Slurry lagoon lining around Bradford

Livestock country north and west of the city

Bradford's urban area has no call for lagoons, but the district stretches a long way out. Grass-based dairy and beef farms in the Aire valley, the Worth Valley and lower Wharfedale produce slurry all winter, and the higher sheep ground beyond them produces less. That is where our work in the district lies.

Many of these farms sit on sloping ground, with the store cut into the hillside below the buildings so slurry can run to it. That puts the downhill bank under the most strain, and it is the one we look at hardest when we check the earthworks.

Pennine rain and an open store

On the Pennine edge, a good deal of what fills an uncovered lagoon is rain rather than slurry. Capacity and freeboard are set by your consultant, and a floating cover is one way the design can stop rainfall eating into storage. Where a cover is specified, we fit it as part of the lining.

Wet weather also governs welding. Fusion needs a dry, clean overlap, so each joint is wiped and dried first, and every morning a sample seam is pulled apart to show the kit is set right for that day's conditions.

The layers, bottom to top

The banks, floor and edge trenches are shaped by whoever is doing your earthworks. We compare them with the drawings, then build the layers the design asks for. On a store with two liners that means:

• A 300gsm needle-punched fleece straight onto the soil
• The secondary sheet in HDPE or LLDPE, fused seam by seam
• A drainage net that guides any leak to a sump you can check
• The primary sheet fused above it
• Filling pipe, outlet and depth marker detailed watertight

Paperwork that stands up to inspection

New stores, and existing ones that are substantially altered, come under the SSAFO rules; your adviser confirms what your farm needs. Our job is a store that doesn't leak and the evidence to prove it: the product list, the weld log and as-built drawings, all in one QA pack.

Existing earth-banked stores can often be lined rather than replaced, after an inspection and some re-profiling of the banks by your contractor. On a farm where space for a new lagoon is short, that is usually the quicker route, and the farm keeps using a store it already knows.