Natural Attenuation
Guidance
A Decision Flowchart for the Use of Monitored Natural Attenuation and Enhanced Attenuation at Sites with Chlorinated Organic Plumes
Interstate Technology & Regulatory Council (ITRC) Enhanced Attenuation/Chlorinated Organics Team. 13 pp, 2007
The flowchart provides a mechanism for transitioning sites through the remediation process, supports decision-making by regulators and site managers, and can be used to determine site remedial change from MNA to active remediation through enhanced attenuation (EA) technologies. EA is a plume remediation strategy to achieve ground-water restoration goals by providing a 'bridge' between MNA and more aggressive methods.
A Decision Framework for Applying Monitored Natural Attenuation Processes to Metals and Radionuclides in Groundwater
Interstate Technology & Regulatory Council (ITRC), Attenuation Processes for Metals and Radionuclides Team. APMR-1, 204 pp, December 2010
Provides a decision framework incorporating key aspects of EPA's three-volume technical background series on MNA for metals and rads in groundwater, guidance on approaches and key issues associated with evaluating attenuation-based remedies, and a process to incorporate enhanced attenuation.
A Framework for Assessing the Sustainability of Monitored Natural Attenuation
Chapelle, F.H., Novak, John, Parker, John, Campbell, B.G., and Widdowson, M.A., 2007, 35 p.
The U.S. Geological Survey, in cooperation with the Strategic Environmental Research and Development Program (SERDP) and Virginia Tech University, has developed a framework for assessing the long-term sustainability of monitored natural attenuation at hazardous waste cleanup sites. The framework consists of methods for assessing the balance between the delivery of contaminants to the environment and their natural attenuation. This methodology, recently published as U.S. Geological Survey Circular 1303, provides environmental planners and managers with a quantitative plan for using monitored natural attenuation as the solution for cleaning up hazardous waste sites.
An Approach for Evaluating the Progress of Natural Attenuation in Groundwater
EPA 600-R-11-204, 2011
The purpose of this document is to present a simple, statistically based approach for evaluating the progress of natural attenuation from the data collected during site characterization and long term monitoring. The intended audience is technical professionals that actually perform the data analyses (i.e., hydrogeologists, engineers) as well as project managers who review those analyses and/or make decisions based on those analyses.
Applicability of Monitored Natural Attenuation at Radioactively Contaminated Sites
IAEA Technical Reports Series No. 445, STI/DOC/010/445, 105 pp, 2006
This report discusses in detail the necessary prerequisites, processes involved, applicability, and limits of MNA as a strategy for dealing with radioactive contamination in the subsurface. The text covers migration and retention mechanisms, the geochemistry of selected radionuclides, data availability and uncertainty, and modeling approaches for assessing MNA potential. Radionuclide geochemistry is described for uranium, neptunium, technetium, cesium, strontium, thorium, radium, and lead.
Aqueous and Mineral Intrinsic Bioremediation Assessment (AMIBA) Protocol (Draft)
2000. Kennedy, L.; J. Everett; J. Gonzales, HQ AFCEE/ER, 286 pp.
Assessment of the Natural Attenuation of NAPL Source Zones and Post-Treatment NAPL Source Zone Residuals
Johnson, P., R. Ekre, R. Krajmalnik-Brown, B. Rittman, P. Lundegard, and R. Hinchee.
ESTCP Project ER-200705, 416 pp, 2013
This project demonstrated a generalized data-driven paradigm for the assessment of source zone natural attenuation (SZNA) at CAHs cleanup sites. The method uses multiple lines of evidence and macroscopic mass balances, leading to confirmation of SZNA and quantification of the total mass loss rate resulting from degradation, dissolved-phase transport, and volatilization. Application of the method was demonstrated at three field sites, with multiple events per site spread out over 3 years. The mass loss rates were relatively consistent over time for each site, but varied from site to site, ranging between 1-10 kg/y at two sites and as high as ~600 kg/y at the third site.
Attenuation Pathways for Munitions Constituents in Soils and Groundwater
Rectanus, H., R. Darlington, K. Kucharzyk, and S. Moore.
TR-NAVFAC EXWC-EV-1503, 81 pp, 2015
This report summarizes recent research findings related to munitions constituent (MC) attenuation pathways in soil and groundwater and discusses lessons learned from monitored natural attenuation and bioremediation applications for MC at DoD sites. The report's scope includes MC issues; physical, chemical, and biological attenuation pathways; technology applications; and eight case studies.
Biogeochemical Transformation Handbook
Darlington , R. and H. Rectanus.
TR-NAVFAC EXWC-EV-1601, 41 pp, 2015
In situ biogeochemical transformation (ISBGT) processes result in the degradation of contaminants through combined biological, mineral, and chemical pathways. This handbook can serve as a key resource in evaluating, selecting, and implementing the ISBGT technology. The handbook presents the fundamentals of ISBGT in a question and answer format; explores the mechanisms that contribute to ISBGT processes; discusses contaminants that can be degraded by ISBGT; identifies key considerations for enhancing, monitoring, and evaluating ISGBT processes; and emphasizes the importance of site characterization in recognizing and accounting for the contributions of ISBGT to natural attenuation.
Calculation and Use of First-Order Rate Constants for Monitored Natural Attenuation Studies. Ground Water Issue
2002. C.J. Newell, et al. EPA 540-S-02-500, 28 pp.
Characterization and Monitoring of Natural Attenuation of Chlorinated Solvents in Ground Water: A Systems Approach, Revision 1
Tyler Gilmore (PNNL); B.B. Looney (SRNL); et al.
WSRC-STI-2006-00084, 65 pp, Aug 2006
Commonly Asked Questions Regarding the Use of Natural Attenuation at Federal Facilities
These pages were developed through a partnership among the U.S. EPA, Air Force, Army, Navy, and Coast Guard. Both chlorinated solvent spills and petroleum-contaminated sites are addressed.
Compatibility of Alternative Chlorinated Solvent Source Treatment Strategies with Monitored Natural Attenuation
2004. Brian B. Looney and Karen M. Vangelas. WSRC-MS-2004-00236, 22 pp.
Delivery and Mixing in the Subsurface: Processes and Design Principles for In Situ Remediation
Kitanidis, P.K. and P.L. McCarty (eds.).
Springer, New York. ISBN: 978-1-4614-2238-9. SERDP-ESTCP Environmental Remediation Technology, Vol. 4, 325 pp, 2012
This technology monograph describes the principles of chemical delivery and mixing systems and their design and implementation for effective in situ remediation. In situ technologies discussed include chemical oxidation, surfactant/cosolvent flushing, subsurface reactors, recirculation systems, PRBs, gas delivery via sparging, and intrinsic remediation in natural-gradient systems. Numerous case studies are provided. Table of contents and abstracts.
Designing Monitoring Programs to Effectively Evaluate the Performance of Natural Attenuation
2000. Wiedemeier, Todd H.; Mary A. Lucas; Patrick E. Haas, AFCEE/ERT, 55 pp.
Determining Source Attenuation History to Support Closure by Natural Attenuation
Newell, C., D. Adamson, T. Sale, B. Parker, and S. Chapman.
ESTCP Project ER-201032, 426 pp, Sep 2013
An innovative approach for reconstructing the contaminant concentration vs. time trend—i.e., the "source history"—for a site uses high-resolution soil data from low permeability zones. Soil cores in these zones essentially serve a similar role as tree rings in that the cores store information about historic environmental conditions. In cases where contaminants have migrated into low permeability zones via diffusion and slow advection, the concentration vs. depth profile can be used to determine if attenuation of the contaminant source in the overlying transmissive zones has occurred--an important line of evidence for evaluating the viability of MNA for site management. Source histories reconstructed at two sites at Naval Air Station Jacksonville illustrate the use of a simple and free software model—the ESTCP Source History Tool. See also the ESTCP Cost and Performance Report
Development of a Quantitative Framework for Evaluating Natural Attenuation of 1,1,1-TCA, 1,1-DCA, 1,1- DCE, and 1,4-Dioxane in Groundwater
Danko, A., D. Adamson, C. Newell, J. Wilson, B. Wilson, D. Freedman, and C. Lebron. ESTCP Project ER-201730, 360 pp, 2021
The objectives of this project were to 1) develop a modified model and framework to evaluate natural attenuation of,1,1-TCA, 1,1-DCA, and 1,1-DCE; 2) develop and validate a protocol to directly measure rate constants for natural biodegradation of 1,4-dioxane using 14C-labeled 1,4-dioxane and groundwater from 10 different field sites; and 3) use the field and lab data to establish if there is consistency between various lines of evidence for 1,4-dioxane attenuation. A new fate and transport model was developed to evaluate historical monitoring data to predict biodegradation rate constants and new decision matrices (flowcharts) guide how to interpret potential lines of evidence for MNA. The tools were then integrated into an existing software platform (BioPIC) that allows users to access the model and the decision matrices. Several approaches were used to generate input data to support and validate the model and framework. Collecting the necessary data and performing a comprehensive MNA evaluation at a single site using the project deliverables was estimated to cost ~$30,000. This assessment could result in substantial savings if the use of MNA is justified versus more aggressive remedies. No regulatory or procurement issues are anticipated during implementation, and end-user concerns are minimal since data can be collected during a single mobilization without disruption to site activities. Additional information: MNA Rate Constant Estimator User's Guide and Tool.
Draft Protocol for Evaluating, Selecting, and Implementing Monitored Natural Attenuation at Explosives-Contaminated Sites
1999. J.C. Pennington; R. Bowen; J.M. Brannon; M. Zakikhani; D.W. Harrelson, Army Engineer Waterways Experiment Station, Vicksburg, MS. WES/TR/EL-99-10, NTIS: ADA369244, 156 pp.
Draft Technical Protocol for Characterizing Natural Attenuation of Chlorinated Solvent Ground-Water Plumes Discharging into Wetlands
Environmental Security Technology Certification Program, ESTCP Project CU-9913, 53 pp, 2006
Enhanced Attenuation: A Reference Guide on Approaches to Increase the Natural Treatment Capacity of a System
Early, T., B. Borden, M. Heitkamp, B.B. Looney, D. Major, W.J. Waugh, G. Wein, T. Wiedemeier, K.M. Vangelas, K.M. Adams, and C.H. Sink.
WSRC-STI-2006-00083, Revision 1, 161 pp, Aug 2006
This guide covers the following EA approaches: (1) hydraulic manipulation to reduce contaminant infiltration using low-permeability barriers, diffusion barriers, covers, encapsulation, and diversion of electron acceptors; (2) passive residual source reduction (e.g., bioventing); (3) increase in system attenuation capacity via biological processes, such as bioaugmentation, biostimulation, and wetlands development and other plant-based methods; (4) abiotic and biologically mediated abiotic attenuation methods; and (5) reactive barriers.
Enhanced Attenuation: Chlorinated Organics
Interstate Technology & Regulatory Council (ITRC), Enhanced Attenuation: Chlorinated Organics Team.
EACO-1, 109 pp, 2008
This guidance contains a protocol to assist in a smooth transition between aggressive remedial actions and MNA. This transition is based on the concept of enhanced attenuation, which encompasses an evaluation of mass balance, a decision framework to provide guidance for site decisions, and a toolbox of potential technologies that optimize aquifer conditions to provide a sustainable treatment or minimize the energy needed to reduce contaminant loading and/or increase the attenuation capacity of an aquifer.
