GROUNDWATER MONITORING IN LITHUANIA

Survey of groundwater monitoring. In 1997 the network of National Groundwater Monitoring included 45 monitoring stations. The monitoring stations as such in most cases are represented by a nest of observational wells drilled to different aquifers. When the monitoring station occupies the areas with different kind of human activities (for instance agricultural fields and forests) it might be represented by two nests of monitoring wells (stations Mikuþiai, Mickûnai). The geological sections and monitored aquifers are shown in Addenda 4 and 5. All in all, in 1997 the monitoring network consisted of 192 observational wells drilled to 7 different aquifers. The differences in number depend on geographical and hydrogeological conditions of each province. Most of the monitoring stations are located in arable lands.

Groundwater monitoring included measurements of levels and water sampling. The both procedures were performed at 25 stations, level measurements without sampling – at 12 stations, and sampling without level measurements – at 6 stations.

Manual water level measurements were used.

Groundwater sampling in 1997 was performed twice: in spring (April–May) and in autumn (October–November). The collected samples were tested for general chemistry and trace elements.

Groundwater monitoring at waterworks included yield registration, measurements of water levels, and water sampling. At present, data bases at Geological Survey contain 233 active waterworks.

In 1997 data concerning groundwater abstraction have been obtained from 166 waterworks. Groundwater sampling was performed at 109 waterworks, all in all in 308 productive wells. The water sampling covers all aquifers usable for drinking water supply.

Monitoring of groundwater quality. The Survey of groundwater quality is based on two data sources: National Groundwater Monitoring and groundwater monitoring at waterworks.

Data of National Groundwater Monitoring are shown In Addendum 3 and Table 10.

The water quality in shallow unconfined aquifer depends essentially upon the station surroundings. The concentrations of all parameters are several times higher in arable lands than on afforested areas. Besides, in arable lands the concentrations of sulphates and nitrates are higher in spring, contrary to the afforested areas where higher concentrations were observed in autumn.

A slight positive trend of concentrations of most ions has been observed during the last three years. It might be resulted by both the influence of human activities and a long-term trend in water level fluctuations.

The influence of agricultural practises on ammonia and nitrates concentrations is established at monitoring stations Lanèiûnava, Alanta, Mikuþiai, Vertininkai. The bimodal distribution of nitrate concentrations also indicates the influence of agriculture.

The trace elements have been analysed by the graphite furnace atomic absorption method. Large part of trace elements (Pb, Cd, Va, Co, Cu) are in the quantities below detection limits. Only iron and stroncium are in relatively large quantities.

In general, the largest quantities of trace elements fall on shallow unconfined aquifer. At the same time the concentrations of trace elements are lower in the afforested areas than in the cultivated lands. The exclusively high quantities of trace elements are found at two monitoring stations (Kojeliai and Dûkðtas). The lowest concentrations are as a rule in water samples collected in afforested areas.

The survey of groundwater quality at waterworks is based on data collected in 1997. The common data overview shows that mean values of water quality parameters are within the limits of existing standards for drinking water. But this cannot be applied to the maximal values. In this sense the most unfavourable situation is in confined Quaternary aquifers usable for drinking water supply. Partially this situation might be explained by hydrogeological conditions as in the case of high concentrations of sulphates as well as high values of total dissolved solids and ammonia. But the high concentrations of nitrates (waterwork Þasliai) as well as the extremely high values of total oxygen demand (waterwork Tauragë) must undoubtfully be treated as a cosequence of human activities.

The variety in water quality of deep Quaternary aquifers depends exclusively upon hydrogeological conditions. The increased concentration values of sulphates and chlorides as well as calcium and ammonia must be explained by leakage of mineralised water from deeper aquifers.

For more information refer to "Groundwater Monitoring In Lithuania 1997" bulletin, Geological Survey Of Lithuania, Vilnius 1998