The Total Maximum Daily Load (TMDL) Program has accounted for the current listing of more than 44,000 impaired waters nationwide and the development of more than 40,000 TMDLs since the program's inception. However, the rate of implementing TMDLs putting into practice the onsite pollution controls called for in the TMDL--long remained virtually undocumented. The TMDL Program was criticized in a 2007 program review by the Office of Inspector General for not being able to estimate the rate of implementing TMDLs in any way. The U.S. Environmental Protection Agency (EPA) subsequently committed to explore sample-based methods for estimating implementation rates, and specifically to conduct a TMDL implementation sampling pilot study in the six north-central states of EPA Region 5. The purpose of the study was to conduct an analysis of Regional TMDL implementation rates and characteristics as represented in a probabilistic sample of Region 5 TMDLs.