Nitrate contamination in a shallow urban aquifer in East Ukraine: evidence from hydrochemical,stable isotopes of nitrate and land use analysis

A combined hydrochemical and stable isotope approach was used to investigate the origin of nitrate in the shallow unconfined groundwater of Kharkiv city, Eastern Ukraine. The contamination was investigated in the context of land use within the catchment area. The observed enrichment of sulfate, chloride and nitrate suggests significant groundwater contamination in the shallow urban aquifer, which is widely used as drinking water source for the urban population. Characteristic nitrate/chloride ratios as well as stable isotope ratios (N and O) of nitrate in the most contaminated springs confirmed that septic waste from leaky sewer systems was the main source of nitrate contamination in the groundwater. Nitrate contamination is linked to the type of land use and sewage treatment regime in the catchment area. It is also modulated by the regional hydrogeology, which determines the susceptibility of a given aquifer toward groundwater pollution. A more quantitative assessment of nitrate sources based on the nitrate isotope analysis alone is rather difficult. However, our study confirms that the combination of hydrochemical tracers, robust land-use analysis and nitrate stable isotope measurements represents a valuable approach to identify the origin of the nitrate contamination.     

Assessing groundwater vulnerability using GIS-based DRASTIC model for Ahmedabad district,India

The present research aims to derive the intrinsic vulnerability of groundwater against contamination using the GIS platform. The study applies DRASTIC model for Ahmedabad district in Gujarat, India. The model uses parameters like depth, recharge, aquifer, soil, topography, vadose zone and hydraulic conductivity, which depict the hydrogeology of the area. The research demonstrates that northern part of district with 46.4% of area is under low vulnerability, the central and southern parts with 48.4% of the area are under moderate vulnerability, while 5.2% of area in the south-east of district is under high vulnerability. It is observed from the study that lower vulnerability in northern part may be mostly due to the greater depth of vadose zone, deeper water tables and alluvial aquifer system with minor clay lenses. The moderate and high vulnerability in central and southern parts of study area may be due to lesser depth to water tables, smaller vadose zone depths, unconfined to semi-confined alluvial aquifer system and greater amount of recharge due to irrigation practices. Further, the map removal and single-parameter sensitivity analysis indicate that groundwater vulnerability index has higher influence of vadose zone, recharge, depth and aquifer parameters for the given study area. The research also contributes to validating the existence of higher concentrations of contaminants/indicators like electrical conductivity, chloride, total dissolved solids, sulphate, nitrate, calcium, sodium and magnesium with respect to groundwater vulnerability status in the study area. The contaminants/indicators exceeding the prescribed limits for drinking water as per Indian Standard 10500 (1991) were mostly found in areas under moderate and high vulnerability. Finally, the research successfully delineates the groundwater vulnerability in the region which can aid land-use policies and norms for activities related to recharge and seepage with respect to existing status of groundwater vulnerability and its quality.     

Nitrate source and fate at the catchment scale of the Vibrata River and aquifer (central Italy): an analysis by integrating component approaches and nitrogen isotopes

The aim of this study is to apply an integrated approach to determine nitrate sources and fate in the alluvial aquifer of the River Vibrata (Abruzzi, central Italy) by coupling the Isotope and the Component approaches. Collected data include concentration and nitrogen isotope composition of groundwater samples from the alluvial aquifer and nitrogen loads arising from agricultural and non-agricultural sources. The adopted methodology identified synthetic fertilizers as main sources of nitrate in the Vibrata alluvial aquifer. At the catchment scale, two different zones have been identified: the Upper Valley, where infiltration to groundwater is dominant and nitrogen easily migrates into the aquifer; in this area, nitrate content in groundwater is stable and normally higher than EU requirements. Moreover, streamwaters are fed by groundwater with a nitrate content likely lowered by denitrification processes occurring in the hyporheic zone. In the Lower Valley, runoff processes dominate and the nitrate content in surface waters is higher. Nevertheless, groundwater is locally affected by denitrification that breaks down the nitrate content, which often reaches values consistent with law limits.     

