Assessing Groundwater Quality for Irrigation and Drinking in Seven Villages along Mara River - Tanzania

Abstract

In this study, the quality of groundwater is examined, and its appropriateness for irrigation and drinking is evaluated. Seven samples from S1 to S7 villages were gathered and examined for several physicochemical and heavy metal characteristics. Chemical data were assessed using US salinity diagrams, Wilcox and water quality index, and a comparison was made with respect to WHO & TBS criteria. The results revealed that pH levels in two villages S4 (pH 5.74) and S5 (pH 5.71) fell below the recommended WHO/TBS. The salinity measurements (EC: 696–938 µS/cm; TDS: 295 – 359 mgL⁻¹) indicated moderate salinity (C2 class), which is appropriate for irrigation with little control. The recorded value of nutrient concentrations was NO^3– (1.22 – 1.82 mgL⁻¹) and PO₄^3– (0.02 – 0.08 mgL⁻¹), which are within safe limits, while that of SO₄^2– (209 –258 mgL⁻¹) neared the 250 mg/L which is the regulatory threshold value. The Ca²⁺ (70 – 78 mgL⁻¹) and Mg²⁺ (25 – 52 mgL⁻¹) complied with the standards, Na⁺ (40 – 58 mgL⁻¹) exceeded recommended levels for Na⁺-sensitive populations. Organic pollution, reflected in COD (14 – 97 mgL⁻¹) and BOD (1.4 – 9.9 mgL⁻¹) values, showed substantial spatial variation, with S5 exhibiting severe contamination. Hydrochemical analysis revealed Ca-Mg-HCO₃/SO₄ water types, accentuating mixed geological and anthropogenic influences. At the same time the SAR ranging between 0.8 – 1.2; Na%: 30 – 40% classified most samples as Excellent to Good. Similarly, most samples were suitable for irrigation based on the US salinity rating. Additionally, the analysis discovered extensive pollution from heavy metals. Iron, chromium, mercury, lead, arsenic, and arsenic concentrations were continuously above WHO drinking water guidelines. Several samples had high cadmium while the amounts of manganese and copper were typically appropriate.