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Advection and Groundwater Flow
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==''In Situ'' Toxicity Identification Evaluation (iTIE)==
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The ''in situ'' Toxicity Identification Evaluation system is a tool to incorporate into weight-of-evidence studies at sites with numerous chemical toxicant classes present. The technology works by continuously sampling site water, immediately fractionating the water using diagnostic sorptive resins, and then exposing test organisms to the water to observe toxicity responses with minimal sample manipulation. It is compatible with various resins, test organisms, and common acute and chronic toxicity tests, and can be deployed at sites with a wide variety of physical and logistical considerations.
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Groundwater migrates from areas of higher [[wikipedia: Hydraulic head | hydraulic head]] (a measure of pressure and gravitational energy) toward lower hydraulic head, transporting dissolved solutes through the combined processes of [[wikipedia: Advection | advection]] and [[wikipedia: Dispersion | dispersion]].  Advection refers to the bulk movement of solutes carried by flowing groundwater.  Dispersion refers to the spreading of the contaminant plume from highly concentrated areas to less concentrated areas. Dispersion coefficients are calculated as the sum of molecular [[wikipedia: Diffusion | diffusion]], mechanical dispersion, and macrodispersion. In many groundwater transport models, solute transport is described by the advection-dispersion-reaction equation.
 
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<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
 
'''Related Article(s):'''
 
'''Related Article(s):'''
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*[[Dispersion and Diffusion]]
 
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*[[Sorption of Organic Contaminants]]
 
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*[[Plume Response Modeling]]
 
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'''CONTRIBUTOR(S):'''
 
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*[[Dr. Charles Newell, P.E.]]
 
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*[[Dr. Robert Borden, P.E.]]
 
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'''Key Resource(s):'''
 
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*[http://hydrogeologistswithoutborders.org/wordpress/1979-english/ Groundwater]<ref name="FandC1979">Freeze, A., and Cherry, J., 1979. Groundwater, Prentice-Hall, Englewood Cliffs, New Jersey, 604 pages. Free download from [http://hydrogeologistswithoutborders.org/wordpress/1979-english/ Hydrogeologists Without Borders].</ref>, Freeze and Cherry, 1979.
 
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*[https://gw-project.org/books/hydrogeologic-properties-of-earth-materials-and-principles-of-groundwater-flow/ Hydrogeologic Properties of Earth Materials and Principals of Groundwater Flow]<ref name="Woessner2020">Woessner, W.W., and Poeter, E.P., 2020. Properties of Earth Materials and Principals of Groundwater Flow, The Groundwater Project, Guelph, Ontario, 207 pages. Free download from [https://gw-project.org/books/hydrogeologic-properties-of-earth-materials-and-principles-of-groundwater-flow/ The Groundwater Project].</ref>, Woessner and Poeter, 2020.
 
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==Groundwater Flow==
 
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[[File:Newell-Article 1-Fig1r.JPG|thumbnail|right|400px|Figure 1. Hydraulic gradient (typically described in units of m/m or ft/ft) is the difference in hydraulic head from Point A to Point B (ΔH) divided by the distance between them (ΔL). In unconfined aquifers, the hydraulic gradient can also be described as the slope of the water table (Adapted from course notes developed by Dr. R.J. Mitchell, Western Washington University).]]
 
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Groundwater will flow from areas of higher [[wikipedia: Hydraulic head | hydraulic head]] toward areas of lower hydraulic head (Figure 1). The rate of change (slope) of the hydraulic head is known as the hydraulic gradient. If groundwater is flowing and contains dissolved contaminants it can transport the contaminants from areas with high hydraulic head toward lower hydraulic head zones, or “downgradient”.
 
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==Darcy's Law==
 
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In unconsolidated geologic settings (gravel, sand, silt, and clay) and highly fractured systems, the rate of groundwater movement can be expressed using [[wikipedia: Darcy's law | Darcy’s Law]]. This law is a fundamental mathematical relationship in the groundwater field and can be expressed this way:
 
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[[File:Newell-Article 1-Equation 1rr.jpg|center|500px]]
 
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::Where:
 
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:::Q = Flow rate (Volume groundwater flow per time, such as m<sup>3</sup>/yr)
 
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:::A = Cross sectional area perpendicular to groundwater flow (length<sup>2</sup>, such as m<sup>2</sup>)
 
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:::V<sub>D</sub> =  “Darcy Velocity”; another way to describe groundwater flow as the flow per unit area (units of length per time, such as ft/yr)
 
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:::K = Hydraulic Conductivity (sometimes called “permeability”) (length per time)
 
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:::ΔH = Difference in hydraulic head between two lateral points (length)
 
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:::ΔL = Length between two lateral points (length)
 
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[[File:Newell-Article 1-Table1r.jpg|550px|thumbnail|left|Table 1. Representative values of total porosity (n), effective porosity (n<sub>e</sub>), and hydraulic conductivity (K) for different aquifer materials<ref name="D&S1998"/><ref>McWhorter, D.B. and Sunada, D.K., 1977. Ground-water hydrology and hydraulics. Water Resources Publication, LLC. 304 pgs. ISBN 978-0-918334-18-3 </ref><ref>Freeze, R.A. and Cherry, J.A., 1979. Groundwater. 604 pgs. ISBN 978-0133653120</ref>.]]
 
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[https://en.wikipedia.org/wiki/Hydraulic_conductivity Hydraulic conductivity] (Table 1 and Fig. 2) is a measure of how easy groundwater flows through a porous medium, or alternatively, how much energy it takes to force water through a porous medium. For example, fine sand (sand with small grains) means smaller pores and more frictional resistance and therefore lower hydraulic conductivity (Fig. 2) compared to coarse sand (sand with large grains), which has less resistance to flow.
 
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Darcy’s Law was first described by Henry Darcy (1856)<ref>Darcy, H., 1856. Les Fontaines Publiques de la Ville de Dijon, Dalmont, Paris. [https://doi.org/10.1029/2001wr000727 doi: 10.1029/2001WR000727]</ref> in a report regarding a water supply system he designed for the city of Dijon, France. He ran experiments and concluded that the amount of water flowing through a closed tube of sand (dark grey box in Figure 3) depends on (a) the change in the hydraulic head between the inlet and outlet of the tube, and (b) the hydraulic conductivity of the sand in the tube. Groundwater flows rapidly in the case of higher pressure (ΔH) and permeable materials such as gravel or coarse sand, but flows slowly when the pressure is lower and low-permeability material such as fine sand or silt.
 
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[[File:Newell-Article 1-Fig2.jpg|475px|thumbnail|right|Figure 2. Hydraulic conductivity of selected rocks<ref>Heath, R.C., 1983. Basic ground-water hydrology, U.S. Geological Survey Water-Supply Paper 2220, 86 pgs. [[Media:Heath-1983-Basic_groundwater_hydrology_water_supply_paper.pdf|Report pdf]]</ref>.]]
 
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[[File:Newell-Article 1-Fig3..JPG|500px|thumbnail|right|Figure 3. Conceptual explanation of Darcy’s Law based on Darcy’s experiment (Adapted from course notes developed by Dr. R.J. Mitchell, Western Washington University).]]<BR CLEAR="left">Since Darcy’s time, Darcy’s Law has been adapted to calculate the actual velocity that the groundwater is moving in units such as meters traveled per year. This quantity is called “interstitial velocity” or “seepage velocity” and is calculated by dividing the Darcy Velocity (flow per unit area) by the actual open pore area where groundwater is flowing, the “effective porosity” (Table 1):
 
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[[File:Newell-Article 1-Equation 2r.jpg|400px]]<br />
 
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:Where:
 
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::V<sub>S</sub> = “interstitial velocity” or “seepage velocity” (units of length per time, such as m/sec)<br />
 
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::V<sub>D</sub> = “Darcy Velocity”; another way to describe groundwater flow as the flow per unit area (units of length per time)<br />
 
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::n<sub>e</sub> = Effective porosity (unitless)
 
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Effective porosity is smaller than total porosity. The difference is that total porosity includes some dead-end pores that do not support groundwater. Typically values for total and effective porosity are shown in Table 1.
 
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[[File:Newell-Article 1-Fig4.JPG|450px|thumbnail|left|Figure 4.  Difference between Darcy Velocity (also called Specific Discharge) and Seepage Velocity (also called Interstitial Velocity).]]
 
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==Darcy Velocity and Seepage Velocity==
 
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In groundwater calculations, Darcy Velocity and Seepage Velocity are two different things used for different purposes. For any calculation where the actual flow rate in units of volume per time (such as liters per day or gallons per minute) is involved, then the original Darcy Equation should be used (calculate V<sub>D</sub>; Equation 1) without using effective porosity. When calculating solute travel time, then the seepage velocity calculation (V<sub>S</sub>; Equation 2) must be used and an estimate of effective porosity is required. Figure 4 illustrates the differences between Darcy Velocity and Seepage Velocity.
 
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==Mobile Porosity==
 
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More recently, data from multiple short-term tracer tests conducted to design in situ remediation systems, have been analyzed to better understand contaminant migration in groundwater<ref name= "Payne2008">Payne, F.C., Quinnan, J.A. and Potter, S.T., 2008. Remediation hydraulics. CRC Press. ISBN 978-1-4200-0684-1</ref>. In these tests, the dissolved solutes were observed to migrate more rapidly through the aquifer than could be explained with typically reported values of n<sub>e</sub>. The interpretation is that the heterogeneity of unconsolidated formations results in a relatively small area of an aquifer cross section carrying most of the water, and so solutes migrate more rapidly than expected. Based on these results, the recommendation is that a quantity called “mobile porosity” should be used in place of n<sub>e</sub> in equation 2 for calculating solute transport velocities. Based on 15 different tracer tests, typical values of mobile porosity range from 0.02 to 0.10 (Table 2). 
 
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[[File:Newell-Article 1-Table2r2.jpg|450px|left|thumbnail|Table 2. Mobile porosity estimates from tracer tests<ref name= "Payne2008"/>.]]
 
