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HomeMy WebLinkAboutWPO201000049 Review Comments Erosion Control Plan 2010-09-17� OF AL ,. vIRGI1`IZP COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road Charlottesville, Virginia 22902 -4596 Phone (434) 296 -5832 Fax (434) 972 -4126 Project: WPO- 2010 - 00049; Meeting Street South Mass Grading (HTC) Plan preparer: Mr. Scott Collins, PE; Collins Engineering Owner or rep.: Plan received date: Date of comments: Reviewer: Route 29 LLC 5 August 2010 17 September 2010 Phil Custer The mass grading plan for Hollymead Towncenter Meeting Street South, received on 5 August 2010, has been reviewed. Engineering review for Current Development can approve the plan once the following comments are addressed. A. General Review Comments 1. VDOT approval is required. At the time of this letter, VDOT approval has not been received. 2. Please include a proposed centerline horizontal alignment, vertical alignment profile, and typical section to confirm that the topography of this grading plan is close to the final grade of Meeting Street. The alignments and sections will be subject to VDOT review. The roadway sections must match the details provided in the application plan of Hollymead A2 (ZMA- 2007- 00001). [32- 8.5.5.4] 3. The stream at this crossing is perennial. The crossing of a perennial stream requires a box culvert, arch culvert, or bridge per 17- 320.D.1. If a box culvert is proposed, please make sure the invert is countersunk 6 ". Please adjust the plan as required and provide calculations showing that the culvert does not backwater onto surrounding properties during a 10 -year storm. 4. This project proposes to disturb a significant amount of critical slopes. Proffers 7.A of ZMA- 2005 -00015 and 9.A of ZMA- 2007 -00001 require the applicant to request a critical slope waiver. The request to disturb critical slopes must meet the requirements of 18- 4.2.5.a. Engineering review will provide a response to the request and schedule the item on a Planning Commission meeting. A site development plan application will be required so the project can be tracked. A fee of $180 for the waiver will be required for "Relief of Condition of Approval" per the Chief of Current Development. Please also shade or hatch all critical slopes on both phases of the ESC plan. 5. Before this ESC plan can be approved, the applicant must provide the county with a copy of the approval from the Army Corps of Engineers or Virginia DEQ for disturbances to the streams and wetlands onsite. 6. Please show the grading for the loft greenway trail at 10% from Meeting Street to a point just north of the sediment basin. Will the trail be located on the embankment of the basin/SWM facility? [32- 8.5.5.4] 7. The downstream slope of the sediment basin must be graded to 3:1 contours. The downstream slope is specified on ESC -4, but the existing contours have been surveyed as steeper than 2:1 in many locations. Sediment Basin 4 appears to be placed at the location of the permanent SWM facility as shown in the latest rezoning application. [32- 8.5.5.4] 8. Please include all information regarding the existing topography shown on this plan including the surveyor, date of the survey, datum, and benchmark. Since the land within the limits of Engineering Review Comments Page 2 of 3 disturbance has been an active construction area for a while, the date of the topography should be recent. 9. Approval of this mass grading plan by the Director of Planning is required. This plan has been transmitted to the Planning Department for their review and approval. [32- 8.5.5.4] B. Erosion and Sediment Control Plan Comments 1. Proffer 7.13 of ZMA- 2005 -00015 and Proffer 9.13 of ZMA- 2007 -00001 requires that the applicant provide additional erosion and sediment controls to achieve a sediment removal rate of 80% as determined by the County Engineer. Please provide a list of these extra measures on the cover sheet of the next submittal so we can evaluate whether they comply with the proffer(s). 2. This area of Hollymead is an active construction site with other open erosion and sediment control permits. Please clearly show the limits of these other plans and identify each plan with their county application number. Is this plan intended to supplement or replace one of these plans? There may be some conflict with the Al ESC plan in the southwestern corner of the Al site where an area of the site is covered by both plans. Please show the ESC measures of the Al plan in this area. 3. In the construction sequence, please reference the requirement for the project to permanently seed the site 9 months after the grading permit is issued, which is required by Proffer 7.0 of the ZMA- 2005 -00015 and Proffer 9.0 of ZMA- 2007 - 00001. The County Engineer may extend this deadline if he feels it is appropriate. 4. In the ESC narrative and on the cover sheet, please list all TMPs that are within the limits of disturbance for this project. If no construction easements have been recorded, each of these parcels will need to be on the bond. Has the Greenway parcel of Al already been dedicated to the County? 5. Please refer to the critical slopes being disturbed, the stream crossing, and the existing site work south of this project's limits as other "critical areas" in the narrative. 6. Please update the general ESC notes from the latest version of the design manual (available online) with a total of 22 notes. 7. Please show the soil boundaries on Phase 1 of the ESC plan and provide descriptions of the soil types in the narrative. Since most of the soil on the east side of the stream has been disturbed with other ESC plans, please adjust the map and descriptions accordingly. 8. Phase 1 of the ESC plan shows the trap and diversion west of the stream being constructed without a stream crossing. Will a temporary stream crossing be installed at any point? If so, please design according to VESCH 3.24. If not, please alter the Phase 1 sheet to include the installation of the culvert and the minimum amount of grading to establish the crossing. Please also adjust the construction sequence accordingly. 9. Please provide a Utility Stream Crossing (USC) symbol at the culvert. This symbol is used to indicate that the stream is to be diverted during the culvert installation. 10. For Erosion and Sediment Control at stream crossings, please refer to the County Engineer's Commentary 5 (available online). Relying on just silt fence as shown for the culvert installation is not acceptable; a few sediment traps adjacent to the stream (in addition to the trap and basin already shown on the plan) will likely be necessary. 11. In phase 1 of the ESC plan provide a diversion south the basin. This may need to be a ROW diversion if construction traffic will be impacting it frequently. 12. Please provide the dewatering orifice calculation. I found an orifice of 4in (rounded down from 4.9in) should be required. 13. Please extend the baffle to the surface water elevation so that the flow path from the diversion is lengthened. 14. Please design a channel where the Meeting Street grading intersects with the mass grading of Engineering Review Comments Page 3 of 3 Area A2. This ditch must be designed to carry the 10 -year storm without overtopping and the 2 -year storm without eroding. Additionally, the seams of the fill at the stream crossing may require riprap to prevent erosion. 15. Please show the 495 contour if it is to be the bottom of the trap. In all phases and the detail, the bottom is shown as 496. 16. Please show the offsite topography to confirm that drainage area to the sediment trap. The topography can be obtained from the GIS department on the county website. 17. Please provide an adequate channel from the outlet of the sediment basin/SWM facility to the stream. 18. The ESC bond will be computed at the time of plan approval.