Steel, overground slurry stores can be an effective way to store large volumes of slurry out far, especially where there is sufficient feed and lying space, but a lack of actual storage. There is increased work in pumping slurry to them in comparison to an underground slatted tank, but those who are limited with ground space, or bedrock that requires breakage, overhead towers can be a more tempting option.

The Department of Agriculture intermittently looks at specifications regarding all manner of farm buildings and infrastructure, and updates specifications as necessary. As such, these specifications should always be followed in relation to farm projects, but they are classed as the minimum standard and must be followed when completing grant aided work, such as TAMS.

S122, the document which covers the minimum specification for proprietary overground circular slurry/effluent stores, had last been updated in late 2016, with a new update on specifications published in December 2024. The new additions to the specifications are listed here.

Steel-sided store with geomembrane liner (SSSGL)

All installers of steel-sided stores with a geomembrane liner (SSSGL) shall be listed on S.122A (accepted installers) and shall use the lining material as submitted as part of the acceptance process. The geomembrane liner used shall have a minimum guarantee of 10 years and a minimum life expectancy of 20 years, and shall be listed on S.122A, along with the accepted installer. The liner manufacturer shall have and maintain ISO 9001 certification. The liner material shall be tested by an EU notified body. It is recommended that the accepted installer has an ISO 9002 Quality Accreditation and uses only materials from an ISO 9001 Quality Approved Manufacturer.

As a minimum, the work shall be performed to a level accepted by a recognised European accreditation body. All work specified in this section shall be the responsibility of the accepted installer, who shall be a specialist in this form of construction, and accepted as such by the Department of Agriculture, Food and the Marine and included on S.122A. The full installation of the geomembrane liner and store sides shall be carried out directly by the accepted installer of the SSSGL.

All other works shall be completed either by the accepted installer, or in accordance with the accepted installer’s instructions. In all cases the installation shall at least meet all the requirements of this specification.

A leak detection system shall be installed under every SSSGL store. The leak detection system shall consist of a 100mm drainage pipe installed below the store base surface, back-filled with 10mm gravel.

The drainage pipe shall be in a circle with a diameter of approximately two-thirds the store diameter, centred to the centre of the store.

This shall be linked to an inspection chamber, on the outside of the store. The inspection chamber shall be of at least 450mm diameter pipe and shall incorporate a lid flush with excavated and/or made-up ground must be finished uniform and smooth and free of any sharp protuberances. In particular, the surfaces to be lined must be free of water, jagged rock, debris, roots or any matter that could damage the lining material.

The area under the liner shall have a minimum 10mm depth of clean sand over the entire surface area. Where the site is excavated to bedrock, a minimum 250mm layer of compacted sub-soil shall be placed over the rock prior to the placement of the sand layer.

Where the sides are steel mesh, the mesh sides shall be lined with a minimum of 1.5mm thick HDPE, with the store liner placed inside the HDPE protection.

Where the sides are corrugated steel sheets, the sides shall be lined with the agreed protection material as listed on S.122A, with the store liner inside the protection material. If slurry in the store is to be agitated with an agitator, the liner shall be protected from damage at the location where the agitator is set up.

Fencing

A fence, minimum of 1.2m high and minimum of 900mm from the silo/tank, shall be constructed around the silo/tank, so as to prevent accidental damage occurring to the silo/tank. The barrier shall be of, at least, IPE 160 or equivalent for both uprights and horizontal sections. An opening 1,200mm wide, incorporating a gate may be left in the barrier to provide access to the valves.

Covers

Store covers shall be of proprietary manufacture and shall be certified by the manufacturer that they are suitable to cover the circular store they are covering. Where covers are being installed at the same time as the rest of the store, the cover shall be installed by the store contractor. Where a floating cover is installed, it shall be of a single piece of geomembrane. The free space between the store wall and the cover floats shall be at least 12cm. All floating covers shall be designed so that any movement of the floating cover does not lead to any damage of the liner or sides of the store.