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Emulsified Vegetable Oil (EVO) is commonly added as a slowly fermentable substrate to stimulate ''in situ'' anaerobic bioremediation. This article summarizes information about EVO transport in the subsurface, consumption during anaerobic bioremediation, and methods for effectively distributing EVO throughout the target treatment zone.
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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>
  
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'''Related Article(s)''':
  
'''Related Article(s):'''
 
*[[Bioremediation - Anaerobic |Anaerobic Bioremediation]]
 
*[[Bioremediation - Anaerobic Design Considerations| Anaerobic Bioremediation Design Considerations]]
 
*[[Chlorinated Solvents]]
 
  
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'''CONTRIBUTOR(S):'''  [[Dr. Samuel Beal]]
  
'''CONTRIBUTOR(S):''' [[Dr. Robert Borden, P.E.]]
 
  
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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):'''
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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)]]
  
*[[media:2017-Borden-Post-Remediation_Evaluation_of_EVO_Treatment.pdf| Post-Remediation Evaluation of EVO Treatment – How Can We Improve Performance?]]<ref name = "Borden2017EVO">Borden, R.C., 2017. Post-Remediation Evaluation of EVO Treatment: How Can We Improve Performance. Environmental Security Technology Certification Program, Alexandria, VA. ER-201581[[media:2017-Borden-Post-Remediation_Evaluation_of_EVO_Treatment.pdf| Report.pdf]]</ref>
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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>.
*[[media:2006-Solutions-IES-Protocol_for_Enhanced_In_Situ_Bioremediation.pdf| Protocol for Enhanced In Situ Bioremediation Using Emulsified Edible Oil (Solutions-IES, 2006)]]<ref>Solutions-IES, 2006.  Protocol for Enhanced In Situ Bioremediation Using Emulsified Edible Oil. Environmental Security Technology Certification Program, Arlington, VA, USA. ER 200221 [[media:2006-Solutions-IES-Protocol_for_Enhanced_In_Situ_Bioremediation.pdf| Report.pdf]]</ref>
 
  
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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>
  
==Introduction==
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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).
  
Emulsified Vegetable Oil (EVO) is commonly added as a slowly fermentable substrate to stimulate the ''in situ''<u> anaerobic bioremediation</u> of chlorinated solvents, explosives, perchlorate, chromate, and other contaminants.  However, effective treatment requires that EVO be distributed throughout the target treatment zone to optimize microbial growth and therefore contaminant degradation.
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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"/>.
  
==EVO Properties, Transport and Retention in the Subsurface==
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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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|-
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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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|}
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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]]
  
[[File:Borden3w2_Fig1.PNG|thumbnail| Figure 1. Photo-micrograph of EVO (0.7 µm median diameter).  White scale bar 25 µm. ]]
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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.
  
EVO is most commonly purchased from a commercial supplier and shipped to the site as a concentrated emulsion containing 45 to 60% vegetable oil.  These factory prepared emulsions are generally stable but do have a finite shelf-life (typically several months), which can be can be significantly shortened by extremes in storage temperature.  Soybean oil is commonly used because of its availability, good handling characteristics, and relatively low cost.  The oil provides a slow release organic substrate to support long-term anaerobic activity.  The remainder of the EVO formulation consists of: (a) more readily fermentable soluble substrates (e.g. fatty acids or alcohols); (b) surfactants to reduce oil droplet interfacial tension, stabilize the emulsion and reduce oil droplet flocculation; and (c) water.  The soluble substrates are first used by bacteria to reduce other terminal electron acceptors (oxygen, ferric iron, sulfate etc) and generate rapid, initial growth of the required bacteria.  In some cases, additional nutrients are added to enhance microbial growth including nitrogen, phosphorus, yeast extract, and vitamin B<sub>12</sub>. The median oil droplet size of factory prepared emulsions is commonly in the range of 0.5 to 2.0 µm, which provides emulsion stability during shipping and also improves transport through typical aquifer materials (Figure 1).  Some product vendors provide more concentrated EVO products containing oil and surfactant that do not contain water to save on shipping costs.  These products must be emulsified in the field by adding water and mixing.  Typically, these field prepared emulsions are not as stable as factory prepared emulsions, and often have much larger oil droplets.
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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)]]
  
