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' Site Conceptual Model . Former MEL BOKIDES PETROLEUM - MANTECA 983 Moffat Boulevard, Manteca, California 10. INTRODUCTION AND SCOPE OF WORK At the request of Mr Nick Bokides of Mel Bokides Petroleum(MBP)Advanced GeoEnvironmental, ' Inc (AGE)has prepared this preliminary Site Conceptual Model(SCM)for 983 Moffat Boulevard, Manteca, California (site) The purposes of the SCM are to 1) identify the type and source(s) of contamination, 2)determine the nature and the extent of the contamination within a hydrogeologic ' framework,3)identify the dominant fate and transport characteristics of the site,4)specify potential exposure pathways, and 5)identify potential receptors that may be impacted by the contamination The site setting is illustrated on Figure 1 Site structures and soil borings and monitoring well ' locations are depicted on Figure 2 The SCM was prepared as directed in the San Joaquin County Environmental Health Department ' (SJCEHD) letter dated 09 August 2004, grid is in accordance with guidelines established by the Central ValleyRegional Water Quality Control Board(CVRWQCB)for the subsurface investigation ' of underground storage tank(UST) sites This preliminary SCM has been prepared utilizing existing data collected during previous subsurface ' . investigations focused on evaluation of dissolved methyl tertiary butyl ether(MTBE) ' 2.0 BACKGROUND The site is located in a business/agricultural area of eastern Manteca, California, in San Joaquin ' County(Figure 1),it is at the intersection of Moffat Boulevard and Cowell Avenue,in an area of low topographic relief, at an elevation of approximately 48 feet above mean sea level (Manteca Quadrangle, 7 5-Minute USGS Topographic) The property currently is being utilized as a gasoline station consisting of one small building at the north side of the site, an asphalt-paved vehicle area on the east side of the site and an active UST system utilized for automobile and truck fueling 21 REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING ' The site is situated within the Great Valley Geomorphic Province of California, a large, elongate northwest trending, asymmetric structural trough The Great Valley Province has been filled with thick sequences of sediment ranging in age from Jurassic to Recent, creating a nearly flat lying ' alluvial plain extending from the Tehachapi Mountains in the south to the Klamath Mountains in the north The western and eastern boundaries of this province are comprised of the California Coast Range and the Sierra Nevada,respectively Rocks composing the basement complex of the province have not been completely defined but are believed to be of metamorphic and igneous origin The • Great Valley Province has been subdivided into two major divisions identified as the Sacramento Advanced GeoEnvlropmental,Inc