What Pollution is in the Air in London?

5 Mains Pollutants in the Air in London

The main sources of air pollution in London are road transport and domestic and commercial heating systems.This leads to a lowering of Air Quality.  These sources emit a variety of pollutants, including:

  • Nitrogen dioxide (NO2): NO2 is a reddish-brown gas that is produced when fossil fuels are burned. It is a major irritant to the lungs and can cause respiratory problems such as asthma, bronchitis, and pneumonia.
  • Particulate matter (PM): PM is a mixture of solid particles and liquid droplets found in the air. It can come from a variety of sources, including car exhaust, wood burning, and construction dust. PM can cause a variety of health problems, including heart disease, stroke, and lung cancer.
  • Ozone (O3): O3 is a gas that is formed when sunlight reacts with NO2 and other pollutants. It is a powerful irritant to the lungs and can cause respiratory problems such as asthma and bronchitis.
  • Sulfur dioxide (SO2): SO2 is a colorless gas that is produced when fossil fuels are burned. It is a major irritant to the lungs and can cause respiratory problems such as asthma and bronchitis.
  • Volatile organic compounds (VOCs): VOCs are a large group of chemicals that are released into the air from a variety of sources, including cars, factories, and paints. Some VOCs are known to be carcinogenic.

Lesser Know Pollutants in the Air in London

In addition to these main pollutants, air in London can also be contaminated with other pollutants such as carbon monoxide, lead, and mercury.

In addition to “chemicals” there is also a wide variety of plastic origin particle mater (POPP), this can come from laundry fibres and car tires.

a map showing air quality in central london yellow and green area are shown as being less polluted whilst red and purple areas are over the safe AQO limit, areas next to big ben and parliament square show as being above air quality objective

London Air Quality Network » Annual Pollution Maps

The levels of air pollution in London vary depending on the location and the time of year. Central London is generally the most polluted area, as it has the highest concentration of vehicles and other sources of pollution. Air pollution levels are also higher during the winter months, when people are more likely to burn wood for heating.

The Mayor of London has set a target of achieving world-class air quality by 2030. To achieve this goal, the city is implementing a variety of measures, including:

  • Reducing traffic emissions: The city is investing in public transportation, cycling infrastructure, and electric vehicles. ULEZs can also help reduce emissions from vehicles.
  • Improving energy efficiency: The city is helping businesses and residents to reduce their energy consumption, which will help to reduce air pollution emissions from heating and power generation. These schemes although available in theory are often difficult to apply for for, and they are not suitable for all people. For example swapping a gas boiler for a heat pump is only possible if your house is well insulated.
  • Planting trees and green spaces: Trees and other plants can help to filter air pollution and improve air quality. Some people even take it upon themselves to plant trees in their local neighbourhoods.

The city is also working with other cities and countries to share best practices and reduce air pollution on a global scale.

If you require an Air Quality Assessment in London or Bristol, or anywhere in the UK we are happy to help. Please contact us.

Critique of Michael Gove’s Nutrient Neutrality Announcement

Critique of Michael Gove’s Nutrient Neutrality Announcement

Below you will find commentary of government plans to reform nutrient neutrality laws. Comments are

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Nutrient Neutrality Announcement

Over 100,000 homes held up due to defective EU laws will be unblocked between now and 2030, delivering an estimated £18 billion boost to the economy, the government has announced today (29 August 2023).

  • Comment: Not all of the nutrient sensitive sites are European sites, some such as SSSIs are international.

Currently, legacy EU laws on nutrient neutrality are blocking the delivery of new homes, including cases where planning permission has already been granted. Nutrients entering our rivers are a real problem, but the contribution made by new homes is very small. These laws which originate from Brussels put a block on new homes in certain areas – taking away control over what is built, and when, from local people.

  • Comment: One house will make a small contribution. 100,000 homes will make a lkare contribution.

Through an amendment to the Levelling Up and Regeneration Bill, the government will do away with this red tape and allow for the delivery of more than 100,000 new homes desperately needed by local communities. Thanks to the government’s action, it is expected that developers could begin construction on these homes in a matter of months.

  • Comment: This is presented as though the whole of society will benefit from this reform. One of the main obstacles to people buying new homes is high interest rates, and high living costs. This is nothing to do with nutrients.

