“The really good thing about it is that it works,” says Darrel Andrews, assistant director of the Environmental Division of the Tarrant Regional Water District in Fort Worth, Texas.

He means the nearly 2,100-acre man-made wetland that filters drinking water for 1.8 million customers in the Dallas-Fort Worth metroplex. Through a partnership with the Texas Parks and Wildlife Department that began in 1997, the wetland was built on the north unit of the wildlife department’s Richland Creek Wildlife Management Area, about 80 miles southeast of Dallas between the Richland-Chambers Reservoir and the Trinity River.

Each day, up to 90 mgd (permitted) of water is pumped from the Trinity River a little more than a mile to five sedimentation basins at the head of the wetlands. With surface areas up to 80 acres, the 6- to 8-foot-deep sedimentation basins retain the river water about 24 hours to remove suspended solids and nutrients.

Over the next seven days, gravity moves the flow from the basins through 20 wetland cells for natural processing and final nutrient removal. “Detention time in the wetland is critical to us,” says Andrews. “That is why we built the project in the first place.”

The native way

The cells vary in size and follow the land formation to increase contact time. Cells are organized in trains of three to five, handling flow variations and downtime. Clarified water from the cells flows through a canal and is lifted into the nearby Richland-Chambers Reservoir before being pumped to Dallas-Fort Worth customers. 

Native vegetation, such as cattails, smartweed, arrowhead and varieties of rushes, sedges and millets, thrive in the wetlands. Not all had to be planted because of existing seed sources in the native soil. “We provided the moisture and they grew,” Andrews says. The soil, the plants and the plants’ associated biofilm work to remove nutrients, mainly nitrogen and phosphorus.

Plant selection and other design parameters were based on results of an eight-year study of a 2 1/2-acre pilot wetland that began in 1992. The study showed that certain plants could remove nutrients and that some plants could outperform others. Determining the optimal water level in which plants could thrive and survive was critical. The wetland was built in a flood plain, and the impact of seasonal flooding needed to be known.

“We had a lot of questions to answer in those early years, and we used that time to determine whether these things were even going to work for our purpose,” says Andrews.

Going to scale

The pilot project’s success led to the first phase of field-scale construction of 250 acres, which began in 2002. After several years of successful operation, the second phase of 200 acres was completed in 2009. The final 1,600-acre expansion was completed in 2013. The entire raw water filtering area is named the George W. Shannon Wetlands.

As part of the parks department’s Richland Creek area, the wetland vegetation provides habitat for songbirds, shorebirds, wading birds and raptors. Residents include egrets, herons, blackbirds, warblers, hawks and bald eagles. Migrating ducks and geese are frequent visitors. Larger wildlife include deer, feral hogs and alligators. Recreational uses include hiking, camping, bird watching and hunting.   

Created as mitigation for construction of the reservoir, the Richland Creek area has many marshes and sloughs and vast bottomland forests of cedar, elm, oak, willow, ash and box elder that also serve as breeding and nesting grounds for resident and migratory birds. 

The Shannon Wetland filtering concept came out of a long-range plan developed by the water district’s staff in the late 1980s. Projected population growth showed the need for additional raw water supply by 2017. Traditionally, a new reservoir would have been the solution, Andrews says. But the close proximity of the Trinity River to the Richland-Chambers Reservoir provided another option.

More on the way

However, during dry months with little runoff, 95 percent of the Trinity River is treated wastewater effluent. Without some pretreatment or filtering, its impact on the reservoir’s water quality would be detrimental. “Our thought was that if we could find a way to treat the river water and get it to the existing reservoir, we could delay construction of a new reservoir for many years,” says Andrews.   

Successful operation of the Shannon Wetland has paved the way for another 2,000-acre wetland to be built in 10 to 15 years. Andrews says the cost will be about half that of a reservoir, and instead of two decades it will take two or three years to construct. “Overall, it is cheaper water and more environmentally friendly,” Andrews says.

The award-winning George W. Shannon Wetlands Water Reuse Project was the first of its kind in the United States. In 2004, it received the Engineering Excellence Grand Award from the American Council of Engineering Companies (ACEC).

In 2009, the WateReuse Association named it Large Project of the Year. In 2014 it was selected by Engineering News-Record as the Best of the Best in the water/environment category. In 2015, it was the winner of the National Association of Environmental Professionals’ award for excellence in environmental management.   

“The ultimate goal of the project was to produce water for delivery into the Richland-Chambers Reservoir that was as good as or better than the water that flows to it naturally from the creeks upstream of the reservoir,” Andrews says. “I am proud to say that it meets that goal for nutrients and far exceeds it for sediment.”