Once injected, the oil droplets are transported through the aquifer pore spaces by flowing groundwater. Experimental and mathematical modeling studies by Soo and Radke<ref>Soo, H. and Radke, C.J., 1984. Flow mechanism of dilute, stable emulsions in porous media. Industrial & engineering chemistry fundamentals, 23(3), pp.342-347. [https://doi.org/10.1021/i100015a014 doi: 10.1021/i100015a014]</ref><ref >Soo, H. and Radke, C.J., 1986. A filtration model for the flow of dilute, stable emulsions in porous media-I. Theory. Chemical Engineering Science, 41(2), pp.263-272. [https://doi.org/10.1016/0009-2509(86)87007-5 doi: 10.1016/0009-2509(86)87007-5]</ref><ref>Soo, H., Williams, M.C. and Radke, C.J., 1986. A filtration model for the flow of dilute, stable emulsions in porous media-II. Parameter evaluation and estimation. Chemical Engineering Science, 41(2), pp.273-281. [https://doi.org/10.1021/es304641b doi: 10.1016/0009-2509(86)87008-7]</ref> have shown that oil droplets larger than the sediment pores are rapidly removed by straining with a large, permanent permeability loss. The median pore size of sand aquifers is typically over 100 µm<ref>Coulibaly, K.M. and Borden, R.C., 2004. Impact of edible oil injection on the permeability of aquifer sands. Journal of Contaminant Hydrology, 71(1-4), pp.219-237. [https://doi.org/10.1016/j.jconhyd.2003.10.002 doi: 10.1016/j.jconhyd.2003.10.002]</ref> which is orders of magnitude greater than the oil droplet diameter (< 2 µm) of factory prepared emulsions, so physical straining is not a significant retention mechanism in sands. However, field prepared emulsions often have larger oil droplets, so physical straining of the large droplets can be significant.
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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.
  
Common factory prepared emulsions are retained by aquifer material when the small oil droplets collide with sediment surfaces and stick (referred to as interception).  Retention of small oil droplets (diameter < 2 µm) by aquifer material can be described by deep-bed filtration theory<ref name= "Ryan1996">Ryan, J.N. and Elimelech, M., 1996. Colloid mobilization and transport in groundwater. Colloids and surfaces A: Physicochemical and engineering aspects, 107, pp.1-56. [https://doi.org/10.1016/0927-7757(95)03384-X doi: 10.1016/0927-7757(95)03384-X]</ref><ref name= "Logan1999">Logan, B.E., 1999. Environmental transport processes. John Wiley & Sons, New York</ref><ref name= "Coulibaly2006">Coulibaly, K.M., Long, C.M. and Borden, R.C., 2006. Transport of edible oil emulsions in clayey sands: One-dimensional column results and model development. Journal of Hydrologic Engineering, 11(3), pp.230-237. [https://doi.org/10.1061/(asce)1084-0699(2006)11:3(230) doi: 10.1061/(ASCE)1084-0699(2006)11:3(230)]</ref> where droplet capture by the sediment surfaces is a function of: (1) the frequency that droplets collide with sediment surfaces; and (2) the collision efficiency, which is the fraction of droplets colliding with the sediment surfaces that are actually retained<ref>Westall, J.C. and Gschwend, P.M., 1993. Mobilizing and depositing colloids. Manipulation of groundwater colloids for environmental restoration. ISBN 9780873718288]</ref><ref name= "Ryan1996"/><ref name= "Logan1999"/>. 
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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>]]
  
Collision frequency between oil droplets and sediment surfaces depends on groundwater flow velocity (advection), Brownian motion (diffusion), and gravitational settling or floatation. Very small droplets vibrate rapidly due to Brownian motion, resulting in frequent collisions with particle surfaces and rapid removal.  Large droplets float, colliding with the roof of the sediment pores, increasing removal.  For vegetable oil emulsions at typical groundwater velocities, the lowest collision frequency occurs at a particle size of 0.5 to 2 µm<ref>Borden, R.C., 2007.  Engineering Delivery of Insoluble Amendments. Partners in Environmental Technology Symposium & Workshop, SERDP, Washington, DC</ref>.
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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.
  
