Special Issue "Natural Background Levels in Groundwater"

A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydrology".

Deadline for manuscript submissions: closed (31 January 2021) | Viewed by 11161

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Special Issue Editors

Dr. Elisabetta Preziosi
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Guest Editor
Consiglio Nazionale delle Ricerche, Istituto di Ricerca sulle Acque, Monterotondo, Italy
Interests: natural background levels; groundwater quality; groundwater monitoring; sustainable water resources management; climate changes; groundwater flow modeling; water framework directive; groundwater directive
Special Issues, Collections and Topics in MDPI journals
Dr. Marco Rotiroti
E-Mail Website
Guest Editor
Department of Earth and Environmental Sciences, University of Milano-Bicocca, Milano, Italy
Interests: hydrogeochemical modelling; trace elements; groundwater quality; groundwater/surface water interactions
Special Issues, Collections and Topics in MDPI journals
Dr. M. Teresa Condesso de Melo
E-Mail Website
Guest Editor
Instituto Superior Técnico, University of Lisbon, Portugal
Interests: groundwater baselines; tracers; saline intrusion; groundwater recharge; groundwater dependent ecosystems; socio-hydrogeology
Dr. Klaus Hinsby
E-Mail Website
Guest Editor
Geological Survey of Denmark and Greenland, Department of Hydrology, Øster Voldgade 10, 1350 Copenhagen K, Denmark
Interests: water resources; global change; hydrogeology; hydrochemistry; climate change; groundwater geochemical and quantitative status; groundwater age and residence times; groundwater dependent terrestrial and associated aquatic ecosystems; EU and UN water policies
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

High levels of inorganic compounds in groundwater represent a significant problem in many parts of the world, with important economic, social, and environmental drawbacks. Natural groundwater composition mainly derives from water–rock interactions, both in vadose and saturated zones, but depends also on biological processes, residence time, and the initial composition of recharge water. Contamination from industrial, agricultural, and urban areas often overlaps on the natural features of groundwater, and the assessment of the impact of anthropogenic activities might be challenging.

This is a fundamental issue in groundwater management, in particular when the concentration of inorganic compounds exceeds the threshold values set for the evaluation of the good groundwater chemical status of groundwater, as requested by many environmental regulations. The distinction of high natural background levels (NBLs) of chemical elements in groundwater from human-derived contamination is needed to clearly define the environmental objectives for groundwater bodies as well as the reclamation targets for contaminated sites.

A variety of methodologies have been adopted by different countries to assess the NBLs of chemical elements in groundwater that are potential contaminants and may be hazardous for human health and groundwater-dependent ecosystems. Recent research has demonstrated the need for an enhanced understanding of the interaction of natural and anthropogenic processes affecting groundwater quality finalised to the assessment of the boundary between pristine and polluted.

This Special Issue aims to update the knowledge on methods and approaches used to derive NBLs, from site-specific to catchement-wide or regional scale. We welcome the submission of papers reporting the development of innovative methods to determine the NBL and new criteria for a correct evaluation of anthropogenic impacts on groundwater quality, including conceptual model definition, monitoring strategies, geochemical modelling, and statistical and spatial analysis of geochemical data. The final goal is a Special Issue bringing together new insights on how the NBL is dealt with, from different regions of the world.

Dr. Elisabetta Preziosi
Dr. Marco Rotiroti
Dr. M. Teresa Condesso de Melo
Sr. Sci. Klaus Hinsby
Guest Editors

Manuscript Submission Information

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Keywords

  • Geochemical modelling
  • Water–rock interactions
  • Spatial analysis
  • Geostatistics
  • Multivariate statistical analysis
  • Threshold values
  • Groundwater pollution.

