Some environmental impacts can be fixed later, but it generally much more expensive to "bolt-on" a fix than to design the project properly in the first place. T

Some environmental impacts can be fixed later, but it generally much more expensive to "bolt-on" a fix than to design the project properly in the first place. This of course means the fix is rarely implemented. According to NEPA, when an impact is identified, the intent is to develop an alternative to avoid the impact entirely. It's only when alternatives are found to be infeasible that other mitigation methods can be considered.