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Home My WebLink About2025-06-13 OUT 2125 Stormwater Report Rev 0 Stormwater Management & Erosion Control Report Submitted to: North Carolina Department of Environmental Quality Prepared for: Cook Out 7245 Market Street, Wilmington, NC 28411 Sambatek Project Ref.: OUT-2125 Prepared by: SAMBATEK NC PC 8312 Creedmoor Road Raleigh, North Carolina 27613 Date: 06/13/2025 Table of Contents: Project Summary ......................................................................................................................... 1 Existing Conditions ...................................................................................................................... 1 Proposed Conditions ................................................................................................................... 2 Post Construction Stormwater Management Criteria ........................................................... 2 Erosion and Sediment Control Measures ................................................................................ 2 Project Sequence ......................................................................................................................... 2 Critical Erosion Areas .................................................................................................................. 3 Silt Fence ....................................................................................................................................... 3 Vegetative Stabilization .............................................................................................................. 3 Temporary Stabilization ............................................................................................................. 3 Temporary Erosion and Sediment Control Maintenance ...................................................... 3 Calculation Methodology ............................................................................................................ 4 List of Appendices: Appendix A – USDA HSG Map Appendix B – USGS Topographic Map Appendix C – FEMA FIRMette Flood Map Appendix D – Pre- & Post-Development Impervious Exhibits OUT-2125 – SWM Report June 13, 2025 Page 1 Project Summary This project is for the redevelopment of a commercial restaurant property located at the at 7245 Market Street in Wilmington, NC. This site is the location of a former Dennys restaurant and the center of property coordinates are 34.274424°, -77.817232°. This stormwater management plan is intended to address compliance with the North Carolina Department of Environmental Quality (NCDEQ) post- construction stormwater and construction phase erosion and sediment control requirements. In particular, this report will discuss the existing NCDEQ permitted stormwater control measures (SCM) that were constructed as part of the 2017 Dennys project which will be preserved and reused following the completion of this redevelopment. The proposed redevelopment activities included in this project include the removal the surface course of a portion of the existing pavements and select concrete curb and gutter, refitting the existing building for Cook Out’s usage, and minor modification to the parking lot area to accommodate the drive-through aisle and updated parking. The Dennys parking lot currently drains to a series of catch basins which drain to a infiltration SCM located beneath the parking areas. These catchments will be protected during construction from sediment laden runoff and will be reused following redevelopment. The infiltration basin will be used to provide post-construction stormwater management per NCDEQ requirements. There is also an above-ground infiltration basin located toward the rear of the site which receives surface runoff from the grassed area comprising rear half of the site. This grassed area and basin will not be impacted by this project. Both the infiltration SCMs were recently maintained, inspected, and certified as compliant with NCDEQ standards in June 2025. The remainder of this report contains a detailed description of the pre- and post-development site conditions, stormwater requirements, and the construction phase erosion and sediment control measures proposed to be used on this project. Existing Conditions The existing parcel is roughly divided in half, with the front of half of the site being fully developed with a vacant restaurant building, paved parking and sidewalk areas, curb and gutter, landscaping areas, and an access driveway onto Market Street. The rear half of the site is undeveloped and is fully grassed with no impervious cover. Each half of the site has its own stormwater management system. The developed area associated with existing building has several catch basins located in the parking lot which direct runoff into an underground infiltration SCM. This SCM includes an interconnected perforated piping system, aggregate storage cells, and an outlet device located near the Market Street right-of-way to allow for the bypass of larger storm runoff volume. The rear of the site features two drainage swales which capture runoff from the rear half of the site and conveys it into an above ground infiltration basin. The infiltration basin consists of a 2-foot deep, grass lined infiltration basin with a rip- rap lined bypass weir located at the northwest end of the basin to provide bypass of larger storm runoff volumes. The USDA Soils Survey list the on-site soils as Le – Leon Sand (HSG A/D) and Se – Seagate Fine Sand (HSG B). Site Area = 1.96 acres