoir at Soldier Canyon (HT-SOL-b). After the runoff period, the reservoir inflow and outflow TOC concentrations are similar.

FIGURE 6.10 - MONTHLY BOXPLOT COMPARISON OF TOC CONCENTRATIONS IN HORSETOOTH RESERVOIR INFLOWS IN HANSEN FEEDER CANAL AND OUTFLOWS IN HANSEN SUPPLY CANAL.

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6.3 HORSETOOTH RESERVOIR TOC, DOC, UVA & SUVA

TOC has been measured at Horsetooth Reservoir since 2005 for the Baseline Monitoring Program, although the TOC data summary presented in this report focuses on the data collected beginning in WY2009, except for March

2008 samples collected by the USGS (see Section 2.3). DOC analysis was begun in WY2011 and UV254 was added to the parameter list in WY2012 for Horsetooth Reservoir (top and bottom). UV254 is used to characterize DOC since naturally occurring, terrestrially-derived humic substances are known to strongly absorb light at a 254-nm wavelength. UV254 and DOC data are used together to calculate Specific UV Absorption (SUVA = UV254/DOC) which indicates whether the DOC is of microbiological (algal) origin or from humic (terrestrial) sources, or a mixture.

Figure 6.11 is a monthly boxplot of TOC concentrations at Spring Canyon and Soldier Canyon Dams at both the 1- meter and bottom depths. Median TOC concentrations at the 1-meter depth are generally the same as or higher than at the reservoir bottom (Figure 6.11). Higher TOC concentrations would be expected near the surface (compared to bottom samples) during the spring and summer since algal production near the surface contributes to the TOC pool. The highest median monthly concentrations for the 1-meter samples, 4.35 mg/L, occur in July.

FIGURE 6.11 - TOC MONTHLY BOXPLOT FOR HORSETOOTH RESERVOIR.

In the summer/fall of 2010, the City of Fort Collins Water Treatment Facility and the Tri-Districts Solider Canyon Filter Plant experienced a significant increase in TOC concentrations in raw water entering their plants from the Horsetooth Reservoir Soldier Canyon outlet. The TOC data collected for Northern Water’s Baseline Monitoring Program show TOC concentrations approaching 4 mg/L at the reservoir bottom at Soldier Canyon during this period (Figure 6.12). This is consistent with the findings from the City of Fort Collins (Billica and Oropeza, 2011) which showed a peak TOC concentration of 4.2 mg/L in October 2010 in raw Horsetooth Reservoir water entering the plant at Soldier Canyon. The Fort Collins data showed a five-year (2005-2009) mean TOC concentration of 3.2 mg/L at this location, which is significantly lower (from a water treatment perspective) than concentrations approaching 4 mg/L. The increase in TOC observed in 2010 is believed to have been caused by a higher than normal

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loading of TOC to Horsetooth Reservoir from the Big Thompson River during the 2010 spring snowmelt runoff period. Since 2010, TOC concentrations around 4 mg/L at the bottom of Soldier Canyon have been measured in sampling events in Oct. 2011, April-May 2012, and July 2012 (Figure 6.12), but dropped to lower values after July 2012. The average TOC concentrations measured at the bottom of Soldier Canyon for Northern Water’s Baseline Monitoring Program have average 3.5 mg/L during the 2009 – 2015 period.

2009-2015 Horsetooth Res TOC Concentrations at Soldier Canyon Dam HT-SOL 1 meter TOC 6.5

6.0 HT-SOL bottom TOC

5.5

5.0

4.5

4.0

3.5 TOC (mg/L) TOC 3.0

2.5 Bottom TOC 2009 - 2015 Avg = 3.52 mg/L 2.0 Bottom TOC Aug 2012 - 2015 Avg = 3.49 mg/L 1.5 12 13 14 09 10 11 09 09 10 10 11 11 12 12 13 14 15 09 10 11 12 13 14 15 12 13 14 15 ------Jul Jul Jul Jul Jul Jul Jul Jan Jan Jan Jan ------Oct Oct Oct Apr Apr Apr Apr Apr Apr Apr Sep Sep Sep Sep Dec Dec Dec ------2 2 2 1 1 1 1 1 1 1 1 1 1 1 2 2 2 1 1 1 1 30 30 30 30 31 31 31 FIGURE 6.12 - TOC CONCENTRATIONS AT HORSETOOTH RESERVOIR, SOLDIER CANYON DAM SITE.

TOC AND DOC COMPARISON

Dissolved organic carbon (DOC) concentrations have been measured in addition to the TOC concentrations from WY2011 through WY2015. The average DOC/TOC ratio for the three Horsetooth Reservoir sites is 0.98 for the 1 meter samples (range of 0.89 to 1.09) and 0.97 for the bottom samples (range of 0.86 to 1.04). These ratios are consistent with the findings of others that have shown that the organic carbon present in water bodies is primarily in the dissolved form. The DOC/TOC ratios on Figure 6.13 that are greater than 1.0 indicate cases where the lab results measured a DOC slightly higher than the TOC. A quality control logic check performed during data review specifies that the Horsetooth Reservoir 2011-2015 DOC:TOC Ratio HT-SPR 1 meter DOC must be 1.5 HT-SPR bottom HT-DIX 1 meter below 110% of the 1.4 HT-DIX bottom TOC; if the 110% 1.3 HT-SOL 1 meter criteria is HT-SOL bottom 1.2 exceeded, the 1.1 incident is further 1.0 investigated and 0.9 the data may be Ratio of of DOC to TOCRatio 0.8 flagged as 0.7 “suspect” or 0.6 “disqualified” and 0.5 not used in data 10 11 12 13 14 15 10 11 12 13 14 11 12 13 14 15 10 11 12 13 14 11 12 13 14 15 11 12 13 14 15 ------Jul Jul Jul Jul Jul - - - - - Oct Oct Oct Oct Oct Sep Dec Dec Dec Dec Dec

Aug Aug Aug Aug Aug analyses. Mar Mar Mar Mar Mar - - - - - May May May May May - 2 1 1 1 1 ------1 2 1 1 1 1 2 1 1 1 1 31 31 30 30 30 31 31 30 30 30 31 30 30 30 30

FIGURE 6.13 - TIME SERIES PLOT OF DOC TO TOC RATIOS.

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UV254 AND SUVA

The TOC that occurs in the surface waters of this report is a complex mixture of naturally occurring organic compounds. TOC concentration data are of importance to water treatment plants since the treatment plants are required to remove a certain fraction of the raw water TOC, but the concentration values do not tell us anything about the source (terrestrially-derived or produced within the water body), composition, or reactivity (with chlorine or other disinfectants) of the compounds that make up the mixture. The characteristics of the mixture influence the amount of TOC that can be removed at the water treatment plant and the potential for the TOC to form DBPs when chlorine is added at the water treatment plant.

Ultraviolet absorbance at a wavelength of 254 nanometers (UV254) is the most common optical measurement used to characterize TOC. Humic substances and other compounds with aromatic (ringed) groupings absorb light strongly at a wavelength of 254 nanometers, so that waters with high terrestrial inputs of TOC have relatively high

UV254. TOC composed of a high fraction of humic substances is easier to remove during the water treatment coagulation process than TOC that is made up of a large fraction of non-humic (algal) organic matter.

The specific UV absorbance (SUVA) of a sample is calculated by dividing UV254 by DOC to obtain a normalized parameter (SUVA) that indicates aromatic carbon content of the DOC independent of DOC concentration [SUVA -1 (L/mg-m) = (UV254 in cm )/(DOC in mg/L) x 100]. SUVA can be used to compare the character of different waters, including samples collected at different locations or at the same location but during different seasons. From AWWA (2011; page 3.65, Table 3-22), SUVA> 4 indicates a high fraction of humic (terrestrially-derived) organic matter, SUVA < 2 indicates a high fraction of non-humic matter (including algal DOC; Nguyen et al, 2005), and 2< SUVA <4 indicates a mix of humic and non-humic matter. The WQCD (2011c), in their prehearing statement in support of the DUWS chlorophyll-a interim value, used SUVA data to help characterize DOC in lakes and reservoirs.

UV254 was added to the parameter list in WY2012 for the lake/reservoir sites (top and bottom) in Northern Water’s

Baseline Monitoring Program, and was measured in samples collected through WY2015. A time series plot of UV254 values measured at the Horsetooth Reservoir Spring Canyon and Soldier Canyon sites are shown along with the values measured at the Grand Lake West Portal Adams Tunnel site (GL-ATW) in Figure 6.14. Analysis for UV254 was not performed on any of the flowing sites, so the data for GL-ATW represent the characteristics of the West Slope water that is transported through the Adams Tunnel. The data show that water in Grand Lake at the Adams

Tunnel has a higher UV254 than the Horsetooth Reservoir sites, indicating the presence of more compounds with aromatic (ringed) groupings assumed to be humic substances of terrestrial origin (washed in from the surrounding watershed).

The DOC data that corresponds to the UV254 data (plotted in Figure 6.14) are plotted on Figure 6.15. The DOC concentrations for GL-ATW are generally similar to those in Horsetooth Reservoir except for the May-June spring runoff peaks that are often pronounced in the Grand Lake data since the lake experiences direct snowmelt runoff from the watershed at this time. Although their DOC concentrations are generally similar, the character of the TOC is different between Grand Lake and Horsetooth Reservoir as indicated by the time series plot of calculated

SUVA (UV254 absorbance per mg/L DOC) on Figure 6.16, and the monthly boxplot of SUVA values on Figure 6.17. Horsetooth Reservoir SUVAs generally fall between 2.0 and 3.0, while SUVAs for GL-ATW range from 2.6 to 3.9. At the bottom of Horsetooth Reservoir at Solder Canyon, near the Soldier Canyon outlet, the SUVA values showed little monthly variability during the WY2012 – WY2015 period with values indicative of a mixture of humic and non- humic substances and in the range of 2.3 to 3.0 L/mg m.

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HT-SPR 1 meter 2012-2015 UV254 (absorption at 254 nanometers) HT-SPR bottom Horsetooth Res & Grand Lake at West Portal Adams Tunnel 0.22 HT-SOL 1 meter 0.2 HT-SOL bottom 0.18 GL-ATW 1 meter 0.16

1) 0.14 -

0.12

0.1

UVA (cm UVA 0.08

0.06

0.04

0.02

0 1-Jul-12 1-Jul-13 1-Jul-14 1-Jul-15 1-Sep-11 1-Mar-12 1-Mar-13 1-Mar-14 1-Mar-15 1-May-12 1-May-13 1-May-14 1-May-15 31-Oct-11 30-Oct-12 30-Oct-13 30-Oct-14 31-Dec-11 30-Dec-12 30-Dec-13 30-Dec-14 30-Aug-12 30-Aug-13 30-Aug-14 30-Aug-15 FIGURE 6.14 - TIME SERIES PLOT OF UV254 DATA FOR HORSETOOTH RESERVOIR SITES & GRAND LAKE AT WEST PORTAL SITE. 2012-2015 DOC concentrations (mg/L) Horsetooth Res & Grand Lake at West Portal Adams Tunnel 6.0

5.5

5.0

4.5

4.0

3.5

3.0 2.5 HT-SPR 1 meter DOC DOC (mg/L) 2.0 HT-SPR bottom 1.5 HT-SOL 1 meter 1.0 HT-SOL bottom 0.5 GL-ATW 1 meter 0.0 1-Jul-12 1-Jul-13 1-Jul-14 1-Jul-15 1-Sep-11 1-Mar-12 1-Mar-13 1-Mar-14 1-Mar-15 1-May-12 1-May-13 1-May-14 1-May-15 31-Oct-11 30-Oct-12 30-Oct-13 30-Oct-14 31-Dec-11 30-Dec-12 30-Dec-13 30-Dec-14 30-Aug-12 30-Aug-13 30-Aug-14 30-Aug-15 FIGURE 6.15 - TIME SERIES PLOT OF DOC DATA FOR HORSETOOTH RESERVOIR SITES & GRAND LAKE AT WEST PORTAL SITE.

2012-2015 SUVA [SUVA = (UV254/DOC) x100] HT-SPR 1 meter Horsetooth Reservoir & Grand Lake at West Portal Adams Tunnel HT-SPR bottom 5.0 HT-SOL 1 meter HT-SOL bottom 4.5 SUVA > 4: High fraction of humic substances; high molecular weight; high aromatic & hydrophobic character GL-ATW 1 meter

4.0

3.5 m) -

3.0

2.5

SUVA (L/mg SUVA 2.0

1.5 SUVA < 2: High fraction of non-humic matter; low molecular weight; high aliphatic & low hydrophobic character

1.0 11 12 13 14 15 11 12 13 14 12 13 14 15 11 12 13 14 12 13 14 15 12 13 14 15 ------Jul Jul Jul Jul - - - - Oct Oct Oct Oct Sep Dec Dec Dec Dec Aug Aug Aug Aug Mar Mar Mar Mar - - - - May May May May - 1 1 1 1 ------1 1 1 1 1 1 1 1 1 31 30 30 30 31 30 30 30 30 30 30 30 FIGURE 6.16 - TIME SERIES PLOT OF SUVA FOR HORSETOOTH RESERVOIR SITES & GRAND LAKE AT WEST PORTAL SITE.

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FIGURE 6.17 - MONTHLY BOXPLOT OF CALCULATED SUVA DATA FOR HORSETOOTH RESERVOIR AT SOLDIER CANYON SITES & GRAND LAKE AT WEST PORTAL SITE.

The character of TOC in Horsetooth Reservoir water is influenced by the character of the West Slope TOC. It is also influenced by the TOC in the Big Thompson River which is highly aromatic during the spring runoff, with SUVA values reported in previous studies of approximately 3.2 L/mg-m (Summers et al, 2013; Beggs et al, 2013). However, the TOC in Horsetooth Reservoir has had time for transformations to occur through photodegradation and microbial breakdown. This results in TOC with different characteristics than the West Slope and Upper Big Thompson River source waters.

The data also indicate that the character of TOC in Horsetooth Reservoir is influenced to some degree by algal activity. A drop in SUVA occurred at Soldier Canyon (1-meter site) in Horsetooth Reservoir at the same time that seasonal peaks in TOC and DOC occurred in July-August 2012 and 2013. These peaks in TOC and DOC were not accompanied by increases in UV254 absorbance, resulting in the drop in SUVA (Figure 6.16). SUVA may go down if algae present in a reservoir begin to contribute a more significant fraction of the dissolved organic matter pool, since algal-derived DOC does not absorb strongly at a wavelength of 254 nanometers. The monthly boxplot for SUVA indicates that lower values occur at the surface of Horsetooth Reservoir during the summer months coincident with algal production. However, although algae may contribute to the DOC pool during some months, the previous, rigorous DOC characterization studies have shown that the dissolved organic matter within Horsetooth Reservoir is dominated by humic-like (terrestrially derived) material (Summers et al, 2013).

6.4 TOTAL SUSPENDED SOLIDS (TSS) Total suspended solids (TSS) are made up of both inorganic and organic particles. Both fractions contribute to water clarity and turbidity. The inorganic fraction includes silts and clays, while the organic fraction includes phytoplankton, zooplankton, and detritus. Detritus is non-living organic matter and can include dead algae, breakdown particles from macrophytes/vascular aquatic plants, and organic particles of terrestrial origin. Sources of suspended solids include soil erosion from the surrounding watersheds, shoreline/bank erosion, re-suspension of sediments, and in- reservoir production of phytoplankton, macrophytes and zooplankton.

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Analysis for TSS began for some sites in 2000 and, although all TSS data are plotted in the time series plots in Appendix C, the box plots only include data beginning in 2009 when there was a consistent detection limit of 1 to 2 mg/L. Prior to this, the TSS detection limit was primarily in the range of 5 to 15 mg/L with many non-detects. The AT-EP and OLY samples were analyzed by the USGS until WY2012 with TSS detection limits of 5 to 10 mg/L (with almost all samples below detection limits), so the boxplots for the AT-EP and OLY sites only include TSS data collected since WY2012. Beginning in WY2012, TSS analysis for these sites was conducted by Huffman Laboratories with a detection limit of 1 mg/L; in WY2014, TSS analysis was conducted by High Sierra Laboratories at a detection limit of 0.1 to 0.3 mg/L.

For the other sites, TSS analysis at a detection limit of 1 mg/L was conducted by Huffman Laboratories beginning in WY2009, and then by High Sierra Laboratories at a detection limit of 0.1 to 0.3 mg/L beginning in WY2014, with a variety of higher detection limits in years prior to WY2009 (Table 1.5). Again, the time series plots for TSS include all data collected since WY2000. However, due to the differences in detection limits prior to WY2009 compared to WY2009 and later, the monthly, annual and spatial boxplots for TSS were constructed with the WY2009 through WY 2015 data only.

A spatial boxplot of TSS data is shown in Figure 6.18(a) and (b), including the Horsetooth Reservoir sites. Figure 6.18(a) shows the full scale (up to a high of 828 mg/L at HFC- BTD on 4/17/14) while Figure 6.18(b) has been re-scaled to better show TSS data up to 80 mg/L.

FIGURE 6.18 (a) - TOTAL SUSPENDED SOLIDS SPATIAL BOXPLOT.

FIGURE 6.18 (b) - TOTAL SUSPENDED SOLIDS SPATIAL BOXPLOT, RE-SCALED TO SHOW LOWER CONCENTRATIONS.

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The Horsetooth Reservoir sites show little variability in TSS concentrations as would be expected since settling of suspended solids is an ongoing process in reservoirs. Median concentrations of the 47 samples used to construct each of the boxes in Figure 18 for the Horsetooth Reservoir sites ranges from 2.0 to 2.8 mg/L. The TSS monthly boxplots for Horsetooth Reservoir (Appendix D) do not show strong seasonal patterns, although elevated TSS concentrations may occur during any given time as a result of such things as increased phytoplankton production and wave action on exposed shorelines.

The largest variability in TSS concentrations occurs in the Big Thompson and Poudre River sites (HFC-BTU, HFC- BTD, HSC-PRU, and HSC-PRD). The river sites experience seasonal peaks during the spring snowmelt runoff period and can also experience increases during significant spring and summer rain events. The river sites have also been directly impacted by the 2012 High Park Fire and the September 2013 flood (Figures 6.19 and 6.20). All TSS concentrations above 50 mg/L at the Big Thompson River sites (HFC-BTU and HFC-BTD) were measured after the September 2013 flood, while all TSS concentrations above 54 mg/L at the Poudre River sites (HSC-PRU and HSC- PRD) were measured after the June 2012 High Park Fire. Runoff from wildfire burn areas and flood events can both produce large sediment loads so high TSS concentrations would be expected. In addition, river and road restoration and construction projects within the Big Thompson Canyon have resulted in an ongoing, occasional elevated TSS concentration at the HFC-BTU and HFC-BTD sites, depending on when sampling occurs relative to restoration/construction activities in the river.

A comparison of the paired upstream and downstream data on Figures 6.19 and 6.20 indicate the diluting effect that the canal flows have on river TSS, with the downstream river concentrations (sites HFC-BTD and HSC-PRD) generally lower than the upstream river concentrations.

Total Suspended Solids 2009 - WY2015 Time Series Plot: Big Thompson River at Hansen Feeder Canal (HFC-BTU & HFC-BTD) 1000 HFC-BTD HFC-BTU Sept 2013 Flood

100 TSS (mg/L) TSS 10

1 12 13 14 15 09 10 11 12 13 14 15 09 10 11 12 09 10 11 12 13 14 15 12 13 14 09 10 11 ------Jul Jul Jul Jul Jul Jul Jul Jan Jan Jan Jan ------Oct Oct Oct Apr Apr Apr Apr Apr Apr Apr Sep Sep Sep Sep Dec Dec Dec ------2 2 2 1 1 1 1 - - - 1 1 1 1 1 1 1 2 2 2 1 1 1 1 30 30 30 30 31 31 31 FIGURE 6.19 - TSS TIME SERIES PLOT FOR BIG THOMPSON RIVER SITES ASSOCIATED WITH THE HFC.

