Natural Source Zone Depletion (NSZD) - Revision history

Admin at 21:15, 3 February 2025

2025-02-03T21:15:44Z

Admin at 20:46, 27 April 2022

2022-04-27T20:46:45Z

Admin at 20:46, 27 April 2022

2022-04-27T20:46:31Z

Debra Tabron at 16:23, 26 August 2019

2019-08-26T16:23:07Z

Jhurley: /* Measuring the NSZD Thermal Expression */

2019-08-21T13:51:53Z

‎Measuring the NSZD Thermal Expression

Jhurley: /* Measuring the NSZD Thermal Expression */

2019-08-21T13:26:31Z

‎Measuring the NSZD Thermal Expression

Jhurley: added author of update to Contributors

2019-07-11T15:16:25Z

added author of update to Contributors

Jhurley: /* Measuring the NSZD Thermal Expression */

2019-07-08T16:18:08Z

‎Measuring the NSZD Thermal Expression

Jhurley: /* Converting Temperature to an NSZD Rate */

2019-06-06T18:46:38Z

‎Converting Temperature to an NSZD Rate

Jhurley: /* Limitations and Challenges */

2019-05-20T20:16:54Z

‎Limitations and Challenges

← Older revision		Revision as of 21:15, 3 February 2025
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−	'''Contributor(s):''' [[Tom Palaia]], [[Jeff Fitzgibbons]] and [[Poonam Kulkarni]]	+	'''Contributor(s):''' [[Tom Palaia]], [[Jeff Fitzgibbons]] and [[Poonam Kulkarni\|Poonam Kulkarni, P.E.]]

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 Natural source zone depletion (NSZD) is a term used to describe the collective, naturally occurring processes of dissolution, volatilization, and biodegradation that result in mass losses of light non-aqueous phase liquid (LNAPL) petroleum hydrocarbon constituents from the subsurface. NSZD is coming to the forefront of decision making at petroleum hydrocarbon remediation sites because much higher source attenuation rates are now being measured compared to previous rates based on incomplete conceptual models<ref>Lundegard, P.D., Johnson, P.C., 2006. Source zone natural attenuation at petroleum hydrocarbon spill sites-II: application to a former oil field. Groundwater Monitoring & Remediation, 26(4), 93-106. [http://dx.doi.org/10.1111/j.1745-6592.2006.00115.x doi:10.1111/j.1745-6592.2006.00115.x]</ref><ref name="McCoy2015">McCoy, K., Zimbron, J., Sale, T., Lyverse, M., 2015. Measurement of natural losses of LNAPL using CO<sub>2</sub> traps. Groundwater, 53(4), 658-667. [http://dx.doi.org/10.1111/gwat.12240 doi: 10.1111/gwat.12240]</ref><ref>Palaia, T. 2016. Natural Source Zone Depletion Rate Assessment. Applied NAPL Science Review (ANSR), Volume 6, Issue 1, May.</ref>. NSZD processes occur at most petroleum release sites and quantifying NSZD rates is an important part of an overall site remediation strategy.
 <div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 '''Related Article(s):'''

← Older revision		Revision as of 20:46, 27 April 2022
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−	'''~~CONTRIBUTOR~~(S):''' [[Tom Palaia]], [[Jeff Fitzgibbons]] and [[Poonam Kulkarni]]	+	'''Contributor(s):''' [[Tom Palaia]], [[Jeff Fitzgibbons]] and [[Poonam Kulkarni]]

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 '''Key Resource(s):'''
 *Quantification of Vapor Phase-Related NSZD Processes<ref>American Petroleum Institute (API), 2017. Quantification of Vapor Phase-Related NSZD Processes, First Edition. API Publication 4784, 124 pages.</ref>
 *[//www.enviro.wiki/images/b/bd/ITRC-2009-Nat_Zone_Depletion.pdf Evaluating Natural Source Zone Depletion at Sites with LNAPL. LNAPL-1. Washington, D.C.: Interstate Technology & Regulatory Council, LNAPLs Team.]<ref name="ITRC2009">Interstate Technology & Regulatory Council (ITRC). 2009. Evaluating Natural Source Zone Depletion at Sites with LNAPL. LNAPL-1. Washington, D.C.: Interstate Technology & Regulatory Council, LNAPLs Team. [//www.enviro.wiki/images/b/bd/ITRC-2009-Nat_Zone_Depletion.pdf Report pdf]</ref>

