In order to meet future water supply requirements, Tarrant Regional Water District is pursuing several options including diverting Trinity River water into two of the District’s reservoirs located downstream of the Dallas-Fort Worth Metroplex. The District’s approach to augment the water supply with reclaimed water involves a multiple-barrier approach including advanced wastewater treatment, retention in the Trinity River, treatment through a constructed wetland system, dilution (maximum of 30 percent of reservoir capacity during drought conditions), retention in the reservoir, and potable water treatment. Data regarding treatment efficiencies from a pilot-scale constructed wetland facility operated from 1992 through 2000 and continuing research at a recently completed field-scale constructed wetland facility will be utilized to determine potential changes in treatment requirements and/or the required dilution rate. The field-scale constructed wetland project has involved a working partnership between the District and the Texas Parks and Wildlife Department (TPWD). The 243-acre field-scale project is constructed on TPWD property under a Memorandum of Understanding between the District and TPWD. Several operation and management issues are being evaluated at the field-scale level in order to adequately quantify impacts. Also, the effectiveness of flow distribution designs (including deep water channels for distribution of inflows and collections of outflows, vegetative baffles, shallow shoals, and deep water zones) and shallow filtering zones immediately above the outflow of the final wetland cell will be determined in the field-scale unit prior to final design of the full-scale system. Applying constructed wetlands for providing additional treatment prior to discharging the reclaimed water into existing water supply reservoirs has proven to be effective in meeting treatment objectives based on more than eight years of performance testing data at a pilot-scale facility and during the initial operation of the field-scale system. The District is continuing its research effort to further examine various performance, operation, and maintenance issues that would be associated with the use of constructed wetlands on a full-scale basis. The District’s efforts to incorporate a multiple barrier approach will ensure that water provided to its customers is not only a dependable but also a safe supply.
The Tarrant Regional Water District’s (District), a political subdivision of the state of Texas agency created in 1924, mission is to provide raw water to its customers that are located within Tarrant and adjacent counties. The District’s current customer base is about 1.5 million residents. To meet the raw water supply needs, the District has constructed and operates four major surface water reservoirs. The District’s water supply system is shown in Figure 1. The legislated requirement for long-term water supply planning, completed in the year 2001, reflected that water demands in areas served by the District would increase from 363,000 acrefeet/year in 2000 to 491,000 acre-feet per year in 2050. In order to meet this future water supply requirement, the District is pursuing several options. One of the options provides an opportunity to increase the District’s water supply in a timely manner by diverting Trinity River water, which
is largely treated wastewater return flows, into two of the District’s downstream reservoirs (Richland-Chambers and Cedar Creek Reservoirs). This paper describes the District’s approach to diverting the Trinity River water and presents an update of the progress of implementing this approach.
The District’s plan to augment the water supply with reclaimed water diverted from the Trinity River is anticipated to provide about 115,500 acre-feet/year (103-MGD average) of additional water. This approach to augment the water supply with reclaimed water involves a multiple-barrier approach.
- Barrier 1: Advanced wastewater treatment
- Barrier 2: Retention in the Trinity River
- Barrier 3: Treatment in a constructed wetland system
- Barrier 4: Dilution (maximum of 30 percent of reservoir capacity during drought conditions)
- Barrier 5: Retention in Reservoir
- Barrier 6 Water treatment
In order to provide a conservative safety margin, a dilution rate of 30 percent of reservoir capacity (during drought conditions) was selected. Data regarding treatment efficiencies from the pilot-scale constructed wetland facility operated from 1992 through 2000 and the on-going operation of a field-scale constructed wetland facility will be utilized to determine potential changes in treatment requirements and/or the required dilution rate.
The District formulated a staged program to perform research to examine the financial aspects, operation and maintenance issues, and treatment performance of the constructed wetland. The staged program involved initially constructing, operating, and testing of a approximately 2.5-acre pilot-scale constructed wetland. Subsequent to gaining required information from the pilot-scale wetland, an approximately 243-acre field-scale wetland was constructed to perform further research regarding the treatment expectations of the wetlands.
This project has involved a working partnership between the District and the Texas Parks and Wildlife Department (TPWD) to bring this reclaimed water concept to reality. Reviewing the roles and responsibilities of the District and TPWD helps to gain an understanding about why the two entities have had enthusiastic interest in working together to achieve the objectives of the project.