Okay, jjust wanted to say, solar observatories are not just telescopes poking out of funny looking rooves. They are also laboratories engaged in scientifiic experiments about solar activity and some experiments might involve the use of machinery that requires radio isotopes.

For example a solar study:

Astronomical detection of radioactive molecule 26AlF in the remnant of an ancient explosion

Tomasz Kamiński, Romuald Tylenda, […]Nimesh A. Patel

My theory is that they received shipment of a needed iisotope by way of the local post office and found upon delivery that the packaging was damaged or opened prior to delivery, and the closure of the post office is due to possible contamination there as well. There is no other reason to involve a post office.