Published Papers (10 papers)

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Editorial

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Editorial
Natural Background Levels in Groundwater
Water 2021, 13(19), 2770; https://doi.org/10.3390/w13192770 - 06 Oct 2021
Viewed by 500
Abstract
High levels of inorganic compounds in groundwater represent a significant problem in many parts of the world, with major economic, social and environmental drawbacks [...] Full article
(This article belongs to the Special Issue Natural Background Levels in Groundwater)

Research

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Article
A Broad-Scale Method for Estimating Natural Background Levels of Dissolved Components in Groundwater Based on Lithology and Anthropogenic Pressure
Water 2021, 13(11), 1531; https://doi.org/10.3390/w13111531 - 29 May 2021
Cited by 3 | Viewed by 1245
Abstract
The Water Framework Directive (WFD) requires EU member states to assess the chemical status of groundwater bodies, a status defined according to threshold values for harmful elements and based on/the natural background level (NBL). The NBL is defined as the expected value of [...] Read more.
The Water Framework Directive (WFD) requires EU member states to assess the chemical status of groundwater bodies, a status defined according to threshold values for harmful elements and based on/the natural background level (NBL). The NBL is defined as the expected value of the concentration of elements naturally present in the environment. The aim of this study is to propose a methodology that will be broadly applicable to a wide range of conditions at the regional and national scale. Using a statistical approach, the methodology seeks to determine NBLs for SO4, As, Cd, Cr, Cu, Ni, Zn, and F based on the lithology of aquifers from which groundwater monitoring data were collected. The methodology was applied in six EU countries to demonstrate validity for a wide range of European regions. An average concentration was calculated for each parameter and chosen water point and linked to a lithology. Based on the dataset created, significant differences between lithologies and pressure categories (urban, agricultural, industrial, and mining) were tested using a nonparametric test. For each parameter, 90th percentiles were calculated to provide an estimation of the maximum natural concentrations possible for each lithology. Full article
(This article belongs to the Special Issue Natural Background Levels in Groundwater)
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Article
Roadmap for Determining Natural Background Levels of Trace Metals in Groundwater
Water 2021, 13(9), 1267; https://doi.org/10.3390/w13091267 - 30 Apr 2021
Cited by 5 | Viewed by 1283
Abstract
Determining natural background levels (NBLs) is a fundamental step in assessing the chemical status of groundwater bodies in the EU, as stipulated by the Water Framework and Groundwater Directives. The major challenges in deriving NBLs for trace metals are understanding the interaction of [...] Read more.
Determining natural background levels (NBLs) is a fundamental step in assessing the chemical status of groundwater bodies in the EU, as stipulated by the Water Framework and Groundwater Directives. The major challenges in deriving NBLs for trace metals are understanding the interaction of natural and anthropogenic processes and identifying the boundary between pristine and polluted groundwater. Thus, the purpose of this paper is to present a roadmap guiding the process of method selection for setting meaningful NBLs of trace metals in groundwater. To develop the roadmap, we compared and critically assessed how three methods for excluding polluted sampling points affect the NBLs for As, Cd, Cr, Cu, Ni, and Zn in Danish aquifers. These methods exclude sampling points based on (1) the primary use of the well (or sampling purpose), (2) the dominating anthropogenic pressure in the vicinity of the well, or (3) a combination of pollution indicators (NO3, pesticides, organic micropollutants). Except for Ni, the NBLs derived from the three methods did not differ significantly, indicating that the data pre-selection based on the primary use of the wells is an important step in assuring the removal of anthropogenically influenced points. However, this pre-selection could limit the data representativity with respect to the different groundwater types. The roadmap (a step-by-step guideline) can be used at the national scale in countries with varying data availability. Full article
(This article belongs to the Special Issue Natural Background Levels in Groundwater)
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Article
Assessing Natural Background Levels in the Groundwater Bodies of the Apulia Region (Southern Italy)
Water 2021, 13(7), 958; https://doi.org/10.3390/w13070958 - 31 Mar 2021
Cited by 6 | Viewed by 964
Abstract
Defining natural background levels (NBL) of geochemical parameters in groundwater is a key element for establishing threshold values and assessing the environmental state of groundwater bodies (GWBs). In the Apulia region (Italy), carbonate sequences and clastic sediments host the 29 regional GWBs. In [...] Read more.
