Groundwater Monitoring Program Research Articles

Bridging gaps in groundwater management in International River Basin Districts (IRBDs) – through harmonized monitoring and data sharing

Study regionEurope, with focus on Scandinavia (Denmark, Norway, Sweden), the Baltic countries (Estonia, Latvia, Lithuania), Finland, Poland, and Ukraine. Study focusThe Water Framework Directive (WFD) aims to obtain harmonised holistic Europe-wide water management based on an integrated river basin management model. This study analyses the efficiency of national groundwater monitoring programmes in meeting cross-border demands for harmonised data in IRBDs. Emphasis is placed on the core parameters, oxygen content, pH, conductivity, nitrate, and ammonium, specified by the WFD to be monitored in surveillance monitoring programmes. The findings offer recommendations for national water authorities on infirmities in groundwater management and how they could improve data transparency and availability for enhanced long-term management of shared resources. New hydrological insights for the regionA questionnaire distributed to nine European countries indicates large national differences in the extent of groundwater monitoring. This study highlights several key recommendations for moving forward with transborder groundwater management. Firstly, it is imperative that all nations adhere to ISO standards for field practices and analysis. Secondly, transborder collaborative projects to harmonise e.g., design of monitoring programmes, sampling, and analysis and cooperation on data analysis must be established. Lastly, there is a need to enhance the accessibility of groundwater data and associated metadata. The achievement of the WFD objectives encounters obstacles, due to weak transborder integration and the effects related to administrative boundaries.

Temporal variation of iodine in Danish groundwater

Iodine is an essential element for human health, and both high and low iodine intake could have negative health outcomes. The spatial variation of iodine in Danish groundwater has been studied before, but to the author’s knowledge, this is the first time that the temporal variation is characterised. Nationwide data from the Danish groundwater monitoring programme (GRUMO) were analysed between 2011 and 2021, including 2924 samples from 1242 well screens at 893 wells. The sampling frequency varied and so the robust coefficient of variation (rCV) was calculated for 930 (75%) of well screens, and time-series analysis was performed for 23 (2%). Key findings are (1) iodine in Danish groundwater varies over time (0–124%, median = 10%), (2) in one quarter of the well screens rCV exceeds 20% and (3) this variation cannot be attributed solely to analytical uncertainty at 14% of the well screens. The impact of temporal variation of iodine in Danish drinking water of groundwater origin should be evaluated in future exposure or epidemiological studies with respect to the study goal, location and time period. Since the temporal variation could not be quantified over the entire concentration range, monitoring of iodine in Danish groundwater should continue.

EFFECT OF ABATTOIR WASTE ON THE PHYSICO-CHEMICAL AND FAECAL COLIFORM LOAD OF SURFACE AND UNDERGROUND WATER BODIES IN UGHELLI, DELTA STATE

This study aimed to evaluate the effects of effluent from the Ogheneweta abattoir on the physico-chemical and faecal coliform load of surface and underground water surrounding the abattoir. The study compared the water quality parameters with the guidelines provided by the Federal Ministry of Environment (FMENV) and the World Health Organization (WHO). The research involved the determination of various factors, including physico-chemical characteristics, microbial activity, and spatial and seasonal variations of water. Four sampling stations were selected for the study, with two focusing on groundwater impact and the other two on surface water impact. Differences between the two types of stations were also analyzed. Field sampling was conducted over a nine-month period, and water quality parameters such as temperature, pH, dissolved oxygen, turbidity, biochemical oxygen demand, and faecal coliform load were measured. Standard methods and instruments were utilized for sample collection and analysis, following established water analysis procedures. Statistical analysis was performed using a paired sample T-test (P<0.05). The results indicated that water temperature ranged from 25.56oC to 27.78oC, pH from 6.52 to 7.11, total dissolved solids (TDS) from 10.67mg/l to 210.78mg/l, electrical conductivity (EC) from 20.95mg/l to 426.05mg/l, dissolved oxygen (DO) from 4.17mg/l to 4.72mg/l, turbidity from 1.95mg/l to 9.67mg/l, and biochemical oxygen demand (BOD) from 1.33mg/l to 1.74mg/l. Faecal coliform counts in underground and surface water samples ranged from 2.00 to 2.22MPN/100L and 2.67 to 7.33MPN/100L, respectively. The study findings revealed that the abattoir activities had a negative impact on the quality of both surface and underground water within the Ogheneweta abattoir area. While most physico-chemical and microbial parameters adhered to FMENV and WHO guidelines, the concentrations of turbidity in surface water and faecal coliform in both surface and underground water exceeded the acceptable limits. Moreover, the study showed distinct seasonal variations in physico-chemical parameters, with higher values recorded for pH, TDS, and turbidity during the rainy season, and lower values observed for conductivity. Based on the results, it is recommended that a groundwater monitoring program be implemented to assess the water quality status of wells near abattoirs, ensuring the protection of local residents’ health. Prompt intervention measures, including the establishment of effluent treatment facilities, are essential for effective waste management at abattoirs in Ughelli.

