Assessment of groundwater safety surrounding contaminated water storage sites using multivariate statistical analysis and Heckman selection model: a case study of Kazakhstan

Abstract

Petrochemical enterprises in Kazakhstan discharge polluted wastewater into special recipients. Contaminants infiltrate through the soil into the groundwater, which potentially affects public health and environment safety. This paper presents the evaluation of a 7-year monitoring program from one of the factories and includes nineteen variables from nine wells during 2013-2019. Several multivariate statistical techniques were used to analyse the data: Pearson's correlation matrix, principal component analysis and cluster analysis. The analysis made it possible to specify the contribution of each contaminant to the overall pollution and to identify the most polluted sites. The results also show that concentrations of pollutants in groundwater exceeded both the World Health Organization and Kazakhstani standards for drinking water. For example, average exceedance for total petroleum hydrocarbons was 4 times, for total dissolved solids-5 times, for chlorides-9 times, for sodium-6 times, and total hardness was more than 6 times. It is concluded that host geology and effluents from the petrochemical industrial cluster influence the groundwater quality. Heckman two-step regression analysis was applied to assess the bias of completed analysis for each pollutant, especially to determine a contribution of toxic pollutants into total contamination. The study confirms a high loading of anthropogenic contamination to groundwater from the petrochemical industry coupled with natural geochemical processes.

Assessing data-scarce contaminated groundwater sites surrounding petrochemical industries

“…Previous research has shown that hydrocarbons, originating from the petrochemical industry, are practically ubiquitous in groundwater, are usually only biodegraded to a limited extent, and the resulting contaminant plumes may be several kilometers long (Balderacchi et al 2013). Measured concentrations in groundwater samples show that the amount of TPH constantly exceeds the permissible limit in all monitoring wells surrounding Sarymsaq, which confirms the presence of groundwater pollution in the area (Radelyuk et al 2021b). The amount of TPH usually has maximum peaks during the spring season, which can be explained by intensive snowmelt and large infiltration of water through the soil profile.…”

“…As residents of the rural area near the industrial zone are using the groundwater from the shallow aquifer for their drinking and domestic purposes (Tussupova et al 2016), an investigation was needed to assess potentially affected sites and to prevent members of the local community from drinking unsafe water. The source of potential contamination in this case study is a recipient pond "Sarymsaq" (Appendix A), where wastewater is discharged by the cluster of local petrochemical industry sites (Radelyuk et al 2021b).…”

“…A steady-state condition is assumed for the model, as there is relatively negligible exploitation of groundwater resources, and there are no significant trends in observed heads during a long-term period, despite seasonal fluctuations (Radelyuk et al 2021b). The average head value was used to assign the initial head for the steady-state modeling.…”

“…However, recent research in the experimental area of this study has shown that pollutant concentrations often exceed permissible levels outside the sanitary zone. Consequently, pollutants at some sites are likely to be spreading towards areas with substantial groundwater use (Radelyuk et al 2021b).…”

Impact of groundwater contamination on human health

“…Karunanidhi et al (2020a, b) described subsurface hydrogeochemical processes in a geologically heterogeneous semi-arid region of south India using mass transfer and fuzzy comprehensive modelling, and reported high influence of silicate weathering, ion exchange and gypsum dissolution on overall quality of the groundwater. Similarly, Radelyuk et al (2020) assessed groundwater safety close to contaminated water storage sites in Kazakhstan using multivariate statistical analysis and Heckman selection model (a very first attempt to evaluate environmental factors) and confirmed a high loading of anthropogenic contamination from the petrochemical industry coupled with natural geochemical processes.…”