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The Desalination and Water Purification Research & Development Program Newsletter - No. 18 - Winter 2000


The Desalination and Water Purification Research & Development (DWPR) Program continues to cooperate with a variety of U.S. organizations involved in water purification and desalting research. These cooperations allow the Federal investment to be maximized in several areas at once and ensure that the highest quality research is accomplished as a result of the DWPR program's competitive bid and peer review processes. Recently, two cost-shared partnerships agreements were awarded, and a significant water management study appraisal report was published. Both are discussed below.


The goal of the Partnerships task is to establish cooperations with water research organizations for the purpose of co-funding others to perform research. Cost-shared awards to water research organizations allow program involvement in an expanded arena of research and provide a unique opportunity to leverage program funds. During fiscal year 2000, proposals to cost-share basic and applied research were sought from responsible water research organizations dedicated to creating new sources of water through research and technology. Recently, awards of $60,000 per year (for up to three years) were made to National Water Research Foundation and to American Water Works Association Research Foundation. The DWPR program looks forward to participating in the project review and selection process each of these organizations uses to perform advanced water treatment research.


The Southern Arizona Regional Water Management Study (SARWMS) is a cooperative effort between the Metropolitan Domestic Water Improvement District, Town of Marana, Town of Oro Valley, Pima County Flood Control District, Central Arizona Water Conservation District, Arizona Department of Water Resources, and Reclamation. The goal of SARWMS is to build on and expand regional cooperation related to water resource management issues in the area. An Appraisal Study titled Alternatives for Using Central Arizona Project Water in the Northwest Tucson Area, dated August 2000, was recently published by Reclamation's Phoenix Area Office.

The issue of water use in the Tucson basin has been controversial and divisive for many years. Currently, local aquifers in much of the study area are productive and vary from relatively high quality to some localized poor quality. However, groundwater levels have been dropping over the years, with the exception of the lower Santa Cruz River area where effluent recharge is occurring. Additionally, the Central Arizona Project (CAP) aqueduct, which supplies Colorado River water, transverses the western portion of the study area. Unfortunately, the northwest municipal water providers do not have the facilities necessary to use CAP water or treated effluent. As a result, sufficient quantities of renewable water supplies within the area present a problem for some municipal providers. Voter-mandated water use initiatives, limited financial resources, sometimes inadequate technical information, and established jurisdictional boundaries all act as barriers to what may be the best and most cost-effective solutions to many of the water resource problems.

A scope of work to address these complex water resource issues was developed by SARWMS that included both operational (common renewable water system infrastructure, data base, etc.) and strategic (assessment of water supply availability and constraints, water quality concerns, identification of alternatives, preliminary appraisal-level design, etc.) components. Four potential potable water use alternatives were developed, as well as an option for nonpotable use. The potable alternatives which could be included in an implementation strategy are: using the existing Tucson water delivery system; direct delivery of CAP water; continued exclusive use wells; and CAP recharge and recovery. A fifth hybrid alternative, raw water delivery, could be used alone or in conjunction with other alternatives. The appraisal study provides conceptual design for each alternative and provides sufficient design information so that costs and other important factors can be compared and informed policy and management decisions can be made.

Unlike the other alternatives, treatment and direct delivery provides the potential for controlling water quality. In order to effectively evaluate this alternative, several methods of treating water were analyzed. The three primary treatment methods that meet existing Safe Drinking Water Act standards include conventional treatment (CT), slowsand filtration (SSF), and microfiltration/ultrafiltration (MF/UF). In addition, reverse osmosis (RO) was evaluated as a desalting method because it lowers the total dissolved solids (TDS) in water.

The "base case" for treatment and direct delivery is CT, typically consisting of filtration and disinfection. However, understanding that water quality is an important consideration, various treatment train options were selected by the SARWMS partners with input from Reclamation's water treatment experts in the Denver Office. These options include: (1) no desalting with variable production plants by (a) CAP water with CT, (b) CAP water with SSF, (c) CAP water with MF or UF; and (2) desalting plants with aquifer storage and recovery by (a) CAP water with CT and RO, (b) CAP water with SSF and RO, (c) CAP water with MF/UF and RO.

As a result of the treatment train comparisons, the overall costs and benefits from desalting as it relates to wastewater effluent reuse were examined. This issue is particularly relevant because effluent reuse will become an increasing important source of renewable supply in the future. When CAP water becomes fully integrated into the Tucson basin's water supply system, the TDS level of effluent is expected to rise from the current 550 mg/L to about 950 mg/L. At 950 mg/L TDS, turf irrigation practices will need to be changed to allow "flushing" of salts from the root zones. However, if CAP water is desalted, wastewater effluent TDS will drop to less than its present level (if CAP water is desalted to 100 mg/L TDS, the wastewater would be about 350 mg/L).

The economic benefits of using low-salinity water are significant for all uses, including residential, commercial, industrial, and water recycling and reuse. Two recent studies (Dames and Moore, 1995; Bookman-Edmonston, 1999) estimated different but nevertheless considerable economic benefits of using low-salinity waters. The estimated impacts of salinity on residential customers as estimated by the two studies is approximately proportional to the TDS of the water. Thus, in evaluating water supplies and treatment processes, the salinity of the finished water is an important economic criteria.

Following the vision of the SARWMS management team, an implementation strategy to address the appraisal study findings will be developed. This implementation strategy includes two major parallel activities: decisionmaking process (public education/input and process for selecting alternatives), and legal/institutional process (discussion of ownership, operation, financing, and repayment).

Reclamation is proud to have assisted in this important water management study. For more information regarding the SARWMS appraisal report, please contact Eric Holler, Study Manager, Phoenix Area Office, (520) 670-4825.


Water from Water is published by Reclamation's Water Treatment Engineering and Research Group - Susan Martella, Editor. For more information about the DWPR program, contact Kevin Price at: Bureau of Reclamation, 86-69000, PO Box 25007, Denver CO 80225; phone (303) 445-2260; or e-mail a message to MPrice@usbr.gov.
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