October 14 - 16, 2025
The Westin
Westminster, CO
Conveniently Located between Boulder & Denver
The Westin
Westminster, CO
Conveniently Located between Boulder & Denver
The Remediation Technology and Emerging Contaminants Summit agenda continues to develop! Check back often for updates!
Due to increasing regulatory pressure on the group of substances known as PFAS, companies worldwide are currently searching for alternatives to replace the many uses of PFAS with safer alternatives. To facilitate the transition, we have recently compiled a database of alternatives for all possible uses of PFAS. The concept of functional substitution is followed to identify the technical function(s) of PFAS, their end-use function(s), and the service(s) they provide in each application. By doing so, we are able to identify various alternatives to PFAS, i.e. chemical alternatives, but also alternative materials, technologies and/or products. The user of the database is thus able to understand the reason why PFAS are used in certain consumer/industrial applications, and to determine whether viable alternatives are available. As highlighted in our previous work, defining the use of a substance of concern following the functional substitution approach can be helpful to evaluate its essentiality. Therefore, the database can be used to identify applications where the technical function provided by PFAS is not needed (i.e. is non-essential) in the final product to deliver its services, and those that do not fulfil the criteria to be considered as necessary for health and safety, or critical for the functioning of society. In this presentation, I will present the database show how it can be a useful tool to facilitate the substitution of PFAS.
Hot on the heels of USEPA’s updated guidance on the Destruction and Disposal of PFAS, demand for conducting demonstrations of PFAS destruction technologies has increased. In the revised guidance, the agency recommends that thermal destruction facilities conduct performance testing prior to accepting and processing PFAS materials and the testing should include Other Test Method (OTM)-45 and OTM-50. These methods provide targeted results for a range of semivolatile and volatile PFAS thought to be the likely products of any incomplete destruction.
This discussion will delve into the intricacies of EPA OTM-45/50, providing the audience with important technical considerations for a successful PFAS air emissions sampling campaign. Attendees will gain insights into the latest advancements in PFAS measurement methods, the opportunities and challenges posed by these methods, and their role in the evolving PFAS regulatory landscape.
Arq Inc. is an environmental technology company specializing in the development and application of advanced activated carbons to remove harmful chemicals and pollutants, such as PFAS, from water supplies, contaminated land sites and air emissions. In this session, we will discuss the design considerations of activated carbon, including the fundamental science behind its development, key features, and strategies for enhancing capacity and sequestration. We will also discuss the challenges and considerations involved in full-scale manufacturing of activated carbon. Through examples of priority and emerging applications, we aim to provide a comprehensive understanding of the application of activated carbons from the perspective of a producer.
A field-scale pilot test of in situ thermal desorption of PFAS from vadose zone soil took place at a former fire training area with PFAS impacts to soil of greater than 1,900 ug/kg. The soil was heated to an average temperature of 403 ºC during the treatment test period of 20.5 weeks using thermal conduction heating. Concentrations of PFAS were measured in soil before and after the pilot test and subsurface vapor collected during system operations was sampled using Other Test Method 45 (OTM-45) and OTM-50 at six time points throughout the heating process. The condensate generated was also regularly sampled for PFAS. The off-gas and condensate were treated using vapor and liquid phase granular activated carbon prior to discharge. PFAS leaching from pre- and post-treatment soils was also measured using the Leaching Environmental Assessment Framework (LEAF) method 1316. Subsamples of the condensate were sent to Colorado School of Mines for hydrothermal alkaline and ultraviolet-sulfite destructive treatment.
Results showed that when a temperature of at least 350 °C was maintained for seven days (following vaporization of soil moisture), a 99.5% average reduction of PFOS in soil was observed. Not all of the treatment area was uniformly treated; suspected long-term shallow water incursion on the eastern side of the test area limited heating to sustained target temperatures. Because of this, removal of PFAS from soil on the eastern side of the test area was hampered. Additionally, several PFAS were present in the eastern side after treatment that were not present before heating, suggesting that transformation occurred during the pilot test. Concentrations in the condensate peaked 30 days after heating began and then decreased. Granular activated carbon and hydrothermal alkaline treatment (HALT) were effective at treating the condensate and vapor to below the discharge limits. Concentrations of PFAS measured in the vapor and condensate streams were used to calculate a mass balance.
Funding provided by ESTCP, Project ER20-5250
Developing analytical methodologies to measure PFAS has been a major challenge for researchers interested in studying PFAS occurrence, fate, transport, and treatment. Recently, the US EPA published two methods: 1) Method 1633, used for the analysis of PFAS in aqueous, solid, biosolids, and tissue samples, and 2) Method 1621, used for the analysis of adsorbable organic fluorine (AOF) in aqueous matrices. However, we have found that Method 1633 was not suitable for the analysis of certain samples, including AFFF-impacted groundwater, soils, and sludges and biosolids. We also have had various challenges with applying Method 1621 to analyze samples containing high concentrations of fluoride. This presentation will discuss how the analytical workflows of Method 1633 and 1621 may be modified to deal with these samples. The presentation will also provide a brief overview of how analytical methodologies for PFAS have evolved over the past 15 years.
Colloidal activated carbon (CAC) is being injected through wells into the pathways of PFAS groundwater plumes at contaminated sites to adsorb PFAS and prevent downgradient migration, thereby reducing risks to potential receptors. Individual PFAS compounds compete with each other for adsorption sites on CAC, and it is presently not clear how this competition will affect the time period that CAC will serve as an effective adsorption barrier. To assess this time period, adsorption isotherms for both individual and mixtures of PFAS on CAC, as well as column breakthrough profiles for the same PFAS on CAC amended soil, were measured. The ideal adsorbed solution theory and the multicomponent Langmuir model were used to assess how well multi-component isotherms could be predicted using both measured and predicted single sorbate isotherms. The isotherms are being used as input to a reactive transport model to predict multicomponent PFAS breakthrough in the columns. These results will be presented, as well as analyses of how long CAC will effectively prevent PFAS migration in the field, and whether simplified methods can be used to predict this breakthrough time.
Hydrothermal alkaline treatment (HALT) as a means for PFAS destruction via fluorine mineralization has received increased attention in recent years due to its efficacy in degrading PFAS and its resilience to co-constituents in complex concentrate matrices. While HALT has been applied to a wide range of matrices in bench-scale batch experiments and full-scale field demonstrations are recently underway, many questions remain as to how HALT may be better optimized to reduce energy requirements, consumable inputs (e.g., concentrated alkali), and reaction times for a variety of feedstocks. Further questions center around how small-scale batch reactions may correlate with upscaled flow-through operations in the field, and whether prediction of full-scale treatment performance is possible. To answer these questions and more, a bench-scale continuous-flow hydrothermal reactor was constructed and operated in tandem with batch HALT reactors to determine the thresholds at which complete defluorination of PFAS may be attained. Reductions in alkali dose, reaction time, temperature, and pressure were explored to better identify rate-limiting parameters of nucleophilic substitution that leads to fluoride release. To that end, a predictive model is under development using reaction kinetics and thermal/alkali inputs to determine the ideal conditions for complete PFAS destruction while streamlining the overall process for improved sustainability and cost-efficiency. Results are contextualized within the scope of life cycle assessment and costing analyses to optimize treatment trains for specific matrices that may exhibit co-constituent interference or hydroxide scavenging (e.g., foam fractionation concentrates and ion exchange brines). Primary goals of this study include the application of the predictive model to inform scale-up decisions for full-scale treatment and the ability to conduct batch reactions that may be used to predict treatment outcomes in the field. Ultimately, identification of how HALT may be tailored to specific matrices may also enable coupling of separation technologies (e.g., membranes and adsorbents) with flow-through HALT reactors for an optimized treatment train with PFAS-free waste streams.
This study examines a range of analytical methods used to measure poly- and perfluoroalkyl substances (PFAS), which are becoming more widely recognized and regulated by water utilities. With the ongoing identification of new PFAS compounds, utilities often encounter challenges in selecting the most effective techniques for evaluating contamination levels. By comparing ten different measurement methods, including US EPA Methods 533 and 1633, we reveal notable differences in the total PFAS and organofluorine concentrations. Importantly, certain compounds may experience significant losses during analysis, particularly during nitrogen drying, which can lead to underreporting of contamination levels. This information is crucial for water utilities and stakeholders, as precise measurements are essential for regulatory compliance and safeguarding public health. Our results offer valuable insights for implementing effective analytical strategies in response to the evolving PFAS landscape.
Hydrothermal alkaline treatment (HALT) is an emerging PFAS destruction technology which relies on the properties of subcritical water (>300 ˚C, >20 MPa) and an alkaline amendment (e.g., NaOH) to destroy PFAS in liquid concentrates. This allows for the implementation of effective PFAS treatment trains, where technologies such as foam fractionation, regenerable sorbents, and/or membranes can be coupled with HALT to facilitate separation, concentration, and destruction of PFAS.
