Trace element hydrochemical assessment of the Calabar Coastal Plain Aquifer,southeastern Nigeria using statistical methods

Groundwater samples from 33 locations within the Coastal Plain Sands aquifer of Calabar (Nigeria) were collected and analysed for 43 trace elements by means of ICP-MS. The aim of this study is to determine the natural background levels of trace elements as a guide for future pollution monitoring of the aquifer. Secondly, this article focuses on the pollution vulnerability of the coastal plain sand aquifer. Statistical methods have been used to determine the source(s) of these elements. Results show that the area is characterised by four types of groundwater, including: Na-HCO₃, Na-HCO₃-Cl, Na-Cl and Ca-Na-HCO₃-Cl. Secondly, all the elements considered are below normal averages. In addition, the Spearman correlation shows significant correlation especially among the lanthanide group of elements (p<0.0001). Factors analyses indicate mainly two groups of elements. The first group being due to the natural geochemical process (weathering/leaching of the basement lithology; characteristics of the elements) and the second is due to tidal flushing of the estuary. This indicates that the source of the trace element in the aquifer is due to a geogenic process and not anthropogenic. Thus, the present data set will serve as a reference source for pollution monitoring in the area.     

Groundwater vulnerability assessment in shallow aquifer of Kathmandu Valley using GIS-based DRASTIC model

In this paper, groundwater aquifer vulnerability map has been developed by incorporating the major geological and hydro-geological factors that affect and control the groundwater contamination using GIS based DRASTIC model. This work demonstrates the potential of GIS to derive a map by overlying various spatially referenced digital data layers that portrays cumulative aquifer sensitivity ratings across the Kathmandu Valley, Nepal, providing a relative indication of groundwater vulnerability to contamination. In fact, the groundwater is the major natural resources in Kathmandu for drinking purpose. The decline in groundwater levels due to the over exploitation and thus extracted water from shallow aquifer has been contaminated by the infiltration of pollutants from polluted river and land surface is continuous and serious. As the demand for water for human and industrial use has escalated and at the same time, the engineering and environmental costs are much higher for new water supplies than maintaining the existing sources already in use. Management of groundwater source and protecting its quality is therefore essential to increase efficient use of existing water supplies. Aquifer vulnerability maps developed in this study are valuable tools for environmental planning and predictive groundwater management. Further, a sensitivity analysis has been performed to evaluate the influence of single parameters on aquifer vulnerability assessment such that some subjectivity can be reduced to some extent and then new weights have been computed for each DRASTIC parameters.     

Groundwater vulnerability and risk mapping of the Angad transboundary aquifer using DRASTIC index method in GIS environment

The protection and preservation of groundwater resources are compulsory, particularly in the arid and semiarid countries where the waters are scarce. The effects of increasing urbanization, economic development, and agricultural activities, along with the erratic and scarce rainfall, contribute to the quantitative and qualitative deterioration of these resources. This paper attempts to produce groundwater vulnerability and risk maps for the Angad transboundary aquifer using DRASTIC model. The data which correspond to the seven parameters of the model were collected and converted to thematic maps in Geographic Information System environment. The modified DRASTIC map, which is the summation of the DRASTIC index and the network fractures maps, shows two degreed of vulnerability: medium and high. This map is then integrated with a land use map to assess the potential risk of groundwater to pollution in the Angad transboundary aquifer. There are three risk zones that are identified: moderate, high, and very high.     

