Drainage Report

en ACS These are small areas at the perimeter of the drainage area that have minimal distariceteravets Lc before exiting the area of analysis. The longest path is Sheet flow 96 If @ 5.73% over grass Tc= 8.7 min Detention basin 4 collects water from the roof of Building D1, the disturbed grass area behind D1 and the roadway on the east side of the site in front of Building D. The drainage in this area drains to the Canoe Brook Tributary. The existing conditions have been modeled with a coverage as woods in good condition as required by the standards with NOAA type D rainfall curves. The table below outlines the results of the routing for this area. Water Quantity without exfiltration EXISTING Permitted Undet. BASIN TOTAL 2YR 1.67 84 33 0.16 Al 10 YR 4.06 2.84 .70 70 1.40 100 YR 9.38 7.50 1.50 5.25 6.75 Water Quality Small scale infiltration basins are listed as green technology for water quality when provided with pre- treatment. Basin 4 has a pre-treatment of a Cascade separator which provides 50% removal and the small-scale infiltration basin in series with it provides a total suspended solid removal of 90% Groundwater Recharge Test pit E1 and E2 were excavated to a depth of 12 and 14 ft with groundwater at 7 and 9 ft below grade respectively. The surface grade of E1 minus the 7 ft to groundwater is the limiting factor establishing the groundwater level at elevation 583. The basin bottom is set at elevation 585 making any groundwater in this area 2 ft below the bottom of the basin. The porous pavement reservoir is in fill over the existing grade for most of this system. The permeability of E1 was determined to be 0.61 in/hr. With a factor of safety of 2 the exfiltration rate from the basin used in the hydrocad calculation was .305 in/hr. See the spreadsheet on page 14 for the summary of groundwater recharge for this basin area and the project. Detention Basin 5 Area The Existing Area of Basin 5 contributing area is 167719 sf of Woods in good condition. The initial 100 LF is sheet flow with a slope of 12% in woods with light underbrush. Tc=10.1 min 9 Anderson Consulting Services LLC 40 Miller Drive, Boonton, NJ 07005 973-975-0703 (O) 973-886-7336 (C) PAndersonpe@gmail.com