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Adsorption of contaminants by soils removes them from solution and slows down contaminant movement to groundwater. The majority of energetic materials experience reversible sorption in soils. In general, organic carbon is the best predictor of extent of adsorption of energetic materials in soils and sediments. However, different groups of energetic materials have different affinities for soils, with nitroaromatic compounds adsorbing more and nitroguanidine (NQ) and 3-nitro-1,2,4-triazol-5-one (NTO) having little adsorption. While overall energetic materials are not strongly adsorbed compared to other organic contaminants, like polycyclic aromatic hydrocarbons (PAHs), adsorption still influences attenuation of energetic materials in soils and can delay their transport to groundwater by 2 - 30 times relative to unreactive compounds under saturated conditions, and more when soil is unsaturated.
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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.  
 
 
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
'''Related Articles:'''
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'''Related Article(s)''':
*[Energetic Materials]
 
  
  
'''CONTRIBUTOR(S):''' [[Dr. Katerina Dontsova]]
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'''CONTRIBUTOR(S):''' [[Dr. Samuel Beal]]
  
  
 
'''Key Resource(s)''':  
 
'''Key Resource(s)''':  
*[https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminants-on-Ranges/Characterizing-Fate-and-Transport/ER-2220 Dissolution of NTO, DNAN, and Insensitive Munitions Formulations and Their Fates in Soils]<ref name="Dontsova2014">Dontsova, K., Taylor, S., Pesce-Rodriguez, R., Brusseau, M., Arthur, J., Mark, N., Walsh, M., Lever, J. and Simunek, J., 2014. Dissolution of NTO, DNAN, and Insensitive Munitions Formulations and Their Fates in Soils (No. ERDC/CRREL-TR-14-23).Engineer Research and Development Center Hanover NH Cold Regions Research and Engineering Lab. [http://www.environmentalrestoration.wiki/images/a/af/Dontsova-2014-Dissolution_and_Fate.pdf Report pdf]</ref>
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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>  
*[https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminants-on-Ranges/Identifying-and-Evaluating-Sources/ER-1691 SERDP project ER-1691: Dissolution Rate of Propellant Energetics from Nitrocellulose Matrices]<ref name="Taylor2012">Taylor, S., Dontsova, K., Bigl, S., Richardson, C., Lever, J., Pitt, J., Bradley, J.P., Walsh, M. and Simunek, J., 2012. Dissolution Rate of Propellant Energetics from Nitrocellulose Matrices (No. ERDC/CRREL-TR-12-9). Engineer Research and Development Center Hanover NH Cold Regions Research and Engineering Lab. [https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminants-on-Ranges/Identifying-and-Evaluating-Sources/ER-1691/ER-1691 ER-1691]</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>
*[https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminants-on-Ranges/Characterizing-Fate-and-Transport/ER-1481 SERDP project ER-1481: Characterization and Fate of Gun and Rocket Propellant Residues on Testing and Training Ranges]<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: Final report, ERDC. CRREL Technical Report TR-11-13, US Army Engineer Research and Development Center-Cold Regions Research and Engineering Laboratory, Hanover, NH. ER-1481. [https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminants-on-Ranges/Characterizing-Fate-and-Transport/ER-1481 ER-1481]</ref>
 
 
 
*[https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminants-on-Ranges/Characterizing-Fate-and-Transport/ER-1155 Distribution and Fate of Energetics on DoD Test and Training Ranges]<ref name= "Pennington2006">Pennington, J.C., Jenkins, T.F., Ampleman G., Thiboutot, S., Brannon, J.M., Hewitt, A.D., Lewis, J., Brochu, S., Diaz, E., Walsh, M.R., Walsh, M.E., Taylor, S., Lynch, J.C., Clausen, J., Ranney, T.A., Ramsey, C.A., Hayes, C.A., Grant, C.L., Collins, C.M., Bigl, S.R., Yost, S., Dontsova, K., 2006.  Distribution and fate of energetics on DoD test and training ranges: Final Report. ERDC TR-06-13. Vicksburg, MS: U.S. Army Engineer Research and Development Center. ER-1155. [http://www.environmentalrestoration.wiki/images/0/07/Pennington-2006-Distribution_and_Fate...Final_Report.pdf Report pdf]</ref>
 
