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Acids are produced during Enhanced Reductive Dechlorination (ERD) which can cause pH to drop, inhibiting treatment. Alkaline materials including hydroxides and carbonates are sometimes added to the aquifer during ERD to maintain a pH of greater than 6, improving bioremediation performance. This article describes a simplified approach and a spreadsheet-based <u>design tool</u> for estimating the total amount of base required to achieve a specified target pH at the end of the treatment period, once all reactions have gone to completion.  To prevent overshoot and excessively high pH, users typically add a fraction of the total base required in several increments spread over time.
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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):'''
 
*[[pH Buffering in Aquifers]]
 
*[[Low pH Inhibition of Reductive Dechlorination]]
 
*[[Bioremediation – Anaerobic]]
 
*[[Chlorinated Solvents]]
 
  
  
'''CONTRIBUTOR(S):''' [[Dr. Robert Borden, P.E.]]
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'''CONTRIBUTOR(S):''' [[Dr. Samuel Beal]]
  
  
'''Key Resource(s):'''
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'''Key Resource(s)''':
*Spreadsheet-based <u>Design Tool -- Base Addition for ERD</u>
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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>
*[[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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*[[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>
  
 
==Introduction==
 
==Introduction==
Aquifer pH lower than 6 can reduce the efficiency of enhanced reductive dechlorination (ERD) and other in situ remediation processes.  This article describes a simplified approach using a spreadsheet-based <u>design tool</u> for estimating the total amount of base required to achieve a specified target pH at the end of the treatment period, once all reactions have gone to completion.  This approach requires simplification of several important processes controlling subsurface pH, and is only appropriate for developing initial estimates of the total amount of base required.  In practice, aquifer pH should be monitored during ERD and periodically adjusted to maintain conditions for optimal microbial growth and contaminant degradation. Early in the bioremediation process, reactions will not have gone to completion and less base will be required to maintain the target pH.  To prevent overshoot and excessively high pH, users typically add a fraction of the total base required in several increments spread over time.
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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)]]
==Background Aquifer pH==
 
In humid areas, rainfall combined with carbonic acid produced in the soil leaches out base cations (Na<sup>+</sup>, K<sup>+</sup>, Ca<sup>2+</sup>, Mg<sup>2+</sup>) gradually acidifying the soil. Figure 1 shows soil pH in the contiguous United States.
 
 
 
(FIGURE 1 HERE)  NEED TO REDUCE FILE SIZE
 
 
 
Groundwater pH is influenced by soil pH, but also by other factors.  As acidic water infiltrates through the soil profile, some of the acidity may be neutralized by dissolution of soil and aquifer minerals.  Silicate minerals including feldspars and micas can hydrolyze over time, consuming acid, and releasing dissolved cations (Na<sup>+</sup>, K<sup>+</sup>, Ca<sup>2+</sup>, Mg<sup>2+</sup>). However, these weathering reactions are slow, and are often not sufficient to prevent pH declines during ERD.  Figure 2 shows a cumulative frequency distribution of groundwater pH at a site in eastern North Carolina. Average soil pH at this site is approximately 5.  The vadose zone and surficial aquifer at the site are predominantly quartz sand and weathered clays, so weathering processes provide minimal buffering capacity.  90% of the groundwater pH measurements were between 4.5 and 6.0 indicating low soil pH at this site was a reasonable predictor of acidic groundwater.  At other sites containing carbonate minerals or relatively young rocks, mineral dissolution often results in greater buffering.
 
 
 
[[File:Borden2w2Fig2.png|thumbnail|left|Figure 2. Cumulative frequency distribution of groundwater pH measurements at site in eastern North Carolina where soil pH is approximately 5. ]]
 
 
 
==Groundwater Acidity==
 
Acidity is the amount of base required to neutralize acids present in a water sample. Since various acids can disassociate to different extents, two solutions with the same pH can have different acidities (see <u>pH Buffering in Aquifers</u>). In most cases, the acidity of the background groundwater is the sum of acidity from strong mineral acids (phosphoric, nitric, sulfuric, and hydrochloric acids), organic acids, and dissolved carbon dioxide.
 
Mineral acidity (also referred to as methyl orange acidity) is determined by titrating a sample with a strong base to pH=3.7 (Standard Method 2310, AWPA 2016).  If the initial pH is greater than 3.7, mineral acidity is zero. The spreadsheet-based <u>design tool</u> presented here uses this measurement to account for the base demand of any strong acids already present in the aquifer. Total acidity (commonly referred to as phenolphthalein acidity) should not be used to calculate the amount of base required because the titration endpoint of this parameter is pH 8.3, which will over-estimate the base requirement for optimal ERD.
 
 
 
Under low pH conditions, organic volatile fatty acids (acetic, propionic, etc.) can accumulate and contribute to acidity. However, in background groundwater, organic acid concentrations are generally low.  In the design tool, acidity from background organic acids is assumed to be negligible.  
 
