ISSN 1691-5402 Environment. Technology. Resources Proceedings of the 9th International Scientific and Practical Conference. Volume 1 © Rēzeknes Augstskola, Rēzekne, RA Izdevniecība, 2013 175 Mining under Kalina and Selisoo Bogs Merle Otsmaa Tallinn University of Technology / Department of Mining Address: Ehitajate tee 5, Tallinn, EE-12618 , Estonia Abstract. Continuous developing of Estonian power engineering on the basis of oil shale requires ever taking into use of new exploration fields. When the reserve of Estonia mine is depleted, mining of the exploration field of Seli has to be started. But that field is located under the Selisoo bog which is defined as a region of the Natura 2000 network and is planned become a nature preserve. Conservationists are interested for what extent oil shale mining under the Selisoo bog and in its immediate nearness will spoil the natural water regime of the bog. To clear up the environmental impact are carried through several investigations in the Selisoo bog. As a result of modeling is proposed a perceptible lowering of water table in peat layer. At the same time we have a positive experience on mining under bogs and water bodies, some kilometers to the north from the Selisoo bog. In Viru mine situated under the Kalina bog there is oil shale mining practically finished for today, but the Kalina bog exists as before, also the Lake Kalina in this bog. The aim of this research is to compare the geological and hydrogeological parameters of the Selisoo and Kalina bogs, clearing up the essential factors owing to which the mining in district of the Selisoo bog could exert a larger influence on environment than under the Kalina bog. In this paper are some measures for diminishing of the environmental impact brought on. Keywords – underground mining, bog, water level, precipitations, water-resistance. I INTRODUCTION Observable Selisoo bog lies in Northeastern Estonia in oil shale area beside of working Estonia mine. About 10 km to the north is located the lake Kalina surrounded by a bog of the same name (Fig. 1). Under that bog the reserve is depleted already. In the Estonia mine mining activities are approaching the bog Selisoo to the west. But Selisoo is defined as a region of the Natura 2000 networkError! Reference source not found. and it is planned become a nature preserve [4][4]. The aim of intended nature preserve is to protect different birds and valuable natural habitats – humus alimentary lakes and lakelets, bogs and bog forests. Therefore all measures to prevent or reduce to a minimum changes in the natural state of Selisoo need to be carefully considered. Above all it is essential that the present water conditions will not be spoiled and biotope of that place will remain. The reserves of Seli exploration field are validated in 01.04.1998. Only in first block the productivity is over 35 GJ/m 2 what meets the requirements of proved resource. The area of proved reserve is 1964.20 ha. 248 ha of planned nature preserve remains above the Estonia mine. Fig. 1. Location of Kalina and Selisoo bogs [2]. II GEOLOGICAL CONDITIONS For preservation of peatlands and water bodies in mined areas is essential the good water-resistance of sediments. In table I there is presented two geological cross-sections of observation wells in comparison [6][6]. The geology of sediments is investigated also just on shore of the Lake Kalina (borehole 1 in fig. 8) [7][7], where the thickness of little-decomposed peat was measured 1.72 m. Under peat was found 0.45 m of lake mud (gyttja) and 2.1 m clay with gravel and pebbles, containing 1 – 6 cm thick bands of sand. Sandy loam is laying in southern part of Lake Kalina, elsewhere is fine sand [7]. TABLE I GEOLOGICAL CROSS-SECTIONS Kalina Selisoo 85 0.5 km in the southeastern of the lake 233 0.8 km in the western of Selisoo Geol. index Description of layer Thick- ness, m Geol. index Description of layer Thick- ness, m QIV Peat 3 gQIII Sandy loam 4.5 lgQIII Varigrained sand 1.5 O2- 3nb Fissured dolostone 9.6 O2jh- kl Fissured dolostone 25 O2rk Fissured dolostone 9.2 O2id Compact limestone 7.87 O2on Clayey limestone 3.3 O2kk Dolostone 0.01 O2kl Limestone 8.05 O2kk argilliit 0.62 O2jh Clayey limestone 10.45 O2kk Dolomitic limestone 6.86 O2id Clayey limestone 7.9 O2kk Oil shale 5.53 O2kk Oil shale 13.7 Depth of oil shale 44.86 Depth of oil shale 53