Groundwater vulnerability assessment in the Melaka State of Malaysia using DRASTIC and GIS techniques

The present work attempts to interpret the groundwater vulnerability of the Melaka State in peninsular Malaysia. The state of groundwater pollution in Melaka is a critical issue particularly in respect of the increasing population, and tourism industry as well as the agricultural, industrial and commercial development. Focusing on this issue, the study illustrates the groundwater vulnerability map for the Melaka State using the DRASTIC model together with remote sensing and geographic information system (GIS). The data which correspond to the seven parameters of the model were collected and converted into thematic maps by GIS. Seven thematic maps defining the depth to water level, net recharge, aquifer media, soil media, topography, impact of vadose zone and hydraulic conductivity were generated to develop the DRASTIC map. In addition, this map was integrated with a land use map for generating the risk map to assess the effect of land use activities on the groundwater vulnerability. Three types of vulnerability zones were assigned for both DRASTIC map and risk map, namely, high, moderate and low. The DRASTIC map illustrates that an area of 11.02 % is low vulnerability, 61.53 % moderate vulnerability and 23.45 % high vulnerability, whereas the risk map indicates that 14.40 % of the area is low vulnerability, 47.34 % moderate vulnerability and 38.26 % high vulnerability in the study area. The most vulnerability area exists around Melaka, Jasin and Alor Gajah cities of the Melaka State.     

基于DRASTIC的含水层脆弱性模糊评价方法与应用

通过分析目前广泛采用的DRASTIC方法存在的主要问题,将含水层脆弱性定义为模糊概念,结合模糊分析评价理论及三标度分两步的层次分析法建立了一套改进的含水层脆弱性评价模型。为测试其可靠性,分别将改进模型和传统DRASTIC模型应用于祁县东观镇含水层脆弱性评价中。研究结果表明:改进模型得到的脆弱性等级变化较后者更灵敏,分布范围及变化情况更精确,更能真实反映含水层脆弱性在空间上的连续变化,且计算简便、脆弱性分区图效果直观,丰富和完善了地下水脆弱性评价方法。     

Vulnerability evaluation of a coastal plain sand aquifer with a case example from Calabar,southeastern Nigeria

A point count index method using a well drillers log and field measurements has been developed following the DRASTIC and SINTACS procedures to map and evaluate the vulnerability of a coastal plain aquifer to surface and near surface contamination. The input parameters with the acronym CALOD include clay layer thickness (C), aquifer media character (A), lateritic layer thickness (L), overlying layer character (O) and the depth to groundwater level (D). The CALOD vulnerability potential index (CALOD index) is computed as the sum of the products of weights and ratings assigned to each of the input parameters. The CALOD index, varying between 15 and 75, is divided into four classes: high (>60), high-medium, (40–60), low-medium (20–40) and low (<20). The CALOD index is then used to produce a vulnerability potential map for the area. From the map, areas of high, high-medium and medium-low are consistent with the upper gravelly aquiferous zone while areas of medium-low and low are restricted to the deeper lower sandy aquiferous layer. The most important parameters affecting groundwater vulnerability to pollution in coastal areas include saturated thickness of the aquifer, depth to groundwater level, lateritic layer thickness and the aquifer media character. The concentration of some chemical pollution indicators (electrical conductivity, K, NO₃, Cl and metal load) are relatively higher for the highly vulnerable shallower upper gravelly unit in comparison to the less vulnerable deeper sandy unit. This method is very suitable for coastal plain sand aquifers especially, where data is scare.     

Evaluation of groundwater vulnerability to pollution using DRASTIC framework and GIS

Groundwater management has a prominent role in the world especially in arid and semi-arid areas which have a shortage of water, and due to this serious problem, many researchers work on that for prevention and managing the water recourses to conserve and monitor sources. DRASTIC index can be put forward for estimating of groundwater vulnerability to such pollution. The main purpose of using the groundwater vulnerability model is to map groundwater susceptibility to pollution in different areas. However, this method has been used in various areas without modification, disregarding the effects of pollution type and characteristics. Thus, this technique must be standardized and approved for Kerman plain. Vulnerability evaluation to explain areas that are more vulnerable to contamination from anthropogenic sources has become a prominent element for land use planning and tangible resource management. This contribution aims at evaluating groundwater vulnerability by applying the DRASTIC index as well as employ sensitivity analyses to evaluate the comparative prominent of the model parameters for groundwater vulnerability in Kerman plain in the southeastern part of Iran. Moreover, the potential of vulnerability to pollution is more accurately assessed by optimizing the weights of the DRASTIC parameters with the single-parameter sensitivity analysis (SPSA). The new weights were calculated. The result of the study revealed that the DRASTIC-Sensitivity analysis exhibit more efficiently than the traditional method for a nonpoint source pollution. Observation of ultimate nitrate showed the result of DRASTIC-SPSA has more accuracy. The GIS method offers an efficient environment for carrying out assessments and greater capabilities for dealing with a huge quantity of spatial data.     

