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The mobility of [https://en.wikipedia.org/wiki/Metalloid '''metals and metalloids'''] (collectively referred to as “metals” in this article) in groundwater is fundamental to assessment of risk these contaminants pose, as well as their remediation. Mobile contaminants are more likely than less mobile contaminants to reach environmental receptors at concentrations that exceed risk-based levels. Geochemical gradients (such as changes in pH, redox potential, and ionic strength over time and space in a plume) cause partitioning of the contaminants to aquifer solids via adsorption and/or precipitation. This partitioning controls the mobility of metal contaminants in groundwater.  
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The heterogeneous distribution of munitions constituents, released as particles from munitions firing and detonations on military training ranges, presents challenges for representative soil sample collection and for defensible decision making. Military range characterization studies and the development of the incremental sampling methodology (ISM) have enabled the development of recommended methods for soil sampling that produce representative and reproducible concentration data for munitions constituents. This article provides a broad overview of recommended soil sampling and processing practices for analysis of munitions constituents on military ranges.  
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<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
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'''Related Article(s)''':  
  
'''Related Articles''':
 
  
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'''CONTRIBUTOR(S):'''  [[Dr. Samuel Beal]]
  
'''CONTRIBUTOR(S):''' [[Dr. Miles Denham]]
 
  
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'''Key Resource(s)''':
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*[[media:Taylor-2011 ERDC-CRREL TR-11-15.pdf| Guidance for Soil Sampling of Energetics and Metals]]<ref name= "Taylor2011">Taylor, S., Jenkins, T.F., Bigl, S., Hewitt, A.D., Walsh, M.E. and Walsh, M.R., 2011. Guidance for Soil Sampling for Energetics and Metals (No. ERDC/CRREL-TR-11-15). [[media:Taylor-2011 ERDC-CRREL TR-11-15.pdf| Report.pdf]]</ref>
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*[[Media:Hewitt-2009 ERDC-CRREL TR-09-6.pdf| Report.pdf | Validation of Sampling Protocol and the Promulgation of Method Modifications for the Characterization of Energetic Residues on Military Testing and Training Ranges]]<ref name= "Hewitt2009">Hewitt, A.D., Jenkins, T.F., Walsh, M.E., Bigl, S.R. and Brochu, S., 2009. Validation of sampling protocol and the promulgation of method modifications for the characterization of energetic residues on military testing and training ranges (No. ERDC/CRREL-TR-09-6). Engineer Research and Development Center / Cold Regions Research and Engineering Lab (ERDC/CRREL) TR-09-6, Hanover, NH, USA. [[Media:Hewitt-2009 ERDC-CRREL TR-09-6.pdf | Report.pdf]]</ref>
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*[[media:Epa-2006-method-8330b.pdf| U.S. EPA SW-846 Method 8330B: Nitroaromatics, Nitramines, and Nitrate Esters by High Performance Liquid Chromatography (HPLC)]]<ref name= "USEPA2006M">U.S. Environmental Protection Agency (USEPA), 2006. Method 8330B (SW-846): Nitroaromatics, Nitramines, and Nitrate Esters by High Performance Liquid Chromatography (HPLC), Rev. 2. Washington, D.C. [[media:Epa-2006-method-8330b.pdf | Report.pdf]]</ref>
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*[[media:Epa-2007-method-8095.pdf | U.S. EPA SW-846 Method 8095: Explosives by Gas Chromatography.]]<ref name= "USEPA2007M">U.S. Environmental Protection Agency (US EPA), 2007. Method 8095 (SW-846): Explosives by Gas Chromatography. Washington, D.C. [[media:Epa-2007-method-8095.pdf| Report.pdf]]</ref>
  
'''Key Resource(s):'''
 
 
 
==Introduction==
 
==Introduction==
Mobility of a contaminant is the rate at which the contaminant moves relative to the rate at which groundwater moves. Highly mobile contaminants move at rates near those of groundwater and travel from sources to receptors in the same timeframe as groundwater. Other contaminants are affected by geochemical reactions that cause them to partition to aquifer solids. The partitioning results in retardation of the contaminant transport relative to groundwater. The degree of retardation depends on the chemical nature of the contaminant, the chemical composition of the groundwater, and the mineralogy of the aquifer. Contaminants that are highly mobile under one set of aquifer conditions may be relatively immobile under different conditions<ref name="Truex2011">Truex, M., Brady,  P., Newell, C.J., Rysz, M., Denham, M., Vangelas, K. 2011. The scenarios approach to attenuation-based remedies for inorganic and radionuclide contaminants. Savannah-River National Laboratory U.S. Department of Energy. [http://www.environmentalrestoration.wiki/images/e/e3/TRUEX-2011-Scenarios_Approach_to_Attenuation-Based_Remedies.pdf Report pdf]</ref>.
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[[File:Beal1w2 Fig1.png|thumb|200 px|left|Figure 1: Downrange distance of visible propellant plume on snow from the firing of different munitions. Note deposition behind firing line for the 84-mm rocket. Data from: Walsh et al.<ref>Walsh, M.R., Walsh, M.E., Ampleman, G., Thiboutot, S., Brochu, S. and Jenkins, T.F., 2012. Munitions propellants residue deposition rates on military training ranges. Propellants, Explosives, Pyrotechnics, 37(4), pp.393-406. [http://dx.doi.org/10.1002/prep.201100105 doi: 10.1002/prep.201100105]</ref><ref>Walsh, M.R., Walsh, M.E., Hewitt, A.D., Collins, C.M., Bigl, S.R., Gagnon, K., Ampleman, G., Thiboutot, S., Poulin, I. and Brochu, S., 2010. Characterization and Fate of Gun and Rocket Propellant Residues on Testing and Training Ranges: Interim Report 2. (ERDC/CRREL TR-10-13. Also: ESTCP Project ER-1481)  [[media:Walsh-2010 ERDC-CRREL TR-11-15 ESTCP ER-1481.pdf| Report]]</ref>]]
 