The move comes alongside new environmental measures that will tackle pollution at source and restore habitats. This includes significantly expanding investment in and evolving the Nutrient Mitigation Scheme run by Natural England, doubling investment to £280 million to ensure it is sufficient to offset the very small amount of additional nutrient discharge attributable to up to 100,000 homes between now and 2030.

  • Comment: On a rural waste treatment works around 700m2 of wetland is required to offset 1 home. To offset 100,000 new homes we will require 70,000,000m2.  Wetland at very best case costs around £4 per m2 to buy land and create. And as such the this extra £140 million is around half the amount required.

Natural England will work with local authorities, the private sector and others to tackle nutrient pollution and work towards the long-term health and resilience of the river systems. The government intends to work with the house building industry to ensure that larger developers make an appropriate and fair contribution to this scheme over the coming years, and is discussing the right structure and approach with the Home Builders Federation.

  • Comment: Natural England have had 3 years to do this already and have not delivered. I am writing this from a small developers perspective because that is who we deal with. But Natural England have taken in some case 3 years to make a decision on some the sites we are working on, which is too slow. This may because of the liabilities that arise from breach of ecological laws.

The government will then accelerate work on full site restoration through further work on new Protected Site Strategies, which Natural England will draw up in partnership with local communities to set protected sites on the path to recovery in the most affected catchments with the highest housing demand.

Secretary of State for Levelling Up, Housing and Communities, Michael Gove MP said:

We are committed to building the homes this country needs and to enhancing our environment. The way EU rules have been applied has held us back. These changes will provide a multi-billion pound boost for the UK economy and see us build more than 100,000 new homes.

Protecting the environment is paramount which is why the measures we’re announcing today will allow us to go further to protect and restore our precious waterways whilst still building the much-needed homes this country needs.

We will work closely with environmental agencies and councils as we deliver these changes.

  • Comment: Not all of this is EU law. Some is international. The phosphate credit market (of which are we are part) will also provide a multi billion pound boost to the economy. These credits scheme also benefit farmers, smaller developers and homeowners, who are often eligible for free septic tank upgrades, or 6 figure sums from changing the way their farm operates. An open phosphate credit market spreads wealth around.

Secretary of State for Environment, Food and Rural Affairs, Thérèse Coffey said:

These new plans will cut nutrients and help support England’s precious habitats whilst unlocking the new homes that local communities need.

We are going to tackle the key causes of nutrients at source with over £200 million of funding to reduce run off from agriculture and plans to upgrade waste water treatment works through conventional upgrades, catchment approaches and nature-based solutions.

  • Comment: This sounds like a tax payer funded bail out of water companies. With taxpayer money going to water companies so they can upgrade their water works. They should have course made less profit and done this work years ago.

This builds on the key commitments made in our 5-year strategy – our Environmental Improvement Plan – as well as our Plan for Water which brings forward more investment, stronger regulation and tougher enforcement to protect our rivers.

Alongside the amendments tabled to the Levelling Up and Regeneration Bill, which is currently in the House of Lords, the government has announced a series of new environmental measures to restore our protected sites, including a commitment to offset the very small amount of additional nutrients attributable to up to 100,000 new homes. Beyond the immediate action that will be driven by Natural England’s Nutrient Mitigation Scheme, this package includes:

Committing to further work on developing Protected Sites Strategies in the catchments most impacted by nutrient neutrality and with the most acute housing pressures. These bespoke plans will help identify specific action needed to restore habitats and species in specific areas. The aim is to agree and implement tangible actions to reduce pollution at source, through nature-based solutions such as wetlands and new innovations.

Reducing nutrients entering the water from new development with new laws expected to drive significant investment from water companies to upgrade wastewater treatment works to the highest technical standards by 2030. The next water company investment cycle will be among the biggest and most ambitious ever.

  • Comment: Who is paying for those upgrades. And how will it impact on water bills.

Conducting at least 4,000, inspections on farms each year – making sure that slurry and other sources of nutrients are being handled in a way that minimises pollution of the water environment.

Reducing nutrient run off into our rivers from farms – supporting our farmers by investing £200 million in grants for improved slurry storage infrastructure and precision spreading equipment. This makes a further £166 million available for new investment into slurry infrastructure.

  • Comment: This is already implemented. But it is difficult to get planning permission for improved slurry storage owing to the calculation methodologies employed in assessing their impact.

Investing £25 million to drive innovation to help farmers manage plant and soil nutrients. This will increase resilience, reduce input costs and improve productivity as part of a more circular economy for nutrients. The effective use of waste has the potential to create new revenue streams. We will also consult this year on modernising our fertiliser product standards to drive increased use of organic and recycled nutrients.

