Contaminant Concentrations In Groundwater Research Articles

Soil and groundwater contamination by crude oil spillage: A review and implications for remediation projects in Nigeria

Management of soil and groundwater resources has been recognized as essential to meeting the sustainable development goals of Agenda 2063 of the African Union. As Africa’s fastest growing population with over 200 million people, Nigeria is responsible for leading the continent’s environmental sustainability goal. Nigeria has seen a sizable number of crude oil spillages that have contaminated its soils and groundwater resources, and several of these contaminated sites are to be cleaned up yet. There needs to be more scientific data to design an effective cleanup and to manage the soil and groundwater resources effectively. So far, the only extensive crude oil-contaminated site remediation project documented is on Ogoniland in the Niger Delta region of Nigeria. However, this project resulted in less effective, albeit temporary, cleanup solutions. This review presents a state-of-the-art synthesis of research on soil and groundwater contamination by crude oil. It includes sections on processes, measurements, predictions, and management, as well as an analysis of the state and challenges in Nigeria. In-depth field, laboratory, and computer models for crude oil contamination investigation have been developed with over 60 years of significant research. However, studies and case projects in Nigeria have relied on point sampling to determine the concentration of crude oil contaminants in soil and groundwater. This method offers limited information on the solute concentration and hydraulic distribution, which regulates pollutant mobility within the subsurface. The absence of baseline and high-resolution subsurface characterization data has also resulted in a need for more process-based knowledge to direct the development of site-specific remediation strategies. As a result, it is challenging to design a conceptual model that is detailed enough to help with predictions of the flow dynamics of crude oil contaminants in the unsaturated and saturated zones. It is anticipated that this review will stimulate further multidisciplinary research through site evaluation and monitoring to provide reliable information that can be used to develop appropriate model-based remediation solutions.

The Contaminate Infiltration Model for Heat and Concentration Transport Within Porous Media Under Electromagnetic Fields

Abstract This paper studies the groundwater model of the influence of physical parameters, including input frequency of the electromagnetic, and input concentration of contaminants in groundwater, on the velocity pattern, temperature distribution, and concentration distribution of convective heat transfer in saturated porous media as soil. The mathematical models have solved seven equations in this simulation study, i.e., Maxwell's equation, heat transfer in fluid and solid phases, momentum, and concentration equations. The effect of frequencies and input concentrations of contaminants on the convective heat transfer and concentration distribution in porous media as soil under an electromagnetic wave is investigated. The results indicate that the electromagnetic wave frequency of 2.45 GHz has the most influence on the temperature distribution, velocity patterns, and concentration distribution of the fluid within the porous media as soil during saturated flow in groundwater. The inlet fluid concentration of the contaminant at 30 mol/dm3 has the most impact on the temperature distribution between the implementation of an electromagnetic wave of 2.45 GHz. So, this numerical model provides simple decision data based on comparing the maximum contaminant concentrations of porous media as soil samples with surface soil screening levels such as petroleum engineering and agricultural engineering. This result can be used by the engineer as a guide to determine whether further investigation is needed.

A pilot study to assess the influence of infiltrated stormwater on groundwater: Hydrology and trace organic contaminants.

Underground infiltration basins (UIBs) mimic the natural hydrologic cycle by allowing stormwater to recharge local groundwater aquifers. However, little is known about the potential transport of organic contaminants to receiving groundwater. We conducted a pilot study in which we collected paired grab samples of stormwater runoff flowing into two UIBs (inflow) and shallow groundwater adjacent to the UIBs. Samples were collected coincident with three rain events and analyzed for volatile organic compounds, semi‐volatile organic compounds, pharmaceuticals, and pesticides. Few contaminants were detected in groundwater, compared with inflow, and groundwater concentrations were typically an order of magnitude less. With one exception (trichloroethene), all groundwater concentrations were at least two orders of magnitude below available guidance or screening values. This short communication highlights information gaps in understanding the hydrologic connectivity between UIBs and receiving groundwater and potential consequent contaminant transport to the subsurface from varying climatic conditions.Practitioner Points Urban stormwater contains organic contaminants including pharmaceuticals, pesticides, and semi‐volatile organic compounds that may be transported to groundwater via infiltration.In general, fewer contaminants were detected in groundwater and at lower concentrations, compared with urban stormwater runoff.Trace organic contaminant concentrations in groundwater were much lower than drinking water guidance/screening values.

