By Karen R. Smith

CASS—the Central Arizona Salinity Study—is a coalition of water and waste water agencies who have come together to evaluate salinity issues affecting the region. The mission of CASS, “is to provide its members with workable alternatives for a quality, cost effective, sustainable and reliable water supply through partnerships and cooperative efforts in regional salinity planning and management.”

Four different subcommittees presented their summary reports and conclusions at the end of June as part of Phase One of the study. The preface to the subcommittee reports states that the first phase concluded, “that about 1.5 million tons of salts are imported into the region annually, primarily from two major surface water sources, but also from agricultural fertilizers and salt contributions to waste water systems, including water softeners and food waste. Since only about 400,000 tons of salts leave the region, more than a million tons are added each year.” Central Arizona’s two main water supply watersheds are the Salt/Verde River and the Colorado River.

Planning
The Planning Subcommittee assessed salt removal options and evaluated the feasibility considerations and costs each would incur. Key findings noted the need for better RO systems—with 15 percent water loss and high energy demands, implementation of such treatment would be a challenge for the state. Concentrate management was identified as the number one issue to be resolved. The Colorado River Basin Salinity Control Program has successfully reduced salinity by over 750,000 tons per year (65 mg/l TDS) and done so cost-effectively. The subcommittee therefore recommended expanding this program (a federal initiative) to achieve further salt reductions.

Salinity control
The increasing use of water softeners by resorts, industries and residences was cited by the Salinity Control at the Wastewater Treatment Plant Subcommittee. Right now, 51 percent of all new homes are installing water softeners. According to the U.S. Bureau of Census and the Real Estate Center at Texas A&M University, 80,778 residential building permits were issued in Arizona in 2004; 2005 is expected to top that number. Preliminary conclusions here stated that salinity is rising and will continue to do so.

Brackish groundwater and concentrate management
Brackish groundwater may be used to meet water quality goals and the subcommittee of that name concluded that RO and/or electrodialysis (EDR) are currently being used in the southwest to desalt this water prior to blending. Long-term viability of sources must be a consideration and concentrate management limitations may be a factor. The subcommittee charged with the latter noted that new technologies and strategies have been developed in the months since the subcommittee began meeting in April of 2004. National and regional research projects are now in progress. However, they concluded that, “there is no magic bullet that will meet all concentrate management needs…and finally, concentrate management can no longer be thought of as a disposal issue, but must be recognized as an integral part of our long-term supply management strategy. There is no new water to import into our desert environment. To survive as a community, we must keep our water here.”

Key findings and conclusions of note (all subcommittees)
When considering the application of salinity control or reduction technologies, guidelines for assessing the need and benefits could include:

  • Will the TDS reduction reduce, postpone, or eliminate development of new or expanded water supplies?
  • Will the TDS reduction eliminate or reduce the use of existing diversions from natural water courses or from aquifers?
  • Will the TDS reduction reduce the demand on existing water supplies?
    Waste water treatment plants are currently receiving TDS without limits on quantity or quality and no cost recovery charges are made to contributors.
  • Local limits to TDS discharge may be difficult to calculate because there are currently no regulatory limits on TDS discharges.
  • Goals need to be refined and should be in a range rather than be specific (see Table 1).
    A possible alternative to local limits may be to develop a surcharge program.
  • An accurate accounting of TDS sources must be made to support a surcharge so that costs can be fairly apportioned.
  • An accurate evaluation of the cost of TDS treatment, including current and new costs for equipment, staff and residuals handling, mut be made to allow developing a cost per pound of TDS treatment.
  • All water users will be impacted by charges for TDS management with the largest contributors paying more
    Local limits may be non-numeric; best management practices or prohibitions may be considered. Examples of best management practices are:
    > Encouraging use of non-self regenerating water softeners (PE units).
    > Encouraging product substitution (KCl instead of NaCl) in water softeners.
    > A prohibition might be limiting point source discharges to a certain number of pounds of TDS per day.

 

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