This report describes the results of a pilot study on the ammonia emission, deposition and critical load exceedances in the ROM area of south-east Friesland in the Netherlands. For this area an emission inventory was made describing the emission on a 1x1 km grid scale. A distinction was made between the emissions from stables and storage, application of manure and meadows. The stable emission of 300 (of a total of 1200) farms situated near areas sensitive to acidification was distinguished from the total stable emissions in the area. Deposition for the current situation (1993) averaged over the whole area, and for each nature area sensitive to acidification (>5 ha), was calculated using the OPS model. A distinction was made between the deposition due to emissions from foreign sources, the Dutch sources outside the ROM area, the sources within the area and the 300 farms. Critical load maps for nature areas, and for groundwater and surface water pollution, were derived from landuse data, species composition maps, the NLOAD model and critical load values for different ecosystems. Exceedances of the critical loads were estimated to determine the current environmental risk. Several scenarios were developed for the ammonia emissions in the area. The deposition and critical load exceedances were also determined for these scenarios. A pilot study on the optimization of emissions, given the critical deposition loads for nature areas, was also carried out. The results of this pilot study showed the optimization to be a good tool for determining future emission levels and spatial distributions to prevent exceedances of critical loads for all sensitive areas.<br>

To support the policy on preventive soil protection a measure to assess the emission to soil has been derived for sustaining soil quality on the basis of target values. This measure can be used to compare different sources of potential soil pollution and to derive directives for emission reduction. The study from which this measure is forthcoming is reported in two parts: Part 1 (report no. 715810015) is devoted to deriving a critical load for the unsaturated top layer of the soil and in part 2 (this report) the critical load is applied to the various combinations of soil, land use and emission sources. Emission reduction percentages were calculated for several combinations of sources and substances. It was concluded that a distinction could be made among a number of combinations as to levels of the critical load and target value exceedance in a 100 year period. Up to 90% emission reduction was calculated for the corrosion of zinc and lead along motorways, copper along railways and zinc in the combination of corrosion of guard-rails and motorways. In a 100-year period target values will certainly be exceeded and intervention values possibly. The method presented could form the base for soil protection policy insight into the extent of problems and for setting priorities. To define emission reduction with respect to priority combinations of sources and substances, further differentiation of specific loads and the loaded surface will be necessary.<br>

Estimates of emissions of pesticides from agricultural soils to the atmosphere and to the groundwater are needed. The most important processes determining the fate of pesticides are transformation, partitioning between the solid, liquid and gas phases, transport, and uptake by plant roots. The interaction between these processes is complex and non-linear. As these processes are functions of soil temperature and soil water status the use of a dynamic simulation model in prediction is indispensable. For this reason, the model PESTRAS has been developed. This model has been composed of existing models, i.e. the soil water transport submodel SWIF, the heat transport model HEATRAS, part of the pesticide leaching and accumulation model PESTLA, and the gas transport model GAS. This report comprises the incorporation of the model GAS and a partitioning point model into the PESTRAS model. A description is given of the model theory, the numerical scheme, and the model verification. Results are presented to show the sensitivity of the model to important input parameters, and the application of the model in a case study for 1,3-dichloropropene. The appendix contains a full manual of the programme. The model will be used on a routine basis for the generation of the annual reports 'State-of-the-Environment', published by RIVM. The model is also used in pesticide registration procedures. The incorporation of a gas transport submodel extends the scope of the model to volatile pesticides (Henry coefficient > 10 exp. -5 m3 m-3).

A large-scale 2-dimensional vertically integrated groundwater model has been constructed to investigate the geohydrological responses to glacial climate conditions. The groundwater model is based on the hydrogeological model of the Cenozoic and Mesozoic sediments in the subsurface of Northwest Europe constructed by the Dutch Geological Survey. Three different layers are distinguished above the relatively impervious base of Palaeozoic and Precambrian rocks. Boundary conditions to simulate groundwater flow related to various stages of the Pleistocene glaciations in the Northwest European lowlands have been inferred from palaeo-environmental reconstructions for the last three glacial cycles. Testing of the model concepts was carried out using a strongly simplified model. Effects of subglacial meltwater infiltration, excess meltwater redistribution and proglacial drainage of the highly pressurized groundwater system were examined. Sensitivity analyses with both the simplified and the large-scale model were carried out to identify important processes and system parameters. The effect of glaciation on the NW European groundwater system was investigated with the large-scale model. First, groundwater heads and velocities during an extreme cold climatic situation were compared with the present situation. Second, the geohydrology during the complete Saalian glacial cycle was studied by means of a sequence of steady-state simulations. This was followed by a final study on the effects of glaciations in the last 480,000 years. Results of the simulations indicate relatively high groundwater velocities and pressures, both in the subglacial areas and ice-marginal permafrost areas during cold periods. Extreme high velocities may develop when the ice sheet advances to the southern margins of the Upper Plio/Pleistocene aquifer in Northwest Europe. Areas with reduced meltwater infiltration which are assumed to be favourable areas for subglacial erosion processes coincide with areas where eskers, tunnel valleys and glacial basins are found. During relatively short periods in the Pleistocene glaciations high groundwater velocities were observed in areas containing the salt formations to be seen as potential repositories for radioactive waste.

