DEVELOPMENT OF A NONPOINT SOURCE BMP CONTROL STRATEGY FOR A WATERSHED TMDL
Abstract:Lake Macatawa is a 1,800-acre drowned river mouth lake located near Holland, Michigan, along the shores of Lake Michigan. The lake is part of the 110,000 acre (175 square mile) Macatawa River Watershed located in Ottawa and Allegan Counties. Lake Macatawa and the surrounding tributaries are a unique and valuable resource for southwest Michigan. In 1996, Lake Macatawa and several of its tributaries were listed by the Michigan Department of Environmental Quality's (MDEQ) 303(d) nonattainment list, due to high nutrient levels, nuisance algae blooms, high turbidity, and poor fish and macroinvertebrate communities. Preliminary water quality data has indicated that high phosphorus concentrations and excessive turbidity are the main contributors to poor water quality.
In response to the listing, the MDEQ received a 104(b) grant from the United States Environmental Protection Agency (EPA) to develop a phosphorus Total Maximum Daily Load (TMDL) for Lake Macatawa. Preliminary results from the TMDL study revealed that the nonpoint sources comprised 91 percent of the total phosphorus load. Average phosphorus levels in Lake Macatawa were measured at 127 micrograms per liter in 1997.
A list of 44 Best Management Practices (BMPs) were considered as controls for reduction of the nonpoint phosphorus load. An objective and quantitative procedure, based on economic production theory and marginal cost analysis, was developed to assign the proposed level of effort and subarea watershed locations for each BMP. The optimum level of effort for each BMP was established for three categories of upstream subareas, designated as urban, agricultural and urbanizing areas. In addition, downstream BMPs were applied to the residual loading entering Lake Macatawa after the implementation of proposed upstream BMPs.
The BMP optimization procedure is based on a graphical approach as developed by Heaney and Nix (1977). This method determines the optimal combination of BMPs and level of effort to achieve any desired level of phosphorus removal using marginal cost analysis. The key benefit of this approach is to provide a defensible method for selecting the lowest cost combination of controls for reducing the nonpoint phosphorus loadings.
In addition to identifying the BMPs that were considered for each land use category a determination was made between the relationship of the BMPs which operate in parallel on the same source of pollutant load and those that are in serial or downstream from the parallel controls.
The recommended levels of effort and opinions of cost developed for the nonpoint loading reduction strategy assumed that existing BMPs already in progress will continue when the proposed controls are implemented. In addition to the level of effort, proposed capital costs were prepared when applicable, as well as annual costs, expected annual phosphorus removals, and unit costs for phosphorus removal. The capital costs for the optimized upstream controls total approximately 1.7 million and require a total annual cost of approximately 1.4 million to implement. These controls can provide approximately 58 percent of the targeted phosphorus reduction of 91,000 pounds per year. Therefore, some level of additional downstream controls will be required.
Three types of downstream controls were considered, including alum treatment, sediment basins, and enhanced or created wetlands. If each of these controls were implemented, the total capital costs are estimated to be 7.6 million, and require a total annual cost of approximately 980,000 to implement. The additional phosphorus removal from these controls is estimated to be 72,750 pounds per year, giving a safety margin of 34,810 pounds per year when compared to the target reduction.
This paper provides a summary of how the BMP optimization method was developed, the input data required to perform the analysis, and how the results were evaluated and refined to address local concerns. This process included gaining the input and validation from the Project Steering Committee, comprised of key Stakeholder Groups.
Document Type: Research Article
Publication date: January 1, 2000
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