Inequities in Drinking Water Quality Among Domestic Well Communities and Community Water Systems, California, 2011‒2019.

Objectives. To evaluate universal access to clean drinking water by characterizing relationships between community sociodemographics and water contaminants in California domestic well areas (DWAs) and community water systems (CWSs). Methods. We integrated domestic well locations, CWS service boundaries, residential parcels, building footprints, and 2013-2017 American Community Survey data to estimate sociodemographic characteristics for DWAs and CWSs statewide. We derived mean drinking and groundwater contaminant concentrations of arsenic, nitrate, and hexavalent chromium (Cr[VI]) between 2011 and 2019 and used multivariate models to estimate relationships between sociodemographic variables and contaminant concentrations. Results. We estimated that more than 1.3 million Californians (3.4%) use domestic wells and more than 370 000 Californians rely on drinking water with average contaminant concentrations at or above regulatory standards for 1 or more of the contaminants considered. Higher proportions of people of color were associated with greater drinking water contamination. Conclusions. Poor water quality disproportionately impacts communities of color in California, with the highest estimated arsenic, nitrate, and Cr(VI) concentrations in areas of domestic well use. Domestic well communities must be included in efforts to achieve California's Human Right to Water. (Am J Public Health. 2022;112(1):88-97. https://doi.org/10.2105/AJPH.2021.306561).

Roles of reactive iron mineral coatings in natural attenuation in redox transition zones preserved from a site with historical contamination

In this study, a protocol was developed to identify reduction-oxidation (redox) transition zones in an effort to exploit natural source zone depletion processes. A sediment core with a total length of 18-m was collected from a site with historical contamination that includes chlorinated benzenes where the redox condition was preserved. In the four redox transition zones investigated, reactive iron coatings are characterized with a suite of analyses under anaerobic conditions. To distinguish surface coating mineralogy, X-ray diffraction, X-ray fluorescence, and field-emission scanning electron microscopy with an energy dispersive X-ray analyzer were applied along with a six-step sequential extraction process. The cycling of Fe and S, as an important contribution and indicator of ongoing natural attenuation processes for constituents of concern (COC), was delineated by using data from multiple and complementary analyses for isolating and identifying iron phases. Along with groundwater chemistry, contaminant concentrations, and microbial genera, attenuation of COCs is expected to be active and sustainable in redox transition zones, where there is an abundance of reactive iron mineral coatings cycling through biogeochemical reactions. Reactions in other redox transition zones may be limited where iron mineral coatings are not dominant.

A Moving Least Squares Based Meshless Element-Free Galerkin Method for the Coupled Simulation of Groundwater Flow and Contaminant Transport in an Aquifer

In this study, a meshless simulation model based on the element-free Galerkin method (EFGM) is proposed for the coupled simulation of groundwater flow and contaminant transport (GFCT) in the two-dimensions. EFGM discretizes the governing GFCT equations using the Galerkin integral approach and shape functions generated through the moving least squares (MLS) approximation method. It results into the stable system of equations for estimating the groundwater head and contaminant concentration values. EFGM computes the several global matrices using the spatial information of the scattered and unconnected field nodes and hence, terminates the meshing procedure unlike the finite difference (FDM) and finite element (FEM) methods. The Kronecker delta function property is missing in EFGM shape functions and hence, the Dirichlet boundary conditions are enforced with some special methods. We have used the penalty method to include them into the presented EFGM model. This method is straightforward and computationally useful for the real field simulations. The proposed model is first validated using both the one- and two-dimensional analytical solutions. The developed coupled model is then applied to solve the hypothetical and real field problems. EFGM results for both the problems are compared with the MODFLOW and MT3DMS results for the head and concentration values respectively. EFGM results are found to be satisfactory for both the cases, and it shows the potential of the proposed approach for the coupled GFCT simulations.

