Tracing multiple sources of groundwater pollution in a complex carbonate aquifer (Tarnowskie Góry, southern Poland) using hydrogeochemical tracers, TCE, PCE, SF₆ and CFCs

Highlights

• CFCs were used as anthropogenic tracers based on the pollution plumes spreading down from the town area.

• Boron was used as an indicator of the pollution coming from the chemical plant.

• TCE and PCE helped to trace specific type of pollution coming from the industrial part of the town.

Abstract

A comprehensive study on the sources of groundwater contamination in the Triassic carbonate aquifer, southern Poland, was conducted. The Gliwice aquifer is an important source of potable water in the Silesia region, the most industrialized part of Poland. Groundwater quality has been deteriorating over the last decades, which encouraged researchers to undertake comprehensive study to identify the sources and fates of the observed pollution. The presented study comprised analyses of major and minor ions, trichloroethylene (TCE) and tetrachloroethylene (PCE), CFC-11, CFC-12, SF₆, Ne and Ar in groundwater. The results showed that shallow groundwater within the Tarnowskie Góry town, located in the recharge zone of the aquifer, was more contaminated than groundwater abstracted from deeper part of the aquifer within the town, as well as groundwater located downgradient. A contamination plume of boron indicated an impact of the closed chemical plant, operating in the 20th century. Groundwater in the vicinity of the chemical plant was significantly altered, which was manifested by elevated concentrations of Cl⁻, SO₄^2-, Na⁺, total Fe and Mn. The study revealed groundwater contamination with CFC-11 and CFC-12. Comparison of concentrations obtained in two field campaigns (in 2010 and 2015) showed an increase in the extent of pollution plumes. The third analysed gaseous tracer, SF₆, did not appear to come from non-atmospheric sources, therefore, it was possible to calculate groundwater age using lumped parameter models. The results showed relatively young ages of the analysed groundwater samples, from 4 to 5 to 30–50 years. The youngest groundwater were found close to the Drama River, suggesting infiltration of the surface water into the carbonate aquifer. This feature of the river was confirmed by the observation of TCE and PCE concentrations in groundwater. Central part of the Tarnowskie Góry town was a source area for TCE and PCE contamination. Two directions of pollutants migration were observed, one of them was induced by the drainage of the historic ore mine and subsequently the Drama River – recipient of water coming from the mine drainage.

Introduction

Groundwater is the major source of drinking water in many countries around the world. It is considered to have generally better quality than surface water and be less vulnerable to pollution from the surface. However, groundwater quality deterioration due to anthropogenic activities is observed all over the world, often resulting in the closure of well-fields (Kowalczyk et al., 2003; Bottrell et al., 2008; Murphy et al., 2011). In areas heavily influenced by anthropogenic activities, groundwater protection issues are of great importance, particularly where groundwater is the main source of drinking water. A proper strategy for water quality protection requires identification of pollution sources and other factors determining changes in the chemical composition of groundwater (Puig et al., 2013; Zendehbad et al., 2019). Carbonate aquifers affected by strong anthropogenic pressures represent particularly difficult research targets, because groundwater flow paths and pollution migration are not as clear as in the case of pore aquifers. The Gliwice aquifer is an example of a triple porosity system (fissured-karst-intergranular), where fracture networks pose a key conduits for migration of water and contaminants. In addition, carbonate minerals, as relatively soluble, can buffer some changes in the physico-chemical parameters of water, making observation of human impact on water chemistry even more difficult.

Research on groundwater quality and active hydrogeochemical processes in carbonate aquifers have been carried out for many years (Hanshaw and Back, 1979; Elliot et al., 1999; Capaccioni et al., 2001; Leybourne et al., 2009; Atekwana and Seeger, 2015; Liang et al., 2018; Sracek et al., 2019). Identification of pollution sources is commonly enhanced by application of stable isotopes (Bӧhlke 2002; Cary et al., 2013; Xing et al., 2013; Urresti-Estala et al., 2015; Jakóbczyk-Karpierz et al., 2017; Najet et al., 2019), groundwater dating (Hӧhener et al., 2003; Darling et al., 2012; Gil-Márquez et al., 2020) and hydrogeochemical tracers (Smedley et al., 2018; Nofal et al., 2019).

This paper focuses on groundwater pollution sources in the Gliwice carbonate aquifer, one of the strategic reservoirs of potable water in the Upper Silesia region, southern Poland, the most industrialized part of the country. The aquifer has been a subject of detailed investigation for many years due to its important role in drinking water supply. Researchers focused primarily on groundwater resources (Kowalczyk, 2003), numerical flow modelling (Kowalczyk et al., 2003; Sitek, 2014), 3D geological modelling (Sitek et al., 2009) as well as groundwater pollution and protection (Różkowski, 1990a; Rubin et al., 1999; Rubin and Witkowski, 2003; Witkowski et al., 2008; Jakóbczyk-Karpierz et al., 2017).

The objective of the present study was to evaluate the extent of human impact on groundwater quality in the eastern and central part of the Gliwice carbonate aquifer using various hydrogeochemical indicators (major and minor ions, boron, trichloroethylene and tetrachloroethylene) and environmental tracers (chlorofluorocarbons and SF₆). Based on the results, general patterns were sought that could be used by other researchers in similar research areas.