Assessment of natural background levels in potentially contaminated coastal aquifers

BRIDGE methodology-based quality standards to assess aquifer chemical status in the southwest Bengal Basin, Bangladesh

Assessment of natural background levels (NBLs) of compositional groundwater parameters helps to identify the potential threats to groundwater resources. This study is the first attempt to apply the pre-selection-based BRIDGE (Background cRiteria for the IDentification of Groundwater thrEshold) methodology to calculate the NBLs and threshold values (TVs) of major groundwater constituents in the southwest Bengal Basin, Bangladesh. A database consisting of 78 groundwater samples was used to assess the NBLs and associated TVs of the major groundwater parameters (EC, Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^-, NO₃^-, SO₄^2-, PO₄^3-, Mn²⁺, and Fe²⁺). NBLs were derived based on 90th and 97.7th percentiles. The status of regional groundwater resources was assessed by applying 90th percentile NBL on a regional dataset (n = 196). Results revealed the "poor" chemical status of shallow aquifers denoting heavy deterioration of the groundwater quality due to anthropogenic interventions. Nitrate contamination and salinization were identified as the major threats to the deep groundwater of the southwest Bengal Basin. Finally, to verify the chemical status of groundwater in a heavily urbanized area, derived TVs were applied throughout the experimental site Khulna. Twenty-five deep groundwater samples were collected for this purpose. Though most of the parameters exhibited "good" chemical status, nitrate demonstrated anthropogenic groundwater contamination in Khulna City. Thus, the developed TVs would provide an early warning system of pollution. On a national scale, it is expected to facilitate the sustainable groundwater management of the country and contribute to achieving the Sustainable Development Goals (SDG) of the United Nations (UN) in Bangladesh.

A systematic approach to derive natural background levels in groundwater: Application to an aquifer in North Lebanon perturbed by various pollution sources

Several efforts have recently emerged to develop methods capable of determining groundwater natural background levels (NBLs) due to their utmost importance in assessing water quality. A recently developed systematic approach to derive NBLs is the Khadra-Stuyfzand (KS) scheme. It has a clear and standardized flow with multi-steps to eliminate biased or contaminated samples, and hence it is capable of dealing with different pollution sources as well as saltwater intrusion. This method was applied to the Koura-Tripoli-Zgharta (KTZ) Miocene aquifer of coastal North Lebanon. It derived baseline conditions for 2 physical, 16 chemical, and 3 bacteriological parameters in addition to 8 trace elements, and 83 pesticides, polynuclear aromatic hydrocarbons, and volatile organic compounds. The results revealed the extent of anthropogenic shift from background levels, and delineated the main contaminated spots. In fact, the established groundwater baseline composition is typical of limestone aquifers with oligohaline-fresh, moderate alkalinity, calcium bicarbonate water, under freshening conditions. Nonetheless, this quality is locally degraded by microbial contamination due to wastewater disposal sites, saltwater intrusion, and minor nutrient loading from agricultural activities and/or urban development. The measured concentrations of major water ions and a variety of drinking water contaminants (e.g. nutrients, pesticides, hydrocarbons, and heavy metals) are below human health benchmarks, but the microbiological content at several spots has exceeded the permissible limits which renders the water unsuitable for domestic use, and calls for prompt mitigation measures.

Assessing Natural Background Levels in the Groundwater Bodies of the Apulia Region (Southern Italy)

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.

Deriving Natural Background Levels of Arsenic at the Meso-Scale Using Site-Specific Datasets: An Unorthodox Method

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.

GuEstNBL: The Software for the Guided Estimation of the Natural Background Levels of the Aquifers

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.

Groundwater pollution assessment in landfill areas: Is it only about the leachate?

Groundwater is the environmental compartment very often involved in the broader issues related to contaminated sites characterization and reclamation. It is not uncommon to find areas in which some substances directly linked to the petrographic composition of the aquifer reach high values exceeding the limits set by the regulations. These concentrations are defined as Natural Background Levels (NBL) and the need to quantify their real contribution, in areas subject to strong anthropogenic pressures, represents an emerging problem. Global statistical analyses and laboratory testing are proposed here to distinguish between the impacts of different forcing influencing water quality in hydrogeological systems. The study focus on the application of a methodology based on the Component Separation analysis for the NBL estimation of selected chemical species in potentially contaminated aquifers flowing in the proximity of landfill areas, and on the subsequent validation of the results through experimental studies of field samples. A site located in Calabria, Italy, and constituting a typical example of an aquifer which has been subjected to possible contact with the leachate produced by waste degradation is considered. The work is keyed to NBLs characterization of aluminum, iron and manganese and to the identification of their natural component for a proper environmental assessment of the site. Estimated NBLs are consistent with the geochemical composition of site samples. The adopted methodology can represent a useful instrument to distinguish effective anthropogenic contamination from natural conditions and to define realistic environmental clean-up goals.

