SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

715 Hunter, Stockton April 27, 2005 Page 2 The analytical results of the soil samples from previous investigations in 2002 indicated significant concentrations of petroleum hydrocarbons existed in the soil in both the vadose and saturated zones. Concentrations of Total Recoverable Petroleum Hydrocarbons (TRPH) and Total Petroleum Hydrocarbons as gasoline (TPI-1-g) in the soil samples collected in the 2002 investigation are as follows (Table 2) : Table 2 Soil Sample Results of TRPH and TPH-g from 2002 Investigation 131- B1- B2- B2- 133- 133- B4- B4- 205bs 30'bs 15'bs 30'bs 15'bs 30'bs 20'bs 30'bs TRPH 23300 23900 26,000 8,000 92 4,100j 4,600 36,000 TPHmg 760 930 550 1 ,200 0.38 33400 13700 8,100 Concentrations in milligrams per kilogram (mg/kg) The concentrations of TPH-g in the vadose zone reported during the subsequent investigation in 2003 were considerably lower than the above-listed 2002 results, but the concentrations of TPH-g remained high in the saturated zone (Table 3) : Table 3 Soil Sample Results of TPHmg from 2003 Investigation MW2- MW2- MW2- MW3- MW3- MW3- MWi- MW1- 25'bs 35'bs 40'bs 20'bsg 30'bs 40'bs 30'bs 40'bs TPHmg 12.0 1270 1620 1 4.2 2,200 490 114 240 Concentrations in milligrams per kilogram (mg/kg) MW-2 is located near soil boring B1 . MW-3 is located near soil boring B2. MW-1 is located near soil boring B3 . The increasing concentrations of dissolved contaminants indicate continuous leaching of contaminants from soil to groundwater in both the vadose and saturated zone. Since a fine sand layer with some silt and clay begins at about 25 feet bsg to 50 feet bsg, where a coarse sand layer begins, the potential vertical and lateral migration of the dissolved contaminants through the sand layers is also high. It is crucial that remediation of the contaminant source in the soil be implemented as soon as possible in order to decrease the amount of contamination leaching into the groundwater and migrating through the sand layers . AGE recommends using soil vapor extraction (SVE) as the remediation alternative. EHD does not agree that using SVE alone is sufficient since SVE technology is for remediation of the vadose zone. Since significant amounts of contaminants exist in both vadose and saturated zones, EHD recommends reviewing other technologies that will remediate both the vadose and saturated zones such as dual phase extraction, or a combination of SVE, and air sparging. Submit a work plan for interim remediation of the impacted zones to EHD by May 31, 2005 . The deepest soil sample results were 210 mg/kg of TPH-g from soil boring B5 at 60 feet bsg. The groundwater contamination plume has not been defined in any direction.