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Pringle A,enue. Suit Ltiain of Cieek � WbodwaTd-C�de Consultants ' 2l . CA CA 9x596--.,.,vJ ' »159a5-3000 April 17, 1986 90304A Mr. Mike so LOF Glass 500 East Louise Lathrop, California 95330 Dear Mr. So: In response to your request we have prepared this letter which addresses the comments given by Mr. Eckman of the Regional Water Quality Control Board (RWQCB) and recommends actions to be taken to recover the remaining free oil from the 1985 spill. A proposal for the investigation and remediation of the February 1986 spill is covered under a separate letter. The recommendations included herein are based on our current knowledge of conditions at the site which does not include details of recovery operations or well measurements undertaken since May of 1985. The issue of contaminated soil removal is only addressed briefly as it is assumed that all free oil will be recovered and no soil removal will be required per Mr. Eckman's statements. The comments in question from Mr. Eckman are the suggestion to artificially raise the water table to enhance oil recovery and his concern of leaving too much oil in the pore spaces with the currently employed water table depression method of recovery. In principal we agree with Mr. Eckman in so much as recovery would be maximized under high water table conditions and that some free oil will remain in the pore spaces during water table drawdown. We do, however, feel that the advantages of raising the water table do not justify the costs and complexities associated with it. We also feel that a drawdown system similar to the current one be used is the most cost-effective method of recovery. Mr. Eckman's suggestion is to inject water into the substrate or flood the surface around the perimeter of the spill in an effort to maintain a high water table and create a hydraulic gradient towards the center of the spill. The oil migrating downgradient can then be recovered at a central location. Mr. Eckman also offers an alternate suggestion which is to raise the water table to ground level where the floating oil can easily be recovered. We evaluated Mr. Eckman's suggestions and found that although it is feasible in theory, several problems are involved with its implementation. Flooding is too difficult to control so additional injection wells would have to be installed to provide a continuous ridge of water around the spill including several inside the LOF building. The wells would require special design and construction to ensure maximum transmission of water to the aquifer. No hydraulic parameters are known about the aquifer but assuming an effective porosity of 15 percent, a Consuiiinq Enc.neers.Geologists rnd Environmental Scientists LIA Offices in Other Principal Cites CW