Physical and Chemical Characteristics of Tertiary and Upper Cretaceous Units in Laramie County, Southeastern Wyoming

Most of Laramie County, located in southeastern Wyoming, is underlain by Tertiary and Upper Cretaceous lithostratigraphic units. Aquifers in the Tertiary lithostratigraphic units (Tertiary aquifers) compose the locally and regionally important High Plains aquifer system. These aquifers have been the primary source of groundwater for domestic, public supply, industrial, and irrigation use in the county, as well as for much of the High Plains area in southeastern Wyoming. Heavily utilization has caused local groundwater levels to decline. Concern about the groundwater-level declines has resulted in special regulation of new groundwater diversions from the aquifer system in these areas, as well as created substantial ongoing debate as to how to arrest the declines and where to obtain additional groundwater supplies within the county.

Consequently, the U.S. Geological Survey, in cooperation with the Wyoming State Engineer’s Office, is conducting studies to improve understanding of the geologic and hydrogeologic characteristics of Tertiary lithostratigraphic units composing the High Plains aquifer system. Additionally, stratigraphically lower and deeper Tertiary and Upper Cretaceous lithostratigraphic units underlying the High Plains aquifer system also are being studied to evaluate potential use as alternative sources of groundwater supply within the county.

The studies include detailed geologic and hydrogeologic characterization of the Tertiary and Upper Cretaceous lithostratigraphic units including lithologic description, lithostratigraphy, groundwater quality, hydraulic properties, groundwater age and recharge, hydraulic head/groundwater flow, and hydrostratigraphy. The detailed hydrogeologic characterization will provide water resources managers of the High Plains aquifer system with greater insight into the possibility of identifying and developing deeper and stratigraphically lower aquifers in Tertiary and Upper Cretaceous lithostratigraphic units.