Conceptual Site Model Research Articles

A Conceptual Site Model for Per‐ and Polyfluoroalkyl Substance Water Supply Impacts in a Residential Community

ABSTRACTAt a Class 4 State Superfund site located in a densely developed residential/commercial area in a suburb of New York City, emerging contaminant sampling for PFAS was performed as part of a statewide data‐gathering project. Two per‐ and polyfluoroalkyl substances (PFAS), perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), were detected at concentrations in excess of drinking water standards in bedrock and overburden monitoring wells at the State Superfund site. A bedrock private water supply well sampling program and a PFAS source investigation, consisting of overburden investigations near potential sources (i.e., sites with a history of known or suspected use, storage, or discharge of PFAS), were undertaken to assess exposures and identify and potentially eliminate sources of PFAS contaminants in the bedrock drinking water supply.Relative ratios of PFAS (i.e., PFAS signatures) were plotted geospatially to facilitate comparison of the characteristics of overburden groundwater sampling results to that of nearby bedrock private water supply sampling results. In addition, total PFAS concentrations in overburden groundwater and bedrock private water supply samples were compared to identify potential sources of bedrock groundwater impacts. The PFAS signature analysis revealed that (1) PFAS signatures of overburden groundwater samples were generally consistent with nearby bedrock private water supply samples; (2) total PFAS concentrations detected in overburden groundwater samples were marginally higher than concentrations detected in nearby bedrock private water supplies; (3) there was generally low variability in PFAS signatures throughout the study area (Assessment Area); and (4) overburden groundwater and bedrock private water supply PFAS signatures were similar to that of the nearby wastewater treatment plant effluent discharge, which represents a composite average PFAS signature for domestic wastewater from the area. Finally, septic system tracers were also detected in bedrock private water supply and overburden groundwater samples. Based on the results of the investigation, multiple lines of evidence support the Conceptual Site Model, which is likely applicable to many PFAS‐contaminated drinking water supplies with conditions similar to the Assessment Area: consumer product use and discharge to domestic septic systems in a densely developed residential area, lacking area‐wide municipal water and sewer, with shallow groundwater and bedrock, and a vertical downward groundwater gradient, have resulted in the widespread presence of PFAS in private water supply wells.

Examining site intervention efficacy and uncertainties with conceptual Bayesian networks: preventing offsite migration of DNAPL and contaminated groundwater.

For contaminated sites, conceptual site models (CSMs) guide the assessment and management of risks, including remediation strategies. Recent research has expanded diagrammatic CSMs with structural causal modeling to develop what are nominally called conceptual Bayesian networks (CBNs) for environmental risk assessment. These CBNs may also be useful for problems of controlling and preventing offsite contaminant migration, especially for sites containing dense nonaqueous phase liquids (DNAPLs). In particular, the CBNs provide greater clarity on the causal relationships between source term, onsite and offsite migration, and remediation effectiveness characterization for contaminated DNAPL sites compared to traditional CSMs. These ideas are demonstrated by the inclusion of modifying variables, causal pathway analysis, and interventions in CBNs. Additionally, several new extensions of the CBN concept are explored including the representation of measurement variables as lines of evidence and alignment with conventional pictorial CSMs for groundwater modeling. Taken as a whole, the CBNs provide a powerful and adaptable knowledge representation tool for remediating subsurface systems contaminated by DNAPL.

