Selenium Removal from Irrigation Drainage in the San Joaquin Valley
* Can selenium be safely removed from irrigation drainage water by treatment with bioreactors or chemical precipitation processes in conjunction with membrane separation to provide increased irrigation water?
Need and Benefit
Over the past several decades, Reclamation has formulated and reformulated different plans to provide drainage service to the San Luis Unit (SLU). In the 1960s it was determined that the best method of providing drainage to the SLU was to construct a 197-mile drain that would convey drainage to the Sacramento delta. By 1975, 82 miles of the drain were completed and the project was suspended due to environmental concerns. In 1978, the lands within Westlands Water District began draining an average of 7, 300 acre-feet of water annually into the drain into Kesterson Reservoir, which had become the temporary terminus of the drain. In 1986, the drains at Westlands were closed because of adverse environmental impacts thought to have been caused by selenium present in the drainage water. The subsequent lack of a drainage outlet for Westlands was detrimental to their farming operations.
The Federal Government was sued shortly thereafter by some of the affected landowners in Westlands. In November 2000, the Ninth Circuit of Appeals ruled in favor of the plaintiffs and ordered the Government to, without delay, provide drainage to the SLU pursuant to the statutory duty imposed by section 1(a) of the San Luis Act. The boundaries of the SLU include all lands within Westlands, Broadview, Pacheco, and Panoche water districts plus the southern portion of San Luis Water Districts. Reclamation's Mid-Pacific (MP) regional office in Sacramento, California and the South-Central California Area Office (SCCAO) in Fresno, California are evaluating alternatives for complying with the court order. One of the final alternatives for drainage service currently being evaluated includes membrane treatment, selenium removal treatment, and evaporation ponds. A field study using pilot-scale equipment to evaluate these technologies will greatly assist the larger effort of analyzing alternatives that provide drainage service.
If we can help solve the selenium issue, it would allow the farmers to reuse at least half of the 7, 300 acre feet of drainage water that now is put into evaporation ponds. It would also free half of the land area that now must be used for evaporation for farming again.
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