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2 pages, 147 KiB

Open AccessEditorial

Contaminant Transport and Fate

by Thomas B. Boving and William J. Blanford

Water 2021, 13(9), 1195; https://doi.org/10.3390/w13091195 - 26 Apr 2021

Viewed by 2414

Abstract

This Special Issue highlights many of the predominant contaminant transport and fate processes that redistribute solutes through natural and engineered surface and subsurface environments [...] Full article

(This article belongs to the Special Issue Contaminant Transport and Fate)

Research

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20 pages, 2666 KiB

Open AccessArticle

Using Concentration–Discharge Relationships to Identify Influences on Surface and Subsurface Water Chemistry along a Watershed Urbanization Gradient

by Jessica A. Balerna, Jacob C. Melone and Karen L. Knee

Water 2021, 13(5), 662; https://doi.org/10.3390/w13050662 - 28 Feb 2021

Cited by 5 | Viewed by 3551

Abstract

Urban development within watersheds impacts the hydrology and water quality of streams, but changes to groundwater–surface water interactions in this “urban stream syndrome” are not yet well understood. This study focused on three stream systems in a northern Virginia (USA) protected area with [...] Read more.

Urban development within watersheds impacts the hydrology and water quality of streams, but changes to groundwater–surface water interactions in this “urban stream syndrome” are not yet well understood. This study focused on three stream systems in a northern Virginia (USA) protected area with 14.2, 31.7, and 66.1% developed land in their watersheds. Surface water was sampled weekly for nutrients, dissolved metals, sulfate, ancillary water quality parameters, and discharge over two non-consecutive years with the hyporheic zone sampled during the second year. Concentration–discharge relationships revealed largely chemostatic behavior in surface water solutes in the least urbanized stream, while in the two more urbanized streams, these relationships tended to have significant positive and negative slopes, indicating diverse delivery pathways depending on the constituent. In the least urbanized stream, linear regressions between discharge and solute concentrations in hyporheic water had exclusively negative slopes, indicating source-limited delivery, while the other two urbanized streams maintained largely chemostatic behavior. Average specific conductance and nitrate + nitrite concentrations in stream surface water reflected an urbanization gradient, while sulfate, Ca, K and Sr concentrations suggested a threshold effect: the stream with a mostly forested watershed had the lowest concentrations, while the other two were higher and similar. Specific conductance indicated salinization of both surface and groundwater at the two more urban streams, possibly threatening aquatic organisms. Metal concentrations in surface and subsurface water were often positively correlated with specific conductance and negatively correlated with pH, suggesting that they may originate from road salt and/or be mobilized by acid precipitation. These results indicate the importance of monitoring both baseflow and stormflow as pathways for pollution. Full article

(This article belongs to the Special Issue Contaminant Transport and Fate)

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24 pages, 3483 KiB

Open AccessFeature PaperArticle

Evaluating Potential for Groundwater Contamination from Surface Spills Associated with Unconventional Oil and Gas Production: Methodology and Application to the South Platte Alluvial Aquifer

by Cynthia Mai Kanno and John E. McCray

Water 2021, 13(3), 353; https://doi.org/10.3390/w13030353 - 30 Jan 2021

Cited by 9 | Viewed by 3335

Abstract

Surface spills occur frequently during unconventional oil and gas production operations and have the potential to impact groundwater quality. A screening-level analysis using contaminant fate and transport simulations was performed to: (1) evaluate whether hypothetical (yet realistic) spills of aqueous produced fluids pose [...] Read more.

Surface spills occur frequently during unconventional oil and gas production operations and have the potential to impact groundwater quality. A screening-level analysis using contaminant fate and transport simulations was performed to: (1) evaluate whether hypothetical (yet realistic) spills of aqueous produced fluids pose risks to groundwater quality in the South Platte Aquifer, (2) identify the key hydrologic and transport factors that determine these risks, and (3) develop a screening-level methodology that could be applied for other sites and pollutants. This assessment considered a range of representative hydrologic conditions and transport behavior for benzene, a regulated pollutant in production fluids. Realistic spill volumes and areas were determined using publicly available data collected by Colorado’s regulatory agency. Risk of groundwater pollution was based on predicted benzene concentrations at the groundwater table. Results suggest that the risk of groundwater contamination from benzene in a produced water spill was relatively low in the South Platte Aquifer. Spill size was the dominant factor influencing whether a contaminant reached the water table. Only statistically larger spills (volume per surface area ≥12.0 cm) posed a clear risk. Storm events following a spill were generally required to transport typical (median)-sized spills (0.38 cm volume per surface area) to the water table; typical spills only posed risk if a 500 or 100 year storm (followed by little degradation or sorption) occurred right after the spill. This methodology could be applied to evaluate spills occurring over other aquifers. Full article

(This article belongs to the Special Issue Contaminant Transport and Fate)

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29 pages, 10773 KiB

Open AccessArticle

Multi-Gene Genetic Programming Regression Model for Prediction of Transient Storage Model Parameters in Natural Rivers

by Hyoseob Noh, Siyoon Kwon, Il Won Seo, Donghae Baek and Sung Hyun Jung

Water 2021, 13(1), 76; https://doi.org/10.3390/w13010076 - 31 Dec 2020

Cited by 22 | Viewed by 3329

Abstract

A Transient Storage Model (TSM), which considers the storage exchange process that induces an abnormal mixing phenomenon, has been widely used to analyze solute transport in natural rivers. The primary step in applying TSM is a calibration of four key parameters: flow zone [...] Read more.

