Hillylaid Pool: what the published measurements show

The Environment Agency has said that sampling at Hillylaid Pool, a body of surface water beside the former ICI Hillhouse works, “concluded that there was a presence of historical PFAS and other industrial type containments” [sic], and that “work is underway to understand the nature and extent of this contamination and the potential risks it may pose.”

Published measurements of that water already exist. This post sets out what they show, and what the study that produced them says about where the contamination came from.

What the words mean

PFAS are a family of manufactured chemicals used to make non-stick and weather-resistant materials. PFOA (perfluorooctanoic acid) is one of them. The International Agency for Research on Cancer classifies it in Group 1, “carcinogenic to humans”. That classification describes how strong the evidence is that the substance can cause cancer. It is not a statement about the level of risk at any particular exposure. EEA-NH4 is a chemical used in fluoropolymer manufacture as a replacement for PFOA.

Concentrations are given in nanograms per litre (ng/L). For scale only, the EU limit for total PFAS in drinking water is 100 ng/L. That limit applies to treated water at the tap. No drinking water is taken from Hillylaid Pool, and the comparison is a unit anchor rather than a safety threshold for this water body.

The February 2023 sampling

A research team led by Joost Dalmijn, with Ian Cousins as senior author, sampled water around the Hillhouse site on a single day. The paper states it plainly: “Duplicate water samples were taken during a single sampling day (12-02-2023)”. It was published in Environmental Science and Technology on 18 July 2025.

The paper is explicit about which point was cleanest, and it is the permitted one:

“Remarkably, the main discharge point (W1) of the process water effluent had the lowest PFAS concentrations compared to all the other sampling points. At the main discharge, ΣPFAS concentrations were 30 ng/L (main discharge in Wyre 1) and 33 ng/L (main discharge in Wyre 2), while the other sampling points all had PFAS levels within the thousand to tens of thousands of ng/L.”

The highest readings were to the north:

“The highest PFAS concentrations were found to the north of the plant at a discharge near a lagoon (DBL) and at a land drain north of the lagoon (WLD) and a leaking part of a long discharge pipe (WLPD) leading to the River Wyre. PFOA was very prominent in these samples, with concentrations ranging from 891 ± 37 ng/L to 20,624 ± 556 ng/L.”

That range covers those three points together. The paper does not give a separate range for the lagoon discharge alone. It also records that PFOA at two of them was high enough to saturate the detector on the primary method and had to be requantified by direct injection.

This is one day’s sampling, in February 2023. It is a snapshot, not a description of how the site operates now.

What the paper says caused it

This is the part that has not been widely reported, and it matters more than any single figure.

“The high PFOA concentrations are likely attributable to the extensive use of APFO for PTFE production at the plant between 1955 and 2012 and unabated emissions of PFOA to the environment during this time. Therefore, it could be that a large reservoir of PFOA and substances related to its production still exists within the perimeter of the industrial site.”

And on why it is still turning up in surface water:

“Elevated PFAS concentrations at these locations could potentially be explained by re-emission from existing on-site PFAS reservoirs.”

So the peer-reviewed source does not describe this as current discharge. It describes a legacy reservoir built up over a period of use running from 1955 to 2012.

That period covers two operators, and it is worth being precise about both. Imperial Chemical Industries ran the site from the 1950s to 1999. AGC Chemicals Europe has run it since 1999, and used and released PFOA there for a further thirteen years. That is not an inference. AGC joined the US Environmental Protection Agency’s 2010/2015 PFOA Stewardship Programme and reported its own emissions under it: 237 kg of PFOA from its non-US plants in 2011, falling to 23.5 kg in 2012, the year it says it stopped using the chemical.

The published record does not break the total down by operator, so we do not know how the 1955 to 2012 releases divide between them, and we do not assert a split.

The paper identifies the lagoon at the highest-reading point as ICI’s:

“This lagoon was used as an effluent pit by Imperial Chemical Industries (ICI), the former operator of the PTFE production plant and was, unfortunately, not accessible during sampling. The high PFAS concentrations measured here indicate this lagoon should be the subject of further investigation.”

We do not assert that PFOA has been released recently, and we have no evidence that it has.

The Agency’s own later sampling

Between September 2024 and January 2025, WSP, working for the Environment Agency, sampled thirteen surface water locations. The published summary records that “PFOA was detected at all 13 sampling locations. The highest concentration (19.2 µg/l) was recorded at Hillylaid Pools.”

That is 19,200 ng/L, in the pool to which W2 discharges. PFOA was found at every location sampled, including points away from this discharge, so the pool sits in a wider affected area rather than at the end of a single identified pathway.

The permit classification of “uncontaminated surface water and roof water” applies to the discharge point W2, not to Hillylaid Pool itself. The 1,744 ng/L EEA-NH4 figure above is a measurement of pool water. The paper reports no separate figure for the discharge point.

