Theme - Modeling
A COMPUTER PROGRAM FOR WATER QUALITY STUDIES
S. Chidambaram1, AL. Ramanathan2, K. Srinivasamoorthy1,
P. Ananadhan1 and S. Vasudevan1
1Department of Geology, Annamalai University, Chidambaram
2School of Environmental Sciences, JNU, New Delhi
The chemical constituents present in the water determine the quality. The water quality studies have become essential to delineate the utility criteria. The study on the quality needs certain constituents like major cations and anions. Some of the parameters like Sodium Absorption ratio, Hardness, Corrosivity index, sodium percentage, index to the base exchange, permeability index, etc., and certain ionic ratios like Na/Ca, Cl/HCO3, Na/Cl, etc., will help to determine certain process like nature of weathering and saltwater intrusion studies. Moreover the classification of water using the standards available like. Wilcox classification (EC), Eaton’s (Na%), Richards (SAR), USGS hardness classification, Styfzands classification, chemical facies and Schollers water type. It becomes a tedious and time-consuming process to calculate all these parameters. So in order to over come this difficulty a computer program was made in C++ using turbo C compiler. The data input requires ppm values of ions like Ca, Mg, Na, K, Cl, HCO3, SO4, H4SiO4, PO4, NO3, F, and parameters like pH, EC and TDS. The program first converts these data fed to epm values and checks for the ionic balance. Large set of data can be fed in and the individual ionic ratios and chemical parameters of the sample can be obtained and also it groups the sample fed into against the above said standard classifications. One of the preliminary and essential need of water is for agriculture. The USSL classification has been used for several years for the same and the plot has also been included in the program along with Doneen’s permeability index plot, Johnson’s water facies plot, Gibbs water chemistry plot and certain standard graphs to establish the linear relationship of the ions. This program substitutes the manual calculation and immediate grouping of the entire data set.
AN APPROACH TO SELECT, BUILD AND DECIDE THE GROUND WATER MODEL
Deeksha and H.S. Bhatia
Civil engineering, Delhi College of Engineering, New Delhi - 110 042
Ground water flow and transport modeling can be useful in making informed and defensible remedial decision. This paper describes method for selecting ground water flow and contaminant transport models. This selection process starts with conceptualisation , which takes in account modeling objectives , environmental characteristic of the site and the phase of remedial process . Parameter estimation describes the various parameters of ground water flow and contaminant transport, which is followed by review and evaluation process that includes calibration and validation mainly done for screening the model. The best suited model that meet site specific modeling are finally used.
Water both groundwater and surface water is the most vital resource, which is contributing a major share in meeting the requirements of domestic, industrial and agricultural needs. Ramanathapuram coast is a semi-arid region, which receives a annual average rainfall of 980 mm. The Northeast monsoon contributes 70 % of rainfall. Nearly 900 naturally formed rainfed tanks in geological past of the study area holds the rainwater during the monsoon and for a short while in the post monsoon too. Twenty-eight samples have been collected during monsoon period of year 2000 from the surface tanks of the study area and analyzed. With the analyzed results, the surface water has been classified using HYCH program. The following thematic maps have been prepared Viz. Total Dissolved Solids, Salinity and Sodium Hazard, Hardness, Chloride / Bi-carbonate ratio and Water Classification using GIS. From these, it is inferred that water resources are affected by the saline water encroachment along the northeastern and Southern coastal regions. Interior parts fall under fresh water having some intermediate water quality. C5S4 type water, which type water having very high Sodium and high Salinity is observed along the above mentioned coastal regions. Similarly brackish salt and permanent hard water have been identified along the same coastal locations. Groundwater is being pumped near Uppur and Valinokkam (Loc.s 9 & 26) for the saltpans and these development activities may enhance the salinity water encroachment of this area.
POTENTIAL OF MEMBRANE SEPARATION TECHNOLOGY FOR FLUORIDE REMOVAL FROM UNDERGROUND WATER
Meenakshi Pahwa and R.C. Maheshwari
Centre for Rural Development and Technology
Indian Institute of Technology, New Delhi
Membrane technology has been established as a proven technology for desalination of seawater to provide drinking water in coastal areas. Yet little attention has been given to explore its potential for treatment of groundwater having some inorganic pollutants. In this study, various membranes were tested to select a suitable membrane for this purpose. Initially, experiments were done with nanofiltration membrane and was observed that all the monovalent ions are rejected less as compared to bivalent ions. But fluoride shows exceptional behavior. This may be due to low solubility product of calcium fluoride. Thus fluoride may precipitate out in hard water and so rejected better. But, the problem associated with nanofiltration membranes is the very low recovery.
