BIOMEDY
Applications BIOREM
Previous
Prj 9023 - Bioremediation of underground water contaminated by tailing ponds of a Uranium Processing Plant
The tailing dump of a level land type covered 2,760,000 m2 and comprised 4 accumulators elevating up to 35 m. The tailing dump was used for 42 years and cumulated 37,000,000 m3 of uranium ore processing tailings.

The underground water was polluted due to infiltration and percolation from tailings. In result of the many years use of the tailing dump there was formed a northward aureole of polluted underground water extending for about 10 km2.

Main contaminating elements were sulfates, nitrates, molybdenum and manganese.

The map shows the position of the wells, the extension of the aureole of pollution and its vertical section
In the tailing dump area there develops a water-bearing horizon dating back to the proluvial-alluvial deposits of Meso-Upper Quaternary age which thickness is perforated by wells for the depth of 400-450 m. Prevalent rocks are gravel of different coarseness with inclusions of boulders and sandy-gravelly-loamy fillings. There are often occurring mild clay lenses and interbeds having thickness 2-17 m, uneven by extension but increasing in the direction south-north.

The water-bearing horizon is perforated by wells deepening 90 m in the southern region of the tailing dump and 45-50 in the area of accumulation. In the northern region there begin a zone of thinning-out of the water-bearing horizon that crops out there.

Velocity of water flow differs significantly both in horizontal and vertical sections. This is explainable with the heterogeneity of the rocks.

The water-bearing horizon is both of pressured and free-flow type. The depth of free flow water is of 97 m in the southern region while ranges 45-50 m in the northern region. Northern the accumulators there appear coeval clays in the roof and the horizon begins to be of pressured type. Water-bearing rock filtration coefficients changes from 0.44 to 137 m/24hours while the average velocity of underground water is of 0.85 m/24hours. Many years observation allowed estimating the average velocity of the movement of the underground water in the area in about 350 m/year (or about 1 m/24hours). Moving further north, the underground water comes into a lithologically checkered section acquiring a pressured character. The underground flow is being split for separate horizons according to inter-bed characteristics. Temperature of the underground water is 13-14°C.

The underground water outside the zone of the tailing dump is mildly mineralized (up to 250-300 mg/l). The background content of sulfates ranges 50-100 mg/l and content of nitrates ranges 20-40 mg/l.

In the vertical section of the contaminated zone, at a depth of 50-100 m it was detected a contamination below the background.

In the upper layer of the contaminated water flow, for a thickness of 30-50 m, it was found most of the source of contamination with a total mineralization of 4000-5000 mg/l. This layer forms the contamination pattern and, for calculation it was assumed an average thickness of 30 m.

For the localization of the aureole of the contaminated water it was perforated a system of interception wells which water returned to the uranium processing plant.

The table above and diagrams below shows the dynamic of decontamination

This techniques allowed to monitor the pollution and to considerably lower its velocity of propagation. Unfortunately the method did not suffice to prevent further pollution.

Thereupon the idea to implement BIOREM by using existing interception wells.