Abstract
Karst aquifers, characterized by a combination of multiple porosity types, discrete flow paths, and variable hydraulic conductivities, create a highly complex and heterogeneous environment that influences both the storage capacity and transport of contaminants in the subsurface. These complexities of karst aquifers present unique challenges for remediating contaminated groundwater. Pilot studies were performed at eight sites at Redstone Arsenal (RSA) in Huntsville, Alabama, to assess the viability of in situ injection-based remedies to treat groundwater impacted by chlorinated volatile organic compounds (CVOCs) and perchlorate in the epikarst, the uppermost, highly weathered rind of karst bedrock. The studies assessed effectiveness of two injection-based in situ remedial technologies: in situ bioremediation (ISB) and in situ biogeochemical reduction (ISBGR). The injected remedial amendment or “substrate” for ISB was emulsified vegetable oil and for ISBGR was a combination of organic carbon and zero-valent iron. ISB injections were performed in the epikarst using permanent injection wells screened across the contact between the overburden and underlying bedrock at each of the eight sites. At six of the eight sites, ISB or ISBGR injections were also performed in the overburden using temporary injection points to evaluate the impact of overburden injections on the treatment of epikarst groundwater. Pilot study areas were co-located in the overburden and epikarst at three of these six sites. Fluorescent dyes were added to the substrate at two sites to evaluate substrate distribution and define the performance monitoring network. Post-injection monitoring confirmed successful substrate delivery, establishment of strongly reducing conditions, and significant declines in CVOCs and perchlorate at several locations, demonstrating that in situ injection-based remedies can be implemented effectively in karst settings. Lessons learned from these pilot studies inform the potential for full-scale remedial implementation and underscore the importance of adaptive injection strategies, robust performance monitoring, and the use of tracers to address site-specific heterogeneity.
DOI
https://doi.org/10.5038/9781967518012.1017
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Remediating Groundwater in a Karst Terrane: Encouraging Results and Lessons Learned
Karst aquifers, characterized by a combination of multiple porosity types, discrete flow paths, and variable hydraulic conductivities, create a highly complex and heterogeneous environment that influences both the storage capacity and transport of contaminants in the subsurface. These complexities of karst aquifers present unique challenges for remediating contaminated groundwater. Pilot studies were performed at eight sites at Redstone Arsenal (RSA) in Huntsville, Alabama, to assess the viability of in situ injection-based remedies to treat groundwater impacted by chlorinated volatile organic compounds (CVOCs) and perchlorate in the epikarst, the uppermost, highly weathered rind of karst bedrock. The studies assessed effectiveness of two injection-based in situ remedial technologies: in situ bioremediation (ISB) and in situ biogeochemical reduction (ISBGR). The injected remedial amendment or “substrate” for ISB was emulsified vegetable oil and for ISBGR was a combination of organic carbon and zero-valent iron. ISB injections were performed in the epikarst using permanent injection wells screened across the contact between the overburden and underlying bedrock at each of the eight sites. At six of the eight sites, ISB or ISBGR injections were also performed in the overburden using temporary injection points to evaluate the impact of overburden injections on the treatment of epikarst groundwater. Pilot study areas were co-located in the overburden and epikarst at three of these six sites. Fluorescent dyes were added to the substrate at two sites to evaluate substrate distribution and define the performance monitoring network. Post-injection monitoring confirmed successful substrate delivery, establishment of strongly reducing conditions, and significant declines in CVOCs and perchlorate at several locations, demonstrating that in situ injection-based remedies can be implemented effectively in karst settings. Lessons learned from these pilot studies inform the potential for full-scale remedial implementation and underscore the importance of adaptive injection strategies, robust performance monitoring, and the use of tracers to address site-specific heterogeneity.