Defining natural background levels (NBL) of geochemical parameters in groundwater is a key element for establishing threshold values and assessing the environmental state of groundwater bodies (GWBs). In the Apulia region (Italy), carbonate sequences and clastic sediments host the 29 regional GWBs. In this study, we applied the Italian guidelines for the assessment of the NBLs, implementing the EU Water Framework Directive, in a south-European region characterized by the typical Mediterranean climatic and hydrologic features. Inorganic compounds were analyzed at GWB scale using groundwater quality data measured half-yearly from 1995 to 2018 in the regional groundwater monitoring network (341 wells and 20 springs). Nitrates, chloride, sulfate, boron, iron, manganese and sporadically fluorides, boron, selenium, arsenic, exceed the national standards, likely due to salt contamination along the coast, agricultural practices or natural reasons. Monitoring sites impacted by evident anthropic activities were excluded from the dataset prior to NBL calculation using a web-based software tool implemented to automate the procedure. The NBLs resulted larger than the law limits for iron, manganese, chlorides, and sulfates. This methodology is suitable to be applied in Mediterranean coastal areas with high anthropic impact and overexploitation of groundwater for agricultural needs. The NBL definition can be considered one of the pillars for sustainable and long-term groundwater management by tracing a clear boundary between natural and anthropic impacts. Full article
(This article belongs to the Special Issue Natural Background Levels in Groundwater)
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Article
Natural Background Levels of Potentially Toxic Elements in Groundwater from a Former Asbestos Mine in Serpentinite (Balangero, North Italy)
Water 2021, 13(5), 735; https://doi.org/10.3390/w13050735 - 08 Mar 2021
Cited by 7 | Viewed by 855
Abstract
The definition of natural background levels (NBLs) for potentially toxic elements (PTEs) in groundwater from mining environments is a real challenge, as anthropogenic activities boost water–rock interactions, further increasing the naturally high concentrations. This study illustrates the procedure followed to derive PTE concentration [...] Read more.
The definition of natural background levels (NBLs) for potentially toxic elements (PTEs) in groundwater from mining environments is a real challenge, as anthropogenic activities boost water–rock interactions, further increasing the naturally high concentrations. This study illustrates the procedure followed to derive PTE concentration values that can be adopted as NBLs for the former Balangero asbestos mine, a “Contaminated Site of National Interest”. A full hydrogeochemical characterisation allowed for defining the dominant Mg-HCO3 facies, tending towards the Mg-SO4 facies with increasing mineralisation. PTE concentrations are high, and often exceed the groundwater quality thresholds for Cr VI, Ni, Mn and Fe (5, 20, 50 and 200 µg/L, respectively). The Italian guidelines for NBL assessment recommend using the median as a representative concentration for each monitoring station. However, this involves discarding half of the measurements and in particular the higher concentrations, thus resulting in too conservative estimates. Using instead all the available measurements and the recommended statistical evaluation, the derived NBLs were: Cr = 39.3, Cr VI = 38.1, Ni = 84, Mn = 71.36, Fe = 58.4, Zn = 232.2 µg/L. These values are compared to literature data from similar hydrogeochemical settings, to support the conclusion on their natural origin. Results highlight the need for a partial rethink of the guidelines for the assessment of NBLs in naturally enriched environmental settings. Full article
(This article belongs to the Special Issue Natural Background Levels in Groundwater)
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Article
Deriving Natural Background Levels of Arsenic at the Meso-Scale Using Site-Specific Datasets: An Unorthodox Method
Water 2021, 13(4), 452; https://doi.org/10.3390/w13040452 - 09 Feb 2021
Cited by 3 | Viewed by 1174
Abstract
Arsenic is found in groundwater above regulatory limits in many countries and its origin is often from natural sources, making the definition of Natural Background Levels (NBLs) crucial. NBL is commonly assessed based on either dedicated small-scale monitoring campaigns or large-scale national/regional groundwater [...] Read more.
Arsenic is found in groundwater above regulatory limits in many countries and its origin is often from natural sources, making the definition of Natural Background Levels (NBLs) crucial. NBL is commonly assessed based on either dedicated small-scale monitoring campaigns or large-scale national/regional groundwater monitoring networks that may not grab local-scale heterogeneities. An alternative method is represented by site-specific monitoring networks in contaminated/polluted sites under remediation. As a main drawback, groundwater quality at these sites is affected by human activities. This paper explores the potential for groundwater data from an assemblage of site-specific datasets of contaminated/polluted sites to define NBLs of arsenic (As) at the meso-scale (order of 1000 km2). Common procedures for the assessment of human influence cannot be applied to this type of dataset due to limited data homogeneity. Thus, an “unorthodox” method is applied involving the definition of a consistent working dataset followed by a statistical identification and critical analysis of the outliers. The study was conducted in a highly anthropized area (Ferrara, N Italy), where As concentrations often exceed national threshold limits in a shallow aquifer. The results show that site-specific datasets, if properly pre-treated, are an effective alternative for the derivation of NBLs when regional monitoring networks fail to catch local-scale variability. Full article
