Surface water quality assessment in the Bach Dang river basin, Vietnam: Using water quality index and Geographical Information System methods

Abstract The study evaluates the surface water quality of Bach Dang river basin. During rainy season, temperature, pH, EC, BOD5, COD, coliforms, ammonium and phosphate values were 27–37 oC, 6.6–8.9, 300–2200 μS/cm, 5–25 mg/L, 5–26 0–3000 MPN/100mL, below 0.01 0.02 respective. dry seasons, Zn, Pb, Cr, As, Fe Mn levels drinking limits. In index varied from 76 to 91, signifying medium excellent quality. most outstanding sites QN12, QN18, QN22. areas had moderate (WQI between 61 93), except for QN01, QN03, QN04, QN05, QN06, QN07, QN11, QN16, QN17, QN19, QN23, where it dropped (61–73). temperatures greater higher EC in southeast. DO concentrations northwest southeast both seasons. southern southeastern regions exhibited more COD BOD5 than western, southwest, north, northeast regions. exceeded permissible limit west, southeast, east, northeast. Coliforms acceptable with during season. addition, Zn Pb are favorably associated Mn, positively correlated coliforms BOD5. pH inversely positively. negatively phosphates. connected alkalinity, while As COD.