March 2015, Vol. 70, No. 3
Features
IPL Will Meet DFW Water Demands Beyond 2030
Spurred by a booming job market, affordable housing, proximity to an international airport and its central location in the U.S., the Dallas-Fort Worth Metroplex has experienced a significant population growth over the last decade.
In 2011, according to the U.S. Census Bureau, the population of the metroplex was more than 6.5 million, making it the largest metropolitan area in the south and the fourth largest in the country. This growing population is expected to surpass 13 million in 2060.
To meet the future water demands resulting from this growth, the Tarrant Regional Water District (TRWD) and the city of Dallas Water Utilities (DWU) are partnering to design, build and operate a massive raw water infrastructure that will deliver an additional 350 million gallons per day (mgd) of water by connecting a network of reservoirs southeast of the metroplex.
The $2.3 billion project, known as the Integrated Pipeline Project (IPL), will consist of 150 miles of pipeline with a series of pump stations and balancing reservoirs from Lake Palestine to Lake Benbrook with connections to Cedar Creek and Richland-Chambers Reservoirs. By sharing resources, TRWD and DWU will save an estimated $500 million in capital expenses and potentially $1 billion in energy savings over the life of the project.
“From a business case standpoint, it made sense to partner with DWU and build one big pipeline instead of the agencies building two separate lines,” said Kathy Berek P.E., M.ASCE, the business director of the IPL program at TRWD. “Also, during the state water planning, we found that both agencies needed an additional water supply of approximately 380 mgd by 2060. Our future water demands were very similar. That is another reason why the two agencies are working together. The IPL program is a win-win for both agencies.”
Section 15-1
The IPL will be completed in five phases. The first phase consists of Section 15-1, Section 15-2 and Sections 12, 13, and 14 (see map). Lockwood, Andrews & Newnam Inc. (LAN), a planning, engineering and program management firm, is the prime designer for Section 15-1, the first section currently under construction in this program. Section 15-1 consists of approximately 16 miles of 108-inch water line, valves, connections and appurtenances along the proposed alignment. Other firms involved in Section 15-1 include Alan Plummer Associates Inc. and CP&Y Inc. Section 15-1, awarded with a bid of $92.9 million, is being constructed by a team of contractors that includes Garney Construction (prime), Oscar Renda (sub) and S.J. Louis (sub).
“The TRWD has existing smaller pipelines that deliver water from Richland-Chambers and Cedar Creek Reservoirs,” said Tony Boyd, P.E., LAN’s senior vice president. “The 90-inch Richland-Chambers pipeline crosses Section 15-1 right in the middle. By connecting to the existing system, TRWD can get more water from this system. The combination of the IPL line and the existing Richland-Chambers pipeline will give TRWD redundancy and increased capacity, enough to meet its water demands for the next 10 years.”
Crossing the 90-inch Richland Chambers pipeline also provided a number of challenges. To accommodate the future construction of the 108-inch line, the existing pipeline first needed to be lowered. LAN had to take into account a number of considerations. To protect the existing pipe, design criteria required no transfer of thrust loading. Also, in order to maintain contracted service to customers, TRWD could only shut down the pipeline for a maintenance period of 45 days during the winter.
LAN evaluated six separate vertical alignments to achieve a balance between protecting the condition of the existing pipeline and meeting the aggressive schedule. Ultimately, the contractor used a 90-inch uncoated, cement mortar lined steel pipe encased in low strength concrete. This allowed for maximum joint length for construction (fewer pieces to install) and provided an alkaline environment compatible with the existing pre-stressed concrete cylinder pipe and cathodic protection system. Construction included removal and lowering of roughly 1,540 linear feet of the existing 90-inch pipeline with part of the length required to handle thrust from vertical bends and some length to avoid creating additional high and low points in the TRWD system.
With design completed more than one year before the allowable maintenance window for construction, sufficient time was available to pre-purchase pipe material and avoid the risk of manufacturing and delivery delays during construction. The pipeline was successfully lowered under a construction-manager-at-risk contract within the allowable 45 day maintenance window without impacting future system operation. The conflict with the proposed IPL line was eliminated.
