INTERNATIONAL WATER SUPPLY ASSOCIATION
ASSOCIATION INTERNATIONALE DES DISTRIBUTIONS D'EAU
IX CONGRESS - NEW YORK - 1972
SPECIAL SUBJECT No. 11
Investigations into Artificial Augmentation of Underground Water Supplies in Poland
TADEUSZ BLASZYK and ANDRZEJ PAWULA
Research Institute of Municipal Economy, Poznań, Poland
Most of the municipal water intakes in Poland are supplied with infiltration water. Water intakes are situated mainly in river valleys and, to a great extent, they use suballuvial natural infiltration.
Artificial ground-water intakes are installed in regions where there is great water demand, coupled with limited ground-water resources. The practicability of constructing an intake of this type depends upon geological and hydrogeological factors, as well as on freedom from contamination of surface water. If, by any chance, the surface water should contain too much dissolved chemical compounds, it is unsuitable for the augmentation of artificial ground-water. The exploitation of surface and ground-water resources is closely connected with environmental control.
Owing to the intensive industrialization of the authors’ country, appreciable chemical pollution of rivers, and of some hydrogeological formations, may now be observed. The utilization of surface water for artificial ground-water development is only possible in the case of large rivers, or with pure mountain streams. In Poland there are a few artificial ground-water intakes dependent upon ponds, trenches, or gallery infiltration systems.
A typical example of an artificial ground-water inlet is the Poznań municipal water intake, dating from 1926. It consists of three lines of infiltration ponds located in the valley of the river Warta. This area, in general, is covered with a layer of sandy-gravel pleistocenic sediments, about 15 m thick. These sandy-gravel sediments are underlain by pleocenic clay.
In acting as a supply system for this water intake, a major portion was derived from water from a stream - about 92%; only 5% came from natural ground-water, and 3% from rainfall.
The exploitation of supplies by means of artificial underground water is achieved by vertical wells connected to three syphons. Fig. 1 shows a hydrodynamical diagram of water-flow lines from the infiltration pond to the wells. The route taken by the underground filtration water is about 75 m long. Supply conditions depend upon the porosity of sediments under the infiltration pond as well as upon those in aquifer.
The mean filtration rate of pleistocenic sediments is about 2,5 m/hour. Filtration velocity is 0,1 m/hour with a hydraulic gradient I = 0,01 and effective porosity m = 0,25. The permeability at the bottom of the infiltration pond will vary with the duration of the exploitation. Initially, after cleaning the bottom of the pond, the filtration velocity is actually 0,1 m/hour, but it decreases, as shown in Fig. 2, due to the deposition of sediments on the bottom, during the period of exploitation (Fig. 5). The amount deposited on the bottom depends, on one hand, upon the mineraI composition of the water in the stream, and, on the other, upon the biocoenosis of the infiltration pond. The assessment of the degree of sediment deposition, and of the period of return to normal at the bottom of the infiltration pond, will require to be worked out afresh for each individual case. For example, fish-culture in an infiltration pond will reduce the quantity of sediments, and thereby extend the period of usefulness of the pond (Jaskowski, 1969)2.
At an observation point for taking readings under an infiltration pond (Spandowska 1969)3, the penetration of Coli type organisms was noted at depths of from 0,75 m to 1,5 m. The numbers of this type of bacteria in the infiltration pond varied between 100 and 1000 cells E. Coli per 100 ml of water (Fig. 3). Investigations have also been carried out on the penetration (Jaskowski 1969), of other micro-organisms from the infiltration pond through to a sand layer. Living micro-organisms, such as blue-green algae, nematodes, infusoria, flagellata, and rotifera have penetrated up to 0,8 m. Penetrations to greater depths, up to 1,0 m, have been noted in the case of diatom shells, and of vegetation detritus also.
Fig. 4 shows the variability of oxygen conditions attendant upon the water purification process during infiltration from the bottom of a pond.
Water from streams employed for the artificial augmentation of ground-water will bring about changes in composition immediately after being pumped to the infiltration ponds, as well as changes in its passage underground.
The general character of the variations in the chemical composition of water is shown in Table 1 and Fig. 5.
Variation of chemical composition of water during flow underground from stream, pond, or welI.
Mineralization of water
Participation of ions [% mval/l]
|Underground water at depth of 13 m and distant 5 m from pond||396||5,43||0,1||17,2||28,4||54,3||0||19,5*||0,1||14,5||65,9|
|Underground water at depth of 13 m, and distant 50 m from pond||432||6,00||0,1||16,0||32,3||51,6||0||15,3*||0,2||14,8||69,7|
* (Na+ + K+) evaluated from difference.
In regard to ionic macro-compounds, a decrease in quantity of calcium and bicarbonates was observed in water pumped from streams to the infiltration ponds. This decrease is connected with the biocoenosis of the pond, as has been mentioned earlier. The rest of the ionic compounds remain unchanged in quantity, but sulphates increase slightly.
Variations in the other chemical indicators are shown in Fig. 6. A small increase was observed in the oxidizability of pond water, in comparison with the water from streams, followed by a decrease during transit through the aquifer, to a value of 4 mg 02/l. A conversion process was also observed to be taking place in regard to the nitrogen compounds, amounting to a reduction, which was indicated by a simultaneous decrease of nitrates and an increase in ammonia ions.
The iron and manganese contents of artificial ground-water were higher than in the infiltration pond. Iron, equally as well as manganese, was precipitated simultaneously with bicarbonates, at the infiltration pond; they increased again in underground water; and this may be explained by the initiation of chemical processes in the mineral compounds from pleistocene sediments.
In Poland, besides the promotion of artificial ground-water improvement schemes in valleys, an idea has been worked out for replenishment of water resources in the deeper geological formations, on a regional scale. This concept is based on developing completely the partly exploited ground-water resources synclines in the chalk.
Fig. 1-6: iwsa.jpg
1. Błaszyk, T., and Pawuła, A. 1971. Rules of underground water intake control (research project), Research Institute of Municipal Economy, Poznań
2. Jaskowski, J. 1969. The influence of biocoenosis on effectiveness of infiltration ponds, shown by an example from Poznań water intake (research project), Research Institute of Municipal Economy, Poznań.
3. Spandowska, S. 1969. Bacteria penetration in underground water, shown by an example from Poznań water intake (research project), Research Institute of Municipal Economy, Poznań.