Extent and Persistence of Secondary Water Quality Impacts after Enhanced Reductive Bioremediation

Electron donor ED addition can be very effective in stimulating enhanced reductive bioremediation ERB of a wide variety of groundwater contaminants. However, ERB can result Secondary Water Quality Impacts SWQI including decreased levels of dissolved oxygen O2, nitrate NO3-, and sulfate SO42-, and elevated levels of dissolved manganese Mn2, dissolved iron Fe2, methane CH4, organic carbon, and naturally occurring hazardous compoundse.g., As. This report summarizes available information on processes controlling the production and natural attenuation of SWQI parameters and can be used as a guide in understanding the magnitude, areal extent and duration of SWQI in ERB treatment zones and the natural attenuation of SWQI parameters as the dissolved solutes migrate down gradient with ambient groundwater flow. This information was compiled from a wide variety of sources including a survey and statistical analysis of SWQI from 47 ERB sites, geochemical model simulations, field studies at sites where organic-rich materials have entered the subsurface e.g., wastewater, landfill leachate and hydrocarbon plumes, and basic information on physical, chemical and biological processes in the subsurface. This information is then integrated to provide a general conceptual model of the major processes controlling the production and attenuation of SWQI production and attenuation.