106 The “Fundamental Intermittent Standards”: Are they suitable for use in 2021 Environment Act?

Guest episode by Philippa C Mohan

Introduction

I have had several people say to me that when it comes to overflows ‘dilution is not the solution for pollution’. It rhymes but is it scientifically accurate? What role will dilution (or its counterpart concentration) play in our assessment on whether environmental harm has occurred from an intermittent overflow discharge under the new 2021 Environment Act in England?????

It is important to note that under the Water Resources Act (1991) an overflow spill is not a pollution incident and is permitted if it is compliant with a discharge permit issued by the Environment Agency (EA). When issuing such permits the EA applies water quality design standards for all new, improved or altered storm overflows. One of the design standards that must be complied with is the Fundamental Intermittent Standards (FIS) and it is FIS that we must examine for the relationship between the environmental harm and the role of pollutant concentration.? In the Storm Overflow Reduction Plan (2023) it has been taken one step further by stating that achieving the Urban Pollution Management (UPM) Manual FIS is the required method to demonstrate ‘no local adverse ecological impact’. But is that a suitable use of FIS??

I acknowledge that the 2021 Environment Act also calls for meeting applicable percentile standards, but I wish to focus on FIS today.? The 2021 Environment Act is only applicable to England, but if other nations across the UK and Ireland wish to use UPM FIS as a standard of harm then implications are equally applicable.

Fundamental Intermittent Standards (FIS)

FIS are acceptable concentration-duration-frequency design standards for dissolved oxygen and unionised ammonia. To understand FIS, you need to know two things: its scientific background and that the standards were created for publication in the Urban Pollution Management (UPM) Manual.

Environmental harm is usually confirmed when the ecosystem is deemed to not be in a ‘healthy’ condition. Environmental health is defined as the condition of an ecosystem in which its attributes are outside of their normal ranges relative to its ecological state of development.? However, this definition lacks the ability to quantify the effect of an attribute being outside its “normal” range (van Andel & Aronson, 2006). Just because something is unusual does not always equate with it having a negative consequence, which is why environmental health is usually paired with the concept of ecosystem integrity. Ecosystem integrity is defined as the condition of an ecosystem that displays its “usual” biodiversity characteristics, such as species composition and community structure, and is fully capable of sustaining “normal” ecosystem functioning (Parrish et al., 2003). Thus, providing us with clear markers against which to judge ecosystems.

Ecotoxicological research was carried out between 1987 and 1992, reported in a National Rivers Authority Report (Milne et al. 1992) to investigate the relative importance of concentration, duration and frequency of reduced dissolved oxygen and elevated unionised ammonia concentrations on the ability for types of fish to reproduce. Reproduction is prevented when either fish have died or there has been considerable damage to their reproductive organs. This research showed that all three components (concentration, duration and frequency) were not just important but interconnected. That the concentration of dissolved oxygen or unionised ammonia a fish could withstand depended on how many times and how long and it had to endure the concentrations. The point of inability to reproduce is important for the definition of environmental harm as it is the point at which species composition and community structure is altered. Thus, it is a point in which ecosystem integrity is compromised.

The first edition of the UPM Manual was published in 1994 to provide technical tools and planning approaches that can be used to manage environmental issues arising from urban drainage system discharges into the environment. Many of the planning concepts and tools it outlines were new, including the development of FIS from scientific results to design standards. The UPM manual is exactly what it says it is; a manual for managing urban pollution. It is not a manual for assessing the impact of urban pollution on the environment. Therefore, its aim is to delivery strategies that are cost effective and avoid over provision of hydraulic or treatment capacity and storage. It should also be noted that the UPM specifically states that it is concerned with the performance of the urban wastewater system during and in the recovery period from rainfall and does not address the performance of systems under dry weather conditions. This is why when you examine FIS in the UPM manual, it is not as straightforward as the fish is dead or cannot reproduce, so harm has therefore occurred. To ensure the system is optimally designed, it should pass FIS with expected rainfall. In the first iteration of UPM this was a series of selected rainfall events but by the 2nd iteration in 1998 it had become a 10-year rainfall time series. It is accepted that any given year may exceed expected rainfall and hence not satisfy FIS, but designing for these events is not cost effective. Discharge events that are not caused by rainfall, but for instance a blockage, under UPM FIS should be discounted as UPM does not address the performance of urban wastewater systems under dry weather conditions.

Using FIS to define Environmental Harm

When we think about water quality environmental issues today, we often jump to the understanding that we get from the Water Framework Directive (WFD) and whether a location achieved good ecological status. But the UPM Manual, and hence FIS, was created in the mid-90s and therefore it predates WFD which was implemented in the year 2000. Thus, it was simply assumed to begin with, partly because of its scientific origins, that FIS was sufficient in defining good ecological status under WFD. This was dependent on the results of a pending review to scrutinise this assumption in more detail. That review was published in 2012, titled; Review of urban pollution management standards against WFD requirements (EA, 2012). ?It concluded that UPM FIS are “fit for purpose” and no modifications were required with respect to the WFD. ?

Firstly, the standards were demonstrated to provide protection to all life-stages of all aquatic life (plants, invertebrates and fish) associated with the specified ecosystem type. This responded to a common criticism of FIS; Why do we focus so heavily on fish when there is a whole ecosystem to protect? It then followed a very similar line of argument to the one I outlined at the start, that the point where aquatic community structure is altered should be the point at which the classification of good ecological status should be lost.

