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HomeMy WebLinkAboutSDP200600041 Review Comments Road Plan and Comps. 2009-04-24� 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: Briarwood; Phases IA-1, 1B -1, 4, and 8 Plan preparer: The Engineering Groupe, Inc. Owner or rep.: Woodbriar Associates Plan received date: 31 March 2009 (ESC, SWM, FSP) (Rev10) 16 March 2009 (RP) Date of comments: 24 April 2009 (Rev10) Reviewer: Phil Custer (Rev10) On 30 April 2008, an engineering review was completed for the Briarwood (Phases 1A, 1B, and 8) site, road, ESC, and SWM plans and contained only administrative comments. Since that time, the applicant has opted to include Phase 4 in this construction set. This letter primarily contains review comments for the Phase 4 section but there are a few comments from the previously reviewed phases that were too important to overlook. A. Road Plan (SDP200600041) 1. VDOT approval is required. At the time of this letter, VDOT approval has not yet been received. 2. The road bond amount which was previously quoted is no longer applicable. A new road bond amount will be completed once the applicant submits a Road Bond request form with an updated schedule of completion. A road bond is not necessary until a final plat is submitted. 3. Please show 200ft of the existing profile for St. Ives. If the road isn't already sloped at 6.27%, a vertical curve must be provided. 4. Please show the 18, 20, and 22 contour lines on sheet 20A. 5. Please show how the extension of St. Ives road will affect the RWSA site and provide a VDOT commercial entrance. The building and driveways in this area appear to be masked. 6. The low point of the cul -de -sac must be carried to the stormwater management facility. Please show either a channel or pipe. 7. Please provide traffic control and street name signs on Sunset Drive. 8. Please label the curb radii at intersections and the cul -de -sac. 9. In the road profiles, please label the existing grade at the 50ft stations. 10. Please show VDOT standard cross - drains in the road profile. B. Final Site and Drainage Plan (SDP200600041) 1. A critical slope waiver is necessary for the disturbance of natural slopes in Phase 4. Only critical slopes disturbed for the roadway construction can be disturbed by the county engineer. Please submit a request for critical slope disturbance and we will schedule it for a Planning Commission Meeting. 2. Before this plan can be approved, ROW dedication and drainage easements are required on all offsite properties. This plat must be recorded before the site and road plan can be approved. Please also provide temporary construction easements for any work outside the ROW dedication and drainage easements. 3. Low maintenance, non - grassed groundcover is needed on all slopes steeper than 3:1. For a list of acceptable groundcovers, please see table 3.37C in the VESCH. Engineering review will Engineering Review Comments Page 2 of 3 also accept other equivalent groundcovers if proposed by the applicant. 4. Please provide drainage computations for the existing drainage structures on St. Ives which will have their drainage areas increased by this development. 5. Please place a drop inlet to capture the concentrated runoff at Sta. 10 +00 on the St. Ives Extension. 6. Please provide a note on the drainage profile sheets stating that all pipes deeper than 12ft require safety slabs (SL -1). There are several structures that currently do not have the safety slab specified. 7. Please provide a note on the drainage profile sheets stating that all inlets must have inlet shaping (IS -1) if the drop from the surface (or pipe) to the bottom is 4ft or greater. 8. Wall details are needed in the site plan set. 9. Provide more spot elevations around the proposed walls. Any wall 4ft or taller will require a handrail. 10. Inlets that do not overflow to a stormwater management facility must be sized for a 6.5in/hr storm. 11. Please design and specify on the plan the size of the ditch to the northwest side of Sunset Drive. 12. Structure ST -415 appears to be a culvert on the plan, but the calculations sheet indicates it is a DI -7. Please clarify. If the structure will be a culvert, please provide a headwater calculation and provide an adequate sump area. Regardless of whether this structure is a DI -7 or an end section, the computation needs to take into account the drainage area to existing structure in the Camelot subdivision. 13. Please specify a small berm on the downstream side of all DI -7's so that the headwater shown in the calculations has the chance to accumulate without bypassing the inlet. 14. Please provide a detail for the pipe from structure 406 under the retaining wall. 15. Please update all four standard Albemarle County Construction notes in the sheet sets. The latest set of notes can be found in the current edition of the design manual, available online. C. Stormwater Management (WPO200600066) 1. Please submit a stormwater management facility maintenance agreement for TMP 32G - -A. Properties 32G -1, 32G - -C, and 32G -02 -97 already have recorded maintenance agreements. 2. For all facilities treating runoff from Phase 4, please use the grass and gravel cells in the modified simple spreadsheet. 