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  • Modelling Groundwater Vulnerability using the DRASTIC model and GIS

    Methods Results & Discussion

    Ivana Baboolal and Clément Pont, GPHY 346: Environmental Modeling, 2013.

    Groundwater is one of Canada’s most important natural resources, providing water for approximately 25% of the population, to cater to their everyday needs [1]. The issue of protection of groundwater as a vital resource has, as of late, come to increased public awareness across the country, and in particular regions where signi�cant risks to it have been identi�ed. One such province is Alberta, where extensive exploitation of oil and gas has led to concerns of groundwater pollution in a number of communities. Groundwater vulnerability mapping can be used to e�ectively quantify the risk of contamination, leading to e�ective infrastructure planning and contamination mitigation strategies. This can be done using the DRASTIC model, proposed by the United States Environmental Protection Agency (EPA).

    DRASTIC is an acronym, representing Depth to Water, Net Recharge, Aquifer Media, Soil Type, Topography, Impact of Vadose Zone and Hydraulic Conductivity. Each of these parame- ters assesses the hydrologic capability of an aquifer to become contaminated. In the GIS environment, these are ranked and weighted in order to produce a groundwater susceptibility map, using the equation and weightings shown below.

    Model Used

    Data Pre-Processing

    (DR×DW) + (RR×RW) + (AR×AW) + (SR×SW) + (TR×TW ) + (IR×IW) + (CR×CW)

    Data used in this model were all acquired from government agencies and included data for precipitation, groundwater, rivers, lakes, bedrock and sur�- cial geology, sediment thic- kness, bedrock topography and the digital elevation model.

    Parameter Weight Depth to Water 5 Net Recharge 4 Aquifer Media 3 Soil Type 2 Topography 1 Impact of Vadose Zone 5 Hydraulic Conductivity 3

    Values for hydraulic conductivity and estimates for groundwater recharge in Alberta were acquired. These data were all processed in the GIS environment to produce the layers required for assessment in the DRASTIC model. These were then combined using the DRASTIC weightings to pro- duce the map of groundwater susceptibility in southern Alberta.

    The groundwater susceptibility map shows that there is a generally low risk of groundwater contamination in the study area. Changes in the DRASTIC index values were due primarily to changes in depth to groundwater, as this had the heaviest weighting of the DRASTIC parameters.


    Fig. 1: Di�erent layers and weightings used in the DRASTIC Model

    Table 1: Description of the DRASTIC parameters

    The DRASTIC model can be used to produce a map which details the vulnerability of groundwater in a region based on seven hydrological factors. Using GIS techniques, this model was performed to assess groundwater vulnerability in southern Alberta, and proved that there is generally low groundwater susceptibility in the region. Validation with published maps indicated that estimates from this model may prove to have values lower than expected, however trends in the models show good consistency. Based on the produced map, e�ective strategies can be implemented whereby regions showing high risk can be further diminished.

    In comparing the results obtained to a published groundwater susceptibility map in the Edmonton-Calgary corridor by the Alberta Geological Survey, similarities were noted however it is notable that the susceptibility was generally higher than the results obtained by this study. This could be due to variation in scale of the data used for interpolation as well as variation in the parameter rankings. Overall, the results of this study are thought to provide a good measure of groundwater susceptibility in southern Alberta.

    Figure 2: Groundwater suscep- tibility map of southern Alberta

    using the DRASTIC model

    Figure 3: DRASTIC groundwater susceptibi- lity map of the Edmonton - Calgary corridor, pro- duced by the Alberta Geo- logical Survey

    Environment Canada, «Groundwater» 13 September 2013. Available at: