Remediation of aquifers

Remediation of aquifers contaminated with NAPLs is a multitask endeavor. NAPL can occur in several forms ... 

The results presented in this section indicate that all surfactants may not be suitable for surfactant-enhanced desorption. Multiple factors may influence the suitability of a surfactant for surfactant-enhanced desorption. These factors have been discussed previously. It is clear that additional research is needed to better understand how surfactant molecular structure and soil composition/chemistry affect the rate of solute desorption. However, the results presented in this chapter and in other studies indicate that surfactant-enhanced remediation of aquifers is a promising technology that needs to be explored. 

Dwarakanath, V., 1997. Characterization and Remediation of Aquifers Contaminated by Nonaque-ous Phase Liquids Using Partitioning Tracers and Surfactants. Ph.D. dissertation. The University of Texas at Austin. 

Fe ) has also been shown to remove As(III) from contaminated soils (15,16), and assist in the remediation of aquifers contaminated with polycyclic aromatic hydrocarbons (26). Other nanomaterials have been developed to act as pollutant sensors, such as the trinitrotoluene (TNT) sensor, which can detect TNT at concentrations as low as 20ng/mL(27). 

Brenoel, M. and R.A. Brown. Remediation of a Leaking Underground Storage Tank with Enhanced Bioreclamation. In Proc. 5th National Symposium and Exposition on Aquifer Restoration and Groundwater Monitoring, National Water Well Association, Worthington, Ohio, 1985. pp. 527. 

Newman LA et al. (1999) Remediation of trichloroethylene in an artificial aquifer with trees a controlled field study. Environ Sci Technol 33 2257-2265. 

Tse KKC, S-L Lo, JWH Wang (2001) Pilot study of in-situ thermal treatment for the remediation of pentachlorophenol-contaminated aquifers. Environ Sci Technol 35 4910-4915. 

Newman LA, X Wang, lA Muizniekls, G Ekuan, M Ruszaj, R Cortelucci, D Domroes, G Karscig, T Newman, RS Crampton, MG Yost, PE Heilman, J Duffy, MP Gordon, SE Strand (1999) Remediation of trichloroethylene in an artificial aquifer with trees a controlled field study. Environ Sci Technol 33 2257-2265. 

Sahoo D, JA Smith, TE Imbrigiotta, HM Mclallan (1998) Surfactant-enhanced remediation of a trichloroeth-ene-contaminated aquifer. 2. Transport of TCE. Environ Sci Technol 32 1686-1693. 

Stroo HP et al. (2003) Remediating chlorinated solvent source zones Environ Sci Technol 37 225A-230A. Tick GR, P Lourenso, AL Wood, ML Brusseau (2003) Pilot-scale demonstration of cyclodextrin as a solubility-enhancement agent for remediation of a tetrachloroethene-contaminated aquifer Environ Sci Technol 37 5829-5834. 

Another important factor is the food/nutrient ratio. Many of the necessary nutrients may already be present in the aquifer, such as K, Mg, Ca, S, Na, Mn, Fe, and trace elements however, N and P may be deficient and need to be added. The optimum ratio of BOD N P is 100 5 1. It is not a good practice to inject a large quantity of nutrients in the aquifer at one go. They should be fed at the required usage rate throughout the cleanup process. Both the organic contaminants and the nutrients should be completely exhausted by the end of the in situ remediation of an aquifer. 

The method or methods employed to remediate an aquifer vary, depending on the type, degree, and extent of contamination. Where pollution is shallow and dispersed over a small area, the sediments can sometimes be dug up and transported to a landfill designed especially to isolate the contaminants. Permeable reaction barriers can be installed to intercept a contaminant plume and strip pollutants from it, if the plume is shallow and narrowly focused. 

Fig. 32.2. Remediation of the aquifer shown in Figure 32.1, as the simulation continues. After water contaminated with Pb++ displaces half of the aquifer s pore volume, clean water is flushed through the aquifer until a total of 30 pore volumes have been replaced. Flushing attenuates Pb++ concentration in the groundwater (top), so that it gradually approaches drinking water standards (MCL, or Maximum Contamination Level), and slowly displaces most of the sorbed metal from the Fe(OH)3 surface, primarily from the weak surface sites.

