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| − | Groundwater migrates from areas of higher [[wikipedia: Hydraulic head | hydraulic head]] toward lower hydraulic head, transporting dissolved solutes through the combined processes of [[wikipedia: Advection | advection]] and [[wikipedia: Dispersion | dispersion]]. Advection refers to the bulk movement of solutes carried by flowing groundwater. Dispersion refers to the spreading of the contaminant plume from highly concentrated areas to less concentrated areas. In many groundwater transport models, solute transport is described by the advection-dispersion-reaction equation in which dispersion coefficients can be calculated as the sum of molecular diffusion, mechanical dispersion, and macrodispersion.
| + | ==Munitions Constituents – Sample Extraction and Analytical Techniques== |
| | + | Munitions Constituents, including [[Wikipedia: Insensitive munition | insensitive munitions]] IM), are a broad category of compounds and, in areas where manufactured or used, can be found in a variety of environmental matrices (waters, soil, and tissues). This presents an analytical challenge when a variety of these munitions are to be quantified. This article discusses sample extraction methods for each typical sample matrix (high level water, low level water, soil and tissue) as well as the accompanying [[Wikipedia: High-performance liquid chromatography | HPLC]]-UV analytical method for 27 compounds of interest (legacy munitions, insensitive munitions, and surrogates). |
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| | <div style="float:right;margin:0 0 2em 2em;">__TOC__</div> | | <div style="float:right;margin:0 0 2em 2em;">__TOC__</div> |
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| | '''Related Article(s):''' | | '''Related Article(s):''' |
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| − | *[[Dispersion and Diffusion]] | + | *[[Munitions Constituents]] |
| − | *[[Sorption of Organic Contaminants]]
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| − | *[[Plume Response Modeling]]
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| − | *[[Matrix Diffusion]]
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| − | '''CONTRIBUTOR(S):''' [[Dr. Charles Newell, P.E.|Dr. Charles Newell]] and [[Dr. Robert Borden, P.E.|Dr. Robert Borden]] | + | '''Contributor(s):''' |
| | + | |
| | + | *Dr. Austin Scircle |
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| | '''Key Resource(s):''' | | '''Key Resource(s):''' |
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| − | *[http://hydrogeologistswithoutborders.org/wordpress/1979-english/ Groundwater]<ref name="FandC1979">Freeze, A., and Cherry, J., 1979. Groundwater, Prentice-Hall, Englewood Cliffs, New Jersey, 604 pages. Free download from [http://hydrogeologistswithoutborders.org/wordpress/1979-english/ Hydrogeologists Without Borders].</ref>, Freeze and Cherry, 1979. | + | *[https://www.epa.gov/sites/default/files/2015-07/documents/epa-8330b.pdf USEPA Method 8330B]<ref name= "8330B">United States Environmental Protection Agency (USEPA), 2006. EPA Method 8330B (SW-846) Nitroaromatics, Nitramines, and Nitrate Esters by High Performance Liquid Chromatography (HPLC), Revision 2. [https://www.epa.gov/esam/epa-method-8330b-sw-846-nitroaromatics-nitramines-and-nitrate-esters-high-performance-liquid USEPA Website] [[Media: epa-8330b.pdf | Method 8330B.pdf]]</ref> |
| − | *[https://gw-project.org/books/hydrogeologic-properties-of-earth-materials-and-principles-of-groundwater-flow/ Hydrogeologic Properties of Earth Materials and Principals of Groundwater Flow]<ref name="Woessner2020">Woessner, W.W., and Poeter, E.P., 2020. Properties of Earth Materials and Principals of Groundwater Flow, The Groundwater Project, Guelph, Ontario, 207 pages. Free download from [https://gw-project.org/books/hydrogeologic-properties-of-earth-materials-and-principles-of-groundwater-flow/ The Groundwater Project].</ref>, Woessner and Poeter, 2020.
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| − | | |
| − | ==Groundwater Flow==
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| − | [[File:Newell-Article 1-Fig1r.JPG|thumbnail|left|400px|Figure 1. Hydraulic gradient (typically described in units of m/m or ft/ft) is the difference in hydraulic head from Point A to Point B (ΔH) divided by the distance between them (ΔL). In unconfined aquifers, the hydraulic gradient can also be described as the slope of the water table (Adapted from course notes developed by Dr. R.J. Mitchell, Western Washington University).]]
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| − | Groundwater flows from areas of higher [[wikipedia: Hydraulic head | hydraulic head]] (a measure of pressure and gravitational energy) toward areas of lower hydraulic head (Figure 1). The rate of change (slope) of the hydraulic head is known as the hydraulic gradient. If groundwater is flowing and contains dissolved contaminants it can transport the contaminants by advection from areas with high hydraulic head toward lower hydraulic head zones, or “downgradient”.
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| − | | |
| − | ===Darcy's Law===
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| − | {| class="wikitable" style="float:right; margin-left:10px;text-align:center;"
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| − | |+Table 1. Representative values of total porosity (''n''), effective porosity (''n<sub>e</sub>''), and hydraulic conductivity (''K'') for different aquifer materials<ref name="D&S1997">Domenico, P.A. and Schwartz, F.W., 1997. Physical and Chemical Hydrogeology, 2nd Ed. John Wiley & Sons, 528 pgs. ISBN 978-0-471-59762-9. Available from: [https://www.wiley.com/en-us/Physical+and+Chemical+Hydrogeology%2C+2nd+Edition-p-9780471597629 Wiley]</ref><ref>McWhorter, D.B. and Sunada, D.K., 1977. Ground-water hydrology and hydraulics. Water Resources Publications, LLC, Highlands Ranch, Colorado, 304 pgs. ISBN-13: 978-1-887201-61-2 Available from: [https://www.wrpllc.com/books/gwhh.html Water Resources Publications]</ref><ref name="FandC1979" />
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| − | |-
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| − | !Aquifer Material
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| − | !Total Porosity<br /><small>(dimensionless)</small>
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| − | !Effective Porosity<br /><small>(dimensionless)</small>
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| − | !Hydraulic Conductivity<br /><small>(meters/second)</small>
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| − | |-
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| − | | colspan="4" style="text-align: left; background-color:white;" |'''Unconsolidated'''
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| − | |-
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| − | |Gravel||0.25 - 0.44||0.13 - 0.44||3×10<sup>-4</sup> - 3×10<sup>-2</sup>
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| − | |-
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| − | |Coarse Sand||0.31 - 0.46||0.18 - 0.43||9×10<sup>-7</sup> - 6×10<sup>-3</sup>
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| − | |-
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| − | |Medium Sand||—||0.16 - 0.46||9×10<sup>-7</sup> - 5×10<sup>-4</sup>
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| − | |-
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| − | |Fine Sand||0.25 - 0.53||0.01 - 0.46||2×10<sup>-7</sup> - 2×10<sup>-4</sup>
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| − | |-
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| − | |Silt, Loess||0.35 - 0.50||0.01 - 0.39||1×10<sup>-9</sup> - 2×10<sup>-5</sup>
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| − | |-
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| − | |Clay||0.40 - 0.70||0.01 - 0.18||1×10<sup>-11</sup> - 4.7×10<sup>-9</sup>
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| − | |-
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| − | | colspan="4" style="text-align: left; background-color:white;" |'''Sedimentary and Crystalline Rocks'''
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| − | |-
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| − | |Karst and Reef Limestone||0.05 - 0.50||—||1×10<sup>-6</sup> - 2×10<sup>-2</sup>
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| − | |-
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| − | |Limestone, Dolomite||0.00 - 0.20||0.01 - 0.24||1×10<sup>-9</sup> - 6×10<sup>-6</sup>
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| − | |-
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| − | |Sandstone||0.05 - 0.30||0.10 - 0.30||3×10<sup>-10</sup> - 6×10<sup>-6</sup>
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| − | |-
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| − | |Siltstone||—||0.21 - 0.41||1×10<sup>-11</sup> - 1.4×10<sup>-8</sup>
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| − | |-
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| − | |Basalt||0.05 - 0.50||—||2×10<sup>-11</sup> - 2×10<sup>-2</sup>
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| − | |-
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| − | |Fractured Crystalline Rock||0.00 - 0.10||—||8×10<sup>-9</sup> - 3×10<sup>-4</sup>
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| − | |-
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| − | |Weathered Granite||0.34 - 0.57||—||3.3×10<sup>-6</sup> - 5.2×10<sup>-5</sup>
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| − | |-
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| − | |Unfractured Crystalline Rock||0.00 - 0.05||—||3×10<sup>-14</sup> - 2×10<sup>-10</sup>
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| − | |}
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| − | In unconsolidated geologic settings (gravel, sand, silt, and clay) and highly fractured systems, the rate of groundwater movement can be expressed using [[wikipedia: Darcy's law | Darcy’s Law]]. This law is a fundamental mathematical relationship in the groundwater field and can be expressed this way:
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| − | | |
| − | [[File:Newell-Article 1-Equation 1rr.jpg|center|500px]]
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| − | | |
| − | ::Where:
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| − | :::''Q'' = Flow rate (Volume of groundwater flow per time, such as m<sup>3</sup>/yr)
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| − | :::''A'' = Cross sectional area perpendicular to groundwater flow (length<sup>2</sup>, such as m<sup>2</sup>)
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| − | :::''V<sub>D</sub>'' = “Darcy Velocity”; describes groundwater flow as the volume of flow through a unit of cross-sectional area (units of length per time, such as ft/yr)
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| − | :::''K'' = Hydraulic Conductivity (sometimes called “permeability”) (length per time)
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| − | :::''ΔH'' = Difference in hydraulic head between two lateral points (length)
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| − | :::''ΔL'' = Distance between two lateral points (length)
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| − | | |
| − | [https://en.wikipedia.org/wiki/Hydraulic_conductivity Hydraulic conductivity] (Table 1 and Figure 2) is a measure of how easily groundwater flows through a porous medium, or alternatively, how much energy it takes to force water through a porous medium. For example, fine sand has smaller pores with more frictional resistance to flow, and therefore lower hydraulic conductivity compared to coarse sand, which has larger pores with less resistance to flow (Figure 2).
