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HomeMy WebLinkAboutWPO202100063 Review Comments WPO VSMP 2022-12-10t� OF ALB County of Albemarle COMMUNITY DEVELOPMENT DEPARTMENT ��BGIN�Q' VSNIP Permit Plan Review 401 McIntire Road, North Wing Charlottesville, VA 22902-4579 Telephone: 434-296-5832 WWW.ALBEMARLE.ORG Project title: Dunlora Village (Farm) VSMP & SWM Plan Project: WPO2021-00063 Plan preparer: Chris Mulligan, PE — Roudabush, Gale & Assoc., Inc. 999 Second Street, SE, Suite 201 Charlottesville, VA 22902 cmulligan(a),,roudabush.com 440 Premier Circle, Suite 200, Charlottesville, VA 22901 Owner /Applicant: E. L. Phillips and Ann P. Phillips Liv. Trust, etal C/O Caroline Molina -Ray 6704 Menchaca Road, Unit 33, Austin TX, 78745 Applicant: Southern Development Homes, 142 South Pantops Dr. Charlottesville, VA 22911 charlesa(a),southem-development.com Plan received date: 8 Nov 2021 (Rev. 1) 6 Dec 2021 (Rev. 2) 20 May 2022 (Rev. 3) 28 Oct 2022 Date of comments: 18 Nov 2021, QC -denied /email sent November 18, 2021 4:25 PM (Rev. 1) 30 Dec 2021 (Rev. 2) 29 jun 2022 30 Jun 2022 5 edit corrections /Minor) (Rev. 3) 10 Dec 2022 Reviewer: John Anderson, PE County Code section 17-410 and Virginia Code §62.1-44.15:34 requires the VSNIP authority to act on any VSMP permit by issuing a project approval or denial. This project is denied for reasons listed below. The VSNIP application content requirements can be found in County Code section 17-401. Recommend virtual (or in -person) meeting to discuss SWM and ESC plan design. Further submittal based on surface sand filter concept is likely unworkable. A. Stormwater Pollution Prevention Plan (SWPPP) The SWPPP content requirements can be found in County Code section 17-405. A SWPPP must contain (1) a PPP, (2) an ESCP, (3) a SWMP, and (4) any TMDL measures necessary. SWPPP 1. Please ensure SWPPP cover includes reference to WP02021-00063. (Rev. 2) Not Addressed, but county approval stamp will identify project. No follow-up required. (SWPPP will be approved once all plan revisions complete, and SWPPP I I" x 17" ESC/SWM plan sheet inserts are revised, as needed). (Rev. 3) Persists. Once plan revisions address review comments, please update SWPPP with I I" x 17" plan sheet inserts, including PPP Exhibit. 2. Submit SWPPP using county template located at: (Rev. 2) All other SWPPP review comments addressed. [remaining 30-Dec comments removed.] B. Pollution Prevention Plan (PPP) —see SWPPP item 2.b., above (Rev. 2) Addressed. The PPP content requirements can be found in County Code section 17-404. C. Stormwater Management Plan (SWMP) Engineering Review Comments Page 2 of 15 VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a SWMP. This plan is disapproved for reasons listed below. The stormwater management plan content requirements can be found in County Code section 17-403. [ Items 1: 9.: 3/9/22 email, Albemarle to RGA — see Additional review detail.] 1. Please provide a separate VaRRM.xls for phased development indicating (by phase lines, and calculations) that minimums (forest -open space easement) shown on plans are sufficient. Sheet 2 lists Ph I, II, III, IV (4.0, 4.0, 4.0, 2.5 Ac.). (Rev. 3) Comment discussed with Applicant / withdrawn. As follow-up, please note that FOS Easement Areas =sufficient (proportional to post-dev impervious area, as possible approach) should be recorded with each platted subdivision phase. Applicant appears to acknowledge circumstance and requirement. 2. Engineering evaluates filtering practices in comparison with VA DEQ Stormwater Design Specification No. 12 (strict evaluation against): a. Maximum contributing CDA of 5 Ac. for surface sand filters, and a maximum CDA of 2 Ac. (recommended for perimeter or underground filters). Revise design per Spec. 12. Applicant response (5/12/22 letter): `Plunge pools and demising walls have been introduced to reduce the maximum drainage area to under 5 acres to each filtration bed.' As ollow-up: 5 Ac. CDA is a design maximum for a surface sand filter. Please revise design. —Also, see Additional review detail. (Rev. 3) Addressed. b. Please note that "filters have been used on larger drainage areas in the past, but greater clogging problems have typically resulted." VA DEQ Tech Spec No. 12,1). 4. (Rev. 2) Reminder. (Rev. 3) NA -Addressed. Item 2.a. above. c. Soil testing requirements: Ref. 6.2, Soil testing requirements, p. BMP specification No. 12. (Rev. 2) Persists. Applicant: `Soil testing will be provided as available.' (Rev. 3) Persists. Design depends on SWM B', `C', `D' (sand filters). Provide test results and summary evaluation with next plan submittal if sand filters continue, central to design. Plan cannot be approved absent soil test data to establish the water table and bedrock elevations and evaluate soil suitability. d. Overall si_n,5 requirem, ;its, Ref 6.1. — see Additional rer, � (Rev. 3) Addressed. Volume and surface areas of Filters provided. e. Depth to water table and bedrock, Ref. p. 4. — see Additional review detail. (Rev. 3) Persists. See item c., above. f. 7.3, Steep Terrain, several key design criteria, including (p. 11): — see Additional review detail. g. 7.4, Cold climate and winter performance (p. 11). — see Additional review detail. h. 6.5, Filter media and surface cover, Impervious drainage area: — see Additional review detail. (Rev. 3) Addressed. Discussed with Applicant. Practice allowed with pervious contributing DA. i. 6.4, Conveyance and overflow (p. 8): — see Additional review detail. (Rev. 3) Not addressed. Clarify /discuss design that addresses VA DEQ Stormwater Design Specification No. 12, 6_4, which reads, in part: `Most filtering practices are designed as off-line systems so that all flows enter the filter storage chamber until it reaches capacity, at which point larger flows are then diverted or bypassed around the filter to an outlet chamber and are not treated. Runoff from larger storm events should be bypassed using an overflow structure or a flow splitter.' As ollow-up: Provide small-scale plan /profile details of overflow structure, flow splitter, etc. for each filter. 