Date of Graduation

8-2012

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Ralph K. Davis

Committee Member

Phillip D. Hays

Second Committee Member

Douglas C. Melton, Jr

Keywords

Earth sciences, Arkansas, Fayetteville Shale, Groundwater evolution, Groundwater quality, Redox

Abstract

This study establishes a spatially distributed domestic water well groundwater quality data set, throughout the Fayetteville Shale Gas Play (FSGP) in central Arkansas. The data set facilitates characterization of the geology and groundwater quality across the study area, benefits residents who may have concerns about the potential impacts on their well water quality, and provides a groundwater quality basis to which complaints can be compared and resolved. The assessment included: research of the study area, site reconnaissance, water sampling and collection, interviews with owners of the property, analytical analysis, Quality Assurance and Quality Control, and groundwater data interpretation.

The study area is a mixture of: agriculture, national forestry, wetlands, pasture/rangeland, residential development, industrial, and natural gas exploration and extraction. Out of 105 samples analyzed, 104 met the EPA's Safe Drinking Water (SDW) Maximum Contaminant Levels with one exceeding the SDW standards for nitrate as nitrogen. Two constituents (iron and manganese) exceeded the EPA's SDW SMCLs in several of the groundwater samples, but pose no health risks to humans. Based on the data of 105 groundwater samples, all wells were within the pre-existing groundwater quality parameters for central Arkansas as compared to historical data from the U.S. Geological Survey, and others. A few groundwater samples showed outliers, possibly due to: anthropogenic conditions, laboratory errors or field collection issues.

The direct rock/water interaction and redox processes that contribute to the groundwater quality in the study area are controlled by three factors 1) recharge percolating through thin organic rich soils 2) domestic water wells withdrawing from vertical fractures that interact with multiple lithologies dominated by sandstones and shales, and 3) normal south-trending faults and very low permeability in the Western Interior Plains Confining system that results in small isolated basins that are dominated by short lateral flow to seeps and springs.

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