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

Abstract

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 long-term 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.

Electro-assisted groundwater bioremediation: Fundamentals, challenges and future perspectives

“…Groundwater is typically located in the soil pore spaces and rock fractures and is usually under insufficient mixing conditions (Lai et al, 2015). In some hydrocarbons-contaminated aquifers, an excess of hydrocarbons (as electron donors) prevails over acceptors (Rivett and Thornton, 2008). Dissolved electron acceptors such as oxygen, nitrate, sulfate in the contaminant plume core are depleted and cannot be readily replenished in the downstream plume due to limited dispersion through the soil matrix (Anneser et al, 2010).…”

A Review on Transport Modeling Of VOCs In Subsoil

“…The vast majority of VOC biodegradation research has been undertaken in the saturated zone and has been driven by monitored natural attenuation interests, both for petroleum Aromatic Hydrocarbons and Chlorinated Aliphatic Hydrocarbons at contaminated sites generally [19]. The basic processes that are included in VOC transport model formulation are:…”

Dynamic changes in microbial community structure and function in phenol-degrading microcosms inoculated with cells from a contaminated aquifer

“…The management and remediation of polluted groundwater is important to ensure water resources, maintain safe drinking water supplies, reduce human health risks and protect the environment. Natural attenuation is a risk‐based strategy for managing polluted groundwater, where it can be shown by appropriate monitoring and technical appraisal using site‐specific assessments that natural processes will reduce the risk to identified receptors within a reasonable timescale (Environment Agency, 2000; Pickup et al , 2001; Röling & van Verseveld, 2002; Rivett & Thornton, 2008). Monitored natural attenuation (MNA) is the use of natural attenuation as a remediation concept for contaminated groundwater, with an emphasis on long‐term assessment of natural attenuation processes and their efficacy in meeting site‐specific management objectives (Thornton et al , 2001a, b; Rivett & Thornton, 2008).…”

“…Natural attenuation is a risk‐based strategy for managing polluted groundwater, where it can be shown by appropriate monitoring and technical appraisal using site‐specific assessments that natural processes will reduce the risk to identified receptors within a reasonable timescale (Environment Agency, 2000; Pickup et al , 2001; Röling & van Verseveld, 2002; Rivett & Thornton, 2008). Monitored natural attenuation (MNA) is the use of natural attenuation as a remediation concept for contaminated groundwater, with an emphasis on long‐term assessment of natural attenuation processes and their efficacy in meeting site‐specific management objectives (Thornton et al , 2001a, b; Rivett & Thornton, 2008). For this, it is necessary to be able to predict the performance and the possible outcome of a MNA programme with some confidence, to ensure that alternative strategies can be selected where natural attenuation is unlikely to succeed (Thornton et al , 2001a; Wilson et al , 2004).…”

“…Natural attenuation comprises a combination of physical, chemical and biological processes, including advection, dispersion, volatilization, sorption and degradation. In groundwater, biodegradation and biotransformation are typically the most important natural attenuation processes for organic contaminants (Environment Agency, 2000; Rivett & Thornton, 2008). However, the microbial communities responsible for biodegradation in aquifers are poorly characterized with respect to community structure, functional interaction and their relationships under different environmental conditions (Pickup et al , 2001).…”