An operational non-hazardous landfill in the Northeast of England was required to update its monitoring network in response to regulatory pressure. The site is contained, with a complex lining system, and sits on a principal aquifer. Monitoring data indicated that there was a leachate escape from the landfill. Elevated concentrations of ammoniacal nitrogen and low dissolved oxygen were detected, which threatened the water quality at a downstream groundwater Public Water Supply (PWS) borehole.
Investigations were undertaken and an abstraction borehole installed to control the spread on the leachate plume in groundwater. Downstream sentinel monitoring boreholes were also installed. An historic source of leachate leakage was identified as overtopping of temporary bund during filling of a cell. The volumes of leachate lost were estimated and the likely spread of the plume was modelled. This enabled the timescales for contaminant concentrations to dissipate to be estimated.
When measured concentrations did not fall in accordance with the model results, further assessment by the operator identified ongoing leakage or leachate through the subbase of a haul road. This breach was sealed. The modelling and monitoring were pivotal in preventing the spread of the plume and protecting the PWS receptor and in the operator maintaining good working relationships with the Environment Agency and water company. Diminishing concentrations at the sentinel boreholes confirmed that the receptor was protected.
