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-"tea <br /> CHEMICAL PROCESSORS, INC. <br /> Northern California Division <br /> i <br /> - • FIRf i <br /> A Burlington <br /> Environmental 4nc. <br /> VED <br /> Company San Joaquin County ENVlR MAR 5 1990 February 22, 1990 <br /> Public Health Services 0NMENIAL NEALT Project #1148 <br /> 1601 E. Hazelton Ave. PERi�i1TjSERVi N <br /> Stockton, CA 95201 CFS <br /> Attention: Darlene Reuss <br /> INTERIM GROUNDWATER REMEDIATION PROJECT <br /> -CHEVRON SERVICE-STAION 49.6465;'-5608 N:PERSHING AVE., 4 � <br /> STOCKTON, CALIFORNIA <br /> { Dear Ms. Reuss:. <br /> Chemical Processors, Inc. (Chempro) has been retained by Chevron to perform a <br /> pumping test at the above captioned site. Groundwater will be extracted from one <br /> well initially and discharged directly to the sanitary sewer once permitted. After the <br /> pumping test has been completed, the extraction system will remain in place and <br /> continue to discharge to the sanitary sewer. Additional extraction wells will be <br /> added if determined necessary by the pumping test. Chempro will proceed under <br /> self direction with the work described herein unless otherwise instructed by San <br /> Joaquin County or Chevron. <br /> AQUIFER TESTING <br /> A pumping test will be conducted in a new extraction well (well #9) to be <br /> constructed east of the underground storage tank complex. The pumping test will <br /> allow us to determine hydraulic properties of the aquifer, and to determine if <br /> additional extraction wells will be needed to capture contaminated groundwater <br /> beneath the site. The pumping test will consist of four parts: (1) step-discharge <br /> pumping, (2) constant discharge pumping, (3) water-level recovery measurements, <br /> _and (4) data analysis. <br /> The step discharge test will be used to determine well efficiency and the sustainable <br /> pumping rate. The constant discharge pumping test will be performed to gather <br /> data needed to determine aquifer properties, including the hydraulic conductivity <br /> and the radius of influence. The continuous pumping test will be run for up to 12 <br /> hours or longer if low hydraulic .conductivity values are estimated during the step <br /> discharge test. The water level recovery will then be recorded by a data logger until <br /> the water level has recovered to-at least 90% of-its original level. The recovery data <br /> will be used to verify the hydraulic conductivity values determined during the <br /> constant discharge test. Several methods (e.g., Jacob, 1963; Theis, 1935; and/or <br /> .Boulton, 1963) will be used to analyze the data. <br /> Water levels in the pumping well 'and up :to three surrounding wells will be <br /> monitored and recorded in the field with a pressure transducer/datalogger system. <br /> These instruments record the water level data automatically for later retrieval by a <br /> i <br /> 950 Gilman Street, Suite B <br /> Berkeley, California 94710 <br /> (415) 524-9372 <br />