Threat of land subsidence in and around Kolkata City and East Kolkata Wetlands,West Bengal,India

This paper attempts to estimate the possible rate of land subsidence of Kolkata City including Salt Lake City and the adjoining East Kolkata Wetlands located at the lower part of the deltaic alluvial plain of South Bengal basin. Demand of groundwater for drinking, agricultural and industrial purposes has increased due to rapid urbanization. The subsurface geology consists of Quaternary sediments comprising a succession of clay, silty clay and sand of various grades. Groundwater occurs mostly under confined condition except in those places where the top aquitard has been obliterated due to the scouring action of past channels. Currently, the piezometric head shows a falling trend and it may be accelerated due to further over-withdrawal of groundwater resulting in land subsidence. The estimated mean land subsidence rate is 13.53 mm/year and for 1 m drop in the piezometric head, the mean subsidence is 3.28 cm. The surface expression of the estimated land subsidence is however, cryptic because of a time lag between the settlement of the thick low-permeable aquitard at the top and its surface expression. Therefore, groundwater of the cities and wetland areas should be developed cautiously based on the groundwater potential to minimize the threat of land subsidence.     

The hydro geochemical characterization of ground waters in Tunisian Chott’s region.

Tunisian Chott’s region is one of the most productive artesian basins in Tunisia. It is located in the southwestern part of the country, and its groundwater resources are developed for water supply and irrigation. The chemical composition of the water is strongly influenced by the interaction with the basinal sediments and by hydrologic characteristics such as the flow pattern and time of residence. The system is composed of an upper unconfined “Plio-Quaternary” aquifer with a varying thickness of 20–200 m, an intermediate confined/unconfined “Complex Terminal” aquifer about 100 m in thickness and a deeper “Continental Intercalaire” aquifer about 150 m in thickness separated by thick clay and marl layers. The dissolution of evaporites and carbonates explains part of the contained Na⁺, Ca²⁺, Mg²⁺, K⁺, SO₄²⁻ and Cl^-, but other processes, such carbonate precipitation, also contributes to the water composition. The stable isotope composition of waters establishes that the deep groundwater (depleted as compared to present corresponding local rainfall) is ancient water recharged probably during the late Pleistocene and the early Holocene periods. The relatively recent water in the Plio-Quaternary aquifer is composed of mixed waters resulting presumably from upward leakage from the deeper groundwater.     

Electrical imaging of the groundwater aquifer at Banting,Selangor, Malaysia

A geophysical study was carried out in the Banting area of Malaysia to delineate groundwater aquifer and marine clay layer of the alluvial Quaternary deposits of Beruas and Gula Formations. The Beruas Formation is formed by peat and clayey materials as well as silt and sands, whereas the Gula Formation consists of clay, silt, sand and gravels. Both Formations were deposited on top of the Carboniferous shale of the Kenny Hill Formation. A 2-D geoelectrical resistivity technique was used. Resistivity measurement was carried out using an ABEM SAS 4000 Terrameter. The 2-D resistivity data of subsurface material for each survey line was calculated through inverse modelling and then compared with borehole data. The resistivity images of all the subsurface material below the survey lines show similar pattern of continuous structure of layering or layers with some lenses with resistivity ranging from 0.1 to 50 Ωm. The upper layer shows resistivity values ranging from 0.1 to 10 Ωm, representing a clay horizon with a thickness up to 45 m. The second layer with depth varies from 45 to 70 m below surface and has resistivity values ranging from 10 to 30 Ωm. Borehole data indicate coarse sand with some gravels for this layer, which is also the groundwater aquifer in the study area. The lowermost layer at a depth of 70 m below ground level shows resistivity values ranging from 30–50 Ωm and can be correlated with metasedimentary rocks consisting of shale and metaquartzite.     

