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10 <br /> San Joaquin County DIRECTOR <br /> Donna Heran,RENS <br /> p.9-U.!N C Environmental Health Department ASSISTANT DIRECTOR <br /> ,aLKf `P <br /> 600 East Main Street Laurie Cotulla,REHS <br /> vii ' , • . < Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> Carl Borgman, REHS <br /> Mike Huggins.REHS,RDI <br /> • c P • Website:www Sjgov.org/ehd Margaret Lagorio,REHS <br /> 4�rFOR� <br /> Phone: (209) 468-3420 Robert McCIellon,REHS <br /> Fax: (209)464-0138 Jeff Carruesw,REHS,RDI <br /> Kasey Foley,REHS <br /> August 11, 2008 <br /> Diggler and Wad LLC Mr. Sergio Moreschalchi <br /> Scott Damouny Atlantic Richfield Company <br /> 2707 E. Fremont St., Suite 14 PO Box 1257 <br /> Stockton, CA 95205 San Ramon, CA 94583 <br /> Subject: former ARCO Gas #443 Site Code: RO-1781 <br /> 2478 E. Oak Street APN: 14124023 <br /> Stockton, CA 95205 Global ID#: T0607798060 <br /> The San Joaquin County Environmental Health Department (END) has reviewed Interim <br /> Remedial Action Plan (TRAP) dated July 10, 2008, prepared by Stantec for the above <br /> subject site, and has the following comments. <br /> The TRAP proposes installing four monitoring wells for the required lateral and vertical <br /> plume delineation investigation and conducting monthly ground water batch extraction <br /> (GWE) from MW-1 S, MW-2S, and MW-1D as the interim remedial action. <br /> Three of the proposed monitoring wells are to be installed with screened intervals <br /> constructed at 40 feet to 60 feet below ground surface ('bgs). One well, MW-8, is <br /> proposed to be "cased"and the screened interval is proposed at 105' to 120' bgs. No <br /> details for this deep well were included in the TRAP. <br /> Construction and material details for the deep monitoring well (MW-8) are required to <br /> be submitted to and approved by the EHD before the well installation can proceed. <br /> Please provide an addendum that includes materials specifications and dimensions of <br /> the conductor casing for MW-8. Centralizers are required for this type of well and the <br /> details for their material and spacing must be included in the addendum. The EHD <br /> requires the cement grout annulus between the soil and the outer diameter (OD) of the <br /> conductor casing and the grout annulus between the OD of the PVC well casing and <br /> the inner diameter (ID) of the conductor casing to be no less than 2 inches. The <br /> addendum is to include a verbal description, as well as a well schematic/diagram of <br /> MW-8 that clearly shows these and all other proposed dimensions of the well. <br /> In addition, the EHD requires continuous coring/sampling from 100' bgs to total depth of <br /> the pilot hole for MW-8. The screened interval for this monitoring well is to be placed at <br /> the most permeable layer identified and the conductor casing is to end in the least <br /> permeable layer just above the well's screened interval. <br />