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HomeMy WebLinkAboutWPO201100019 Review Comments Erosion Control Plan 2011-04-26� 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 Plan (WPO- 2011 - 00019) Plan preparer: Mr. Mike Myers, PE; Dominion Engineering Owner or rep.: Stonehaus Plan received date: 18 March 2011 (plan date 14 September 2007) Date of comments: 26 April 2011 Reviewer: Phil Custer The first submittal of the ESC Plan for Whittington Phase A (WPO- 2011 - 00019) received 18 March 2011, has been reviewed. The comments from the review of the road and stormwater management plans will be provided at a later date. The general review comment section will be included in the road -swm review letter and comments may be added to it. Engineering can approve the ESC plan 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. 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 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 Albemarle County Community Development Engineering Review Comments Page 2 of 2 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. 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. 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. 5. Please number the lots in the same manner as the application plan. 6. Lot 82 currently violates proffer 2. 7. Please update all note lists with the latest available standard county notes found in the current edition of the design manual, available online. 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. 9. The water main is proposed as being constructed now in the alignment of Road A to 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. 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. 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. B. Erosion and Sediment Control Plan Review (WPO- 2011 - 00019) 1. Please provide all state and federal permits for the utility work across the stream on the north end of the property. 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. 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. 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 Albemarle County Community Development Engineering Review Comments Page 3 of 3 necessary symbol and design of the crossing. 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. 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. 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. 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. 9. The diameters in detail 8/S7 do not match the design information for either basin in the set and calculations. 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. 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. 12. The following comments are provided on the adequate channel calculations: 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. b. The analysis must continue until the 1% rule is reached. The development area used in the 1 % calculation must include the acreage of the total development and not just the phase currently being constructed now. 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. d. An analysis of the channel on site between the outlet of SWM -2 and the first northern cross - section is needed. 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. f. Cross - section A4 does not appear to be a designed channel. 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 Albemarle County Community Development Engineering Review Comments Page 4 of 4 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. 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). i. The cross - sections should be labeled on the map. j. Additional comments may be necessary based on the review of the SWM plan and any issues discovered with the facility routings. 13. After the plans have been approved, please provide a completed Bond Estimate Request Form to the County Engineer to receive an ESC Bond.