Difference between pages "1,4-Dioxane" and "NAPL Mobility"

From Enviro Wiki
(Difference between pages)
Jump to: navigation, search
m
 
m
 
Line 1: Line 1:
−
[[wikipedia: 1,4-Dioxane | 1,4-Dioxane]] (14D) is a heterocyclic synthetic organic chemical that contains two ether bonds, is miscible with water, does not strongly sorb to natural or engineered materials, and does not biodegrade in many environments, all of which results in its persistence and rapid transport in aqueous environments.  14D is a suspected human carcinogen, which has resulted in relatively strict standards for drinking water sources.  [[wikipedia: Advanced oxidation process | Advanced oxidation processes]] (AOPs) are the most well-developed technologies for removal of 14D from potable water supplies.  Several treatment technologies are being developed for ''in situ'' treatment of 14D including [[Chemical Oxidation (In Situ - ISCO) | chemical oxidation]], [[Biodegradation - Cometabolic | cometabolic bioremediation]], and [[Thermal Remediation | thermally enhanced]] [[Soil Vapor Extraction (SVE) | soil vapor extraction]].
+
[[Wikipedia: Light non-aqueous phase liquid | Light non-aqueous phase liquid (LNAPL)]] source zones evolve over time, from a short period of expanding LNAPL bodies, to mature sites where LNAPL mobility becomes much lower or zero.  The recent development of [[Wikipedia:LNAPL transmissivity | LNAPL transmissivity]] testing provides an improved metric for understanding whether mobile LNAPL can be effectively recovered from hydrocarbon sites.
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
−
'''Related Article(s):'''
+
'''Related Article(s)''':
 +
*LNAPL Source Zone Conceptual Models (Coming soon)
 +
*LNAPL Remediation Technologies (Coming soon)
  
−
*[[Biodegradation - 1,4-Dioxane]]
 
−
*[[Biodegradation - Cometabolic]]
 
  
−
'''CONTRIBUTOR(S):''' [[Matthew Zenker]], [[Dr. Shaily Mahendra | Shaily Mahendra]], and [[Dr. Michael Hyman | Michael Hyman]]
+
'''CONTRIBUTOR(S):''' [[Andrew Kirkman]]
  
  
−
'''Key Resource(s)''':
+
'''Key Resource(s)''':  
 +
*[https://lnapl-3.itrcweb.org LNAPL Site Management: LCSM Evolution, Decision Process, and Remedial Technologies]<ref name= "ITRC2018">ITRC, 2018. LNAPL Site Management: LCSM evolution, decision process, and remedial technologies (LNAPL-3). Interstate Technical and Regulatory Council https://lnapl-3.itrcweb.org/</ref>. Section 3 provides an introductory discussion of LNAPL mobility concepts. 
 +
*[https://www.api.org/oil-and-natural-gas/environment/clean-water/ground-water/lnapl/ldrm API LNAPL Distribution and Recovery Model (LDRM), API 4760] <ref name= "Charbeneau2007">Charbeneau, R.J., 2007. LNAPL Distribution and Recovery Model. Distribution and Recovery of Petroleum Hydrocarbon Liquids in Porous Media. Vol. 1. API Publication 4760. [[media:API2007_LDRM.pdf | Report.pdf]] https://www.api.org/oil-and-natural-gas/environment/clean-water/ground-water/lnapl/ldrm</ref>.  Provides detailed discussion of LNAPL mobility as related to saturation, soil properties and capillary pressure.
 +
*[https://www.crccare.com/files/dmfile/CRCCARETechnicalreport44_TechnicalmeasurementguidanceforLNAPLnaturalsourcezonedepletion.pdf Technical measurement guidance for LNAPL natural source zone depletion]<ref name= "CRCCARE2018">CRC CARE, 2018. Technical measurement guidance for LNAPL natural source zone depletion. Cooperative Research Centre for Contamination Assessment and Remediation of the Environment, Newcastle, Australia. Technical Report no. 44. 254p [[media:CRCCARE2018_Measurement_Guidance_for_LNAPL_NSZD.pdf | Report.pdf]]  https://www.crccare.com/files/dmfile/CRCCARETechnicalreport44_TechnicalmeasurementguidanceforLNAPLnaturalsourcezonedepletion.pdf</ref>. Section 6 provides a discussion of compositional changes to LNAPL over time and how to use those changes to calculate natural source zone depletion rates. 
  
−
*[https://doi.org/10.1201/EBK1566706629 Environmental Investigation and Remediation: 1,4-Dioxane and other solvent stabilizers]<ref name="Mohr2010">Mohr, T.K., Stickney, J.A. and DiGuiseppi, W.H., 2010. Environmental investigation and remediation: 1, 4-dioxane and other solvent stabilizers. CRC Press. Boca Raton. 550 pages. [https://doi.org/10.1201/EBK1566706629 doi: 10.1201/EBK1566706629]</ref>
+
==Introduction==
 +
LNAPL can be found in the subsurface in three different states:
 +
#'''Residual LNAPL''' is trapped and immobile but can undergo composition change and generate dissolved hydrocarbon plumes and/or vapor sources in the unsaturated zones.
 +
#'''Mobile LNAPL''' is LNAPL at greater than the residual saturation which can therefore accumulate in a well where it is potentially recoverable. However, in this state LNAPL saturation is insufficient to drive migration (i.e., the LNAPL body is not expanding).
 +
#'''Migrating LNAPL''' is LNAPL at greater than the residual saturation that expands into previously unimpacted locations over time (e.g., LNAPL appears in a monitoring well that had no previous detections).
  
−
==Properties, Fate and Transport==
+
When released to the subsurface, light non-aqueous phase liquids form source zones which evolve over time with changing impacts to soil, groundwater, and at some sites surface water. Shallow unsaturated soils may also be impacted by intrusion of vapors released by the LNAPL. (See [[Vapor Intrusion - Separation Distances from Petroleum Sources]].) LNAPL mobility is typically highest during the time of the release to the environment.  Once the release stops, LNAPL mobility and the potential for migration rapidly decrease.  The LNAPL body may initially contain mobile LNAPL near the release point.  However, as the LNAPL body spreads, the driving head and pressure gradient decrease, and the LNAPL thickness (a key factor in mobility) decreases. The LNAPL body also begins to weather, losing volatiles and biodegradable compounds.  Over time, this weathering process alters the LNAPL composition and stabilizes the LNAPL body, and the fraction of LNAPL that remains mobile therefore decreases<ref name= "ITRC2018"/><ref name= "CRCCARE2018"/><ref>Mahler, N., Sale, T. and Lyverse, M., 2012. A mass balance approach to resolving LNAPL stability. Groundwater, 50(6), pp.861-871. [https://doi.org/10.1111/j.1745-6584.2012.00949.x  [10.1111/j.1745-6584.2012.00949.x  10.1111/j.1745-6584.2012.00949.x]</ref>.  LNAPL bodies from historical releases are dominated by immobile residual LNAPL. 
−
1,4-Dioxane (14D) is a heterocyclic organic compound, and the most commonly encountered of the three dioxane isomers (1,2-, 1,3- and 1,4-dioxane). Key physical and chemical properties of 14D are listed in Table 1.  The heterocyclic, polar structure of 1,4-dioxane causes it to be miscible with water and also unable to strongly sorb or partition to aquifer solids or engineered sorbents (i.e. activated carbon).  While 14D has a moderate vapor pressure, the high aqueous solubility results in limited volatilization.  
+
 
−
   
+
Because LNAPL bodies evolve over time, LNAPL mobility is a much more significant concern during and immediately after the release period than it is after the release is halted.  Tools are now available to assess the magnitude of LNAPL mobility at individual release sites to support decision making regarding potential remedial actions. One such tool is the American Petroleum Institute’s [https://www.api.org/oil-and-natural-gas/environment/clean-water/ground-water/lnapl/ldrm LNAPL Distribution and Recovery Model (LDRM)] which is available as a free download. Please see the LNAPL Mobility and Recovery section below for a more complete discussion of modeling tools.
−
{| class="wikitable" style="float:right; margin-left: 10px;"
+
 
−
|+Table 1. Properties of 1,4-Dioxane
+
In order to understand LNAPL mobility, key concepts from the science of multiphase flow in porous media (e.g. soil and aquifer material) are important.  Consider dry soil to which a small amount of water is added.  The open pore space in the soil, initially filled with 100 percent air, now contains a mix of air and water. Therefore, a soil can have more than one fluid within the pores (“multiphase”).  The fraction of pore space filled with a given fluid is termed “saturation”.  The air saturation of the initially dry soil was 100% and the water saturation was zero.  When considering a petroleum release site, three different fluids may exist in the pore space: air, water and LNAPL.  The sum of the saturation of the three fluids is 100%. All three fluids can exist within the subsurface with varying saturations.
 +
 
 +
==LNAPL Mobility Conceptualized==
 +
[[File:Kirkman1w2Fig1.png|thumb|left|Figure 1.  LNAPL Distribution in a research sand tank<ref>Hawkins, A. M., 2013.  Processes Controlling the behavior of LNAPLs at groundwater surface water interfaces, Master of Science Thesis, Colorado State University, Ft. Collins, Colorado.  [[media:Hawkins2013_LNAPL_at_GW_SW_Interfaces.pdf | Report.pdf]]</ref>.]]
 +
Figure 1 shows a research tank with a well screen in a porous media (sand) containing LNAPL.  The LNAPL fluoresces under ultraviolet (UV) light, while water and air do not.  The column of yellow fluorescence in the well represents the gauged LNAPL thickness and corresponds to the vertical interval over which LNAPL flows in the formation<ref name= "Huntley2000">Huntley, D., 2000. Analytic determination of hydrocarbon transmissivity from baildown tests. Groundwater, 38(1), pp.46-52. [https://doi.org/10.1111/j.1745-6584.2000.tb00201.x doi: 10.1111/j.1745-6584.2000.tb00201.x]</ref>.  The yellow fluorescence to the left of the well represents LNAPL occurring within soil pores.  Below the potentiometric surface line, the pores are dominated by water (dark pores) and LNAPL.  Above this line LNAPL and water still exist in pores, but the air saturation increases with elevation.  The incomplete yellow fluorescence in the formation illustrates how water and LNAPL occupy pores over the mobile interval.  This occurs because the mobile LNAPL cannot displace all of the water from the pores.
 +
 
 +
[[File:Kirkman1w2Fig2.png|thumb|Figure 2.  Hypothetical relative permeability curves for water and an LNAPL in a porous medium<ref name= "USEPA1996"/><ref>Newell, C. J., Acree*, S. D., Ross, R.R., and Huling, S.G. 1995. Light non-aqueous phase liquid. U.S. Environmental Protection Agency, Washington, DC. EPA/540/S-95/500 (NTIS 95-267738) [[media:Newell1995_EPA_540_S-95_500_lnapl.pdf | Report.pdf]]</ref><ref>Williams, D.E. and Wilder, D.G., 1971. Gasoline Pollution of a Ground‐Water Reservoir—A Case History. Groundwater, 9(6), pp.50-56. [https://doi.org/10.1111/j.1745-6584.1971.tb03577.x doi: 10.1111/j.1745-6584.1971.tb03577.x]</ref>.]]
 +
LNAPL mobility can be described mathematically by Darcy’s Law, an empirically derived equation describing the flow of fluids through porous media where the specific discharge, ''q'', is equal to the product of the hydraulic conductivity, ''K'', and the hydraulic gradient, ''i''.  While this is the same Darcy’s Law that is used to describe groundwater flow (see [[Advection and Groundwater Flow]]), there is an important additional term, Relative Permeability, that is included when using Darcy’s Law to describe the flow of LNAPL in the subsurface.  Relative permeability is the ratio of the effective permeability of a fluid at a specified saturation to the intrinsic permeability of the medium at 100-percent saturation<ref>Mercer, J.W. and Cohen, R.M., 1990. A review of immiscible fluids in the subsurface: properties, models, characterization and remediation. Journal of contaminant hydrology, 6(2), pp.107-163. [https://doi.org/10.1016/0169-7722(90)90043-G doi: 10.1016/0169-7722(90)90043-G]</ref>.  The USEPA (1996)<ref name= "USEPA1996">USEPA, 1996.  How to effectively recover free product at leaking underground storage sites.  A guide for state regulators.  USEPA 510-R-96-001.  U.S. Environmental Protection Agency, 162 pp. [[media:USEPA1996_510_R-96_001_Recover_Free_Prod_at_LUSTS.pdf| Report.pdf]]</ref> describes relative permeability this way:
 +
 