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 ==Measuring the NSZD Thermal Expression==
-[[File: NSZD2019Fig6.png |thumb|left|450px| Figure 6a. Conceptual Model of Thermal Monitoring<ref name="ThermalNSZD2018">Thermal NSZD, 2018. Thermal NSZD: Continuous Remote Monitoring of Natural Source Zone Depletion</ref>.]][[File:4860_NSZD_Short.mp4 |thumb|450px| Figure 6b. Thermal monitoring video.]]
+[[File: NSZD2019Fig6.png |thumb|left|450px| Figure 6a. Conceptual Model of Thermal Monitoring<ref name="ThermalNSZD2018">Thermal NSZD, 2018. Thermal NSZD: Continuous Remote Monitoring of Natural Source Zone Depletion [https://www.thermalnszd.com/index.php Thermal NSZD LLC]</ref>.]][[File:4860_NSZD_Short.mp4 |thumb|450px| Figure 6b. Thermal monitoring video.]]
 Analogous to a compost pile which generates heat, microbial biodegradation of LNAPL is an exothermic process that results in heat being transferred to the surroundings. As seen in Figure 6a, microbial reactions include: i) methane generation in an anaerobic zone (both above and below the water table); and ii) methane oxidation in the unsaturated zone by bacteria which releases heat<ref name="ITRC2018" /><ref name="Sale2018" />. For instance, subsurface temperatures in LNAPL-impacted locations have been found to be higher than background areas, with increases ranging from 2-2.5 °C<ref name="Sweeney2014">Sweeney, R.E., Ririe, G.T., 2014. Temperature as a tool to evaluate aerobic biodegradation in hydrocarbon contaminated soil. Groundwater Monitoring & Remediation, 34(3), 41-50. [http://onlinelibrary.wiley.com/wol1/doi/10.1111/gwmr.12064/abstract doi:10.1111/gwmr.12064]</ref>, and up to 2.7 °C<ref name="Warren2015"> Warren, E., Bekins, B.A., 2015. Relating subsurface temperature changes to microbial activity at a crude oil-contaminated site. Journal of Contaminant Hydrology, 182, 183-193. [http://dx.doi.org/10.1016/j.jconhyd.2015.09.007 doi:10.1016/j.jconhyd.2015.09.007]</ref>. A video summary of Thermal Monitoring technology is presented in Figure 6b.
 [[File:NSZD2019Fig7a.png|thumb|250px|left| Figure 7a. Thermocouples to be installed on drill rods.]][[File:NSZD2019Fig7b.png|thumb|250px| Figure 7b. Conventional Drill Rig.]]

