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Z. Michalczyk, M. Łoś

the ground water table was also raised. Accumulation of peats and alluvia (alluvial soils) in the river valleys was accelerated, resulting in the filling-out of ponds and, in conseąuence, their becomming shallow. Drainage carried out locally was to bring the reverse effect. However, it was not of great importance because it did not change the water table in the Bystrzyca river valley which remained a natural drainage ground of underground and top waters.

By the 19th c., the economic significance of the water installations built earlier on the Bystrzyca and Czechowka rivers was decreasing. The silted-up ponds brought smali profits, and the river valley bottoms hampered spatial development of the city because it was difficult to get them under control. The rivers and their valleys served as natural reservoirs for municipal sewage, constituting a big threat to the inhabitants. Therefore, some of the ponds were liąuidated in the 19th c., and in the others the amounts of water damming up was reduced. Due to this, local lowering of the underground water table occurred by about 1—2 m in the areas adjacent to the ponds. Further lowering of the table, probably considerable, was caused by sinking wells to get water to satisfy communal und industrial demands.

In the second half of the 19th c. a fast demographic development of Lublin occurred; the population increased from 21,300 in 1870 to 80,100 in 1914. In the years 1875—1916, the area of the city was 8.7 km² (Kierek 1965). The city compounds extended beyond the Bystrzyca and Czechowka river valleys (Fig. 2). The central part of Lublin is situated in the fork area of the two valleys, and then residential and industrial suburbs developed. To supply the city with water, morę and morę wells were sunk. In the 19th c. there were about 90 wells in Lublin, sunk most often in ąuaternary deposits in river valleys and interfluves (Brunner et al. 1893). Because of relatively limited exploitation of underground waters and bad sanitary conditions of top waters epidemics of infectious diseases occurred. To improve the sanitary state of the city three deep wells were sunk (the 'Central’ source) for the second waterworks in the history of the city. In the years 1898—1914 the waterworks supplying the central part of the city was developed. The building of a sewer system was also started.

In 1916, neighbouring villages were incorporated into Lublin, whereby its area increased to 30.1 km² (Fig. 2). The number of inhabitants increased from 86,700 in 1920 to 120,000 in 1939 (Kierek 1975). The building of a modern waterworks, which came into operation in 1929, was indispensable. Water was taken from Upper Cretaceous rocks by means of 8 wells in Wrotkow suburb in the Bystrzyca river valley. In 1930, about one million m³ of water were obtained from both sources (the old 'Central’ and the new Wrotkow’), and in 1938 1,300,000 m³ (Marczuk 1978). In addition, underground water was exploited at an amount reaching 0.3 million m³/year from the wells of industrial plants. The sewer system was developed in parallel reaching a length of 55.7 km in 1938. The communal treatment plant received 0.8 million m³ of wastewater and about 0.9 million m³ of rain water (Kierek