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