MPCA Site Assessment: Vapor Intrusion Investigation. Remediation Division Superfund Unit 1

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1 MPCA Site Assessment: Vapor Intrusion Investigation Remediation Division Superfund Unit 1

2 MPCA Project Team Doug Wetzstein, Supervisor Dave Moore, Project Leader Dave Scheer, Hydrogeologist Hydrogeologist

3 EPA Emergency Response Team Partners Sonia Vega, Project Manager Gary Newhart, Technical Assistance

4 Reductive Dechlorination Process The chlorinated hydrocarbon (chlorinated ethene) is used as an electron acceptor, chlorine atom is removed and replaced with a hydrogen atom: C 2 Cl 4 (PCE) + H + + 2e- ÆC 2 HCl 3 (TCE) + Cl - (1) C 2 HCl 3 (TCE) + H + +2e- ÆC 2 H 2 Cl 2 (cis-dce) + Cl - (2) C 2 H 2 Cl 2 (cis-dce) + H + + 2e- ÆC 2 H 3 Cl (VC) + Cl - (3) C 2 H 3 Cl (VC) + H + + 2e- ÆC 2 H 4 (ethene) + Cl - (4) In general, the transformation of chlorinated ethenes occurs by sequential dechlorination from PCE to TCE to DCE to VC to ethane.

5 Vinyl Chloride (VC). Introduction Chemicals of Concern: 1,1,2,2-Tetrachloroethylene (PCE), 1,1,2-Trichloroethylene (TCE), cis-1,2-dichloroethene (cis-dce),

6 Perchloroethylene (PCE) Commonly uses: Fabric care industry-dry Cleaning Solvent Metal Degreaser-Metal Plating, Metal Fabrication, Print Shops, Plastic Injection Mold cleaning.

7 St. Louis Park Vapor Intrusion Site

8 VOC Concentrations in Drift Aquifer

9 VOC Concentrations in Platteville- Glenwood Formation GW

10 Direct Push Investigation Geoprobe Post Run Tubing Method Drill 1.5 inch diameter hole 8 bgs

11 Purge Line Gas is drawn through 1/4 diameter tube by triple gas meter. Line is purged until O 2 and CO 2 readings stabilize.

12 Collect PID Readings Soil vapor drawn into Photo Ionization Detector (PID) to measure the concentration of total organic vapors.

13 Collect Subsurface Vapor Sample Collect soil gas into Summa Canister. Analyze for contaminants of concern at laboratory.

14 Indoor Air Screening Values Chemical CAS # Residential Concentration ug/m 3 Commercial Concentration ug/m 3 Target Organs PCE Cancer TCE Cancer Cis-1,2-DCE Vinyl Chloride Cancer, liver

15 Investigation Results PCE or TCE vapor concentrations greater than 100X screening values near well 437. PCE or TCE vapor concentrations greater than 1000X screening values detected in samples from residential neighborhood southeast of well 437.

16 Overview Quantitative data Low detection levels Accurate Expense: $25, Probes installed at site (12-15 probes per day). Up to 2 week laboratory turn around.

17 Passive Diffusion Sampler (Gore ) ½ inch drive rotary hammer drill. Electric generator. One inch diameter hole to a depth of approximately three feet bgs.

18 Insert module into hole

Collect Data Module exposure period (usually 10-14 days).

19 Collect Data Module exposure period (usually days). Ship exposed modules back to vendor via over night courier.

20 TCE SURVEY RESULTS

21 PCE SURVEY RESULTS

22 Hand held equipment allows access to tight locations. Overview 79 Diffusion samplers deployed over three days. Qualitative Data. Cost $50,000 Gore data results available 30 days after submittal.

23 Next Phase of Investigation EPA TAGA Bus Trace Atmospheric Gas Analyzer

24 Capable of running one sample every six minutes

25 Sub Slab Sample Port

26 Sub Slab Sample Collection

27 Sub slab Sampling Samples collected at 269 properties; 220 residential properties; 49 industrial/commercial properties.

28 Sub Slab Sampling Results Sub Slab Exceedances: 41 Residential 12 Commercial

29 Indoor Air Sampling Collected Indoor Air Samples from 52 Properties: 40 residential (1 denied access) 12 commercial/industrial

30 Indoor Air Sampling Results Indoor Air Exceedances 11 Residential 5 Industrial

31 Northern Area Subslab Conc. > Screening Value

32 Southern Area Subslab Conc. > Screening Value

33 Mitigation System Installation 40 residential mitigation systems installed; Mitigation systems at industrial properties are responsibility of commercial entity.