THE STATUS OF VAPOR INTRUSION ASSESSMENT AND MITIGATION IN OREGON

Transcription

1 THE STATUS OF VAPOR INTRUSION ASSESSMENT AND MITIGATION IN OREGON By Don Hanson, Oregon DEQ SCRD May 2012 Oklahoma City

2 OREGON PUBLISHED VI GUIDANCE IN MARCH 2010 Guidance for Assessing and Remediating Vapor Intrusion in Buildings onguidance.pdf Stepped away from predictive models (J&E) Derived soil gas attenuation factors (AFs) Using 2008 subsurface vapor and indoor air data set AF of 200 Residential AF of 1,000 Industrial AFs applied to residential or occupational ambient air RBCs (RBCs set at 10E-6 risk in OR) Step-wise procedure (groundwater, soil gas, indoor air) Removal (mitigation) possible at any step

3 RISK BASED CONCENTRATIONS (RBCs) HAVE NOW BEEN ADDED RBCs for soil gas were added to Oregon s RBC Table RBCs are based on 1 X 10-6 excess cancer risk or HI of 1 (non-cancer) RBCs based on AFs in Guidance Soil Gas RBCs Applied to both soil gas, sub-slab samples Guidance stipulates sampling procedures No need to apply AFs Just use RBCs

4 CRAWL SPACE SITUATIONS Sample soil gas near or beneath building (5-ft bgs) Compare to SG RBCs Sample Crawl Space Compare to air RBCs (guidance assumes no attenuation between crawlspace and indoor air

5 TYPICAL VI ASSESSMENT PROCESS AT OREGON DRYCLEANER 1. Initial soil & groundwater assessment 2. Compare soil and water data against VI RBCs 3. If above RBCs, move to soil gas sampling Around or beneath buildings (prefer beneath) Soil gas (5 ) or sub-slab Sub-slab simple and more representative of concentration potential to affect indoor air. Temporary (direct push) or permanent sampling probes Permanent better to monitor seasonal variations 4. If data exceed RBCs (consistently?), mitigate or consider indoor air sampling This is a big deal!

6 Preference for Sub-Slab Samples

7 AIR SAMPLING PROBLEMS Its Complicated AIR SAMPLING Problems with background Outdoor/background samples important Guidance allows subtracting out background This can be complicated Due to the high variability in air concentrations, determining the value to be subtracted may be difficult, particularly if the difference between indoor air and ambient levels is within the range of sampling and normal method-specific analytical error. Therefore, this procedure may be subject to considerable professional judgment and should be considered in the context of all available evidence. DEQ Guidance Footnote (P. 27)

8 PROBLEMS WITH AIR SAMPLING, CONTINUED Risk Communication When indoor air concentrations are not attributable to subsurface vapors The recognition that these chemicals (PCE and others*) are all around us The recognition that residents might be contaminating themselves with household chemicals *Limit analyte list to contaminants of concern when possible

9 THE TREND TOWARD MITIGATION WHEN SOIL GAS CONCENTRATIONS ARE VERY HIGH May choose to skip air sampling and move directly to mitigation Sub-slab depressurization Crawl space venting/depressurization below vapor barrier HVAC controls Floor sealing Or combination of technologies

10 2012 CHANGES IN EPA SLOPE FACTORS (in IRIS) FOR PCE Oregon had already been using conservative (lower) slope factor for PCE DEQ s RBCs (based on 1 x 10-6 excess cancer risk) went UP about 2 orders of magnitude w/ 2012 IRIS revisions Example: Soil Gas VI to Indoor air RBC (residential) Was 82 µg/m 3 Now 1,900 µg/m 3

11 IMPLICATIONS FOR DRY CLEANER INVESTIGATIONS AND CLEANUPS BIG affect in Oregon Lower risk overall (= fewer cleanups) In some cases non-cancer may drive cleanups in Oregon Hot Spot (HS) = preference for treatment under Oregon Law HS = 1 X 10-4 excess cancer risk or 10 times non-cancer HS = Concentrations above Cancer RBC X 100 OR HS = Concentrations above Non-Cancer RBC X 10

12 OREGON PCE HOT SPOT ISSUE HIGHLIGHTED Vapor Intrusion RBC for Soil Gas (Residential) 1,900 µg/m 3 based on cancer risk 8,300 µg/m 3 based on non-cancer Cancer Drives Non- Hot Spot Risk Hot Spot Thresholds (Residential) 190,000 µg/m 3 based on cancer risk 83,000 µg/m 3 based on non-cancer Non-Cancer Drives Hot Spot and preference for treatment* *Hot Spot Criteria are used to drive/trigger Orphan cleanups and Dry Cleaner Program cleanups *Orphan/Dry Cleaner Cleanup/funding for removal/mitigation may be postponed if no Hot Spot exists

13 CASE STUDY NuWay II Cleaners Lebanon, Oregon

14 NuWay II Cleaners, Lebanon, Oregon PCE dry cleaners Orphan Program One source of Area-wide groundwater contamination in downtown area Groundwater remediation on-site (source area) Site selected for soil gas assessment based on historically high (previous) PCE concentrations Groundwater in vicinity of buildings < VI RBCs before soil gas sampling Release mechanism/source never well understood no soil removal was ever conducted

15 Department of Environmental Groundwater Concentrations Quality Historically > VI RBC < RBCs at time of VI Assessment NuWay II Cleaners Groundwater Treatment Area Main PCE/TCE Plume Assumed Release Area

16 APRIL INITIAL SOIL GAS ASSESSMENT RESULTS Department of Environmental Quality PCE in GW ND Soil Gas April ug/m 3 Sub Slab Oct ,520 ug/m 3 PCE in GW ND Soil Gas April ug/m 3 Oct ,500 ug/m 3

17 FEB SUB SLAB SOIL GAS ASSESSMENT RESULTS Department of Environmental Quality Residential RBC 82 ug/m 3 /1,900 ug/m 3 Urban Res. RBC 220 ug/m 3 /5,100 ug/m 200 ug/m ug/m 3 7,060 ug/m ug/m ug/m 3 31 ug/m 3 2,400 ug/m 3

18 NuWay II Cleaners PCE Changes Implications After one sampling event Pre-2012 RBCs showed Risk for residence (urban residential) and one location in nail salon (Occupational) 2012 RBCs showed risk only at residence (urban residential OR residential exposure)

19 NUWAY II VAPOR INTRUSION ASSESSMENT NEXT STEPS Last sampled in February 2011 Re-Sample all vapor points in September 2012 to measure for seasonal variation Compare Results to 2012 PCE and other COC Risk Based Concentrations Compare results against Hot Spot Concentrations Determine which areas, if any, require mitigation (sub slab depressurization)

20 NUWAY II CLEANERS VAPOR INTRUSION STUDY QUESTIONS? Don Hanson Oregon Department of Environmental Quality (541)