1130 90TH ST SW 2025-07-29 - Laserfiche WebLink

basin within unit 3 or an off-site catch basin located in the gutter on the east side of 11th Place W. The on-site catch basin pipes its runoff to the off-site catch basin. From the offsite catch basin the runoff is piped south approximately 500-feet to a detention pond. Said detention pond is located on the east side of the cul-de-sac of 11th Place W. The outfall of the detention pond overflow west on the adjacent golf course. The runoff converance system of the golf course includes a catch basin within 100' of the outfall of the detention pond. From said catch basin the runoff is piped south approximately 1,800 feet to the end of the golf course. From there the water is directed west. It is unclear if the piped runoff outfalls to an unnamed stream approximately 1,200 feet from the last point of interest or if the runoff outfalls into Swamp Creek approximately 2,200 feet from the last point of interest. Either way both streams flow south and merge together approximately '/2 mile downstream from where the runoff would be introduced into either stream. Based on the site observations these stream systems would be considered the receiving water body for this project and the downstream analysis can be stopped at that point. Based on the fact that the new NPGIS runoff will be dispersed with splash blocks and infiltrated into the subsurface to the maximum extent possible with swales, and that the PGIS will be dispersed using transition zones to sheet flow runoff over the future amended soils and landscaping before the runoff leaves the site, and that this project only proposes to increase the total combined impervious surfaces of all 4 units on the site by less than 5,000 sf the developed flows are expected to be slightly more than in the existing conditions. During the site visit and review of the downstream system no portion of the system appeared to be inadequate. 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: 0.39 acres Average slope for the site: <2% (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 each of the 4 units will need to be completely cleared. Based on the above information and the fact that the area of the site to be disturbed is flat and construction site runoff will pass through silt fencing or other perimeter filtration features prior to leaving the site, and that if site conditions warrant, additional BMP's can be implemented as corrective measures the Risk Category for this site is Low Risk. OLYMPIC TERRACE CONDOS 13-0605 June 2013 Page 7