volV) (0123456789().,-volV) can move into the groundwater specified in the exposure assessment option as well as the magnitude of residues in groundwater. The objective may also include determining degradation rates in soil as a function of depth, persistence and movement of residues in groundwater, efficacy of mitigation measures, or confirmation of more detailed studies on a wider range of sites. Sampling schedules should consider the expected time required for an active substance to move through the soil into groundwater, as well as expected persistence in both soil and groundwater. Movement and persistence can be affected by both site characteristics and properties of the active substance and its metabolites. The need to tailor study designs to objectives, exposure assessment options, compound properties and site characteristics complicates the development of standardised study designs. Therefore, this report includes a number of example designs.Other key points that must be addressed by study designs are the vulnerability of the chosen sites compared to the vulnerability of all use areas supported by the study, the product use before and during the study, and the connectivity of the sampled groundwater to treated fields. Demonstrating connectivity (a quality criterion in the EU assessment of monitoring sites to exclude false negative measurements) is more challenging for catchment or aquifer monitoring compared to shallow wells installed as part of in-field or edge-of-field studies. This report includes an extensive discussion on assessing vulnerability of monitoring sites. This includes information on different approaches to vulnerability assessment and mapping as well as for setting monitoring sites into context. Lists of available methods and data sources available at the European level are also included. In addition to information on study design and estimating vulnerability, this report includes information on a number of other topics: avoiding contamination during sampling and/or analysis, avoiding influencing residue movement as a result of purging during sampling, and proper study documentation (Good Laboratory Practices and/or quality criteria). Procedures that are discussed include site selection (new or existing wells), installation of monitoring wells, sample collection, and analysis of samples. The report also provides information on causes of outliers (abnormally high concentrations not the result of normal leaching through soil), the use of public monitoring data, information on further hydrological characterisation (such as use of tracers, groundwater age dating, and geophysical methods), and information that should be included in reports providing results of groundwater studies. AbstractGroundwater monitoring is recommended as a higher-tier option in the regulatory groundwater assessment of crop protection products in the European Union. However, to date little guidance has been provided on the study designs. The SETAC EMAG-Pest GW group (a mixture of regulatory, academic, and industry scien...

Sediment-water fluxes of hydrophobic organic chemicals (HOC) may affect the quality of surface waters. Here, we present an approach to derive such fluxes from (a) in situ HOC concentration gradients measured with passive samplers and (b) mass transfer coefficients measured with a novel flux method using Empore disks. For eight undisturbed sediments, this method identified whether the sediment acted as a source or as a sink for HOCs. The analysis also identified which type of transport resistance governed sediment water exchange. For seven inland locations, exchange was limited by benthic boundary layer transport, showing no dependencies on sediment or chemical properties other than concentration. For one river mouth location, exchange was limited by slow in-bed intraparticle diffusion. A biphasic dual compartment radial diffusion model adequately described the data for this location. Fast desorption was interpreted as molecular diffusion retarded by microscale dual domain sorption to amorphous as well as black carbon (BC). Slow desorption was invariant with LogK(ow) and consistent with intraorganic matter diffusion through BC particles. Finally, it is discussed how these findings can be translated into a general framework for flux based exposure assessment.

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GeoPEARL_NL is used as a higher tier instrument in the leaching assessment of plant protection products in the Netherlands. Because the soil organic matter contents in arable soils in the current version were too high, a new soil organic matter for the Netherlands was needed. The new 3D organic matter map has been generated in two steps; first a trend model was developed based on data at 1210 locations selected using a well-defined stratified random sampling scheme followed by interpolation of the residuals using about 770 000 determinations of organic matter content from the Dutch Soil Information System (BIS-Nederland). In general, the predicted soil organic matter contents in the top layer of arable soils correspond well with those measured. Because preliminary calculations showed higher leaching concentrations using the new GeoPEARL version, the consequences of this new version in combination with the Dutch Decision Tree for leaching to groundwater was investigated. The results of the computations revealed that the PEC90 calculated using GeoPEARL in tier 2 is higher than the PEC80 calculated using FOCUSPEARL in many cases. This inconsistency between the first and second tiers could be remedied by the introduction of a calibration factor.Calibration factors of 5 and 10 are necessary to ensure consistency between these tiers for spring and autumn applications, respectively. Suggestions are given for improvement and justification of the calibration factors in the Decision Tree. It is recommended to systematically compare the predicted leaching concentration in groundwater abstraction areas with that in the Dutch agricultural area as a whole. To improve the reliability of model predictions for these smaller areas, development a more flexible schematisation is needed.Keywords: decision tree, GeoPEARL, groundwater, leaching, national authorisation, plant protection product, pesticide, soil organic matter • Acquisition, duplication and transmission of this publication is permitted with clear acknowledgement of the source.• Acquisition, duplication and transmission is not permitted for commercial purposes and/or monetary gain.• Acquisition, duplication and transmission is not permitted of any parts of this publication for which the copyrights clearly rest with other parties and/or are reserved. Analysis of the data showed that the organic matter content in the top 0.3 m of arable soil profiles in GeoPEARL was 1.5. to 2 times higher than that measured in these soils. This difference was introduced in the schematisation at the time of the development of the schematisation, because the aim was to estimate the average organic matter content in a grid cell, which results from a mixture of grassland and arable soil profiles. The consequence of the error in the organic matter content of arable soils is that the leaching concentrations to groundwater are underestimated. To remedy this, the Working Group on the Dutch Decision Tree for Leaching to Groundwater started to work on the improvement of the soil schematisation for G...