Hidrológiai Közlöny 1971 (51. évfolyam)

1. szám - Dr. Erdélyi Mihály: Hidrogeológiai tényezők hatása a felszínalatti vizek minőségére

6 Hidrológiai Közlöny 1971. 1. sz. Special Conference Number, Szebellédy, L. minerals and rocks, and alsó the poor reliability of analyses. 2. Gy. Gondos investigated the locally important iron- and manganese content of groundwater in the alluvial coarse deposits of rivers in Hungary. The data of pumping tests carried out in 121 wells, 203 water-analyses and 36 mineralogical tests were evaluated. The river water was in each case of a eomposition excluding the possibility of enrichment, thus the cause had to be looked for in the aquifer. 30 to 75% of the heavy mineral fractions were ferrous garnet, amphibole and magnetite. The aquifer contained an amount of iron, which, if only a fraction of it had been dissolved would have reached the highest observed anomaly value. High-iron groundwater was found to occur whcre: a) the contours of the area coincide with those of a depression, b) there is no impermeable cover but a "window" for infiltrating precipitation. Most of the precipitation reaches the aquifer in such places. Decaying plants create the redueing médium, where the iron is dissolved. No shifting ofthese spots in the direction of fiow was observed. An enrichment in manganese in groundwater was not always observed under the same surface as that of iron. Manganese may substitute bivalent iron in minerals. Distilled water saturated with C0

2 was found to dissolve from 5 gr powdered garnet 14.4 mg/l iron and 2.2 mg/l manganese, in 30 days. In their papers S. Karácsonyi and Gy. Scheuer investigate the origin and recharge of waters at great dephts in porous and karstic rocks, giving excellent interpretation of geological and hydrochemistry data. The investigations were carried out — and rightly so — at two boundary areas of the Great Hungárián Plains, where the disturbing effects can be better eliminated. 3. There are four water horizons in the Upper Pannonian formation, at the Gyöngyös research area. The at-rest level of the uppermost layer is t he highest, its yield is moderate. The at-rest level of the deeper aquifers decreases downwards, indicating a deterioration of recharge. The groundwater is of a Ca—Mg hydrogen-carbonate type, with a totál hardness of 12—50 Germán degrees and 400—1000 mg/l totál dry residue. The totál hardness in the uppermost layer is still 13 —17 Germán degrees, the totál salt content — calcium hydrogen carbonate — is average. Probing at greater depths the Ca—Mg content as well as hardness decrease, the Na-content increases and thus a gradual transition can be observed towards the sodium hydrogen carbonate watertype. The top layer of the upper Pannonian formation is thus recharged directly from groundwater, the deviation in the ratio of individual ions is caused by the dissolving of minerals contained in the waterbearing layer. At the bottom of the formation — below 300 m. the water contains little Ca ang Mg, similarly to springs originating from andesite. It may be supposed that in the deeper waterbearing horizons, in direct contact with the andesite or communicating with it over a fault, the "dilute" water of andesite is transformed by being enriched with dissolved mineral matter from the layer. Between these two extreme water types all transitory types of water occur. The data indicates that the quantitative change in salt content is independent from the temperature. Evaluating the analytical data of groundwater near the surface, from different depths in the Upper-Pannonian formation and from springs in andesite on the mountain fringe, authors observed the extent of recharge to have a decreasing tendency and thus to be in agreement with the hydrodynamic interpretation. 4. In their second paper authors state that in the vicinity of Eger all conditions are fulfilled. which enable the origin of waters from karstic, deep sources to be investigated. a) The surface karst with descending karstic water is present. b) In the area of the Tertiary, impermeable rock on the bordér of mountain ranges the confined deep karstic water is drained at a single spot only, in the lukewarm ascending springs in a limestone horst near the surface. c) Farther away from the borders of mountain ranges, the water of the deep karst is explored by three deep boreholes. The results of the investigation indicate that the amount of components in the karstic water, the concentration of dissolved matter, increases graduallv with rising temperatures. The increase of the totál salts content with temperature is not linear, here the difference in flow velocitv resulting from the inhomogeneity of the aquifer plays an important role. The earlier observation of G. Szalontay, concerning Budapest thermal waters are thus coníirmed [28]. The shift in the relatíve proportions of individual components is alsó caused by a dissolving of the cover rock. More intense dissolving is possible mainly along the several hundred meter long faults, where the aquifer is in contact with the impermeable cover along a large surface. 5. The paper by T. Kecskés is an excellent complete review of the subject matter from the point of water supply and civil engineering. The role of water temperature, gas content, sediment, flow rate and level change, further mineralogical factors (rock type, rock structure, minerals) is considered from the aspect of dissolving. The importance of time is correctly emphasised. An analysis of the origin of water quality components is alsó presented in the paper. 6. The paper by A. Rónai is a good example for an excellent summingup ofthe origin and movement of subsurface waters, with many data and documentation, in a major hydrogeological unit (the socalled Hungárián Basin). This summing up is