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10 August 1998 AGE-NC Project No. 98-0471 Page 7 of 8 were mostly peat or light weight, highly organic soils which typically have higher porosity and permeability, and therefore weigh less, than typical soils (sand or clay). • The greatest concentrations of petroleum hydrocarbons were detected in samples collected from the trench established west of the active 1,000-gallon AST(Trench T1). Hydrocarbon impacted soils were observed and quantified at high concentrations below the buried portion of the AST system. This distribution of the contaminants indicates that the buried portion of the fueling system may have been leaking and may still be releasing petroleum products. • Impacted soils are limited to a depth of eight feet bsg, based on analytical data of soil samples collected from both AST locations. • The more intensely impacted soils are limited to the area of the active 1,000-gallon AST dispenser lines. Soil data from samples collected from trenches established surrounding Trench T1 indicted the presence of low concentrations of TPH-g and BTE&X compounds. • The release of petroleum has impacted the ground water beneath the active 1,000-gallon AST on the site. The date of initiation of the release cannot be determined, however, some quantities of the petroleum released contained MTBE, the fuel additive present in some gasoline formulations since the late 1970s and in most gasoline formulations since the late 1980s and early 1990s. The percentages of gasoline compounds present in the trench T1 water sample,high benzene to TPH-g ratios, indicate that unmodified fuels are present at the site. Figure 3 depicts the known distribution of dissolved hydrocarbons. 5.0. RECOMMENDATIONS Based upon data collected over the quarter at site, AGE recommends the following: • Cease use of the active AST system to remove the soils impacted by the release of petroleum in the subsurface. • Install secondary containment systems under the AST systems. • Install groundwater monitoring wells to determine the chemical characteristics of the dissolved plume and to assess the stability of the dissolved plume. Advanced GeoEnvironmental,Inc.