Geomorph Site Characterization Report March 2008 Update

GeoMorph® Site Characterization Report March 2008 Update

Tittabawassee River and Floodplain Soils Midland, Michigan

Prepared by:

Ann Arbor Technical Services, Inc. 290 South Wagner Road Ann Arbor, Michigan 48103

Prepared for:

The Dow Chemical Company 1790 Building Midland, Michigan 48674

March 1, 2008

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SECTION NO. TITLE PAGE NO.

1. INTRODUCTION...... 1-1 1.1 GEOMORPH® 2007 SAP OBJECTIVES ...... 1-3 1.2 GEOMORPH® SITE CHARACTERIZATION UPDATE DELIVERABLES...... 1-3 1.3 REPORT ORGANIZATION ...... 1-4

2. BACKGROUND...... 2-1 2.1 STUDY AREA OVERVIEW...... 2-1 2.1.1 Tittabawassee River...... 2-1 2.1.2 2007 Study Area ...... 2-1 2.2 OVERVIEW OF 2007 INVESTIGATION ACTIVITIES...... 2-3 2.3 PROJECT CONSTRAINTS AND LIMITATIONS ...... 2-3 2.4 SUMMARY OF FIELD OPERATIONS AND METHODS...... 2-3 2.4.1 Sample Identification...... 2-4 2.4.1.1 Soil and Sediment Sample Locations...... 2-4 2.4.1.2 Soil and Sediment Sample Identification ...... 2-6 2.4.1.3 Erosion Scar Locations ...... 2-6 2.4.1.4 Field Duplicates ...... 2-6 2.4.1.5 Field Blanks...... 2-7 2.4.2 Sampling Methods...... 2-7 2.4.2.1 General Sampling Guidelines...... 2-8 2.4.2.2 Sample Locations and Field Positioning...... 2-8 2.4.2.3 In-channel Sediment Sampling ...... 2-9 2.4.2.4 Floodplain, Overbank, and Tributary Samples ...... 2-11 2.4.2.5 Field Equipment Decontamination...... 2-13 2.4.2.6 Soil and Sediment Core Processing...... 2-13 2.4.3 Field Documentation and Recordkeeping ...... 2-14 2.4.3.1 Field Sample Data Collection ...... 2-14 2.4.3.2 Chain of Custody, Sample Shipping, and Long-term Storage ...... 2-15 2.4.4 Geophysical Surveys ...... 2-16 2.5 SOIL CLASSIFICATION...... 2-18 2.5.1 Soil Formation ...... 2-18 2.5.2 Soil Profile...... 2-19 2.5.2.1 Soil Genesis ...... 2-19 2.5.2.2 Soil Horizon Nomenclature ...... 2-19 2.5.3 Soil Physical & Mineralogical Properties...... 2-20 2.5.4 Soil Classification...... 2-21

3. TITTABAWASSEE RIVER FLUVIAL GEOMORPHOLOGY OVERVIEW...... 3-1 3.1 TITTABAWASSEE RIVER HYDROLOGY...... 3-1 3.2 WATERSHED AND TRIBUTARIES ...... 3-2 3.3 ANTHROPOGENIC INFLUENCES...... 3-2 3.4 CHARACTERISTIC DEPOSITIONAL FEATURES OF THE UPPER AND MIDDLE TITTABAWASSEE RIVER AND FLOODPLAIN...... 3-3 3.4.1 Floodplain Deposition ...... 3-4 3.4.1.1 Levees (Natural and Historic Natural Levees)...... 3-5 3.4.1.2 Ridge and Swale Complexes...... 3-6 3.4.1.3 Crevasse Splays ...... 3-6

3.4.1.4 Deltaic Overbank Deposition Areas...... 3-7 3.4.1.5 Tributary and Wetland Deposition Areas...... 3-7 3.4.2 In-channel Features...... 3-8 3.4.2.1 Buried Deposits ...... 3-9 3.4.2.2 Alleviated Deposit...... 3-10 3.4.2.3 Riffle and Pool...... 3-10 3.4.2.4 Erosional Features ...... 3-10

4. HISTORICAL AND EXISTING CONDITIONS...... 4-1 4.1 GEOLOGY AND SOILS...... 4-1 4.1.1 Glacial and Post-Glacial History ...... 4-1 4.1.1.1 Ice Cover...... 4-1 4.1.1.2 Formation of the Port Huron End Moraine ...... 4-2 4.1.1.3 Inland Lakes ...... 4-3 4.1.1.4 Ice Retreat and Lower Lake Levels ...... 4-7 4.1.1.5 Rising Water Levels ...... 4-9 4.1.2 River Evolution...... 4-9 4.1.3 Soil Development ...... 4-11 4.2 HYDROLOGY AND FLOOD SERIES ANALYSIS ...... 4-14 4.2.1 Flood Series Analysis/Flood Recurrence Interval Calculations ...... 4-14 4.2.2 Flood Series Analysis/Flood Recurrence Estimates of Peak Recorded Discharges...4-16 4.2.3 Stage and Discharge ...... 4-18 4.2.3.1 Data Collection...... 4-18 4.2.3.2 Data Analysis and Results ...... 4-18 4.3 LAND USE OVERVIEW ...... 4-22 4.3.1 Historical Aerial Photograph Review...... 4-22 4.3.1.1 Preparation of photographs ...... 4-22 4.3.1.2 Review and analysis...... 4-23 4.3.2 Anthropogenic Influences...... 4-23 4.3.2.1 Logging and Agricultural Practices ...... 4-23 4.3.2.2 Areas Physically Disturbed after European Settlement ...... 4-31 4.3.2.3 Berms...... 4-33 4.3.2.4 Bank Protection ...... 4-33 4.3.2.5 Bridges...... 4-34 4.3.2.6 Recreational Areas ...... 4-44 4.3.3 Present Land Use Tax Classification...... 4-46 4.4 CHANNEL, FLOODPLAIN, AND VALLEY MORPHOLOGY...... 4-46 4.4.1 Introduction to Stream Classification ...... 4-46 4.4.1.1 Delineation of Regions ...... 4-48 4.4.2 Existing Channel Morphology and Mapping ...... 4-56 4.4.3 Existing Floodway Morphology and Mapping...... 4-58 4.5 HYDRODYNAMIC MODELING...... 4-59 4.5.1 Updates to EFDC Model ...... 4-59 4.5.2 Flood Events...... 4-59 4.5.3 Streamline Analyses ...... 4-60 4.5.4 Stream Power Analyses Performed Using Results of EFDC Simulations ...... 4-61 4.6 TRIBUTARY AND WETLAND HYDRODYNAMIC INFLUENCES ...... 4-61 4.6.1 Tributaries Upstream of Midland ...... 4-62 4.6.2 Tributaries and Wetlands between Midland and the Confluence Area ...... 4-63

4.7 CONSTITUENTS OF INTEREST ...... 4-64 4.7.1 Definition of Primary and Secondary Constituents of Interest (COI) ...... 4-64 4.7.2 Primary COI ...... 4-64 4.7.3 Secondary COI ...... 4-65 4.8 GEOCHEMISTRY ...... 4-71 4.8.1 Background...... 4-71 4.8.2 Protocol Development ...... 4-71 4.8.3 Fraction Analysis - 2006 and 2007 Samples ...... 4-71

5. UTR AND MTR CHARACTERIZATION...... 5-1 5.1 RIVER REGION I: “UPSTREAM OF DOW DAM” (REACHES A - D) ...... 5-1 5.1.1 Geomorphology...... 5-2 5.1.2 Anthropogenic Influences...... 5-2 5.1.2.1 Reach D Interim Response Action: Historic Wastewater Flume Deposit ...... 5-2 5.1.3 Lateral Channel Migration...... 5-3 5.1.4 Primary COI Data - Summary ...... 5-3 5.1.5 Secondary COI Data...... 5-6 5.2 RIVER REGION II: “NEAR PLANT AREA” (REACHES E - H) ...... 5-7 5.2.1 Geomorphology...... 5-7 5.2.2 Anthropogenic Influences...... 5-7 5.2.3 Lateral Channel Migration...... 5-8 5.2.4 Sediment Thickness and Glacial Till...... 5-8 5.2.5 Primary COI Data - Summary ...... 5-9 5.2.6 Secondary COI Data...... 5-12 5.3 RIVER REGION II: “DOWNSTREAM” (REACHES I - K)...... 5-12 5.3.1 Geomorphology...... 5-13 5.3.2 Anthropogenic Influences...... 5-13 5.3.2.1 Reach J/K Interim Response Action: Bank and Overbank Area...... 5-14 5.3.3 Lateral Channel Migration...... 5-14 5.3.4 Primary COI Data - Summary ...... 5-15 5.3.5 Secondary COI Data...... 5-18 5.4 RIVER REGION III (REACHES L – Y)...... 5-18 5.4.1 Geomorphology...... 5-18 5.4.2 Anthropogenic Influences...... 5-19 5.4.2.1 Reach O Interim Response Activities: In-channel Deposit at RO-332+00 ....5-19 5.4.3 Lateral Channel Migration...... 5-19 5.4.4 In-Channel Sediment Thickness and Glacial Till...... 5-20 5.4.5 Surface Water Flow During Flood Events...... 5-20 5.4.6 Primary COI Data - Summary ...... 5-21 5.4.7 Secondary COI Data...... 5-28 5.5 RIVER REGION IV (REACHES Z – DD)...... 5-29 5.5.1 Geomorphology...... 5-29 5.5.2 Anthropogenic Influences...... 5-30 5.5.3 Surface Water Flow during Flood Events ...... 5-30 5.5.4 Primary COI Data - Summary ...... 5-31 5.5.5 Secondary COI Data...... 5-33 5.6 RIVER REGION V (REACHES EE – II)...... 5-33 5.6.1 Geomorphology...... 5-33 5.6.2 Anthropogenic Influences...... 5-35

5.6.3 Lateral Channel Migration...... 5-35 5.6.4 Surface Water Flow during Flood Events ...... 5-36 5.6.5 Primary COI Data - Summary ...... 5-37 5.6.6 Secondary COI Data...... 5-40 5.7 RIVER REGION VI (REACHES II – KK) ...... 5-40 5.7.1 Geomorphology...... 5-40 5.7.2 Surface Water Flow during Flood Events ...... 5-40 5.7.3 Primary COI Data - Summary ...... 5-41 5.7.4 Secondary COI Data...... 5-43 5.8 RIVER REGION VII (REACHES LL – PP) ...... 5-43 5.8.1 Geomorphology...... 5-44 5.8.2 Surface Water Flow during Flood Events ...... 5-44 5.8.3 Primary COI Data - Summary ...... 5-44 5.8.4 Secondary COI Data...... 5-46 5.9 RIVER REGION VIII (REACHES QQ – UU)...... 5-46 5.10 RIVER REGION IX (REACHES VV – YY) ...... 5-47

6. STATISTICAL EVALUATION OF GEOMORPHIC INVESTIGATION FINDINGS...... 6-1 6.1 BACKGROUND...... 6-1 6.2 STATISTICS IN SUPPORT OF NATURE AND EXTENT ...... 6-2 6.2.1 Soil Profile Descriptions -Maturity & Stability Indicators...... 6-2 6.2.2 Geomorphic Surface & Spatial Relationship to Furan and Dioxin Distribution ...... 6-5 6.2.2.1 Geomorphic Surface and TEQ Concentration as a Function of Depth...... 6-5 6.2.2.2 TEQ Concentration as a Function of Sample Distance from River...... 6-6 6.2.2.3 Differences in Frequency Distributions of Maximum TEQ by Geomorphic Surface ...... 6-8 6.2.3 Geomorphic Surface and Proximity Statistical Summary ...... 6-9 6.2.3.1 Descriptive Statistics-Geomorphic Surface and Proximity Combinations...... 6-9 6.2.3.2 Maximum TEQ Concentration Probability ...... 6-12 6.2.3.3 Significance Tests ...... 6-12 6.3 EXPOSURE UNIT SAMPLING AND EVALUATION ON PRIORITY 1 AND 2 PROPERTIES...... 6-17 6.4 SURFACE WEIGHTED AVERAGE CONCENTRATION ANALYSIS ...... 6-20 6.4.1 Geomorphic Characterization and SWAC Polygons...... 6-20 6.4.1.1 Geomorphic Surface Mapping...... 6-20 6.4.1.2 Soil/Sediment Profiling and Geomorphic Surface Verification...... 6-21 6.4.1.3 Verification Geomorphic/SWAC Polygons...... 6-22 6.4.2 Geomorphic Surface Weighted Concentration Analysis...... 6-22 6.4.2.1 Statistical Evaluation of SWAC Polygons ...... 6-23 6.4.2.2 Current Condition SWAC Process: ...... 6-24

7. 2007 SUPPLEMENTAL ACTIVITIES...... 7-1 7.1 SUPERFUND REMOVAL ACTIONS...... 7-1 7.2 PCAP STEP OUT PROCESS AND DECISION TREE ...... 7-1 7.3 BANK ASSESSMENT ...... 7-2 7.3.1 Baseline Model...... 7-2 7.3.2 Sensitivity Evaluations ...... 7-3 7.3.3 Preliminary Bank Assessment Findings ...... 7-4

8. REFERENCES ...... 8-1

9. GLOSSARY...... 9-1

10. ACRONYMS AND ABBREVIATIONS ...... 10-1

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LIST OF FIGURES (IN TEXT)

FIGURE 1-1 STUDY AREA FIGURE 3-1 DISTRIBUTION OF TEQ CONCENTRATIONS IN THE OVERBANK IN THE UPPER AND MIDDLE TITTABAWASSEE RIVER FIGURE 3-2 DISTRIBUTION OF TEQ CONCENTRATIONS IN THE TRIBUTARIES IN THE UPPER AND MIDDLE TITTABAWASSEE RIVER FIGURE 3-3 DISTRIBUTION OF TEQ CONCENTRATIONS IN-CHANNEL IN THE UPPER AND MIDDLE TITTABAWASSEE RIVER FIGURE 4-1 MAJOR ICE READVANCES DURING THE RETREAT OF THE LAURENTIDE ICE SHEET FIGURE 4-2 SURFACE WATER DRAINAGE AND GLACIAL LAKES ASSOCIATED WITH RETREAT OF THE LAURENTIDE ICE SHEET FIGURE 4-3 TITTABAWASSEE RIVER SOIL PROFILES RELATIVE TO GEOMORPHIC SURFACE FIGURE 4-4 EFDC MODEL USGS FIELD MEASUREMENT STAGE AND DISCHARGE COMPARISONS AT THE TITTABAWASSEE RIVER USGS GAGE FIGURE 4-5 PREDICTED DISCHARGE AS A FUNCTION OF STAGE FOR AVAILABLE TITTABAWASSEE RIVER USGS GAGE RATING CURVES FIGURE 4-6 DETAIL OF LOWER END OF RATING CURVE OF PREDICTED DISCHARGE AS A FUNCTION OF TITTABAWASSEE RIVER USGS GAGE RATING CURVE FIGURE 4-7 GAGE ELEVATION FOR A GIVEN DISCHARGE AS A FUNCTION OF TIME AT THE TITTABAWASSEE RIVER USGS GAGE FIGURE 4-8 LOGJAM ON THE TITTABAWASSEE RIVER FIGURE 4-9 ERODED LANDSCAPE POST LOGGING FIGURE 4-10 ROSGEN STREAM ASSESSMENT LEVEL 1 STREAM TYPES FIGURE 4-11 PLAN VIEW OF TITTABAWASSEE RIVER REGIONS FIGURE 4-12 DENSITY SEPARATION PHOTOMICROGRAPHS

LIST OF FIGURES (IN TEXT) - CONTINUED

FIGURE 5-1 REGION I: “UPSTREAM” (REACHES A-C) IN-CHANNEL DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-2 REGION I: “UPSTREAM” (REACHES A-C) OVERBANK DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-3 REGION I: “UPSTREAM” (REACHES A-C) TRIBUTARY DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-4 REGION II: “NEAR PLANT” (REACHES D-H) IN-CHANNEL DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-5 REGION II: “NEAR PLANT” (REACHES D-H) OVERBANK DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-6 REGION II: “NEAR PLANT” (REACHES D-H) TRIBUTARY DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-7 REGION II: “DOWNSTREAM” (REACHES I-K) IN-CHANNEL DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-8 REGION II: “DOWNSTREAM” (REACHES I-K) OVERBANK DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-9 REGION II: “DOWNSTREAM” (REACHES I-K) TRIBUTARY DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-10 REGION III: “UPPER” (REACHES L-O) IN-CHANNEL DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-11 REGION III: “MIDDLE” (REACHES P-V) IN-CHANNEL DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-12 REGION III: “UPPER” (REACHES L-O) OVERBANK DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-13 REGION III: “UPPER” (REACHES L-O) TRIBUTARY DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-14 REGION III: “MIDDLE” (REACHES P-V) OVERBANK DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-15 REGION III: “MIDDLE” (REACHES P-V) TRIBUTARY DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-16 REGION III: “LOWER” (REACHES W-Y) OVERBANK DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-17 REGION III: “LOWER” (REACHES W-Y) TRIBUTARY DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-18 REGION IV: (REACHES Z-DD) OVERBANK DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-19 REGION IV: (REACHES Z-DD) TRIBUTARY DISTRIBUTION OF TEQ BY LOCATION

LIST OF FIGURES (IN TEXT) - CONTINUED

FIGURE 5-20 REGION V: (REACHES EE-II UPPER) OVERBANK DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-21 REGION V: (REACHES EE-II UPPER) TRIBUTARY DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-22 REGION VI: (REACHES II LOWER -KK) OVERBANK DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-23 REGION VI: (REACHES II LOWER -KK) TRIBUTARY DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-24 REGION VII: (REACHES LL-MM) OVERBANK DISTRIBUTION OF TEQ BY LOCATION FIGURE 5-25 REGION VII: (REACHES LL-MM) TRIBUTARY DISTRIBUTION OF TEQ BY LOCATION

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LIST OF TABLES (IN TEXT)

TABLE 2-1 2007 TITTABAWASSEE RIVER INVESTIGATION REACH DESIGNATIONS AND RIVER REGIONS TABLE 4-1 WATER SURFACE ELEVATION COMPARISONS BETWEEN THE EFDC MODEL AND A STAGE DISCHARGE CURVE BASED ON TITTABAWASSEE RIVER USGS READINGS TABLE 4-2 CALCULATED RECURRENCE INTERVALS FOR THE TOP TWENTY EVENTS IN THE HISTORICAL RECORD OF USGS ANNUAL PEAK FLOW DATA TABLE 4-3 SAGINAW COUNTY TAX CLASS SUMMARY - TITTABAWASSEE RIVER STUDY AREA TABLE 4-4 SUMMARY OF TITTABAWASSEE RIVER REGIONS TABLE 4-5 SUMMARY OF RIVER CLASSIFICATION BY REGION TABLE 4-6 WATERSHED AREAS OF SELECTED TRIBUTARIES DOWNSTREAM OF MIDLAND TABLE 4-7 2006 SECONDARY COI SAMPLE LOCATIONS AND INTERVALS TABLE 4-8 2007 SECONDARY COI SAMPLE LOCATIONS AND INTERVALS TABLE 4-9 GEOCHEMISTRY FRACTION ANALYSIS TABLE 4-10 PARTICLE SIZE FRACTION SUMMARY TABLE 5-1 REGION I: “UPSTREAM” (REACHES A-C) IN-CHANNEL TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-2 REGION I: “UPSTREAM” (REACHES A-C) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-3 REGION II: “NEAR PLANT” (REACHES D-H) IN-CHANNEL TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-4 REGION II: “NEAR PLANT” (REACHES D-H) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-5 REGION II: “DOWNSTREAM” (REACHES I-K) IN-CHANNEL TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-6 REGION II: “DOWNSTREAM” (REACHES I-K) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

LIST OF TABLES (IN TEXT) - CONTINUED

TABLE 5-7 REGION III: “UPPER” (REACHES L-O) IN-CHANNEL TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-8 REGION III: “MIDDLE” (REACHES P-V) IN-CHANNEL TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-9 REGION III: “UPPER” (REACHES L-O) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-10 REGION III: “MIDDLE” (REACHES P-V) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-11 REGION III: “LOWER” (REACHES W-Y) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-12 REGION IV: (REACHES Z-DD) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-13 REGION V: (REACHES EE-II UPPER) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-14 REGION VI: (REACHES II LOWER-KK) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-15 REGION VII: (REACHES LL-PP) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-16 REGION VIII: (REACHES QQ-UU) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION TABLE 5-17 REGION IX: (REACHES VV-YY) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION TABLE 6-1 TYPICAL RELATIONSHIPS BETWEEN DEPTH AND TEQ TABLE 6-2 DESCRIPTIVE STATISTICS FOR ALL GEOMORPHIC SURFACE AND PROXIMITY COMBINATIONS TABLE 6-3 MAXIMUM TEQ PROBABILITY RANGES FOR EACH GEOMORPHIC SURFACE TABLE 6-4 MAXIMUM TEQ STATISTICAL SIGNIFICANCE TEST (ENTIRE MTR) KRUSKAL-WALLIS AND DUNN’S MULTIPLE COMPARISON METHOD GEOMORPHIC SURFACE

LIST OF TABLES (IN TEXT) - CONTINUED

TABLE 6-5 MAXIMUM TEQ STATISTICAL SIGNIFICANCE TEST (ENTIRE MTR) KRUSKAL-WALLIS AND DUNN’S ULTIPLE COMPARISON METHOD PROXIMITY

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LIST OF ATTACHMENTS

ATTACHMENT A RIVER REGIONS AND REACHES FOR THE UPPER, MIDDLE, AND LOWER TITTABAWASSEE RIVER ATTACHMENT B GEOPHYSICAL SURVEY ATTACHMENT B-1 2007 BATHYMETRY CHARTS ATTACHMENT B-2 TECHNICAL MEMORANDUM: CALIBRATION OF IN-CHANNEL GEOPHYSICAL SURVEY RESULTS USING STRATIGRAPHIC AND CONTAMINANT PROFILE ATTACHMENT C TYPICAL TITTABAWASSEE RIVER AND FLOODPLAIN DEPOSITIONAL LANDSCAPE PATTERNS ATTACHMENT D FLOOD EXTENT RESULTS FOR MODELED EVENTS ATTACHMENT E HISTORICAL CHANNEL ALIGNMENT FIGURES ATTACHMENT F 2007 SAMPLING LOCATIONS, TITTABAWASSEE RIVER ATTACHMENT G MIDDLE AND LOWER TITTABAWASSEE RIVER LAND USE TAX CLASSIFICATION FIGURE ATTACHMENT H STREAM CLASSIFICATION REPORT, TITTABAWASSEE RIVER ATTACHMENT I EFDC MODEL OUTPUTS, TITTABAWASSEE RIVER ATTACHMENT J FIGURES DEPICTING FLOOD TIME SERIES AND EFFECTS OF TRIBUTARIES AND WETLANDS, TITTABAWASSEE RIVER ATTACHMENT K 2006 AND 2007 TARGET AND EXTENDED TARGET SECONDARY CONSTITUENTS OF INTEREST, TITTABAWASSEE RIVER ATTACHMENT L ELEVATION OF TITTABAWASSEE RIVER BOTTOM AND GLACIAL TILL BY RIVER STATION ATTACHMENT M STATISTICS IN SUPPORT OF 2007 NATURE AND EXTENT INVESTIGATION – FIGURES AND TABLES, TITTABAWASSEE RIVER ATTACHMENT N SWAC ANALYSIS AND EXPOSURE UNIT EVALUATION, TITTABAWASSEE RIVER ATTACHMENT N-1 SWAC SURFACE TEQ MAPS

LIST OF ATTACHMENTS - CONTINUED

ATTACHMENT N-2 SWAC SURFACE TEQ CALCULATION TABLES ATTACHMENT N-3 EXPOSURE UNIT DESCRIPTIVE STATISTICS ATTACHMENT N-4 EXPOSURE UNIT ADEQUACY OF CHARACTERIZATION ANALYSIS ATTACHMENT O IRA/PCAP DECISION TREE, DATED APRIL 30, 2007 AND IRA/PCAP SAMPLING PLAN, TITTABAWASSEE RIVER ATTACHMENT P BANK STABILITY PRELIMINARY ASSESSMENT, TITTABAWASSEE RIVER ATTACHMENT Q SUMMARY TABLES OF IRA/PCAP STEP-OUT SAMPLES COMPLETED 2007 AND PLANNED FOR 2008, TITTABAWASSEE RIVER ATTACHMENT R SURFACE TEQ FIGURES ATTACHMENT S MAXIMUM TEQ FIGURES ATTACHMENT T TITTABAWASSEE RIVER CROSS-SECTIONS ATTACHMENT U DATA SUMMARY REPORTS, TITTABAWASSEE RIVER ATTACHMENT U-1 2006 AND 2007 SITE CHARACTERIZATION DATA SUMMARY IN-CHANNEL AND OVERBANK ATTACHMENT U-2 2006 AND 2007 SITE CHARACTERIZATION DATA SUMMARY EROSION SCAR ATTACHMENT U-3 2006 AND 2007 PRIMARY CONSTITUENTS OF INTEREST/SECONDARY CONSTITUENTS OF INTEREST DATA SUMMARY ATTACHMENT U-4 2006 AND 2007 PRIMARY CONSTITUENTS OF INTEREST/SECONDARY CONSTITUENTS OF INTEREST SITE POSITIVES SUMMARY ATTACHMENT U-5 2006 AND 2007 PRIMARY CONSTITUENTS OF INTEREST/SECONDARY CONSTITUENTS OF INTEREST SUMMARY STATISTICS

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

1. INTRODUCTION

This GeoMorph® Site Characterization Report Update has been prepared for the Study Area consisting of the river channels and floodplains of the Tittabawassee River (TR) beginning at the confluence of the Tittabawassee and Chippewa Rivers and extending 22 miles downstream to the confluence of the Shiawassee and Tittabawassee Rivers downstream of Green Point Island. This Report has been prepared pursuant to Section 1.1 of the 2007 GeoMorph® Sampling and Analysis Plan (SAP) dated July 2, 2007 (ATS, 2007b). The SAP, approved by the Michigan Department of Environmental Quality (MDEQ) on July 12, 2007, and incorporated herein by reference, describes the sampling strategy, sampling locations, and procedures to determine the horizontal and vertical extent of constituents of interest (COI) contamination in the Study Area. A map showing the location of the Study Area is provided in Figure 1- 1.

The Tittabawassee River has been the focus of several investigations over the past several decades. These studies have primarily been directed toward gaining an understanding of flows and solids transport in the river and its floodplain over a range of flow conditions, and the distribution of contaminants in the river water, sediments, fish, and more recently floodplain soils.

The comprehensive Remedial Investigation Work Plan for the Tittabawassee River and Floodplain Soils dated September 17, 2007 (RIWP) (ATS, 2007a) includes within its scope the investigative work reported in this Site Characterization Report, March 2008 Update (SCR). Findings from the GeoMorph® investigative work on the UTR during the summer and fall of 2006 are reported in the GeoMorph® Pilot Site Characterization Report, dated February 1, 2007, and incorporated herein by reference (ATS, 2007c). This Site Characterization Update Report builds upon the information presented in these prior reports; and includes, in summary form, the information that has become available through February 4, 2008 from the 2007 SAP (ATS, 2007b) investigation activities.

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® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

Figure 1-1. Study Area

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® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

1.1 GEOMORPH® 2007 SAP OBJECTIVES The 2007 SAP provides a detailed description of the approach used to investigate and evaluate the COIs related to historic releases from the Dow Midland Plant that may be present in in-channel sediments along the UTR/MTR and in floodplain soils along the MTR and limited portions of the LTR. The 2007 SAP is an addendum to the UTR GeoMorph® Sampling and Analysis Plan (UTR SAP) (ATS, 2007b) dated July 7, 2006. The 2007 SAP and the updated 2007 Tittabawassee River Project Quality Assurance Project Plan (QAPP) (ATS, 2007d) describe the means and methods for conducting the 2007 GeoMorph® SAP activities.

Objectives of the 2007 investigation include use of high resolution geophysical techniques to locate in-channel erosion and deposition areas in the UTR/MTR and then to focus sampling in these depositional areas, to delineate in-channel deposits containing sediments with elevated concentrations of COI, and to provide a geomorphology-based characterization of overbank and floodplain soils along the MTR.

1.2 GEOMORPH® SITE CHARACTERIZATION UPDATE DELIVERABLES UTR/MTR In-channel Sediment Characterization

• Bathymetry charts of the in-channel river bottom of the UTR/MTR; • Graphical and tabular reports of the identified locations and depths of sediment deposits and layers with elevated concentrations of furans and dioxins; • Cross-sections for in-channel confirmatory sediment poling and core sampling; • Summary tables, surface TEQ and maximum TEQ figures, sediment profile logs, and chemistry/ geologic cross-sections, with all locations described by reach and stationing coordinates; • Evaluation of channel migration over time using digitized channel positions from historical aerial photographs; • Graphical and tabular reports of the identified locations and depths of deposits and layers with elevated secondary constituents of interest (SCOI) concentrations including the depiction of SCOI concentrations on maps and cross-sections.

MTR Overbank and Floodplain Soil Characterization

• Detailed one-foot contour topographic mapping of the MTR project area with mapped geomorphic surfaces; • Historical aerial photographic and anthropogenic analysis for the period of interest; • Detailed geomorphic surface mapping of the MTR;

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

• Summary tables and concentration maps of the overbank soil sampling information with all locations described by reach and stationing coordinates; • Surface TEQ and maximum TEQ figures, soil profile logs, and chemistry geologic cross-sections; • Land use characterization and zoning designations; • Graphical and tabular reports of the identified locations and depths of deposits and layers with elevated SCOI concentrations including the depiction of SCOI concentrations on maps and cross sections; • Surface weighted average concentration (SWAC) analysis; • Sediment geochemistry.

1.3 REPORT ORGANIZATION This Report is organized into the following sections:

Section 1 – Introduction: presents the general objectives, deliverables, and organization for this report.

Section 2 – Background: presents an overview of the Study Area and the 2007 investigation activities, including a summary of field operations and project constraints and limitations.

Section 3 – Tittabawassee River Fluvial Geomorphology Overview: provides an overview of key geomorphologic and fluvial features of the Tittabawassee River that integrates the information necessary to understand how furans, dioxins, and other COI move through the Study Area and come into contact with the environment.

Section 4 – Historical and Existing Condition: presents updated information on Study Area geology and soils, land use and anthropogenic influences, fluvial morphology, hydrodynamic modeling, tributary and wetland influences, constituents of interest, and geochemistry.

Section 5 – GeoMorph® Discussion of Results: provides a synthesis and discussion of the findings from the 2007 investigation activities.

Section 6 – Statistical Evaluation of Geomorphic Investigation Findings: presents the results of the statistical evaluations in support of nature and extent, exposure unit sampling and evaluation of Priority 1 and 2 properties, and the geomorphic surface weighted concentration analysis.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

Section 7 – 2007 Supplemental Activities: presents a summary of 2007 Superfund removal actions, the pilot corrective action program (PCAP) step out process and decision tree, and the preliminary bank stability assessment.

Section 8 – References: lists the references cited in this report.

Section 9 – Glossary: lists terms and related definitions used in this report.

Section 10 – Acronyms and Abbreviations: lists the acronyms and abbreviations used in this report.

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2. BACKGROUND

This section provides a description of the Study Area, a summary of the 2007 Field Operations and Methods, and a brief description of the Soil Classifications and Methodology.

2.1 STUDY AREA OVERVIEW 2.1.1 Tittabawassee River The Tittabawassee River is a tributary to the Saginaw River, draining 2,400 square miles of land in the Saginaw River Watershed. The Tittabawassee River, along with the Shiawassee, Flint, and Cass Rivers, comprise approximately 84 percent of the total Saginaw River drainage area (MDNR, 1988). The Tittabawassee has the largest drainage area covering 39 percent of the total area draining to the Saginaw River.

There are a number of dams on the upstream portion of the Tittabawassee River. In 1918, a hydroelectric dam was constructed near Beaverton. In 1925, dams at Secord, Smallwood, Edenville, and Sanford were constructed to generate hydroelectric power and provide limited storage and flood control for the Cities of Midland and Saginaw. The current operation of the hydroelectric station at Sanford results in water releases from Sanford Dam during peak electricity usage periods to provide peaking power to Consumer’s Energy. Sanford Lake has limited flood storage capacity due to a narrow range of permitted lake levels. The Dow Dam was constructed in 1940 to provide sufficient water depth behind the dam to supply a reliable source of water to Dow. Below the Dow Dam in Midland, the river is free flowing to the confluence with the Shiawassee and Saginaw Rivers.

Various industrial and municipal wastewaters discharge into the Tittabawassee River and its major tributaries, the Salt, Tobacco, and Chippewa Rivers. Past industrial discharges include wastes from chemical, plastics, can manufacturing, and photographic industries (Rossman, et al., 1983). A smaller, significant tributary, the Lingle Drain, located east and south of the Midland Plant, has received both municipal and industrial discharges over time.

2.1.2 2007 Study Area The Study Area for the 2007 investigation activities encompasses the section of the Tittabawassee River commencing at the confluence of the Tittabawassee and Chippewa Rivers and extending approximately 22 miles downstream to the confluence of the Tittabawassee and

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Shiawassee Rivers downstream of Green Point Island. Figure 1-1 provides a depiction of the Study Area.

For communication purposes, a numerical stationing system was established for the River. The numerical stationing was established down the middle of the River at 50 foot intervals. In addition, reach designations and river regions were developed based on valley width and slope; channel sinuosity, pattern, and slope; geomorphic features; and depositional setting. These are summarized in Table 2-1 below and graphically depicted in Attachment A.

Table 2-1. 2007 Tittabawassee River Investigation Reach Designations and River Regions

River Regions and Reach Designation Stationing Reach Length (ft) Upper Tittabawassee River Region I Reach A 0+00 to 12+00 1,200 Reach B 12+00 to 37+50 2,550 Reach C 37+50 to 46+50 900 Reach D 46+50 to 57+50 1,100 Region II Reach E 57+50 to 81+00 2,350 Reach F 81+00 to 115+00 3,400 Reach G 115+00 to 141+00 2,600 Reach H 141+00 to 163+50 2,250 Reach I 163+50 to 185+50 2,200 Reach J 185+50 to 196+50 1,100 Reach K 196+50 to 233+50 3,700 Region III Reach L 233+50 to 261+50 2,800 Reach M 261+50 to 286+00 2,450 Reach N 286+00 to 320+00 3,400 Reach O 320+00 to 335+50 1,550 Middle Tittabawassee River Reach P 335+50 to 358+00 2,250 Reach Q 358+00 to 377+50 1,950 Reach R 377+50 to 401+00 2,350 Reach S 401+00 to 429+00 2,800 Reach T 429+00 to 440+00 1,100 Reach U 440+00 to 464+00 2,400 Reach V 464+00 to 486+00 2,200 Reach W 486+00 to 505+50 1,950 Reach X 505+50 to 529+00 2,350 Reach Y 529+00 to 546+50 1,750 Region IV Reach Z 546+50 to 567+00 2,050 Reach AA 567+00 to 602+50 3,550 Reach BB 602+50 to 632+50 3,000 Reach CC 632+50 to 656+50 2,400 Reach DD 656+50 to 678+00 2,150 Region V Reach EE 678+00 to 694+50 1,650 Reach FF 694+50 to 723+50 2,900 Reach GG 723+50 to 742+50 1,900 Reach HH 742+50 to 770+50 2,800 Reach II (upper) 770+50 to 783+00 1,250 Region VI Reach II (lower) 783+00 to 814+50 3,150

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River Regions and Reach Designation Stationing Reach Length (ft) Reach JJ 814+50 to 853+50 3,900 Reach KK 853+50 to 872+50 1,900 Region VII Reach LL 872+50 to 896+00 2,350 Reach MM 896+00 to 927+00 3,100 Lower Tittabawassee River Reach NN 927+00 to 966+50 3,950 Reach OO 966+50 to 983+50 1,700 Reach PP 983+50 to 1014+50 3,100 Region VIII Reach QQ 1014+50 to 1030+50 1,600 Reach RR 1030+50 to 1051+50 2,100 Reach SS 1051+50 to 1087+50 3,600 Reach TT 1087+50 to 1118+50 3,100 Reach UU 1118+50 to 1145+50 2,700 Region IX Reach VV 1145+50 to 1176+50 3,100 Reach WW 1176+50 to 1218+50 4,200 Reach XX 1218+50 to 1256+00 3,750 Reach YY 1256+00 to 1281+00 2,500

2.2 OVERVIEW OF 2007 INVESTIGATION ACTIVITIES The 2007 investigation activities continued and expanded on the investigative work started in 2006 to understand the nature and extent of historical deposition of the constituents of concern within the Upper, Middle, and portions of the Lower Tittabawassee River and its floodplain. The 2007 activities included sampling and analysis of river sediment and overbank soils within the Upper and Middle TR and review and analysis of the effect of geologic, historic anthropogenic land use, fluvial geomorphologic character, and hydrodynamic influences on sediment movement and deposition within the TR system. An update of historical and current conditions is presented in detail in Section 4. A discussion of results is presented in Section 5 of this report.

2.3 PROJECT CONSTRAINTS AND LIMITATIONS After a diligent effort by Dow to obtain property access along both banks of the Study Area, 35 property owners denied Dow property access for their sampling crews during the 2007 site investigation activities; this number includes two property owners who withdrew access permission to multiple parcels while the field investigation efforts were underway. As a result, there are sections of the Study Area where sampling of the overbank did not occur during the 2007 site investigation. These sections are identified on the graphics presented in this report.

2.4 SUMMARY OF FIELD OPERATIONS AND METHODS The 2007 SAP and 2007 QAPP incorporated herein by reference (ATS, 2007b; ATS, 2007d) provide a thorough description of the 2007 field investigation protocols. The following sections provide an overview of the sample identification, sampling and sample handling procedures, and recordkeeping

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used during the 2007 GeoMorph® Tittabawassee River investigation. Summaries of the geophysical survey and the soil classification methodologies are also included. A summary of 2007 sample locations is provided in Attachment F.

2.4.1 Sample Identification A systematic process was used to identify locations and samples. This process was built upon the numerical river stationing to provide unique labels for each sample location that assists in identifying the sample location when reviewing data. The following sections describe the identification system used for sampling locations and for individual soil and sediment samples, field duplicate samples, and erosion scar samples.

2.4.1.1 Soil and Sediment Sample Locations Each sample location was identified with a unique identification that relates to the location and type of the sample. The structure of these identifiers is described below. Prior to sampling, a Field Location was assigned to each sampling point. After the sample locations were surveyed, the locations were converted to a final Sample Location that incorporated more accurate information regarding the position of the Sample Location.

The unique identifier assigned to each sample location was made up of four sample descriptors in a specific order. Below is a description of the Field Location identification and the Final Location identification.

Field Location Identification

RReach – Station Number - Orientation Sequence Number

Where:

RReach = The first letter R represents the word Reach followed by a one or two letter designation indicating the reach of the Tittabawassee River. For example: RBB represents Reach BB. Presently, reaches within the 2007 study areas of the TR are as follows:

Upper Tittabawassee River (UTR) are in reaches A – O Middle Tittabawassee River (MTR) are in reaches P – MM Lower Tittabawassee River (LTR) are in reaches NN – YY

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Station Number = Approximate location of sample point along longitudinal stationing of Tittabawassee River.

Sample Orientation = a spatial reference locating the sample in relation to the river; designated as N for overbank samples on the northeast side of the river, S for overbank samples on the southwest side of the river, and C for in-channel samples.

Sequence Number = a sequential one or two digit designation of the sampling location along a transect. Note that for overbank (N or S) locations, the sequence number typically starts at the bank and increases as you move away from the bank, with zero being reserved for erosion scar sample locations. For in-channel locations, the sequence number typically begins at the NE bank and increases as you move to the SW channel bank, starting at “1”.

Example: RBB-607+00-S1

The core sample in this example would be collected from Reach BB, the transect is located on or near station 607+00, and the sampling location is the first one from the overbank along the southwest side of the river.

Final Location Identification

After the survey data were collected for a sample location, the Sample Orientation and Sequence Number were modified as described below:

Sample Orientation = The sample orientation is changed as follows

N is changed to NE S is changed to SW C is changed to IC

Sequence Number = The sequence number is changed to be the approximate distance from the river bank to the sample location.

Field Location Example: RBB-607+00-S1

Final Location Example: RBB-607+00-SW4

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2.4.1.2 Soil and Sediment Sample Identification Soil and sediment samples had the depth interval of the sample added to the end of the location identification to create a unique identifier for the samples. In-channel sediment sample depths were measured from the sediment surface and do not include the water depth above the sediments. A soil or sediment sample with a sample depth beginning with a zero indicates the sample was collected from the soil or sediment surface.

Analytical Sample Example: RBB-607+00-SW4-0.0-1.0

The sample in this example would be collected from Reach BB, the transect is located on or near station 607+00, the sample point is located 4 feet southwest of the channel bank, and the sample depth is 0.0 to 1.0 foot below ground surface.

2.4.1.3 Erosion Scar Locations Erosion scars were sampled to confirm the geomorphological or chemical profile at that location. In these cases, erosion scar samples and locations were named according to the nomenclature described above. In the unique Field Location identification, the sequence number “zero” specifically denotes erosion scar sample locations. In the unique Final Location identification, the sample orientation was NE or SW and the distance from channel number was “zero” to specifically denote erosion scar samples. An example of each field and final identifiers for the same location are shown below:

Field Location Identification

RN-290+00-N0

Final Location Identification

RN-290+00-NE0

Final Location Identification (for analytical samples)

RN-290+00-NE0-0.0-1.0

2.4.1.4 Field Duplicates Field duplicate samples were also named according to the nomenclature described above with the addition of the letters “DUP” added as a suffix yielding the following scheme:

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Reach – Station Number – Distance from Channel – Sample Depth – DUP

If a duplicate was collected along with a sample used in the example above, the sample ID would be as follows:

Example: RBB-607+00-SW4-0.0-1.0-DUP

2.4.1.5 Field Blanks Field rinsate blank samples (Field Blanks) were named according to the nomenclature described below:

FB – Equipment – Number Rinsate - Date

Where:

FB = Field Blank

Equipment = apparatus that comes in contact with the sample, is used for more than one sample, and is not fitted with a CAB liner. Examples include the following:

Bowl = Bowl and spoon or trowel

Auger = Bucket auger

Number Rinsate = the chronological number for that particular rinsate sample of the series of rinsates for that type of equipment for that event.

Date = date of collection of the sample.

Example: FB-BOWL-2-072607

The Field Blank in this example was collected from a rinsate of the stainless steel bowl and spoon or trowel used to mix, it was the second “bowl” blank for the event, and it was collected on July 26, 2007.

