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==Contaminated Sediment Risk Assessment==
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==Lysimeters for Measuring PFAS Concentrations in the Vadose Zone==  
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[[Contaminated Sediments - Introduction | Contaminated sediments]] in rivers and streams, lakes, coastal harbors, and estuaries have the potential to pose ecological and human health risks. The goals of risk assessment applied to contaminated sediments are to characterize the nature and magnitude of the current and potential threats to human health, wildlife and ecosystem functioning posed by contamination; identify the key factors contributing to the potential health and ecological risks; evaluate how implementation of one or more remedy actions will mitigate the risks in the short and long term; and evaluate the risks and impacts from sediment management, both during and after any dredging or other remedy construction activities.  
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[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]] are frequently introduced to the environment through soil surface applications which then transport through the vadose zone to reach underlying groundwater receptors. Due to their unique properties and resulting transport and retention behaviors, PFAS in the vadose zone can be a persistent contaminant source to underlying groundwater systems. Determining the fraction of PFAS present in the mobile porewater relative to the total concentrations in soils is critical to understanding the risk posed by PFAS in vadose zone source areas. Lysimeters are instruments that have been used by agronomists and vadose zone researchers for decades to determine water flux and solute concentrations in unsaturated porewater. Lysimeters have recently been developed as a critical tool for field investigations and characterizations of PFAS impacted source zones.  
 
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<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
 
'''Related Article(s):'''
 
'''Related Article(s):'''
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*[[Contaminated Sediments - Introduction]]
 
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*[[In Situ Treatment of Contaminated Sediments with Activated Carbon]]
 
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*[[Sediment Capping]]
 
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*[[Passive Sampling of Sediments]]
 
  
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'''Contributor(s):'''
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*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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*Richard J. Wenning
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*[[PFAS Transport and Fate]]
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*Sabine E. Apitz
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*[[PFAS Toxicology and Risk Assessment]]
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*[[Mass Flux and Mass Discharge]]
  
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'''Key Resource(s):'''
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'''Contributors:''' Dr. John F. Stults, Dr. Charles Schaefer
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* Contaminated Sediment Remediation Guidance for Hazardous Waste Sites<ref name="USEPA2005">United States Environmental Protection Agency (USEPA), 2005. Contaminated Sediment Remediation Guidance for Hazardous Waste Sites. Office of Solid Waste and Emergency Response, Washington, D.C. EPA-540-R-05-012. OSWER 9355.0-85.  Free download from: [https://semspub.epa.gov/work/HQ/174471.pdf USEPA]&nbsp;&nbsp; [[Media: 2005-USEPA-Contaminated_Sediment_Remediation_Guidance_for_Hazardous_Waste_Sites.pdf | Report.pdf]]</ref>
 
  
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* Principles for Environmental Risk Assessment of the Sediment Compartment<ref name="Tarazona2014">Tarazona, J.V., Versonnen, B., Janssen, C., De Laender, F., Vangheluwe, M. and Knight, D., 2014. Principles for Environmental Risk Assessment of the Sediment Compartment: Proceedings of the Topical Scientific Workshop. 7-8 May 2013. European Chemicals Agency, Helsinki. Document ECHA-14-R-13-EN. Free download from: [https://echa.europa.eu/documents/10162/22816050/environmental_risk_assessment_final_en.pdf/3515b685-6601-40ce-bd48-3f8d5332c0f8 European Chemicals Agency]&nbsp;&nbsp; [[Media: ECHA-14-R-13-EN.pdf | Report.pdf]]</ref>
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'''Key Resources:'''
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*Assessment of PFAS in Collocated Soil and Porewater Samples at an AFFF-Impacted Source Zone: Field-Scale Validation of Suction Lysimeters<ref name="AndersonEtAl2022"/>
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* Assessing and managing contaminated sediments:  
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*PFAS Concentrations in Soil versus Soil Porewater: Mass Distributions and the Impact of Adsorption at Air-Water Interfaces<ref name="BrusseauGuo2022"/>
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:: Part I, Developing an Effective Investigation and Risk Evaluation Strategy<ref name="Apitz2005a">Apitz, S.E., Davis, J.W., Finkelstein, K., Hohreiter, D.W., Hoke, R., Jensen, R.H., Jersak, J., Kirtay, V.J., Mack, E.E., Magar, V.S. and Moore, D., 2005. Assessing and Managing Contaminated Sediments: Part I, Developing an Effective Investigation and Risk Evaluation Strategy. Integrated Environmental Assessment and Management, 1(1), pp. 2-8. [https://doi.org/10.1897/IEAM_2004a-002.1 DOI: 10.1897/IEAM_2004a-002.1] Free access article from: [https://setac.onlinelibrary.wiley.com/doi/epdf/10.1897/IEAM_2004a-002.1 Society of Environmental Toxicology and Chemistry]&nbsp;&nbsp; [[Media: Apitz2005a.pdf | Report.pdf]]</ref>
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*Using Suction Lysimeters for Determining the Potential of Per- and Polyfluoroalkyl Substances to Leach from Soil to Groundwater: A Review<ref name="CostanzaEtAl2025"/>
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:: Part II, Evaluating Risk and Monitoring Sediment Remedy Effectiveness<ref name="Apitz2005b">Apitz, S.E., Davis, J.W., Finkelstein, K., Hohreiter, D.W., Hoke, R., Jensen, R.H., Jersak, J., Kirtay, V.J., Mack, E.E., Magar, V.S. and Moore, D., 2005b. Assessing and Managing Contaminated Sediments: Part II, Evaluating Risk and Monitoring Sediment Remedy Effectiveness. Integrated Environmental Assessment and Management, 1(1), pp.e1-e14. [https://doi.org/10.1897/IEAM_2004a-002e.1 DOI: 10.1897/IEAM_2004a-002e.1]</ref>
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*Use of Lysimeters for Monitoring Soil Water Balance Parameters and Nutrient Leaching<ref name="MeissnerEtAl2020"/>
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*PFAS Porewater Concentrations in Unsaturated Soil: Field and Laboratory Comparisons Inform on PFAS Accumulation at Air-Water Interfaces<ref name="SchaeferEtAl2024"/>
  
