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il wlggq� S i 3 Clayton EV`.1R0A�tF\i4� C01,SLLSA`TS 2. The depth to water below grade and below the excavation; 3. If lire excavation was deeper than 10.5 feet, the reasons for not collecting confirmatory soil samples from the base of the excavation." Clayton's response to the above comments are as follows: Clayton initially removed approximately 1,000 cubic yards of soil from the excavation. Some of the soil appeared to be uncontaminated, based on readings from the organic vapor meter (OVM) and visual observation. Other soil was saturated with water. In some areas the groundwater table was encountered, but it was not continuous throughout the bottom of the excavation. ,.. Wben the; initial excavation was completed,we collected seven soil samples from the base of the walls at approximately 10.5 feet below the ground surface (bgs). The samples taken from the north and east walls had concentrations of petroleum hydrocarbons above the remediation objectives. We also collected a water sample from the excavation: This sample had a total recoverable hydrocarbon concentration of 2 parts per million (ppm). Based on this initial excavation, Clayton recommended additional excavation of soil from the A' north and east walls. The excavation in the vicinity of the soil samples collected in the initial excavation from the north and east walls was deepened to approximately 12 feet below grade until either soil appeared to be clean based on visual observation and readings from the OVM, or the groundwater table was intersected. In some areas, the excavation was deepened below the water table. The walls of the excavation were expanded to the north and to the east. On August 9, 1990, a concrete, underground septic tank was encountered. Ms. Diane Hinson of the SJC/EHD I oversaw the septic tank removal and soil sampling on August 17, 1990. The excavation was des entd to approximately 13 feet below grade in the vicinity.of the I ,.,, former septic tank (4 feet below the bottom of the tank) and two soil samples were collected. ! s Petroleum hydrocarbons were below detectable levels in these samples. This overexcavation included the area where soil sample ME-1 was collected. Four new confirmation samples were collected from the north and east walls after any soil that showed evidence of potential contamination was excavated. These samples did not contain detectable Levels of petroleum hydrocarbons. I A total of about 1,650 cubic yards of,soil was excavated to achieve removal of all soils with t concentrations exceeding 3.6 mg/kg of&a GUne and 80 mg/kg of oil and grease. Ms. Thayer raised the following concert; about soil samples fain the installation of well MW- 3B: "The soil samples from MW-3B indicated soil contamination of 770 ppb total recoverable hydrocarbons at 4 feet and 20 ppb at 9 feet. The fractions of hydrocarbons were not identified. f I loin