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2021699.7004 t.ammersMle School District July 16, 1990 3.0 REGIONAL GEOLOGY AND HYDROLOGY Joaqu The Lammersville School District site is located in the northwest irds of thetGreat Cent al Valley portion of Sly of The Sart Joaquin Valley constitutes approximately the southern two -thirds th California; to the north.ttte Sacramento-San Joaquin Delta and the Sacramento Valley beyond occupy the remaining third of the Great Central Valley. The San Joaquin Valley is bordered on t eDa east and and southeast by the Sierra Nevada geomorphic province and on the west by the Coast Mang es (others, 1959). The San Joaquin Valley floor slopes gradually toward the northwest and ddips to a Valley at its its center line. A low, broad and indistinct divide interrupts the lengthwise slope basins:the San Joaquin Basin to the north.which drains to the midpoint and separates, .o hydrologic pacific ocean,and the Tulare Basin to the south,whit Basina(Stateet only when of CalitorniaaDepartmentflows carry its ofWate water across the divide and into the San Joaquin Resources, 19131Y site is located within the Tracy Groundwater Basin, a politically designated portion The subjectarea is being degraded by of the San Joaquin Groundwater Basin. The water quality in the Tracy Stockton and intrusion of saline connate groundwater as a result of overdrafttwesteof rn boqundary uifers softehe San Joaquin Tracy areas. Shallow groundwater is generally poor along the Groundwater Basin. 4.0 BACKGROUND One underground gasoline tank was formerly located on the site for fueling the school buses that serviced the LammersviAe School District. The gasoline tank was removed and LammersviAe School relik sampling and analysis program to conDistrict retained Groundwater Technotl afifte hecund rlys Ig soils and groundwater. Results of the determine if leakage from the tank had initial investigation were presented in Groundwater Technology'sorin su(MW lcthr{oughcMW$)I were drilled Report', dated August 10, 1987. On June 19, 1987, by g extent to and around the tank excavation in an attempt to define the veksste cal s armed aiut n June f adjacent petroleum hydrocarbons in the soil and groundwater(Figure 2) The initial wor - — _ �. �1 GROUNDLVATER..... TECHNOLOGY,INC.