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Remediation Technologies Screening Matrix, Version 4.0 4.30 Natural Attenuation
(In Situ GW Remediation Technology)
  Description Synonyms Applicability Limitations Site Information Points of Contact
Data Needs Performance Cost References Vendor Info. Health & Safety
Table of Contents
Technology>>Ground Water, Surface Water, and Leachate

>>3.9 In Situ Biological Treatment

      >>4.30 Monitored Natural Attenuation
Introduction>> Natural subsurface processes—such as dilution, volatilization, biodegradation, adsorption, and chemical reactions with subsurface materials—are allowed to reduce contaminant concentrations to acceptable levels.


Figure 4-30:
Typical Monitoring Well Construction Diagram
Natural subsurface processes such as dilution, volatilization, biodegradation, adsorption, and chemical reactions with subsurface materials are allowed to reduce contaminant concentrations to acceptable levels. Natural attenuation is not a "technology" per se, and there is significant debate among technical experts about its use at hazardous waste sites. Consideration of this option usually requires modeling and evaluation of contaminant degradation rates and pathways and predicting contaminant concentration at down gradient receptor points, especially when plume is still expanding/migrating. The primary objective of site modeling is to demonstrate that natural processes of contaminant degradation will reduce contaminant concentrations below regulatory standards or risk-based levels before potential exposure pathways are completed. In addition, long term monitoring must be conducted throughout the process to confirm that degradation is proceeding at rates consistent with meeting cleanup objectives.

Natural attenuation is not the same as "no action," although it often is perceived as such. CERCLA requires evaluation of a "no action" alternative but does not require evaluation of natural attenuation. Natural attenuation is considered in the Superfund program on a case-by-case basis, and guidance on its use is still evolving. 

Compared with other remediation technologies, natural attenuation has the following advantages:

  • Less generation or transfer of remediation wastes;
  • Less intrusive as few surface structures are required;
  • May be applied to all or part of a given site, depending on site conditions and cleanup objectives;
  • Natural attenuation may be used in conjunction with, or as a follow-up to, other (active) remedial measures; and
  • Overall cost will likely be lower than active remediation.

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Intrinsic Remediation; Bioattenuation; Intrinsic Bioremediation; Monitored Natural Attenuation (MNA).
DSERTS Code: F3 (Natural Attenuation)

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Target contaminants for natural attenuation are VOCs and SVOCs and fuel hydrocarbons. Fuel and halogenated VOCs are commonly evaluated for natural attenuation. Pesticides also can be allowed to naturally attenuate, but the process may be less effective and may be applicable to only some compounds within the group. Additionally, natural attenuation may be appropriate for some metals when natural attenuation processes result in a change in the valence state of the metal that results in immobilization (e.g., chromium).

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Factors that may limit applicability and effectiveness include:
  • Data used as input parameters for modeling need be collected.
  • Intermediate degradation products may be more mobile and more toxic than the original contaminant.
  • Natural attenuation is not appropriate where imminent site risks are present.
  • Contaminants may migrate before they are degraded.
  • Institutional controls may be required, and the site may not be available for reuse until contaminant levels are reduced.
  • If free product exists, it may have to be removed.
  • Some inorganics can be immobilized, such as mercury, but they will not be degraded.
  • Long term monitoring and associated costs.
  • Longer time frames may be required to achieve remediation objectives, compared to active remediation.
  • The hydrologic and geochemical conditions amenable to natural attenuation are likely to change over time and could result in renewed mobility of previously stabilized contaminants and may adversely impact remedial effectiveness; and
  • More extensive outreach efforts may be required in order to gain public acceptance of natural attenuation.

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Data Needs:

A detailed discussion of these data elements is provided in Subsection 2.2.2. (Data Requirements for Groundwater, Surface Water, and Leachate).

The extent of contaminant degradation depends on a variety of parameters, such as contaminant types and concentrations, temperature, moisture, and availability of nutrients/electron acceptors (e.g., oxygen, nitrate).