Introducing from 2024 payment premiums into our environmental land management schemes. This will accelerate take up of certain high priority options, including those that provide benefits for water quality.

Publishing a River Wye action plan this autumn to tackle the unique issues in Herefordshire.

Ensuring new homes built do not place undue stress on already stressed local water networks by consulting this year on new requirements where needed for Sustainable Drainage Solutions to reduce pressure on storm overflows from new homes and flood risk.

All of this builds on our Plan for Water, which sets out measures to transform and integrate our water system, address sources of pollution and boost our water supplies through more investment, stronger regulation, and tougher enforcement.

Our nutrient reduction plan will also help deliver on our legal target to reduce nutrient runoff from agriculture by at least 40% by 2038, and by 15% in nutrient neutrality catchments by 2028, and to reduce phosphorus loadings from wastewater by 80% by 2038, and by 50% by 2028.

  • Comment: How will this be delivered without increasing dependency on food imports.

The government has a strong record on housebuilding, with more than 2.2 million homes delivered since 2010. The Secretary of State for Housing recently set out his long-term plan to go even further and unlock more development across the country.

Changes to nutrient neutrality rules and wider planning reforms will allow the government to go even further towards its target of delivering one million homes this Parliament.

The environmental measures announced today lead on from the government’s Plan for Water published in April which set out actions to address all sources of water pollution, including through accelerating £2.2 billion of water company infrastructure investment to prevent storm overflow discharges and improve drought resilience, and unlimited fines for environmental polluters.

  • Comment: Who is paying for these upgrades. Do this shift financial burden from house builders and water companies on to tax paper / bill payer.

The current EU-derived regulations have required Natural England to issue guidance to 62 local authority areas that new development must be ‘nutrient neutral’ in their area, including Somerset, Norfolk, Teesside, Kent, Wiltshire and the Solent. This has blocked or delayed new development – including around a large number of homes that already have planning permission and local communities have already said they want.

The amendment today will remove this requirement, allowing Natural England greater freedom to develop catchment-specific solutions to the causes of nutrient pollution in partnership with each community, supported by government and private investment.

  • Comment: Natural England already have that ability.

SWEL’s Opinion

The problem with nutrient neutrality is not the law, or the lack of solutions. The problem stems from:

  1. Lack of staff in Councils and Natural England
  2. Lack of effective decision making by Councils and Natural England

We have been offering solutions, for over 3 years. However, there has been little urgency on the part of planning officials and natural england to approve these, or to provide advice. In situation where we have found a way through, it has taken years to do so.

Some ideas, that might work:

  1. Doubling staffing levels of National England
  2. Doubling Staffing Levels in Planning Offices
  3. Pay Natural England extra money for each home passed off.
  4. Leave the rules as they are.

Considerations for Landscape and Townscape Assessment in Bristol

We have recently produced a Landscape and Townscape Assessment in Bristol. In doing so we have considered the following:

Bristol’s Landscape Character

Bristol is a city with a diverse landscape character, ranging from the rolling hills of the Mendip Hills to the urban waterfront of the River Avon. Any development proposal must be carefully considered in the context of the surrounding landscape, and should not unduly harm its character.

View from Castle Park Bristol

View Corridors

Bristol is a city with many important view corridors, both within the city itself and to the surrounding countryside. Any development proposal must be carefully considered in the context of these view corridors, and should not obstruct important views.


Bristol is committed to sustainability, and any development proposal must be sustainable in its design and construction. This includes consideration of factors such as energy efficiency, water conservation, and the use of local materials.

Community Impact

Any development proposal must be considered in the context of its impact on the local community. This includes factors such as traffic congestion, noise pollution, and the loss of green space.

In addition to these general considerations, there are also a number of specific considerations that may apply to particular development proposals in Bristol. For example, if a development proposal is located in a conservation area, it will need to be carefully considered in the context of the area’s special character. Similarly, if a development proposal is located in a floodplain, it will need to be designed to mitigate the risk of flooding.


The landscape and townscape assessment process is an important part of ensuring that development in Bristol is sustainable and sensitive to its surroundings. By carefully considering the factors outlined above, developers can help to ensure that their proposals make a positive contribution to the city’s landscape and townscape.

