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• <br /> Stantec Consulting Corporation <br /> L� 3017 Kilgore Road Suite 100 <br /> Rancho Cordova CA 95670 <br /> Tel:(916)861-0400 <br /> Fax:(916)861-0461-04 30 <br /> Stantec <br /> G1r�';AL1 <br /> October 17, 2008 <br /> Mr. Mike Infurna <br /> San Joaquin County Environmental Health Department <br /> 600 East Main Street � <br /> Stockton, California 95202 <br /> RE: Addendum to Interim Remediation Action Plan <br /> Former ARCO Service Station No. 443 <br /> 2478 E. Oak Street <br /> Stockton, California 95205 <br /> File No.: 77BP.00443.02.0136 <br /> Dear Mr. Infurna: <br /> This letter, prepared by Stantec Consulting Corporation (Stantec) on behalf of Atlantic Richfield <br /> Company (ARC), a BP Affiliated Company, presents an addendum to the Interim Remediation <br /> Action Plan dated July 10, 2008 and the Addendum to Interim Remediation Action Plan dated <br /> September 10, 2008 for the site referenced above. The original work plan called for the <br /> installation of four groundwater monitoring wells and the initiation of monthly groundwater <br /> extraction via vacuum truck. Based upon conversations with the regulator on October 6, 2008, <br /> and with the drilling company, the following modifications to the work plan have been prepared <br /> to address the regulator's concerns.. <br /> The soil boring for well MW-8 will initially be advanced to approximately 95 feet (ft) below <br /> ground surface (bgs) using a drill-rig equipped with an eight-inch diameter, continuous flight, <br /> hollow-stem auger as a pilot hole. Afterward, the soil boring will be advanced to a depth of 95 ft <br /> bgs using a drill-rig equipped with an 18-inch diameter, continuous flight, hollow-stem auger <br /> centered on the eight-inch pilot hole. An ten and 1/4 inch inside diameter, flush-threaded, steel <br /> casing will be set within the annulus of the auger. The final casing depth will be determined in <br /> the field based upon observed conditions in order to set the bottom of the casing in an <br /> impermeable layer. The area between the outside of the steel casing and the wall of the boring <br /> will then be filled with cement and/or grout to surface grade and allowed to set. The inside of <br /> the steel casing will be covered with a plug. After the boring has set for at least 24 hours, a drill- <br /> rig equipped with an ten-inch diameter, continuous flight, hollow-stem auger will be advanced <br /> down the inside of the steel casing of the boring to a depth of 120 ft. <br /> During advancement of the pilot hole and the advancement to terminal depth, soil samples will <br /> be collected at five-foot intervals using a steel split-spoon sampler driven approximately 24 <br /> inches using a 140-Ib hammer that is dropped 30 inches. A continuous core will be collected <br /> from MW-8 in two ft long samples beginning at a depth of 75 ft bgs. An attending geologist will <br /> log cuttings and sample in accordance with American Society for Testing and Materials (ASTM) <br /> D-2488 — Standard Practice for Description and Identification of Soils (Visual-Manual <br /> Procedure) under the direction of a State of California Professional Geologist or Professional <br /> Engineer. Soil cores will be screened in the field for the presence of volatile organic compounds <br /> using a photo-ionization detector(PID). All down-hole drilling equipment will be decontaminated <br /> 443 1RAP Addendum 10-08.doc 1 <br />