Vízügyi Közlemények, 1969 (51. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(102) Considerable difficulties are due to industrial wastes, the volume and composition of which depends on the manufacturing program of individual plants. P'or this reason these should be made responsible for removing harmful consistuents from their own wastes before discharging them into the recipient. Thermal pollution due to cooling waters tends to retard the process of selfpurification. Wastes irrigation can be practiced only where loose soils of high absorbing capacity are available and even then large areas are required. In Hungary wastes irrigation has been introduced — with an experimental character over 14 hectares— in the vicinity of Debrecen. Detergents play an important role among the pollutants of domestic wastes. Neither are the "soft" detergents harmless since their decomposition products, such as N and P, are important plant nutrients and are conducive to the prolification of algae —especially in slowly flowing or standing waters, making water objectionable for use. 5. Garbage disposal as a water problem. Although soil is an excellent filter material, it is inevitable that polluting materials should be leached from domestic wastes and garbage by precipitation water, regardless what method of treatment is applied. The amount of garbage may be estimated at 250 to 300 kg per capita and year. It is for this reason that in large cities the problem of garbage disposal is not only of sanitary significance but affects pollution control as well. 6. Oil is the most dangerous polluting agent. The most severe hazard to water resourses is due to mineral oil and its products. Oil may find access to surface waters or by seepage to groundwater at the point of production and refinement, during transportation — owing to accidence and rupture of pipelines —, in the course of storage, distribution and carelessness in use and finally as a consequence of improper disposal of used oils. The growing menace ifc illustrated by the increasing oil production, by the growing number of motorcars and the growing popularity of oil heating. Oil hazards are concentrated in large towns and in their immediate surroundings and are made especially severe by the fact that taste complaints occur even at a dilution of 1:1,000.000 and the adverse effect is conserved for several decades. Pollution control measures (operation instructions, handling specifications, regulations concerning the construction of underground reservoirs and pipelines, quality supervision and accident prevention service) are therefore of special significance in large towns. Effective protection of water quality in Hungary is ensured by a governmental decree of 1967. For the implementation responsibility is vested by the Water Quality Supervision of the Water Resources Management Center, and by the corresponding agencies of individual district water authorities. 7. Variations of the groundwater table. The effect of urbanization on groundwater regime is also a significant one. Recharge to groundwater is diminished by growing impervious areas (roofs, pavements of streets and roads, etc.), as well as by higher rates of runoff (gutters, sinks and organized snow-removal). On the other hand, sprinkling of green areas presents a source of additional recharge. The groundwater table may be raised locally by civil engineering structures whereas underground conduits in the city may exert a drawdown effect. Leekage from municipal sewers at damage points may introduce seepage water into the surrounding soil especially at high rates of flow, whereas in other instances, the groundwater may be drained especially by deep sewers. No generalization is possible but the designer should always bear in mind the potential adverse effects of civil engineering structures. 8. Drainage of precipitation water. Owing to the growth of impervious areas and to accelerated runoff the wave

5 passing down the sewers tend to increase in intensity. The peak discharge resulting from a particular rainfall may be four times as large as in the period before urbanization. In the case of smaller rainfalls this is obviously of no consequence, still a growing number of cases is reported where deeper basements and elevator shafts are flooded by shower water. Earlier sewers in rapidly developing areas may become insufficient, while the reconstruction of major highways may be of the saine effect since by cutting through watersheds the area drained by a particular sewer may be changed suddenly.