This work pays attention to the possibility of formation leakage through reinforced concrete walls of sewage tanks. Leakage can be caused by the action of aggressive components of wastewater on concrete. Hardened cement paste can be damaged by chloride and ammonium ions present in significant quantities in the post-production waters from coking plants. This important kind of concrete corrosion was precisely recognized in laboratory conditions. Specimens of cement pastes made from two different cements were immersed in saturated water solutions of ammonium chloride. The test results of porosity, chloride ion concentrations, and content of crystal phases showed large changes in the microstructure of hardened cement pastes. We found that the Portland cement used in the postwar years provide better durability than the slag cement currently recommended for constructing environmental protection facilities.