Monitored Natural Attenuation (MNA) of Metal and Metalloids - Revision history

Admin at 20:40, 27 April 2022

2022-04-27T20:40:15Z

Jhurley at 19:31, 13 March 2020

2020-03-13T19:31:59Z

Jhurley: /* MNA as a Remedy Guidance */

2020-03-13T19:22:53Z

‎MNA as a Remedy Guidance

Jhurley: /* Attenuation of Metals and Metalloids */

2020-03-13T19:20:47Z

‎Attenuation of Metals and Metalloids

Jhurley: /* Attenuation of Metals and Metalloids */

2020-03-13T19:19:59Z

‎Attenuation of Metals and Metalloids

Jhurley: /* The Scenarios Approach to Attenuation-Based Remedies */

2020-03-13T19:15:17Z

‎The Scenarios Approach to Attenuation-Based Remedies

Jhurley at 15:40, 27 November 2019

2019-11-27T15:40:49Z

Admin: 1 revision imported

2018-05-04T20:57:36Z

1 revision imported

Admin: 1 revision imported

2018-05-04T20:53:46Z

1 revision imported

Admin: 1 revision imported

2018-05-04T20:50:27Z

1 revision imported

← Older revision		Revision as of 20:40, 27 April 2022
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−	'''~~CONTRIBUTOR~~(S):''' [[Dr. Miles Denham]] and [[Dr. Charles Newell, P.E.]]	+	'''Contributor(s):''' [[Dr. Miles Denham]] and [[Dr. Charles Newell, P.E.]]