This coupled treatment train approach facilities PFAS treatment for groundwater, landfill leachate, fire training ponds, municipal wastewater, and industrial wastewater. Aquagga has demonstrated these applications in both bench and pilot-scale studies, often achieving over 99.9% total PFAS destruction efficiencies.
This talk will present a state-of-the-art for the HALT technology, along with the current status of commercialization and implementation. Recent advancements at the Colorado School of Mines and University of Washington have elucidated the reaction mechanisms and pathways for PFAS degradation under HALT conditions, along with opportunities for process optimization. A brief overview of the reaction chemistry will be given, showing the multiple lines of evidence used to prove the efficacy of HALT in destroying PFAS. Additionally, Aquagga is engaged in several demonstration / validation projects for HALT, mostly funded by the DoD, at various stages of completion. A summary of these projects and the various outcomes and stages of completion will be presented. Finally, a future outlook for HALT will be shared, based on strengths and weaknesses of HALT in the context of other destruction technologies, along with commercial use cases which have been validated by the Aquagga team.
The total oxidizable precursor (TOP) assay has been extensively used for detecting PFAS pollutants that do not have analytical standards. It uses hydroxyl radical (HO•) from the heat-activation of persulfate under alkaline pH to convert H-containing precursors to perfluoroalkyl carboxylates (PFCAs) for target analysis. However, the current TOP assay oxidation method does not apply to emerging PFAS because (i) many structures do not contain C−H bonds for HO• attack and (ii) the transformation products are not necessarily PFCAs.
In this study, we explored the use of classic acidic persulfate digestion, which generates sulfate radical (SO4−•), to extend the capability of TOP assay. We first examined the oxidation of Nafion-related ether sulfonates that contain C−H or −COO−, characterized the oxidation products, and quantified the F atom balance. The SO4−• oxidation greatly expanded the scope of oxidizable precursors. The transformation was initiated by decarboxylation, followed by various spontaneous steps such as HF elimination and ester hydrolysis.
We further compared the oxidation of legacy fluorotelomers using SO4−• versus HO•. The results suggest novel product distribution patterns depending on the functional group and oxidant dose. The general trends and strategies were also validated by analyzing a mixture of 100,000- or 10,000-fold diluted aqueous film-forming foam (containing various fluorotelomer surfactants and organics) and a spiked Nafion precursor.
Therefore, (1) the combined use of SO4−• and HO• oxidation, (2) the expanded list of standard chemicals, and (3) further elucidation of SO4−• oxidation mechanisms will provide more critical information to probe emerging PFAS pollutants."
There are hundreds if not thousands of fuel oil tanker spills and fires that have been controlled by AFFF, and they always occur on roads and highways and often at remote locations or within urban areas.
Cascade will present the results of bench scale testing, full scale remediation design and implementation, and full-scale performance testing for in situ remediation of PFAS by colloidal activated carbon.
The spill, 2022, occurred on the Atlantic City Freeway in NJ, and we believe this is the first remediation project addressing tanker spills that have contaminated groundwater.
The utility of an environmental field sampling program is predicated on the collection of representative and unbiased field data; much moreso when the constituents of concern include PFAS. Previous studies have been useful towards building an understanding of the different types of PFAS that may potentially leach from various sample materials (Denly et al., 2019; Rodowa et al., 2020). These studies identified leaching behavior from several materials sampled, however other materials were left untested and the testing methodologies employed may not have been completely representative of field conditions.
To augment the results of these previously reported studies, Ramboll and Eurofins undertook a study of 25 common materials of sampling, ranging from disposable shop wipe towels, to various bladder and tubing materials, to protective Tyvek suits, in addition to the pump bodies of five different common rental groundwater sampling pumps and an artificial groundwater sample made up of a pH 9.4 leaching solution collected from the pumped discharge of each pump studied. The 25 different materials of sampling were subjected to a modified EPA LEAF 1315 extraction methodology, using a pH 9.4 solution and a 24-hour leaching period to simulate a worst-case but realistic exposure condition (considering many types of the equipment tested are often used as “dedicated” equipment and remain in contact with environmental media indefinitely). Analysis was performed using a modified EPA Method 537 Isotope Dilution procedure with a target analyte list of 70 individual PFAS compounds.
This presentation will review the results and findings of the study, including a brief overview of the methods and materials and a more in-depth evaluation of the study related to implications for field sampling activities and published sampling protocol guidance and procedures (e.g., ASTM, 2007; USEPA, 2019).
The purpose of this study was to quantify the field performance of a colloidal activated carbon (CAC) barrier based on monitoring data collected during the initial 18 months of a pilot test. The In-Situ Remediation Model (ISR-MT3DMS) was calibrated to match concentration versus time profiles for ten short- and long-chain PFAS at two in-barrier and two downgradient monitoring wells. A two-dimensional cross-section model representing CAC heterogeneity with depth was needed to match PFAS trends at in-barrier wells. The effects of CAC heterogeneity on long-term barrier performance are discussed. The ISR-MT3DMS model was also used to demonstrate that PFAS downgradient of the CAC barrier exhibit rate-limited desorption. A focused cost-benefit analysis is conducted for a hypothetical AFFF-impacted site, to assess the benefits and limitations of source control when a CAC barrier is employed in a downgradient plume. Options for short-term and longer-term PFAS groundwater remedial goals are discussed, as well as potential future options for treating spent CAC barriers. Modeling results demonstrate that CAC barriers do not need to be designed to prevent PFBS breakthrough based on recent EPA MCL and hazard index regulations.
As PFAS measurement needs expand from targeted analysis of a select group of PFAS to cover the thousands of uncharacterized/partially characterized entities, the use of high-resolution accurate mass (HRAM) analysis has increased significantly. From the discovery of previously uncharacterized factory emissions in North Carolina and New Jersey, to their use in source characterization, source attribution and forensics, the vast majority if this work has been carried out in academic, government and non-profit institutions. While this work continues to provide valuable information on uncharacterized PFAS and suspect screening, scale on adoption of these techniques will need development of capabilities at commercial and contract laboratories.
Our objectives with this study were to understand and elucidate the major challenges with untargeted PFAS workflows from a commercial lab perspective such as 1) technical instrument capabilities, sensitivity of the instruments, speed, resolution and capabilities to generate actionable information on suspect screening workflows and untargeted workflows, 2) data analysis and reporting workflows, 3) standardization and benchmarking for untargeted PFAS analysis, and 4) alignment of technical needs of workflow with analyst skillset available in a commercial lab.
Preliminary results indicate that all instruments were in general able to detect the 40 target PFAS in 1633 at the default low calibration level with a few exceptions. There were instrument-specific differences in relative sensitivity by PFAS structure type. With suspect screening workflows, the number of available PFAS with previously compiled information, integration with publicly available databases and general ease of use of workflow varied significantly between the options tested. Results for the untargeted workflow are being compared using Kendrick Mass Defect results, number of features detected, Schymanski scale evaluation for confidence of detection, ease of use of instrument-specific software, integration with publicly available software such as MZmine and Fluoromatch and will be presented.
This presentation will provide an overview of the laboratory approach for a new rapid turnaround-time Direct Inject Analysis method. As the demand for PFAS testing increases, the laboratory's ability to hit required turnaround times becomes increasingly critical to project success. A rapid turnaround time procedure based on EPA 8327 and ASTM D-8421 methods was developed for analysis of up to 63 compounds using Isotope Dilution with results available in as little as 1-2 business days. A basic overview of the approved and promulgated methods currently available (including EPA 537.1, 533, and Draft 1633) will be provided, as well as an overview of the newly developed Direct Inject Analysis technique which will cover the approach, challenges, and solutions to developing this method through the use of comparative data from real-world samples.
The effective degradation of emerging contaminants in drinking water and wastewater matrices remains a critical challenge, particularly in terms of sustainable and scalable solutions. This study aims to explore the removal of emerging contaminants using laccase-inspired bionanozymes, focusing on their potential to degrade endocrine-disrupting chemicals (EDCs).
A novel synthesis of laccase-mimicking bionanozymes using single amino acids (histidine and cysteine) conjugated with copper ions (Cu2+) was developed, mimicking the active site of the natural laccase enzyme. Characterization using Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) confirmed successful complex formation, while Cu2+ ion content analysis revealed the influence of amino acid composition on copper retention. The amino acid composition also impacts the catalytic activity, showing variable performance towards compounds containing phenolic hydroxyl groups. Spectrophotometric and electron paramagnetic resonance (EPR) analyses showed the formation of hydroxyl (·OH) and superoxide (O2·-) radicals during the oxidation of phenolic substances such as 2-aminophenol, 2,4-dichlorophenol, and 2,6-dimethoxyphenol. Bionanozymes with optimal catalytic activity demonstrated superior stability and reusability compared to natural laccase. In this presentation, we will discuss the application of the laccase-mimicking bionanozymes for the degradation of various bisphenol EDCs, and their effectiveness under conditions relevant to practical water and wastewater treatment.
The simplicity and green synthesis of these bionanozymes make them a promising alternative for large-scale applications. Future research will focus on optimizing the bionanozyme formulations and potential immobilization expanding their applicability to a wider range of contaminants and scenarios.
