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HomeMy WebLinkAboutWPO200800045 Review Comments Erosion Control Plan 2009-01-28ALg�,�� �'IRGINZ� COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road Charlottesville, Virginia 22902 -4596 Phone (434) 296 -5832 Fax (434) 972 -4126 Project: WPO- 2008 - 00045, SDP - 2008 -00074 Blue Ridge Co- Housing Plan preparer: Mr. Kevin Conner, CLA; Gay and Neel Inc. [kconner @gayandneel.com] Owner or rep.: Crozet Co- Housing, LLC fax (unknown) Date received: (Rev. 3) 17 December 2008 (Rev. 2) 7 October 2008 (Rev. 1) 31 July 2008 29 April 2008 Date of Comment: (Rev. 3) 28 January 2009 (Rev. 2) 25 November 2008 (Rev. 1) 14 August 2008 15 May 2008 (SRC Final Site Plan Comments) 13 June 2008 (Road Plans, SWM Plans, ESC Plans) Engineer: (Rev. 1, 2, and 3) Phil Custer Jonathan Sharp A. Final Site Plans (comments from 15 May 2008) 1. Please provide copies of federal and state permits for stream disturbance (Army Corps, VDEQ, etc.). (Rev. 1) Comment has not been addressed. (Rev. 2) Comment has not been addressed. (Rev. 3) Comment has not been addressed. 4. Please provide all copies of necessary offsite easements. For example, easements to construct water and sewer, road improvements, offsite construction and access easements, drainage easements, etc. (Rev. 1) Comment has not been addressed. The only offsite easement obtained has been for the construction within the private ROW. Permanent easements are needed for this project that must be obtained before approval is granted. Temporary construction easements also appear necessary on adjacent parcels affected by the roadway upgrade and construction of the SCC's to the streams. (Rev. 2) Comment has not been addressed. An easement plat has not yet been reviewed by the County. Comments from a full review of the plat will be given under a separate cover. Over the last several months, most of the discussion regarding offsite easements has revolved around the roadway culvert and drainage channels. Please be aware that in addition to the drainage easements in this area, the following easements will be required: - drainage easements will be needed for the channels downstream of SWM facilities 3 and 5 - construction easements for the sediment traps shown on the ESC plan, and - a swm easement on the 56 -76B encompassing the embankment of SWM facility 5. A letter from the property owner will be enough to address our concerns about the construction of the sediment traps. (Rev. 3) A letter from the owner of 56 -67B acknowledging and permitting the construction activity taking place on his /her parcel is required before plan approval. Comments from the review of the easement plat will be given in a separate letter (SUB- 2008 - 00285). The easement plat must be recorded before the site plan can be approved. 15. Please show the sight distance lines at the entrance of the site on Parkview Drive. (Rev. 1) Comment has not been addressed. A vertical profile of this sight line may be needed because of the existing grading of Park View Drive. (Rev. 2) Comment has not been addressed. (Rev. 3) Comment has not been addressed. The sight distance lines shown in this set are from Parkview Drive onto Route 240 as opposed to from the site onto Parkview Drive. There is some concern that the sight line from the site looking north is obstructed because of the crest curve in the roadway. 16. VDOT approval is required for any work affecting the public right -of -way. (Rev. 1) VDOT approval has not yet been received. (Rev. 2) VDOT approval has been received. 17. Parking areas cannot exceed 5% in grade, in any direction. (Rev. 1) Comment has been addressed. (Rev. 2) Grading has been amended and the plan is now currently in violation of 18- 4.12.15c. (Rev. 3) There is a spot elevation west of the existing house that should be changed from 652.5 to 653. This change will bring the site into compliance with the parking lot grade requirements. B. Road Plans 37. Guardrail must be specified over all fill slopes and culverts, with 3' additional shoulder, using VDOT designations. Guardrail end sections must be labeled. (Rev. 1) Comment has not been addressed. The shoulder has not been increased an additional aft when the guardrail is necessary. Guardrail is needed over a larger span than what is specified. The guardrail should be accounted for in the roadway section as well. (Rev. 2) The applicant seems to have replaced 2:1 slopes with 3:1 slopes for most areas on the latest plan. Considering this change and the wide clear zone on the north side of the road, guardrails are no longer needed. If the applicant wishes to keep the guardrails along the roadway, then the guardrails must be placed in a f at area of 2 010, not on the 3:1 slope. Please be sure to update the roadway section to match what has been changed in plan view. (Rev. 3) Guardrail is still shown on the east side of the roadway. It is not necessary at this location because of the grade of the slope. However, if it is still proposed, it should be shown on a relatively mild grade, not 3:1. 