A Modified DRASTIC Approach to Shallow Groundwater Vulnerability in the West Lake Watershed in Hangzhou, China

The quality of shallow groundwater in the West Lake watershed was investigated from March to July 2000. Integrating with Blackland GRASS GIS system, the DRASTIC model was used to compile the groundwater vulnerability map. A land use factor was added to the DRASTIC model and the modified model (LDRASTIC) increased the accuracy of prediction from 26.9% to 51.3%. The vulnerability map showed that the lowly, moderately and highly susceptible area predicted occupied about 11.6%, 70.9% and 17.5% of the whole watershed, respectively. Compared with the observed values of nitrate and electric conductivity, the LDRASTIC index improved the Pearson correlation coefficients from -0.010 to 0.237 and 0.380 to 0.503;both the improved coefficients were significant at the 0.01 level. The modified DRASTIC analysis showed a great potential as a screening tool for policy decision-making in groundwater management.``