Environmental Molecular Diagnostics: New Site Characterization and Remediation Enhancement Tools
Interstate Technology & Regulatory Council (ITRC), Environmental Molecular Diagnostics
Team. EMD-2, 363 pp, Apr 2013
EMD technologies can be classified into two major categories of analytical techniques: chemical technologies (i.e., CSIA), and different molecular biological techniques. A detailed description of each major EMD is illustrated with case studies of their application and recommendations regarding appropriate uses. Frequently asked questions regarding the underlying science, including stable isotope chemistry and fundamental molecular biology, are addressed in the appendices. Also available as a PDF file
Estimating Cleanup Times Associated with Combining Source-Area Remediation with Monitored Natural Attenuation
M. Widdowson, F. Chapelle, C. Casey, and M. Kram.
NFESC TR-2288-ENV, 192 pp, 2008
U.S. EPA guidance specifically requires a reasonable time frame for MNA to achieve site-specific cleanup objectives; thus, it is necessary to provide estimates of cleanup times whenever MNA is proposed as part of a cleanup strategy. The U.S. Navy, USGS, and Virginia Tech have developed Natural Attenuation Software (NAS) as a screening tool designed for estimating time of remediation for MNA with varying degrees of source area remediation. This report describes the software and the results of its use at 8 sites contaminated primarily with chlorinated ethenes.
Field-Scale Evaluation of Monitored Natural Attenuation for Dissolved Chlorinated Solvent Plumes
AFCEE, 455 pp, 2009
This report 1) presents a strategy and framework for quantitatively assessing the sustainability of MNA-based remedies for groundwater at chlorinated solvent-impacted sites, 2) provides case-study reviews using existing long-term monitoring data sets from multiple U.S. Air Force sites where chlorinated solvents exceed closure criteria, and 3) summarizes observations and recommendations that were developed when working through the case study examples. The 3 principal components of the sustainability assessment framework described in this report are analysis of plume stability, estimation of remediation timeframes, and estimation of the longevity of specific chlorinated aliphatic hydrocarbon degradation processes.
Framework for Site Characterization for Monitored Natural Attenuation of Volatile Organic Compounds in Ground Water
Pivetz, B.E., D. Abshire, W. Brandon, S. Mangion, B. Roberts, B. Stuart, L. Vanderpool, B. Wilson, and S.D. Acree.
EPA 600-R-12-712, 89 pp, 2012
Site characterization is essential to provide site-specific data and interpretations to determine if site remedial goals can be met with MNA in appropriate remedial time frames, and to provide site-specific data and interpretations to determine the necessary performance monitoring parameters, locations, and frequency for monitoring. A broad overview of technical issues includes development of a conceptual site model, characterization variables, sampling locations and frequencies, problematic issues encountered at MNA sites and approaches to overcome them, and the interpretations related to the MNA decision-making process.
Frequently Asked Questions about Monitored Natural Attenuation in Groundwater
Adamson, D. and C. Newell.
ESTCP Project ER-201211, 91 pp, 2014
This new report covers MNA as an evolving technology, the basis for MNA, new contaminants for the MNA lineup, new techniques and tools, emerging issues for evaluating MNA as a remedy, and implementation and site closure. See also the Web-based interactive version.
Ground Water Issue Paper: Synthesis Report on State of Understanding of Chlorinated Solvent Transformation
Pivetz, B., A. Keeley, E. Weber, J. Weaver, J. Wilson, and C. Ma.
EPA 600-R-13-237, 44 pp, 2013
This paper summarizes the biotic and abiotic transformations of chlorinated solvents used at industrial and dry-cleaning facilities: PCE, TCE, TCA, and daughter products. It briefly describes the factors that affect the transformation mechanisms as well as the measurements necessary to distinguish among the mechanisms. The paper serves as a guide for developing an advanced groundwater transport model, with governing equations for simulating these processes in models.
Guidance Protocol: Application of Nucleic Acid-Based Tools for Monitoring Monitored Natural Attenuation (MNA), Biostimulation, and Bioaugmentation at Chlorinated Solvent Sites
ESTCP Project ER-0518, 34 pp, 2011
This protocol summarizes the current state of the practice of molecular biological tools (MBTs), specifically nucleic-acid based tools commercially available to identify relevant Dehalococcoides bacteria. It is intended to provide a technically sound and practical approach to MBT use. This document provides recommendations regarding sampling approaches and criteria in evaluation of data for use in bioremediation decision making. See also the Project ER-0518 Final Report and the ESTCP Cost and Performance Report.
Guidance for Monitoring Passive Groundwater Remedies Over Extended Time Scales
Fritz, B.G., M.J. Truex, V.L. Freedman, C. Bagwell, R.J. Cameron, J. Counts, L.E. Martino, K.C. Picel, J. Quinn, and E.Y. Yan. Pacific Northwest National Laboratory, 66 pp, 2020
This document provides guidance for implementing an extended-scale monitoring (ESM) approach appropriate for long-duration passive remediation. It is intended to facilitate the development of site-specific monitoring plans that consider local site conditions and the selection of appropriate monitoring techniques. ESM applies to slow-moving groundwater contaminant plumes and emphasizes monitoring primarily of potential exposure pathways. The nature of an ESM plan is not to fully understand the dynamics of plume behavior. Rather, ESM confirms that the plume stays within the controlled zone and verifies that the plume behaves as predicted, consistent with the conceptual site model. A standard monitoring tool may be implemented in a nontraditional manner to verify performance. Alternatives to standard monitoring techniques such as well-based sampling and analysis may also be appropriate for some aspects of ESM. A portfolio of approaches is described in this document, including sampling methods currently under development that may reduce costs associated with long-term monitoring.
