79 since 1961 BALTICA Volume 29 Number 2 December 2016: 79–92 http://dx.doi.org/10.5200/baltica.2016.29.08 Impact of human activity on groundwater chemistry (Wielkopolska region, Poland) Krzysztof Dragon Dragon, K., 2016. Impact of human activity on groundwater chemistry (Wielkopolska region, Poland). Baltica, 29 (2), 79–92. Vilnius. ISSN 0067–3064. Manuscript submitted 15 July 2016 / Accepted 20 November 2016 / Published online 10 December 2016 © Baltica 2016 Abstract The article identifes the effects of human activity on groundwater chemistry in the regional aquifer system located in the Wielkopolska region (western Poland). It was documented using statistical methods, that the main process infuencing the groundwater chemistry is connected to contamination. The impact of contamination is evident in regions without sewers and where the aquitard is relative thin. Chloride and sul- phatewere found most infuenced by pollution from surface sources. Total hardness is also sensitive, but its behavior is controlled by geogenic processes as well. Factor analyses are a reliable tool for recognizing con- tamination’s impact on groundwater chemistry, especially for cases with a relatively low contamination level, when contamination is related to natural occurring water components. This research is important for imple- menting groundwater protection plans at the regional scale. These interpretations may be used to manage water resources better at the regional scale. Keywords • groundwater contamination • factor analysis • groundwater chemistry Krzysztof Dragon (smok@amu.edu.pl), Adam Mickiewicz University Poznan, Institute of Geology, Department of Hydrogeology and Water Protection, Makow Polnych Street 16, 61–606 Poznan, Poland INTRODUCTION Groundwater is the main source of water for the population and industrial uses in Poland. Contami- nation leads to deterioration in groundwater quality. Therefore, groundwater pollution can cause both health and economic consequences (Choi et al. 2005). Contamination increases the cost of water treatment and infuences the effectiveness of equipment used to extract, treat and distribute water. In extreme cases, impurities can lead to closures of water infrastructure (Dragon & Gorski 2008). Groundwater is increasingly contaminated due to human activities all over the world. This effect is particularly apparent in shallow, unconfned aquifers. However, evidences of contamination are also ob- served in deeper aquifers covered by a thick aquitard. It is important factor for groundwater management strategies because it is common tendency to relocate water exploitation to deeper aquifers due to shallow groundwater contamination (Jeong 2001). Therefore, recognizing the impact of human acti vity on groundwater chemistry is critical (Lawrence et al. 2000; Jeong 2001; Cronin et al. 2003) and should be the starting point for implementing groundwater protection zoning (Nel et al. 2009; Jime´nezMadrid et al. 2012). For such actions to be effective, they should be undertaken even at sites with low levels of anthropogenic change to groundwater chemistry. Recognizing the frst symptoms of anthropogenic contamination is a diffcult scientifc research prob- lem, especially when the contamination concerns only naturally occurring groundwater components such as Cl and SO 4 ions. In this case, an assessment of anthro- pogenic impact must be performed based on recog- nizing natural geochemical processes, hydrochemical zoning and natural background concentrations. For groundwater chemistry recognition due to the cost of establishing not specially dedicated monitor- ing boreholes but pre–existing pumping wells are typically used (Netzer et al. 2011). The depth and de- gree at which contaminants penetrate aquifers remain poorly understood among other factors due to a lack of depth–specifc sampling (Cronin et al. 2003).