East Hennepin Avenue Site

1. East Hennepin Avenue Site Presented to MPCA and EPA December 12, 2011

2. Overview • Site History • Closure Evaluations • Pump Out System Shutdown – One Year of Monitoring Results • Recent Vapor Intrusion Investigation Methods & Results • Next Steps

3. Site History • Located in residential neighborhood just north of U of MN campus • GMI research laboratory 1930s - 1970s • Solvents disposed of on site 1940s -1960s • Property sold in 1977 – currently mixed commercial/industrial use at site buildings I-35W Dinkytown U of MN

4. Site History – Characterization • Began site characterization work and disposal pit excavated in early 1980s • Solvents impacted shallow groundwater (glacial drift) and uppermost bedrock aquifers with VOCs, primarily TCE • Monitoring well network in four hydrogeologic units • Shallow groundwater plume extends off site to the south-southwest • 1984 Response Order by Consent between GMI and MPCA

5. Site History – Generalized Geologic Section

6. Site History – Groundwater Remediation • Operation of pump out systems in glacial drift and uppermost bedrock began in 1985 – operated continuously since then • Objectives were to contain the plume and reduce concentrations • GMI began pursuing site closure and delisting in 2010 – MPCA concurred and requested several closure evaluations • Pump out systems shut down September 2010 with one year of subsequent groundwater monitoring Onsite air stripper tower for groundwater treatment

7. Closure Evaluations • Groundwater • Monitor groundwater for one year after pump out system shutdown • 1997 well survey indicated no potable use nearby – to be updated before closure • Recent MPCA surface water assessment indicated no concern for adverse impact to Mississippi River • Soil • 2001 onsite soil investigation indicated no concern • Vapor Intrusion • 1997 vapor survey at onsite building basements/tunnels and nearby buried utilities using field instruments (i.e., PID) indicated no concern • Additional vapor intrusion work completed in November 2011 based on recent MPCA guidance • Institutional Controls • BBD Holdings, Inc. (current Property owner) placed a Restrictive Covenant in 2004 – to be updated following closure

8. Groundwater Monitoring after Shutdown • Pump out systems in glacial drift • Two wells (109, 110) treated with onsite air stripper and discharged to storm sewer • Three downgradient wells (111, 112, 113) discharge directly to storm sewer • Pump out systems in Magnolia Member of the Platteville Formation • Two on-site pump out wells (MG-1 and MG-2) discharge directly to storm sewer

9. Groundwater Monitoring after Shutdown • Four rounds of quarterly monitoring in all pump out wells and selected “sentinel” glacial drift and Magnolia Member wells to monitor any plume migration • September 2010 through June 2011 • Continued annual (one round) of monitoring at other wells including Carimona Member and St. Peter Sandstone

10. Groundwater Monitoring after Shutdown – Groundwater Elevations • Flow direction in glacial drift remained to the southwest as was the case both before and during pump out system operation • Flow direction back to pre-pump out system operation directions in the Magnolia Member (northwest) • Water levels similar to previous years with exception of pump out wells (water levels increased)

11. Groundwater Monitoring after Shutdown – TCE Concentrations Groundwater Flow Direction

12. Groundwater Monitoring Before & After Shutdown – TCE Concentrations Shutdown Sept. 2010

13. Groundwater Monitoring Before & After Shutdown – TCE Concentrations Shutdown Sept. 2010

14. Groundwater Monitoring after Shutdown – TCE Concentrations Groundwater Flow Direction

15. Groundwater Monitoring Before & After Shutdown – TCE Concentrations Shutdown Sept. 2010

16. Groundwater Monitoring after Shutdown • Generally, data is favorable • TCE concentrations stable or decreasing in most glacial drift and Magnolia Member wells • Immediate increase in concentration at glacial drift well V following shutdown – concentrations stable since then • One round of monitoring in 2012 would be useful to continue to evaluate effect of pump out system shutdown

17. Simplified Vapor Intrusion Model • MPCA has developed screening values for volatile contaminants in groundwater, soil gas, and indoor air • TCE in groundwater: 20 ug/L • TCE in soil gas: 30 ug/m3 • TCE in indoor air: 3 ug/m3 From MPCA August 2010 Vapor Intrusion Technical Support Document

18. VI Evaluation Steps in September 2011 Work Plan • Step 1 – Groundwater Screening and Receptor Survey • determine if vapor intrusion should be further evaluated based on site conditions and existing groundwater data • Step 2 – Soil Gas Investigations • 2A – Soil gas investigation work using existing monitoring well network (if needed based on results of Step 1) • 2B – Soil gas investigation on site (if needed based on results of Step 2A) • 2C – Soil gas investigation in City R-O-W (if needed based on results of Steps 2A and/or 2B) • Step 3 – Building Specific Investigations (if needed based on results from Steps 2B and 2C) • Step 4 – Response Actions at Buildings (if needed based on results from Step 3)

19. Groundwater Screening and Receptor Survey

20. Surrounding Neighborhood

21. Surrounding Neighborhood

22. Evaluation Steps in September 2011 Work Plan • Step 1 – Groundwater Screening and Receptor Survey -> done as part of Work Plan • Step 2 – Soil Gas Investigations • 2A – Soil gas investigation work using existing monitoring well network -> needed based on results of Step 1 – work completed November 2011 • 2B – Soil gas investigation on site (if needed based on results of Step 2A) • 2C – Soil gas investigation in City R-O-W (if needed based on results of Steps 2A and/or 2B) • Step 3 – Building Specific Investigations (if needed based on results from Steps 2B and 2C) • Step 4 – Response Actions at Buildings (if needed based on results from Step 3)

23. Recent Investigation Methods & Results – Part 1: Vertical Groundwater Profiling • Investigation to determine if TCE concentrations vary with depth in the shallow groundwater • If shallowest water is “clean” VI might not be a concern • Used passive bags in existing groundwater wells and analyzed water in bags for TCE Well cap Wire hanging assembly for sampler bags Ground surface Soil column Groundwater table Sampler bags deployed for two weeks at varying depths Weight Vertical Profiling Investigation at Existing Groundwater Well

24. Recent Investigation Methods & Results – Part 2: Soil Gas Sampling at Existing Wells • Collect soil gas samples from existing monitoring wells • Results better evidence of potential VI risk than groundwater sampling but are worst-case since collected at the water table Vacuum canister to collect soil gas sample after purging with vacuum pump Seal Ground surface Soil column Soil gas drawn into well screen under vacuum Groundwater table Soil Gas Sampling at Existing Monitoring Well

25. Soil gas sampling at monitoring well S

26. Recent Investigation Methods – Sample Locations

27. Results – Summary Table

29. Next Steps • Work Plan calls for onsite soil gas investigation in soil column if Step 2A results exceed screening values • One round of groundwater monitoring in 2012 to continue to evaluate effect of pump out system shutdown

30. Questions/Discussion