2.4.2 Sampling Methods In-channel sediment, floodplain, overbank, tributary, and erosion scar soil sampling was conducted following the SOPs in the 2007 Quality Assurance Project Plan (QAPP) (ATS,

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2007d), incorporated herein by reference (2007 QAPP). To address field conditions, an additional sampling method was added for in-channel sampling during the field season. A portion of the in-channel sediment sampling was accomplished using a sonic drill rig mounted on a hovercraft. This enabled field crews to access portions of the river inaccessible by boat. With the sonic drill rig, field crews were able to drill to deeper depths as compared to conventional hand methods.

The sections that follow provide a generalized summary of the sampling methods. In most cases, the in-channel and overbank floodplain soil sampling were conducted along transects perpendicular to the river channel to determine the depositional environment in that sub-reach of the river. Erosion scar sample locations were located along the edge of the river banks. The following procedures were used for in-channel sediment sampling, overbank, tributary, and erosion scar soil sampling during the 2007 GeoMorph® TR investigation.

2.4.2.1 General Sampling Guidelines The following general protocols were employed during all GeoMorph® sample collection activities:

• Prior to arriving at the site, all field equipment was examined to verify that it was in good operating condition. After each use, the sampling equipment was washed with a laboratory grade soap and rinsed with clean, distilled or deionized water; • Field sampling crew members used a new pair of disposable nitrile gloves at each location to be sampled, and changed the nitrile gloves as appropriate when torn or soiled; • Field blank (rinsate) samples were collected once per day when non-dedicated sampling equipment was used to collect samples. Field blanks consisted of distilled water that had been routed through decontaminated sampling equipment and collected into the appropriate containers; • All sampling generated wastes (i.e., gloves, Tyvek, etc.) were collected, containerized, and labeled for proper transport and disposal; • The core liners were labeled at the time of sample collection, using the unique site identifier, sample depth, top of core, and time and date of collection;

2.4.2.2 Sample Locations and Field Positioning In 2007, a permanent Tittabawassee River Geodetic Control Network (TGCN) was established to assure a single consistent coordinate system for all positioning on the Tittabawassee River project. The system consists of permanent physical monuments, with published horizontal and vertical coordinates, spaced at one mile intervals along

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existing road systems that parallel both sides of the Tittabawassee River. All in-channel, floodplain, overbank, tributary, and erosion scar sample locations were marked and/or surveyed during the project to the extent practical using a dual frequency Real-Time Kinematic Global Positioning System (RTK/GPS) with a connection to the Michigan Spatial Reference Network (MSRN). To insure project uniformity in data collection, the GPS equipment was checked against one, or more, of the published TGCN control points at the start and end of each collection session.

Data collected in the field was reviewed for positional compliance, prior to acceptance into the database.

GPS was not used in areas under heavy tree canopy or other significant obstructions where the required project accuracies were unattainable. In the event that GPS could not meet project expectations, traditional surveying methods were used. In these situations, a minimum of two temporary control points were GPS located outside the area of concern. A land survey Total Station verified the relative position and elevation of the control points prior to locating any points of interest.

The horizontal coordinate system was based on the Michigan State Plane Coordinate System of 1983 (MSPCS83 or MSC 83), South Zone, as defined in Michigan Public Act 9 of 1964 and amended on June 14, 1988. The coordinates were derived from geodetic coordinates (latitude and longitude) based on the North American Datum of 1983 (NAD 83) and expressed in international feet. All elevations were based on the North American Vertical Datum of 1988 (NAVD88).

The Standard Operating Procedure, provided in the 2007 QAPP, describes the RTK/GPS and land surveying data generation, collection, quality control, data acceptance, and data reporting procedures. Attachment F contains a summary of sampling locations an associated survey coordinates.

2.4.2.3 In-channel Sediment Sampling The in-channel sediment sampling was conducted from the top of the sediment into the underlying native soil until refusal or until the core encountered the underlying silty-clay or clay till. Sampling was conducted from a hovercraft in shallow water and a boat in deeper water.

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Hovercraft Sampling Methods A hovercraft equipped with a sonic drill rig was used on the river to collect continuous sediment cores. Two sampling methods, a check valve sampler and a sonic macro core sampler, were used in conjunction with the sonic drill rig. Both sampling methods were advanced using the sonic drill rig.

The check valve sampler was fitted with a five foot long, 2.7 inch diameter PVC tube and was used for the top 5 feet of sediment depth. The check valve sampler was advanced slowly from top of sediment to 5 feet or until refusal. The depth interval was recorded and the sampler was extracted from the river sediment. Both ends of the sediment core were immediately capped and taped. The core was then labeled as specified in the SOP from the 2007 QAPP and secured for transport.

For sediment depths greater than 5 feet, a closed piston, sonic macro core sampler was used. The sonic macro core sampler, equipped with a 5 foot, 2.25 inch diameter Polyethylene Terephthalate Glycol (PETG) liner, was slowly advanced to the desired depth. The sampler was opened and advanced an additional 5 feet, or until refusal. The depth interval was recorded and the sampler was then extracted from the river sediment. The PETG liner was extracted from the core barrel, immediately capped, taped, and labeled as specified in the SOP from the 2007 QAPP. This process was repeated until refusal due to clay or other physical obstacle.

All sediment cores were transported to 1111 Washington Street for logging and processing.

Boat Sampling Methods A modified pontoon boat was used on the river to collect continuous sediment cores. Three methods were used to collect sediment cores, depending on sampling depth and conditions: a hand driven check valve sampler, a jack hammer driven macro core barrel sampler, and a slide hammer driven soggy bottom sampler.

The check valve sampler was fitted with a four foot long, 2.75 inch in diameter PVC tube and was used for the top 4 feet of sediment depth. The check valve sampler was advanced slowly from top of sediment to refusal or terminal depth (4 feet). Once the sampler met refusal or terminal depth, the depth interval was recorded and the sampler

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was extracted from the river sediment. Both ends of the sediment core were immediately capped and taped. The core was then labeled as specified in the SOP from the 2007 QAPP and secured for transport.

For sediment depths greater than 4 feet, a closed piston, macro core sampler was used. The macro core sampler, equipped with a four foot, 1.75 inches in diameter PVC liner, was slowly advanced to the desired depth. The sampler was opened and advanced an additional 4 feet, or until refusal. The depth interval was recorded and the sampler was then extracted from the river sediment. The PVC liner was extracted from the core barrel, immediately capped, taped, and labeled as specified in the SOP from the 2007 QAPP. This process was repeated until refusal due to clay or any other physical obstacle.

The soggy bottom sampler operated in the same manner as the macro core sampler. However, the PVC liners used in the soggy bottom sampler were 1.5 inches in diameter. The soggy bottom sampler was hand driven by a slide hammer as opposed to being driven by a gas powered jack hammer as the macro core sampler.

All sediment cores were transported to 1111 Washington Street for logging and processing.

2.4.2.4 Floodplain, Overbank, and Tributary Samples The floodplain, overbank, and tributary sampling was conducted from the top of the soil into the underlying native soil until terminal depth, collapse of borehole, or refusal due to clay fill or other physical obstacle. Hand sampling and direct push methods were used to collect samples.

Hand Sampling Methods Hand sampling methods were used by field crews to develop a greater understanding of the soils and geomorphic features, and to collect samples for quantitative chemical analysis. A 1.1 foot stainless steel sampling tube, equipped with a new acetate liner, was pushed vertically into the ground to a depth of 1.1 feet either by hand or by using a dead- blow hammer. The sampling tube was then extracted and the acetate liner removed. After retrieval of the interval sample (e.g., 0.0-1.1 feet), a bucket auger was used to auger down over this interval allowing passage of a clean tube for sampling the next 1.1 foot interval (e.g. 1.1-2.2 feet, 2.2-3.3 feet, etc.) without interference from the sidewall of the

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previous interval. Measurements were taken after each step to verify interval depths. Sample cores were immediately capped and labeled as specified in the SOP from the 2007 QAPP. This process was repeated to target depth, refusal, or until collapse of the borehole. Used equipment was stored in a plastic container, away from clean equipment, until decontamination.

All soil cores were transported to 1111 Washington Street for logging and processing.

Direct Push Sampling Methods Direct push drilling methods were utilized to reach deeper depths than hand sampling allowed. A four foot long macro core sampling barrel, equipped with a new PVC liner, was advanced into the ground to a depth of approximately 4 feet. The sampling barrel was then extracted from the ground and the PVC liner removed. After retrieval of the sample core interval (e.g., 0.0-4.0 feet), the sampling barrel (decontaminated and equipped with a new PVC liner) was advanced into the next 4 foot interval (e.g. 4.0-8.0 feet, 8.0-12.0 feet, etc.). Measurements were taken after each step to verify interval depths. Sample cores were immediately capped and labeled as specified in the SOP from the 2007 QAPP. This process was repeated to target depth or refusal.

All soil cores were transported to 1111 Washington Street for logging and processing.

Erosion Scar Sampling Erosion scars along the river banks were observed in areas where erosion may be caused by high river velocities and shear stress along the river bank face during storm events, or by undercutting of river banks due to daily river level fluctuations. The erosion scar face represents the soil present in the feature deposit that has not yet eroded but has been disturbed through the erosion process.

Erosion scar sampling was conducted from a ladder that was lowered down the bank and tied off to a tree at the top. Three points along a transect down the face of the erosion scar location were chosen as sampling points. These sampling points were approximately equidistant down the face of the erosion scar, depending on the surface features of the erosion scar. At each sampling point, a 1.1 foot stainless steel sampling tube, equipped with a new acetate liner, was pushed horizontally into the erosion scar to a depth of 1 foot. The sample tube was then extracted from the bank and the acetate liner removed.

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This process was repeated for the remaining two sample points along the erosion scar transect location. The sample cores were immediately capped, labeled, and transported to 1111 Washington Street for processing. The three sample cores from each erosion scar location were composited and sampled for laboratory analysis. Used equipment was stored in a plastic container, away from the clean equipment, until decontamination.

2.4.2.5 Field Equipment Decontamination All non-dedicated sampling equipment used in the sampling process, including the one inch sample tubes, stainless steel bowls and utensils, were decontaminated prior to initial use, between sample intervals, and between sampling locations. Hand augers were decontaminated prior to initial use and between sample locations. Decontamination procedures included washing and scrubbing of the equipment with a laboratory grade soap solution, rinsing with distilled water, and air-drying. Rinsate water was containerized and properly disposed off-site.

2.4.2.6 Soil and Sediment Core Processing Overbank, floodplain, and tributary soil cores were processed and logged according to the SOP for “Core Logging and Processing” provided in Appendix E of the 2007 QAPP. Soil profile descriptions including color (Munsell Color Chart), USCS soil texture, USDA-SCS soil texture, moisture, root content, mottling, clay skin development, and other soil features such as the presence of shell fragments, sand or gravel lenses, iron concretions, wood fragments and odors were recorded electronically on a tablet PC or PC workstation. Soil profile descriptions were completed to the depth of the native soil horizon, as determined by the geomorphologist.

Following completion of the soil profiles, sample intervals or subsamples were selected for chemical analysis based on geomorphic setting and related determination of soil horizons. Although soil cores were obtained in one foot intervals, the sample interval specified for chemical analysis may vary based on the soil horizons encountered. Distinct soil horizons significantly greater than 2 feet were divided into smaller intervals and subsampled for laboratory analysis. Both grab and composite samples were used in determining the extent of impact, depending on the soil horizons encountered and an assessment of the best interval to obtain representative contaminant concentrations.

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2.4.3 Field Documentation and Recordkeeping

2.4.3.1 Field Sample Data Collection Sample data were recorded real-time using a GIS-based system as field crews collected soil cores and samples. GPS coordinates were recorded at all sample locations prior to soil sampling and linked to a base map created using ESRI ArcPad software. At each location, logs of soil cores, sample method, geographic features, sample anomalies, or problems encountered during sample collection were entered into the field computer and tied to the sample location. Data were merged into the database daily. Another data transfer was used to query the database for sample information and incorporate the data into an electronic chain of custody.

Paper back-up forms were used if the computer equipment or database was temporarily inaccessible. Once the electronic systems availability was returned, the data recorded on the paper back-up forms were entered electronically.

Observations, measurements, and sample information were recorded using the field specific computer equipment. Project-specific forms and dropdown lists were custom programmed into the ESRI ArcPad software for electronic data acquisition. All information relevant to sampling activities was recorded on these forms and stored electronically in an Access Database format. Entries on these forms included:

• Names of field crew members • Date and time of soil logging • Date and time of sample collection • Number and volume of samples collected • Location of sampling activity • Sampling method • Date and time of core collection • Sample identification • Soil horizon descriptions • Field measurements • Field observations

Information collected using the electronic forms was reviewed for quality assurance purposes. As appropriate, field quality assurance corrective actions were recorded in the

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Corrective Action section of the database. Electronic field records were chosen as the preferred means for data collection to eliminate transcription errors as field data was transferred to the database. Additionally, the use of standardized forms and drop-down menus provided continuity to the field data across field crews. These records are part of the permanent project file.

2.4.3.2 Chain of Custody, Sample Shipping, and Long-term Storage A designated sample custodian was responsible for the care and custody of samples until they were transferred to the appropriate laboratory. To minimize sample handling errors as few people as possible handled the samples. Chain of custody (COC) records were initiated electronically and populated by the sample custodian. COCs contained the following information:

• Laboratory identification, address, and contact; • Sample custodian’s name, date, and time of shipment; • Method of shipment, carrier, and tracking number (if applicable); • Sample identification, date, and time; • Sample type (composite or grab); • Number of containers; • Priority number; • Applicable analytical method; and • Sample matrix.

When the sample custodian transferred possession of the samples, the COC was signed, dated and the time was noted.

An electronic version of the COC was distributed via email to the appropriate laboratory, designated lab personnel, and the ATS GeoMorph® team senior staff. A signed hard copy version of the COC followed each lot of samples from initial shipment, through the laboratories, and until samples were received at 1111 Washington Street for archiving.

The sample custodian properly packaged the samples for shipment in strong, tamper- proof coolers that were uniquely identified. Individual sample containers were isolated from contamination by placing them in re-sealable, liquid-tight bags. Each sample container was placed into appropriate sized bubble wrap bags to protect against breakage. Ice bags, double bagged to prevent leakage, were added to the coolers to maintain a

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temperature of 4°C. Free space within the cooler was consumed with additional packing materials to prevent breakage. A hard copy of the COC was placed in the appropriate cooler during shipment/delivery. Each cooler was sealed with packing tape and two signed and dated custody seals. Samples sent by commercial carrier included a bill of lading with a unique record number for computer tracking. Tracking numbers were recorded as part of the permanent custody documentation. Upon receipt of the samples at the laboratory, a Sample Receipt Form (SRF) was completed and attached to the chain of custody record. The SRF documented the condition of the chain of custody seal, time of receipt and the laboratory storage location.

All unconsumed samples were shipped, according to the procedure stated above, from the laboratory back to 1111 Washington Street for archiving. Upon receipt, samples were verified against the appropriate COC and the record was signed and closed. Individual sample containers were inspected for integrity and defects. Samples were sorted, cataloged, and referenced according to reach, transect, and COC number. Finally the samples were boxed, labeled with indelible ink, and stored at -10°C.

2.4.4 Geophysical Surveys Prior to implementing the detailed in-channel characterization of the UTR/MTR, a series of pilot geophysical surveys were conducted in Reach O during April 2007 to evaluate geophysical tools and techniques for bathymetric and sub-bottom profiling of Tittabawassee River channel bottom. The geophysical instruments evaluated during the April 2007 work included: multibeam sonar, interferometric sidescan sonar, dual frequency single beam echosounder, and chirp sub-bottom profilers (multiple frequencies). These geophysical techniques provided high resolution detail of river bottom morphology, and located a number of submerged/buried structures and objects.

Bathymetry Multibeam sonar in combination with precision GPS-based positioning provided superior results on the Upper and Middle portions of the Tittabawassee River for high resolution bathymetric mapping when compared to interferometric sidescan sonar and the single beam echosounder. To map the erosional and depositional surfaces in of the UTR and MTR channel bottom, high resolution multibeam bathymetry was collected during the April-June 2007 time period. Representative in-channel sampling locations were selected for Reaches E though V based on bathymetry, sediment thickness, and a review of the channel velocities, shear stresses,

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and streamlines from EFDC modeling outputs. The 2007 bathymetry charts for Reaches A through C and E through V are provided in Attachment B-1. Bathymetric survey of the remaining reaches of the Tittabawassee River will be conducted in 2008, weather and river conditions permitting.

Sub-bottom Profiling Acoustic sub-bottom profile geophysical surveys were conducted concurrently with bathymetric surveys of in-channel deposits in the UTR and upper MTR, from Reach A through V. Sub- bottom profiling can be useful in non-intrusive delineation of sediment deposits consisting of layered materials with different acoustic impedances (e.g., clay, silt, sand, gravel, and bedrock interfaces). Where the layered materials are suitable, it can provide useful information concerning discontinuities and/or irregularities in sediment deposits.

Maximum penetration of acoustic signals used in sub-bottom profiling is generally limited by water depth at the point the acoustical profile is recorded, and by acoustic absorption of the sediment materials themselves. In the 2007 UTR and upper MTR work to date, both factors limited the information that could be obtained from sub-bottom profile surveys. At the river flow rates present during the April-June 2007 survey period, the maximum useful sub-bottom penetration was approximately three to 9 feet. Virtually all sub-bottom information below this depth was obscured by acoustic multiples in the profile and was thereby lost. This maximum theoretical penetration was further reduced because the deposits in the Tittabawassee River are predominantly acoustically “hard” sands and gravels. A detailed summary of sub-bottom profiling work and the calibration of in-channel geophysical survey results using stratigraphic and contaminant profile information is provided in Attachment B-2. In general, while the sub- bottom profiles did indicate heterogeneous, multi-layer sequences in the sub-surface, they did not provide definitive information on the occurrence/location of wood layers. Nor did they provide information on woody material occurring within discrete sand and gravel layers. Further, the sub-bottom profiles did not consistently provide information on the elevation of the basal clay when present beneath acoustically “hard” deposits such as sands and gravels. As a consequence, while the sub-bottom profiles can be useful in selecting sampling locations, they could not be relied upon exclusively to determine sampling locations.

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2.5 SOIL CLASSIFICATION Soil descriptions have been used to support the Tittabawassee River Study Area investigation soil sampling effort and also the development of a conceptual model that explains occurrence of furans and dioxins in the fluvial landscape.

The following overview provides a basis for understanding the soil descriptions used in the GeoMorph® investigation of the TR Study Area. The overview describes basic soil processes and terms relating to soil formation, soil properties, soil horizon descriptive nomenclature, and soil classification. The characteristics of soils in a fluvial landscape are also discussed.

2.5.1 Soil Formation Soils are three-dimensional natural bodies of unconsolidated mineral or organic material on the immediate surface of the earth that are dynamic, having properties derived from the combined effects of climate, topography, and biotic activities, acting on parent material(s) over time (SSSA, 1997; Brady and Weil, 1999).

Soil development, which results in unique soil profiles and characteristic soil horizons, is due to the five soil forming factors including parent material and those factors that influence weathering and soil development, such as climate, biotic activity, topography, and time.

Soils form from parent materials that occur through geologic processes. The nature of parent material influences the properties of soils that are developed including texture and chemical/mineralogical composition.

Parent materials may develop from residual rock, transported material, or accumulated plant debris (organic soils). Residual rock parent material develops in place from the weathering of the underlying bedrock. Parent material may form in one place and be transported and deposited in another location through gravity (colluvial), river systems (fluvial), oceans (marine), lakes (lacustrine), ice (glacial), and wind (eolian) processes.

Climate through precipitation and temperature determines the nature and intensity of parent material weathering and soil development. Biotic activity influences organic matter accumulation, soil aggregate stability, weathering, nutrient cycling, and leaching of iron and aluminum metals. Topography influences runoff, soil water content, solar energy, vegetation, and soluble salt accumulation in semiarid areas. Soil-forming processes including weathering

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and soil profile development require time. The time for a soil to develop may range from less than 40 years to more than 1,000 years depending on the other four soil forming factors.

2.5.2 Soil Profile

2.5.2.1 Soil Genesis Accumulation of parent material through bedrock weathering or deposition of geologic materials may precede, or more commonly, occur simultaneously with the development of soil horizons or layers that are parallel to the soil surface. Soil horizons are soil layers that are different in terms of physical, chemical, and biological properties. The soil profile is the vertical exposure of the sequence of layered soil horizons.

During formation or genesis of a soil the parent material is subjected to soil forming processes that can be classified into four broad categories: transformations, translocations, additions, and losses. Transformations include mineral weathering and organic mater decomposition, by which constituents are modified, totally altered, and synthesized. Translocations are movements of inorganics and organics within the soil profile from one horizon to another (up and/or down) by water and soil organisms. Soil profile additions include input of materials from plant matter (organics), atmospheric dust, or perhaps salts from groundwater. Soil profile losses include leaching of constituents from the profile and erosion of surface materials.

Soil genesis results in the development of unique soil profiles with distinct horizons. The nature of the soil profile and distinguishing horizons from one landscape to another is dependent on the soil forming factors described above.

2.5.2.2 Soil Horizon Nomenclature Horizons with similar characteristics are classified in the United States Department of Agriculture Soil Classification System (USDA-SCS) as master soil horizons. The master soil horizons beginning from the soil surface include O, A, E, B, and C horizons. Soils may include one or more of the master horizons. More mature soils often have more and better developed horizons within the soil profile as compared to recent soils with fewer horizons and less horizon development.

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The O horizon is a predominantly organic layer consisting of plant and/or animal mass that is in various stages of decomposition and occurs above a mineral soil or in an organic soil (e.g. wetland soil).

The A horizon is typically the upper mineral horizon (unless buried) that contains sufficient partially decomposed organic matter to impart a darker color as compared to lower horizons. A horizons often have granular structure due to the binding from soil organic compounds.

The E horizon is characterized as a layer of maximum leaching or eluviation. Clay and iron/aluminum oxides are typically leached from this layer and transported downward to the lower horizon(s). The E horizon is typically lighter in color from the horizon above or below and is often composed of more resistant materials such as quartz.

The B horizon is often a horizon of accumulation, typically by illuviation from above. The B horizon has been subjected to sufficient change so that the structure of the parent material is not discernable. The materials of accumulation often include those leached from the overlaying A or E horizons including silicate clays and iron/aluminum oxides.

The C horizon is below the zone of greatest biological activity and has not been sufficiently altered by soil genesis to be classified as a B horizon. The C horizon may include some of the structural characteristics of the parent material.

2.5.3 Soil Physical & Mineralogical Properties Soils are typically characterized based on physical, chemical, and mineralogical properties. Vertical core samples or the vertical exposure of excavated pits are often characterized using physical parameters to define soil horizons of a soil profile.

The following describes the parameters that were used in this investigation to describe soil based on the USDA-SCS:

Color Munsell color charts are used to describe soil color. Soil color provides insights into dominant soil forming processes since color is often derived from the soil coatings of organic matter (dark), iron oxides (yellow, red, brown), and salts (white, in semiarid areas). Soils subject to periodic wet periods or fluctuating water tables typically have mottles or blotches (red, yellow, brown) dispersed within the dominant soil color. Soils that are saturated for extended periods result in reduction of iron oxides to a gleyed color (grey, bluish, gray-green). Soil color is used,

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often along with other soil properties, to differentiate soil horizon boundaries and reduction- oxidation status due to soil water condition (e.g. fluctuating water table, perched water, saturated)

Texture Soil texture, the relative proportion of particle size classes (sand, silt, clay), is typically determined in the field using the 'feel method'. Soil texture classes for this investigation were defined using the USDA-SCS and also the Unified Soil Classification System. The soil textures for a range of USDA-SCS soil textural classes were determined using the hydrometer method. Samples of these laboratory determined textures (sand, sandy loam, loamy sand, loam, sandy clay loam, and clay loam) were maintained on site to support (calibrate) textural determinations of soil using the 'feel method'.

Structure Soil structure or the arrangement of primary soil particles into cohesive aggregates or peds influences soil porosity, aeration, permeability, and erosion potential. The four principal soil structure shapes, and examples of each USDA-SCS type include spheroidal (granular), platy (platy), prismlike (prismatic), and blocklike (subangular blocky). Structure is also useful for horizon differentiation since surface A horizons often have granular structure and subsurface horizons (B, C) often do not have granular structure.

Rupture Resistance Rupture resistance using the USDA-SCS describes the resistance of a soil ped to mechanical stress or deformation at a dry or moist condition. Rupture resistance was determined by squeezing the soil ped between the thumb and forefinger. Examples of rupture resistance for a moist soil from less to more resistance are: loose, very friable, friable, firm, very firm, and extremely firm. The rupture resistance may be used along with other parameters to indirectly evaluate soil strength, which influences potential for mass failure.

Plasticity Plasticity characterizes the degree to which moist to near wet reworked soil can be permanently deformed without rupturing. In this investigation, the evaluation was done by hand forming or rolling the thinnest possible wire at the most optimum soil water content. Examples of soil plasticity from less to more plastic soils are: non-plastic, slightly plastic, moderately plastic, and very plastic. The soil plasticity is typically dependent on soil clay content with higher clay content resulting in a more plastic soil. Plasticity influences soil erodibility and compactibility.

Water Content The soil water content (dry, moist wet) provides information that may reflect soil permeability, soil water storage capability, and relationship to groundwater.

2.5.4 Soil Classification In the United States, soils are classified and mapped by the USDA-Natural Resource Conservation Service (NRCS) based on soil properties and characteristic horizons. County Soil Survey Reports are generally available through county USDA-NRCS offices. The benefit of the report is dependent on the mapping scale that is required to achieve project objectives.

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Although the soil survey reports were helpful for predicting the soil profiles and horizon types that would be encountered during the TR investigation, the USDA-NRCS mapping scale was not sufficient to capture all soil types and variability within the fluvial landscape.

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3. TITTABAWASSEE RIVER FLUVIAL GEOMORPHOLOGY OVERVIEW

This section provides an overview of flows and solids transport in the Tittabawassee River and floodplain, and explains how natural and anthropogenic forces have brought about the characteristic fluvial geomorphologic land forms within the Tittabawassee River bed and its floodplain. These findings are discussed in more detail in Section 4. Section 5 relates the extent and distribution of the primary constituents of interest, as characterized in this investigation, to these characteristic land forms.

The primary constituents of interest, furans and dioxins, are hydrophobic organics that tend to strongly partition to solids. Where present in the Tittabawassee River and floodplain, these chemicals are often associated with particles of graphitic carbon as a result of the chlorination of coal tar binders in graphitic electrodes used in historic brine electrolysis production at the Dow Midland plant. An understanding of the movement and deposition of solids over time within the dynamic Tittabawassee River fluvial system is therefore essential to understanding the movement and distribution of the primary constituents of interest.

3.1 TITTABAWASSEE RIVER HYDROLOGY The Tittabawassee River is a river of annual variation, with energetics that change substantially throughout the year. For much of the time, the Tittabawassee River is a relatively low-energy system; typical conditions include a median flow of about 1,000 cfs, an average depth ranging from about one to 8 feet, and average water surface width extending from about 200 to 400 feet. High-energy events channel flows from an extensive river watershed that drains a large portion of Michigan’s lower peninsula through a narrow channel and floodplain, extending from Midland to the Shiawassee River confluence. These high flows are most often experienced during major rain events and periods of snow melt throughout late winter, spring, and fall. For example, a 1-year storm event results in an average flow of about 10,000 cfs, which is approximately 10 times median flow. Water depths during a 1-year event increase to as much as 16 feet, and the maximum extent of the water surface widens to about 3000 feet in portions of the floodplain. Flows as high as 38,700 cfs have been recorded, almost 40 times median flow.

Flows in the Tittabawassee are so variable because there is little storage capacity within the river system to buffer the impact of flooding. Although there are several dams along the river, these dams are “run of the river” and do not create flow buffering impoundments of significant volume, relative to peak flows.

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During high flow events, the ability of the river system to erode and move solid particles is greatest. As flows recede, and during the intervening low-flow periods, particles in suspension can settle and form new deposits. Much of the characteristic geomorphic features of Tittabawassee River and floodplain have formed as result of these alternating high- and low-energy environments.

3.2 WATERSHED AND TRIBUTARIES Most of the watershed area (approximately 96 percent) is located upstream of Midland. It is drained by three major tributaries, the Pine, Chippewa, and Tobacco Rivers, along with the mainstem of the Tittabawassee River. Downstream of Midland, tributaries are much smaller and the river is confined within a narrow floodplain, flanked by escarpments.

The tributaries deliver not only flows but also watershed solids to the river and floodplain, affecting the erosional and depositional characteristics of the river. The sediment load carried by tributaries from upland areas to the river is especially pronounced during and following storm events, and these events also provide the energy to erode and move sediment, in spots where shear stress applied to bed and banks is greatest.

Deposition of new solids, and movement of solids already present in the stream bed, result in changes to channel width and depth. Where event velocity is greatest, there is potential for erosion of the banks and the deepening and/or movement of the incised channel known as the thalweg. At higher flows, the river overtops its banks and enters the floodplain. Velocities are lower as flow overtops the banks and spreads out across the floodplain, so that solids deposit along the banks and into the floodplain. New bank features and the filling in of the channel and thalweg occur as the event recedes and flow and velocity decrease.

Below Midland, smaller tributaries deliver limited flow and solids to river. They also provide channels/conduits by which flood flows can reach the floodplain, carrying sediment load from the river into upland areas adjacent to the tributary. As low points in floodplain topography, tributaries provide deeper areas for solids-laden river flows to lose velocity, decreasing their ability to carry solids. Some tributaries also create a backwater effect occurring early in flood events, providing a channel through nearshore levees and allowing relatively still waters to inundate floodplain areas adjacent to the channel.

3.3 ANTHROPOGENIC INFLUENCES In addition to climate-driven natural dynamics, the river system also has been profoundly affected by impacts of European settlement and uses of watershed. Michigan was extensively lumbered in the

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late 19th Century, and the clear-cutting practices that were employed caused catastrophic deforestation, stripping land of its vegetative cover. Use of the river for log transport to sawmills loaded the river with lumber and scoured its banks. Lumbering activity also sent loads of woody debris into the river. Where layers of woody material are found in the sediment bed, they may provide a way to date sediments located above and below, relative to the beginning and end of the era of peak lumbering.

Agricultural and industrial development of the Midland area added to this transformation of the landscape, changing both flood frequencies and solids loads to the Tittabawassee River. These changes affected both erosion and deposition, contributing to changes in river channel and floodplain land forms. Higher runoff volumes increased the energy applied to the River’s bed and banks. The higher flows also increased the River’s ability to transport solids along the river bed and into the floodplain. Larger loads of solids were also delivered from the upstream watershed to the river below Midland. Channel and floodplain topographic features reflect this legacy of increased flows and solids loads.

Extractive activities, such as sand mining and clay extraction in the overbank areas, have also had an impact on sediment load and transport. In certain locations, these floodplain disturbances may have significantly modified deposition patterns and distribution of constituents of interest by creating low spots in the over bank that modify overland flow and sediment transport patterns, and by increasing sediment load to tributaries and the river causing changes to the river channel.

Other anthropogenic changes influencing the shape of the river and floodplain include dams, bridges, bank armoring, earth work, man-made tributaries, and outfall structures. Each of these features has affected river and floodplain hydrology, sediment transport, and geomorphology.

3.4 CHARACTERISTIC DEPOSITIONAL FEATURES OF THE UPPER AND MIDDLE TITTABAWASSEE RIVER AND FLOODPLAIN The extent, magnitude, frequency, and duration of the river’s responses to natural and anthropogenic influences were analyzed through a systematic, quantitative assessment. This assessment provides the ability to separate natural and anthropogenic influences and to predict how the river will reach an equilibrium state through a balance of energy and sediment supply. To assist in this assessment the Tittabawassee River was classified into nine distinct River Regions based on valley type, width and slope, and channel sinuosity, pattern, profile, and cross-sectional characteristics.

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There are two general types of deposition within the Tittabawassee River system: lateral accretion and vertical accretion. Lateral accretion occurs cross-wise to the river flow as a result of eroding banks that mobilize alluvium (detritus) into the channel flow which carries this material downstream and deposits it in point bars (crescent shaped ridges of sand and gravel that develop on the inside of a growing meander bend). This type of accretion tends to consist of mixed coarse-grain materials.

Vertical accretion occurs when the stream floods and is the process underlying development of natural levees. This type of accretion generally tends to consist of finer-grained materials, with the coarsest-grained materials located nearer to the channel and progressively finer-grained materials depositing farther away from the channel.

3.4.1 Floodplain Deposition Highly variable Tittabawassee River flows, combined with regional geology, river geomorphology and topography, soil formation analysis, and the legacy of past lumbering, agricultural, and extractive practices, have contributed to identification of five typical floodplain depositional landscape features in the Upper and Middle Tittabawassee River:

• levees; • ridge and swale complexes; • crevasse splays; • deltaic overbank deposition areas; and • tributary and wetland deposition areas.

Each of these features was formed by solids delivered by the river, carried over bank, and deposited onto the floodplain. Each feature was created by a distinct set of local hydrological conditions, leading to deposition of different soils types of varying thicknesses.

Soil analyses have been instrumental in identifying these recurring features along the floodplain. Primary to this analysis is an understanding of the maturity and thickness of soil formation processes, which can provide insight into the fluvial deposition and movement of soils within the floodplain. Soil formation analysis is based on parent material and those factors that influence weathering and soil development such as climate, biotic activity, topography, and time. Relative thicknesses of soils of different types in locations around the floodplain are strong indicators of different patterns of deposition. In particular, occurrences and thicknesses

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of the following layers have been critical in identifying geomorphological surfaces of different types:

• litter layer (Type O horizon); • topsoil (Type A horizon); • illuivial horizon (Type B horizon); • and weathered parent material (Type C horizon).

Figure 3-1 presents the distribution of TEQ concentrations in the overbank of the Upper and Middle Tittabawassee River based on the results of the 2006 and 2007 investigations. Many of the elevated concentrations were found buried in the natural levees above a woody debris layer. Where isolated elevated concentrations of constituents of interest were found distant from the natural levees, their presence was usually found in one of four additional depositional landscapes typical of the Upper and Middle Tittabawassee River.

Figure 3-1.

3.4.1.1 Levees (Natural and Historic Natural Levees) Levees are elongated, raised ridges formed at the channel-floodplain boundary during overbank flow events. As the river overflows its banks, the flood water moving from the

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channel to the floodplain encounters a loss of momentum. Velocity differential results in the preferential deposition of material at the edge of the channel. As sediment-laden waters spill over the channel banks, coarser solids deposit near the former bank. In this way, natural levees are built up in parallel to the river channel, to a level higher than the outer floodplain. Levee heights are scaled to channel size and their presence suggests relative channel planform stability.

The Tittabawassee floodplain includes a series of parallel levees. The presence of multiple levees in this River system represents the changes in river dynamics as a result of the narrowing of the channel due to increased sediment load following the logging and early agricultural development era. In this report, the most recent levees found adjacent to the river channel are called “natural levees” and those that are found farther from the channel are called “historic natural levees” representing the pre-industrial era.

Attachment C provides a figure showing a typical configuration of levees, with the historic natural levee located just beyond the natural levee along an outer bend of the river. As the profile inset shows, both levees are raised ridges with the elevation of the floodplain dropping with distance away from the river.

3.4.1.2 Ridge and Swale Complexes Similar processes of solids deposition during flood events at a succession of distances from the river channel have led to the formation of parallel ridges and swales. Typically, ridge and swale complexes are comprised of scroll bars with each scroll representing the former location of a point bar. The resulting ridge and swale complexes consist of higher ridges separated by topographic lows or swales. These are a common occurrence in meandering river system. Attachment C provides a figure showing a typical set of ridges and swales. Similar to levees, the ridge deposits contain relatively coarse soils.

3.4.1.3 Crevasse Splays Crevasse splays are floodplain deposits typically comprised of sandy or silty material, formed by floodwaters that have breached the levees. The floodwaters deposit sediment when velocity slows as it moves across the floodplain. Splays arise in locations where the channel is sinuous and floodwaters take a more direct route when they overtop the banks, scattering course solids near and at an angle to the former bank, with finer materials deposited farther from the channel.

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Attachment C provides a figure showing a typical splay (aerial photo, TIN topography, geomorphic surface map, and geologic cross-section). The aerial photograph of this splay clearly shows lighter-colored surficial sand deposits spread across the bank in a direction of overbank event flow. The splay shown in the figure extends well into the floodplain, and has appreciable thickness as evident in the geologic profile.

3.4.1.4 Deltaic Overbank Deposition Areas Like splays, these are deposits formed where floodwaters overtop banks at an angle to flow direction. These are broad areas of vertical accretion. As the flood waters move across the overbank plain, the decreasing velocity of the flow results in a progressive sorting of deposits from coarse to fine as flow moves farther away from the channel.

Attachment C provides a figure showing a typical deltaic overbank deposition area (aerial photo, TIN topography, geomorphic surface map, and geologic cross-section). The deltaic overbank area shown in the figure extends well into the floodplain, and has resulted in a relatively large deposit extending away from the channel. Deltaic overbank soils are generally finer than levee and splay soils, reflecting a greater transport distance from the channel.

3.4.1.5 Tributary and Wetland Deposition Areas As floodwaters rise, they can breach banks at tributaries and begin to fill portions of the floodplain. The bottoms of tributaries and wetlands in the floodplain generally have the lowest elevations, so that floodwaters in these locations are the deepest and slowest. In the early stages of floods, tributaries and wetlands can even be stagnant backwaters. In either case, the effect is the creation of preferential areas of deposition for solids suspended in floodwaters.

Attachment C provides a figure showing a typical course of a major flood event in Reaches FF to II, which includes a lowland area around a former oxbow. The snapshots simulate the inundation of this area during the first few days of an 8-year event in 2004. Subsequent snapshots show relatively low simulated velocities in and around the oxbow throughout the event. Tributary and wetland area deposits are relatively fine, reflecting the low energy of flows in these areas.

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Figure 3-2 presents the distribution of TEQ concentrations by number of locations in the tributaries of the Upper and Middle Tittabawassee River based on the 2006 and 2007 investigations.

Figure 3-2

3.4.2 In-channel Features Like the floodplain, the sediment bed is subject to both high- and low-energy flow regimes. Much of the year is characterized by lower flows and stream velocities. During this time the bed experiences low velocities and shear stresses, so that solids delivered from upstream can deposit, especially in eddies and deep spots where velocity is lowest, including inner bends. Higher flows during events of intermediate size increase stream velocities, shear stresses, and the potential for erosion, especially where velocities are greatest, such as along outer bends. At a certain flow rate, the channel banks fill, and any additional flow is spread over the banks and into the floodplain. This spreading of higher flows across the floodplain attenuates further increases in shear stress experienced by the bed and banks.

Erosion of the upstream watershed delivers a mix of finer and coarser solids to the Tittabawassee River below Midland. Finer sediments require less energy to keep in suspension, tending to remain in suspension except at the lower stream velocities. For this reason, in

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general, the finest sediments (such as silts and clays) are found deposited in areas experiencing the lowest velocities and shear stresses, while only coarser sediments(such as sand and gravel) can deposit and remain in place in higher energy areas. Because the Tittabawassee River regularly experiences high flow events, with associated velocities and sheer stresses, coarse sediments predominate with a high proportion of sand, and lesser proportion of silt and clay. Because of the legacy of lumbering in the watershed and use of the river to transport logs to sawmills on the Saginaw, the sediment bed also includes layers of woody debris, as well as buried logs.

Figure 3-3 presents the distribution of TEQ concentrations by in-channel locations in the Upper and Middle Tittabawassee River based on the 2006 and 2007 investigations.

Figure 3-3

3.4.2.1 Buried Deposits Where the river is sinuous, its velocity is generally greater along outer bends than inner bends, making inner bends more likely places to find deposits. These inner bend deposits, known as point bars, in combination with erosion of the opposite bank, can result in a gradual shifting of the channel from the inner toward the outer bend. Nearby tributaries can also contribute to point bars by delivering solids to the river during rain

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events. These loads of solids from a tributary to the river may deposit at the first low- velocity location they encounter in the river, such as an inner bend.

As is the case in the floodplain, buried wood is a good indicator of deposits created during the logging era. Wood is present in sediments in many locations, and can assist in differentiating 20th Century deposits from those created at an earlier time.

3.4.2.2 Alleviated Deposit Where flow is restricted, such as upstream of bridge abutments, the channel depth can be increased and its velocity reduced. Sediment that accumulates at these locations due to the reduced velocity is called an alleviated deposit. The more recently the anthropogenic modification to flow, the more surficial is the resulting deposit.

3.4.2.3 Riffle and Pool Riffle and pool sequences are commonly found in rivers with shallow bed slopes, such as the Upper and Middle Tittabawassee River. Riffles are shallow areas with steeply sloped facets (i.e. microscale sediment formations), while pools are deep with shallow-sloped facets. Riffles and pools typically occur at relatively constant spacing in response to dynamic variations in velocity and shear stress. Attachment C provides a figure showing a typical Tittabawassee River riffle and pool sequence, with pools scoured out along successive outer bends and riffles populating the stream in between the two pools.

Changes in flows and solids loads can bring about changes in the riffle and pool sequence. In particular, higher flows can scour out new pool areas, and higher solids loads during storms can fill in existing pools with flood debris and support formation of new riffles. Thus, it is possible that high flows and solids loads associated with lumbering and subsequent agricultural and industrial development have led to long-term pattern modification in riffle and pool sequences.

3.4.2.4 Erosional Features In general, erosion is greatest in areas of the river where velocities and shear stresses are highest. The coarsest materials are found in these areas. When the river is contained within its banks, this occurs in shallower areas and along outer bends. High shear stresses along outer bends during bankfull conditions can also give rise to bank instability. At high flows, when banks are overtopped, the tops of levees generally

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experience very high shear stresses, and solids eroded from the levees and other suspended loads can be delivered to the floodplain in the predominant direction of flow. At high flow, the stream paths along which suspended solids move are more direct and less sinuous than at low flow, because flow can follow the predominant fall direction with less constraint imposed by the banks.

The erodibility of the stream bed and banks is attenuated during high-flow events by a phenomenon known as “armoring”. High shear stresses sort surficial grains, resuspending fines while leaving coarser grains in place. This process increases the surface sediment layer’s resistance to erosion. Coarse grains can also be delivered by a process of rolling and sliding of particles along the bed, known as “bed load”. Coarse particles delivered as bed load may come to rest when a low spot is encountered, such as where fines have been eroded by rising flows. In this way, bed load enhances armoring, by providing additional coarse particles to replace resuspended fines and reduce erodibility.

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4. HISTORICAL AND EXISTING CONDITIONS

The following sections provide updated information on historical and current conditions within the Study Area with an emphasis on the Middle Tittabawassee River based on the 2007 analysis of geology and soils, hydrology, land use including anthropogenic influences, river system morphology, hydrodynamic modeling, tributary and wetland hydrodynamic influences, and constituents of interest, and geochemistry.

