High on Trenchless: Denver Metro Projects Accommodate Urban Expansion
The Denver Metropolitan area has had one of the hottest economies of any U.S. city in recent years. A 2019 Denver Post article noted Colorado’s GDP increased 3.5 percent in 2018 and ranked seventh overall among states for economic growth in the past year, citing U.S. Bureau of Economic Analysis data.
According to the Colorado Office of Economic Development and International Trade, the state is home to approximately 9,800 infrastructure engineering-related companies employing nearly 140,000 people. Statistics from the office also note that about 17 of every 1,000 employees in the Denver metro area are in engineering. There are also more female civil engineers in Colorado than in any other field of engineering.
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In addition, the Denver metro area is home to several engineering firms with a presence in the underground sector, including: CH2M (based in Englewood, Colo., and now part of Jacobs Engineering Group), which has regularly ranked atop Trenchless Technology’s Top 50 Trenchless Engineering Firms; MWH Global (based in Broomfield, Colo., and now part of Stantec); Arcadis North America (Highlands Ranch, Colo.); Cardno Inc. (Lone Tree, Colo.); Lithos Engineering (Lakewood and Ft. Collins, Colo.); and Brierley Associates (Denver).
“There’s a lot of momentum with trenchless both in new installations and rehabilitation in the Colorado market, particularly in Denver and the Front Range area,” says Jeff Maier, water infrastructure practice leader at engineering firm Garver. “There’s also a wide range of acceptance with trenchless technologies, which have hit a mature level in the industry. The area has really adopted a lot of it. I think Colorado is one of the leading trenchless markets in the country.”
Maier notes that while the use of trenchless is not new in the area, population growth and the presence of companies specializing in high-tech have been drivers for the increase in construction to accommodate development, with trenchless being a significant component.
“I think popularity of the area and a more progressive view on technology have been factors for the acceptance,” adds Maier, who also serves on the board of directors for the North American Society for Trenchless Technology (NASTT) and has held a number of positions in the trenchless sector working in the Rocky Mountain region. “A lot of engineering consulting firms have hubs of operation in the Denver metro area, and that provides the resources from a technical standpoint to support that.”
He notes some of the large municipalities and utilities in the area including the Metro Wastewater Reclamation District (MWRD), Denver Water and the City of Aurora have been big proponents leading the charge. He also notes Fort Collins as a willing adopter of alternative project delivery methods. Here’s a look at some of the trenchless work happening across the Denver metro area and some projects that have been completed by various utilities and municipalities in recent years.
City and County of Denver
The City and County of Denver has a capital projects group, Wastewater Infrastructure Project Management (IPM), that is responsible for expanding and upgrading the City’s storm and sanitary sewer infrastructure and waterways.
Separately, the Wastewater Management Division of the City and County manages annual hard bid contracts focused on critical and preventative sewer lining in the city. For its critical maintenance, the Wastewater Management Division has a program that addresses unforeseen issues discovered by sewer inspection using CCTV that it does in-house. The division has an annual fund set aside for these projects and rehabilitates lines in many cases using trenchless. Separately, the division performs emergency repairs that are addressed by its in-house construction team.
The Wastewater Management Division’s preventative maintenance work includes addressing pipelines that are known to be problematic due to factors like age, material type, corrosion or other failures that need point repairs. Those lines are also inspected using CCTV before a plan is implemented by the division’s engineering team prior to contractors being on the job.
“We have a lot of flexibility in our operations because we have in-house CCTV and in-house construction crews to perform work ahead of the contractor to decrease the cost of lining and potentially help eliminate change orders,” says Selena Klosowski, engineering supervisor for the Wastewater Management Division.
Klosowski’s engineering team does design work independent of needing to hire outside design consutlants for wastewater critical and preventative maintenance. Other work that can be completed by the division’s in-house construction crews are manhole repairs and other preliminary work before contractors arrive on the job. In addition, the City also performs vac and jet work to clean wastewater infrastructure as a part of its preventive maintenance and to minimize sewer backups.