 
 
==Energetic Materials==
 
'''Energetic materials''' are compounds that release large amounts of energy upon oxidation. They typically have high number of N-O bonds, often in the form of nitro groups. They are used in explosives, such as '''traditional and insensitive munitions, and propellants''', which are used to propel projectiles. Common energetic materials used on US training grounds include trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 2,4-dinitrotoluene (2,4-DNT), nitroglycerin (NG), nitroguanidine (NQ), 2,4-dinitroanisole (DNAN), and 3-nitro-1,2,4-triazol-5-one (NTO) (Fig. 1). Liquid propellants, like perchlorate, are not discussed here.
 
[[File:Dontsova-Article 1-Figure 1.PNG|500px|thumbnail|right|Figure 1. Common energetic materials, modified from Taylor et al., 2015<ref name="Taylor2015">Taylor, S., Halasz, A., Dontsova, K., Hawari, J., Thiboutot, S., Ampleman, G., 2015. Munitions Related Contamination: Source Characterization, Fate, and Transport. Technical Reference Document AVT197 / RTG063. NATO Science and Technology Organization (STO)</ref>.]]
 
 
 
'''Trinitrotoluene (TNT) ''' is used directly without mixing with other components as a fill for the projectiles, for example in howitzers, but is also part of a number of traditional formulations. Due to relatively low melting temperature (80.35°C), it is often used as a matrix in the melt cast formulations, such as Composition B (Comp B). Comp B (60% RDX, 39% TNT and 1% wax) is one of the most common traditional formulations and is used in both artillery and mortar shells. In Comp B, particles of RDX, material with higher melting temperature, are dispersed in a TNT (material with lower melting temperature) matrix allowing mixing of the two components of the formulation and filling of the shells.  Other formulations with TNT include '''Tritonal''' (a mixture of 80% TNT and 20% Al used in aerial bombs), Octol, and Comp H-6.
 
 
 
'''Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)''' is another common explosive material. In addition to Composition B, it is a main constituent in '''C4''', a demolition explosive composed mostly of military-grade RDX (91%), as well as polyisobutylene, a binder, oil, and di(2-ethylhexyl)sebacate, a plasticizer; '''Comp A4''' (97% RDX and 3% wax used in 40-mm grenades), and Comp H-6 (44% RDX and 29.5% TNT, 21% Al) among many others. RDX is also used in new insensitive munitions formulations '''IMX 104''' and '''PAX 21'''.
 
 
 
'''Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) ''' is an explosive in its own right and is used as main component in '''Octol''' (75% HMX and 25% TNT), a fill for antitank rockets, but also appears in formulations that contain RDX as an impurity (about 10% in industrial grade RDX).  
 
 
 
'''2,4-dinitrotoluene (2,4-DNT) ''' and its isomer 2,6-dinitrotoluene (2,6-DNT), which is present as an admixture in formulations containing 2,4-DNT, are components of solid propellant formulations. Solid propellant formulations have insoluble nitrocellulose matrix and depending on other components present in formulation, are classified as single base, double base, or triple base. Single base propellants include nitrocellulose only or nitrocellulose and 2,4-DNT. Example of the single base propellant is '''M1''' which has 10% 2,4-DNT and is used in howitzers.
 
 
 
'''Nitroglycerin (NG) ''' is a constituent in double base propellants, which can include 10 to 40% NG in addition to the nitrocellulose. Double base propellants are used in small arms, mortars, and howitzers.
 
 
 
'''Nitroguanidine (NQ)''' is a part of the triple base propellants, which in addition to nitrocellulose have NG and NQ. M31 used in artillery shells has 20% NG and 55% NQ. NQ is also used in new insensitive munitions formulation '''IMX 101'''.
 
