A study of the hydrogeochemical processes in the national capital territory of India was carried out with the objective of identifying the geochemical processes and their relation with groundwater quality as well as to get an insight into the hydrochemical evalution of groundwater. Salinity and nitrate contamination are the two major problems in the area, which is alarming considering the use of this water for drinking. Various graphical plots and statistical analyses have been carried out using chemical data to deduce a hydrochemical evaluation of the aquifer system based on the ionic constituents, water types, hydrochemical facies and factors controlling groundwater quality. The prevailing hydrochemical processes operating here are simple dissolution, mixing, weathering of carbonate minerals, locally known as ‘kankar’, and of silicate, ion exchange, and surface water interaction. Limited reverse ion exchange has been noticed in a few parts of the study area especially in post-monsoon periods. Periodic seasonal switch-over has been clearly noticed in these hydrogeochemical processes that control groundwater quality of the area. The number of factors that control the overall mineralization and water quality of Delhi vary from season to season. In pre-monsoon, there are four factors while in post-monsoon it increases to five. The study highlights the descriptive capabilities of conventional and multivariate techniques as effective tools in groundwater evaluation.

Identification and evaluation of hydrogeochemical processes in the groundwater environment of Delhi, India

The Palar and Cheyyar River Basins in Tamil Nadu state of Southern India are characterised by different geological formations, and groundwater is the major source for domestic, agricultural and other water-related activities. Hydrogeochemical studies were carried out in this area with the objective of identifying the geochemical processes and their relation to groundwater quality. Groundwater samples were collected once a month from 43 groundwater wells in this area from January 1998 to July 1999. Sampling procedures and chemical analysis were carried out as per the standard methods. Chemical data are used for mathematical calculations and graphical plots to understand the chemical process and its relation to the groundwater quality. The chemical composition of groundwater in the central part of the study area mainly depends on the recharge from lakes and the river, which is explained by a mixing mechanism. In addition, weathering of silicate minerals controls the concentration of major ions such as sodium, calcium, magnesium and potassium in the groundwater of this area. Further, the activity ratios indicate that the groundwater is in equilibrium with kaolinite, smectite and montmorrillonite. The reverse ion exchange process controls the concentration of calcium, magnesium and sodium in hard rock formations, and dissolution of carbonate minerals and accessory minerals is the source of Ca and Mg, in addition to cation exchange in the sedimentary formations. In general, the chemical composition of the groundwater in this area is influenced by rock–water interaction, dissolution and deposition of carbonate and silicate minerals, ion exchange, and surface water interactions.

Identification and evolution of hydrogeochemical processes in the groundwater environment in an area of the Palar and Cheyyar River Basins, Southern India

Solute and isotopic geochemistry and ground water flow in the central Wasatch Range, Utah

Hydrogeochemical investigations were carried out in Chithar River basin, Tamil Nadu, India to identify the major geochemical processes that regulate groundwater chemistry. For this study, long-term (1991-1997) and recent water quality data (2001-2002) for 30 groundwater wells spread over the study area were used to understand the groundwater geochemistry and hydrogeochemical process regulating groundwater quality. Groundwater quality data obtained from more than 400 water samples were employed. Results of electrical conductivity and chloride express large variation between minimum and maximum values and high standard deviation, which suggests that the water chemistry in the study region is not homogeneous and influenced by complex contamination sources and geochemical process. Nitrate and depth to water table expose the influences of surface contamination sources, whereas dissolved silica, fluoride and alkalinity strongly suggest the effect of rock-water interaction. In the study region, weathering of carbonate and silicate minerals and ion exchange reactions predominantly regulate major ion chemistry. Besides, the concentrations of sulphate, chloride and nitrate firmly suggest the impact of agricultural activities such as irrigation return flow, fertiliser application, etc on water chemistry in the study region.

Groundwater geochemistry and identification of hydrogeochemical processes in a hard rock region, Southern India.

https://www.uni-muenster.de/imperia/md/content/landschaftsoekologie/hydrologiebodenkunde/profblodauliteratur/_23__blodau_2006.pdf

A review of acidity generation and consumption in acidic coal mine lakes and their watersheds.

In this case study, we have demonstrated how a minimal amount of relatively inexpensive isotopic data can be used to help solve a complex Hydrogeologie problem.



Acidic (pH 3 to 4) and neutral (pH 6.0 to 7.7) mine drain waters have been identified and sampled in the mining districts in the central Wasatch Range of Utah. The chemical evolution of acid and neutral mine waters follow fundamentally different chemical and isotopic evolutionary pathways which reflect fundamentally different flow histories. Most neutral mine discharges are either low iron calcium-bicarbonate waters or iron and sulfate rich waters. Stable isotopic values of δ2 H and δ18 O plot near and parallel to the meteoric water line (MWL), suggesting a meteoric origin for all mine waters. 3H concentrations (20.9 to 40.8 TU) and 14C activities (46.2 to 96.3 pmc) indicate mine waters have a major component of modern recharge water. Shallow circulation of most mine discharges is suggested by low TDS, nonthermal discharge temperatures and the proximity of most mine workings to the surface.



The δ34 S values of mine discharge waters tend to cluster about two nodes. Neutral mine drainages with low SO42- contents cluster about δ34 S = 0/o, whereas neutral mine drainages with high Su42 contents cluster about δ34S =+5.5%o. An acid mine drainage also has a 534 S value of about 0 %o. δ34 S values of ∼ 0 %o are attributed to the oxidation ofpyrite and other sulfide minerals, whereas more positive isotopic values are attributed to isotopic fractionation accompanying the dissolution of gypsum and anhydrite. Only mine discharges with a δ34S δ 0%o have the potential to produce acid drainage. Geologic and δ13C data suggest acid mine waters (mean δ13C =−15.0%o) discharge from ground-water flow systems generally devoid of carbonate rocks. Neutral mine waters (mean δ13C =− 9.7%o) discharge from aquifers containing abundant carbonate rocks which neutralize excess H+ ions released by the oxidization of sulfide minerals.

Mark D. Loucks

Papers

Solute and isotopic geochemistry and ground water flow in the central Wasatch Range, Utah

The Use of Solute and Isotopic Chemistry to Identify Flow Patterns and Factors Which Limit Acid Mine Drainage in the Wasatch Range, Utah