Under 33 CFR §151.05, 'clean ballast' is determined by one of two methods. When an oil discharge monitoring and control system approved by the flag state is used, what oil content threshold in the effluent is determinative that the ballast qualifies as clean ballast?

Why C is correct

33 CFR §151.05 defines clean ballast and states that when discharged through an approved oil discharge monitoring and control system, evidence that the oil content of the effluent does not exceed 15 ppm is determinative that the ballast is clean. The visual test — no visible traces of oil on the surface or shorelines and no sludge or emulsion deposited — is the alternative method when no such system is used.