 
 
'''2,4-Dinitroanisole (DNAN)''' and '''3-nitro-1,2,4-triazol-5-one (NTO)''' are energetic materials used in '''insensitive munitions''', new explosive formulations developed to decrease risk of unintended detonation due to shock or temperature and to ensure safe handling. These formulations include '''IMX 101''' (43% DNAN, 37% NQ, 20% NTO), '''IMX 104''' (53% NTO, 32% DNAN, 15% RDX), and '''PAX 21''' (34% DNAN, 30% ammonium perchlorate [AP], and 31% RDX). IMX 101 is a more stable replacement for TNT and has been used to fill artillery shells, while IMX 104 is analogous to Composition B and used as a fill for mortar shells. PAX 21 has been developed for mortars but has been shown to have high potential to deposit ammonium perchlorate during detonations<ref>Walsh, M.R., Walsh, M.E., Ramsey, C.A., Brochu, S., Thiboutot, S. and Ampleman, G., 2013. Perchlorate contamination from the detonation of insensitive high-explosive rounds. Journal of hazardous materials, 262, pp.228-233. [http://dx.doi.org/10.1016/j.jhazmat.2013.08.045 doi: 10.1016/j.jhazmat.2013.08.04]</ref> and was therefore discontinued.
 
 
 
Dissolved energetic materials can sorb to soil, slowing their movement and potentially affecting degradation through biological and abiotic mechanisms. Depending on their structure, energetic materials have different chemical properties and different affinity for soils. Soils are heterogeneous mixtures of inorganic and organic components, charged and not charged, non-polar and polar, with different affinities to different energetic materials. Many organic contaminants (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs)) are non-polar, so they have low affinity for water and have very high affinity to non-polar organic solvents, where they accumulate (“partition”) from water. Similarly, soil organic matter can also attract non-polar compounds from soil solution. The majority of energetic compounds, however, are polar. They can also partition to organic matter, but to a smaller extent than non-polar compounds (like PAHs and PCBs). For compounds that exhibit hydrophobic partitioning behavior, polarity of the compound and amount of organic matter in the soil determines how much they will adsorb; lower polarity and greater amount of organic matter results in greater adsorption. Ionic compounds do not partition, but can adsorb to charged parts of the soil through different mechanisms. Clay minerals and metal oxides and hydroxides (present as small “clay-sized” particles in soils) have charge. Clay minerals are negatively charged and oxides and hydroxides can be either positively or negatively charged depending on soil pH. Negatively charged minerals strongly adsorb positive compounds (not common among energetics) and do not adsorb negatively charged ones, while positively charged oxides can adsorb negatively charged compounds. Since pH influences charge of both energetics and soil constituents, it can also influence adsorption of energetics. In addition, there other types of interactions that can influence adsorption of nitroaromatic explosives discussed below.
 
 
 
To quantify soil adsorption soil scientists and environmental professionals use adsorption coefficient, ''K<sub>d</sub>'', a ratio between concentration of compound in soil (C<sub>s</sub>) and solution (C<sub>w</sub>) at equilibrium:
 
 
 
K<sub>d</sub> = C<sub>s</sub> / C<sub>w</sub>
 
  
Since organic matter is often the main part of the soil that influences adsorption, adsorption coefficients can be normalized to the amount of organic matter in the soil (usually expressed as fraction of organic carbon, ''f<sub>OC</sub>''). The resulting coefficient, ''K<sub>OC</sub>'', is defined as follows:
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==Introduction==
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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)]]
  
''K<sub>OC</sub>'' = ''K<sub>d</sub> / f<sub>OC</sub>''
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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>.
  
''K<sub>d</sub>'' describes linear adsorption where affinity of compounds for soil does not change with its concentration. This is generally true for partitioning-type adsorption. However, if other mechanisms are involved, it may no longer remain accurate. For example, if specific sites on soil surface, rather than organic matter in general, are participating in adsorption, these sites can be all occupied at high contaminant concentrations and no longer able to adsorb, resulting in decreased affinity.  
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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>
  
The Freundlich equation can be used to describe systems where there is a finite capacity for adsorption:
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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).
  
