Abstract: An Investigation of Potential Groundwater Impact by San Emidio New Town Development, Southern San Joaquin Basin, California

Bryan L. Bruce, Janice M. Gillespie

Dale Poe Development Corporation desires to pump as much as 20,000 acre-feet of ground water per year in the area of the proposed San Emidio Ranch Project located in the southernmost portion of the San Joaquin Valley. The goal of this study is to determine the effects of these withdrawals upon water levels in the aquifer. A simulation model based on the Theis well equation was used to predict the response of the water table to pumpage. Scenarios were run with a "best case" having transmissivity and pumpage rate values of 204,400 gal/day/ft and 12,390 gal/min, respectively, and a "worst case" with 69,050 gal/day/ft and 12,390 gal/min, respectively. The transmissivity values were based on data from a pump test described in the Environmental Impact Report (EIR). The maximum pumpage rate as taken from EIR estimates; the minimum pumpage rate was calculated from the minimum value required to supplement reduced surface water supplies during drought periods for the estimated 63,000 residents. Results from the two simulations were plotted to illustrate the amount of drawdown that would occur under each scenario after a 25-yr period. It was determined that even under the worst case scenario the area of water-table decline would remain almost completely within the project area and should have minimal impact on surrounding farms and ranches.

AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994