Desert Dunes Riparian Habitat Study

City of Yuma, 
Arizona

Desert Dunes Riparian Habitat Study

Flow Augmentation in Yuma's East Wetlands

Awards: 
2008 Public Works Project of the Year - American Public Works Association, Arizona Chapter
2008 Public Works Project of the Year - American Public Works Association, National
Combined restoration project will revitalize 1,400 acres in the Yuma East Wetlands.
Combined restoration project will revitalize 1,400 acres in the Yuma East Wetlands.

Carollo worked with the City of Yuma, Arizona to obtain the environmental permits and implement operational changes at the Main Street WTP that enabled the discharge of spent filter backwash water from the Main Street WTP to support the Yuma East Wetlands. The spent filter backwash water augments flow and improves water quality in the Yuma East Wetlands, which is a 1,400-acre habitat restoration project occurring along the banks of the Colorado River near Yuma. The project will restore native riparian, wetland, and aquatic habitat, including habitat for threatened and endangered species. In addition, the restored wetlands will provide opportunities for environmental education, recreation, and eco-tourism. The City’s discharge of spent filter backwash water is an innovative beneficial use for this used water flowstream. The discharge is critical to augment flow through the wetlands during summertime low flow conditions and to reduce salt concentrations in the wetlands that result from inflows of agricultural return water. Before the City began discharging spent filter backwash water to the Yuma East Wetlands, it was simply recycled within the Main Street WTP.

Discharging from the Main Street WTP to the Yuma East Wetlands required a discharge permit from the Arizona Department of Environmental Quality. Total residual chlorine and selenium concentrations in the backwash water had the potential to exceed water quality standards in the Colorado River. Copper in the backwash water was also a concern. The City could have abandoned plans to discharge the spent filter backwash water and continued to recycle it within the WTP. Ultimately, the City and Carollo partnered with the Arizona Department of Environmental Quality and the U.S. Fish and Wildlife Service to develop a solution that recognized the importance of the discharge for the viability and health of the Yuma East Wetlands, was economically feasible for the City, and protected fish and wildlife in the wetlands.

To reduce the use of copper and chlorine at the Main Street WTP, the City implemented a fast-track project to design, procure, and install a chlorine dioxide generation system at the WTP. Carollo designed a chlorine dioxide generation and feed system to replace the use of copper sulfate and chlorine as pre-oxidants/ algaecides in the sedimentation basins at the WTP. The City procured and implemented the system themselves, saving time and money. Use of chlorine dioxide reduced copper concentrations to acceptable levels in the spent filter backwash water.

In addition to the operational changes at the Main Street WTP, Carollo worked with the City to successfully change the surface water quality standards for chlorine and selenium in the Colorado River at the Yuma East Wetlands. The revised standards are less stringent to accommodate the Main Street WTP discharge but are still protective of wildlife. The standards change was accomplished through the “net ecological benefit” provision of Arizona state law, which required the City and Carollo to demonstrate that the balance of ecological benefits from discharging far outweighed any possible environmental impact from the alternative standards. This project is the first successful application of “net ecological benefit” in Arizona.