Loading...
HomeMy WebLinkAboutSUB201100029 Review Comments Road Plan and Comps. 2011-12-07� 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: Whittington Phase A ESC and Road Plan (WPO- 2011 -00019 & SUB - 2011 - 00029) Plan preparer: Mr. Mike Myers, PE; Dominion Engineering Owner or rep.: Stonehaus Plan received date: 18 March 2011 (plan date 14 September 2007) (Rev. 1) 25 August 2011 (Rev. 2) 7 November 2011 Date of comments: 5 May 2011 (Rev. 1) 10 October 2011 (Rev. 2) 7 December 2011 Reviewer: Phil Custer The second resubmittal of the Road and ESC plans for Whittington Phase A (SUB- 2011 -00029 and WPO- 2011- 00029) received 7 November 2011, has been reviewed. Engineering can approve the plans after the following comments have been addressed. A. General Review 1. In VDOT's review of the plan, the engineer noted that the current layout of this development does not meet VDOT's latest Subdivision Street Acceptance requirements, which requires multiple connections in multiple directions to adjacent parcels and the reconfiguration of internal streets to meet a specific interconnectivity index. Under my current understanding of state law, the applicant/owner is not required to make any modification to the development plan that would require "significant government action ". In this case, a significant government action would be a required action by the Board of Supervisors; a modification subject to the variation procedures outlined in 18- 8.5.5.3 of the County Ordinance would not be significant enough to automatically grandfather the previous road layout. The Zoning Department has informed me that many, if not all, of the road alignment modifications that would allow the development to meet current VDOT acceptance requirements can be varied by the Planning Director and will NOT need to go back to the Board of Supervisors. I will forward an official response from the Zoning Department once I receive it. Please prepare a variation request to the Planning Director to alter the road network to meet VDOT's current acceptance guidelines. I recommend discussing this with county staff and VDOT during one of our Monday afternoon "pre -app" meetings before making any of the alterations to the road plan. (Rev. 1) A variation request has been received by the Planning Department. Once I get a response from the Director of Planning, I will forward it to the applicant. It is my understanding that the requested variations to the road alignment will meet VDOT's acceptance requirements for the subdivision. Official VDOT approval is required. (Rev. 2) The variation has been approved. However, the county is still awaiting VDOT approval. 2. VDOT has also commented on the lack of pedestrian facilities and stated that a sidewalk or path will be needed on at least one side of the streets within this subdivision. I believe Albemarle County Community Development Engineering Review Comments Page 2 of 8 there are provisions in the state code that allow the developer to provide these paths or trails outside of the ROW, but it is unclear what the standard and proximity to lots these paths would need to be. In other words, the primitive trail in the few locations indicated on the application may not be adequate for the replacement of a path parallel to the road. At a minimum, the primitive trail shown on the application plan behind lots 48, 50, and 77 will need to be constructed in this phase. Additional paths around and behind nearly all lots and of an greater standard may be required. All modifications to the trail or road sections will require that a variation be approved by the Planning Department. (Rev. 1) VDOT approval is required. The trail system should connect across road A west of Lot 48 rather than directing pedestrians onto the Loop Road and Road E. (Rev. 2) The trail modification has been made. However, the county is still awaiting VDOT approval. 3. An overlot grading plan must be provided before any subdivision plat is approved. It would benefit all parties if this plan was included in this application so: -all disturbances could be protected with one ESC plan - post - development stormwater management plan and ditch calculations could be based on more accurate estimations of lot disturbance, yards (affecting the hydrologic coefficient, and watershed boundaries The overlot grading plan must include all of the requirements of Proffer 4c -4h. Please also provide more likely estimates for final yard, driveway, and house dimensions. The current estimates are optimistic and will inhibit the house construction process if more disturbance is desired by a builder than what was shown on the grading plan. (Rev. 1) Staff has found the following deficiencies with the overlot grading plan: a. Please provide vertical profiles of the driveways to Lots 49, 50, 52, 53, 54, 56, and 86 so that staff can review whether it's feasible driveways can be graded so undercarriages of vehicles do not scrape the ground. b. The driveway for Lot 54 is steeper than 20 %. c. The requirement stipulated in Proffer 4h seems to not be complied with on several lots. Please show house entrances and walking paths with slopes clearly labeled. (Rev. 2) All previous comments have been addressed. However, in addressing these comments the applicant has added 2:1 slopes throughout the plan. Please either convert these to 3:1 slopes (the county's preference) or specify a low maintenance, non - grassed groundcover over these areas. 