Introduction

The treatment of Per- and polyfluoroalkyl substances (“PFAS”) and other pollutants of concern is exposing deep tensions in the regulatory framework governing water and urban wastewater infrastructure. From environmental permitting to the adequacy of Environmental Impact Assessments (“EIA”), the legal risks are mounting. This blog, which is co-authored by planning and environment barrister Claire Nevin and PFAS expert witness Geraint Williams, examines some of the technical and legal challenges associated with water infrastructure consenting in a rapidly evolving regulatory landscape for PFAS and other pollutants of concern. It is essential reading for those working in the water infrastructure and development consenting sectors.

When the cure is worse than the disease: the PFAS treatment technology gap

PFAS are a diverse class of synthetic chemicals characterised by their persistence, mobility, and potential toxicity.  Long-chain perfluoroalkyl acids (“PFAAs”), in particular, present significant environmental and regulatory challenges. Their widespread use across industrial, commercial, and domestic applications poses a significant issue for UK water companies, which must balance investment decisions, regulatory compliance, and growing public scrutiny.

Influent entering wastewater treatment works (“WWTW”) originates from a wide range of sources, resulting in highly variable PFAS compositions. These sources can include industrial discharges from primary manufacturers, sites where Aqueous Film-Forming Foams (“AFFF”) have been extensively used (such as airports, oil and gas facilities, and fire stations), as well as landfills, textile, carpet and leather industries, paper and cardboard manufacturing, metal finishing operations, agricultural runoff, and other diffuse inputs. This diversity makes source identification and control particularly challenging. 

Historically, regulatory focus has centred on perfluorooctanoic acid (“PFOA”) and perfluorooctane sulfonic acid (“PFOS”), both long-chain PFAAs. However, as global restrictions have limited their use, the industry has shifted towards replacement PFAS, including short-chain substitutes. Substances such as trifluoroacetic acid (“TFA”) and other ultra-short chain PFAS are increasingly detected in wastewater but remain less well understood.  Consequently, monitoring programmes - such as the UK Chemical Investigations Programme (“CIP 4”) - are expanding their scope to include these emerging contaminants. Work on delivering CIP 4 is well underway, and the findings will be available from 2027. CIP 5 will begin in 2030.

Conventional wastewater treatment processes are generally ineffective at removing PFAS. Physical, chemical, and biological treatments may instead transform precursor PFAS into intermediates or more stable terminal PFAAs. During primary treatment (e.g. sedimentation and clarification) and secondary treatment (e.g. aerobic biodegradation), these transformations can alter PFAS composition without achieving meaningful removal. As a result, elevated concentrations of terminal PFAAs are often observed in effluent and receiving environments downstream of WWTW.

A key analytical challenge is that routine laboratory methods typically focus on a limited suite of PFAS (such as those listed by the Drinking Water Inspectorate), primarily detecting terminal PFAAs. Many polyfluorinated precursors are not captured by these standard analyses and require more advanced techniques for accurate characterisation. This can lead to an incomplete understanding of total PFAS loading and transformation pathways.

In addition to treated effluent discharges, there is increasing focus on PFAS partitioning into sewage sludge (biosolids) and on potential emissions through volatilisation and aerosol formation, particularly from fluorotelomer alcohols. The UK Government is currently reviewing the use of sewage sludge in agriculture, with particular attention to the potential for PFAS to enter the food chain and how biosolids might contribute to diffuse contamination into surface waters. 

Emerging treatment technologies are currently being trialled to address PFAS contamination; however, these solutions require substantial capital investment and careful evaluation of their long-term sustainability. The high costs associated with both implementation and ongoing energy consumption must be balanced with efforts to strengthen source control. In response, many water companies are undertaking comprehensive catchment risk assessments to identify key sources of PFAS inputs. These assessments typically combine desktop studies, the review of documentary evidence, and analysis of Environment Agency data, alongside field investigations such as site walkovers, drone surveys, and targeted sampling of groundwater and surface water.

Legal challenges for development consents

The evolving legal and regulatory landscape

The growing gap between scientific understanding of PFAS and other pollutants of concern and the treatment technologies deployed to address them raises serious legal and regulatory challenges for the water infrastructure and development consenting sectors.

The Urban Waste Water Treatment (England and Wales) Regulations 1994 (“the Regulations”) seek to ensure that wastewater is treated to a minimum standard before it is discharged from public sewers, sewage treatment plants, or from industrial installations. Notably, the Regulations do not contain any provisions addressing PFAS, nor do they impose any PFAS-specific discharge limits or require operators to deploy treatment processes that are capable of PFAS removal.

