Cottonwood Drive Widening Project

The Cottonwood Drive widening is an important capital improvement project for the Town of Parker, Colorado. It features the expansion of the roadway from two traffic lanes to four lanes between Cottonwood Way and Jordan Road, the renovation of an existing bridge spanning Cherry Creek, and the construction of a new adjacent bridge to accommodate the added lanes of traffic. As part of the redevelopment, the Town had to develop a plan to comply with the local stormwater discharge regulations.

STORMWATER REGULATIONS 

Because the project is located in the Cherry Creek Reservoir watershed, it has to meet some more stringent ordinances for stormwater discharge than the typical state MS4 requirements. As outlined by the Cherry Creek Basin Water Quality Authority and the Town of Parker criteria manuals, all new development or redevelopment is categorized in tiers based on land disturbance and new or increased impervious areas.

“This was a large road widening and fell under Tier 3 water quality requirements,” explained Michael Grabczyk, PE, CFM, Stormwater Project Manager for the Town of Parker. “We had to provide full water quality capture volume and prescribed BMP as outlined by the flood district and state or provide an alternative treatment device that reduces the total suspended solids (TSS) concentration to below the median value of 30mg/L.”

STORMWATER MANAGEMENT SOLUTION

After considering the alternatives for the project, an above-ground pond and two SiteSavers, hydrodynamic separators, were selected to meet the stormwater volume and water quality requirements. The first SiteSaver was installed near Cherry Creek under the new bridge and the second was placed near Jordan Street. The two devices will be used to remove pollutants like trash, hydrocarbons, and sediment from the road’s stormwater runoff before draining into Cherry Creek.

“SiteSaver was chosen for this project for meeting the stormwater requirements, exceeding in all the Town’s maintenance needs, and making the price work,” stated Grabczyk.

PROJECT CHALLENGES

The project team faced challenges regarding site constraints, timing, and changing stormwater regulations. This project is an improvement of existing infrastructure that was a couple of decades old. A lot had changed in terms of water quality requirements since its construction, and the area was surrounded by existing developments, so there was no space available to go outwards to meet the new requirements. “It was a site constraint and space issue,” affirmed Grabczyk.

In addition, the time between when the project started and when it was bid was long. The first design was created in the early 2010s, and it was shelved for many years. Since then, stormwater regulations have changed as well as the technical details about new and existing treatment devices.

The existing drainage report was written with standards that were no longer relevant, and a lot had to be considered for the location of the new BMPs and to make sure they would meet the Cherry Creek Basin Water Quality Authority regulations.

MAINTENANCE 

The Town of Parker has a stormwater utility department that is responsible for maintaining and managing all the town’s stormwater infrastructure, including drainage ways and storm sewers. Stormwater ponds and any kind of BMP devices are inspected regularly.

The SiteSaver devices will be inspected every six months for the first few years to determine the site-specific rate at which the internal reservoir fills with pollutants (sediment, trash, hydrocarbons, etc.). A long-term maintenance schedule will be implemented based on these inspections and adjusted as needed.  Maintenance will be done by replacing the disposable net component and using a vacuum truck to remove sediment, hydrocarbons, and water within the unit.

“We had a great experience with StormTrap. The sales representatives were responsive and very knowledgeable; they assisted us from initial project phases to completion,” affirmed the City’s Stormwater Project Manager.