ARCHIVED REPORTS_XR0007143 - Laserfiche WebLink

Home Browse Search

' work involved drilling and sampling five additional soil borings and the installation of three additional on-site monitoring wells The Applied Consultants report concluded that the source of hydrocarbons in soil ' was located near bonng B7 Analytical results of soil samples indicated that hydrocarbons were present at 70 and 75 feet bgs, the depth to groundwater at that time Analytical results of groundwater samples indicated that the hydrocarbon plume in groundwater was centered near monitoring well MW-1 Benzene concentrations exceeded the California action level in groundwater samples from each of the six monitoring wells SOTA conducted further assessment of groundwater conditions with the installation of one on-site and one ' off-site groundwater monitoring well in 1995 These monitoring wells (MW-7 and MW-8) were included in the quarterly monitoring program in October 1995 Results of the October 1995 quarterly monitoring ' and sampling event indicated that the depth to groundwater was between approximately 63 to 66 feet bgs and the groundwater flow direction was toward the southwest Analytical results indicated that hydrocarbon concentrations exceeded California action levels in groundwater samples from five of the seven on-site ' monitoring wells Results also indicated that elevated hydrocarbon concentrations were present in groundwater from the off-site monitoring well (MW-7) 1 Between November 1994 and September 1997, SOTA conducted groundwater monitoring at the site During this period, the screen intervals of the on-site monitor wells had been submerged (Table 2) 23 RECEn GROUNDWATERI ' Blaes performed groundwater monitoring at the site in March and September 1999 Groundwater depth measurements collected on March 24, 1999 indicated groundwater levels between approximately 36 and 39 ' feet bgs, approximately 25 feet higher than previous measurements collected by SOTA on September 24, 1997 (Table 2) The apparent groundwater flow direction on March 24, 1999 was toward the south (Appendix A) Dissolved benzene concentrations ranged from 0 9 to 45 micrograms per liter (Vg/I_) in groundwater ' samples collected from six of the seven on-site wells in March 1999 Histoncal analytical data indicate that groundwater from monitor wells MW-1, MW-4 and MW-6 have typically had higher dissolved hydrocarbons concentrations than the other monitor wells (Table 2) Groundwater depth measurements collected on September 3, 1999 indicated that groundwater levels ranged ' from 46 25 to 49 80 feet bgs, approximately 10 feet lower than measurements taken in March 1999 The apparent groundwater flow direction was toward the northwest (Figure 4) ' 4