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L 4 <br /> R603 UPDATE-15 4/8/93 <br /> [ stripping inside the "ConVault°' was obtained for certified <br /> - ! laboratory analysis, before dumping approximately 600 gallons of <br /> kthis water to the City of Stocktons sanitary sewer, see Table 4 <br /> ; and Appendix A. <br /> � As of February 18, 1993 , a total of 16806 gallons of gasoline <br /> grange hydrocarbons have been removed from the soil and ground <br /> : water beneath this site . Previously removed floating product <br /> (40 . 25 gallons) , condensation. from vapor extraction (48 .5 <br /> ' , gallons) , projected petroleum hydrocarbon in situ oxidation CO2 ' <br /> � . , vapor recovery (43242 pounds/6 . 25 pounds/gallon = 6.918 . 7 gallons) <br /> and vapor extraction-destruction of hydrocarbons (61242 <br /> pounds/6 . 25 = 9798 . 7 gallons) . No chlorinated solvents were t <br /> detected in chromatogram- comparisons; "i.e . " 1 2 -Dichloroethane <br /> (DCE) - retention time 2 . 079 minutes, Trichloroethylene (TCE) - <br /> rretention time 3 . 023 minutes and Tetrachloroethylene (PCE) - <br /> Iretention time 3 . 75 minutes . <br /> UPDATE STATUS REPORT 15 (FEBRUARY 25, - MARCH 18, 1993) . <br /> k 2 .0 GROUND WATER <br /> I <br /> k2. 1 LOCAL GROUND WATER FLOW f <br /> iGround 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 /> :r Joaquin Delta. At present, encroachment of saline waters from 11 <br /> Tithe Delta is impairing the quality of the ground water in the <br /> Stockton area. <br /> i <br /> lBased upon ground water elevation measurements - obtained <br /> kthroughout the evaluation of this site, the overall local flow <br /> Idirection 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 /> r ' 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 cycle is occurring. If the ground water surface <br /> ; indicates flow from MW2 towards MW1, a discharge cycle is <br /> occurring. Starting on December 1, 1992, LTT has been <br /> a tperforming twice a week purging of selected wells; the recharge <br /> hand 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) . The twice a week well purging is <br /> creating a ground water low "cone of depression" beneath the site i . <br /> near MW1 and MW2 , see Figures 4A - Janaury, 1993 and . 4B - <br /> February, 1993 . l <br /> ,� If I, • <br /> PAGE 2 <br />