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Revised Work Plan For Soil and Groundwater Assessment 4 <br /> Ranch Market,23569 South Santa Fe Road Riverbank California April 25,2000 <br /> Groundwater Assessment <br /> Details concerning the completion of well MW-1,MW-2, MW-3, and MW-4 are provided in <br /> Table 2. One grab water sample was collected from boring B-1 in January 1998 contained <br /> elevated concentrations of BTEX and TPHg(Table 3). The four Site related wells were <br /> monitored and sampled in December 1998 and December 1999. Groundwater samples <br /> collected from the four wells contain reportable concentrations of BTEX, TPHg, and MtBE. <br /> No reportable concentrations of TBA, DIPE, ETBE, TAME, EDB, or 1,2-dichloroethane(1- <br /> 2,DCA) were detected in the water samples collected from the four wells. <br /> Domestic Well Sampling <br /> As detailed below and shown on Figure 2, four domestic water supply wells are located within <br /> 340 feet of the former tank pit. <br /> Well# Location from Tank Pit Comments <br /> DW-1 90 feet west of tank pit Onsite well <br /> DW-2 120 feet south of tank pit Down gradient of tank pit (well idle) <br /> DW-3 245 feet south-southeast Down gradient of tank pit <br /> DW-4 340 feet south of tank pit Down gradient of tank pit <br /> Referring to Table 3,water samples collected from the four domestic water wells have been <br /> analyzed for the presence of BTEX, TPHg,MtBE, TBA,DIPE, ETBE, TAME, EDB, and 1-2- <br /> DCA. Since water sample collected from well DW-2 contained reportable concentrations of <br /> MtBE, the well taken out of service. Well DW-1 is now used to supply water to the Site and <br /> adjacent residence that used well DW-2. <br /> Hydrogeology <br /> The depth to groundwater ranged from 25.90 to 28.69 feet bgs in the four wells. During the <br /> monitoring events conducted in December 1998 and December 1999 the groundwater flow <br /> direction was been southerly with a gradient of 0.0015 foot per foot. Surface drainage is to the <br /> southeast, towards the Stanislaus River, located approximately 750 feet south of the Site. <br /> Stratigraphy <br /> Based on the soil samples collected from the onsite soil borings, the lithology from grade to 40 <br /> feet bgs consists of silty sand grading at depth to poorly graded course grained sand. <br /> Fik:RB-C P. Wdl.LW <br />