 
==Introduction==
 
==Introduction==
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Improving the management of [[Contaminated Sediments - Introduction | contaminated sediments]] is of growing concern globally. Sediment processes in both marine and freshwater environments are important to the function of aquatic ecosystems<ref name="Apitz2012">Apitz, S.E., 2012. Conceptualizing the role of sediment in sustaining ecosystem services: Sediment-Ecosystem Regional Assessment (SEcoRA), Science of the Total Environment, 415, pp. 9-30. [https://doi.org/10.1016/j.scitotenv.2011.05.060 DOI:10.1016/j.scitotenv.2011.05.060] Free download from: [https://d1wqtxts1xzle7.cloudfront.net/7588577/Apitz_SEcoRA%202012.pdf?1326618388=&response-content-disposition=inline%3B+filename%3DConceptualizing_the_role_of_sediment_in.pdf&Expires=1637094311&Signature=c2wczG59XxkitPjmBhc9PaODHJ8Vufg3gyzdG8tqGD6~mIVhLoz30E7eQNIghfMlH~jbch3KTVxMqD2AQFMQCSeXghIwqH~lXjGrEP07MJXCEgntzSW-V8Gws~33it5pEm9Ied64fSOvMLJR-PUXVr2OVTsVHQJHurHdGrtEmhUd90bKrC0NNlD28YLGQpkVUOlqa75e0K4sjPngwPUwUxhq18NAH6-1Uc3fQU5g5AjXwGph-VNe7EwzT-0do5OD056AsG-Eg8xIZi0ABJqMsg1wb92tIPpmmNy6ntdklHeN6tq~3IJFB7Tg8XYntQ-CGT8pYV9S7Kz14GhXVm9OQA__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA Academia.edu]</ref>, and many organisms rely on certain sediment quality and quantity characteristics for their life cycle<ref name="Hauer2018">Hauer, C., Leitner, P., Unfer, G., Pulg, U., Habersack, H. and Graf, W., 2018. The Role of Sediment and Sediment Dynamics in the Aquatic Environment. In: Schmutz S., Sendzimir J. (ed.s) Riverine Ecosystem Management. Aquatic Ecology Series, vol. 8, pp. 151-169. Springer. [https://doi.org/10.1007/978-3-319-73250-3_8 DOI: 10.1007/978-3-319-73250-3_8]  Open access book from: [https://library.oapen.org/bitstream/handle/20.500.12657/27726/1002280.pdf?seque#page=153 SpringerOpen]</ref>. Human health can also be affected by sediment conditions, either via direct contact, as a result of sediment impacts on water quality, or because of the strong influence sediments can have on the quality of fish and shellfish consumed by people<ref name="Greenfield2015">Greenfield, B.K., Melwani, A.R. and Bay, S.M., 2015. A Tiered Assessment Framework to Evaluate Human Health Risk of Contaminated Sediment. Integrated Environmental Assessment and Management, 11(3), pp. 459-473. [https://doi.org/10.1002/ieam.1610 DOI: 10.1002/ieam.1610]</ref>. A common approach to achieving the explicit management goals inherent in different sediment assessment frameworks in North America and elsewhere is the use of the ecological risk assessment (ERA)<ref name="USEPA1997a">US Environmental Protection Agency (USEPA), 1997. The Incidence and Severity of Sediment Contamination in Surface Waters of the United States: Volume 1, National Sediment Quality Survey. EPA-823R-97-006. Washington, DC. [[Media: EPA-823-R-97-006.pdf | Report.pdf]]</ref>. An ERA “evaluates the likelihood and magnitude of adverse effects from exposure to a chemical for organisms, such as animals, plants, or microbes, in the environment”<ref name="SETAC2018">Society of Environmental Toxicology and Chemistry (SETAC), 2018. Technical Issue Paper: Environmental Risk Assessment of Chemicals. SETAC, Pensacola, FL. 5 pp. Free download from: [https://cdn.ymaws.com/www.setac.org/resource/resmgr/publications_and_resources/setac_tip_era.pdf SETAC]&nbsp;&nbsp; [[Media: setac_tip_era2018.pdf | Report.pdf]]</ref>. An ERA provides information relevant to the management decision-making process<ref name="Stahl2001">Stahl, R.G., Bachman, R., Barton, A., Clark, J., deFur, P., Ells, S., Pittinger, C., Slimak, M., Wentsel, R., 2001. Risk Management: Ecological Risk-Based Decision Making. SETAC Press, Pensacola, FL, 222 pp. ISBN: 978-1-880611-26-5</ref>. It should be performed in a scientifically based, defensible manner that is cost-effective and protective of human health and the environment<ref name="CNO1999">Chief of Naval Operations (CNO), 1999. Navy Policy for Conducting Ecological Risk Assessments, Letter 5090, Ser N453E/9U595355, dated 05 April 99. Department of the Navy, Washington, DC. Free download from: [https://www.navfac.navy.mil/content/dam/navfac/Specialty%20Centers/Engineering%20and%20Expeditionary%20Warfare%20Center/Environmental/Restoration/er_pdfs/gpr/cno-ev-pol-era-19990405.pdf the US Navy]&nbsp;&nbsp; [[Media: CNO1999.pdf | Report.pdf]]</ref>. Therefore, science-based methods for assessing sediment quality and use of risk-based decision-making in sediment management are important for identifying conditions suspected to adversely affect ecological and human services provided by sediments, and predicting the likely consequences of different sediment management actions<ref name="Bridges2006">Bridges, T.S., Apitz, S.E., Evison, L., Keckler, K., Logan, M., Nadeau, S. and Wenning, R.J., 2006. Risk‐Based Decision Making to Manage Contaminated Sediments. Integrated Environmental Assessment and Management, 2(1), pp. 51-58. [https://doi.org/10.1002/ieam.5630020110 DOI: 10.1002/ieam.5630020110] Free access article from: [https://setac.onlinelibrary.wiley.com/doi/epdf/10.1002/ieam.5630020110 SETAC]</ref><ref name="Apitz2011">Apitz, S.E., 2011. Integrated Risk Assessments for the Management of Contaminated Sediments in Estuaries and Coastal Systems. In: Wolanski, E. and McLusky, D.S. (eds.) Treatise on Estuarine and Coastal Science, Vol 4, pp. 311–338. Waltham: Academic Press. ISBN: 9780123747112</ref>.
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Lysimeters are devices that are placed in the subsurface above the groundwater table to monitor the movement of water through the soil<ref name="GossEhlers2009">Goss, M.J., Ehlers, W., 2009. The Role of Lysimeters in the Development of Our Understanding of Soil Water and Nutrient Dynamics in Ecosystems. Soil Use and Management, 25(3), pp. 213–223. [https://doi.org/10.1111/j.1475-2743.2009.00230.x doi: 10.1111/j.1475-2743.2009.00230.x]</ref><ref>Pütz, T., Fank, J., Flury, M., 2018. Lysimeters in Vadose Zone Research. Vadose Zone Journal, 17 (1), pp. 1-4. [https://doi.org/10.2136/vzj2018.02.0035 doi: 10.2136/vzj2018.02.0035]&nbsp; [[Media: PutzEtAl2018.pdf | Open Access Article]]</ref><ref name="CostanzaEtAl2025">Costanza, J., Clabaugh, C.D., Leibli, C., Ferreira, J., Wilkin, R.T., 2025. Using Suction Lysimeters for Determining the Potential of Per- and Polyfluoroalkyl Substances to Leach from Soil to Groundwater: A Review. Environmental Science and Technology, 59(9), pp. 4215-4229. [https://doi.org/10.1021/acs.est.4c10246 doi: 10.1021/acs.est.4c10246]</ref>. Lysimeters have historically been used in agricultural sciences for monitoring nutrient or contaminant movement, soil moisture release curves, natural drainage patterns, and dynamics of plant-water interactions<ref name="GossEhlers2009"/><ref>Bergström, L., 1990. Use of Lysimeters to Estimate Leaching of Pesticides in Agricultural Soils. Environmental Pollution, 67 (4), 325–347. [https://doi.org/10.1016/0269-7491(90)90070-S doi: 10.1016/0269-7491(90)90070-S]</ref><ref>Dabrowska, D., Rykala, W., 2021. A Review of Lysimeter Experiments Carried Out on Municipal Landfill Waste. Toxics, 9(2), Article 26. [https://doi.org/10.3390/toxics9020026 doi: 10.3390/toxics9020026]&nbsp; [[Media: Dabrowska Rykala2021.pdf | Open Access Article]]</ref><ref>Fernando, S.U., Galagedara, L., Krishnapillai, M., Cuss, C.W., 2023. Lysimeter Sampling System for Optimal Determination of Trace Elements in Soil Solutions. Water, 15(18), Article 3277. [https://doi.org/10.3390/w15183277 doi: 10.3390/w15183277]&nbsp; [[Media: FernandoEtAl2023.pdf | Open Access Article]]</ref><ref name="MeissnerEtAl2020">Meissner, R., Rupp, H., Haselow, L., 2020. Use of Lysimeters for Monitoring Soil Water Balance Parameters and Nutrient Leaching. In: Climate Change and Soil Interactions. Elsevier, pp. 171-205. [https://doi.org/10.1016/B978-0-12-818032-7.00007-2 doi: 10.1016/B978-0-12-818032-7.00007-2]</ref><ref name="RogersMcConnell1993">Rogers, R.D., McConnell, J.W. Jr., 1993. Lysimeter Literature Review, Nuclear Regulatory Commission Report Numbers: NUREG/CR--6073, EGG--2706. [https://www.osti.gov/] ID: 10183270. [https://doi.org/10.2172/10183270 doi: 10.2172/10183270]&nbsp; [[Media: RogersMcConnell1993.pdf | Open  Access Article]]</ref><ref>Sołtysiak, M., Rakoczy, M., 2019. An Overview of the Experimental Research Use of Lysimeters. Environmental and Socio-Economic Studies, 7(2), pp. 49-56. [https://doi.org/10.2478/environ-2019-0012 doi: 10.2478/environ-2019-0012]&nbsp; [[Media: SołtysiakRakoczy2019.pdf | Open Access Article]]</ref><ref name="Stannard1992">Stannard, D.I., 1992. Tensiometers—Theory, Construction, and Use. Geotechnical Testing Journal, 15(1), pp. 48-58. [https://doi.org/10.1520/GTJ10224J doi: 10.1520/GTJ10224J]</ref><ref name="WintonWeber1996">Winton, K., Weber, J.B., 1996. A Review of Field Lysimeter Studies to Describe the Environmental Fate of Pesticides. Weed Technology, 10(1), pp. 202-209. [https://doi.org/10.1017/S0890037X00045929 doi: 10.1017/S0890037X00045929]</ref>. Recently, there has been strong interest in the use of lysimeters to measure and monitor movement of per- and polyfluoroalkyl substances (PFAS) through the vadose zone<ref name="Anderson2021">Anderson, R.H., 2021. The Case for Direct Measures of Soil-to-Groundwater Contaminant Mass Discharge at AFFF-Impacted Sites. Environmental Science and Technology, 55(10), pp. 6580-6583. [https://doi.org/10.1021/acs.est.1c01543 doi: 10.1021/acs.est.1c01543]</ref><ref name="AndersonEtAl2022">Anderson, R.H., Feild, J.B., Dieffenbach-Carle, H., Elsharnouby, O., Krebs, R.K., 2022. Assessment of PFAS in Collocated Soil and Porewater Samples at an AFFF-Impacted Source Zone: Field-Scale Validation of Suction Lysimeters. Chemosphere, 308(1), Article 136247. [https://doi.org/10.1016/j.chemosphere.2022.136247 doi: 10.1016/j.chemosphere.2022.136247]</ref><ref name="SchaeferEtAl2024">Schaefer, C.E., Nguyen, D., Fang, Y., Gonda, N., Zhang, C., Shea, S., Higgins, C.P., 2024. PFAS Porewater Concentrations in Unsaturated Soil: Field and Laboratory Comparisons Inform on PFAS Accumulation at Air-Water Interfaces. Journal of Contaminant Hydrology, 264, Article 104359. [https://doi.org/10.1016/j.jconhyd.2024.104359 doi: 10.1016/j.jconhyd.2024.104359]&nbsp; [[Media: SchaeferEtAl2024.pdf | Open Access Manuscript]]</ref><ref name="SchaeferEtAl2023">Schaefer, C.E., Lavorgna, G.M., Lippincott, D.R., Nguyen, D., Schaum, A., Higgins, C.P., Field, J., 2023. Leaching of Perfluoroalkyl Acids During Unsaturated Zone Flushing at a Field Site Impacted with Aqueous Film Forming Foam. Environmental Science and Technology, 57(5), pp. 1940-1948. [https://doi.org/10.1021/acs.est.2c06903 doi: 10.1021/acs.est.2c06903]</ref><ref name="SchaeferEtAl2022">Schaefer, C.E., Lavorgna, G.M., Lippincott, D.R., Nguyen, D., Christie, E., Shea, S., O’Hare, S., Lemes, M.C.S., Higgins, C.P., Field, J., 2022. A Field Study to Assess the Role of Air-Water Interfacial Sorption on PFAS Leaching in an AFFF Source Area. Journal of Contaminant Hydrology, 248, Article 104001. [https://doi.org/10.1016/j.jconhyd.2022.104001 doi: 10.1016/j.jconhyd.2022.104001]&nbsp; [[Media: SchaeferEtAl2022.pdf | Open Access Manuscript]]</ref><ref name="QuinnanEtAl2021">Quinnan, J., Rossi, M., Curry, P., Lupo, M., Miller, M., Korb, H., Orth, C., Hasbrouck, K., 2021. Application of PFAS-Mobile Lab to Support Adaptive Characterization and Flux-Based Conceptual Site Models at AFFF Releases. Remediation, 31(3), pp. 7-26. [https://doi.org/10.1002/rem.21680 doi: 10.1002/rem.21680]</ref>. PFAS are frequently introduced to the environment through land surface application and have been found to be strongly retained within the upper 5 feet of soil<ref name="BrusseauEtAl2020">Brusseau, M.L., Anderson, R.H., Guo, B., 2020. PFAS Concentrations in Soils: Background Levels versus Contaminated Sites. Science of The Total Environment, 740, Article 140017. [https://doi.org/10.1016/j.scitotenv.2020.140017 doi: 10.1016/j.scitotenv.2020.140017]</ref><ref name="BiglerEtAl2024">Bigler, M.C., Brusseau, M.L., Guo, B., Jones, S.L., Pritchard, J.C., Higgins, C.P., Hatton, J., 2024. High-Resolution Depth-Discrete Analysis of PFAS Distribution and Leaching for a Vadose-Zone Source at an AFFF-Impacted Site. Environmental Science and Technology, 58(22), pp. 9863-9874. [https://doi.org/10.1021/acs.est.4c01615 doi: 10.1021/acs.est.4c01615]</ref>. PFAS recalcitrance in the vadose zone means that environmental program managers and consultants need a cost-effective way of monitoring concentration conditions within the vadose zone. Repeated soil sampling and extraction processes are time consuming and only give a representative concentration of total PFAS in the matrix<ref name="NickersonEtAl2020">Nickerson, A., Maizel, A.C., Kulkarni, P.R., Adamson, D.T., Kornuc, J. J., Higgins, C.P., 2020. Enhanced Extraction of AFFF-Associated PFASs from Source Zone Soils. Environmental Science and Technology, 54(8), pp. 4952-4962. [https://doi.org/10.1021/acs.est.0c00792 doi: 10.1021/acs.est.0c00792]</ref>, not what is readily transportable in mobile porewater<ref name="SchaeferEtAl2023"/><ref name="StultsEtAl2024">Stults, J.F., Schaefer, C.E., Fang, Y., Devon, J., Nguyen, D., Real, I., Hao, S., Guelfo, J.L., 2024. Air-Water Interfacial Collapse and Rate-Limited Solid Desorption Control Perfluoroalkyl Acid Leaching from the Vadose Zone. Journal of Contaminant Hydrology, 265, Article 104382. [https://doi.org/10.1016/j.jconhyd.2024.104382 doi: 10.1016/j.jconhyd.2024.104382]&nbsp; [[Media: StultsEtAl2024.pdf | Open Access Manuscript]]</ref><ref name="StultsEtAl2023">Stults, J.F., Choi, Y.J., Rockwell, C., Schaefer, C.E., Nguyen, D.D., Knappe, D.R.U., Illangasekare, T.H., Higgins, C.P., 2023. Predicting Concentration- and Ionic-Strength-Dependent Air–Water Interfacial Partitioning Parameters of PFASs Using Quantitative Structure–Property Relationships (QSPRs). Environmental Science and Technology, 57(13), pp. 5203-5215. [https://doi.org/10.1021/acs.est.2c07316 doi: 10.1021/acs.est.2c07316]</ref><ref name="BrusseauGuo2022">Brusseau, M.L., Guo, B., 2022. PFAS Concentrations in Soil versus Soil Porewater: Mass Distributions and the Impact of Adsorption at Air-Water Interfaces. Chemosphere, 302, Article 134938. [https://doi.org/10.1016/j.chemosphere.2022.134938 doi: 10.1016/j.chemosphere.2022.134938]&nbsp; [[Media: BrusseauGuo2022.pdf | Open Access Manuscript]]</ref>. Fortunately, lysimeters have been found to be a viable option for monitoring the concentration of PFAS in the mobile porewater phase in the vadose zone<ref name="Anderson2021"/><ref name="AndersonEtAl2022"/>. Note that while some lysimeters, known as weighing lysimeters, can directly measure water flux, the most commonly utilized lysimeters in PFAS investigations only provide measurements of porewater concentrations.
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Sediment risk assessment is increasingly used by governmental agencies to support sediment management in freshwater, estuarine, and marine environments. Strategies for sediment management encompass a wide variety of actions, from removal, capping or treatment of contaminated sediment to the monitoring of natural processes, including sedimentation, binding, and bio- and photo-degradation that serve to reduce the potential threat to aquatic life over time. It is not uncommon to revisit a sediment risk assessment periodically to check how changed environmental conditions reflected in sediment and biotic sampling work has either reduced or exacerbated the threats identified in the initial assessment.
 
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At present, several countries lack common recommendations specific to conducting risk assessment of contaminated sediments<ref name="Bruce2020">Bruce, P., Sobek, A., Ohlsson, Y. and Bradshaw, C., 2020. Risk assessments of contaminated sediments from the perspective of weight of evidence strategies – a Swedish case study. Human and Ecological Risk Assessment, 27(5), pp. 1366-1387. [https://doi.org/10.1080/10807039.2020.1848414 DOI: 10.1080/10807039.2020.1848414]&nbsp;&nbsp; [https://www.tandfonline.com/doi/full/10.1080/10807039.2020.1848414 Website]</ref>. In the European Union, sediment has played a secondary role in the Water Framework Directive (WFD), with most quality standards being focused on water with the option for the development of national standards for sediment and biota for bioaccumulative compounds. The Common Implementation Strategy (CIS) in 2010 provided guidance on the monitoring of contaminants in sediments and biota, but not on risk-based decision-making<ref name="EC2010">European Commission, 2010. Common Implementation Strategy For The Water Framework Directive (2000/60/EC), Technical Report - 2010 – 041; Guidance document No. 25 On Chemical Monitoring Of Sediment And Biota Under The Water Framework Directive. 82pp. ISBN 978-92-79-16224-4.  [https://op.europa.eu/en/publication-detail/-/publication/5ff7a8ec-995b-4d90-a140-0cc9b4bf980d  Free download]</ref>. There are efforts underway to incorporate guidance for management of contaminated sediment in the Common Implementation Strategy in 2021<ref name="Brils2020">Brils, J., 2020. Including sediment in European River Basin Management Plans: Twenty years of work by SedNet. Journal of Soils and Sediments, 20(12), pp.4229-4237. [https://doi.org/10.1007/s11368-020-02782-1 DOI: 10.1007/s11368-020-02782-1]&nbsp;&nbsp; [https://link.springer.com/content/pdf/10.1007/s11368-020-02782-1.pdf Open Access Article]</ref>. Sediment risk assessment guidance from Norway, Canada, the Netherlands, and the US are most often referenced when assessing the risks from contaminated sediments<ref name="Bruce2020"/><ref name="Birch2018">Birch, G.F., 2018. A review of chemical-based sediment quality assessment methodologies for the marine environment. Marine Pollution Bulletin, 133, pp.218-232. [https://doi.org/10.1016/j.marpolbul.2018.05.039 DOI: 10.1016/j.marpolbul.2018.05.039]</ref><ref name="Kwok2014">Kwok, K.W., Batley, G.E., Wenning, R.J., Zhu, L., Vangheluwe, M. and Lee, S., 2014. Sediment quality guidelines: challenges and opportunities for improving sediment management. Environmental Science and Pollution Research, 21(1), pp. 17-27. [https://doi.org/10.1007/s11356-013-1778-7 DOI: 10.1007/s11356-013-1778-7] Free download from: [https://www.researchgate.net/profile/Graeme-Batley/publication/236836992_Sediment_quality_guidelines_Challenges_and_opportunities_for_improving_sediment_management/links/0c96052b8a8f5ad0c6000000/Sediment-quality-guidelines-Challenges-and-opportunities-for-improving-sediment-management.pdf ResearchGate]</ref>. Some European countries, such as Norway, have focused their risk assessment guidance on the assessment of sediment conditions relative to general chemical thresholds, while in North America, risk assessment guidance focuses on site- or region-specific conditions<ref name="Apitz2008">Apitz, S.E., 2008. Is risk-based, sustainable sediment management consistent with European policy?. Journal of Soils and Sediments, 8(6), p.461-466. [https://doi.org/10.1007/s11368-008-0039-8 DOI: 10.1007/s11368-008-0039-8]&nbsp;&nbsp; Free download from: [https://d1wqtxts1xzle7.cloudfront.net/7081664/apitz%20jss%20risk-based%20europe-with-cover-page-v2.pdf?Expires=1637274548&Signature=KqIoYyQ6VPAFN7lKHJMVC3bbn00RRMCR68bsQNBGrFJ9kbX5BnI-aucFCqRgVUNUb1lu0Q4tzUkCjPXJRGBsTA3OnbH8Ol9sNoXZ001aOwG7tKuV8qEblGiqtQUHh9GdiNAPQsm50f~E1iozL9a6imApWjqK8oFCfdUbcUd1oaW7PCDu28KWN-k5ddefWNZBAzGIdaWt3mBJ1EYeKRrp4F6Codlny3pWCT5MpA~c4c0IKq8L7Uj~-VxH5LXjFDd7cm07JeOY8S5rlxgF1zMoTIggMo5v2M3AS3CO2SAqy7yR3HC-IjUx3RsMqKa5eS2jT1ADiXcqeVygCdCCXza05g__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA Academia.edu]</ref>.
 
