ARCHIVED REPORTS_XR0002803 - Laserfiche WebLink

Home Browse Search

3.0 RESULTS OF THE INVESTIGATION 31 Geology and Hydrogeology Based on the CPT soundings, subsurface soils to a depth of 125 feet consist of massive intervals of fine-grained silt and clay mixtures, interrupted by thin (i e , up to five-foot thick), groundwater- bearing, coarser-grained intervals Groundwater-bearing intervals were identified at approximately 45, 75, 90, and 125 feet bgs The interval at 125 feet appears to consist of gravelly sand of undetermined thickness A soil boring log is included in the CPT report (Appendix D) On August 24, 2000, the static depth to the groundwater table, as measured in the nine groundwater monitoring wells, ranged from 37 12 feet bgs in MW-4 to 40 79 feet bgs in MW-7 MW-7 is completed above-grade and protected with a monument casing To incorporate MW-1, VW-1, and VW-2 into the soil vapor extraction and air sparging systems, ENSR previously modified the wellheads and compromised the survey In the other monitoring wells, the groundwater elevation ranged from a high of 22 38 feet below mean sea level (MSL) in MW-2 to a low of 22 67 feet below MSL in MW-5 Groundwater levels have dropped an average of 3 28 feet, since groundwater levels were last measured on May 19, 2000 In the past year, groundwater levels have dropped an average of 0 52 feet Since May 1992, the groundwater levels have risen approximately 29 29 feet The cumulative groundwater monitoring data are summarized in Table 4 The groundwater flow direction and gradient are illustrated on the groundwater surface map (Figure 6) The groundwater gradient was calculated at 0 0022 foottfoot in a northeasterly direction This is consistent with the prevailing historical groundwater gradient and flow direction 32 Analytical Results iOnly three of the ten soil samples collected from beneath the former UST contained detectable concentrations of gasoline constituent compounds The sample collected at 10 feet contained 560 milligrams per kilogram (mg/kg) of TPH-as-gasoline and 0 1 mg/kg of MTBE The sample collected at 20 feet only contained 4 5 mg/kg of TPH-as-gasoline, and the sample collected at 40 feet only contained 00087 mg/kg of MTBE The soil samples collected at 30, 50, 60, 70, 80, 90, and 100 feet did not contain detectable concentrations of any of the compounds analyzed These soil sample results are summarized in Table 2 and the laboratory report and chain-of-custody are included in Appendix E 9