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 Current NSZD practice is to evaluate the petroleum hydrocarbon stoichiometric equivalent of biodegradation in both the aqueous phase and gaseous (vapor) phase<ref name="ITRC2009" />. This section covers the gaseous component.
-At one site, the gaseous expression of NSZD has been shown to account for >70% of the hydrocarbon biodegradation that occurs in the subsurface<ref>Molins, S., Mayer, K.U., Amos, R.T., Bekins, B.A., 2010. Vadose zone attenuation of organic compounds at a crude oil spill site - Interactions between biogeochemical reactions and multicomponent gas transport. Journal of Contaminant Hydrology, 112(1), 15-29. [http://dx.doi.org/10.1016/j.jconhyd.2009.09.002 doi: 10.1016/j.jconhyd.2009.09.002]</ref><ref name="Ng et al 2015">Ng, G-H.C., Bekins, B.A., Cozzarelli, I.M., Baedecker, M.J., Bennett, P.C., Amos, R.T., Herkelrath, W.N., 2015. Reactive transport modeling of geochemical controls on secondary water quality impacts at a crude oil spill site near Bemidji, MN. Water Resources Research, (51) pp 4156–4183. [http://dx.doi.org/10.1002/2015wr016964 doi:10.1002/2015WR016964][//www.enviro.wiki/images/6/6c/Ng_et_al_2015.pdf  report.pdf]</ref>. Three methods to monitor the vapor phase-related portion of NSZD are currently available and widely used. These are the gradient, passive flux trap, and dynamic closed chamber (DCC) methods elaborated on below. Method choice for a particular project is a site-specific judgment based on data quality, monitoring objectives, and site conditions.
+At one site, the gaseous expression of NSZD has been shown to account for >70% of the hydrocarbon biodegradation that occurs in the subsurface<ref>Molins, S., Mayer, K.U., Amos, R.T., Bekins, B.A., 2010. Vadose zone attenuation of organic compounds at a crude oil spill site - Interactions between biogeochemical reactions and multicomponent gas transport. Journal of Contaminant Hydrology, 112(1), 15-29. [http://dx.doi.org/10.1016/j.jconhyd.2009.09.002 doi: 10.1016/j.jconhyd.2009.09.002]</ref><ref name="Ng et al 2015">Ng, G-H.C., Bekins, B.A., Cozzarelli, I.M., Baedecker, M.J., Bennett, P.C., Amos, R.T., Herkelrath, W.N., 2015. Reactive transport modeling of geochemical controls on secondary water quality impacts at a crude oil spill site near Bemidji, MN. Water Resources Research, (51) pp 4156–4183. [http://dx.doi.org/10.1002/2015wr016964 doi:10.1002/2015WR016964][//www.enviro.wiki/images/6/6c/Ng_et_al_2015.pdf report.pdf]</ref>. Three methods to monitor the vapor phase-related portion of NSZD are currently available and widely used. These are the gradient, passive flux trap, and dynamic closed chamber (DCC) methods elaborated on below. Method choice for a particular project is a site-specific judgment based on data quality, monitoring objectives, and site conditions.
 [[File:Palaia-Article 1-Figure 2.PNG|450px|thumbnail|Figure 2c. Schematic of a typical gradient method monitoring setup (excerpt from Johnson et al. (2006)<ref name="Johnson2006" />).]]
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 ==Measuring the NSZD Thermal Expression==
 [[File: NSZD2019Fig6.png |thumb|left|450px| Figure 6a. Conceptual Model of Thermal Monitoring<ref name="ThermalNSZD2018">Thermal NSZD, 2018. Thermal NSZD: Continuous Remote Monitoring of Natural Source Zone Depletion</ref>.]][[File:4860_NSZD_Short.mp4 |thumb|450px| Figure 6b. Thermal monitoring video.]]
-Analogous to a compost pile which generates heat, microbial biodegradation of LNAPL is an exothermic process that results in heat being transferred to the surroundings. As seen in Figure 6, microbial reactions include: i) methane generation in an anaerobic zone (both above and below the water table); and ii) methane oxidation in the unsaturated zone by bacteria which releases heat<ref name="ITRC2018" /><ref name="Sale2018" />. For instance, subsurface temperatures in LNAPL-impacted locations have been found to be consistently higher than background areas, with increases ranging from 2-2.5 °C<ref name="Sweeney2014">Sweeney, R.E., Ririe, G.T., 2014. Temperature as a tool to evaluate aerobic biodegradation in hydrocarbon contaminated soil. Groundwater Monitoring & Remediation, 34(3), 41-50. [http://onlinelibrary.wiley.com/wol1/doi/10.1111/gwmr.12064/abstract doi:10.1111/gwmr.12064]</ref>, and up to 2.7 °C<ref name="Warren2015"> Warren, E., Bekins, B.A., 2015. Relating subsurface temperature changes to microbial activity at a crude oil-contaminated site. Journal of Contaminant Hydrology, 182, 183-193. [http://dx.doi.org/10.1016/j.jconhyd.2015.09.007 doi:10.1016/j.jconhyd.2015.09.007]</ref>.
+Analogous to a compost pile which generates heat, microbial biodegradation of LNAPL is an exothermic process that results in heat being transferred to the surroundings. As seen in Figure 6a, microbial reactions include: i) methane generation in an anaerobic zone (both above and below the water table); and ii) methane oxidation in the unsaturated zone by bacteria which releases heat<ref name="ITRC2018" /><ref name="Sale2018" />. For instance, subsurface temperatures in LNAPL-impacted locations have been found to be higher than background areas, with increases ranging from 2-2.5 °C<ref name="Sweeney2014">Sweeney, R.E., Ririe, G.T., 2014. Temperature as a tool to evaluate aerobic biodegradation in hydrocarbon contaminated soil. Groundwater Monitoring & Remediation, 34(3), 41-50. [http://onlinelibrary.wiley.com/wol1/doi/10.1111/gwmr.12064/abstract doi:10.1111/gwmr.12064]</ref>, and up to 2.7 °C<ref name="Warren2015"> Warren, E., Bekins, B.A., 2015. Relating subsurface temperature changes to microbial activity at a crude oil-contaminated site. Journal of Contaminant Hydrology, 182, 183-193. [http://dx.doi.org/10.1016/j.jconhyd.2015.09.007 doi:10.1016/j.jconhyd.2015.09.007]</ref>. A video summary of Thermal Monitoring technology is presented in Figure 6b.