3D GeoRemediation: A Digital Hydrogeophysical–Chemical Clone and Virtual Hydraulic Barrier with Groundwater Circulation Wells (GCWs) for Groundwater Remediation

Identification of contamination sources and delineation of plumes in the geological environment stand as pivotal elements in reconstructing the conceptual site model (CSM) and devising remediation strategies tailored to specific physicochemical traits. This study endeavors to showcase the capabilities of a 3D digital interface, seamlessly integrating multi-source data, to elucidate site-specific contamination dynamics and steer the implementation of remediation strategies harmoniously aligned with the ethos of remediation geology. In a site historically marred by chlorinated solvent contamination, the digitization of stratigraphic, piezometric, chemical, and membrane interface probe (MIP) data underpins geomodeling endeavors and yields a meticulously crafted, data-driven CSM. The hydrogeochemical and hydrogeophysical data were interpolated to build a volumetric, digital 3D model illustrating data-driven elements. The comprehensive 3D clone adeptly delineates secondary contamination sources and renders visible the contamination plume within a georeferenced framework, mirroring the nuanced interplay of stratigraphic nuances and groundwater path. A data-centric approach to modeling facilitates the design of the first hydraulic virtual barrier leveraging groundwater circulation well (GCW) technology, its geometry finely attuned to intercept the contamination plume originating from source dissolution and aligning with preferential groundwater flow trajectories. Conventional hydrochemical monitoring and multilevel sampling substantiate the discernible reduction in chlorinated solvent concentrations across various depths within the aquifer horizon, affirming the efficacy of GCWs in their virtual barrier configuration. The findings highlight the effectiveness and limited groundwater consumption of the virtual barrier compared to the on-site pump-and-stock system. This research underscores the potency of a multi-faceted evidence-driven puzzle in conceptualizing contamination mechanisms within the geological milieu, thereby fostering the application of cutting-edge, effective, and sustainable remediation strategies.

Data Evaluation Framework for Refining PFAS Conceptual Site Models

AbstractContaminated sites with per‐ and polyfluoroalkyl substances (PFASs) are the cause of environmental, health, and financial concerns. Understanding and addressing PFASs at their source areas is important for effective characterization, risk assessment, and remediation. This paper introduces a framework that relies on commonly available PFAS data to assist in identifying PFAS source areas and assess PFAS fate and transport considerations along flowpaths. Currently accepted PFAS physical and chemical behaviors have been incorporated into metrics that can be evaluated geospatially, and/or over time, to build a weight‐of‐evidence approach to refine conceptual site models (CSMs). Graphical representation of data according to a PFAS “family tree” is also proposed for more consistent interpretation and pattern recognition. Combined, these tools create a PFAS data evaluation framework (PFAS Framework) that consists of a tiered analysis approach based on data availability and site complexity. Case studies from real sites are presented to demonstrate the capabilities of the PFAS Framework in identifying source areas.

Polydimethylsiloxane dialysis passive sampler monitoring of chlorinated solvent contaminated sites – A field study

The complexity of the subsurface contaminated by chlorinated solvents such as trichloroethylene (TCE) makes it challenging to gain a complete understanding of contamination distribution and establish a conceptual site model (CSM). High-resolution vertical contaminant concentration profiling across both the unsaturated zone and the saturated aquifer is desirable for mapping the distribution of contamination. A Fick's law-based polydimethylsiloxane (PDMS) dialysis passive sampler was developed and evaluated on a field scale for its potential application. This study tests the passive sampler at two TCE contaminated sites, and the sampling results were compared with the results from different sampling methods based on the relative percent difference. The PDMS dialysis passive sampler obtained more representative soil gas concentrations in the unsaturated zone than a portable monitoring and sampling device, which caused soil gas flow disturbance by soil gas pumping during sample collection. In the saturated aquifer sampling, the results obtained by the PDMS dialysis passive sampler correlated well with those obtained by a commercial polyethylene passive diffusion bag, and exhibited higher sensitivity under low TCE concentration conditions. Furthermore, the PDMS dialysis passive samplers were densely deployed inside each monitoring well at multiple depths, at two sites, to achieve high-resolution monitoring across the unsaturated zone and saturated aquifer. Based on the PDMS dialysis sampler data, a more comprehensive three-dimensional CSM was systematically established.

