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® 4r App/!ea/ �eaSy�tems 4191-E Power Inn Road, Sacramemo, CA 95826 (916)452.2901 •FREMONT e COSTA MESA Y SACRAMENTO e HOUSTON 4 September 14, 1988 0728SEPP AGS job No. 86102-3 Mr. Steve Epperson Beacon Oil Company 525 West Third Street Hanford, California 93230 Subject: Letter report of quarterly ground-water monitoring at Beacon Station No. 3-492, 470 North Main Street, Manteca, California. Mr. Epperson: s A geologist from our office visited the site referenced above on June 7, 1988, to purge and sample three ground-water monitoring wells. This work was completed at the request of Beacon Oil Company as part of our ongoing environmental investigation. The site is located on the southeast corner of of the intersection of North Main Street and Alameda Street in Manteca. The site Vicinity Map, Plate P-1, shows the location of the station. Applied GeoSystems previously installed three 4-inch- . diameter ground-water monitoring wells (AGS Report No. 86102-1, dated December 16, 2986) . The locations of the wells relative to the site facilities are depicted on the Generalized Site Plan, y Plate P-2. Previous work, summarized in our Work Plan (AGS Report No. 86102-2, dated May 26, 1987) , suggests that soil in- thn a.�ea immediately adjacent to and below the tank cavity is contaminated with hydrocarbons. Depth-to-.,j--and-water measurements were taken in each monitoring well prio,: to ;surging and sampling. When corrected for changes in topography .:hese data indicate that the change in elevation of the ground-wafter surface between the three wells is less than f the instrument crror (0.02 foot over the required distance) ; therefore, the ground-water potentiometric surface is inferred to - be-e:= lntially-flat.__-flat. --obtained during -.--- _-- --- --- I f.