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removed A 1500-gallon concrete septic tank was then excavated and broken up, and portions of the asphalt pavement were removed to provide access to the planned excavation areas All demolition debris was removed and disposed of at a Class III landfill 4 2 2 Soil Excavation and Sampling Estimates of the lateral and vertical extent of soil impacted from the underground tanks were estimated in previous investigations (JHKA, 1987 and Dames & Moore, 1988) It was apparent that soils had been impacted by TPH/D from 10 to 30 feet bgs on the east end of the former maintenance shop in ' the vicinity of the former 500 gallon waste oil tank Soils to the west of the shop, in the vicinity of the 10,000 gallon diesel UST had been impacted from 10 to 20 feet bgs (Dames & Moore, 1988) All ' previous investigations suggested that impacted soil extended directly below the former maintenance shop The approximate extent of the excavations along with geologic cross sections are presented in Figure 4 2 and 43 A VA1n,5�f�� All excavation activities were conducted under the th and Safety Plan presented in the Soil t Remediation and Groundwater Monitoring Workplan es& Moore, 1990) which was consistent with the state and federal Occupational Safety and Heal thee Dames & Moore Site Safety Officers conducted "tailgate" Health and Safety meetings wi l subcontractors prior to the start of each day's activities Both excavations and stockpiled soils in the biotreatment cell were monitored for organic vapors using an organic vapor meter (OVM) as directed by the Health and Safety Plan OVM readings greater than 50 ppm would cause all workers in the vicinity to use personal protective breathing apparatus Excavated soils were screened for TPHID in the field by using a thin layer chromatography (TLC) method to rapidly assess TPHID concentrations Soils which were stained or gave detectable ' OVM readings were transported directly to the biotreatment cell Soils with TLC values for TPHID greater than 10,000 mg/kg were also transported directly to the biotreatment cell Soils with lower TLC values, were segregated into two stockpiles Soils with TLC-TPH/D concentrations less than 100 mg/kg were placed in a stockpile to the south of the site designated OBC (Figure 4 4) Soils with TLC-TPHID from 100 to 10,000 mg/kg were stockpile adjacent to the eastern excavation, labeled OB2 (Figure 4 4) All stockpiled soil was resampled and analyzed by a California Department of Health Services (DHS) certified laboratory ' Excavation of impacted soil and bioremediation treatment cell construction were performed by CKC, Inc of Paso Robles, California between June 11 and June 20, 1990 Excavation at the west end of the former maintenance building was performed with a track-mounted hydraulic excavator When all stained soils appeared to be removed, and each of the four walls then the walls and the floor of the SAC36 046 16