 
 
In theory, acidity from dissolved carbon dioxide can be measured using a modification of Standard Method 2310<ref name = "APWA2016">American Public Health Association, American Water Works Association and Water Environment Federation (APWA, AWWA, and WEF), 2016. Standard Method 2320 Alkalinity, Standard methods for the examination of water and wastewater. [[media:2016-APWA-Standard_Method_2320_Alkalinity.pdf| Report.pdf]]</ref> in which the sample is titrated to a target pH using a strong base. When using this approach, special precautions should be taken to prevent any pH shift due to degassing of dissolved carbon dioxide from the sample during transport to the laboratory or during analysis of the sample. In the design tool, acidity from background dissolved carbon dioxide is instead calculated from the dissolved inorganic carbon concentration (DIC) and background pH. This eliminates the problem of pH shift due to dissolved carbon dioxide degassing.  Commercial laboratories can measure DIC using a modification of the Total Organic Carbon (TOC) procedure.
 
 
 
==Aquifer Buffering Capacity==
 
An aquifer’s buffering capacity is the resistance to pH change and is primarily due to two processes: (1) buffering by dissolved and solid carbonates; and (2) surface complexation and/or ion exchange reactions on mineral surfaces. While mineral weathering processes do influence long-term pH changes, weathering reactions are often too slow to prevent pH declines due to HCl and CO<sub>2</sub> production during ERD.
 
 
 
[[File:Borden2w2Fig3.png|thumbnail|right|400 px|Figure 3. Distribution of H<sub>2</sub>CO<sub>3</sub>*, HCO<sub>3</sub><sup>-</sup> and CO<sub>3</sub><sup>2-</sup> as a function of pH. ]]
 
 
 
''Buffering by Dissolved and Solid Carbonates''
 
In natural aqueous systems, pH buffers are predominantly weak acid anions that easily bind and release hydrogen ions. The most common are the weak acid anions produced by dissolved CO<sub>2</sub> <ref>Langmuir, D., 1997, Aqueous Environmental Geochemistry. Prentice-Hall, Inc. Upper Saddle River, NJ ISBN: 978-0023674129.</ref><ref>Drever, J.I., The Geochemistry of Natural Waters: Surface and Groundwater Environments. Prentice-Hall, Inc., ISBN 0132727900.</ref>.  When CO<sub>2</sub> dissolves in water, some CO<sub>2</sub> combines with H<sub>2</sub>O forming carbonic acid (H<sub>2</sub>CO<sub>3</sub>).  For convenience, the sum of dissolved CO<sub>2</sub> and H<sub>2</sub>CO<sub>3</sub> is often written as H<sub>2</sub>CO<sub>3</sub>*. H<sub>2</sub>CO<sub>3</sub>*can then disassociate releasing a bicarbonate ion (HCO<sub>3</sub><sup>-</sup>) and one H<sup>+</sup> or a carbonate ion (CO<sub>3</sub><sup>2-</sup>) and two H<sup>+</sup> by the following<ref name= "Stumm1996">Stumm, W. and Morgan, J.J., 1996. Aquatic chemistry; an introduction emphasizing chemical equilibria in natural waters. ISBN-13: 978-0471091738 and ISBN-10: 0471091731</ref>:
 
 
 
<div class="center"><big>H<sub>2</sub>CO<sub>3</sub>* &hArr; H<sup>+</sup> + HCO<sub>3</sub><sup>-</sup> &hArr; 2 H<sup>+</sup> + CO<sub>3</sub><sup>2-</sup>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</big> ''Reactions 1 and 2''</div>
 
 
 
Figure 3 shows the relative distribution of these solutes as a function of pH. The reactions are reversible so that (a) an influx of acid will cause the HCO<sub>3</sub><sup>-</sup> and CO<sub>3</sub><sup>2-</sup> ions to protonate, consuming the acid, or (b) an influx of base will cause dissociation (deprotonation) of H<sub>2</sub>CO<sub>3</sub>* and the bicarbonate ion to consume the base. The maximum resistance to pH change (buffering capacity) occurs when the pH is equal to the dissociation constant of either carbonic acid (pH = 6.3 @ 25°C) or of the bicarbonate ion (pH = 10.3 @ 25°C).  The buffering capacity of groundwater is measured with an alkalinity titration<ref>U.S. Geological Survey, 2015. National field manual for the collection of water-quality field data,  Alkalinity and acid neutralizing capacity.  US Geological Survey Techniques of Water-Resources Investigations, book 9, chap. A6., sec. 6.6. [[media:USGS-2015-Natl_Field_Manual.pdf| Report pdf]</ref><ref name= "APWA2016"/>.  The units of alkalinity can be given as milliequivalents (meq) per liter, but are often reported as mg CaCO<sub>3</sub>/L (milligrams of CaCO<sub>3</sub> per liter) using the following equation:
 
 
 
<div class="center">'''Alkalinity''' (mg CaCO<sub>3</sub>/L) '''= Alkalinity''' (meq/L) '''&times; 50''' (mg CaCO<sub>3</sub>/meq) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;''Equation 1''</div>
 
 
 
For a system open to a large reservoir of carbon dioxide (e.g. the atmosphere), the buffering capacity (assuming no soluble minerals are present) is a function of the partial pressure of carbon dioxide in the reservoir. Near the water table, groundwater is open to the atmosphere and can release excess dissolved CO<sub>2</sub> gas if its partial pressure is greater than the reservoir’s, essentially stripping some acid out of the groundwater by partially reversing the above reactions.  
 
