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This aquifer is under threat from the nearby oil shale

mining operations -- the underground mines of

Ahtme and Estonia to the West, and the opencast

mines of Viivikonna and Sirgala to the East.

The Ordovician aquifer, within the area where oil

shale is mined, has been largely depleted because of

mine drainage. The latter amounts to around

600,000 m

3

/day, whereas groundwater consumption

in rural areas from this aquifer is estimated to be

about 3,444 m

3

/day.

The inability to exploit the Ordovician aquifer in

mining areas results in overexploitation of the deep

aquifers of Voronka and Gdov. Deep boreholes in

these aquifers supply 82% of the county's ground-

water consumption, but the water contains high salt

levels, often exceeding permitted limits for potable

water. Furthermore, intensive exploitation has created

a deep depression in the aquifer, centred on the

conurbations of Jôhvi and Sillamäe, although this

problem has been slowly resolving since 1990.

Unfortunately, replenishment might come from salt

water from the Gulf of Finland.

48

Contamination and degradation of water

resources by mining

In themining region,undergroundworkinghas affected

the stability of the land, leading to subsidence, in

particular after mines have been closed down and are

no longer maintained. It has also resulted in chemical

pollution of water resources.

The Ordovician aquifer, within the area where

oil shale is mined, has been largely depleted

because of mine drainage.

The latter amounts to around 600,000 m

3

/day,

whereas groundwater consumption in rural

areas from this aquifer is estimated to be

about 3,444 m

3

/day.

Aquifer

Aquitard

40

20

0

-20

-40

-60

-80

-100

-120

-140

-160

-180

-200

-220

-240

-260

-280

-300

-320

Age

Quaternary

Devonian

Ordovician

Cambrian

Vendian

(Precambrian)

Precambrian

sustainable water resource management

Fig. 1: South-North

hydro-geological cross section

of Ida-Viru County (Estonia).

Fig. 1 : Coupe schématique

hydrogéologique Nord-Sud du

Comté Ida-Viru (Estonie).

Source :Estonian Geological Survey