Incremental and Average Control Costs in a Model of Water Quality Trading with Discrete Abatement Units

This paper answers three questions related to the discrete nature of pollution abatement: (i) does a source's incremental control cost (as defined by the U.S. Environmental Protection Agency) necessarily exceed its average control cost, (ii) is incremental control cost a better approximation of a source's willingness to pay for abatement credits than average control cost, and (iii) exactly how does trading in discrete and continuous abatement markets differ? We find that the answer to the first two questions are both "no", suggesting that the U.S. Environmental Protection Agency needs to refine its reliance on incremental control cost as the sole measure upon which to assess the financial feasibility of water quality trading. In answer to the third question, the outcome of bilateral trading in the presence of discrete abatement can be determined through a process of implicit sequential consistency. For the general case where trading partners' average control cost curves "cross," the trading outcome is inherently sensitive to the initial allocation of abatement responsibilities