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Home My WebLink AboutWPO202000053 Correspondence 2021-02-02® COLLINS ENGINEERING January 29, 2021 Emily Cox Department of Community Development 401 McIntire Road Charlottesville, VA 22902 RE: Pleasant Green Phase ll—VSMP (WP0202000053) 200 GARRETT ST, SUITE K CHARLOTTESVILLE VA 22902 ��434.293.3719 PH 434.293.2813 FX www.coll ns-eng ineeri ng.com Thank you for your comments dated December 23, 2020 on the above referenced project. Please see the detailed responses below describing how the remaining comments were addressed. A. Stormwater Pollution Prevention Plan (SWPPP) 1. An updated registration statement has been inserted into the revised SWPPP. 2. An updated registration statement has been inserted into the revised SWPPP. B. Pollution Prevention Plan (PPP) 1. A PPP specific to phase II has been created and inserted into the revised SWPPP. C. Stormwater Management Plan (SWMP) 1. The previous submittal contained a typographical error where the upper 'Phase III' label should have read 'Phase 11'. The revised plans have corrected this label and the data shown is accurate. 2. Sheet 1's'Generol Note' entitled 'Preserved/Managed Slopes' was updated to address this comment. 3. The FDP Plan number will be provided prior to final approval. It is the applicant's hope that all construction plan - related comments have been addressed with this resubmission and the administrative items outside the scope of the 24N36" construction plan sheets can be provided subsequent to this submission. 4. Sheet 2, in the upper -right portion of the page, has been updated to show the removal of the approved culvert in the vicinity of the existing cul-de-sac if it has been constructed at the time of this plan's construction. 5. Sheet 2 has been updated to include a note that reads 'cemetery shall not be disturbed'. 6. Sheets 8, 9 and 10 have been added to the back of the VSMP plans. A note beneath sheet 1's'Sheet Index Table' has also been added reading 'The grading & drainage plan sheets have been added to this set for informational purposes only. These sheets demonstrate that positive drainage has been provided away from the houses for a minimum o f10'. These sheets also show the top &bottom elevations of the retaining walls. These three excerpts have been taken from the subdivision plan and the final approval of that plan will dedicate the final construction grades.' Per a phone conversation between Ms. Cox and Mr. Murray of Collins Engineering on January 10, this was deemed an acceptable method for addressing this comment. 7. The three areas below the proposed level spreaders were staked in the field on January 2V. Collins Engineering met with County Engineering onsite on January 25th. During this meeting it was determined that the area below Level Spreader 'B'was sufficient for a conservation area/easement, but that the areas below Level Spreaders'C' and 'D' would need to be modified to be vegetated filter strips. Consequently, the plans and calculations have been updated accordingly. 8. Please see the response above to comment C.7. 9. Currently, there are no recorded/existing forest & open space easements located in Pleasant Green Phase II. Collins Engineering forwarded the plat for phase II to County Engineering on January 141h indicating this. Following this e- mail, Collins Engineering met with County Engineering onsite on January 21't, as noted above. This meeting resulted in a change to the SWM plan and a minor loss in water quality credit. To offset this loss, new SWM Forest & Open Easements are now proposed with this plan, located within the limits of Pleasant Green's phase II. Also, in the January 21`t meeting County Engineering advised the applicant the two easements could overlap. Despite this, the applicant cautiously designed the proposed SWM Forest & Open Space easements to be outside the limits of the conserved open space and vegetated filter strips beneath the three level spreaders. 