38. Ditches must be dimensioned at 1' depth min., and 4' min. width from shoulder to ditch centerline. (Rev. 1) Comment has been addressed. 39. Please provide a profile for the roadway culvert. (Rev. 1) The profile of the roadway culvert is adequate but a drainage easement will be needed over the pipe where it exists outside of the ROW. The easement should be placed at the width specified by the formula in the design manual. (Rev. 2) All vertical or horizontal changes in direction or changes in material require a VDOT structure. It appears the latest revision to the culvert design requires 2 structures. The pipe diameters cannot decrease in a pipe system. (Rev. 3) Comment has been addressed. The profile as shown is acceptable. Changes to the profile may be required due to comments regarding the calculations. 40. Please provide culvert calculations. (Rev. 1) Comment has not been addressed. The computations appear to be for the existing culvert that will be replaced with this plan. (Rev. 2) Comment has not been addressed. The calculations provided appear to be for a pipe in a storm sewer network instead of a culvert calculation. The capacity of a 24in culvert at 2% is smaller than of a 24in pipe in a stormsewer system because of the headwater conditions. The culvert calculations should show that headwater for the pipe during a 10 -year storm is less than 1.5 times the diameter. Depending on the slope, my calculations show that a 30 or 36 inch culvert may be needed. (Rev. 3) Calculations for the culvert require the following changes: - The drainage area map is not correct. There is an existing drainage system along Route 240 that directs some runoff from the south side of Route 240 across to the stream. Another drainage system picks up water from the second storage building on TMP 56A3 -7. Please adjust the map. - The calculations do not accurately reflect the proposed condition. Please provide a calculation for a 20ft 30" culvert sloped at 3.48% with a tailwater condition of the height of the water through the existing culvert. Also provide two storm drain calculations for the existing CMP pipe and proposed the 38ft RCP pipe. The culvert must meet all requirements listed above (head cannot be greater than 1.5 x diameter, etc.). C. Stormwater Management Plan 49. Cross - section details of each facility must be provided, including: embankments, principle and emergency spillways, sediment forebays, and biofilter floor dimensions. See the County Engineering design manual checklist for all cross - section detail requirements. (Rev. 1) The provided details are missing critical pieces of information. Please list the embankment elevation, embankment width, bed elevation, spillway elevation and TOW (if applicable). And, for all biofilters adjacent to walls, please show the gravel backfill behind the biofilters and any tie backs and how it relates to the mix in the biofilter. Engineering review is concerned about water escaping the mix without treatment by passing through the backfill. Please also provide details for the spillway through the retaining wall. (Rev. 2) Please show and dimension the check dam forebays in plan view as they have been designed in the calculations package. Check dams should be cleaned out or replaced at the time of biofilter construction conversion. The channels in the check dam forebay calculations do not appear to match the dimensions in the SCC calculations. As an alternative, the applicant may place stone horse -shoe shaped dams in the biofilter bed at the inlet point as long as they are sized correctly. (Please contact me to discuss this possibility further.) (Rev. 1) The grading plan does not show the swales and checkdams. The calculations do not consider the slope of the swale either. The calculations double count a large percentage of the water. I do not believe there is enough room in the swales for the checkdams to act as forebays. More extensive calculations should be submitted or, as an alternative, the applicant may place stone forebays in the biofilter bed. A forebay should also be provided in SWM 3. 50. For facilities with embankments 3 feet or higher, the 10 yr. and 100 yr. high water elevations must be shown on the cross - section details. With an emergency spillway, 1 foot of freeboard for the 100 yr. storm must be provided. Without an emergency spillway, 2 feet of freeboard for the 100 yr. storm must be provided. (Rev. 1) Comment has not been addressed. It appears that all facilities lack adequate free board. (Rev. 2) Freeboard appears to have been met on all facilities. Please remove "MIN" from the spillway callout on the biofilter detail sheets. The weir must be the length specified on the plan. If it were widened in the field, discharges would be higher and may not meet the pre- development rate. (Rev. 2) Comment has not been addressed. "MIN" has not been removed from the description of each spillway. 