3. It is unclear if filtering practices with associated upslope forebays and distilling ponds are capable of meeting energy balance at release points to natural conveyances: (Rev. 3) Not addressed. Applicant: `Point of Analysis for each concentrated outfall is summarized on Outfall Compliance Sheet.' Asfollow- up: Current plan and lack of comprehensive calculation packet do not address comments in a meaningful way. Response to this or other comments requesting comprehensive approach to calcs./compliance narrative appears to be table titled `Stormwater Outfill Point of Analysis' on sheet 15, reproduced, below. This table appears to be sole response to prior comments on topic of energy balance for each outfill, request for combined calculation packet, calculations for flood protection, analysis to limits of analysis, and discrete ELS design. Engineering is unable to evaluate revised plan, absent detailed calculations that correlate design features, discharge points, points of analysis, and SWM facilities with state stormwater quality and quantity requirements, and struggles for more helpful language to guide revisions or to direct attention to requirements listed at 9VAC25-870-66. Comments persist. Engineering Review Comments Page 3 of 15 Stormwater Outfall Point of Analysis Location Pre -Developed Events Post -Developed Events l year 2year 10year Iyear 2year 10year POA#1 4.45 9.18 27.7 2.45 12.1 48 80%Reduction SWM A diverted to ELS#1 POA#2 1.36 2.98 9.57 Minimal DA-Preserved FOS POA#3 4.21 7.63 20.3 3.37 4.79 18.3 80%Reduction POA#4 3.5 7.61 23.9 2.87 4.22 7.13 80%Reduction POA#5 0.49 1.07 3.43 Minimal DA-Preserved FOS POA#6 0.58 1.23 3.76 Minimal DA-Preserved FOS POA#7 4.35 9.66 31.9 2.87 4.22 11.1 80%Reduction POA#8 0.35 0.71 2.13 Minimal DA-Preserved FOS a. Each discharge to a natural channel or terrain feature is required to meet 9VAC25-870-66.B.3, Energy balance. (Rev. 2) Partially addressed. Applicant: `Shown for each concentrated outfall proposed. In addition, all capturable sheet -flow is to be directed to the SWM devices. Perimeter terrain offers some limitations to achieving this goal, and is depicted on the Outfall Summary Sheet.' As follow-up: i. A combined calculation packet with water quality /quantity tabulated Qj_n data for each of the 8 outfalls depicted, with narrative (numeric /summary) information is required. Initial submittal included a series of individual routings. Please combine individual routings to create a single calculation packet with compliance narrative for each outfall. ii. Provide /show (in calc. packet) energy balance equation for each outfall to a natural receiving stream using equation listed at state administrative code 9VAC25-870-66.B.3. iii. Provide calculations for flood protection for each outfall, ref. 9VAC25-870-66.C. (Rev. 3) Not addressed. Applicant: `Summarized on Outfall Compliance Sheet, correspondence with the calculation packet was improvedFlabeled and numbered to coordinate with plan references.' Asfollow-up: If correspondence with calculation packet was submitted, please notify plan reviewer immediately. Items received 10/28/22: VSMP /WPO application, SWM Forest and Open Space Easement Exhibit d. 9/28/22' 8- pg. comment response, 10/20/22, 28-sheet revised WO plan, 10/28/22, and transmittal, 10/28/22, image, below: Ouantty Descri lion ➢ Revised WPO Plan ➢ WPO plication Comme County ➢ HydroCAD Reports ➢ ediment Basi i n Forms Information included _ilxnp packagex ➢ VRRM Spreadsheet As Comments: r� t� Items submitted 10/28 listed, below. It's possible that the digital file VSMP Combined Documents was mistakenly a copy of the VSMP-WPO plan, since when we open this file, it is the 28-sheet plan. RGA may have intended to submit a single combined calculation packet, but it was not received. Given extent of comments relating to calculations, Engineering will make every effort to comment within 3-weeks of receipt of comments and next plan revision submittal, but this depends on work demands at the time these items are received. Engineering Review Comments Page 4 of 15 Name WPO202100063 Resubmission Form 10/28/2022 WPO202100063 Resubmission FOREST OPEN SPACE EXHIBIT-20221026 '® WPO202100063 Resubmission Dunlora VSMP Combined Documents WPO202100063 Resubmission Dunlora Village_WPO Application_28Oct22 WPO202100063 Resubmission Dunlora Village VSMP WPO202100063 Resubmission Albemarle Co. Transmittal WPO202100063 Resubmission Alb Co3rd Round CRL iv. Perform analysis to limits of analysis (9VAC25-870-66.B.4 /9VAC25-870-66.C.3.). v. Sheet 12 depicts a series of Level Spreaders (ELS); for each ELS: (Rev. 3) Partially addressed. As follow-up: Please see initial review, 3.a.v.1.2., below. Also please see New items beginning with SWM Plan item 11. below. 1. Provide discrete design: plan /profile (at a scale small enough to discern detail). 2. Reference ELS design criteria at VA DEQ Storrnwater Design Specification No. 2, Sheet Flow to Filter or Open Space, Table 2.2. b. Can RGA provide detail or at a conceptual outline of how proposed SWM concept meets energy balance at each discharge point? (Rev. 2) Persists. Applicant: `Runoff Reduction Calculations including pre/post mapping provided with this submittal.' Unless overlooked, calculations (single document) not attached to May submittal. Please see item 3.a. for information requested. (Rev. 3) Partially addressed. Applicant: `Overall site shown w/ outfall locations & stormwater runoff labels to support routings, design and runoff reduction requirements. SWM Compliance sheet compares the preceding Pre & Post independent analysis sheets for concentrated runoff not controlled by an ELS.' This potion of Applicant response may relate to material contained in a combined calculation packet. If so, material will be reviewed when a combined calc. packet is received. As follow-up: Please see Rev. 3 comments, elsewhere, above and below. c. — see Additional review detail. d. — see Additional review detail. 4. Given BMP design criteria, Engineering evaluates concept plan (as presented): —see Additional review detail. a. Likely requires adjustment /concept revision to ensure compliance with: — see Additional review detail. i. Max. CDA ii. Impervious CDA iii. Steep terrain design criteria iv. SWM quality /quantity requirements (likely not met with limited number of filtering devices proposed) v. Note: Numerous, smaller, strategically placed filtering practices may be required. vi. Engineering cannot approve, per ordinance (17-408.C.2.), BMP design that does not attain BMP Clearinghouse Website design criteria. Design that deviates from BMP Clearinghouse design criteria is an unapproved BMP (design). vii. — see Additional review detail. 