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Home My WebLink AboutWPO201300032 Review Comments Erosion Control Plan 2014-06-02�pF A vt�r�1Q COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road, Room 227 Charlottesville, Virginia 22902 -4596 Phone (434) 296 -5832 Fax (434) 972 -4126 Project: Plan preparer: Owner or rep.: Plan received date; Date of comments: Reviewer: Cascadia - WPO Dominion Engineering [434- 979 -8121 ] Cascadia Development, LLC 13 May 2014 30 May 2014 Michelle Roberge Engineering has completed the review of application WP0201300032. A. Erosion & Sediment Control Plan and SWM Plan (WP0201300032) 1) [Comment] The application states Early Grading Permit. For this type of application, there should be no structures shown on this plan. Please clarify how you would like to pursue application. Even though this may be an early grading plan application, I have reviewed plans for E &S and SWM just in case it was a typo on the application. [Revision 11 The title should include "Early Grading Plan." Also, remove all hardscapes: proposed roads, proposed single family homes, proposed sidewalks, etc. This early grading plan should only include E &S control measures and grading for Phase 1 and Phase 2. 2) [Comment] On sheet SW3, please label preserved and managed slopes. [Revision 11 Comment no longer required. The critical slopes are shown on plan. The critical slopes waiver was already approved with the ZMA. At this point there is no need to differentiate managed slopes from preserved slopes. Also, the ZMA was approved prior to the adoption of the new critical slopes section in the ordinance. 3) [Comment] Temporary slope drains are not designed per VESCH standards. Typical designs show a compacted earthen dike to divert runoff to slope drains. Please show. [Revision 11 Comment partially addressed. DDs still need to be shown for TSD draining to SB -2. 4) [Comment] Per meeting on Feb 6, 2014, we discussed revising the existing topography. Please address. A sewerline was installed along northern and eastern portion of the site. We discussed possibly using this road as a means to divert runoff to a sediment trap. [Revision 11 Comment partially addressed. Applicant has not designed sediment traps near the access road (built for the existing sewerline). Sediment traps will need to be designed. Remove the DDs that split the site and size the sediment traps for new drainage areas. Engineering Review Comments Page 2 of 4 5) [Comment] For phase 1 (northern and eastern portion), it will make more sense to have diversion dikes at bottom of slopes to sediment traps. Then grade up the steep slopes. These diversion dike are partially shown for the eastern portion of site. [Revision 11 Comment partially addressed. Diversion dikes are proposed at the bottom of fill slopes, but it appears that the construction of the walls will be required to satisfy the proposed grades on the early grading plan. The retaining walls can only be built if the site plan is approved and at this time it is still under review. Also, as previously mentioned in comment 1, an early grading plan should not show hardscapes. Please clarify how you would like to proceed since an early grading plan will not allow you to construct the walls necessary to grade the eastern portion to the final grades on plan. 6) [Comment] The diversion dikes which splits the site on sheet SW8 and SW 13 does not appear to work for clearing, grubbing and grading. This coincides with comment 4. I suggest removing these diversion dikes and enlarging sediment trap 1. The diversion dikes at the bottom of the slope should be extended for more capture to sediment trap 1. [Revision 11 Comment partially addressed. There is still a diversion dike #3 that splits the site. This will not work as it will be difficult to maintain as the site is being cleared, grubbed and graded. Address with comment 4. 7) [Comment] The challenge is how to address erosion control in Phase 2 once the walls on eastern side are installed. The dd's behind homes will not work. [Revision 11 Comment partially addressed. This is only an early grading plan. The walls need to be built to construct the DDs at the top of the fill slope. See comment 5. 