4.1 GEOLOGY AND SOILS 4.1.1 Glacial and Post-Glacial History During the Pleistocene epoch, glaciers intermittently covered Michigan starting around 780,000 years before present (780 ka; 1 ka equal 1,000 years). Along the Tittabawassee River, the glaciers advanced and receded multiple times and left a thick (typically, >100 feet) sequence of unconsolidated materials deposited on top of the bedrock. The current landforms near Midland and Saginaw are a mixture of landforms left during the glacial period and landforms created after the recession of the glaciers by re-working of these materials. In addition, the unique shape of the Tittabawassee River watershed, with a very narrow watershed width between Midland and Saginaw, is also influenced by the glacial land forms. This discussion presents the major periods that have affected the land forms and the sequence of unconsolidated materials underlying the watershed and river.

4.1.1.1 Ice Cover Thick continental glaciers spread across Canada and advanced into, and retreated from, the Midland/Saginaw area during the Pleistocene glaciation. These glaciers advanced into the Midland/Saginaw area starting as early as 780 ka, with major ice sheets advancing and retreating on approximately 100,000 year cycles (Larson and Schaetzl, 2001). The most recent periods of glaciation are the Illinoian (302 ka to 132 ka) and the Wisconsin (79 ka to 10 ka) (Larson and Schaetzl, 2001).

The ice sheets were centered in Canada and had a thickness estimated at 2,500 m to 3,000 m (Larson and Schaetzl, 2001). The ice sheets thinned away from the center, and over the Great Lakes watershed, the ice is estimated to have exceeded 750 m (Larson and Schaetzl, 2001). The thick ice sheet had a significant mass

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that compressed and ground underlying sediment and bedrock. This mass also caused the crust of the earth to subside slightly in response to the additional mass. The ice was thickest north and northeast of Midland and Saginaw, causing more subsidence to the north and northeast of the study area and less subsidence south and southwest of the study area.

During the glacial advance, a till was laid down that is observed under the sediments in the Tittabawassee River and floodplain. This till was compressed by the weight of the Wisconsin glaciers’ ice sheets resulting in the very stiff glacial till. The till observed in the Study Area is usually a sandy clay loam with less than 15 percent subangular embedded pea size gravel. The till matrix varies somewhat with some samples showing a matrix of silty clay loam, clay loam, loamy sand, or sandy loam. The till can be observed by walking along the upland scarp along Saginaw Road on the northeast bank in Reach I. The till also contains localized areas of other grain sizes, such as sand units, that have also been compressed by the thick ice sheet.

4.1.1.2 Formation of the Port Huron End Moraine The Laurentide ice sheet extended across Michigan during the Wisconsin glaciation between 79 and 10 ka. The retreat of the Laurentide ice sheet was interrupted by major re-advances of the ice that reached their maximum extent at intervals of approximately 15.5, 13.0, 11.8, and 10.0 ka. (Figure 4-1 depicts these glacial advances and retreats.) The Saginaw Lobe re-advance of 15.5 ka covered the entire area around Midland and Saginaw. During the readvance that peaked at 13.0 ka, the Saginaw Lobe advanced inland from the Saginaw Bay depression as far as Saginaw and just east of Midland, Michigan.

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Figure 4-1. Major Ice Readvances during the Retreat of the Laurentide Ice Sheet. (Larson and Schaetzl, 2001)

The farthest extent of the glacier at 13.0 ka created a terminal moraine referred to as the Outer Port Huron end moraine. The Outer Port Huron end moraine runs parallel to, and just east of the Tittabawassee River valley along much of the distance from Midland to Saginaw. This moraine system continues north of Midland where it can be traced across the northern part of the lower peninsula of Michigan and continues around to the southeast and east beyond Saginaw where it can be traced into the Ontario basin (Larson and Schaetzl, 2001; Dorr and Eschman, 1970). This moraine forms a still visible linear ridge that extends toward the north northwest from Saginaw past the east side of Midland (Farrand and Bell, 1982; USGS, 1973a-f; USGS, 1975a-b). This terminal moraine influenced the drainage pattern for the Tittabawassee River water shed.

The later re-advances of the Laurentide ice sheet at 11.8 and 10.0 ka did not extend into the Midland/Saginaw area (Larson and Schaetzl, 2001; Dorr and Eschman, 1970).

4.1.1.3 Inland Lakes The elevations of the surface water in lakes that affect the study area were significantly changed by the glacial and post-glacial processes. Surface water levels in the Lake Huron basin were controlled by the elevation of outlets or

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spillways for this drainage system. When the Laurentide ice sheet advanced into Michigan, the ice blocked many of the spillways, and this blockage caused water to back-up and find higher spillways out of the drainage basin. As the ice sheet retreated, removal of the ice from these spillways initially exposed lower outlets, allowing lake levels to decline significantly. After the glacial ice was gone, isostatic rebound caused the land surface and the elevation of these outlets to rise. With this isostatic rebound the water levels in the Great Lakes rose again and eventually found alternate spillways that did not have significant rebound. The major surface water bodies and drainage systems are presented in Figure 4-2 and discussed further below.

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Figure 4-2. Surface Water Drainage and Glacial Lakes associated with the Retreat of the Laurentide Ice Sheet. (Larson and Schaetzl, 2001)

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During the ice retreat following the readvance of 15.5 ka, the ice sheet blocked the northern drainage of the current Saginaw Bay watershed. Glacial melt water formed glacial Lake Arkona that flowed west through the glacial Maple-Grand River Valley and into glacial Lake Chicago (in the southern end of the current Lake Michigan basin) and then into the Mississippi River watershed (Larson and Schaetzl, 2001; Farrand, 1988). The elevation of glacial Lake Arkona was controlled by the outlet into the glacial Maple-Grand River valley near Maple Rapids, Michigan. As this outlet or spillway was eroded by the drainage through the glacial Maple-Grand River, the level of the glacial lake lowered, resulting in successive beach ridges, still visible in the Saginaw Bay region. Glacial Lake Arkona extended up against the Laurentide ice sheet as the ice sheet retreated. Eventually, the retreating ice exposed a lower outlet in Ontario, and glacial Lake Arkona was drained to a water level closer to the current Saginaw Bay (Larson and Schaetzl, 2001; Dorr and Eschman, 1970).

During the re-advance of the Laurentide ice sheet and the creation of the Port Huron end moraine (approximately 13 ka), the lower drainage outlet through Canada was again blocked by ice, and waters backed up to form glacial Lake Saginaw just west of the Tittabawassee River between Midland and Saginaw. Glacial Lake Saginaw also drained down the glacial Maple-Grand River Valley through an outlet near Maple Rapids, Michigan (Larson and Schaetzl, 2001; Farrand, 1988). After down cutting of the outlet near Maple Rapids, the lake level dropped and formed glacial Lake Warren, continuing to occupy the area west of the Port Huron end moraine (Larson and Schaetzl, 2001; Farrand, 1988; Dorr and Eschman, 1970).

The glacial lakes that covered the area between and east of Midland and Saginaw (Arkona, Saginaw, and Warren) received fine sands, silts and clays from the melting glaciers, resulting in the flat silty-clay loam that is used as productive farmland east of the Study Area. This old lakebed is characterized by a low slope and is currently drained by incised ditches to promote the agricultural use of the land. These lake bed sediments are soft and have been removed from the current

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Tittabawassee River flood path between the upland scarps where the river has eroded down into the underlying stiff glacial till.

The inland lake had sandy shorelines that are still present as beach ridges that arc across the Saginaw Bay region. These shorelines consist of well sorted sands from the old beach and dune complexes that are present on top of the lake bed clay at the transition out of the flat farmed areas. North of the Study Area, these beach ridges, representing successive glacial lake shorelines, are common (Farrand and Bell, 1982). One major series of shorelines runs in a curved arc that approaches the Tittabawassee River at Reaches M and N, near the location of the large sand ridge mapped as an Upland Surface within the river valley from Station 286+00 to Station 312+00 on the northeast side of the river.

4.1.1.4 Ice Retreat and Lower Lake Levels As the Laurentide ice sheet retreated, leaving the Port Huron end moraine, lower outlets for the current Lake Huron basin were exposed. Initially waters flowed through a lower outlet near Buffalo, New York and the lake west of the Port Huron Moraine was drained (Larson and Schaetzl, 2001). By 12.5 ka, the outlet for Lake Erie at Niagara Falls, New York was ice free and the water drained along the current Detroit River through Lake Erie (Larson and Schaetzl, 2001). Eventually, a still lower outlet near Trenton, Canada was exposed, and the water level in the drainage basin lowered further to a level significantly below the current water level in Saginaw Bay. With the readvances of the ice sheet in 11.8 and 10.0 ka, the water level in the current Lake Huron basin rose and fell as ice again filled and closed the outlets and then retreated from and opened the outlets. It is not clear if the glacial lakes that formed at these later times extend into the Port Huron end moraine (Larson and Schaetzl, 2001).

The retreat of the Laurentide ice sheet opened successively lower outlets, and the glacial lakes and post-glacial lakes never again extended inland as far as the Port Huron end moraine (Larson and Schaetzl, 2001; Farrand, 1988). As the ice retreated further into Canada, a much lower drainage outlet for the area was exposed. The lowest outlet was through the Ottawa River in Canada, when the drainage of the current Lake Huron basin completely bypassed Lake Erie and

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Lake Ontario. By approximately 9.5 ka, the elevation of the surface water in the Lake Huron basin was 290 feet above mean sea level, forming Lake Stanley which was located in the northern part of the current Lake Huron (Larson and Schaetzl, 2001; Farrand, 1998; Dorr and Eschman, 1970). This water level was approximately 300 feet lower than the current level of Lake Huron.

Drops in the lake levels may have occurred rapidly when lower outlets were opened. During the glacial maximums, the ice blocked the flow of water out of the lower spillways for this area. As the ice retreated, there came a point in time when the remaining ice served only to dam the lower outfalls. There are places where these ice dams broke and released water over a relatively short period of time. Currently it has not been determined how rapid the changes in the water levels were when the inland lakes were drained from the area around Midland and Saginaw.

The lower elevation of surface water in the current Lake Huron and Saginaw Bay footprint had a significant impact on the southern portion of the Tittabawassee River. With the water level lower in Saginaw Bay, the Saginaw River incised into the underlying glacial and lacustrine soils, lowering the water level in the Saginaw River at Saginaw. This created a subsequent change in the water level of the lower Tittabawassee River with an impact on the gradient in the Tittabawassee River some distance up the river from its confluence with the Shiawassee River. Currently, the water level in all of the Saginaw River and in the southern portion of the Tittabawassee River is moderated by the water level in Saginaw Bay.

As the ice retreated, the mass of the ice was removed from the crust of the earth. As a result of the decrease in mass caused by the melting of thousands of feet of overlying ice, the crust of the earth began to rebound. Since there had been more ice loading to the north and northeast, there was measurably more rebound to the north and northeast and less rebound to the south and southwest. This differentiation is observable by mapping ancient shorelines within Michigan and may have caused slight differential rebound within areas the size of the Study Area.

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Locally, rebound may have increased the gradient along a southwest-northeast axis through this area over a long period of time. This change may now be reflected in the directional drainage and apparent slope of the ancient lakebed toward the south.

This isostatic rebound may also have influenced and changed historic drainage patterns. To the north, this rebound may have influenced which areas drained to the south behind the moraine system and entered the Tittabawassee River.

4.1.1.5 Rising Water Levels Isostatic rebound caused the lower outlets of the Lake Huron basin to rise in elevation. Eventually there was sufficient isostatic rebound to result in surface water flow preferentially following the Detroit River into Lake Erie and Lake Ontario. Over the last 6,000 years, the outlet for Lake Huron has remained at its current location, stabilizing water levels in Saginaw Bay and Lake Huron (Farrand, 1988; Larson and Schaetzl, 2001).

With the rise in water level in Lake Huron and Saginaw Bay, surface water backed up into the Saginaw River. This resulted in a shallow gradient in the Saginaw River between Saginaw and Lake Huron, resulting in increased water levels farther upstream and likely affecting the gradient of the lower Tittabawassee River. The backwater in the flooded river systems also created broad wetlands on the low permeable clays in the areas along the Saginaw River and throughout the Shiawassee watershed.

4.1.2 River Evolution The final glacier advancement and retreat of about 13 ka likely had the most influence on the landscape, leaving geomorphic surfaces composed of glacial till and outwash deposits. During glacial advancement and retreat, till typically consisting of poorly sorted finer-grained sediment, was deposited directly by the glacier. As the glaciers retreated north of the Tittabawassee River valley, coarse-grained outwash sediments were transported by glacial melt water and deposited over the till deposits in the Tittabawassee River valley. Melt water extended across the valley with flow contained by the upland scarps. As the glaciers continued to retreat, the melt water decreased, and

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the flow was contained in a channel that meandered within a valley delineated by the upland scarps.

Since glaciation, many factors have influenced river and geomorphic surface development including: watershed characteristics (e.g., area, shape, slope, vegetation, and land use), channel characteristics (e.g., width, height, and gradient), sediment characteristics (e.g., load and particle size), and flood characteristics (e.g., frequency, duration, and magnitude).

Following the decrease of flow from glacial melt water, the river was confined to a channel except for flooding. The decrease in channel width and subsequent increase in hydraulic energy from concentrated channel flows resulted in channel incision (e.g., down-cutting). The channel incision eroded fine-grained channel sediment, which was transported downstream. Likewise, channel banks subjected to hydraulic forces also eroded. The channel incision and bank erosion process continued until less erodible deposits (e.g., coarser-grained sediment) or bedrock are encountered and/or hydraulic equilibrium was achieved.

The geomorphic surfaces within the floodplain represent historic river channel bed incision and abandonment of channel beds as a result of lateral migration. Development of these geomorphic surfaces from oldest to youngest progressed as follows: upper high surface, high surface, intermediate surface, low surface, historic natural levees, natural levees, and shorelines. The lateral migration of the river over time erodes geomorphic surfaces so the resulting landscape will often include remnants of these surfaces. In the Tittabawassee River, the upper high surface is a good example of a historical surface that has remnants present on the current landscape.

Geomorphic surfaces are mature when vertical accretion on the surface occurs at a low recurrence interval. In this situation, the surface is exposed for a long enough period between inundation to experience chemical and physical breakdown of the fluvial deposits and to develop sufficient sustainable vegetative growth to begin the soil forming process. A geomorphic surface that receives flood deposition every year is immature. In the Tittabawassee River valley, the historic natural levee and geomorphic surfaces have

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been sufficiently mature to begin soil development. The shoreline and natural levees are examples of immature geomorphic surfaces.

4.1.3 Soil Development Most of the soils in the Tittabawassee River floodplain developed from parent materials that were deposited either from glacial activity and/or from fluvial deposits associated with later flooding and channel adjustments. Soil profile differences between soils in the Tittabawassee River floodplain often are influenced by topography and the hydraulic energy of the flow system. Topography is a major soil forming factor that results in soil property differences along a landscape. Hydraulic energy of river flow affects sediment transport and deposition rates relative to particle size, which is a process that determines soil parent material, another soil forming factor. The soils near the existing river corridor at lower elevations often consist of coarse-grained, well-drained sand that developed from fluvial deposits. These soils, associated with specific geomorphic surfaces, including levees or low surfaces, often either have no significant horizon development (C horizon only) or a weakly developed soil profile (thin A horizon over C horizon) indicating a relatively recent soil formation in terms of the geologic time frame.

Soils with more developed profiles including A, E and/or B, and C master horizons often occur further from the existing river corridor on slightly higher elevations on intermediate and high geomorphic surfaces. The surface soils (A & B horizons ) at some of these slightly higher elevation locations are often finer-grained as compared to near river soils, with USDA-SCS textures that may include loamy sand, sandy loam, loam, sandy clay loam, and clay loam. The finer-grained soil textures reflect fluvial transport and depositional processes whereby finer-grained soil particles settled further from the river corridor. The soils on these slightly elevated surfaces away from the river, with more developed soil profiles, typically represent a more stable environment (less flooding and low energy flow system) and are presumed to be more mature as compared to the soils with no or weakly developed soil profiles.

Soils that are saturated or near saturation for extended periods during flooding occur near or away from the river corridor, on lower elevations on a surface defined as geomorphic wetland. Geomorphic wetlands, however, are not determined using US Army-Corps of Engineer methods for jurisdictional wetland delineation based on soils,

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hydrology, and vegetation. Geomorphic wetland soils may include an organic horizon composed of partially decomposed plant matter (O horizon) and/or an A horizon. The A horizon typically consists of medium to fine-grained soil (e.g., USDA-SCS: loam, silt loam, silt, clay loam). The wetland soils have developed from fluvial deposits in low elevation backwater areas where hydraulic conditions were optimum (low energy flow system) for the transport and settlement of medium to finer-grained soil particles.

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The following Figure 4-3 presents typical soil profiles from geomorphic surfaces that extend from near the Tittabawassee River (less mature) to higher elevations away from the river (more mature).

Figure 4-3 Tittabawassee River Soil Profiles Relative to Geomorphic Surface Natural Historic Geomorphic Intermediate Levee Natural Levee Wetland Surface RQ-367+00-SW17 RDD-658+ 50-SW35 RP-356+50-SW340 RS-416+00-NE552

C-horizon A-horizon A-horizon A-horizon

0.0 to 10+ ft 0.0 to 0.4 ft 0.0 to 1.0 ft 0.0 to 1.0 ft Brown and very dark Black loamy sand, Dark grey loam, Black loam, granular, grayish brown and granular, non-plastic granular, slightly slightly plastic dark grey, loamy sand plastic C-horizon and sandy loam, single grain and 0.4 to 6.0+ ft subangular blocky, Very dark grayish Bw-horizon E-horizon slightly plastic and brown and brown and non-plastic dark yellowish brown 1.0 to 1.6 ft 1.0 to 1.8 ft sand, single grain, Dark grayish brown, Grayish brown non-plastic (strong brown (yellowish brown mottles) clay loam, mottles), fine sand, subangular blocky, single grain, non- moderately plastic plastic

C-horizon

1.6 to 8.0+ ft

Brown and dark grey Bs-horizon clay loam and loamy sand, subangular 1.8 to 2.5 ft blocky and single Brown fine sand, grain, moderately single grain, non- plastic and non-plastic plastic

C-horizon

2.5 to 4.0+ ft

Brown fine sand, single grain, non- plastic

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4.2 HYDROLOGY AND FLOOD SERIES ANALYSIS 4.2.1 Flood Series Analysis/Flood Recurrence Interval Calculations The two-dimensional Environmental Fluid Dynamics Code (EFDC) model of the Tittabawassee River and floodplain was used to develop estimates of flooding extent for various flooding recurrence intervals. Estimates of flooding extent aids in the understanding of inundation frequency for various portions of the floodplain and associated locations of river and floodplain contaminants.

Model Setup Steady state upstream and downstream boundary conditions for the two-dimensional EFDC model of the Tittabawassee River and Floodplain were developed for the following recurrence intervals: the 1, 1.5, 2, 5, 10, 25, 50, 75, 100, and 500-year events. The upstream boundary of the EFDC model is a flow-based boundary and flows specified at this boundary were based on a log Pearson Type III recurrence interval analysis, described in Section 4.2.2. The downstream boundary of the EFDC model at the confluence of the Tittabawassee River with the Shiawassee River is a water-level- based boundary and was set using results obtained from the 1-dimensional full equations model (FEQ) of the Saginaw River and floodplain. Flow rates for the FEQ model were determined using a log Pearson Type III recurrence interval analysis of available USGS gage data. The downstream boundary of the FEQ model was set based on a median Lake Huron water surface elevation at Essexville, Michigan. For larger recurrence intervals, the number of potentially active cells in higher elevations of the potential 100- year and 500-year floodplains was increased to insure that the model extent itself did not limit the floodable area for these larger events.

Model Results The two-dimensional EFDC model was run for each recurrence interval listed above, and flooding extent estimates were made for each recurrence interval. These extent estimates were used to better understand the flooding frequencies for various locations within the Tittabawassee River floodplain. Velocity and shear stress values were also calculated for each recurrence interval. These estimates can be used to determine whether areas are likely erosional or depositional when flooded. The use of steady flows for each event in setting upstream and downstream boundary conditions provides conservative estimates of flooding extent, because in reality the peak flood flow rate

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would be transitory, and would tend to attenuate in both flow and stage as it moved down the river. The more extreme 100-year and 500-year flood results are likely to slightly under predict flood extent due to the absence of bridge decks in the EFDC model. The obstruction caused by these bridge decks under flood conditions would tend to increase the depth of flow in the river and increase flooding extent for the more extreme events. In addition, the Dow tertiary treatment ponds were not included as part of the EFDC model extent and so are not shown as inundated under these extreme events.

Model predicted water surface elevations at the site of the Tittabawassee River USGS gage downstream of Midland for these steady state flooding events were also compared with available USGS-predicted water surface elevations for various flooding events. USGS-predicted water surface elevations were taken from the current USGS stage discharge curve, and show broad agreement with EFDC-predicted water surface elevations. Comparisons are shown in Table 4- 1.

Table 4-1. Water Surface Elevation Comparisons Between the EFDC Model and a Stage-Discharge Curve Based on Tittabawassee River USGS Gage Readings Water Surface Elevation (Ft, NGVD29)

Event Modeled EFDC USGS Stage Discharge Curve Median Flow 590.7 590.6 1 Year Event 600.8 599.4 1.5 Year Event 601.3 600.0 2 Year Event 602.9 601.9 5 Year Event 606.1 606.2 10 Year Event 607.9 608.6 25 Year Event 609.7 611.3 50 Year Event 610.9 613.1 75 Year Event 611.6 614.0

Results of the EFDC model-predicted water surface elevations at the site of the Tittabawassee River USGS gage were also compared with 132 available physical stage and discharge measurements taken at the gage and posted on the USGS Water Watch website (USGS, 2008). Physical measurements posted on the website were taken between March 13, 1985 and December 11, 2007, with the exception of 4 measurements taken on March 1 and 4, 1959, March 1, 1960 and on September 3, 1975. Comparison of the EFDC model-predicted water surface elevations and stage/discharge

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measurements made by the USGS show good agreement between model output and USGS field data. These results are shown in Figure 4-4.

Figure 4-4. EFDC Model USGS Field Measurement Stage and Discharge Comparisons at the Tittabawassee River USGS Gage

50,000

45,000

40,000

35,000

s) 30,000 cf ( e rg a 25,000 h c is D20,000

15,000

10,000

5,000

0 585 590 595 600 605 610 615 620 WSE (ft, NGVD29) USGS measurement EFDC prediction

Model simulations indicate that large portions of the floodplain are flooded under the 1- year event and that flood extent reaches from one valley wall to another for the majority of the floodplain in the 5-year event scenario. Simulations performed predict that the bank full flood has a recurrence interval of less than 1-year. Flood extent results for all events modeled are provided in Attachment D.

4.2.2 Flood Series Analysis/Flood Recurrence Estimates of Peak Recorded Discharges The following presents a summary of the flood frequency calculations performed for the Tittabawassee River at USGS gage 04156000, located 2,000 feet downstream of the Dow Dam on the Tittabawassee River. Available peak water year discharges as reported by the USGS were used to calculate flood recurrence intervals using several methodologies. Flood recurrence estimates of the top twenty peak annual discharges were also calculated. Results of these analyses are presented below.

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Peak water year measurements as reported by the USGS were also analyzed to determine the recurrence intervals of various events in the historical record. The top twenty flows in a given water year were sorted and a recurrence interval was calculated for each event based on the flood recurrence analysis of the historical record. Table 4-2 details the calculated recurrence interval for these twenty events.

Table 4-2. Calculated Recurrence Intervals for the Top Twenty Events in the Historical Record of USGS Annual Peak Flow Data Calculated Calculated Calculated Log Weibull Gumbel Pearson Type III Water Peak Flow Recurrence Recurrence Recurrence Year Rate (cfs) Interval (yrs) Interval (yrs) Interval (yrs) 1986 38,700 98.0 84.7 77.2 1916 34,800 49.0 45.1 39.8 1948 34,000 32.7 39.6 34.8 1912 32,800 24.5 32.7 28.7 1946 31,200 19.6 25.3 22.2 1919 29,200 16.3 18.4 16.3 1945 28,000 14.0 15.2 13.5 1959 27,300 12.3 13.6 12.2 1950 27,200 10.9 13.4 12.0 1929 26,800 9.8 12.6 11.3 1976 26,400 8.9 11.8 10.6 1942 26,000 8.2 11.1 10.0 1960 24,600 7.5 9.0 8.2 1965 24,200 7.0 8.4 7.7 2004 23,900 6.5 8.1 7.4 1933 23,600 6.1 7.7 7.1 2006 23,000 5.8 7.0 6.5 1975 22,200 5.4 6.2 5.8 1957 22,000 5.2 6.1 5.7 1928 21,800 4.9 5.9 5.5

The greatest differences in estimates of recurrence intervals for events correspond to larger recurrence intervals and higher flow values. This is to be expected since larger flows and recurrence intervals have less data available to make a prediction. The log Pearson Type III method has been recommended for use by the U.S. Interagency Advisory Committee on Water Data when calculating recurrence intervals for a location of interest (Bedient and Huber, 1992). The Gumbel method has been recommended for use within the United Kingdom (Linsley et al, 1982). Both methods provide reasonable estimates of peak stream flow and recurrence interval for large storm events.

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4.2.3 Stage and Discharge Historic stage/discharge rating tables developed by the USGS for the Tittabawassee River USGS gage (gage 04156000) were analyzed to determine whether any trends in the relationship between stage and discharge at the gage could be observed over time. An analysis of the rating tables showed an apparent decrease in stage over time at the gage for a given discharge, which may be a result of channel degradation through channel deepening or widening at the gage. This apparent decrease was seen for a range of discharges, excluding the highest discharges.

4.2.3.1 Data Collection Thirty-three separate historical gage rating table records were provided by the Grayling, Michigan office of the USGS for Tittabawassee River USGS gage 04156000. These records encompassed dates from March 24, 1936 through the present, and spanned the entire period of record of available daily flow data, with rating table gaps in the record between October 1, 1940 and November 8, 1943, April 1, 1965 and April 30, 1965, and between October 1, 1967 and March 25, 1968. A rating table for dates between May 13, 1962 and March 27, 1963 was also received but was not legible. These rating tables are based on three different elevation datums, with the present datum for the gage set at 580.08 feet NGVD29. Prior to October 1, 1955 the gage datum was set at an elevation 10.2 feet higher and between October 1, 1955 and September 30, 1993 the gage datum was set at an elevation 0.2 feet higher. Initial gage rating tables had a lower peak discharge that was based on available stage data at the time of table development. For example, the first rating table was defined up to a discharge of 8,250 cfs. Rating table discharges were increased as needed to predict discharges for gage measured stage measurements. Updated gage rating tables were also created as additional stage and discharge field measurements were collected. Seven hundred sixty-six field measurements have been collected since 1936 to support the development of various gage rating tables for this gage.

4.2.3.2 Data Analysis and Results Stage and discharge values from these tables were copied into a Microsoft Excel workbook and the stage of each table was adjusted to match the present datum.

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Figure 4-5 presents a plot of discharge versus stage for each available rating curve.

Figure 4-5. Predicted Discharge as a Function of Stage for Available Tittabawassee River USGS Gage Rating Curves

45,000

40,000

35,000

30,000

25,000 (cfs)

20,000 Discharge

15,000

10,000

5,000

0 5 101520253035

Stage at the Tittabawassee River USGS Gage (ft) Rating Curve Numbers 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

A review of the available rating curves shows that the relationship between stage and discharge at the gage, as reflected in best-fitting curves, has changed through time. This is likely due in part to the collection of additional field data at the gage. It may also reflect changes in bathymetry and floodplain elevation at the gage, as well as changes over time in methods of estimating discharge. A review of the lower end of the rating curves, presenting discharges for lower stage values, shows a similar spread between rating curves: a more detailed view of this section of the various rating curves is shown in Figure 4-6.

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Figure 4-6. Detail of Lower End of Rating Curve of Predicted Discharge as a Function of Stage for Available Tittabawassee River USGS Gage Rating Curves

10,000

9,000

8,000

7,000

6,000 (cfs)

5,000 Discharge 4,000

3,000

2,000

1,000

0 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Stage at the Tittabawassee River USGS Gage (ft) Rating Curve Numbers 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

In general, discharges for a given river stage measured at the gage are higher in the more recent tables developed by the USGS for the Tittabawassee River gage, indicating that the river near the gage may have experienced some erosion in the channel and/or banks over time.

Figure 4-7 presents an apparent time trend in elevation at a given discharge at the Tittabawassee River gage. Each line in the figure represents elevations over time for a particular discharge, as interpolated from available rating tables.

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Figure 4-7. Gage Elevation for a Given Discharge as a Function of Time at the Tittabawassee River USGS Gage

615

610

605 NGVD29)

600 (ft,

Elevation

595

590

585 1934 1939 1945 1950 1956 1961 1967 1972 1978 1983 1988 1994 1999 2005 2010

Year Flows in CFS 500 1,000 1,500 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 12,500 15,000 17,500 20,000 25,000 30,000 35,000

An analysis of available USGS rating curves spanning the period 1936-present shows that the elevation as predicted by the gage rating tables for a given flow has been dropping over time for a broad range of flow rates. This suggests that over the long term, the river at the gage may have degraded its channel, either in the bed or banks or both. Degradation of the river channel over time increases the cross sectional area below a particular water surface elevation available to convey flow. Consequently, a larger discharge is passed for a given elevation at the gage.

At higher discharges, stage elevations do not change as much in the various rating tables, likely due to a scarcity of data available to estimate discharge for the more extreme stage elevations, and possibly also due to less change over time in cross- sectional area and wetted perimeter of the river and floodplain for larger events. The stage and discharge values for larger events are also affected more by river and floodplain conditions a greater distance downstream from the gage, making it

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more difficult to attribute apparent changes in bathymetry and floodplain elevation to the immediate neighborhood of the gage.

4.3 LAND USE OVERVIEW The effects of land use and specific anthropogenic influences on the horizontal and vertical distribution of contamination in the Study Area are still under study. Final conclusions will be presented in the final 2009 report. Only those anthropogenic features or land use activities with a major influence on the Upper and Middle Tittabawassee River hydrology, geomorphology, and sediment transport or with a significant influence on the horizontal and vertical distribution of constituents of interest are presented here. Upstream anthropogenic structures and features that influence the MTR are discussed in the Remedial Investigation Work Plan. (ATS, 2007a)

4.3.1 Historical Aerial Photograph Review Historical aerial photographs representing approximate ten year intervals dating back to the 1930s were used to document fluvial geomorphologic patterns within the Study Area and to review changes in land use, vegetation cover, and anthropogenic activity pertinent to understanding sediment transport and deposition.

4.3.1.1 Preparation of photographs Mosaic aerial photographs were obtained for 2004, 2006, and 2007 from The Dow Chemical Company and from National Aerial Resources of Albany, New York for the length of the Study Area.

Individual aerial photographs were also obtained from National Aerial Resources for the following chronologic intervals:

• 1938 to 1941 • 1952 to 1955 • 1970 to 1973 • 1980 • 1992

Individual aerial photographs were converted from an Adobe PDF to a TIFF format using Adobe Photoshop software at 300 dpi resolution to support

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georeferencing using ESRI ArcGIS ArcMap-ArcInfo. Spatial referencing was based on the following datums:

• GCS North American 1983 • NAD 1983 State Plane Michigan South FIPS 2113 Feet Intl • North American Datum of 1983 • Geodetic Reference System 80

Drawing from base layers developed by others for the Study Area, centerlines of road intersections and property corners were used as the preferential reference points. Wherever possible, control points were selected throughout the aerial coverage of each digital photograph.

Following spline transformation, the raster dataset was permanently transformed and the rectified images saved as new TIFF images. Data accuracy of the rectified TIFF images (1938 through 1992) is subject to the accuracy of the base layers used to georeferenced the individual TIFF files.

4.3.1.2 Review and analysis The georeferenced aerial photographs were used to provide insight in fluvial deposition patterns within the floodplain as discussed in Section 4.4.1.and to assess the general migration pattern of the river channel over time. Attachment E provides a comparison of channel alignment within the Study Area. For the most part, the channel has maintained a general alignment with little migration.

4.3.2 Anthropogenic Influences

4.3.2.1 Logging and Agricultural Practices

4.3.2.1.1 Logging The Tittabawassee River watershed has undergone extensive changes over the last 150 years. The most dramatic changes took place in the mid 1800’s when the Tittabawassee River watershed was extensively logged. Clear cut logging operations in the Saginaw watershed started in earnest in 1847, reached their peak in the watershed in the early 1880’s, and

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continued through about 1898 (AIM, undated). These operations were intensive, with the forest being completely logged and little standing timber remaining. The transport and milling of the logs also had profound impacts on the Saginaw and its tributaries, choking the rivers with logs and generating great volumes of sawdust.

The environmental costs of these logging activities were large and their effects are still seen in the watershed today. They included an increase in the sediment load to the river and floodplain, intentional changes in river morphology, and induced changes in bed shear stresses under high-flow conditions.

Changes in flows and solids loads Clear-cutting of forests, with logs rejected by company inspectors left in place, set the stage for massive fires, leaving lands barren in many areas until reforestation in the 1930’s and 1950’s (AIM, undated). Increased runoff and resulting erosion brought increased loads of sediment into the Tittabawassee and other Saginaw River tributaries.

The sawing of logs also generated great masses of sawdust, especially in the early decades of the lumbering boom, when thick saw blades resulted in one-fourth to nearly one-half of the log being turned to sawdust. Much of this sawdust was generated along the Saginaw River, because it was accessible to Great Lakes shipping. Disposal sites for sawdust included the river and floodplain until the practice of producing salt from brine, which began locally in the 1860’s, began using sawdust for fuel (AIM, undated).

Direct impacts on river morphology Logs were transported to the river during winter, taking advantage of ice and snow to reduce friction on land, and then floated downstream. Transport practices likely stripped vegetation that remained on the forest floor. Stream channels were deepened and straightened to prevent log jams and dams were constructed to raise water levels and store logs.

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These dams would subsequently be broken to flush logs downstream to larger rivers (Bassett, 1988). Sluiceways were built to convey logs around dams, falls, and rapids. Rivers filled with logs and it was difficult to prevent massive log jams, despite the improvements. Scour of the bed and banks were an inevitable result. The Saginaw was also dredged to facilitate shipping. (AIM, undated)

Figure 4-8. Logjam on the Tittabawassee River (AIM, undated)

Responses of river to lumbering impacts Before logging, this vegetation reduced the intensity and volume of overland flow caused by rainfall and snowmelt and held solids in place on the land. Clear-cutting and subsequent fires in the watershed denuded the landscape of trees, brush, and other groundcover resulting in a flashier response to wet-weather events, allowing sediment to be mobilized and washed into tributary streams and the Tittabawassee River itself, increasing loads of sediment in the watershed.

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Figure 4-9. Eroded Landscape Post-Logging (Center for Michigan History Studies)

Higher peak flows would be expected to have caused increased channelization of the river, reinforcing the straightening that was done to facilitate movement of logs. Because of this increased flashiness, and the scouring effects of log flows in the river, much of the increased solids load can be expected to have been transported downstream and redeposited in the riverbed and deposited on riverbanks and floodplains during flood events. The coarsest sediments would have been transported only under the highest flows and would have had the shortest transport paths within the floodplain, contributing to the formation of levees along the river bank. Finer sediments would have been transported farther away from the river within the floodplain and farther downstream, including low-flow events. Logs trapped in sediment, some of which are still visible today, may have had the opposite effect, reinforcing the bed and providing greater local stability under high-flow conditions.

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Similar environmental effects due to logging and other similar historical disturbances have been seen within other upper Midwest watersheds that underwent heavy logging. Watersheds studied in Wisconsin in the Mississippi River and Lake Superior Drainage Basins have shown large amounts of sediment movement due to clear cutting of forests. Large post-logging sediment loads and inundation of old floodplains, and the filling of the river bed and floodplain, have been documented in these locations as well. It has been shown that these watersheds are still adjusting to and recovering from the effects of logging in the watersheds late in the 19th century. Furthermore, these watersheds are accommodating the large amount of sediment delivered post logging by adjusting to a new geomorphologic state and this adjustment is still ongoing today (Fitzpatrick, 2006). In the long term, the episodic movement of sediment due to logging activities could cause these systems to come to a new geomorphologic equilibrium that is different than conditions pre-logging. These processes can be seen on the Tittabawassee River as well, where the river and floodplain show large amounts of long term sediment deposition as the river comes to a different geomorphologic equilibrium that is different than the morphology present pre-logging.

Fisheries studies done within the Hiawatha National Forest in upper Michigan have seen similar ecological degradation and sedimentation in rivers within the national forest. Fisheries workers there have found saw logs dating from the 1890 buried under 5 feet of sand and 2 to 4 feet of sand burying extensive deposits of gravel and cobblestone in streams (Bassett, 1988). Historical accounts of these northern Michigan rivers describe large accumulations of fallen trees in northern Michigan rivers and streams. These same accounts have little to no mention of bank erosion. To facilitate logging, these stream channels were cleared of large woody debris in the river channel that stabilized the channel morphology, reduced peak flows by increasing channel resistance to flow and held sediment in place. This removal of in river debris adversely affected channel morphology, allowing severe bank erosion to take place, and

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allowing gravel and sand to be washed downstream. Subsequent clear cutting of near bank trees eliminated future sources of logs that could trap gravel and reduce erosion (Bassett, 1988).

4.3.2.1.2 Past and Present Agricultural Activities Post logging agricultural practices contributed further to the release of soils and sediments into the Tittabawassee River watershed. After logging occurred, portions of the watershed were used for agriculture. Tributaries in the watershed would have been further modified and straightened to promote land drainage, and to increase flood runoff from poorly drained soils. Swampland would also have been drained to create arable farmland. Past agricultural practices did not use best management practices such as riparian buffers to protect streams and other drainage courses. Rather farming would likely have occurred up to the edge of a stream channel, preventing re-vegetation and bank stabilization.

As tributaries were further modified to support farming of land within the watershed post-logging, these modifications would have provided a continual source of sediment to the Tittabawassee River watershed, and would have increased sediment loads where land improvements took place. Trimble (1983) observed large increases in sediment loads in a creek in Wisconsin post logging which he attributed to upland sheet, rill, and gully erosion due to poor farming practices in the creek watershed, with additional sediment coming from bed and bank erosion of straightened tributaries and dug drainage ditches. These effects were not mitigated until the United States government formed the Soil Conservation Service in 1935 to reduce erosion, partly through educating farmers on how to employ best management practices to conserve soil and sediments on farmed land.

Post-logging agricultural activities within the Tittabawassee River watershed continue to influence the watershed response to significant storm events today. Most of the agricultural land within the watershed is maintained through the use of drain tile. This drain tile keeps farmland

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free from standing water and allows agricultural crops to develop root systems in the spring. If this drain tile were not present, it is likely that these lands would have reverted back to forested/marshy areas with low runoff potential.

The Tittabawassee watershed upstream of Midland is dominated by clayey, poorly drained soils (MDNR 1994). Because this soil has poor drainage potential and tight void space, the soil is easily saturated in the spring, even when drain tile is used. When rain and snowmelt events occur, saturated soils do not have capacity to infiltrate the excess water which would typically pool on the land surface. Instead, excess water is forced from the saturated soil into tile drains and these drains quickly route this water to nearby streams. These drain tile systems deliver water to creeks and streams much faster than this water could have traveled in the forested pre-logging environment. The Tittabawassee watershed has very little relief, and drain tile systems provide a quick route for water to travel. Therefore the watershed, though less flashy than in the years when much of the watershed was denuded of trees, still has a faster rainfall/snowmelt response in the spring than when compared to the pre- logging and settlement era.

4.3.2.1.3 Effects of Logging and Post Logging Agricultural Practices There are several lines of evidence that support large scale post-logging sediment transport and sedimentation. First, the presence of timber cut during the logging era buried in the Tittabawassee riverbed is evidence of sedimentation. These buried logs also show how the increased river channel and floodplain sediment load has raised portions of the riverbed. Logs at several locations have been found buried to a depth of several feet. Few non-historic logs have been found on the surface of the riverbed, with the exception of logs that were driven vertically into the riverbed to aid in logging activities.

The presence of one or more woody debris layers buried several feet below the surface has been found in many cores at many locations in the

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Tittabawassee Riverbed. These debris layers were likely generated by watershed logging activities and subsequent fires provide markers that show the amount of sedimentation that has taken place within the Tittabawassee River system since the beginning of logging operations. Debris layers can be seen in areas of the riverbed associated with riverbed sections such as the thalweg, riffle/pool areas and in areas adjacent to point bars, indicating that sedimentation is occurring in river locations with varied geomorphology.

Abrupt changes in soil/sediment layers can be seen throughout the riverbed and floodplain. Coarser sand and silt layers can be seen in the riverbed, in levees adjacent to the river, and in the floodplain bottomlands. Coarse sand and gravel deposits likely resulting from post logging erosion can be seen above woody debris layers and silt/clay layers in the riverbed. Review of available coring data shows that newer natural levee systems have developed along the riverbanks of the Tittabawassee River. These levee systems are composed primarily of sand sized particles to a great depth. These levees often occur on the streamside of historic natural levee systems, which have more developed finer grained soil horizons at depth. Floodplain soils also show developed soil horizons in several locations that have been buried by new sediments. These buried soil structures likely result from the large sediment load resulting from previous logging activities. Logging-mobilized sediments would be deposited adjacent to and on top of existing levee systems. Coarser sediments would be deposited at or near to the river’s edge, and newer levee systems would develop that would restrict the main river channel. Sediments that were washed over levee systems would tend to deposit into the floodplain as river-carrying capacity decreased with distance from the river, and would deposit in thin layers.

These abrupt changes in buried soil and sediment layers observed throughout the Tittabawassee River in the riverbed, in levee systems and in the floodplain have been caused to a large extent by the large sediment

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load increase resulting from historic logging operations. Subsequent post logging agricultural use of the land further contributed to soil erosion and sedimentation of the riverbed, levees and floodplain due to poor farming practices. Elevated sediment loads continue to affect the geomorphology of the river at present, and need to be accounted for in any remedial investigation or corrective action.

Logging and post logging agricultural activities within the Tittabawassee watershed provided the catalyst that created the present hydraulics and sediment transport mechanisms within the river and floodplain and caused a large increase in sediment loads, river response to rainfall and snowmelt, and changes in the depositional characteristics of the river and floodplain. The sediment load present within the river and floodplain is much higher, sediment sizes are larger, and there is less resistance within the river system due to river straightening, improvements, and debris removal. The net effect is to increase the carrying capacity of the Tittabawassee River, a tendency for large amounts of coarse grained sediment deposition in the riverbed, natural levees, and in the floodplain, and a tendency for the river and floodplain to develop into a more coarser grained and higher energy equilibrium geomorphologic state, different than the geomorphology present before logging operations began. Soil and contaminant profiles also support a broad trend towards a geomorphologic river system at a different equilibrium than was present pre-logging and settlement.

