Drainage Report and Supplement 82625

Cunningham Engineering & Design, LLC Certificate of Authorization No, 24GA28204400 213 Newton Swartswood Road, Newton, New Jersey 07860 973-219-7546 RMCNJPE@YAHOO.COM DRAINAGE REPORT FOR PROPOSED SITE IMPROVEMENTS BLOCK 152.02, LOTS 176, 179 & 186 TOWNSHIP OF WEST ORANGE ESSEX COUNTY, NEW JERSEY APPLICANT MONTCLAIR STABLES LLC PREPARED BY __________________________________________ ROBERT M. CUNNINGHAM, PE NEW JERSEY LICENSE #GE31540 Revised August 26, 2025

INTRODUCTION This report is submitted in support of an application to the Board of Adjustment of The Township of West Orange for site plan and variance approval. The Applicant, Montclair Stables LLC, has purchased the existing equine facility on Woodland Avenue and proposes to make improvements to the site. The primary improvements are the re-orientation and reconstruction of the existing outdoor sand riding arena and the re-location of the paved parking lot and driveways. The Applicant also proposes to make improvements to Nicholas Avenue; a paper street located at the rear of the property. This facility has used part of Nicholas Avenue as a driveway for decades. The proposed improvements include extending the driveway to connect to the paved portion of Nicholas Avenue near its intersection with Cannon Street. The driveway would function as a one-way driveway which would exit near the Cannon Street intersection and there would be new security gates at both ends. There are presently two buildings on the site, a barn and an indoor riding arena which are connected by a one-story concourse. There are no changes proposed to the configuration of these buildings. The Existing Drainage Area Plan, as well as the Existing Conditions Plan in the application set, depict a dwelling and related improvements which existed on Lot 176 until recently. The dwelling was removed under a demolition permit issued by the West Orange Construction Code Office. The trees that are scheduled for removal are indicated on Sheet SE-2 of the application set as well as on the Landscape Architect’s drawings. Due to the total surface area that will be disturbed under the present definition of disturbance in the Stormwater Management Regulations, this project is considered a major project. Over one acre of land area will be disturbed. Since less than one quarter of an acre of new “vehicular surface”, the required water quality standards are satisfied by the proposed project. The project is located in the Metropolitan Planning Area PA-1 on the State Plan Policy Map, therefore, the project is exempt from complying with the groundwater recharge provisions of the local stormwater management ordinance. The drainage analysis and calculations presented herein are intended to document compliance with the stormwater runoff quantity standards found in section 25-29.4r of the West Orange Land

t ordinance. The drainage analysis and calculations presented herein are intended to document compliance with the stormwater runoff quantity standards found in section 25-29.4r of the West Orange Land Use Regulations: Section 25-29 Stormwater Control. EXISTING DRAINAGE The existing drainage patterns are indicated on the attached Existing Drainage Areas Plan. The area considered includes the site, a portion of Nicholas Avenue, a small portion of adjacent Lot 132 and an existing bridle path on Lots 1 and 2 in Block 152.26. An easement for the bridle path appears on the Tax Map. The total study area includes 175,847 square feet, or 4.037 acres. Under present conditions, two primary drainage areas were delineated and are shown on the Existing Drainage Areas Plan along with the surface coverage summary for each drainage area. This plan also indicates the time of concentration travel paths with the land slope and flow type for each reach. Page 1

Drainage Area E-1 includes the front yards of the buildings, a small portion of the roof area, the existing paved parking lot and most of Lot 176. Area E-1 drains to Woodland Avenue. The surface area is 32,101 square feet. Drainage Area E-2 includes the remainder of the study area and has 143,746 square feet of surface area. This drainage area drains toward Nicholas Avenue with a slight portion of it draining toward the residential properties on Terrace Avenue and Nicholas Avenue. The portion of Nicholas Avenue that the Applicant proposes to improve is also included in drainage area E-1. Under present conditions, no formal drainage system exists for the parking lot and runoff from the roofs simply drips from the roof edges onto the ground. PROPOSED DRAINAGE IMPROVEMENTS The applicant proposes to construct a drainage system for the re-configured parking lot which will include a type D inlet, 15” RCP pipe, and a doghouse manhole at the connection point to the existing storm drain in Woodland Avenue. A road opening permit will be required for this work. The applicant also proposes installing gutters on the barn and on the indoor riding arena. Downspouts will be piped to collector pipes which will connect to the existing drainage systems as shown on Sheet SE-4 of the application set. The reconstruction of the outdoor riding arena will also be an improvement to stormwater runoff and groundwater recharge. The new arena will be totally level and will capture the rainfall over its entire area. The arena will consist of a 6” thick sand surface over a layer of filter fabric over a 15” thick layer of 1 ½” clean crushed stone. The subgrade below the stone will be scarified prior to stone installation. A flush concrete curb will surround the entire arena and will serve to confine the sand and stone as well as rainfall. A subsurface bulkhead wall will be installed to separate the sections of the new riding arena that will drain toward Nicholas Avenue and toward Woodland Avenue. Each section of the riding arena will have an independent perforated pipe subdrain with the inverts being 3” above the soil subgrade. At maximum capacity, we estimate that the riding arena will be able to store approximately 4 ½” of rainfall in the clean stone bed. The Applicant also proposes to locate, expose, and make any necessary repairs to an existing inlet that is part of the municipal

