Report 4 13 2026

​ENSURPLAN, INC.​ ​ ww.Ensurplan.​​net​ w ​ ivil Engineers & Land Surveyors C Ph: (732) 469-0400​ ​Certificate of Authorization 24GA27997700​ ​STORMWATER DRAINAGE REPORT​ ​04/13/26​ ​Minor Subdivision 15 Ridgeway Ave West Orange, NJ​ ​Design Discussion​​(continued)​ ​ rainage areas connected directly via roof drain piping or indirectly via flow through the​ D ​impervious pavement are shown in purple,​ ​ rainage areas shown in green generate runoff which will flow overland via sheet flow to the​ D ​inlet at the rear of the site, bypassing the infiltration system.​ ​Diagram of Proposed Drainage Areas​ ​6​ ​Mailing Address: Post Office Box 4304, Warren, NJ 07059​

​ENSURPLAN, INC.​ ​ ww.Ensurplan.​​net​ w ​ ivil Engineers & Land Surveyors C Ph: (732) 469-0400​ ​Certificate of Authorization 24GA27997700​ ​STORMWATER DRAINAGE REPORT​ ​04/13/26​ ​Minor Subdivision 15 Ridgeway Ave West Orange, NJ​ ​Design Discussion​ ​(continued)​ ​ he below grade infiltration basin has been sized as required to restrict the volumes of the​ T ​design storms and provide the necessary reductions in rate. It is also required that the designed​ ​pond volume can drain within 72 hours via infiltration.​ ​The maximum storage for the projected 100 year storm is 3,667 cf.​ ​Time to empty: (3,667 cf max / (125.5’ x 12.75’) sf flat bottom) x 12”/ft / 0.5”/hr = 55 hrs​ ​The maximum volume within the pond 4,026 cf.​ ​Time to empty: (4,026 cf max / (125.5’ x 12.75’) sf flat bottom) x 12”/ft / 0.5”/hr = 60 hrs​ ​ he infiltration rate utilized in the design analysis is 0.5”/hour which is half of the infiltration rate​ T ​measured of 1.00”/hr at the soil log situated within the infiltration bed.​ ​7​ ​Mailing Address: Post Office Box 4304, Warren, NJ 07059​

​ENSURPLAN, INC.​ ​ ww.Ensurplan.​​net​ w ​ ivil Engineers & Land Surveyors C Ph: (732) 469-0400​ ​Certificate of Authorization 24GA27997700​ ​STORMWATER DRAINAGE REPORT​ ​04/13/26​ ​Minor Subdivision 15 Ridgeway Ave West Orange, NJ​ ​Stormwater Analysis​ ​Stormwater Quantity​ ​Requirements​ ​ o comply with the Major Stormwater regulations quantity control restrictions, stormwater​ T ​management measures shall be designed so that the post-construction peak runoff rates for the​ ​current and projected 2-, 10 and 100 year storm events, as defined and determined pursuant to​ ​N.J.A.C. 7:8-5.7(c) and (d), respectively, are 50, 75 and 80 percent, respectively, of the​ ​preconstruction peak runoff rates. The percentages apply only to the post-construction​ ​stormwater runoff that is attributable to the portion of the site on which the proposed​ ​development or project is to be constructed.​ ​Design Methodology/Discussion​ ​ he runoff rates from the existing condition were determined. The runoff rates from the​ T ​proposed conditions were determined. A study point is modeled at the existing inlet to the rear​ ​of the site at which all runoff from the studied area is collected. A comparison to the pre​ ​construction and post construction rates along with the maximum allowed reduced rates follows.​ ​Current Intensity Storm​ ​Pre Construction​​Rate​ ​Maximum​ ​Post Construction Rate​ ​2 Year Storm 0.38 cfs 0.19 cfs 0.19 cfs​ ​10 Year Storm 0.95 cfs 0.71 cfs 0.66 cfs​ ​100 Year Storm 2.26 cfs 1.81 cfs 1.80 cfs​ ​8​ ​Mailing Address: Post

s 1.80 cfs​ ​8​ ​Mailing Address: Post Office Box 4304, Warren, NJ 07059​

​ENSURPLAN, INC.​ ​ ww.Ensurplan.​​net​ w ​ ivil Engineers & Land Surveyors C Ph: (732) 469-0400​ ​Certificate of Authorization 24GA27997700​ ​STORMWATER DRAINAGE REPORT​ ​04/13/26​ ​Minor Subdivision 15 Ridgeway Ave West Orange, NJ​ ​Design Methodology/Discussion​​(continued)​ ​Projected Intensity Storm​ ​Pre Construction Rate​ ​Maximum​ ​Post Construction Rate​ ​2 Year Storm 0.57 cfs 0.29 cfs 0.26 cfs​ ​10 Year Storm 1.31 cfs 0.98 cfs 0.90 cfs​ ​100 Year Storm 3.17 cfs 2.54 cfs 2.33 cfs​ ​Stormwater Recharge​ ​Requirements​ ​ o comply with the Major Stormwater regulations recharge requirements, stormwater​ T ​management measures shall be designed to demonstrate through hydrologic and hydraulic​ ​analysis that the increase of stormwater runoff volume from pre-construction to​ ​post-construction for the projected two-year storm, as defined and determined pursuant to​ ​N.J.A.C. 7:8- 5.7(d), is infiltrated.​ ​Design Methodology/Discussion​ ​ echarge has been provided by the use of a small scale infiltration basin and has been​ R ​analyzed by utilizing the New Jersey Groundwater Recharge Spreadsheet (NJGRS)​ ​ s the NJGRS cannot model infiltration from a system which is simultaneously discharging​ A ​outflow through an orifice the study area is limited to a 2” thick stone bed set below the system​ ​outlet.The BMP variable is the depth from the surface invert of the discharge orifice or 48”. The​ ​depth to the lower surface is 50” and the effective depth of the BMP is 1.6” or 0.4 voids x 2”​ ​stone depth.​ ​9​ ​Mailing Address: Post Office

