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HomeMy WebLinkAboutWPO200800033 Review Comments Stormwater Management Plan 2008-09-22� 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: Wickham Pond Phase 2 Block 2 [SDP200800056, WP02008000331 Plan preparer: The Timmons Group Owner or rep.: Charlotte B. Dammann Plan received date: 25 March 2008 04 June 2008 (Rev]) 14 August 2008 (Rev2) Date of comments: 9 May 2008 21 July 2008 (Revl ) 22 September (Rev2) Reviewer: Phil Custer Jonathan Sharp (Revl ) Phil Custer (Rev2) The site, SWM, and ESC plans for Wickham Pond Phase 2 Block 2 have been reviewed. The plans cannot be approved as submitted and will require the following changes. A. Final Site Plan 1. Please provide a benchmark on the plan with a set elevation. A benchmark is referred to but is not near the project area and must be shown on the plan. [DM] Rev]: comments addressed. 2. Please specify a VDOT standard entrance for each site access point onto the roadway. Rev]: comment addressed. 3. Sight distance does not appear to be shown to the VDOT standard for entrances onto the roadway. One hundred feet of sight distance is required for all internal intersections and not entrances onto VDOT ROW. Rev]: Adequate sight distances should be provided on Wickham Way. Rev2: Comment has been addressed. 4. Please show the necessary walls and pillars from the structural plans for the garage on sheet S -1. The garage configuration and layout must be approved by the Zoning department in order to waive the 100ft internal sight distance requirement specified in our ordinance. Revl: The plans still do not show whether or not all parking and travelway ordinances are met, as the elevations of the garage and the footprint of the underground parking structure are not shown. Only the travelway widths and parking dimensions appear to meet the ordinances. One hundred foot sight distances and grade restrictions will need to be maintained unless a waiver is granted from the Zoning Administrator. Please show the footprint for the design of the underground parking garage, including the location of walls, columns, footers, etc. as these will affect sight distances. All proposed grading on site is required, including grading for the underground parking structure. [18- 32.6.6b, h6] Rev2: Please remove the note on sheet 3 referencing the garage layout being subject to change. Replace these three sentences with a note stating "Any deviation from this site plan will require an amendment to be approved by the county." Please also include this note on sheet 3. Many of the parking spaces are not 18ft in length due to the diameter of the columns. Engineering Albemarle County Community Development Engineering Review Comments Page 2 of 5 review does not support a waiver of this requirement. 5. Please provide traffic control devices on the site. There appears to be several conflict points in the garage and surrounding drive aisle that may need signage. Rev]: comments not addressed. Traffic control design for all parking areas must be provided prior to final site plan approval. Rev2: Please provide signs specifying the advisory speed inside the garage is 5mph. This is a condition of the waiver of the sight distance requirement in the parking garage. 6. The dumpster and loading space configurations are not currently acceptable to engineering review. The dump trucks and vehicles using the loading spaces will not be permitted to back out into the roadway. The loading spaces also cannot block the dumpsters. [18- 32.7.2] Rev1: I am unsure as to how underground trash collection will work. Will there not be a dumpster? Underground parking garages tend to have very low ceilings and garbage trucks would not be able to pick the dumpsters up. [18- 32.7.2] Rev2: The ordinance specifies that the loading spaces must have a clearance height of 14.5ft. It is clear that the garage does not have this height. [18- 4.12.18] The county would like more information regarding the waste disposal plan for this site. The areas for trash collection appear too small considering the residential and commercial units on site. Please also address the county's concern that the trash truck may be too tall for the garage. Please provide sections estimating the height required from the lowest beam in the garage to the finished floors and the courtyard. 7. Please provide greater detail with regards to grading throughout the site, specifically of the garage, courtyard, and access aisles from the roadway to the garage. Entrances cannot exceed 4% for the first 40' from the intersected street. Across the garage there appears to be a vertical drop of loft. Rev1: comments not addressed. Proposed grading is required. All proposed grading for travelways and parking areas must meet zoning ordinances. [18- 32.6.6b] Rev2: Travelway grades cannot exceed 10% measured at any location on the travelway. The county will not require the full landing requirement of 40ft at 4 %. Only 20ft at 4% will be needed at each entrance. The eastern travelway also appears to conflict with Building B. All grade changes should have a reasonable vertical curve. 8. Please provide more detail in reference to the "stairs to elevator" specified on sheet S -1. Rev1: All proposed grading should be shown. Any drops of 4' or greater require safety railing. [DM] Rev2: Show the grading around the travelways into the garage with relation to the surrounding grades in the grass. It appears that walls are needed in both entrances. Please provide wall details with the safety railing as required. 