Groundwater quality assessment for domestic uses in the micro- geomorphological units of Lagos, Nigeria

Abstract

This study focused on physic-chemical and trace metals concentrations in hand dug wells across four micro geomorphological units of Lagos Nigeria. Water samples were collected from 12 selected wells used for domestic purposes in the metropolis between November 2009 and March 2010. Four (4) parameters – pH, EC, DO and salinity were determined with portable pH/conductivity meters, handheld M90 Mettler Toledo AG DO meter and handheld Omega salinity meter respectively. The remaining seven (7) parameters - total dissolved solids (TDS), total hardness (TH), chloride (Cl^-), nitrate (NO₃^-), iron (Fe), manganese (Mn) and zinc (Zn) were determined using atomic spectrophotometer, gravimetric, chlorometric and titrimetric methods. The results reveal that pH levels ranged between 5.2 and 8.2 with mean of 6.4±0.90, EC between 34.0 and 340.0mg/l with mean of 177±121mg/l, DO between 1.7 and 4.0mg/l with mean of 2.6±0.7mg/l, TDS between 5 and 241mg/l with mean of 88.1±95mg/l, TH between 6.3 and 109mg/l with mean of 39.7±27.2mg/l, salinity between 17.0 and 497.0mg/l with mean of 111±168mg/l, Cl^- between 3.5 and 55mg/l with mean of 20±19.9 mg/l, NO₃^- between 7.7 and 62.0mg/l with mean of 26.1±19.6mg/l, Fe between 0.02 and 1.5mg/l with mean of 0.2±0.41mg/l, Mn between 0.02 and 0.2mg/l with mean of 0.1±0.05mg/l, and, Zn between 0.0 and 0.3mg/l with mean of 0.1±0.08mg/l. EC, TDS, TH, salinity, Cl^- and Zn concentrations in all sampled wells fall within the WHO recommended limits. NO₃^- and Fe concentrations ranged above WHO limits in some cases. The results suggest that the variation in concentrations could be attributed to the surrounding geomorphological units except heavy metals which are traced to leachates around landfill areas. Nevertheless, the results of concentration of the analyzed parameters, heavy metals in particular do not follow a significantly identified trend across the geomorphological units

Keywords: Groundwater, physic-chemical, trace metals, geomorphic units, Lagos