A systematic examination of the literature on pollution has revealed almost no mention of monitoring prior to the Stockholm conference in 1972 (Harvey 1981). Since then, there has been a significant increase in the attention paid to monitoring. In the environmental science literature, however, ‘considerable confusion has resulted from the contradictory way in which terminology relating to the monitoring concept has been used’ (Harvey 1981). For the purposes of this chapter, therefore, monitoring is defined as an activity undertaken to provide specific information on the characteristics and functioning of environmental and social variables in space and time.
With this definition, it is clear that monitoring fulfils a number of important functions in EIA. The main uses of monitoring data are in impact monitoring and in ‘audit studies’. Again, the term ‘audit’ does not have, as yet, an agreed meaning in environmental science literature. Increasingly the term is used to describe the process of comparing the impacts predicted in an EIA with those which actually occur after implementation in order to assess whether the impact prediction process performs satisfactorily (see, for example, Andrews et al. 1974, Bisset 1984). In this chapter the significance of impact monitoring and audits in EIA are considered in detail.
The aim of impact monitoring is to detect an impact if it has occurred and to estimate its magnitude. An essential part of the process is to establish that the perceived change is a consequence of the project and not the function of some other cause. The changes might result, for example, from natural variations in the parameter monitored or may be the result of some other development in the vicinity and, thus, not related to the project under consideration. This is not an easy task and great care and attention has to be paid to experimental design in order to achieve this objective.
The only way of ensuring that an impact can be assigned correctly to a project is to use ‘reference’ monitoring locations, comparable to the controls in classical