28. Water quality assessment and VN_WQI determination of the Tam Dao stream, Vinh Phuc province

Abstract

Tam Dao stream water samples were collected at 6 points along the stream, originating from the water supply pumping station (watershed area) to Thac Bac. Water samples were taken 4 times (2 times during the dry season and 2 times during the rainy season in 2022 and 2023. The analysis results showed that the water quality at TD1 and TD2 points was good, in accordance with standard A of QCVN 08: 2023/BTNMT. However, the water quality gradually decreased along the flow. Specifically, PO₄^3- increased by 10 to 40 times, NO₃^- increased by 2 to 5 times, and heat-resistant Coliform increased by 45 to 465 times, while the concentration of dissolved oxygen decreased. Assessing the quality of Tam Dao Spring water according to the VN_WQI index also shows that the WQI index gradually decreases from 94 at the watershed point to 41 at the end point. Over time, the quality of spring water was declining, the color of the water smelled worse and worse, and the NO₃^- parameter in 2012 was 19 times higher than in 1998-2001. That shows that the water quality in the watershed area, where there was little human impact, is still good, but the downstream water quality decreased due to the receipt of domestic wastewater from residential areas in the area.