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h Y <br /> � F <br /> T <br /> a.i I <br /> 1 <br /> I Quarterly Monitoring, First Quarter 1991. May 23, 1991 <br /> �. Former Unocal Station 2859. Stockton, California AGS 38012-7 <br /> Sacramento, California (Hazardous Waste Testing Uboratory No. F.773). The results of � <br /> mese and previous analyses are summarized in Table 2. Copies of lne laboratory analysis <br /> reports are included with this report. <br /> Results of laboratory analyses indicated TPHg was detected in the samples collected from <br /> wells MW-4 and MW-5 at concentrations of 110 parts per billion (ppb) and 45 ppb, <br /> respectively. Benzene and toluene were riot detected in the water samples collected from <br /> monitoring wells MW-4 and MW-5. Concenit ations of ethyibenzene, and total xylene <br /> isomer were detected in the water collected from well MW-4 at 0.8 and 1.5 ppb respectively., <br /> the _ two compounds were not detected in water sampled from well i`1W-5. <br /> vnriusions and Recommendations <br /> Results indicate BTi?X concentrations have not been detected in water sampled from well <br /> MW-5 for two consecutive quarters. Concentrations of dissolved hydrocarbons detected in <br /> water sampled from well MW-4 were below maximum concentrations levels in drinking <br /> water outlined in Title 22, California Code of Regulation, Sections 64444. Based on l <br /> dissolved hydrocarbon concentrations detected in well MW-4, we recommend continuing <br /> quarterly monitoring. We have scheduled the next sampling for the week of May 13, 1991. <br /> In addition a work plan is in preparation for drilling a vapor-extraction well onsite for use <br /> in a vapor-extraction teat. <br /> , <br /> 3 _ <br /> AjO71led G60SYS1,Of s - - <br />