LOW-ENERGY ALTERNATIVES
disposal of filter media in permeable reactive barriers. Above- ground treatment is also easier to monitor and maintain than filter media in reactive barriers. The other alternative of non- pumped wells offers the convenience of easily replaced filter cartridges; however, a very substantial infrastructure (large number of wells) was necessary to contain the contaminant plume onsite.
the plume onsite. Based upon required infrastructure and timeframe for contaminant removal, the low-capacity extrac- tion-injection well pair was most effective and is worthwhile to consider as a remediation alternative in practice.
References
1. EPA (US Environmental Protection Agency) (2002) Economic analysis of the implementation of permeable reactive barriers for remediation of contaminated ground water. Washington, DC: US Environmental Protection Agency.
2. Ludwig RD, McGregor RG, Blowes DW, et al. (2002) A permeable reactive barrier for treatment of heavy metals. Ground Water; 40(1):59-66.
3. Gilbert O, Pablo J, Cortina J-L, et al. (2010) In situ removal of arsenic from groundwater by using permeable reactive barriers of organic matter/limestone/zero-valent iron mixtures. Environ Geochem Health; 32(4):373-8.
4. Guerin TF, Horner S, McGovern T, et al. (2002) An application of permeable reactive barrier technology to petroleum hydrocarbon contaminated groundwater. Water Research; 36(1):15-24.
5. Robertson WD, Blowes DW, Cherry JA (2000) Long- term performance of in situ reactive barriers for nitrate remediation. Ground Water; 38(5):689-695.
6. Lai KCK, Lo IMC, Birkelund V, et al. (2006) Field moni- toring of a permeable reactive barrier for removal of chlo- rinated organics. J Environ Engineering; 132(2):199-210.
Figure 3. Map of selected flow lines (top) and remaining contam- inant plume after 500 d (bottom) with injection-extraction well pair; contours in mg/L.
Alternatives outlined above share certain features. Each requires groundwater to carry dissolved contaminants, while involving hydrodynamic dispersion and dilution to lower con- taminant concentrations. Active alternatives removed similar contaminant mass: 15.55 kg for the permeable reactive barrier; 15.12 kg for the non-pumped wells; and 15.53 kg for the extrac- tion well. Furthermore, each alternative enabled portions of the contaminant plume to migrate past the structure, but ultimately contained the plume onsite. The results outlined above indicate that enabling a contaminant plume to travel and attenuate within an onsite buffer zone can help remediate contaminated groundwater.
Some field conditions would render the above alternatives less effective. In particular, low seepage velocities and low solubility would delay or prevent contaminants from moving into reactive barriers, filter cartridges, or extraction wells. In practice, groundwater remediation systems are highly dependent upon site-specific conditions and require careful monitoring to verify operational efficiency.
Conclusions
The objective of this study was to evaluate alternatives of no-action and three active remediation scenarios to contain and remove a plume of contaminated groundwater. A modest seepage velocity and relatively narrow contaminant plume were simulated. The active alternatives included a permeable reactive barrier, non-pumped wells with filter media, and a low-capacity extraction-injection well pair downgradient of the contaminant plume. The no-action alternative did not contain
7. Blowes DW, Ptacek CJ, Benner SG, et al. (2000) Treatment of inorganic contaminants using permeable reactive bar- riers. J Contam Hydrol; 45(1):123-137.
8. Gupta N, Fox TC (1999) Hydrogeologic modeling for per- meable reactive barriers. J Hazardous Materials; 68(1):19- 39.
9. Elder CR, Benson CH, Eykholt GR (2002) Effects of het- erogeneity on influent and effluent concentration from horizontal permeable reactive barriers. Water Resour Research; 38(8):1152, doi:10.1029/2001WR001259.
10. Painter BDM (2004) Reactive barriers: Hydraulic per- formance and design enhancements. Ground Water; 42(4):609-619.
11. Hemsi PS, Shackelford CD (2006) An evaluation of the influence of aquifer heterogeneity on permeable reac- tive barrier design. Water Resour Research; 42:W03402, doi:10.1029/2005WR004629.
12. Hudak, PF (2007) Mass transport in groundwater near hanging-wall interceptors. J Environ Sci Health; 42(3):317-321.
13. USGS (US Geological Survey) (1999) Deep aquifer remediation tools (DARTs): A new technology for ground- water remediation. Reston, VA: US Geological Survey Fact Sheet 156-99.
14. Hudak PF (2009) Internal versus external configurations of passive wells with filter cartridges for cleaning contami- nated groundwater. Remediation; 20(1):133-141.
15. Hudak PF (2008) Evaluation of reactive well networks for remediating heterogeneous aquifers. J Environ Sci Health; 43:731-7.
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