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[[File:Beal1w2 Fig2.png|thumb|left|200 px|Figure 2: A low-order detonation mortar round (top) with surrounding discrete soil samples produced concentrations spanning six orders of magnitude within a 10m by 10m area (bottom). (Photo and data: A.D. Hewitt)]]
Aqueous [https://en.wikipedia.org/wiki/Speciation '''speciation'''] reactions, [https://en.wikipedia.org/wiki/Adsorption '''adsorption'''], and [https://en.wikipedia.org/wiki/Precipitation '''precipitation'''] control the partitioning of metals to aquifer solids, and hence their mobility. Adsorption and precipitation cause partitioning of the contaminant to aquifer solids and aqueous speciation reactions can strongly influence the extent to which adsorption and precipitation occur. These processes can be considered as chemical reactions in which constituents react to form products to the extent determined by equilibrium constants. Discussions of adsorption, precipitation and aqueous speciation can be found in most aqueous geochemistry textbooks (e.g., <ref name = "Stumm1981">Stumm, W., and Morgan J. J. 1981. Aquatic chemistry: An introduction emphasizing chemical equilibria in natural waters. John Wiley & Sons.</ref><ref name="Langmuir1997">Langmuir, D., 1997, Aqueous Environmental Geochemistry. Prentice-Hall, Inc. Upper Saddle River, NJ ISBN: 978-0023674129.</ref><ref name= "Dreverj">Drever, J.I., The Geochemistry of Natural Waters: Surface and Groundwater Environments. Prentice-Hall, Inc., ISBN 0132727900.</ref>) of and other references discuss how these apply to specific metals are available<ref name="Truex2011"/><ref>United States Environmental Protection Agency (USEPA), 2007. Monitored Natural Attenuation of Inorganic Contaminants in Groundwater, Volume 2 - Assessment for Non-Radionulcides Including Arsenic, Cadmium, Chromium, Copper, Lead, Nickel, Nitrate, Perchlorate, and Selenium, Edited by R.G. Ford, R.T. Wilkin, and R.W. Puls. U.S. Environmental Protection Agency, EPA/600/R-07/140. [http://www.environmentalrestoration.wiki/images/3/3a/USEPA-2007-MNA_of_Inorganic_Contaminants_in_GW%2C_Vol_2.pdf Report pdf]</ref><ref>U.S. Environmental Protection Agency (USEPA), 2007. Monitored natural attenuation of inorganic contaminants in groundwater, Volume 3 Assessment for Radionuclides Including Tritium, Radon, Strontium, Technetium, Uranium, Iodine, Radium, Thorium, Cesium, and Plutonium-Americium, Edited by R.G. Ford and R.T. Wilkin. U.S. Environmental Protection Agency, EPA/600/R-10/093. [http://www.environmentalrestoration.wiki/images/0/05/USEPA-2010-MNA_of_Inorganic_Contaminants_in_GW%2C_Vol_3.pdf Report pdf]</ref><ref>Wilkin, R.T., 2007. Metal attenuation processes at mining sites. Ground Water Issue. Environmental Protection Agency, EPA/600/R-07/092. [http://www.environmentalrestoration.wiki/images/d/d0/Wilkin-2007-Metal_Attenuation_Processes_at_Mining_Sites.pdf Report pdf]</ref>.
 
  
A discussion of reactions responsible for aqueous speciation, adsorption, and precipitation requires a brief discussion of equilibrium constants<ref>U.C. Davis, The Equilibrium Constant, found in http://chemwiki.ucdavis.edu/Core/Physical_Chemistry/Equilibria/Chemical_Equilibria/The_Equilibrium_Constant . Contributor: Heather Voigt.</ref> and activity. Any reaction:
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Munitions constituents are released on military testing and training ranges through several common mechanisms. Some are locally dispersed as solid particles from incomplete combustion during firing and detonation. Also, small residual particles containing propellant compounds (e.g., [[Wikipedia: Nitroglycerin | nitroglycerin [NG]]] and [[Wikipedia: 2,4-Dinitrotoluene | 2,4-dinitrotoluene [2,4-DNT]]]) are distributed in front of and surrounding target practice firing lines (Figure 1). At impact areas and demolition areas, high order detonations typically yield very small amounts (<1 to 10 mg/round) of residual high explosive compounds (e.g., [[Wikipedia: TNT | TNT ]], [[Wikipedia: RDX | RDX ]] and [[Wikipedia: HMX | HMX ]]) that are distributed up to and sometimes greater than) 24 m from the site of detonation<ref name= "Walsh2017">Walsh, M.R., Temple, T., Bigl, M.F., Tshabalala, S.F., Mai, N. and Ladyman, M., 2017. Investigation of Energetic Particle Distribution from High‐Order Detonations of Munitions. Propellants, Explosives, Pyrotechnics, 42(8), pp.932-941. [https://doi.org/10.1002/prep.201700089 doi: 10.1002/prep.201700089] [[media: Walsh-2017-High-Order-Detonation-Residues-Particle-Distribution-PEP.pdf| Report.pdf]]</ref>.
  
wA + xB = yC + zD
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Low-order detonations and duds are thought to be the primary source of munitions constituents on ranges<ref>Hewitt, A.D., Jenkins, T.F., Walsh, M.E., Walsh, M.R. and Taylor, S., 2005. RDX and TNT residues from live-fire and blow-in-place detonations. Chemosphere, 61(6), pp.888-894. [https://doi.org/10.1016/j.chemosphere.2005.04.058 doi: 10.1016/j.chemosphere.2005.04.058]</ref><ref>Walsh, M.R., Walsh, M.E., Poulin, I., Taylor, S. and Douglas, T.A., 2011. Energetic residues from the detonation of common US ordnance. International Journal of Energetic Materials and Chemical Propulsion, 10(2). [https://doi.org/10.1615/intjenergeticmaterialschemprop.2012004956 doi: 10.1615/IntJEnergeticMaterialsChemProp.2012004956] [[media:Walsh-2011-Energetic-Residues-Common-US-Ordnance.pdf| Report.pdf]]</ref>. Duds are initially intact but may become perforated or fragmented into micrometer to centimeter;o0i0k-sized particles by nearby detonations<ref>Walsh, M.R., Thiboutot, S., Walsh, M.E., Ampleman, G., Martel, R., Poulin, I. and Taylor, S., 2011. Characterization and fate of gun and rocket propellant residues on testing and training ranges (No. ERDC/CRREL-TR-11-13). Engineer Research and Development Center / Cold Regions Research and Engineering Lab (ERDC/CRREL) TR-11-13, Hanover, NH, USA. [[media:Epa-2006-method-8330b.pdf| Report.pdf]]</ref>. Low-order detonations can scatter micrometer to centimeter-sized particles up to 20 m from the site of detonation<ref name= "Taylor2004">Taylor, S., Hewitt, A., Lever, J., Hayes, C., Perovich, L., Thorne, P. and Daghlian, C., 2004. TNT particle size distributions from detonated 155-mm howitzer rounds. Chemosphere, 55(3), pp.357-367.[[media:Taylor-2004 TNT PSDs.pdf| Report.pdf]]</ref>
  
where w, x, y, and z are coefficients of the reaction stoichiometry and A, B, C, and D are chemical constituents, has an equilibrium constant that defines whether the reaction will tend to proceed to the right, to the left, or not at all. The important metric is this ratio:
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The particulate nature of munitions constituents in the environment presents a distinct challenge to representative soil sampling. Figure 2 shows an array of discrete soil samples collected around the site of a low-order detonation – resultant soil concentrations vary by orders of magnitude within centimeters of each other. The inadequacy of discrete sampling is apparent in characterization studies from actual ranges which show wide-ranging concentrations and poor precision (Table 1).
[[File:Denham-Article 2-Equation 1.PNG|150px|center]]
 
  
where α<sub>i</sub> is the activity (effective concentration; [https://en.wikipedia.org/wiki/Thermodynamic_activity thermodynamic activity]) of constituent i. When this ratio is less than the equilibrium constant, the reaction will tend to proceed to the left and vice versa. If the ratio equals the equilibrium constant, the reaction is at equilibrium and will not proceed in either direction. Most college level introductory chemistry textbooks will have a complete discussion of [https://en.wikipedia.org/wiki/Equilibrium_constant '''equilibrium constants'''] and activity<ref>Brown, T.L., H.E. LeMay, B.E. Bursten, and J.R. Burdge, 2015 13th Ed. Chemistry: The Central Science. Prentice Hall, Upper Saddle River, NJ. ISBN: 978-0321910417.</ref>.
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In comparison to discrete sampling, incremental sampling tends to yield reproducible concentrations (low relative standard deviation [RSD]) that statistically better represent an area of interest<ref name= "Hewitt2009"/>.
  
