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• 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, Califorma, 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 QUARTERLY MONITORING ACTIVITIES Smith Technology performed quarterly groundwater momtormg and sampling on December 17, 1996 Field work included measuring the depth-to-water in wells MW I through MW6 and purging and sampling the water from wells MW2 through MW4 and the nearby community well (Thornton 42) The samples were analyzed for the presence of dissolved petroleum hydrocarbons The water table elevation has increased an average of approximately 104 feet since the last monitoring event in September 1996 Groundwater monitoring data are summarized in Table 1 Groundwater beneath the site generally flows in a west-southwesterly direction with average gradient of 0 001 ft/ft, or approximately 5 3 feet/mile A groundwater gradient map for the December 17, 1996 monitoring episode is shown on Figure 2 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 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 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 MW3 and MW4 The laboratory method detection levels for BTEX and TPHg were 0 50 and 50 ppb, respectively The analytical results are generally consistent with historical levels Analytical results are summarized in Table 1 Laboratory reports and chain-of-custody documentation are presented in Attachment 2 �j w 1943261quart1yl4gr-1996 doc 2 • SMTN