Assessment of Groundwater Quality and Health Risk in the Oil and Gas Field of Dingbian County, Northwest China

In order to determine the groundwater quality status and health risks caused by target pollutants in the oil and gas field of Dingbian County, 30 groundwater samples were collected and quantitative analyses of 20 parameters. Hydrogeochemical characteristics of groundwater was analysed using Durov diagram, statistical analysis, Gibbs diagram and correlation analysis. Entropy weighted water quality index evaluated groundwater quality. Health risk assessment model was used to evaluate the health risk to adults and children caused by target pollutants (NO3 (-), NH4 (+), NO2 (-), F-, Mn, Zn, Ba2+, As and Cr6+) through direct ingestion and dermal absorption. The results show that the groundwater is alkaline in the study area and the abundance of cations is Na+ > Mg2+ > Ca2+ > K+ and anions is SO4 (2-) > Cl- > HCO3 (-). All evaluation indicators except K+, NH4 (+), Zn and Ba2+ in groundwater exceed the permissible limits of drinking water. Gibbs diagrams display that evaporation crystallisation and rock weathering control the groundwater hydrochemical components. The study shows 53.4% of groundwater samples are not suitable for drinking in the study area. Total dissolved solids (TDS), Mg2+, Na+, SO4 (2-), Cl- and total hardness are the main contaminants which mainly come from industrial activities. The health risk assessment shows that the total risks of carcinogens (As and Cr6+) to adults and children are 4.20 x 10(-4) and 1.14 x 10(-3) per year, respectively, which are far higher than the International Commission on Radiologic Protection recommended maximum acceptable annual level (5.0 x 10(-6) per year).