Six urban drainage basins in Atlanta, Georgia, served by combined and separate sewers, were studied to determine the major pollution sources during storm events. Rainfall frequency analysis and simulation techniques were utilized to obtain design criteria for alternative pollution abatement schemes. High frequency storms cause the worst impact and most of the pollution from combined sewer areas. Annual BOD from these areas is 2,078,000 pounds, or 460 lbs/acre, of which 57 percent is due to storms of two--week or higher frequency. Bypassing of wastewater treatment plant flows during storms adds 690,000 pounds BOD/year. Runoff from storm--sewered areas, at 253 lbs/acre, adds 5,577,000 pounds/year. Overflows and bypassed flows have severe impact upon the South River, due to their high deoxygenation rates and coliform concentrations. Annual BOD reduction from combined sewer areas of 57 percent may be achieved for a total annual cost of $165,000, by modifying the three regulators and treating 80 percent of the overflows, in conjunction with storage sufficient to contain a two--week storm. (Author)