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Prepared in cooperation with the U.S. Air Force Aeronautical Systems Center, Environmental Management Directorate

Hydrogeology at Air Force Plant 4 and Vicinity and Water Quality of the Paluxy Aquifer, Fort Worth, Texas

By E.L. Kuniansky, S.A. Jones, R.D. Brock, and M.D. Williams

U.S. Geological Survey
Water-Resources Investigations Report 96–4091


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CONTENTS

Abstract

Introduction

Purpose and Scope

Description of Study Area

Previous Investigations

Approach

Hydrogeology

Water Quality

Acknowledgments

Hydrogeology

Geology, Extent, and Water-Yielding Characteristics

Terrace Alluvial Aquifer

Goodland-Walnut Confining Unit

Paluxy Aquifer

Paluxy "Upper Sand" and Upper Zone of the Paluxy Aquifer

Middle and Lower Zones of the Paluxy Aquifer

Glen Rose Confining Unit

Twin Mountains Aquifer

Ground-Water Movement

Terrace Alluvial Aquifer

Goodland-Walnut Confining Unit

Paluxy Aquifer

Horizontal Movement

Vertical Movement

Hydraulic Connection With Lake Worth

Water Quality of the Paluxy Aquifer

Trichloroethylene and Other Volatile Organic Compounds

Chromium

Iron and Manganese

Other Trace Metals

Conclusions

Selected References

Glossary of Common Hydrogeologic and Chemical Terms

FIGURES

1-3.   Maps showing:
  1.   Location of study area
  2.   Location of selected wells at Air Force Plant 4 and vicinity, Fort Worth, Texas
  3.   Surface geology in western Tarrant County, Texas
4.   Generalized hydrogeologic section at Air Force Plant 4 and Naval Air Station, Fort Worth, Texas
5.   Generalized hydrogeologic diagram of the aquifer system underlying Air Force Plant 4, Fort Worth, Texas
6-10.   Maps showing:
  6.   Top of the Goodland-Walnut confining unit at Air Force Plant 4 and vicinity, Fort Worth, Texas
  7.   Water-level altitudes and flow direction in the terrace alluvial aquifer at Air Force Plant 4 and vicinity, Fort Worth, Texas, May 1993
  8.   Water-level altitudes in the Paluxy "upper sand" at Air Force Plant 4, Fort Worth, Texas, May 1993
  9.   Regional water-level altitudes and flow direction in the Paluxy aquifer at Air Force Plant 4 and vicinity, Fort Worth, Texas, May 1993
  10.   Trichloroethylene concentrations in the terrace alluvial aquifer at Air Force Plant 4 and vicinity, Fort Worth, Texas
11.   Graph showing concentrations of iron and manganese, and the corresponding secondary maximum contaminant level (SMCL), at domestic water-supply wells northwest of Air Force Plant 4, Fort Worth, Texas, April 1995

TABLES

1.   Well information for domestic water-supply wells sampled northwest of Air Force Plant 4, Fort Worth, Texas
2.   Analyses performed for water-quality surveys of domestic water-supply wells northwest of Air Force Plant 4, Fort Worth, Texas, April 1993 and April 1995
3.   Constituents analyzed for and laboratory reporting limits
4.   Stratigraphic units at Air Force Plant 4 and Naval Air Station, Fort Worth, Texas
5.   Water-level data for U.S. Geological Survey nested wells near Lake Worth, Fort Worth, Texas, February 1994
6.   Selected results of laboratory analyses for volatile organic compounds, total trace metals, and field-measured properties for domestic water-supply wells sampled northwest of Air Force Plant 4, Fort Worth, Texas, April 1993
7.   Selected results of laboratory analyses for volatile organic compounds, total trace metals, major anions, and field-measured properties for domestic water-supply wells sampled northwest of Air Force Plant 4, Fort Worth, Texas, April 1995

Abstract

Ground water in the surficial terrace alluvial aquifer is contaminated at Air Force Plant 4, Fort Worth, Texas, and at the adjacent Naval Air Station. Some of the contaminated water has leaked from the terrace alluvial aquifer to an uppermost interval of the Paluxy Formation (the Paluxy "upper sand") beneath the east parking lot, east of the assembly building, and to the upper and middle zones of the Paluxy aquifer near Bomber Road, west of the assembly building. Citizens are concerned that contaminants from the plant, principally trichloroethylene and chromium might enter nearby municipal and domestic wells that pump water from the middle and lower zones of the Paluxy aquifer.

Geologic formations that crop out in the study area, from oldest to youngest, are the Paluxy Formation (aquifer), Walnut Formation (confining unit), and Goodland Limestone (confining unit). Beneath the Paluxy Formation is the Glen Rose Formation (confining unit) and Twin Mountains Formation (aquifer). The terrace alluvial deposits overlie these Cretaceous rocks.

The terrace alluvial aquifer, which is not used for municipal water supply, is separated from the Paluxy aquifer by the Goodland-Walnut confining unit. The confining unit restricts the flow of ground water between these aquifers in most places; however, downward leakage to the Paluxy aquifer might occur through the "window," where the confining unit is thin or absent.

The Paluxy aquifer is divided into upper, middle, and lower zones. The Paluxy "upper sand" underlying the "window" is an apparently isolated, mostly unsaturated, sandy lens within the uppermost part of the upper zone. The Paluxy aquifer is recharged by leakage from Lake Worth and by precipitation on the outcrop area. Discharge from the aquifer primarily occurs as pumpage from municipal and domestic wells. The Paluxy aquifer is separated from the underlying Twin Mountains aquifer by the Glen Rose confining unit.

Water-level maps indicate that (1) ground water in the terrace alluvial aquifer appears to flow outward, away from Air Force Plant 4; (2) a ground-water mound, possibly caused by downward leakage from the terrace alluvial aquifer, is present in the Paluxy "upper sand" beneath the "window;" and (3) lateral ground-water flow in regionally extensive parts of the Paluxy aquifer is from west to east-southeast.

Trichloroethylene concentrations at Air Force Plant 4 have ranged from about 10,000 to about 100,000 micrograms per liter in the terrace alluvial aquifer, from 8,000 to 11,000 micrograms per liter in the Paluxy "upper sand," and from 2 to 50 micrograms per liter in the upper and middle zones of the Paluxy aquifer. Chromium concentrations at Air Force Plant 4 have ranged from 0 to 629 micrograms per liter in the terrace alluvial aquifer.

The seven municipal wells mostly west and south of Air Force Plant 4 are not along a flowpath for leakage of contaminants from the plant because ground-water flow in the Paluxy aquifer is toward the east-southeast. Furthermore, trichloroethylene was not detected in any of these wells in 1993 when all were sampled for water quality.

The results of water-quality sampling at 10 domestic wells northwest of the Air Force Plant 4 during April 1993 and April 1995 indicated that neither trichloroethylene nor chromium had migrated off-site to these wells.

 


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