GROUNDWATER CHEMISTRY AND MODELING OF AQUIFER DEPTH AROUND UBURU-OKPOSI SALT LAKES, SOUTH EASTERN NIGERIA
The study area comprised Uburu and Okposi towns in Ohazara Local Government Area, Ebonyi state and it lies between latitudes 6000’N and 6005’N, and longitudes 7044’E and 7050’E. The area belongs to the saline hydrogeological groundwater basin of Albian Asu River Group in Cross River Basin. Three major outcrops of saline groundwater in the study area are: Umuchime- Uburu lake, Ivu-Ezizo and Amaechi-Okposi lakes. The saline lakes support long production of salts by rural women via local means. 20 water samples from the lakes, dug-wells and boreholes were analyzed to determine the hydrogeochemical constituents of the area. Values of total dissolved solids (TDS) in the samples range between 130 and 256,100mg/l. Calcium(Ca2+), magnesium (Mg2+) and sodium (Na2+) show significant concentrations of cations between 6 and 1440mg/l, 2 and 245mg/l and, 7 and 1231mg/l respectively. Chloride is the most dominant anion and it ranges between 1000 and 1,153640mg/l. Total prdissolved solids (TDS), chloride (Cl-) and calcium (Ca2+) concentrations are observed to be above objectionable limits for drinking water in the area. The chemical constituents revealed two saline groundwater types in the area; Ca-Cl and Mg-Cl waters. The Ca2+ and Mg2+ constituents generated hard water in the study area. The calculated sodium absorption ratio (SAR) indicated depletion of sodium in the water and, as a result, the saline groundwaters are suitable for irrigation. Vertical Electrical Soundings revealed that the saline groundwaters with low resistivities are in the less permeable medium like clay, plastic shale and siltstone units. The best aquifers observed are the permeable sandstone units at the depth of 20m and fractured shale at 53m depth.