Abiotic degradation of PCE and TCE favors Reductive ß-elimination reactions through acetylene. Anaerobic biological reactions follow sequential hydrogenolysis [2].Monitored natural attenuation (MNA) can be an effective and low-cost approach for remediation of contaminated sites. MNA includes physical, chemical and biological processes that reduce contaminant mass or concentration in soil or groundwater under intrinsic condtions. SiREM provides comprehensive and customizable testing packages (SiREMNA™,) to evaluate the viability of MNA for a variety of both organic and inorganic contaminants.
SiREMNA™ – Natural Attenuation Testing for VOCs
In support of MNA remedies, SiREM is pleased to offer SiREMNA™, a comprehensive analytical package that can be customized to identify and quantify reactive minerals, dechlorinating bacteria and other indicator parameters for abiotic and biotic degradation of chlorinated volatile organic compounds (cVOCs). The most common MNA mechanisms at cVOC contaminated sites are anaerobic biodegradation and abiotic/chemical reduction. Biodegradation involves key bacteria that are capable of degrading cVOCs to non-toxic end products. Abiotic degradation of cVOCs is mediated by naturally occurring reduced iron and sulfur minerals, and although often unrecognized, is now considered a key process in natural attenuation of these compounds. The analyses can be performed directly on aquifer materials or used to complement SiREM’s bench-scale treatability testing services, including batch microcosm and column testing to:
- Characterize site conditions for MNA evaluation and remediation decision tools such as BioPIC.
- Assess the effectiveness and sustainability of biotic degradation of cVOCs.
- Determine the role of abiotic reductive dechlorination by biogenic reactive minerals that occur in naturally reducing aquifers, and include iron sulfides, green rusts, pyrite, magnetite, biotite and siderite.
- Support design and monitor performance of enhanced in-situ chemical reduction (ISCR).
- Assess the role of abiotic dechlorination by biogenic reactive minerals formed by iron and sulfate reducing bacteria (SRB) at enhanced reductive dechlorination (ERD) bioremediation applications.
SiREMNA™ Methods for Evaluation of Abiotic and Biotic Natural Attenuation Processes For Chlorinated Volatile Organic Compounds
SiREMNA™ – Inorganics Natural Attenuation Testing
SiREM has developed and expanded the SiREMNA™,testing program for a comprehensive SiREMNA™,-Inorganics testing package to evaluate the viability of MNA remedies for metals and other inorganic contaminants. The package is designed to provide data to assess the viability of MNA and for designing testing protocols in MNA remedies including:
- The chemical and mineralogical characteristics of aquifer solids that provide attenuation capacity
- The aqueous and solid phase chemical speciation of contaminants within the plume as well as unaffected upgradient and downgradient areas
- Quantification of immobilization and/or sequestration process that may control contaminant attenuation
- Collection of site-specific data to demonstrate the long-term stability of immobilized inorganic constituents
*Adsorption onto iron oxyhydroxides is shown
What Makes Inorganics Different?
Under different conditions, natural processes may reduce the mobility, toxicity or bioavailability of inorganic constituents by precipitation as new minerals, co-precipitation, adsorption to the surfaces of soil particles or incorporation into soil particles.
In contrast to organic compounds that are degradable which results in their destruction, inorganic attenuation often involves immobilization via reversible/irreversible processes.
SiREMNA™ Methods for Evaluation of Natural Attenuation Processes For Inorganic Compounds
*Tiered MNA evaluation approach (Ref. 2): Tier 1. Demonstration of active contaminant removal from ground water & dissolved plume stability; Tier 2. Determination of the mechanism and rate of attenuation; Tier 3. Determination of the long-term capacity for attenuation and stability of immobilized contaminants; and Tier 4. Design of performance monitoring program.
