Summary:

The aim of this study was the application of the triangle method for the calculation of the infiltration and inflow volume entering the sanitary sewer system operating in the Cracow County (Lesser Poland Voivodeship). The analyzed, 10 km long, sewer system is made of vitrified clay pipes with diameters of 200, 250 and 300 mm. Infiltration and inflow, also called extraneous water, adversely affect the operation of sewer systems and sewage treatment plants, what in turn may result in water contamination in the receiver. Amount of extraneous water in the inflows to sewer systems should be estimated using the available computational methods and their causes should be eliminated on an ongoing basis. The conducted study showed an alarming amount of extraneous water flowing into the analyzed sewer system, i.e. in 2010 it accounted for 41.1% (40033 m3), in 2011 - 28.7% (22224 m3), while in 2012 - 23.4% (16848 m3) of the total annual volume of polluted water. The volume of infiltration and inflow entering the examined sewer system depended primarily on the frequency of precipitation, and - to a lesser extent - on its annual total amount. Illegal connections of yard inlets or gutters to the sewage drains are the main cause of extraneous water inflow to the analyzed sewer system, as determined based on field inspections and smoke tests, conducted by the water supply company.