Aplicação de Redes Neurais Artificiais Para Simulação de Fluxo e Transporte de Contaminantes Sob Incerteza de Condutividade Hidráulica

A incerteza relacionada à variabilidade espacial da condutividade hidráulica (K) é um importante aspecto a ser considerado nas simulações da migração de plumas de contaminantes e, consequentemente no gerenciamento ambiental de áreas contaminadas. A utilização de modelos estocásticos de K em conjunto com a simulação de fluxo e o transporte de contaminantes é frequente em pesquisas para a previsão do comportamento da pluma, bem como para projetos de remediação sob a incerteza deste parâmetro hidrogeológico. No entanto, as técnicas tradicionais de modelagem de fluxo e de contaminantes, como o MODFLOW e o MT3D, baseadas no método de diferenças finitas, normalmente são lentas e exigem bastante esforço computacional. Dessa maneira, esta pesquisa aplicou redes neurais artificias (RNA) em 100 cenários de condutividade hidráulica, realizados por métodos estocásticos, a fim de avaliar a incerteza de K na migração de uma pluma. Além disso, foi possível validar a utilização de RNA como ferramenta de decisão para a estimativa da concentração média de contaminantes nas águas subterrâneas ao longo de três anos de simulação. Com base nos resultados obtidos, foi possível avaliar possíveis técnicas de remediação para a área de pesquisa em função da migração da pluma sob a incerteza da condutividade hidráulica.

Assessing the Transport of Pharmaceutical Compounds in a Layered Aquifer Discharging to a Stream.

A groundwater plume containing high concentrations of pharmaceutical compounds, mainly sulfonamides, barbiturates, and ethyl urethane, in addition to chlorinated ethenes and benzene was investigated. The contamination originating from a former pharmaceutical industry discharges into a multilayered aquifer system and a downgradient stream. In this study, geological and hydrogeological data were integrated into a numerical flow model to examine identified trends using statistical approaches, including principal component analysis and hierarchal cluster analysis. A joint interpretation of the groundwater flow paths and contaminant concentrations in the different compartments (i.e., groundwater and hyporheic zone) provided insight on the transport processes of the different contaminant plumes to the stream. The analysis of historical groundwater concentrations of pharmaceutical compounds at the site suggested these compounds are slowly degrading. The pharmaceutical compounds migrate in both a deep semiconfined aquifer, as well as in the shallow unconfined aquifer, and enter the stream along a 2-km stretch. This contrasted with the chlorinated ethenes, which mainly discharge to the stream as a focused plume from the unconfined aquifer. The integrated approach developed here, combining groundwater flow modeling and statistical analyses of the contaminant concentration data collected in groundwater and the hyporheic zone, lead to an improved understanding of the observed distribution of contaminants in the unconfined and semiconfined aquifers, and thus to their discharge to the stream. This approach is particularly relevant for large and long-lasting contaminant sources and plumes, such as abandoned landfills and industrial production sites, where field investigations may be very expensive.

Estimation of Interstitial Velocity Using a Direct Drive High-Resolution Passive Profiler.

The fate and transport of groundwater contaminants depends partially on groundwater velocity, which can vary appreciably in highly stratified aquifers. A high-resolution passive profiler (HRPP) was developed to evaluate groundwater velocity, contaminant concentrations, and microbial community structure at ∼20 cm vertical depth resolution in shallow heterogeneous aquifers. The objective of this study was to use mass transfer of bromide (Br- ), a conservative tracer released from cells in the HRPP, to estimate interstitial velocity. Laboratory experiments were conducted to empirically relate velocity and the mass transfer coefficient of Br- based on the relative loss of Br- from HRPP cells. Laboratory-scale HRPPs were deployed in flow boxes containing saturated soils with differing porosities, and the mass transfer coefficient of Br- was measured at multiple interstitial velocities (0 to 100 cm/day). A two-dimensional (2D) quasi-steady-state model was used to relate velocity to mass transfer of Br- for a range of soil porosities (0.2-0.5). The laboratory data indicate that the mass transfer coefficient of Br- , which was directly-but non-linearly-related to velocity, can be determined with a single 3-week deployment of the HRPP. The mass transfer coefficient was relatively unaffected by sampler orientation, length of deployment time, or porosity. The model closely simulated the experimental results. The data suggest that the HRPP will be applicable for estimating groundwater velocity ranging from 1 to 100 cm/day in the field at a minimum depth resolution of 10 cm, depending on sampler design.

