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<br /> ENVIRONMENTAL RESOLUTIONS, INC.
<br /> July 30, 1999
<br /> ERI 227903 R02
<br />' Mr Bob Boust
<br /> Union Oil Company of California
<br /> 2121 North California Boulevard, Suite 250
<br /> Walnut Creek, California 94596
<br /> Subject Supplemental Environmental Investigation, Former Unocal Service Station 5098,
<br /> 5606 Pacific Avenue, Stockton, California
<br /> Mr Boust
<br /> 1 At the request of Union Oil Company of California (Unocal), Environmental Resolutions Inc ERI
<br /> drilled twelve soil borings and installed nine groundwater monitoring wells at and in the vicinity of the
<br /> subject site The purpose of the work was to further evaluate the extent of residual petroleum
<br /> hydrocarbons in soil and dissolved petroleum hydrocarbons in groundwater ERI performed the work
<br /> in accordance with ERI's Work Plan for Supplemental Environmental Investigation, dated
<br /> November 12, 1998, and ERI's Addendum to Work Plan for Supplemental Environmental Investigation,
<br /> bpi dated December 9, 1998 The Work Plan and Addendum were approved by the San Joaquin County
<br /> Public Health Services, Environmental Health Division (the County) in a letter dated November 20,
<br /> 1998, and an approval dated January 13, 1999 (sent via facsimile) The approval letters are provided
<br /> in Attachment A Specifically, the work included
<br /> O Obtaining an encroachment permit from the City of Stockton Public Works Department (the City)
<br /> to drill in City of Stockton right-of-way,
<br /> C Obtaining permits from the County to drill 12 soil borings and install nine groundwater monitoring
<br />' wells at or in the vicinity of the site,
<br /> • Drilling 12 soil borings (Bl, B2, MW 10A, MW 14A, MW 18, MW 19S, MW 19D, MW21S,
<br /> MW21D, MW22S, MW22D, and HPI) to depths ranging from approximately 49 to 81 5 feet
<br /> below ground surface (bgs),
<br /> • Collecting soil samples from the borings for laboratory analysis and to evaluate soil stratigraphy,
<br /> Collecting three discrete groundwater samples from various depths from boring HPI,
<br /> • Constructing groundwater monitoring wells MW 10A, MW 14A, MW 18, MW 19S, MW 19D,
<br /> MW21S, MW211), MW22S, and MW22D in the respective borings,
<br /> • Submitting select soil samples from the borings and groundwater samples from HPI for laboratory
<br /> analysis for petroleum hydrocarbons and associated constituents,
<br /> e Developing the newly-installed groundwater monitoring wells,
<br /> Coordinating groundwater monitoring and sampling of the newly-installed monitoring wells with
<br /> Unocal to coincide with quarterly monitoring and sampling of previously-existing wells, and,
<br /> o Preparing this report documenting the procedures and results of the investigation
<br /> i
<br />' 73 Digital Drive, Suite 100, Novato, California 94949-5791 415-382-9105 (FAX 415-382-1856)
<br /> Lake Forest • Novato • Seattle
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