Monitored natural attenuation of organic contaminants in groundwater: principles and application

This paper reviews the conceptual and technical basis underpinning the use of monitored natural attenuation (MNA) for the management of organic contaminants in groundwater. MNA has important advantages over engineered remediation technologies for groundwater. Its significance will increase across the international community generally and its application for the management of petroleum hydrocarbons and other aromatic compounds will expand. Its application to other contaminants such as chlorinated solvents requires further qualification, although it has demonstrable potential for these. Long-term dissolution of non-aqueous-phase liquid (NAPL) sources is a major issue affecting remediation time-frames for MNA. Source zone remediation in conjunction with MNA will be required for many contaminated sites to meet typical regulatory time-frames permitted for MNA application. Internationally, there is general consensus in the scientific basis and assessment methods included in the technical guidance or protocols supporting the application of MNA. It is not a 'do-nothing' remediation strategy, but requires site-specific characterisation, scientifically based analysis and a longterm commitment to monitoring, data collection and rigorous technical evaluation for ongoing performance assessment. Additional remediation technologies may be required to support MNA during the remediation programme and the decision to implement MNA should consider the large body of MNA literature that now exists and is summarised here.