Big Blue River Watershed Water Quality Impairment: Total Phosphorus and Ph

KANSAS-LOWER REPUBLICAN BASIN TOTAL MAXIMUM DAILY LOAD

Waterbody/Assessment Unit: Big Blue River Watershed Water Quality Impairment: Total Phosphorus and pH

1. INTRODUCTION AND PROBLEM IDENTIFICATION

Subbasin: Lower Big Blue, Lower Little Blue Counties: Marshall, Washington HUC8: 10270205 HUC10 (12): 01 (03, 04) 02 (01, 02, 03, 04) 05 (01, 02, 03)

HUC8: 10270207 HUC10 (12): 06 (06)

Ecoregion: Smoky Hills (27a), Flint Hills (28a), and Loess and Glacial Drift Hills (47i)

Drainage Are a: Approximately 383 square miles (mi2)

Water Quality Limited Segments Covered Under TMDL (designated uses for main stem and tributary segments are detailed in Table 1):

Main Stem Segment Tributaries Tributaries HUC8: 10270205 Big Blue R (21) Deer Cr (36) Scotch Cr (38) Bommer Cr (40) Elm Cr, North (41) Mission Cr (22) Murdock Cr (42)

Big Blue R (20) Horseshoe Cr (26) Raemer Cr (33) Indian Cr (37) Meadow Cr (34) Little Indian Cr (35)

Big Blue R (18) Dutch Cr (44) Hop Cr (43) Spring Cr (19) Schell Cr (45) Lily Cr (39)

Big Blue R (17) Elm Cr (46)

HUC8: 10270207 Fawn Cr (45)

Table 1. Designated uses for main stem and tributary segments in the watershed (Kansas Department of Health and Environment, 2013). Stream Segment Expected Contact Domestic Food Ground Industrial Irrigation Livestock # Aquatic Recreation Supply Procurement Water Water Use Use Watering Life Recharge Use HUC8: 10270205 Big Blue R 17 E B X X X X X X Elm Cr 46 E b X X X X X X Big Blue R 18 E B X X X X X X Dutch Cr 44 E b O O O O O O Hop Cr 43 E b O X X O X X Spring Cr 19 E B X X X X X X Schell Cr 45 E b X X X X X X Lily Cr 39 E b X X X X X X Big Blue R 20 E C X X X X X X Deer Cr 36 E b X X X X X X Scotch Cr 38 E b O O O O O X Bommer Cr 40 E b X O X X X X Big Blue R 21 E C X X X X X X Mission Cr 22 E C X X X X X X Murdock Cr 42 E b X O X X X X Horseshoe Cr 26 E C X X X X X X Raemer Cr 33 E b X X X X X X Indian Cr 37 E b X X X X X X Meadow Cr 34 E b X X X X X X Little Indian Cr 35 E b X X X X X X Elm Cr, North 41 S b X X X X X X HUC8: 10270207 Fawn Cr 45 E b X O X X X X X=use is designated; O=use is not designated; E=Expected aquatic life; S=Special aquatic life; B, C=Primary contact recreation; b=Secondary contact recreation

Impaired Use: Expected aquatic life, contact recreation, domestic water supply

303(d) Listings: Kansas stream segments monitored by station SC731 (Figure 1), North Elm Creek near Oketo, are cited as impaired by total phosphorus (TP) in 2008, 2010, 2012, 2014, 2016, and 2018.

Kansas stream segments monitored by station SC233, Big Blue River near Oketo, are cited as impaired by: TP in 2008, 2010, 2012, 2014, 2016, and 2018; pH in 2002, 2004, 2008, 2010, 2012, 2014, 2016, and 2018; and biology in 2004, 2008, 2010, 2012, 2014, 2016, and 2018.

Kansas stream segments monitored by station SC717, Horseshoe Creek near Marysville, are cited as impaired by TP in 2008, 2010, 2012, 2014, 2016, and 2018.

Kansas stream segments monitored by station SC240, Big Blue River near Blue Rapids, are cited as impaired by TP in 2008, 2010, 2012, 2014, 2016, and 2018 and by pH in 2004, 2008, 2010, 2012, 2014, 2016, and 2018.

Figure 1. Map of contributing area for KDHE stream chemistry stations SC731, SC233, SC717, and SC240.

Water Quality Criteria: Nutrients -- Narrative: The introduction of plant nutrients into streams, lakes, or wetlands from artificial sources shall be controlled to prevent the accelerated succession or replacement of aquatic biota or the production of undesirable quantities or kinds of aquatic life (K.A.R. 28-16- 28e(d)(2)(A)).

The introduction of plant nutrients into surface waters designated for primary or secondary contact recreational use shall be controlled to prevent the development of objectionable concentrations of algae or algal by-products or nuisance growths of submersed, floating, or emergent aquatic vegetation (K.A.R. 28-16-28e(d)(7)(A)).

The introduction of plant nutrient into surface waters designated for domestic water supply use shall be controlled to prevent interference with the production of drinking water (K.A.R. 28-16- 28e(d)(3)(D)).

Taste-producing and odor-producing substances of artificial origin shall not occur in surface waters at concentrations that interfere with the production of potable water by conventional water treatment processes, that impart an unpalatable flavor to edible aquatic or semiaquatic life or terrestrial wildlife, or that result in noticeable odors in the vicinity of surface waters (K.A.R. 28-16-28e(b)(7)).

Dissolved Oxygen -- Numeric: The concentration of dissolved oxygen in surface waters shall not be lowered by the influence of artificial sources of pollution. The Dissolved Oxygen criterion is 5 mg/L (K.A.R. 28-16-28e(e), Table 1g).

pH -- Numeric: Artificial sources of pollution shall not cause the pH of any surface water outside of a zone of initial dilution to be below 6.5 and above 8.5 (K.A.R. 28-16-28e(e), Table 1g).

2. CURRENT WATER QUALITY CONDITIONS AND DESIRED ENDPOINT

Level of Support for Designated Uses under the 2018 303(d) List: Phosphorus levels in Big Blue River near Oketo (SC233), Big Blue River near Blue Rapids (SC240), Horseshoe Creek near Marysville (SC717), and North Elm Creek near Oketo (SC731) are consistently high. Excessive nutrients are not being controlled and are thus impairing aquatic life, domestic water supply, and contact recreation uses. The ultimate endpoint of this Total Maximum Daily Load (TMDL) will be to achieve the Kansas Surface Water Quality Standards by eliminating excessive primary productivity and impairment to aquatic life, recreation, and domestic water supply associated with excessive phosphorus.

Station Location and Period of Record: Stream Chemistry (SC) Monitoring Station: SC731: Active rotational station on North Elm Creek near Oketo, located on a county road bridge 1.75 miles north of Oketo. Sampled quarterly every four years in the period of record from April 16, 2001 to December 4, 2017.

SC233: Active permanent station on Big Blue River near Oketo, located on a K-233 highway bridge 0.5 miles south and 0.5 mile west of Oketo. Sampled quarterly in the period of record from March 13, 1990 to October 15, 2018. SC717: Active rotational station on Horseshoe Creek near Marysville, located on a U.S. 77 highway bridge 1.2 miles west and 3.75 miles north of Marysville. Sampled quarterly every four years in the period of record from January 26, 1998 to December 4, 2017. SC240: Active permanent station on Big Blue River near Blue Rapids, located on a U.S. 77 highway bridge 1.4 miles east of Blue Rapids. Sampled quarterly in the period of record from March 13, 1990 to October 15, 2018.

Stream Biology (SB) Monitoring Stations: SB233: Active station on Big Blue River 1 mile west of Oketo. Period of record: April 3, 1990 to June 27, 2017. SB240: Active station on Big Blue River on U.S. Highway 77, 1.4 miles northeast of Blue Rapids. Period of record: July 17, 2013 to August 16, 2016. SB374: Inactive station on North Elm Creek at a county road bridge 2 miles east and 2.5 miles North of Oketo. Period of record: July 13, 1999 to October 17, 2000. SB475: Inactive station on Horseshoe Creek on a county road bridge 2.1 miles north of Herkimer. Period of record: October 6, 2010 to October 13, 2015. SB476: Inactive station on Spring Creek on a county road bridge 0.6 miles south of Marysville. Period of record: October 6, 2010 to October 13, 2015.

Stream Probabilistic (SP) Monitoring Stations: SP826: North Elm Creek. Period of record: 2006, 2008, and 2011. SPA066: Horseshoe Creek. Period of record: 2006. SPB514: Indian Creek. Period of record: 2016. SPB172: Spring Creek. Period of record: 2012. SPB642: Schell Creek. Period of record: 2017. SPA285: Dutch Creek. Period of record: 2008 and 2017. SPB173: Fawn Creek. Period of record: 2012.

Streamflow Gage: U.S. Geological Survey 06882510: Big Blue River at Marysville. Period of record: January 1, 1990 to December 31, 2018. U.S. Geological Survey 06814000: Turkey Creek near Seneca. Period of record: January 1, 1990 to December 31, 2018.

Hydrology: Streamflow conditions were developed using U.S. Geological Survey (USGS) streamgage data from the Big Blue River at Marysville (06882510) and Turkey Creek near Seneca (06814000). Total flow at KDHE stream chemistry (SC) stations SC233 and SC240 is based on the watershed ratio between values from Big Blue River segments located in Marshall County (as determined by USGS in Perry et. al., 2004) and the contributing drainage area of USGS gage 06882510, including flow originating in Nebraska. The calculations for the discreet drainage areas within Kansas measured at SC233 and SC240 applied the ratio of the watershed size of the KDHE SC station to the area of the USGS gage. Streamflow conditions for SC717 and SC731 were developed using the ratio of their respective watershed areas to that of the

streamgage in Turkey Creek near Seneca. The resulting estimated flows are displayed in cubic feet per second (cfs) in Table 2 over the January 1, 1990 through December 31, 2018 period of record for the four SC stations within the TMDL watershed.

Table 2. Estimated flow conditions at stream chemistry (SC) stations for Big Blue River near Oketo (SC233) and Blue Rapids (SC240), Horseshoe Creek near Marysville (SC717), and North Elm Creek near Oketo (SC731) and monitored flow conditions at U.S. Geological Survey (USGS) gages for the 1990 through 2018 period of record. Mean Percent Flow Exceedance (cfs) Drainage Stream Station Flow Area (mi2) 90% 75% 50% 25% 10% (cfs)

Turkey Creek USGS 276 129 2.10 7.40 22.0 69.0 203 06814000

KDHE North Elm Creek 21.3 8.84 0.170 0.497 1.54 4.55 13.4 SC731

USGS Big Blue River 4,777 984 153 239 367 729 2,090 06882510

KDHE Big Blue River SC233 4,670 962 150 234 359 713 2,043

Big Blue River KDHE Discreet Flow for SC233 31.1 6.41 0.996 1.56 2.39 4.75 13.6 Drainage Area SC233

KDHE Horseshoe Creek 82.3 34.2 0.656 1.92 5.93 17.6 51.6 SC717

KDHE Big Blue River 8,490 1,749 272 425 652 1,296 3,714 SC240

Big Blue River: KDHE Discreet Flow for SC240 249 51.3 7.98 12.5 19.1 38.0 109 Drainage Area SC240

In Figure 2 and Table 3, flows are split between the 1990 through 1999 and 2000 through 2018 periods of record revealing reduced flow in both Turkey Creek and the Big Blue River in the more recent period. Interstate flow in the Big Blue River is managed under the Kansas-Nebraska Big Blue River Compact. Entered into 1971, the purpose of the compact is to promote interstate comity, achieve equitable apportionment of the waters of the Big Blue River Basin and promote the orderly development thereof, and to encourage an active pollution abatement program in each state. The Compact provides for minimum target flows to reach the Kansas state line on the Big Blue River during the months of May (45 cfs), June (45 cfs), July (80 cfs), August (90 cfs), and September (65 cfs; Kansas Department of Agriculture, 2019). Long-term estimated flows for the Big Blue River and its tributaries can be found in Table 4 (Perry et. al, 2004).

Figure 2. Estimated flow duration curve for KDHE stream chemistry stations in the Big Blue River Watershed above Tuttle Creek Reservoir for the 1990 through 1999 and 2000 through 2018 periods of record. Flow Duration Curves for the Big Blue River near Oketo and Blue Rapids, North Elm Creek and Horseshoe Creek 1990-1999 & 2000-2018 100000

10000

1000

100

10 Flow (cfS)

1990-1999 SC731 North Elm Cr 2000-2018 SC731 North Elm Cr 0.1 1990-1999 SC233 Big Blue R nr Oketo 2000-2018 SC233 Big Blue R nr Oketo 1990-1999 SC717 Horseshoe Cr 0.01 2000-2018 SC717 Horseshoe Cr 1990-1999 SC240 Big Blue R nr Blue Rapids 2000-2018 SC240 Big Blue R nr Blue Rapids 0.001 0 10 20 30 40 50 60 70 80 90 100 Percent of Time Flow Exceeded

Table 3. Streamflow in Turkey Creek and the Big Blue River during the 1990 through 1999 and 2000 through 2018 periods of record. Mean USGS Watershed Period of Percent Flow Exceedance (cfs) Stream Flow Gage Area (mi2) Record (cfs) 90% 75% 50% 25% 10% 1990-1999 158 5.00 10.0 32.5 77.0 242 Turkey Creek 06814000 276 2000-2018 91.8 1.50 4.79 15.6 46.4 145 1990-1999 1,228 208 292 474 972 2,810 Big Blue River 06882510 4,777 2000-2018 856 138 206 326 600 1,730

Table 4. U.S. Geological Survey long-term estimated flows for the Big Blue River and its tributaries (Perry et.al, 2004, Marshall County). Drainage Mean Flow Exceedance (%) 2-year Stream Site ID Area Flow Peak 90% 75% 50% 25% 10% (mi2) (cfs) (cfs) Murdock Cr 50 12.1 4.19 0 0 0 0.34 3.03 945 Mission Cr 37 47.9 17.3 0 0 1.47 5.91 19.3 2,792 Big Blue R 145 4,640 570 91.8 139 233 429 1,120 17,888 North Elm Cr 182 25.1 8.75 0 0 0.43 2.29 8.58 1,393 Big Blue R 210 4,670 498 89.1 133 221 383 959 17,966 Bommer Cr 222 8.66 2.85 0 0 0 0 1.64 741 Big Blue R 284 4,690 470 88.0 130 217 365 895 17,964 Scotch Cr 308 9.26 2.91 0 0 0 0 1.58 766 Big Blue R 294 4,700 511 94.4 139 231 397 992 17,991 Deer Cr 295 24.2 8.64 0 0 0.98 3.14 9.42 1,322 Big Blue R 306 4,720 613 110 161 267 477 1,230 18,098 Little Indian 173 11.3 3.81 0 0 0.17 0.75 3.18 839 Meadow Cr 186 6.48 1.93 0 0 0 0 0.80 613 Indian Cr 211 17.3 6.33 0 0 0.68 2.14 6.63 1,086 Raemer Cr 321 10.6 3.60 0 0 0.19 0.74 3.06 795 Horseshoe Cr 307 128 42.1 0.10 1.70 6.57 19.9 56.2 3,172 Big Blue R 396 4,860 1,190 200 286 467 924 2,590 19,100 Lily Cr 400 9.42 2.90 0 0 0 0 1.53 772 Schell Cr 465 8.07 2.54 0 0 0 0 1.19 713 Spring Cr 408 65.6 22.7 0 0 2.11 8.17 26.3 2,624 Big Blue R 445 4,930 1,200 200 286 467 928 2,610 19,273 Hop Cr 446 16.6 5.96 0 0 0.62 1.97 6.13 1,045 Big Blue R 484 4,950 1,210 201 287 468 930 2,610 19,316 Dutch Cr 485 10.6 3.85 0 0 0.33 0.99 3.51 819 Big Blue R 611 4,980 1,210 201 287 469 934 2,620 19,127 Fawn Cr 762 29.5 13.1 0 0.21 2.15 6.25 16.8 1,571 Big Blue R 667 8,450 1,480 255 352 530 1,070 2,910 23,396 Elm Cr 666 24.1 9.92 0 0 1.05 3.70 11.3 1,392 Big Blue R 769 8,490 1,490 255 354 533 1,080 2,930 23,316

At all SC sites, high annual mean and median flows occurred in 1993, and the lowest annual mean flow occurred in 2012 (Figures 3-6). The lowest annual median flows in the Big Blue River occurred in 2012, while the lowest median flows in Horseshoe and North Elm Creeks occurred in 2006. Annual flows generally coincide with National Oceanic and Atmospheric Administration (NOAA) annual total precipitation from Blue Rapids station USC00140911. Monthly, the highest mean flows occurred in June in the Big Blue River and in May in the tributaries North Elm and Horseshoe Creeks (Figures 7-10). Seasonally, the spring (April through June) records the highest mean and median across the watershed (Figure 11). Winter (March through November) records the lowest mean flows at all stations, as well as the lowest median flow in the Big Blue River (Table 5). The magnitude of the difference between summer- fall (July through October) and winter flows is much smaller in the tributaries than in the main stem. The lowest median values recorded for the tributaries is during the summer-fall season.