==Aqueous Speciation==
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{| class="wikitable" style="float: right; text-align: center; margin-left: auto; margin-right: auto;"
Single, or free, dissolved ions of metals and metalloids can combine with other dissolved ions to form different dissolved species, called aqueous complexes, with chemical properties different from the original ions. Metal contaminants form aqueous complexes with ions that are relatively abundant in groundwater. For example, the dissolved mercury ion Hg<sup>+2</sup> readily combines with the chloride ion under mildly acidic conditions by the reaction:
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|+ Table 1. Soil Sample Concentrations and Precision from Military Ranges Using Discrete and Incremental Sampling. (Data from Taylor et al. <ref name= "Taylor2011"/> and references therein.)
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! Military Range Type !! Analyte !! Range<br/>(mg/kg) !! Median<br/>(mg/kg) !! RSD<br/>(%)
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|-
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| colspan="5" style="text-align: left;" | '''Discrete Samples'''
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|-
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| Artillery FP || 2,4-DNT || <0.04 – 6.4 || 0.65 || 110
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|-
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| Antitank Rocket || HMX || 5.8 – 1,200 || 200 || 99
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|-
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| Bombing || TNT || 0.15 – 780 || 6.4 || 274
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|-
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| Mortar || RDX || <0.04 – 2,400 || 1.7 || 441
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|-
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| Artillery || RDX || <0.04 – 170 || <0.04 || 454
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|-
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| colspan="5" style="text-align: left;" | '''Incremental Samples*'''
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|-
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| Artillery FP || 2,4-DNT || 0.60 – 1.4 || 0.92 || 26
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|-
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| Bombing || TNT || 13 – 17 || 14 || 17
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|-
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| Artillery/Bombing || RDX || 3.9 – 9.4 || 4.8 || 38
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|-
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| Thermal Treatment || HMX || 3.96 – 4.26 || 4.16 || 4
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|-
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| colspan="5" style="text-align: left; background-color: white;" | * For incremental samples, 30-100 increments and 3-10 replicate samples were collected.
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|}
  
Hg<sup>+2</sup> + 2Cl<sup>-</sup> = HgCl<sub>2</sub><sup>o</sup> (where HgCl<sub>2</sub><sup>o</sup> is a dissolved species)
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==Incremental Sampling Approach==
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ISM is a requisite for representative and reproducible sampling of training ranges, but it is an involved process that is detailed thoroughly elsewhere<ref name= "Hewitt2009"/><ref name= "Taylor2011"/><ref name= "USEPA2006M"/>. In short, ISM involves the collection of many (30 to >100) increments in a systematic pattern within a decision unit (DU). The DU may cover an area where releases are thought to have occurred or may represent an area relevant to ecological receptors (e.g., sensitive species). Figure 3 shows the ISM sampling pattern in a simplified (5x5 square) DU. Increments are collected at a random starting point with systematic distances between increments. Replicate samples can be collected by starting at a different random starting point, often at a different corner of the DU. Practically, this grid pattern can often be followed with flagging or lathe marking DU boundaries and/or sampling lanes and with individual pacing keeping systematic distances between increments. As an example, an artillery firing point might include a 100x100 m DU with 81 increments.
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[[File:Beal1w2 Fig3.png|thumb|200 px|left|Figure 3. Example ISM sampling pattern on a square decision unit. Replicates are collected in a systematic pattern from a random starting point at a corner of the DU. Typically more than the 25 increments shown are collected]]
  
This reaction has an association, or equilibrium, constant that governs the proportions of Hg<sup>+2</sup>, Cl<sup>-</sup> and HgCl<sub>2</sub><sup>o</sup> that can exist in solution at equilibrium. Mercury can form many other aqueous complexes and its distribution among these aqueous complexes is known as the aqueous speciation of mercury. Furthermore, aqueous speciation can change as conditions in the groundwater change. For example, let’s investigate the calculated aqueous speciation of uranium on an Eh-pH diagram (Fig. 1). The dominant species is different at different pH and Eh values (species activities are equal along the red lines between species dominance fields). [https://en.wikipedia.org/wiki/Redox '''Eh'''] is a measure of the tendency of electrons to flow from one ion to another<ref name="Langmuir1997"/><ref name= "Dreverj"/> while [https://en.wikipedia.org/wiki/PH'''pH'''] is an indicator of how acidic or basic the groundwater is. The aqueous speciation is also different when other components involved in speciation reactions have different activities (e.g., calcium and [https://en.wikipedia.org/wiki/Fugacity '''fugacity ''']) of CO<sub>2</sub> in equilibrium with the system).
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DUs can vary in shape (Figure 4), size, number of increments, and number of replicates according to a project’s data quality objectives.
  
[[File:Denham-Article 2-Figure 1.PNG|500px|thumbnail|right|Figure 1: Aqueous speciation of uranium (diagram produced with The Geochemist’s Workbench® <ref>Bethke, C.M. and S. Yeakel, 2015. The geochemist’s workbench®, Release 10.0. Latest version available at [www.gwb.com www.gwb.com]</ref>), PCO<sub>2</sub> = 0.01 atm., [Ca] = 10 mg/L.]]
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[[File:Beal1w2 Fig4.png|thumb|right|250 px|Figure 4: Incremental sampling of a circular DU on snow shows sampling lanes with a two-person team in process of collecting the second replicate in a perpendicular path to the first replicate. (Photo: Matthew Bigl)]]
  
Speciation affects adsorption of a metal because different species are adsorbed to different degrees by aquifer minerals. This is because the charge and hydrated radii on aqueous species differs and these properties are important influences on adsorption. Aqueous speciation affects precipitation because the solubility of a mineral is defined by a single species. For example, if the solubility of the mineral anglesite is defined by the ion Pb<sup>+2</sup>, but Pb<sup>+2</sup>, is only a minor species in the aqueous speciation of lead, then the real solubility will be higher than that calculated from the “relation”:
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==Sampling Tools==
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In many cases, energetic compounds are expected to reside within the soil surface. Figure 5 shows soil depth profiles on some studied impact areas and firing points. Overall, the energetic compound concentrations below 5-cm soil depth are negligible relative to overlying soil concentrations. For conventional munitions, this is to be expected as the energetic particles are relatively insoluble, and any dissolved compounds readily adsorb to most soils<ref>Pennington, J.C., Jenkins, T.F., Ampleman, G., Thiboutot, S., Brannon, J.M., Hewitt, A.D., Lewis, J., Brochu, S., 2006. Distribution and fate of energetics on DoD test and training ranges: Final Report. ERDC TR-06-13, Vicksburg, MS, USA. Also: SERDP/ESTCP Project ER-1155. [[media:Pennington-2006_ERDC-TR-06-13_ESTCP-ER-1155-FR.pdf| Report.pdf]]</ref>. Physical disturbance, as on hand grenade ranges, may require deeper sampling either with a soil profile or a corer/auger.
  
K<sub>sp</sub> = aPb<sup>+2</sup> X aSO<sub>4</sub><sup>-2</sup>
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[[File:Beal1w2 Fig5.png|thumb|left|200 px|Figure 5. Depth profiles of high explosive compounds at impact areas (bottom) and of propellant compounds at firing points (top). Data from: Hewitt et al. <ref>Hewitt, A.D., Jenkins, T.F., Ramsey, C.A., Bjella, K.L., Ranney, T.A. and Perron, N.M., 2005. Estimating energetic residue loading on military artillery ranges: Large decision units (No. ERDC/CRREL-TR-05-7). [[media:Hewitt-2005 ERDC-CRREL TR-05-7.pdf| Report.pdf]]</ref> and Jenkins et al. <ref>Jenkins, T.F., Ampleman, G., Thiboutot, S., Bigl, S.R., Taylor, S., Walsh, M.R., Faucher, D., Mantel, R., Poulin, I., Dontsova, K.M. and Walsh, M.E., 2008. Characterization and fate of gun and rocket propellant residues on testing and training ranges (No. ERDC-TR-08-1). [[media:Jenkins-2008 ERDC TR-08-1.pdf| Report.pdf]]</ref>]]
  
Where K<sub>sp</sub> is the solubility product constant, or the equilibrium constant for solid substance dissolving in an aqueous solution and “a” is the activity, or effective concentration, of each one of the different species in the reaction.
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Soil sampling with the Cold Regions Research and Engineering Laboratory (CRREL) Multi-Increment Sampling Tool (CMIST) or similar device is an easy way to collect ISM samples rapidly and reproducibly. This tool has an adjustable diameter size corer and adjustable depth to collect surface soil plugs (Figure 6). The CMIST can be used at almost a walking pace (Figure 7) using a two-person sampling team, with one person operating the CMIST and the other carrying the sample container and recording the number of increments collected. The CMIST with a small diameter tip works best in soils with low cohesion, otherwise conventional scoops may be used. Maintaining consistent soil increment dimensions is critical.
  
