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-a. .ate -a <br /> 11�1 <br /> a <br /> PRELIMINARY HYDROGEOLOGIST ASSESSMENT REPORT <br /> 148N West Frontage Road <br /> Manteca, California <br /> Delta Project No. 40-88-479 <br /> Page 8 <br /> 3.4 Site Hydroeeolot!y <br /> The depth to ground water at the site was measured on May 23, 1989, and ranged from 28.36 feet below <br /> grade in MW-4 to 29.84 feet below grade in MW-3. Ground water levels recorded in monitoring wells <br /> at.the.site to date are presented iwTable ,Contours of the water table shown in Figure 6 are based <br /> on the May 23, 1989,monitoring event. The water table surface is relatively uniform. The ground water <br /> elevation contour map indicates flow to the northeast with an approximate gradient of 0.0027 foot/foot. <br /> From the hydrograph, Figure 7, a decrease in the water table of over 1 foot is noted between the June <br /> 7, 1989, and the June 27, 1989, monitoring events. <br /> To determine the hydraulic conductivity of the water-bearing materials at the site, slug tests were <br /> performed in each monitoring well in accordance with methods presented by Bower and Rice (1976). <br /> I: Results of the slag tests are summarized in Table 5. Hydraulic conductivity values range from 2.14 <br /> feet/day at MW-4 to a high of 8.69 feet/day at MW-3. The average hydraulic conductivity of the four <br /> monitoring wells is 6.28 feetiday. The average linear velocity is expected to shift periodically with <br /> hydraulic gradient changes related to seasonal ground water level fluctuations. The average rate of ground <br /> water movement at the site based on the average hydraulic conductivity and.an estimated effective porosity <br /> i> <br /> �- (0.30)equals 0.0565 feet/day. The average Iinear velocity is expected to shift periodically with changes <br /> Fin the hydraulic gradient related to seasonal ground water level fluctuations. The average velocity of 0.056 <br /> footlday was derived from the following equation (Freeze and Chzrry, 1979): <br /> V — KI <br /> n <br /> Where: V = Average linear velocity <br /> K = Hydraulic conductivity. <br /> I = Hydraulic gradient. <br /> R = Effective porosity. <br /> At the site: V = (6.28 feet/ft�0027 fect/feet) <br /> 0.30 <br /> V = 0.0565 feet/day = 20.6 feet/year <br /> NOTE: n - Estimated. <br /> k:-Averaged. <br />