4.3.2.2 Areas Physically Disturbed after European Settlement The logging era influences discussed above represent the greatest physical disturbance to the river and overbank areas during post glacial times, and the watershed is still recovering from this massive disturbance. Following this era, the fertile land surface in the MTR Study Area was largely developed into agricultural uses where the hydrologic and geomorphic conditions were considered suitable. To a lesser extent, land adjacent to the river was used for

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extractive purposes. Drainage channels and access roads were constructed to support these post-logging era land uses.

Available historical aerial photographs document the changing land uses since 1937. Aerial photographs from the following years were examined during the course of the 2007 MTR investigations: 1937, 1941, 1955, 1963, 1970, 1980, 1992, 2004, 2006, and 2007. High resolution aerial stereogrammetric contour mapping obtained from the 2006 aerial photography reveals current land surface forms and aids in identifying areas where earthworks may have occurred since the first European settlement in the 1830’s. This information, when considered along with soil layering and chemistry information from the 2007 site investigations, provides a useful characterization of the types and extent of land surface changes, both natural and manmade, that have taken place along the MTR since European settlement and allows an assessment of their influences on the horizontal and vertical distribution of contaminants.

From a review of these multiple lines of evidence, modern agricultural activities (including plowing and tilling) has likely had little discernable impact on the distribution of contaminants. Agricultural activity can be seen in the historical aerial photographs to have diminished in extent over time due to withdrawal of marginally productive lands from active agricultural production, and growing residential, commercial, and recreational uses along the river.

Where highly intrusive activities have taken place in the floodplain of the MTR, such as improvements to tributaries and large drainage channel construction (especially where breaches in the natural levee have occurred), the horizontal and vertical distribution of contaminants on the overbank differ from the contaminant distribution patterns that exist due to purely fluvial geomorphological processes. In certain areas of the MTR, the land surface has been substantially modified by extractive activities, such as sand excavation for a multitude of purposes and clay excavation for the brickworks popular in the region in the 19th century (Saginaw Township, 1877).

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Some of these historical disturbances have allowed deposits from contemporary secondary sources to come to rest where they otherwise would not have if the natural fluvial processes had not been altered by land surface disturbances. Historical soil extraction in the floodplain has resulted in deposition zones of substantial vertical accretion of contaminated sediments well away from the river. This is a variation from the normal extent of contamination in the floodplain that has occurred from purely fluvial geomorphological processes. Examples of this variation can be found in Reach S Northeast, Reach V Southwest, and Reach FF Northeast.

Alluvial soils are also known to have been used or removed during bridge construction during the 20th century, although the precise identification of the relocated deposits has not been possible. In general, bridges have required import of soils for construction of the approach roads, so soils “borrowed” from surrounding areas may be buried in the bridge approaches.

Areas identified as anthropogenically disturbed from the review of historical aerial photographs and high resolution contour mapping are shown with a cross-hatched “disturbed symbol” on the maximum and surface TEQ figures provided in Attachments R and S.

4.3.2.3 Berms Other than natural levees and areas where bank protection has been installed, there are no artificial “berms” in the MTR as there are in the upper reaches of the UTR. Small berms, generally transverse to direction of river flow, have resulted from drainage channel improvements across the floodplain. These berms and the associated channels and tributaries are discussed in Section 4.6.2.

4.3.2.4 Bank Protection Bank protection has been installed on the channel banks in several areas of the MTR. Bank protection measures for the bridges are described in the discussion below of each bridge’s influences. Based on the low level, high resolution aerial photography of the river performed in 2007 and observations by the ATS field sampling crews, bank protection armoring also exists in the following areas:

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• Stone Riprap, Reach V, southwest bank, Station RV-480+00 to 485+00, Freeland Festival Park; • Broken Concrete Riprap, Reach FF, northeast bank, RFF-716+00 to 731+00, Agricultural Field; • Heavy Stone Riprap, Reach FF, southwest bank, Station RFF-730+50 to 734+50, River Road Embankment; • Broken Concrete Riprap, Reach II, northeast bank, Station RII-780+00 to 782+50, Forested Mouth of Former Oxbow; • Stone Riprap, Reach II, northeast bank, Station RII-786+00 to 792+00, Imerman Park; • Heavy Stone Riprap, Reach II, southwest bank, Station RII-804+00 to 811+50, River Road Embankment.

4.3.2.5 Bridges Three bridges presently span the MTR. There are also abutment and pier foundations remaining in the river channel from historic bridges that no longer exist. Bridges in the UTR have been previously described in prior reports. (ATS, 2007a) Two UTR bridges, one at Gordonville and one at Smith Crossing, will be discussed here in greater detail as a result of the nearby ATS channel sediment sampling, laboratory analysis and bathymetric survey work performed in 2007 and recent data gathering on the bridges.

Gordonville Road Bridge

Gordonville Road Bridge (County classification: Bridge B1 of 56-12-26) is located at Station RK 233+00, at the boundary between Reaches K and L. The original bridge structure was constructed in 1974 and 1975. The bridge decking was rehabilitated in 2007. The structure consists of two concrete abutments spaced 485 feet apart, with heavy riprap from the bottom of the channel to the normal high water elevation of 600 feet msl, five concrete piers, and reinforced concrete deck spans. The concrete piers are 3 feet wide at the water line, spaced on 80 foot centers, and placed at a 55 degree angle to the curving center-line of the bridge deck so as to be parallel to the river flow at the location of the bridge (Midland County, 2007). A review of historical aerial photographs indicates that no bridge existed at this location prior to 1974.

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The Gordonville Road Bridge has two principal influences on the river geomorphology. During high flow conditions, the bridge abutments act as a restrictive orifice and the bridge approaches act as dams for overbank flow. These structures constrict upriver flow from the floodplains down to the relatively narrow channel between the bridge abutments. Most flood flow passes between the Gordonville Road Bridge abutments even during a 100-year flood event. Immediately upon passing the bridge, some flood stream lines begin leaving the channel, but the majority of the streamlines continue straight down the channel for several hundred feet. All lines of evidence suggest that the bridge piers are acting as flow straightening “vanes.” This straightening of the streamlines is a pronounced influence of the bridge.

Of the flood event frequencies modeled to date (see Section 4.5), the 1 to 1.5-year recurrence interval storm is commonly regarded as the “principal channel forming” event. The EFDC modeling indicates that during a 3-year storm event some streamlines begin crossing the northeast bank into the floodplain approximately 200 feet downstream of the bridge piers, but the majority of streamline departures from the channel do not occur until approximately 540 feet downstream of the piers. Comparing channel boundaries from 1937 to 2006, the northeast outside bend channel location has been relatively stable from the bridge to a distance of approximately 540 feet downstream. At this location, there has been a distinct lateral movement of the outside bend toward the northeast.

Further downstream on the left bank, approximately 1,000 feet from the bridge piers, a maximum lateral migration of approximately 37 feet has occurred in the outside bend since 1937. Erosion scars were noted at this location of maximum migration by site investigation observers during the 2006 UTR site investigation (ATS, 2007c).

At this same river station, the southwest inside bend bank has migrated 80 feet to the northeast since 1937. The net effect of lateral migration of both banks has been to narrow the channel width at this location from 311 feet in 1937 to 260 feet in 2006. This narrowing is primarily due to aggradation on the inside bend point bar on the southwest side of the river.

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Review of the 2007 bathymetry indicates that the most irregular near-bank bathymetry begins at the 540 foot distance downstream where the lateral migration of the northeast bank begins to occur. The shape of the near bank irregularities in the channel bathymetry is suggestive of minor bank collapses over time. These irregularities occur on both sides of the river from this location in Reach L downstream to the abandoned Smith’s Crossing Bridge, as discussed further below.

The flow straightening effects of the bridge piers are also evident in the 2007 high resolution channel bottom bathymetry. The river bottom formations can be divided into four distinct bands for several hundred feet downstream of the bridge, with the dividing lines between each formation falling approximately parallel to the slightly curving shorelines of Reach L. Each dividing line can be traced upstream to a point near each of the central three piers of the Gordonville Road Bridge.

There are two distinct dune formations in the center of the river channel downstream of the bridge, with the centerline of the channel (where the center pier of the bridge is located) approximating the dividing line between the two types of dune formations.

The different dune types represent different rates of transport, bottom friction, and levels of bed movement. “River dune” profiles are typically triangular in shape with long gentle upstream slopes and short steep downstream slopes. (Simmons, 1966)

The spring 2007 dune profiles to the southwest of the centerline of the river in upper Reach L have a typical wavelength (distance from crest to crest) of between 9 and 13 feet, whereas the dune profiles to the northeast of the centerline have a typical wavelength of between 20 and 40 feet. The dividing line between the two formations is distinct and can be traced upstream to the center pier (Pier #3) of the Gordonville Road Bridge.

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The channel bottom surfaces proximal to the channel banks for the first few hundred feet downstream of the bridge piers in Reach L are relatively flat. Further downstream, the channel bottom irregularities discussed above begin to emerge. There are no dune formations in the near-bank bands of the channel bottom.

The dividing lines between the distinctive near-bank channel bottom characteristics and the central dune formations are also reasonably discernable. They can be traced back upstream to Pier #2 on the southwestern side of the river, and to Pier #4 on the northeastern side of the river. Piers #1 and #5 are very close to the toe of the channel banks and have no noticeable effect on downstream channel sediment patterns.

Impacted sediments in upper Reach L are generally buried below more than a foot of sandy surficial sediments having low TEQ concentrations. Given the physical positioning and character of sediments and woody deposits exhibiting elevated concentrations, these deposits are likely to have been deposited during the first part of the 20th century, whereas the Gordonville Road Bridge was built in 1974.

The character of the dune formations overlying the contaminated deposits varies during the season. Erosion chains have been spaced throughout the upper portions of Reach L and are currently under study to evaluate channel bed stability.

In summary, the principal anthropogenic influences of the Gordonville Road Bridge are 1) to act as an orifice constraining high flow events to the relatively narrow channel between the bridge abutments, and 2) to act to straighten flow for the first few hundred feet downstream of the bridge piers, which serve as straightening vanes. These piers have the effect of creating divisions between the wavelengths of the dune formations in the center of the river and also between the dune formations and the near-bank channel bottom shape. Except for stabilizing the northeast outside bend bank for several hundred feet downstream, multiple lines of evidence support the conclusion that the bridge is not affecting either the net lateral migration of the river channel or the migration of bottom sediments.

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As discussed above, on-going studies of the channel bed stability are being conducted to monitor the seasonal dynamics of the channel bed in upper Reach L.

Smith’s Crossing Bridge

Smith’s Crossing Road Bridge, now abandoned, is located at Station RL 261+50 at the boundary between Reaches L and M. Smith’s Crossing Bridge was built in 1907 and is typical of the pin connected iron truss bridges that were built throughout the region in the early part of the 20th century (www.historicbridges.org, 2008). The abutments are 290 feet apart and there is one pier at the center of the bridge. The channel width between the abutments is 242 feet compared to a channel width of approximately 300 feet immediately upstream.

As with the Gordonville Road Bridge, the center pier of Smith’s Crossing Bridge creates a division in the dune formations in the center of the channel for several hundred feet downstream of the bridge. There is not, however, a significant differentiation of wavelengths in the dune formations on either side of the centerline as evident downstream of the Gordonville Road Bridge.

EFDC modeling indicates that the earthen approaches to the bridge act to constrict flood flows to the channel between the concrete abutments for 1 to 3-year frequency flood events. For the 8 and 100-year frequency flood events, the bridge approaches are overtopped by floodwaters. During a 100-year flood, the southwestern approach is inundated to a distance of approximately 600 feet toward the southwest; the northeastern approach is inundated for a distance of nearly 1,000 feet toward the northeast. During the larger flood events, the Smith’s Crossing Bridge approaches tend to act as horizontal weirs or submerged dams across the floodplain.

An aggrading area is evident in the middle of the river channel upstream of Smith’s Crossing Bridge. This area is several feet thick and extends approximately 900 feet upstream of the bridge. From river Station RL 252+00 to about RL 57+00, the deposit spans the river, and the thalweg is difficult to discern

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in the 2007 bathymetry. This sand accumulation is likely the result of the orifice constriction and backwater effects of Smith’s Crossing Bridge combined with a historical overabundance of sediment load.

Hydrodynamically, EFDC streamline modeling for the 3-year frequency storm indicates that water streamlines begin to leave the channel over the southwest bank immediately downstream of the bridge. On the northeast bank, modeling indicates that the majority of the streamlines during a 3-year storm begin to leave the channel approximately 600 feet downstream of the bridge.

These streamline channel departure locations are consistent with the position of the beginning of erosion scars noted downstream of the bridge during the 2006 field observations (ATS, 2007c). On the northeast bank, erosion scars began 600 feet downstream of the bridge and continued intermittently for approximately 2,000 feet downstream throughout Reach M and into upper Reach N. On the southwest bank, erosion scars began immediately downstream of the bridge abutment and continued for approximately 600 feet downstream (on what is otherwise a net aggrading and laterally accreting bank).

Based on the historical aerial photograph review, the Smith’s Crossing Bridge appears to have had a straightening effect on the channel for several hundred feet downstream. In 1937 there was a gentle bend downstream of the bridge, with the outside bend on the southwest bank, and inside bend on the northeast bank. Recent aerial photographs indicate that the river has experienced a lateral migration of 50 to 70 feet toward the northeast into the former inside bend since 1937. This lateral migration toward an inside bend is the reverse of what could normally be expected on a river meander, and is likely the result of the bridge construction in 1907.

Erosion pins were placed in a number of locations in Reach M banks during the 2007 site investigation, and the banks were surveyed on a 100 feet transect spacing by a licensed surveyor. Monitoring of the erosion pins and bank cross- sections is planned for the 2008 site investigation.

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Freeland Road Bridge

The next bridge downstream of Smith’s Crossing Bridge is the Freeland Road Bridge (County classification: Bridge B1 of 73-26-20) at Station RL 486+00. This location is also the boundary line between Reaches V and W. The Freeland Road Bridge consists of two principal bridge sections separated by approximately 300 feet of roadway built on an earthen embankment across wetlands. The “main” section of the bridge that spans the river channel was completed in November 1976 (Saginaw County, 2008), and consists of five reinforced concrete spans supported by six concrete piers and two abutments. The abutments are spaced 354 feet apart. The combined design discharge capacity of the two bridges (main channel and overflow) is 49,400 cfs. The drainage area contributing to this crossing is shown on 1992 plans to be 2530 square miles (Saginaw County, 1992).

The 1976 main channel bridge replaced a pin connected steel girder bridge (probably built around 1931) that had two 150 foot center spans, with an 18 foot long steel stringer span attached to the eastern abutment and 140 feet of trestle spans on steel piers attached to the western abutment, for a total bridge length of 458 feet. There were three steel piers under the central steel girder sections and seven steel piers under the western approach spans. All of the historical structures were to be removed during the 1977 bridge replacement (Saginaw County, 1976).

An early plat map of Tittabawassee Township indicates that a bridge existed across the river at this location as early as 1877 (Beers, 1877). Immediately south of the current main span, two historic bridge pier foundations are revealed by the 2007 high resolution bathymetry. The historic pier foundations are 50 feet long and spaced 100 feet apart to divide the channel into thirds. They are having no noticeable influence on river hydrodynamics or sediment patterns at the time of this writing.

The present “overflow” span west of the main channel bridge span was reconstructed in 1993. The reconstruction used the original substructure of the 1931 steel girder bridge that it replaced. The distance between the abutments is 200 feet and there are three evenly spaced piers between the abutments. There is

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normally no flow beneath this bridge section. During flooding it is designed to pass a discharge of 8,630 cfs. During a 3-year flood frequency, the EFDC modeling indicates that this overflow accepts streamlines flowing along the toe of the southwestern scarp. The modeling indicates that these western floodplain streamlines emerge from the river channel in Reaches Q and R. The overflow span also accepts 3-year flood event streamlines that emerge from the river channel in Reach U, in an anthropogenically depressed area just upstream of the bridges.

At this time, there appears to be no significant hydrodynamic, geomorphic or TEQ distribution influences from these bridge spans or from the Freeland Festival Park improvements, except for constricting streamlines to flow through the bridge abutments during storm flows, creating a slight backwater effect, a deepening of the thalweg immediately upstream of the main span, and probably straightening streamlines downstream of the main span piers. High resolution bathymetry is not presently available more than 100 feet south of the bridge. No erosion scars were noted during the field surveys that could be attributed to the bridge spans. The aerial photo history indicates that the position of the channel banks have been relatively stable for several hundred feet downstream of the Freeland Road Bridge since 1937.

Tittabawassee Road Bridge

The Tittabawassee Road Bridge (County classification: Bridge B1 of 73-25-28) is located at Station RDD 678+00 at the boundary between river Reaches DD and EE and river Regions IV and V. Construction of the present bridge structure was completed in 1966 (Saginaw County, 2008). The decking was rehabilitated in 2002 (Saginaw, 2001). The bridge consists of seven reinforced concrete spans resting on six concrete piers and two abutments. The total width of the bridge between abutments is 485 feet. The piers supporting the spans are 70 feet apart. The piers are placed at a 70 degree angle to the bridge centerline so as to be parallel to river flow at the location of the bridge. Cofferdams built around Piers #3 and #5 during the 2002 rehabilitation were intentionally left in place for additional structural support. The abutment side slopes beneath the bridge consist

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of poured concrete, with additional heavy riprap placed in 2002 just downstream of the concrete channel slopes under the bridge. A water main is buried across the river channel approximately 40 feet south of the bridge piers.

Based on review of available historical aerial photographs, no bridge existed at this location prior to the 1966 structure. Historical documents indicate that the Kapitan Ferry (a hand pulled cable ferry) was located near the present bridge. The ferry was abandoned in 1909 (Ederer, 1980).

Field observations and aerial photographs from 2006 and 2007 reveal substantial build up of woody debris against the upstream side of the two eastern piers and along the eastern abutment slope of the main channel bridge. This debris buildup is periodically cleared, but when present, it diverts much of the channel flow to pass under the two spans located on the western side of the channel.

The EFDC modeling indicates that river streamlines from all flood event frequencies are constricted, principally on the west side, to pass almost entirely through the channel between the abutments, although the modeling indicates that the western approach to the bridge is inundated to a distance of 265 feet from the channel during a 3-year flood event, and to an approximate distance of 400 feet from the channel during a 100-year flood event. The modeling indicates that the 3-year flood event streamlines rapidly expand laterally past the bridge abutment on the western side of the bridge to flow out into the southwestern floodplain during all significant flood events. There is little or no expansion (or constriction) to the northeast because the eastern abutment of the bridge is situated on the eastern scarp of the river valley. The construction plans for the bridge report that the maximum velocity in the channel immediately downstream of the bridge during a 100-year flood event is 4.9 feet/second (1.5 meters/second) (Saginaw County, 2001).

There have been no significant erosion scars noted in the vicinity of the bridge during the 2007 field investigation. A high resolution bathymetric survey is planned for the area of the Tittabawassee Road Bridge in 2008. There is no bank

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armoring in the vicinity of the bridge, except at the abutments, and no discernable impact on channel migration since 1937.

State Street Bridge

State Street Bridge (County classification: Bridge B1 of 73-25-23) crosses the river at Station RMM 927+00, which is the lower boundary of river Reach MM of the MTR. The present bridge is a reinforced concrete bridge on reinforced concrete piers spaced on 70 foot centers. Construction of the current structure was completed in 1980 (Saginaw County, 2008). There are five spans between the concrete abutments for a total bridge width of 350 feet.

There is an additional bridge span on State Street that crosses a tributary within the floodplain approximately 3,400 feet to the west of the main bridge. This western span crosses a historic tributary that is clearly evident in historical plat maps of the area and can be discerned in the current high resolution aerial topography. The bridge is approximately 340 feet wide between abutments with three concrete piers spaced approximately 50 feet apart. The date of construction of the current structure is unknown, although a bridge span is observed at this location in the 1937 aerial photograph. The EFDC modeling indicates that this western bridge passes streamlines during a 3-year flood event that have left the main channel as far north as Tittabawassee Road to flow along the western scarp down to State Street. No significant constriction of 3-year flood streamlines is apparent from the modeling at this western bridge location.

At the main channel of the State Street Bridge, EFDC modeling indicates that there is little to no constriction of flood streamlines from the western floodplain during a 3-year flood event; some constriction during an 8-year event; and a moderate constriction of streamlines during a 100-year event. The eastern side of the channel is constrained by the eastern scarp of the river valley. The river channel at and near the bridge has moved 20 to 45 feet to the west toward the outside bend/eastern scarp between 1937 and 2006. There has been a net increase in channel width at the bridge location during this period of approximately 30 feet. The present bridge structure does not appear to be having an effect on this natural

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channel movement toward the outside bend. ATS field teams did not observe any significant erosion scars in this area of the river.

Other Abandoned Bridge Crossings

Recent field observations and high resolution aerial photography have revealed the location of an abandoned bridge crossing at river Station RMM 901+50 in upper Reach MM. Four stone in-channel pier footings and shoreline abutments can be clearly seen in the 2007 aerial photography taken during low water conditions on the river. An 1877 plat map of the area shows that Hospital Road, due north of these remnant footings, once crossed the river at this location. The 1877 plat map also reveals that there was a brickworks on the northeastern side of the river near the historical bridge (Saginaw Township, 1877). Remnants of the bridge piers, abandoned road and the brickworks can be seen (albeit with poor photographic resolution) in the 1937 aerial photograph of the area.

EFDC modeling indicates that the abandoned bridge pier foundations in this area are having no significant effect on hydrodynamic conditions through this area of the river. No erosion scars were observed that could be attributed to the abandoned foundations.

4.3.2.6 Recreational Areas Three recreational areas have been developed along the MTR in recent time: Freeland Festival Park, Tittabawassee Township Park, and Imerman Memorial Park

Freeland Festival Park is located in Tittabawassee Township on the western shoreline and overbank of the river in Reach V, just north of Freeland Road Bridge. The present improvements were constructed between June and September of 2005 as a part of an Interim Response Action (IRA) at this location funded by Dow. A detailed description of the park construction activities, present facilities, and IRA measures are included in the RIWP for the Tittabawassee River and Floodplain (ATS, 2007a).

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Tittabawassee Township Park is located along portions of Reach S on the northeastern overbank of the river between Stations RS 406+00 and RS 412+00. The majority of the park improvements lie outside the 100-year floodplain northeast of “Old Midland” Road. Within the floodplain, the only improvements consist of paved drives and parking areas adjacent to the river in the forested areas of the park. There is no improved river access at this location. Based on a review of the high resolution 2006 aerial topography, the only earthworks within the 100- year floodplain boundary in the park was placement of the fill for the access road leading from Old Midland Road down to the shoreline.

Imerman Memorial Park is a 96 acre park with significant improvements located within the 100-year floodplain of the river along Reaches II and JJ. From a review of historical aerial photographs and the 2006 high resolution aerial topography, the only discernable recent earth change activities consisted of placement of the fill for the paved access road through the park, the excavation for the boat launch, creation of two small mounds to raise pumped toilet facilities above the floodplain elevation, and improvements to the drainage channel at the southern end of the park. The main access road into the park was started in or around 1963 and the principal park improvements were completed by 1992. Until recently, the area of the park was zoned “Extractive” and there is some indication of sand mining in the 2006 high resolution topography of the site, especially in the inside bend levee systems at the southern end of the park. There are visual indications of partially re-vegetated mining activities in these southern levees in the 1937 aerial photograph. By 1941 the southern levee areas were re-vegetated. From 1937 to 1963, the area of the present day park was partially farmed and partially forested.

Interim Response Activities (IRAs) funded by Dow were conducted within the 100-year floodplain boundaries of Imerman Memorial Park between November 2004 and April 2006 to mitigate the potential for direct contact exposure to surface soils in high use areas of the park and to address erosion along the river at the northern end of the park near the present observation deck and riprap armoring. A detailed description of the 2004 to 2006 park construction activities,

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present recreational facilities, and IRA measures are included in the RIWP for the Tittabawassee River and Floodplain (ATS, 2007a).

4.3.3 Present Land Use Tax Classification A review of the 2007 land use designations assigned by the Saginaw County Zoning Department found a substantial difference in the boundaries for “Residential” land use from those identified in earlier reports. A reanalysis of land use was conducted using the Saginaw County land use tax classification dataset for the FEMA 100-year floodplain within the Tittabawassee River watershed boundary. The dominant land use tax classes within Saginaw County in the Study Area are residential (45 percent) and agricultural (27 percent). The exempt and institutional tax class accounts for approximately 11 percent. As presented in Attachment G, agricultural tax class areas are located primarily between Reach Q and Y and between Reach FF and NN and residential tax class areas are located primarily between Reach Z and JJ and between NN and YY. Table 4-3 provides a summary of the total acreage for each land use tax class in Saginaw County within the Study Area.

Table 4-3 Saginaw County Tax Class Summary – Tittabawassee River Study Area

Tax Class Description Acreage Percentage Unassigned 140 3% Agricultural 1,493 27% Commercial 463 8% Developmental/Transitional 158 3% Exempt/Institutional 586 11% Industrial 218 4% Residential 2,516 45% Total 5,574 100%

4.4 CHANNEL, FLOODPLAIN, AND VALLEY MORPHOLOGY 4.4.1 Introduction to Stream Classification For more than a century, the Tittabawassee River has undergone numerous changes in its floodplain and channel as a result of anthropogenic influence. Floodplain impacts have included removal of vegetation, changes in vegetation density and type, alterations in landforms and construction of encroachments that block the flow-path of flood flows, including roadway embankments and pipeline crossings. The channel itself has been

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impacted by changes in its boundary conditions, including removal of vegetation and artificial hardening with levees and sheet-pile walls. The construction of several dams upstream of the Midland Plant has likely created conditions of “clear water discharge”, changing the rivers sediment supply downstream. All of these anthropogenic influences have likely, in some way, affected river stability and sediment supply, thereby creating the potential for negative impacts in the form of excess erosion and deposition.

The extent, magnitude, frequency, and duration of the responses of the Tittabawassee river to these influences can be analyzed through a systematic, quantitative assessment of historic land use changes, channel processes, sediment supply, and future evolution of the river. Essential to this assessment is the ability to separate natural and anthropogenic influences, and to predict how the river will reach an equilibrium state through a balance of energy and sediment supply (Rosgen, 2006). While this assessment necessarily involves numerous levels of data collection, analysis, and prediction, it begins with a broad-level classification of the river. Such a classification helps provide an overview of the general state of the river, allows separation of the river into areas of distinct morphology, and elucidates future data collection and analysis needs.

For this investigation, Rosgen Level I and Level II classification methodology (Rosgen, 1996) provided the framework for this classification. However, deviations have been necessary due the lack of field-verified bankfull elevations. Since Level I and Level II classification does not require a great deal of field survey data, the approximations made for this classification are a reasonable deviation from standard methodology. It is not expected that acquisition of more detailed field verified data will alter the results of the classification for the River Regions discussed below. Later, more detailed levels of classification will incorporate a greater amount of data collection and involve a higher level of analysis that comports with the river assessment standards established by the US Environmental Protection Agency (USEPA), and the Rosgen methodology. This assessment provided a broad, general classification that allows for a rapid initial delineation of stream types and illustrates the distribution of these types that would be encountered within a given study area. The Level I classification and delineation process provides a general characterization of valley types, and identifies the corresponding major stream types, A through G. Illustrations of the Level I stream types are shown in Figure 4-10.

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Figure 4-10. Level I Stream Types

Attachment H presents the complete stream classification report including a detailed description of methodology.

4.4.1.1 Delineation of Regions A “Region” for the purposes of this report means a section of the river valley, floodplain, and channel which displays similar valley type, width and slope, and similar channel sinuosity, pattern, profile and cross-sectional dimension. Once these approximate Regions were delineated, more precise measurements of dimension, pattern, and profile were undertaken in each Region to facilitate analysis at higher levels of classification.

Nine river Regions were delineated, based on observation of valley and fluvial pattern trends, an examination of average water surface slope between significant fluvial features, and profiles of the median water surface elevation data and the thalweg. To the extent reasonable, the beginning and ending stations of the River Regions were placed to correspond with the beginning and ending stations of the

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River Reach designations developed during earlier phases of the Tittabawassee River investigation. These Regions and respective station limits are presented in Table 4-4. The table also provides valley length, stream length, and sinuosity measurements.

Table 4-4. Summary of Tittabawassee River Regions River Classification Station Range Valley Length Stream Sinuosity (Stream Region Start End (ft) Length (ft) Length/Valley Length) Region I RA 0+00 RD 57+50 15,050 16,350 1.09 Region II RE 57+50 RK 233+50 6,592 7,000 1.06 Region III RL 233+50 RY 546+50 30,781 31,300 1.02 Region IV RZ 546+50 RDD 678+00 11,512 13,150 1.14 Region V REE 678+00 RII 783+00 9,033 10,500 1.16 Region VI RII 783+00 RKK 872+50 8,243 8,950 1.09 Region VII RLL 872+50 RPP 1014+50 11,818 14,200 1.20 Region VIII RQQ 1014+50 RUU 1145+50 11,212 13,050 1.16 Region IX RVV 1145+50 RYY 1280+00 13,671 14,750 1.08

Following the delineation of the Tittabawassee River into distinct Regions, a more detailed analysis of plan, profile, and cross-section of the river was undertaken. The broad-level classification of rivers is based on morphological features associated with stream patterns, shape (width/depth ratio) and vertical containment (entrenchment ratio) (Rosgen, 2006). To begin this classification, river transect data surveyed from bathymetry were obtained from other investigators and entered into RiverMorph® software. Several transects were selected in each River Region as representative of river features (pool, riffle, etc.) for that Region. Field-measured bankfull data was not available for this analysis. Therefore, an approximate bankfull elevation was estimated for each cross-section by finding a feature that most closely resembles a bankfull indicator that would be located in the field (e.g., the top of the shoreline surface depositional feature below the floodplain, an inflection point on the top of a point bar, or the topmost point of an area of scour). To verify the approximation, “regional curves” were used. These are regression equations which show the relationship between the drainage area of river and its width, mean depth, flow and cross-sectional area at bankfull stage, in similar physiographic regions. In most cases, the regional curve bankfull area was very close to the bankfull areas calculated at each cross-section. Where great differences were apparent between the two values, the bankfull elevation of the cross-section was adjusted to match the area with the regional

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curve value to see if it corresponded with an inflection point along the graph. On cross-sections where the regional curve area did correspond to a point on the graph, the bankfull was left at this elevation.

The results of the broad level classification for each River Region are summarized in Table 4-5. Figure 4-11 presents a plan view of the entire river, with the limits of each River Region. Short descriptions of each Region are also provided below.

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Table 4-5. Summary of River Classification by Region

Stream Type Stream River Classification River Classification Region Bankfull Width (Wbkf) (ft) Bankfull Depth (dbkf) (ft) Bankfull X-Section ft) (sq. Area (Abkf) Width/Depth Ratio (ft/ft) (Wbkf/dbkf) Maximum Depth (ft) (dmbkf) Width of Flood-Prone (ft) Area (Wfpa) Ratio Entrenchment (ft/ft) (ER) Channel Materials (Particle Size Index) (mm) D50 Water Surface Slope (S) (ft/ft) Channel Sinuosity (k) Typical "C" < .001 - >12 >2.2* >1.2* Characteristics .039 Region I Region I cannot be accurately classified according to the classification system for natural rivers due to anthropogenic impacts Region II 247.7 10.9 2,709 22.6 17.4 1,206 4.9 0.26 0.00012 1.06 C5c- Region III 298.6 9.9 2,952 30.2 15.0 3,003 10.1 0.33 0.0001 1.02 C5c- Region IV 283.2 5.1 1,438 55.7 7.5 1,345 4.7 0.24 0.00006 1.14 C5c Region V 142.0 6.9 1,956 20.6 7.6 2,706 19.1 0.19 0.00022 1.16 C5c- Region VI 379.9 8.4 3,174 45.4 11.1 2,028 5.3 2.1 0.0001 1.09 C4c- Region VII 400.0 9.0 3,586 44.6 15.9 2,070 5.2 1.8 0.00021 1.20 C5c- Region VIII 337.5 11.8 3,987 28.6 14.9 2,800 8.3 0.18 0.00005 1.16 C5c- Region IX 410.5 10.5 4,299 39.2 14.2 1,200 2.9 0.47 0.0001 1.08 C5c- *Values are guidelines, and use of judgement may place values that are close to the typical stream type chararacteritics within that stream type.

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Figure 4-11. Plan View of Tittabawassee River Regions

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Region I Region I extends from the beginning of the Tittabawassee River study area at Station RA 0+00 to the Dow Dam, located at Station RD 57+50, and encompasses Reaches A through D. The distinguishing characteristic of this Region is the Dow Dam, which likely affects the sediment regime of the river downstream. While the river upstream of the Dow Dam appears similar in its planform to the river downstream due to the influence of the Midland Plant, it is hypothesized that the sedimentological differences between upstream and downstream are great enough to warrant using the Dow Dam as the separating point between Region I and Region II. Sediment data were not available for this level of analysis, however dams and impoundments often create conditions of “clear water discharge”, which can significantly affect the sediment regime of a river downstream of the dam. “Clear water discharge”, also referred to as “hungry water”, describes the effect of interrupting the continuity of sediment transport through a system with either a dam, impoundment, or mining activities, and thereby creating flow that is sediment-starved downstream of the activity. This sediment-starved flow is prone to erode channel bed and banks and create channel incision (Kondolf, 1997).

The valley of Region I appears to be almost completely anthropogenically modified, to the point of being unable to classify the valley type accurately. There is a levee or berm along the banks of the river for the entire length of this Region. Additionally, the floodplain is occupied by the industrial complex of the Dow Midland Plant. The width of the valley is much narrower here than at other Regions along the river. Visualization of bathymetry shows that, while several deep pools are present along this Region, the influence of the Dow Dam and levees may be causing a general trend of aggradation in the channel.

Region II Region II lies between Stations RE 57+50 and RK 233+50, corresponding with Reaches E through K. It is bounded on the upstream and lower ends by the Dow Dam and E. Gordonville Road respectively. The Region was delineated within these bounds primarily due to the influence of the dam, which may be creating conditions of “clear water discharge”, the increasing valley width along this Region, the significant decrease in the belt width of the river, and an increase in water surface slope. This Region appears to be a transition between the anthropogenically impacted floodplain and narrow valley of Region I, and the low belt width, but wider valley of Region III.

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This Region is bounded on the west by a brine pond and the artificial embankment associated with it, and on the East by agricultural fields and extensive ditching. A levee is present along both banks of this Region for all of its length. Bathymetric data shows the channel to contain several transverse bars, a trend that is continued into Region III.

Region III Region III is the longest of all the Regions, extending 5.9 miles from Station RL 233+50 to Station RY 546+00. It begins just downstream of the East Gordonville Road Bridge and continues to just downstream of the Town of Freeland, and corresponds with Reaches L through Y. Within Region III the valley is significantly wider than in Region I and II, ranging from 1,000 to 3,000 feet in width. A levee is present along both sides of the river; however, there are occasional ‘breaks’ in the levee from streams flowing into the river as well as several locations where the levee is absent. Land use of the valley within this Region is primarily a mix of woodlands, pastureland, and agricultural land. Some of the wooded areas appear to be quite wet, occurring in localized depressions.

Region IV Region IV is located between Stations of RZ 546+50 and RDD 678+00, and includes River Reaches Z through DD. The downstream station limit of this region is defined by the crossing of Tittabawassee Road. Region IV is characterized by a decrease in overall valley/floodplain width from Region III, but with a marked increase in observed beltwidth. Unlike Region III, the meanders of this Region stretch laterally to meet the sheer valley walls. From aerial photography, the floodplain appears to be a mixture of forest and cropland, with Midland Road and North River Road defining the floodplain boundaries on the sides of the valley. The channel itself contains 3 significantly long pools, located not on the meander bends, but rather in the straight sections of the river, which is the reverse of what is normally observed in a natural river system. The meander bends themselves are comprised of relatively long point bars, lateral bars and transverse bars. According to geomorphic surface data, the channel is bordered by historic natural levees.

Region V Region V is a somewhat unique section of the Tittibawassee River because of the occurrence of a historic oxbow, a wide flood-prone overbank, and channel processes that create relatively high sinuosity. This Region is approximately 10,500 feet in length and

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corresponds with all or part of Reaches EE, FF, GG, and HH. Region V is bounded on the upstream end by Tittabawassee Road and on the lower end by significant contraction in the width of the flood-prone overbank. The Region was delineated within these bounds primarily due to the increasing valley width, the occurrence of the oxbow, and the change in pattern when the area is observed in plan view.

This Region is bounded on the NE by a broad overbank floodplain with a classic historic oxbow formation. High, medium, and low terraces occur on the NE overbank floodplain moving from high to low away from the channel. The oxbow provides evidence of the historical changes in the River’s pattern in response to the increased flood-prone overbank width. Region V is bounded on the SW by the varying widths of floodplain with the floodplain actually disappearing at one point where the channel strikes the valley wall (glacial till) at a fairly sharp, meander bend. A levee is present along the SW bank as the channel approaches the valley wall and along the NE meander bend. This meander, located in Reach GG, is unique in pattern when compared to the rest of the river and likely indicates a changing planform. The bathymetric data shows a contraction in the vicinity of this meander and supports observations of a changing planform for this Region.

Region VI Region VI is located between Stations RII 783+00 and RKK 872+50, and is a relatively short section extending only 8,950 linear feet. The first 2,000 foot stretch exhibits a classic meandering pattern with clearly identified pools and riffles that is characteristic of a “C-type” stream. However, the rest of this Region is almost straight, and the river has become over widened which has caused sediment to begin to deposit in a long riffle. The

particle analysis supports this observation, as the D50 particle size has increased from 0.19 mm to 2.1 mm compared to the Region V (Table 4-5).

Region VII Region VII is bounded by Stations RLL 872+50 and RPP 1014+50. This Region is characterized by an increase in floodplain and valley width, which continues to widen downstream into Regions VIII and IX. The floodplain in this Region is defined by the presence of sheer valley walls (upland scarp), on top of which is a greater degree of residential and commercial development than upstream, while the floodplain itself is comprised of cropland and forested areas. The floodplain in this Region is also

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encroached by State Road, which cuts across the Region near Station RNN 927+00. The channel possesses a historic natural levee along its length. Perhaps the most significant aspect of this Region is that it has the steepest water surface slope of any of the river Regions, and possesses several relatively long and steep riffles.

Region VIII Region VIII extends 2.5 miles from Stations RQQ 1014+50 to RUU 1145+50. This Region begins at the Gratiot Road Bridge and continues downstream to the South Center Road Bridge, and corresponds with Reaches QQ through UU. The overbank valley is relatively wide through this Region extending in some locations for over a mile. Adjacent land use within the valley varies from undeveloped woodland to pastureland to developed residential and commercial areas. The roads and the railroad located near the midpoint of this Region provide a constriction within the valley. While a small levee appears to be present adjacent to the river banks there are numerous breaks, and it likely does not restrict access to the floodplain as much as in other Regions.

Region IX Region IX is comprised of the most downstream section of the Tittabawassee River before its confluence with the Shiawassee and Saginaw Rivers. This Region is approximately 13,450 feet in length and corresponds with all or part of Reaches UU, WW, XX, YY. Region IX is bounded on the upstream end by North Center Road and on the lower end by the confluence with the Saginaw River. The Region was delineated within these bounds primarily due to the increasing valley width and the perceived backwater effects from the Saginaw River.

This region is bounded on the NE by a broad floodplain that is predominately made up of low terrace features. Natural levees exist on both banks of the river in this Region. The River is bounded on the SW by a broad floodplain that extends to the Saginaw River. Levees are intermittently present along both banks and on several inside meanders. The bathymetric data shows a consistent pattern of riffles, pools, and classic point bar formation.

4.4.2 Existing Channel Morphology and Mapping In-channel sample locations were selected based on transects identified during the 2006 field season based on changes in channel width and sinuosity. The 2007 in-channel sample locations

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between Station RA 0+00 at the upstream edge of Reach A through Station RV 486+00 at the downstream edge of Reach V were based on the bathymetric survey conducted in 2007 of the river channel bottom to define areas of potential deposition and channel scour.

River systems develop a pool and riffle sequence as a result of sediment transport dynamics within the riverine system. The pools represent depositional areas where the channel gradient flattens resulting in deeper water and slower water velocities. The riffles represent areas of steeper channel gradient, shallower water, and increased water velocities. Because of the differences in water velocity, the bed load particle size varies between pools and riffles. The 2007 bathymetry maps show a distinct, yet irregular pool and riffle system. The distance between and length of the pools and riffles varies greatly in the Tittabawassee River system.

River channels develop distinct sediment deposition patterns based on sediment grain size, bed geometry, water velocity, shear stress, anthropogenic influences, sinuosity of the channel, and water depth. The thalweg is the portion of the river channel with the highest water velocity and maximum depth in the channel cross section. The thalweg has the least amount of deposition in the channel cross section. In a straight reach of the river, the thalweg will be present in the middle of the channel. In a meandering river, the thalweg will alternate from the outside of the meander bend, cross the channel between meanders, and continue on the outside of the meander bend on the opposite bank from the upstream meander, creating an “S” shape.

In-channel deposition in a straight reach of the river occurs in braid bars which are areas of sediment accumulation near the middle of the channel. The sediment deposition pattern present in a meandering river reach stores sediment in point bars on the inside of the meander bend. In- channel deposits are most stable in the point bars as a result of lower water velocities on the inside of the meander bend.

Sample locations in the Tittabawassee River were selected along transects perpendicular to river flow where changes in depositional patterns were observed. Along each transect, sample locations were placed within each distinct depositional area. For example, in a typical transect, one sample location would be selected from the thalweg, one from the near thalweg deposits, one from the point bar, and one from the near bank point bar deposits. This sampling approach provided a representative sediment profile, representative of localized depositional patterns within the transect and of areas immediately upstream and downstream that demonstrated a similar deposition channel cross section.

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4.4.3 Existing Floodway Morphology and Mapping Detailed surface mapping of the location and extent of fluvial geomorphic landforms within Middle Tittabawassee River valley, between river Stations RP 335+50 and RMM 927+00, was initially developed prior to the 2007 field season. This section of the Tittabawassee River valley is composed of eight distinct geomorphic surfaces, each representing a unique depositional and/or erosional environment produced by the river over time.

Shoreline surfaces are located adjacent to the channel and are frequently flooded, often remaining submerged during periods of high water. Natural levees and historic natural levees are usually found within 100 feet of the main channel and represent topographically elevated deposits largely consisting of sandy overbank flood sediments. Low, intermediate, high, and upper high surfaces occur across the width of the river valley and each constitutes a depositional unit of like elevation representing a unique suite of fluvial processes. Interspersed among other surfaces, geomorphic wetlands occupy closed or partially confined depressions and are seasonally or perennially saturated. Areas outside of the river valley were mapped as upland.

Initial mapping was completed using a combination of detailed topographic and aerial imagery. One-foot contours were used as a base on which to initially map the geomorphic surfaces, paying particular attention to the specific topographic “signatures” of each surface. For example, levees could often be identified by a very narrow set of closed contours running adjacent and parallel to the channel banks. Aerial photographs were used to refine geomorphic wetland boundaries and identify topography affected by anthropogenic disturbance (e.g., man- made ditches, roadbeds, etc.).

