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Home My WebLink AboutWPO201400031 Review Comments 2016-09-29Short Review Comments Report for: WPO201400031 SubApplication Type: Westlake Hills Phase II, III, & IV - Road Plans Stormwater Management/BMP Plan Erosion and Sediment Control Plan Stream Buffer Mitigation Plan Date Completed:05/12/2014 Reviewer:John Anderson CDD Engineering Review Status:Requested Changes Reviews Comments: Division: Date Completed:05/12/2014 Reviewer:John Anderson CDD Engineering Review Status:Requested Changes Reviews Comments: Division: Date Completed:05/12/2014 Reviewer:John Anderson CDD Engineering Review Status:Requested Changes Reviews Comments: Division: Date Completed:07/21/2014 Reviewer:John Anderson CDD Engineering Review Status:Requested Changes Reviews Comments: Division: Date Completed:07/21/2014 Reviewer:John Anderson CDD Engineering Review Status:Requested Changes Reviews Comments: Division: Date Completed:07/21/2014 Reviewer:John Anderson CDD Engineering Review Status:Requested Changes Reviews Comments: Division: Date Completed:10/13/2014 Reviewer:John Anderson CDD Engineering Review Status:Denied Reviews Comments: Division: Date Completed:10/20/2014 Reviewer:John Anderson CDD Engineering Review Status:Denied Reviews Comments: Division: Date Completed:10/21/2014 Reviewer:John Anderson CDD Engineering Review Status:Approved Reviews Comments: Division: Page:1 of 2 County of Albemarle Printed On:January 20, 2017 Date Completed:09/29/2016 Reviewer:John Anderson CDD Engineering Review Status:See Recommendations Reviews Comments:Phase II ONLY Lickinghole Fee $ 9,452.87 Division: Page:2 of 2 County of Albemarle Printed On:January 20, 2017 x-n vIRGIN�A 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 (Rev. 1) (Rev. 2) (Rev. 3) (Rev. 4) Date of comments: (Rev. 1) (Rev. 2) (Rev. 3) (Rev. 4) Reviewer: Approval Westlake Hills Phase I1, 111, & IV Scott Collins; Collins Engineering [200 Garrett St., Suite K, Charlottesville, VA 22902, scott&collins -en ing eering corn] Lickinghole Creek, LLC [P. O. Box 1467, Charlottesville VA 22902, alankriverbenddev.com] 16 April 2014 6 June 2014 (Road Plan/ESC /SWM/Mitigation) 28 August 2014 (Road Plan/ESC /SWM/Mitigation) 15 October 2014 (�/ SWPPP- PPP/ESC /SWM/Mitigation) 21 October 2014 (SWPPP -PPP; WPO Cover sheet) 12 May 2014 18 July 2014 (21 July 2014; SMW Items 15 -20) 13 October 2014 (Road Plan/ESC /SWM/Mitigation) 19 October 2014 (Read-Plan/SWPPP- PPP/ESC /SWM /Mitigation) 21 October 2014 (SWPPP- PPP/ESC /SWM /Mitigation) Approved John Anderson The erosion & sediment control, stormwater management, stormwater pollution prevention, and pollution prevention plans (WP0201400031) submitted Oct -15 (or rev. Oct -21), 2014 are approved. The forms and instructions to request the Water Protection Ordinance and Subdivision Ordinance bond amounts can be found on the Community Development Department website shown below. You may contact Ana Kilmer (Albemarle County Department of Community Development) at ext. 3246 for further information on bonding procedures and maintenance agreements. Link — bonds: http:// www. albemarle. org /deptforms.asp ?department--bonds Please refer to p. 7 of review letter dated 19- Oct -14 sent as e- attachment 20- Oct -14 for next -step guidance (Process). Once construction begins, should the County inspector find limits of disturbance increased or a need for additional control measures required to protect the site, additional fees will be required. Prior review comments are available in the County -view database system. Thank you. File: Approv- WP0201400031- westlake hills, phase II,III,IV- 102114 vIRGIN�A 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 (Rev. 1) (Rev. 2) (Rev. 3) Date of comments: (Rev. 1) (Rev. 2) (Rev. 3) Reviewer: VSMP Permit plan review Westlake Hills Phase 11,11I, & IV Scott Collins; Collins Engineering [200 Garrett St., Suite K, Charlottesville, VA 