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r ter' ,y December 2000 AGE-NC Project No. 9-5-0114 Pac of 8 2.3. REGIONAL GEOLOGICAL S11:I'"FCNG "I71t site is Situated within the Great Valley Gcomol'phic Province of California, a large, elongate northwest tending. asymmetric structural tough. 1'he Great Valley Province has been tilled witl� thick sequcltces of sediment rangI g in age Irom Jurassic tii 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 oCtlle province have not been colIipl0tel%2 defined but arc hellcvcd to be of metamorphic and igneous 01-11'111. the Great Vallee Province has been subdivided into two major divisions identified as the Sacramento and all Joaquin Vallcvs. The Vlode,to. Riverbank and -I'unlock Lake Formations and overlying Recent alluvium are the principal sources of'doinestic ground water in the 13.500-square mile Sail Joaquin VallCV Ground Water Basin (Basin 5-22). This basin is drained primarily by the San Joaquin River. 2.4, Gl\MUND SVA L=R DF.1' I ll AND HA.M' DIRECTION 13ascd on review of the I,17CS nj Lyu(rl I)eIxh In 1999 map published by the San Joaquin County Flood Control District and Water Conservation District(FCD&rW('D). the estimated depth to groUnd water at the site to be 30 feet hs,,. Review of the map Lines gI'l:qual Elevalion ol Cirurrrx:Irccl7c:r.SJ�rit� r 199E (FCDc,W('F)) depicts the regional ground water t7owv direction towards the northwest and west. Between Mav 1993 and current, the elevation of")round water 114easured from wells on the site have shown an increase of the depth to ground water from 50 feet bsg to approximatcly 22 feet hso, vwith a -eneral !around water tlow direction towards the east and northeast. Ground water elevation contour maps for the site wcrt included in previt}u, quarterlN report, prepared by AGF Recievw of-previous around water monitoring at the site and historical depth to ground water maps (FCD&WCD) dating hack to 1971 sLlggests that ground water depth near the site has fluctuated hetween 6(_l fleet bs(-, and 40 feet bsg 3.0. SCOPE OF WORK T11C ,cope of the work includes installatiOn of Uround water monitoring and extraction wells, performance ofa<�round water extraction pump test, analysis of grab w°ater samples and soil samples to assess the horizontal and vertical extent ol'impacted media. and analysis of selected soil samples for permeability and porosity. .A large monitoring well or ground eater extraction well should he installed within the 10rmer [IST excavation, the area of the highest concentration dissolved hydrocarbons as Stoddard. .4drnnced Gc4 IF:11cironInenta1, Inc.