3505 UPLAND AVE 2020-09-08 - Laserfiche WebLink

Sound would be considered the receiving water body for this project and the downstream • analysis can be stopped at that point. The new and replaced NPGIS runoff on-site will be collected and conveyed to an on-site detention system prior to release to the downstream system. Roof downspouts will be conveyed directly to the system via 6" PVC collection lines. Runoff from driveways will be dispersed as sheet flow over vegetated landscaping/amended soils before being collected by yard drains and conveyed to the detention system. Also, this project proposes to make improvements to the drainage systems within the City ROW. Portions of the existing roadway along this projects frontage will be improved and some new CBs and pipes will be installed to collect and convey some of this new runoff. Approximately 3,400 sf of new impervious surfaces will be constructed within the City ROW. Therefore, an equivalent area of new and existing impervious surfaces will be collected and conveyed to the detention system for flow control. This equivalent area is calculated to be 3,500 sf which is slightly greater than the proposed new impervious. The combination of the proposed improvements, as stated above, are designed to mitigate the impacts of the proposed improvements and better match the existing conditions. 4. SWPPP NARRATIVE The intent of this section is to provide the information necessary to support the engineering plans in order to implement a design that will; reduce, eliminate or prevent the discharge of stormwater pollutants, meet or exceed the water quality and sediment management standards for the City and State, and prevent adverse impacts to the receiving waters for this project. Note; this narrative is intended to support the SWPPP that is included with the Targeted Drainage Plans also a part of this submittal package to the City. A. SITE GRADING/EROSION CONTROL RISK ASSESSMENT Area proposed to be cleared/worked: 27,006 sf= 0.62 acres Average slope for the site: 5% (Area of Disturbance Only) Erosion Hazard of Soil Low Critical Areas downslope No Site is upstream of an ESA Stream No In order to complete the proposed project, it is expected that the majority of lots 1, 2 and 3 will need to be disturbed. Based on the above information and the fact that the area to be disturbed is flat to moderate and construction site runoff will pass through silt fencing or other perimeter filtration features prior to leaving the site and entering the off-site open ditch/stream, and that if site conditions warrant, additional BMP's can be implemented as corrective measures the Risk Category for this site is Low Risk. Uplands Short Plat 14-0108 June, 2016 Page 6