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. , .. <br /> � State �; ter Resources Contra'� Board <br /> Division of Clean Water Programs, <br /> Winston H. Hickox 2014 T Street•Sacramento,California 95814,(916) GrayDavis <br /> Mailing Address: P.O.Box 944212•Sacramento,Californiai•'94244-2.120E <br /> Secretaryfor Governor <br /> Environmental FAX(916)227-4349•Internet Address: http://www.swreb.ca.gov <br /> Protection 991 JUL 26 Phi 1. 16 <br /> JUL 2 2 a <br /> 1 <br /> Ms. Donna Heran, Director <br /> Environmental Health Division <br /> San Joaquin County Public Health Services <br /> 304 East Weber Avenue <br /> Stockton, CA 95202 <br /> Dear Ms. Heran: <br /> PETITION OF UNOCAL CORPORATION FOR REVIEW OF DENIAL OF PETROLEUM <br /> UNDERGROUND STORAGE TANK (UST) SITE CLOSURE AT 1665 PACIFIC AVENUE <br /> IN THE CITY OF STOCKTON <br /> Unocal Corporation filed a petition on June 17, 1997 for review of a denial by your agency staff <br /> of site closure at the above UST site. I have decided to defer taking this petition to the State <br /> Water Resources Control Board pending an evaluation of the results of an additional year of site j <br /> monitoring. However, I do not believe that further site assessment is warranted. The reasons for <br /> my decision are explained below. <br /> Geologists on my staff completed a technical review (enclosed) of the facts pertaining to the <br /> subject site. The review concluded the following: <br /> • Primary source removal and over-excavation occurred in 1988. I <br /> • The site was actively remediated with soil vapor extraction for nearly one year in 1996. <br /> • Biodegradation of petroleum BTEX compounds over a ten year period has reduced the extent of <br /> shallow groundwater exceeding drinking water standards to within 70 feet down-gradient of the site. <br /> • MTBE concentrations are very low, consistent with a pre-1988 release. <br /> • Shallow groundwater at this site is already significantly degraded by "background"levels of nitrate <br /> in excess of primary drinking water standards and total dissolved solids (TDS) and chlorides above <br /> secondary drinking water standards due to extensive sea water intrusion over the past 50 years. <br /> • If shallow groundwater were recharging deeper groundwater to any appreciable extent, significant <br /> impacts from nitrate, TDS and chlorides would have been evident. <br /> California Environmental Protection Agency <br /> $a Recycled Paper <br />