Groundwater occurrence and aquifer vulnerability assessment of Magodo Area,Lagos, Southwestern Nigeria

A combination of vertical electrical soundings (VES), 2D electrical resistivity imaging (ERI) surveys and borehole logs were conducted at Magodo, Government Reserve Area (GRA) Phase 1, Isheri, Southwestern Nigeria, with the aim of delineating the different aquifers present and assessing the groundwater safety in the area. The Schlumberger electrode array was adopted for the VES and dipole-dipole array was used for the 2D imaging. The maximum current electrode spread (AB) was 800 m and the 2D traverse range between 280 and 350 m in the east-west direction. The thickness of impermeable layer overlying the confined aquifer was used for the vulnerability ratings of the study area. Five lithological units were delineated: the topsoil, clayey sand, unconsolidated sand which is the first aquifer, a clay stratum and the sand layer that constitutes the confined aquifer horizon. The topsoil thickness varies from 0.6 to 2.6 m, while its resistivity values vary between 55.4 and 510.6 Ω/m. The clayey sand layers have resistivity values ranging from 104.2 to 143.9 Ω/m with thickness varying between 0.6 and 14.7 m. The resistivity values of the upper sandy layer range from 120.7 to 2195.2 Ω/m and thickness varies from 3.3 to 94.0 m. The resistivity of the clay layer varies from 11.3 to 96.1 Ω/m and the thickness ranges from 29.6 to 76.1 m. The resistivity value of the confined aquifer ranges between 223 and 1197.4 Ω/m. The longitudinal conductance (0.0017–0.02 mhos) assessment of the topsoil shows that the topsoil within the study area has poor overburden protective capacity, and the compacted impermeable clay layer shows that the underlying confined aquifer is well protected from contamination and can be utilized as a source of portable groundwater in the study area. This study therefore enabled the delineation of shallow aquifers, the variation of their thicknesses and presented a basis for safety assessment of groundwater potential zones in the study area.     

An integrated approach for aquifer vulnerability mapping using GIS and rough sets: study from an alluvial aquifer in North India

A modified DRASTIC model in a geographic information system (GIS) environment coupled with an information-analytic technique called ‘rough sets’ is used to understand the aquifer vulnerability characteristics of a segment of the lower Kali watershed in western Uttar Pradesh, India. Since the region is a flat plain, topography (T) is removed as a potential control. Other parameters are the same as in DRASTIC, hence the new model is termed as DRASIC. The rough set technique is employed to provide insight into the relative vulnerabilities of different administrative units (blocks) within the study area. Using rough sets, three important factors are computed: strength, certainty and coverage. Strength indicates how the vulnerability characteristics vary in the entire area, certainty gives the relative fractions of low, medium and high vulnerability regions within a particular block, and coverage computes the percentage of a particular vulnerability state in each block. The purpose of the work is to demonstrate the utility of this integrated approach in classifying different administrative blocks in the study area according to their aquifer vulnerability characteristics. This approach is particularly useful for block-level planning and decision making for sustainable management of groundwater resources.     

