Using time to event modeling to assess the ecological risk of produced water discharges
Since 1991, the North Sea countries (the United Kingdom, the Netherlands, Norway and Denmark) have been developing a decision support system to legislate the use and discharge of offshore exploration, drilling and production chemicals. The heart of this “Harmonized Mandatory Control System” is the CHARM model (Chemical Hazard Assessment and Risk
Management). This model enables the ranking of chemicals on the basis of their intrinsic properties, using a realistic worst-case scenario (i.e., 95 percentile of known field conditions occurring in the North Sea). To meet the prerequisites of the model (simple and transparent calculation rules), the CHARM model uses a fixed dilution factor, assuming equal and constant dispersion of chemicals around the platform. Although such a model is suitable for an internationally harmonized control system, a more realistic prediction is required to assess the actual risk of produced water. Because of increasing environmental concerns about the impacts of oil and gas exploration and production, and a shift toward self-regulation, the Norwegian Exploration and Production Industry initiated the development of a more detailed risk assessment model. In this model (DREAM: Dose Related Effect Assessment Model), environmental risk is dependent on the type of organism and its sensitivity as a function of exposure time. The DREAM project began in 1998 and is expected to be completed in 2001. Most effort will be put into the development of time to event models for representative chemicals and organisms. These models will be derived using the results of an extensive experimental program.