5. — see Additional review detail. As follow-up: Engineering anticipates FOS easement will be proposed with phased final subdivision plats. Also, related comments, elsewhere. (Rev. 3) Duplicate. See item 1., p. 2, above. 6. Rooftop runoff not captured /conveyed to SWM facilities: SWM /WPO plan design (and later, independent homebuilders) may not propose release of concentrated downspout runoff to fill or cut slopes (Ref. 18- 4.3.3.C.4). (Rev. 2) Persists. Applicant: `Noted in plans. Physically capturable rear yard drainage is being directed via rear yard swales toward stormwater inlets of facilities.' As follow-up: ... Proposed grading (unless overlooked) does not clearly define Swale conveyance to stormwater inlets of facilities. Sheet 17 includes detail titled sheet flow measure-uncaptured, non-SWMareas with caption that reads `Note: Utilize measure as necessary or required to prevent re -concentration of runoff from adjacent impervious surfaces. Rear yards shall be directed to an approved SWM facility when possible. Engineering Review Comments Page 5 of 15 Concentrated runoff leaving the rear yard toward steep slopes without sheet -flow management or storm - water management controls is prohibited.' Sheet 17 note that reflects ordinance requirement/s, prohibition, measures as needed, while helpful, lacks detail required to prevent rooftop runoff (concentrated storm runoff) release without capture /treatment. (Rev. 3) Persists. Applicant: `Rear yard swales have been designed to capture and convey all disturbed areas to either a SWM facility or a concentrated runoff location defined by a specific POA. Uncontrolled runoff to POA locations are controlled via Outlet Protection since contributing area or runoff is reduced from pre -developed conditions.' Surface runoff may not cross more than 3 lot lines. Swales across yards are likely to be removed by homeowners and are not anticipated to persist /function in any practical capacity once homes are occupied. Also, item 5.c., below. 7. Please exercise caution when representing uncollected runoff as sheet flow, in post -developed condition, for example: rooftop runoff requires transition to sheet flow, if not conveyed to a dedicated SWM facility. (Rev. 2) Persists. Applicant: `Since the uncollected runoff areas were not included /treated as a portion of the necessary stormwater compliance strategy, areas of concentration are being directed to Level Spreaders, so as to achieve sheet -flow. Smaller, more remote and uncapturable areas —due to terrain constraints —shall have graded yards to initiate the sheet -flow conditions.' As follow-up: Please see comments related to ELS, elsewhere. (Rev. 3) Persists. Applicant: `Revised rear yards to capture & convey all impervious runoff from exiting the disturbed area onto steep slopes and have been directed with ditches to controlled outfall (POA locations) or storm sewer inlets and treated and detained to meet runoff requirements.' See item 7. above. 8. Items above relate to compliant filtering practice design (Engineering evaluates against BMP specifications), compliance with 9VAC25-870-66.B.3, and 9VAC205-870-69. 9. Additional comment may be possible with additional detail. (Rev. 3) Additional comments possible with additional detail. best, J. Anderson [ Items 1: 10., below, based upon 30-Dec 2021 review comments —Also, see Additional review detail.] 1. General (Rev. 2, 3) Items below persist. a. Provide access easement to each permanent SWM facility. (Rev. 3) Not addressed. For example, Sheet 15 does not show vehicular access for SWM facilities in series, or to ELS at lower elevation. Provide vehicular access to all SWM facilities. Please see ACDSM p. 12, Best Management Practices for Storrnwater Management. b. Provide easement for each SWM facility. (Rev. 3) Partially addressed. As follow-up: Please label Var width SWM easement, SWM `E,' Sheet 19. Also, wherever SWM discharges to pipe to ELS, extend SWM easement to include ELSs at lower elevations since ELSs provide element of SWM control. c. Provide forest -open space easement. (Rev. 3) Partially addressed via Exhibit d. 9/28/22. As ollow-up: Revise sheet 15 and sheets as needed to include proposed FOS linework. The exhibit is an overall depiction that does not allow comparison with design elements. For example: Exhibit v. sheet 15, there is no linework on sheet 15 to match the proposed limits of FOS easement shown on the Exhibit. Plans should depict proposed FOS. Exhibit is helpful but additional plan detail is required to evaluate possibility and practicality of broad extent of FOS proposed. Exhibit, 9/28/22 (except) v. sheet 15: Engineering Review Comments Page 6 of 15 Sheet 15 4131-5770 0both • opm=z»: o",poq I 0000l=nan. � � I 2. OI101•v25dv 1 OItO]I.20.Otiv vast-Ma[pv By-vax I 061 .9®cls I � ooml-ssln. I \ON.IRI m.ari FOREST -PRESERVED OPEN SPACE -SEE EXHIBIT 'NO LAND DISTURBANCE s 1 PERMITTED' ,a\.... DA=18.5 AC (SITE TOTAL) _ i w-za b. 1 / OIII-IID W� 1 om •em n. 1 y � 161 = — OIO]I-155Cp 1 1 5 1 1 (` 2) Engineered Level Sureader d. Provide public drainage easement downstream of SWM facilities to the point discharge reaches a natural receiving stream, or to the property line [see 14428]. (Rev. 3) May persist. Please direct reviewer to plan sheet that depicts and labels public drainage easement downstream of SWM. e. Note: Easements La, b, e, d may be recorded with a final subdivision plat. Off -site easement (or written agreement) needed to construct /maintain temporary ESC measures, sediment basins or Engineering Review Comments Page 7 of 15 outfalls, for example, must be recorded (or copy of the written agreement provided to county) prior to WPO plan approval. f. Nutrient credit purchase is required prior to receiving a grading permit, but is not required for WPO plan approval. 2. Provide Calculation packet: (Rev. 2) May persist. — see Additional review detail. (Rev. 3) Items a, b, e, below, persist. Applicant: `Routings are now easier to follow as of software upgrade/reorganized/named/ sequenced.' Asfollow-up: Please see comments concerning missing calc. packet, item. 3. p. 2. Also, item e. discussed briefly /tel. Sheet runoff should be depicted /shown graphically or discussed narratively either in Calc. packet or on the plan. Please direct reviewer to plan or calculation design narrative or depiction of post-dev sheet runoff, including consideration of whether post-dev sheet flow contributes to down -gradient erosion, or flooding. 