Study of land subsidence by radar interferometry and hot spot analysis techniques in the Peshawar Basin, Pakistan

Land subsidence caused by anthropogenic activities is frequently reported in many megacities worldwide, affecting over 500 million residents. For the first time, this work is reporting substantial ground subsidence in the fifth largest city of Pakistan. Observation of surface deformation using the Small Baseline Subset (SBAS), Interferometric Synthetic Aperture Radar (InSAR) technique on Sentinel-1A datasets from 2015 to 2019 show subsidence up to 3.23 cm. Geologically, this region is going through active deformation associated with Himalayan orogeny. From August 1973 till December 2018, around ten thousand low- to moderate-magnitude earthquakes are reported.We used the emerging hot spot analysis on InSAR and earthquake data to assess the role of seismicity on subsidence. Four variables were analyzed; ground displacement measured by InSAR, earthquake count, earthquake depth, and earthquake magnitude. Analysis of InSAR data indicates that the vast majority of the area is subsiding. This investigation also reveals that earthquake activity near Peshawar is decreasing. In contrast, the earthquake activity is unstable but high in the direction of Tarbela Dam, which is the world's largest earth-filled dam.No systematic groundwater monitoring program has been implemented, and limited published data suggest that the water demand quadrupled in the last decade. A decline in the water table is also reported. Optimized hot spot analysis of water pumping data for 2017 shows a few isolated mild hot spots in the urban center. Excessive groundwater demand and Land-use change from agriculture to urban may have played a significant role in land subsidence in this region.

From Spatial Characterisation to Prediction Maps of the Naturally Occurring Radioactivity in Groundwaters Intended for Human Consumption of Duero Basin, Castilla y León (Spain)

According to the European Council Directive 51/2013 EURATOM, the radionuclide content in human consumption waters must comply with the stated recommendations to ensure the protection of public health. The radiological characterisation assessed in Laboratorio de Radiaciones Ionizantes y Datación of Universidad de Salamanca, in more than 400 groundwater samples gathered from intakes intended for human consumption from the Castilla y León region (Spain), has provided worthwhile data for evaluating the spatial distribution of the radioactivity content in the Duero basin. For this purpose, geostatistical exploration and interpolation analysis, using the inverse distance weighting (IDW) method, was performed. The IDW prediction maps showed higher radioactivity occurrence in western and southern areas of the study region, mainly related to the mineralogical influence of the igneous and metamorphosed outcroppings in the Cenozoic sediments that formed the porous detritic aquifers of the Duero basin edges. The hydraulic characteristics promote the distribution of these radioactivity levels towards the centre of the basin as a consequence of the unconfined nature of the aquifers. Prediction maps provide a worthwhile tool that can be used for better planning and managing of groundwater monitoring programmes.