In spring 2007, the preliminary mapping was field verified by visual observation for accuracy. Prior to emergence of spring vegetation, all parcels with property access were walked and surfaces were visually identified and compared to the preliminary mapping. A tablet PC and Leica GPS unit were used to record areas where discrepancies existed between the visual observation and the initial desktop mapping to facilitate follow-up changes. Areas with restricted or prohibited access were not field verified.

During and after the 2007 field season, additional field verification was made based on the soils and analytical data obtained during the field season. Changes in property access rights also allowed for additional field verification to be completed. Because certain surfaces contain distinct soil and/or contaminant profiles, such data provided an additional means by which to

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verify the initial mapping. Locations where soil and/or contaminant profiles did not match nearby locations on similar geomorphic surfaces were flagged for additional field verification. Final field verification was completed in December 2007, following the fall loss of vegetation. Flagged locations were revisited and final surface mapping determinations were made using a combination of visual, soil, and analytical indicators.

4.5 HYDRODYNAMIC MODELING During the 2007 investigation, incremental updates and improvements were made to the two dimensional environmental fluid dynamics code (EFDC) model of the Tittabawassee River and floodplain. Initial model development is detailed in Appendix J of the GeoMorph® Pilot Site Characterization Report, Upper Tittabawassee River and Floodplain Soils (ATS, 2007c). Since this report, incremental changes have been made to the model with old events being re-run through the model and new events being run as needed.

4.5.1 Updates to EFDC Model Incremental updates were made to both the model topography and bathymetry as more detailed data sets became available. Topography for the entire model domain, extending from the Dow Dam downstream to the confluence of the Tittabawassee and Shiawassee River, was updated in the model. Information for this updated topography was collected in 2006 and processed in 2007 by Advance Mapping Technologies Inc. Bathymetry from the upstream edge of Reach E (i.e., Dow Dam) extending to the downstream edge of Reach V (i.e., the Freeland Road Bridge) was also updated in the EFDC model. The bathymetry was collected and processed in 2007 by TetraTech EC, Inc. Information on topography and bathymetry detail, collection and processing methods and topographical extent is provided in Section 2.4 and Attachments B-1 and B-2.

4.5.2 Flood Events After updates to the topography and bathymetry were made, the simulations of the March 2004 and May 2004 flood events (used previously for calibration) were run again using the EFDC model and the new outputs compared to available data. As before, EFDC model results compared well with available stage, flood extent, and velocity data and no additional calibration was necessary. The 1986 event (the largest event in the USGS period of record) was also run through the updated EFDC model.

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Analyses of the 1-year, 1.5-year, 2-year, 5-year, 10-year, 25-year, 50-year, 75-year, 100-year, and 500-year recurrence interval flooding events were also performed using the EFDC model. These simulations were run using a steady upstream flow rate and downstream water surface elevation as boundary conditions. Similar to the unsteady flow simulations, the downstream boundary of the EFDC model at the confluence area was set using results obtained from the 1- dimensional full equations model (FEQ) of the Saginaw River and floodplain. Flow rates for the FEQ model were determined using available USGS gage data. The downstream boundary was set based on a median Lake Huron water surface elevation at Essexville Michigan. For both the EFDC model and the FEQ model, flow rates for various recurrence intervals were selected based on a log Pearson Type III recurrence interval analysis of available USGS gage data, discussed in more detail in Section 4.2.2. Outputs of the unsteady and steady flow EFDC runs included flood extent and stage and velocities and shear stress values in the river and floodplain. These outputs were used to assist in the development of a conceptual site model for the Tittabawassee River and floodplain. Complete river and floodplain EFDC Model peak velocity and sheer stress output for the 1-year recurrence interval event, the 1.5-year recurrence interval event, the March 2004 (~8-year recurrence), May 2004 (~3-year recurrence), and the 1986 event (~77-year recurrence) is provided in Attachments I. Flood extent results for the 1- year, 1.5-year, 2-year, 5-year, 10-year, 25-year, 50-year, 75-year, 100-year, and 500-year recurrence interval flooding events are discussed in Section 4.2.1.

4.5.3 Streamline Analyses In addition to the velocity, shear stress, and flood extent estimates calculated by the EFDC model itself, model output was processed to develop streamlines from locations of interest. Streamlines represent the paths that neutrally buoyant individual particles follow in a flow field. For each streamline, a point of origin was first selected within the model river or floodplain model domain. A velocity magnitude and direction was next interpolated from the EFDC velocity output data at the point of interest, and the next point along the streamline was then determined by calculating the distance a neutrally buoyant particle would travel in a small period of time using the previously interpolated velocity. This process was repeated until the boundary of the model domain was reached, resulting in streamlines that extended from the point of interest both upstream and downstream, in the river and floodplain. For this modeling effort, streamlines were created for sample points of interest in the Tittabawassee River and floodplain. Processed streamlines were used to assist in the understanding of stream flow paths in the river and floodplain, and provided an understanding of how predicted flow paths of water

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and sediment contributed to development of the observed geomorphic depositional features described in Section 3.

4.5.4 Stream Power Analyses Performed Using Results of EFDC Simulations Estimates of in-river and floodplain stream power values were also calculated using EFDC model output. The concept of stream power is essentially the amount of work per unit time (power) available within the river at a particular location and is directly related to the sediment carrying capacity of the river at this location. Stream power can also be normalized as stream power per unit length, called unit stream power (watts/m), or stream power per area, called specific stream power (watts/m2). Stream power estimates can be related to the sediment carrying capacity of river and floodplain flows at various locations throughout an event, provide estimates on the mobility of sediments at a particular location, help predict riverbed morphology for a given sediment size, and provide an estimate of likely erosional and depositional zones in the river and floodplain throughout an event. Calculations of specific stream power were made for the entire river and floodplain and these results were used to assist in the development of a conceptual site model for the Tittabawassee River and floodplain. A typical output of calculated specific stream power near Reach L is provided in Attachment I. The complete river and floodplain EFDC Model peak stream power output for the 1-year recurrence interval event, the1.5-year recurrence interval event, the March 2004 (~8-year recurrence), May 2004 (~3-year recurrence), and the 1986 event (~77-year recurrence) is also provided in Attachment I.

4.6 TRIBUTARY AND WETLAND HYDRODYNAMIC INFLUENCES This section presents a discussion of the hydrodynamic influences of the Tittabawassee River tributaries and wetlands, with a primary focus on those located upstream of Midland. A separate discussion is also provided of tributaries and wetlands located between Midland and the confluence of the Tittabawassee and Shiawassee Rivers. These discussions are separated because of the very different characteristics of the sub-watersheds above and below Midland. Above Midland, the Tittabawassee is fed by major tributaries that contribute a significant fraction of total flow. The Tittabawassee River system drains approximately 6 percent of Michigan’s Lower Peninsula. Flows and solids delivered by the river at Midland are the product of this upstream portion of the watershed. Between Midland and the confluence, the watershed is largely confined to the floodplain adjacent to the river, and tributaries are limited to drains and small streams, which contribute proportionately little flow to the mainstem of the river. These features are nevertheless important as topographic features affect flow velocities and solids deposition.

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4.6.1 Tributaries Upstream of Midland Most of the area (96 percent) of the Tittabawassee River watershed is located upstream of Midland. Major tributaries that feed the Tittabawassee upstream of Midland include the Pine River, the Chippewa River, the Tobacco River, and the main stem of the Tittabawassee River itself. Based on an overview of total drainage area, much of the flow in the river originates in its upstream tributaries.

These tributaries are also important sources of sediment to the Tittabawassee River. The 1995 Saginaw River and Bay Remedial Action Plan (MDNR, 1994) indicates that a large portion of the soils in the tributaries above Midland are of poor quality, with a high risk of erosion. Nineteenth century clear-cut logging practices, which are discussed in Section 4.3.2.1, made soils in previously forested lands vulnerable to erosion, and conversion of those forested lands to tilled farmland provided a continuing source of solids to the Tittabawassee and its tributaries. The widespread use of drainage tile to eliminate wetlands, making them available for farming, has decreased the time of concentration for flood events, increasing the flashiness of the river system.

Suspended solids loads have been measured at several bridges downstream of Midland, and these data indicate that the solids load is large during wet weather events (LTI, 2004). TSS concentrations of up to 88 mg/liter were measured on the Tittabawassee River bridges downstream of Midland during wet weather events and a TSS sample of 320 mg/liter was recorded by an ISCO sampling device at the Downstream end of the Tittabawassee River near the confluence, though peak wet weather TSS values near 100 mg/liter were more typical. Bed load, which is the movement of coarse particles by saltation along the sediment bed, may be another important mode of solids transport in the Tittabawassee as evidenced by the presence of dune bed forms in many areas of the sediment bed. Additional information will be obtained during 2008 to better understand the extent of bed load present within the river system at various flow rates. Dams on the Tittabawassee are all “run-of-the-river”, including the Dow Dam in Midland, and provide little storage or control of wet-weather flows, also allowing passage of solids at higher flows. The Pine River has no dams and may be a significant contributor of solids to the Tittabawassee, based on its contribution to flow. TSS measurements on the Chippewa just downstream of the Pine/Chippewa River confluence taken by an ISCO sampling device measured concentrations as high as 180 mg/liter during wet weather events (LTI, 2004).

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4.6.2 Tributaries and Wetlands between Midland and the Confluence Area In contrast, the tributaries between Midland and the confluence of the Tittabawassee and the Shiawassee Rivers bring only minor proportions of flows and solids into the Tittabawassee River system, based on an analysis of drainage area. Their primary significance is as topographic features that can increase river and floodplain water and sediment interchange during events, and can also affect water depth and velocity. Table 4-6 gives the watershed area and percentage of total watershed of four creeks and drains downstream of the Tittabawassee river confluence in Midland.

Table 4-6. Watershed Areas of Selected Tributaries Downstream of Midland Percentage of Watershed Tributary Total Area miles2 Watershed Bullock Creek 31.6 1.3% Lingle Drain 3.6 0.1% Sarle Drain 0.6 0.0% Shaffer and Major Drains 4.7 0.2% Ref: Watershed estimates calculated from state and federal GIS sources.

Where tributaries cut through levees, they provide a direct flow path from the main channel to floodplain bottom lands. Flow velocities decline as flows pass from the channel to the adjacent floodplain. This decline in energy promotes net solids deposition in floodplain areas near minor tributaries, with the coarsest sediments tending to be found nearest to the river channel as measured along event flow paths. These tributaries are also a local source of sediments at lower flows, where they meet the main Tittabawassee River channel. As tributaries meet the deeper waters of the channel, in-channel bars often form, as identified in Reach O during the 2006 UTR site investigation (ATS, 2007c).

Under flooding conditions, tributaries and wetlands in the floodplain become deep spots in a widened river, with lower flow velocities and longer durations of flooding than other floodplain areas. For this reason they can preferentially collect sediments, with the coarsest sediments tending to be found nearest to the river channel along event flowpaths. The minor tributaries include constructed ditches, and along the sides of some of these ditches there are piles of dredge spoils in the form of berms; an example is located in Reach O. These berms retain floodwaters at the falling limbs of major flow events, potentially enhancing net solids deposition behind the berms. Attachment J provides figures presenting the backwater effects of tributaries and wetlands over the course of a flood event.

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4.7 CONSTITUENTS OF INTEREST 4.7.1 Definition of Primary and Secondary Constituents of Interest (COI) The Tittabawassee River Sampling and Analysis Plans (SAPs) and Quality Assurance Project Plans (QAPPs) specify the 17 chlorinated dibenzofurans and dibenzodioxins used to calculate TEQ as the Primary Constituents of Interest (COI) in the Tittabawassee River investigation (ATS, 2006a-b; ATS, 2007b & d). However, because of the long and complex history of the Midland Plant as a manufacturer of chemicals, and the likelihood of other potential contributors of chemicals to the Tittabawassee River watershed, other potential constituents of interest (PCOI) are being evaluated as part of the site characterization. The SAP and QAPP documents identify these additional substances as site-specific, Secondary COI.

4.7.2 Primary COI Seventeen chlorinated dibenzofurans and dibenzodioxins used to calculate TEQ are the primary Constituents of Interest (Primary COI) in this investigation. These substances are known to be environmentally persistent. Certain furan congeners predominate in the mixture of furan-dioxin congeners present in Tittabawassee River sediments and floodplain soils downstream of Midland. Most of the Total TEQ is attributable to these furan congeners. As a result, a selected subset of selected furans and dioxins constitutes a useful suite of contaminants to assess the presence of sediment and soil impact.

Primary COI are measured using either Methods 1613-TRP/RT or 1613B. The details of these HRGC/MS methods, and their suitability for the TR project is discussed in the project QAPP (ATS, 2007d). Method 1613-TRP/RT is used to provide rapid-turnaround, near-real-time data based on site-specific congeners. Method 1613B is used for confirmation analysis when atypical congener patterns are encountered, or when information is needed on a specific furan or dioxin congener not included in the 1613-TRP/RT site-specific indicators.

A method comparability study of data generated by the two methods in 2006 found very good to excellent correlation over a concentration range of 10 ppt TEQ to 36,000 ppt TEQ, the range of samples evaluated (ATS, 2007e). The correlation coefficient (R-squared) for an unbiased data set (n=24) was 0.994 to 0.996, depending on whether second column confirmation was used for 1613B. The correlation coefficient for a data set biased to reflect atypical congener patterns (n=60) was 0.978 to 0.982, again depending on the use of second column confirmation for 1613B.

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For 2007 site characterization, the process of evaluating congener patterns and selecting samples for 1613B confirmation was automated using the following triggers developed from evaluation of the 3,800 samples analyzed in 2006:

• If the ETEQ concentration is greater than 50 ppt TEQ, and the 2,3,7,8-TCDD contribution to ETEQ exceeds 10 percent, the 1613-TRP/RT results are flagged for confirmation; • If the ETEQ concentration is greater than 50 ppt TEQ, and the ratio of (1,2,3,4,7,8- HxCDF + 1,2,3,6,7,8-HxCDF) to 2,3,4,7,8-PCDF exceeds 1.7x, the 1613-TRP/RT results are flagged for confirmation.

Flagging for either condition results in a QA/QC review of the congener pattern, and routing of the sample extract for 1613B confirmation using the extended, second column procedure. Approximately 5 percent of the samples analyzed in 2007 received such confirmation based on these triggers. Data from 1613B confirmation analysis replaced flagged 1613-TRP/RT results in the site characterization data summary reports and graphics as they became available. Method 1613B is a labor and time intensive procedure, and not all such confirmation results from 2007 samples were available at the time this report was prepared.

4.7.3 Secondary COI

PCOI/COI Evaluation Process Evaluation of Secondary COI for the Tittabawassee River investigation was a large and complex task, given the chemical manufacturing history of the 100+ year old Dow Midland Plant. This evaluation was undertaken in a collaborative effort between Dow, MDEQ, USEPA, and ATS in the summer and fall of 2006. The end products of this effort included a chemical database of more than 1,000 substances used and/or produced over the history of the Midland Plant, along with important physical properties, chemical properties, and analytical method references. This database was used to generate a series of method-based Target Analyte Lists (TALs) which identified the site-specific Secondary COI for Tittabawassee River samples, and assigned the Secondary COI to USEPA methods that would be used to measure them. The PCOI evaluation process was documented in a Technical Memorandum issued by ATS on December 1, 2006, and included as Attachment G in the Tittabawassee River Remedial Investigation Work Plan (RIWP) issued on that same day (ATS, 2006c-d). The list of target and extended target analytes for 2006 and 2007 samples is given in Attachment K.

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Secondary COI Sample Selection Criteria Sediment Deposition Zones The GeoMorph® investigation of the Tittabawassee River is based upon a site model that incorporates the environmental chemistry of specific contaminants with their fate and transport, as mediated by the hydrology and morphology of the river. In this way, the distribution of contaminants associated with river sediments can be mapped along with the erosion and deposition zones of the river. This is equally true for fine-grained sediments as well as medium/coarse grained sediments.

Because of the unique nature of the graphitic carbon source material for furan and dioxin Primary COI, these contaminants occur in all sediment size fractions. Geochemistry fractionation studies have confirmed they can occur in fine grained, silt and clay-sized material, as well as in larger material the size of medium and coarse-grained sands (Dow, 2007a-b). Accordingly, they are useful indicators of impact in all sediments of the Tittabawassee River. Based on the Primary COI, impacted deposition zones within the Upper and Middle Tittabawassee River include the following morphologic units:

• in-channel deposits • levees • ridge and swale complexes • wetlands • near-channel over-bank areas (e.g. immediately downstream from eroding, contaminated levee) • tributaries

Samples for characterization of Secondary COI are selected from deposits accreted over the past 150 years within each of these morphologic units and along the entire length of the river. Secondary COI samples are selected to be inclusive of deposited sediments spanning the entire range of furan/dioxin impact, and the entire range of particle size fractions up to large gravel/small cobble.

Other Factors In addition to sediment deposition zones, the following criteria are also used to select samples for Secondary COI:

• atypical furan/dioxin congener patterns;

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• proximity to historic outfalls; • evidence during coring or logging of visual, olfactory, or other characteristics suggestive of impact.

Atypical congener patterns can include elevated TCDD/PCDD content, indicative of residues from trichlorophenol processes, and/or elevated HxCDF content, indicative of residues from pentachlorophenol processes. An analysis of the location of historic outfalls was made in preparing the RIWP, and sampling transects have been located to provide information on residual impact, if any exists. In certain samples, visual or other physical clues suggest the possibility of impact.

Secondary COI Using USEPA Appendix IX – 2006 Samples While the 2006 field activities were underway and the PCOI evaluation process was being finalized, MDEQ and Dow agreed to gather some information on Secondary COI using the current USEPA Appendix IX list of target analytes and analytical methods. For this, a set of 24 samples from 22 in-channel and over-bank locations were selected from the 2006 UTR sample set. Included were a number of samples from the following locations selected to provide information about sediment composition at transects adjacent to known historic outfalls:

RD-55+00-IC-C RD-55+00-IC-SW2 RD-55+05-IC-NE RG-117+00-IC-C RG-130+50-IC-C RG-130+50-IC-SW RG-130+50-NE10 RG-130+50-NE30 RH-161+50-T-NE50 RH-161+50-T-NE265 RH-162+00-IC-C

The results of this analysis were presented in the February 1, 2007 Site Characterization Report (ATS, 2007c). Of the 221 target analytes, a total of 94 substances were detected in these samples.

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Site-Specific Secondary COI – 2006 Samples Using the selection criteria identified above, ATS collaborated with MDEQ in early 2007 to select samples from the 2006 UTR sample set for analysis of site-specific, Secondary COI. These included all 24 samples of the Appendix IX list, plus an additional 62 in-channel and over-bank samples. The number of locations and sample intervals for the morphologic units and river reaches are summarized in Table 4-7. A subset of six of these samples were also fractionated for particle size using the geochemistry study protocol, as described in Section 4.8 below, and Secondary COI were analyzed in the individual fractions.

The results of this analysis were reported to MDEQ and USEPA in July and August 2007. Of the 178 site-specific target analytes, a total of 117 substances were detected in these samples.

Site-Specific Secondary COI – 2007 Samples Based upon the criteria identified above, a total of 319 samples from 80 locations were selected for analysis of Secondary COI from the 2007 site characterization sample set. The specific locations and sample intervals are summarized in Table 4-8. Included are a number of samples from the following locations selected to provide information about sediment composition at transects adjacent to known historic outfalls:

RG-138+00-IC115 RH-151-50-IC33 RI-164+50-IC (three locations)

Of the 178 site-specific target analytes, a total of 123 substances were detected in these samples. These data, along with corresponding data from the 2006 samples, are discussed along with the Primary COI chemistry results in Section 5 below.

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Table 4-7.

290 South Wagner Road 2006 Secondary COI List (rev. 08.01.2007) Ann Arbor, Michigan 48103 Tittabawassee River Site Investigation Tel. 734/995-0995 Fax. 734/995-3731 Midland, Michigan Michigan Laboratory ID: 9604 Wisconsin Laboratory ID: 998321720

Deposition Zones

In-channel Levee Complex Ridge and Swale Wetland Complex Other Overbank Areas Tributaries

Reach Locations Samples Locations Samples Locations Samples Locations Samples Locations Samples Locations Samples

Reach A 2 2 Reach B 1 1 Reach C 1 1 Reach D 4 4 Reach E 2 2 Reach F 1 1 Reach G 3 3 26 Reach H 1 1 22 Reach I 1 3 Reach J Reach K 3 9 2 6 Reach L 1 1 3 15 Reach M 1 1 2 2 12 Reach N 1 6 Reach O 3 3 2 11 1 4

Subtotal 21 23 11 43 0 0 3 10 3 8 2 2

Locations (total) 40 Samples (total) 86

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Table 4-8.

290 South Wagner Road 2007 Secondary COI List (rev. 12.17.2007) Ann Arbor, Michigan 48103 Tittabawassee River Site Investigation Tel. 734/995-0995 Fax. 734/995-3731 Midland, Michigan Michigan Laboratory ID: 9604 Wisconsin Laboratory ID: 998321720

Deposition Zones In-channel Levee Complex Ridge and Swale Wetland Complex Other Overbank Areas Tributaries Reach Locations Samples Locations Samples Locations Samples Locations Samples Locations Samples Locations Samples

Reach E Reach F Reach G 1 3 Reach H 2 11 Reach I 8 27 Reach J 2 14 Reach K - - Reach L 5 12 Reach M 3 3 Reach N Reach O Reach P 1 1 1 5 1 6 Reach Q 2 15 3 12 1 1 Reach R 1 1 Reach S 2101 2 Reach T 1 5 3 12 2 9 1 1 Reach U Reach V 1 9 Reach W Reach X 24 Reach Y 11 Reach Z 2 8 2 8 Reach AA 16 11 13 Reach BB 2 6 1 1 Reach CC 1 9 1 1 Reach DD Reach EE 14 Reach FF 5 34 2 7 1 3 Reach GG 1 1 Reach HH 16 Reach II 1 10 1 9 1 5 Reach JJ 1 11 1 3 2 3 Reach KK 1 1 Reach LL 2 9 Reach MM 1 5 1 1

Subtotal 25 95 25 124 13 56 10 27 4 10 3 7

Locations (total) 80 Samples (total) 319

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4.8 GEOCHEMISTRY 4.8.1 Background The 2006 UTR site characterization confirmed previous findings of elevated furan and dioxin concentrations in medium and coarse grained soils and sediments, quite atypical for hydrophobic organic compounds. Further, the congener pattern of these residues was unique in that it was predominated by chlorinated furans. This is distinctly different from congener patterns characteristic of chlorophenol products and processes. Evaluation of the congener pattern, and analysis of the release history for the Midland plant, revealed these residues are most likely to have originated from direct chlorination of dibenzofuran in the coal tar binder of graphic carbon electrodes used in chlorine electrolytic cells.

4.8.2 Protocol Development Because the significance of this is important in the fate and transport-based GeoMorph® site characterization, a geochemistry fractionation protocol was developed in 2006 to provide empirical evidence. The protocol utilizes a combination of dry sieving and wet sieving/Stokes Law settling to obtain discrete particle size cuts. Each fraction is then characterized for:

• moisture content; • particle size distribution; • total organic carbon content; • “black carbon” content; • furan/dioxin concentration.

The protocol incorporates manual procedures that are labor and time intensive, therefore the number of samples that can be processed at a given time is limited.

4.8.3 Fraction Analysis - 2006 and 2007 Samples Thirteen sediment/soil samples from the 2006 UTR sample set were selected collaboratively with MDEQ for the initial set of analyses. The results, contained in a report issued to MDEQ and USEPA on March 30, 2007, confirmed the presence of elevated furans and dioxins in all particle size fractions, including medium coarse grained materials (Dow, 2007a). Further, the report concluded that subsample variability can be expected to increase as the furan/dioxin concentration increases. This unusual circumstance results from the presence of heterogeneously distributed particles of source material containing the furans/dioxins.

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The results from this fractionation work are summarized in Table 4-9. One of the samples in this group, RL-246+00-SW20 (5.0-6.0), taken from an industrial-age levee, contained relatively high concentrations of approximately 20,000 ppt ETEQ in the clay and silt fractions, and an unusually high concentration of 150,000 ppt ETEQ in the sand fraction. Two sand fractions, 53-2,000 µm (very fine to very coarse) and 250-2,000 µm (medium to very coarse), were further fractionated based on density using a cesium chloride solution. The objective was to separate siliceous material, having a density of approximately 1.7, from carbonaceous materials having substantially lower densities. In this density separation, carbonaecous material such as coal tar impregnated graphitic carbon, having a density of approximately 1.15, would be expected to separate with the light fraction.

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Table 4-9.

290 South Wagner Road GEOCHEMISTRY FRACTION ANALYSIS Ann Arbor, Michigan 48103 Tel. 734/995-0995 Fax. 734/995-3731 Michigan Laboratory ID: 9604 Wisconsin Laboratory ID: 998321720

Location Depth Interval (ft bgs) Geomorphic Unit Clay Fraction Analysis Silt Fraction Analysis Sand Fraction Analysis (<5 um) (5-53 um) (53-2000 um) ETEQ Fraction of Total ETEQ Fraction of Total ETEQ Fraction of Total (ppt) % (w/w) (ppt) % (w/w) (ppt) % (w/w)

2006 UTR Samples

RG-130+50-NE30 7.2-7.9 Low surface - <1.0* 6,700 2.1 96 94.3 " 7.9-8.8 " - <1.0* 4,000 3.8 2,100 93.9

RL-246+00-SW20 3.0-4.0 Natural levee 1,700 8.7 1,200 15.5 210 74.0 " 4.0-5.0 " 3,200 10.8 2,200 21.1 570 63.2 " 5.0-6.0 " 21,000 5.1 14,000 11.3 150,000 80.5 " 6.0-7.5 " 22,000 10.2 16,000 16.1 4,200 68.4 " 7.5-8.5 " 16,000 9.1 12,000 14.0 1,500 72.7

RL-246+00-SW85 0.0-0.6 High surface 7,200 4.0 4,100 9.4 670 84.2 " 0.6-1.5 " 5,000 4.5 3,100 6.6 640 86.3 " 1.5-2.5 " 305 3.8 230 6.4 0 89.4

RL-246+00-SW265 0.0-0.8 Geomorphic wetland 870 19.6 660 44.4 1,500 31.5 " 0.8-1.1 " 1,400 23.1 1,100 41.2 1,400 28.0 " 1.1-3.1 " 77 31.9 68 39.1 49 22.3

2007 UTR Samples

RD-55+10-IC-NE composite Waste deposit - <1.0* 29,100 52.0 11,400 52.4

RL-258+50-IC135 2.0-3.5 In-channel deposit - <1.0* - <1.0* 468 97.3

RL-258+50-IC196 1.5-4.0 In-channel deposit - <1.0* 11,300 5.3 4,060 94.9

RM-262+00-IC126 0.5-2.3 In-channel deposit - <1.0* - <1.0* 1.0 98.7

RO-321+50-IC155 1.7-4.0 In-channel deposit - <1.0* 128 1.5 8.2 97.5

RO-334+00-IC113 1.6-4.0 In-channel deposit - <1.0* 30,500 0.8 115 100.2

Notes: (*) indicates clay fraction was combined with silt fraction for analysis.

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The density separation gave visually distinct residues that are clearly evident in the following photomicrographs, where “#1” is the 53-2,000 µm fraction sample, and “#2” is the 250-2,000 µm fraction sample: Figure 4-12. Density Separation Photomicrographs

The lightly colored and heavier siliceous material is shown on the left. It contrasts starkly with the more darkly colored “light” fraction shown on the right. From these micrographs it is clear that, like the heavier sand, the material composing the “light” fraction exists in a range of particle sizes. The relative weight of the fractions was as follows:

Table 4-10. Particle Size Fraction Summary

Weight- Heavy Weight- Light Particle Size Fraction Fraction (g) Fraction (g) #1 (53-2,000µm) 12.36 0.13 #2 (250-2,000µm) 12.55 0.14

In both cases, the heavier siliceous material comprised approximately 99 percent of the sample but contained less than 2 percent of the TEQ mass. Conversely, though the light fractions constitute only 1 percent of the sample mass, they contain 98 percent of the furan and dioxin residue measured in the fractions.

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5. UTR AND MTR CHARACTERIZATION

A river is a dynamic system that strives toward equilibrium in terms of energy associated with flow and sediment transport. River patterns and channel shapes and the associated landforms or geomorphic features associated with the fluvial landscape are products of this process of striving towards equilibrium and are influenced by many variables including discharge, longitudinal slope, sediment load, bank resistance, vegetation, and geology.

The following discussion presents a consolidation of the findings from the 2006 and 2007 field investigations, and includes summary discussions of the geomorphology, analytical results, horizontal and vertical extent of contamination, and the nature of contamination in relation to the predominant geomorphologic features and hydrodynamic conditions. The discussion is referenced to River Regions, River Reaches, and River Stationing, which are summarized in Section 2.1.2.

These summary discussions are best read while referring to Surface TEQ Concentration Maps contained in Attachment R, Maximum TEQ Concentration Maps contained in Attachment S, and Geologic Cross- Sections prepared for UTR and MTR transects presented in Attachment T. In addition, the Site Characterization Data Summary reports, containing soil profile descriptions for each sampling location, the geomorphic setting of each location, and the analytical results for each soil horizon sampled are presented in Attachment U-1 and U-2. These attachments and the following discussion taken together provide a comprehensive narrative and graphical description of the database presently available for the UTR and MTR.

5.1 RIVER REGION I: “UPSTREAM OF DOW DAM” (REACHES A - D) The “Upstream of Dow Dam” river segment includes Reach A through Reach D, which combined comprise the upper portion of River Region I. This area of Region I extends from the City of Midland Tridge at the confluence of the Chippewa and Tittabawassee Rivers (Station RA 0+00) downstream to the Dow Dam (Station RD 57+50). This area of the river is relatively stable with minimal evidence of erosion, scour, and/or deposition, presumably due to the backwater influence from the Dow Dam.

The river channel associated with Reach A and Reach B is relatively natural. Downstream from Reach B, the river channel is influenced by anthropogenic structures including embankments, rip-rap, and sheet pile. The channel hydraulic gradient is less than 0.001 ft/ft or less than 1 foot of vertical change over the entire 5,750 foot channel length. The channel is relatively straight, except for a

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meander towards the south in Reach B, resulting in low channel sinuosity, or ratio of channel length to valley length, which is representative of a stable river. The channel width is relatively uniform and ranges from about 200 to 400 feet.

5.1.1 Geomorphology The predominant geomorphic features in this river segment include low surfaces and upland. Shoreline and intermediate surfaces areas do occur, but to a much lesser extent. Throughout most of the river segment, overbank flow is contained within a relatively narrow corridor due to embankments and upland.

5.1.2 Anthropogenic Influences The most significant land uses are associated with industrial and commercial facilities including buildings, roads, surface water impoundments, and grass areas along the river and adjacent to the surface water impoundments. Prominent anthropogenic modifications adjacent to or near the river include the Poseyville Road Bridge, a drainage channel that discharges into the west bank of the river near Station RB 30+00, the water intake basin (constructed channel expansion) upstream of the Dow Dam on the west bank, and the Dow Dam.

The area of the UTR “Upstream of Dow Dam” is highly channelized by the berms and armoring on both sides of the river as it passes between the Dow Midland Plant operations to the northeast and the T-Ponds to the southwest. All samples collected in this area are from in- channel or from southwest overbank locations. Sampling in the overbank was not performed on City of Midland property or in areas of the Dow Midland plant on-site corrective action activities. In addition, the highly industrialized nature and historic construction activities along the downstream end of this river segment has narrowed the floodplain and resulted in limited geomorphic feature development.

5.1.2.1 Reach D Interim Response Action: Historic Wastewater Flume Deposit Two in-channel sampling locations in Reach D (RD-55+05-IC-NE and RD-55+10-IC- NE) were actually located in a deposit occurring between sheet piling walls of a historic wastewater flume located along the northeast shore. The flume was created with sheet piling installed parallel to and approximately 20 feet from the northeastern bank of the river. The purpose of the flume was to constrain wastewater discharges to flow adjacent to the northeastern side of the river, bypassing the industrial water intake located on the southwestern side of the river just above the dam. The flume was used prior to the

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construction of the Tertiary Ponds in the early 1970’s. The sediment within this historic flume was contained on three sides by sheet piling and on the downstream end by the Dow dam. The sheeting on the east side is a component of the RGIS system, and serves as the Tittabawassee River bank.

The composition and consistency of these sediments were consistent with discharge of brine wastes from the production of chlorine by the electrolysis of salt brine. The sediments in this flume deposit area were removed as part of an CERCLA Interim Response Activities removal action in the summer and fall of 2007. This work is described in a separate report from Dow to be submitted to USEPA under separate cover. Because of the unique characteristics of the areas and sediments sampled in Reach D, information about in-channel borings, samples, and sample data from this portion of Region I are addressed with those of the “Near Plant Area” Reaches in Region II, discussed below.

5.1.3 Lateral Channel Migration The river upstream of the Dow Dam has been migrating to the northeast, based on comparison of aerial photographs (1937 to 2004), with erosion and accretion occurring on the outside and inside of the meander bend, respectively. The ponding or backwater from the dam is evident from the contrast in channel configuration beginning in Reach B and continuing through Reach D. Lateral channel migration is not observed downstream of RB-30+00 in Reach B. The present channel width based on the 2004 aerial is greater than 1937 channel width starting about midway through Reach B, due to backwater from the downstream dam, which was installed sometime between 1937 and 1945.

5.1.4 Primary COI Data - Summary In-Channel Samples In-channel sampling of Reaches A through D in River Region I took place in 2006. The number of boring locations and samples resulting from this effort in Reaches A through C are summarized in the following table:

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Table 5-1.

REGION I: "UPSTREAM" (REACHES A - C) IN-CHANNEL TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 A515150000 B1264640000 C624240000

The concentration frequency distribution by location is summarized in the following histogram:

Figure 5-1.

Because of the unique characteristics of areas sampled in Reach D, information about in- channel borings, samples, and sample data are included in the discussion of River Region II below.

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Overbank and Tributary Samples Overbank and tributary sampling of Reaches A through D in River Region I took place in 2006. The number of boring locations and samples resulting from this effort are summarized in the following table:

Table 5-2.

REGION I: "UPSTREAM" (REACHES A - C) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 A0000000 B739363000 C423194000

The concentration frequency distribution by location is summarized in the following histograms:

Figure 5-2.

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Figure 5-3.

Because of the uniqueness of some of the deposits in Reach D, information about overbank and tributary borings, samples, and sample data are included in the discussion of River Region II below.

The three dimensional spatial distribution of TEQ is best illustrated by the Surface TEQ and Maximum TEQ plan view graphics for this River Region, found in Attachments R and S, and the corresponding geologic cross-sections, found in Attachment T. It is important when using the Maximum TEQ graphic to keep in mind that this a two-dimensional presentation of three- dimensional data.

In summary, Reaches A through C of Region I constitute good site background. Except for the two wastewater flume locations in Reach D discussed below, all locations in-channel samples upstream of the Dow Dam are <100 ppt TEQ. Similarly, all overbank and tributary samples upstream of the Dow Dam are <200 ppt TEQ.

5.1.5 Secondary COI Data A total of four samples from deposition zones in River Region I were analyzed in for Secondary COI compounds. A summary of the Secondary COI target analytes found, the frequency they were found, and the range of concentrations found are summarized in the table titled Region I –

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Reaches A – C: Primary and Secondary COI “Positives” Summary in Attachment U-4. Concentration data and summary statistics for all Secondary COI analytes are contained in Attachments U-3 and U-5.

5.2 RIVER REGION II: “NEAR PLANT AREA” (REACHES E - H) The “Near Plant Area” of River Region II includes Reaches E through H and has a river length of 10,425 feet. This downstream portion of Region II extends from the Dow Dam at Station RE 57+50 downstream to the facility Pipe Bridge at Station RH 163+50. The entire river channel is adjacent to either the Midland Plant or MCV properties. The “Near Plant” area downstream of the Dow Dam is a highly channelized river segment with the presence of steep slopes along both sides of the river. Dow Midland Plant property exists on the northeast side of the river. Dow Midland Plant property also exists on the southwest side in Reaches E and F; with MCV property on the southwest side through Reaches G and H. The highly industrialized land use and historic construction activities along this river segment has narrowed the floodplain, increased channel velocities, and resulted in limited geomorphic feature development.

The channel hydraulic gradient is less than 0.001 ft/ft or less than 2 feet of vertical change over the entire 10,600 foot channel length. The channel is relatively straight, except for a meander downstream of the Dow Dam and a meander near the boundary between Reach G and Reach H. Therefore, the channel sinuosity, or ratio of channel length to valley length, is relatively low and representative of a stable river. The channel width is relatively uniform and ranges from about 200 to 350 feet.

5.2.1 Geomorphology Geomorphic features include floodplain, wetland, tributaries, natural levee, low, low intermediate, intermediate, high and upland surfaces. Throughout most of the river segment, overbank flow is contained within a relatively narrow corridor due to embankments and upland.

5.2.2 Anthropogenic Influences The most significant land uses are associated with industrial and commercial facilities (Dow, MCV) including buildings, roads, surface water impoundments, drainage channels, and grass areas along the river and adjacent to surface water impoundments. Prominent anthropogenic modifications adjacent to or near the river include the Dow Dam, large surface water impoundments greater than 40 acres in size along most of the southwest bank, and significant

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drainage channels that discharge from the southwest bank (Reach F/G boundary) and northeast bank (Reach H/I).

5.2.3 Lateral Channel Migration The channel width in the Near Plant Portion of the UTR has increased along the entire length (Reaches E through H) based on comparisons of 1937 to 2004 aerial photographs. The increase in channel width is attributed to anthropogenic influences including the Dow Dam, sheet pile, rip rap, and the water discharge locations (Bullock Creek, Dow Midland Plant, and Lingle Drain). Downstream from the Dow Dam, the river has widened to the northeast due to increased water velocity from the dam. Erosion has occurred in Reach F and H, on the southwest bank, due to the sheet pile and rip rap installed along the northeast bank adjacent to the Dow Plant. The river channel has shifted to the southwest in Reach G due to the former Dow wastewater treatment plant discharge, the RGIS system installation, and the sheet pile along the northeast bank.

The present river channel is relatively stable with minimal evidence of erosion, scour, and/or deposition. The most significant indication of bank erosion occurs along the southwest outside bank of the meander, with respect to downstream flow, just downstream of the Dow Dam. An erosion scar was observed along this outside bank, which experiences greater hydraulic forces as compared to the inside bank. Energy associated with the dam and the sheet pile located along the northeast bank of the river are the likely sources of the erosion along this unarmored bank segment.

5.2.4 Sediment Thickness and Glacial Till The Tittabawassee River has eroded a channel into the underlying glacial till in this section of the river. For approximately 4,000 feet in Region I, the maximum thickness of the sediments is less than 8 feet and the elevation of the till is generally above 580 feet above msl. Throughout this section of Region II, most soil borings penetrated into the till. One anomalous boring at RF-90+50-IC56 penetrated 15 feet of sediment (to 571.8 feet above msl) before terminating at refusal without entering the glacial till. Downstream of Station RF 90+50, the maximum thickness of the sediments gradually increases to 9 to 14 feet thick. In the many locations within this Near Plant Area of Region II, the glacial till is present at or near the bottom of the river with no overlying soft sediment.

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This pattern of coherent glacial till present on the outside bend or just down river of a bend continues downstream through River Regions II and III to the downstream end of Reach Y. This provides stability to the current meanders in the river. The Figure TILLGRAPH in Attachment L presents the elevation of the top of the sediment for each boring and also the elevation at which the till was identified. If the boring reached its terminal depth before reaching the glacial till the elevation of the bottom of the boring is shown and the elevation of the glacial till must be beneath that elevation.

5.2.5 Primary COI Data - Summary In-Channel Samples In-channel sampling of Reach D in Region I, and Reaches E through H in Region II, took place in 2006 and 2007. The number of boring locations and samples resulting from this effort in Reaches D through H are summarized in the following table:

Table 5-3.

REGION II: "NEAR PLANT" (REACHES D - H) IN-CHANNEL TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 D946351226 E2084794100 F361861707621 G301331273100 H 31 145 116 20 8 0 1

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The concentration frequency distribution by location is summarized in the following histogram:

Figure 5-4.

Overbank and Tributary Samples Overbank and tributary sampling of Reaches in Region II took place in 2006. The number of boring locations and samples resulting from this effort are summarized in the following table:

Table 5-4.

REGION II: "NEAR PLANT" (REACHES D - H) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 D4990000 E 289069164 1 0 F 42 197 143 52 2 0 0 G 30 202 126 67 9 0 0 H 158660224 0 0

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The concentration frequency distribution by location is summarized in the following histograms:

Figure 5-5.

Figure 5-6.

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While the data from Reach D from Region I have been included in these data sets for statistical analysis purposes, the sediments from within the historical flume have been removed as part of the CERCLA removal action in 2007.

The three dimensional spatial distribution of TEQ is best illustrated by the Surface TEQ and Maximum TEQ plan-view graphics for this River Region, found in Attachments R and S, and the corresponding geologic cross-sections, found in Attachment T. It is important when using the Maximum TEQ graphic to keep in mind that this is a two-dimensional presentation of three- dimensional data.

In summary, in this Region there are four in-channel deposits that contain TEQ concentrations greater than 5,000 ppt, all but one of which occur in sediment layers buried beneath relatively clean sand with TEQ of <1,000 ppt. The exception, at RH-151+50-IC152, is a thin layer (0.0- 0.6 feet bss) of limited spacial extent. In the overbank, there is one location with a TEQ concentration greater than 5,000 ppt, and it occurs at depth, buried beneath clean soil.

5.2.6 Secondary COI Data A total of 31 samples from deposition zones in River Region II “Near Plant” (including samples from Reach D) were analyzed for Secondary COI compounds. A summary of the Secondary COI target analytes found, the frequency they were found, and the range of concentrations found are summarized in the table titled Region II – “Near-Plant”(Reaches D –H): Primary and Secondary COI “Positives” Summary in Attachment U-4. Concentration data and summary statistics for all Secondary COI analytes are contained in Attachments U-3 and U-5. As mentioned above, while the data from Reach D from Region I have been included in this data set for statistical analysis purposes, the sediments from within the historical flume have been removed as part of the CERCLA removal action in 2007.

5.3 RIVER REGION II: “DOWNSTREAM” (REACHES I - K) The upper portion of the “natural river” section of the UTR begins in River Region II, downstream of the Dow plant site. Region II “Downstream” is comprised of Reaches I through K, and has a river centerline distance of 7,000 feet. These reaches extend from the Dow facility Pipe Bridge (Station RI 163+50) to Gordonville Road (Station RK 233+50). Most of the river channel is adjacent to Midland Plant, MCV, or privately owned properties that are undeveloped. Throughout the majority of this river segment, overbank flow is not contained with in a relatively narrow corridor by embankments and upland as is the case upstream in River Region II “Near Plant” discussed above.

