SITE INFORMATION AND CORRESPONDENCE_FILE 2

Home Browse Search

collected for chemical analysis at 10, 11, and 12 fbg. Maximum adsorbed-phase TPH-G, TPH-D, and benzene concentrations were 590, 3,700, and 6.6 ppm, respectively. • A review of the field descriptions of select soil samples collected from the aquifer in AW- 10, AW-11, and AW-12 indicates the material to be sand with fines, with content varying from 20 to 44 per cent by weight. Values of hydraulic conductivities (K) for these soil types range from a high of approximately 2 x 1W to less than 2 x 10' ft/min (for silty sand [Freeze and Cherry 1979]). • Aquifer testing estimated the shallow aquifer could yield approximately 2.0 gpm from AW- 9. CONCLUSIONS Based on the results of this and past investigations, Alton Geoscience concludes: • No free product is present on ground water beneath the site. • Based on the results of field activities and laboratory analyses, the lateral extent of dissolved-phase hydrocarbons in ground water is adequately characterized. Dissolved-phase hydrocarbons appear limited to the north/northwest portion of the property (in the vicinity of AW-3 and AW-9), and may extend offsite under Grantline Road. The results of ground water analyses indicate that dissolved-phase hydrocarbons are not present along the north side of Grantiine Road. • Concentrations of dissolved-phase hydrocarbons as detected in monitoring wells have generally decreased through time. • Remedial excavation efforts have removed petroleum hydrocarbons to the fullest practical extent. • Adsorbed-phase hydrocarbons in the vicinity of the former aboveground storage tanks and underground storage tank are present within the capillary fringe only and extend vertically to below ground water. Remedial excavation operations in 1990 have effectively removed hydrocarbon-affected soil from the vadose zone in the vicinity of the former storage tanks. • The presence of adsorbed-phase hydrocarbons below static water level appears to indicate a smear zone due to water table fluctuations. It can be expected that concentrations attenuate rapidly with depth as in MW-12. • Estimations of hydraulic conductivity (K), transmissivity (T), storativity (S), and average linear velocity were made from data collected during the aquifer pumping test. The K value estimated from aquifer testing is 7.47 x 10' ft/min; this compares favorably with those ranges of values given by Freeze and Cherry for similar soil types. Transmissivity was estimated at a low 1.35 x 10-2 ft2/min. For comparison, Freeze and Cherry indicate that