Published October 2007

STORM: Finessing the Fleet

By Jim Force (page 28)

Denver employs a variety of jet/vacuum vehicles to remove debris from stormwater catch basins, laterals, and improve urban water quality.

What might seem like a minor operation is having a big impact on the quality of the water environment in metropolitan Denver, Colo. The city has adopted diverse methods for removing debris from its stormwater catch basins and lines, and the procedures are helping make the Mile High City’s parks and waterways more appealing.

Lupé Martinez, manager I with the city’s Wastewater Management Division, explains that prior to 2000, the primary pieces of equipment for routine storm drain maintenance in Denver were “flush trucks.”

Four 1,000-gallon-capacity tankers with power-assisted flushing systems moved through the city on an annual basis, flushing the system from top to bottom, ultimately sending most of the flushed material into the South Platte River.

Today, the city uses vacuum trucks and jet rodders to regularly clean each catch basin and lateral, removing debris from the system so it doesn’t foul the waterways and spoil the riverbanks. The new procedure has also reduced backups and overflows.

“In the past, we experienced high levels of bacteria in the South Platte and Cherry Creek,” Martinez says. “Now, by maintaining our basins and laterals instead of simply flushing them, we’re helping make the environment more conducive to kayaking, hiking, and picnicking.” The basin cleaning program has become a key element in Mayor John W. Hickenlooper’s Green-print Denver program (see sidebar) to improve the environment.

A flexible fleet

Workhorses of the new maintenance program are sewer cleaners from Vactor Mfg., provided to the city by Boyle Equipment Co., the Colorado Vactor dealer in Commerce City.

The fleet includes:

• Two Model 2112 combination jet/vac units with 12-cubic-yard debris tanks, 1,500-gallon water tanks, and pumps delivering 80 gpm/2,500 psi.

• Three Model 2115CB catch basin cleaners with 15-cubic-yard debris tanks, 500-gallon water tanks, and pumps delivering 10 gpm/ 700 psi.

• Four Model 2105CB single-axle catch basin cleaners with 5-cubic-yard debris tanks, 500-gallon water tanks, and pumps delivering 10 gpm/700 psi.

The fleet gives the city the versatility it needs, says Jim Hermosillo, operations supervisor with the division. The 2115 and 2105 models break up clogged material with high-pressure water streams and vacuum the material out of the basins. The smaller 2105 units can squeeze into tight spaces, such as the city’s downtown alleys.

“Some of these alleys are only 12 to 14 feet wide,” says Hermosillo. The 2105s span about 10 feet, mirror to mirror, and they can maneuver more easily than larger units in downtown traffic.

Cleaning power

The 2112 combination units provide the solution for removing material from storm sewer laterals. They scour material out with high-pressure jet rodders, then vacuum the debris into the onboard hopper.

Each vehicle is staffed by a crew of two. They situate the unit next to the storm drain and pull the cover. If necessary, they set out safety cones to divert traffic. To clean a basin, the operators first break up clogged material with the waterjet. Then, using a joy-stick controller, they position the boom and 8-inch suction hose.

The boom can telescope to eight feet and can turn 180 degrees. At the pivot point, a durable synthetic material permits the boom to twist as necessary. Once the tube is positioned in the basin, high pressure air — delivered by a centrifugal compressor and dynamically and statically balanced aluminum fan — draws the material out of the basin and deposits it in the debris hopper.

The combination units have a similar vacuum capability, but also are equipped with a 1-inch high pressure jet rodder to clean out lateral lines. The rodder can extend to 800 feet down the lines, although Hermasillo says the lengths encountered in Denver are typically 25 to 50 feet.

The trucks haul the debris to the wastewater treatment plant, where it is placed in a 30-cubic-yard roll-off container that is ultimately taken to a landfill. A screen in the roll-off allows water to be drained and routed to the treatment process.

Scheduling and maintenance

With more than 26,000 stormwater catch basins and 900-plus miles of storm sewer lines, Denver’s crews need about 14 months to complete a full circuit and clean every storm drain. Crews travel a pre-planned daily route to assure complete coverage. A typical cleaning stop may take 10 to 15 minutes, although the time depends heavily on weather conditions, Martinez and Hermosillo point out.

When called for, the city can divert equipment to areas in need of emergency cleaning. The department prides itself on a half-hour response time in these situations.

In the winter, crews manually clear snow and ice from the storm drains. They do not use the waterjet systems until the temperature is above freezing.

The Denver team relies on a Cityworks software program to log the maintenance history of each basin and lateral. Developed by Azteca, Cityworks is a GIS-based asset management system specifically designed to manage capital assets and infrastructure.

To avoid critical downtime and keep the cleaning fleet on the street on a continuous basis, each Vactor unit is brought in for a routine two-hour cleaning and maintenance checkup every week. Every three months, each vehicle is taken out of service for a more rigorous four-hour preventive maintenance procedure, performed by an on-staff mechanic.

“We get the units in and out as quickly as possible,” says Martinez. “The maintenance program has very little impact on the cleaning schedule.”

Results are evident

Though storm drains and basins are pretty much out of the public eye, the Denver catch basin cleaning program is showing results. A series of articles last summer in the Denver Post reported on the renaissance of the South Platte River, which is recovering its natural beauty and recreational functions after years of neglect and pollution.

“I know that our cleaning and maintenance program has had a lot to do with the river’s improvement,” says Martinez. “Keeping our urban waterways clean, as part of the Greenprint Denver program, is the major storm sewer challenge here. It’s good to really see the benefit of our work.”