Exploratory study of groundwater infiltration in lough arrow using thermal imagery and geochemical tracers

abstract: Groundwater dynamics were investigated in Lough Arrow in the north-west of Ireland. The lake is designated under the EU Habitats Directive (92/43/EEC) for its representative Annex I habitat from which charophytes are the main feature of interest. Groundwater interactions are considered a significant component of the lough's hydrology with its Annex I archetype deemed vulnerable to the pressures of nutrient pollution. This study utilised thermal imagery and geochemical tracers to detect and quantify groundwater inputs. Landsat 7 Thermal Infrared Imagery from two dates in both summer and winter was processed to investigate the potential occurrence of localised seepage points of groundwater captured as anomalous spatial plumes. In situ surveys of radon were undertaken in summer to confirm the presence of groundwater in the lake. Results were subsequently modelled to estimate the total groundwater discharge into the lake during the survey period. Additionally, a conceptual site model was created to characterise potential pressures to the lake from groundwater interactions within the catchment. Thermal imaging failed to conclusively identify thermal plumes consistent with localised groundwater inputs in Lough Arrow. However, the radon inventory applied to the mass balance estimated the lake was subject to 6,722m3 of groundwater influx per day at the time of the survey. The conceptual site model determined the lake was subject to potential pollution pressures from groundwater due to the catchment's physical attributes and land use activities. This is primarily due to the presence of a karst aquifer in the majority of the catchment coupled with significant agricultural and forestry practices. The vulnerability of the aquifer and the influx of groundwater to the lake highlights the potential threat groundwater contamination may pose to the favourable conservation condition of Lough Arrow's Annex I habitat.

Critical review of the environmental management of a DNAPL contaminated site in Resende, Rio de Janeiro, Brazil

The current nonconformity of most Brazilian states regarding the environmental guidelines established by the Conama 420 resolution makes clear that there are still many challenges to be faced on the management field of contaminated sites. The analysis of a factual remediation operation in an industrial site in the city of Resende, Rio de Janeiro state, show that traditional site investigation techniques are still being applied as main tools of characterization, data collection and decision-making in the management of the area. The site has had its investigation start in the late 90’s through multiple soil sampling and monitoring wells installation, pointing DNAPLs (dense non-aqueous phase liquids) among the chemicals of interest. The industrial site has undergone remediation for over 10 years now and has not been closed yet. More recently, the efficiency reduction of the primary remediation system, a dual-phase extraction system with over 50 installed wells, led to the implementation of in-situ stimulated bioremediation. Performance reports show lower efficiency than expected, hinting that a lackluster CSM (conceptual site model) might be leading to poor decision making. Despite being adequate remediation techniques, previous efforts and literature indicate that the site must undergo new investigation steps employing high-resolution site characterization (HRSC) techniques such as the MIP (membrane interface probe), allowing the refinement of the current CSM and the optimization of current remediation efforts.

Delineation of a PFOA Plume and Assessment of Data Gaps in its Conceptual Model Using PlumeSeeker™.

An accurate conceptual site model (CSM) and plume-delineation at contamination sites are pre-requisites for successful remediation and for satisfying regulators and stakeholders. PlumeSeeker™ is well-suited for assessing data gaps in CSMs by using available site data and for identifying the optimal number and locations of sampling locations to delineate contaminant plumes. It is an enhancement of a university research code for plume delineation using geostatistical and stochastic modeling integrated with the groundwater modeling software MODFLOW-SURFACT™. PlumeSeeker™ increases the overall confidence in the location of the plume boundary through a variance-reduction approach that selects existing- or new monitoring wells for sampling based on minimizing the uncertainty in plume boundary and on new field information. Applicable at sites with or without existing monitoring wells, PlumeSeeker™ is particularly powerful for optimally allocating project resources (labor, well installation, and laboratory costs) between existing wells and sampling at new locations. An application of PlumeSeeker™ at Lakehurst, the naval component of Joint Base McGuire-Dix-Lakehurst in New Jersey, demonstrates how the cost of delineating the migration pathway of a perfluorooctanoic acid (PFOA) plume can be minimized by requiring only 9 new sampling locations in addition to samples from 2 existing wells for achieving a 70% reduction in plume uncertainty. In addition, the use of available site data in three different scenarios identified CSM data-gaps in the source area and in the interaction between Manapaqua Branch and groundwater, where the observed high concentration in this area could have resulted from a combination of groundwater migration and induced infiltration.

