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Geo(oglcafTechnics Inc. <br /> 2741 Riw,?oad <br /> Mo&!sto,Caafomia 95351 <br /> (209)538-6424/'faX#538-5852 <br /> WORK PLAN <br /> FATE & TRANSPORT MODEL <br /> Former Moresco Property. <br /> .16865 Gawne Road <br /> Stockton, California <br /> Project No. 251.2 <br /> March 21, 1997 <br /> 1.0 INTRODUCTION <br /> The exploratory work at this site has shown that gasoline was released from the former <br /> residential ;UST and impacted the subsurface soils down to about 70 feet below ground <br /> surface (bgs). Gasoline with the fuel oxygenate. compound Methyl Tertiary Butyl Ether <br /> (MTBE)' has been found at this site at elevated concentration. The center of the highest <br /> contaminant mass is migrating away from the source and moving down towards groundwater. <br /> Groundwater monitoring has not occurred, but groundwater depth is approximately 110 feet <br /> bgs. Mass balance calculations show that approximately 1,675 gallons of gasoline are present <br /> in the subsurface. <br />{ Site geologic conditions are dominated by sandy sediments with a thin gravel layer at 63 feet, <br /> and four,fine grained lenses or layers down to 100 feet bgs. The .presence of MTBE in the <br /> gasoline and evidence of chemical mass transfer through the subsurface soils away from.the <br /> original tank source suggest that the gasoline contaminant may encounter groundwater and <br /> potentially impact the property's domestic well located 200 feet-east of the former tank <br /> location. <br /> Chemical fate and transport and risk evaluation modeling was recommended by Geological <br /> i Technics Inc. and approved by Mr. Ron Rowe of San Joaquin County. The purpose of this <br /> work plands to present 'a conceptual model and the specific parameters to be used in the <br /> 4 model. <br /> 2.0 CONCEPTUAL MODEL <br /> In orderto develop a range of variability for the physical parameters, a combination of <br /> previously„obtained soil classification information and laboratory data was used. Previous <br /> reports have resulted in a good understanding,of the subsurface stratigraphy at the site. <br /> Based on the available information previously submitted to the San Joaquin County <br /> Department of Environmental Health and the Regional Water Quality Control Board <br /> (agencies),-,a conceptual model for the site has been developed and is presented in this section. <br /> II <br />