ASPEN – Aspen City Council agreed Monday to drill five or six test borings under the city’s golf course and to dig as many as eight test pits on the course as part of a feasibility study of an underground reservoir.
The City Council will add $116,000 to an existing $53,000 contract with Deere and Ault Inc., an engineering firm from Longmont, to study water storage options under and on the 148-acre golf course.
The amended contract added “open water storage,” or surface reservoirs, as a potential option in the next phase of the Deere and Ault study.
“I think we’re on the right track to say, ‘Hey, listen, how much water do we really need and where do we want to store it?'” Councilman Adam Frisch said of the city’s ongoing look into water needs.
On Tuesday, the City Council has a work session to look at Aspen’s water supply and demands for the future.
Of the $116,000 approved Monday, $18,000 is for drilling the borings and $4,400 is for digging the test pits, which are meant to help determine the quality of the gravel under the golf course, according to information provided by Deere and Ault. Other major costs include $48,000 for geotechnical investigation, $16,800 for project management and $12,600 for conceptual layout of a reservoir.
Don Deere, a principal at Deere and Ault, told the council in May after an initial conceptual screening that an underground, or in-situ, reservoir beneath the Aspen Golf Club, as the city’s golf course is called, could hold 1,200 acre-feet of water.
To better estimate storage capacity and cost, Deere said test bores would confirm his early analysis that the area sits on about 75 feet of gravel deposited over bedrock.
“The borings will provide information on depth to bedrock, the approximate location of any boulder layers and permeability data for the bedrock,” according to information from Deere and Ault as part of the contract amendment. “The test pit excavations will … look for fine-grained soils that could be used for embankment or slope liner construction as well as the potential for supplemental fines for slurry wall construction.”
Deere said in a recent interview that underground boulders can significantly increase the cost of construction of an in-situ reservoir.
“We understand some gravel deposits in the area may contain boulders, so if adequate exposures are found, we will conduct a boulder count to estimate the locations and maximum size of boulders in the deposit,” Deere told the city.
According to Deere’s conceptual analysis, building an in-situ reservoir under the golf course would cost between $12 million and $72 million, depending on soil conditions.
Dave Hornbacher, the city’s utilities director, said at Monday’s meeting he wasn’t sure where the holes would be drilled, but “they should not be near somebody’s home.”
A June 30 memo from Margaret Medellin, the city’s utilities portfolio manager, said an in-situ reservoir would “create sub-surface water storage through the installation of slurry walls extending from the surface to bedrock.
“With suitable geology, these slurry walls can create an in-place, subsurface storage vessel,” she wrote. “As needed, water would be withdrawn form the in-situ reservoir via wells and pumped to a treatment facility.”
The city is studying water storage options because it is looking for alternatives to building two dams on upper Maroon and Castle creeks.
The proposed Castle Creek project would hold 9,062 acre-feet of water behind a 170-foot-tall dam and the proposed Maroon Creek project would hold 4,567 acre-feet behind a 155-foot-tall dam at the confluence of East and West Maroon creeks.
The city filed two due diligence applications in October in Division 5 water court seeking to maintain its conditional storage rights for another six years, and told the state, as it has since 1965, that it intends to build both dams if necessary to meet future water demands.
Ten parties, including the U.S. Forest Service, Pitkin County, four wealthy landowners, and four environmental groups, are opposing the city’s most recent diligence claims in water court. The next settlement conference in the two cases is set for Aug. 2.
When the City Council voted to submit its latest diligence application, it also directed staff to study alternatives to the two dams.
As part of that effort, the city also has contracted with Headwaters Corp., “a natural resources management consulting firm” with offices in Lakewood and Nebraska, to study water supply and demand, especially in the face of a hotter climate.
Preliminary results of that effort are to be presented at today’s work session at 4 p.m.
George Oamek, an agricultural economist at Headwaters, prepared a report on July 3 for the council on his ongoing “risk analysis” of Aspen’s water needs. And he said more information is needed before he can come up with a specific recommendation regarding storage.
He found that the existing data about historic flows in Maroon and Castle creeks may not be adequate for his purposes, especially as there are not water gauges on either creek.
Oamek also found that recent climate data is not specific enough to show potential impacts to Castle and Maroon creeks, and that the city will need to fine-tune its demand projections by analyzing land-use plans in both the city and the county.
Editor’s note: Aspen Journalism, an independent nonprofit news organization, is collaborating with The Aspen Times on water coverage. The Times published this story on Tuesday, July 11, 2017.