- water
- water-quality
Dilution is the mixing of a discharged pollutant load into the clean flow of the receiving water. Because a stream is weakest at low flow, water-quality-based effluent limits are sized against the design low flow — the 7Q10 — so the discharge still meets criteria under the worst realistic dilution. Regulators may recognize a bounded mixing zone immediately downstream of an outfall where criteria are allowed to be met at the zone's edge rather than the pipe.
Dilution is the hinge between the water-quality thread and the data-center thread of this record. A large consumptive cooling withdrawal removes flow from the same reach that dilutes a downstream discharge, so it shrinks the assimilative capacity available to every permitted load below the intake — a coupling the water-balance model makes explicit rather than assuming away.