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Total Suspended Solids 2009 - WY2015 Time Series Plot: Poudre River at Hansen Supply Canal (HSC-PRU & HSC-PRD) 1000 HSC-PRD June 2012 High Park Fire HSC-PRU

100

TSS (mg/L) TSS 10

FIGURE 6.20 - TSS TIME SERIES PLOT FOR 1 POUDRE RIVER 12 13 14 15 09 10 11 12 13 14 15 09 10 11 12 09 10 11 12 13 14 15 12 13 14 09 10 11 ------SITES Jul Jul Jul Jul Jul Jul Jul Jan Jan Jan Jan ------Oct Oct Oct Apr Apr Apr Apr Apr Apr Apr Sep Sep Sep Sep Dec Dec Dec ------2 2 2 1 1 1 1 - - -

1 1 1 1 ASSOCIATED 1 1 1 2 2 2 1 1 1 1 30 30 30 30 31 31 31 WITH THE HSC.

6.5 TIME TREND ANALYSIS RESULTS FOR TOC & MAJOR IONS The trend analysis results for TOC and the major ions are summarized in Table 6.1 while raw data output from the Seasonal Kendall Test are included in Appendix I. The test was performed at a 90% confidence level (critical p-value = 0.10), which means that there is at most a 10% chance of concluding that a statistically significant trend exists when in fact there is no trend. If a computed p-value is less than 0.10, a statistically significant time trend is concluded to exist. For cases where a statistically significant trend is concluded to exist, the “Sen slope as a percent of the mean” is used to evaluate the magnitude of the trend in a relative manner. Cases where the absolute value of the Sen slope is greater than 4% of the mean are highlighted in Table 6.1 with an up or down arrow, where 4% was selected to allow for a focus on those parameters with the highest trend magnitudes (i.e., trends that are more likely to have significance from a practical standpoint). Note that if the Sen Slope is equal to 4% of the mean value calculated over the study period, the annual average parameter concentration would change by 100% of that value in 25 years (or 4% of that value each year), assuming the trend continues over time.

Of particular interest here are the TOC time trend results. For the canal/tunnel sites, the Hansen Feeder Canal at the Horsetooth inlet and the Hansen Supply Canal show a statistically significant increasing trend in TOC concentrations although the magnitude of the trends are relatively small (Sen Slope is 0.5 % of the mean at HFC-HT and 1.2% of the mean at HSC-PR). These trend results differ from those reported previously by others for Horsetooth Reservoir and waters in the Hansen Feeder Canal.

There is some history related to the analysis and reporting of trends in increasing TOC concentrations. A data analysis report prepared for the BTWF (Haby and Loftis, 2007) showed a statistically significant increasing trend in TOC concentrations in Horsetooth Reservoir and Hansen Feeder Canal sites over the period of 2001 through 2006. An increasing trend in TOC concentrations in Horsetooth Reservoir was also observed by the City of Fort Collins in their 1997-2009 data. In the 2010 Big Thompson State of the Watershed report (Hydros Consulting, 2011), which included data for the period WY2000-WY2009, statistically significant increasing trends in TOC concentrations were reported for the East Portal Adams Tunnel, Olympus Tunnel, and in the Hansen Feeder Canal sites HFC-FRD and HFC-BT as well as the Big Thompson River sites HFC-BTU and HFC-BTD (Horsetooth Reservoir was not included in that report). In the most recent BTWF report (Hydros Consulting, 2015), which included data for the period WY2000-WY2014, TOC concentrations continued to show a statistically significant increase at the East Portal Adams Tunnel, Olympus Tunnel, and in the Hansen Feeder Canal sites HFC-FRD and HFC-BT as well as the Big Thompson River sites HFC-BTU and HFC-BTD, and HFC-HT was added to this list of

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sites with increasing TOC. However, Hydros Consulting (2015) noted that the increasing TOC trends may have recently begun to plateau.

For the TOC trend analysis results presented in Table 6.1 and Appendix I, the flowing sites upstream of Horsetooth Reservoir are based on 149 to 199 data points for each site collected over the period of 2000 (or 2002) through September 2015. Many of the data are the same data that are included in the BTWF database since they were collected for both Northern Water and the BTWF. The Horsetooth Reservoir results presented in Table 6.1 are based on 62 data points at each location (62 at the 1 meter depth and 62 at the bottom) collected over the period of March 2008 through September 2015. Visual inspection of the time series plots in Appendix C and the annual boxplots in Appendix E do not show any obvious trends in TOC concentrations over time, consistent with the statistical trend analysis results (from both a statistical and practical standpoint). Of the trend analysis results presented in Table 6.1, the only site which may have questionable results is the Poudre River site upstream of the Hansen Supply Canal (HSC-PRU) since there were only 36 TOC data points included in Northern Water’s database; there are significantly more Poudre River TOC data collected by the City of Fort Collins that could be used to better assess time trends in the Poudre River TOC concentrations.

TABLE 6.1 - SUMMARY OF SEASONAL KENDALL TREND TEST RESULTS FOR TOC AND MAJOR IONS TOC & Major Ions

Site ID System Feature TOC Alkalinity Calcium Magnesium Potassium Sodium Chloride Sulfate AT-EP Adams Tunnel OLY Olympus Tunnel HFC-FRD Hansen Feeder Canal, Flatiron HFC-BTU Big Thompson Riv, upstream HFC HFC-BT Hansen Feeder Canal, Big Thomp Riv HFC-BTD Big Thompson Riv, downstream HFC HFC-HT Hansen Feeder Canal, Horsetooth Res

HT-SPR-1 Horsetooth Res, Spring Can, 1 meter ↑ HT-SPR-b Horsetooth Res, Spring Can, bottom ↑ HT-DIX-1 Horsetooth Res,Dixon Can, 1 meter ↑ HT-DIX-b Horsetooth Res, Dixon Can, bottom ↑ HT-SOL-1 Horsetooth Res, Soldier Can, 1 meter ↑ HT-SOL-b Horsetooth Res, Soldier Can, bottom ↑

HSC-PRU Poudre River, upstream HSC HSC-PR Hansen Supply Canal ↑ HSC-PRD Poudre River, downstream HSC

Note: all trend tests are at the 90% confidence level (significant trend if p-value ≤ 0.10)

Chloride. The other trend analysis result of note in Table 6.1 is the increasing trend in chloride concentrations in Horsetooth Reservoir and the Hansen Supply Canal. The Sen slope for these sites ranged from 6.7% to 11.1% of the mean. The cause of this increasing trend is unknown. However, maximum chloride concentrations measured in Horsetooth Reservoir are around 3 mg/L, so the concentrations have remained relatively low.

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7. NUTRIENTS

Nitrogen and phosphorus are major nutrients that support algal growth in water. Concentrations of these nutrients are linked to the biological condition and productivity status of a water body. The solutions to water quality problems related to algae are ultimately tied to the control of sources of phosphorus and/or nitrogen, and depend on what nutrient is limiting algal growth and biomass. Natural sources of nutrients include precipitation, phosphorus- rich rocks, and biochemical processes. Anthropogenic sources of nutrients include urban runoff, domestic wastewater treatment plant effluent, failing and/or poorly maintained septic systems, livestock waste, fertilizer applications to agricultural lands/golf courses/lawns, and soil erosion.

The forms of nitrogen and phosphorus that are analyzed for the Baseline Monitoring Program are summarized on Table 7.1, along with their significance and associated water quality standards.

TABLE 7.1 - FORMS OF NITROGEN AND PHOSPHORUS MEASURED FOR THE BASELINE MONITORING PROGRAM. Form in Nutrient Water Quality Significance Regulatory Standards Water A primary source of nitrogen for algae; released during decomposition NH3 (un-ionized of organic matter; when oxygen is form) present, ammonia is converted Un-ionized form toxic to aquatic life. Ammonia and (oxidized) to nitrate in a process Aquatic Life water quality standard: table value NH4+ (ionized called nitrification; ammonia can depends on pH and water temperature. form; ammonium accumulate in the hypolimnion near ion) the sediments under anoxic conditions. A primary source of nitrogen for High concentrations of nitrate causes "blue baby" Nitrate NO3- algae; nitrate is created during the syndrome (methemoglobinemia); Drinking water oxidation of ammonia (nitrification). max. contaminant level = 10 mg/L as N Nitrate + High concentrations of nitrite causes a condition Nitrite Available for uptake by algae, but in fish called "brown blood disease" rarely encountered at significant (methemoglobinemia); Aquatic Life standard = Nitrite NO2- concentrations; intermediate product 0.05 mg/L formed during nitrification but High concentrations of nitrite causes "blue baby" quickly converted to nitrate. syndrome (methemoglobinemia); Drinking water max. contaminant level = 1 mg/L as N Ammonia + Indicates organic loading from Organic Nitrogen phytoplankton, aquatic weeds and Total Kjeldahl compounds external sources; represents the Nitrogen (proteins, amino total amount of oxidizable nitrogen (TKN) acids, peptides, (i.e., nitrogen compounds that can etc) eventually be converted to nitrate). Colorado WQCC: TN = 0.426 mg/L cold water Total Calculated: lakes/res, July 1- Sept 30 avg in mixed layer; TN = Nitrogen TN = TKN + 1.25 mg/L cold water streams, annual median; (TN) NO3- + NO2- values do not yet apply to water bodies in this report. Form of phosphorous that is At 6

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Section 7.1 summarizes the phosphorus data collected during the reporting period, while the nitrogen data are summarized in Section 7.2. Section 7.3 presents nitrogen to phosphorus ratios for Horsetooth Reservoir to evaluate if nitrogen or phosphorus (or both) are limiting the growth and biomass of algae. Section 7.4 presents the results of the nutrient time trend analysis. Time series plots, monthly boxplots, annual boxplots, and spatial boxplots for all of the sites are contained in Appendix C, D, E, and F, respectively.

Nutrient analysis for the Baseline Monitoring Program began in different years depending on the nutrient and site (Table 1.2). The time series plots for the nutrient data (Appendix C) include all the data collected since WY2000, except for data flagged as “suspect” in the database as discussed in Section 2.3. For some sites and parameters, boxplots were constructed using a subset of the data, with some data and parameters excluded due to high detection limits resulting in many non-detected values that can skew the boxes. Data excluded from the boxplots were summarized on Table 2.1.

7.1 PHOSPHORUS Ortho-phosphate (ortho-P) is the only form of phosphorus that is immediately available for uptake by algae. Total phosphorus (TP) includes dissolved, particulate, adsorbed, organic, and inorganic forms of phosphorus, and includes phosphorus that is bound to sediments and phosphorus that is tied up within organic matter and phytoplankton. TP is generally considered the best value for assessing phosphorus in a water body because of the dynamic nature of the phosphorus cycle and the ability of phosphorus to be transformed and change from one form to another. However, since ortho-P is the form that is immediately available for algal uptake, it is the focus of much of the discussion here.

Organic and inorganic particles that contain phosphorus settle to the bottom of the water bodies where they accumulate in the sediments. The bottom sediments serve as both a sink and a source of phosphorus. The release of soluble phosphorus (ortho-P) from the bottom sediments of a lake/reservoir to the overlying water is very complex (e.g., Hupfer and Lewandowski, 2008; and others) and includes biotic and chemical processes that are impacted by dissolved oxygen, redox conditions, pH, temperature, and the concentrations of other inorganic and organic compounds.

Within the C-BT Project watersheds, natural sources of phosphorous include the decay of plant debris and other organic matter. Phosphorus is also present in the minerals that make up the rocks, soils and sediments and can be present in atmospheric particulate dry fallout. Anthropogenic sources of phosphorus include wastewater treatment plant effluent, failing individual sewage disposal systems (ISDSs), runoff from agricultural lands and urban areas, and erosion of stream channels, dirt roads, construction sites, and other land surfaces.

TP is often used to estimate algal biomass and the trophic state or biological condition of a lake or reservoir. Under a trophic state classification system (Carlson and Simpson, 1996), TP concentrations greater than 0.024 mg/L in a lake/reservoir correspond to eutrophic conditions (nutrient rich with high algal production), while TP concentrations less than 0.012 mg/L correspond to oligotrophic conditions (nutrient poor with low algal production). Mesotrophic conditions lie between oligotrophic and eutrophic. In order to prevent nutrient enrichment of water bodies and to protect their designated beneficial uses, the Colorado Water Quality Control Commission adopted an interim TP numeric value of 0.025 mg/L for cold water lakes and reservoirs to be assessed as a July 1- Sept 30 average of values in the mixed layer (epilimnion). An interim TP numeric value of 0.110 mg/L was adopted for cold water rivers and streams and 0.17 mg/L for warm water rivers and streams, both assessed as an annual median. TP numeric values have not been adopted as a water quality standard for Horsetooth Reservoir and the other sites covered in this report.

Figures 7.1 and 7.2 are spatial boxplots of TP and ortho-P concentrations, respectively. The three Horsetooth Reservoir sites include separate boxes for the 1 meter below surface and the 1 meter above bottom depths. The

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highest median TP concentration (0.06 mg/L) occurs at the HFC-BTU site (Big Thompson River above the Hansen Feeder Canal). The lowest median TP concentration of 0.012 mg/L occurs at the East Portal Adams Tunnel (AT-EP), Horsetooth Reservoir at Soldier Canyon 1-meter depth (HT-SOL-1), and at the Hansen Supply Canal (HSC-PR) site. The river sites experience the highest TP concentrations since TP is associated with sediments that are mobilized during snowmelt runoff and significant rainfall events. The Big Thompson River sites have been impacted by the 2013 flood, while the Poudre River sites have been additionally impacted by the 2012 High Park Fire. The highest TSS concentrations observed at the river sites associated with these events (Section 6.4) have also produced the highest TP concentrations.

FIGURE 7.1 - SPATIAL BOXPLOT OF TOTAL PHOSPHOROUS.

FIGURE 7.2 - SPATIAL BOXPLOT OF ORTHO-P.

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The lowest ortho-P concentrations are found at the East Portal Adams Tunnel, the 1-meter Horsetooth Reservoir sites, and the Hansen Supply Canal. The highest ortho-P concentrations are found at the Big Thompson River sites which are downstream of the wastewater treatment plant effluent discharge for both the Estes Park Sanitation District and the Upper Thompson Sanitation District. High nutrient concentrations in Big Thompson River water upstream of the Dille Tunnel (HFC-BTU) can impact nutrient concentrations in the Hansen Feeder Canal during diversions at the Dille Tunnel, but these diversions generally occur during higher flows when nutrient concentrations in the Big Thompson River are diluted. The impact of wastewater treatment plant effluent on nutrient concentrations within the mainstem Big Thompson River is further discussed in the 2015 BTWF State of the Watershed Report (Hydros Consulting, 2015). In Horsetooth Reservoir, the 1-meter samples have low ortho-P concentrations compared to the bottom samples. The median ortho-P concentrations in the Horsetooth Reservoir 1-meter samples is 0.001 mg/L and reflects the fact that ortho-P near the surface is readily taken up by phytoplankton as it becomes available. Ortho-P is also removed from the water column by adsorbing onto the surfaces of clays and metal oxides (i.e., inorganic sediments) and then settling to the reservoir bottom.

In water bodies such as Horsetooth Reservoir that strongly stratify, ortho-P concentrations (and consequently TP concentrations) increase in the hypolimnion over the months prior to turnover. There are two main processes by which this occurs. In the first process, organic matter that has settled down into the hypolimnion and onto the lake/reservoir bottoms undergoes decomposition by microorganisms. This process consumes oxygen and liberates ortho-P and nitrogen. If this organic matter is assumed to consist of algal biomass, its decomposition by microorganisms can be conceptually represented by the following stoichiometric equation (Stumm and Morgan, 1981, page 562; although note that the exact elemental composition of algal cells, particularly the proportion of N and P shown in the equation below as a 16:1 molar ratio, varies between phytoplankton species and also varies in space and time for any given species depending on environmental conditions):

Breakdown by {algal biomass} microorganisms - 2- + {(CH2O)106(NH3)16(H3PO4)} + 138O2 106CO2 + 16NO3 + HPO4 + 122H2O + 18H + trace elements + energy

2- If enough oxygen is present, some of the liberated ortho-P (shown as HPO4 in the equation above) will adsorb onto the surfaces of clays and metal oxides and be stored in the sediments. Some of this ortho-P is also taken up by microorganisms that live in the hypolimnion (bacteria). However, the net result is the accumulation of ortho-P and nitrogen in the hypolimnetic waters as organic matter is decomposed and oxygen concentrations drop. This accumulation of ortho-P begins when stratification sets in and ends at turnover.

The second main process that results in an increase in ortho-P in the hypolimnion occurs when oxygen levels at the reservoir bottom decrease to 0 mg/L. At this time, there can be an abrupt increase in ortho-P concentrations as ortho-P is released from the bottom sediments and diffuses into the overlying hypolimnetic waters. This is seen at Horsetooth Reservoir when anoxic conditions exist at Spring Canyon Dam. Among the many complicated processes that occur within the sediments, ortho-P that has been adsorbed onto iron and manganese oxide surfaces is released into the sediment pore water as the iron and manganese oxides are dissolved under chemically reducing/anoxic conditions.

At Horsetooth Reservoir, monthly boxplots for the Spring Canyon Dam site (HT-SPR) show significant increases in median ortho-P concentrations at the reservoir bottom through the summer and into the fall, with the highest concentrations occurring prior to fall turnover (Figure 7.3). The bottom ortho-P concentrations at the Spring Canyon Dam site reach higher levels than at any of the other West and East Slope C-BT Project reservoirs except

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Willow Creek Reservoir. When oxygen levels at the reservoir bottom decrease to near 0 mg/L, ortho-P concentrations at the HT-SPR bottom site often abruptly increase further as ortho-P is also released from the sediments. At Horsetooth Reservoir, anoxic conditions occurred at the HT-SPR bottom site in October 2008, 2009, 2012 and 2013 (Figure 5.11), prior to fall turnover. High ortho-P concentrations at the reservoir bottom at the Spring Canyon Dam site in October result in an increase in ortho-P concentrations in the 1-meter samples at Spring Canyon Dam in November after the fall turnover (Figure 7.3).

The bottom ortho-P concentrations at the Dixon Canyon site (HT-DIX) also increase through the summer and into the fall, but are lower than at Spring Canyon. A similar increase is not seen at the Soldier Canyon site (HT-SOL) since hypolimnetic waters are released at the Soldier Canyon Outlet and limit the accumulation of ortho-P at the reservoir bottom (Figure 7.3).

FIGURE 7.3 - MONTHLY BOXPLOTS OF ORTHO-P CONCENTRATIONS FOR HORSETOOTH RESERVOIR: SPRING, DIXON & SOLDIER CANYON SITES.

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7.2 NITROGEN Sources of nitrogen to the surface waters include biological nitrogen fixation by some cyanobacteria; decay of plant debris; and atmospheric particulate dry fallout and precipitation falling directly onto the water body surfaces. Anthropogenic sources of nitrogen include wastewater treatment plant effluent, failing individual sewage disposal systems, and runoff from fertilized agricultural lands, golf courses and lawns.

Within a water body, ammonia is released during the biological decomposition of organic matter (remains of dead plants and animals) in a process called ammonification (Figure 7.4). In the presence of oxygen, this ammonia is readily converted to nitrite N2 Atmospheric nitrogen and then nitrate in a biological process called nitrification. Total Kjeldahl nitrogen (TKN) Nitrogen fixation by N2 Aqueous nitrogen some cyanobacteria is the sum of ammonia and •Wastewater effluent organic nitrogen and •Watershed runoff Denitrification represents the total amount of •Atmospheric deposition (anoxic conditions) oxidizable nitrogen (i.e., nitrogen compounds that can

- + - NO3 be converted to nitrate). NH4 NO2 Bottom Nitrite Nitrate Sediments Ammonia TKN concentrations can Nitrification (oxic conditions) fluctuate with phytoplankton Ammonification activity and with inputs of Uptake Uptake organic matter from other sources. Organic N - dissolved & Algae particulate (Decomposing algal biomass and other plant & animal matter/wastes) Animals

FIGURE 7.4 - SIMPLIFIED NITROGEN CYCLE IN AQUATIC SYSTEMS

In order to prevent nutrient enrichment of water bodies and to protect their designated beneficial uses, the Colorado Water Quality Control Commission adopted an interim total nitrogen (TN) numeric value of 0.426 mg/L for cold water lakes and reservoirs to be assessed as a July 1- Sept 30 average of values in the mixed layer (epilimnion). An interim TN numeric value of 1.25 mg/L was adopted for cold water rivers and streams, assessed as an annual median. TN includes organic nitrogen, ammonia, nitrate and nitrite. There is a delayed implementation of the TN numeric value and it has not been adopted as a water quality standard for specific water bodies in Colorado, including the water bodies in this report. There are drinking water standards for nitrate and nitrite (10 mg/L and 1mg/L, respectively), but concentrations in the water bodies covered in this report are all significantly lower than these standards.

