There is no EPA "mandate." The nutrient TMDL for the lake is simply a number that reflects what the science tells us is needed to fully restore water quality and beneficial uses of the lake. Whether we do that or not is up to us. EPA cannot force the state to spend money to achieve the TMDL. EPA does have the authority to force some dischargers (e.g. municipal treatment plants and some stormwater sources) to adopt more stringent pollution control measures but it fully understands that this would impose exorbitant costs for very little benefit and accordingly it has not exercised this authority. Nor is there any likelihood that the current administration would do so. Indeed the Trump EPA will be an obstacle to cleaning up the lake.
Thanks to Act 64 Vermont has a framework to make progress on addressing the severe pollution problems that have turned Missisquoi and St Albans bays into dangerous cesspools fed by the nutrient pollution pouring off tiled agricultural lands in Franklin County. There is no cheap way to do it. The question is how much is a clean and healthy lake worth to current and future generations.