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c <br /> PUBLIC HEALTH SERVICE <br /> SAN JOAQUIN COUNTY <br /> ENVIRONMENTAL HEALTH DIVISION H : < <br /> Ernest M. Fujimoto, M. D., M.P.H., Acting Health Officer ;• <br /> 304 East Weber Avenue, Third Floor • Stockton, CA 95202 °4t;FORa`� <br /> 209/468-3420 <br /> cl 7D � <br /> £D RALSTON <br /> UNOCAL CORPORATION JUL 0 1 '1991, <br /> 2000 CROW CANYON PLACE STE 400 <br /> SAN RAMON CA 94583 <br /> RE: UNOCAL STATION#5886 SITE CODE: 1176 <br /> 2701 MARCH LANE <br /> STOCKTON CA <br /> As a result of reviewing site specific data from the most recent quarterly groundwater monitoring event, <br /> past groundwater and soil sampling events and the Supplemental Evaluation and Investigation Report dated <br /> June 3, 1997, San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) <br /> provides the following comments and directives. <br /> Data received from soil and ground water sampling events at the above referenced site provide <br /> documentation of past and new contaminant distribution as petroleum hydrocarbons. <br /> MTBE (Methyl tertiary butyl ether), benzene,xylenes and total petroleum hydrocarbons as gasoline and <br /> diesel were detected in hand augered soil(pea gravel)samples taken from directly beneath three of six site <br /> sheet flow drains which were recently removed as directed by the City of Stockton and San Joaquin County <br /> Public Health Services Environmental Health Division (PHS/EHD). As discussed with Environmental <br /> Resolutions Incorporated(ERI)personnel Keith Romstad and Unocal representative Adadu Yemane onsite <br /> the day of sampling, "soil and ground water beneath all drains should be sampled to avoid remobilization <br /> costs and delays in documentation of contaminant distribution' as recommended by site inspector Ron <br /> Rowe of PHS/EHD. <br /> i <br /> These engineered receptacles and pea gravel fill materials were placed at the site recently during <br /> comprehensive site renovation and underground tank system upgrades which supports the concept of <br /> introduction of new contaminants to this site. It is important to note that these drains were placed directly <br /> in front and at the base of all fuel dispensers on site creating a potential direct conduit to the subsurface <br /> environment (soil & ground water). The likely source of these new contaminants new the drains includes <br /> but is not limited to overfills and spills of petroleum products from routine vehicle fueling activities. <br /> PHS/EHD staff have documented these activities and photographs are available for review. It is clear from <br /> the laboratory data that although only three drains of six were sampled, all six are likely contaminant <br /> source areas. These surface drain areas are considered by PHS/EHD to be contaminant source areas and <br /> must be completely evaluated in the next scope of work. <br /> With regard to ground water contamination it is apparent that MTBE concentrations are significant(as high <br /> as 20,000 µg/1 in MW-3) and have likely migrated off site realizing that the southern property line is less i <br /> than 20 feet from MW-6S&D which is impacted by fuel hydrocarbon constituents(MTBE at 480 µg/1). In <br /> accordance with PHS/EHD directives issued in correspondence to Unocal in March of 1997 four dual <br /> completion monitoring wells were installed at the above referenced site near the property boundaries. <br /> I <br /> A Division of San Joaquin County Health Care Services <br />