 +
<q>''The relative permeability of a particular geologic media that is completely saturated with a particular fluid is equal to the intrinsic permeability. When more than one fluid (i.e., air, water, petroleum hydrocarbon) exists in a porous medium, the fluids compete for pore space thereby reducing the relative permeability of the media and the mobility of the fluid. This reduction can be quantified by multiplying the intrinsic permeability of the geologic media by the relative permeability. As with saturation, the mobility of each fluid phase present varies from zero (0% saturation) to one (100% saturation).''</q>
 +
 
 +
Figure 2 shows an example of relative permeability curves for a water-LNAPL system. The curves representing water saturation (starting at top right, blue line) and hydrocarbon saturation (starting at top left, red line) are contrary to one another and divide the figure into three flow zones. Zone I, where hydrocarbon saturation is relatively high, is dominated by hydrocarbon flow.  Water saturation is relatively high in Zone III, and therefore water flow is dominant. Flow of both water and LNAPL characterizes Zone II.
 +
 
 +
The relative permeability term scales the LNAPL conductivity to the fraction of pores occupied by LNAPL.  If LNAPL occupies 50 percent of the pores, then it will only flow through LNAPL-filled pores and therefore does not use the entire permeability of the soil.  If the sum of the pores is considered a pipe, then a pipe half full will transmit less LNAPL than a pipe completely full for a given pressure gradient. The relative permeability term is used to account for this effect.
 +
 
 +
[[File:Kirkman1w2Fig3.png|thumb|left|Figure 3.  Aquifer transmissivity versus hydraulic conductivity.]]
 +
LNAPL saturation varies with elevation across the gauged LNAPL thickness, where LNAPL conductivity is lowest near the oil/water interface and highest near the air/LNAPL interface.  To provide a single metric for LNAPL mobility, the conductivity must be summed across the mobile LNAPL interval to give the LNAPL transmissivity.
 +
 
 +
LNAPL transmissivity has been identified as a key metric for evaluating the likely effectiveness of direct LNAPL recovery compared to traditional measurements such as gauged LNAPL thickness in monitoring wells<ref>Kolhatkar, R., Kremesec, V., Rubin, S., Yukawa, C. and Senn, R., 1999. Application of field and analytical techniques to evaluate recoverability of subsurface free phase hydrocarbons. Petroleum Hydrocarbons and Organic Chemicals in Ground Water, pp.5-15.</ref><ref>Lundy, D.A. and Zimmerman, L.M., 1996, May. Assessing the recoverability of LNAPL plumes for recovery system conceptual design. In Proceedings of the 10th National Outdoor Action Conference and Expo (pp. 13-15).</ref><ref name= "Huntley2000"/><ref name= "Kirman2013">Kirkman, A.J., 2013. Refinement of Bouwer‐Rice baildown test analysis. Groundwater Monitoring & Remediation, 33(1), pp.105-110. [https://doi.org/10.1111/j.1745-6592.2012.01411.x  doi: 10.1111/j.1745-6592.2012.01411.x]</ref><ref name= "ASTM2013">ASTM, 2013.  ASTM E2856-13, Standard guide for estimation of LNAPL transmissivity, ASTM International, West Conshohocken, PA.</ref><ref name= "Charbeneau2016">Charbeneau, R., Kirkman, A., and Muthu, R., 2016.  API LNAPL Transmissivity Workbook: A Tool for Baildown Test Analysis – User Guide.  American Petroleum Institute Publication 4762.</ref><ref name= "Palmier2016">Palmier, C., Dodt, M. and Atteia, O., 2016. Comparison of Oil Transmissivity Methods Using Bail‐Down Test Data. Groundwater Monitoring & Remediation, 36(3), pp.73-83.[[media:Palmier2016_LNAPLBaildownTesting.pdf| Report.pdf]]</ref><ref>Lenhard, R.J., Rayner, J.L. and Davis, G.B., 2017. A practical tool for estimating subsurface LNAPL distributions and transmissivity using current and historical fluid levels in groundwater wells: Effects of entrapped and residual LNAPL. Journal of contaminant hydrology, 205, pp.1-11. [[media:Lenhard2017_Estimating_Subsurface_LNAPL.pdf | Report.pdf]]</ref>.  LNAPL transmissivity represents the volume of LNAPL flow a formation can produce per unit time over a unit width for a unit hydraulic gradient.  Aquifer transmissivity is the primary metric for evaluating how much water can be produced from a water bearing unit in the subsurface and accounts for the thickness of the saturated aquifer and the ease with which the aquifer can transmit a given fluid per unit volume. The concept of transmissivity is illustrated in Figure 3.  It is reasonable to apply similar thinking to estimation of the amount of LNAPL that could be produced by a particular subsurface matrix, and therefore transmissivity has become a key metric used to predict whether direct recovery (direct pumping) of LNAPL is likely to be effective.
 +
 
 +
The average LNAPL recovery rate was shown to be closely related to the average LNAPL transmissivity as well as to the LNAPL thickness in a series of 10-hour pump tests of three wells at an LNAPL-impacted site (Table 1, ITRC 2018)<ref name= "ITRC2018"/>.  The measured LNAPL thickness in the source well (MW-1) was 3.7 times higher than in the LNAPL fringe well (MW-3), while the ratio of their average LNAPL transmissivities was 5. The average recovery rate was 12 times greater at the source well than at the fringe well.  In this study, LNAPL thickness, average transmissivity and average recovery rate were all strongly correlated, with correlation coefficients of 0.94 and above.
 +
{| class="wikitable" style="float:right; margin-left:10px;text-align:center;"
 +
|+ Table 1. LNAPL Transmissivity Results from One LNAPL Site<ref name= "ITRC2018"/>
 
|-
 
|-
−
!Property
+
! Well ID
−
!Value
+
! Well Location
−
!Reference
+
! LNAPL Thickness in Well<br/>(ft)
 +
! Average LNAPL Transmissivity<br/>(ft<sup>2</sup>/day)
 +
! Average LNAPL Recovery Rate<br/>(gallons/minute)
 
|-
 
|-
−
|Chemical Formula||C<sub>4</sub>H<sub>8</sub>O<sub>2</sub>||
+
| '''MW-1''' || Source || 8.13 || 100 || 1.2
 
|-
 
|-
−
|Chemical Abstracts Service (CAS) Number||123-91-1||
+
| '''MW-2''' || Mid-point || 4.39 || 60 || 0.3
 
|-
 
|-
−
|Appearance||Colorless Liquid||NIOSH, 2007<ref name="NIOSH2007">Barsan, M.E., 2007. NIOSH pocket guide to chemical hazards. [//www.enviro.wiki/images/3/3b/2007-NIOSH_Pocket_Guide_to_Chemical_Hazards.pdf Report.pdf]</ref>
+
| '''MW-3''' || LNAPL || 2.2 || 20 || 0.1
 
|-
 
|-
−
|Molecular Weight||88.105 g/mol||NIST, 2018<ref>NIST, 2018. NIST Chemistry WebBook: Standard Reference Database 69. US Department of Commerce. https://webbook.nist.gov/chemistry/</ref>
+
| colspan="2" | '''Ratio of MW-1 to MW-3''' || 3.7 || 5.0 || 12
−
|-
 
−
|Water Solubility||Miscible||NIOSH, 2007<ref name="NIOSH2007" />
 
−
|-
 
−
|Specific Gravity||1.03||NIOSH, 2007<ref name="NIOSH2007" />
 
−
|-
 
−
|Vapor Pressure at 25&deg; C||38.1 mm Hg||US EPA, 2017<ref name="USEPA2017Z">US EPA, 2017. Technical Fact Sheet – 1,4-Dioxane. Publication number: EPA 505-F-17-001. [//www.enviro.wiki/images/2/2e/2017-USEPA-_Technical_Fact_Sheet.pdf Report.pdf]</ref>
 
−
|-
 
−
|Henry’s Law Constant at 25&deg; C||4.80 X 10<sup>-6</sup> atm-m<sup>3</sup>/mol||US EPA, 2017<ref name="USEPA2017Z" />
 
−
|-
 
−
|Octanol-Water Partition Coefficient (log ''K<sub>ow</sub>'')||-0.27||US EPA, 2017<ref name="USEPA2017Z" />
 
−
|-
 
−
|Organic Carbon Partition Coefficient (log ''K<sub>oc</sub>'')||1.23||Lyman et al., 1990<ref>Lyman, W.J., W.F. Reehl , D.H. Rosenblatt, and N.P.E. Vermeulen, 1990. Handbook of Chemical Property Estimation Methods. American Chemical Society, 110(2), 61-61. [https://doi.org/10.1002/recl.19911100212 doi: 10.1002/recl.19911100212]</ref>
 
