Report 4 13 2026

ENSURPLAN, INC. www.Ensurplan.net Civil Engineers & Land Surveyors Ph: (732) 469-0400 Certificate of Authorization 24GA27997700 April 13, 2026 File: 29906 STORMWATER MANAGEMENT REPORT PREPARED FOR PROPOSED TWO LOT MINOR SUBDIVISION Located at 15 RIDGEWAY AVENUE BLOCK 158 LOT 28.01 Within The TOWNSHIP OF WEST ORANGE ESSEX COUNTY, NJ Wi ME NJ License GE44863 1 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​ ​Introduction and Major Stormwater Justification​ ​ his report has been prepared to demonstrate that the runoff from the proposed improvements​ T ​to the site, which result in an increase of impervious coverage, is properly mitigated in accord​ ​with the Township of West Orange requirements for a major stormwater project, and will pose no​ ​negative impact to any surrounding downstream properties.​ ​ o ensure that the design complies with the requirements and goals of the Township Stormwater​ T ​Ordinance a detailed analysis of the site condition was performed. A soils evaluator tested​ ​various areas of the site to identify both seasonal high water levels and the ability of the soil to​ ​infiltrate runoff. Additionally areas allowing for use of low impact development were identified;​ ​including potential preservation of large deciduous trees, lessening the slope of surfaces and​ ​elongation of drainage paths. This study focused the design on the area of the site which​ ​would allow for use of infiltration.​ ​ small scale sub-surface extended detention infiltration basin (a system allowing for infiltration​ A ​and controlled release) was chosen as the green infrastructure BMP to provide infiltration,​ ​recharge and reduction of runoff quantity. The basin is located at the area of the site where the​ ​soils evaluation determined an acceptable infiltration rate for design (A factor of safety was​ ​applied to the analysis by utilizing ½ of the measured infiltration rate in all calculations).​ ​ he basin shall be a shared system, accepting runoff from both lots, therefore an easement​ T ​allowing for common use and maintenance shall be established. Operations and maintenance​ ​requirements and responsibilities shall be filed with the record owner deeds.​ ​ ermeable

e an easement​ T ​allowing for common use and maintenance shall be established. Operations and maintenance​ ​requirements and responsibilities shall be filed with the record owner deeds.​ ​ ermeable pavement, another green infrastructure BMP, is specified for all driveway surfaces.​ P ​This system is rated for 80% total suspended solids reduction providing water quality treatment​ ​for the site.​ ​ he analysis shows that the runoff from the developed portion of the site directed towards the​ T ​infiltration basin when combined with the runoff rate from the developed portions of the site​ ​which bypass the system, has been reduced to no more than 50% of the two year storm rate.​ ​75% of the 10 year storm rate and 80% for the 100 year storm rate from what would have​ ​occurred if the design area were an undeveloped wooded lot.​ ​2​ ​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​ ​Introduction and Major Stormwater Justification​​(continued)​ I​n addition to the utilization of two green infrastructure BMPs low impact development measures​ ​are implemented throughout the unstudied portion of the site (not experiencing placement of​ ​impervious cover and maintaining existing lawn surfaces) which will serve to lessen the overall​ ​stormwater runoff from the site. These measures include; preservation of large trees, lessening​ ​of slopes and increasing drainage paths to increase time of concentration. These items are​ ​shown on the Land Use Planning and Source Control Plan within the site plan set.​ ​Property Description​ ​ he project site is an existing flag lot with a stem portion containing the driveway which fronts on​ T ​Ridgeway Avenue The 1.219 acre property was previously developed with a single family​ ​dwelling with attached garage, covered parking or storage area, retaining walls, bocci court and​ ​koi pond. The property is located within an existing residential neighborhood. The existing home​ ​is served by public utilities which are located within the bed of Ridgeway Avenue.​ ​ rainage from a small portion of the property (approximately 3,000 sf) flows overland from a​ D ​highpoint on the driveway stem towards Ridgeway Avenue. The remainder of the site drains​ ​overland from South to the North towards the rear of Lot 21.01 at which point runoff from the site​ ​is collected by an existing inlet and piped through Lot 21.01 to the Township storm sewer​ ​system. No existing stormwater management facilities were found on the site.​ ​ here are no protected steep slopes on the site; slopes on the property are predominantly​ T ​between 1.5% and 8%.​ ​ he soils on the site are silt loam to loamy sand noted as BouB Boonton Urban Land

