Environmental fate modelling is now actively used for the registration of plant protection products (PPPs). Yet, to be efficient in a harmonized registration process, the quality of PEC modelling needs to be assured.
Quality assurance of mathematical modelling implies the validation, documentation and maintenance of the modelling codes and scenarios. The FOrum for the Co-ordination of pesticide fate models and their USe (FOCUS) defined the procedures for realizing tier 1 PEC groundwater calculations for active substances at the pan-European level. The FOCUS working groups also identified a range of uncertainties related to the validity of the leaching models and scenarios. To mitigate some of these problems, the EU project APECOP (Effective approaches for predicting environmental concentrations of pesticides) was designed. The major objective of the project is to improve modelling concepts for PEC groundwater and air, and to increase the validity status of the modelling codes. In addition a methodology was developed and implemented to evaluate the representativity of the current tier 1 groundwater scenarios such as recommended by the FOCUS groundwater scenarios working group. In this paper, we summarize the methodologies that were used in this project. More detailed information is given in the subsequent papers.