Geochemistry of groundwater,Burdwan District,West Bengal,India

Hydrogeochemical investigations are carried out in the different blocks of Burdwan district, West Bengal, India in order to assess its suitability for drinking as well as irrigation water purpose. Altogether 49 representative groundwater samples are collected from bore wells and the water chemistry of various ions viz. Ca²⁺, Mg²⁺, Na⁺, K⁺, CO₃²⁻, HCO₃⁻, Cl⁻, SO₄²⁻ and NO₃⁻ are carried out. The chemical relationships in Piper and Gibbs diagram suggest that the groundwater mainly belongs to alkali type and Cl⁻ group and are controlled by rock dominance. A comparison of groundwater quality in relation to drinking water quality standards proves that most of the water samples are suitable for drinking water purpose whereas groundwater in some areas of the district has high salinity and high sodium adsorption ratio (SAR), indicating unsuitability for irrigation water and needs adequate drainage.     

Groundwater arsenic biogeochemistry-Key questions and use of tracers to understand arsenic-prone groundwater systems

Over 100,000,000 people worldwide are exposed to high arsenic groundwater utilised for drinking or cooking.The consequent global avoidable disease burden is estimated to be of the order of 100,000 avoidable deaths or more per annum from just direct exposures — i.e.excluding indirect exposure(from rice and other foods)and excluding morbidity.Notwithstanding 1000 s of papers published on arsenic(hydro)(bio)geochemistry,there remain a number of key outstanding questions to be addressed in relation to arsenic geoscience-these include questions related to:(i)the role of human activities —irrigation,agriculture and other land uses — on arsenic mobilisation in groundwaters;(ii)the specific sources,nature and role of organics,minerals and microbial communities involved in arsenic mobilisation;(iii)the relationship to microscopic to macroscopic scale geological(including tectonic)and evolution processes;(iv)unravelling the over-printing of multiple processes in complex highly heterogeneous aquifer systems and(v)using increasing understanding of the controls of arsenic mobility in groundwaters systems to informing improved locally-relevant remediation and mitigation approaches.This article further summarises how the 9 further papers in this Special Issue address some of these questions through the use of chemical and/or isotopic tracers.     

Fracture and stress orientation from borehole image logs: A case study from Cambay basin,India

The Deccan trap basalt, laid down by multiple lava flows during upper Cretaceous to Paleocene times forms the basement of current study in Cambay basin. As such, there is great interest and value in fracture detection and evaluation of fractured basement reservoirs in the Cambay basin. The procedure for identification and evaluation of natural as well as induced fractures in basaltic basement of the Cambay basin is presented in this work. In this study formation micro-imager (FMI) and extended range micro-imager (XRMI) log data for fracture identification is used. The Deccan trap basaltic basement of the study area, comprising five wells in the Tarapur-Cambay block, has potential for holding commercial hydrocarbon due to the presence of fractures and weathered basement. Both image logs (FMI, XRMI) identify three types of fracture including open (conductive), partially open and closed (resistive) fractures, of which open and partially open fractures are important for hydrocarbon accumulation. Fracture dip ranges from 10° to 80°. Image logs have also identified washout, breakout and drilling-induced fracture zones. The strike direction of the open natural fractures for four wells varies from N60°E to N30°E whereas the strike direction of most natural fracture in the fifth well is oriented towards N20°W. The orientations of drilling-induced fractures and breakouts may be interpreted for the in-situ stress direction over the logged interval. Drilling-induced tensile fractures, identified over the depth interval of 1969–1972 m, and borehole breakouts over the interval of 1953–1955 m in one well, suggest an orientation of maximum in-situ horizontal compressive stress (S_H) lies in the north-south direction. The azimuths of open natural fractures in the same well vary from north-south to N30°E. It is expected that the direction of fluid flow will be controlled by open natural fractures and therefore would be in a direction parallel to the S_H direction, which is orthogonal to the minimum horizontal stress (S_h) direction. The orientations observed are consistent with the present day S_H direction in the study area of Cambay basin.     

Disk luminosity and angular momentum for accreting,weak field neutron stars in the ‘Slow’ rotation approximation

For accretion on to neutron stars possessing weak surface magnetic fields and substantial rotation rates (corresponding to the secular instability limit), we calculate the disk and surface layer luminosities general relativistically using the Hartle & Thorne formalism, and illustrate these quantities for a set of representative neutron star equations of state. We also discuss the related problem of the angular momentum evolution of such neutron stars and give a quantitative estimate for this accretion driven change in angular momentum. Rotation always increases the disk luminosity and reduces the rate of angular momentum evolution. These effects have relevance for observations of low-mass X-ray binaries.     