4. The lot layout may need to be modified when the subdivision plat is reviewed by a Current Development Planner because it does not match the layout shown on the application plan. (Rev. 1) This comment is to be reviewed with a subdivision plat application. 5. Please number the lots in the same manner as the application plan. (Rev. 1) Comment has been addressed. 6. Lot 82 currently violates proffer 2. (Rev. 1) Comment has been addressed. 7. Please update all note lists with the latest available standard county notes found in the current edition of the design manual, available online. (Rev. 1) Comment has been addressed. 8. Please make sure all critical slopes are shaded. For instance, there is a slope on Lot 1 that changes 8ft vertically in 20ft horizontally. (Rev. 1) Comment has been addressed. 9. The water main is proposed as being constructed now in the alignment of Road A to Albemarle County Community Development Engineering Review Comments Page 3 of 8 nearly the highest elevation of the subdivision. I recommend that the applicant submit this road segment for review by the county and VDOT so the waterline will not need to be adjusted later based on road geometry issues. (Rev. 1) Please forward ACSA approval to county staff. Approval of this set does not constitute county approval of the vertical alignment for this roadway. (Rev. 2) Comment remains unchanged. 10. Is there an existing easement for the offsite sanitary sewer connection? If so, please clearly show its limits and label it with the deedbook and page number. If not, this easement must be recorded prior to issuance of a grading permit or approval of the final subdivision plat. (Rev. 1) Comment has not yet been addressed. (Rev. 2) Comment has been addressed. Easement has been recorded in DB 4099 PG 73. 11. There are solid black squares and rectangles throughout the set containing the ESC and SWM plans that seem to be a graphical error. Additional comments may be necessary on all applications for the areas and proposals obstructed by these shapes. (Rev. 1) Comment has been addressed. 12. In order for the plan to move forward, a variation must also be given by the Planning Director for the modifications shown to the stormwater management plan. Engineering review prefers the stormwater concept shown in the application plan because nearly all of the lots can be treated by the in -line facilities. (Rev. 1) A variation request has been received by the Planning Department. Once I get a response from the Director of Planning, I will forward it to the applicant. (Rev. 2) Comment has been addressed. B. Erosion and Sediment Control Plan Review (WPO- 2011 - 00019) Please provide all state and federal permits for the utility work across the stream on the north end of the property. (Rev. 1) Comment has not been addressed. (Rev. 2) Comment has been addressed. 2. Is the ravine in the area of lots 92 -96 being filled in at this time? If so, please include within the limits of construction, provide adequate access, and design adequate ESC protection measures. If not, please remove all grading indicating construction in this area from all sheets in all sets. (Rev. I) Comment has been addressed. 3. The applicant has indicated that the utility stream crossing will be constructed by damming the stream and diverting flow around in a manmade channel. Please provide the USC symbol at the crossing on the plan and include Plate 3.25 -1 in the construction set. In the detail, please provide the cross - section, liner the contractor is to use, and which side of the stream the diversion is to be constructed on. The cross - section should be designed to pass the two year storm. (Rev. 1) Please provide sizing calculations for the culvert and the diversion channel. (Rev. 2) Dimensions of the culvert and temporary channel are adequate. Please provide a construction entrance off of Singleton Lane in the easement. Otherwise, the diversion channel cannot be constructed without placing another culvert. 