Correct. Do keep an ear out to see if that control channel rotates to other frequencies as that may narrow down the initial search. Also, the use of the ETrunk program can be helpful in IDing new LCNs.
You may be receiving the NDW's Naval Academy (Annapolis) site control channel. I recall picking up another EDACS control channel in the military VHF-high band (while listening in Montgomery County) but I was not able to confirm its use.
I know there are two or three Navy VHF EDACS systems in the Washington area. And I've heard that the Naval Academy may be using one of them. However, I believe 138.51/138.515 is fairly strong in the immediate DC area. This would seem to indicate that this control channel does not belong to the Naval Academy. Or maybe they just run a very strong system.
You might ask this question on the Scan DC list at qth.net.
you might want to try the frequency of 138.5125. that part of the spectrum goes in either 12.5 or 25 khz steps. depending on what is using them at the time, being military aircraft or military bases. 8)