The sa lin ity of ground wa ter in Meso zoic and Ce no zoic aq ui fers of NW Po land ori gin and evo lu tion 2

Transcription

1 STU DIA GEO LOGICA PO LO NICA Vol. 126, Kraków 2006, pp Hydrogeology and Hydrogeochemistry Ed ited by J. Dowgia³³o Part II Dorota KAC ZOR 1 The sa lin ity of ground wa ter in Meso zoic and Ce no zoic aq ui fers of NW Po land ori gin and evo lu tion 2 (Figs 1 33; Tabs 1 4) Abstract. Chemi cal com po si tion of sa line groundwaters occurring in the Mesozoic deposits of NW Po land, based on 285 ar chi val chemi cal analy ses from 113 deep bore holes, shows much simi lar ity within par ticu lar aq ui fers. These are mostly chloride- sodium wa ters. Chloride- sodium- calcium wa ters pre domi nate only within the Lower Tri assic aquifer. Chloride-sodium-magnesium waters ap pear only at iso lated lo ca tions. All the wa ters stud ied are typi cal of a high min er ali za tion (TDS), the lat ter in creases with the aq ui fer depth up to a maxi mum of 328 g/dm 3 (Ob jez ierze IG-1 well). The TDS of these brines, meas ured sys tem ati cally over the last 40 years at pro duc tion wells in the health re sorts Ko³obr zeg, Ka mieñ Po mor ski, Œwi nou jœcie and Po³czyn Zdrój, is nearly con stant and di rectly pro por tional to the con cen tra tion of Cl ion. The brines in Meso zoic aq ui fers of NW Po land are poly ge netic. Their main com po nents are fos sil sea wa ter and me te oric wa ter. Holo cene in fil tra tion wa ter is a lo cal ad mix ture in the up per part of the Meso zoic suc ces sion only. The hy dro chemi cal in di ca tors (Br :J, Cl :J, Cl :Br, Ca 2+ :Sr 2+, rna + :rcl ) and the iso tope ra tios of oxy gen, hy dro gen and stron tium sug gest that the sa lin ity of wa ters in the Meso zoic de pos its is re lated to their ma rine ori gin and, to a lesser ex tent, to the dis so lu tion of Zechstein and Tri as sic salts. Dis so lu tion of Zechstein salts could oc cur in con tact zones with ground wa ters within the Meso zoic un til the chemi cal bal ance be tween them has been es tab lished. Such con tacts are cur rently ob served at base of the Lower Tri as sic rock as well as in 18 salt struc tures pierc ing the Tri as sic aq ui fers. Brines within the Tri as sic rock con tain an ad mix ture of residual (evaporite-related) liquids associated with the Zechstein and Tri as sic salt se ries. The sa line wa ters within the Meso zoic rock com plex are un der pres sure, which en ables their up ward mi gra tion through a sys tem of frac tures and faults to wards the Ce no zoic aq ui fers. This pro cess is most in tense in hydro geo logi cal win dows de vel oped in ar eas of ero sional re duc tion of the over ly ing Oli go cene clays on up lifted tec tonic blocks and salt- cored an ti clines. The ex tent of in creased ground wa ter sa lin ity zones in Ce no zoic de pos its de pends on flow di rec tions in the ac tive cir cu la tion zones. There fore, these sa lin ity zones, which oc cupy 33% of the study area, do not al ways co in cide with the zones of brine as cen sion. 1 In sti tute of Geo logi cal Sci ences, Pol ish Acad emy of Sci ences, ul. Twarda 51/55, Warszawa, Po land; e- mail: dkacz@op.pl 2 Manu script re ceived Oc to ber 16, Manu script accepted for publication December 4th 2006.

2 6 D. KACZOR The as cent of sa line wa ter is haz ard ous to the qual ity of Ma jor Ground wa ter Res er voirs (MGR). This con cerns the MGRs of Uznam (101) and Wo lin is lands (102), Roœc ino (103) and Dêbno (134), as well as large mu nici pal ground wa ter in takes, such as those in Œwi nou jœcie ( Wydrzany ), Wo lin, Trze bi atów, Gry fice, Ko³obr zeg ( Roœciêc ino and Bogucino ), Koszalin, Goleniów, Nowogard, Gry fino ( Tywa and Dolna Odra ), Krzypnica, Star gard Szcze ci ñski, Choszc zno, Wa³cz and Czarnków lo ca tions. Key words: Ground wa ter, sa lin ity, brine as cen sion, NW Poland. INTRODUCTION The knowl edge of the ori gin, chemi cal com po si tion, and con di tions of oc cur - rence of sa line ground wa ters in the Meso zoic de pos its of NW Po land is im por tant for proper ground wa ter man age ment. These wa ters have been util ized for salt pro - duc tion in Ko³obr zeg since the 8th cen tury (Le cie jewicz, 1960). Be gin ning from the 19th cen tury, they have been ex ploited for thera peu tic pur poses in the health re - sorts of Ko³obr zeg, Ka mieñ Po mor ski, Œwi nou jœcie and, af ter World War II, also at Po³czyn Zdrój. By the end of the 20th cen tury, brines from the Meso zoic de pos its have be come the sub ject of in ter est as a source of ther mal en ergy, e.g. in geo ther mal heat ing plants at Pyrzyce and Star gard Szcze ci ñski. Pro duc tion of this en ergy is fa - voured by suit able geo logi cal con di tions in the area. The knowl edge of geo logi cal con di tions un der which the brines oc cur has a cru - cial sig nifi cance for proper man age ment of fresh ground wa ter. As cend ing brines are haz ard ous to the qual ity of us able aq ui fers (Kac zor, 2005). Due to this pro cess, a number of ground wa ter in takes have al ready been closed in West Pom era nia, e.g. those at Œwi nou jœcie, Ka mieñ Po mor ski, Strze ewo, ó³cin, and Bia³ogard. There - fore, the rec og ni tion of zones of as cen sion of sa line wa ters and the de ter mi na tion of mecha nisms of this pro cess are of par ticu lar im por tance for the pro tec tion of us able ground wa ter re serves. The main pur pose of this pa per is to elu ci date the ori gin of sa lin ity of ground wa - ters in the Meso zoic de pos its of NW Po land, and to char ac ter ize sa lin ity of the as so - ci ated Ce no zoic aq ui fers that are in flu enced by as cend ing brines. The study area cov ers ap proxi mately 26,000 km 2, be ing con fined by the Bal tic Sea coast line, the state bor der with Ger many, the Warta and No teæ River val leys, and the me rid ian 17 E (Figs 1, 2). The pa per sum ma rizes data con cern ing the chemi cal com po si tion of ground wa ters in the Meso zoic aq ui fers and in the health re sort in takes (the lat ter were collected over the last 40 years). The pa per also ad dresses im por tant prob lems of sa lin ity caused by an thro po genic con tami na tion, as well as the sa lin ity re lated to coastal in tru sions of Bal tic sea- water. The avail able hy dro chemi cal data were care - fully se lected and veri fied in an at tempt to elimi nate meas ure ments in di cat ing that the sa lin ity origi nates from the above- mentioned sources. Pos si ble haz ard to the Ma jor Ground wa ter Res er voirs and to the main ground wa ter in takes due to de vel - op ment of the up ward mi gra tion of sa line wa ters from the Meso zoic aq ui fers is discussed.

