In-Situ Groundwater Remediation

Contaminant Removal to Non-Detect With Re-Circulating Wells

In-Situ Groundwater Remediation is a simple patented technology that removes contaminants from groundwater within the well. It does not pump the water to the surface or otherwise remove it from the aquifer. The groundwater is pumped more vigorously than in a pump-and-treat or air sparging approach, circulated several times through a treatment zone established around the ISGR well, and treated for removal of contaminants during each of several passes through the well.

While there are numerous possible configurations, each optimized for a different set of geologic conditions, the most basic approach is also the most commonly used. Figure 1 shows the basic configuration.

The well penetrates to the maximum depth of the contamination, with a normal inlet screen across the lower several feet of the contaminated thickness.
The well incorporates a second screen, an outlet screen, usually at or near the normal water table.
The functions of the two screens can be reversed, with the upper screen serving as the inlet screen and the lower screen serving as the outlet screen.
The inlet portion of the well is separated from the outlet portion by a packer.
The size of the well casing increases just below ground surface to a diameter of a few feet, to accommodate placement of an adsorptive or reactive treatment medium in the well. A central pipe is located in this larger-diameter portion of the well. The central pipe serves to collect the water after treatment and convey it back to the lower, smaller-diameter portion of the well.
The water is pumped by a submersible pump to the larger-diameter portion of the well, where it is pumped through the treatment medium.
The treated water exits the treatment medium and is conveyed by the central pipe back to the smaller-diameter portion of the well. From this point, the water is conveyed through the smaller-diameter portion of the well to the exit screen. The water then flows, under gravity and/or applied pressure, through the outlet screen and flows back into the aquifer through the sand pack and the aquifer materials.
At the exit screen, higher than normal pressures are formed, resulting in higher head values near the well.
The treated water flows outward from the well and downward under the influence of the vertical gradients created by the extraction process at the bottom of the well and the mounding at the water table. Because aquifer materials are typically anisotropic, allowing horizontal flows more readily than vertical flows, the flows tend to be more outward than downward.
A recirculation zone is created that typically returns the majority of the treated water to the inlet screen. The shape and size of the treatment zone are largely determined by the treated thickness, the hydraulic conductivity, the anisotropy of the aquifer, and the pumping rate.
The water cycles through the treatment zone several times, on average, before escaping down gradient. The treatment process does not have to achieve final cleanup levels in a single pass, since the water will return for additional treatment. Five passes through the well, even at only 85% removal on each pass, easily exceeds 97% removal. Using activated carbon as an adsorptive medium, treatment is usually 100% in a single pass through the well.
There are no above-ground systems or equipment. Typically, the only above-ground appearance of an ISGR system is a manhole with an adjacent power pole that has a utility meter and a control panel.

While the basic configuration and process are straightforward, even for this simplest case there are many considerations in designing and installing In-Situ Groundwater Remediation systems. Well diameter, optimal pumping rate, number of wells and well placement, length of the outlet screen, special development procedures, controls and instrumentation, in-well plumbing configuration, constructability, and many other factors must be addressed in developing a complete design. For more complex or challenging geology, there are additional considerations such as confined aquifer configurations and multiple rows of wells.

The general advantages of In-Situ Groundwater Remediation and specifically the advantages of ISGR over air sparging and pump-and-treat technologies are listed below.

Figure 1 - In-Situ Groundwater Remediation Wells - Click to see a larger image

Major Advantages Of In-Situ Groundwater Remediation
With Re-Circulating Wells

No surface equipment

Constructed entirely below ground, ISGR systems take up no aboveground space.
Silent operation

Faster

Faster than pump and treat or air sparging. Much less than the 30 to 50 years commonly estimated for pump-and-treat systems.
More vigorous than pump-and-treat approaches. Pump-and-treat is passive in nature, extracting the water that is easiest to extract and waiting for contaminants to diffuse from lower permeability zones. Re-circulating wells induce vertical gradients to vigorously circulate and treat all of the water in the aquifer multiple times.

Cheaper

Lower initial capital costs, lower maintenance costs, and faster cleanups result in lower life-cycle costs.
Fewer wells. Well spacing typically 2 to 5 times depth of contamination. At a site with 50 feet of saturated zone, well spacing can be 200+ feet.
Lower pressures than air sparging systems, typically just the pressure required to pump the water to near ground surface. Pumping an incompressible fluid (water instead of air), energy costs are lower than for air sparging.

More flexible

Large well spacings at many sites allow great flexibility in placing wells.
Tolerant of variable geology. Rather than being impeded by thin silt lenses and discontinuous clay layers, re-circulation patterns are enhanced by these typical real-world features.
Pumping rate can be adjusted after installation to match actual aquifer response. Pumping rate and even screen placement can be modified to meet changing conditions during cleanup.
Does not affect adjacent plumes. Because groundwater is not extracted, adjacent plumes are not drawn toward a re-circulating well. Specific plumes or parts of a plume can be targeted.
Can be used to distribute nutrients in the groundwater to enhance bioremediation.
Compatible with soil vapor extraction systems.

Regulatory advantages

No extraction of groundwater. Does not lower groundwater levels. No re-injection problems. Eliminates the need for water treatment at the surface.
No air emissions. Re-circulating wells can be operated with zero discharge.