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The Economics of TMDLs Case Study: North Bosque River TMDLs
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Pp. 204-210 in Total Maximum Daily Load (TMDL) Environmental Regulations: Proceedings of the March 11-13, 2002 Conference, (Fort Worth, Texas, USA) 701P0102.(doi:10.13031/2013.7558)
Authors: K. O. Keplinger and C. Santhi
Keywords: Economics, Cost-effectiveness, TMDL, Water quality, Nutrient pollution, Phosphorus, BMPs, Dairy, Wastewater treatment plants, Simulation, Bosque River
Because the total maximum daily load (TMDL) process sets quantitative environmental targets
but does not specify the means for achieving those targets, TMDLs are natural candidates for
cost-effectiveness analysis. In cases where more than one control strategy can achieve targets,
an investigation of cost-effectiveness ratios may indicate the least costly control strategy.
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A cost-effectiveness analysis is applied to the N. Bosque River, where impairment is attributed to
phosphorus (P) loading from dairy waste application fields (WAFs) and municipal wastewater
treatment plants (WWTPs). On average, soluble reactive P (SRP) loads and concentrations need
to be reduced by 65 and 70 percent respectively from potential future growth levels, which
assume fully permitted flows at WWTPs and fully permitted cow numbers. A baseline scenario
and six P control scenarios were simulated assuming fully permitted conditions. Three dairy best
management practices (BMPs) were simulated: haul out of dairy manure, field application of
manure at the P rate, and reduced P in dairy diet formulations. Phosphorus control at WWTPs
and two combined strategies were also considered. The reduced P diet provided benefits
(negative costs) to producers, while P control at WWTPs was the next most cost-effective control
measure for reducing both P loads and concentrations. These control measures alone, however,
do not achieve numeric targets for either SRP loads or concentrations. A combined strategy
involving manure application at the P rate on existing WAFs, the haul out of excess manure, and
implementation of a reduced P diets in combination with P reduction at WWTPs was estimated
to reduce both P loads and concentrations by 87 percent of that needed to achieve targets. In this
application, opportunities for reducing the total cost of achieving targets is limited because 1)
both P loads and concentrations are targeted, and 2) the levels of those targets require substantial
implementation of all control measures considered.