Using Generic and Pesticide DRASTIC GIS-based models for vulnerability assessment of the Quaternary aquifer at Sohag, Egypt

Groundwater resources in the Sohag area, Egypt are currently threatened by contamination from municipal and industrial activities, and agricultural pesticides. To cope with the growing population, there has been development in the desert zone on both sides of the Nile Valley including agricultural investment areas, wastewater disposal sites, new urban areas, and industry. Use of agrochemicals in the old cultivated and newly reclaimed lands and wastewater disposal sites in the study area represent the most hazardous contamination sources. Prevention of contamination and management of the Quaternary aquifer is urgently needed. To address vulnerability assessment of the Quaternary aquifer, the Generic and Pesticide DRASTIC GIS-based models have been used. The Generic DRASTIC index ranged between 94 and 189, and the Pesticide DRASTIC index ranged between 94 and 226. The results showed that 83% of the Quaternary aquifer is characterized by the high and very high vulnerability classes to municipal, industrial and agricultural pesticides contamination. It was found that nearly all the development projects are located in the very high vulnerability class areas. Management alternatives for the Quaternary aquifer may be improved by application of these models, allowing sensitive groundwater sources to be protected for continuing use in the future.     

Aquifer vulnerability assessment using the DRASTIC model at Russeifa landfill,northeast Jordan

Groundwater is inherently susceptible to contamination from anthropogenic activities and remediation is very difficult and expensive. Prevention of contamination is hence critical in effective groundwater management. In this paper an attempt has been made to assess aquifer vulnerability at the Russeifa solid waste landfill. This disposal site is placed at the most important aquifer in Jordan, which is known as Amman-Wadi Sir (B2/A7). The daily-generated leachate within the landfill is about 160 m³/day and there is no system for collecting and treating this leachate. Therefore, the leachate infiltrates to groundwater and degrades the quality of the groundwater. The area is strongly vulnerable to pollution due to the presence of intensive agricultural activity, the solid waste disposal site and industries. Increasing groundwater demand makes the protection of the aquifer from pollution crucial. Physical and hydrogeological characteristics make the aquifer susceptible to pollution. The vulnerability of groundwater to contamination in the study area was quantified using the DRASTIC model. The DRASTIC model uses the following seven parameters: depth to water, recharge, aquifer media, soil media, topography, impact on vadose zone and hydraulic conductivity. The water level data were measured in the observation wells within the disposal site. The recharge is derived based on precipitation, land use and soil characteristics. The aquifer media was obtained from a geological map of the area. The topography is obtained from the Natural Resources Authority of Jordan, 1:50,000 scale topographic map. The impact on the vadose zone is defined by the soil permeability and depth to water. The hydraulic conductivity was obtained from the field pumping tests. The calculated DRASTIC index number indicates a moderate pollution potential for the study area.     

地下水易污性评价方法——DRASTIC指标体系

本文较详细地介绍了目前欧美国家在地下水易污性评价中所广泛采用的ＤＲＡＳＴＩＣ指标体系方法,对其中所含的地下水埋深,含水层的净补给,岩性,土壤类型,渗流区介质,水力传导系数７个参数的评分以及在评分过程中所应注意的问题进行了具体的阐述,最后简要介绍了ＤＲＡＳＴＩＣ易污性指标体系法在大连沿海地区地下水易污性评价中应用的情况,实际应用表明该方法可适用于我国广大地区的地下水易污性评价工作。     

Assessment of aquifer vulnerability based on GIS and DRASTIC methods: a case study of the Senirkent-Uluborlu Basin (Isparta, Turkey)

Aquifer vulnerability has been assessed in the Senirkent-Uluborlu Basin within the Egirdir Lake catchment (Turkey) using the DRASTIC method, based on a geographic information system (GIS). There is widespread agriculture in the basin, and fertilizer (nitrate) and pesticide applications have caused groundwater contamination as a result of leaching. According to hydrogeological data from the study area, surface water and groundwater flow are towards Egirdir Lake. Hence, aquifer vulnerability in the basin should be determined by water quality in Egirdir Lake. DRASTIC layers were prepared using data such as rainfall, groundwater level, aquifer type, and hydraulic conductivity. These data were obtained from hydrogeological investigations and literature. A regional-scale aquifer-vulnerability map of the basin was prepared using overlay analysis with the aid of GIS. A DRASTIC vulnerability map, verified by nitrate in groundwater data, shows that the defined areas are compatible with land-use data. It is concluded that 20.8% of the basin area is highly vulnerable and urgent pollution-preventions measures should be taken for every kind of relevant activity within the whole basin.     