Additionally, the 90-inch Richland-Chambers line operated at a higher pressure than the planned 108-inch IPL line, providing another significant design challenge. To reduce pressure from the existing line before it reaches the new pipeline, the project team designed a $5 million structure called the Richland-Chambers interconnection facility on a 40-acre site.
“It’s basically a pump station without the pump,” said Boyd. “While it’s not uncommon to reduce pressure to a connecting pipe, the challenge for us was to provide a high level of operational flexibility that could accommodate future pipelines. The IPL rights-of-way could eventually accommodate two more large pipelines and the Richland-Chambers rights-of-way could have an additional pipeline. Essentially, you could have up to five pipelines crossing the 40-acre site in different directions at different operating pressures. We had to figure out how to accommodate interconnection of all these pipelines and still maintain pressure.”
Other project challenges
To install Section 15-1, the project team also had to tunnel under an active Union Pacific Railroad (UPRR) line and under Interstate 45. Both UPRR and the Texas Department of Transportation had strict settlement requirements – no more than one-quarter inch for the railroad and one-half inch for the highway. To accommodate their requirements, the project team performed extensive geo-technical investigations and incorporated a complex network of monitoring equipment in design specifications to ensure that the tunnels stayed within the agreed-upon parameters.
“The biggest challenge was the size of the pipeline,” said Boyd. “Normally, crossing roadways and railroads is not a significant technical issue, but when you put a 12-foot diameter hole in the ground, it changes the way people think. Considering that we were removing so much dirt, a quarter-inch and half-inch settlement wasn’t much to work with. We developed a performance-based specification for bidding, allowing hand mining or the use of a tunnel boring machine with detailed monitoring requirements. Ultimately, the contractor elected to hand mine all of the relatively short tunnels on this project.”
Boyd says the design team was very complex, with LAN, Alan Plummer Associates and CP&Y working side by side and many different design specialties engaged for pipe design, valve design, interconnection hydraulics, transient analysis, stream restoration and traffic control, just as a sampling. They interfaced with as many as 15 design firms working on other phases at the program level, he says.
“We had weekly chats and calls with the three project teams that were working in parallel on various aspects of the pipeline and interconnection design, monthly workshops with the project managers, quarterly specification calls and even meetings with the principal of each firm,” said Boyd. “The scale of the project added another layer of complexity. Section 15-1 will include roughly 2,000 pieces of pipe when constructed, and each piece of pipe weighs upwards of 40,000 pounds. When you consider the embedment material required for the pipe and hauling of any spoils material from the excavation, we’re talking about a lot of heavy trucks traveling through rural county roadways. Along with TRWD and program level consultants, we put in a lot of effort to coordinate with the counties so everybody could be on the same page.”
Conclusion
Despite these challenges, Section 15-1 is on track for completion in August 2015. Phase 1 will be operational by 2018. The final phase of the IPL is currently scheduled for completion in 2030.
Once built, IPL will deliver enough water to meet Dallas–Fort Worth Metroplex water demands beyond 2030. Additionally, over the past decade, TRWD and DWU have embraced conservation efforts such as restricting lawn watering during dry periods. These conservation efforts have bought the district another 10 years’ worth of water supply.
“We are continuing to be good partners for our community,” said Berek. “While the population growth in the metroplex is a good thing, we also need to ensure that our water infrastructure keeps pace with that growth. We are glad that our proactive efforts are starting to pay off.”
ABOUT THE AUTHOR: Justin Reeves is an Associate and Team Leader at Lockwood, Andrews & Newnam, Inc. (LAN), a planning, engineering and program management firm. He can be contacted at JReeves@lan-inc.com.
FOR MORE INFORMATION:
Lockwood, Andrews & Newnam (LAN) Inc., (713) 266-6900, http://www.lan-inc.com/
Alan Plummer Associates Inc. (Fort Worth Office), (817) 806-1700, http://www.apaienv.com/
CP&Y, (512) 349-0700, http://www.cpyi.com/
Garney Construction, (816) 741-4600, http://www.garney.com
Oscar Renda Contracting, (817) 491-2703, http://www.oscarrenda.com
S.J. Louis Construction, (210) 340-9998, http://www.sjlouis.com
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