Farm Waste Structures: Guidance on Construction, Repair and Maintenance

Separation of clean and dirty water. Dirty water storage. Yard area construction.

Note No: CGN 008, July 2000
Prepared by ADAS National Building Design Team. Funded by The Department for Environment, Food & Rural Affairs.

Figure 1

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Figure 2

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Example: a scheme for dealing with dirty and clean water

Contaminated rainwater from the yards drains by gravity into the sectional pre-cast concrete reception pit, Figure 2 centre, and seen under construction in Figure 1. This is then pumped into the above ground concrete storage tank, Figure 2 left.The brickwork chamber, Figure 2 centre left, houses two lockable valves in the tank outlet pipe.The large eaves gutter to the building, Figure 2 top right, collects and conveys clean rainwater to a down pipe seen at the corner of the building. The down pipe is connected to a drain that discharges the roof water into a consented outfall in a nearby ditch.


  • Dirty water collection, storage and disposal systems must conform to the Control of Pollution Regulations. Refer to the Water Code (See References 1 & 2).
  • Carry out a site survey and draw a plan to scale. The survey should include:-
    • All roof areas and rainwater collection systems eg gutters, rainwater pipes, gullies.
    • All rainfall or wash water catchment areas such as yards, roads and collecting yards.
    • Levels and contours of catchment areas.
    • Layout of existing drainage systems including pipe sizes, manholes and invert levels.
    • Drain inlets and outlets and identification of type i.e. dirty or clean system.
  • Use the information to calculate the separate areas identified as clean or dirty.
  • Obtain the appropriate rainfall figures to use for design purposes from the Environment Agency or directly from the Meteorological Office.
  • Determine the quantities of clean and dirty water for the appropriate storage requirement i.e. reception pits minimum capacity two days waste production, slurry storage 120 days or as determined by a Farm Waste Management Plan (See Reference 2).
  • Include wash water and effluent run-off from stores.

Separation of clean water

  • Change practices to minimise dirty areas. Use kerbs, sleeping policemen and re-adjust yard levels to separate clean run-off.
  • Prepare detailed designs for clean water drains based upon BS 8301 (See Reference 3).
    • Ensure that gutters are adequate to collect roof rainwater.
    • Provide adequate rainwater pipes that discharge directly to a clean water drain.
    • Protect down pipes against impact damage.
    • Kerb and protect gullies at yard level from accidental contamination.
  • Consult the Environment Agency about your assessment of clean water and about discharge consents.

The Environment Agency may require an oil interceptor to be fitted in water drainage systems from roads and yards used by traffic. Information on oil interceptors is given in CIRIA Report No 164 (See Reference 4).

Dirty Water Storage

  • Roofing over fouled yard areas will help reduce volumes of dirty water. This may be a cost effective solution in some circumstances.
  • Refer to leaflets CGN 001, 003 and 004 for information about storage tanks. Dirty water may be drained directly or indirectly into an earth-banked store or a below ground tank, (see leaflet CGN 002)

Yard area construction

  • Specify at least 150mm thickness of compacted type 1 hardcore laid on the compacted and graded formation after topsoil removal (See Reference 5).
  • Use a 150mm thick slab using RC40 concrete mix to BS 5328 laid to BS 8110 requirements. It is recommended that the slab be reinforced with at least an A252 steel fabric to minimise cracking. Seek expert advice where heavy traffic is likely. Seal joints with a sealant to BS 6213 (See References 6, 7 & 8).
  • Contour and kerb yards to contain the dirty water.
  • Lay to falls. At appropriate locations, form surface depressions to provide an adequate channel leading towards the reception pit or store. Maintain the slab thickness beneath the channel.

Reception Pits

  • Obtain expert advice if intending to self-build or to use a second hand tank.
  • Design below ground pits/tanks to withstand BS 5502 Part 50 loading (See Reference 9).
  • Suitable proprietary tanks, conforming to the Control of Pollution Regulations, include pre-cast concrete and glass reinforced plastic construction (See Reference 5).


  • Refer to CIRIA Reports 126 and 164 for further information about constructing a dirty water installation (See References 4 & 5).
  • If you intend to engage a building contractor refer to Leaflet CGN 100.

Repair and Maintenance

  • Obtain information for operation and maintenance from the designer or installer.
  • Operate and maintain pumps correctly.
  • Repair defective gutters and rain water pipes.
  • Repair defective kerbs and channels.
  • Seek expert advice about major structural defects and concrete decay.
  • Seek expert advice about exposed and corroded reinforcement.
  • Floor joints must be inspected every year. If defective, properly prepare and repair with sealant.
  • Joints with defective concrete may require special attention.
  • Check and rectify damage and blockages to drains and reception pits. Be aware of danger and take precautions against toxic gases during inspections.
  • Refer to CIRIA Report 126 for specialist techniques and repair practice (See Reference 5).
  • Refer to Leaflets CGN 001, 002, 003 and 004 for information about the maintenance of slurry stores.


  1. The Control of Pollution (Silage, Slurry and Agricultural Fuel Oil) Regulations 1991 (as amended).
  2. The Code of Good Agricultural Practice for Water; MAFF (Free publication).
  3. British Standard 8301: Building drainage; British Standards Institution.
  4. CIRIA Report No 164: Design of containment systems for the prevention of water pollution.
  5. CIRIA Report No 126: Farm waste storage- Guidelines for construction.
  6. British Standard 5328: Concrete specifications and procedures; British Standards Institution.
  7. British Standard 8110: Structural use of concrete; British Standards Institution.
  8. British Standard 6213: Selection of construction sealants; British Standards Institution.
  9. British Standard 5502: Buildings and structures for agriculture (Parts 20 and 22); British Standards Institution.

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