22902, scottncollins- engineering com] Lickinghole Creek, LLC [P. O. Box 1467, Charlottesville VA 22902, alan(ariverbenddev.com] 16 April 2014 6 June 2014 (Road Plan/ESC /SWM/Mitigation) 28 August 2014 (Road Plan/ESC /SWM /Mitigation) 15 October 2014 (Read-Plan/ SWPPP- PPP /ESC /SWM/Mitigation) 12 May 2014 18 July 2014 (21 July 2014; SMW Items 15 -20) 13 October 2014 (Road Plan/ESC /SWM/Mitigation) 19 October 2014 (R ^ /SWPPP- PPP/ESC /SWM /Mitigation) John Anderson County Code section 17 -410 and Virginia Code §62.1- 44.15:34 require the VSMP authority to act on any VSMP permit by issuing a project approval or denial. This project is denied. The rationale is given in the comments below. The application may be resubmitted for approval if all of the items below are satisfactorily addressed. The VSMP application content requirements can be found in County Code section 17 -401. 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. — Furnish SWPPP, similar to WP0201400059, WP0201400030 (Briarwood/Collins Engineering). 1. (Rev. 3) Comment partially addressed. Please revise, or include. a. WP0201400031, plan sheet 1 Existing conditions b. Certification Statement, p. 28 —print certification statement exactly as shown at Part III K 4, CGP (VAR10). c. Document header: If SWPPP covers Phase I, include reference to Phase I (not just II, III, & IV). d. WP0201500016 sheets (11" x 17 ") as New Appendix if SWPPP covers Phase I. —All sheets. e. Update p. i -26 (as necessary) to specifically include Phase I Narrative -text: include control, containment, spill prevention measures specific to Phase I if not identical with Phase 11, III, & IV. This item will be reviewed carefully. f. Appendix B — Include CGP Letter of Coverage dated 12- Sep -14. g. Appendix D — Revise Inspection Form, p. 5, Certification Statement exactly as at Part III K 4. h. Appendix E — Revise Corrective Action Form, p. 2, Certification Statement exactly as at Part III K i. Phase II, III, & IV plan inserts— replace cover sheet with corrected version. See SWMP comments, Engineering Review Comments Page 2 of 7 below. j. Revise Exhibit (Concrete Wash out, Porta johns, Fueling Area) to include containment details —ref Briarwood project Exhibit. Also: show dumpster location draining to ST. Please call to discuss. k. Page 25: Rain gauge is applicable; revise. Identify general location of rain gauge: Phase I, as well as Phase II,III, & IV. 1. Page 17: Sediment Basin Control #1 —ref. sheet 13 -14 rather than sheet 10. m. Page 16: Soil Compaction Control #1 —ref actual sheet # rather than sheet X. n. Revise cover: Make it explicitly clear that SWPPP /PPP covers All Phases: I, II, III, & IV. o. Page 1 — Revise Operator(s) to Piedmont Neighborhoods, LP rather than SM Charlottesville LC. VAR10F988 is issued to Piedmont Neighborhoods LP. B. Pollution Prevention Plan (PPP) — Since PPP included with SWPPP, PPP comments included with SWPPP comments, above. The PPP content requirements can be found in County Code section 17 -404. — Furnish PPP, similar to WP0201400059, WP0201400030 (Briarwood/Collins Engineering). C. Stormwater Management Plan (SWMP, WP0201400031) — All prior comments addressed. Remaining (New) comments: correct COVER SHEET: total project area = 139.93 Ac; sheets =15 pages; title: Westlake Hills Subdivision, Phase II, III, & IV WPO Plan, WP0201400031. SWMP approved, pending corrections. Please submit 4 copies SWM Plan cover sheet only, with corrections. Revise SWPPP (All Phases). See Page 7 for important Phase I Pre - construction meeting note. Tentative: 22- Oct -14; confirm with Mark Hopkins, ACCD. VSMP Regulation 9VAC25- 870 -108 requires the VSMP authority to approve or disapprove a SWMP. This plan is disapproved; comments above (All relate to cover sheet). SWMP requirements can be found in County Code section 17 -403. Separate out the WPO plans. They cannot be approved as part of a road plan set. (Rev. 1) Comment partially addressed. Please restore plan sheets 2 (existing conditions), 5, and 5A (grading plan) to WPO plan set, as grading and existing conditions are essential to WPO review /approval. These sheets should remain with the road plan set, as well. (Rev. 2) Comment addressed. 