$**$FLOWRATE $1$ ONLY $**$

$3-13$ The wastewater treatment plant has been experiencing high wastewater flowrates during the wet$-$weather months. The average monthly flows for four flow regimes are reported below $($flow regime to be selected by instructor$).$ The rapid increase in flows during the winter months is due mainly to increased infiltration$/$inflow$.$ Infiltration is estimated to be $67$ percent of the excess flow. The lengths of the collection system pipelines that need to be repaired are also listed below. The average repair cost is $$200,\frac{000}{k}m$ and the repair will be effective in reducing the infiltration by $30$ percent. How many years from now will it take to pay back the cost of the sewer repair program based on the annual savings in treatment cost, assuming the future annual flowrates are

equal to those in the table below? The current cost of treatment is $$\frac{1\mathrm{.}50}{m^3}$ and the future cost of treatment is estimated to escalate at $6$ percent per year. Assume the sewer repair will be complete in three years for Areas $1$ and $2,$ and four years for Areas $3$ and $4.$

$\backslash$table$[[$Month$,$Average monthly flowrate, $\frac{m^3}{d}$