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Ms. Katie Larsen 07/03/2025 Page 2 Peltier Ponds Development - Engineering Review 8. All swale grades to meet minimum 2% slopes • Stormwater Management Stormwater management for the Peltier Ponds site consists of multiple sedimentation basins and irrigation reuse to provide treatment. Additional stormwater management requirements are set beyond standard City and RCWD rules based on the site’s location within the Northeast Drainage Area Comprehensive Stormwater Management Plan (CSMP). Based on City interpretation of the CSMP, it appears the design is generally compliant with these requirements, though additional information is requested. Existing and proposed discharge rates are summarized below. Pre- and Post- Development Discharge Rates (cfs) Condition 2-Year 10-Year 100-Year 10-Day Snowmelt Existing 28.35 67.29 162.34 N/A Proposed 24.81 57.29 127.92 N/A Trunkline – 0.1 cfs/acre N/A N/A 3.39 N/A Trunkline – Proposed N/A N/A 2.49 N/A Comments: 1. This development falls within the CSMP area and as such is beholden to additional rate control and volume reduction requirements. These volume reductions are demonstrated for flows to/through Wetland 4 and the 0.1 cfs/acre flows are demonstrated for tributary area to the 60” trunkline. Please confirm with RCWD that these are the only offsite flows with additional requirements. 2. An additional requirement for development within the CSMP is provision of more detailed water quality/reuse calculations. Please provide existing and proposed TP/TSS loading calculations for the proposed BMPs, including stormwater reuse. Additionally, please request a copy of the Reuse Design Worksheet from RCWD to quantify potential reuse volumes. 3. Provide profile plans of proposed storm sewer, including utility crossings, for more detailed review and comment. 4. Provide calculations demonstrating spread at the catchbasins is 10’ or less for the 3- year storm event. 5. Rational method pipe capacity calculations must be provided showing storm sewer is sized to convey the 10-year storm event and flow velocities are minimum 3 ft/s. 6. Confirm constructability of connecting proposed storm outlets into the existing trunkline manholes. 7. As the proposed ACD 72 ditch realignment will no longer need to provide subsurface drainage, nonperforated pipe can be specified in order to reduce loading to the tile. 8. Impervious area calculations should be based on actual site impervious, not the percentages in HydroCAD land use types. 9. Pond areas 2.5a and b should each be sized for NURP dead storage volumes separately according to their tributary areas. Pond flows only combine through