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K C E I N F E L D F R 1 EXECUTIVE SUMMARY This report presents results for the first semi-annual sampling event (2000 groundwater sampling), a sensitive receptor survey, and additional soil and groundwater-sampling using push probes This work was conducted in the vicinity of a former underground storage tank (UST) located at the ' subject site (Plate 1) Ms Jan Thompson of Wilbur-Ellis Company retained Kleinfelder to conduct the limited receptor survey and push probe assessment in accordance with our "Workplan" for the subject site (File number 20-4439-01 E01, dated April 25, 2000) The semi-annual groundwater assessment was conducted according to our proposal/cost estimate titled, "Semi-Annual Groundwater Monitoring, Former Underground Storage Tank Site, 212 Industrial Drive, Stockton, CA 95206", dated June 5, 2000 (Kleinfelder File No 20-YPO-171) In summary A total of seven "sensitive receptors," including six wells and one canal, were identified, which were potentially located within a 2,000-foot radius of a former underground storage tank (UST) at the subject site It is Kleinfelder's opinion that the contaminant plume at the subject site has not impacted these receptors Groundwater flow direction during the July 7, 2000 semi-annual sampling event was the northeast at a gradient of 0 005 ft/ft This flow direction and gradient are generally consistent with previous groundwater elevation data ' Total petroleum hydrocarbons as referenced to gasoline and/or benzene were detected in groundwater samples collected from the three onsite monitoring wells (MW-1 through MW-3) ' and one or more push probe groundwater samples (GP-3 through GP-5) located in the vicinity of the former UST None of the five oxygenates (ETBE, DIPE, MTBE, TAME or TBA) or ethanol and methanol were detected during the push probe assessment conducted on June 1, 2000 ' Benzene was detected in groundwater samples in each of the three-onsite monitoring wells MW- Be gr p 1, MW-2 and MW-3 and in a single push probe groundwater sample The benzene ' concentrations ranged from 10 µg/1 from groundwater collected from MW-2 to 1,100 µg/1 from a groundwater sample collected from MW-1 These benzene concentrations are at or exceed ' State and Federal MCLS of 1 µg/1 and 5 gg/l, respectively Petroleum constituents detected in groundwater from the three onsite monitoring wells have decreased from previous sampling events (Table 1) ' The contaminant plume appears be on the shape of an oval in the vicinity of the former UST and measures approximately 220 by 160 feet The plume appears to be contained to the subject site although the northern extent appears in close proximity to the northern property boundary near Industrial Drive 20-4439-01 E0112000R726 Page I of 17 Copynght 2000 Kleinfelder, Inc October 16 2000