9VAC25-870-66.D. lists important design and review considerations, vis-a-vis post - developed sheet flow. A calculation packet (single .PDF document) that includes analytic values, compliance values, tables, and narrative correlated to plan —to individual SWM facilities, pre- /post-dev maps, storm culvert design tables, etc. —is essential to review /plan approval. We believe it may have inadvertently not been submitted with other items. See item 3., p. 2, above. a. Combine multiple routing documents submitted 12/6/21 into a single document. (Rev. 3) Not addressed. Also, item 3. p. 2, above. b. Provide stormwater quantity and quality narrative that indicates compliance for overall development, and at each discharge point. (Rev. 2) Persists. (Rev. 3) Not addressed. Calc. packet is logical location to present point discharge compliance narrative. c. — see Additional review detail. (Rev. 2) Addressed. d. Include VaRRM.xls. (Rev. 2) Partially addressed. As follow-up: Comments elsewhere request VaRRM.x1s to show post -developed forested condition for phased development, with minimum post -development land cover (forest) values that correspond with intent to develop Dunlora Village in phases. These min. values are likely to be 4,4,4,2.5 Ac. for Phases I, II, III, and IV. (Rev. 3) Addressed. Exhibit d. 9/28/22 depicts forest & open space areas totaling 18.5 Ac. Additional comments possible once a single -document Calc. packet with VRRM.xls is submitted. e. Discuss runoff where plan indicates post -developed condition is sheet flow. Please note requirements for sheet flow analysis at 9VAC25-870-66.D. (Rev. 2) Persists. Also, seefollow-up at (email) review items 3.a.v., and 6., above. — see Additional review detail. (Rev. 3) Persists. D. Increased volumes of sheet flow resulting from pervious or disconnected impervious areas, or from physical spreading of concentrated flow through level spreaders, must be identified and evaluated for potential impacts on down -gradient properties or resources. Increased volumes of sheet flow that will cause or contribute to erosion, sedimentation, or flooding of down gradient properties or resources shall be diverted to a stormwater management facility or a stormwater conveyance system that conveys the runoff without causing down - gradient erosion, sedimentation, or flooding. If all runoff from the site is sheet flow and the conditions of this subsection are met, no further water quantity controls are required. €. T-rans€et Sheet 16 uting-da•ohe Caluula4ion packet. Rev. 2) Persists. g. — see Additional review detail. (Rev. 2) Withdrawn. Ref. email to RGA, June 24, 2022 8:25 AM. h. Revise VaRRM.xls to reflect post -developed forest -open space land cover available to be placed in permanent deeded easement, that meets DEQ concept of FOS. (Rev. 2) Persists. Please see comment request for individual VaRRM.xls tied to each phased plat, since plan indicates a minimum area to be platted as FOS easement, with each of (the 4) final subdivision plats. 3. —see Additional review detail -(Rev. 2) Addressed, also, see 3/9/22 email section, above. 4. — see Additional review detail. (Rev. 2) Withdrawn —Engineering accepts design is consistent with Steep Slopes Exhibit, 5. Sheet 40 (Rev. 3) Sheet 11 a. —see Additional review detail. (Rev. 2) Withdrawn. See item 2.g., this page. b. Please label lots. (Rev. 2) Persists. (Rev. 3) Persists. Applicant: `Overall Phasing & Lot #'s provided.' As follow-up: Please direct reviewer to sheet depicting overall phasing and lot #s. c. Show roof leader line runoff discharge to stormwater conveyance system. — see Additional review detail. Please ref. email review item 7. above, for follow-up comments. (Rev. 3) Not addressed. Engineering Review Comments Page 8 of 15 Applicant: `Rear yard ditches were implemented to provide full capture of impervious surface and conveyance to managed outfall locations.' As follow-up: Proposed storm ditches on sheet 11 close to rear of structures must be abandoned as a design strategy. Policy disallows overland runoff that crosses more than 3 lots. Drainage Plan Checklistfor plan reviewers: `Provisions and easements for drainage across 3 or more lots. Dense development where fencing, decking, etc is expected should provide yard inlets and pipes in easements, rather than ditches' — Please revise design to provide yard inlet -pipe capture /conveyance with next submittal to limit cross -lot drainage to 3 or fewer lots. Yard inlets with 6"-8"42" HDPE pipe conveyance are common in comparable residential developments. d. Label SWM facilities. (Rev. 2) Partially addressed. As follow- Please review plan sheets that display SWM facility design, and ensure facilities are labeled in plan view: SWM `A', B', etc. (Rev. 3) Partially addressed. Please ensure each SWM facility is identified on Sheet 15, for example, SWM-1 near N property boundary does not appear to be labeled. e. At each SWM facility outfall, indicate discharge is to an adequate receiving channel. SWM facility discharge must be to an adequate receiving channel. (Rev. 2) Persists. Please ref email review item 3.a.iii-iv. above, for follow-up comments. (Rev. 3) Persists. Applicant: `See Sheet 12, Stormwater Compliance & Sheet 11 Post-Dev DA Map.' As follow-up: Sheet 11 and 12 do not provide analysis of adequate channel: ability to convey Q2-n without erosion, Qjo-n Vol. (CFS) within receiving channel. Provide (or direct reviewer) to adequate channel analysis. Sheet 15 table, Stormwater Outfall Point ofAnalysis lists POA#1-POA#8, with values that likely correlate to calc. packet routings. Cannot evaluate without Calc. packet. Also, unclear if 2-yr values are Vel. or Vol. Request narrative to interpret `80% reduction' label. Given gap in ability to review, recommend we schedule meeting to discuss review comments in detail to shorten time to plan approval. f. All SWM facilities appear to discharge to natural terrain. Provide energy balance equations for each SWM facility discharge to natural terrain. Also, please see Calculation packet comment, below. (Rev. 2) Persists. Please ref email review item 3.a./3.a.ii., above, for follow-up comments. (Rev. 3) Persists. Applicant: `See sheet 12, Stormwater Compliance.' As follow-up: Please see Rev. 3 comments concerning calc. packet. g. Delineate Forest /Open Space Easement for SWM purposes. (Rev. 2) Partially addressed. Please ref. item 2.d. this page, for follow-up comments. (Rev. 3) Partially addressed. See item l.c. p. 5, above. h. —see Additional review detail. (Rev. 2) Addressed. 