Application of groundwater modelling for sustainable management: Few case studies from India

111-116Few case studies on groundwater models applied to understand the flow and solute transport in parts of southern India are presented. These examples showcase the ability of mathematical models to aid in decision making processes towards sustainable management of groundwater resources

Cross comparison of five popular groundwater pollution vulnerability index approaches

Identification of a suitable overlay and index method to map vulnerable zones for pollution in weathered rock aquifers was carried out in this study. DRASTIC and four models derived from it, namely Pesticide DRASTIC, modified DRASTIC, modified Pesticide DRASTIC and Susceptibility Index (SI) were compared by applying them to a weathered rock aquifer in southern India. The results were validated with the measured geochemical data. This study also introduces the use of temporal variation in the groundwater level and nitrate concentration in groundwater as input and for validation respectively to obtain more reliable and meaningful results. Sensitivity analysis of the vulnerability index maps highlight the importance of one parameter over another for a given hydrogeological setting, which will help to plan the field investigations based on the most or the least influential parameter. It is recommended to use modified Pesticide DRASTIC for weathered rock regions with irrigation practises and shallow aquifers (<20 m bgl). The crucial input due to land use should not be neglected and to be considered in any hydrogeological setting. It is better to estimate the specific vulnerability wherever possible rather than the intrinsic vulnerability as overlay and index methods are more suited for this purpose. It is also necessary to consider the maximum and minimum values of input parameters measured during a normal year in the models used for decision making

Geochemical modelling of the effects of a proposed uranium tailings pond on groundwater quality. Technical article

The impact of a proposed uranium tailings pond on groundwater quality was assessed by geochemical modelling. Groundwater samples were collected from six dug wells in the Nalgonda district, Andhra Pradesh, in southern India, once every 2 months from March 2008 to January 2010, and analysed for calcium, magnesium, sodium, potassium, chloride, sulphate, carbonate, bicarbonate, and uranium. Prediction of groundwater quality was carried out for 100 years using PHREEQC to assess the effects of infiltration of water from the proposed tailings pond. The sensitivity of the model for variations in porosity, hydraulic gradient, hydraulic conductivity, and concentration of uranium in the tailings was evaluated. Geochemical modelling predicts that if the chemical composition of the tailings water is maintained at about the expected mean concentrations, and an appropriate liner is installed with an infiltration rate B1.0 9 10-9 m/s, the concentration of solutes in the groundwater will be increased from present background levels for a down-gradient distance of up to 500 m for the anticipated life of the mine, i.e. 16 years. The concentration of ions in groundwater would exceed background concentrations for up to 100 m at the end of 100 years. This study was used to predict the optimum chemical composition for the tailings and the extent, in terms of time and distance, that the groundwater concentration of various ions would be increased by infiltration of wastes from the tailings pond

Hydrochemical characteristics of groundwater for domestic and irrigation purposes in Madhuranthakam, Tamil Nadu, India

Hydrochemical study was carried out in Madhuranthakam located near Chennai in Tamil Nadu, India with an objective of understanding the suitability of local groundwater quality for domestic and irrigation purposes. Twenty groundwater samples were collected in February 2002 and analysed for physical and chemical parameters. Groundwater in this area was found to be within the desirable Bureau of Indian Standards and World Health Organisation limits for drinking water. Ca-HCO3 was the dominant groundwater type. Groundwater in this area was assessed for irrigation purposes on the basis of sodium percentage (Na%), magnesium hazard (MH), residual sodium carbonate (RSC), sodium absorption ratio (SAR), permeability index (PI) and United States Department of Agriculture (USDA) classification. Most of the groundwater samples were suitable for irrigation, except in a few locations (15%) based on MH. Overall the groundwater quality was suitable for drinking and domestic purposes and permissible for irrigation activities

Geological and geomorphological controls on groundwater occurrence in a hard rock region

Remote sensing and GIS tools have broadly helped hydrogeologists to delineate the groundwater prospective zones for watershed development and management. The origin, movement and existence of groundwater depends on several factors such as slope, drainage density, land use, geology, lineament density and geomorphology. Based on these, the mapping and identification of groundwater potential zones were carried out in a part of Nalgonda district, Telangana, India. The regions were categorised as high, moderate and low groundwater potential, and they were validated with the groundwater levels and yield of wells located in the corresponding zones. Extensive possibility for watershed development is possible in 41 % of the total 724 km2 and 46 % of the area offers moderate options. Any groundwater management project implemented in these favourable areas will bring maximum benefit. Similar studies should be considered necessary before designing a water resource development activity as it will reduce the cost on detailed field visits which are time-consuming

Groundwater quality and its hydrochemical characteristics in a shallow weathered rock aquifer of southern India