8) [Comment] The temporary slope drains on phase II erosion control on eastern portion will not work. They should outlet into perimeter controls, such as as sediment trap. [Revision 11 Comment partially addressed. Clarify the gravel outlet on SW14 as no sediment shall leave the site. 9) [Comment] S13-1 on calcs appear to be SB -2. Please revise name and note "post condition ". [Revision 11 Comment not addressed. The calcs were not submitted with this submission. Also the SB -1 on calcs should be relabeled to SB -2 post conditions. This submittal should also show the post drainage areas in phase 2 of early grading plan. All design of SB or ST shall be for higher DA of pre and post conditions. 10) [Comment] On SW -5, SB -1 is an existing pond. Please correct label. This should not be used as a sediment pond. What is the benefit of reducing the amount of drainage area to existing pond 1 when both ponds are owned by Dr Hurt. [Revision 11 Comment partially addressed. Before the SCC and ditch (for Fontana development) can be fully functional, final grading will need to be completed. Then ditches will be constructed. I recommend showing a designed berm greater than 18" with SCC to divert water to SB -1 and SB -2 as a perimeter control measure in Phase 1 and Phase 2. SCC to SB -2 can be designed with SWM plan. 11) [Comment] Also, it appears that the ponds proposed does not match the approved ZMA2002 -04 plans. Please clarify. This may have been discussed already while Michael Koslow was the reviewer. [Revision 11 Applicant has stated the proposed pond design has been approved by Engineering Review Comments Page 3 of 4 the ARB. This was previously coordinated with original plan reviewer, Michael Koslow. 12) [Comment] On SW24, the pond labels do not match report. Please revise. [Revision 11 This is an early grading plan. Applicant will revise on SWM plans. 13) [Comment] It appears that the target phosphorous removal is 43 %, not including the future development. Please take the future development into account. The current proposed development shows the retention pond to be sized to treat 4* WQV (Retention Pond II), 275,880 cu -ft. When you add the future development, the BMP choice may change. Page 6 on your report reflects the correct impervious areas, but this is not reflected in removal rate calcs. Please revise removal rate calcs. [Revision 11 This is an early grading plan. Applicant will revise on SWM plans. 14) [Comment] Once 13 is addressed, please meet all three below if site has inadequate channels: a) Detain the WQV (1" runoff) and release over 48 hours. b) Detain the 1 year 24 -hour storm and release over 24 hours. c) Detain and reduce the peak flow for a 1.5, 2 and 10 year 24 -hour storm, to the following level; peak flow <= Qf (Vf/Vpost), where Qf is flow from the site in a well forested condition (C = 0.25, or CN = 51), and Vf is volume from the site in a well forested condition. [Revision 11 This is an early grading plan. Applicant will revise on SWM plans. 15) [Comment] Show detail of emergency spillway. [Revision 11 This is an early grading plan. Applicant will revise on SWM plans. 16) [Comment] It appears that a majority of the eastern portion is untreated. I recommend increasing the size of the biofilter on the north and addressing more treatment on eastern portion of site. [Revision 11 This is an early grading plan. Applicant will revise on SWM plans. 17) [Comment] Please provide SCC calculations. [Revision 11 Comment partially addressed. I recommend a new SCC on western boundary of site in conjunction with proposed DD #8. The velocity was higher than 4 f /s. Please show appropriate grass lining on detail. The proposed ditch on southern boundary should also state acreage on calcs. The velocity was higher than 4 f /s. Please show appropriate grass lining. SCC to SB -2 can be designed with SWM plan. 18) [Comment] All plans and calculations shall be signed, sealed and dated when it is ready to approve. [Revision 11 Comment not addressed. No calcs for E &S has been submitted. Applicant will submit calcs for SWM with appropriate swm plans. New comment 19) On SW -5, one of the new excavated sediment traps is missing. Please add. Engineering Review Comments Page 4 of 4 20) On SW -12, show the silt fence behind the DD. 21) On SW -13, the rip -rap ditch appears to be part of the SWM facility design. Please confirm. This can be shown later with the SWM facility design. Also, please note there is a proposed pedestrian trail crossing this ditch. A culvert should be proposed. 22) DD6 will not work. This splits the site also. I recommend removing DD and sizing excavated sediment trap to work with drainage area. Sincerely, Michelle Roberge