Residuals Management of Agricultural Drainage Treatment in the San Joaquin Valley, CA

The handling of agricultural drainage in the San Luis Unit consists of four processes: evapotranspiration, reverse osmosis, biotreatment of selenium, and an evaporation pond system. Most of the drainage from commercial farms is delivered to agricultural reuse areas where approximately 73 percent of the water is removed by evapotranspiration through irrigation of salt tolerant crops. Up to the limits of solubility, the salts and other dissolved components remain in the water. The effluent from the reuse areas and some water that bypasses the reuse areas form the feedwater for the reverse osmosis plants. The reverse osmosis plants operate at approximately 50 percent recovery. The half of the volumetric flow from which most of the salt has been removed is returned to local districts for some beneficial use. The half containing most of the salt would be delivered to the biotreatment plants where most of the selenium would be removed. The effluent from the biotreatment plants would be delivered to the evaporation ponds for final disposal. This manuscript describes the latter three processes, reverse osmosis (RO), biotreatment of selenium, and an evaporation pond system in the context of piloting and a Feasibility level design.