So, it seems counties in northeast Nebraska are retaining 39.90 for use as some sort of point to point interop system (which was really what it was back in the day).
Nebraska Emergency Management still has their documentation referring to 39.900 as an emergency channel for communications between LEOPs. It seems they are not fully embracing the "ROC" channels on the SRS yet. I'm guessing all of the LEOPs will still have 39.9 until their transmitters break down and they can't get parts. Below is an excerpt from the Nebraska State Emergency Management Plan.
https://nema.nebraska.gov/sites/nema.nebraska.gov/files/doc/nebraska-seop.pdf
"State actions:
When a warning is received, the operator at the State Warning Point will clear the
NAWAS network of all traffic, transmit the warning and then receive acknowledgement of
the warning from each Warning Point. The Alternate State Warning Point provides a
backup means of disseminating tactical warnings. The area Warning Points will
immediately send any warnings to assigned locations using a secondary warning
network, 39.9 MHz or telephone"
On a side note, it you have not monitored NAWAS, there is a lot of good stuff that comes across here. They do regular nationwide and statewide calling tests. In the event of a major National Emergency, this would be a good frequency to have ready.
NAWAS is primarily a phone based network, but I know of 3 NAWAS transmitters in Nebraska. There may be more, but these are the only ones that have been reported to Radio Reference by scanner listeners. I'm not sure if there are any of these gems transmitting around the Sioux City area, but let us know if you find them.
156.000 Grand Island
453.650 Lincoln
155.550 Papillion (Omaha Metro Area)