2. Drainage areas are confusing. Drainage divides' upper boundaries should coincide with topographical high points (see post - development, Areas IA, 4A). Downslope drainage area boundaries are somewhat subjective, but areas included in post - development plans (and runoff calculations) are excluded as undisturbed on ESC sheets 26 and 27. Drainage area divides should coincide with actual existing and proposed finished grades. (Rev. 1) Comment addressed. 3. Runoff from Areas I & 4A should be controlled and treated to the extent practicable. Area 4A is controlled during construction by a sediment trap (ST1), sediment basin (SB5), and temporary diversions. Area lA runoff is diverted to SB 1 during construction. These temporary structures are eliminated and not replaced with permanent SWM features. Please consider permanent SWM basin or berm structures located to avoid conflict with allowable use of lots. A berm, for example, on the downslope (western) boundary of drainage area I may divert runoff to SWM basin 1. Grading Plan (sheet 5A) does not reflect alteration of contours likely to occur with removal of SB5. Show grades that result from removing S135 (pre- existing contours will be altered). (Rev. 1) Comment addressed. 4. Use 1 -2% existing impervious area to calculate %RR, for all drainage areas. 8% pre - development impervious area is too high. Proposed SWM Facilities are Extended Detention (2WQV) with phosphorus removal efficiency of 35 %, but %RR for Areas 1, 2, 3, are 47, 40, 46, respectively, so extended detention will not provide minimum water quality pollutant removal. Once %RR is re- calculated for Area 4 using 1 -2% existing impervious area, Engineering Review Comments Page 3 of 7 extended detention may not be suitable as SWM for Area 4, as well. Extended detention is appropriate for a required removal rate of 35 %. (Rev. 1) As follow -up to discussion with Scott Collins and ACCD staff on 18 -Jul, comment withdrawn / Extended detention basins are suitable, except SWM Facility #1; ref. 15 -20, below. Re£ short version BMP computations for worksheets 2 — 6. Use yards / cultivated turf = Area X 0.08. Check effect of change (0.08) on V, water quality volume (21- Jul). Also, see comment #14 below, Summary of Watershed tables. please Note:. The County has received a list of projects which have applied for general permit coverage from DEQ. This project (all phases) does not appear on that list. Without a current permit, conditional permit, or permit continuation by DEQ, we cannot approve the stormwater management plan. This proj ect would have to apply for a new permit, and meet the current state requirements. Please provide copies of documents demonstrating current DEQ VSMP general permit coverage, or apply for a new VSMP general permit with the County. (Rev. 2) Comment partially addressed —ref. 9/12/14 Letter; VDEQ to Piedmont Neighborhoods, LP. Also, email, ACCD to Collins, 10/13/2014 2:37 PM, re VAR10F988. Project covered under VAR10F988, but VPDES permit is assigned to Piedmont Neighborhoods, LP, which differs from name of owner on file with ACCD, or, apparently, recorded in County Land Records. (Rev. 3) Comment addressed per conversation with Frederick Cunningham, Director, Office of Water Quality Permits, VDEQ (Richmond), VPDES permit operator and owner of land being developed may be separate entities. 5. The shape of SWM Facility 2 is problematic; the area between sediment forebay and retention basin is so narrow it constricts flow. Floor width at transition from forebay to basin is 4 -ft, which is susceptible to sedimentation and obstruction. Please use less narrow configuration for SWM Facility 42. (Rev. 1) Comment addressed — dimensions revised slightly (4 - 6 ft); further revision recommended (not mandated). 