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:-d y ro t PROGRESS REPORT/REMEDIATION FEASIBILITY STUDY _ Holt Brothers 1541 West Charter Way Stockton, California (Figure 1) In May of 198,9, seven (7) underground storage tanks (UST's) were removed from the site. During removal of the UST's evidence of soil contaminatlon was noted. The initial investigation work conducted by Dames & Moore (January 1989), included the installatio.. of four (4) monitoring wells (MW1, MW2, MW3, and MW4). Soil wimples collected from MW1 exhibited soil contamination. No contamination of soils was found during the installation of wells MW2, MW3, ox Mw4. Grr--undwater samples collected from wells MW1 and MW2 contained petroleum hydrocarbons, and halogenated volatile organic hydrocarbons. Halogenated organics were not found in MW3 A and MW4. Phase II site investigations 'Sep-rember of 1989) conducted by Bio National Cor;1r,ration in conjunction with Dames & Moore, included the drilling of free (5) soil borings with the completion of two (2) borings as monitoring wells (h;W5 and MW6). In December of 1989 Bio National Cctporation installed a cycle skimmer pump and prototype biologic treatment system operating on effluent from MW1. on January 9, 1991 WaterWork Corp, performed a. short, term step drawdown test and longer term (4 hr) constant rate pumping test using well MW6. During the test, drawdown in wells MW1, MW5, and MW6 were mon'tor{ad. The step drawdown test was performed to, (1), evaluate the productivity and efficiency of the well, and (2), to determine 'the optimum rate for the lunger term constant rata test. The step test indicated the well does not exhibit significant well f losses and is reasonably efficient. The semilog plot of the step test data is contained in Attachment 1. A rate of 1.5 gallons per minute (gpm) was selected for the longer term constant ::ate test. Semilog plots of drawdown versus time for wells MWl, MW5, and, MW6 are contained in Attachment 1 along with the semilog plot of •che recovery data from well MW6. The formation transmissivity and storage coefficient calculated from the test data are shown on fable 1. Interpretation of the monitoring well data is complicated somewhat by the effects of partial penetration. Because MW6 is screened in sand 5-8 feet deeper than wells MW1 and MW5 (Table 1) the hydrauli communication is potentially limited particularly fcr MW1. Well logs indicate a well, MW5, was drilled and sandpacked to a depth of 45 feet although casing extends only 37.5 ft. The uncased but i HSLR402.wp 1 _ -