A Transient Storage Model (TSM), which considers the storage exchange process that induces an abnormal mixing phenomenon, has been widely used to analyze solute transport in natural rivers. The primary step in applying TSM is a calibration of four key parameters: flow zone dispersion coefficient (

K_{f}

), main flow zone area (

A_{f}

), storage zone area (

A_{s}

), and storage exchange rate (

α

); by fitting the measured Breakthrough Curves (BTCs). In this study, to overcome the costly tracer tests necessary for parameter calibration, two dimensionless empirical models were derived to estimate TSM parameters, using multi-gene genetic programming (MGGP) and principal components regression (PCR). A total of 128 datasets with complete variables from 14 published papers were chosen from an extensive meta-analysis and were applied to derivations. The performance comparison revealed that the MGGP-based equations yielded superior prediction results. According to TSM analysis of field experiment data from Cheongmi Creek, South Korea, although all assessed empirical equations produced acceptable BTCs, the MGGP model was superior to the other models in parameter values. The predicted BTCs obtained by the empirical models in some highly complicated reaches were biased due to misprediction of

A_{f}

. Sensitivity analyses of MGGP models showed that the sinuosity is the most influential factor in

K_{f}

, while

A_{f}

,

A_{s}

, and

α

, are more sensitive to

U / U_{*}

. This study proves that the MGGP-based model can be used for economic TSM analysis, thus providing an alternative option to direct calibration and the inverse modeling initial parameters. Full article

(This article belongs to the Special Issue Contaminant Transport and Fate)

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16 pages, 1500 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Manganese Dioxide and Permanganate as Amendments with Persulfate for Aqueous 1,4-Dioxane Oxidation

by Logan Bridges, Ruba A. M. Mohamed, Naima A. Khan, Mark L. Brusseau and Kenneth C. Carroll

Water 2020, 12(11), 3061; https://doi.org/10.3390/w12113061 - 1 Nov 2020

Cited by 8 | Viewed by 4696

Abstract

Persulfate (PS) is widely used to degrade emerging organic contaminants in groundwater and soil systems, and various PS activation methods (e.g., energy or chemical inputs) have been considered to increase oxidation strength. This study investigates PS activation through manganese amendment in the form [...] Read more.

Persulfate (PS) is widely used to degrade emerging organic contaminants in groundwater and soil systems, and various PS activation methods (e.g., energy or chemical inputs) have been considered to increase oxidation strength. This study investigates PS activation through manganese amendment in the form of potassium permanganate (KMnO₄) and manganese dioxide (MnO₂) to subsequently degrade the emerging and recalcitrant groundwater contaminant 1,4-dioxane (1,4-D). The activation of PS by MnO₂ was confirmed by radical trap and by product formation. The degradation kinetics of 1,4-D by PS was also compared with varying amendments of KMnO₄ and MnO₂. The results showed that MnO₂ activated PS, which increased the degradation rate constant of 1,4-D. KMnO₄ activation of PS was not observed even though the binary oxidant mixture did enhance the degradation of 1,4-D. These results have implications for applying in situ chemical oxidation in subsurface systems, especially for conditions wherein manganese exists naturally in groundwater or aquifer minerals to support possible PS activation. Full article

(This article belongs to the Special Issue Contaminant Transport and Fate)

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23 pages, 7848 KiB

Open AccessEditor’s ChoiceArticle

A Modified HYDRUS Model for Simulating PFAS Transport in the Vadose Zone

by Jeff Allen Kai Silva, Jiří Šimůnek and John E. McCray

Water 2020, 12(10), 2758; https://doi.org/10.3390/w12102758 - 3 Oct 2020

Cited by 74 | Viewed by 8528

Abstract

The HYDRUS unsaturated flow and transport model was modified to simulate the effects of non-linear air-water interfacial (AWI) adsorption, solution surface tension-induced flow, and variable solution viscosity on the unsaturated transport of per- and polyfluoroalkyl substances (PFAS) within the vadose zone. These modifications [...] Read more.