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There is some evidence of erosion, scour, and/or deposition along portions of this river segment. Erosion scars occur throughout this segment and are common along both channel banks within and downstream from lower Reach K. The river segment has fewer anthropogenic structures, as compared to the previously discussed upstream river segments. The channel hydraulic gradient is less than 0.001 ft/ft. There are several gradual meanders throughout the river segment. The meanders are within a relatively narrow corridor, therefore, the channel sinuosity, or ratio of channel length to valley length, is relatively low and representative of a stable river. The channel width is relatively uniform and ranges from about 200 to 400 feet.

5.3.1 Geomorphology The geomorphic features include shoreline, wetland, tributaries, natural (industrial age) levee, historic natural (pre-industrial age) levee, low, intermediate, high, and upper high, and upland surfaces. Throughout most of the river segment, overbank flow is not contained within a relatively narrow corridor by embankments and upland, as compared to the river segments immediately upstream.

5.3.2 Anthropogenic Influences The most significant land uses include a surface water impoundment and woodland. Prominent anthropogenic modifications adjacent to or near the river include: a large MCV surface water impoundment (greater than 40 acres in size) and associated drainage channels, extending from Reach I through upper Reach K; a constructed drainage tributary that discharges into the UTR within lower Reach K on the SW side; and, the Gordonville Road Bridge in downstream boundary of Reach K and Region II.

This section of the UTR includes the first large inside bend of the river downstream of the Midland Plant. A large wetland bounds the area along most of its northeastern side, with Saginaw Road further to the northeast beyond the wetland. The Caldwell boat launch bounds the downstream end of Reach K.

From geomorphological and anthropogenic perspectives areas included in Reach I through K have a rich history. As discussed in the RIWP (ATS, 2007), the deforestation, fires and flooding of the logging era, followed by the installation of the series of upriver hydroelectric and flood control dams in 1925, likely combined to create the double series of levees (“pre- industrial age” and “industrial age”) that remain along much of the UTR, especially along inside bends. In Reach K, as in many downstream areas of the UTR, the industrial age natural levees

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closest to the river have relatively low concentrations near the ground surface, with concentrations of furan and dioxins increasing to a maximum level in the three to eight foot depth range (reflecting industrial-age levee building with contaminated sediments in the past). The historic, pre-industrial natural levee, along with the intermediate surfaces adjacent to river and wetlands, generally have the opposite concentration profile, with higher concentrations closest to the ground surface and the with the zone of impact extending one to 3 feet bgs. These vertical concentration profiles are exhibited throughout Reaches K though I.

5.3.2.1 Reach J/K Interim Response Action: Bank and Overbank Area Interim Response Activities were undertaken on the northeastern bank and overbank of Reaches J and K during the summer and fall of 2007. This work is described in a separate report from Dow to be submitted to USEPA under separate cover.

5.3.3 Lateral Channel Migration Based on a comparison of 1937 to 2004 aerial photographs, Reaches I through K portions of the river have been expanding to the northeast with erosion occurring on the inside of the meander bend and limited accretion on the outside of the meander bend which is an unusual pattern of channel movement. This lateral movement to the northeast into the inside bend is most likely due to: hydrodynamic effects of the progressive channeling and berm construction along the river just upstream of Reach K through the Midland Plant and MCV areas just upstream of Reach K; installation of the Dow dam in 1945; and, the narrowing of the river channel by 100 feet at the beginning of Reach K. The plant construction and the embankment of Saginaw Road just upstream of Reach K constrain flood flows to a very narrow, essentially manmade, channelized floodway until river station RJ 190+00, at which point the floodway immediately widens out into the low terrace area on the northeast side of the river.

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5.3.4 Primary COI Data - Summary In-Channel Samples In-channel sampling of Reaches I through K in Region II, took place in 2006 and 2007. The number of boring locations and samples resulting from this effort in Reaches I through K are summarized in the following table:

Table 5-5.

REGION II: "DOWNSTREAM" (REACHES I - K) IN-CHANNEL TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 I 51 283 254 20 7 2 0 J 30 158 129 17 7 2 3 K 43 192 167 17 4 2 2

The concentration frequency distribution by location is summarized in the following histogram:

Figure 5-7.

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Overbank and Tributary Samples Overbank and tributary sampling of Reaches I through K in Region II took place in 2006. The number of boring locations and samples resulting from this effort are summarized in the following table:

Table 5-6.

REGION II: "DOWNSTREAM" (REACHES I - K) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 I 20 124 75 34 13 2 0 J 17 105 70 27 5 2 1 K 75 475 253 117 62 25 18

The concentration frequency distribution by location is summarized in the following histograms:

Figure 5-8.

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Figure 5-9.

The three dimensional spatial distribution of TEQ is best illustrated by the Surface TEQ and Maximum TEQ plan view graphics for this River Region, found in Attachments R and S, and the corresponding geologic cross-sections, found in Attachment T. It is important when using the Maximum TEQ graphic to keep in mind that this is a two-dimensional presentation of three- dimensional data.

In summary, in Reaches I through K there are two in-channel deposits that contain TEQ concentrations greater than 5,000 ppt. The first occurs in a buried deposit immediately downstream from the Dow facility Pipe Bridge, at RI 163+50-IC81. The other occurs in buried layers of a point bar on the inside of the meander bend centered at transect RK 196+50. In both cases, these deposits are buried beneath relatively clean sand with TEQ of <1,000 ppt. In the overbank, there is one location in Reach I with a TEQ concentration greater than 5,000 ppt at RI 172+00-SW290 in a deposit buried beneath soil with TEQ of <1,000 ppt. In Reaches J and K there a number of locations where soils exceed 5,000 ppt TEQ at depth in industrial age levees, and five locations in Reach K where they exceed 5,000 ppt TEQ at the surface. These surface locations have been addressed through the Reach J/K Interim Response Action.

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5.3.5 Secondary COI Data A total of 58 samples from deposition zones in River Region II/Reaches I – K were analyzed for Secondary COI compounds. A summary of the Secondary COI target analytes found, the frequency they were found, and the range of concentrations found are summarized in the table titled Region II – Reaches I – K: Primary and Secondary COI “Positives” Summary in Attachment U-4. Concentration data and summary statistics for all Secondary COI analytes are contained in Attachments U-3 and U-5.

5.4 RIVER REGION III (REACHES L – Y) Region III is the longest River Region, extending 31,500 feet from the Gordonville Road Bridge at RL 233+50, at the beginning of Reach L, downstream to RY 546+50 at the end of Reach Y. Through this Region, the river valley opens up from 1,000 feet to 3,000 feet wide between the scarps. Region III is characterized by the lowest sinuosity (1.02) of any of the Regions of the Tittabawassee River downstream of Midland. The meanders in Region III do not reach from upland scarp to upland scarp, but rather form narrower meander patterns within the river valley.

5.4.1 Geomorphology A well developed levee system runs through River Region III. The levee system has a generally recurring sequence of a broader high or intermediate surface where floodwaters crest the overbank from the main channel, followed by a narrower levee system near the apex of the meander bend, and then an area where the levees are lower and less well developed at the point where overbank flow re-enters the river channel.

Broad high and intermediate surfaces are typically present along the Tittabawassee River where flood waters from the main channel crest the bank and flow onto the overbank. These “deltaic overbank” deposits are typically not as broad in River Region III as they are in other locations on the river because the meanders are narrower. The areas where high or intermediate surfaces are combined with natural levees exist downstream from the following river bends:

RQ 359+00 through RQ 371+00 NE RR 379+00 through RS 402+00 SW RS 413+00 through RS 420+00 NE RT 432+00 through RU 440+00 SW RU 448+00 through RY 456+00 NE

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A splay area exists between Stations RP 344+00 and RQ 372+00 NE where floodwaters flow into the overbank along an inside meander bend. Ridge and swale complexes are frequently observed on narrow bends in Region III. The ridges in these sequences represent a series of parallel historic levees that are lower in elevation than the current industrial age natural levees. Ridge and swale complexes exist between Stations RS 405+00 and RS 418+00 SW and between Stations RU 441+00 and RU 454+00 SW.

Between the levee system and the channel water line there exist recently accreted surfaces that are designated as “Shoreline Surfaces” in this report. These surfaces are well below the bank full elevation. Shoreline surfaces are present in front of the levees between Stations RQ 358+50 and RQ 361+50 SW and between Stations RQ 367+00 and RQ 369+00 SW.

5.4.2 Anthropogenic Influences The overbank areas in River Region III are dominantly natural land forms. Anthropogenic features along River Region III include the following three bridges:

• Gordonville Road Bridge, built in 1974 at Station RL 233+50 which marks the beginning of Region III and Reach L; • Smiths Crossing Bridge, now abandoned, was built in 1097 and is located at Station RM 261+50, the boundary between Reaches L and M; • Freeland Road Bridge is located at Station RV 485+00. The present structure was completed in 1976 although various bridges have existed at this location since 1877.

Significant fill along the scarp in the NE overbank is evident in Reach L. In addition, historic filling and excavation activities have modified the overbank in some areas. The anthropogenic effects of the bridges and other land form changes are discussed in detail in Section 4.3.2.

5.4.2.1 Reach O Interim Response Activities: In-channel Deposit at RO-332+00 An Interim Response Action (IRA) was performed during 2007 in Reach O. The IRA consisted of temporary installation of sheet pile coffer dams and removal of river sediments. Sediments represented by many of the 2006 sample locations in Reach O were removed as part of this response action. The details of the Reach O IRA are discussed in a separate report being prepared by Dow for submittal to USEPA.

5.4.3 Lateral Channel Migration Review of aerial photographs reveals that the river channel in River Region III has been relatively stable over the 70 years from 1937 and 2007 compared to other sections of the river.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

5.4.4 In-Channel Sediment Thickness and Glacial Till The presence and elevation of the underlying highly compacted glacial till at the bottom of the river directly relate to the pattern of the narrow meanders that are typical in Region III. Glacial till was observed at or near the surface of the river channel along the outside of most bends, and often extended down river from the bend. See the Figure TILLELEV in Attachment L. The thickness of softer sediment thickness overlying the till varies throughout Region III from zero to over 10 feet.

5.4.5 Surface Water Flow During Flood Events Throughout Region III, water moves between the overbank and the main channel as the river meanders to the NE and SW. Typically during a flood event, when the channel bends to the NE, water moves from the main channel onto the SW overbank. Similarly, when the channel bends to the SW, flood streamlines crest the bank onto the NE overbank and streamlines moving along the SW overbank return back into the main channel.

Typically in locations where the distance between the main channel and the upland scarp widens, flood waters flow onto the widened overbank from the main channel. Wherever the upland scarp approaches the river channel, the overbank narrows and flow returns to the river. As long as the river bend does not abut the upland scarp, some of the overbank floodwater continues to flow along the overbank and does not immediately re-enter the main channel. In areas where the river is fairly straight, the overbank flow is nearly parallel with the main channel flow during flood events. An example of where this occurs is the SW overbank in Reaches X and Y, from Station RX 505+50 to RY 546+50, where there is minimal flow exchange between the channel and the overbank.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

5.4.6 Primary COI Data - Summary In-Channel Samples In-channel sampling of Reaches L through V in River Region III took place in 2006 and 2007. The number of boring locations and samples resulting from this effort are summarized in the following tables:

Table 5-7.

REGION III: "UPPER" (REACHES L - O) IN-CHANNEL TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 L 81 442 343 53 21 19 6 M 41 239 203 25 8 2 1 N341221118300 O 67 189 156 12 11 6 4

Table 5-8.

REGION III: "MIDDLE" (REACHES P - V) IN-CHANNEL TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 P201251177100 Q 219680111 2 2 R251661555303 S 24 148 117 19 4 7 1 T 138668113 2 2 U211211134220 V221351268100

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The concentration frequency distribution by location is summarized in the following histograms:

Figure 5-10.

Figure 5-11.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

Note that for completeness the in-channel data for Reach O have been included in the table and histogram for that portion of Region III, however these data do not represent present conditions since the deposit at RO 322+00 / RO 328+00 was removed as part of the Reach O Interim Response Action in 2007.

Overbank and Tributary Samples Overbank sampling of Reaches L through Y in River Region III took place in 2006 and 2007. The number of boring locations and samples resulting from this effort are summarized in the following tables:

Table 5-9.

REGION III: "UPPER" (REACHES L - O) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 L 100 461 271 112 47 24 7 M 69 532 302 109 73 30 18 N 79 498 289 102 63 33 11 O 75 463 287 99 59 12 6

Table 5-10.

REGION III: "MIDDLE" (REACHES P - V) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 P 86 488 295 92 79 18 4 Q 73 423 215 96 82 24 6 R 32 135 73 23 29 7 3 S 61 271 115 62 79 14 1 T 14712322260 0 U 45 169 75 48 40 4 2 V 36 151 87 34 22 7 1

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Table 5-11.

REGION III: "LOWER" (REACHES W - Y) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 W1348316 110 0 X 55 240 108 58 55 13 6 Y 29 139 79 31 21 5 3

The concentration frequency distribution by location is summarized in the following histograms:

Figure 5-12.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

Figure 5-13.

Figure 5-14.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

Figure 5-15.

Figure 5-16.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

Figure 5-17.

Summarizing the in-channel results for Region III, there are eleven in-channel deposits throughout Reaches L through V that contain TEQ concentrations greater than 5,000 ppt. They occur in point bars along inside meander bends, or downstream from such point bars, at the following river locations:

RL 236+25 / RL 239+50 RL 256+00 / RL 258+50 RM 273+00 RQ 359+00 RQ 365+50 RR 388+00 RR 398+50 RS 417+50 RT 424+00

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

RT 434+00/RT 439+50 RU 452+00 / RU 456+00

In general the sediment layers containing these elevated TEQ concentrations are buried beneath sand containing <1,000 ppt TEQ. However, in seven of these locations sediments with concentrations greater than 5,000 ppt TEQ are exposed at the surface.

In the overbank, the highest concentrations TEQ concentrations and the thickest deposits containing TEQ are located in the industrial age natural levees immediately adjacent to the river. The industrial age natural levees in the central portion of this Region had maximum soil concentrations greater than 15,000 ppt TEQ, typically buried 2 feet or more below the ground surface. Pre-industrial age historic natural levees occur behind natural levees, and along non- aggrading banks of the river. They contain lower TEQ concentrations than the natural levees and the vertical concentration profile is markedly different. In the historic natural levees the TEQ are found in surficial materials, typically at depths of 6 feet or less below ground surface.

The natural levees and historic natural levees gradually transition into intermediate surfaces, or in some cases high surfaces, on the back side of the levee complex. Concentrations typically decrease with distance from the river in these intermediate surfaces. Where the flow of water from the river channel onto the overbank during flood events created deltaic overbank deposition patterns, the intermediate and high surfaces extended farther back into the floodplain, and the TEQ concentrations decrease more slowly with distance from the river. In these deltaic overbank deposition patterns, concentrations between 1,000 and 5,000 ppt TEQ are common.

Further from the river, typically in the low surfaces and geomorphic wetland surfaces, the concentrations drop to below 1,000 ppt TEQ. This is especially true in areas where the overbank flow has remained outside of the channel for some distance in stretches of the wide overbank in Region III.

5.4.7 Secondary COI Data A total of 149 samples from deposition zones in River Region III (59 from Upper, 86 from Middle and 4 from Lower) were analyzed for Secondary COI compounds. A summary of the Secondary COI target analytes found, the frequency they were found, and the range of concentrations found are summarized in three tables titled as follows in Attachment U-4:

Region III – “Upper” (Reaches L-O): Primary and Secondary COI “Positives” Summary

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

Region III – “Middle” (Reaches P-V): Primary and Secondary COI “Positives” Summary

Region III – “Lower” (Reaches W-Y): Primary and Secondary COI “Positives” Summary

Concentration data and summary statistics for all Secondary COI analytes are contained in Attachments U-3 and U-5.

5.5 RIVER REGION IV (REACHES Z – DD) River Region IV extends 13,150 feet from River Station RZ 546+50 at the beginning of Reach Z downstream to the East Tittabawassee Road Bridge at River Station RDD 678+00 at the end of Reach DD. This Region is characterized by a higher sinuosity (1.14) than Region III (1.02) with meanders extending either all of the way or nearly all of the way to the upland scarps.

5.5.1 Geomorphology Where the river pulls away from the NE upland scarp, deltaic overbank deposition has resulted in a broad intermediate or high surface adjacent to the river. Where the river abuts and then pulls away from the upland scarp, the deltaic overbank deposition extends to the upland scarp, within the intermediate and high surfaces on the SW overbank between Station RAA 597+00 and Station RSS 606+00. Where the main channel does not abut the upland scarp, and some overbank flow with a lower sediment load flows onto the widening overbank, the overbank deltaic deposition pattern does not extend to the upland scarp. This is present in the high surface on the NE overbank between Station RBB 619+00 and Station RBB 626+00 and in the high surface on the SW overbank between Station RCC 648+00 and Station RCC 643+00. Along the wider sections of overbank where the width is relatively stable, the more classic, narrow natural levees and historic natural levees transition into high or intermediate surfaces in the levee complex and then into low surfaces or geomorphic wetlands.

The height of the levee complex decreases as the river approaches an upland scarp and the width of the overbank narrows. Where the river abuts the upland scarp and the overbank disappears, the lower end section of the levee complex serves as a low surface between Station RZ 562+00 and Station RZ 566+00). Where the river does not abut the upland scarp, the flow in the remaining narrow section of the overbank is parallel to the main channel, and a distinct natural levee formed, as seen along the SW overbank between Station RCC 640+00 and Station RCC 647+00 or, alternatively, a narrow intermediate surface formed, as seen along the NE overbank between Station RBB 604+00 and Station RBB 614+00 where a tributary intercepts the river bank.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

5.5.2 Anthropogenic Influences Within Region IV, the NE overbank has been significantly modified by the historic removal of sand from Station RZ 555+50 through Station RAA 598+00. In Reaches Z and AA, the main channel initially pulls away from the NE upland scarp as the NE overbank widens from 200 feet to over 1,300 feet wide. The river then meanders back to within 200 feet of the SW upland scarp near Station RBB 615+00. For the majority of this section of the NE overbank, most of the overbank behind the levee has been significantly modified.

From Station RAA 600+00 to RCC 654+00, while the upland scarp has been modified by houses built into this area, the overbank area does not have any discernable large scale anthropogenic modifications.

The SW overbank is also significantly anthropogenically modified from Station RCC 654+00 through Station RDD 678+00. At the approach for the Tittabawassee Road Bridge, the SW overbank has been graded and/or excavated. An elevated access drive off from Tittabawassee Road is still present in this section.

5.5.3 Surface Water Flow during Flood Events Within River Region IV, the river channel meanders nearly from upland scarp to upland scarp between each turn. The width of the overbank widens as the river pulls away from the upland scarp in each meander, and then the width of the overbank contracts significantly as the river re- approaches the same upland scarp downstream. Flow of water during flood events is significantly influenced by the interaction between the flow in the main channel and the flow boundary along the upland scarp. When the river pulls away from the upland scarp, creating a wider overbank, flood water from the main channel flows out onto the overbank. When the width of the overbank is relatively stable near its maximum width, the overbank flow is nearly parallel to the main channel. As the river re-approaches the upland scarp, the overbank flow is re-directed toward into the main channel.

In two of the meanders the river approaches to within 200 feet of the upland scarp. This occurs at Station RBB 614+00 on the SW overbank and at Station RCC 644+00 on the NE overbank. At these locations, most of the overbank flood flow is directed back into the main channel, while some of the overbank flow remains within this thin stretch of the overbank. The overbank flow that does not re-enter the channel experiences slower velocities than the main channel and unlikely transports sediment to the same degree as the channel flow.

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Near the end of River Region IV, the main channel lies adjacent to the NE upland scarp and the SW overbank widens to 1,300 feet. The approach for the Tittabawassee Road Bridge at the end of Region IV serves to direct the floodwater flow on the SW overbank into the single span of the bridge over the main channel. Approximately 230 feet away from the river channel, an access roadway extends approximately 500 feet north-northwest along the overbank and then turns and goes about 400 feet to the east into the overbank. This roadway further constricts the flow of flood water in the lower portion of this overbank area. During flood events, flood waters are trapped behind this roadway and preferentially flow back into the main channel at the tributary cut near Station RDD 660+00. During the peak flow of a 100-year flood event, the access roadway into the overbank is topped and the overbank flow recharges into the main channel down river from the tributary. During the subsidence of a 100-year flood, the break in the levee at Station RDD 660+00 experiences a significant flow as the flood waters contained in overbank area drain back into the river.

5.5.4 Primary COI Data - Summary In-Channel Samples No in-channel samples were collected from River Region IV in 2006 or 2007.

Overbank and Tributary Samples Overbank sampling of Reaches in River Region IV took place in 2007. The number of boring locations and samples resulting from this effort are summarized in the following table:

Table 5-12.

REGION IV: (REACHES Z - DD) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 Z 58 238 110 58 44 20 6 AA 47 262 159 65 30 5 3 BB 50 280 132 78 62 7 1 CC 36 178 107 38 22 10 1 DD 51 186 82 54 43 5 2

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

The concentration frequency distribution by location is summarized in the following histograms:

Figure 5-18.

Figure 5-19.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

In summary, the highest concentrations of furans and dioxins, and the thickest sequence of sediments containing furans and dioxins are again found adjacent to the main channel in the industrial age natural levees. Within these natural levees, the highest concentrations are typically present in intervals that start deeper then 2 feet below grade. The concentrations of furans and dioxins decrease behind the natural levees. Concentrations in the low surface and geomorphic wetlands are typically below 2,000 ppt TEQ, and decrease in samples moving toward the upland scarp.

5.5.5 Secondary COI Data A total of 40 samples from deposition zones in River Region IV were analyzed for Secondary COI compounds. A summary of the Secondary COI target analytes found, the frequency they were found, and the range of concentrations found are summarized in the table titled Region IV – Reaches Z – DD: Primary and Secondary COI “Positives” Summary in Attachment U-4. Concentration data and summary statistics for all Secondary COI analytes are contained in Attachments U-3 and U-5.

5.6 RIVER REGION V (REACHES EE – II) River Region V extends 10,500 feet downstream from Station REE 678+00 at the beginning of Reach EE, where the river lies adjacent to the NE upland scarp and where the approach for the Tittabawassee Road Bridge constricts the SW overbank. It concludes at Station RII 783+00 midway into Reach II, where the width of the flood path has narrowed and the channel is within 500 feet of the NE upland scarp.

In River Region V the flood path in the overbank widens to over 3,000 feet as the river channel meanders from the NE upland scarp to the SW upland scarp. The wide NE overbank contains an abandoned river channel in the form of an oxbow wetland.

5.6.1 Geomorphology In the northern quarter of this Region, the river lies adjacent to the NE upland scarp. A golf course and an aqua driving range have modified the SW overbank. The aqua driving range

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

consists of two ponds that have been excavated into the remnant of the levee complex. Along the golf course, a double levee is present running parallel to the river, with the narrowest levee representing the natural levee. Further south from the golf course (starting at Station RFF 707+00) the elevation of the levee decreases and forms a ridge and swale complex. As the channel approaches the upland scarp and the overbank flow returns toward the channel, the elevation of the levee decreases and the historic levees transition from an intermediate surface to a low surface. Behind this levee complex, the elevation of the overbank decreases to a low surface and then to a geomorphic wetland.

Where the NE overbank widens out to over 3,000 feet, a broad overbank deltaic deposition pattern consists of high surfaces and intermediate surfaces that extend down to the top of the oxbow. Soils along this broad overbank depositional pattern consist of poorly graded and well graded sands with some fines.

Through the wide section of the NE overbank, the river and overbank flows are parallel during flood events and a double levee system is present here. Behind this levee system the NE overbank decreases in elevation towards an intermediate surface behind the levee. As the channel re-approaches the NE upland scarp, and the overbank flood flow returns to the main channel, the elevation of the levee system decreases to a low surface.

Behind the natural levee system on the NE overbank, the land falls off to drained low surface, intermediate surface and geomorphic wetlands. The abandoned oxbow is currently a mixture of geomorphic wetlands and low surfaces. The north end of the oxbow has been filled in with sands that have entered from the south extent of the deltaic overbank deposition area. One creek has incised down the western side of the eastern lobe of the oxbow and now enters the main channel at RII 780+00. The historic levee from the oxbow is also present as an intermediate surface along the western lobe of the oxbow.

The SW overbank from Station RHH 746+00 through the end of Region V does not follow a typical pattern. The land forms in this section have been influenced by the avulsion of the river that created the oxbow structure, and the river channel is still adjusting to this change. This section does not contain the typical sequence of a long levee along the river that transitions back through an intermediate surface to a low back levee area (low surface or geomorphic wetland). Instead, this section contains remnant land forms from the avulsion that caused the oxbow feature. A review of historic maps from before the logging era indicates that the avulsion had

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

occurred prior to early mapping. In the upper end of this section, Reach HH, the SW overbank contains the old river channel that was present prior to the avulsion that caused the oxbow. This area has filled in and is currently a combination of geomorphic wetlands and low and intermediate surfaces. In this section, the SW edge of the main channel has been relatively stable since 1937. In the southern half of this section, the SW overbank presents a ridge and swale complex that consists of a series of geomorphic wetlands, low surfaces, and intermediate surfaces, with the lower elevation on the down river portion of the ridge and swales. This ridge and swale sequence formed as the channel adjusted to a new path after the avulsion.

5.6.2 Anthropogenic Influences Two areas in Reach EE and FF on the SW overbank have been anthropogenically modified to support current land uses: (1) a golf course with grading to create greens, tees, sand traps, and ponds and (2) an aqua-drive golf driving range consisting of two large ponds. Property access for sampling of these properties was not granted in 2007.

A tributary enters the overbank in a ravine along the upland scarp west of Station RFF 701+00. The tributary appears to have historically drained into the geomorphic wetland surface and is now drained by a straight ditch that has been dug along the upland scarp. Although the natural drainage course meanders through the levee complex and enters the river at Station RFF 715+00, the incised ditch splits from this course and continues along the upland scarp and enters the river at Station RGG 739+00.

5.6.3 Lateral Channel Migration Although most of the channel boundaries in Region V have been stable over the last 70 years (1937 through 2007), the channel has migrated in two locations. Aerial photographs indicate the channel boundary migrated in Reaches FF and GG, where the river channel has cut into the NE bank between Stations RFF 712+00 and RGG 732+00. Much of this migration was concurrent with the formation of a peninsula along the SW bank. As much as 220 feet of the NE bank has eroded over the past 70 years near Station RGG 725+50. In addition, between Stations RFF 719+00 and RGG 730+00, immediately upstream from where the channel abuts the SW upland scarp, a sand bar has accreted on the SW shoreline, extending the overbank area up to 240 feet into the historic channel. This sand bar is located just before the main channel reaches the upland scarp, encounters the coherent glacial till, and takes an abrupt turn to the left.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

In Reach V the channel is still responding to the avulsion that formed the oxbow. Between Stations RHH 770+50 and RII 781+50, the channel has eroded into the SW overbank, with a maximum cut of 100 feet near Station RII 778+00. Further downstream, where the overbank flow returns to the main channel, the channel boundary has moved up to 50 feet into the channel creating a new overbank on the SW side between Stations RII 782+00 and RII 803+00.

5.6.4 Surface Water Flow during Flood Events During flood events, all of the river water is restricted to the width of the Tittabawassee Road Bridge at Station REE 678+00 at the upper end of Region V. Downstream of the bridge, water flows onto the SW overbank, across the aqua-range golf course. During low and high flood events, the deep, man-made ponds offer a preferential flow path for the flood water leaving the river. The flood waters continue to flow across the ponds onto the low surface and geomorphic wetlands.

Between Station REE 694+00 and Station RGG 728+00 the main channel moves away from the NE upland scarp to the SW upland scarp, resulting in a broad 3,000 foot NE overbank. Through this section of the river, surface water flows from the main channel onto the NE overbank from Station RGG 694+00 where the channel pulls away from the upland scarp through Station RGG 728+00 near the sharp bend in the main channel as it encounters the SW upland scarp.

There are two overbank deposition patterns in this Region. A typical deltaic overbank depositional pattern is observed along the NE side between Station REE 694+00 and Station RFF 710+00. In this area, water flows onto the overbank across historically deposited materials on the deltaic deposition area along the high surface toward the northern edge of the abandoned oxbow. The second deposition pattern is observed between Station RFF 717+00 and Station RFF 719+00 where a cut in the levee system provides a preferential flow path for flood water toward the northern end of the oxbow.

During larger flood events, such as the 8-year and 100-year floods, NE overbank flow roughly parallels the river channel between Stations RFF 720+00 and RHH 760+00. Flow re-enters the main channel some distance downstream between Stations RII 775+00 and RII 782+00 where the expanse of NE overbank reduces from approximately 3,000 feet to approximately 600 feet in width. During smaller, more frequent flood events, the water level in the channel slightly recharges water held in the overbank.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

As the river slowly pulls away from the SW upland scarp, surface water from the channel enters the widening SW overbank between Station RHH 742+50 and Station RII 782+00. Flow re- enters the main channel between Station RII 782+00 and Station RII 801+00 (in Region VI) where the channel lies close to the scarp. Overbank flood flow in this area is influenced by topographic features within the Region. The historic levee system, prior to the avulsion that caused the oxbow area on the NE overbank area, has a low spot at Station RHH 767+00 that provides a preferential flow path during smaller, more frequent flood events. In addition, there is a low trough across the overbank that starts near Station RII 773+00 that also provides a preferential flow path during floods.

5.6.5 Primary COI Data - Summary In-Channel Samples No in-channel samples were collected from River Region V in 2006 or 2007.

Overbank and Tributary Samples Overbank sampling of Reaches in River Region V took place in 2007. The number of boring locations and samples resulting from this effort are summarized in the following table:

Table 5-13.

REGION V: (REACHES EE - II UPPER) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 EE 31 110 35 57 16 2 0 FF 77 393 135 108 102 38 10 GG 30 164 78 45 31 9 1 HH 42 247 134 65 36 12 0 II UPPER 36 217 89 63 45 13 7

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

The concentration frequency distribution by location is summarized in the following histograms:

Figure 5-20.

Figure 5-21.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

The three dimensional spatial distribution of TEQ is best illustrated by the Surface TEQ and Maximum TEQ plan view graphics for this River Region, found in Attachments R and S, and the corresponding geologic cross-sections, found in Attachment T. It is important when using the Maximum TEQ graphic to keep in mind it is a two-dimensional presentation of three- dimensional data.

In the upstream portion of Region V access was restricted along the SW bank on the property occupied by the aqua driving range ponds, so no information is available there. However, a significant number of samples were collected west of that property. All but one of these samples were less than 5,000 ppt TEQ, with concentrations declining moving away from the river and most being less than 1,000 ppt TEQ. The exception was 7,300 ppt TEQ on an intermediate surface at REE 688+50-SW48 in the backwater area downstream of the bridge.

Where the overbank flow resulted in deltaic overbank deposition and created broad intermediate and high surfaces on the NE overbank, concentrations of furans and dioxins over 5,000 ppt TEQ extend farther inland and are thicker than observed in other Regions. These concentrations decline moving south, away from the bank. South of RGG 727+00, concentrations behind the levee system on the NE overbank typically have decreased to less than 1,000 ppt TEQ. Within the footprint of the abandoned oxbow, the profile containing furans and dioxins is thicker than in adjacent areas outside the oxbow. This is particularly evident near the northern end of the oxbow that has received more deposition from the broad deltaic overbank deposition flow (see RFF 719+00-NE1430). At the south end of the abandoned oxbow, near RII 779+50-NE115, the old channel for the oxbow influenced the distribution of furans and dioxins. Borings placed in the old river channel have buried deposits containing furans and dioxins deeper than typically observed in the down river end of a Region (see RII 779+50-NE151 and RII 779+50-NE158).

On the SW overbank in Reach HH, the distribution of furans and dioxins are also linked to the location of the abandoned channel prior to the avulsion. The areas within the footprint of the old channel have buried deposits with concentrations up to 12,000 ppt TEQ at RHH 766+00- SW149, in the interval 3.7 to 5.0 feet bgs. In this area, the impacted interval extends to a depth of 3 to 8 feet bgs, with the highest concentrations buried beneath cleaner material. In the intermediate surface representing the old levee behind the old channel, concentrations are typically below 300 ppt TEQ, with the highest concentration occurring in the surface samples (transects RHH 761+00 and RHH 766+00).

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

5.6.6 Secondary COI Data A total of 76 samples from deposition zones in River Region VI were analyzed for Secondary COI compounds. A summary of the Secondary COI target analytes found, the frequency they were found, and the range of concentrations found are summarized in the table titled Region V – Reaches EE – II Upper: Primary and Secondary COI “Positives” Summary in Attachment U- 4. Concentration data and summary statistics for all Secondary COI analytes are contained in Attachments U-3 and U-5.

5.7 RIVER REGION VI (REACHES II – KK) River Region VI is characterized by the narrowing of the river flood path after Region V. Region VI starts at Station RII 783+00 midway into Reach II and continues to the end of Reach KK at RKK 872+50. The first 2,000 foot stretch of Region V exhibits a classic meandering pattern between Stations RII 783+00 and RII 804+00 before becoming relatively straight between Stations RII 804+00 and RKK 872+50. Region VI depositional features include a classic deltaic depositional pattern at the northern end and a classic double levee system with a low surface farther from the river along the straight stretch. The overall sinuosity of Region VI is 1.09.

5.7.1 Geomorphology A deltaic depositional pattern occurs in the upper portion of Region VI where the channel flows onto the NE overbank (high surfaces and intermediate surfaces from Station RII 783+00 through Station RII 804+50). This broad overbank deposition is present in the NE overbank through Station RII 811+00. A double levee system is present on both sides of the river along the long straight stretch from Station RII 804+50 through Station RII 872+50. Behind the levees in the long central section, the overbank transitions back to broad low surfaces and geomorphic wetlands. These low surfaces and wetlands drain towards the SW where three outlets drain the area into the main channel at Stations RJJ 822+50, RKK 854+00 and RMM 907+00 (in Region VII).

Anthropogenic influences in this area include (1) The presence of bank reinforcement at Imerman Park; (2) the addition of Imerman Park boat launch; (3) farming activities; and (4) the entrenchment of drainage ditches in the NE overbank.

5.7.2 Surface Water Flow during Flood Events Region VI begins with the main channel lying within 500 feet of the NE upland scarp. Within the first quarter of Region VI, the channel meanders across to abut the SW upland scarp as the

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NE overbank widens. Flood water from the channel flows onto the NE overbank between Stations RII 785+00 and RII 790+00. The overbank flow then moves down river roughly parallel to the main channel through the rest of this Region. The overbank flow re-enters the channel in Region VII where the channel approaches the upland scarp along the NE bank.

Along the SW bank, the river runs adjacent to the upland scarp for almost 2,000 feet from Station RII 802+50 through Station RJJ 821+50. As the river begins to pull away from the SW upland scarp, water enters the overbank area at approximately Station RJJ 850+00. After this, the width of the SW overbank is relatively consistent, and overbank flow parallels the flow in the main channel until Station RKK 872+50.

5.7.3 Primary COI Data - Summary In-Channel Samples No in-channel samples were collected from River Region VI in 2006 or 2007.

Overbank and Tributary Samples Overbank sampling of Reaches in River Region VI took place in 2007. The number of boring locations and samples resulting from this effort are summarized in the following table:

Table 5-14.

REGION VI: (REACHES II LOWER - KK) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 II LOWER 48 286 123 77 65 17 4 JJ 104 446 225 122 85 8 6 KK33173794439110

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The concentration frequency distribution by location is summarized in the following histograms:

Figure 5-22.

Figure 5-23.

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The three dimensional spatial distribution of TEQ is best illustrated by the Surface TEQ and Maximum TEQ plan view graphics for this River Region, found in Attachments R and S, and the corresponding geologic cross-sections, found in Attachment T. It is important when using the Maximum TEQ graphic to keep in mind it is a two-dimensional presentation of three- dimensional data.

In summary, within the overbank soil samples, the highest concentrations and thickest deposits containing furans and dioxins were located within the natural levee immediately adjacent to the river. Furans and dioxins within the natural levees had maximum concentrations greater than 15,000 ppt TEQ, buried at depths greater that 6 feet bgs. Two interior samples had over 5,000 ppt TEQ, and both were located within the 1,000 feet of the channel along the deltaic overbank deposition at RII 796+00-NE950 and RII 802+00-NE802. From 1,000 feet to 2,000 feet downstream from the channel flow entering the overbank, most of the overbank samples contained a maximum of 1,000 to 5,000 ppt TEQ. Further downstream, overbank samples containing a maximum concentration of less than 1,000 ppt TEQ became more prevalent until the majority of overbank borings had a maximum concentration of less than 1,000 ppt TEQ toward the end of this Region.

5.7.4 Secondary COI Data A total of 18 samples from deposition zones in River Region IV were analyzed for Secondary COI compounds. A summary of the Secondary COI target analytes found, the frequency they were found, and the range of concentrations found are summarized in the table titled Region VI – Reaches II Lower – KK: Primary and Secondary COI “Positives” Summary in Attachment U-4. Concentration data and summary statistics for all Secondary COI analytes are contained in Attachments U-3 and U-5.

5.8 RIVER REGION VII (REACHES LL – PP) River Region VII is bounded by River Stations RLL 872+50 at the beginning of Reach LL and RPP 1014+50 at the end of Reach PP. This Region is characterized by an increase in floodplain and valley width, which continues to widen downstream into Regions VIII and IX. The first 5,450 feet of Region VII exhibits a classic meandering pattern from Station RLL 872+50 through Station RMM 927+00 where the floodplain is encroached by State Road. Overbank sampling activities were limited along this Region due to the encroachment of the NE upland scarp and a broad area along the SW bank with no access between Stations RLL 878+50 and RMM 927+00. Depositional features along Region VII include a classic double levee system along the SW inside meander bend. The

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pattern of Region VII exhibits one of the highest sinuosity of all the River Regions at approximately 1.2.

5.8.1 Geomorphology A classic levee system is present along the inside meander bend from Station RLL 872+50 through Station RMM 927+00. Behind the levee, the overbank transitions back to broad low surfaces and geomorphic wetlands. These low surfaces and geomorphic wetlands drain towards the secondary bridge along the State Road approach. Along the NE bank between Stations RLL 880+00 and RMM 904+00, the levee system is a low surface where floodwaters from Region VI flow back into the river channel.

5.8.2 Surface Water Flow during Flood Events During flood events, water from the channel enters the SW overbank between Stations RLL 874+00 and RMM 904+00 and either flows back into the river channel or flows through the secondary bridge along the approach for the State Street Bridge. Floodwaters along the NE bank flow back into the river channel between Stations RLL 888+00 and RMM 904+00 where the river channel approaches the upland scarp.

5.8.3 Primary COI Data - Summary In-Channel Samples No in-channel samples were collected from River Region VII in 2006 or 2007.

Overbank and Tributary Samples Overbank sampling of Reaches in River Region VII took place in 2007. The number of boring locations and samples resulting from this effort are summarized in the following table:

Table 5-15.

REGION VII: (REACHES LL - PP) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 LL 30 175 88 40 28 15 4 MM 10 43 16 12 15 0 0 NN419181000 OO0000000 PP0000000

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The concentration frequency distribution by location is summarized in the following histograms:

Figure 5-24.

Figure 5-25.

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The three dimensional spatial distribution of TEQ is best illustrated by the Surface TEQ and Maximum TEQ planview graphics for this River Region, found in Attachments R and S, and the corresponding geologic cross-sections, found in Attachment T. It is important when using the Maximum TEQ graphic to keep in mind it is a two-dimensional presentation of three- dimensional data.

In summary, limited overbank soil samples were collected along Region VII. The highest concentrations and thickest deposits of furans and dioxins were located within the industrial age natural levee located at the beginning of Region VII. Furans and dioxins within the natural levees between Stations RLL 872+50 and RLL 885+50 had maximum soil concentrations greater than 15,000 ppt, buried to depths greater than 5 feet bgs.

5.8.4 Secondary COI Data A total of 150 samples from deposition zones in River Region VII were analyzed for Secondary COI compounds. A summary of the Secondary COI target analytes found, the frequency they were found, and the range of concentrations found are summarized in the table titled Region IV – Reaches LL – MM: Primary and Secondary COI “Positives” Summary in Attachment U-4. Concentration data and summary statistics for all Secondary COI analytes are contained in Attachments U-3 and U-5.

5.9 RIVER REGION VIII (REACHES QQ – UU) Region VIII extends 2.5 miles from Station RQQ 1014+50 at the beginning of Reach QQ to Station RUU 1145+50 at the end of Reach UU. This Region begins at the Gratiot Road bridge and continues downstream to the South Center Road Bridge, and corresponds with Reaches QQ through UU. The valley is relatively wide through this Region extending in some locations for over a mile. Adjacent land use within the valley varies from undeveloped woodland to pastureland to developed residential and commercial areas. Both the roads along with a railroad towards the midpoint of this Region provide a constriction within the valley. Region VIII has a sinuosity of 1.16 and is one of the more sinuous River Regions.

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At the request of the MDEQ limited overbank sampling was conducted in Reaches RR, SS, and TT in 2007. The number of boring locations and samples resulting from this effort are summarized in the following table:

Table 5-16.

REGION VIII: (REACHES QQ - UU) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 QQ0000000 RR622211000 SS740298300 TT429176420 UU0000000

Surface TEQ and Maximum TEQ plan-view graphics for this River Region are found in Attachments R and S. It is important when using the Maximum TEQ graphic to keep in mind it is a two-dimensional presentation of three-dimensional data.

5.10 RIVER REGION IX (REACHES VV – YY) Region IX is comprised of the most downstream section of the Tittabawassee River before its confluence with the Shiawassee and Saginaw Rivers. This Region is approximately 13,450 feet in length and corresponds with all or part of Reaches VV, WW, XX, YY, beginning at River Station RVV 1145+50 and ending at RYY 1281+00. It is bounded on the upstream end by North Center Road and on the lower end by the confluence. This Region was delineated within these bounds primarily due to the increasing valley width and the perceived backwater effects from the Saginaw River. Region IX has a sinuosity of approximately 1.08.

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At the request of the MDEQ limited overbank sampling was conducted in Reaches XX and YY in 2007. The number of boring locations and samples resulting from this effort are summarized in the following table:

Table 5-17.

REGION IX: (REACHES VV - YY) OVERBANK AND TRIBUTARY TEQ DATA FREQUENCY DISTRIBUTION

Reach Borings Total Samples Concentration (ppt TEQ) <100 100-999 1000-4,999 5,000-14,999 >15,000 VV0000000 WW0000000 XX1951120 YY315122100

Surface TEQ and Maximum TEQ plan view graphics for this River Region are found in Attachments R and S. It is important when using the Maximum TEQ graphic to keep in mind it is a two- dimensional presentation of three-dimensional data.