 
|}
 
|}
  
−
Biodegradation of 14D is limited in many environments including surface water, groundwater and wastewater treatment plants.  Currently, there is little evidence that 14D biodegrades under anaerobic conditions<ref>Shen, W., Chen, H. and Pan, S., 2008. Anaerobic biodegradation of 1, 4-dioxane by sludge enriched with iron-reducing microorganisms. Bioresource technology, 99(7), pp.2483-2487. [https://doi.org/10.1016/j.biortech.2007.04.054 doi: 10.1016/j.biortech.2007.04.054]</ref><ref name="Zhang2017">Zhang, S., Gedalanga, P.B. and Mahendra, S., 2017. Advances in bioremediation of 1, 4-dioxane-contaminated waters. Journal of environmental management, 204, pp.765-774. [https://doi.org/10.1016/j.jenvman.2017.05.033 doi: 10.1016/j.jenvman.2017.05.033]</ref>.  In contrast, under aerobic conditions, several bacteria and fungi<ref>Skinner, K., Cuiffetti, L. and Hyman, M., 2009. Metabolism and cometabolism of cyclic ethers by a filamentous fungus, a Graphium sp. Appl. Environ. Microbiol., 75(17), pp.5514-5522. [https://doi.org/10.1128/aem.00078-09 doi:10.1128/AEM.00078-09]</ref> can grow on 14D as a sole source of carbon and energy, including well-characterized strains such as ''Pseudonocardia dioxanivorans'' CB1190<ref name="Parales1994">Parales, R.E., Adamus, J.E., White, N. and May, H.D., 1994. Degradation of 1, 4-dioxane by an actinomycete in pure culture. Applied and Environmental Microbiology, 60(12), pp.4527-4530. [//www.enviro.wiki/images/c/cd/1994-Parales-Degradation_of_1%2C4-Dioxane_by_an_Actinomycete_in_Pure_Culture.pdf Report.pdf]</ref><ref name="Mahendra2006">Mahendra, S. and Alvarez-Cohen, L., 2006. Kinetics of 1, 4-dioxane biodegradation by monooxygenase-expressing bacteria. Environmental Science & Technology, 40(17), pp.5435-5442. [https://doi.org/10.1021/es060714v [https://doi.org/10.1021/es060714v doi: 10.1021/es060714v]</ref> and other closely related [[wikipedia: Actinomycetales | actinomycetes]]<ref name="Zhang2017" /><ref>Yamamoto, N., Saito, Y., Inoue, D., Sei, K. and Ike, M., 2018. Characterization of newly isolated Pseudonocardia sp. N23 with high 1, 4-dioxane-degrading ability. Journal of bioscience and bioengineering, 125(5), pp.552-558. [https://doi.org/10.1016/j.jbiosc.2017.12.005 doi: 10.1016/j.jbiosc.2017.12.005]</ref><ref>Inoue, D., Tsunoda, T., Sawada, K., Yamamoto, N., Saito, Y., Sei, K. and Ike, M., 2016. 1, 4-Dioxane degradation potential of members of the genera Pseudonocardia and Rhodococcus. Biodegradation, 27(4-6), pp.277-286. [https://doi.org/10.1007/s10532-016-9772-7 doi: 10.1007/s10532-016-9772-7]</ref><ref>Kim, Y.M., Jeon, J.R., Murugesan, K., Kim, E.J. and Chang, Y.S., 2009. Biodegradation of 1, 4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06. Biodegradation, 20(4), p.511. [https://doi.org/10.1007/s10532-008-9240-0 doi: 10.1007/s10532-008-9240-0]</ref>. However, growth of these organisms on 14D is slow<ref>Barajas-Rodriguez, F.J. and Freedman, D.L., 2018. Aerobic biodegradation kinetics for 1, 4-dioxane under metabolic and cometabolic conditions. Journal of hazardous materials, 350, pp.180-188. [https://doi.org/10.1016/j.jhazmat.2018.02.030 doi: 10.1016/j.jhazmat.2018.02.030]</ref>, and as a consequence, 14D-metabolizing microorganisms are generally not effective in degrading 14D at the lower concentrations (≤100 &mu;g/L) commonly observed in surface water and groundwater <ref name="Adamson2014">Adamson, D.T., Mahendra, S., Walker Jr, K.L., Rauch, S.R., Sengupta, S. and Newell, C.J., 2014. A multisite survey to identify the scale of the 1, 4-dioxane problem at contaminated groundwater sites. Environmental Science & Technology Letters, 1(5), pp.254-258. [https://doi.org/10.1021/ez500092u doi: 10.1021/ez500092u]</ref><ref name="Knappe2016">Knappe, D., Lopez-Velandia, C., Hopkins, Z. and Sun, M., 2016. Occurrence of 1, 4-Dioxane in the Cape Fear River Watershed and Effectiveness of Water Treatment Options for 1, 4-Dioxane Control. NC Water Resources Research Institute of The University of North Carolina, Report No. 478. [//www.enviro.wiki/images/a/a4/2016-Knappe-Occurrence_of_1%2C4-dioxane_in_the_Cape_Fear_River.pdf Report.pdf]</ref>. 
+
An example in which LNAPL transmissivity would be better than LNAPL thickness at predicting LNAPL recoverability is shown in Figure 4.  At this site there was little or no change in LNAPL thickness over 10 years of LNAPL recovery using a vacuum truck.  If the LNAPL thickness were affected by the ongoing recovery action, a clear trend of decreasing LNAPL thickness over time would have been observed, which would have resulted in clustering of early time data on the right side of the graph and late time data on the left<ref name= "ITRC2018"/>.  
 +
[[File:Kirkman1w2Fig4.png|thumb|left|Figure 4. Gauged LNAPL thickness versus potentiometric surface elevation through time<ref name= "ITRC2018"/><ref name= "Kirkman2_2013">Kirkman, A.J., Adamski, M. and Hawthorne, J.M., 2013. Identification and assessment of confined and perched LNAPL conditions. Groundwater Monitoring & Remediation, 33(1), pp.75-86. [https://doi.org/10.1111/j.1745-6592.2012.01412.x  doi: 10.1111/j.1745-6592.2012.01412.x]</ref>), showing 10 years of LNAPL recovery with little to no change in LNAPL thickness.]]
  
−
While 14D is not commonly used as a microbial growth substrate at ambient concentrations, there are a wide variety of microorganisms that can [[Biodegradation_-_Cometabolic | cometabolically biodegrade]] 14D when grown on a different (primary) substrate. During cometabolism, the primary substrate supports production of active biomass and induces the appropriate enzymes that can then fortuitously biodegrade 14D. Primary substrates that have been shown to support cometabolic biodegradation of 14D include [[wikipedia: Tetrahydrofuran | tetrahydrofuran]] (THF), [[wikipedia: Toluene | toluene]], [[wikipedia: Methane | methane]], [[wikipedia: Ethane | ethane]], [[wikipedia: Propane | propane]], and [[wikipedia: Isobutane | isobutane]]<ref name="Mahendra2006" /><ref>Vainberg, S., McClay, K., Masuda, H., Root, D., Condee, C., Zylstra, G.J. and Steffan, R.J., 2006. Biodegradation of ether pollutants by Pseudonocardia sp. strain ENV478. Appl. Environ. Microbiol., 72(8), pp.5218-5224. [https://doi.org/10.1128/aem.00160-06 doi: 10.1128/AEM.00160-06]</ref><ref>Hatzinger, P.B., Banerjee, R., Rezes, R., Streger, S.H., McClay, K. and Schaefer, C.E., 2017. Potential for cometabolic biodegradation of 1, 4-dioxane in aquifers with methane or ethane as primary substrates. Biodegradation, 28(5-6), pp.453-468. [https://doi.org/10.1007/s10532-017-9808-7 doi: 0.1007/s10532-017-9808-7]</ref><ref>Bennett, P., Hyman, M., Smith, C., El Mugammar, H., Chu, M.Y., Nickelsen, M. and Aravena, R., 2018. Enrichment with carbon-13 and deuterium during monooxygenase-mediated biodegradation of 1, 4-dioxane. Environmental Science & Technology Letters, 5(3), pp.148-153. [https://doi.org/10.1021/acs.estlett.7b00565 doi: 10.1021/acs.estlett.7b00565]</ref><ref>Deng, D., Li, F., Wu, C. and Li, M., 2018. Synchronic Biotransformation of 1, 4-Dioxane and 1, 1-Dichloroethylene by a Gram-Negative Propanotroph Azoarcus sp. DD4. Environmental Science & Technology Letters, 5(8), pp.526-532. [https://doi.org/10.1021/acs.estlett.8b00312 doi: 10.1021/acs.estlett.8b00312]</ref>. Recent field studies have demonstrated that propane-stimulated cometabolic biodegradation can reduce 14D to below 2-3 µg/L under appropriate conditions<ref name="Lippincott2015">Lippincott, D., Streger, S.H., Schaefer, C.E., Hinkle, J., Stormo, J. and Steffan, R.J., 2015. Bioaugmentation and propane biosparging for in situ biodegradation of 1, 4‐dioxane. Groundwater Monitoring & Remediation, 35(2), pp.81-92. [https://doi.org/10.1111/gwmr.12093 doi: 10.1111/gwmr.12093]</ref><ref name="Chu2018">Chu, M.Y.J., Bennett, P.J., Dolan, M.E., Hyman, M.R., Peacock, A.D., Bodour, A., Anderson, R.H., Mackay, D.M. and Goltz, M.N., 2018. Concurrent Treatment of 1, 4‐Dioxane and Chlorinated Aliphatics in a Groundwater Recirculation System Via Aerobic Cometabolism. Groundwater Monitoring & Remediation, 38(3), pp.53-64. [https://doi.org/10.1111/gwmr.12293 doi: 10.1111/gwmr.12293]</ref>.
+
Based on the practical experience from five LNAPL sites, the ITRC proposed a threshold LNAPL transmissivity for recoverability: values below 0.1 to 0.8 ft<sup>2</sup>/day indicate low recoverability. Therefore, the majority of the LNAPL at a site in this category is in a state of lesser mobility, and the remaining source is dominated by residual saturation <ref name= "ITRC2018"/>. For the five LNAPL sites, the ITRC concluded: “These sites were closed or granted no further action after developing comprehensive LNAPL Conceptual Site Models and operating LNAPL recovery systems. All sites demonstrated achievement of the impracticable limit (i.e., the lack of LNAPL recoverability) irrespective of in-well LNAPL thickness remaining. Since that time, data from four additional sites, with comprehensive LCSMs based on high-resolution data, were analyzed and affirmed the proposed limits.”  The ITRC (2018)<ref name= "ITRC2018"/> recently expanded the technical basis for this important LNAPL transmissivity threshold with more technical background and additional case studies.
  
−
As a result of the low sorption, low volatilization and low biodegradation, attenuation of 14D is often limited in groundwater<ref>Nyer, E., Boettcher, G. and Morello, B., 1991. Using the properties of organic compounds to help design a treatment system. Groundwater Monitoring & Remediation, 11(4), pp.81-86. [https://doi.org/10.1111/j.1745-6592.1991.tb00395.x doi: 10.1111/j.1745-6592.1991.tb00395.x]</ref><ref>Jackson, R.E. and Dwarakanath, V., 1999. Chlorinated decreasing solvents: physical‐chemical properties affecting aquifer contamination and remediation. Groundwater Monitoring & Remediation, 19(4), pp.102-110. [https://doi.org/10.1111/j.1745-6592.1999.tb00246.x doi: 10.1111/j.1745-6592.1999.tb00246.x]</ref>, surface water<ref name="Knappe2016" /> and traditional potable and wastewater treatment systems<ref name="Stepien2014">Stepien, D.K., Diehl, P., Helm, J., Thoms, A. and Püttmann, W., 2014. Fate of 1, 4-dioxane in the aquatic environment: From sewage to drinking water. Water Research, 48, pp.406-419. [https://doi.org/10.1016/j.watres.2013.09.057 doi: 10.1016/j.watres.2013.09.057]</ref>.  In groundwater, the limited sorption of 14D results in relatively low concentrations in the source area and large dilute plumes<ref name="Adamson2014" />. Under these conditions, much of the 14D mass will be present in the downgradient plume and aggressive treatment of the source area is generally less effective in reducing 14D migration.
+
==Characterization of LNAPL Mobility==
 +
Field testing for LNAPL transmissivity transforms the gauged LNAPL thickness, fluid parameters of density and viscosity and the relative permeability into a single value. As saturation decreases, the interconnectivity of the pores decreases, and the ability of the soil to transmit LNAPL for a given gradient decreases.  
  
−
==Toxicity and Regulatory Standards (updated 2018)==
+
LNAPL transmissivity can be estimated with LNAPL baildown or other well testing techniques where the well screen intersects the entire interval of mobile LNAPL.  ASTM (2013)<ref name= "ASTM2013"/> and Gatsios et al. (2018)<ref>Gatsios, E., García-Rincón, J., Rayner, J.L., McLaughlan, R.G. and Davis, G.B., 2018. LNAPL transmissivity as a remediation metric in complex sites under water table fluctuations. Journal of Environmental Management, 215, pp.40-48. [[media:Gatsios2018_LNAPL_Transmissivity_as_Metric.pdf | Report.pdf]]</ref> describe four methods:
−
The U.S. Department of Health and Human Services<ref>ATSDR, 2012. Toxicological profile for 1,4-dioxane. Agency for Toxic Substances and Disease Registry [//www.enviro.wiki/images/d/df/2012-ASTDR._Toxicological_profile_for_1%2C4-dioxane.pdf Report.pdf]</ref> classifies 14D as a reasonably anticipated human carcinogen, and the International Agency for Research on Cancer<ref name="IARC1999">IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, International Agency for Research on Cancer and World Health Organization, 1999. Re-evaluation of some organic chemicals, hydrazine and hydrogen peroxide. IARC.</ref><ref>Stickney, J.A., Sager, S.L., Clarkson, J.R., Smith, L.A., Locey, B.J., Bock, M.J., Hartung, R. and Olp, S.F., 2003. An updated evaluation of the carcinogenic potential of 1, 4-dioxane. Regulatory Toxicology and Pharmacology, 38(2), pp.183-195. [https://doi.org/10.1016/S0273-2300(03)00090-4 doi: 10.1016/S0273-2300(03)00090-4]</ref> regards 14D as possibly carcinogenic to humans (Group 2B).  These classifications are primarily based on research on mice, rats and guinea pigs<ref name="IARC1999" />. One human epidemiological study reported no increased deaths from cancer in workers exposed to 14D<ref>Buffler, P.A., Wood, S.M., Suarez, L. and Kilian, D.J., 1978. Mortality follow-up of workers exposed to 1, 4-dioxane. Journal of occupational medicine.: official publication of the Industrial Medical Association, 20(4), pp.255-259.</ref>.
 