So, to overcome this problem hyperfiltration membrane was used and experiments were done at varying range of operating pressure, feed flow rate, pH of feed water, temp. of feed water and concentration of feed water, because the membrane separation efficiency depends upon operating conditions and chemical composition of feed water. Thus, optimum conditions for maximum efficiency were selected and the water samples collected from rural areas of district Gurgaon were treated at the optimum operating conditions. The results showed that at high pressure, hyperfiltration membrane rejects almost the all the ions upto 99%, thus leading to need of remineralization and cost is also high due to high pressure requirements. But at low pressure, rejection is in the range of 88% to 93%, which allows some essential minerals to remain in water and also the cost of process is reduced.
ASSESSMENT OF GROUNDWATER POLLUTION THROUGH MASS TRANSPORT MODELING
V.V.S. Gurunadha Rao
National Geophysical Research Institute, Hyderabad - 500 007
Effective management of groundwater requires the ability to predict subsurface flow and transport of solutes, and the response of fluid and solute flux to changes in natural and man made stresses. One popular tool evolved during last three decades is the deterministic, distributed parameter, computer simulation model for analyzing flow and solute transport in groundwater systems. Recently, the visual MODFLOW and MT3D (Mass transport in three dimensions) models have become popular for groundwater flow and mass transport simulation respectively, with the advantages of pre-processing and post-processing facilities attached to the basic modeling software. The number and types of equations to be solved in flow and mass transport modeling are determined by the concepts of the dominant governing processes. The coefficients of the equations are the parameters that are measures of the properties, boundaries, and stresses of the system; dependent variables of the equation are the measures of the state of the system. These are mathematically determined by the solution of the governing equations. Two case studies have been presented to illustrate the application of mass transport modeling for assessment of groundwater contamination.
First case study deals with likely groundwater contamination from red mud stacking from a proposed allumina plant near Doragarha, Rayagada district, Orissa. The allumina plant produces fine red-mud residue and the liquor contains Sodium Carbonate (Na2CO3). The concentration of Na2CO3 may be as high as 3500 mg/l. The red mud slurry is pumped to the disposal area where it is spread in layers known as red mud stacking layers. The water drained from the red mud stacking area is collected in two ponds for recycling. Seepage from tanks may carry the effluent to the groundwater regime. The red mud ponds are located in a Khondalitic terrane of Eastern Ghats. Geophysical surveys have been carried out to understand aquifer geometry, identify significant structural features controlling the groundwater flow. A groundwater flow and mass transport model was constructed to analyze likely migration of contaminants from the red mud ponds for 50 years. The predictions showed that the contaminants might take more than 50 years to reach the Baraha nadi, a perennial stream in the area.
Mass transport modeling in the Bolaram Industrial Development area near Hyderabad illustrates the study of groundwater contamination due to discharge of effluents from the pharmaceutical and bulk drug industries in effluent settlement tanks/ponds and stream channels during last 20 years. The seepage from the beds of these tanks/ponds and along the Pamula vagu stream acted as a diffuse source of contamination. The mass transport model has been calibrated for a period of 20 years and later used for assessment of contaminant migration for next 20 years. The contaminant migration is restricted to a narrow patch with elevated TDS concentrations due to low permeability of the aquifer in the granitic terrain.
