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I w` Mr. Kyle Christie February 27, 1995 Page 3 Between July and September 1993, the single-walled USTs and associated piping were replaced with double-walled fiberglass USTs and double containment piping. The UST replacement process was overseen by Roux. Soil samples were collected from the UST cavity sidewalls and the bottom of the piping trenches as directed by the County. The analytical results of these samples indicated that generally minor hydrocarbon concentrations were present in the soil in the piping trenches and UST cavity. Significant hydrocarbon concentrations were identified (2,600 parts per million (ppm) total petroleum hydrocarbon as w gasoline (TPH-G) and 1,600 ppm TPH-G) in the samples collected from the north center sidewall of the UST cavity and adjacent to the-pump island closest to the building. In addition to replacing the USTs and piping, vault boxes and remediation piping were installed to accommodate future installation of a soil vapor extraction/ air sparge remediation system. Details of this work are presented in Roux and Associates October 14, 1993 Underground Storage Tank Removal and Soil Sampling Report. { Field Work i During September 19 to 26, 1994, wells S-1 through S-3, VES-1 through VES-7, and SMW-1 were installed. -BC personnel were on-site to oversee the drilling, sampling, and construction of the wells. The wells were installed by Turner Explorations, Inc., of Rancho Cordova, California. The installation of the wells was conducted in accordance with BC's work plan dated August 9, 1994. Table 1 presents the well completion details for all of the newly installed wells.. Upon completion, well SMW-1 was surveyed for elevation by BC personnel because data from this well will be used in quarterly groundwater monitoring and sampling. { The seven dual completion soil vapor extraction/air sparge wells were drilled and constructed as presented in the work plan with the following exceptions. Heaving sand was encountered in boreholes S-3, SMW-2, VES-5 and VES-7. As a result, the depth of the sparge well casing I is 0.5 to 2.5 feet less than stated in the work plan. This change will not affect the operation of these wells because the screened interval is still well below the top of the saturated zone. E The thickness of the shallow(above the vapor extraction screened interval) he transition seals ranged from 0.5 feet to 1 feet. The thickness of the transition seals were reduced (from the 1 to 2 feet thickness stated in the work plan to accommodate a thicker cement grout seal above the transition seal. i s The drill cuttings were temporarily stored enveloped in plastic sheeting on the west side of { the site. At the conclusion of the drilling, BC personnel collected a composite soil sample of the stockpiled soil for laboratory analysis for waste characterization. The soil was removed from the site by, Dillard Trucking Company of Byron, California, under contract with ARCO. Upon completion, groundwater monitoring well SMW-1 was developed by BC personnel. Approximately 25 gallons of groundwater were generated during the development process. The development water was contained in a labeled 55-gallon Department:of Transportation (DOT) drum and temporarily stored on site. The development water and equipment steam- 1)2124M\E.'\7524Vt£PORTS\7524-0LL-I QMS-PS2200 J