4. How is the area north of the stream to be accessed`? If it is to be off of Singleton, please provide a construction entrance. If the stream is to be crossed, please provide the necessary symbol and design of the crossing. (Rev. I) Comment has been addressed. Albemarle County Community Development Engineering Review Comments Page 4 of 8 5. Biofilter 1 must be designed as a sediment trap to treat the 450ft of road until it is stabilized. Diversion dikes flanking on both sides of this sediment trap will be needed. (Rev. 1) This sediment trap must be designed for more than 2.06 acres because its watershed is larger during the first few days of land disturbance and only shrinks to 2.06 acres once final grades are reached. Please increase the size of this trap. Also, a cleanwater diversion is not a state - authorized ESC measure. If the reduction of the watershed adjacent to Lot 48 is necessary, show it as a constructed SCC and provide instant stabilization with sod or riprap from the existing swale on the lot (next to the CWD symbol) to the clearing. Keep the standard diversion to sediment trap I in the plan. Because construction vehicles will need to cross these two conveyances please provide an appropriately sized culvert crossing of the cleanwater SCC and either a culvert crossing for the normal diversion or provide a RWD. (Rev. 2) The plan has been redesigned and a sediment basin added for the entire drainage area. The concept is acceptable and the design of the basin is adequate except for the dimensions of the embankment. Because the top is 509, the embankment is drawn too narrow. Please widen the embankment 6ft. Please also extend the baffle to the southeast so the flow path is actually lengthened. 6. Please provide a diversion on the west side of sediment basin 1 to collect as much of the grading required from with lot 3 as much as possible. This diversion ditch should be kept in place in the post development scenario to treat as much runoff as possible in the SWM facility. The lot facilities may no longer be necessary in Lot 3. (Rev. 1) The diversion has been correctly added, though please design it as an SCC so its permanence is clear. (Rev. 2) Comment has been addressed. 7. The diversion on the east side of sediment basin 2 should be lowered as much as possible and extended to direct as much runoff from Lots 57 and 58 into the basin. This diversion ditch should be kept in place in the post development scenario to treat as much runoff as possible in the SWM facility. The lot facilities may not be necessary for a few of these lots. (Rev. 1) The diversion has been correctly added, though please design it as an SCC so its permanence is clear. (Rev. 2) Comment has been addressed. 8. The details for the sediment basins refer to a RCP anti -vortex and trash rack device but sheet S7 also includes the standard detail from the corrugated metal anti -vortex device. Please replace this detail with an RCP anti -vortex device. Please also include a stage - discharge graph for the top if it differs from Plate 3.14 -8 of VESCH. (Rev. I) Comment has been addressed. Although, I strongly recommend designing the sediment basin so the riser can remain almost untouched when a conversion to the stormwater basin needs to be performed. Currently, the crests of both basin risers are the same in ESC and SWM phases, but the CMP antivortex device would need to be swapped out with an RCP structure. (Note that detail 71E13 incorrectly indicates the riser for SB -I needs to be lowered to convert the facility to a swm facility.) 9. The diameters in detail 8/S7 do not match the design information for either basin in the set and calculations. (Rev. 1) The dewatering orifice for Basin I is too large. The calculation should be based off of geometrics for required volume (h/2< 0.65ft), not provided volume. The resulting diameter should be rounded down, not up. (Rev. 2) Comment has been addressed. Albemarle County Community Development Engineering Review Comments Page 5 of 8 10. There are no sediment control measures for the water line construction work. Since silt fence will likely not be an adequate solution given the existing topography, the applicant should consider constructing the road A grades with this plan and provide sediment basins /traps at the stream buffer edge. I doubt the applicant/contractor would want to fill in the trench completely in areas where it is known that the road will be in cut. (Rev. 1) Comment has not been addressed. Silt fence must not be placed perpendicular to sheet flow. Check dams are not an appropriate settling measure. (Rev. 2) After consultation with other county staff, it has been determined that just silt fence for this area of work is acceptable. However, in the latest submittal the silt fence was placed on the uphill side of the construction in some places. Please modify the plan so the silt fence is proposed in the same location as it was in the August submittal. 11. Will the selective thinning of the landscape buffer require the uprooting of stumps? If so, silt fence will be needed for this work where runoff does not already drain to a sediment basin and the work to the north will need to be shown on an ESC sheet. (Rev. I) Comment has been addressed. Please note that approval of this ESC does not constitute compliance with proffer 8. This proffer will be checked during the review of the plats for this project. 