Natural Attenuation for Groundwater Remediation (2000) / Chapter Skim
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1 Introduction: Using Natural Processes in Groundwater Restoration
1 Introduction: Using Natural Processes in Groundwater Restoration
Pages 20-36
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. The first large-scale attempts to restore contaminated sites, initiated after the Love Canal incident and passage of the Superfund~ law in 1980, employed engineered systems to attempt to remove contamination from groundwater and soil.
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, which are components of gasoline that are commonly found at leaking underground storage tank sites. In 1993, the National Research Council (NRC)
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Cleanup strategies based on natural attenuation, instead of the more strictly defined intrinsic bioremediation, are the predominant choices being pursued today. Whether natural attenuation is an appropriate strategy for managing contaminated sites has become a politically controversial issue.
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It answers several important questions: Why are informed members of the public near contaminated sites often skeptical about this approach? What does science tell about when natural processes can work in cleaning up a site?
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Earlier estimates, prior to closure of a large number of leaking underground gasoline storage tanks, placed the number of such sites at approximately 300,000 to 400,000 (NRC, 1994~. (See Chapter 3 for information about typical sources of groundwater and soil contaminants and the fate of these contaminants in the subsurface.)
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As Figure 1-2 shows, natural attenuation is the leading remedy used at more than 15,000 sites for groundwater contaminated by leaking underground storage tanks. It is the fourth most common remedy used at more than 6,000 sites for cleanup of soil contaminated by leaking underground storage tanks (see Figure 1-3~.
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Soil washing Biopiles Bioventing Tar o ~ Monitored natural attenuation Q Incineration Thermal Resorption Landfarming Soil vapor extraction Landfilling 547 644 Alternative technologies Traditional options 6,823 1 3.906 28,492 0 10,000 20,000 30,000 Number of Sites FIGURE 1-3 Methods used to clean up soil contamination from leaking underground storage tanks as of 1997, according to a survey of state program managers. SOURCE: Tulis et al., 1998.
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More recently, discovery of methyl tert-butyl ether (MTBE) , a fuel oxygenate used to decrease air pollution from automobiles, in plumes of contamination from underground storage tanks has slowed regulatory approval of natural attenuation remedies for these sites, especially in California.
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INCREASING VARIETY OF CONTAMINANTS CONSIDERED FOR NATURAL ATTENUATION Scientists have demonstrated convincingly that natural processes can substantially destroy some contaminants, primarily from gasoline and other fuels, but this level of scientific confidence is not as high for most other common groundwater contaminants. A strong scientific foundation for understanding how petroleum hydrocarbons biodegrade in the environment was available before empirical studies, such as the Livermore report, documented the effectiveness of natural attenuation of
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For example, regulators have approved the use of natural attenuation for the treatment of a plume of trinitrotoluene, an explosive, at the Sierra Army Depot in Herlong, California (Ground Water Newsletter, 1996~. Natural attenuation has also been approved for treating vinyl chloride, which is a potent carcinogen once thought to be extremely recalcitrant to natural degradation, at a chemical manufacturing site (Leetham and Larson, 1997~.
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According to citizen group representatives, a key concern of communities affected by contaminated sites is that natural attenuation is being used to justify the dilution of contaminants and the transfer of contaminants from one environmental medium to another. Community leader Diane Heminway of Citizens' Environmental Coalition in Medina, New York, observed, At both the state and federal levels, it has been the goal to remove as many sites as possible from the Superfund list.
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Second, at many contaminated sites, documenting the occurrence of transformation and immobilization processes is likely to be essential to community acceptance and successful use of natural attenuation. SUMMARY Natural attenuation is replacing or augmenting engineered remediation systems at an increasing number of sites with contaminated groundwater and soil.
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1999. Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites.
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1995. Technical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in Groundwater, Vols.
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