[https://en.wikipedia.org/wiki/Redox Oxidation-reduction] '''chemistry''' plays an important role in aqueous speciation of certain metals such as arsenic (As), chromium (Cr), copper (Cu), mercury (Hg), selenium (Se), and uranium (U). These contaminants can exist in more than one oxidation state over the range of conditions found in contaminated groundwater. A change in oxidation state can profoundly change the adsorption behavior and solubility of a metal or metalloid (For example, see the two chromium species in '''Figure 2 in MNA of Metal and Metalloid Contaminants'''). Reactions that change the oxidation state of metals are often kinetically limited, but can be catalyzed by microbial interactions<ref>NABIR, 2003. Bioremediation of metals and radionuclides - what it is and how It works. LBNL-42595, Lawrence Berkeley National Laboratory for the Natural and Accelerated Bioremediation Research Program, Office of Science, U.S. Department of Energy [http://www.environmentalrestoration.wiki/images/9/97/NABIR-2003-Bioremediation_of_Metals_and_Radionuclides.pdf Report pdf]</ref><ref name= "USEPA2007V1">United States Environmental Protection Agency (USEPA), 2007. Monitored natural attenuation of inorganic contaminants in groundwater, Volume 1 Technical basis for assessment, Edited by R.G. Ford, R.T. Wilkin, and R.W. Puls. U.S. Environmental Protection Agency, EPA/600/R-07/139.  [http://www.environmentalrestoration.wiki/images/c/c1/USEPA-2007-MNA_of_Inorganic_Contaminants_in_GW%2C_Vol_1_Technical_Basis_for_Assessment.pdf Report pdf]</ref>. Thus, for metals that are sensitive to oxidation-reduction potential, it is important to consider microbial activity and potential interactions with the contaminants when assessing mobility. 
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The sampling tool should be cleaned between replicates and between DUs to minimize potential for cross-contamination<ref>Walsh, M.R., 2009. User’s manual for the CRREL Multi-Increment Sampling Tool. Engineer Research and Development Center / Cold Regions Research and Engineering Lab (ERDC/CRREL) SR-09-1, Hanover, NH, USA.  [[media:Walsh-2009 ERDC-CRREL SR-09-1.pdf | Report.pdf]]</ref>.
  
==Adsorption==
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==Sample Processing==
Adsorption can be defined as the partitioning of a constituent to the surface of an aquifer solid phase as a 2-dimensional “coating”<ref>United States Environmental Protection Agency (USEPA), 1999. Understanding variation in partition coefficient, Kd, values, Volume 1 - The Kd model, methods of measurement, and application of chemical reaction codes. EPA 402-R-99-004A [http://www.environmentalrestoration.wiki/images/7/75/USEPA-1999-Understanding_variation_in_partition_coefficient%2C_Kd_values-Vol_1.pdf Report pdf]</ref>. For aqueous species carrying an electrical charge, partitioning is driven by electrostatic attraction and then potential bonding of the constituent to the surface of the solid. Uncharged (neutral) species may adsorb onto aquifer solid surfaces because they are repulsed, driven out of the aqueous phase, by energetically more favorable attraction of water molecules to each other.
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While only 10 g of soil is typically used for chemical analysis, incremental sampling generates a sample weighing on the order of 1 kg. Splitting of a sample, either in the field or laboratory, seems like an easy way to reduce sample mass; however this approach has been found to produce high uncertainty for explosives and propellants, with a median RSD of 43.1%<ref name= "Hewitt2009"/>. Even greater error is associated with removing a discrete sub-sample from an unground sample. Appendix A in [https://www.epa.gov/sites/production/files/2015-07/documents/epa-8330b.pdf U.S. EPA Method 8330B]<ref name= "USEPA2006M"/> provides details on recommended ISM sample processing procedures.
The surface of most aquifer minerals carries an electrical charge that varies with pH. For oxides and silicates, the charge is mostly the result of partially-bonded oxygen atoms at the surface. The resulting negative charge attracts positively charged ions. One of the most common and energetically favorable ions available to bond with the surface oxygens is the hydrogen ion. Hence, as pH of groundwater decreases and hydrogen ions are more abundant, more hydrogen ions approach surface oxygens, neutralizing the negative charge (Fig. 2). The pH at which all charge has been neutralized is called the zero point of charge (ZPC). At pH values below the ZPC, the mineral surface becomes positively charged. This variable surface charge behavior of aquifer minerals is an important control on adsorption of metal and metalloid contaminants. Those contaminants that exist in groundwater primarily as ''cations'' tend to adsorb more strongly as pH increases. Those that exist primarily as ''anions'' tend to adsorb more strongly as pH decreases.
 
  
[[File:Denham-Article 2-Figure 2.PNG|thumbnail|500px|Figure 2: Mineral surface exchanging hydrogen ions with varying pH (from ITRC, 2010<ref>ITRC, 2010. A Decision Framework for Applying Monitored Natural Attenuation Processes to Metals and Radionuclides, Interstate Technology and Regulatory Council, Technical/Regulatory Guidance AMPR-1. [http://www.environmentalrestoration.wiki/images/a/ac/ITRC-2010-A_Decision_Framework.pdf Report pdf]</ref>).]]
+
Incremental soil samples are typically air dried over the course of a few days. Oven drying thermally degrades some energetic compounds and should be avoided<ref>Cragin, J.H., Leggett, D.C., Foley, B.T., and Schumacher, P.W., 1985. TNT, RDX and HMX explosives in soils and sediments: Analysis techniques and drying losses. (CRREL Report 85-15) Hanover, NH, USA. [[media:Cragin-1985 CRREL 85-15.pdf| Report.pdf]]</ref>. Once dry, the samples are sieved with a 2-mm screen, with only the less than 2-mm fraction processed further. This size fraction represents the USDA definition of soil. Aggregate soil particles should be broken up and vegetation shredded to pass through the sieve. Samples from impact or demolition areas may contain explosive particles from low order detonations that are greater than 2 mm and should be identified, given appropriate caution, and potentially weighed.
  
