Hydrogeologic impacts in the Estonian oil shale deposit

Abstract

The article describes the hydrogeological problems related to water influx to the mine and water sulphate content association with underground oil shale mining in an environmentally sensitive area of Estonia. The water balance method was used to calculate the ratio of mine water outflow/inflow. Water balance calculations are needed for estimating the groundwater transversal flow into closed mines. Before oil shale mining groundwater geochemical processes are characterised by low sulphate content. Dewatering of oil shale mines lowered groundwater level in the Keila-Kukruse aquifer, and caused an about 50-fold increase in sulphate by intensive oxidation of pyrite of natural origin. The mobile sulphate ion may serve as an indicator of changes occurring in the sulphate content of groundwater stored in the Keila-Kukruse and Lasnama¨e-Kunda aquifers of the Ordovician system in the area of closed and working mines. Using the method of inverse mixing, sulphate ion distribution is a possibility to study the movement of groundwater in lateral and transversal directions.

Impact of Oil Shale Mining on Flow Regimes in Northeast Estonia

“…The dominant control on hydrogeology of the limestone is, however, mine pumping operations, which have completely drained the Ordovician aquifer. As a result, an extensive cone of depression (Erg and Pastarus 2008;Golf 1968) stretching up to 35 m in depth and 2.5 km outside of the mining area (Erg and Pastarus 2008;Kattai et al 2000) creates groundwater flow gradients towards the mines. The size of the cone of depression depends on the depth of the mine (Kattai et al 2000).…”

Impact of the shale mine on the River Purtse hydrological regime in north-east Estonia

“…Due to mining activity, the underlying Ordovician limestone deposits and the aquifer complex have been totally drained by mine pumping operations. As a result, it has created the effect commonly known as 'cone of pumping depression' (Erg & Pastarus 2008). This effect stretches up to 35 m in depth and 2.51cm outside of the mining area (Kattai et al 2000), creating groundwater infiltration to the mines.…”

Analysis of long term hydrological records to assess the changing regime and pathways in oil shale mining districts of North East Estonia

“…Due to mining activity and pumping operations, the underlying Ordovician limestone deposits and aquifer complex have been totally drained. As a result an extensive cone of depression [18] stretching up to 35 m in depth and 2.5 km outside of the mining area [19] creates groundwater flow gradients towards the mines. After closure of mines in the last two decades, new massive underground water bodies have developed in the mine voids [12,13].…”