Background/Objectives. 1,4-Dioxane (dioxane) is a probable carcinogen and persistent groundwater pollutant often found comingled with chlorinated solvents (e.g., trichloroethylene, dichloroethylene, and trichloroethane). Because of dioxane’s high mobility in groundwater, dioxane plumes tend to be large and dilute. Proposed EPA risk guidelines for dioxane in drinking water are as low as 0.35 μg/L. Reaching this low clean-up guideline through remediation has proven to be particularly difficult and costly. Utilizing aggressive pump-and-treat and ex-situ technologies such as advanced oxidation (AO) on dilute dioxane plumes is often prohibitively expensive. Monitored natural attenuation (MNA) is a low-cost alternative, but it can have difficulty reaching stringent clean-up concentrations. Utilizing aggressive pump-and-treat and ex-situ technologies such as advanced oxidation (AO) on dilute dioxane plumes is often prohibitively expensive. Alternatively, phytoremediation using poplar trees has been proposed as a cost-effective clean-up strategy. Another promising solution is to pump the contaminated water onto plantations of trees and to bioaugment the poplar rhizosphere with dioxane-degrading bacteria to speed remediation. In prior laboratory studies, we evaluated metabolic dioxane degraders Pseudonocardia dioxanivorans CB1190 and Mycobacterium sp. PH-06 as bioaugmentation candidates to speed the degradation rate of dioxane by hybrid poplar (Populus deltoides x nigra, DN34) via bioaugmentation. However, these strains are often ineffective at relatively low dioxane concentrations (< 100 µg/L) commonly encountered in the field. In addition, chlorinated solvents have been shown to inhibit dioxane degradation by CB1190. In our recent work, we have identified Rhodococcus ruber 219 as a strong alternative candidate for field bioaugmentation. With the addition of B-vitamins, the strain can sustain metabolic degradation in dilute dioxane concentrations (< 100 µg/L) and degrade dioxane to below health advisory levels (< 0.35 µg/L).
Approach/Activities. Our current research aims to demonstrate that bioaugmented phytoremediation offers a reliable and cost-effective treatment solution for 1,4-dioxane and chlorinated solvent co-contaminants. To validate this, we conducted initial flow-through groundwater column experiments to evaluate dilute dioxane (~100 µg/L) metabolism by R. ruber 219 with or without hybrid poplar. Furthermore, we are conducting a pilot-scale demonstration at the former Twin Cities Army Ammunition Plant (TCAAP) in Arden Hills, MN. This site has a significant 1,4-dioxane and chlorinated solvent plume extending 6 miles offsite, contaminating nearby community drinking water wells. During this demonstration, we are evaluating bioaugmented phytoremediation utilizing above-ground Phyto Attached Growth Reactors (PhAGRs®) developed by project partner Ecolotree, Inc. These PhAGRs are planted with poplar or willow trees and bioaugmented with R. ruber 219 to treat irrigated groundwater contaminated with dioxane and chlorinated solvents.
Results/Lessons Learned. We report results from flow-through column experiments in which R. ruber 219 maintained the metabolism of dilute dioxane (~100 µg/L) to 0.5-5 µg/L for one month. In addition, we report the results of the first two years of our field demonstration. In May 2023, twenty-four PhAGRs filled with perlite were deployed to TCAAP and bioaugmented with R. ruber 219. Following irrigation with TCAAP groundwater, the effluent was recycled continually to the top of each PhAGR by drip irrigation to ensure treatment of 1,4-dioxane and chlorinated solvent co-contaminants. This successful strategy achieved sustained 1,4-dioxane effluent concentrations below 1 µg/L. In addition, chlorinated solvent co-contaminants were effectively removed to below Minnesota Pollution Control Agency (MPCA) advisory levels. Using qPCR, we also report the remarkable resilience of R. ruber 219 despite low initial 1,4-dioxane concentrations (~30 µg/L) in the TCAAP groundwater, an exceedingly low substrate concentration for metabolic degraders. Ongoing work aims to further optimize the system to increase treatment volume while ensuring sustained treatment. In addition, we strive to bolster the system’s performance to reach effluent dioxane concentrations below 0.35 µg/L. We expect this demonstration to yield a cost-effective treatment strategy for source control at many dioxane-contaminated DoD sites.
Sulfolane is used to sweeten sour gas and for CO2 capture, and it is found as a contaminant in groundwater. While sulfolane is miscible in pure water, sulfate salts decrease its miscibility. As a result, sulfates hinder sulfolane migration in model clayey fractures. Chloride salts have a less marked effect than sulfates, but they promote partitioning of sulfolane in hydrocarbons when these are present as co-contaminants. This delays the vertical migration of sulfolane in a model sandy aquifer.
Amines such as diisopropylamine are used alongside sulfolane in industrial processes and are thus found as co-contaminants in groundwater. Diisopropylamine can be dispersed in water yielding electrically charged droplets that can be separated through electrokinetic methods. Similar to sulfolane, its miscibility in water decreases with salts. Without salts, sulfolane promotes the miscibility of diisopropylamine in water and hampers its sorption onto different minerals, possibly enhancing its migration in aquifers with low salinity.
N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD)-quinone (6PPD-Q), a transformation byproduct of the widely used tire antioxidant and antiozonant 6PPD, has recently been identified as the primary cause of acute lethal toxicity to coho salmon in urban storm runoff. The asphalt concrete (AC) surface layer, which contacts 6PPD-Q upon its release from
tires, plays a critical role in its environmental fate. The incorporation of recycled tire rubber (RTR) into asphalt mixtures is a common practice, necessitating an urgent investigation into the interactions of 6PPD-Q at the asphalt-water interface.
This study evaluates the sorption and desorption dynamics of 6PPD-Q in both compacted and crushed loose (∼5 mm) rubberized asphalt mixtures, as well as its mobilization during simulated rainfall events. The crushed loose mixtures reflect the physicochemical properties of asphalt materials, while the compacted mixtures simulate in-service AC layers. Sorption equilibrium for
6PPD-Q was achieved within 12 days, with coefficients ranging from 151.57 to 257.51 L/kg for compacted asphalt. Desorption rates after 12 days varied from 0.01 to 0.09 μg/L for crushed loose mixtures and 0.025 to 0.05 μg/L for compacted mixtures when exposed to double deionized water and synthetic stormwater. Rainfall simulation experiments revealed 6PPD-Q concentrations in runoff water of 0.0015 to 0.0049 μg/L, significantly below the lethal concentrations (LC50) of 0.095 μg/L for coho salmon and 308.67 μg/L for zebrafish larvae.
These findings suggest that while the release of 6PPD-Q from compacted rubberized asphalt mixtures is minimal, these materials can effectively act as sorbents for this emerging contaminant, highlighting their potential role in mitigating urban runoff toxicity.
Background/Objectives. 1,4-Dioxane is a groundwater contaminant that is a growing concern and is commonly associated with chlorinated solvent plumes. Removal of 1,4-dioxane using traditional physical-chemical water treatment technologies can be difficult, and many existing groundwater pump and treat (P&T) systems are not equipped to remove chlorinated solvents and 1,4-dioxane. While advanced oxidation processes (AOPs) can reliably destroy 1,4-dioxane, other treatment methods are emerging – with bioremediation serving as a reliable, safe, sustainable, and economical alternative to AOPs. Bioreactors are an attractive option for retrofitting existing P&T systems when 1,4-dioxane treatment is required, or as a technology to incorporate into new construction. The focus of ESTCP project (ER22-7226) is the biodegradation of 1,4-dioxane using propane as a primary substrate in an aerobic membrane biofilm reactor (MBfR). The objectives of this project are to demonstrate the effectiveness of the technology to destroy 1,4-dioxane in groundwater to below relevant regulatory standards and compare MBfRs to AOPs on the basis of economics and sustainability.
Approach/Activities. This project combines two previously demonstrated remedial technologies: propane-mediated biodegradation of 1,4-dioxane and MBfRs. Biodegradation of 1,4-dioxane typically occurs via aerobic pathways. Engineered bioremediation approaches have been implemented at the pilot-scale and full-scale and have commonly utilized propane as a primary substrate. Using gaseous species to foster biologically mediated reactions in conventional engineered bioreactors can be challenging, specifically related to achieving adequate gas transfer. An MBfR eliminates this challenge by utilizing pressure-controlled gas-transfer membranes by providing gaseous substrate directly to the biofilm via membrane diffusion. Gas supply to the biofilm is driven by the concentration gradients induced via biochemical demand, making the MBfR a self-regulating system. The first phase of this project initiates with bench-scale testing to configure commercially available membranes for 1,4-dioxane biological treatment. A field demonstration will then be conducted at Arnold Air Force Base, in Tennessee, to gather the data required to take this technology to full scale.
