Ammonia assessments: initial screening and evidence gathering (GN 020)

The first stage is to gather evidence in order to make your assessment. We advise using a tool called SCAIL to make the initial screening assessment .  

In order to use SCAIL and if required, carry out further detailed modelling, you will need the following information. 

Please note:

  • SCAIL can only be used to assess impacts over 250 metres from the development 
  • SCAIL should only be used in the Conservative MET option 
  • SCAIL cannot be used for in combination assessments 
  • The output should be printed to pdf as evidence.  

Screening distances to be used 

 The screening distance of 5 kilometres should be used unless your development is listed below. If your development is listed, please use the appropriate screening distance. For developments that propose the use of scrubbers, 5 km is the maximum screening distance required.

  • For 32000 or fewer free range layers with manure belt removal : 3 km
  • For 140 or fewer Beef cattle : 3 km
  • For 32000 caged layers : 10 km
  • For 100 000 or more free range layers : 10 km
  • For 200 000 broilers : 10 km
  • For 400 or more dairy cows : 10km
  • For 32000 or more other poultry (non chicken) : 10km
  • For 1500 pigs or more : 10 km

For anaerobic digestion with a storage capacity for feedstock and/or digestate of 1000 cubic metres or more  : 10 km

In your assessment you need to consider the sensitive sites within the appropriate screening distance. 

Sensitive sites 

We consider a sensitive site to be an area that holds habitat in which species that cannot tolerate high levels of nitrogen are critical to habitat/ecosystem function. The sensitive sites can only tolerate a certain level of ammonia, the level is referred to as the Critical Level (Cle).

Some of the most sensitives sites will have a critical level of 1 µg/m3 whilst others will have critical levels of 3 µg/m3. All the sensitive sites we currently want to be assessed by applicants are on a map layer you can access below.  

The Map 

View areas considered to be sensitive on our open data map

Please follow the link, unclick the NRW operational assets and select the Air Quality tab select your area of the interactive map and zoom in to an appropriate level. In the layer list select ‘SSSI NH3 Critical Levels’ and ‘N Sensitive Ancient Woodlands and Parkland’.

This will show the areas we are concerned about and the critical level above which the habitats and species will be adversely affected, this is the appropriate critical level to use in your assessment and will either be 1 µg/m3 or 3 µg/m3.

This version of the map may be updated in future as evidence emerges of the need to protect further areas. Any changes will be advertised 3 months in advance and the evidence provided for public scrutiny. 

Other sources of ammonia 

Ammonia from other existing sources and ammonia from your proposed sources may act in-combination at sensitive sites where they overlap. Your assessment must take account of these other sources of ammonia not included in the background.

You can find out background values from the Air Pollution Information Service (APIS) website 

Ammonia background concentration from the Air Pollution Information System (APIS) is given as an average over three years. Other sources of ammonia include proposed sites and existing sites that started operating after the 31st December of the second year of the three year APIS average’. Details of other ammonia sources can be found on the Local Planning Portal.

Find information on other sources of ammonia emission on the Local Planning Authority website

Contributions of ammonia from your proposal, existing background, and any other sources must be added together. The total is assessed against the critical level at each habitat site in your assessment.

For example, during your assessment for a free range chicken farm with 50,000 birds you find an area of a Site of Special Scientific Interest (SSSI) within your 5km screening distance. A search of your Local Planning Portal finds a 200,000 bird broiler farm that is not included in the APIS background. The 10km screening distance of this source overlaps with the SSSI area that lies inside your 5km screening distance. Impacts of ammonia from your proposal must be added to the ammonia from the identified broiler farm and the background ammonia at the SSSI where they overlap.

Find information on other sources of ammonia emission on the Local Planning Authority website

Read How to carry out detailed modelling

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