The European Union Water Framework Directive (2000) is sending a strong signal for environmental protection. By recommending the use of total costs, it seeks to take into account environmental damages as a whole in the decisionmaking process of environmental policies. It is also a strong signal for environmental economists since they will now have to include accurately the environmental damages to be assessed. Yet, when dealing with land planning in sensitive environments, existing methods are reaching some limits. International and european agreements seem to support the development of compensatory mitigation based on the american design (mitigation banking). At the same time, these agreements require an increased use of economic valuation mechanisms. In this paper, we suggest to combine this two approaches by using compensatory mitigation process as an assessment of the "pur" environmental damages costs. They would come as a complement to traditional mechanisms such as contingent valuation and stated choice methods which, regarding complex natural systems, fail to assess accurate nonuse values or existence values.