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Mr. Michael T. Goldstein October 14 , 1985 Page 3 above the top of each wells sand pack to the land surface. Figures 1 through 5 show well locations, and construction information, and a north south geologic cross section through the basin using the latest lithologic information from the new monitoring wells. Following installation, each well was developed and sampled. Development consisted of pumping or bailing a number of casing and borehole volumes from each well . The volume of water removed from each well during development is given on the well log. Wells BC12 and BC14 could be pumped without going dry, and during development , at least 100 gallons of water was removed prior to sampling. Well BC13 , the well monitoring the deeper, previously unsampled zone, would not readily yield water during development. The water level in the well dropped from a static water level abut 32. 5 feet to approximately 80 feet while being pumped at an estimated rate of less than one-quarter gallon per minute. The well was sampled after approximately 25 gallons of water had been removed. Each well was sampled using a nitrogen-powered bladder pump, equipped with a Teflon discharge tube. Samples were obtained for chloroform analysis following well development and these results are shown on Table 1 . The initial sampling of BC12, BC13, and BC14 occurred on August 30 , September 3 , and September 5 , respectively. Chloroform Concentrations Samples have been obtained for chloroform analysis from the monitoring wells , the recovery well, the air-stripping tower, and the Tracy South Area well on a regular basis since late June. The results of chloroform analyses are given in Table 1. Chloroform concentrations in the groundwater pumped from the recovery well and the wells adjacent to the basin reached their highest levels in August. As Figure 5 shows , the peak concentrations recorded in Wells BC7 and BC10 occurred prior to the 1 week discharge of the water from the air-stripper column to the basin floor. This indicates that capture of a downgradient plume occurred at this time. Subsequent chloroform concentrations decreased in Wells BC7 and BC10 and increased in Well BC2 while water was being discharged to the basin floor. Chloroform has not been detected and confirmed in water samples from the Tracy South Area well. Chloroform was reported in one sample and duplicate from the well , however, we believe that this was a laboratory or sampling error. Subsequent sampling did not confirm the presence of chloroform in the water. Groundwater Levels Water level data are summarized in Table 2 and Figure 6 is a generalized water table contour map drawn from data obtained on September 16 . The figure shows that pumping the recovery well produces a small cone of depression. BROWN AND CALDWELL PO BOX 8045 WALNUI CREEK.CA 945961220• (415)9379010 TELL X336490-OFFICE AT 3480BUSK IRK AVLNUE PLEASANT 11 I L 194523