Figure 3. Annual mean and median flows for North Elm Creek near Oketo (SC731) and annual total precipitation at the NOAA station in Blue Rapids (USC00140911). Annual Mean and Median Flow in North Elm Creek (SC731) and Annual Precipitation at Blue Rapids 45 60

30 40 Precipitation (in)

Flow (cfs) 20

15 20

0 0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Mean Median 1990-2018 Period of Record Mean Flow Precipitation

Figure 4. Annual mean and median flows for Big Blue River near Oketo (SC233) and annual total precipitation at the NOAA station in Blue Rapids (USC00140911). Annual Mean and Median Flow in the Big Blue River near Oketo (SC233) and Annual Precipitation at Blue Rapids 3500 60

3000 50

2500

40 Precipitation (in) 2000

30 Flow (cfs) 1500

1000

10 500

0 0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Mean Median 1990-2018 Period of Reord Mean Flow Precipitation

Figure 5. Annual mean and median flows for Horseshoe Creek near Marysville (SC717) and annual total precipitation at the NOAA station in Blue Rapids (USC00140911). Annual Mean and Median Flow in Horshoe Creek (SC717) and Annual Precipitation at Blue Rapids 160 60

140 50

120

40 100 Precipitation (in)

80 30 Flow (cfs)

60 20

10 20

Figure 6. Annual mean and median flows for the Big Blue River near Blue Rapids (SC240) and annual total precipitation at the NOAA station in Blue Rapids (USC00140911). Annual Mean and Median Flow in the Big Blue River near Blue Rapids (SC240) and Annual Precipitation at Blue Rapids 6000 60

5000 50

4000 40 Precipitation (in)

3000 30 Flow (cfs)

2000 20

1000 10

Figure 7. Estimated monthly mean and median flows for the North Elm Creek near Oketo (SC731). 1990-2018 Mean and Median Monthly Flow in North Elm Creek (SC731) 25

15 Flow (cfs)

0 January February March April May June July August September October November December Mean Median

Figure 8. Estimated monthly mean and median flows for the Big Blue River near Oketo (SC233). 1990-2018 Mean and Median Monthly Flow in the Big Blue River near Oketo (SC233) 2500

2000

1500 Flow (cfs)

1000

500

0 January February March April May June July August September October November December Mean Median

Figure 9. Estimated monthly mean and median flows for the Horseshoe Creek near Marysville (SC717). 1990-2018 Mean and Median Monthly Flow in Horseshoe Creek (SC717) 90

Flow (cfs) 40

0 January February March April May June July August September October November December Mean Median

Figure 10. Estimated monthly mean and median flows for the Big Blue River near Blue Rapids (SC240). 1990-2018 Mean and Median Monthly Flow in the Big Blue River near Blue Rapids (SC240) 4500

4000

3500

3000

2500

Flow (cfs) 2000

1500

1000

500

0 January February March April May June July August September October November December Mean Median

Figure 11. Flow by season in the Big Blue River Watershed. Big Blue River flows reflect watershed areas of 4,670 mi2 and 8,490 mi2 near Oketo and Blue Rapids, respectively.

Seasonal Flow in North Elm Creek (SC731) 1990-2018 Seasonal Flow in Horseshoe Creek (SC717) 1990-2018 30 Season Season Spring 100 Spring Summer-Fall Summer-Fall Winter Winter

75 20 ) ) s s f f c c ( (

w w 50 o o l l F F

0 0

Spring Summer-Fall Winter Spring Summer-Fall Winter

Seasonal Flow in the Big Blue River near Oketo (SC233) 1990-2018 Seasonal Flow in the Big Blue River near Blue Rapids (SC240) 1990-2018 4000 Season Season Spring Spring 6000 Summer-Fall Summer-Fall Winter Winter 3000 4500 ) ) s s f f c c ( ( 2000 w w

o o 3000 l l F F

1000 1500

0 0

Spring Summer-Fall Winter Spring Summer-Fall Winter

Table 5. Seasonal flows in the Big Blue River (SC233 and SC240), North Elm Creek (SC731), and Horseshoe Creek (SC717). Big Blue River flows reflect watershed areas of 4,670 and 8,490 mi2 near Oketo and Blue Rapids, respectively. Mean (cfs) Median (cfs) Stream Spring S/F Winter Spring S/F Winter North Elm Creek (SC731) 17.0 7.19 5.29 4.00 0.772 1.31 Big Blue River near Oketo (SC233) 1,700 914 559 656 325 305 Horseshoe Creek (SC717) 65.6 27.8 20.4 15.4 2.98 5.07 Big Blue River near Blue Rapids (SC240) 3,087 1,661 1,016 1,193 590 555

Total Phosphorus: Total phosphorus (TP) loading in the watershed reflects the seasonal flow pattern, with higher concentrations occurring during the spring season indicating an increase in frequency of runoff events caused by precipitation (Figure 12). The exception to this pattern is in North Elm Creek where slightly higher TP concentrations are recorded in the summer-fall season. Figure 13 and Table 6 display a pattern typical of watersheds primarily influenced by nonpoint source loading, with the highest concentrations occurring during the high flow condition of 0-25% flow exceedance. Concentrations diminish over the 26-50% and 51-75% flow exceedance values; however, there is an uptick in concentrations when streams are at the low flow condition of 76-100% flow exceedance. Overall, mean and median TP concentrations are highest in the Big Blue River near Oketo (SC233) at 0.905 and 0.781 mg/L, respectively. TP concentrations in both tributaries are markedly lower and contribute to decreased concentrations seen downstream in the Big Blue River near Blue Rapids (SC240; Figure 14; Table 7).

Figure 12. Box plot of total phosphorus by season in the Big Blue River near Blue Rapids (SC240), Big Blue River near Oketo (SC233), Horseshoe Creek near Marysville (SC717), and North Elm Creek near Oketo (SC731).

Total Phoshorus by Season and Station

2.5 Season Spring Summer-Fall Winter

) 2.0 L / g m (

u 1.5 r o h p s o

h 1.0 P

l a t o T 0.5

0.0

SC731 SC233 SC717 SC240

Figure 13. Box plot of total phosphorus by flow condition for the Big Blue River near Blue Rapids (SC240), Big Blue River near Oketo (SC233), Horseshoe Creek near Marysville (SC717), and North Elm Creek near Oketo (SC731).

Total Phosphorus by Percent Flow Exceedance and Station

North Elm Cr (SC731) 2.5 Big Blue nr Oketo (SC233) Horseshoe Cr (SC717) Big Blue nr Blue Rapids (SC240) ) L

/ 2.0 g m (

s u r 1.5 o h p s o h

P 1.0

l a t o T 0.5

0.0

% % % % % % % % % % % % % % % % 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 2 5 7 0 2 5 7 0 2 5 7 0 2 5 7 0 - - 1- -1 - - 1- -1 - - 1- -1 - - 1- -1 0 6 5 6 0 6 5 6 0 6 5 6 0 6 5 6 2 7 2 7 2 7 2 7 Percent Flow Exceedance (%)

Table 6. Total phosphorus concentration mean, median, and number of samples (N) by season (spring: April through June, summer-fall: July through October, winter: November through March), flow range, and station for the 1990 through 2018 period of record. Flow Total Phosphorus (mg/L) Exceedance Spring Summer-Fall Winter All (%) Mean Median N Mean Median N Mean Median N Mean Median N North Elm Creek (SC731) 0-25 0.342 0.320 8 0.435 0.469 4 0.257 0.184 5 0.339 0.284 17 26-50 0.164 0.162 4 0.372 0.390 3 0.121 0.063 7 0.187 0.154 14 51-75 0.286 0.219 3 0.204 0.202 3 0.125 0.047 5 0.190 0.133 11 76-100 0.158 0.158 2 0.225 0.227 8 0.145 0.139 7 0.185 0.200 17 0-100 0.269 0.219 17 0.293 0.239 18 0.157 0.107 24 0.231 0.200 59 Big Blue River near Oketo (SC233) 0-25 1.31 1.21 18 1.14 1.09 16 1.13 0.766 7 1.21 1.09 41 26-50 0.939 0.842 11 0.900 0.878 10 0.633 0.619 16 0.796 0.746 37 51-75 0.587 0.530 7 0.786 0.739 8 0.684 0.685 20 0.688 0.693 35 76-100 0.760 0.717 3 0.850 0.855 18 0.939 0.948 12 0.874 0.860 33 0-100 1.03 0.882 39 0.940 0.865 52 0.781 0.700 55 0.905 0.781 146 Horseshoe Creek (SC717) 0-25 0.698 0.698 2 0.196 0.196 1 0.599 0.46 4 0.570 0.572 7 26-50 0.233 0.180 3 0.512 0.395 3 0.287 0.287 1 0.361 0.329 7 51-75 0.271 0.271 2 0.183 0.183 1 0.092 0.0915 4 0.156 0.116 7 76-100 - - - 0.108 0.108 2 0.428 0.428 2 0.268 0.126 4 0-100 0.377 0.348 7 0.305 0.196 7 0.355 0.135 11 0.347 0.196 25 Big Blue River near Blue Rapids (SC240) 0-25 1.35 1.23 18 1.17 1.122 16 0.878 0.728 8 1.19 1.06 42 26-50 0.719 0.549 12 0.818 0.792 10 0.478 0.430 18 0.635 0.524 40 51-75 0.380 0.320 7 0.631 0.527 8 0.489 0.460 22 0.499 0.460 37 76-100 0.517 0.587 3 0.558 0.515 18 0.590 0.597 12 0.566 0.549 33 0-100 0.930 0.669 40 0.807 0.659 52 0.558 0.501 60 0.741 0.588 152 Definition: – - no data

Figure 14. Box plot of total phosphorus over the respective periods of record for stream chemistry stations in the Big Blue River near Oketo and its tributary North Elm Creek (SC731) and in the Big Blue River near Blue Rapids (SC240) and its tributary Horseshoe Creek (SC717).

Total Phosphorus Concentrations by KDHE Stream Chemistry Station

1.8 North Elm Cr (SC731) 1.6 Big Blue R nr Oketo (SC233) Horseshoe Cr (SC717) 1.4 Big Blue R nr Blue Rapids (SC240) ) L / g 1.2 m (

s u

r 1.0 o h p s 0.8 0.772 o h P

l 0.6 0.593 a t o

T 0.4

0.2 0.200 0.203

0.0 SC731 SC233 SC717 SC240

In addition to routinely sampled, permanent and rotational KDHE SC stations, there are seven stream probabilist ic (SP) stations located on tributaries within the TMDL Watershed (Table 7). Stream probabilistic stations are selected randomly as part of the SP Program and are sampled three to six times in a single year. The data generated by the SP Program is used by KDHE to develop the biennial 305b report and as supporting data during analysis of stream water quality, such as TMDL development. Due to the sporadic nature of the data, only the TP data is presented here for analysis. It should be noted that the same site is sometimes sampled more than one year, as is the case with North Elm Creek and Dutch Creek.

Table 7. Total phosphorus (TP) concentration mean, median and number of samples (N) for stream probabilistic (SP) stations located within the TMDL Watershed. SP/Associated Median TP Mean TP Stream Sample Year N SC Watershed (mg/L) (mg/L) 2006 0.220 0.318 4 North Elm Cr SP826/SC731 2008 0.349 0.353 7 2011 0.340 0.310 4 Horseshoe Cr SPA066/SC717 2006 0.540 0.654 3 Indian Cr SPB514/SC717 2016 0.275 0.275 4 Spring Cr SPB172/SC240 2012 0.435 0.477 4 Schell Cr SPB642/SC240 2017 0.125 0.126 4 2008 0.145 0.173 4 Dutch Cr SPA285/SC240 2017 0.037 0.044 4 Fawn Cr SPB173/SC240 2012 0.087 0.149 4

Figure 15 displays annual median and mean TP concentrations in the Big Blue River near Oketo (SC233) and in North Elm Creek (SC731), a tributary to the main stem Big Blue River. In both cases, a trend line calculated from annual medians indicate increasing concentrations across the period of record. Similarly, Figure 16 displays an upward trend in annual median concentrations in the Big Blue River near Blue Rapids (SC240) and its tributary Horseshoe Creek (717) over the period of record. Annual high median and mean values occurred in 2016 at both Big Blue River stations while North Elm Creek and Horseshoe Creek recorded their high annual median and mean values in 2008 and 2005, respectively (Table 8). When the TP period of record is split and assessed over the 1990 through 1999 and 2000 through 2018 periods of record, all main stem median and mean values are higher for the later period of record. Tributary stations have smaller data sets and less defined patterns, with no 1990 through 1999 period of record for North Elm Creek and a higher mean and lower median for Horseshoe Creek.

