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A missing element in most approved TMDLs is an evaluation component. TMDLs identify the point source and nonpoint source load reductions necessary to achieve water quality standards. The point source load reductions are implemented and monitored through the NPDES Program. The nonpoint source load reductions to be achieved are identified by pollutant source or subwatershed. A water quality-based watershed plan that provides the implementation details also needs to be developed to support the achievement of the necessary NPS reductions. The plan identifies the Best Management Practices (BMPs) that will be supported, necessary information and education activities, monitoring effort, implementation schedule, cost (administrative, technical and financial incentives), and responsibilities. In order to ensure the necessary nonpoint source load reductions are achieved, an adaptive management approach is recommended for inclusion in the watershed management plan. The most defensible measure of the watershed management efforts performance is a well-designed and implemented monitoring effort that examines statistically the relationship between the projects activities and changes in water quality. Monitoring during the nonpoint source implementation phase of a TMDL is done primarily to ensure the management plan is correctly carried out. The monitoring results should be able to check if assumptions about the direct, indirect and cumulative effects of management activities on resources are valid. Thus, the monitoring effort is the key element in the adaptive management of a watershed. There are five common designs utilized in watershed monitoring. Each design relies on a different level and intensity of monitoring and answers different questions at various levels of confidence. The watershed level monitoring effort enables the implementing entity and the public to measure progress toward meeting pollutant load reductions.

Since there is a lag time between when BMPs are installed and water quality improvements can be expected, evaluation of NPS implementation needs to be more than just water quality monitoring. At a minimum, NPS TMDL evaluations should consist of a mixture of administrative, social and environmental measures. Establishing an Evaluation Framework will provide the basis for organizing a monitoring and assessment effort to collect, analyze and utilize data to not only document what has been accomplished, but to improve ongoing implementation. The combination of administrative, social and environmental measures provides the crucial information for guiding management decisions through successive iterations of the adaptive management cycle. This paper will present a TMDL Evaluation Framework in support of the implementation of a NPS TMDL.