SITE INFORMATION AND CORRESPONDENCE

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ACTON • �' MICKELSON van DAM,INC. # 2 Consulting Scientists.Engineers,and Geologists l l February 13, 1995 RECEIVED F E e 2 11995 .Mr. Kenneth Earnest ENVIRONMENTAL HEALTH Ultramar Inc. PERMIT/SERVICES 525 West Third Street Hanford, California 93230 19005.1617 Subject: Work Plan for Assessment of Vapor Extraction System Effectiveness Former Beacon Station No.494,2185 East Fremont Street;'Stockton, California Dear Mr. Earnest: Acton • Mickelson • van Dam,Inc. (AMV), has been authorized by Ultramar Inc. (Ultramar) to submit a work plan to assess the effectiveness of remedial activities at the subject site (Figures 1 and 2). Proposed work includes the advancement of four soil borings at the site (designated as CB-1 through CB-4,Figure 3). Soil boring advancement and related soil sample SAN JOAQUIN COUNTS analysis are intended to determine the presence or absence of petroleum hydrocarbon constituents in soil beneath the site and assess whether soil vapor extraction should continue at the site. PUBLIC HEALTH SERVICES ENVIRONMENTAL HEALTH DIVISION Background Information P. 0. BOX 2009, STOCKTON,CA 96021 A total of five monitoring wells and four vapor extraction wells were installed by AMV during PHONE:(209)468-3420 April and December 1992. Previous investigations by AMV had indicated the presence of a petroleum hydrocarbon constituents in soil and ground water beneath the site. Three monitoring wells(MW-1, MW-2, and MW-3)were installed at the site by AMV in April 1992. Depth to `j��( Approved ground water beneath the site ranged from 71.29(MW-3)to 72.02(MW-2)feet below respective casing risers. Two additional monitoring wells (MW-4 and MW-5)and four vapor extraction l] Approved with changes-;See Re.=& wells were installed at the site by AMV in December 1992. Ground water gradient was calculated at 0.035 foot per foot(ft/ft) in December 1992 with an inferred direction of flow toward the west. ❑ Disapproved; See RefrArki Ground water samples collected as part of the quarterly monitoring schedule at the site on ReMarks February 4, 1993, indicated that the highest concentration of dissolved benzene was present in monitoring well MW-3,located south of the underground storage tanks(USTs). A ground water sample collected on that date from monitoring well MW-4, located southeast of the USTs, S �� reported the highest concentration of total petroleum hydrocarbons as gasoline(ITHgy)at 1,20o Date B micrograms per liter(µgl1). all Approval of these pians extends only to that which is shown and described hereon but 4511 Golden Foothill Parkway.Suite 1 4916p 939-7550 does not authorize or approve any omissiofl EI Dorado Hills,California 95762 Fax 49161 939.7570 or deviation of recluirementS of State 'laws rw ,oca l Ordinances.