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�_ .. .. e 2•'34-. - <br /> 1 . <br /> Chevron U.S.A. <br /> Page 2 <br /> Ground water samples obtained from the monitoring wells installed at the <br /> subject property were 'chemical:ly analyzed,' and reported as non-detected for the <br /> presence of petroleum hydrocarbons contamination as of the date of the report. <br /> In an effort to reduce the potential for further migration of 'the noted <br /> contamination at the subject property, Dames & Moore has prepared the following <br /> remedial action plan for the contaminated subsoils observed at the subject <br /> property. <br /> PROPOSED REMEDIAL PLAN <br /> Subsoil contamination was observed at two -of the three previous dispenser <br /> island locations drilled and sampled at the subject property. Analysis of samples <br /> obtained from the soil boring advanced through the. previous tank removal backfill <br /> area Were interpreted to suggest residual liquid contamination was not present in <br /> that area. <br /> Based upon those observations, Dames & Moore has assumed that each of the <br /> dispenser island may have experienced unauthorized releases over the life of the <br /> previous service station. Therefore, the dispenser island which was not drilled <br /> and sampled during the previous investigation is assumed to also possibly have <br /> contamination present, and is included in the remedial plan for the subject <br /> property. <br /> It is proposed that. soil excavation be conducted in the. vicinity of each <br /> dispenser island location to remove gasoline contaminated soils, and excavated <br /> soil 'be `aerated. The anticipated maximum depth of the excavations at the <br /> dispenser island locations will be 20 feet below the existing grade. Field <br /> screening of ,excavated soils with a portable photoionization detector will be <br /> .utilized to help 'describe contamination persistence in a lateral relationship to <br /> each previous dispenser location. Soil samples will be obtained at the limits of <br /> each excavation for chemical analysis to help evaluate contamination removal <br /> parameters. <br /> Upon completion of excavation of contaminated subsoils in the vicinity of <br /> each- of- the previous dispenser islands, -excavated soils will be spread' to an <br /> approximate thickness of 5 inches over plastic sheeting on the subject site for <br /> aeration. Aerating soil will be disked or otherwise mechanically mixed on a <br /> weekly basis to aid aeration. Aerating soils will be segregated on-site in a . <br /> locked temporarily-fenced area which limits general access. <br /> • i <br /> Periodic composite sampling of the aerating soils will be conducted in order <br /> -to evaluate the aeration process. Soil samples obtained from the limits of <br /> excavation and from composite sampling of aerating soils will be chemically . <br /> analyzed at a .state-approved laboratory for the presence and concentration of <br /> benzene, toluene, ethylbenz.ene, xylenes, and total petroleum hydrocarbons. <br /> Excavated areas will be backfilled with soil and- compacted as specified by <br /> local -codes. Uponcompletion of- treatment, aerated soils will be transported to a <br /> local landfill for appropriate disposal, or spread uniformly over the subject <br /> site area. <br /> .DAMES & MOORE <br />