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pt I. LATHROP PROPERTY WKA No. 1184.02 January 30, 1992 Page 7 Soil types and elevations of iithologic change were found to be consistent at the boring locations, generally comprised of light brown silty fine to medium-grained sands (SM) from the ground surface to approximately ;') feet below ground sviface (bgs); at most boring locations, a less silty medium to coarse grained grey sand (SP)exists from 10 to 15-feet bgs. The sand unit is .underlain by an olive-grey to light brown clayey silt (ML) with cemented 1 e nodules. Ground water was encountered in the borings between 10 to 15 feet bgs. The i thickness of the clayey silt layer was not determined, because it appeared, based on visual • and olfactory field evidence ..uring drilling, that the clayey silt layer had not boon S contaminated by petroleum hydrocarbons. This was confirmed by analysis of subsurface samples obtained from the bottom of the borings, each of whiuh terminated within the a uppermost portion of the clayey s. ilt layer. Flowing sands prevented bottom sample retrieval only in Boring P1. All other bottom oamples contained non-detectable concentrations of petroleum hydrocarbons. ' ins r The clayey silt layer is very likely an a luitard between "first water"beneath the property and fef� •, deeper aquifers. Given the absence of petroleum hydrocarbon contamination of the clayey silt layer, we did not find justification to fully penetrate it. This course of action significantly lowered the potential fcr the creation of a vertical conduit between first water and deeper i ground waters. i } f Soils Excavatinn Soils excavation was accomplished January 11 and 12,,,1,99.1;with a J0790D-LC excavator equipped with a 1-5/8-cubic-yard bucket operated by Lee Senge;a six-cubic-yard dumptruck was utilized to place the excavated soils in appropriate locations on the property. Mr. Senge ;. and our field personnel were ir, compliance with OSHA Hazardous Waste Cperations and s Emergency Response Standard (29 CFR 1910.1.20(e)1 and we prepared a January 10, 1991, Project Site Safety Plan that was read and signed by the property owners and Mr. Bongo .r - during a site "tailgate meeting" prior to excavating activities. r" "" ` -1 "overburden" soils.were -removed from the .t, Approximately. nine vertical feet of ccan. . I ` excavation area (Plate'2)10rior,to contaminated soiis'removal: Overburden was removod't'o uniform depth below original site grade, the easterly end of the excavation was "ramped" 4 4 and then excavation of contaminated soils was accomplished. overburden was temporarily stockpiled on the central portion of the property while contaminated soils were placed on and . WALL-ACE•RUkl. - 6A5500ATZL INC. -