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Comprehensive Stormwater Management Plan Northeast Lino Lakes Drainage Improvement Project WSB Project No. 2929-79 Page 19 6 RCWD RULE C REQUIREMENTS 6.1 Rule C Overview The Northeast Lino Lakes CSMP area is located within a single resource of concern drainage area (Figure 3, Appendix A). General drainage patterns as documented in this CSMP will be maintained with any future developments so that stormwater runoff will remain within the Peltier Lake ROC drainage area and be managed to meet RCWD’s Rule C requirements. As allowed for under RCWD Rule C.5(f), this CSMP has been prepared as an alternative means to meet the requirements of Rule C.6 Water Quality Treatment and Rule C.7 Peak Stormwater Runoff Control for the development of the area, which is anticipated to be completed in several distinct phases. The peak runoff control and water quality treatment requirements will be met, in aggregate, for the area as a whole. 6.2 Water Quality Treatment [RCWD Rule C.6] RCWD’s water quality treatment requirements will be met through a variety of measures, including stormwater detention ponds, biofiltration, and infiltration, as is feasible. Figure 14, Appendix A shows the locations and suggested types of regional BMPs. It is anticipated that the study area will include water quality treatment trains with sedimentation BMPs located in upland areas designed to remove solids and particulate matter. These will be combined with surface and media filtration to remove dissolved particulates, nitrogen, and phosphorus prior to entering the new system and discharging into the regional BMPs. Total phosphorus loading under existing and proposed land use conditions was estimated using event mean concentrations from the Minnesota Stormwater Manual (Minnesota Pollution Control Agency 2016). Under existing conditions, the CSMP area contributes approximately 12.6 pounds of total phosphorus annually to Peltier Lake. With the proposed full-build out land uses, in absence of any stormwater treatment, the CSMP area loading would increase to approximately 14.4 pounds per year (Table 6-1 and Appendix E). Table 6-1. Summary of Total Phosphorus (TP) Loading by Region without Stormwater Treatment REGION Area [ac] Existing TP Load [lb] Proposed TP Load [lb] TP Load Change [lb] HUGO 215.6 0.72 1.36 +0.64 EAST 553.9 4.90 6.43 +1.53 CENTRAL 447.3 5.89 6.30 +0.41 WEST 152.5 1.06 0.31 -0.75 TOTALS 1,349 12.6 14.4 +1.83 The proposed land uses in the West region, including the wetland management corridor and medium density residential have a lower total phosphorus concentration (0.03 and 0.3 mg/L, respectively) than the existing land use of agricultural row crops (0.32 mg/L) and contribute to the reduction in the proposed total phosphorus loading. However, as required by RCWD Rule C.6, water quality treatment is a necessary component of development and we expect the TP loading to be reduced significantly with the required stormwater treatment practices in place. A challenge for the CSMP area will be to infiltrate stormwater to meet the water quality volume reduction in Rule C.6. Review of the CSMP area led to the development of Figure 15, Appendix A (Infiltration Suitability). This map was developed using the following four criteria: