25 Pa. Code § 236.506
For determining classification for waste that contains a mixture of radionuclides, it is necessary to determine the sum of fractions by dividing each radionuclide's concentration by the appropriate limit and adding the resulting values. The appropriate limits shall be taken from the same column of the same table. The sum of the fractions for the column shall be less than, or equal to, 1 if the waste class is to be determined by that column.
Example: A waste contains Sr-90 in a concentration of 50 Ci/m (1.85 TBq/m) and Cs-137 in a concentration of 22 Ci/m (814 GBq/m). Since the concentrations both exceed the values in Table 2 of § 236.503, Column 1, they must be compared to Column 2 values. For Sr-90 fraction, 50/150 = 0.33; for Cs-137 fraction, 22/44 = .5; the sum of the fractions = 0.83. Since the sum is less than 1, the waste is Class B.
25 Pa. Code § 236.506
This section cited in 25 Pa. Code § 236.503 (relating to waste classification).