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==References==
 
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<references/>
 
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==See Also==
 
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*[http://iwmi.dhigroup.com/solute_transport/advection.html International Water Management Institute Animations]
 
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*[http://www2.nau.edu/~doetqp-p/courses/env303a/lec32/lec32.htm NAU Lecture Notes on Advective Transport]
 
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*[https://www.youtube.com/watch?v=00btLB6u6DY MIT Open CourseWare Solute Transport: Advection with Dispersion Video]
 
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*[https://www.youtube.com/watch?v=AtJyKiA1vcY Physical Groundwater Model Video]
 
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*[https://www.coursera.org/learn/natural-attenuation-of-groundwater-contaminants/lecture/UzS8q/groundwater-flow-review Online Lecture Course - Groundwater Flow]
 
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*[[Contaminated Sediments - Introduction]]
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*[[Contaminated Sediment Risk Assessment]]
  
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'''Contributors:''' Dr. G. Allen Burton Jr., Austin Crane
  
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'''Key Resources:'''
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*A Novel In Situ Toxicity Identification Evaluation (iTIE) System for Determining which Chemicals Drive Impairments at Contaminated Sites<ref name="BurtonEtAl2020">Burton, G.A., Cervi, E.C., Meyer, K., Steigmeyer, A., Verhamme, E., Daley, J., Hudson, M., Colvin, M.,  Rosen, G., 2020. A novel In Situ Toxicity Identification Evaluation (iTIE) System for Determining which Chemicals Drive Impairments at Contaminated Sites. Environmental Toxicology and Chemistry, 39(9), pp. 1746-1754. [https://doi.org/10.1002/etc.4799 doi: 10.1002/etc.4799]</ref>
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*An in situ toxicity identification and evaluation water analysis system: Laboratory validation<ref name="SteigmeyerEtAl2017">Steigmeyer, A.J., Zhang, J., Daley, J.M., Zhang, X., Burton, G.A. Jr., 2017. An in situ toxicity identification and evaluation water analysis system: Laboratory validation. Environmental Toxicology and Chemistry, 36(6), pp. 1636-1643. [https://doi.org/10.1002/etc.3696 doi: 10.1002/etc.3696]</ref>
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*Sediment Toxicity Identification Evaluation (TIE) Phases I, II, and III Guidance Document- <ref>United States Environmental Protection Agency, 2007.  Sediment Toxicity Identification Evaluation (TIE) Phases I, II, and III Guidance Document, EPA/600/R-07/080. 145 pages. [https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P1003GR1.txt Free Download]&nbsp; [[Media: EPA2007.pdf | Report.pdf]]</ref>
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*In Situ Toxicity Identification Evaluation (iTIE) Technology for Assessing Contaminated Sediments, Remediation Success, Recontamination and Source Identification- <ref>In Situ Toxicity Identification Evaluation (iTIE) Technology for Assessing Contaminated Sediments, Remediation Success, Recontamination and Source Identification [https://serdp-estcp.mil/projects/details/88a8f9ba-542b-4b98-bfa4-f693435535cd/er18-1181-project-overview Project Website]&nbsp; [[Media: ER18-1181Ph.II.pdf | Final Report.pdf]]</ref>
  
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==Introduction==
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In waterways impacted by numerous naturally occurring and anthropogenic chemical stressors, it is crucial for environmental practitioners to be able to identify which chemical classes are causing the highest degrees of toxicity to aquatic life. Previously developed methods, including the Toxicity Identification Evaluation (TIE) protocol developed by the US Environmental Protection Agency (EPA)<ref>Norberg-King, T., Mount, D.I., Amato, J.R., Jensen, D.A., Thompson, J.A., 1992. Toxicity identification evaluation: Characterization of chronically toxic effluents: Phase I. Publication No. EPA/600/6-91/005F. U.S. Environmental Protection Agency, Office of Research and Development. [https://www.epa.gov/sites/default/files/2015-09/documents/owm0255.pdf Free Download from US EPA]&nbsp; [[Media: usepa1992.pdf | Report.pdf]]</ref>, can be confounded by sample manipulation artifacts and temporal limitations of ''ex situ'' organism exposures<ref name="BurtonEtAl2020"/>. These factors may disrupt causal linkages and mislead investigators during site characterization and management decision-making. The ''in situ'' Toxicity Identification Evaluation (iTIE) technology was developed to allow users to strengthen stressor-causality linkages and rank chemical classes of concern at impaired sites, with high degrees of ecological realism.
  
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The technology has undergone a series of improvements in recent years, with the most recent prototype being robust, operable in a wide variety of site conditions, and cost-effective compared to alternative site characterization methods<ref>Burton, G.A. Jr., Nordstrom, J.F., 2004. An in situ toxicity identification evaluation method part I: Laboratory validation. Environmental Toxicology and Chemistry, 23(12), pp. 2844-2850. [https://doi.org/10.1897/03-409.1 doi: 10.1897/03-409.1]</ref><ref>Burton, G.A. Jr., Nordstrom, J.F., 2004. An in situ toxicity identification evaluation method part II: Field validation. Environmental Toxicology and Chemistry, 23(12), pp. 2851-2855. [https://doi.org/10.1897/03-468.1 doi: 10.1897/03-468.1]</ref><ref name="BurtonEtAl2020"/><ref name="SteigmeyerEtAl2017"/>. The latest prototype can be used in any of the following settings: in marine, estuarine, or freshwater sites; to study surface water or sediment pore water; in shallow waters easily accessible by foot or in deep waters only accessible by pier or boat. It can be used to study sites impacted by a wide variety of stressors including ammonia, [[Metal and Metalloid Contaminants | metals]], pesticides, polychlorinated biphenyls (PCB), [[Polycyclic Aromatic Hydrocarbons (PAHs) | polycyclic aromatic hydrocarbons (PAH)]], and [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | per- and polyfluoroalkyl substances (PFAS)]], among others. The technology is applicable to studies of acute toxicity via organism survival or of chronic toxicity via responses in growth, reproduction, or gene expression<ref name="BurtonEtAl2020"/>.
  
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==System Components and Validation==
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[[File: CraneFig1.png | thumb | 600 px | Figure 1: A schematic diagram of the iTIE system prototype. The system is divided into three sub-systems: 1) the Pore Water/Surface Water Collection Sub-System (blue); 2) the Pumping Sub-System (red); and 3) the iTIE Resin, Exposure, and Sampling Sub-System (green). Water first enters the system through the Pore Water/Surface Water Collection Sub-System. Porewater can be collected using Trident-style probes, or surface water can be collected using a simple weighted probe. The water is composited in a manifold before being pumped to the rest of the iTIE system by the booster pump. Once in the iTIE Resin, Exposure, and Sampling Sub-System, the water is gently oxygenated by the Oxygen Coil, separated from gas bubbles by the Drip Chamber, and diverted to separate iTIE Resin and Exposure Chambers (or iTIE units) by the Splitting Manifold. Water movement through each iTIE unit is controlled by a dedicated Regulation Pump. Finally, the water is gathered in Sample Collection bottles for analysis.]]
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The latest iTIE prototype consists of an array of sorptive resins that differentially fractionate sampled water, and a series of corresponding flow-through organism chambers that receive the treated water ''in situ''. Resin treatments can be selected depending on the chemicals suspected to be present at each site to selectively sequester certain chemical of concern (CoC) classes from the whole water, leaving a smaller subset of chemicals in the resulting water fraction for chemical and toxicological characterization. Test organism species and life stages can also be chosen depending on factors including site characteristics and study goals. In the full iTIE protocol, site water is continuously sampled either from the sediment pore spaces or the water column at a site, gently oxygenated, diverted to different iTIE units for fractionation and organism exposure, and collected in sample bottles for off-site chemical analysis (Figure 1). All iTIE system components are housed within waterproof Pelican cases, which allow for ease of transport and temperature control.
  
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===Porewater and Surface Water Collection Sub-system===
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[[File: CraneFig2.png | thumb | 600 px | Figure 2: a) Trident probe with auxiliary sensors attached, b) a Trident probe with end caps removed (the red arrow identifies the intermediate space where glass beads are packed to filter suspended solids), c) a Trident probe being installed using a series of push poles and a fence post driver]]
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Given&nbsp;the&nbsp;importance&nbsp;of sediment porewater to ecosystem structure and function, investigators may employ the iTIE system to evaluate the toxic effects associated with the impacted sediment porewater. To accomplish this, the iTIE system utilizes the Trident probe, originally developed for Department of Defense site characterization studies<ref>Chadwick, D.B., Harre, B., Smith, C.F., Groves, J.G., Paulsen, R.J., 2003. Coastal Contaminant Migration Monitoring: The Trident Probe and UltraSeep System. Hardware Description, Protocols, and Procedures. Technical Report 1902. Space and Naval Warfare Systems Center.</ref>. The main body of the Trident is comprised of a stainless-steel frame with six hollow probes (Figure 2). Each probe contains a layer of inert glass beads, which filters suspended solids from the sampled water. The water is drawn through each probe into a composite manifold and transported to the rest of the iTIE system using a high-precision peristaltic pump.
  
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The Trident also includes an adjustable stopper plate, which forms a seal against the sediment and prevents the inadvertent dilution of porewater samples with surface water. (Figure 2). Preliminary laboratory results indicate that the Trident is extremely effective in collecting porewater samples with minimal surface water infiltration in sediments ranging from coarse sand to fine clay. Underwater cameras, sensors, passive samplers, and other auxiliary equipment can be attached to the Trident probe frame to provide supplemental data.
  
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Alternatively, practitioners may employ the iTIE system to evaluate site surface water. To sample surface water, weighted intake tubes can collect surface water from the water column using a peristaltic pump.
  
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===Oxygen Coil, Overflow Bag and Drip Chamber===
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[[File: CraneFig3.png | thumb | left | 400 px | Figure 3. Contents of the iTIE system cooler. The pictured HDPE rack (47.6 cm length x 29.7 cm width x 33.7 cm height) is removable from the iTIE cooler. Water enters the system at the red circle, flows through the oxygen coil, and then travels to each of the individual iTIE units where diagnostic resins and organisms are located. The water then briefly leaves the cooler to travel through peristaltic regulation pumps before being gathered in sample collection bottles.]]
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Porewater&nbsp;is&nbsp;naturally&nbsp;anoxic due to limited mixing with aerated surface water and high oxygen demand of sediments, which may cause organism mortality and interfere with iTIE results. To preclude this, sampled porewater is exposed to an oxygen coil. This consists of an interior silicone tube connected to a pressurized oxygen canister, threaded through an exterior reinforced PVC tube through which water is slowly pumped (Figure 3). Pump rates are optimized to ensure adequate aeration of the water. In addition to elevating DO levels, the oxygen coil facilitates the oxidation of dissolved sulfides, which naturally occur in some marine sediments and may otherwise cause toxicity to organisms if left in its reduced form.
  
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Gas bubbles may form in the oxygen coil over the course of a deployment. These can be disruptive, decreasing water sample volumes and posing a danger to sensitive organisms like daphnids. To account for this, the water travels to a drip chamber after exiting the oxygen coil, which allows gas bubbles to be separated and diverted to an overflow system. The sample water then flows to a manifold which divides the flow into different paths to each of the treatment units for fractionation and organism exposure.
  