Tracking sources of groundwater nitrate contamination using nitrogen and oxygen stable isotopes at Beijing area,China

The identification of sources and behavior of contaminants is important to control and manage groundwater quality of aquifer systems in urban areas. In this study, hydrogeochemistry of major constituents and stable isotope ratios of nitrate in groundwater were determined to identify contamination sources and transformation processes occurring in soils and deeper groundwater of Beijing with intense human activities. The nitrogen and oxygen isotopic compositions of nitrate in pore water extracts from groundwater samples indicate at least three potential sources of nitrate in groundwaters at Beijing. Stable isotope analyses from this study site, which has atmospheric, chemical fertilizer and human waste nitrate sources, provide a tool to distinguish nitrate sources in a confined aquifer where concentrations alone do not. These data indicate that the most common sources of high nitrate concentrations in groundwater at Beijing are wastewater and denitrification process occurred specially in the Central area. NO₃–N and cation and anion concentrations (Ca²⁺, Mg²⁺ Cl^? and SO ₄ ² ) showed strong correlations indicating that they originated from the same sources. This study demonstrates that a thorough evaluation of hydrodynamic and hydrochemical parameters with dual isotopes of NO₃ ^? constitutes an effective approach for identifying sources and transformation processes of NO₃ ^? in deeper groundwater systems.     

Assessment of regional change in nitrate concentrations in groundwater in the Central Valley, California, USA, 1950s–2000s

A regional assessment of multi-decadal changes in nitrate concentrations was done using historical data and a spatially stratified non-biased approach. Data were stratified into physiographic subregions on the basis of geomorphology and soils data to represent zones of historical recharge and discharge patterns in the basin. Data were also stratified by depth to represent a shallow zone generally representing domestic drinking-water supplies and a deep zone generally representing public drinking-water supplies. These stratifications were designed to characterize the regional extent of groundwater with common redox and age characteristics, two factors expected to influence changes in nitrate concentrations over time. Overall, increasing trends in nitrate concentrations and the proportion of nitrate concentrations above 5 mg/L were observed in the east fans subregion of the Central Valley. Whereas the west fans subregion has elevated nitrate concentrations, temporal trends were not detected, likely due to the heterogeneous nature of the water quality in this area and geologic sources of nitrate, combined with sparse and uneven data coverage. Generally low nitrate concentrations in the basin subregion are consistent with reduced geochemical conditions resulting from low permeability soils and higher organic content, reflecting the distal portions of alluvial fans and historical groundwater discharge areas. Very small increases in the shallow aquifer in the basin subregion may reflect downgradient movement of high nitrate groundwater from adjacent areas or overlying intensive agricultural inputs. Because of the general lack of regionally extensive long-term monitoring networks, the results from this study highlight the importance of placing studies of trends in water quality into regional context. Earlier work concluded that nitrate concentrations were steadily increasing over time in the eastern San Joaquin Valley, but clearly those trends do not apply to other physiographic subregions within the Central Valley, even where land use and climate are similar.     

An aquifer vulnerability assessment of the Benin Formation aquifer,Calabar, southeastern Nigeria,using DRASTIC and GIS approach

An aquifer vulnerability of the Benin Formation aquifer (Calabar, southern Nigeria) has been assessed using a combination of DRASTIC index and GIS technology. The assessment was necessitated by the fact that uncontrolled disposal of domestic, industrial and agricultural wastes have caused groundwater contamination. Therefore, prevention of contamination, monitoring and management of the aquifer was urgently required to increase the efficient use of the current water supplies. The DRASTIC method uses seven parameters (depth to groundwater table, net recharge, aquifer media, soil media, topography, influence of vadose zone and hydraulic conductivity), which were used to produce vulnerability maps. The drastic vulnerability index ranged between 124 and 170. The vulnerability map shows that the aquifer is highly vulnerable in southeastern parts of the area covering about 22 %. The medium vulnerability area covers about 56.8 % of Calabar extending from the southwest to northern parts. 21.2 % of the area covering the central and northern parts the area lies within the low vulnerability zone. The present industrial and activities are located in the eastern and western parts, which falls within the low-medium vulnerability areas. Documented nitrate concentration in hand-dug wells and boreholes are in agreement with vulnerability zones. Sensitivity analysis was performed to evaluate the sensitivity of each parameter between map layers such that subjectivity can be reduced to an extent and new weights computed for each DRASTIC parameter. As management options sensitive areas, especially in the southern parts of Calabar area, should be protected from future development.     

