Question about sizing the silt trap

Hi, We are trying to pursue both storm water quality control and quantity control credits. When we calculate the 2 year - 24 hour design storm it comes to about 6.75 inches and 25% of that we are going catch in a catchment area. Then there will be an overflow from the catchment area and that we intend to release through a silt trap. The confusing part is that we are in the wet zone and the quality control credit requires us to design the silt trap for 1 inch rainfall per 24 hours. But from the catchment area there will be overflow in the range of 75% of 6.75 inch 2 year - 24 hour design storm. That is about 5 inches and only 1 inch of that will be handled effectively by the silt trap. If we try to make the silt trap to handle a 5 inch storm then it becomes so large. Am I making the correct reasoning here? Or how should I handle this situation? Please advise. Thank you.