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REG 603 UPDATE-6 2/21/92 <br /> • <br /> south, southwest and southeast with a ridge forming in the slower <br /> velocity sediments from MW2 towards MW10 and then out to MW4. <br /> This figure indicates that the period of discharge has met its <br /> limit with a pronounced valley forming at MW1 and pronounced <br /> ridges forming at the lower velocity wells MW2, MW10, MW4 and MW9, <br /> see Figure 4B. <br /> Figure 4C represents the ground water gradient from measurements <br /> obtained during the December 17, 1991, quarterly ground water <br /> sampling. The flow direction is generally to the east and <br /> northeast with a basin at MW10 . This figure represents a period <br /> of recharge, most likely from the precipitation that occurred in <br /> the Stockton area during late November and early December. The <br /> basin at MW10 can be attributed to two factors; the slower <br /> recovery of the silty clayey sands and also to vapor extraction, <br /> dewatering of the well. <br /> Depth to ground water measurements obtained on January 21, 1992, <br /> show a continuation of the recharge cycle with a trough extending <br /> from MW1 towards MW2 primarily be produced by vapor extraction, <br />. see Figure 4D. <br /> 2. 2 GROUND WATER QUARTERLY SAMPLING AND PROCEDURES <br /> Ground water samples have been collected since December 9, 1988, <br /> see Table 1. These samples were collected by a WEGE geologist and <br /> "Chain of Custody" hand delivered on ice to a state certified <br /> testing laboratory (McLaren Analytical or Chemtech (MATRIX) <br /> Analytical Laboratories) for chemical analyses. These samples <br /> were analyzed for TPH, and BTEX concentrations using EPA Methods <br /> 8015 and 602 respectively. Since diesel has never shown up in the <br /> sample results, the samples obtained from 11/27/90 and later were <br /> analyzed using EPA methods 5030 and 602 for Total Fuel <br /> Hydrocarbons and BTEX, see Appendix B. Complete chemical results <br /> are presented in Table 1 of this report. <br /> Before water "purging" or sampling commenced, a ground water <br /> interface probe (resistivity meter) was lowered into each well and <br /> A. ptI, tv water „a as— m nt-o tier re�i+r deli 1�Tavi- a �]'1 Ll l+ia71V <br /> e ei ..ae u.�ui eAK as a.0 nc:.�.e LarVVL...V\.a. as.r.r..., t"-- l <br /> designed bailer was lowered into the water to determine if <br /> gasoline product was floating on the water. If product was <br /> observed, product thickness was measured and ground water <br /> elevations were recalculated to compensate for the weight of <br /> gasoline. Monitor wells that contained gasoline product were then <br /> "Purged" until depletion of the floating product was observed. <br /> Approximately a quart of gasoline was recovered by this method <br /> from MW1 on 11/27/90. The recovered product is presently being <br /> stored with the ground water produced from "purging" the monitor <br /> wells for sampling, on site in the 1000 gallon "ConVault" . <br /> PAGE 4 <br />