Hydrogeothermal Conditions in Éire - Geological Survey of Ireland

- 13 -11-6. Hydrochemical CharacteristicsInvestigators of one or other of the warm springs have in the pasttaken samples and had chemical analyses made. In this respect, the reportof Plunkett & Studdert (1883) on the Mallow Spa spring is of interest;Fahy (1974, 1975) also had some chemical analyses made on the Enfield (1005)spring. But it was only towards the end of 1979 that there was asystematic sampling of almost all of the known springs, with the analysescarried out under uniform conditions at the State Laboratory in the Collegeof Science. The results of these analyses are presented here in Table 3and 4. The results are strictly comparable, though the absolute valuesof some of the trace elements (not normally determined in water in thislaboratory) are less certain. The percentage amounts of the major ions areplotted on the triangular diagram of Fig. 4, while the trace elements siand I are plotted against temperatures on Fig. 5.(i) Major Anions and Cations. In general, the major ionsindicate rather normal groundwater issuing from these springs. TDS tendto lie in the range of 280 to 480 ppm, which is normal for Irish groundwatersfrom limestone aquifers. Much of the chlorine is in the 15 to 30 mg/litrange, normal for such waters and reflecting the rather high Cl content ofIrish groundwaters (as Burdon & Cullen, 1980). However, it is clear thatthere are three springs in Leinster which have definitely abnormal chemicalcharacteristics and this is also well-marked on Fig. 4.They are:NO. 1001 (Louisa Bridge) with Cl = 446 and TDS = 1160; No. 1004 (st. Patrick'sWell) with Cl = 142 and TDS = 636; and No. 1009 (St. Margarets) with Cl = 39and TDS = 582. From Fig. 2, it can be seen that these three springs havealready been grouped together as lying "along the synclinal structureinferred from two Tournaisian outcrops" (Item 11-2. (i». It is unfortunatethat No. 1010 was not sampled in December, 1979, and that the existenceof No. 1014 (Clonee) was reported only when this study had almost beencompleted. Repeated chemical analyses from these five springs (1009, 1014, JOO]1004 and 1010) will be awaited with interest.It will be noted that the other high Cl values (45 and 47 mg/lit)come from springs Nos. 1005 and 1006, which are close together, but whichdiffer much in temperature.In fact, all efforts to find a direct relationship between themajor anions and cations in solution and the temperatures of the springsproved unavailing. It may be said that the main chemical composition ofthe Irish warm springs is not related to the temperature of these springs.The most mineralized (No. 1001, Louisa Bridge) had a temperature of l6.2 o Con 7.12.79; the hottest (No. 1005, Enfield) has but some 400 ppm of TDS,but a temperature of 23.3 0 C on 7.12.79. The coolest is also rather highlymineralized.(ii) Trace Elements. The trace elements determined were Si, I,F, B, Se and Ba, as in Table 4. In addition total Fe and dissolved Fe weredetermined, though it seemed improbable that they would yield diagnosticinformation. The accuracy of some of the determinations is doubtful, sincesuch elements are not normally determined in water analyses. It can be seenthat they are erratic. Efforts were made to relate them to temperature.In the cases of Si and I, there was some limited success, as shown on Fig. 5.