Geochemical Barriers and Mineral Precipitation for Groundwater Remediation: Advances in Natural and Engineered Systems

Groundwater across North America is still vulnerable to widespread contamination by metals and metalloids, left over from historic-industrial and mine activities. This review explores natural and engineered techniques employing geochemical barriers and precipitates to immobilize contaminants. Natural attenuating processes like arsenic removal by iron hydroxide at Elizabeth City, NC, and carbonate buffering at Sudbury Basin and Faro Mine, YK, highlight inherent systems' capacities to attenuate pollutant mobility. However, these are subject to stable geochemical environments and long-term management, especially with respect to increasing climate variability and its effect on hydrological regimes (Arnold, 2010). Engineered remedies like zero-valent permeable reactive iron barriers at Denver Federal Center, CO, and lead immobilization by phosphate amendment at Butte, MT, show high removal capacities; however, engineered remedies are limited by clogging and side reactions and by evolving regulatory standards. New techniques like nanoscale hydroxides and biomineralization through sulfate-reducing bacteria hold promise for inexpensive and sustainable remediation, though large-scale validation is required. The remediation guidelines enacted by U.S. EPA and by Canadian agencies set cleanup goals and monitoring schemes and cost-benefit analyses show passive systems to have long-term economic and societal advantage even at large initial characterization costs. Future remediation work needs to incorporate adaptive management schemes and by planning for climatic change can ensure sustainable aquifer protection.