''C<sub>s</sub> = K<sub>f </sub>C<sub>w</sub><sup>n</sup>''
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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"/>.
  
where ''K<sub>f</sub>'' is Freundlich adsorption coefficient, and n is a parameter that indicates change in affinity of compound with concentration. If n equals 1, adsorption becomes linear. Non-linear adsorption does not allow identification of the sorption mechanism, but indicates that partitioning is not the only mechanism involved in compound adsorption.
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{| class="wikitable" style="float: right; text-align: center; margin-left: auto; margin-right: auto;"
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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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|-
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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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| Artillery FP || 2,4-DNT || <0.04 – 6.4 || 0.65 || 110
 +
|-
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| Antitank Rocket || HMX || 5.8 – 1,200 || 200 || 99
 +
|-
 +
| Bombing || TNT || 0.15 – 780 || 6.4 || 274
 +
|-
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| Mortar || RDX || <0.04 – 2,400 || 1.7 || 441
 +
|-
 +
| 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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|-
 +
| Artillery FP || 2,4-DNT || 0.60 – 1.4 || 0.92 || 26
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|-
 +
| Bombing || TNT || 13 – 17 || 14 || 17
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|-
 +
| Artillery/Bombing || RDX || 3.9 – 9.4 || 4.8 || 38
 +
|-
 +
| Thermal Treatment || HMX || 3.96 – 4.26 || 4.16 || 4
 +
|-
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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.
 +
|}
  
There is a retardation factor, R, which indicates how much arrival of compound will be delayed relative to the unreactive tracer. It can be calculated from adsorption coefficients (''K<sub>d</sub>''), bulk density of the soils (''ρ<sub>b</sub>) and moisture content (''θ''),  
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==Incremental Sampling Approach==
which for saturated conditions would be equal to soil porosity:
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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.
 +
[[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]]
  
''R = 1 + ρ<sub>b </sub> K <sub>d </sub> / θ''
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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.
  
For a compound that does not adsorb to soils, R = 1, while sorbing compounds will have values > 1. The larger the retardation, the longer it would take for compound to reach ground water.
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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)]]
  
The major chemical groups of energetics are nitroaromatics (TNT, 2,4-DNT and 2,6-DNT, and DNAN) and nitramines (RDX and HMX). Nitroglycerin, nitroguanidine, and NTO (nitrotriazole) are the most common representatives of their chemical groups, which also include derivative energetic materials. Below we describe sortion behavior for each of these groups.
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==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<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.
  
==Nitroaromatic Compounds==
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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>]]
  
'''Nitroaromatic compounds''' used as explosives include '''2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT) ''', and a new insensitive munition material '''2,4-dinitroanisole (DNAN) '''. Nitroaromatics have been shown to have similar behavior in the soils.  
+
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.
  
When adsorption of organic compounds is driven by hydrophobic partitioning to the organic matter in the soils, the polarity of the molecule is an indication of how well it will adsorb to the soils. Octanol water partitioning coefficient (K<sub>ow</sub>) is used as a measure of compound polarity, with Kow of 1 indicating equal affinity for polar water and non-polar octanol and higher numbers indicating higher affinity of compound for non-polar solvent and, by extension, for soil organic matter. Nitroaromatic energetic materials have octanol water partitioning coefficients values between 40 and 100 (Log K<sub>ow</sub> at 25° C for TNT is 1.86 - 2.00, for 2,4-DNT is 1.98, and for DNAN 1.64), meaning that they would be present in 40 to a 100 times higher concentrations in polar solvent than in water, and therefore are also likely to partition to soil organic matter. This is reflected in relatively high soil adsorption coefficients normalized to organic carbon (log''K<sub>OC</sub>'') values for TNT (2.48-3.04)<ref>Agency for Toxic Substances and Disease Registry (ATSDR), 1995. Toxicological profile for 2,4,6-trinitrotoluene. pp. 87-113. U.S. Department of Health and Human Services, Public Health Service.  [http://www.environmentalrestoration.wiki/images/c/c8/ATSDR-1995-2%2C4%2C6-trinitrotoluene.pdf Report pdf]</ref> and DNAN (2.24 ± 0.20<ref name= "Dontsova2014"/><ref>Arthur, J.D., Mark, N.W., Taylor, S., Brusseau, M.L., Simunek, J., Dontsova, K.M., in review. Batch soil adsorption and column transport studies of 2, 4-dinitroanisole (DNAN) in soils. J. Contam. Hydrol.</ref> to 2.45 ± 0.16<ref name= "Hawari2015">Hawari, J., Monteil-Rivera, F., Perreault, N.N., Halasz, A., Paquet, L., Radovic-Hrapovic, Z., Deschamps, S., Thiboutot, S. and Ampleman, G., 2015. Environmental fate of 2, 4-dinitroanisole (DNAN) and its reduced products. Chemosphere, 119, pp.16-23. [http://dx.doi.org/10.1016/j.chemosphere.2014.05.047 doi:10.1016/j.chemosphere.2014.05.047]</ref>).  
+
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>.
  