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| − | | |
| − | [[File:AdvectionFig2.PNG|400px|thumbnail|left|Figure 2. Hydraulic conductivity of selected rocks<ref>Heath, R.C., 1983. Basic ground-water hydrology, U.S. Geological Survey Water-Supply Paper 2220, 86 pgs. [//www.enviro.wiki/images/c/c4/Heath-1983-Basic_groundwater_hydrology_water_supply_paper.pdf Report pdf]</ref>.]]
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| − | Darcy’s Law was first described by Henry Darcy (1856)<ref>Brown, G.O., 2002. Henry Darcy and the making of a law. Water Resources Research, 38(7), p. 1106. [https://doi.org/10.1029/2001wr000727 DOI: 10.1029/2001WR000727] [//www.enviro.wiki/images/4/40/Darcy2002.pdf Report.pdf]</ref> in a report regarding a water supply system he designed for the city of Dijon, France. Based on his experiments, he concluded that the amount of water flowing through a closed tube of sand (dark grey box in Figure 3) depends on (a) the change in the hydraulic head between the inlet and outlet of the tube, and (b) the hydraulic conductivity of the sand in the tube. Groundwater flows rapidly in the case of higher pressure (ΔH) or more permeable materials such as gravel or coarse sand, but flows slowly when the pressure difference is lower or the material is less permeable, such as fine sand or silt.
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| − | | |
| − | [[File:Newell-Article 1-Fig3..JPG|500px|thumbnail|right|Figure 3. Conceptual explanation of Darcy’s Law based on Darcy’s experiment (Adapted from course notes developed by Dr. R.J. Mitchell, Western Washington University).]]
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| − | Since Darcy’s time, Darcy’s Law has been extended to develop a useful variation of Darcy's formula that is used to to calculate the actual velocity that the groundwater is moving in units such as meters traveled per year. This quantity is called “interstitial velocity” or “seepage velocity” and is calculated by dividing the Darcy Velocity (flow per unit area) by the actual open pore area where groundwater is flowing, the “effective porosity” (Table 1):
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| − | | |
| − | [[File:Newell-Article 1-Equation 2r.jpg|400px]]
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| − | | |
| − | :Where:
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| − | ::''V<sub>S</sub>'' = “interstitial velocity” or “seepage velocity” (units of length per time, such as m/sec)<br />
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| − | ::''V<sub>D</sub>'' = “Darcy Velocity”; describes groundwater flow as the volume of flow per unit area per time (also units of length per time)<br />
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| − | ::''n<sub>e</sub>'' = Effective porosity - fraction of cross section available for groundwater flow (unitless)
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| − | | |
| − | Effective porosity is smaller than total porosity. The difference is that total porosity includes some dead-end pores that do not support groundwater. Typical values for total and effective porosity are shown in Table 1.
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| − | | |
| − | [[File:Newell-Article 1-Fig4.JPG|500px|thumbnail|left|Figure 4. Difference between Darcy Velocity (also called Specific Discharge) and Seepage Velocity (also called Interstitial Velocity).]]
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| − | | |
| − | ===Darcy Velocity and Seepage Velocity===
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| − | In groundwater calculations, Darcy Velocity and Seepage Velocity are used for different purposes. For any calculation where the actual flow rate in units of volume per time (such as liters per day or gallons per minute) is involved, then the original Darcy Equation should be used (calculate ''V<sub>D</sub>'', Equation 1) without using effective porosity. When calculating solute travel time however, the seepage velocity calculation (''V<sub>S</sub>'', Equation 2) must be used and an estimate of effective porosity is required. Figure 4 illustrates the differences between Darcy Velocity and Seepage Velocity.
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| − | | |
| − | ===Mobile Porosity===
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| − | {| class="wikitable" style="float:right; margin-left:10px; text-align:center;"
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| − | |+Table 2. Mobile porosity estimates from 15 tracer tests<ref name="Payne2008">Payne, F.C., Quinnan, J.A. and Potter, S.T., 2008. Remediation Hydraulics. CRC Press. ISBN 9780849372490 Available from: [https://www.routledge.com/Remediation-Hydraulics/Payne-Quinnan-Potter/p/book/9780849372490 CRC Press]</ref>
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| − | |-
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| − | !Aquifer Material
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| − | !Mobile Porosity<br /><small>(volume fraction)</small>
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| − | |-
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| − | |Poorly sorted sand and gravel||0.085
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| − | |-
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| − | |Poorly sorted sand and gravel||0.04 - 0.07
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| − | |-
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| − | |Poorly sorted sand and gravel||0.09
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| − | |-
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| − | |Fractured sandstone||0.001 - 0.007
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| − | |-
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| − | |Alluvial formation||0.102
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| − | |-
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| − | |Glacial outwash||0.145
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| − | |-
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| − | |Weathered mudstone regolith||0.07 - 0.10
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| − | |-
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| − | |Alluvial formation||0.07
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| − | |-
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| − | |Alluvial formation||0.07
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| − | |-
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| − | |Silty sand||0.05
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| − | |-
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| − | |Fractured sandstone||0.0008 - 0.001
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| − | |-
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| − | |Alluvium, sand and gravel||0.017
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| − | |-
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| − | |Alluvium, poorly sorted sand and gravel||0.003 - 0.017
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| − | |-
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| − | |Alluvium, sand and gravel||0.11 - 0.18
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| − | |-
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| − | |Siltstone, sandstone, mudstone||0.01 - 0.05
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| − | |}
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| − | | |
| − | Payne et al. (2008) reported the results from multiple short-term tracer tests conducted to aid the design of amendment injection systems<ref name="Payne2008" />. In these tests, the dissolved solutes were observed to migrate more rapidly through the aquifer than could be explained with typically reported values of ''n<sub>e</sub>''. They concluded that the heterogeneity of unconsolidated formations results in a relatively small area of an aquifer cross section carrying most of the water, and therefore solutes migrate more rapidly than expected. Based on these results, they recommend that a quantity called “mobile porosity” should be used in place of ''n<sub>e</sub>'' in equation 2 for calculating solute transport velocities. Based on 15 different tracer tests, typical values of mobile porosity range from 0.02 to 0.10 (Table 2).
