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r The site's station building and garage were demolished in December 1994 to facilitate corrective action activities including the removal of hydrocarbon contaminated soil which was present beneath the station building The demolition of the station building was requested in PHS/EHD correspondence dated July 7, 1994 A required demolition asbestos survey conducted previously on the station building, determined the presence of asbestos containing materials E T Abatement, of Modesto California, properly removed and disposed of the site's suspected asbestos containing materials on November 11, 1994 In February 1995, Smith Environmental personnel supervised the excavation of approximately 1,400 cubic yards of soil from the vicinity of the former underground storage tanks Approximately 10,000 gallons of groundwater was pumped from the open excavation into an on- site Baker Tank The excavation pit was subsequently backfilled with imported self compacting material Excavation activities are discussed in detail in Smith Environmental's Excavation Summary Report, dated October 24, 1995 FIELD ACTIVITIES Smith Technology performed quarterly groundwater monitoring and sampling on September 30, 1996 Field work included measuring the depth-to-water in wells MW 1 through MW6, purging and sampling the water from wells MW 1 through MW6 and analyzing the samples for the presence of dissolved petroleum hydrocarbons The nearby community well (Thornton #2) was sampled on October 4, 1996, due to a scheduling conflict with San Joaquin County Utilities Maintenance District The water table elevation has decreased an average of approximately 3 19 feet since the last monitoring event in June 1996 Groundwater monitoring data are summarized in Table 1 Groundwater beneath the site generally flows in a south-southwesterly direction with average gradient of 0 001 ft/ft, or approximately 5 3 feet/mile This is a slight departure from historic groundwater monitoring data winch has depicted a predominately westerly flow direction A groundwater gradient map for the September 30, 1996 monitoring episode is shown on Figure 2 Groundwater samples were collected from wells NMI through MW6 after purging and stabilization of physical parameters (pH, electrical conductivity, and temperature) The monitoring wells were purged and sampled according to RESNA Industry's Quality Assurance/Quality Control Plan, on file with PHS/EHD Well purge logs are included in Attachment 1 The community well was sampled through an existing sampling port Additionally, during the October 4, 1996 visit, approximately one cubic yard of soil was backfilled into a surface depression adjacent to MW3 and leveled evenly with the ground surface to protect the wellhead of MW3 and remedy the potential physical hazard This localized depression is apparently the result of subsidence of backfill material which was placed in the former excavation in addition to post office patrons occasionally driving and parking an automobile on-site w1943261QUARTLY\3QR-1996 DOC 2 • SMITH