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Home My WebLink AboutWPO201600009 Approval - County 2018-07-30COUNTY 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.: Received date: (Rev. 1) (Rev. 2) (Rev. 3) Date of comments: (Rev. 1) (Rev. 2) (Rev. 3) Reviewer: VSMP Plan review Amendment Old Trail Village Blocks 10, 16, 17, 18 & 30 —SWM Plan Amendment Jimmy Taggart, PE; Bill Ledbetter —Roudabush, Gale & Associates, Inc. [BLedbettergroudabush.com; JTaggartgroudabush.com ] 914 Monticello Road, Charlottesville, VA 22902 March Mountain Properties LLC [1005 Heathercroft Circle, Suite 100] Dave Brockman, dave a oldtrailvilla eg com 21 May 2018 12 Jul 2018 (.PDF) 24 Jul 2018 (.PDF) 30 Jul 2018 (.PDF) 5 Jul 2018 17 Jul 2018 28 Jul 2018 30 Jul 2018 Approved 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 /pg. 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 approved. 1. Water Quantity requirements are met: Q2, Qlo 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: htips:Hlis.vireinia.cov/cci-bin/legp6O4.exe?000+ree+9VAC25-870-96 ) Engineering Review Comments Page 2 of 3 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 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 (L3) for appropriate level of design detail. (Rev. 1) Partially addressed. As follow-up, please see New comments, below. * Link NSWMH: https://www.deq.vir ig nia.gov/Portals/O/DEQ/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. (Rev. 2) Partially addressed. As follow-up, please label floor dimensions to aid construction inspection. (Rev. 3) Addressed. 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. (Rev. 2) Addressed. (Link /Min. Std. 3.07: https://www.deq.virginia.gov/Portals/0/DEO/Water/Publications/HndbkVolumeLpdf ) 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. (Rev. 2) Addressed. As follow-up: Please compare weir elevation (633') with sediment forebay stage storage data: if 3,349 CF required at elevation < 633', capacity of forebay appears insufficient. Please revise, or call if review comment an oversight error. VSWMH First Edit. 1999, Fig. 3.04-2 appears to indicate weir volume /capacity tied to weir elevation. (Rev. 3) Addressed. ►11 SEDIMENT FOREBAY STAGE STORAGE Elev(Fq-- aS lCFl 631.000 0.000 632-000 410.206 634.000 1825.670 636.000 7660.118 REQUIRED: 3,349 CIF AVAJLABLE: 4.743 CIF C. Provide fixed, vertical, sediment depth marker for the forebay; show on plans (Ref. VSWMH, Std. 3.04-3 /Maintenance, para. 2). (Rev. 2) Addressed. d. Include text hele, from Min. Std. 3.04 (pg. 3.04-3) Maintenance, on plans: (Rev. 2) Addressed. 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. (Rev. 2) Addressed. f. Provide profile showing features equivalent to those shown in Fig. 3.07-2b, Enhanced Engineering Review Comments Page 3 of 3 Extended Detention Basin —Section. Marsh features are required; marsh distinguishes Enhanced Ex. Detention. (Rev. 2) Addressed. g. Reference narrative design information, tables and figures in VSWMH, Min. Std. 3.07; this information guides design, review, inspection and construction. (Rev. 2) Addressed. h. Provide liner to prevent infiltration, per pg. 3.07-22, else infiltration may prevent the shallow marsh from holding water. (Rev. 2) Addressed. Applicant response: a note has been added to state that a geotechnical engineer must test the area for determining the necessity of a geosynthetic pond liner in the marsh design area. i. Reference buffer zone recommendation, Min. Std. 3.07, pg. 3.07-24. Show on plans, as necessary, via note. (Rev. 2) Addressed. 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. (Rev. 2) Addressed. 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). (Rev. 2) Addressed. 1. Also, include maintenance and inspection guidelines, items L-7., Min. Std. 3.01, pg. 3.01-17/18, on plans. (Rev. 2) Addressed. 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 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. (Rev. 2) Addressed. Applicant acknowledges; All geotech reports relative to the construction of the embankmentibasin parameters will be submitted with the as - built drawing. C. VSMP: SWPPP: Erosion Control Plan (WP02016-00009) —NA D. Mitigation Plan (WP02016-00009) NA Process: Now approved, please call if March Mountain wishes to adjust existing SWM Plan bond amount. Albemarle accepts current amount as a relatively reasonable estimate of expense to construct revised SWM facility, but Applicant may wish to review previously -approved and bonded SWM facility (L-3) to avoid unnecessary avoidable bond expense, should enhanced extended detention pond bond amount appear to be less than the original SWM facility L3 bond amount. County forms can be found on the county website forms center under engineering; http://www.albemarle.org/deptforms.asp?department=cdeng)Uo Please feel free to call if any questions. Thank you 434.872-4501 —0069 WP0201600009—OTV blocks 10, 16, 17, 18—VSMP_Amendment 073018approv