Surface impoundment

Surface impoundment means a waste management unit which is a natural topographic depression, man-made excavation, or diked area formed primarily of earthen materials (although it may be lined with man-made materials), which is designed to hold an accumulation of liquid wastes or waste containing free liquids, and which is not an injection well. Examples of surface impoundments are holding, storage, settling, and aeration pits, ponds, and lagoons.

Source

40 CFR § 61.341

Scoping language

Benzene concentration means the fraction by weight of benzene in a waste as determined in accordance with the procedures specified in 61.355 of this subpart.