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: Temporal and spatial variations of the concentration and the isotopic composition of groundwater sulfate in an unconfined sandy aquifer covered by peatland have been studied to better understand the sources and biogeochemical processes that affect sulfate distribution in shallow groundwater systems influenced by organic rich sediments. The groundwater monitoring was carried out for one year at hydrogeological station Pożary located within the protected zone of the Kampinos National Park. Sulfur (34SSO4) and oxygen (18OSO4) isotopic composition of dissolved sulfates were analyzed together with oxygen (18OH2O) and hydrogen (2HH2O) isotopic composition of water and major ions concentration at monthly intervals. The research revealed three main sources of sulfates dissolved in groundwater, namely, (a) atmospheric sulfates—supplied to the aquifer by atmospheric deposition (rain and snow melt), (b) sulfates formed by dissolution of evaporite sulfate minerals, mainly gypsum—considerably enriched in 34S and 18O, and (c) sulfate formed during oxidation of reduced inorganic sulfur compounds (RIS), mainly pyrite—depleted in 34S and 18O. The final isotopic composition and concentration of dissolved SO42− in groundwater are the result of overlapping processes of dissimilatory sulfate reduction, oxidation of sulfide minerals, and mixing of water in aquifer profile.

Chemical and isotopic analyses of groundwater from piezometers localized around a reclaimed landfill were performed in order to identify the boundaries of groundwater contamination zone. Spatial distribution of dissolved inorganic carbon (DIC) concentration and stable carbon isotopes in the groundwater was used to distinguish the piezometers localized within the contaminated aquifer. Background groundwater was characterized by low DIC concentration (from 1.8 to 5.0 mmol/L) and negative values of δC (from -20.6‰ to -12.4‰). Higher DIC concentrations (from 6.0 to 12.5 mmol/L) and higher values of δC (from -10.9 to +3.6‰) were determined in groundwater contaminated by landfill leachate. The study confirmed that δC value in the groundwater was a useful tracer in determining the extent of the contamination zone around the landfill. In general, upgradient from the landfill, carbon isotopic composition of groundwater depended on natural sources of carbon and δC values were negative. Downgradient from the landfill, where groundwater was contaminated by the landfill leachate, δC values were higher, sometimes even positive.

Measurement and calculation of the carbon isotopic composition of groundwater from piezometers located around a reclaimed landfill were performed in order to test the method to distinguish the piezometers localized within the contaminated area and to identify the boundaries of the leachate plume. In order to select the best method for delineation of the leachate plume it was analyzed: chemical composition, the stable carbon isotopic composition in groundwater, and the calculation of carbon isotopic composition in groundwater. Comparison of the different methods for delineation of the leachate plume indicate, that the best method appear to be method based on the measurement and calculation of the carbon isotopic composition in groundwater. The proposed method has been tested using the data from Otwock landfill (Poland), but it can also be used in other contaminated areas.

Accurate projection of gas generation from landfills poses numerous difficulties. One needs to select and use an appropriate method from among several available options, and consider local and individual conditions of a landfill. These aspects are crucial for the economic management of the landfill gas in new landfills, and for assessing the impact of the gas on soil-water environment in old landfills. This paper is aimed at reviewing the research methods that can be used to assess the activity of new municipal waste landfills currently in operation, and of old, closed landfills after reclamation. Landfill activity can be assessed using different models and analysis of the produced gas. The actual data on the investigated municipal landfill showed that the landfill activity can be accurately assessed based on the quantitative determination of biogas formation using the LandGEM method, and the analysis of gas phase variability in the landfill accounting for oxygen, methane, carbon dioxide and hydrogen sulfide share/presence. Each landfill is different and calls for an individual approach or methodological modifications.