Processes Affecting the Natural Attenuation of Gasoline in Ground Water -- Galloway Township, New Jersey

Research focused on three interrelated themes: groundwater contaminant geochemistry; estimation of microbial degradation rates of hydrocarbons on the basis of rates of gas transport in the unsaturated zone; and vapor-extraction remediation design. Contaminant geochemistry work produced a water-quality database that indicated zones of aerobic biodegradation adjacent to zones of anaerobic degradation with sharp chemcial-concentration gradients in narrow interfacial zones. The analysis of gas transport in the unsaturated zone provided a method for quantifying rates of aerobic biodegradation in the capillary zone and shallow groundwater. Mathematical models were developed to simulate vapor extraction remediation and to optimize system design.

Research Objectives

The research objectives for this site are to:

• Characterize the ground-water geochemistry to identify the important biogeochemical processes and microbial degradation pathways
• Develop field and laboratory methods to quantify rates of hydrocarbon transport and microbial degradation in the subsurface
• Determine the factors controlling the performance of vapor-extraction remediation

Approach

Field experiments were performed to quantify the fate of gasoline hydrocarbons associated with engineered (vapor extraction)- and natural-attenuation remediation. A network of vapor probes and ground-water wells were sampled to obtain detailed resolution of the biogeochemical signatures of hydrocarbon degradation above and below the water table. Vapor extraction wells were sampled to determine hydrocarbon biodegradation and mass-removal rates.

Laboratory column experiments were performed to examine the direct response of microbes in controlled systems, emulative of field conditions. The column experiments were also used to determine air-phase permeabilities and effective diffusion coefficients of unsaturated-zone sediments. Open and closed microcosm experiments were conducted to investigate stoichiometric-degradation relations and biodegradation pathways.

Mathematical models provide a means to predict and quantify the transport and biodegradation of hydrocarbons in the subsurface. These models are applied to analyze field and laboratory experiments and to test microbial-kinetic hypotheses. The mathematical models help insure maximum transfer value of the methods to the public.

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The following investigators have contributed to the Galloway research project (* indicates core member):

U.S. Geological Survey, West Trenton, NJ

Arthur L. Baehr*

Jeffrey M. Fischer

Ronald J. Baker*

Matthew A. Lahvis*

Nicholas P. Smith

Jacob Gibs

Program coordination, site hydrogeology, instrumentation, unsaturated-zone vapor analysis, in-situ estimates of microbial degradation, laboratory experiments of hydrocarbon diffusion and microbial degradation, bioventing remediation, mathematical model development

U.S. Geological Survey, National Research Program, Reston VA

Mary Jo Baedecker

Isabelle M. Cozzarelli

Jessica A. Hopple

Curtis S. Phinney

Shallow ground-water analysis, geochemistry and microbiology

Drexel University, Philadelphia, PA

Claire Welty

Craig J. Joss

Jonathan J. Dillow

John G. Nolan

Airflow and induced hydrocarbon transport modeling, coupled transport and optimization modeling, microcosm experiments

University of Virginia, Charlottesville, VA

Aaron L. Mills

Susan E. Randali

Microbial analysis of sediments

University of Lowell, Lowell, MA

Clifford J. Bruell

Craig D. Gilbert

Dense-vapor laboratory experiments