12. The following comments are provided on the adequate channel calculations: (Rev. 1) There are issues with both directions of the adequate channel analysis. I recommend a combination of downstream improvements and redesigning the stormwater facilities to the requirements outlined at the bottom of page 7 (of 35) of the County's Design Manual. a. The downstream adequate channel analysis must be performed using the 24 -hour storm. The rational method is not acceptable. It may be easier to do the SWM detention calculations using the SCS method so the outputs can be used with channel analysis. This routing procedure is also helpful when it comes to adding hydrographs as the project becomes more developed over the years. (Rev. I) Comment has been addressed. b. The analysis must continue until the I% rule is reached. The development area used in the I% calculation must include the acreage of the total development and not just the phase currently being constructed now. (Rev. I) The limits of the study are now acceptable. c. No culverts appear to have been analyzed using the 10 -year storm. Downstream of SWM -1, there appears to be a 15" culvert underneath a driveway and a larger culvert underneath Old Lynchburg Road. On the northside of the property, there is a large culvert underneath Singleton Lane which drains to another large culvert underneath Old Lynchburg Road. More culverts may need to be analyzed base upon where the 1% rule is met. (Rev. 1) Existing culvert 1 must be upgraded. This manmade "channel" is not adequate for the 10 -year discharge from SWM -1. The applicant has noted that the Old Lynchburg Road culverts are not adequate for the 10 -year storm. According to adequate channel law, these VDOT culverts will need to be upgraded or further reductions from the SWM facilities will need to be designed. In past projects, if VDOT hydraulic engineers determine upgrades are not necessary, this MS -19 requirement will not be enforced by the county. Please work with VDOT regarding this matter and copy me on all correspondence with their engineers. d. An analysis of the channel on site between the outlet of SWM -2 and the first northern cross - section is needed. Albemarle County Community Development Engineering Review Comments Page 6 of 8 (Rev. 1) The applicant has correctly shown a new riprapped channel from SWM - 2 to the stream. However, the segment of the stream represented by cross - section B7 experiences a significant, erosive velocity. It is not "well stabilized" and is presently eroding. Without significant upgrades to this channel, SWM -2 must be redesigned to meet the three requirements listed on page 7 (of 35) of the County's Design Manual. e. The longitudinal slopes used in the analysis of the southern channel are too flat. County topography found slopes of 6.66 %, 5.2 %, 8.5 %, and 4.5% between the contours in the channel on the way to the larger stream. (Rev. I) Comment has been addressed. f. Cross - section A4 does not appear to be a designed channel. (Rev. 1) Having walked the downstream channel with the applicant, the selected cross - sections are not indicative of the whole length of the channel from the pond outlet to the stream. There is practically no channel on TMP 90 -42. A culvert was not analyzed on this property either. On TMP 90 -44, the existing flow deltas randomly through a shallow depressed area, across tree trunks and exposed roots. One defined channel is not present. g. What is the permissible velocity for each segment of each channel cross - section? Please use Table 5 -22 of the VESCH. There are many computed velocities that are higher than the values in this table. These channels are not adequate. Channel improvements and/or reductions to 2 -year storm release rates will be necessary. (Rev. 1) Comment has not been addressed. The permissible velocity varies across a channel's cross - section. h. The velocity within the channel varies across its width. Please provide a velocity output for each channel segment of each cross - section. This velocity should be compared with each segment's permissible velocity (see previous comment). (Rev. 1) Comment has not been addressed. Please refer to the county's design manual for more detail on expectations for adequate channel calculations. i. The cross - sections should be labeled on the map. (Rev. I) Comment has been addressed. j. Additional comments may be necessary based on the review of the SWM plan and any issues discovered with the facility routings. (Rev. I) Additional comments after the review of the SWM plan are nW necessary. (Rev. 2) Considering the applicant's analysis of the downstream channels, the proposed upgrade to the channel downstream of SWM -I shown on sheet E6, VDOT's determination that