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HomeMy WebLinkAboutSDP200800031 Review Comments Minor Amendment 2008-06-03� OF AL ,. vIRGI1`IZP 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: Free Union Country School [SDP200800031, WP0200800018] Plan preparer: Hunter McCardle [email: hmccardle @mckeecarson.com] Plan received date: 26 Feb 2008 21 Apr 2008 (Revl) Date of comments: 02 Apr 2008 03 June 2008 (Revl) Reviewer: Jonathan Sharp A. Minor Amendment 1. Please provide the date and source of the topographic information: All topography should be field verified by the designer within the last year. Rev]: comments addressed. 2. Please provide the benchmark location, elevation and datum for topography. Rev]: comments addressed. 3. Please show the WPO buffer limits on the plan. Rev]: Buffer disturbance is shown on the plans. Please remove all work and grading outside the buffer. 4. Please show all critical slopes on the plans. Rev]: comments addressed. 5. The existing topography for the contour line 476 breaks north of the proposed sport court. Rev]: comments not addressed. Show proposed contours tying to existing contours for the demolition of the building. Final topography should show no grading breaks. 6. Proposed slopes steeper than 3:1 require low maintenance (not grass) ground cover specified on the plans. Rev]: comments addressed. 7. Please provide the Albemarle County general construction notes on the plans, verbatim. Rev]: comments not addressed. There are 9 County general construction notes, the plans only show 8. 8. Please provide drainage profiles for the storm pipes on the plans, in accordance with the County Engineering Design Manual Checklist. Rev]: Pipe profiles are required for all proposed pipes. 9. Please provide pipe computations for all pipes, in accordance with the County Engineering Design Manual Checklist. Revl: comments addressed. 10. Please show any roof drains that will tie into the SWM facility. Rev]: comments addressed. 11. The proposed sport court is on a 4.5% slope. This is a very steep slope for a sport/basketball court. The previous court was on a slope of 1 %, which is a more appropriate slope for a basketball court. Rev]: comments addressed. B. Stormwater Management Plan (WP0200700022) 12. Please provide a completed copy of the standard stormwater maintenance agreement and fee for recordation. The SWM facility is located on TMP 29 -15D. Albemarle County Community Development Engineering Review Comments Page 2 of 3 Rev]: comments not addressed. 13. The proposed drainage area map is confusing. Please delineate each of the 3 drainage areas on the sheet: DA #1, DA #2, and DA- Bioiilter. The narrative states that DA #2 does not change from pre - development to post - development, but it appears to be changing based on the drainage area maps. Rev]: comments addressed. 14. Will the SWM facility be sized for the future building additions? Please clarify this in the SWM narrative. Include assumed impervious values for any future development included in the calculations. Rev]: This is still unclear. See comment #15. 15. For redevelopment or expansion sites with no previous SWM facilites, please identify the overall increase in impervious area on site. The proposed SWM facility must, at a minimum, treat an area comparable to the net increase of imperviousness on site. You may be above and beyond the requirements based on the proposed design, but it is difficult to tell. Describing the increase of imperviousness in the SWM narrative may suffice. Rev]: It is unclear if the biofilter is treating enough impervious area for the proposed area or for future improvements. Engineering analysis of pre and post impervious areas is approximated as follows: Ip,e = 0.50 acres Ioost = 0.70 acres Ipost + Ipost ft., = 0.85 acres Iinc,ease = 0.35 acres The plans are only showing treating 0.15 acres of impervious area. At a minimum 0.2 acres of impervious area should drain to the facility. To include future improvements, 0.35 acres of impervious area should be treated. 16. Please provide the Albemarle County general SWM notes on the plans, verbatim. Rev]: comments addressed. 17. An adequate trash rack is required on the riser in the facility. Rev]: coments not addressed. 18. If concentrated discharges are proposed to the facility (such as roof drains), sediment forebays are required. Also, concentrated discharges should not short- circuit in the biofilter with respect to their proximity to the principle spillway. Rev]: Will there be no gutters or downspouts from the roof? These would be considered concentrated discharge. Also, baffles are not permitted in permanent facilities, only for ESC basins. 19. Please label the minimum floor dimensions of the biofilter on the plans. Rev]: comments addressed. 20. Please label elevations on the cross - section detail of the biofilter. Rev]: comments addressed. 21. Areas of sheet flow draining to the facility should be protected by appropriate scour protection stone. Rev]: comments not addressed. 22. Please provide under drains in the biofilter. Cleanouts should be provided at the end of the underdrain pipes, and every 50 feet. The underdrain and cleanout locations should be shown on the plans. Rev]: comments addressed. 23. Removal Rate calculations should not include offsite areas on the plans. Please remove the areas not included on the parcel. It does not appear that these changes necessitate the need for a different type of proposed facility. Rev]: comments addressed. Albemarle County Community Development Engineering Review Comments Page 3 of 3 24. Please provide routing hydrographs for the 2 yr, 10 yr, and 100 yr storm. Rev]: comments addressed. 25. Please use realistic critical durations. Durations should be representative of actual rainfall events (such as the rainfall model for a SCS 24 hr duration storm). Typically, storm events in excess of 30 -45 minutes are unrealistic. (As a result of using shorter durations, peak flow rates typically decrease.) Rev]: comments addressed. 26. The provided detention computations use incorrect outlet structure information. A weir of 0.2 feet is specified, but a 12" diameter weir riser is shown on the plans. Also, the structure information for the outlet barrel is not included in the computations. Rev]: comments addressed. 27. A SWM bond will be computed by the County once the plans have been approved. C. Erosion and Sediment Control Plan (WPO200700022) 28. The soils description in the narrative should provide a description of each type of soil on site. Rev]: comments addressed. 29. The limits of clearing and grading should include all buildings to be demolished. Rev]: comments addressed. 30. Please provide the dust control symbol (DC) on the plans. Rev]: comments addressed. 31. Tree protection must be provided on the drip line of trees proposed to be saved. Please distinguish silt fence from tree protection with different delineations. Rev]: comments addressed. 32. Please extend the Diversion Dike from the Construction Entrance to the proposed sediment trap. Rev]: comments addressed. 33. Please remove the Diversion Dike east of the existing main building. It only causes unnecessary disturbance and concentrates flow. Rev]: comments addressed. 34. The parking area, staging area, and stockpile location are located in the way of construction and grading. Rev]: comments addressed. 35. The proposed outfall location for the ESC trap /SWM facility will cause concentrated discharge onto the neighboring parcel before reaching the downhill swale. Please revise the configuration to keep discharge on the parcel before it reaches the swale. Rev]: comments not addressed. 36. The proposed drop inlet sediment trap does not meet VESCH minimum standards (3.07). 134 cu yd /acre of wet storage is required, and wet storage cannot exceed 2 feet in depth. Engineering recommends either providing as shallow wet storage as possible (1 ft min) or eliminating the trap because of its proximity to the play area as safety is a concern. Please specify safety fencing around the sediment trap. Rev]: comments addressed. 37. The invert elevations of the sediment trap do not match the drainage plans. The invert in of the downstream pipe is 471 while the bottom of the trap is 470.5. The top of the riser for the SWM facility is 475 while the top of the inlet for the sediment trap is 474. Rev]: comments addressed. 38. An ESC bond will be computed by the County once the plans have been approved.