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The comprehensive characterization of per- and polyfluoroalkyl substances (PFASs) is necessary for the effective assessment and management of risk at contaminated sites. While current analytical methods are capable of quantitatively measuring a number of specific PFASs, they do not provide a complete picture of the thousands of PFASs that are utilized in commercial products and potentially released into the environment. These unmeasured PFASs include many PFAS precursors, which may be converted into related PFAS chemicals through oxidation. The total oxidizable precursor (TOP) assay offers a means of bridging this gap by oxidizing unknown PFAS precursors and intermediates and converting them into stable PFASs with established analytical standards. The application of the TOP assay to samples from PFAS-contaminated sites has generated several new insights, but it has also presented various technical challenges for laboratories. Despite the increased number of literature studies that include the TOP assay, there is a critical and growing gap in the application of this method beyond researchers in academia. This article outlines the benefits and challenges of using the TOP assay with aqueous samples for site assessments and suggests ways to address some of its limitations.

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Persistent arsenic (As) pollution sources from anthropogenic activities pose a serious threat to groundwater quality. This work aims to illustrate the application of an innovative remediation technology to remove As from a heavily contaminated fractured aquifer at a historically polluted industrial site. Groundwater circulation well (GCW) technology was tested to significantly increase and accelerate the mobilization and removal of As in the source area. The GCW extracts and re-injects groundwater at different depths of a vertical circulation well. By pumping out and reinjecting in different screen sections of the well, the resulting vertical hydraulic gradients create recirculation cells and affect and mobilize trapped contaminants that cannot be influenced by traditional pumping systems. The first 45-m deep IEG-GCW® system was installed in 2020, equipped with 4 screen sections at different depths and with an above-ground As removal system by oxidation and filtration on Macrolite (Enki). A geomodeling approach supports both remediation and multi-source data interpretation. The first months of operation demonstrate the hydraulic effectiveness of the IEG-GCW® system in the fractured rock aquifer and the ability to significantly enhance As removal compared to conventional pumping wells currently feeding a centralized treatment system. The recirculation flow rate amounts to about 2 m3/h. Water pumped and treated by the GCW system is reintroduced with As concentrations reduced by an average of 20%-60%. During the pilot test, the recirculating system removed 23 kg As whilst the entire central pump-and-treat (P&T) system removed 129 kg, although it treated 100 times more water volume. The P&T plant removed 259 mg As per m3 of pumped and treated groundwater while the GCW removed 4814 mg As per m3 of the treated groundwater. The results offer the opportunity for a more environmentally sustainable remediation approach by actively attacking the contamination source rather than containing the plume.

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RESUMO Este trabalho apresenta os resultados da utilização de duas técnicas de investigação geoambiental em alta resolução: investigação passiva de vapores do solo e investigação com o uso de Membrane Interface Probe (MIP), em uma área contaminada por hidrocarbonetos de petróleo, localizada no município de Duque de Caxias, Rio de Janeiro. O processo de gerenciamento ambiental da área iniciou-se em 2012 e contemplou as etapas preconizadas nas legislações vigentes. Os resultados obtidos a partir das investigações tradicionais foram insuficientes para a compreensão das características físicas e geoquímicas necessária para o sucesso das fases de diagnóstico e, consequentemente, da remediação. Portanto, duas investigações em alta resolução foram conduzidas com o objetivo de refinar o modelo conceitual de forma a atender adequadamente à Resolução CONAMA nº 420/09 e à Resolução CONEMA nº 44/12, permitindo ações futuras mais eficientes. A investigação passiva de vapores do solo utilizou amostradores compostos por materiais adsorventes granulares, encapsulados em uma membrana microporosa hidrofóbica e quimicamente inerte que permite a difusão dos vapores presentes no meio. Os resultados representam qualitativamente a presença de contaminação no subsolo. O MIP é uma ferramenta de direct push com medição em tempo real, que detecta a presença da contaminação tanto em meios insaturados quanto saturados inconsolidados. A partir dos resultados integrados, foi possível constatar que a distribuição de compostos orgânicos voláteis (volatile organic compounds (VOCs)) em água subterrânea ocorre de forma descontínua ao longo da área, sendo possível identificar cinco hotspots distintos e suas diferentes áreas fonte, incluindo uma região com presença de fase livre.