Mechanistic theories of adsorption consider the structure of ions attracted to the surface of a mineral. In general, there are ions that are touching the mineral surface because they have lost some or all of their waters of solvation. There are also ions that retain their waters of solvation and exist in a diffuse layer that carries less of an electrical charge with distance from the mineral surface. Adsorption of ions that touch the mineral surface are bonded more strongly to the surface. This type of adsorption is referred to in various sources as inner-sphere adsorption or complexation, specific adsorption, or chemisorption (chemical adsorption). Adsorption of ions that retain their waters of solvation in the diffuse layer is referred to as outer sphere adsorption or complexation, non-specific adsorption, or physisorption (physical adsorption). Detailed discussion of adsorption can be found in Dzombak and Morel, 1990<ref>Dzombak, D.A. and Morel, F.M., 1990. Surface complexation modeling: hydrous ferric oxide. John Wiley & Sons. ISBN 0-471-63731-9</ref>, Stumm, 1992<ref name="Stumm1992">Stumm, W. 1992. Chemistry of the Solid-Water Interface - Processes at the Mineral-Water and Particle-Water Interface in Natural Systems. John Wiley & Sons, Inc., ISBN 0-471-57672-7. </ref>, Stumm, 1995<ref>Stumm, W. 1995. The inner sphere surface complex - A key to understanding surface reactivity. C.P. Huang, C.R. O’Melia, and J.J. Morgan (Eds.) Aquatic Chemistry - Interfacial and Interspecies Processes. American Chemical Society, Washington DC. [https://doi.org/10.1021/ba-1995-0244.ch001 doi: 10.1021/ba-1995-0244.ch001]</ref>, and Sposito, 1995<ref>Sposito, G. 1995. Adsorption as a problem in coordination chemistry - The concept of the surface complex. C.P. Huang, C.R. O’Melia, and J.J. Morgan (Eds.) Aquatic Chemistry - Interfacial and Interspecies Processes. American Chemical Society, Washington DC. [https://doi.org/10.1021/ba-1995-0244.ch002 doi: 10.1021/ba-1995-0244.ch002]</ref>. Reviews of adsorption can be found in Stumm and Morgan, 1981<ref name = "Stumm1981"/>, Langmuir, 1997<ref name="Langmuir1997"/>, and Drever<ref name= "Dreverj"/>.
+
The <2-mm soil fraction is typically still ≥1 kg and impractical to extract in full for analysis. However, subsampling at this stage is not possible due to compositional heterogeneity, with the energetic compounds generally present as <0.5 mm particles<ref name= "Walsh2017"/><ref name= "Taylor2004"/>. Particle size reduction is required to achieve a representative and precise measure of the sample concentration. Grinding in a puck mill to a soil particle size <75 µm has been found to be required for representative/reproducible sub-sampling (Figure 8). For samples thought to contain propellant particles, a prolonged milling time is required to break down these polymerized particles and achieve acceptable precision (Figure 9). Due to the multi-use nature of some ranges, a 5-minute puck milling period can be used for all soils. Cooling periods between 1-minute milling intervals are recommended to avoid thermal degradation. Similar to field sampling, sub-sampling is done incrementally by spreading the sample out to a thin layer and collecting systematic random increments of consistent volume to a total mass for extraction of 10 g (Figure 10).
  
Ion exchange can be treated as a type of adsorption but its definition varies in the literature. Certain minerals, such as smectite clays and zeolites, exchange cations whereas some minerals exchange anions between their crystal structure and groundwater. Ions also exchange at the layer of outer sphere complexes and in the diffuse layer of ions at the interface of groundwater. Broadly, ion exchange includes all forms of ion exchange. A more restrictive definition of ion exchange is sometimes used in soil science that includes only “readily exchanged” ions as outer sphere complexes or in the diffuse layer<ref>Dzombak, D.A. and J.M. Hudson, 1995. Ion exchange - The contributions of diffuse layer sorption and surface complexation. C.P. Huang, C.R. O’Melia, and J.J. Morgan (Eds.) Aquatic Chemistry - Interfacial and Interspecies Processes. American Chemical Society, Washington DC. [https://doi.org/10.1021/ba-1995-0244.ch003 doi: 10.1021/ba-1995-0244.ch003]</ref><ref>Bourg, I.C. and G. Sposito, 2011. Ion Exchange Phenomena. LBNL-4940E, Lawrence Berkeley National Laboratory</ref><ref name= "DavisUC">U.C. Davis/ Solubility Product Constant, in http://chemwiki.ucdavis.edu/Core/Physical_Chemistry/Equilibria/Solubilty/Solubility_Product_Constant,_Ksp > Contributors: Kathryn Rashe, Lisa Peterson.</ref>. To maintain electrical neutrality in the groundwater, the moles of charge exchanged must be equal. This can either mean: 1) ions of the same charge exchange in a stoichiometry that results in a zero net change of charge in the groundwater, or 2) cations and anions exchange in a stoichiometry that results in a zero net change of charge in the groundwater.
+
<li style="display: inline-block;">[[File:Beal1w2 Fig6.png|thumb|200 px|Figure 6: CMIST soil sampling tool (top) and with ejected increment core using a large diameter tip (bottom).]]</li>
 +
<li style="display: inline-block;">[[File:Beal1w2 Fig7.png|thumb|200 px|Figure 7: Two person sampling team using CMIST, bag-lined bucket, and increment counter. (Photos: Matthew Bigl)]]</li>
 +
<li style="display: inline-block;">[[File:Beal1w2 Fig8.png|thumb|200 px|Figure 8: Effect of machine grinding on RDX and TNT concentration and precision in soil from a hand grenade range. Data from Walsh et al.<ref>Walsh, M.E., Ramsey, C.A. and Jenkins, T.F., 2002. The effect of particle size reduction by grinding on subsampling variance for explosives residues in soil. Chemosphere, 49(10), pp.1267-1273. [https://doi.org/10.1016/S0045-6535(02)00528-3 doi: 10.1016/S0045-6535(02)00528-3]</ref> ]]</li>
 +
<li style="display: inline-block;">[[File:Beal1w2 Fig9.png|thumb|200 px|Figure 9: Effect of puck milling time on 2,4-DNT concentration and precision in soil from a firing point. Data from Walsh et al.<ref>Walsh, M.E., Ramsey, C.A., Collins, C.M., Hewitt, A.D., Walsh, M.R., Bjella, K.L., Lambert, D.J. and Perron, N.M., 2005. Collection methods and laboratory processing of samples from Donnelly Training Area Firing Points, Alaska, 2003 (No. ERDC/CRREL-TR-05-6). [[media:Walsh-2005 ERDC-CRREL TR-05-6.pdf| Report.pdf]]</ref>.]]</li>
 +
<li style="display: inline-block;">[[File:Beal1w2 Fig10.png|thumb|200 px|center|Figure 10: Incremental sub-sampling of a milled soil sample spread out on aluminum foil.]]</li>
  
The capacity of aquifer solids to exchange cations or anions can be measured using standardized methods. These are good indicators of whether an aquifer can accommodate sufficient adsorption of contaminant metals. It must be remembered, however, that the measurements are made under a specific set of conditions. Adsorption may be less or more under the conditions of the contaminated aquifer.  The effect of cation exchange capacity on the mobility of several metals is incorporated in the scenarios system for evaluating MNA for inorganics<ref name="Truex2011"/>.
+
==Analysis==
 
+
Soil sub-samples are extracted and analyzed following [[Media: epa-2006-method-8330b.pdf | EPA Method 8330B]]<ref name= "USEPA2006M"/> and [[Media:epa-2007-method-8095.pdf | Method 8095]]<ref name= "USEPA2007M"/> using [[Wikipedia: High-performance liquid chromatography | High Performance Liquid Chromatography (HPLC)]] and [[Wikipedia: Gas chromatography | Gas Chromatography (GC)]], respectively. Common estimated reporting limits for these analysis methods are listed in Table 2.
==Precipitation==
 