Nitrate contamination in groundwater in the Sidi Aïch–Gafsa oases region, Southern Tunisia

Groundwater pumped from the semi-confined Complex Terminal (CT) aquifer is an important production factor in irrigated oases agriculture in southern Tunisia. A rise in the groundwater salinity has been observed as a consequence of increasing abstraction from the aquifer during the last few decades. All sources of contamination were investigated using hydrochemical data available from the 1990s. Water samples were taken from wells tapping both the CT and the shallow aquifers and analyzed with regard to chemistry tracers. Hydrochemical and water quality data obtained through a sampling period (December 2010) and analysis program indicate that nitrate pollution can be a serious problem affecting groundwater due to the use of nitrogen (N) fertilizers–pesticides in agriculture. The concentration of nitrate in an groundwater-irrigated area in Gafsa oases basin was studied, where abstraction from an unconfined CT aquifer has increased threefold over 25 years to 34 million m³/year; groundwater levels are falling at up to 0.7 m/year; and groundwater is increasingly mineralised (TDS increase from 500 to 4,000 mg/L), with nitrate concentrations ranging from 16 to 320 mg/L.     

Pollutant transport in a shallow unconfined aquifer in Perry,Ohio

The groundwater system in northern Perry Township in Lake County, Ohio, is a shallow, unconfined aquifer consisting of periglacial lake beach deposits and less permeable lacustrine plain deposits. Groundwater flow is generally toward Lake Erie from south to north and is controlled by the top of the Ashtabula Till, but strong, local variations are caused by northward flowing streams During the study period, water levels in most wells exhibited a seasonal fluctuation of less than 0 3 m from their mean values. The areal distributions of chloride and nitrate concentrations indicate that road salt runoff easily infiltrates the aquifer and that nitrate may be sourced from fertilizer application. Ground-water flow and solute transport models indicate that in excess of 27 years are required to obtain chemical steady-state under hydrologic steady-state conditions. The simulations also demonstrate that nitrate loading must occur in more than one cultivated field in order to obtain the observed wide-spread nitrate distribution.     

Assessment of Groundwater Vulnerability in Upper Betwa River Watershed using GIS based DRASTIC Model

Groundwater, the most vital water resource being used for irrigation, domestic and industrial purposes is nowadays under severe threat of contamination. Groundwater contamination risk assessment is an effective tool for groundwater management. In the study, a DRASTIC model which is based on the seven hydrogeological parameters viz: depth of water, net-recharge, aquifer media, soil media, topography, impact of vadose zone and hydraulic conductivity was used to evaluate the groundwater pollution potentiality of upper Betwa watershed. ArcGIS was used to create the ground water vulnerability map by overlaying the seven layers. Based on groundwater vulnerability map, the watershed has been divided in three vulnerable zones viz; low vulnerability zone with 42.83 km² of area, moderate with 369.21 km² area and high having 270.96 km² of area. Furthermore, the DRASTIC model has been validated by nitrate concentration over the area. Results of validation have shown that in low vulnerable zone, no nitrate contamination has been recorded. While in the moderate zone nitrate has been found in the range of 1.6-10ppm. However, in high vulnerable zone 11-40ppm of nitrate concentration in groundwater has been recorded, which proves that the DRASTIC model is applicable for the prediction of groundwater vulnerability in the watershed and in similar areas too.     

An assessment of the risk associated with urban development in the Thiaroye area (Senegal)

Water quality data from 56 wells, aquifer characteristics, soil types and land use in the city suburb of Dakar were compared to assess the effects of land use on the Thiaroye groundwater quality. The study area encompassed an unsewered densely populated zone, agricultural land, low density villages, and undeveloped land located in the sand dunes. A method similar to GIS technologies was applied to evaluate the degree of vulnerability of the different parts of the aquifer in relation to urban development, land use and aquifer characteristics. The aquifer parameters (hydraulic conductivity, groundwater level depth, recharge, soil type) were re-evaluated qualitatively into three class rankings (high, moderate and low), depending on the likelihood for contaminants reaching the water table, then combined using the two matrix Boolean logic based approaches to identify the nine classes of vulnerability assessed in the aquifer domain. An attempt was made to explain the distribution of nitrate concentration with the assessed vulnerability. In the area assessed, in the densely populated zone running from Pikine, to Thiaroye and Yeumbeul, very high nitrate concentrations correspond with the highest vulnerability index (H1). Nitrate contamination in this area is a consequence of point-source seepage from individual septic systems improperly built in this area. In the eastern part of the aquifer, high nitrate concentrations at Deni B. Ndao, Mbawane and Golam localities coincide with a moderate vulnerability assessment. The major source of nitrate in these areas is induced by agricultural activities.     

