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Find out How a Slurry Lagoon is Constructed

Watch as Our Operations Director, Pat Browne speaks to Bertie Troy of Grasstec Group about constructing a typical lined farm effluent storage lagoon.


The lagoon is excavated to the required dimensions, keeping the sides of the lagoon at 45 degrees as shown in the picture.

The floor of the lagoon should have a slight fall of between 150-300mm towards one corner. In this corner a pipe is placed out through the bank at a slight fall away from the lagoon towards the Leak Detection Manhole. A Leak Detection system has to be installed to meet Department of Agriculture specifications, if the farmer is claiming for grant aid on the lagoon. Our company supplies the Leak Detection system and is included in our price list.

Once the lagoon in fully excavated, the floor of the lagoon is covered with 3 inches of Pea-Gravel (half inch rounded stone) and the sloping sides are covered with 2 inches of quarry dust (quarter inch to fines). At this stage the floor and sides are ready to be lined with our heavy duty 2.5mm slurry lagoon liners.

Slurry Lagoon Excavation

Leak Detection System

Leak Detection System

This picture shows where the leak detection system is positioned. As can be seen there is approximately 800mm (2 1/2ft) between the manhole and the nearest piece of liner. This space is needed as an anchor trench is dug there and the liner is buried in it to keep it secured soundly to the ground.

The Manhole itself has a sealed base and travels down 1m (3ft) below the floor of the lagoon. A 160mm (6 inch) pipe exits the manhole 1m (3ft) from the bottom. It extends in just under the lagoon liner at the base of the lagoon. Should there be a leak in the lagoon the slurry will travel into through the leak detection manhole, where it can be sampled. With 20 years experience in both industrial & agricultural sealing projects, we have not yet had any leaks in our projects using lagoon liners.


The slurry lagoon can be agitated by either pump or propeller type agitators. We would recommend the use of the propeller type as this offers the farmer reduced costs for both lining and concrete. Furthermore, propeller agitators usually require less horsepower to drive and can easily generate substantial currents in the lagoon due to the liner’s smooth surface. The addition of a hydraulic top linkage makes it even easier to break up a thick crust by rising the propeller through the crust. As a rule of thumb, for square lagoons, one agitation point is needed for every 200,000 gallons of storage. For long and narrow lagoons additional points are usually required.

Slurry Stores Mixing Point and Slope Fab

Mixing Point and Slope Fab

Propeller Type Agitation

Propeller Type AgitationUsed in 99% of slurry lagoons. The concrete pad is usually 3m (10ft) wide and 160mm (6 inches) thick. It extends out 2m (6ft) out onto the floor also to absorb the agitation currents. At ground level the concrete extends out enough so that the four wheels of the tractor willl fit on it. About 6m3 of 40N concrete is needed for each agitation point. Estimated at €100 per cubic meter, it will cost approximately €600 per point. Propeller agitators can be bought new from approximately €2,000 up to €3,500 for high output versions. They are also widely available second hand and most slurry contractors carry one.

Pump Type Agitation

Slurry Pump Agitator

Slurry Pump Agitator

With the pump type agitation point a concrete structure needs to be built so that a tractor can reverse out onto it. This is poured before any lining has started. The walls are 300mm (1ft) thick and are made from reinforced concrete with steel. The average cost to get one poured is approximately €2,500. A substantial amount of extra work is required to line around the concrete wall and is charged at an additional €1,500 per agitation point. Therefore at €4,000 extra, the pump type agitation point can become expensive, particularly if more than one is required.

Scraping into the Lagoon

Scraping Into The LagoonWhether using an automatic or a tractor scraper the concrete needs to be poured on top of the liner as you can see in the picture. The 300mm (1ft) high kerb walls directs the slurry to the lagoon. The picture refers to an automatic scraper. If a tractor scraper was to be used concrete wheel stops would need to be installed to prevent the tractor reversing into the lagoon. These are shown in the following photographs.

Safety: Agitation Point Gate

Agitation Point GateThis picture shows a perfectly fenced agitation point to grant specification. The gate itself has no horizontal bars other than the top and bottom bar. Rigid galvanised steel mesh is then welded directly onto the gates frame. The gate needs to be made in such a way that it can be locked securely. It must be 1.8m (6ft) high. The posts that it hangs from are usually either 100mm (4 inch) or 150mm (6 inch) galvanised tubular steel

Safety: Agitation Point Handrail

Agitation Point HandrailThe gate needs to be opened to agitate or empty the lagoon so behind the gate additional safety features are required. As can be seen a waist high 50mm (2 inch) galvanised tubular steel handrail is provided. To make room for the agitator the centre bar can slide to the right, out of the way.

Safety: Wheel Stops

Wheel StopsThe wheel stops prevent the tractor from reversing into the lagoon accidentally. The concrete wheel stops shown are 300mm (1ft) high, 300mm (1ft) thick and 900mm (3ft) wide. The maximum space that can be left between them is 1.2m (4ft). They need to be connected to the concrete pad below them with 12mm High Yield reinforcing steel rods. As can be seen from this angle the wheel stops are kept out to the edge of the lagoon to take full advantage of the reach of the agitator

Safety: Tyre Ladders

Tyre LaddersTyre ladders are provided as a means of emergency escape from the lagoon in the unlikely event of someone falling in. They are usually located in the four corners of the lagoon, but to meet Department of Agriculture specification S126 they should also be placed every 8m along the sides of the lagoon. The ropes are tied off at the bottom of the fence posts.

Safety: Fencing

  • FencingGrant specification fencing requires a 2.5mm chain link fence to be 1.8m (6ft) high.
  • The posts can be either 75mm (3 inch) galvanised tubular steel with a 3.2mm wall thickness, or concrete with a 125mm X 125mm (5 inch X 5 inch) butt end.
  • Posts can be no further than 3m (10 ft) apart. The posts also need to be embedded in 600mm (2ft) of concrete.
  • Four strands of plain wire shall be strained and stapled or tied to the uprights with tying wire.
  • One strand of 2.5mm barbed wire shall be placed along the top of the fence.

Flow Channel

 farm slurry storage flow chanel

Farm Slurry Storage Flow Channel

This picture shows how a flow channel can be incorporated into a lagoon. The walls here are of block-work construction that has been plastered on both sides. They can also be poured concrete. The lip at the front is approximately 230mm (9 inches) high. The height of these lips varies from channel to channel particularly as the channels get longer, the lip usually gets higher.

Completed Lagoons

These pictures show some completed lagoons. Please note some did not have their fencing installed at the time the pictures were taken.

300,000 Gallon Lagoon near Athlone, Co. Westmeath

300,000 Gallon Lagoon near Mallow, Co. Cork

780,000 Gallon Lagoon near Portlaoise, Co. Laois

500,000 Gallon Lagoon near Listowel, Co. Kerry

300,000 Gallon Lagoon near Mallow, Co. Cork

500,000 Gallon Lagoon near Listowel, Co. Kerry

Lagoon Technical Details

Automatic scraper linked to lagoon

Handrail open

Handrail detail

Handrail locking pin

Handrail detail

Lagoon gate and wheel stops

Agitation Point

Permanent pipe mounting joint

Fencing wire clip


To get a site visit, quote, more information or just some advice about your slurry lagoon please don't hesitate to contact us. You can call, email or simply complete our query form and we will contact you.

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