  
−
There is currently no maximum contaminant level (MCL) for 14D.  However, tap water screening (0.46 µg/L) and drinking water equivalent levels (1 mg/L)<ref>U.S. Environmental Protection Agency (USEPA), 2018(a). Edition of the Drinking Water Standards and Health Advisories. EPA 822-F-18-001 [//www.enviro.wiki/images/3/36/2018-USEPA-Edition_of_the_Drinking_Water_Standards_and_Health_Advisories.pdf Report.pdf]</ref> have been established.  For soil contamination, the US EPA has calculated a residential soil screening level (SSL) of 5.3 milligrams per kilogram (mg/kg), an industrial SSL of 24 mg/kg and leach-based SSL of 9.4 x 10<sup>-5</sup> mg/kg <ref>U.S. Environmental Protection Agency (USEPA), 2018(b). Regional Screening Level (RSL) Summary Tables. https://www.epa.gov/risk/regional-screening-levels-rsls-generic-tables</ref>.  Many states have established drinking water and groundwater standards, which range from 0.25 (New Hampshire) to 9.1 µg/L (Texas)<ref>Suthersan, S., Quinnan, J., Horst, J., Ross, I., Kalve, E., Bell, C. and Pancras, T., 2016. Making strides in the management of “emerging contaminants”. Groundwater Monitoring & Remediation, 36(1), pp.15-25. [https://doi.org/10.1111/gwmr.12143 doi: 10.1111/gwmr.12143]</ref>.
+
*Short-Term Baildown Tests:  LNAPL is quickly removed from a well, and data showing how quickly LNAPL refills the well are collected.  These data are analyzed using methods similar to analyzing slug tests.  An easy to use spreadsheet<ref name= "Charbeneau2016"/> is available [https://www.api.org/oil-and-natural-gas/environment/clean-water/ground-water/lnapl/transmissivity-workbook here] to help process the data generated by short-term baildown tests and obtain an LNAPL transmissivity estimate.  Short-term baildown tests are the most commonly used method. 
 +
*Manual Skimming Method:  LNAPL is repeatedly recovered over time (on the order of several days), gauging the well as it recovers, and then initiating another recovery event before the LNAPL level rebounds by more than 25% of the original drawdown. This is done until the LNAPL removal rate stabilizes, and then this rate is used to calculate transmissivity.
 +
*Long-Term Recovery-Based Methods:  Typically applied to sites with on-going LNAPL recovery.  There are several equations which can be used to calculate LNAPL transmissivity from the long-term recovery data.
 +
*Tracer-Based Method: An emerging, less common method involving placing fluorescent dyes that are soluble in LNAPL but not water into a well. The dye concentration is measured over time to calculate the LNAPL flux through the well.
  
−
==History of Use and Release to Environment==
+
Two comparative studies have shown that different LNAPL transmissivity measurement techniques yield similar results<ref name= "Palmier2016"/><ref name= "Kirman2013"/>).  For sites with more complex conditions such as perched LNAPL, confined LNAPL, and changes in potentiometric surface, see ASTM Standard E2856-13<ref name= "ASTM2013"/> and Kirkman et al. (2013)<ref name= "Kirkman2_2013"/>.
−
The most common use of 14D has been as a solvent stabilizer for [[wikipedia: 1,1,1-Trichloroethane | 1,1,1-Trichloroethane]] (TCA) utilized in metal degreasing operations.  The addition of 14D to degreasing solvents such as TCA inhibits the formation of metal salts, which can result in solvent breakdown<ref name="Mohr2010" />. Approximately 90% of 14D produced in the 1980s was used as a stabilizer for TCA<ref name="Mohr2010" />.  Following the [[wikipedia: Montreal Protocol | phase-out of ozone depleting chemicals]] including TCA, the production and use of 14D has declined.  Beyond its use as a solvent stabilizer, 14D has also been used in textile, paint and ink, cellulose acetate membrane and adhesive manufacturing operations<ref name="Mohr2010" />.
 
  
−
14D is an un-intended byproduct of some organic chemical synthesis processes<ref name="Mohr2010" />.  14D can be produced during manufacture of [[wikipedia: Ethoxylation | alcohol ethoxylates]] which are used in a wide variety of consumer products including soaps and detergents, cosmetics and food.  In 2001, ethoxylated raw materials were found to contain up to 1.4% 14D<ref>Black, R.E., Hurley, F.J. and Havery, D.C., 2001. Occurrence of 1, 4-dioxane in cosmetic raw materials and finished cosmetic products. Journal of AOAC international, 84(3), pp.666-670. [//www.enviro.wiki/images/7/7d/2001-Black-Occurrence_of_1%2C4-dioxane_in_cosmetic_raw_materials....pdf Report.pdf]</ref>. Once this issue was recognized, measures were put into place to reduce 14D levels.  14D levels in the final product can be reduced by controlling the production process<ref>Ortega, J.A.T., 2012. Sulfonation/sulfation processing technology for anionic surfactant manufacture. In Advances in Chemical Engineering. IntechOpen. [//www.enviro.wiki/images/f/fa/2012-Ortega-Sulfonation_sulfation.pdf Report.pdf]</ref> and by treatment of finished products by several approaches including vacuum stripping, steam stripping, and drying<ref>Sachdeva, Y.P. and Gabriel, R.L., Pharm-Eco Laboratories Inc, 1997. Apparatus for decontaminating a liquid surfactant of dioxane. U.S. Patent 5,643,408. [//www.enviro.wiki/images/f/f0/1997-Sachdeva-Apparatus_for_decontaminating_a_liquid_surfractant.pdf Report.pdf]</ref>. 14D is produced as a byproduct during production of [[wikipedia: Polyethylene terephthalate| polyethylene terephthalate]] (PET), polyester and strong surfactants, as well as many other products<ref>Ellis, R.A. and Thomas, J.S., Wellman Inc, 1998. Destroying 1, 4-dioxane in byproduct streams formed during polyester synthesis. U.S. Patent 5,817,910. [//www.enviro.wiki/images/b/b3/1998-Ellis-Destroying_1%2C4-dioxane_in_byproduct_streams_formed_during_polyester.pdf report.pdf]</ref>. Treated industrial wastewater containing 14D may be released to surface water or groundwater<ref name="Knappe2016" /><ref name="Grady1997">Grady, C.P.L., Sock, S.M. and Cowan, R.M., 1997. Biotreatability Kinetics: A Critical Component in the Scale-up of Wastewater Treatment Systems. Environmental Science Research, 54, pp.307-322. [https://doi.org/10.1007/978-1-4615-5395-3_28 doi: 10.1007/978-1-4615-5395-3_28]</ref><ref name="Zenker 2000">Zenker, M.J., Borden, R.C. and Barlaz, M.A., 2000. Mineralization of 1, 4-dioxane in the presence of a structural analog. Biodegradation, 11(4), pp.239-246. [https://doi.org/10.1023/A:1011156924700 doi: 10.1023/A:1011156924700]</ref>.
+
In addition to field testing, LNAPL transmissivity can also be estimated using an appropriate computer-based model, although it is best to calibrate the model to observed field values initially. Please see LNAPL Mobility and Recovery Models (below) for more on this topic.
  
−
[[File:14D_Plume_Length.mp4 | 600px | thumb | right | Figure 1. Results of 14D plume length study.]]14D has been detected in air, potable water, wastewater and groundwater.  14D was detected in ambient air in several studies<ref>Harkov, R., Katz, R., Bozzelli, J. and Kebbekus, B., 1981. Toxic and carcinogenic air pollutants in New Jersey volatile organic substances. Proceedings of the International Technical Conference of Toxic Air Contaminants, p.245. Pittsburgh, PA: Air Pollution Control Association</ref><ref>Shah, J.J. and Singh, H.B., 1988. Distribution of volatile organic chemicals in outdoor and indoor air: A national VOCs data base. Environmental Science & Technology, 22(12), pp.1381-1388. [https://pubs.acs.org/doi/abs/10.1021/es00177a001 doi: 10.1021/es00177a001]</ref><ref>Keel, L. and A. Franzmann, 2000. Downtown Bellingham air toxics screening project, 1995-1999 staff report. Northwest Air Pollution Authority (NWAPA). [//www.enviro.wiki/images/d/d0/2000-Keel-Downtown_Bellingham_Air_Toxics_Screening_Project.pdf Report.pdf]</ref>).  In a survey of 4,864 public drinking water systems, 14D was detected in 21% of the systems and exceeded the health-based reference concentration of 0.35 &mu;g/L in 6.9%<ref name="Adamson2017a">Adamson, D.T., Piña, E.A., Cartwright, A.E., Rauch, S.R., Anderson, R.H., Mohr, T. and Connor, J.A., 2017. 1, 4-Dioxane drinking water occurrence data from the third unregulated contaminant monitoring rule. Science of the Total Environment, 596, pp.236-245. [https://doi.org/10.1016/j.scitotenv.2017.04.085 doi: 10.1016/j.scitotenv.2017.04.085]</ref>. Municipal wastewater<ref>Abe, A., 1999. Distribution of 1, 4-dioxane in relation to possible sources in the water environment. Science of the Total Environment, 227(1), pp.41-47. [https://doi.org/10.1016/S0048-9697(99)00003-0 doi: 10.1016/S0048-9697(99)00003-0]</ref><ref>Westerhoff, P., Yoon, Y., Snyder, S. and Wert, E., 2005. Fate of endocrine-disruptor, pharmaceutical, and personal care product chemicals during simulated drinking water treatment processes. Environmental Science & Technology, 39(17), pp.6649-6663. [https://doi.org/10.1021/es0484799 doi: 10.1021/es0484799]</ref> and landfill leachates<ref>DeWalle, F.B. and Chian, E.S., 1981. Detection of trace organics in well water near a solid waste landfill. Journal‐American Water Works Association, 73(4), pp.206-211. [https://doi.org/10.1002/j.1551-8833.1981.tb04681.x doi: 10.1002/j.1551-8833.1981.tb04681.x]</ref><ref>Fujiwara, T., Tamada, T., Kurata, Y., Ono, Y., Kose, T., Ono, Y., Nishimura, F. and Ohtoshi, K., 2008. Investigation of 1, 4-dioxane originating from incineration residues produced by incineration of municipal solid waste. Chemosphere, 71(5), pp.894-901. [https://doi.org/10.1016/j.chemosphere.2007.11.011 doi: 10.1016/j.chemosphere.2007.11.011]</ref> also frequently contain 14D.  
+
==Why is LNAPL mobility important?==
 +
All LNAPL starts out mobile during the release and the resulting pore-invading process, often referred to as “drainage” conditions (because as the LNAPL enters a pore, the water or air is “drained” out).  LNAPL must displace fluids such as water and air to invade the pores. While larger pores in a given soil can be easily entered by LNAPL that has relatively low driving [[Wikipedia: Hydraulic head | head]] (pressure) relative to water or air, smaller pores require larger heads relative to those fluids. This behavior results in incomplete LNAPL saturation of the pores, as shown in Figure 1.
  
−
In groundwater, 14D is frequently observed as a co-contaminant with TCA<ref name="Adamson2014" /><ref name="Anderson2012">Anderson, R.H., Anderson, J.K. and Bower, P.A., 2012. Co‐occurrence of 1,4‐dioxane with trichloroethylene in chlorinated solvent groundwater plumes at US Air Force installations: Fact or fiction. Integrated Environmental Assessment and Management, 8(4), pp.731-737. [https://doi.org/10.1002/ieam.1306 doi: 10.1002/ieam.1306]</ref>. As 14D was often utilized as an additive to degreasing solvents<ref name="Mohr2010" />, its presence is positively correlated with other [[Chlorinated Solvents | chlorinated organics]] such as TCA, [[wikipedia: Trichloroethylene | trichloroethene]] (TCE), and [[wikipedia: 1,1-Dichloroethene | 1,1-Dichloroethene]] (1,1-DCE)<ref name="Adamson2017a" />.  In one study, TCA and/or TCE were observed in 94% of the monitoring wells with detectable 14D<ref name="Anderson2012" />.
+
Concerns with LNAPL mobility are primarily focused on preventing additional migration and on reduction of the source volume. Consider a release of LNAPL to the subsurface. During the invasion process LNAPL is migrating down to the water table while spreading. Pores at the front of the migration are interconnected as saturation is increasing. Hence all LNAPL is mobile. Once the release stops, pores near the release point and in the center of the LNAPL body will have more LNAPL flowing out of them than is flowing in. LNAPL saturations decrease as pores are evacuated of LNAPL. During this evacuation (also referred to as “imbibition”) the pores become disconnected and some LNAPL is left in smaller, now disconnected, pores. This phenomenon is due to capillary forces inhibiting gravity drain/hydraulic gradient mechanisms. This is similar to the fraction of water that will not drain out of a sponge. This behavior, a key feature of multiphase flow in porous media, results in incomplete removal of LNAPL from the soil and the formation of residual LNAPL (which can be conceptualized as a disconnected single LNAPL blob in a single pore).  The fraction of LNAPL retained is termed “residual LNAPL saturation” and is a function of the pore size distribution or the soil type, the maximum saturation LNAPL initially achieved and the water saturation.  
  