here are no protected steep slopes on the site; slopes on the property are predominantly​ T ​between 1.5% and 8%.​ ​ he soils on the site are silt loam to loamy sand noted as BouB Boonton Urban Land within​ T ​hydrologic soil type “C”, with a seasonal water table depth exceeding 80” in depth and a​ ​moderately low to moderately high infiltration rate of the most restrictive soil layer of 0.06 to 0.20​ ​in/hr (USDA NRCS Soil Survey).​ ​3​ ​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​ ​Property Description​ ​(continued)​ ​ n site soils testing revealed a depth to seasonal high water varying from 5’ to 7.5’ with an​ O ​infiltration rate varying from 0.32”/hr to 1.00”/hr. Testing was done towards the four corners of​ ​the site. Only the southwest portion of the site yielded permeability rates great enough to​ ​support an infiltration system.​ ​ he vegetation on the site is predominantly well established lawn, with a number of large​ T ​deciduous trees located predominantly along the exterior boundary of the site with a lesser​ ​concentration within the site interior.​ ​ review of the NJ Geoweb site along with a site inspection by the engineer did not reveal any​ A ​indications of wetlands, waterways or presence of protected species which might impact the​ ​development of the site.​ ​Project Scope and Stormwater Management System Overview​ I​t is proposed to subdivide the property into two lots. One lot will contain the existing home to​ ​the northeast of the site and a new home will be constructed on the second lot. Both lots will​ ​share a driveway access centered on the stem portions of the lots accessing Ridgeway Avenue.​ ​ tility services for the homes shall be provided through the stem portions of the lot connecting to​ U ​the mains on Ridgeway Ave.​ ​ enovations and reconfiguration of the existing home was undertaken pursuant to an approved​ R ​zoning permit. During the course of demolition the builder removed a significant portion of the​ ​existing dwelling leaving only the garage as a standing structure. Therefore from a stormwater​ ​modeling perspective the project shall be now considered the construction of two new homes.​ ​ shared stormwater management system shall be constructed on the two lots. All proposed​ A ​vehicle surfaces shall be

spective the project shall be now considered the construction of two new homes.​ ​ shared stormwater management system shall be constructed on the two lots. All proposed​ A ​vehicle surfaces shall be constructed with permeable pavement. The driveway surfaces shall be​ ​underlain with a stone bed and an interconnecting perforated pipe system, both of which will​ ​collect runoff from the driveway and direct it towards a proposed basin at the southwest corner​ ​of the site. Runoff from all roof surfaces which will receive pre-treatment through the use of a​ ​gutter screening system, will also be directed directly to the proposed basin or into the stone​ ​bed below the driveway surface.​ ​4​ ​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​ ​Project Scope and Stormwater Management System Overview​​(continued)​ I​nfiltration may be used in the model of the stormwater basin routing as all runoff entering the​ ​system from developed surfaces receives pretreatment by either a gutter screening system or​ ​by passing through the permeable pavement layer. The basin shall, through the use of​ ​infiltration and orifice control, provide the required stormwater quantity reductions, recharge​ ​volumes and the required 80% reduction of total suspended solids for water quality.​ ​Design Discussion​ ​ tormwater analysis of the project is accomplished utilizing HydroCAD version 10.20-8a​ S ​Software furnished by HydroCAD Software Solutions LLC. The SCS-TR20 methodology is used​ ​to analyze NOAA 24 hr type C storms for both the current (2020) and projected (2050) 2, 10 and​ ​100 year rainfalls along with the NJDEP 2 hour water quality design storm.​ ​ he model of this project focuses solely on the “developed” area of the site within the drainage​ T ​area directed towards the residential properties to the north. As the Township stormwater​ ​ordinance defines the reconstruction of a home or milling or replacement of pavement as​ ​placement of new impervious surface, all impervious surfaces within this area whether driveway​ ​or existing roofs shall be considered “new” and altered from a good condition wood ground​ ​cover. The remaining portions of this drainage area which shall not be proposed with an​ ​impervious cover are considered existing lawn conditions to remain, and therefore are not​ ​included within the study.​ ​ small portion of the paved driveway stem from which runoff flows from the existing highpoint​ A ​towards Ridgeway Ave is considered as replacement as it has existed prior to 1980 and​

the study.​ ​ small portion of the paved driveway stem from which runoff flows from the existing highpoint​ A ​towards Ridgeway Ave is considered as replacement as it has existed prior to 1980 and​ ​continues to drain towards Ridgway Ave.​ ​These areas are depicted on the drainage area map.​ ​ he area of the site to be studied in the existing condition is modeled as type “C” HSG with​ T ​ground cover type of “good condition woods” with a curve number of 70. The time of​ ​concentration was calculated as 10.9 minutes consisting of sheet and shallow concentrated flow​ ​from the rear of the proposed homes travelling to the study point which shall be the existing inlet​ ​to the rear of the site. The existing study area totals 18,843 sf.​ ​4​ ​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 areas of the site to be studied in the proposed condition are modeled as impervious​ T ​surfaces with a curve number of 98, The proposed study area is 18,843 sf, equaling the existing​ ​condition study area. The proposed condition is modeled into two sub areas, both fully​ ​impervious, one contributing runoff to the infiltration system and the other bypassing the​ ​infiltration system with runoff traveling overland to the inlet at the rear of the property.​ ​A diagram of the drainage analysis follows…​ ​Diagram of Proposed Stormwater Management Study​ ​5​ ​Mailing Address: Post Office Box 4304, Warren, NJ 07059​