Figure 15. Annual mean and median total phosphorus concentrations in the Big Blue River near Oketo (SC233) and its tributary North Elm Creek (SC731) with median trend lines. Annual Average and Median TP in the Big Blue River near Oketo and in its Trib North Elm Creek with Median Trendlines

1.6

1.5

1.4

1.3

1.2

1.1

0.9

0.8

0.7

Total Phosphours (mg/L) 0.6

0.5

0.4

0.3

0.2

0.1

0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2015 2016 2017 2018 2014

SC731 North Elm Cr Mean SC731 North Elm Cr Median SC233 Big Blue R nr Oketo Mean

SC233 Big Blue R nr Oketo Median Linear (SC731 North Elm Cr Median) Linear (SC233 Big Blue R nr Oketo Median)

Figure 16. Annual mean and median total phosphorus concentrations in the Big Blue River near Blue Rapids (SC240) and its tributary Horseshoe Creek (SC717) with median trend lines. Annual Average and Median TP in the Big Blue River near Blue Rapids and in its Trib Horseshoe Creek with Median Trendlines

1.6

1.5

1.4

1.3

1.2

1.1

0.9

0.8

0.7

Total Phosphours (mg/L) 0.6

0.5

0.4

0.3

0.2

0.1

0 1990 1991 1992 1993 1994 1995 1996 1997 2000 2001 2002 2003 2004 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2018 1998 1999 2005 2016 2017

SC717 Horseshoe Cr Mean SC717 Horseshoe Cr Median SC240 Big Blue R nr Blue Rapids Mean

SC240 Big Blue R nr Blue Rapids Median Linear (SC717 Horseshoe Cr Median) Linear (SC240 Big Blue R nr Blue Rapids Median)

Table 8. Annual total phosphorus mean and median concentrations in the Big Blue River Watershed, March 13, 1990 to December 4, 2018. Values with no data are denoted with a – symbol. Total Phosphorus (mg/L) SC240 Year SC731 SC233 SC717 Big Blue R nr Blue North Elm Cr Big Blue R nr Oketo Horseshoe Cr Rapids Mean Median N Mean Median N Mean Median N Mean Median N 1990 - - - 0.640 0.640 5 - - - 0.444 0.430 5 1991 - - - 1.04 0.795 6 - - - 0.822 0.525 6 1992 - - - 0.845 0.700 6 - - - 0.785 0.490 6 1993 - - - 0.612 0.650 5 - - - 0.704 0.490 5 1994 - - - 0.704 0.690 5 - - - 0.612 0.190 10 1995 - - - 0.693 0.687 6 - - - 0.571 0.547 8 1996 - - - 0.944 0.686 5 - - - 0.986 0.483 5 1997 - - - 0.782 0.799 6 - - - 0.691 0.603 6 1998 - - - 0.717 0.650 7 0.324 0.270 6 0.616 0.535 6 1999 - - - 0.961 0.859 6 - - - 0.929 0.703 6 2000 - - - 0.774 0.750 6 - - - 0.759 0.575 6 2001 0.148 0.128 5 0.920 0.760 6 - - - 0.895 0.573 7 2002 0.147 0.152 6 0.885 0.885 6 - - - 0.613 0.480 6 2003 0.220 0.209 4 1.06 0.866 5 - - - 0.756 0.616 5 2004 0.175 0.184 4 0.947 0.842 5 - - - 0.715 0.697 5 2005 0.294 0.220 6 1.14 1.10 6 0.597 0.581 6 0.951 0.913 6 2006 0.298 0.220 5 0.946 0.970 5 - - - 0.723 0.593 5 2007 0.290 0.250 6 1.12 1.19 5 - - - 0.835 0.904 5 2008 0.353 0.349 6 0.857 0.754 6 - - - 0.769 0.615 6 2009 0.166 0.147 5 1.09 0.701 4 0.268 0.183 5 0.589 0.492 5 2010 - - - 0.772 0.804 4 - - - 0.822 0.599 4 2011 0.310 0.340 4 0.794 0.783 4 - - - 0.737 0.686 4 2012 - - - 0.850 0.836 4 - - - 0.714 0.572 4 2013 0.189 0.167 4 0.920 0.872 4 0.345 0.294 4 0.748 0.653 4 2014 - - - 1.21 1.20 4 - - - 1.05 0.950 4 2015 - - - 0.930 0.895 4 - - - 0.710 0.570 4 2016 - - - 1.60 1.50 4 - - - 1.16 1.07 4 2017 0.120 0.111 4 0.863 0.825 4 0.108 0.099 4 0.588 0.515 4 2018 - - - 0.843 0.970 4 - - - 0.720 0.815 4 1990-1999 - - 0 0.795 0.689 56 0.324 0.270 6 0.708 0.508 61 2000-2018 0.226 0.196 59 0.975 0.866 90 0.329 0.239 19 0.774 0.615 91

Daily samples of TP concentrations show that nearly 30% of the daily samples in the Big Blue River near Oketo (SC233) are greater than 1 mg/L while 20% of the samples in the Big Blue River near Blue Rapids (SC240) are greater than 1 mg/L (Figures 17-18). Over the period of record, only one tributary sample, taken on February 14, 2005 in Horseshoe Creek (SC717) and measuring 1.35 mg/L, measured greater than 1 mg/L. No samples rose above that mark in North Elm Creek (SC731). Single sample highs in the Big Blue River occurred on June 8, 2009 at SC233 (2.65 mg/L) and May 13, 1996 at SC240 (2.81 mg/L).

Figure 17. Daily sample concentrations at KDHE stream chemistry stations in the Big Blue River near Oketo (SC233) and in its tributary North Elm Creek (SC731). Single Sample TP Concentrations in the Big Blue R near Oketo and in North Elm Cr 3

2.5

1.5 Total Phosphorus (mg/L) 1

0.5

0 8/2/2010 6/6/2011 1/8/2018 4/28/1997 3/23/1998 9/21/1998 3/17/2008 9/15/2008 4/20/2009 1/10/2012 3/13/1990 9/10/1990 4/22/1991 3/16/1992 9/21/1992 6/14/1993 7/18/1994 2/13/1995 8/21/1995 3/18/1996 9/16/1996 4/19/1999 3/20/2000 9/18/2000 4/16/2001 3/18/2002 9/16/2002 4/14/2003 7/19/2004 2/14/2005 8/15/2005 1/23/2006 9/18/2006 4/16/2007 10/9/2012 8/13/2013 6/10/2014 1/12/2015 8/15/2016 6/12/2017 10/28/1991 12/13/1993 10/27/1997 10/18/1999 10/15/2001 10/20/2003 10/15/2007 12/14/2009 10/19/2015 10/15/2018 Sample Collection Date Big Blue nr Oketo (SC233) North Elm Cr (SC731)

Figure 18. Daily sample concentrations at KDHE stream chemistry stations in the Big Blue River near Blue Rapids (SC240) and in its tributary Horseshoe Creek (SC717). Single Sample TP Concentrations in the Big Blue R near Blue Rapids and in Horseshoe Creek 3

2.5

1.5 Total Phosphorus (mg/L) 1

0.5

0 8/2/2010 6/6/2011 1/8/2018 3/13/1990 9/10/1990 4/22/1991 6/14/1993 7/18/1994 3/18/1996 9/16/1996 4/28/1997 9/21/1998 4/19/1999 3/20/2000 9/18/2000 4/16/2007 8/13/2013 6/10/2014 1/12/2015 3/16/1992 9/21/1992 2/13/1995 8/21/1995 3/23/1998 4/16/2001 3/18/2002 9/16/2002 4/14/2003 7/19/2004 2/14/2005 8/15/2005 1/23/2006 9/18/2006 3/17/2008 9/15/2008 4/20/2009 1/10/2012 10/9/2012 8/15/2016 6/12/2017 10/28/1991 12/13/1993 10/27/1997 10/18/1999 10/15/2001 10/20/2003 10/15/2007 12/14/2009 10/19/2015 10/15/2018 Sample Collection Date Big Blue R nr Blue Rapids (SC240) Horseshoe Creek (SC717)

Assessment of samples taken on the same day at the upstream (SC233) and downstream (SC240) SC stations in the Big Blue River show that most of the time concentrations at the state-line are significantly higher than those seen at the downstream station (Figure 19). These lower concentrations seen at Blue Rapids indicate dilution and assimilation of TP concentrations at the border are routinely occurring along the reaches of the Big Blue River in Kansas, resulting in lower TP concentrations entering Tuttle Creek Reservoir than those entering the state.

Figure 19. Total phosphorus concentrations in samples taken on the same day at upstream and downstream KDHE sampling sites in the Big Blue River.

Same Day Upstream and Downstream TP Concentrations Big Blue River near Oketo (Upstream) and Blue Rapids (Downstream)

3.0 2.8

L 2.6 / g 2.4 1:1 Line m 2.2 P T 2.0 ) 0

4 1.8 2

C 1.6 S (

1.4

m 1.2 a e

r 1.0 t s

n 0.8

w 0.6 o

D 0.4 0.2 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 Upstream (SC233) TP mg/L

Figures 20-23 display single sample TP concentrations by flow condition and season. Higher TP concentrations during higher flow is indicative of nonpoint source loading to the watershed and can be seen particularly well in the datasets for the Big Blue River at SC233 and SC240 (Figures 21 and 23). Tributaries North Elm Creek (SC731) and Horseshoe Creek (SC717) have smaller datasets and are not located on the stream segment where the USGS gage used to derive flows is located. The result is a noisier pattern with datapoints that plot up outside of the expected nonpoint source loading pattern; however, the trend generally holds true with higher TP concentrations occurring during higher flow conditions (Figures 20 and 22).

Figure 20. Total phosphorus by percent flow exceedance and season for the North Elm Creek near Oketo (SC731).

Total Phosphorus by Percent Flow Exceedance and Season for North Elm Creek (SC731) 0.9 Season 0.8 Spring Summer-Fall

) Winter

L 0.7 / g m

( 0.6

s u r 0.5 o h p

s 0.4 o h P

l 0.3 a t o

T 0.2

0.1

0.0 0 10 20 30 40 50 60 70 80 90 100 Flow Exceedance (%)

Figure 21. Total phosphorus by percent flow exceedance and season for the Big Blue River near Oketo (SC233).

Total Phosphorus by Percent Flow Exceedance and Season for the Big Blue River near Oketo (SC233) 3.0 Season Spring 2.5 Summer-Fall

) Winter L / g m

( 2.0

s u r o

h 1.5 p s o h P

l 1.0 a t o T 0.5

0.0 0 10 20 30 40 50 60 70 80 90 100 Flow Exceedance (%)

Figure 22. Total phosphorus by percent flow exceedance and season for the Horseshoe Creek near Marysville (SC717).

Total Phosphorus by Percent Flow Exceedance and Season for Horseshoe Creek near Marysville (SC717) 1.4 Season Spring 1.2 Summer-Fall

) Winter L /

g 1.0 m (

s u

r 0.8 o h p s

o 0.6 h P

l a

t 0.4 o T

0.2

0.0 0 10 20 30 40 50 60 70 80 90 100 Flow Exceedance (%)

Figure 23. Total phosphorus by percent flow exceedance and season for the Big Blue River near Blue Rapids (SC240).

Total Phosphorus by Percent Flow Exceedance and Season for the Big Blue River near Blue Rapids (SC240) 3.0 Season Spring 2.5 Summer-Fall

) Winter L / g m

( 2.0

s u r o

h 1.5 p s o h P

l 1.0 a t o T 0.5

0.0 0 10 20 30 40 50 60 70 80 90 100 Flow Exceedance (%)

To further assess TP loading in the Big Blue River Watershed, a mass balance for TP was estimated under low (75%), median (50%), and high (25%) flow conditions (Table 9). The mass

balance begins with an accounting of the incoming loads from the Little Blue River Watershed, as measured at SC741, then calculates loads originating in the North Elm Creek (SC731), Horseshoe Creek (SC717), and upper Big Blue River (SC233) watersheds. Next it estimates the load coming from the unaccounted-for watershed between SC233 and SC240. Finally, it balances the individual watershed loads against the total load measured at the Big Blue River near Blue Rapids (SC240), located just above Tuttle Creek Reservoir.

Across all flow conditions, the bulk of the TP load entering Tuttle Creek Reservoir is originating in the watershed measured by SC233, the Big Blue River near Oketo. The SC233 watershed size is estimated at 4,670 mi2; however, only 31.1 mi2 is located within Kansas borders, meaning 85%, 72%, and 56% of the TP load entering Tuttle Creek Reservoir originates in Nebraska under low, median, and high flow conditions, respectively. Contributions from Nebraska show a relative decrease with increasing flow. This pattern reverses in the Little Blue watershed, where the bulk of the remaining load originates, and loads increase with increasing flow. Loads from the tributaries North Elm Creek and Horseshoe Creek start small and increase only slightly with increasing flow. Estimated loads for the unmonitored area of the TMDL Watershed lying between SC233 and SC240 show assimilation of TP is occurring under low flow conditions. With increased flow conditions, up to 12% of the total load originates here.

Table 9. Estimated mass balance for total phosphorus loads under various flow conditions. Percent of Drainage Total Load Flow Flow TP TP Watershed Area Measured Exceedance (cfs) (mg/L) (lbs/day) (mi2) at SC240 (%) Little Blue River near Waterville (SC741) 3,460 157 0.289 245 19% North Elm Creek (SC731) 25.1 0.585 0.185 0.6 0.1% Big Blue River near Oketo (SC233) 4,670 234 0.874 1,104 85% 75% Horseshoe Creek (SC717) 128 1.92 0.268 2.8 0.2% Contributing area between SC233 & SC240 3,627 n/a n/a -54 -4% Total load measured in the Big Blue River at SC240 8,450 425 0.566 1,299 100% Little Blue River near Waterville (SC741) 3,460 246 0.386 512.8 26% North Elm Creek (SC731) 25.1 1.81 0.189 1.8 0.1% Big Blue River near Oketo (SC233) 4,670 359 0.743 1,440 72% 50% Horseshoe Creek (SC717) 128 5.93 0.258 8.3 0.4% Contributing area between SC233 & SC240 3,627 n/a n/a 43.6 2% Total load measured in the Big Blue River at SC240 8,450 652 0.57 2,007 100% Little Blue River near Waterville (SC741) 3,460 460 1.03 2,559 31% North Elm Creek (SC731) 25.1 5.37 0.339 10 0.1% Big Blue River near Oketo (SC233) 4,670 713 1.22 4,697 56% 25% Horseshoe Creek (SC717) 128 17.6 0.57 54 0.7% Contributing area between SC233 & SC240 3,627 n/a n/a 1,008 12% Total load measured in the Big Blue River at SC240 8,450 1,296 1.19 8,328 100%

Total Phosphorus and Water Quality Parameters: Total phosphorus has well-established and defined relationships with orthophosphate (OP) and total suspended solids (TSS). These relationships are examined further to delineate potential sources of TP loading.

Orthophosphate The soluble portion of TP that is readily available for biological use is OP. It can be indicative of of runoff from livestock operations, instream livestock watering, and failing septic systems in watersheds primarily influenced by nonpoint sources of pollution. Because of the relatively high reporting limit of orthophosphate beginning in 2002, it should be noted that only samples measuring above the reporting limit are included in the analysis presented which likely overestimates true OP concentration means. Reporting limits for OP have changed throughout the period of record: 0.01 mg/L from 1995-1996, 0.02 mg/L from 1997 to February 2002, and 0.25 mg/L from March 2002 to current (Figure 24). The OP concentrations greater than the reporting limit by station are: the Big Blue River near Oketo (SC233) has a total of 96 averaging 0.49 mg/L; the Big Blue River near Blue Rapids (SC240) has a total of 81 averaging 0.36 mg/L; North Elm Creek has a total of eight averaging 0.25 mg/L; Horseshoe Creek (SC717) has a total of five averaging 0.36 mg/L (Table 10). Of the winter samples from the Big Blue River near Oketo (SC233), 100% measured above the reporting limit. Of all the samples in the watershed, 64% measure over the reporting limit with an average of 0.40 mg/L.

Figure 24. Orthophosphate samples measuring greater than the reporting limit for the Big Blue River near Blue Rapids (SC240), Big Blue River near Oketo (SC233), Horseshoe Creek near Marysville (SC717), and North Elm Creek near Oketo (SC731).

Orthophosphate by Station 1.2 SC233 SC240 SC717 1.0

) SC731 L

/ Reporting Limit g

m 0.8 (

e t a

h 0.6 p s o h p

o 0.4 h t r O 0.2

0.0 1 1 7 7 7 7 7 3 5 0 4 8 5 2 2 9 8 0 3 4 5 5 8 6 5 6 8 9 2 3 3 6 8 9 0 1 1 1 1 1 0 1 1 1 1 1 0 9 0 0 0 0 9 0 0 0 9 0 0 0 0 0 0 9 9 9 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9 0 0 0 0 9 0 0 0 9 0 0 0 0 0 0 9 9 9 9 0 0 0 2 2 1 2 2 2 1 1 2 2 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / 1 1 1 6 7 3 3 4 0 5 3 0 4 5 9 0 3 5 5 7 6 7 7 0 9 3 2 2 0 8 4 9 4 5 5 / / 1 1 / 1 1 2 1 2 1 1 1 / 1 2 1 1 1 1 1 1 2 1 2 1 1 1 1 1 2 / / 2 / / 2 2 2 / / / / 2 6 / / 1 / / / / / / 2 / / / / / / / / / / / 1 / / / / 1 1 7 3 1 8 9 4 1 1 7 2 2 0 6 7 4 0 3 8 3 8 1 4 2 8 2 9 2 7 1 0 4 1 1 1 1 1

Table 10. Average of orthophosphate concentrations measuring above the reporting limit at both steam chemistry stations in the Big Blue River and the North Elm and Horseshoe tributary creeks. 1995-2018 By Season Sampling Site Sample Info Summer/ All Spring Fall Winter Seasons Average OP > RL (mg/L) 0.17 0.20 0.34 0.25 North Elm Creek OP > RL/Total # of Samples 2/18 3/17 3/25 8/60 SC731 % samples with OP > RL 11% 18% 12% 13% Average OP > RL (mg/L) 0.39 0.53 0.51 0.49 Big Blue River OP > RL/Total # of Samples 24/30 31/36 41/41 96/107 SC233 % samples with OP > RL 80% 86% 100% 90% Average OP > RL (mg/L) 0.31 - 0.40 0.36 Horseshoe Creek OP > RL/Total # of Samples 2/6 0/5 3/8 5/19 SC717 % samples with OP > RL 33% 0% 38% 26% Average OP > RL (mg/L) 0.31 0.39 0.36 0.36 Big Blue River OP > RL/Total # of Samples 17/30 24/35 40/44 81/109 SC240 % samples with OP > RL 57% 66% 91% 74% Average OP > RL (mg/L) 0.35 0.45 0.43 0.40 All Sites OP > RL/Total # of Samples 45/84 58/93 87/118 190/295 % samples with OP > RL 54% 62% 74% 64%

Total Suspended Solids Phosphorus is typically linked to sediment or TSS because of the propensity of those solids to adsorb phosphorus. Figures 25-28 display the relationship between TP and TSS in the Big Blue River near Oketo (SC233) and Blue Rapids (SC240) and in the tributary stations North Elm Creek (SC731) and Horseshoe Creek (SC717). Generally, the figures display that once TSS concentrations increase to 100 mg/L, the relationship improves as the source of TP becomes tied to sediment loading. Below 100 mg/L the relationship weakens with TP concentrations outpacing TSS concentrations and could be an indication of TP sources from sources other than those tied to sediment, such as livestock in riparian areas.

