ARCHIVED REPORTS XR0008268 - Laserfiche WebLink

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/diS6o/A t 0 Working To Restore Nature hydrocarbon constituents in soil borings MW2 and SBI at respective depths of 10 5 and 5 feet below grade Only xylenes were detected in soil boring MW2 at 0 009 ppm, marginally above the detection limit of 0 005 ppm (Table 2) Analytical results of groundwater samples collected from the site monitoring wells detected petroleum hydrocarbon constituents in well MW2 only The groundwater flow was determined to be in the southern direction Field activities performed during the initial investigation are discussed in detail in WaterWork's Preliminary Report, dated June 17, 1991 At the request of San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD), RESNA Industries Inc (RESNA) began quarterly monitoring and sampling of site monitoring wells MWI, MW2, and MW3 in January 1992 Groundwater flow was determined to be consistently in the southern direction During a file review of the site's historical groundwater data, errors were discovered in the calculations used to determine the monitoring wellhead elevations A resurvey of relative wellhead elevations conducted in December 1992 verified that the original survey data was accurate, however the calculated wellhead elevations were incorrect Using the original survey data, wellhead and groundwater elevations were recalculated The correct groundwater elevation data are shown on Table 3 Using a kriging program, groundwater gradient maps were recreated for all past monitoring episodes The figures depicted a consistently east-northeast groundwater flow direction This is OR congruent with the regional groundwater gradient direction which flows northeasterly toward a groundwater depression located east of Stockton (San Joaquin County Flood Control and Water Conservation District, Spi ing 1992) Analyses of collected water samples detected only xylenes at 0 6 parts per billion (ppb) in well MW2 in July 1992 To date, no other analytes have been detected in the site monitoring wells Table 4 summarizes laboratory results for groundwater since March 1991 In January 1993 RESNA supervised the drilling of five additional soil borings (SB3 through SB7) in the vicinity of the former tanks as shown on Figure 2 Slight product odor was observed in soil borings S136 and SB7 and moderate to strong odor was noted in boring SB4 Groundwater was encountered at approximately 6 feet below grade during drilling activities in January 1993 Cored soil samples were collected and submitted for laboratory analysis Petroleum hydrocarbon analytes were detected in borings SB3, SB -4 and SB -6 Soil sampling results are summarized in Table 2 These activities defined the approximate extent of soil contamination FIELD ACTIVITIES The following scope of work was based upon the information collected during previous site investigations The work was designed to remove the remaining impacted soil in the vicinity of the former tanks All field work was performed under the supervision of RESNA personnel in SXR1293 DRF 2