ATTACHMENT 5


Industrial Hygiene Field Station                  Oct. 30, 1950
Box "illegible" Fort Douglas Station
Salt Lake City, Utah

Mr. D.C. Viles
Vice President                               CONFIDENTIAL
Vanadium Corporation of America
Durango, Colorado

Dear Mr. Vile:

     We have received the analysis on the radon samples which we
took in the Prospector No. 1 mine at Marysvale after the forced
ventilation fan had been installed and was operating.  These
samples showed that the atmospheric radon concentrations in the
mine had been reduced by a factor of about 500.  Both samples
were taken at approximately the same location as the previous one
which showed a level of 25,900 micromicrocuries of radon per
liter.  The fan had been turned off for about two hours when the
first sample was taken and had been in operation for about 40
minutes when the second flask was filled.  In both cases the
atmospheric radon concentration was about 500 micromicrocuries
per liter.  Both samples should represent the highest radon level
in the occupied areas of the mine as the fresh air was introduced
in the opposite end of the mine drift and most if it went up the
entrance incline without passing through the area that was being
worked.

     It is encouraging to see how much the radon concentrations
in this mine have been reduced by the use of ventilation and it
is my opinion that if fresh air were introduced to the working
faces of the drift the radon levels would be lowered still
further.

                              Yours very truly,


                              Duncan A. Holaday
                              Senior Sanitary Engineer
                              Industrial Hygiene Field Station

"Illegible"