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_ .x. � yi g _ �• t <br /> Problem Assessment Report December 5, 1989 <br /> USA Petroleum Station No. 65, Lodi, California AGS 87050-3 <br /> 4 <br /> FIELD WORK AND METHODS <br /> The field work performed in this investigation that has not been previously reported <br /> included: 1) drilling four soil borings offsite,2)collecting soil samples and classifying them <br /> according to the Unified Soil Classification System, 3) installing four ground-water <br /> monitoring wells in the borings, 4)sampling ground water from the seven monitoring wells <br /> i at the site, 5) surveying the elevations of the wells by a licensed surveyor, 6) performing <br /> i <br /> bailer tests to obtain preliminary estimate of transmissivity and hydraulic conductivity of the <br /> aquifer, 7).,&valuating the groundwater flow direction at the time of sampling, and 8) s _ <br /> evaluating the zero line of contamination. ; <br /> Ground-water monitoring well MW-4 was drilled and installed on January 17, 1989; well <br /> MW-5 was drilled and installed on January 18, 1989. At the request of USA, permits were <br /> obtained for two additional wells to further delineate the limits of ground-water <br /> contamination. Well MW-6 was drilled and installed on February 23, 1989, and well MW-. <br /> N <br /> 7 was drilled and installed on March 28, 1989, <br /> Y � <br /> 'fhe location of the four offsite borings and monitoring wells in relation to adjacent property <br /> , <br /> i are depicted on Plate P-2. The placement of. the wells was''based on the previous <br /> ----- <br /> - evaluation of the groundwater gradient across the site. Borings were drilled to 20 feet <br /> ;A <br /> s �, <br /> MIN=IN ills <br />