(This article belongs to the Special Issue Natural Background Levels in Groundwater)
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Article
eNaBLe, an On-Line Tool to Evaluate Natural Background Levels in Groundwater Bodies
Water 2021, 13(1), 74; https://doi.org/10.3390/w13010074 - 31 Dec 2020
Cited by 6 | Viewed by 963
Abstract
Inorganic compounds in groundwater may derive from both natural processes and anthropogenic activities. The assessment of natural background levels (NBLs) is often useful to distinguish these sources. The approaches for the NBLs assessment can be classified as geochemical (e.g., the well-known pre-selection method) [...] Read more.
Inorganic compounds in groundwater may derive from both natural processes and anthropogenic activities. The assessment of natural background levels (NBLs) is often useful to distinguish these sources. The approaches for the NBLs assessment can be classified as geochemical (e.g., the well-known pre-selection method) or statistical, the latter involving the application of statistical procedures to separate natural and anthropogenic populations. National Guidelines for the NBLs assessment in groundwater have been published in Italy (ISPRA 155/2017), based mainly on the pre-selection method. The Guidelines propose different assessment paths according to the sample size in spatial/temporal dimension and the type of the distribution of the pre-selected dataset, taking also into account the redox conditions of the groundwater body. The obtained NBLs are labelled with a different confidence level in function of number of total observations/monitoring sites, extension of groundwater body and aquifer type (confined or unconfined). To support the implementation of the Guidelines, the on-line tool evaluation of natural background levels (eNaBLe), written in PHP and using MySQL as DBMS (DataBase Management System), has been developed. The main goal of this paper is to describe the functioning of eNaBLe and test the tool on a case study in central Italy. We calculated the NBLs of As, F, Fe and Mn in the southern portion of the Mounts Vulsini groundwater body, within the volcanic province of Latium (Central Italy), also separating the reducing and oxidizing facies. Specific results aside, this study allowed to verify the functioning and possible improvements of the online tool and to identify some criticalities in the procedure NBLs assessment at the groundwater body scale Full article
(This article belongs to the Special Issue Natural Background Levels in Groundwater)
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Article
An Integrated Use of GIS, Geostatistical and Map Overlay Techniques for Spatio-Temporal Variability Analysis of Groundwater Quality and Level in the Punjab Province of Pakistan, South Asia
Water 2020, 12(12), 3555; https://doi.org/10.3390/w12123555 - 17 Dec 2020
Cited by 4 | Viewed by 1190
Abstract
The rapidly changing climatic scenario is demanding periodic evaluation of groundwater quality at the temporal and spatial scale in any region for its effectual management. The statistical, geographic information system (GIS), geostatistical, and map overlay approaches were applied for investigating the spatio-temporal variation [...] Read more.
The rapidly changing climatic scenario is demanding periodic evaluation of groundwater quality at the temporal and spatial scale in any region for its effectual management. The statistical, geographic information system (GIS), geostatistical, and map overlay approaches were applied for investigating the spatio-temporal variation in groundwater quality and level data of 242 monitoring wells in Punjab, Pakistan during pre-monsoon and post-monsoon seasons of the years 2015 and 2016. The analysis indicated the higher variation in data for both the seasons (pre-monsoon and post-monsoon) as coefficient of variation (CV) values were found in the range of 84–175% for groundwater quality parameters. Based on the t-test values, the marginal improvement in groundwater electrical conductivity (EC), sodium absorption ratio (SAR) and residual sodium carbonate (RSC) and decrease in groundwater level (GWL) were observed in 2016 as compared to 2015 (p = 0.05). The spatial distribution analysis of groundwater EC, SAR and RSC indicated that the groundwater quality was unfit for irrigation in the lower south-east part of the study area. The groundwater level (GWL) was also higher in that part of the study area during the pre-monsoon and post-monsoon seasons in 2015 and 2016. The overlay analysis also indicated that the groundwater EC, RSC and GWL values were higher in south-east parts of the study area during pre-monsoon and post-monsoon seasons of 2015 and 2016. Hence, there is an instant need to apply groundwater management practices in the rest of the region (especially in the lower south-east part) to overcome the future degradation of groundwater quality. Full article
