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Frontier Transportation B23502.01A January 2, 1996 Page 6 The borings will be drilled using a Central Mine Equipment model 75 (CME-75), mobile hollow-stem auger drill rig. Drilling services will be provided by Twining's Drilling Services Division (C57 Contractors License No. 506159) under to supervision of a Twining geologist. Proposed soil boring locations are also shown on Drawing 4. The final boring locations may be adjusted in the field due to underground utilities and other site improvements. The proposed soil borings will not be drilled in an easement or right-of-way controlled by a municipal government. Therefore, municipal permits will not be required for this assessment. An application for a soil boring permit will be submitted to the SJCPHS with this work plan. The vertical extent of PPC migration beneath the former gasoline USTs excavation will not be investigated at this time since the excavation remains open preventing drill rig access. The lateral extent of PPC migration in soil will be assessed by drilling soil borings B4, B-2, and B-3 at various distances north, east, and south of the former gasoline USTs to a depth of 15 feet BSG. The western extent of PPC migration in soil will be assessed by drilling angle boring B-4 beneath the existing building to a depth of 15 feet BSG. Soil samples will be collected at 10 and 15 feet BSG in each of the four soil borings. Soil samples will be field screened for the purpose of preparing lithologic logs and for evidence of PPCs. Soil samples collected will be preserved in the field for laboratory analysis consistent with our SOPs. Soil samples will be submitted for laboratory analysis based on the results of the field screening with the PID and SJCPHS criteria for subsurface assessment. Based on the planned depth of 15 feet, two soil samples ( 10 and 15 feet BSG) will be analyzed for each boring. The analytical results of soil samples collected from these soil borings are expected to provide data on PPC concentrations in subsurface soil. This data will be used to evaluate the lateral extent of PPC migration in soil. After completion of the soil sampling, the soil borings will be backfilled with a sand/cement slurry. The slurry will be pumped through the annulus in the hollow-stem augers. Backfill will be placed in one continuous operation from the bottom to the top of the borehole. When the annulus fills with the slurry, auger flights will be removed ( 10 feet at a time) from the borehole, allowing the slurry to uniformly fill the borehole to the surface. 4. 1.2 Monitoring Well Installation and Development: Based upon the adsorbed phase PPC concentrations detected in soil samples collected during UST removal and the observed shallow depth to groundwater at the site, a groundwater investigation will also be conducted as part of this site characterization. Twining proposes to install three groundwater monitoring wells (MW- 1 through MW 3) at the proposed locations illustrated in Drawing 4. Boreholes for the monitoring wells will be drilled using a CME-75, mobile hollow-stem auger drill rig. Drilling services will be provided by Twining's Drilling Services Division