“Soil horizon” means a distinct layer of soil running parallel to the soil surface, designated as the O, A, B, or C horizon proceeding vertically through the soil profile from the soil surface downward.

Source. (See Revision Notes #1 and #2 at chapter heading for Env-Wq 1000) #11184, eff 10-1-16; ss by #14486, eff 2-1-26, EXPIRES: 2-1-36 (formerly Env-Wq 1002.67)