Tittabawassee River Floodplain

Transcription

1 Tittabawassee River, Saginaw River & Bay Site Tittabawassee River Floodplain Mary P. Logan U.S. EPA CAG Meeting March 17, 2014

2 Agenda Overview Floodplain conditions Why clean up the floodplain? Remedy options What s next?

3 Overview Tittabawassee River (TR) floodplain is part of larger Tittabawassee River, Saginaw River & Bay site Dioxins (primarily furans) are the driving contaminant in floodplain soil Remedy options include: Soil removal and disposal Soil cover Land use management will be included, where needed Major issues/challenges Trigger for action/cleanup goals Scope, size, and timing of project Coordination with property owners

4 Site Video Dow developed a video in 2013 to explain the site history and current conditions Contaminant sources and status of source control Nature, extent, fate, and transport of contaminants Potential exposure pathways

5 FLOODPLAIN CONDITIONS

6 Segmenting the Site ~ 24 miles of the Tittabawassee River TR divided into seven segments around 3 to 5 miles each Work upstream to downstream Segment 1 largely complete Segment 2 to start 2014

7 Tittabawassee River 8-Year Floodplain Frequently flooded (8-year floodplain) area along the TR is shown in the blue About 4,500 acres in the 8-year floodplain Dioxin/furan distribution is not uniform Not all areas will need cleanup

8 TR 8-Year Floodplain Land Types Pond 1% Emergent wetland 2% Maintained 5% Forested/ shrub wetland 14% Hard surface > 1% Active agriculture 18% Unforested upland 11% Forest 48%

9 TR 8-Year Floodplain Land Types Segment 3

10 TR 8-Year Floodplain Land Uses Commercial 4% Public recreation 3% Residential maintained 5% Active agriculture 18% Shiawassee NWR 16% Undeveloped/ low use/ natural 54%

11 TR 8-Year Floodplain Land Uses Segment 3

12 Floodplain Assessment Transect-based sampling Geomorphic units used to help locate samples Step out samples Segment 3

13 Floodplain Assessment (cont.) Samples primarily from Study divided into upper, middle, and lower TR Dioxin samples ~ 1,835 locations ~ 9,200 samples Furans dominate the TEQ More than 220 other chemicals assessed ~ 200 locations ~ 625 samples Biased sampling Dioxin floodplain sample locations

14 Floodplain Assessment (cont.) Evaluating the range of TEQ surface concentrations Evaluating depth, geomorphic type, etc. Additional data to support design and implementation Segment 2

15 WHY CLEAN UP THE FLOODPLAIN?

16 What are the Health Impacts of Dioxin* Cancer Exposure to dioxins at high enough levels may cause a number of adverse health effects, including cancer. Factsheet-2012.pdf Non-cancer The most obvious non-cancer health effect if exposed to large amounts of dioxin is chloracne (severe skin disease with acne-like lesions), Developmental and reproductive effects, Damage to the immune system, and Interference with hormones * From Helen Dawson s April 2012 CAG presentation

17 Potential Environmental Risk* In general terms, potential risk depends on the following three factors: EPA headquarters-determined values: 1. The toxicity of the chemical: The dioxin RfD relates to non-cancer toxicity. Site-specific factors: 2. How much of a chemical is present in an environmental medium (e.g., soil, sediment). 3. How much exposure a person has: Contact with the contaminated environmental medium, and How much is bioavailable ; that is, how much is absorbed into the body relative to how much is ingested. * From Helen Dawson s April 2012 CAG presentation

18 Superfund Human Health Risk Assessment Framework* Planning & Scoping (Data Collection and Evaluation) Toxicity Assessment (Cancer and Non-cancer) Risk Characterization Exposure Assessment * From Helen Dawson s April 2012 CAG presentation

19 Risk Assessment, Risk Characterization, and Risk Management within Superfund* Risk Assessment Risk Management Data Collection Toxicity Assessment Exposure Assessment Risk Characterization Statutory/Legal Considerations Community Considerations Social/Economic Factors Remedy Selection & Cleanup Levels Adapted from Risk Assessment in the Federal Government: Managing the Process (NRC 1983)

20 Overview of Floodplain Cleanup Goals Overarching goal: Limit people s exposure to TEQ from Tittabawassee River floodplain soil How to meet the goal: Conduct cleanups that reduce surface soil TEQ levels Establish or maintain land uses that result in lower human exposures

21 REMEDY OPTIONS

22 Floodplain Cleanup Options In areas that need cleanup: Soil Removal & Disposal Dig up contaminated soil Backfill with clean soil, if needed Transport & dispose contaminated soil Soil Cover Place a cover of clean material over contaminated soil Monitoring required, and maintenance if needed Combination of these two

23 Floodplain Cleanup Options (cont.) Soil removal and/or cover would be combined with land use management ( institutional controls or ICs ), where needed Legal and administrative tools Often an important part of the overall cleanup Designed to lower the potential for people to be exposed to contamination Can keep areas in natural condition ICs already in place in the floodplain

24 Site-Specific Cleanup Goals Considering cleanup goals for two land uses: Residential maintained Other land uses Goals based on potential human exposures How much soil people accidentally eat How much is absorbed through the skin Goals will be protective for both non-cancer and cancer potential risks

25 Example Scenario Maintained Residential Property: Other Land Use If a polygon is > 1000 ppt implement remedy on polygon regardless of SWAC. If resulting SWAC > 250 ppt implement remedy on polygon(s) to accomplish a resulting SWAC < 250 ppt. Residential Maintained River 8-Year FP Boundary 25

26 EPA s Evaluation Criteria Effectiveness Implementability Cost Reduction of toxicity, mobility, or volume Short-term effectiveness Long-term effectiveness and permanence

27 Options Screened Out No Action Not protective In-place Treatment (i.e., activated carbon amendment) uncertain effectiveness and implementability issues Monitored Natural Attenuation uncertain effectiveness and timeframe Treatment after removal (i.e., incineration) implementability and cost issues

28 WHAT S NEXT?

29 Areas Under Development Triggers for Action/ Cleanup Goals Planning 2014 outreach Refining schedule Developing the recommended cleanup Preparing a proposal Public comment Selection of cleanup plan

30 Floodplain Outreach Floodplain outreach started in spring 2013 The information will help shape EPA s cleanup proposal (expected 2014) and the selected remedy

31 Process and Timing EPA, working with MDEQ, issues a proposed cleanup plan for public comment Late summer or fall 2014 EPA, working with MDEQ, considers and responds to comments and selects the cleanup option(s) Fall 2014 Dow begins Phase I designs Fall 2014 into spring/summer 2015 Construction start planned for 2015 Will start adjacent to Segment 2 Will work with affected property owners

32 Projected Schedule Segment 1 First season of field work Remobilize to finish field work Segment 2 Develop cleanup plan Propose cleanup plan to public Finalize cleanup plan First season of field work (anticipate two field seasons) Remobilize to finish field work Tittabawassee River Floodplain Engage floodplain stakeholders regarding cleanup options & tradeoffs Develop cleanup plan Propose cleanup plan to public Finalize cleanup plan First season of field work Segment 3 Develop cleanup plan Propose cleanup plan to public Finalize cleanup plan

33 QUESTIONS?