Precipitation of contaminant metals can be an effective attenuation mechanism. Precipitation differs from adsorption in that the contaminant is bound in a 3-dimensional structure of a mineral or an amorphous precursor to a mineral. The mineral can be composed of the contaminant bound to counterions from the groundwater. For example, lead can combine with the sulfate ion and form the mineral anglesite (PbSO<sub>4</sub>) by the reaction:
 
 
 
Pb<sup>+2</sup> + SO<sub>4</sub><sup>-2</sup> = PbSO<sub>4</sub>
 
 
 
The equilibrium constant of this reaction, often referred to as the K<sub>sp</sub> (solubility product)<ref name= "DavisUC"/> is defined as:
 
 
 
K<sub>sp</sub> = aPb<sup>+2</sup>  X  aSO<sub>4</sub><sup>-2</sup>
 
 
 
where ai is the activity, or effective concentration, of the species i. When the product of the aPb<sup>+2</sup> and aSO<sub>4</sub><sup>-2</sup> equals the K<sub>sp</sub>, the groundwater is said to be saturated with anglesite. If the product exceeds the K<sub>sp</sub> then it is thermodynamically favorable for anglesite to precipitate. Note that the K<sub>sp</sub> refers specifically to the Pb<sup>+2</sup> ion and the SO<sub>4</sub><sup>-2</sup> ion. Lead in other dissolved species such as PbCl<sub>2</sub><sup>o</sup>, PbCO<sub>3</sub><sup>o</sup>, or even PbSO<sub>4</sub><sup>o</sup> is not considered. Hence, the aqueous speciation of a metal is important in controlling whether or not it will precipitate from groundwater. The measurement of the concentrations of lead and sulfate in groundwater provides the total dissolved concentration of each constituent that may be distributed among many species. Precipitation of minerals in aquifers is discussed in most aqueous geochemistry textbooks (e.g.,<ref name="Truex2011"/><ref name = "Stumm1981"/><ref name="Langmuir1997"/>).
 
 
 
There are several special cases of precipitation. One, known as coprecipitation, is when the contaminant is a minor component of a precipitating mineral. A metal can be coprecipitated in a mineral either because it chemically resembles a primary component of the mineral or because it adsorbs to the surface of the mineral as precipitation occurs, becoming “trapped” as the mineral continues to precipitate. Another is surface precipitation, the nucleation and precipitation of one mineral on the surface of another. In this case adsorption of ions that compose the precipitating mineral causes activities of the pertinent ions to become high enough that the layer of water at the surface of the host mineral becomes saturated with the precipitating mineral. The precipitating mineral may be saturated at the surface of the host mineral, but undersaturated in the bulk groundwater. Surface precipitation is discussed in detail by Stumm, 1992<ref name="Stumm1992"/>, and briefly discussed in U.S.E.P.A., 2007<ref name= "USEPA2007V1"/>.
 
 
 
Microbial reactions can also affect the mobility of metals and metalloids by causing them to precipitate from groundwater<ref name= "USEPA2007V1"/>. Under strongly reducing conditions metals catalyze the reduction of sulfate to sulfide. Metals such as zinc (Zn), lead (Pb), nickel (Ni), and cadmium (Cd), as well as redox sensitive arsenic (As) copper (Cu), and mercury (Hg), will readily precipitate as sulfide minerals<ref>Diels, L., Geets, J., Dejonghe, W., Van Roy, S., Vanbroekhoven, K., Szewczyk, A. and Malina, G., 2010, January. Heavy metal immobilization in groundwater by in situ bioprecipitation: comments and questions about efficiency and sustainability of the process. In Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy (Vol. 11, Article 7).</ref>. Such reducing conditions are generally caused by a series of microbial reactions that deplete the system of oxidants such as oxygen, nitrate, and ferric iron. For other metals, like chromium (Cr) and uranium (U), the reducing conditions caused by microbes changes the oxidized and mobile forms (Cr(VI) and U(VI)) into reduced forms (Cr(III) and (UIV)) that precipitate as hydroxides or oxides.
 
 
 
==Colloidal Transport==
 
Contaminants can be transported in groundwater by [https://en.wikipedia.org/wiki/Colloid colloidal] particles and this can enhance the mobility of metals and metalloids<ref name="Stumm1992"/><ref>McCarthy, J.F. and Zachara, J.M., 1989. Subsurface transport of contaminants. Environmental Science & Technology, 23(5), pp.496-502. [https://doi.org/10.1021/es00063a001 doi: 10.1021/es00063a001]</ref><ref>Puls, R.W., R.M. Powell, D.A. Clark, and C.J. Paul, 1991. Facilitated transport of inorganic contaminants in groundwater: part II. colloidal transport. U.S Environmental Protection Agency EPA/600/M-91/040. [http://www.environmentalrestoration.wiki/images/d/d6/Puls-1991-Facilitated_Transport.pdf Report pdf]</ref><ref>Takala, M. and Manninen, P., 2006. Sampling and analysis of groundwater colloids. A literature review (No. POSIVA-WR--06-15). Posiva Oy.</ref>. This occurs when contaminants attach to mobile colloidal particles of minerals or when contaminants precipitate from groundwater, but remain mobile as colloidal particles. The mobility of colloidal particles depends on the surface charge of the particles relative to each other and relative to aquifer mineral surfaces. These are most sensitive to pH and ionic strength. Despite the widespread occurrence of contaminants associated with colloidal particles, it is unusual that the concentration of contaminant carried by colloidal particles is the primary cause for exceeding regulatory standards at an exposure point. 
 
 
 
==Simple Guide to Mobility of Metals in Groundwater==
 
All concepts described above were incorporated into a “scenarios approach” guidance document to help groundwater professionals to evaluate the mobility of several metals and inorganics ('''Fig. 2 in MNA of Metal and Metalloid Contaminants'''). It shows how shows how three primary factors (oxidation/reduction potential (ORP); cation exchange capacity (CEC), and sediment iron oxide coatings and solids), combine with three secondary factors (pH, sulfur/sulfide, and total dissolved solids) to provide a semi-qualitative indicator of mobility.
 
  
 +
{| class="wikitable" style="float: center; text-align: center; margin-left: auto; margin-right: auto;"
 +
|+ Table 2. Typical Method Reporting Limits for Energetic Compounds in Soil. (Data from Hewitt et al.<ref>Hewitt, A., Bigl, S., Walsh, M., Brochu, S., Bjella, K. and Lambert, D., 2007. Processing of training range soils for the analysis of energetic compounds (No. ERDC/CRREL-TR-07-15). Hanover, NH, USA. [[media:Hewitt-2007 ERDC-CRREL TR-07-15.pdf| Report.pdf]]</ref>)
 +
|-
 +
! rowspan="2" | Compound
 +
! colspan="2" | Soil Reporting Limit (mg/kg)
 +
|-
 +
! HPLC (8330)
 +
! GC (8095)
 +
|-
 +
| HMX || 0.04 || 0.01
 +
|-
 +
| RDX || 0.04 || 0.006
 +
|-
 +
| [[Wikipedia: 1,3,5-Trinitrobenzene | TNB]] || 0.04 || 0.003
 +
|-
 +
| TNT || 0.04 || 0.002
 +
|-
 +
| [[Wikipedia: 2,6-Dinitrotoluene | 2,6-DNT]] || 0.08 || 0.002
 +
|-
 +
| 2,4-DNT || 0.04 || 0.002
 +
|-
 +
| 2-ADNT || 0.08 || 0.002
 +
|-
 +
| 4-ADNT || 0.08 || 0.002
 +
|-
 +
| NG || 0.1 || 0.01
 +
|-
 +
| [[Wikipedia: Dinitrobenzene | DNB ]] || 0.04 || 0.002
 +
|-
 +
| [[Wikipedia: Tetryl | Tetryl ]]  || 0.04 || 0.01
 +
|-
 +
| [[Wikipedia: Pentaerythritol tetranitrate | PETN ]] || 0.2 || 0.016
 +
|}
  
