Sacramento Turns to Trenchless for LNWI, UNWI Projects
The County of Sacramento, Calif., recently completed some of the most extensive and challenging underground infrastructure work ever done in the United States.
The cost, personnel and technology involved set new standards in terms of innovation, creativity and minimal disruption to residents and businesses.
Trenchless technology was critical to the success of two massive and much publicized interceptor projects — the Lower Northwest Interceptor (LNWI) and Upper Northwest Interceptor (UNWI) — that were part of a vital expansion program by the Sacramento Regional County Sanitation District (SRCSD) to address the growing needs of its customers. But trenchless technology has been used elsewhere in that area, including water projects that upgraded and expanded lines for the Sacramento County Water Agency, proving again that its use is essential to our underground infrastructure.
The use of trenchless technology — specifically microtunneling and pipe jacking — in the Sacramento area on these interceptor projects and others shows the forward-thinking and proactive approach of the public works officials and engineers in addressing these critical links, which cost more than $900 million dollars to design and construct and more than a decade to complete.
An interesting aspect to the LNWI and UNWI programs was that the work shone a bright light on the use of trenchless technology at a time when the industry was really just coming of age in the late 1990s and microtunneling was a little used and thought of construction method in North America. These projects became a tremendous platform to show what trenchless technology brings to North America’s infrastructure needs.
Interceptor Program
The Sacramento Regional County Sanitation District provides regional wastewater conveyance and treatment services to residential, industrial and commercial customers throughout unincorporated Sacramento County; the cities of Citrus Heights, Elk Grove, Folsom, Rancho Cordova, Sacramento and West Sacramento; and the communities of Courtland and Walnut Grove. The wastewater travels through 177 miles of interceptor pipelines to the Sacramento Regional Wastewater Treatment Plant in Elk Grove, where approximately 150 million gals of wastewater are treated each day and safely discharged into the Sacramento River.
SRCSD was formed in 1973, and in 1982 the Sacramento Regional Wastewater Treatment Plant began service. But by the early 1980s, the SRCSD board knew the district had to expand and upgrade its sewer network to serve the growing population and businesses in the Sacramento area.
“The original interceptor system was designed to accommodate 20 years of growth,” said Kyle Frazier, SRCSD senior civil engineer.
Formulation of the SRCSD’s expansion program began in the 1980s and ramped up during the 1990s, with serious discussion of how to construct the network. Best value design options were discussed and researched and open-cut played a big role. But alternatives were also needed and that’s where trenchless technology came into play.
Design and construction of the Lower Northwest Interceptor and Upper Northwest Interceptor got under way during the 2000s, with completion of both by 2010, with LNWI done by 2007. “We have doubled the size of our system during that expansion. We currently have 58 miles of pressure pipes and 110 miles of gravity pipes ranging from 24 to 144 in. in diameter, with a majority being 48 to 66 in. in diameter,” Frazier said.
Combined, the Lower and Upper Northwest Interceptors mark completion of SRCSD’s longest interceptor reach that extends nearly 40 miles from Citrus Heights to North Natomas through West Sacramento and to the treatment plant in Elk Grove. It consists of pipe sizes ranging from 36 to 144 in. in diameter, as well as three large pump stations, the largest of which is rated for 221 mgd.
To complete these projects using strictly open-cut methods would have made the work less costly but longer and much more intrusive to the public. SRCSD wanted to keep the disruption to a minimum, if possible, and find creative ways to go under challenging rivers like the Sacramento and American rivers, levees, railroad crossings and high-traversed roads and highways.
Trenchless technology availed to SRCSD the alternative construction methods that would drastically impact the success of these huge construction endeavors, as well as expand and grow the workload for trenchless engineers, contractors and manufacturers on the West Coast for the next decade. SRCSD officials were a kind of trailblazer of sorts when it came to selecting microtunneling for key segments of the interceptor program. Microtunneling, though a well-accepted installation method outside of North America, was still trying to make inroads here when the program was first being discussed.
“We had a lot of challenges related to construction of our expanded system, especially trying to put large diameter pipes into narrow populated corridors and having major obstacles such as streams, rivers and levees,” Frazier said. “The use of trenchless technology in these areas allowed us to successfully complete these projects.”
Each of these interceptor projects were divided into multiple segments for engineering/design and construction and each of those segments further divided, creating even more work for trenchless personnel in that area. For example, UNWI was divvied into nine segments and within those segments, broken down even further. Of the more than 120,000 ft of pipeline installed during UNWI, trenchless technology was used to construct more than 70,000 ft. For the LNWI, approximately 30 percent of the total footage was installed using trenchless technology. As one engineer put it, “This was an impressive trenchless program.”
The interceptor program took more than a decade to design and construct, with completion of both by 2010. This program became the hub of trenchless work in the Sacramento area for a slew of engineering firms serving as designers, construction managers and program overseers. These included but not limited to CH2M Hill, Black and Veatch, Montgomery Watson, URS, Jacobs Associates, Parsons Brinckerhoff, Bennett Trenchless, Hatch Mott McDonald, CDM, and Brown and Caldwell. Among the trenchless contractors who contributed to these amazing projects were: Vadnais Corp., Steve Rados Inc., Walter C. Smith Co., Michels Pipeline Construction, Nada Pacific and Traylor Bros.
