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+wGENs OESICJEAS[U6LLiM'f5 Table 3 Hydraulic Conductivity ' Well Kfeet/min ( ) K (cm/sec) ' MW-4 1 47 x 10-3 7 47 x 101 MW-6 1.497 x IV 7 61 x 10-4 IL MW-8 2 17 x 10-3 1 10 X 10-3 ' The geometric mean hydraulic conductivity value is 8 6 x 10-3 cm/sec (1 7 x 10-3 ft/min) The calculated hydraulic conductivities for MW-4 and MW-6 are typical for silty sand and sand for MW-8 (Freeze and Cherry, 1979) To study the effect of tidal fluctuations on groundwater elevation at the site, WESTON measured groundwater levels during a 4.5 hour period in November 1991. Between high and low tide a ' total groundwater elevation decrease of 0 18 feet in MW-4 was observed During the same period the tidal elevation at the Port of Stockton decreased by approximately 1.7 feet ' 2.2.5 Effective Porosit Because of the difficulties involved in accurately determining effective porosity, accepted literature values for the type of soil comprising Zone 4 were used to estimate this parameter Freeze and Cherry (1979) give a range of effective porosity for silt of 0 25 to 0 5 To be conservative the effective porosity of Zone 4 is assumed to be 0 4 I2.2.6 Advective Groundwater Velocity ' The advective velocity of ground water in the direction parallel to ground water flow is given by ' v = -Ki/ne where v = average advective ground water velocity (seepage velocity) (L/T) ' K = hydraulic conductivity (L/T) (1 7 x 10-4 ft/min) I = gradient (0 003) ne = effective porosity (0 4) Using this relationship in conjunction with site-specific data, the average advective groundwater ' velocity at the site is 0 018 feet per day (ft/day) or approximately 6 7 feet/year 2.2.7 Inor anic Groundwater Chemistry and Geochemical Indicators of Biodegradation ' A variety of water quality parameters were analyzed from groundwater samples collected from MW-2A, MW-7 and MW-9 in September 1997 These parameters are important for evaluating water quality conditions and as geochemical indicators of biodegradation of fuel hydrocarbons LSPROJECr555ANJ000ISMACr1ONPL 11