be able to store approximately 4 ½” of rainfall in the clean stone bed. The Applicant also proposes to locate, expose, and make any necessary repairs to an existing inlet that is part of the municipal drainage system in Nicholas Avenue. This inlet was identified on the original topographic survey but is not visible at this time. POST CONSTRUCTION DRAINAGE AREAS. Post Construction Drainage Area P-1 contains 32,238 square feet of area including most of the front yards of the buildings, a small portion of the building roofs, the re-configured parking lot and 11,500 square feet of the re-configured riding arena. Drainage area P-1 drains toward Woodland Avenue Post Construction Drainage Area P-2 contains143,609 square feet of surface area including most of the building roof area, the courtyard between the riding ring and the barn, the paddocks and driveway at the east end of the site, 22,575 square feet of the sand riding arena, the paddocks at the west end of the site and the portion of Nicholas Avenue under consideration. Page 2.

SUMMARY OF DRAINAGE CALCULATIONS The drainage calculations are intended to document that the stormwater runoff quantity provisions of the Ordinance are met, the drainage pipe sizes proposed are adequate, and to provide the carrying capacity of the existing open riprap channel in Nicholas Avenue as requested by the Township Engineer. The reader will notice that the computer modeling output was prepared by Stonefield Engineering & Design LLC. I engaged Stonefield to assist with computer modeling. Stonefield is also serving as the Professional Planning Consultants on this project. Stonefield performed the calculations at my direction and their output was reviewed and approved by me. The flow paths for the times of concentration for Existing Drainage Area E-1 and Proposed Drainage Area P-1 vary somewhat while the flow paths and times of concentration for Existing Drainage Area E-2 and Proposed Drainage Area P-2 are virtually identical. The stormwater runoff from the existing and proposed drainage areas was calculated for the 2-, 10-, and 100-year return period storms for the required 2020 rainfall totals and for the required projected 2050 rainfall totals. The runoff curve numbers for the existing conditions were assigned with the assumption that all existing surfaces are in “good” condition. To demonstrate compliance with the runoff quantity requirements the existing and proposed runoff hydrographs were compared in a “curve under curve” analysis for each of the required return periods. In all instances the proposed runoff hydrographs remain “under” the existing runoff hydrographs. Therefore, the project complies with the requirements. We believe that the runoff hydrographs for the proposed conditions may be less than the calculated hydrographs indicate. The runoff curve number for the proposed sand riding arena was kept somewhat high to provide a factor of safety in the calculations, especially for the lower return period storm events. The 3” depth of stone below the invert of the perforated drains in the riding arena will still hold water in the stone voids after the stored water above the inverts has drained out. The Soil Survey data indicates that the lowest expected infiltration rate for the existing soils will be 0.06 inches per hour. If the 3” stone depth below the drain inverts was actually 100% water, it would drain within 50 hours. The calculations

expected infiltration rate for the existing soils will be 0.06 inches per hour. If the 3” stone depth below the drain inverts was actually 100% water, it would drain within 50 hours. The calculations also indicate that the proposed pipe sizes for the leader drain system and for the 15” parking lot drain are more than adequate to carry runoff from the 25 year return period storm. The capacity of the riprap channel was evaluated at a flow depth of 15 inches, even though the depth of the channel is deeper. A flow depth of 15 Inches was chosen because the outlet pipe is a 15” diameter pipe. The calculated flow capacity for the channel is 47.68 c.f.s. which is obviously greater than the capacity of the downstream 15” pipe. Page 3.

CONCLUSION The designer believes that the proposal complies with the provisions of the Stormwater Management Ordinance, reduces stormwater runoff to adjacent properties and public roads and does not create increased demand on the public drainage system. ENCLOSURES Appendix 1: Drainage Runoff Calculations Output Existing Drainage Areas Plan Proposed Conditions Drainage Areas Plan Proposed Piping Calculation Plan Page 4.

563110 563190 563270 563350 563430 563510 563590 563670 563750 4518110 4518110 4518030 4518030 4517950 4517950 4517870 4517870 563030 563110 563190 4517790 563270 563350 563430 Map Scale: 1:3,540 if printed on A landscape (11" x 8.5") sheet. N Meters 300 Feet 0 150 300 600 900 Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 18N WGS84 0 50 Natural Resources Conservation Service 100 200 Web Soil Survey National Cooperative Soil Survey 563510 563590 563670 563750 74° 14' 37'' W 4517790 Soil Map may not be valid at this scale. 74° 15' 10'' W 40° 48' 30'' N 40° 48' 47'' N 4518190 4518190 4518270 4518270 563030 40° 48' 47'' N 74° 14' 37'' W 74° 15' 10'' W Soil Map—Essex County, New Jersey (12 Woodland Avenue) 1/5/2025 Page 1 of 3 40° 48' 30'' N

Soil Map—Essex County, New Jersey (12 Woodland Avenue) MAP LEGEND Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp MAP INFORMATION Spoil Area Stony Spot The soil surveys that comprise your AOI were mapped at 1:12,000. Very Stony Spot Warning: Soil Map may not be valid at this scale. Wet Spot Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography Mine or Quarry Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Essex County, New Jersey Survey Area Data: Version 20, Sep 3, 2024 Miscellaneous Water Perennial Water Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Rock Outcrop Date(s) aerial images were photographed: 16, 2022 Saline Spot Sandy Spot Oct 10, 2022—Oct The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 1/5/2025 Page 2 of 3