DuPont Pompton Lakes
Air Modeling Frequently Asked Questions (FAQs)
The following FAQs pertain to the April 2010 NJDEP report entitled “Tetrachloroethylene (PCE) and Trichloroethylene (TCE) Air Dispersion Modeling and Risk Assessment, Pompton Lakes, Passaic County, April 2010” [pdf]: The report, in its entirety, can be viewed at http://www.nj.gov/dep/srp/community/sites/dupont_pompton_lakes/
Were TCE and PCE levels from inside the homes used to model emission rates for the sub-slab systems?
The air modeling considered three sources of PCE and TCE: 1) the permitted air stripper at the DuPont facility, 2) vapors coming off the groundwater which are emitted through the soils throughout the plume area and, 3) the samples that detected PCE and TCE out of the 335 ambient (outside) air samples, modeled as stack emissions. All three sources modeled used conservative assumptions and the assessment shows there is negligible cancer and non-cancer risk. In fact, the emissions calculations coming from groundwater through soils fully account for the entire off site groundwater plume contribution to the vapors in the outside air. To be very conservative the ambient air samples were also used to provide an additive emission factor.
Were sub-slab soil gas levels from beneath the slabs of the homes tested used to model emission rates for the vapor mitigation systems?
As subslab soil gas levels do not represent a continual source of air contamination at the concentrations measured under the homes, they were not used to conduct the air dispersion modeling and risk assessment. However, subslab soil gas levels under homes in the ground water plume area remain elevated and therefore a potential source of indoor air contamination. For this reason the NJDEP, EPA, New Jersey Department of Health and the Agency for Toxic Substances and Disease Registry have consistently recommended the installation of vapor mitigation systems in homes located over the groundwater plume.
Under “Modeling Methodology” the report states that “Rural dispersion coefficients were assumed." What is that and does it account for atmospheric inversions?
Dispersion coefficients are determined based on land use and population density. In this case, rural dispersion modeling applied. This modeling does account for atmospheric inversions. The meteorological data used for this model is used for pollutant permitting and air toxic assessments in northeast New Jersey. In addition ambient air data continues to be collected and evaluated as part of the DuPont investigation.
DuPont - Pompton Lakes Works
Pompton Lakes, Passaic County
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