泰安市第四系水文地质结构对浅层地下水污染敏感性控制作用研究

通过对泰安市第四系水文地质结构研究发现, 浅层地下水的污染受地层结构的控制, 在包气带岩性及含水层岩性相同的条件下, 包气带的厚度越大, 其防污性能越高, 含水层遭受污染的程度越小; 在地面环境质量及包气带岩性和厚度相近的条件下, 粗砂含水层较粉质粘土含水层更易遭受污染      

Groundwater pollution risk mapping for the Eocene aquifer of the Oum Er-Rabia basin, Morocco

Sustainable development requires the management and preservation of water resources indispensable for all human activities. When groundwater constitutes the main water resource, vulnerability maps therefore are an important tool for identifying zones of high pollution risk and taking preventive measures in potential pollution sites. The vulnerability assessment for the Eocene aquifer in the Moroccan basin of Oum Er-Rabia is based on the DRASTIC method that uses seven parameters summarizing climatic, geological, and hydrogeological conditions controlling the seepage of pollutant substances to groundwater. Vulnerability maps were produced by using GIS techniques and applying the “generic” and “agricultural” models according to the DRASTIC charter. Resulting maps revealed that the aquifer is highly vulnerable in the western part of the basin and areas being under high contamination risk are more extensive when the “agricultural” model was applied.     

The impact of the geologic setting on the Quaternary aquifer,El-Tur area,Southwest Sinai,Egypt

The groundwater extracted from the unconfined Quaternary aquifer is the main source of water supply in El-Tur area. The area is bounded from the east by the elevated basement complex of Southern Sinai and from the west by El-Qabaliyat Ridge. The wadis dissecting these highlands form effective watersheds of the Quaternary aquifer. These wadis form areas of focused recharge. Recharge also occurs directly via the Quaternary sediments covering El-Qaa Plain. Subsurface lateral groundwater flow from the fractured basement contributes significant recharge to the aquifer as well. The aquifer sediment facies affect the type and quality of groundwater. In the eastern part where the aquifer is composed mainly of gravel and coarse sand with fragments of weathered basement, the Na-Cl-SO₄ water dominates. In the west where the facies change is rapid and complex, many water types arise. The base exchange index (BEX) is positive in this part reflecting the role of clay minerals in changing the water types via cation exchange. In the east where clays are insignificant in the aquifer, the BEX is negative. In the western part next to El-Qabaliyat Ridge, the wells discharging from the calcareous sand zone have low groundwater salinities compared to the wells discharging from the alluvium. In general, the groundwater salinity increases in the direction of groundwater flow from the northeast to the southwest which reflects the dissolution of aquifer sediments. The concentration relationships between the major ions on one hand and chloride on the other reflect the dissolution of calcium carbonates, precipitation of K- and Mg-bearing minerals, and cation exchange of Ca for Na on clay minerals. The hydrochemical models support these reactions. In addition, they show that the effect of evaporation on the recharge water in the western catchment is about four times its effect on the eastern recharge water which reflects the rapid recharge through the wadis draining the fractured basement. Moreover, the contribution from the eastern catchment in sample No. 23 is more than four-folds the contribution from the western recharge area. The stable isotopes (²H and ¹⁸O) show that the Quaternary aquifer is recharging from recent rainfall. However, upward leakage of Paleogene groundwater (depleted in ¹⁸O) also occurs. The groundwater level map shows strong overpumping impact especially in the areas close to El-Tur city.     

Using lithologic modeling techniques for aquifer characterization and groundwater flow modeling of the Sohag area, Egypt

Three dimensional lithologic modeling techniques have been used for detailed characterization and groundwater flow modeling of the Quaternary aquifer system of the Sohag area, Egypt. Well log data were used for building the lithologic model using RockWorks. A groundwater flow model, facilitated by MODFLOW 2000, was built using results of the lithologic model. The obtained lithologic model honored the well log data and revealed a complex sedimentary system, which is mainly composed of six lithologic categories: clay, clay and sand, fine sand, coarse sand, sand and gravel, and gravel. Inter-fingering and presence of lenses are the main characteristics of the sedimentary basin in the study area. A wide range of hydraulic conductivities is present, which vary spatially and control the groundwater flow. Heterogeneity of the aquifer system is spatially represented where different hydraulic conductivities are found in the different directions. Sandy layers tend to be connected. Hydraulic continuity is represented by inter-fingering and connection of sandy materials within the aquifer system.     

