Soakaway installation in Nottingham

Good infiltration over a drinking-water aquifer

Sherwood Sandstone is soft, sandy and permeable, which is why percolation results on it are often strong. It is also one of the country's principal aquifers, pumped for public supply. That cuts both ways: the ground welcomes clean roof water, but the engineer has to think about what else goes into it.

Expect the design to separate the two. Roof runoff may go straight to the soakaway, while water from drives and yards passes through silt and oil management first, or goes elsewhere. Source protection zones and the depth to the water table are checked by your engineer before the crates are sized.

Keeping sand out of the crates

Weathered sandstone breaks down into loose sand, and pit sides on these plots can slump while they're open. Our crew works promptly once the hole is formed. The permeable geotextile goes in first and wraps the whole structure, so fine sand stays outside while water moves freely through.

Over the years, it's sediment that kills a soakaway, not the crates. We connect the catchpits and filters shown on the design, so grit is trapped where someone can lift a cover and empty it, rather than settling in the voids where nobody can reach it.

Where infiltration runs out

Not all of Greater Nottingham drains. Cross the Trent towards Radcliffe, Bingham and Cotgrave and the mudstone takes over. On the river terraces, the water table can be too shallow to leave the clearance a soakaway needs beneath it. In both cases the engineer will usually move to sealed attenuation, and we install that as well.

• New homes and small estates on the sandy land north of the city
• Barn conversions and rural plots around Calverton and Blidworth
• Extensions to schools and community buildings
• Light commercial units where the roof drains to ground

A day on a Nottingham soakaway

Before the dig we read the volume, depth and position off the engineer's drawing, including the distance from the house that Approved Document H expects. On the day, we look at the base the groundworker has formed and make sure it's level and free of loose spoil. Then the wrap goes in, the crates are built up inside it to the designed size, the inlet and silt connections are made, and the geotextile is folded over and closed. Your groundworker backfills; we leave inspection records for building control.