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01, <br /> ,; � - '- ,ter <br /> On <br /> w <br /> r-:y -_-CM r�r F�� �•e. ,yam'^ ra -.i�. <br /> ...-w- :.- .�ia�i+JJ+35- J� ,•i- ,....�"iLwswsaaa�.w` .�veCY`R-•=-_. ._.�. _.:d.,�,� .�s�i. icc�c' - - '; <br />�7 <br /> p. <br /> i <br /> j <br /> f <br /> i <br /> I <br /> April 30, 1991 <br /> 0109rsis <br /> AGS 38012-4 <br /> Mr. Rick Sisk <br /> Unocal Corporation <br /> P.O. Box 5155 <br /> San Ramon, California 94583 <br /> Subject: Quarterly Ground-Water Monitoring,Fourth Quarter 1990,at Dormer Unocal <br /> Station No. 2859, 1665 Pacific Avenue, Stockton, California. <br /> Mr. Sisk: <br /> This report summarizes the results of the fourth quarter 1990 groundwater monitoring that <br /> Applied GeoSystems, Inc. (Applied GeoSystems) conducted at the request of Unocal <br /> Corporation at the subje^t site. The site location is shown on the Site Vicinity flap (Plate <br /> P-1). The purpose of quarterly sampling is to monitor changes in concentrations of gasoline <br /> hydrocarbons in the ground water and changes in the groundwater gradient. <br /> The work for this monitoring phase included subjectively analyzing ground water in two <br /> monitoring wells (wells MW-4 and MW-S) and collecting and analyzing groundwater <br /> samples for hydrocarbon constituents. We did not collect water samples from wells MW-1 <br /> through MW-3 or measure depths to water in these wells because the wells were dry. As <br /> a result,we could not evaluate the groundwater gradient beneath the site. The locations <br /> of the monitoring wells are shown on the Generalized Site Plan (Plate P-2). <br /> Previous Work <br /> Five soil borings were drilled at the site in January 1988 as part of a subsurface <br /> environmental investigation conducted by J.H. Kleinfelde• & Associates (Kleinfelder) of <br /> Sacramento, California. Results of that investigation indicated that hydrocarbons were <br /> present in soil underlying the site (Kleinfelder, March 3, 1988, Report No. 24-2081-01). <br /> Applied GeoSystems began an environmental investigation in conjunction with underground- <br /> storage tank removal in March and April 1988. During this irivestigation, a geologist <br /> observed removal of the underground storage tanks and collected soil samples for laboratory <br /> analysis of hydrocarbons. <br />