ARCHIVED REPORTS XR0001497 - Laserfiche WebLink

Home Browse Search

1 4.0 SITE CLOSURE 4.1 Hydrocarbon Impacted Soil As stated in the October 1993 and Apnl 1994 Quarterly Reports prepared by GeoAudit, trace concentrations of benzene (0 006 ppm) and toluene (0 007 ppm) were detected in an excavation soil sample at a depth of 39 feet (Table 2), benzene (0 0079 ppm) was detected in a soil sample from MW-2 (MW2-45, Table 4) Additionally, samples from depths of 40 and 50 feet in B-1, near the center of the former gasoline tank excavation (Table 3), ' contained low concentrations of hydrocarbons. However,all detected concentrations are very low and most are just above reporting limits ' Figure 8 is a cross section of the site showing soil sample locations and remaining hydrocarbon impacted soil The volume of remaining impacted soil at the site can be estimated by viewing the remaining impacted soil as a cylinder with an approximate radius of 12 feet and an average thickness of thickness of 4 feet This estimation yields a remaining impacted soil volume of 67 cubic yards Using the concentrations of soil samples from the excavation, soil borings and monitonng wells, we estimate the remaining volume of gasoline to be approximately 0 12 gallons Calculations and assumptions are included in Appendix F rIt is unlikely that the impacted soil remaining at the site poses a health risk, due to the extremely low concentrations of hydrocarbons and remote location from Human ieceptors Furthermore, the impacted soil has shown no impact to groundwater for moie than one year, and any attempt at remediation of such a small volume of soil (and low level) would likely be ineffective and not cost efficient 4.2 Groundwater During the March 1993 sampling event, low concentrations of benzene (3 7 ppb) and xylene:, (11 ppb) were detected in MW-2 However, the presence of petroleum hydrocarbon impacted groundwater was not confirmed in subsequent samplings During the January 1994 event benzene, toluene, and xylene were initially reported in MW-3, but reanalysis of the sample did not confirm the presence of detectable hydrocarbons Although the reanalysis was not performed until 17 days after the sample was collected, it is unlikely that impacted groundwater is present at the site Since no petroleum hydrocarbons have been detected in groundwater for five consecutive sampling events, we believe that the extremely low concentrations of hydrocarbons initially reported (March 1993) are not representative of site conditions and no impacted groundwater remains at the site 4.3 Site Closure In accordance with the "Central Valley Regional Board Requests for Site Closure - 0.65-t A.W s.wo.,h� 11 i" W."2--d CUMAL eaw