Secondly, for most concentrations, durations and frequency combinations, the standards provide a margin of safety (see Table 1 EA, 2012). The boxes that are yellow are standards where there is less than a 5% margin of safety, and the boxes that are green provided more than 5% margin of safety.? The largest margin of safety applied is 463%. Therefore, meeting FIS, should result in no long-term behavioural or physiological effects and no short-term fish and macroinvertebrate mortality. This therefore satisfies WFD requirements to ensure that the existing good quality status of a water body is not compromised by intermittent discharges from the wastewater systems network.

The table below shows a summary comparison of estimated thresholds limits developed from the effect matrix against the existing UPM2 FIS for dissolved oxygen and unionised ammonia for salmonid and cyprinid fisheries (EA, 2012).

This argument is logical from a design perspective. That you would want to design a system that when implemented does not cause harm. However, there is a possible argument that in some locations we could be designing to massive over protection leading to significant over investment and excessive carbon emissions. It is however not being used to define if harm has occurred. In passing FIS, you can confidently state no environmental harm has occurred as you have not reached the point at which species composition and community structure is altered. But in failing FIS you cannot assert that harm has occurred. You may simply be in the safety margin (which can be considerable). This is a significant flaw with using FIS, to define adverse ecological impact as proposed under the Storm Overflow Reduction Plan. There also currently seems to be a lack of transparency within the UPM FIS about the margins of safety that are incorporated. These margins of safety are a quantified expression of the water industry aversion to taking risks with the aquatic environment. Environmental risk should be explicitly written down and expressed to all stakeholders involved. But it isn’t. One principal underlying the Environment Act (2021) is transparency. There is no narrative around how we design to higher standards than are scientifically required. If anything, it is often implied that if a location fails FIS, harm has certainly occurred, which is not necessarily true. For an example I took water quality data (supplied by a UK water company) from 5 locations that I have used in my PhD and applied the 1 hour 1 month DO thresholds for cyprid fisheries with and without the 20% margin of safety (see the table below). With the FIS margin of safety 3 out of 5 locations would have 10 or more regulatory exceedances, but only 1 location would have 10 or more without the margin of safety. The other 2 locations did not have large numbers of FIS exceedances.

This poses an issue for the transitioning of using FIS from design standards as they were developed under UPM manual to an assessment framework as proposed under Storm Overflow Reduction Plan. The not knowing if harm has occurred is firstly a confusing narrative for stakeholders and the public to grasp and secondly makes regulating harder than required. There is also the question of what to do with the assumptions the UPM manual makes, like requiring 10 years’ worth of data, to prove an average score of passing FIS under expected rainfall. To disregard it is to not follow the principal assumptions of FIS, but at the same time the public probably will not be satisfied with the answer that you need 10 years’ worth of data to answer the question, are the fish dead or severely damaged.

Should FIS be used in the 2021 Environment Act?

Personally, I think the principle of FIS should be applied but the UPM FIS should be left as a design standard, as the UPM intended it to be. The Storm Overflow Reduction Plan is correct in stating that it is our best currently available measure. Having concentration-duration-frequency standards for low dissolved oxygen and elevated unionised ammonia based on the ecotoxicological research carried out by National Rivers Authority really could provide an invaluable insight into environmental harm caused by intermittent spills from SSOs. That argument has already been scrutinised by the EA. But the concentration thresholds must be set at the point that aquatic community structure is altered to gain that insight. Therefore, I propose that there are two sets of FIS. UPM FIS, which is left alone. It is used as a design standard and has all the requirements as stipulated by the UPM manual including it being tested against 10 years’ worth of data. Then a second set of standards; Assessment FIS, which is used to state if harm has occurred. This set of standards would not have the margins of safety and would also not require 10 years’ worth of data. Once the return period has been exceeded twice that location would be deemed to cause harm. Then once two thresholds are known, the industry could even go on to have open transparent discussions between all stakeholders on whether the margins of safety are a suitable level of protection in designing costly solutions to prevent environmental harm. The premium that stakeholders would be required to pay for the margin of safety would also now be clear and an informed, open debate on cost-effectiveness could now be had.

Reference / links to documents

EA (2012), Review of urban pollution management standards against WFD requirements, Bristol, available: https://assets.publishing.service.gov.uk/media/5a7c56d840f0b62dffde1747/LIT_7373_b2855a.pdf , accessed: 19/09/2024

Milne, I., Mallett, M.J., Clarke, S., Flower, T.G., Holmes, D. and Chambers, R.G. (1992) Combined sewer overflows, ecotoxicology and water quality standards. NRA R&D Note 123. National Rivers Authority, Bristol.

Parrish, J. D.,?Braun, D. P., &?Unnasch, R. S.?(2003).?Are we conserving what we say we are? Measuring ecological integrity within protected areas.?Bioscience,?53(9),?851–860.

Storm Overflow Reduction Plan (2023) available: https://assets.publishing.service.gov.uk/media/6537e1c55e47a50014989910/Expanded_Storm_Overflows_Discharge_Reduction_Plan.pdf accessed: 19/09/2024

Urban Pollution Management (UPM)? https://fwr.org/wp-content/uploads/2018/09/UPM-manual.pdf

Van Andel, J., & Aronson, J. (Eds.). (2006). Restoration ecology: The new frontier. Oxford, UK: Blackwell Science

Water Resources Act (1991) available: https://www.legislation.gov.uk/ukpga/1991/57/contents accessed: 19/09/2024