Collision efficiency varies due to a variety of factors including pH, droplet and matrix grain surface coatings, ionic strength, surface roughness, sediment surface charge heterogeneity, and blocking of the sediment surface with previously retained droplets<ref>Bolster, C.H., Mills, A.L., Hornberger, G.M. and Herman, J.S., 2001. Effect of surface coatings, grain size, and ionic strength on the maximum attainable coverage of bacteria on sand surfaces. Journal of Contaminant Hydrology, 50(3-4), pp.287-305. [https://doi.org/10.1016/S0169-7722(01)00106-1 doi: 10.1016/S0169-7722(01)00106-1]</ref><ref>Johnson, P.R. and Elimelech, M., 1995. Dynamics of colloid deposition in porous media: Blocking based on random sequential adsorption. Langmuir, 11(3), pp.801-812. [https://doi.org/10.1021/la00003a023 doi: 10.1021/la00003a023]</ref><ref>Rijnaarts, H.H., Norde, W., Bouwer, E.J., Lyklema, J. and Zehnder, A.J., 1996. Bacterial deposition in porous media related to the clean bed collision efficiency and to substratum blocking by attached cells. Environmental Science & Technology, 30(10), pp.2869-2876. [https://doi.org/10.1021/es960597b doi: 10.1021/es960597b]</ref><ref>Rijnaarts, H.H., Norde, W., Bouwer, E.J., Lyklema, J. and Zehnder, A.J., 1996. Bacterial deposition in porous media: effects of cell-coating, substratum hydrophobicity, and electrolyte concentration. Environmental Science & Technology, 30(10), pp.2877-2883. [https://doi.org/10.1021/es9605984 doi: 10.1021/es9605984]</ref>. Oil droplets and sediment particles typically take on an electrical charge and are surrounded by a <u>double layer</u> of charged ions.  When both the oil droplets and sediment surfaces have a negative charge, the oil droplets tend to be repelled by the sediments, reducing oil retention by the sediments.  When the oil droplets are negatively charged and the sediments are positive or neutral, the oil droplets are more likely to stick and be retained by the sediment. 
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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>.
  
[[File:Borden3w2 Fig2.png|thumbnail|Figure 2. Animation illustrating oil droplet transport and retention in porous media]]
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==Sample Processing==
As a dilute emulsion containing millions of negatively charged oil droplets migrates through the aquifer pore spaces, it encounters some positively charged locations. If the oil droplet ‘bumps into the sediment’ at that location, the droplet will likely stick and fill up that site (Figure 2).  Additional oil droplets will be repelled by the attached droplet and migrate further through the aquifer, gradually filling up the available attachment sites.  In this way, the emulsion gradually saturates the available attachment sites and continues to migrate with the flowing groundwater. The maximum amount of oil that can be retained by an aquifer is a function of the oil droplet properties (diameter, surface charge), chemical characteristics of the sediment surface (e.g., presence of organic or iron oxide coatings), and surface area available for droplet attachment. Sediments with a high clay content are expected to have a higher maximum oil retention because of the greater surface area and number of sites available for oil droplet attachment. Fine grain sediments will also have smaller pores, so physical straining of oil droplets becomes more important.
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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.
  
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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.
  
'''Droplet transport mp4 file here (cannot upload)'''
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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).
  
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<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>
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<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>
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<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>
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<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>
  
A common measure of suspension or emulsion stability is <u>zeta potential</u> which is the potential difference between the bulk fluid and the stationary fluid layer attached to the particle surface.  Particles that have a highly negative (or highly positive) zeta potential will not flocculate.  However, when zeta potential is close to zero, attractive forces may exceed the electrostatic repulsion and the emulsion may break and flocculate. Typical rules of thumb for negatively charged emulsions (zeta potential < 0) are ([https://en.wikipedia.org/wiki/Zeta_potential Zeta Potential]):
+
==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>)
 
|-
 
|-
|align=left|- rapid flocculation||&nbsp;&nbsp;&nbsp;&nbsp; 0 mV||&nbsp;&nbsp;&nbsp;&nbsp; < ||&nbsp;&nbsp;&nbsp;&nbsp; zeta potential ||&nbsp;&nbsp;&nbsp;&nbsp; <||&nbsp;&nbsp;&nbsp;&nbsp; -5 mV
+
! rowspan="2" | Compound
 +
! colspan="2" | Soil Reporting Limit (mg/kg)
 
|-
 
|-
|align=left|- incipient instability||&nbsp;&nbsp;&nbsp;&nbsp;-10 mV ||&nbsp;&nbsp;&nbsp;&nbsp; < ||&nbsp;&nbsp;&nbsp;&nbsp; zeta potential ||&nbsp;&nbsp;&nbsp;&nbsp; <||&nbsp;&nbsp;&nbsp;&nbsp; -30 mV
+
! HPLC (8330)
 +
! GC (8095)
 
|-
 
|-
|align=left|- moderate stability||&nbsp;&nbsp;&nbsp;&nbsp; -30 mV||&nbsp;&nbsp;&nbsp;&nbsp; < ||&nbsp;&nbsp;&nbsp;&nbsp; zeta potential ||&nbsp;&nbsp;&nbsp;&nbsp; <||&nbsp;&nbsp;&nbsp;&nbsp; -40 mV
+
| HMX || 0.04 || 0.01
 
