Chapter 7.3, Page 2 of 4

Hydrogeologic Units

The principal bedrock aquifer in North Park is the Coalmont Formation that is as much as 6,500 feet thick. The Coalmont Formation is a basin-fill unit derived from the surrounding uplifted mountains, and consists of a complex, interfingering of coarse- and fine-grained sediments. The hydraulic characteristics and water quality of this aquifer are dependent upon the compositional variability of the Coalmont Formation within the basin. An estimated 39 million acre-feet of recoverable, good quality water are available for withdrawal. A hydro-stratigraphic table of the North Park basin is presented as Table 7.3-1.

Table 7.3-1 Hydrogeologic Units of North Park
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Ground water in Middle Park is highly influenced by the depositional complexity, thrust faulting, and variable thickness of the rock units.  The Troublesome Formation (lake bed deposits) represents the most important bedrock aquifer for many parts of the Middle Park Basin.  The Troublesome attains a thickness of at least 800 feet in the Fraser subbasin and possibly 1,000 feet in the Granby area.  This aquifer contains an estimated two million acre-feet of ground water in storage.  The underlying Middle Park Formation can be from 2,500 to 5,000 feet thick (Voegeli, 1965) and is an aquifer in the upper part where it consists of conglomerate and sandstone (Table 7.3-2).

Table 7.3-2 Hydrogeologic Units of Middle Park
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Chapter 7.3, Page 2 of 4