Hefty project aims to improve Straight Creek’s water quality

SUMMIT COUNTY — Several construction projects slated for this summer near the Eisenhower Tunnel will aim to improve the fish habitat and water quality in Straight Creek, which supplies the drinking water to Dillon and Dillon Valley.

Straight Creek is listed as “impaired” under the Clean Water Act because of the amount of sediment — mostly sand and small pebbles — in the water, which can disrupt the fish spawning cycle.

The sediment also can create a costly filtration process for the town of Dillon and the Dillon Valley District.

“In the big runoff years, a lot of that sand washes down and fills in our diversion structure that runs to the water plant and we have to dig that out,” town of Dillon engineer Dan Burroughs said.

The sediment problem isn’t new, said Colorado Department of Transportation (CDOT) environmental planner Terri Tiehen.

“We’ve been working on this for over 15 years,” Tiehen said. “It’s a land management issue for the Forest Service and a drinking water issue for the town of Dillon.”

All the land surrounding I-70 near the tunnel is owned by the U.S. Forest Service, although CDOT has an easement for the interstate.

Though the sediment doesn’t actually pollute Dillon or Dillon Valley’s drinking water, it does make it tougher to treat the water, Tiehen said.

CDOT will begin the first of three projects to rectify the situation later this summer:

Project 1: Collecting runoff

CDOT will spend $1 million from federal and highway funds to overhaul its storm water drainage system.

The new system will collect highway runoff that is currently flowing into the culvert that carries Straight Creek under the interstate.

When the project is done, highway runoff near the west portal of the tunnel will be diverted from Straight Creek into a nearby sediment basin.

Straight Creek currently flows through the same basin, but will be rerouted and placed back into its original channel in hopes of reducing the contaminants in the creek.

Two smaller projects (listed below) will also be constructed in conjunction with the larger undertaking, but will be paid for primarily with grant money from the Environmental Protection Agency (EPA), which is doled out by the state health department, Tiehen said.

The town of Dillon and the Dillon Valley District will also contribute $5,000 each toward the effort, while CDOT will provide $114,000.

Where is Straight Creek? Straight Creek begins near the Eisenhower Tunnel, and runs through a culvert underneath Interstate 70, then parallels the highway and eventually meets up with the Blue River in Silverthorne. The town of Dillon and Dillon Valley District have a diversion structure where Laskey Gulch flows into Straight Creek, just after milepost 208.

Project 2: Separating runoff flows

Another project will separate groundwater spring flows from highway runoff flows, which are currently mixed. CDOT will construct a drainage pipe in the gravel along westbound I-70 at approximately milepost 212 that will allow spring flows to be diverted to the nearest clean water tributary culvert.

Project 3: Keeping sediment out of snow piles

One more project will be a snow slide at the tunnel parking lot above Straight Creek. The idea is to keep sediment out of the snow piles in the lot which will reduce the amount of sand carried to the creek during snowmelt.

A concrete barrier will provide an opening above the snow slide so plow drivers can push snow down onto the slide. Below the slide, a concrete structure will be built to collect all the sediment.

Tiehen estimates 50-100 tons of sand will be captured each year by the new structure.

CDOT already picks up 25 percent of the sand it puts on the roads every year, she said.

Together, the two smaller projects will cost about $500,000.

The work is expected to be completed by the end of next summer.

Monitoring the results

When the work is done, extensive monitoring will be continued for many years, with several measuring sticks to determine how successful the projects have been.

For instance, the amount and size of sediment in the stream and its pools will be measured. Monitoring stations will be used to count the number of age classes of fish in the creek, with five being the goal.

Sediment problems in Straight Creek date back to the completion of Interstate 70 in the 1970s due to sanding from winter road maintenance and sediment loading from exposed cut and fill slopes along the highway.

In 1991, the Straight Creek Clean-up Committee was formed to come up with a program to monitor the water.

The committee is comprised of representatives from the town of Dillon, the county, Northwest Council of Governments, the Forest Service, the state health department, the EPA and some citizens.

In 1998, the water quality control commission put Straight Creek on the impaired list and in 2000, a total maximum daily load was completed, which is a plan identifying an approach to fix the stream so it meets water quality standards.

Nicole Formosa can be reached at (970) 668-3998, ext. 229, or at nformosa@summitdaily.com