Useful Tips

Here are some additional tips for landscape and townscape assessment in Bristol:

  • Consult with local stakeholders: It is important to consult with local stakeholders, such as residents, businesses, and community groups, to get their input on development proposals. This can help to ensure that proposals are compatible with the needs and priorities of the local community.
  • Use visual impact assessment: Visual impact assessment can be a useful tool for assessing the potential impact of a development proposal on the surrounding landscape and townscape. This can help to identify potential problems early on in the planning process, and to develop mitigation measures to address them.
  • Consider the long-term impact: It is important to consider the long-term impact of a development proposal, not just the immediate impact. This includes factors such as the impact on the environment, the economy, and the quality of life for residents.
  • Be creative and innovative: There are often ways to mitigate the negative impacts of development on the landscape and townscape. For example, developers can use green roofs and walls to add greenery to buildings, and they can plant trees and shrubs to screen unsightly development from view.

5 Air Quality Problems in London

London has a long history of poor air quality, and the problem has only worsened in recent years. The city’s air quality is now among the most polluted in Europe, and it is estimated that poor air quality contributes to the deaths of thousands of Londoners each year.

There are a number of factors that contribute to London’s poor air quality problem, including:

  • Road transport: Traffic congestion is a major source of poor air quality in London. Cars, buses, and trucks emit a variety of pollutants, including nitrogen dioxide (NO2), particulate matter (PM), and carbon monoxide (CO).
  • Domestic heating: The burning of wood, coal, and other fuels for heating homes and businesses also contributes to poor air quality. These fuels emit a variety of pollutants, including NO2, PM, and sulfur dioxide (SO2).
  • Industry: Industrial activities, such as power generation and manufacturing, also emit a variety of pollutants. These pollutants can include NO2, PM, SO2, and heavy metals.
  • Construction: Construction activities, such as demolition and roadwork, can also contribute to poor air quality. These activities can generate dust and other pollutants that can be harmful to human health.
  • Agriculture: Agriculture can also contribute to poor air quality, particularly from the use of pesticides and fertilizers. These pollutants can be carried by the wind and can end up in the air in urban areas.

The effects of poor air quality can be far-reaching. Short-term exposure to poor air quality can cause respiratory problems, such as asthma, bronchitis, and pneumonia. Long-term exposure to poor air quality can increase the risk of heart disease, stroke, cancer, and respiratory diseases. Poor air quality can also contribute to premature death.

The city of London is taking steps to address the poor air quality problem. These steps include:

  • Investing in public transportation: The city is investing in public transportation, such as buses, trains, and trams. This will help to reduce the number of cars on the road and, in turn, reduce poor air quality.
  • Introducing clean air zones: The city has introduced clean air zones in central London. These zones charge vehicles that do not meet certain emissions standards. The aim of these zones is to reduce the number of polluting vehicles in the city center.
  • Encouraging people to walk and cycle: The city is encouraging people to walk and cycle more. This will help to reduce the number of cars on the road and, in turn, reduce poor air quality.
  • Working with businesses to reduce emissions: The city is working with businesses to reduce their emissions. This includes providing financial incentives and technical assistance to help businesses switch to cleaner technologies.

The city of London is making progress in addressing the poor air quality problem. However, there is still more work to be done. The city needs to continue to invest in public transportation, introduce clean air zones, and encourage people to walk and cycle more. Only then will London be able to achieve a healthy and sustainable air quality.

In addition to the city’s efforts, there are a number of things that individuals can do to reduce their impact on poor air quality. These include:

  • Drive less: If possible, walk, cycle, or take public transportation instead of driving.
  • Choose a fuel-efficient car: When you do need to drive, choose a car that is fuel-efficient.
  • Carpool or vanpool: If you can, carpool or vanpool with others to work or school.
  • Use public transportation: When possible, use public transportation instead of driving.
  • Walk or bike: If your destination is within walking or biking distance, walk or bike instead of driving.
  • Avoid idling your car: When you are stopped in traffic, turn off your car engine.
  • Keep your car well-maintained: Make sure your car is properly maintained, including regular oil changes and tune-ups.
  • Use less energy at home: You can reduce your energy use at home by making small changes, such as turning off lights when you leave a room, unplugging appliances when they are not in use, and weatherizing your home.
  • Plant trees: Trees help to improve air quality by absorbing pollutants and releasing oxygen.

By taking these steps, individuals can help to reduce poor air quality and improve the quality of life for everyone in London.

