Abstract: Hydrogeology and Structure of the Bluewater Springs Area South Central Montana

Curtis E. Padilla, Thomas J. Osborne

The Bluewater springs area in south central Montana was the site of oil and gas exploration in the first half of this century. Though no significant oil was found, artesian water wells produced over 3,000 gallons per minute. Artesian springs in the area produce tufa deposits over faulted, northwest dipping Mesozoic and upper Paleozoic sediments. Two new faults were mapped in the vicinity, one of these a high angle vertical fault dissects an anticline. The Tensleep and Madison aquifers (700-1,000 ft deep) leak water to the surface through faults and fractures, producing variable water quality depending on the minerals dissolved from overlying rock formations.

Evaluation of limited aquifer data reveals the following:

-- hydraulic conductivity of 40,000 to 300,000 gpd/ft

-- hydrostatic head greater than 400 feet above land surface.

-- total dissolved solids concentrations were 2,370 ppm in Big Bluewater Springs, but only 1,200 ppm in a Tensleep well in the vicinity.

Flowing wells 45 to 70 years old have failed leading to major yield reductions, and cessation of flow. Potentially corrosive groundwater coupled with excessive flow velocities and inadequate well construction has likely led to well failures. In response, major uncontrolled alterations of groundwater flow systems have occurred with outbreaks of new springs and sinkholes near failed wells. New wells must be carefully planned, constructed and tested to avoid excessive interference, depressurization and failure.

AAPG Search and Discovery Article #90952©1996 AAPG Rocky Mountain Section Meeting, Billings, Montana