6. Plan views of each SWM facility (1,2,3,4) are drawn to scale. Please furnish profile views of each facility drawn to scale. Include entire culvert pipe (outfall). Typical sections do not reflect design heights listed as 6, 2, 8, and 10 -ft for SWM Facilities 1, 2, 3, and 4, respectively. (Rev. 1) Comment addressed. 7. If SWM Facilities #1, 2 appear to be constructed by down- cutting existing terrain. There are wetlands between these two SWM facilities. Soil borings are needed for these proposed SWM facility locations. Groundwater depth is a practical concern at each location. (Rev. 1) Comment addressed. 8. Drainage: Please ensure the carryover at any on -grade inlet is included in downstream inlet calculations (structure 30, for example, with carryover to structure 2813). Evaluate last on -grade inlet or inlets with carryover located prior to sump inlets, often in cul -de -sacs, to ensure that final roadway grades and drive entrance details allow on -grade inlet carryover to reach a point of entry to stormwater collection system. In the case of structure 30, for example, will carryover reach structure 2813, or will it find lower outlet at drive entrances to Lot 79, 80, or 81 (prefer no carryover at such last on -grade inlets)? (Rev. 1) Comment addressed. Please superimpose critical slopes that appear on sheet 2 on sheets 5 and 5A to facilitate review of proposed development on critical slopes. (Rev. 1) Comment addressed, but show Approved critical slope impact layer (dark shading, as shown on sheet 2, 16 -Apr plans; ref. #1, above). This will guide inspection and construction, help avoid misunderstandings that easily arise. 10. Please ensure that spread at inlet Str. 84B (San Marcos Way) does not exceed 9 -ft, and at Str. 38 (Westhall Drive) does not exceed 10 -ft. Furnish flanking inlets upslope of structures 20 and 22 on Westhall Drive, since spread at each inlet is > 10.2 -ft. (Rev. 1) Comment addressed. 11. As many as 26 inlets have a calculated required throat length greater than design throat length (sheets 19, 20). Please use engineering judgment to provide design at least equal the calculated required throat length. There are Engineering Review Comments Page 4 of 7 examples of slight mismatch: 12 -ft vs. 12.06 (rate insignificant), and greater disparity: 12 -ft vs. 14.47 -ft, for example. It is cases of greater disparity that will benefit from design that meets calculated requirements. (Rev. 1) Comment addressed. Note- number of inlets fell from 26 to 0 if use 4 " /hr table, to 12 if use 6.5 "/hr table (sheets 19/20, SUB201400067). 5 out of 12 show design v. calculated difference < 0.15' (2 "). Thank you. 12. Minor: Titles of computations (tables) on sheet 22 should reference SWM Facility #3 and #4. Also, using a start elevation of 547.5 to model SWM Facility #1 yields negative elevations. Should start elevation for SWM Facility #1 be 542.00 instead? (Rev. 1) Comment addressed. New 13. Label PERMANENT DITCH # 1 (detail, sheet 6) on sheet 3, where drainage area divide line obscures this new design feature, and on sheet 5 once sheets 5A and 5 are restored to WPO plan set (comment #1, above). (Rev. 2) Comment addressed. 14. Summary of Watershed tables, sheets 3, 4, and 5 — revise to clarify that values are peak flow (cfs) values. Confirm SCS routing compares pre - development peak flow using pre - development DA acreage against post - development peak flow using post - developed DA acreage. Acreage varies: pre -post development. (Rev. 2) Comment addressed. 