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STATE OF CALIFORNIA GEORGE DRXMLOAN,&Vwnor <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL B�ARD— <br /> CENTRAL VALLEY REGION <br /> 3443 ROUTIER ROAD <br /> 8ACUMENTO,CA 48827-3048 <br /> 25 May 1989 <br /> Ms. Diane Hinson 3 <br /> San Joaquin Local Health District <br /> P. 0+ Box 2009 <br /> Stockton, CA 95201 <br /> WORK PLAN FOR ARCO STATION 434, 601 KETTLEMAN LANE, LODI, SAN JOAQUIN COUNTY <br /> We reviewed the 10 March 1989 work plan and supplied our comments to ARCO in a <br /> 27 March 1989 letter. Brown and Caldwell En ineering submitted a 25 April <br /> 1989 response to our letter. Our comments on this latest submittal by Brown <br /> and Caldwell are as follows: <br /> Soil Characterization Work <br /> 1 . The extent of contaminated soil west and north of borehole B-2 needs to <br /> be defined, Brown and Caldwell believes that additional borings west <br /> and north of B-2 are not "necessary for soil characterization purposes" . <br /> They have not explained their reasoning. There is a zone of highly <br /> t contaminated soil (hazardous waste levels) immediately above the ground <br /> 4 water surface that has not been delineated. We agree that it may have <br /> been transported there on ground water or the capillary fringe, but the <br /> source of the contamination was the leaking product line at the ARCO <br /> station, We recommend that ARCO have their consultant accurately <br /> delineate the lateral and vertical distribution of the contaminants in <br /> the soil . <br /> 3. We have no objection to Brown and Caldwell 's request not to take vapor <br /> meter readings on the nine continuous core samples. <br /> Proposed Modification to the Soil Characterization Work <br /> 1. We have no objections to vapor recovery wells being installed in <br /> the boreholes proposed to delineate soil contamination. Our only <br /> concern is that Brown and Caldwell proposes to screen these wells from 7 <br /> to 45 feet below grade, and have supplied no rationale for selecting <br /> this interval . Discreet screened intervals place at zones of <br /> x_ __ .contaminati_on_would facilitate_avmore_,efficient and cost effective soil <br /> remedfat'lon. � Ideally, we recommend that analytical results' of soil <br /> samples be used to identify the zones of contamination and the screened <br /> intervals should be designed accordingly, but the continuous core <br /> samples may make it possible to design' the screen interval of each well <br /> based on field data. They plan to use' field evidence to select the ' <br /> boreholes for vapor recovery well instlallations. We suggest that this <br /> field evidence also be used to select the best screen interval (s) for <br /> each well . <br /> ,4 I <br /> E <br /> -ti. <br />