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 Demonstrating that adsorption and/or precipitation are sufficiently limiting the mobility of a contaminant metal or metalloid is the strongest evidence that MNA is an appropriate remedy. Adsorption and precipitation may occur when a metal or metalloid enters groundwater because the contaminant, and often the composition of fluids carrying the contaminant, cause perturbations of the near steady-state condition of the groundwater system. This promotes reactions that tend to return the groundwater system toward its original state and these often result in contaminant adsorption, precipitation, or both.
-[[File:Denham-Article 3-Figure 1.PNG|thumb|600px|Figure 1. Typical contaminant plume evolution in an aquifer showing leading and trailing gradients<ref name= "ITRC2010"/>.]]
+[[File:Denham-Article 3-Figure 1.PNG|thumb| 600px | left |Figure 1. Typical contaminant plume evolution in an aquifer showing leading and trailing gradients<ref name= "ITRC2010"/>.]]
 Consider the evolution of a contamination plume in an aquifer (Figure 1). As contamination enters the aquifer, a ''geochemical gradient'' forms at the leading edge of the plume<ref name="Truex2011"/>. This leading gradient may simply be a concentration gradient of the contaminant, where the concentration is higher on the side of the plume opposite of the direction of flow. In many cases, the leading gradient also includes gradients in concentrations of other constituents associated with the contaminant source. For example, contamination plumes often have different pH, oxidation-reduction potential, or ionic strength than the native groundwater. In any event, reactions tend to occur that counter the geochemical gradient and can cause adsorption of the contaminant to aquifer mineral surfaces or precipitation of the contaminant.
 The rate of the reactions and the supply of reactants in the aquifer at the leading gradient of a contamination plume influence the rate at which the contamination plume moves. The supply of reactants includes the concentration of reactive minerals and the concentration of available adsorption sites and is called the aquifer attenuation capacity. Once the source of contamination has been eliminated, the migration rate of the leading edge or gradient of the contaminant plume will be zero or near zero if rates of adsorption or precipitation are fast relative to groundwater flow and attenuation capacity is sufficient to react with all the contamination in the aquifer<ref name= "USEPA2007V1"/><ref name="Truex2011"/><ref>Bekins, B., Rittmann, B.E. and MacDonald, J.A., 2001. Natural attenuation strategy for groundwater cleanup focuses on demonstrating cause and effect. Eos Trans. American Geophysical Union, 82(5), 53-58. [http://dx.doi.org/10.1029/01eo00028 doi: 10.1029/01EO00028]</ref>. These conditions are necessary for MNA to be a viable remedy for metal and metalloid contaminants.
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 ==MNA as a Remedy Guidance==
-[[File:Denham-Article 3-Table 1.PNG|550px|thumbnail|Table 1. Tiered four-phase approach to demonstrating MNA for inorganic compounds<ref name="EPA2015" />.]]In 2015, the U.S. EPA published guidance for use of MNA for inorganic contaminants<ref name="EPA2015" />. This approach and criteria for using MNA integrates the framework of guidance issued in 1999 on using MNA for organic contaminants<ref name="EPA2015"/> with the technical approaches for inorganic contaminants issued in 2007<ref name="EPA1999" />. Companion documents exist<ref name= "USEPA2007V1"/> that provide characterization and technical guidance to demonstrating MNA for specific nonradioactive inorganic contaminants<ref name="USEPA2007a"/> and radionuclides<ref name="USEPA2010"/>. In addition, the Interstate Technology and Regulatory Council published a Technical/Regulatory Guidance document that provides a decision framework for applying the EPA guidance, as well as providing the perspective of some state regulatory agencies and stakeholders<ref name= "ITRC2010"/>.
+In 2015, the U.S. EPA published guidance for use of MNA for inorganic contaminants<ref name="EPA2015" />. This approach and criteria for using MNA integrates the framework of guidance issued in 1999 on using MNA for organic contaminants<ref name="EPA2015"/> with the technical approaches for inorganic contaminants issued in 2007<ref name="EPA1999" />. Companion documents exist<ref name= "USEPA2007V1"/> that provide characterization and technical guidance to demonstrating MNA for specific nonradioactive inorganic contaminants<ref name="USEPA2007a"/> and radionuclides<ref name="USEPA2010"/>. In addition, the Interstate Technology and Regulatory Council published a Technical/Regulatory Guidance document that provides a decision framework for applying the EPA guidance, as well as providing the perspective of some state regulatory agencies and stakeholders<ref name= "ITRC2010"/>.
 The basis for demonstrating MNA for inorganic contaminants, such as metals and metalloids, is a tiered four-phase strategy (outlined in Table 1).
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 ==The Scenarios Approach to Attenuation-Based Remedies==
-[[File:Denham-Article 3-Table 2.PNG|thumb| 600 px|left|Figure 2. Six scenarios for evaluating inorganic monitored natural attenuation<ref name="Truex2011"/>.]]
+[[File:Denham-Article 3-Table 2.PNG|thumb| 550 px|left|Figure 2. Six scenarios for evaluating inorganic monitored natural attenuation<ref name="Truex2011"/>.]]
-[[File:Denham-Article 3-Figure 2.PNG|750px|thumbnail|right|Table 2. Summary of inorganic contaminant mobility for 4 < pH < 9 for six scenarios<ref name="Truex2011"/>.]]
+[[File:Denham-Article 3-Figure 2.PNG|650px|thumbnail|right|Table 2. Summary of inorganic contaminant mobility for 4 < pH < 9 for six scenarios<ref name="Truex2011"/>.]]
-[[File:MNA_of_metals.mp4 | 600px | left | Figure 3. The Scenarios Approach for MNA of Inorganics and Radionuclides.]]
+[[File:MNA_of_metals.mp4 | thumb | 550px | left | Figure 3. The Scenarios Approach for MNA of Inorganics and Radionuclides.]]
 In 2011, the U.S. Department of Energy published the “Scenarios Approach to Attenuation‐Based Remedies for Inorganic and Radionuclide Contaminants”<ref name="Truex2011"/> to serve as a technical resource to guide waste site owners, regulators, stakeholders, or other interested parties through the process of evaluating attenuation-based remedies for sites contaminated with inorganic or radionuclide contaminants. A structured approach is provided where:
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 There are six scenarios that are a function of three primary factors: oxidation/reduction potential (ORP); cation exchange capacity (CEC), and sediment iron oxide coatings and solids (Fig. 2). There are three primary factors and three secondary factors (pH, sulfur/sulfide, and total dissolved solids) that combine with the six scenarios to provide a semi-quantitative indicator of mobility (i.e., low mobility is defined as a retardation factor of 1000+) (Table 2). The Scenarios Approach for MNA of Inorganics and Radionuclides is explained in more detail in the [[Media:MNA_of_metals.mp4 | video]] shown in Figure 3.
+<br clear="left">
 ==References==

