FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

15 July I999 AGE-NC Project No. 98-0504 Page 4 of 5 5.0. RESULTS A total of nine soil samples were collected from the floor and sidewalls of the over-excavation. TPH-g was detected at concentrations up to 80 mg/kg in the sample from the north wall, east end of the excavation. TPH-g was not detect in soil samples collected from the south,northwest, and east wall of the over excavation. Additionally, TPH-g was not detected in the samples collected from the south end of the west wall and from the floor of the excavation. BTEX compounds were detected at concentrations up to 1 mg/kg, benzene was only detected in the north west wall sample. MTBE and TBA were detected at concentrations up to 1.30 mg/kg and 8.9 mg/kg, respectively. MTBE was detected at the highest concentrations in the northern portion of the over excavation, especially in the northern west wall sample, located at the northwest edge of the site under Monroe Avenue. Analytical results of soil samples are sununarized in Table 1. The laboratory reports and chain-of-custody forms are included in Appendix B. 6.0. DISCUSSION The analytical results of samples collected during the 22 September 1998 UST removal indicated significant MTBE-impact to soil at approximately 11 feet bsg near the north end of USTs #1 and #2. The laboratory results from samples collected on 10 November 1998 after the over-excavation indicated lower concentrations from samples collected from the floor at 13 feet bsg. The samples collected from the south wall of the excavation did not have concentrations of the analytes of concern that exceeded the analytical method detection limits. Based on visual evidence of the condition of the tanks at the time of their removal and the laboratory data from samples collected, the hydrocarbon impact appears to have originated from the dispenser island and/or piping area. The vertical and lateral extent of impacted soil is not known at this time. Further subsurface investigation is necessary to determine the extent of the hydrocarbon-impact. 7.0. RECOMMENDATIONS Based upon the detection of MTBE at concentrations as great as 1,300 ug/kg in soil at depths as great as i 1 feet bsg, AGE recommends further subsurface investigation at the site to assess the MTBE-impact to soil and ground water. Ground water is currently approximately 30 feet bsg. The ground water flow direction onsite is inferred to have a northerly direction. AGE recommends one soil boring located in the dispenser area, advanced to the historic low ground water level of approximately 50 feet bsg.AGE recommends three additional soil probe borings advanced to ground water, a total depth of approximately 30 feet bsg, encompassing the former UST system. One soil Advanced GeoEnr ironmental,Inc.