Assessing mercury pollution at a primary ore site with both ancient and industrial mining and smelting activities

The Minamata Convention on Mercury has mandated a renewed global effort to tackle Hg pollution. The present study evaluates Hg pollution at a primary Hg production site exploited since the Qin Dynasty (200s BC), with intensive industrial scale production over the past four decades. This single location accounts for over 95% total Hg production in China in recent years. To assess the environmental risk and effectiveness of recently implemented control measures, we collected 90 soil samples, 60 plant tissue samples, 47 sediment samples, and 47 river water samples from the site and its vicinity. A site-specific conceptual site model was established based on the sources, migration transformation pathways of Hg pollutant and its exposure scenarios. The maximum soil Hg concentration reached 10,451 mg kg−1, posing a high health and ecological risk. Vegetable and crop Hg concentrations outside the site reached 0.23 mg kg−1 in rice grains and 4.24 mg kg−1 in green onion. The highest health risk, with a hazard quotient of 130.66, was observed in the Ore Storage Site, which reduced to 17.14 when Hg bioavailability was considered. Risk control measures implemented in recent years included a stormwater collection system and capping of the tailing pond area with clean imported soil. These measures were generally successful; however, Hg in the tailings were found to be contaminating the imported surficial soil due to rainfall saturation and upward migration, suggesting a need for long-term post remedial site monitoring and maintenance. We also found that mining and smelting activities have contaminated a 6 km stretch of a nearby river, with sediment Hg concentrations reaching 2819 mg kg−1, and water column concentrations reaching 193.21 ng L−1. The sediment and water concentrations are highly correlated (R2 = 0.78), suggesting that, with risk control measures in place, a reservoir of Hg in polluted river sediment is now driving pollution in the water column. This work demonstrates that primary Hg mining has caused widespread and serious soil and water pollution. Risk control measures can reduce human health and ecological risks, but robust monitoring and maintenance are required for remediation to be effective in the long-term.

PEST and AEM Modeling for Data Acquisition Planning.

A well-planned field data collection program should be designed to (1) collect a sufficient set of data of the right types at the right locations, and (2) collect a parsimonious set of data to avoid unnecessary costs. Combining PEST and a simple analytic element method (AEM) groundwater flow model for the site of interest provides a relatively simple, low-cost method of developing such a program. AEM models are well suited to this approach because they are quick to develop yet hydraulically accurate, reducing impacts on project budgets at early data collection planning stages; and quick to run, solving rapidly for the many iterations that PEST requires to generate good parameter estimates. This article shows two examples of this method: one for a steady state watershed model, and one for a transient pumping test project to demonstrate that PEST coupled with a simple AEM model that sketches out the key features of a site conceptual model can be an efficient tool in planning key parts of a hydrogeologic site investigation.

Pump-and-treat (P&T) vs groundwater circulation wells (GCW): Which approach delivers more sustainable and effective groundwater remediation?