Guidance for Using Compound Specific Isotope Analysis (CSIA) to Document the Biodegradation and Natural Attenuation of RDX
Hatzinger, P., P.K van Groos, M. Fuller, and N.C. Sturchio.
ESTCP Project ER-201208, 40 pp, 2019
This project developed and validated a CSIA method to confirm and constrain rates of aerobic and anaerobic biodegradation of RDX at field sites. This technique can be utilized to provide critical data to support monitored natural attenuation as a remedy for treating this energetic in groundwater and to confirm the effectiveness of in situ enhanced bioremediation remedies when implemented.
Guidance on Natural Attenuation for Petroleum Releases
2003. Wisconsin Dept. of Natural Resources. PUB-RR-614, 104 pp.
Guidance on Natural Source Zone Depletion
CL:AIRE (Contaminated Land: Applications in Real Environments), Reading. ISBN 978-1905046-44-7, 98 pp, 2024
This document captures recent advances in natural source zone depletion (NSZD) alongside a decision-making framework to provide technical guidance for practitioners, regulators, and liability owners on the science and practical considerations for the application of NSZD-based risk management strategies in the UK. The framework is a three-stage procedure designed to mesh with existing risk management procedures. The stepwise framework includes 1) Screening NSZD feasibility by confirming that LNAPL and NSZD processes do not pose risks to receptors, and evaluating technical, practical, economic, sustainability, and regulatory constraints; 2) Demonstrating that the NSZD rate can achieve remediation objectives, through good quality data collection supporting defensible conceptualization of NSZD processes; and 3) Implementing a long-term performance monitoring program to confirm that NSZD continues to be protective of receptors and capable of achieving remediation objectives, resulting in eventual closure of risk-management measures for LNAPL.
Guidance on Remediation of Petroleum-Contaminated Ground Water by Natural Attenuation
Washington State Department of Ecology, Toxics Cleanup Program.
Publication 05-09-091, 143 pp, 2005.
Guidance on the Assessment and Monitoring of Natural Attenuation of Contaminants in Groundwater
CL:AIRE (Contaminated Land: Applications in Real Environments), Reading. ISBN 978-1-905046-42-3, 137 pp, 2024
This guidance updates the UK Environment Agency's technical guidance for monitored natural attenuation (MNA) published in 2000. It captures significant scientific advances that have been made in understanding contaminant behavior and reactive transport in the subsurface, alongside ongoing developments in site characterization, monitoring, and predictive modeling approaches and technologies. These evolving methods enhance contaminant and process-specific understanding required to develop advanced conceptual site models for MNA, addressing complexities and uncertainties that were previously challenging to deal with.
Historical and Retrospective Survey of Monitored Natural Attenuation: Lines of Inquiry Supporting Monitored Natural Attenuation and Enhanced Passive Remediation of Chlorinated Solvents
2004. T.M. McGuire, C.J. Newell, B.B. Looney, and K.M. Vangelas. WSRC-TR-2003-00333, Rev. 1, 96 pp.
Implementing Monitored Natural Attenuation and Expediting Closure at Fuel-Release Sites
2004. J.S. Brauner, D.C. Downey, J.R. Hicks, B.M. Henry, J.E. Hansen. Air Force Center for Environmental Excellence Technology Transfer and Defense Logistics Agency. NTIS: ADA426387, 247 pp.
This text is an addendum to the Technical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in Groundwater (AFCEE, 1995). The 1995 AFCEE protocol is to be retained, with this addendum providing expanded guidance on developing and implementing expedited closure plans and formal exit strategies for fuel-release sites.
Management of Large Dilute Plumes of Chloroethenes and 1,4-Dioxane via Monitored Natural Attenuation (MNA) and MNA Augmentation
Rhea, L.K. and C. Clark. Remediation 32(1-2):97-118(2022)
This article summarizes EPA research on monitored natural attenuation (MNA) of CVOC plumes produced in the past twenty years, including evidence of the biological degradation of dioxane. Based on the summarized reports, EPA work documented elsewhere, and the work of others, under appropriate conditions, MNA or augmented MNA remain viable management options for CVOC plumes. Unlike MNA of plumes containing only CVOCs, however, MNA of large dilute comingled plumes should be expected to occur by cometabolic oxidation rather than direct metabolic processes.
Manual for Biological Remediation Techniques
International Centre for Soil and Contaminated Sites, 81 pp, 2006
Provides an initial overview of selected organic contaminants, describes their susceptibility to microbial degradation in soil and groundwater, and reviews their treatment potential by land farming, biobeds, bioreactors, bioslurping, bioventing, biosparging, bioscreen, bioaugmentation, and monitored natural attenuation. Monitoring of bioremediation progress is also discussed.
Mass Balance: A Key to Advancing Monitored and Enhanced Attenuation For Chlorinated Solvents
B.B. Looney, K. Vangelas, K.M. Adams, F.H. Chappelle, T.O. Early, and C.H. Sink.
WSRC-STI-2006-00082, 91 pp, 2006
This report introduces the mass balance concept, examines the contributions and significance of various components of the mass balance, and provides an initial assessment of promising development areas.
Methodology for Estimating Times of Remediation Associated with Monitored Natural Attenuation
2003
This report outlines a method for estimating timeframes required for natural attenuation processes, such as dispersion, sorption, and biodegradation, to lower contaminant concentrations and mass to predetermined regulatory goals in groundwater systems. The time-of-remediation (TOR) problem described in this report is formulated as three interactive components: (1) estimating the length of a contaminant plume once it has achieved a steady-state configuration from a source area of constant contaminant concentration, (2) estimating the time required for a plume to shrink to a smaller, regulatoryacceptable configuration when source-area contaminant concentrations are lowered by engineered methods, and (3) estimating the time needed for nonaqueous phase liquid (NAPL) contaminants to dissolve, disperse, and biodegrade below predetermined levels in contaminant source areas.
