Summit County renovates, renews Old Dillon Reservoir

Elise Reuter
Representatives from Summit County, Dillon and Silverthorne came together to cut the ribbon for the "new" Old Dillon Reservoir, which was rebuilt and expanded from a capacity of less than 50 acre feet to more than 300 acre feet. Pictured left to right are County Commisioners Thomas Davidson, Karn Stiegelmeier and Dan Gibbs, Silverthorne Utility Manager Zach Margolis, County Manager Gary Martinez, and Dillon Town Engineer Dan Burroughs.
Courtesy of Bill Linfield |

Thursday marked the culmination of five years of work, as Summit County Commissioners, and Dillon and Silverthorne leaders cut the ribbon in front of the expanded and renovated Old Dillon Reservoir.

Located between Interstate 70 and Dillon Dam Road, the “new” Old Dillon Reservoir’s capacity was multiplied from 46 acre-feet to 303 acre-feet of water. A new recreation trail was also constructed around the reservoir, highlighting the surrounding acres of wetlands that were recently replanted.

“The newly expanded Old Dillon Reservoir gives Summit County, Dillon and Silverthorne new flexibility and certainty in managing our water rights and our municipal water supplies,” Summit County manager Gary Martinez said in a statement. “We’ll be able to put this water to great use in a variety of ways throughout the county, including river restorations, workforce housing projects and emergency preparedness.”

The three entities pulled together in 2010, forming the Old Dillon Reservoir Water Authority. The $5.7 million project broke ground in 2011, and was completed by 2014. Annual operating costs of $50,000 will be divided between the county, Dillon and Silverthorne. Some years, the water authority will have access to more than 303-acre feet of water with approved refill rights.

Once construction was completed, the reservoir was refilled this year, and stocked with golden trout by Colorado Park and Wildlife. Once the fish population has matured, it will be open to catch-and-release fishing. More than 2 acres of wetlands were planted in 2013 and 2014 that will be maintained using water redirected from Salt Lake Gulch.

“The wetlands have a continuous water source so they should thrive,” Martinez said. “The wetlands that were there before were starting to go away quickly … A year or two before we even started expansion, there was an order from the state to drain the reservoir. They had concerns about the existing dams and so on.”

Martinez added that the authority hopes to improve the trail and parking area in the future.

A call for change

Originally constructed in the 1930s as a water supply source for Dillon, the state called for the dam to be rebuilt as it had become unusable in recent years. The reservoir required major upgrades to meet current safety standards, which involved draining the reservoir, removing the old dams, and constructing newer, safer dams using onsite materials.

“The reservoir that was there was inadequate,” Martinez said. “It was never going to be an adequately sized reservoir, and it was not built for modern standards.”

The crews also relocated the Salt Lick Gulch headgate upstream from its original location, constructing a new spillway and outlet to Salt Lick Gulch and a new outlet to the Dillon Reservoir.

In the future, Dillon and Silverthorne hope to be able to use the Old Dillon Reservoir to augment their water supplies. The idea is that the reservoir would add to water from Silverthorne’s well gallery. In the event of a spill into Straight Creek, Dillon’s primary water source, the reservoir could serve as a backup source if more improvements are made.

Dillon will study this possibility within the next decade, to see if water could be released from the Old Dillon Reservoir into the Lake Dillon Reservoir, and then brought up to Dillon’s water treatment plant, or if a direct pipeline could be established. A third option would be to create a small pump space and treatment process near the base of the town.

“There is always a potential right now that we would have a hazardous spill on I-70 and not get water from Straight Creek,” said Robert Buras, chief plant operator with Dillon’s Water Department. “The whole reason for the Old Dillon Reservoir is to give us an alternative source away from Straight Creek not affected by this. It’s planning things out and executing them over a period of time.”

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