In the case of engineering firm Bennett Trenchless, David Bennett relocated his operations from Mississippi to the Sacramento area in the late 1990s when his firm was contracted to aid SRCSD on some test projects to determine whether microtunneling would be a good fit. “The area had challenges with its geology,” said Bennett. “The pioneering spirit of SRCSD shone through in its spending of several million in research dollars on these test projects. They really embraced trenchless technology early on.”
Now firmly established in the Sacramento area as a leading engineering firm, Bennett and his senior project engineer, Matt Wallin, say the volume of work generated by SRCSD over the last decade was incredible, bringing with it inventiveness and innovation by the design and construction teams. And trenchless technology benefited from a good deal of it, they said.
“Since 2001, we have worked on at least 15 different projects with SRCSD,” Wallin said. “SRCSD sort of single-handedly supported the trenchless industry in this area for over a decade from designers to contractors.”
Dan Schitae, project manager with Vadnais Corp., a microtunneling contractor in Vista, Calif., said Vadnais was involved in many of the trenchless contracts for the interceptor projects and the work enabled the contracting firm to grow in experience with each project — something that could be said of many of the contractors involved.
“The program was quite a boon for trenchless contractors,” he said. “When the LNWI program kicked off, it added a lot of trenchless work for contractors. In 2000, Vadnais also did some long crossings of the American River for the City of Sacramento as part of its 48-in. water line. For UNWI, we worked Segment 9 that involved almost 30,000 ft of microtunneling.”
The interceptor work Vadnais allowed the contractor to refine its in-house slurry separation technique, which produces a more efficient separation of spoils from the slurry. “By the time we got up to Segment 9, where we were doing 30,000 ft down the center of a street, there wasn’t a drop of slurry that hit the ground,” Schitae said
Frazier said that microtunneling was used in the areas that made the most sense in terms of soils, elevations and public disruption. “We used trenchless technology extensively in areas where it made sense or was the only available technique, such as for major river crossings like the Sacramento and American Rivers,” he said. “We relied on our engineering consultants who brought in tunneling experts such as David Bennett, for example. The trenchless field has been maturing over the last few decades. There were a lot of lessons learned over the years that we used to help us choose the right type of construction and the best way to put it together in a package.”
Andrew Finney, a senior geotechnical engineer with CH2M Hill, was intimately involved with UNWI Segments 3-4, in which CH2M Hill served as the lead design firm (Michels Pipeline Construction was the contractor). His role was the overall tunnel lead for the contract through its design and construction, teaming with Bennett Trenchless and Jacobs Associates. He said the interceptor program opened a lot people’s eyes — including his own due to his limited experience with trenchless at that time — to what trenchless can do.
“We were working in challenging soil conditions due to the Sacramento River and shallow groundwater,” Finney said. “We actually microtunneled under levees, which was the first time microtunneling was used under a levee. Before that the U.S. Army Corp of Engineers only allowed horizontal directional drilling to be used under levees.
“The impact that these and other trenchless projects in this area had on the trenchless industry has been huge,” Finney said. “Projects like these raise the awareness of the technology and how it can be employed. Sacramento [officials] were very willing to embrace a higher cost but lower impact solutions for their projects.”
And Finney is quick to note that there are more projects in Sacramento than just LNWI and UNWI. He noted that projects such as U and S Streets Inline Storage Project that increased drainage in the downtown Sacramento area by providing inline storage and peak-flow delivery capacity to the Sump 1A pump Station used microtunneling as did the Freeport Intake water project.
The Freeport Regional Water Authority Project was the result of the Sacramento County Water Agency (SCWA) and the East Bay Municipal Utility District (EBMUD) recognizing a common need to meet and improve their current and future demand for water supplies more reliably. The two entities came together to construct a joint development of a regional water supply project at a cost of more than $350 million; project construction took place between 2007 and 2010. The project involved construction of giant two-story pumps to pull the water out of the Sacramento River into an underground vault. A special system was built to rid the water of sediment and provide enough clean water for 1.6 million customers.
“This project crossed Interstate 5, Highway 99, had railroad crossings and crossed a number of environmentally sensitive areas,” said Forrest Williams, program manager for the joint venture of SCWA and EBMUD. “We used trenchless technology, specifically microtunneling, in order to satisfy environmental concerns and the conditions of crossing railroad easements and to avoid utilities already installed.”
Unfortunately for Sacramento customers — and trenchless contractors and designers — public works officials have curtailed their infrastructure projects over the last few years as the housing market bottomed out, even though they had more projects on their books.
“Given the current economic conditions, this [new] system is going to have to last longer than initially planned when designed. The growth has slowed,” said Frazier.
But Frazier noted that SRCSD is moving toward applying an asset management program to look at the condition of its pipes and focus on inspection using techniques such as CCTV, sonar, laser and electromagnetic. “This is just in the planning stages right now,” he said.
Sharon M. Bueno is managing editor of Trenchless Technology.