6. Sheets 12-15 (Rev. 2) Partially addressed. Please see email item 2_i., above, for follow-up comments. a. Label primary spillway outfall elevation on profile. b. Label primary spillway pipe type, length, slope, INV IN/OUT on profile 7.— see Additional rer1. 11.2)Addressed. 8. — see Additional review detail. (Rev. 2) Addressed. 9. — see Additional review detail. (Rev. 2) Addressed. Ref. sheet 17. 10. — see Additional review detail. (Rev. 2) Addressed. New (Rev. 3) 11. Sheet 26 a. STRM 214 — ELS#3 profile: Revise retaining wall per 18-4.3.3.A.1. 10' Max. ht., retaining walls. b. Str. 210 or other structure with INV IN — INV OUT >4.0', provide V2" steel plate in floor of MH /Str. c. Provide ELS #3 profile: label elements of design, critical elevations, and dimensions (L xW xD). Ref sheet 25 Hemico County Environmental Program Manual 9.01-3 for type information to present with ELS #3 PROFILE. d. Label outfall protection (riprap): CI./size; L x W x D, unless detail provided on separate sheet. e. Provide vehicular access to ELS #3 and energy dissipator below retaining wall. Future maintenance may require material /equipment access, foot trail or no access are inadequate. f. Grading at top of retaining concentrates runoff in swales, as it should. Provide grate inlet /pipe conveyance for this runoff, at low point in swales. Swale may not release runoff across top of Engineering Review Comments Page 9 of 15 wall. Depict swale-structure connection of TW swales with Str. 210 in plan and profile views. See Str. 214 a typ. grate likely suitable for swale collection. g. Provide lintel design detail for 15" HDPE at thru-wall penetration, provide plan view label ref to lintel detail. Ensure HDPE thru wall is shielded from vertical or lateral displacement or force at this location. h. Provide LD-229 storm drain design computations, or direct reviewer to location of culv. table. 12. Sheet25 a. Provide ELS 92 profile: label elements of design, critical elevations, and dimensions (L xW xD). Also, see item 1 l.c. above. b. Show pipe in ELS detail, with adequate cover for pipe and proper end section (ES). Label ES. c. Detail title is `SWM A -Level 1 Extended Detention, by-pass and Engineered Level Spreader #1, but other references are to ELS#2. Please revise ref. as needed, for clarity and accuracy. d. Detail Phase 1, Engineered Level Spreader #2: Label Str and pipes: IDs, rim elev. INV IN/OUT, %:" steel plate labels, slope, DIA, pipe material, ES -type, etc. e. Label outfall protection (riprap): CI./size; L x W x D, unless detail provided on separate sheet. f Provide LD-229 storm drain design computations, or direct reviewer to location of culv. table. 13. Sheet24 a. Similar to comments above, label E.L.S. #1 profile pipes and structures. Add labels for SL-I safety slab for any structure>12'. b. Provide ELS #1 profile: label elements of design, critical elevations, and dimensions (L xW xD). Also, see items I I.c., 12.a.., above. c. Revise outlet protection label to ref. OP IA detail on sheet 21 rather than sheet 17. d. Retaining wall ht. >3' requires building permit. e. Retaining wall ht. >4' requires PE -sealed geotechnical design, not generic design. RW design required prior to WO plan approval. Engineering review is separate from building inspections review for building permit. Sheet 28 Anchor Diamond Wall details are insufficient for wall ht. >4-ft. f Add station labels to E.L.S. #1 profile corresponding with plan view stations (10+00 — 21+60f). g. Provide LD-229 storm drain design computations, or direct reviewer to location of culv. table. 14. Sheet2l a. Level Spreader -POA 1, SWM `A' Outfall detail caption reads see sheet 12 for location and dimensions. Sheet 12 does not include design detail or dimensions for ELS, SWM `A'. Revise. 15. Sheet20 a. SWM Pond 4 profile: Str SB4 Riser, provide SL-1 label. (SL-1 = safety slab) b. Ext'd Detention Facility `E': Provide required geotechnical testing / VA DEQ Stormwater Design Specification No. 15. Sec. 6.3. 6.3. Required Geotechnical Testing Soil borings should be taken below the proposed embankment, in the vicinity of the proposed outlet area, and in at least two locations within the proposed ED pond treatment area. Soil boring data is needed to (1) determine the physical characteristics of the excavated material, (2) determine its adequacy for use as structural fill or spoil, (3) provide data for structural designs of the outlet works (e.g., bearing capacity and buoyancy), (4) determine compaction/composition needs for the embankment, (5) determine the depth to groundwater and bedrock and (6) evaluate potential infiltration losses (and the potential need for a liner). c. Label internal slope, longitudinal slope through the ED pond (Max. should be — 0.5% to 1%). d. Label ED pond floor INV elevation (-366'). e. Plan and profile, SWM `E' do not match, revise for consistency. For example, plan view L to R displays emergency overflow, forebay, micro -pool, and inlet pipe plunge pool, with elevation breaks between features. Profile shows emergency overflow and 2 lower features, not 3. Also, SWM riser location appears inaccurate in profile view, not centered, as shown in plan view. f. Provide, show, label and dimension facility `E' riser base (likely, concrete, with riser embedded). g. Provide riser base buoyancy calculations. Engineering Review Comments Page 10 of 15 h. Revise outlet protection label to ref. ON detail on sheet 21 rather than sheet 17. i. Provide, label vehicular SWM facility access from Tarleton Drive paved surface to rim of Ext'd detention facility `E'. With road plan, show section of ribbon curb for maintenance vehicles, CG- 6 not designed to be mounted by vehicles. Comment may apply to other facilities. All SWM facilities require vehicular access from paved surface to facility rim, or dam embankment. j. Storm Sewer Schedule is same as schedule on Sheet 19, ensure table corresponding with Facility `E' shown on this sheet. k. Pipe from 402 to 402A exceeds pipe max slope 16% (VDOT Drainage Manual 9.4.8.7. and Alb. County Drainage Plan checklist for plan reviewers). Provide anchors /anchor detail for culvert pipe installed at grade >16% (proposed % slope=19.14%). 