Environmental examination of tailing ponds by geophysical methods

Abstract

The "Alkaloida" pharmaceutical factory located at the village of Tiszavasvári was established in 1927. Its main profile was to produce morphine from dry poppy-heads. During the decades, the activity of the factory and production of goods grew continuously, thus parallelly the amount of industrial wastes increased as well. The largest modification in the production circle took part in 1970 when the production of synthetic plant-protecting agents, fungicides and herbicides started, in addition to the traditional products of pharmaceutical industry. Until 1964, the communal and industrial waste water produced by the factory has been run into the Hortobágy Main Canal, after a. simple precipitation. Later the toxic waste waters which could not be cleaned biologically, were deposited in the abandoned clay pits of the neighbouring brickworks. The remediation program of the site started in 1997. The general task was to dewater the whole area, to separate it from the surroundings by slot walls, and later a complete recultivation. We carried out reconnaissance geophysical measurements in the site, the results of which were sufficient to start a detailed survey. The morphology of the site is quite plain, surface shaping by rivers can be detected, although these traces have been mixed with eolic sediments. The waste water tailing ponds are located on a plain ridge. The ponds are surrounded by earth dams. The River Tisza runs about 10 km far from the site, the most important irrigation canal of the country, the East Main Canal can be found at a distance of 1.8 km. Near the ponds to the south there are apple plantations, and about 200 m to the southwest fish pond are to be found. Thickness of the strongly stratified Pleistocene sediments is about 150 m. According to the different phases of fluvial sedimentation highly permeable sand and gravel layers alternate with impermeable layers of clay, silt and mud. A number of information on the near surface layers are available: archive drilling data and results of Engineering Geophysical Soundings, an advanced version of Cone Penetrating Tests. Moreover, aerial photos of the site taken in·1956 and 1994 are available in a scale of M = 1 : 5000. On the basis of investigation of the monitoring wells the groundwater table is between 1.0 and 2.0 m in the average, the direction of the groundwater flow is W. The task of geophysics was to delineate the deposited contaminating material both in horizontal and vertical directions, and to detect the pollution occurred. Moreover, the depth, thickness and hydraulic conductivity of the impermeable clay layer should also be determined. An important requirement was that the shallow impermeable clay layer be unsettled in the possible slightest degree. Ground geophysical methods meet these demands; four of them were chosen: