U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

For more information on Natural Attenuation, please contact:

Ed Gilbert
Technology Assessment Branch

PH: 202-566-0928 | Email:

Natural Attenuation


Adobe PDF LogoApplication of Monitored Natural Attenuation and Risk-Based Corrective Action at a Chlorinated-Hydrocarbon Contaminated Site for Risk Management
Dai W.C., T.T. Tsai, C.M. Kao, Y.M. Chang, and H.C. His.
Research Journal of Chemistry and Environment 16(3):87-97(2012)

This paper presents a case study of the feasibility of MNA for risk reduction of TCE and 1,1-DCE at a spill site. The objectives were to (1) evaluate the possible exposure routes and human health risks from the contaminated groundwater using tiered risk assessment approach; (2) apply the BIOCHLOR model to assess the effectiveness of natural attenuation for the contaminant plume; (3) apply probability and Monte Carlo analyses to develop more practical remediation goals; and (4) develop a realistic streamlined process and risk-based decision-making strategies for site management.

Adobe PDF LogoAssessment of Post Remediation Performance of a Biobarrier Oxygen Injection System at a Methyl Tert-Butyl Ether (MTBE)-Contaminated Site, Marine Corps Base Camp Pendleton, San Diego, California
Neil, K., T. Chaudhry, K.H. Kucharzyk, H.V. Rectanus, C. Bartling, P. Chang, and S. Rosansky.
ESTCP Project ER-201588, 284 pp, 2017

This project was conducted to evaluate the long-term performance of natural attenuation of MTBE after shutdown of a biobarrier system. The long-term impact of the biobarrier system on formation permeability was assessed via slug tests. In addition to evaluating data collected using conventional monitoring techniques, this project applied metagenomics and metaproteomics to improve the understanding of long-term impacts of the remedy on biodegradation at the site.

Benzene Degradation in Contaminated Aquifers: Enhancing Natural Attenuation by Injecting Nitrate (Abstract)
Muller, C., K. Knoller, R. Lucas, S. Kleinsteuber, R. Trabitzsch, H. Weiß, R. Stollberg, H.H. Richnow, and C. Vogt. Journal of Contaminant Hydrology 238:103759(2021)

A field experiment was conducted to stimulate benzene biodegradation by injecting nitrate (NO3) into a sulfidic benzene plume. The experiment aimed to recycle sulfate by nitrate-dependent sulfide oxidation and use NO3 as direct electron acceptor for benzene oxidation. Over 60 days, 6.74 tons of sodium nitrate were injected into the lower aquifer. Biogeochemical changes within the benzene plume were monitored for more than one year. Nitrate was microbiologically consumed, but benzene was not biodegraded by sulfate-reducing consortia. However, small carbon isotope fractionation of benzene suggested the presence of in situ benzene biodegradation processes in the plume, probably supported by nitrate. In conclusion, nitrate injection resulted in changing redox conditions and recycling of sulfate in the benzene plume due to microbial oxidation of reduced sulfur species, potentially leading to conditions favorable for in situ benzene biodegradation.

Adobe PDF LogoChallenges in Planning for Groundwater Remedy Transition at a Complex Site
O'Steen, W.N. and R.O. Howard, Jr. U.S. EPA Region 4, 12 pp, 2014

Complex groundwater contamination sites require comprehensive, structured groundwater monitoring in planning for transition to a new groundwater remedy. This paper provides as an example the Medley Farm Superfund site, a former waste solvent dump located in South Carolina. PCE, TCE, and their degradation products in the groundwater were addressed with pump and treat from 1995 to 2004. Between October 2004 and April 2012, injection of a lactate solution to promote enhanced reductive dechlorination (ERD) was conducted on multiple occasions, with positive responses in hydrogeochemistry and groundwater quality. In 2012, EPA issued an amended ROD, changing the groundwater remedy to ERD. MNA was selected as a contingency remedy in anticipation that as cleanup progresses, ERD may transition to MNA. Restructuring the site's monitoring and data evaluation program will enable EPA to discern treatment effects more clearly and facilitate MNA evaluation.

