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SOMA Quarterly Report and Closure Request,Site Code 1203 Stockton Regional Wastewater Treatment Facility 2500 W Navy Dnve,Stockton,CA Project No W0366 01 Page 2 On October 16, and 17, 1989, five soil borings were drilled to depths ranging from 11 to 29 feet below grade (Figure 2) Four of the borings were completed as groundwater monitoring wells No soil contamination was noted in any boring with the exception of SBI, which was located approximately 30 feet north of the former tank. TPHD was detected in SBI at 378 parts per million in a soil sample collected from 10 feet below grade, however, no volatile constituents (BTEX) were detected in the sample No soil impaction was evident above 10 feet below grade, based upon field observations (PID, visual) Based upon analytical results of water samples collected from monitoring wells MWI, MW2, MW3, and MW4 on October 30, 1989, groundwater beneath the site was not significantly impacted by dissolved hydrocarbons Only xylene was detected in well MW3 at 0 55 parts per billion (ppb), marginally above the detection limit of 0 3 ppb The groundwater flow was determined to be in the northeasterly direction Field activities performed during the initial investigation are discussed in detail in WaterWork's Problem Assessment Report, dated January 15, 1990 Analytical results for soil and groundwater are summarized on Table 1 and 2, respectively Groundwater monitoring and sampling of wells MWI, MW2, and MW3 was performed by RESNA on March 17, 1992 Analytical results did not detect petroleum hydrocarbon constituents (Table 2) Well MW4 could not be located Groundwater flow direction was determined to be north-northeasterly During June 1992, monitoring well MW4 was located and repaired The well had inadvertently been paved over with asphalt The well was redeveloped and sampled on June 24, 1992, in conjunction with the sampling of monitoring wells MWI, MW2, and MW3 In accordance with a written request by PHS/EHD, RESNA advanced three hand augured borings on June 24 and 25, 1992, in the vicinity of soil boring SBI to further characterize subsurface soil conditions at the site The borings were advanced to depths of approximately 9 feet below grade Two soil borings (SB5 and SB6) were placed near SBI and one (SB4) near the former tank where soils were previously found to contain residual diesel hydrocarbons at 378 ppm and 11 ppm, respectively Samples were collected from the bottom of each bonng (8 5-9 feet) and analyzed Toluene, ethylbenzene, and xylenes were detected (Table 1) at levels below State Maximum Contaminant Levels (MCLs) TPHD was detected only in boring SB4 (near the former tank) at 1 9 ppm Benzene was not detected in any samples collected at the site Groundwater monitoring and sampling of all site monitoring wells was conducted on June 24, 1992 Laboratory analyses did not detect the presence of dissolved petroleum hydrocarbons in any collected samples (Table 2) Groundwater flow direction was determined to be northeasterly 4QR-1992 FNL