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R603 UPDATE-12 12/22/92 UPDATE STATUS REPORT 12 NOVEMBER 17 - DECEMBER 18 1992 2 . 0 GROUND WATER 2. I LOCAL GROUND WATER FLOW Ground water flow direction in this region is to the west and towards south Stockton from the foothills of the Sierra Nevada Mountain Ranges, and towards the east from the Sacramento-San Joaquin Delta At present, encroachment of saline waters from the Delta is impairing the quality of the ground water in the Stockton area Based upon ground water elevation measurements obtained throughout the evaluation of this site, the overall local flow direction beneath this site is to the east--northeast at a relatively flat slope Slug tests performed on the monitoring wells (May 25, 1990) indicated hydraulic conductivity (K) , ranging from highs of 45 43 and 33 48 feet/day at MW9 and MWl respectively, to lows of 0 . 52 and 1 99 feet/day at monitoring wells MW2 and MW10 respectively These drastically different K values (in the above mentioned wells) along with the monthly depth to ground water measurements help determine if the ground water beneath the site is in a recharge or a discharge cycle If the ground water surface indicates flow from MW1 towards MW2 , a recharge cycle is occurring If the ground water surface + indicates flow from MW2 towards MWI, a discharge cycle is I occurring Measurements obtained on November 11, 1992 , (Figure 4A) , show a rise in ground water elevations . The flow direction is towards MW1 and MW5 The flow towards MW1 can be attributed to vapor extraction removing moisture from the vadose zone and capillary fringe with water replacement being provided by the water table This lowering of the ground water at MW1 is localized at the vapor recovery wells MW1, MW2 , MW3 and MW10 The flow gradient towards MW5 can be considered the normal gradient near this site This figure represents an end of the discharge cycle that started in February, 1992 and the beginning of a recharge cycle with the start of the rainy season. Figure 4B, represents the gradient beneath the site from ground water measurements obtained December 9, 1992 This figure is very similar to the November, 1992 measurements and shows a continual recharge in ground water elevations with the exception of MW5 , which showed a slight drop in ground water elevation m�- �.�or+ ;..ere obrai ned After the initiation of the lllese measureme a♦�s interim well purging by LTT and the decrease in ground water elevation at MW5 could be attributed to the purging activities by LTT. The dewatering valley created by vapor extraction at MW1, MW2 , MW3 and MW10 is more pronounced and indicates a larger area lJl. L r,1influence,14G, out to MWA frnm var�nr extraction on the ground vu water. PAGE 3