The U.S. Environmental Protection Agency (EPA or the Agency) developed environmental standards for the disposal of defense-related transuranic wastes for the U.S. Department of Energy’s (DOE or the Department) Waste Isolation Pilot Plant (WIPP). EPA implements these standards for WIPP, which has been in operation for over ten years. The general environmental standards are set forth in the Agency’s 40 CFR Part 191 Environmental Radiation Protection Standards for the Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Wastes [1]. These standards are implemented by site-specific compliance criteria [2]. The WIPP Land Withdrawal Act requires DOE to submit a re-certification application every five years after the initial receipt of waste. DOE submitted the latest WIPP re-certification application in March 2009. For re-certification, DOE must identify changes that have occurred over the previous five years and analyze their impact on the potential long-term performance of the repository. Once EPA determines that the re-certification application is complete, the Agency has six months to review the application and make a final decision. During this review, EPA solicits and incorporates public comment where appropriate. During the first re-certification in 2004, several stakeholder groups brought up issues (e.g., karst) that were addressed in the original certification. EPA has received comments again raising some of these same issues for the 2009 re-certification. In addition, DOE must submit proposed changes to the WIPP repository to EPA for review and approval. This paper describes selected issues of concern to WIPP and highlights interactions between EPA as the regulatory authority and DOE as the implementing organization. In general EPA’s experience points out the importance of communication, documentation and the regulator’s responsibility in determining “how much is enough.”