Nitrate + Nitrite. A spatial boxplot of nitrite plus nitrate is plotted on Figure 7.5. The lowest median concentrations of nitrate+nitrite are found at the Horsetooth Reservoir 1 meter depth due to algal uptake. The highest median nitrate+nitrite concentrations are found in the Big Thompson River sites, which are downstream of wastewater treatment plants, and the sites at the bottom of Horsetooth Reservoir.

At the bottoms of stratified water bodies such as Horsetooth Reservoir, nitrate concentrations increase as organic matter settles to the bottom, ammonia is released during decomposition of the organic matter, and the ammonia is oxidized to nitrate through nitrification. Under anoxic conditions (oxygen concentration of 0 mg/L), nitrification

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ceases and denitrification takes place. During denitrification (Figure 7.4), nitrate undergoes bacterial reduction to

N2 which is coupled with the decomposition or oxidation of organic matter (where nitrate serves as the oxidant).

At Horsetooth Reservoir, the nitrate+nitrite concentrations at the reservoir bottom show significant increases through the summer and into the fall (Figure 7.6; see Appendix C for HT-DIX site). The nitrate+nitrite concentrations at the bottom of Spring Canyon (HT-SPR) and Dixon Canyon (HT-DIX) just prior to fall turnover are the highest among all the C-BT Project West and East Slope lake/reservoir sites. An increase in nitrate+nitrite concentrations also occurs through the summer at the Soldier Canyon site (HT-SOL; Figure 7.6), but the magnitude of the increase is less since hypolimnetic waters are released at the Soldier Canyon Outlet.

FIGURE 7.5 - SPATIAL BOXPLOT OF NITRATE PLUS NITRITE.

FIGURE 7.6 - MONTHLY BOXPLOTS OF NITRATE + NITRITE CONCENTRATIONS FOR HORSETOOTH RES (HT-SPR AND HT-SOL).

At the 1-meter depth in Horsetooth Reservoir, nitrate concentrations are generally highest in the March - May period (Figure 7.6). However, Figure 7.6 indicates that the high bottom nitrate+nitrite concentrations that occur right before fall turnover can result in an increase in nitrate+nitrite concentrations in the 1-meter samples in

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November. With the fall turnover, the nitrate+nitrite that has accumulated in the hypolimnetic waters is distributed throughout the entire water column.

Figure 7.7 is a monthly boxplot that compares nitrate+nitrite concentrations in the Hansen Feeder Canal upstream of Horsetooth (HFC-HT), the top and bottom concentrations in Horsetooth at Soldier Canyon (HT-SOL-1 and HT- SOL-b), and the concentrations in the Hansen Supply Canal downstream of Horsetooth (HSC-PR). The elevated nitrate+nitrite concentrations in the hypolimnion at Soldier Canyon result in an increase in nitrate+nitrite concentrations in the Hansen Supply Canal (HSC-PR) in August through October (Figure 7.7), but the concentrations are still low and do not appear to significantly impact nitrate+nitrite concentrations in the Poudre River downstream of the Hansen Supply Canal. Figure 7.7 indicates that the nitrate + nitrite concentrations in the Hansen Feeder Canal inflow to Horsetooth Reservoir (HFC-HT) is generally higher than at the Soldier Canyon and Hansen Feeder Canal sites during May and June.

FIGURE 7.7 - MONTHLY BOXPLOT OF NITRATE+NITRITE CONCENTRATIONS AT HFC-HT, HT-SOL-1, HT-SOL-b, AND HSC-PR.

Ammonia. A spatial boxplot of ammonia concentrations is plotted on Figure 7.8. The highest ammonia concentrations occur at the Big Thompson River sites, which are downstream of wastewater treatment plants, and at the bottom of Horsetooth Reservoir.

FIGURE 7.8 - SPATIAL BOXPLOT OF AMMONIA.

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Ammonia concentrations at the bottom of Horsetooth Reservoir are generally low (median concentrations ranging from 0.003 to 0.005 mg/L) since the ammonia produced during the decomposition of organic matter (ammonification) is quickly converted to nitrate through nitrification. However, when anoxic conditions exist at a reservoir bottom, nitrification ceases and ammonia can accumulate as decomposition of organic matter and ammonification continue. Reservoir turnover generally takes place before anoxic conditions and significant ammonia accumulation occurs, although an exception to this often occurs at Spring Canyon.

Total Kjeldahl Nitrogen (TKN). A spatial boxplot of TKN concentrations is plotted on Figure 7.9. TKN is the sum of ammonia and organic nitrogen concentrations and, with ammonia concentrations relatively low, most of the TKN is made up of organic nitrogen (in particulate and dissolved forms). The highest TKN concentrations occur at the Big Thompson River sites, which are downstream of wastewater treatment plants, and at the Poudre River sites. The highest TKN concentrations measured at the Poudre River sites occurred during the year after the 2012 High Park Fire, including peaks during the 2013 spring runoff and in September 2013 at the beginning of the 2013 Flood event.

FIGURE 7.9 - SPATIAL BOXPLOT OF TOTAL KJELDAHL NITROGEN (TKN).

Total Nitrogen (TN). TN includes organic nitrogen, ammonia, nitrate and nitrite and is calculated here as the sum of TKN plus nitrate+nitrite. A spatial boxplot of TN concentrations is plotted on Figure 7.10.

The 1-meter TN concentrations at the Horsetooth Reservoir sites are well below the 0.426 mg/L interim value as indicated on Figure 7.10, with the median concentration for all TN data at each Horsetooth site within the range of 0.24 to 0.26 mg/L and maximum values below 0.35 mg/L. Most of the TN at the 1-meter depth is comprised of organic nitrogen, with the ammonia, nitrate and nitrite concentrations all very low.

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FIGURE 7.10 - SPATIAL BOXPLOT OF TOTAL NITROGEN.

7.3 HORSETOOTH RES NITROGEN TO PHOSPHORUS RATIOS Water column Total Nitrogen:Total Phosphorus (TN:TP) ratios are commonly used to assess whether nitrogen, phosphorus or both are limiting phytoplankton growth and biomass within lakes and reservoirs. The N:P ratio of phytoplankton cells averages approximately 7.2:1 on a weight basis (the Redfield ratio; e.g., Wetzel, 2001, page 278; Stumm and Morgan, 1981, page 562; or 16:1 on a molar basis) and is the basis for assessing nutrient limitations using TN:TP ratios calculated from TP and TN concentrations in the water column. At the simplest level (and assuming that the phytoplankton community in a specific water body has a N:P ratio of 7.2), water samples with a TN:TP < 7.2 would indicate that the water body is N limited, while a TN:TP > 7.2 would indicate that the water body is P limited. However, optimal N:P ratios vary over a wide range across the variety of freshwater phytoplankton (from 4 to 38 or higher; Downing and McCauley, 1992; Wang and Wang, 2009). The addition of the limiting nutrient to a water body will cause an increase in the algal population.

The literature shows that a range of TN:TP ratios have been used to assess the nutrient limitation status of lakes and reservoirs (Table 7.2). For a specific lake or reservoir, the exact ratio at which a nutrient becomes limiting depends on the community of phytoplankton species that are present and their specific TN:TP ratios. Because of this, TN:TP ratios calculated for the water column often do not do a very good job of predicting the nutrient that limits phytoplankton growth; Wang and Wang (2009) suggested that the method is unreliable. Nutrient enrichment experiments are required for a more accurate assessment.

TABLE 7.2 - TP:TN RATIOS (WEIGHT BASIS) REPORTED IN THE LITERATURE FOR PREDICTING NUTRIENT LIMITATIONS. N-Limitation Co- P-Limitation (N deficiency) Limitation (P deficiency) Guildford and Hecky (2000) TN:TP < 9 9 > TN:TP < 22 TN:TP > 22

Downing and McCauley (1992) TN:TP <14

Jassby and Goldman (2003), page 40 TN:TP < 4 4 > TN:TP < 14 TN:TP > 14

Sakamato (1966) TN:TP < 10 10 > TN:TP < 17 TN:TP > 17

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TN:TP ratios have also been used to predict the dominance of the phytoplankton population by cyanobacteria (blue- green algae), with low TN:TP ratios (in water bodies enriched with P) favoring nitrogen-fixing species of cyanobacteria. An analysis presented by Smith (1983) indicated that lakes with epilimnetic TN:TP ratios >29:1 (weight basis) will typically be characterized by low proportions (by volume) of cyanobacteria. However, Downing et al (2001) showed that the risk of dominance by cyanobacteria is more strongly associated with the concentrations of TP, TN or algal biomass than the ratio of TN:TP. More recent work (Harris, 2012) showed a significant reduction in cyanobacteria biovolume and a shift to phytoplankton that are a more favorable food source for zooplankton when nitrogen was added to large-scale in situ mesocosms to achieve high TN:TP ratios > 75:1 (by weight).

Nutrient limitations have been previously assessed by others for the C-BT lake/reservoirs. Jassby and Goldman (1999, page 17) assessed nutrient limitations in Horsetooth Reservoir and Carter Lake based on nutrient data collected in 1998 and 1999. They used the ranges shown in Table 7.2 above that were reported by Sakamoto (1966), where TN:TP > 17 indicates P limitation and TN:TP < 10 indicates N limitation. Their analysis indicated P limitation approximately 60% of the time and N limitation less than 20% of the time in both Horsetooth Reservoir and Carter Lake Reservoir.

Lieberman (2008) assessed nutrient limitations in Horsetooth Reservoir during the period 2005 -2007. This analysis used the TN:TP ranges shown in Table 7.2 that were suggested by Jassby and Goldman (2003), where TN:TP > 14 indicates P limitation, and co-limitation was assumed to occur when 4 < TN:TP < 14. The analysis indicated that these water bodies were usually P limited with some instances of N + P co-limitation (Tables 27 to 37, page 219- 229, in Lieberman, 2008).

Data collected during the Baseline Monitoring Program from WY2008 through WY2015 were used to calculate TN:TP ratios for Horsetooth Reservoir. The calculated TN:TP ratios are summarized for the Horsetooth Reservoir sites in the time series plot shown in Figure 7.11. The TN:TP ratio for a specific water body can vary over a season or from year to year, and indicates shifts in nutrient limitation from one nutrient to the other or to co-limitation.

Reference lines were drawn on Figure 7.11 at a TN:TP ratio of 10 (to indicate the approximate N limitation threshold) and at a TN:TP ratio of 17 (to indicate the approximate P limitation threshold) as suggested by Sakamoto (1966). Based on these thresholds and the calculated TN:TP ratios, it would be concluded that Horsetooth Reservoir is either P limited or co-limited.

Horsetooth Reservoir TN:TP Ratio WY2008 - WY2015 HT-SPR TN:TP 1-meter TN & TP data HT-SOL TN:TP 60

30 TN:TP Ratio Probable P 20 Limitation

10 Probable N Limitation 0

10/01/07 12/31/07 03/31/08 06/30/08 09/30/08 12/30/08 03/31/09 06/30/09 09/30/09 12/30/09 03/31/10 06/30/10 09/30/10 12/30/10 03/31/11 06/30/11 09/30/11 12/30/11 03/30/12 06/29/12 09/29/12 12/29/12 03/30/13 06/29/13 09/29/13 12/29/13 03/30/14 06/29/14 09/29/14 12/29/14 03/30/15 06/29/15 09/29/15 FIGURE 7.11 - TIME SERIES PLOT OF HORSETOOTH RESERVOIR CALCULATED TN:TP RATIOS

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TN and TP concentrations include significant amounts of nitrogen and phosphorus that are not available for immediate uptake by phytoplankton. Because of this, nutrient limitation may be better assessed from the concentrations of the readily available nutrients: nitrate+nitrite, ammonia, and ortho-P. However, concentrations of these parameters in the epilimnion are generally very low since they are rapidly taken up by phytoplankton. Sometimes their concentrations are below their respective detection limits, making it difficult to calculate accurate ratios. It is for this reason that assessments of nutrient limitations have relied primarily on ratios calculated from TN and TP.

[TIN]:[ortho-P] ratios were calculated using the TIN (TIN = total inorganic nitrogen = nitrate + nitrite + ammonia) and ortho-P 1-meter data collected in WY2008-WY2015 in order to see how they compare to the TN:TP ratios. For this data set, when “non-detects” occur, they occur in the ortho-P data (approximately 10% of the 1-meter ortho-P measurements made during this period were reported as not detected, with a detection limit of 0.001 mg/L), with no “non-detects” in the nitrate+nitrite and ammonia data. Note that the median 1-meter ortho-P concentration was 0.001 mg/L (the median ortho-P measured at a concentration equal to the detection limit). Spatial boxplots of these ratios are shown on Figure 7.12.

Reference lines were drawn on Figure 7.12 at a [TIN]:[Ortho-P] ratio of 10 (to indicate the approximate N limitation threshold) and at a [TIN]:[Ortho-P] ratio of 17 (to indicate the approximate P limitation threshold). Based on these thresholds and the calculated [TIN]:[Ortho-P] ratios, different conclusions would be drawn compared to the TN:TP boxplots shown in Figure 7.11. Figure 7.12 indicates that Horsetooth Reservoir can be nitrogen limited, co-limited, or P-limited, with P limitation occurring primarily in the spring and fall, and N limitation occurring over the summer.

Horsetooth Reservoir TIN:Ortho-P Ratio WY2008 - WY2015 HT-SPR TIN:Ortho-P 1-meter TIN (= ammonia + nitrate+nitrite) & ortho-P data HT-SOL TIN:Ortho-P

50 P Ratio

- 40

30 TIN:Ortho Probable P 20 Limitation

10 Probable N Limitation 0

10/01/07 12/31/07 03/31/08 06/30/08 09/30/08 12/30/08 03/31/09 06/30/09 09/30/09 12/30/09 03/31/10 06/30/10 09/30/10 12/30/10 03/31/11 06/30/11 09/30/11 12/30/11 03/30/12 06/29/12 09/29/12 12/29/12 03/30/13 06/29/13 09/29/13 12/29/13 03/30/14 06/29/14 09/29/14 12/29/14 03/30/15 06/29/15 09/29/15 FIGURE 7.12 - TIME SERIES PLOT OF HORSETOOTH RESERVOIR [TIN]:[ORTHO-P] RATIOS WITH NON-DETECTED ORTHO-P EVALUATED AT 1.0 X DL (ORTHO-P DL = 0.001 MG/L).

7.4 TIME TREND ANALYSIS RESULTS FOR NUTRIENTS The trend analysis results for nutrients are summarized in Table 7.3 while raw data output from the Seasonal Kendall Test are included in Appendix I. The test was performed at a 90% confidence level (critical p-value = 0.10), which means that there is at most a 10% chance of concluding that a statistically significant trend exists when in fact there is no trend. If a computed p-value is less than 0.10, a statistically significant time trend is concluded to exist. For cases where a statistically significant trend is concluded to exist, the “Sen slope as a percent of the mean” is used to

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evaluate the magnitude of the trend in a relative manner. Cases where the absolute value of the Sen slope is greater than 4% of the mean are highlighted in Table 7.3 with an up or down arrow, where 4% was selected to allow for a focus on those parameters with the highest trend magnitudes (i.e., trends that are more likely to have significance from a practical standpoint). Note that if the Sen Slope is equal to 4% of the mean value calculated over the study period, the annual average parameter concentration would change by 100% of that value in 25 years (or 4% of that value each year), assuming the trend continues over time.

Table 7.3 - Summary of Seasonal Kendall Trend Test Results for Nutrients

Nutrients

Site ID System Feature Ammonia N Nitrate + NitriteTotal N Kjeldahl NOrtho PhosphateTotal Phosphorus AT-EP Adams Tunnel ↓ OLY Olympus Tunnel HFC-FRD Hansen Feeder Canal, Flatiron HFC-BTU Big Thompson Riv, upstream HFC HFC-BT Hansen Feeder Canal, Big Thomp Riv ↓ HFC-BTD Big Thompson Riv, downstream HFC ↑ HFC-HT Hansen Feeder Canal, Horsetooth Res ↓

HT-SPR-1 Horsetooth Res, Spring Can, 1 meter ↓ HT-SPR-b Horsetooth Res, Spring Can, bottom HT-DIX-1 Horsetooth Res,Dixon Can, 1 meter ↓ HT-DIX-b Horsetooth Res, Dixon Can, bottom ↓ ↓ ↓ HT-SOL-1 Horsetooth Res, Soldier Can, 1 meter ↓ HT-SOL-b Horsetooth Res, Soldier Can, bottom

HSC-PRU Poudre River, upstream HSC ↓ ↑ ↑ HSC-PR Hansen Supply Canal ↓ ↓ HSC-PRD Poudre River, downstream HSC ↓ ↑ ↑ ↑

Note: all trend tests are at the 90% confidence level (significant trend if p-value ≤ 0.10)

The time trend analysis for the ammonia data indicate statistically significant decreasing trends for many of the sites (Table 7.3), including Hansen Feeder Canal and Horsetooth Reservoir sites with relatively high trend magnitudes. However, the ammonia trend analysis is impacted by the changing detection limits (lowering over time) and the high number of nondetects, with the percent above the detection limit ranging from 58 to 88% for all sites. This also applies to the ortho-P results where, for the tunnel/canal sites upstream of Horsetooth Reservoir, the percent of the data points above the detection limit ranged from 20% to 50%. The statistically significant decreasing trend in ortho-P at the Adams Tunnel site is influenced by the fact that only 20% of the values at this site were above the detection limit. As a comparison, the percent detected above the detection limit for the nitrate+nitrite data ranges from 80 to 100% across all sites.

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At the Poudre River sites (HSC-PRU and HSC-PRD), increasing trends in nitrate, TKN, ortho-P and Total P are influenced by the 2012 High Park Fire as can be seen on the time series plots (Appendix C) and the annual boxplots (Appendix E). Also note that the Poudre River sites have not been sampled at the same frequency over the years so that the upstream and downstream trend analysis results may not be consistent.

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8. METALS

The metals currently included in the Baseline Monitoring Program are arsenic (As), boron (B), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni), selenium (Se), silver (Ag), uranium (U), and zinc (Zn). All metals are analyzed for the dissolved form (analysis conducted on samples filtered through a 0.45-micron filter) except for arsenic, chromium and iron which are analyzed for both the dissolved and total recoverable forms. The decision to analyze for the dissolved form and/or the total form is based on the applicable water quality standards.

Metals analysis for the Baseline Monitoring Program began in different years depending on the metal and site (Table 1.2). Metals analysis with low level detection limits began in 2009 (Table 1.5). The time series plots for the metals data (contained in Appendix C) include all the data collected since WY2000. The boxplots were constructed using a subset of the data, with some data and parameters excluded due to high detection limits resulting in many non- detected values that can skew the boxes. Data excluded from the metals boxplots were summarized on Table 2.1. The monthly, annual, and spatial boxplots for metals are included in Appendix D, E, and F, respectively. Boxplots for total arsenic, boron, chromium (dissolved and total), and uranium were constructed from only two or three years of data, and the boxplots show the individual data points (in open circles).

Metals are important because, in higher concentrations, they are toxic to aquatic life and humans. Copper, iron, manganese, silver and zinc can also cause aesthetic issues in treated drinking water if their concentrations are elevated. Concentrations of metals are regulated under both the Federal Clean Water Act and the Safe Drinking Water Act through standards adopted by the Colorado Water Quality Control Commission (WQCC) and implemented by the CDPHE. Although comparisons are made in this section to the applicable standards (Table 8.1), a rigorous standards compliance assessment is not conducted. The comparisons to water quality standards are conducted only to provide a frame of reference and some context for the observed data.

Acute and chronic aquatic life standards for cadmium, copper, lead, manganese, nickel, silver and zinc are based on hardness, with metals toxicity increasing with decreasing hardness since more of the metal is present in a bioavailable form at lower hardness. Because of this, the metals standards are lower for waters that have a lower hardness. Equations to calculate the hardness-based acute (ac) and chronic (ch) metals standards are contained in Colorado Regulation No. 31 (5 CCR 1002-31) The Basic Standards and Methodologies for Surface Water, Table III Metal Parameters. Table 8.1 indicates a range of values that correspond to the range of hardness values that are generally observed at the East Slope – North End sites: 10 to 40 mg/L as CaCO3. The spatial boxplot of hardness values (Figure 8.1) calculated from the calcium and magnesium concentrations shows that most of the hardness values fall within this range, with sites upstream of Horsetooth Reservoir having median values of about 20 mg/L while the Horsetooth sites have median hardness values closer to 30 mg/L.

