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• MEMORANDUM • <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION <br /> 3443 Routier Road, Suite A Phone: (916) 255-3000 <br /> Sacramento, CA 95827-3098 CALNET: 8-494-3000 <br /> TO: Antonia K. J. Vorster FROM- James Taylor <br /> Senior WRC Engineer Associate Engineering Geo ogist <br /> DATE: 12 April 1993 SIGNATURE: <br /> SUBJECT: DRAFT COMPREHENSIVE REMEDIAL INVESTIGATION/FE BILITY STUDY (RI/FS) WORK <br /> PLAN AMENDMENTS AND EVALUATION OF DETECTION LIMITS FOR THE COMPREHENSIVE <br /> PHASE I REMEDIAL INVESTIGATION (RI), DEFENSE DISTRIBUTION REGION WEST <br /> (DDRW), TRACY, SAN JOAQUIN COUNTY <br /> I have reviewed the Draft Comprehensive RI/FS Work Plan Amendments for DDRW, Tracy <br /> submitted on 11 February 1993. I have also reviewed the Evaluation of Detection <br /> Limits for the Comprehensive Phase I RI submitted on 20 January 1993. These <br /> submittals were prepared by Montgomery Watson Engineers for the Corps of Engineers <br /> (CoE) . The amendments to the Comprehensive RI/FS Work Plan and the detection limits <br /> proposed for the Phase I RI are acceptable. However, there are some important <br /> omissions and concerns regarding Montgomery Watson's approach to the Phase I RI that <br /> need to be addressed. The omissions include Board comments that were addressed in <br /> Response to Comments prepared by Woodward-Clyde Consultants, but failed to be <br /> incorporated into Montgomery Watson's approach to the Phase I RI field activities. <br /> These omissions and concerns were pointed out at the 23 March 1993 Project Manager's <br /> meeting to discuss the upcoming Phase I RI activities and are discussed in more <br /> detail below. <br /> MAJOR CONCERNS <br /> Underground Storage Tank (UST) Investigation. At the 23 March 1993 meeting <br /> Montgomery Watson presented an outline, Overview of Phase I RI/FS Field <br /> Investigation Activities. This outline includes a figure, Conceptual Model for Soil <br /> Boring/HydroPunchTM Investigation. The figure illustrates that proposed soil <br /> borings will be drilled outside former UST excavations. This concept does not <br /> follow the Tri-Regional Board Staff Recommendations for Preliminary Investigation <br /> and Evaluation of Underground Tank Sites. Sampling should be based on the size of <br /> the tank and located within the former tank excavation. For example, a tank with a <br /> capacity greater than 10,000 gallons requires that three or more samples be <br /> collected at the ends and middle, or generally spaced along the length, of the tank. <br /> A tank with a capacity of 1000 to 10,000 gallons requires that two samples be <br /> collected, one at each end of the tank. The proposed methods of investigation are <br /> unacceptable and must be modified prior to implementation of fieldwork. <br /> Hydro Punch'" samples should be located downgradient and as close as possible to the <br /> former UST excavation. <br /> During the 23 March 1993 meeting, DDRW, Tracy pointed out that many of the former <br /> UST sites were sampled during tank removal . As previously recommended in our <br /> 9 April 1993 letter, existing data must be reviewed to reduce the number of samples <br /> proposed for sites that may test negative for contamination. This would allow for <br /> increased sampling at sites where contamination is suspected or unknown at little or <br /> no additional expense. EPA expressed concern about the quality of that data, but <br /> agreed that it was a worthwhile exercise. Existing UST data were previously <br />