Assessment of Shallow Aquifers Contamination by Failure of on-Site Sewage Disposal System in Ughelli, Western Niger Delta, Nigeria

Abstract

Hydrochemical quality of shallow groundwater aquifers was investigated to assess the potential of contamination by on-site sewage disposal systems in Ughelli. The results are; pH(5.47 – 7.45 ), Ec (105-483.2µscm), TDS( 58.95-294.7mg/l), Na⁺(1.8-10.95mg/l ), K⁺(2.64-9.87mg/l ), Mg²⁺( 2.40-9.89mg/l), Ca²⁺(3.01-14.90mg/l) and Fe²⁺ ( 0.02-0.87mg/l). Others include NO₃ (0.04-31.24mg/l), NH₃⁺ (0.015-6.98 mg/l), Cl^- (8.5 - 104mg/l), SO₄^-(2.24-45.75mg/l), PO₄^-(0.21-2.25mg/l). The quality of most groundwater samples from shallow aquifers falls within the tolerance limits stipulated by the WHO and NSDWQ. However, some groundwater samples revealed the presence of high microbial population including total coliform bacteria count (1.78 – 25MNP/100ml) and Escherichia coli (1.35-9.66 MNP/100ml) above the WHO and NSDWQ standards.  Interaction between on-site sewage disposal systems and shallow groundwater aquifers was established  by the presence of microbial population, high concentration of NH₃⁺ and slightly elevated concentration  of NO₃, electrical conductivity and TDS in some the groundwater samples. The extent of contamination of groundwater is strongly influenced by depth of the aquifers, high recharge rate during the wet seasons and availability of permeable soil beneath on-site sewage disposal systems. Consequently the paper recommends that groundwater should be sourced from deeper aquifers and those sourced from shallow aquifer in the area should be disinfected before being used.

Key words; Groundwater, aquifer, coliform, contamination, on-site disposal systems, WHO and NSDWQ