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6. STATISTICAL EVALUATION OF GEOMORPHIC INVESTIGATION FINDINGS

6.1 BACKGROUND One of the principles of the GeoMorph® sampling design centers on the understanding that there is an association between furan and dioxin concentrations in soils and distinct fluvial deposition areas. Such a sampling design is based on collecting representative soil samples from distinct fluvial geomorphic surfaces to characterize the furan and dioxin concentrations associated with the soils from those geomorphic surfaces.

During the development of the 2006 SAP for the Upper Tittabawassee River (ATS, 2006a), MDEQ expressed a desire to statistically calibrate and verify the sample design by comparing the efficiencies and results generated by the fate and transport-based GeoMorph® process to that of random sampling designs. During 2006, this site characterization process was validated against classic investigation methods (fixed-transect and random-on-grid sampling schemes) using standard statistical tools. As reported in the February 1, 2007 UTR GeoMorph® Pilot Site Characterization Report (ATS, 2007c), the results of this analysis concluded that geomorphologic information can make sampling strategies more efficient, both by reducing the number of samples needed to characterize the spatial distribution of contamination and by targeting areas where contaminants occur preferentially over areas where they do not.

During the development of the 2007 SAP (ATS, 2007b), MDEQ expressed a desire to expand the statistical calibration and verification of the GeoMorph® sample design to include an evaluation of Exposure Units according to Michigan PA 451, Parts 201 and 111. MDEQ formally included this requirement in the July 24, 2007 Compliance Schedule for the Tittabawassee River Site Investigation (Compliance Schedule). In response to this Compliance Schedule, a process outline for assessing adequacy of site characterization and providing the basis for Exposure Unit evaluations on Priority 1 and 2 was submitted to MDEQ on August 3, 2007. On September 17, 2007, ATS proposed sampling locations for evaluation of Exposure Units on Priority 1 and 2 properties within the Lower Tittabawassee River (LTR) Study Area. On October 15, 2007 the 2007 GeoMorph® Work Plan for Exposure Unit Sampling and Evaluation was submitted to MDEQ pursuant to the July 24, 2007 MDEQ Compliance Schedule. A “Technical Memorandum for SWAC analysis” was submitted to MDEQ on October 31, 2007 pursuant to the July 12, 2007 GeoMorph® SAP. MDEQ did not provide comments and so Dow proceeded with the work described in these work plans.

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6.2 STATISTICS IN SUPPORT OF NATURE AND EXTENT The distribution of furans and dioxins in the overbank soils supports the use of geomorphic features to characterize the nature and extent of the furans and dioxins. The evaluation presented below first discusses the soil profiles and how they relate to the stability of the ground surface in the geomorphic surfaces; then addresses the distribution of furans and dioxins in the geomorphic surfaces, and finally presents summary statistics for the geomorphic surfaces along with a statistical comparison between the surfaces.

6.2.1 Soil Profile Descriptions -Maturity & Stability Indicators Soil profiles provide insight into the fluvial sediments deposited in the overbank. Soil profile characteristics, including degree of soil profile development, reflect the relative maturity and stability of the geomorphic surfaces. In addition, the presence of wood and of shells in the soil column provides a marker for the bottom of the profile containing furans and dioxins in the natural levees.

Soil profiles provide information on the maturity of soil development. More developed soil profiles (A, B, or E horizons) correlate with more mature soil surfaces, and less developed soil profiles (C horizons) correlate with areas of more rapid deposition or erosion. In the Tittabawassee River fluvial system, soil profiles are often undeveloped or weak on the natural levees and shoreline surfaces near the river where the ground surface is subject to continuous deposition or transport. In contrast, soil profiles in geomorphic wetlands and upper high surfaces away from the river at greater elevations are often more developed, indicating a more stable and mature condition. Each of the soil profile horizons is discussed below. The distribution of wood debris and snails is also evaluated.

A horizon The A horizon develops on the ground surface and contains relatively higher organic matter than other horizons. The organic matter causes a darker color in sandy and silty soils. Within the MTR, no A horizon was present at many of the sample locations on the natural levees. These surfaces have received recent deposition (or erosion) and are not stable enough to support soil development. Shoreline and tributary A horizons are also immature, with an average A horizon thickness of 0.6 and 0.8 feet, respectively. The typical A horizon thickness for low, intermediate, and high surfaces and some uplands is near 1.0 foot indicating the greatest relative stability and maturity of the overbank surfaces.

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B horizon The presence of a B horizon is also an indicator of relative soil stability and maturity. The development of a B horizon involves the translocation of soil constituents such as clay, iron, or aluminum into the horizon and represents a level of soil development and stability beyond that of only an A horizon formation. In general, the percentage of locations with B horizons increases on geomorphic surfaces away from the river as depicted in Figure 1 of Attachment M. None of the samples on shoreline surfaces contained B horizons, as would be expected. Only 6 percent of natural levee sample locations have B horizons, and where present show very weak development (Bw). Approximately 25 percent of the sample locations on low surfaces, the most extensive geomorphic surface in the MTR, exhibit B horizons. Slightly higher intermediate surfaces have B horizons at 27 percent of the sampled locations; and 38 percent of high surface locations have B horizons. The overall pattern is one of greater soil stability with distance from the river and increase in elevation. Geomorphic wetlands, which are widely dispersed between the bank and the upland scarp both laterally and topographically, exhibit B horizons in 29 percent of sampled locations.

E horizon The development of an E horizon represents a level of soil stability greater than that required for B horizon development. An E horizon is usually located between the A horizon and the B horizon and represents a zone in the soil column where leaching has removed materials such as clay, iron, and/or aluminum. The formation of an E horizon is not common on floodplain soils that are relatively young. Only 2 percent of sampled locations exhibit E horizons.

C horizon The C horizon represents the portion of the soil column that shows no or limited development from soil forming processes. In the overbank cores, the C horizons consisted of the sands, silts, and clays deposited in the overbank by fluvial processes. The C horizon was the primary horizon represented in the majority of the cores within the natural levees. Furans and dioxins were found within the C horizons of the natural levees.

Wood fragments - natural levees The presence of wood appears to provide a marker that corresponds to past logging in the watershed. Logging activities began and peaked before industrialization of the Midland area and before the release history of furans and dioxins. Wood materials entered the watershed during the logging era from erosion from upland forested areas, from natural abrasion of the

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thousands of logs rafted down the Tittabawassee River, and from occasional sawing activities that may have occurred near the banks of the Tittabawassee River. Wood is typically observed as a secondary component in a sand or silt matrix, but can also occur as the main matrix in some samples. The depth of the wood material and association with natural levees supports the hypothesis that the wood material represents soils deposited during or shortly after the logging era. Once these wood deposits were buried by further sediments, wood became less common in the samples.

Wood fragments are most commonly found in the accreting banks of a natural levee adjacent to the main channel. Almost half of the samples containing wood (49.7 percent or 161 of 324 samples) were collected in a natural levee. Another quarter of the samples (24.4 percent or 79 of 324 samples) were from low surfaces, and the remaining samples were at less than 10 percent across other geomorphic surfaces. The frequency of natural levee samples containing wood fragments is highest between 8 and 10 feet below the surface (Figure 2 in Attachment M). The frequency of samples with wood fragments decreases both above and below this depth interval. Approximately 90 percent of all natural levee samples with wood fragments are below a depth of 6.0 feet. This supports the hypothesis that the natural levees formed after the logging era, with the sediments toward the bottom of many natural levees being deposited in the late 1800s or early 1900s.

Data from the 2007 field season indicates that the mean maximum TEQ concentration interval for MTR natural levees is 4.4 to 6.0 feet, just above the major depositional interval for wood fragments. While furans and dioxins are detected in some soil samples containing wood, the wood is typically observed at the bottom of the soil profile containing furans and dioxins. The interval containing wood also typically extends below the interval containing furans and dioxins. Seventy percent (70 percent) of the natural levee samples with wood fragments had a TEQ concentration less than 100 ppt TEQ. In contrast, only 25 percent of the natural levee samples without wood fragments had concentrations less than 100 ppt TEQ. The median TEQ concentration of natural levee samples with wood fragments is 13 ppt. The median TEQ concentration of natural levee samples without wood fragments is 1,200 ppt TEQ. Therefore, the presence of wood fragments is a good marker for the bottom of the interval containing furans and dioxins.

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Presence of shells or shell fragments in overbank soil samples The presence of shells or shell fragments indicates an increased probability of low TEQ concentration at and below the sample depth. The shell fragments appear to represent a historic period when the shells were more common in the watershed. Figure 3 in Attachment M shows the frequency of samples with shells as related to TEQ concentration range. The 562 overbank samples that contained shell fragments are distributed across samples from low surfaces (26 percent), intermediate surfaces (17 percent), natural levees (17 percent), and wetlands (16 percent) with less than 10 percent of the samples in other geomorphic surfaces. Approximately 45 percent of all MTR overbank samples had a TEQ concentration less than 100 ppt and a 75 percent had a TEQ less than 1,000 ppt. In contrast, approximately 75 percent of MTR overbank samples that had shells or shell fragments had a TEQ concentration less than 100 ppt and 95 percent of overbank samples that had shells or shell fragments had a TEQ concentration less than 1,000 ppt. Therefore, shell fragments also provide an indication that the samples with shells tend to have lower concentrations of furans and dioxins, but not as strong of an indication as the presence of wood.

6.2.2 Geomorphic Surface & Spatial Relationship to Furan and Dioxin Distribution Both the maximum concentration and the depth of the furans and dioxins are related to the geomorphic surfaces. In addition, certain geomorphic surfaces with higher furan and dioxin concentrations occur closer to the river (such as natural levees) while other surfaces with lower furan and dioxin concentrations occur farther from the river (such as upper high surfaces).

This distribution is observed in a relationship between proximity to the river and furan and dioxin concentrations. Confidence intervals were developed for the mean and median of the maximum TEQ concentration on different geomorphic surfaces. As an example, the 95 percent confidence intervals for the mean of the maximum TEQ concentration in samples from upland surfaces and from upper high surfaces are both below 100 ppt TEQ.

6.2.2.1 Geomorphic Surface and TEQ Concentration as a Function of Depth For most geomorphic surfaces there is a relationship between sample depth and corresponding TEQ concentration. Typical relationships of high and low TEQ concentrations as a function of depth within each geomorphic surface are provided in Table 6-1 below.

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Table 6-1. Typical Relationships Between Depth and TEQ Geomorphic Surface Typical Depth Range* Typical TEQ Range* Shoreline 0 to 1.1 feet > 600 ppt (Figure 4) 0 to 6 feet up to 600 ppt > 6 feet minimal Natural Levee ~ 4 feet > 30,000 ppt (Figure 5) 3 to 6 feet > 25,000 ppt 2 to 6 feet > 20,000 ppt 2 to 8 feet > 15,000 ppt 1 to 9 feet > 10,000 ppt > 12 feet minimal Historic Natural Levee 0 to 3 feet up to 11,000 ppt (Figure 6) 3 to 5 feet up to 1,000 ppt > 5 feet minimal Low 0 to 3 feet up to 10,000 ppt (Figure 7) 3 to 7 feet up to 5,000 ppt > 7 feet minimal Intermediate 0 to 1 foot > 10,000 ppt (Figure 8) 1 to 3 feet up to 10,000 ppt 3 to 4 feet up to 3,000 ppt 4 to 7 feet up to 1,000 ppt > 7 feet minimal High 0 to 1 foot up to 7,000 ppt (Figure 9) 1 to 4 feet up to 500 ppt > 4 feet minimal Geomorphic Wetland 0 to 1 foot up to 6,000 ppt (Figure 10) 1 to 4 feet up to 2,000 ppt > 4 feet minimal Tributary 0 to 1 foot up to 2,000 ppt (Figure 11) 1 to 3 feet up to 5,000 ppt > 3 feet minimal * Typical TEQ Range and Typical Depth Range include the typical ranges of TEQ and depth for most samples.

The referenced figures, provided in Attachment M, show the TEQ concentration as a function of depth for each of the specified geomorphic surfaces. There are two general patterns in the data. In natural levee and tributary samples the highest TEQ concentrations typically occur at depth and not near the surface. For all other geomorphic surfaces elevated TEQ concentrations, when they occur, are typically found near the surface and are then underlain by samples with low or no TEQ.

6.2.2.2 TEQ Concentration as a Function of Sample Distance from River There is a relationship between the geomorphic features and the distance away from the main channel. Typically, the highest TEQ concentrations are found within the industrial age natural levees which were formed at the edge of the river channel through deposition of predominantly coarse-grained sediment (e.g., sand) throughout the release history.

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Natural levees in the Tittabawassee River typically display the highest TEQ concentrations at depth, with concentrations decreasing at shallower depths. This reflects the decline in source load from the river over time. Upper high surfaces typically occur away from the river. These surfaces flood less frequently and display lower TEQ concentrations. Therefore, a relationship can be shown between the distance away from the river and the concentrations of furans and dioxins.

Depth to Low TEQ Concentration Within a geomorphic surface type, the depth to reach a specified low TEQ (<10 to <90 ppt) decreases with distance from the river for some of the geomorphic surfaces. Attachment M provides graphical representations of the relationship between the depth to TEQ concentration <10 and <90 ppt TEQ and distance from the river for the various geomorphic surfaces: historic natural levees (Figures 12 and 13), low surfaces (Figures 14 and 15), intermediate surfaces (Figures 16 and 17), high surfaces (Figures 18 and 19), and geomorphic wetlands (Figures 20 and 21).

Most shoreline locations are between 0 and 10 feet from the river and most natural levee locations are between 5 and 40 feet from the river; no trend is evident in these surfaces as sample locations move away from the river. Trends are most distinct for surfaces having numerous samples across a wide range of distances away from the river (i.e. low and intermediate surfaces). These surfaces often represent different geomorphic features closer to the river than they do farther from the river. For example, a ridge and swale complex may have low and intermediate surfaces that are part of the levee complex near the river and broader overbank areas when located away from the river channel. Intermediate and high surfaces may represent a deltaic overbank deposit near the river channel and broader overbank areas when located away from the river channel.

Maximum TEQ Concentration Low, intermediate, and high surfaces, geomorphic wetlands, and tributaries, show a decrease in the maximum TEQ concentration with distance away from the river. The range in maximum TEQ concentrations for low, intermediate, and high surfaces and for tributary locations decreases considerably a short distance inland from the river. For some geomorphic surfaces, maximum TEQ concentrations decrease from >15,000 ppt to <3,000 ppt over an approximate distance of 200 feet. These decreases often represent the

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change in geomorphic setting of these geomorphic surfaces as you move away from the river.

Attachment M provides graphical representations of the relationship between the maximum TEQ concentration and distance away from the river for low surfaces (Figure 22), intermediate surfaces (Figure 23), high surfaces (Figure 24), geomorphic wetlands (Figure 25), and tributaries (Figure 26). These graphics also identify sample locations that contain higher concentrations farther away from the river. Most of these samples occur in Reaches RFF and RGG where the deltaic overbank deposition has transported furans and dioxins further inland than in many of the other reaches. The deltaic overbank deposition feature was classified during the 2007 field sampling efforts, and this geomorphic feature, and the related fluvial processes that form them, have a significant influence on the concentrations of furans and dioxins in the floodplain. Incorporating a sound understanding of the geomorphology, including features such as the deltaic overbank deposits, can explain the distribution of furans and dioxins better than a simple relationship between distance from the river and the concentration of furans and dioxins.

6.2.2.3 Differences in Frequency Distributions of Maximum TEQ by Geomorphic Surface Attachment M provides the frequency distributions of maximum TEQ concentrations for the various geomorphic surfaces: shoreline (Figure 27), natural levee (Figure 28), historic natural levee (Figure 29), low surface (Figure 30), intermediate surface (Figure 31), high surface (Figure 32), wetland (Figure 33), and tributary (Figure 34). Maximum TEQ concentrations for shoreline locations were generally between 1,001 and 5,000 ppt. Maximum TEQ concentrations for natural levee locations were always greater than 1,000 ppt. A majority of historic natural levee locations (59 percent) had maximum TEQ concentrations between 1,001 and 5,000 ppt. Most low and intermediate surface locations had maximum TEQ concentrations between 101 and 5,000 ppt.

The frequency distribution of maximum TEQ concentrations for high surface locations was bimodal. Approximately 40 percent of locations had maximum TEQ concentrations less than 100 ppt, while 36 percent of the locations had max TEQs between 1,001 and 5,000 ppt. In many areas, this bimodality is related to the different geomorphic features covered by a high geomorphic surface. These geomorphic features include the transition

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to the upland scarp where concentrations are lower and also the deltaic overbank deposition where concentrations are higher.

Most geomorphic wetland locations had maximum TEQ concentrations between 101 and 5,000 ppt. A majority of tributary locations (59 percent) had maximum TEQ concentrations between 101 and 1,000 ppt. Ninety-two percent (92 percent) of the upper high and upland locations had maximum TEQ concentrations less than 100 ppt.

6.2.3 Geomorphic Surface and Proximity Statistical Summary To analyze the effects of geomorphic surface and proximity on TEQ concentration, the MTR data was sorted three different ways using different categories for each sort: 1) geomorphic surface, 2) proximity (to river) and 3) paired combinations of geomorphic surface- proximity. Statistical procedures were performed using the software application SigmaStat.

Descriptive statistics of maximum TEQ concentrations were developed for each of the three categories. Maximum TEQ concentration probabilities (probable range of concentrations) were also developed for geomorphic surface subsets. Statistical significance tests using maximum TEQ concentrations were conducted on paired geomorphic surface subsets (e.g. natural levee vs. low surface). Statistical significance tests using maximum TEQ concentrations were also conducted on paired proximity subsets (e.g. bank vs. away). The significance tests were used to determine if the null hypothesis that the two populations are from the same population (e.g., no significant difference in concentrations between the paired subsets) could be rejected in favor of the alternate hypothesis that the two subsets represent different populations (e.g., significant difference in concentrations between the paired subsets).

6.2.3.1 Descriptive Statistics-Geomorphic Surface and Proximity Combinations The descriptive statistics for the 21 geomorphic surface and proximity combinations are provided in Table 6-2. For all samples analyzed as not detectable at a specified detection limit, the detection limit was used as the value (e.g. a value of 10 was used for <10 ppt TEQ). The data shows that the average (mean and median) and most common (mode) concentrations follow the relationships described above, i.e. concentrations are typically greater for those geomorphic surface-proximity subsets near the river (e.g. natural levee- bank) and decreases with those subsets that are located away from the river (e.g. high- away). As the sample locations approach the upland scarp, the concentrations drop off.

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The mean and median concentrations of the sample sets fall below 100 ppt TEQ in the high surface away, upper high surface away, and the upland surface.

As discussed earlier, the population of the combined high surfaces samples was bimodal. This difference was partially attributed to the distribution of high surfaces over multiple geomorphic features such as deltaic overbank deposition and the away transitions to the upland scarp. The summary statistics provide further support for a more detailed review of the geomorphic features within the high and intermediate surfaces. The confidence intervals for the mean of the away samples on both the intermediate and high surfaces (High—Away and Intermediate—Away on Table 6-2) do not overlap with the confidence intervals of the mean for the other proximity classifications for the high and intermediate surfaces. This distinction supports the further evaluation of the geomorphic features within the intermediate and high surfaces during the 2008 field period.

There is a considerable range of data variability between subsets as shown by the coefficient of variation (ratio of standard deviation to mean) which ranges from 0.08 for upper high surface-away to 3.67 for tributary- in-channel. The 95 percent confidence interval of the maximum TEQ mean concentration also shows the variability between the subsets with intervals from 10-11ppt for Upper High surface-Away to 0-3, 161 ppt for Tributary-In-channel.

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Table 6-2. Descriptive Statistics for All Geomorphic Surface and Proximity Combinations

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6.2.3.2 Maximum TEQ Concentration Probability Maximum TEQ concentration probabilities for geomorphic surface subsets were developed by transforming data to obtain normal probability data distributions and using a standard normal probability table. For all samples analyzed as not detectable at a specified detection limit, the detection limit was used as the value (e.g. a value of 10 was used for <10 ppt TEQ). All data sets were log transformed using the natural log (ln) and then evaluated for normality. The log normal assumption was strongest on the larger data sets with the exception of the bimodal high surface which had the weakest relationship to a log normal distribution. The small sample sizes were also marginally log normal (shoreline, upland, and upper high surfaces). The probability ranges were calculated on the natural log transformed data and the resulting values were converted through an inverse log function. Table 6-3 presents the lowest maximum TEQ concentration for probabilities ranging from 2.5 percent to 97.5 percent for each geomorphic surface. The subsets with the highest maximum TEQ concentrations at the 95 percent probability level from highest to lowest are natural levee, historical natural levee, and high surface.

Table 6-3. Maximum TEQ Probability Ranges for Each Geometric Surface 50% (Geometric Geomorphic Surface n 2.5% 5% 25% Mean) 75% 95% 97.5% Shoreline 12 136 198 634 1,422 3,193 10,206 14,885 Natural Levee 83 2,251 2,853 5,916 9,828 16,327 33,862 42,913 Historic Natural Levee 54 278 389 1,099 2,262 4,658 13,150 18,420 Low 240 65 98 348 836 2,013 7,109 10,710 Intermediate 152 37 61 283 819 2,371 10,926 17,944 High 53 <10 <10 69 310 1,403 12,274 24,824 Upper High 7 <10 <10 <10 <10 11 12 12 Upland 8 <10 <10 <10 18 35 88 120 Geomorphic Wetland 102 65 96 316 721 1,648 5,402 7,943 Tributary 50 12 20 107 340 1,082 5,707 9,793

6.2.3.3 Significance Tests Significance tests were conducted on MTR maximum TEQ concentration data by comparing geomorphic surface subsets using the non-parametric Kruskall-Wallis and Dunn's Multiple Comparison Method. These significance tests were also conducted on proximity data subsets. For all samples analyzed as not detectable at a specified detection limit, the detection limit was used as the value (e.g. a value of 10 was used for <10 ppt TEQ). The significance tests were used to determine if the null hypothesis that the two populations are from the same population could be rejected in favor of the

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alternate hypothesis that the two subsets represent different populations. If there is a statistically significant difference in the populations, then there is likely a difference in the transport and/or depositional characteristics between the combinations. Tables 6-4 and 6-5 provide the results of the significance tests for geomorphic surface and proximity.

The comparison of MTR maximum TEQ geomorphic surface data shows that compared data for most geomorphic surfaces are significantly different (P<0.05). Twenty of the 28 comparisons concluded that the samples from the different pairs of geomorphic surfaces were different.

Samples from natural levee and historic natural levees were statistically different from samples from all of the other geomorphic surfaces, including each other. Therefore, the natural levees represent a unique depositional environment that is different from the other overbank geomorphic surfaces.

Similarly, the combined upper high surface and upland surface data set was statistically different from samples from all of the other geomorphic surfaces. The mean concentrations on these surfaces are below the mean concentrations on all other surfaces. This multiple comparison test supports the conclusion that the upper high and upland surfaces represent different deposition characteristics than the rest of the overbank.

Within the low, intermediate, high and geomorphic wetland surfaces, the differences between geomorphic surfaces were less pronounced. While only eight out of 28 comparisons made were not significant, 6 of the 8 not-significant conclusions occurred between these four geomorphic surfaces: low vs. intermediate, low vs. high, intermediate vs. high, high vs. wetland, intermediate vs. wetland, and low vs. wetland. This is consistent with the conclusion that additional geomorphic features need to be included in the evaluation of these surfaces, such as ridge and swale, deltaic overbank deposition, and away transition to upland scarps.

The comparison of MTR maximum TEQ proximity data shows that 10 of the 15 compared data sets for proximity subsets are also significantly different (P<0.05). Only 5 out of 15 comparisons were not significant (near bank vs. ridge and swale, near bank vs.

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wetland, ridge & swale vs. wetland, away vs. in-channel (tributary), wetland vs. in- channel (tributary).

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Table 6-4. Maximum TEQ Statistical Significance Test (Entire MTR) Kruskal-Wallis and Dunn’s Multiple Comparison Method Geomorphic Surface

Surface Hist. Nat. Lev. Low Interm. High Upper High & Upland Geo. Wetland Tributary Natural Levee yes yes yes yes yes yes yes Historical Natural Levee yes yes yes yes yes yes Low surface no no yes no yes Intermediate Surface no yes no yes High Surface yes no no Upper High and Upland Surface yes yes Geomorphic Wetland no

Summary Statistics n Max Min Median Mean Std Dev Natural Levee 85 41,000 1,800 11,000 12,864 8,634 Historical Natural Levee 56 26,000 100 2,200 3,826 4,173 Low surface 240 30,000 22 855 1,875 3,206 Intermediate Surface 155 20,000 10 920 2,240 3,271 High Surface 53 12,000 10 580 1,577 2,361 Upper High and Upland Surface 15 160 10 10 22 39 Geomorphic Wetland 104 25,000 41 650 1,519 2,862 Tributary 51 40,000 10 400 1,524 5,620

P<0.05 = Probability of falsely rejecting the null hypothesis (the two data sets are from the same population) n = number of locations

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Table 6-5. Maximum TEQ Statistical Significance Test (Entire MTR) Kruskal-Wallis and Dunn’s Multiple Comparison Method Proximity

Near-Bank Ridge and Swale Away Wetland Complex In-Channel (Trib) Bank yes yes yes yes yes Near-bank no yes no yes Ridge and Swale yes no yes Away yes no Wetland Complex no

Summary Statistics n Max Min Median Mean Std Dev Bank 160 41,000 140 5,750 8,678 8,338 Near Bank 115 26,000 16 1,100 2,191 3,283 Ridge and Swale 104 20,000 44 1,045 2,085 2,892 Away 134 10,000 10 160 535 1,264 Wetland Complex 91 25,000 41 640 1,495 2,993 In-Channel Tributary 51 40,000 10 400 1,524 5,620

P<0.05 = Probability of falsely rejecting the null hypothesis (the two data sets are from the same population) n = number of locations

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6.3 EXPOSURE UNIT SAMPLING AND EVALUATION ON PRIORITY 1 AND 2 PROPERTIES A statistical evaluation was used to validate that the GeoMorph® investigation process adequately characterized exposure unit area concentrations on Priority 1 and 2 properties in the Middle and Lower Tittabawassee River study areas. The GeoMorph® investigation developed subsets of data on Priority 1 and 2 properties for different geomorphic surfaces, and these data subsets represent exposure units for comparison to action levels. The action levels for the exposure units have not been finalized, so this approach includes a sensitivity analysis. This process also includes an evaluation of the adequacy of characterization at different action levels.

Sample Design During the summer and fall of 2007 ATS conducted overbank sampling in the MTR and select Reaches of the LTR. One goal of this sampling was to determine which Priority 1 and 2 properties with 2007 “residential” land use designations have concentrations that exceed the IRA/PCAP Decision Tree thresholds. The IRA/PCAP Decision Tree and IRA/PCAP Step-out Sampling Plan are provided in Attachment O.

This evaluation utilizes the MTR and LTR overbank samples collected during 2007. Sixteen overbank samples on eight parcels along the MTR triggered the Decision Tree threshold for concentrations >10,000 ppt TEQ in the upper 1-foot of soil. Three hundred sixty-two samples at 273 locations sampled on 37 parcels within the overbank of the MTR and LTR triggered the significantly lower residential land use threshold of >1,000 ppt TEQ in the upper 1-foot of soil. In total, the IRA/PCAP Decision Tree resulted in the collection of more than 320 step-out samples. The combination of GeoMorph® site characterization samples and the IRA/PCAP Step-out Samples provided more than 825 surface TEQ results that provided the dataset used for the statistical evaluation of exposure unit area concentrations on Priority 1 and 2 properties in the Middle and Lower Tittabawassee River study areas.

Statistical Evaluation The statistical approach used to evaluate exposure unit areas for the Tittabawassee River study area is described in the October 12, 2007, Work Plan for Exposure Unit Sampling, Middle and Lower Tittabawassee River (ATS, 2007g). This approach was utilized to conduct this evaluation.

Initially, the data set of 825 surface TEQ results was divided into sub-populations, or individual data sets, that represented exposure units within each residential property. The sample locations were grouped into these individual data sets based first on property boundaries and geomorphic surfaces,

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and then further grouped or divided based upon additional geomorphic properties such as geomorphic proximity categories, soil development, and contaminant profile. These data sets were used to develop descriptive statistics on populations and/or sub-populations, considering a number of variables including number of data values, satisfaction of normal distribution model assumptions (independence, normal distribution), and potential influence of outliers on data analyses to select the most appropriate parametric and/or nonparametric statistical tests. The types of descriptive statistics included:

• Population distribution type (normal or lognormal); • Shape of the distribution (coefficient of variation, skewness, and kurtosis); • Test for outliers (Grubbs’ Test); • Measures of central tendency (mean, geometric mean, median); • Measures of statistical variability (standard deviation); • Measures of confidence (95 % mean LCL/UCL, 95% median LCL/UCL, 95% geometric mean LCL/UCL, lambda test, mean vs. action level sensitivity analysis)

Data Analysis One hundred thirty-seven individual data sets were established based on property boundaries, geomorphic surfaces, geomorphic proximity categories, soil development, and contaminant profiles. To enhance comparability between the GeoMorph® sample design and the MDEQ Sampling Strategies and Statistics Training Material (S3TM) (MDEQ, 2002) for the purposes of evaluating exposure unit area concentrations, only surface TEQ were used. Where sample duplicates occurred, the maximum detected TEQ was used to represent the concentration at that location.

The individual datasets were evaluated for data normality. Based on the size of the individual datasets, the evaluation of the coefficient of variance (CV), skewness, and kurtosis were used to screen for data distribution. One hundred eighteen individual datasets conformed to the expectations of a normal distribution and these individual datasets were subsequently screened for outliers utilizing Grubbs’ Test (Barnett and Lewis, 1994). Within these 118 normal data sets, sixteen results were identified as possible outliers and were appropriately flagged.

It is important to have sufficient data on the soil concentrations to estimate a representative concentration for a given geomorphic surface. Another important objective in any sampling program is to obtain the most accurate and representative data possible while minimizing the associated costs (MDEQ, 2002). Lambda tests, 95% UCL/LCL, and a mean value vs. action level sensitivity analyses were performed to evaluate the adequacy of characterization for each data set.

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To provide for an evaluation of the sensitivity, Lambda tests were performed for each individual

dataset, using four potential action levels of 100 ppt TEQ (λ100), 1,000 ppt TEQ (λ1000), 5,000 ppt

TEQ (λ5000), and 10,000 ppt TEQ (λ10000). In general, the lower action level value for lambda (λn) the more samples are required to maintain a specified level of confidence. In addition, as the mean

values approach an action level, lambda (λn) becomes small and additional sampling may be warranted to maintain a certain level of confidence.

Confidence limits (95% LCL/UCL) for the mean values were calculated to compare GeoMorph® site characterization data to selected action levels. The tabulated individual datasets with the descriptive statistics, lambda tests, and confidence intervals is provided in Attachment N-3. These action levels compare the following null and alternative hypotheses:

Null hypothesis, Ho: Mean TEQ in a given geomorphic surface is less than or equal to the selected action level.

Alternative hypothesis, Ha: Mean TEQ in a given geomorphic surface is greater than the selected action level.

If the mean TEQ for a geomorphic surface is greater than or equal to the action level, then a 95% UCL for the mean will be above the applicable action level and collection of additional samples is not likely to result in a UCL for the mean that is below that action level. Therefore, it can be concluded that contaminants are present above the applicable action level and no additional sampling is warranted until such time as a risk-based action level has been selected for the area.

If the 95% LCL for the mean for a geomorphic surface is greater than or equal to the action level, then collection of additional samples is not likely to result in a LCL or UCL for the mean that is below that action level. Therefore, it can be concluded that contaminants are present above the applicable action level and no additional sampling is warranted until such time as a risk-based action level has been selected for the area.

Further analysis was performed comparing mean values and action levels to evaluate the adequacy of characterization for each dataset. This analysis calculates the sample size necessary to achieve specified false positive and false negative rates. Attachment N-4 provides a completed adequacy of characterization analysis that summarizes the sample size necessary to achieve specific false positive and false negative rates.

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The statistical analysis documents that the GeoMorph® sampling design does a superior job over traditional sampling techniques in a variety of areas: 1) the GeoMorph® sampling design segregates the variation of TEQ into meaningful data sets that can be used for the evaluation of exposure, 2) the GeoMorph® sampling design accurately identifies areas with elevated levels of TEQ and accurately identifies areas with little or no TEQ.

6.4 SURFACE WEIGHTED AVERAGE CONCENTRATION ANALYSIS The following section provides the results from the surface weighted average concentration analysis (SWAC) conducted on the geomorphic surfaces in the Upper and Middle Tittabawassee River.

6.4.1 Geomorphic Characterization and SWAC Polygons In preparation for the SWAC analysis, polygons representing different geomorphic surfaces were developed. The following provides a summary of this process.

6.4.1.1 Geomorphic Surface Mapping Preliminary geomorphic feature mapping is conducted to define specific landform and channel features that result from and/or influence fluvial geomorphologic processes. For the Tittabawassee River, geomorphic surfaces such as shorelines, low, intermediate, high, and uplands are often distinguished by elevation differences. For that reason, the mapping of these surfaces is done on high resolution topographic maps. Based on this method, defined geomorphic surfaces can be compared to similar surfaces within a given Reach.

The Reach is used as a basis for geomorphic mapping to provide a practical means to evaluate the river system. The different Reaches along the TR were defined by delineating river segments with similar geomorphologic and/or hydraulic characteristics. This method provides a means to define significant geomorphic surfaces, many of which can be correlated throughout the Reach. The preliminary geomorphic mapping is then used to establish soil sample locations. Most overbank soil samples are arrayed along transects that are generally perpendicular to river flow and extend away from each river bank. Sample locations are typically selected to represent each geomorphic surface type.

Geomorphic surfaces with the same classification are not always considered “similar” since proximity to the river and geomorphic setting need to be considered when attempting to group similar surfaces. To illustrate, an intermediate surface adjacent to a

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river channel is a distinctly different surface when compared to an intermediate surface separated from the river channel by a low surface. To provide an understanding of the spatial variability of contaminants across geomorphic surfaces, more than one sample is generally collected from each specific surface type in a given Reach. Soil descriptions and chemical profiles obtained during site characterization activities are used to confirm or revise preliminary geomorphic surface delineation and geomorphic surface classifications for overbank deposits.

Most in-channel sediment samples are arrayed along transects that are generally perpendicular to river flow. The absolute number and location of in-channel samples is established for each deposit based on available geophysical data (bathymetry and mapping of in-channel deposition and erosion areas) and the relative size of the depositional areas with respect to the Reach (de minimis, small, medium, and large deposits). To provide an understanding of the spatial variability of contaminants across in-channel deposits, multiple samples are generally collected across each specific deposit in a given Reach. Sediment profile descriptions obtained during site characterization activities are used to confirm or revise preliminary mapping of in-channel deposits.

6.4.1.2 Soil/Sediment Profiling and Geomorphic Surface Verification In a river environment, it is important to relate one geomorphic surface to another when evaluating depositional environments. Soil profiles are described and compared to determine if overbank surfaces have been influenced by similar depositional and/or erosional factors. The selection of soil sample locations is based on parameters that influence the development of geomorphic surfaces including the channel gradient, channel configuration (e.g., meander versus straight, bankfull width, meander width, meander wavelength, radius of curvature, and belt width), surface elevation, aggradation/degradation potential (deposition/erosion), and thalweg position.

In the overbank environment it is important to identify and group like surfaces based on similar soil profiles. The soil and contaminant profiles are compared to determine the similarity and differences within a geomorphic surface and across geomorphic surfaces. The data from similar surfaces can be extrapolated on the surface to estimate the depositional pattern. The boundaries of the extrapolation are based on the soil development processes and the homogeneity of the deposition pattern. Similar soil profiles and a homogeneous deposition pattern allow broader extrapolation boundaries.

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The in-channel sediment is the most dynamic portion of the river regime. The changes in water velocity, discharge, sediment load, and size due to seasonal and single flood events influence aggradation and degradation patterns. Detailed mapping and sampling of the in-channel sediments is necessary to understand river bed surfaces and to establish relative bed stability. It is also important to confirm in-channel deposits based on similar sediment profiles. Common in-channel stable bed features include riffles, runs, pools, and glides. Riffles typically occur at the flow cross-over locations and have a poorly defined thalweg. Runs typically have greater depths and higher velocities than riffles and have a well defined thalweg. Pools are the deepest locations, and are often located at the outside of meander bends. Glides are located downstream from pools and typically have a channel bed with a negative slope while the water slope is positive.

6.4.1.3 Verification Geomorphic/SWAC Polygons SWAC polygons are graphic representations of geomorphic surfaces with similar characteristics. They are developed by applying knowledge of the river geomorphology, detailed topographic information, mapping in-channel/overbank areas, and correlating those surfaces to soil/sediment and contaminant profiles. In some cases, geomorphic surfaces may have one or more SWAC polygons based on the complexity of the depositional and erosional pattern. Once SWAC polygons are selected, applicable attenuation factors associated with the aggradation/degradation potential can be applied to the SWAC polygons. Example work product outputs for the SWAC polygons with surface TEQ concentrations are included in Attachments N-1 and N-2.

6.4.2 Geomorphic Surface Weighted Concentration Analysis A current condition Surface Weighted Average Concentration (SWAC) analysis was performed for each SWAC polygon of interest. The SWAC polygon boundaries were established using the following criteria:

• Soil Profile Information: the profile information for each sample location was classified as either a sandy depositional environment or a fine-grained depositional environment. Each sample location was assigned one of these categories. • Max and Surface TEQ: TEQ concentrations were divided into the following classes:

a) 0-100 ppt TEQ

b) 100-1,000 ppt TEQ

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c) 1,000-5,000 ppt TEQ

d) 5,000-15,000 ppt TEQ

e) >15,000 ppt TEQ

f) Geomorphic Surface: when possible, SWAC polygon boundaries were drawn following geomorphic surfaces. When TEQ concentrations and soils were similar across geomorphic surfaces, SWAC polygon boundaries were drawn across geomorphic surfaces. The Geomorphic Surface categories: in- channel, shoreline, low, low intermediate, intermediate, high, natural levee (post-industrial levee), historic natural levee (pre-industrial levee), geomorphic wetland, upper high, upland, island, and tributary;

g) Geomorphic Proximity Categories: bank, near bank, ridge and swale, near bank, wetland complex, away, and disturbed/other.

Each SWAC polygon was drawn according to these criteria for Surface TEQ.

The SWAC analysis will be prepared using data collected from the site characterization to establish COI concentrations for SWAC polygons following a statistical evaluation of select, representative populations and/or sub-populations (individual geomorphic surfaces, and reach level grouping of like surfaces, as appropriate).

6.4.2.1 Statistical Evaluation of SWAC Polygons The approach that was used to evaluate SWAC polygons for the Tittabawassee River study areas is as follows:

Established statistical populations and sub-populations, based on geomorphic surfaces, geomorphic proximity categories, soil development, and contaminant profile;

Developed descriptive statistics on populations and/or sub-populations (individual geomorphic surfaces and possible river reach or region level grouping of like surfaces/features, as appropriate); statistical evaluations considered a number of variables including number of data values, satisfaction of normal distribution model assumptions (independence, normal distribution), and potential influence of outliers on data analyses to select the most appropriate parametric and/or nonparametric statistical tests. Example descriptive statistics include:

a) Population Distribution Type (normal, lognormal);

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b) Shape of the Distribution (coefficient of variation, skewness or kurtosis, etc.);

c) Test for Outliers (Grubbs, Dixon’s, Rosner’s, etc.);

d) Measures of central tendency (mean, median, every 10th percentile, mode, interquartile mean, etc.);

e) Measures of statistical variability (standard deviation, variance, range, interquartile range, average deviation, etc.);

f) Establish measures of confidence (95% mean UCL, 95% median UCL, etc.);

6.4.2.2 Current Condition SWAC Process: The current condition SWAC was developed by applying knowledge of the geomorphology of the river system, detailed site characterization data, and information on the overbank and in-channel areas to establish boundary conditions for the spatial analysis. COI concentration data and factors used in a SWAC analysis depended on the exposure vectors being evaluated, and the relationship of site concentration data to numeric thresholds for concern. Following verification of SWAC polygons, COI concentrations and applicable attenuation factors associated with the aggradation/degradation (i.e., erosion/deposition) potential were assigned to in-channel and overbank SWAC polygons.

In-channel SWAC Analysis

Because the bed load and wash load components of sediment transport are significant in the Tittabawassee River, the surface layers of in-channel deposits are dynamic. In order to assign the aggradation/degradation factors for in-channel deposits differential measurements must be taken of the bed elevation and form. Differential high resolution bathymetry will be used for this purpose. Initial bathymetry was recorded for Reaches A through V in 2007. A follow-up survey is planned for spring 2008. Together with calibration ground control measurements, these bathymetric survey data sets will be used to determine the aggradation/degradation patterns, and assign the corresponding factors for the in-channel SWAC analysis. Completion of this SWAC analysis is planned for July 2008.

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Overbank SWAC Analysis

The SWAC calculation used for overbank polygons applied an assigned erosion factor

(EF, reflecting potential to erode based on proximity), an assigned depth attenuation

factor (DAF, based on depth of COI), and other relevant factors to the average soil concentration (arithmetic or geometric mean) for the individual SWAC polygon. If a sample concentration fell below the detection limit, one half of the detection limit was used for the sample value. The adjusted concentration was multiplied by the surface area of the SWAC polygon (sq. ft.) to obtain a product of “Adjusted COI concentration times SWAC Polygon Area.” The total SWAC value for a Reach equaled the sum of the “Adjusted COI concentration times SWAC Polygon Area”, divided by the sum of the SWAC Polygon Areas for a Reach of the river.

The formula for the SWAC polygon calculation is:

Pa = C × E f × Daf × A

Where:

Pa = Product of Adjusted Concentration x SWAC Polygon Surface Area (ppt TEQ x sq. ft.)

C = Average Sample Concentration of SWAC Polygon (ppt TEQ)

Ef = Erosion Factor

• High Erosion Potential or Aquatic Setting = 1.0 • Medium Erosion Potential = 0.5 • Low Erosion Potential = 0.25 • Very Low Erosion Potential = 0.1

Daf = Depth Attenuation Factor

• High: Direct Contact or ≤0.5 ft of Soil/Sediment Cover = 1.0 • Medium: >0.5ft – 1.0 ft Soil/Sediment Cover = 0.5 • Low: >1.0ft Soil/Sediment Cover = 0.1

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• Very Low: >1.0 ft Soil/Sediment Cover plus Rip Rap, Geotextile, or Other Engineered Stabilization = 0.01

A = Surface Area of SWAC Polygon (sq. ft.)

The Reach SWAC value equals the sum of the “Adjusted COI concentration times SWAC Polygon Area”, divided by the sum of the SWAC Polygon Areas for a Reach of the river.