(This article belongs to the Special Issue Natural Background Levels in Groundwater)
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Article
GuEstNBL: The Software for the Guided Estimation of the Natural Background Levels of the Aquifers
Water 2020, 12(10), 2728; https://doi.org/10.3390/w12102728 - 29 Sep 2020
Cited by 5 | Viewed by 943
Abstract
Natural background levels (NBLs) for targeted chemical elements characterize a specific groundwater body, the knowledge of which represents a fundamental information for environmental agencies responsible for the protection, management, and remediation of territory. The large number of areas subject to strong anthropogenic pressures [...] Read more.
Natural background levels (NBLs) for targeted chemical elements characterize a specific groundwater body, the knowledge of which represents a fundamental information for environmental agencies responsible for the protection, management, and remediation of territory. The large number of areas subject to strong anthropogenic pressures of a different nature and magnitude makes the job of control authorities particularly difficult. The process to distinguish effective anthropogenic contamination from natural conditions and to define realistic environmental clean-up goals goes through the computation of several mutually dependent statistical methods, some of which have non-trivial resolution and interpretation. In this study, we presented a new tool designed to drive those working in the sector into an articulated path towards NBL assessment. The application software was developed in order to read environmental input data provided by a user-friendly web-based geographic information system (GIS) and to return the NBL estimate of a given chemical element following a wizard that allows for the implementation of two methodologies, i.e., component separation or pre-selection. The project was born from a collaboration between the Department of Environmental Engineering of the University of Calabria and the Department of Environmental Policies of the Calabria Region. The software was used to estimate NBLs in selected chemical species at potentially contaminated industrial sites located in Lamezia Terme, Italy. In the future, the developed calculation program will be the official evaluation tool of the Calabria Region for identifying groundwater thresholds. Full article
(This article belongs to the Special Issue Natural Background Levels in Groundwater)
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Article
Ambient Background Values of Selected Chemical Substances in Four Groundwater Bodies in the Pannonian Region of Croatia
Water 2020, 12(10), 2671; https://doi.org/10.3390/w12102671 - 24 Sep 2020
Cited by 4 | Viewed by 920
Abstract
Groundwater quality is a consequence of cumulative effects of natural and anthropogenic processes occurring in unsaturated and saturated zone, which, in certain conditions, can lead to elevated concentrations of chemical substances in groundwater. In this paper, the concept of determining the ambient background [...] Read more.
Groundwater quality is a consequence of cumulative effects of natural and anthropogenic processes occurring in unsaturated and saturated zone, which, in certain conditions, can lead to elevated concentrations of chemical substances in groundwater. In this paper, the concept of determining the ambient background value of a chemical substance in groundwater was applied, because the long-term effects of human activity influence the increase in concentrations of substances in the environment. The upper limits of ranges of ambient background values were estimated for targeted chemical substances in four groundwater bodies in the Pannonian region of Croatia, according to the demands of the EU Groundwater Directive. The selected groundwater bodies are typical, according to the aquifer typology, for the Pannonian region of Croatia. Probability plot (PP), the modified Lepeltier method, as well as the simple pre-selection method, were used in this paper, depending on a number of chemical data in analysed data sets and in relation to the proportion of <limit of quantification (LOQ) values in a data set for each groundwater body. Estimates obtained by using PP and the modified Lepeltier method are comparable when data variability is low to moderate, otherwise differences between estimates are notable. These methods should not be used if the proportion of <LOQ values in a data set is higher than 30%; however, the integration of results of both methods can increase the confidence of estimation. If the proportion of <LOQ values is higher than 30%, it is recommended to use the robust pre-selection method with the adequate confidence level. For highly skewed data, the 90th percentile of the pre-selected data set is comparable with other methods and preferable over the 95th percentile. The estimates obtained for inert and mobile substances are comparable on different scales. For highly redox-sensitive substances, estimates may differ by one to two orders of magnitude, in relation to the observed heterogeneity of the aquifer systems. The critical issue in the estimation process is the determination of hydrogeological and geochemical homogeneous units within the heterogeneous aquifer system. Full article
(This article belongs to the Special Issue Natural Background Levels in Groundwater)
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