7.27 Two alternative projects to control flooding from rare, but sometimes heavy, rainfalls in the arid southwest will have the cash flows shown. Determine which alternative should be selected on the basis of a B/C analysis at i = 8% per year and a 20-year study period. Table Summary: Table divided into three columns compares two alternative options of a 20 years long flooding project at an 8% rate of interest. Column 1 represents the factors. Columns 2 to 3 are marked as: sanitary sewers (SS) and open channels (OC). Sanitary Sewers (SS) Open Channels (OC) First cost, $ 26 million 53 million M&O cost, $ per year 1.4 million 30,000 Sanitary Sewers (SS) Open Channels (OC) Homeowner cleanup costs, $ per year 950,000 0 8.