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===iTIE Units: Fractionation and Organism Exposure Chambers===
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[[File: CraneFig4.png | thumb | 300px | Figure 4. A diagram of the iTIE prototype. Water flows upward into each resin chamber through the unit bottom. After being chemically fractionated in the resin chamber, water travels into the organism chamber, where test organisms have been placed. Water is drawn through the units by high-precision peristaltic pumps.]]
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At the core of the iTIE system are separate dual-chamber iTIE units, each with a resin fractionation chamber and an organism exposure chamber (Figure 4). Developed by Burton ''et al.''<ref name="BurtonEtAl2020"/>, the iTIE prototype is constructed from acrylic, with rubber O-rings to connect each piece. Each iTIE unit can contain a different diagnostic resin matrix, customizable to remove specific chemical classes from the water. Sampled water flows into each unit through the bottom and is differentially fractionated by the resin matrix as it travels upward. Then it reaches the organism chamber, where test organisms are placed for exposure. The organism chamber inlet and outlet are covered by mesh to prevent the escape of the test organisms. This continuous flow-through design allows practitioners to capture the temporal heterogeneity of ambient water conditions over the duration of an in situ exposure. Currently, the iTIE system can support four independent iTIE treatment units.
  
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After being exposed to test organisms, water is collected in sample bottles. The bottles can be pre-loaded with preservation reagents to allow for later chemical analysis. Sample bottles can be composed of polyethylene, glass or other materials depending on the CoC.
  
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===Pumping Sub-system===
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[[File: CraneFig5.png | thumb | 300px | Figure 5. The iTIE system pumping sub-system. The sub-system consists of: A) a single booster pump, which is directly connected to the water sampling device and feeds water to the rest of the iTIE system, and B) a set of four regulation pumps, which each connect to the outflow of an individual iTIE unit. Each pump set is housed in a waterproof case with self-contained rechargeable battery power. A tablet is mounted inside the lid of the four pump case, which can be used to program and operate all of the pumps when connected to the internet.]]
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Water movement through the system is driven by a series of high-precision, programmable peristaltic pumps ([https://ecotechmarine.com/ EcoTech Marine]). Each pump set is housed in a Pelican storm travel case. Power is supplied to each pump by internal rechargeable lithium-iron phosphate batteries ([https://www.bioennopower.com/ Bioenno Power]).
  
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First, water is supplied to the system by a booster pump (Figure 5A). This pump is situated between the water sampling sub-system and the oxygen coil. The booster pump: 1) facilitates pore water collection, especially from sediments with high fine particle fractions; 2) helps water overcome vertical lifts to travel to the iTIE system; and 3) prevents vacuums from forming in the iTIE system interior, which can accelerate the formation of disruptive gas bubbles in the oxygen coil. The booster pump should be programmed to supply an excess of water to prevent vacuum formation.
  
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Second, a set of four regulation pumps ensure precise flow rates through each independent iTIE unit (Figure 5B). Each regulation pump pulls water from the top of an iTIE unit and then dispenses that water into a sample bottle for further analysis.
  
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==Study Design Considerations==
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===Diagnostic Resin Treatments===
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Several commercially available resins have been verified for use in the iTIE system. Investigators can select resins based on stressor classes of interest at each site. Each resin selectively removes a CoC class from site water prior to organism exposure.
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*[https://www.dupont.com/products/ambersorb560.html DuPont Ambersorb 560] for removal of 1,4-dioxane and other organic chemicals<ref>Woodard, S., Mohr, T., 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>
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*C18 for nonpolar organic chemicals
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*[https://www.bio-rad.com/en-us Bio-Rad] [https://www.bio-rad.com/en-us/product/chelex-100-resin?ID=6448ab3e-b96a-4162-9124-7b7d2330288e Chelex] for metals
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*Granular activated carbon for metals, general organic chemicals, sulfide<ref>Lemos, B.R.S., Teixeira, I.F., de Mesquita, J.P., Ribeiro, R.R., Donnici, C.L., Lago, R.M., 2012. Use of modified activated carbon for the oxidation of aqueous sulfide. Carbon, 50(3), pp. 1386-1393. [https://doi.org/10.1016/j.carbon.2011.11.011 doi: 10.1016/j.carbon.2011.11.011]</ref>
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*[https://www.waters.com/nextgen/us/en.html Waters] [https://www.waters.com/nextgen/us/en/search.html?category=Shop&isocode=en_US&keyword=oasis%20hlb&multiselect=true&page=1&rows=12&sort=best-sellers&xcid=ppc-ppc_23916&gad_source=1&gad_campaignid=14746094146&gbraid=0AAAAAD_uR00nhlNwrhhegNh06pBODTgiN&gclid=CjwKCAiAtLvMBhB_EiwA1u6_PsppE0raci2IhvGnAAe5ijciNcetLaGZo5qA3g3r4Z_La7YAPJtzShoC6LoQAvD_BwE Oasis HLB] for general organic chemicals<ref name="SteigmeyerEtAl2017"/>
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*[https://www.waters.com/nextgen/us/en.html Waters] [https://www.waters.com/nextgen/us/en/search.html?category=All&enableHL=true&isocode=en_US&keyword=Oasis%20WAX%20&multiselect=true&page=1&rows=12&sort=most-relevant Oasis WAX] for PFAS, organic chemicals of mixed polarity<ref>Iannone, A., Carriera, F., Di Fiore, C., Avino, P., 2024. Poly- and Perfluoroalkyl Substance (PFAS) Analysis in Environmental Matrices: An Overview of the Extraction and Chromatographic Detection Methods. Analytica, 5(2), pp. 187-202. [https://doi.org/10.3390/analytica5020012 doi: 10.3390/analytica5020012]&nbsp; [[Media: IannoneEtAl2024.pdf | Open Access Article]]</ref>
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*Zeolite for ammonia, other organic chemicals
  
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Resins must be adequately conditioned prior to use. Otherwise, they may inadequately adsorb toxicants or cause stress to organisms. New resins should be tested for efficacy and toxicity before being used in an iTIE system.   
  
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===Test Organism Species and Life Stages===
  
  
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<br clear="left"/>
  
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A Conceptual Site Model (CSM) is a collection of information about a contaminated site that integrates the available evidence regarding its hydrogeologic setting, contaminant sources, exposure pathways, potential receptors, and site history.  A CSM for a [[Wikipedia: Light non-aqueous phase liquid | Light Non-Aqueous Phase Liquid (LNAPL)]] site focuses on several key concepts: the stage in the LNAPL site life cycle, LNAPL distribution in the subsurface and the resulting mobility of the LNAPL, LNAPL as a source of dissolved and vapor plumes, and the attenuation of LNAPL sources over time.
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==Advantages==
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<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
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A UV/sulfite treatment system offers significant advantages for PFAS destruction compared to other technologies, including high defluorination percentage, high treatment efficiency for short-chain PFAS without mass transfer limitation, selective reactivity by ''e<sub><small>aq</small></sub><sup><big>'''-'''</big></sup>'', low energy consumption, and the production of no harmful byproducts. A summary of these advantages is provided below:
 +
*'''High efficiency for short- and ultrashort-chain PFAS:''' While the degradation efficiency for short-chain PFAS is challenging for some treatment technologies<ref>Singh, R.K., Brown, E., Mededovic Thagard, S., Holson, T.M., 2021. Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor. Journal of Hazardous Materials, 408, Article 124452. [https://doi.org/10.1016/j.jhazmat.2020.124452 doi: 10.1016/j.jhazmat.2020.124452]</ref><ref>Singh, R.K., Multari, N., Nau-Hix, C., Woodard, S., Nickelsen, M., Mededovic Thagard, S., Holson, T.M., 2020. Removal of Poly- and Per-Fluorinated Compounds from Ion Exchange Regenerant Still Bottom Samples in a Plasma Reactor. Environmental Science and Technology, 54(21), pp. 13973-80. [https://doi.org/10.1021/acs.est.0c02158 doi: 10.1021/acs.est.0c02158]</ref><ref>Nau-Hix, C., Multari, N., Singh, R.K., Richardson, S., Kulkarni, P., Anderson, R.H., Holsen, T.M., Mededovic Thagard S., 2021. Field Demonstration of a Pilot-Scale Plasma Reactor for the Rapid Removal of Poly- and Perfluoroalkyl Substances in Groundwater. American Chemical Society’s Environmental Science and Technology (ES&T) Water, 1(3), pp. 680-87. [https://doi.org/10.1021/acsestwater.0c00170 doi: 10.1021/acsestwater.0c00170]</ref>, the UV/sulfite process demonstrates excellent defluorination efficiency for both short- and ultrashort-chain PFAS, including [[Wikipedia: Trifluoroacetic acid | trifluoroacetic acid (TFA)]] and [[Wikipedia: Perfluoropropionic acid | perfluoropropionic acid (PFPrA)]].   
 +
*'''High defluorination ratio:''' As shown in Figure 3, the UV/sulfite treatment system has demonstrated near 100% defluorination for various PFAS under both laboratory and field conditions.
 +
*'''No harmful byproducts:''' While some oxidative technologies, such as electrochemical oxidation, generate toxic byproducts, including perchlorate, bromate, and chlorate, the UV/sulfite system employs a reductive mechanism and does not generate these byproducts.
 +
*'''Ambient pressure and low temperature:''' The system operates under ambient pressure and low temperature (<60°C), as it utilizes UV light and common chemicals to degrade PFAS. 
 +
*'''Low energy consumption:''' The electrical energy per order values for the degradation of [[Wikipedia: Perfluoroalkyl carboxylic acids | perfluorocarboxylic acids (PFCAs)]] by UV/sulfite have been reduced to less than 1.5 kilowatt-hours (kWh) per cubic meter under laboratory conditions. The energy consumption is orders of magnitude lower than that for many other destructive PFAS treatment technologies (e.g., [[Supercritical Water Oxidation (SCWO) | supercritical water oxidation]])<ref>Nzeribe, B.N., Crimi, M., Mededovic Thagard, S., Holsen, T.M., 2019. Physico-Chemical Processes for the Treatment of Per- And Polyfluoroalkyl Substances (PFAS): A Review. Critical Reviews in Environmental Science and Technology, 49(10), pp. 866-915. [https://doi.org/10.1080/10643389.2018.1542916 doi: 10.1080/10643389.2018.1542916]</ref>.
 +
*'''Co-contaminant destruction:''' The UV/sulfite system has also been reported effective in destroying certain co-contaminants in wastewater. For example, UV/sulfite is reported to be effective in reductive dechlorination of chlorinated volatile organic compounds, such as trichloroethene, 1,2-dichloroethane, and vinyl chloride<ref>Jung, B., Farzaneh, H., Khodary, A., Abdel-Wahab, A., 2015. Photochemical degradation of trichloroethylene by sulfite-mediated UV irradiation. Journal of Environmental Chemical Engineering, 3(3), pp. 2194-2202. [https://doi.org/10.1016/j.jece.2015.07.026 doi: 10.1016/j.jece.2015.07.026]</ref><ref>Liu, X., Yoon, S., Batchelor, B., Abdel-Wahab, A., 2013. Photochemical degradation of vinyl chloride with an Advanced Reduction Process (ARP) – Effects of reagents and pH. Chemical Engineering Journal, 215-216, pp. 868-875. [https://doi.org/10.1016/j.cej.2012.11.086 doi: 10.1016/j.cej.2012.11.086]</ref><ref>Li, X., Ma, J., Liu, G., Fang, J., Yue, S., Guan, Y., Chen, L., Liu, X., 2012. Efficient Reductive Dechlorination of Monochloroacetic Acid by Sulfite/UV Process. Environmental Science and Technology, 46(13), pp. 7342-49. [https://doi.org/10.1021/es3008535 doi: 10.1021/es3008535]</ref><ref>Li, X., Fang, J., Liu, G., Zhang, S., Pan, B., Ma, J., 2014. Kinetics and efficiency of the hydrated electron-induced dehalogenation by the sulfite/UV process. Water Research, 62, pp. 220-228. [https://doi.org/10.1016/j.watres.2014.05.051 doi: 10.1016/j.watres.2014.05.051]</ref>.
  
