Field Measurement of Fluorescent Dissolved Organic Material as a Means of Early Detection of Leachate Plumes

Early detection of landfill leachate plumes may minimise aquifer degradation and financial expenditure for the landfill operator. Current methods of landfill leachate monitoring typically include analysis of groundwater field parameters such as electrical conductivity (EC), coupled with laboratory analysis of a selection of major cations and anions. In many instances, background influences can mask the impact of leachate, which only becomes apparent once a significant impact has occurred. Here, we investigate the potential for changes in fluorescent dissolved organic material (FDOM) concentration to be used as an indicator of leachate impact. The research was undertaken in a fractured rock aquifer located downgradient of a local government-operated putrescible landfill in Central West NSW, Australia. Field measurement of groundwater FDOM was undertaken using an in situ fluorometer (FDOM probe) which provides a relative measurement of FDOM. To quantify the FDOM values, a bench fluorescence spectrophotometer was used to collect excitation/emission spectra. A plume of elevated FDOM and EC levels within the fractured rock system up to 600 m downgradient of the landfill was identified, whereas analysis of major cations and anions from boreholes within the plume did not detect leachate impacts above background. Excitation/emission matrices of groundwater from these locations confirmed that similar fluorescence signatures to those collected from the landfill were present. Photodegradation experiments were conducted to determine if fluorescent whitening agents (FWAs) were a component of the fluorescence signal. Observed photodegradation of 40 % compared to background (8 %) suggests that a component of the fluorescence signal can be attributed to FWAs. FDOM in groundwater therefore provides an indicator of low-level (up to 98 % dilution) leachate influence, and the identification of FWAs within groundwater can be considered confirmation of a leachate signal.