|-
 
|-
|align=left|- good stability ||&nbsp;&nbsp;&nbsp;&nbsp; -40 mV||&nbsp;&nbsp;&nbsp;&nbsp; < ||&nbsp;&nbsp;&nbsp;&nbsp; zeta potential ||&nbsp;&nbsp;&nbsp;&nbsp; <||&nbsp;&nbsp;&nbsp;&nbsp; -61 mV
+
| RDX || 0.04 || 0.006
 
|-
 
|-
|align=left|- excellent stability||&nbsp;&nbsp;&nbsp;&nbsp; ||&nbsp;&nbsp;&nbsp;&nbsp;  ||&nbsp;&nbsp;&nbsp;&nbsp; zeta potential ||&nbsp;&nbsp;&nbsp;&nbsp; <||&nbsp;&nbsp;&nbsp;&nbsp; -61 mV
+
| [[Wikipedia: 1,3,5-Trinitrobenzene | TNB]] || 0.04 || 0.003
|}
 
 
 
Zeta potential and maximum oil retention were measured in sediments from two sites (SA17 Zone B and OU2) using either deionized water (DI water) or a solution of 200 mg/L CaCl<sub>2</sub><ref name = "Borden2017EVO"/>. In DI water, the zeta potential of the EVO (EOS 598B42) was -43 mV indicating good stability, while the zeta potential of the soil varied from -20 to -30 mV indicating incipient instability (Table 1).  However, in the CaCl<sub>2</sub> solution, zeta potential of the soils and emulsion were much closer to zero indicating rapid flocculation.  The much weaker repulsion of the oil droplets by the sediment particles in the CaCl<sub>2</sub> solution resulted in a large increase in maximum oil retention (Table 2). These results are consistent with the common practice of adding multivalent cations to water treatment systems to reduce zeta potential and enhance flocculation of suspended particles.  In general, trivalent cations (Fe<sup>+3</sup>, Al<sup>+3</sup>) are more effective flocculants than divalent cations (Ca<sup>+2</sup>, Mg<sup>+2</sup>, Fe<sup>+2</sup>, Mn<sup>+2</sup>), which are more effective than mono-valent cations (Na<sup>+</sup>, K<sup>+</sup>).
 
 
 
These results demonstrate that dissolved cation concentration (Na<sup>+</sup>, K<sup>+</sup>, Ca<sup>+2</sup>, Mg<sup>+2</sup>, Mn<sup>+2</sup>, Fe<sup>+2</sup>) can have a major impact on zeta potential and oil retention.  High concentations of dissolved cations will occur naturally in aquifers with high total dissolved solids (Na<sup>+</sup>, K<sup>+</sup>) or with carbonate minerals (Ca<sup>+2</sup>, Mg<sup>+2</sup>).  In situ bioremediation can increase cation concentration by release of dissolved Mn<sup>+2</sup> or Fe<sup>+2</sup> and by addition of alkaline materials (NaHCO<sub>3</sub>, Mg(OH) <sub>2</sub>), if needed to raise pH. 
 
 
 
{| class="wikitable" style="text-align: center;"
 
|+ colspan="3" | Table 1. Effect of solution composition on zeta potential
 
 
|-
 
|-
! rowspan="2" | Colloid
+
| TNT || 0.04 || 0.002
! colspan="2" | Average Zeta Potential (mV) (standard deviation)
 
 
|-
 
|-
! DI Water
+
| [[Wikipedia: 2,6-Dinitrotoluene | 2,6-DNT]] || 0.08 || 0.002
! 200 mg/L CaCl<sub>2</sub>
 
 
|-
 
|-
| SA17 Soil 15-23’ || -29.4 (0.8) || -8.5 (0.5)
+
| 2,4-DNT || 0.04 || 0.002
 
|-
 
|-
| SA17 Soil 30-40’|| -22.3 (0.9) || -7.5 (0.9)
+
| 2-ADNT || 0.08 || 0.002
 
|-
 
|-
| OU2 Soil 37-40’ || -19.9 (0.5) || -12.2 (0.9)
+
| 4-ADNT || 0.08 || 0.002
 
|-
 
|-
| EOS 598B42|| -43.0 (0.7) || -10.3 (0.4)
+
| NG || 0.1 || 0.01
|}
 
 
 
