Vapor Intrusion Panel Discussion. SCRD Fall 2009 Meeting Terry Evanson Wisconsin DNR,

Transcription

1 Vapor Intrusion Panel Discussion SCRD Fall 2009 Meeting Terry Evanson Wisconsin DNR,

2 VI Issues at WI Dry Cleaner Sites Assessment of the vapor pathway at operating dry cleaners & SSDS installation Field QC for sub-slab sampling Assessing sub-slab vapor using soil samples Placement of exhaust stacks for SSDS

3 VI Assessment at Operating Dry Cleaners in WI WI routinely requires sub-slab samples for assessing vapor pathway Usually collect sub-slab soil and sub-slab vapor samples, although not necessarily in the same locations. Do not collect indoor air samples at operating dc facility Do collect indoor air samples at adjacent occupied structures

4 Controversies Sub-slab PCE usually very high beneath dry cleaner Occasionally dig up flooring and underlying contaminated soil, but not commonly WI DNR recommends installation of SSDS primarily to limit vapor movement away from the dry cleaner portion of the building and to address land use changes in the future.

5 Controversies Adjacent structures often have high sub-slab PCE levels and may have high indoor air PCE Can t easily separate IA PCE source HVAC systems vs. vapor intrusion Typically ask building owner adjust HVAC in addition to installing a SSDS Post-SSDS installation, building ventilation & pressure may need to be rebalanced by a mechanical engineer.

6 QC in Sub-slab vapor sampling Good QC is critical to all environmental samples; vapor samples are no exception Major concern with vapor sampling is atmospheric AIR LEAKS into the sample. Use of IPA & 1,1-DFE identifies leaks POST sampling. Can not justify adjusting sample concentrations based on tracer gas concentrations in sample. QC for leaks PRIOR to collecting samples.

7 Recommended QC in Sub-slab sampling Helium leak detection of seal around the probe. Use shroud with small amount of He added (different sources recommend 10 40% of air volume) Shut-in test to ensure there are no leaks in the compression connections to the canister. Requires equipment to measure vacuum in sample lines

8 QA/QC of Sub-slab sampling

9 Reference for Leak Detection Testing EPRI Reference Handbook for Site-Specific Assessment of Sub-Surface Vapor Intrusion to Indoor Air pdf

10 Saukville Fabricare

11 Strip Mall location of Saukville Cleaners

12 Saukville Fabricare Plan View

13 HVAC or VI? (IA screening value, PCE = 21 ug/m 3, 10-5 risk)

14 Saukville Fabricare - HVAC Connection Back hallway entry to dry cleaner. Laundry entrance to left. Air intake for the laundry is in the ceiling adjacent to the light.

15 Vacant Space mostly open, dirt floor

16 Sealed dirt floor with plastic

17 Saukville Fabricare Plan View QC Issues

18 Example of impact of air leaks Sample # (within strip mall) Round 1 Isopropyl Alcohol (ug/m 3 ) Round 1 PCE (ug/m 3 ) Round 2 (with He/shut-in) PCE (ug/m 3 ) 1 18, ,500, ,000 5 < , ,000

19 Our recommendations All vapor sample results be accompanied by a description of QA/QC measures used to collect the sample. If isopropyl alcohol is used for leak detection and is detected in the sample, consultant should expect to resample the probes. If no QC procedure has been used in sample collection, consultant should expect to resample using good QC.

20 Sub-slab vapor concentrations vs. soil concentrations Can not reliably estimate soil vapor concentrations from bulk soil values, but consultants routinely want to screen the vapor pathway in this manner.

21 Example: Soil concentration vs Subslab vapor concentration (PCE) Soil (ug/kg) Sub-slab vapor (ug/m 3 ) Vapor Screening Value (ug/m 3 ) 1,500 2,500, ,

22 Venting SSDS stacks Can be difficult to find a location to vent stacks and avoid building air intakes. Left to the judgment of the installer (usually a contractor experienced in radon mitigation).

23 Roof Vent for Coin Laundry Sub-slab vent Air Intake West North

24 Roof Vents for Dance Studio & Sandman Co. Vent #3 Vent #2