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--------------- SECOR % �'96r'Aoa0,Suile 100 INTERNATIONAL Rancho Cordova,CA 95670 S E C 0 R INCORPORATED 916-061-0400 TEL 916-061-0430 FAX July 15, 2005 Mr. Mike Infurna f_[Ecaya San Joaquin County Environmental Health Department +� u 304 Webber Avenue, 3" Floor Stockton, California JUL $ 8 2005 ENVIRONMENT HEALTH RE: Second Addendum Work Plan for the Installation of Well MW-�JRMIT/SER VICES 76 Service Station No. 11195 16500 North 1-5 Lathrop, California SECOR Project No.: 77CP.60195.02.0001 Dear Mr. Infurna: On behalf of ConocoPhillips, SECOR International Incorporated (SECOR) has prepared this letter, which presents a second addendum to SECOR's September 13, 2004 Work Plan for Additional Site Assessment. The initial work plan proposed the installation of three additional off-site wells (MW-22 through MW-24) for further delineation of the lateral extent of the dissolved plume off-site at the site referenced above (Figure 1). In accordance with the September 13, 2004 work plan, SECOR supervised the installation of wells MW-23 and MW-24 by Cascade Drilling (Cascade) on May 19, 2005. Due to the presence of storm water and water fines identified within five feet of the proposed location of well MW-22 during pre-drilling activities, SECOR did not complete the installation of well MW-22 on the scheduled drilling date. On June 17, 2005, SECOR submitted an Addendum Work Plan for the Installation of Well MW-22, which presented an alternative method of installing well at the same location proposed in the September 13, 2004 work plan, with modifications to the well construction details. The addendum included a proposal to install the well by advancing 3.25-inch outer diameter Geoprobe drive rods through the initial 1.5-inch outer diameter borehole advanced for soil sampling. The borehole would then be converted to a one-inch diameter, Schedule 40 polyvinyl chloride (PVC) well with approximately 15 feet of 0.020-inch, slotted screen extending from approximately 7 feet to 22 feet bgs. Following the receipt of the addendum work plan, Mr. Infurna of the San Joaquin County Environmental Health Department (SJCEHD) contacted SECOR, and indicated that the proposed well construction details were not in compliance with the California Department of Water Resources (DWR) Water Well Standards, which require a minimum of two inches of annular space between the well casing and the borehole. In response, SECOR has prepared this secondary addendum work plan, proposing to install well MW-22 at an alternative location on the Holiday Inn property (16855 Harlan Road), utilizing the hollow stern auger drill method as initially proposed in SECOR's September 13, 2004 Work Plan for Additional Site Assessment. A summary of the proposed modified scope of work is = `-? presented below.