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

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

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

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

Site History – Generalized Geologic Section

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

Closure Evaluations Groundwater Soil Vapor Intrusion 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

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

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

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)

Groundwater Monitoring after Shutdown – TCE Concentrations Groundwater Flow Direction

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

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

Groundwater Monitoring after Shutdown – TCE Concentrations Groundwater Flow Direction

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

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

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 Describe general concept. From MPCA August 2010 Vapor Intrusion Technical Support Document

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)

Groundwater Screening and Receptor Survey Assumed Property Use # of Properties (Estimated) Residential 304 School/day care 2 Recreational (Van Cleve Park) 1 (4 parcels) Commercial 6 Industrial (the Site) 1 Vacant/undeveloped (no structures) 19 TOTAL 336 Describe potential magnitude of problem – area shown in yellow is approximately 78-acres.

Surrounding Neighborhood

Surrounding Neighborhood

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)

Vertical Profiling Investigation at Existing Groundwater Well 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

Soil Gas Sampling at Existing Monitoring Well 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 Groundwater table Seal Ground surface Vacuum canister to collect soil gas sample after purging with vacuum pump Soil column Soil gas drawn into well screen under vacuum Note that MPCA suggested this method/step Soil Gas Sampling at Existing Monitoring Well

Soil gas sampling at monitoring well S

Recent Investigation Methods – Sample Locations Wells selected based on construction (screen length, length of exposed screen) and location (inside of plume, outside of plume). Sampling at existing wells to minimize intrusion/disturbance of nearby neighborhood.

Results – Summary Table CAN PROBABLY DELETE THIS SLIDE – REDUNDANT WITH FOLLOWING FIGURE. Groundwater ISV is 20 ug/L. Some variation with TCE concentration with depth. 10x ISV is 30 ug/m3 (more investigation per our workplan) – shown in pink. Building specific investigations required at 100x ISV (300 ug/m3). Acute ISV is 2,000 ug/m3 (potential short term exposure health risks in indoor air). Remind that our results are not “true” soil gas results but are “worst-case” screening results.

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

Questions/Discussion