ARCHIVED REPORTS XR0000240 - Laserfiche WebLink

Home Browse Search

Geocon has performed quarterly groundwater monitoring at the site since March 1995, with the most recent fourth quarter 1996 event completed on October 23, 1996. The fourth quarter 1996 groundwater monitoring report has been prepared and released separately from this report. A summary of the results of the previous site investigation work performed at the subject site are as follows: • The UST excavation samples indicate that releases of fuel hydrocarbons into the vadose zone soils has occurred. Excavation sample UST 1-1 collected from the west end of the unleaded fuel UST excavation contained total petroleum hydrocarbons as gasoline (TPHg) at a concentration of 2,000 milligrams per kilogram(mg/kg)and excavation sample UST 2-1 collected from the east end of the diesel fuel UST contained total petroleum hydrocarbons as diesel (TPHd) at a concentration of 58 mg/kg.A summary of the UST removal data is presented in Appendix A. • TPHg and TPHd were detected in vadose zone soil in borings SB-1 and MW-3 at a depth of 46 feet bgs at concentrations up to 120 mg/kg TPHg in boring SB-1 and 31 mg/kg TPHd in boring MW-3. TPHg and TPHd were not detected in borings SB-2, MW-1 and MW-2 with the exception of 1.0 mg/kg TPHg reported at 46 feet bgs in boring MW-2. • TPHg was detected in vadose zone soil in boring VW-2 between the depths of 26 to 51 feet bgs with a maximum concentration of 550 mg/kg at 46 feet bgs. TPHg and TPHd were detected in vadose zone soil at a depth of 45 feet bgs in boring MW-5 at concentrations of 17 and 12 mg/kg, respectively.TPHg was further detected in boring MW-9 at a depth of 41 feet bgs. • TPHg was detected in capillary fringe soil in borings VW-1 and VW-2 at depths of 65 and 61 feet bgs at a concentration of 1.3 mg/kg. Benzene exists in capillary fringe soil beneath the former fuel USTs with concentrations in borings VW-1 and VW-2 of 0.13 and 0.088 mg/kg,respectively. • Based on the October 1996 groundwater monitoring data, groundwater exits beneath the project boundaries at a depth of approximately 60 feet bgs with a general flow direction to the east at a relatively flat gradient of 0.0008 ft/ft. • Groundwater quality data from October 1996 indicates that dissolved petroleum hydrocarbon impacts exist beneath the site at maximum reported concentrations of 570 micrograms per liter (ug/1) TPHd, 17,000 ug/l TPHg, 4,200 ug/benzene and.43 ug/l methyl tert-butyl ether(MTBE) in well VW-2. The locations of the former USTs, existing groundwater monitoring and vapor wells, soil borings and the current site improvements are depicted on the Site Plan, Figure 2. Cumulative soil analytical data is presented in Tables 1 and 2. Cumulative groundwater analytical data is presented in Table 3. 1_3 Summary of Current Environmental Study In accordance with the request of Caltrans, Geocon performed a vapor extraction pilot test (VET) and prepared this PAR/CAP. I I Project No.58100-06-11C -2- December 17,1996 I