Spatial Analysis to Evaluate Groundwater Vulnerability to Contamination of Unconfined Aquifer in Semarang Lowland Area Using DRASTIC Method

Abstract

The increasing population up to 1.67% per year in the urban coastal city such as Semarang affects enormous stress on the natural resources - groundwater, in particular. To assess groundwater vulnerability to contamination the DRASTIC method was applied. DRASTIC was one method in compiling a zone of groundwater vulnerability to contamination. This method required seven parameters, namely D (water table depth), R (recharge zone), A (media aquifer), S (soil media), T (topography), I (vadose zone), and C (hydraulic conductivity). Processing of each parameter to calculate the Drastic Index (DI) was developed by using spatial analysis in ArcGIS. The results conduct there is three-level of groundwater vulnerability to contamination namely low, medium, and high. The low vulnerability has the number of DI of 61 to 100, while the DI of moderate is around 101-140. The high level is represented by 141-180 of DI. The low level is distributed in some areas in the south of Semarang, while the medium is dominated in the Ngaliyan area, Gajahmungkur, Semarang Selatan, also found in Tugu, Semarang Barat, Candisari, and some areas in the Semarang Tengah. Indeed, the high level is found in the plains areas in the northern, in the western, and eastern part of Semarang.