A COST-BASED STRATEGY FOR TMDL ALLOCATION

Abstract

Many states are actively involved with the load allocation phase of the Total Maximum DailyLoad (TMDL) Program. The Environmental Protection Agency (EPA) directs that TMDLs mustinclude establishment of reasonable and equitable load allocations among point sources thatwill, alone or in conjunction with other management and restoration activities, provide for theattainment of designated water uses (water quality standards) and the restoration of impairedwaters(FDEP, 2002). Allocation of load reductions must include an evaluation of the most costeffectiveapproach, however, specific guidelines do not address how this should beaccomplished. The TMDL process is technically complex enough without the inclusion of costoptimization. What are the benefits to be derived from including cost into the allocation?Preliminary EPA reports project a median savings of 75% (with a range of 21% to 92%) inimplementation cost for BOD and Nutrients reduction when a Cost-effective TMDL Programapproach is followed (EPA, 2001). The EPA evaluation involved a simple linear comparison ofallocation alternatives. Unfortunately, the highly non-linear nature of the implementation costswas not taken into consideration. With the potential for savings, it is imperative to develop asystematic optimization approach that seeks to minimize costs of implementation whileincorporating the non-linear nature of the cost functions. The objective of this paper is to present a mathematical model that that uses a mixed integer nonlinearoptimization approach to reduce the potential costs associated with alternative allocationstrategies. The mathematical model was developed for the fecal coliform TMDL allocation forthe Muddy Creek sub-watershed (Muddy 3) located in Rockingham County, Virginia. TheVirginia TMDL Program has historically allocated the fecal reductions as follows (ASAE, 2002): 90-100% direct deposits of cattle manure in streams 100% of all unpermitted point sources 0-95% in nonpoint sources 35-85% in wildlife fecal materials in streams The mathematical model has the potential for considerable cost savings when a flexible (non-rulebased) allocation strategy is adopted that focuses on maximum environmental contribution for agiven expenditure.