Annually, the Wastewater Management Division does about $3.9 million in relining using CIPP. Under its annual contract, the division generally rehabilitates 80,000 to 120,000 lf of sewer pipe including some storm sewer. That program has been managed by the Wastewater Management Division since 2017.
“Trenchless rehabilitation just allows us to prolong the lifespan of our infrastructure without even having to open cut to remove and replace them,” Klosowski says. “In the City, open cut can generally be more disruptive, time consuming and costly than trenchless methods. We see trenchless as a best management practice because it’s more effective with the budget we have.”
Denver’s Metro Wastewater Reclamation District is the wastewater treatment authority for much of metropolitan Denver and parts of northern Colorado. The utility serves roughly 2 million people in a 715-sq-mile area that includes Denver, Arvada, Aurora, Brighton, Lakewood, Thornton and Westminster.
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MWRD declined to be interviewed for this story, but the district, which also performs preventative maintenance, has been active in rehabilitation work on its interceptor sewers.
In 2016, under its Interceptor Condition Assessment Initiative, MWRD’s engineering staff identified 83 pipe segments throughout four interceptors – the Bear Creek, Cherry Creek, Harvard Gulch and Sand Creek Interceptors – and identified severely corroded or damaged pipe segments in need of rehabilitation or repair. Two diversion structures on its West and Southside interceptors were also identified as very poor due to inoperability and a potential safety hazard for entrants. The 2017 Interceptor Rehabilitation Project was initiated in late 2016 to address the identified rehabilitation and repairs. The design and bidding phase work was completed in-house by engineering staff and MWRD entered into a contract with Insituform Technologies for the construction.
Insituform began CIPP insertions in January 2018. Work completed included the following items:
- Several thousand linear feet of the MWRD’s Harvard Gulch Interceptor Pipe (42- and 48-in. diameter) were rehabilitated using CIPP.
- Several thousand linear feet of its Bear Creek Interceptor Pipe (36- and 39-in. diameter) was rehabilitated using CIPP.
- Four different phases of wastewater bypass systems were designed, assembled, tested and operated to accommodate CIPP lining activities.
Another project currently in motion, MWRD’s Second Creek pipeline, will enable portions of Aurora, Brighton, Commerce City, Denver, Denver International Airport and South Adams County to be served by MWRD’s Northern Treatment Plant. The pipeline will be approximately 20 miles long and ranges in diameter from 24 to 60 in. and will be constructed 5 to 50 ft underground. The project will involve 17 tunnels and the general contractor, Garney Construction, has issued qualifications for hand mining, non-pressurized TBMs, guided auger boring/pipe ramming and pressurized microtunneling.
Denver Water’s collection system covers more than 4,000 square miles and the utility operates facilities in 12 counties. It also operates and maintains more than 3,000 miles of distribution pipe. Denver Water has dabbled in trenchless in recent years where applicable, according to the utility’s communications specialist Jose Salas.
According to Salas, in spring 2018, 29th Avenue was partially closed between Sheridan Boulevard and Fenton Street for a rehabilitation project on a 36-in. steel pipe originally installed in the 1920s as one of the final phases of its Ashland Reservoir Tank Replacement project.
Denver Water engineers looked into sliplining the existing 36-in. pipeline with a 30-in. fusible PVC pipe. At the time, the largest PVC pipe Denver Water had used in its system was 24-in., making this the largest PVC pressure pipe install to date. It was determined that fusible PVC from Underground Solutions would adequately supply the flow demands of that system segment while providing a new non-corrosive asset. The 30-in. pipe was fused and installed through a 1,200-ft segment in one week, while the project was originally slated to last three weeks. The project was highlighted in a paper and presented at NASTT’s No-Dig Show in Chicago earlier this year.
As a side note on Denver Water, the utility made headlines earlier this summer when it announced a commitment to replace its remining lead pipes with copper lines over the next 15 years. There are an estimated 90,000 residences in the Denver area that have lead service line connections for potable water and the plan put forth by Denver Water thus far is pending EPA approval.
City of Aurora
Aurora, Colorado, located about 20 miles east of downtown Denver, has been one of the most active municipalities in the metro area when it comes to underground construction, according to Maier.