{| class="wikitable" style="text-align: center;"
 
|+ colspan="3" | Table 2.  Oil retention in laboratory columns flushed with EOS598B42 and either DI water or 200 mg/L CaCl<sub>2</sub>
 
 
|-
 
|-
! rowspan="2" | Aquifer Material
+
| [[Wikipedia: Dinitrobenzene | DNB ]] || 0.04 || 0.002
! colspan="2" | Average Oil Retention (g oil/g sediment) (standard deviation)
 
 
|-
 
|-
! DI Water
+
| [[Wikipedia: Tetryl | Tetryl ]]  || 0.04 || 0.01
! 200 mg/L CaCl<sub>2</sub>
 
 
|-
 
|-
| SA17 Zone B || 0.0027 (0.0027)|| 0.0133 (0.0060)
+
| [[Wikipedia: Pentaerythritol tetranitrate | PETN ]] || 0.2 || 0.016
|-
 
| OU2 || 0.0144 (0.0018)|| 0.0381 (0.0114)
 
 
|}
 
|}
 
Detailed laboratory column, sandbox, and field studies have shown that EVO can be transported substantial distances through fine silty or clayey sand and fractured rock<ref name= "Coulibaly2006"/> <ref>Jung, Y., Coulibaly, K.M. and Borden, R.C., 2006. Transport of edible oil emulsions in clayey sands: 3D sandbox results and model validation. Journal of Hydrologic Engineering, 11(3), pp.238-244. [https://doi.org/10.1061/(asce)1084-0699(2006)11:3(238)  doi: 10.1061/(asce)1084-0699(2006)11:3(238)]</ref><ref name= "Borden2007a">Borden, R.C., 2007. Effective distribution of emulsified edible oil for enhanced anaerobic bioremediation. Journal of Contaminant Hydrology, 94(1-2), pp.1-12. [https://doi.org/10.1016/j.jconhyd.2007.06.001 doi: 10.1016/j.jconhyd.2007.06.001]</ref><ref>Borden, R.C., Beckwith, W.J., Lieberman, M.T., Akladiss, N. and Hill, S.R., 2007. Enhanced anaerobic bioremediation of a TCE source at the Tarheel Army Missile Plant using EOS. Remediation Journal: The Journal of Environmental Cleanup Costs, Technologies & Techniques, 17(3), pp.5-19. [https://doi.org/10.1002/rem.20130 doi: 10.1002/rem.20130]</ref><ref>Riha, B.D., Looney, B.B., Noonkester, J.V., Hyde, K. and Solutions, S.R.N., 2009. Treatability Study for Edible Oil Deployment for Enhanced cVOC Attenuation for T-Area, Savannah River Site: Interim Report–Year One. Technical Report SRNL-RP-2009-00539. Savannah River National Laboratory, Aiken, SC. [[media:2009-Riha-Treatability_Study_for_Edible_deployment..._SRNL-RP-2009-00539-F.pdf| Report.pdf]]</ref> <ref>Kovacich, M.S., Beck, D., Rabideau, T., Pettypiece, K.S., Noel, M., Zack, M.J. and Cannaert, M.T., 2007, May. Full-scale bioaugmentation to create a passive biobarrier to remediate a TCE groundwater plume. In Proceedings: Ninth International In Situ and On-Site Bioremediation Symposium, Baltimore, Maryland, USA. [[media:2007-Kovacich-Full-Scale_Bioaugmentation_to_Create_a_Passive_Biobarrier....pdf| Report.pdf]]</ref><ref name = "Watson2013">Watson, D.B., Wu, W.M., Mehlhorn, T., Tang, G., Earles, J., Lowe, K., Gihring, T.M., Zhang, G., Phillips, J., Boyanov, M.I. and Spalding, B.P., 2013. In situ bioremediation of uranium with emulsified vegetable oil as the electron donor. Environmental science & technology, 47(12), pp.6440-6448. [https://doi.org/10.1021/es3033555 doi: 10.1021/es3033555]</ref>.  However, once oil droplets attach to soil surfaces, they are strongly retained and do not migrate further.  Much effort has focused on developing EVO formulations with low retention to reduce the amount of oil required to treat a given volume of aquifer.  However, in some cases, higher oil retention is required to treat very high permeability gravels or fractured rock.  In these cases, EVO with large oil droplets can be used.  The large droplets increase oil retention by straining and by oil droplet buoyancy which causes the large droplets to collide with the roof of the sediment pores.
 