Results/Lessons Learned. Work to date has focused on quantification of oxygen and propane fluxes through two types of commercially available membranes. Additionally, bench-scale MBfRs have been operating to degrade 1,4-dioxane in the presence of two types of bioaugmentation cultures and under various operating conditions. Initial bench-scale MBfR results demonstrate 93% to 99.9% 1,4-dioxane removal when provided at high concentrations (e.g., 1 mg/L to ~60 mg/L) as the sole carbon source. Propane-mediated cometabolic tests resulted in ~50% to >99% removal of 1,4-dioxane, starting at approximately 100 µg/L, to less than 5 µg/L for various configurations and operating conditions. The molar ratio of 1,4-dioxane to propane has been varied between 1:200 to nearly 1:30000 to test treatment sensitivity and identify optimal operating conditions for the future field demonstration at Arnold Air Force Base.
Sulfolane is a constituent of concern at former oil and gas sites where is it used in the Sulfinol process for sweetening gas. Sulfolane is an emerging contaminant with chemical properties that promote transport in groundwater, including high solubility, low sorption potential and low volatility. While biodegradation of sulfolane under aerobic conditions has been demonstrated in laboratory and field-scale studies, it is critical to establish the site-specific intrinsic capacity for sulfolane biodegradation and to evaluate remedial strategies to enhance sulfolane biodegradation, for full-scale remedial design.
A former gas plant was piloted for enhanced attenuation via biosparging by amending the groundwater with oxygen to enhance the growth of aerobic sulfolane-degrading microorganisms and increase sulfolane degradation rates. Field-scale biosparging resulted in sulfolane biodegradation to below criteria. To confirm and understand the observed decreases in sulfolane concentrations, multiple lines of evidence were employed, including traditional site data combined with culture-based techniques, and molecular biological tools to enrich, identify and assess microbial sulfolane-degraders.
A multi-year study, with the goal of characterizing sulfolane degraders in site groundwater, included propagating sulfolane degraders from groundwater on a microbial growth media containing sulfolane, followed by comprehensive studies of the microbial population including 16S rRNA amplicon sequencing to characterize the culture’s microbial community and to assess changes due to varying sulfolane concentrations. Culture based methods were used to isolate putative sulfolane degraders, and genomics and proteomics were used in biomarker discovery, specifically identifying genes and proteins integral to sulfolane degradation.
In summary, we have developed a culture capable of degrading sulfolane, identified two potential novel putative sulfolane-degraders and putative genes and enzymes involved in the sulfolane degradation process. Future work includes understanding how these microbes cooperate in the sulfolane degradation pathway and deploying tests targeting identified biomarkers to assess sulfolane bioremediation potential at sulfolane sites.
Background. Per- and polyfluoroalkyl substances (PFAS) are commonly found in municipal wastewater/biosolids. PFAS originate from various industrial and municipal sources, including papermaking, textile mills, and down-the-drain discharges in residences. These compounds include commonly studied chemicals such as PFOS and PFOA, but short-chain PFAS and polyfluorinated compounds pose challenges for removal in wastewater treatment plants (WWTPs). Despite uncertain and variable removal efficiency previously reported, understanding PFAS fate in treatment processes is crucial, especially considering their potential transformation into the more stable PFOS and PFOA.
Wet Air Oxidation (WAO), an advanced oxidation technology, has been effective in treating complex organic pollutants in wastewater since its development in the 1950s. Operating under elevated temperatures and pressures, WAO utilizes oxygen, purified or from air, to oxidize organic compounds into simpler, inorganic substances. While primarily involving free-radical reactions, WAO's specific impact on PFAS and their precursors remains uncertain. The Total Oxidizable Precursors (TOP) assay, designed to transform all oxidizable PFAS precursors into measurable PFAAs, offers insights into precursor concentrations in various environmental matrices. However, its efficacy, particularly in organically rich matrices like WWTP solids, requires further investigation. Comparing WAO and TOP assay outcomes provides valuable insights into PFAS oxidation potentials, and the specific compounds generated during WAO. Understanding these processes' implications aids in managing PFAS release into the environment through effluent discharge or biosolids. In summary, a comprehensive comparison between WAO and TOP assay characterizes the PFAS oxidation mechanisms and precursor quantification, informing wastewater treatment plant practices and environmental management strategies for PFAS contamination.
Material/Methods. Sample Collection: As part of a comprehensive monitoring study of multiple WWTPs, extensive sampling was conducted at each WWTP, we are focusing on one WWTP employing WAO for biosolids treatment. Two sets of samples of biosolids and aqueous media were collected: pre-WAO and post-WAO process. Post-WAO samples comprised treated biosolids and aqueous decant samples. Samples were collected concurrently during each sampling event from specified locations within the WWTP. PFAS Analysis Methods: The samples were analyzed with EPA Method 1633 and an adapted version of laboratory-specific EPA Method 537.1 (LS-Method 537) and total organofluorine (TOF). Quality assurance and control samples were incorporated in each sampling event. Samples with High Solid Content: Analytical challenges in treating samples with high solid content were addressed by centrifugation and analyzing both phases separately. This approach ensured accurate detection of PFAS compounds present in different phases. TOP Assay: Samples pre- and post-WAO underwent TOP assay treatment following previously described procedures. Liquid samples were spiked with TOP assay reagents, incubated, underwent SPE, and analyzed by LC-MS. For solid samples, sequential solvent extraction was conducted, followed by oxidation using TOP assay reagents. Total Organic Fluorine Measurement: Samples were analyzed for total organic fluorine (TOF) content using combustion ion chromatography (CIC). Liquid samples were analyzed for adsorbable organic fluorine (AOF) based on EPA 1621, while solid samples were analyzed for extractable organic fluorine (EOF). These methods ensured comprehensive analysis of PFAS and organic fluorine content in both liquid and solid samples collected from the WWTP before and after WAO treatment.
Results/Discussion. This presentation describes our findings including: 1) PFAS composition and analytical challenges in samples pre-WAO and post-WAO: Average PFAS treatment through WAO over 34 sampling events. The diverse composition of PFAS compounds and the complexities in their detection and quantification across matrices presented unique analytical challenges. PFAS composition differed between solids before and after WAO and the decant. For example, 5:3 fluorotelomer carboxylic acid (5:3 FTCA) was only detected in the decant samples with concentrations ranging between ~60 to 1,600 ng/L. 2) PFAS mass balance through WAO and potential intermediate generation: Mass balance calculations based on EPA Method 1633 consistently indicated potential intermediate generation or losses of precursors during the WAO process. In particular, a mass balance for 5:3 FTCA revealed increasing concentrations during treatment implying incomplete conversion of related precursors during WAO. 3) Cumulative probability plots: Statistical analysis using cumulative distribution plots further supported precursor transformation during the WAO process and intermediates generation for all sampling events. 4) TOP assay: Results showed PFSAs and some intermediates including FTCAs generated in most of the sampling events in pre-WAO samples with negligible PFCA generation after the TOP assay. Conversely, high pH conditions during the TOP treatment may contribute to PFSA formation through sample hydrolysis compared to more neutral conditions during WAO. 5) Comparison between WAO and TOP assay: Comparison between WAO and TOP assay outcomes provides insights into PFAS oxidation levels and precursor quantification, aiding in understanding the WAO effectiveness and the use of TOP in WWTP analysis. Overall higher conversion factors up to 2 times the precursor to intermediates were observed for WAO compared to TOP assay implying a more favorable precursor oxidation process in WAO. 6) Total organofluorine (TOF) analysis: TOF content of the pre-WAO samples were mostly undetectable which was attributed to analytical challenges and limitations associated with TOF methods for complex matrices. Finally, we will discuss the implications for WAO and other oxidizable processes on WWTP operation which have significant implications for optimizing WWTP operation for effective PFAS removal strategies.
The extensive use of per- and polyfluoroalkyl substances (PFAS) in consumer products and industrial processes has resulted in widespread environmental contamination. Remediation efforts will lead to the accumulation of large amounts of solid waste, such as excavated soils, pavements, and spent water treatment materials (e.g., granular activated carbon [GAC]). Incineration is a practical method for managing these waste stockpiles; however, the thermal destruction of PFAS requires extremely high temperatures (>1,000 °C) and may release undesirable products of incomplete destruction (PIDs) in the flue gas.
In this presentation, I will discuss our efforts to enhance PFAS mineralization in solid wastes at lower temperatures using alkali and alkaline-earth metal additives. While the temperature required to initiate PFAS thermal destruction was the same with or without additives—indicating similar initial reaction steps—the presence of additives significantly improved the mineralization process. The additives not only increased the reaction rate but also reduced the formation of PIDs. For instance, when GAC contaminated with perfluorooctane sulfonate (PFOS) was treated at 800 °C for 15 minutes without additives, only 49% of the PFOS was mineralized. In contrast, using Ca(OH)2 as an additive resulted in 98% mineralization in less than 3 minutes. The additive's ability to increase the reaction rate and alter byproduct selectivity suggests it acts as a catalyst. Additionally, it prevented the release of HF in the flue gas by forming CaF2 in the ash. These findings highlight the potential of catalytic additives to lower operating costs and mitigate the environmental impacts of incinerating PFAS-contaminated solid wastes.