Pump-and-treat (P&T) is commonly used to remediate contaminated groundwater sites. The scientific community is currently engaged in a debate regarding the long-term effectiveness and sustainability of P&T for groundwater remediation. This work aims to provide a quantitative comparative analysis of the performance of an alternative system to traditional P&T, to support the development of sustainable groundwater remediation plans. Two industrial sites with unique geological frameworks and contamination with dense non-aqueous phase liquid (DNAPL) and arsenic (As) respectively, were selected for the study. At both locations, attempts were made for decades to clean up groundwater contamination by pump-and-treat. In response to persistently high levels of pollutants, groundwater circulation wells (GCWs) were installed to explore the possibility of accelerating the remediation process in unconsolidated and rock deposits. This comparative evaluation focuses on the different mobilization patterns observed, resulting variations in contaminant concentration, mass discharge, and volume of extracted groundwater. To facilitate the fusion of multi-source data, including geological, hydrological, hydraulic, and chemical information, and enable the continuous extraction of time-sensitive information, a geodatabase-supported conceptual site model (CSM) is utilized as a dynamic and interactive interface. This approach is used to assess the performance of GCW and P&T at the investigated sites. At Site 1, the GCW stimulated microbiological reductive dichlorination and mobilized significantly higher 1,2-DCE concentrations than P&T, despite recirculating a smaller volume of groundwater. At Site 2, As removal rate by GCW resulted generally higher than pumping wells. One conventional well mobilized higher masses of As in the early stages of P&T. This reflected the P&T's impact on accessible contaminant pools in early operational periods. P&T withdrew a significantly larger volume of groundwater than the GCW. The outcomes unveil the diverse contaminant removal behavior characterizing two distinct remediation strategies in different geological environments, revealing the dynamics and decontamination mechanisms that feature GCWs and P&T and emphasizing the limitations of traditional groundwater extraction systems in targeting aged pollution sources. GCWs have been shown to reduce remediation time, increase mass removal, and minimize the significant water consumption associated with P&T. These benefits pave the way for more sustainable groundwater remediation approaches in various hydrogeochemical scenarios.

Development of public exposure scenarios for land sites with residual radioactive contamination

The article considers the experience of development of public exposure scenarios for land sites with residual radioactive contamination on the example of three sites located in Moscow and St. Petersburg. The study was intended to identify the anticipated groups of land users and select parameters for calculating radiation doses. Exposure scenarios regarding use of land sites for living or working were described by such parameters as duration of the stay, staying indoors or outdoors, physical activity, etc. Exposure pathways for selected users were identified using the conceptual site model approach. For calculations within a number of scenarios, geomigration modeling of radionuclide transport in the environment was performed using the GeRa code. Exposure doses for population groups were calculated using the Ecorad-Aqua software module. Doses were calculated for each exposure pathway. The study demonstrates that the proposed scenario “Office worker” can be applied to various sites that are planned for placing administrative, industrial, scientific, commercial buildings and structures, scenario “Construction worker” – for sites with construction and excavation activities underway. The parameters of the “Resident” scenario allow for its application for the multiapartment residential development in large cities. In the future, it is practical to develop a typical scenario for an outdoor worker whose activity is to provide care and maintenance of the site. These scenarios can be used as ready-made solutions for calculating radiation doses for the population from residual radioactivity at the nuclear sites under decommissioning and remediated areas. Estimates of annual effective doses for the population are needed for decommissioning and remediation planning and determination of the values of radiation factors in the relevant projects.

Long-term leaching through clayey till of N,N-dimethylsulfamide, a Persistent and Mobile Organic Compound (PMOC)

