RP24: Lined biobed plus pesticide loading and washdown area
Source: gov.uk (2025-02-03)

Find out about eligibility and requirements for the lined biobed plus pesticide loading and washdown area item.

This item is part of Capital Grants 2025. You must read the Capital Grants 2025 guidance (https://www.gov.uk/government/publications/capital-grants-2025) to understand the rules and how to apply. If you’re applying for this item as part of a Countryside Stewardship Higher Tier (CSHT) application, you must read the CSHT applicant’s guide (https://www.gov.uk/government/publications/countryside-stewardship-higher-tier-csht) to understand the rules and how to apply.

How much you’ll be paid

£119.77 per square metre (m2).

How this item benefits the environment

This item contains and collects pesticide residues that result from loading and washdown handling activities and degrades them in a biobed. It helps prevent pesticides from entering drains or water bodies, reducing the risk of water pollution.

This item can help you protect, recover and improve biodiversity on your land.

Where you can use this item

You can only use this item in areas targeted for the reduction of water pollution from agriculture, with support from Catchment Sensitive Farming (https://www.gov.uk/guidance/catchment-sensitive-farming-reduce-agricultural-water-pollution).

Catchment Sensitive Farming provides advice where there are water quality or flood risk issues linked to farming.

You cannot use this item:
- within 10 metres (m) of a watercourse
- within 50m of a spring, borehole or well which is not used to supply water for domestic use or food production without prior agreement from the Environment Agency (https://www.gov.uk/government/organisations/environment-agency#org-contacts)
- within 250m of a borehole used to supply water for domestic use or food production purposes without prior agreement from the Environment Agency
- in an area that’s designated as a Groundwater Source Protection Zone 1 (https://www.gov.uk/guidance/groundwater-source-protection-zones-spzs) without prior agreement from the Environment Agency
- without relevant advice, consents or waste management licence from the Environment Agency
- on historic or archaeological features identified in your Historic Environment Farm Environment Record (https://hefer-data.org.uk/) (HEFER)
- on areas of wildlife interest identified on your Farm Environment Record (FER) or on MAGIC (https://magic.defra.gov.uk/MagicMap.aspx)
Get permission to use this item

You’ll need to get advice, consents and any required permits from the Environment Agency (https://www.gov.uk/guidance/check-if-you-need-an-environmental-permit) before you start work. You also must make sure you can comply with the T32 exemption requirements (https://www.gov.uk/guidance/waste-exemption-t32-treatment-of-waste-in-a-biobed-or-biofilter).

What you must do to use this item

You must follow the specifications below when constructing this item.

Installing a loading and washdown area

You must install:
- a bunded concrete loading and washdown area
- holding tanks
- fixed pumps and pipes to remove washings from the tank
To do this, you must:
- remove topsoil and excavate an area for the washdown area and tank
- remove or divert any field drains that cross the site
- cover the site with 140 millimetres (mm) to 160mm of well compacted hardcore and at least 25mm of sand blinding, prior to installing the damp proof membrane
- lay a damp-proof membrane (at least 1200 gauge)
- lay a reinforced concrete slab at least 150mm thick to falls of at least 1:100
- construct a raised concrete barrier (‘bund’) around the perimeter of the slab, making sure that all concrete joints are sealed with a proprietary sealant
- make sure the bund is at least 100mm high so that it can contain liquids
- make sure the concrete-bunded area is as wide as the sprayer plus 2m, and as long as the sprayer plus 1.5m
- direct the drain containing the silt trap to a tank or chamber (no larger than 1500 litres) from which you can pump out and dispose of pesticide washings
- make sure the holding tank is made from seamless polyethylene, glass-reinforced plastic (GRP) or pre-cast concrete
- make sure the holding tank is sized according to local rainfall and the area of concrete (if there’s no roof or cover)
- make sure the whole structure is impermeable
Drainage in the loading and washdown area

You must also make sure the bunded concrete slab contains a slotted-cover type drain connected to a silt trap. It must have a removable cover that has a nominal capacity of 250mm below the inlet, so it allows liquid to drain.

Alternatively, you can lay the concrete so it’s sloping 4 ways to a drain in the centre of the slab. The drain should have a silt trap within it.

Installing a biobed

To install a biobed below ground level, you must:
- excavate an area for the biobed
- remove and block off any field drains
- compact and slope the sides of the earth bank to 30 to 35 degrees (about 1 in 1.5) towards the base
- lay an impermeable synthetic liner at least 1.2mm thick (pesticide grade) on top of a geotextile membrane underlay (190g per m2) and add 25mm of sand blinding
To construct a biobed above ground level, you must:
- use pre-cast or reinforced concrete and a 1.2mm thick liner, or an impermeable pesticide grade container
- follow the manufacturer’s installation instructions for the liner
You must then install any necessary holding tanks, pumps and pipes for the below or above-ground biobed.