−
'''Related Article(s)'''
+
==Limitations==
−
* [[LNAPL Remediation Technologies]]
+
Several environmental factors and potential issues have been identified that may impact the performance of the UV/sulfite treatment system, as listed below. Solutions to address these issues are also proposed.
−
* [[NAPL Mobility]]
+
*Environmental factors, such as the presence of elevated concentrations of natural organic matter (NOM), dissolved oxygen, or nitrate, can inhibit the efficacy of UV/sulfite treatment systems by scavenging available hydrated electrons. Those interferences are commonly managed through chemical additions, reaction optimization, and/or dilution, and are therefore not considered likely to hinder treatment success.
−
* [[Natural Source Zone Depletion (NSZD)]]
+
*Coloration in waste streams may also impact the effectiveness of the UV/sulfite treatment system by blocking the transmission of UV light, thus reducing the UV lamp's effective path length. To address this, pre-treatment may be necessary to enable UV/sulfite destruction of PFAS in the waste stream. Pre-treatment may include the use of strong oxidants or coagulants to consume or remove UV-absorbing constituents.
−
* [[Natural Attenuation in Source Zone and Groundwater Plume - Bemidji Crude Oil Spill]]
+
*The degradation efficiency is strongly influenced by PFAS molecular structure, with fluorotelomer sulfonates (FTS) and [[Wikipedia: Perfluorobutanesulfonic acid | perfluorobutanesulfonate (PFBS)]] exhibiting greater resistance to degradation by UV/sulfite treatment compared to other PFAS compounds.
−
* [[Monitored Natural Attenuation (MNA)]]  
 
−
* [[Biodegradation - Hydrocarbons]]
 
  
−
'''CONTRIBUTOR(S):''' [[Dr. Charles Newell, P.E. | Charles Newell]]
+
==State of the Practice==
−
 
+
[[File: XiongFig2.png | thumb | 500 px | Figure 2. Field demonstration of EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> for PFAS destruction in a concentrated waste stream in a Mid-Atlantic Naval Air Station: a) Target PFAS at each step of the treatment shows that about 99% of PFAS were destroyed; meanwhile, the final degradation product, i.e., fluoride, increased to 15 mg/L in concentration, demonstrating effective PFAS destruction; b) AOF concentrations at each step of the treatment provided additional evidence to show near-complete mineralization of PFAS. Average results from multiple batches of treatment are shown here.]]
−
'''Key Resource(s):'''
+
[[File: XiongFig3.png | thumb | 500 px | Figure 3. Field demonstration of a treatment train (SAFF + EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>) for groundwater PFAS separation and destruction at an Air Force base in California: a) Two main components of the treatment train, i.e. SAFF and EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>; b) Results showed the effective destruction of various PFAS in the foam fractionate. The target PFAS at each step of the treatment shows that about 99.9% of PFAS were destroyed. Meanwhile, the final degradation product, i.e., fluoride, increased to 30 mg/L in concentration, demonstrating effective destruction of PFAS in a foam fractionate concentrate. After a polishing treatment step (GAC) via the onsite groundwater extraction and treatment system, all PFAS were removed to concentrations below their MCLs.]]  
−
* LNAPL Site Management: LCSM Evolution, Decision Process, and Remedial Technologies. LNAPL-3. ITRC.<ref name="LNAPL-3">Interstate Technology and Regulatory Council (ITRC), 2018. LNAPL Site Management: LCSM Evolution, Decision Process, and Remedial Technologies. LNAPL-3. ITRC, LNAPL Update Team, Washington, DC.  [https://lnapl-3.itrcweb.org LNAPL-3 Website]</ref>
+
The effectiveness of UV/sulfite technology for treating PFAS has been evaluated in two field demonstrations using the EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> system. Aqueous samples collected from the system were analyzed using EPA Method 1633, the [[Wikipedia: TOP Assay | total oxidizable precursor (TOP) assay]], adsorbable organic fluorine (AOF) method, and non-target analysis. A summary of each demonstration and their corresponding PFAS treatment efficiency is provided below.  
−
 
+
*Under the [https://serdp-estcp.mil/ Environmental Security Technology Certification Program (ESTCP)] [https://serdp-estcp.mil/projects/details/4c073623-e73e-4f07-a36d-e35c7acc75b6/er21-5152-project-overview Project ER21-5152], a field demonstration of EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> was conducted at a Navy site on the east coast, and results showed that the technology was highly effective in destroying various PFAS in a liquid concentrate produced from an ''in situ'' foam fractionation groundwater treatment system. As shown in Figure 2a, total PFAS concentrations were reduced from 17,366 micrograms per liter (µg/L) to 195 µg/L at the end of the UV/sulfite reaction, representing 99% destruction. After the ion exchange resin polishing step, all residual PFAS had been removed to the non-detect level, except one compound (PFOS) reported as 1.5 nanograms per liter (ng/L), which is below the current Maximum Contaminant Level (MCL) of 4 ng/L. Meanwhile, the fluoride concentration increased up to 15 milligrams per liter (mg/L), confirming near complete defluorination. Figure 2b shows the adsorbable organic fluorine results from the same treatment test, which similarly demonstrates destruction of 99% of PFAS.
−
* Managing Risk at LNAPL Sites - Frequently Asked Questions, 2nd Edition. API.<ref name="Sale2018"> Sale, T., Hopkins, H., and Kirkman, A., 2018.  Managing Risk at LNAPL Sites - Frequently Asked Questions, 2nd Edition. American Petroleum Institute (API), Washington, DC. 72 pages. [https://www.api.org/oil-and-natural-gas/environment/clean-water/ground-water/lnapl/lnapl-faqs Free download from API.] [https://www.enviro.wiki/index.php?title=File:Sale-2018_LNAPL_FAQs_2nd_ed.pdf Report.pdf]</ref>
+
*Another field demonstration was completed at an Air Force base in California, where a treatment train combining [https://serdp-estcp.mil/projects/details/263f9b50-8665-4ecc-81bd-d96b74445ca2 Surface Active Foam Fractionation (SAFF)] and EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> was used to treat PFAS in groundwater. As shown in Figure 3, PFAS analytical data and fluoride results demonstrated near-complete destruction of various PFAS. In addition, this demonstration showed: a) high PFAS destruction ratio was achieved in the foam fractionate, even in very high concentration (up to 1,700 mg/L of booster), and b) the effluent from EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> was sent back to the influent of the SAFF system for further concentration and treatment, resulting in a closed-loop treatment system and no waste discharge from EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>. This field demonstration was conducted with the approval of three regulatory agencies (United States Environmental Protection Agency, California Regional Water Quality Control Board, and California Department of Toxic Substances Control).
−
 
 
−
==Life Cycle of LNAPL Sites==
 
−
[[File:Newell1w2Fig1.png |thumb|left|250px| Figure 1. Early, Middle, and Late Stage LNAPL releases<ref name= "Sale2018"/>.  The key distinctions are the presence of continuous LNAPL that can be mobile and the amount of time that has elapsed for NSZD to remove LNAPL.]]
 
−
A Conceptual Site Model (CSM) is a collection of information about a contaminated site that integrates the available evidence regarding its hydrogeologic setting, contaminant sources, exposure pathways, potential receptors, and site history (see ASTM E1689-95(2014)<ref name="ASTM2014a"> ASTM, 2014. Standard Guide for Developing Conceptual Site Models for Contaminated Sites. ASTM E1689-95(2014), ASTM International, West Conshohocken, PA. [https://doi.org/10.1520/E1689-95R14 DOI: 10.1520/E1689-95R14]  http://www.astm.org/cgi-bin/resolver.cgi?E1689</ref> and ASTM E2531-06(2014)<ref name="ASTM2014b"> ASTM, 2014. Standard Guide for Development of Conceptual Site Models and Remediation Strategies for Light Nonaqueous-Phase Liquids Released to the Subsurface. ASTM E2531-06(2014), ASTM International, West Conshohocken, PA. [https://doi.org/10.1520/E2531-06R14  DOI: 10.1520/E2531-06R14]  http://www.astm.org/cgi-bin/resolver.cgi?E2531</ref>).  When developing a CSM for an LNAPL site, it is important to understand that LNAPL releases evolve and change from what are referred to as Early Stage sites to Middle Stage and then to Late Stage sites<ref name="Sale2018"/> (Figure 1). 
 
−
 
 
−
An Early Stage site is characterized by the presence of a continuous LNAPL zone where a thick layer of LNAPL accumulation (also known as free product) is observed in monitoring wells. The continuous LNAPL zone (or LNAPL body) may be mobile at Early Stage sites, migrating into previously non-impacted areas. Removal of significant LNAPL mass by active pumping may be feasible at these sites. Early Stage sites are now relatively rare in the United States due to stringent environmental regulations enacted in the 1980s which emphasized preventing releases.
 
