CONCLUSIONS FROM A NEGATIVE TRACER TEST IN THE URBAN THERMAL KARST AREA, BUDAPEST, HUNGARY

Abstract

To prove the hydraulic connection between the urban Rozsadomb recharge area (Buda Thermal Karst System, Budapest, Hungary) - through its hydrothermal inactive caves - and the springs at the foothills has been an important question since the 1980s. These cold and lukewarm springs have been utilized as thermal baths since Roman times, and in modem times, occasionally, chemical and bacterial contaminants of human origin have been detected in them. It is hence of considerable importance to know whether these contaminants originated from the Rozsadomb recharge area or from close to the discharge points. According to the results of a previous test in a cave passage high upon the hill, it was tempting to suppose direct connection between the Rozsadomb area and the Boltiv Spring in the foothills. The expected breakthrough-time predicted from this previous study was between 10 hours and 42 days. The tracer test documented in this present work showed that no breakthrough occurred. It is proposed therefore that the risk of the Boltiv Spring being contaminated by infiltration in the Rozsadomb recharge area is low as compared with the possible contamination from sources near the discharge area. We suggest that in this case the negative tracer test clearly helped to prove and to understand better the role of "natural attenuation" in the Rozsadomb area. The efficient dilution observed in the tracer test facilitated the prediction of a hitherto unknown, large, phreatic cave-system as well.