San Antonio Fast Tracks Filtration Plant

In Texas, where water is an especially precious resource, San Antonio has tapped a new drinking water source. The $21 million International Business Park Water Production Facility (WPF) looks beyond the region's traditional groundwater source and employs ultrafiltration membrane technology to purify surface water.

The WPF is the first ever design/build/operate contract for a municipal ultrafiltration surface-water treatment plant in the United States. It also is among the first water treatment plants in the United States taking advantage of state-of-the-art ultrafiltration membrane technology, as well as the first water treatment plant in San Antonio treating river or lake water.

The nine mgd WPF officially opened for operation Dec. 7, 1999, just 18 months after initial groundbreaking. On time and within budget, the fast-track design/build approach saved approximately two years in construction over conventional design-bid-build scenarios.

Fast-Track Approach

The Bexar Metropolitan Water District is the second largest water purveyor in the metropolitan San Antonio area, serving some 250,000 customers. The area relied on the Edwards Aquifer for its water supply, but rapid growth and recent droughts caused severe drops in the water table. Anticipating shortages, the local groundwater agency mandated reductions in groundwater withdrawals.

In response, the BMWD initiated the $21 million project, which is an example of successful fast-track design/build teamwork. According to BMWD officials, the speed of the WPF design and construction was critical to meeting the area's pressing water needs.

Adopting an innovative funding approach helped speed the project. Montgomery Watson, BMWD officials and plant operator United Water Services agreed to fund various portions of the development costs. Meanwhile, the District sought traditional bond funding. Once final construction contracts were in place and bond funding was obtained, the BMWD reimbursed the development costs to the team partners in the first construction progress payment.

To further speed completion, the team cooperated extensively to deliver the materials and applications. For example, the design team took full advantage of its subcontractors' familiarity with roofing and piping system materials to find the most suitable choices for these jobs, saving money and improving the facility's design and expected longevity.

Project Scope

As one of Montgomery Watson's largest design-build contracts, the project encompassed raw-water intake facilities, pipeline, reservoir and sludge lagoons, as well as the cutting-edge membrane filtration treatment plant, one million gallons of storage and a high service pump station.

As drinking water regulations become increasingly stringent, conventional treatment technologies approach their limits. Some industry experts believe that ultrafiltration processes will surpass the performance and reliability of conventional systems. This new facility supports their theory and offers the industry a full-scale example of ultrafiltration at work.

Pilot Testing

As the first major water treatment plant in the United States to use ultrafiltration membrane technology on highly turbid surface water, the WPF challenged engineers to fully assess the limits of the process, via pilot testing.

The team established a performance evaluation with membrane filtration equipment vendors. The pilot test involved a full-scale demonstration of the technology operating on the WPF site over the course of 90 days. Montgomery Watson engineers constructed a complete water treatment process using water drawn from the Medina River and a pretreatment process duplicating the one to be used by the new plant.

The compressed and overlapping activities increased the project management complexity. The permitting process through the state and local agencies proved to be the project's most challenging task. These agencies were very new to the design/build/construction scenario. Montgomery Watson and its subconsultants worked closely with them to keep the project on time and on budget.

Plant Design

The consulting engineering company worked with United Water Services of Harrington Park, N.J., to implement the ultrafiltration water treatment technology. The WPF introduces a number of innovative design and construction techniques and technologies, particularly in the area of ultrafiltration.

San Antonio's new Water Production Facility draws surface water from the Medina River.

The WPF draws surface water from the Medina River via the new raw water intake facility. A variable height weir constructed at the river creates a small pool. The weir can be adjusted form zero to 5.5 feet depending on the water conditions in the river.

Three submersible pumps, each with a nominal capacity of five million gallons per day (mgd), pump the water via a 30 inch diameter pipeline to the WPF. Two of the pumps incorporate a variable frequency speed adjustment from 2.5 mgd to five mgd to match the raw water pumping rate to plant production.

Because the raw water facility is built in the Medina River flood plain, all mechanical equipment including the pumps and weir are designed to be submersible. The water is pumped from the raw water facility over a distance of about 7000 feet to a Superpulsator clarifier at the WPF site. Ferric sulfate is used as for coagulation and powdered activated carbon can be fed in to control taste and odor problems.

Membrane Ultrafiltration

Once the raw water is clarified, it is pumped via three variable speed pumps (5 mgd each) through a 24-inch diameter pipeline to the 9 mgd ultrafiltration facility. There the water passes through three self-cleaning, 200-micron pre-filters that then feed the membranes. A water-quality monitoring panel mounted on the wall supports operator activities during the treatment process.

The ultrafiltration membranes consist of seven racks with 48 modules per rack with a surface area of 592 square feet per module. The microscopic membranes catch the smallest bacteria and any particles. The system automatically, and sequentially, backwashes the membranes once an hour, and recycles all backwash water.

Once filtered, the water flows to a 0.5 million gallon tank that operates as a disinfection contact basin as well as storage tank. Water from this storage tank is transferred about five miles to another tank, where high service pumps then deliver the water to the distribution system.

Operations Facilities

Operations facilities are located adjacent to the membrane process area. These include a control room, kitchenette, and laboratory. The operator can monitor and control all raw water pumping station and plant functions from the control room. The SCADA system can control the entire plant automatically, as well.

The new entrance lobby is equipped with audio-visual equipment to enhance plant tours. The BMWD manages approximately 30 acres on which the facility is located. This allows room for future expansions.

Contractor Montgomery Watson received the prestigious Honor Award from the Consulting Engineers Council of Texas (CEC-Texas) in its 2000 Engineering Excellence Competition for the design and construction of the facility. Montgomery Watson, Inc. provides engineering design, procurement, construction, technology and program management services.