Innovative applications of subgrade biogeochemical reactors: Three case studies

AbstractSubgrade biogeochemical reactors (SBGRs) are an in situ remediation technology shown to be effective in treating contaminant source areas and groundwater hot spots, while being sustainable and economical. This technology has been applied for over a decade to treat chlorinated volatile organic compound source areas where groundwater is shallow (e.g., less than approximately 30 feet below ground surface [ft bgs]). However, this article provides three case studies describing innovative SBGR configurations recently developed and tested that are outside of this norm, which enable use of this technology under more challenging site conditions or for treatment of alternative contaminant classes. The first SBGR case study addresses a site with groundwater deeper than 30 ft bgs and limited space for construction, where an SBGR column configuration reduced the maximum trichloroethene (TCE) groundwater concentration from 9,900 micrograms per liter (μg/L) to <1 μg/L (nondetect) within approximately 15 months. The second SBGR is a recirculating trench configuration that is supporting remediation of a 5.7‐acre TCE plume, which has significant surface footprint constraints due to the presence of endangered species habitat. The third SBGR was constructed with a new amendment mixture and reduced groundwater contaminant concentrations in a petroleum hydrocarbon source area by over 97% within approximately 1 year. Additionally, a summary is provided for new SBGR configurations that are planned for treatment of additional classes of contaminants (e.g., hexavalent chromium, 1,4‐dioxane, dissolved explosives constituents, etc.). A discussion is also provided describing research being conducted to further understand and optimize treatment mechanisms within SBGRs, including a recently developed sampling approach called the aquifer matrix probe.

Remember Groundwater Flow

Groundwater flow is governed by groundwater hydraulics and is key to understanding the subsurface migration of groundwater, dissolved contaminants, and emplaced injection fluids. Yet groundwater flow appears to be largely forgotten or ignored in many subsurface injection-based remedial studies. Over the past decade, numerous studies of subsurface injection technologies (in situ oxidation, enhanced biodegradation, etc.) have been presented at conferences and published as peer-reviewed papers. These studies discuss the effectiveness of these remediation technologies and present chemical and biological data to support their results. However, rarely do these studies consider the impact of groundwater flow on data interpretation and their results. Often the studies do not even provide basic information on groundwater seepage velocities. I recently read a professional paper, an in situ oxidation (ISCO) study, that prompted me to write this editorial. I will use this unnamed study as an example, but I could equally use one of numerous other studies as an example. This ISCO study showed reductions in contaminant concentrations with some rebound and, in many respects, was well designed and well documented. The groundwater seepage velocity was reported to be about 46 ft/year. Three ISCO injection events were completed, during a period of about 9 months, at the source and at other injection locations extending about 30 ft downgradient from the source. The monitoring network consisted of three transects of discrete monitoring wells located 15, 45, and 75 ft downgradient from the source injection location. Evaluations of the effectiveness of the injections were completed based on a groundwater sampling event 3 months after the last injection. A final groundwater sampling event, which occurred 11 months after the last injection event, was used to evaluate rebound. Do you see what troubles me here? Consider this ISCO study and assume idealized horizontal groundwater flow while disregarding aquifer heterogeneity that complicates groundwater flow. Based on the distances of the monitoring transects (15, 45, and 75 ft downgradient) and the groundwater seepage velocity (46 ft/year), it would take approximately 119 (almost 4 months), 357, and 595 days for the injected ISCO fluid from the source injection to flow past the three monitoring transects, respectively. Yet this ISCO study evaluated the results and effectiveness of the ISCO injections based on groundwater samples collected 3 months after the last injection, before the injected fluid had migrated past the closest monitoring well transect. During the final sampling event, 11 months postinjection, the injected fluid would be expected to be found around two of the three well transects under these idealized groundwater flow conditions. The real world is not homogeneous and isotropic. Heterogeneity can result in varying migration rates for injected fluid and can affect the composition of well samples. Injected fluids in higher permeable zones will flow past downgradient monitoring wells faster than injected fluids in lower permeable zones. Groundwater samples reflect a combination of groundwater from the different permeability zones intersected by the well. If a groundwater sample is collected from a well that intersects both a higher permeable zone, where the original contaminated groundwater has displaced the injected fluid, and a lower permeable zone, which still has the noncontaminated injected fluid, the resulting groundwater sample would reflect a mixture of groundwater from these two zones. If, for example, 70% of the sample water comes from the higher permeable zone and 30% of the sample water comes from the lower permeable zone, the resulting groundwater sample would indicate a contaminant concentration 30% lower than the original groundwater contaminant concentration. This could be interpreted to suggest that the postinjection groundwater concentrations had declined by 30%. Groundwater flow needs to be understood and specifically addressed during studies of injection-based in situ remediation because groundwater flow is key to understanding the subsurface migration of groundwater and emplaced injection fluids. The characterization and heterogeneity of groundwater flow need to be integral to the design, data collection, and data interpretation of injection-based remedial studies if we wish to truly understand the effectiveness of our in situ injection remedial technologies. Therefore, for the design, implementation, interpretation, and presentation of studies involving injection based in situ remedial technologies, remember groundwater flow. Guy Swenson, BA, MS, Marcellus, NY; [email protected]