Adobe PDF LogoCharacterizing Natural Degradation of Tetrachloroethene (PCE) Using A Multidisciplinary Approach
Kesson, S.A., C.J. Sparrenbom, C.J. Paul, R. Jansson, and H. Holmstrand.
Ambio 50:1074-1088(2021)

Conventional groundwater analysis combined with compound-specific isotope data of carbon, microbial DNA analysis, and geoelectrical tomography techniques was used to investigate chlorinated solvents originating from a former drycleaning site in Sweden. The zone where natural degradation occurred was identified in the transition between two geological units, an observation confirmed by all methods. The change in hydraulic conductivity in this transition may have facilitated biofilm formation and microbial activity. The examination of the impact of geological conditions on the biotransformation process was facilitated by the unique combination of the applied methods. The extended array of investigation methods was thus beneficial with the potential to reduce remediation.

Delineation and Characterization of the Borden MTBE Plume: An Evaluation of Eight Years of Natural Attenuation Processes
1998. American Petroleum Institute (API). Publication no. 4668.

Evaluation of the Protocol for the Natural Attenuation of Chlorinated Solvents: Case Study at the Twin Cities Army Ammunition Plant
2001. Wilson, John T. (U.S. EPA, Subsurface Protection and Remediation Div., Ada, OK); Don H. Kampbell; Mark Ferrey (Site Remediation Section, Minnesota Pollution Control Agency, St. Paul); Paul Estuesta. Report No: EPA 600-R-01-025, 49 pp.

Expedited Approach to a Carbon Tetrachloride Spill Interim Remedial Action
1998. C. Cowdery; A. Primrose; J. Uhland; N. Castaneda. RFP-5191, NTIS: DE98003480, 8 pp.

Monitored natural attenuation was selected as an interim measure for a carbon tetrachloride spill at a Rocky Flats site where source removal or in situ treatment could not be implemented due to the surrounding infrastructure.

Field, Laboratory and Modeling Evidence for Strong Attenuation of a Cr(VI) Plume in a Mudstone Aquifer Due to Matrix Diffusion and Reaction Processes
Chapman, S., B. Parker, T. Al, R. Wilkin, D. Cutt, K. Mishkin, and S. Nelson. Soil Systems 5(18)(2021)

Both conventional and high-resolution field and laboratory methods were used to investigate processes that attenuate a Cr(VI) plume in sedimentary bedrock. Cr(VI) concentrations in the plume at a former industrial facility declined by more than three orders of magnitude over 900 m downgradient. Internal plume concentrations generally are stable or declining due to diffusive and reactive transport in the low-permeability matrix as fluxes from the source dissipate due to natural depletion and active remediation. The strong attenuation is attributed to diffusion from mobile groundwater in fractures to immobile porewater in the rock matrix and reactions causing transformation of aqueous Cr(VI) to low-solubility Cr(III) precipitates. Field characterization data for the fracture network and matrix properties were used to inform 2-D numerical model simulations that quantify attenuation due to diffusion and reaction processes. The field, laboratory, and modeling evidence demonstrate effects of matrix diffusion and reaction processes causing strong attenuation of a Cr(VI) plume in a sedimentary bedrock aquifer.

Adobe PDF LogoFive-Year Enhanced Natural Attenuation of Historically Coal-Tar-Contaminated Soil: Analysis of Polycyclic Aromatic Hydrocarbon and Phenol Contents
Telesinski1, A. and A. Kiepas-Kokot. ǀ International Journal of Environmental Research and Public Health 18:2265(2021)

A study assessed concentrations of phenols and PAHs following enhanced natural attenuation (ENA) at an industrial waste area where coal tar was processed. Soil in the investigation area was formed from a layer of uncompacted fill. Twelve sampling points were established to collect soil samples. A previous study did not detect heavy metals, BTEX, or cyanide concentrations though PAHs and phenols were detected at concentrations higher than permitted by Polish norms. Repeated analyses of phenols and PAHs were conducted in 2020 to determine ENA effectiveness. Results showed that ENA efficiently degraded phenols and naphthalene; concentrations were not elevated compared to the standards for industrial waste areas. The three- and four-ring hydrocarbons were degraded at a lower intensity. Based on the mean decrease in content following five years of ENA, the compounds can be arranged in the following order: phenols > naphthalene > phenanthrene > fluoranthene > benzo(a)anthracene > chrysene > anthracene.