Figure 25. Total phosphorus versus total suspended solids for North Elm Creek near Oketo (SC731).

Total Phosphorus versus Total Suspended Solids North Elm Creek (SC731)

200 500 SC731 TSS < 100 mg/L SC731 TSS > 100 mg/L 1 R-Sq=0.41 0.9 R-Sq=0.64 )

L 0.8 /

g 0.7 m (

s 0.6 u r o

h 0.5 p s o

h 0.4 P

a 0.1 t o

T 0.3

1 10 100 Total Suspended Solids (mg/L)

Figure 26. Total phosphorus versus total suspended solids for the Big Blue River near Oketo (SC233).

Total Phosphorus versus Total Suspended Solids Big Blue River near Oketo (SC233)

100 1000 SC233 TSS < 100 mg/L SC233 TSS > 100 mg/L 3 R-Sq=0 R-Sq=0.42 )

L 2 /

g 1

m 1.5 ( 0.9

u 0.8 r

o 0.7 1 h 0.9 p s 0.6 0.8 o 0.7 h P

0.6

l 0.5 a

t 0.5 o

T 0.4 0.4

0.3 0.3 10 100 Total Suspended Solids (mg/L)

Figure 27. Total phosphorus versus total suspended solids for Horseshoe Creek near Marysville (SC717).

Total Phosphorus versus Total Suspended Solids Horseshoe Creek (SC717)

100 200 500 SC717 TSS < 100 mg/L SC717 TSS > 100 mg/L 0.8 1.5 0.7 R-Sq=0.49 R-Sq=0.78

) 0.6 L

/ 1

g .5 0 0.9 m

( 0.8 0.4 s

u 0.7 r

o 0.6

h 0.3 p

s 0.5 o h

P 0.4

0.2 l a t

o 0.15 0.3 T

0.1 0.2 0.09 10 20 50 Total Suspended Solids (mg/L)

Figure 28. Total phosphorus versus total suspended solids concentrations greater and less than 100 mg/L for the Big Blue River near Blue Rapids (SC240).

Total Phosphorus versus Total Suspended Solids Big Blue River near Blue Rapids (SC240)

100 1000 SC240 TSS < 100 mg/L SC240 TSS > 100 mg/L 0.9 R-Sq=0 R-Sq=0.57

) 0.8 L / 0.7 g m (

0.6 s

u 1 r

o 0.5 h p s

o 0.4 h P

l a t

o 0.3 T

0.2 0.1 10 20 50 100 Total Suspended Solids (mg/L)

Total Phosphorus and Biological Indicators: The narrative criteria of the Kansas Surface Water Quality Standards are based on conditions of the prevailing biological community. Excessive primary productivity may be indicated by extreme shifts in dissolved oxygen (DO), dissolved oxygen saturation (DO saturation), and pH as the chemical reactions of photosynthesis and respiration alter the ambient levels of oxygen and acid-base balance of the stream. These extreme shifts, in turn, can result in undesirable regime shifts in the algal biomass and biological community within the stream.

Dissolved Oxygen Of all samples measured for DO in the TMDL Watershed, only four measured below the water quality criterion of 5.0 mg/L (Figures 29-32). Two excursions occurred in the North Elm Creek (SC731) in October 2003 (4.8 mg/L) and June 2011 (4.2 mg/L), and two occurred in the Big Blue River near Blue Rapids (SC240) in July 1992 (3.8 mg/L) and July 2000 (4.4 mg/L). The frequency of the DO excursions has not warranted a 303(d) listing at either station. As expected, dissolved oxygen and temperature are inversely related and correspond to seasonal changes as oxygen becomes less soluble in water as temperatures increase (Table 12).

Figure 29. Dissolved oxygen by date and dissolved oxygen versus temperature for North Elm Creek near Oketo (SC731).

Dissolved Oxygen by Date for Dissolved Oxygen versus Temperature for North Elm Creek (SC731) North Elm Creek (SC731) 15.0 15.0

12.5 12.5 ) ) L L / / g g m m ( (

n n e 10.0 e 10.0 g g y y x x O O

d d e e v v l l o o s s s s i 7.5 i 7.5 D D

Water Quality Criterion Water Quality Criterion 5.0 5.0

01 01 2 3 4 5 6 7 8 8 9 11 17 17 0 10 20 30 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 2 0 0 0 0 0 0 0 0 0 2 2 2 / / /2 /2 2 /2 /2 /2 /2 /2 /2 / / / 6 7 6 8 / 5 7 6 8 7 2 2 3 4 /1 /1 1 1 20 1 1 1 2 1 1 /1 /1 / 2 / / / / / / / 1/ / 2 3 2 Temperature (°C) 4 1 9 8 9 8 7 4 1 1 10 1 1

Figure 30. Dissolved oxygen by date and dissolved oxygen versus temperature for the Big Blue River near Oketo (SC233).

Dissolved Oxygen by Date for Dissolved Oxygen versus Temperature for the Big Blue River (SC233) the Big Blue River (SC233) 17.5 17.5

15.0 15.0 ) ) L L / / g g m m (

12.5 ( 12.5

n n e e g g y y x x O O

d d

e 10.0 e 10.0 v v l l o o s s s s i i D D

7.5 7.5

Water Quality Criterion Water Quality Criterion 5.0 5.0

1 1 0 9 3 5 7 8 0 2 3 5 7 9 1 13 16 18 9 9 9 9 9 9 0 0 0 0 0 0 0 0 0 0 0 10 20 30 19 1 19 19 19 19 20 20 20 20 20 20 2 2 2 2 / / / / / / / / / / / / / / / / 3 8 6 9 8 0 5 2 0 7 0 0 /6 5 6 5 /1 /2 /1 /1 2 3 1 2 2 1 2 2 6 1/ /1 /1 3 0 8 6 4/ 1/ 5/ 1/ / 0/ / / 1 5 0 1 1 10 1 8 4 1 Temperature (°C)

Figure 31. Dissolved oxygen by date and dissolved oxygen versus temperature for Horseshoe Creek near Marysville (SC717).

Dissolved Oxygen by Date for Dissolved Oxygen versus Temperature for Horseshoe Creek (SC717) Horseshoe Creek (SC717) 17.5 17.5

15.0 15.0 ) ) L L / / g g m m ( 12.5 ( 12.5

n n e e g g y y x x O O

d d e

10.0 e v 10.0 v l l o o s s s s i i D D

7.5 7.5

Water Quality Criterion 5.0 Water Quality Criterion 5.0

8 8 8 5 5 5 5 9 9 9 13 13 17 17 9 9 9 0 0 0 0 0 0 0 0 0 0 0 19 19 19 0 0 0 0 0 0 0 2 2 2 2 0 6 12 18 24 / / / /2 /2 /2 /2 /2 /2 /2 / / / / 3 8 1 4 3 5 9 6 8 2 2 3 3 11 2 /1 /2 1 1 1 1 1 / 1 /1 /1 /1 / / 5 9 / / / / / 6 / 2 8 3 9 3 2 6 8 12 2 10 Temperature (°C)

Figure 32. Dissolved oxygen by date and dissolved oxygen versus temperature for the Big Blue River near Blue Rapids (SC240).

Dissolved Oxygen by Date for Dissolved Oxygen versus Temperature for the Big Blue River (SC240) the Big Blue River (SC240) 17.5 17.5

15.0 15.0 ) ) L L / / g g 12.5 12.5 m m ( (

n n e e g g y y x x O O 10.0 10.0

d d e e v v l l o o s s s s i i D D 7.5 7.5

Water Quality Criterion .0 5.0 5 Water Quality Criterion

0 1 3 4 5 7 9 1 2 4 6 8 9 2 4 7 8 0 10 20 30 9 99 9 9 9 9 9 00 0 0 0 0 0 01 01 01 01 19 1 19 19 19 19 19 2 0 0 0 0 0 2 2 2 2 / / / / / / / / /2 /2 /2 /2 /2 / / / / 3 8 6 9 1 7 4 2 2 9 5 8 2 0 6 3 5 /1 / 2 /1 /1 /1 2 /1 /1 2 1 1 2 1 /1 /1 /1 /1 Temperature (°C) 3 0 8 9 2 / 6 2 / / / / / 1 9 3 0 1 1 10 7 7 5 1 10 1

Table 12. Mean temperature, dissolved oxygen, and dissolved oxygen saturation, as well as median pH, by season for the Big Blue River Watershed. Station Spring Summer-Fall Winter All Seasons Temperature (°C) North Elm Creek (SC731) 20.1 20.8 5.0 14.1 Big Blue River (SC233) 18.4 20.8 5.0 14.2 Horseshoe Creek (SC717) 21.7 19.9 4.9 13.8 Big Blue River (SC240) 18.1 20.3 4.4 13.6 Dissolved Oxygen (mg/L) North Elm Creek (SC731) 8.1 7.5 12.1 9.5 Big Blue River (SC233) 9.5 9 13.1 10.7 Horseshoe Creek (SC717) 9.6 8.6 13.1 10.9 Big Blue River (SC240) 9.1 8.4 12.6 10.3 Dissolved Oxygen Saturation (%) North Elm Creek (SC731) 87.9 83.1 93.9 88.9 Big Blue River (SC233) 99.9 98.6 102 100 Horseshoe Creek (SC717) 109 92.7 102 101 Big Blue River (SC240) 95.1 91.9 96.5 94.2 pH North Elm Creek (SC731) 7.8 7.7 7.8 7.8 Big Blue River (SC233) 8.1 8.2 8.2 8.2 Horseshoe Creek (SC717) 7.8 7.7 7.8 7.7 Big Blue River (SC240) 8.0 8.1 8.1 8.1

Dissolved Oxygen Saturation

Primary productivity increases in the spring and summer-fall, when temperatures are higher and DO concentrations are lower. When primary productivity is excessive, oxygen from aquatic photosynthesis can create DO concentrations that exceed the natural oxygen equilibrium of the stream at a given temperature. Supersaturated conditions occur when the ratio of the oxygen capacity of the stream at a given temperature to the oxygen concentration in the stream exceeds 110%. The Big Blue River near Oketo (SC233), which is uncoincidentally the station most highly enriched by TP, strongly displays this pattern with an uptick in DO saturation frequency beginning in the 2000s (Figure 33). Over the period of record, each station has DO saturation values greater than 110%: North Elm Creek (SC731) has one, the Big Blue River near Oketo (SC233) has 35, Horseshoe Creek (SC717) has seven, and the Big Blue River near Blue Rapids (SC240) has 14.

Figure 33. Dissolved oxygen saturation by date for stations in the TMDL Watershed.

% DO Saturation by Date % DO Saturation by Date North Elm Creek (SC731) Horseshoe Creek (SC717)

200 200 n n o o i

i 150

150 t t a a r r u u t t a a S S 110 Supersaturation 110 Supersaturation O

O 100

100 D D

% %

50 50 8 8 8 5 5 5 9 9 9 3 3 7 7 9 9 9 0 0 0 0 0 0 1 1 1 1 1 1 1 2 2 2 3 3 4 4 5 5 5 6 6 7 7 7 8 8 8 9 9 9 1 1 3 3 7 7 9 9 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 / 1 /1 /1 2 2 2 2 2 2 / 2 /2 /2 / 2 20 2 0 20 20 20 2 0 2 0 20 20 2 0 2 0 20 20 2 0 2 0 20 20 20 2 0 20 20 20 2 0 2 0 20 20 2 0 2 0 20 20 6 8 1 / / / / / / 4 5 2 4 / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / 2 1 2 1 4 13 17 16 / 8 1 4 1 / 1 / 1 6 20 17 18 2 2 1 8 14 20 1 7 1 5 18 15 1 9 1 5 18 19 18 1 5 28 19 15 1 6 / 8 14 /6 1 2 1 4 /5 12 / 4 / / / / / / / 6 / / 11 / 2 4 / 8 / 2/ 3/ 7/ 1 / 4/ 0/ 5/ 1 / 4 / 8/ 2/ 5 / 9 / 2/ 6/ 0 / 1 / 5/ 9/ 2 / 6 2/ 6 2/ 5 / 11 6/ 12 1 5 9 2 6 0 2 2 5 6 1 1 1 1 1 1 1 1 1 1 1

Collection Date Collection Date

% DO Saturation by Date % DO Saturation by Date Big Blue River near Oketo (SC233) Big Blue River near Blue Rapids (SC240)

200 200 n n o o

i 150 i 150 t t a a r r u u t t

a a Supersaturation S S Supersaturation 110 110 O 100 O 100 D D

% %

50 50

9 0 90 9 1 9 2 93 94 9 5 9 6 97 98 9 8 9 9 00 01 02 0 3 04 05 05 0 6 07 08 09 1 1 1 2 13 14 1 6 1 7 18 9 0 9 0 91 9 2 93 9 4 94 95 96 97 9 8 98 9 9 00 0 1 02 0 3 04 05 05 06 0 7 08 0 9 10 1 2 13 1 4 15 17 18 19 19 19 1 9 19 19 19 1 9 1 9 19 19 1 9 2 0 20 20 2 0 2 0 20 20 2 0 2 0 20 20 20 2 0 20 20 20 2 0 2 0 19 1 9 19 1 9 19 1 9 19 1 9 19 1 9 19 19 19 20 2 0 20 2 0 20 2 0 20 2 0 20 20 20 20 2 0 20 2 0 20 2 0 20 / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / 1 3 29 2 8 13 16 18 1 9 13 28 26 3 0 1 8 17 18 1 8 1 7 15 14 1 9 1 3 17 15 12 / 7 24 13 /9 2 3 1 2 23 1 3 2 9 28 1 3 16 16 13 19 1 3 28 2 6 30 1 8 17 1 8 18 17 15 14 1 9 13 1 7 15 1 2 /1 1 0 14 1 6 19 13 / 9 3 / 0/ 0 / 7 / 8/ 7/ 6 / 5 / 4/ 1/ 1/ 0 / 7/ 6/ 3/ 2 / 3 / 2/ 2/ 1 / 2 / 9/ 0/ 3 4 / 8/ 12 2/ 6 / 7/ 3 / 0 / 0/ 7 / 8/ 5 / 2/ 6 / 5/ 4/ 1/ 1/ 0 / 7/ 6 / 3/ 2 / 3/ 2 / 2/ 1/ 2/ 9/ 0 / 11 1 / 5/ 9 / 0/ 3 / 4 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Collection Date Collection Date

pH Another water quality indicator of primary productivity is pH, as photosynthesis can increase pH via consumption of carbon dioxide in the water. The numeric water quality criteria for pH is a range from 6.5 to 8.5 with binomial analysis of excursions applied to determine 303(d) listing status. Both sites in the Big Blue River are listed as impaired for pH, with 25 excursions greater than 8.5 at SC233 near Oketo and 22 excursions greater than 8.5 at SC240 near Blue Rapids (Table 13; Figures 34-35).