10. The 'Stormwater Management Water Quality Narrative' shown on sheet 16 was updated to address this comment. This plan's SWM strategy was updated to include a Level II wet pond where SWM Facility'B' is located. This revision, coupled with the aforementioned SWM Forest & Open Space Easements, results in a surplus of water quality credit. The surplus will be applied to the Connector Road's VSMP plan. Also, two VRRM analyses were performed. One analysis is shown in the attached calculations to show that the phosphorous removal rates associated with Phases II & III are sufficient for this plan. And the second analysis is shown in the calculations packet, and on sheet 16, demonstrating that the Phases II & III water quality credit is sufficient to cover the impacts from the Connector Road with extra credits in reserve. The result is this plan is no longer dependent upon the approval of the Connector Road VSMP plan (WPO 201900027). Conversely, the Connector Road VSMP plan (WPO 201900027) is now dependent upon this plan's approval. Please also note, the approval of the VUE's amendment #1 to WPO 201600069 is still required prior to the approval of the Connector Road VSMP plan (WPO 201900027), however the approval of Amendment #1 to the VUE is no longer required for this plan's Phases II & III approval. 11. The minimum stormwater quantity requirements set forth in 9VAC25-870-66 are met with this plan. Furthermore, per the January 141h phone conversation noted above it was determined that the outfalls for the larger storm events below SWM facilities'B','C' and'D'should be extended to defined channels to address this comment. As a result, these outfalls have been revised to address this comment. 12. The previous submittal for SWM Facility'D' showed an open-air dry basin that provided stormwater quantity, not stormwater quality, treatment. This plan has been revised to now provide an underground detention system instead of the dry basin. This revision allowed for the removal of the adjacent retaining walls, hereby making this comment no longer applicable. 13. Sheets 8, 9 and 10 have been added to this plan showing the top and bottom elevations of the proposed retaining walls, hereby addressing this comment. D. Erosion and Sediment Control Plan (ESCP) 1. The topography was field verified in November of 2020. Sheet 1's'General Note' under subsection 'Topo & Survey' was updated accordingly. 2. The tree protection fencing is now shown inside the limit of disturbance. 3. The slopes in excess of 3:1 grades are now identified on the plans. These slopes require blanket matting and native steep slope mix are indicated with a cross hatch and BM symbol. 4. Dust control and temporary seeding are now shown in Phase 1. 5. A diversion approximately paralleling the property is now shown and outfalls into Sediment Basin B. Sediment Trap B has been upgraded and renamed to Sediment Basin E (Phase 1&2)/Trap E (Phase 3). This upgrade was a result of additional runoff entering sediment basin/trap E with the shift of the diversion paralleling the property line. The drainage areas to these diversion dikes are now reduced below the 5 acre maximum. Also, ESC phase I was modified to direct the runoff below the cul-de-sac to sediment basin V. This ensures additional runoff will not enter sediment basin 'Cs contributing diversion, and that the diversion's total subarea is below the maximum 5 acre threshold. This receives 2.28 acres of drainage in phase 1. The diversion dike to the west (left) of Sediment Basin C receives 0.88 acres of drainage. The remainder of the 8.12 ac total drainage area to Sediment Basin C reaches the basin directly as overland flow now with slight regrading of the ditch below the cul-de-sac. In Phase 2, the east (right) diversion for Sediment Basin C receives 3.79 acres, while the diversion to the west (left) receives 0.21 acres with a slight change to the overlot intermediate grading. 6. Outlet protection is now provided at the outfalls of any diversion dike exceeding 300 LF. 7. Silt fence is now extended around sediment basin D adjacent to Rambling Brook Lane. 8. McComb Street is now provided inlet protection. 9. The names of the sediment traps and basins are now provided in the sequence on sheet 5. 10. Sediment Trap'A' now outfalls via a riser and barrel system that connects into the existing storm sewer. Per the January 14"' phone conversation between Ms. Cox and Mr. Murray, this was deemed an acceptable method for resolving this comment. 11. The anti -vortex plate is now checked on the trash rack detail. This detail is now shown on 19. E. Mitigation Plan 1. All disturbances in the buffer are now accounted for, including the areas level spreaders. Should you have any questions, please feel free to contact Scott Collins at scott@collins-engineering.com or Graham Murray at ¢raham@collins-eneineerine.com . Sincerely, Graham Murray, PE