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Chandrashekar, Hanumanthaiah 
  
plane country. The western portion of Taluk is jungly and marketed by continues hills. The atmosphere is neither 
very humid nor dry. The Annual precipitation of this region is 890mm. 
Anekal Taluk has a typical hydrogeolocic setting. The entire Taluk comprise of mainly Granitic gneiss belonging to 
pre-Cambrian age. The granetic gneiss is exposed as a continuous chain of mounds raising from 300 to 500 feet 
above ground level. The depth of weathering is gentle. The central and eastern portions of taluk show maximum 
thickness of weathered mantle. 
The population mainly depends on agriculture for their subsistence. The farming is mainly dry farming, as Taluk has 
not got any big rivers. Irrigation is mainly carried out by means of tanks and wells. The principle dry crops are ragi 
and gram. The wet crops consist of paddy, sugarcane and jowar. In addition to other crops arreca, betlevine, 
coconut, grapes, banana sugarcane, ground nut, vegetables etc., are also raised to some extent mulberry cultivation is 
also seen here and these. 
DRASTIC METHDOLOGY: 
DRASTIC - DRASTIC is a ground water pollution vulnerability assessment spatial deterministic model. 
DRASTIC uses a set if seven hydrogeologic key parameters to classify the vulnerability or pollution potential of an 
aquifer. The parameters are weighed with respect to their relative importance to the pollution potential of the 
aquifer. The DRASTIC parameters are 
The Impact of vadose zone 
€ The Depth to ground water 
€ The Recharge due to rainfall 
9 The Aquifer media 
® The Soil media 
€ The Topography 
® 
® 
The hydraulic conductivity 
DRASTIC INDEX (DI) = Dg Dy * Rag Rw +Ar Aw + Sp Sy *Tg Tw +Ir Iw + Cr Cv 
R refers to rating of the parameter ranges and W refers to the weighting of the parameter. Rating varying from 1 to 
10, are intended to reflect the relative significance of classes with in each factor. The weightages and rating for 
various DRASTIC parameters is given in Table (1 to 7) 
Depth to water is an important primary data, which determines the depth of material through which a contaminant 
must travel before reaching the Aquifer. The published reports of department of mines and geology are used for 
finding depth to water in the study area. Recharge is defined as the total quantity of water, which is applied on the 
ground surface. Recharged water is the principle vehicle for leaching and transporting solid and liquid contaminants 
to water table. The rainfall data of fixed rain gauge stations with sixteen years of observations has used. The 
recharge value polygons are obtained using revised norms of ground water estimation committee report. Aquifer 
media refers to the consolidated or unconsolidated rock, which serves as storage of water. In preparation of 
polygonal unit of aquifer media satellite remote sensing derived hydrogeomorphological maps and geological maps 
are used. The soil map from NBLUSS centre Bangalore was enlarged to 1:50,000 scale the soil units represented on 
maps are suitably combined into various textural unit polygons representing varied ability of a contaminant to move 
vertically into vadose zone. Topography refers to Slope and slope variability of the land surface. The slope map is 
derived using SOI top sheets. The impact vadose zone in complex phenomena combining aquifer media and 
topography characteristics. Hydraulic conductivity refers to the ability of the aquifer material to transmit water. The 
hydraulic conductivity values are calculated after calculating transmistivity from pumping test data. The weightages 
are assigned using, US EPA (works of Aller) for all the DRASTIC parameters. 
Suitable modification are done in assigning ranges depending on the parameter values in hydrogeologic setting for 
Anekal Taluk. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 259