to a uniform rollback that measured

to a uniform rollback that measured loadings by county with the objective of a 30 percent reduction in total nitrogen loadings. Using a least-cost mathematical programming model, Schwabe finds that the uniform rollback is the more cost-effective strategy, especially since the 30 percent reduction target would be unlikely to be met using the initial rule. However, the author notes that the dominance of the uniform strategy is specific to this particular setting and should
not be taken as a general proposition. The fact that point and nonpoint sources have received such different treatment from the EPA suggests the possibility that costs could be lowered by a more careful balancing of these control options. Point sources have received the most attention and have cleaned up considerably. Nonpoint sources have received very little atten-tion. This suggests that perhaps the marginal cost of additional abatement for point sources is now significantly high that it justifies moving control toward nonpoint sources. Figure 18.3 portrays the current situation. The marginal cost of abatement of point sources is consistently lower than the marginal cost of abatement of nonpoint sources. However, consider a case in which point sources have already cleaned up 50 percent of their discharges. If nonpoint sources have not cleaned up any, then the marginal cost of the next unit of cleanup is actually lower for the nonpoint sources! Suppose the regulatory agency is seeking additional cleanup. Can you see how the total cost of this additional abatement would be less for the nonpoint source than the point source?