Cyclonic microzonation

A procedure for cyclonic microzonation of coastal regions with the help of the cyclone track records is outlined using a sound method of statistical forecast and finding wind speed at a site with the help of standard wind field model. The procedure can be adopted for regions where directly measured wind speeds are scarce like, coastal regions of the developing and under developed countries. For the purpose of microzonation, the regions along with the available cyclone tracks are mapped using GIS. The area is then divided into a number of grids. The centre of the grid (site) is taken as the centre of the circle of influence. The cyclonic wind speeds at the site are estimated from the tracks falling within the influence circle. Distribution of the cyclonic wind speed at the site is then obtained from the estimated cyclonic wind speeds. Assuming the arrival of cyclone to be a Poisson process, a cyclone hazard curve, denoting the annual probability of exceedance versus cyclonic wind speed is determined. From the hazard curves drawn for different sites of the region, cyclonic microzonation map is prepared for different return periods of the cyclonic wind speed. The procedure is illustrated by applying it to microzone a very crucial coastal region of Andhra Pradesh in India, for which cyclone track records are available.     

Kinetics of oxytetracycline sorption on magnetite nanoparticles

Iron oxide nanoparticles (nano-Fe) have been widely used in environmental remediation, including that of emerging contaminants, such as antibiotics. Magnetite nanoparticles (nano-Fe₃O₄) have been reported to form on the outer surface of nano-Fe and have the potential to be a good sorbent for certain antibiotics. This study reports, for the first time, the kinetics and thermodynamics of adsorption of a common tetracycline group antibiotic, oxytetracycline (OTC), on nano-Fe₃O₄. Batch sorption kinetics were evaluated by varying initial OTC concentration (0.25–2 mM), nano-Fe₃O₄ concentration (2.5–20 g L^?1), pH (3.8–7.6), temperature (5, 15, 35 °C), and ionic strength (0.01–0.5 M KCl) to derive thermodynamic and kinetic constants. Results show that OTC sorption kinetics is rapid and increases with increasing temperature. The derived thermodynamic constants suggest a surface chemical-controlled reaction that proceeds via an associative mechanism. Results indicate the potential of developing a nano-magnetite-based remediation system for tetracycline group of antibiotics.     

The nature and engineering behavior of carbonate soils at Bombay High,India

Abstract

This paper presents the results of a laboratory investigation undertaken to study the nature of two submarine carbonate soils from Bombay High off the west coast of India, as well as to study the shear and plasticity behavior of their sand and silt‐clay fractions, respectively. Scanning electron micrographs reveal that the carbonate content in both soils is comprised primarily of nonskeletal particles of various types. X‐ray diffraction and infrared absorption analyses indicate that in one soil the carbonate fraction consists of calcite and aragonite minerals, whereas in the other soil dolomite is also present. The non‐carbonate fraction of both soils is comprised primarily of quartz and feldspar, and also some clay minerals. The nature of the carbonate fraction of the two soils indicates that they were formed by different depositional processes.

During drained triaxial shear the nonskeletal sand grains of both soils exhibit a lower degree of crushing when compared with that of the skeletal carbonate sands, and thus appear to be stronger foundation material.

Although the carbonate contents of the silt‐clay fractions of the two soils are similar, they exhibit markedly different plasticity characteristics . This is probably because of the microlevel cementation produced by carbonate material in one soil.

This study leads one to the conclusion that carbonate content alone should not be treated as a parameter which controls the engineering behavior of submarine soils; the nature and form of carbonate material must also be identified.     

Shear Behaviour of Loose and Compacted Pond Ash

Massive utilization of pond ash in earth works requires thorough understanding of its geotechnical characteristics, especially strength characteristics. Here in this paper, a detailed experimental study carried on the strength and other geotechnical characteristics of pond ash samples, collected from inflow and outflow points of two ash ponds in India, are presented. Strength characteristics were investigated using consolidated drained (CD) and undrained ( [`(\textCU)] \overline{\text{CU}} ) triaxial tests with pore water pressure measurements, conducted on loose and compacted specimens of pond ash samples under different confining pressures. Ash samples from inflow point exhibited behaviour similar to sandy soils in many respects. They exhibited higher strengths than reference material (Yamuna sand), though their specific gravity and compacted maximum dry densities are significantly lower than sands. Ash samples from outflow point exhibited significant differences in their properties and values, compared to samples from inflow point. Shear strength of the ash samples from outflow point are observed to be low, particularly in loose state where static liquefaction is observed.