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t <br />PARS(Orms • <br />Parsons Engineering Science, Inc. A Unit of Parsons Infrastructure & Technology Group Inc. OjC G� <br />2101 Webster Street • Suite 700 • Oakland, California 94612 • (510) 891-9085 • Fax (510) 835-rTk <br />G <br />March 10, 1999 _ <br />Ref: 729801 <br />California Regional Water Quality Control Board1 +r U / <br />Central Valley Region 3 A�j t� <br />3443 Routier Road, Suite A <br />Sacramento, California 95827-3098 <br />Attention: Mr. Philip S. Isorena <br />Subject: Response to Comments on Letter Reports from Parsons Engineering Science <br />and Quarterly Monitoring Report No. 4 for 1998 <br />App re e�iornia <br />e ruc ures orporation Facility <br />Stockton, C <br />Reference: Review of Several Documents, <br />BP Oil/Applied Aerospace, Stockton, San Joaquin County <br />Letter from Philip Isorena, CRWQCB, to Werner Sicvol, BP Oil Company <br />Dated: 11 February 1999 <br />Dear Mr. Isorena: <br />This letter is submitted by Parsons Engineering Science, Inc. (Parsons) on behalf of BP <br />Oil Company. It addresses your comments and reiterates points discussed in our <br />telephone conversation on February 18. The comments are addressed in their order of <br />appearance in the above -referenced letter. The final topic of this letter is a proposal to <br />address the leading edge of the main plume (e.g. MW -5R) and the more dilute plume <br />northeast of the AASC facility through a program of further sampling, modeling, and <br />alternatives analysis. The details of this program are subject to modification based on the <br />outcome of the field investigation, results of model simulations, and additional <br />information that may be gained through operation of the remedial wells. <br />RWQCB Comments on Simulation of Proposed Groundwater Extraction System <br />Response to Item 1. The groundwater extraction and treatment system (GWETS) is not <br />expected to capture groundwater contamination that has already migrated downgradient <br />of the capture zone depicted in the capture zone simulation report (Parsons, 1998c). <br />However, MW -5R, 6, 8 and other wells will be in the downgradient "shadow" of the <br />capture zone of the GWETS and are expected to exhibit decreasing concentrations in the <br />future due to mass removal by the treatment system. <br />Response to Item 2. The groundwater extraction pump intakes are set approximately four <br />feet from the bottom of each well. The drawdown at each well is controlled by a high - <br />'i <br />LED PARSONS <br />