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 ==MNA as a Remedy Guidance==
-In 2015, the U.S. EPA published guidance for use of MNA for inorganic contaminants<ref name="EPA2015" />. This approach and criteria for using MNA integrates the framework of guidance issued in 1999 on using MNA for organic contaminants<ref name="EPA2015"/> with the technical approaches for inorganic contaminants issued in 2007<ref name="EPA1999" />. Companion documents exist<ref name= "USEPA2007V1"/> that provide characterization and technical guidance to demonstrating MNA for specific nonradioactive inorganic contaminants<ref name="USEPA2007a"/> and radionuclides<ref name="USEPA2010"/>. In addition, the Interstate Technology and Regulatory Council published a Technical/Regulatory Guidance document that provides a decision framework for applying the EPA guidance, as well as providing the perspective of some state regulatory agencies and stakeholders<ref name= "ITRC2010"/>.
+[[File:Denham-Article 3-Table 1.PNG|550px|thumbnail|Table 1. Tiered four-phase approach to demonstrating MNA for inorganic compounds<ref name="EPA2015" />.]]In 2015, the U.S. EPA published guidance for use of MNA for inorganic contaminants<ref name="EPA2015" />. This approach and criteria for using MNA integrates the framework of guidance issued in 1999 on using MNA for organic contaminants<ref name="EPA2015"/> with the technical approaches for inorganic contaminants issued in 2007<ref name="EPA1999" />. Companion documents exist<ref name= "USEPA2007V1"/> that provide characterization and technical guidance to demonstrating MNA for specific nonradioactive inorganic contaminants<ref name="USEPA2007a"/> and radionuclides<ref name="USEPA2010"/>. In addition, the Interstate Technology and Regulatory Council published a Technical/Regulatory Guidance document that provides a decision framework for applying the EPA guidance, as well as providing the perspective of some state regulatory agencies and stakeholders<ref name= "ITRC2010"/>.
 The basis for demonstrating MNA for inorganic contaminants, such as metals and metalloids, is a tiered four-phase strategy (outlined in Table 1).
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 Throughout these documents, it is repeatedly emphasized that MNA is not a “do nothing” remedy. This is certainly the case, given the burden of proof required to successfully demonstrate MNA as a viable remedy for metal and metalloid contamination.
 ==The Scenarios Approach to Attenuation-Based Remedies==

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 The rate of the reactions and the supply of reactants in the aquifer at the leading gradient of a contamination plume influence the rate at which the contamination plume moves. The supply of reactants includes the concentration of reactive minerals and the concentration of available adsorption sites and is called the aquifer attenuation capacity. Once the source of contamination has been eliminated, the migration rate of the leading edge or gradient of the contaminant plume will be zero or near zero if rates of adsorption or precipitation are fast relative to groundwater flow and attenuation capacity is sufficient to react with all the contamination in the aquifer<ref name= "USEPA2007V1"/><ref name="Truex2011"/><ref>Bekins, B., Rittmann, B.E. and MacDonald, J.A., 2001. Natural attenuation strategy for groundwater cleanup focuses on demonstrating cause and effect. Eos Trans. American Geophysical Union, 82(5), 53-58. [http://dx.doi.org/10.1029/01eo00028 doi: 10.1029/01EO00028]</ref>. These conditions are necessary for MNA to be a viable remedy for metal and metalloid contaminants.
-Another necessary condition for MNA viability is that the flux of contaminants from the zone of attenuation must be too low now and in the future to present a hazard. Just as there is a leading gradient of a contamination plume, there is also a trailing gradient (Fig. 1) caused by influx of native (“clean”) groundwater into the attenuation zone. If reactions in the trailing gradient cause contaminants to desorb or dissolve at a rate that produces a flux of contaminants from the attenuation zone that presents a hazard, then MNA is not a viable remedy.
+Another necessary condition for MNA viability is that the flux of contaminants from the zone of attenuation must be too low now and in the future to present a hazard. Just as there is a leading gradient of a contamination plume, there is also a trailing gradient (Figure 1) caused by influx of native (“clean”) groundwater into the attenuation zone. If reactions in the trailing gradient cause contaminants to desorb or dissolve at a rate that produces a flux of contaminants from the attenuation zone that presents a hazard, then MNA is not a viable remedy.
 Characterization and study of reactions in the leading geochemical gradient of a contaminant plume identify attenuation mechanisms and quantify attenuation capacity. Characterization and study of reactions in the trailing geochemical gradient determine whether attenuation will be long-lived enough for MNA to be viable as a remedy.

