For the initial phase of its water supply project, the Brushy Creek Regional Utility Authority opted to construct a temporary floating intake structure on Lake Travis, rather than build a permanent deep-water intake now. Courtesy of BCRUA
Three cities teamed up to build a single, expandable water treatment facility, as well as raw and finished water conveyance pipelines and a temporary, floating intake structure that can be replaced as demand increases.
August 14, 2012—A new drinking water system serving three rapidly growing Texas communities in the suburbs of Austin recently went into operation. Completed on time and substantially under budget, the $131-million project represents the first phase of a $331-million effort to ensure adequate water supplies for the cities through at least 2040.
In 2006 the Texas cities of Cedar Park, Leander, and Round Rock established the Brushy Creek Regional Utility Authority (BCRUA), which is based in Round Rock. The body was created as a partnership that would enable the three municipalities to jointly design and construct a regional system for procuring additional supplies of treated water from Lake Travis, a large reservoir formed by Mansfield Dam, which is on the Colorado River northwest of Austin. The cities previously had been pursuing individual plans for meeting anticipated increases in demand. However, the three communities realized that by joining forces they could obtain a more timely and cost-effective solution, says Michael Thuss, P.E., M.ASCE, the program manager for the BCRUA.
The first fruits of the partnership—a water supply system comprising a new water intake, pipelines for conveying raw and finished water, and the 17 mgd Brushy Creek Regional Water Treatment Plant—achieved substantial completion in late June, enabling operations to begin. For the project’s initial phase, the BCRUA opted to construct a temporary floating intake structure rather than build a permanent deepwater intake. Because the deepwater intake would have had to be sized to accommodate the project’s ultimate capacity, constructing the smaller, temporary intake was deemed more cost-effective for now, Thuss says.
The 30 mgd floating intake was designed by the Marine Dynamics Corporation, of Longview, Texas, based on specifications developed by HDR, of Omaha, Nebraska. Situated on a 64 by 52 ft barge held in place by four rock anchors, the floating intake includes four 700 hp vertical turbine pumps, one of which has a variable-frequency drive to optimize motor speed, says Matt Cannon, the project manager for Excel Construction Services, LLC, of Leander, which constructed the temporary intake. The water is pumped through flexible hoses to a manifold valve and then into a 0.75 mi long underwater pipeline that connects to a 78 in. diameter steel pipeline located onshore. All told, the pumps on the barge convey the raw water 700 ft upward in elevation and a distance of roughly 5 mi to the treatment plant. Jacobs Engineering Group, Inc., of Pasadena, California, designed the underwater transmission line and the onshore raw water pipeline. The underwater transmission line was constructed by W.L. Hailey and Company, Inc.—which has since changed its name to the Layne Christensen Company, of Mission Woods, Kansas—while the onshore raw water pipeline was built by S.J. Louis Construction of Texas, Ltd., of Austin.
Constructed to have an initial treatment capacity of 17 mgd, the Brushy Creek Regional Water Treatment Plant can be readily expanded as needed in the coming decades, says Steven Lynk, P.E., BCEE, a vice president in the Austin office of CDM Smith. Headquartered in Cambridge, Massachusetts, CDM Smith designed the Brushy Creek plant, and construction was handled by Pepper-Lawson Construction, L.P., of Houston. Ultimately, it will be possible to configure the facility to have a treatment capacity of 106 mgd. With that goal in mind, all pipelines within the treatment plant were sized to accommodate the planned expansions. However, additional treatment structures will be added in “bite sizes,” Lynk says. Therefore, the site was laid out so that operations would not be disrupted during future plant expansions, an arrangement that “makes for a better project,” Lynk says.
The Brushy Creek Regional Utility Authority’s water supply project
includes new raw and finished water pipelines, an expandable
water treatment facility, and a temporary floating intake.
A permanent, deep-water intake can be constructed in the future.
Courtesy of BCRUA
Upon its arrival at the facility, the raw water undergoes rapid mixing, with chemical coagulants and polymer added to promote coagulation. The water then enters flocculation chambers, followed by sedimentation basins, before passing through one of five high-rate filters containing a combination of anthracite and sand. Next the filtered water undergoes disinfection by means of sodium hypochlorite and liquid ammonium sulfate, and it is then treated with sodium permanganate to control taste and odors. Finished water enters a 4 million gal clear well before being pumped to a 2 million gal elevated storage tank located on-site.
Solids generated during the sedimentation process are pumped to a gravity thickener and then further dewatered by means of belt filter presses. After the dewatering process, the solids are transported to a landfill. Water removed during the dewatering goes to a wash water decant basin, which also receives the backwash water used to clean the filters. Water leaving the decant basin is returned to the head of the plant, thereby minimizing the amount of water lost during the treatment process. All told, the plant has a treatment efficiency ranging from 95 to 98 percent, Lynk says.
After being treated, the finished water is distributed by means of 7 mi of steel pipe ranging in diameter from 72 to 78 in. The finished water pipeline was delivered in two segments, the first designed by Lockwood, Andrews & Newman, Inc., of Houston, and constructed by S.J. Louis Construction. The second segment was designed by K Friese and Associates, Inc., of Austin, and constructed by BRH Garver Construction LP, of Houston.
Originally budgeted to cost $171 million, the first phase of the BCRUA’s water supply project cost only $131 million, Thuss says. The nearly 25 percent savings were realized mainly from construction bids lower than anticipated. The bids were submitted at the height of the recent economic downturn. “Contractors were hungry at the time,” Thuss says.
As for future project phases, the BCRUA intends to construct a deepwater intake at a permanent location on Lake Travis, along with 2 mi of new raw water pipeline connecting the intake to the existing onshore pipeline, says Chris Lippe, the authority’s general manager. The deepwater intake will be needed to accommodate the larger pumping capacities that will be required in the future, Lippe says. Although the intake’s initial capacity will be 30 mgd, pumps will be added to increase capacity to 140 mgd, an amount that includes water that will be treated at existing facilities operated by Cedar Park and Leander. Estimated to cost $160 million, the permanent intake and additional raw water pipeline could be completed as early as the end of 2016, Lippe says. However, the exact time frame will depend to a great extent on water supply conditions in Lake Travis.