Fred Henderson of Hendco Services and Paul Morgan of Colorado Geological Survey recently completed a study and issued a report providing new data about the Poncha Hot Springs geothermal resource.

The report lists several conclusions based upon information compiled during the study:

  • The study area contains the highest "thermal gradient anomaly" measured to date in Colorado.
  • Geological fault structures, including the main east-west Poncha Hot Springs fault and subsidiary faults to the north, appear to control the upwelling and flow of geothermal water from a deep geothermal source.
  • Previous geothermometry studies indicate the possible presence of a deep, high-temperature reservoir.
  • Scientific observations suggest existence of a deep, high-temperature reservoir capable of producing electricity in significant amounts.
  • Findings support conducting a magnetotelluric survey followed by one or two 1,000-1,500-foot-deep thermal gradient holes to further validate and locate a potential deep geothermal reservoir.

Henderson and Morgan performed detailed surface fault mapping and compiled that information and data from previous studies into a geographic information system database.

The scientists used the database to determine the best locations for drilling holes in which to measure temperatures and determine the thermal gradient - the rate at which temperature increases with depth.

Four thermal gradient holes were drilled about 260 feet deep, and an existing hole was reopened to a depth of 280 feet.

Data from the five holes was combined with data collected during 2010 from a 650-foot well east of the hot springs and four shallow wells drilled in the late 1970s and early '80s north of the area.

Analysis of all available data revealed hot water rising from the north-northeast along a fault that reaches the surface at the hot springs east of the former Boy Scout camp.

In addition, the study identified a large underground volume of hot water that bypasses the Salida collection system and flows west toward U.S. 285.

Based upon results of thermal gradient drilling and data compiled from available sources, the report indicates a potential deep, hot reservoir probably lies north-northeast of the hot springs.

To help define the geothermal resource and identify the best location for drilling a deeper thermal gradient hole, the report recommends conducting a magnetotelluric survey in the area.

During the Dec. 6 Salida City Council meeting, council members voted to enter an agreement with Mt. Princeton Geothermal, LLC, for a magnetotelluric survey.

The survey will be conducted by Dewhurst Group, LLC, and is expected to be done in January. Dewhurst specializes in geothermal exploration and is conducting a magnetotelluric survey of geothermal resources near Mount Princeton.

Magnetotelluric testing will use specialized subsurface imaging in conjunction with temperature data to identify areas appearing suitable for commercial geothermal electricity generation.

Magnetotelluric testing will help identify the source of thermal water associated with hydrological features that need to be preserved, including Poncha Hot Springs which supply water for Salida Hot Springs Aquatic Center.

The thermal gradient study was financed by a $50,000 grant from the Governor's Energy Office.

A complete copy of the report is at http://cityofsalida.com/projects/hot-springs-source.

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