 
==References==
 
==References==
 
 
<references/>
 
<references/>
  
 
==See Also==
 
==See Also==
 +
*[https://itrcweb.org/ Interstate Technology and Regulatory Council]
 +
*[http://www.hawaiidoh.org/tgm.aspx Hawaii Department of Health]
 +
*[http://envirostat.org/ Envirostat]

Latest revision as of 18:58, 29 April 2020

The heterogeneous distribution of munitions constituents, released as particles from munitions firing and detonations on military training ranges, presents challenges for representative soil sample collection and for defensible decision making. Military range characterization studies and the development of the incremental sampling methodology (ISM) have enabled the development of recommended methods for soil sampling that produce representative and reproducible concentration data for munitions constituents. This article provides a broad overview of recommended soil sampling and processing practices for analysis of munitions constituents on military ranges.

Related Article(s):


CONTRIBUTOR(S): Dr. Samuel Beal


Key Resource(s):

Introduction

Figure 1: Downrange distance of visible propellant plume on snow from the firing of different munitions. Note deposition behind firing line for the 84-mm rocket. Data from: Walsh et al.[5][6]
Figure 2: A low-order detonation mortar round (top) with surrounding discrete soil samples produced concentrations spanning six orders of magnitude within a 10m by 10m area (bottom). (Photo and data: A.D. Hewitt)

Munitions constituents are released on military testing and training ranges through several common mechanisms. Some are locally dispersed as solid particles from incomplete combustion during firing and detonation. Also, small residual particles containing propellant compounds (e.g., nitroglycerin [NG] and 2,4-dinitrotoluene [2,4-DNT]) are distributed in front of and surrounding target practice firing lines (Figure 1). At impact areas and demolition areas, high order detonations typically yield very small amounts (<1 to 10 mg/round) of residual high explosive compounds (e.g., TNT , RDX and HMX ) that are distributed up to and sometimes greater than) 24 m from the site of detonation[7].

Low-order detonations and duds are thought to be the primary source of munitions constituents on ranges[8][9]. Duds are initially intact but may become perforated or fragmented into micrometer to centimeter;o0i0k-sized particles by nearby detonations[10]. Low-order detonations can scatter micrometer to centimeter-sized particles up to 20 m from the site of detonation[11]

The particulate nature of munitions constituents in the environment presents a distinct challenge to representative soil sampling. Figure 2 shows an array of discrete soil samples collected around the site of a low-order detonation – resultant soil concentrations vary by orders of magnitude within centimeters of each other. The inadequacy of discrete sampling is apparent in characterization studies from actual ranges which show wide-ranging concentrations and poor precision (Table 1).

In comparison to discrete sampling, incremental sampling tends to yield reproducible concentrations (low relative standard deviation [RSD]) that statistically better represent an area of interest[2].

Table 1. Soil Sample Concentrations and Precision from Military Ranges Using Discrete and Incremental Sampling. (Data from Taylor et al. [1] and references therein.)
Military Range Type Analyte Range
(mg/kg)
Median
(mg/kg)
RSD
(%)
Discrete Samples
Artillery FP 2,4-DNT <0.04 – 6.4 0.65 110
Antitank Rocket HMX 5.8 – 1,200 200 99
Bombing TNT 0.15 – 780 6.4 274
Mortar RDX <0.04 – 2,400 1.7 441
Artillery RDX <0.04 – 170 <0.04 454
Incremental Samples*
Artillery FP 2,4-DNT 0.60 – 1.4 0.92 26
Bombing TNT 13 – 17 14 17
Artillery/Bombing RDX 3.9 – 9.4 4.8 38
Thermal Treatment HMX 3.96 – 4.26 4.16 4
* For incremental samples, 30-100 increments and 3-10 replicate samples were collected.

Incremental Sampling Approach

ISM is a requisite for representative and reproducible sampling of training ranges, but it is an involved process that is detailed thoroughly elsewhere[2][1][3]. In short, ISM involves the collection of many (30 to >100) increments in a systematic pattern within a decision unit (DU). The DU may cover an area where releases are thought to have occurred or may represent an area relevant to ecological receptors (e.g., sensitive species). Figure 3 shows the ISM sampling pattern in a simplified (5x5 square) DU. Increments are collected at a random starting point with systematic distances between increments. Replicate samples can be collected by starting at a different random starting point, often at a different corner of the DU. Practically, this grid pattern can often be followed with flagging or lathe marking DU boundaries and/or sampling lanes and with individual pacing keeping systematic distances between increments. As an example, an artillery firing point might include a 100x100 m DU with 81 increments.

Figure 3. Example ISM sampling pattern on a square decision unit. Replicates are collected in a systematic pattern from a random starting point at a corner of the DU. Typically more than the 25 increments shown are collected

DUs can vary in shape (Figure 4), size, number of increments, and number of replicates according to a project’s data quality objectives.

Figure 4: Incremental sampling of a circular DU on snow shows sampling lanes with a two-person team in process of collecting the second replicate in a perpendicular path to the first replicate. (Photo: Matthew Bigl)

Sampling Tools

In many cases, energetic compounds are expected to reside within the soil surface. Figure 5 shows soil depth profiles on some studied impact areas and firing points. Overall, the energetic compound concentrations below 5-cm soil depth are negligible relative to overlying soil concentrations. For conventional munitions, this is to be expected as the energetic particles are relatively insoluble, and any dissolved compounds readily adsorb to most soils[12]. Physical disturbance, as on hand grenade ranges, may require deeper sampling either with a soil profile or a corer/auger.

Figure 5. Depth profiles of high explosive compounds at impact areas (bottom) and of propellant compounds at firing points (top). Data from: Hewitt et al. [13] and Jenkins et al. [14]

Soil sampling with the Cold Regions Research and Engineering Laboratory (CRREL) Multi-Increment Sampling Tool (CMIST) or similar device is an easy way to collect ISM samples rapidly and reproducibly. This tool has an adjustable diameter size corer and adjustable depth to collect surface soil plugs (Figure 6). The CMIST can be used at almost a walking pace (Figure 7) using a two-person sampling team, with one person operating the CMIST and the other carrying the sample container and recording the number of increments collected. The CMIST with a small diameter tip works best in soils with low cohesion, otherwise conventional scoops may be used. Maintaining consistent soil increment dimensions is critical.

The sampling tool should be cleaned between replicates and between DUs to minimize potential for cross-contamination[15].

Sample Processing

While only 10 g of soil is typically used for chemical analysis, incremental sampling generates a sample weighing on the order of 1 kg. Splitting of a sample, either in the field or laboratory, seems like an easy way to reduce sample mass; however this approach has been found to produce high uncertainty for explosives and propellants, with a median RSD of 43.1%[2]. Even greater error is associated with removing a discrete sub-sample from an unground sample. Appendix A in U.S. EPA Method 8330B[3] provides details on recommended ISM sample processing procedures.

Incremental soil samples are typically air dried over the course of a few days. Oven drying thermally degrades some energetic compounds and should be avoided[16]. Once dry, the samples are sieved with a 2-mm screen, with only the less than 2-mm fraction processed further. This size fraction represents the USDA definition of soil. Aggregate soil particles should be broken up and vegetation shredded to pass through the sieve. Samples from impact or demolition areas may contain explosive particles from low order detonations that are greater than 2 mm and should be identified, given appropriate caution, and potentially weighed.

