OF-13-08 Gilcrest/LaSalle Pilot Project Hydrogeologic Characterization Report


The Gilcrest/LaSalle Hydrogeologic Characterization Report is a component of the Gilcrest/LaSalle Pilot Project conducted by the Colorado Division of Water Resources (DWR) and funded by the Colorado Water Conservation Board (CWCB). The Gilcrest/LaSalle Pilot Project goal is to evaluate high groundwater conditions in the South Platte alluvial aquifer near Gilcrest and LaSalle, Colorado. For this study the CGS compiled, analyzed, and reinterpreted existing hydrogeologic data from previously published regional studies. Digital PDF download. OF-13-08D

NOTE: Subsequent to the original Gilcrest/LaSalle Pilot Project Hydrogeologic Characterization Report, the CGS has prepared two addenda. In 2015, a technical memorandum (2015 Addendum) was prepared using 2013-2014 water level data. A second technical memorandum (2017 Addendum) was prepared in October 2017 to present additional groundwater maps from 2015-2017 water level data. Included are brief descriptions of activities undertaken to generate additional spring and fall groundwater maps, water level data, and the findings. Both these addenda are included at the end of the main report, following the appendices.

The integration of previous investigations along with new analysis added significantly to the Study Area hydrogeologic characterization, and provided insight into the South Platte alluvial aquifer depositional model, particularly with respect to discontinuous low permeability beds within the central portion of the alluvial aquifer, and lower permeability beds on the aquifer flanks.

Specifically, the CGS hydrogeologic characterization has:

  1. Developed a hydrograph template to facilitate HydroBase data analysis;
  2. Refined alluvial aquifer extent mapping;
  3. Combined surficial geology from different sources to revise surficial mapping;
  4. Refined the bedrock and alluvial surface geologic mapping;
  5. Refined the alluvial aquifer lithologic and depositional conceptual models;
  6. Compiled driller’s logs from 448 boreholes into a digital lithologic dataset;
  7. Developed updated localized time-series water table contour and depth-to-groundwater maps;
  8. Evaluated groundwater flow in detail;
  9. Identified local-scale water level data gaps;
  10. Identified existing candidate wells for additional water level monitoring and aquifer testing.

Additionally, the study determined that, despite a large number and distribution of wells monitored, the overall data set contains significant areal gaps. These gaps limit the ability to analyze detailed long-term groundwater level trends and to map detailed water table surfaces across portions of the Study Area over long periods.