15. Check revised V, required treatment volume, .xIs (cy), against Extended Detention Facility Data, cf, each SWM basin. (SWM Facility #1,!k-Jun plans: V (.xls) = 281.3 cy = 7595 cf - Extended detention facility data reports = 11,704 cf, for example. Remaining basins: SWM Facility #2, 6 -Jun plans: V (.xls) = 153.9 cy = 4155 cf - Extended detention facility data reports = 2,465 cf. SWM Facility #3, 6 -Jun plans: V (.xls) _ 258.6 cy = 6982 cf - Extended detention facility data reports = 6,233 cf. SWM Facility 44, 6 -Jun plans: V (.xls) _ 267.2 cy = 7214 cf - Extended detention facility data reports = 4,188 c£) Ensure WQV and 2 X WQV required are accurate since basis of SWM basin design. Check SWM facility design against 2 X water quality volume. (Rev. 2) Comment addressed. 16. Revise % RR calc, DA #1, 2,3,4A-4B: Use 'C' = 0.70 only (instead of 0.76, 0.28, 0.44, 0.36. C, pollutant concentration,is not a variable, but a constant, mg/L, phosphorous, New Development in Development Areas. (Rev. 2) Comment addressed. 17. Revise .xIs (Short Version BMP Computations): Use post - developed D.A. areas to calculate L ost . ( All pre - and post - development Drainage Areas differ: 1, 2, 3, 4A - 4B ) (Rev. 2) Comment addressed 18. SWM basin #1: Extended Detention for D.A. #1 is not suitable. %RR — 67. Re- evaluate SWM control for DA # 1. Sheets 4 -5: Update Notes re. Lickinghole Creek Prorata share (Rev. 2) Comment addressed. 19. Revise Runoff Curve Number Table, DA #4A, Developed: revise Woods= 3.36 Acres; Area negligible, once lots developed. (Sheet 3, 6 -June -2014 plan set) (Rev. 2) Comment addressed. 20. Re -run SCS routing using: revised 1% meadow -woods pre - developed condition (12- May -14, comment #4); L(post) [ revised using post - developed D.A. areas ]; (revised) required 2 X WQV; revised basin geometry (if revised); alternate SWM Facility #1; and higher post - developed CN, DA #4A. Also, see 94, above. (Rev. 2) Comment addressed. 21. Reconcile impervious area, DA #4, post - developed. Runoff Curve Number Table lists as 2.31 Ac; Short Version BMP.xIs lists as 3.01 Ac. (Rev. 2) Comment not addressed, but discrepancy inconsequential. New, Rev -2 1. Title p. —INDEX, list mitigation plan as sheet 15. (Rev. 3) Comment addressed. 2. Wherever possible, label proposed public drainage easements beyond public RW as proposed rp ivate drainage easements —sheet 4, for example. (Rev. 3) Comment addressed. Engineering Review Comments Page 5 of 7 D. Erosion Control Plan (ESCP - WP0201400031) Virginia Code §62.1- 44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This ESC plan is annroved. The erosion control plan content requirements can be found in County Code section 17 -402. 1. Separate out the WPO plans. They cannot be approved as part of a road plan set. (Rev. 1) Partially addressed, see item #1, SWM plan, above. Restore sheets. (Rev. 2) Comment addressed. 2. Super silt fence is proposed as single perimeter control at various locations with 160 -200 ft upslope drainage areas. VESCH details design criteria, planning considerations, construction specifications, and conditions where silt fence may be used, and does not recognize super silt fence. Please eliminate reference to super silt fence wherever it occurs (at least 1,600 LF are shown as perimeter controls measures for Drainage Areas 3, 4). Please revise design to include measures consistent with topography, percent grade, length, acreage, and suitability per VESCH. Silt fence should not be installed cross- contour, but on- contour with minimal rise or fall along its length. Diversion dikes and sediment traps (or basins) may be more appropriate in many locations currently shown to be controlled with super silt fence. Request for variance is an option. (Rev. 1) Comment partially addressed. Sheet 9: show IP [VESCH Plate 3.07 -1] at each of 24" yard drain inlets [`A' —`O'; 16 -Apr, sheets 5 -5A]. Pipes between yard drain inlets are 12" DIA. Grading and runoff are significant. Q, from system `N'- `M' -`L' = 3.5cfs, at structure 44. IP required at each inlet, A -0. [Concho Lane: A -D; Lampasas Dr: E,F; Pecos Ct: G,H; Westhall Dr: 1, J, K; and Area between San Marcos Way - Westhall Dr: M,N,L] (Rev. 2) Comment addressed. 