Following a request from the European Commission, the Panel on Plant Protection Products and their Residues (PPR) was asked to deliver a scientific opinion on the report of the FOCUS groundwater working group (FOCUS, 2009) with respect to the higher tier leaching assessments. The PPR Panel is of the general opinion that, as suggested in the FOCUS report, substance parameter refinement can be applied in risk assessment. State of the art knowledge has developed to such an extent that scenario refinement is feasible as well, but will make assessment more complex unless embedded in basic tools and adequate guidance. The same is true for spatial modelling but establishment of adequate databases will require quite some effort. The Panel considers current knowledge on groundwater hydrology insufficient for implementation of monitoring as the highest tier of the assessment at the European level. The implementation of scenario refinement and spatial modelling requires clear criteria on the extent of arable surface areas with estimated leaching rates below the threshold level.