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25 Cupania Circle <br /> Monterey Park, CA 91755 <br /> (YVATCPhone(323)517-9780 <br /> Fax 323 <br /> A 6 SOCIATES INC ax )517-9781 <br /> Engineering Individual So/cations <br /> www.atcassociates.com <br /> April 13, 2011 <br /> Mr. Mike Infurna <br /> San Joaquin County Environmental Health Department <br /> 600 East Main Street <br /> Stockton, California 95202 <br /> RE: Letter Addendum to Stantec's Addendum to July 8, 2010 Work Plan for Monitoring Well Destruction <br /> and Replacement, and Additional Path Forward <br /> Former Thrifty Oil Co. Station No. 172 <br /> ConocoPhillips Site No. 5449 <br /> 7647 Pacific Avenue <br /> Stockton, California <br /> Dear Mr. Infurna: <br /> This letter, prepared on behalf of ConocoPhillips Company (COP) by ATC Associates (ATC) for ConocoPhillips <br /> Site No. 5449, located at 7647 Pacific Avenue, Stockton, California addends Stantec Consulting Corporation's <br /> (Stantec's) Work Plan for Monitoring Well Destruction and Replacement, dated July 8, 2010, and Addendum to <br /> July 8, 2010 Work Plan for Monitoring Well Destruction and Replacement, and Additional Path Forward, dated <br /> September 23, 2010. ATC has recently taken over the role of lead consultant for the open environmental case at <br /> the site from Stantec Consulting (Stantec) and has reviewed the content and applicability of the September 23, <br /> 2010 work plan addendum (Attachment 1). <br /> It is ATC's opinion that the work proposed in Stantec's September 23, 2010 work plan addendum is appropriate in <br /> scope and methodology; accordingly, ATC will utilize Stantec's September 23, 2010 work plan addendum <br /> (included as Attachment 1) as the work plan for well installation and well recovery activities. It should be noted, <br /> that Stantec completed the proposed well destruction and well protection activities, as documented in Stantec's <br /> Well Destruction and Well Protection Report, dated March 15, 2011. <br /> Scope of Work <br /> The work ATC will perform will consist of: 1) recovering previously-protected wells MW-3, MW-7, and MW-12R; <br /> 2) installing shallow-screened on-site wells MW-4R, MW-14, and MW-15; 3) installing deep-screened on-site well <br /> MW-13; and 4) installing shallow-screened off-site well MW-16. While the lengths of the proposed well screens <br /> were not stated in Stantec's September 23, 2010 work plan addendum, ATC's proposed well construction details <br /> are summarized on Table 1. All other activities associated with the well installation and well repair activities (utility <br /> locating, soil and groundwater sampling, well development, etc.) will be performed by ATC in accordance with <br /> Stantec's September 23, 2010 work plan addendum. <br /> Schedule <br /> In recent conversations held between ATC and Miller Pacific Inc. (the company performing the site redevelopment <br /> activities), ATC was advised that well installation and well recovery activities would be possible starting the week <br /> of May 16, 2011. Assuming pending site redevelopment activities are not delayed, and timely receipt of all <br />