Methyl tert-Butyl Ether (MTBE): Its Movement and Fate in the Environment and Potential for Natural Attenuation
1999. Parsons Engineering Science, Inc., 221 pp.
This report presents an overview of the physical and chemical characteristics of MTBE, summarizes the literature regarding its degradation, and provides recommendations for data collection and analysis in support of natural attenuation supplemented with long-term monitoring for restoration of ground water contaminated with MTBE.
Microbial Mineralization of cis-Dichloroethene and Vinyl Chloride as a Component of Natural Attenuation of Chloroethene Contaminants under Conditions Identified in the Field as Anoxic
Bradley, P.M.
U.S. Geological Survey Scientific Investigations Report 2012-5032, 41 pp, 2012
Oxygen-based microbial mineralization of DCE and VC can be substantial under field conditions characterized as anoxic. A modified framework is detailed for assessing the potential importance of oxygen during chloroethene biodegradation.
Monitored Natural Attenuation
2004. Chapter IX in How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers. U.S. EPA, Office of Underground Storage Tanks, EPA 510-R-04-002, 77 pp.
Monitored Natural Attenuation Technical Guidance
New Jersey Department of Environmental Protection, Site Remediation Program, 175 pp, 2012
This technical guidance discusses MNA of organic compounds (particularly petroleum hydrocarbons and chlorinated solvents), inorganics, and radionuclides for groundwater sites in New Jersey. Numerous references are listed for additional information, and excerpts from selected references are provided in the appendices.
Monitored Natural Attenuation of Inorganic Contaminants in Ground Water, Volume 1: Technical Basis for Assessment
EPA 600-R-07-139, 2007
Volume 1 of 3 consists of three sections that describe 1) the conceptual background for natural attenuation for inorganic contaminants, 2) the technical basis for attenuation of inorganic contaminants in ground water, and 3) approaches to site characterization to support evaluation of MNA. Emphasis is placed on characterization of immobilization and/or degradation processes that may control contaminant attenuation, as well as technical approaches to assess performance characteristics of the MNA remedy. A tiered analysis approach is presented to assist in organizing site characterization tasks in a manner designed to reduce uncertainty in remedy selection.
In a separate chapter for each listed contaminant, Volume 2 of 3 describes (1) the natural immobilization or degradation processes that can result in the attenuation of the contaminant and (2) data requirements to be met during site characterization. The document emphasizes characterization of immobilization and/or degradation processes that may control contaminant attenuation, as well as technical approaches to assess performance characteristics of the MNA remedy. A tiered analysis approach is presented to assist in organizing site characterization tasks.
In a separate chapter for each listed contaminant, Volume 3 of 3 describes (1) the natural radioactive decay or immobilization processes that can result in the attenuation of the contaminant and (2) data requirements to be met during site characterization. The document emphasizes characterization of immobilization and/or radioactive decay processes that may control contaminant attenuation or flux reduction, as well as technical approaches to assess performance characteristics of the MNA remedy. A tiered analysis approach is presented to assist in organizing site characterization tasks.
Monitored Natural Attenuation of MTBE as a Risk Management Option at Leaking Underground Storage Tank Sites
J.T. Wilson, P.M. Kaiser, and C. Adair, U.S. EPA, National Risk Management Research Laboratory, Ada, OK. EPA 600-R-04-179, 89 pp, Jan 2005
This report reviews the current state of knowledge on the transport and fate of MTBE in ground water, with emphasis on the natural processes that can be used to manage the risk associated with MTBE in ground water or that contribute to natural attenuation of MTBE as a remedy. It provides recommendations on the site characterization data necessary to manage risk or to evaluate monitored natural attenuation (MNA) of MTBE, and it illustrates procedures that can be used to work up data to evaluate risk or assess MNA at a specific site. The information is intended to allow state regulators to determine whether they have adequate information to evaluate MNA of fuel oxygenates at a site and to allow the regulators to separate sites where MNA of fuel oxygenates may be an appropriate risk management alternative from sites where MNA is not appropriate.
Monitored Natural Attenuation of Tertiary Butyl Alcohol (TBA) in Ground Water at Gasoline Spill Sites
J.T. Wilson and C. Adair.
EPA 600-R-07-100, 55 pp, 2007
Although TBA generally is considered to be more readily degradable in ground water than MTBE, a close examination of the available information indicates that a default presumption that TBA is readily degraded in anaerobic ground water is not justified. The authors review the prospects for using monitored natural attenuation to manage the risk from TBA in ground water at gasoline spill sites.
Monitored Natural Attenuation to Manage PFAS Impacts to Groundwater: Potential Guidelines
Newell, C.J., D.T. Adamson, P.R. Kulkarni, B.N. Nzeribe, J.A. Connor, J. Popovic, and H.F. Stroo | Remediation 31(4):7-17(2021)
Guidelines based on a three-tiered line of evidence (LOE) approach were developed to evaluate MNA at PFAS-impacted groundwater sites using the scientific basis described in a companion paper. The approach applies direct and indirect measurements, calculations, and field and modeling methods to assess PFAS retention in the subsurface. The paper identifies data requirements to assess LOEs to quantify retention in both the vadose and saturated zones and provides tools that can be used to address key questions about PFAS MNA. Finally, the paper lists potential methods to enhance PFAS MNA for sites where MNA alone may not effectively manage PFAS.
Monitoring and Assessment of In-Situ Biocontainment of Petroleum Contaminated Ground-Water Plumes
EPA 600-R-98-020, 1998. NTIS: PB98-145329, 218 pp.