A subagging regression method for estimating the qualitative and quantitative state of groundwater

A subsample aggregating (subagging) regression (SBR) method for the analysis of groundwater data pertaining to trend-estimation-associated uncertainty is proposed. The SBR method is validated against synthetic data competitively with other conventional robust and non-robust methods. From the results, it is verified that the estimation accuracies of the SBR method are consistent and superior to those of other methods, and the uncertainties are reasonably estimated; the others have no uncertainty analysis option. To validate further, actual groundwater data are employed and analyzed comparatively with Gaussian process regression (GPR). For all cases, the trend and the associated uncertainties are reasonably estimated by both SBR and GPR regardless of Gaussian or non-Gaussian skewed data. However, it is expected that GPR has a limitation in applications to severely corrupted data by outliers owing to its non-robustness. From the implementations, it is determined that the SBR method has the potential to be further developed as an effective tool of anomaly detection or outlier identification in groundwater state data such as the groundwater level and contaminant concentration.

Evaluation of groundwater pollution risk (GPR) from agricultural activities using DRASTIC model and GIS

Groundwater Pollution risk (GPR) map which utilized groundwater quality is important in order to prevent the groundwater contaminant concentration due to the agricultural activities. DRASTIC model and GIS application are two important tools that had been used for accessing and predicting the quality of groundwater. These supplementary tools are calculating, visualizing, and presenting the GPR by using DRASTIC index for each hydrogeologic factor through ArcGIS software. This study was covered approximately Selangor basin area where the GPR has been defined. There are four categories of agricultural activities in the Selangor basin which are animal husbandary areas, horticultural lands, short term crops and tree, palm and other permanent crops. The map showed that the “low” zones of GPR occupied 56% of the east side of the Selangor basin, 34% of the west side of the Selangor basin exposed to “medium” zones of GPR and the “high” zones of GPR covered 10% at the north side and the south to the west side of the Selangor basin. As a particular, for agricultural activities which is 52% of Selangor basin area, the “low”, ‘’medium” and “high” zones of GPR was occupied as 42%, 43% and 15% respectively. Based on four categories of agricultural landuse, GPR map validated by nitrate distribution map, shows that the 99% of the variation in nitrate distribution zones are explained by GPR zones. In conclusion, groundwater pollution risk was affected by agricultural activities.

