ARCHIVED REPORTS_XR0011036 - Laserfiche WebLink

Home Browse Search

k1T !i F � Executive Summary The Disco site is the location of three former 10,000-gallon gasoline tai 6' 16 iel6�ed gasoline constituents into the soil and groundwater. The current property owner of the Disco site is Del Monte Foods (Del Monte). Del Monte has conducted soil and groundwater investigation activities at the Disco site at the direction of San Joaquin County's Public Health Services, Environmental Health Division (PHS/EHD). Del Monte also has constructed and is operating a treatment system designed to'remove the source of gasoline. This report summarizes the progress of the air sparging and soil vapor extraction (AS/SVE) I processes intended to remove gasoline contamination at the source, presents the findings of the supplemental site characterization and monitoring performed through March 1995, delineates the extent of the gasoline plume, evaluates remedial options for the dissolved- phase gasoline plume in the groundwater, and presents a final remediation plan. AS/SVE Progress Summary and Conclusions : The AS/SVE system is achieving gasoline removal in three ways. Through SVE, gasoline is removed at an estimated rate of 20 to.50 pounds per day. This rate is expected to decline rapidly and to approach-an asymptotic rate of 2 to 4 pounds per day after 6 months or so. Gasoline is being removed at approximately 1 pound per month by biodegradation in the . groundwater; it is also being degraded in the vadose zone. m The SVE system has a radius of influence of more than 20 to 2S feet, or enough coverage area to effect remediation of all known nonaqueous phase liquid (NAPE) gasoline in the vadose zone. As soil vapor concentration declines, exchange of the engine for vapor phase { granular activated carbon treatment and-blower cycling should be considered to improve groundwater mixing and reduce operating cost. l Site Character Summary Groundwater at the Disco site has a small horizontal gradient (0.001 ft/ft) and a vertical gradient of 0.012 ft/ft. The natural rate of horizontal movement is perhaps 5 to 10 feet per year, and the vertical movement is an order. of magnitude slower. The direction of the horizontal shallow gradient has been highly variable in 3.5 years of monitoring. Historic fluctuations of over 50 feet in groundwater elevation since closure of the Disco Service Station 20 years ago are likely to have smeared NAPL gasoline both above and below the present groundwater elevation. Groundwater is probably on the rise due to extreme precipitation/infiltration this winter. Vertical groundwater fluctuations together with a variable horizontal gradient have spread gasoline and created a groundwater plume that has migrated approximately 200 feet to the west and northwest and 100 feet to the east. ( Groundwater modeling indicates that the shallow groundwater at the Disco site is not likely to have been influenced by former Del Monte production well pumping. Pumping at very SF010030991.DOC ES-1 i