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y Page 2 Ms. Vicki McCartney, REHS February 20, 2004 The facility once had four USTs. A former 10,000 -gallon diesel -fuel tank and two 6,000 -gallon 1 gasoline tanks were located near the southwest corner of the main building in the vicinity of monitoring well MW -1 (shown in Figure 2). A 20,000 -gallon diesel -fuel tank was located on the • east side of the facility nearer to South Airport Way. The gasoline tanks near the southwest building corner were permanently removed in April 1987. The eastern -most gasoline tank had previously been taken out of service and abandoned in place by removing the fuel and filling it with sand. The western -most gasoline tank failed a tank integrity test in December 1986, which initiated the permanent removal of both USTs. The two t diesel -fuel USTs were removed in September 1989. w Following the December 1986 detection of the leak in the western -most gasoline UST, l Environmental Science & Engineering (ESE) drilled five borings around the perimeter of the two ` adjacent gasoline USTs and collected soil samples for analysis. ESE's results, contained as an appendix in Anderson Consulting Group's (ACG) December 19, 1991 Problem Assessment Report, indicated that petroleum hydrocarbon impact in soil extended to a depth of at least 28 feet. L, During the April 1987 UST removals, impacted soil was overexcavated to 28 feet, which included the area where ESE had placed their borings. Approximately 450 cubic yards of soil, including some 120 cubic yards that was noted to be impacted with gasoline, was land -farmed A., with guidance from the San Joaquin Air Pollution Control District (SJAPCD). L In July and September 1987, ESE installed three groundwater monitoring wells (MW -1 through MW -3). In January 1988, ACG installed wells MW -4 and MW -5. ACG subsequently drilled soil borings 90-1 and 90-2 and installed wells MW -6 and MW -7 in February 1990 and then MW -8 in September 1990. PSC (formerly Burlington Environmental) installed wells MW -9 through L MW -13 in March 1994, and piezometers PZ -1 and PZ -2 and air sparging well SP -1 in September 1994. PSC performed a soil venting and air sparging pilot test in October and November of 1994 to evaluate the effectiveness of this remediation technology. Soil venting tests were performed using well MW -1, and air sparging tests were performed using well SPA. Results of the tests, contained in PSC's February 1, 1995 Final Remediation Plan, indicated that soil venting and air sparging would be effective in remediating hydrocarbon impact. In June 1995, PSC proceeded with the installation of air sparging wells SP -2 through SP -6. However, implementation of the sparge and vent remediation was postponed due to naturally occurring petroleum hydrocarbon concentration reductions that were observed at the time. 1 In May 1999, PSC performed a subsurface investigation using cone penetrometer (CPT) 4 technology. Three CPT borings (CPT -1 through CPT -3) were driven, and soil and groundwater 4 KLEINFELDER .3077 Fite Circle, Sacramento, CA 95827-1815 (916) 366-1701 (916) 366-7013 fax