Towards a better understanding of the Oulmes hydrogeological system (Mid-Atlas,Morocco)

Located in the Mid-Atlas (Morocco), the Oulmes plateau is famous for its mineral water springs “Sidi Ali” and “Lalla Haya” commercialised by the company “Les Eaux minérales d’Oulmès S.A”. Additionally, groundwater of the Oulmes plateau is intensively exploited for irrigation. The objective of this study, essentially performed from data collected during isotopic (summer 2004) and piezometric and hydrogeochemical field campaigns (spring 2007), is to improve the understanding of the Oulmes hydrogeological system. Analyses and interpretation of these data lead to the statement that this system is constituted by a main deep aquifer of large extension and by minor aquifers in a perched position. However, these aquifers interact enough to be in total equilibrium during the cold and wet period. As highlighted by isotopes, the origin of groundwater is mainly infiltration water except a small part of old groundwater with dissolved gas rising up from the granite through the schists.     

Assessment of aquifer vulnerability to contamination in Khanyounis Governorate, Gaza Strip—Palestine, using the DRASTIC model within GIS environment

Groundwater is a very important natural resource in Khanyounis Governorate (the study area) for water supply and development. Historically, the exploitation of aquifers in Khanyounis Governorate has been undertaken without proper concern for environmental impact. In view of the importance of quality groundwater, it might be expected that aquifer protection to prevent groundwater quality deterioration would have received due attention. In the long term, however, protection of groundwater resources is of direct practical importance because, once pollution of groundwater has been allowed to occur, the scale and persistence of such pollution makes restoration technically difficult and costly. In order to maintain basin aquifer as a source of water for the area, it is necessary to find out, whether certain locations in this groundwater basin are susceptible to receive and transmit contamination. This study aims to: (1) assess the vulnerability of the aquifer to contamination in Khanyounis governorate, (2) find out the groundwater vulnerable zones to contamination in the aquifer of the study area, and (3) provide a spatial analysis of the parameters and conditions under which groundwater may become contaminate. To achieve that, DRASTIC model within geographic information system (GIS) environment was applied. The model uses seven environmental parameters: depth of water table, net recharge, aquifer media, soil media, topography, impact of vadose zone, and hydraulic conductivity to evaluate aquifer vulnerability. Based on this model and by using ArcGIS 9.3 software, an attempt was made to create vulnerability maps for the study area. According to the DRASTIC model index, the study has shown that in the western part of the study area the vulnerability to contamination ranges between high and very high due to the relatively shallow water table with moderate to high recharge potential, and permeable soils. To the east of the previous part and in the south-eastern part, vulnerability to contamination is moderate. In the central and the eastern part, vulnerability to contamination is low due to depth of water table. Vulnerability analysis of the DRASTIC Model indicates that the highest risk of contamination of groundwater in the study area originates from the soil media. The impact of vadose zone, depth to water level, and hydraulic conductivity imply moderate risks of contamination, while net recharge, aquifer media, and topography impose a low risk of aquifer contamination. The coefficient of variation indicates that a high contribution to the variation of vulnerability index is made by the topography. Moderate contribution is made by the depth to water level, and net recharge, while impact of vadose zone, hydraulic conductivity, soil media, and Aquifer media are the least variable parameters. The low variability of the parameters implies a smaller contribution to the variation of the vulnerability index across the study area. Moreover, the “effective” weights of the DRASTIC parameters obtained in this study exhibited some deviation from that of the “theoretical” weights. Soil media and the impact of vadose zone were the most effective parameters in the vulnerability assessment because their mean “effective” weights were higher than their respective “theoretical” weights. The depth of water table showed that both “effective” and “theoretical” weights were equal. The rest of the parameters exhibit lower “effective” weights compared with the “theoretical” weights. This explains the importance of soil media and vadose layers in the DRASTIC model. Therefore, it is important to get the accurate and detailed information of these two specific parameters. The GIS technique has provided an efficient environment for analysis and high capabilities of handling large spatial data. Considering these results, DRASTIC model highlights as a useful tool that can be used by national authorities and decision makers especially in the agricultural areas applying chemicals and pesticides which are most likely to contaminate groundwater resources.     

