10521 19TH AVE SE 2022-05-23 - Laserfiche WebLink

Silver Lake Plaza Lawn and landscaped areas: • Post -Construction Soil Quality and Depth BMP T5.13 in accordance with guidelines stated within the handout provided by SoilsforSalmon.org. See Appendix IV of this report for handout information. Roofs feasibility description: 1. Full Dispersion per BMP T5.30 or Downspout Full Infiltration per BMP T5.10A. i. Full Dispersion is infeasible due to insufficient flow path length and lack of native forest vegetation. Full Infiltration is infeasible due to inadequate soil quality according to the geotechnical engineer. 2. Bioretention per Volume V, Chapter 7. i. Due to limited available pervious area on -site, along with the fact that the entire site consists of inadequate soil quality for infiltration (according to Geotech Report by Robinson Noble), bioretention facilities are infeasible. 3. Downspout Dispersion Systems in accordance with BMP T5.1013. i. Downspout Dispersion is infeasible due to insufficient flow path length (i.e. less than 25' vegetated flow paths surrounding the entire site). 4. Perforated Stub -out Connections in accordance with BMP T5.10C. i. Due to Perforated Stub -out Connections not allowed under impervious or heavily compacted surfaces along with the need for them to meet the same setbacks as infiltration facilities or 10', perforated stub out connections cannot be designed in any suitable location. There are no feasible areas on the site that are at least 10' downstream of the building that do not contain an impervious or highly compacted surface/subsurface. Instead, all roof runoff will be tight lined to the on -site drainage/detention. Other Hard Surfaces feasibility description: 1. Full Dispersion per BMP T5.30 i. As noted above, Full Dispersion is infeasible due to insufficient flow path length and lack of native forest vegetation. 2. Permeable Pavement per BMP T5.15 i. Per a geotechnical engineering report by Robinson Noble, Inc. infiltration BMPs, such as permeable pavement, are not recommended. 3. Biorention per Volume V, Chapter 7. i. Due to limited available area on -site and infiltration infeasibility, bioretention facilities are infeasible. 4. Sheet Flow Dispersion in accordance with BMP T5.12 or BMP T5.11. i. As noted above, dispersion BMPs are infeasible due to insufficient flow path length. Instead, runoff from other hard surfaces will be conveyed to an on -site detention pipe and will be managed with a control riser. WESTERN ENGINEERS, INC. 14 PROJECT: 15-1415-A