The formula for the Reach SWAC value calculation is:

P ∑ a = Re ach SWAC Value ∑ A

Where:

A = Surface Area of SWAC Polygon (sq. ft.)

Pa = Product of Adjusted Concentration x SWAC Polygon Surface Area (ppt TEQ x sq. ft.)

The UTR and MTR SWAC calculation table using surface TEQ concentrations is provided in Attachment N-2. The UTR and MTR surface TEQ SWAC Maps is provided

in Attachment N-1. A assigned default value of 1 was used for erosion factor (EF) and

depth attenuation factor (DAF). As appropriate, the total SWAC for a river region (combination of reaches, based on river morphology) can also be calculated by combining the sum of the “Total Reach Adjusted COI concentration times SWAC Polygon Area”, divided by the sum of the “Total Reach SWAC Polygon Area.”

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7. 2007 SUPPLEMENTAL ACTIVITIES

7.1 SUPERFUND REMOVAL ACTIONS In three Administrative Settlement Agreements and Orders on Consent for Removal Action (AOC) between the United States Environmental Protection Agency (USEPA) and The Dow Chemical Company (Dow) dated July 12, 2007, Dow agreed to take actions to remove impacted sediments in sections of Reach D and O, and impacted soils in Reaches J/K during 2007. Dow completed all removal actions within the AOC defined schedules and is in the process of preparing final reports.

Actions in Reach D included removal of river sediments within a historic wastewater discharge flume bounded by the remnants of a sheet pile wall that once paralleled the Dow property immediately upstream of the Dow Dam on the NE side of the river. Site activities were completed in 2007.

Actions in Reaches J/K included removal of impacted soils along the bank/levee and overbank terrace on the northeast side of the Tittabawassee River, approximately 3.6 miles downstream of the confluence of the Chippewa and Tittabawassee Rivers. The area is located on Dow property and is bounded to the northeast by a wetland, by Saginaw Road further northeast of the wetland, to the south by the Caldwell Boat Launch (located just west of the Saginaw/Waldo Road intersection in Midland, Michigan) and to the west by the east channel of the Tittabawassee River. Site activities began August 6, 2007 with completion of the site restoration work on December 13, 2007.

Actions in Reach O included removal of river sediments from a 1,300 foot long point bar located off the NE bank of the Tittabawassee River approximately 6 miles downstream of the confluence of the Chippewa and Tittabawassee Rivers. The area is located immediately adjacent to Dow property, south of Saginaw Road in Ingersoll Township. Site activities began August 13, 2007 with completion of in-river sediment removal activities on October 26, 2007.

7.2 PCAP STEP OUT PROCESS AND DECISION TREE In accordance with the IRA/PCAP Implementation Decision Tree, dated April 30, 2007, additional step-out sampling is required when sediment concentrations exceed 10,000 ppt TEQ at any depth in- channel, when sediment and soil concentrations exceed 10,000 ppt TEQ in the upper 1 foot of soil in the overbank, or when concentration from samples from residential land use conditions exceed 1,000 ppt TEQ in the upper 1 foot of soil. Attachment O provides a copy of the IRA/PCAP Implementation Decision Tree.

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A summary table in Attachment Q provides soil profile and analytical details for the various locations where TEQ concentrations triggered the Decision Tree and for the completed step-out samples. The table also provides a list of the in-channel and residential overbank locations where step-out sampling is planned during the 2008 investigation.

7.3 BANK ASSESSMENT A preliminary assessment of bank stability, using available physical data from specific locations within the UTR and MTR, and the United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Bank Stability and Toe Erosion Model (Version 4.1) was conducted to:

• assess bank stability based on available physical data (bank profile and soil profile textural characterization); • compare model predicted bank stability with field observations; • assess model use for future decision-making regarding channel modifications and bank stabilization practices.

Although the model has capability to predict bank and toe erosion based on overall channel flow, channel slope, and soil material erodibility, the focus of this preliminary effort was to evaluate the potential for bank failure.

The bank failure component of the model includes methods to predict conditions suitable for wedge failures within saturated and unsaturated soil. Bank failure can be characterized by the shape of the failure surface and/or the mode of failure. The bank stability model assumes gravitational failure in one of three modes: planar (slab), cantilever (undercutting & overhang), and a modification of planar failure that considers the influence of tension cracks. The primary output from the model was the predicted bank stability (Fs) value. The bank stability value is the ratio of the shear strength (resisting force) of soil bank material to the driving force (gravitational). Fs values of 1.3 or greater represent a stable bank conditions, Fs values between 1.0 and less than 1.3 represent a conditionally stable bank, and Fs values less than 1.0 represent an unstable bank.

A summary of the baseline model and sensitivity analysis is provided below. Attachment P provides the full preliminary assessment report.

7.3.1 Baseline Model The baseline simulation represented conditions based on bank and profile inputs from field measurements, and model estimates of soil and bank parameters. Field measurements included

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soil type, which was used to determine the soil profiles, soil layering, bank composition and soil friction angle. Model-estimated parameters included the soil friction angle and shear surface angle. Soil friction angles for specific soil types were determined by the model. Soil profile descriptions for the UTR and MTR were used in selecting the soil friction angle for specific soil types. The shear surface angle was generated by the model. The shear emergence location on the bank was defined as 0, since shear surfaces on the bank slope were not observed. Soil layers were determined based on the soil horizon data available from soil profile descriptions. The bank profile included three layers of angular fine sand and two layers of angular coarse sand. The toe material was composed of coarse sand. The banks consisted of predominantly excessively well drained sands; therefore, the bank water table and the channel flow elevations were assumed near the channel-full/bank top elevation for the baseline simulation. The channel slope was determined from existing channel profile data. A channel flow duration of 12 hours was used to represent relatively frequent flow events. The baseline simulation did not include either man-made bank stability measures or any vegetation cover.

The resulting Fs from the baseline model was 7.0, indicating that the bank for the baseline condition is stable.

7.3.2 Sensitivity Evaluations Sensitivity simulations were conducted by changing the value of one or more input parameters. These simulations were done to evaluate the sensitivity of the model to specific input parameters and also to represent potential conditions that may result in bank instability.

The sensitivity simulations indicated model predictions were most sensitive to: (1) the shear surface angle (determined by bank angle, soil type, soil friction angle, and pore water pressure); (2) the shear plane emergence along the bank and its relationship to channel flow and bank water table elevations; (3) the differential, if present, between bank and channel flow elevations; and, (4) the bank height.

Most of the sensitivity simulations predicted banks that were relatively stable with Fs values that range from 1.8 to 10.4. Unstable banks were predicted for the following conditions:

• When the shear surface plane emerged about midway along the bank slope, and channel flow and bank water table elevations were above the emergence plane at about three feet from the bank surface; • When the bank water table is about 6.5 feet or more than the channel flow;

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• When the bank height is more than 33 feet.

The Fs values for the unstable/conditional unstable conditions ranged from 0.8 to 1.2. The predicted Fs values were dependent on several variables: (1) shear plane emergence location; (2) bank water table elevation; (3) channel flow elevation; and, (4) the separation between bank water table and channel flow elevations. In general, bank stability was predicted when bank water table and channel flow elevations occurred below the shear plane emergence or when channel flow was well above the shear plane emergence.

7.3.3 Preliminary Bank Assessment Findings The preliminary model results indicated that the banks typical of the UTR and MTR are relatively stable with respect to bank mass failure. These results are consistent with general observations in the UTR and MTR, where bank mass failure is rarely observed.

The bank soil layers in the UTR and MTR are predominantly sand. Sand is a relatively noncohesive material. Generally, in noncohesive banks the shear strength increases more rapidly with depth than does the shear stress. Therefore, bank failure is most likely to occur at shallow depths from dislodgement of individual particles or failure along shallow slip surfaces (Langendoen, 2000). Sand is also typically not subject to failures associated with tension cracks.

Attachment P provides photographs of the natural levee banks in the UTR, Reaches M and N. The photographs, taken in early November, 2007, show 100 pecent vegetation cover on the banks. The photographs also show the ordinary high water mark at the base of the slope, identified by the line where vegetation is present above the mark and is non-vegetated below the mark.

Tasks necessary for further evaluation of bank stability and erosion along the Tittabawassee River include:

• Use visual characterization to classify bank types (estimated height & slope, profile) within those reaches where erosion and bank stability are significant concerns based on the presence of COI. Document (map) bank failure locations and shear planes, if existing, with respect to Reach characteristics (e.g. outside meander), similar to the process presently used for mapping bank erosion scars, and document conditions that may contribute to failure (e.g. undercutting, lack of vegetative cover, surcharge from overhanging trees). • Use data and observations from bank erosion monitoring to assess bank stability.

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• Monitor soil pore water pressure in bank profiles to evaluate the influence of soil water conditions on soil strength and bank stability. • Conduct analysis of existing hydrologic data from USGS Midland gaging station to assess the frequency and duration of the top of bank flood stage. The duration of the top of bank flood stage is significant to bank stability because it influences the degree and extent of bank saturation. • Conduct analysis of existing hydrologic data from USGS Midland gaging station to estimate rate of channel stage decline for a range of flow events. • If necessary, conduct borehole shear tests to document bank soil strength.

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8. REFERENCES

AIM (undated). Allis Information Management, Inc., The Logging Industry in the Saginaw Watershed 1847-1898. ATS (2006a). Ann Arbor Technical Services, Inc., GeoMorph® Sampling and Analysis Plan, Upper Tittabawassee River, Midland, Michigan, July. ATS (2006b). Ann Arbor Technical Services, Inc., Quality Assurance Project Plan (QAPP), GeoMorph® Investigation, Upper Tittabawassee River, Midland, Michigan, July. ATS (2006c). Ann Arbor Technical Services, Inc., Technical Memorandum: PCOICOI/TAL Evaluation & Target Analyte List Development, December. ATS (2006d). Ann Arbor Technical Services, Inc., Remedial Investigation Work Plan: Tittabawassee River and Floodplain Soils, Midland, Michigan, December. ATS (2007a). Ann Arbor Technical Services, Inc., Remedial Investigation Work Plan, Tittabawassee River and Floodplain Soils, Midland, Michigan, December 2006; revised September 2007. ATS (2007b). Ann Arbor Technical Services, Inc., 2007 GeoMorph® Sampling and Analysis Plan, Upper and Middle Tittabawassee River, Midland, Michigan, July. ATS (2007c). Ann Arbor Technical Services, Inc., GeoMorph® Pilot Site Characterization Report, Upper Tittabawassee River and Floodplain Soils, Midland, Michigan, February. ATS (2007d). Ann Arbor Technical Services, Inc., 2007 Quality Assurance Project Plan, GeoMorph® Investigation, Tittabawassee River, Midland, Michigan, July. ATS (2007e). Ann Arbor Technical Services, Inc., Technical Memorandum: Method Comparability Study – Chlorinated Dioxins and Furans by Methods 1613B and 1613- TRP/RT, March. ATS (2007f). Ann Arbor Technical Services, Inc., Technical Memorandum: Secondary COI Sample Selection Strategy, Tittabawassee River, Midland, Michigan, December. ATS (2007g). Ann Arbor Technical Services, Inc., Work Plan for Exposure Unit Sampling, Middle and Lower Tittabawassee River, Midland, Michigan, October. Barnett, V. and Lewis, T. (1994). Outliers in Statistical Data, 3rd edition. Wiley: Chichester New York. Basset, C.E. (1988). USDA, Rivers of Sand: Restoration of Fish Habitat on the Hiawatha National Forest. Integrating Forest Management for Fish and Wildlife. U. S. Department of Agriculture, Forest Service, North Central Forest Experimental Station. pp 43-48. Bedient, P. and Huber, W (1992). Hydrology and Floodplain Analysis, Addison Wesley, New York Beers (1877). Tittabawassee Township [Plat Map], Saginaw County, Michigan, F.W. Beers & Co., 1877, (http://www.historicmapworks.com/Sections/Maps/viewPlateUS-22917.htm)

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Brady, N. C. and Weil, R.R., (1999). The Nature and Properties of Soils. 12 ed., Prentice Hall, Upper Saddle River, NJ. CMHS (2008). Center for Michigan History Studies, undated, http://www.michiganepic.org/lumbering/photoarchive/archive4/pages/Stumps.htm, Online, February. Dorr, J.A., Eschman, D.F., (1970). Geology of Michigan. The University of Michigan Press. Dow (2007a). The Dow Chemical Company, Distribution of Polychlorinated Dibenzo-p- Dioxin/Dibenzofurans on Fractionated Soils from the Tittabawassee River Floodplain, March. Dow (2007b). The Dow Chemical Company, Distribution of Polychlorinated Dibenzo-p- Dioxin/Dibenzofurans in Sediments and Their Particle Size Fractions from the Tittabawassee River, August. Ederer, R. (1980). Images of America, Thomas Township, Michigan Farrand, W.L., Bell, D.L., (1982). Quaternary Geology of Southern Michigan. [Map] http://www.michigan.gov/documents/Quaternary_Geology_Map_19609_7.pdf) Farrand, W.R., (1988). Michigan Geological Survey, Division of the Michigan Department of Environmental Quality; The Glacial Lakes around Michigan Bulletin 4; revised 1988. http://www.deq.state.mi.us/documents/deq-gsd-info-geology-BU4.pdf Fitzpatrick, F., (2006). US Geological Survey, From Landslides to Levees, Important Links Among Episodic Sediment Movement, Fluvial Landforms, Geologic Setting, and Aquatic Habitat. USGS. Lansing MI. October. Kondolf, G.M. (1997). Hungry Water: Effects of Dams and Gravel Mining on River Channels. Environmental Management 21(4):533-551. Langendoen, E.J., (2000). Concepts – Conservation Channel Evolution and Pollutant Transport System, Version 1.0, Research Report No. 16, USDA-ARS National Sedimentation Laboratory, Oxford, MS. December. Larson, G., and Schaetzl, R., (2001). Origin and Evolution of the Great Lake, Great Lakes Research Volume 27, number 4, pages 518-546 (International Association of Great Lakes Research). http://www.geo.msu.edu/schaetzl/publication_list.html Linsley, R., Kohler, M. and Paulhus, J. (1982). Hydrology for Engineers, McGraw Hill, New York. LTI (2004). Limno-Tech, Inc., Preliminary Flow and Solids Monitoring, 2003-2004, Tittabawassee River, Michigan. November. Mainville, A. and Craymer, M.R. (2005). Present-day Tilting of the Great Lakes Region Based on Water Level Gauges, GSA Bulletin, Vol. 117, no. 7/8, pp 1070-1080. MDEQ, (2002). Michigan Department of Environmental Quality, Sampling Strategies and Statistics Training Materials for Part 201 Cleanup Criteria. MDNR (1988). Michigan Department of Natural Resources, Remedial Action Plan for Saginaw River and Saginaw Bay Area of Concern, September.

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MDNR (1994). Saginaw River/Bay Remedial Action Plan, Draft 1995 Biennial Report, Volume 1. Michigan Department of Natural Resources. Lansing, MI. Midland County (2007). Midland County Road Commission, Plan and Profile of Proposed Gordonville Road Over the Tittabawassee River Bridge Rehabilitation Project, Job # 86275A, 2/12/2007. Rosgen, D. (1996). Applied River Morphology. Wildland Hydrology, Pagosa Springs, CO. Rosgen, D. (2006). Watershed Assessment of River Stability and Sediment Supply. Wildland Hydrology, Fort Collins, Colorado. Saginaw County (1976). Saginaw County Road Commission, General Plan of Site, Bridge Crossing the Tittabawassee River on W. Freeland Road, Job # 09170A, Revised 3/15/1976. Saginaw County (1992). Saginaw County Road Commission, General Plan of Site, Freeland Road Tittabawassee River Overflow, Job # DB-1107-2, December. Saginaw Township (1877) http://www.saginawtownship.org/oldsite/Historic%20Photos/township%20composite%2 0map.htm Saginaw County (2001). Saginaw County Road Commission, General Plan of Structure, Tittabawassee Road over Tittabawassee River, Job # DB-1153-19, November. Saginaw County (2008). Saginaw County Road Commission, personal communication with Periard, J.G., January. Sherwood, J. and Huitger, C (2005). Bankfull Characteristics of Ohio Streams and Their Relation to Peak Streamflows. USGS Scientific Investigations Report 2005–5153. Simmons (1966). USGS, Resistance to Flow in Alluvial Channels, Simmons D. B., and E. V. Richardson, U.S. Geological Survey Professional Paper 422-J, 1966. SSSA, (1996). Glossary of Soil Science Terms. Soil Science Society of America, 677 South Segoe Road, Madison, WI Trimble, S.W. (1983). A Sediment Budget for Coon Creek Basin in the Driftless Area, Wisconsin, 1853-1977, Trimble, S.W., American Journal of Science, Vol. 283, pg 454- 474, May. USACE (2007). US Army Corps of Engineers, Detroit District, Prehistoric Glacial Movements and Lake Shapes, http://gis.glin.net/maps/ Online, December. USGS (undated). U.S. Geological Survey Programs in Michigan, U.S. Geological Survey Fact Sheet, FS-022-96 USGS (1973a). U.S. Geological Survey, Averill Quadrangle. USGS (1973b). U.S. Geological Survey, Midland North Quadrangle; 1962, Photo revised. USGS (1973c). U.S. Geological Survey, Midland South Quadrangle; 1962, Photo revised. USGS (1973d). U.S. Geological Survey, Gordonville Quadrangle. USGS (1973e). U.S. Geological Survey, Auburn Quadrangle; 1962, Photo revised. USGS (1973f). U.S. Geological Survey, Saginaw Quadrangle; 1967, Photo revised.

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USGS (1975a). U.S. Geological Survey, Hemlock Quadrangle. USGS (1975b). U.S. Geological Survey, Shields Quadrangle. USGS (2008). U.S. Geological Survey, Streamflow Measurements for Michigan, USGS 04156000 Tittabawassee River at Midland, MI. http://nwis.waterdata.usgs.gov/mi/nwis/measurements/?site_no=04156000&agencycd=U SGS Online February 6, 2008. USGS, (2008). U.S. Geological Survey, Peak Streamflow for Michigan, USGS 04156000 Tittabawassee River at Midland MI. http://nwis.waterdata.usgs.gov/mi/nwis/peak?site_no=04156000&agency_cd=USGS&for mat=html accessed January 8, 2008. www.historicbridges.org, (2008). www.historicbridges.org/truss/smithscrossing, accessed 1/17/2008

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9. GLOSSARY

Accelerated erosion Erosion at a rate greater than normal, usually associated with activities of man which reduce plant cover and increase runoff. (See geologic erosion.) Accretion The gradual addition of new land to old by the deposition of sediment carried by the water. Aggradation The geologic process by which stream bed, floodplains, and the bottoms of other water bodies are raised in elevation by the deposition of material eroded and transported from other areas. It is the opposite of degradation. Alleviation The process of accumulating sediment deposits at places where the flow is retarded. Alluvial Pertaining to processes or materials associated with transportation and/or deposition by flowing water. Alluvial deposit Clay, silt, sand, gravel, or other sediment deposited by the action of running or receding water. Alluvial stream A stream whose channel boundary is composed of appreciable quantities of the sediments transported by the flow, and which generally changes it bed forms as the rate of flow changes. Alluvium Sediments deposited directly or indirectly by flowing water of (modern) streams and rivers, including the sediments laid down in riverbeds, floodplains, deltas, alluvial fans, and estuaries. Antidunes Bed forms that occur at a velocity higher than that velocity which forms dunes and plane beds. Antidunes commonly move upstream, and are accompanied by and in phase with waves on the water surface. Aquifer A subsurface strata or zone that is sufficiently permeable to conduct groundwater and to yield economically significant quantities of water to wells and springs. Aquitard A confining bed that retards but does not prevent the flow of water to or from an adjacent aquifer; a leaky confining bed. It does not readily yield water to wells or springs, but may serve as a storage unit for groundwater. Armoring The formation of a resistant layer of relatively large particles resulting from removal of finer particles by erosion. Avulsion A sudden change in the course of a stream channel, such as the cutting off of a meander. Bankfull Discharge The discharge and corresponding stage at the incipient point of flooding. It is often associated with a return period, on the average, of 1.5 years. It is expressed as the momentary maximum of instantaneous peak flows rather than the mean daily discharge. Bankfull mean The mean depth of flow at the bankfull stage, determined as the cross-sectional depth area (sum of the products of unit width times depth) divided by the bankfull surface width. Bankfull stage The elevation of the water surface associated with the bankfull discharge. Bankfull width The surface width of the stream measured at the bankfull stage. Bathymetry The measurement of the depth of bodies of water. The fluvial equivalent of topography. Bed material The unconsolidated sediment mixture of which the bed is composed. Bedload The part of a river’s load that is moved on or immediately above the stream bed, such as the larger or heavier particles (boulders, pebbles, gravel) rolled along the bottom; the part of the load that is not continuously in suspension or solution. Bedload discharge The quantity of bedload passing through a cross-sectional area of stream in a specified unit of time.

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Belt width The width of the full lateral extent of the bankfull channel measured perpendicular to the fall of the valley. Benchmark value Published generic risk-based values for human and ecological exposure. Bottomset bed Fine-grained material (usually silts and clays) slowly deposited on the bed of a quiescent body of water at the advancing edge of a delta Boulder (fluvial A detached rock mass larger than a cobble, having a diameter greater than 256 sediment) mm (10 in) being somewhat rounded or otherwise distinctively shaped by abrasion in the course of transport. Channel A natural or artificial waterway that periodically or continuously contains moving water, or which links two quiescent bodies of water. Channel-fill deposits Deposits of sediment within a channel, partly or completely filling the channel (Such materials accumulate where the transporting capacity has been insufficient to remove it as rapidly as it has been delivered.) Clay 1) The soil size fraction consisting of particles less than 0.002 mm (2 microns) in diameter. 2) Fine-grained minerals (often phyllosilicate minerals) that become plastic with the appropriate water content and harden as they dry. 3) A soil textural class for soils containing more than 40 percent clay and less than 40 percent silt and less than 45 percent sand. Clay size (fluvial A term used in sedimentology for a particle having an equivalent spherical sediment) diameter equal to or less than 1/256 mm (0.00016 in). Cobbles A rock larger than a pebble and smaller than a boulder, having a diameter in the range of 76-250 mm being somewhat rounded or otherwise modified by (fluvial sediment) abrasion in the course of transport. Cohesive sediments Sediments whose resistance to initial movement or erosion is affected mostly by cohesive bonds between particles. Colloids (fluvial Finely divided solids that do not settle in a liquid but which may be removed by sediment) coagulation or biochemical action. Smaller than 0.00024 mm. Confinement The lateral containment of rivers as quantitatively determined by meander width ratio (meander width ratio is determined by dividing belt width by bankfull width see meander width ratio. Confluence The point where two or more rivers meet. Constituents of The lists of COI for this project are derived from the PCOI, and reflect those Interest (COI) substances that are likely to have been released to the environment during the period of interest for the study. Because of the large number of PCOI, the COI lists have been organized by chemical class to facilitate evaluation of physical/chemical properties and selection of analytical methods. COI may or may not have suitable analytical methods, and therefore may or may not be included on the Target Analyte List.(TAL) Contaminant of A Target Analyte List (TAL) chemical present in soil or sediment at a Potential Concern concentration that is greater than background concentrations and relevant risk- (CoPC) based screening values for human health derived either by MDEQ or EPA. Contaminant of Any contaminant that is shown to pose possible ecological risk. Potential Ecological Concern (COPEC) Crevasse Splay Floodplain deposit typically composed of sandy or silty material where floodwaters have breached levees or banks and deposited suspended sediment as velocity decreases. Critical tractive The minimum force necessary to initiate movement of sediment particles in the force stream bed. Cut bank The steep or overhanging slope on the outside bend of a river meander. It is produced by lateral erosion of the river.

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Degradation The geologic process by which stream beds are lowered in elevation by the removal of material through erosion and scouring. The opposite of aggradation. Delta A deposit of sediment formed where moving water (as from a stream at its mouth) is slowed by a body of standing water. . Deltaic Overbank A deposit of sediment formed where moving water (as from a stream at the point Deposition Area where bankfull discharge is exceeded) tops its normal banks and the resultant velocity decrease deposits (along the longitudinal flow path) the coarsest part of its load first, medium grained material next, followed by fine grained material. The resulting deposition pattern is thicker deposits on the upstream side and thinner deposits downstream, similar to a delta pattern. Deposition The mechanical or chemical processes through which sediments accumulate in a resting place. Drainage basin The total area that contributes surface water flow through a single point (usually the confluence of two rivers) on the landscape. (See also watershed.) Dunes (stream) Bed forms of coarse sediment generally transverse to the direction of flow, with a triangular profile having a gentle upstream slope (dunes advance downstream by the movement of sediment along the upstream slope and by the deposition of sediment on the steep downstream slope. Dunes move downstream at low velocities compared to the stream flow velocity.) Dynamic A condition of a river system in which there is a balanced inflow and outflow of Equilibrium materials (Glossary of Geology 5th Edition) Entrenchment Ratio The quantitative index of the vertical containment of rivers as determined by dividing the flood-prone area width by the bankfull width. (The flood-prone area width is measured at twice the maximum bankfull depth - see flood-prone area width). Erosion The wearing away of the land surface by detachment and movement of soil and rock fragments through the action of moving water, wind, ice, or a combination of these agents. Fill Man-made deposits of natural earth material (e.g., rock, soil, sand) and/or waste materials (e.g., tailings or excavation spoils), used to fill an area. Fine material Particles of a size finer than the particles present in appreciable quantities in the bed material; normally silt and clay particles (particles finer than 0.062 mm). Flashy River flow regime characterized by a rapid rate of change. Floodplain That portion of a river valley, adjacent to the channel, which is built of sediments deposited during the present regimen of the river and is covered with water when the river overflows its banks at flood stages. It is available to the river to accommodate flows greater than the bankfull discharge (see bankfull stage). There is not a constant frequency of occurrence of flood discharge associated with the floodplain, as the depth of flow over the floodplain is a function of the width of the floodplain and the magnitude of the flood peak. The estimated 8-year and 100-year Floodplains represent the extent of the floodplain inundated during floods with recurrence intervals of 8 years and 100 years, respectively. Flood-prone area The width associated with a value of twice the bankfull depth. It is the area width including the floodplain of the river and often the low terrace of alluvial streams. This value when divided by the bankfull width is used to determine entrenchment ratio. Fluvial Of or pertaining to rivers. Fluvial sediment Particles derived from rocks or biological materials that are transported by, suspended in, or deposited by streams.

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Foreset bed Inclined sediment layers deposited upon or along the advancing front of a delta in the direction of stream flow. Foreset beds cover bottomset beds, and in turn are covered by topset beds as the delta continues to grow. Gaging station A specific location along a river, lake, or other body or water where hydrologic data are measured. Geochronology Study of time in relationship to the history of the earth. Geologic or natural the erosion process on or in a given land form undisturbed by activities of man erosion and his agents. Geomorphic The two-dimensional mapped representation of a geomorphic surface. The polygon polygon boundaries are based on soil and analytical data. Geomorphic Surface An identifiable natural landform, such as a levee or river terrace formed from river processes. Geomorphology The science that treats the general configuration of the earth’s surface; specifically, the study of the classification, description, nature, origin, and development of landforms and their relationships to underlying structures and the history of geologic changes as recorded by these surface features. Gley A soil condition resulting from prolonged soil saturation, which is manifested by the presence of bluish or greenish colors through the soil mass. Gleying occurs under reducing conditions, by which iron is reduced to the ferrous state. Graded stream A stream in which the gradient has been adjusted to balance discharge and sediment load. Grading Degree of mixing of size classes in sedimentary material. Well graded implies a generally equal sediment size distribution, from coarse to fine. Poorly graded refers to a nearly uniform grain size distribution. Granule A rock fragment larger than very coarse sand grain and smaller than a pebble, having a diameter in the range of 2-4 mm (1/12 – 1/6 in) being somewhat rounded or otherwise modified by abrasion in the course of transport. Gravel An unconsolidated, natural accumulation of typically rounded rock fragments resulting from erosion, consisting predominantly of particles larger than sand (between2 mm and 76 mm), such as boulders, cobbles, pebbles, granules, or any combination of these fragments. Gully erosion The enlargement of rills into channels 300 mm or more in depth by ephemeral concentrated flow of water. Hazardous Any substance that the Michigan Department of Environmental Quality substance demonstrates, on a case-by-case basis, poses an unacceptable risk to public health, safety, or welfare, or the environment, considering the state of the material, dose-response, toxicity, or adverse impact on natural resources. Hydrophobic Lacking strong affinity for water. Lacustrine Sediment deposited in a lake environment. Lag deposits Coarser, heavier materials left behind after finer materials have been washed away. Lateral accretion Sediment deposits formed along the inner (convex) sides of channel bends. See deposits point bar. Longitudinal Profile The profile of a stream or valley, drawn along its length from source to mouth. Meander A curve, bend, or loop produced by a laterally migrating stream or river. Midland Plant The Dow Chemical Company Midland Plant in Midland, Michigan Morphology The observation of the form of lands. Mottles Spots or blotches of different color or shades of color interspersed with the dominant soil color. Munsell Color A color designation system that specifies the relative degrees of the three simple System variables of color: hue, value and chroma.

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Natural levee A ridge or embankment of sand and silt, built by a river on its floodplain along both banks of its channel, especially in times of flood when water overflowing the normal banks is forced to deposit the coarsest part of its load. Noncohesive Sediments consisting of discrete particles. The movement of such particles sediments depends on the properties of shape, size, and density, and on their position with respect to surrounding particles. Overbank deposit Silt and clay deposited from suspension on floodplain by floodwaters that cannot be contained within the river channel. Palustrine Pertaining to material growing or deposited in a marsh. Parent Material The unconsolidated and more or less chemically weathered mineral or organic matter from which the surface soil (A, E, & B horizons) is developed from soil forming processes. Particle size A linear dimension, usually designated as "diameter," used to characterize the size of a particle. The dimension may be determined by any of several different techniques, including sedimentation, sieving, micrometric measurement, or direct measurement. Particle-size The frequency distribution (sometimes cumulative) of particles within specified distribution size ranges. Relative amounts are usually expressed as percentages by mass. Pavement (streams) A coarse surface layer on the streambed that is rarely disrupted. Pebble A rock fragment larger than a granule and smaller than a cobble, having a diameter in the range of 4-64 mm (1/6 – 2.5 in) being somewhat rounded or otherwise modified by abrasion in the course of transport. Ped A unit of soil structure such as a block, column, granule, plate, or prism, formed by natural processes. Pedogenic The natural process of soil formation and development, including erosion and leaching. Referring to soils or soil genesis. Photolysis Chemical decomposition induced by light or other radiant energy. Photo-oxidation Oxidation under the influence of radiant energy (as light). Point bar One or a series of low, crescent-shaped ridges of sand and gravel developed on the inside of a growing meander of a river or stream by the slow addition of individual accretions accompanying migration of the channel toward the outer bank. Potential The PCOI for this project consist of those substances on the master list of Constituent of chemicals submitted by The Dow Chemical Company to MDEQ on June 1, Interest (PCOI) 2006, plus those substances found in biomonitoring of the Tittabawassee and Saginaw Rivers. It is recognized that not all substances on the Dow master list will have significance as environmental contaminants, nor that the substances found in biomonitoring of the two rivers are necessarily related to Dow operations in Midland. Regimen (of a Characteristics of a stream with respect to flow duration, channel capacity to stream) transport sediment, and amount of material supplied for transportation. Reservoir An impounded body of water or controlled lake where water is collected and stored. Residue Material that remains after gases, liquids, or solids have been removed. Riffle/pool channel Alluvial channels with bed features composed of a series of pools (deep and flat slope facets) and riffles (shallow and steep slope facets). The pool-to-pool sequence is related to the meander geometry of rivers and is associated with Y2 meander wavelength (approximately 5-7 bankfull widths). Rill erosion An intermediate form of erosion by running water between sheet erosion and gully erosion that leaves a pattern of small well defined incisions on the land surface less than 300 mm in depth.

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Ripple Small triangular-shaped bed forms that are similar to dunes but have much smaller heights and lengths of 0.3 m or less. Scoping Study Tittabawassee River Floodplain Scoping Study: CH2M Hill 2005b Scour Enlargement of a flow section by the removal of the boundary material by the motion of the fluid. Sediment Solid material, both mineral and organic, that is in suspension, is being transported, or has been moved from its site of origin by air, water, or ice, and has come to rest on the earth’s surface either above or below sea level. Sediment sample A quantity of water-sediment mixture or deposited sediment that is collected to characterize some property or properties of the sampled medium. Settling The downward movement of suspended-sediment particles. Shear stress Force produced at the sediment bed as a result of friction between the flowing (hydraulic) water and the solid bottom. Sheet erosion The more or less uniform removal of soil from an area by raindrop splash and overland flow without the development of water channels. Silt Individual mineral particles that range in diameter from 0.0024 to 0.02 mm. Silt is also a textural class for soil containing > 80 percent silt, <20 percent sand, and <12 percent clay Sinuosity The ratio of stream length to down valley distance. It is also the ratio of valley slope to channel slope. Sloughs A stagnant or sluggish channel of water occurring in a floodplain. Soil Unconsolidated mineral and/or organic matter that has been modified due to climate, organisms, relief, and/or parent material all over time such that it is different from the parent material from which it was derived. Soil Genesis The mode of origin of the soil with special reference to the processes or soil forming factors responsible for the formation of the A, E, & B horizons. Soil Horizon A layer of soil about parallel to the land surface and differing from adjacent genetically related layers in physical, chemical, and biological properties or characteristics. Soil Profile A vertical section of the soil through all its horizons and extending into the C horizon. Soil Texture The relative proportions of US Department of Agriculture-Natural Resources Conservation Service (USDA-NRCS) particle size separates (major separates: sand, silt, clay) in a soil as described by the classes of USDA-NRCS soil texture. Classes include sand, loamy sand, sandy loam, sandy clay loam, sandy clay, loam, clay loam, silt loam, silt, silty clay loam, silty clay, and clay. The textural classes may be modified by the addition of suitable adjectives when rock fragments are present. Sorting The process by which sedimentary particles are selectively separated from associated but dissimilar particles by flowing water. Stable Equilibrium A state of equilibrium of a body, such as a pendulum, when it tends to return to its original position after being displaced (Glossary of Geology 5th Edition) Stream discharge The water volume passing through a cross-sectional stream area in a defined unit of time. Stream slope Determined by the change in elevation of the bed surface over a measured length of channel. It is expressed as a ratio of elevation (rise) over distance (run) in ft/ft. Stream stability The ability of a stream to transport the water and sediment of its watershed in such a manner as to maintain its dimension, pattern, and profile over time, without either aggrading or degrading.

® GEOMORPH SCR - MARCH 2008 UPDATE TITTABAWASSEE RIVER

Stream Terrace A former floodplain of a stream channel abandoned as the stream downcut into its valley and created a new, topographically lower, floodplain. Streambank erosion The removal of bank material by flowing water. Streamline Predicted flow path of a particle under different flow conditions. Study Area The Study Area is the river channels and FEMA Q3 100 year floodplains for the 22 miles of the Tittabawassee River between the Chippewa and Saginaw Rivers. Suspended load Finer particles that are suspended in the water column. Suspended-sediment The mass of suspended-sediment passing through a stream cross-sectional area discharge in a defined unit of time. Suspended-sediment The mass of sediment particles suspended in the water column of a stream or load river. Target Analyte (TA) An analyte include on the Target Analyte Lists (see below). Target Analyte Lists The Target Analyte Lists are compilations of those substances (elements or (TALs) chemicals) that will be analyzed in samples from the Study Area. TALs are method specific, and are integral components of the project QAPP and method SOPs. Because of the large number of COI and project samples, not all samples will be analyzed for all TAs. Texture The relative proportions of the three major soil separates, sand, silt, and clay, in a soil. Thalweg The line drawn to join the lowest points along the entire length of a river bed or valley. Till Unstratified drift deposited directly by a glacier without reworking by water, and consisting of a mixture of clay, silt, sand, gravel, and boulders ranging widely in size and shape. Topset bed A layer of sediment deposited on the top surface of an advancing delta that is continuous with the landward alluvial plain. Transportation The complex process of moving sediment particles by water. The principal factors affecting transportation are turbulence, ratio of settling velocity to water velocity, shape, size, density, and quantity of particles, and saltation. Turbidity A measure of the optical properties of a liquid (usually water) which lead to light rays being scattered and absorbed rather than transmitted in straight lines. Turbidity of water is caused by the presence of suspended and dissolved matter such as clay, silt, finely divided organic matter, plankton, other microscopic organisms, organic acids, or dyes suspended in the water column. Turbulence The irregular motion of a flowing fluid. Unconsolidated A sediment that is loosely arranged or unstratified, or whose particles are not cemented together, occurring either at the surface or at depth. Valley trenching Gully erosion occurring on floodplains. Vertical accretion Floodplain deposits formed by the vertical accumulation of suspended sediments deposits deposited during overbank flooding. Vertical The degree to which the stream has abandoned its floodplain as determined by containment/channel Bank-Height Ratio (lowest bank height divided by bankfull height). incision Water surface slope Means the slope of the stream as measured at the water surface rather than the bed surface. It is often used as the average energy grade of the stream. Water surface slope measurements are often obtained for various stages of streamflow. Slope values will vary somewhat for riffles and pools for the low flow stage compared to the bankfull stage. Watershed All lands enclosed by a continuous hydrologic surface drainage divide and lying upslope from a specified point on a stream. Width/depth ratio The ratio of bankfull width to bankfull mean depth.

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SITE CHARACTERIZATION REPORT UPPER TITTABAWASSEE RIVER

10. ACRONYMS AND ABBREVIATIONS

°C Degrees Celsius 1984 Report Point Sources and Environmental Levels of 2,3,7,8-TCDD (2,3,7,8 – Tetrachlorodibenzo-p-Dioxin) on the Midland Plant Site of The Dow Chemical Company of Midland, Michigan (November 5, 1984) ANOVA Analysis of Variance ATS Ann Arbor Technical Services, Inc. ATSDR Agency for Toxic Substances and Disease Registry BERA Baseline Ecological Risk Assessment bgs Below ground surface bss Below sediment surface CDD Chlorinated dibenzodioxins CDF Chlorinated dibenzofurans cfm Cubic feet per minute cfs Cubic feet per second CIC Community Information Centers Cm/sec Centimeters per second COC Chain of Custody COI Constituent of Interest: The lists of COI for this project are derived from the PCOI, and reflect those substances that are likely to have been released to the environment during the period of interest for the study. Because of the large number of PCOI, the COI lists have been organized by chemical class to facilitate evaluation of physical/chemical properties and selection of analytical methods. COI may or may not have suitable analytical methods, and therefore may or may not be included on the Target Analyte List.(TAL) CoPC Contaminant of Potential Concern: A Target Analyte List (TAL) chemical present in soil or sediment at a concentration that is greater than background concentrations and relevant risk-based screening values for human health derived either by MDEQ or EPA. CSM Conceptual Site Model CWS Clear Water Sewer DDD Dichloro-diphenyl-dichloroethane DDT 4,4’-(2,2,2-Trichloroethane-1,1-diyl)bis(chlorobenzene) DGPS Digital Global Positioning System dioxin Polychlorinated dibenzo-p-dioxin Dow The Dow Chemical Company EDD Electronic Data Deliverable EF Erosion Factor EFDC Environmental Fluid Dynamics Code EPA Environmental Protection Agency

SITE CHARACTERIZATION REPORT UPPER TITTABAWASSEE RIVER

ERA Ecological Risk Assessment ETEQ Estimated Toxic Equivalent Quotient FEMA Federal Emergency Management Agency FTP File Transfer Protocol furan Polychlorinated dibenzo-p-furan Fv Vapor Pressure GIS Geographic Information System GPS Global Positioning System HASP Health and Safety Plan HHRA Human Health Risk Assessment IWS Ionizing Wet Scrubber LCS Laboratory Control Sample License Hazardous waste management facility operating license LiDAR Light Detection and Ranging ln Natural Logarithm LTI Limno-Tech, Inc. MACT Maximum Achievable Control Technology MCV Midland Cogeneration Venture MDCH Michigan Department of Community Health MDEQ Michigan Department of Environmental Quality MDNR Michigan Department of Natural Resources mg/L Milligrams per liter MNFI Michigan natural features inventory msl Mean sea level MSU Michigan State University NELAC National Environmental Laboratory Accreditation Conference NOD Notice of Deficiency NPDES Nation Pollutant Discharge Elimination System NRCS Natural Resources conservation Service NRT Near-Real-Time PAH Polynuclear Aromatic Hydrocarbons PCB Polychlorinated Biphenyls PCOI Potential Constituent of Interest: The PCOI for this project consist of those substances on the master list of chemicals submitted by The Dow Chemical Company to MDEQ on June 1, 2006, plus those substances found in biomonitoring of the Tittabawassee and Saginaw Rivers. It is recognized that not all substances on the Dow master list will have significance as environmental contaminants, nor that the substances found in biomonitoring of the two rivers are necessarily related to Dow operations in Midland. PCSM Preliminary Conceptual Site Model PNA Polynuclear Aromatic Hydrocarbons ppt Parts per trillion or picograms per gram

SITE CHARACTERIZATION REPORT UPPER TITTABAWASSEE RIVER

PRM Probalistic Risk Assessment QA/QC Quality Assurance/Quality Control QAPP Quality Assurance Project Plan R 299.5528 Michigan Administrative Code, Rule 299.5528 RCRA Resource Conservation and Recovery Act RGIS Revetment Groundwater Interception System RI Remedial Investigation RIWP Remedial Investigation Work Plan S3TM Sampling Strategies and Statistics Training Materials for Part 201 Cleanup Criteria: MDEQ 2003b SAP Sampling and Analysis Plan SCR Site Characterization Report SCS Soil Classification System SLERA Screening-Level Ecological Risk Assessment SLRA Screening-Level Risk Assessment SOP Standard Operating Procedure SOW Scope of Work SRF Sample Receipt Form SSCC Site-Specific Cleanup Criteria SVOC Semivolatile Organic Compound SWAC Surface Weighted Average Concentration TA Target Analyte TAL Target Analyte List: The Target Analyte Lists are compilations of those substances (elements or chemicals) that will be analyzed in samples from the Study Area. TALs are method specific, and are integral components of the project QAPP and method SOPs. Because of the large number of COI and project samples, not all samples will be analyzed for all TAs. TCDD 2,3,7,8-Tetrachloro-dibenzo-p-dioxin TEF Toxic Equivalency Factor TIC Tentatively Identified Compounds TEQ Toxic Equivalent Quotient TOC Total Organic Carbon TR Tittabawassee River USCS Unified Soil Classification System USDA-SCS United States Department of Agriculture - Soil Classification System USEPA United States Environmental Protection Agency USGS United States Geological Survey USR Upper Saginaw River UTR Upper Tittabawassee River VOC Volatile organic compound WHO World Health Organization WSS Water Settling Sewer (?)

SITE CHARACTERIZATION REPORT UPPER TITTABAWASSEE RIVER

WWTP Wastewater Treatment Plant