9. Please provide more information regarding the drainage system around the buildings, in the plaza, and around the parking structure. Will the buildings have roofdrains taking runoff to the biofilter or is there an underground drainage system taking water around the parking structure? How is infiltrated water from the courtyard reaching the biofilter? Please also show the trenchdrains. Rev1: The plans indicate that Post DA 4 and 6 are piped to structure 163, but no pipes or drains have been provided. Rev2: Please provide more detail regarding the parking garage drainage system and grinder pump. This system will be subject to the approval of the county engineer. 10. Please provide a section detail for the replacement of the paved pedestrian path. Rev1: comments not addressed. Rev2: The applicant has provided a detail for sidewalks. The sidewalk detail should include the strength requirement of 3000psi at 28 days. A detail for the replaced pedestrian path (along Route 240 that is disrupted by the TSD) is still needed. Albemarle County Community Development Engineering Review Comments Page 3 of 5 11. Please do not provide an entrance from the VDOT ROW for the biofilter maintenance path. The access must be given from another entrance on site. Rev]: comments addressed. 12. On all slopes steeper than 3:1, please specify a low- maintenance groundcover. [DM] Rev]: comments addressed. 13. Additional comments may be forthcoming on the next submittal due to the required changes. a. (Revl) Engineering recommends redesigning the concrete area between buildings C and D, as the grade is shown at 10%. Is there a reason why the elevation at building C is at 654? What is the crest elevation of Wickham Place adjacent to building C? The elevation at building C could be lowered to provide a more suitable grade between buildings C and D. (Rev.2) Water is directed towards Building D. Please amend the grading. b. Engineering recommends directing drainage away from the proposed "stairs to underground parking garage." (Rev.2) Comment has been addressed. B. Stormwater Management Plan 14. The Lickinghole SWM basin pro -rata fee will be computed once the site plan has been approved. Revl: The Lickinghole SWM basin pro -rata fee will be computed once the site plan has been approved. Rev2: The Lickinghole SWM basin pro -rata fee will be computed once the site plan has been approved. 15. The hydrologic characteristics of Post - Development Drainage area 1 are not reasonable. I do not see how the time of concentration increases from 16 minutes to 19 minutes. I believe a post - development time of concentration between 5 and 10 minutes would be much more reasonable. Please provide a breakdown of the C coefficient for the DA 1. It is likely that grassed area over the courtyard will be highly compacted and a coefficient of around 0.6, rather than 0.3, should be used. Rev]: comments addressed. 16. Please submit a modified simple spreadsheet for DA 1. Rev]: Please provide adequate Water Quality Calculations for the entire site (calculations have only been provided for the area draining toward Three Notched Road). During the rezoning, was it the intent to provide additional water quality for Wickham Pond Phase II block 2? If so, adequate water quality measures should be provided per the rezoning. Otherwise, water quality is provided per payment of a pro rata share to the Lickinghole Basin. Rev2: Water Quality requirements will be taken care of with the Lickinghole Basin fee. 17. The project area data seems to be incorrect in Table 12. Rev]: comments addressed. 18. Please provide a detention compliance summary. Revl: Detention computations are required. If detention is provided offsite, please provide calculations verifying that the offsite facilities are adequately providing detention for the proposed site. Rev2: Comment not addressed. Please submit calculations and all other exhibits showing detention compliance. This plan has a separate file and should be exclusive of other files. The calculations should reflect the latest proposed conditions. 19. Please remove any reference to the luckstone mix from the biofilter detail. The county now requires that the biofilter mix meets the approved state standard. Rev]: comments addressed. 20. Please provide lft freeboard of the 100 -year storm in the biofilter facility. Albemarle County Community Development Engineering Review Comments Page 4 of 5 Rev]: comments addressed. 21. The post - development drainage area does not appear to be accurate. Rev]: comments addressed. 22. The planting plan for the biofilter should be amended. All required plantings should be provided in the bed area. Based on the bed area of the facility, there should be close to 83 trees /shrubs while maintaining a tree to shrub ratio between 2:1 and 3:1. Please adjust the "R -ARA" typo in the lower right corner of the planting detail for the biofilter. Rev]: comments addressed. 23. The minimum pipe size out of the facility is 15 ". [DM] Rev]: comments addressed. 24. A bond amount will be computed by the County when the plans have been approved. Revl: A bond amount will be computed by the County when the plans have been approved. Rev2: A bond amount will be computed by the County when the plans have been approved. 