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ZE%RI r <br /> ENVIRONMENTAL.PES:QLUT1Oin, INC. <br /> April 3, 1997 <br /> ERI 205503.A01 <br /> Mr. Ronald Rowe, Sr. <br /> Site Mitigation Unit <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> 304 East Weber Avenue, Third Floor <br /> Stockton, California 95202 <br /> Subject: Addendum to Work Plan for Supplemental Environmental Investigation at Unocal <br /> Service Station 5886, 2701 March Lane, Stockton, California. <br /> Mr. Rowe: <br /> At the request of 76 Products Company, and pursuant to correspondence from San Joaquin County <br /> Public Health Services, Environmental Health Division (PHS/EHD) dated April 1, 1997, <br /> Environmental Resolutions, Inc. (ERI) is submitting this addendum to our work plan (dated March <br /> 28, 1997) for the subject site. The addendum addresses the vertical distribution of methyl tert-butyl <br /> ether (MTBE) detected in groundwater beneath the site and discloses the chemicals utilized in fuel <br /> mixtures by 76 Products Company. <br /> Work outlined in ERI's Work Plan includes: 1) obtaining and reviewing MTBE data from a previous <br /> investigation and fuel inventory reconciliation records; 2) obtaining appropriate well permits and <br /> drilling four on-site soil borings; collecting soil samples; constructing groundwater monitoring wells <br /> in these borings; developing and purging the new wells; collecting groundwater samples; analyzing <br /> selected soil and groundwater samples; and 3) interpreting the data to evaluate the source and extent <br /> of residual hydrocarbons in soil and lateral extent of dissolved MTBE in groundwater, and preparing <br /> a report. <br /> The San Joaquin County PHS/EHD response to the work plan requested 76 Products Company <br /> address the vertical distribution of MTBE in groundwater and disclose the chemicals utilized in fuel <br /> mixtures by 76 Products Company. In accordance with the correspondence and request from the San <br /> Joaquin County PHS/EHD, analyses of select soil samples and groundwater samples will include total <br /> petroleum hydrocarbons as gasoline (TPHg) and diesel fuel (TEPHd) and benzene, toluene, <br /> ethylbenzene, and total xylene isomers (BTEX) as well as MTBE. Select soil samples will also be <br /> analyzed for permeability, dry bulk density, porosity, and moisture content. No samples will be <br /> collected beneath the existing drains during this investigation. It is our understanding 76 Products <br /> Company is following appropriate procedures to close the drains. ERI will collect samples of native <br /> soil from beneath the drains by either coring the concrete and collecting a sample of native soil from <br /> beneath each drain, or hand angering at an angle to beneath each drain and collecting a sample of <br /> native soil. <br /> To address the vertical distribution of MTBE in groundwater, ERI will revise the construction of the <br /> proposed monitoring wells to incorporate duel casings within the proposed borings with discreet <br /> 74 Digital Drive,Suite 6, Novato, California 94949 415-382-9105 (FAX 415-382-1856) <br /> Irvine • Novato • Seattle <br />