How are permit limits expressed?

Permits may contain several different types of limitations on a given pollutant. For instance, permits often limit both the total amount of a pollutant (usually in terms of pounds per day) and its average concentration in the wastewater (usually in terms of milligrams per liter) over given time periods. These limits may be expressed in terms of a daily maximum and a monthly average. Permits may also spell out an acceptable range of particular parameters such as pH. To comply, a permittee must keep the discharge within all these limits; exceeding just one constitutes a violation.

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