All,
Thank you so much for the variety and depth of your responses. In short, I think I can conclude that there is no direct, clear, black and white answer. Once again, life is grey and murky at best. In response to the last post from urgross, I have done numerous Federal projects on military bases and you are correct. The Federal Government does not bow to any State or Local requirements but can abide by them voluntarily if they so choose. Likewise, they may or may not follow their own standards (which they do have).
In my specific case, my main concern was being the designer of record and the enforcer of all the Federal, State and local stormwater regulations that exist at the same time. The conflict, in my mind, exists that if I, as the designer, design to meet all of these requirements in private practice, then the regulator who enforces the laws that I must abide by as a designer can enforce that which I missed or misinterpreted without threat of impunity (note the sovereign immunity doctrine cited in an earlier post above). However, if I am under threat of losing my job at worst or potentially stunting my advancement or pay raises because I adhere to both the design and enforcement of laws created by others that are not necessarily engineers, that could create a perceived conflict of interest. The appearance of such a conflict of interest could lead to the accusation that I purposely did not design it correctly (as opposed to an omission error or misinterpretation) or I pressured my enforcement staff to not enforce things correctly in order to protect my reputation. Again, with ethics, it is not just "not doing the wrong thing" but also not "appearing to do the wrong thing". By virtue of my position as both designer and enforcer, my concern is that a simple mistake or omission would "appear" to be, in reality, purposeful. Hence the question of a conflict of interest...
This has been a great discussion and I think has flushed out many issues for us all to consider. In the end, I have discovered that it is not clearly legislated in my exact circumstance (although I think it would be wise to enact such clear legislation for exact examples such as I have proposed). Therefore, in the end, it is a personal decision that I must make without any real clear answer. I think all of you have helped me to frame my reasoning as what any other reasonable engineer would do in the same situation should I ever be challenged. Thank you!