Geochemical matrix differently affects the response of internal standards and target analytes for pesticide transformation products measured in groundwater samples

Electrospray ionization (ESI) is the most common technique in liquid chromatography coupled to tandem mass spectrometry (LC-MS-MS) allowing for sensitive detection of polar compounds with online water concentration. The technique is popular in groundwater monitoring programs and has permitted great progress in the detection and quantification of polar pesticide transformation products (TP) in recent years. However, ESI is also known to be prone to matrix effects. The common solution to this potential bias is the use of labelled internal standards. Unfortunately, these are not available for all target compounds, which leads to the linkage of target compounds to non-homologue internal standards with unknown consequences for quantification in variable geochemical settings. We investigated these matrix effects for polar TP with a molecular mass range of 225–350 Da and logDpH7 between −0.27 and −1.7 as well as for parent compounds with logDpH3 between 0.84 and 3.22. The acquired internal standards were tested on a gradient of DOC, anions, conductivity and inorganic carbon with a set of ten carefully chosen groundwater samples. Internal standards that were measured in positive ionization mode proved to be insensitive to geochemical variations while those that were measured in negative ionization mode showed reduced response with increasing anion concentration. All pairs of internal standards and target analytes were investigated for deviating matrix effects using standard addition experiments. Positive ionization compounds and target compounds with deuterated homologues showed little deviation while non-homologue pairs in negative mode proved to be strongly biased. Although bias was up to factor five for some compounds it was remarkably stable over the entire gradient studied, suggesting an identical suppression mode at varying matrix levels for different compounds. We advocate the conduct of standard addition experiments if homologue internal standards are not available.

DETERMINATION OF THE TOTAL 14C CONCENTRATION OF WATER SAMPLES USING THE COD METHOD AND AMS

ABSTRACTRadiocarbon (14C) is the one of the most important radionuclides released from the nuclear facilities to the environment. Currently, inorganic 14C is checked during regular environmental monitoring as part of the groundwater monitoring program of the Paks Nuclear Power Plant. Several studies have shown that organic 14C can be also an important and sensitive tool for detection of possible leakage of nuclear technological systems. For this reason, a wet oxidation method was developed for the accelerator mass spectrometry (AMS) 14C measurement technique to determine the 14C activity concentration of the total dissolved carbon content of water samples, coming from environmental monitoring wells. The overall efficiency of the oxidation was around 94 ± 5% for different types of tested organic compounds. The typical 14C background (1–2 pMC) is obtained by preparation of blank samples, which allows a detection level of around 5·10–5 Bq L–1. The activity of the organic fraction can be calculated using the formula presented in the study. The method was applied for water samples deriving from environmental monitoring wells of a pressurized-water reactor (PWR) type of NPP. The results of our investigations over the 14 different water samples around the Paks NPP show that DO14C contribution to the total 14C activity concentration was between 5–25%.

Spatiotemporal dynamics of Escherichia coli presence and magnitude across a national groundwater monitoring network, Republic of Ireland, 2011–2020

Groundwater is a vital drinking water resource and its protection from microbiological contamination is paramount to safeguard public health. The Republic of Ireland (RoI) is characterised by the highest incidence of verocytotoxigenic Escherichia coli (VTEC) enteritis in the European Union (EU), linked to high reliance on unregulated groundwater sources (~16% of the population). Yet, the spatio-temporal factors influencing the frequency and magnitude of microbial contamination remain largely unknown, with past studies typically constrained to spatio-temporally ‘limited’ sampling campaigns. Accordingly, the current investigation sought to analyse an extensive spatially distributed time-series (2011−2020) of groundwater monitoring data in the RoI. The dataset, compiled by the Environmental Protection Agency (EPA), showed ‘high’ contamination rates, with 66.7% (88/132) of supplies testing positive for E. coli, and 29.5% (39/132) exceeding concentrations of 10MPN/100 ml (i.e. gross contamination) at least once during the 10-year monitoring period. Seasonal decomposition analyses indicate that E. coli detection rates peak during late autumn/early winter, coinciding with increases in annual rainfall, while gross contamination peaks in spring (May) and late-summer (August), likely reflecting seasonal shifts in agricultural practices. Mixed effects logistic regression modelling indicates that monitoring sources located in karst limestone are statistically associated with E. coli presence (OR = 2.76, p = 0.03) and gross contamination (OR = 2.54, p = 0.037) when compared to poorly productive aquifers (i.e., transmissivity below 10m2/d). Moreover, 5-day and 30-day antecedent rainfall increased the likelihood of E. coli contamination (OR = 1.027, p < 0.001 and OR = 1.005, p = 0.016, respectively), with the former also being associated with gross contamination (OR = 1.042, p < 0.001). As such, it is inferred that preferential flow and direct ingress of surface runoff are the most likely ingress mechanisms associated with E. coli groundwater supply contamination. The results presented are expected to inform policy change around groundwater source protection and provide insight for the development of groundwater monitoring programmes in geologically heterogeneous regions.

