9512 EVERGREEN WAY 2022-08-29 - Laserfiche WebLink

LAWN AND LANDSCAPED AREAS Post -Construction Soil Quality and Depth: The native topsoil will be maintained to the maximum extent practical. In areas requiring grading, the topsoil will be removed and stockpiled onsite in a designated controlled area, not adjacent to public resources or critical areas, to be reapplied on other portions of the site. Areas of new fill not covered by impervious surfaces shall have topsoil modified as needed to meet BMP T5.13 requirements. ROOFS Full Dispersion or Downspout Full Infiltration: Full dispersion is not feasible as the project cannot accommodate the required vegetated flow paths. Downspout full infiltration is not feasible as the water table is relatively shallow at the building addition location. Bioretention: The proposed addition's roof drains are immediately piped underground into the existing roof leader system. It is not feasible to daylight this system to the bioretention cell at the handicapped parking bay. Downspout Dispersion Systems: Downspout dispersion is infeasible for this development as the downspout systems are immediately piped underground into the existing roof leader system. Perforated Stub -Out Connections: Perforated stub -out connections are infeasible due to the high groundwater table. See Appendix F for geotechnical report documenting the groundwater levels. OTHER HARD SURFACES Full Dispersion: Full dispersion is not feasible as the project cannot accommodate the required 100' native vegetated flow paths. Permeable Pavement: Permeable pavements are not feasible as the native soils below the parking lot do not meet the soil suitability criteria for providing treatment. Bioretention: Bioretention is used to capture much of the new pedestrian pavement at the library entrance. Additionally, the bioretention cell provides water quality treatment for the handicapped parking bay and surrounding drive aisle. Evergreen Branch Library Expansion — Dykeman, Inc. 5