Table 13. pH by percent flow exceedance and season at stream chemistry stations in the TMDL Watershed. pH Flow Spring Summer-Fall Winter All Exceedance # > 8.5/ # > 8.5/ # > 8.5/ # > 8.5/ (%) Mean Median Mean Median Mean Median Mean Median Total # Total # Total # Total # North Elm Creek (SC731) 0-25 7.7 7.6 0/8 7.4 7.2 0/4 7.6 7.7 0/5 7.6 7.6 0/17 26-50 7.9 7.8 0/4 7.4 7.4 0/3 7.9 8.0 0/7 7.8 7.8 0/14 51-75 7.9 7.9 0/3 7.8 8.0 0/3 7.7 7.7 0/5 7.8 7.8 0/11 76-100 8.0 8.0 0/2 7.9 7.9 0/8 7.8 7.8 0/7 7.8 7.8 0/17 0-100 7.8 7.8 0/17 7.7 7.7 0/18 7.8 7.8 0/24 7.8 7.8 0/59 Big Blue River near Oketo (SC233) 0-25 7.7 7.7 0/18 7.6 7.6 0/16 7.7 7.8 0/7 7.7 7.6 0/41 26-50 8.1 8.0 1/11 8.2 8.2 0/10 8.2 8.2 2/16 8.2 8.2 3/37 51-75 8.8 8.9 6/7 8.4 8.4 2/8 8.3 8.2 2/20 8.4 8.4 10/35 76-100 8.8 8.8 3/3 8.6 8.5 8/18 8.2 8.2 1/12 8.5 8.4 12/33 0-100 8.1 8.1 10/39 8.2 8.3 10/52 8.2 8.2 5/55 8.2 8.2 25/146 Horseshoe Creek (SC717) 0-25 7.6 7.6 0/2 8.0 8.0 0/1 7.9 8.0 0/4 7.8 7.8 0/7 26-50 7.8 7.9 0/3 7.5 7.5 0/3 7.3 7.3 0/1 7.6 7.7 0/7 51-75 8.0 8.0 0/2 7.5 7.5 0/1 7.9 7.9 0/4 7.9 7.9 0/7 76-100 - - - 7.8 7.8 0/2 7.5 7.5 0/2 7.7 7.8 0/4 0-100 7.8 7.9 0/7 7.7 7.8 0/7 7.8 7.8 0/11 7.7 7.8 0/25 Big Blue River near Blue Rapids (SC240) 0-25 7.7 7.7 0/18 7.6 7.7 1/16 7.8 7.8 1/7 7.7 7.7 2/41 26-50 8.1 8.0 0/11 8.1 8.2 2/10 8.2 8.3 1/16 8.1 8.1 3/37 51-75 8.4 8.5 2/7 8.4 8.3 3/8 8.2 8.2 2/20 8.3 8.3 7/35 76-100 8.6 8.5 2/3 8.5 8.6 7/18 8.1 8.1 1/12 8.3 8.5 10/33 0-100 8.0 8.0 4/39 8.1 8.2 13/52 8.1 8.1 5/55 8.1 8.1 22/146

Although most of the excursions in the Big Blue River occurred during the summer-fall season under lower flow conditions, there were excursions across the seasons and at flows as high as 38% flow exceedance (Figures 36-37). This indicates the river is excessively enriched by nutrients, leading to excessive primary productivity that goes unabated even during cooler conditions and increased flow. There are no pH excursions for Horseshoe Creek (SC717) or North Elm Creek (SC731), and the flow and temperature patterns seen in pH in streams impacted by excessive primary productivity are absent (Figures 38-39).

Figure 34. pH by sampling date in the Big Blue River near Oketo (SC233).

pH by Date Big Blue River near Oketo (SC233)

9.5

9.0

8.5 8.5

H 8.0 p

7.5

7.0

6.5 6.5

0 0 1 2 3 4 5 6 7 8 8 9 0 1 2 3 4 5 5 6 7 8 9 1 2 3 4 6 7 8 9 9 9 9 9 9 9 9 9 9 9 9 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 9 9 9 9 9 9 9 9 9 9 9 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 /1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 /2 2 2 2 2 2 2 / / 8 / / / / / / / / / / / / / / / / / / / / 7 / / / / / / 13 9 2 13 16 18 19 13 8 6 0 18 7 18 8 7 5 4 9 3 17 5 2 / 4 13 /9 3 12 3 / 2 / / / / / / /2 2 3 / /1 / 1 /1 1 1 1 1 / 1 1 3 2 / 2 / 2 3 / 0 7 8 7 6 5 4 1/ 1/ 0 7 6 / 2 / / / 1/ 2 / / / 8 12 / 6 7/ 10 1 1 1 3 3 2 12 1 1 9 10 4 2 Collection Date

Figure 35. pH by sampling date in the Big Blue River near Blue Rapids (SC240).

pH by Date Big Blue River near Blue Rapids (SC240)

9.5

9.0

8.5 8.5

H 8.0 p

7.5

7.0

6.5 6.5

0 0 1 2 3 4 4 5 6 7 8 8 9 0 1 2 3 4 5 5 6 7 8 9 0 2 3 4 5 7 8 9 9 9 9 9 9 9 9 9 9 9 9 9 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 9 9 9 9 9 9 9 9 9 9 9 9 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 /1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 / / 8 / / / / / / / / / / / / / / / / / / / / / 1/ / / / / / / 13 9 2 13 16 16 13 19 13 8 6 0 18 7 18 8 7 5 4 9 3 17 5 2 / 10 14 16 19 13 /9 / 2 / / / / / / / /2 2 3 / /1 / 1 /1 1 1 1 1 / 1 1 1 / / / / / 3 / 0 7 8 5 2 6 5 4 1/ 1/ 0 7 6 / 2 / / / 1/ 2 / / 1 1 5 9 0 3 4 10 1 1 1 1 3 3 2 12 1 1 9 10 1 Collection Date

Figure 36. pH by percent flow exceedance and season in the Big Blue River near Oketo (SC233). pH vs % Flow Exceedance Big Blue River near Oketo (SC233) 9.5 Season Spring Summer-Fall 9.0 Winter

8.5 8.5

H 8.0 p

7.5

7.0

6.5 6.5

0 10 20 30 40 50 60 70 80 90 100 % Flow Exceedance

Figure 37. pH by percent flow exceedance and season in the Big Blue River near Blue Rapids (SC240). pH vs % Flow Exceedance Big Blue River near Blue Rapids (SC240) 9.5 Season Spring Summer-Fall 9.0 Winter

8.5 8.5

H 8.0 p

7.5

7.0

6.5 6.5

0 10 20 30 40 50 60 70 80 90 100 % Flow Exceedance

Figure 38. pH by sampling date in North Elm Creek (SC731) and Horseshoe Creek (SC717).

pH by Date pH by Date North Elm Creek (SC731) Horseshoe Creek (SC717)

8.5 8.5 8.5 8.5

8.0 8.0 H H

p 7.5

7.0 7.0

6.5 6.5 6.5 6.5 1 1 1 1 1 3 3 7 2 4 2 3 4 5 5 6 6 7 7 8 8 9 7 5 7 9 9 2 8 3 1 1 0 1 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 8 5 9 3 7

2 2 9 9 0 0 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

/ / 9 9 0 0 0 0 / / / / / / / / / / / / / / / / / / / / / / / / / / / / 1 1 2 2 2 2 6 2 6 4 5 2 7 0 4 / / / / / / 8 5 8 4 7 8 5 5 8 9 8 9 5 6 9 5 8 4 2 8 0

/ 1 6 1 3 1 1 / 1 1 / 5 8 4 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 / 1 2 1 2 2 2 / 2 1 / / / 6 / 1 / / / / / / / / / / / / / / / / / 2 / / / / / / / / / 6 / 6 2 2 1 1 9 8 2 1 1 4 5 6 1 8 1 8 3 4 5 4 8 2 5 9 2 6 0 1 5 9 2 2 0 7 1 1 1 1 1 1 1 1 Collection Date Collection Date

Figure 39. pH by percent flow exceedance and season North Elm Creek (SC731) and Horseshoe Creek (SC717).

pH vs % Flow Exceedance pH vs % Flow Exceedance Horseshoe Creek (SC731) North Elm Creek (SC717)

8.5 8.5 8.5 8.5

8.0 8.0

H 7.5 H 7.5 p p

7.0 7.0 Season Season Spring Spring Summer-Fall Summer-Fall Winter Winter

6.5 6.5 6.5 6.5

0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 % Flow Exceedance % Flow Exceedance

Algal Biomass Although stream samples are not routinely analyzed for chlorophyll-a, there is some data available for North Elm Creek and the Big Blue River near Oketo (Figure 40; Table 14). The relatively small data set for North Elm Creek shows algae growth under control during the cooler winter temperatures and increased concentrations coinciding with the warmer seasons. For the period of record that includes data collected at the same site by both the stream chemistry and stream probablistic programs, North Elm Creek has an overall mean of 12.0 µg/L chlorophyll-a. In the Big Blue River near Oketo, chlorophyll-a concentrations are excessively high throughout the year though the winter season shows a relative decline. The spring season records the highest average over the period of record at 198 µg/L chlorophyll-a.

Figure 40. Chlorophyll-a concentrations by season at sites in the Big Blue Watershed.

Chlorophyll a By Season North Elm Cr (SC731_SP826) and Big Blue River nr Oketo (SC233) 1000 SITE_NAME Season_1 SC233 spring SC233 summer-fall SC233 winter )

L SC731_SP826 spring / 100

g SC731_SP826 summer-fall u

( SC731_SP826 winter

l l y h

p 10 o r o l h C

1 1 1 1 7 7 7 7 7 7 5 9 0 8 3 4 4 6 2 3 4 5 5 6 6 8 8 9 5 3 4 5 6 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 / 2 2 / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / 7 2 2 2 4 2 9 7 0 2 9 3 0 7 7 9 6 7 7 / 9 2 9 3 8 5 4 8 3 5 8 9 6 1 1 1 / / / 1 1 1 / 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 / / 2 / 3 / / 2 2 / / / / / / 2 / / / / 8 4 / / / / / / / / / 2 / / / 2 9 7 6 1 1 2 7 2 1 4 2 5 7 2 4 0 2 0 8 3 2 4 1 5 1 5 2 1 8 1 1 1 1 1 Collection Date

Table 14. Chlorophyll-a data by season at stream chemistry stations in the TMDL Watershed. Spring Summer-Fall Winter All Period of Mean Mean Mean Mean Stream Record N Chl a N Chl a N Chl a N Chl a (µg/L) (µg/L) (µg/L) (µg/L) North Elm Cr 3/15/04 – 5 13.3 6 19.3 9 6.5 20 12.0 (SC731_SP826) 12/12/11 Big Blue R 2/17/03 – 10 198 12 115 21 70.3 43 113 (SC233) 4/19/18

Biology Data regarding macroinvertebrate organisms and community within the TMDL Watershed are collected at KDHE stream biology (SB) stations on the Big Blue River at SB233, co-located with SC233, and SB240, co-located with SC240. North Elm Creek is monitoried for biology at SB374, located just upstream from SC731. Horseshoe Creek is monitored for biology at SB475, upstream from Horshoe Creek’s confluence with Raemer Creek. Additionally, Spring Creek (CUSEGA 1027020519) is monitored just above its confluence with the Big Blue River at SB476. KDHE’s Stream Biological Monitoring Program uses the Aquatic Life Use Support Index (ALUS Index) to assess stream biology as described in Kansas’ 2018 303(d) Methodology. The ALUS Index consists of five categorizations of biotic condition that, once measured, are assigned a score (Table 15). Scores are then tallied, and a support category is assigned according to Table 16.

Biology metrics used in the ALUS Index include: 1. Macroinvertebrate Biotic Index (MBI): A statistical measure that evaluates the effects of nutrients and oxygen demanding substances on macroinvertebrates based on the relative abundance of certain indicator taxa (orders and families). 2. Ephemeroptera, Plecoptera, and Trichoptera (EPT) abundance as a percentage of the total abundance of macroinvertebrates. 3. Kansas Biotic Index for Nutrients (KBI-N): Mathematically equivalent to the MBI, however, the tolerance values are species specific and restricted to aquatic insect orders. 4. EPT Percent of Count (EPT % CNT): The percentage of organisms in a sample consisting of individuals belonging to the EPT orders. 5. Shannon’s Evenness (SHN EVN): A measure of diversity that describes how evenly distributed the numbers of individuals are among the taxa in a sample.

Table 15. ALUS Index metrics with scoring ranges. MBI KBI-N EPT EPT % CNT SHN EVN Score <= 4.18 <= 2.52 >= 16 >= 65 >= 0.849 4 4.19-4.38 2.53-2.64 14-15 56-64 0.826-0.848 3 4.39-4.57 2.65-2.75 12-13 48-55 0.802-0.825 2 4.58-4.88 2.76-2.87 10-11 38-47 0.767-0.801 1 >= 4.89 >= 2.88 < = 9 <= 37 <= 0.766 0

Table 16. ALUS Index score range, interpretation of biotic condition, and support category. ALUS Index Score Biotic Condition Support Category >16 - 20 Very Good Supporting >13 - 16 Good >7 - 13 Fair Partially Supporting >3 - 6 Poor Non-Supporting 0 - 3 Very Poor

Biotic conditions were sampled in the Big Blue River at SB233 from 1990 to 2017 and downstream at SB240 from 2013 to 2017, in North Elm Creek (SB374) from 1999 to 2000, in Horseshoe Creek (SB475) from 2010 to 2015, and in Spring Creek (SC476) from 2010 to 2015.

Generally, annual sampling at a KDHE SB site consists of duplicate samples taken on a single day in the spring or summer-fall season; however, intensive sampling occurred in Horseshoe Creek and Spring Creek over the 2011 through 2015 time period as part of a sub-watershed study. Daily sample data is displayed in Figure 41, while Table 17 displays the annual average of all samples taken during a year. The Big Blue River site at SB233 has been sampled 27 times between 1990 and 2017. This station has a mean ALUS Index of 12, indicating that aquatic life has been partially supported over the period of record. A closer look at Figure 41 shows the biotic condition at SB233 declined over the 2000-2003 period, after which conditions began to improve in 2013. The Big Blue River at SB240 was sampled in 2013, 2014, and 2016 and has a mean ALUS Index of 15, indicating biotic conditions were supportive of aquatic life during those years. The North Elm Creek at SB374 was sampled during 1999 and 2000, with ALUS Index of 10 and 7, respectively, indicating biotic conditions were fair and partially supportive of aquatic life during the years sampled. Horseshoe Creek at SB475 and Spring Creek at SB476 have been sampled 15 times: once in 2010; twice in 2011; and three times per year in 2012, 2013, 2014, and 2015. Biotic conditions in Horseshoe Creek have ranged from poor to fair, while conditions in Spring Creek have ranged from very poor to fair over their respective periods of record.

Figure 41. Aquatic Life Use Support Index scores in the Big Blue River watershed, 1990 to 2017.