Natural background levels and threshold values for groundwater in fluvial Pleistocene and Tertiary marine aquifers in Flanders,Belgium

Aquifers from the same typology can have strongly different groundwater chemistry. Deducing the groundwater quality of less well-characterized aquifers from well-documented aquifers belonging to the same typology should be done with great reserve, and can only be considered as a preliminary approach. In the EU’s 6th FP BRIDGE project “Background cRiteria for the IDentification of Groundwater thrEsholds”, a methodology for the derivation of threshold values (TV) for groundwater bodies is proposed. This methodology is tested on four aquifers in Flanders of the sand and gravel typology. The methodology works well for all but the Ledo-Paniselian aquifer, where the subdivision into a fresh and saline part is disproved, as a gradual natural transition from fresh to saline conditions in the aquifer is observed. The 90 percentile is proposed as natural background level (NBL) for the unconfined Pleistocene deposits, ascribing the outliers to possible influence of pollution. For the Tertiary aquifers, high values for different parameters have a natural origin and the 97.7 percentile is preferred as NBL. The methodology leads to high TVs for parameters presenting low NBL, when compared to the standard used as a reference. This would allow for substantial anthropogenic inputs of these parameters.     

Groundwater flow in an arsenic-contaminated aquifer,Mekong Delta,Cambodia

To advance understanding of hydrological influences on As concentrations within groundwaters of Southeast Asia, the flow system of an As-rich aquifer on the Mekong Delta in Cambodia where flow patterns have not been disturbed by irrigation well pumping was examined. Monitoring of water levels in a network of installed wells, extending over a 50 km² area, indicates that groundwater flow is dominated by seasonally-variable gradients developed between the river and the inland wetland basins. While the gradient inverts annually, net groundwater flow is from the wetlands to the river. Hydraulic parameters of the aquifer (K ≈ 10⁻⁴ ms⁻¹) and overlying clay aquitard (K ≈ 10⁻⁸ ms⁻¹) were determined using grain size, permeameter and slug test analyses; when coupled with observed gradients, they indicate a net groundwater flow velocity of 0.04–0.4 ma⁻¹ downward through the clay and 1–13 ma⁻¹ horizontally within the sand aquifer, producing aquifer residence times on the order 100–1000 a. The results of numerical modeling support this conceptual model of the flow system and, when integrated with observed spatial trends in dissolved As concentrations, reveal that the shallow sediments (upper 2–10 m of fine-grained material) are an important source of As to the underlying aquifer.     

Evaluation of hydrogeochemical processes in the Pleistocene aquifers of Middle Ganga Plain, Uttar Pradesh, India

Evaluation of major ion chemistry and solute acquisition process controlling water chemical composition were studied by collecting a total of fifty-one groundwater samples in shallow (<25 m) and deep aquifer (>25 m) in the Varanasi area. Hydrochemical facies, Mg-HCO₃ dominated in the largest part of shallow groundwater followed by Na-HCO₃ and Ca-HCO₃ whereas Ca-HCO₃ is dominated in deep groundwater followed by Mg-HCO₃ and Na-HCO₃. High As concentration (>50 μg/l) is found in some of the villages situated in northeastern parts (i.e. adjacent to the concave part of the meandering Ganga river) of the Varanasi area. Arsenic contamination is confined mostly in tube wells (hand pump) within the Holocene newer alluvium deposits, whereas older alluvial aquifers are having arsenic free groundwater. Geochemical modeling using WATEQ4F enabled prediction of saturation state of minerals and indicated dissolution and precipitation reactions occurring in groundwater. Majority of shallow and deep groundwater samples of the study area are oversaturated with carbonate bearing minerals and under-saturated with respect to sulfur and amorphous silica bearing minerals. Sluggish hydraulic conductivity in shallow aquifer results in higher mineralization of groundwater than in deep aquifer. But the major processes in deep aquifer are leakage of shallow aquifer followed by dominant ion-exchange and weathering of silicate minerals.     

