MWH Constructors and Denver Water Partner on Upgrades to Combat Denver Population Boom
When aging infrastructure bumps up against population growth, utilities are often caught in the middle. Denver is working through the thick of that phenomenon right now. Built in the early 1960s, the water facility on the south side of the city originally featured two 15-million-gallon reservoirs. A pump station was added just a few years later. But time has taken its toll on the facility, and John Kolkman, Project Manager at MWH Constructors, now part of Stantec Construction Group (Constructors), says, "It's over 50 years old and there have been some wear and tear that comes with age."
Since the initial construction, Denver's population has also continued to grow, placing greater demand on the storage and pumping facilities. To ensure the continued reliability of the system and to address increased consumption by the city's communities, Denver Water decided to upgrade and expand the site. "We're replacing those two existing reservoirs with three new 15-million-gallon circular post-tensioned tanks," Kolkman says. "At the same time, there will be a new pump station constructed to replace the existing one." The Hillcrest reservoir project will tackle the intersection of outdated facilities and a burgeoning local customer base, and provide Denver Water with a more stable path forward.
Funding and Bid Packages
Denver Water is funded through a number of routes, including water rates, bond sales and hydropower sales. "We use those dollars to maintain and upgrade the water system," says Martin Garcia, P.E., PMP, Senior Engineer at Denver Water. The project, with an overall budget of $100 million, is being delivered using a construction manager at risk (CMAR) approach. Constructors are the designated CMAR contractor, and Garcia says, "They were engaged early in the design phase, and they provided input to constructability and cost estimating." Once the design packages were released, then developed bid packages for subcontracting and material procurement.
The project is separated out into five work packages. That process of splitting the overall scope into smaller chunks has resulted in a number of benefits for the contractor team and Denver Water. The first package, for example, consisted primarily of the large diameter piping and associated valves needed for the project. Though that early package wasn't large - only about $1.3 million - Kolkman says, "It allowed Denver Water to confirm design for that section and it also allowed us to do procurement early."
Though a number of key materials had long lead times, the team was still able to get the pipe delivered to the site before the next phase was ready to launch. "We could start work right away, which was important because the pipe needed to go in early," Kolkman explains. Given the space constraints of the site, the team planned to stack about 200,000 cubic yards of dirt on top of the newly installed pipe almost immediately.
Bundled in the second work package was the majority of the dirt work, where the team conducted mass excavation and subgrade development with a lime-stabilized soil treatment, along with associated minor items. The strategy allowed the geotechnical engineer to complete the necessary preliminary work without delaying later activities. "If we had waited for all of the design to be done, the start date would have been pushed out by several quarters," Kolkman says.
The third package is the construction of the three new tanks. Work package number four is scheduled to launch in 2018, and will cover replacement of the pump station. The last work package will wrap up a variety of close-out items. "It will take care of landscaping, paving, new fences and finishing off the site," Kolkman says.
Staging the work in this manner has involved more overhead on Constructors' part, as opposed to simply tackling the entire task list at one time. The end result, however, has been more efficient scheduling and less downtime. It also provided additional opportunities within the local subcontractor community, where smaller businesses are sometimes unable to bid on very large projects.
"We held an outreach in Denver that was well attended, and we tried to include those companies so they could participate in the project," Kolkman says. "We wanted to think about parceling the work into small enough packages so they're manageable for smaller businesses." Through the process, Constructors identified several local firms that will benefit from the project, and Kolkman adds, "The project has benefitted from using them, as well."
As with most construction efforts, the Hillcrest reservoir project includes a number of weather-dependent activities within its scope. Cold temperatures and precipitation can wreak havoc with schedules. "It does cause some angst about how we handle some of the larger concrete placements," Kolkman says.
Because traffic and other issues often complicate concrete work, the large slabs that will support the 310-foot diameter tanks - and the corresponding roof pours - are done on Saturdays. "When we schedule those, we're typically scheduling four or six months in advance," Kolkman explains. If the weather presents challenges on that day, the slab pour must be bumped by a full week. "We had to do contingent planning around that," Kolkman says of the tricky scheduling.
A rather extensive temporary drainage system also had to be installed around the construction area. "There's a lot that goes into handling snow and wet conditions on the site," Kolkman says. He adds that spring flooding only made the situation worse, so Constructors came up with provisions to control the water. "We had to maintain access to the construction areas, as well as out to the tanks, which are sitting in a large, open excavation." Fortunately, the team has had more flexibility on the tank walls, which are smaller, weekday-friendly pours, and can be more easily blanketed and protected from weather.
With its long-standing commitment to environmental stewardship, the utility found an opportunity to pursue greater sustainability as part of the Hillcrest project. Paul Ries, P.E., Senior Mechanical Engineer at Denver Water, says the building envelope of the new pump station will include increased thermal barriers to help lower the energy demand of the HVAC units.
"The HVAC equipment will consist of efficient evaporative cooling units for the pump gallery and heat pump units for the office and electrical areas," he explains. "All of the HVAC units will utilize full economizing capabilities to provide natural heating and cooling through simple building ventilation." With nearly 7,000 horsepower on tap to convey an estimated 115 million gallons of water a day, the team specified premium efficiency motors for the pumps. The result will be greater capacity from the facility without sacrificing pump efficiency.
Building Strong Community Connections
Communications with nearby residents have been carefully orchestrated to ensure the public is aware of the project's long-term goals and short-term impacts. The jobsite is located adjacent to a main north-south freeway, and is surrounded on the other three sides by residential neighborhoods. "Outreach events were held during preconstruction, before we started, with each of the neighborhoods," Kolkman says.
Denver Water and Constructors participated in town hall-style meetings that were held at the local high school and in the meeting facility of a nearby condominium complex. These gatherings provided residents with the opportunity to ask questions and better understand the construction events that might periodically disrupt traffic flows or other activities. "Denver Water also did additional renderings of what the finished site will look like, so neighbors know what to expect," Kolkman says.
These early sessions were augmented by the mailing of a brochure to residents near the property boundary. "It outlined what neighbors could expect to see and experience over the four-year duration of the project, including our communication commitments," Garcia says. In addition to updates posted to Denver Water's website, other platforms were also used to keep residents informed about the project's progress. Among those were an opt-in e-mail distribution list and the use of the Nextdoor application to provide regular updates to neighbors.
Face-to-face discussions have been ongoing, and Garcia explains, "Denver Water and contractor communications representatives conduct annual walk-throughs of the neighborhood immediately adjacent to the work site to check in with neighbors, answer questions and address issues." By adopting a communication strategy that's in tune with the community and its needs, the Hillcrest project team has been able to maintain good information flows and leverage the most effective tools and discussion platforms for its audience.