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R603 UPDATE-14 3/25/93 <br /> UPDATE STATUS REPORT 14 JANUARY 19 - FEBRUARY 25 1993) . <br /> 2. 0 GROUND WATER <br /> 2 I LOCAL GROUND WATER FLOW <br /> Ground water flow direction in this region is to the west and <br /> towards south Stockton from the foothills of the Sierra Nevada <br /> Mountain Ranges, and towards the east from the Sacramento-San <br /> Joaquin Delta At present, encroachment of saline waters from <br /> the Delta is impairing the quality of the ground water in the <br /> Stockton area. <br /> Based upon ground water elevation measurements obtained <br /> throughout the evaluation of this site, the overall local flow <br /> direction beneath this site is to the east-northeast at a <br /> relatively flat slope . Slug tests performed on the monitoring <br /> wells (May 25 , 1990) indicated hydraulic conductivity (K) , <br /> ranging from highs of 45 43 and 33 48 feet/day at MW9 and MW1 <br /> respectively, to lows of 0 52 and 1 . 99 feet/day at monitoring <br /> wells MW2 and MW10 respectively These drastically different K <br /> values (in the above mentioned wells) along with the monthly <br /> depth to ground water measurements help determine if the ground <br /> water beneath the site is in a recharge or a discharge cycle . If <br /> the ground water surface indicates flow from MW1 towards MW2 , a <br /> recharge cycle is occurring. If the ground water surface <br /> indicates flow from MW2 towards MWI, a discharge cycle is <br /> occurring Starting on December 1, 1992 , LTT has been <br /> performing twice a week purging of selected wells, the recharge <br /> and discharge cycles can now only be determined by the relative <br /> elevations of wells that are not being purged by LTT (MW4, MW5, <br /> MW6, MW7, MW9, MW11 and MW12) <br /> Figure 4 , represents the gradient beneath the site from ground <br /> water measurements obtained February 8 , 1993 . This figure shows <br /> a continued rise of the ground water beneath this site in the <br /> wells that are not being purged by LTT. The dewatering valley <br /> created by vapor extraction at MW1, MW2, MW3 and MW10 , and the <br /> purging of these wells along with MW8 , is more pronounced and <br /> indicates a larger area of influence than previously shown in <br /> UPDATE REPORT 13 (January 15, 1993 ground water gradient map) . <br /> 2 2 GROUND WATER QUARTERLY SAMPLING <br /> Ground water samples were collected on December 9, 1992 , see <br /> Table 1 . These samples were collected by a WEGE sample <br /> technician and "Chain of Custody" hand delivered on ice to a <br /> state certified testing laboratory (MATRIX Analytical <br /> Laboratories) for chemical analyses These samples were analyzed <br /> for TPH and BTEX concentrations using EPA Methods 8015 and 602 <br /> respectively. Since diesel has never shown up in the sample <br /> results, the samples obtained on 11/27/90 and later were analyzed <br /> using EPA methods 5030 and 602 for Total Fuel Hydrocarbons and <br /> BTEX. The next quarterly sampling will occur in March, 1993 . <br /> PAGE 3 <br />