Groundwater recirculation can increase the effectiveness and speed of in-situ remediation activities at contaminated sites!
Many sites with groundwater contamination require an in-situ remedial approach that can treat difficult or hard to reach contaminants in the subsurface. Excavating these impacts is often disruptive, costly or even impossible! These were some of the initial impetuses for the development of in-situ remediation technologies in the first place.
Sometimes subsurface conditions at a site can limit the effectiveness or speed of in-situ remediation methods due to limited access to the plume of contamination or the slow pace of groundwater flow. In many cases, especially with remedial solutions, in-situ approaches rely on groundwater transport to carry the prescribed amendments across the target treatment areas or to modify some specific element of the groundwater geochemistry (e.g. pH) to support the degradation processes in the subsurface. Enter greater flexibility in the in-situ remediation realm by way of groundwater extraction and recirculation systems.
Groundwater recirculation systems can overcome what are sometimes limitations of in-situ injection programs since they can:
- Manipulate groundwater flow velocities and travel times;
- Provide quicker and more complete distribution of remedial amendments;
- Reach remote areas of sites where direct injections are not possible; and
- Better target contaminated areas.
Additional benefits of recirculation systems include the ability to:
- Reduce the need for costly or unnecessary off-site disposal of impacted groundwater by extracting, dosing and re-injecting impacted groundwater;
- Inject and move large volumes of remedial solutions;
- Alter natural groundwater flow patterns;
- Enhance hydraulic containment; and
- Transport amendments greater distances in the subsurface before they are consumed.
Here at Vertex we recently updated our mobile Environmental Compliance Approval (ECA) for in-situ remediation with the Ontario Ministry of Environment, Conservation, and Parks (MECP). This allows the incorporation of groundwater recirculation into in-situ remediation processes designed to treat soil and groundwater at sites contaminated with a wide variety of organic and/or inorganic compounds. With this amended ECA, Vertex can easily incorporate groundwater recirculation at any sites that can benefit from the associated advantages.
At a site in the GTA, Vertex designed and implemented a groundwater extraction and recirculation system to help address groundwater contaminated with excess levels of a common, nitrogen-based, liquid fertilizer. For various reasons at this operating facility the preferred approach was in-situ remediation. However, two of the largest hurdles to overcome at this site were the lack of groundwater hydraulic control and the relatively limited areas of the site that were physically accessible for injection purposes.
The obvious solution was to enhance groundwater flow velocities and control the distribution of remedial amendments in the subsurface via a groundwater recirculation system. Vertex designed, installed and tested a system that included several rows of injection and extraction wells placed as far as 35 m apart. An enhanced hydraulic gradient was established at the site by extracting groundwater from downgradient wells, filtering and dosing the water with remedial amendments, and then reinjecting the amended groundwater at the upgradient wells. This system increased the hydraulic gradient across the otherwise inaccessible contaminant plume by 10% to 20%, increasing the speed of amendment distribution proportionately. It also allowed greater control over groundwater flow patterns at the site and, as an added benefit, provided better hydraulic control of the contaminant plume in the coarse-grained sands. Remediation is being completed via enhanced, anaerobic biological denitrification. The first season of treatment was completed last fall and preliminary results are highly promising!
So, the next time you encounter a site that has what might normally be considered impediments to an in-situ remedial approach, ask Vertex if an enhanced program using groundwater recirculation might do the trick.
To learn more about Vertex’s approach with groundwater recirculation systems or other in-situ remediation techniques, please contact us.