HomeMy WebLinkAboutApplication Files_85048_pg0184 provide pre-treatment of runoff from the respective parking lots prior to discharge into
Baskin. :#6. or sizing sheet"rovid$&in Appendix f2 inate thAt unifq
will provide 65% and 71% removal of sediment prior to discharge into Basin #6. The
large permanent pool of Basin #6 exceeds the required water quality volume for the
contributing watershed. Together, the basins and sediment chambers will facilitate the
removal of suspended solids via settling prior to discharge. Additional treatment
' measures include vegetation within the basins, two-foot sumps in all catch basins for the
initial removal of suspended solids from the stormwater and an oil/trap hood installed in
the last catch basin in line prior to discharge into the basins.
F. Pipe Outfall Protection
Outfall protection for the pipe discharges into the basins consists of riprap aprons
extending from the pipe ends down into the permanent pool of the basin. The widths of
the aprons in all cases are in excess of 3 times the pipe diameter.
' The outfall from CB#35 into Basin #6 was designed a little differently because the
permanent pool does not extend up near the pipe outlet. However, in reviewing the
IHydroCAD data sheets, the water surface in Basin #6 does back up to above the outlet
flowline of this pipe in each of the design storms. Thus, the energy resulting from
discharges during the design storms will be dissipated by the elevated water in the basin.
' As a result, the outfall need only be sized for much smaller storms where the water
surface does not back up to the pipe outlet. To be conservative,the apron was sized with
a minimum 12' apron length and 8' width which, according to the DOT Drainage Manual
Table 8.7.1 provided in Appendix 7, is more than sufficient for the 2-year design storm
(4.21 cfs discharge from the 24-inch diameter pipe).
' G. Summary of Results
The proposed design and analysis indicates that there will be no increase in peak runoff from the
site for the indicated design storms. In addition, the treatment measures discussed will provide
pollutant removal prior to discharge of the stormwater.
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