[FG28_Kodiak]

Stationaries are not Actors!

You can use

        public static void RemoveStaticAt(double xPos, double yPos, double radius)
        {
            
            foreach (GroundStationary stationary in GamePlay.gpGroundStationarys(xPos, yPos, radius))
            {
                stationary.Destroy();
            }

        }

GamePlay.gpGroundStationarys is overloaded:
GamePlay.gpGroundStationarys(double x, double y, double radius)
GamePlay.gpGroundStationarys(string country)
GamePlay.gpGroundStationarys(string country, double y, double radius)

you get a Array of GroundStationary on a Position with a given radius, additional you can specify a country. Or you can get all Stationaries of a country you specify.