Establishment of undergroundwater quality index (GWQI) and application to Hai Lang district, Quang Tri province

Abstract

In this study a Ground Water Quality Index (GWQI) was established and applied to Hai Lang district in Quang Tri province. Ten basic water quality parameters selected for establishment of the GWQI consisted of: pH, TDS, hardness (HARD); SO4, COD, N-NH4, N-NO3, Fe, Mn and Total coliform (TC). Principal component analysis (PCA) was applied to the monitoring data set of the period 2015-2018 in the district to determine the weights (w_i) of the parameters. The linear sub-index functions (q_i) were set up basing on the allowable limits of the parameters specified in the National Technical Regulation on Domestic Water Quality (QCVN 01-1:2018/BYT) issued by the Ministry of Health. Three (3) different methods were used to calculate index GWQI_M (multiplicate form), GWQI_A (additive form) and GWQI_Ref (reference form) for the water quality data set. The indexes were all funtions of sub-index q_i and weights w_i. The obtained results show that the index GWQI_M is more suitable than GWQI_A and GWQI_Ref in reflecting the groundwater quality. Applying the GWQI_M to the water quality data set of the period 2019 - 2021 in the district indicated that there are 89% of GWQI_M values classified as Very good or Good water quality, 7% as Medium 1% as Poor and 3% as Very poor (or Unfit for drinking).