PFAS are found in shallow soil worldwide at sites with no onsite discharges and far from known sources. Environmental regulations are generally predicated on the assumption that contaminants were discharged at a site. Regulatory programs often allow consideration of ambient background concentrations (ABCs) to determine if a contaminant release has occurred at a site and if so, utilize those ABCs in development of site-specific cleanup standards. The concept of ABC is especially relevant to PFAS due to their ubiquity and promulgation of very stringent cleanup standards.
We collected 100 surface soil samples (0- to 6-inch depth) from across Massachusetts for analysis of 36 PFAS compounds to evaluate ABCs. Samples were collected under double-blind sample protocols to preserve anonymity of the owners, from 25 publicly- and privately-owned, undeveloped or minimally developed, parks, woodlands, and conservation areas with no known PFAS discharges or nearby industrial sources. PFOS (range 0.19 to 6.0 ng/g, median 1.0 ng/g) and PFOA (range 0.072 to 4.2 ng/g, median 0.61 ng/g) were detected in every sample. Four other compounds (PFBA, PFNA, PFHpA, and PFUnA) were detected in at least 80% of the samples.
The significance of these background soil PFAS concentrations is highlighted by comparison of the individual and population background results with current Massachusetts soil cleanup standards, and implications of those results under current regulations. At least one compound from 64 of the 100 individual samples, and samples from 21 of the 25 properties, exceed reportable concentrations. Thus, if this study was not conducted under double-blind protocols, the owners of those 21 properties would be obligated to notify the Massachusetts Department of Environmental Protection (MassDEP). MassDEP may then identify the presence of these compounds as a “release” and require further investigation and remediation, regardless of the characterization of these properties as background with no onsite source or discharge of PFAS.
The most stringent Massachusetts soil standards (S-1/GW-1 standards) are based upon an assumption that PFAS could leach from soil into an underlying aquifer at a concentration exceeding drinking water standards. Statewide average background concentrations exceed the S-1/GW-1 standards for PFOS, PFOA, PFNA, and PFDA. Considering the number and widespread distribution of the sample locations, widespread PFAS groundwater contamination at concentrations exceeding drinking water criteria is expected. MassDEP reports PFAS data for 1,669 samples from private wells from 85 towns in which 60% or more of the residences utilize private wells for their primary drinking water supply. PFAS were detected at concentrations above the GW-1 groundwater standard in 6% of private wells across the state. This frequency is far less than the frequency of sample locations (64%) or properties (84%) at which the S-1/GW-1 soil criteria were exceeded in our study, which implies that the model underlying the S-1/GW-1 standard derivation may be inappropriate or apply overly conservative assumptions.
Our results highlight the potential liabilities for innocent landowners even though no discharge has occurred at their site. PFAS were routinely detected at concentrations exceeding current soil cleanup criteria, in undeveloped, open-space and conservation areas with no known PFAS discharges and far from known sources. Under current regulations, those landowners could be subject to costly investigation and remediation even though no discharge has occurred at their site.
Filtration methods are commonly used for the large-scale treatment of PFAS-impacted water, resulting in the transfer of PFAS to solid media which must be reactivated or disposed of. Depending on influent PFAS concentrations and effluent standards, treatment by filtration can generate large quantities of solid waste whose fate by reactivation can be costly and whose fate by disposal may face regulatory uncertainty. Surface active foam fractionation (SAFF) provides an alternative solution to filtration by injecting air into impacted water to generate PFAS-rich foam. Removal of the foam results in large reductions in PFAS concentrations in the treated water and a highly concentrated, small volume waste stream that can be disposed of or treated by numerous PFAS destruction technologies. The purpose of this study was to evaluate the effectiveness of SAFF at treating impacted groundwater in the eastern Twin Cities, Minnesota metro area and to determine whether SAFF is a feasible technology to address impacted waters in a full-scale treatment system as a method to increase the time between changeouts of filtration media required to provide safe drinking water to the affected communities.
This study unfolded across two stages. The purpose of the first stage was to evaluate the effectiveness of SAFF at treating low-foaming, impacted groundwater in the eastern Twin Cities, Minnesota metro area and to determine the operational parameters which achieve optimal removal efficiencies. The second stage, which is currently in progress, uses the effluent rendered by these optimized settings for RSSCT column studies to determine the extent to which SAFF pretreatment can reduce consumption of filtration media in a full-scale drinking water treatment system. The results of these RSSCT column studies can inform cost and energy savings associated with extending the lifespan of filtration media.
The pilot study was conducted with a SAFF®20 (EPOC Systems, Australia) to determine the PFAS removal efficiency when treating impacted groundwater from the Shakopee and Jordan Aquifers, both of which are used for drinking water by communities in the area. No amendments were used during this pilot study to improve removal. Operational settings including air injection rate and treatment time were varied with each water source to evaluate the effect on removal efficiency during primary fractionation. Performance variability was then evaluated over a longer treatment duration across several weeks for the optimized settings, which allowed for fine-tuning of the secondary fractionation stage and evaluation of long-term concentrate production. To evaluate the potential extension in lifespan of filtration media to achieve drinking water standards, rapid small scale column tests (RSSCTs) will be completed with granular activated carbon (GAC) and ion exchange resin with raw water and SAFF-treated water from the Shakopee Aquifer.
No foam was observed during the SAFF treatment of groundwater during primary fractionation because of its low total organic content. This was an anomaly when compared to other readily-foaming influent waters typically supplied to SAFF systems. Even without the formation of visible foam, removal efficiencies exceeded 99% for PFOS and 98% for PFOA during treatment of the more impacted Shakopee Aquifer, resulting in a reduction of PFOS and PFOA concentrations from approximately 800 ng/L and 300 ng/L, respectively, to 3 ng/L PFOS and below detection limits for PFOA. Initial PFAS concentrations were lower in the Jordan Aquifer at 5 ng/L PFOS and 40 ng/L PFOA. Although the resulting removal efficiencies were lower, effluent PFOS and PFOA concentrations were below 2 ng/L. The longer duration studies showed that with the treatment of approximately 35,000 gallons per day, less than a gallon of concentrate was produced each day.
This pilot study demonstrated that significant PFAS removal can be achieved with a SAFF system even without the presence of other organic chemicals that can promote the formation of foam. While this pilot study demonstrated significant removal of PFOS and PFOA, effluent concentrations remained in exceedance of Minnesota Department of Health (MDH) Health Risk Limits (HRLs), signifying that a polishing step using filtration media would be required to achieve the required concentrations for drinking water. Ongoing work is evaluating the extent to which pretreatment with SAFF can reduce the amount of granular activated carbon (GAC) and ion exchange resin required to achieve the drinking water standard. These results will then be incorporated into a feasibility study and used to evaluate the extent to which SAFF can be used to provide clean drinking water to communities in the eastern Twin Cities.
Wastewater treatment plants (WWTPs) are sources of Per- and Polyfluoroalkyl Substances (PFAS) pollution, yet PFAS monitoring and fate assessment in WWTPs remain insufficient. We compiled a public WWTP-PFAS-CA statewide database (2020 - 2023), encompassing information from over 200 WWTPs across California. This database includes PFAS concentrations in influent, effluent, and biosolids and included data on sampling dates, wastewater sources, and treatment processes. Our analysis revealed that more than 80% of WWTPs exhibit increased total PFAS concentrations in the effluent. Individual PFAS were positively correlated with each other within the same wastewater matrix. Additionally, we developed a machine learning tool for PFAS monitoring (assessing total PFAS , individual PFAS occurrence, and predicting specific PFAS concentrations) in WWTPs. The AUROC/accuracy for the prediction of total PFAS risks were ~80%. Our machine learning models achieved ~80% accuracy in predicting total PFAS risk in WWTPs and identified key influencers of PFAS fate in influent, effluent and biosolids, including WWTP size, wastewater source, county population, and GDP.
Sorption-based processes are recognized among the most effective technologies for the sequestration of per- and polyfluoroalkyl substances (PFAS). However, the adsorption performance of both selective and nonselective adsorbents is often hindered by several factors, particularly the presence of dissolved organic matter, which poses a substantial challenge in the treatment of complex water matrices. This talk discusses the current and emerging challenges associated with PFAS removal via sorption-based processes, emphasizing the impact of increasingly stringent regulatory frameworks on shaping the development of advanced treatment strategies to mitigate these limitations.