3 SALINITY OF GROUNDWATER, NW POLAND 7 Fig. 1. Geo log i cal map of NW Po land with out Ce no zoic de pos its (af ter Dadlez ed., 2000) The main sub ject of in ter est of the pres ent pa per is ground wa ter from Meso zoic for ma tions, with ref er ence to the defi ni tion of sa line wa ter pre sented in the Hydro - geo logi cal Glos sary (Dow gia³³o et al., ed., 2002). For Ce no zoic aq ui fers, ground - wa ter with con cen tra tion of chlo ride ion >30 mg/dm 3, caused by brines as cend ing from the Meso zoic com plex, was taken into con sid era tion. This bound ary value is con sid ered to be in dica tive of a de vel op ing pro cess in sali ni za tion of us able fresh ground wa ters (Ma cioszc zyk, 1991; Grube, 2000; Gór ski, 2001). PREVIOUS RESEARCH Sci en tific pa pers pub lished in the 18th and 19th cen tu ries gave de scrip tions of nu mer ous nat u ral springs and out flows of sa line wa ters, sin gle chem i cal anal y ses of

4 8 D. KACZOR Fig. 2. Sketch map of tec tonic units of the study area (af ter Po aryski, ed., 1974) brines as well as in di cated halophyte sites near Mrze yno, Ko³obrzeg, Bia³ogard, Pyrzyce and Miedwie Lake (Brüggemann, 1799; Ascherson, 1859; Deecke, 1898). Halophytes are salinity indicator plants for near-surface groundwater. Research on and prospection for ther a peu tic wa ters, bi tu mens and ther mal wa ters gave rise to a num ber of re ports de scrib ing oc cur rence con di tions of sa line wa ters in the Pol ish Low lands (Œwidziñski, 1954; Kolago, 1957, 1964; Dowgia³³o, 1961, 1965a, b; Bojarski & Depowski, 1963; Pazdro & Agopsowicz, 1964; Depowski et al., 1965; Bojarska & Bojarski, 1968; Bojarski, 1966, 1970, 1993; Bojarski et al., 1977; D¹browski, 1973; P³ochniewski & Stachowiak, 1980; Soko³owska & Soko³owski, 1990; Górecki (ed.), 1995; Górecki & Szczepañski, 1991; Soko³owski et al., 1993, 1995; Bojarski & Soko³owski, 1994; Soko³owski, 1997; Kapuœciñski et al., 1997: Bojarski & Sadurski, 2000). The prin ci pal pro cesses con trol ling the for ma tion of sa line wa ters and brines are the fol low ing ones: sea wa ter evap o ra tion, dis so lu tion of salt-bear ing rocks, re ac - tions be tween wa ter and the rock, and mem brane fil tra tion (Land & Prezbindowski, 1981; Leœniak, 2005; Stoessell & Moore, 1983; McCaffrey et al., 1987; Con nolly et al., 1990a; Fisher & Boles, 1990; Fontes & Matray, 1993a, b; Nativ, 1996; Chi & Savard, 1997; Davisson et al., 1994; Davisson & Criss, 1996; Branks et al., 2002; Tijani, 2004). Sea wa ter re tained in the rock and dis so lu tion of ha lite are the sources

5 SALINITY OF GROUNDWATER, NW POLAND 9 of ground wa ter sa lin ity, most of ten re ported by re search work ers (Egeberg & Aagaard, 1989; Fisher & Boles, 1990; Davisson et al., 1994; Nativ, 1996; Chi & Savard, 1997; Branks et al., 2002; Tijani, 2004). There are two dom i nant hy poth e ses in the de bate on the causes of sa lin ity in wa - ters within Me so zoic aqui fers of the Pol ish Low lands. In nu mer ous, par tic u larly ear lier pa pers, a view was ex pressed that the sa lin ity re sulted from dis so lu tion of Zechstein salts by me te oric wa ter cir cu lat ing within the rock mass see Samsonowicz (1928, 1954), Œwidziñski (1954), Kolago (1957, 1964), Dowgia³³o (1965a), Kleczkowski (1966), Prochazka (1970), Zuber & Grabczak (1991), Krawiec (1999a, b), Krawiec et al. (2000), Kwaterkiewicz et al. (1999, 2000). An es sen tial role of fos sil sea wa ter in the evo lu tion of chem i cal com po si tion of brines was pos - tu lated by Dowgia³³o (1965b, 1971, 1988), Paczyñski & Pa³ys (1970), Dowgia³³o & Tongiorgi (1972), Kleczkowski (1979), Macioszczyk (1979), Weil (1981), and Szpakiewicz (1983). Re sults of iso to pic in ves ti ga tions of ground wa ter, first car ried out on sam ples from Po land by Dowgia³³o (1971), had a fun da men tal sig nif i cance for this hy poth e sis. De ter mi na tions of ox y gen, hy dro gen and sul phur sta ble iso tope ra tios gave rise to a con cept that sa line wa ters in Me so zoic de pos its of NW Po land are of a mixed or i gin (fos sil and me te oric wa ters) with a pre vail ing con tri bu tion of con nate sea wa ter or sea wa ter which in fil trated into consolideted rocks dur ing trans gres sion pe ri ods (Dowgia³³o, 1971; Dowgia³³o & Tongiorgi, 1972; Ró - kowski & Przew³ocki, 1974). The hy poth e sis that the main com po nent of ground - wa ter within in the Me so zoic is a mix ture of fos sil wa ters, and that only groundwa - ters within the Triassic are dominated by residual (evaporite-related) liquids, was confirmed by the later work of Dowgia³³o (1988). The geogenic sa lin ity of wa ters within Ce no zoic aqui fers in the Pol ish Low - lands was ini tially seen as a re sult of dis so lu tion of salt struc tures (Gumu³ka, 1964; Prochazka, 1970). Sub se quently, some au thors pointed out to a pos si bil ity of up - ward mi gra tion of brines from Me so zoic rocks. Their chem i cal com po si tion in - volved mix ing of rel ict sea wa ter with so lu tions formed by leach ing of rock salt (Macioszczyk et al., 1972, 1980; Macioszczyk, 1973, 1979, 1980; Gmurczyk, 1999). In the cen tral Wielkopolska re gion (West ern Po land), the de vel op ment of ground wa ter sa lin ity in the Mio cene aqui fer is re lated to faults and tec tonic de pres - sions ob served at the top of the Me so zoic se quence, whereas in the case of Pleis to - cene aqui fers to discharge zones along river valleys (Górski, 1989). The pro cess of sa line wa ter as cen sion from Me so zoic rocks might have been in - ten si fied by Pleis to cene glacioisostatic move ments (Michalski, 1985; Michalski & Starnawska, 1987; Boniecka et al., 1988; Dowgia³³o et al., 1988a, 1990; Dowgia³³o & Nowicki, 1991, 1997). In the Bal tic coastal zone, wa ter sa lin ity in the Ce no zoic aqui fers could orig i nate from both the as cent of sa line ground wa ter and in gres sions of Bal tic sea wa ter, as re ported by Matkowska (1983), K³yza (1988), Kucharski & Twarogowski (1993), Kachnic (1999), Krawiec (1999c), Kozerski & Kwaterkiewicz (1984, 1988, 1997), Zuber et al. (1988), Dowgia³³o et al. (1988b), Burzyñski et al. (1999) and Kwaterkiewicz et al. (1999, 2000). A syn thetic char ac teri sa tion of sa line wa ters of Po land was also pre sented in a