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| − | | |
| − | A data mining analysis of 43 sites in California by Kulkarni et al. (2020) showed that on average 90% of the groundwater flow occurred in about 30% of cross sectional area perpendicular to groundwater flow. These data provided “moderate (but not confirmatory) support for the mobile porosity concept.”<ref name="Kulkarni2020">Kulkarni, P.R., Godwin, W.R., Long, J.A., Newell, R.C., Newell, C.J., 2020. How much heterogeneity? Flow versus area from a big data perspective. Remediation 30(2), pp. 15-23. [https://doi.org/10.1002/rem.21639 DOI: 10.1002/rem.21639] [//www.enviro.wiki/images/9/9b/Kulkarni2020.pdf Report.pdf]</ref>
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| − | ==Advection-Dispersion-Reaction Equation==
| + | *Methods for simultaneous quantification of legacy and insensitive munition (IM) constituents in aqueous, soil/sediment, and tissue matrices<ref name="CrouchEtAl2020">Crouch, R.A., Smith, J.C., Stromer, B.S., Hubley, C.T., Beal, S., Lotufo, G.R., Butler, A.D., Wynter, M.T., Russell, A.L., Coleman, J.G., Wayne, K.M., Clausen, J.L., Bednar, A.J., 2020. Methods for simultaneous determination of legacy and insensitive munition (IM) constituents in aqueous, soil/sediment, and tissue matrices. Talanta, 217, Article 121008. [https://doi.org/10.1016/j.talanta.2020.121008 doi: 10.1016/j.talanta.2020.121008] [[Media: CrouchEtAl2020.pdf | Open Access Manuscript.pdf]]</ref> |
| − | The transport of dissolved solutes in groundwater is often modeled using the Advection-Dispersion-Reaction (ADR) equation. As shown below (Equation 3), the ADR equation describes the change in dissolved solute concentration (''C'') over time (''t'') where groundwater flow is oriented along the ''x'' direction.
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| | | | |
| − | {|
| + | ==Introduction== |
| − | | || [[File:AdvectionEq3r.PNG|center|635px]]
| + | [[File: ScircleFig1.png | thumb | 400px | Figure 1. Primary Method labeled chromatograms]] |
| − | |-
| + | [[File: ScircleFig2.png | thumb | 400px | Figure 2. Secondary Method labeled chromatograms]] |
| − | | Where: ||
| + | The primary intention of the analytical methods presented here is to support the monitoring of legacy and insensitive munitions contamination on test and training ranges, however legacy and insensitive munitions often accompany each other at demilitarization facilities, manufacturing facilities, and other environmental sites. Energetic materials typically appear on ranges as small, solid particulates and due to their varying functional groups and polarities, can partition in various environmental compartments<ref>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]</ref>. To ensure that contaminants are monitored and controlled at these sites and to sustainably manage them a variety of sample matrices (surface or groundwater, process waters, soil, and tissues) must be considered. (Process water refers to water used during industrial manufacturing or processing of legacy and insensitive munitions.) Furthermore, additional analytes must be added to existing methodologies as the usage of IM compounds changes and as new degradation compounds are identified. Of note, relatively new IM formulations containing NTO, DNAN, and NQ are seeing use in [[Wikipedia: IMX-101 | IMX-101]], IMX-104, Pax-21 and Pax-41 (Table 1)<ref>Mainiero, C. 2015. Picatinny Employees Recognized for Insensitive Munitions. U.S. Army, Picatinny Arsenal Public Affairs. [https://www.army.mil/article/148873/picatinny_employees_recognized_for_insensitive_munitions Open Access Press Release]</ref><ref>Frem, D., 2022. A Review on IMX-101 and IMX-104 Melt-Cast Explosives: Insensitive Formulations for the Next-Generation Munition Systems. Propellants, Explosives, Pyrotechnics, 48(1), e202100312. [https://doi.org/10.1002/prep.202100312 doi: 10.1002/prep.202100312]</ref>. |
| − | |- | |
| − | |
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| − | :''D<sub>x</sub>, D<sub>y</sub>, and D<sub>z</sub>''
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| − | | are hydrodynamic dispersion coefficients in the ''x, y'' and ''z'' directions (L<sup>2</sup>/T),
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| − | |-
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| − | |
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| − | :''v''
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| − | | is the advective transport or seepage velocity in the ''x'' direction (L/T), and
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| − | |- | |
| − | |
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| − | :''λ''
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| − | | is an effective first order decay rate due to combined biotic and abiotic processes (1/T).
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| − | |-
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| − | |
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| − | :''R'' | |
| − | | is the linear, equilibrium retardation factor (see [[Sorption of Organic Contaminants]]),
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| − | |}
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| | | | |
| − | The term on the left side of the equation is the rate of mass change per unit volume. On the right side are terms representing the solute flux due to dispersion in the ''x, y'', and ''z'' directions, the advective flux in the ''x'' direction, and the first order decay due to biotic and abiotic processes. Dispersion coefficients (''D<sub>x,y,z</sub>'') are commonly estimated using the following relationships (Equation 4):
| + | Sampling procedures for legacy and insensitive munitions are identical and utilize multi-increment sampling procedures found in USEPA Method 8330B Appendix A<ref name= "8330B"/>. Sample hold times, subsampling and quality control requirements are also unchanged. The key differences lie in the extraction methods and instrumental methods. Briefly, legacy munitions analysis of low concentration waters uses a single cartridge reverse phase [[Wikipedia: Solid-phase extraction | SPE]] procedure, and [[Wikipedia: Acetonitrile | acetonitrile]] (ACN) is used for both extraction and [[Wikipedia: Elution | elution]] for aqueous and solid samples<ref name= "8330B"/><ref>United States Environmental Protection Agency (USEPA), 2007. EPA Method 3535A (SW-846) Solid-Phase Extraction (SPE), Revision 1. [https://www.epa.gov/esam/epa-method-3535a-sw-846-solid-phase-extraction-spe USEPA Website] [[Media: epa-3535a.pdf | Method 3535A.pdf]]</ref>. An [[Wikipedia: High-performance_liquid_chromatography#Isocratic_and_gradient_elution | isocratic]] separation via reversed-phase C-18 column with 50:50 methanol:water mobile phase or a C-8 column with 15:85 isopropanol:water mobile phase is used to separate legacy munitions<ref name= "8330B"/>. While these procedures are sufficient for analysis of legacy munitions, alternative solvents, additional SPE cartridges, and a gradient elution are all required for the combined analysis of legacy and insensitive munitions. |
| | | | |
| − | {|
| + | Previously, analysis of legacy and insensitive munitions required multiple analytical techniques, however the methods presented here combine the two munitions categories resulting in an HPLC-UV method and accompanying extraction methods for a variety of common sample matrices. A secondary HPLC-UV method and a HPLC-MS method were also developed as confirmatory methods. The methods discussed in this article were validated extensively by single-blind round robin testing and subsequent statistical treatment as part of ESTCP [https://serdp-estcp.mil/projects/details/d05c1982-bbfa-42f8-811d-51b540d7ebda ER19-5078]. Wherever possible, the quality control criteria in the Department of Defense Quality Systems Manual for Environmental Laboratories were adhered to<ref>US Department of Defense and US Department of Energy, 2021. Consolidated Quality Systems Manual (QSM) for Environmental Laboratories, Version 5.4. 387 pages. [https://www.denix.osd.mil/edqw/denix-files/sites/43/2021/10/QSM-Version-5.4-FINAL.pdf Free Download] [[Media: QSM-Version-5.4.pdf | QSM Version 5.4.pdf]]</ref>. Analytes included in these methods are found in Table 1. |
| − | | || [[File:AdvectionEq4.PNG|center|360px]]
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| − | |-
| |
| − | | Where: ||
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| − | |-
| |
| − | |
| |
| − | :''D<sub>m</sub>''
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| − | | is the molecular diffusion coefficient (L<sup>2</sup>/T), and
| |
| − | |-
| |
| − | |
| |
| − | :''α<sub>L</sub>, α<sub>T</sub>'', and ''α<sub>V</sub>''
| |
| − | | are the longitudinal, transverse and vertical dispersivities (L), respectively. | |
| − | |}
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| | | | |
| − | ===ADR Applications===
| + | The chromatograms produced by the primary and secondary HPLC-UV methods are shown in Figure 1 and Figure 2, respectively. Chromatograms for each detector wavelength used are shown (315, 254, and 210 nm). |
| − | [[File:AdvectionFig5.png | thumb | right | 350px | Figure 5. Curves of concentration versus distance (a) and concentration versus time (b) generated by solving the ADR equation for a continuous source of a non-reactive tracer with ''R'' = 1, λ = 0, ''v'' = 5 m/yr, and ''D<sub>x</sub>'' = 10 m<sup>2</sup>/yr.]]
