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26056 N. Thornton Road, Stockton <br />Page 2 <br />screen intervals may be more appropriate. Continuous core soil sampling or <br />cone pentrometer testing should be used to determine the length and location of <br />the screen interval for the deeper screened monitoring wells. <br />The reason or justification for measuring the water levels in monitoring well MW1, <br />MW2 and MW4 every 20 minutes for a five-day period was not clear. Provide a <br />justification for this work and explain how it will be used as a preliminary <br />evaluation for performing groundwater extraction from MW3 and MW4. <br />The work plan states that a well performance test (step drawdown test) will be <br />performed on MW3 and MW4. Provide details on how the test will be conducted. <br />if needed, a constant rate pumping test should be designed and conducted to <br />derive aquifer parameters that can be used to quantify plume capture if <br />groundwater extraction is necessary for remediation. EHD does agree that the <br />extracted water will have to be disposed of off-site. <br />EHD has directed you to collect groundwater samples from all the monitoring <br />wells and the Thornton municipal well each quarter of the calendar year, have <br />the samples analyzed for TPH-g, benzene, toluene, ethyl-benzene, xylene, <br />MTBE, DIPE, ETBE, TAME, TBA, 1,2-DCA and EDB using EPA Method 8260B <br />and submit the data and quarterly report to Geotracker, the State Water <br />Resources Control Board data base. Ron Rall at the San Joaquin County Public <br />Works Department (209 468-3090) is to be contacted to gain access for <br />collection of groundwater samples from the Thornton municipal well and copies <br />of the analytical results of those water samples are to be submitted to him. This <br />sampling and analysis must be initiated by February 15, 2006. <br />If you have any questions contact me at (209) 468-3449 or Harlin Knoll, Senior <br />REHS at (209) 468-3442. <br />Donna Heran, REHS, Director <br />Environmental Health Department <br />IYAA.Att.AJ <br />Margaret Lagorio, Supervising REHS <br />Unit IV <br />c: H2OGEOL — Gary Lowe <br />San Joaquin County Public Works — Ron Rail <br />CVRWQCB — Jim Barton