A Preliminary Study of the Hydrogeology of the Dakota Formation in Douglas, Sarpy and Washington Counties, Eastern Nebraska

Authors

Thomas Mark O'Connor, University of Nebraska-Lincoln

First Advisor

Jerry F. Ayers

Date of this Version

8-1987

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College of the University of Nebraska in partial fulfillment of requirement for the degree of Master of Science

Department of Geology

Under the supervision of Jerry F. Ayers

Lincoln, Nebraska, August 1987

Page i is missing containing the first part of the abstract

Comments

Copyright 1987, Thomas Mark O'Connor. Used by permission

Abstract

This study provides preliminary information on the hydrogeology of the Dakota Formation within a 1,000 square-mile area in eastern Nebraska. Isopach maps of the Dakota Formation and individual sand and gravel beds were constructed using a computer contouring program. Hydraulic conductivity values for water-bearing sand beds in the Dakota were estimated using the equation for calculating the specific capacity of wells and results from a grain-size analysis. Concentrations of major dissolved species were determined for samples collected from twenty five wells. The Dakota Formation is characterized by an increase in thickkness and an increase in percentage of clay versus sand beds toward the north and west. Relatively thick sand deposits are located along the eastern and southern margins of the subcrop area. These deposits form the major aquifer system within the Dakota Formation. Use of the specific capacity equation and grain-size data yielded reasonable esimates for hydraulic conductivity in this area. Estimates of hydraulic conductivity ranged from 14 feet per day to 300 feet per day and averaged 55 feet per day. Groundwater from the Dakota Formation is predominantly a calcium-bicarbonate type, although calcium-sulfate type water was found in deeper wells located in the northern part of the study area. Groundwater was found to be saturated with respect to calcite in all but three samples. Recharge is predominantly from percolation of meteoric water, however recharge from underlying Paleozoic limestones is possible.

Statement of purpose

The purpose of this study is to provide information on the hydrogeology of the Dakota Formation within the Papio Natural Resources District (NRD). Information on the geology of the Dakota Formation and the quantity and quality of water available from the Dakota aquifer is needed by the Papio NRD for present and future groundwater management decisions and as a data base for evaluating long-term trends in groundwater quality and supply.

Advisor: Jerry F. Ayers