16. Sheet 19 a. Label SWM Pond 3 design features, including but not limited to: sand filter bottom, top, depth, and all structure and pipe critical design elements (material, pipe DIA, L, %slope, IDs, etc.). Note: Sheet 18 SWM B& C profile illustrates comprehensive profile data. b. SWM Pond 3 design incl. retaining wall, Sta. 11+21.12, that appears >10' ht. Ref. 18-4.3.3.A.1. Revise design as needed. c. Provide lintel design for pipe passing beneath retaining wall. Ensure pipe is shielded from lateral and vertical displacement, and forces. d. Unless VDOT 2016 R&B Std. requires, SL-1 required for structures > 12' (likely not required for Str. ht <12'). e. SWM Pond 3 profile: Label ES. f. Storm Sewer Schedule is same as schedule on Sheet 20, ensure table corresponding with Facility `D' shown on this sheet. g. Pipe from 402 to 402A exceeds pipe max slope 16% (VDOT Drainage Manual 9.4.8.7. and Alb. County Drainage Plan checklist for plan reviewers). Provide anchors /anchor detail for culvert pipe installed at grade >16%. h. SWM Pond 3 profile includes text box label that reads: Connects to SWM E via downstream future storm sewer system. Revise to show phased design to guide review /construction since design proposes elements of a SWM train with downstream elements of SWM not built with initial SWM. It is critical that first -phase construction include interim downstream design, including pipes, outfalls, and outfall protection. 17. Sheet 18 a. Profile label indicates 4" HDPE slotted under -drain to connect to DI-1 riser; IW (OUT)=397.00 (1%min slope), but base DI-1 appears >399'elevation. Connection with DI-1 appears infeasible. Review and revise design as needed. b. SWM Pond 2 profile shows 159' — 15" HDPE at 19.56% slope. Revise. Also, item 15.k., above. c. Revise outlet protection label to ref. OP2 /2A detail on sheet 21, rather than sheet 17. d. Revise `runoff reduction facility' labels to BMP type in DEQ clearinghouse or 1999 VA SWMH. e. SWM `C' emergency spillway is ambiguous in plan view. Clearly delineate location in plan view. If plunge pool WSE activates emergency spillway, define emergency spillway discharge path, and provide detailed emergency spillway design data similar to runoffreduction emer. spillway data. f. Provide /label vehicular access to SWM B' `C' and runoff reduction facility. Provide SWM access easement over vehicular access. g. Provide section `A -A' profile to clarify design intent: Engineering Review Comments Page 11 of 15 -EMERGENCY SPILLWAY 455 --'- p I , _ W379` _ \ INVE.50' p L=16.31 SSLOPES 1 61CONC. FILTRATION SAND FILTERS07 4 CONCRETE 390' �. 1B' RECOMMENDED MIN_ DEMISING WALL 1 TOP = 374.0 At = 2 @ 25 x 32 BOTTOM=371.0 (MINIMUM RECTANGLE) I (SEE DETAILS) / TOP SAND = 372.00 / J A' PERFO IATED HPDE / UNDER -DRAIN W/A'SITE 100 YR WSE - 36D.91 380 1 INSPECTION PORT, 6' �J / IISE 2YR WSE M.22� - Up ABOVE FINISHED GRADE t� I YR WSE-300.00 R- ' ! Vs - 0 75 • Tv 100 YR W. 13.956 c.1. 10 YR. WEE PI O ELEV.=373.53 2 YR WSI POO GRAVEL DIAPHRAGM / 1 YR WSI ADJACENT TO //� / 1NOFF REDUCTION .�1S - PLUNGE POOL / � '� (SEE DETAILS) / _ / \ / VAAWBLE WIC SWMEASEME / / .a0 � - � PROTECTgN / TOP OF DAM = 2,00 - / / SEE DETAIL oPzc 3WID0T7' / / & MINIMUM TOP WIDTH � A00�/ � ON SHEET I7 ET PROTECTION D� O' PLUNGE SEE DETAIL 0112 i9 / l` - PRE-TAEATMENr ON SHEET 17 / / VOLUME=2.763 tl / � / p ELEV. = 372A0 w10 i 18. Sheet17 a. Label distilling basin and forebay in plan view. b. Label distilling basin, forebay, and micro pool floor elevations, in profile. c. Provide label for V2" steel plate in floor of Str. 100B. d. Recommend SL-1 label at Str. 100C in profile view, in addition to table on sheet 18. e. Label all earthen embankment side -slopes, 2:1, 3:1, etc. f. Design of Str. 100D serves as a bypass, with 24" DIA pipe upstream, 12" downstream g. Profile label for Str. 100D references detail on Sheet 20. Detail does not appear on sheet 20. Include Str. 100D bypass detail on this sheet, if possible. Else direct reviewer to detail. Additional comments possible. It. Increase pipe DIA downslope of Str. 100D to 15", which is Min. pipe DIA in public drainage easement. Ref. Drainage Plan checklist for plan reviewers, Drainage Computations, item 1, subitem 2. i. Provide and label SWM facility and public drainage easement/s in plan view. I. Provide /label vehicular SWM facility access from paved surface to ELS#L k. Label lots. 1. Label streets. in. Provide additional proposed grade contours. n. Provide reverse slope benches, as needed. See 184.3.3.C.1. 19. Sheet16 a. Label sediment basin floor dimensions (L x W). b. Label emergency spillway riprap dimensions (L x W x D). c. At least several plan and profile view elevations do not match, for example: top of SB embankment, top of riser. Check all plan /profile data for consistency/accuracy. Please check sediment basin design, and storm routing calculations for consistency/accuracy. d. Provide additional proposed grade contours. Provide reverse slope benches, as needed. See 18- 4.3.3.C.1. X Engineering Review Comments Page 12 of 15 D. Erosion and Sediment Control Plan (ESCP) Virginia Code §62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This plan is disapproved for reasons listed, below. The erosion control plan content requirements can be found in County Code section 17-402. 1. Provide Notes, sheets 6 and 7 a. Preserved steep slopes (>25%) to be marked in the field and reviewed by Albemarle County ESC inspector prior to land disturbance. (Rev. 2) Partially addressed. Asfollow-W � Please revise Note 3, sheet 6, 7, to read: "Preserved steep slopes (>25%) to be marked in field by contractor and reviewed by Albemarle County ESC inspector prior to land disturbance." That is: Albemarle does not mark slopes, but reviews contractor /engineer flagging. (Rev. 3) Addressed. b. — see Additional review detail. (Rev. 2) Addressed. c. No permanent or temporary disturbance of preserved steep slopes is permissible. (Rev. 2) Partially addressed. As follow -UP: Please revise Note 5, sheet 6, 7, to read: "No permanent or temporary disturbance of preserved steep slopes is permissible unless related to storm or utility line installation, and only if No alternative exists, impacts are minimized, slopes are immediately stabilized, and pipe location across steep slopes is shown on an approved WPO or site plan." That is: extremely limited temporary disturbance is permissible for utility line or storm pipe installation only, where no other utility corridor exists, or is impracticable. (Rev. 3) Not addressed. Asfollow- up: Please review verbatim request for Note 5. text revision. 