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Water-Resources Investigations Report 00–4241

Contribution from the National Water Quality Assessment Program

Relation of shallow water quality in the Central Oklahoma aquifer to geology, soils, and land use

By Alan H. Rea, Scott C. Christenson, and William J. Andrews

Abstract

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The purpose of this report is to identify, describe, and explain relations between natural and land-use factors and ground-water quality in the Central Oklahoma aquifer NAWQA study unit. Natural factors compared to water quality included the geologic unit in which the sampled wells were completed and the properties of soils in the areas surrounding the wells. Land-use factors included types of land use and population densities surrounding sampled wells. Ground-water quality was characterized by concentrations of inorganic constituents, and by frequencies of detection of volatile organic compounds and pesticides. Water-quality data were from samples collected from wells 91 meters (300 feet) or less in depth as part of Permian and Quaternary geologic unit survey networks and from an urban survey network.

Concentrations of many inorganic constituents were significantly related to geology. In addition, concentrations of many inorganic constituents were greater in water from wells from the Oklahoma City urban sampling network than in water from wells from low-density survey networks designed to evaluate ambient water quality in the Central Oklahoma aquifer study unit. However, sampling bias may have been induced by differences in hydrogeologic factors between sampling networks, limiting the ability to determine land-use effects on concentrations of inorganic constituents.

Frequencies of detection of pesticide and volatile organic compounds (VOC's) in ground-water samples were related to land use and popuĀ­lation density, with these compounds being more frequently detected in densely-populated areas. Geology and soil properties were not significantly correlated to pesticide or VOC occurrence in ground water. Lesser frequencies of detection of pesticides in water from wells in rural areas may be due to low to moderate use of those compounds on agricultural lands in the study unit, with livestock production being the primary agriĀ­cultural activity. There are many possible sources of pesticides and VOC's in the urban areas of Central Oklahoma. Because only existing water-supply wells were sampled, it is not clear from the data collected whether pesticides and VOC's: (1) occur in low concentrations throughout upper portions of the aquifer in urban areas, or (2) are present in ground water only in the immediate vicinity of the wells due to back-flow of those chemicals into the wells or to inflow around cement seals and through gravel packs surrounding well casings of surface runoff containing those compounds.

 

Version 1.0

Posted August 2008


Suggested citation:

Rea, A.H., Christenson, S.C., and Andrews, W.J.., 2001, Relation of shallow water quality in the Central Oklahoma aquifer to geology, soils, and land use: U.S. Geological Survey Water-Resources Investigations Report 00-4241, 31 p.


Contents

Abstract

Introduction

Methods of Data Compilation, Association, and Analysis

Compilation of areally-distributed attributes

Geologic setting

Soil properties

Land use

Associating point data with areally-distributed attributes

Stratification based on geology and land use

Buffer-overlay analysis

Particle-tracking analysis

Statistical analysis

Hypothesis testing

Sampling biases

Relation of Geologic Setting to Ground-Water Quality

Inorganic constituents

Organic compounds

Relation of Soil Properties to Ground-Water Quality

Inorganic constituents

Organic compounds

Relation of Land Use to Ground-Water Quality

Inorganic constituents

Organic compounds

Relation of Population Density to Ground-Water Quality

Inorganic constituents

Organic compounds

Relation of Multiple Factors to Detection of Organic Compounds

Possible Sources of Contaminants

Inorganic constituents

Organic compounds

Conclusions

References



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