DNO Substation, Worcestershire
Several tonnes of electrical insulating oil were released from a grid transformer during a fault. An unknown proportion entered the ground beneath via soakaway drainage. A nearby stream and SSSI were at risk of pollution. Ground investigation was required to define the distribution of oil in the subsurface, assess the risks to environmental receptors and the options for product recovery.
We installed a perimeter interception trench to prevent oil from migrating beyond the site boundary. A series of boreholes were drilled to confirm geological and hydrogeological conditions and delineate the contamination. A remediation pilot trial was undertaken to determine the most appropriate technique for recovery of free product. Product distribution and migration were found to be governed by a complex hydrogeological scenario.
Free product had bypassed perched water and entered a lower, confined aquifer. Data from the ground investigation and pilot trial were used to demonstrate the heterogeneity of product distribution, slow rate of migration and low recoverable volume. Risk assessment, monitoring and product bailing were agreed with The Environment Agency as suitable to protect environmental receptors and address client liabilities.
A report was issued in Spring 2012 demonstrating completion of the works to the satisfaction of The Environment Agency and our client.