Research

24 pages, 4765 KiB

Open AccessFeature PaperArticle

Arsenic in Petroleum-Contaminated Groundwater near Bemidji, Minnesota Is Predicted to Persist for Centuries

by Brady A. Ziegler, G.-H. Crystal Ng, Isabelle M. Cozzarelli, Aubrey J. Dunshee and Madeline E. Schreiber

Water 2021, 13(11), 1485; https://doi.org/10.3390/w13111485 - 26 May 2021

Cited by 5 | Viewed by 2730

Abstract

We used a reactive transport model to investigate the cycling of geogenic arsenic (As) in a petroleum-contaminated aquifer. We simulated As mobilization and sequestration using surface complexation reactions with Fe(OH)₃ during petroleum biodegradation coupled with Fe-reduction. Model results predict that dissolved As [...] Read more.

We used a reactive transport model to investigate the cycling of geogenic arsenic (As) in a petroleum-contaminated aquifer. We simulated As mobilization and sequestration using surface complexation reactions with Fe(OH)₃ during petroleum biodegradation coupled with Fe-reduction. Model results predict that dissolved As in the plume will exceed the U.S. and EU 10 µg/L drinking water standard for ~400 years. Non-volatile dissolved organic carbon (NVDOC) in the model promotes As mobilization by exerting oxygen demand, which maintains anoxic conditions in the aquifer. After NVDOC degrades, As re-associates with Fe(OH)₃ as oxygenated conditions are re-established. Over the 400-year simulation, As transport resembles a “roll front” in which: (1) arsenic sorbed to Fe(OH)₃ is released during Fe-reduction coupled to petroleum biodegradation; (2) dissolved As resorbs to Fe(OH)₃ at the plume’s leading edge; and (3) over time, the plume expands, and resorbed As is re-released into groundwater. This “roll front” behavior underscores the transience of sorption as an As attenuation mechanism. Over the plume’s lifespan, simulations suggest that As will contaminate more groundwater than benzene from the oil spill. At its maximum, the model simulates that ~5.7× more groundwater will be contaminated by As than benzene, suggesting that As could pose a greater long-term water quality threat than benzene in this petroleum-contaminated aquifer. Full article

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

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12 pages, 1357 KiB

Open AccessArticle

Occurrence of Pharmaceutical Compounds in Groundwater from the Gran Canaria Island (Spain)

by Sarah Montesdeoca-Esponda, María del Pino Palacios-Díaz, Esmeralda Estévez, Zoraida Sosa-Ferrera, José Juan Santana-Rodríguez and María del Carmen Cabrera

Water 2021, 13(3), 262; https://doi.org/10.3390/w13030262 - 22 Jan 2021

Cited by 16 | Viewed by 2502

Abstract

The presence of pharmaceutical compounds in the whole environment is a growing concern. These compounds might be present in the effluents of wastewater treatment plants and, hence, irrigation with treated sewage may be a source of groundwater pollution. The volcanic aquifer that lies [...] Read more.

The presence of pharmaceutical compounds in the whole environment is a growing concern. These compounds might be present in the effluents of wastewater treatment plants and, hence, irrigation with treated sewage may be a source of groundwater pollution. The volcanic aquifer that lies NE of Gran Canaria (Spain) was studied to address the relationship of the occurrence of pharmaceutical compounds and a golf course that has been irrigated with regenerated water since 1973. Of the 14 analyzed groundwater samples, five wells were chosen to perform annual monitoring. Irrigation water and soil leachate were also evaluated. The target analytes were atenolol, metamizole, fluoxetine, ibuprofen, nicotine, permethrin, caffeine, and their metabolite paraxanthine. The environmental risk is limited as the concentrations of the pharmaceuticals measured in the sampled wells were always below 60 ng·L⁻¹ (lower than the detected caffeine and nicotine concentrations). Wide variations for the same wells were measured among sampling campaigns, and also among the different wells. The study points to the importance of sample conservation during transport and the need to perform analyses immediately, or to follow an in-situ extraction procedure to carry concentrated samples under better conditions. Full article

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

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19 pages, 3583 KiB

Open AccessEditor’s ChoiceArticle

Screening and Distribution of Contaminants of Emerging Concern and Regulated Organic Pollutants in the Heavily Modified Guadalhorce River Basin, Southern Spain

by Marta Llamas, Iñaki Vadillo-Pérez, Lucila Candela, Pablo Jiménez-Gavilán, Carmen Corada-Fernández and Antonio F. Castro-Gámez

