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- • Jam- . � - " •- _ Y- - -- - <br /> a. <br /> Groundwater gradient directions have been calculated from the <br /> gauging data in Table 1 using the three-point method (Billings <br /> 1972 ) or by contouring the groundwater elevations. <br /> In-the two years from 1988 to 1990, the downgradient direction <br /> has been generally toward the northeast, and the gradient has <br /> j been very shallow ( less than 0.002 as measured from MW1 to MW2 ) . <br /> The nearest surface water is a channeli.,ed intermittent tributary <br /> of the west-flowing Fivemile Creek, which passes within 100 yards <br /> of the site (see Figure 1 ). Fivemile Creek ^arries surface run- <br /> j off westward to the waters of the San Joaquin River system. Flow <br /> in Fivemile Creek may contribute to recharge of the shallow <br /> � '--s aquifers beneath the site during periods of precipitation. <br /> � s <br /> 1 .3 DI5TRIBUT'ION OF PETROLEUM HYDROCARBONS IN GROUNDWATER <br /> � E <br /> . Groundwater has been sampled and analyzed 11 times at the site <br /> since wells were first installed in November 1986 Throughout <br /> this sampling period,: MW3.:has:.:contained `the:.;highast :'concentra=- <br /> �.r� tions:,,,of .dissolved;hydrocarbons of;.:-the;,f ive<-:wells Water .samples <br /> ( � <br /> .. . from MW1 , MW2,: MW4, and MW5 have contained only very low concert-- <br /> trations of petroleum contaminants or. have not contained petro- <br /> .. p"1 , <br /> leum aomP onndsabove method detection limits. Contaminant t <br /> concentrations in the wells have generally decreased with time <br /> The gradient calculations 'indicate that well MW2 is located down- <br /> gradient from well MW3. Throughout the sampling period, water <br /> from.MW2 has contained much lower levels of dissolved hydro- <br /> - � - <br /> raw carbons than has water from MW3. Dissolved hydrocarbons have not <br /> fbeen_.detected in concentrations above method detection limits in i <br /> water: from .MW2 .since January 1989 (last five sampling rounds} <br /> These;-,data,suggest that ahe- contaminated._groundwater:'plume_::is. <br /> confined :_to.;.the--,'polrtion .of:,.the .aquifer.4 around :MW3.,.:, <br /> e42/71050/7=90/tx 3 <br /> T <br />