ABSTRACT This paper presents the results of two high-resolution site characterization (HRSC) techniques: passive investigation of soil vapors and investigation using Membrane Interface Probe (MIP), in an area contaminated by petroleum hydrocarbon, located in the municipality of Duque de Caxias, Rio de Janeiro. The environmental management process in the area began in 2012 and contemplated the stages recommended by the current legislation. The results obtained from the traditional investigations were insufficient for the understanding of the physical and geochemical aspects for the success of the diagnostic phases and, consequently, the remediation phase. Therefore, it was conducted two high-resolution investigations with the objective of improving the conceptual model in order to comply adequately with CONAMA Resolution 420/09 and CONEMA Resolution 44/12, allowing future actions more efficient. The soil gas passive investigation used samplers composed of granular adsorbent materials, encapsulated in a hydrophobic and chemically inert microporous membrane that allows the diffusion of the vapors present in the media. The results qualitatively represent the presence of contamination in the subsoil. MIP is a direct push tool with real-time measurement, which detect the presence of contamination in both unsaturated and saturated media. From the integrated results, it was possible to verify that the distribution of volatile organic compounds (VOCs) in groundwater occurs in a discontinuous way throughout the area. It was possible to identify five distinct hotspots and their different source areas, including a region with the presence of free-phase.

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A life cycle conceptual site model (LC-CSM) can represent the actual spatial distribution and migration of pollution of a site very accurately and be beneficial in supporting decisions for accurate site remediation or risk management. A volatile chlorinated hydrocarbon contaminated site in the Beijing-Tianjin-Hebei region was chosen as the study case. LC-CSMs were established following the site assessment, preliminary investigation, detailed investigation, and supplementary investigation of each stage. The application of field screening tests such as a membrane interface probe and the multi-electrode resistivity method assisted in identifying potential pollution sources and hot points. Concurrently, a large amount of vinyl chloride, the end product of chlorinated hydrocarbon degradation, was detected in some boreholes, indicating that pollutant biodegradation had occurred at this site. Some typical boreholes and cross-sections were chosen to analyze the biodegradation indicators and chemical fingerprints, combining the results of the comprehensive score of chlorinated hydrocarbon anaerobic biodegradability in groundwater reaching 22. It is judged that the site has strong anaerobic biodegradability. This step-by-step optimization forms an LC-CSM for site investigation, which provides scientific support for accurate site characterization.

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High-resolution characterisation tools such as Laser-Induced Fluorescence (LIF) logging represent a step forward towards a more effective management of sites contaminated by light non-aqueous phase liquid (LNAPL) petroleum hydrocarbons. In this paper, the applicability of LIF response as an indicator of LNAPL mobility at one site with an unconsolidated aquifer was investigated. LIF profiles were logged adjacent to twin coring locations and wells with LNAPL transmissivity (Tn) measurements in a heterogeneous gasoline contaminated site in Western Australia. LIF response was correlated to Tn to a greater extent than LNAPL saturation (Sn) measurements from coring. In particular, LIF signal maxima were a better indicator of Tn than the integral LIF signal. Furthermore, LIF allowed rapid identification of areas with long-term near-immobile LNAPL (entrapped and residual) because of the multi-wavelength waveforms associated with distinct subsurface characteristics. It was also demonstrated that the delineation of presumably less-mobile intervals could be enhanced by using the relative LIF response in the 350 nm wavelength channel. Thus, this work gave evidence that LIF logging provides valuable information about LNAPL distribution and mobility in commonly found subsurface settings, despite generally poor correlations with Sn measurements. LIF probes can be successfully used to guide the installation and application of more costly conventional methods in addition to the development of existing site models.