Time series study for groundwater level evaluation in monitoring well

Climate and hydrogeological conditions of the Brazilian semi-arid demand sustainable and efficient water solutions. Groundwater monitoring programs are tools to subsidize the decision-making in this sense. In Ceará state, the monitoring of Araripe sedimentary basin aquifers is important for the development of the region. In this scenario, the present work aimed to study the groundwater level through an exploratory analysis of time series. The study area covered the eastern portion of the Araripe sedimentary basin, in the municipality of Milagres, in Ceará state. As the object of this study, it was obtained the time series of monthly average groundwater levels in a monitoring well of RIMAS/CPRM and installed in the Middle Aquifer System. Graphical and numerical methods were applied for the identification and description of time series main characteristics. Precipitation data in the study area were used to evaluate the system recharge. Results were discussed according to the environmental aspects of the study area. As a result, it was possible the identification and description of time series patterns such as trend and seasonality through the applied methods. It is also highlighted the sharp drawdown of groundwater levels in long term in the time series, reflecting the quantitative state of the aquifer system, as well as the groundwater recharge during the rainy season of the region, evidenced by the study of time series seasonality together with the precipitation data..

Impacts of changing watershed conditions in the assessment of future groundwater contamination risk

Rural regions, which are commonly reliant on groundwater for water supply, often face groundwater quality challenges related to agricultural activity. To sustainably manage and protect groundwater resources, it is necessary to have a clear understanding of inherent groundwater vulnerability and the contamination risk posed by pollutant loading. Index-based methods typically assess groundwater contamination risk in a static manner and commonly represent agricultural land as a single land use class despite the complexity of land management practices that may be present. This paper illustrates modification of the conventional DRASTIC-LU methodology, through a newly developed DRASTIC-AgLU-CC approach, to better understand how groundwater contamination risk may change by mid-century while simultaneously examining the potential influence of land use scheme complexity on model performance and prediction. Recharge, depth to water table, and land use are treated as dynamic factors through the integration of downscaled global climate model data, empirically estimated water table fluctuation and recharge, and trend-based land change modelling. The Upper Parkhill watershed in southwestern Ontario, Canada serves as a case study for method application. Study results indicate that more detailed agricultural land use representation, specifically the inclusion of crop rotation and tile drainage data, has the potential to improve model predictive ability; furthermore, predicted future changes in groundwater contamination risk may vary depending on the manner in which land use is represented. Within the Upper Parkhill watershed, mid-century land use and climate conditions may increase groundwater contamination risk, although minimal change is anticipated. The presented approach provides a valuable screening tool to better understand the potential for changing groundwater contamination risk in rural regions and can be used to guide groundwater monitoring programs and water supply development.

Evaluation of non-uniform groundwater level data using spatiotemporal modeling

Groundwater is one of the main sources of freshwater. To ensure its sustainability, it is important to know its current status and changing pattern over time, through the essential groundwater monitoring program conducted by water management planners, groundwater modelers and urban developers. However, uniformly distributed data is hardly available in most catchments. In this study, the Spatiotemporal Regression Kriging method (Rkriging) was adopted to derive a spatiotemporal pattern for Harvey River Catchment in Western Australia, using the limited groundwater data in the catchment. The accuracy of the estimation was investigated using the Leave-One-Out Cross-Validation approach. Time-series analysis (i.e., auto-correlation and cross-correlation) was then employed to provide a better understanding of the estimated groundwater level change (ΔGWL) over time. To gain insight into the change of groundwater levels, the correlation between groundwater level (GWL) and precipitation pattern with possible time-lag was explored. The results showed that the Rkriging method is satisfactory and the findings were consistent with the previously published results in literature in the area. The estimated decreasing GWL trend matched the precipitation pattern in the catchment. Such shallow groundwater levels in Harvey Catchment resulted in a short time-lag between the precipitation and GWL time-series. The proposed method should be applied to other catchments with limited groundwater data and can be a useful approach for catchments with irregular temporal and spatial data.