Although many potential suppliers perform the modeling, sampling, and sample analysis required for monitoring natural attenuation, the evaluation of natural attenuation is often not straightforward and will require expertise in several technical areas including microbiology/bioremediation, hydrogeology, and geochemistry. When available, information to be obtained during data review includes:

  • Soil and ground water quality data:
    • Three-dimensional distribution of residual-, free-, and dissolved-phase contaminants. The distribution of residual- and free-phase contaminants will be used to define the dissolved-phase plume source area.
    • Historical water quality data showing variations in contaminant concentrations through time.
    • Chemical and physical characteristics of the contaminants.
    • Geochemical data to assess the potential for biodegradation of the contaminants.
  • Location of potential receptors:
    • Ground water wells.
    • Surface water discharge points.

The operation and maintenance (O&M) duration is determined from natural attenuation evaluation and regulatory requirements. The process is expected to continue for several years until desired degradation levels are achieved. The duration of O&M is dependent on all of the data and information listed above.

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Performance Data:

Natural attenuation has been selected by AFCEE for remediation at 45 sites.

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There are costs for modeling and monitoring. Modeling determines whether natural attenuation is a feasible remedial alternative. The most significant costs associated with natural attenuation are most often due to monitoring requirements, which include two major parts - site characterization and performance monitoring. Site characterization determines the extent of contamination and contaminant degradation rates. Performance monitoring tracks down contaminants migration and degradation and cleanup status.

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Treatment Technologies for Site Cleanup: Annual Status Report (ASR), Tenth Edition, EPA 542-R-01-004

Innovative Remediation Technologies:  Field Scale Demonstration Project in North America, 2nd Edition

Remediation Technology Cost Compendium - Year 2000

Treatment Experiences at RCRA Corrective Actions, December 2000, EPA 542-F-00-020

Abstracts of Remediation Case Studies, Volume 4,  June, 2000, EPA 542-R-00-006

Guide to Documenting and Managing Cost and Performance Information for Remediation Projects - Revised Version, October, 1998, EPA 542-B-98-007

NATO/CCMS Pilot Study on Evaluation of Demonstrated and Emerging Technologies for the Treatment and Clean Up of Contaminated Land and Groundwater (Phase II Final Report)

A Citizen's Guide to Monitored Natural Attenuation (English Version), EPA 542-F-01-004

An overview of this technology, including installation protocols, provided by the Air Force Center for Environmental Excellence (AFCEE) is located at
American Society For Testing and Materials(ASTM), 1998, Guide for Remediation by Natural Attenuation, E 1943-98.

Barker, J.F., et al., 1987. "Natural Attenuation of Aromatic Hydrocarbons in a Shallow Sand Aquifer," Groundwater Monitoring Review, Winter 1987.

Bredehoeft, J.D., and L.F. Konikow, 1993. "Ground-Water Models - Validate or Invalidate," Ground Water, Vol. 31, No. 2, pp. 178-179.

Bruce, L., T. Miller, and B. Hockman, 1991. "Solubility Versus Equilibrium Saturation of Gasoline Compounds - A Method To Estimate Fuel/Water Partition Coefficient Using Solubility or Koc", in Proceedings of the NWWA/API Conference on Petroleum Hydrocarbons in Ground Water, A. Stanley, Editor, NWWA/API, pp. 571-582.

Chiang, C.Y., J.P. Salanitro, E.Y. Chai, J.D. Colthart, and C.L. Klein, 1989. "Aerobic Biodegradation of Benzene, Toluene, and Xylene in a Sandy Aquifer - Data Analysis and Computer Modeling", Ground Water, Vol. 27, No. 6, pp. 823-834.

EPA, 1994. Natural Attenuation of Hexavalent Chromium in Groundwater and Soils, EPA/540/S-94/505.

EPA, 1995. Natural Bioattenuation of Trichloroethene at the St. Joseph, Michigan Superfund Site. Project Summary, EPA/600/SV-95/001.

