LECTURE 13MONITORED NATURAL ATTENUATIONMonitored Natural AttenuationHistorical development of MNA1988 Guidance on Ground Water1993 and 1994 – NRC Studies1995 – AFCEE Technical Protocol1996 – EPA Symposium on Natural Attenuation1996 – Draft Technical Protocol1997 – MNA Policy Directive1998 – MNA SeminarsDefinition of MNA (continued)Elements of Natural AttenuationComponents of MNADemonstrating efficacy of MNAAerobic biodegradation of fuel hydrocarbonsBiodegradation sequenceDenitrificationDenitrificationIron reductionIron reductionSulfate reductionMethanogenesis (Methane fermentation)MethanogenesisCarbon dioxide neutralizationAnalytical protocolAnalytical protocolAnalytical protocolAverage Relative Contribution of BTEX Biodegradation Processes in Site Ground Water at 42 sitesAverage Relative Contribution of BTEX Biodegradation Processes in Site Ground Water at 42 sitesTreatability Study Results (continued)BIOSCREENAnaerobic transformation of carbon tetrachlorideAbiotic degradation of TCAAnaerobic dechlorination of TCAAnaerobic degradation of PCE & TCEAnalytical protocolAnalytical protocolsExtent of Chlorinated Solvents and BTEXBTEX and Electron AcceptorsBTEX and Metabolic ByproductsChlorinated Solvents and ByproductsPlot of TCE, DCE, VC, and Ethene versus Distance DowngradientPlume ClassificationBIOCHLORDiffusive disappearanceLECTURE 13MONITORED NATURAL ATTENUATIONMonitored Natural AttenuationAs defined by U.S. EPA:reliance on natural processes to achieve site-specific remedial objectives Source: Pope, D. F., and J. N. Jones, 1999. Monitored Natural Attenuation of Chlorinated Solvents. U.S. EPA Remedial Technology Fact Sheet. Report Number EPA/600/F-98/022. Office of Research and Development, U.S. Environmental Protection Agency, Washington, D.C. May 1999. (http://www.epa.gov/ada/download/fact/chl-solv.pdf).Dispersionand DilutionSorptionChemical ReactionsVolatilization(Evaporation)BiodegradationProcesses ofNATURALATTENUATIONof Petroleum HydrocarbonsHistorical development of MNAHistorical development• 1985 – Always a remedial alternative: EPA says it was used in Superfund as early as 1985• 1988 – Guidance on Remedial Actions for Contaminated Ground Water at Superfund Sites discusses natural attenuation, but mostly as a comparison standard for active remediation. Natural attenuation is not encouraged• Began to be more commonplace with recognition of intractability of DNAPL cleanups and inadequacy of pump and treat technology• Simultaneously, there was increasing recognition that in situ processes were containing or cleaning up contamination• 1993-94 – Two key studies by National Research Council:• In Situ Bioremediation – When does it work? – 1993study discusses intrinsic bioremediation• Alternatives for Ground Water Cleanup – 1994• 1995 – Technical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in Groundwater• Prepared by Air Force Center for Environmental Excellence working with U.S. EPA research laboratory• Defines procedure to show intrinsic remediation is occurring• September 1996 – EPA Symposium on Natural Attenuation of Chlorinated Organics in Ground Water• November 1996 – Draft Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Groundwater (Final in Sept. 1998)• December 1997 – OSWER Policy Directive: Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites• Sept.-Dec. 1998 – EPA Seminars on Monitored Natural Attenuation in nine cities around the US1988 Guidance on Ground Water1993 and 1994 – NRC Studies"In Situ Bioremediation. When does it work?" National Research Council. "Alternatives for Ground Water Cleanup." National Research Council.1995 – AFCEE Technical ProtocolTechnical Protocol for Implementing IntrinsicRemediation with Long-Term Monitoring for Natural Attenuationof Fuel Contamination Dissolved in GroundwaterVolume 1ByTodd WiedemeierJohn T. Wilson and Donald H. KampbellRoss N. Miller and Jerry E. HansenAir Force Center for Environmental ExcellenceTechnology Transfer DivisionBrooks AFB, San Antonio, TexasParsons Engineering Science, Inc.Denver, ColoradoU.S. Environmental Protection AgencyRobert S. Kerr LaboratoryAda, OklahomaAir Force Center for Environmental ExcellenceTechnology Transfer DivisionBrooks AFB, San Antonio, Texas1996 – EPA Symposium on Natural Attenuation1996 – Draft Technical ProtocolNov. 1996 – DraftSept. 1998 - Final1997 – MNA Policy Directive1998 – MNA SeminarsDefinition of MNA (continued)May be physical, chemical or biologicalAct without human intervention to reduce the mass, toxicity, mobility, volume, or concentration of contaminants in soil or ground waterProcesses include:biodegradationdispersiondilutionsorptionvolatilizationchemical or biological stabilization, transformation, or destructionSource: Pope, D. F., and J. N. Jones, 1999. Monitored Natural Attenuation of Chlorinated Solvents. U.S. EPA Remedial Technology Fact Sheet. Report Number EPA/600/F-98/022. Office of Research and Development, U.S. Environmental Protection Agency, Washington, D.C. May 1999. (http://www.epa.gov/ada/download/fact/chl-solv.pdf).Elements of Natural AttenuationMNA is not:No-action alternativePresumptive or default remedyMNA must be:Evaluated along with other alternativesSelected only is it meets remediation objectivesWork in reasonable time frame (30 years)Used very cautiously as sole remedyComponents of MNARequired components of MNA:Source controlPerformance monitoringPrerequisite for MNA:Site-specific characterization data and analysisDemonstrating efficacy of MNA1. Historical chemical data showing clear trend of decreasing mass or concentration.2. Hydrogeologic or geochemical data that indirectly demonstrate natural attenuation processes3. Field or microcosm studies that directly demonstrate natural attenuation processesAerobic biodegradation of fuel hydrocarbonsOxygen used as electron acceptor2C6H6+ 15O2→ 12CO2+ 6H2OIndicators of biodegradation:Reduction in dissolved oxygen (3 mg DO needed to metabolize 1 mg of benzene)Reduction in hydrocarbon concentrationBiodegradation sequenceOrder of aerobic biodegradation:Ethyl benzeneTolueneBenzeneXyleneDenitrificationNitrate is electron acceptor6NO3–+ 6H++ C6H6→ 6CO2↑ + 6H2O + 3N2 ↑Actually occurs in multiple steps mediated by different bacteria:NO3 –→ NO2–→