31 Mar 2008
BAE Systems Environmental
Failure of the construction in an internally bunded tank released a substantial quantity of domestic grade kerosene into ground beneath this former farm in rural Kent where BAE Systems Environmental were commissioned to determine the extent and nature of the fuel spill including a full environmental risk assessment.
The Site was in a sensitive location within a Source Protection Zone being underlain by sandy gravel Head deposits overlying limestone and sandstone of the Hythe Formation. Intrusive investigations were conducted and a phased assessment and evaluation approach provided a progressively updated conceptual model.
A plume of affected soil was shown to have formed beneath the spill extending horizontally to a radius of approximately 7m from the point source and through the Head deposits into more competent strata some 4m below existing ground level.
Rotary borehole drilling with core recovery was the only method likely to provide adequately precise characterisation and sampling of the Hythe Formation. Four boreholes were constructed to assess plan area of the plume and to encounter deep groundwater. In addition, a further borehole was drilled at an inclined angle of 45o to intercept beneath the point source.
It was demonstrated that the entire quantity of hydrocarbons released had been immobilised by the buffer capacity of the near-surface strata and no plausible pollutant linkage to groundwater was established.
A quantitative risk assessment for controlled waters confirmed that concentrations of hydrocarbons in near surface strata presented no significant risk to groundwater beneath the site, even if contact was established.
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