ARCHIVED REPORTS_XR0011438 - Laserfiche WebLink

Home Browse Search

24 April 2000 AGE-NC Project No. 97-0327 ' Page 5 of 6 ' by laboratory analysis. The analytical results of the selected soil samples are summarized in Table 1- The laboratory reports (Castle Analytical Laboratory Reference No. 2813 and McCampbell Analytical Inc. Lab I.D. No. 30783 through 30785) and chain-of-custody forms are included in Appendix D. 4.0. DISCUSSION AND CONCLUSIONS The following conclusions were drawn from the results of this investigation: • Saturated soil at the site was encountered at approximately 55 feet bsg. The static water level was measured at approximately 51 feet below the tops of the monitoring well casings. • The lithology underlying the site is dominated by fine sandy silt and silty fine sand. Generally, a fine sandy silt interval was encountered from 10 feet bsg to 25 feet bsg, which ' was underlain by a silty fine sand interval from 25 feet bsg to 40 feet bsg. A fine sandy silt layer was also encountered from 40 feet bsg to 50 feet bsg and was underlain by a silty fine sand interval from 50 feet to 70 feet bsg. The modeled site stratigraphy is shown in Figures ' 3 and 4. • The deepest soil horizon found to be impacted by petroleum hydrocarbons and/or oxygenated fuel additives was at 40 feet bsg (P6, P8, MW-1 and MW-2) and 45 feet bsg (MW-3). Locally, impacted soil was encountered at depths ranging from 25 feet bsg to 30 feet bsg(P3, P4 and P5), but more commonly, shallower soil, even close to the former UST excavation a, (P3, P6, P7and P8) was not found to be impacted. This distribution of contaminants, in conjunction with the site stratigraphy as described above, suggests a narrow, vertical plume of impacted soil descending from the former UST pit that spread laterally upon encountering the silt interval at 40 to 50 feet bsg. This model is shown in Figures 8 and 9. • The low concentrations of petroleum hydrocarbons and oxygenated fuel additives in ground ' water samples, reported in AGE's Ground Water Monitoring Report - 1 st Quarter, dated 21 April 2000, suggests that locally, at least a small volume of impacted soil has extended to ground water at approximately 51 feet bsg, probably in the former UST area. The petroleum hydrocarbon-impacted soil appears to extend horizontally from the UST area to MW-1, a minimum distance of approximately 53 feet toward the southeast. The detection of only MTBE, at a concentration of 0.6µg/kg, is suggestive of the plume margin. • The horizontal extent of petroleum hydrocarbon-impacted soil is relatively unknown east, northeast, north, northwest, west and southwest of the former UST area. Advanced GcoEnvironmcntal,lnc. I I. s