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Home My WebLink AboutWPO201600009 Review Comments WPO VSMP 2018-07-17COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road, Room 227 Charlottesville, Virginia 22902-4596 Phone (434) 296-5832 Fax (434) 972-4126 VSMP Plan review Amendment Project: Old Trail Village Blocks 10, 16, 17, 18 & 30 —SWM Plan Amendment Plan preparer: Jimmy Taggart, PE; Bill Ledbetter —Roudabush, Gale & Associates, Inc. [BLedbettergroudabush.com; JTaggartgroudabush.com ] 914 Monticello Road, Charlottesville, VA 22902 Owner or rep.: March Mountain Properties LLC [1005 Heathercroft Circle, Suite 100] Dave Brockman, dave a,oldtrailvilla eg com Received date: 21 May 2018 (Rev. 1) 12 Jul 2018 (.PDF) Date of comments: 5 Jul 2018 (Rev. 1) 17 Jul 2018 Reviewer: John Anderson SWPPP, ESOP, Mitigation Plans not reviewed with this correspondence —NA (SWM Plan Amendment) WP0201600009 —Amendment to SWM Facility L-3 (Also see Stantec Stormwater Management Design Summary —East Side, Old Trail Village, Rev. 6/27/16 /ne. 4.5: Quantity Compliance Summary. Also, p. 10 of .PDF Attached to this correspondence: Water Quantity Compliance Summary Table, Node ID L3, showing Q2, Qio pre -development =4.71 and 14.32 cfs, respectively.) A. Stormwater Pollution Prevention Plan (SWPPP) —NA B. VSMP: SWPPP: Stormwater Management Plan (WP0201600009) VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a SWMP. This plan is disapproved; please see comments below. The stormwater management plan content requirements can be found in County Code section 17-403. 1. Water Quantity requirements are met: Q2, Q10 pre -development =4.71 and 14.32 cfs, respectively* while Q2, Qio proposed peak developed discharge =1.97 and 11.91 cfs, respectively. * Ref. Stantec Report, rev. 6/27/16, Table 1 p. 4.5 (Also, p. 5 of Attached 6/19/16 SWMP review comments) 2. Water Quality Compliance is met* since the approved bioretention basin and proposed extended detention -enhanced SWM facilities are equivalent at phosphorus removal efficiency. 9VAC25-870-96; Link: httns:Hlis.virginia.gov/cci-bin/leay604.exe?000+ree+9VAC25-870-96 Bioretention basin 50% Bioretention filter 50% Extended detention -enhanced 50% 38-66% Retention basin II (4 x WQ Vol) 50% Infiltration (1 x WQ Vol) 50% *pending additional design review Engineering Review Comments Page 2 of 3 3. Please provide additional (enhanced extended detention) SWM facility detail, including details at least comparable to VSWMH Vol. 1, Min. Std. 3.07, Fig. 3.07-1a and Fig 3.07-1b* and Fig. 12, Stantec Stormwater Master Plan, Old Trail Village, approved April 25, 2016. Level of detail provided on sheets 4 and 5 is insufficient to guide review, construction, or inspection. Please see Attached (Fig. 12). Also, note level of detail provided with Sheet 10, L-3 Bioretention Grading and Layout, Stantec, 5/20/16, included as plan sheet 3 with this submittal. Please reference Stantec (5/20/16) plan and profile (LL=3) for appropriate level of design detail. (Rev. 1) Partially addressed. As follow-up, please see New comments, below. * Link NSWMH: hgps://www.deg.virginia.gov/Portals/O/DEO/Water/Publications/HndbkVolumeI.pdf 4. Minor: a. Riser top elevation, sheet 4 (Outlet #1 /Routing), 636.22 does not match sheet 5 profile. Please reconcile. (Rev. 1) Addressed. b. Sheet 2 and 4, 201.15' 36" RCP is inconsistent with sheet 5 As -built, HDPE. Please reconcile. (Rev, 1) Addressed. 5. With additional design detail for enhanced extended detention, additional comments are possible. New: 1. Sheet 4: Please label floor dimensions, forebay and extended detention. 