The primary natural sources of metals in surface waters are the geologic formations and soils that make up the surrounding watersheds. As rainfall and snowmelt water move through weathered rocks and soil, metals in dissolved or particulate forms are picked up and transported to surface water bodies. Geothermal waters are also natural sources of metals. Anthropogenic sources of metals in surface waters include municipal and industrial wastewater discharges, urban runoff, and discharges/runoff associated with mining, industrial, and agricultural activities. Metals emitted to the atmosphere from coal-fired power plants, ore processing facilities, smelter facilities, waste incineration, automobile exhaust, wildfires, volcanic eruptions, windblown dust, etc. can enter surface waters through wet or dry deposition of particulates. The relative lack of mining and industrial activity in the local watersheds generally limits the trace metals to low concentrations.

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TABLE 8.1 - WATER QUALITY STANDARDS FOR BASELINE MONITORING PROGRAM METALS. Federal Safe Drinking Water Federal Clean Water Act & Colorado WQCC Regs 31, 33, 38 Act & Colorado WQCC Reg 5 CCR 1003-1 Use Classification Primary Secondary Metal Aquatic Life (b) Domestic Maximum Maximum Contaminant Contaminant Water Water (c) Level (MCL) Level Acute (a) Chronic (a) Supply + Fish or Action Level (SMCL) (µg/L) (µg/L) (µg/L) (µg/L)(d) (µg/L) (µg/L) 0.02 – 10 Arsenic 340 150 0.02 (tot. rec.) 10 (30-day)

Boron

Trout: Cadmium 0.07 – 0.21 5 (1-day) 5 0.23 – 0.77

Chromium 16 (Cr VI) 11 (Cr VI) 50 (1-day)

1,000 Copper 1.5 – 5.7 1.3 – 4.1 1,300 1,300 1,000 (30-day) 300 Iron 1,000 (tot. rec.) 300 (dis.; 30-day) 50 Lead 5 - 24 0.19 – 0.92 15 (1-day) 50 Manganese 1,387 – 2,200 766 – 1,216 50 (dis.; 30 day) 100 Nickel 67 - 216 7.4 - 24 610 (30-day) 50 Selenium 18.4 4.6 170 50 (30-day) Trout: 100 Silver 0.039 – 0.42 100 0.001 – 0.016 (1-day) 16.8 – 30 Uranium (30-day) 5,000 Zinc 20 - 66 17 - 57 7,400 5,000 (30-day)

(a) Aquatic life standards for cadmium, copper, lead, manganese, nickel, silver and zinc are calculated based on hardness; the two values given in this table for these metals correspond to the values calculated for a representative hardness range of 10 to 40 mg/L as CaCO3, respectively. Standards for the other metals are table values and are not calculated. (b) Metals for aquatic life use are dissolved unless otherwise specified; acute standards are evaluated by comparison of individual sample values to the assigned standard, and non-attainment of the acute standard occurs if the standard is exceeded more frequently than once in three years; chronic standards are assessed based on the 85th percentile of the ranked data. (c) Metals for domestic water supply use are stated as total recoverable unless otherwise specified. (d) Applicable to Class 1 aquatic life segments that also have a water supply classification.

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FIGURE 8.1 - HARDNESS SPATIAL BOXPLOT

8.1 ARSENIC (DISSOLVED & TOTAL RECOVERABLE) Arsenic is associated with an increased cancer risk, skin lesions, and other human health problems. A primary maximum contaminant level (MCL) of 10 µg/L and an MCL goal of 0 µg/L have been set for arsenic by the U.S EPA and the CDPHE for the protection of human health in treated drinking water. For the protection of aquatic life, an acute limit of 340 µg/L and a chronic limit of 150 µg/L have been set for arsenic. For the protection of domestic water supplies, the CDPHE has set a hybrid total recoverable arsenic criteria of 0.02 – 10 µg/L (where 0.02 µg/L is the human health-based value and 10 µg/L is the MCL). If a water body is both a drinking water supply and used by the public for fishing, the CDPHE has set a human health-based total recoverable arsenic standard of 0.02 µg/L (“water + fish ingestion” criteria). The 0.02 µg/L standard applies automatically to segments with Aquatic Life Cold 1 and Water Supply Use Classifications, including the sites in this report.

Low levels of dissolved arsenic are detected at all sampling sites (Figure 8.2). The Horsetooth Reservoir sites and the Hansen Supply Canal and Poudre River sites generally have higher concentrations than the tunnel sites, Hansen Feeder Canal sites and Big Thompson River sites. The highest concentrations have been detected at the bottom of Horsetooth Reservoir at Spring Canyon Dam prior to fall turnover. Arsenic adsorbs onto iron oxide particulate material and, after settling to the bottom of a water body, this arsenic can be released into solution when iron oxides dissolve under anoxic/reducing conditions. The highest dissolved arsenic concentration in Horsetooth Reservoir, 1.6 µg/L, occurred on 10/9/12 at the bottom of Spring Canyon, with lower concentrations on this date at the bottom of Horsetooth Reservoir at Dixon and Soldier Canyon Dams, 0.72 µg/L and 0.65 µg/L, respectively.

In 2012, Horsetooth Reservoir was placed on the 303(d) list of impaired waters for arsenic. Sections of the Big Thompson River and the Poudre River that are monitored by HFC-BTU, HFC-BTD, HSC-PRU and HSC-PRD were placed on the 303(d) list of impaired waters for arsenic in 2016. The arsenic impairments are related to the exceedance of the chronic total recoverable arsenic standard of 0.02 µg/L for “water + fish ingestion.” In WY2013, Northern Water began analysis for total arsenic with a detection limit of either 0.1 µg/L or 0.4 µg/L (both higher than the standard). The data collected to date are shown on the spatial boxplot in Figure 8.3. Since the plot only includes three years of data, the individual data points are shown in the figure as open circles. Many of the samples did not have concentrations above the detection limits (Figure 8.3). Elevated total arsenic concentrations were

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measured at the Poudre River sites in the spring and fall of 2013, including 1.5 µg/L at HSC-PRU and 2.4 µg/L at HSC-PRD, both on 9/9/13. These elevated concentrations may be related to runoff from the High Park Fire burn area during the 2013 flood event. A total arsenic concentration of 1.83 µg/L was measured at the bottom of Horsetooth Reservoir at Spring Canyon on 10/9/12, coincident with the high dissolved arsenic concentration of 1.6 µg/L measured on that date.

FIGURE 8.2 - DISSOLVED ARSENIC SPATIAL BOXPLOT

FIGURE 8.3 - TOTAL ARSENIC SPATIAL BOXPLOT

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8.2 BORON (DISSOLVED) Analysis for boron began in WY2014, and the spatial boxplot presented in Figure 8.4 only includes two years of data. From this limited data set, the Hansen Feeder Canal, Big Thompson River, and Poudre River sites have the largest range of values with the highest concentrations. Horsetooth Reservoir concentrations are around 5 µg/L and fall within a narrow range of values. There are no drinking water or aquatic life standards for boron, but there is a 750 µg/L agricultural standard to protect sensitive crops during long-term irrigation.

FIGURE 8.4 - DISSOLVED BORON SPATIAL BOXPLOT

8.3 CADMIUM (DISSOLVED) Cadmium has a primary drinking water MCL of 5 µg/L, and long-term exposure above the MCL may result in kidney damage. The aquatic life standards for cadmium are based on hardness; for an average hardness within the range of

10 to 40 mg/L as CaCO3, the acute trout standard ranges from 0.23 to 0.77 µg/L while the chronic standard ranges from 0.07 to 0.21 µg/L.

Cadmium detection limits have varied over the years, but concentrations are usually below the detection limit (Figure 8.5). The highest concentrations at the sites covered in this report include 0.24 µg/L at the Olympus Tunnel on 8/14/07 and 0.3 µg/L at the Big Thompson River below the Hansen Feeder Canal site on 7/12/05, both outliers compared to the rest of the data at those sites. FIGURE 8.5 - DISSOLVED CADMIUM SPATIAL BOXPLOT

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8.4 CHROMIUM (DISSOLVED & TOTAL RECOVERABLE) Analysis for dissolved and total chromium began in WY2014, and the spatial boxplots presented in Figures 8.6 and 8.7 only include two years of data. From this limited data set, the highest dissolved chromium concentrations have been measured in the Hansen Feeder Canal sites, with all concentrations below 1.8 µg/L and well below the acute and chronic aquatic life standards of 16 and 11 µg/L, respectively. The lowest dissolved chromium concentrations have occurred in the Horsetooth Reservoir and Hansen Supply Canal sites, with all values below 0.3 µg/L.

The highest total chromium concentrations have occurred in the two Big Thompson River sites, HFC-BTU and HFC- BTD. The highest concentration measured to date was 8 µg/L at HFC-BTD, well below the total chromium drinking water supply standard of 50 µg/L.

FIGURE 8.6 - DISSOLVED CHROMIUM SPATIAL BOXPLOT

FIGURE 8.7 - TOTAL CHROMIUM SPATIAL BOXPLOT

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8.5 COPPER (DISSOLVED) Low levels of copper occur in waters from weathering of geologic formations. Elevated concentrations of copper in the C-BT system have been attributed to the use of copper sulfate for the control of nuisance algae in the East Slope canals. Application of copper sulfate to the east slope canals was discontinued in April 2008 by Northern Water and in 2012 by Reclamation. The use of copper sulfate is of concern because, at low concentrations, copper can impact various non-target aquatic organisms including zooplankton and fish. Dissolved copper is rapidly converted to particulate forms (through its high affinity for organic matter and inorganic suspended particles) and settles out in the bottom sediments where it accumulates (Haughey, et al, 2000).

A secondary maximum contaminant level (SMCL) of 1,000 µg/L has been set for dissolved copper in drinking water leaving a treatment plant. SMCLs are non-enforceable guidelines regulating contaminants that may cause aesthetic effects in treated drinking water. Levels above the copper SMCL can result in a metallic taste and blue-green staining. A primary MCL of 1,300 µg/L has been set for the protection of human health. Much lower levels of copper have been set to protect aquatic life, with acute and chronic values calculated based on hardness. For waters with an average hardness within the range of 10 to 40 mg/L as CaCO3, the acute standard ranges from 1.5 to 5.7 µg/L while the chronic standard ranges from 1.3 to 4.1 µg/L.

Data collected since WY2002 show that the highest dissolved copper concentrations have historically been found at the Hansen Feeder Canal and Hansen Supply Canal sites, while the lowest concentrations have generally occurred at the Horsetooth Reservoir and Poudre River sites (Figure 8.8).

FIGURE 8.8 - DISSOLVED COPPER SPATIAL BOXPLOT FOR WY2002 – WY2015 PERIOD.

Copper concentrations in the canals have decreased since the use of copper sulfate was discontinued, as indicated in the annual boxplots shown in Figure 8.9 for the Hansen Feeder Canal below Flatiron Reservoir, Hansen Feeder Canal upstream of Horsetooth Reservoir, Horsetooth Reservoir, and the Hansen Supply Canal.

The annual boxplot for the East Portal Adams Tunnel (Figure 8.9) indicates some higher copper concentrations (≥ 4 µg/L) during the WY2010 to WY 2014 period, compared to the earlier years. The North Inlet to Grand Lake was added to the State 303(d) List for copper in 2016. However, copper concentrations measured at Northern Water’s North Inlet site (NI-GLU) have averaged 0.96 µg/L during this period, with a maximum value of 1.8 µg/L, and is not a cause of elevated copper at the Adams Tunnel. The 303(d) listing at the North Inlet is related to the very low hardness at that site, which results in a very low aquatic life standard for copper. The cause of elevated copper concentrations at the East Portal Adams Tunnel site is not known.

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FIGURE 8.9 - ANNUAL BOXPLOTS FOR COPPER: ADAMS TUNNEL, HANSEN FEEDER CANAL, HANSEN SUPPLY CANAL & HORSETOOTH RES SITES.

Since all copper sulfate applications were stopped in 2012, the copper spatial boxplot takes on a new pattern as shown in Figure 8.10 for the WY2012 to WY2015 data. The highest median concentrations now occur at the Big Thompson River sites, followed by the Adams Tunnel and Olympus Tunnel sites. The highest concentrations in the Hansen Feeder Canal sites shown on Figure 8.10 (3.5 to 3.9 µg/L) occurred in samples collected on Oct. 3, 2013 when these sites were impacted by floodwater that had entered Lake Estes and was then pumped through the Olympus Tunnel to Pinewood and Flatiron Reservoirs, and subsequently released to the Hansen Feeder Canal.

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FIGURE 8.10 - DISSOLVED COPPER SPATIAL BOXPLOT FOR WY2012 – WY2015 PERIOD.

8.6 IRON (DISSOLVED AND TOTAL RECOVERABLE) Iron is the second most abundant metal in the earth’s outer crust (Hem, 1985) and high total iron concentrations can exist when inorganic suspended solids concentrations are high. Dissolved iron concentrations are generally low except under conditions of oxygen depletion (such as what can occur at reservoir/lake bottoms) and/or low pH. An SMCL of 300 µg/L has been set for dissolved iron (Table 8.1) in treated drinking water. Levels above the SMCL can result in a metallic taste and reddish/orange staining of laundry and plumbing fixtures. For the protection of aquatic life, there is a chronic total recoverable iron standard of 1,000 µg/L.

Dissolved iron concentrations at all sites are generally below the drinking water SMCL except for some occurrences above 300 µg/L at the Hansen Feeder Canal sites, Olympus Tunnel, Big Thompson River and Poudre River (Figure 8.11). The highest dissolved iron concentrations (not shown on Figure 8.11) include 1,170 µg/L at HFC-FRD, 1,090 µg/L at HFC-BT, and 1,110 µg/L at HFC-HT, in samples collected on Oct. 3, 2013 when these sites were impacted by floodwater that had entered Lake Estes and was then pumped through the Olympus Tunnel to Pinewood and Flatiron Reservoirs, and subsequently released to the Hansen Feeder Canal.

A spatial boxplot for total iron is shown on Figure 8.12. Total iron concentrations include both the dissolved and particulate fractions. The highest total iron concentrations are generally associated with higher total suspended solids (TSS) concentrations and have occurred at the Big Thompson River and Poudre River sites. This can be seen, for example in Figures 8.13 and 8.14 which are time series plots of both TSS and total iron data for the Big Thompson River below the Hansen Feeder Canal (HFC-BTD) and the Poudre River below the Hansen Supply Canal. These figures show that the annual peaks in total iron are coincident with the annual peaks in TSS and generally occur during the spring runoff, but have been exacerbated by the High Park Fire in the Poudre Watershed and the 2013 Flood. The total iron concentration in the Big Thompson River reached a maximum value of 35,700 µg/L at HFC- BTD in April 2014, during the spring runoff after the river had been damaged by the September 2013 flood. Total iron concentrations are expected to remain elevated along with the TSS as restoration work continues in the Big Thompson Canyon.

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FIGURE 8.11 - DISSOLVED IRON SPATIAL BOXPLOT

FIGURE 8.12 - TOTAL IRON SPATIAL BOXPLOT

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Total Suspended Solids & Total Iron 2009 - WY2015 Time Series Plot: HFC-BTD TSS Big Thompson River below Hansen Feeder Canal (HFC-BTD) HFC-BTD Total Iron

Sept 2013 Flood 10000

Tot Rec Iron Chronic Std = 1,000 ug/L 1000

100

10 Total Iron (ug/L) or TSS (mg/L) (ug/L)TSS orIron Total

1 2-Jul-09 2-Jul-10 2-Jul-11 1-Jul-12 1-Jul-13 1-Jul-14 1-Jul-15 1-Jan-09 1-Jan-10 1-Jan-11 1-Jan-12 1-Oct-09 1-Oct-10 1-Oct-11 2-Apr-09 2-Apr-10 2-Apr-11 1-Apr-12 1-Apr-13 1-Apr-14 1-Apr-15 30-Sep-12 30-Sep-13 30-Sep-14 30-Sep-15 31-Dec-12 31-Dec-13 31-Dec-14 FIGURE 8.13 - TIME SERIES PLOT OF TSS AND TOTAL IRON CONCENTRATIONS IN THE BIG THOMPSON RIVER AT HFC-BTD.

Total Suspended Solids 2009 - WY2015 Time Series Plot: HSC-PRD TSS Poudre River below Hansen Supply Canal (HSC-PRD) HSC-PRD Total Iron

10000 June 2012 High Park Fire

Tot Rec Iron Chronic Std = 1,000 ug/L 1000

100

10 Total Iron (ug/L) or TSS (mg/L)(ug/L) TSS orIron Total

FIGURE 8.14 - TIME SERIES PLOT OF TSS AND TOTAL IRON CONCENTRATIONS IN THE POUDRE RIVER AT HSC-PRD.

8.7 LEAD (DISSOLVED) Lead has a primary drinking water action level of 15 µg/L and a public health goal of 0 µg/L to protect infants and children from delays in physical/mental development, and to protect adults from kidney problems and other health issues. The aquatic life standards for lead are based on hardness; for hardness within the range of 10 to 40 mg/L as

CaCO3 (which generally covers the hardness range for the water bodies in this report), the acute standard ranges from 5 to 24 µg/L while the chronic standard ranges from 0.19 to 0.92 µg/L.

Although dissolved lead is commonly measured above the detection limits (which have varied over the years), concentrations are low and have generally been below 0.1 µg/L (Figure 8.15). Many of the values over 0.1 µg/L occurred during the WY2005 – WY2007 period (see time series plots in Appendix C). However, elevated concentrations (0.50 to 0.55 µg/L) were measured at the Hansen Feeder Canal sites in October 2013 when these

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sites were impacted by floodwater that had entered Lake Estes and was then pumped through the Olympus Tunnel to Pinewood and Flatiron Reservoirs, and subsequently released to the Hansen Feeder Canal. Elevated concentrations in the Poudre River occurred after the High Park Fire and Sept 2013 Flood (up to 0.38 µg/L), while elevated concentrations in the Big Thompson River (up to 0.54 µg/L) occurred after the Sept 2013 Flood.

FIGURE 8.15 - DISSOLVED LEAD SPATIAL BOXPLOT.

8.8 MANGANESE (DISSOLVED) Manganese is a significant component of the earth’s crust, although it is much less abundant than iron. When the dissolved oxygen at a reservoir/lake bottom is low (< 2 mg/L), manganese bound in the bottom sediments is released into solution. As the oxygen level and the redox potential decrease at the reservoir bottom, manganese is released into solution before iron (Drever, 1988; Wetzel, 2001, pg. 250, 295) resulting in a greater chance of occurrence of problematic levels of high manganese. When turnover occurs, dilution and increased dissolved oxygen levels cause the dissolved manganese concentrations to return to low levels at the reservoir bottom.

The U.S. EPA and CDPHE have set a SMCL of 50 µg/L for dissolved manganese in treated drinking water. If not sufficiently removed during water treatment, dissolved manganese can change to a solid form and cause “brown water” episodes that stain plumbing fixtures and laundry. Levels above the SMCL also result in a bitter metallic taste. These conditions result in customer complaints to drinking water treatment plants. The City of Fort Collins Water Treatment Facility has set a target manganese concentration in treated water of 5 µg/L because of customer complaints that occur at levels much lower than the SMCL. The aquatic life standards for manganese are based on hardness. For hardness within the range of 10 to 40 mg/L as CaCO3 (which generally covers the hardness range for the water bodies in this report), the acute standard ranges from 1,387 to 2,200 µg/L while the chronic standard ranges from 766 to 1,216 µg/L.

The spatial boxplot (Figure 8.16) shows occurrences of high manganese (> 50 µg/L) at the bottom of Horsetooth Reservoir (HT-SPR-b, HT-DIX-b, and HT-SOL-b). High dissolved manganese concentrations occur during periods of low dissolved oxygen prior to fall turnover. At the HFC-BTD Big Thompson River site, all concentrations above

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50 µg/L occurred after the 2013 Flood. The highest dissolved manganese concentrations at the Poudre River sites occurred within 12 months after the 2012 High Park Fire.

FIGURE 8.16 - DISSOLVED MANGANESE SPATIAL BOXPLOT.