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There is general consensus from a regulatory perspective, globally, on the importance of sediment risk assessment. Technical guidance documents prepared by Canada<ref name="Fletcher2008">Fletcher, R., Welsh, P. and Fletcher, T., 2008. Guidelines for Identifying, Assessing, and Managing Contaminated Sediments in Ontario. Ontario Ministry of the Environment. PIBS6658e. [http://www.ene.gov.on.ca/publications/6658e Website]</ref><ref name="HealthCanada2017">Health Canada, 2017. Supplemental Guidance on Human Health Risk Assessment of Contaminated Sediments: Direct Contact Pathway, Federal Contaminated Site Risk Assessment in Canada. ISBN: 978-0-660-07989-9. Cat.: H144-41/2017E-PDF. Pub. 160382. Free download from: [https://publications.gc.ca/collections/collection_2018/sc-hc/H144-41-2017-eng.pdf Health Canada]&nbsp;&nbsp; [[Media: HealthCanada2117.pdf | Report.pdf]]</ref> , the European Union<ref name="Tarazona2014"/>, and the United States Environmental Protection Agency (USEPA)<ref name="USEPA2005"/> advise a flexible, tiered approach for sediment risk assessment. Sediment quality guidelines in many countries reflect the scientific importance of including certain sediment-specific measurement and biotic assessment endpoints, as well as certain physical sediment processes and chemical transformation processes potentially affecting biotic responses to contaminant exposure in the sediment<ref name="Wenning2005">Wenning, R.J. Batley, G.E., Ingersoll, C.G., and Moore, D.W., (eds), 2005. Use Of Sediment Quality Guidelines And Related Tools For The Assessment Of Contaminated Sediments. SETAC, Pensacola, FL. 815 pp. ISBN 1-880611-71-6.</ref>. New risk assessment methods continue to emerge in the scientific literature<ref name="Benson2018">Benson, N.U., Adedapo, A.E., Fred-Ahmadu, O.H., Williams, A.B., Udosen, E.D., Ayejuyo, O.O. and Olajire, A.A., 2018. A new method for assessment of sediment-associated contamination risks using multivariate statistical approach. MethodsX, 5, pp. 268-276. [https://doi.org/10.1016/j.mex.2018.03.005 DOI: 10.1016/j.mex.2018.03.005]&nbsp;&nbsp; [https://www.sciencedirect.com/science/article/pii/S2215016118300438/pdfft?md5=85b8a3a1062310e4c7c4a06e670e66c4&pid=1-s2.0-S2215016118300438-main.pdf  Free Access Article]&nbsp;&nbsp; [[Media: Benson2018.pdf | Report.pdf]]</ref><ref name="Saeedi2015">Saeedi, M. and Jamshidi-Zanjani, A., 2015. Development of a new aggregative index to assess potential effect of metals pollution in aquatic sediments. Ecological Indicators, 58, pp. 235-243. [https://doi.org/10.1016/j.ecolind.2015.05.047 DOI: 10.1016/j.ecolind.2015.05.047]  Free download from: [https://www.academia.edu/download/49801572/mRAC_published.pdf Academis.edu]</ref><ref name="Vaananen2018">Väänänen, K., Leppänen, M.T., Chen, X. and Akkanen, J., 2018. Metal bioavailability in ecological risk assessment of freshwater ecosystems: from science to environmental management. Ecotoxicology and Environmental Safety, 147, pp. 430-446.  [https://doi.org/10.1016/j.ecoenv.2017.08.064 DOI: 10.1016/j.ecoenv.2017.08.064]</ref>. These new methods, however, are likely to be considered supplemental to the more generalized framework shared globally.
 
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==Fundamentals of Sediment Risk Assessment==
 
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[[File: SedRiskFig1.PNG | thumb |700px|Figure 1. Schematic of the sediment risk assessment process]]
 
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Whereas there is strong evidence of anthropogenic impacts on the benthic community at many sediment sites, the degree of toxicity (or even its presence or absence) cannot be predicted with absolute certainty using contaminant concentrations alone<ref name="Apitz2011"/>. A sediment ERA should include lines of evidence (LOEs) derived from several different investigations<ref name="Wenning2005"/>. One common approach to develop several of these LOEs in a decision framework is the triad approach. Triad-based assessment frameworks require evidence based on sediment chemistry, toxicity, and benthic community structure (possibly including evidence of bioaccumulation) to designate sediment as toxic and requiring management or control<ref name="Chapman1996">Chapman, P.M., Paine, M.D., Arthur, A.D., Taylor, L.A., 1996. A triad study of sediment quality associated with a major, relatively untreated marine sewage discharge. Marine Pollution Bulletin 32(1), pp. 47–64.  [https://doi.org/10.1016/0025-326X(95)00108-Y DOI: 10.1016/0025-326X(95)00108-Y]</ref>. In some decision frameworks, particularly those used to establish and rank risks in national or regional programs, all components of the triad are carried out simultaneously, with the various LOEs combined to support weight of evidence (WOE) decision making. In other frameworks, LOEs are tiered to minimize costs by collecting only the data required to make a decision and leaving some potential consequences and uncertainties unresolved.
 
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Figure 1 provides an overview of a sediment risk assessment process. The first step, and a fundamental requirement, in sediment risk assessment, involves scoping and planning prior to undertaking work. This is important for optimizing the available assessment resource and conducting an assessment at the appropriate level of detail that is transparent and free, to the extent possible, of any bias or preconceived beliefs concerning the outcome<ref name="Hill2000">Hill, R.A., Chapman, P.M., Mann, G.S. and Lawrence, G.S., 2000. Level of Detail in Ecological Risk Assessments. Marine Pollution Bulletin, 40(6), pp. 471-477. [https://doi.org/10.1016/S0025-326X(00)00036-9 DOI: 10.1016/S0025-326X(00)00036-9]</ref>.
 
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===Screening-Level Risk Assessment (SLRA)===
 
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Technical guidance in many countries strongly encourages sediment risk assessment to begin with a Screening-Level Risk Assessment (SLRA)<ref name="USEPA2005"/><ref name="Tarazona2014"/><ref name="Fletcher2008"/>. The SLRA is a simplified risk assessment conducted using limited data and often assuming certain, generally conservative and generic, sediment characteristics, sediment contaminant levels, and exposure parameters in the absence of sufficient readily available information<ref name="Hope2006">Hope, B.K., 2006. An examination of ecological risk assessment and management practices. Environment International, 32(8), pp. 983-995.  [https://doi.org/10.1016/j.envint.2006.06.005 DOI: 10.1016/j.envint.2006.06.005]</ref><ref name="Weinstein2010">Weinstein, J.E., Crawford, K.D., Garner, T.R. and Flemming, A.J., 2010. Screening-level ecological and human health risk assessment of polycyclic aromatic hydrocarbons in stormwater detention pond sediments of Coastal South Carolina, USA. Journal of Hazardous Materials, 178(1-3), pp. 906-916.  [https://doi.org/10.1016/j.jhazmat.2010.02.024 DOI: 10.1016/j.jhazmat.2010.02.024]</ref><ref name="Rak2008">Rak, A., Maly, M.E., Tracey, G., 2008. A Guide to Screening Level Ecological Risk Assessment, TG-090801. Tri-Services Ecological Risk Assessment Working Group (TSERAWG), U.S. Army Biological Technical Assistance Group (BTAG), Aberdeen Proving Ground, MD. 26 pp.  [https://usaphcapps.amedd.army.mil/erawg/SLERA.pdf Free Download]&nbsp;&nbsp; [[Media: Rak2008.pdf | Report.pdf]]</ref><ref name="USEPA2001">US Environmental Protection Agency (USEPA), 2001. ECO Update. The Role of Screening-Level Risk Assessments and Refining Contaminants of Concern in Baseline Ecological Risk Assessments. EPA 540/F-01/014. Washington, D.C. [https://www.epa.gov/sites/default/files/2015-09/documents/slera0601.pdf  Website]&nbsp;&nbsp; [[Media: EPA 540_F-01_014.pdf  | Report.pdf]]</ref>.
 
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The analysis is often semi-quantitative, and typically includes comparisons of various chemical and physical sediment conditions to threshold limits established in national or international regulations or by generally accepted scientific interpretations. US technical guidance encourages the comparison of contaminant measurements in water, sediment, or soil to National Oceanographic and Atmospheric Administration (NOAA) sediment screening quick reference tables, or SQuiRT cards, which list quality guidelines from a range of sources, based on differing narrative intent<ref name="Buchman2008">Buchman, M.F., 2008. Screening Quick Reference Tables (SQuiRTs), NOAA OR&R Report 08-1. National Oceanographic and Atmospheric Administration (NOAA), Coastal Protection and Restoration Protection Division. 34 pp. [https://repository.library.noaa.gov/view/noaa/9327  website]&nbsp;&nbsp; [[Media: SQuiRTs2008.pdf | Report.pdf]]</ref>.
 
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The screening level approach is intended to minimize the chances of concluding that there is no risk when, in fact, risk may exist. Thus, the results of an SLRA may indicate contaminants or sediments in certain locations in the original study area initially thought to be of concern are acceptable (i.e., contaminant levels are below threshold levels), or that contaminant levels are high enough to indicate immediate action without further assessment (e.g., contaminant levels are well above probable-effects guidelines). In other cases, or at other locations, SLRA may indicate the need for further examination. Further study may apply site-specific, rather than generic and conservative assumptions, to reduce uncertainty.
 
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===Detailed Risk Assessment===
 
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Detailed sediment risk assessment is conducted when SLRA results indicate one or more sediment contaminants exceed background conditions or regulatory threshold limits. For some contaminants, such as the dioxins and other persistent, bioaccumulative, and toxic substances (PBTs), technical guidance may mandate further examination, regardless of whether threshold levels are exceeded<ref name="Solomon2013">Solomon, K., Matthies, M., and Vighi, M., 2013. Assessment of PBTs in the European Union: a critical assessment of the proposed evaluation scheme with reference to plant protection products. Environmental Sciences Europe, 25(1), pp. 1-17.  [https://doi.org/10.1186/2190-4715-25-10 DOI: 10.1186/2190-4715-25-10]&nbsp;&nbsp; [https://enveurope.springeropen.com/articles/10.1186/2190-4715-25-10 Open Access Article]</ref><ref name="Matthies2016">Matthies, M., Solomon, K., Vighi, M., Gilman, A. and Tarazona, J.V., 2016. The origin and evolution of assessment criteria for persistent, bioaccumulative and toxic (PBT) chemicals and persistent organic pollutants (POPs). Environmental Science: Processes and Impacts, 18(9), pp. 1114-1128.  [https://doi.org/10.1039/C6EM00311G DOI: 10.1039/C6EM00311G]</ref>. Detailed sediment risk assessment typically follows a three-step framework similar to that described for ecological risk assessment - problem formulation, exposure analysis, and risk characterization<ref name="Suter2008">Suter, G.W., 2008. Ecological Risk Assessment in the United States Environmental Protection Agency: A Historical Overview. Integrated Environmental Assessment And Management, 4(3), pp. 285-289.  [https://doi.org/10.1897/IEAM_2007-062.1 DOI: 10.1897/IEAM_2007-062.1]&nbsp;&nbsp; Free download from: [https://bioone.org/journals/integrated-environmental-assessment-and-management/volume-4/issue-3/IEAM_2007-062.1/Ecological-Risk-Assessment-in-the-United-States-Environmental-Protection-Agency/10.1897/IEAM_2007-062.1.pdf?casa_token=ieq3Cnc-YdIAAAAA:_MH-gpnwpJKvZSV2Qew43Y4ocdgADq1HvugpvmrblcGONMJgvIjYB52zQnXn_oAUW0gTy5GAkfY BioOne]</ref>.
 
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US sediment management guidance describes a detailed risk assessment process similar to that followed for US ecological risk assessment<ref name="USEPA2005"/>. The first step is problem formulation. It involves defining chemical and physical conditions, delineating the spatial footprint of the sediment area to be examined, and identifying the human uses and ecological features of the sediment. Historical data are included in this initial step to better understand the results of biota, sediment, and water sampling as well as laboratory toxicity testing results. The SLRA is often included as a part of problem formulation.
 
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The second step is exposure analysis. This step includes the identification of pathways by which human and aquatic organisms might directly or indirectly contact contaminants in the sediment. The exposure route (i.e., ingestion, dermal, or inhalation of particulates or gaseous emissions) and both the frequency and duration of contact (i.e., hourly, daily, or seasonally) are determined for each contaminant exposure pathway and human and ecological receptor. The environmental fate of the contaminant, factors affecting uptake, and the overall exposure dose are included in the calculation of the level of contaminant exposure. The exposure analysis also includes an effects assessment, whereby the biological response and associated level required to manifest different biological responses are determined for each contaminant.
 
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The third step is risk-characterization. It involves calculating the risks for each human and ecological receptor posed by each sediment contaminant, as well as the cumulative risk associated with the combined exposure to all contaminants exerting similar biological effects. An uncertainty analysis is often included in this step of the risk assessment to convey where knowledge or data are lacking regarding the presence of the contaminant in the sediment, the biological response associated with exposure to the contaminant, or the behavior of the receptor with respect to contact with the sediment. A sensitivity analysis also may be conducted to convey the range of exposures (lowest, typical, and worst-case) and risks associated with changes in key assumptions and parameter values used in the exposure calculations and effects assessment.
 