Groundwater quality degradation as a result of overpumping in the delta Wadi El-Arish area,Sinai Peninsula,Egypt

The delta Wadi El-Arish area of the Sinai Peninsula is one of the most important parts of Egypt for industrial and agricultural expansion projects because of its relatively abundant supply of groundwater. This study focuses on the hydrogeology and hydrochemistry of the Quaternary aquifer in the delta Wadi El-Arish area and on the impacts pumping has had on groundwater quality. The objectives were to determine the relationships between groundwater pumping and water levels and water quality, to estimate the hydraulic parameters of the Quaternary aquifer, and to determine the hydrochemistry of groundwater in the Quaternary aquifer and its suitability for irrigation. The conclusions are: (1) potentiometric surface elevations have declined by an average of about 0.5 m since 1981 in response to an increase in pumping, (2) the transmissivity of the lower Pleistocene calcareous sandstone (kurkar) unit is higher than the transmissivity of the upper Pleistocene alluvium, (3) groundwater in the Pleistocene aquifer is augmented with groundwater leaking from the overlying Holocene sand dune deposits through the intervening sandy clay aquitard, (4) groundwater in the kurkar is of lower quality than groundwater in the alluvium, (5) total dissolved solids (TDS) concentrations have increased by an average of about 1500 ppm since 1962, (6) an increase in saltwater intrusion has occurred in the northern part of the study area, and (7) the irrigation suitability of groundwater pumped from wells in much of the area is limited to salt tolerant crops. Our recommendations are: (1) no new pumping wells should be drilled and no increase in pumping rates should be allowed in the delta Wadi El-Arish area, (2) reliable estimates of the quantity of groundwater recharge should be made, (3) flood irrigation systems should be replaced by either drip or sprinkler     

The use of geoprocessing to assess vulnerability on the east coast aquifers of Rio de Janeiro State,Brazil

The east coast of Rio de Janeiro State, Brazil, shows a worrying overlap between areas with intrinsic groundwater vulnerability and the most significant urban expansion zones. It experienced a rapid population growth in recent years, mainly due to the tourism industry, resulting in a significant pressure on drinking groundwater resources. In this regard, development and use of techniques to control and protect areas susceptible to contamination is crucial. The elaboration of aquifer vulnerability maps is thus extremely helpful to support water resources management. The aim of the work is to present the methodological approach in the use of Geoprocessing techniques to obtain a suitable groundwater vulnerability model in Rio de Janeiro east coast. Considering the existing problems and the current land use and characteristics of the study region, it is clear that the most vulnerable areas (that is, “extreme” and “very high” vulnerability areas), coincide with the most significant zones of urban occupation, corresponding to 11% of the total study area, demanding adoption of urgent measures in the near future. Geoprocessing tools and remote sensing for characterization of Rio de Janeiro’s east coast aquifer vulnerability gave good results, representing a satisfactory method for management actions at low cost.     