8.9 NICKEL (DISSOLVED) Although a treated drinking water standard does not exist for nickel, a total recoverable nickel concentration of 100 µg/L has been set to protect domestic water supplies. For the protection of aquatic life, the acute standard for dissolved nickel ranges from 67 to 216 µg/L while the chronic standard ranges from 7.4 to 24 µg/L for waters with a hardness within the range of 10 to

40 mg/L as CaCO3. Dissolved nickel is detected at all of the sampling sites (Figure 8.17), but concentrations have generally been below 1.5 µg/L.

FIGURE 8.17 - DISSOLVED NICKEL SPATIAL BOXPLOT.

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8.10 SELENIUM (DISSOLVED) A primary MCL of 50 µg/L has been set for selenium to protect human health. Lower levels of selenium have been set to protect aquatic life, including an acute standard of 18.4 µg/L and a chronic standard of 4.6 µg/L. Dissolved selenium is present at all of the sampling sites, but concentrations have been low, generally below 0.3 µg/L (Figure 8.18). Higher concentrations of selenium commonly occur in other parts of Colorado, including downstream segments of the Big Thompson River (Hydros Consulting, 2015), due to the presence of naturally occurring selenium-rich shales.

FIGURE 8.18 - DISSOLVED SELENIUM SPATIAL BOXPLOT.

8.11 SILVER (DISSOLVED) Silver is one of the most toxic metals to aquatic life as reflected by low acute and chronic standards. The aquatic life standards for silver are based on hardness; for average hardness within the range of 10 to 40 mg/L as CaCO3, the acute standard ranges from 0.039 to 0.42 µg/L, while the chronic (trout) standard ranges from 0.001 to 0.016 µg/L. The U.S. EPA and CDPHE have set an SMCL of 100 µg/L for silver in treated drinking water. If not sufficiently removed during water treatment, silver can result in skin discoloration (a cosmetic effect). Silver has rarely been detected and most lab results have indicated that silver is not present above the detection limits, which have varied over the years (Figure 8.19). Figure 8.19 summarizes a total of 1,348 data points, with 59 data points (4%) detected values, and 32 of the detected values having concentrations of 0.009 µg/L or less. The three highest values shown on Figure 8.19 (0.13 to 0.2 µg/L) all occurred during the June 2003 sampling event.

FIGURE 8.19 - DISSOLVED SILVER SPATIAL BOXPLOT.

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8.12 URANIUM (DISSOLVED) A primary MCL of 30 µg/L has been set for uranium in treated drinking water to protect human health. Aquatic life standards for uranium are based on hardness; for hardness within the range of 10 to 40 mg/L as CaCO3, the acute standard ranges from 190 to 875 µg/L, while the chronic standard ranges from 119 to 547 µg/L. However, uranium standards have not been adopted for the Big Thompson River, Poudre River or Horsetooth Reservoir.

Analysis for uranium began in WY2014, and the spatial boxplot presented in Figure 8.20 only includes two years of data. From this limited data set, uranium is present at concentrations below 2.5 µg/L. The lowest concentrations have been measured in Horsetooth Reservoir and the Hansen Supply Canal with median concentrations there of approximately 0.2 µg/L.

FIGURE 8.20 - DISSOLVED URANIUM SPATIAL BOXPLOT.

8.13 ZINC (DISSOLVED) The U.S. EPA and CDPHE have set an SMCL of 5,000 µg/L for zinc in treated drinking water. If not sufficiently removed during water treatment, zinc can impart a metallic taste to water. The aquatic life standards for zinc are based on hardness. For average hardness within the range of 10 to 40 mg/L as CaCO3, the acute standard ranges from 20 to 66 µg/L while the chronic standard ranges from 17.5 to 57 µg/L. Dissolved zinc is routinely detected at all sites, although most concentrations have been below 10 µg/L (Figure 8.21). All concentrations above 10 µg/L occurred prior to 2008 and are most likely a result of the lab method and not due to a change in water quality.

FIGURE 8.21 - DISSOLVED ZINC SPATIAL BOXPLOT.

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The segment of the Big Thompson River that includes Northern Water’s two monitoring sites, HFC-BTU and HFC- BTD (Segment COSPBT02), was on the 2012 303(d) list for zinc, but was de-listed for zinc in 2016. The time series plots (Appendix C) indicate that the highest concentrations at HFC-BTU were measured during the 2002-2004 period. During the 2005-2009 period, a high detection limit (10 µg/L) resulted in no useful information since all samples collected at HFC-BTU during that time were below the detection limit. Concentrations in samples collected after 2009 have all been below 5 µg/L.

8.14 TIME TREND ANALYSIS RESULTS FOR METALS Time trend analysis was not conducted for the full suite of metals due to a short period of record for some metals and a high number of non-detected values for others. The trend analysis results for metals are summarized in Table 8.2 while raw data output from the Seasonal Kendall Test are contained in Appendix I.

TABLE 8.2 - SUMMARY OF SEASONAL KENDALL TREND TEST RESULTS FOR METALS Metals

Site ID System Feature Arsenic, dis Copper, dis Iron, dis Iron, total Manganese, disNickel, dis Selenium, dis Zinc, dis AT-EP Adams Tunnel ↑ ↑ ↓ OLY Olympus Tunnel ↑ ↑ ↓ HFC-FRD Hansen Feeder Canal, Flatiron ↓ HFC-BTU Big Thompson Riv, upstream HFC ↑ HFC-BT Hansen Feeder Canal, Big Thomp Riv ↓ HFC-BTD Big Thompson Riv, downstream HFC HFC-HT Hansen Feeder Canal, Horsetooth Res ↓ ↓

HT-SPR-1 Horsetooth Res, Spring Can, 1 meter ↓ ↓ ↓ ↓ HT-SPR-b Horsetooth Res, Spring Can, bottom ↓ ↓ HT-DIX-1 Horsetooth Res,Dixon Can, 1 meter ↓ ↓ ↓ ↓ HT-DIX-b Horsetooth Res, Dixon Can, bottom ↓ HT-SOL-1 Horsetooth Res, Soldier Can, 1 meter ↓ ↓ HT-SOL-b Horsetooth Res, Soldier Can, bottom ↓

HSC-PRU Poudre River, upstream HSC ↑ ↑ ↓ HSC-PR Hansen Supply Canal ↓ ↑ ↓ ↑ ↓ HSC-PRD Poudre River, downstream HSC ↓ ↑ ↑

Note: all trend tests are at the 90% confidence level (significant trend if p-value ≤ 0.10)

The test was performed at a 90% confidence level (critical p-value = 0.10), which means that there is at most a 10% chance of concluding that a statistically significant trend exists when in fact there is no trend. If a computed p-value is less than 0.10, a statistically significant time trend is concluded to exist. For cases where a statistically significant trend is concluded to exist, the “Sen slope as a percent of the mean” is used to evaluate the magnitude of the trend in a relative manner. Cases where the absolute value of the Sen slope is greater than 4% of the mean are highlighted

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in Table 8.2 with an up or down arrow, where 4% was selected to allow for a focus on those parameters with the highest trend magnitudes (i.e., trends that are more likely to have significance from a practical standpoint). Note that if the Sen Slope is equal to 4% of the mean value calculated over the study period, the annual average parameter concentration would change by 100% of that value in 25 years (or 4% of that value each year), assuming the trend continues over time.

Copper. The trend analysis results in Table 8.2 for copper are consistent with the annual boxplots that were shown in Figure 8.9 and the time series plots in Appendix C. Copper concentrations in the canals have decreased since the use of copper sulfate was discontinued during the 2008 – 2011 period. The cause of the statistically significant increasing trend in copper concentrations at the Adams Tunnel and Olympus Tunnel sites is not known. Copper concentrations in the Poudre River downstream of the Hansen Supply Canal (HSC-PRD) show a statistically significant decreasing trend, coincident with the discontinued use of copper sulfate in the Hansen Supply Canal in 2008.

Iron & Manganese at Flowing sites above Horsetooth Reservoir. Manganese concentrations at all the flowing sites upstream of Horsetooth Reservoir were elevated after the September 2013 flood (as can be seen on the time series plots in Appendix C) which influenced the statistically significant increasing trends found at these sites (Table 8.2). The dissolved and total iron increasing trends were influenced by the fact that maximum concentrations at these sites were measured after Sept 2013, near the end of the trend period.

Dissolved Iron & Manganese at Horsetooth Reservoir. Statistically significant decreasing trends in dissolved iron and manganese concentrations are indicated in Table 8.2 for the 1-meter Horsetooth Reservoir sites. Note, however, that the manganese concentrations at the 1-meter depth are typically low (< 10 µg/L) over the period of record.

Manganese & total iron at Poudre River sites. At the Poudre River sites (HSC-PRU and HSC-PRD), increasing trends in manganese and total iron concentrations were influenced by the 2012 High Park Fire as can be seen on the time series plots (Appendix C) and the annual boxplots (Appendix E). Also note that the Poudre River sites have not been sampled at the same frequency over the years so that the upstream and downstream trend analysis results may not be consistent.

Zinc. A statistically significant decreasing trend in zinc concentrations is indicated in Table 8.2 for a number of sites. Note that zinc analysis for the Horsetooth Reservoir sites began in March 2008 and only includes around 20 data points per site, with all values ≤ 6 µg/L, so the practical significance of this trend is limited. The decreasing trend at the HSC-PR and HSC-PRU sites is influenced by higher values during the 2002-2004 period, with a maximum value of 13 µg/L during that time, compared to all values ≤ 2.7 µg/L since 2009. The trend at HFC-HT was also influenced by higher values during the 2002-2004 period, with a maximum value of nearly 25 µg/L during that time, compared to all values <4 µg/L since 2009. At the Adams Tunnel and Olympus Tunnel, higher zinc concentrations that occurred during 2007, combined with a drop in the detection limit in 2012, contributed to the statistically significant decreasing trends observed at those sites. These trends in zinc concentrations are most likely a result of the lab method and not a change in water quality.

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9. HORSETOOTH RES PHYTOPLANKTON, CHLOROPHYLL & ZOOPLANKTON

Horsetooth Reservoir phytoplankton productivity in terms of phytoplankton genera and species, phytoplankton densities (cell counts), and phytoplankton biovolume is presented in Section 9.1. Since chlorophyll-a is found in all species of phytoplankton, it is used to represent and estimate the fresh phytoplankton biomass; Horsetooth Reservoir chlorophyll-a data are summarized in Section 9.2, including an evaluation of the data with respect to the 5 µg/L value established for DUWS lakes/reservoirs (but not adopted for Horsetooth Reservoir). Trophic status of the reservoir is assessed in Section 9.3 using the chlorophyll-a data. Geosmin data from the City of Fort Collins related to the sites in this report are presented and evaluated in Section 9.4. Finally, Horsetooth Reservoir zooplankton data are summarized in Section 9.5.

9.1 PHYTOPLANKTON Algal populations considered in this report are restricted to the phytoplankton, those algae and cyanobacteria species that exist as free-floating organisms in the open water. Phytoplankton are photosynthetic, microscopic organisms that can be further characterized as unicellular, colonial, or filamentous. They all contain chlorophyll-a, one of the primary pigments that allows for the conversion of water, carbon dioxide, and sunlight into carbohydrates during photosynthesis.

Phytoplankton form the base of the food web in lakes and reservoirs and are, therefore, an essential component of the aquatic ecosystem. However, a rapid increase in the population of a group or a species of phytoplankton can result in a nuisance algae bloom. Algae blooms occur as a result of an input of nutrients (nitrogen and/or phosphorus) and/or a change in some other growth-controlling environmental condition such as water temperature, hydraulic residence time, or the zooplankton population that feeds on phytoplankton. Algae blooms can result in impacts to the recreational, aquatic life, and water supply uses of a water body. Potential water quality impacts associated with algae blooms include:

• Discoloration and reduced clarity of the water.

• An increase in pH (during photosynthesis by the algae) near the water surface that can impact aquatic life.

• Depletion of oxygen levels (during degradation of the algal bloom) near the water surface that can impact aquatic life.

• Increase in biomass that settles to the lake/reservoir bottom, undergoes microbial degradation that depletes oxygen levels, and results in the release of metals and nutrients from the bottom sediments.

• Production of taste and odor compounds (such as geosmin).

• Production of toxins by cyanobacteria.

• An increase in TOC that could lead to an increase in the production of disinfection byproducts at drinking water treatment plants.

• Filter clogging issues at drinking water treatment plants.

Phytoplankton sampling at each site in Horsetooth Reservoir consists of the collection of composite samples representing the 0 to 5 meter depth interval. This depth interval corresponds to the depth interval for the chlorophyll-a data. Composite samples representing the 5 to 10 meter depth interval were also collected through WY2013, but are not discussed here. Phytoplankton analyses include identification to the species level (or lowest possible taxonomic level), cell density or abundance (cells/mL), and cell biovolume (cubic micrometer/milliliter, or µm3/mL). The laboratory method for phytoplankton analyses changed in WY2010. Prior to WY2010, the Sedgwick-

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Rafter method was used with a maximum 400x magnification. Beginning in WY2010, the Membrane Filtration method was used with a 630x magnification.

The average cell volume (µm3/cell) for each species is determined by obtaining mean cell dimensions from a representative number of cells and applying these dimensions to the formula for the solid geometric shape that most closely matches the cell shape (sphere, cylinder, etc). The number of cells counted per mL of water sample (cells/mL) is multiplied by the average cell volume (µm3/cell) to obtain the total cell biovolume (µm3/mL) for that species.

There is a large range in cell sizes between the various phytoplankton species. For species with a very small cell size, a high cell count (cells/mL) may over-emphasize their apparent fraction of biomass. Because of this, total phytoplankton cell biovolume is sometimes considered to provide a more accurate way to evaluate and compare algal populations. Cell biovolume can be used to estimate fresh phytoplankton biomass (in units of mg/L) by multiplying the cell biovolume (µm3/mL) by a factor of 1x10-6 (AWWA, 2010, pg. 63).

Phytoplankton present in Horsetooth Reservoir include species from seven groups: Bacillariophyta (diatoms), Chlorophyta (green algae), Chrysophyta (golden-brown algae), Cryptophyta (cryptomonads), Cyanophyta (blue- green algae or cyanobacteria), Pyrrhophyta (dinoflagellates), and Euglenophyta (euglenoids). Appendix G contains bar graphs of density, percent composition by density, biovolume, and percent composition by biovolume for the seven phytoplankton groups for each Horsetooth Reservoir sampling site for the 0-5 meter depth interval. Shifts in the dominant phytoplankton groups from season to season and year to year can be identified by visual inspection of these graphs. However, the factors controlling the phytoplankton populations and their seasonal and annual shifts are complex and include temperature, sunlight, flow, hydraulic residence time, nutrient concentrations, and grazing by zooplankton.

Dominant phytoplankton population by density. The Horsetooth Reservoir phytoplankton population is generally dominated by diatoms, green algae and cryptomonads by density (cells/mL). Occasionally, cyanobacteria, or golden-brown algae may be a dominant algal group by density. The maximum phytoplankton densities measured in Horsetooth Reservoir occurred on September 13, 2011 during a bloom of the very small cyanobacteria Aphanothece clathrata, with cell counts ranging up to 67,100 cells/mL at Spring Canyon Dam (0-5 meters). High total phytoplankton densities have also occurred in Summer 2012 (ranging up to 19,300 cells/mL at HT-SPR on 8/14/12, with 83% of the counts comprised of cyanobacteria, primarily Anabaena planctonica and the small-celled Pannus) and Summer 2014 (ranging up to 47,035 cells/mL at HT-DIX on 7/16/14, with 85% of the counts comprised of the small- celled cyanobacteria Aphanocapsa).

Dominant phytoplankton population by biovolume. Diatoms dominate the phytoplankton population by biovolume (µm3/mL). Cryptomonads and golden-brown algae may also be dominant by biovolume. Occasionally, the presence of the dinoflagellate Ceratium hirundinella at low densities (<200 cells/mL) can dominate the phytoplankton biovolume due to their large size. There is typically a late spring/early summer and a late fall seasonal peak in phytoplankton biovolume. Maximum biovolume levels measured within Horsetooth Reservoir include 14,200,000 µm3/L at Spring Canyon (0-5 meters, 12/19/11, 98% diatoms), 11,000,000 µm3/L at Dixon Canyon (0-5 meters, 12/19/11, 99.6% diatoms), and 11,100,000 µm3/L at Soldier Canyon (0-5 meters, 6/17/14, 97% diatoms). Biovolumes greater than 10,000,000 µm3/L have also occurred at Spring Canyon on 10/9/12 (92% dinoflagellates) and on 2/11/15 (98% diatoms), and at Soldier Canyon on 12/19/11 (99% diatoms).

Common genera in Horsetooth Reservoir. The most common genera of diatoms in Horsetooth Reservoir include Asterionella, Aulacoseira, Cyclotella, Discostella, Fragilaria, Stephanodiscus, Synedra, and Tabellaria. Cryptomonas and Rhodomonas are the genera of cryptomonads found in Horsetooth Reservoir. Some genera of green algae commonly found in Horsetooth Reservoir include Chlorella, Oocystis, Pyramimonas, and Sphaerocystis. Dinobryon is the most abundant genus of golden-brown algae found in Horsetooth Reservoir. Finally, when they are present,

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the cyanobacteria density in Horsetooth Reservoir is generally dominated by four genera – Anabaena, Aphanocapsa, Aphanothece, and Chroococcus.

Occurrence of Cyanobacteria in Horsetooth Reservoir. Although cyanobacteria “blooms” in Horsetooth Reservoir do not occur very often, the data indicate that when they do occur, they generally result from large densities (cell counts) of the small-celled Aphanocapsa, Aphanothece, Chroococcus, and Pannus, as shown for example on Figure 9.1 for the 0-5 m samples collected at HT-SPR. The highest cyanobacteria density measured in Horsetooth Reservoir occurred during the September 13, 2011 sampling event at HT-SPR, with the phytoplankton population made up almost exclusively of Aphanothece clathrata. Cyanobacteria densities ranged from 21,900 cells/mL at Soldier Canyon (0-5 meter depth), to 12,400 cells/mL at Dixon Canyon (0-5 meter depth), to 65,400 cells/mL at Spring Canyon (0-5 meter depth). However, while cyanobacteria made up over 90 percent of the total cell counts on that date, the group made up less than 10 percent of the total phytoplankton biovolume due to the very small cell size of Aphanothece clathrata. Aphanothece clathrata is not a known geosmin or cyanotoxin producer and does not present problems for water treatment plants.

Horsetooth Res at Spring Canyon (HT-SPR): Densities (cells/mL) of dominant Cyanobacteria Species (0-5 m) 20,000 2007 2008 2009 2010 2011 2012 2013 2014 2015 18,000 65,399 cells/mL 16,000

14,000

12,000

10,000

8,000

6,000 Density Density (number of cells/mL) 4,000

2,000

0 9-Oct-12 4-Sep-07 8-Sep-08 6-Sep-12 8-Aug-07 15-Jul-08 17-Jul-12 16-Jul-13 16-Jul-14 14-Jul-15 8-Nov-12 10-Jun-08 14-Jun-11 26-Jun-12 11-Jun-13 17-Jun-14 16-Jun-15 11-Oct-07 28-Oct-08 19-Oct-09 13-Oct-10 18-Oct-11 17-Oct-13 14-Oct-14 13-Oct-15 17-Apr-12 29-Apr-13 14-Apr-15 27-Sep-06 19-Sep-07 22-Sep-08 24-Sep-09 13-Sep-11 17-Sep-13 10-Sep-14 16-Sep-15 19-Dec-11 18-Aug-08 14-Aug-12 13-Aug-13 11-Aug-14 11-Aug-15 17-Nov-09 15-Nov-10 15-Nov-11 29-Nov-11 19-Nov-13 20-Nov-14 10-Nov-15 20-May-08 15-May-12 14-May-13 20-May-15

Aphanocapsa delicatissima Aphanocapsa sp. Aphanothece clathrata Chroococcus microscopicus Pannus sp. Anabaena planctonica Anabaena flos-aquae FIGURE 9.1 - DENSITIES OF DOMINANT CYANOBACTERIA AT HORSETOOTH RES AT SPRING CANYON (HT-SPR), 0-5 M DEPTH.