| |
| − | The ADR equation can be solved to find the spatial and temporal distribution of solutes using a variety of analytical and numerical approaches. The design tools [https://www.epa.gov/water-research/bioscreen-natural-attenuation-decision-support-system BIOSCREEN]<ref name="Newell1996">Newell, C.J., McLeod, R.K. and Gonzales, J.R., 1996. BIOSCREEN: Natural Attenuation Decision Support System - User's Manual, Version 1.3. US Environmental Protection Agency, EPA/600/R-96/087. [https://www.enviro.wiki/index.php?title=File:Newell-1996-Bioscreen_Natural_Attenuation_Decision_Support_System.pdf Report.pdf] [https://www.epa.gov/water-research/bioscreen-natural-attenuation-decision-support-system BIOSCREEN website]</ref>, [https://www.epa.gov/water-research/biochlor-natural-attenuation-decision-support-system BIOCHLOR]<ref name="Aziz2000">Aziz, C.E., Newell, C.J., Gonzales, J.R., Haas, P.E., Clement, T.P. and Sun, Y., 2000. BIOCHLOR Natural Attenuation Decision Support System. User’s Manual - Version 1.0. US Environmental Protection Agency, EPA/600/R-00/008. [https://www.enviro.wiki/index.php?title=File:Aziz-2000-BIOCHLOR-Natural_Attenuation_Dec_Support.pdf Report.pdf] [https://www.epa.gov/water-research/biochlor-natural-attenuation-decision-support-system BIOCHLOR website]</ref>, and [https://www.epa.gov/water-research/remediation-evaluation-model-chlorinated-solvents-remchlor REMChlor]<ref name="Falta2007">Falta, R.W., Stacy, M.B., Ahsanuzzaman, A.N.M., Wang, M. and Earle, R.C., 2007. REMChlor Remediation Evaluation Model for Chlorinated Solvents - User’s Manual, Version 1.0. US Environmental Protection Agency. Center for Subsurface Modeling Support, Ada, OK. [[Media:REMChlorUserManual.pdf | Report.pdf]] [https://www.epa.gov/water-research/remediation-evaluation-model-chlorinated-solvents-remchlor REMChlor website]</ref> (see also [[REMChlor - MD]]) employ an analytical solution of the ADR equation. [https://www.usgs.gov/software/mt3d-usgs-groundwater-solute-transport-simulator-modflow MT3DMS]<ref name="Zheng1999">Zheng, C. and Wang, P.P., 1999. MT3DMS: A Modular Three-Dimensional Multispecies Transport Model for Simulation of Advection, Dispersion, and Chemical Reactions of Contaminants in Groundwater Systems; Documentation and User’s Guide. Contract Report SERDP-99-1 U.S. Army Engineer Research and Development Center, Vicksburg, MS. [[Media:Mt3dmanual.pdf | Report.pdf]] [https://www.usgs.gov/software/mt3d-usgs-groundwater-solute-transport-simulator-modflow MT3DMS website]</ref> uses a numerical method to solve the ADR equation using the head distribution generated by the groundwater flow model MODFLOW<ref name="McDonald1988">McDonald, M.G. and Harbaugh, A.W., 1988. A Modular Three-dimensional Finite-difference Ground-water Flow Model, Techniques of Water-Resources Investigations, Book 6, Modeling Techniques. U.S. Geological Survey, 586 pages. [https://doi.org/10.3133/twri06A1 DOI: 10.3133/twri06A1] [[Media: McDonald1988.pdf | Report.pdf]] Free MODFLOW download from: [https://www.usgs.gov/mission-areas/water-resources/science/modflow-and-related-programs?qt-science_center_objects=0#qt-science_center_objects USGS]</ref>.
| |
| | | | |
| − | Figures 5a and 5b were generated using a numerical solution of the ADR equation for a non-reactive tracer (''R'' = 1; λ = 0) with ''v'' = 5 m/yr and ''D<sub>x</sub>'' = 10 m<sup>2</sup>/yr. Figure 5a shows the predicted change in concentration of the tracer, chloride, versus distance downgradient from the continuous contaminant source at different times (0, 1, 2, and 4 years). Figure 5b shows the change in concentration versus time (commonly referred to as the breakthrough curve or BTC) at different downgradient distances (10, 20, 30 and 40 m). At 2 years, the mid-point of the concentration versus distance curve (Figure 5a) is located 10 m downgradient (x = 5 m/yr * 2 yr). At 20 m downgradient, the mid-point of the concentration versus time curves (Figure 5b) occurs at 4 years (t = 20 m / 5 m/yr).
| + | ==Extraction Methods== |
| | + | ===High Concentration Waters (> 1 ppm)=== |
| | + | Aqueous samples suspected to contain the compounds of interest at concentrations detectable without any extraction or pre-concentration are suitable for analysis by direct injection. The method deviates from USEPA Method 8330B by adding a pH adjustment and use of MeOH rather than ACN for dilution<ref name= "8330B"/>. The pH adjustment is needed to ensure method accuracy for ionic compounds (like NTO or PA) in basic samples. A solution of 1% HCl/MeOH is added to both acidify and dilute the samples to a final acid concentration of 0.5% (vol/vol) and a final solvent ratio of 1:1 MeOH/H<sub>2</sub>O. The direct injection samples are then ready for analysis. |
| | | | |
| − | ===Modeling Dispersion=== | + | ===Low Concentration Waters (< 1 ppm)=== |
| − | Mechanical dispersion (hydrodynamic dispersion) results from groundwater moving at rates both greater and less than the average linear velocity. This is due to: 1) fluids moving faster through the center of the pores than along the edges, 2) fluids traveling shorter pathways and/or splitting or branching to the sides, and 3) fluids traveling faster through larger pores than through smaller pores<ref>Fetter, C.W., 1994. Applied Hydrogeology: Macmillan College Publishing Company. New York New York. ISBN-13:978-0130882394</ref>. Because the invading solute-containing water does not travel at the same velocity everywhere, mixing occurs along flow paths. This mixing is called mechanical dispersion and results in distribution of the solute at the advancing edge of flow. The mixing that occurs in the direction of flow is called longitudinal dispersion. Spreading normal to the direction of flow from splitting and branching out to the sides is called transverse dispersion (Figure 6). Typical values of the mechanical dispersivity measured in laboratory column tests are on the order of 0.01 to 1 cm<ref name="Anderson1979">Anderson, M.P. and Cherry, J.A., 1979. Using models to simulate the movement of contaminants through groundwater flow systems. Critical Reviews in Environmental Science and Technology, 9(2), pp.97-156. [https://doi.org/10.1080/10643387909381669 DOI: 10.1080/10643387909381669]</ref>.
| + | Aqueous samples suspected to contain the compounds of interest at low concentrations require extraction and pre-concentration using solid phase extraction (SPE). The SPE setup described here uses a triple cartridge setup shown in '''Figure 3'''. Briefly, the extraction procedure loads analytes of interest onto the cartridges in this order: Strata<sup><small>TM</small></sup> X, Strata<sup><small>TM</small></sup> X-A, and Envi-Carb<sup><small>TM</small></sup>. Then the cartridge order is reversed, and analytes are eluted via a two-step elution, resulting in 2 extracts (which are combined prior to analysis). Five milliliters of MeOH is used for the first elution, while 5 mL of acidified MeOH (2% HCl) is used for the second elution. The particular SPE cartridges used are noncritical so long as cartridge chemistries are comparable to those above. |
| − | [[File:Fig2 dispanddiff.JPG|thumbnail|left|400px|Figure 6. Conceptual depiction of mechanical dispersion (adapted from ITRC (2011)<ref name="ITRC2011">ITRC Integrated DNAPL Site Strategy Team, 2011. Integrated DNAPL Site Strategy. Technical/Regulatory Guidance Document, 209 pgs. [//www.enviro.wiki/images/d/d9/ITRC-2011-Integrated_DNAPL.pdf Report pdf]</ref>).]]