​stone depth.​ ​9​ ​Mailing Address: Post Office Box 4304, Warren, NJ 07059​

​ENSURPLAN, INC.​ ​ ww.Ensurplan.​​net​ w ​ ivil Engineers & Land Surveyors C Ph: (732) 469-0400​ ​Certificate of Authorization 24GA27997700​ ​STORMWATER DRAINAGE REPORT​ ​04/13/26​ ​Minor Subdivision 15 Ridgeway Ave West Orange, NJ​ ​Design Methodology/Discussion​​(continued)​ ​ he NJGRS calculation sheet was used to solve for the minimum allowable infiltration footprint​ T ​and checked against the provided area. The minimum area was calculated to be 1,339 sf while​ ​the provided infiltration footprint is 1,600 sf.​ ​As shown on the following two exhibits the required recharge volume is provided.​ ​Recharge Work Sheet One​ ​10​ ​Mailing Address: Post Office Box 4304, Warren, NJ 07059​

​ENSURPLAN, INC.​ ​ ww.Ensurplan.​​net​ w ​ ivil Engineers & Land Surveyors C Ph: (732) 469-0400​ ​Certificate of Authorization 24GA27997700​ ​STORMWATER DRAINAGE REPORT​ ​04/13/26​ ​Minor Subdivision 15 Ridgeway Ave West Orange, NJ​ ​Design Methodology/Discussion​​(continued)​ ​Recharge Work Sheet Two​ ​11​ ​Mailing Address: Post Office Box 4304, Warren, NJ 07059​

​ENSURPLAN, INC.​ ​ ww.Ensurplan.​​net​ w ​ ivil Engineers & Land Surveyors C Ph: (732) 469-0400​ ​Certificate of Authorization 24GA27997700​ ​STORMWATER DRAINAGE REPORT​ ​04/13/26​ ​Minor Subdivision 15 Ridgeway Ave West Orange, NJ​ ​Stormwater Quality​ ​ o comply with the Major Stormwater regulations water quality requirements, stormwater​ T ​management measures shall be designed to provide 80% reduction of the post-construction​ ​load of total suspended solids (TSS) in stormwater runoff generated from the water quality​ ​design storm over the net increase of motor vehicle surface.​ ​Design Methodology/Discussion​ ​ lean roof runoff and runoff from lawns, walkways, patios or decks do not have to be treated for​ C ​TSS removal.​ ​ herefore discussion of water quality provision on site is limited to the remaining impervious​ T ​surface comprising driveway cover. All proposed driveways on the site are specified to be​ ​constructed of a permeable pavement system. The system is rated to provide 80% TSS removal​ ​if the storage bed below the pavement can accommodate the water quality storm.​ ​ onstruction details provide a non-woven geotextile fabric underlain stone bed under all​ C ​permeable pavement with a minimum depth of 12” Void storage at a 40% ratio provides an​ ​effective depth of 4.8” well in excess of the water quality storm depth of 1.25”​ ​12​ ​Mailing Address: Post Office Box 4304, Warren, NJ 07059​

​ENSURPLAN, INC.​ ​ ww.Ensurplan.​​net​ w ​ ivil Engineers & Land Surveyors C Ph: (732) 469-0400​ ​Certificate of Authorization 24GA27997700​ ​STORMWATER DRAINAGE REPORT​ ​04/13/26​ ​Minor Subdivision 15 Ridgeway Ave West Orange, NJ​ ​Infiltration Mounding Analysis​ ​ he mounding of the infiltrated water below the basin bottom is modeled utilizing the Hantush​ T ​spreadsheet calculator downloaded from the NJDEP.​ ​ epth for the mounding analysis is based on the maximum depth of the projected 100 year​ D ​storm or 3.44 feet.​ ​The initial calculation inputs are as follows​ ​ he recharge rate, R,or the permeability rate utilized is ½ of the measured rate of 1.0”/hr​ T ​R=0.5 “/hr​ ​ he basin dimensions for spread sheet entry were 65’’ x 6.5’. Because the basin shape is linear​ T ​the spread sheet is run twice with the x and y values transposed.​ ​The specific yield utilized was the default value of 0.15.​ ​The horizontal hydraulic conductivity was set equal to the design permeability rate of 0.5”/hr.​ ​The duration of the infiltration period was calculated as follows.​ ​Infiltrated Vol (0.045 af) (43,560 sf) (12”) / Footprint (1,600 sf) (0.5”/hr) = 29 hrs​ ​The initial thickness of the saturated zone utilized was the default value of 10 feet.​ ​ esults indicate a zero change in mounding at a distance 23.5’ from the long axis of the pond​ R ​and a zero change in mounding at a distance 25’ from the long axis of the pond. There are no​ ​building structures with a basement within the area which would experience an increase of​ ​ground water elevation.​ ​13​ ​Mailing Address: Post Office Box 4304, Warren, NJ 07059​