Slurry lagoon lining around Birmingham

The farms just outside the city

Past Sutton Coldfield and Walmley the built-up area gives way to farmland within a few miles: dairy and beef units, mixed farms and livery yards running out into North Warwickshire and south Staffordshire. Those farms sit close to housing and to the Tame and its brooks, so a store that leaks is noticed quickly by neighbours and by the watercourse.

There is also digestate. Anaerobic digestion plants that take farm or food waste need lagoons for what comes out, and those stores tend to be bigger and more heavily specified than a dairy farm's.

Being near our Tamworth base helps here. A lining crew can get to site at short notice to catch a dry spell, and come back again if the fill points have to wait for the pipework.

A Tame valley lagoon of ours

Bodymoor Heath, on the far side of Sutton Coldfield, is where we lined 2,000m² of farm lagoon for slurry and wastewater. The welded LLDPE sits between two layers of 300g/m² fleece, the lower one guarding against stones in the formation and the upper one against livestock. Rain set in during the job, so we reordered the work to stay on programme and ran our final checks across the whole lining before handing it back.

Layers, from simple to double-lined

Which layers go in is set by the contents and by the farm's consultant or permit. A dirty-water store on a small unit may need only fleece and one welded liner; a digestate lagoon serving an AD plant may need two with a detection layer between.

On these jobs the banks, base and anchor trenches are cut and shaped by the farm's earthworks contractor. Before our membrane is delivered we walk the batters and trench line against the lining drawings, and on the first day a trial weld is cut, tested and logged.

• Non-woven protection fleece laid over the base and banks
• A welded HDPE or LLDPE liner, joined panel to panel
• A drainage layer and second liner for leak detection, where specified
• Fill pipes, draw-off and a level gauge sealed through the membrane
• A floating cover where rain and odour must be controlled

Records for the inspector and the insurer

A lagoon is judged on its paperwork as well as its workmanship. Ours comes as one QA file: what was delivered and laid, how each seam tested, and drawings of the store as finished. That file is what an inspection visit and the farm's insurer will both ask to see.