6 10 D. KACZOR num ber of at lases (Dowgia³³o et al., 1974; Turek, ed., 1977; Górecki, ed., 1995; Bojarski, 1996; Paczyñski & P³ochniewski, 1996). Ar eas of in creased sa lin ity in us able aqui fers were shown in the Hydrogeological Map of Po land, scales 1:200,000 and 1:50,000 pub lished by the Pol ish Geo log i cal Institute. DATA SOURCES AND RE SEARCH METH ODS The pres ent re search was based on both un pub lished (ar chi val) and pub lished data, as well as on au thor s own in ves ti ga tions. Un pub lished data were col lected from the fol low ing sources: Cen tral Geo log i cal Ar chives in War saw, ar chives of the Oil & Gas Drill ing Com pany in Pi³a and Zielona Góra, BPiUBU Balneoprojekt in War saw, Geo log i cal En ter prise Polgeol in War saw, health re sorts of Kamieñ Pomorski, Ko³obrzeg and Po³czyn Zdrój, Geotermia En ter prises at Pyrzyce and Stargard Szczeciñski, Szczecin Voivodship Of fice and HY DRO Bank Da ta base (CBDH) in War saw. Ar chi val ma te ri als in cluded pri mar ily geo log i cal logs and re sults of chemical analyses of groundwater from deep bore holes drilled by pe tro leum com pa nies (68) and the Pol ish Geo log i cal In sti tute (22), from health re sort wells (13), geo ther mal drillings (6) and other wa ter wells (7650). Some in for ma tion was also de rived from geo log i cal and hydrogeological documentations and re ports. Out of pub lished re ports, the fol low ing were used: Pro file g³êbokich otworów wiertniczych Instytutu Geologicznego (Bojarski, 1972 Kamieñ Pomorski IG-1; Bojarski, 1973 Szczecin IG-1; Bojarski, 1975 Wolin IG-1; Bojarski, 1977a Chociwel IG-1; Bojarski, 1977b Koszalin IG-1; Bojarski, 1979 Po³czyn IG-1; Bojarski, 1986 Ustronie IG-1). The re search was also based on re sults of pub lished chem i cal anal y ses (Dowgia³³o, 1965a, 1969; Szmytówna, 1970; Jarocka, ed., 1976) and iso to pic de ter mi na - tions (Dowgia³³o 1971; Dowgia³³o & Tiongiorgi 1972; Dowgia³³o, 1988; Zuber & Grabczak 1991; Krawiec 1999a, b, 2005; Krawiec et al., 2000; Krawiec & Dulski, 2004). The pres ent au thor also used re sults of 42 chem i cal anal y ses of ground wa ter sam ples col lected by her self from Ce no zoic de pos its dur ing map ping work on the map sheets of Goleniów (191), Jenikowo (192) and Tucze (193) for pur poses of the Hydrogeological Map of Po land, scale 1:50,000. These anal y ses were car ried out at the Cen tral Geo log i cal Lab o ra tory of the Pol ish Geo log i cal In sti tute in War saw. The range de ter mi na tions in cluded: ph, con duc tiv ity, al ka lin ity, HCO 3, SO 4, Cl, NO 3, NO 2, F, HPO 4, SiO 2, NH 4, Ca, Mg, Na, K, Fe, Mn, Zn, Cr, Cu, Pb, Sr, Ba, Al and B. Mea sure ments of sta ble ox y gen and hy dro gen iso tope ra tios were also done for 3 wa ter sam ples col lected from the Li assic aqui fer of the geo ther mal wells GT-1 at Pyrzyce (2 sam ples) and GT-1 at Stargard Szczeciñski (1 sam ple), and for 1 sam - ple from the Up per Cre ta ceous aqui fer of a well at Pniewo. In ad di tion, the ra tios of stron tium iso topes 87 Sr/ 86 Sr were mea sured in 2 sam ples taken from the Li assic aqui fer in well GT-1 at Pyrzyce and well Ed ward II at Kamieñ Pomorski. Iso to pic re search was con ducted at the laboratories of the Institute of Geological Sciences Polish Academy of Sciences. The use of un pub lished ma te ri als was pre ceded by the as sess ment of their re li - abil ity. As far as data from wa ters oc cur ring within Me so zoic rock com plexes are concerned, the results of chemical analyses performed by petroleum companies were treated with spe cial cau tion. The pro cess of data se lec tion in cluded also a ver i - fi ca tion car ried out by Bojarski (1996) dur ing con struc tion of the Hydrochemical

7 SALINITY OF GROUNDWATER, NW POLAND 11 and hy dro dy namic at las of the Palaeozoic and Me so zoic and ascensive salinity of ground waters in Polish Lowlands. The as sess ment of re li abil ity of wa ter data for in di vid ual Ce no zoic ho ri zons re - lied on elim i na tion of those re sults of anal y ses which could in di cate that wa ter sa - lin ity was caused ei ther by Bal tic sea wa ter in gres sions or by anthropogenic pollution. In elim i nat ing anal y ses which could sug gest the con tam i na tion by the Bal tic sea wa ter of chem i cal com po si tion of groundwaters in Ce no zoic aqui fers, depth to the sam pled aqui fer and the Cl ion con cen tra tion, were the main fac tors con sid - ered. The au thor used the same mode of in ter pre ta tion of the or i gin of ground wa ter salinization in coastal ar eas as that pre vi ously ap plied by Kwaterkiewicz et al. (1999, 2000) in the nearby eba re gion. Ac cord ing to that in ter pre ta tion based on iso to pic de ter mi na tions, it was pos si ble to find out that the sa lin ity of the first, un - con fined, aqui fer is a re sult of the Bal tic sea wa ter in flu ence, whereas in the sec ond aqui fer, con fined by a sev eral tens of centi metres thick till layer, sa line ground wa - ter co mes from Me so zoic rocks. Fol low ing this as sump tion, the re sults of chem i cal anal y ses of wa ter sam ples col lected from the un con fined aqui fer were elim i nated. The only mea sure ments used, were those of chlo ride con cen tra tion ex ceed ing the av er age ob tained for the Bal tic sea wa ter, i.e mg/dm 3 (K³yza, 1988). Par tic u lar at ten tion was paid to the re sults of anal y ses of ground wa ter ex tracted for pub lic use in cit ies where the prob a bil ity of anthropogenic pol lu tion of ground - wa ter is high. The ba sic in di ca tor of anthropogenic or i gin of chlo rides in ground - wa ter is an in creased con cen tra tion of sulphates and ni tro gen com pounds, as sug - gested by Macioszczyk (1991) and Górski (2001). Mea sure ments show ing the amount of ni trates in wa ter of >0.1 mg/dm 3, and that of sulphates of >40 mg/dm 3 in con fined aqui fers, and 75 mg/dm 3 in unconfined ones, were rejected. Depths to the sam pled aqui fers and the lo cal land use pat tern were ad di tional cri - te ria taken into con sid er ation. The as sess ment of vari abil ity of chlo ride con cen tra - tions com bined with the depth to the aqui fer (Kaczor, 2005) shows that the de crease in Cl con cen tra tions to the amount be low 30 mg/dm 3 takes place at depths of about m be low the sur face in the area con sid ered. In creased con cen tra tions of chlo - rides, re corded at greater depths, should rather be re lated to saline groundwater rise. To il lus trate chem i cal com po si tion of sa line ground wa ter within Me so zoic for - ma tions, 285 chem i cal anal y ses per formed in the years were used. The col lected data en abled iden ti fi ca tion of chem i cal types of the wa ters us ing the clas - si fi ca tion of Shchukarev-Priklonsky (Priklonsky & Laptev, 1955). This clas si fi ca - tion is based on the most com monly de ter mined ions: Cl, SO 4 2, HCO 3, Na +, Ca 2+ and Mg 2+ found in amounts ex ceed ing 20% meq, assumintg that the to tal sums of these an ions and cat ions equiv a lents equal 100% each. The con cen tra tions of Na + and K + are pre sented jointly due to the usu ally small con tent of the K + and the dif fi - culty in its de ter mi na tions. The pres ent pa per de scribes the spa tial vari abil ity of the ground wa ter chem i cal com po si tion in 8 ma jor Me so zoic aqui fers, pro vid ing maps for the best doc u mented aqui fers namely the Lower Triassic (see Fig. 6) and the Lower Jurassic (see Fig. 7) ones.

