The plant has been around since at least the 1970s. At the time it likely was on the edge of town, but through 50 years of urban sprawl, the town grew around it.
It may be even older than that. My source for the age of the site is this 1970 NASA ALSEP supplier list (from the moon program!), which lists the address as an approved manufacturer on page 38: https://www.lpi.usra.edu/lunar/ALSEP/pdf/31111000671279.pdf
Surely they've had to get new permits over time as their operations changed? And why didn't the presence of the plant prevent the town from growing around it?
There's a home 430 feet away from it. At that point you didn't even try to create a buffer zone.