Abstract

Groundwater is an important freshwater resource in Tanzania. However, rapid urbanization, informal/unplanned settlements and agricultural intensification in major basins threaten its sustainability. Most groundwater aquifers in the country are not monitored or managed, thus exposing them to potential contamination and overexploitation. This paper is based on a research conducted in the months of February and March, 2014, to assess how hydrogeological parameters and human activities impact on groundwater resources in Hombolo catchment. Thirty water samples collected from boreholes and shallow wells in the catchment were found to have high nitrate concentrations of 51.35 and 37.91 mg/L, respectively. Nitrate concentration varied by land use types with agricultural areas being the largest contributor (exceeding 154 mg/L) while wells in residential areas had relatively low concentrations (about 2.97 mg/L). However, the nitrate results do not represent the whole year; it is limited to two (2) months of field study. Using DRASTIC overlay and index method, 37.5 and 6.6% of the catchment were classifed as moderate and high vulnerability, respectively. However, when DRASTIC governing equation was explicitly integrated with human activities rating, areas with high vulnerability increased from 6.6 to 17.5%. Increased human activities, changed groundwater vulnerability over time and moderate areas in 1987 had changed to high vulnerability by 2014. Integrating human activities in the methodology is more suitable for groundwater vulnerability assessment.

Key words: Groundwater contamination, risk assessment, vulnerability, human activities.