8 12 D. KACZOR One of the au thor s aims was to iden tify the re la tion ships be tween vari a tions in chem i cal com po si tion of ground wa ter and the tec ton ics of the Perm ian Me so zoic struc tural com plex. Thus, hydrochemical data are pre sented against the back - ground of the fault pat tern and salt tec tonic struc tures, in clud ing also the poorly de - vel oped ones (see Fig. 3). The pa per pro vides also char ac ter is tics of spa tial and temporal variations in the total water mineralization of Mesozoic aquifers. The ver - ti cal vari abil ity in to tal min er al iza tion is pre sented on geo log i cal-hydrochemical cross-sec tions (see Fig. 9 12) and in the graph show ing the ra tio be tween wa ter min er al iza tion and depth (see Fig. 8). The tem po ral vari abil ity over the last 40 years is il lus trated in graphs show ing the vari a tion in to tal min er al iza tion of brines from pro duc tive wells in the Œwinoujœcie, Kamieñ Pomorski, Ko³obrzeg and Po³czyn Zdrój health resorts (see Fig. 13). An at tempt to ex plain the or i gin of ground wa ter sa lin ity of Me so zoic aqui fers was based mainly on anal y sis of ge netic hydrochemical and iso to pic in di ca tors in - clud ing the most com monly ap plied ra tios: Br :J, Cl :J, Cl :Br, Ca 2+ :Sr 2+ and rna + :rcl. Re sults of four au thor s own de ter mi na tions of sta ble iso topes of ox y gen and hy dro gen, and 20 cou ples of pub lished de ter mi na tions (Dowgia³³o 1971; Dowgia³³o & Tiongiorgi 1972; Dowgia³³o 1988; Zuber & Grabczak 1991; Krawiec 1999a, b, 2005; Krawiec et al., 2000; Krawiec & Dulski, 2004) were also used (see Tab. 2). The re la tions be tween 18 O to 2 H (see Fig. 18), 18 O and to tal min er al iza - tion (see Fig. 19), and be tween 18 O and the depth to the sam pled aqui fer (see Fig. 20) were ana lysed. An at tempt was also made to cal cu late the 87 Sr to 86 Sr ra tio in ground wa ter, com par ing the re sults with the av er age value of this ra tio in mod ern sea wa ter and in Phanerozoic sed i men tary rocks (see Figs 21, 22). The char ac teri sa - tion of ground wa ter sa lin ity in Ce no zoic de pos its is based on 7747 mea sure ments of Cl con cen tra tion, and on maps of Cl con cen tra tion in groundwaters of Qua ter - nary (see Fig. 24), and Neo gene and Palaeogene aqui fers (see Fig. 32). The vari a - tion in sa lin ity dis played by groundwaters from Ce no zoic lay ers was dis cussed against the back ground of both the tec tonic set ting of Perm ian Me so zoic formations and a scheme of ground wa ter cir cu la tion sys tem in Ce no zoic de pos its (Paczyñski, ed., 1993). GEOLOGICAL SETTING Sub-Me so zoic base ment The Zechstein salt-bear ing de pos its, which form the sub-me so zoic base ment, are the most im por tant for ma tion in volved in the dis cus sion on the or i gin of salinization of ground wa ter. The Zechstein sec tion in cludes rocks of the Werra, Stassfurt, Leine and Aller cyclothems (Marek & Pajchlowa, eds, 1997). The top of the Zechstein strata lies at depths rang ing from 500 m be low sea level in the north - ern part of the Pom er a nian Synclinorium to > 4000 m be low sea level in the Szczecin Synclinorium, ris ing over the Goleniów salt stock up to 690 m be low sea level (Jaskowiak-Schoeneichowa, ed., 1979). The Zechstein suc ces sion is rep re -

9 SALINITY OF GROUNDWATER, NW POLAND 13 sented by rock salt and po tas sium-mag ne sium salts with lime stone, anhydrite, do - lo mite and clay in ter ca la tions. Me so zoic for ma tions Lower Tri as sic de pos its are rep re sented by a mudstone-claystone-sand stone com plex. The Röth (Lower Tri as sic) sec tion of the Szczecin Synclinorium in cludes two evaporitic se ries com posed of rock salt and an hyd rites with in ter ca la tions of dolomites, marls and clastics, 5 to 47 m thick (Jaskowiak-Schoeneichowa, ed., 1979). In the Pom er a nian Anticlinorium and Synclinorium, claystones with anhydritic con cen tra tions are equiv a lent to the evaporitic se ries (Dadlez, ed., 1976; Raczyñska, ed., 1987). Mid dle Tri as sic de pos its are rep re sented by marly lime - stones with clastic ad mix ture, and by claystones and dolomites with abun dant anhydritic con cen tra tions. These rocks oc cur through out the whole re gion, ex cept for the area of well de vel oped salt diapirs in the cen tral part of the Szczecin Synclinorium (Marek & Pajchlowa, eds, 1997). The Up per Tri as sic sec tion con - sists of the Keuper sand stone-claystone de pos its with plant re mains, the lower gyp - sum beds (claystones with anhydrite, gyp sum, do lo mite and sand stone in ter ca la - tions) and the up per gyp sum beds (claystones with anhydrite and gyp sum con cen - tra tions). The two lat ter are sep a rated by sand stone-mudstone rocks of the reed sand stone (Dadlez, ed., 1976; Jaskowiak-Schoeneichowa, ed., 1979; Raczyñska, ed., 1987). The over ly ing Rhaetian rocks are rep re sented largely by var ie gated dolomitic claystones with con glom er ate and sand stone in ter ca la tions and con cen - tra tions of coalified plant de tri tus. The Lower Ju ras sic de pos its are com posed of quartz sand stones, most fre - quently fine-grained, dolomitic, si der it ic and cal car e ous, interbedded by claystone and mudstone con tain ing plant re mains, py rite con cre tions and spherosiderites. Thick ness of the Li assic suc ces sion var ies from 20 m in the Pom er a nian Synclinorium to 1100 m in the Pom er a nian Anticlinorium. Near Œwidwin, and close to the Goleniów salt diapir, these rocks were re moved by ero sion (Dadlez, ed., 1976; Jaskowiak-Schoeneichowa, ed., 1979; Raczyñska, ed., 1987). The Mid dle Ju ras sic de pos its are rep re sented mainly by claystones and mud shales ac com pa nied by fine-grained sand stones with plant de tri tus, rang ing in thick ness from about 10 m to over 500 m. The Upper Ju ras sic rocks are pre served in the Szczecin and Pom er a - nian synclinoria, in the east ern part of the Fore-Sudetic Monocline, along slopes of the Pom er a nian Anticlinorium, and in the Trzebiatów Syncline (see Fig. 1). They con sist of mudstones, marls, sand stones and claystones over lain by car bon ates, marls, mudstones, and fine-grained sand stones with glauconite, as well as by dolomites, marls and lime stones. An evaporitic se ries (Up per Portlandian) rep re - sented by gyp sum and anhydrite beds is ob served in the south-east of the Szczecin Synclinorium and near Szczecinek. The Cre ta ceous de pos its oc cur in the Szczecin and Pom er a nian synclinoria, the Fore-Sudetic Monocline and in the Trzebiatów Syncline of the Pom er a nian Anticlinorium (see Fig. 1). Lower Cre ta ceous com plex is rep re sented by marly