Effect of phytoremediation on concentrations of benzene, toluene, naphthalene, and dissolved oxygen in groundwater at a former manufactured gas plant site, Charleston, South Carolina, USA, 1998–2014

Concentrations of benzene, toluene, naphthalene, and dissolved oxygen in groundwater at a former manufactured gas plant site near Charleston, South Carolina, USA, have been monitored since the installation of a phytoremediation system of hybrid poplar trees in 1998. Between 2000 and 2014, the concentrations of benzene, toluene, and naphthalene (BTN this pathway of uptake by trees was confirmed by the detection of benzene, toluene, and naphthalene in trees during sampling events in 2002, and later in the study in 2012. These data suggest that the phytoremediation system affects the groundwater contaminants on a seasonal basis and, over multiple years, has resulted in a cumulative decrease in dissolved-phase contaminant concentrations in groundwater. The removal of dissolved organic contaminants from the aquifer has resulted in a lower demand on dissolved oxygen supplied by recharge and, as a result, the redox status of the groundwater has changed from anoxic to oxic conditions. This study provides much needed information for water managers and other scientists on the viability of the long-term effectiveness of phytoremediation in decreasing groundwater contaminants and increasing dissolved oxygen at sites contaminated by benzene, toluene, and naphthalene.

Refining the site conceptual model at a former uranium mill site in Riverton, Wyoming, USA

Milling activities at a former uranium mill site near Riverton, Wyoming, USA, contaminated the shallow groundwater beneath and downgradient of the site. Although the mill operated for <6 years (1958–1963), its impact remains an environmental liability. Groundwater modeling predicted that natural flushing would achieve compliance with applicable groundwater protection standards by the year 2098. A decade of groundwater monitoring indicated that contaminant concentrations were declining steadily, which confirmed the conceptual site model (CSM). However, local flooding in 2010 mobilized contaminants that migrated downgradient from the Riverton site and resulted in a dramatic increase in groundwater contaminant concentrations. This observation indicated that the original CSM was inadequate to explain site conditions and needed to be refined. In response to the new observations after the flood, a collaborative investigation to better understand site conditions and processes commenced. This investigation included installing 103 boreholes to collect soil and groundwater samples, sampling and analysis of evaporite minerals along the bank of the Little Wind River, an analysis of evapotranspiration in the shallow aquifer, and sampling naturally organic-rich sediments near groundwater discharge areas. The enhanced characterization revealed that the existing CSM did not account for high uranium concentrations in groundwater remaining on the former mill site and groundwater plume stagnation near the Little Wind River. Observations from the flood and subsequent investigations indicate that additional characterization is still needed to continue refining the CSM and determine the viability of the natural flushing compliance strategy. Additional sampling, analysis, and testing of soil and groundwater are necessary to investigate secondary contaminant sources, mobilization of contaminants during floods, geochemical processes, contaminant plume stagnation, distribution of evaporite minerals and organic-rich sediments, and mechanisms and rates of contaminant transfer from soil to groundwater. Future data collection will be used to continually revise the CSM and evaluate the compliance strategy at the site.

Parametric fate and transport profiling for selective groundwater monitoring at closed landfills: A case study

Monitoring contaminant concentrations in groundwater near closed municipal solid waste landfills requires long term monitoring program which can require significant investment for monitoring efforts. The groundwater monitoring data from a closed landfill in Florida was analyzed to reduce the monitoring efforts. The available groundwater monitoring data (collected over 20years) were analyzed (i.e., type, concentration and detection level) to identify the trends in concentrations of contaminants and spatial mobility characteristics of groundwater (i.e., groundwater direction, retardation characteristics of contaminants, groundwater well depth, subsoil characteristics), to identify critical monitoring locations. Among the 7 groundwater monitoring well clusters (totaling 22 wells) in landfill, the data from two monitoring well clusters (totaling 7 wells) located along direction of groundwater flow showed similarities (the highest concentrations and same contaminants). These wells were used to assess the transport characteristics of the contaminants. Some parameters (e.g., iron, sodium, ammonia as N, chlorobenzene, 1,4-dichlorobenzene) showed decreasing trends in the groundwater due to soil absorption and retardation. Metals were retarded by ion exchange and their concentration increased by depth indicating soil reached breakthrough over time. Soil depth did not have a significant effect on the concentrations of volatile organic contaminants. Based on the analyses, selective groundwater monitoring modifications were developed for effective monitoring to acquire data from the most critical locations which may be impacted by leachate mobility. The adjustments in the sampling strategy reduced the amount of data collected by as much as 97.7% (i.e., total number of parameters monitored). Effective groundwater sampling strategies can save time, effort and monitoring costs while improving the quality of sample handling and data analyses for better utilization of post closure monitoring funds.

