STF80MK A06368As a response to the Norwegian authorities’ requirements in 1997 of “zero discharges to sea” by the end of 2005, the operating companies on the Norwegian shelf initiated the development of the DREAM (Dose-related Risk and Effect Assessment Model) model, including the framework for calculating the Environmental Impact Factor for produced water (EIFPW). The DREAM model has successfully been used for years as a basis for calculation of EIFs for produced water discharges, assisting the oil companies in choosing among different technological produced water treatment solutions. The success of the EIFPW as an environmental management tool inspired the industry to initiate a Joint Industry Project (JIP), ERMS (Environmental Risk Management System), to develop a similar tool for drilling discharges: the Environmental Impact Factor for drilling discharges (EIFDD). Similar to the EIFPW, the EIFDD was designed to be an environmental risk-based decision support tool, to assist the oil industry in establishing cost-effective mitigation measures for reducing potential harmful discharges to the marine environment. The concept of the EIFDD is based on the PEC/PNEC ratio approach as described in the European technical Guidance Document (2003) on environmental risk assessment. Its calculation is implemented in the DREAM model. The companies involved in the development are using the EIFDD as a management tool to evaluate the risk connected to discharges and to evaluate the effects of alternate mitigation measures, for instance changing the chemical composition during drilling operations offshore.