WRIR 03-4089


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Davis, J. Hal, 2003, Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, U.S. Naval Air Station, Jacksonville, Florida: U.S. Geological Survey Water Resources Investigations Report 03-4089, 61 p.

ABSTRACT:

The Jacksonville Naval Air Station occupies 3,800 acres adjacent to the St. Johns River in Jacksonville, Florida. Two underground storage tanks at Hangar 1000 contained solvents from the late 1960s until they were removed in 1994. Ground-water samples at one of the tank sites had levels of trichloroethene (TCE) and total dichloroethene (DCE) of 8,710 micrograms per liter (mg/L) and 4,280 mg/L, respectively. Vinyl chloride (VC) at the site is the result of the biodegradation of DCE. Ground water beneath Hangar 1000 flows toward a storm sewer. TCE and DCE plumes travel with the ground water and presumably have reached the storm sewer, which discharges to the St. Johns River. Simulation of solute transport indicates that the traveltime from the storage tank site to the storm sewer is 16, 14, and 12 years for TCE, DCE, and VC respectively. TCE has the longest traveltime because it has the highest retardation factor at 2.5, DCE takes less time with a retardation factor of 2.0, and VC has the quickest traveltime because it has the lowest retardation factor of 1.7. Based on modeling results, the release of contaminants in the aquifer occurred more than 16 years ago.

Model-derived dispersivity values at Hangar 1000 were: longitudinal 1.5 feet (ft), transverse 0.27 ft, and vertical 0.27 ft. The model-derived first order decay rates for biodegradation of TCE, DCE, and VC were 0.0002 per day (d-1), 0.0002 d-1, and 0.06 d-1, respectively. These rates are equivalent to half-lives of 13.7 years for TCE and DCE and 17 days for VC.

Source area reductions in contaminant concentrations of 50 and 100 percent were modeled to simulate remediation. As expected, reducing the source concentration by 50 percent resulted in eventual TCE, DCE, and VC concentrations that were half of the original concentrations. About 16 years were needed for new steady-state TCE concentrations to develop, about 14 years for DCE, and about 12 years for VC. Reducing the source area concentrations by 100 percent in the model eventually resulted in zero concentrations of TCE, DCE, and VC. The modeled period of time for the contaminants to be removed from the aquifer once the source was removed was about 17 years for TCE, 15 years for DCE, and 13 years for VC.

TABLE OF CONTENTS

Abstract Introduction

Purpose and Scope
Previous Modeling at the Jacksonville Naval Air Station
Acknowledgments
Methods Hydrologic Setting Occurrence and Factors Affecting the Movement of Trichloroethene, Dichloroethene, and Vinyl Chloride Ground-Water Flow Simulation at the Station
Original Subregional Model
Recalibration of the Subregional Model
Ground-Water Budget
Sensitivity Analysis
Ground-Water Flow Model Limitations Fate and Transport Simulations of Trichloroethene, Dichloroethene, and Vinyl Chloride Movement at Hangar
Model Construction
Flow Path Analysis
Fate and Transport Modeling Overview
Calibration to Current Distribution Trichloroethene, Dichloroethene, and Vinyl Chloride
Predicted Movement of Trichloroethene, Dichloroethene, and Vinyl Chloride Assuming Source Reduction of 50 Percent
Predicted Movement of Trichloroethene, Dichloroethene, and Vinyl Chloride Assuming Source Reduction of 100 Percent
Measurement Error and Effect of Parameter Variation on Fate and Transport Modeling Results Summary
References