−
[[File:Newell1w2Fig2a.png |thumb|500px| Figure 2a. Time lapse conceptualization of the formation of an LNAPL body<ref name="ITRC2019"> Interstate Technology and Regulatory Council (ITRC), 2019. LNAPL Training: Connecting the Science to Managing Sites. Part 1: Understanding LNAPL Behavior in the Subsurface. ITRC, Washington, DC. [[Media: ITRC2019_LNAPLtrainingPart1.pdf | Slides.pdf]]</ref>.]]
 
−
[[File:Newell1w2Fig2b.png |thumb|500px| Figure 2b.  Sand tank experiment of an LNAPL release<ref name="ITRC2019"/>.]]
 
−
 
 
−
Many sites in the U.S. are now considered to be in the Middle Stage, where the LNAPL thickness in wells has been largely depleted by natural spreading of the LNAPL body, [[Natural Source Zone Depletion (NSZD)]], smearing of the water table, and/or active remediation, and where the LNAPL bodies are stable or shrinking<ref name="LNAPL-3"/><ref name="Sale2018"/> (Figure 1).  Active pumping characteristically only recovers LNAPL at relatively low rates of under 100 gallons per acre per year at Middle Stage sites, but NSZD rates may be much higher, on the order of 100s to 1,000s of gallons per acre per year.  Middle Stage dissolved phase plumes, typically comprised of monoaromatics such as benzene, toluene, ethyl benzene, and xylenes, are stable or shrinking over time.
 
−
 
 
−
Late Stage sites only have a sparse distribution of residual (trapped) LNAPL due to long-term NSZD and any active remediation that has been performed at the site.  The potential risks to receptors are typically low at Late Stage sites due to relatively low concentrations of LNAPL constituents in the dissolved phase and/or vapor plumes.
 
−
 
 
−
==LNAPL Body Formation==
 
−
LNAPLs released from tanks, pits, pipelines, or other sources will percolate downwards under the influence of gravity through permeable pathways in the unsaturated zone (e.g., soil pore space, fractures, and macropores) depending on the volume and pressure head of the LNAPL release, until encountering an impermeable layer or the water table, causing the LNAPL body to spread laterally.  The Interstate Technology and Regulatory Council (ITRC)<ref name="LNAPL-3"/> describes this downward movement toward the water table this way:
 
−
 
 
−
<blockquote>''During the downward movement of LNAPL through the soil, the presence of confining layers, subsurface heterogeneities, or other preferential pathways may result in irregular and complex lateral spreading and/or perching of LNAPL before the water table is encountered. Once at the water table, the LNAPL will spread laterally in a radial fashion as well as penetrate vertically downward into the saturated zone, displacing water to some depth proportional to the driving force of the vertical LNAPL column (or LNAPL head). The vertical penetration of LNAPL into the saturated zone will continue to occur as long as the downward force produced by the LNAPL head or pressure from the LNAPL release exceeds the counteracting forces produced by the resistance of the soil matrix and the buoyancy resulting from the density difference between LNAPL and groundwater.''<ref name="LNAPL-3"/></blockquote>
 
−
 
 
−
While the release at the surface is still active, the LNAPL body can expand until the LNAPL addition rate is equal to the NSZD depletion rate.  However, once the release at the surface is stopped, the expansion will stop relatively quickly, and the LNAPL body will stabilize.  Figure 2a shows a conceptual depiction of this release scenario and Figure 2b shows a sand tank experiment of an LNAPL release.  Because of the buoyancy effects, LNAPL releases that reach the water table will form LNAPL bodies that “like icebergs, are partially above and below the water table”.<ref name="Sale2018"/>
 
−
 
 
−
==Key Implications of the LNAPL Conceptual Site Model==
 
−
The nature of multi-phase flow processes in porous media (e.g., the interaction of LNAPL, water, and air in the pore spaces of an unconsolidated aquifer) has several important implications for environmental professionals in areas including interpretation of LNAPL thickness in monitoring wells and assessment of the long-term risk associated with LNAPL source zones. A few of the key implications are described below.
 
−
 
 
−
===Three States of LNAPL===
 
−
LNAPL can be found in the subsurface in three different states:
 
−
 
 
−
# '''Residual LNAPL''' is trapped and immobile but can undergo composition and phase changes and generate dissolved hydrocarbon plumes in saturated zones and/or vapors in unsaturated zones. The fraction of the total pore space occupied by this discontinuous LNAPL is referred to as the residual saturation, with other phases such as water and air in the remainder of the pore space.
 
−
# '''Mobile LNAPL''' is LNAPL at greater than the residual saturation. Mobile LNAPL can accumulate in a well and is potentially recoverable, but is not migrating (i.e., the LNAPL body is not expanding).
 
−
# '''Migrating LNAPL''' is LNAPL at greater than the residual concentration which is observed to expand into previously non-impacted locations over time (e.g., LNAPL appears in a monitoring well that had previously been clean).   
 
−
 
 
−
These three LNAPL states can cause different concerns and in some cases require different remediation goals.
 
−
 
 
−
===LNAPL “Apparent Thickness” is a Poor Metric for Risk Management===
 
−
[[File:Newell1w2Fig3.png |thumb|left|600px| Figure 3.  Five LNAPL Thickness Scenarios for five different physical settings<ref name="Sale2018"/>.]]
 
−
[[File:Newell1w2Fig4.png |thumb|350px| Figure 4.  Apparent LNAPL thickness versus LNAPL transmissivity, showing no correlation<ref name="Hawthorne2015">Hawthorne, J.M., 2015.  Nationwide (USA) Statistical Analysis of LNAPL Transmissivity, in: R. Darlington and A.C. Barton (Chairs), Bioremediation and Sustainable Environmental Technologies—2015. Third International Symposium on Bioremediation and Sustainable Environmental Technologies (Miami, FL), page C-017, Battelle Memorial Institute, Columbus, OH.  www.battelle.org/biosymp  [[Media:Hawthorne2015.pdf | Abstract.pdf]]</ref>.]]
 
−
LNAPL thickness in monitoring wells is often referred to as the “apparent LNAPL thickness” because at first glance this LNAPL thickness might be expected to be the thickness of LNAPL that is in the formation, but in reality it is not well correlated with the thickness of the LNAPL zone in the subsurface for several reasons.
 
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−
First, different physical settings can produce different LNAPL thicknesses in monitoring wells.  Sale et al. (2018) show five different scenarios that produce very different responses with regard to apparent LNAPL thickness (Figure 3).  Scenario A shows an LNAPL apparent thickness in the monitoring well that is at static equilibrium with LNAPL in an unconfined aquifer.  Scenario B, while also an unconfined aquifer, is comprised of very fine-grained soils that cause the LNAPL thickness in the well to be much higher than in Scenario A.  In Scenario C, the LNAPL has accumulated under a confined unit (likely due to an underground release of LNAPL below the confining unit), and the LNAPL has risen above the groundwater potentiometric surface, leading to a large (and misleading) LNAPL thickness in the monitoring well.  Scenario D, LNAPL in a perched unit, also shows a very different response from the other scenarios.  Scenario E, LNAPL in fractured system, shows that the LNAPL can penetrate below the water table, and that LNAPL thickness in a well is dependent on the pressure from accumulation of LNAPL in the fractures<ref name="Sale2018"/>.
 
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−
Second, apparent LNAPL thickness is affected by changes in the groundwater surface elevation (or water table). Generally, when groundwater elevations are higher than typical, the LNAPL thickness in monitoring wells will decrease or go to zero because the groundwater will redistribute any mobile LNAPL into what previously was the unsaturated zone.  During lower groundwater elevation periods, much more of the LNAPL will occur as a continuous phase near the water table, leading to higher LNAPL thicknesses in wells.
 
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−
Overall, LNAPL thickness measurements are useful for delineating the extent of mobile LNAPL in the saturated zone and can provide useful data for understanding the vertical distribution of LNAPL in the formation<ref name="Hawthorne2011">Hawthorne, J.M., 2011. Diagnostic Gauge Plots—Simple Yet Powerful LCSM Tools. Applied NAPL Science Review (ANSR), 1(2). [http://naplansr.com/diagnostic-gauge-plots-volume-1-issue-2-february-2011/ Website] [[Media:Hawthorne2011.pdf | Report.pdf]]</ref><ref name="Kirkman2013">Kirkman, A.J., Adamski, M., and Hawthorne, M., 2013. Identification and Assessment of Confined and Perched LNAPL Conditions. Groundwater Monitoring and 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>. But LNAPL thickness by itself is a very poor indicator of the feasibility of LNAPL recovery<ref name="LNAPL-2">Interstate Technology and Regulatory Council (ITRC), 2009. Evaluating LNAPL Remedial Technologies for Achieving Project Goals. LNAPL-2. ITRC, LNAPLs Team, Washington, DC. www.itrcweb.org  [[Media:ITRC-LNAPL-2.pdf | Report.pdf]]</ref><ref name="Hawthorne2015"/> (see [[NAPL Mobility]]) (Figure 4).  Because there is little correlation between apparent LNAPL thickness and LNAPL mobility, there is also little correlation between apparent thickness and the risk to receptors from the LNAPL.
 
−
 
 
−
===Complete LNAPL Remediation Is Very Challenging===
 
−
Sale et al. (2018) described the problems with attaining complete LNAPL remediation this way:
 
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−
<blockquote>''Experience of the last few decades has taught us: 1) our best efforts often leave some LNAPL in place, and 2) the remaining LNAPL often sustains exceedances of drinking water standards in release areas for extended periods. Entrapment of LNAPLs at residual saturations is a primary factor constraining our success. Other challenges include the low solubility of LNAPL, the complexity of the subsurface geologic environment, access limitations associated with surface structures, and concentration goals that are often three to five orders of magnitude less than typical initial concentrations within LNAPL zones.''<ref name="Sale2018"/></blockquote>
 
−
 
 
−
In particular, the discontinuous residual LNAPL cannot be removed (or recovered) by pumping, and ''in situ'' remediation is expensive and not completely effective (see [[LNAPL Remediation Technologies]]).  However, many regulatory programs require “LNAPL recovery to the extent practicable.”  The lack of quantitative metrics and the lack of correlation between apparent LNAPL thicknesses and subsurface LNAPL makes this a problematic requirement in many cases and the ITRC (2018) cautions “Thickness or concentration data alone may not provide a sound basis for defining the point at which a cleanup objective is achieved.”<ref name="LNAPL-3"/>  However, Sale et al. (2018) describe metrics such as LNAPL transmissivity, limited/infrequent well thicknesses, decline curve analysis, asymptotic analysis, and comparison to NSZD rates that can be used to determine when LNAPL has been removed the extent practicable<ref name="Sale2018"/>.
 