Hydrology of part of the Oramiriukwa River basin,southeast of Owerri,Imo State,Nigeria

The Oramiriukwa River is within the sandy coastal plain strata of the Benin formation (Miocene–Recent). The base flow is very high ranging from 79.13–98.56%, which is caused by the excellent hydraulic interconnection between the river and the adjacent unconfined aquifer. Recharge rates are high, estimated to range from 1.8×10¹²–2.5×10¹² m³/year. Coastal sands are medium-to-coarse grained, moderately-to-poorly sorted, angular to subangular, with lenses of clay and clayey fine-grained sands. The coastal sands and clay lenses form aquifer and aquitard systems, which are unconfined to semi-confined. Groundwater recharge potential is high. Runoff from precipitation is low. Groundwater and surface water are fairly acidic; pH ranges from 5.5–6.1 (groundwater) and 5.8–6.5 (surface water), and hardness is generally low. Chemical analysis and percentage sodium show that groundwater and surface water are somewhat potable after some pH modification of the surface water. The waters are good for agricultural use, especially for irrigation and poultry water supply. However, pollution from landfill leachate is serious. Electronic Publication     

Socio-economic constraints of groundwater in Capital La Rioja, Argentina

Historically, the arid conditions of La Rioja, Argentina have been the main controlling factor in its development. The shortage of surface water, which is fully used, makes groundwater a potential source for development. The government encouraged investment in early 1979, resulting in a 20-fold increase of groundwater extraction by 1998 (0.076–1.450 m³/s, respectively) to cover related needs of agriculture, industry and population growth. This extraction created unjustified uncertainties derived from negative results obtained in hydrological balances. However, a 0.5 m lowering of the water-table surface was experienced. A knowledge of groundwater functioning was required to establish a reliable frame of reference for development and, at the same time, to find possible scenarios of feasible economic activities in harmony with accessible water resources and aptitude of the environment. The flow regime was found to be composed of three main systems: a regional, an intermediate and several local. The intermediate system provides water for the extraction boreholes, and discharges naturally in Salina La Antigua. From the chemical perspective the intermediate system has three groundwater groups. Group I has an outstanding fluoride concentration (1.98–3.10 mg/l) defined to the north of the City of la Rioja and the highest temperature (26.8–33.0°C), the lowest lithium content (0.029–0.059 mg/l) and moderate arsenic (≤0.038 mg/l). Group II has the moderate arsenic content (≤0.38 mg/l) detected to the south of the City of La Rioja and high lithium (0.024–0.085 mg/l), Group III has the lowest TDS (456–931 mg/l) and arsenic (0.007–0.012 mg/l) and the highest lithium (0.067–0.141 mg/l). to A regional flow is represented by Group IV with one order of magnitude higher strontium (4.870 mg/l), lead (0.021 mg/l) and uranium (0.362 mg/l) content than the other groups. Results provide evidence to eliminate several well-established hydro-myths such as “the boreholes are getting dry” and “boreholes are getting saline water”. The aquifer (granular Tertiary and Quaternary material) thickness (≈750m) was defined with the aid of the geological framework, geothermometers and Modflow modelling. The aquifer extent extends far beyond the limits of the study area. Several economic activities were found to be feasible with available groundwater resources and without bordening the environment (fish farming, bottled-water marketing, SPA activities and farming of endangered species).     

Sustainable groundwater resources, Heretaunga Plains, Hawke's Bay, New Zealand

 The Heretaunga Plains, Hawke's Bay, New Zealand, is underlain by Quaternary fluvial, estuarine-lagoonal, and marine deposits infilling a subsiding syncline. Within the depositional sequence, river-channel gravels form one of the most important aquifer systems in New Zealand. An interconnected unconfined–confined aquifer system contains groundwater recharged from the Ngaruroro River bed at the inland margin of the plain, 20 km from the coast. At the coast, gravel aquifers extend to a depth of 250 m. In 1994–95, 66 Mm³ of high quality groundwater was abstracted for city and rural water supply, agriculture, industry, and horticulture. Use of groundwater, particularly for irrigation, has increased in the last 5 years. Concern as to the sustainability of the groundwater resource led to a research programme (1991–96). This paper presents the results and recommends specific monitoring and research work to refine the groundwater balance, and define and maintain the sustainable yield of the aquifer system. Three critical management factors are identified. These are (1) to ensure maintenance of consistent, unimpeded groundwater recharge from the Ngaruroro River; (2) to specifically monitor groundwater levels and quality at the margins of the aquifer system, where transmissivity is <5000 m²/d and summer groundwater levels indicate that abstraction exceeds recharge; (3) to review groundwater-quality programs to ensure that areas where contamination vulnerability is identified as being highest are covered by regular monitoring. Received, January 1998 / Revised, August 1998, March 1999 / Accepted, April 1999     

