SITE INFORMATION AND CORRESPONDENCE

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fir • San Joaquin County DIRECTOR Donna Heran,REHS Environmental Health Department ,p ASSISTANT DIRECTOR 600 East Main Street Laurie Cotulla,REHS Stockton, California 95202-3029 PROGRAM COORDINATORS 1 lY_ Carl Borgman,REHS RDI °q . ' - �°' • Website:www.s/gov.o9r /ehd Mike Huggins,REHS, �r F oRt� Margaret Lagorio,REHS Phone: (209)468-3420 Robert McClellon,REHS Fax: (209) 464-0138 Jeff Carruesco,REHS,RDI Kasey Foley,REHS August 11, 2008 Diggler and Wad LLC Mr. Sergio Moreschalchi Scott Damouny Atlantic Richfield Company 2707 E. Fremont St., Suite 14 PO Box 1257 Stockton, CA 95205 San Ramon, CA 94583 Subject: former ARCO Gas #443 Site Code: RO-1781 2478 E. Oak Street APN: 14124023 Stockton, CA 95205 Global ID#: T0607798060 The San Joaquin County Environmental Health Department (EHD) has reviewed Interim Remedial Action Plan (TRAP) dated July 10, 2008, prepared by Stantec for the above subject site, and has the following comments. The IRAP proposes installing four monitoring wells for the required lateral and vertical plume delineation investigation and conducting monthly ground water batch extraction (GWE) from MW-1 S, MW-2S, and MWAD as the interim remedial action. Three of the proposed monitoring wells are to be installed with screened intervals constructed at 40 feet to 60 feet below ground surface ('bgs). One well, MW-8, is proposed to be "cased" and the screened interval is proposed at 105' to 120' bgs. No details for this deep well were included in the TRAP. Construction and material details for the deep monitoring well (MW-8) are required to be submitted to and approved by the EHD before the well installation can proceed. Please provide an addendum that includes materials specifications and dimensions of the conductor casing for MW-8. Centralizers are required for this type of well and the details for their material and spacing must be included in the addendum. The EHD requires the cement grout annulus between the soil and the outer diameter (OD) of the conductor casing and the grout annulus between the OD of the PVC well casing and the inner diameter (ID) of the conductor casing to be no less than 2 inches. The addendum is to include a verbal description, as well as a well schematic/diagram of MW-8 that clearly shows these and all other proposed dimensions of the well. In addition, the EHD requires continuous coring/sampling from 100' bgs to total depth of the pilot hole for MW-8. The screened interval for this monitoring well is to be placed at the most permeable layer identified and the conductor casing is to end in the least permeable layer just above the well's screened interval.