Noble gas signatures constrain oil-field water as the carrier phase of hydrocarbons occurring in shallow aquifers in the San Joaquin Basin, USA

Noble gases record fluid interactions in multiphase subsurface environments through fractionation processes during fluid equilibration. Water in the presence of hydrocarbons at the subsurface acquires a distinct elemental signature due to the difference in solubility between these two fluids. We find the atmospheric noble gas signature in produced water is partially preserved after hydrocarbons production and water disposal to unlined ponds at the surface. This signature is distinct from meteoric water and can be used to trace oil-field water seepage into groundwater aquifers. We analyse groundwater (n = 30) and fluid disposal pond (n = 2) samples from areas overlying or adjacent to the Fruitvale, Lost Hills, and South Belridge Oil Fields in the San Joaquin Basin, California, USA. Methane (2.8 × 10−7 to 3 × 10−2 cm3 STP/cm3) was detected in 27 of 30 groundwater samples. Using atmospheric noble gas signatures, the presence of oil-field water was identified in 3 samples, which had equilibrated with thermogenic hydrocarbons in the reservoir. Two (of the three) samples also had a shallow microbial methane component, acquired when produced water was deposited in a disposal pond at the surface. An additional 6 samples contained benzene and toluene, indicative of interaction with oil-field water; however, the noble gas signatures of these samples are not anomalous. Based on low tritium and 14C contents (≤ 0.3 TU and 0.87–6.9 pcm, respectively), the source of oil-field water is likely deep, which could include both anthropogenic and natural processes. Incorporating noble gas analytical techniques into the groundwater monitoring programme allows us to 1) differentiate between thermogenic and microbial hydrocarbon gas sources in instances when methane isotope data are unavailable, 2) identify the carrier phase of oil-field constituents in the aquifer (gas, oil-field water, or a combination), and 3) differentiate between leakage from a surface source (disposal ponds) and from the hydrocarbon reservoir (either along natural or anthropogenic pathways such as faulty wells).

A systematic multi-isotope approach to unravel methane origin in groundwater: Example of an aquifer above a gas field in southern New Brunswick (Canada)

Following the large increase in unconventional hydrocarbon production in North America and elsewhere in the last 15 years, many jurisdictions have implemented groundwater monitoring programs to verify whether these subsurface industrial activities impact shallow groundwater quality. The interpretation of groundwater monitoring results typically relies mostly on dissolved alkane chemical and isotopic composition to infer the potential presence of thermogenic hydrocarbons presumed to originate from a deep source, which may indicate contamination. However, ambiguous results are frequently obtained, and post-genetic processes are often suspected to have modified the original gas composition. Here, we present a systematic approach to identify alkane origin with greater certainty, by thoroughly investigating four processes that may affect dissolved hydrocarbon gas: 1) late-stage methanogenesis, 2) oxidation (of methane or higher alkanes), 3) mixing between different gas sources, and 4) secondary methanogenesis. This is achieved by using empirical equations and fractionation factors available in the literature, combined to site-specific isotopic tracers (δ13CCH4, δ2HCH4, δ2HH2O, δ13CDIC) in groundwater samples. This approach is being tested and applied to a study area located in southern New Brunswick, Canada. The area overlies the McCully gas field from which unconventional natural gas is produced since 2003, and the nearby Elgin area, a prospective area for condensates. Results demonstrate that the presence of methane in groundwater is not related to the proximity of gas wells. In a few shallow wells located very close to producing gas wells in the McCully gas field, methane and ethane were detected, and the compositional and isotopic data sometimes seemed to point towards a thermogenic origin. However, consideration of the four processes led to the conclusion that the gas was of microbial origin, and that it had been oxidized to various levels. In contrast, thermogenic gas was detected in groundwater in the Elgin area, where no commercial production has yet taken place. In this area the natural hydrocarbon gas context is more complex, and the gas from some of the wells was affected by mixing, oxidation, and late-stage methanogenesis. Finally, the approach used in this paper has proven capable of disentangling the original isotopic signature from post-genetic modifications and, despite initial ambiguity, has shown no evidence that past hydraulic fracturing in the McCully gas field has affected shallow groundwater quality.

