USGS

 

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 02-4121


Distribution and Mass Loss of Volatile Organic Compounds in the Surficial Aquifer at Sites FT03, LF13, and WP14/ LF15, Dover Air Force Base, Delaware, November 2001–February 2002

By Jeffrey R. Barbaro and Pradumna P. Neupane

 

This report is available as a pdf.

 

ABSTRACT

Ground-water and surface-water sampling was conducted in the natural attenuation study area in the East Management Unit of Dover Air Force Base, Delaware to determine the distributions of volatile organic compounds in the vicinity of four sites—Fire Training Area Three, the Rubble Area Landfill, the Receiver Station Landfill, and the Liquid Waste Disposal Landfill. This work was done by the U.S. Geological Survey, in cooperation with the U.S. Air Force, as part of an ongoing assessment of the effectiveness of natural attenuation at these sites. The specific objectives of the study were to (1) determine the areal and vertical extent of the contaminant plumes and source areas, (2) measure volatile organic compound concentrations in ground-water discharge areas and in surface water under base-flow conditions, (3) evaluate the potential for off-site migration of the mapped plumes, and (4) estimate the amount of mass loss downgradient of the Liquid Waste Disposal and Receiver Station Landfills. A direct-push drill rig and previously installed multilevel piezometers were used to determine the three-dimensional distributions of volatile organic compounds in the 30–60-foot-thick surficial aquifer underlying the natural attenuation study area. A hand-driven mini-piezometer was used to collect ground-water samples in ground-water discharge areas. A total of 319 ground-water and 4 surface-water samples were collected from November 2000 to February 2001 and analyzed for chlorinated solvents and fuel hydrocarbons.

The contaminant plumes migrating from Fire Training Area Three and the Rubble Area Landfill are approximately 500 feet and 800 feet, respectively, in length. These plumes consist predominantly of cis-1,2-dichloroethene, a daughter product, indicating that extensive dechlorination of tetrachloroethene and trichloroethene has occurred at these sites. With an approximate length of 2,200 feet, the plume migrating from the Receiver Station and Liquid Waste Disposal Landfills is the largest of the three plumes in the East Management Unit. In this plume, the parent compounds, tetrachloroethene and trichloroethene, as well as cis-1,2-dichloroethene, are present downgradient of the source. Vinyl chloride was not detected in the natural attenuation study area. Vertical waterquality profiles indicate that volatile organic compounds are present mainly in the upper part of the surficial aquifer. Plumes of fuel hydrocarbon constituents were not detected in the natural attenuation study area.

Volatile organic compounds were present at concentrations above detection limits in 6 of 14 samples collected from the aquifer underlying the bed of Pipe Elm Branch and the drainage ditch adjacent to Fire Training Area Three, indicating that the plumes migrating from Fire Training Area Three and the Receiver Station and Liquid Waste Disposal Landfills are reaching these groundwater discharge areas. In contrast, sampling results indicated that the plume from the Rubble Area Landfill does not reach these ground-water discharge areas. Trichloroethene was present above detection limits in one of four surface-water samples collected from Pipe Elm Branch and the drainage ditch adjacent to Fire Training Area Three. The trichloroethene concentration is below applicable Delaware Department of Natural Resources and Environmental Control surfacewater- quality standards for human health.

An assessment of chlorinated-solvent mass loss in the plume migrating from the Receiver Station and Liquid Waste Disposal Landfills indicates that tetrachloroethene and trichloroethene mass loss downgradient of the source is negligible. Cis-1,2- dichloroethene, however, appears to biodegrade by an unidentified reaction in the plume. Plan-view maps of the plume migrating from the Receiver Station and Liquid Waste Disposal Landfills indicate that tetrachloroethene, trichloroethene, and cis-1,2-dichloroethene may migrate off Dover Air Force Base property approximately 1,500 feet downgradient of the source areas. In this downgradient area, the direction of plume migration is roughly parallel to the Dover Air Force Base boundary, which probably restricts the extent of off-site migration. Sampling results indicate that off-site migration of the other two plumes in the East Management Unit is unlikely. The groundand surface-water samples collected in this study led to an improved understanding of the areal and vertical extent of the volatile organic compound plumes, the occurrence and fate of volatile organic compounds in the ground-water discharge areas, and the amount of intrinsic biodegradation downgradient of the Receiver Station and Liquid Waste Disposal Landfills.

 

TABLE OF CONTENTS

Abstract

Introduction

Purpose and scope

Description of study area

Intended use for data

Acknowledgments

Methods of investigation

Ground-water sample collection

Direct-push drill rig

Mini-piezometer

Multilevel piezometers

Surface-water sample collection

Quality-control sample collection

Analytical methods

Distribution of volatile organic compounds

Ground water

FT03

LF13

WP14/LF15

Ground-water discharge areas

Surface water

Quality-control samples

Assessment of volatile organic compound mass loss at WP14/LF15

Mass flux

Concentration ratios

Mole fractions

Summary and conclusions

References cited

Appendixes


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For more information about USGS activities in Maryland, Delaware and the District of Columbia contact:

 

Director
U.S. Geological Survey
Maryland, Delaware, D.C. Water Science Center
8987 Yellow Brick Road
Baltimore, MD 21237
Telephone: (410) 238-4200
Fax: (410) 238-4210

 

or access the USGS Water Resources of Maryland, Delaware, and District of Columbia home page at:  http://md.water.usgs.gov/.




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