SALT-GRADIENT SOLAR PONDS FROM CONCENTRATED SUBSURFACE AGRICULTURAL DRAINAGE WATERS OF THE SAN-JOAQUIN VALLEY, CALIFORNIA

Over 100,000 acre-feet of agricultural drainage water must be disposed of annually in the San Joaquin Valley in an environmentally safe manner. Almost all the proposed management strategies involve the final disposal of highly concentrated brines evolved from this water. Salt-gradient solar ponds, for thermal and electrical power production, are proposed to accomplish this until a permanent salt-sink is designated. Numerous research papers and reports, based on field testing, have been published. The California Department of Water Resources operated a 0.5-acre solar pond from 1985 to 1989 at its Los Banos Demonstration Desalting Facility. Salt-gradient solar ponds consist, in part, of agricultural drainage water, initially with a salinity of 10,000 milligrams per liter (mg/L), concentrated 30-fold to a concentration of 300,000 mg/L or higher. Many well-established techniques are available to achieve this concentration. Approximately 100 million gallons of drainage water per acre of solar pond are needed. The energy stored in a salt-gradient solar pond can be used to provide the elevated temperatures for the biological selenium removal systems being developed, for the driving force in distillation systems used for pond maintenance, or for electrical power.