For discharges to perennial streams or lakes, permittees must use receiving water collected as close to the point of discharge as possible but unaffected by the discharge. Receiving water must be collected outside the regulatory mixing zone for discharges to lakes. If the receiving water control fails to fulfill the test acceptability criteria in OAC 252:606-6-38, the permittee must substitute synthetic dilution water for the receiving water in all subsequent tests, provided:

1. (1) a synthetic dilution water control which fulfills the test acceptability requirements in OAC 252:606-6-38 was run concurrently with the receiving water control.
2. (2) the test indicating receiving water toxicity was carried out to completion.
3. (3) the synthetic dilution water had a pH, hardness and alkalinity similar to that of the receiving water, provided the magnitude of these three parameters did not cause toxicity in the synthetic dilution water.
4. (4) the receiving water test must be conducted at the start of each permitting cycle.

Added at 41 Ok Reg, Number 23, effective 9-15-24