Atkins has developed an environmental reporting tool, which has assisted the UK water industry in meeting the challenge of reporting on pollutant loads released to the environment through WwTWs.

The estimator tool, Chemical Discharges to Water Database,

also has a role to play in improving understanding of the pollution burden from domestic and diffuse sources – a key step in developing future controls to meet objectives set under the Water Framework Directive (WFD).

Every year, the English and Welsh water companies and Scottish Water are required to report to the regulators, the Environment Agency (EA) and the Scottish Environment Protection Agency (SEPA) the annual load of key substances discharged to surface water from their WwTWs. This is no small task because each company may have hundreds of WwTWs, and there are about 80 chemicals to report against for each works. Atkins was commissioned by UK Water Industry Research (UKWIR) and the EA to develop and deliver a cost-effective reporting protocol for the water companies to produce their annual returns to the Pollution Inventory. The resulting software is now being used by all nine of England’s water service companies, and has subsequently been adopted by Scottish Water and SEPA.


These returns by the English water companies and Scottish Water report on current substances of potential environmental concern, both internationally and in the UK. The returns are collated within the EA’s Pollution Inventory and SEPA’s Scottish Pollutant Release Inventory respectively, along with similar information from other industry sectors.

Currently, the UK uses this information to report to Europe for the European Pollutant Emission Register (EPER). However, releases from WwTWs are not required to be included. However, under the

proposed European Pollutant Release and Transfer (E-PRTR)

regulations, which will extend the EPER protocol, releases from municipal WwTWs will be included.

The purpose of these inventories is two-fold. Firstly to provide

publicly available data on industrial emissions to the environment

at a local and national level (for example the EA’s What’s in Your Backyard), and secondly to inform regulation of industry by improving the level of information and understanding of pollutant releases

to the environment.

The public’s ‘right to know’ is increasingly becoming a feature of environmental policy. The current EPER protocol and the proposed

E-PRTR are driven by an OECD recommendation, which calls on

countries to implement comprehensive publicly available Pollutant Release and Transfer Registers. In addition, under the WFD, stakeholder participation and engagement plays a key role in the development of management plans for achieving environmental targets.

The Department for Environment, Food and Rural Affairs (DEFRA) is required to provide the general public with opportunities to discuss the preparation of its proposed measures. Clearly, for this to be

effective, the public must have access to information in order to understand the pollution issues.

Why is an estimator tool useful?

The estimator was developed in response to the inherent problems associated with producing these returns for all the substances at

hundreds of WwTWs. One key problem is that monitoring uniformly for all these substances is not financially feasible for the water companies, nor is this the intention of the regulators.

The Ministerial Direction, which outlines the reporting requirements for the water industry, states that DEFRA “does not intend that

reporting for the Pollution Inventory should involve any extra monitoring above that required for other purpose”. In addition, it would not be possible to detect many of the substances in the effluent due to low concentrations and the limits of detection.

Recognising these issues, the estimator tool was developed jointly by the EA and UKWIR as a practicable and cost-effective means of providing an assessment of loads from WwTWs. Crucially, it is acceptable both to the water industry and to the regulators.

Other benefits include reducing the administrative effort of reporting, and improving the efficiency of data handling by minimising the likelihood of transcription errors. For the English water companies’ returns, they can be uploaded automatically to the EA’s website by the estimator.

How are the estimates made?

Substances arise at WwTWs from a range of sources, broadly categorised as either point or diffuse. Point sources are specific, identifiable discharges, such as an industrial discharge, and are usually consented (as trade effluent). Diffuse sources, however, are dispersed across a catchment and may be individually minor but significant collectively. Due to their nature, they are more difficult to control. The major diffuse sources of chemicals entering the sewerage system are domestic properties, services (such as hairdressers, dentists, hospitals) and run-off.

The protocol

estimates the load

discharged from the WwTW by building up an estimate of the inputs, and then applying a removal rate depending on the type of treatment. In order to make the tool easy to use and practicable, the inputs to the sewer from these diffuse

elements are derived from basic parameters such as dry weather flow and connected population. As trade effluent is site specific, it

is not possible to generalise this, and trade effluent data is added separately to the estimator.

A comprehensive review of national and international data relating to the substances was undertaken to understand how these

substances are used within these sources.

