The evaluation of pump-and-treat groundwater remediation techniques for gasoline with emphasis on in situ bioremediation

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Virginia Tech

The purpose of this research was to evaluate the use of conventional groundwater pump-and-treat technology in the remediation of a gasoline contaminated groundwater, and to discuss the benefits of incorporating biotransformation mechanisms in the groundwater cleanup process. Physical and chemical fate and transport mechanisms occurring in the subsurface were investigated to identify potentially rate limiting phenomena. The overall objective was to describe the processes involved in the conceptual design of an in situ groundwater biotreatment system which utilizes naturally occurring microorganisms.

Transport of gasoline in the subsurface as a result of bulk movement and advection was investigated to determine the hydrologic parameters of importance in a groundwater remediation scheme. Saturated and unsaturated flow conditions were included due to the suspected importance of vadose zone storage capabilities. Additional fate and transport phenomena including contaminant dispersion, adsorption, and vapor transport are discussed as they relate to the cleanup process. Biotransformation processes responsible for degrading gasoline organics are given, along with the rate limiting parameters of a groundwater bioremediation system.

Design of a groundwater remediation system using naturally occurring microorganisms must be preceded by a thorough investigation of subsurface hydrologic conditions, biological conditions, and geochemical properties analysis. The hydrologic properties of interest in the aquifer are obtained through aquifer pumping tests and include aquifer transmissivity, conductivity and storage coefficients. This allows a calculation of well pumping rates and the zone of influence of recovery/injection areas. It further allows a mechanism for determining the suitability of bioremediation utilizing this approach.

Subsurface biological conditions and geochemical properties are closely tied together and are critical to the feasibility of biological groundwater remediation. Demonstration of microbiological culture presence and growth potential is performed utilizing standard microbiological mediums as well as a hydrocarbon medium. Groundwater cation and anion analysis is performed along with nutrient optimization studies to identify design formulations.