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==Key Considerations==
 
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===Stakeholder Engagement===
 
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Stakeholder involvement is widely acknowledged as an important element of [[Wikipedia: Dredging | dredged]] material management<ref name="Collier2014">Collier, Z.A., Bates, M.E., Wood, M.D. and Linkov, I., 2014. Stakeholder engagement in dredged material management decisions. Science of the Total Environment, 496, pp. 248-256.  [https://doi.org/10.1016/j.scitotenv.2014.07.044 DOI: 10.1016/j.scitotenv.2014.07.044]  Free download from: [https://www.researchgate.net/profile/Matthew-Bates-9/publication/264460412_Stakeholder_Engagement_in_Dredged_Material_Management_Decisions/links/5a9d50fbaca2721e3f32adea/Stakeholder-Engagement-in-Dredged-Material-Management-Decisions.pdf ResearchGate]</ref>, sediment remediation<ref name="Oen2010">Oen, A.M.P., Sparrevik, M., Barton, D.N., Nagothu, U.S., Ellen, G.J., Breedveld, G.D., Skei, J. and Slob, A., 2010. Sediment and society: an approach for assessing management of contaminated sediments and stakeholder involvement in Norway. Journal of Soils and Sediments, 10(2), pp. 202-208.  [https://doi.org/10.1007/s11368-009-0182-x DOI: 10.1007/s11368-009-0182-x]</ref>, and other environmental and sediment related activities<ref name="Gerrits2004">Gerrits, L. and Edelenbos, J., 2004. Management of Sediments Through Stakeholder Involvement. Journal of Soils and Sediments, 4(4), pp. 239-246.  [https://doi.org/10.1007/BF02991120 DOI: 10.1007/BF02991120]</ref><ref name="Braun2019">Braun, A.B., da Silva Trentin, A.W., Visentin, C. and Thomé, A., 2019. Sustainable remediation through the risk management perspective and stakeholder involvement: A systematic and bibliometric view of the literature. Environmental Pollution, 255(1), p.113221.  [https://doi.org/10.1016/j.envpol.2019.113221 DOI: 10.1016/j.envpol.2019.113221]</ref>.
 
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Sediment management, particularly at the river basin scale, involves a wide variety of different environmental, governmental, and societal issues<ref name="Liu2018">Liu, C., Walling, D.E. and He, Y., 2018. The International Sediment Initiative case studies of sediment problems in river basins and their management. International Journal of Sediment Research, 33(2), pp. 216-219.  [https://doi.org/10.1016/j.ijsrc.2017.05.005 DOI: 10.1016/j.ijsrc.2017.05.005]  Free download from: [https://www.researchgate.net/profile/Cheng-Liu-43/publication/317032034_Review_The_International_Sediment_Initiative_Case_Studies_of_sediment_problems_in_river_basins_and_their_management/links/5f4f37d2299bf13a319703df/Review-The-International-Sediment-Initiative-Case-Studies-of-sediment-problems-in-river-basins-and-their-management.pdf ResearchGate]</ref>. Incorporating these different views, interests, and perspectives into a form that builds consensus for whatever actions and goals are in mind (e.g., commercial ports and shipping, navigation, flood protection, or habitat restoration) necessitates a formal stakeholder engagement process<ref name="Slob2008">Slob, A.F.L., Ellen, G.J. and Gerrits, L., 2008. Sediment management and stakeholder involvement. In: Sustainable Management of Sediment Resources, Vol. 4: Sediment Management at the River Basin Scale, Owens, P.N. (ed.), pp. 199-216. Elsevier.  [https://doi.org/10.1016/S1872-1990(08)80009-8 DOI: 10.1016/S1872-1990(08)80009-8]</ref>.
 
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Results from a three-year (2008-2010) [https://www.ngi.no/eng/Projects/Sediment-and-society Sediment and Society] research project funded by the Norwegian Research Council point to three important challenges that must be resolved for successful stakeholder engagement: (1) how to include people who have important management information and local knowledge, but not much influence in the decision-making process; (2) how to secure resources to ensure participation and (3) how to engage and motivate stakeholders to participate early in the sediment remediation planning process<ref name="Oen2010"/>.
 
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===Conceptual Site Model===
 
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The preparation of a conceptual site model (CSM) is a fundamental component of problem formulation and the first step in detailed sediment risk assessment. The CSM is a narrative and/or illustrative representation of the physical, chemical and biological processes that control the transport, migration and actual or potential impacts of sediment contamination to human and/or ecological receptors<ref name="NJDEP2019">New Jersey Department of Environmental Protection, 2019. Technical Guidance for Preparation and Submission of a Conceptual Site Model. Version 1.1. Site Remediation and Waste Management Program, Trenton, NJ. 46 pp. [https://www.nj.gov/dep/srp/guidance/srra/csm_tech_guidance.pdf Free download].</ref><ref name="USEPA2011">US Environmental Protection Agency, 2011. Guidance for the Development of Conceptual Models for a Problem Formulation Developed for Registration Review. Environmental Fate and Effects Division, Office of Pesticide Programs, Washington, D.C. [https://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/guidance-development-conceptual-models-problem Website]</ref>. The CSM should include a “food web” because the aquatic food web is an important exposure pathway by which contaminants in the sediment reach humans and pelagic aquatic life<ref name="Arnot2004">Arnot, J.A. and Gobas, F.A., 2004. A Food Web Bioaccumulation Model for Organic Chemicals in Aquatic Ecosystems. Environmental Toxicology and Chemistry, 23(10), pp. 2343-2355.  [https://doi.org/10.1897/03-438 DOI: 10.1897/03-438]</ref>.
 
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The CSM provides an early opportunity for critical examination of the interactions between sediment and the water column and the influence of groundwater inputs, surface runoff, and hydrodynamics. For example, there are situations where impacts in the aquatic food web can be driven by ongoing inputs to the water column from upstream sources, but mistakenly connected to polluted sediments. Other considerations included in a CSM can be socio-economic and include linkages to the ecosystem services provided by sediments<ref name="Broszeit2019">Broszeit, S., Beaumont, N.J., Hooper, T.L., Somerfield, P.J. and Austen, M.C., 2019. Developing conceptual models that link multiple ecosystem services to ecological research to aid management and policy, the UK marine example. Marine Pollution Bulletin, 141, pp.236-243.  [https://doi.org/10.1016/j.marpolbul.2019.02.051 DOI: 10.1016/j.marpolbul.2019.02.051]&nbsp;&nbsp; [https://www.sciencedirect.com/science/article/pii/S0025326X19301511/pdfft?md5=34993d6c3a57b6fb18a8b6329597fcb9&pid=1-s2.0-S0025326X19301511-main.pdf Open Access Article.]</ref><ref name="Wang2021">Wang, J., Lautz, L.S., Nolte, T.M., Posthuma, L., Koopman, K.R., Leuven, R.S. and Hendriks, A.J., 2021. Towards a systematic method for assessing the impact of chemical pollution on ecosystem services of water systems. Journal of Environmental Management, 281, p. 111873.  [https://doi.org/10.1016/j.jenvman.2020.111873 DOI: 10.1016/j.jenvman.2020.111873]&nbsp;&nbsp; [https://www.sciencedirect.com/science/article/pii/S0301479720317989/pdfft?md5=daff5e94f8aed44ffce6508afef2308c&pid=1-s2.0-S0301479720317989-main.pdf  Open Access Article.]</ref>, or the social, economic and environmental impacts of sediment management alternatives. In such a case, when risk assessment seeks to compare risks of various management actions (including no action), the CSM can be termed a sustainability CSM, or SustCSM<ref name="McNally2020">McNally, A.D., Fitzpatrick, A.G., Harrison, D., Busey, A., and Apitz, S.E., 2020. Tiered approach to sustainability analysis in sediment remediation decision making. Remediation Journal, 31(1), pp. 29-44.  [https://doi.org/10.1002/rem.21661 DOI: 10.1002/rem.21661]&nbsp;&nbsp; [https://onlinelibrary.wiley.com/doi/epdf/10.1002/rem.21661 Open Access Article].</ref><ref name="Holland2011">Holland, K.S., Lewis, R.E., Tipton, K., Karnis, S., Dona, C., Petrovskis, E., and Hook, C., 2011. Framework for Integrating Sustainability Into Remediation Projects. Remediation Journal, 21(3), pp. 7-38. [https://doi.org/10.1002/rem.20288 DOI: 10.1002/rem.20288].</ref>. At a minimum, however, the purpose of the CSM is to illustrate the scope of the risk assessment and guide the quantification of exposure and risk.
 
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===Environmental Fate===
 
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An important consideration in exposure analysis is the determination of the bioavailable fraction of the contaminant in the sediment. There are two considerations. First, the adverse condition may be buried deep enough in sediments to be below the biologically available zone; typically, conditions in sediment below a depth of 5 cm will not contact burrowing benthic organisms<ref name="Anderson2010">Anderson, R.H., Prues, A.G. and Kravitz, M.J., 2010. Determination of the biologically relevant sampling depth for terrestrial ecological risk assessments. Geoderma, 154(3-4), pp.336-339.  [https://doi.org/10.1016/j.geoderma.2009.11.004 DOI: 10.1016/j.geoderma.2009.11.004]</ref>. If there is no prospect for the adverse condition to come closer to the surface, then the risk assessment could conclude the risk of exposure is insignificant. The second consideration relates to chemistry and the factors involved in the binding to sediment particles or the chemical form of the substance in the sediment<ref name="Eggleton2004">Eggleton, J. and Thomas, K.V., 2004. A review of factors affecting the release and bioavailability of contaminants during sediment disturbance events. Environment International, 30(7), pp. 973-980.  [https://doi.org/10.1016/j.envint.2004.03.001 DOI: 10.1016/j.envint.2004.03.001]</ref>. However, these assumptions should be examined in the context of [[Climate Change Primer | climate change]], and the likelihood of more frequent and extreme events, putting burial at risk, higher temperatures and changing biogeochemical conditions, which may alter environmental fate of contaminants, compared to historical studies.
 
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The above contaminant bioavailability considerations are important factors influencing assumptions in the risk assessment about contaminant exposure<ref name="Peijnenburg2020">Peijnenburg, W.J., 2020. Implementation of bioavailability in prospective and retrospective risk assessment of chemicals in soils and sediments. In: The Handbook of Environmental Chemistry, vol 100, Bioavailability of Organic Chemicals in Soil and Sediment, Ortega-Calvo, J.J., Parsons, J.R. (ed.s), pp.391-422. Springer.  [https://doi.org/10.1007/698_2020_516 DOI: 10.1007/698_2020_516]</ref><ref name="Ortega-Calvo2015">Ortega-Calvo, J.J., Harmsen, J., Parsons, J.R., Semple, K.T., Aitken, M.D., Ajao, C., Eadsforth, C., Galay-Burgos, M., Naidu, R., Oliver, R. and Peijnenburg, W.J., 2015. From Bioavailability Science to Regulation of Organic Chemicals. Environmental Science and Technology, 49, 10255−10264. [https://doi.org/10.1021/acs.est.5b02412 DOI: 10.1021/acs.est.5b02412]&nbsp;&nbsp; [https://pubs.acs.org/doi/pdf/10.1021/acs.est.5b02412 Open Access Article].</ref>. There have been recent advances in the use of sorbent amendments applied to contaminated sediments that alter sediment geochemistry, increase contaminant binding, and reduce contaminant exposure risks to people and the environment<ref name="Ghosh2011">Ghosh, U., Luthy, R.G., Cornelissen, G., Werner, D. and Menzie, C.A., 2011. In-situ sorbent amendments: a new direction in contaminated sediment management. Environmental Science and Technology, 45, 4, 1163–1168.  [https://doi.org/10.1021/es102694h DOI: 10.1021/es102694h]&nbsp;&nbsp; [https://pubs.acs.org/doi/pdf/10.1021/es102694h Open Access Article]</ref>. [[Passive Sampling of Sediments | Passive sampling techniques]] have emerged to quantify chemical binding to sediment and determine the freely dissolved concentration that is bioavailable.
 
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===Assessment and Measurement Endpoints===
 
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Assessment and measurement endpoints used in sediment risk assessment are comparable to those described in USEPA ecological risk assessment guidance<ref name="USEPA2005"/><ref name="USEPA1992">US Environmental Protection Agency (USEPA), 1992. Framework for Ecological Risk Assessment, EPA/630/R-92/001. Risk Assessment Forum, Washington DC.  [[Media: EPA-630-R-92-001.pdf | Report.pdf]]</ref><ref name="USEPA1996">US Environmental Protection Agency (USEPA), 1996. Eco Update: Ecological Significance and Selection of Candidate Assessment Endpoints. EPA/540/F-95/037. Office of Solid Waste and Emergency Response, Washington DC.  [[Media: EPA 540-F-95-037.pdf | Report.pdf]]</ref><ref name="USEPA1997b">US Environmental Protection Agency (USEPA), 1997. Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments - Interim Final, EPA 540/R-97/006. Office of Solid Waste and Emergency Response, Washington DC.  [[Media: EPA 540-R-97-006.pdf | Report.pdf]]</ref><ref name="USEPA1998">US Environmental Protection Agency (USEPA), 1998. Guidelines for Ecological Risk Assessment. EPA/630/R-95/002F. Risk Assessment Forum, Washington DC.  [[Media: EPA 630-R-95-002F.pdf | Report.pdf]]</ref>. A sediment risk assessment, and ecological risk assessments more broadly, must have clearly defined endpoints that are socially and biologically relevant, accessible to prediction and measurement, and susceptible to the hazard being assessed<ref name="USEPA1992"/>.
 
−
 
 
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Assessment endpoints for humans include both carcinogenic and noncarcinogenic effects. Due to their assumed higher levels of exposure, human receptors used in sediment risk assessment typically include recreational, commercial, and subsistence fishermen, i.e., people who might be at increased risk from eating fish or contacting the sediment or water on a regular basis such as indigenous peoples, immigrants from fishing cultures, and subsistence fishers who rely upon fish as a major source of protein. Special considerations are given to women of child-bearing age, pregnant women and young children. Assessment endpoints for ecological receptors focus on benthic organisms, resident fish, piscivorous and other predatory birds and marine mammals. Endpoints typically include mortality, reproductive success and population susceptibility to disease or similar adverse chronic conditions.
 
−
 
 
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Measurement endpoints are related quantitatively to each assessment endpoint. Whenever practical, multiple measurement endpoints are chosen to provide additional lines of evidence for each assessment endpoint. For example, for humans, it might be possible to measure contaminant levels in both food items and human blood or tissue. For predatory fish, birds and mammals, it might be possible to measure contaminants in both prey and predator tissues. Measurement endpoints can be selected to assess non-chemical stressors as well, such as habitat alteration and water turbidity. Typically, measurement endpoints are compared to measurements at a reference site to ascertain the degree of departure from local natural or background conditions.
 