Optimization of the DRASTIC method for groundwater vulnerability assessment via the use of simple statistical methods and GIS

The assessment of groundwater vulnerability to pollution has proved to be an effective tool for the delineation of protection zones in areas affected by groundwater contamination due to intensive fertilizer applications. By modifying and optimizing the well known and widely used DRASTIC model it was possible to predict the intrinsic vulnerability to pollution as well as the groundwater pollution risk more accurately. This method incorporated the use of simple statistical and geostatistical techniques for the revision of the factor ratings and weightings of all the DRASTIC parameters under a GIS environment. The criterion for these modifications was the correlation coefficient of each parameter with the nitrates concentration in groundwater. On the basis of their statistical significance, some parameters were subtracted from the DRASTIC equation, while land use was considered as an additional DRASTIC parameter. Following the above-mentioned modifications, the correlation coefficient between groundwater pollution risk and nitrates concentration was considerably improved and rose to 33% higher than the original method. The model was applied to a part of Trifilia province, Greece, which is considered to be a typical Mediterranean region with readily available hydrogeological and hydrochemical data.

---

Resumen La evaluación de vulnerabilidad del agua subterránea a la contaminación ha demostrado ser una herramienta efectiva para la delimitación de zonas de protección en áreas afectadas por contaminación de aguas subterráneas debido a aplicaciones intensivas de fertilizantes. Mediante la modificación y optimización del bien conocido y ampliamente utilizado modelo DRASTIC fue posible predecir la vulnerabilidad intrínseca a la contaminación así como el riesgo a la contaminación del agua subterránea con mayor precisión. Este método incorporó el uso de técnicas estadísticas y geoestadísticas simples para la revisión del pesaje y establecimiento de rangos de factores de todos los parámetros DRASTIC bajo un ambiente SIG. El criterio para estas modificaciones fue el coeficiente de correlación de cada parámetro con las concentraciones de nitraros en agua subterránea. En base al grado significativo estadístico algunos parámetros fueros sustraídos de la ecuación DRASTIC, mientras que se consideró el uso de la tierra como un parámetro adicional de DRASTIC. Siguiendo las modificaciones antes mencionadas se mejoró considerablemente el coeficiente de correlación entre el riesgo a la contaminación del agua subterránea y las concentraciones de nitratos incrementando en 33% su valor en relación al método original. El modelo se aplicó en una parte de la provincia Trifilia, Grecia, la cual se considera ser una región Mediterránea típica con datos hidroquímicos e hidrogeológicos fácilmente disponibles.

---

Résumé L’évaluation de la vulnérabilité des eaux souterraines à la pollution a montré qu’elle est un outil efficace pour délimiter les zones de protection dans les zones affectées par la contamination des eaux souterraines due à l’utilisation intensive de fertilisants. En modifiant et optimisant le modèle DRASTIC, bien connu et souvent utilisé, il a été possible de prédire la vulnérabilité intrinsèque à la pollution, et de définir plus précisément le risque de pollution. Cette méthode incorpore l’utilisation de simples techniques statistiques et géostatistiques, pour la révision des facteurs d’estimation et de pondération de tous les paramètres de DRASTIC sous S.I.G. Le critère de ces modifications était le coefficient de corrélation de chaque paramètre avec la concentration en nitrates dans les eaux souterraines. Sur la base de leur signification statistique, certains paramètres ont été soustraits de l’équation DRASTIC. Suivant les modifications mentionnées ci-dessus, le coefficient de corrélation entre les concentrations en nitrate et le risque de pollution des eaux souterraines a été considérablement amélioré de 33% par rapport à la méthode originale. Le modèle a été appliqué sur une partie de la province de Trifilia en Grèce, qui est considérée comme une région typiquement méditerranéenne avec des données hydrogéologiques et hydrochimiques aisément accessibles.

