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GEOCON 0 0 CONSULTANTS,INC. GEOTECH N ICAL ■ E N V I R O N M E N T A t ■ MATERIALS low Project No. 59482-06-02 January 5, 2012 Mr. Mike Infuma San Joaquin County Environmental Health Department 600 East Main Street Stockton, California 95202-3029 Subject: 5400 AND 5606 PACIFIC AVENUE STOCKTON, CALIFORNIA CLEANUP AND ABATEMENT, ORDER NO. 5-00-707 CASE NUMBERS 390258 AND 390014 CHEVRON#306620(FORMER UNOCAL#5098) WELL DESTRUCTION WORKPLAN ADDENDUM Dear Mr. Infuma: As requested by the San Joaquin County Environmental Health Department (SJCEHD), we have prepared this addendum to AECOM's Well Destruction Workplan (Workplan) dated April 2011 for groundwater monitoring and remediation well destruction activities to be conducted at the former Montgomery Wards, LLC (Wards) auto service center located at 5400 Pacific Avenue and the former Unocal service station #5098 (Chevron Facility No. 306620), located at 5606 Pacific Avenue in Stockton, California. The Wards and Unocal sites are collectively referred to as the Site. These revisions are a result of multiple email conversations with Mike Infuma and Nuel Henderson of the SJCEHD regarding concerns with the procedures and methods outlined in the Workplan. The approximate site location is shown on Figure 1. The approximate locations of the wells to be destroyed are depicted on Figure 2. SCOPE OF SERVICES Field Activities Eighty-nine groundwater and remediation wells will be destroyed by either pressure grouting or overdrilling techniques. The proposed destruction method for each individual well is shown on Table 1. Descriptions of the methods and procedures involved with each of these proposed methods are presented below. Drilling Out 2-Inch-Diameter and 4-Inch-Diameter Polyvinyl Chloride (PVC) Wells Using a Hollow-Stem Auger Drilling Rig Welts MW-2, MW-3, MW-11, MW-16, MW-32, AS-33, VEW-IA, VEW-113, VEW-2A, VEW-213, VEW-3, VEW-4 and VEW-5 will be destroyed by drilling out the casing and annulus to the total depth of each well using a hollow-stem auger drilling rig equipped with a self-centering "stinger" bit. If the self-centering "stinger bit" should malfunction or be deemed unsuitable, appropriately sized drilling rods will be placed down the annulus of the well and angered around to ensure the augers stay centered on the well. The augers used to drill out each well will be at least the same size as was used when the wells were installed (8-, 11- and 12-inch-diameter). These wells are constructed of 2-, 3- and 3160 Gold Valley Drive,Suits 800 0 Randa Cordova,CA 95742-7515 0 Telephone 916.852.9118 0 Fax9l6.852.9132