Relatively high cyanobacteria densities also occurred during 2012, 2014 and 2015. The Summer 2012 event is different from the other years in that Anabaena planctonica made up a significant fraction of the total cyanobacteria density. At HT-SPR, there was a total cyanobacteria density of 15,991 cells/mL on 8/14/12, with an Anabaena planctonica density of 5,536 cells/mL and 10,199 cells/mL of the small-celled Pannus (Figure 9.1). This is similar to what was observed at the HT-SOL site during the 8/14/12 sampling event. At HT-DIX, the peak 2012 cyanobacteria density occurred during the 7/17/12 event, with a total density of 17,749 cells/mL, which included 3,358 cells/mL of Anabaena planctonica and 14,391 cells/mL of the small-celled Aphanothece. Because of the presence of Anabaena planctonica in the Summer 2012 samples, the cyanobacteria biovolume made up a larger fraction of the total phytoplankton biovolume, 37% at HT-DIX on 7/17/12, and 15% at HT-SPR and 19% at HT-SOL on 8/14/12.

Small-celled genera made up the entire cyanobacteria population during early summer 2014 sampling events, with an Aphanocapsa density of 40,110 cells/mL at HT-DIX on 7/16/14, and Chroococcus densities of 8,556 cells/mL at HT- SOL on 7/16/14, and 7,290 cells/mL at HT-SPR on 6/17/14. In 2015, the small-celled Aphanocapsa made up the entire cyanobacteria population at HT-SPR during the 7/14/15 sampling event at 12,729 cells/mL.

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Two identified producers of geosmin, Anabaena circinalis and Aphanizomenon flos-aquae, have occasionally been found in Horsetooth Reservoir, but densities have been very low. Anabaena circinalis was found during Sept. 2009 and Oct. 2010 in Horsetooth Reservoir at very low densities (less than 14 cells/mL in Sept. 2009, and 0.4 cells/mL in Oct. 2010). Aphanizomenon flos-aquae was found in May and September 2008 at densities of 60 and 54 cells/mL, respectively, at Spring Canyon Dam (0-5 meter depth). Aphanizomenon flos-aquae was also found in June 2015 at Soldier Canyon Dam (0-5 m depth) at a density of 57 cells/mL, and in Nov. 2015 at Spring Canyon Dam (0-5 meter depth) at a density of 12 cells/mL.

9.2 CHLOROPHYLL-A Chlorophyll is a group of pigments found in plants that allow for the conversion of water, carbon dioxide, and sunlight into carbohydrates during photosynthesis. Chlorophyll-a is the primary photosynthetic pigment and is present in all species of algae and cyanobacteria (Wetzel, 2001). Chlorophyll-b is found in green algae and the euglenophytes, while chlorophyll-c is present in the diatoms, golden-brown algae, cryptomonads, and the dinoflagellates. Although the Baseline Monitoring Program has included the analysis of these three chlorophylls (USBR lab only, data prior to WY2015), this report summarizes the chlorophyll-a data only. Standard Method 10200-H2 (Spectrophotometric Determination of Chlorophyll) is the laboratory method used for the determination of chlorophyll concentrations. Pheophytin, a common degradation product of chlorophyll, is also determined with this method. The chlorophyll-a data summarized here have been corrected for pheophytin (corrected chlorophyll-a is obtained by subtracting out the pheophytin concentration from the chlorophyll-a concentration).

9.2.1 CHLOROPHYLL-a DATA REVIEW The Baseline Monitoring program currently includes the collection of composite samples within the 0-5 meter depth interval for chlorophyll analysis. The 0-5 meter chlorophyll-a data and the 0-5 meter phytoplankton data are for the same 0-5 meter composite sample. Time series plots for the 0-5 meter corrected chlorophyll-a data are included in Appendix C; note that units of mg/m3 are equivalent to µg/L. A monthly boxplot of corrected chlorophyll-a data is shown on Figure 9.2, summarizing the seasonal changes in the chlorophyll-a data for Horsetooth Reservoir. FIGURE 9.2 - HORSETOOTH RES CORRECTED CHLOROPHYLL-A (0-5 M) MONTHLY BOXPLOT.

The seasonal peaks in chlorophyll-a in Horsetooth Reservoir are typically less than 10 µg/L and coincide with the summer (July) and fall (Sept-Nov) peaks in biovolume that are often dominated by diatoms. The highest Horsetooth Reservoir chlorophyll-a concentrations were 12.1 µg/L on 11/24/08 at Soldier Canyon Dam and 16.3 µg/L on 10/9/12 at Spring Canyon Dam. The 11/24/08 peak was coincident with an annual peak in phytoplankton biovolume dominated by the diatom Tabellaria. The 10/9/12 peak was coincident with an annual peak in phytoplankton biovolume dominated by the dinoflagellate Ceratium hirundinella (the biovolume for Ceratium hirundinella was

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12,700,000 µm3/L, or 92% of the total biovolume, although the density was only 196 cells/mL; they can make up a significant fraction of the total biovolume due to their large size).

Median chlorophyll-a concentrations in Horsetooth Reservoir are 3.2, 3.2 and 3.1µg/L at Spring Canyon Dam (HT-SPR), Dixon Dam (HT-DIX), and Soldier Canyon Dam (HT-SOL), respectively, for all March – November data from the 2005-2015 monitoring period (Figure 9.3). The March – November averages are slightly higher than the medians during this period, at 3.8, 3.3 and 3.3µg/L at HT- SPR, HT-DIX, and HT-SOL, respectively (circles in the boxes on Figure 9.3). The boxplots in Figure 9.3 summarize a total of 83 data points at each site.

FIGURE 9.3 - BOXPLOT OF HORSETOOTH RES SITES WY2005 – WY2015 MARCH-NOV 0-5 M CHLOROPHYLL-A DATA.

The hydraulic residence time of water in Horsetooth Reservoir was significantly higher in WY2014 and WY2015 (1.8 and 1.5 years, respectively; see Section 4.3) compared to the period WY2006 - WY2012 (range of 0.7 to 0.95 years). Long hydraulic residence times can favor some phytoplankton, including cyanobacteria. However, the chlorophyll-a and phytoplankton data do not show any obvious increases coincident with these longer hydraulic residence times.

9.2.2 COMPARISON OF CHLOROPHYLL-a AND PHYTOPLANKTON BIOVOLUME Since chlorophyll-a is found in all species of phytoplankton, it is used to represent and estimate the fresh phytoplankton biomass. Phytoplankton biovolume is also used to estimate fresh phytoplankton biomass. The chlorophyll-a content of a phytoplankton cell depends on the phytoplankton group, species, size, season, environmental conditions, and general condition of the cells. Because of this, there is often not a strong relationship between chlorophyll-a concentrations and the total phytoplankton biovolume data. This can be seen in Figure 9.4 which is a plot of corrected chlorophyll-a data and total phytoplankton biovolume data for the 0-5 meter depth interval for Horsetooth Res at Spring Canyon (HT-SPR): Total Phytoplankton Biovolume 0-5 m Comparison of Total Phytoplankton Biovolume & Chlorophyll-a Concentrations Horsetooth 14,000,000 Chlorophyll-a 0-5 m 21 Reservoir

12,000,000 18 at HT-SPR.

10,000,000 15

a a (ug/L) 8,000,000 12 -

6,000,000 9

Chlorophyll 4,000,000 6

Phytoplankton Phytoplankton Biovolume (um3/mL) 2,000,000 3

0 0 10 10 10 11 11 11 11 12 12 12 13 13 13 14 14 14 15 15 10 10 10 11 11 12 12 13 13 14 15 13 14 15 10 11 12 13 14 15 10 11 12 13 14 15 10 11 12 13 14 15 ------Jul Jul Jul Jul Jul Jul Apr Apr Oct Apr Oct Apr Oct Apr Oct Apr Apr ------Jun Jun Jun Jun Jun Jun Mar Mar Feb Aug Sep Nov Aug Sep Nov Dec Aug Sep Nov Aug Sep Nov Aug Sep Nov Aug Sep ------May May May May May May ------20 12 17 16 16 14 01 21 13 01 18 17 09 29 17 08 14 08 14 26 11 17 16

20 06 11 15 29 19 08 19 20 10 14 09 13 14 06 13 17 11 10 11 16 20 18 15 14 14 20

FIGURE 9.4 - COMPARISON OF TOTAL PHYTOPLANKTON BIOVOLUME & CHL-A DATA FOR HORSETOOTH RES (HT-SPR).

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9.2.3 DIRECT USE WATER SUPPLY RESERVOIRS AND CHLOROPHYLL-a In 2012, the Colorado Water Quality Control Commission established a chlorophyll-a interim value that applies to Direct Use Water Supply (DUWS) lakes and reservoirs. DUWS lakes and reservoirs have a drinking water treatment plant intake in the lake or reservoir, or a man-made conveyance from the lake/reservoir that provides water directly to a water treatment plant (WQCC, 2016c, page 41). A March1 to November 30 average chlorophyll-a value of 5 µg/L in the mixed layer (epilimnion) was established for DUWS lakes/reservoirs with an allowable exceedance frequency of 1-in-5 years (WQCC, 2016c, page 66). The purpose of this chlorophyll-a standard is to minimize water treatment issues related to algae, particularly taste and odor problems and the formation of regulated disinfection byproducts from algal-produced organic carbon.

Horsetooth Reservoir has been classified as a DUWS reservoir, but the 5 µg/L interim value has not been adopted for this reservoir. However, in order to evaluate how the existing conditions in the reservoir compare to the 5 µg/L chlorophyll-a value, the annual March-November averages were calculated using the 0-5 meter WY2005 – WY2015 chlorophyll-a data. The number of data points used to calculate the March-Nov averages varied from year to year, and ranged from 4 to 11 at each sampling location. For the most recent 5 years of data, the 5 µg/L interim value was exceeded once at Spring Canyon (March-Nov average of 5.2 µg/L in 2012), with no exceedances at Soldier Canyon (Figures 9.5 and 9.6). Although not shown here, data for Dixon Canyon (HT-DIX) are similar to HT-SOL with no March-Nov averages that exceed the 5 µg/L chlorophyll-a interim value.

FIGURE 9.5 - WY2005-WY2015 MARCH - NOV CHLOROPHYLL-A DATA & AVERAGES FOR HORSETOOTH RES AT SPRING CANYON (HT-SPR).

FIGURE 9.6 - WY2005-WY2015 MARCH - NOV CHLOROPHYLL-A DATA & AVERAGES FOR HORSETOOTH RES AT SOLDIER CANYON (HT-SOL).

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One of the primary purposes of the DUWS chlorophyll-a standard is to address the potential for increased algal production in lakes and reservoirs to result in an increase in TOC concentrations, which can lead to an increase in disinfection byproducts during water treatment. If algae are a significant contributor to TOC within a reservoir, the TOC concentrations would be expected to increase with chlorophyll-a concentrations. The WY2009-WY2015 one-meter TOC concentrations are plotted against the 0-5 meter corrected chlorophyll-a concentrations for Horsetooth Reservoir on Figure 9.7. This plot indicates that TOC concentrations are not correlated to chlorophyll- a concentrations in Horsetooth Reservoir, and current chlorophyll-a levels are not having an obvious impact on TOC concentrations. This is consistent with the findings of Summers et al (2013; e.g., pages 97, 116, 124) who indicated that the TOC in Horsetooth Reservoir and in water flowing out of the East Portal Adams Tunnel is dominated by terrestrial, humic-like materials and does not strongly exhibit microbial (algal) characteristics.

TOC vs Chl-a: Horsetooth Res WY2009-WY2015 data 1-meter TOC & 0-5 m Chl-a data 7.0 HT-SPR HT-DIX 6.5 HT-SOL 6.0

5.5

5.0

4.5

4.0

TOC (mg/L) TOC 3.5

3.0

2.5

2.0

1.5 0 2 4 6 8 10 12 14 16 18 Chl-a (ug/L)

FIGURE 9.7 - HORSETOOTH RES WY2009 TO WY2015 TOC VERSUS CHLOROPHYLL-A CONCENTRATIONS.

9.3 TROPHIC STATE Lakes and reservoirs are often classified based on algal productivity (abundance and biomass). Water bodies with low algal productivity are considered oligotrophic, water bodies with moderate algal abundance are mesotrophic, while water bodies with high algal productivity are eutrophic, or the even higher hyper-eutrophic. These categories are termed trophic states and are generally associated with other characteristics of a water body as outlined on Table 9.1 (from Carlson and Simpson, 1996).

A water body can be categorized into trophic state using chlorophyll-a, Secchi depth, Total P, total nitrogen and/or other data. Chlorophyll-a is considered the best measure of algal biomass and, if chlorophyll-a data are available, should be used to assess trophic state. There are several classification systems used to delineate boundaries between trophic states (see, for example, Table 2 in WQCD, 2011b). Carlson (1977) developed a trophic state index (TSI) that uses three equations based on the three variables chlorophyll-a, Secchi depth, and Total P:

TSI based on chlorophyll-a: TSI(CHL) = 9.81 ln(chlorophyll-a in µg/L) + 30.6

TSI based on Secchi depth: TSI(SD) = 60 – 14.41 ln(Secchi depth in meters)

TSI based on Total P: TSI(TP) = 14.42 ln(TP in µg//L) + 4.15 where “ln” is the natural logarithm. Each 10-unit increase of the TSI scale (from 30 to 40, 40 to 50, etc) represents a halving of the Secchi depth, a doubling of Total P, and a 2.8-fold increase in chlorophyll-a. Table 9.1 shows the

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chlorophyll-a, Secchi depth and Total P values that correspond to the major divisions of Carlson’s TSI scale. Ranges of the TSI scale have also been related to the trophic state terms oligotrophic, mesotrophic, and eutrophic.

Carlson’s TSI is widely used by others and it is applied here to estimate the trophic state of Horsetooth Reservoir. It is generally applied by using seasonal average values of chlorophyll-a, Secchi depth, and/or Total P in the epilimnion. For this report, the July 1 through September 30 average values of chlorophyll-a were calculated for each year during the WY2005-WY2015 time period using data from the Spring Canyon site (Figure 9.8) and Soldier Canyon (Figure 9.9). Visual assessment of these figures indicates that Horsetooth Reservoir is in the mesotrophic range based on chlorophyll-a data. Note that the number of data points used to calculate the annual July-Sept averages plotted on Figures 9.8 and 9.9 is generally 3 (monthly sampling during July, August and September), but ranges from 2 to 5. Although algae populations can change quickly and one monthly sampling event does not capture the full range of conditions, the WY2005-WY2015 data are consistently in the mesotrophic range.

TABLE 9.1 - TROPHIC CLASSIFICATION OF LAKES & RESERVOIRS BASED ON CHL-A, SECCHI DEPTH & TOTAL P (FROM CARLSON AND SIMPSON, 1996). Carlson’s Trophic Fisheries & Secchi Trophic Water Body Water Supply Chl-a Total P State Recreation Depth Status characteristics characteristics (ug/L) (mg/L) Index characteristics (m) (TSI) Clear water, Water may be oxygen suitable for an Salmonid fisheries <30 throughout the < 0.95 > 8 < 0.006 unfiltered water dominate year in the supply. Oligotrophic hypolimnion

Hypolimnion of shallower lakes Salmonid fisheries 0.95- 0.006- 30-40 8-4 may become in deep lakes only 2.6 0.012 anoxic. Water Iron, manganese, moderately clear; Hypolimnetic taste & odor increasing anoxia results in problems; raw 0.012 - Mesotrophic 40-50 probability of loss of salmonids; 2.6-7.3 4-2 water turbidity 0.024 hypolimnetic walleye may requires anoxia during predominate. filtration. summer Anoxic Warm-water hypolimnion, fisheries 0.024 - 50-60 7.3-20 2-1 macrophyte only. Bass may 0.048 problems dominate. Macrophytes, algal Eutrophic Blue-green algae scums & low dominate; algal Episodes of clarity may 0.048 - 60-70 scums & severe taste & 20-56 1-0.5 discourage 0.096 macrophyte odor possible. swimming & problems boating.

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FIGURE 9.8 - HORSETOOTH AT SPRING CANYON: TROPHIC CLASSIFICATION BASED ON JULY-SEPT AVG CHLOROPHYLL-A.

FIGURE 9.9 - HORSETOOTH AT SOLDIER CANYON: TROPHIC CLASSIFICATION BASED ON JULY-SEPT AVG CHLOROPHYLL-A.

9.4 CITY OF FORT COLLINS GEOSMIN DATA The City of Fort Collins has monitored geosmin concentrations at Horsetooth Reservoir sites since 2008 and at the East Portal of the Adams Tunnel and Hansen Feeder Canal sites since 2009 (Billica et al, 2010; Billica and Oropeza, 2011, page 27). Geosmin data collected by the City of Fort Collins were obtained by Northern Water and are presented and evaluated here since geosmin is an important constituent of concern for drinking water treatment plants. The data evaluation and summary presented in this section is an update of the summary presented in Billica et al (2010).

The City of Fort Collins geosmin data collected through 2015 for the Horsetooth Reservoir Spring Canyon Dam and Soldier Canyon sites (1 meter and bottom samples) are plotted on Figure 9.10, while the geosmin data for the Adams Tunnel and Hansen Feeder Canal sites are plotted on Figure 9.11. The data are summarized in annual boxplots in Figures 9.12 and 9.13 (note that geosmin samples were not collected for the Horsetooth Reservoir sites in 2015). Samples for geosmin analysis are generally collected August through November, with the number of samples collected each year ranging from 2 to 7 (Figures 9.12 and 9.13 show the individual data points). Geosmin

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analysis was conducted through 2015 by Dr. Keith Elmund of the City of Fort Collins using solid phase microextraction as per Standard Method 6040D (2005), and gas chromatography/mass spectrometry.

Figures 9.10 and 9.12 show that high geosmin concentrations were measured in Horsetooth Reservoir in 2008, but have been near or below the 5 nanograms/L (ng/L) odor threshold since 2010. Peak geosmin concentrations in Horsetooth Reservoir occurred in Nov. 2008 including nearly 53 ng/L at Spring Canyon (1-meter depth) and 28 ng/L at the bottom of Solder Canyon Dam where the intake to the treatment plants is located. In 2009, the geosmin concentrations within the reservoir were less, but still of concern, with a peak concentration of 18 ng/L at Spring Canyon (1-meter depth), although concentrations measured at the bottom of Soldier Canyon Dam remained less than 5 ng/L. The conditions that allowed for the high geosmin concentrations within Horsetooth Reservoir in 2008 and 2009, but not in the 2010-2014 period, are unknown and difficult to determine due to the many contributing factors. As discussed in Section 9.1, two identified producers of geosmin, Anabaena circinalis and Aphanizomenon flos- aquae, have occasionally been found in Horsetooth Reservoir, but densities have been very low, and at levels that would not be expected to result in taste and odor issues.

Figures 9.11 and 9.13 show that relatively high geosmin concentrations (greater than the odor threshold of 5 ng/L) are often detected at the East Portal Adams Tunnel and in the Hansen Feeder Canal downstream of Flatiron Reservoir. Geosmin is relatively stable in the environment, can persist in the open water, and can be transported by water movement (AWWA, 2010, pg. 361). At the same time, geosmin is subject to both volatilization and biodegradation that impact its fate in aquatic ecosystems. However, the detection of geosmin at the Hansen Feeder Canal just upstream of Horsetooth Reservoir (HFC-HT; Figures 9.11and 9.13) indicates that some portion of the geosmin found in Horsetooth Reservoir is transported to the reservoir from upstream sources.

Potential sources of geosmin that are upstream of Horsetooth Reservoir include periphyton (attached algae) in the Hansen Feeder Canal between Flatiron Reservoir and Horsetooth Reservoir, phytoplankton in the small reservoirs between the Adams Tunnel and the Hansen Feeder Canal (including Lake Estes and Flatiron Reservoir), and phytoplankton in the West Slope reservoirs. Phytoplankton sampling is not conducted in the reservoirs between the Adams Tunnel and the Hansen Feeder Canal, but periphyton sampling is conducted for the Hansen Feeder Canal and phytoplankton sampling is conducted in the West Slope reservoirs. These data are reviewed below with respect to possible sources of geosmin entering Horsetooth Reservoir.

