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Sampling Density in Stratified Sediment Bedforms for Estimating Surface-Area Weighed Average Concentrations

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Sampling Density in Stratified Sediment Bedforms for Estimating Surface-Area Weighed Average Concentrations How Much is Too Much? Sampling Density in Stratified Sediment Bedforms for Estimating Surface-Area Weighed Average Concentrations Evan Thomas, PE Senior Environmental Engineer WEDA Virtual Summit June 15, 2021 woodplc.com Kalamazoo River Superfund Site – Michigan Designated a Superfund Site in 1990 and placed on NPL due to the presence of PCBs in the river’s fish, sediment, and surface water 80 miles of the Kalamazoo River, 1,000s of acres of lakes and floodplain Site split into seven areas for sequential Supplemental Remedial Investigations (SRI)/Feasibility Studies (FS), Remedial Design (RD), and Remedial Action (RA) 2 A presentation by Wood. WEDA June 2021 Area 5 • 9.1- mile reach with normal flow near 1,100 cfs • 110-acre lake • Trowbridge and Allegan City Dam (RM 35.9 to 44.8) Area 6 Beginning Downstream Extent of Channelized Flow Area 5 Beginning Upstream Extent of Impounded Lake 3 A presentation by Wood. WEDA June 2021 Sampling objectives • Unbiased investigation strategy that is defensible, reproducible and provides a robust dataset for statistical evaluation at the level needed to make decisions in a Feasibility Study (FS) and inform future remedial design sampling • Optimize sampling plan by using – higher density sampling where variance is higher to reduce uncertainty – lower density sampling where variance is less and uncertainty is already low 4 A presentation by Wood. WEDA June 2021 Area 5 timeline Spring 2017 Fall 2017 Summer 2018 Summer 2019 Summer 2020 Anticipated 2022 Recon I Recon II Phase I Phase II SRI FS ► Begin CSM ► Sample to ► Describe Nature ► Collect bathymetry support SRI/FS and Extent ► Identify potential risk (SWAC) ► Identify bedform ► Develop Remedial groups and sampling ► Fill remaining Alternatives density for Phase I data gaps as ► Collect physical data necessary 5 A presentation by Wood. WEDA June 2021 Approach Recon I Recon II Phase I Phase II SRI FS 6 A presentation by Wood. Recon with sample design in mind • Stratified, random sampling – Strata = Bedforms based on similar characteristics – Sample core density based on bedform group • Recon Activities – Collect bathymetry data – Limited sediment cores with physical characteristics and PCB analysis to quantify variability 7 A presentation by Wood. WEDA June 2021 Bathymetry 8 A presentation by Wood. WEDA June 2021 Contour over bathymetry 9 A presentation by Wood. WEDA June 2021 Water depth 10 A presentation by Wood. WEDA June 2021 Slope 11 A presentation by Wood. WEDA June 2021 Curvature 12 A presentation by Wood. WEDA June 2021 Aspect 13 A presentation by Wood. WEDA June 2021 Individual bedform mapping 14 A presentation by Wood. WEDA June 2021 Simplified bedform mapping 15 A presentation by Wood. WEDA June 2021 Bedform classifications pre-Recon II Simplified Category Bedform Acreage Simplified Category Acreage Riffle 27.8 Ripple Marks 7.7 Run 53.6 Likely Coarse 105.9 Scour Trough 5.0 Steep Side Slope 11.9 Anabranch 20.5 Backwater 29.3 Likely Fine 60.2 Oxbow 10.4 Anthropogenic 11.1 Glide 8.4 Island 18.8 Mouth Bar 34.6 Plane Bed 5.0 Likely Coarse and Fine 168.4 Point Bar 18.7 Pool 46.1 Sediment Bar 13.6 Side Channel 12.2 Sums 334.5 334.5 16 A presentation by Wood. WEDA June 2021 Recon II Results Recon I Recon II Phase I Phase II SRI FS 17 A presentation by Wood. PCB distributions by bedform PCB data consistent with CSM Sediment PRG 18 A presentation by Wood. WEDA June 2021 Cluster analysis of channelized flow multivariate data Data used in cluster analysis • Sediment thickness • Surface gradation – Percent fines – Percent fine sand – Percent medium sand – Percent coarse sand or greater • Hydrodynamic Model Results (1100, 3200, 4900, 8400, 12000 cfs) – WSE – Water depth – Velocity – Shear stress Data not used in cluster analysis • PCB concentrations • Bathymetry and derivatives (e.g., slope, aspect, curvature) 19 A presentation by Wood. WEDA June 2021 Individual sample hierarchical cluster analysis Fine Bedform Coarse Bedform Group Group Fine Bedform Coarse Bedform Group Group 20 A presentation by Wood. WEDA June 2021 PCB population statistics by cluster Individual Bedforms Bedform Strata Sediment PRG 21 A presentation by Wood. WEDA June 2021 Phase I sampling design for channelized flow 238 locations • 194 Phase I locations – 73 in Coarse Bedform Group – 121 in Fine Bedform Group • 44 Recon II locations – 24 in Coarse Bedform Group – 20 in Fine Bedform Group Coarse Bedform layout with streamtubes Fine Bedform layout as stratified sampling in bedforms 23 A presentation by Wood. WEDA June 2021 Phase I Results Recon I Recon II Phase I Phase II SRI FS 24 A presentation by Wood. Recon II & Phase I PCBs by bedform – channelized flow sediments Int 1 Int 2 Int 3 SED-362 Int 3 SED-394 Int 4 Int 4 Sediment PRG 25 A presentation by Wood. WEDA June 2021 Recon I Recon II Phase I Phase II SRI FS 29 A presentation by Wood. Conclusions • Sampling results support conceptual site model (CSM) • Fine bedforms have variable PCB concentrations • Coarse bedforms tend to have low PCB concentrations and low variability • Reduced sample density overall and reduced uncertainty • Useful in defining remedial footprints in FS 30 A presentation by Wood. WEDA June 2021 Questions? Jerry Eykholt, PE, PhD Project Engineer Greg Horstmeier Project Engineer Heidi Fogell Area 5 Manager Cynthia Draper, PE Evan Thomas, PE Program Manager Project Engineer Madison, WI Kalamazoo River Team [email protected] 32 A presentation by Wood. WEDA June 2021 .
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