About 90 years ago a natural depression in the vicinity of the town of Zwickau was filled with waste left after floatation of coal exploited in the area. Later on the locality became a dumping site for municipal and industrial waste from the town of Zwickau. Waste was disposed for years without any records, and at the present time the town faces an uneasy task of securing a harmless and controlled operation of the waste dump in accordance with environmental laws now in effect in Germany. A project has been launched sponsored by the ENMOTEC GmbH, company. Tübingen, subsidiaries Freiberg and Zwickau. At the initial stages of the project an important role was played by geophysical methods applied in mapping the tectonic structure of the dumping area including other desirable geological information, mapping the extent, distribution and thickness of floatation coal layers within the mound, and mapping the disposed refuse itself. The following geoelectric methods were applied: resistivity profiling, VLF and VES. They proved to be effective tools of investigation in the specific conditions of an operating dump. Results of these measurements are presented in graphic form in schematic situation of tectonic faults and lithological boundary-lines and in a geological profile of the dump. On the basis of geophysical results monitoring boreholes were placed in the vicinity of the dump. Layers of floatation coal and of municipal and industrial waste were delineated. Another aim of the geophysical survey was to find out whether there were any active processes going on in the disposed coal refuse. A temperature survey was carried out over the dumping area in a network of points at two depth levels, 0.5 and 1 m under the surface. Localitions of anomalous temperatures with a relative increase of over 20°C and maximum values of over 40°C at 1 m depth were mapped. At the final stage of the geophysical survey logging measurements were conducted in 10 cased monitoring boreholes in the surrounding of the dump. Measurements of total gamma activity of rocks were carried out, and measurements of physical properties of fluids in the boreholes: temperature (TM), transparency (FM) and resistivity (RM). Resistivity fluid log and photometry were applied for determination of groundwater dynamics in boreholes by measuring the time cycle of RM and FM curves after sodium chloride or nigrosine dye had been added to the mud fluid. These special measurements resulted in locating water inflows and leakages from the boreholes, and in mapping water circulation in the boreholes. Information on groundwater quality, stratification, temperature and filtration rate served as a basis for projecting and installing an effective monitoring system.
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