3. Please review sediment basin design. Please provide emergency spillway exit channel length calculations or narrative supporting exit channel lengths of 2.4, 4, 4, and 15 -41. Please explain (narrative is okay) why sediment basin #5 does not have an emergency spillway. Revise anti -seep collar dimensions for all 5 sediment basins (size at least 4 -11 larger than barrel diameter / VSMH, 1999, p. 5 -68). SB 1 requires 3 collars given length of barrel in saturated zone = 57.68 -ft. SB 1 upstream face slope must be 2.5:1 (or flatter) given embankment height = 12 -ft. (Rev. 1) Comment addressed. 4. Invert in -out for three sediment basin outfall pipes is identical and does not correspond with invert information on details; please revise invert data for SB 1, 2, and 4 (sheet 27), as necessary. (Rev. 1) Partially addressed — please reconcile plan and profile culvert slope and INV information for S134. Comment partially addressed — Minor, please edit plan view revise slope to read 2.51 %. (Rev. 3) Comment addressed. 5. Please draw sediment basin profiles to scale. Show actual existing contours with relative scale. Generic section views are furnished. Existing ground is shown no higher than invert of outfall of culverts through embankments, at base of 3:1 slope. Actual slopes are flatter. Embankment heights are given as 6, 2, 8, 12, 6 -ft (SB 1, 2, 3, 4, and 5, respectively). Note: embankment height of S134 and SWM Facility 44 are not identical (SWM #4 embankment height is given as 10 -ft). (Rev. 1) Comment addressed. 6. Show baffles on plan view details for S134 and SBS. (Rev. 1) Comment addressed. 7. Show soil stockpiles. Show staging areas. Identify any off -site borrow or spoils sites. (Rev. 1) Comment addressed. 8. Minor: Titles of Erosion and Sediment Control Plans Phase I and Phase II are reversed (sheets 26, 27). (Rev. 1) Comment addressed. New 9. Revise line of 24" berm between SB2 and SB3, redraw uphill portion. (Rev. 2) Comment addressed. Engineering Review Comments Page 6 of 7 10. Minor: Sheet 7 —Re -label Temporary Diversion detail to read Temporary 24 " Diversion Berm. If temporary right -of -way diversions are used, show where practice will be used (plan view), else delete detail. It is confusing given second temporary diversion detail. Sheet 8 — please label 100 -yr floodplain and Lickinghole Creek. Sheet 10 —label ESC BASIN 3 profile. (Rev. 2) Comments addressed. 11. Sheet 8 — Restore SF between S132 and S133 (make continuous; ref 16 -Apr, sheet 26). (Rev. 2) Comment addressed. 12. Sheet 8 — S134 — Extend SF east with tree protection line, 80 -100', as initially shown, 16 -Apr. (Rev. 2) Comment addressed. 13. Sheet 8 —Show additional SF north and west of SBS, unless existing land cover is woods. (Rev. 2) Comment addressed. 14. Sheet 8 —Label CE paved, plan view. [Ref. Sequence of Construction, Note 4] (Rev. 2) Comment addressed. As follow -up, please include paved wash rack detail with ESC details, sheet 10. (Rev. 3) Comment addressed. 15. Sheet 9 —PS -DC shown; show TS -MU as well. (Rev. 2) Comment addressed. 16. Sheet 9 — Relocate IP symbol and label to yard drain inlet between Concho Lane and Lampasas Drive. (Rev. 2) Comment addressed. C. Road plans (SUB201400067) — Not revised or submitted with WPO SWPPP/PPP /SWM/ESC plans -NA 1. Intersection of San Marcos Way and Weshall Drive does not continue the 2% intersected cross grade for a minimum of 20' from the edge of pavement of the intersected street (ref. Sta. 14 +03.17, San Marcos Way). (Rev. 1; Rev. 2) Defer to VDOT. 2. Furnish Route Number for Jonna Street (show on plans). (Rev. 1) Comment addressed. 3. ACCD defers to VDOT. All streets are proposed as public roads. (Rev. 1) Comment acknowledged. 4. VDOT approval is required. (Rev. 1) Comment acknowledged. D. Mitigation plans (WP0201400031) 1. 100 -ft. stream buffer (unnamed tributary to Lickinghole Creek) appears to be different on several sheets (4A, 26, and 32). Stream buffers should not shift from one sheet to the next. (Rev. 1) Comment addressed. 