Choosing an approach and defining risk management zone
The results of the inventory of the existing information, including the boundary conditions, and a preliminary description of the contamination situation, may confirm that the site of concern can be considered a megasite. Due to its complexity in terms of the contamination situation (inventory of information) and the site-specific conditions (boundary conditions), it might be difficult or even impossible to meet the requirements of the EU-Water Framework Directive (WFD) at a megasite. Therefore, a megasite in most cases requires an approach deviating from the standard approach usually applied to contaminated sites. In that case, a risk-based approach is recommended, which can be supported by the Integrated Management Strategy (IMS) at hand.
As a basis for the decision to opt for a risk-based approach and the IMS, an assessment should be carried out, whether the existing or potential groundwater contamination at the megasite of concern can be treated fulfilling the regulations of the WFD - i.e. until 2015 (for The Netherlands 2030) - and by proportionate means. The assessment is done taking into consideration the technical and economic feasibility of the megasite clean-up.
This assessment is based on an expert evaluation and carried out at the preliminary estimation level. The result of this assessment is a technical and economical argumentation that is a basis for the discussion of the group of stakeholders (GOS) regarding the further management of the megasite.
If it is concluded that the regulations of the WFD cannot be met in terms of timeframe and proportionality, and a risk-based approach is applicable to the megasite of concern, a preliminary Risk Management Zone (RMZ) should be defined. The RMZ embraces an area, in which an impact on groundwater is accepted for a period of time that exceeds the requirements of the WFD. The RMZ is delineated based on the existing or predictable groundwater contamination. Based on this determination, the risks to other receptors inside the RMZ can be assessed and managed without considering the quality standards for groundwater. For the time being, the groundwater as a receptor inside the RMZ is addressed in terms of assessing its reduction to quality targets below the "good quality" - target of the WFD (local standard) by proportionate means, aiming for example at the use of groundwater as industrial water.
Output
The output of this step is the stakeholders' agreement on the need for a risk-based approach supported by the IMS. As a basis for the management of the megasite, a preliminary RMZ is defined.