their existing facilities do not need to be updated, and the proposed release rates of the two detention facilities, the county considers MS -19 satisfied. However, it is my understanding that an easement has not yet been recorded for the proposed work on TMP 90 -44. A precedent has been set by the county with the approval of Northtown Center to approve an ESC plan pending downstream easement recordation. If the downstream owner is unwilling to provide these easements, the proposed offsite work is not required. Please add the following note to sheet E6: An easement has not yet been obtained for the work shown on TMP 90 -44. The applicant shall request permission from the downstream property owner upon issuance of the grading permit. If permission is not provided by the downstream property owner within nine months, the offsite work will not be required by the county. Attempts to acquire the downstream easement must be documented. Albemarle County Community Development Engineering Review Comments Page 7 of 8 13. After the plans have been approved, please provide a completed Bond Estimate Request Form to the County Engineer to receive an ESC Bond. (Rev. 1) Comment remains unchanged. (Rev. 2) Comment remains unchanged. C. Road Plan Review (SUB- 2011 - 00029) 1. VDOT approval is required. (Rev. 1) VDOT approval has not yet been received. (Rev. 2) Comment remains unchanged. 2. Please use the full buildout ADT estimates for the design of the pavement cross - sections. For instance, road A will likely have close to 900 vehicles a day travelling on it and Road E will have more through traffic than just the lots shown on this plan. Please update the pavement design based on these new estimates. (Rev. 1) The stronger pavement section of Road E should be extended to Sta. 16 +00. Otherwise, all pavement cross - sections are acceptable. (Rev. 2) Comment has been addressed. 3. The private sanitary sewer laterals across the VDOT roads may be an issue. Please provide confirmation from VDOT that these laterals are acceptable within their ROW. (Rev. 1) This will be reviewed with comment C. I. 4. Please show sight distance triangles at all intersections including the sight distance line looking southwest from the road yet to be built between lot 59 and 86. The crest of Road E may create a problem vertically at this intersection. (Rev. 1) The sight distances on Road E are acceptable. However, the sight distance onto Road A from the Loop Road and Road E should be 280ft based on the design speed of the roadway. (Rev. 2) Comment has been addressed. 5. Please show all street name, stop, and all other necessary traffic control signs. (Rev. 1) Comment has been addressed. 6. The street cross - sections do not match the cross - sections of the approved application plan. Please request a variation to deviate from the approved cross - sections. (Rev. 1) A variation request has been received by the Planning Department. Once I get a response from the Director of Planning, I will forward it to the applicant. (Rev. 2) Comment has been addressed. 7. The median is poorly aligned with the approach of the eastbound lane. The median should be centered on the centerline of the roadway and the south side of the road should be flared similar to the north side so this transition isn't so abrupt. (Rev. I) Comment has been addressed. 8. The ROW should be widened where the median was added so that the clear zone is controlled by VDOT. (Rev. 1) Comment has been addressed. 9. Please label all edge -of- pavement radii at intersections and turnarounds /culdesacs. (Rev. 1) Comment has been addressed. 10. Many more crossdrains are needed throughout the set. At least two CD- ls are needed on the loop road. At least two CD- ls and one CD -2 are needed on Road E. (Rev. 1) Additional crossdrains may be necessary, but I will let VDOT determine whether they are or not. 11. Show all utility line crossings in the drainage profiles. (Rev. 1) The laterals for Lot I may require the storm line to be deeper. I do not believe that the service authority would allow the line between the top of pipe and the surface nor do I believe they would allow the lateral to be placed below the storm line. Please confirm with ACSA that Albemarle County Community Development Engineering Review Comments Page 8 of 8 either of these solutions would be acceptable or design this pipe deeper in the ground so a lateral can pass between the top of pipe and the ground. (Rev. 2) Comment has been addressed. 12. Show outlet protection tables and graphics /details in the road plan set. (Rev. I) Comment has been addressed. 13. Please clearly label the sump and callout its depth at ST -7. (Rev. I) Comment has been addressed. 14. Please provide a summary table for the driveway culverts. It seems most culverts can be 15" in diameter, but some may need to be larger to pass the 10 -year storm. (Rev. I) Comment has been addressed.