10 14 D. KACZOR claystones and sandy-cal car e ous mudstones with bi valve shell de tri tus, over lain by claystones with sid er ite in ter ca la tions and fine-grained sand stone. The Up per Cre - ta ceous suc ces sion is com posed of car bon ate rocks (chalk, marls, lime stones with flints), gaizes, marly claystones and mudstones com monly con tain ing glauconite and quartz grains. Lo cally sandstones and sandy limestones occur. The above-de scribed li thol ogy of the Me so zoic suc ces sion makes it pos si ble to draw some palaeohydrogeological con clu sions con cern ing the area un der con sid - er ation. Through most of the Me so zoic era, ma rine con di tions pre vailed over the area under consideration. Thus, mainly seawater filled the sedimentary basins, while intercalations of salt and sulphate rocks indicate periodical increases in water sa lin ity due to in tense evap o ra tion. Only dur ing the Late Rhaetian and, pe ri od i - cally, dur ing the Early and Mid dle Ju ras sic and the Early Cre ta ceous, non-ma rine con di tions pre vailed over the area, while the ma rine ba sin was con fined to the deep - est zones of the Mid-Pol ish Trough (Marek & Pajchlowa, eds, 1997). In fil tra tion of rain wa ter, caus ing re moval of con nate sea wa ter from the top most part of the geo - log i cal sec tion, was possible only during relatively short periods. Cenozoic deposits The Palaeogene and Neo gene sed i men tary cover of the Me so zoic com plex shows nu mer ous ero sional hi a tuses (see Figs 24, 32). The lon gest one cov ers north - ern part of the Pom er a nian Synclinorium (Ciuk & Piwocki, 1988), shorter hi a tuses have been rec og nized over the Szczecin Synclinorium near Œwinoujœcie and over salt-cored anticlines of Nowe Warpno, Szczecin, Gryfino and Choszczno (Kurzawa, 2000, 2003). The Palaeogene and Neo gene de pos its, 100 to 200 m thick, are rep re sented mostly by sands, grav els, muds and clays (Ciuk, 1972). The Lower Oligocene (Rupelian) clays and claystones ( septarian clays ), and brack ish siltstones cor re spond ing to the Toruñ clays (Peryt & Piwocki, ed., 2004), which sep - a rate Ce no zoic aqui fers from the Me so zoic ones con tain ing sa line wa ters, are im - por tant in terms of sa lin ity of Ce no zoic wa ters caused by ground wa ter as cent. The septarian clays are best de vel oped over the Szczecin Synclinorium with the av er - age thick ness of 62 m, lo cally ex ceed ing 100 m. In the east of the study area, there oc cur the Toruñ clays (Czempiñ For ma tion), from sev eral m. to over 50 m thick. In the south-east ern area, ground wa ter occuring within Qua ter nary sed i ments is pro tected by up to 50 m-thick Lower Plio cene clays and muds, the so-called var ie - gated clays. The Qua ter nary de pos its are a con tin u ous com plex com monly less than 100 m thick (max i mum 237 m), de creas ing to sev eral tens of metres and even be low 10 m in the up lifted north ern area of the Pom er a nian Anticlinorium and over salt-cored anticlines (Kurzawa, 2000). The Pleis to cene suc ces sion in cludes 10 gla cial till ho - ri zons rep re sent ing the Narew, San, Nida, Odra, Warta and Vistula glaciations, and ac com pa nied by sandy-grav elly and muddy-clayey glaciofluvial and ice-dam lake se ries (Mojski, 1984). The Ho lo cene sec tion con sists mainly of organogenic de pos -

11 SALINITY OF GROUNDWATER, NW POLAND 15 its (peat and gyttja) and a sev eral metres thick sandy-muddy se ries filling river valleys and lake basins. Tectonic setting As far as the sub-perm ian struc tural pat tern is concerned, the study area is lo - cated within the West Eu ro pean Palaeozoic Plat form, and its east ern ex tremes ad - join the mar ginal zone of the East Eu ro pean Pre cam brian Plat form (Dadlez, 1974). The area in cludes parts of the four sec ond-or der tec tonic units: the Pom er a nian and Szczecin synclinoria, the Pom er a nian Anticlinorium and the Fore-Sudetic Monocline along with the Gorzów Wielkopolski Block (Po aryski, ed., 1974). Bound ary be tween the Pom er a nian Synclinorium and the Pom er a nian Anticlinorium runs along the Karlino-Szczecinek fault zone, be tween the Pom er a nian Anticlinorium and the Szczecin Synclinorium along the Œwinoujœcie-Drawsko fault zone, and be tween the Szczecin Synclinorium and the Fore-Sudetic Monocline along the Pyrzyce-Krzy zone. The south ern bound ary of the Gorzów Wielkopolski Block runs along the Lower Warta fault zone as iden ti fied on seis mic pro files (Fig. 2). The trends, na ture and pa ram e ters of the ma jor fault zones are in ad e quately known. The most com pre hen sive char ac ter is tics re fers to those sec tors of faults which sep a rate the Pom er a nian Anticlinorium from the Szczecin and Pom er a nian Synclinoria; this ar eas was well ex plored by seis mic sur veys. These faults cross the Palaeozoic base ment and the en tire Me so zoic se quence, and their pres ence is man i - fested by var ied re lief and struc tural fea tures of the top sur face of the Me so zoic com plex. The scale of up lift or throw along the fault planes, de fined by Dadlez (1987) as the in ver sion di men sion, is m in the coastal Bal tic Sea re gion, and up to 3000 m in cen tral and south-east ern parts of the Pom er a nian Anticlinorium. The downfaulting and shift ing of faulted blocks re sults in for ma tion of a system of mobile blocks. The Mid-Pol ish Trough de vel oped at the end of the Car bon if er ous be tween the mar ginal zone of the East Eu ro pean Plat form and the Variscan orogen. Its ax ial zone ap prox i mately co in cides with the pres ent-day po si tion of the Pom er a nian Anticlinorium (Marek & Pajchlowa, eds, 1997). Since the Zechstein, through the Late Cre ta ceous, the Mid-Pol ish Trough was the main path way for ma rine trans - gres sions, be ing sub ject to load-in duced sub si dence due to in creas ing burial. Dur - ing the Late Cre ta ceous, the trough be gan to in vert, re sult ing in an up lift of the Pom - eranian Anticlinorium. Intense erosional processes affected the Cretaceous and Jurassic rocks during Early Tertiary times. Typ i cal tec tonic fea tures of the north ern area of the Pom er a nian Anticlinorium are synsedimentary grabens de vel oped dur ing the Late Tri as sic and Early Ju ras sic (Dadlez, 1987). The graben-bound ing faults show a near-me rid i o nal ori en ta tion and are ob served in the ar eas of Kamieñ Pomorski, Trzebiatów and Ko³obrzeg (Fig. 3). In this sec tor of the Mid-Pol ish Trough, the most in tense fault ing, reach ing deep base ment, oc curred dur ing the Perm ian. Dur ing Late Cre ta ceous, these faults be - came re ac ti vated (Krzywiec, 2000). The best sur veyed Perm ian Me so zoic faults