 
 
In a closed system (e.g. below the water table), the buffering capacity is a function of the total dissolved carbonates (H<sub>2</sub>CO<sub>3</sub>*, HCO<sub>3</sub><sup>-</sup>, and CO<sub>3</sub></sub><sup>-2</sup>). When solid carbonate minerals are present (CaCO<sub>3</sub>, MgCO<sub>3</sub>, CaMg(CO<sub>3</sub>)<sub>2</sub>, FeCO<sub>3</sub>), carbonate mineral dissolution can limit pH declines caused by strong acids (e.g. HCl).  For example, in an aquifer containing solid CaCO<sub>3</sub>, the ambient groundwater is saturated with CaCO<sub>3</sub> (s). When HCl is produced by ERD, groundwater pH declines, and dissolved CO<sub>3</sub><sup>2-</sup> also declines as the carbonate ion is protonated by the added H<sup>+</sup> ions causing an increase in HCO<sub>3</sub><sup>-</sup> and/or H<sub>2</sub>CO<sub>3</sub>* (see Figure 3). The groundwater is now under-saturated and CaCO<sub>3</sub> will dissolve, consuming H<sup>+</sup> by the following reaction:
 
 
 
<div class="center"><big>CaCO<sub>3</sub>(s) + H<sup>+</sup> &rArr; Ca<sup>2+</sup> + HCO<sub>3</sub><sup>-</sup> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </big> ''Reaction 3''</div>
 
 
 
[[File:Borden2w2Fig4.png|thumbnail|right|400 px|Figure 4. Buffering capacity of aquifer solids from SA-17 and OU-2 measured in DI water<ref name = "Borden2017EVO"/>. The legend shows depth below ground surface in feet for individual samples. ]]
 
However, the solubility of carbonate minerals is relatively low, so solid carbonates are much less effective in limiting pH declines due to CO<sub>2</sub> production in the saturated zone.  Below the water table, CO<sub>2</sub> may not degas, causing a buildup of HCO<sub>3</sub><sup>-</sup>.  Geochemical modeling<ref name="Robinson2009">Robinson, C., Barry, D.A., McCarty, P.L., Gerhard, J.I. and Kouznetsova, I., 2009. pH control for enhanced reductive bioremediation of chlorinated solvent source zones. Science of the Total Environment, 407(16), pp.4560-4573. [http://dx.doi.org/10.1016/j.scitotenv.2009.03.029 doi:10.1016/j.scitotenv.2009.03.029]</ref> indicates that the aquifer can become supersaturated with CaCO<sub>3</sub> during ERD, causing carbonate dissolution to stop. As additional CO<sub>2</sub> is produced, CaCO<sub>3</sub> (s) will precipitate producing H<sup>+</sup> by the following reaction:  
 
 
 
<div class="center"><big>H<sub>2</sub>CO<sub>3</sub>* + Ca<sup>2+</sup> + CO<sub>3</sub><sup>2-</sup> &rArr; H<sup>+</sup> + HCO<sub>3</sub><sup>-</sup> + CaCO<sub>3</sub>(s) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </big> ''Reaction 4''</div>
 
 
 
[[File:Borden2w2Fig5.png|thumbnail|right| 400 px|Figure 5. Aquifer buffering capacity (pHBC) from multiple ERD sites<ref name = "Borden2017EVO"/>.]]
 
 
 
''Surface Complexation and Ion Exchange Reactions''
 
H<sup>+</sup> sorption to Fe and Al oxyhydroxides and clay minerals through surface complexation and ion exchange reactions can have a major impact on pH.  H<sup>+</sup> adsorbs strongly to some mineral surfaces, which can accumulate large amounts of H<sup>+</sup> as the solution pH declines and release the H<sup>+</sup> back to solution as the pH rises<ref>Davis, J.A. and Kent, D.B., 1990. Surface complexation modeling in aqueous geochemistry. Reviews in Mineralogy and Geochemistry, 23(1), pp.177-260. [https://doi.org/10.1021/es980312q doi: 10.1021/es980312q ]</ref><ref>Davis, J.A., Coston, J.A., Kent, D.B. and Fuller, C.C., 1998. Application of the surface complexation concept to complex mineral assemblages. Environmental Science & Technology, 32(19), pp.2820-2828. [https://doi.org/10.1021/es980312q  doi: 10.1021/es980312q]</ref>.  This strong buffer can reduce the pH decline in many systems, but can also greatly increase the amount of base required to increase aquifer pH.
 