Two methods have been developed to determine the maximum ammonia emissions and ammonia distribution across the country, provided the critical loads for ammonia for natural areas are not exceeded. Using critical nitrogen loads for seven types of natural areas from the literature, we derived the relative contribution of current nitrogen deposition to total nitrogen deposition, and 'corrected' for this, to obtain ranges of critical ammonia loads for natural areas. The first method uses an optimisation program to determine the optimal maximum emission distribution, while the second method uses source- receptor matrices and receptor-source matrices to iteratively determine the emission distribution. The second method leads to lower emission values because the distribution is not 'optimal'. If complete protection from NH3 deposition (i.e. the lowest critical ammonia loads for the existing natural areas) is offered, the maximum emission is 46 (method 2) to 66 kton (method 1). The highest emissions can be found in areas remote from natural areas, i.e. north of the provinces of Groningen and Friesland, and in Noord-Holland, the west of Zuid-Holland and Zeeland. If the national ecological network of protected areas (EHS), where nature areas will be developed in the future, is also taken into account, the maximum emission drops to 40 - 52 kton NH3. These methods are valuable in illustrating the effects of making possible choices in nature development or protection. If, for example, a limited exceedance of maximally 20% is tolerated, the maximum emission will increase by 10 - 45 kton.

The National Groundwater Quality Monitoring Network was set up by the RIVM in 1979. Since 1984 groundwater has been sampled every year at about 400 locations at depths of about 10 and 25 metres below land surface. After 1989 the number of locations increased because several Provincial Groundwater Quality Networks joined the National Network. In 1992 groundwater was sampled at about 600 locations. About 25 chemical components and some physical properties were measured. Information on sampling depth, soil- and land use and region in the Netherlands was used to classify the data into groups. This study resulted in estimates of mean concentrations and areal percentages of target value exceedance for the year 1992 and target value exceedance per region presented in the form of maps. The change in groundwater quality per group and region in the period 1984-1993 is also investigated. Correlation analysis was used to examine the relationship between concentrations and time.<br>

The distribution of calculated potential exposure due to soil contamination is quantified to gain insight into the reliability of the human exposure calculated with the CSOIL model. The study is focused on the distribution of exposure due to uncertainty in the input parameters caused by spatial variability and lack of information. A Monte Carlo-based sensitivity and uncertainty analysis is performed for this purpose using the UNCSAM computer package. Also investigated is the chance of occurrence of the deterministically calculated potential exposure underlying the intervention values, using the probability density function of the calculated potential exposure. Finally, the most important input parameters for the exposure distribution are derived for both potential and actual exposure. The study is focused on five contaminants, differing widely in their contaminant characteristics. The exposure via separate exposure routes is also evaluated so as to indicate the distribution of the exposure and contribution of the input parameters to exposure to other contaminants. To achieve this, other contaminants have to be characterised according to the contribution of these separate exposure routes to the total exposure. Because of large uncertainties in the calculation of the contents in the contact media (indoor air, plant content), for some contaminants one should consider performing measurements in these contact media. On the basis of probalistically derived exposure, Maximal Permissable Risk (MPR) for intake and ecotoxicological serious soil-contamination concentration (ECOTOX EBVC), it is recommended in the future to consider deriving probalistically based guidelines (e.g. intervention values) or other environmental quality objectives (e.g. final contaminant level after remediation).<br>

Analogous to the CSOIL model, which estimates human exposure to contaminated soils, an exposure model called SEDISOIL has been developed to quantify human exposure to sediments. When using this model it should be kept in mind that calculations are not very accurate, certainly when measurements in surface water and on fish have not been performed. SEDISOIL can be used for determinating the urgency of remediation in the case of seriously contaminated soils.<br>

For future versions of the integrated reports: Environmental Balance and Environmental Outlook, RIVM has chosen to present an overview of environmental issues, especially those related to actual and future environmental policies in the Netherlands. In terms of so-called target and related policy monitoring indicators. These environmental indicators are represented by a limited numbers of concise and appealing parameters to present the vast amount of information on environmental pressure and quality. This report defines Environmental indicators for the extent of soil pollution and the progress of soil remediation and of soil protection restricted to point sources. The most important gaps and discrepancies between definition of indicators and quantification (collecting data) are listed. It is concluded that for the present quantifying the majority of the listed indicators, for instance where information structures are lacking or relevant parameters are not collected, is not possible.

The first results of the National Soil Quality Monitoring Network of the Netherlands are described. The network is a cooperative effort of the National Institute of Public Health and the Environment (RIVM), the Agricultural Economic Research Institute (LEI-DLO) and the Research Institute for Agrobiology and Soil Fertility (AB-DLO). The primary objective of the network is to establish changes in soil quality over time. Secondary objective is to establish the actual quality of soil and upper groundwater. Attention is focussed primarily on the rural part of the country. The monitoring program is divided evenly in time units: about 40 locations are sampled yearly. The network started in 1993 with the sampling of soil and upper groundwater on 35 cattle farms in the sandy regions of the Netherlands. The farms are divided into two categories: extensive (19) and intensive (16). These farms represent 25% of the agricultural area in the sandy regions and 12% of the total agricultural area of the Netherlands. The report contains information on concentrations of heavy metals, polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides in the topsoil (0-10 cm). Information on concentrations of macroparameters, nutrients and heavy metals in groundwater is also presented. The measured concentrations are compared with the Dutch objectives for soil and groundwater quality (target values). No exceedance of target values was observed for heavy metals in soil. Target values for a number of individual PAHs and organochlorine pesticides were exceeded in soil. The same holds for nitrate and for a number of metals in groundwater. There are no statistical significant differences between both categories with respect to heavy metal, PAH and organochlorine concentrations in the soil. Heavy metal balances have been computed at farm level for cadmium, copper, lead and zinc. There is a balance surplus for all metals involved due to the net result of input through atmospheric deposition and farming practice (feedstuff, manure and fertilizer) and output as a result of leaching to the groundwater. Therefore it is concluded that accumulation of heavy metals occurs. However, there is no correlation between the actual balance surplus and present metal concentrations in the soil. On the basis of these balance computations and taking into account the local variation in concentrations, 1998 is estimated to be the proper time to repeat the sampling on the farms in the categories visited in 1993.