12 16 D. KACZOR which fol low the sub-perm ian frac ture sys tem are those in the Pom er a nian Anticlinorium (Dadlez, ed., 1976). Trends of youn ger faults only partly co in cide with sub-perm ian dis con ti nu ity zones, be ing of ten in de pend ent of older faults. Also fault throw di rec tions have changed through time. Ac tive faults transecting the Me - so zoic for ma tions could play a role of mi gra tion path ways for brines, al though, in some cases, they could also act as hy dro dy namic bar ri ers. Closer iden ti fi ca tion of their sig nif i cance for the de vel op ment of salinization affecting groundwater in Mesozoic aquifers is, however, difficult. Block move ments of the sub-zechstein base ment trig gered pro cesses of mi gra - tion of Zechstein salt. These pro cesses have con tin ued since Late Tri as sic, re sult ing in de for ma tion of the over ly ing rock se ries (Dadlez, 1979). Salt move ments gave rise to the for ma tion of salt struc tures, i.e. con vex forms such as salt-cored anticlines and domes (Dadlez & Jaroszewski, 1994). The salt body may partly or com - pletely pierce the over ly ing rocks, or oc curs as swells with out break ing the con ti nu - ity of the over ly ing strata. When pierc ing the over bur den, the salts form salt plugs (salt diapirs) that in clude salt stocks (oval in plan view) and salt walls (elon gated in shape). Domed salt bod ies which de vel oped with out pierc ing through the over bur - den are re ferred to as salt pil lows (more or less iso met ric forms) or salt walls (ani so - met ric in shape). In the area of the max i mum thick ness of Zechstein de pos its, within the so-called cen tral zone of salt tec ton ics, there are salt walls and stocks partly pierc ing the Me so zoic overburden, mostly the Lower Triassic rocks (see Fig. 3). These are salt plugs of: Grzêzno, Oœwino, Maszewo, Drawno, Goleniów, Wierzchos³awiec, Nowogard, Ostrzyca, Dominikowo, Cz³opa and Szamotu³y, and small, close-to-faults salt in tru sions near Przytór, Miêdzyzdroje, Dargob¹dz and Kodr¹b. Poorly de vel oped struc tures, rep re sented by salt walls and pil lows not pierc ing Me so zoic rocks, oc cur in the so-called mar ginal zone of salt tec ton ics. These are salt pil lows of: Po³czyn, Barwice, Lotyñ, Œwidwin, Rokita, Resko, obez, Drawsko, Pi³a, and the salt walls of Krajenka and Miros³awiec-Trzcianka, lo cated in the east ern mar ginal zone. Salt pil lows of Nowe Warpno, Krakówko, Maszewo, Gryfino, Pyrzyce, Marianowo, Recz, Choszczno, Widuchowa, Banie, Lipiany, Karsk, Pe³czyce, Drezdenko, Chojna, Myœlibórz, Dêbno, Cedynia and Czelin, and salt walls of P³awno and Szczecin were de vel oped in the west ern marginal zone. The move ment of salt, largely be long ing to the cyclothem Z2 (Leine), oc curred since the Late Tri as sic. The pro cess was most in tense dur ing the Late Tri as sic and Late Cre ta ceous times. A first gen er a tion of salt walls and pil lows de vel oped within the cen tral zone of salt tec ton ics dur ing the Late Tri as sic. Sub se quently, they evolved into salt stocks and walls dur ing the Late Cre ta ceous (Dadlez, 1979). Qua - ter nary glacioisostatic pro cesses as so ci ated with ice-sheet load ing-deloading cy - cles (Liszkowski, 1993), reactivatied salt tec tonic move ments, as ev i denced by thick ness re duc tion and strati graphic hi a tuses ob served in the Pleis to cene sec tion above salt-cored anticlines as compared with synclinal areas (Kurzawa, 2003). HYDROGEOLOGICAL CONDITIONS Wa ter-bear ing Me so zoic de pos its, rep re sented largely by sand stones with interbedding mudstone-claystone se ries, and by Mid dle Tri as sic, Ju ras sic and Cre -

13 SALINITY OF GROUNDWATER, NW POLAND 17 ta ceous car bon ate rocks, oc cur over most of the study area, ex cept for the north ern and cen tral parts of the Pom er a nian Anticlinorium where Cre ta ceous and Mid dle to Up per Ju ras sic de pos its were re moved by ero sion. Near Œwidwin and Czaplinek, there are also small ar eas lack ing Lower Ju ras sic and Up per Tri as sic de pos its. In the west of the Fore-Sudetic Monocline, no Mid dle to Up per Ju ras sic and Lower Cre ta - ceous rocks oc cur. The Me so zoic rocks con tain pre dom i nantly sa line wa ters and brines. Nonsaline (fresh) groundwaters have been found only in the north ern part of the Pom er a nian Anticlinorium which is de void of Palaeogene and Neo gene de pos - its and cov ered only by a thin Pleis to cene se quence. Depths to the nonsaline wa ters range here be tween 300 and 500 m be low sur face, as for ex am ple near Œwidwin, Szczecinek and Pi³a (Turek, ed., 1977). Of par tic u lar sig nif i cance is the Li assic aqui fer be ing the ma jor res er voir of ther mal wa ters in the Pol ish Low lands, with geo ther mal gra di ents rang ing from 1.5 to 5.5 C/100m (Górecki, ed., 1995). The per cent age con tri bu tion of thick ness of wa ter-bear ing sand stone lay ers in the Lower Ju ras sic sec tion var ies be tween 50 and 80%. Con sid er able re sources of ther - mal wa ters are also stored in the Lower Cre ta ceous aqui fer. Water-bearing Cenozoic deposits are represented mainly by Miocene sands, subordinately by Oligocene sands and Pleis to cene glaciofluvial sands interbedded by poorly per me able gla cial tills. They are sat u rated with fresh wa ters re charg ing us able aqui fers. Only in ar eas of slow wa ter ex change, these groundwaters are col - oured and show in creased min er al iza tion and oxidability (Macioszczyk et al., 1972; Górski, 1989). Groundwaters are con fined, ex cept of shal low aqui fers, most of them oc cur ring in river valleys (Malinowski, ed., 1991). Both re gional and lo cal ground wa ter sys tems may be ob served in the study area. A re gional sys tem con sists of sa line wa ters stored in Me so zoic de pos its. It is re - charged di rectly through in fil tra tion of me te oric wa ter in ar eas of aqui fer out crops lo cated in the Fore-Sudetic Monocline, the north ern mar gin of the Holy Cross Mts, the Suwa³ki-Mazury El e va tion and the eba El e va tion (Bojarski & Sadurski, 2000; Malicki & Szczepañski, 1991). In di rect re charge oc curs by in fil tra tion of wa ter through Ce no zoic de pos its. The vari abil ity in re duced ground wa ter heads of the Lower Ju ras sic (Fig. 4) and the Lower Cre ta ceous aqui fers (Fig. 5) sug gests that brines of the Me so zoic com plex mi grate very slowly north wards, to wards the Bal - tic Sea. These groundwaters are con fined and their head gra di ent ranges be tween 0.9x10 3 and 1.1x10 3 hpa/10m (Bojarski, 1996). The ground wa ter ta ble in most of the tested wells sta bi lizes within Ce no zoic de pos its above the top of the Me so zoic rocks. In the wells Kamieñ Pomorski IG-1, Ustronie IG-1 (see Fig. 9), Huta Szklana 1 (see Fig. 12), Ed ward II in Kamieñ Pomorski, Józef in Dziwnówek, Anastazja in Podczele (see Fig. 9), B-1 and B-2 in Ko³obrzeg, Jatki II, Goœcino IG-1, Ko³obrzeg PN1, Jarkowo 1, Gorzów Wielkopolski IG-1, Marianowo 1 (see Fig. 10) and Pi³a IG-1 (see Fig. 11), spon ta ne ous out flow of brines was ob served, or even oc curs at pres ent. This in di cates fa vour able con di tions of their as cent to wards us able aqui fers. Through close-to-faults and highly frac tured zones, the brines mi - grate up wards, from Me so zoic into the Ce no zoic aqui fers, to be mixed with fresh wa ters in the ac tive cir cu la tion zone. Wa ters of this zone form lo cal ground wa ter

14 18 D. KACZOR Fig ) Hy dro dy namic field of the Lower Ju ras sic geo ther mal wa ter res er voir (af ter Górecki, ed., sys tems in clud ing ei ther par tic u lar aqui fers or their groups. The de gree of ground - wa ter salinization within Ce no zoic de pos its due to the as cent of brines de pends on the dis tance trav elled by sa line so lu tions which un dergo di lu tion within the ground - wa ter res er voir. There fore, the up ward mi gra tion of brines does not ev ery- where lead to no tice able salinization of us able aquifers. Flow di rec tions of groundwaters within the Ce no zoic com plex of the study area are con trolled both by the po si tion of the Odra and Warta river val leys and by the vi - cin ity of the Bal tic Sea coast see Fig. 24 (Paczyñski, ed., 1993). In lower-or der ground wa ter res er voirs, these di rec tions are re lated to the po si tion of lo cal re charge and dis charge zones. The Drawsko Lakeland is such a re charge area sup ply ing ground wa ter to the Ce no zoic aqui fers, where the high est re corded ground wa ter ta - ble al ti tude reaches 140 m above sea level (Paczyñski, ed., 1993). This is also an area of deep in fil tra tion of fresh wa ters into Me so zoic aqui fers (Dowgia³³o, 1965a), as ev i denced by the Po³czyn 2 well ex tract ing an al most fresh wa ter from the Up per Tri as sic aqui fer at depths of m below the surface (Krawiec & Dulski, 2004).

