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+� 16 September 1996 <br /> AGE-NC Project No. 95-0168 <br /> Page 2 of 5 <br /> UW <br /> t approximately 450 miles. The valley is enclosed by the granitic Sierra Nevada Mountains on the east <br /> L. and the sedimentary and metamorphic Franciscan Coast Range on the west. The surf cial and upper <br /> several thousand feet of subsurface layers consist primarily of unconsolidated and consolidated <br /> r alluvial and floodplain sheet deposits (predominantly sand, silt and clay)of Quaternary age, which <br /> is derived from the Sierra Nevada Mountains. Beneath the upper sedimentary deposits lies a thick <br /> sequence of marine deposits of Mesozoic age, which in turn is underlain by a pre-Jurassic.complex <br /> of igneous and metamorphic rock. <br /> V► <br /> t <br /> Lo <br /> 2.4. UNDERGROUND STORAGE-TANK REMOVAL <br /> Two 500-gallon and one 250-gallon underground storage tanks (USTs: Tank#l, Tank 42 and Tank <br /> L #3)were removed from three separate excavations on the property in January 1988. One additional <br /> 250-gallon UST,located under the building on-site,was.slurry filled with concrete under observation <br /> r by the PHS-EHD. <br /> I.W <br /> Soil samples were collected from beneath each removed UST and analyzed for total petroleum <br /> hydrocarbons (TPH), volatile aromatics (benzene, toluene, ethyl benzene and xylenes: BTE&X) <br /> ethylene dibromide(EDB)and total lead. Analytical results of soil samples indicated that significant <br /> TPH and BTE&X concentrations were present in soil samples beneath Tank 43 (250-gallon), located <br /> near the southern portion of the site. The sample collected from beneath the southern tank contained <br /> `W TPH at 2,500 milligrams per kilograms: mg/kg (parts per million: ppm). The results of the UST <br /> removals are summarized in Table 1. A copy of the laboratory report is included as Appendix A. <br /> t 3.0. SITE ASSESSMENT AND REMEDIATION <br /> 3.1. EXCAVATION OF HYDROCARBON-IMPACTED SOIL <br /> r <br /> On 17 August 1995, hydrocarbon-impacted soil was removed from the former Tank#3 area under <br /> the supervision of EnviroSearch of Bakersfield, California. Excavation procedures were directed by <br /> representatives of AGE. The excavated soil was stockpiled on-site. <br /> Six soil samples were collected from the floor and sidewalls of the excavation by AGE. <br /> Additionally, five composite soil sample were collected from the stockpiled soil. Analytical results <br /> of soil samples indicated that hydrocarbon-impacted soil remained in place at the eastern wall of the <br /> excavation at a depth of 14 feet below surface grade(bsg). Soil sample E-1 contained total petroleum <br /> hydrocarbons quantified as gasoline (TPH-g) at 340 ppm. Soil samples from the north, west and <br /> south walls and floor of the excavation either did not contain detectable concentrations of the <br /> petroleum hydrocarbons, or had concentrations below levels of concern. Analytical results of soil <br /> r <br />