Environmental assessments play an important role among environmental protection instruments in the economy. Three main cases of such assessments can be distinguished: forecasts of the effects of the implementation of the plan, program, strategy (i.e. the so-called strategic assessments), environmental impact assessment of planned projects, as well as environmental audits, including post-implementation assessments, of existing installations and facilities. In each case, the objectives of the procedure can be different and the assessment methods are defined differently too (Barczak and Kulig, 2017; Zarra et al., 2014). Generally, it is to show that a newly built facility, also modernized or extended, meets the environmental protection standards included in legal regulations and administrative decisions. In the case of modernization or extension of the facility, it must additionally be shown that the ecological goal of the project has been achieved. As far as odour effects are concerned, the main goal of the research is to determine whether the plant (installation) being potential source of odorants emission put into operation will not be nuisance for other users of the area and residents in general. In the article, the methodological aspects of odour testing in post-implementation assessments in sewage management were analysed on the example of a modernized and expanded wastewater treatment plant (installation of the WWTP) located in Central Poland. Field studies on the impact on the environment were carried out based on scented air pollution of objects causing odour nuisance in the analysed area.