Only a very limited number of PFAS are subject to statutory environmental standards in England and Wales. PFOS is identified as a priority hazardous substance under the Water Environment (Water Framework Directive) (England and Wales) Regulations 2017, which define "the table of priority substances" as the table in Part A of Annex I to the Environmental Quality Standards Directive, which contains PFOS. Both PFOS and PFOA are controlled as persistent organic pollutants through the Persistent Organic Pollutants Regulations 2007 which designate the Environment Agency (in England) and Natural Resources Body for Wales as both the competent authority and the enforcement authority. The Environmental Permitting (England and Wales) Regulations 2016 provide the permitting mechanism through which these external standards can take effect in individual discharge permits for wastewater treatment works, but the 2016 Regulations themselves contain no PFAS-specific substance list. Currently, the Environment Agency regulates PFAS pursuant to its powers under the 2016 Regulations by issuing notices and requesting information in relation to PFAS from operators of high-risk sectors and sites. Although, the Environment Agency notes that this is being done in a phased approach due to the complexity and scale of the challenge. 

These frameworks appear increasingly dated given the significant developments in scientific understanding and the legal and regulatory framework for PFAS since 1994. For example, a notable counterpoint to the UK is the EU’s revised Urban Wastewater Treatment Directive which entered into force on 1 January 2025 and includes revised standards and monitoring obligations to address new pollutants such as PFAS, microplastics and micro-pollutants. It also requires Member States to monitor the disposal and reuse of sewage sludge to ensure that it is being done safely and in an environmentally responsible manner.

The rapidly evolving legal and regulatory landscape on PFAS is further underscored by the Government’s PFAS Plan which was published on the 3rd of February 2026 (the webinar delivered by FTB barristers Andrew Fraser-Urquhart KC, Claire Nevin and Emma Rowland on the PFAS Plan is available here).

The Plan’s objective is to understand the impacts of PFAS on public health and the environment and build towards coordinated actions to minimise risks. Elements of the PFAS plan which will be of particular interest to the water and wastewater treatment industries include:

(i) The Government’s commitment to reform the UK REACH regime by 2028 to ensure that PFAS controls are more aligned with the EU after post-Brexit regulatory divergence led the UK to fall behind the EU on the risk management of PFAS and other pollutants of concern (see here for Claire Nevin’s blog post on the regulatory regimes governing the use of PFAS, including an explanation of UK and EU REACH). Specifically, reform of UK REACH will place additional constraints on the wastewater treatment industry to identify and manage the risks associated with sewage sludge and other outputs following treatment that contain chemicals not yet captured by UK REACH.

(ii) The PFAS Plan commits to undertaking a public consultation on the introduction of statutory limits for PFAS in England’s drinking water. If such limits are implemented, the water industry will need to ensure that its infrastructure and treatment facilities contain adequate PFAS-filtering technology and testing mechanisms to ensure compliance with these limits. In the US, the significant financial burden on water companies of ensuring their infrastructure and treatment facilities are fit for purpose has already produced substantial litigation as water companies deploy the “polluter pays” principle to hold polluters liable for the PFAS treatment costs incurred by water companies. Similar litigation may yet be brought in the UK as the water industry faces the significant burden of updating its infrastructure and treatment facilities to tackle chemical pollution caused by polluting industries.

(iii) The Government's commitment to producing cross-sector guidance on reducing emissions and improving the handling, monitoring and disposal of PFAS includes a commitment under Action 2.13 of the PFAS Plan to work with industry and regulators to identify and require the use of best available techniques ("BAT") to prevent or minimise emissions of PFAS. Whilst this presents an opportunity for the water and wastewater industries to play a key role in shaping what BAT looks like in a PFAS context, it also foreshadows a clear expectation that these industries will upgrade existing facilities and commission new infrastructure capable of treating PFAS effectively.

For those financing, consenting and delivering water and wastewater infrastructure, it is therefore clear that PFAS is quickly transitioning from a future regulatory risk to a present-day constraint that must be designed for. Moreover, if PFAS treatment upgrades are to happen at scale, they will need to be built into future Asset Management Period submissions to Ofwat.

The Finch Effect: Downstream Chemical Pollution and the Environmental Impact Assessment (“EIA”) Challenge for Wastewater Infrastructure

In addition to navigating the complexities of substantial technical upgrades, those seeking development consent for wastewater infrastructure will need to engage with potential PFAS contamination throughout the consenting process in their environmental assessments. For the purposes of this blog post, we focus on EIA because R (Finch on behalf of the Weald Action Group) v Surrey County Council and others [2024] UKSC 20 raises important questions about how downstream or indirect environmental effects should be assessed, including whether ineffective wastewater treatment - where, as explained by Geraint Williams earlier in this post, treated effluent may paradoxically be more environmentally harmful than the untreated wastewater entering the system - must be considered as part of the assessment.

A failure to identify or assess a likely significant effect of a proposed development in accordance with the Environmental Impact Assessment Regulations 2017 may lead to the quashing of a decision to grant permission for development. Therefore, if there is cogent evidence to demonstrate that PFAS contamination resulting from a proposed wastewater infrastructure development is likely to have significant effects on the environment or human health, and no baseline assessment of contamination or of the effects of development on that contamination has been taken into account, that is a legal error and is likely to lead to the quashing of any decision to grant consent for that proposed development.

