Economic TMDL allocation: An optimization framework

The Total Maximum Daily Load (TMDL) approach currently used by the US Environmental Protection Agency (USEPA), to restore an impaired stream by allocating allowable loads to the polluters, does not mandate any economic analysis. The need for a cost effective allocation process has long been identified but no single best way to accomplish this has yet been developed. This research is an effort to incorporate economic criteria in the traditional TMDL allocation framework.; The main objective of this work is to improve the cost-effectiveness of pollution reduction measures at the load allocation stage. To achieve that goal an optimization procedure was developed to allocate loads subject to water quality criteria while minimizing the costs of load reductions. The cost of pollutant reduction is a function of the level of reduction achieved through a specific control option. The cost-effectiveness relationships were established for vegetative buffer strips to control agricultural land-based loads; streamside fencing to prohibit cattle from entering the stream; and septic system repair and installation. Wildlife and pet waste management options were also considered.; A portion of the Muddy Creek watershed and the entire Roses Creek watershed, both located in the Commonwealth of Virginia, were selected as case studies for this analysis. The TMDL allocation presented in the TMDL documents for the two watersheds were used to compare the model results. The pollutant load distribution in the Muddy Creek watershed does not allow full utilization of the model. The Muddy Creek watershed has only one feasible load allocation scenario whereas the optimization process proposed in this research is most valuable when there are multiple feasible scenarios. The application of the strategy to the Roses Creek watershed verifies the effectiveness of the model and realizes the following results; (1) The allocation recommended in the published Roses Creek TMDL is infeasible either due to the limitations on control measures' effectiveness or a very stringent water quality requirement ('upper percentile' E. coli criteria of 235 count/100 ml). (2) An economically superior (82 percent savings) allocation scenario is found in comparison with the published TMDL scenario, which satisfies the 30-day geometric mean E. coli criteria with a 5 percent margin of safety (120 counts/100 ml).; The research effort revealed additional findings. The incorporation of a model which relates pollutant reduction efficiency to cost of compliance enables the evaluation of the feasibility of the load allocation for the selected control measures. Similarly the feasibility of attaining the water quality criteria with best control strategies can be assessed. The optimization framework may also be useful to pollutant traders who are interested in investigating alternate TMDL allocations for cost savings.