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Subsurface Investigation, Well installation, and Sample Analyses Results Page I4 <br /> Cintra Park Phase II Development, <br /> Tract 2705, Tracy, California <br /> July 23, 1998 CTE Job No. 20-0445B <br /> 5.2 Groundwater Sample Analyses Results <br /> Relatively low,but detectable concentrations of TPH-G,benzene,toluene, ethyl benzene, and xylene <br /> r <br /> were observed in groundwater sampled on April 8, 1998; however, for the May 13, 1998 sampling, <br /> all analytical constituents were below the laboratory reporting limit (Figure 7 and Table 4). <br /> Maximum TPH-G concentrations for the April 8th sampling were 50 pg/L(PMW-1, and PMW-3), <br /> which is at the Iaboratory reporting limit. Maximum benzene/toluene/ethyl-benzene/xylene(BTEX) <br /> 1 . <br /> concentrations for the April 8th sampling were 0.75/5.1/0.62/4.6 pg/L,respectively, in well PMW-1. <br /> Concentrations of MTBE in both sampling events and ethanol/methanol in the May 13th sampling <br /> F <br /> event were below the laboratory reporting limit. <br /> r� <br /> We believe that the reason that TPH-G and BTEX constituents were observed in selected samples <br /> r from the April 8, 1998 sampling, but not from the May 13, 1998 sampling or the grab sample <br /> collected from SB-3 (March 11, 1998) was the differing sampling method used between these <br /> � a <br /> events. Samples were collected from the pump on April 8th and were collected using a disposable <br /> bailer on March 11th and May 13th. Therefore,we believe that concentrations in samples collected <br /> on April 8th, albeit relatively low,represent a false positive, and that the samples collected on March <br /> 11th(SB-3 only) and May 13th more accurately represent true groundwater concentrations. <br /> il+ <br /> CATEEL FILES%CINTRA PARKICINTRA7-13.DOC <br /> i <br /> A . <br />