Laserfiche WebLink
4 .3 Stratigraphy <br />' The stratigraphy at this site was discussed in moderate detail in <br /> GeoAudit' s ammended FRP. Two zones of oxidized sediment are present <br /> in the upper 70 feet, and appear to represent paleosols. These <br />' zones are overlain by reduced sediment. The contact between <br /> oxidized and reduced zones is interpreted as a major erosion <br /> surface between depositional sequences. Each sequence is further <br /> subdivided into several upward-fining fluvial sequences. These <br />' sequences are illustrated in Figures 5 and 6 of the FRP. <br /> The new wells (VW-5 through VW-7) encountered these sequences. The <br />' uppermost seugence is present from approximately 22 feet to ground <br /> surface, and forms an upward-fining sequence of medium- to fine- <br /> grained sand and silty sand. Brown to reddish-brown, moderately <br />' oxidized sand and sandy silt was present .from approximately 30 to <br /> 38 feet. Light grey to light brown, reduced sand was present to <br /> approximately 45 feet. The lower erosion surface is present near 45 <br /> feet in VW-5 and near 58 feet in VW-6; sediment below this depth is <br />' oxidized to dark brown or reddish brown. <br /> 4 .3 Soil Contamination <br /> TPH as gasoline and BTE&X were detected in all of the analyzed soil <br /> samples (Table 5) . The greatest concentration of hydrocarbons was <br /> at depths between 30 and 45 feet, which is in accord with <br /> observations from the vadose zone wells drilled in May 1993 . <br /> Appendix A shows that the remedial wells are screened through this <br /> contaminated interval . The laboratory report and chain-of-custody <br /> for the soil samples is included in Appendix C. <br />' 5. 0 CONCLUSIONS AND RECOMMENDATIONS <br /> 5, 1 Groundwater <br />' The depth to groundwater has increased 2 feet throughout the site <br /> area since measurements were made in June 1993 . The groundwater <br /> flow direction continues to be to the south-southwest. <br />' Significant changes in groundwater contamination have occurred <br /> since the June sampling event. Concentrations of TPH and BTE&X have <br />' dropped markedly in MW-14 , but have risen considerably in EW-1. <br /> These two wells continue to be the most contaminated. <br /> The sample from MW-11 supports the suggestion in GeoAudit' s FRP <br />' that the June 1993 data from MW-11 are questionable (Figures 15 and <br /> 16 of the FRP) . In contrast to previous monitoring events, TPH and <br /> BTE&X were reported in MW-11 in June. A sampling or laboratory <br /> labeling error may have occurred in the June event. No <br /> contamination was detected in MW-11 in the September event. <br />' 14 <br />