The <2-mm soil fraction is typically still ≥1 kg and impractical to extract in full for analysis. However, subsampling at this stage is not possible due to compositional heterogeneity, with the energetic compounds generally present as <0.5 mm particles[7][11]. Particle size reduction is required to achieve a representative and precise measure of the sample concentration. Grinding in a puck mill to a soil particle size <75 µm has been found to be required for representative/reproducible sub-sampling (Figure 8). For samples thought to contain propellant particles, a prolonged milling time is required to break down these polymerized particles and achieve acceptable precision (Figure 9). Due to the multi-use nature of some ranges, a 5-minute puck milling period can be used for all soils. Cooling periods between 1-minute milling intervals are recommended to avoid thermal degradation. Similar to field sampling, sub-sampling is done incrementally by spreading the sample out to a thin layer and collecting systematic random increments of consistent volume to a total mass for extraction of 10 g (Figure 10).

  • Figure 6: CMIST soil sampling tool (top) and with ejected increment core using a large diameter tip (bottom).
  • Figure 7: Two person sampling team using CMIST, bag-lined bucket, and increment counter. (Photos: Matthew Bigl)
  • Figure 8: Effect of machine grinding on RDX and TNT concentration and precision in soil from a hand grenade range. Data from Walsh et al.[17]
  • Figure 9: Effect of puck milling time on 2,4-DNT concentration and precision in soil from a firing point. Data from Walsh et al.[18].
  • Figure 10: Incremental sub-sampling of a milled soil sample spread out on aluminum foil.
  • Analysis

    Soil sub-samples are extracted and analyzed following EPA Method 8330B[3] and Method 8095[4] using High Performance Liquid Chromatography (HPLC) and Gas Chromatography (GC), respectively. Common estimated reporting limits for these analysis methods are listed in Table 2.

    Table 2. Typical Method Reporting Limits for Energetic Compounds in Soil. (Data from Hewitt et al.[19])
    Compound Soil Reporting Limit (mg/kg)
    HPLC (8330) GC (8095)
    HMX 0.04 0.01
    RDX 0.04 0.006
    TNB 0.04 0.003
    TNT 0.04 0.002
    2,6-DNT 0.08 0.002
    2,4-DNT 0.04 0.002
    2-ADNT 0.08 0.002
    4-ADNT 0.08 0.002
    NG 0.1 0.01
    DNB 0.04 0.002
    Tetryl 0.04 0.01
    PETN 0.2 0.016

    References

    1. ^ 1.0 1.1 1.2 Taylor, S., Jenkins, T.F., Bigl, S., Hewitt, A.D., Walsh, M.E. and Walsh, M.R., 2011. Guidance for Soil Sampling for Energetics and Metals (No. ERDC/CRREL-TR-11-15). Report.pdf
    2. ^ 2.0 2.1 2.2 2.3 Hewitt, A.D., Jenkins, T.F., Walsh, M.E., Bigl, S.R. and Brochu, S., 2009. Validation of sampling protocol and the promulgation of method modifications for the characterization of energetic residues on military testing and training ranges (No. ERDC/CRREL-TR-09-6). Engineer Research and Development Center / Cold Regions Research and Engineering Lab (ERDC/CRREL) TR-09-6, Hanover, NH, USA. Report.pdf
    3. ^ 3.0 3.1 3.2 3.3 U.S. Environmental Protection Agency (USEPA), 2006. Method 8330B (SW-846): Nitroaromatics, Nitramines, and Nitrate Esters by High Performance Liquid Chromatography (HPLC), Rev. 2. Washington, D.C. Report.pdf
    4. ^ 4.0 4.1 U.S. Environmental Protection Agency (US EPA), 2007. Method 8095 (SW-846): Explosives by Gas Chromatography. Washington, D.C. Report.pdf
    5. ^ Walsh, M.R., Walsh, M.E., Ampleman, G., Thiboutot, S., Brochu, S. and Jenkins, T.F., 2012. Munitions propellants residue deposition rates on military training ranges. Propellants, Explosives, Pyrotechnics, 37(4), pp.393-406. doi: 10.1002/prep.201100105
    6. ^ Walsh, M.R., Walsh, M.E., Hewitt, A.D., Collins, C.M., Bigl, S.R., Gagnon, K., Ampleman, G., Thiboutot, S., Poulin, I. and Brochu, S., 2010. Characterization and Fate of Gun and Rocket Propellant Residues on Testing and Training Ranges: Interim Report 2. (ERDC/CRREL TR-10-13. Also: ESTCP Project ER-1481) Report
    7. ^ 7.0 7.1 Walsh, M.R., Temple, T., Bigl, M.F., Tshabalala, S.F., Mai, N. and Ladyman, M., 2017. Investigation of Energetic Particle Distribution from High‐Order Detonations of Munitions. Propellants, Explosives, Pyrotechnics, 42(8), pp.932-941. doi: 10.1002/prep.201700089 Report.pdf
    8. ^ Hewitt, A.D., Jenkins, T.F., Walsh, M.E., Walsh, M.R. and Taylor, S., 2005. RDX and TNT residues from live-fire and blow-in-place detonations. Chemosphere, 61(6), pp.888-894. doi: 10.1016/j.chemosphere.2005.04.058
    9. ^ Walsh, M.R., Walsh, M.E., Poulin, I., Taylor, S. and Douglas, T.A., 2011. Energetic residues from the detonation of common US ordnance. International Journal of Energetic Materials and Chemical Propulsion, 10(2). doi: 10.1615/IntJEnergeticMaterialsChemProp.2012004956 Report.pdf
    10. ^ Walsh, M.R., Thiboutot, S., Walsh, M.E., Ampleman, G., Martel, R., Poulin, I. and Taylor, S., 2011. Characterization and fate of gun and rocket propellant residues on testing and training ranges (No. ERDC/CRREL-TR-11-13). Engineer Research and Development Center / Cold Regions Research and Engineering Lab (ERDC/CRREL) TR-11-13, Hanover, NH, USA. Report.pdf
    11. ^ 11.0 11.1 Taylor, S., Hewitt, A., Lever, J., Hayes, C., Perovich, L., Thorne, P. and Daghlian, C., 2004. TNT particle size distributions from detonated 155-mm howitzer rounds. Chemosphere, 55(3), pp.357-367. Report.pdf
    12. ^ Pennington, J.C., Jenkins, T.F., Ampleman, G., Thiboutot, S., Brannon, J.M., Hewitt, A.D., Lewis, J., Brochu, S., 2006. Distribution and fate of energetics on DoD test and training ranges: Final Report. ERDC TR-06-13, Vicksburg, MS, USA. Also: SERDP/ESTCP Project ER-1155. Report.pdf
    13. ^ Hewitt, A.D., Jenkins, T.F., Ramsey, C.A., Bjella, K.L., Ranney, T.A. and Perron, N.M., 2005. Estimating energetic residue loading on military artillery ranges: Large decision units (No. ERDC/CRREL-TR-05-7). Report.pdf
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    18. ^ Walsh, M.E., Ramsey, C.A., Collins, C.M., Hewitt, A.D., Walsh, M.R., Bjella, K.L., Lambert, D.J. and Perron, N.M., 2005. Collection methods and laboratory processing of samples from Donnelly Training Area Firing Points, Alaska, 2003 (No. ERDC/CRREL-TR-05-6). Report.pdf
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    See Also