ALUS Scores at SB Sites in the Big Blue River TMDL Watershed

20 SB233-Upper Big Blue Fully Supporting SB240-Lower Big Blue 18 SB374-North Elm Cr SB475-Horseshoe Cr 16 SB476-Spring Cr 14 e

r 13 o Partially Supporting c 12 S

S 10 U L 8 A 6 6

4 2 Not Supporting 0 1 1 1 1 7 7 7 5 2 5 5 2 2 4 5 3 0 0 3 3 4 4 0 3 3 2 5 9 3 4 6 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 9 1 1 1 1 1 9 0 0 9 9 0 0 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9 0 0 0 0 0 9 0 0 9 9 0 0 9 1 2 2 2 1 2 2 2 1 2 2 2 2 1 2 2 2 2 2 2 2 2 2 1 2 2 2 2 2 / 2 2 / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / 7 8 2 8 3 7 7 1 7 0 6 3 5 2 2 5 6 5 8 6 8 9 5 5 3 6 0 9 9 1 4 6 1 1 / / / 1 1 1 1 1 1 1 / / / 2 / / 1 1 1 1 2 2 2 2 2 / / / / / / / / 2 / / / / / / / / / 9 5 5 7 / / / / / 0 0 4 5 / 9 5 6 7 4 8 7 7 7 7 7 0 0 0 6 8 1 1 6 4 8 8 9 8 1 6 1 1 Collection Date

Table 17. Number of samples (N) and mean ALUS Index Score by sampling station and year. SB233 Upper SB475 SB240 SB374 North SB476 Big Blue Horseshoe Lower Big Elm Creek Spring Creek Year River Creek Blue River N Mean N Mean N Mean N Mean N Mean 1990 - - 1 14 ------1991 - - 1 10 ------1992 - - 1 17 ------1993 - - 1 13 ------1994 - - 1 13 ------1995 - - 1 12 ------1996 - - 1 14 ------1997 - - 1 16 ------1998 - - 1 18 ------1999 2 10 1 16 ------2000 1 7 1 7 ------2001 - - 1 12 ------2002 - - 1 6 ------2003 - - 1 3 ------2004 - - 1 18 ------2005 - - 1 11 ------2006 - - 1 10 ------2007 - - 1 12 ------2008 ------2009 - - 1 8 ------2010 - - 1 14 2 6 2 6 - - 2011 - - 1 10 4 3 4 8 - - 2012 - - 1 7 6 3 6 6 - - 2013 - - 1 13 6 6 6 8 1 15 2014 - - 1 13 6 6 6 9 1 16 2015 - - 1 16 6 3 6 7 - - 2016 - - 1 13 - - - - 1 13 2017 - - 1 17 ------Period of Re cord Total Samples and 3 9 27 12 30 4 30 8 3 15 ALUS Score Average Definition – - no data

Desired Endpoints for Water Quality (Implied Load Capacity) for the Big Blue River Watershed from the Kansas-Nebraska State Line to Tuttle Creek Reservoir. The ultimate desired water quality endpoints of this TMDL will be to achieve the Kansas Water Quality Standards by eliminating the impacts to aquatic life, domestic water supply, and contact recreation associated with excessive phosphorus and objectionable flora as described in the narrative criteria pertaining to nutrients. There are currently no existing numeric phosphorus criteria in Kansas.

The Big Blue River Watershed lies within U.S. EPA Level IV Ecoregion Smoky Hills (27a), Rolling Plains and Breaks (27b), Flint Hills (28a), and Loess and Glacial Drift Hills (47i). Assessment of 49 KDHE SC stations within these Level IV Ecoregions and the Kansas-Lower Republican River Basin with TP data from 2000 to 2018 indicates a 25th percentile of station medians of 0.120 mg/L and a 50th percentile of station medians of 0.216 mg/L (Table 18).

Table 18. Summary of Kansas Department of Health and Environment (KDHE) stream chemistry stations within the Level IV Ecoregions and Kansas-Lower Republican River Basin from 2000 to 2018. 50th Number 25th 75th Number Percentile of Percentile of Percentile of U.S. EPA Level 4 Ecoregions of of KDHE Medians Medians Samples Medians Stations (mg/L) (mg/L) (mg/L) Smoky Hills (27a) 12 620 0.233 0.303 0.401 Rolling Plains and Breaks (27b) 4 147 0.235 0.278 0.451 Flint Hills (28a) 21 1,120 0.046 0.117 0.177 Loess and Glacial Drift Hills (47i) 12 603 0.188 0.223 0.263 Aggregated Ecoregions 49 2,490 0.120 0.216 0.309

Within the combined Level III Ecoregions Central Great Plains (27), Flint Hills (28), and Western Corn Belt Plains (47), there are 54 KDHE stations with both SB and SC data. An analysis of the mean ALUS Index versus the median TP concentration at those sites indicates there is a general decline in biology with increasing TP concentrations (Figure 42). There is one SB station fully supporting biology that is unimpaired for TP, while most unimpaired stations are partially supporting biology. This variability in the relationship of the mean ALUS Index versus the median TP concentration is due to the numerous factors impacting biological health. Such variability supports an adaptive management approach to reduce current TP concentrations and loads in phases, rather than establishing a single, definitive threshold.

This TMDL seeks to establish an adaptive management approach to observe and respond to biological metrics in order to assess the impact of TP reductions. As such, the primary measure of phosphorus load reduction in the TMDL for impaired segments of Big Blue River Watershed will be an improved ALUS Index. An ALUS Index greater than 13 at SB stations will serve to establish that the biological community reflects recovered or renewed diversity and minimal disruption by the impacts described in the narrative criteria for nutrients on aquatic life, recreation, and domestic water supply.

Figure 42. Aquatic Life Use Support (ALUS) Index versus median total phosphorus for stream biology and stream chemistry stations within the Level III Ecoregions from 2000 to 2018.

Of the SC stations within the Level IV Ecoregions and the Kansas-Lower Republican River Basin used for the TP milestone analysis, 13 SC stations with a total of 250 samples have corresponding chlorophyll-a data. An analysis of the relationship between chlorophyll-a versus TP indicates that there is a positive correlation between the variables (Figure 43). In this relationship, the 25th percentile of station medians of 0.120 mg/L yields a chlorophyll-a concentration of 7.7 µg/L and the 50th percentile of station medians of 0.216 mg/L yields a chlorophyll-a concentration of 13.4 µg/L. These chlorophyll-a concentrations bracket the desired chlorophyll-a endpoint of 10 µg/L. The chlorophyll-a concentration will serve as an additional biological measure of nutrient loading reduction in order to assess improvements in primary productivity and address its impacts as described in the narrative criteria for nutrients on aquatic life, recreation, and domestic water supply.

Furthermore, secondary indicators of the health of the aquatic biological community will be assessed at SC stations. Dissolved oxygen concentrations will be monitored to ensure concentrations are greater than 5.0 mg/L. According to the Kansas Water Quality Standards, concentrations below this are low enough to put aquatic life under stress. Dissolved oxygen saturation will also be monitored for indication of overactive primary productivity, as indicated by supersaturated values greater than 110%. The pH will be monitored, as well, to ensure that overactive primary productivity is not altering SC; values should remain between 6.5 and 8.5 in order to protect aquatic life according to the Kansas Water Quality Standards.

Figure 43. Chlorophyll-a versus total phosphorus for stream chemistry stations within the Level IV Ecoregions and the Kansas-Lower Republican River Basin from 2000 to 2018.

Therefore, the numeric endpoints for this TMDL indicating attainment of water quality standards within the watershed are: 1. An ALUS Index score greater than 13 at SB stations. 2. Maintain median sestonic chlorophyll-a concentration equal to or below 10 µg/L at SC stations. 3. Dissolved oxygen concentrations greater than 5.0 mg/L at SC stations. 4. Dissolved oxygen saturation below 110% at SC stations. 5. pH values within the range of 6.5 to 8.5 at SC stations.

All five endpoints must be maintained over three consecutive years to constitute full support of the designated uses of the Big Blue River Watershed and its tributaries. After the endpoints are attained, simultaneous digression of these endpoints more than once every three years on average constitutes a resumption of impaired conditions in the stream.

There are no existing numeric phosphorus criteria currently in Kansas. Hence, the series of endpoints established by this TMDL will be the measures used to indicate full support of the designated uses for the creeks and river. These endpoints will be evaluated periodically as phosphorus levels decline in the watershed over time with achievement of the ALUS Index endpoint indicating restored status of the aquatic life use in the river.

This TMDL looks to establish phased TP endpoints that will be the cue to examine for altered, improved biological conditions in the creeks and river. Assessment of the biological community in the watershed will be initiated once concentrations approach the Phase I management milestone of a median concentration of 0.216 mg/L. Should aquatic life not respond positively,

Phase II will commence with a TP milestone concentration of 0.121 mg/L (Table 19). Simultaneous achievement of the chlorophyll-a, dissolved oxygen, oxygen saturation, and pH endpoints will signal phosphorus reductions are addressing the accelerated succession of aquatic biota and the development of objectionable concentrations of algae and algae byproducts, thereby restoring the domestic water supply, aquatic life, and contact recreation uses in the creek.

Table 19. Current condition (2000 through 2018) TP concentration and Phase I and Phase II TP milestones for the TMDL Watershed. Current TMDL Phase I TMDL Phase II Condition Stream Chemistry Station Reduction in TP Reduction in TP Median TP TP Milestone from Current TP Milestone from Current (mg/L) (mg/L) (mg/L) Concentration Concentration North Elm Creek 0.196 0.196 0% 0.120 39% (SC731) Big Blue River (SC233) 0.866 0.216 75% 0.120 86% Horseshoe Creek 0.239 0.216 10% 0.120 50% (SC717) Big Blue River (SC240) 0.615 0.216 65% 0.120 80%

Additionally, reductions in TP loading will reduce the degree of primary productivity occurring in the river as determined by chlorophyll-a concentrations measuring below 10 µg/L. Exceedances of the pH criterion of 8.5 can occur because of excessive primary productivity, particularly during the summer months. During photosynthesis, carbon dioxide and water are converted to sugar, oxygen, and hydroxyl ions leading to increased pH levels. The target of 10 µg/L chlorophyll-a should indicate primary productivity is under control and pH exceedances, particularly during the summer months, should abate. Achievement of the pH endpoint in the Big Blue River near Oketo (SC233) and Big Blue River near Blue Rapids (SC240) indicates pH in the river has been restored to a degree that it is now meeting the Kansas Surface Water Quality Standard for pH. As such, the Big Blue River near Oketo (SC233), Big Blue River near Blue Rapids (SC240), and their related segments will be eligible for delisting during the following 303(d) cycle.

3. SOURCE INVENTORY AND ASSESSMENT

Point Sources: There are 11 National Pollution Discharge Elimination System (NPDES) permits in the Big Blue River Watershed (Table 20; Figure 44). All of the 11 permitted facilities are in the contributing area for SC240, located on the Big Blue River near Blue Rapids. Of the 11 permitted facilities, four are lagoons discharging domestic waste, one is a non-discharging lagoon, one is a discharging industrial permit, three are permits for industrial pretreatment, one is for pit dewatering at a concrete plant, and one is a quarry.

Three of the four discharging lagoon systems are required to monitor for TP in their effluent quarterly, when discharging. The City of Blue Rapids has discharged 12 of the last 48 quarters and report an average TP concentration of 2.8 mg/L. The City of Waterville has reported an average TP concentration of 1.9 mg/L and has discharged 15 of the last 48 quarters. The Home

City Sewer District #1 has discharged during four of 48 quarters with an average TP concentration of 2.3 mg/L. The fourth facility, a large lagoon facility operated by the City of Marysville, is permitted to discharge at a rate of 0.6 million gallons per day (MGD) and is required to monitor flow on weekdays and TP monthly. On average, the City of Marysville discharges 0.42 MGD with an effluent concentration of 2.2 mg/L TP. As discharging lagoons, these four facilities are considered contributors to the TP impairment and are assigned a TP wasteload allocation (WLA) by this TMDL. Conversely, USD #498 Valley Heights operates a lagoon facility treating domestic waste that is prohibited from discharging. It will not be assigned a WLA for TP as it is not considered a contributor to the impairment in the Big Blue River near Blue Rapids.

There is an industrial facility, GP Industrial Plasters – Blue Rapids, discharging non-cooling contact water, reverse osmosis concentrates, and mine dewatering to the watershed. Although this facility has not been required to monitor for TP, it will be assigned a nominal WLA for TP by this TMDL and will be required to monitor for TP at the next permit renewal. There are also three industrial pretreatment facilities discharging in the watershed. Two facilities, Rafter M Trailers and Titan MFG Plant #1, are discharging to the City of Waterville Wastewater Treatment Plant (WWTP), while Landol Corporation #1 is discharging to the City of Marysville WWTP. As their TP WLAs are effectively incorporated into the TP allocations assigned to the municipalities to which they discharge, these facilities will not be assigned individual WLAs by this TMDL.

Lastly, the Marysville Ready Mix Co., Inc. concrete operation and Or-al Quarries Inc. – Hanover Quarry operation are not prohibited from discharging but are not expected to contribute to the TP impairment in the watershed. Therefore, they will be assigned a TP WLA of zero by this TMDL.

Table 20. National Pollution Discharge Elimination System (NPDES) facilities in the Big Blue River Watershed. Current Kansas NPDES TP Current Design Receiving Permit TP Permittee Permit Permit Facility Type Monitoring Flow Flow Stream Expiration Mean Number Number Frequency (MGD) (MGD) (mg/L) M- 3-Cell City of Blue Big Blue BB04- KS0024775 Discharging 3/31/20 Quarterly - 0.160 2.8 Rapids OO01 Lagoon River M- 4-Cell City of Big Blue BB13- KS0092142 Discharging 3/31/20 Monthly 0.42 0.60 2.2 Marysville River OO02 lagoon M- 4-Cell City of Little Blue BB22- KS0048429 Discharging 9/30/20 Quarterly - 0.0925 1.9 Waterville River OO01 lagoon M- 4-Cell Home City Unnamed BB27- KS0095435 Discharging 3/31/20 Quarterly - 0.020 2.3 SD #1 Tributary OO01 lagoon USD #498 M- Non-discharging Valley BB22- KSJ000431 NA 1/31/21 NA NA NA NA Lagoon Heights NO01 Landol P- City of Industrial Corporation BB13- KSP000014 Marysville 3/31/22 NA NA NA NA pretreatment #1 OO01 WWTP P- City of Rafter M Industrial BB22- KSP000057 Waterville 6/30/22 NA NA NA NA Trailers pretreatment OO02 WWTP P- City of Titan MFG Industrial BB22- KSP000068 Waterville 11/20/23 NA NA NA NA Plant #1 pretreatment OO01 WWTP Non-contact Unnamed GP Industrial cooling I-BB04- Tributary Plasters - KS0002135 water/RO 3/31/25 NA - 0.046 - PO01 & Elm Blue Rapids concentrate/mine Creek dewatering Marysville I-BB13- Unnamed Ready Mix KSG110114 Concrete Plant 9/30/22 NA NA 0 NA PR01 Tributary Co., Inc. Or-al Quarries, Inc. I-BB22- Fawn KS0095125 Quarry 12/31/19 NA NA 0 NA - Hanover PO01 Creek Quarry Definitions: NA: Not applicable; -: No data

Figure 44. Map of sources in the Big Blue River TMDL Watershed.

Livestock and Waste Management Systems: There are 10 certified or permitted Confined Animal Feeding Operations (CAFOs) within the Big Blue River Watershed, none of which are of a size to require a federal permit (Table 21). Of the permitted facilities, one is in the North Elm Creek Watershed, six are in the Horseshoe Creek Watershed, and three are in the Big Blue River Watershed near Blue Rapids. All these livestock facilities have waste management systems designed to retain an anticipated two weeks of normal wastewater from their operations and contain a 25-year, 24-hour rainfall/runoff event. Typically, this rainfall event coincides with streamflow that occurs less than 1-5% of the time. Additionally, facility waste management systems are designed to minimize runoff entering operations and detain runoff emanating from operations. It is unlikely TP loading would be attributable to properly operating permitted facilities, though extensive loading may occur if any of these facilities were in violation and discharged. All CAFOs are assigned a WLA of 0 lbs/day TP.

Table 21. Confined Animal Feeding Operations in the Big Blue River Watershed. KS Permit SC Animal County Livestock Type Type Number Watershed Numbers A-BBMS-B005 SC731 Marshall Beef 500 Permit A-BBMS-BA01 SC717 Marshall Beef 500 Certification A-BBMS-M019 SC717 Marshall Dairy 200 Certification A-BBMS-T001 SC717 Marshall Commercial Truck Wash 6 Permit A-BBMS-S036 SC717 Marshall Swine 1,882 Permit A-BBMS-S047 SC717 Marshall Beef, Swine 1,860 Permit A-BBMS-B006 SC717 Marshall Beef 900 Permit A-BBMS-BA03 SC240 Marshall Beef 495 Certification A-BBMS-BA10 SC240 Marshall Beef, Swine 286 Certification A-BBMS-BA04 SC240 Marshall Beef 185 Certification

Overall, the number of head of livestock have increased in both counties where the watershed is located between 2012 and 2017 (U.S. Department of Agriculture, 2012 and 2019). The largest increase in Marshall County was in the number of cattle and calves, while the number of chickens saw a 43% increase in Washington County over the same time period (Table 22).

