A decade ago, Pima County's Regional Wastewater Reclamation Dept., or RWRD, was facing a problem: The Arizona Dept. of Environmental Quality had ruled that the levels of nitrogen coming from RWRD's network of 10 wastewater-stripping and treatment plants were too high. At that point, the 41- million-gallons-a-day Roger Road plant was releasing wastewater with nitrogen levels between 30 milligrams and 57 mg per liter, well above the 10 mg/l requirement, say county officials.
While nitrogen is known to be harmful to aquatic life, experts say that, when its levels are higher than would occur naturally, it also can be harmful to children and babies. Two of the system's plants—the facilities at Roger Road and Ina Road—discharge directly into the Santa Cruz River and thus presented a potential threat to health.
Although the county regularly monitors the quality of water and no local water providers draw from the groundwater near the Roger Road and Ina Road facilities, the county and Arizona Dept. of Environmental Quality (DEQ) officials were concerned that effluent discharged into the river could percolate into local groundwater and increase nitrogen and ammonia levels in the aquifer.
The Arizona DEQ, in accordance with federal requirements, had set permissible nitrogen and ammonia limits to a range of 8 mg/l to 10 mg/l. By 2006, the DEQ told Pima County officials they would need to meet the new requirements at the Ina Road facility by Jan. 1, 2014, and at the Roger Road facility by Jan. 1, 2015.
As a result, RWRD embarked on a $720-million Regional Optimization Plan (ROMP) to improve the quality of its effluent. The program is using innovative techniques as it expands and upgrades the 37.5-million-gallons-a-day Ina Road plant to 50 mgd and replaces an aging, outdated 41-mgd wastewater stripping plant with a new, state-of-the-art 32-mgd water reclamation plant at Roger Road. The plan also includes an interceptor sewer that reroutes flows from the Roger Road plant to the Ina Road facility, which was completed in December 2010.
New Way of Doing Business
For ROMP, the county opted to use alternative delivery methods on the projects, says Jackson Jenkins, utility director for the Pima County RWRD. With $720 million at stake in the ROMP program—the largest such undertaking in the county's history—officials decided "the time was ripe to take a look at some other methods," Jenkins says.
For the Pima County Water Reclamation Facility (WRF) at Roger Road, "we decided that a DBO [a design-build-operate contract] was the best value to the ratepayer and to the region. Based on how things have come out in the building and completion of this project, I think we made the right choice," Jenkins adds.
CH2M Hill won a $164-million portion of the design-build-operate contract in December 2010. The project's total cost for the capital phase is $172 million. The Englewood, Colo.-based firm will operate the facility for 20 years, using primarily local labor.
MWH Constructors Inc., Broomfield, Colo., is the construction manager-at-risk on the project's $227-million Ina Road upgrade and expansion, CH2M Hill is the designer, and Jacobs Field Services of North America is the program manager.
In contrast to the traditional design-bid-build process, the entire team on both projects used an integrated planning process, working collaboratively to scare off potential hiccups. John Cevaal, MWH Constructors vice president and western U.S. operations director, says, "If [the county] had tried to fully design [the Ina Road project] and bid this out, I really think they would have had multiple claims for schedule delays as well as unforeseen conditions that they would have had to navigate their way through."
Doug Post—senior project manager for the Phoenix office of Archer Western Contractors, which is serving as a subcontractor to CH2M Hill on the Roger Road WRF—says his firm was present during the design meetings with CH2M Hill and provided input on the constructibility of the design.
"We would chime in and give input on constructibility and how we were going to build it at the same time they were figuring out the design of it. We were able to fix most of the headaches that you'd see on a regular hard-bid job where you don't have that input. That was extremely helpful and made the job go quite well from a construction standpoint," Post says.
Archer Western performed earthwork, excavation and backfill, built all underground piping and poured structural concrete for the WRF project, which is on schedule and expected to be complete by May 2014, well ahead of the Jan. 1, 2015, deadline.
