EVALUATING SURFACE WATER QUALITY AND TESTING FREQUENCY IN TIEN AND HAU RIVERS, AN GIANG PROVINCE, USING 10-YEAR MONITORING DATA

The study aimed to assess the variation of surface water quality and evaluate the monitoring frequency at threecontinuous monitoring stations on the Tien river (MT1 station) and Hau river (MH1 and MH2 station) over a 10-year period (2009-2018), with a monitoring frequency of 12 times per year (monthly). The water quality variables comprised of temperature (oC), pH, dissolved oxygen (DO, mg/L), total suspended solids (TSS, mg/L), nitrate (N-NO- 3 , mg/L), orthophosphate (P-PO3 4- mg/L), chemical oxygen demand (COD, mg/L), and coliforms (MPN/100 mL). The individual water quality parameters were assessed by comparison with National Technical Regulation on surface water quality (QCVN 08-MT: 2015/BTNMT). Monitoring frequency was evaluatedusing Cluster Analysis (CA). The findings revealed that surface water on both Tien and Hau rivers was perpetually polluted with suspended solids, organic matter, nutrients, and microorganisms. The CA identified that the frequencies of current water monitoring could be reduced from 12 times to 5 times per year, resulting in a 58% reduction in monitoring costs. Future study should focus on evaluating water quality parameters toencompass all water quality characteristics in the Tien and Hau rivers. International collaboration with countries that impact the river before flowing into Vietnam in water management should be enhanced to solve continuing water problems.