Department
of Earth Science |
Northeastern
Illinois University
Aqueous Geochemistry
Earth Science 406
Fall 2002
Department
of Earth Science |Northeastern
Illinois University
Conference Presentation Abstract
Journal Article: Geochemical evolution of Ground Water in the Great Plains (Dakota) Aquifer of Nebraska: Implications for the Management of a Regional Aquifer system by David C. Gosselin, F. Edwin Harvey, and Carol D. Frost. Published in “ Ground Water” journal, vol. 39, N.1, January-February 2001. Pg.98-101.
Abstract written by Lefter Jani
The Great Plains (Dakota) aquifer is one of the most extensive aquifer system in North America and underlines approximately 94% of Nebraska. Urban expansion and development of Nebraska’s metropolitan areas placed increased demands for water from Dakotas Aquifer system. The solution for this problem was strongly related with two major hypothesis: 1) The quality of water, which was one of the primary constrains in use of Dakota Aquifer as a primary source. 2) The determination of a first hand management strategy that did not exist. The solution of this problem was the object and the scope of this study.
The use of water chemistry data for major ions, from 203 wells in 19
counties in Eastern Nebraska, with sufficient information about dO18, dD
and dSr87 and two geochemical models PHREEQC and SNORM made possible the
determination of three primary sources of water from Dakota formation:
1. Meteoric water
2. NaCl brines from underlying formations
3. Cold glacial melt water
In accordance with this type of water sources and geochemical evolution
of various type of waters the corresponding first order management strategies
were suggested: Pleistocene – age glacial melt water is the source in those
areas where CaSO 4 and Ca-NaSO 4 type waters occurs. This type of water
is not easily renewed. Before an extensive development occurs, a detailed
evaluation was recommended to be done. The Ca (+/-Mg)HCO3 type waters is
from recharge by local precipitation and should be managed to maintain
them as a renewable source. In mixed ground water type areas the water
chemistry indicates an interaction of two distinct types – Meteoric water
and either CaSO4, Ca-NaSO4 or NaCl type water. If relatively fresh
ground water is extracted at a rate that changes the location of interference
between the end members, than monitoring the changes of water chemistry
in a well over the time, can be used as an early indicator or warning system
for onset of potential problems related to overpumping.
This objective was achieved using the major – ion water chemistry data from 203 wells in 19 counties in Eastern Nebraska, reconnaissance of dO18 and dD and geochemical model PHREEQCI.
Modern meteoric water, NaCl brines from underlying formations and glacial melt water was determined that are the primary sources for water in the Dakota aquifer. The recommendations and the suggested strategies were given based on these three water types and the geochemical evaluation of other water resources as below:
The areas where CaSO4 and Ca – NaSO4 type occurs, Pleistocene age glacial melt water is the source. The fact that this type of water is a not easily renewable brings in attention that detailed water resource evaluation should be conducted before extensive development occurs. The source of Ca( +/- Mg) HCO3 type of water is from recharge by local precipitation and should be managed to maintain them as renewable resource. The mixed ground water type areas, which water chemistry reflects a composition of two distinct type of waters: meteoric and the other is (CaSO4 and Ca – NaSO4 ) or NaCl type water. The rate at which the fresh ground water is extracted influences the location of the interference between end members, and by monitoring the changes in water chemistry, this (interference) can be used as an early indicator system for the onset of potential problems related to over pumping.
Last updated December 2, 2002