Air Quality Assessment London 

Direct Debit “Southwest Envrion”

We received around 5 or 6 phone calls per year with people asking about Direct Debits or Recurring Card Payments from “Southwest Environ”.

These payments relate to Paignton Zoo!

We trade as – Southwest Environmental Limited

Paignton Zoo trade as “Paignton Zoo”, but their holding company is Southwest Environmental Parks Limited.

So I hope that helps.

We don’t use direct debit for any payments, we issue invoices to people and they pay us via BACs.

All the best,

Kind regards,

Will – Managing Director  – Southwest Environmental Limited

Visual Impact Assessment Bath

We have recently been asked to provide a Visual Impact Assessment for a site in Bath.

This was an unusual request given the scale of the building which is quite small, given the range of buildings and structures we typically see requiring a visual impact assessment.

Ordinarily we would carry out visual impact assessments for projects such as wind turbines, or solar farms, but in this instance the project comprises of a extension to an existing domestic garage, to create a two storey building.

picture of a timber clad building (university of dundee library)

The project is in a suburban area, but is relatively close to Bath’s historic centre. Perhaps this is the reason a Visual Impact Assessment has been requested by Bath and North East Somerset Council (BANES).

We will visit the area surrounding site and take photos so as to represent views from different aspects, we will then make a qualitative review of ht e situation and prescribe a magnitude of impact.

If you require a visual impact assessment for any type of project please do contact us.

A visual impact assessment is process by which the visual impact of a project is assessed. For example the visual impact of a new or altered building may have on onlookers. This differs to a landscape impact assessment where the impact is assessed in relation to the landscape, no a conceptual onlooker.

Image: PFord, Public domain, via Wikimedia Commons

Special Treatment Establishment Licences

Special Treatment Establishment Licences relates to licenses sought in connection with Beauty Treatments and Sun Beds and associated practices:


We were recently contacted by a prospective client asking about planning application for Beauty Salon. She informed us that the application for for a Special Treatment Establishment Licence, states the requirement for planning permission.

The proposed site for the Beauty Parlor is already a retail outlet, selling electric bicycles, and as such we thought we would research the exact requirements as full planning application may not be required.

You will need to check with the Council’s Planning team to confirm whether any planning consent or permission is required. If the premises has previously operated as something other than a special treatment premises, you may require a change of use.

But does this cover premises with existing generic use classes such as Use Class E?

Typically it is not the change of use that requires a planning application it is any alteration to the shop frontage or signage. From Government Guide on Signs:

Class 13 allows advertisements to be displayed on a site that has been used continually for the preceding ten years for the display of advertisements. Class 13 does not permit any substantial increase in the extent, or alteration in the manner, of the use of the site or the display of the advertisement.

So there is some scope for making alterations, but you would need to evidence 10 years of prior use.

If you need help with a planning application then please do get in touch. 




Environmental Product Declaration (EPD)

Environmental Product Declaration (EPD) Consultants

Southwest Environmental Limited can apply for an Environmental Product Declaration (EPD) on your behalf. We are based in the UK, and provide our services Worldwide.

We have been successfully carrying out life cycle assessments of goods and services for over a decade. We can provide help and support in getting an Environmental Product Declaration (EPD) issued for your products or services.

How does an Environmental Product Declaration Work?

An Environmental Product Declaration is a short report (often backed up by a larger report) that sets out the impacts of you product or service. For example let us pretend we are obtaining an EPD for a Hammer made by “Company A”.

We would need to find out the impacts created in the manufacturing, transport, use and disposal of the product. In Fact there are potentially 17 subdivisions to include for.

Most if the lifecycle work we undertake is based around Carbon Footprinting, but with an EPD there are special requirements that result in a broader scope:

  • GWP-fossil
  • GWP-biogenic
  • GWP- luluc
  • GWP- total
  • ODP
  • EP-freshwater
  • EP- marine
  • EP-terrestrial
  • POCP
  • ADP-minerals&metals*
  • ADP-fossil*
  • WDP*

The list extends to about 30 factors which need to be footprint, it is quite time consuming, but luckily we can find most of these values in prepared databases.

You wood find footprints for EN1508 materials or services ,and add these together to make up you final footprint and publish an EPD.

A Lot of Numbers. . .

Why Do I need an Environmental Product Declaration EPD?

You probably need one because you customer is asking for one. If they use you products as part of the service they deliver then they will need to feed in data from your EPD, in to their EPD. In that way they can work out their footprint.

