Research, assessing and water quality change trends in the Holocene and Pleistocene layers to meet water supply requirements for the coastal area of Binh Thuan province, Vietnam

The study conducted water sampling at 30 well locations in 3 aquifers with different water depths (X15 m, X24 m, X36 m) in the Holocene and Pleistocene aquifers in the coastal area of Binh Thuan province, Vietnam. Water quality index calculation methods, correlation analysis, and principal component analysis were applied. The results showed that the Groundwater Quality Index fluctuated at “Excellent”, accounting for 18.61 %; “Good” accounts for 38.05 %; “Poor” accounts for 20.55 %; the remaining “Very Poor” and “Inappropriate” account for 22.79 %. The most “inappropriateˮ part is in Ham Thuan, Phan Thiet. Some well sites are not suitable for water supply. In the coastal area of Phan Thiet, the average chloride content during the year is higher than the allowed standard. During 3 years of monitoring, in the dry season, the highest chloride content was 478 mg.L–1 at sites GWBT16, GWBT20, and 521 mg.L–1 at GWBT24. The results of the principal component correlation analysis of water quality in the X15 m aquifer show a tendency to be more severely affected by high tides during the rainy season.