Monitored Natural Attenuation
Monitored Natural Attenuation is a desirable remediation strategy that relies on physical, chemical or biological processes that act to clean up contaminated groundwater without human intervention, within a reasonable time frame and without compromising the protection of human health and the environment. A related term is monitored natural attenuation (MNA). Frequently MNA can be used to affect cleanup of groundwater more cost effectively than other strategies, albeit it sometimes requires more time.
MNA is most appropriate as a cleanup strategy when the site’s groundwater conditions are fully delineated and the source of contamination has been removed or mitigated. Frequently, bringing a site to closure where MNA would be acceptable to regulatory authorities requires a full evaluation of sensitive receptors and modeling of groundwater flow, fate and transport.
GHR has effectively remediated a number of sites using MNA as the sole cleanup approach and in other instances, where natural attenuation has been used in combination with other technologies.
When aggressive means of remediation are necessary to bring a site to cleanup in the shortest possible time, GHR evaluates chemical oxidation technologies against site-specific contaminant criteria. Ozone, hydrogen peroxide, Fentons Reagent, persulfate compounds and permanganate all have been successfully employed for this purpose. Combinations of oxidants are frequently more successful than single oxidant. Chemical oxidation has also been used in combination with enhanced natural attenuation.
GHR can determine the most advantageous chemical oxidants to achieve optimum results for each site's conditions.
Enhanced Managed Attenuation
GHR has designed and implemented a variety of types of enhanced managed attenuation systems. One example uses a pump and treat system with an aboveground, fixed film bioreactor where air, or pure oxygen, is used to augment and speed up the natural biodegradation process. Frequently, this technology results in stabilizing and/or immobilizing the contaminant plume by providing hydraulic control of the contaminated site. The effluent from the bioreactor enriched in oxygen and biochemically active, is returned to the groundwater on site. This approach promotes in situ biochemical oxidation in addition to the aboveground treatment.
GHR has also been very successful with in-situ enhanced natural managed using pure oxygen and an innovative down-well gas delivery system. Extremely high levels of dissolved oxygen are delivered to the groundwater, typically upgradient of the contaminant plume. The technology also can be employed as a “fence” at the upgradient boundary of a property to prevent off-site contamination from impacting the target property. Similarly, the technology can be used as a “screen” at the down gradient limit of the property to prevent contamination from moving off-site.
The oxygen infusion technology is applicable to any contamination that is biodegradable, either aerobically or anaerobically, including sites contaminated with chlorinated solvents. To learn more about oxygen infusion technology, visit the official iSOC™ site.