The effects of ascent recharge on deep exploitable aquifers on the North European Plain (a case study of the Rogoźno salt anticline, Poland)

Abstract

1 Adam Mickiewicz Uni ver sity, Fac ulty of Geo graph ical and Geo log i cal Sci ences, In sti tute of Ge ol ogy, De part ment for Hydrogeology and Wa ter Pro tec tion, Krygowskiego 12, 61-680 Poznañ, Po land Rasa³a, M., Ja¿dzewska, J., 2017. The ef fects of as cent re charge on deep ex ploit able aqui fers on the North Eu ro pean Plain (a case study of the RogoŸno salt anticline, Po land). Geo log i cal Quar terly, 61 (4): 962-972, doi: 10.7306/gq.1387In the pa per, we an a lyse the im pact of as cend ing brines from the Me so zoic base ment on the for ma tion of hydrogeological con di tions of deep ex ploit able aqui fers. In the North Eu ro pean Plain, there are nu mer ous salt struc tures with as so ci ated tectonic de for ma tions, which form mi gra tion zones of sa line wa ters from the Me so zoic base ment to the Ce no zoic cover. This cre ates a geogenic threat to ex ploit able aqui fers, es pe cially in terms of ground wa ter ex ploi ta tion con di tions. Pre vi ous studies of these phe nom ena had been con ducted on a re gional scale and fo cused mainly on the dis tri bu tion of chlo rides in receiver aqui fers with out de tailed anal y sis of hydrodynamical and hydrogeochemical ef fects of the as cent. As part of re search into the topic, it is nec es sary at this point to de velop the meth od ol ogy of as sess ment of geogenic risks for ground wa ter, for ex am ple for rea sons of pro tec tion of fresh ground wa ter re sources. As the re search area, a halotectonic anticline re gion was cho sen, where the Me so zoic base ment is char ac ter ized by strong tec tonic de for ma tion, and the deep est Ce no zoic aqui fer has a re gional spread. Some sim ple anal y ses al lowed to clearly iden tify the zones of sa line ground wa ter as cent along tectonic dis con ti nu ities of the Me so zoic bed rock. This phe nom e non causes the ap pear ance of wa ters with a mineralisation up to 2000 mg/L in the ex ploit able aqui fer. As cent re charge through ac tive faults causes the pres ence of zones with an omalously high piezometric pres sure in the cover of the fault over lay. The shape of these zones is cor re lated with the course of tec tonic de for ma tions. In flu ence of geogenic pol lu tion is greater in the mar ginal zones of the anticline than above it. For the full as sess ment of as cent im pact on hydrogeological con di tions of the re ceiver, it is nec es sary not only to an a lyse chlo ride con cen tra tions, but also other ground wa ter com po nents -i.e. sulphates. Hydrogeochemical anal y sis may al low for iden ti fica tion of the shal lower and deeper as cent re charge zones from the Me so zoic base ment. Com pre hen sive iden ti fi ca tion of these fac tors, even in the case of poor tec tonic con trol, can con trib ute to op ti mi za tion of ground wa ter ex ploi ta tion and pro tection con di tions in the ar eas po ten tially and ac tu ally threat ened by as cent.Key words: ground wa ter, as cend ing brines, hy dro dy namic anom a lies, hydrogeochemical anom a lies, salt struc tures, palaeo...