ARCHIVED REPORTS_XR0013078 - Laserfiche WebLink

Home Browse Search

15 June 2009 AGE-NC Project No.05-1306 r.. Page 7 of 33 The CPT-generated soil types from near-surface to approximately 90 feet bgs at the CPT-1 location '"" consisted dominantly of fine-grained soil (silt, sandy silt, clayey silt, silty clay and clay). Sand and silty sand was identified at approximate depths from 19 feet to 40 feet bgs, 46 feet to 54 feet bgs, 64 feet to 65 feet bgs, and 86 feet to 90 feet bgs, which is consistent with the geology identified in `" Section 2.1 Regional Geologic/Hydrogeologic Setting. CPT computer-generated boring logs are included in Appendix F. 2.6. HYDROGEOLOGY The subsurface material underlying the site consists primarily of fine-grained (e.g., clay and silt) material with zones of sand. The uppermost fine-grained clay and silt material exists from ground surface to a depth of approximately 15 feet bgs under which lies a zone composed primarily of sand- sized material to a depth of approximately 41 feet bgs. An approximately 5-foot thick clay zone is reported to exist from approximately 41 feet to 46 feet bgs (the clay was confirmed as noted on the tips of each piece of shoring installed for the excavation project) followed again by sand-sized material to a depth of approximately 52 feet bgs, which is the total depth of the explored site. Measured depth to ground water in the area of the former UST has ranged from 7.97 feet to 14.29 feet below bgs (off-site ground surface elevations near MW-5 and MW-6 are approximately 4 feet to 5 feet lower than the site, and corresponding depth to water measurements vary accordingly).The direction of the horizontal hydraulic gradient ranges from approximately southeast �- to southwest. ` 3.0. ASSESSMENT OF TPH-D-IMPACTED SOIL The highest concentrations of TPH-d were detected in boring MW2, within the former tank excavation area. TPH-d concentrations in boring MW2 were as high as 14,000 mg/kg, in a sample collected at a depth of 20 feet bgs. The maximum detection of TPH-g in soil was 870 mg/kg, detected in the same sample. These soil samples were collected below the water table and in the former UST area. Soils associated with these samples were removed during remediation.Therefore, these results are no longer representative of the site. L. Soil samples collected in borings HA-8 and HA-9 had detection of TPH-d at 690 mg/kg and 1,500 mg/kg. The area where the maximum TPH concentrations were detected is defined by HA-9, SB-1, MW-2, SB-2, and MW-4. This area extends approximately 20 feet beyond the former UST excavation, and may represent a smear zone below the current water table. TPH-d concentrations were primarily detected between 15 feet bgs to 25 feet bgs. w w. Advanced GeoEnvironmental,Inc. i..