Lessons from Large Groundwater Plume Sites Redfield and Wall Vapor Intrusion Workshop 18th Annual West Coast Conference on Soils, Sediments and Water, San Diego, California, March 13, 2008 Ian Hers, Golder Associates Dave Folkes, Envirogroup Paul Sanders, NJDEP Soil Contamination (residual or mobile NAPL) Indoor Air Chemical Vapour Transport Groundwater Contamination
Wall Township, NJ
Wall Township, NJ PCE in groundwater Dry cleaners source of two large PCE plumes (1.5 by 2 miles!), sand, distance building-groundwater = 10.5 Dry cleaners decommissioned prior to 1991 PCE detected in private wells 1997 Indoor air testing began 2001
Wall Township, Indoor Air Max indoor PCE concentration!: Residential houses ~ 2000 ug/m 3, Commercial (1 building) ~ 1500 ug/m 3 LEGEND PCE concentration indoor air (ug/m 3 )
Wall Township, NJ
Wall Township, Groundwater vs. Indoor Air 3 PCE Indoor Air Conc. (ug/m ) 250 200 150 100 50 0 0 50000 100000 150000 200000 3 Calculated PCE Vapor Conc. from groundwater (ug/m )
Wall Township, Groundwater Alpha Data Groundwater PCE Alpha 1.E-02 NJDEP GWSL defaults, 1 m depth BFL (a = 1.06-03) 1.E-03 NJDEP GWSL defaults, 3.2 m depth BFL (a = 8.27-04) 1.E-04 1.E-05 1.E-06 1.E+04 1.E+05 1.E+06 Predicted PCE Vapor Conc. from groundwater (ug/m3) Maximum: 1.11x10-2 95th: 1.42x10-3 75th: 3.14x10-4 50th: 8.16x10-5 25th: 3.11x10-5 5th: 1.73x10-5 Minimum: 1.35x10-6
Wall Township, Influence of Sump Groundwater PCE Alpha 1.E-02 Gdw Alpha Sump Median Alpha = 2.6E-04 Gdw Alpha No Sump Median Alpha = 4.4E-05 1.E-03 1.E-04 1.E-05 1.E-06 1.E+04 1.E+05 1.E+06 Predicted PCE Vapor Conc. from groundwater (ug/m3)
Wall Township, Subslab Alpha Data Subslab PCE Alpha 1.E+00 1.E-01 Generic NJDEP Subslab Alpha (0.02) 1.E-02 1.E-03 1.E-04 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 3 Subslab PCE Concentration (ug/m ) 1.E+05
Wall Township, Comparison Subslab and External Soil Gas PCE Soil Vapor Conc.(ug/m3) 1.E+05 Ratios similar elevation external/subslab = 0.017, 0.47, 0.72 and 1.27. Subslab Soil Vapor External Shallow Soil Vapor Depth to external soil vapor 2.4 1.E+04 2.3 1.8 1.E+03 1.5 2.3 2.4 1.8 1.E+02 1.7 1.8 1.E+01 1 2 3 4 5 Houses 6 7 8 9
Redfield, Denver, CO (all Redfield slides from D.Folkes, Envirogroup) Site > 11-DCE action level in air (0.49 ug/m3) Large TCE, 1,1DCE & TCE plume below residential area See Folkes March 2004 AEHS San Diego presentation (as well as others) for additional info
Redfield Background Info 1,1-DCE indoor air measurements > 700 homes - limited (or no) influence background Variable geology consisting of sand, silt, clay, weathered sedimentary rock described as silty, clay loess with sand lenses in database Variable distance building to groundwater (< 3 to > 30 ) Variable house construction (slab-on-grade, basement, crawlspace) Variable HVAC systems/operation
Redfield, Groundwater Concentration Used Database used maximum interpolated groundwater concentration within 100 feet of building, Reason was observed AFs were higher for lower groundwater concentrations and there were some outliers with AF above 10-3
Redfield, Denver, CO Alpha versus Season
Redfield, Denver, CO Alpha versus Season
Measured 11-DCE Indoor Conc. (ug/m3) Redfield, Groundwater vs. Indoor Air 140 120 100 80 60 40 20 0 0 100000 200000 300000 400000 500000 600000 700000 Predicted 11-DCE Vapor Conc. from Groundwater (ug/m3)
Redfield, CO (first phase)
Redfield, Groundwater Alpha Groundwater Alpha 1E-02 1E-03 Basement N=244 AF=7.6E-05 Maximum: 1.78x10-3 Crawlspace N=72 AF=6.9E-05 Slab-at-grade N=14 AF=2.2E-05 95th: 4.68x10-4 75th: 1.52x10-4 50th: 7.31x10-5 1E-04 25th: 2.82x10-5 5th: 7.84x10-6 1E-05 Minimum: 1.68x10-6 Lognormal Distribution 1E-06 0 10 20 30 40 Geometric Distance from building to water table (ft.) mean =
Redfield - Alpha Observations AF vary over 2 orders-of-magnitude, what are some possible reasons for variability: Depth (relatively small effect) Foundation (relatively small effect) Analytical precision (likely small effect) Groundwater concentration variability -? House variability (HVAC, occupant use) -? Geologic variability (vadose zone soil, capillary zone, backfill around house -?)
Redfield, Influence of Soil Type 1.E-02 Groundwater Alpha Sand lenses median alpha = 5.8E-05 Silty clay loess soil median alpha = 3.8E-05 1.E-03 1.E-04 1.E-05 1.E-06 0 10 20 30 40 Depth to water table from ground surface (ft) 50
Redfield, Alpha Temporal Effects There is some variability in groundwater concentrations Changes in groundwater concentrations may take weeks or months to translate to possible changes in indoor air concentrations Longer-term attenuation factor data resolves some of this temporal variability and may be better predictor of representative attenuation factors
Redfield, Groundwater Data Groundwater DCE, ug/l 1000 100 10 1 0.1 Mar-97 Jul-98 Dec-99 Apr-01 Sep-02 Jan-04 Sample Date H1 H2 H3 H4 H5 May-05 Oct-06
Redfield, Indoor Air Data Indoor Air DCE, ug/m3 10 1 0.1 0.01 Mar-97 Jul-98 Dec-99 Apr-01 Sep-02 Jan-04 Sample Date H1 H2 H3 H4 H5 May-05 Oct-06
Redfield, Alpha Versus Time 1.E-04 1.E-05 1.E-06 Sample Date H1 H2 H3 H4 H5 Oct-06 May-05 Jan-04 Sep-02 Apr-01 Dec-99 Jul-98 1.E-07 Mar-97 Attenuation Factor 1.E-03
Redfield, Single Point vs Average Alpha 100% 90% Cumulative Percent 80% 70% 60% 50% 40% 30% 20% 10% 0% 1.0E-06 1.0E-05 1.0E-04 Attenuation Factor Singe Point Alphas Average Alpha Geomean Alpha 1.0E-03
Conclusions Over 2 orders-of-magnitude variability in AFs observed, which is to be expected given sources of variability However, within this variability internally consistent patterns and trends were observed Redfield: Foundation type did not appear to influence AF while soil type did, no fresh water lens Wall: Sump did appear to influence AF (although data limited), appeared to be fresh water lens