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−
===Attenuation Processes are Active and Important===
 
−
Both LNAPL source zones and their dissolved phase hydrocarbon plumes are attenuated by biodegradation and other attenuation process.  In the source zone, this attenuation is called [[Natural Source Zone Depletion (NSZD)]] (see also [[Natural Attenuation in Source Zone and Groundwater Plume - Bemidji Crude Oil Spill]]).  In the dissolved plume it is called [[Monitored Natural Attenuation (MNA)]] (see also  [[Biodegradation - Hydrocarbons]]). These processes generally limit the length of dissolved phase hydrocarbon plumes to a few hundred feet<ref name="Newell1998">Newell, C.J., and Connor, J.A., 1998. Characteristics of Dissolved Hydrocarbon Plumes: Results from Four Studies, Version 1.1. American Petroleum Institute, Soil/Groundwater Technical Task Force, Washington, DC. [https://www.enviro.wiki/index.php?title=File:Newell-1998-chararacterization_of_dissolved_Pet._Hydro_Plumes.pdf  Report.pdf]</ref> via processes that have been well known and understood since the mid-1990s.
 
−
 
 
−
However, NSZD is “by far, the biggest new idea for LNAPLs in the last decade.”<ref name="Sale2018"/>  Originally, LNAPL bodies were thought to attenuate very slowly via dissolution and volatilization.  In 2006, it was discovered that NSZD rates are orders of magnitude higher than originally thought, largely due to direct biodegradation of LNAPL constituents to methane and carbon dioxide by methanogenic consortiums of naturally occurring bacteria<ref name="Lundegard2006">Lundegard, P.D., and Johnson, P.C., 2006. Source Zone Natural Attenuation at Petroleum Spill Sites—II: Application to a Former Oil Field. Groundwater Monitoring and Remediation. 26(4), pp. 93-106.  [https://doi.org/10.1111/j.1745-6592.2006.00115.x  DOI: 10.1111/j.1745-6592.2006.00115.x]</ref><ref name="Garg2017">Garg, S., Newell, C., Kulkarni, P., King, D., Adamson, D.T., Irianni Renno, M., and Sale, T., 2017. Overview of Natural Source Zone Depletion: Processes, Controlling Factors, and Composition Change. Groundwater Monitoring and Remediation, 37(3), pp. 62-81.  [https://doi.org/10.1111/gwmr.12219 DOI:  10.1111/gwmr.12219] [[Media:Garg2017gwmr.12219.pdf | Report.pdf]]</ref>.  NSZD processes play an important role in risk mitigation and the long-term stability of LNAPL bodies<ref name="Mahler2012">
 
−
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 DOI: 10.1111/j.1745-6584.2012.00949.x]</ref><ref name="LNAPL-3"/>.
 
−
 
 
−
===Risk from LNAPL Source Zones Diminishes Over Time===
 
−
At Early Stage LNAPL sites, the expansion of the LNAPL body is a risk that needs to be addressed. Fortunately, this type of site is relatively rare.  For Middle and Late Stage sites, the primary risks are associated with phase changes (dissolution of the LNAPL forming a dissolved plume and volatilization from the LNAPL or dissolved plume forming hydrocarbon vapors).  As described above, MNA can often control the dissolved phase (see [[Monitored Natural Attenuation (MNA) of Fuels]]), while aerobic biodegradation in the unsaturated zone greatly reduces the vapor intrusion risk from hydrocarbon vapors (see [[Vapor Intrusion - Separation Distances from Petroleum Sources]]).
 
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Understanding LNAPL body mobility and stability is important to understand the potential risks posed by LNAPL.  The relative magnitude of LNAPL mobility can be determined by measuring the LNAPL transmissivity (see [[NAPL Mobility]]).  If the transmissivity is below a threshold level (in the range of 0.1 to 0.8 ft<sup>2</sup>/day) then the LNAPL likely cannot be recovered efficiently by pumping, but above this transmissivity level recovery is feasible<ref name="LNAPL-3"/>.  Michigan’s LNAPL guidance states “if the NAPL has a transmissivity greater than 0.5 ft<sup>2</sup>/day, it is likely that the NAPL can be recovered in a cost-effective and efficient manner unless a demonstration is made to show otherwise.”  Kansas LNAPL guidance requires “recovery of all LNAPL with a transmissivity greater than 0.8 ft<sup>2</sup>/day that can be recovered in an efficient, cost-effective manner.”<ref name="LNAPL-3"/>.  The stability of the entire LNAPL body can be evaluated using statistical tools to determine if migration of LNAPL is occurring<ref name="Hawthorne2013">Hawthorne, J.M., Stone, C.D., Helsel, D., 2013. LNAPL Body Stability Part 2: Daughter Plume Stability via Spatial Moments Analysis. Applied NAPL Science Review (ANSR), 3(5).  [http://naplansr.com/lnapl-body-stability-part-2-daughter-plume-stability-via-spatial-moments-analysis-volume-3-issue-5-september-2013/ Website] [[Media:Hawthorne2013.pdf | Report.pdf]]</ref>.
 
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==Overview of Modern LNAPL Conceptual Site Model==
 
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[[File:Newell1w2Fig5.png |thumb|500px| Figure 5.  A higher tier of LNAPL CSM is useful as LNAPL site complexity increases<ref name="LNAPL-3"/>.]]
 
−
The ITRC (2018) describes the typical evolution of an LCSM over the course of the remediation process which can be broken into three separate stages:
 
−
* An ''Initial LCSM'' focuses on identifying the LNAPL concerns, such as a risk to health or safety, any LNAPL migration, LNAPL-specific regulations, and physical or aesthetic impacts.
 
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* A ''Remedy Selection LCSM'' supports remedial technology evaluation by characterizing aspects of the LNAPL and site subsurface that may impact remedial technology performance.
 
−
* A ''Design and Performance LCSM'' focuses on presenting the technical information needed to establish remediation objectives, design and implement remedies or control measures, and track progress toward defined remediation endpoints.
 
−
 
 
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One key question when developing an LCSM is “how much data is enough.”  In general, the answer is that the existing data is sufficient for the current stage of the remediation project when it allows the stakeholders to agree on a path forward<ref name="LNAPL-3"/>.  Figure 5 shows that as the level of complexity of a site increases, a higher tier of LCSM is useful to provide enough information for making decisions<ref name="LNAPL-3"/><ref name="ASTM2014a"/>. The higher tier of information could be higher data density, additional tools for a given line of evidence, or other evaluations.
 
−
 
 
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==LNAPL Concerns, Remediation Goals and Objectives==
 
−
Finally, the ITRC (2018) provides a methodology for identifying LNAPL concerns, verifying those concerns, selecting LNAPL remediation goals, and determining LNAPL remediation objectives.  Examples of each of these concepts are provided below:
 
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* '''Potential Concerns:'''  Human or ecological risk concerns, fire or explosivity issues, LNAPL migration, LNAPL-specific regulatory concerns, other concerns such as odors or geotechnical issues.
 
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* '''Verifying Concerns:'''  Measure LNAPL transmissivity to determine if it is recoverable; measure vertical and horizontal separation distances between buildings and LNAPL bodies to screen for vapor intrusion concerns.
 
−
* '''Remediation Goals:'''  Reduce mobile LNAPL saturation, abate unacceptable soil concentrations, terminate LNAPL body migration, abate unacceptable constituent concentrations in dissolved and vapor phases.
 
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* '''Remediation Objectives:'''  Recover LNAPL to the extent practicable based on transmissivity, reduce soil concentrations to below regulatory limits, stop LNAPL migration with a barrier, contain migrating groundwater plume (if present), reduce groundwater and vapor concentration to acceptable levels.
 
−
* '''Remediation Technologies:'''  LNAPL Mass Recovery technologies, LNAPL phase change technologies, LNAPL Mass Control technologies, combinations of technologies.
 
−
 
 
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Overall, a LNAPL Conceptual Site Model that integrates key site specific information and current technical knowledge about LNAPL sites in general is instrumental to successful site management, where LNAPL concerns drive remediation goals, goals drive remediation objectives, and the objectives form the basis for the selection of remediation technologies.  
 
  
 
==References==
 
==References==
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+
<references />
−
<references/>
 
  
 
==See Also==
 
==See Also==
−
American Petroleum Institute (API), 2006. API Interactive LNAPL Guide Version 2.0.4. API, Soil and Groundwater Technical Task Force.  [https://www.api.org/oil-and-natural-gas/environment/clean-water/ground-water/lnapl/interactive-guide Free download from API] 
 

Latest revision as of 10:17, 13 February 2026

In Situ Toxicity Identification Evaluation (iTIE)

The in situ Toxicity Identification Evaluation system is a tool to incorporate into weight-of-evidence studies at sites with numerous chemical toxicant classes present. The technology works by continuously sampling site water, immediately fractionating the water using diagnostic sorptive resins, and then exposing test organisms to the water to observe toxicity responses with minimal sample manipulation. It is compatible with various resins, test organisms, and common acute and chronic toxicity tests, and can be deployed at sites with a wide variety of physical and logistical considerations.

Related Article(s):

Contributors: Dr. G. Allen Burton Jr., Austin Crane

Key Resources:

  • A Novel In Situ Toxicity Identification Evaluation (iTIE) System for Determining which Chemicals Drive Impairments at Contaminated Sites[1]
  • An in situ toxicity identification and evaluation water analysis system: Laboratory validation[2]
  • Sediment Toxicity Identification Evaluation (TIE) Phases I, II, and III Guidance Document- [3]
  • In Situ Toxicity Identification Evaluation (iTIE) Technology for Assessing Contaminated Sediments, Remediation Success, Recontamination and Source Identification- [4]

Introduction

In waterways impacted by numerous naturally occurring and anthropogenic chemical stressors, it is crucial for environmental practitioners to be able to identify which chemical classes are causing the highest degrees of toxicity to aquatic life. Previously developed methods, including the Toxicity Identification Evaluation (TIE) protocol developed by the US Environmental Protection Agency (EPA)[5], can be confounded by sample manipulation artifacts and temporal limitations of ex situ organism exposures[1]. These factors may disrupt causal linkages and mislead investigators during site characterization and management decision-making. The in situ Toxicity Identification Evaluation (iTIE) technology was developed to allow users to strengthen stressor-causality linkages and rank chemical classes of concern at impaired sites, with high degrees of ecological realism.