−
A comprehensive evaluation of a large multi-site dataset<ref name="Adamson2017b">Adamson, D., Newell, C., Mahendra, S., Bryant, D. and Wong, M., 2017. In Situ Treatment and Management Strategies for 1,4-Dioxane-Contaminated Groundwater. SERDP Project [[Media:2017Adamson_et_al_ER-2307.pdf | ER-2307]].</ref> found that 14D was detected, when analyzed for, at 52% of sites containing TCE, 70% of sites with 1,1,1-TCA, and 69% of sites with 1,1-DCE. The spatial extent of the 14D plumes typically fell within a similar or smaller footprint than the co-occurring chlorinated solvent plumes.  The more limited migration of 14D, compared to chlorinated solvents, may be due to the timing of the 14D release. TCE was used at many sites prior to the use of TCA.  As a result, TCE (and its by-products) may have been released before TCA and 14D and could have a “head-start”. The results were somewhat surprising given the high migration potential of 14D, as explained in the [[Media:14D_Plume_Length.mp4 | video]] shown in Figure 1. The maximum historical dioxane concentrations were below 365 μg/L for half of 194 sites with detectable 14D<ref name="Adamson2014" />. Overall, 14D plumes are generally so dilute that source zones may be difficult to identify.
+
Multiple researchers<ref>Lenhard, R.J., Oostrom, M. and Dane, J.H., 2004. A constitutive model for air-NAPL-water flow in the vadose zone accounting for immobile, non-occluded (residual) NAPL in strongly water-wet porous media. Journal of Contaminant Hydrology, Vol. 73(1-4), pp 283-304 [[media:Lenhard2004_air-NAPL-water_flow.pdf| Report.pdf]]</ref><ref name= "Johnston2005">Johnston, C.D. and Adamski, M., 2005, August. Relationship between initial and residual LNAPL saturation for different soil types. In Proceedings of the 2005 Petroleum Hydrocarbons and Organic Chemicals in Groundwater®: Prevention, Assessment, and Remediation Conference (pp. 17-19). [[media:Johnston2005_Residual_LNAPL_Saturation.pdf| Report.pdf]]</ref> have investigated the range of expected values of residual saturation in soils at LNAPL release sites. The overall conclusion of this work is that residual saturation depends on the amount of LNAPL initially present in the pores (initial saturation, S<sub>ni</sub>), the soil type and the water saturation. Figure 5 illustrates how residual saturation values in the vadose zone vary with soil type and initial LNAPL saturation<ref name= "Johnston2005"/>. Key points from Figure 5 include: a) finer-grained soils like silts (ML) and clays (CL) often have higher residual saturation values than sands (SC or SP); and b) higher initial saturation values result in higher residual saturation values.  
  
−
The common presence of 14D in potable water supplies is a concern because 14D removal is low in many unit processes commonly employed in publicly owned treatment works (POTW) due to the high solubility, low volatility, and relative resistance to biodegradation (see section on physical/chemical treatment).  14D removal was not observed in several physical/chemical water treatment processes including coagulation, oxidation and air stripping processes<ref name="McGuire1978">McGuire, M.J., Suffet, I.H. and Radziul, J.V., 1978. Assessment of unit processes for the removal of trace organic compounds from drinking water. Journal‐American Water Works Association, 70(10), pp.565-572. [https://doi.org/10.1002/j.1551-8833.1978.tb04244.x doi: 10.1002/j.1551-8833.1978.tb04244.x]</ref>.  Activated carbon adsorption is somewhat more successful, with reported removal efficiencies ranging from 50 to 67 percent<ref name="McGuire1978" /><ref>Johns, M.M., Marshall, W.E. and Toles, C.A., 1998. Agricultural by‐products as granular activated carbons for adsorbing dissolved metals and organics. Journal of Chemical Technology & Biotechnology: International Research in Process, Environmental and Clean Technology, 71(2), pp.131-140. [https://doi.org/10.1002/(SICI)1097-4660(199802)71:2 <131::AID-JCTB821>3.0.CO;2-K doi: 10.1002/(SICI)1097-4660(199802)71:2<131::AID-JCTB821>3.0.CO;2-K]</ref>. Stepien<ref name="Stepien2014" /> reported that 14D removal was not observed in four domestic wastewater treatment plants in Germany.  In a study of North Carolina water treatment facilities, 14D removal was not observed at two of the facilities, but was reduced by 65% at a third which employed ozonation of raw and settled water<ref name="Knappe2016" />.
+
==LNAPL Mobility and Recovery Models==
 +
LNAPL distribution and mobility can be evaluated using public domain computer models.  The LNAPL Distribution and Recovery Model estimates LNAPL transmissivity, saturation and overall volume in the subsurface and aids in assessing the potential effectiveness of recovery efforts to reduce LNAPL source volume.  The Hydrocarbon Spill Screening Model is a US EPA model for evaluating the infiltration of LNAPL following a release and the resulting risks as LNAPL reaches the water-table and spreads laterally.
  
−
==Above Ground Treatment==
+
*[https://www.api.org/oil-and-natural-gas/environment/clean-water/ground-water/lnapl/ldrm API LNAPL Distribution and Recovery Model (LDRM), API 4760]<ref name= "Charbeneau2007"/> – Addresses the recoverability of LNAPL in terms of time, induced drawdown, well spacing and residual fraction.
−
Air stripping is generally not effective for removing 14D from contaminated water due its low [[wikipedia: Henry’s law | Henry’s Law]] constant. While 14D can be removed from water by sorption to granular activated carbon (GAC), sorption capacities are low resulting in high capital and operating costs<ref name="Woodard2014">Woodard, S., Mohr, T. and Nickelsen, M.G., 2014. Synthetic Media: A Promising New Treatment Technology for 1, 4‐Dioxane. Remediation Journal, 24(4), pp.27-40. [https://doi.org/10.1002/rem.21402 doi:10.1002/rem.21402]</ref>. In contrast, polymeric sorbents (e.g. Ambersorb<sup>TM</sup> 560) are reported to have 5 to 10 times the sorption capacity of GAC, making sorption a more attractive alternative, though with additional operational requirements of adsorbent regeneration and proper disposal of spent waste<ref name="Woodard2014" />. While 14D can be degraded by high energy UV radiation in high purity water<ref>Hentz, R.R. and Parrish, C.F., 1971. Photolysis of gaseous 1, 4-dioxane at 1470 Ang. The Journal of Physical Chemistry, 75(25), pp.3899-3901. [https://doi.org/10.1021/j100694a023 doi: 10.1021/j100694a023]</ref>, direct ultraviolet photolysis is not economically viable due to operational challenges and high costs<ref name="Mohr2010" />.
+
*[https://www.epa.gov/water-research/hydrocarbon-spill-screening-model-hssm-windows-version Hydrocarbon Spill Screening Model (HSSM)]<ref>Weaver, J.W., Charbeneau, R.J., Tauxe, J.D., Lien, B.K. and Provost, J.B., 1995. The Hydrocarbon spill screening model (HSSM) Volume 1: User’s Guide. US EPA, publication EPA/600/R-94/039a, 229pp. [[media:Weaver1995_HSSMv1.pdf | Report.pdf]]</ref> – Evaluates potential risks of releases and promotes continuing improvement towards prevention.
  
−
Advanced oxidation processes (AOPs) using combinations of ozone (O<sub>3</sub>), hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) and ultraviolet (UV) radiation produce highly reactive [[wikipedia: Hydroxyl radical | hydroxyl radicals]] (•OH) which are effective in destroying 14D.  In the peroxone process (O<sub>3</sub> + H<sub>2</sub>O<sub>2</sub>), O<sub>3</sub> reacts with H<sub>2</sub>O<sub>2</sub> giving rise to hydroxyl radicals<ref>Fleming, E.C., Zappi, M.E., Toro, E., Hernandez, R., Myers, K., Kodukula, P. and Gilbertson, R., 1997. Laboratory assessment of advanced oxidation processes for treatment of explosives and chlorinated solvents in groundwater from the former Nebraska Ordnance Plant. Technical Report SERDP-97-3 [//www.enviro.wiki/images/b/b5/1997-Fleming-Laboratory_assessment_of_advanced_oxidation_process.pdf Report.pdf]</ref>.  In a variation of this approach ([http://aptwater.com/hipox/technology/overview-advanced-oxidation-process-for-water-treatment/ HiPOx™ process]), H<sub>2</sub>O<sub>2</sub> is added first followed by high pressure O<sub>3</sub><ref>Bowman, R.H., Lahey, T. and Herlihy, P., Applied Process Tech Inc, 2007. System and method for remediating contaminated soil and groundwater in situ. U.S. Patent 7,264,419. [//www.enviro.wiki/images/6/61/2007-Bowman-System_and_method_fo_remediating_contaminated_soil_and_groundwater.pdf Report.pdf]</ref>.  Hydroxyl radicals are produced in UV + H<sub>2</sub>O<sub>2</sub> systems by direct photolysis of H<sub>2</sub>O<sub>2</sub> caused by absorption of energy from an ultraviolet lamp<ref>Omura, K. and Matsuura, T., 1968. Photo-induced reactions—IX: The hydroxylation of phenols by the photo-decomposition of hydrogen peroxide in aqueous media. Tetrahedron, 24(8), pp.3475-3487. [https://doi.org/10.1016/S0040-4020(01)92645-6 doi: 10.1016/S0040-4020(01)92645-6]</ref><ref>Stefan, M.I. and Bolton, J.R., 1998. Mechanism of the degradation of 1, 4-dioxane in dilute aqueous solution using the UV/hydrogen peroxide process. Environmental Science & Technology, 32(11), pp.1588-1595. [https://doi.org/10.1021/es970633m doi: 10.1021/es970633m]</ref>.
+
==LNAPL Mobility and Risk ==
 +
Residual LNAPL poses the same risk of groundwater contamination and [[Vapor Intrusion - Separation Distances from Petroleum Sources | petroleum vapor intrusion]] as mobile LNAPL<ref name= "ITRC2018"/>. The LNAPL composition, not the LNAPL thickness or saturation in soil, drives the concentrations in vapor and groundwater phases and therefore the risk to receptors.  Once most of the LNAPL is immobile and residual LNAPL dominates the source area, removal of any small remaining mobile fraction is not expected to reduce risks of groundwater contamination or petroleum vapor intrusion in a meaningful way.
  