Water 2020, 12(11), 3012; https://doi.org/10.3390/w12113012 - 27 Oct 2020

Cited by 14 | Viewed by 2858

Abstract

Emerging pollutants have aroused an increasing concern due to their ubiquitous presence in the environment and harmful potential. Both emerging (e.g., pharmaceuticals and personal care products) and regulated organic pollutants pose a serious threat to water quality and their presence and spatial distribution [...] Read more.

Emerging pollutants have aroused an increasing concern due to their ubiquitous presence in the environment and harmful potential. Both emerging (e.g., pharmaceuticals and personal care products) and regulated organic pollutants pose a serious threat to water quality and their presence and spatial distribution are complicated to address as they can derive from several factors: distribution of point and diffuse sources, environmental conditions, hydrogeological features of the region and inherent properties of the considered contaminants. In this study, a ground and surface water monitoring campaign was conducted in the three main detritic groundwater bodies of an extensive and heavily modified river basin in order to draft an initial description of the occurrence and distribution of a wide range of organic contaminants. In total, 63 out of 185 target pollutants were detected. An attempt to understand the importance of different factors governing the distribution of some of the most frequently found pollutants was made. Antibiotics spatial distribution is potentially influenced by the hydrogeological functioning of the basin modified by hydraulic infrastructures (reflected by hydrochemistry and environmental tracers δ²H and δ¹⁸O), not directly related to the distribution of potential sources. The presence of other organic pollutants does not reflect an evident correlation with flow pathways. Differences in contaminant occurrence are potentially attributed to the way pollutants are released into the environment as well as physico-chemical properties. Full article

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

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20 pages, 6775 KiB

Open AccessEditor’s ChoiceArticle

Redox Dependent Arsenic Occurrence and Partitioning in an Industrial Coastal Aquifer: Evidence from High Spatial Resolution Characterization of Groundwater and Sediments

by Chiara Sbarbati, Maurizio Barbieri, Alyssa Barron, Benjamin Bostick, Nicolò Colombani, Micòl Mastrocicco, Henning Prommer, Stefania Passaretti, Yan Zheng and Marco Petitta

Water 2020, 12(10), 2932; https://doi.org/10.3390/w12102932 - 20 Oct 2020

Cited by 16 | Viewed by 3033

Abstract

Superlative levels of arsenic (As) in groundwater and sediment often result from industrial pollution, as is the case for a coastal aquifer in Southern Italy, with a fertilizer plant atop. Understanding conditions under which As is mobilized from the sediments, the source of [...] Read more.

Superlative levels of arsenic (As) in groundwater and sediment often result from industrial pollution, as is the case for a coastal aquifer in Southern Italy, with a fertilizer plant atop. Understanding conditions under which As is mobilized from the sediments, the source of that As, is necessary for developing effective remediation plans. Here, we examine hydrogeological and geochemical factors that affect groundwater As concentrations in a contaminated coastal aquifer. Groundwater has been subject to pump-and-treat at a massive scale for more than 15 years and is still ongoing. Nevertheless, As concentrations (0.01 to 100 mg/L) that are four orders of magnitude more than Italian drinking water standard of 10 μg/L are still present in groundwater collected from about 50 monitoring wells over three years (2011, 2016, and 2018). As was quantified in three different locations by sequential extractions of 29 sediment cores in 2018 (depth 2.5 m to −16.5 m b.g.l.), combined with groundwater As composition, the aqueous and solid partitioning of As were evaluated by partition coefficient (K_d) in order to infer the evolution of the contaminant plumes. Most sediment As is found in easily extractable and/or adsorbed on amorphous iron oxides/hydroxides fractions based on sequential extractions. The study shows that As contamination persists, even after many years of active remediation due to the partitioning to sediment solids. This implies that the choice of remediation techniques requires an improved understanding of the biogeochemical As-cycling and high spatial resolution characterization of both aqueous and solid phases for sites of interest. Full article

