Credit: Photo: Troy Ogilvie, city of Dallas
The Bachman Water Treatment Plant uses a traditional flocculation, sedimentation, and filtration process.
Renovating and expanding a 75-year-old facility into a modern, state-of-the-art purification facility while maintaining the flavor of the existing architecture isn't as easy as it sounds, but it can be done.
In 2002, AEC firm Chiang, Patel & Yerby Inc. (CP&Y) was asked to improve the Bachman Water Treatment Plant in Dallas and help the plant comply with the Safe Drinking Water Act.
To meet the U.S. Environmental Protection Agency's Enhanced Surface Water and Disinfection By-Product Rules, the design included improvements to expand the plant's capacity to serve the growing needs of Dallas Water Utilities' (DWU) customers. Improvements also were intended to enhance plant performance and reliability, and improve DWU's ability to increase capacity over several years.
The project included hydraulic improvements to expand the plant's capacity to 150 mgd, a new low-service pump station, a high-service pump station/clearwells, chemical system renovation, ozone disinfection system, filter renovations, sedimentation rehabilitation, electrical renovations, and an improved supervisory control and data acquisition system.
Luckily, the plant is strategically located in the heart of Dallas. “Dallas' water distribution system literally grew up around the Bachman Water Treatment Plant; therefore, the plant is the most economical of the city's three treatment plants in terms of cost to produce and deliver water,” said Edward M. Motley, P.E., D.E.E., senior vice president of CP&Y.
With the plant needing significant improvements and the city needing additional water treatment capacity to serve its growing population, Dallas' staff decided to both renovate and expand the plant. The original plan called for a modest 15 mgd expansion, but CP&Y showed how the plant could be expanded by an additional 20 mgd, bringing the total expansion to 35 mgd and resulting in a 150 mgd plant.
In addition to the expansion, the plant was totally renovated, giving Dallas a modern 150 mgd water treatment plant in the heart of its distribution system. This feat was achieved for only $0.75 per mgd of water treatment capacity.
The biggest challenges were limited space and multiple contracts. The plant is sandwiched between a lake, a park, an airport, and an industrial area. The project was divided into six construction contracts so that as many as five contracts would be concurrent.
As a result, said Motley, the team learned the need for communication. A construction manager was retained to manage the onsite activities, an essential strategy for the project.
The city's main challenges revolved around keeping the plant in service during construction. “Having a construction manager onsite played a huge role in making this a successful project,” said Charles Stringer, P.E., assistant director of water operations for DWU. “Also, having good engineering firms producing good plans and specifications added to the project's success. Finally, having two good contractors working on the project made things happen smoothly.”Bachman Water Treatment Plant
Project completion date: May 7, 2005
Total cost: $126.9 million
AEC firm: Chiang, Patel & Yerby Inc.
Neat stat: Five contractors worked simultaneously on a small urban site with literally hundreds of interfaces; work was completed with a change order record of less than 3%.