15 SALINITY OF GROUNDWATER, NW POLAND 19 Fig. 5. Hy dro dy namic field of the Lower Cre ta ceous geo ther mal wa ter res er voir (af ter Górecki, ed., 1995) CHEMICAL COMPOSITION OF GROUNDWATERS IN MESOZOIC AQUIFERS Com po si tion of groundwaters oc cur ring within Me so zoic aqui fers is based on the re sults of 285 chem i cal anal y ses. These wa ters are mostly of the Cl-Na, type al - though the Cl-Na-Ca wa ter is dom i nant in the Tri as sic aqui fer (Tab. 1). Only the wa ter anal y ses from the bore holes Przytór 1 and Sadlno 1 (Lower Tri as sic aqui fer), Cz³opa 3 and Dargob¹dz 2 (Lower Ju ras sic aqui fer) re vealed the pres ence of Cl-Na-Mg type wa ter with high Mg (>20 meq%). In Cre ta ceous aqui fers, a lo cal in - flu ence of fresh meteroric wa ter in fil tra tion is marked. It re sults in the for ma tion of Cl-HCO 3 -Na wa ters (Oœwino IG-1, Biesiekierz 1 and Rokita IG-1 bore holes). Sa - line groundwaters in Me so zoic aqui fers are char ac ter ised by a high to tal min er al - iza tion reach ing 328 g/dm 3 (Objezierze IG-1 bore hole see Fig. 6). Their chem i cal com po si tion shows much sim i lar ity within both par tic u lar strati graphic units and ma jor struc tural units within the Me so zoic com plex (see Tab. 1). The most fre quent are Cl an ions with con cen tra tion rang ing from 54.2 to 99.7 meq% (see Tab. 1). Bi -

16 20 D. KACZOR Aquifer Upper Cretaceous Upper Jurassic Middle Jurassic Lower Jurassic Upper Triassic Middle Triassic Table 1 Chem i cal com po si tion of sa line groundwaters in Me so zoic aqui fers Chemical type of groundwater Number of analyses TDS g/dm 3 Cl-Na Cl-HCO 3-Ca- Na Cl-HCO3-Na Cl-Na Cl-Na Cl-Na Cl-Mg Cl-Na Cl-Na-Ca-Mg Cl-Na-Mg Cl-Mg-Na Cl-Na 29 Cl-Na-Ca Cl-Na-Mg Cl-Na Cl-Na Cl-Na-Ca Abridged notation of chemical composition meq % Iodine Bromine concentration concentramg/dm 3 mg/dm 3 Cl SO HCO Na Ca Mg Cl 58.7 SO HCO Na 40.2 Ca Cl SO HCO Na Ca Mg Cl SO HCO Na Ca Mg Cl SO HCO Na Ca Mg Cl SO HCO Na Ca Mg Cl 91.5 SO HCO 30.2 Na 14.9 Ca 2.3 Mg Cl SO HCO Na Ca Mg Cl 99.0 SO HCO Na 48.8 Ca 23.5 Mg Cl 94.0 SO HCO Na 61.9 Ca 6.9 Mg Cl 91.6 SO HCO Na 21.4 Ca 3.8 Mg Cl SO HCO Na Ca Mg Cl SO HCO Na Ca Mg Cl 94.7 SO HCO Na 71.2 Ca 4.0 Mg Cl SO HCO Na Ca Mg Cl SO HCO Na Ca Mg Cl 98.8 SO HCO Na 64.7 Ca 20.4 Mg Lower Cretaceous

17 SALINITY OF GROUNDWATER, NW POLAND 21 car bon ates and sulphates show a much smaller con tri bu tion, com monly below 1 meq%. In creased con cen tra tions of bi car bon ates above 20 meq% were re corded only in sev eral ground wa ter sam ples taken from Cre ta ceous de pos its, and the max i - mum value re corded was 42.3 meq% (Oœwino IG-1 bore hole). The high est amount of sulphates 526 meq/dm 3 (18.5 meq%) was found in the Lower Tri as sic aqui fer (Gozd 3 bore hole). The most com mon cat ion Na +, is dom i nant in all aqui fers. Its share var ies be tween 14.9 to 97.6 meq% (see Tab. 1). The cal cium con tri bu tion is smaller, rang ing from sev eral to a dozen or so meq% (1619 meq/dm 3 in the Lower Tri as sic aqui fer Huta Szklana 1 bore hole). The share of Mg +2 is meq%, ex cept for the Mid dle and Lower Ju ras sic aqui fers where it amounts to 82.7 meq% and to 74.2 meq%, re spec tively (the Dargob¹dz 2 bore hole, see Tab. 1). Sa line wa - ters within the Me so zoic com plex are char ac ter ised by high con cen tra tions of biophile el e ments such as bro mine and io dine. The max i mum bro mine con cen tra - tion reaches 2000 mg/dm 3 (Po³czyn IG-1 bore hole), the io dine con cen tra tion co - mes up to 17.0 mg/dm 3 (Moracz IG-1 bore hole). Both max ima were found in the Lower Tri as sic aqui fer (see Tab. 1). Chem i cal anal y ses of cu ra tive wa ters pro duced by wells in health re sorts pro vided also data on the con cen tra tions of stron tium ( mg/dm 3 ), lith ium (< mg/dm 3 ), bar ium (< mg/dm 3 ), bo ron in the form of bo ric acid ( mg/dm 3 ), and sil i con in the form of silicic acid ( mg/dm 3 ). The chem i cal vari abil ity of brines within the Me so zoic for ma tions does not show any dis tinct re la tion ship to the po si tion of lo cal tec tonic units, fault zones or salt tec tonic struc tures, as dis played on the maps of chem i cal com po si tion of wa ters in the Lower Tri as sic (Fig. 6) and the Lower Ju ras sic for ma - tions (Fig. 7). Re la tion ship be tween the to tal min er al iza tion of groundwaters within Mesozoic aquifers and tectonics of the Permian Mesozoic sequence A dis tinct re la tion ship be tween wa ter min er al iza tion and the pat tern of tec tonic units is ob served in the study area. The high est TDS val ues were found in the cen - tral part of the Szczecin Synclinorium, the low est ones were noted in the Pom er a - nian Synclinorium and the Fore-Sudetic Monocline (see Figs 6, 7). The high wa ter min er al iza tion in the cen tral part of the Szczecin Synclinorium may be re lated to the oc cur rence of salt diapirs partly pierc ing the Me so zoic strata. The Iñsko and Wierzchos³awiec diapirs pierce through the Lower Tri as sic de pos its, the Cz³opa, Szamotu³y, Domikowo, Drawno, Ostrzyca and Nowogard diapirs through the Lower and Mid dle Tri as sic ones. Only the Oœwino and Grzêzno diapirs reach the top of the Tri as sic strata, and the Goleniów salt stock cuts up also the Lower and Mid dle Ju ras sic rocks (see Figs 3, 6, 7). Dur ing the rise of these struc tures, salt was mov ing up wards, be ing in con tact with wa ters pres ent in the pierced rocks. Just at that time, the Zechstein salts could have been leached out by the sur round ing groundwaters, in par tic u lar those in Tri as sic aqui fers. For ex am ple, in the Cz³opa 1 bore hole, ground wa ter sam pled from Up per Tri as sic sed i ments which oc cur at depths of m be low the sur face and di rectly over lie Zechstein salts,