The technology has undergone a series of improvements in recent years, with the most recent prototype being robust, operable in a wide variety of site conditions, and cost-effective compared to alternative site characterization methods[6][7][1][2]. The latest prototype can be used in any of the following settings: in marine, estuarine, or freshwater sites; to study surface water or sediment pore water; in shallow waters easily accessible by foot or in deep waters only accessible by pier or boat. It can be used to study sites impacted by a wide variety of stressors including ammonia, metals, pesticides, polychlorinated biphenyls (PCB), polycyclic aromatic hydrocarbons (PAH), and per- and polyfluoroalkyl substances (PFAS), among others. The technology is applicable to studies of acute toxicity via organism survival or of chronic toxicity via responses in growth, reproduction, or gene expression[1].

System Components and Validation

Figure 1: A schematic diagram of the iTIE system prototype. The system is divided into three sub-systems: 1) the Pore Water/Surface Water Collection Sub-System (blue); 2) the Pumping Sub-System (red); and 3) the iTIE Resin, Exposure, and Sampling Sub-System (green). Water first enters the system through the Pore Water/Surface Water Collection Sub-System. Porewater can be collected using Trident-style probes, or surface water can be collected using a simple weighted probe. The water is composited in a manifold before being pumped to the rest of the iTIE system by the booster pump. Once in the iTIE Resin, Exposure, and Sampling Sub-System, the water is gently oxygenated by the Oxygen Coil, separated from gas bubbles by the Drip Chamber, and diverted to separate iTIE Resin and Exposure Chambers (or iTIE units) by the Splitting Manifold. Water movement through each iTIE unit is controlled by a dedicated Regulation Pump. Finally, the water is gathered in Sample Collection bottles for analysis.

The latest iTIE prototype consists of an array of sorptive resins that differentially fractionate sampled water, and a series of corresponding flow-through organism chambers that receive the treated water in situ. Resin treatments can be selected depending on the chemicals suspected to be present at each site to selectively sequester certain chemical of concern (CoC) classes from the whole water, leaving a smaller subset of chemicals in the resulting water fraction for chemical and toxicological characterization. Test organism species and life stages can also be chosen depending on factors including site characteristics and study goals. In the full iTIE protocol, site water is continuously sampled either from the sediment pore spaces or the water column at a site, gently oxygenated, diverted to different iTIE units for fractionation and organism exposure, and collected in sample bottles for off-site chemical analysis (Figure 1). All iTIE system components are housed within waterproof Pelican cases, which allow for ease of transport and temperature control.

Porewater and Surface Water Collection Sub-system

Figure 2: a) Trident probe with auxiliary sensors attached, b) a Trident probe with end caps removed (the red arrow identifies the intermediate space where glass beads are packed to filter suspended solids), c) a Trident probe being installed using a series of push poles and a fence post driver

Given the importance of sediment porewater to ecosystem structure and function, investigators may employ the iTIE system to evaluate the toxic effects associated with the impacted sediment porewater. To accomplish this, the iTIE system utilizes the Trident probe, originally developed for Department of Defense site characterization studies[8]. The main body of the Trident is comprised of a stainless-steel frame with six hollow probes (Figure 2). Each probe contains a layer of inert glass beads, which filters suspended solids from the sampled water. The water is drawn through each probe into a composite manifold and transported to the rest of the iTIE system using a high-precision peristaltic pump.

The Trident also includes an adjustable stopper plate, which forms a seal against the sediment and prevents the inadvertent dilution of porewater samples with surface water. (Figure 2). Preliminary laboratory results indicate that the Trident is extremely effective in collecting porewater samples with minimal surface water infiltration in sediments ranging from coarse sand to fine clay. Underwater cameras, sensors, passive samplers, and other auxiliary equipment can be attached to the Trident probe frame to provide supplemental data.

Alternatively, practitioners may employ the iTIE system to evaluate site surface water. To sample surface water, weighted intake tubes can collect surface water from the water column using a peristaltic pump.

Oxygen Coil, Overflow Bag and Drip Chamber

Figure 3. Contents of the iTIE system cooler. The pictured HDPE rack (47.6 cm length x 29.7 cm width x 33.7 cm height) is removable from the iTIE cooler. Water enters the system at the red circle, flows through the oxygen coil, and then travels to each of the individual iTIE units where diagnostic resins and organisms are located. The water then briefly leaves the cooler to travel through peristaltic regulation pumps before being gathered in sample collection bottles.

Porewater is naturally anoxic due to limited mixing with aerated surface water and high oxygen demand of sediments, which may cause organism mortality and interfere with iTIE results. To preclude this, sampled porewater is exposed to an oxygen coil. This consists of an interior silicone tube connected to a pressurized oxygen canister, threaded through an exterior reinforced PVC tube through which water is slowly pumped (Figure 3). Pump rates are optimized to ensure adequate aeration of the water. In addition to elevating DO levels, the oxygen coil facilitates the oxidation of dissolved sulfides, which naturally occur in some marine sediments and may otherwise cause toxicity to organisms if left in its reduced form.

Gas bubbles may form in the oxygen coil over the course of a deployment. These can be disruptive, decreasing water sample volumes and posing a danger to sensitive organisms like daphnids. To account for this, the water travels to a drip chamber after exiting the oxygen coil, which allows gas bubbles to be separated and diverted to an overflow system. The sample water then flows to a manifold which divides the flow into different paths to each of the treatment units for fractionation and organism exposure.

iTIE Units: Fractionation and Organism Exposure Chambers

Figure 4. A diagram of the iTIE prototype. Water flows upward into each resin chamber through the unit bottom. After being chemically fractionated in the resin chamber, water travels into the organism chamber, where test organisms have been placed. Water is drawn through the units by high-precision peristaltic pumps.

At the core of the iTIE system are separate dual-chamber iTIE units, each with a resin fractionation chamber and an organism exposure chamber (Figure 4). Developed by Burton et al.[1], the iTIE prototype is constructed from acrylic, with rubber O-rings to connect each piece. Each iTIE unit can contain a different diagnostic resin matrix, customizable to remove specific chemical classes from the water. Sampled water flows into each unit through the bottom and is differentially fractionated by the resin matrix as it travels upward. Then it reaches the organism chamber, where test organisms are placed for exposure. The organism chamber inlet and outlet are covered by mesh to prevent the escape of the test organisms. This continuous flow-through design allows practitioners to capture the temporal heterogeneity of ambient water conditions over the duration of an in situ exposure. Currently, the iTIE system can support four independent iTIE treatment units.

After being exposed to test organisms, water is collected in sample bottles. The bottles can be pre-loaded with preservation reagents to allow for later chemical analysis. Sample bottles can be composed of polyethylene, glass or other materials depending on the CoC.

Pumping Sub-system

Figure 5. The iTIE system pumping sub-system. The sub-system consists of: A) a single booster pump, which is directly connected to the water sampling device and feeds water to the rest of the iTIE system, and B) a set of four regulation pumps, which each connect to the outflow of an individual iTIE unit. Each pump set is housed in a waterproof case with self-contained rechargeable battery power. A tablet is mounted inside the lid of the four pump case, which can be used to program and operate all of the pumps when connected to the internet.

Water movement through the system is driven by a series of high-precision, programmable peristaltic pumps (EcoTech Marine). Each pump set is housed in a Pelican storm travel case. Power is supplied to each pump by internal rechargeable lithium-iron phosphate batteries (Bioenno Power).

First, water is supplied to the system by a booster pump (Figure 5A). This pump is situated between the water sampling sub-system and the oxygen coil. The booster pump: 1) facilitates pore water collection, especially from sediments with high fine particle fractions; 2) helps water overcome vertical lifts to travel to the iTIE system; and 3) prevents vacuums from forming in the iTIE system interior, which can accelerate the formation of disruptive gas bubbles in the oxygen coil. The booster pump should be programmed to supply an excess of water to prevent vacuum formation.

Second, a set of four regulation pumps ensure precise flow rates through each independent iTIE unit (Figure 5B). Each regulation pump pulls water from the top of an iTIE unit and then dispenses that water into a sample bottle for further analysis.

Study Design Considerations

Diagnostic Resin Treatments

Several commercially available resins have been verified for use in the iTIE system. Investigators can select resins based on stressor classes of interest at each site. Each resin selectively removes a CoC class from site water prior to organism exposure.

Resins must be adequately conditioned prior to use. Otherwise, they may inadequately adsorb toxicants or cause stress to organisms. New resins should be tested for efficacy and toxicity before being used in an iTIE system.

Test Organism Species and Life Stages


Advantages

A UV/sulfite treatment system offers significant advantages for PFAS destruction compared to other technologies, including high defluorination percentage, high treatment efficiency for short-chain PFAS without mass transfer limitation, selective reactivity by eaq-, low energy consumption, and the production of no harmful byproducts. A summary of these advantages is provided below:

  • High efficiency for short- and ultrashort-chain PFAS: While the degradation efficiency for short-chain PFAS is challenging for some treatment technologies[12][13][14], the UV/sulfite process demonstrates excellent defluorination efficiency for both short- and ultrashort-chain PFAS, including trifluoroacetic acid (TFA) and perfluoropropionic acid (PFPrA).
  • High defluorination ratio: As shown in Figure 3, the UV/sulfite treatment system has demonstrated near 100% defluorination for various PFAS under both laboratory and field conditions.
  • No harmful byproducts: While some oxidative technologies, such as electrochemical oxidation, generate toxic byproducts, including perchlorate, bromate, and chlorate, the UV/sulfite system employs a reductive mechanism and does not generate these byproducts.
  • Ambient pressure and low temperature: The system operates under ambient pressure and low temperature (<60°C), as it utilizes UV light and common chemicals to degrade PFAS.
  • Low energy consumption: The electrical energy per order values for the degradation of perfluorocarboxylic acids (PFCAs) by UV/sulfite have been reduced to less than 1.5 kilowatt-hours (kWh) per cubic meter under laboratory conditions. The energy consumption is orders of magnitude lower than that for many other destructive PFAS treatment technologies (e.g., supercritical water oxidation)[15].
  • Co-contaminant destruction: The UV/sulfite system has also been reported effective in destroying certain co-contaminants in wastewater. For example, UV/sulfite is reported to be effective in reductive dechlorination of chlorinated volatile organic compounds, such as trichloroethene, 1,2-dichloroethane, and vinyl chloride[16][17][18][19].

Limitations

Several environmental factors and potential issues have been identified that may impact the performance of the UV/sulfite treatment system, as listed below. Solutions to address these issues are also proposed.