−
AOPs are commonly employed for 14D treatment because of their high removal efficiencies with low contact times<ref name="Mohr2010" /><ref name="Ikehata">Ikehata, K., Jodeiri Naghashkar, N. and Gamal El-Din, M., 2006. Degradation of aqueous pharmaceuticals by ozonation and advanced oxidation processes: a review. Ozone: Science and Engineering, 28(6), pp.353-414. [https://doi.org/10.1080/01919510600985937 doi: 10.1080/01919510600985937]</ref>.  The degradation mechanisms and kinetics of these processes are well understood, with multiple systems in current use<ref name="Mohr2010" />.  All of these systems are effective in destroying 14D, but have some limitations including the potential for bromate formation (when Br is present), reduced efficiency in the presence of free radical scavengers (e.g. HCO<sub>3</sub>) and high capital and operating costs associated with energy and chemical consumption<ref name="Mohr2010" /><ref>Woodward, C., Shulmeister, J., Larsen, J., Jacobsen, G.E. and Zawadzki, A., 2014. The hydrological legacy of deforestation on global wetlands. Science, 346(6211), pp.844-847. [https://doi.org/10.1126/science.1260510 doi: 10.1126/science.1260510]</ref>.
+
==Summary and Key Conclusions==
 +
Mobile LNAPL can pose a risk where continued migration and expansion of the LNAPL footprint is occurring.  LNAPL recovery efforts should focus on sites where LNAPL migration has the potential to expand the LNAPL footprint and where LNAPL recovery can significantly reduce the overall source volume.  Where most of the LNAPL is immobile, recovery of a small amount of mobile LNAPL is not expected to substantially reduce risks of groundwater contamination or petroleum vapor intrusion.
  
−
Biological wastewater treatment has not been widely applied for 14D removal.  While high concentrations of 14D will support growth of 14D degraders<ref>Sock, S.M., 1993. A comprehensive evaluation of biodegradation as a treatment alternative for the removal of 1, 4-dioxane (Doctoral dissertation, Clemson University)</ref> growth rates on 14D are slow<ref name="Grady1997" /><ref name="Parales1994" /><ref>Roy, D., Anagnostu, G. and Chaphalkar, P., 1994. Biodegradation of dioxane and diglyme in industrial waste. Journal of Environmental Science & Health Part A, 29(1), pp.129-147. [https://doi.org/10.1080/10934529409376026 doi: 10.1080/10934529409376026]</ref><ref>Bernhardt, D. and Diekmann, H., 1991. Degradation of dioxane, tetrahydrofuran and other cyclic ethers by an environmental Rhodococcus strain. Applied Microbiology and Biotechnology, 36(1), pp.120-123. [https://doi.org/10.1007/bf00164711 doi: 10.1007/BF00164711]</ref>, and the low 14D concentrations in many systems are not sufficient to maintain an adequate level of 14D degraders for effective treatment.  To overcome this problem, 14D degrading biomass was supported by addition of tetrahydrofuran (THF) to a continuously fed trickling filter for over one year.  The system was effective in reducing 14D concentrations by 93–97% while influent 14D concentrations were varied from 200 to 1,200 µg/L<ref>Zenker, M.J., Borden, R.C. and Barlaz, M.A., 2003. Occurrence and treatment of 1, 4-dioxane in aqueous environments. Environmental Engineering Science, 20(5), pp.423-432. [https://doi.org/10.1089/109287503768335913 doi: 10.1089/109287503768335913]</ref>.  This basic approach was applied to full-scale treatment of leachate from the Lowry Landfill Superfund site where both THF and 14D were present as co-contaminants<ref>Shangraw, T. and Plaehn, W.  2012. Full-scale treatment of 1,4-dioxane using a bioreactor. Federal Remediation Technologies Roundtable Meeting. [//www.enviro.wiki/images/9/98/2012-Shangraw-Full-scale_Treatment_of_1%2C4-dioxane.pdf Report.pdf]</ref>.
+
The ITRC (2018)<ref name= "ITRC2018"/> discusses lines of evidence for evaluating LNAPL Migration risk as well as the benefits of LNAPL recovery in source reduction.  Often LNAPL sites exhibiting low transmissivity values (i.e. 0.1 to 0.8 ft<sup>2</sup>/day) or with stable LNAPL bodies that are comprised of mostly residual LNAPL will not benefit from recovery attempts to remove mobile LNAPL.   
−
 
 
−
==''In-Situ'' Treatment==
 
−
A variety of methods have been attempted for ''in situ'' treatment of 14D impacted soil and groundwater including [[Chemical Oxidation (In Situ - ISCO) | ''in situ'' chemical oxidation (ISCO)]], thermally enhanced [[Soil Vapor Extraction (SVE) | soil vapor extraction]], bioremediation, phytoremediation, and [[Monitored Natural Attenuation (MNA) | monitored natural attenuation (MNA)]].
 
−
 
 
−
ISCO can be used to degrade 14D in source areas with a variety of oxidants including [[wikipedia: Permanganate | permanganate]]<ref>Waldemer, R.H. and Tratnyek, P.G., 2006. Kinetics of contaminant degradation by permanganate. Environmental Science & Technology, 40(3), pp.1055-1061. [https://doi.org/10.1021/es051330s doi: https://doi.org/10.1021/es051330s]</ref>, [[wikipedia: Persulfate | persulfate]]<ref>Félix-Navarro, R.M., Lin-Ho, S.W., Barrera-Díaz, N. and Pérez-Sicairos, S., 2007. Kinetics of the degradation of 1, 4-dioxane using persulfate. Journal of the Mexican Chemical Society, 51(2), pp.67-71. ISSN 1870-249X</ref>, [[wikipedia: Fenton’s reagent | Fenton’s reagent]]<ref>Kiker, J.H., Connolly, J.B., Murray, W.A., Pearson, S.C.P., Reed, S.E.R. and Tess, R.J., 2010. Ex-situ wellhead treatment of 1, 4-dioxane using fenton's reagent. In Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy (Vol. 15, No. 1, p. 18).</ref> and ozone<ref name="Ikehata" />.  However, ISCO treatment of 14D in source areas is not common because much of the mass is in the downgradient plume.  Dilute plumes can potentially be treated using cylinders placed in wells that slowly release oxidant over time. In a field demonstration, a system of slow release persulfate cylinders was effective in reducing 14D and chlorinated solvent concentrations by over 99% for 119 days<ref>Evans, P., Hooper, J., Lamar, M., Nguyen, D., Dugan, P., Crimi, M. and Ruiz, N., 2018. Sustained In situ Chemical Oxidation (ISCO) of 1, 4 Dioxane and Chlorinated VOCs Using Slow release Chemical Oxidant Cylinders. ESTCP Cost and Performance Report, ER-201324. [//www.enviro.wiki/images/7/7e/2018-Evans-ER-201324_Cost_%26_Performance_Report.pdf Report.pdf]</ref>.
 
−
 
 
−
[[Thermal Remediation | Thermal remediation]] of source areas is not frequently utilized for 14D remediation because much of the 14D mass is in the dissolved plume.  However, when applied to treat a source area, thermal remediation can be effective. Following electrical resistive heating of a chlorinated solvent source area, 14D levels in groundwater were reduced by >99%<ref>Oberle, D., Crownover, E. and Kluger, M., 2015. In situ remediation of 1, 4‐dioxane using electrical resistance heating. Remediation Journal, 25(2), pp.35-42. [https://doi.org/10.1002/rem.21422 doi: 10.1002/rem.21422]</ref>.  14D source areas can also be treated using a combination of heated air injection and focused air extraction from areas with elevated 14D concentrations.  In a field demonstration, thermally enhanced [[Soil Vapor Extraction (SVE) | soil vapor extraction]] reduced 14D levels by 94%<ref>Hinchee, R.E., P.C. Johnson, P.R. Dahlen, and D.R. Durris, 2017. 1,4-Dioxane remediation by extreme soil vapor extraction (XSVE). Final Report ESTCP Project 201326 [//www.enviro.wiki/images/9/99/2017-Hinchee-1.4_Dioxane_remediation_by_extreme_soil_XSVE_ER-201326_Final_Report.pdf Report.pdf]</ref><ref>Hinchee, R.E., Dahlen, P.R., Johnson, P.C. and Burris, D.R., 2018. 1, 4‐Dioxane Soil Remediation Using Enhanced Soil Vapor Extraction: I. Field Demonstration. Groundwater Monitoring & Remediation, 38(2), pp.40-48. [https://doi.org/10.1111/gwmr.12264 doi: doi.org/10.1111/gwmr.12264]</ref>.  Modeling results indicate that removal increases with increasing air injection temperature and relative humidity and decreases with initial soil moisture content<ref>Burris, D.R., Johnson, P.C., Hinchee, R.E. and Dahlen, P.R., 2018. 1, 4‐Dioxane Soil Remediation Using Enhanced Soil Vapor Extraction (XSVE): II. Modeling. Groundwater Monitoring & Remediation, 38(2), pp.49-56. [https://doi.org/10.1111/gwmr.12277 doi: 10.1111/gwmr.12277]</ref>.
 
−
 
 
−
''In situ'' bioremediation has not been commonly applied to 14D treatment due to the slow growth of bacteria using 14D as a growth substrate.  However, there has been some success in stimulating cometabolic biodegradation of 14D using gaseous substrates.  In a biosparging pilot test, air amended with propane was injected into a single well that was bioaugmented with the propanotroph [[wikipedia: Rhodococcus | ''Rhodococcus ruber'']] ENV425.  14D levels decreased by >99% in the sparge well and two nearby monitoring wells<ref name="Lippincott2015" />. A propane-stimulated groundwater recirculation system has also recently been reported to effectively reduce concentrations of 14D as well as several chlorinated aliphatics such as TCE and 1,2-dichloroethane<ref name="Chu2018" />.
 
−
 
 
−
Phytoremediation has been reported as a viable treatment alternative for 14D<ref>Aitchison, E.W., Kelley, S.L., Alvarez, P.J. and Schnoor, J.L., 2000. Phytoremediation of 1, 4-dioxane by hybrid poplar trees. Water Environment Research, 72(3), pp.313-321. [https://doi.org/10.2175/106143000X137536 doi: 10.2175/106143000X137536]</ref>.  The primary removal process is via phytovolatilization, which involves transpiration of chemicals from the leaf surfaces to the atmosphere<ref>Ouyang, Y., 2002. Phytoremediation: modeling plant uptake and contaminant transport in the soil–plant–atmosphere continuum. Journal of Hydrology, 266(1-2), pp.66-82. [https://doi.org/10.2175/106143000X137536 doi: 10.2175/106143000X137536]</ref>. Addition of 14D degrading bacteria (e.g. CB1190) and appropriate co-substrates can further enhance the removal of 14D in soil planted with poplar trees<ref>Kelley, S.L., Aitchison, E.W., Deshpande, M., Schnoor, J.L. and Alvarez, P.J., 2001. Biodegradation of 1, 4-dioxane in planted and unplanted soil: effect of bioaugmentation with Amycolata sp. CB1190. Water Research, 35(16), pp.3791-3800. [https://doi.org/10.1016/S0043-1354(01)00129-4 doi: 10.1016/S0043-1354(01)00129-4]</ref>.
 
−
 
 
−
Early microcosm studies indicated that 14D did not degrade in the presence of impacted aquifer material under ''in situ'' conditions<ref name="Zenker 2000" />. However, a statistical analysis of multiple Air Force and California sites found evidence of 14D removal in 19% of the sites<ref name="Adamson2015">Adamson, D.T., Anderson, R.H., Mahendra, S. and Newell, C.J., 2015. Evidence of 1, 4-dioxane attenuation at groundwater sites contaminated with chlorinated solvents and 1, 4-dioxane. Environmental Science & Sechnology, 49(11), pp.6510-6518.[ https://doi.org/10.1021/acs.est.5b00964 doi:10.1021/acs.est.5b00964]</ref>, similar to other chlorinated VOCs (TCE and 1,1-DCE).  The decay rates were positively correlated to dissolved oxygen, and negatively correlated to high metals and chlorinated VOC concentrations<ref name="Adamson2015" />.  14D decay has also been positively correlated to the presence of oxidizing enzymes<ref name="Li2013">Li, M., Mathieu, J., Yang, Y., Fiorenza, S., Deng, Y., He, Z., Zhou, J. and Alvarez, P.J., 2013. Widespread distribution of soluble di-iron monooxygenase (SDIMO) genes in arctic groundwater impacted by 1, 4-dioxane. Environmental science & technology, 47(17), pp.9950-9958. [https://doi.org/10.1021/es402228x doi: 10.1021/es402228x]</ref><ref>Gedalanga, P.B., Pornwongthong, P., Mora, R., Chiang, S.Y.D., Baldwin, B., Ogles, D. and Mahendra, S., 2014. Identification of biomarker genes to predict biodegradation of 1, 4-dioxane. Appl. Environ. Microbiol., 80(10), pp.3209-3218. [https://doi.org/10.1128/aem.04162-13 doi: 10.1128/AEM.04162-13]</ref>. Native 14D degrading microorganisms have also been detected in field studies using a number of environmental diagnostic assays, such as [[wikipedia: Microarray | microarray]]<ref name="Li2013" /> and [[Stable Isotope Probing (SIP) | stable isotope probing]]<ref>Chiang, S.Y.D., Mora, R., Diguiseppi, W.H., Davis, G., Sublette, K., Gedalanga, P. and Mahendra, S., 2012. Characterizing the intrinsic bioremediation potential of 1, 4-dioxane and trichloroethene using innovative environmental diagnostic tools. Journal of Environmental Monitoring, 14(9), pp.2317-2326. [https://doi.org/10.1039/c2em30358b doi: 10.1039/C2EM30358B]</ref><ref>Li, M., Liu, Y., He, Y., Mathieu, J., Hatton, J., DiGuiseppi, W. and Alvarez, P.J., 2017. Hindrance of 1, 4-dioxane biodegradation in microcosms biostimulated with inducing or non-inducing auxiliary substrates. Water Research, 112, pp.217-225. [http://dx.doi.org/10.1016/j.watres.2017.01.047 doi: 10.1016/j.watres.2017.01.047]</ref>, suggesting that monitored natural attenuation (MNA) may be a feasible and cost-efficient alternative to mitigate 14D at some sites.
 
