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MMIN ATTACHMENT 1: ASSESSMENT ACTIVITIES WESTERN GEOLOGIC RESOURCES, 1989 WGR performed a soil-vapor survey in 1989 Twelve temporary soil-vapor sampling points were installed at the locations shown in Figure 2 Vapor samples were collected from each location at 5 feet below ground surface (bgs) and at 15 feet bgs The highest concentration of total volatile hydrocarbons (TVH) found at 5 feet bgs was 2,500 ppm, at VP-11 Vapor Points VR-1 and VP-12 also contained elevated concentrations of TVH at 5 feet bgs (680 ppm and 390 ppm, respectively) Soil-vapor samples collected from 15 feet bgs contained concentrations as high as 91,000 ppm TVH (VP-11). Concentrations of TVH in excess of 50,000 ppm were found in Vapor Points VP-1 and VP-12 at 15 feet bgs Volatile hydrocarbons were also found in Vapor Points VP-2, VP-3, VP-4, VP-9, and VP-10, but at lower concentrations (3,100 ppm, 410 ppm, 15 ppm, 220 ppm, and 1,800 ppm, respectively) The highest concentrations were in the vicinity of the former tank pit Following the soil-vapor survey, WGR installed five monitoring wells Five borings were drilled on the site and were completed as Monitoring Wells MW-1 through MW-5 in February and March 1989 Groundwater sampling confirmed that the highest concentrations were in the vicinity of the former tank pit EARTH TECHNOLOGY CORPORATION, 1991 In 1991, Earth conducted cone penetrometer tests (CPT) and groundwater sampling at the site The CPT data provide general lithologic descriptions as well as the ability to collect discrete ground- water samples (Earth,November 1991) This work further confirmed that the highest concentrations were in the vicinity of the former tank pit. GROUNDWATER TECHNOLOGY, INC., 1992 In March 1992, GTI installed Monitoring Wells MW-6 and MW-7 as well as Vapor Well VW-1 at the locations shown in Figure 2 Well MW-6 was installed across Plymouth Road, down- gradient from the site,to determine the extent of the plume Well MW-7 was installed upgradient of the known extent of contamination to further delineate the plume Well VW-1 was completed in the vadose zone,to be used as a vapor-extraction well in the future Monitoring Well MW-8 was installed in December 1993 to further define the downgradient limits of the plume extending from the property • GM_,WCHMONADATA.CHEVRON CHEV N-Z%T&V t"COM-ACT AtI41&c