58. A SWM bond will be computed by the County once the plans have been approved. (Rev. 1) Comment has been noted by the applicant. (Rev. 2) Comment has been noted by the applicant. (Rev. 3) Comment has been noted by the applicant. D. Mitigation Plan 59. A mitigation plan is required for any stream buffer disturbance. Please provide a mitigation application, plan, and fee. a. (Rev. 1) Please provide the disturbance detail showing a shaded areas of the proposed stream buffer disturbance so that the 0.32 acres can be confirmed. This area must match the ESC plan. [DM] (Rev. 2) Comment not addressed. The stream buffer at the crossing is actually 200ft (100ft on both sides of the stream). The stream buffer layer should be adjusted and the mitigation plan recalculated. Please note that the buffer disturbance line should match the limits of disturbance on the ESC plan. There is also a discrepancy between sheet 5 and 9 to how much stream buffer has been disturbed. (Rev. 3) The mitigation plan does not appear to be sufficient. The disturbance of the buffer for the construction of sediment traps 3 -6 does not appear to be included in the buffer disturbed area. Also, the calculation does not appear to be computed correctly. With the limits as shown on the latest plan, about 17,200sf are disturbed. Our ordinance requires that the mitigation for this disturbance be replanted at a 2:1 ratio which then makes the total to consider 34,400sf. This number should then be divided by 400 (as detailed in Option la of the Design Manual in the mitigation section) to find the number of sets of plantings required. 60. A Mitigation bond will be computed by the County once the plans have been approved. (Rev. 1) Comment has been noted. (Rev. 2) Comment has been noted. (Rev. 3) Comment has been noted. E. Erosion and Sediment Control Plan 61. It appears that inadequate perimeter control is provided. See comment #24. (Rev. 1) Comment has not been addressed. b. The construction of ST -1 will require a retaining wall. This wall needs to be the first measure installed and should be noted in the construction sequence and shown on sheet 4. (Rev. 2) Comment has been addressed. c. The grading for the sediment traps 1 and 2 are not correct. It appears the grading is being shown is the grading of the biofilters which appear on sheet 7. Please correct. It is difficult checking the compliance with the sediment trap calculations without the necessary grading. Additional comments may be necessary once the grading is shown. (Rev. 2) Please remove the silt fence and note stating that silt fence is to be installed on the uphill side of the biofilters. The biofilters will not be installed until after stabilization. This means that builings 6, 7, and 11 will be built after site stabilization. This should be called out more clearly on the plan so the contractor is more aware of the phasing. Silt fence on the downhill side of SWM 3 is required. Please label contours and show the weirs for traps 1 and 2. Volumes will be confirmed once the contours have been labeled. (Rev. 3) The wet storage of trap 1 is steeper than 1:1. The calculation table for trap 2 requires 6ft from the bottom of the trap to the top of the embankment, but only 5ft is provided in the grading, there does not appear to be enough volume in this trap. Traps 3 -6 should be moved inline with the ditches so that the fill from the roadway can be directed into the traps. 62. Silt fence must not be used across contours in place of diversion dikes. Silt fence is limited to areas of sheet flow with 1/a acre per 100ft of level on -grade silt fence. (Rev. 1) Comment has been addressed. 63. Please provide ESC measures for the road improvements and sewer line improvements. (Rev. 1) Comment has not been addressed. The grading for the sediment traps need to be shown. I do not see any ESC measures for the construction of the sewer line. (Rev. 2) Comment has not been addressed. Please show silt fence for utility work in the VDOT ROW. Please also label the contours of traps 3 -6 to confirm the dimensions of the traps with the tables. The stone weirs should also be shown. (Rev. 3) Traps 3 -6 should be moved inline with the ditches so that the fill from the roadway can be directed into the traps. 64. Stream crossings and diversions must be provided at all stream crossings. A detailed sequence of construction must be provided for the replacement of the existing culvert and work within the live stream. (Rev. 1) Comment has not been addressed. (Rev. 2) Comment has not been addressed. (Rev. 3) Please provide a USC symbol on the plan and include a copy of Plate 3.25 -3 next to the pump detail. Engineering review recommends, but will not require, constructing a new pipe parallel to the existing culvert to simplify the work near the stream. 76. An ESC bond will be computed by the County once the plans have been approved. (Rev. 1) Comment noted. (Rev. 2) Comment noted. (Rev. 3) Comment has been noted by the applicant. File: E5_esc swm rp fsp mp_PBC_sdp08074 + wpo08045 Blue Ridge Co- Housing.doc