Multiple Lines of Evidence for Estimating NSZD Rates Overlying A Shallow LNAPL Source Zone
Wozney, A., I. Hers, K. Stevenson, C. Campbell, N. Nickerson, and C. Gosse.
Groundwater Monitoring & Remediation 42(3):86-104(2022) [Abstract]
An applied research and development program was conducted at a former refinery site over 4 years to study quantitative technologies for evaluating natural source zone depletion (NSZD) of petroleum hydrocarbon LNAPL present within a shallow soil zone. Discrete CO2 efflux measurements from dynamic closed chambers were compared with estimates obtained using static traps and continuous monitoring using forced diffusion technology. Thermistor strings along a transect were used to monitor hourly thermal gradients and assess NSZD rates using the temperature gradient method. Discrete soil-gas data were used to quantify the vertical oxygen gradient to estimate NSZD rates using the concentration gradient method (CGM). Results of discrete and continuous monitoring methods provided monthly NSZD rate estimates that ranged seasonally from 80-1300 gal/acre/year using radiocarbon corrected CO2 efflux method for decane (C10H22) equivalent, 120 to 1600 gal/acre/year using CGM (for wet to dry conditions) and 400-2000 gal/acre/year using the temperature gradient method. Both seasonal temperature and precipitation fluctuations contributed to variability in rates.
Natural Attenuation General Data Guide
1999. M.L. Kram; F. Goetz, Naval Facilities Engineering Service Center, Port Hueneme, CA. NAVFAC-UG-2035-ENV, NTIS: ADA361097, 38 pp.
This guide is a decision-making tool to help remedial project managers (RPMs) determine whether natural attenuation can be used as a remedial option at contaminant release sites. Data requirements and methodology to evaluate the potential for using natural attenuation are presented. Tables of commonly measured parameters, general data collection rationale, and interpretation guidance are included to help the RPM recognize data gaps, interpret data, construct a conceptual site model, and develop a sampling and analysis plan for evaluation and monitoring purposes.
Natural Attenuation of Chlorinated Solvents in Groundwater: Principles and Practices
1999. Interstate Technology and Regulatory Cooperation (ITRC) Working Group. 117 pp.
Natural Attenuation of Metals and Radionuclides -- An Overview of the Sandia/ DOE Approach
1998. R.D. Waters; P.V. Brady; D.J. Borns. SAND--98-0415C, NTIS: DE98003135, 14 pp.
Sandia National Laboratories is developing guidelines that outline the technical basis for relying on natural attenuation for the remediation of metals and radionuclide-contaminated soils and groundwaters at DOE sites for those specific cases where natural processes are effective at ameliorating soil and ground-water toxicity.
Natural Attenuation of Perchlorate in Groundwater: Processes, Tools and Monitoring Techniques: Protocol Report
M.T. Lieberman and R.C. Borden.
ESTCP, Project ER-0428, 80 pp, 2008
This document provides information on fate, transport, and transformation of perchlorate in different geochemical environments; emerging and/or specialized technologies for evaluating perchlorate attenuation in groundwater; and a tiered approach for evaluating MNA of perchlorate.
Natural Source Zone Depletion (NSZD): From Process Understanding to Effective Implementation at LNAPL-Impacted Sites
Smith, J.W.N., G.B. Davis, G.E. DeVaull, S. Garg, C.J. Newell, and M.O. Rivett.
Quarterly Journal of Engineering Geology and Hydrogeology 55(4): qjegh2021-166(2022)
This paper summarizes the proceedings of a Special Session on natural source zone depletion (NSZD) research at the June 2021 virtual AquaConSoil conference. Investigations have focused on a range of hydrocarbon products, such as gasoline, diesel, jet fuel, and crude oil. Key NSZD processes include aerobic biodegradation, fermentation and methanogenesis of LNAPL constituents, dissolution of LNAPL constituents into groundwater and volatilization of LNAPL constituents into the unsaturated zone. Methanogenesis of organic materials has long been recognized in municipal landfills and natural anoxic environments, such as peat and wetlands. Recognition of similar processes in light non-aqueous phase liquid (LNAPL) source zones in the past decade and high rates of aerobic biodegradation observed in unsaturated zones above LNAPL-impacted areas has significantly revised the conceptual model of LNAPL source zone behavior and persistence. Several NSZD monitoring approaches have been developed and are being applied in field studies. While the quantitative NSZD rates derived can vary between techniques, they all demonstrate that NSZD LNAPL removal can exceed that delivered by engineered LNAPL recovery techniques, particularly for mature LNAPL bodies.
Natural and Enhanced Attenuation of Chlorinated Solvents Using RT3D
C.D. Johnson, M.J. Truex, and T.P. Clement.
PNNL-15937, 77 pp, 2006
This document describes the context for applying RT3D (Reactive Transport in 3 Dimensions) to monitored natural attenuation of chlorinated solvent contamination in ground water. It also discusses dechlorination reactions that may occur and the general approach for using RT3D reaction modules (including a summary of the RT3D reaction modules that are available) to model fate and transport of chlorinated solvents as part of MNA or for combinations of MNA and selected types of active remediation.
Performance Monitoring of MNA Remedies for VOCs in Ground Water
EPA 600-R-04-027, 2004
This document provides technical recommendations regarding the types of monitoring parameters and analyses useful for evaluating the effectiveness of the natural attenuation component of ground-water remedial actions. The information will be helpful during the design of the performance monitoring plan as well as during its implementation.
Providing Additional Support for MNA by Including Quantitative Lines of Evidence for Abiotic Degradation and Co-metabolic Oxidation of Chlorinated Ethylenes
Wiedemeier, T.H., J.T. Wilson, D.L. Freedman, and B. Lee.
