Groundwater Contamination Dynamics in Peri-Urban Nigeria: Insight from Septic Tank Proximity and Water Quality Index

This study examines the relationship between septic tank proximity and groundwater contamination in Aluu, a developing peri-urban community in Rivers State. Six water samples from boreholes were analyzed for physicochemical parameters (pH, total dissolved solids, alkalinity, and heavy metals: lead, cadmium, and chromium) and microbes (total coliform and E. coli). Bacteria indicator ratio and weighted arithmetic water quality index (WA-WQI) were employed to assess effluent infiltration and suitability for human consumption. Results revealed that 67% of sampled boreholes failed to meet the minimum 20-meter separation distance from septic tanks as set by the Nigerian Industrial Standard (NIS) guidelines. While heavy metals and total dissolved solids (TDS) remained within permissible standards, all samples exceeded Nigerian Standard for Drinking Water Quality (NSDWQ) limits for total coliform and E. coli. Biochemical oxygen demand (BOD) exceeded guidelines in some samples, suggesting organic pollution. WA-WQI scores classified samples as very poor (76.32), poor (51.25 – 68.03) and good (48.58). Cd and BOD were identified as the major chemical pollutants with Cd and BOD having contributory shares of 41.03 to 59.05 % and 34 to 43.76 % respectively. All other chemical parameters had contributory share of 6.94 to 23.14%. The total coliform to E. coli ratio for all samples was low (2 to 5.7:1) confirming septic effluent infiltration. Correlation analysis did not directly link proximity as the major factor responsible for effluent infiltration. The study recommends groundwater evaluation in peri-urban areas, and treatment of all water samples before consumption.