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

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20 pages, 28827 KiB

Open AccessArticle

Nitrate Contamination in Brazilian Urban Aquifers: A Tenacious Problem

by Ricardo Hirata, Fabiana Cagnon, Aline Bernice, Carlos Henrique Maldaner, Paulo Galvão, Carlos Marques, Rafael Terada, Claudia Varnier, M. Cathryn Ryan and Reginaldo Bertolo

Water 2020, 12(10), 2709; https://doi.org/10.3390/w12102709 - 27 Sep 2020

Cited by 21 | Viewed by 3201

Abstract

This study follows the geochemistry of nitrogen in a Cretaceous and unconfined sedimentary aquifer in the city of Urânia (Brazil) over 20 years. Although the sewer network was built in the 1970s, the nitrate contamination problem (>45 mg/L-NO₃⁻) persists to [...] Read more.

This study follows the geochemistry of nitrogen in a Cretaceous and unconfined sedimentary aquifer in the city of Urânia (Brazil) over 20 years. Although the sewer network was built in the 1970s, the nitrate contamination problem (>45 mg/L-NO₃⁻) persists to this day. The oldest urbanization areas located in the north of the city initially used cesspits for wastewater and currently present the highest nitrate concentrations (>120 mg/L-NO₃⁻), with the plume reaching the deeper aquifer portions (up to 100 m). The contamination is not as dramatic in the south part of the city, where urbanization including installation of the sewage network with PVC pipes that are more resistant to leak than the old ceramic networks occurred after 1985. Based on the constructive well profiles, three hydrogeochemical zones were established: shallow (<20 m deep), with average nitrate of 63 mg/L-NO₃⁻; intermediate (20–60 m), with 30 mg/L-NO₃⁻; and deep (>60 m), with 17 mg/L-NO₃⁻. The current total nitrate mass in the aquifer exceeds 731 kg-NO₃⁻. Numerical flow (Modflow) and transport (MT3D) model scenarios support the hypothesis that the nitrate contamination is caused by substantial infiltration of nitrogen through the cesspits until the 1970s, but after the 1990s, leaks from the sewer network should be responsible for the maintenance of the recently observed high concentrations of nitrate. Full article

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

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30 pages, 12151 KiB

Open AccessArticle

Underground Barrier Wall Evaluation for Controlling Saltwater Intrusion in Sloping Unconfined Coastal Aquifers

by Asaad M. Armanuos, Nadhir Al-Ansari and Zaher Mundher Yaseen

Water 2020, 12(9), 2403; https://doi.org/10.3390/w12092403 - 27 Aug 2020

Cited by 15 | Viewed by 3285

Abstract

Barrier walls are considered one of the most effective methods for facilitating the retreat of saltwater intrusion (SWI). This research plans to examine the effect of using barrier walls for controlling of SWI in sloped unconfined aquifers. The sloping unconfined aquifer is considered [...] Read more.

Barrier walls are considered one of the most effective methods for facilitating the retreat of saltwater intrusion (SWI). This research plans to examine the effect of using barrier walls for controlling of SWI in sloped unconfined aquifers. The sloping unconfined aquifer is considered with three different bed slopes. The SEAWAT model is implemented to simulate the SWI. For model validation, the numerical results of the seawater wedge at steady state were compared with the analytical solution. Increasing the ratio of flow barrier depth (d_b/d) forced the saltwater interface to move seaward and increased the repulsion ratio (R). With a positive sloping bed, further embedding the barrier wall from 0.2 to 0.7 caused R to increase from 0.3% to 59%, while it increased from 1.8% to 41.7% and from 3.4% to 46.9% in the case of negative and horizontal slopes, respectively. Embedding the barrier wall to a d_b/d value of more than 0.4 achieved a greater R value in the three bed-sloping cases. Installing the barrier wall near the saltwater side with greater depth contributed to the retreat of the SWI. With a negative bed slope, moving the barrier wall from X_b/L_o = 1.0 toward the saltwater side (X_b/L_o = 0.2) increased R from 7.21% to 68.75%, whereas R increased from 5.3% to 67% for the horizontal sloping bed and from 5.1% to 64% for the positive sloping bed. The numerical results for the Akrotiri coastal aquifer confirm that the embedment of the barrier wall significantly affects the controlling of SWI by increasing the repulsion ratio (R) and decreasing the SWI length ratio (L/L_a). Cost-benefit analysis is recommended to determine the optimal design of barrier walls for increasing the cost-effectiveness of the application of barrier walls as a countermeasure for controlling and preventing SWI in sloped unconfined aquifers. Full article

