ARCHIVED REPORTS_2019 SOIL MGMT PLAN (MAY)

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Brusea File No. 137-002 Page 3 December 27, 2018 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 methane, 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 December 2018 soil gas samples collected from SGMW1 and SGMW2 did not contain methane at a concentration above the laboratory reporting limits of 0.00023% 0.00024% for these samples, respectively. Methane concern at the site is not indicated by October 2018 data. The soil gas samples collected from monitoring wells SGMW1 and SGMW2 in December 2018 contained the VOCs acetone 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 considered Regional Screening Levels (RSLs) published by the US Environmental Protection Agency (USEPA) and Environmental Screening Levels (ESLs) published by the San Francisco Bay Regional Water Quality Control Board (SFBRWQCB). The applicable screening values for acetone 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 0.001 to simulate the attenuation that could occur from soil gas to the indoor air environment. As shown on Table I, the concentrations of acetone detected in the soil gas samples in December 2018 are well below the commercial/industrial agency screening values considered, and, as such, are not considered a concern. SUMMARY AND CLOSING As described herein, our firm conducted monitoring/sampling of the two soil gas monitoring wells (SGMW1 and SGMW2) at the subject property in December 2018. The purpose of the soil gas monitoring program is to evaluate whether soil gas contaminants, including methane and VOCs, exist at the westerly margin of the property as a result of uncharacterized subsurface wastes that reportedly exist offsite to the west of the subject property. Data from the December 2018 monitoring event (as well as all previous soil gas monitoring data) do not indicate elevated concentrations of methane or VOCs in soil gas at the monitoring well locations. The soil gas monitoring performed in December 2018 completes a full year of monthly soil gas monitoring at the site. Per agency directives, subsequent soil gas will be performed on a quarterly basis. The next monitoring event will take place in the first quarter of 2019.