Slurry lagoon lining in Solihull

Farming in the Meriden Gap

Lagoon work in the borough is a handful of farms rather than a farming district. It sits in the open country east of the M42, around Barston, Berkswell and Balsall Common, and over the boundary into Warwickshire, where we cover the same ground.

Many of these stores are older earth-banked lagoons dug decades ago. Some were never lined. Others have a liner that has aged, been patched or pulled from its anchorage. The banks may be clay, but clay banks crack and slump, and slurry finds the weak point.

From a single liner to a double-lined store

The build-up follows what is being stored and what your consultant or permit asks for. A dirty-water store taking yard washings can be as simple as fleece under a single welded sheet. A slurry store close to a watercourse may need a primary and a secondary liner separated by a drainage medium, so any seepage through the upper sheet is caught and can be checked at an inspection point before it gets near the soil.

• 300gsm protection fleece on the prepared profile
• Welded HDPE or LLDPE, single or double
• Leak-detection layer between liners where specified
• Floating cover where the design calls for one
• Sealed details at the fill pipe, the draw-off and the depth gauge

Who does what

Shaping the store is the earthworks contractor's job: banks, base and the trench along the crest. Before our liner is delivered we walk the finished shape with the lining drawing in hand, because a soft bank or a sharp stone left in the base will show up later as a leak. Then we lay, weld and detail, make a recorded test weld, and leave the farm a QA pack: the products used, the seam log with its trial weld, and as-built drawings for an inspector or insurer.

Weather, emptying and timing

Arden clay turns sticky within hours of rain, and membrane welds best in dry, settled conditions. On a reline the old store also has to be emptied and cleaned out first, which fits around the farm's spreading calendar. We plan the lining around both, and keep the farm told if the forecast moves the dates.

Our nearest lagoon job shows how that works. North Warwickshire's Bodymoor Heath, a short run up the M42, is where we lined a 2,000m² store in welded LLDPE, sandwiched between two 300g/m² fleeces so stones beneath and cattle above can't damage it. Rain interrupted the install; we resequenced the work and the farm still had its store on programme.