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PROBLEM ASSESSMENT REPORT 8131 Pacific Ave , Stockton, CA Aegis Project No 90-020 Page 9 3. 3 HYdroaeoZogic Conditions Monitoring wells were drilled to 10 feet below first ground water which was encountered approximately 55 feet below grade. Ground ' water elevations were measured on July 23 , 1990, prior to collecting ground water samples. All water level measurements were made from the surveyed well head elevations and measured to . 01 feet. Well head elevations were surveyed and referenced to an assumed datum of 100 feet above sea level by a California Licensed Surveyor. Table 3 summarizes the ground water elevations. Figure 5 is a ground water elevation contour map. As indicated by Figure 5 ground water flow direction is to the southeast. The calculated hydraulic gradient is 0. 008 ft/ft. A slug test was performed in monitoring well MW-3 to estimate the transmissivity (T) , storativity (S) , and hydraulic conductivity ' (K) in the aquifer. The slug test consisted of dropping a five foot long, three inch diameter PVC pipe, capped at both ends and filled with clean sand into the well (slug in) . A pressure transducer was placed below the slug and connected to an Aqua Star data logger which recorded the changes in water level over time. The same process was followed when the slug was removed (slug out) . A software package titled Graphical Well Analysis Package (Dansby, GWAP, 1987) was used to analyze the data. GWAP consists of a curve matching program that utilizes the Cooper, Bredehoeft and Papadopulos method (Cooper, et. al . 1967 . ) . The I values for S ranged from 1. 111 x 10-4 to 1. 111 x 10-2 , T ranged from = 1. 499 x 102 to 1. 845 x 102 gallons per day per foot (gpd/ft) and K ranged from 1. 478 x 102 to 1.819 x 102 gallons per day per square foot (gpd/sq ft) . Data from the slug test is included in Appendix F. The well identification number indicates the type of slug test completed MW3d is the slug in test and MW3u3 is the slug out test. 3.4 Ground Water Analysis Ground water samples were collected from the monitoring wells on July 23 and 24 1990. Ground water samples were analyzed for PHV EPA Method 5030/GC/FID and BTEX by EPA Method 602 . Additionally, ground water samples collected from MW-1 and MW-3 were analyzed for total and fecal coliform. Analyses of ground water samples for total and fecal coliforfu was requesr-ed by San Joaquin County. Table 4 summarizes the ground water analytical results. All three ground water samples contained PHV above detection limits. The ground water sample collected from MW-1 contained 0 . 35 ppm PHV, 0 . 0019 ppm benzene, 0. 0015 ppm toluene, 0 . 006 ppm ethyl benzene, and 0. 002 ppm xylenes. The ground water sample collected from MW-2 contained 1. 9 ppm PHV, 0. 044 ppm benzene, 0. 042 ppm toluene, 0. 0071 ppm ethyl benzene, and 0. 021 ppm xylenes. The ground water sample collected from MW-3 contained 63 ppm PHV, 10 ppm benzene, 18 ppm toluene, 1.8 ppm ethyl benzene, and 11 ppm xylenes.