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HomeMy WebLinkAboutWPO201300023 Review Comments Mitigation Plan 2013-05-23�� OF A i" A COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road, Room 227 Charlottesville, Virginia 22902 -4596 Phone (434) 296 -5832 Fax (434) 972 -4126 Project: Edenbrook Park (WP02013- 00023) Plan preparer: Perkins & Orrison [tel 540- 464 -5009] Owner or rep.: March Mountain Properties, LLC Plan received date: 3 April 2013 Date of comments: 23 May 2013 Reviewer: Michael Koslow The first erosion and sediment control, stormwater management, and mitigation plan (WPO201300023) submitted 27 March 2013 has received Engineering Review and does not appear to meet Albemarle County minimum checklist items for approval. Please adequately address the following comments for final approval: A. Application Information 1) After plan approval but prior to grading permit issuance, a pro -rated share payment to Lickinghole Basin will be required. 2) Please provide US Army Corps permission or permit for proposed work in flood plain of Unnamed Tributary to Slabtown Branch. 3) After plan approval but prior to grading permit issuance, an owner - signed stormwater maintenance agreement and recordation fee ($17) will be required for maintenance of any proposed stormwater management (SWM) facilities. B. Title Information 1) Title sheet of final plans will require a date and professional engineer signature prior to approval. C. Proposed Plan View Information 1) Please include labeled stormwater management easements over all proposed facilities and associated structures. 2) Please label drainage structure numbers in grading plan. Please include drainage structure profile sheet from final site plans (sheet 10 of SDP2013- 00020) or a reference to this sheet by note. Engineering Review Comments Page 2 of 3 D. Erosion and Sediment Control (ESC) Plan 1) Albemarle County requires a paved construction entrance (see Design Standards Manual for detail). Please delete proposed stone construction entrance detail and revise "CE" legend description to "Temporary paved construction entrance" on sheet 5. 2) Please indicate dust control for each proposed phase of ESC. 3) Please ensure there are no erosion control measures in the way of construction access or grading. Please propose R/W Diversions for portions of proposed Diversion Dikes which cross proposed road construction as shown in ESC Phase Il or reconfigure proposed sediment traps based on reconfigured drainage divides associated with road construction. 4) Please provide an adequate channel analysis for runoff from proposed construction. Analysis could be proven given: a) adherence to VESCH MS -19 requirements (see 4VAC50- 30 -40, MS -19 sec. b (1)): The applicant shall demonstrate that total drainage area to the point of analysis within the channel is one hundred times greater than the contributing drainage areas of the project in question. A report or plan depiction with analysis to this point could prove channel adequacy. b) adherence to VA code 10.1- 603.4(7): essentially, the required condition for an on -site solution without looking downstream for a 24 hour 1. 5, 2, and 10 -year intensity event - (post - development) Peak flow rate <= Pf*VfNp Where Pf = peak flow rate in a forested condition Vf = runoff volume in a forested condition Vp = runoff volume proposed Please note: if all project outfalls drain directly to a stream which has 100x the drainage area compared with the 5.53 Acres of proposed land disturbance, an exhibit showing the drainage area and statement as much will prove Adequate Channel outfall for this project. E. Stormwater Management Plan 1) Please provide a plan view depiction of existing conditions proposed to drain to the proposed bioretention basin (could be a modification of ESC drainage divides map on sheet 8). Depiction should include: a) Drainage divides for all drainage areas to proposed facilities as used in computations b) Acreage of each drainage area, labeled on the map area and matching comps c) Drainage divides for total drainage areas to proposed facilities, matching comps 2) Please provide a plan view depiction of proposed conditions proposed to drain to the proposed bioretention basin (could be a modification of post development drainage divides map on sheet 8). Depiction should include: a) Drainage divides for all drainage areas to proposed facilities as used in computations b) Acreage of each drainage area, labeled on the map area and matching comps c) Drainage divides for total drainage areas to proposed facilities, matching comps Engineering Review Comments Page 3 of 3 3) Please provide cross section details for Bio -filter A, Bio -filter B, Bio -filter C, and Bio - filter D showing and labeling dimensions of: a. Embankments b. Principal Spillway c. Emergency Spillway (could expand, label, draw to scale and 4x duplicate "Bioretention Filter (VSHM Std 3.11) with Underdrain Detention" detail on sheet 6). 4) Due to high concentration of contributing impervious surface to the proposed bio- filters, please include sediment forebays for all proposed bio - filters. The forebays should be sized to 0.25" of runoff per impervious acre (this can be included in the water quality volume). 5) Please remove "bio -filter area shown on master plan — not proposed" from plan sheet 4 6) Please transpose apparent mis- labeled R -Tank HD orifice "A" and "B" invert elevation labels on "Bioretention Filter (VSHM Std 3.11) with Underdrain Detention" detail on sheet 6. 7) Please include a manufacturer's detail for proposed R -Tank HD (or equivalent) storage modules. 8) Please provide 4' diameter minimum inspection access for proposed R -Tank HD storage modules. This could be accomplished by oversizing the riser pipe. F. Mitigation Plan 1) For permanent stream buffer impacts proposed with this submittal, proposed mitigation plan is adequate. Current Development Engineering is available from 2:30 -4 PM on Thursdays to discuss these review comments. Please contact Michael Koslow at 434 - 296 -5832 ext. 3297 or email mkoslowgalbemarle.or to schedule an appointment. [17- 204.f1 An application for an erosion and sediment control plan that requires modifications, terns, or conditions to be included in order for it to be approved shall be deemed to be withdrawn if the owner fails to submit a revised plan addressing the omitted modifications, terms or conditions within six (6) months after the owner is informed of the omitted information as provided under paragraph (B).