One interesting project came in late 2018 when the City needed to rehabilitate manholes as part of rehabilitation work on the Sand Creek Interceptor. According to Chris Larson, chief operations officer at trenchless contractor C&L Water Solutions, previously-used coatings and high H2S levels had left the interceptor with dilapidated manholes and more than 60 of them needed to be replaced, some as deep as 25 ft.
C&L was selected as the contractor on Aurora Water’s Manhole Insert Rehabilitation Phase 2 project. Larson says Aurora had experimented with the idea of manhole inserts in the past and was confident in the process. C&L used fiberglass manhole liners from Giddings, Texas-based LFM, a manufacturer of liners designed specifically to fit inside deteriorated manholes. Diameters of the manhole liners are sized 6-in. smaller than the host manhole diameter. The manholes needing replacement on this project ranged from 24 to 42 in. in diameter.
“The City chose the fiberglass inserts because it wanted an inorganic material that’s not subject to corrosion like concrete,” says Larson.
The installation process involved rehabilitating the benches, installing the insert and filling the annular space with a flowable fill or urethane grout. The insert technology gave the City a new manhole at a fraction of the cost and disruption.
“On average, it took about three days to do each of these,” Larson says, with the project taking a total of about 180 days. “A lot of the manholes had high flows, but thankfully they were able to be diverted to parallel interceptors.”
Larson adds the state of trenchless construction has been strong for some time across the state of Colorado, noting the Consolidated Mutual Water Company in Lakewood, Colorado, which began pipe bursting more than 20,000 ft of water pipe annually in 2010.
“I’d say the greater Denver area seems to be very receptive to trenchless as a whole,” Larson adds. “They’ve been very progressive with rehabilitation programs. If anything, it’s slowed down from our perspective. In prior years, we’ve seen some cities doing 100,000-ft projects every year that they’re now doing every other year or every third year. But we’re seeing a lot more rehab work now in the northern and southern parts of Colorado.”
The City of Aurora has also been active on the new installation side in its use of trenchless construction. One such project is the Fitzsimons-Peoria Stormwater Outfall project currently in progress for Aurora Water. This project will upgrade an existing storm drainage basin and infrastructure to convey a 100-year storm event in response to recent flooding and urban revitalization.
The job involves a pair of microtunnel drives being completed by trenchless contractor BTrenchless, which has completed a number of trenchless installations across the Rocky Mountain region. The first is a 72-in. nominal ID Hobas pipe that will be 320 ft using an Akkerman SL74 MTBM. The next drive out of the same pit will be a 48-in. nominal ID Hobas pipe using an SL51 Akkerman MTBM that will be 148 ft.
The project also involves two TBM tunnels that will start this fall, one of which is a 54-in. ID Hobas direct jack TBM that will be 240 ft long and a final drive that will be 96-in. diameter spanning about 280 ft. Those projects are slated to begin in early 2020.
City of Brighton
In the City of Brighton, about 20 miles northwest of downtown Denver, BTrenchless also completed a 660-ft, 72-in. diameter microtunnel under the Union Pacific Rail Yard in 2018. The job installed steel interlocking pipe from Perma-Lok for a new storm sewer. The project was done for the city and Urban Drainage & Flood Control District, which was taking emergency action to alleviate flooding in the area.
Chris Knott, director of business development at BTrenchless, notes the high number of projects in response to storms in the Denver area roughly five years ago that caused significant flooding in the region.
“Everybody really put a keen eye on looking at what systems can handle,” he says. “It’s been a lot of upgrading of storm sewers since then.”
Knott adds that beyond flood control, many of the trenchless projects happening in the Denver metro area reflect the trends in infrastructure construction across much of the United States.
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“I think Denver, like most other cities, is at a point where infrastructure has to be updated,” he says. “It doesn’t matter what it is. It’s all been in the ground a long time, especially in larger cities. Not only are those capacities for water or sewer not sufficient, but it’s also telecommunications, for example. Everything has to be upgraded to match the growth, not just here but everywhere.”