Pima County Upgrades Water Facilities to Reduce Nitrogen Threat
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."