However, partitioning to soil organic carbon is not the only mechanism of adsorption for nitroaromatic energetics. Nitroaromatics have less affinity for soils as their concentration increases indicating that they are adsorbed to specific functional groups in the soils. Clay minerals, also called layer silicates or phyllosilicate clays, a common component in fine reactive fraction of the soils, strongly adsorb TNT, 2,4-DNT, and DNAN<ref name="Haderlein1996">Haderlein, S.B., Weissmahr, K.W. and Schwarzenbach, R.P., 1996. Specific adsorption of nitroaromatic explosives and pesticides to clay minerals. Environmental Science & Technology, 30(2), pp.612-622. [https://doi.org/10.1021/es9503701 doi:10.1021/es9503701]</ref><ref name="Linker2015">Linker, B.R., Khatiwada, R., Perdrial, N., Abrell, L., Sierra-Alvarez, R., Field, J.A. and Chorover, J., 2015. Adsorption of novel insensitive munitions compounds at clay mineral and metal oxide surfaces. Environmental Chemistry, 12(1), pp.74-84. [https://doi.org/10.1071/en14065 doi:10.1071/en14065]</ref>. Adsorption is increased when potassium is exchangeable cation neutralizing the negative charge in clay structures and in swelling clays with larger number of surfaces available for sorption. There are several explanations for mechanism of interaction between clays and nitroaromatics, either direct bond between clay silicate surfaces and nitroaromatic ring structures or indirect through exchangeable cations and nitro-groups of nitroaromatics. In soils, nitroaromatic adsorption by clays is decreased by mixed clay mineralogy, mixed cation composition, and organic and oxide coatings on soil clays<ref>Weissmahr, K.W., Hildenbrand, M., Schwarzenbach, R.P. and Haderlein, S.B., 1999. Laboratory and field scale evaluation of geochemical controls on groundwater transport of nitroaromatic ammunition residues. Environmental Science & Technology, 33(15), pp.2593-2600. [https://doi.org/10.1021/es981107d doi:10.1021/es981107d]</ref><ref name="Dontsova2009">Dontsova, K.M., Hayes, C., Pennington, J.C. and Porter, B., 2009. Sorption of high explosives to water-dispersible clay: Influence of organic carbon, aluminosilicate clay, and extractable iron. Journal of Environmental Quality, 38(4), pp.1458-1465. [https://doi.org/10.2134/jeq2008.0183 doi:10.2134/jeq2008.0183]</ref>.
+
==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%<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.
Because of the great variability between soils, in order to predict affinity of energetic compounds to any particular soil it is beneficial to be able to identify soil properties that are easily measured and related to already measured adsorption coefficients for other soils. Soil organic carbon and cation exchange capacity of the soils are both good predictors of soil adsorption for nitroaromatic compounds (Fig. 2). Organic carbon can adsorb nitroaromatics through hydrophobic partitioning and other mechanisms, while cation exchange capacity is a good indicator of a type of clay mineral present in the soil.
 
