Water banking in the Southwest is an increasingly important tool in the conservation arsenal. In West Phoenix, Arizona, the NAUSP facility is operated by Salt River Project (SRP), the third largest private water utility in the United States. At this facility, re-claimed water from the surrounding 4 municipalities is mixed with Colorado River water, via the Central Arizona Project canal system, and delivered to the facility, which consists of six 20 to 25 acre percolation basins. There the water slowly percolates into the ground water table below, for future retrieval and use. The NAUSP facility is a major success story in the arid southwest having effectively banked almost one million acre feet of water into the ground in the past 5 years.

As is common in other similar facilities, “black plug layer” (an anaerobic slime layer) forms in the top layer of soil “capping” the percolation pond and inhibiting the absorption of water into the ground. The problem had become so severe at NAUSP that water banking operations had ground to a halt. The resolution was to mobilize a bulldozer equipped with a 7 foot long steel tooth to till the earth in an attempt to re-open the soil and continue operations. The equipment was used on all basins, except one. This sixth basin was treated with CBX.

SRP was looking for a solution that was effective and less costly than the $500,000 spent on tilling the basins, and were interested in proving CBX as that solution. CBX contains numerous aerobic strains of active biologicals, which have proven extremely effective in other similar situations, and because of the relative low cost of the product and its application, it appeared to be a valuable alternative.

CBX was applied at NAUSP on March 31ST at a rate of 2 gallons per acre. Water was applied soon thereafter, and the basin was filled over the course of the next two weeks. Prior to the application of CBX, it normally took 3 days to fill the basin. After CBX, it required two weeks. The gates were closed, and the water in the basin drained within 48 hours. 

An additional delivery of water was released on April 24TH, the gates closed on April 27TH, and again the water has drained within 48 hours. Almost 24 acre feet of water (8 million gallons) banked in a basin that previously took 2-3 months to accomplish the same. The cost per basin of using equipment to accomplish repairs was $100,000. The cost of CBX per basin $3,437.50. Ultimately, the black plug layer will re-form in the mechanically repaired basins at a depth beyond that which equipment can be used. At this point, soil will have to be removed and disposed of as hazardous waste, because of the reclaimed water. Continued treatments of CBX should keep the layer from reforming and facilitate continued conservation of water. CBX is an effective, less expensive solution to poorly percolating soils in retention basins. The proof is in the pictures.