Pump-and-treat groundwater remediation

Mercer, J.W., Skipp, D.C., and Giffin, D. Basics of pump-and-treat groundwater remediation technology, U.S. EPA Report... 

If required, pump-and-treat groundwater remediation and/ or in situ bioremediation are options, but unlike with soil excavation, it may take years for contaminant concentrations to reach the agreed end point. The postclosure part of the closeout activities plan should contain a well-defined exit strategy for any necessary postclosure remediation, based on a sampling methodology that defines progress and determines when the end point is reached. 

Natural attenuation by itself, however, often is not sufficient to achieve a desired extent or rate of contaminant removal from an aquifer. In these instances, one remedial option may be to enhance the natural rate of biodegradation of pollutant chemicals in the aquifer. This strategy, called in situ bioremediation, is considered to be one of the most attractive remedial techniques from a cost perspective, because many of the high costs associated with pumping and treating groundwater or excavating contaminated aquifer material are avoided. Furthermore, the potential exposure of cleanup workers to pollutant chemicals is reduced if many of the contaminants are mineralized while still in the aquifer. 

Following the implementation of the remedy, the state or the potentially responsible party (PRP) assumes responsibility for the operation and maintenance (O M) of the site, which may include activities such as groundwater pump and treat, and cap maintenance. Once U.S. EPA has determined that all appropriate response actions have been taken and cleanup goals have been achieved, the site is deleted from the NPL through a formal rulemaking process. 

The pump-and-treat methodology is effective for groundwater remediation. It is also an effective way to prevent the further extension of a contaminated area. The cleanup involves two steps ... 

For the site remediation case shown in Figure 16.21, this alternative consists of in situ SVE of TCE-contaminated soil (Area 2), in situ soil fixation of lead-contaminated soil (Area 1), cap (Area 1), and the groundwater pump-and-treat components of Alternative 3. 

This alternative includes components of Alternatives 3 and 4 and introduces a thermal destruction component to address the TCE-contaminated soil. For the site remediation case shown in Figure 16.21, the lead-contaminated soil in Area 1 would be fixed and covered with a soil/clay cap, as described in Alternative 4. The groundwater would be addressed through pumping and treating, via an air stripper, as described in Alternatives 3 and 4. The TCE-contaminated soil in Area 2 would be excavated and treated on site by a thermal destruction unit comprisng a mobilized rotary kiln. 

The relatively low Henry s constants (the ratio of a compound s concentration in air relative to its concentration in water) of oxygenates can result in them being more difficult to strip from contaminated groundwater via air sparging or air stripping as part of a pump-and-treat remedy. 

For practitioners of in situ technologies, note that U.S. EPA has issued a policy statement that reinjection of contaminated groundwater is allowed under Resource Conservation and Recovery Act (RCRA)35 36 as long as certain conditions are met. This policy is intended to apply to remedies involving in situ bioremediation and other forms of in situ treatment. Under this policy, groundwater may be reinjected if it is treated aboveground prior to reinjection. Treatment may be by a pump-and-treat system or by the addition of amendments meant to facilitate subsurface treatment. Also, the treatment must be intended to substantially reduce hazardous constituents in the groundwater (either before or after reinjection) the cleanup must be protective of human health and the environment and the injection must be part of a response action intended to clean up the environment.37... 

MPE provides several advantages when compared with the use of SVE or pump-and-treat alone. MPE provides for an increase in groundwater recovery rates, an increase in ROI in individual ground-water recovery wells, and recovery of shallow free product. By depressing the groundwater table in the vicinity of the extraction wells, MPE provides for remediation of the capillary fringe and smear zone, and remediation of volatile, residual contaminants located above and below the water table.46... 

From the 323 projects in U.S. EPA s MTBE Treatment Profiles dataset, 85 projects were identified where MTBE in groundwater was remediated using pump-and-treat along with 15 additional projects that treated MTBE in drinking water (collectively referred to as pump-and-treat projects). Information on the treatment of other oxygenates was reported for 20 of these 100 projects 16 projects reported TBA, 6 projects reported TAME, 2 projects reported ethanol, and 1 project reported DIPE as a contaminant in addition to MTBE. 

Aboveground Treatment Technologies Used at 70 Groundwater Pump-and-Treat Remediation and Drinking Water Treatment Projects... 

In addition, cover systems are also used in the remediation of hazardous waste sites. For example, cover systems may be applied to source areas contaminated at or near the ground surface or at abandoned dumps. In such cases, the cover system may be used alone or in conjunction with other technologies to contain the waste (e.g., slurry walls and groundwater pump and treat systems). 

We construct in this section a model of how inorganic lead reacts as it infiltrates and contaminates an aquifer, and then as the aquifer is flushed with fresh water during pump-and-treat remediation (Bethke, 1997 Bethke and Brady, 2000). We assume groundwater in the aquifer contacts hydrous ferric oxide [Fe(OH)3, for simplicity] which sorbs Pb++ ions according to the surface complexation model of Dzombak and Morel (1990), as discussed in Chapter 10. 

According to the technology developer, the total cost for using the in situ microbial filter technology is approximately half of the estimated pump-and-treat cost, while involving only about 10% of the usual volume of groundwater used in pump-and-treat remediation (D152103, p. 1). 

A site-specific, cost-benefit analysis is required to determine if an active remediation system or MNA would be the most effective remediation option (D11322U, p. 8). In 1999, the U.S. Army prepared an analysis of the cost of MNA, in situ bioremediation, and pump-and-treat systems for the treatment of explosives-contaminated groundwater at the Louisiana Army Ammunition Plant in Min den, Louisiana (D22026Y). This comparison is summarized in Table 1. 

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