Relative risk of groundwater-quality degradation near California (USA) oil fields estimated from 3H, 14C, and 4He

Relative risks of groundwater-quality degradation near selected California oil fields are estimated by examining spatial and temporal patterns in chemical and isotopic data in the context of groundwater-age categories defined by tritium and carbon-14. In the Coastal basins, western San Joaquin Valley (SJV), and eastern SJV; 82, 76, and 0% of samples are premodern (pre-1953 recharge), respectively; and 3, 0, and 31% are modern (recharged during or after 1953), respectively. Carbon-14 and helium-4 data indicate most premodern samples are 1000 to 10,000 (33%) or >10,000 (50%) years old. Organic chemicals that could be associated with deeper hydrocarbon reservoirs (e.g. thermogenic gases and benzene) occur most frequently in premodern groundwater, suggesting premodern groundwater has a higher risk of degradation from upward migration of hydrocarbons than modern and mixed-age groundwater. Low sulfate concentrations in some premodern groundwater containing high thermogenic-methane concentrations (>28 mg/L) indicate methane attenuation associated with sulfate reduction can be limited in premodern groundwater. The more common occurrence of manufactured compounds, like tetrachloroethene, in modern and mixed-age groundwater than in premodern groundwater indicates modern and mixed-age groundwater has a higher risk of degradation from land-surface sources than premodern groundwater. Time-series data for chloride in groundwater affected by disposal of oil-field water in unlined ponds indicate some modern and mixed-age groundwater are susceptible to chemical migration within 2–3 km of surface sources. Timescales for diluting chloride concentrations in groundwater with fresh recharge once disposal ponds are decommissioned are shorter in mixed-age groundwater with large fractions of modern water (9–14 years in one example) than in mixed-age groundwater with large fractions of premodern water (no evidence of dilution after 12 years of monitoring in one example). The presence of predominantly premodern groundwater in the Coastal basins and western SJV indicates these areas have relatively high risk from upward migration of hydrocarbons, reduced methane attenuation capacity, and long dilution times, whereas predominantly modern- and mixed-age groundwater in the eastern SJV indicates this area has relatively high risk from chemical migration from land-surface sources and subsequent extensive spreading. Age-based characterizations of relative risk could inform the design of groundwater-monitoring programs near oil fields in terms of the spatial distribution of monitoring points relative to source areas and monitoring frequency and duration.

Estimating pesticides in public drinking water at the household level in Denmark

Pesticide pollution has raised public concern in Denmark due to potential negative health impacts and frequent findings of new substances after a recent expansion of the groundwater monitoring programme. Danish drinking water comes entirely from groundwater. Both the raw groundwater and the treated drinking water are regularly monitored, and the chemical analyses are reported to a publicly available national database (Jupiter). Based on these data, in this study we (1) provide a status of pesticide content in drinking water supplied by public waterworks in Denmark and (2) assess the proportion of Danish households exposed to pesticides from drinking water. ‘Pesticides’ here refers also to their metabolites, degradation and reaction products. The cleaned dataset represents 3004 public waterworks distributed throughout the country and includes 39 798 samples of treated drinking water analysed for 449 pesticides (971 723 analyses total) for the period 2002–2019. Of all these chemical analyses, 0.5% (n = 4925) contained a quantified pesticide (&gt;0.03 μg/l). Pesticides were found at least once in the treated drinking water at 29% of all sampled public waterworks for the period 2002–2019 and at 21% of the waterworks for the recent period 2015–2019. We estimate that 56% of all Danish households were potentially exposed at least once to pesticides in drinking water at concentrations of 0.03–4.00 μg/l between 2002 and 2019. However, in 2015–2019, the proportion of the Danish households exposed to pesticides (0.03–4.00 μg/l) was 41%. The proportion of Danish households potentially exposed at least once to pesticides above the maximum allowed concentration (0.1 μg/l) according to the EU Drinking Water Directive (and the Danish drinking water standard) was 19% for 2002–2019 and 11% for 2015–2019. However, the maximum concentrations were lower than the World Health Organization’s compound-specific guidelines. Lastly, we explore data complexity and discuss the limitations imposed by data heterogeneity to facilitate future epidemiological studies.