Correlation between nitrate concentration in groundwater and parameters affecting aquifer intrinsic vulnerability

This paper is the result of a study which was carried out in order to verify if the traditional methods to evaluate the intrinsic vulnerability or vulnerability related parameters, are able to clarify the problem of nitrate pollution in groundwater. In particular, the aim was to evaluate limitations and problems connected to aquifer vulnerability methods applied to nitrate contamination prevision in groundwater. The investigation was carried out by comparing NO₃ ⁻ concentrations, measured in March and November 2004 in the shallow aquifer, and the vulnerability classes, obtained by using GOD and TOT methods. Moreover, it deals with a comparison between NO₃ ⁻ concentrations and single parameters (depth to water table, land use and nitrogen input). The study area is the plain sector of Piemonte (Northern Italy), where an unconfined aquifer nitrate contamination exists. In this area the anthropogenic presence is remarkable and the input of N-fertilizers and zootechnical effluents to the soil cause a growing amount of nitrates in groundwater. This approach, used in a large area (about 10,000 km²) and in several monitoring wells (about 500), allowed to compare the efficiency of different vulnerability methods and to verify the importance of every parameter on the nitrate concentrations in the aquifer. Furthermore it allowed to obtain interesting correlations in different hydrogeological situations. Correlations between depth to water table, land use and nitrogen input to the soil with nitrate concentrations in groundwater show unclear situations: in fact these comparisons describe the phenomenon trend and highlight the maximum nitrate concentrations for each circumstance but often show wide ranges of possible nitrate concentrations. The same situation could be observed by comparing vulnerability indexes and nitrate concentrations in groundwater. These results suggest that neither single parameters nor vulnerability methods (GOD and TOT) are able to describe individually the complex phenomena affecting nitrate concentrations in soil, subsoil and groundwater. In particular, the traditional methods for vulnerability analysis do not analyze physical processes in aquifers, such as denitrification and nitrate dilution. According to a recent study in the shallow unconfined aquifer of the Piemonte plain, dilution can be considered as the main cause for nitrate attenuation in groundwater.     

Degradation of groundwater quality in coastal aquifer of Sabratah area,NW Libya

Overextraction of groundwater is widely occurring along the coast where good quality groundwater is at risk, due to urbanization, tourist development and intensive agriculture. The Sabratah area at the northern central part of Jifarah Plain, Northwest Libya, is a typical area where the contamination of the aquifer in the form of saltwater intrusion, gypsum/anhydrite dissolution and high nitrate concentrations is very developed. Fifty groundwater samples were collected from the study area and analysed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters electrical conductivity, sodium, potassium, magnesium, chloride and sulphate which can be attributed to seawater intrusion. The intensive extraction of groundwater from the aquifer reduces freshwater outflow to the sea, creates drawdown cones and lowering of the water table to as much as 30 m below mean sea level. Irrigation with nitrogen fertilizers and domestic sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for the high nitrate concentration towards the south of the region. Seawater intrusion and deep salt water upconing result in general high SO₄ ^2? concentrations in groundwater near the shoreline, where localized SO₄ ^2? anomalies are also due to the dissolution of sebkha deposits for few wells in the nearby sebkhas. Upstream, the increase in SO₄ ^2? concentrations in the south is ascribed to the dissolution of gypsum at depth in the upper aquifer.     

Hydrogeochemistry of the Saloum (Senegal) superficial coastal aquifer

Seawater has entered and concentrated in the Saloum hydrologic system up to 100 km upstream, contaminating both the surface water and the superficial 'Continental terminal' (CT) groundwater resources, and large proportions of cultivated lands. In the areas affected by saltwater contamination, chloride concentrations as high as 3,195 mg/l have been measured in the groundwater samples collected from wells located in the vicinity of the Saloum River, making the water inadequate for drinking water purposes. This paper presents the results of a study designed to characterise the current extent of the saline groundwater and the mechanism of saline surface water body/fresh groundwater mixing in relation to the groundwater flow trends. It also describes the groundwater chemical and isotopic composition and geochemical processes controlling the chemical patterns. Four major water types occur in the study area, namely Na-rich saline groundwater, Ca-Na-rich saline groundwater, Na-dominant fresh groundwater and Ca-dominant fresh groundwater. A hydrogeochemical zonation of the aquifer, based on the presence of different water families and on the groundwater flow, led to the identification of the main processes controlling the groundwater chemistry. Cation exchange reactions on the kaolinite clay mineral, calcite dissolution in the eastern zone where calcite minerals have been identified, reverse cation exchange reactions in the saline-contaminated band along the Saloum River and, to a lesser extent, a gypsum dissolution are the predominant processes. Results of i¹⁸O and iD analysis in 15 groundwater samples compared with the local meteoric line indicate that the groundwater has been affected by evaporation, and the groundwater is isotopically lighter as the depth of water table increases. In this study, i¹⁸O data were used in conjunction with chloride data to identify the source of high chloride. Results show a departure of the contaminated water samples from the seawater mixing line, which indicates that other processes rather than mixing between modern seawater and native groundwater alone increase the chloride concentrations.     

