Laserfiche WebLink
_ Hunan Health Risk Assessment <br /> Former Mobil Oil Bulk Plant 04-343 <br /> 500 East Grant Line Road <br /> Tracy, California <br /> Well efficiency calculations, which refer to the percentage of head loss caused by friction and <br /> turbulence, were attempted based on the relative change in well drawdown with increased <br /> ' pumping rate during the step drawdown test. Data scatter prevented tlie use of this method as <br /> well as the more rigorous Birsoy-Summers method. Data scatter may represent aquifer <br /> stratification and/or delayed yield effects of the unconfined aquifer. <br /> 1 <br /> Short-term well yield is defined directly by step test data. The maximum pumping rate during <br /> ' testing was 2.86 gpm, which caused AW-9 to be overpumped in approximately 20 minutes. <br /> Longer-term well yields are projected based on efficiency and hypothetical target drawdown. <br /> The logarithmic stabilization of the pumping rate for a desired drawdown determines the <br /> maximum long-term yield. <br /> Constant-Rate Pump Test <br /> ' Constant-rate testing is conducted by pumping water from a well at a constant rate for an <br /> extended period of time, generally greater than 24 hours, and monitoring water level drawdown <br /> in the pumping well and observation wells with pressure transducers connected to an automatic <br /> data logger. <br /> ' From April 14 to 16, 1993, data were collected for 2,840.5 minutes (1.9 days) of pumping at <br /> approximately 2.0 gpm and 333 minutes of recovery (0.2 days). The constant-rate pump test <br /> ' data were analyzed using the Theis equation for a confined aquift r and the Cooper-Jacob <br /> approximation to the Theis equation. Prior to the analysis, the pump test data were corrected <br /> using the Jacob correction for an unconfined aquifer. This correction is necessary to accurately <br />' predict drawdown in an unconfined aquifer. <br /> ' Both the Theis equation analysis and the Cooper-Jacob approximation to the Theis equation <br /> predicted the transmissivity and storativity to be 1.3 x 102 square feet per minute (ft'/min) and <br /> ' 1.0 x 10', respectively. <br /> 30-0136-11 <br /> 1 1-9 <br />