Evaluation of some groundwater quality parameters using geostatistics in the urban coastal aquifer of Bosaso plain, Somalia

Groundwater is a major drinking water resource in arid coastal regions. The groundwater quality of Bosaso city experienced degradation due to rapid urbanization and industrialization. This study was carried out to delineate the spatial distribution of groundwater quality parameters and evaluate groundwater suitability for drinking and irrigation uses. The groundwater samples were collected from Bosaso Plain to determine the pH, electrical conductivity (EC), total dissolved solids (TDS), and sodium and chloride concentrations. To categorize water quality for irrigation purposes, sodium adsorption ratio (SAR) was calculated. Ordinary kriging procedure was performed in order to map the spatial distribution of groundwater quality parameters. The interpretation of laboratory analysis results revealed that the most of groundwater wells in the study area is unsafe for drinking purposes due to high salinity, except for the central area (Biyo Kulule). In terms of irrigation uses, the minor area may be under the risk of alkalinity or sodium hazard. However, all groundwater supply points are not suitable for irrigation due to the salinization risk and can be only used to irrigate high salt-tolerant crops. The final maps show that the groundwater quality decreases from southeast to the north of the plain. This indicates that the groundwater is probably subjected to the seawater intrusion. In this regard, the implementation of a groundwater monitoring program is necessary to achieve concrete results. Nevertheless, the most suitable groundwater quality is found to be at the central part of the Bosaso plain.

Hydrogeological investigation of soil salinity adjacent to a flood protection infrastructure

Groundwater modelling is a commonly used technique to determine the influence of surficial processes on subsurface aquifers. In this study, a groundwater monitoring study was conducted on an agricultural field adjacent to a large drainage canal to determine the effects of the canal's operation as it relates to soil salinity during periods around flood events. The groundwater monitoring program consisted of twenty standpipes instrumented with groundwater pressure transducers that took four daily measurements. A finite element model was generated using data collected from the 2017 flood year to determine the effect of the flood on the local groundwater regime within one area consisting of four standpipes. The analysis of the model calibration yielded good to excellent results using the Nash–Sutcliffe Model Efficiency technique, with three of the four standpipes. The salt content within the model area was primarily gypsum initially derived from the underlying till and bedrock units. Model analysis indicated that various processes might impact soil salinity, including canal seepage, evapotranspiration and excessive snowmelt/recharge. The largest flood event on record for the canal was used in the calibrated model to determine the maximum extent of influence the canal has on the adjacent lands. The maximum extent of impact was found to be 112 m in the alluvial sediments and 240 m in the surficial sand structure.

Regulatory groundwater monitoring: Realistic residues of pinoxaden and metabolites at vulnerable locations

A bespoke groundwater monitoring programme was designed to generate a database of pinoxaden and metabolite concentrations in shallow groundwater at agricultural locations across Europe. The data generated from this programme represent a higher tier refinement of modelled exposure estimates and provide realistic information on groundwater quality at vulnerable locations which will aid plant protection product (PPP) assessment in Europe in relation to Regulation (EC) No. 1107/2009.The Regulatory GeoPEARL_3.3.3 model developed by RIVM was used to estimate the vulnerability of cereal growing regions to leaching of two pinoxaden metabolites across the entire EU at a 1 km2 level using 20 years of daily weather data (MARS, EU JRC). Seventy sites located within the upper 50th percentile of leaching vulnerability from this modelling exercise, crop density and shallow groundwater were selected for monitoring groundwater.Retrospective and prospective pinoxaden product applications at candidate sites were recorded and these data used to place sites in the distribution for Europe. The 70 sites all fulfil the site assessment criteria and have no confining layers which may prevent or delay leaching. All sites equipped with groundwater wells had a minimum of two pinoxaden applications in the preceding four years to cereal crops.A total of 1326 samples were analysed from up to 90 down hydraulic gradient wells at 70 locations between June 2015 and July 2018. Results indicate that pinoxaden and pinoxaden metabolites are very unlikely to reach shallow groundwater at concentrations greater than 0.1 μg/L for relevant metabolites, or 10 μg/L for non-relevant metabolites, respectively (Sanco/221/2000-rev.10). Over 38 months of groundwater monitoring the annual average and 90th percentile for pinoxaden or its metabolites never exceeded 0.1 μg/L and it is proposed that these data infer that exposure to these metabolites is minimal.

