Revised Standard Version translates verse 30 as an independent statement, but it is better as a consequence of verse 29, as in Good News Translation.

The waters become hard like stone translates the Hebrew “the waters hide themselves.” The word translated as “hide” has a variant form which means “harden,” and so become hard, and this suits the context better than “hide.” Habel analyzes the problem as a poetic case where the verb in the first line provides the sense for the verb in the second line, and the second for the first also. Normally the “deep is hidden” and water “freezes over,” but here the verbs are reversed so as to apply to the subject in the other line. Even if this is the case, it is normally necessary to adjust the wording in order to make the meaning clear. Therefore it is best to translate line a, for example, as “which make the water hard like stone.” In line b face of the deep refers to the surface of the ocean. The verb translated as is frozen means “to become set, to solidify or form a solid mass,” and so Good News Translation has “and freeze the face of the sea.” In languages unacquainted with freezing it may be possible to say “and the surface of the sea becomes hard” or “becomes cold and hard.”

Quoted with permission from Reyburn, Wiliam. A Handbook on Job. (UBS Helps for Translators). New York: UBS, 1992. For this and other handbooks for translators see here .