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600 N Holt Road Project No.06304-01 Page 12 <br /> 2.0 SITE DESCRIPTION <br /> The Site is a former agricultural airplane landing strip (D&D Flying Service) located at 600 N Holt <br /> Road in the City of Stockton, California. The subject property is located approximately 1,500 feet <br /> east of N Holt Road,with access located off W House Road, adjacent to the northeast portion of the <br /> subject property with APN: 131-210-20. The approximately 81-acre Site is currently utilized as <br /> commercial farmland. Irrigation canals followed by agricultural fields border the subject properties <br /> perimeter. The northeast boundary of the subject property is adjacent to W House Road, with <br /> access to the Site.The Former D&D Flying Service operations ceased in approximately 1988. <br /> The Site topographyz is relatively flat, with a gentle topographic gradient to the west-southwest, <br /> with an approximate elevation of 0 feet above mean sea level (msl).The general area is agricultural, <br /> interspersed with some rural agricultural residential housing. <br /> A general location map (Vicinity Map - Plate 1) and a general site map showing the former landing <br /> strip and AG plane rinse area locations (Site Map - Plate 2) are attached to this report in Appendix <br /> A. <br /> 3.0 CONCEPTUAL SITE MODEL <br /> The conceptual site model (CSM) is a tool used to identify primary sources of contaminants of <br /> potential concern (COPC) at a Site, mechanisms of release for COPCs, points of exposure at the Site, <br /> and exposure pathways (ingestion, inhalation, and dermal contact) for the screening level <br /> evaluation of health risks. The CSM also serves the purpose of guiding the progression of the risk <br /> assessment process, thereby functioning both as an organizational tool and as a check against <br /> omissions that might result in underestimations of health risk. Three of the most important <br /> elements of the CSM are land use, potential receptors, and potential exposure pathways. The <br /> workplan begins with a base evaluation considering the unrestricted residential land use scenario. <br /> The following summarize a basic CSM based on a review of available regulatory databases for the <br /> Site and adjacent properties. <br /> 3.1 Hydrogeology <br /> According to the most detailed Geologic Map3 covering the subject property and vicinity, the site is <br /> underlain by Holocene Dos Palos Alluvium (Qdp) mixed alluvium dominantly from granitic sources. <br /> The site soil consists primarily of Peltier mucky clay loam which has slow infiltration rates and is <br /> poorly drained4. The soil underlying the AG plane rinse area is compacted from years of farm <br /> operations. <br /> Groundwater elevation maps were not available for the region. One well/pump permit on file with <br /> the San Joaquin County Environmental Health Department for a parcel located approximately 1,000 <br /> feet east of the subject property (situs address 1510 N Inland Drive) was obtained during a public <br /> Z US Geological Survey, 2018,7.5'Topographic Map,California, Holt Quadrangle. <br /> 3 California Geological Survey D.L.Wagner, E.J. Bortugno,and R.D. McJunkin, 1991,Geologic Map of the San Francisco—San Jose <br /> Quadrangle,California. Scale 1:250,000 <br /> ^UC Davis California Soil Resource Lab,SoilWeb. <br /> Petralogix Engineering,Inc. <br /> 26675 Bruella Road,Galt,Ca 95632 <br /> 12091-400-5729 <br /> U <br /> www.petralogix.com <br />