Environmental pollution with Persistent and Mobile Organic Compounds (PMOC) from anthropogenic activities is an increasing cause for concern. These compounds are readily leached to groundwater aquifers and are likely to resist degradation, putting pressure on groundwater resources. Pesticides can form PMOCs upon degradation in the environment. The PMOC N,N-dimethylsulfamide (DMS) was the most frequently detected pesticide metabolite in Danish drinking water wells in 2020, although the pesticidal use of the last parent compound (tolylfluanid) ended in 2007. This study aimed to improve the understanding of the leaching of the PMOC DMS from clayey tills by combining a review of compound properties, sources and use, comprehensive field observations and numerical flow and solute transport modeling. The modeling explored the mechanisms of DMS retention during vertical transport in clayey till and the fingerprint in the underlying aquifer. The results were supported by detailed field observations at an agricultural site with strawberry production. Porewater samples were collected from clayey till to a depth of 12 m bgs by a custom designed installation method of suction cups. Groundwater sampling (249 samples) was designed to provide vertical concentration profiles at various distances from the presumed sources. The review of properties showed that the parent compounds and intermediates degrade quickly in topsoil, releasing the highly persistent and mobile DMS. We tested the effect of fractures on transport with different hydraulic apertures and a scenario without fractures by numerical modeling. The results showed that the presence of fractures can smooth the breakthrough curve below the clayey till, leading to faster breakthrough, lower maximum concentration, and several decades of prolonged leaching in simulations with the largest aperture (20 μm). The fracture-matrix interaction is a possible explanation for the observed delay of leaching from clayey till. The vertical concentration profiles in groundwater were used for identifying the sources at the field site and testing source strengths. Assigning one point source (200 μg/L) and two diffuse sources (40–50 μg/L) to the model produced vertical concentration profiles that compared well with observed field data in clayey till and the aquifer. All results were integrated into a conceptual model for the environmental fate of PMOCs in soil and groundwater. The findings of this study imply that the presence of fractures in clayey till should be considered in conceptual site models, since they can substantially prolong the leaching of PMOCs to groundwater. The integration of comprehensive field investigations and numerical modeling is key to understand the fate of PMOCs in complex field systems with different source types. Together with widespread occurrences of PMOCs in groundwater systems, the results highlight the need for improved approval procedures for pesticides and biocides which considers their persistent and mobile metabolites.

Comprehensive assessment of soil and dust heavy metal(loid)s exposure scenarios at residential playgrounds in Beijing, China

Small playgrounds situated within residential communities are popular recreational areas. However, heavy metal(loid)s (HMs) in soil or equipment dust may pose a public health risk. This study provides a comprehensive assessment of the health risk associated with HMs exposure at residential playgrounds in cities, a field that has not been thoroughly investigated previously. 70 soil and 70 equipment dust samples were collected from 30 urban and 40 suburban playgrounds in Beijing. Results indicated significant enrichment of Cu, As, and Ni in the soil with Enrichment Factors (EFs) >5 from both anthropogenic and lithogenic sources. Correlation analyses showed that the levels of Be, Cr, Mn, Co, Ni in soil and Be, Mn, As, Cd in dust were positively correlated with the distance to the nearest highway, with p-values < 0.01. Enrichment and correlation analyses contributed to a better understanding of the sources and transport pathways of HMs in urban environment. Based on a site-specific Conceptual Site Model (CSM), the carcinogenic risks (CRs) and Hazard Quotients (HQs) were quantified for residents as the ratio of HMs exposure to reference doses. Risk assessment indicated the mean predicted CR for children and adults exposed to soil was 3.75 × 10−6 and 5.29 × 10−6, respectively, while that at dust exposure scenarios was lower, at 2.47 × 10−6 and 3.49 × 10−6, respectively, all of which were at the upper end of U.S. EPA's acceptable criteria of 1 × 10−6 to 1 × 10−4. Among the HMs, As and Ni were identified as the priority control contaminants due to significant contribution to CRs. Furthermore, the spatial distribution revealed an increasing trend in health risk from the urban center to the suburbs. This study emphasizes the need for effective measures to mitigate potential health risk and enhance the safety of recreational areas, particularly for susceptible individuals.

DRASTIC-Fm-URBAN index: an updated and reliable GIS vulnerability mapping for the assessment of fractured rock media in urban areas