The reaction front reaches the end of the aquifer in the simulation after somewhat less than three pore volumes have been displaced. At this point, the contaminant begins to pass out of the domain. Remediation of the aquifer, however, proceeds slowly, as shown in Figure 32.2. Even after 30 pore volumes have been flushed, some lead remains sorbed to weak sites in the aquifer sediments, and the Pb++ concentration in the groundwater remains above the limits sets as drinking water... 

During the later phases of remediation of an aquifer, it has often been suggested that the expense of continuing LNAPL recovery is not worth the effort, considering the remaining small quantities of recoverable product. The implication of this argument has been that the product will eventually go into solution and therefore will be recovered as part of the dissolved contaminant recovery. Experience has demonstrated that this is not usually a viable option, because the time required and treatment costs to accomplish the task are much greater than with respect to LNAPL product recovery efforts. 

Remediation of petroleum-impacted aquifers where LNAPL is present is typically a phased process. These phases can be simplified as follows ... 

Sanchez, M. and Ely, R., 1998, Recovery of Trichloroethylene from a Bench-Scale Aquifer by Density Manipulations In Nonaqueous-Phase Liquids — Remediation of Chlorinated and Recalcitrant Compounds (edited by G. B. Wickramanayake and R. E. Hinchee), Battelle Press, Columbus, OH, pp. 181-185. 

The issue of dissolved fractions, in terms of aquifer restoration objectives, would be more appropriately addressed at a phase of the remediation program after the source of the dissolved contamination is controlled. Of course, containment of the dissolved plume remains a priority throughout the program. For large-scale recovery programs, requiring treatment prior to reinjection would place an excessive economic burden on the overall remediation effort without technical justification, at least during the course of NAPL recovery. 

Laney, D. F., 1988, Hydrocarbon Recovery as Remediation of Vadose Zone Soil/Gas Contamination In Proceedings of the National Water Well Association Second National Outdoor Conference on Aquifer Restoration, Groundwater Monitoring and Geophysical Methods, Vol. Ill, Las Vegas, NV, May, pp. 1147-1171. 

Nadim R, Hoag GE, Liu SL, Carley RJ, Zack P (2000) Detection and remediation of soil and aquifer systems contaminated with petroleum products An overview. J Pet Sci Eng 26 169-178... 

Kun Z, Hui C, Guanghe L, et al. 1998. In situ remediation of petroleum compounds in groundwater aquifer with chlorine dioxide. Water Res 32(5) 1471-1480. 

Laboratory studies indicate that aquathermolysis can be used to aid in the remediation of waste oils, chromium (Cr VI) and volatile organic compounds (VOCs) in contaminated soils and aquifers. Aquathermolysis is particularly useful in lowering the viscosity of oil and increasing its mobility to facilitate further treatment. Potential applications range from treating household and industrial refuse to destruction of chemical warfare agents. 

The use of vegetable oil for remediation of organic contaminants in an aquifer or unsaturated zone has been smdied at Pacific Northwest Laboratory. The oil strips organic compounds from the aqueous phase or particulate matter and is then pumped out for recovery. In addition, the oil can be used as a carbon source by microorganisms, hence encouraging in situ bioremediation. The technology has not proceeded beyond bench-scale testing and is not commercially available. 

You are involved in the remediation of an aquifer that has been contaminated with 2-methylnaphthalene. Similar to the toluene case discussed in Illustrative Example 14.2, the aquifer is flushed with air-saturated water that is pumped into the ground at one place and withdrawn nearby. Calculate how much water is at least required to supply sufficient oxygen for the microbial mineralization of 1 kg of 2-methyl-naphthalene assuming that the water contains 10 mg 02 L 1. 

Similarly, bioemulsifiers, such as emulsan produced by Acinetobacter calcoaceticus, have been shown to aid in removal of metals. Potential for remediation of soils using bacterial exopolymers is indicated by a study which showed that purified exopolymers from 13 bacterial isolates removed cadmium and lead from an aquifer sand with efficiencies ranging from 12 to 91% (Chen et al., 1995). Although such molecules have much larger molecular weights ( 106) than biosurfactants, this study showed that sorption by the aquifer sand was low, suggesting that in a porous medium with a sufficiently. large mean pore size, use of exopolymers may be feasible. 

Remediation of Poisoned Aquifers. Means for correcting polluted underground water systems are limited and costly. To the knowledgeable would-be polluter, the costs and time involved serve as incentives for preventing such damage in the first place. 

Aksoy, A., and Culver, T. B. (2000). "Effect of sorption assumptions on the optimization of aquifer remediation designs." Ground Water, 38(2), 200-208. 

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