Existing Impervious Area = 0.86 acres Existing Pervious Area = 1.10 acres OUT-2125 – SWM Report June 13, 2025 Page 2 Proposed Conditions Prior to the start of construction, the site will be prepared for land disturbance through the installation of erosion and sedimentation control measures as detailed in the construction plan set. As noted on the demolition plans, the existing pavements will be sawcut and a portion of the parking area will be removed to accommodate for the construction of an updated parking area and a drive through aisle for the retrofitted building. Stormwater runoff will continue to follow existing drainage conditions, with runoff entering catch basins with the parking lot prior to flowing into/through the underground infiltration SCM. The existing underground infiltration SCM serving the front half of the site and the above ground system serving the rear of the site will remain in their current condition and will not be impacted by the small area of grading included in these redevelopment activities. Site Area = 1.96 acres Proposed Impervious Area = 0.87 acres Proposed Pervious Area = 1.09 acres Post Construction Stormwater Management Criteria In accordance with the NCDEQ Post Construction Stormwater Permitting Map, this project is located within a coastal county and is subject to the Coastal State Stormwater Permitting Program administered by NCDEQ. As mentioned in previous sections of this report, this redevelopment will maintain the two NCDEQ permitted SCMs that are currently present and operational on site. This redevelopment does not propose a substantial change in use from the current permitted usage and does not propose any revisions to the drainage going to either of these two SCMs. This project does not propose to construct any new SCMs or modifications to the existing SCMs and will not result in negative impacts to the existing SCMs, the adjoining properties, or downstream waterways. Erosion and Sediment Control Measures All vegetative practices and erosion and sediment control features shall be designed, constructed, and maintained in accordance with NCDEQ requirements requirements. The erosion and sediment control plan shall be kept on site in a mailbox type structure located immediately adjacent to the posted permits if needed. Sediment shall be removed from the sediment control structures as necessary, but at a minimum, when the design capacity of each structure is reduced by 50%. Project Sequence A site-specific project sequence has been prepared and included within the construction drawings. This project sequence details the full schedule of events to be completed during the construction of this project including pre-construction permitting and compliance activities as well as construction-phase erosion and sediment control, inspections, and approvals. Please refer to the construction drawings for further information. OUT-2125 – SWM Report June 13, 2025 Page 3 Critical Erosion Areas The most critical erosion area will be the surface of the working areas during construction operations. If areas being demolished and re-paved are not provided the appropriate erosion protection, there is a significant potential for the construction areas to be eroded and for sediment to be carried away onto the existing right of way, negatively impacting locations downstream. To minimize the potential for erosion, covered areas that are temporarily inactive will be seeded within 14 calendar days after placement of the soil cover and BMPs installed to prevent runoff from being carried away offsite. Silt Fence Sediment fences will be provided down gradient of the proposed site grading at the locations shown on the drawings. Silt fences are not to be used across channels or in areas of concentrated flows. Vegetative Stabilization Vegetative cover shall be re-established within 14 calendar days after completion of the activity. Refer to plans for temporary and permanent seeding schedule and specifications. Temporary Stabilization Disturbed areas will be vegetated in accordance with NCDEQ requirements. Temporary control features will remain in place and will be maintained until the up-gradient disturbed area has been stabilized with vegetative cover. Temporary Erosion and Sediment Control Maintenance All erosion and sediment control measures will be checked for stability and operation following every runoff-producing rainfall but in no case less than twice every week, at least 72 hours apart. Any necessary repairs will be made immediately to maintain all measures as designed. Sediment fences and inlet protection shall be inspected at least twice every week, at least 72 hours apart. Repairs shall be made immediately. Sediment deposits shall be removed as needed to provide adequate storage volume for the next rainfall event, and to reduce pressure on the silt fence. Fencing materials and sediment deposits shall be removed, and the area brought to grade following stabilization of upgradient disturbed areas and approval of the site. OUT-2125 – SWM Report June 13, 2025 Page 4 Calculation Methodology · Soils data for the site was taken from the NRCS USDA web soil survey website (http://websoilsurvey.nrcs.usda.gov/). · The on- and off-site topography used in the analysis is from a field survey by Sambatek. OUT-2125 – SWM Report June 13, 2025 Appendix A: USDA HSG Map OUT-2125 – SWM Report June 13, 2025 Appendix B: USGS Topographic Map OUT-2125 – SWM Report June 13, 2025 Appendix C: FEMA FIRMette Flood Map OUT-2125 – SWM Report June 13, 2025 Appendix D: Pre- & Post-Development Impervious Exhibits