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===Sediment Toxicity Testing===
 
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Sediment bioassays are an integral part of effects characterization when assessing the risks posed by contaminated sediments and developing sediment quality guidelines<ref name="USEPA2014">US Environmental Protection Agency (USEPA), 2014. Toxicity Testing and Ecological Risk Assessment Guidance for Benthic Invertebrates. Office of Chemical Safety and Pollution Prevention, Washington DC.  [https://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/toxicity-testing-and-ecological-risk-assessment Website]&nbsp;&nbsp; [[Media: USEPA2014.pdf | Report.pdf]]</ref><ref name="Simpson2016a">Simpson, S., Campana, O., Ho, K., 2016. Chapter 7, Sediment Toxicity Testing. In: J. Blasco, P.M. Chapman, O. Campana, M. Hampel (ed.s), Marine Ecotoxicology: Current Knowledge and Future Issues. Academic Press Incorporated. pp. 199-237.  [https://doi.org/10.1016/B978-0-12-803371-5.00007-2 DOI: 10.1016/B978-0-12-803371-5.00007-2]</ref>. The selection of appropriate sediment bioassays is dependent on the questions being addressed, the physical and chemical characteristics of the sediment matrix, the nature of the contaminant(s) of concern, and preferences of the supervising regulatory authority for the test method and test organisms<ref name="Amiard-Triquet2015">Amiard-Triquet, C., Amiard, J.C. and Mouneyrac, C. (ed.s), 2015. Aquatic Ecotoxicology: Advancing Tools For Dealing With Emerging Risks. Academic Press, NY. ISBN #9780128009499.  [https://doi.org/10.1016/B978-0-12-800949-9.12001-7 DOI: 10.1016/B978-0-12-800949-9.12001-7]</ref>. Bioassay procedures have been standardized in several countries, and it is not unusual for different test methods to be required in different countries for the same sediment management purpose<ref name="DelValls2004">DelValls, T.A., Andres, A., Belzunce, M.J., Buceta, J.L., Casado-Martinez, M.C., Castro, R., Riba, I., Viguri, J.R. and Blasco, J., 2004. Chemical and ecotoxicological guidelines for managing disposal of dredged material. TrAC Trends in Analytical Chemistry, 23(10-11), pp. 819-828.  [https://doi.org/10.1016/j.trac.2004.07.014 DOI: 10.1016/j.trac.2004.07.014]&nbsp;&nbsp; Free download from: [https://d1wqtxts1xzle7.cloudfront.net/46085251/Chemical_and_Ecotoxicological_Guidelines20160530-23122-4fooj2-with-cover-page-v2.pdf?Expires=1637618385&Signature=aNsOfciO0HPhucL8S713nenRlvviD2dbLi8y63n93iGX~Cc7CHwyYQ2bfNlT6VnjuFJeVT83M01Xog6esr14gyvL9pmlo3hw5fQp5J9vA8gqXcT9kQfM1T2Q0Ig883yGMFmtgUrrU6p8c8V~8rh5DTKDD5ZsiL4zloGgF6Gs4F2ecEDqyFBZ17yYpXGVVBmpfm87sUpaPY0Ix9iWJ~5nxM~HF6XYl1sA1rgFSerT-Y5W8Ma7-XMljnYHQ7hW7eqMjyN66IDj7pwafG7Ox-Hnp07IuD-oMY1dHHrzTOmHpXpWgMYLn2zf1BSmy~tqIFHE6UjZn5ako93PgExuzEjEiw__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA Academia.edu]</ref>. Guidance documents in Australia, Canada, Europe and the US cover the wide range of sediment bioassay procedures most often used in risk assessment<ref name="Bat2005">Bat, L., 2005. A Review of Sediment Toxicity Bioassays Using the Amphipods and Polychaetes. Turkish Journal of Fisheries and Aquatic Sciences, 5(2), pp. 119-139.  [https://dergipark.org.tr/en/pub/trjfas-ayrildi/issue/13287/160604 Free download]&nbsp;&nbsp; [[Media: Bat2005.pdf | Report.pdf]]</ref><ref name="Keddy1995">Keddy, C.J., Greene, J.C. and Bonnell, M.A., 1995. Review of Whole-Organism Bioassays: Soil, Freshwater Sediment, and Freshwater Assessment in Canada. Ecotoxicology and Environmental Safety, 30(3), pp. 221-251.  [https://doi.org/10.1006/eesa.1995.1027 DOI: 10.1006/eesa.1995.1027]</ref><ref name="Giesy1990">Giesy, J.P., Rosiu, C.J., Graney, R.L. and Henry, M.G., 1990. Benthic invertebrate bioassays with toxic sediment and pore water. Environmental Toxicology and Chemistry, 9(2), pp. 233-248.  [https://doi.org/10.1002/etc.5620090214 DOI: 10.1002/etc.5620090214]</ref><ref name="Simpson2016b">Simpson, S. and Batley, G. (ed.s), 2016. Sediment Quality Assessment: A Practical Guide, Second Edition. 358 pp. CSIRO Publishing, Australia. ISBN # 9781486303847.</ref><ref name="Moore2019">Moore, D.W., Farrar, D., Altman, S. and Bridges, T.S., 2019. Comparison of Acute and Chronic Toxicity Laboratory Bioassay Endpoints with Benthic Community Responses in Field‐Exposed Contaminated Sediments. Environmental Toxicology and Chemistry, 38(8), pp. 1784-1802.  [https://doi.org/10.1002/etc.4454 DOI: 10.1002/etc.4454]</ref>.
 
  
−
In general, sediment toxicity tests focus on either (acute) lethality in whole organisms (typically benthic infaunal species such as amphipods and polychaetes) following short-term or acute exposures (<14 days) or (chronic) sublethal responses (e.g., reduced growth or reproduction or both) following longer-term exposures<ref name="Simpson2016a"/>. It is not unusual in sediment risk assessment to rely on more than one sediment bioassay. Both acute and chronic tests involving either solid-phase or pore-water sediment fractions can be useful to discern the contributions of different contaminants in whole sediment by examining the response of different endpoints in different test organisms<ref name="Keddy1995"/><ref name="Giesy1990"/>. The application of more specialized techniques such as toxicity identification evaluations (TIEs) have also proved useful to help identify contaminants or contaminant classes most likely responsible for toxicity and to exclude potentially confounding factors such as ammonia<ref name="Ho2013">Ho, K.T. and Burgess, R.M., 2013. What's causing toxicity in sediments? Results of 20 years of toxicity identification and evaluations. Environmental Toxicology and Chemistry, 32(11), pp. 2424-2432. [https://doi.org/10.1002/etc.2359 DOI: 10.1002/etc.2359]</ref><ref name="Bailey2016">Bailey, H.C., Curran, C.A., Arth, P., Lo, B.P. and Gossett, R., 2016. Application of sediment toxicity identification evaluation techniques to a site with multiple contaminants. Environmental Toxicology and Chemistry, 35(10), pp. 2456-2465. [https://doi.org/10.1002/etc.3488 DOI: 10.1002/etc.3488]</ref>.
+
==PFAS Background==
 +
PFAS are a broad class of chemicals with highly variable chemical structures<ref>Moody, C.A., Field, J.A., 1999. Determination of Perfluorocarboxylates in Groundwater Impacted by Fire-Fighting Activity. Environmental Science and Technology, 33(16), pp. 2800-2806. [https://doi.org/10.1021/es981355+ doi: 10.1021/es981355+]</ref><ref name="MoodyField2000">Moody, C.A., Field, J.A., 2000. Perfluorinated Surfactants and the Environmental Implications of Their Use in Fire-Fighting Foams. Environmental Science and Technology, 34(18), pp. 3864-3870. [https://doi.org/10.1021/es991359u doi: 10.1021/es991359u]</ref><ref name="GlügeEtAl2020">Glüge, J., Scheringer, M., Cousins, I.T., DeWitt, J.C., Goldenman, G., Herzke, D., Lohmann, R., Ng, C.A., Trier, X., Wang, Z., 2020. An Overview of the Uses of Per- and Polyfluoroalkyl Substances (PFAS). Environmental Science: Processes and Impacts, 22(12), pp. 2345-2373. [https://doi.org/10.1039/D0EM00291G doi: 10.1039/D0EM00291G]&nbsp; [[Media: GlügeEtAl2020.pdf | Open Access Article]]</ref>. One characteristic feature of PFAS is that they are fluorosurfactants, distinct from more traditional hydrocarbon surfactants<ref name="MoodyField2000"/><ref name="Brusseau2018">Brusseau, M.L., 2018. Assessing the Potential Contributions of Additional Retention Processes to PFAS Retardation in the Subsurface. Science of The Total Environment, 613-614, pp. 176-185. [https://doi.org/10.1016/j.scitotenv.2017.09.065 doi: 10.1016/j.scitotenv.2017.09.065]&nbsp; [[Media: Brusseau2018.pdf | Open Access Manuscript]]</ref><ref>Dave, N., Joshi, T., 2017. A Concise Review on Surfactants and Its Significance. International Journal of Applied Chemistry, 13(3), pp. 663-672. [https://doi.org/10.37622/IJAC/13.3.2017.663-672 doi: 10.37622/IJAC/13.3.2017.663-672]&nbsp; [[Media: DaveJoshi2017.pdf  | Open Access Article]]</ref><ref>García, R.A., Chiaia-Hernández, A.C., Lara-Martin, P.A., Loos, M., Hollender, J., Oetjen, K., Higgins, C.P., Field, J.A., 2019. Suspect Screening of Hydrocarbon Surfactants in Afffs and Afff-Contaminated Groundwater by High-Resolution Mass Spectrometry. Environmental Science and Technology, 53(14), pp. 8068-8077. [https://doi.org/10.1021/acs.est.9b01895 doi: 10.1021/acs.est.9b01895]</ref>. Fluorosurfactants typically have a fully or partially fluorinated, hydrophobic tail with ionic (cationic, zwitterionic, or anionic) head group that is hydrophilic<ref name="MoodyField2000"/><ref name="GlügeEtAl2020"/>. The hydrophobic tail and ionic head group mean PFAS are very stable at hydrophobic adsorption interfaces when present in the aqueous phase<ref>Krafft, M.P., Riess, J.G., 2015. Per- and Polyfluorinated Substances (PFASs): Environmental Challenges. Current Opinion in Colloid and Interface Science, 20(3), pp. 192-212. [https://doi.org/10.1016/j.cocis.2015.07.004 doi: 10.1016/j.cocis.2015.07.004]</ref>. Examples of these interfaces include naturally occurring organic matter in soils and the air-water interface in the vadose zone<ref>Schaefer, C.E., Culina, V., Nguyen, D., Field, J., 2019. Uptake of Poly- and Perfluoroalkyl Substances at the Air–Water Interface. Environmental Science and Technology, 53(21), pp. 12442-12448. [https://doi.org/10.1021/acs.est.9b04008 doi: 10.1021/acs.est.9b04008]</ref><ref>Lyu, Y., Brusseau, M.L., Chen, W., Yan, N., Fu, X., Lin, X., 2018. Adsorption of PFOA at the Air–Water Interface during Transport in Unsaturated Porous Media. Environmental Science and Technology, 52(14), pp. 7745-7753. [https://doi.org/10.1021/acs.est.8b02348 doi: 10.1021/acs.est.8b02348]</ref><ref>Costanza, J., Arshadi, M., Abriola, L.M., Pennell, K.D., 2019. Accumulation of PFOA and PFOS at the Air-Water Interface. Environmental Science and Technology Letters, 6(8), pp. 487-491. [https://doi.org/10.1021/acs.estlett.9b00355 doi: 10.1021/acs.estlett.9b00355]</ref><ref>Li, F., Fang, X., Zhou, Z., Liao, X., Zou, J., Yuan, B., Sun, W., 2019. Adsorption of Perfluorinated Acids onto Soils: Kinetics, Isotherms, and Influences of Soil Properties. Science of The Total Environment, 649, pp. 504-514. [https://doi.org/10.1016/j.scitotenv.2018.08.209 doi: 10.1016/j.scitotenv.2018.08.209]</ref><ref>Nguyen, T.M.H., Bräunig, J., Thompson, K., Thompson, J., Kabiri, S., Navarro, D.A., Kookana, R.S., Grimison, C., Barnes, C.M., Higgins, C.P., McLaughlin, M.J., Mueller, J.F., 2020. Influences of Chemical Properties, Soil Properties, and Solution pH on Soil–Water Partitioning Coefficients of Per- and Polyfluoroalkyl Substances (PFASs). Environmental Science and Technology, 54(24), pp. 15883-15892. [https://doi.org/10.1021/acs.est.0c05705 doi: 10.1021/acs.est.0c05705]&nbsp; [[Media: NguyenEtAl2020.pdf  | Open Access Article]]</ref>. Their strong adsorption to both soil organic matter and the air-water interface is a major contributor to elevated concentrations of PFAS observed in the upper 5 feet of the soil column<ref name="BrusseauEtAl2020"/><ref name="BiglerEtAl2024"/>. While several other PFAS partitioning processes exist<ref name="Brusseau2018"/>, adsorption to solid phase soils and air-water interfaces are the two primary processes present at nearly all PFAS sites<ref>Brusseau, M.L., Yan, N., Van Glubt, S., Wang, Y., Chen, W., Lyu, Y., Dungan, B., Carroll, K.C., Holguin, F.O., 2019. Comprehensive Retention Model for PFAS Transport in Subsurface Systems. Water Research, 148, pp. 41-50. [https://doi.org/10.1016/j.watres.2018.10.035 doi: 10.1016/j.watres.2018.10.035]</ref>. The total PFAS mass obtained from a vadose zone soil sample contains the solid phase, air-water interfacial, and aqueous phase PFAS mass, which can be converted to porewater concentrations using Equation 1<ref name="BrusseauGuo2022"/>.</br>
 +
:: <big>'''Equation 1:'''</big>&nbsp;&nbsp; [[File: StultsEq1.png | 400 px]]</br>
 +
Where ''C<sub>p</sub>'' is the porewater concentration, ''C<sub>t</sub>'' is the total PFAS concentration, ''ρ<sub>b</sub>'' is the bulk density of the soil, ''θ<sub>w</sub>'' is the volumetric water content, ''R<sub>d</sub>'' is the PFAS retardation factor, ''K<sub>d</sub>'' is the solid phase adsorption coefficient, ''K<sub>ia</sub>'' is the air-water interfacial adsorption coefficient, and ''A<sub>aw</sub>'' is the air-water interfacial area. The air-water interfacial area of the soil is primarily a function of both the soil properties and the degree of volumetric water saturation in the soil. There are several methods of estimating air-water interfacial areas including thermodynamic functions based on the soil moisture retention curve. However, the thermodynamic function has been shown to underestimate air-water interfacial area<ref name="Brusseau2023">Brusseau, M.L., 2023. Determining Air-Water Interfacial Areas for the Retention and Transport of PFAS and Other Interfacially Active Solutes in Unsaturated Porous Media. Science of The Total Environment, 884, Article 163730. [https://doi.org/10.1016/j.scitotenv.2023.163730 doi: 10.1016/j.scitotenv.2023.163730]&nbsp; [[Media: Brusseau2023.pdf  | Open Access Article]]</ref>, and must typically be scaled using empirical scaling factors. An empirical method recently developed to estimate air-water interfacial area is presented in Equation 2<ref name="Brusseau2023"/>.</br>
 +
:: <big>'''Equation 2:'''</big>&nbsp;&nbsp; [[File: StultsEq2.png | 400 px]]</br>
 +
Where ''S<sub>w</sub>'' is the water phase saturation as a ratio of the water content over the volumetric soil porosity, and ''d<sub>50</sub>'' is the median grain diameter.
  
