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1119jj%'Q�1111 MEMO= <br /> 7-Eleven/Stockton 10 <br /> August 1990 <br /> This subsurface geologic model also suggests that the <br /> highest concentrations of hydzocarbons in the adsorbed phase may <br /> be primarily restricted to the unsaturated upper stratigraphic <br /> sequence, particularly the basal gravelly coarse sand unit. This <br /> is supported by the sharp permeability contrast which exists at <br /> -- the base of the gravelly coarse sand and the marked attenuation <br /> of the lateral extent of the dissolved-hydrocarbon plume <br /> coincident with the decline of the groundwater elevation below <br /> the base of the gravelly coarse sand. <br /> SCOPE OF WORK <br /> Services performed by Groundwater Technology during this <br /> rkportii,g period consisted primarily of regularly scheduled <br /> operation and maintenance of -the groundwater--treatment system, <br /> - and monitoring and sampling of the groundwater-monitoring wells. <br /> Specifically, the following services have been conducted since <br /> the previous reporting period deadline of March 31, 1990; <br /> o Monitored on--site and off-site wells for depth-to-water <br /> and depth-to-product on three separate occasions. <br /> o Sampled groundwater from twelve monitoring wells, two <br /> monitoring clusters, and one recovery well in May, <br /> 1990. <br /> o Sampled groundwater from domestic wells TMG 1912, 1927, <br /> 8968, 9140, 9156, 9160, and 9172 three times. <br /> o Analyses for the presence of hydrocarbons in <br /> groundwater samples from monitoring wells MW-15a and <br /> MW-15b showed TPH-as-gasoline concentrations of 120 ppb <br /> ~ and 98 pph, respectively, in the May sampling round. <br /> --"� CRUZ'\IIlS':1T1>Id <br /> Tkcimoincv.Nc <br />