CORRESPONDENCE_2019 - Laserfiche WebLink

Home Browse Search

Brusca File No. 137-002 Page 3 June 25, 2019 Murphy Parkway Property Soil Gas Monitoring SOIL GAS LABORATORY TESTING The soil gas samples collected from soil gas monitoring wells SGMW1 and SGMW2 were transported to a State-certified laboratory for analysis. Both soil gas samples were analyzed for met hane, oxygen, carbon dioxide, and nitrogen by ASTM Method D1946. The samples also were analyzed for VOCs by EPA Test Method TO-15. The analytical laboratory results are summarized on the attached Table I, along with data from past monitoring. The laboratory reports, internal laboratory QA/QC data, and chain-of-custody documentation also are attached. RESULTS AND DISCUSSION As shown on Table I, the June 2019 soil gas sample s collected from SGMW1 and SGMW2 did not contain methane at a concentration above the laboratory reporting limit s of 0.00021% 0.00026% for these samples, respectively. Methane concern at the site is not indicated by June 2019 data. The soil gas samples collected from monitoring wells SGMW1 and SGMW2 in June 2019 contained the VOCs acetone, chloroform and/or carbon disulfide at very low concentrations. To evaluate the significance of the concentrations of acetone detected in the soil gas samples (particularly with respect to the potential for vapor intrusion into indoor air spaces at concentrations that could be considered a human health concern), we have co nsidered Regional Screening Levels (RSLs) published by the US Environmental Protection Agency (USEPA) and Environmental Screening Levels (ESL s) published by the San Francisco Bay Regional Water Quality Control Board (SFBRWQCB). The applicable screening values for acetone, chloroform, and carbon disulfide are shown on Table I along with the analytical data from the soil gas monitoring wells . The published RSL values are for indoor air VOC concentrations. For use in the screening evaluation for the subject site, the indoor air RSL values have been adjusted by an attenuation factor of 0.03 to simulate the attenuation that could occur from soil gas to the indoor air environment. As shown on Table I, the concentrations of acetone, chloroform, and carbon disulfide detected in the soil gas sample s in June 2019 are below the commercial/industrial agency screening values considered, except for the chloroform concentration detected in the soil gas sample collected from SGMW1. The soil gas sample collected from SGM W1 contained 3 4 ug/m3 chloroform which slightly exceeds the screening level considered (18 ug/m3). The source of the chloroform detected in the SGMW1 sample is unknown. Chloroform occurs naturally in certain settings, although ant hro pogenic sources are responsible fo r much of the chloro fo rm in the environment. A common anthropogenic source of chlorofo rm in the environment is the discharge of chlorinated drinking water. It is possible that the detected chloroform in soil gas at the SGMW1 location is related to the recent initiation of landscape irrigation in the area of SGMW1 utilizing municipal water. Nonetheless, it is our opinion that the slightly elevated concentration of chloroform detected at the SGMW1 location in June 2019 would not represent an unacceptable vapor intrusion health risk at the onsite warehouse building, due to the distance to the building and the nature of flo or slab system associated with the building. As mentioned above, the soil gas screening levels considered were developed using an attenuation factor of 0.03, which most