Improving Long-Term Monitoring of Contaminated Groundwater at Sites Where Attenuation-Based Remedies are Deployed (Abstract)
Denham, M.E., M.B Amidon, H.M. Wainwright, B. Dafflon, J. Ajo-Franklin, and C.A. Eddy-Dilek. | Environmental Management 66:1142-1161(2020)

A long-term monitoring strategy is proposed for contaminated groundwater with residual contamination on the subsurface. The strategy focuses on measuring the hydrological and geochemical parameters that control attenuation or remobilization of contaminants while de-emphasizing contaminant-concentration measurements. The approach was demonstrated at a site in South Carolina where groundwater is contaminated by several radionuclides, and a comprehensive enhanced attenuation remedy was implemented to minimize discharge of contamination to surface water. The proposed long-term monitoring strategy combines subsurface and surface measurements using spectroscopic tools, geophysical tools, and sensors to monitor the parameters controlling contaminant attenuation. This approach can detect the possibility of contaminant remobilization from engineered and natural attenuation zones, allowing potential adverse changes to be mitigated before contaminant attenuation is reversed.

Adobe PDF LogoMonitored Natural Attenuation (MNA) of Contaminated Soils: State of the Art in Europe — A Critical Evaluation
Declercq, I., V. Cappuyns, and Y. Duclos.
Science of the Total Environment 426:393-405(2012)

This paper presents a snapshot of the state of the art for MNA implementation in six European countries, including a comparison between countries, an overview of some existing MNA cases, and relevant aspects related to return on experience. Although MNA is currently being applied in most of the study countries, some (e.g., Finland) still do not recognize it as an official remediation technique. This study also illustrates the differences in MNA approach that exist between countries, as well as the differences in application levels.

Adobe PDF LogoMonitored Natural Attenuation of Perchlorate in Groundwater: ESTCP Cost and Performance Report
ESTCP, Project ER-200428, 51 pp, 2010

To test the processes and methods needed to obtain lines of evidence to support MNA as a remedy for perchlorate-contaminated groundwater, this project applied the tiered approach developed and described in the 2008 perchlorate MNA protocol to two field demonstration sites in Maryland, the first at the Naval Surface Warfare Center, Indian Head, and the second at a manufacturing facility in Elkton where perchlorate commingled with TCE. Indian Head Site DemonstrationAdobe PDF Logo; Elkton Site DemonstrationAdobe PDF Logo

Adobe PDF LogoNATO/CCMS Pilot Study for the Evaluation of Demonstrated and Emerging Technologies for the Treatment and Clean Up of Contaminated Land and Groundwater (Phase III) 1999 Special Session: Monitored Natural Attenuation
EPA 542-R-99-008, 1999

This publication represents the proceedings of the Monitored Natural Attention Session in May 1999. This session was chaired by Fran Kremer, Ph.D. of the U. S. Environmental Protection Agency and Anja Sinke, Ph.D. from the Dutch TNO Institute of Environmental Science. It was presented at the second meeting of the Phase III Pilot Study.

Adobe PDF LogoNatural Attenuation and Biostimulation for In Situ Treatment of 1,2-Dibromoethane (EDB)
Koster van Groos, P., P. Hatzinger, G. Lavorgna, P. Philip, and T. Kuder. ESTCP Project ER-201331, 782 pp, 2022

The goals of this project were to improve understanding of EDB attenuation, particularly novel compound-specific isotope analysis tools, and determine whether biostimulation or bioaugmentation could effectively enhance in situ treatment of EDB. Improved methods to measure carbon isotope composition with low EDB concentrations were developed and applied. Differences in the isotopic composition of EDB among field samples provided valuable insights into EDB degradation processes. A lactate-based anaerobic in situ bioremediation approach was also applied in an impacted source area for chlorinated VOCs. The ISB effort aimed to demonstrate that higher EDB concentration source areas can be treated when attenuation processes are insufficient to protect receptors.