Constructing a biobed outlet

To construct a biobed outlet (except for evaporation systems), you must:
- insert a drain through the liner to create a 100mm bonded outlet at the lowest point of excavation or create an internal sump (pit where water collects) when digging the biobed pit
- lay the liner to incorporate the sump
- make sure the liner is not perforated
- insert a central, permeable, vertical access tube that’s 0.5m in diameter to allow water to flow into the sump base
- install a pump within the tube that’s operated by a float switch setting
- place a ring of perforated drainage pipe into the base of the biobed and on top of tthe liner – this will help the pump flow
- install pumps to carry the treated discharge from the biobed to a vegetated area for irrigation, or pump it to a storage tank for irrigation or re-use
Using offset biobeds

When using an offset biobed (which is separate to the concrete area you drive the sprayer on to), you must:
- collect pesticide washings from an existing pesticide loading and washdown area in a storage tank
- pump them for treatment in the offset biobed
Installing drive-over biobeds

When installing a drive-over biobed, you must:
- construct a bunded drive-over grid above the biobed (with supporting foundations)
- make sure the grid and its foundations are suitable for the loading of any equipment driven over the grid
How to use evaporation systems (biobeds designed to work by evaporation)

To use evaporation systems, you must:
- cover the biobed with roof sheeting, using side ventilation to allow evaporation to occur without rainfall entering the system
- prepare the biomix as detailed for a non-evaporation system, but with a 50:50 ratio of soil and straw, and without turfing over it
- base the treatment volumes on (https://voluntaryinitiative.org.uk/water/biobeds/) evaporation calculations
- get advice on design and volume calculations from specialists with experience in these systems
How to prepare the biomix

To prepare the biomix, you must:
- mix one part peat-free compost, one part topsoil and 2 parts straw (wheat or barley) by volume
- allow the biomix to compost for 30 to 90 days before using it to fill the biobed to an effective depth of 1m, topping it up if there’s any settlement
- use at least 1 cubic metre of biomix for every 1000 litres of liquid treated in any 12-month period
- turf over the biomix (except for evaporation systems)
- lay perforated pipes to distribute pesticide washings across the surface
The biobed does not need a cover or roof unless it’s an evaporation system.

You must not treat more than 15,000 litres of pesticide washings (excluding rainfall) in any 12-month period.

Evidence you must keep

You must keep written support from your Catchment Sensitive Farming adviser and provide this with your application.

You must also keep and provide with your claim:
- photographs of the site during the different stages of construction or contracts, invoices or other documents confirming the technical specification for the completed works
- photographs of the completed works in place and installed
- any consents or permissions connected with the work
You must also keep and provide on request:
- receipted invoices or bank statements where a receipted invoice is unavailable
- photographs of the site before works start
- documents (including records of treatment in the biobed) associated with the T32 exemption for the treatment of waste in a biobed or biofilter (https://www.gov.uk/waste-exemption-t32-treatment-of-waste-in-a-biobed-or-biofilter) registered with the Environment Agency
Read the record keeping and site visit requirements in the Agreement holder’s guide: Capital Grants, Higher Tier capital grants and Protection and Infrastructure grants (https://www.gov.uk/government/publications/agreement-holders-guide-capital-grants-higher-tier-capital-grants-and-protection-and-infrastructure-grants-2025) for more information.

If you’re applying for this item as part of a Countryside Stewardship Higher Tier (CSHT) application, read the record keeping and site visit requirements in the CSHT agreement holder’s guide (https://www.gov.uk/government/publications/countryside-stewardship-higher-tier-csht).

Other capital items you can use with this item

You can use this item alongside RP28: Roofing (sprayer washdown area, manure storage area, livestock gathering area, slurry stores, silage stores) (https://www.gov.uk/countryside-stewardship-grants/roofing-sprayer-washdown-area-manure-storage-area-livestock-gathering-area-slurry-stores-silage-stores-rp28) on areas you can cover.

Advice to help you use this item

The following advice may help you to use this item, but you do not have to follow it to get paid. It’s not part of this item’s requirements.

British Standards

Check to make sure the work meets relevant British Standards (https://www.bsigroup.com/en-GB/products-and-services/standards/).

Choosing a location

Construct the biobed in an area:
- set aside for pesticide loading and washing operations
- where there’s no other traffic
Measuring up for a biobed

You can read advice on the Voluntary Initiative website (https://voluntaryinitiative.org.uk/water/biobeds/) about:
- how to measure the loading and washdown area
- how to measure holding tanks
- pesticide handling areas and biobeds including sizing and volume calculations
Maintaining the biobed

Add fresh, pre-composted biomix to the biobed every year to maintain 1m depth. Replace the biomix every 5 years. You’ll need a U10 (https://www.gov.uk/search?q=U10+exemption&filter_organisations%5B%5D=environment-agency) or U11 exemption (https://www.gov.uk/search?q=U11+exemption&filter_organisations%5B%5D=environment-agency) to spread the biomix to land. Only use the biobed to treat pesticide washings. Take care removing the biomix from the biobed to ensure the liner is not damaged.

Maintaining the slab, bund and pumps

You should inspect the concrete slab and bund regularly. Repair any damage or deterioration. Check the pumps regularly to make sure they’re operating properly.

You’ll also need to make sure that:
- the area is not used for any purpose other than pesticide handling operations
- the concrete is not damaged, so the area becomes impermeable
- the storage tank does not overflow