Pump and treat remediation

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. 

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

Remediation more commonly proceeds by a pump-and-treat scheme in which contaminated water is drawn from the aquifer and treated at the surface to remove contaminant metals, before being discharged or reinjected into the aquifer. A pump-and-treat remedy can be prolonged, projected not uncommonly to proceed over the course of many decades before the contaminants might be largely flushed from the aquifer. 

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. 

K( results predict that flushing only a few pore volumes of clean water through the aquifer can displace the contamination, suggesting pump-and-treat remediation will be quick and effective. Models constructed with the surface complexation model, in contrast, depict pump-and-treat as a considerably slower and less effective remedy. 

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). 

Maryland Supeifund Site Natural attenuation enabled new development at 70-acre Superfund site approximately 20 miles northwest of Baltimore, Maryland. This property had been contaminated by a printed circuit board manufacturing company. According to a manager, the pump-and-treat remediation system failed to meet groundwater treatment goals, though it cost over 1 million to construct and more than 200,000 a year to operate. It was estimated that this approach could cost as much as 5 million over 10 years and would still not achieve the cleanup objectives of the Maryland Department of Environment (D17452R). 

Mackay, D. M., and J. A. Cherry, Groundwater contamination Pump-and-treat remediation , Environ. Sci. Technol, 23, 630-636 (1989). 

In general, the design objective is to determine the most cost-effective remedial design. The cost functions for pump-and-treat remediation using granular activated carbon (GAC) derived by Culver and Shenk (1998) were adapted for this analysis. In addition to the operating costs and the treatment capital costs considered by Culver and Shenk (1998), the capital costs of well installation have also been included, and the carbon utilization costs are calculated at every simulation time step. Thus the objective function can be described as follows ... 

Keely, J. F. (1989). "Performance evaluations of pump-and-treat remediations. Rep. No. 

Mackay D. M. and Cherry J. A. (1989) Groundwater contamination pump and treat remediation. Environmental Science Technology 23, 630-636. 

Figure 9. Map of field site at Picatinny Arsenal, NJ showing the location of 10 g/L trichloroethene (TCE) plume boundary, subsurface air pressure and moisture content sampling site, and withdrawal wells for the pump-and-treat remediation system.

Fig. 8 Predicted HCBD in a withdrawal well during pump and treat remediation of a 10-m contaminated zone at the PPI site...

West, C.C. 1992. Surfactant-enhanced solubilization of tetrachloroethylene and degradation products in pump and treat remediation, p. 149-158. In D.A. Sabatini and R.C. Knox (ed.) Transport and remediation of subsurface contaminants. Colloidal, interfacial, and surfactant phenomena. ACS, Washington, DC. 

The presence of contaminants in predominantly clay soils poses a difficult and potentially costly remediation problem. The low hydraulic conductivity of these soils prohibits the use of traditional pump-and-treat remediation techniques. Other treatment methods involving excavation and employing various thermal treatments are costly, energy intensive, and could themselves create other adverse environmental impacts. Incomplete remediation of contaminated clay could lead to posttreatment seepage and recontamination of the remainder of the site. For these reasons, much research has been done to advance the field of electrokinetic (EK)... 

Berglund, S. Cvetkovic, V (1995) Pump-and-treat remediation of heterogeneous aquifers Effects of rate-limited mass transfer. Ground Water 33 (4), 675-685. 

The system is simple to operate, reliable and requires a minimum of operator attention or maintenance once the membrane has been formed. The stability of the system makes it particularly suitable for Itmg-term use as is necessary for extended pump and treat remedial programs. 

Based on the observations from the demonstration, it is feasible that the membrane system can be effectively and reliably operated over an extended time period as would be necessary for pump and treat remediations. 

Table 4 shows the total annual cleanup cost to range between 514,180 and 1,209,700. This is based on the assumption that the remediation will take one year. Most applications for this technology will require several years, as in pump-and-treat remedial projects. Since many of the cost factors are one-time, the overall /galIon cost will go down as the length of the project increases. This is illustrated in the hypothetical site example in the subsequent sub-section. The total cost is also highly dependent on whether concentrate treatment and disposal is considered as part of the... 

The EPA has long ago concluded that the enviromnental pump-and-treat remediation technology that has been used for removing NAPL hydrocarbon contaminants from aquifers is not working [2]. Indeed, field demonstrations of soil flushing have illustrated potential problems [13], and aquifers contaminated with DNAPLs were shown to be extremely difficult to remediate with the standard pump-and-treat methods. 

Several field demonstration studies were conducted in the United States, mainly in the 1990s. These demonstrations have shown that surfactant-enhanced subsurface remediation (SER) is relatively rapid and economical, and can be competitive with conventional pump and treat remediation, if—in ex situ bioremediation—surfactant losses can be minimized, contaminated elution maximized, and surfactant-contaminant separation and the former s reuse implemented [46]. 

Pahner, C.D. and Fish, W., 1992. Chemical enhancements to pump and treat remediation, USEPA, EPA 540-S-92-001. 

The conventional remediation method of pump and treat involves pumping of contaminated water followed by treatment at the surface by air stripping, steam stripping, activated carbon filtration and various other means. Pump and treat is limited by parameters such as flow rates, NAPL composition and mass transfer rates, and the surface area available for mass transfer of NAPL constituents from the NAPL to the water [3-5]. Furthermore, dilution effects [6] caused by hydrodynamic dispersion and mixing of contaminated and uncontaminated water adversely affect pump and treat remediation operations. Even in those cases where a pool has formed and has been located and DNAPL pumped out, large amounts of residual NAPL remain to dissolve and pollute the water [7]. The need for cost effective alternatives to pump and treat is compelling. 

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