EPA, 1997.  Bioremediation of BTEX, Naphthalene, nad Phenanthrene in Aquifer Material Using Mixwed Oxygen/Nitrate Electron Acceptor Conditions, EPA/600/SR-97/120.

EPA, 1997. Federal Register Notice - 62 FR 64588-64589 Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites; OSWER Directive 9200.4-17; Interim Final.

EPA, 1997. Proceedings of the Symposium on Natural Attenuation of Chlorinated Organics in Ground Water, EPA/540/R-97/504.

EPA, 1997. Symposium on Natural Attenuation of Ground Water, EPA/540/R-97/504.

EPA, 1997. Use of Monitored Natural Attentuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites, OSWER Directive 9200.4-17.

EPA, 1998. Handouts from the Monitored Natural Attenuation seminars conducted by EPA Office of Research and Development. EPA/625/K-98/001.

EPA, 1998. Issues Associated With Natural Attenuation, EPA/OUST.

EPA, 1998. Monitoring and Assessment of In-Situ Biocontainment of Petroleum Contaminated Ground-Water Plumes. Project Summary EPA/600/SR-98/020.

EPA, 1998. Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water, EPA/600/R-98/128.

Lee, M.D., 1988. "Biorestoration of Aquifers Contaminated with Organic Compounds," CRC Critical Reviews in Environmental Control, Vol. 18, pp. 29-89.

Lorah, M.M., L. D. Olsen, B.L. Smith, M.A. Johnson, and W.B. Fleck, 1997. Natural Attenuation of Chlorinated Volatile Organic Compounds in a Freshwater Tidal Wetland, Aberdeen Proving Ground, Maryland, USGS/WRIR-97-4171.

MacIntyre, W.G., M. Boggs, C.P. Antworth, and T.B. Staufer, 1993. "Degradation Kinetics of Aromatic Organic Solutes Introduced into a Heterogeneous Aquifer," Water Resources Research, Vol. 29, No. 12, pp. 4045-4051.

Vroblesky, D.A., M.D. Petkewich, P.M. Bradley, and J.F. Robertson, 1998. Natural Attenuation Assessment of Contaminated Ground Water at a Gas-Turbine Manufacturing Plant, Greenville, South Carolina (Abstract), USGS/WRIR-98-4165.

Weidemeier, T.H., P.R. Guest, R.L. Henry, and C.B. Keith, 1993. "The Use of BIOPLUME to Support Regulatory Negotiations at a Fuel Spill Site Near Denver, Colorado," in Proceedings of the Petroleum Hydrocarbons and Organic Chemicals in Groundwater Prevention, Detection, and Restoration Conference, NWWA/API, pp. 445-449.

Weidemeier, T.H., B. Blicker, and P.R. Guest, 1994b. "Risk-Based Approach to Bioremediation of Fuel Hydrocarbons at a Major Airport," in Proceedings of the Federal Environmental Restoration III & Waste Minimization Conference & Exhibition.

Weidemeier, T.H., D.C. Downey, J.T. Wilson, D.H. Kampbell, R.N. Miller, and J.E. Hansen, 1994. "Technical Protocol for Implementing the Intrinsic Remediation (Natural attenuation) with Long-Term Monitoring Option for Dissolved-Phase Fuel Contamination in Ground Water", AFCEE, San Antonio, TX.

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Site Information:

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Points of Contact:

General FRTR Agency Contacts

Technology Specific Web Sites:

Government Web Sites

Non Government Web Sites

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Vendor Information:

A list of vendors offering In Situ Biological Water Treatment is available from  EPA REACH IT which combines information from three established EPA databases, the Vendor Information System for Innovative Treatment Technologies (VISITT), the Vendor Field Analytical and Characterization Technologies System (Vendor FACTS), and the Innovative Treatment Technologies (ITT), to give users access to comprehensive information about treatment and characterization technologies and their applications.

Government Disclaimer

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Health and Safety:

To be added

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