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===Uncertainty===
+
==Lysimeters Background==
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As part of the overall analysis of risk from exposure to certain sediment conditions, it is generally understood there is a moderate degree of uncertainty associated with sampling and the environmental fate of contaminants; an order of magnitude of uncertainty associated with ecological exposure and dose-response; and greater than an order of magnitude of uncertainty associated with the quantification of potential human health effects<ref name="DiGuardo2018">Di Guardo, A., Gouin, T., MacLeod, M. and Scheringer, M., 2018. Environmental fate and exposure models: advances and challenges in 21st century chemical risk assessment. Environmental Science: Processes and Impacts, 20(1), pp. 58-71.  [https://doi.org/10.1039/C7EM00568G DOI: 10.1039/C7EM00568G]&nbsp;&nbsp; [https://pubs.rsc.org/en/content/articlehtml/2018/em/c7em00568g  Open access article]</ref>. The sources of uncertainty and significance to sediment risk assessment can vary widely, thereby affecting confidence in the decisions made based on risk assessment<ref name="Reckhow1994">Reckhow, K.H., 1994. Water quality simulation modeling and uncertainty analysis for risk assessment and decision making. Ecological Modelling, 72(1-2), pp.1-20.  [https://doi.org/10.1016/0304-3800(94)90143-0 DOI: 10.1016/0304-3800(94)90143-0]</ref><ref name="Chapman2002">Chapman, P.M., Ho, K.T., Munns Jr, W.R., Solomon, K. and Weinstein, M.P., 2002. Issues in sediment toxicity and ecological risk assessment. Marine Pollution Bulletin, 44(4), pp. 271-278. [https://doi.org/10.1016/S0025-326X(01)00329-0 DOI: 10.1016/S0025-326X(01)00329-0]</ref>.
+
[[File: StultsFig1.png |thumb|600 px|Figure 1. (a) A field suction lysimeter with labeled parts typically used in field settings – Credit: Bibek Acharya and Dr. Vivek Sharma, UF/IFAS, https://edis.ifas.ufl.edu/publication/AE581. (b) Laboratory suction lysimeters used in Schaefer ''et al.'' 2024<ref name="SchaeferEtAl2024"/>, which employed the use of micro-sampling suction lysimeters. (c) A field lysimeter used in Schaefer ''et al.'' 2023<ref name="SchaeferEtAl2023"/>. (d) Diagram of a drainage wicking lysimeter – Credit: Edaphic Scientific, https://edaphic.com.au/products/water/lysimeter-wick-for-drainage/]]
 +
Lysimeters,&nbsp;generally&nbsp;speaking, refer to instruments which collect water from unsaturated soils<ref name="MeissnerEtAl2020"/><ref name="RogersMcConnell1993"/>. However, there are multiple types of lysimeters which can be employed in field or laboratory settings. There are three primary types of lysimeters relevant to PFAS listed here and shown in Figure 1a-d.
 +
# <u>Suction Lysimeters (Figure 1a,b):</u> These lysimeters are the most relevant for PFAS sampling and are the majority of discussion in this article. These lysimeters operate by extracting liquid from the unsaturated vadose zone by applying negative suction pressure at the sampling head<ref name="CostanzaEtAl2025"/><ref name="SchaeferEtAl2024"/><ref name="QuinnanEtAl2021"/>. The sampling head is typically constructed of porous ceramic or stainless steel. A PVC case or stainless-steel case is attached to the sampling head and extends upward above the ground surface. Suction lysimeters are typically installed between 1 and 9 feet below ground surface, but can extend as deep as 40-60 feet in some cases<ref name="CostanzaEtAl2025"/>. Shallow lysimeters (< 10 feet) are typically installed using a hand auger. For ceramic lysimeters, a silica flour slurry should be placed at the base of the bore hole and allowed to cover the ceramic head before backfilling the hole partially with natural soil. Once the hole is partially backfilled with soil to cover the sampling head, the remainder of the casing should be sealed with hydrated bentonite chips. When sampling events occur, suction is applied at the ground surface using a rubber gasket seal and a hand pump or electric pump. After sufficient porewater is collected (the time for which can vary greatly based on the soil permeability and moisture content), the seal can be removed and a peristaltic pump used to extract liquid from the lysimeter.
 +
# <u>Field Lysimeters (Figure 1c):</u> These large lysimeters can be constructed from plastic or metal sidings. They can range from approximately 2 feet in diameter to as large as several meters in diameter<ref name="MeissnerEtAl2020"/>. Instrumentation such as soil moisture probes and tensiometers, or even multiple suction lysimeters, are typically placed throughout the lysimeter to measure the movement of water and determine characteristic soil moisture release curves<ref name="Stannard1992"/><ref name="WintonWeber1996"/><ref name="SchaeferEtAl2023"/><ref name="SchaeferEtAl2022"/><ref>van Genuchten, M.Th. , 1980. A Closed‐form Equation for Predicting the Hydraulic Conductivity of Unsaturated Soils. Soil Science Society of America Journal, 44(5), pp. 892-898. [https://doi.org/10.2136/sssaj1980.03615995004400050002x doi: 10.2136/sssaj1980.03615995004400050002x]</ref>. Water is typically collected at the base of the field lysimeter to determine net recharge through the system. These field lysimeters are intended to represent more realistic, intermediate scale conditions of field systems.
 +
# <u>Drainage Lysimeters (Figure 1d):</u> Also known as a “wick” lysimeter, these lysimeters typically consist of a hollow cup attached to a spout which protrudes above ground to relieve air pressure from the system and act as a sampling port. The hollow cup typically has filters and wicking devices at the base to collect water from the soil. The cup is filled with natural soil and collects water as it percolates through the vadose zone. These lysimeters are used to directly monitor net recharge from the vadose zone to the groundwater table and could be useful in determining PFAS mass flux.
  
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Consequently, technical guidance in several countries encourages including a quantitative uncertainty analysis in sediment risk assessment<ref name="USEPA2005"/><ref name="Tarazona2014"/><ref name="Apitz2005a"/><ref name="Apitz2005b"/>. The aim of uncertainty analysis is to express either quantitatively or qualitatively the limitations inherent in predicting exposures and effects and, ultimately, the level of overall risk posed by sediment conditions<ref name="Batley2002">Batley, G.E., Burton, G.A., Chapman, P.M. and Forbes, V.E., 2002. Uncertainties in Sediment Quality Weight-of-Evidence (WOE) Assessments. Human and Ecological Risk Assessment, 8(7), pp. 1517-1547.  [https://doi.org/10.1080/20028091057466 DOI: 10.1080/20028091057466]</ref>. Sediment risk assessment increasingly relies on a weight-of-evidence process to improve the certainty of conclusions about whether or not impairment exists due to sediment contamination, and, if so, which stressors and biological species (or ecological responses) are of greatest concern<ref name="Burton2002">Burton, G.A., Batley, G.E., Chapman, P.M., Forbes, V.E., Smith, E.P., Reynoldson, T., Schlekat, C.E., Besten, P.J.D., Bailer, A.J., Green, A.S. and Dwyer, R.L., 2002. A Weight-of-Evidence Framework for Assessing Sediment (or Other) Contamination: Improving Certainty in the Decision-Making Process. Human and Ecological Risk Assessment, 8(7), pp. 1675-1696.  [https://doi.org/10.1080/20028091056854 DOI: 10.1080/20028091056854]</ref>. Recent advancements, including the use of Bayesian networks and geographic information systems, also help capture the range of variability in both measured and predicted exposures and responses<ref name="Holsman2017">Holsman, K., Samhouri, J., Cook, G., Hazen, E., Olsen, E., Dillard, M., Kasperski, S., Gaichas, S., Kelble, C.R., Fogarty, M. and Andrews, K., 2017. An ecosystem‐based approach to marine risk assessment. Ecosystem Health and Sustainability, 3(1), p. e01256.  [https://doi.org/10.1002/ehs2.1256 DOI: 10.1002/ehs2.1256]&nbsp;&nbsp; [https://www.tandfonline.com/doi/full/10.1002/ehs2.1256 Open access article]</ref><ref name="Marcot2019">Marcot, B.G. and Penman, T.D., 2019. Advances in Bayesian network modelling: Integration of modelling technologies. Environmental Modelling and Software, 111, pp. 386-393.  [https://doi.org/10.1016/j.envsoft.2018.09.016 DOI: 10.1016/j.envsoft.2018.09.016]</ref><ref name="Men2019">Men, C., Liu, R., Wang, Q., Guo, L., Miao, Y. and Shen, Z., 2019. Uncertainty analysis in source apportionment of heavy metals in road dust based on positive matrix factorization model and geographic information system. Science of The Total Environment, 652, pp. 27-39.  [https://doi.org/10.1016/j.scitotenv.2018.10.212 DOI: 10.1016/j.scitotenv.2018.10.212]</ref>. The level of sophistication applied to the uncertainty analysis is a subjective consideration and often decided by regulatory pressures, public perceptions and the likely cost (not only economic, but also social and environmental) of mitigating or removing the contamination.
+
==Analysis of PFAS Concentrations in Soil and Porewater==
 +
{| class="wikitable mw-collapsible" style="float:left; margin-right:20px; text-align:center;"
 +
|+Table 1. Measured and Predicted PFAS Concentrations in Porewater for Select PFAS in Three Different Soils
 +
|-
 +
!Site
 +
!PFAS
 +
!Field</br>Porewater</br>Concentration</br>(&mu;g/L)
 +
!Lab Core</br>Porewater</br>Concentration</br>(&mu;g/L)
 +
!Predicted</br>Porewater</br>Concentration</br>(&mu;g/L)
 +
|-
 +
|Site A||PFOS||6.2 ± 3.4||3.0 ± 0.37||6.6 ± 3.3
 +
|-
 +
|Site B||PFOS||2.2 ± 2.0||0.78 ± 0.38||2.8
 +
|-
 +
|rowspan="3"|Site C||PFOS||13 ± 4.1||680 ± 460||164 ± 75
 +
|-
 +
|8:2 FTS||1.2 ± 0.46||52 ± 13||16 ± 6.0
 +
|-
 +
|PFHpS||0.36 ± 0.051||2.9 ± 2.0||5.9 ± 3.4
 +
|}
 +
[[File: StultsFig2.png | thumb | 600 px | Figure 2. Field Measured PFAS concentration Data (Orange) and Lab Core Measured Concentration Data (Blue) for four PFAS impacted sites<ref name="AndersonEtAl2022"/>]]
 +
[[File: StultsFig3.png | thumb | 400 px | Figure 3. Measured and predicted data for PFAS concentrations from a single site field lysimeter study. Model predictions both with and without PFAS sorption to the air-water interface were considered<ref name="SchaeferEtAl2023"/>.]]
 +
Schaefer&nbsp;''et&nbsp;al.''<ref name="SchaeferEtAl2024"/>&nbsp;measured&nbsp;PFAS porewater concentrations with field and laboratory suction lysimeters across several sites. Intact cores from the site were collected for soil water extraction using laboratory lysimeters. The lysimeters were used to directly compare field derived measurements of PFAS concentration in the mobile porewater phase. Results from measurements are for four sites presented in Figure 2.
  