TRANSPORT OF POLLUTANTS IN OPEN CHANNEL WITH SHORT WAVES
Sandeep Patil and A. K. Rastogi
Dept of Civil Engg., IIT, Bombay - 400 076
Assessment of the surface water quality in open channels is of greater importance today due to the increasing load of pollutants that is diverted to these systems. Computation of dispersion coefficient plays an important role for an adequate prediction of the pollutants movement in open channels. Apart from the advection dispersion, short period wave on the water surface also contribute to this process, which exists on any water body open to the atmosphere. Effect of ambient wavy environment on the transport of pollutants through open channel is examined in the present study. Equation for the short period surface wave is coupled with the one dimensional dispersion equation to get an accurate and applicable solution of concentration distribution of pollutants. The existing equation of longitudinal dispersion coefficient is modified to consider the short period wave. Initially, experiments were conducted involving non wavy flow in open channel and values of the longitudinal dispersion coefficient were found out by the method of least square. The observed values of longitudinal dispersion coefficient matched closely with the values predicted by the empirical law given by Won Seo II (1998). After verifying the model for non wavy environment short waves of various amplitude and period were generated on the flow with the help of wave generator. Experiments were conducted to note the spread of pollutant values, which were substituted in the analytical solutions to compute the values of wave induced longitudinal dispersion coefficient (WILDC). For non wavy cases, it is well known that the longitudinal dispersion coefficient depends on aspect ratio and friction factor. In case of wavy environment, it was decided to segregate the effect of waves from these parameters. Dimensional analysis was conducted using Buckingham’s P theorem and a new parameter ( a/TU* ) named as wave parameter was found out. The analysis shows that WILDC depends on three parameters instead of two. Outlier in the scatter diagram were detected by Grubb’s analysis and discarded. Uncertainty analysis was conducted and confidence interval was calculated which is stated as predicted data ± 0.092043. This is the range in which true value of dimensionless WILDC is lying with high probability. Expression for WILDC was analytically developed by using two-dimensional depth averaged mass transport equation. Longitudinal dispersion coefficient was integrated over depth as well as one wave period for practical consideration. Equation of Won Seo II was modified for wavy environment by adding local depth averaged velocity due to wave in the flow velocity and the vertical water surface displacement in the mean water depth. The equation is then integrated over a wave period by gauss quadrature method to get the final model of WILDC. The model shows that WILDC remains independent of longitudinal distance. It was observed that negative horizontal vector component of orbital velocity due to wave is the governing factor which decided the value of wave induced longitudinal dispersion coefficient. More the magnitude of negative component, more the churning action, which further increases mixing of pollutants and therefore increases the mixing coefficient. Sensitivity analysis suggested that growth in the wave amplitude and wave period increases the magnitude of longitudinal dispersion coefficient. But the effect of amplitude was found to be more intense than wave period. Further, as depth of flow to wave length ratio increases, effect of wave on the mixing reduces. The concentration verses time curves were plotted which shows that the maximum percentage increase in the concentration occurs at a point of inflection attributed to the wave superposition. As particle traveling under the wave follows orbital motion, superposition of wave increases the longitudinal dispersion coefficient. The study suggests that the concentration distribution of pollutants calculated under wavy environment provided more correct and applicable solution to the real phenomena at the river sites.
GIS BASED AUTOCORRELATION ANALYSIS OF GEOCHEMICAL SPECIES PRESENT IN THE GROUNDWATER OF MEHSANA DISTRICT
S. D. Dhiman1 and Ashok K. Keshari2
1 Department of Civil Engineering, Birla Vishvakarma Mahavidyalaya, Vallabh Vidyanagar, 388120. 2Department of Civil Engineering, Indian Institute of Technology, Delhi, New Delhi - 110016
A Geographic Information System (GIS) can be used as an effective tool to manage environmental, climatic, and hydrologic data to support decision making and meet regulatory requirements. GIS based autocorrelation is a statistical technique by which the correlation between pixel values of raster map and pixel values of same raster map with different shifts (lags), k, in horizontal or vertical direction are generated. In this paper, the GIS based autocorrelation analysis is performed for a study area located in the Mehsana district of Gujarat State. In this particular study, the raster-based maps obtained for the geochemical species present in groundwater are used for autocorrelation analysis. The geochemical species considered for analysis are calcium, magnesium, potassium, sodium, chloride, fluoride, sulfate, nitrate, alkalinity, and pH along with other parameters like electrical conductivity and total hardness. The spatial dependence of a geochemical species present in the groundwater is investigated at 5% significance level. The autocorrelation coefficients (rk,) for each of the geochemical species in horizontal and vertical direction for the rasterized maps are computed at different shifts, and the horizontal and vertical correlograms for these geochemical species are obtained for the area under consideration. The upper and lower tolerance limits for horizontal correlogram at 5% significance level (rk, ¼ k £ 749) are 0.07 and -0.073, respectively. Results reveal that horizontal correlograms for calcium, chloride, nitrate, sulfate, fluoride and electrical conductivity (EC) have all the autocorrelation coefficients falling outside the tolerance band. A very small number of autocorrelation coefficients for sodium, magnesium, potassium, total hardness, bicarbonate and pH are inside the tolerance band. It is thus evident that the geochemical data analyzed for pixels in horizontal direction are not independent. In case of the vertical correlogram for calcium, fluoride, pH, bicarbonate and magnesium, all the autocorrelation coefficients fall outside the tolerance band. However for EC, nitrate, chloride, potassium, sulfate, sodium and total hardness, very few autocorrelation coefficients fall inside the tolerance band limits (rk, ¼ k £ 635) of 0.076 and -0.079. This signifies that the pixels of geochemical species analyzed in vertical direction are also not independent. Such studies on testing the hypothesis of the spatial dependence of geochemical species help in understanding the significance of the geochemical reactions controlling the variability of individual species concentration within the groundwater regimes.