An innovative procedure to assess multi-scale temporal trends in groundwater quality: Example of the nitrate in the Seine–Normandy basin, France

• Large and heterogeneous dataset: how to improve the assessment of trends. • Punctual and regional assessment of groundwater quality. • Homogeneity and nonparametric tests to determine recent groundwater quality trends. • We modify geostatistical approach to create spatial unit for regional trend analysis. • Improving the management of groundwater in compliance with the WFD requirements. The European Water Framework Directive (WFD) asks Member States to identify trends in contaminant concentrations in groundwater and to take measures to reach a good chemical status by 2015. In this study, carried out in a large hydrological basin (95,300 km 2 ), an innovative procedure is described for the assessment of recent trends in groundwater nitrate concentrations both at sampling point and regional scales. Temporal variograms of piezometric and nitrate concentration time series are automatically calculated and fitted in order to classify groundwater according to their temporal pattern. These results are then coupled with aquifer lithology to map spatial units within which the modes of diffuse transport of contaminants towards groundwater are assumed to be the same at all points. These spatial units are suitable for evaluating regional trends. The stability over time of the time series is tested based on the cumulative sum principle, to determine the time period during which the trend should be sought. The Mann–Kendall and Regional-Kendall nonparametric tests for monotonic trends, coupled with the Sen-slope test, are applied to the periods following the point breaks thus determined at both the sampling point or regional scales. This novel procedure is robust and enables rapid processing of large databases of raw data. It would therefore be useful for managing groundwater quality in compliance with the aims of the WFD.

Modelling spatial oscillations in soil borehole bacteria

Spatial oscillations in groundwater contaminant concentrations can be successfully explained by consideration of a competitive microbial community in conditions of poor nutrient supply, in which the effects of spatial diffusion of the nutrient sources are included. In previous work we showed that the microbial competition itself allowed oscillations to occur, and, in common with other reaction–diffusion systems, the addition of spatial diffusion transforms these temporal oscillations into travelling waves, sometimes chaotic. We therefore suggest that irregular chemical profiles sometimes found in contaminant plume borehole profiles may be a consequence of this competition.

The influence of a municipal solid waste landfill on groundwater quality: a modeling case study for râureni�râmnicu vâlcea (romania)

Municipal solid waste landfi lls are potential long-term sources of pollution for both humans and the environment and need to be managed properly both during their lifetime and after closure. This paper analyzes the infl uence of the Râureni-Râmnicu Vâlcea landfi ll (Romania) on the concentration of pollutant reaching the groundwater and the nearby Olt River. Prediction of contaminant concentration in groundwater is based on a simple mathematical model of solute transport. Model parameters are determined from fi eld data and scale analysis. Despite its recent closure after 32 years of activity, this landfi ll has the potential to continue to pollute both the Olt River and the groundwater for decades. Sensitivity analyses are performed to determine the impact of varying the dispersivity coeffi cients on the resulting contaminant transport and distribution in the aquifer. Aquifer pollution is predicted for twenty years beyond the landfi ll closure. Enhanced landfi ll monitoring and establishment of a shared data portal for Romanian environmental data is highly recommended.

Optimal groundwater remediation design of pump and treat systems via a simulation–optimization approach and firefly algorithm

In the present study, an optimization approach based on the firefly algorithm (FA) is combined with a finite element simulation method (FEM) to determine the optimum design of pump and treat remediation systems. Three multi-objective functions in which pumping rate and clean-up time are design variables are considered and the proposed FA-FEM model is used to minimize operating costs, total pumping volumes and total pumping rates in three scenarios while meeting water quality requirements. The groundwater lift and contaminant concentration are also minimized through the optimization process. The obtained results show the applicability of the FA in conjunction with the FEM for the optimal design of groundwater remediation systems. The performance of the FA is also compared with the genetic algorithm (GA) and the FA is found to have a better convergence rate than the GA.