Assessing groundwater availability and the response of the groundwater system to intensive exploitation in the North China Plain by analysis of long-term isotopic tracer data

The use of isotope tracers as a tool for assessing aquifer responses to intensive exploitation is demonstrated and used to attain a better understanding of the sustainability of intensively exploited aquifers in the North China Plain. Eleven well sites were selected that have long-term (years 1985–2014) analysis data of isotopic tracers. The stable isotopes δ¹⁸O and δ²H and hydrochemistry were used to understand the hydrodynamic responses of the aquifer system, including unconfined and confined aquifers, to groundwater abstraction. The time series data of ¹⁴C activity were also used to assess groundwater age, thereby contributing to an understanding of groundwater sustainability and aquifer depletion. Enrichment of the heavy oxygen isotope (¹⁸O) and elevated concentrations of chloride, sulfate, and nitrate were found in groundwater abstracted from the unconfined aquifer, which suggests that intensive exploitation might induce the potential for aquifer contamination. The time series data of ¹⁴C activity showed an increase of groundwater age with exploitation of the confined parts of the aquifer system, which indicates that a larger fraction of old water has been exploited over time, and that the groundwater from the deep aquifer has been mined. The current water demand exceeds the sustainable production capabilities of the aquifer system in the North China Plain. Some measures must be taken to ensure major cuts in groundwater withdrawals from the aquifers after a long period of depletion.     

Assessing the vulnerability of over-exploited volcanic aquifer systems using multi-parameter analysis,Toluca Basin,Mexico

The potential for contamination of groundwater in an over-exploited system led to this investigation on aspects of aquifer vulnerability in the Toluca Basin, Mexico. This study involved the use of various hydrogeological, geochemical and isotopic tools to better understand the susceptibility to contamination where heavy groundwater extraction along with industrial extensive development is concentrated. Geochemical and isotopic analyses of groundwater from production wells along the mountain boundary show little evidence of contamination at present time. Radiocarbon and tritium data collected in piezometers and wells penetrating the Lower basalt aquifer indicate that the groundwater is of varying age and quality. These data, in addition to stable isotope and chemical data also indicate evidence of contamination in the Lower aquifer; which could be associated with fast recharge in the mountains or injection of waste water by illegal wells. Evidence found in this study of low downward gradients in the valley fill sediments and the presence of low permeability aquitard deposits suggest that the aquifer system is currently not highly threatened by surface sources of contamination. However, where urban and industrial development occurs, in the centre of the valley and along the flanks of the Basin, the vulnerability of the aquifer system increases significantly.     

Denitrification coupled to pyrite oxidation and changes in groundwater quality in a shallow sandy aquifer

This study focuses on denitrification in a sandy aquifer using geochemical analyses of both sediment and groundwater, combined with groundwater age dating (³H/³He). The study sites are located underneath cultivated fields and an adjacent forested area at Oostrum, The Netherlands. Shallow groundwater in the region has high nitrate concentrations (up to 8 mM) due to intense fertilizer application. Nitrate removal from the groundwater below cultivated fields correlates with sulfate production, and the release of dissolved Fe²⁺ and pyrite-associated trace metals (e.g. As, Ni, Co and Zn). These results, and the presence of pyrite in the sediment matrix within the nitrate removal zone, indicate that denitrification coupled to pyrite oxidation is a major process in the aquifer. Significant nitrate loss coupled to sulfate production is further confirmed by comparing historical estimates of regional sulfate and nitrate loadings to age-dated groundwater sulfate and nitrate concentrations, for the period 1950-2000. However, the observed increases in sulfate concentration are about 50% lower than would be expected from complete oxidation of pyrite to sulfate, possibly due to the accumulation of intermediate oxidation state sulfur compounds, such as elemental sulfur. Pollutant concentrations (NO₃, Cl, As, Co and Ni) measured in the groundwater beneath the agricultural areas in 1996 and 2006 show systematic decreases most likely due to declining fertilizer use.     