 [[File:NSZD2019Fig7a.png|thumb|250px|left| Figure 7a. Thermocouples to be installed on drill rods.]][[File:NSZD2019Fig7b.png|thumb|250px| Figure 7b. Conventional Drill Rig.]]
 [[File:NSZD2019Fig7c.png|thumb|250px| Figure 7c. Weatherproof surface equipment enclosure with solar power.]]
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 ===Converting Temperature to an NSZD Rate===
-Subsurface temperature data from a background location (i.e., clean, no LNAPL impacts and with similar geology and surface type) is needed in order to subtract local temperature variations from the LNAPL-impacted location temperatures (Figures 8a and 8b). In cases where representative background temperature measurements may not be available at a site, it is possible to estimate background temperature using mathematical models<ref name="Sweeney2014" /><ref name="Hillel1977">Hillel, D., 1977. Computer simulation of soil-water dynamics: a compendium of recent work. IDRC-082e. International Development Research Centre, Ottawa, ON, CA. [//www.enviro.wiki/images/8/8a/Hillel1977.pdf report.pdf]</ref>.
+Subsurface temperature data from a background location (i.e., clean, no underlying LNAPL impacts, away from other heat sources such as subgrade pipelines, and with similar geology, surface type and solar aspect/shading) is needed in order to subtract local temperature variations from the LNAPL-impacted location temperatures (Figures 8a and 8b). In cases where representative background temperature measurements may not be available at a site, it is possible to estimate background temperature using mathematical models<ref name="Sweeney2014" /><ref name="Hillel1977">Hillel, D., 1977. Computer simulation of soil-water dynamics: a compendium of recent work. IDRC-082e. International Development Research Centre, Ottawa, ON, CA. [//www.enviro.wiki/images/8/8a/Hillel1977.pdf report.pdf]</ref>.
 Conversion of the background-corrected temperature data requires: i) evaluation of the heat flux; and ii) conversion to an NSZD rate using the heat of reaction<ref name="Sale2018" />.
-Heat conduction in the subsurface can be quantified using [[wikipedia: Thermal conduction | Fourier’s Law]] for heat flux in the vertical direction (Figure 8a) as follows:<br>
+Heat conduction in the subsurface can be quantified using [[wikipedia: Thermal conduction | Fourier’s Law]] for heat flux in the vertical direction as follows:<br>
 ::::''qh'' = ''‐K<sub>T</sub>(ΔT/Δz)''
@@ Line 131: / Line 131: @@
 ::''K<sub>T</sub>'' is the thermal conductivity (J/m-K),<br>
 ::''ΔT'' is the change in temperature (K), and<br>
-::''Δz'' (m) is the depth interval across which heat flux is calculated. <br>
+::''Δz''  is the depth interval (m) across which heat flux is calculated. <br>
 The total heat flux (sum of heat flux to ground surface and heat flux downward) is converted to an NSZD rate (in gallons LNAPL degraded per acre per year) using the heat of reaction of hydrocarbon biodegradation. The approximate heat released during the complete mineralization of decane is 6,779 kJ/mol<ref name="Stockwell2015">Stockwell, E.B., 2015. Continuous NAPL loss rates using subsurface temperatures (Doctoral dissertation, Colorado State University). [//www.enviro.wiki/images/9/97/Stockwell2015.pdf report.pdf]</ref>.
@@ Line 140: / Line 140: @@
 NSZD rates measured using the methods described above quantify total hydrocarbon mass loss and do not speciate loss or degradation rates of individual chemicals such as benzene or naphthalene from soil or LNAPL phases. Therefore, the use of NSZD data for assessment of remedial timeframe, if based on time to achieve chemical-specific cleanup criteria in groundwater, for example, is limited. Current research is focused on correlating NSZD rates to better established remediation metrics such as LNAPL transmissivity and chemical-specific degradation rates. For example, Ng et al. (2015)<ref name="Ng et al 2015" /> developed a mass balance model that provides some insights on the contributions of various hydrocarbon constituent classes to the overall NSZD rate at a crude oil research site.
-Thermal monitoring requires background correction, similar to methods that measure vadose zone gas transport. Proper placement of temperature transducers in LNAPL-impacted as well as background locations is necessary in order to avoid errors in interpretation of the temperature data. Background thermal monitors should be located in areas with no LNAPL impacts, but with similar geology and surface cover type (e.g., vegetation). Additionally, both LNAPL-impacted and background monitors should be placed in areas without any additional sources of subsurface heat (e.g., active pipelines).
+Thermal monitoring requires background correction, similar to methods that measure vadose zone gas transport. Proper placement of temperature transducers in LNAPL-impacted as well as background locations is necessary in order to avoid errors in interpretation of the temperature data. Background thermal monitors should be located in areas with no LNAPL impacts, but with similar geology, surface cover type (e.g., vegetation), and solar aspect/shading. Additionally, both LNAPL-impacted and background monitors should be placed in areas without any additional sources of subsurface heat (e.g., active pipelines).
 Lastly, NSZD rates can be variable. They can fluctuate seasonally with change in ambient temperature which may induce cold/warm temperature cycles in the subsurface and also fluctuate with changes in surrounding water use (e.g., irrigation pumping). Additionally, each method has its own unique procedure and inherent assumptions, which make its measurement results difficult to compare with others.