 
 
''Estimating Aquifer Buffering Capacity''
 
 
 
When carbonate minerals are present, geochemical models<ref name="Robinson2009"/> are needed to determine the amount of buffering provided by carbonate mineral dissolution.  However, in many naturally low pH aquifers, carbonate minerals are absent and the extent of buffering can be estimated by adding a strong base to the aquifer solids, equilibrating for several days, and measuring the resulting pH.  These buffering curves are typically linear in the pH range of 4.5 to 6.5<ref>Magdoff, F.R. and Bartlett, R.J., 1985. Soil pH Buffering Revisited 1. Soil Science Society of America Journal, 49(1), pp.145-148. [https://doi.org/10.2136/sssaj1985.03615995004900010029x doi: 10.2136/sssaj1985.03615995004900010029x]</ref><ref>Liu, M., Kissel, D.E., Cabrera, M.L. and Vendrell, P.F., 2005. Soil lime requirement by direct titration with a single addition of calcium hydroxide. Soil Science Society of America Journal, 69(2), pp.522-530. [https://doi.org/10.2136/sssaj2005.0522 doi:10.2136/sssaj2005.0522]</ref><ref>Aitken, R.L. and Moody, P.W., 1994. The effect of valence and ionic-strength on the measurement of pH buffer capacity. Soil Research, 32(5), pp.975-984. [https://doi.org/10.1071/SR9940975 doi: 10.1071/SR9940975]</ref> recommend carrying out the titrations in a uniform ionic strength solution, most commonly 0.01 M CaCl<sub>2</sub>. 
 
  
Figure 4 shows the measured final pH versus meq of OH- added per kg of dry aquifer material. Incremental base addition results in a nearly linear increase in pH. The slopes of these curves were estimated by linear regression. pH buffer capacity (pHBC) is calculated as the inverse of the slope and is reported in units of milliequivalents per kilogram (meq/kg) per pH unit.
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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>.
  
Figure 5 shows cumulative frequency distributions for pHBC in 6 different contaminated aquifers in the eastern U.S. Within a single unit, pHBC values are reasonably constant, with the middle 50% of measurements varying by a factor of two. However, median pHBC values can vary by a factor of ten between sites and even between sandy versus clayey units on the same site.
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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>
  
==Acid and Base Production==
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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).
  
Multiple processes can produce or consume acidity during ERD including redox, precipitation, and hydrolysis reactions.  Table 1 shows the amount of H<sup>+</sup> released from some important redox reactions.  
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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"/>.
  
{| class="wikitable" style="text-align: center;"
+
{| class="wikitable" style="float: right; text-align: center; margin-left: auto; margin-right: auto;"
|+ colspan="5" | Table 1. Net Acid Production from Important Redox Reactions
+
|+ 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.)
 
|-
 
|-
! e<sup>-</sup> Acceptor
+
! Military Range Type !! Analyte !! Range<br/>(mg/kg) !! Median<br/>(mg/kg) !! RSD<br/>(%)
! e<sup>-</sup> Donor
 
! Product
 
! Reaction
 
! H<sup>+</sup> Produced<br/><span style="font-weight: normal; font-size: 85%;">per mole e<sup>-</sup> donor</span>
 
 
|-
 
|-
| PCE || H<sub>2</sub> || TCE || C<sub>2</sub>Cl<sub>4</sub> + H<sub>2</sub> → C<sub>2</sub>H<sub>3</sub>Cl<sub>3</sub> + H<sup>+</sup> + Cl<sup>-</sup> || 1
+
| colspan="5" style="text-align: left;" | '''Discrete Samples'''
 
|-
 
|-
| TCE || H<sub>2</sub> || ''c''DCE || C<sub>2</sub>HCl<sub>3</sub> + H<sub>2</sub> → C<sub>2</sub>H<sub>2</sub>Cl<sub>2</sub> + H<sup>+</sup> + Cl<sup>-</sup> || 1
+
| Artillery FP || 2,4-DNT || <0.04 – 6.4 || 0.65 || 110
 
|-
 
|-
| ''c''DCE || H<sub>2</sub> ||VC || C<sub>2</sub>H<sub>2</sub>Cl<sub>2</sub> + H<sub>2</sub> → C<sub>2</sub>H<sub>3</sub>Cl + H<sup>+</sup> + Cl<sup>-</sup> || 1
+
| Antitank Rocket || HMX || 5.8 – 1,200 || 200 || 99
 
|-
 
|-
| VC || H<sub>2</sub> ||Ethene || C<sub>2</sub>H<sub>3</sub>Cl + H<sub>2</sub> → C<sub>2</sub>H<sub>4</sub> + H<sup>+</sup> + Cl<sup>-</sup> || 1
+
| Bombing || TNT || 0.15 – 780 || 6.4 || 274
 
|-
 
|-
| H<sub>2</sub>O || Acetic Acid ||H<sub>2</sub>, HCO<sub>3</sub><sup>-</sup> || C<sub>2</sub>H<sub>4</sub>O<sub>2</sub> + 4 H<sub>2</sub>O → 2 H<sub>2</sub>CO<sub>3</sub>* + 4 H<sub>2</sub> || 2 (1 - &alpha;)
+
| Mortar || RDX || <0.04 – 2,400 || 1.7 || 441
 
