Trends Winter 2009 | Page 3

n 2006, the northern Colorado city of Fort Collins started noticing a big problem at its raw water treatment plant that the City could not ignore: An onslaught of pine needles, leaves, and other debris was plugging valves integral to controlling flow in the water treatment process. Without continual cleaning, the debris shut down flow from the Pleasant Valley Pipeline and eliminated one water source for the two local water treatment facilities. The pipeline brings water fresh from the Rocky Mountains down through the Poudre River and then through an irrigation ditch and into the treatment plants, serving as a secondary supply for the City and three surrounding water districts. The following year, the City installed a temporary screen to trap debris farther upstream from the treatment plant at the entrance to the pipeline. However, during peak spring runoff the screen needed to be cleaned as much as every two hours, around the clock. “It was labor intensive and costly,” said Owen Randall, City of Fort Collins senior utility engineer. Compounding the problem was the fact that an infestation of pine beetles – which are deadly to mountain pines – was quickly spreading through the Rocky Mountain forests, bringing with it increasing debris from beetle-killed trees. The City knew it had to find a more permanent fix by peak runoff season in March 2008, a virtually impossible timeline considering it was starting with no feasible plan, Randall said. Although a previous plan had called for a large sedimentation basin to settle organics out of the ditch water before entering the pipeline, this was deemed too costly and difficult to maintain. “So we really had no idea what we’d end up with. We were literally starting with a blank sheet of paper. I was really concerned the timeline was just not feasible,” Randall said. Using its Alternate Project Delivery System, or APDS, the City quickly assembled its consultant, Ayres Associates, and general contractor, Hydro Construction, to work in concert with the City utility to find a solution. Rather than a typical design-bid-build process, the APDS requires that the owner, consultant, and contractor work together from the start of the project through its completion. After exhausting many options during brainstorming sessions, the group zeroed in on a traveling screen technology, which is more commonly used for wastewater applications. Ayres Associates project manager Chris Pletcher found that the energy efficiency of the screen combined with the reliability from its use in primary screening wastewater applications was the ideal combination for this debris problem. “The traveling screen looks like a giant band that continuously rotates so when one section is trapping debris, the other I