Assessment of a degree of geochemical maturation and activity of a closed landfill site in Poland

The study was conducted around a reclaimed municipal landfill site, located in the suburbs of Otwock, about 25 km south-west of Warsaw (Poland). The research was carried out about 15 years after the landfill site ceased operation. According to the regulations on landfills sites in Poland (J. of Laws of 2002 No. 220 item 1858, Regulation of the Minister of Environment of 9 December 2002 on the scope, time, manner and conditions of landfill monitoring; J. of Laws of 2010 No. 238 item 1588, Regulation of the Minister of Environment of 8 December 2010 amending the regulation on the scope, time, manner and conditions of landfill monitoring), the monitoring period will end in 2021. Despite reclamation, the landfill site still affects the environment. The aim of this study was to assess the geochemical maturation of the stored waste and the landfill site activity by determining the current phase of the landfill site lifetime. This was achieved by means of non-standard application of carbon stable isotopes for the assessment of the landfill activity combined with conventional methods for measuring COD, BOD, DOC, BOD/COD ratio, and H2S and O-2 content in biogas. An analysis of carbon isotopic composition and COD, BOD, DOC of the leachate-contaminated groundwater and O-2 concentration in biogas indicated that the landfill site was between the methanogenic phase and air intrusion phase. However, BOD/COD ratio and H2S concentration in the biogas suggested that the landfill site is still active and the wastes contain readily biodegradable organic matter. The impact of the landfill site on the environment seems quite significant. In this case, and in other situations when the impact of a landfill site on the environment is high after the post-closure stage, the monitoring period should be extended.