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The conceptual site model (CSM) has been designed for Inactive/abandoned mines in the SW part of Cuddapah basin, which gives an overview of Inactive/abandoned mine characterization in terms of physical impacts such as vertical openings, dangerous impoundments, location of steep slopes, waste processing facilities, steep portal abandoned barite mine and assessment of groundwater analytical data. To evaluate the groundwater quality and its suitability for domestic, drinking purposes, 44 groundwater samples were collected from the southwestern part of the Cuddapah basin, were examined for major cations and anions. The suitability of groundwater for drinking purposes is assessed by comparing with the World Health Organization (W.H.O) and Indian standards (IS).

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Model-based decision making is commonly used in performance assessments to assure water resource protection for both human health and the environment for hundreds of years into the future. To make decisions regarding aquifer protection against potential contamination, a conceptual site model (CSM) describing the hydrodynamic behavior needs to account for subsurface heterogeneities in sufficient detail. When site-specific data are sparse, larger-scale geologic descriptions are adopted with the consequence of losing small-scale features (at the cm scale) that can control contaminant transport. In this study, a multiple lines of evidence approach is used to construct vadose zone CSMs based on an evaluation of several types of data, including geologic logs, borehole moisture content and concentration data, geophysical spectral gamma logging data, and groundwater concentration data for a tank farm at the Hanford Site in southeastern Washington State. The resulting CSMs of the unsaturated zone represent a synthesis of what is known about flow and transport processes at the site-scale and maintain consistency with knowledge that has been accumulated at the regional scale. Through a process of extensive data analyses, a systematic approach is described to create an evidence base that supports the evaluation and development of CSMs. Numerical models are then used to evaluate the impact that smaller-scale heterogeneities have on contaminant transport through the vadose zone for a performance assessment on waste tank closure. Together, the field data and the numerical experiments suggest that although small-scale features close to source releases can have an impact on horizontal spreading, overall there is a relatively minor impact on transport for the site under study as evaluated by differences in peak fluxes and arrival times for historical leak events, and for potential releases resulting from waste tank closure. Use of alternative CSMs, developed through careful examination of available characterization and monitoring data, provides confidence that geologic heterogeneities do not impact contaminant transport behavior significantly enough to alter the assessment of risk for closure at this site.

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The goal of the paper is to highlight the management of the complexities and risks for light non-aqueous phase liquid (LNAPL) sites, and how the Illustrated Handbook of LNAPL Transport and Fate in the Subsurface (CL:AIRE, London. ISBN 978-1-905046-24-9. http://www.claire.co.uk/LNAPL; "LNAPL illustrated handbook") is useful guidance and a tool for professionals to understand these complexities and risks. The LNAPL illustrated handbook provides a clear and concise best-practice guidance document, which is a valuable decision support tool for use in discussions and negotiations regarding LNAPL impacted sites with respect to the risks of LNAPL. The LNAPL illustrated handbook is a user-friendly overview of the nature of LNAPL contamination in various geological settings including unconsolidated, consolidated, and fractured rock environments to best understand its fate and behavior leading to the appropriate management and/or remedial approach of the two major risks associated with a LNAPL source. As a source term, LNAPL has chemicals that form dissolved- and vapor-phase plumes, which are referred to as composition-based risks; and being a liquid there is the risk that the source may expand impacting a greater volume of the aquifer, which are referred to as saturation-based risks. There have been significant developments in recent years on the understanding of the complex behavior of LNAPL and associated groundwater and vapor plumes; however, the state of practice has often lagged these improvements in knowledge. The LNAPL illustrated handbook aids the site investigator, site owners, and regulators to understand these risks, and understand how these risks behave through better conceptual understanding of LNAPL transport and fate in the subsurface.

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