Pump and Treat Remediation Strategies

In order to determine an appropriate strategy to manage the contaminated groundwater, it is necessary first to evaluate site conditions and define remediation goals.

Mostly, the goal of groundwater remediation is to protect human health and the environment and to restore groundwater to beneficial uses where practicable.

For groundwater that is or may be used for drinking, clean-up goals can be set at drinking water standards. Whereas when groundwater that is not used for drinking, clean-up goals can be set as per regulatory requirements.

The strategies for managing groundwater contamination using the pump and treat technology includes:

(1) Hydraulic/physical containment

(2) Groundwater quality restoration

(3) Mixed objective strategies

Several ground-water contamination management strategies using P&T technology (after NRC, 1994; Cherry et al., 1992)

Hydraulic Containment

Hydraulic containment is the attempt of confining the movement of contaminated groundwater in order to prevent the continued expansion of the contamination zone.

P&T systems are frequently designed to hydraulically control the movement of contaminated groundwater.

At sites where the contaminant source cannot be removed (e.g., a landfill or bedrock with DNAPLs), hydraulic containment is an option to achieve source control. Hydraulic containment of dissolved contaminants by pumping groundwater from wells or drains.

The physical containment options (e.g., subsurface barrier walls and surface covers to limit inflow) can enhance hydraulic containment systems by reducing the pumping rate required to maintain containment.

Examples of hydraulic containment in plan view and cross-section using an extraction well (a), a drain (b), and a well within a barrier wall (c).

Groundwater Quality Restoration/Cleanup

P&T technology designed for aquifer restoration generally combines hydraulic containment with more aggressive manipulation of groundwater (i.e., higher pumping rates) to attain clean-up goals during a finite period.

Ground-water cleanup is typically much more difficult to achieve than hydraulic containment.

Mixed Objective Strategies

P&T systems can be used to contain the contaminant source areas and attempt restoration of downgradient dissolved plumes. A mixed P&T strategy is appropriate, therefore, at sites where different portions of the contaminated region are amenable to remediation using different methods.

At sites contaminated with LNAPLs (lighter-than-water NAPLs), for example, a mixed remedial strategy may include:

(1) Vacuum-enhanced pumping to recover free product, affect hydraulic containment, and stimulate bioremediation in the LNAPL release area; and

(2) Restoring downgradient ground water via natural attenuation, P&T, and/or air sparging.

There are several other innovative technologies, such as air sparging, engineered bioremediation, and permeable treatment walls can be used in conjunction with P&T, or alone, to address these ground-water remediation objectives.

At some sites, natural attenuation processes may limit the need for P&T. The management strategy selected depends on site-specific hydrogeologic and contaminant conditions, and remediation goals.

References: Design Guidelines for Conventional Pump-and-Treat Systems, Robert M. Cohen1 , James W. Mercer1