Geochemical and isotope evidence for groundwater mineralization in a semi-arid river basin, Sri Lanka

Mineralization of groundwater has become a major concern in the coastal, arid, and semi-arid regions throughout the world. The lower segment of the Walawe river stretches through a semi-arid region in Southern Sri Lanka, and groundwater has become an important source of freshwater for the region. A hydrogeochemical study was carried out to identify the sources and processes of groundwater mineralization in the lower region of the Walawe river basin. The groundwater composition was analysed using samples collected from 32 locations during the pre- and post-monsoon periods. The analysis of groundwater revealed that the groundwater composition of the region was dominated by HCO3−, Cl−, and SO42-, which were mostly balanced by Na+, Ca2+, and Mg2+. Ionic relationships of major solutes indicated that anthropogenic influences such as effects of fertilizer applications during the post-monsoon period and notable effects of evaporation during both periods. δ18O and δ2H signatures of the groundwater in the region showed deviations from the regional meteoric water line suggesting intensive evaporation events (δ2H = 5.6 *δ18O – 1.37, r = 0.98). Particularly, isotope values of pre-monsoon samples in the study region indicated contributions of north-east monsoon and first inter-monsoon. Solute geochemistry and stable isotope evidences from the region indicate that groundwater salinity in the area is mainly caused by anthropogenic inputs of solutes through agricultural activities and modified heavily by intensive evaporation. Principle Component Analysis indicated higher heavy metal concentrations in the groundwater during the post-monsoon period in comparison to that of the pre-monsoon period possibly originated from anthropogenic activities. The finding of this study suggested the need for comprehensive groundwater management plans and monitoring programs for ensuring sustainable management of groundwater in the lower Walawe river basin.

Distinct bacterial communities in tropical island aquifers

The groundwater biome is a poorly characterized habitat hypothesized to harbor uniquely diverse bacterial communities; the degree to which these communities differ from associated soils is a central question in environmental microbiology. We characterized the Bacterial community composition in 37 aquifer and 32 surface soil samples across the island of O‘ahu, Hawaiʻi. Several bacterial phyla (Acetothermia, Omnitrophica, Parcubacteria, Peregrinibacteria) relatively abundant in the aquifer samples were rare to absent in the soils. Immense bacterial diversity detected in the deep aquifers indicates that these environments are not as homogenous as expected, but provide various niches and energy sources for wide variety of bacteria. A small proportion of OTUs were widespread in all the basal (0.63%) and all the dike aquifer (0.31%) samples. However, these core bacteria comprised an average of 31.8% (ranging 16.2%-62.0%) and 15.4% (0.1%-31.5%) of all sequences isolated from the basal and dike aquifers respectively. Bacterial community composition correlated significantly with the sodium, sulfate, potassium, total dissolved solids, nitrate, conductivity, and pH in the basal aquifers, while phosphate and bicarbonate levels were also highly important when dike water samples were included in the analyses. This was consistent with high relative abundance of putative chemolithoautoroph taxa in the aquifer communities relative to soils. Targeted molecular and culture-based fecal indicator microbial analyses indicated good water quality of aquifers. The dominance of unique, deeply branching lineages in tropical aquifers emphasizes a large adaptive potential in O‘ahu’s aquifers; variability among groundwater samples suggests that aquifer habitats are surprisingly variable potentially harboring a variety of chemolithotrophic energy sources. Although parallel analyses of conventional and alternative indicators indicated good groundwater quality, this study calls for groundwater monitoring programs which would consider public as well as ecosystem health.