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| | | | |
| − | The dispersion coefficient in the ADR equation accounts for the combined effects of mechanical dispersion and molecular diffusion, both of which cause spreading of the contaminant plume from highly concentrated areas toward less concentrated areas. [[wikipedia:Molecular diffusion | Molecular diffusion]] is the result of the thermal motion of individual molecules which causes a flux of dissolved solutes from areas of higher concentration to areas of lower concentration.
| + | ===Soils=== |
| | + | Soil collection, storage, drying and grinding procedures are identical to the USEPA Method 8330B procedures<ref name= "8330B"/>; however, the solvent extraction procedure differs in the number of sonication steps, sample mass and solvent used. A flow chart of the soil extraction procedure is shown in '''Figure 4'''. Soil masses of approximately 2 g and a sample to solvent ratio of 1:5 (g/mL) are used for soil extraction. The extraction is carried out in a sonication bath chilled below 20 ⁰C and is a two-part extraction, first extracting in MeOH (6 hours) followed by a second sonication in 1:1 MeOH:H<sub>2</sub>O solution (14 hours). The extracts are centrifuged, and the supernatant is filtered through a 0.45 μm PTFE disk filter. |
| | | | |
| − | ===Modeling Diffusion===
| + | The solvent volume should generally be 10 mL but if different soil masses are required, solvent volume should be 5 mL/g. The extraction results in 2 separate extracts (MeOH and MeOH:H<sub>2</sub>O) that are combined prior to analysis. |
| − | [[File:Fig1 dispanddiff.JPG|thumbnail|right|400px|Figure 7. Conceptual depiction of diffusion of a dissolved chemical recently placed in a container at Time 1 (left panel) and then distributed throughout the container (right panel) at Time 2.]]
| |
| − | [[wikipedia: Molecular diffusion | Molecular diffusion]] is the result of the thermal motion of individual molecules which causes a flux of dissolved solutes from areas of higher concentration to areas of lower concentration (Figure 7). The diffusion coefficient is a proportionality constant between the molar flux due to molecular diffusion and the concentration gradient and is a function of the temperature and molecular weight. In locations where advective flux is low (clayey aquitards and sedimentary rock), diffusion is often the dominant transport mechanism.
| |
| | | | |
| − | The diffusive flux ''J'' (M/L<sup>2</sup>/T) in groundwater is calculated using [[wikipedia:Fick's laws of diffusion | Fick’s Law]]:
| + | ===Tissues=== |
| | + | Tissue matrices are extracted by 18-hour sonication using a ratio of 1 gram of wet tissue per 5 mL of MeOH. This extraction is performed in a sonication bath chilled below 20 ⁰C and the supernatant (MeOH) is filtered through a 0.45 μm PTFE disk filter. |
| | | | |
| − | {|
| + | Due to the complexity of tissue matrices, an additional tissue cleanup step, adapted from prior research, can be used to reduce interferences<ref name="RussellEtAl2014">Russell, A.L., Seiter, J.M., Coleman, J.G., Winstead, B., Bednar, A.J., 2014. Analysis of munitions constituents in IMX formulations by HPLC and HPLC-MS. Talanta, 128, pp. 524–530. [https://doi.org/10.1016/j.talanta.2014.02.013 doi: 10.1016/j.talanta.2014.02.013]</ref><ref name="CrouchEtAl2020"/>. The cleanup procedure uses small scale chromatography columns prepared by loading 5 ¾” borosilicate pipettes with 0.2 g activated silica gel (100–200 mesh). The columns are wetted with 1 mL MeOH, which is allowed to fully elute and then discarded prior to loading with 1 mL of extract and collecting in a new amber vial. After the extract is loaded, a 1 mL aliquot of MeOH followed by a 1 mL aliquot of 2% HCL/MeOH is added. This results in a 3 mL silica treated tissue extract. This extract is vortexed and diluted to a final solvent ratio of 1:1 MeOH/H<sub>2</sub>O before analysis. |
| − | |
| |
| − | |<big>'''''J = -D<sub>e</sub> dC/dx'''''</big> (Equation 5)
| |
| − | |-
| |
| − | |Where:||
| |
| − | |-
| |
| − | |
| |
| − | :''D<sub>e</sub>''
| |
| − | |is the effective diffusion coefficient and
| |
| − | |-
| |
| − | |
| |
| − | :''dC/dx''
| |
| − | |is the concentration gradient.
| |
| − | |}
| |
| − | The effective diffusion coefficient for transport through the porous media, ''D<sub>e</sub>, is estimated as:''
| |
| − | {|
| |
| − | |
| |
| − | |<big>'''''D<sub>e</sub> = D<sub>m</sub> n<sub>e</sub> δ/Τ'''''</big> (Equation 6)
| |
| − | |-
| |
| − | |Where:||
| |
| − | |-
| |
| − | |
| |
| − | :''D<sub>m</sub>''
| |
| − | |is the [[wikipedia:Mass diffusivity | diffusion coefficient]] of the solute in water,
| |
| − | |-
| |
| − | |
| |
| − | :''n<sub>e</sub>''
| |
| − | |is the effective porosity (dimensionless),
| |
| − | |-
| |
| − | |
| |
| − | :''δ''
| |
| − | |is the constrictivity (dimensionless) which reflects the restricted motion of particles in narrow pores<ref name="Grathwohl1998">Grathwohl, P., 1998. Diffusion in Natural Porous Media: Contaminant Transport, Sorption/Desorption and Dissolution Kinetics. Kluwer Academic Publishers, Boston. DOI: 10.1007/978-1-4615-5683-1 Available from: [https://link.springer.com/book/10.1007/978-1-4615-5683-1 Springer.com]</ref>, and
| |
| − | |-
| |
| − | |
| |
| − | :''Τ''
| |
| − | |is the [[wikipedia:Tortuosity | tortuosity]] (dimensionless) which reflects the longer diffusion path in porous media around sediment particles<ref name="Carey2016">Carey, G.R., McBean, E.A. and Feenstra, S., 2016. Estimating Tortuosity Coefficients Based on Hydraulic Conductivity. Groundwater, 54(4), pp.476-487. [https://doi.org/10.1111/gwat.12406 DOI:10.1111/gwat.12406] Available from: [https://ngwa.onlinelibrary.wiley.com/doi/abs/10.1111/gwat.12406 NGWA]</ref>.
| |
| − | |}
| |
| − | ''D<sub>m</sub>'' is a function of the temperature, fluid viscosity and molecular weight. Values of ''D<sub>m</sub>'' for common groundwater solutes are shown in Table 3.
| |
| | | | |
| − | {| class="wikitable" style="float:left; margin-right:20px; text-align:center;"
| + | ==HPLC-UV and MS Methods== |
| − | |+Table 3. Diffusion Coefficients (''D<sub>m</sub>'') for Common Groundwater Solutes.