The domestic contribution is estimated using agreed contribution rates per connected population. Service discharges are estimated using agreed contribution rates and standardised per capita numbers of the service. Using one example of the

service sector to illustrate the point, based on the total number of dentists within the UK and the total population, a number of dentists per head of population can be estimated.

Literature reviews indicate the quantities of substances such as mercury that are released to sewer, therefore an estimate of the quantity of mercury reaching a WwTW from dentists can be made using the connected population to the WwTW.

A literature review was conducted into substances likely to

be present in road run-off, and factors for these contributions

were also included.

A comprehensive literature review into representative removal rates for the different substances was conducted and where necessary expert knowledge on the operation of the WwTW and the physico-chemical properties of the substance was used to determine the

likely fate of a substance in treatment.

It was acknowledged within the report that there is significant

variation in removal rates that are reported in the literature. The range of results was presented, together with the justification for the removal rate used in the estimator.

The estimates were peer-reviewed by UKWIR and the EA and, as far as possible, the outputs with the estimator were verified against actual monitoring data provided by the water companies or the EA.

A sensitivity analysis was also carried out on the values to better understand the impact of these limitations.

Clearly, the quality of the outputs from the software is largely determined by the quality of information available to produce the estimates. The estimator tool has been designed so that the key values can be revised when better data becomes available as research develops.

This applies to most values within the estimator, for example the domestic contribution factors, the water supply characteristics, and the removal rates. If a water company has better information available,

it can override the estimator values, and an audit trail facility provided

in all fields of the estimator can be used to record deviation

from standard values.

While the protocol offers substantial benefit to the water industry and the regulators, it is important that its limitations are understood so that the results are not used for applications for which they were not originally intended. This is particularly important as the information is in the public domain.

The Pollution Inventory estimates represent a very high-level assessment of how a generic WwTW of a particular size may be expected to reduce the pollutant load received. The estimator does not account for actual performance of a WwTW due to the lack of appropriate data on the relationships between performance criteria and treatment efficiency. Therefore the tool should not be used as an indicator of discharge compliance at a particular works, or as the basis for discharge consent setting.

Improving understanding of diffuse pollution

The implementation of the WFD and the potential significant tightening of environmental quality standards for chemicals in the water environment means that diffuse pollution is now perceived as a real issue for the regulators and the water industry. The principles outlined within the estimator tool help to increase understanding of the pollution burden from domestic and diffuse sources.

The water industry wants to be in a strong position to exert a positive influence in reducing the amounts of the substances received at the WwTWs and determine the best way to treat substances that are unavoidably received. UKWIR has funded a number of projects which investigate and develop best advice concerning diffuse sources of pollution, including domestic inputs, service, industries and run-off, and the fate of the substances during treatment.

These are being developed further to ensure that UKWIR remains at the forefront of research and development in this area. The initial results of the ongoing studies are being shared with the regulators and DEFRA, and have helped to improve the understanding of the cost of the WFD implementation across Europe.

Studies such as these being carried out by UKWIR to improve our understanding of the sources of specific chemicals reflect the concern of the EA on the significance of diffuse pollution. The results of

the EA’s latest annual General Quality Assessment have highlighted that diffuse pollution must be tackled in order to meet EU standards.

They identified that in England it is farming and urban run-off,

and in Wales it is farming that are showing up as the most

widespread pollution risks.

What’s on the horizon?

Environmental reporting is increasingly important as public participation and awareness becomes more central in environmental policy. The content and coverage of the Pollution Inventory will continue to

evolve to reflect this.

The EA and SEPA (along with the Northern Ireland Environment and Heritage Service) have recently consulted on revisions to the inventories, which would mean an extension of water companies’ reporting requirements to bring them in line with other industries and to standardise across the UK. Key changes are likely to be the requirement to report on emissions to air and off-site waste transfers.

Through the use of the estimator tool developed by Atkins and collaboration with the regulators, the UK water industry is able to meet its reporting requirements and raise awareness and understanding of the significance of diffuse and domestic sources.

This is a fundamentally important step in the identification of future controls required under the WFD. And ongoing research by UKWIR among others will not only help to refine the estimates within the protocol but also provide a robust platform from which the industry can support the development of future controls.

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