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' � ^ � ., � rW'-., 3 i:.. �,i e � 4�� r � � "v� s� �� 3_ 'e e�,#,�•r� �E �' . ^.`r'.`�'' R",.` �K �.my N. 3 '�G PmE-cT RUGAL,60.3 2-10-89 1.3 GROUND WATER OCCURANCH IN THE KION ARBA Ground water production in this region is predominantly from the sands and gravels associated with the Laguna and Mehrten fo"natio Undnon- ying ne the (continental)sediment deposits of P1io-Plei3t0cene age). Y is Mehrten formation is the Valley Springs Formation,nundifferentiated (continental)sediments that unconformally overlay !he marine Markley-Noxtonville formation (see figure ti). Ground water recnarg e to the above:mentioned formations and to the youtnger formations,surfsm to near surface deposits situated above them (the Quaternary age Alluvium faro and basin deposits and the Pleistocene Victor Formation),is predominantly vertical leakage and lateral movement downdip along the less permeable layers.The Mehrten formation can be found outcropping to the east of Stockton in the foothills of the Sierra Nevada Mountain Ranges. Ground water recharge to this funwtion is predominantly from its exposures in the foothills with some vertical leakage from the overlying formations. The Laguna formation,which overlays the Mehrten does not outcrop in the foothills of this disignated area, but outcrops further north,east of Lodi. Ground water recharge for the Laguna formation is also pm4orninantly from its exposures in the foothills an seepage from the Mokeluume and Calaveras Rivers. The overlaying Vidor Formation and Alluvium deposits are recharged front surfer exposures, and laverns leakage from the ee surface Basin and I� n� Rivers, nterfasoil layersin the area. leakagefro The direction of free ground water movement in this region is to the west and towards south Stockton from the foothills of the Sierra evada Mountain Ranges,and east from the Sacramento -San Joaquin Delta. At present,intrusion of waters from the Delta tyre hnparing the quality of the gnouud water in the Stockton area (sec figure 7 and 8). 1A PREVIOUS WORK EXXON,Inc. contracted Hardy Lawson to perform a site evaluation prior to el conducted a site visit but subleasing lite station. Hardy Lawson persona borings:withi�r the time were unable to obtain permits to� exploratory g frame available to them (see their report dated June 17, 1988 appendix C). On October 21, 1988 Town and Country (T&C)removed the du= underground storage tanks. One tank each of regular leaded, regular unleaded and premium unleaded gasoline. Upon removal, the Tanks were visually inspected by T&C for any suggestion of failure,and were found to be tight. Sample results of soil taken from beneath the removed tanks showed the soil conte gasoline rsary soilesamplscngr(osexs.ta table lied c 1 and GeoSystems (AGS) performed the appendix D). 8.