Expert Witness Report: Three Successive Soakaway Failures Since 1987

Overview

WCI Consulting Engineers was instructed by Porter Dodson solicitors to provide an independent expert witness assessment of a shared foul drainage system at the centre of a five-month neighbour dispute – identifying the root cause of three successive failures and providing a clear remedial pathway.

The Challenge

The Long House and Old Court Barn shared a foul drainage system that had failed repeatedly since 1987, with extensions in 2017 and 2021 also failing. Septic effluent was outcropping on the grounds. An independent technical assessment capable of withstanding legal scrutiny was required.

The WCI Solution

WCI Consulting Engineers analysed all three iterations of the soakaway against BS 6297:2007+A1:2008 and BRE Digest 365, cross-referenced with BGS soil data. The original 20-metre drain was grossly undersized for a 12PE system. The subsequent crates were surface water attenuation products – fundamentally unsuitable for foul drainage. No percolation testing had ever been undertaken. Having systematically discounted all other causes, the report concluded that poor design was the underlying cause of every failure. The recommended pathway: BS 6297 percolation testing, with STP upgrade and watercourse discharge if rates prove inadequate.

The Outcome

Both legal teams received objective, technically rigorous analysis and a constructive route forward to resolve the dispute.

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