(a) OPM establishes a post differential by rulemaking if Government agencies require it for recruitment purposes and if one or more of the following conditions exist:

(1) Extraordinarily difficult living conditions,

(2) Excessive physical hardship, and/or

(3) Notably unhealthful conditions.

(b) OPM periodically reviews with Federal agencies whether conditions of environment have changed in the post differential areas and whether payment of the post differential continues to be warranted as a recruitment incentive.