  
 
==References==
 
==References==
−
 
+
<references/>
−
<references />
 
  
 
==See Also==
 
==See Also==
−
*[https://www.youtube.com/watch?v=y9hIBss4E5c&t=2s 1,4-Dioxane: Do We Have the Right Conceptual Site Model for Managing Contaminated Groundwater Sites?]
 
−
*[https://clu-in.org/contaminantfocus/default.focus/sec/1,4-Dioxane/cat/Overview/ CLU-IN: 1,4-Dioxane]
 
−
*[[wikipedia: 1,4-Dioxane | Wikipedia: 1,4-Dioxane]]
 

Revision as of 11:31, 6 February 2020

Light non-aqueous phase liquid (LNAPL) source zones evolve over time, from a short period of expanding LNAPL bodies, to mature sites where LNAPL mobility becomes much lower or zero. The recent development of LNAPL transmissivity testing provides an improved metric for understanding whether mobile LNAPL can be effectively recovered from hydrocarbon sites.

Related Article(s):

  • LNAPL Source Zone Conceptual Models (Coming soon)
  • LNAPL Remediation Technologies (Coming soon)


CONTRIBUTOR(S): Andrew Kirkman


Key Resource(s):

Introduction

LNAPL can be found in the subsurface in three different states:

  1. Residual LNAPL is trapped and immobile but can undergo composition change and generate dissolved hydrocarbon plumes and/or vapor sources in the unsaturated zones.
  2. Mobile LNAPL is LNAPL at greater than the residual saturation which can therefore accumulate in a well where it is potentially recoverable. However, in this state LNAPL saturation is insufficient to drive migration (i.e., the LNAPL body is not expanding).
  3. Migrating LNAPL is LNAPL at greater than the residual saturation that expands into previously unimpacted locations over time (e.g., LNAPL appears in a monitoring well that had no previous detections).

When released to the subsurface, light non-aqueous phase liquids form source zones which evolve over time with changing impacts to soil, groundwater, and at some sites surface water. Shallow unsaturated soils may also be impacted by intrusion of vapors released by the LNAPL. (See Vapor Intrusion - Separation Distances from Petroleum Sources.) LNAPL mobility is typically highest during the time of the release to the environment. Once the release stops, LNAPL mobility and the potential for migration rapidly decrease. The LNAPL body may initially contain mobile LNAPL near the release point. However, as the LNAPL body spreads, the driving head and pressure gradient decrease, and the LNAPL thickness (a key factor in mobility) decreases. The LNAPL body also begins to weather, losing volatiles and biodegradable compounds. Over time, this weathering process alters the LNAPL composition and stabilizes the LNAPL body, and the fraction of LNAPL that remains mobile therefore decreases[1][3][4]. LNAPL bodies from historical releases are dominated by immobile residual LNAPL.

Because LNAPL bodies evolve over time, LNAPL mobility is a much more significant concern during and immediately after the release period than it is after the release is halted. Tools are now available to assess the magnitude of LNAPL mobility at individual release sites to support decision making regarding potential remedial actions. One such tool is the American Petroleum Institute’s LNAPL Distribution and Recovery Model (LDRM) which is available as a free download. Please see the LNAPL Mobility and Recovery section below for a more complete discussion of modeling tools.

In order to understand LNAPL mobility, key concepts from the science of multiphase flow in porous media (e.g. soil and aquifer material) are important. Consider dry soil to which a small amount of water is added. The open pore space in the soil, initially filled with 100 percent air, now contains a mix of air and water. Therefore, a soil can have more than one fluid within the pores (“multiphase”). The fraction of pore space filled with a given fluid is termed “saturation”. The air saturation of the initially dry soil was 100% and the water saturation was zero. When considering a petroleum release site, three different fluids may exist in the pore space: air, water and LNAPL. The sum of the saturation of the three fluids is 100%. All three fluids can exist within the subsurface with varying saturations.

LNAPL Mobility Conceptualized

Figure 1. LNAPL Distribution in a research sand tank[5].

Figure 1 shows a research tank with a well screen in a porous media (sand) containing LNAPL. The LNAPL fluoresces under ultraviolet (UV) light, while water and air do not. The column of yellow fluorescence in the well represents the gauged LNAPL thickness and corresponds to the vertical interval over which LNAPL flows in the formation[6]. The yellow fluorescence to the left of the well represents LNAPL occurring within soil pores. Below the potentiometric surface line, the pores are dominated by water (dark pores) and LNAPL. Above this line LNAPL and water still exist in pores, but the air saturation increases with elevation. The incomplete yellow fluorescence in the formation illustrates how water and LNAPL occupy pores over the mobile interval. This occurs because the mobile LNAPL cannot displace all of the water from the pores.

Figure 2. Hypothetical relative permeability curves for water and an LNAPL in a porous medium[7][8][9].

LNAPL mobility can be described mathematically by Darcy’s Law, an empirically derived equation describing the flow of fluids through porous media where the specific discharge, q, is equal to the product of the hydraulic conductivity, K, and the hydraulic gradient, i. While this is the same Darcy’s Law that is used to describe groundwater flow (see Advection and Groundwater Flow), there is an important additional term, Relative Permeability, that is included when using Darcy’s Law to describe the flow of LNAPL in the subsurface. Relative permeability is the ratio of the effective permeability of a fluid at a specified saturation to the intrinsic permeability of the medium at 100-percent saturation[10]. The USEPA (1996)[7] describes relative permeability this way:

The relative permeability of a particular geologic media that is completely saturated with a particular fluid is equal to the intrinsic permeability. When more than one fluid (i.e., air, water, petroleum hydrocarbon) exists in a porous medium, the fluids compete for pore space thereby reducing the relative permeability of the media and the mobility of the fluid. This reduction can be quantified by multiplying the intrinsic permeability of the geologic media by the relative permeability. As with saturation, the mobility of each fluid phase present varies from zero (0% saturation) to one (100% saturation).

Figure 2 shows an example of relative permeability curves for a water-LNAPL system. The curves representing water saturation (starting at top right, blue line) and hydrocarbon saturation (starting at top left, red line) are contrary to one another and divide the figure into three flow zones. Zone I, where hydrocarbon saturation is relatively high, is dominated by hydrocarbon flow. Water saturation is relatively high in Zone III, and therefore water flow is dominant. Flow of both water and LNAPL characterizes Zone II.

The relative permeability term scales the LNAPL conductivity to the fraction of pores occupied by LNAPL. If LNAPL occupies 50 percent of the pores, then it will only flow through LNAPL-filled pores and therefore does not use the entire permeability of the soil. If the sum of the pores is considered a pipe, then a pipe half full will transmit less LNAPL than a pipe completely full for a given pressure gradient. The relative permeability term is used to account for this effect.

Figure 3. Aquifer transmissivity versus hydraulic conductivity.

LNAPL saturation varies with elevation across the gauged LNAPL thickness, where LNAPL conductivity is lowest near the oil/water interface and highest near the air/LNAPL interface. To provide a single metric for LNAPL mobility, the conductivity must be summed across the mobile LNAPL interval to give the LNAPL transmissivity.

LNAPL transmissivity has been identified as a key metric for evaluating the likely effectiveness of direct LNAPL recovery compared to traditional measurements such as gauged LNAPL thickness in monitoring wells[11][12][6][13][14][15][16][17]. LNAPL transmissivity represents the volume of LNAPL flow a formation can produce per unit time over a unit width for a unit hydraulic gradient. Aquifer transmissivity is the primary metric for evaluating how much water can be produced from a water bearing unit in the subsurface and accounts for the thickness of the saturated aquifer and the ease with which the aquifer can transmit a given fluid per unit volume. The concept of transmissivity is illustrated in Figure 3. It is reasonable to apply similar thinking to estimation of the amount of LNAPL that could be produced by a particular subsurface matrix, and therefore transmissivity has become a key metric used to predict whether direct recovery (direct pumping) of LNAPL is likely to be effective.

The average LNAPL recovery rate was shown to be closely related to the average LNAPL transmissivity as well as to the LNAPL thickness in a series of 10-hour pump tests of three wells at an LNAPL-impacted site (Table 1, ITRC 2018)[1]. The measured LNAPL thickness in the source well (MW-1) was 3.7 times higher than in the LNAPL fringe well (MW-3), while the ratio of their average LNAPL transmissivities was 5. The average recovery rate was 12 times greater at the source well than at the fringe well. In this study, LNAPL thickness, average transmissivity and average recovery rate were all strongly correlated, with correlation coefficients of 0.94 and above.

Table 1. LNAPL Transmissivity Results from One LNAPL Site[1]
Well ID Well Location LNAPL Thickness in Well
(ft) 		Average LNAPL Transmissivity
(ft2/day) 		Average LNAPL Recovery Rate
(gallons/minute)
MW-1 Source 8.13 100 1.2
MW-2 Mid-point 4.39 60 0.3
MW-3 LNAPL 2.2 20 0.1
Ratio of MW-1 to MW-3 3.7 5.0 12

An example in which LNAPL transmissivity would be better than LNAPL thickness at predicting LNAPL recoverability is shown in Figure 4. At this site there was little or no change in LNAPL thickness over 10 years of LNAPL recovery using a vacuum truck. If the LNAPL thickness were affected by the ongoing recovery action, a clear trend of decreasing LNAPL thickness over time would have been observed, which would have resulted in clustering of early time data on the right side of the graph and late time data on the left[1].

Figure 4. Gauged LNAPL thickness versus potentiometric surface elevation through time[1][18]), showing 10 years of LNAPL recovery with little to no change in LNAPL thickness.

Based on the practical experience from five LNAPL sites, the ITRC proposed a threshold LNAPL transmissivity for recoverability: values below 0.1 to 0.8 ft2/day indicate low recoverability. Therefore, the majority of the LNAPL at a site in this category is in a state of lesser mobility, and the remaining source is dominated by residual saturation [1]. For the five LNAPL sites, the ITRC concluded: “These sites were closed or granted no further action after developing comprehensive LNAPL Conceptual Site Models and operating LNAPL recovery systems. All sites demonstrated achievement of the impracticable limit (i.e., the lack of LNAPL recoverability) irrespective of in-well LNAPL thickness remaining. Since that time, data from four additional sites, with comprehensive LCSMs based on high-resolution data, were analyzed and affirmed the proposed limits.” The ITRC (2018)[1] recently expanded the technical basis for this important LNAPL transmissivity threshold with more technical background and additional case studies.

Characterization of LNAPL Mobility

Field testing for LNAPL transmissivity transforms the gauged LNAPL thickness, fluid parameters of density and viscosity and the relative permeability into a single value. As saturation decreases, the interconnectivity of the pores decreases, and the ability of the soil to transmit LNAPL for a given gradient decreases.

