Localized Mercury Bioaccumulation Study Presented to the SFEI 20 February 2008

2 Outline 1.Project Overview 2.Results 3.Conclusions 4.Outreach Component 5.Next Steps

3 Approximate location of SRWTP outfall diffuser

4 Study Design’s (Null) Hypothesis: [MeHg] in bioindicator organisms (clams) does not vary according to space (upstream vs. downstream site) or time (i.e., between different sampling periods).

5 “Hot spot”, Defined Technical: The null hypothesis is rejected because of a measurable effect of SRWTP effluent. ~ AND ~ Policy: Evidence of localized environmental risk that is so clear and convincing that a reasonable decision maker would conclude that some action must be taken.

6 Project Team SRCSD Reg. Larry Walker Assoc. UCD – F. Schilling UCD – D. Slotton Applied Marine Science SRCSD Lab Caltest Lab Studio Geochimica Lab Cindy Brown Brock Bernstein Robert Mason Tech. Adv. Comm.

7 Conceptual Model River Flow Streambed Sediments Water Surface Effluent Clam Diet Organic Carbon Phytoplankton Phaeophytin Zooplankton Bacteria Fish Diet Pelagic: Small Fish Zooplankton Benthic: Clams Plants Worms Sorption/ Desorption Methylation/ Demethylation Deposition/ Erosion * * * * * * * * * * * * * * * * * * * * * * * * Biouptake/ Bioaccumulation Exposure [MeHg] Factors DO Organic Carbon TSS pH Salinity Redox Potential Sulfate Reactive Mercury Sulfides Nutrients (N, P, Si) Complexation Factors Mercury Organic Carbon TSS DO / Redox Potential pH Salinity Sulfides Diffusion Sorption/ Desorption

8 Monitoring Stations in the 5-mile Study Reach Monitoring Stations R-3 RM44 R-2b R-1 GB E-001

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11 Fish – Locally in Fall Proposed TMDL Goal

12 Fish – Sac. R. Watershed Feather R Ham. City (80 mi) Colusa Drain Yolo Bypass Putah Ck Cache Ck American River Mile 44 Scale 50 ng/g Prickly Sculpin, Fall 2006 Garcia Bend Veteran’s Bridge TMDL WQO = 30 ng/g in fish < 50 mm long

13 Silverside Fall 2006 Mercury Spatial Distribution, following high runoff and flooding winter and spring (40 mi) (90 mi)

14 Effluent Mercury – Local Effects Summary 1) MeHg_sed, Transp. Clams, Resident Clams, Silversides, Juv. Blk. Bass 3) THg_wtr, THg_sed, Sculpin 2) MeHg_wtr Distance from Outfall ~10%

15 Models Developed Independent Variable Partial Correlation with Dry- weight MeHg in Clams Resident Clams: TOC in Sediment Particulate MeHg in Water [1] TSS in Water Transplanted Clams: Suspended MeHg in Water Dissolved MeHg from Effluent Dissolved MeHg in Water [1] [1] Unexpected negative relationships.

16 SRWTP effluent contributes about the same amount of mercury to bioaccumulation as expected from effluent load estimates. The evidence presented by this study argues that:

17 Methylmercury in aquatic organisms near the SRWTP outfall is not outstanding compared to other areas of the Sacramento River Watershed and the Delta. The evidence presented by this study argues that:

18 Technical: The null hypothesis is rejected because of a measurable (i.e., statistically significant) effect of SRWTP effluent. ~ BUT ~ Policy: Is evidence of localized environmental risk so clear and convincing that a reasonable decision maker would conclude that some action must be taken locally?

19 Monitoring Stations R-3 RM44 R-2b R-1 GB E-001 Fishing Areas Shore fishing

20 5. Next Steps