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Mr. James L. Barton <br /> October 19, 2007 <br /> Page 3 <br /> the drilling of the soil boring using 8-inch diameter hollow stem augers. The air knifing will clear the <br /> borehole to 8-inch diameter. <br /> The drilling will now consist of the following sequence: The initial four feet of the boring will be advanced <br /> using an air-knife to clear the boring to 8 inches in diameter. The boring will then be hand-augered to five <br /> feet bgs to allow for sample collection with minimal volatile organic compound (VOC) volatilization from the <br /> air-knifing. Following the collection of the soil sample from approximately five feet bgs, the boring will be <br /> advanced to eight feet bgs using the air-knife to a diameter of approximately 8 inches. The boring will then <br /> be advanced from 8 feet to 43 feet bgs using an 8-inch diameter hollow stem auger drilling equipment. <br /> The air knife potion of the boring is proposed to further confirm the absence of subsurface utilities and <br /> subsurface obstructions and is consistent with Chevron-mandated field procedures. <br /> SCHEDULE <br /> Contingent upon the availability of subcontractors and securing appropriate permits from San Joaquin <br /> County Environmental Health Department, ENSR proposes to commence work immediately upon receipt <br /> of regulatory approval. Tentatively, ENSR has scheduled October 31, 2007 for the installation of MW-15R. <br /> A report of activities will be submitted approximately 60 days after completion of well installation. <br /> REMARKS/SIGNATURES <br /> The interpretations contained in this addendum represent ENSR's professional opinions and are based in <br /> part on information supplied by the client. These opinions are based on currently available information <br /> and are arrived at in accordance with currently accepted hydrogeologic and engineering practices at this <br /> time and location. Other than this, no warranty is implied or intended. <br /> If you have any questions regarding this project, please contact Jennifer Johnston at(916) 362-7100. <br /> Sincerely, <br /> ENSR Corporation <br /> �� + � /00& _'D G <br /> ennrfer Johnston Mark Capps, P.G. #6561 <br /> Project Manager Senior Project ManagerCAM <br /> �m <br /> 'D2 <br /> cc: Mr. Mark Inglis, EMC <br /> Mr. Mike Infurna, San Joaquin County, Environmental Health Division <br /> Mr. Jay Allen, Stone Brothers Management Company <br /> Ms. Nicole Gleason, Downey Brand Oe <br /> 01231-154 ENSR AECOM <br />