Table 22. Agricultural census results for livestock in Marshall and Washington counties from 2012 and 2017 (U.S. Department of Agriculture, 2012 and 2019). Marshall Washington Livestock 2012 2017 % Difference 2012 2017 % Difference Cattle and Calves 29,585 40,561 37% 70,551 71,976 2% Sheep and Lambs 123 2,129 1,631% 531 - - Chickens, Layers 910 1,097 21% 778 1,110 43% Hogs and Pigs 4,474 - - 86,002 95,046 11% Goats 196 138 -30% 675 622 -8% Total 35,288 43,925 24% 158,537 168,754 6% Definition: - data not available

Points of Diversion: Within Marshall and Washington counties, there are 677 unique water rights and 1,123 unique points of diversion. In these counties, groundwater is diverted in greater quantities than surface water (Figure 45; Water Information Management and Analysis System, 2019). The predominant use for diverted water in these counties is irrigation. Diversions for irrigation tend to vary based on environmental conditions; irrigation increases by several thousand-acre feet from a dry year to an average year, as demonstrated in 2017.

Figure 45. Diverted water by source and use according to the Water Information Management and Analysis System (WIMAS) for a dry (2012) and average (2017) year for the Big Blue River Watershed. Diverted Water by Year and Diverted Water by Year and Use Use 12,000 16,000

14,000 10,000 12,000

8,000 10,000

8,000 6,000 6,000 4,000 4,000

2,000 2,000

- - 2012 2017 Surface Ground Domestic Industrial Irrigation 2012 2017 Munucipal Recreation Stockwater

Land Use: The 2011 National Land Cover Database (NLCD) shows the dominant land use is cultivated crops (57.2%) and the secondary land use is hay/pastureland (28.2%) in the watershed (Table 23; Figure 46). Cultivated cropland has an increased potential for nutrient runoff from fertilizers, which can contribute to TP loads in the watershed. Additionally, 5.4% of the watershed is developed, with the most development occurring near Marysville and Blue Rapids. Built infrastructure and impervious surfaces in urban environments increase runoff, which can contribute to TP loads in the watershed, particularly during precipitation runoff events.

Table 23. Percent land use by stream chemistry (SC) contributing area in the TMDL Watershed. Contributing Area Land Use SC731 SC233 SC717 SC240 Total TMDL Watershed Open Water 0.1% 1.4% 0.5% 1.6% 1.2% Developed 4.1% 3.8% 4.2% 6.3% 5.4% Forest 5.5% 7.3% 6.9% 7.2% 7.0% Hay/Pasture 13.3% 22.8% 29.6% 30.1% 28.2% Cultivated Crops 76.9% 64.2% 58.5% 53.5% 57.2% Wetlands 0.1% 0.6% 0.4% 1.3% 0.9%

Figure 46. Map of land cover in the Big Blue River Watershed (NLCD, 2011).

Population Density: Population within the counties where the watershed lies is on the decline in Marshall and Washington according to the 2000 and 2010 censuses (Table 24).

Table 24. County census results from 2000 and 2010 (U.S. Census Bureau, 2010). Population Change, County Population, 2000 Population, 2010 2000 to 2010 (%) Marshall 10,965 10,117 -7.7 Washington 6,483 5,799 -10.6

On-Site Waste Systems: The population of the Big Blue River Watershed is predominantly rural. Urban populations are typically served by municipal sewer systems; however, rural populations may not be connected to the municipal sewer system. According to the U.S. Environmental Protection Agency’s Spreadsheet Tool for Estimating Pollutant Load (STEPL), there are a total of 742 septic systems located in the TMDL Watershed. Septic systems in Kansas typically have an estimated 10-15% failure rate (Electric Power Research Institute, 2000). Failing on-site septic systems have the potential to contribute to nutrient loading in the watershed. However, because of their small flows and the proclivity of phosphorus to adsorb to soil, failing on-site septic systems are considered a minor source of TP loading within the watershed and are not expected to significantly contribute to the TP impairment.

Contributing Runoff: Runoff is primarily generated as infiltration excess with rainfall intensities greater than soil permeability. As the watershed’s soil profiles become saturated, excess overland flow is produced. According to the NRCS STATSGO database, the Big Blue River Watershed has a mean soil permeability of 1.15 inches/hour (Figure 47). Permeability in the watershed ranges from 0.01 to 7.59 inches/hour with approximately 45.7% of the watershed having a low soil permeability of 1.29 inches/hour. According to a USGS open-file report, the threshold soil permeability values are set at 3.43 inches/hour for very high, 2.86 inches/hour for high, 2.29 inches/hour for moderate, 1.71 inches/hour for low, 1.14 inches/hour for very low, and 0.57 inches/hour for extremely low soil permeability (Juracek, 2000). Approximately 98.6% of the Big Blue River Watershed is below the low (1.71 inches/hour) threshold.

Background Levels: Phosphorus is present over the landscape and in the soil profile. It is also present in terrestrial and aquatic biota. Wildlife can contribute to phosphorus loadings, particularly if they congregate to a density that exceeds the assimilative capacity of the land or water.

Figure 47. Map of Natural Resources Conservation Service State Soil Geographic Database soil permeability in the Big Blue River Watershed.

4. ALLOCATION OF POLLUTANT REDUCTION RESPONSIBILITY

The endpoints for these TMDLs are based on the biological condition as described in the Desired Endpoint Section. Additionally, as TP concentrations improve, the pH impairment in the Big Blue River as measured at SC233 and SC240 is expected to improve, thereby restoring conditions of full support of the designated uses in North Elm Creek, Horseshoe Creek, and Big Blue River from the Nebraska-Kansas state line to Tuttle Creek Reservoir.

These TMDLs are established in two phases and apply adaptive management to reductions in TP concentrations in the watershed, triggering periodic assessments of the biological condition as TP concentrations decline. The Phase I TP concentration is established at 0.216 mg/L in Horseshoe Creek and the Big Blue River. The North Elm Creek TP concentration is expected to remain at or below its current condition of 0.196 mg/L during Phase I implementation. There are no municipal mechanical WWTPs discharging to the watershed; hence, Phase I reductions will occur through implementation of agricultural best management practices (BMPs).

Once concentrations in Horseshoe Creek and the Big Blue River approach 0.216 mg/L TP, an intensive assessment of macroinvertebrate abundance and diversity will be performed to determine compliance with the narrative nutrient criteria. The biological condition and endpoints will also be assessed in North Elm Creek. Presuming one or more of the numeric endpoints are not met at the end of Phase I, Phase II will commence with a TP milestone of 0.121 mg/L. Phase II will be achieved via further implementation and application of nonpoint source reduction practices and technologies.

Point Sources: All currently permitted, discharging facilities are located within the contributing area of SC240, the Big Blue River near Blue Rapids. The absence of the potential to upgrade municipal mechanical WWTPs to enhanced nutrient reduction technology leads to Phase I and Phase II wasteload allocations (WLAs) being equivalent under this TMDL. For the lagoon systems treating domestic waste, WLAs are calculated using facility design flow and 2 mg/L TP, an effluent concentration commonly seen in Kansas lagoon systems (Table 25). The industrial permit for GP Industrial Plasters WLA is calculated using design flow and a nominal TP concentration of 0.2 mg/L TP. The concrete plant and quarry are assigned WLAs of 0 pounds per day (lbs/day), as are all CAFOs, as they are not expected to contribute to the impairment. Additionally, a reserve WLA has been incorporated to account for future growth. This reserve is reflective of an effluent concentration of 0.5 mg/L and a design flow of 1 MGD and may be applied whole or in part to a new or expanded discharge in any one of the contributing areas covered by this TMDL.

Nonpoint Source Load Allocation: The load allocation for nonpoint sources is the remaining load capacity after wasteloads and reserves for NPDES dischargers have been accounted for. The load allocation grows proportionately as normal conditions occur and continues to increase with wet weather conditions, thereby accounting for increased runoff from contributing areas. Because only the Big Blue River near Blue Rapids (SC240) Watershed has WLA to account for, the load allocation in each of the upstream watersheds is equivalent to the respective watershed’s load capacity, or TMDL.

Table 25. Phase I and II total phosphorus wasteload allocations for facilities permitted to discharge to the TMDL Watershed. Anticipated TP SC Design Flow TP Wasteload Allocation Permit Permittee Concentration Watershed (MGD) (mg/L) lbs/day lbs/year City of Blue M-BB04-OO01 0.16 2 2.7 985.5 Rapids City of M-BB13-OO02 0.60 2 10.0 3,650 Marysville City of M-BB22-OO01 0.0925 2 1.5 547.5 Waterville Home City SD M-BB27-OO01 0.020 2 0.3 109.5 #1 SC240 GP Industrial Plasters - Blue I-BB04-PO01 0.046 0.2 0.1 36.50 Rapids Marysville I-BB13-PR01 * 0 0 0 Ready Mix Co. OR-AL I-BB22-PO01 * 0 0 0 Quarries, Inc Phase I and Phase II SC240 Subtotal 14.6 5,329 Phase I and Phase II Reserve Wasteload Allocation 4.2 1,533 Phase I and Phase II Total TMDL Watershed Wasteload Allocation 18.8 6,862 Definition: *Not available

To account for TP contributions arising within Kansas, flow conditions for Phase I and Phase II load capacities were developed using incremental flow calculated for the contributing areas of the KDHE stream stations (Figures 48-51; Tables 26-29). Additionally, a TMDL for the the Big Blue River CUSEGA 1027020517 terminus was calculated and includes the reserve WLA that may be applied to the other TMDL Watersheds (Figure 52; Table 30). In all cases, the 2000 to 2018 flow record was utilized to develop the loading scenarios below. Additionally, current condition loads utilized the median TP value over the 2000 to 2018 period of record.

Figure 48. Total phosphorus TMDL with seasonal loading displayed for North Elm Creek (SC731). Phase I & II TP TMDL for North Elm Creek (SC731) 10000

1000

100

10 lbs/day 1

0.1

0.01

0.001 0 10 20 30 40 50 60 70 80 90 100 Percent Flow Exceedance

Phase I TMDL Phase I Load Allocation Phase II TMDL Phase II Load Allocation Spring Loads Summer-Fall Loads Winter Loads

Table 26. Phase I and Phase II current condition, load capacity, and load allocations for North Elm Creek (SC731). Flows are based on the 2000 to 2018 period of record. Current condition is calculated using the 2000 to 2018 median TP value of 0.196 mg/L. Percent of Time Flow Current Condition Load Capacity Load Allocation Flow Exceeds (cfs) (lbs/day) (lbs/day) (lbs/day) Phase I 90% 0.12 0.12 0.12 0.12 75% 0.37 0.39 0.39 0.39 50% 1.20 1.27 1.27 1.27 25% 3.58 3.79 3.79 3.79 10% 11.2 11.8 11.8 11.8 Phase II 90% 0.12 0.12 0.08 0.08 75% 0.37 0.39 0.24 0.24 50% 1.20 1.27 0.78 0.78 25% 3.58 3.79 2.32 2.32 10% 11.2 11.8 7.25 7.25

Figure 49. Total phosphorus TMDL with seasonal loading displayed for the Big Blue River near Oketo (SC233). Phase I & II TP TMDL (Incremental Load) for Big Blue River near Oketo (SC233) 1000

100

10 lbs/day

0.1

0.01 0 10 20 30 40 50 60 70 80 90 100 Percent Flow Exceedance

Phase I TMDL Phase I Load Allocation Phase II TMDL Phase II Load Allocation Spring Loads Summer-Fall Loads Winter Loads

Table 27. Phase I and Phase II current condition, load capacity, and load allocations for the Big Blue River near Oketo (SC233) Watershed. Flows are based on the SC station contributing area of 31.1 mi2 over the 2000 to 2018 period of record. Current condition is calculated using the 2000 to 2018 median TP value of 0.866 mg/L. Percent of Time Flow Current Condition Load Capacity Load Allocation Flow Exceeds (cfs) (lbs/day) (lbs/day) (lbs/day) Phase I 90% 0.90 4.20 1.05 1.05 75% 1.34 6.27 1.56 1.56 50% 2.12 9.93 2.48 2.48 25% 3.91 18.27 4.56 4.56 10% 11.3 52.7 13.1 13.1 Phase II 90% 0.90 4.20 0.58 0.58 75% 1.34 6.27 0.87 0.87 50% 2.12 9.93 1.38 1.38 25% 3.91 18.27 2.53 2.53 10% 11.3 52.7 7.30 7.30

Figure 50. Total phosphorus TMDL with seasonal loading displayed for Horseshoe Creek (SC717). Phase I & II TP TMDL for Horseshoe Creek (SC717) 10000

1000

100

10 lbs/day

0.1

0.01 0 10 20 30 40 50 60 70 80 90 100 Percent Flow Exceedance

Phase I TMDL Phase I Load Allocation Phase II TMDL Phase II Load Allocation Spring Loads Summer-Fall Loads Winter Loads

Table 28. Phase I and Phase II current condition, load capacity, and load allocations for the Horseshoe Creek (SC717) Watershed. Flows are based on the 2000 to 2018 period of record. Current condition is calculated using the 2000 to 2018 median TP value of 0.239 mg/L. Percent of Time Flow Current Condition Load Capacity Load Allocation Flow Exceeds (cfs) (lbs/day) (lbs/day) (lbs/day) Phase I 90% 0.45 0.58 0.52 0.52 75% 1.43 1.84 1.67 1.67 50% 4.64 5.98 5.41 5.41 25% 13.8 17.9 16.1 16.1 10% 43.2 55.8 50.4 50.4 Phase II 90% 0.45 0.58 0.29 0.29 75% 1.43 1.84 0.93 0.93 50% 4.64 5.98 3.00 3.00 25% 13.8 17.9 9.00 9.00 10% 43.2 55.8 28.0 28.0

Figure 51. Total phosphorus TMDL with seasonal loading displayed for the Big Blue River near Blue Rapids (SC240) based on incremental loading. Phase I TP TMDL (Incremental Load) for Big Blue River near Blue Rapids (SC240) 10000

1000

100 lbs/day

0.1 0 10 20 30 40 50 60 70 80 90 100 Percent Flow Exceedance

Phase I TMDL Phase I Load Allocation Phase I WLA (14.6 lbs/day) Spring Loads Summer-Fall Loads Winter Loads

Table 29. Phase I and Phase II current condition, load capacity, and load allocations for the Big Blue River near Blue Rapids (SC240) Watershed. Flows are based on the SC station contributing area of 249 mi2 over the 2000 to 2018 period of record. Current condition is calculated using the 2000 to 2018 median TP value of 0.615 mg/L. Percent of Current Load Wasteload Load Flow Time Flow Condition Capacity Allocation Allocation (cfs) Exceeds (lbs/day) (lbs/day) (lbs/day) (lbs/day) Phase I 90% 7.18 23.9 8.38 8.38 0.00 75% 10.7 35.6 12.5 12.5 0.00 50% 17.0 56.4 19.8 14.6 5.20 25% 31.2 104 36.4 14.6 21.8 10% 90.1 299 105 14.6 90.5 Phase II 90% 7.18 23.9 4.66 4.66 0.00 75% 10.7 35.6 6.95 6.95 0.00 50% 17.0 56.4 11.0 11.0 0.00 25% 31.2 104 20.2 14.6 5.64 10% 90.1 299 58.4 14.6 43.8

Figure 52. Total phosphorus TMDL in the Big Blue River near Blue Rapids based on flow measured at USGS 06882510 adjusted to account for the watershed size of the segment terminus above Tuttle Creek Reservoir. Phase I & II TP TMDL (Cumulative Load) for Big Blue River near Blue Rapids (SC240) 100000

10000

1000 lbs/day

100

1 0 10 20 30 40 50 60 70 80 90 100 Percent Flow Exceedance

Phase I TMDL Phase I Load Allocation Phase I & II Total WLA (18.8 lbs/day) Phase II TMDL Phase II Load Allocation

Table 30. Phase I and Phase II current condition, load capacity, and load allocations for the Big Blue River Watershed. Flows are based on flow seen at segment terminus (watershed area of 8,490 mi2) above Tuttle Creek Reservoir over the 2000 to 2018 period of record. Current condition is calculated using the 2000 to 2018 median TP value at SC240 of 0.615 mg/L. Percent of Current Load Wasteload Reserve Wasteload Load Flow Time Flow Condition Capacity Allocation Allocation Allocation (cfs) Exceeds (lbs/day) (lbs/day) (lbs/day) (lbs/day) (lbs/day) Phase I 90% 245 815 286 14.6 4.2 267 75% 366 1,216 427 14.6 4.2 408 50% 579 1,924 676 14.6 4.2 657 25% 1,066 3,541 1,244 14.6 4.2 1,225 10% 3,075 10,211 3,586 14.6 4.2 3,567 Phase II 90% 245 815 159 14.6 4.2 140 75% 366 1,216 237 14.6 4.2 218 50% 579 1,924 375 14.6 4.2 357 25% 1,066 3,541 691 14.6 4.2 672 10% 3,075 10,211 1,992 14.6 4.2 1,974

Defined Margin of Safety The margin of safety provides some hedge against the uncertainty in phosphorus loading into the Big Blue River. This TMDL uses an implicit margin of safety, relying on conservative assumptions. First, there are five endpoints that are established by this TMDL. Second, the chlorophyll a and biological endpoints used to assess compliance with the narrative criteria have to be maintained for three consecutive years before attainment of water quality standards can be claimed. Finally, wasteload allocations were set using facility design flow although most are discharging well under design flow.