|-
 
|-
| H<sub>2</sub>O || Lactic Acid ||H<sub>2</sub>, HCO<sub>3</sub><sup>-</sup> || C<sub>3</sub>H<sub>6</sub>O<sub>3</sub> + 3 H<sub>2</sub>O → 3 H<sub>2</sub>CO<sub>3</sub>* + 6 H<sub>2</sub> || 3 (1 - &alpha;)
+
| Artillery || RDX || <0.04 – 170 || <0.04 || 454
 
|-
 
|-
| H<sub>2</sub>O || Glucose ||H<sub>2</sub>, HCO<sub>3</sub><sup>-</sup> || C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> + 12 H<sub>2</sub>O → 6 H<sub>2</sub>CO<sub>3</sub>* + 12 H<sub>2</sub> || 6 (1 - &alpha;)
+
| colspan="5" style="text-align: left;" | '''Incremental Samples*'''
 
|-
 
|-
| H<sub>2</sub>O || Soybean Oil ||H<sub>2</sub>, HCO<sub>3</sub><sup>-</sup> || C<sub>56</sub>H<sub>100</sub>O<sub>6</sub> + 162 H<sub>2</sub>O → 56 H<sub>2</sub>CO<sub>3</sub>* + 156 H<sub>2</sub> || 56 (1 - &alpha;)
+
| Artillery FP || 2,4-DNT || 0.60 – 1.4 || 0.92 || 26
 
|-
 
|-
| Oxygen || H<sub>2</sub> ||H<sub>2</sub>O || O<sub>2</sub> + 2 H<sub>2</sub> → 2 H<sub>2</sub>O || 0
+
| Bombing || TNT || 13 – 17 || 14 || 17
 
|-
 
|-
| Nitrate || H<sub>2</sub> ||N<sub>2</sub>, OH<sup>-</sup> || NO<sub>3</sub><sup>-</sup> + 2 ½ H<sub>2</sub> → 2 H<sub>2</sub>O + ½ N<sub>2</sub> + OH<sup>-</sup>|| -1
+
| Artillery/Bombing || RDX || 3.9 – 9.4 || 4.8 || 38
 +
|-  
 +
| Thermal Treatment || HMX || 3.96 – 4.26 || 4.16 || 4
 
|-
 
|-
| Goethite || H<sub>2</sub> ||Fe<sup>2+</sup>, OH<sup>-</sup> || FeO(OH) + ½ H<sub>2</sub> → Fe<sup>2+</sup> + 2 OH<sup>-</sup>|| -2
+
| colspan="5" style="text-align: left; background-color: white;" | * For incremental samples, 30-100 increments and 3-10 replicate samples were collected.
|-
 
| Sulfate || H<sub>2</sub> || HS<sup>-</sup> || SO<sub>4</sub><sup>2-</sup> + 4 H<sub>2</sub> + Fe<sup>2+</sup> → FeS + 4 H<sub>2</sub>O || 0
 
|-
 
| H<sub>2</sub>CO<sub>3</sub>* || H<sub>2</sub> || CH<sub>4</sub> || H<sub>2</sub>CO<sub>3</sub>* + 4 H<sub>2</sub> → CH<sub>4</sub> + 2 H<sub>2</sub>O|| &alpha; - 1
 
 
|}
 
|}
  
During reductive dechlorination of PCE (C<sub>2</sub>Cl<sub>4</sub>) to TCE (C<sub>2</sub>HCl<sub>3</sub>), a chlorine atom (Cl) is replaced with hydrogen (H<sub>2</sub>) releasing one proton (H<sup>+</sup>) and one chloride (Cl<sup>-</sup>).
+
==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<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]]
  
<div class="center"><big>C<sub>2</sub>Cl<sub>4</sub> + H<sub>2</sub> &rArr; C<sub>2</sub>HCl<sub>3</sub> + H<sup>+</sup> + Cl<sup>-</sup>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </big> ''Reaction 5''</div>
+
DUs can vary in shape (Figure 4), size, number of increments, and number of replicates according to a project’s data quality objectives.
  
As TCE is further dechlorinated to ''c''DCE, VC and ethene, an additional proton is released for each chlorine removed. As a result, ERD can release large amounts of acid.  For example, complete reduction of one kilogram of PCE to ethene produces 0.9 kilograms of HCl.
+
[[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)]]
  
Organic substrates added as electron donors ferment in oxygen-poor environments, releasing H<sub>2</sub> and acetic acid. Acetic acid rarely accumulates during ERD, because it can be used by various cohorts of organisms for reduction of PCE and TCE, for reduction of background electron acceptors, or for fermentation to methane (CH<sub>4</sub>). Consumption of acetic acid by all of these processes produces H<sub>2</sub>CO<sub>3</sub>*. The amount of H<sub>2</sub>CO<sub>3</sub>* produced during fermentation of different substrates can be estimated with the following formula:
+
==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.
  