Assessment of groundwater vulnerability using a specific vulnerability method: Case of Maritime Djeffara shallow aquifer (Southeastern Tunisia)

Groundwater resources are vulnerable to contamination especially in shallow aquifers. The aquifer hydrogeological parameters and the Land Uses category combinations lead to subdivide areas according to their contamination likelihood. In arid and semi-arid regions, shallow aquifers are more exposed to groundwater contamination due to high population densities (extensive uses) and agricultural activities (nitrate contamination). Moreover, these regions are characterized by low rainfall and high evaporation. Furthermore, the spread of farmland, industrial and domestic sectors, is the principal contaminant producer which threats the groundwater quality. To protect these limited resources, the groundwater vulnerability assessment was developed in Maritime Djeffara shallow aquifer (Southeastern Tunisia). The study area is essentially occupied by agricultural areas (intensive use of chemical fertilizers) in addition to the discharge of industrial zones. The main objective of this study is to assess the aquifer vulnerability using the Susceptibility Index (SI) method as a specific vulnerability model. The results show that the study area is classified into five classes of vulnerability: very low, low, medium, high, and very high (1.54, 20, 41.54, 35.9, and 1.02%, respectively) with an uneven spatial distribution. The risk results exhibit three degrees: low, moderate, and high. The validation of the vulnerability model was performed by using salinity values and nitrate concentrations with a correlation coefficient of about 57 and 55%, respectively. This study could serve as a scientific basis for sustainable land use planning and groundwater management in the study area.     

Hydrogeochemical characterization of major factors affecting the quality of groundwater in southern Iran,Janah Plain

The Janah alluvial aquifer is located in southern Iran with an arid climate. The type of groundwater in this aquifer is dominantly of sodium chloride and total dissolved solid of groundwater samples range from 1.63 to 335 g/L which confirms that groundwater quality has been severely degraded by salinization. Hydrogeochemical and isotopic investigations were conducted to identify the source of salinity. Total dissolved solids and major ion concentrations were measured at 51 selected sampling sites including springs, wells and surface waters. In addition stable isotopic composition (oxygen-18 and deuterium) was measured in 6 sampling points.The study indicates that the sources of salinity of the Janah aquifer include dissolution of salt diapir and evaporite rocks, a geothermal spring and intrusion of the river water which function individually or together in different parts of the aquifer. Based on the hydrogeochemical and geological studies conceptual flow models were prepared for different parts of the aquifer which illustrate how each source of salinity deteriorates the quality of the alluvial aquifer. We proposed few remediation methods including construction of cemented channel and sealed basins to improve groundwater quality. These methods would prevent infiltration of low quality water into the alluvial aquifer.     

Temporal variations in the depth-specific hydrochemistry and sewage-related microbiology of an urban sandstone aquifer,Nottingham, United Kingdom

The temporal and spatial characteristics of groundwater recharge in urban environments remain poorly understood. Depth-specific monitoring of groundwater quality in the Triassic Sandstone underlying the city of Nottingham, UK, indicates that contamination results primarily from sewage and atmospheric sources. The temporal and depth-specific characteristics of microbial and inorganic (e.g. nitrate, chloride, sulphate) contamination over the investigation period differ significantly and reflect the contrasting transport characteristics of surface-loaded solutes and particulate microbial species (bacteria and viruses) in the Triassic Sandstone. Differences result from a variety of factors, which include microbial die-off, dilution, and the contaminant-source characteristics. Observations in this study show that low levels of microbial contamination should be expected at depth in fissured sandstone due to aquifer heterogeneities such as fissuring and the occurrence of mudstone bands, though the magnitude of this contamination will vary over time. Furthermore, urban groundwater-protection measures based on solute-transport estimates may not be applicable to microbial contamination. Electronic Publication     

A graphic expression of salinization and pollution of groundwater The case of Israel's groundwater

 Anthropogenic activities create various contaminated leachate, which can migrate downward from the vadose zone to groundwater, transferring contaminants, including some hazardous ones. When these various sources of contamination influence the groundwater aquifer simultaneously, the effects of contamination are enhanced. The major concern of this study has been to determine whether the shape of a groundwater chlorograph might be the result of such deterministic effects as accumulation of one or more particular processes of groundwater contamination, and how this might relate to specific hydrological situations. This study proposes a classification of groundwater contamination on the basis of properties of the main components of groundwater quality graphs and the corresponding hydrogeological/environmental situation. The study further suggests that contamination of groundwater in any hydrogeological situation (e.g. sea water) may be graphically expressed. A variety of chlorographs and nitrographs, representative of various groundwater aquifers sampled from a number of wells throughout Israel attest to this. The study thus indicates that groundwater quality graphs may be considered as a complementary tool for groundwater quality control and better understanding aquifer situations.