07-08-2019 Council Packet - Laserfiche WebLink

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Memorandum To: Katie Larsen, City Planner From: Ed Youngquist, WSB & Associates Diane Hankee, City Engineer Date: June 3, 2019 Re: 6650 Enid Trail – Lot Impervious Variance As requested by City Staff, WSB and Associates, Inc. has reviewed the grading revisions for 6650 Enid Trail (Lot 3, Block 2, St. Clair Estates) prepared by Sharper Homes and received on May 7, 2019. The following documents were reviewed: • Project Narrative • Exhibit A - Grading Concept Sketch with Infiltration/Rain Garden Area • Declaration of Building Covenants for St. Clair Estates Project Background The property owner of 6650 Enid Trail, Sharper Homes, submitted a Land Use Application for an impervious surface coverage variance. They are requesting an impervious surface coverage of 43.7% be allowed. The City’s Shoreland Management Overlay ordinance allows for a maximum impervious surface coverage of 30%. The grading exhibit provided shows a proposed swale along the southerly property line directing water towards the rear lot line, discharging into a small infiltration basin located in the northeast corner of the lot. This basin has a proposed emergency overflow of 902.0. The basin discharges northerly – onto adjacent property. Comments: 1. Exhibit A suggests the infiltration basin is sized for 30% impervious lot coverage. The proposed lot coverage is 43.7% impervious. 2. Soils information and stormwater modeling not provided to support infiltration basin design. 3. Infiltration basin design required (cross section, materials, infiltration calcs) 4. The E.O.F. of the basin meets the requirement for separation from low opening. 5. Stormwater maintenance agreement required for the infiltration basin. 6. Drainage and utility easement required if city maintained. 7. Proposed house falls off the constructed house pad – correction needed. 8. Revised grading plan for St. Clair Estates will be required. Conclusions: 1. A stormwater management plan was reviewed and approved for the entire St. Clair Estates development. We do not recommend the practice of stormwater management for individual lots within a subdivision to accommodate non-compliant site construction for the following reasons: a. Overall functionality and longevity of the storm sewer system (BMP) in question. b. Tracking of potential BMP modification by current or future homeowner an issue. c. Need for private stormwater maintenance agreement recorded against the property in perpetuity.