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ENVIRONMENTAL INC Q � 20STi��TUJUN nQ4 3330 Cameron Park Drive Ste 550 <br /> Cameron Park California 95682 <br /> ENVIRONMENT ISE (530)676-6004--Fax (530)676-6005 <br /> PERIM ERVICES <br /> May 27, 2004 <br /> Project No U6100 <br /> Mr Nuel Henderson, Jr <br /> San Joaquin County <br /> Environmental Health Department <br /> 304 East Weber Avenue, Third Floor <br /> Stockton, California 95202 <br /> Re Work Plan Addendum <br /> ARCO Facility No 6100 <br /> 25775 Patterson Pass Road <br /> Tracy, California <br /> Dear Mr Henderson <br /> On behalf of Atlantic Richfield Company (ARCO — a BP affiliated company), Stratus <br /> Environmental, Inc (Stratus) has prepared this Work Plan Addendum for ARCO Facility No <br /> 6100, located at 25775 Patterson Pass Road, Tracy, California <br /> After completing exploratory soil borings adjacent to the site in February 2004, Stratus elected to <br /> complete two monitoring well clusters (MW-10/MW-13 and MW-1I/MW-14) in the Patterson <br /> Pass Road right-of-way On May 25, 2004, well MW-11 was installed to approximately 108 feet <br /> below ground surface (bgs) During the advancement of the boring (B-43) adjacent to well MW- <br /> I1 on May 27, 2004, the hollow stem augers used to advance boring B-43 came into contact with <br /> well MW-11, damaging the well Apparently either well boring MW-11 or MW-14 were not <br /> advanced completely perpendicular to the ground surface Since well MW-11 was damaged, and <br /> may not have been installed completely vertical, Stratus is recommending that the well be <br /> properly abandoned by overdrilling, and backfilling with neat cement Stratus is also <br /> recommending that boring B-43 be properly abandoned by backfilling with neat cement <br /> Stratus is recommending that new borings be advanced to complete the remaining well <br /> installations The recommended locations for the remaining well installations are shown on the <br /> attached figure A discussion regarding the placement of the remaining wells is presented below <br /> The remaining shallow screened monitoring well will be completed as MW-14, and the <br /> remaining deeper screened monitoring well will be completed as MW-15 <br /> Between May 25 and May 27, 2004, Stratus monitored deeper screened wells MW-10, MW-11, <br /> . and MW-12 for the presence of groundwater Groundwater was observed in wells MW-10 and <br /> MW-12, however, well MW-11 was dry The groundwater level observed in well MW-10 <br /> P 16p Arco for URS161001Work Plans16140-work plan addendurn doe <br />