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U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 01-4252

Simulation of Ground-Water Flow and Potential Contaminant Transport at Area 6 Landfill, Naval Air Station Whidbey Island, Island County, Washington

Prepared in cooperation with
DEPARTMENT OF THE NAVY
ENGINEERING FIELD ACTIVITY NORTHWEST
NAVAL FACILITIES ENGINEERING COMMAND

By F. William Simonds

ABSTRACT

A three-dimensional finite-difference steady-state ground-water flow model was developed to simulate hydraulic conditions at the Area 6 Landfill, Naval Air Station Whidbey Island, near Oak Harbor, Washington. Remediation efforts were started in 1995 in an attempt to contain trichloroethene and other contaminants in the ground water. The model was developed as a tool to test the effectiveness of the pump-and-treat remediation efforts as well as alternative remediation strategies. The model utilized stratigraphic data from approximately 76 Navy and 19 private wells to define the geometry of the shallow, intermediate, and deep aquifers and the intervening confining layers. Initial aquifer parameters and recharge estimates from aquifer tests and published remedial investigation reports were used in the model and then adjusted until simulated water levels closely matched observed water-level data collected prior to the onset of remediation in 1995. The calibrated model was then modified to depict the remedial pump-and-treat system, in which contaminated ground water is extracted, treated, and returned to the ground surface for infiltration. The water levels simulated by the modified model were compared with observed water levels for the 1998 calendar year, during which time the pump-and-treat system was in nearly continuous operation and the ground-water system had equilibrated to steady-state conditions. Although artificial boundaries were used in the model, the choice of model boundary conditions was simulation in the area of primary concern surrounding the western contaminant plume and extraction wells. Particle tracking results indicate that the model can effectively simulate the advective transport of contaminants from the source area to the pumping wells and thus be used to test alternative remedial pumping strategies.

CONTENTS

Abstract
Introduction
Hydrogeology of the Ground-Water Flow System
Steady-State Simulation of the Ground-Water Flow System
Steady-State Simulation of Post-Remediation Conditions
Discussion of Ground-Water Flow Simulation
Summary and Conclusions
References Cited

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Send questions or comments about this report to the author, Bill Simonds (wsimonds@usgs.gov) 253.428.3600 ext. 2669.

For more information about USGS activities in Washington, visit the USGS Washington District home page.

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