WATER QUALITY ASSESSMENT AND POLLUTION STATUS OF UPPER GANGA CANAL

Abstract

Availability of good quality water is an indispensable feature for irrigation to improve the quality of agriculture and crop production, as well as for livestock and human drinking purposes to prevent the diseases through water consumption. Undesirable changes in the physicochemical nature and the toxicity of heavy metals in available water can be dangerous, thereby making it unsuitable for domestic and agricultural uses. The Upper Ganga Canal (UGC), Roorkee is being polluted due to disposal of sewage, industrial waste and other human activities. Keeping this in mind, the present study has been carried out to assess the UGC water quality for irrigation, livestock drinking, human drinking, and numerical modelling of pollution dispersion. In this study, water samples were collected from 18 different sampling sites at monthly interval from November- 2014 to October- 2015. Several instruments and standard methods were employed for determination of the physicochemical parameters and trace metals in the UGC water. Further, the most important 15 physicochemical parameters (pH, EC, TDS, Ca2+, Mg2+, Na+, K+, HCO3-, CO32-, Cl-, SO42-, NO3–N, DO, COD and B), and 11 trace metals (Al, As, Cd, Cr, Co, Cu, Fe, Hg, Pb, Mn and Zn) were analyzed on seasonal time-scale. Numerous irrigation water quality metrics i.e. Sodium Adsorption Ratio (SAR), Residual Sodium Content (RSC), Residual Sodium Bicarbonate (RSBC), Sodium Soluble Percentage (SSP), Magnesium Adsorption Ratio (MR), Permeability Index (PI) and Kelley`s Index Ratio (KR) were studied and evaluated for suitability of UGC water. The arithmetic weightage based Water Quality Index (WQI) values were computed to evaluate the water quality for irrigation, livestock drinking, human drinking. Further, a three-dimensional geometry has been developed, from old canal bridge to Ganeshpur bridge, Roorkee, for numerical modelling of pollutant dispersion at five different locations by varying density and size of the solid particles. For irrigation, only the concentration of Mg2+ was higher than the prescribed standard range. On seasonal basis, Boron value was within the permissible limits at all sites, except at sites S4, S5 and S7 in summer, and at site S5 in winter. However, the other physicochemical parameters are within permissible limit at all sites of the UGC, Roorkee and hence, the UGC water is suitable for irrigation purpose. In case of toxic trace metals, concentrations of the Mn during winter, the Zn during winter as well as summer, and the Co during all three seasons were beyond the allowable limits for irrigation at only three sites. The water quality metrics namely SAR, SSP, EC and TDS were ‘excellent’; RSC and RSBC were ‘safe’, and KR was ‘good’ for irrigation. The WQI values of the UGC water ranged from 18.78 to 89.31 (mean of 45.56 and iv SD of 29.79) in winter; from 25.99 to 84.94 (mean of 53.84 and SD of 18.99) in summer; and from 15.58 to 57.76 (mean of 34.02 and SD value of 12.91) in monsoon seasons, revealing suitability of the UGC water for irrigation purpose. Furthermore, inter-relationship analysis depicted that the sensitivity of trace metals varies with the seasonal changes. High sensitivity amongst all metals was observed in monsoon season, followed by winter and summer seasons. For livestock drinking, all the physicochemical parameters considered in this study were within the permissible limits. Also, most of the toxic trace metals in the UGC water at all the sites, except at S4, S5 and S7, were within the permissible limits. The WQI values of the UGC water sites ranged from 22.79 to 190.46 (mean of 66.30 and SD of 55.37) in winter, from 36.12 to 170.52 (mean of 72.95 and SD of 45.77) in summer, and from 15.36 to 172.99 (mean of 62.17 and SD value of 49.39) in monsoon seasons. However, the WQI values were more than 100 for sites S4, S5 and S7 during all the seasons, whereas for other sites it was within permissible limit. Therefore, UGC water can be used for livestock drinking purpose. For human drinking, the physicochemical parameters viz., Ca, K, B, DO and COD were beyond the permissible limits. Most of the toxic trace metals in the UGC water have higher concentration compared to the authentic standards. The WQI values of the UGC water sites ranged from 104.64 to 1485.64 (mean of 443.48 and SD of 459.28) in winter; from 127.65 to 1518.1 (mean of 458.51 and SD of 463.52) in summer; and from 104.24 to 1484.66 (mean of 434.71 and SD value of 455.38) in monsoon seasons. Therefore, UGC water is not suitable for human drinking. Numerical modelling of the UGC water showed that the rate of sewage pollutant dispersion and mass fraction increases with high sewage inlet velocity. Result shows that the inlet of sewage pollutant in canal water leads to maximum change in concentration near the canal banks, and have minimal effect at the center. The mass fraction of sewage pollutant increased from 0.006 to 0.018 in flow time of 50 minutes, when velocity of sewage was increased from 0.2 m/s to 0.4 m/s. The study of solid particle insertion along with the sewage pollutant revealed that the solid particles of large size (diameter of the order of 80 μm to 150 μm) and high density have high affinity to get settle down at the canal base, whereas the particles of small size (below 25 μm diameter) and less density floats with the canal water and travel large distance to settle down. This study will explore the suitability of the UGC water considering physicochemical parameters and toxic trace metals, and provide numerical modelling framework for pollutant dispersion study which would be a value addition for water quality assessment.