ARCHIVED REPORTS_XR0004263 - Laserfiche WebLink

Home Browse Search

Frontier Transportation, Inc. B23502.01 October 16, 1996 Page 6 The lateral extent of PPC migration in soil was assessed by drilling soil borings B-1, B-2, and B-3 at various distances north, east, and south of the former gasoline USTs to a depths ranging from 10 to 12.5 feet BSG. The western extent of PPC migration in soil was assessed by drilling angle boring B-4 beneath the existing building to a vertical depth of 10 feet BSG. Drawing 5 illustrates the cross-section of angle boring B-4. Soil samples were collected at selected depths in each of the four soil borings. Soil samples were field screened using a photoionization detector (PID) and visually observed for evidence of PPCs. The soil samples were also observed for the preparation of lithologic logs. During drilling of the boreholes for monitoring wells MW-1, MW-2, and MW-3 at the originally proposed locations, Twining encountered evidence of PPCs in soil above groundwater. As a result, the borehole for monitoring well MW-1 was relocated twice and the borehole for MW-2 was relocated once. The abandoned boreholes were labeled MW- 1RA, MW-1RB, and MW-2RA respectively. Twining collected soil samples from each of the abandoned boreholes and submitted these soil samples for laboratory analysis. Soil samples MW-IRA and MW-IRB provide additional soil delineation toward the northwest �� aM soil sample MW-2RA provide additional delineation toward the northeast. ' ) p,41'? The boreholes for monitoring wells MW-2 and MW-3 exhibited evidence of PPCs in soil; however, due to the proximity of these wells to the eastern property boundary, the wells could not be relocated without moving offsite. Soil samples collected for laboratory analysis were preserved in the field consistent with our SOPs. Soil borings logs have been included as Appendix B. Soil samples were submitted for laboratory analysis based on the results of the field screening with the PID and SJCEHD criteria for subsurface assessment. After completion of the soil sampling, the soil borings were backfilled with a sand/cement slurry. Based upon the shallow depth of the soil borings and the fine grained soils encountered, Mr. Harlin Knoll of SJCEHD allowed the hollow-stem augers to be removed prior to backfilling. The slurry was poured through the annulus of the boring. Backfill was placed in one continuous operation from the bottom to the top of the borehole. 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 was also conducted as part of this site characterization. On August 15 and 16, 1996, Twining installed three groundwater monitoring wells (MW-1 through MW-3) at the locations illustrated on Drawing 4. Boreholes for the monitoring wells were drilled using a CME-75, mobile hollow-stem auger drill rig. Drilling services were provided by Twining's Drilling Services Division (C57 Contractors License No. 506159) under the supervision of a Twining geologist. Soil samples I