Abstract
DRASTIC is a model that is commonly used to assess vulnerability to groundwater contamination at the landscape scale. When sparse data are available to populate the layers of
the model, it can be difcult to ascertain the true usefulness of the model produced map.
In this research, an alluvial aquifer in Kermanshah province of western Iran was mapped
using the generic DRASTIC model. The data available for populating the model layers
were generally sparse. The model was validated using a nitrate concentration map constructed from well water measurements within the DRASTIC map area. Based on the data
collected and analyzed, a range of values from 107 to 177 was found. Therefore, the fnal
vulnerability map was divided into only two classifcations, moderate and high, instead of
the normal fve classifcations typically used. The results showed that there was no signifcant relationship with nitrate concentration by statistical methods. However, the feld
conditions and the method used have good accuracy. Field evaluations showed that karst
water recharge acts as a factor in diluting nitrate concentrations. Evaluation of all fnal map
classifcation methods (generic DRASTIC, natural breaks (Jenks), equal intervals, quantile,
geometrical interval, and fuzzy classifers) showed that based on cross-validation, the most
consistent classifer is the generic DRASTIC based one with 62% and the quantile method
is in second place with 36%. Changing the weights and rates of layers to justify the model
within the measured nitrate concentrations does not show the inherent nature of the aquifer
to contamination. The results of this model emphasize the use of generic DRASTIC with
correct data and feld study before any optimization. In addition, if optimization is to be
performed, it is necessary to add a layer or layers that relate to those factors having the
greatest impact on aquifer pollution or dilution of the ionic content of groundwater in the
study area. Based on the results obtained from this research, it is concluded that the DRASTIC model can be used to produce a reliable result, useful for planning to reduce groundwater contamination potential, particularly in vulnerable areas.
