3 March 2000

More reasons to bring your

slurry store up to scratch

With yet more pollution control measures to be introduced

towards the end of this year, now is the time to check

whether your set-up is up to scratch, says Royal Agricultural

College senior buildings lecturer Graeme Lochhead

IT is a sad fact, but most UK slurry storage facilities are getting distinctly long-in-the-tooth. Grants for such storage ended in the early 1990s and many stores are now more than 10-years-old. Quite a few, indeed, are more than 20-years-old.

Anything built before Sept 1991 is exempt from the Control of Pollution (slurry, silage and agricultural fuel oil) regulations (1991). But such stores can only retain this status by ensuring that pollution or a significant risk of pollution does not occur.

Given the state of farming, it is important to extend the life of these older stores, but that can only be done through tip-top maintenance and good management.

Clean up your act

Cleanliness is next to godliness, so apply this to your farmyard. Identify clean and dirty areas and minimise the dirty areas where possible.

Start by looking at the clean water drains, roof water, etc, and repairing where needed.

Locate or construct a single point for this clean water to be piped to where it is likely to be used. Consider storing this water for use around the farm and carry out a budgeting exercise on the possible savings in water charges.

Analyse animal and vehicle traffic-flows and try to see how these could help in eliminating external dirty yards. Could the layout of the buildings be altered to allow animals to be moved under cover at all times during the housing period? This would significantly reduce the dirty water element and might even go some way to reducing the time involved in scraping and cleaning.

Dispose of all contaminated water, or, alternatively, store this waste and spread it through a dirty water irrigation system designed to spread at pre-determined levels on fields with minimal slope.

Slurry and solid

waste storage

Farmyard manure from bedded yards can be stored in a clamp area or spread on the field.

The latter is by far the best option, the only restriction being that you must not spread closer than 10m (33ft) to a water course.

This method allows for composting, but the downside is the location of many clamps. Most are next to gateways from fields on to public roads. Good for year-round access, but that seepage from the heap will inevitably leach into the drain and find the nearest stream or watercourse.

Semi-solid waste is best dealt with through weeping wall systems. These provide good storage for all farm waste from different types of facilities, but you need to identify the type of waste before choosing this option.

Weeping wall set-ups need a well designed dirty water system to dispose of the run-off and liquor properly. Separators are another way of using the solid fraction of the slurry and waste.

Whatever the system, pay close attention to maintenance of plant and equipment. It has to work in a hostile environment, so regular servicing is essential. This is best carried out in the spring to ensure equipment will operate the following winter.

When the store is empty, inspect the walls and floors for problems and take remedial action if necessary. If you use a lagoon, check the base and walls and inspect liners for rips and tears.

Slurry stores fall into two types: Earth lagoons (as above) and constructed tanks using concrete or steel. Below-slat slurry stores are designed to have a 20-year life with care and good maintenance, but rarely get inspected .

A lot of these are now exceeding their design life and have probably never received any maintenance or inspection. But before you try to carry out any work, remember that they may contain poisonous gases that are heavier that air and should be evacuated before entering the facility. Only inspect these if you have reason to think that there might be a leak or other potential cause of pollution.

Above-ground stores fall into the same age category but can be readily inspected and checked. If the store is between 15 to 20 years old then this inspection should take place at yearly intervals. Check as follows:

&#8226 Check base for leakage points, observing flow rate.

&#8226 Check for any ground movement below the base.

&#8226 Look for external signs of corrosion.

&#8226 Check for mechanical damage from machines, pumps and stirrers.

&#8226 Check protective coatings.

&#8226 Check fixings, looking for corrosion of nuts and bolts and faulty sealant.

&#8226 Check sluice gates (when empty) for signs of warping and corrosion.

Silage clamps

The thought of major capital investment in silage clamps is pretty daunting and can probably be avoided, but maximising the life of your clamps requires maintenance when they are both empty and full.

Regular checking, timely repair, avoiding mechanical damage and refraining from overfilling are all essential criteria to observe.

The main source of pollution for clamps is through the floors. This is usually caused by old age, poor or made-up ground, poor construction and excessive corrosion.

Make sure your yearly checks are carried out early enough to give you time to repair and cure before ensiling starts. When you check the floor look carefully at the following areas: Joints, movement of concrete slabs, significant cracks in the floor and excessive corrosion, particularly at the front of the clamp.

Check walls, too, for evidence of corrosion and cracking and pay particular attention to signs of overloading and potential collapse. Drainage systems need to be clean and free-flowing and all traps and grids free from silt and dirt. The effluent tank should only be checked if there is a fear of failure and only then with breathing apparatus.

Decide whether to repair, upgrade or renew the clamp and then choose the appropriate repair method. The floor is the most likely area to show severe signs of corrosion, so most repair methods concentrate on this area. Three main techniques are available:

&#8226 Overlay with new concrete.

&#8226 Overlay with a concrete screed likely to contain epoxy resin.

&#8226 Overlay with hot rolled asphalt.

Expect to pay £10 to £20/sq m for these repairs, depending on whether you do it yourself or call in a specialist contractor.

Remember, failures normally occur during or immediately after filling. That is due to the high moisture content of the silage, the speed of filling and the high thrust load on the walls. The important aspect of this is to remove the effluent as quickly as possible from the clamp thus reducing the pressure on the wall. This can be achieved by placing a plastic drainage pipe at the meeting point of the floor and wall when filling.

Agricultural fuel oils

Pollution from failed diesel tanks is not uncommon; the resultant clean-up can be costly, too, and there is always the possibility of prosecution.

Although only new tanks legally have to be bunded, it is good practice to consider bunding your existing one. A brick or block bund with a liner will do, but it must provide 110% (185% in a nitrogen vulnerable zone) of the capacity of the tank. You must also ensure that rainwater cannot enter the bund. Having done this, check your insurance cover in case of leakage; in some cases the cost of cleaning up a spillage is not covered.

Waste management

planning

Last, consider having a waste audit carried out. This tries to identify the type of waste and volume produced, the application rates for the land, slopes that can be used throughout the year and the times of the year suitable for spreading.

Most pollution incidents occur from run-off rather than failures of structures, so good management is essential. Every farm should have a copy of the codes of practice for the protection of water, air and soil, which set out accepted good practice. If you do not produce a site-specific waste management plan, then ensure that you at least follow the codes.

Above: Reduce external dirty yards to a minimum. Large dirty areas create volume problems and are time-consuming to clean. Below: Solid waste stores need regular checking to ensure that they do not overspill. Close attention to spreading opportunities will avoid this problem.

Floor repairs – clean off and prime surface before applying new surface (follow recommendations on label).

This form of propping will only last for a certain amount of time, so take time out to check

the clamp before filling.