<div class="center"><big>C<sub>''&theta;''</sub>H<sub>''&beta;''</sub>O<sub>''&gamma;''</sub> + (3''&theta;'' - ''&gamma;'')H<sub>2</sub>O &rArr; ''&theta;''H<sub>2</sub>CO<sub>3</sub>* + (2''&theta;'' + ''&beta;''/2 - ''&gamma;'')H<sub>2</sub>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </big> ''Reaction 6''</div>
+
[[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>]]
  
{|
+
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.
|-
+
 
|where:
+
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>.
|-
 
| ''&theta;'' || is the number of carbon atoms per mole of substrate
 
|-
 
| ''&beta;'' || is the number of hydrogen atoms per mole of substrate
 
|-
 
| ''&gamma;'' || is the number of oxygen atoms per mole of substrate
 
|}
 
<br/>
 
  
[[File:Borden2w2Fig6.png|thumbnail|left|Figure 6. Fraction of H<sub>2</sub>CO<sub>3</sub>* not ionized (&alpha;) versus pH. ]]
+
==Sample Processing==
As shown in Figure 3, CO<sub>3</sub><sup>2-</sup> is only present in significant concentrations at pH > 8. For pH ranges relevant for ERD (5>pH>8), H<sup>+</sup> release from H<sub>2</sub>CO<sub>3</sub>* can be represented by the following reaction<ref name= "Stumm1996"/>.
+
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.
  
<div class="center"><big>H<sub>2</sub>CO<sub>3</sub>* &rArr; ''&alpha;'' H<sub>2</sub>CO<sub>3</sub>* + (1 - ''&alpha;'') H<sup>+</sup> +  (1 - ''&alpha;'') HCO<sub>3</sub><sup>-</sup> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </big> ''Reaction 7''</div>
+
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.
  
where &alpha; is the fraction of H<sub>2</sub>CO<sub>3</sub>* that does NOT ionize at the target pH with &alpha; = (1+ 10<sup>-6.352</sup> / [H<sup>+</sup>])<sup>-1</sup>. Figure 6 shows the variation in &alpha; as a function of pH.  At pH 6, &alpha; = 0.69, so 0.31 moles of H<sup>+</sup> are released for every mole of CO<sub>2</sub> produced. However at pH 7, &alpha; = 0.18, so 0.82 moles of H<sup>+</sup> are released for every mole of CO<sub>2</sub> produced.
+
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).
  
Reduction of some electron acceptors produces OH<sup>-</sup>, counter-acting acid produced from dechlorination and CO<sub>2</sub> production. Representative reactions for reduction of nitrate (NO<sub>3</sub><sup>-</sup>), iron oxides, sulfate  (SO<sub>4</sub><sup>2-</sup>) and bicarbonate (HCO<sub>3</sub><sup>-</sup>) are included in Table 1.  Goethite [FeO(OH)] is used as a typical iron oxide for these calculations.
+
<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>
  
==Base Addition==
+
==Analysis==
A variety of different bases have been used to raise the aquifer pH to stimulate ERD including soluble and solid carbonates, soluble and solid hydroxides, phosphates and silicate minerals. The carbonates and hydroxides are used most commonly because of their relatively low cost and easy availability.  Table 2 summarizes the physical properties of common basic salts used to raise pH.  
+
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="text-align: center;"
+
{| class="wikitable" style="float: center; text-align: center; margin-left: auto; margin-right: auto;"
|+ colspan="7" | Table 2. Physical Properties of Common Basic Salts used for pH Control
+
|+ 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
 
|-
 
|-
! Base
+
| [[Wikipedia: 2,6-Dinitrotoluene | 2,6-DNT]] || 0.08 || 0.002
! Formula
 
! Molecular<br/>Weight<br/><span style="font-weight: normal; font-size: 85%;">(g/mole)</span>
 
! OH<sup>-</sup><br/><span style="font-weight: normal; font-size: 85%;">(eq/mole)</span>
 
! OH<sup>-</sup><br/><span style="font-weight: normal; font-size: 85%;">(eq/kg Base)</span>
 
! Solubility<br/><span style="font-weight: normal; font-size: 85%;">(g/L)</span>
 
! Saturated<br/>solution pH
 
 
|-
 
|-
| Caustic Soda || NaOH || 40.0 || 1 || 25.0 || 1,100 || >14
+
| 2,4-DNT || 0.04 || 0.002
|-  
+
|-
| Caustic Potash || KOH || 56.1 || 1 || 17.8 || 1,200 || >14
+
| 2-ADNT || 0.08 || 0.002
 +
|-
 +
| 4-ADNT || 0.08 || 0.002
 
|-
 
|-
| Soda Ash || Na<sub>2</sub>CO<sub>3</sub> || 106 || 1 + &alpha; || 11.2 || 300 || ~11.7
+
| NG || 0.1 || 0.01
 
|-
 
|-
| Baking Soda || NaHCO<sub>3</sub> || 84 || &alpha; || 2.2 || 78 || ~8.3
+
| [[Wikipedia: Dinitrobenzene | DNB ]] || 0.04 || 0.002
 
