Among several different contracts for the Waukesha, Wisc., 36-mile pipeline and stations, one included 8.5 miles of water supply pipeline, with three horizontal directional drilling and eight tunnel crossings. Contractor Super Excavators sub-contracted the HDD work to ECI Contracting while Lithos Engineering/GEI Consultants provided engineering support.
One of the HDDs was 1,610-feet of 36-inch diameter high-density polyethylene (HDPE).
“It was fun being able to help the city and my hometown with a sustainable water source and return water back to Lake Michigan. But there was nothing particularly unusual about the HDD,” commented Matthew Olson, Lithos engineer. At least, that was the initial thinking.
That all changed early on, when an unlocated 48-inch sanitary sewer, unknown to the project team, was discovered directly in line with the bore path. Sanitary flow from the damaged sewer caused a nearby sinkhole. After setting up a bypass, repairing the sewer and backfilling the sinkhole, the team went back to the drawing board.
“We knew the crossing would have to be re-designed, deeper and longer to avoid the recently repaired sewer,” said Rob Hotz, general manager, ECI contracting.
This required additional geotechnical exploration to extend the borings sufficiently deep for the modified profile. Lithos recommended boring locations, depths and laboratory testing.
“The revised design was approximately 2,117 linear feet – 507 linear feet longer than the original – with 2,000-foot bend radii, and 10-degree entry/exit angles,” said Olson. “The re-design was also 45-feet deep to pipe crown, versus 26 feet in the original.”
The project now also faced an environmental challenge.
“When the drill was extended, it meant going through contaminated soils, where ductile iron pipe (DIP) would be required,” said Hotz.
If the contaminated soils were shallow, the HDD could have been installed with HDPE pipe and the DIP pipe installed via open cut through the contaminated zone. In this case, the contaminated zone was deep and would have required an expensive and time-consuming deep excavation extending approximately 470 feet or changing the HDD pipe to DIP for the entire length. And the HDPE product was already on site.
“In the end, changes are expensive,” said Olson. “We always have Plan ‘A’ with a reasonable contingency plan, but this was far beyond that.”
Cure for a Cure-All
Historically, Waukesha, Wisc., was known for its spring water. In 1868 Colonel Richard Dunbar, a railroad contractor from New York, announced he had been cured of diabetes by drinking 12 glasses of water in a single day from one of the springs. Water from more than 60 natural springs was bottled and sold with tales of curing liver disease, kidney disease, rheumatism, yellow fever, depression, constipation and countless other ailments.
Known as Spring City, the area attracted well-known names such as Richard Sears and Abraham Lincoln’s widow, Mary Todd Lincoln. At the height of its mineral spring popularity, Waukesha drew 25 trainloads per day of tourists, many from Chicago. The water was so prized that when an entrepreneur attempted to pipe it to Chicago for the 1893 World’s Fair, the Waukesha townspeople fended off his crews with pistols and rifles.
Eventually, the springs lost their luster and as the city grew, it needed a new water source for the numerous factories. Wells were installed to reach approximately 2,000 feet into the St. Peter Sandstone Aquifer to meet the increased demand.
By 1987, Waukesha started to realize a problem with its water supply. Despite the fourth-largest lake in the world being less than 20 miles away; numerous creeks, rivers, and lakes; and an annual rainfall/snowfall of 35 and 40 inches, respectively, water levels in the aquifer were decreasing.
In search of a sustainable water source for future use by the southeast Wisconsin communities, the city determined that Lake Michigan was the only alternative that had long-term reliability. The Waukesha Water Utility (WWU) worked with the Great Lakes Common Council, the Environmental Protection Agency (EPA), the Wisconsin Department of Natural Resources (DNR), and local municipalities to gain approval to use Lake Michigan as its water source. As part of the agreement, WWU is required to return an equal volume of water to the lake as is taken out.
A project was initiated to construct a 36-mile pipeline to source from and return the water to the lake, along with a pump station to connect the Milwaukee water distribution system to Waukesha’s network, a booster pumping station in Waukesha, and an outfall station to discharge clean water to Lake Michigan via the Root River. Overall, the infrastructure will convey approximately 8 million gallons per day and serve 16 local communities.
Once this critical piece of the 36-mile pipeline is complete, the city of Waukesha will be able to take water from Lake Michigan and provide a reliable and sustainable water source for its customers – about 8 million gallons per day – and 15 other nearby municipalities. It will also increase water flow in the Root River. Since 1966, its base flow has been too low to support water quality, recreation and fishery goals for trout and salmon sustainability.
Unique solution
Now the project represented a prime example of all stakeholders (owner, contractor and their engineers) working together to innovate a reasonable solution to meet project goals and minimize change cost.
“The project team worked together in an efficient manner to keep the project moving, which has obvious cost advantages,” said Hotz.
The solution was novel: pull both types of pipe (HDPE and DIP) at the same time. But it would be restrained joint (RJ) DIP to enable the pipe to curve, acting like a chain.
“It was designed to include HDD engineering analysis for pulling back approximately 1,646 feet of HDPE pipe connected to approximately 477 feet of RJ-DIP,” said Olson.
The contracting team decided to devise a connection appurtenance to join the HDPE to RJ-DIP above ground and pull the entire pipe string in with the HDD rig. This combined HDPE/RJ-DIP pull would be a much more economical and environmentally friendly way to install the DIP where required.
The team also collaborated on the different components/fittings to transition from HDPE to RJ-DIP; none of them were “off-the-shelf” fittings.
And there were no hybrid pipe design standards to follow.
“We modified pull force and pipe stress calculations from standard approaches for the separate pipe types to estimate factors of safety on pull force and pipe stress – not just on the pipe but also the fittings,” explained Olson.
It was a novel engineering approach.
“To our understanding, this is the first occurrence of pulling a pipe string combined of HDPE and RJ-DIP in an HDD application,” said Hotz.
Novel construction
It was unique from the construction perspective, too.
“I have been involved in pipe pulls of HDPE and steel pipe, but never both pipe pulls at the same time,” said Mike Schibursky, ECI project manager.
While novel, no one hesitated.
“Everyone was eager to try something new,” he added. “We saw it as a great opportunity to prove what we could do.”
The contractor team also modified standard approaches to reduce risk pulling in this unique pipe string and employed several construction risk mitigation techniques.
A Prime Drilling PD 300/900 RP drill rig drill was set up on the west (left) side of the bore, which was also the lower elevation end of the alignment.
“We did this to reduce probability of inadvertent returns (IR) and so the rig would be in position for pullback after reaming of the borehole. Product pipe was lined up to the east/right,” Schibursky explained. “We set up a turbidity curtain in the Root River to capture any IR should it occur.”
Pipe was pulled in using water for ballast to reduce installation stresses.
ECI brough a variety of reamers for multiple soil conditions and fabricated eight different fittings.
“One of the most important risk-mitigation tactics was the steel sleeve constructed around the connection appurtenance to prevent any protrusions from grabbing or catching on the borehole wall,” he added.
Another example of great coordination and cooperation was road and lane closure for the pullback. “The city was fantastic in helping make the operation successful,” said Schibursky. “We were bringing pipe down the center of the roadway and were able to keep the flow of traffic and maintain access to businesses and residential areas.”
Construction started in April 2023 and took 62 days to complete. UI
FOR MORE INFORMATION
ECI Contracting, (888) 527-2294
Lithos Engineering/GEI Consultants, (303) 625-9502