2008 - 2015 City of Fort Collins Geosmin Data - Horsetooth Res - Spring & Soldier Canyon Dams, top & bottom 35 Not shown: HT-SPR-1 = 52.6 ng/L 11/4/08 HT-SPR-1 30 HT-SPR-b

HT-SOL-1 25 HT-SOL-b 20

15 Geosmin ng/LGeosmin

Odor threshold ≤ 5 ng/L 5

0 29-Feb-12 28-Feb-13 28-Feb-14 28-Feb-15 30-Aug-08 30-Aug-09 30-Aug-10 30-Aug-11 29-Aug-12 29-Aug-13 29-Aug-14 29-Aug-15 29-Nov-08 29-Nov-09 29-Nov-10 29-Nov-11 28-Nov-12 28-Nov-13 28-Nov-14 28-Nov-15 01-Mar-08 01-Mar-09 01-Mar-10 01-Mar-11 31-May-08 31-May-09 31-May-10 31-May-11 30-May-12 30-May-13 30-May-14 30-May-15 FIGURE 9.10 - 2008-2015 GEOSMIN TIME SERIES PLOT FOR HORSETOOOTH RESERVOIR SITES (DATA FROM CITY OF FORT COLLINS).

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2008 - 2015 City of Fort Collins Geosmin Data - Hansen Feeder Canal & Big Thompson R. 35 AT-EP

30 HFC-FRD

HFC-BT 25 HFC-BTU

HFC-HT 20

15 Geosmin ng/LGeosmin

Odor threshold ≤ 5 ng/L 5

0 29-Feb-12 28-Feb-13 28-Feb-14 28-Feb-15 30-Aug-08 30-Aug-09 30-Aug-10 30-Aug-11 29-Aug-12 29-Aug-13 29-Aug-14 29-Aug-15 29-Nov-08 29-Nov-09 29-Nov-10 29-Nov-11 28-Nov-12 28-Nov-13 28-Nov-14 28-Nov-15 01-Mar-08 01-Mar-09 01-Mar-10 01-Mar-11 31-May-08 31-May-09 31-May-10 31-May-11 30-May-12 30-May-13 30-May-14 30-May-15 FIGURE 9.11 - 2009-2015 GEOSMIN TIME SERIES PLOT FOR ADAMS TUNNEL & HANSEN FEEDER CANAL SITES (DATA FROM CITY OF FORT COLLINS).

FIGURE 9.12 - ANNUAL BOXPLOT OF CITY OF FORT COLLINS GEOSMIN DATA FOR HORSETOOTH RESERVOIR SPRING CANYON & SOLDIER CANYON 1 METER AND BOTTOM SITES.

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FIGURE 9.13 - ANNUAL BOXPLOT OF CITY OF FORT COLLINS GEOSMIN DATA FOR ADAMS TUNNEL & HANSEN FEEDER CANAL SITES.

Periphyton sampling in the Hansen Feeder Canal is conducted by Northern Water zero to four times per year to provide information for canal O&M and herbicide application effectiveness (Northern Water, 2016). Of particular note is the fact that significant fractions of the total periphyton biomass collected at the Hansen Feeder Canal site downstream of Flatiron Reservoir (HFC-FRD) are occasionally made up of the cyanobacteria Phormidium autumnale, including 100% of the biomass in Sept 2008, 45% of the biomass in Aug 2009, 35% of the biomass in Oct 2009, and 90% of the biomass in Sept 2013. Juttner and Watson (2007) indicate that a number of species of Phormidium are geosmin producers, but they do not specifically identify Phormidium autumnale as a geosmin producer. Note that no periphyton samples were collected in Sept 2009, no samples throughout 2010, and no samples in Aug-Oct 2011, making it difficult to observe a relationship between the presence of Phormidium autumnale and elevated geosmin concentrations.

The existing Hansen Feeder Canal data are mixed, with elevated geosmin concentrations at HFC-FRD combined with a high percent of the biomass made up of Phormidium autumnale in 2009, but very low geosmin concentrations with a high percent of the biomass made up of Phormidium autumnale in 2013. And, although no periphyton samples were collected at HFC-FRD in Aug-Oct 2011, the geosmin concentration at HFC-FRD during the 10/4/11 sampling event was elevated at 12.6 ng/L, compared to a concentration of 3.3 measured at the Adams Tunnel on that date, indicating a source downstream of the Adams Tunnel, or a travel-time lag between the sampling sites. Again, Phormidium autumnale is not a confirmed geosmin producer, and the available data do not allow for conclusions regarding the periphyton in the Hansen Feeder Canal as a source of geosmin. Phormidium autumnale has not been found to date in periphyton samples collected at the other Hansen Feeder Canal sites (HFC-BT and HFC-HT).

In the West Slope reservoirs, blooms of cyanobacteria often occur in August and September in Grand Lake and Shadow Mountain Reservoir (Billica, 2013). Algal production in Grand Lake and Shadow Mountain Reservoir is impacted by many factors including C-BT Project operations that dictate the flows from Shadow Mountain Reservoir to Grand Lake and influence the hydraulic detention times and water temperatures in Shadow Mountain Reservoir. For example, in 2013, there was an extended period of no Farr pumping (July 24 – Sept 2, conducted to restrict Shadow Mountain flows to Grand Lake to benefit clarity in Grand Lake), that resulted in a higher than normal July- Sept average hydraulic detention time (41 days) in Shadow Mountain Reservoir (Hawley and Boyer, 2016) with warmer water temperatures and high algal production in Shadow Mountain Reservoir. In 2012, which was a dry year with continuous Farr pumping and high flows from Shadow Mountain Reservoir through Grand Lake to the

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Adams Tunnel and to the East Slope reservoirs, the summer hydraulic detention time in Shadow Mountain Reservoir was lower (15 days) with lower surface water temperatures and low peak chlorophyll-a concentrations (Hawley and Boyer, 2014).

Anabaena and Aphanizomenon density data (cells/mL) are presented in Figures 9.14 and 9.15 for Grand Lake at the Adams tunnel (GL-ATW) and Shadow Mountain Reservoir at the middle site (SM-MID). Grand Lake and Shadow Mountain Reservoir often have significant populations of Anabaena planctonica, including a peak density of 26,800 cells/mL at SM-MID in Aug 2013 during the no-pumping period, but this species has not been identified in the literature as a geosmin producer. Two identified producers of geosmin, Anabaena circinalis and Aphanizomenon flos- aquae, have occasionally been found in Grand Lake and Shadow Mountain Reservoir, but densities have been very low and Anabaena circinalis has not been found since 2010.

Grand Lake at Adams Tunnel (GL-ATW): Densities (cells/mL) of Cyanobacteria Species (0-5 m) - Genera of Geosmin Producers 20,000 2008 2009 2010 2011 2012 2013 2014 2015 18,000

16,000

14,000

12,000

10,000

8,000

6,000 Density Density (number of cells/mL)

4,000

2,000

0 7-Jul-14 6-Jul-15 8-Jun-10 9-Jun-14 8-Jun-15 5-Oct-15 3-Apr-13 9-Sep-08 6-Sep-10 7-Sep-10 4-Sep-12 2-Sep-14 8-Sep-15 5-Aug-08 9-Aug-10 6-Aug-12 4-Aug-14 3-Aug-15 16-Jul-08 14-Jul-09 12-Jul-10 25-Jul-11 24-Jul-12 16-Jul-13 25-Jan-10 25-Jan-11 12-Jun-08 28-Jun-11 19-Jun-12 18-Jun-13 29-Oct-08 13-Oct-09 28-Oct-10 17-Oct-11 23-Oct-12 21-Oct-13 23-Sep-08 14-Sep-09 28-Sep-09 20-Sep-10 12-Sep-11 26-Sep-11 17-Sep-12 19-Sep-12 10-Sep-13 25-Sep-13 15-Sep-14 21-Sep-15 19-Aug-08 10-Aug-09 24-Aug-09 11-Aug-10 23-Aug-10 15-Aug-11 29-Aug-11 21-Aug-12 23-Aug-12 12-Aug-13 27-Aug-13 18-Aug-14 17-Aug-15 31-Mar-10 30-Mar-11 25-Mar-13 21-May-08 17-May-10 19-May-10 26-May-11 21-May-12 20-May-13 19-May-14 11-May-15 Anabaena planctonica Anabaena flos-aquae Anabaena sp. Anabaena circinalis - geosmin producer Aphanizomenon flos - aquae - geosmin producer

FIGURE 9.14 - DENSITIES OF CYANOBACTERIA ANABAENA & APHANIZOMENON AT GRAND LAKE – ADAMS TUNNEL (GL-ATW), 0-5 M.

Shadow Mountain - middle (SM-MID): Densities (cells/mL) of Cyanobacteria Species (0-5 m) - Genera of Geosmin Producers 20,000 26,833 2008 2009 2010 2011 2012 2013 cells/mL 2014 2015 18,000

16,000

14,000

12,000

10,000

8,000

6,000 Density Density (number of cells/mL) 4,000

2,000

FIGURE 9.15 - DENSITIES OF CYANOBACTERIA ANABAENA & APHANIZOMENON AT SHADOW MTN RES - MID (SM-MID), 0-5 M.

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Anabaena and Aphanizomenon density data (cells/mL) are presented in Figure 9.16 for Willow Creek Reservoir (WC-DAM). At Willow Creek Reservoir, densities of the geosmin producers Aphanizomenon flos-aquae and Aphanizomenon gracile are significantly higher than at any of the other C-BT Project water bodies, and peak counts have occurred every fall since monitoring began (Figure 9.16). The highest density of Aphanizomenon flos-aquae measured in Willow Creek Reservoir was 24,748 cells/mL during the Oct 19, 2011 sampling event (0-5 meter depth). High counts of Anabaena (various species) often occur in July (Figure 9.16). The geosmin producer Anabaena circinalis has been present during only two sampling events, at a density of 250 cells/mL in Aug. 2008, and at a much higher density of 6,900 cells/mL in July 2010 (both values for 0-5 meter depth).

Willow Ck Reservoir (WC-DAM): Densities (cells/mL) of Cyanobacteria Species (0-5 m) - Genera of Geosmin Producers

24,000 2008 2009 2010 2011 2012 2013 2014 2015 22,000

20,000

18,000

16,000

14,000

12,000

10,000

8,000 Density Density (number of cells/mL) 6,000

4,000

2,000

0 6-Oct-15 9-Sep-08 7-Sep-10 4-Sep-12 2-Sep-14 9-Sep-15 5-Aug-08 7-Aug-12 5-Aug-15 16-Jul-08 15-Jul-09 14-Jul-10 26-Jul-11 25-Jul-12 16-Jul-13 3-Nov-10 17-Jun-09 19-Jun-12 24-Jun-15 15-Oct-09 19-Oct-11 29-Oct-13 16-Sep-09 30-Sep-09 22-Sep-10 13-Sep-11 27-Sep-11 18-Sep-12 10-Sep-13 24-Sep-13 15-Sep-14 19-Aug-08 12-Aug-09 26-Aug-09 11-Aug-10 24-Aug-10 16-Aug-11 30-Aug-11 21-Aug-12 12-Aug-13 27-Aug-13 18-Aug-14 Anabaena planctonica Anabaena flos-aquae Anabaena sp. Anabaena circinalis - geosmin producer Aphanizomenon gracile - geosmin producer Aphanizomenon flos - aquae - geosmin producer FIGURE 9.16 - DENSITIES OF CYANOBACTERIA ANABAENA & APHANIZOMENON AT WILLOW CK RESERVOIR (WC-DAM), 0-5 M.

Given the densities of Aphanizomenon flos-aquae and Aphanizomenon gracile measured in Willow Creek Reservoir, the presence of geosmin is suspected although sampling for geosmin has not been conducted at any of the West Slope reservoirs. Of particular concern would be the potential transport of geosmin from Willow Creek Reservoir in water pumped to the Three Lakes and through the Adams Tunnel. The majority of Willow Creek Reservoir water is pumped to Granby Reservoir during the spring and early summer, prior to the seasonal presence of potential geosmin-producing cyanobacteria. However, a small amount of water is generally pumped to Granby Reservoir in the fall. This water could be impacted by the presence of Aphanizomenon flos-aquae and Aphanizomenon gracile, although the pumped volume is very small and would be diluted in Granby Reservoir. For the water that is pumped from Willow Creek Reservoir during the spring runoff period, it is unlikely that geosmin produced during the summer and fall of one year would be present at detectable levels in Willow Creek Reservoir during the spring of the following year. Dissolved geosmin is relatively stable to chemical and microbiological degradation and can persist in the open water for some time depending on environmental conditions such as temperature (Juttner and Watson, 2007). However, degradation does occur and, in addition, the snowmelt runoff flows would serve to significantly dilute these compounds if they were still present in Willow Creek Reservoir in early spring.

In summary, geosmin concentrations in Horsetooth Reservoir have been near or below the 5 ng/L odor threshold since 2010. At the same time, concentrations above 5 ng/L have been measured at the Adams Tunnel and in the Hansen Feeder Canal. Phytoplankton data collected for Grand Lake and Shadow Mountain Reservoir and periphyton data collected in the Hansen Feeder Canal have not allowed for the identification of geosmin production sites. The large geographical extent of the C-BT Project and the annual variations in operations, as well as the many

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environmental factors, all complicate the fate and transport of geosmin and its spatial variation. These factors together continue to prevent the establishment of cause and effect relationships for geosmin.

9.5 ZOOPLANKTON Zooplankton are microscopic invertebrates (animals without backbones) that live suspended in the water column. Although they have some capability for locomotion or swimming, they cannot swim against currents. They are an essential part of all lake/reservoir ecosystems since they are a direct link in the aquatic food chain, as greatly simplified in Figure 9.17. Zooplankton populations are impacted by the phytoplankton population (zooplankton food source), the population of fish and other predators, water temperature, reservoir operations, and many other factors.

Zooplankton sampling at each Horsetooth Sunlight + CO2 Nutrients Reservoir site consists of the collection of composite samples. From WY2005 – WY2013, two composites were collected Phytoplankton at each site, one representing the 0 to 5 meter depth interval, and the second representing the 5 to 10 meter depth interval. Beginning in WY2014, one 0-10 Herbivorous meter composite is collected at each site. Zooplankton Zooplankton analysis has been conducted during the WY2005-WY2015 period by Carnivorous BSA Environmental Services, Inc. using the Zooplankton Utermohl chamber counting method. Analysis includes identification to the Planktivorous Fish species level (or lowest practical taxonomic level) and abundance (number of individuals per liter). Piscivorous Fish (fish eaters)

FIGURE 9.17 - SIMPLIFIED AQUATIC FOOD CHAIN.

9.5.1 OVERVIEW OF ZOOPLANKTON GROUPS The zooplankton identified in the C-BT Project lake/reservoirs fall into one of three groups: rotifers, cladocerans, and copepods. Representatives of these groups are shown in the photographs in Figure 9.18 while general characteristics of each group are discussed below.

Rotifers are soft-bodied multi-cellular animals that are generally 0.2 to 0.5 millimeter (mm) in length. One of their distinguishing features is a ciliated crown on the anterior (head) end which is used for food gathering and locomotion. They also have a jaw-like structure for grinding and crushing up food particles (http://www.ucmp.berkeley.edu/phyla/rotifera/rotifera.html). They have no legs, and some species have spines and/or a shell-like protective outer covering (lorica). They are generally transparent and colorless. They eat particulate organic detritus, phytoplankton and bacteria. The dominant rotifers found in Horsetooth Reservoir include species of Kellicottia, Keratella (Figure 9.18 A), Polyarthra, and Synchaeta.

Cladocerans are crustaceans (animals with segmented limbs and a hardened external skeleton) and are commonly referred to as “water fleas”. They generally range in size from 0.2 mm to 3.0 mm (Wetzel, 2001, page 484).

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Distinguishing physical characteristics include a head that bends downward (Figure 9.18 B), large antennae used for locomotion, and the presence of a large compound eye. They are covered by a transparent shell (bivalve carapace). Cladocerans are filter feeders; they use their appendages to strain suspended particulate organic detritus, bacteria, and phytoplankton of desirable sizes out of the water. Cladocerans have diurnal vertical migration patterns where they migrate upwards toward the surface at dusk and downward at dawn. Fish depend on cladocerans as a significant food source. The dominant cladocerans found in Horsetooth Reservoir include species of Bosmina, Daphnia, and Eubosmina.

Daphnia lumholtzi is an invasive waterflea that was first confirmed in Colorado in 2013 and is now known to be present in 24 Colorado water bodies including Horsetooth Reservoir as reported by Colorado Parks and Wildlife (http://cpw.state.co.us/Documents/ANS/Fact-Sheet-Waterfleas.pdf). Northern Water’s zooplankton data show the presence of Daphnia lumholtzi during one sampling event at one site (at HT-SPR on 9/8/08).

(A) ROTIFER: Keratella (B) CLADOCERAN: Daphnia (C) COPEPOD: Dicyclops

FIGURE 9.18 - PHOTOGRAPHS OF REPRESENTATIVE ZOOPLANKTON FOUND IN THE LAKE/RESERVOIRS, (A) ROTIFER: Keratella, (B) CLADOCERAN: Daphnia, AND (C) COPEPOD: Dicyclops (photos taken by BSA Environmental Services Inc, Beachwood, OH; included with permission).

Copepods are also crustaceans and have a prominent exoskeleton. They range in size from less than 0.5 mm to over 2 mm in length (http://academics.smcvt.edu/dfacey/AquaticBiology/Freshwater%20Pages/Copepods.html). Adult copepods have a tear-drop shaped (Figure 9.18 C), segmented body that includes a pair of long antennae on the head section used for locomotion, five pairs of legs along the middle used for swimming, and a tail-like appendage at the end. Depending on the species, their mouth parts and appendages near their mouth provide for filtering, seizing, capturing, and/or biting. Copepods feed on algae, bacteria, or other zooplankton (such as rotifers, small cladocerans, and juvenile copepods). The dominant copepods found in Horsetooth Reservoir are in the two orders Cyclopoid (including the genus Diacyclops) and Calanoid (including the genera Leptodiaptomus and Skistodiaptomus). Copepods in the larval stages (termed nauplii) and or in later (still immature) developmental stages (termed copepodids or copepodites) have also been commonly identified in the water samples collected from Horsetooth Reservoir, and are often the dominant contributors to the total copepod count.

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9.5.2 SUMMARY OF HORSETOOTH RESERVOIR ZOOPLANKTON DATA Appendix H contains bar graphs of density (number of individuals per liter) and percent total composition for the three zooplankton groups for Horsetooth Reservoir. The timing of the annual peak in total zooplankton density varies by site and from year to year. The data collected to date indicate that the annual peaks in total density generally occur in Horsetooth Reservoir in the spring and/or fall, as shown in the monthly boxplot (Figure 9.19) for the 0-5 meter samples collected at HT-SPR during the WY2005-WY2013 period (note composite sampling changed to 0-10 meters in WY2014).

FIGURE 9.19 - MONTHLY BOXPLOT OF TOTAL ZOOPLANKTON DENSITY AT HT-SPR.

Cladocerans are generally present at low densities in Horsetooth Reservoir, and make up a small fraction of the total density. A monthly boxplot of total cladoceran density is shown in Figure 9.20 for Spring Canyon, and note that the y-axis scale only goes to 200/L. Annual peaks usually occur in the early spring, although a peak density of 181/L occurred at HT-SPR on 11/8/2012 and made up 60% of the total zooplankton density on that date.

FIGURE 9.20 - MONTHLY BOXPLOT OF TOTAL CLADOCERAN DENSITY AT HT-SPR.

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Rotifers and copepods make up the majority of the total zooplankton population at Horsetooth Reservoir. Monthly boxplots for total rotifer density and total copepod density at Spring Canyon are shown on Figures 9.21 and 9.22, respectively. Most of the peaks in total zooplankton density are dominated by rotifers.

FIGURE 9.21 - MONTHLY BOXPLOT OF TOTAL ROTIFER DENSITY AT HT-SPR.

FIGURE 9.22 - MONTHLY BOXPLOT OF TOTAL COPEPOD DENSITY AT HT-SPR.

9.6 FOOD WEB INTERACTIONS Food web interactions are complex and it is outside the scope of this report to provide detailed interpretation of the WY2005-WY2015 zooplankton data and the effects of the food web structure on water quality. The database of specific genera and species of rotifers, copepods and cladocerans for all sampling locations and sampling dates is available for independent review at http://www.northernwater.org/DynData/WQDataMain.aspx. Studies and analyses conducted by others have revealed important food web interactions present in the C-BT water bodies including Horsetooth Reservoir. Some of these studies are summarized below.

