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Site History • 14000 Highway 88,Lockeford,CA Time Oil Property No 04-049 average decrease in groundwater elevation of 0 44 feet across the site Groundwater flow direction remained consistent with previously collected data, however, gradient decreased somewhat The variations in groundwater elevation and gradient were most likely due to seasonal variation Analyses identified 3,400 ppb gasoline, 200 ppb benzene, 850 ppb toluene, 120 ppb ethylbenzene, and 560 ppb xylenes in the sample collected from MW 1(located nearest to the existing pump islands) The sample collected from MW-3, located to the southeast of the former tank bed (downgradient), contained 1,800 ppb gasoline, 140 ppb benzene, 180 ppb toluene, 78 ppb ethylbenzene, and 260 ppb xylenes, and the sample collected from MW-4, located to the southwest of the former tank bed (sidegradient), contained 410 ppb gasoline, 65 ppb benzene, 3 6 ppb toluene, 28 ppb ethylbenzene, and 4 1 ppb xylenes The sample collected from MW-2, located to the east of the former tank bed (side gradient), was not found to contain detectable concentrations of gasoline or its constituents Based on this data, the extent of groundwater impacts had not been defined in any direction Between the Third and Fourth Quarters of 1995, gasoline and BTEX concentrations increased slightly in MW-4, however, they decreased in MW-1 MW-2, and MW-3 The observed fluctuations in hydrocarbon concentrations were likely a result of seasonal variation in groundwater levels and/or a result of bioattenuation, however, not enough data had been collected to evaluate their significance SECOR's "Quarterly Monitoring Report - December 1996" dated February 5, 1996 was forwarded to the appropriate regulatory agencies on February 13, 1996 • Workplan for Additional Sod and Groundwater investigation-January 1996 Based on the results of the previous investigation, a workplan was prepared for the installation of six additional groundwater monitoring wells to define the extent of sod and groundwater impacts associated with the former underground storage tanks at the subject site On January 25, 1996, SECOR's "Quarterly Status Report and Work Plan for Additional Environmental Investigation" was forwarded to the appropriate regulatory agencies Briefly, proposed site activities consist of the following 1 Six borings would be advanced to approximately 100 feet below ground surface (or to 10 feet below first encountered groundwater) 2 Sod samples would be collected from each boring at 5-foot intervals and submitted for gasoline and BTEX analyses based on visual observation and field instrumentation readings A minimum of three samples would be submitted from each boring 3 Two-inch diameter groundwater monitonng wells would be installed in each of the bonngs Each of the wells would be screened from 5 feet above to at least 10 feet below the first encountered groundwater 4 The completed wells would be developed, surveyed, and sampled Should the results of the additional investigation indicate that the extent of soil and groundwater contamination is been defined, a Problem Assessment Report would be generated Otherwise, a report containing details of the additional field activities, well construction details, and analytical results would be prepared The PHS/EHD approved this workplan in correspondence dated March 6, 1996 7