Application of aqueous film-forming foam (AFFF) for firefighting activities can contaminate concrete and asphalt pavement materials with per- and poly-fluoroalkyl substances (PFAS), which can subsequently migrate and leach into the environments. This laboratory study was conducted to evaluate PFAS leachability potential from contaminated concrete and asphalt in their milled and intact forms. PFAS concentrations in contaminated concrete and asphalt varied substantially. The relative leachability of PFAS from concrete and asphalt materials was also found to be substantially different, with PFAS from concrete being more leachable than from asphalt. The functional group and chain length of PFAS were key factors in determining their leachability from both types of materials. The PFAS leachability from milled concrete was not affected by time; whereas for asphalt, it increased somewhat after 24 h. Particle size had a significant effect on PFAS leachability from concrete as well as from asphalt, with a greater proportion of PFAS leaching from smaller particles than from large particles. While the temperature did not affect PFAS leaching from milled concrete, relatively greater proportions of PFAS were found to leach at a higher temperature from the milled asphalt. PFAS leachability from milled concrete increased with a reduction in pH. PFAS leachability from intact concrete and asphalt half-pucks was found to be time-dependent. The short-chain PFAS were more prone to leaching than the long-chain PFAS from both materials. Furthermore, a greater proportion of PFAS leached from the intact concrete and asphalt materials with relatively lower levels of contamination than with higher PFAS concentrations.
We present a new technology which promises to be economically and environmentally advantageous for regeneration of spent ion exchange resins (IX) used for per- and polyfluoroalkyl substances (PFAS) water treatment. Unlike traditional methods that rely on methanol and brine, followed by costly methanol recovery through distillation, our technology eliminates methanol entirely, reducing both process complexity and energy costs and potentially paving the way for potable water applications. Results from batch and small-column desorption experiments highlight the impact of solution chemistry and additive type and concentration on regeneration efficiency. Compared to traditional methanol/brine mixtures, our all-aqueous formulation offers remarkable regeneration performance of spent IX resins used to treat groundwater impacted by aqueous film-forming foams (AFFF). These findings offer insights into improving sorbent reuse and PFAS degradation in regenerant solutions, providing a promising path toward safer and more sustainable water treatment technologies.
Concrete exposed to AFFF through spills or repeated fire training exercises may contain PFAS (Baduel et al., 2015) and may present a secondary source of PFAS. The leachate from intact concrete cores has
100s of ug/L of PFAS (Thai et al., 2022). Runoff from impacted concrete may contribute to stormwater discharge and have the potential to impact surface water receptors.
One possible mitigation is to apply a concrete sealant to the impacted material. This ESTCP-funded project is testing commercially available sealants for their ability to minimize the leaching of PFAS from concrete in both laboratory and field tests. The field tests are being conducted in three different climate
regimes to compare the performance of the sealants across a range of conditions. The initial phases of the project have investigated AFFF impacts at DoD sites across the U.S. These results, presented here, show a wide variability of PFAS concentration in concrete and are reflective of the type of AFFF used at
the sites. The surficial concrete has some PFAS at mg/kg concentration levels.
Concurrent with the field site selection was the selection of sealants for laboratory screening. Sealant selection is a complex process. Not only are physical performance characteristics, such as ability to withstand freeze/thaw cycles and heavy traffic (Doyle et al.,2021) important, but surface preparation requirements and application methods are critical factors that must be considered. These factors will be discussed. As with other remediation technologies, the preferred sealant will vary with a site’s specific
characteristics and needs.
In the laboratory, leaching tests have compared sealant performance using cores from three different DoD sites. Three methods of measuring leaching from PFAS-impacted concrete cores were used; the first is an adaptation of US EPA Method 1315 and two are published methods for evaluating leaching of PFAS from an intact concrete (Thai et al., 2022). These results will be presented in this presentation. The methods of application of the selected sealants in the field will also be presented.
At the RemTEC conference, we will present our research findings on the regeneration of spent GAC for the removal of PFAS from contaminated water. Our presentation will focus on (1) Preliminary findings on GAC regeneration in batch and column experiments, (2) Investigating fluorine mole balances during the regeneration process and (3) The performance of regenerated GAC while examining the adsorption/desorption mechanisms. We will discuss the experimental setup, including batch experiments with virgin and regenerated GAC, effect of different PFAS concentrations, evaluation of sorption kinetics and capacity. Also, we will make every effort to provide preliminary findings regarding the performance of various destruction technologies such as electrochemical oxidation and supercritical water oxidation (SCWO) on PFAS destruction in the residuals. We will highlight the importance of understanding PFAS fate during regeneration and the implications for sustainable water treatment practices. This technology exhibits considerable scalability potential and can be tailored for implementation at new sites with subsequent optimization.
The rapidly evolving science of PFAS raise many questions and concerns regarding the implementation of existing guidance, often resulting in requests for clarification and development of new policies and guidance. But existing CERCLA guidance has proven to be remarkably flexible to address the challenges of emerging contaminants, including PFAS. For example, EPA’s Risk Assessment Guidance for Superfund Volume I, Human Health Evaluation Manual (Part A) (RAGS) provides detailed instructions on calculating intakes from multiple exposure pathways, identification of toxicity values, calculating risks for multiple substances, and combining risks across exposure pathways. RAGS also provides information on, dealing with chemicals that we know are there but cannot quantify and assessing potential impact of chemicals that lack toxicity values. This presentation will review EPA expectations on how existing guidance and policies can be used to assess PFAS, in conjunction with other chemicals that may be co-occurring. We will also discuss the challenges of decision-making upon completion of the risk assessment, including consideration of ARARs and the selection of a trigger for action.
Bioaccumulation of per- and polyfluoroalkyl substances (PFAS) strongly influence PFAS toxicity thresholds in zebrafish (Danio rerio) where perfluorooctane sulfonic acid (PFOS) is among the most strongly bioaccumulative and potent. As part of a multi-generational PFOS toxicity investigation in zebrafish, PFOS bioaccumulation measurements and calculations of bioconcentration factors (BCF) were made over extended life-time water exposures through 180 days post fertilization (dpf) in parental generation (P) and first filial generation (F1) fish from a continuous exposure to environmentally-relevant PFOS concentrations (0, 0.1, 0.6, 3.2, 20, 100 µg/L PFOS, nominal, measured used in analyses) including 5 replicates per exposure and 50 fish per replicate. At 14 and 29 dpf, fish from the P generation were collected from each of the 5 replicate tanks and flash frozen for tissue analysis. Additionally, male and female fish were individually collected from 5 replicate tanks for each the P and F1 generations at 180 dpf and flash frozen. PFOS was extracted from whole-body tissues for all experimental replicates, measured by liquid chromatography tandem mass spectrometry (LC-MS/MS), and tissue concentrations calculated based on wet weights. PFOS bioaccumulation reached an apparent steady state at ≤ 14 dpf where whole-body tissue concentrations remained largely constant through 180 dpf in the P generation. Comparative tests of measured BCFs among PFOS exposure concentrations revealed multiple instances of significantly lower factors for the 20 and 100 µg/L PFOS exposures relative to the sub-µg/L exposures, 0.1 and 0.6 µg/L, indicating concentration-dependance. PFOS was highly bioaccumulative in zebrafish tissues with mean BCFs based on tissue wet weight values ranging from 255 to 2,136 L/kg. Statistically significant increases in PFOS bioaccumulation and BCF were observed in male fish relative to females where values were approximately doubled in males across PFOS exposure concentrations in 180 dpf fish from both the P and F1 generations. To assess the predictive potential of these data, we developed a toxicokinetic (TK) model for the zebrafish lifecycle that incorporates fertilization and spawning of embryos, their growth, hatching, and development into reproductive adulthood across a population exposed to PFOS, and are using it to simulate exposure of adults to PFOS followed by growth and development of progeny under long-term exposure conditions. The model is being refined and used to calculate BCFs in both P and F1 generations, the result of which will also be reported. Overall, PFOS accumulates rapidly in zebrafish tissues where apparent steady state concentrations remain stable through constant life-time exposure durations, with greater bio-accumulative potential for male fish.
The widespread presence of per- and polyfluoroalkyl substances (PFAS) in environmental media is being realized across urban, commercial, industrial and residential land use areas where expected and unexpected sources are undoubtedly present. This should not be an unexpected finding considering the widespread presence of PFAS in consumer products, firefighting foams (AFFF), and commercial/industrial materials associated with manufacturing and services. This situation presents challenges in conceptual site model (CSM) development, attribution of impacts to responsible parties, and in an evolving regulatory landscape with few comparative standards and guidance, assessing investigative results to determine what levels constitute the need for remedial action. This presentation explores several case studies of site investigation for PFAS in environmental media including air, groundwater, surface water and wastewater using various techniques to examine source to environmental pathways to receptors for development of CSMs that become the basis for determining the need for potential remedial actions.