ESTCP Project ER-201584, 632 pp, 2017
This report shows that an inexpensive downhole sonde (probe) can be used in existing 2- and 4-inch PVC groundwater monitoring wells to quantify magnetic susceptibility of aquifer material. Objectives are to (1) provide a method to readily and inexpensively acquire the magnetic susceptibility data required to evaluate the abiotic degradation of TCE by magnetite in aquifer materials using existing non-metallic groundwater monitoring wells, and (2) provide a method to readily and inexpensively acquire the data required to evaluate and quantify the rate constant for aerobic biological co-oxidation of TCE. Additional information: ESTCP Cost and Performance Report
Remedy Evaluation Framework for Inorganic, Non-Volatile Contaminants in the Vadose Zone
Truex, M.J. and K.C. Carroll.
PNNL-21815; RPT -DVZ-AFRI-004 , 67 pp, 2013
This report presents a remedy evaluation framework that uses an adaptation of the established EPA MNA evaluation approach and a conceptual model-based approach focused on identifying and quantifying features and processes that control contaminant flux through the vadose zone. Structuring evaluation of vadose zone waste sites to use an MNA-based approach provides information necessary to either select MNA as the remedy, if appropriate, or to quantify how much additional attenuation would need to be induced by a remedial action to augment the natural attenuation processes and meet groundwater protection goals.
Remedy Selection and Optimization Considerations for Monitored Natural Attenuation
Naval Facilities Engineering Command fact sheet, 6 pp, November 2022
Monitored natural attenuation (MNA) is a remedial option for monitoring the reduction of concentration, toxicity, and/or mobility of chemicals in groundwater. MNA can serve as a standalone remedy or be implemented as part of a treatment train through a transition from active treatment to a more passive treatment approach over time. Several lines of evidence are needed to achieve regulatory acceptance when selecting MNA as a primary remedy or transitioning to MNA as part of remedy optimization. This fact sheet shares lessons learned related to gathering robust lines of evidence to accelerate regulatory acceptance of MNA as a viable remedial approach.
Scenarios Evaluation Tool for Chlorinated Solvent MNA
M.J. Truex, C.J. Newell, B.B. Looney, and K.M. Vangelas.
WSRC-STI-2006-00096, Revision 2, 194 pp, 2007
This approach presents a framework that links the MNA evaluation and associated decision logic to key site characteristics and known NA phenomena. The tool consists of a user's guide and 13 scenarios built around general site and hydrogeologic conditions.
Screening of the Bacterial Reductive Dechlorination Potential of Chlorinated Ethenes in Contaminated Aquifers: A Technical Assistance Manual for Assessment of Natural Attenuation of Chloroethenes ‐ Contaminated Sites
Tarnawski, S.-E., P. Rossi, and C. Holliger.
Swiss Federal Office for Environment, 86 pp, 2016
The original contribution of this methodology is the use of statistics derived from numerical ecology tools for analysis of the physicochemistry and bacteriological status of a contaminated aquifer.
Site Characterization to Support Use of Monitored Natural Attenuation for Remediation of Inorganic Contaminants in Ground Water
R.G. Ford, R.T. Wilkin, and S. Acree.
EPA 600-R-08-114, 16 pp, 2008
This Issue Paper highlights at what stage of the process solid-phase characterization techniques need to be implemented during site characterization and describes two case studies (one site affected by arsenic, lead, and chromium, and the other by uranium) where the results of these techniques were critical to evaluation of MNA as a potential component of ground-water cleanup.
Standardized Procedures for Use of Nucleic Acid-Based Tools: Recommendations for Groundwater Sampling and Analysis Using qPCR
Lebron, C., P. Dennis, C. Acheson, N. Barros, D. Major, E. Petrovskis, F. Loeffler, K. Ritalahti,
C. Yeager, E. Edwards, J. Hatt, and D. Ogles. SERDP Project ER-1561, 12 pp, 2014
SERDP project ER-1561 focused on identifying and minimizing the causes of variability during quantitative real-time polymerase chain reaction (qPCR) enumeration of genes of interest in groundwater, with the goal of developing of the knowledge needed to standardize methods for collecting, preserving, transporting, storing, and processing environmental samples for qPCR analysis. This document summarizes the project conclusions and recommends procedures for using qPCR analyses that will provide data of sufficient accuracy and reproducibility to allow site management decisions regarding bioremediation or MNA. Further details are available in the ER-1561 Final Report (Lebron et al. 2014, 220 pages).
Subsurface Contaminant Focus Area: Monitored Natural Attenuation (MNA) — Programmatic, Technical, and Regulatory Issues
2001. Krupka, K.M.; W.J. Martin, Pacific Northwest National Laboratory, Richland, WA.Report No: PNNL-13569, 138 pp.
Technical Guide: Monitored Natural Recovery at Contaminated Sediment Sites
V.S. Magar, D.B. Chadwick, T.S. Bridges, P.C. Fuchsman, J.M. Conder, T.J. Dekker, J.A. Steevens, K.E. Gustavson, and M.A. Mills.
ESTCP Project ER-0622, 276 pp, 2009
This technical guide focuses on the role of natural recovery processes in the remediation of contaminated sediments by providing case studies and generic examples to demonstrate concepts at work in real-world situations. This document provides a step-by-step conceptual primer for applying MNR at sediment sites.
Technical Measurement Guidance for LNAPL Natural Source Zone Depletion
CRC for Contamination Assessment and Remediation of the Environment, CRC CARE Technical Report No. 44, 281 pp, 2018
Natural source zone depletion (NSZD) is a term used to extend the traditional understanding of natural attenuation to the LNAPL source zone. NSZD describes the collective, naturally occurring processes of dissolution, volatilization, and biodegradation that result in mass losses of LNAPL petroleum hydrocarbon constituents from the subsurface. This document provides a knowledge base and procedures for consistency in the measurement of NSZD by a variety of methods, including aqueous, soil gas flux, biogenic heat, and LNAPL compositional change based on chemical analysis of oil.
Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water
EPA 600-R-98-128, 1998
Provides guidance for environmental managers on the steps that must be taken to understand the rate and extent to which natural processes are reducing contaminant concentrations at sites that are contaminated by chlorinated solvents. Data collected with this protocol can be used to evaluate natural attenuation through biological processes as part of a protective overall site remedy. The protocol is the result of a collaborative field and laboratory research effort involving researchers from U.S. EPA/ORD, the U. S. Air Force, and the U.S. Geological Survey.
Technical Protocol for Evaluating the Natural Attenuation of MtBE
API Publication 4761, 2007
Technical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in Groundwater, Vol. I
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 1, ADA324248, 323 pp.
This document presents a technical protocol for data collection and analysis in support of intrinsic remediation (natural attenuation) with long term monitoring (LTM) for restoration of ground water contaminated with fuel hydrocarbons. The protocol is designed to evaluate the fate in ground water of fuel hydrocarbons that have regulatory standards.
Technical Resource Document on Monitored Natural Recovery
U.S. EPA, National Risk Management Research Laboratory, Cincinnati, OH.
EPA 600-R-14-083, 251 pp, 2014
This technical resource document is designed to complement Chapter 4 on monitored natural recovery (MNR) in EPA's 2005 Contaminated Sediment Remediation Guidance for Hazardous Waste Sites by providing detailed information on field-scale methodologies and approaches that can be used to measure or predict natural processes that contribute to receptor risk reduction at contaminated sediment sites.
The Importance of Abiotic Transformations in Natural Attenuation of Contaminated Groundwater
Naval Facilities Engineering Systems Command, 4 pp, 2022
This fact sheet focuses on abiotic transformations in the natural attenuation of chlorinated ethenes in groundwater. For sites where active remediation has been in place for many years, documenting the occurrence of abiotic processes may facilitate a transition to monitored natural attenuation (MNA), defined by EPA as "the reliance on natural attenuation processes (within the context of a carefully controlled and monitored site cleanup approach) to achieve site-specific remediation objectives within a timeframe that is reasonable compared to that offered by other more active methods."
The Scenarios Approach to Attenuation-Based Remedies for Inorganic and Radionuclide Contaminants
Truex, M., P. Brady, C. Newell, M. Rysz, M. Denham, and K. Vangelas.
SRNL-STI-2011-00459, 111 pp, Aug 2011
This document was developed as a technical resource to guide interested parties through the process of evaluating attenuation-based remedies for sites contaminated with inorganic or radionuclide contaminants. The six scenarios are based on aquifer geochemical properties: oxidation-reduction potential, cation exchange capacity, and ferric iron oxide content. Section 1 steps the reader through using the scenarios approach, including how to choose a scenario, the parameters on which the scenarios are based, and worksheets to organize data. Section 2 discusses specific attenuation processes affecting contaminant mobility, shows how to use a scenario to develop a site conceptual model, discusses how to apply MNA and EA to specific scenarios, and ties the scenarios approach to U.S. EPA's four tiers of evidence for demonstrating MNA. Section 3 provides detail on attenuation mechanisms and development of conceptual models, discusses the EPA four-tiered approach in more detail, and includes additional information on geochemical reactions, monitoring, remediation, and costs. Appendix B contains a synopsis of mercury chemistry.
Understanding Chlorinated Hydrocarbon Behavior in Groundwater: Investigation, Assessment and Limitations of Monitored Natural Attenuation
2003. Wisconsin Department of Natural Resources. RR-699, 104 pp.
This Directive provides guidance to EPA staff, the public, and the regulated community on how EPA intends to exercise its discretion in implementing national policy on the use of Monitored Natural Attenuation for the remediation of contaminated soil and groundwater at sites regulated under Office of Solid Waste and Emergency Response (OSWER) programs.
Use of Monitored Natural Attenuation for Inorganic Contaminants in Ground Water at Superfund Sites
2015
This new MNA directive for inorganic contaminants expands on and is designed to be a companion to the 1999 MNA guidance. Both policy directives say that multiple lines of evidence should be obtained to evaluate the feasibility of including MNA in the site's selected response action as well as tiered analysis of site characteristics that control and sustain attenuation. This new guidance recommends a phased analytical approach tailored specifically for inorganic contaminants.
Using Advanced Analysis Approaches to Complete Long-Term Evaluations of Natural Attenuation Processes on the Remediation of Dissolved Chlorinated Solvent Contamination
J.S. Brauner, D.C. Downey, and R. Miller.
SERDP Project ER-1348, 462 pp, 2008
This report presents a strategy and framework for quantitatively assessing the sustainability of MNA-based remedies for groundwater at chlorinated solvent sites and summarizes observations and recommendations developed when working through the case studies. The case study reviews use existing long-term monitoring data sets from U.S. Air Force sites where chlorinated solvents exceed closure criteria. The described methods can also be used for the assessment of active remedies.
Verification of Methods for Assessing the Sustainability of Monitored Natural Attenuation (MNA)
Lebron, C.A., F.H. Chapelle, M.A. Widdowson, J.T. Novak, J.C. Parker, and M.A. Singletary.
ESTCP Project ER-0824, CR-NAVFAC EXWC-EV-1302, 109 pp, 2013
ESTCP funded a technology demonstration at 17 chlorinated solvent sites to validate an approach for assessing MNA sustainability based on three components: potentially bioavailable organic carbon (PBOC), the source zone depletion (SZD) function, and long-term sustainability (LTS) using PBOC and dissolved oxygen concentration data. The estimated cost for running a single PBOC test is $75 per sample. Additional information: ESTCP Cost & Performance Report; Project ER-200824 Final Debrief
