The Clean Water Act (CWA)prohibits the discharge into protected waters of any pollutant by any person, unless a discharge permit has been secured from D. Both D and the counterpart state agency play a role. The precise role depends on whether D has delegated permit issuing authority to the state; but no such delegation is present here. Puerto Rico is treated as a state for purposes of the CWA, and its local agency is the Environmental Quality Board (EQB). D held a discharge permit for its oil refining facility. On May 27, 1988, P submitted an application to renew the permit for its facility. D forwarded the application to EQB, requesting that a draft certification be prepared promptly. On January 25, 1989, EQB released a tentative certification--essentially a draft document that facilitates public comment on the proposed state certification and proposed federal permit. The draft certification in this case probably came as a surprise to P. The earlier permit had employed a 'mixing zone' analysis in setting the pollution limitations. The draft certificate did not include a mixing zone analysis. D has used a mixing zone, a defined area of the receiving body of water, after the pollutant has been diluted by that water to measure pollutants. Measuring pollutants at the edge of the mixing zone is widespread in the application of the CWA. Whether to establish such a mixing zone policy is a matter of State discretion. Practically every state and Puerto Rico have adopted mixing zone criteria. The 'mixing zone' determination is basically a cost-benefit judgment on a given set of environmental facts, rather than any sort of 'scientific' determination. EQB's draft certification neither continued in force the old mixing zone criteria temporarily nor made the certificate subject to the new criteria still under development. D's draft permit and request for public comment, therefore, used no mixing zone analysis. EQB had used a mixing zone analysis in the past and was proposing to do so in the future. Just as P moved to correct the EQB certification, D moved even more swiftly to adopt a final permit based on the EQB certificate that omitted a mixing zone analysis. P sought administrative review within D. In June 1992 D's regional administrator issued a decision reaffirming the new permit without a mixing zone provision but continuing the stay of the new permit pending a further administrative appeal. D's Environmental Appeals Board issued a lengthy decision refusing further review. P appealed.