August Mack News

The in-situ remedial technology of Monitored Natural Attenuation (MNA) utilizes natural attenuation processes and requires long-term performance monitoring. It an agency approved remediation technology but is considered to be a passive technology.

The advantages of Monitored Natural Attenuation are the following:

• Overall costs may be lower.
• Minimal disturbance to the site operations.
• Potential use below buildings and other areas that cannot be excavated.
• Does not generate remediation wastes.
• Reduced potential for cross-media transfer of contaminants commonly associated with ex-situ treatment.
• Reduced risk of human exposure to contaminants near the source area.
• Natural biodegradation may result in the complete destruction of contaminants in-situ.
• May be used in conjunction with, or as follow-up to, active remedial measures.

• Much less effective where TPH concentrations in soil are high (> 20,000 to 25,000 mg/kg). Not suitable in the presence of free product.
• Not suitable when contamination has impacted a receptor (e.g., impacted ground water supply well, VI in building).
• Longer periods of time to mitigate contamination (especially for heavier petroleum products).
• Site characterization will be more detailed, and may include additional parameters. Site characterization will be more costly.
• Institutional controls may be necessary to ensure long term protectiveness.
• Performance monitoring will require more monitoring locations and a longer period of time.
• May be accompanied by changes in groundwater geochemistry that can mobilize other contaminants.