Fractured media hydrosystems sources are valuable worldwide for irrigation, water supply, and industrial purposes. Mapping and evaluating intrinsic groundwater vulnerability is a balanced integrative methodology to describe the potential groundwater contamination or pollution. The Geographical Information System (GIS) overlay mapping technique and multi-parametric methodology are largely employed to evaluate vulnerability in groundwater systems. However, the DRASTIC index methodology is often used for regional approaches and is the most recognised for groundwater vulnerability assessment for general purposes. Therefore, several adaptations were proposed, such as the DRASTIC‐Fm methodology focused on fractured rock media. This study proposes an updated multi-parametric DRASTIC-Fm-URBAN methodology’s concept, importance, and applicability, which supports the potential groundwater vulnerability on fractured media assessment for urban areas. This approach is more accurate, particularly on regional to local scales. The analytic hierarchy process (AHP) was applied to define the weight of each assessment parameter. In addition, the index DISCO-URBAN, SI and GODS were used in the historic springs of the Porto and Vila Nova de Gaia riverside urban area. In fact, coupling DRASTIC-Fm-URBAN and DISCO-URBAN vulnerability indexes are reliable approaches to be included as a tool to develop a robust hydrogeological conceptual site model for urban areas.

Using Multiple Geophysical Methods to Refine a Stratigraphic Conceptual Site Model at a Nuclear Waste Site

Using Multiple Geophysical Methods to Refine a Stratigraphic Conceptual Site Model at a Nuclear Waste Site

Predicting future well performance for environmental remediation design using deep learning

In this study, we developed a deep learning (DL) framework with a multi-channel three-dimensional convolutional neural network (MC3D-CNN) to predict well performance and thereby assist future environmental remediation design. Such prediction of extraction well performance at designated locations is critical for configuring pump-and-treat (P&T) well network design and operation, setting reasonable target closure dates for overall remedying, and estimating remedy costs. The framework is developed with operational and monitoring data routinely collected during P&T remedy operations, including well extraction and injection rates as well as in situ contaminant concentrations. Traditionally, the collected data were rarely used for purposes other than assessing past well performance and the accuracy of the conceptual site model. However, recent advances in data-driven computational approaches enable better use of the large datasets to inform future well performance, enhance site characterization, and improve remediation planning. In this study, we established a DL framework to integrate transient three-dimensional contaminant plumes and multiple aquifer properties (e.g., hydraulic conductivity and hydrostratigraphic maps) to identify characteristic patterns controlling and representing extraction well mass recovery, aiming at providing future mass recovery estimates for existing wells and candidate wells at any proposed locations. We evaluated our framework by using a realistic synthetic dataset generated from a well-calibrated flow and transport model used in the 200 West Area of the U.S. Department of Energy’s Hanford Site in southeastern Washington state. The multi-channel feature in our framework allows integration of various types and temporal densities of training datasets for DL model development. Overall, we found that the trained DL model achieved an accuracy of over 90% in ranking extraction well performance in validation datasets, and over 80% in predicting high-performance-ranking well locations. This data-informed approach provides a flexible tool to support adaptive site management, streamline decision-making, and potentially reduce remediation time and costs. Our DL framework can be used as a filtering tool to improve the current P&T network optimization design by reducing the number of candidate well locations.

Codeployment of Passive Samplers and Mussels Reveals Major Source of Ongoing PCB Inputs to the Anacostia River in Washington, DC.

Remedial investigations of sites contaminated with legacy pollutants like polychlorinated biphenyls (PCBs) have traditionally focused on mapping sediment contamination to develop a site conceptual model and select remedy options. Ignoring dissolved concentrations that drive transport and bioaccumulation often leads to an incomplete assessment of ongoing inputs to the water column and overestimation of potential effectiveness of sediment remediation. Here, we demonstrate the utility of codeployment of passive equilibrium samplers and freshwater mussels as dual lines of evidence to identify ongoing sources of PCBs from eight main tributaries of the Anacostia River in Washington, DC, that has been historically polluted from industrial and other human activities. The freely dissolved PCB concentrations measured using passive samplers tracked well with the accumulation in mussels and allowed predictions of biouptake within a factor of 2 for total PCBs and a factor of 4 for most congeners. One tributary was identified as the primary source of PCBs to the water column and became a focus of additional ongoing investigations. Codeployment of passive samplers and mussels provides strong lines of evidence to refine site conceptual models and identify ongoing sources critical to control to achieve river water quality standards and reduce bioaccumulation in the aquatic food web.

