NITRATE CONTAMINATION IN GROUNDWATER AROUND KEFFI TOWN, NORTHCENTRAL NIGERIA

Ten (10) vertical electrical soundings (VES) were carried out in the study area, the field data obtained were then interpreted using partial curve matching and a 1-D inversion algorithm. Resistivity results indicate the presence of top soil (<300 ohm-m), weathered basement (100 to 150 ohm-m) and fractured basement (<3000 ohm-m). The thickness of the topsoil is generally less than 2m while the weathered basement varies from 5m to 30m. Fifteen (15) groundwater samples were collected from different locations across the Keffi area and analysed for their NO3-N concentration. Groundwater sampling were restricted to well-covered shallow hand-dug wells (SHW), medium depth hand pumps (MHP) and motorised boreholes (DMBH). In all the groundwater samples analysed, 10.5% of them exhibited NO3-N contents higher than 0.03mgL-1 and 65% of the samples collected from the agricultural fields contained NO3-N higher than 0.03mgL-1 in contrast to 15% of samples from residential areas. Results also revealed an inverse relationship between the NO3-N concentrations and the depth of the sampling aquifers (SHW>MHP>DMBH). Most of the analysed samples contained NO3-N load less than the fixed threshold limit by WHO (2006) for drinking purposes of below 10mgL-1, thus, rendering the waters safe for drinking purposes.