Priority HUC12s: As this watershed has no major point source dischargers, reductions in nonpoint sources from BMP implementation in those HUC12s most impacted by TP loading will be necessary to achieve the TMDL (Figure 53; Table 31). The Big Blue River TMDL Watershed consists of 10 HUC12s. According to STEPL, the high priority HUC12s are 102702050202, 102702050501, and 102702050201, and 102702050204. Proactive entities may implement BMPs at any time, with an emphasis on priority HUC12s likely yielding the greatest TP reductions to the watershed.

Figure 53. Map of priority HUC12s by total phosphorus load according to estimations from the Spreadsheet Tool for Estimating Pollutant Load for the Big Blue River TMDL Watershed.

Table 31. Priority HUC12s by total phosphorus load according to estimations from the Spreadsheet Tool for Estimating Pollutant Load for the Big Blue River TMDL Watershed. Land Area Total Phosphorus Total Watershed (acres) (lbs/year) (lbs/year/acre) 102702050202 36.3 82,587 2.65 102702050501 59.5 93,145 2.59 102702050201 42.9 67,006 2.57 102702050204 44.5 63,914 2.39 102702050103 20.4 78,229 2.33 102702050606 47.9 59,205 2.11 102702050203 46.8 68,675 2.09 102702050502 54.1 58,562 1.84 102702050104 1.0 27,640 1.84 102702050503 58.1 56,716 1.64 Definition: Bold - Priority HUC12s

Nutrient Reduction Framework Priority Ranking: This watershed lies within the Lower Big Blue (HUC8 10270205) and Lower Little Blue (HUC8 10270207) subbasin. This subbasin is among the top 16 HUC8s targeted for state action to reduce nutrients.

State Water Plan Implementation Priority: Due to the prevalence of high TP concentrations in the watershed, this TMDL focuses on reducing TP loading to the watershed. Primary reductions in TP loadings will need to be achieved through effective riparian and land management. Due to the need to reduce the high nutrient loading to Tuttle Creek Reservoir, an important public water supply source, this TMDL will be High Priority for implementation.

5. IMPLEMENTATION

Desired Implementation Activities 1. Facilitate wastewater reuse for treated municipal wastewater. 2. Renew state and federal permits and inspect permitted facilities for permit compliance. 3. Ensure proper on-site waste system operations in proximity to main stem and tributary segments. 4. Improve riparian conditions along stream systems by installing grass and/or forest buffer strips along the streams and drainage channels in the watershed. 5. Implement and maintain conservation farming practices—including conservation rotation, no-till farming, and contour farming—in order to reduce runoff and cropland erosion of agricultural areas in the watershed. 6. Perform extensive soil testing to ensure excess phosphorus is not unnecessarily applied. 7. Ensure labeled application rates for chemical fertilizers are followed to reduce runoff. 8. Encourage use of subsurface applications for fertilizer. 9. Implement nutrient management plans and ensure that land-applied manure is properly managed to reduce runoff. 10. Establish pasture management practices, including proper stock density, to reduce soil erosion and stormwater runoff.

11. Install alternative livestock watering systems and relocate livestock feeding areas away from riparian areas. 12. Establish alternative livestock foraging areas, collaborate with producers to develop areas for grazing cover crops, and implement rotational grazing systems. 13. Provide education and outreach opportunities on topics such as soil health, nutrient management, and livestock management. 14. Support BMP implementation efforts of the Tuttle Creek Lake WRAPS.

Implementing these practices will reduce nutrient loading in the Big Blue River. Particular emphasis on agricultural BMPs will be needed in this watershed in order to address nonpoint sources of loading and meet Phase I of this TDML (Table 32).

Table 32. Load allocation (nonpoint source) reduction required to meet the Phase I and Phase II TMDLs for the Big Blue River near Blue Rapids (SC240) by flow condition. Loading has been adjusted to reflect loads originating in the Big Blue River TMDL area within Kansas (383 mi2). Nonpoint Flow Estimated Current Load Wasteload Load Nonpoint Load Load Exceedance Flow Condition Capacity Allocation Allocation Reduction Needed Reduction (%) (cfs) (lbs/year) (lbs/year) (lbs/year) (lbs/year) (lbs/year) Needed (%) Phase I 90 11.1 13,426 4,715 4,715 0.0 8,710 75 16.5 20,041 7,039 6,862 177 13,002 50 26.2 31,716 11,139 6,862 4,277 20,577 65% 25 48.2 58,373 20,502 6,862 13,640 37,871 10 139 168,308 59,113 6,862 52,251 109,195 Phase II 90 11.1 13,426 2,641 2,641 0.0 10,784 75 16.5 20,041 3,943 3,943 0.0 16,098 50 26.2 31,716 6,240 6,240 0.0 25,476 80% 25 48.2 58,373 11,485 6,862 4,623 46,888 10 139 168,308 33,114 6,862 26,252 135,194

Implementation Program Guidance NPDES and State Permits – KDHE a. Continue to monitor influent to and effluent from the permitted discharging WWTFs, encourage wastewater reuse and irrigation disposal, and ensure compliance and proper operation of WWTFs to control phosphorus in wastewater effluent. b. Manage the WLA for the watershed to accommodate growth as needed. c. Manure management plans, detailing proper land application rates and practices, will be implemented to prevent runoff of applied manure. d. Inspect permitted livestock facilities to ensure compliance. e. Inspect new permitted livestock facilities for integrity of applied pollution prevention technologies. f. Apply pollution prevention technologies to new registered livestock facilities with less than 300 animal units.

Nonpoint Source Pollution Technical Assistance – KDHE a. Support Section 319 implementation projects for nutrient management through reduction of phosphorus runoff from agricultural activities. b. Provide technical assistance on practices to establish vegetative buffer strips. c. Support implementation efforts of the Tuttle Creek Lake WRAPS and incorporate long term objectives of this TMDL into their 9-element watershed plans. d. Provide technical assistance on nutrient management for livestock facilities and practices which minimize impacts of small livestock operations in the watershed to reduce impacts to stream resources.

Water Resource Cost Share and Nonpoint Source Pollution Control Program – Kansas Department of Agriculture-Division of Conservation (KDA-DOC) a. Apply conservation farming practices—including no-till, terraces, and contours—and erosion control structures, including sediment control basins and constructed wetlands. b. Provide sediment control practices to minimize erosion and sediment transport from cropland and grassland in the watershed. c. Encourage residue management to reduce phosphorus loss and transport from cropland runoff in the watershed. d. Implement manure management plans. e. Install livestock waste management systems for manure storage.

Riparian Protection Program – KDA-DOC a. Protect, establish, or re-establish natural riparian systems, including vegetative filter strips and streambank vegetation. b. Develop riparian restoration projects along targeted stream segments, especially those areas with base flow. c. Promote wetland construction to reduce runoff and assimilate loadings. d. Coordinate riparian management within the watershed and develop riparian restoration projects.

Buffer Initiative Program – KDA-DOC a. Install grass buffer strips near streams. b. Leverage Conservation Reserve Enhancement Programs to hold riparian land out of production.

Extension Outreach and Technical Assistance – Kansas State University a. Educate agricultural producers on sediment, nutrient, and pasture management. b. Provide technical assistance on buffer strip design and minimizing cropland runoff. c. Encourage annual soil testing to determine capacity of field to hold phosphorus. d. Educate residents, landowners, and watershed stakeholders about nonpoint source pollution. e. Promote and utilize the Watershed Restoration and Protection Strategy (WRAPS) efforts for pollution prevention, runoff control, and resource management. f. Educate livestock producers on livestock waste management, land-applied manure applications, and nutrient management plans.

g. Provide technical assistance on livestock waste management systems and nutrient management plans. h. Repair or replace failing septic systems which are located within 100 feet of the Big Blue River or its tributaries.

Timeframe for Implementation: Rural runoff management should expand from 2020 to 2029 to ensure nutrients are addressed. Pollutant reduction practices should be installed within the priority sub-watersheds after 2019 with follow-up implementation and monitoring continuing through 2040. If biology in the watershed has not responded to Phase I reductions by 2040 then Phase II nutrient reduction practices are expected to commence in 2040.

Targeted Participants: The primary participant for implementation of this TMDL is the Tuttle Creek Lake WRAPS. Agricultural operations immediately adjacent to the Big Blue River and its tributaries will be encouraged to implement appropriate practices to further reduce phosphorus loads. Watershed coordinators, technical staff of the WRAPS group, conservation district personnel, and county extension agents should coordinate to assess possible nutrient sources adjacent to streams. Implementation activities to address nonpoint sources should focus on those areas with the greatest potential to impact nutrient loading to the river.

Targeted agricultural activities to focus attention toward include: 1. Denuded riparian vegetation and poor riparian areas along the stream. 2. Conservation compliance on highly erodible areas. 3. Unbuffered cropland adjacent to the stream. 4. Total row crop acreage and gully locations. 5. No till or residue management on cropland. 6. Increasing no-till and precision agricultural practices, including cover crops. 7. Sites where drainage runs through or adjacent to livestock areas. 8. Sites where livestock have full access to the stream and it is their primary water supply.

Milestone for 2025: The Tuttle Creek Lake WRAPS is beginning a three-year funding cycle in 2019 to mitigate nutrient and sediment loads to the watershed. The WRAPS has been active for 10 years and, to date, has successfully achieved 39% of their reduction goals for phosphorus. The current initiative addresses HUC8s 102702070505, 102702070601, 102702070602, 102702070603, and 102702070606. The WRAPS seeks to reduce agricultural and livestock impacts in these targeted HUC12s. Additional livestock management strategies will be implemented within the watershed with the coordination of a Kansas State University watershed specialist. With these efforts, TP data from the Big Blue River near Blue Rapids (SC240) should show indication of declining TP concentrations relative to the pre-2019 data by 2025.

Delivery Agents: The primary delivery agents for program participation will be the State of Nebraska, KDHE, and the Tuttle Creek Lake WRAPS.

Reasonable Assurances Authorities The following authorities may be used to direct activities in the watershed to reduce pollution:

1. K.S.A. 65-164 and 165 empowers the Secretary of KDHE to regulate the discharge of sewage into the waters of the state. 2. K.S.A. 65-171d empowers the Secretary of KDHE to prevent water pollution and to protect the beneficial uses of the waters of the state through required treatment of sewage and established water quality standards and to require permits by persons having a potential to discharge pollutants into the waters of the state. 3. K.S.A. 2002 Supp. 82a-2001 identifies the classes of recreation use and defines impairment for streams. 4. K.A.R. 28-16-69 through 71 implements water quality protection by KDHE through the establishment and administration of critical water quality management areas on a watershed basis. 5. K.S.A. 2-1915 empowers the State Conservation Commission to develop programs to assist the protection, conservation, and management of soil and water resources in the state, including riparian areas. 6. K.S.A. 75-5657 empowers the State Conservation Commission to provide financial assistance for local project work plans developed to control nonpoint source pollution. 7. K.S.A. 82a-901, et. seq. empowers the Kansas Water Office to develop a state water plan directing the protection and maintenance of surface water quality for the waters of the state. 8. K.S.A. 82a-951 creates the State Water Plan Fund to finance the implementation of the Kansas Water Plan, including selected WRAPS. 9. The Kansas Water Plan provides the guidance to state agencies to coordinate programs intent on protecting water quality and to target those programs to geographic areas of the state for high priority in implementation.

Funding The State Water Plan annually generates $12-13 million and is the primary funding mechanism for implementing water quality protection and pollution reduction activities in the state through the Kansas Water Plan. The state water planning process, overseen by the Kansas Water Office, coordinates and directs programs and funding toward watershed and water resources by priority. Typically, the state allocates at least 50% of the fund to programs supporting water quality protection. This watershed and its TMDL are located within a High Priority area and should receive support for pollution abatement practices that lower the loading of sediment and nutrients.

Effectiveness Agricultural nutrient control has been proven effective through conservation tillage, contour farming, and use of grass waterways and buffer strips; additionally, the proper implementation of comprehensive livestock waste management plans has proven effective at reducing nutrient runoff associated with livestock facilities. Presuming the Phase I milestone is not met, this TMDL will be evaluated after 2029 to assess the reductions in phosphorus loads that have taken place with guidance provided to targeted participants regarding follow-up implementation activities.

6. MONITORING

Monitoring for TP will continue at KDHE stations for the tributaries North Elm Creek (SC731) and Horseshoe Creek (SC717) and at the main stem Big Blue River stations near Oketo (SC233) and Blue Rapids (SC240). Biological monitoring will continue at main stem stations SB233 and SB240. Other sites in the watershed may be sampled for biology to assess compliance with the narrative nutrient criteria in the river, as well. Based on the sampling data, the status of the watershed will be re-evaluated during the Section 303(d) listing process in 2030.

7. FEEDBACK

Public Notice: An active website is established at http://www.kdheks.gov/tmdl/planning_ mgmt.htm to convey information to the public on the general establishment of TMDLs and to provide specific TMDLs by river basin. This TMDL was posted to the Kansas-Lower Republican River Basin on this site on January 16, 2020 for public review.

Public Hearing: A public hearing was held on this TMDL on January 31, 2020 in Topeka, Kansas to receive public comments. No comments were received.

Milestone Evaluation: In 2029, evaluation will be made as to the degree of implementation that occurred within the watershed. Subsequent decisions will be made through consultation with local stakeholders and the WRAPS team regarding implementation of nonpoint source reduction strategies and development of additional implementation strategies for the watershed.

Consideration for Section 303(d) Delisting: The segments covered by this TMDL will be evaluated for delisting under Section 303(d) based on the monitoring data from 2020 to 2029. Therefore, the decision for delisting will ensue in the preparation for the 2030 Section 303(d) list. Should modifications be made to the applicable water quality criteria during the implementation period, consideration for delisting, desired endpoints of this TMDL, and implementation activities may be adjusted accordingly.

Incorporation into the TMDL Vision Process, Water Quality Management Plan, and the Kansas Water Planning Process: Under the current version of the Kansas TMDL Vision Process, the next anticipated revision of this TMDL will be after 2025. The revision will emphasize further implementation of WRAPS activities and incorporation of this TMDL into the WRAPS plan. Recommendations for this TMDL will be considered in the Kansas Water Plan implementation decisions under the State Water Planning Process for fiscal years 2020 to 2029.

Developed: June 10, 2020

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