Ecologia was instructed to undertake emergency excavation works, after an accidental loss of approximately 850 litres of kerosene heating oil from a faulty above-ground storage tank at a private domestic property in Kent. The loss occurred above a Principal Aquifer in close proximity to a major drinking water abstraction point.
The emergency works initially comprised hand augering and trial pitting, with on-site and laboratory testing of soils, in order to categorise and delineate the contamination and to assess the risks to receptors such as groundwater and human health.
The emergency works identified that the oil had migrated vertically through fractures within the unsaturated zone of the chalk. Lateral contaminant migration was found to be minimal, however, significant contamination was found to have migrated vertically to depth. Risks to the groundwater and the Principal Aquifer were identified as very high.
In order to assess contaminant migration pathways and any impact to the principal aquifer a total of four deep groundwater monitoring boreholes were installed around the point of loss after consultation with the Environment Agency. Drilling methods comprised hollow stem augering and rotary single coring without the use of water flush. These methods ensured efficient drilling of the chalk without aiding any contaminant migration, whilst allowing undisturbed samples of the chalk to be taken at groundwater level.
The boreholes were drilled to 40m below ground level (bgl) intercepting the aquifer located at approximately 32m bgl in order to allow continuous groundwater monitoring.
Next stage of work will include groundwater monitoring, derivation of remedial targets protective of the principal chalk aquifer and appraisal of appropriate remedial options with the Environment Agency, if deemed necessary.