Connate Groundwater from the Precambrian, South Park, Colorado

Groundwater supply investigations in fractured Precambrian metamorphic rocks for a cattle ranch near South Park, Colorado have revealed two separate aquifers: an upper, low-TDS aquifer fed by meteoric recharge, and an anomalous deeper aquifer of trapped, highly saline, CO₂-saturated water. The ranch is located near the western margin of the Elkhorn Thrust, where during the Laramide Orogeny, Precambrian igneous and metamorphic rocks were thrust over existing sedimentary rocks, such as the Cretaceous Pierre Shale. Geochemical and stable isotopic analyses of the water reveal the water is near-connate. It is postulated that the underlying sedimentary rocks are the source of this carbonated connate water.

After grouting the lower portion of the well to minimize the boundary effects of the lower aquifer, a method for tapping the upper, high-quality groundwater was developed and implemented. The method includes an in-hole transducer that measures and records electroconductivity, turning the well on and off using set upper and lower thresholds found to be acceptable to the cattle operation.