There must be means of confirming that disposals of radioactive waste do not result in members of the public receiving radiation doses in excess of the ICRP recommended limit. It is rarely practicable to measure doses to individuals by direct means and in most cases they can only be estimated from the in­formation gained through environmental monitoring programmes. Furthermore, information must be avail­able from which collective doses to populations can be estimated; again environmental monitoring pro­grammes are a source of such data.

Before an authorisation to dispose of radioactive waste to the environment is granted by the Authorising Government Departments (MAFF and DoE in England or Welsh Office in Wales), an assessment is made of the environmental pathways by which the radionuclides may be returned to man. Environmental monitoring is needed to confirm the assessment made in arriving at the authorised disposal limits and to confirm that the control objectives are being met.

In order to demonstrate compliance with the terms of authorisations granted to dispose of radioactive waste, the responsible Minister is empowered to direct the operator to take and analyse samples of the waste and environmental materials. Results of this monitor­ing are reported to the authorising departments, whose representatives check periodically on the accuracy and effectiveness of such monitoring. It is thus seen that monitoring is carried out in two separate stages, the sampling of disposable waste (discharge monitoring) and the sampling of environmental materials (environ­mental monitoring).

Environmental monitoring must begin before any new major installation comes into operation. This makes it possible to determine the normal level of background radiation in the area, which includes nat­ural radiation, and to establish and rehearse proce­dures for when the establishment becomes operational. Measurements taken when the installation is opera­tional may be compared with pre-operational mea­surements and, where necessary, an assessment may be made of the contribution from radioactive waste discharges.

The purposes of environmental monitoring may be defined as follows:

(a) To assess the radiation exposure of the public This is the fundamental objective of environmen­tal monitoring for radioactivity. In most cases the direct measurement of radiation exposure of the public is not practicable. Instead exposure must be assessed from environmental measurements used in association with data on the habits of the po­pulation concerned.

(b) To confirm control measures The sampling and analysis of radioactive waste discharges serve as a check on the discharge control system. Environ­mental monitoring provides a further check and may result in the detection of releases that might otherwise have gone unnoticed. Monitoring for this purpose may include sampling indicator materials such as fresh water mosses and inedible seaweeds which have no radiological significance. Such monitoring is particularly valuable in the early stages of development of a nuclear facility when discharges are too low to be measurable in those pathways contributing to public radiation expo­sure. It can also give an early warning of changes which may subsequently have a bearing on public radiation exposure.

(c) To contribute to research Monitoring carried out for purposes of the control system — items (a) and (b) — may add to the overall state of knowledge of the behaviour of radionuclides in the environment. It is however, sometimes ne­cessary to improve that state of knowledge by carrying out more extensive studies on a research basis. In particular, at such time as an authorised discharge has resulted in measurable radioactivity in the environment, it is usual to engage in a comprehensive monitoring programme in order to re-assess the relationship between discharges and levels in the environment. Measurements are made embracing the pathways which lead to public exposure. Some of the pathways will be found to be critical.

(d) To provide public information and assurance It is important to provide public information and assurance on the safety discharges from nuclear establishments. Monitoring, based strictly on those discharges and pathways which give rise to envi­ronmental radioactivity leading to a significant level of public radiation exposure, may not on its own be sufficient to satisfy the public of the safety of discharges. It is quite often necessary to engage in monitoring which equivocally demon­strates the safety of discharges, even when such monitoring shows that measured levels are in all senses trivial and in some cases are not discern­ible from natural background levels. Monitoring carried out for this purpose is often based on potentially critical pathways, but there are also occasions when monitoring with little scientific justification is required.

(e) To establish pre-operational ambient levels of radiation Monitoring programmes are needed to determine background levels of radiation and radioactivity in order that long term variations may be observed. Information derived from such programmes serves to describe the state of the environment, that state being made up of radio­activity levels produced by nature and by man.

(f) To help decide on the action required during an emergency In the event of an emergency there must exist the capability to initiate monitoring immediately. The existence of gamma dose rate monitoring programmes which serve to provide an assessment of environmental levels of radioac­tivity will in many cases also enable an emergency programme to be launched without delay.

Monitoring near CEGB sites may be divided into three parts; Land gamma radiation measurements, Land samples and Marine environmental monitor­ing. The three parts may be described briefly as follows, noting that there are minor variations among stations.