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R603 UPDATE--13 2/15/93 UPDATE STATUS REPORT 13 DECEMBER 18 1992 - JANUARY 19 1993) . 2 . 0 GROUND WATER 2. 1 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 MW1 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 MW1, a discharge cycle is occurring Starting on December 1, 1992, LTT has been performing twice a week purging of selected wells, the recharge and discharge cycles can now only be determined by the relative elevations of wells that are not being purged by LTT (MW4 , MW5, MW6, MW7 , MW9, MW11 and MW12) . Figure 4 , represents the gradient beneath the site from ground water measurements obtained January 15, 1993 . This figure shows a continuation of the rising of the ground water beneath this site in the wells that are not being purged by LTT. The dewatering valley created by vapor extraction at MW1, MW2, MW3 and MW10 and the purging of these wells along with MW8 is more pronounced and indicates a larger area of influence as was previously shown in UPDATE REPORT 12 (December 9, 1992 ground water gradient map) 2. 2 GROUND WATER QUARTERLY SAMPLING Ground water samples were collected on December 9, 1992 , see Table 1 . These samples were collected by a WEGE sample technician and "Chain of Custody" hand delivered on ice to a state certified testing laboratory (MATRIX Analytical Laboratories) for chemical analyses These samples were analyzed for TPH and BTEX concentrations using EPA Methods 8015 and 602 respectively. Since diesel has never shown up in the sample results, the samples obtained on 11/27/90 and later were analyzed using EPA methods 5030 and 602 for Total Fuel Hydrocarbons and PAGE 3