Suitability of groundwater for domestic and irrigation purposes as well as its hydrochemical characteristics was estimated in a part of Nalgonda district, Telangana state in southern India. Water samples were collected from 45 wells once every 2 months from March 2008 to January 2010. EC and pH were measured in situ while concentrations of calcium, magnesium, sodium, potassium, sulphate and chloride in groundwater were analysed using ion chromatograph. Carbonate and bicarbonate concentration were determined by acid base titration. General order of dominance of cations in the groundwater of this study area is Na?[Ca2?[Mg2?[ K? while that for anions is HCO3 -[Cl-[SO4-2. Ca–HCO3, Na–Cl, mixed Ca–Na–HCO3 and mixed Ca–Mg–Cl types of groundwater were dominant in this area. Groundwater is generally fresh with medium to high salinity and low alkalinity. Chloride and bicarbonate concentrations were present within the permissible limits for drinking whereas, some samples exceed the permissible limits of the Bureau of Indian Standards for pH, TDS, TH,sodium, calcium, magnesium and sulphate. Potassium exceeded the maximum permissible limits for drinking proposed by World Health Organisation. Sodium adsorption ratio, sodium percentage, residual sodium carbonate and permeability index indicates that the groundwater quality was suitable for irrigation in most parts of the study area

Identification of salinization by bromide and fluoride concentration in coastal aquifers near Chennai, southern India

This study aims to use fluoride as an additional indicator for seawater intrusion apart from the known effective geochemical indicators such as EC, TDS, sodium, chloride and bromide. Groundwater in a coastal part of Arani-Koratalaiyar river basin located north of Chennai, Tamil Nadu, India was assessed to determine its suitability for domestic purpose and to delineate the region affected by seawater intrusion. Fluoride concentration in groundwater samples from forty nine locations varied from 0.02 mg/l to 2.9 mg/l with an average of 0.5 mg/l. As per the Bureau of Indian Standards, the permissible range of fluoride in drinking water is 0.6–1.5 mg/l. Fluoride concentration in groundwater of this area exceeds 1.5 mg/l in 6% of the groundwater samples and is below 0.6 mg/l in 74% of the groundwater samples. There is no known geological source for fluoride in this area. Spatial variation in fluoride concentration in groundwater indicates that the coastal areas have comparatively high fluoride due to seawater intrusion which was similar in comparison with EC and bromide concentration measured in groundwater. This study indicates that fluoride can be used as an indicator of seawater intrusion in coastal areas

Fluoride in weathered rock aquifers of southern India: managed aquifer recharge for mitigation

Climatic condition, geology, and geochemical processes in an area play a major role on groundwater quality. Impact of these on the fluoride content of groundwater was studied in three regions-part of Nalgonda district in Telangana, Pambar River basin, and Vaniyar River basin in Tamil Nadu, southern India, which experience semi-arid climate and are predominantly made of Precambrian rocks. High concentration of fluoride in groundwater above 4 mg/l was recorded. Human exposure dose for fluoride through groundwater was higher in Nalgonda than the other areas. With evaporation and rainfall being one of the major contributors for high fluoride apart from the weathering of fluoride rich minerals from rocks, the effect of increase in groundwater level on fluoride concentration was studied. This study reveals that groundwater in shallow environment of all three regions shows dilution effect due to rainfall recharge. Suitable managed aquifer recharge (MAR) methods can be adopted to dilute the fluoride rich groundwater in such regions which is explained with two case studies. However, in deep groundwater, increase in fluoride concentration with increase in groundwater level due to leaching of fluoride rich salts from the unsaturated zone was observed. Occurrence of fluoride above 1.5 mg/l was more in areas with deeper groundwater environment. Hence, practicing MAR in these regions will increase the fluoride content in groundwater and so physica or chemical treatment has to be adopted. This study brought out the fact that MAR cannot be practiced in all regions for dilution of ions in groundwater and that it is essential to analyze the fluctuation in groundwater level and the fluoride content before suggesting it as a suitable solution. Also, this study emphasizes that long-term monitoring of these factors is an important criterion for choosing the recharge areas

Geochemical characteristics and groundwater quality in the Vientiane Plain, Laos

Groundwater from the shallow aquifers of the Vientiane Plain, Laos is used for domestic needs including to some extent for drinking and for household gardening. The objective of this study is to assess the groundwater quality for drinking and irrigation activities and to determine the processes that lead to the presence of major ions in groundwater. Twenty groundwater samples were collected from a village on the Plain in December 2014, January 2015, and May 2015, and analysed for major ions and selected suite of minor ions and heavy metals. Groundwater is largely acidic, fresh and soft in nature. Geochemistry showed dominant Ca–Mg–HCO3 and mixed Ca–Na–HCO3 groundwater. Sodium impacts the suitability of water for irrigation to some extent. Hydrogeochemical processes identified and verified through factor analysis indicate weathering, carbonate dissolution, ion exchange, and anthropogenic sources including salinisation, due to irrigation and use of fertilizers as sources for the occurrence of major ions at such concentrations in this area. Only concentrations of lead and iron were above the permissible limits with arsenic, copper, zinc, mercury, and uranium found to be within safe limits. Background sample (groundwater) collected 5 km from the study area and the bottled water sample were all within suitable limits for drinking. This study is the first to provide a local-level assessment of geochemical processes in groundwater of this area indicating that the groundwater does not pose any threat to human health if used for drinking based on major ions, minor ions and a suite heavy metals except for iron and lead