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In Horsetooth Reservoir, rainbow smelt were introduced in 1983 as potential prey for walleye. Rainbow smelt feed on zooplankton. Very high numbers of smelt in the late 1980’s are believed to have resulted in a significant drop in cladocerans (Daphnia) and other zooplankton that feed on phytoplankton. This coincided with an increase in phytoplankton biomass and the onset of nuisance manganese conditions in Horsetooth Reservoir as dissolved oxygen was depleted during the breakdown of increased amounts of organic matter that had settled to the reservoir bottom (Jassby and Goldman, 1996, page 11). The rainbow smelt population subsequently decreased with a dramatic increase in the zooplankton population (including Daphnia) by the mid-1990’s (Jassby and Goldman, 1999, page 34; Johnson and Goettl, 1999). A significant increase in the Horsetooth Reservoir rainbow smelt population was observed again in 2012 (personal communication with Dr. Jesse Lepak, Colorado Parks and Wildlife), although the impact of this increase on zooplankton and the food web dynamics is not known.

Mysis shrimp (Mysis relicta) were introduced into Colorado lakes/reservoirs as a supplemental food source for fish. Mysids prey heavily on zooplankton, particularly cladocerans (and specifically Daphnia), resulting in a shift in the zooplankton community. High densities of Mysis shrimp have impacted the zooplankton populations in the C-BT system lake/reservoirs, with populations of Daphnia spp. nearly disappearing from Grand Lake (Martinez and Bergersen, 1989).

On the East Slope, Johnson and Hobgood (2000) reported an abundance of Mysis shrimp in Carter Lake that has been a factor influencing the differences in the zooplankton population between Horsetooth Reservoir and Carter Lake (including seasonal patterns of abundance, and Daphnia spp. that are significantly smaller in Carter). Johnson and Hobgood (2000) indicated that the rainbow smelt population in Horsetooth Reservoir may have eliminated Mysis relicta from that reservoir.

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10. SUMMARY OF FINDINGS & RECOMMENDATIONS

10.1 SUMMARY OF KEY FINDINGS The purpose of this report was to characterize the water quality conditions in Horsetooth Reservoir and the flowing waters (rivers and canals) of the C-BT system from the Adams Tunnel east to Flatiron Reservoir, and then north to Horsetooth Reservoir and the Poudre River, as revealed by data collected for the Baseline Monitoring Program during the 16-year period WY2000 through WY2015. This characterization is an update of the data summaries and findings presented in two previous Northern Water reports, the 2010 Flowing Sites Report (covering WY2000 – WY2009) and the 2013 Lake and Reservoirs Report (covering WY2005 – WY2011); http://www.northernwater.org/WaterQuality/WaterQualityReports1.aspx. However, the two previous reports summarized data collected at all (West Slope and East Slope) Baseline Monitoring Program sites, while this report has a focused geographical scope and provides for the evaluation of Horsetooth Reservoir together with its associated upstream and downstream flowing sites.

This section summarizes the results of the data analysis presented in this report, including spatial and seasonal patterns, time trend analysis, and Horsetooth Reservoir biological parameters (chlorophyll-a and phytoplankton data).

10.1.1 SPATIAL & SEASONAL PATTERNS The geographical scope of this report allows for visualization of the spatial patterns that include Horsetooth Reservoir together with its associated upstream and downstream flowing sites. Horsetooth Reservoir is directly influenced by the upstream water sources, but its water quality is different due to the detention time within the reservoir and the different biological, physical, and chemical processes that take place within the reservoir. Downstream of Horsetooth Reservoir, water in the Hansen Supply Canal takes on characteristics of the reservoir water and does not appear to have any detrimental impact on the Poudre River. Some key spatial and seasonal patterns are summarized below.

Major Ions. The Baseline Monitoring Program shows that concentrations of the major ions are low at all the East Slope - North End sites. The highest median concentrations of calcium, magnesium, sulfate, alkalinity and hardness occur in Horsetooth Reservoir and downstream in the Hansen Supply Canal, with concentrations at these sites falling within narrow ranges. The flowing sites (river and canal sites, except for the Hanen Supply Canal) exhibit wider ranges of major ion concentrations than Horsetooth Reservoir due to the pronounced seasonal variability experienced by the flowing sites, with concentrations diluted during the spring runoff.

TOC. The flowing sites (except for the Hansen Supply Canal) show a wider range in TOC concentrations than Horsetooth Reservoir due to seasonal variability, with increased concentrations during the spring snowmelt runoff period. The Horsetooth Reservoir bottom sites show the narrowest range in concentrations, and influence the narrow range also observed at the downstream Hansen Supply Canal site.

Water from the Adams Tunnel mixes with Big Thompson River water at Lake Estes and the water leaving Lake Estes in the Olympus Tunnel has a blend of characteristics from both sources. During the spring snowmelt runoff period (generally May through June), higher TOC concentrations in the Big Thompson River above Lake Estes result in TOC concentrations in the Olympus Tunnel and Hansen Feeder Canal that are generally higher than at the Adams Tunnel, depending on the relative flows from each source. High TOC water in the Big Thompson River can also be diverted to the Hansen Feeder Canal at the Dille Tunnel during the spring runoff, contributing to elevated TOC concentrations in the Hansen Feeder Canal at Horsetooth during this period.

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Before and after the spring runoff (generally July through March), the TOC concentrations in the Hansen Feeder Canal are primarily influenced by the concentrations in the West Slope water as measured at the Adams Tunnel. This would be expected since flows in the Big Thompson River are low compared to the Adams Tunnel flows during this time. TOC concentrations in the Hansen Feeder Canal at Horsetooth are similar to concentrations measured at the Adams Tunnel, and both are higher than the TOC concentrations in the Big Thompson River above Lake Estes after the spring runoff.

TOC concentrations in water entering Horsetooth Reservoir in the Hansen Feeder Canal (HFC-HT) are highest during the spring runoff period, May – June, and are significantly higher than the reservoir outflow concentrations during this time as measured at the Hansen Supply Canal site (HSC-PR). TOC concentrations at HSC-PR are relatively constant from month to month, with median monthly concentrations of about 3.4 mg/L, and reflect the concentrations measured at the bottom of Horsetooth Reservoir at Soldier Canyon (HT-SOL-b). After the runoff period, the reservoir inflow and outflow TOC concentrations are similar

TOC concentrations at the Horsetooth Reservoir 1-meter depth are generally the same as or higher than at the reservoir bottom. Higher TOC concentrations would be expected near the reservoir surface (compared to bottom samples) during the spring and summer months since algal production near the surface contributes to the TOC pool.

Phosphorous. Ortho-P concentrations are generally highest at the Big Thompson River sites since these sites are influenced by the WWTPs located upstream at Estes Park, and at the bottom of Horsetooth Reservoir at Spring Canyon due to release from bottom sediments during summer stratification. The Big Thompson River and Poudre River sites experience the highest Total P concentrations since Total P is associated with sediments that are mobilized during snowmelt runoff and significant rainfall events. Higher Total P concentrations at the Big Thompson River sites are associated with impacts of the 2013 flood, while the Total P concentrations at the Poudre River sites have been additionally impacted by stormwater runoff from the 2012 High Park Fire burn areas.

Nitrogen. The highest median nitrate+nitrite concentrations are found at the Big Thompson River sites, which are downstream of wastewater treatment plants. The sites at the bottom of Horsetooth Reservoir have elevated nitrate+nitrite concentrations during the late summer and fall. At the bottoms of stratified water bodies such as Horsetooth Reservoir, nitrate concentrations increase as a result of the decomposition of settled organic matter (which releases ammonia that is then converted to nitrate when oxygen is present). The lowest median concentrations of nitrate+nitrite are found at the Horsetooth Reservoir 1 meter depth due to algal uptake.

Metals. The metals currently included in the Baseline Monitoring Program are arsenic (dissolved and total), boron (dissolved), cadmium (dissolved), chromium (total and dissolved), copper (dissolved), iron (total and dissolved), lead (dissolved), manganese (dissolved), nickel (dissolved), selenium (dissolved), silver (dissolved), uranium (dissolved), and zinc (dissolved). Sampling for total arsenic, boron, chromium (dissolved and total), and uranium began in WY2013 or WY2014, so it is premature to make conclusions about the spatial and seasonal patterns for these parameters. Cadmium and silver have rarely been detected and most lab results have indicated that these trace metals are not present above their respective detection limits, which have varied over the years. Many of the other metals do not show strong spatial or seasonal variability. Some specific observations for dissolved arsenic, copper, total and dissolved iron, and manganese are discussed below.

Dissolved Arsenic. Low levels of dissolved arsenic are detected at all sampling sites. The Horsetooth Reservoir sites and the Hansen Supply Canal sites generally have higher concentrations (median of about 0.3 µg/L) than the tunnel sites, Hansen Feeder Canal sites and Big Thompson River sites (median of about 0.2 µg/L). The highest concentrations (up to 1.6 µg/L) have been detected at the bottom of Horsetooth Reservoir at Spring Canyon Dam prior to fall turnover. Arsenic adsorbs onto iron oxide particulate material and, after settling to the bottom of a water body, this arsenic can be released into solution when iron oxides dissolve under anoxic/reducing conditions that can occur at the reservoir bottom prior to fall turnover.

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Copper. Data collected since WY2002 show that the highest dissolved copper concentrations have historically been found at the Hansen Feeder Canal and Hansen Supply Canal sites (median concentrations of 2.1 – 3.4 µg/L). Since all copper sulfate applications were stopped in 2012, the copper spatial boxplot takes on a new pattern with only the WY2012 to WY2015 data. The highest median concentrations now occur at the Big Thompson River sites (median concentrations of 1.5 - 1.8 µg/L), followed by the Adams Tunnel and Olympus Tunnel sites (median concentrations of 1.4 µg/L).

Dissolved Iron. Dissolved iron concentrations at all sites are generally below the drinking water secondary MCL except for some occurrences above 300 µg/L at the Hansen Feeder Canal sites, Olympus Tunnel, Big Thompson River, and Poudre River. The highest dissolved iron concentrations include 1,170 µg/L at HFC-FRD, 1,090 µg/L at HFC-BT, and 1,110 µg/L at HFC-HT, in samples collected on Oct. 3, 2013 when these sites were impacted by floodwater that had entered Lake Estes and was then pumped through the Olympus Tunnel to Pinewood and Flatiron Reservoirs, and subsequently released to the Hansen Feeder Canal.

Manganese. Elevated manganese concentrations (> 50 µg/L, the drinking water secondary MCL) occur at the bottom of Horsetooth Reservoir during periods of low dissolved oxygen, generally in September and October at the end of the summer stratification period. Occasional concentrations above 50 µg/L have also occurred at the Big Thompson River and Poudre River sites.

10.1.2 TREND ANALYSIS The analysis of water quality data conducted for this report included the determination of the statistical significance and magnitude of time trends to address the questions of whether and how much water quality has changed over the period of record. The Seasonal Kendall Test was used to provide a quantitative test for the statistical significance of trends in the concentration time series data. It is a test for monotonic changes in a data series (i.e., a change in only one direction, increasing or decreasing).

The results of the trend analysis conducted for this report are summarized in Table 10.1 while raw data output from the Seasonal Kendall Test are contained in Appendix I. The test was performed at a 90% confidence level (critical p-value = 0.10), which means that there is at most a 10% chance of concluding that a statistically significant trend exists when in fact there is no trend. If a computed p-value is less than 0.10, a statistically significant time trend is concluded to exist. For cases where a statistically significant trend is concluded to exist, the “Sen slope as a percent of the mean” is used to evaluate the magnitude of the trend in a relative manner. Cases where the absolute value of the Sen slope is greater than 4% of the mean are highlighted in Table 10.1 with an up or down arrow, where 4% was selected to allow for a focus on those parameters with the highest trend magnitudes (i.e., trends that are more likely to have significance from a practical standpoint). Note that if the Sen Slope is equal to 4% of the mean value calculated over the study period, the annual average parameter concentration would change by 100% of that value in 25 years (or 4% of that value each year), assuming the trend continues over time.

Although the trend analysis was conducted for many parameters as indicated in Table 10.1 and a number of parameters showed statistically significant trends (increasing or decreasing), the results for copper, TOC, nutrients,

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and Horsetooth Reservoir Secchi depth and chlorophyll-a concentrations are the most noteworthy and of the most practical significance within the geographical scope of this report.

TABLE 10.1 - SUMMARY OF SEASONAL KENDALL TREND TEST RESULTS TOC & Major Ions Nutrients Metals Other

HSC-PRU Poudre River, upstream HSC ↓ ↑ ↑ ↑ ↑ ↓ HSC-PR Hansen Supply Canal ↑ ↓ ↓ ↓ ↑ ↓ ↑ ↓ HSC-PRD Poudre River, downstream HSC ↓ ↑ ↑ ↑ ↓ ↑ ↑

Note: all trend tests are at the 90% confidence level (significant trend if p-value ≤ 0.10)

Copper. The trend analysis results in Table 10.1 show statistically and practically significant decreasing trends in copper concentrations in the canals and Horsetooth Reservoir. Copper concentrations in the canals and downstream Horsetooth Reservoir have dropped since the use of copper sulfate was discontinued during the 2008 – 2011 period. Copper concentrations in the Poudre River downstream of the Hansen Supply Canal (HSC-PRD) show a statistically significant decreasing trend, coincident with the discontinued use of copper sulfate in the Hansen Supply Canal in 2008. At the Adams Tunnel and Olympus Tunnel sites, the analysis showed a statistically significant increasing trend in copper concentrations, although the cause of this is not known.

TOC. Only two canal/tunnel sites, the Hansen Feeder Canal at the Horsetooth inlet and the Hansen Supply Canal, show statistically significant increasing trends in TOC concentrations although the magnitude of the trends are relatively small. The TOC trend results shown in Table 10.1 differ from those reported previously by others for Horsetooth Reservoir and waters in the Hansen Feeder Canal, where previous studies have consistently indicated statistically significant increasing trends in TOC at many of the sites. For example, in the most recent BTWF report (Hydros Consulting, 2015), which included data for the period WY2000 – WY2014, TOC concentrations continued to show a statistically significant increasing trend at the east portal Adams Tunnel, Olympus Tunnel, and in the Hansen Feeder Canal sites HFC-FRD and HFC-BT, and HFC-HT was added to this list of sites with increasing TOC.

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Visual inspection of the time series plots in Appendix C and the annual boxplots in Appendix E do not show any obvious trends in TOC concentrations over time, consistent with the statistical trend analysis results (from both a statistical and practical standpoint).

Nutrients. The time trend analysis for the ammonia data indicate statistically significant decreasing trends for many of the sites (Table 10.1), including Hansen Feeder Canal and Horsetooth Reservoir sites with relatively high trend magnitudes. However, the ammonia trend analysis is impacted by the changing detection limits (lowering over time) and the high number of non-detected values. The statistically significant decreasing trend in ortho-P at the Adams Tunnel site is influenced by the fact that only 20% of the values at this site were above the detection limit. At the Poudre River sites (HSC-PRU and HSC-PRD), increasing trends in nitrate, TKN, ortho-P and Total P are influenced by the increasing concentrations of these parameters that occurred after the 2012 High Park Fire.

10.1.3 HORSETOOTH RESERVOIR PHYTOPLANKTON, CHLOROPHYLL-a & GEOSMIN The Horsetooth Reservoir phytoplankton population is generally dominated by diatoms, green algae and cryptomonads by density (cells/mL). Occasionally, cyanobacteria, or golden-brown algae may be a dominant algal group by density. Diatoms dominate the phytoplankton population by biovolume (µm3/mL). Cryptomonads and golden-brown algae may also be dominant by biovolume.

Although cyanobacteria “blooms” in Horsetooth Reservoir do not occur very often, the data indicate that when they do occur, they generally result from large densities (cell counts) of the small-celled Aphanocapsa, Aphanothece, Chroococcus, and Pannus. Two identified producers of geosmin, Anabaena circinalis and Aphanizomenon flos-aquae, have occasionally been found in Horsetooth Reservoir, but densities have been very low (≤ 60 cells/mL).

Median chlorophyll-a concentrations in Horsetooth Reservoir are 3.2, 3.2 and 3.1µg/L at Spring Canyon Dam (HT- SPR), Dixon Dam (HT-DIX), and Soldier Canyon Dam (HT-SOL), respectively, for all March – November data from the WY2005-WY2015 monitoring period. The seasonal peaks in chlorophyll-a in Horsetooth Reservoir are typically less than 10 µg/L and coincide with the summer (July) and fall peaks in biovolume that are dominated by diatoms. The highest Horsetooth Reservoir chlorophyll-a concentrations were 12.1 µg/L on 11/24/08 at Soldier Canyon Dam and 16.3 µg/L on 10/9/12 at Spring Canyon Dam. The 11/24/08 peak was coincident with an annual peak in phytoplankton biovolume dominated by the diatom Tabellaria. The 10/9/12 peak was coincident with an annual peak in phytoplankton biovolume dominated by the large dinoflagellate Ceratium hirundinella.

In 2012, the Colorado Water Quality Control Commission established a 5 µg/L chlorophyll-a interim value (March- November average, with a 1-in-5 year exceedance frequency) that applies to the epilimnion of Direct Use Water Supply (DUWS) lakes and reservoirs. Horsetooth Reservoir has been classified as a DUWS reservoir, but the 5 µg/L interim value has not been adopted for this reservoir. However, to evaluate how the existing conditions in the reservoir compare to the 5 µg/L chlorophyll-a value, the annual March-November averages were calculated using the 0-5 meter WY2005 – WY2015 chlorophyll-a data. For the most recent 5 years of data, the 5 µg/L interim value was exceeded once at Spring Canyon (March-Nov average of 5.2 µg/L in 2012), with no exceedances at the Soldier Canyon and Dixon Canyon sampling sites.

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Carlson’s trophic state index (TSI) is widely used by others and was applied here to characterize the trophic state of Horsetooth Reservoir. It is generally applied by using seasonal average values of chlorophyll-a, Secchi depth, and/or Total P in the epilimnion. For this report, TSI values were calculated for each year during the WY2005- WY2015 period using the July 1 through September 30 average chlorophyll-a concentrations. The calculated TSI values indicate that Horsetooth Reservoir continues to be in the mesotrophic range.

The City of Fort Collins has monitored geosmin concentrations at Horsetooth Reservoir sites since 2008 and at the East Portal of the Adams Tunnel and Hansen Feeder Canal sites since 2009. Geosmin data collected by the City of Fort Collins were obtained by Northern Water and presented in this report since geosmin is an important taste and odor constituent of concern for drinking water treatment plants. High geosmin concentrations were measured in Horsetooth Reservoir in 2008 (nearly 53 ng/L at Spring Canyon 1-meter depth and 28 ng/L at the bottom of Solder Canyon Dam), but have been near or below the 5 ng/L odor threshold since 2010. In 2009, the geosmin concentrations within the reservoir were less, but still of concern, with a peak concentration of 18 ng/L at Spring Canyon (1-meter depth).

The conditions that allowed for the elevated geosmin concentrations within Horsetooth Reservoir in 2008 and 2009, but not in the 2010-2015 period, are unknown and difficult to determine due to the many contributing factors. Two identified producers of geosmin, Anabaena circinalis and Aphanizomenon flos-aquae, have occasionally been found in Horsetooth Reservoir, but densities have been very low, and at levels that would not be expected to result in taste and odor issues. Relatively high geosmin concentrations (greater than the odor threshold of 5 ng/L) are often detected at the East Portal Adams Tunnel and in the Hansen Feeder Canal downstream of Flatiron Reservoir. The large geographical extent of the C-BT Project and the annual variations in operations, as well as the varying environmental conditions, all complicate the fate and transport of geosmin and its spatial variation. These factors together continue to prevent the establishment of cause and effect relationships for the occurrence of geosmin in Horsetooth Reservoir.

10.2 RECOMMENDATIONS FOR BASELINE MONITORING AND FUTURE SPECIAL STUDIES

Some changes in parameters and sampling frequency have been made over the years to Northern Water’s Baseline Monitoring Program such that it is currently meeting the objectives of the program, including at the East Slope - North End sites. Changes to the program in the East Slope – North End geographical area are not recommended at this time.

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11. REFERENCES

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APPENDICES

A - SUMMARY STATISTICS

B - HORSETOOTH RESERVOIR PROFILES

C - TIME SERIES PLOTS

D - MONTHLY BOX PLOTS

E - ANNUAL BOX PLOTS

F - BOX PLOTS OF SPATIAL VARIABILITY

G - HORSETOOTH RESERVOIR PHYTOPLANKTON DENSITY & BIOVOLUME PLOTS

H - HORSETOOTH RESERVOIR ZOOPLANKTON DENSITY PLOTS

I - STATISTICAL TREND ANALYSIS RESULTS

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