Raw Water Supply Enhancement Through Creative Indirect Reuse – Upper Trinity Regional Water District's Chapman Lake Water Reuse Program
Abstract:The Upper Trinity Regional Water District (UTRWD) was created by the Texas Legislature in 1989 to meet the water utility needs of more than 20 communities in Denton County, and parts of Collin County in North Texas. Services provided include long-range water supply, potable water, wastewater treatment, water reclamation, conservation and watershed protection. Upper Trinity currently secures its water entirely from Lewisville, Ray Roberts and Chapman Lakes. Water reuse will play a large role in UTRWD's development of future water supplies to meet its ever-increasing system demands.
In 1997, the Texas Legislature passed legislation to ensure that water providers planned for the future water needs in Texas. UTRWD's service area is included in Region C, an area, which encompasses all, or part of 16 counties in North Central Texas. The population of Region C is projected to grow from 5 million in the year 2000 to over 13 million in 2060; the planning horizon in the legislation. Correspondingly, water use is projected to increase during that 60-year period from 1.4 million to 3.3 million acre-feet per year. The currently connected supplies in the Region will meet less than 50 percent of the projected 2060 demand. Primary water management strategies for the Region C plan are: water conservation, inter-basin transfers, development of new supplies, and water reuse. Of these, reuse and conservation comprise approximately 25 percent of the needed supply.
UTRWD partnered with the City of Irving in 1990 to secure water rights from Chapman Lake in East Texas. In June of 2003, a 90-mile 72-inch diameter pipeline was completed and delivery of Chapman water to the Trinity Basin was initiated. UTRWD receives an average of 14 mgd from Chapman Lake. In order to achieve the maximum benefit of this new water source, UTRWD submitted an application in August 2001 to the Texas Commission on Environmental Quality (TCEQ) seeking reuse of treated Chapman Lake water. In May 2002, TCEQ declared the application administratively complete. The draft permit was released in September of 2005. The permit allows UTRWD to re-use up to 9,664 acre-feet per year (8.6 mgd) of Chapman Lake derived effluent discharged from UTRWD or its customer's treatment facilities in to Lewisville Lake.
This indirect reuse project is unique in that the Chapman water return flows are discharged into Lewisville Lake, which serves as UTRWD's primary raw water supply source. However, the District has no water or storage rights in the lake. The water UTRWD diverts from Lewisville Lake is either Chapman water passed through Lewisville Lake or raw water purchased from the City of Dallas or the City of Denton. As a result, extensive negotiations and creative approaches to account for the water and return flows were required. In order to use the Chapman return flows, pass-through agreements were developed between the District and Dallas and Denton and submitted to the TCEQ for incorporation into the State water rights permit.
Several innovative requirements have been incorporated into the permit as a result of this collaboration. UTRWD's reuse is limited to a maximum of 60 percent of treated Chapman Lake water delivered to the Trinity River Basin. The reuse is further limited to a single pass through Lewisville Lake. Therefore, if the return flows are not captured/used the day following their discharge, UTRWD loses its rights to their use. Agreements with Dallas and Denton required that UTRWD develop an accounting system that tracks Chapman water on a daily basis through supply, delivery and treatment facilities, and back to Lewisville Lake. The accounting system uses available metered quantities, accounts for water losses within the various delivery systems, and uses these data to compute return flow factors. The treated Chapman water volumes are multiplied by the return flow factors to determine how much water can be claimed by UTRWD. Due to the large quantity of data associated with this accounting system, a Microsoft Access (MS Access) database was developed to input, store, and process the data. Reports have been developed within MS Access to assist with quality control, to support the District in operational management of its various water supplies, and to provide required information to the Cities of Dallas and Denton.
As available water supplies continue to become more scarce, effluent reuse, and especially indirect reuse (supply augmentation), will become a more attractive alternative to the development of new water sources. The UTRWD infrastructure is uniquely suited to take advantage of this type of project since its wastewater facilities discharge into Lewisville Lake, which is the raw water supply source for its 70 mgd Regional Water Treatment Plant. Full reuse of the available Chapman Lake water effectively reduces the Chapman raw water cost by 37 percent. This reduction in cost for a rapidly growing utility helps stabilize rates and frees up funds for much-needed capital projects.
UTRWD is projected to need approximately 155,000 acre-feet per year (138 mgd) to provide for its demands in 2060. Its existing supplies provide for approximately 78 mgd. UTRWD's reuse strategies will provide for slightly more than 20 percent of the needed new supplies. Every gallon of effluent that can be reused allows the District to defer the cost of developing new supplies and divert the savings into improving its infrastructure and/or maintaining rate stability.
Document Type: Research Article
Publication date: 2006-01-01
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