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I � S IEC0R ARCO 595 . May 5, 2004 Page 2 sod analytical data is Included in Table 1 and historical sampling locations are Included in Attachment 2 s� In June 2000, four groundwater monitoring wells (MW-1 through MW-4) and three sod borings (8-1, B-2, and B-3) were completed at the site The subsurface assessment confirmed that petroleum hydrocarbons had Impacted the soil and groundwater beneath the site Results of this Investigation are Included In SECOR's Site Assessment Report, dated October 2, 2000 Historical sod analytical data is Included in Table 1 Well construction details are Included in Table 2 and soil boring logs are Included in Attachment 3 In July 2001, three additional groundwater monitoring wells (MW-5 through MW-7) and two deep soil borings (PSB-1 and PSB-2) were drilled to further delineate the lateral and vertical extent of petroleum hydrocarbons In soil and groundwater beneath and downgradient of the site, and in the vicinity of on-sate domestic water supply well WSW With the exception of minor concentrations of benzene, toluene, and xylenes in the 15-foot, 25-foot, and 55-foot samples from the boring for MW-5, petroleum hydrocarbons and fuel oxygenates were not detected in any soil samples collected during the assessment With the exception of minor concentrations of benzene, toluene, ethylbenzene, and xylenes (BTEX) constituents in boring PSB-2 at 95 feet bgs, concentrations of TPHg and BTEX were not detected in discrete-depth groundwater samples and groundwater monitoring well samples MtBE (EPA Method 8260B) and 1,2-DCA were reported in discrete-depth groundwater samples from boring PSB-1 (75 feet and 90 feet bgs), discrete-depth groundwater samples collected from boring PSB-2 (64 feet and 90 feet bgs), and in wells MW-5 and MW-7 at concentrations up to 94 ppb (MW- 7, August 2001) and 23 ppb (MW-7, August 2001), respectively Approximately 10 cubic yards of soil was generated during fieldwork activities, and disposed of at Forward Landfill in Manteca, California Results of this Investigation are documented in SECOR's Site Assessment Report, dated December • 11, 2001 The historical groundwater gradient direction within the shallow zone at the site has generally been to the northwest at gradients ranging from 0 0004 to 0 01 feet per foot The historical groundwater gradient direction within the deep zone at the site has ranged from the northeast to the southwest at gradients ranging from 0 0007 to 0 11 feet per foot Supply Well Survey Documented in SECOR's Site Assessment Report, dated October 2, 2000, a water supply well survey was performed to Identify the location of permitted water supply wells within a Y2-mile radius of f the site The water well survey consisted of a review of California Department of Water Resources (DWR) files for the area Additionally, SECOR contacted the City of Stockton and the County of San x Joaquin, Department of Public Works (CSJDPW), which are the local water purveyors According to the City of Stockton and the CSJDPW, no municipal wells owned and operated by these agencies are located within the '/-mile search radius However, a total of five water supply wells were identified within the search area, one of which Is an active domestic well located on the southwest corner of the Atlantic Richfield Company property Well search map and data are included in Attachment 3 Also in 2001, SECOR performed a 500-foot radius, door-to-door water supply well survey Water supply well survey forms were submitted to four adjacent businesses (EI Rancho Motel, Weinerschnitzel, Auto Factory, and Denny Boy Restaurant) and one residential property (8100 North Highway 99) The returned survey form from Weinerschnitzel Indicated the presence of a domestic well (well 61DW-1), which supplies the restaurant The well was constructed of 6-Inch steel casing, however, the total depth of the well could not be verified, though the manager of Weinerschnitzel estimated its depth to be approximately 170 feet Subsequent sampling of this well for petroleum hydrocarbon constituents indicated that the well had been impacted by 1, 2-DCA Well head treat was initiated and Is discussed in a later section i IARCO\05951Reports\Site Conceptual Model doc �F