An Integrated Approach for Evaluating Water Quality between 2007–2015 in Santa Cruz Island in the Galapagos Archipelago

Water quality in Galápagos has been deteriorating by increased human impacts over the past few decades. Water quality is a key environmental component and issue in need to be evaluated in the Pelican Bay Watershed, the biggest urban and economic development of Santa Cruz Island, for better management and regulation of water resources. This study assesses coastal and ground water bodies of Pelican Bay by employing a 9-year dataset obtained during a local water quality monitoring program conducted by the Galápagos National Park. Physical-chemical and microbial parameters were evaluated with respect to national and international water quality standards. A statistical integrated approach was performed to calculate environmental background levels of water quality parameters and to explore their seasonal and spatial variation. In addition, a sensitivity analysis was conducted to evaluate the impact of changes in tourism and residents in San Cruz Island in the degradation of water sources. Results highlighted are: (a) water is not suitable for drinking and domestic use at some inland sites; (b) saline water is used for irrigation in the highlands; (c) the presence of parameters of concern at coastal sites represent a risk for human and ecosystem health; (d) background levels may serve for defining site-specific limits to control water quality, and; (e) the influence of population change on water quality conditions varied at each site with a higher effect at coastal sites relatively to inland sites. This study provided valuable information of the water quality status in Santa Cruz Island and can serve as a baseline for effective water management and control of pollution.

Groundwater diffuse pollution in functional urban areas: The need to define anthropogenic diffuse pollution background levels

Groundwater status in highly urbanized areas is particularly affected by anthropogenic influence due to diffuse pollution deriving from many sources. This makes very often challenging to determine whether the observed groundwater conditions are the result of localized pollutant sources (PS-Point Sources). In the EU legislative framework it is accepted that, when Natural Background Levels (NBLs) of undesirable elements are proven to be higher than specific Groundwater Quality Standards (GQSs), NBLs should be assumed as GQSs. No procedure is instead defined when anthropogenic Diffuse Pollution Background levels (DBPLs) are higher than GQSs and make unfeasible any remediation strategy. Among the many contaminants affecting groundwater, the chlorinated solvents, tetrachloroethylene (PCE), trichloroethylene (TCE) and trichloromethane (TCM) among the organics and hexavalent chromium, among the inorganics, having been widely used in several industries all over Europe, are very often the most prevalent contaminants in soil and groundwater. Aim of this paper is to discuss a multivariate statistical approach to address the issue of identification of anthropogenic Diffuse Pollution Background Levels. With such aim, an area of about 1600 km², including the Functional Urban Area of Milan, was considered and 10 independent geochemical datasets, provided by local and regional agencies, and covering the period 2003-2014 were merged into a single database after homogenization and multiple quality checks. A total of 618,258 chemical analyses from 3477 sampling wells were considered, being all samples collected and analyzed through internally consistent protocols. The analysis enabled to identify five main clusters, having specific hydrogeological characteristics, different temporal profiles and pollutant background concentration levels, which were also found to respond differently to meteo-climatic changes. This study offers a robust knowledge basis for drafting a diffuse pollution management plan of the area.

Assessing background levels of specific conductivity using weight of evidence

There are many ways to estimate background levels, and many types of evidence may contribute to determining whether a water, air, or soil is at background. As a result, it is important to define background in each case and to weigh the available evidence to determine the best estimate of background. A weight-of-evidence approach is demonstrated that assesses whether the background SC is sufficiently similar in streams of Ecoregion 70 in West Virginia and Ohio. During planning, five relevant considerations were identified to assess background SC: physical properties, measured SC, spatial distribution of low SC sites, biological properties, and data relevance and reliability. For each consideration, diverse types of evidence were generated, evaluated, and synthesized using weight of evidence. In the example, evidence was weighed for the hypothesis that background SC is similar in two areas in Ecoregion 70, the Western Allegheny Plateau in the eastern United States. Where, as in this case, background is not well characterized by measurements, because data sets are small or sampling designs or anthropogenic inputs may influence estimates of background, it is suggested that information about regional properties, related to and affected by SC, may be used to determine whether SC in the less characterized area is sufficiently similar to a well characterized area.

Air quality study in the coastal city of Crotone (Southern Italy) hosting a small-size harbor

Particulate polycyclic aromatic hydrocarbons (PAHs), n-alkanes, and gaseous pollutants were collected from the harbor and the urban area of Crotone (Southern Italy) in October 2015. The atmospheric concentrations of organic substances associated to PM₁₀ were determined daily, while gaseous pollutants (BTEX, O₃, SO_2, NO_x, NO₂, and NH₃) were monitored on monthly basis by means of diffusive sampling. Total PAHs reached, on the average, 1.56 ± 0.72, 0.33 ± 0.14, and 0.59 ± 0.37 ng/m³ at the urban monitoring stations (Fiore, Fermi) and at the harbor, respectively. The percent distribution and diagnostic concentration ratios of PAHs were similar at Fermi and harbor, whereas differences were found through comparison with Fiore site. Biogenic n-alkanes (n-C₂₉, and n-C₃₁) were the most abundant components, indicating the important impact of terrestrial higher plants in all sites. On the other hand, n-C₂₃-n-C₂₅ homologs originated from incomplete combustion of fossil fuel were not negligible (CPI_2.5 = 2.4) in harbor, confirming the role of anthropogenic sources there. Inside the harbor, SO₂ concentrations ranged from 5.6 to 14.8 μg/m³ showing the maximum value within the old part of the harbor (touristic port). A statistical significant difference between the harbor and the surroundings was indeed observed for this pollutant, which is a specific marker of ship emissions. The other gaseous species monitored did not exhibit the same distribution, with exception of NH₃ and benzene, whose concentration values ranged from 2.8 to 6.9 μg/m³ and 0.3 to 1.4 μg/m³, respectively, and peaked at the same harbor site. Similarities were found in NO_x, NO₂, and O₃ concentration distributions, showing high values in the New Port area.