<Root>
     <Location>
         <DepartureBoundary>
            <DepartureBoundaryRadius>600</DepartureBoundaryRadius>
         </DepartureBoundary>
     </Location>
     <Location>
         <DepartureBoundary>
            <DepartureBoundaryRadius>600</DepartureBoundaryRadius>
         </DepartureBoundary>
     </Location>
</Root>

XDocument locationsDoc = XDocument.Load("file.xml");
DepartureLocationBoundaryRadius = null;
List<DepartureBoundaryRadius> radiusList = new List<DepartureBoundaryRadius>();

foreach (XElement locationElement in locationsDoc.Descendants("Root"))
{
    foreach (XElement locationSubElement in locationsDoc.Descendants("Location"))
    {
        foreach (XElement departureElement in locationsDoc.Descendants("DepartureBoundary"))
        {
             DepartureLocationBoundaryRadius =  departureElement.Element("DepartureRadius").Value));
             radiusList.Add(DepartureLocationBoundaryRadius);
        }
    }
}