  • Environmental factors, such as the presence of elevated concentrations of natural organic matter (NOM), dissolved oxygen, or nitrate, can inhibit the efficacy of UV/sulfite treatment systems by scavenging available hydrated electrons. Those interferences are commonly managed through chemical additions, reaction optimization, and/or dilution, and are therefore not considered likely to hinder treatment success.
  • Coloration in waste streams may also impact the effectiveness of the UV/sulfite treatment system by blocking the transmission of UV light, thus reducing the UV lamp's effective path length. To address this, pre-treatment may be necessary to enable UV/sulfite destruction of PFAS in the waste stream. Pre-treatment may include the use of strong oxidants or coagulants to consume or remove UV-absorbing constituents.
  • The degradation efficiency is strongly influenced by PFAS molecular structure, with fluorotelomer sulfonates (FTS) and perfluorobutanesulfonate (PFBS) exhibiting greater resistance to degradation by UV/sulfite treatment compared to other PFAS compounds.

State of the Practice

Figure 2. Field demonstration of EradiFluorTM[20] for PFAS destruction in a concentrated waste stream in a Mid-Atlantic Naval Air Station: a) Target PFAS at each step of the treatment shows that about 99% of PFAS were destroyed; meanwhile, the final degradation product, i.e., fluoride, increased to 15 mg/L in concentration, demonstrating effective PFAS destruction; b) AOF concentrations at each step of the treatment provided additional evidence to show near-complete mineralization of PFAS. Average results from multiple batches of treatment are shown here.
Figure 3. Field demonstration of a treatment train (SAFF + EradiFluorTM[20]) for groundwater PFAS separation and destruction at an Air Force base in California: a) Two main components of the treatment train, i.e. SAFF and EradiFluorTM[20]; b) Results showed the effective destruction of various PFAS in the foam fractionate. The target PFAS at each step of the treatment shows that about 99.9% of PFAS were destroyed. Meanwhile, the final degradation product, i.e., fluoride, increased to 30 mg/L in concentration, demonstrating effective destruction of PFAS in a foam fractionate concentrate. After a polishing treatment step (GAC) via the onsite groundwater extraction and treatment system, all PFAS were removed to concentrations below their MCLs.

The effectiveness of UV/sulfite technology for treating PFAS has been evaluated in two field demonstrations using the EradiFluorTM[20] system. Aqueous samples collected from the system were analyzed using EPA Method 1633, the total oxidizable precursor (TOP) assay, adsorbable organic fluorine (AOF) method, and non-target analysis. A summary of each demonstration and their corresponding PFAS treatment efficiency is provided below.

  • Under the Environmental Security Technology Certification Program (ESTCP) Project ER21-5152, a field demonstration of EradiFluorTM[20] was conducted at a Navy site on the east coast, and results showed that the technology was highly effective in destroying various PFAS in a liquid concentrate produced from an in situ foam fractionation groundwater treatment system. As shown in Figure 2a, total PFAS concentrations were reduced from 17,366 micrograms per liter (µg/L) to 195 µg/L at the end of the UV/sulfite reaction, representing 99% destruction. After the ion exchange resin polishing step, all residual PFAS had been removed to the non-detect level, except one compound (PFOS) reported as 1.5 nanograms per liter (ng/L), which is below the current Maximum Contaminant Level (MCL) of 4 ng/L. Meanwhile, the fluoride concentration increased up to 15 milligrams per liter (mg/L), confirming near complete defluorination. Figure 2b shows the adsorbable organic fluorine results from the same treatment test, which similarly demonstrates destruction of 99% of PFAS.
  • Another field demonstration was completed at an Air Force base in California, where a treatment train combining Surface Active Foam Fractionation (SAFF) and EradiFluorTM[20] was used to treat PFAS in groundwater. As shown in Figure 3, PFAS analytical data and fluoride results demonstrated near-complete destruction of various PFAS. In addition, this demonstration showed: a) high PFAS destruction ratio was achieved in the foam fractionate, even in very high concentration (up to 1,700 mg/L of booster), and b) the effluent from EradiFluorTM[20] was sent back to the influent of the SAFF system for further concentration and treatment, resulting in a closed-loop treatment system and no waste discharge from EradiFluorTM[20]. This field demonstration was conducted with the approval of three regulatory agencies (United States Environmental Protection Agency, California Regional Water Quality Control Board, and California Department of Toxic Substances Control).

References

  1. ^ 1.0 1.1 1.2 1.3 1.4 Burton, G.A., Cervi, E.C., Meyer, K., Steigmeyer, A., Verhamme, E., Daley, J., Hudson, M., Colvin, M., Rosen, G., 2020. A novel In Situ Toxicity Identification Evaluation (iTIE) System for Determining which Chemicals Drive Impairments at Contaminated Sites. Environmental Toxicology and Chemistry, 39(9), pp. 1746-1754. doi: 10.1002/etc.4799
  2. ^ 2.0 2.1 2.2 Steigmeyer, A.J., Zhang, J., Daley, J.M., Zhang, X., Burton, G.A. Jr., 2017. An in situ toxicity identification and evaluation water analysis system: Laboratory validation. Environmental Toxicology and Chemistry, 36(6), pp. 1636-1643. doi: 10.1002/etc.3696
  3. ^ United States Environmental Protection Agency, 2007. Sediment Toxicity Identification Evaluation (TIE) Phases I, II, and III Guidance Document, EPA/600/R-07/080. 145 pages. Free Download  Report.pdf
  4. ^ In Situ Toxicity Identification Evaluation (iTIE) Technology for Assessing Contaminated Sediments, Remediation Success, Recontamination and Source Identification Project Website  Final Report.pdf
  5. ^ Norberg-King, T., Mount, D.I., Amato, J.R., Jensen, D.A., Thompson, J.A., 1992. Toxicity identification evaluation: Characterization of chronically toxic effluents: Phase I. Publication No. EPA/600/6-91/005F. U.S. Environmental Protection Agency, Office of Research and Development. Free Download from US EPA  Report.pdf
  6. ^ Burton, G.A. Jr., Nordstrom, J.F., 2004. An in situ toxicity identification evaluation method part I: Laboratory validation. Environmental Toxicology and Chemistry, 23(12), pp. 2844-2850. doi: 10.1897/03-409.1
  7. ^ Burton, G.A. Jr., Nordstrom, J.F., 2004. An in situ toxicity identification evaluation method part II: Field validation. Environmental Toxicology and Chemistry, 23(12), pp. 2851-2855. doi: 10.1897/03-468.1
  8. ^ Chadwick, D.B., Harre, B., Smith, C.F., Groves, J.G., Paulsen, R.J., 2003. Coastal Contaminant Migration Monitoring: The Trident Probe and UltraSeep System. Hardware Description, Protocols, and Procedures. Technical Report 1902. Space and Naval Warfare Systems Center.
  9. ^ Woodard, S., Mohr, T., Nickelsen, M.G., 2014. Synthetic media: A promising new treatment technology for 1,4-dioxane. Remediation Journal, 24(4), pp. 27-40. doi: 10.1002/rem.21402
  10. ^ Lemos, B.R.S., Teixeira, I.F., de Mesquita, J.P., Ribeiro, R.R., Donnici, C.L., Lago, R.M., 2012. Use of modified activated carbon for the oxidation of aqueous sulfide. Carbon, 50(3), pp. 1386-1393. doi: 10.1016/j.carbon.2011.11.011
  11. ^ Iannone, A., Carriera, F., Di Fiore, C., Avino, P., 2024. Poly- and Perfluoroalkyl Substance (PFAS) Analysis in Environmental Matrices: An Overview of the Extraction and Chromatographic Detection Methods. Analytica, 5(2), pp. 187-202. doi: 10.3390/analytica5020012  Open Access Article
  12. ^ Singh, R.K., Brown, E., Mededovic Thagard, S., Holson, T.M., 2021. Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor. Journal of Hazardous Materials, 408, Article 124452. doi: 10.1016/j.jhazmat.2020.124452
  13. ^ Singh, R.K., Multari, N., Nau-Hix, C., Woodard, S., Nickelsen, M., Mededovic Thagard, S., Holson, T.M., 2020. Removal of Poly- and Per-Fluorinated Compounds from Ion Exchange Regenerant Still Bottom Samples in a Plasma Reactor. Environmental Science and Technology, 54(21), pp. 13973-80. doi: 10.1021/acs.est.0c02158
  14. ^ Nau-Hix, C., Multari, N., Singh, R.K., Richardson, S., Kulkarni, P., Anderson, R.H., Holsen, T.M., Mededovic Thagard S., 2021. Field Demonstration of a Pilot-Scale Plasma Reactor for the Rapid Removal of Poly- and Perfluoroalkyl Substances in Groundwater. American Chemical Society’s Environmental Science and Technology (ES&T) Water, 1(3), pp. 680-87. doi: 10.1021/acsestwater.0c00170
  15. ^ Nzeribe, B.N., Crimi, M., Mededovic Thagard, S., Holsen, T.M., 2019. Physico-Chemical Processes for the Treatment of Per- And Polyfluoroalkyl Substances (PFAS): A Review. Critical Reviews in Environmental Science and Technology, 49(10), pp. 866-915. doi: 10.1080/10643389.2018.1542916
  16. ^ Jung, B., Farzaneh, H., Khodary, A., Abdel-Wahab, A., 2015. Photochemical degradation of trichloroethylene by sulfite-mediated UV irradiation. Journal of Environmental Chemical Engineering, 3(3), pp. 2194-2202. doi: 10.1016/j.jece.2015.07.026
  17. ^ Liu, X., Yoon, S., Batchelor, B., Abdel-Wahab, A., 2013. Photochemical degradation of vinyl chloride with an Advanced Reduction Process (ARP) – Effects of reagents and pH. Chemical Engineering Journal, 215-216, pp. 868-875. doi: 10.1016/j.cej.2012.11.086
  18. ^ Li, X., Ma, J., Liu, G., Fang, J., Yue, S., Guan, Y., Chen, L., Liu, X., 2012. Efficient Reductive Dechlorination of Monochloroacetic Acid by Sulfite/UV Process. Environmental Science and Technology, 46(13), pp. 7342-49. doi: 10.1021/es3008535
  19. ^ Li, X., Fang, J., Liu, G., Zhang, S., Pan, B., Ma, J., 2014. Kinetics and efficiency of the hydrated electron-induced dehalogenation by the sulfite/UV process. Water Research, 62, pp. 220-228. doi: 10.1016/j.watres.2014.05.051
  20. ^ 20.0 20.1 20.2 20.3 20.4 20.5 20.6 20.7 Cite error: Invalid <ref> tag; no text was provided for refs named EradiFluor

See Also

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