@@ Line 32: / Line 32: @@
 Demonstrating that adsorption and/or precipitation are sufficiently limiting the mobility of a contaminant metal or metalloid is the strongest evidence that MNA is an appropriate remedy. Adsorption and precipitation may occur when a metal or metalloid enters groundwater because the contaminant, and often the composition of fluids carrying the contaminant, cause perturbations of the near steady-state condition of the groundwater system. This promotes reactions that tend to return the groundwater system toward its original state and these often result in contaminant adsorption, precipitation, or both.
-Consider the evolution of a contamination plume in an aquifer (Fig. 1). As contamination enters the aquifer, a ''geochemical gradient'' forms at the leading edge of the plume<ref name="Truex2011"/>. This leading gradient may simply be a concentration gradient of the contaminant, where the concentration is higher on the side of the plume opposite of the direction of flow. In many cases, the leading gradient also includes gradients in concentrations of other constituents associated with the contaminant source. For example, contamination plumes often have different pH, oxidation-reduction potential, or ionic strength than the native groundwater. In any event, reactions tend to occur that counter the geochemical gradient and can cause adsorption of the contaminant to aquifer mineral surfaces or precipitation of the contaminant.
+[[File:Denham-Article 3-Figure 1.PNG|thumb|600px|Figure 1. Typical contaminant plume evolution in an aquifer showing leading and trailing gradients<ref name= "ITRC2010"/>.]]
+Consider the evolution of a contamination plume in an aquifer (Figure 1). As contamination enters the aquifer, a ''geochemical gradient'' forms at the leading edge of the plume<ref name="Truex2011"/>. This leading gradient may simply be a concentration gradient of the contaminant, where the concentration is higher on the side of the plume opposite of the direction of flow. In many cases, the leading gradient also includes gradients in concentrations of other constituents associated with the contaminant source. For example, contamination plumes often have different pH, oxidation-reduction potential, or ionic strength than the native groundwater. In any event, reactions tend to occur that counter the geochemical gradient and can cause adsorption of the contaminant to aquifer mineral surfaces or precipitation of the contaminant.
 The rate of the reactions and the supply of reactants in the aquifer at the leading gradient of a contamination plume influence the rate at which the contamination plume moves. The supply of reactants includes the concentration of reactive minerals and the concentration of available adsorption sites and is called the aquifer attenuation capacity. Once the source of contamination has been eliminated, the migration rate of the leading edge or gradient of the contaminant plume will be zero or near zero if rates of adsorption or precipitation are fast relative to groundwater flow and attenuation capacity is sufficient to react with all the contamination in the aquifer<ref name= "USEPA2007V1"/><ref name="Truex2011"/><ref>Bekins, B., Rittmann, B.E. and MacDonald, J.A., 2001. Natural attenuation strategy for groundwater cleanup focuses on demonstrating cause and effect. Eos Trans. American Geophysical Union, 82(5), 53-58. [http://dx.doi.org/10.1029/01eo00028 doi: 10.1029/01EO00028]</ref>. These conditions are necessary for MNA to be a viable remedy for metal and metalloid contaminants.

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 '''Related Article(s)''':
 *[[Metal and Metalloid Contaminants]]
 *[[Metals and Metalloids - Mobility in Groundwater]]
 *[[Metal and Metalloids - Remediation]]

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