 
==EVO Consumption==
 
Shortly after injection, most oil droplets are immobilized on sediment surfaces.  The soluble substrates are rapidly consumed during reduction of background electron acceptors (oxygen, nitrate, manganese, iron and sulfate).  The oil (triglyceride) is fermented to hydrogen and acetic acid through a two-step process where the ester linkages between the glycerol (an alcohol) and the long-chain fatty acids (LCFAs) are hydrolyzed releasing free fatty acids and glycerol to solution.  Glycerol is very soluble and relatively easy to biodegrade, so this material is quickly consumed releasing 1,3-propanediol and then H<sub>2</sub> and acetate.  The LCFAs undergo further breakdown by ''beta''-oxidation releasing hydrogen (H<sub>2</sub>), one molecule of acetic acid (C<sub>2</sub>H<sub>4</sub>O<sub>2</sub>), and a new acid derivative with two fewer carbon atoms<ref name= "Sawyer1994">Sawyer, C.N., P.L. McCarty, and G.F. Parkin. 1994. Chemistry for Environmental Engineering. McGraw-Hill Inc. ISBN 10: 0070549788 / ISBN 13: 9780070549784</ref>. 
 
 
<div class="center"><big>C<sub>n</sub>H<sub>2n</sub>O<sub>2</sub> + 2 H<sub>2</sub>O &rArr; 2 H<sub>2</sub> + C<sub>2</sub>H<sub>4</sub>O<sub>2</sub> + C<sub>n-2</sub>H<sub>2n-4</sub>O<sub>2</sub>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</big> ''Reaction 1''</div>
 
 
By successive oxidation at the ''beta'' carbon atom, long-chain fatty acids (LCFAs) are whittled into short chain fatty acids (SCFAs) and acetic acid.  Four hydrogen atoms are released from saturated fatty acids for each acetic acid unit produced<ref name= "Sawyer1994"/>.  Unsaturated fatty acids undergo the same general process, but release two atoms of hydrogen for each acetic acid unit. 
 
 
Microcosm, modeling, and field studies by Tang et al.<ref>Tang, G., Wu, W.M., Watson, D.B., Parker, J.C., Schadt, C.W., Shi, X. and Brooks, S.C., 2013. U (VI) bioreduction with emulsified vegetable oil as the electron donor–microcosm tests and model development. Environmental science & technology, 47(7), pp.3209-3217. [https://doi.org/10.1021/es304641b doi: 10.1021/es304641b]</ref><ref>Tang, G., Watson, D.B., Wu, W.M., Schadt, C.W., Parker, J.C. and Brooks, S.C., 2013. U (VI) bioreduction with emulsified vegetable oil as the electron donor–model application to a field test. Environmental science & technology, 47(7), pp.3218-3225. [https://doi.org/10.1021/es304643h doi: 10.1021/es304643h]</ref>, and Watson et al <ref name = "Watson2013"/> indicate that the LCFA consumption rate, and associated H<sub>2</sub> and acetate production rate, is controlled by LCFA solubility.  LCFAs have a relatively low aqueous solubility and will precipitate in the presence of divalent cations (Ca<sup>+2</sup>, Mg<sup>+2</sup>, Mn<sup>+2</sup>, Fe<sup>+2</sup>) or sorb to clay<ref>Angelidaki, I., Petersen, S.P. and Ahring, B.K., 1990. Effects of lipids on thermophilic anaerobic digestion and reduction of lipid inhibition upon addition of bentonite. Applied Microbiology and Biotechnology, 33(4), pp.469-472. [https://doi.org/10.1007/BF00176668 doi: 10.1007/BF00176668]</ref>, reducing their bioavailability and fermentation rate.  Since LCFA precipitation/sorption is an equilibrium process, a portion of LCFA will be in the aqueous phase and available for fermentation.  The short chain fatty acids are much more soluble and sorption/precipitation of these materials is not a significant factor.
 
