AWWA MTC57592

In February 2000, the U.S. Court of Appeals affirmed a lower court ruling that the US Bureau ofReclamation must provide drainage service to the irrigators in the San Luis Unit whichcomprises an area of more than 700,000 acres. Reclamation recently completed a yearlongeffort to evaluate various alternatives for the treatment and disposal of about150,000 acre-ft/year of drainwater, that is 134 million gallons per day if spread outevenly throughout the year. The final preferred alternative consists of the followingcomponents:drainwater collection and reuse;biological treatment;desalination; and,disposal to evaporation ponds.The next phase of the project is a feasibility study which consists of field investigationsand preparation of detailed designs and cost estimates. The feasibility study will be usedto obtain congressional authorization and funding to implement drainage service andcomply with the court order.Water quality analyses and projections of future water quality indicate there will besubstantial challenges for desalting the drainwater. The total dissolved solidsconcentration is expected to range between 5,000 and 20,000 mg/L across the Valleyover the 50-year planning period. Recovery will be limited by hardness which exceeds2,000 mg/L as CaCO3 at some locations. The drainwater contains boron (>20 mg/L)which is not well rejected by reverse osmosis membranes below pH 10. The productwater would be reused for irrigation of commercial agricultural crops, many of which areadversely impacted by boron concentrations as low as 5 mg/L. Valley soils contributeselenium to the drainwater which is well rejected by the membranes. The reverseosmosis concentrate, therefore, will be difficult to dispose of because it will containelevated levels of selenium that already have proven toxic to wildlife within existingimpoundments of concentrated drainwater.The field investigation for desalination involves pilot testing of reverse osmosis andnanofiltration membranes at two or more locations in the Valley. Reclamation ispartnering with the California Department of Water Resources, local farmers, waterdistricts, and membrane manufacturers for the pilot tests. A pilot system has beendeployed and is currently evaluating pretreatment requirements. The next six monthswill provide information needed to address the challenges, determine the constraints forsuccessful operation, and perform a detailed design and cost estimate for a full-scaledesalination plant. This portion of the study will evaluate RO pretreatment requirements,performance, and chemical precipitation or absorption of selenium from the concentrate. Includes 3 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

03/05/2003

Number of Pages:

10

File Size:

1 file , 480 KB