The site. A plot at Little Moor Hill, Smethwick, near Birmingham, where soakaways were proposed for the surface water.
What we did. Four test locations were planned. Tests A and B were carried out in natural ground to BRE 365.
What we found. Neither pit fell the required 25% while we were on site, so infiltration was far too slow. The rest of the site was covered in a large amount of fill material, so tests C and D could not be carried out in natural ground.
What it meant. Soakaways weren’t a viable way to discharge surface water from this site, and the drainage strategy had to use another route.
The lesson. Made ground is common across the Black Country and Sandwell. A soakaway in fill is rarely accepted, so the natural ground beneath is what counts.