Receiving Water

Receiving water is the water body, river, estuary, coastal sea, or aquifer, into which an effluent or runoff is discharged and where its impact is assessed. Its assimilative capacity, the load it can absorb without breaching water quality criteria, sets how stringent a discharge permit must be. In the United States, NPDES permits derive water-quality-based effluent limits from the receiving water’s designated uses and ambient criteria, and a total maximum daily load apportions the allowable pollutant load across sources when the water is impaired. Dilution, mixing-zone behavior, residence time, and stratification of the receiving water govern how a sewage outfall or stormwater discharge actually disperses.