Natural Attenuation of a Chlorinated Ethene Plume Discharging to a Stream: Integrated Assessment of Hydrogeological, Chemical and Microbial Interactions
Ottosen, C.B., V. Ronde, U.S. McKnight, M.D. Annable, M.M. Broholm, J.F. Devlin, et al.
Water Research 186:116332(2020)

Several methods were combined in a multi-scale interdisciplinary in situ approach to assess and quantify the near-stream attenuation of a plume, primarily consisting of cDCE and VC that is discharging to a stream. Monitoring was conducted over seven years. At first, the site exhibited limited degradation from 2012-16 despite seemingly optimal conditions but presented notable degradation levels in 2019. A conceptualization of flow, transport, and processes clarified that hydrogeology was the main control on the natural attenuation, as short residence times of 0.5-37 days restricted the time in which dechlorination could occur. Longer Abstract

Adobe PDF LogoNatural Attenuation of Chlorinated Solvents: Performance and Cost Results From Multiple Air Force Demonstration Sites. Technology Demonstration Technical Summary Report
1999. Air Force Center for Environmental Excellence Technology Transfer Division, 101 pp.

Adobe PDF LogoNatural Attenuation of Chlorinated Volatile Organic Compounds in a Freshwater Tidal Wetland, Aberdeen Proving Ground, Maryland
1997. M.M. Lorah; L.D. Olsen; B.L. Smith; M.A. Johnson; W.B. Fleck, USGS. Publication WRI 97-4171, 108 pp.

Adobe PDF LogoNatural Attenuation of Fuel Hydrocarbons: Performance and Cost Results From Multiple Air Force Demonstration Sites. Technology Demonstration Technical Summary Report
1999. Air Force Center for Environmental Excellence Technology Transfer Division, 67 pp.

Natural Attenuation of Trichloroethene at the St. Joseph, Michigan, Superfund Site [video]
EPA 600-V-95-001, 1995

Request Video from SRIC (580-436-8651).

Proceedings: SNOWMAN Network Conference on Monitored Natural Attenuation, November 7, 2011, Salon du Relais, Paris

Six separate reports concerning the use of MNA in Belgium, Denmark, France, Germany, the Netherlands, and Sweden are included in the proceedings. A summary report inventories the significant differences observed among the countries in MNA definitions and implementation.

Pump and Treat and In Situ Bioremediation of Contaminated Groundwater at the French Ltd. Superfund Site, Crosby, Texas: Cost and Performance Report
1998. Federal Remediation Technologies Roundtable. 16 pp.

Adobe PDF LogoRegion 5 Monitored Natural Attenuation Report

This report describes a natural attenuation field study conducted jointly by the U. S. EPA Region 5, Wisconsin Department of Natural Resources (WDNR), the Illinois Environmental Protection Agency (IEPA), and Amoco Corporation (Amoco) since October 1994. To obtain the appendices to this report, please contact

Adobe PDF LogoSite-Specific Work Plan [Monitored Natural Attenuation]: Brown & Bryant Superfund Site, 600 South Derby Street, Arvin, California
U.S. Army Corps of Engineers (USACE), 68 pp, 2012

This plan describes the actual performance of the natural attenuation remedy. It is expected that by using a predictive model, the rate of attenuation of the contaminants of concern (1,2-dichloropropane, 1,3-dichloropropane, 1,2,3-trichloropropane, chloroform, Dinoseb, 1,2-dibromo-3-chloropropane, and ethylene dibromide) can be described, thus providing a measure to gauge progress. If monitoring data indicate that the contaminant levels do not continue to decline in accordance with expectation as defined by this model, USACE and EPA will reconsider the remedy decision.

Adobe PDF LogoTechnical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in Groundwater, Vol. II
1999. T. Wiedemeier; J.T. Wilson; D.H. Kampbell; R.N. Miller; J.E. Hansen, Air Force Center for Environmental Excellence (AFCEE) Technology Transfer Division, Brooks AFB, San Antonio, TX. Volume 2, ADA324247, 343 pp.

Volume II presents the results of intrinsic remediation demonstrations at Hill AFB, Utah, and Patrick AFB, Florida. Engineering evaluation/cost analyses (EE/CAs) were conducted to evaluate the use of intrinsic remediation (natural attenuation) with long-term monitoring (LTM) for remediation of BTEX contamination dissolved in ground water.

USGS Research on Variability in Composition of an Oil Spill After More Than 30 Years of Natural Attenuation
U.S. Geological Survey

The objective of the project is to improve the understanding of the mobilization, transport, and fate of crude oil in the shallow subsurface. The U.S. Geological Survey Toxic Substances Hydrology Program began an interdisciplinary research project in 1983 at the site of a crude-oil spill near Bemidji, Minnesota.