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Tre a a CRA M ..OMPANY <br /> October 30, 1996 <br /> Mr. Alex MacDonald <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 3443 Routier Road, Suite A. <br /> Sacramento, California 95827-3098 <br /> SUBJECT: Review of Regulatory Comments to the August 2, 1996 Permanent <br /> Monitoring Well Replacement Workplan-Lathrop Groundwater Remedial <br /> Program. Reference #197. <br /> Dear Alex: <br /> Occidental Chemical Company's consultant, TreaTek-CRA Company (TreaTek) has <br /> completed a review of the comments contained in your October 2, 1996 correspondence. <br /> These comments were in regards to several issues pertaining to the. Permanent <br /> Monitoring Well Replacement Workplan for the Lathrop Groundwater Remedial Program. <br /> In response to the comments and issues raised in the correspondence, TreaTek has <br /> prepared the following amendments to the Permanent Monitoring Well Replacement <br /> Workplan: <br /> o TreaTek agrees that the selection of screen slot size and the appropriate <br /> filter pack should be based on aquifer material characteristics. To <br /> determine aquifer characteristics, a small diameter mud rotary pilot <br /> borehole will be installed adjacent to each scheduled replacement <br /> monitoring well location. The boreholes will be drilled to a depth of ten feet <br /> above the preselected mid-screen depth of the monitoring well being <br /> replaced. The borehole will then be advanced and continuously sampled <br /> an additional 20 feet. The 20 foot continuous core will be placed in core <br /> boxes and logged by a registered geologist. A best available <br /> representative sample of permeable aquifer material will be collected and <br /> submitted to a materials laboratory for grain size distribution analyses. <br /> Based upon these analyses, design calculations will be performed to <br /> determine the most efficient well intake system (screen slot size/length and <br /> Environmental Technology & Remediation Systems <br /> 2055 Niagara Falls Blvd. 2441 Crowne Point Drive 202 Val Dervin Parkway <br /> Suite Three Cincinnati, OH 45241 Suite 400 <br /> Niagara Falls, NY 14304 513/326-7600 Stockton, CA 95206 <br /> 716/297-2160 FAX 513/326-7601 209/983-6810 <br /> FAX 716/297-2265 FAX 209/983-6960 <br />