     

Groundwater vulnerability and risk mapping of the Hajeb-jelma aquifer (Central Tunisia) using a GIS-based DRASTIC model

The aim of this study is to elaborate a synthetic document for the assessment of groundwater vulnerability to pollution in the Hajeb-Jelma aquifer. The specific object is to incorporate the Geographical Information System (GIS) to generate groundwater vulnerability and risk maps with DRASTIC model. Indeed, GIS could help to make the results of a complicated model more clear through visual representation, providing an applicable tool for decision makers. The vulnerability map of Hajeb-Jelma watershed shows three classes: moderate, high and very high depending on the intrinsic properties. The risk map shows a very high risk dependant on hydrogeological characteristics, land use and human impacts in major part of the Hajeb-Jelma region. These maps could serve as a scientific basis for sustainable land use planning and groundwater management in the Hajeb-Jelma region.     

Determining shallow aquifer vulnerability by the DRASTIC model and hydrochemistry in granitic terrain,southern India

Shallow aquifer vulnerability has been assessed using GIS-based DRASTIC model by incorporating the major geological and hydrogeological factors that affect and control the groundwater contamination in a granitic terrain. It provides a relative indication of aquifer vulnerability to the contamination. Further, it has been cross-verified with hydrochemical signatures such as total dissolved solids (TDS), \(\hbox {Cl}^{-},\, \hbox {HCO}_{3}^{-},\, \hbox {SO}_{4}^{2-}\) and \(\hbox {Cl}^{-}/\hbox {HCO}_{3}^{-}\) molar ratios. The results show four zones of aquifer vulnerability (i.e., negligible, low, moderate and high) based on the variation of DRASTIC Vulnerability Index (DVI) between 39 and 132. About 57% area in the central part is found moderately and highly contaminated due to the 80 functional tannery disposals and is more prone to groundwater aquifer vulnerability. The high range values of TDS (2304–39,100 mg/l); \(\hbox {Na}^{+}\)(239– 6,046 mg/l) and \(\hbox {Cl}^{-}\) (532–13,652 mg/l) are well correlated with the observed high vulnerable zones. The values of \(\hbox {Cl}^{-}/\hbox {HCO}_{3}^{-}\) (molar ratios: 1.4–106.8) in the high vulnerable zone obviously indicate deterioration of the aquifer due to contamination. Further cumulative probability distributions of these parameters indicate several threshold values which are able to demarcate the diverse vulnerability zones in granitic terrain.     

Comparison of DRASTIC and DC resistivity modeling for assessing aquifer vulnerability in the central Nile Delta,Egypt

DRASTIC indexing and integrated electrical conductivity (IEC) modeling are approaches for assessing aquifer vulnerability to surface pollution. DRASTIC indexing is more common, but IEC modeling is faster and more cost-effective because it requires less data and fewer processing steps. This study aimed to compare DRASTIC indexing with IEC modeling to determine whether the latter is sufficient on its own. Both approaches are utilized to determine zones vulnerable to groundwater pollution in the Nile Delta. Hence, assessing the nature and degree of risk are important for realizing effective measures toward damage minimization. For DRASTIC indexing, hydrogeological factors such as depth to aquifer, recharge rate, aquifer media, soil permeability, topography, impact of the vadose zone, and hydraulic conductivity were combined in a geographical information system environment for assessing the aquifer vulnerability. For IEC modeling, DC resistivity data were collected from 36 surface sounding points to cover the entire area and used to estimate the IEC index. Additionally, the vulnerable zones identified by both approaches were tested using a local-scale resistivity survey in the form of 1D and 2D resistivity imaging to determine the permeable pathways in the vadose zone. A correlation of 0.82 was obtained between the DRASTIC indexing and IEC modeling results. For additional benefit, the obtained DRASTIC and IEC models were used together to develop a vulnerability map. This map showed a very high vulnerability zone, a high-vulnerability zone, and moderate- and low-vulnerability zones constituting 19.89, 41, 27, and 12%, respectively, of the study area. Identifying where groundwater is more vulnerable to pollution enables more effective protection and management of groundwater resources in vulnerable areas.