| + | The Primary HPLC method uses a Phenomenex Synergi 4 µm Hydro-RP column (80Å, 250 x 4.6 mm), or comparable, and is based on both the HPLC method found in USEPA 8330B and previous work<ref name= "8330B"/><ref name="RussellEtAl2014"/><ref name="CrouchEtAl2020"/>. This separation relies on a reverse phase column and uses a gradient elution, shown in Table 2. Depending on the analyst’s needs and equipment availability, the method has been proven to work with either 0.1% TFA or 0.25% FA (vol/vol) mobile phase. Addition of a guard column like a Phenomenex SecurityGuard AQ C18 pre-column guard cartridge can be optionally used. These optional changes to the method have no impact on the method’s performance. |
| − | |-
| + | The Secondary HPLC method uses a Restek Pinnacle II Biphenyl 5 µm (150 x 4.6 mm) or comparable column and is intended as a confirmatory method. Like the Primary method, this method can use an optional guard column and utilizes a gradient elution, shown in Table 3. |
| − | !Aqueous Diffusion Coefficient
| + | |
| − | !Temperature<br /><small>(°C)</small>
| + | For instruments equipped with a mass spectrometer (MS), a secondary MS method is available and was developed alongside the Primary UV method. The method was designed for use with a single quadrupole MS equipped with an atmospheric pressure chemical ionization (APCI) source, such as an Agilent 6120B. A majority of the analytes, shown in Table 1, are amenable to this MS method, however nitroglycerine (which is covered extensively in USEPA method 8332) and 2-,3-, and 4-nitrotoluene compounds aren’t compatible with the MS method. MS method parameters are shown in Table 4. |
| − | !''D<sub>m</sub>''<br /><small>(cm<sup>2</sup>/s)</small>
| + | |
| − | !Reference
| + | ==Summary== |
| − | |-
| + | The extraction methods and instrumental methods in this article build upon prior munitions analytical methods by adding new compounds, combining legacy and insensitive munitions analysis, and expanding usable sample matrices. These methods have been verified through extensive round robin testing and validation, and while the methods are somewhat challenging, they are crucial when simultaneous analysis of both insensitive and legacy munitions is needed. |
| − | |Acetone||25|| 1.16x10<sup>-5</sup> ||Cussler 1997 <ref name="Cussler1997">Cussler, E.L., 1997. Diffusion: Mass Transfer in Fluid Systems, Cambridge University Press, New York, 580 pages. ISBN: 9780521450782</ref>
| |
| − | |-
| |
| − | |Benzene||20||1.02x10<sup>-5</sup>||Bonoli and Witherspoon 1968 <ref name="Bonoli1968">Bonoli, L. and Witherspoon, P.A., 1968. Diffusion of Aromatic and Cycloparaffin Hydrocarbons in Water from 2 to 60 deg. The Journal of Physical Chemistry, 72(7), pp.2532-2534. [https://doi.org/10.1021/j100853a045 DOI: 10.1021/j100853a045]</ref>
| |
| − | |-
| |
| − | |Carbon dioxide||25||1.92x10<sup>-5</sup>||Cussler 1997 <ref name="Cussler1997"/>
| |
| − | |-
| |
| − | |Carbon tetrachloride||25||9.55x10<sup>-6</sup>||Yaws 1995 <ref name="Yaws1995">Yaws, C.L., 1995. Handbook of Transport Property Data: Viscosity, Thermal Conductivity and Diffusion Coefficients of Liquids and Gases, Gulf Publishing Company, Houston, TX. ISBN: 0884153924</ref>
| |
| − | |-
| |
| − | |Chloroform||25||1.08x10<sup>-5</sup>||Yaws 1995 <ref name="Yaws1995"/>
| |
| − | |-
| |
| − | |Dichloroethene||25||1.12x10<sup>-5</sup>||Yaws 1995 <ref name="Yaws1995"/>
| |
| − | |-
| |
| − | |1,4-Dioxane||25||1.02x10<sup>-5</sup>||Yaws 1995 <ref name="Yaws1995"/>
| |
| − | |-
| |
| − | |Ethane||25||1.52x10<sup>-5</sup>||Witherspoon and Saraf 1965 <ref name="Witherspoon1965">Witherspoon, P.A. and Saraf, D.N., 1965. Diffusion of Methane, Ethane, Propane, and n-Butane in Water from 25 to 43°. The Journal of Physical Chemistry, 69(11), pp. 3752-3755. [https://doi.org/10.1021/j100895a017 DOI: 10.1021/j100895a017]</ref>
| |
| − | |-
| |
| − | |Ethylbenzene||20||8.10x10<sup>-6</sup>||Bonoli and Witherspoon 1968 <ref name="Bonoli1968"/>
| |
| − | |-
| |
| − | |Ethene||25||1.87x10<sup>-5</sup>||Cussler 1997 <ref name="Cussler1997"/>
| |
| − | |-
| |
| − | |Helium||25||6.28x10<sup>-5</sup>||Cussler 1997 <ref name="Cussler1997"/>
| |
| − | |-
| |
| − | |Hydrogen||25||4.50x10<sup>-5</sup>||Cussler 1997 <ref name="Cussler1997"/>
| |
| − | |-
| |
| − | |Methane||25||1.88x10<sup>-5</sup>||Witherspoon and Saraf 1965 <ref name="Witherspoon1965"/>
| |
| − | |-
| |
| − | |Nitrogen||25||1.88x10<sup>-5</sup>||Cussler 1997 <ref name="Cussler1997"/>
| |
| − | |-
| |
| − | |Oxygen||25||2.10x10<sup>-5</sup>||Cussler 1997 <ref name="Cussler1997"/>
| |
| − | |-
| |
| − | |Perfluorooctanoic acid (PFOA)||20||4.80x10<sup>-6</sup>||Schaefer et al. 2019 <ref name="Schaefer2019">Schaefer, C.E., Drennan, D.M., Tran, D.N., Garcia, R., Christie, E., Higgins, C.P. and Field, J.A., 2019. Measurement of Aqueous Diffusivities for Perfluoroalkyl Acids. Journal of Environmental Engineering, 145(11). [https://doi.org/10.1061/(ASCE)EE.1943-7870.0001585 DOI: 10.1061/(ASCE)EE.1943-7870.0001585]</ref>
| |
| − | |-
| |
| − | |Perfluorooctane sulfonic acid (PFOS)||20||5.40x10<sup>-6</sup>||Schaefer et al. 2019 <ref name="Schaefer2019"/>
| |
| − | |-
| |
| − | |Tetrachloroethene||25||8.99x10<sup>-6</sup>||Yaws 1995 <ref name="Yaws1995"/>
| |
| − | |-
| |
| − | |Toluene||20||8.50x10<sup>-6</sup>||Bonoli and Witherspoon 1968 <ref name="Bonoli1968"/>
| |
| − | |-
| |
| − | |Trichloroethene||25||8.16x10<sup>-6</sup>||Rossi et al. 2015 <ref name="Rossi2015">Rossi, F., Cucciniello, R., Intiso, A., Proto, A., Motta, O. and Marchettini, N., 2015. Determination of the Trichloroethylene Diffusion Coefficient in Water. American Institute of Chemical Engineers Journal, 61(10), pp.3511-3515. [https://doi.org/10.1002/aic.14861 DOI: 10.1002/aic.14861]</ref>
| |
| − | |-
| |
| − | |Vinyl chloride||25||1.34x10<sup>-5</sup>||Yaws 1995 <ref name="Yaws1995"/>
| |
| − | |}
| |
| − | </br>
| |
| − | ===Macrodispersion===
| |
| − | [[File:ADRFig2.PNG | thumb | right | 350px | Figure 8. Predicted variation in macrodispersivity with distance for varying ''σ<sup>2</sup>Y'' and correlation length = 3 m.]]
| |
| − | [[File:NewThinkingAboutDispersion.mp4 |thumbnail|right|500px|Figure 9. Matrix diffusion processes and their effects on plume persistence and attenuation.]]
| |
| − | Spatial variations in hydraulic conductivity can increase the apparent spreading of solute plumes observed in groundwater monitoring wells. For example, in an aquifer composed of alternating layers of lower hydraulic conductivity (''K'') silty sand and higher ''K'' sandy gravel layers, the dissolved solute rapidly migrates downgradient through the sandy gravel layers resulting in relatively high concentration fingers surrounded by relatively uncontaminated material. Over time, contaminants in lower ''K'' layers eventually breakthrough at the monitoring well, causing a more gradual further increase in measured concentrations. This rapid breakthrough followed by gradual increases in solute concentrations gives the appearance of a plume with a very large dispersion coefficient. This spreading of the solute caused by large-scale heterogeneities in the aquifer and the associated spatial variations in advective transport velocity is referred to as macrodispersion.
