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• 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 onsite 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 GROUNDWATER MONITORING AND SAMPLING Smith Environmental performed quarterly groundwater monitoring and sampling on December 29, 1995 Field work included measuring the depth-to-water in wells MW through MW6, purging and sampling the water from wells MW2 through MW4, and analyzing the samples for the presence of dissolved petroleum hydrocarbons The water table elevation has increased an average of approximately 0 71 feet since the last monitoring event in September 1995 Groundwater monitoring data are summarized in Table 1 Groundwater beneath the site generally flows southwest with an overall gradient of 0 001 ft/ft, or approximately 6 feet/mile This is consistent with the previous monitoring data A groundwater gradient map for the • December 29, 1995 monitoring episode is shown on Figure 2 depicting an apparent mounding of groundwater in the vicinity of the former excavation Groundwater samples were collected from wells MW2 through MW4 after purging and stabilization of physical parameters (pH, electrical conductivity, and temperature) The monitoring wells were purged and sampled according to RESNA Industries' Quality Assurance/Quality Control Plan, on file with PHS/EHD Well purge logs are included in Attachment 1 LABORATORY ANALYSIS Collected groundwater samples were placed on ice and transported under chain-of-custody protocol to state certified Argon Laboratories Samples were analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX) and TPHg by EPA methods 8020 and modified 8015, respectively Laboratory analyses detected elevated concentrations of petroleum hydrocarbons in the samples collected from wells MW2, MW3, and MW4 The laboratory method detection levels of BTEX and TPHg were 0 50 and 50 ppb, respectively Results are generally consistent with historical levels Analytical results are summarized in Table 2 Laboratory reports and chain-of-custody documentation are presented in Attachment 2 In accordance with PHS/EHD correspondence dated December 27, 1993, the sampling schedule of NMI has been reduced to annually and wells MW5 and MW6 to semi-annually Wells MW2, MW3 and MW4 will continue to be sampled quarterly This schedule is based upon historical groundwater analytical data w 1943261QUARTLYI4QR-1995 DOC 2 • SMTH