In Finch, the Supreme Court held that the indirect "downstream" (scope 3) greenhouse gas emissions from an onshore oil drilling project in Surrey should be included in the Environmental Statement. This raises important and complex questions for wastewater infrastructure projects, particularly given the current lack of effective technical solutions for treating PFAS. In some circumstances, as explained above, the treatment process itself may have the indirect and unintended consequence of transforming PFAS compounds into different, more mobile, or potentially more harmful forms. Accordingly, it will be necessary not only to establish the baseline levels and characteristics of PFAS present prior to treatment (itself a difficult task given the current patchwork nature of the UK’s regulatory framework for PFAS) but also to assess the downstream environmental effects of post-treatment discharges. It follows that applicants seeking consent for new or upgraded wastewater treatment facilities that lack effective PFAS treatment technology must also assess the likely significant environmental effects arising from the post-treatment transformation and release of PFAS compounds.

Environmental Statements should also assess the technology, measures and techniques that can realistically be deployed to avoid, prevent or reduce any significant adverse effects on the environment from the treatment of wastewater containing PFAS and other pollutants of concern. However, as consenting authorities can only impose conditions or mitigation measures after having assessed the risk of environmental harm, it would not be lawful under the EIA Regulations to grant permission in reliance on potential technical solutions or other mitigation measures for PFAS impacts that are speculative, unknown or whose effectiveness is not guaranteed. As the Court of Appeal held at [46] in Bellway Urban Renewal Southern v Gillespie [2003] EWCA Civ 400, in order to be relied on, the “nature, availability and effectiveness” of mitigation measures must be “already plainly established and plainly uncontroversial.”

Furthermore, whereas a parallel can be drawn with the "Rochdale envelope" principle used in Nationally Significant Infrastructure Projects under the Planning Act 2008 (where projects can be consented with a degree of design flexibility built in), the issues raised by PFAS in a wastewater treatment context are arguably different and more complex. This is because the uncertainty is not just about design parameters but whether there may be chemical reactions that produce unforeseen outputs not factored into the original design. Furthermore, an approach centred and dependent on design flexibility and potentially uncertain technologies would be unlawful if it had the consequence of underassessing the likely significant environmental effects, including the worst case parameters, of PFAS contamination.

Conclusions

The above demonstrates the scale of only some of the challenges facing the water industry and those seeking development consent for new or upgraded urban wastewater treatment plants. Although PFAS is not yet routinely considered as part of environmental assessments for infrastructure projects and other development in the UK, any application falling within the environmental assessment regimes that has the potential to exert likely significant effects on the environment due to PFAS or other pollutants of concern would face material legal risk if left unaddressed.

Faced with these significant challenges, what should those seeking consent for wastewater treatment facilities and other water infrastructure actually do?

First, international developments and the Government’s new PFAS Plan demonstrate that the legal and regulatory direction of travel for PFAS will only intensify. However, operators and developers should not wait for reform to crystallise before acting. Existing permit conditions should be reviewed against emerging PFAS science and environmental assessments for new or upgraded wastewater infrastructure must address chemical outputs, not just inputs.

Second, proposed mitigation must meet the Bellway threshold of being plainly established and uncontroversial.

Third, those financing and delivering water infrastructure should be building PFAS treatment obligations into future AMP submissions to Ofwat.

Finally, three reform processes in particular deserve close attention: the UK REACH reform programme due by December 2028, the forthcoming consultation on statutory PFAS limits in drinking water, and the planned consultation on the sewage sludge regulatory framework. Each has the potential to materially reshape legal obligations and costs for the water and wastewater industries.

Claire Nevin is a planning and environmental barrister at FTB. She is regularly instructed on chemicals, including PFAS, and wider pollution and contaminated land matters for a range of clients including local authorities, businesses including multinational conglomerates, resident groups and NGOs. Claire is also called to the Bar of Ireland, where she has advised on development proposals raising PFAS issues.

Geraint Williams is an Associate Technical Director in the Environment and Climate Change Division at HKA.  With over 28 years of experience, he provides expert opinions, analysis, and advice on high-value and complex environmental claims in litigation. Geraint is widely recognised for his leadership in contaminated land and PFAS. He co-authored the UK’s first industry guidance on PFAS in soil and water, published by CIRIA (Construction Industry Research and Information Association), and is actively involved in shaping best practice across the sector.  He is Chair-Elect of the Association of Geotechnical and Geoenvironmental Specialists (AGS) and previously chaired the Technical Panel of the Society of Brownfield Risk Assessment. He also contributes to national standards and policy development through his role on the British Standards Committee for Soil Quality (EH/4) and the National Brownfield Forum.