Assessment of Groundwater Quality Using GIS - A Case Study of the Churu District of Rajasthan - page 04

Calculation of the WQI

Case I:

The parameter's standard range (Acceptable limit by IS/WHO) is given in Table 2 and it is used to calculate the WQI for the study area.

8 physico-chemical parameters consisting of Temperature, Colour, Turbidity, pH, Nitrate as NO3-, Nitrite as NO2-, Fluoride as F-, and TDS were considered in the calculation of the WQI. Water Quality Index (WQI) calculation involves three stages. The equations used in it are mentioned above from B1 to B3. The spatial distribution of the quality index for both monsoons is shown in Figure 3a and 3b respectively.

Case II:

The weight of 1-5 depending on the values of the parameters are given. If the difference between the value and the acceptable value range is low, then the weight of 1 is given and if the difference is high than the weight is 5. The Weight (w) has been assigned according to its concentration and relative importance in the overall quality of water for drinking purposes (Table 2). The relative weight has also been calculated and given in Table 3.

The following 8 physico-chemical parameters were considered in the calculation of WQI: Temperature, Colour, Turbidity, pH, Nitrate as NO3-, Nitrite as NO2-, Fluoride as F-, and TDS. In it, a few of the locations had negative values of WQI which were treated as zero as no value is below zero in any of the quality indexes.

A set of equations from A1 to A5 were used to calculate the WQI. Figures 5a and 5b show the spatial distribution of the water quality indexes in the study area for both monsoons.

 

Results and Discussion

Table 1 shows the range of various parameters in the study area. The main data indicates the average values of pH as 7.4 and 7.5 for Pre Monsoon and Post Monsoon which indicates a basic (alkaline) condition of the groundwater samples. TDS indicates the different types of minerals present the in water, and from this study, it indicates an average value of 2196.52 mg/l in pre monsoon and 2077.55 mg/l in post monsoon. The mean value of TDS is above the recommended limit of IS: 10500. the anions reveal average values of Nitrate as NO3- (151.15 mg/l in pre monsoon and 175.57 mg/l in post monsoon), Nitrite as NO2- (0.02 mg/l in pre monsoon and 0.01 in post monsoon), Fluoride as F- (0.91 mg/l in pre monsoon and 1.45 mg/l in post monsoon duration) respectively. All the mean concentrations of the parameters are above IS: 10500 recommended limits except Colour and Turbidity. The mean values of anions reveal an order of abundance as NO3- > F- > NO2-.

 

Tab02-03

 

Fig03a
Figure 3a: Spatial Distribution of Water Quality Index (case I) in the study area for Pre Monsoon duration.

 

Fig03b
Figure 3b: Spatial Distribution of Water Quality Index (case I) in the study area for Post Monsoon duration.

 

Fig04
Figure 4: Water Quality Index (case I) of groundwater samples location for Pre & Post Monsoon duration.

 

Tab04