Aspen School District digs deep for clean geothermal energy

Thanks to a relatively easy and extremely rare drill test down to 1,000 feet under the high school football field, Aspen School District will be a key proof-of-concept project for a state-backed push into Colorado’s rich geothermal energy sources. 

Ground-source geothermal heat pumps circulate water deep underground to gain energy from stable temperatures. In zero-degree surface temperatures in winter, the circulating lines bring up 55-degree water as the starting point for heating. In summer, that 55 degrees is the base for cooling. Aspen plans to use the new system to bring clean, low-carbon energy to school and administration buildings across its campus. 

But first, construction consultants McKinstry and drillers PanTerra Energy had to prove it could be done. Most commercial-scale geothermal projects in Colorado stop at about 500 feet underground. The first few hundred feet in Aspen is actually the hardest, with drillers having to cope with varied conditions of “cobble” near the surface. 

Drilling sped up the deeper it went into Aspen’s bedrock, and PanTerra reached the 1,000-foot mark that only a Hayden-area project has targeted for geothermal energy, project officials said in an interview. The base temperature at 1,000 feet is a few degrees higher, and more stable, than shallower bore holes. 

The Aspen success bodes well for geothermal energy in Colorado, a research and development focus of Gov. Jared Polis and the Colorado Energy Office. Overhauling Aspen School District’s energy sources has been made possible by a combination of federal and state grants and tax credits, and a local bond issue. 

“We’ve really seen an uptick in these projects, and I think we’re finally able to help drive some of these studies and look at constructability and how can we make them more financially viable, get contractors and drillers more familiar with the technology and being able to move these from study through implementation,” said Ashley Brasovan, a senior account executive with consultant McKinstry. 

“Building a strong project pipeline is one of the best ways to grow Colorado’s geothermal market,” said Lauren Suhrbier of the Western Slope nonprofit consultant Clean Energy Economy for the Region. The successful depth of Aspen’s main bore could cut the number of required bore holes to 150 from 300 for the project, but that 150 would still represent a big share of Colorado’s planned geothermal activity in the next two years, Suhrbier said. 

“Projects at this scale help contractors build experience, train crews, expand fleets and create opportunities for new firms to enter the market,” Suhrbier said. 

With a starting temperature of 50 to 55 degrees, geothermal heat pumps can cut the fossil fuel energy needed to reach comfortable indoor temperatures by up to 70%. 

A successful deep bore offers multiple lessons from mountainous areas like Aspen lacking flat open spaces. Taking one hole deeper saves time from getting the same total depth out of more than one hole, project engineer Stephan Rank said. While it took about four days of drilling to get through the first few hundred feet of mixed “cobble,” he said, the next 750 feet of bedrock only took a day and a half. 

Cutting the number of bores in half through deeper drills means Aspen may only have to use half the field space of other geothermal projects, a McKinstry spokesperson said. 

Each major drill is a learning experience, Rank said. 

“We contracted for 1,000 feet,” he said. “but you don’t really know until you do it.”