|-
 
|-
| Hydrated Lime || Ca(OH)<sub>2</sub> || 74.1 || 2 || 27.0 || 1.85 || ~12.4
+
| [[Wikipedia: Tetryl | Tetryl ]]  || 0.04 || 0.01
 
|-
 
|-
| Magnesium<br/>Hydroxide ||Mg(OH)<sub>2</sub> || 58.3 || 2 || 34.3 || <0.01 || ~10.3
+
| [[Wikipedia: Pentaerythritol tetranitrate | PETN ]] || 0.2 || 0.016
 
|}
 
|}
<br/>
 
NaOH and KOH provide a large number of OH- equivalents (eq) per kg and are very soluble so only small volumes of base are required to raise the aquifer pH.  However, concentrated solutions of NaOH and KOH have pH > 14 which is inhibitory to bacteria, would expose workers to safety hazards, and can partially dissolve aluminosilicates.
 
 
As described above, solid calcium carbonate (CaCO<sub>3</sub>) is generally not effective in raising pH during ERD because of its low aqueous solubility.  Na<sub>2</sub>CO<sub>3</sub> and NaHCO<sub>3</sub> are much more soluble and can be effective in raising aquifer pH.  The amount of H<sup>+</sup> consumed per mole varies as a function of pH between pH 5 and 8<ref name= "Stumm1996"/>.  For closed conditions (below water table where CO<sub>2</sub> cannot degas) and pH < 8, NaHCO<sub>3</sub> and Na<sub>2</sub>CO<sub>3</sub> disassociate to H<sub>2</sub>CO<sub>3</sub>* and HCO<sub>3</sub><sup>-</sup>, consuming H<sup>+</sup> by the following reactions.
 
 
<div class="center"><big>NaHCO<sub>3</sub> + ''&alpha;'' H<sup>+</sup> &rArr; Na<sup>+</sup> + ''&alpha; '' H<sub>2</sub>CO<sub>3</sub>* + (1 – ''&alpha;'') HCO<sub>3</sub><sup>-</sup> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </big> ''Reaction 8''</div>
 
 
<div class="center"><big>Na<sub>2</sub>CO<sub>3</sub> + (1 + ''&alpha;'') H<sup>+</sup> &rArr; 2 Na<sup>+</sup> + ''&alpha;'' H<sub>2</sub>CO<sub>3</sub>* + (1 – ''&alpha;'') HCO<sub>3</sub><sup>-</sup> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </big> ''Reaction 9''</div>
 
 
At pH = 6, &alpha; = 0.69 so 0.69 moles of H<sup>+</sup> are consumed per mole of NaHCO<sub>3</sub> and 1.69 moles of H<sup>+</sup> consumed per mole of Na<sub>2</sub>CO<sub>3</sub> (Figure 6).  However at pH = 7, &alpha; = 0.18 so only 0.18 moles of H<sup>+</sup> are consumed per mole of NaHCO<sub>3</sub> and 1.18 moles of H<sup>+</sup> consumed per mole of Na2CO<sub>3</sub>.  As a result, bicarbonates and carbonates are relatively effective at raising the pH to 6.  However, these materials provide less alkalinity per unit mass at pH =7, increasing the amount of material required.
 
 
Ca(OH) <sub>2</sub> and Mg(OH) <sub>2</sub> provide large amounts of OH- per kg.  However, these materials have a low aqueous solubility, making them more difficult to distribute in the subsurface.<ref>Borden, R.C., Lai, Y.S., Overmeyer, J., Yuncu, B. and Allen, J.P., 2016.  In situ pH adjustment with colloidal Mg(OH)<sub>2</sub>.  Environmental Engineer and Scientist: Applied Research and Practice, accepted for publication, Vol 17, pp.28-33.</ref> describe the use of a colloidal form of Mg(OH) <sub>2</sub> with improved transport properties.
 
 
==Design Tool==
 
An MS Excel based <u>design tool</u> was developed to aid in estimating the amount of base required to achieve a specified target pH at the end of the treatment period, once all reactions have gone to completion<ref name = "Borden2017EVO"/>.  The general approach and calculations were presented in the previous sections.  The design tool is specifically focused on pH adjustment for ERD and calculation procedures include the following assumptions.
 
 
#The target pH is between 5 and 8.
 
#The carbonate system is the primary aqueous pH buffer.
 
#Organic acids including volatile fatty acids (acetic, propionic, etc.) are consumed and do not accumulate.
 
#Any H<sub>2</sub> or acetate produced by substrate fermentation that is not consumed through reduction of chlorinated solvents and background electron acceptors (O<sub>2</sub>, NO<sub>3</sub>, iron oxides, and SO<sub>4</sub>) is consumed by methanogenesis.
 
#All processes and reactions have gone to completion. The calculated total base requirement is for the end of the treatment period once all acids (HCl and H<sub>2</sub>CO<sub>3</sub>) have been produced. 
 
 
In general, the most important factors controlling base requirement are: a) initial and target pH; b) amount of substrate consumed; c) aquifer buffering capacity (pHBC); and d) amount of iron oxides reduced.  To calculate base requirement, design tool users must enter the following information.
 
