Steve may have more to add to this, perhaps, but we have a real challenge, I would agree. It's very difficult to understand the overall carrying capacity, if you will, of an ecosystem, a drainage basin, or an airshed in the context of individual environmental assessments.
What we do is require proponents to look at past history to determine the extent to which impacts have occurred in the area already. We ask proponents to look at the future, to the extent that we know what the future is and whether or not there are other projects being proposed. Finally, we try to ensure that proponents minimize impacts to the extent possible to avoid reaching thresholds.