The site. A site at Appleby, Buildwas, in the Severn valley near Telford.
What we did. Trial pits at different points across the site, tested to BRE 365.
What we found. The ground conditions varied across the site, and the soils were cohesive (clay-rich), holding water rather than letting it soak away.
What it meant. We did not recommend soakaways for this site. The surface water strategy needed another route, which is what the testing was there to establish.
The lesson. Ground can change within one site. More than one pit, in the right places, is what makes a result reliable.