At the Roger Road WRF project, CH2M Hill made several innovative design decisions. First, the design team opted to use a dissolved air flotation (DAF) system at the beginning of the process train rather than at the end, where DAF systems are usually located in wastewater treatment systems. This is the first such DAF application in the U.S., says Greg Fischer, projects program manager for CH2M Hill. By placing the DAF at the start of the process, the county eliminated the need for four extra primary clarification tanks, Fischer says.
For nitrogen removal, the county required a five-stage Bardenpho process, which passes the flow through an anaerobic zone and then through alternating anoxic and aerobic zones. After consulting with firms such as Greeley and Hansen of Chicago, county officials decided that, as part of the ROMP approach, the Bardenpho process would be the most effective at removing nitrogen, ammonia, phosphorus and other key elements. CH2M Hill expanded on this concept by incorporating step-feed and simultaneous nitrification and denitrification features. According to CH2M Hill officials, the overall plant system is designed to provide operational flexibility. Further, it will achieve higher effluent-water quality at lower capital and life-cycle costs than other treatment alternatives that were evaluated.
A two-pronged approach confronted odor reduction. The team developed one system that deploys a carbon adsorber system for serving the bioreactor, consisting of an odor exhaust fan, two dual-bed carbon adsorber vessels and a bypass stack assembly. The team also designed an engineered biofilter system that has two large odor exhaust fans that will draw air from both the sewage's plant entry point and the DAF; then, the air is drawn into a three-cell, long-life engineered media biofilter system. The biofilter system will be covered, and the headspace air will be routed out of a common 30-ft-tall stack via stack exhaust fans.
A Discovery at Ina Road
During the design phase in 2009, the county discovered that parts of the plant were sitting on a veritable historical treasure: an irrigation and canal system dating back to the San Pedro period, between 1250 B.C. and 750 B.C. An archeological team was brought in to evaluate and document the findings.
"The site of Las Capas at the Ina Road wastewater expansion project is the earliest and most complicated and sophisticated agricultural irrigation system discovered in North America so far," says Loy Neff, program manager with Pima County's office of sustainability and conservation. Archeology magazine cited the discovery as one of the top archeological finds of 2009.
MWH's Cevaal says the archeological team needed about six months to unearth and document the findings. However, the excavation and archeological work unfolded during the design phase, and the county provided extra personnel to get the job done quickly. As a result, the construction schedule did not slip. "When they were done mapping it, we could go in and complete the excavation and start the construction of our basins," Cevaal says.
Work at Ina Road
The work at the Ina Road facility includes constructing a new 25-mgd ammonia-, nitrogen- and nutrient-removal process system—that is, the five-stage Bardenpho process—to replace an existing 25-mgd high-purity oxygen train; upgrading an existing 12.5-mgd biological-nutrient-activated-sludge process train for additional nutrient removal; and constructing another 12.5-mgd capacity ammonia-, nitrogen- and nutrient-removal process system. Cevaal says the project is expected to be complete by October 2013, well ahead of the Jan. 1, 2014, deadline.
The plant's construction is fairly intricate, Cevaal notes. Every time workers connect two pipes or replace an existing pipe with a new one, they have to perform a maintenance of plant operations (MOPO), essentially shutting down some of the plant to allow the work to be completed. Cevaal estimates there will be more than 100 MOPOs before the project is completed. Moreover, the team likely will have to shut the complete plant down about eight times. "Every time we touch an existing pipe or an existing part of the process, it's a very extensive and collaborative process that we go through between [ourselves], the designer, Jacobs, the plant's operators—sometimes literally going minute by minute of what we have to do to make that tie-in successful," Cevaal says.
Between hiring top-tier firms to create innovative projects and using progressive delivery methods, the Pima County RWRD is proud of what the ROMP program has achieved, Jenkins says.
In the past, the department used a delivery method that was "design, bid, build, litigate," Jenkins quips, because contractors and subcontractors would frequently get into disputes with the county over pricing and other issues. But things have turned around significantly, he says. The ROMP program has gone very smoothly. "Now we have a good story to tell."