 
Immediately adjoining the precipitated LCFAs, H<sub>2</sub> and acetate will be produced, and aquifer redox conditions will become sulfate-reducing to methanogenic with H<sub>2</sub> varying between 1 and 10 nM<ref>Chapelle, F.H., Haack, S.K., Adriaens, P., Henry, M.A. and Bradley, P.M., 1996. Comparison of E h and H<sub>2</sub> Measurements for Delineating Redox Processes in a Contaminated Aquifer. Environmental Science & Technology, 30(12), pp.3565-3569. [https://doi.org/10.1021/es960249 doi: 10.1021/es960249]</ref> and acetate varying between 10<sup>5</sup> to 10<sup>7</sup> nM (6 to 600 mg/L).  H<sub>2</sub> concentrations are maintained at low levels by rapid consumption of background electron acceptors or chlorinated solvents.  If the chlorinated solvents and other electron acceptors are depleted in the area immediately adjoining the LCFAs, H<sub>2</sub> will be fermented to CH<sub>4</sub> and will no longer be available for enhanced reductive dechlorination (ERD).  In contrast, acetate turnover is much slower, and dissolved acetate can migrate with flowing groundwater, eventually reaching contaminated portions of the aquifer, stimulating the reduction of PCE, TCE and other more highly chlorinated compounds.  However, ''c''DCE and VC are only efficiently degraded by <u>Dehalococcoides spp.</u> which require H<sub>2</sub> as an electron donor.  Since elevated H<sub>2</sub> levels only occur near where LCFAs are being fermented, ''c''DCE and VC will only be reduced to ethene in close proximity to the precipitated LCFAs. 
 
 
Given that the contaminant distribution in the aquifer is almost never known, the best approach is to distribute EVO as uniformly as possible throughout the target treatment zone. 
 
 
[[File:Borden3w2 Fig3.png|thumbnail| Figure 3. EVO mixed in field during early pilot test]]
 
 
==Injection System Design==
 
There are a variety of different approaches that can be used to <u>inject emulsions</u> in the subsurface including: (a) injection only using grids of temporary or permanent wells; (b) recirculation using systems of injection and pumping wells; and (c) barriers.  Each of these approaches has advantages and disadvantages with the ‘best’ approach dependent on site-specific conditions.  For each approach, cost and effectiveness are a function of the well layout and injection sequence.
 
 
Projects involving injection of oil emulsions typically, but not always, involve the following steps: (1) installation of injection wells and associated equipment; (2) preparation or purchase of a concentrated emulsion; and (3) dilution of the concentrated emulsion with water and (4) injection.  Emulsions can be injected through the end of <u>direct push</u> tools, through temporary direct-push wells, or through permanent conventionally-drilled wells.  The selection of the most appropriate method for installing injection points depends on site-specific conditions including drilling costs, flow rate per well, and volume of fluid that must be injected. 
 
 
Using properly prepared emulsions, it is possible to move injected emulsions 10, 20, or in some cases even 50 ft away from the injection point.  However, achieving effective distribution of the emulsified oil often requires injecting large volumes of water.  Depending on the injection well layout and formation permeability, emulsion injection can require an hour to several days per well.  For greater efficiency, several wells may be injected at one time using a simple injection system manifold.
 
 
Modeling studies by Clayton and Borden (2009)<ref>Clayton, M.H. and Borden, R.C., 2009. Numerical modeling of emulsified oil distribution in heterogeneous aquifers. Groundwater, 47(2), pp.246-258. [https://doi.org/10.1111/j.1745-6584.2008.00531.x doi: 10.1111/j.1745-6584.2008.00531.x]</ref> showed that EVO distribution throughout a target treatment zone is controlled by: (1) injection point spacing; (2) mass of oil injected relative to the maximum oil retention capacity of the treatment zone (Mass Scaling Factor, SF<sub>M</sub>); (3) volume of dilute emulsion and/or chase water injected to distribute the emulsion relative to the total treatment zone pore volume (Volume Scaling Factor, SF<sub>V</sub>); and (4) timing of injection into different wells.  If too little oil is injected or too little fluid is injected, the oil will be retained by the sediment close to the injection wells and large portions of the aquifer will remain untreated.  Figure 4 shows the effect of SF<sub>M</sub> and SF<sub>V</sub> on volume contact efficiency (the fraction of treatment zone contacted) for a moderately heterogeneous aquifer treated with a uniform grid of injection wells.  For SF<sub>M</sub>> 0.4 and SF<sub>V</sub>>0.4, contact efficiencies greater than 50% can be achieved.  However, contact efficiencies greater than 70% are very difficult to achieve due to the spatial variations in permeability common to most aquifers. 
 
