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Chemn <br /> Chevron U S A Inc <br /> 2410 Camino Ramon, San Ramon, California• Phone (415) 842-9500 <br /> q Mail Address PO Box 5004,San Haman CA 94583[1804 <br /> Marketing Department April 18, 1991 <br /> Ms Diane Hinson <br /> San Joaquin County Environmental Health <br /> P.O. Box 2009 <br /> Stockton, CA 95201 <br /> Re Chevron S.S #9-6465 APR 2 5 °""i <br /> 5608 North Pershing Avenue, Stockton, C6NVIRONMFNTAL HEALTH <br /> PERMIT/SERVICES <br /> Dear Ms Hinson <br /> Enclosed is a report dated March 8, 1991 which describes groundwater monitoring by Chevron's <br /> consultant, Alton, on January 18, 1991 at the site referenced above <br /> Chevron has been monitoring the groundwater at this site since the installation of groundwater <br /> monitoring wells in February of 1988 Chevron's three year groundwater program has generated <br /> the following information- <br /> (1) Direction of groundwater gradient has consistently been in a northeast <br /> direction <br /> (2) The horizontal extent of dissolved phase hydrocarbons in the groundwater <br /> has been consistent since several damaged well heads were repaired in June 1990 to <br /> prevent surface runoff from compromising the integrity of groundwater samples <br /> collected from the wells <br /> (3) The latest data indicates that levels of dissolved benzene in the groundwater <br /> are only slightly in excess of the stringent California drinking water standards <br /> As a result of the consistency of the groundwater information gathered since the well head <br /> reconstruction and the relatively low levels of dissolved phase hydrocarbons present in the <br /> groundwater at this site, Chevron feels that continued monrtonng on a quarterly basis will not <br /> contribute any significant new information, but rather will merely generate a large quantity of <br /> redundant data. Chevron feels that a revision of its monitoring program is warranted at this time <br /> and has instructed its consultant, Alton, to follow the monitoring and reporting programs defined <br /> below: <br /> Monitoring <br /> • Measure the groundwater elevations in all wells(MW-1 through MW-11) on <br /> a semi-annual basis during the first and third quarters of each year <br /> I <br />