Although the US Park Police in the Washington DC area do use this frequency, it can be assigned to several other agencies as well. I have allocations on this frequency for the US Department of the Interior, which includes the Bureau of Land Management (BLM), Bureau of Reclamation and the National Park Service. It's also allocated to the US Fish and Wildlife Service nationwide. There are a few other oddball local assignments to the military and the Justice Department as well.
You will have to keep monitoring for some additional information on what the frequency is being used for and you will probably be able to figure out which DoI agency it is...
- Chris