The HYDRUS unsaturated flow and transport model was modified to simulate the effects of non-linear air-water interfacial (AWI) adsorption, solution surface tension-induced flow, and variable solution viscosity on the unsaturated transport of per- and polyfluoroalkyl substances (PFAS) within the vadose zone. These modifications were made and completed between March 2019 and May 2019, and were implemented into both the one-dimensional (1D) and two-dimensional (2D) versions of HYDRUS. Herein, the model modifications are described and validated against the available literature-derived PFAS transport data (i.e., 1D experimental column transport data). The results of both 1D and 2D example simulations are presented to highlight the function and utility of the model to capture the dynamic and transient nature of the temporally and spatially variable interfacial area of the AWI (

A_{a w}

) as it changes with soil moisture content (

Θ_{w}

) and how it affects PFAS unsaturated transport. Specifically, the simulated examples show that while AWI adsorption of PFAS can be a significant source of retention within the vadose zone, it is not always the dominant source of retention. The contribution of solid-phase sorption can be considerable in many PFAS-contaminated vadose zones. How the selection of an appropriate

A_{a w} (Θ_{w})

function can impact PFAS transport and how both mechanisms contribute to PFAS mass flux to an underlying groundwater source is also demonstrated. Finally, the effects of soil textural heterogeneities on PFAS unsaturated transport are demonstrated in the results of both 1D and 2D example simulations. Full article

(This article belongs to the Special Issue Contaminant Transport and Fate)

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14 pages, 2647 KiB

Open AccessEditor’s ChoiceArticle

Nonlinear Autoregressive Neural Networks to Predict Hydraulic Fracturing Fluid Leakage into Shallow Groundwater

by Reza Taherdangkoo, Alexandru Tatomir, Mohammad Taherdangkoo, Pengxiang Qiu and Martin Sauter

Water 2020, 12(3), 841; https://doi.org/10.3390/w12030841 - 17 Mar 2020

Cited by 38 | Viewed by 4383

Abstract

Hydraulic fracturing of horizontal wells is an essential technology for the exploitation of unconventional resources, but led to environmental concerns. Fracturing fluid upward migration from deep gas reservoirs along abandoned wells may pose contamination threats to shallow groundwater. This study describes the novel [...] Read more.

Hydraulic fracturing of horizontal wells is an essential technology for the exploitation of unconventional resources, but led to environmental concerns. Fracturing fluid upward migration from deep gas reservoirs along abandoned wells may pose contamination threats to shallow groundwater. This study describes the novel application of a nonlinear autoregressive (NAR) neural network to estimate fracturing fluid flow rate to shallow aquifers in the presence of an abandoned well. The NAR network is trained using the Levenberg–Marquardt (LM) and Bayesian Regularization (BR) algorithms and the results were compared to identify the optimal network architecture. For NAR-LM model, the coefficient of determination (R²) between measured and predicted values is 0.923 and the mean squared error (MSE) is 4.2 × 10⁻⁴, and the values of R² = 0.944 and MSE = 2.4 × 10⁻⁴ were obtained for the NAR-BR model. The results indicate the robustness and compatibility of NAR-LM and NAR-BR models in predicting fracturing fluid flow rate to shallow aquifers. This study shows that NAR neural networks can be useful and hold considerable potential for assessing the groundwater impacts of unconventional gas development. Full article

(This article belongs to the Special Issue Contaminant Transport and Fate)

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14 pages, 1873 KiB

Open AccessArticle

N-Nitrosodimethylamine Formation from Treatment of Seasonally and Spatially Varying Source Water

by Maxwell C. Meadows, Soni M. Pradhanang, Takahiro Fujioka, Hitoshi Kodamatani, Menu B. Leddy and Thomas B. Boving

Water 2019, 11(10), 2019; https://doi.org/10.3390/w11102019 - 28 Sep 2019

Cited by 4 | Viewed by 3840

Abstract

N-nitrosodimethylamine (NDMA) is a disinfection by-product (DBP) that has been classified as a probable human carcinogen in multiple risk assessments. NDMA presence in drinking water is widespread and dependent on source water, disinfectant type, precursors, and water treatment strategies. The objectives of this [...] Read more.

N-nitrosodimethylamine (NDMA) is a disinfection by-product (DBP) that has been classified as a probable human carcinogen in multiple risk assessments. NDMA presence in drinking water is widespread and dependent on source water, disinfectant type, precursors, and water treatment strategies. The objectives of this study were to investigate NDMA formation potential in a modeled monochloramine water treatment plant (WTP) fed by seasonally and spatially varying source water; and to optimize DBP precursor removal by combining conventional and additional treatment techniques. After NDMA analysis, it was found that NDMA formation was significantly dependent on source water type and monochloramine contact time (CT); e.g., at 24 h CT, Cork Brook produced 12.2 ng/L NDMA and Bailey Brook produced 4.2 ng/L NDMA, compared with 72 h CT, Cork Brook produced 4.1 ng/L NDMA and Bailey Brook produced 3.4 ng/L NDMA. No correlations were found between traditional DBP precursors such as total organic carbon and total nitrogen, and the formation of NDMA. The laboratory bench-top treatment system was highly effective at removing traditional DBP precursors, highlighting the need for WTPs to alter their current treatment methods to best accommodate the complex system of DBP control. Full article

(This article belongs to the Special Issue Contaminant Transport and Fate)

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