3. The flow path in Stormwater management 3 from structure 4 -406 should be longer. I recommend moving the outfall to the eastern corner and providing a loft wide access path to the forebay. 4. All water deeper than 6ft should not be considered as part of the 4xWQv. Please adjust the calculation for SWM facility 3 in this regard. 5. Please eliminate the vegetated filter strip and extend channels for facility 3 and 5 to collect this water. 6. Facility 5 must have a 3:1 downstream slope. 7. The minimum drainage area for wet ponds is 10 acres. Facility 5 cannot be a wet pond. 8. If a biofilter is sized to provide a 65% removal rate, it must have a bed equal to 4% of the impervious area draining to it. The biofilter shown in the plan possesses a removal rate of 50 %. 9. Please show the cutoff trench and impervious core in the embankment detail for all ponds. 10. The biofilter detail is hard to read. Please clarify. Additional comments may be necessary after the change. The biofilter characteristics must match those listed in the engineering review checklist. To simplify design, review, construction, and inspection, I recommend combining this facility with Facility 5. 11. The ponding within a biofilter must be Ift when using the 2.5% or 4% calculation method specified in the design manual. If a 6" ponding depth is desired, the applicant should provide a volume calculation showing that the water quality volume is provided. Engineering Review Comments Page 3 of 3 12. The SWM bond will need to be recalculated. The calculation will occur once the plan is closer to approval. D. Erosion Control Plan (WPO200600066) 1. The ESC bond will need to be recalculated. The calculation will occur once the plan is closer to approval. 2. Adequate channel calculations must be provided from the outlet of all stormwater management facilities in Phase 4, Pond 1, and Pond 2. For the outfall of Pond 2, the analysis may terminate once the road culvert is analyzed. The channel from this pond should be designed using proposed contours and not existing because this area will have been previously disturbed with the sediment basin. All other analyses may terminate once the river is reached. The analyses should meet all requirements specified in the latest edition of the design manual. 3. The concept for the ESC plan in phase 4 is problematic and should be amended. The transition from Phase 1 to Phase 2 has many issues that would leave portions of the site unprotected. Given the existing and proposed topography, it appears an intermediate phase is needed showing the traps and basins in place at the time the road and drainage system is constructed. Once the road and drainage system is constructed, the measures in the low points (traps 2 and 3) can be replaced with silt fence since the majority of the drainage area is diverted to Basin 5 and the trap/basin that will be permanent facility 5. This would require relocating several sections of the drainage system. We recommend setting up a meeting to discuss the ESC plan corrections prior to the next submittal. The use of the temporary slopes drain across the active construction area will not be permitted. Additional comments may be required. 4. Sediment Basin 5 should be designed using the maximum drainage area to it. 5. Please lightly hatch all critical slopes on the ESC plan. 6. Please update the disturbed area in the ESC narrative. 7. Please show the ESC measures for the Route 29 improvements. It appears as though check dam, ditch matting, and inlet protection are needed. 8. The construction entrance for the site does not appear to drain to the sediment basin because of the difference in elevations. Please provide a trap downhill of the construction entrance. 9. Please provide a note on the plan at the four other entrances that access to the site will be limited to only the entrance at Briarwood Drive. 10. Show the erosion and sediment control measures needed around the St. Ives cul -de -sac. 11. Work is shown in a wooded area close to the property line of many existing lots in the Camelot subdivision. Though the limit of construction line is within the subject parcel, there have been cases throughout the county where, because of damage to trees and root systems, disturbance has crossed property lines. Please provide a note on the plans stating that damage to trees close to the property line is a critical area and the contractor must be careful not to disturb adjacent parcels. 12. The location of ST -1 is in the middle of construction. Please move the trap to the corner of the property at the start of the St. Ives extension. 13. ST -2 should be located farther downhill so the retaining walls can be constructed without disturbance of the sediment trap. Otherwise, a more detailed phased plan may be required. 14. Pond 5 should be designed as a sediment trap for the ESC phase. A diversion should carry runoff from construction area around the St. Ives cul -de -sac. 15. Please provide matting calculations for all proposed channels. 16. Please label the contours in all traps so that the volumes can be verified. 17. Please provide DC, TS, and PS symbols on the plan where applicable.