LNAPL transmissivity can be estimated with LNAPL baildown or other well testing techniques where the well screen intersects the entire interval of mobile LNAPL. ASTM (2013)[14] and Gatsios et al. (2018)[19] describe four methods:

  • Short-Term Baildown Tests: LNAPL is quickly removed from a well, and data showing how quickly LNAPL refills the well are collected. These data are analyzed using methods similar to analyzing slug tests. An easy to use spreadsheet[15] is available here to help process the data generated by short-term baildown tests and obtain an LNAPL transmissivity estimate. Short-term baildown tests are the most commonly used method.
  • Manual Skimming Method: LNAPL is repeatedly recovered over time (on the order of several days), gauging the well as it recovers, and then initiating another recovery event before the LNAPL level rebounds by more than 25% of the original drawdown. This is done until the LNAPL removal rate stabilizes, and then this rate is used to calculate transmissivity.
  • Long-Term Recovery-Based Methods: Typically applied to sites with on-going LNAPL recovery. There are several equations which can be used to calculate LNAPL transmissivity from the long-term recovery data.
  • Tracer-Based Method: An emerging, less common method involving placing fluorescent dyes that are soluble in LNAPL but not water into a well. The dye concentration is measured over time to calculate the LNAPL flux through the well.

Two comparative studies have shown that different LNAPL transmissivity measurement techniques yield similar results[16][13]). For sites with more complex conditions such as perched LNAPL, confined LNAPL, and changes in potentiometric surface, see ASTM Standard E2856-13[14] and Kirkman et al. (2013)[18].

In addition to field testing, LNAPL transmissivity can also be estimated using an appropriate computer-based model, although it is best to calibrate the model to observed field values initially. Please see LNAPL Mobility and Recovery Models (below) for more on this topic.

Why is LNAPL mobility important?

All LNAPL starts out mobile during the release and the resulting pore-invading process, often referred to as “drainage” conditions (because as the LNAPL enters a pore, the water or air is “drained” out). LNAPL must displace fluids such as water and air to invade the pores. While larger pores in a given soil can be easily entered by LNAPL that has relatively low driving head (pressure) relative to water or air, smaller pores require larger heads relative to those fluids. This behavior results in incomplete LNAPL saturation of the pores, as shown in Figure 1.

Concerns with LNAPL mobility are primarily focused on preventing additional migration and on reduction of the source volume. Consider a release of LNAPL to the subsurface. During the invasion process LNAPL is migrating down to the water table while spreading. Pores at the front of the migration are interconnected as saturation is increasing. Hence all LNAPL is mobile. Once the release stops, pores near the release point and in the center of the LNAPL body will have more LNAPL flowing out of them than is flowing in. LNAPL saturations decrease as pores are evacuated of LNAPL. During this evacuation (also referred to as “imbibition”) the pores become disconnected and some LNAPL is left in smaller, now disconnected, pores. This phenomenon is due to capillary forces inhibiting gravity drain/hydraulic gradient mechanisms. This is similar to the fraction of water that will not drain out of a sponge. This behavior, a key feature of multiphase flow in porous media, results in incomplete removal of LNAPL from the soil and the formation of residual LNAPL (which can be conceptualized as a disconnected single LNAPL blob in a single pore). The fraction of LNAPL retained is termed “residual LNAPL saturation” and is a function of the pore size distribution or the soil type, the maximum saturation LNAPL initially achieved and the water saturation.

Multiple researchers[20][21] have investigated the range of expected values of residual saturation in soils at LNAPL release sites. The overall conclusion of this work is that residual saturation depends on the amount of LNAPL initially present in the pores (initial saturation, Sni), the soil type and the water saturation. Figure 5 illustrates how residual saturation values in the vadose zone vary with soil type and initial LNAPL saturation[21]. Key points from Figure 5 include: a) finer-grained soils like silts (ML) and clays (CL) often have higher residual saturation values than sands (SC or SP); and b) higher initial saturation values result in higher residual saturation values.

LNAPL Mobility and Recovery Models

LNAPL distribution and mobility can be evaluated using public domain computer models. The LNAPL Distribution and Recovery Model estimates LNAPL transmissivity, saturation and overall volume in the subsurface and aids in assessing the potential effectiveness of recovery efforts to reduce LNAPL source volume. The Hydrocarbon Spill Screening Model is a US EPA model for evaluating the infiltration of LNAPL following a release and the resulting risks as LNAPL reaches the water-table and spreads laterally.

LNAPL Mobility and Risk

Residual LNAPL poses the same risk of groundwater contamination and petroleum vapor intrusion as mobile LNAPL[1]. The LNAPL composition, not the LNAPL thickness or saturation in soil, drives the concentrations in vapor and groundwater phases and therefore the risk to receptors. Once most of the LNAPL is immobile and residual LNAPL dominates the source area, removal of any small remaining mobile fraction is not expected to reduce risks of groundwater contamination or petroleum vapor intrusion in a meaningful way.

Summary and Key Conclusions

Mobile LNAPL can pose a risk where continued migration and expansion of the LNAPL footprint is occurring. LNAPL recovery efforts should focus on sites where LNAPL migration has the potential to expand the LNAPL footprint and where LNAPL recovery can significantly reduce the overall source volume. Where most of the LNAPL is immobile, recovery of a small amount of mobile LNAPL is not expected to substantially reduce risks of groundwater contamination or petroleum vapor intrusion.

The ITRC (2018)[1] discusses lines of evidence for evaluating LNAPL Migration risk as well as the benefits of LNAPL recovery in source reduction. Often LNAPL sites exhibiting low transmissivity values (i.e. 0.1 to 0.8 ft2/day) or with stable LNAPL bodies that are comprised of mostly residual LNAPL will not benefit from recovery attempts to remove mobile LNAPL.

References

  1. ^ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 ITRC, 2018. LNAPL Site Management: LCSM evolution, decision process, and remedial technologies (LNAPL-3). Interstate Technical and Regulatory Council https://lnapl-3.itrcweb.org/
  2. ^ 2.0 2.1 Charbeneau, R.J., 2007. LNAPL Distribution and Recovery Model. Distribution and Recovery of Petroleum Hydrocarbon Liquids in Porous Media. Vol. 1. API Publication 4760. Report.pdf https://www.api.org/oil-and-natural-gas/environment/clean-water/ground-water/lnapl/ldrm
  3. ^ 3.0 3.1 CRC CARE, 2018. Technical measurement guidance for LNAPL natural source zone depletion. Cooperative Research Centre for Contamination Assessment and Remediation of the Environment, Newcastle, Australia. Technical Report no. 44. 254p Report.pdf https://www.crccare.com/files/dmfile/CRCCARETechnicalreport44_TechnicalmeasurementguidanceforLNAPLnaturalsourcezonedepletion.pdf
  4. ^ Mahler, N., Sale, T. and Lyverse, M., 2012. A mass balance approach to resolving LNAPL stability. Groundwater, 50(6), pp.861-871. [10.1111/j.1745-6584.2012.00949.x 10.1111/j.1745-6584.2012.00949.x
  5. ^ Hawkins, A. M., 2013. Processes Controlling the behavior of LNAPLs at groundwater surface water interfaces, Master of Science Thesis, Colorado State University, Ft. Collins, Colorado. Report.pdf
  6. ^ 6.0 6.1 Huntley, D., 2000. Analytic determination of hydrocarbon transmissivity from baildown tests. Groundwater, 38(1), pp.46-52. doi: 10.1111/j.1745-6584.2000.tb00201.x
  7. ^ 7.0 7.1 USEPA, 1996. How to effectively recover free product at leaking underground storage sites. A guide for state regulators. USEPA 510-R-96-001. U.S. Environmental Protection Agency, 162 pp. Report.pdf
  8. ^ Newell, C. J., Acree*, S. D., Ross, R.R., and Huling, S.G. 1995. Light non-aqueous phase liquid. U.S. Environmental Protection Agency, Washington, DC. EPA/540/S-95/500 (NTIS 95-267738) Report.pdf
  9. ^ Williams, D.E. and Wilder, D.G., 1971. Gasoline Pollution of a Ground‐Water Reservoir—A Case History. Groundwater, 9(6), pp.50-56. doi: 10.1111/j.1745-6584.1971.tb03577.x
  10. ^ Mercer, J.W. and Cohen, R.M., 1990. A review of immiscible fluids in the subsurface: properties, models, characterization and remediation. Journal of contaminant hydrology, 6(2), pp.107-163. doi: 10.1016/0169-7722(90)90043-G
  11. ^ Kolhatkar, R., Kremesec, V., Rubin, S., Yukawa, C. and Senn, R., 1999. Application of field and analytical techniques to evaluate recoverability of subsurface free phase hydrocarbons. Petroleum Hydrocarbons and Organic Chemicals in Ground Water, pp.5-15.
  12. ^ Lundy, D.A. and Zimmerman, L.M., 1996, May. Assessing the recoverability of LNAPL plumes for recovery system conceptual design. In Proceedings of the 10th National Outdoor Action Conference and Expo (pp. 13-15).
  13. ^ 13.0 13.1 Kirkman, A.J., 2013. Refinement of Bouwer‐Rice baildown test analysis. Groundwater Monitoring & Remediation, 33(1), pp.105-110. doi: 10.1111/j.1745-6592.2012.01411.x
  14. ^ 14.0 14.1 14.2 ASTM, 2013. ASTM E2856-13, Standard guide for estimation of LNAPL transmissivity, ASTM International, West Conshohocken, PA.
  15. ^ 15.0 15.1 Charbeneau, R., Kirkman, A., and Muthu, R., 2016. API LNAPL Transmissivity Workbook: A Tool for Baildown Test Analysis – User Guide. American Petroleum Institute Publication 4762.
  16. ^ 16.0 16.1 Palmier, C., Dodt, M. and Atteia, O., 2016. Comparison of Oil Transmissivity Methods Using Bail‐Down Test Data. Groundwater Monitoring & Remediation, 36(3), pp.73-83. Report.pdf
  17. ^ Lenhard, R.J., Rayner, J.L. and Davis, G.B., 2017. A practical tool for estimating subsurface LNAPL distributions and transmissivity using current and historical fluid levels in groundwater wells: Effects of entrapped and residual LNAPL. Journal of contaminant hydrology, 205, pp.1-11. Report.pdf
  18. ^ 18.0 18.1 Kirkman, A.J., Adamski, M. and Hawthorne, J.M., 2013. Identification and assessment of confined and perched LNAPL conditions. Groundwater Monitoring & Remediation, 33(1), pp.75-86. doi: 10.1111/j.1745-6592.2012.01412.x
  19. ^ Gatsios, E., García-Rincón, J., Rayner, J.L., McLaughlan, R.G. and Davis, G.B., 2018. LNAPL transmissivity as a remediation metric in complex sites under water table fluctuations. Journal of Environmental Management, 215, pp.40-48. Report.pdf
  20. ^ Lenhard, R.J., Oostrom, M. and Dane, J.H., 2004. A constitutive model for air-NAPL-water flow in the vadose zone accounting for immobile, non-occluded (residual) NAPL in strongly water-wet porous media. Journal of Contaminant Hydrology, Vol. 73(1-4), pp 283-304 Report.pdf
  21. ^ 21.0 21.1 Johnston, C.D. and Adamski, M., 2005, August. Relationship between initial and residual LNAPL saturation for different soil types. In Proceedings of the 2005 Petroleum Hydrocarbons and Organic Chemicals in Groundwater®: Prevention, Assessment, and Remediation Conference (pp. 17-19). Report.pdf
  22. ^ Weaver, J.W., Charbeneau, R.J., Tauxe, J.D., Lien, B.K. and Provost, J.B., 1995. The Hydrocarbon spill screening model (HSSM) Volume 1: User’s Guide. US EPA, publication EPA/600/R-94/039a, 229pp. Report.pdf

See Also

Retrieved from "https://www.enviro.wiki/index.php?title=1,4-Dioxane&oldid=13333"