 
[[File:Borden3w2 Fig4.png|thumbnail|Figure 4. Effect of volume scaling factor (SFV) and mass scaling factor (SFM) on volume contact efficiency for a moderately heterogeneous aquifer with well spacing approximately equal to row spacing<ref name = "Borden2008">Borden, R.C., Clayton, M., Weispfenning, A.M., Simpkin, T. and Lieberman, M.T., 2008. Development of a design tool for planning aqueous amendment injection systems. Environmental Security Technology Certification Program, Arlington, Virginia. ESTCP Project ER-0626. [[media:2008-Borden-Development_of_a_design_tool_for_injections.pdf| Report.pdf]]</ref>. ]]
 
 
Designing an effective and efficient injection system is challenging due to the trade-offs between cost and performance.  In general, closer well spacing with more oil and more distribution water will improve contact efficiency, but also increase costs.  There are also trade-offs between costs for injection point installation and labor for fluid injection.  Increasing the separation between injection wells will reduce the number of wells, reducing drilling costs.  However, a larger well spacing can also increase the time required for injection, increasing labor costs.  An Excel spreadsheet-based <u>design tool</u> is available to assist in developing efficient and effective injection systems<ref name= "Borden2008"/><ref>Weispfenning, A.M. and Borden, R.C., 2008. A design tool for planning emulsified oil‐injection systems. Remediation Journal: The Journal of Environmental Cleanup Costs, Technologies & Techniques, 18(4), pp.33-47. [https://doi.org/10.1002/rem.20180 doi: 10.1002/rem.20180]</ref>.
 
 
Once the well spacing and injection volumes are selected, there are two basic approaches to injecting emulsions: (1) injection of a small volume of more concentrated emulsion (typically 10 to 20% oil by volume) followed by additional chase water to distribute the emulsion throughout the formation; or (2) continuous injection of a more dilute emulsion (typically 0.5 to 2% oil by volume).  Numerical modeling results indicate that the two approaches are both effective in distributing emulsion<ref name= "Borden2007a"/> and the choice should be based on personal preferences and site logistics.  In all cases, the concentrated emulsion should be diluted with enough water to reduce the viscosity to near that of water, reducing injection pressures.  After emulsion injection is complete, clean water should be injected at the end to push mobile oil out away from the injection point to reduce well fouling with bacteria and oil. 
 
 
==Summary==
 
Emulsified Vegetable Oil (EVO) is commonly added as a slowly fermentable substrate to stimulate ''in situ'' anaerobic bioremediation.  Commercially available EVO typically contains a mixture of 45 to 60% vegetable oil present in small (0.5 to 2.0 µm) droplets, more readily fermentable soluble substrates (e.g. fatty acids or alcohols), surfactants, nutrients and water.  Oil droplets are retained by aquifer material when they collide with sediment surfaces and stick (referred to as interception).  The tendency of oil droplets to stick to aquifer material varies due to a number of factors including pH, droplet and matrix grain surface coatings, ionic strength, surface roughness, sediment surface charge heterogeneity, and blocking of the sediment surface with previously retained droplets.  Following injection, the vegetable oil is hydrolyzed to glycerol and long-chain fatty acids (LCFAs), which are subsequently fermented to hydrogen (H<sub>2</sub>) and acetate.  The rate of LCFA fermentation and resulting H<sub>2</sub> production is limited by sorption to sediment surfaces and/or precipitation with divalent cations (Ca<sup>+2</sup>, Mg<sup>+2</sup>, Mn<sup>+2</sup>, Fe<sup>+2</sup>).  Since H<sub>2</sub> is rapidly consumed near where it is produced, the oil droplets should be distributed as uniformly as possible throughout the target treatment zone.  This involves injecting sufficient EVO and sufficient water to distribute the EVO throughout the treatment zone.
 
  
 
==References==
 
==References==
 
 
<references/>
 
<references/>
  
 
==See Also==
 
==See Also==
*[https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminated-Groundwater/ER-1205/ER-1205 Development of Permeable Reactive Barriers Using Edible Oils]
+
*[https://itrcweb.org/ Interstate Technology and Regulatory Council]
*[https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminated-Groundwater/ER-200221/ER-200221 Edible Oil Barriers for Treatment of Chlorinated Solvent- and Perchlorate-Contaminated Groundwater]
+
*[http://www.hawaiidoh.org/tgm.aspx Hawaii Department of Health]
*[https://www.serdp-estcp.org/Tools-and-Training/Environmental-Restoration/Groundwater-Plume-Treatment/Protocol-for-Enhanced-In-Situ-Bioremediation-Using-Emulsified-Edible-Oil Protocol for Enhanced In Situ Bioremediation Using Emulsified Edible Oil]
+
*[http://envirostat.org/ Envirostat]
*[https://www.serdp-estcp.org/Tools-and-Training/Environmental-Restoration/Groundwater-Plume-Treatment/Emulsion-Design-Tool-Kit Emulsion Design Tool Kit]
 

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