2. Sheets 6, 7 a. Label limits of disturbance, x.xx Ac. (Rev. 2) May persist. Please direct reviewer to label (x.xx Ac.) on plan sheet 6 or 7, if overlooked. (Rev. 3) Addressed, via Note 61 sheet 7. b. — see Additional review detail. (Rev. 2) Addressed. c. — see Additional review detail. (Rev. 2) Addressed, Note: SB#3 emergency spillway removed. d. — see Additional review detail. (Rev. 2) Addressed. e. — see Additional review detail (Rev. 2) Addressed. f — see Additional review detail. (Rev. 2) Addressed. g. — see Additional review detail. (Rev. 2) Addressed. It. — see Additional review detail. (Rev. 2) Addressed. i. — see Additional review detail. (Rev. 2) Addressed. j. Sediment basin and sediment trap outfalls are problematic: i. Provide off -site permanent public drainage easement for SB#4 outfall (OP4 is off -site). (Rev. 2) Persists. Space for future maintenance problematic: limited or non-existent where detail shows SB#4 emergency spillway touching property line. (Rev. 3) Addressed. Applicant: SB#4 & SWM `E' were pulled back to avoid offsite encroachments. As follow- Please also see item 2.j.iii.3.. below. i. N. 2) Addressed. [image removed with Rev. 2 comments]: iii. Revise SB#3 Emergency Spillway: (Rev. 2) Persists. Emergency spillway eliminated with revision. Plan now shows sediment trap spillway weir at property line, which does not address concern expressed with initial review comment (reprinted as 1.,2.,3., below). 1. Eliminate curved exit. Design using straight exit channel, per DEQ ref. doc. From p. 3, DEQ Emergency Spillway document: The topography most be carefully considered when constructing an emergency spillway. The alignment of the exit channel must be straight to a point far enough below the embankment to insure that any flow escaping the exit channel cannot damage the embankment. This may result in additional clearing and/or grading requirements beside the abutments, property line, etc. 2. Current design overlaps emergency spillway and fill slope at base of fill slope. There is a relatively high likelihood that flow may escape the exist channel and erode the embankment. Revise design. Engineering Review Comments Page 13 of 15 3. Insufficient space: Emergency spillway is coincident with development property line. There must be adequate space to construct /maintain the spillway on the development parcel. Alternatively, off -site easement is required prior to WPO plan approval. Easements in connection with ESC measures may not be deferred until final subdivision plat, but any easement (or written agreements) required to implement VESCP measures must be in place prior to WPO plan approval. (Rev. 3) Partially addressed. Applicant: `SB#3&4, including spillway designs were revised to address concerns.' As follow-up: Provide revised SB#3 and SB#4 designs in profile view. Label critical sediment basin design elements, including riser and basin floor elevations, orifices, side -slopes, etc., or direct reviewer to SB#3/4 profiles. Additional comments possible. iv. SB#4 Emergency spillway: (Rev. 2) Not addressed. 1. Revise to avoid undercutting fill slope SB embankment. Provide straight exit. (Rev. 3) Addressed. Applicant: `SB#4 revised to eliminate need for emergency Spillway. Over -sized.' v. Provide armored emergency spillway design for any SB emergency spillway proposed to be in fill rather than cut. Consider velocity, channel dimensions, riprap classification, etc. Provide calculations for armored emergency spillways. (Rev. 2) May persist. Please see item 2.i.iii, above. (Rev. 3) Addressed. Applicant: `All specified spillway sections remain in cut locations.' vi. SB#1 Emergency spillway: (Rev. 2) Not addressed. (Rev. 3) Addressed. Applicant: `Spillway riprap and overflow riprap channel section from SB# 1 extended to existing channel is located in cut.' 1. Revise, since armored spillway terminates at top of fill slope, extend armor to base of fill slope. Adhere to DEQ Vegetated Emergency Spillway design criteria, and guidance 3. Sheet 8 a. — see Additional review detail. (Rev. 2) Addressed. i. Revise bottom trap dimensions to L x W, for each ST. ii. Provide weir length, each ST. 4. Sheets 12-15 a. Since each SB is destined for permanent service as a SWM facility, include relevant geotechnical design, construction, inspection, and maintenance notes on the plan. Ref. VA DEQ Stormwater Design Specification, Appendix A, Earthen Embankment. Without these notes, there is risk or likelihood of inadequate geotechnical material testing, inspection, etc. during construction of embankments that transition from VESCP measure to permanent SWM facility. (Rev. 2) Not addressed. Geotechnical considerations are critical for earthen embankments. (Rev. 3) Partially addressed. Applicant: `Geo-technical notes added, including soil testing specifications.' As follow-up: While geotechnical testing /monitoring requirements on sheet 5 (3 notes) consider need to assess bedrock at SWM facilities and testing relative to filtering practices, there is insufficient guidance for earthen embankments. Please provide geotechnical test guidance notes for earthen embankments, for sediment basins. b. Provide sediment basin profiles. Do not combine SB and SWM detention as a single profile. SBs are temporary ESC measures, bonded, built, inspected, and maintained independent of future use as a SWM facility. Segregate ESC profiles from SWM profiles. (Rev. 2, �) Partially addressed. As ollow-up: i. SB#1, sheet 13 (comments (may) also apply to SB#2, SB#3, SB#4): 1. SB 41 profile indicates 1,380.2 CY storage required, 749.0 CY storage provided. SB# 1 appears undersized. If so, revise SB# 1 to provide sufficient stored volume. (Rev. 3) Addressed. Applicant: `Design change. Pond regraded and re- designed to meet requirements.' 2. Provide profile consistent with VESCH Plate 3.14-2, to include these elevations (in addition to top of dam and riser crest top elevations provided): (Rev. 3) Not Engineering Review Comments Page 14 of 15 addressed. Applicant: `SWM a [A] is currently Level 1 extended detention w/forebay and micro -pools. Dewatering added for maintenance.' As follow-up: Comment pertains to sediment basin design, not SWM facility design. Please provide items a, c, d, e, below. a. design high water b. top 4 dam c. dewatering device d. sediment clean -out point e. bottom of base of riser structure 3. Show continuous proposed grade across floor of sediment basin # 1. (Rev. 3) Addressed. 