About five years ago, the city of Alamosa, Colo., was facing arsenic levels of 30 ppb in its drinking water—far beyond the U.S. Environmental Protection Agency’s (EPA) limit of 10 ppb. The city’s public works director, Don Koskelin, realized Alamosa needed a treatment process in place quickly to deal with this problem.
According to Koskelin, the city felt it was heading into uncharted territory. It had never had a treatment process for its drinking water before, and at the time arsenic removal was still a fairly new and developing science.
“We couldn’t just take something off the shelf and replace it. We had to build the shelf first,” said Koskelin. The city began working with Arber Associates, a planning and design engineering firm for water/wastewater projects out of Lakewood, Colo.
The Planning Phase
The city and Arber agreed that a brand new arsenic treatment plant should be constructed. Most of the project’s challenges came in the initial planning phases of the new plant. There was not much previous research and testing done on arsenic removal technology, and the fact that the city’s drinking water had high amounts of dissolved silica posed a challenge as well.
“The high levels [of dissolved silica] made it difficult to choose more common methods of arsenic removal,” Koskelin said.
In determining the process that would best fit their needs, the city and Arber looked closely at the current distribution system and storage capabilities, both of which would be affected by the new plant. The two parties narrowed down their choices to these two: an ion exchange process, or a coagulation process followed by membrane filtration. After comparing them in terms of cost, maintenance and efficiency, it was agreed that they would treat the arsenic by coagulation and membrane filtration.
Picking the right membranes was also a challenge because the type of membrane would determine the design of the new plant; therefore, Alamosa staff and Arber had to pick the membranes first. The city did a lot of field testing with different membranes and subsequently picked GE/Zenon submerged membranes, which performed well.
Another hurdle for the city was designing and constructing a new facility on a previously developed site. A developed industrial/commercial site located in the central part of the Alamosa was designated for the new plant. Although strategically located next to an existing city well, the site posed limitations for the size of the facility and construction techniques.
Arber worked closely with the city, GE/Zenon and general contractor Moltz Construction during the design to develop a facility layout that would be functional and operational on the existing site, make the required site improvements that were necessary prior to construction and address site constraints in order to build the plant within the required 15 ft of the city’s main well.
“The WTP as constructed is not only functional, but is aesthetically pleasing as compared to the site prior to construction,” said Steve Ravel, P.E., project manager for Arber Associates.
Construction & Community Reaction A plan was put into place to build a $10.5- million arsenic treatment plant. Moltz Construction began building in March 2007.
For the 11,000 people the drinking water system serves, there was a mixed reaction about the new treatment plant.
“We heard a lot of feedback. Many people really questioned if there was a need to do this, and it was hard to convince people that it was truly necessary,” said Koskelin. “Others were more accepting and more open to the new research done through the EPA about [the effects of] arsenic. They were very happy that we’ve been so proactive and got this done so soon.”
The project was funded in four different ways: a state grant, money from the Colorado Department of Local Affairs, the city’s reserved fund and money from the federal Revolving Loan Fund.
Plant operators have already begun rigorously testing the system and filtering water. Koskelin said he expects the plant to be in final completion stages and online in September 2008. The parties involved overcame all of the challenges by planning very carefully, performing test after test and working together.
“[This process] has been educational for all of us,” Koskelin said. “Moltz Construction and Arber have been a joy to work with.”