Ultraviolet Absorbers (Stabilizers)

Compounds that when mixed with thermoplastic resin selectively absorb ultraviolet rays protecting the resins from ultraviolet attack.

Unanticipated Return

See inadvertent return.

Uncased Bore

Any bore without a lining or pipe inserted, i.e. self-supporting, whether temporary or permanent.

Underdrain

See subdrain.

Underground Utility

Active or inactive services or utilities below ground level.