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------------ <br /> - URS <br /> --- --URs <br /> September 14, 2005 b <br /> r. <br /> Ms. Lori Duncan,REHS 2168 h <br /> Unit IV-Site Mitigation 0664 <br /> San Joaquin County Environmental Health Department <br /> 304 East Weber Avenue,Third Floor <br /> Stockton,California 95202-2708 <br /> k <br /> RE: Workplan for the Abandonment of a Groundwater Monitoring Well, Installation of an <br /> Interim Soil Vapor Extraction/Air Sparge Groundwater Treatment System, and <br /> Installation of Groundwater Monitoring Wells—Addendum <br /> Former ARCO Station No. 2168 f <br /> 441 West Charter Way 6 <br /> Stockton,California 94570 <br /> Dear Ms.Duncan: <br /> On behalf of Atlantic Richfield Company (ARCO, a BP-affiliated company), URS Corporation <br /> Americas (URS)has prepared this addendum to the URS submitted Workplan for the Abandonment of a <br /> Groundwater Monitoring Well, Installation of an Interim Soil Vapor Extraction/Air Sparge Ground- <br /> water Treatment System, and Installation of Groundwater Monitoring Wells dated June 9, 2005 to <br /> present the following modifications to the scope of work: <br /> • Abandonment of seven onsite vapor wells; <br /> • Installation of one additional groundwater monitoring well;and <br /> k <br /> • Installation of remediation wells below grade with an asphalt covering. <br /> MODIFIED SCOPE OF WORK <br /> Well Destructions <br /> Vapor wells VW-2, VW-3, VW4, VW-5, VW-6, VW-9, VW-12, and VW-13 will be abandoned <br /> properly by a licensed drilling contractor at the direction of a URS geologist. The other on-site vapor <br /> wells will be included as part of the interim remediation system Vapor well locations are shown on <br /> Sheet 1. <br /> Vapor wells will be destroyed by pressure grouting and then overdrilling the top 5 feet with 10-inch, <br /> outside-diameter (OD),hollow-stem augers (HSAs) and filling with a Portland cement grout containing <br /> <5%bentonite powder(grout)to the surface. <br /> Groundwater Monitoring Well Installation <br /> One additional groundwater monitoring well will be installed in the north eastern portion of the site.The <br /> boring will be drilled with an 8-inch OD HAS-equipped drill rig.Soil samples will be collected at 5-foot <br /> intervals during drilling using a modified California split-spoon sampler. Soil samples will be used for <br /> URS Group,Inc. <br /> Crown Corporate Center j <br /> 2870 Gateway Oaks Drive,Suite 300 <br /> Sacramento,CA 95833 <br /> Tel:916.679.2000 <br /> Fax 916.679.2900 KAWprocessUS BP ARCW2168\2005 System lnstallation%SVE-AS SyslnsWP Addendum.doc 1 <br /> r <br />