25. Please submit signed copy of the Stormwater Maintenance Agreement and $17 fee to the County. Revl: Please provide easements for the use of the offsite SWM facilities. Rev2: Comment has not been addressed. The Block 2 site plan cannot be approved until a plat is approved showing the stormwater management easement for the pond and all necessary drainage easements. 26. Additional comments may be forthcoming on the next submittal due to the required changes. Rev2: No additional comments appear to be necessary. C. Erosion and Sediment Control Plan 27. Please remove the "Silt Trap to Biofilter Conversion detail ". The detail shown in the Stormwater management sheet is acceptable and another detail does not need to be included in the ESC plan. Rev]: comments addressed. 28. Please provide a soil stockpile area. Revl: The stockpile area is shown in a location of cut (for the underground parking structure). Where will all the excess cut be stockpiled? There does not appear to be enough room onsite as shown. Rev2: To the note in the construction sequence, please add that the offsite location needs to have an approved ESC plan and the ESC inspector needs to be notified. Please update the "Offsite Areas" section of the narrative to include all of this information. 29. Please show the outlet to the sediment trap to scale. Rev]: comments not addressed. Rev2: Comment has been addressed. 30. How is site runoff flowing out of the sediment trap to pass the paved pedestrian path? A method to pass the pedestrian path should be accounted for in the ESC plan. Rev]: comments not addressed. Adequate downstream channels should be provided from the outlet of the sediment trap while the sediment trap is in place. At a minimum, an adequate channel should be provided to the existing ditch below. Rev2: Please specify a diameter to the slope drain. The slope drain should go under the trail so users of the trail do not have an obstacle to avoid. 31. In the construction sequence, please move the biofilter conversion step to the end of the sequence and note the conversion is only authorized by the County Water Protection Inspector. Rev]: comments addressed. 32. Please do not show tree protection fencing within the dripline of trees. On the northern side of the property, it may be best to put the fencing south of the paved pathway. Please note that ARB requirement for tree protection fencing is 5ft from the dripline of a protected tree. Please coordinate ESC with ARB tree conversation plans. Albemarle County Community Development Engineering Review Comments Page 5 of 5 Rev]: comments addressed. 33. Please move the construction entrance into the watershed of the sediment trap and provide a diversion on the northside of the CE direction water into the trap. Rev1: comments addressed. 34. Please replace the silt fence on the western portion of the property with a diversion direction water into the sediment trap. Rev]: comments addressed. 35. A bond amount will be computed by the County when the plans have been approved. Rev]: A bond amount will be computed by the County when the plans have been approved. Rev2: A bond amount will be computed by the County when the plans have been approved. 36. Additional comments may be forthcoming on the next submittal due to the required changes. a. (Revl) Outlet protection in Phase I of the ESC plans is shown outside the limits of disturbance. (Rev2) The temporary slope drain should be included in the limits of disturbance. The slope drain should be placed underneath the paved pedestrian path so as not to disturb use of the path. b. (Revl) Please show a Construction Entrance (CE) and limits of disturbance on phase II of the ESC plans. (Rev2) Comment has been addressed. c. (Rev I) The plans show proposed grading and improvements for Wickham Pond Phase II Block 1 as existing. The proposed ESC plans may not work if construction begins prior to the completion of Block 1. (Rev2) Comment has been acknowledged by the applicant. d. (Revl) The proposed sediment basin is very close in proximity to the construction of the proposed underground parking structure. The plans may need to revised to avoid ESC measures in the way of construction or grading. (Rev2) Comment has not been addressed. The edge of the sediment trap (elevation 538) is located 10ft from the inside wall of the garage. Considering the thickness of the wall section and the depth of the foundation in relation to the elevation of the trap grading, the sediment will be an obstacle during the construction of the garage and should be modified. e. (Rev I) As the proposed buildings and structures are very close to the proposed Wickham Place and Wickham Way and encompass the majority of the back half of the site, construction access and coordination may be required in the right -of -way. If Block 1 is constructed prior to Block 2, cordination may be required to divert traffic through Wickham Pond Phase 1 during the construction of Block 2. (Rev2) Comment has been acknowledged by the applicant. f. (Revl) Please provide adequate channel calculations for the outfall following structure 403 and for the pipe systems from stuctures 127 and 163 to the pond in phase I. [MS -19] (Rev2) Comment has not been addressed. A drainage area map supporting the pipe calculations should be submitted with this MS -19 analysis. Also, no channel calculations for the ditch west of structure 401 were submitted.