Archana Deodhar

Geochemical characterization of groundwater from an arid region in India

A study on the geochemical processes in arid region of western India (Kachchh district) was carried out using major, minor, trace metal data and isotopic composition (δ2H, δ18O) of groundwaters. Results indicate that the distribution of chemical species in groundwater of this district is controlled by leaching of marine sediments, dissolution of salts in root zone and incongruent dissolution of carbonate minerals. Common inorganic contaminants such as fluoride, nitrate and phosphate are within drinking water permissible limits. However, most of the samples analyzed contain total dissolved salts more than desirable limits and fall in doubtful to unsuitable category with regard to irrigational purpose. Trace metal data indicates no contamination from toxic elements such as arsenic and lead. An increased salt content is observed in groundwater at shallower depths indicating mixing with surface water sources. The chemical characteristics of the groundwater have found to be strongly dependent on the local lithological composition. Environmental isotopic data indicates that the groundwater is of meteoric origin and has undergone limited modification before its recharge. The processes responsible for observed brackishness are identified using chemical and isotope indicators, which are in agreement with subsurface lithology and hydrochemistry. These data though represent hydrochemical scenario of 2001 can still be used for understanding the long-term fluctuations in water chemistry and would be quite useful for the planners in validating groundwater quality models.

Recovery of 137Cs from Laboratory Waste using Solvent Extraction with Sodium Tetraphenylboron (TPB)

The paper describes a method for the recovery of 137Cs from an aqueous radioactive laboratory waste solution containing 137Cs (2 µg/mL) in the presence of high concentration of Na+ using solvent extraction technique. The method comprises of adjustment of pH to the acidic range (pH = 2), contacting the aqueous radioactive solution with sodium tetraphenylboron (TPB) in nitrobenzene, whereby 137Cs binds with tetraphenylboron anions and gets separated. Results of this investigation indicate that 137Cs could be efficiently and selectively extracted from an aqueous solution media containing high concentration of Na+ under mildly acidic pH into an organic phase and back extracted with small volume of 3 M HNO3, thus enabling concentration. The proposed method was successfully applied in real samples.

A multi-isotope approach (O, H, C, S, B and Sr) to understand the source of water and solutes in some the thermal springs from West Coast geothermal area, India

The West Coast belt, consisting of nearly 60 thermal springs, is one of the most diversified geothermal fields in India. The present work describes the multi-isotopic (O, H, C, S, B and Sr) characterization of thermal waters carried out in the Tural-Rajwadi geothermal field, situated in southern sector of the west coast geothermal area. The aim of this study is to delineate the origin of thermal water as well as to ascertain the sources of carbon, sulphur, boron and strontium dissolved in those thermal springs. The stable isotopes (δ2H and δ18O) and tritium data indicate that these thermal springs are not recently recharged rain water rather, it contains very old component of water. Oxygen-18 shift is observed due to rock-water interaction over a long period of time. Carbon isotopic composition of DIC points out to the silicate weathering with soil CO2 coming from C3 type of plants whereas δ34S of dissolved sulphate confirms the marine origin of sulphate. This marine signature is basically derived from paleo-seawater possibly entrapped within the flows. Boron isotopic data reveals that both the seawater and rock dissolution are the sources of boron in the thermal waters whereas high 87Sr/86Sr ratios (0.7220–0.7512) of the thermal waters conclusively establishes that archean granitic basement is the predominant rock source of strontium, not the Deccan flood basalts. In addition, like strontium, concentrations of lithium, rubidium and caesium are also governed by the rock-water interaction. Thus, the combined use of this multi-isotope technique coupled with trace element concentrations proves to be an effective tool to establish the sources of solutes in the thermal water.

Distribution of environmental tritium in rivers, groundwater, mine water and precipitation in Goa, India

Tritium concentration in rivers, groundwater, precipitation and mine pits water, all over Goa state was characterized to find out spatial and temporal variability of tritium. Twenty four water samples were collected during pre-monsoon and post-monsoon and analyzed for their tritium concentration. The mean tritium concentration in surface and sub-surface hydrosphere is 2.5 (±0.6) TU. The mean concentration of tritium in rivers, groundwater, mines pits water and rain water are 2.9 (±0.5) TU, 1.95 (±0.5) TU, 2.5(±0.3) TU and 3.1(±0.1) TU respectively. The tritium distribution in all the samples shows modern precipitation (post-1950) component in surface and sub-surface hydrosphere of Goa. The HYSPLIT4.0 air mass trajectory model and atmospheric circulation pattern suggest that the moisture origin was from the Arabian Sea and this low tritium moisture is diluting the tritium concentration of surface hydrosphere near the coastal area. The tritium concentration in surface hydrosphere shows more and more enrichment as one move inland (i.e. away from the coast). Significant seasonal change is observed in the surface hydrosphere. The pre-monsoon samples showed higher tritium concentration than post-monsoon samples. This may be due to high rate of re-evaporation of water and a reduction in the supply of oceanic moisture during the summer (pre-monsoon).

Isotope Hydrogeological Factors Control Transport of Radon-222 in Hard Rock Fractured Aquifer of Bangalore, Karnataka

Radon-222 is a daughter element of radium-226 and are member of the uranium decay series. Radon-222 concentrations in groundwater of Bangalore city in different geological units were measured in 42 tube wells. The study area is underlain by Granite, Migmatite, Granodiorite and Gneiss rock and many dolerite dykes. The radon-222 concentration in groundwater is widely varying and ranging from 14 to 1000 Bq/L with an average value of 172.4 Bq/L. Significant differences in the radon-222 concentrations in groundwater among geological units were observed. The radon-222 distribution in groundwater is related to the presence of uranium in aquifer materials of the various rock types. Uranium concentration in groundwater is ranging from 0.2 to 523 μg/L. Transport of radon-222 through bedrock by water depends mainly on the percolation of water through the pore and along fractured planes of the rocks. Rn-222 cannot travel farther than several hundred meters away from their origin because of its short half-life of 3.8 days. It may travel the farthest within fractured or fissured geological formation where groundwater movement is fastest. The study shows that radon concentration in groundwater is controlled by geohydrological and hydrochemical characteristics of the study area.