Hydrogeological envoronment in the agglomeration area of Irkutsk

Sholokhov P.A.

Institute of the Earth crust, Irkutsk, Russia

Sholokhov@crust.irk.ru

At present time Irkutsk have urban population of about 1,000,000. Centralized water supply to this city is drawn from the Irkutsk water storage and the Angara river. According to chemical and bacteriological indicators the quality of surface water is relatively poor. Therefore supply water is subjected to chlorinization and hypochlorinization in the warm season. The water also contains benzopyrenes and petroleum products with concentration exceeding standards. In this connection steps are being considered to transfer Irkutsk to underground sources of water supply. This idea is well supported by the available resources and technical feasibility. Within the periphery of the Irkutsk agglomeration area there are several prospected large bodies of fresh groundwater with estimated reserves. Within the agglomeration area bedrock groundwater is used only by self-sustained industrial and agricultural enterprises as domestic or process water. In the urban area groundwater is considerably polluted.

A radical transformation of the hydrogeological situation occurred after the Irkutsk Hydro water storage was filled/ The water level rise up to 28 m in the upper reach led to the formation of a confined aquifer in previously dry gravel-shingle sediments of the third overflooding terrace. The high recharge by seepage into the water-bearing materials, a reliable protection against surface pollution sources and the extremely favorable supply conditions contributed to the formation of a very large body of high-quality groundwater. Simultaneously the entire layer is host to the main volume of by-pass seepage which has ensured a groundwater level rise of 1,0-1,5 meter in the central part of the Irkutsk city without exceeding a critical point and no underflooding of this area occurred.

Over the past 60 years anthropogenic impact has caused a transformation of the thermal and salt balances of groundwater in the upper part of the hydrogeological sequence. The main result of the alterations implies an abrupt increase in inputs to the water balance accompanied by a rapid rise in groundwater mineralization and temperature as well as by a change in the groundwater chemical composition.

The transformation of natural hydrogeological conditions within the agglomeration has progressed to the point where active intervention needed to prevent further degradation. It is necessary to develop alternative engineering anti-underflooding schemes for the city. Also there is a need to minimize damage to surface water quality caused by uncontrolled pollution brought about by groundwater runoff. There comes a time where consideration should be given to future reasonable ecological rehabilitation of the geological environment, one of the most mobile elements of which is groundwater. Restoration of groundwater levels to a safe depth and decrease in the discharge of chemical and thermal pollutants into the Angara river are impossible without specialized hydrogeological mapping of the urban agglomeration. In this connection centralized groundwater supply to the Irkutsk is in stage of project proposals now.