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Mr Harlan Knoll S E C ® R July 3, 2003 Page 2 Ball Park Well Construction Details The Ball Park well is screened from 570 feet bgs to 732 feet bgs and from, 850 feet bgs to 874 feet bgs Cement grout extends from surface grade to 490 feet bgs, past the confining layers Static water level in the Ball Park well was measured at 71 feet bgs ,a r� Data Analysis Analysis of the data indicates a relationship between the Ball Park well and site monitoring wells screened at greater depths (MW-5 and MW-6B) The Ball Park well pump was operational from approximately 16 30 to 21 30 daily Displacement versus time plots indicate water level w increased in deeper screened wells when the Ball Park pump was operational, and that the water level decreased when the Ball Park pump was turned off, Figures 3 and 4, respectively ; Displacement versus time plots Indicate that the Ball Park well does not have a significant influence on water levels in MW-6A (Figure 5) It appears that the confined aquifer remains ; saturated when the Ball Park well pump is operational Increase in water level the wells in the unconfined aquifer wells may be due to a response known as the °Noordbergum" effect, (Verrugt, 1969)' Pumping of groundwater from the confined aquifer in the Ball Park well results in a lowering of the hydraulic head in the confined aquifer of 'k approximately 170 feet The head loss causes an increase in the load carried by aquifer grains and pore water within the entire groundwater system in and above the confined aquifer When 41 the increase in load is applied instantaneously as with the periodic pumping of the Ball Park well, the pore water will initially carry the load This results in an increase in pore pressure, which ; causes a rise of the water level in the overlying aquifer This response is generally observed, and is more predominant, in fine-grained material (Bouwer, 1978)2 CONCLUSIONS x The data does not indicate a hydrogeologic communication between the shallow aquifer through which site monitoring wells are screened, and the deeper aquifer beneath the Corcoran Clay in which the City of Tracy's Ball Park Well is screened Pumping in the Ball Park well influences the shallow aquifer, although the influence appears to be mechanical and not hydrogeological If you have any questions, please feel free to call Bob Jackson (916) 861-0400 extension 283 or Robert J (Bob) Cochran with Chevron at (925) 842-9655 - FN Sincerely, SECOR International Incorporated ob Jackso Acott OEGable5R G Staff Geologist Principle Geologist r 3 ' Verrugt A 1969 Elastic storage of aquifers In Flow through Porous Media, R J M DeWeist �ed ) Academic Press, New York, pp 331-376 Bouwer H 1978 Groundwater Hydrology McGraw HIII Book Company pp 326-333 1 IChevron1986321Reports120031Transducer study doc r ra