In-Situ Subsurface Microbial Transformation of Selenium as Source Control in Backfilled Phosphate Overburden

EPA Grant Number: F07D20692
Title: In-Situ Subsurface Microbial Transformation of Selenium as Source Control in Backfilled Phosphate Overburden
Investigators: Kirk, Lisa Bithell
Institution: Montana State University
EPA Project Officer: Lee, Sonja
Project Period: January 1, 2007 through January 1, 2010
RFA: STAR Graduate Fellowships (2007) RFA Text |  Recipients Lists
Research Category: Hazardous Waste/Remediation , Academic Fellowships , Fellowship - Microbial Geochemistry


Selenium release associated with weathering mine waste has been recognized as a threat to human health and the environment. This study of subsurface microbial ecology, as it affects selenium transformation and attenuation in backfilled mine waste, addresses potential for selenate reduction by indigenous microorganisms using naturally available carbon at phosphate mine sites in Southeast Idaho. The ultimate objective of this research is to define how backfilled mine environments might be ecologically engineered to support optimal levels of selenate reduction as a method of source control, through selective handling and rock placement, compaction, management of water, and control of gas exchange. Biobarriers would then be constructed during routine mining operations to limit potential groundwater impacts.


For regulators and miners to rely on natural attenuation of selenium via microbial reduction in subsurface backfills, they must know the identify and distribution of the microorganisms involved, and the environmental factors that influence populations levels and activity. Samples of groundwater and mine waste have been collected under sterile, environmentally controlled conditions from sonic drill holes, with insitu measurements of oxygen, carbon dioxide, moisture content, temperature, and geochemistry. Three principal objectives have been defined for this research:

  1. Identify and enumerate selenate-reducing organisms. Organisms capable of selenate reduction will isolated and identified using both cultivation and non-cultivation dependent (e.g., PCR, DGGE, clone libraries, and genomic analysis) methods. Enumerate organisms based on lithology and aerobic tolerance using most probable number method.
  2. Determine which backfill-relevant environmental factors influence microbial selenate reduction, using microcosm experiments to evaluate the influence of key variables such as oxygen, moisture content, available form of organic carbon, and concentrations of potential inhibitors (sulfate, nitrate, and manganese) on magnitude and rate of selenate reduction.
  3. Determine selenium reduction rates under environmentally relevant conditions of lithologic variation, moisture, flow rate, and oxygen exposure, using column leach test methods.

Expected Results:

This research will identify the indigenous organisms and conditions capable of promoting in-situ microbial reduction of selenate in backfilled phosphate mine waste, thereby providing a foundation for development of reactive barrier designs. Results of this work will improve understanding of subsurface microbial ecology, enhancing efforts to integrate the biogeochemical processes into environmental management of impacted subsurface sites.

Supplemental Keywords:

selenium, selenate reduction, microbial transformation, SE Idaho phosphate mine waste, subsurface microbial ecology, natural attenuation,, Scientific Discipline

Progress and Final Reports:

  • 2007
  • 2008
  • Final