−
==Role in Sediment Management==
+
Data from sites A and B showed reasonably good agreement (within ½ order of magnitude) for most PFAS measured in the systems. At site C, more hydrophobic constituents (> C6 PFAS) tended to have higher concentrations in the lab core than the field site while less hydrophobic constituents (< C6) had higher concentrations in the field than lab cores. Site D showed substantially greater (1 order of magnitude or more) PFAS concentrations measured in the laboratory-collected porewater sample compared to what was measured in the field lysimeters. This discrepancy for the Site D soil can likely be attributed to soil heterogeneity (as indicated by ground penetrating radar) and the fact that the soil consisted of back-filled materials rather than undisturbed native soils.  
−
Whether or not remediation of contaminated sediments is warranted depends on the magnitude of direct or indirect health risks to humans, ecological threats to aquatic biota, and the extent of risk reduction that can be achieved by removal or containment of the contamination<ref name="Kvasnicka2020">Kvasnicka, J., Burton Jr, G.A., Semrau, J. and Jolliet, O., 2020. Dredging Contaminated Sediments: Is it Worth the Risks? Environmental Toxicology and Chemistry, 39(3), pp. 515-516.  [https://setac.onlinelibrary.wiley.com/doi/pdfdirect/10.1002/etc.4679 DOI: 10.1002/etc.4679]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/pdfdirect/10.1002/etc.4679 Open access article]</ref>. As all sediment management also introduces risk pathways, such as sediment re-suspension leading to contaminant release, possible impacts due to land, water and energy usage, and risk to workers, remedial decision-making should also consider the risks posed by the remedial process. There are two types of remediation risks inherent in sediment remediation - engineering and biological. Sediment remedy implementation risks are predominantly short-term engineering issues associated with applying the remedy such as worker and community health and safety, equipment failures, and accident rates<ref name="Wenning2006">Wenning, R.J., Sorensen, M. and Magar, V.S., 2006. Importance of Implementation and Residual Risk Analyses in Sediment Remediation. Integrated Environmental Assessment and Management, 2(1), pp. 59-65.  [https://doi.org/10.1002/ieam.5630020111 DOI: 10.1002/ieam.5630020111]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/full/10.1002/ieam.5630020111 Open access article]</ref>. Sediment residual risks are predominantly longer-term changes in exposure and effects to humans, aquatic biota, and wildlife after the remedy has been implemented<ref name="Wenning2006"/>.
+
   
 +
Site&nbsp;C&nbsp;showed&nbsp;elevated PFAS concentrations in the laboratory collected porewater for the more surface-active compounds. This increase was attributed to the soil wetting that occurred at the bench scale, which was reasonably described by the model shown in Equations 1 and 2 (see Table 1<ref name="AndersonEtAl2022"/>). Equations 1 and 2 were also used to predict PFAS porewater concentrations (using porous cup lysimeters) in a highly instrumented test cell<ref name="SchaeferEtAl2023"/>(Figure 3). The ability to predict soil concentrations from recurring porewater samples is critical to the practical application of lysimeters in field settings<ref name="AndersonEtAl2022"/>.
  
−
In addition to evaluating sediment conditions prior to remediation, sediment risk assessment can be useful to understand how the engineering risks, the contaminant exposure pathways, and which human and wildlife populations are at risk might change with different remediation options<ref name="NRC2001">National Research Council (NRC), 2001. A Risk‐Management Strategy For PCB Contaminated Sediments. Committee On Remediation Of PCB‐Contaminated Sediments, Board On Environmental Studies And Toxicology. National Academies Press, Washington DC. 452 pp. ISBN: 0-309-58873-1 [https://doi.org/10.17226/10041 DOI: 10.17226/10041]&nbsp;&nbsp; Free download from: [https://www.nap.edu/catalog/10041/a-risk-management-strategy-for-pcb-contaminated-sediments The National Academies Press]</ref>. Decision tools such as multi-criteria decision analysis (MCDA), or sustainability assessment<ref name="Apitz2018">Apitz, S.E., Fitzpatrick, A., McNally, A., Harrison, D., Coughlin, C., and Edwards, D.A., 2018. Stakeholder Value-Linked Sustainability Assessment: Evaluating Remedial Alternatives for the Portland Harbor Superfund Site, Portland, Oregon, USA. Integrated Environmental Assessment and Management, 14(1), pp. 43-62. [https://doi.org/10.1002/ieam.1998 DOI: 10.1002/ieam.1998]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/full/10.1002/ieam.1998 Open access article]</ref><ref name="Fitzpatrick2018">Fitzpatrick, A., Apitz, S.E., Harrison, D., Ruffle, B., and Edwards, D.A., 2018. The Portland Harbor Superfund Site Sustainability Project:  Introduction. Integrated Environmental Assessment and Management, 14(1), pp. 17-21. [https://doi.org/10.1002/ieam.1997 DOI: 10.1002/ieam.197]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/full/10.1002/ieam.1997 Open access article]</ref>, for example, incorporate elements from sediment risk assessment to support remediation decision making<ref name="Linkov2006a">Linkov, I., Satterstrom, F.K., Kiker, G., Seager, T.P., Bridges, T., Gardner, K.H., Rogers, S.H., Belluck, D.A. and Meyer, A., 2006. Multicriteria Decision Analysis: A Comprehensive Decision Approach for Management of Contaminated Sediments. Risk Analysis, 26(1), pp. 61-78.  [https://doi.org/10.1111/j.1539-6924.2006.00713.x DOI: 10.1111/j.1539-6924.2006.00713.x]&nbsp;&nbsp; Free download from: [https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1164&context=usarmyceomaha US Army Corps of Engineers]</ref>. Sediment risk assessment also plays an important role in the implementation of monitored natural recovery (MNR) as a remediation strategy<ref name="Magar2006">Magar, V.S. and Wenning, R.J., 2006. The role of monitored natural recovery in sediment remediation. Integrated Environmental Assessment and Management, 2(1), pp. 66-74.  [https://doi.org/10.1002/ieam.5630020112 DOI: 10.1002/ieam.5630020112]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/full/10.1002/ieam.5630020112 Open access article]</ref>. Insofar as ecological recovery is affected by surface‐sediment‐contaminant concentrations, the primary recovery processes for MNR are natural sediment burial and transformation of the contaminant to less toxic forms by biological or chemical processes<ref name="Magar2009">Magar, V.S., Chadwick, D.B., Bridges, T.S., Fuchsman, P.C., Conder, J.M., Dekker, T.J., Steevens, J.A., Gustavson, K.E. and Mills, M.A., 2009. Technical Guide: Monitored Natural Recovery at Contaminated Sediment Sites. Environmental Security Technology Certification Program (ESTCP) Project ER-0622. 277 pp.  [https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminated-Sediments/In-place-Remediation/ER-200622/(language)/eng-US Website]&nbsp;&nbsp; [https://apps.dtic.mil/sti/pdfs/ADA512822.pdf Free download]</ref>.
+
Results from suction lysimeters studies and field lysimeter studies show that PFAS concentrations in porewater predicted from soil concentrations using Equations 1 and 2 generally have reasonable agreement with measured ''in situ'' porewater data when air-water interfacial partitioning is considered. Results show that for less hydrophobic components like PFOA, the impact of air-water interfacial adsorption is less significant than for highly hydrophobic components like PFOS. The soil for the field lysimeter in Figure 3 was a sandy soil with a relatively low air-water interfacial area. The effect of air-water interfacial partitioning is expected to be much more significant for a greater range of PFAS in soils with high capillary pressure (i.e. silts/clays) with higher associated air-water interfacial areas<ref name="Brusseau2023"/><ref>Peng, S., Brusseau, M.L., 2012. Air-Water Interfacial Area and Capillary Pressure: Porous-Medium Texture Effects and an Empirical Function. Journal of Hydrologic Engineering, 17(7), pp. 829-832. [https://doi.org/10.1061/(asce)he.1943-5584.0000515 doi: 10.1061/(asce)he.1943-5584.0000515]</ref><ref>Brusseau, M.L., Peng, S., Schnaar, G., Costanza-Robinson, M.S., 2006. Relationships among Air-Water Interfacial Area, Capillary Pressure, and Water Saturation for a Sandy Porous Medium. Water Resources Research, 42(3), Article W03501, 5 pages. [https://doi.org/10.1029/2005WR004058 doi: 10.1029/2005WR004058]&nbsp; [[Media: BrusseauEtAl2006.pdf | Free Access Article]]</ref>.
  
−
Since risk reduction is the long‐term goal of contaminated sediment management<ref name="Apitz2002">Apitz, S.E. and Power, E.A., 2002. From Risk Assessment to Sediment Management: An International Perspective. Journal of Soils and Sediments, 2(2), pp. 61-66.  [https://doi.org/10.1007/BF02987872 DOI: 10.1007/BF02987872]&nbsp;&nbsp; Free download from: [https://www.researchgate.net/profile/Sabine-Apitz/publication/225649107_From_risk_assessment_to_sediment_management_An_international_perspective/links/09e4150cb2df7c6331000000/From-risk-assessment-to-sediment-management-An-international-perspective.pdf ResearchGate]</ref>, predicting the rate at which contaminant exposures and risks are mitigated by sedimentation and degradation over time can be aided by including parameters in the risk assessment that calculate the rate of contaminant removal or decay in the sediment. Evaluating sediment management options in terms of risk reduction involves assessing risks under the diverse set of conditions that include the current state of the site as well as the conditions that would occur both during the implementation work and long after the work is complete and the ecosystem stabilizes<ref name="Linkov2006b">Linkov, I., Satterstrom, F.K., Kiker, G.A., Bridges, T.S., Benjamin, S.L. and Belluck, D.A., 2006. From Optimization to Adaptation: Shifting Paradigms in Environmental Management and Their Application to Remedial Decisions. Integrated Environmental Assessment and Management, 2(1), pp. 92-98.  [https://doi.org/10.1002/ieam.5630020116 DOI: 10.1002/ieam.5630020116]&nbsp;&nbsp; [https://setac.onlinelibrary.wiley.com/doi/epdf/10.1002/ieam.5630020116 Open access article]</ref><ref name="Reible2003">Reible, D., Hayes, D., Lue-Hing, C., Patterson, J., Bhowmik, N., Johnson, M. and Teal, J., 2003. Comparison of the Long-Term Risks of Removal and In Situ Management of Contaminated Sediments in the Fox River. Soil and Sediment Contamination, 12(3), pp. 325-344.  [https://doi.org/10.1080/713610975 DOI: 10.1080/713610975]</ref>.
+
==Summary and Recommendations==
 +
The majority of research with lysimeters for PFAS site investigations has been done using porous cup suction lysimeters<ref name="CostanzaEtAl2025"/><ref name="AndersonEtAl2022"/><ref name="SchaeferEtAl2024"/><ref name="QuinnanEtAl2021"/>. Porous cup suction lysimeters are advantageous because they can be routinely sampled or sampled after specific wetting or drying events much like groundwater wells. This sampling is easier and more efficient than routinely collecting soil samples from the same locations. Co-locating lysimeters with soil samples is important for establishing the baseline soil concentration levels at the lysimeter location and developing correlations between the soil concentrations and the mobile porewater concentration<ref name="CostanzaEtAl2025"/>. Appropriate standard operation procedures for lysimeter installation and operation have been established and have been reviewed in recent literature<ref name="CostanzaEtAl2025"/><ref name="SchaeferEtAl2024"/>. Lysimeters should typically be installed near the source area and just above the maximum groundwater level elevation to obtain accurate results of porewater concentrations year round. Depending upon the geology and vertical PFAS distribution in the soil, multilevel lysimeter installations should also be considered.
  
−
==Summary==
+
Results from several lysimeters studies across multiple field sites and modelling analysis has shown that lysimeters can produce reasonable results between field and laboratory studies<ref name="SchaeferEtAl2024"/><ref name="SchaeferEtAl2023"/><ref name="SchaeferEtAl2022"/>. Transient effects of wetting and drying as well as media heterogeneity affects appear to be responsible for some variability and uncertainty in lysimeter based PFAS measurements in the vadose zone. These mobile porewater concentrations can be coupled with effective recharge estimates and simplified modelling approaches to determine mass flux from the vadose zone to the underlying groundwater<ref name="Anderson2021"/><ref name="StultsEtAl2024"/><ref name="BrusseauGuo2022"/><ref>Stults, J.F., Schaefer, C.E., MacBeth, T., Fang, Y., Devon, J., Real, I., Liu, F., Kosson, D., Guelfo, J.L., 2025. Laboratory Validation of a Simplified Model for Estimating Equilibrium PFAS Mass Leaching from Unsaturated Soils. Science of The Total Environment, 970, Article 179036. [https://doi.org/10.1016/j.scitotenv.2025.179036 doi: 10.1016/j.scitotenv.2025.179036]</ref><ref>Smith, J. Brusseau, M.L., Guo, B., 2024. An Integrated Analytical Modeling Framework for Determining Site-Specific Soil Screening Levels for PFAS. Water Research, 252, Article121236. [https://doi.org/10.1016/j.watres.2024.121236 doi: 10.1016/j.watres.2024.121236]</ref>.
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Effective sediment risk assessment begins with an initial scoping and planning exercise. The work proceeds to a SLRA and, if warranted, detailed risk assessment using a process comparable to ecological risk assessment. The key elements of sediment risk assessment must include a well‐designed and site‐specific CSM; a transparent and well‐thought‐out biological and chemical data collection and analysis plan; carefully selected reference sites and decision criteria; and an explicit discussion of uncertainty. If the risk assessment concludes that unacceptable risks exist, risk‐management strategies must be evaluated, selected, implemented, and their success evaluated.
 
  
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Sediment risk assessments are designed to simulate and predict plausible interactions between contaminants or other stressors and both ecological and human receptors. The intent is to derive meaningful insights that provide conclusions that are both rational and protective, in that they err on the side of over-estimating the likely environmental risks. Although conservative assumptions should always be used early in the sediment risk assessment process, final decisions should be supported by refined, realistic estimates of risk provided by site‐specific data and sound analytical approaches. It is increasingly evident after nearly 50 years of application that sediment risk assessment is most useful when supported by a well‐designed, site‐specific, and tiered assessment process<ref name="Bridges2005">Bridges, T., Berry, W., Della Sala, S., Dorn, P., Ells, S., Gries, T., Ireland, S., Maher, E., Menzie, C., Porebski, L., and Stronkhorst, J., 2005. Chapter 6: A framework for assessing and managing risks from contaminated sediments. In: Use of sediment quality guidelines and related tools for the assessment of contaminated sediments. Wenning, Batley, Ingersoll, and Moore, editors. Society of Environmental Toxicology and Chemistry (SETAC), pp. 227–266. ISBN: 1-880611-71-6</ref>.
+
Future research opportunities should address the current key uncertainties related to the use of lysimeters for PFAS investigations, including:
 +
#<u>Collect larger datasets of PFAS concentrations</u> to determine how transient wetting or drying periods and media type affect PFAS concentrations in the mobile porewater. Some research has shown that non-equilibrium processes can occur in the vadose zone, which can affect grab sample concentration in the porewater at specific time periods.
 +
#<u>More work should be done with flux averaging lysimeters</u> like the drainage cup or wicking lysimeter. These lysimeters can directly measure net recharge and provide time averaged concentrations of PFAS in water over the sampling period. However, there is little work detailing their potential applications in PFAS research, or operational considerations for their use in remedial investigations for PFAS.
 +
#<u>Lysimeters should be coupled with monitoring of wetting and drying</u> in the vadose zone using ''in situ'' soil moisture sensors or tensiometers and groundwater levels. Direct measurements of soil saturation at field sites are vital to directly correlate porewater concentrations with soil concentrations. Similarly, groundwater level fluctuations can inform net recharge estimates. By collecting these data we can continue to improve partitioning and leaching models which can relate porewater concentrations to total PFAS mass in soils and PFAS leaching at field sites.
 +
#<u>Comparisons of various bench-scale leaching or desorption tests to field-based lysimeter data</u> are recommended. The ability to correlate field measurements of PFAS concentrations with estimates of leaching from laboratory studies would provide a powerful method to empirically estimate PFAS leaching from field sites.
  