Hydrogeochemical stratification of the unconfined Samobor aquifer (Zagreb,Croatia)

In the western part of the city of Zagreb, Croatia, hydrogeochemical and isotopic investigations of the Samobor aquifer were carried out with the aim of determining the differences in hydrogeochemical characteristics at increasing aquifer depths. The aquifer comprises 40-m thick gravelly–sandy deposits, with lenses and interlayers of silt and clay. The analyses have proven that with increasing aquifer depth, there are decreases in groundwater temperature and the values of electrical conductivity and increases in the sodium, iron and manganese concentrations. The δ¹³C distribution shows an evident increase in biogenic carbon concentrations with increasing aquifer depth. The measured specific ¹⁴C activities showed that the deeper part of the aquifer is characterized by slow water exchange, while the shallower part is influenced by current recharge, although the pumping wells located on the well-field downstream penetrate the aquifer fully. A direct exchange of water from the Sava River and groundwater occurs in the near vicinity of the river. This exchange weakens further away, while the difference in hydrogeochemical characteristics between the Sava River water and groundwater increases.     

Environmental geological assessment of a solid waste disposal site: a case study in Sivas, Turkey

The selection of the disposal site is probably the most important step in the development of solid waste management. In site selection, geology plays a determining role. This study evaluates the characteristics of the environment on the basis of the geological, hydrogeological and geo-engineering properties of the solid waste site of the Sivas city, Turkey. The area is underlain by the Oligocene-Miocene rocks which have limited aquifer properties. Thin Quaternary alluvium and soil cover overlie the Oligo-Miocene rocks, which are represented as well graded sand and inorganic silt of low plasticity. The Quaternary alluvium and soil cover are classified as inorganic clays having a low plasticity and the permeability varies from 1.2×10⁻⁶ to 3.11×10⁻⁶ m/s. These values are much higher than 1×10⁻⁸ m/s, which is accepted for waste disposal standards. Seepage waters have a potential to pollute the ground water and the Kızılırmak River, which is 500 m to the southwest of the waste disposal area and because the disposal site is close to the river, the potential for flash flooding poses a high pollution risk. The waste disposal area must be covered by clay layers or an impervious artificial membrane. In addition, seepage must be controlled and removed from the site.     

Identifying sources of groundwater recharge in the Merguellil basin (Tunisia) using isotopic methods: implication of dam reservoir water accounting

Thirty-two groundwater samples collected from the Merguellil Wadi basin (central Tunisia) complemented by the Haouareb dam reservoir water samples have been isotopically analysed in order to investigate the implication of the reservoir water to recharging the aquifer, and also to infer the sources, relative ages and mixing processes in the aquifer system. Plots of the stable isotopes data against the local meteoric lines of Tunis-Carthage and Sfax indicate a strong implication of the dam water noticeable up to a distance of 6–7 km. A contribution as much as 80% of the pumped water has been evidenced using isotopic mass balance. In addition, poorly distinguished water clusters in the stable isotope plots, but clearly identified in the diagrams δ¹⁸O versus ³H and ³H versus ¹⁴C, indicate various water types related to sources and timing of recharge. The isotopic signatures of the dam accounting water, the “old” and “native” recharged waters, have been evidenced in relation to their geographical distribution and also to their radiogenic isotopes (³H and ¹⁴C) contents. In the south-western part of the aquifer, mixing process occurs between the dam reservoir water and both the “old” and “native” water components.