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

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22 pages, 5629 KiB

Open AccessArticle

Meteorological Variability and Groundwater Quality: Examples in Different Hydrogeological Settings

by Manuela Lasagna, Daniela Ducci, Mariangela Sellerino, Susanna Mancini and Domenico Antonio De Luca

Water 2020, 12(5), 1297; https://doi.org/10.3390/w12051297 - 03 May 2020

Cited by 24 | Viewed by 4084

Abstract

Rainfall and temperature variability causes changes in groundwater recharge that can also influence groundwater quality by different processes. The aim of this study is the analysis of the hydrogeochemical variations over time due to meteorological variability in two different study areas in Italy: [...] Read more.

Rainfall and temperature variability causes changes in groundwater recharge that can also influence groundwater quality by different processes. The aim of this study is the analysis of the hydrogeochemical variations over time due to meteorological variability in two different study areas in Italy: an alluvial aquifer in the Piedmont Po plain and an alluvial-pyroclastic aquifer in the Campanian plain. The examined plains show groundwater with natural quality not satisfying the European drinking water standards, or anthropogenic contamination. The peculiar natural quality is due, in the Campanian plain, to the closeness of volcanic areas, and to the presence of reducing conditions. In Piedmont plain a test site is characterized by a point-source contamination by heavy metals, due to the presence of past industrial activities. In all the examined areas there is a diffuse nitrate contamination. The fluctuations of the ions As, F, Fe, Mn, Cr VI, NO₃, and Cl were analyzed and compared, using statistical methods, with the variations over time in precipitation, temperature, and piezometric levels, sometimes significant. Results highlight the importance of the groundwater and meteorological monitoring and the key role of the recharge variation in the hydrogeochemical processes. The linking degree between rainfall/temperature variability and hydrogeochemistry is variable, in function of the typology of chemical species, their origin, and of the aquifer characteristics. The fluctuation of climate variables determines sudden changes in the geochemistry of shallow unconfined aquifers (e.g., in the Piedmont plain), while semiconfined or confined aquifers (e.g., in the Volturno-Regi Lagni plain) react with a greater delay to these variations. Moreover, natural quality is more affected by climatic variations than anthropogenic contamination, which is the result of multiple environmental and anthropic factors. Full article

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

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26 pages, 47030 KiB

Open AccessArticle

Interplay between Fingering Instabilities and Initial Soil Moisture in Solute Transport through the Vadose Zone

by Luis Cueto-Felgueroso, María José Suarez-Navarro, Xiaojing Fu and Ruben Juanes

Water 2020, 12(3), 917; https://doi.org/10.3390/w12030917 - 24 Mar 2020

Cited by 4 | Viewed by 3807

Abstract

Modeling water flow and solute transport in the vadose zone is essential to understanding the fate of soil pollutants and their travel times towards groundwater bodies. It also helps design better irrigation strategies to control solute concentrations and fluxes in semiarid and arid [...] Read more.

Modeling water flow and solute transport in the vadose zone is essential to understanding the fate of soil pollutants and their travel times towards groundwater bodies. It also helps design better irrigation strategies to control solute concentrations and fluxes in semiarid and arid regions. Heterogeneity, soil texture and wetting front instabilities determine the flow patterns and solute transport mechanisms in dry soils. When water is already present in the soil, the flow of an infiltration pulse depends on the spatial distribution of soil water and on its mobility. We present numerical simulations of passive solute transport during unstable infiltration of water into sandy soils that are prone to wetting front instability. We study the impact of the initial soil state, in terms of spatial distribution of water content, on the infiltration of a solute-rich water pulse. We generate random fields of initial moisture content with spatial structure, through multigaussian fields with prescribed correlation lengths. We characterize the patterns of water flow and solute transport, as well as the mass fluxes through the soil column. Our results indicate a strong interplay between preferential flow and channeling due to fingering and the spatial distribution of soil water at the beginning of infiltration. Fingering and initial water saturation fields have a strong effect on solute diffusion and dilution into the ambient water during infiltration, suggesting an effective separation between mobile and inmobile transport domains that are controlled by the preferential flow paths due to fingering. Full article

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

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