Monitoring at W2

Discharge point classifications and monitoring requirements are set by the Environment Agency in the permit it issues, not chosen by the operator. Under this classification the Agency set no PFAS limits at W2 and required no PFAS monitoring there. We have not seen the Agency’s basis for the classification, or whether it has been reviewed.

AGC has also given a practical reason relating to W2. In a July 2023 presentation to the Environment Agency, the company is recorded as saying “not sure we have access to W2”. On a shared estate with multiple operators, an access difficulty is plausible. We hold this through a third-party compilation of Environmental Information Regulations material rather than from the primary record, and we have not yet obtained the primary document.

What is being done

The Environment Agency says work is underway to understand the nature and extent of the contamination, and that it will “continue to monitor the area for potential impacts on the wider environment and take appropriate regulatory action where necessary.”

AGC is carrying out voluntary environmental investigations at Hillylaid Pools and other locations, under Environment Agency oversight. The Agency’s own contractor records that it continues to engage with the company, that a voluntary inspection of the main site is under way, and that a site investigation was planned with reporting expected in early 2026.

So this is not a situation where nothing is happening. What is not yet clear is what statutory route is being taken, and on what timetable.

Contaminated land, and why the position here is different

Two allotment sites near the plant have been considered under Part 2A of the Environmental Protection Act 1990, the legal process for formally designating land as contaminated.

In March 2026 the Environment Agency concluded that Occupation Road Allotments meets the statutory criteria. Sandringham Avenue Allotments was recommended for determination on 3 July 2026. In both cases the Agency recommends and the local authority makes the determination. We have not been able to confirm from public records whether Wyre Council has since formally determined either site.

In both cases the route was soil where people grow and eat produce.

The Act is not limited to soil. Section 78A(2) covers land where “significant pollution of controlled waters is being caused or there is a significant possibility of such pollution being caused.”

But Part 2A is a backstop. Section 78YB restricts its use where the pollution is being, or can be, dealt with under the environmental permitting regime. The Hillhouse site is permitted, so that restriction may be a substantial part of the answer to why this route has not been taken. We do not know whether it has been considered and set aside, or not reached yet.

What is not confirmed in available documents

• Whether Hillylaid Pool is “controlled waters” within the meaning of the Water Resources Act 1991. The Part 2A water limb depends on this and we have not established it.
• Who is responsible for the DBL discharge and the other unpermitted points. The paper identifies the lagoon as the former ICI effluent pit but does not attribute the discharges themselves to any current operator. Hillhouse is a shared estate.
• Whether the monitoring position at W2 has changed since. We have not seen current monitoring requirements for that point.
• What the Environment Agency’s Regulation 61 Notice produced. The Agency served a notice under permit EPR/BU5453IY on 3 October 2023 compelling information on historic PFAS releases from the site; AGC responded in December 2023 with a historic mass balance. We have not seen the notice or the response.
• When the Agency became aware of the February 2023 results, and what assessment followed between the paper’s publication in July 2025 and this statement. We make no suggestion that any party caused or contributed to that interval.
• The July 2023 access statement reaches us through a third-party compilation rather than the primary record. We are seeking the primary document.
• The date of the Agency’s statement. The Gazette page carries 3 August 2026; the headline appeared in feeds on 2 August.
• The Gazette records the Agency’s wording as “containments”. We take this as a transcription of “contaminants”.

Context that cuts the other way

• The peer-reviewed source attributes the high PFOA to use between 1955 and 2012 and to a reservoir remaining on site, not to current discharge.
• The lagoon at the highest-reading point is identified in that source as ICI’s former effluent pit. ICI operated the site until 1999. This does not put AGC outside the period: it operated the site from 1999 and reported its own PFOA emissions until 2012.
• AGC’s documentation states PFOA use ceased in 2012, and PFOA has been prohibited in the UK since 4 July 2020 under retained Commission Delegated Regulation (EU) 2020/784.
• The main permitted discharge was the cleanest point sampled.
• The Environment Agency, not the operator, sets permit classifications and monitoring requirements.
• The Agency’s contractor found PFOA at all thirteen locations it sampled, including upstream points, and also recorded non-PFAS contaminants in the wider area. Hillylaid Pool has more than one possible contamination history.

The questions

Is Hillylaid Pool being addressed under the environmental permitting regime, and if so what does that require and by when?

To the Environment Agency: on what basis was discharge point W2 classified as uncontaminated surface water, and has that classification been reviewed in light of the measurements since?

Given that the paper identifies the lagoon as a former ICI effluent pit and recommends it “should be the subject of further investigation”, has that lagoon been investigated, and by whom?

What is the scope of the voluntary investigations at Hillylaid Pools, and will the results be published?