| Monitored Natural Attenuation (MNA) is a methodology for remediation that relies upon naturally occurring chemical, biological, and physical processes to reduce the toxicity, mobility, mass or concentrations of contaminants.; Natural attenuation of liquid phase and dissolved phase petroleum hydrocarbons is likely occurring to various degrees at railroad sites. The interpretation of geochemical indicators (e.g., comparison of dissolved oxygen, oxidation-reduction potential, nitrate, ferrous iron, sulfate and methane concentrations detected within the source zone versus background zones) is important in providing evidence that the contaminant mass is being degraded.; Based on a literature review and an in depth analysis of historical groundwater data for two Canadian Pacific Railway sites, MNA can be valuable component of site remediation strategies once source control actions are implemented. When properly applied and where protective of human and environmental health, MNA offers the potential to significantly reduce site remediation costs. |
