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1 <br /> ERI <br /> ENVIRONMENTAL RESOLUTIONS, INC. <br /> 4 _ December 9, 1998 <br /> ERI 227903 W02 <br /> DEC 0 9 1998 <br /> Mr Robert Boust : —11 Ne , ,�i,�- (7 <br /> Unocal DBG/AMG <br /> ;C„ <br /> 2121 North California Boulevard, Suite 250 PCF�1,�� } t.;�. <br /> Walnut Creek, California 94596 <br /> Subject Addendum to Work Plan for Supplemental Environmental Investigation at Former Unocal <br /> Service Station 5098, 5606 Pacific Avenue, Stockton, California <br /> Mr Boust <br /> At the request of Union Oil Company of California (Unocal), Environmental Resolutions, Inc (ERI) <br /> submitted a Work Plan entitled Work Plan for Supplemental Environmental Investigation at Former <br /> Unocal Service Station 5098, dated November 12, 1998 for the subject site The San Joaquin County <br /> Public Health Services, Environmental Health Division (the County) provided comments to the Work <br /> Plan in a letter dated November 20, 1998 and requested an addendum be submitted by December 2, <br /> 1998 A copy of the County's letter is provided in Attachment A Pursuant to a written request by <br /> ERI, the County granted an extension of the submittal date to December 9, 1998 The County's <br /> . approval is provided in Attachment B <br /> The following presents the information requested in the County's comment letter <br /> Item 1 - Well Construction Details <br /> As requested, " Diagrams and specifications are to be included for the wells that detail the size, <br /> length, placement depths, intervals, and materials to be included in the construction of the well " Well <br /> construction details for both the shallow and deep wells are provided in Attachment C In addition, as <br /> requested, the screen length of deep wells will be no greater than five feet and the screened interval of <br /> the deep monitoring wells shall be placed in the most permeable soil layer closest to the historical <br /> deepest depth to groundwater (i e , approximately 60 feet below ground surface) To facilitate the <br /> recognition of permeable zones, borings drilled for deep well installation will be continuously cored <br /> beneath 40 feet <br /> Item 2 - AiialNtical AnaINsis of Soil Samples from Groundwater Monitoring Well Borings <br /> As requested in the County's letter "Soil samples collected from the monitoring well installations shall <br /> be additionally analyzed for the seven oxygenates listed in the enclosed PHS-EHD policy" Although <br /> Unocal has agreed to perform analyses for oxygenated compounds, it should be noted that Unocal has <br /> not used any other oxygenated compounds other than methyl tertiary butyl ether (MTBE) in its gasoline <br /> in California Soil sampling of borings for lithologic and potential laboratory analysis will be <br /> performed at 5-foot intervals from the surface to total depth of the deep wells for wells proposed as <br /> side-by side completion For shallow wells only (i e , a deep well not proposed nearby), soil sampling <br /> 74 Digital Drive, Suite 6, Novato, Caldomia 94949 415-382-9105 (FAX 415-382-1856) <br /> Lake Forest • Novato - Seattle <br />