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Ms. Katie Larsen 08/06/2025 Page 3 Nature Refuge North Addition Engineering Review Existing 0.26 0.95 8.68 Needed if basins landlocked Proposed 0.45 1.07 7.46 Needed if basins landlocked Comments: 1. Outflow rates increase for all modeled storm events beyond what can be attributed to model accuracy. Further attempts at providing rate control must be made. For example, ditching flows from back yards to the inlets routing to BMPs, lowering the FES north of Wetland 50 to better route flows into Pond 500, or small rate-control basins at areas that cannot reasonably be routed into a BMP. a. If increases cannot be avoided, it must be demonstrated that they will not cause an adverse downstream impact. Carlson (4/25/2025) Flows have been adjusted and plans modified. WSB (5/23/2025) Updated modeling shows the total existing flow rates are maintained, decrease, or increase within model tolerance. Rate control is met with this current design. 2. The SWMP water quality calculations show 0.90 acres of existing impervious, however the HydroCAD existing modeling has 3.57 acres of unconnected roof land cover. Please clarify these differences. Carlson (4/25/2025) Existing impervious adjusted within water quality calculations. WSB (5/23/2025) Complete 3. Please revise the Water Quality calculations in the SWMP as they do not match HydroCAD modeling. For instance, HydroCAD modeling shows 16.86 total acres and 7.52 acres of impervious routed to Pond 600, but the SWMP has a total area of 9.77 acres and 0.196 acres of impervious. Carlson (4/25/2025) Water quality calculation updated. WSB (5/23/2025) The SWMP still shows incorrect land covers for the Water Quality calculations of Pond 500 and 600. The planned drainage areas well exceed 0.973 and 2.511 acres, respectively. Additionally, 9.02 acres of impervious area are claimed to be directed to ponds 500 and 600, but the submitted HydroCAD models only include 8.59 acres of impervious in the pond subcatchments. Compared to the 11.19 acres of total proposed impervious, there is significantly more than the 15% limit of new impervious not being treated for water quality as required in RCWD Rule C.6.(e). Comment remains open. The Water Quality calculation pages still need to be corrected and total impervious not routed to BMPs is still over the 15% threshold. Carlson (6/6/2025) Revised. Note that within Pond 600 calculations, Subcatchments 25B, 30, 35, 600 & 601 will flow into Pond 600. Pond 500 has 1 subcatchment. Also added calculations for runoff control at the water quality volume for both ponds. Per discussion, the impervious not being treated is all rear yard drainage. These areas will be filtered through grassed yards, wooded outlots, wetlands, and a dry pond. TSS and TP removals will occur and can be calculated through a MIDS model if necessary. Assumption is that most if not all the TSS and TP will be removed. WSB (6/25/2025) Complete 4. NURP criteria specify a maximum depth of 10’. Pond 500 has a depth of 11’, raising the bottom elevation to 10’ will bring it into NURP compliance and still keep the majority of its dead volume. Carlson (4/25/2025) Pond 500 has been revised to a depth of 10’ Page 109 of 168