 
 
Transformation products of TNT and DNT, where nitro groups are reduced to amino-groups, can also adsorb to organic matter in the soils, both reversibly<ref name= "Brannon2002">Brannon, J.M. and Pennington, J.C., 2002. Environmental fate and transport process descriptors for explosives (No. ERDC/EL-TR-02-10). Engineer Research and Development Center Vicksburg MS Enviornmental Lab. [http://www.environmentalrestoration.wiki/images/9/9e/TR-02-10.pdf Report pdf]</ref><ref>Dontsova, K.M., Yost, S.L., Šimunek, J., Pennington, J.C. and Williford, C.W., 2006. Dissolution and transport of TNT, RDX, and Composition B in saturated soil columns. Journal of Environmental Quality, 35(6), pp.2043-2054. [https://doi.org/10.2134/jeq2006.0007 doi:10.2134/jeq2006.0007]</ref> and irreversibly<ref>Thorn, K.A. and Kennedy, K.R., 2002. 15N NMR investigation of the covalent binding of reduced TNT amines to soil humic acid, model compounds, and lignocellulose. Environmental Science & Technology, 36(17), pp.3787-3796. [https://doi.org/10.1021/es011383j doi:10.1021/es011383j]</ref><ref>Thorn, K.A., Pennington, J.C., Kennedy, K.R., Cox, L.G., Hayes, C.A. and Porter, B.E., 2008. N-15 NMR study of the immobilization of 2, 4-and 2, 6-dinitrotoluene in aerobic compost. Environmental Science & Technology, 42(7), pp.2542-2550. [https://doi.org/10.1021/es0720659 doi: 10.1021/es0720659]</ref><ref name= "Hawari2015"/>.
 
[[File:Dontsova-Article 1-Figure 2.PNG|800px|thumbnail|center|Figure 2. Linear correlation between a) measured TNT soil adsorption coefficients (''K<sub>d</sub>'') and cation exchange capacity (CEC) that accounts for clay and OM in the soil (P = 1.5 * 10<sup>-10</sup>; Data from Brannon and Pennington, 2002<ref name= "Brannon2002"/> and b) measured 2,4-DNT ''K<sub>d</sub>'' values and percent organic carbon (%OC) in the soil (P = 7.61 * 10<sup>-8</sup>; Data from Brannon and Pennington, 2002<ref name= "Brannon2002"/> and Taylor at al., 2012<ref name="Taylor2012"/>. P values < 0.01 indicate a highly significant correlation. Modified from Taylor et al., 2015<ref name="Taylor2015"/> and Dontsova et al., 2014.<ref name= "Dontsova2014"/>).]]
 
 
 
==Cyclic Nitramines==
 
[[File:Dontsova-Article 1-Figure 3.PNG|right|400 px|thumbnail|Figure 3. Linear correlation between percent organic carbon in soil and adsorption coefficients (''K<sub>d</sub>''), L kg<sup>-1</sup> equivalent to cm<sup>3</sup> g<sup>−1</sup>, for RDX<ref name="Tucker2002"/>.]]
 
 
 
Cyclic nitramines include '''hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)''' and '''octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)'''. RDX and HMX are more polar and have smaller octanol-water partitioning coefficients (''K<sub>ow</sub>'') values, 0.86 - 0.90 for RDX and 0.17 for HMX, than the nitro-aromatic compounds, TNT, DNT, and DNAN. RDX also has a lower affinity for soils<ref name= "Brannon2002"/><ref name="Tucker2002">Tucker, W.A., Murphy, G.J. and Arenberg, E.D., 2002. Adsorption of RDX to soil with low organic carbon: Laboratory results, field observations, remedial implications. Soil and Sediment Contamination, 11(6), pp.809-826. [http://dx.doi.org/10.1080/20025891107104 doi:10.1080/20025891107104]</ref><ref name="Tucker2002"/>. RDX is not adsorbed by clays or iron oxides<ref name="Haderlein1996"/><ref name="Dontsova2009"/>. Adsorption of RDX happens through hydrophobic partitioning to organic matter (isotherms are linear and reversible) and amount of organic carbon in the soils determines extent of RDX adsorption. Significant correlation between RDX ''K<sub>d</sub>'' values and soil organic-carbon content is observed (Fig. 3). HMX has a similar behavior to RDX, but higher ''K<sub>d</sub>'' values.
 
