Objective

Anaerobic bioremediation has emerged as an effective technology for aquifers contaminated with chlorinated solvents, chromate, explosives, and other contaminants. Typically, a readily biodegradable, soluble, organic substrate (e.g., molasses, lactate, whey) is flushed through the treatment zone. The substrate ferments to hydrogen and acetate, which support pollutant biodegradation and transformation. Important advantages of this process include: (1) a wide variety of pollutants can be treated to very low levels; (2) energy inputs are low; (3) the primary inputs are renewable materials; (3) no wastes are produced requiring treatment or disposal; (4) worker exposure to contaminants is minimal; and (5) capital and operating costs are low. As a result, anaerobic bioremediation is now one of the most commonly employed technologies for chlorinated solvent remediation.

However, anaerobic bioremediation can result in near- and long-term impacts to groundwater quality. Adverse impacts may occur under certain conditions, including release of dissolved organic carbon, methane, hydrogen sulfide, and a variety of naturally occurring metals and metalloids (e.g., iron, manganese, and arsenic). Preliminary data suggests that many of these contaminants do naturally attenuate. However, the factors controlling the rate and extent of natural attenuation are still poorly understood.

The objective of this project is to develop an improved understanding of the near- and long-term impacts to groundwater quality after implementation of in situ anaerobic bioremediation processes. This will include development and application of a general modeling approach for describing the natural attenuation of important secondary water quality impacts associated with electron donor addition.