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This research is aimed at delineating the groundwater potential zones in Gombe and environs using Dar Zarrouk parameters. The study area is located within longitudes 11°7′0″E to 11°14′0″E, and latitudes 10°15′0″N to 10°21′0″N, it is basically underlain by basement Complex rocks represented by Diorite and Granites, and Cretaceous sedimentary rocks represented by Bima, Yolde, Fika and Gombe Formations. Thirty two (32) vertical electric soundings (VES) using Schlumberger array method with the aid of ABEM Signal Averaging System (SAS) Terrameter was used for the data acquisition. The result of the interpretation shows four to six geo-electric layers. The geo-electric section revealed the major aquifers to be confined and semi confined and consist of Medium grain sandstones, with varying thicknesses. The aquifer hydraulic characteristics indicated that the transverse resistance, ranges from 235.2Ωm 2 to 6317.87Ωm 2 with an average value of 1789.50Ωm 2 . The Longitudinal conductance, S, ranges from 0.1415Ωm to 31.933Ωm with an average of 2.002Ωm. The Hydraulic conductivity value range from 2.62m/day to 138.66 m/day with a mean value of 20.662 m/day. The transmissivity values obtained for the various layers range from 78.34 m 2 /day to 13284.02m 2 /day, with the average value been 893.57 m 2 /day. Four groundwater potential zones were delineated including medium grain sandstones, Sandstones, clayey sand and shaly sand.

The aim of the study is to assess the occurrence of fluoride in the groundwater of Kaltungo area and environs. Consumption of high fluoride waters clearly manifests in the majority inhabitant of the area in form of dental fluorosis especially in the majority of the populace. Thirty groundwater samples were collected from hand-dug wells and boreholes using standard method and were analyzed to determine the fluoride level. The results revealed that the Fluoride in the waters ranges from 0.8 to 1.94 mg/l with a mean value of 1.65 mg/l. No clear variations in fluoride content have been observed in both the borehole samples and those from the hand-dug wells. Ca-Mg-HCO 3 and Ca-Mg-Cl are the two major water types obtained in the area, which have a good association with fluoride. Negative correlation is observed between fluoride and temperature, fluoride and magnesium, fluoride and potassium and poor correlation is observed between fluoride and chloride, fluoride and nitrate, fluoride and phosphates which rules out the possibility of anthropogenic source of the fluoride in the waters. Positive correlation between fluoride and iron, indicates that the presence of fluoride in the water is as a result of dissolution of biotite within the host rock (Basalt).

Groundwater is the most essential natural resource, which forms the core of the ecological system and thus, become the major source of domestic supply, agricultural, industrial, recreational, as well as environmental activities (Kwami et al., 2019). Groundwater is that water found within the saturated voids beneath the ground (Abdulrahmanet al., 2017). The source of groundwater is chiefly from precipitating atmospheric moisture which has percolated down into the soil and subsoil layers. In the last few decades, there has been a tremendous increase in the demand for fresh water due to rapid population growth and the accelerated pace of industrialization. However, in developing countries, like Nigeria, human health is threatened by most of the agricultural activities particularly in relation to excessive fertilizers application and improper sanitary conditions. Also, the quality and availability of groundwater have been affected due to adverse effect of excessive groundwater withdrawal and improper waste management, especially in rapid developing cities (Ramakrishnaiah et al., 2009). Intensive irrigated agricultural discharges into the groundwater can led to considerable change in the groundwater quality. Therefore, once the groundwater is contaminated, its quality cannot be restored by stopping the pollutants from the sources. The ground water quality evaluation and determination for human consumption is essential for the wellbeing of the ever-increasing population (Ishaku, 2011).It therefore becomes imperative to regularly monitor the quality of groundwater and to device ways and means to protect it. Water quality index (WQI) is one of the most effective tools to communicate information on the quality of water to the concerned citizens and policy makers (Kwami et al., 2018). Therefore, becomes an important parameter for the assessment and management of groundwater. Water quality index is defined as a rating reflecting the composite influence of different water quality parameters on the overall quality of water (Tiwari and Manzoor, 1988, Ramakrishnaiah et al., 2009). Horten (1965) proposed the concept of WQI that represent gradation in water quality and calculated in such a way that presents the suitability of groundwater for human consumption. This study is aimed at discussing the application of water quality index (WQI) in the assessments of groundwater suitability for human consumption.