Pima County Upgrades Water Facilities to Reduce Nitrogen Threat
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.
Another design-assist subcontractor, McDade-Woodcock of Albuquerque, has worked with CH2M-Hill on a number of projects, including performing all electrical, instrumentation and control at Roger Road.
“By being engaged early, we are able to work with their designers and keep their designers focused on the important process critical items,” says Rob Rives, president and CEO of McDade-Woodcock. “We’ve done the ancillary work enough, and we know their standards, so we are able to do that ourselves and free up their engineers to focus on their cost-driving items.”
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.