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 NSZD is occurring at most petroleum release sites, however, site-specific conditions will drive the magnitude of rates. For example, the presence of a “typical” gaseous expression of NSZD (Figure 1) is contingent upon the presence of LNAPL and free exchange of atmospheric oxygen with the subsurface. If the site contains predominantly impervious ground cover, then NSZD processes will deviate from that described herein, and procedures to measure it must be adapted accordingly. Many other site conditions such as low permeability soil layers, perching water or wet vadose zones, shallow water tables, and cold climates can also affect NSZD processes and must also be taken into account during the design of any NSZD monitoring plan.
-NSZD rates measured using the methods described above quantify total hydrocarbon mass loss and do not speciate loss or degradation rates of individual chemicals such as benzene or naphthalene from soil or LNAPL phases. Therefore, the use of NSZD data for assessment of remedial timeframe, if based on time to achieve chemical-specific cleanup criteria in groundwater, for example, is limited. Current research is focused on correlating NSZD rates to better established remediation metrics such as LNAPL transmissivity and chemical-specific degradation rates. For example, Ng et al. (2015)<ref>Ng, G.-H. C., B. A. Bekins, I. M. Cozzarelli, M. J. Baedecker, P. C. Bennett, R. T. Amos, Herkelrath, W. N., 2015. Reactive transport modeling of geochemical controls on secondary water quality impacts at a crude oil spill site near Bemidji, MN, Water Resoures Research., 51, 4156–4183. [http://onlinelibrary.wiley.com/doi/10.1002/2015WR016964/abstract doi: 10.1002/2015WR016964]</ref> developed a mass balance model that provides some insights on the contributions of various hydrocarbon constituent classes to the overall NSZD rate at a crude oil research site.
+NSZD rates measured using the methods described above quantify total hydrocarbon mass loss and do not speciate loss or degradation rates of individual chemicals such as benzene or naphthalene from soil or LNAPL phases. Therefore, the use of NSZD data for assessment of remedial timeframe, if based on time to achieve chemical-specific cleanup criteria in groundwater, for example, is limited. Current research is focused on correlating NSZD rates to better established remediation metrics such as LNAPL transmissivity and chemical-specific degradation rates. For example, Ng et al. (2015)<ref name="Ng et al 2015" /> developed a mass balance model that provides some insights on the contributions of various hydrocarbon constituent classes to the overall NSZD rate at a crude oil research site.
 Thermal monitoring requires background correction, similar to methods that measure vadose zone gas transport. Proper placement of temperature transducers in LNAPL-impacted as well as background locations is necessary in order to avoid errors in interpretation of the temperature data. Background thermal monitors should be located in areas with no LNAPL impacts, but with similar geology and surface cover type (e.g., vegetation). Additionally, both LNAPL-impacted and background monitors should be placed in areas without any additional sources of subsurface heat (e.g., active pipelines).