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v1117 Lone Palm Avenue, Suite B <br /> Modesto, CA 95351 <br /> www.atcassociates.com <br /> 209-579-2221 <br /> ASSOCIATES I N C . Fax 209-579-2225 <br /> Environmental,Geotechnical and Materials Engineers <br /> May 2, 2006 <br /> 54.22493.0001 <br /> MAY 9' ,, 2006 <br /> Ms. Lori Duncan ENVIRONMENT HEALTH <br /> San Joaquin County Environmental Health Department PERMIT/SERVICES <br /> 304 E. Weber Street, Third Floor <br /> Stockton, California 95202 <br /> Subject: Addendum to Proposed Work for 1112 East Harding Way, Stockton, California <br /> Dear Ms. Duncan: <br /> 9 ) x-1 <br /> ATC Associates Inc. has prepared this letter to serve as an addendum to ATC's Amg�005 <br /> Corrective Action Plan prepared on behalf of Mr. Robert Egginian for the installation of three <br /> vapor wells and one air sparge well, and the performance of a vapor extraction/air sparge pilot <br /> test at the above referenced site (Figure 1). <br /> SCOPE OF WORK <br /> Planning and Permits <br /> Upon approval of this addendum and boring locations by the EHD, ATC will,prepare an <br /> application to advance the borings in the City of Stockton right-of-way property. Upon receipt <br /> of the city's encroachment permit, ATC will provide a copy to the EHD and submit a permit and <br /> fees to the EHD. ATC will also schedule field personnel and equipment, notify Underground <br /> U Services Alert to locate underground utilities as required, and perform any other necessary field <br /> I preparation and job start-up activities. <br /> Construction of Air Some and Vapor Wells <br /> �y y To determine the lateral and vertical extent of soil and groundwater contamination at the site, and <br /> to evaluate the feasibility of vapor extraction as a remedial alternative for cleanup at the site, a <br /> t total of three vapor extraction wells and one air sparge well will be installed at the project site <br /> � / (Figure 2). <br /> The vapor extraction wells will be constructed of 2-inch diameter, schedule 40 PVC casing and <br /> 0.010 slot size screen (Figure 3). The bottom of the screen interval will be fitted with an end <br /> plug and the top of the casing will be fitted with an expandable, water-tight, locking cap. A well <br /> screen length in the vapor extraction wells will extend from a depth of 20 to 40 feet bgs. Above <br /> the screen will be a sand layer from 18 to 40 feet bgs, a bentonite layer from 15 to 18 feet bgs, <br /> 1 <br />