Forensic Analytical Approach for Hydrocarbon Fingerprinting in Soil Vapor Samplings: Example of a Residential Neighborhood in Brazil

Conventional analytical methods determine the concentration of compounds used to estimate the presence of environmental contamination capable of posing risk to human and ecological receptors (Murphy and Morrison, 2007). While these target analytes help regulators and environmental professional identify and manage potentially harmful conditions, these compounds can be generated by many natural and anthropogenic (man-made) sources and conventional methods alone fail to compositionally differentiate subsurface sources of contamination in complex environments (Morrison, 2000; Wang and Fingas, 2003; Gouvêa et al, 2019; Douglas et al, 2007). This case study demonstrates the advantage of using both conventional and forensic testing methods to accurately identify the source(s) of volatile hydrocarbon contamination in soil vapor samples for the development of an accurate conceptual site model in a neighbourhood near industrial facilities in Rio de Janeiro State, Brazil. The goal of this study was to differentiate potential impacts from a local steelmaking plant from fugitive hydrocarbons associated with more generic human activity in urban settings. This case study demonstrated the advantage of constructing chemical fingerprints from conventional volatile organic compound (VOC) method TO 15 and a forensic volatile hydrocarbon method using an enhanced version of method TO 15 (PIANO). The chemical fingerprints of vapor samples collected from subsurface soil gas and sewers were analysed and compared to laboratory reference samples. These data determined that the VOCs detected in neighbourhood soil vapor samples were associated with fugitive petroleum products migrating in the sewer pipelines and not with the steelmaking wastes emplaced near the residential area. This article discusses the forensic data and chemical signatures that support these findings, and the use of environmental forensic techniques to evaluate environmental data associated with complex scenarios, involving multiple contamination sources.

A novel concept for estimating the contaminant mass discharge of chlorinated ethenes emanating from clay till sites

Interest in using contaminant mass discharge (CMD) for risk assessment of contaminated sites has increased over the years, as it accounts for the contaminant mass that is moving and posing a risk to water resources and receptors. The most common investigation of CMD involves a transect of multilevel wells; however, this is an expensive undertaking, and it is difficult to place it in the right position in a plume. Additionally, infrastructure at the site needs to be considered. To derive an initial CMD estimate at a contaminated site and to allow for the prioritization of further investigations and remedial actions, the ProfileFlux method has been developed. It is targeted at former industrial sites with a source zone in a low conductivity layer with primarily vertical flow overlying an aquifer with primarily horizontal groundwater flow. The ProfileFlux method was developed for mature chlorinated solvent plumes, typically originating from more than 30 to 50-year-old spills, as the usage of chlorinated solvents is mainly historical. Thus, it is assumed that the contaminant had time to distribute in the low conductivity layer by mainly diffusive processes. Today the contamination is continuously released to the underlying aquifer, where advection and dispersive (other than diffusive) processes are of higher importance. The approach combines high-resolution, depth-discrete vertical concentration profiles and a simple 2D flow and transport model to estimate CMD by comparing measured and simulated concentration profiles in the aquifer. The study presented herein includes a global sensitivity analysis, in order to identify crucial field parameters, and of particular importance in this regard are source length, groundwater flux and infiltration. The ProfileFlux method was tested at a well-examined industrial site primarily contaminated with trichloroethylene, thereby allowing a comparison between CMD from the ProfileFlux method and the traditional transect method. CMD was estimated at 117–170 g/year, when using the ProfileFlux method, against 143 g/year with the transect method, thus validating ProfileFlux method's ability to estimate CMD. In addition, applying the method identified weak points in the conceptual site model. The method will be incorporated into a user-friendly online tool directed at environmental consultants and decision-makers working on the risk assessment and prioritization of contaminated sites with the specific hydrogeological conditions of an aquifer with an overlying low permeability layer.