SITE INFORMATION AND CORRESPONDENCE

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UQ UQ . . - VR AN INTERNATIONAL PROFESSIONAL SERVICES ORGANIZATION 1989), which is most likely .acting as a groundwater barrier isolating the shallow groundwater zones of both sites:r-Thejshallow wells at M & B are designed to detect sinking contaminants (heavier than water) and are therefore predominantly screened-below first groundwater, across the first permeable sand zone encountered (referred to as the "A" Zone in the M& B Summary Report). Because the contaminants associated with the Union Ice Investigation are floaters(lighter than water), the shallow wells at Union Ice need to be screened across first groundwater, above.the M& B "A" Zone. In addition,since the M&B shallow wells are screened below the water surface, groundwater elevations from'.-the M & B shallow wells may not be truly representative of actual first groundwater elevations because of possible 5 vertical gradients. Moreover, the"A" Zonc at M* B is continuously pumped at a rate of 7 gallons per minute from 'Well A-8 further influencing the groundwater elevation measurements at M & A. As for stratigraphic data,'the- "A" Zone at M & B has been tentatively correlated. However, it is not considered to represent a continuous lithologic unit. It'may or may not be present beneath the Union Ice Site. This zone is generally found below the M& B site. at a depth of approximately 30 to ` 40 feet below grade. If present below the. Union Ice site, this zone will be I used to represent the next deepest aquifer zone below first groundwater,and will be screened by the proposed deeper wells.i! Total completion depth of these deeper wells will be 40 to 50, feet depending on the depth at which the. i "A" Zone is encountered (if present). If the "A" Zone is not encountered, the deep wells will be screened from the' 40 to 50 feet depth interval (approximately. 15 to 20,feet below the shallow:;wells.screening interval). 1 k Comment: 2. The proposed workplan does not include a sampling plan. Selected soil i samples shall be submitted to the laboratory for`bcnzene, toluene, xylene, & ethyl benzene and total petroleum hydrocarbons detected as gasoline and diesel. Attached is the Minimum Verification Lab Analysis form suggesting those recommended lab analysis. URS Consultants should specify field screening techniques for selecting soil samples for submittal to the laboratory. Response: Soil contamination was not addressed in the Workplan because the tank bottom was within first groundwater and soil contamination appeared to be limited to the soils immediately adjacent to the tank (backfill) and gasoline was observed floating on groundwater.within the`tank excavation. However, to evaluate the amount of contaminated `soil present; URS proposes to re- excavate the tank.excavation to groundwater and collect samples from the excavation.side walls. During excavation,Y excavated soils will be .screened for petroleum hydrocarbons using an Organic Vapor Analyzer (OVA). When the OVA readings are not above background, two soil samples will be collected from the center of each excavation side wall (a't the S foot and ten foot depths). All excavated soils will be stockpiled on asphalt pavement and covered with plastic sheeting until final disposition is,determined, whether it be onsite treatment or offsite disposal. Four-soil samples will be colected from the excavated .soils for compositing•at.the laboratory. 65550,01/07249/Unionlce.giw 2