Hi Bob, I used the map at the top of this message board for my claim, which I won. The "Full Build Out map of Takhli" has a scale and I figured out the 500 meter drift area based on the scale and highlighted that distance all around the base. The munitions area, end of runway and some living areas are within that distance. A good description of your daily duties as a crew chief and emphasis on the number of times you were within these areas is important.
Good luck and don't give up, if you do they win! If I can help let me know I was a wrench with the 333rd TFS in 1966. LouB.