Colorado River Management Section

Overview - Water Quality

Maintaining the quality of the Colorado River water supply is important.  A number of contaminants, both naturally occurring and manmade, could impact the quality of Colorado River water including salinity, nutrients, metals, endocrine disrupting compounds, perchlorate, bacteria, pathogens and sediment.  Programs and planning efforts exist to monitor and address these water quality threats.

Salinity

Increased salinity levels in the Colorado River affect agricultural, municipal and industrial users.  Agricultural water users suffer economic damage due to reduced crop yields, added labor costs for irrigation management and added drainage requirements. Urban users must replace plumbing and water-using appliances more often, or spend money on water softeners or bottled water. Industrial users and water and wastewater treatment facilities incur reductions in the useful life of system infrastructure.  Damages in the United States are estimated at $330 million per year, and while economic damage in Mexico is not quantified it is also a significant concern.

In 1972, EPA required development of water quality standards for salinity in the Colorado River in accordance with Clean Water Act Section 303. The seven Colorado River Basin States formed the Colorado River Basin Salinity Control Forum (the Forum) in 1973. The Forum has developed numeric salinity standards for three locations in the Lower Basin as well as a basin-wide plan of implementation. The EPA has approved the standards and the plan of implementation adopted by the Colorado River Basin States.  The water quality standards establish a flow-weighted average annual salinity standard that must be maintained on the lower Colorado River at the following locations:

Below Hoover Dam (to Parker Dam) - 723 mg/L
Below Parker Dam (to Imperial Dam) - 747 mg/L
At Imperial Dam - 879 mg/L

Implementation of the salinity control plan has ensured compliance with the numeric criteria while the Basin States continue to develop the water allocated to them by the Colorado River Compact.  Millions of dollars have been spent to prevent 1.9 million tons of salt from entering the river. The following websites contain additional information about salinity control:

United States Bureau of Reclamation: http://www.usbr.gov/uc/progact/salinity/index.html
Colorado River Basin Salinity Control Forum: http://www.coloradoriversalinity.org/

The salinity of Colorado River water has also been a contentious issue with regard to the quality of water delivered to Mexico pursuant to the Mexican Water Treaty of 1944 (Treaty).  In a normal water year the Treaty requires the United States to deliver 1.5 million acre-feet of Colorado River water to Mexico. Salinity impacts to water users in Mexico became an issue after the Wellton-Mohawk Irrigation and Drainage District began discharging saline groundwater and return flows to the Colorado River above Morelos Dam, Mexico’s primary diversion point.

In 1961, Mexico lodged a formal protest with the United States, claiming damages to agriculture in Mexico.  The United States began a process to address Mexico’s concerns, which culminated in the passage of the Colorado River Basin Salinity Control Act of June 24, 1974, Public Law 93-320 (the Salinity Control Act). The Salinity Control Act authorized a temporary measure to reduce the salinity of the Treaty water delivery by redirecting the brackish Wellton-Mohawk drainage water from the Colorado River (where it had been counted as part of Mexico’s treaty allocation of 1.5 million acre-feet) to the Cienega de Santa Clara (Cienega) in Mexico (where it is not counted against the treaty allocation).  Each year, approximately 109,000 acre-feet of water is delivered to the Cienega.  The Salinity Control Act authorized the construction of the Yuma Desalting Plant, which was intended to capture and treat the drainage water flowing to the Cienega, and return most of it (71,000 to 85,000 acre-feet) to the River for delivery as part of the annual Treaty obligation. 

The Yuma Desalting Plant was built and operated briefly, at one-third capacity in 1992/1993, but that test run was cut short when flood flows on the Gila River damaged the intake canal.  The Plant hasn’t been operated since that time, but remains in ready-reserved status.  As a result, an average of an additional 109,000 acre-feet of water is delivered from system storage each year to replace the water that is bypassed to the Cienega.  Although water users in the lower Colorado River Basin States are concerned about potential water supply reductions resulting from continued storage losses, the bypass flow to the Cienega de Santa Clara currently supports a large wetland habitat that is home to many species of birds and other animals. 

The Central Arizona Water Conservation District organized a stakeholder group to identify measures to address water supply and environmental concerns associated with operation of the Yuma Desalting Plant.  The group formulated some alternatives to minimize the risk of shortage to water users in the lower Colorado River basin resulting from lost system storage while minimizing environmental impacts to the Cienega.  The group issued a report with their recommendations titled Balancing Water Needs on the Lower Colorado River: Recommendations of the Yuma Desalting Plant/Cienega de Santa Clara Workgroup, April 22, 2005. 

Increased water demand in each of the three Lower Basin States has intensified the need for more efficient water management of the Colorado River system. This, coupled with the effects of a prolonged drought over the entire Colorado River Basin, has increased interest in replacing and/or recovering bypass flows to Mexico in order to conserve storage in the Colorado River reservoirs.

Other Water Quality Issues
In 2005, the Governor of Arizona appointed The Clean Colorado River Alliance (Alliance) stakeholder group to address water quality issues for the Colorado River.  In addition to salinity, the Alliance identified several other water quality concerns including nutrients, metals, endocrine disrupting compounds, perchlorate, bacteria and pathogens, and sediment.  The Alliance issued a report titled Clean Colorado River Alliance Recommendations to Address Colorado River Water Quality, January 2006.  The report includes a number of recommendations to monitor and mitigate the impacts of these pollutants.  The Alliance report can be found at: http://www.azdeq.gov/environ/water/download/ccra06.pdf.

 

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