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Clayton <br /> f\l IKI 4\11G\7{� <br /> ( 7\SIII i\S <br /> 2 The do nth :o water below grade and below the excavation, <br /> 3 If the excavation was deeper than 10 S feet, the reasons for not collecting confirmatory <br /> soil samples from the base of the excavation" <br /> -� Clayton's response to the above comments are as follows. <br /> Clayton initially removed approximately 1,000 cubic yard of soil from the excavation Some <br /> of the soil appeared to be uncontaminated, based on readings from the organic vapor meter <br /> (OVM) and visual observation Other soil was saturated with water. Iii some areas the <br /> groundwater table was encountered, but it was not continuous throughout the bottom of the <br /> excavation. x <br /> � z <br /> 4..}7 <br /> When the ordtial excavation was completzd,we collected seven soil samples from the base of <br /> i the walls aL approximately 10.5 feet below the ground surface (bgs) The samples taken from <br /> r� the north and east walls had concentrations of petroleum hydrocarbons above the <br /> remediation objectives. We also collected a water same;e from the excavation. This sample <br /> r' had a total recoverable hydrocarbon concentration of 2 parts pei million (ppm). <br /> Based on this initial excavation, Cigyton recomm4nded additional excavation of soil from the <br /> north and east waUs. The excavation in the vicinity of the soil samples collected in the initial <br /> ' excavation from the north and east walls was deepened to approximately 12 feet below grade <br /> until either soil appeared to be clean based on visual observation and readings from the <br /> �. OVM, or-ttle groundwater table was intersected. In some areas, the excavation was <br /> deepened"below the water table. <br /> isz �a The walls of the excavation were expanded to the north and to the east. On August 9, 1990, <br /> a concrete, underground septic tank was encountered. Ms. Diane Hinson of the SSC/EI <br /> oversaw the septic tank removal and soil sampling on August 17, 1990 <br />� xp's+ t4 x <br /> The excavation was deepened to approximately 13 feet below grade m the vicinity of the <br /> former septic tank (4 feet below the bottom of the tank) and two soil samples were collected. <br /> Pet roleum,hydrocarbons were below detectable levels m these samples This overexcavation <br /> µ included the area where soil sample ME-1 was collected. <br /> Four new confirmation samples were collected from the north and east walls after any soil <br /> that showed evidence of potential cGntammation'was excavated. These samples did not <br /> contain detectable levels of petroleum hydrocarbons. <br /> A total of about 1,650 cubic yards of soil was excavated to achieve removal of all soils with <br /> concentrations exceeding 3.6 mg/kg of gasoline and 80 mg/kg of oil and grease. <br />` I. Ms. Thayer raised the following concern about soil samples from the installation of well MW- <br /> R 3B: <br /> Ili "The soil samples from MW-3B indicated sod contamination of 770 ppb total recoverable <br /> r hydrocarbons at a feet and 20 ppb at 9 feet. The fractions of hydrocarbons were not <br /> identified. <br /> 4 6I ' <br /> S � <br /> s <br />