Chandrashekar, Hanumanthaiah 
  
TABLE: 6 
Impact of Vadose Zone 
  
  
  
  
  
  
  
  
  
  
Ranges Ratings 
Granetic Gneiss S 
Weathered Granetic Gneiss 6 
Fractured Granetic Gneiss 7 
Weathered Fractured 8 
Granetic Gneiss 
Valley Fills, Recent Sand Deposits 9 
WEIGHT:5 
TABLE :7 
Hydraulic Conductivity of Aquifer 
20-40 
60-80 
80-100 
Weight: 3 
  
USE OF G.LS. IN ARIVING AT DRASTIC INDEX: 
DRASTIC parameter layers were put as polygon coverages. THE G.LS. approach provides the decision-makers 
powerful tools for collecting, storing, retrieving, analyzing and displaying the parameter layers of data. The 
assigning weightages for DRASTIC parameter values in the accompanying text files is done. Finally the range of 
each DRASTIC parameter is multiplied with weights and a layer by addition resulted in a final number called 
DRASTIC index. DRASTIC INDEX ranges were ranged from less than 110 as first category up to seventh category 
which is having DRASTIC INDEX greater than 160. Thus pollution potential map with minute grid obtained. 
The water quality parameters like Py, TDS, EC, HCO,. C1. SO,, Ca, Mg,Na, and SAR value for twenty two 
locations in Anekal taluk is assessed in laboratory. The water quality assessment is made for monsoon and non- 
mansoon. These are compared with the standard values and DRASTIC Indices. The DRASTIC Indices ranges are 
future classified as very high, moderate, low, and low ground water pollution vulnerability. 
«DRASTIC INDEX MAP" or *POLLUTION POTENTIAL MAP" prepared using G.LS. is compared with the 
manually prepared pollution potential map. The result show that variation between Drastic Index Map prepared 
using G.LS. and Drastic Index Map prepared manually is quite small. 
Assuming non-linearity between DRASTIC indices and water quality parameters, spearmans rank correlation co- 
efficient in calculated (Ref. Table9). The spearman rank correlation co-efficient lying between 0.85-0.90 show that 
water quality parameters and DRASTIC indices are positively correlated. 
The pollution potential map or D.I map so prepared helps in classifying areas into different vulnerability classes. 
This classification helps in identifying the areas and villages, which are more vulnerable to ground water pollution. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 261