| |
| − | | |
| − | In some groundwater modeling projects, large values of the dispersion coefficient are used as an adjustment factor to better represent the observed large-scale spreading of plumes<ref name="ITRC2011"/>. Theoretical studies suggest that macrodispersivity will increase with distance near the source, and then increase more slowly farther downgradient, eventually approaching an asymptotic value<ref name="Gelhar1979">Gelhar, L.W., Gutjahr, A.L. and Naff, R.L., 1979. Stochastic analysis of macrodispersion in a stratified aquifer. Water Resources Research, 15(6), pp.1387-1397. [https://doi.org/10.1029/WR015i006p01387 DOI:10.1029/WR015i006p01387]</ref><ref name="Gelhar1983">Gelhar, L.W. and Axness, C.L., 1983. Three‐dimensional stochastic analysis of macrodispersion in aquifers. Water Resources Research, 19(1), pp.161-180. [https://doi.org/10.1029/WR019i001p00161 DOI:10.1029/WR019i001p00161]</ref><ref name="Dagan1988">Dagan, G., 1988. Time‐dependent macrodispersion for solute transport in anisotropic heterogeneous aquifers. Water Resources Research, 24(9), pp.1491-1500. [https://doi.org/10.1029/WR024i009p01491 DOI:10.1029/WR024i009p01491]</ref>. Figure 8 shows values of macrodispersivity calculated using the theory of Dagan<ref name="Dagan1988"/> with an autocorrelation length of 3 m and several different values of the variance of ''Y'' (σ<small><sup>2</sup><sub>''Y''</sub></small>) where ''Y'' = Log ''K''. The calculated macrodispersivity increases more rapidly and approaches higher asymptotic values for more heterogeneous aquifers with greater variations in ''K'' (larger σ<small><sup>2</sup><sub>''Y''</sub></small>). The maximum predicted dispersivity values were in the range of 0.5 to 5 m. Zech, et al. (2015)<ref>Zech, A., Attinger, S., Cvetkovic, V., Dagan, G., Dietrich, P., Fiori, A., Rubin, Y. and Teutsch, G., 2015. Is unique scaling of aquifer macrodispersivity supported by field data? Water Resources Research, 51(9), pp.7662-7679. [https://doi.org/10.1002/2015WR017220 DOI: 10.1002/2015WR017220] Free access article from [https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2015WR017220 American Geophysical Union]</ref> presented moderate and high reliability measurements of longitudinal macrodispersivity versus distance. Typical values of the longitudinal macrodispersivity varied from 0.1 to 10 m, with much lower values for transverse and vertical dispersivities.
| |
| − | | |
| − | ===Matrix Diffusion=== | |
| − | Recently, an alternate conceptual model for describing large-scale plume spreading in heterogeneous soils has been proposed<ref name="ITRC2011" /><ref name="Payne2008"/><ref name="Hadley2014">Hadley, P.W. and Newell, C., 2014. The new potential for understanding groundwater contaminant transport. Groundwater, 52(2), pp.174-186. [http://dx.doi.org/10.1111/gwat.12135 doi:10.1111/gwat.12135]</ref>. In this approach, solute transport in the transmissive zones is reasonably well described by the advection-dispersion equation using relatively small dispersion coefficients representing mechanical dispersion. However, over time, molecular diffusion slowly transports solutes into lower permeability zones. As the transmissive zones are remediated, these solutes slowly diffuse back out, causing a long extended tail to the flushout curve. This process, referred to as [[Matrix Diffusion |matrix diffusion]], is controlled by [[wikipedia: Molecular diffusion | molecular diffusion]] and the presence of geologic heterogeneity with sharp contrasts between transmissive and low permeability media<ref>Sale, T.C., Illangasekare, T., Zimbron, J., Rodriguez, D., Wilkins, B. and Marinelli, F., 2007. AFCEE source zone initiative. Report Prepared for the Air Force Center for Environmental Excellence by Colorado State University and Colorado School of Mines. [//www.enviro.wiki/images/0/08/AFCEE-2007-Sale.pdf Report pdf]</ref> as discussed in the [//www.enviro.wiki/images/8/8a/NewThinkingAboutDispersion.mp4 video] shown in Figure 9. In some cases, matrix diffusion can maintain contaminant concentrations in more permeable zones at greater than target cleanup goals for decades or even centuries after the primary sources have been addressed<ref>Chapman, S.W. and Parker, B.L., 2005. Plume persistence due to aquitard back diffusion following dense nonaqueous phase liquid source removal or isolation. Water Resources Research, 41(12): W12411. [https://doi.org/10.1029/2005WR004224 DOI: 10.1029/2005WR004224] Free access article from [https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2005WR004224 American Geophysical Union]</ref>.
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| | ==References== | | ==References== |
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| | <references /> | | <references /> |
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| | ==See Also== | | ==See Also== |
| − | | + | *[https://serdp-estcp.mil/focusareas/9f7a342a-1b13-4ce5-bda0-d7693cf2b82d/uxo#subtopics SERDP/ESTCP Focus Areas – UXO – Munitions Constituents] |
| − | *[http://iwmi.dhigroup.com/solute_transport/advection.html International Water Management Institute Animations] | + | *[https://denix.osd.mil/edqw/home/ Environmental Data Quality Workgroup] |
| − | *[http://www2.nau.edu/~doetqp-p/courses/env303a/lec32/lec32.htm NAU Lecture Notes on Advective Transport]
| |
| − | *[https://www.youtube.com/watch?v=00btLB6u6DY MIT Open CourseWare Solute Transport: Advection with Dispersion Video] | |
| − | *[https://www.youtube.com/watch?v=AtJyKiA1vcY Physical Groundwater Model Video]
| |
| − | *[https://www.coursera.org/learn/natural-attenuation-of-groundwater-contaminants/lecture/UzS8q/groundwater-flow-review Online Lecture Course - Groundwater Flow]
| |
Munitions Constituents – Sample Extraction and Analytical Techniques
Munitions Constituents, including insensitive munitions IM), are a broad category of compounds and, in areas where manufactured or used, can be found in a variety of environmental matrices (waters, soil, and tissues). This presents an analytical challenge when a variety of these munitions are to be quantified. This article discusses sample extraction methods for each typical sample matrix (high level water, low level water, soil and tissue) as well as the accompanying HPLC-UV analytical method for 27 compounds of interest (legacy munitions, insensitive munitions, and surrogates).
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- Methods for simultaneous quantification of legacy and insensitive munition (IM) constituents in aqueous, soil/sediment, and tissue matrices[2]
Introduction
Figure 1. Primary Method labeled chromatograms
Figure 2. Secondary Method labeled chromatograms
The primary intention of the analytical methods presented here is to support the monitoring of legacy and insensitive munitions contamination on test and training ranges, however legacy and insensitive munitions often accompany each other at demilitarization facilities, manufacturing facilities, and other environmental sites. Energetic materials typically appear on ranges as small, solid particulates and due to their varying functional groups and polarities, can partition in various environmental compartments[3]. To ensure that contaminants are monitored and controlled at these sites and to sustainably manage them a variety of sample matrices (surface or groundwater, process waters, soil, and tissues) must be considered. (Process water refers to water used during industrial manufacturing or processing of legacy and insensitive munitions.) Furthermore, additional analytes must be added to existing methodologies as the usage of IM compounds changes and as new degradation compounds are identified. Of note, relatively new IM formulations containing NTO, DNAN, and NQ are seeing use in IMX-101, IMX-104, Pax-21 and Pax-41 (Table 1)[4][5].
Sampling procedures for legacy and insensitive munitions are identical and utilize multi-increment sampling procedures found in USEPA Method 8330B Appendix A[1]. Sample hold times, subsampling and quality control requirements are also unchanged. The key differences lie in the extraction methods and instrumental methods. Briefly, legacy munitions analysis of low concentration waters uses a single cartridge reverse phase SPE procedure, and acetonitrile (ACN) is used for both extraction and elution for aqueous and solid samples[1][6]. An isocratic separation via reversed-phase C-18 column with 50:50 methanol:water mobile phase or a C-8 column with 15:85 isopropanol:water mobile phase is used to separate legacy munitions[1]. While these procedures are sufficient for analysis of legacy munitions, alternative solvents, additional SPE cartridges, and a gradient elution are all required for the combined analysis of legacy and insensitive munitions.