 
#Treatment zone dimensions and design period for this phase of remediation. 
 
#Site characteristics including average hydraulic conductivity (K), porosity, hydraulic gradient, contaminant concentrations in aquifer material and groundwater, and amount of electron acceptors to be produced (i.e. CH<sub>4</sub>) or consumed (O<sub>2</sub>, NO<sub>3</sub>, Fe, SO<sub>4</sub>).
 
#Background pH, total inorganic carbon, mineral acidity, and pH buffering capacity (pHBC).  A database of pHBC measurements is provided to aid users in selecting design values when laboratory measurements are not available.
 
#Mass of organic substrate and base to be injected.
 
#When vegetable oil is used as a substrate, the fraction of injected oil that is consumed during the design period.
 
#Target pH
 
 
Users are reminded that the design tool calculates the total amount of base required '''once all reactions go to completion'''.  Early in the bioremediation process, reactions will not have gone to completion and less base will be required to maintain the target pH.  To prevent overshoot and excessively high pH, users typically add a fraction of the total base required in several increments spread over time.
 
 
[[File:Borden2w2Fig7.png|400 px|thumbnail|right|Figure 7. Required base addition for PRB for different target pH values.]]
 
==Case Study==
 
The design tool was used to estimate the amount of base required to stimulate ERD in a 435 ft long emulsified vegetable oil (EVO) biobarrier at Operable Unit 2 (OU2) on the former Naval Training Center (NTC) in Orlando, FL<ref name = "Borden2017EVO"/>.  The biobarrier consists of two rows of injection wells spaced approximately 30 ft on center which were treated with a total of 20,224 lb of vegetable oil.  The vertical treatment thickness was 10 ft, influent groundwater pH ~5, and pHBC = 8 meq/kg/pH.  To provide guidance on amounts of base required, the design tool was used to estimate the amount of NaOH, Na<sub>2</sub>CO<sub>3</sub>, NaHCO<sub>3</sub>, or Mg(OH) <sub>2</sub> required to achieve different pH values at the end of the five year treatment period.  Results presented in Figure 7 indicate that the amount of base required is very sensitive to the target pH.  For target pH values < 5.4, little or no base is required.  Increasing the target pH to 6 or 7, requires progressively greater amounts of base because of the soil acidity and carbonic acid released from substrate fermentation.
 
 
To achieve a pH of approximately 7, 10,200 lb of NaOH or 7,400 lb of Mg(OH) <sub>2</sub> are required, which is equivalent to 50% or 37% respectively (by weight) of the vegetable oil injected.  Multiple NaOH injections would be required since a single injection would result in an excessively high initial pH and the base would migrate out of the treatment zone over time with flowing groundwater.  The total mass of Mg(OH) <sub>2</sub> required is less than NaOH, since two moles of OH- are released per mole of Mg(OH) <sub>2.</sub>  However, Mg(OH) <sub>2</sub> has a very low aqueous solubility, so the material must be injected in a colloidal form.  Since the material is a solid and would not migrate downgradient, 100% of the required Mg(OH) <sub>2</sub> could be injected simultaneously with the EVO.  The pH of a pure slurry of Mg(OH)<sub>2</sub> is relatively high (~10.3).  However once injected, CO<sub>3</sub><sup>2-</sup> precipitates on the surface of the Mg(OH) <sub>2</sub> particles forming a MgCO<sub>3</sub> coating that maintains the aquifer pH between 7 and 8<ref>Hiortdahl, K.M. and Borden, R.C., 2013. Enhanced reductive dechlorination of tetrachloroethene dense nonaqueous phase liquid with EVO and Mg (OH)2. Environmental science & technology, 48(1), pp.624-631. [https://doi.org/10.1021/es4042379 doi: 10.1021/es4042379]</ref>.  In general, it is not practical to raise the pH to near 7 with NaHCO<sub>3</sub> due to the small amount of H<sup>+</sup> consumed by this material at near neutral pH.  Na<sub>2</sub>CO<sub>3</sub> could be effective, but would require multiple injections due to the high pH (~11.7) and downgradient migration with groundwater flow.
 
 
==Summary==
 
Alkaline materials are commonly added during ERD to maintain an aquifer pH of greater than 6.  A simplified approach and spreadsheet-based design tool are presented for estimating the total amount of base required to achieve a specified target pH at the end of the treatment period, once all reactions have gone to completion.  To prevent overshoot and excessively high pH, users typically add a fraction of the total base required in several increments spread over time.  Users should be aware that results are very sensitive to variations in the target pH since the amount of H<sup>+</sup> released from carbon dioxide and consumed by NaHCO<sub>3</sub> and Na<sub>2</sub>CO<sub>3</sub> is a function of pH.
 
  
 
==References==
 
==References==
<references />
+
<references/>
  
 
==See Also==
 
==See Also==
 
+
*[https://itrcweb.org/ Interstate Technology and Regulatory Council]
*[https://infoscience.epfl.ch/record/124950 BUCHLORAC: Program for predicting the bicarbonate requirement for anaerobic bioremediation of chlorinated solvents]
+
*[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