Chlorinated solvents, including tetrachloroethene (PCE) and trichloroethylene (TCE), are among the most commonly-detected chemicals at cleanup sites and it is not uncommon for large plumes covering wide swaths of urban industrial areas to mask multiple sources. Identifying sources and disentangling multiple potential sources in commingled groundwater plumes are critical yet challenging components of forensic investigations to identify, and where appropriate, allocate sources to a plume. Herein, we propose a new methodology for disentangling large, chlorinated solvent plumes by identifying and delineating the impacts of smaller downgradient sources hidden within a larger plume emanating from an upgradient source or sources. This new approach involves the combination of three methodologies in two steps. A first step employs chlorinated solvent “fingerprints” consisting of “pie-charts” of PCE and its daughter products to identify unique downgradient fingerprints which cannot be explained by the upgradient source. A second step consists of plotting contaminant concentrations along the centerline of a plume and modeling the expected concentrations of the upgradient source migrating beneath the downgradient source by fitting a “most likely” decay curve (e.g., first order decay) to observed data from the upgradient source. Application of this new methodology at a large commingled PCE/TCE plume identified a number of different fingerprints (e.g., different ratios of PCE and its daughter products) which could not be explained by the upgradient source, and most likely represented previously unidentified sources of TCE/PCE releases. A number of these different fingerprints matched the locations on historical Sanborn maps of industrial operations that, based on historical operations and chemical uses, reasonably would have the potential to have used chlorinated solvents, and potentially released them into the environment. The second step, involving modeling the plume decay along the centerline of the plume, allowed us to delineate the extent of the upgradient plume that was masked by additional downgradient sources. In conclusion, this new methodology allowed us to identify at least two previously unknown TCE-contributing sites within the larger chlorinated solvent plume and delineate the extent of the impacts from the upgradient source.
The abstract discusses the challenges in distinguishing sources of Poly and Perfluoroalkyl Substances (PFAS) due to their widespread presence and persistence. Various forensic techniques, including identification of indicator compounds, concentration ratios, and multivariate analysis such as Principal Component Analysis (PCA), are utilized for source appointment. The study focuses on PFAS source areas at two Department of Defense (DoD) installations in the Western United States. Analytical data from impacted sites are compiled and transformed using different techniques like Z-score normalization and log ratios before PCA analysis. Preliminary results reveal distinct PFAS signatures associated with different sources, such as AFFF and automotive repair, or landfill leachate. The study emphasizes the importance of choosing appropriate data transformation techniques for accurate interpretation of PCA results, which may vary between sites. These findings aim to guide future research in optimizing variance explained in multivariate analysis of compositional data to inform resource allocation and decision-making for PFAS-impacted sites.
All groundwater projects are challenged by the uncertainty of subsurface conditions, particularly the permeability structure and the impact on groundwater flow paths. Different types of geologic models (conceptual, visual, and numerical) with varying degrees of sophistication are increasingly in use to address the stratigraphic heterogeneity that is the root cause of uncertainty. However, the accuracy and relevance of the geologic model developed for a site is highly dependent on the practitioner’s knowledge of depositional environments and ability to leverage all site data to correlate geologically plausible stratigraphic geometries. Environmental Sequence Stratigraphy (ESS) is a best practice to guide correlations, leverage existing data, and develop geologic models and parameters. ESS uses stratigraphic principles to better define and map the hydrostratigraphic framework of the subsurface and identify data gaps. Project examples from a range of environments are provided that illustrate models supported by ESS analysis vs. those developed using traditional lithostratigraphic approaches.
The recent regulatory focus on PFAS is likely to result in significantly more sites investigating potential impacts from PFAS. While PFOA and PFOS have previously been the main focus for regulations and risk assessment, that is slowly shifting as we learn more about PFAS beyond PFOS and PFOA. These changes highlight the importance of using ecological risk assessment to better understand site-specific risk from PFAS at impacted sites. The refinement of risk assessment tools and our understanding of PFAS exposure for wildlife at sites enhances our ability to assess risks to wildlife at sites with potential impacts from PFAS.
Hydrogen compound-specific isotope analysis (CSIA) is a mainstream isotope tool applied in contaminant assessment, both for contaminant source apportionment and for characterizing degradation processes. It is well recognized that hydrogen CSIA applications must necessarily be restricted to analysis of hydrogen that is not subject to exchange with water, if the results are to be representative of the contaminant source and/or of contaminant transformations. Hydrogen atoms readily exchange with water in polar functional groups (e.g., alcohol, carboxylic acids), but carbon-bound hydrogen atoms are generally thought to be recalcitrant with respect to this process. In contrast, we have recently demonstrated that carbon-bound hydrogen exchange with water is relatively fast for aqueous trichloroethene (TCE) at above-neutral pH and/or at temperatures corresponding to groundwater in warm climates. Under these conditions, the hydrogen isotope composition of TCE would be significantly altered by the exchange within the lifespan of a contaminant plume (Kuder and Ojeda, ACS EST Water 2023, 3, 712−719). In this presentation, we will discuss the implications of these recent findings with the focus on the assessment of the sources and fate of TCE. Whereas the exchange complicates the legacy applications of using hydrogen isotope data as a line of evidence for apportionment of TCE sources, it opens an interesting and novel avenue of contamination age dating applications.
In the presentation, we will summarize the results from batch equilibration experiments which permitted determination of TCE-water hydrogen exchange rates. Next, we will discuss how this evidence limits interpretations when using hydrogen isotope data as a line of evidence to apportion the sources of TCE (TCE solvent vs TCE product of reductive dechlorination). Finally, we will present examples of historical field data sets produced by the OU Laboratory to illustrate the convergence of the hydrogen isotope composition of TCE with that of ambient water over the timescales of residence in groundwater time.
The results from laboratory experiments demonstrate hydrogen exchange with half-lives well below 10 years projected for certain environments, such as for alkaline waters in carbonate aquifers. While the rates of the exchange are significantly slower in acidic groundwater and at lower temperatures, the traditional focus on using hydrogen CSIA data for TCE source apportionment appears poorly warranted. On the other hand, hydrogen data have the potential to constrain the time of residence of TCE in the environment, in that the detection of isotope signatures trending towards equilibrium with local water would indicate certain minimum residence times which can be calculated using known rate constraints of the exchange reaction. Conversely, detection of highly 2H-enriched TCE typical of manufactured solvent in waters conducive to rapid exchange would be a strong indication of recently dissolved TCE and a likely presence of an active DNAPL source. The same principle of data interpretation can be extrapolated to other compounds susceptible to the exchange.
Per- and polyfluoroalkyl substances (PFAS) concentrations in groundwater exceeded state regulatory thresholds at an industrial facility that spray-applied polytetrafluoroethylene (PTFE) and other fluoropolymer coatings onto medical devices for over 40 years. The facility is in a groundwater resource area where groundwater is used by nearby public and private water supply wells. The conceptual site model (CSM) developed for the site identified historical air emissions via spray booth and oven stacks at the facility as a primary source of PFAS to the environment that occurred primarily during former operations. PFAS were deposited and accumulated onto nearby soils, the facility roof and process equipment. These continue to be the primary and secondary sources, respectively, of PFAS to groundwater via leaching through the vadose zone and infiltration of stormwater runoff from the facility roof. PFAS concentrations in the site soils, groundwater, public water supply well, and some nearby private wells exceeded regulatory thresholds for PFAS.
This case study will provide highlights of the site investigations and mitigation activities and, in particular, will discuss:
• the multiple complexities in developing the CSM for the site and identifying the sources of PFAS at this industrial facility,
• challenges in mitigating accumulated PFAS in process equipment as a long-term secondary source of PFAS,
• addressing stormwater as a secondary PFAS source and design of the SCTS in the absence of guidance or stormwater criteria,
• the approved remedy for the site addressing, and
• lessons learned as part of the multi-year investigations at the site.
One of the most challenging elements of any groundwater project is the uncertainty of the subsurface. The complexity of the subsurface has confounded the progress, delayed remediation goals, and caused project-budget overruns for many remediation efforts at contaminated sites worldwide. This is oftentimes due to the oversimplification of the geologic model by assuming homogeneous, isotropic conditions when heterogeneity is the rule. The focus on the geologic model needs to be about teasing out the details of the subsurface heterogeneity that controls groundwater flow and contaminant migration. Geology-focused CSMs (applying concepts of Environmental Sequence Stratigraphy - ESS) have proven to be a best practice for resolving the challenges of geologic heterogeneity. This best practice was recognized by the U.S. Environmental Protection Agency in their 2017 Groundwater Technical Issue Paper. A geology-focused approach applies not only to environmental-restoration projects but is also relevant and beneficial to groundwater resources/sustainable groundwater management.
Diisopropyl ether (DIPE) is a branched ether that is byproduct of isopropyl alcohol (IPA) manufacturing. The extent and rate of in situ biodegradation of DIPE in groundwater at a former manufacturing facility were evaluated in a laboratory microcosm study. The study consisted of two phases: a 2022 microcosm study that assessed DIPE degradation under different electron acceptor and nutrient amendments, and a 2023 microcosm study that assessed DIPE degradation under intrinsic site conditions without amendments.
The 2022 microcosm study used groundwater and geologic material collected from four monitoring wells at the site, representing different DIPE concentrations and geochemical conditions. The microcosms were constructed under aerobic conditions and selected microcosms were amended with iron, manganese, and diammonium phosphate. One set of microcosms was also bioaugmented with a DIPE-degrading enriched microbial population from an on-site aerobic bioreactor. The results showed that DIPE degradation occurred in all microcosms except for the sterile controls, indicating the presence of indigenous DIPE-degrading microorganisms. Importantly, complete DIPE degradation was observed in intrinsic control microcosms without any further addition of oxygen and without addition of amendments for biostimulation and bioaugmentation. The DIPE degradation rates ranged from 0.002 to 0.022 per day, with half-lives of 31 to 347 days. Next Generation Sequencing analysis revealed the diversity and abundance of microbial communities in the microcosms and identified potential DIPE-degrading taxa. A comparison of the microbial communities in the microcosms and the on-site bioreactor indicated similarities in microbial composition.