Previously, analysis of legacy and insensitive munitions required multiple analytical techniques, however the methods presented here combine the two munitions categories resulting in an HPLC-UV method and accompanying extraction methods for a variety of common sample matrices. A secondary HPLC-UV method and a HPLC-MS method were also developed as confirmatory methods. The methods discussed in this article were validated extensively by single-blind round robin testing and subsequent statistical treatment as part of ESTCP ER19-5078. Wherever possible, the quality control criteria in the Department of Defense Quality Systems Manual for Environmental Laboratories were adhered to[7]. Analytes included in these methods are found in Table 1.
The chromatograms produced by the primary and secondary HPLC-UV methods are shown in Figure 1 and Figure 2, respectively. Chromatograms for each detector wavelength used are shown (315, 254, and 210 nm).
High Concentration Waters (> 1 ppm)
Aqueous samples suspected to contain the compounds of interest at concentrations detectable without any extraction or pre-concentration are suitable for analysis by direct injection. The method deviates from USEPA Method 8330B by adding a pH adjustment and use of MeOH rather than ACN for dilution[1]. The pH adjustment is needed to ensure method accuracy for ionic compounds (like NTO or PA) in basic samples. A solution of 1% HCl/MeOH is added to both acidify and dilute the samples to a final acid concentration of 0.5% (vol/vol) and a final solvent ratio of 1:1 MeOH/H2O. The direct injection samples are then ready for analysis.
Low Concentration Waters (< 1 ppm)
Aqueous samples suspected to contain the compounds of interest at low concentrations require extraction and pre-concentration using solid phase extraction (SPE). The SPE setup described here uses a triple cartridge setup shown in Figure 3. Briefly, the extraction procedure loads analytes of interest onto the cartridges in this order: StrataTM X, StrataTM X-A, and Envi-CarbTM. Then the cartridge order is reversed, and analytes are eluted via a two-step elution, resulting in 2 extracts (which are combined prior to analysis). Five milliliters of MeOH is used for the first elution, while 5 mL of acidified MeOH (2% HCl) is used for the second elution. The particular SPE cartridges used are noncritical so long as cartridge chemistries are comparable to those above.
Soils
Soil collection, storage, drying and grinding procedures are identical to the USEPA Method 8330B procedures[1]; however, the solvent extraction procedure differs in the number of sonication steps, sample mass and solvent used. A flow chart of the soil extraction procedure is shown in Figure 4. Soil masses of approximately 2 g and a sample to solvent ratio of 1:5 (g/mL) are used for soil extraction. The extraction is carried out in a sonication bath chilled below 20 ⁰C and is a two-part extraction, first extracting in MeOH (6 hours) followed by a second sonication in 1:1 MeOH:H2O solution (14 hours). The extracts are centrifuged, and the supernatant is filtered through a 0.45 μm PTFE disk filter.
The solvent volume should generally be 10 mL but if different soil masses are required, solvent volume should be 5 mL/g. The extraction results in 2 separate extracts (MeOH and MeOH:H2O) that are combined prior to analysis.
Tissues
Tissue matrices are extracted by 18-hour sonication using a ratio of 1 gram of wet tissue per 5 mL of MeOH. This extraction is performed in a sonication bath chilled below 20 ⁰C and the supernatant (MeOH) is filtered through a 0.45 μm PTFE disk filter.
Due to the complexity of tissue matrices, an additional tissue cleanup step, adapted from prior research, can be used to reduce interferences[8][2]. The cleanup procedure uses small scale chromatography columns prepared by loading 5 ¾” borosilicate pipettes with 0.2 g activated silica gel (100–200 mesh). The columns are wetted with 1 mL MeOH, which is allowed to fully elute and then discarded prior to loading with 1 mL of extract and collecting in a new amber vial. After the extract is loaded, a 1 mL aliquot of MeOH followed by a 1 mL aliquot of 2% HCL/MeOH is added. This results in a 3 mL silica treated tissue extract. This extract is vortexed and diluted to a final solvent ratio of 1:1 MeOH/H2O before analysis.
HPLC-UV and MS Methods
The Primary HPLC method uses a Phenomenex Synergi 4 µm Hydro-RP column (80Å, 250 x 4.6 mm), or comparable, and is based on both the HPLC method found in USEPA 8330B and previous work[1][8][2]. This separation relies on a reverse phase column and uses a gradient elution, shown in Table 2. Depending on the analyst’s needs and equipment availability, the method has been proven to work with either 0.1% TFA or 0.25% FA (vol/vol) mobile phase. Addition of a guard column like a Phenomenex SecurityGuard AQ C18 pre-column guard cartridge can be optionally used. These optional changes to the method have no impact on the method’s performance.
The Secondary HPLC method uses a Restek Pinnacle II Biphenyl 5 µm (150 x 4.6 mm) or comparable column and is intended as a confirmatory method. Like the Primary method, this method can use an optional guard column and utilizes a gradient elution, shown in Table 3.
For instruments equipped with a mass spectrometer (MS), a secondary MS method is available and was developed alongside the Primary UV method. The method was designed for use with a single quadrupole MS equipped with an atmospheric pressure chemical ionization (APCI) source, such as an Agilent 6120B. A majority of the analytes, shown in Table 1, are amenable to this MS method, however nitroglycerine (which is covered extensively in USEPA method 8332) and 2-,3-, and 4-nitrotoluene compounds aren’t compatible with the MS method. MS method parameters are shown in Table 4.
Summary
The extraction methods and instrumental methods in this article build upon prior munitions analytical methods by adding new compounds, combining legacy and insensitive munitions analysis, and expanding usable sample matrices. These methods have been verified through extensive round robin testing and validation, and while the methods are somewhat challenging, they are crucial when simultaneous analysis of both insensitive and legacy munitions is needed.
References
- ^ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 United States Environmental Protection Agency (USEPA), 2006. EPA Method 8330B (SW-846) Nitroaromatics, Nitramines, and Nitrate Esters by High Performance Liquid Chromatography (HPLC), Revision 2. USEPA Website Method 8330B.pdf
- ^ 2.0 2.1 2.2 Crouch, R.A., Smith, J.C., Stromer, B.S., Hubley, C.T., Beal, S., Lotufo, G.R., Butler, A.D., Wynter, M.T., Russell, A.L., Coleman, J.G., Wayne, K.M., Clausen, J.L., Bednar, A.J., 2020. Methods for simultaneous determination of legacy and insensitive munition (IM) constituents in aqueous, soil/sediment, and tissue matrices. Talanta, 217, Article 121008. doi: 10.1016/j.talanta.2020.121008 Open Access Manuscript.pdf
- ^ 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
- ^ Mainiero, C. 2015. Picatinny Employees Recognized for Insensitive Munitions. U.S. Army, Picatinny Arsenal Public Affairs. Open Access Press Release
- ^ Frem, D., 2022. A Review on IMX-101 and IMX-104 Melt-Cast Explosives: Insensitive Formulations for the Next-Generation Munition Systems. Propellants, Explosives, Pyrotechnics, 48(1), e202100312. doi: 10.1002/prep.202100312
- ^ United States Environmental Protection Agency (USEPA), 2007. EPA Method 3535A (SW-846) Solid-Phase Extraction (SPE), Revision 1. USEPA Website Method 3535A.pdf
- ^ US Department of Defense and US Department of Energy, 2021. Consolidated Quality Systems Manual (QSM) for Environmental Laboratories, Version 5.4. 387 pages. Free Download QSM Version 5.4.pdf
- ^ 8.0 8.1 Russell, A.L., Seiter, J.M., Coleman, J.G., Winstead, B., Bednar, A.J., 2014. Analysis of munitions constituents in IMX formulations by HPLC and HPLC-MS. Talanta, 128, pp. 524–530. doi: 10.1016/j.talanta.2014.02.013
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