 
 
==Nitroglycerin (NG)==
 
Reported '''nitroglycerin''' soil adsorption coefficients range from 0.08 to 3.8 cm<sup>3</sup> g<sup>−1</sup> (estimated retardation factors between 1.2 and 11 for saturated conditions assuming soil bulk density of 1.3 g cm<sup>-3</sup>), lower than the ones determined for 2,4-DNT. This agrees within a factor of two lower ''K<sub>ow</sub>'' values (log ''K<sub>ow</sub>'' of 1.62), though a larger difference was measured in ''K<sub>d</sub>'' values than in ''K<sub>ow</sub> values for the two compounds. NG adsorption coefficients are not correlated with organic matter content (P = 0.4945), suggesting that other mechanisms are responsible for adsorption. NG is a polar molecule<ref>Winkler, D.A., 1985. Conformational analysis of nitroglycerin. Propellants, Explosives, Pyrotechnics, 10(2), pp.43-46. [https://doi.org/10.1002/prep.19850100204 doi:10.1002/prep.19850100204]</ref> and may form dipole-dipole and hydrogen bonds with polar moieties in the soils.
 
 
 
==Nitroguanidine (NQ)==
 
'''NQ''' is a polar compound, and can become negatively charged due to loss of proton from one of the amino groups (acid dissociation constant of ''pK<sub>a</sub>'' = 12.8), but it is not charged at environmental pH range<ref>Spanggord, R.J., Chou, T.W., Mill, T., Podoll, R.T. and Harper, J.C., 1985. Environmental Fate of Nitroguanidine, Diethyleneglycol Dinitrate, and Hexachloroethane Smoke. Phase 1. SRI International Menlo Park CA. [http://www.environmentalrestoration.wiki/images/0/0a/Spanggord-1985-Env.Fate.pdf Report pdf]</ref>. It is very weakly adsorbed by soils with reported adsorption coefficients for NTO below 0.60 cm<sup>3</sup>g<sup>–1</sup> (estimated retardation factor below 2.5 for saturated conditions)<ref name= "Pennington2006"/><ref name="Dontsova2007">Dontsova, K.M., Pennington, J.C., Yost, S., Hayes, C., 2007. Transport of nitroglycerin, nitroguanidine and diphenylamine in soils. Characterization and Fate of Gun and Rocket Propellant Residues on Testing and Training Ranges: Interim Report 1. Engineer Research and Development Center, Vicksburg, MS. [http://www.environmentalrestoration.wiki/images/4/44/Dontsova-2007-Charact._and_Fate.pdf Report pdf]</ref><ref name="Taylor2012"/>. Measured adsorption coefficients normalized to the organic carbon content (log ''K<sub>oc</sub>'') for NQ range between 0.81 and 1.66<ref name= "Pennington2006"/><ref name="Dontsova2007"/><ref name="Taylor2012"/>. However, organic carbon content is not a good predictor of NQ adsorption. NQ is a polar compound, has negative or low positive log ''K<sub>ow</sub>'' values (-0.89, 0.148)<ref>Haag, W.R., Spanggord, R., Mill, T., Podoll, R.T., Chou, T.W., Tse, D.S. and Harper, J.C., 1990. Aquatic environmental fate of nitroguanidine.Environmental Toxicology and Chemistry, 9(11), pp.1359-1367. [http://dx.doi.org/10.1002/etc.5620091105 doi:10.1002/etc.5620091105]</ref> and therefore is not expected to partition to the organic matter.  
 
  
 +
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.
  
 +
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).
  
 +
<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>
  
 +
==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.
  
 +
{| 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
    14. ^ 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). Report.pdf
    15. ^ 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. Report.pdf
    16. ^ 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. Report.pdf
    17. ^ 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. doi: 10.1016/S0045-6535(02)00528-3
    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
    19. ^ 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. Report.pdf

    See Also