4. Show clay core, cutoff trench, collars, as needed. Sheet 17 typical provides inadequate detail. (Rev. 3) May persist. Applicant: `Facility is currently extended detention and does not permanently impound large quantities of water. Detail/notes revised accordingly. Clay core and earthen dam construction notes added.' As follow-up. Please direct reviewer to notes /sheet. Note: comment pertains to ESC /sediment basin design, not permanent SWM facility. 5. If collars required, show in profile, and label collar dimensions. (Rev. 3) Partially addressed. Applicant: `NA.' As follow-up: Provide sediment basin design sheets with calc. packet or with plan incl. calcs. to indicate collar/s not required. 6. Show /label 24" pipe end section (VDOT ES-1, for example). (Rev. 3) Persists. Pipe end sections not labeled in all profiles. Please incl. VDOT nomenclature. 7. Permanent riser In. >12' requires safety slab (VDO. SL-1). (Rev. 3) Addressed via table notes. As follow-up: Recommend label structures requiring SL-1 in profile view. 8. Label SB# I floor dimensions (L x W). (Rev. 3) Addressed. 9. Provide baffles, as needed. (Rev. 3) Addressed. Applicant: `NA' 10. Label 24" pipe INV OUT. (Rev. 3) Not addressed. Label INV OUT, profile view. ii. SB#2, sheet 14 1. Label ST414 in plan view. (Rev. 3) Addressed. 2. Apply SB#1 comments to SB#2, as needed. (Rev. 3) Items may persist. Additional review comments possible. 3. WQV (storage) required /provided not listed on profile. (Rev. 3) Addressed. iii. SB#3 & Outfall to SB#4 (sheet 15) 1. Recommend compaction note for MH /pipe nearly entirely in fill section_ (Rev 3) Withdrawn. MH/pipe no longer in fill - sheet 19. 2. Comments for SB#1 above may also apply. (Rev. 3) Items may persist. Additional review comments possible. 3. Label is confusing: `Sediment basin 3 shall be a sediment trap until the storm sewer outfall into sediment basin 4 is constructed (limit contributing drainage area to less than 3 Acres). Note: Divert all runoff to SB#4 until basin & SWM `D' outfall is operational'. Clarify proposed sequence /interdependence of SB#3 (basin/trap), SB44, SWM `D'. (Rev. 3) Addressed. Applicant: `Attempted to clarify. Issue is associated with phasing. SWM `D' will likely be converted to permanent Filtration prior to conversion of SB#4 into Ext'd detention. In addition, the phasing would not `construct' the storm sewer outfall system from SB#3, until Phase 4. Ultimately SB#4 is large enough to accommodate the entirety, but needed the sediment trap initially to `capture' the graded slope w/o [runoff] escaping the site or attempting the use of silt fence, primarily due to lack of an adequate or manageable outfall location.' Engineering Review Comments Page 15 of 15 iv. SB#4, sheetl6: Apply SB#1 comments, as needed. (Rev. 3) Items may persist. Additional review comments possible. c. Provide Sediment basin design (tables), per VESCH, 3.14 (size, baffles, collars, spillways, etc.). (Rev. 2) Not addressed. 5. New (Rev. 3) Sheet 19, inset detail upper left — Label for sediment basin #3 references detail, sheet 14. Correct ref. No SB#3 detail on sheet 14. Also, see ESC plan item 42.6.iii.3., above. Process: After approval, plans will have to be bonded. The bonding process is begun by submitting a bond estimate request form and fee to the Department of Community Development. One of the plan reviewers will prepare estimates and check parcel and easement information based on the approved plans. The County's Management Analyst will prepare bond agreement forms, which will have to be completed by the owner and submitted along with cash, certificates or sureties for the amounts specified. The agreements will have to be approved and signed by the County Attorney and County Engineer. This may take 24 weeks to obtain all the correct signatures and forms. Stormwater Management Facilities Maintenance agreements will also have to be completed and are recorded. The County's Management Analyst or other staff will prepare the forms and check for ownership and signature information. The completed forms will have to be submitted along with court recording fees. This project appears to propose nutrient credit purchase, may require off -site written agreements or easement to support ESC measures, and requires forest -open space easement (for SWM purposes), SWM facility and SWM facility access easement, and public drainage easement. (Off -site easement or written agreement with adjacent landowners required to construct or maintain temporary ESC measures is required for WPO plan approval.) After bonding and agreements are complete, county staff will enter project information in a DEQ database for state application processing. DEQ will review the application information based on local VSMP authority approval. At this time, the DEQ portion of the application fees will have to be paid directly to the state. For fastest processing, this is done electronically with the emails provided on the application. DEQ should notify applicants with instructions on how to pay fees. When DEQ approves the application, they will issue a permit coverage letter. This should be copied to the county. After DEQ coverage is issued, via the coverage letter, the County can hold a pre -construction conference. Applicants must complete the request for a pre -construction conference form, and pay the remainder of the application fee. The form identifies the contractor and responsible land disturber, and the fee remaining to be paid. This will be checked by county staff, and upon approval, a pre -construction conference will be scheduled with the County inspector. At the pre -construction conference, should everything proceed satisfactorily, a joint VSMP and grading permit will be issued by the County so that work may begin. County forms can be found on the county website forms center under Engineering Applications: https://www.albemarle. org/government/community-develoi)ment/aooly-for/engineering-anol ications Thank you. Please call if any questions — tel. 434.296-5832-x3069, or email ianderson2(a)albemarle.org . WPO202100063_Dunlora Farm-Village_I21022rev3