2. VSWMH, First Edition, 1999, Min. Std. 3.07 guides review, please: a. Provide shallow marsh. Show in plan /profile —adjust design to reflect Min. Std. 3.07 guidance relative to shallow marsh size, depth, plantings, etc. Ref., for example, pg. 3.07-19, pool volume /depth of an extended detention shallow marsh. (Link /Min. Std. 3.07: hM2s://www.deg.vir ig nia.2ov/Portals/O/DEO/Water/PublicationsiHndbkVolumeLpdf ) b. Provide sediment forebay sizing calculation that shows that the sediment forebay is sized to hold 0.25 inches of runoff per impervious acre of contributing drainage area, with an absolute minimum of 0.1 inches per impervious acre. Ref. VSWMH, Min. Std. 3.04, pg. 3.04- 3, Volume. C. Provide fixed, vertical, sediment depth marker for the forebay; show on plans (Ref. VSWMH, Std. 3.04-3 /Maintenance, para. 2). d. Include text below, from Min. Std. 3.04 (pg. 3.04-3) Maintenance, on plans: In general, sediment should be removed from the forebay every 3 to 5 years, or when 6 to 12 inches have accumulated, whichever comes first. To clean the forebay, draining or pumping and a possible temporary partial drawdown of the pool area may be required. Refer to the VESCH, 1992 edition for proper dewatering methods_ e. Provide schematic showing features equivalent to those shown in Fig. 3.07-2a, Enhanced Extended Detention Basin Plan. Marsh features are required; marsh distinguishes Enhanced ED, by definition. f. Provide profile showing features equivalent to those shown in Fig. 3.07-2b, Enhanced Extended Detention Basin —Section. Marsh features are required; marsh distinguishes Enhanced Ex. Detention. g. Reference narrative design information, tables and figures in VSWMH, Min. Std. 3.07; this information guides design, review, inspection and construction. h. Provide liner to prevent infiltration, per pg. 3.07-22, else infiltration may prevent the shallow marsh from holding water. i. Reference buffer zone recommendation, Min. Std. 3.07, pg. 3.07-24. Show on plans, as necessary, via note. j. Add plan note requiring removal of sediment and other debris during conversion of sediment basin to enhanced ED; ref. pg. 3.07-17, 3. k. Reference Inspections, pg. 3.07-28, and include Chapter 3 Appendix annual inspection checklist (Attached to these comments) on the plans (transfer to plans). 1. Also, include maintenance and inspection guidelines, items L-7., Min. Std. 3.01, pg. 3.01-17/18, on plans. 3. Note: Looking ahead to VSMP As -built, please consider and ensure that earthen embankment (already constructed) meets Minimum Std. 3.01, Earthen Embankment requirements with respect to material, core, compaction, inspection, etc. A (geotechnical) inspection report with details of Engineering Review Comments Page 3 of 3 construction is expected, and is a minimum requirement. Min. Std. 3.01, p. 3.01-13, Embankment Construction, states: "A geotechnical or construction inspector should be on site during embankment construction. Inspectors should be required to more than just test fill compaction, i.e., observe foundation preparation, pipe installation, riser construction, filter installation, etc." Albemarle requests construction inspection observations and test results with As -built drawing for enhanced extended detention basin earthen embankment, already constructed. The fact that the embankment is nearly entirely in cut may simplify the task. Note:.PDF preview welcome, prior to print submittal; reviewer out -of -office: AuO—Aug20. C. VSMP: SWPPP: Erosion Control Plan (WP02016-00009) —NA D. Mitigation Plan (WP02016-00009) —NA Engineering plan review staff are available from 2-4 PM on Thursdays, should you require a meeting to discuss this review. Process: Please call to discuss bonding —in interest of sending comments, have not evaluated relative expense of change in Approved BMP. Albemarle will check on this, and Applicant may also want to review previously -approved and bonded SWM facility L-3 to avoid unnecessary or avoidable bond expense, should an enhanced extended detention pond bond amount be less than original SWM facility L-3 bond amount. County forms can be found on the county website forms center under engineering; http://www.albemarle.oriz/deptforms.asp?department=cdengWo Please feel free to call if any questions. Thank you 434.872-4501 —0069 WP0201600009 OTV blocks 10, 16, 17, 18 VSMP Amendment 071718rev1