Publication Date

1997

Document Type

Dissertation/Thesis

First Advisor

Booth, Colin J.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Geology

LCSH

Mine subsidences--Illinois; Longwall mining--Illinois; Water chemistry; Groundwater--Illinois

Abstract

The purpose of this study is to characterize and explain the changes that occur in groundwater chemistry over longwall mines. The sites chosen for study are both located in the southern Illinois coalfields. The emphasis at both sites is on the surficial drift and bedrock units over each longwall panel. This study uses data collected above two mines: one located in Jefferson County and the other in Saline County. Forty-nine wells were used to characterize the chemistry at these two sites. Previous studies made under the support of the Illinois Mine Subsidence Research Program and the Office of Surface Mining have concentrated on characterizing hydraulic parameters, piezometric changes, or small-scale chemical studies. Prior to this study, observations of water levels in mine-panel bedrock piezometers indicate an aquifer can be affected by subsidence. This study adds to earlier work and incorporates new data taken at both sites. The data was used to determine the overall geochemical effects of longwall mining on near surface aquifers. Samples were taken directly from a downhole pump and analyzed for major cations and anions. Chemical parameters including pH, Eh, dissolved oxygen, electrical conductivity, and temperature were recorded from field observations taken from a surface flow-through tube. The chemical results indicate that the drift units at both the Jefferson County and Saline County sites have not been affected by mining; the bedrock units can be affected by leakage from overlying units or by the changes in water residence time. The degree of chemical change is attributed to the geological and hydraulic parameters of the aquifer. It can be minimized by low aquifer hydraulic conductivity but some changes in composition and ionic concentrations still occur. Large changes in chemistry can occur through vertical leakage of high concentrations of ions or an influx of oxygenated water into the aquifer. Additionally, changes can occur as a result of the amount of time that chemical reactions have to proceed within the aquifer, which can be influenced by increases in hydraulic conductivity. Thus, this study has found that chemical changes can occur in subsided aquifers due to one of the following causes: changes in water residence time, an influx of oxygenated water, or an influx of more brackish water from an overlying aquifer.

Comments

Includes bibliographical references (pages [261]-267)

Extent

xiii, 287 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type

Text

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