A History of the Trinity River Wastewater Treatment Plants

WEFTEC®.06

OUR FAMILY ALBUM: A HISTORY OF THE TRINITY RIVER WASTEWATER TREATMENT PLANTS

Richard M. Browning, Ph. D. Trinity River Authority P.O. Box 60 Arlington, Texas 76004

ABSTRACT

Wastewater collection and treatment systems in the Trinity River basin serve a population of over 6 million and handle flows in excess of 700 million gallons per day. The population is growing at a rate of over 2.7% per year. One hundred years ago, the population was a few tens of thousands and there was little or no wastewater collection and treatment. Groundwater in the basin is limited, summers are hot and dry and streams often cease to flow. Extensive development of water supplies and wastewater collection and treatment has occurred. The overall process has benefited from regionalized systems and from cooperation between those systems. The quality of wastewater treatment has greatly improved, and the quality of the river has changed from a state of disrepute to one that now sustains many uses, including recreation and reuse.

KEYWORDS

Trinity River, Texas, regionalization, reuse, wastewater treatment, Dallas-Fort Worth area

SUMMARY

History

The Trinity River Basin, and particularly the upper basin, lies between the relatively high precipitation of east Texas and arid west Texas. Its prairies support farming and ranching, and in the late 1800’s the Dallas-Fort Worth area at its center began to grow into a major metropolitan area. However, rainfall is sporadic, and groundwater is limited. Development of surface water supplies became necessary, and by the start of the twentieth century wastewater collection and treatment became necessary for public health and safety. The first major wastewater systems were constructed in the 1910-20 period, but with the basic treatment available plus loadings from slaughterhouses and other industries, the limited assimilative capacity of the Trinity River was still overwhelmed. The basic standard technology was secondary treatment, but funding was limited, particularly during the Depression and World War II. Until about 1970, the history was one of catching up with growth and the river was in poor shape.

Regionalization

The core cities of Dallas and Fort Worth in the mid-twentieth century began to provide wastewater treatment to suburban municipalities that were in the watersheds of their treatment plants. Fort Worth now serves its entire area with a collection system leading to one treatment plant, the Village Creek plant. Dallas treats the flow from its area at its Central and Southside plants. The Trinity River Authority began in the late 1950’s to treat wastewater at its Central plant from cities between Dallas and Fort Worth. These four plants now treat the majority of all wastewater from the area. In addition, the Trinity River Authority has developed four smaller systems serving cities in watersheds south and north of the four central systems. In the 1970’s, the North Texas Municipal Water District began providing regional services to municipalities in the East Fork watershed. The District’s system includes the Mesquite Creek plant in the lower East Fork watershed, the Rowlett Creek plant in the Lake Ray Hubbard watershed, the Wilson Creek plant in the Lake Lavon watershed, and several smaller systems. Also, since the 1990’s the Upper Trinity Regional Water District has begun regional wastewater services in southeastern Denton County.

The first four of the above entities, the cities of Dallas and Fort Worth, the North Texas Municipal Water District, and the Trinity River Authority, formed the Upper Trinity River Water Quality Compact in 1975, in order to cooperate in monitoring the river and in working on regulatory, planning and related matters. The North Central Texas Council of Governments through its Water Resources Council is also an important forum for discussion and cooperation on planning and regulatory matters. It maintains the Water Quality Management Plan for the area under the Clean Water Act and also coordinates activities of cities and others subject to municipal stormwater permitting and regulation.

Regionalized treatment has efficiently achieved advanced levels of treatment at the fewest number of plants. It has achieved economies of scale in facilities, expertise, and logistics. It has facilitated planning of service areas and treatment improvements. It has also made the work of the regulatory agencies more efficient by enabling them to deal with fewer entities and facilities. There are limits to the advantages of size, but regionalization includes the ability to develop small systems and also to develop satellite treatment facilities within larger systems.

TECHNOLOGY

The first plants provided little more than primary treatment, but by the late 1930’s secondary treatment was adopted as the standard for designs approved by the Texas Department of Health. However, actual achievement of secondary treatment was inconsistent because of shortcomings in operations and maintenance, and overloading. In the late 1960’s, most major plants in the Dallas-Fort Worth area were not achieving secondary treatment and needed expansion. The Texas Water Quality Board insisted that expansion must be accompanied by the highest levels of treatment that had been demonstrated in large systems. The state issued discharge permits for 10 mg/l BOD and 10 mg/l TSS before the passage of the federal Clean Water Act, and they became the

standard and goal for plant improvements that continued through the 1970’s. The treatment included primary, extended aeration, and sand filters. In the mid 1980’s, fine bubble aeration became available and enabled nitrification to be added, in most cases within the existing treatment units. A new wasteload allocation was issued in 1985 requiring nitrification and raising the stream standard for dissolved oxygen accordingly. Since then, many different refinements in operation and design have enabled further lowering of effluent limits.

Current technology enables advanced treatment to be installed from the start in newer and small systems. Nutrient removal is installed in the Wilson Creek plant on Lake Lavon. UV and other variations in disinfection have been used in some locations. Land application, wetland treatment, and many other technologies have been employed in many cases.

REGULATION

The first major regulation of wastewater in Texas was under the state Department of Health, but it was mainly limited to the approval of wastewater treatment plant designs and occasional case-by-case investigations. In the early 1960’s the Department began issuing discharge permits specifying effluents limits. In 1967 the Texas Water Quality Board was created and began issuing the permits. The first permits were all technology based; water quality models were not used to make wasteload allocations. In the 1970’s the first dissolved oxygen model was calibrated for the upper Trinity River. It has been recalibrated several time for use in updated wasteload allocations.

IMPROVEMENTS IN THE RECEIVING WATERS

The upper Trinity River for a long time was considered an open sewer: little or no treatment, slaughterhouse and stockyard wastes, bypasses, “black rises” (resuspended organic sediments after a rain), extremely limited fish life, and fish kills. Beginning with the treatment improvements of the 1970’s great improvement in the river has been achieved. Loadings have been reduced by a factor of five while flows have more than doubled. Dissolved oxygen has improved from zero in a large reach to consistently above five mg/l. A broad biological community thrives. The reputation lingers, but the river is now suitable for a wide range of uses and gradually the perception is changing. It is prominent in the major efforts to develop the river for waterside urban development and recreation in Fort Worth and Dallas, and in park development in the mid-cities.

REUSE

The quality of the reclaimed water from the treatment plants is such that it is suitable and attractive for reuse. Various projects have already been conceived for reuse, and there will be many more in the foreseeable future, given increased demands and costs of alternatives, plus improved effectiveness and decreased cost of membrane treatment and other technologies. This development in recent years has also initiated much activity and uncertainty regarding water rights.

FUTURE ISSUES

Growth, technology, regulation, recreation, reuse, and water rights will drive wastewater planning and design for the foreseeable future. All these factors are already intense and are increasing.