 
==References==
 
==References==

Latest revision as of 15:50, 15 January 2026

Lysimeters for Measuring PFAS Concentrations in the Vadose Zone

PFAS are frequently introduced to the environment through soil surface applications which then transport through the vadose zone to reach underlying groundwater receptors. Due to their unique properties and resulting transport and retention behaviors, PFAS in the vadose zone can be a persistent contaminant source to underlying groundwater systems. Determining the fraction of PFAS present in the mobile porewater relative to the total concentrations in soils is critical to understanding the risk posed by PFAS in vadose zone source areas. Lysimeters are instruments that have been used by agronomists and vadose zone researchers for decades to determine water flux and solute concentrations in unsaturated porewater. Lysimeters have recently been developed as a critical tool for field investigations and characterizations of PFAS impacted source zones.

Related Article(s):

Contributors: Dr. John F. Stults, Dr. Charles Schaefer

Key Resources:

  • Assessment of PFAS in Collocated Soil and Porewater Samples at an AFFF-Impacted Source Zone: Field-Scale Validation of Suction Lysimeters[1]
  • PFAS Concentrations in Soil versus Soil Porewater: Mass Distributions and the Impact of Adsorption at Air-Water Interfaces[2]
  • Using Suction Lysimeters for Determining the Potential of Per- and Polyfluoroalkyl Substances to Leach from Soil to Groundwater: A Review[3]
  • Use of Lysimeters for Monitoring Soil Water Balance Parameters and Nutrient Leaching[4]
  • PFAS Porewater Concentrations in Unsaturated Soil: Field and Laboratory Comparisons Inform on PFAS Accumulation at Air-Water Interfaces[5]

Introduction

Lysimeters are devices that are placed in the subsurface above the groundwater table to monitor the movement of water through the soil[6][7][3]. Lysimeters have historically been used in agricultural sciences for monitoring nutrient or contaminant movement, soil moisture release curves, natural drainage patterns, and dynamics of plant-water interactions[6][8][9][10][4][11][12][13][14]. Recently, there has been strong interest in the use of lysimeters to measure and monitor movement of per- and polyfluoroalkyl substances (PFAS) through the vadose zone[15][1][5][16][17][18]. PFAS are frequently introduced to the environment through land surface application and have been found to be strongly retained within the upper 5 feet of soil[19][20]. PFAS recalcitrance in the vadose zone means that environmental program managers and consultants need a cost-effective way of monitoring concentration conditions within the vadose zone. Repeated soil sampling and extraction processes are time consuming and only give a representative concentration of total PFAS in the matrix[21], not what is readily transportable in mobile porewater[16][22][23][2]. Fortunately, lysimeters have been found to be a viable option for monitoring the concentration of PFAS in the mobile porewater phase in the vadose zone[15][1]. Note that while some lysimeters, known as weighing lysimeters, can directly measure water flux, the most commonly utilized lysimeters in PFAS investigations only provide measurements of porewater concentrations.

PFAS Background

PFAS are a broad class of chemicals with highly variable chemical structures[24][25][26]. One characteristic feature of PFAS is that they are fluorosurfactants, distinct from more traditional hydrocarbon surfactants[25][27][28][29]. Fluorosurfactants typically have a fully or partially fluorinated, hydrophobic tail with ionic (cationic, zwitterionic, or anionic) head group that is hydrophilic[25][26]. The hydrophobic tail and ionic head group mean PFAS are very stable at hydrophobic adsorption interfaces when present in the aqueous phase[30]. Examples of these interfaces include naturally occurring organic matter in soils and the air-water interface in the vadose zone[31][32][33][34][35]. Their strong adsorption to both soil organic matter and the air-water interface is a major contributor to elevated concentrations of PFAS observed in the upper 5 feet of the soil column[19][20]. While several other PFAS partitioning processes exist[27], adsorption to solid phase soils and air-water interfaces are the two primary processes present at nearly all PFAS sites[36]. The total PFAS mass obtained from a vadose zone soil sample contains the solid phase, air-water interfacial, and aqueous phase PFAS mass, which can be converted to porewater concentrations using Equation 1[2].

Equation 1:   StultsEq1.png

Where Cp is the porewater concentration, Ct is the total PFAS concentration, ρb is the bulk density of the soil, θw is the volumetric water content, Rd is the PFAS retardation factor, Kd is the solid phase adsorption coefficient, Kia is the air-water interfacial adsorption coefficient, and Aaw is the air-water interfacial area. The air-water interfacial area of the soil is primarily a function of both the soil properties and the degree of volumetric water saturation in the soil. There are several methods of estimating air-water interfacial areas including thermodynamic functions based on the soil moisture retention curve. However, the thermodynamic function has been shown to underestimate air-water interfacial area[37], and must typically be scaled using empirical scaling factors. An empirical method recently developed to estimate air-water interfacial area is presented in Equation 2[37].

Equation 2:   StultsEq2.png

Where Sw is the water phase saturation as a ratio of the water content over the volumetric soil porosity, and d50 is the median grain diameter.

Lysimeters Background

Figure 1. (a) A field suction lysimeter with labeled parts typically used in field settings – Credit: Bibek Acharya and Dr. Vivek Sharma, UF/IFAS, https://edis.ifas.ufl.edu/publication/AE581. (b) Laboratory suction lysimeters used in Schaefer et al. 2024[5], which employed the use of micro-sampling suction lysimeters. (c) A field lysimeter used in Schaefer et al. 2023[16]. (d) Diagram of a drainage wicking lysimeter – Credit: Edaphic Scientific, https://edaphic.com.au/products/water/lysimeter-wick-for-drainage/

Lysimeters, generally speaking, refer to instruments which collect water from unsaturated soils[4][11]. However, there are multiple types of lysimeters which can be employed in field or laboratory settings. There are three primary types of lysimeters relevant to PFAS listed here and shown in Figure 1a-d.

  1. Suction Lysimeters (Figure 1a,b): These lysimeters are the most relevant for PFAS sampling and are the majority of discussion in this article. These lysimeters operate by extracting liquid from the unsaturated vadose zone by applying negative suction pressure at the sampling head[3][5][18]. The sampling head is typically constructed of porous ceramic or stainless steel. A PVC case or stainless-steel case is attached to the sampling head and extends upward above the ground surface. Suction lysimeters are typically installed between 1 and 9 feet below ground surface, but can extend as deep as 40-60 feet in some cases[3]. Shallow lysimeters (< 10 feet) are typically installed using a hand auger. For ceramic lysimeters, a silica flour slurry should be placed at the base of the bore hole and allowed to cover the ceramic head before backfilling the hole partially with natural soil. Once the hole is partially backfilled with soil to cover the sampling head, the remainder of the casing should be sealed with hydrated bentonite chips. When sampling events occur, suction is applied at the ground surface using a rubber gasket seal and a hand pump or electric pump. After sufficient porewater is collected (the time for which can vary greatly based on the soil permeability and moisture content), the seal can be removed and a peristaltic pump used to extract liquid from the lysimeter.
  2. Field Lysimeters (Figure 1c): These large lysimeters can be constructed from plastic or metal sidings. They can range from approximately 2 feet in diameter to as large as several meters in diameter[4]. Instrumentation such as soil moisture probes and tensiometers, or even multiple suction lysimeters, are typically placed throughout the lysimeter to measure the movement of water and determine characteristic soil moisture release curves[13][14][16][17][38]. Water is typically collected at the base of the field lysimeter to determine net recharge through the system. These field lysimeters are intended to represent more realistic, intermediate scale conditions of field systems.
  3. Drainage Lysimeters (Figure 1d): Also known as a “wick” lysimeter, these lysimeters typically consist of a hollow cup attached to a spout which protrudes above ground to relieve air pressure from the system and act as a sampling port. The hollow cup typically has filters and wicking devices at the base to collect water from the soil. The cup is filled with natural soil and collects water as it percolates through the vadose zone. These lysimeters are used to directly monitor net recharge from the vadose zone to the groundwater table and could be useful in determining PFAS mass flux.

Analysis of PFAS Concentrations in Soil and Porewater

Table 1. Measured and Predicted PFAS Concentrations in Porewater for Select PFAS in Three Different Soils
Site PFAS Field
Porewater
Concentration
(μg/L) 		Lab Core
Porewater
Concentration
(μg/L) 		Predicted
Porewater
Concentration
(μg/L)
Site A PFOS 6.2 ± 3.4 3.0 ± 0.37 6.6 ± 3.3
Site B PFOS 2.2 ± 2.0 0.78 ± 0.38 2.8
Site C PFOS 13 ± 4.1 680 ± 460 164 ± 75
8:2 FTS 1.2 ± 0.46 52 ± 13 16 ± 6.0
PFHpS 0.36 ± 0.051 2.9 ± 2.0 5.9 ± 3.4
Figure 2. Field Measured PFAS concentration Data (Orange) and Lab Core Measured Concentration Data (Blue) for four PFAS impacted sites[1]
Figure 3. Measured and predicted data for PFAS concentrations from a single site field lysimeter study. Model predictions both with and without PFAS sorption to the air-water interface were considered[16].

Schaefer et al.[5] measured PFAS porewater concentrations with field and laboratory suction lysimeters across several sites. Intact cores from the site were collected for soil water extraction using laboratory lysimeters. The lysimeters were used to directly compare field derived measurements of PFAS concentration in the mobile porewater phase. Results from measurements are for four sites presented in Figure 2.

Data from sites A and B showed reasonably good agreement (within ½ order of magnitude) for most PFAS measured in the systems. At site C, more hydrophobic constituents (> C6 PFAS) tended to have higher concentrations in the lab core than the field site while less hydrophobic constituents (< C6) had higher concentrations in the field than lab cores. Site D showed substantially greater (1 order of magnitude or more) PFAS concentrations measured in the laboratory-collected porewater sample compared to what was measured in the field lysimeters. This discrepancy for the Site D soil can likely be attributed to soil heterogeneity (as indicated by ground penetrating radar) and the fact that the soil consisted of back-filled materials rather than undisturbed native soils.

Site C showed elevated PFAS concentrations in the laboratory collected porewater for the more surface-active compounds. This increase was attributed to the soil wetting that occurred at the bench scale, which was reasonably described by the model shown in Equations 1 and 2 (see Table 1[1]). Equations 1 and 2 were also used to predict PFAS porewater concentrations (using porous cup lysimeters) in a highly instrumented test cell[16](Figure 3). The ability to predict soil concentrations from recurring porewater samples is critical to the practical application of lysimeters in field settings[1].

Results from suction lysimeters studies and field lysimeter studies show that PFAS concentrations in porewater predicted from soil concentrations using Equations 1 and 2 generally have reasonable agreement with measured in situ porewater data when air-water interfacial partitioning is considered. Results show that for less hydrophobic components like PFOA, the impact of air-water interfacial adsorption is less significant than for highly hydrophobic components like PFOS. The soil for the field lysimeter in Figure 3 was a sandy soil with a relatively low air-water interfacial area. The effect of air-water interfacial partitioning is expected to be much more significant for a greater range of PFAS in soils with high capillary pressure (i.e. silts/clays) with higher associated air-water interfacial areas[37][39][40].

Summary and Recommendations

The majority of research with lysimeters for PFAS site investigations has been done using porous cup suction lysimeters[3][1][5][18]. Porous cup suction lysimeters are advantageous because they can be routinely sampled or sampled after specific wetting or drying events much like groundwater wells. This sampling is easier and more efficient than routinely collecting soil samples from the same locations. Co-locating lysimeters with soil samples is important for establishing the baseline soil concentration levels at the lysimeter location and developing correlations between the soil concentrations and the mobile porewater concentration[3]. Appropriate standard operation procedures for lysimeter installation and operation have been established and have been reviewed in recent literature[3][5]. Lysimeters should typically be installed near the source area and just above the maximum groundwater level elevation to obtain accurate results of porewater concentrations year round. Depending upon the geology and vertical PFAS distribution in the soil, multilevel lysimeter installations should also be considered.

Results from several lysimeters studies across multiple field sites and modelling analysis has shown that lysimeters can produce reasonable results between field and laboratory studies[5][16][17]. Transient effects of wetting and drying as well as media heterogeneity affects appear to be responsible for some variability and uncertainty in lysimeter based PFAS measurements in the vadose zone. These mobile porewater concentrations can be coupled with effective recharge estimates and simplified modelling approaches to determine mass flux from the vadose zone to the underlying groundwater[15][22][2][41][42].

Future research opportunities should address the current key uncertainties related to the use of lysimeters for PFAS investigations, including:

  1. Collect larger datasets of PFAS concentrations to determine how transient wetting or drying periods and media type affect PFAS concentrations in the mobile porewater. Some research has shown that non-equilibrium processes can occur in the vadose zone, which can affect grab sample concentration in the porewater at specific time periods.
  2. More work should be done with flux averaging lysimeters like the drainage cup or wicking lysimeter. These lysimeters can directly measure net recharge and provide time averaged concentrations of PFAS in water over the sampling period. However, there is little work detailing their potential applications in PFAS research, or operational considerations for their use in remedial investigations for PFAS.
  3. Lysimeters should be coupled with monitoring of wetting and drying in the vadose zone using in situ soil moisture sensors or tensiometers and groundwater levels. Direct measurements of soil saturation at field sites are vital to directly correlate porewater concentrations with soil concentrations. Similarly, groundwater level fluctuations can inform net recharge estimates. By collecting these data we can continue to improve partitioning and leaching models which can relate porewater concentrations to total PFAS mass in soils and PFAS leaching at field sites.
  4. Comparisons of various bench-scale leaching or desorption tests to field-based lysimeter data are recommended. The ability to correlate field measurements of PFAS concentrations with estimates of leaching from laboratory studies would provide a powerful method to empirically estimate PFAS leaching from field sites.

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See Also

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