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Langston's Market, 15615 Seventh Street, Lathrop, California Work Plan-Phase HLateral& Vertical Extent of January 10, 1996 Second Ground►vater Aquifer, Revised Page: Z the capillary fnnge zone, and the water table, with little Iateral spreading Figure 2 shows the lateral extent of both the soil and groundwater contarrunation as determined by the April 1992 investigation Although no groundwater monitoring wells were installed at that time, soil vapor samples were collected from above the water table in all borings and screened in the field using a 580B OVM Although not conclusive, this preliminary investigation provided a reasonable estimate of the extent of contamination in both the soil and groundwater, and has formed the basis for the location of exploratory soil bonngs and groundwater monitoring wells The drilling activities were performed under the supervision of a California Registered Geologist who selected the boring locations and logged the borings as they were drilled During drilling, soil samples were collected at appropriate depth intervals (9, 14, and 17 feet) using a driven tube sampler egalpped with extension rods and a single clean one-inch diameter stainless steel tube Soil samples were collected at 9, 14, and 17 feet below the ground surface The 9-foot sample would correspond to a depth appy oximately equal to the bottom of the tank, while the !7-foot sample would be representative of the capillary fringe zone The presence of contamination ir, the sample collected from 17 feet would indicate that grcundwater at that location is contanunated OVM readings represent the maximum reading registered by the 580B instrument during the screening of each sample Although OVM readings do not precisely correspond to chenucal analysis the ieadings apprommate the amount of gasoline present in the soil in parts-per-ini'llion +.ppm), of total petroleum hydrocarbon constituents A s.grufic.ant amount of gasoline remains in the Vadose zone soil at the site Ori;+ borings SB-3, I SB-77, and SB-8 appeared to be fiecy of significant amount of total petroleum hydrocarbons Due to the shallow depth of the water table (17 5 fret), it iS therefore not surprising to find that groundwater quality has been ict:��acted by the release of nearly 1,200 gallor_s of gasoline from the failed underground fuel tank Borings SE-5 Asn{ SB-6 were drilled directly beneath the center and the failed end of the former tank respectively The highest OVM readings were found throughout the soil column in these two locations, cont-hr-rung that the source of the gasoline in the soil originated from the former underground fuel tank On July 27, 1995, WIC, Inc , in conjunction with SEMCO, Inc , under a San Joaquin County approved work plan, dated October 11, 1994 began interim remedial activities at this site with the removal of surface structures and trench slotting to further define the limits of contamination The water table was measured at approximately ib'/z feet below ground level The four existing Igroundwater monitoring wells were then abandoned, under permit, to avoid the possibility of cross-contamination Excavation of uncontaminated soil continued down to approximately 15'/z feet below ground level Excavation of contaminated soil continued down to an average depth of 25 feet, with the aide of a de-watering well Contaminated soil was trucked directly to Forward Landfill, Stockton, California and stockpiled for characterization and disposal Pumped water was treated and discharged to the City of Lathrop sewer system and City of Manteca treatment plant After the excavation had progressed to its maximum limit due to roads and utilities,