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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.

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Concentration of heavy metals from surface and groundwater within the communities were determined in order to assess the health risks linked to the use/consumption of same. Furthermore, the cancer risk for adults in surface water revealed medium to high cancer risk for arsenic (As); low to medium cancer risk for cadmium (Cd) and very high cancer risk for chromium (Cr). In addition, the cancer risk for adults in groundwater is as follows: high cancer risk for As; low cancer risk for Cd and very high cancer risk for Cr while that for children is very high cancer risk for As and Cr and then low cancer risk for Cd. The findings from this research confirm that the inhabitants within the study area are at direct health risk (carcinogenic and non-carcinogenic) due to the alternate use of surface and groundwater without any form of treatment.

Geochemical evaluation of the Gongila Formation of Bornu (Chad) Basin indicated mineralogical compositions of quartz, feldspar, anatase, gypsum, smectite and kaolinite from XRD analysis. Corresponding major oxides from XRF analysis indicated the dominance of SiO2 with an average of 54.91 wt % followed by Al2O3 with 15.92 wt %. CaO, NaO, K2O, MgO, MnO, Fe2O3 TiO2 and P2O5 occurred with average compositions of 1.87%, 1.02%, 2.15%, 1.17%, 0.06%, 3.04%, 0.03% and 1.52 % respectively. Alteration indexes derivations from these oxides consisting of Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA) and Chemical Index of Weathering (CIW) accounted for a dominantly moderate weathering condition for the formation. Discriminant plots of Fe2O3+MgO versus TiO2 indicated a tectonically passive source area composed of generally intermediate igneous rocks, affirmed by Al2O3 versus TiO2 bivariate model with skewed plot along the granite line. The dominance of smectite suggests prevalence of arid to semi-arid paleoclimatic conditions during the deposition of shales of the Gongila Formation. Intermittent phases of superposed tropical climate are also depicted by the subordinate kaolinite mineralization.