Desalting and ground water management in the San Joaquin Valley, California

Abstract

Desalting brackish ground water can be combined with ground water management in the San Joaquin Valley to partially alleviate environmental and economic problems caused by agricultural drainage water. Desalting subsurface drainage water produced from on—farm shallow drainage systems is costly due to high salinity and the potential for scaling and fouling of reverse osmosis (RO) membranes. When subsurface drainage water is transported in open canals, algal growth and accompanying organic transformations present pretreatment problems that have yet to be solved. Similar problems have been experienced at desalting facilities outside the San Joaquin Valley using comparable feed waters. The proposed pumping of usable ground water from the semiconfined aquifer on the Valley's west side to lower the shallow water table and thus eliminate waterlogging of crop root zones may result in degradation and mining of usable ground water and contamination of the confined aquifer below the Corcoran clay, the principal confining layer in the Valley. A combination of brackish ground water desalting and ground water management by pumping unusable shallow ground water from an interval between the crop root zones and the usable water body at the bottom of the semiconfined aquifer would result in (1) a lower salinity feed water that will reduce the cost of desalting, (2) a feed water that requires little, if any, filtration to protect RO membranes, and (3) the removal of the body of water containing high levels of salt and selenium that endanger usable water in both aquifers. The combination of brackish ground water desalting and ground water management would result in the production of usable quantities of fresh water for California's ever-increasing population and a reduction in the cost of reclaiming and managing drainage water by desalination.