18 22 D. KACZOR shows the min er al iza tion of 58.6 g/dm 3, while at a depth of m be low the sur face in the same aqui fer g/dm 3 (see Fig. 11). Such an in crease in min er al - iza tion along a rel a tively short depth in ter val sug gests the de vel op ment of a min er - al iza tion au re ole due to leach ing of salts from the Cz³opa salt wall. Sim i lar signs of the Zechstein salts leach ing can be in ferred from brine anal y sis of the Wolin IG-1 borehole where, in the Lower Jurassic aquifer, the maximum water mineralization of g/dm 3 (see Fig. 12) was re corded at a depth of m be low the sur - face. This bore hole was drilled close to a small close-to-fault salt struc ture of Miêdzyzdroje, within which the top of Zechstein salt oc curs at the depth of 1460 m be low the sur face, and is di rectly over lain by Up per Ju ras sic de pos its. A dis tinct in - crease in wa ter min er al iza tion was also ob served in brines from the Up per Ju ras sic aqui fer of the bore holes Grzêzno 5 (89 g/dm 3 ), Oœwino IG-1 (96 g/dm 3 ) and Chociwel 3 (104.4 g/dm 3 ) see Fig. 10, drilled near the Grzêzno and Oœwino salt diapirs (see Fig. 3). In the case of other salt struc tures con sid ered, no rep re sen ta tive data are avail able. In ar eas of weakly de vel oped salt walls and pil lows, no dis tinct in crease in wa ter min er al iza tion has been ob served. This is best pro nounced in the Lower Tri as sic aqui fer which is in a di rect con tact with salts of these struc tures (see Fig. 6). How ever, the lack of drillings above the salt walls and pil lows does not al - low to prove such re la tion ship. Highly min er al ized ground wa ter of 314 g/dm 3 was ob served only near the P³awno salt wall (Huta Szklana 1 bore hole), sug gest ing oc - cur rence of salt dis so lu tion (see Fig. 6). High min er al iza tion val ues (>200 g/dm 3 ) were re corded also above the Drezdenko (Strzelce Krajeñskie IG-1 bore hole), Rokita (Rokita IG-1 and Moracz 1 bore holes) and Po³czyn salt pil lows (Po³czyn IG-1 bore hole) see Fig. 6. Re la tion ship be tween the min er al iza tion of sa line groundwaters in Me so zoic aqui fers and depth of their oc cur rence Min er al iza tion vari abil ity of wa ters within the Me so zoic com plex, in con nec - tion with depth of their oc cur rence, was ana lysed tak ing into ac count 220 de ter mi - na tions dis played as points on a graph (Fig. 8). A re gres sion line is de ter mined by the lin ear equa tion: M = 0.08H 2.4 (where M stands for min er al iza tion, H for the depth to the sam pled aqui fer). This re la tion ship is most ap par ent within the depth in ter val of 800 to 1800 m be low the sur face within which the great est num ber of points is grouped close to the re gres sion line. The in crease in min er al iza tion with depth is less pro nounced at depths less than 800 m be low the sur face, which may be a re sult of me te oric wa ter re charge. Sim i larly, the re la tion ship is less pro nounced at depths be low 1800 m be low the sur face. There are only few points sit u ated near the re gres sion line, the other ones (those cor re spond ing to sam ples col lected mainly from the Lower Tri as sic aqui fer) are shifted to the right of the line. This can sug gest an in creas ing min er al iza tion caused ei ther by an ad mix ture of strongly min er al ized re sid ual liq uids of the Zechstein ba sin (and, pos si bly, smaller, Tri as sic ba sin un der - go ing evap o ra tion), or by a con tact of these wa ters with Zechstein salts. The graph (see Fig. 8) also shows the re gres sion lines cal cu lated by Dowgia³³o (1971) for

19 SALINITY OF GROUNDWATER, NW POLAND 23 Fig. 8. The re la tion ship be tween ground wa ter mineralization and depth of occurrence groundwaters in Me so zoic aqiufers of north ern Po land, and by Weil (1981) for min er al ized groundwaters oc cur ring within the War saw Trough. Com par i son of the curves in di cates that the in crease in min er al iza tion of groundwaters in Me so - zoic aqui fers with depth is most dis tinctly ex pressed in north-west ern Po land. This re la tion is also il lus trated in hydrogeochemical cross-sec tions (Figs 9 12) show ing that wa ter min er al iza tion does not de pend ei ther on lith o logic or strati graphic fac -

20 24 D. KACZOR tors. The con tours of ground wa ter min er al iza tion, cor re spond ing to the val ues of 50, 100, 200 and 300 g/dm 3, cross the bound aries of lithological com plexes and strati graphic units. Ex am ples of a dis tinct in crease in min er al iza tion with depth are ob served in the Ko³czewo 1, Ustronie IG-1 (see Fig. 9), Chociwel 3, Oœwino IG-1 (see Fig. 10), Chabowo 3, Cz³opa 3, Cz³opa 1 and Pi³a IG-1 bore holes (see Fig. 11). The phe nom e non of min er al iza tion in creas ing with depth is typ i cal of deep sed i - men tary bas ins (Rittenhouse et al., 1969). It is of ten ex plained by the pro cess of ultrafiltration which re lies on pref er en tial sep a ra tion (re tain ing) of some ions, which are con tained in ground wa ter, by clay sed i ments act ing as semipermeable mem branes (Berry, 1969; Dowgia³³o, 1971, Hanshaw & Coplen, 1973; Kharaka & Berry, 1973; Graf, 1982; Philips & Bentley, 1987; Kharaka & Carothers, 1986; Hem, 1989; Drever, 1997). The course of this pro cess de pends pri mar ily on elec tro - chem i cal prop er ties of clay min er als, as well as on pres sure and tem per a ture within the res er voir, in par tic u lar dur ing com pac tion of sed i ments. Out of the ions con - tained in the brines in ves ti gated, Na + and Cl ions are the most susceptible ones to be retained. On the other hand, how ever, the ef fec tive ness of ultrafiltration pro cess and, first of all, its abil ity to pro duce con sid er able vol umes of brines, has been chal lenged by some au thors (Knauth & Beeunas, 1986; Egeberg & Aagard, 1989; Con nolly et al., 1990a; Fontes & Matray, 1993a; Hanor, 1994; Tijani, 2004). The main counter - argu ments against the sig nif i cance of the ultrafiltration pro cess are the lack of suf fi - ciently high pres sures, un usual in nat u ral geo log i cal con di tions (Knauth & Beeunas, 1986; Tijani, 2004), and the lack of clay de pos its in the lith o logic pro file (Land & Prezbindowski, 1981). Nev er the less, high pres sures oc cur within compressional zones as so ci ated with tec tonic ac tiv ity. Such a compressional zone ex isted at the end of the Me so zoic in north-west ern Po land, as ev i denced both by the de vel op ment of in ver sion faults cut ting the Perm ian Me so zoic struc tural com - plex and its base ment, and by the evo lu tion of salt struc tures (Marek & Pajchlowa, eds, 1997; Krzywiec, 2000). The ultrafiltration pro cess in the area of in ter est could have also been fa voured by the lithological types of Me so zoic de pos its rep re sented mainly by mudstone-claystone-sand stone com plexes. Car bon ate rocks are dom i - nant only in the Middle Triassic, uppermost Upper Jurassic and Upper Cretaceous sections. Vari abil ity in time of sa line ground wa ter min er al iza tion in Me so zoic aqui fers Data con cern ing the vari abil ity in time of the to tal ground wa ter min er al iza tion, and its re la tion ship with the con cen tra tion of chlo rides, orig i nate from sys tem atic mon i tor ing car ried out dur ing the pe riod of by the Balneoprojekt En - ter prise on me dic i nal wa ters in takes: Ed ward II at Kamieñ Pomorski, B-1 and Emilia (No 6) at Ko³obrzeg, Jantar at Œwinoujœcie and Po³czyn IG-1 at Po³czyn Zdrój. The anal y ses are shown in the form of graphs il lus trat ing both vari a tions in min er al iza tion and con cen tra tions of Cl ion as a function of time (Fig. 13).