If another supplier has a published EPD, they can also compare your product to the other supplier and see who has the lowest carbon.

Environmental Product Declaration EPD Costs

You can get an EPD issued for one simple products for perhaps £8000, this would include our fees and the fees to the 3rd party verifier, and the certification costs. However, costs go up very quickly for more complex products. Even a simple report will be backed up with 50 plus pages of spreadsheet calculations. Unfortunately there is no such thing as an Life Cycle Assessment that can be completed in “One Click”.

Please contact us to talk about your requirements.

Life Cycle Assessment for Amazon Product

Life Cycle Assessment for Amazon Product

We have recently been commissioned to undertake a Life Cycle Assessment for a product being sold on Amazon Marketplace. Despite offering Life Cycle Assessment Services for over 10 years this is the first time we have produced a Life Cycle Assessment for Amazon Product.

Climate Pledge Friendly

If you have been shopping for drones or vegetables on Amazon recently you may have noticed the Climate Pledge Friendly tick box. If you select this, then only Climate Pledge Friendly items will show up in your search.

In order to back up this green claim, it is required that you submit a life cycle assessment (whole life or size reduction) and have it assessed by a third party.

How it Works

We can arrange all aspects of this process for you. We will carry out the required data collections, and or calculations to prove a size reduction, or carbon footprint for your product. We will then provide this information to a 3rd party certification body. Who will also offer you various choices in terms of  carbon offsets.

Once this has been completed we will provide information to you so it can be submitted to Amazon, and you product be included under Climate Pledge Friendly category.

We point out at this point that we are no endorsed in any way by Amazon. But we have been carrying out Life Cycle Assessments for over 10 years. Contact Us to find out more.

Phosphates in Wales

This week, we have had our first taste of the Phosphate Planning Issues arising in Wales. This relates to the trickle down from the Dutch N Ruling (2018) which has been affecting various parts of the UK, since late 2020.

The Afon Teifi, Afon Tywi (River Towy), River Wye and Afon Cleddau are located in special areas of conservation, and as such affected by the ruling.

For this our first report in Wales relating to the Phosphate situation we have encountered some key differences, between Wales and England.


So Far only Carmarthenshire has release a budget calculator. Compared to the the calculators we have been using in Somerset and Cornwall, it is quite limited, although it is good that it can be used offline, so we can save a copy for later use, or reference! Take note Somerset and Cornwall (probably not though).

The Carmarthenshire calculator does not automatically calculate mitigation options. This leaves sizing of wetlands for example up to the applicant / agent / consultant. And we would consider this problematic, as even with agree methods (as indicated in Somerset / Cornwall Calculators) there is enough detail to contest, without added variability.

Treatment Works

Unlike the Sewage Treatment Works (STWs) we have seen in England, many of the welsch plants have no consent limit for Phosphates. They are also for the most part way over capacity, as some of them run in overflow mode (raw sewage in rivers) for 50% of the year.

This lack of consent limit is an advantage for developers and open the possibility of pre-treating waste water from mains connected sites, to provide a benefit.

Some Similar Problems

However, some things remain the same:

In Somerset and Cornwall we have had very little feedback on sites with wetlands, or sites which use extant uses to offset new uses, or that use off-site schemes. They are all in limbo, I wouldn’t mind some critique because at least that might seam as though things were moving along. I expect this to be the same in Wales.

There have been queries on other application in Wales that seek to discredit the accuracy of treatment efficiencies. We have seen this in England and Wales. Wetlands for example for a project in cornwall have been called in to question. With regards to banking coefficients yes they will vary. But so do treatment efficiencies of manufactured solutions, and phosphate concentrations of effluent, and as such I do not think it is meaningfully practical to adjust banking coefficients.

As with all things environmental science we are trying to take a non-numerical highly variable system (a human urinating in a toilet) and apply maths to the resultant processes. It cannot be done 100% accurately. So uncertainty has to be accounted for. If a study were undertaken of say 50 systems, monitoring for inputs and outputs after 5 years we might arrive a c. 95% certainty that certain banking coefficint would be met. But in these early stages some uncertainty will have to be accepted. 

In the majority of reported cases the 99% filtration rate is achieved, and we have agreed to monitor outfall in long term, so very little remainder risk here.

In summary we need someone in NRW (or NE in England) to start making decisions on this promptly. IF not all the benefit that could occur driven by the real need for clean rivers could be written out of existence by the stroke of a pen by Llywodraeth Cymru.