SITE INFORMATION AND CORRESPONDENCE

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r Ms.Lori Duncan November 15,2011 RE: 2911 E.Fremont St,Stockton,CA Page 8 of 14 comparing the various ESLs established by RWQCB SF Bay,site concentrations are well below the ESLs based upon direct exposure, which is not an exposure pathway at the site because contaminated soils remaining exist at depths greater than 15 feet and are overlain by concrete and asphalt. In addition, groundwater sampling at the site detected only very low levels of PCE, but no residual gasoline consitituents,which suggests that native clay and silt zones present between the residual contamination and the known water table at the site act as an effective barrier to migration of contaminants downward to the water table. INDOOR AIR SAMPLING AND RISK EVALUATION Although direct contact with employees is not an exposure pathway and groundwater sampling has shown that groundwater beneath the former clarifier has not been significantly impacted, the residual soil contamination remaining beneath the former clarifier could pose a potential vapor intrusion concern. To investigate the potential vapor intrusion risk,L&P personnel collected air samples both inside and outside the warehouse building that housed the former clarifier. The samples were collected in general accordance with guidelines prepared by the California Environmental Protection Agency,Department of Toxic Substance Control, (CaVEPA-DTSC, October 2011). Pre-Sampling Site Visit and Interviews Prior to collecting indoor and outdoor air samples,L&P conducted a site visit to determine the pattern of use for the area in question(Warehouse#2). L&P conducted informal interviews with staff including the operations manager,dispatch manager and several employees working outside near the warehouse. Site personnel indicated that Warehouse#2 is used as storage of merchandise and the doors typically remain closed during site operations. The warehouse was fairly empty during the site visit. There were no visible chemicals stored within the warehouse. Activity outside the warehouse includes vehicle fueling (above ground storage tanks in a covered fueling area) and equipment loading. The yard office is located 80 feet east of the warehouse. The predominant wind direction is from the northwest. Upwind properties include residences and a school. Air Sampling and Analysis The air samples were collected on October 12,2011 and analyzed by the laboratory on October 17,2011. The indoor and ambient air samples were collected into 6-liter Summa Canisters using a flow controller set by the laboratory to collect time-weighted samples over an 8-hour period. One indoor air sample(602-IAI) was collected immediately over the excavated area,one indoor air sample(602-IA2)was collected at the rear of the warehouse,one ambient air sample(602-AA 1)was collected next to the yard office(approximately 80 feet east of the excavated area),and one ambient air sample(602-AA2)was collected at the eastern property boundary. A slight wind originated from the northwest. Although no chemicals were stored in the warehouse 10759-EXC SUMMARY LTR