12 2026 02 12 Crestmont CC Stormwater Management Report

requirements. 3.2.2 Design Methodology The proposed stormwater quality BMPs that have been chosen for the project design consist of small-scale bioretention basins and a porous asphalt pavement system. Small-Scale Bioretention Basin 2 (SSBB-2) has been designed in accordance with Chapter 9.7 of the BMP Manual to achieve 80% TSS removal, meaning that it has been designed with a 24-inch deep soil bed planted site-tolerant meadow mix grasses, and can store the entire water quality design storm event runoff volume below the first orifice opening of the outlet control structure with the water surface elevations not exceeding 12 inches. Small-Scale Bioretention Basin 1 (SSBB-1) has been designed to achieve 90% TSS removal, meaning that it has been designed with a 24-inch deep soil bed planted with a terrestrial forested community, and can store the entire water quality design storm event runoff volume below the first orifice opening of the outlet control structure with the water surface elevations not exceeding 12 inches. Both bioretention basins have been design with underdrains due to the relatively poor-draining in-situ soils, as well as to minimize any potential infiltration in areas of potential karst formations. Refer to the supporting calculations in Appendix E of this report. The proposed porous pavement system (PAPS-1) has been designed to achieve 80% TSS removal. The system consists of a porous asphalt surface course, a choker course that will filter pollutants, and an underlying stone storage bed subbase. The stone storage bed layer of the porous pavement system has been adequately sized to route the 100-year design storm event; therefore, there is more than adequate capacity to store the water quality storm event runoff volume, thus meeting the criteria to achieve 80% TSS removal. The porous asphalt pavement system meets all the design criteria set forth in Chapter 9.6 of the BMP Manual. Refer to the supporting calculations in Appendix E of this report. 3.2.3 Design Summary Approximately 1.09± acres of the total 1.48± acres of proposed regulated motor vehicle surface in the area of redevelopment will be treated by a combination of small-scale bioretention basins and the porous asphalt pavement system. As part of the proposed stormwater management design, approximately 0.77± acres of existing regulated motor vehicle surface, located outside of the

ntion basins and the porous asphalt pavement system. As part of the proposed stormwater management design, approximately 0.77± acres of existing regulated motor vehicle surface, located outside of the proposed limit of disturbance area, will be captured and conveyed to the proposed BMPs for water quality treatment. The proposed TSS removal rate for the project has been calculated to be 68.2%, which is greater than the 67.2% that is required. Refer to Figure 9 – Proposed Water Quality Treatment Map for a map indicating which portions of regulated motor vehicle surface are being treated at what TSS removal rate based upon the proposed BMPs that are 17