Based on the results of the 2022 study which demonstrated aerobic DIPE biodegradation that did not require biostimulation or bioaugmentation, an additional treatability study was conducted in 2023 to confirm that DIPE degradation was also occurring under more anoxic conditions. The 2023 microcosm study used groundwater and geologic material collected from the same four monitoring wells as the 2022 study but constructed the microcosms under anaerobic conditions to enable observations of DIPE biodegradation at dissolved oxygen concentrations similar to those within the DIPE plume at the site. The microcosms for the 2023 study were not amended with any electron acceptors or nutrients. The results showed that DIPE degradation occurred in all microcosms except for the sterile controls, confirming the intrinsic biodegradation potential of the site. The DIPE degradation rates ranged from 0.001 to 0.005 per day, with half-lives of 139 to 693 days. Next Generation Sequencing analysis revealed the diversity and abundance of microbial communities in the microcosms and identified a shift in DIPE-degrading taxa from more aerobic to anaerobic communities.
These laboratory microcosm studies demonstrated that DIPE biodegradation can occur under both aerobic and anaerobic conditions with varying rates. The study also provided insights into the microbial ecology and functional genes involved in DIPE degradation.
Groundwater remediation at many Air Force installations is inherently complex due to long histories of multiple releases, multiple source areas and numerous chemicals of concern including emerging contaminants. This presentation will introduce the decision logic and approach for using Environmental Sequence Stratigraphy (ESS) principles to refine a conceptual site model (CSM) and support optimization of groundwater treatment systems to reduce life-cycle costs and accelerate remedial systems towards cleanup goals. Case studies in different geologic settings will be presented to show how application of ESS principles to better understand complex subsurface geology can accelerate projects towards cleanup goals by reducing uncertainty with respect to the nature, extent, and fate and transport of groundwater impacts.
Stormwater Best Management Practices (BMPs), including bioretention and bioinfiltration systems, are specifically designed to capture suspended sediments, including microplastics. Recent laboratory studies have demonstrated that these BMPs can remove 90% or more of microplastics; however, most of these particles remain concentrated in the upper 5 cm of the soil or filter media, primarily due to straining. Since plastics are non-biodegradable and expected to persist beyond the design life of stormwater BMPs, the accumulation of microplastics in the filter layer presents a potential environmental concern. Over time, the deposited microplastics may be resuspended and subsequently discharged into the effluent, potentially transforming the BMP into a secondary source of microplastic pollution. This presentation outlines when and how resuspension could become a critical factor in releasing previously captured microplastics from BMPs. Our results show that approximately 40% of the deposited microplastics can be resuspended and washed away during a single rainfall event, with resuspension occurring predominantly within the first few seconds of overflow. This phenomenon was found to be more pronounced for microplastics than for other sediments, a result attributed to the reduced adhesion of plastic particles to the filter media and their higher buoyancy, as plastics are lighter than sediments. We also show that adding a gravel layer above the filter media may mitigate the resuspension of microplastics by dissipating the energy of stormwater flow and trapping the buoyant plastic particles. These findings highlight the significant role of resuspension in diminishing the overall effectiveness of stormwater BMPs in microplastic removal and propose a straightforward engineering solution to reduce the associated risks.
PFAS-containing soils are found in source material of large groundwater plumes and in some cases stock-piled, like at Eielson Air Force Base (AFB) in Alaska, awaiting treatment. Under the Department of Defense’s Environmental Security Technology Certification Program (ESTCP), TRS implemented two pilot demonstrations of thermal desorption. Laboratory and field testing have shown near complete elimination of PFAS at 400oC. These demonstrations were completed to document PFAS reductions achievable at the field scale using thermal conduction heating (TCH) to temperatures around 400oC, both in situ at Eielson AFB and ex situ at Beale AFB.
At Eielson, a small soil pile was chosen for the demonstration, containing approximately 134 cubic yards of soil. The soil contained PFOS at an estimated starting concentration of 230 µg/kg (two orders of magnitude higher than the Alaska cleanup objective of 3.0 µg/kg). Heater borings were installed through the soil pile and the surface was covered and insulated. Heating was performed for 100 days, reaching temperatures in the pile between 350 and 450oC.
At Beale AFB, an in-situ location was chosen in a former fire training area. The treatment volume was approximately 120 cubic yds, with a maximum concentration of 1,750 µg/kg PFOS prior to treatment. The soil was treated with a TCH, vapor recovery and treatment system nearly identical to the Eielson AFB demonstration.
At Eielson, all the soil samples from locations which reached 400oC were below laboratory detection limits for PFOA and PFOS. Many of the lessons learned at Eielson were implemented at Beale AFB. The in situ project resulted in similar results – substantial reductions where the soils reached 350-400oC.
Based on these two successful demonstrations, TRS Group has been asked to implement an ex situ thermal treatment at Joint Base Elmendorf-Richardson through a partnership between ESTCP and the Defense Innovation Unit (DIU) called the Environmental Remediation & Restoration from PFAS Initiative. For this demonstration, 2,000 cubic yards of PFAS impacted soil will be treated during the spring and summer of 2024. The soil will be heated to 400°C using electrically powered horizontal heaters arranged in triangular arrays. Once the target temperature is achieved, heating will continue until the PFAS soil concentration performance objectives are met. The heating duration is anticipated to require approximately 120 days, with a vapor and process water treatment system similar to Eielson AFB.
For large-scale field applications, the energy usage and associated costs and sustainability impacts are major factors for thermal treatment. Energy densities in the range of 600-800 kWh per cubic yard treated means that the cost of the energy will be in the order of $80-150 per cubic yard depending on local electricity costs. With PFOA and PFOS scheduled to be added to the CERCLA list of hazardous compounds, such treatment costs may be competitive with alternate solutions such as landfilling.
Smoldering is an energy-efficient, flameless form of combustion that has been applied both in situ and ex situ to treat a wide range of contaminated soils and other organic wastes, including per- and polyfluoroalkyl substances (PFAS). Smoldering can be self-sustaining after a one-time, local ignition event by using low-volatility, high-energy contaminants as the fuel. Although PFAS do not support smoldering combustion in and of themselves and their high thermal stability often requires temperatures greater than 900°C for destruction, a supplementary fuel can be used to reach these temperatures in a smoldering combustion reaction to facilitate the destruction of PFAS.
A previous scale-up study conducted under the US Department of Defense (DoD) Strategic Environmental Research Program (SERDP) demonstrated reduction of PFAS concentrations in soil and granular activated carbon (GAC) to near or below detection limits using smoldering. Detailed sampling was also implemented to develop an excellent understanding of the fluorine mass balance (80 – 128% mass recovery). Further work evaluated commercial scale applications of smoldering for treatment of PFAS-impacted soils and spent media. This includes design and fabrication of a new, rapidly deployable ex situ treatment system (the STARxpress) in partnership with the Defense Innovation Unit (DIU). Results of the first deployment of the STARxpress to Joint Base Elmendorf-Richardson (JBER) for treating stockpiled PFAS-impacted soil will be presented.
Additional case studies will also be presented to highlight smoldering demonstration projects with the US Air Force Civil Engineer Center (AFCEC) and the Environmental Security Technology Certification Program (ESTCP). The AFCEC project includes a series of ex situ smoldering tests to evaluate treatment of PFAS-impacted soils, sediments, and spent GAC. The influence of soil type, moisture content, and PFAS and co-contaminant concentrations on treatment robustness and effectiveness will be discussed. Preliminary results from the ESTCP demonstration evaluating smoldering treatment of a PFAS source zone in situ will also be presented. This demonstration includes in situ soil mixing to distribute a powder activated carbon (PAC) supplementary fuel solution through the source zone prior to implementation of in situ smoldering.
The Mobile Remediation System (MRS-1), developed by ASRC Consulting & Environmental Services (ACES), utilizes electric induction to heat contaminated soils and remove per- and polyfluoroalkyl substances (PFAS) through thermal desorption. To enhance performance, an electric plasma torch was integrated into the system to power the Thermal Oxidizer Unit (TOU), achieving temperatures above 1100°C necessary for PFAS destruction without the use of hydrocarbons.
Initial testing demonstrated the effectiveness of this energy-efficient approach, significantly reducing PFAS concentrations in soil. The first large-scale deployment on the upgraded system is currently underway at Joint Base Elmendorf-Richardson (JBER) as part of an ESTCP demonstration, treating approximately 3,500 cubic yards of PFAS-impacted soil. This presentation will discuss the integration of the plasma torch, early results from JBER, and the broader potential of MRS-1 for scalable, on-site PFAS remediation across Department of Defense (DoD) sites and beyond.