2. These sheets do not accurately capture installation impacts required to establish sewer line in the vicinity of MH- 11. Sheet 32 does not calculate impact for this sanitary line. These impacts are permanent in that maintenance requires permanent, clear access to sanitary facilities. Calculate and offset impacts to areas of stream buffer impacted by sanitary sewer line installation (see portions of lots 61, 62, 80, and 81; sheet 32). (Rev. 1) Comment addressed. 3. SWM basins #I and #2 cannot be installed without impact to stream buffers. They may be drawn to show no impact, but final grade lines that touch buffer boundaries cannot be achieved without permanent alteration of landscape within the 100 -ft stream buffer or 100 -year floodplain. Delineate a reasonable zone for construction equipment operation and alteration or loss of vegetative cover during construction or maintenance of downslope embankments. Show reasonable buffer and floodplain impacts on sheet 32. As drawn, design assumes no impact more than 10 -ft downslope of top of embankment of SWM #1, or more than 9 -ft downslope of top of embankment of SWM #2. This is unrealistic. (Rev. 1) Comment addressed. 4. Mitigation area proposed with this plan should increase above 1.04 Acres. (Rev. 1) Comment addressed. New 5. Label PERMANENT DITCH #I (detail, sheet 6) on sheet 12. (Rev. 2) Comment addressed. Engineering Review Comments Page 7 of 7 The VSMP permit application and WPO plan cover sheet, and SWPPP/PPP (Westlake Hills Subdivision Phase I II, III, & IV) may be resubmitted for approval when all comments have been satisfactorily addressed. For re- submittal, please provide 4 copies of WPO plan cover she 3 copies of SWPPP/PPP (19 phases), with a completed application form. No plan review fee is required. Engineering plan review staff is available from 2 -4 PM on Thursdays, should you require a meeting to discuss this review. Mr. Anderson and Mr. Collins spoke on 17 -Oct. Westlake Hills (Phase I) is eligible for a pre - construction meeting. Mr. Anderson sent note, 17 -Oct, explaining meeting will be scheduled at Mr. Hopkins' convenience. This date appears to be Wed, 22- Oct -14. Please confirm with Mark Hopkins. Process for Phase II, III, & IV (WP0201400031) is outlined below: Surety/bond; Lickinghole Basin Fee; SWM Facilities Maintenance agreements (signed, received, and recorded). Process: (Disre aeference to DEQ, below: Project has received General VPDES Permit No. VARIOF988. 12- Sep -14) After approval, plans will need 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 need to be completed by the owner and submitted along with cash, certificates or sureties for the amounts specified. The agreements will need to be approved and signed by the County Attorney and County Engineer. This may take 2 -4 weeks to obtain all the correct signatures and forms. Stormwater Management Facilities Maintenance agreements will also need to be completed and recorded. The County's Management Analyst or other staff will prepare the forms and check for ownership and signature information. The completed forms will need to be submitted along with court recording fees. After bonding and agreements are complete, county staff will need to 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 need 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 will need to 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: http://www.albemarle.org/dotfonns.asp?dgpartment--cdengmTo File: WPO201400031-Westlake Hills- 101914 -Rev3 C O L L t N "" 200 tistitttt St..Suite K.Charlottestiille.VA 22902 434.2933719 PH 434.293.2813 FX www i.(ohm. t#19ir10.0t 010 CJ19tH October 21, 2014 John Anderson Albemarle County Department of Community Development 401 McIntire Road Charlottesville,VA 22902 RE: Westlake Hills Phase II,III, &IV VSMP Permit Plan Review Dear John: Thank you for your comments dated October 19, 2014 on the above-referenced project. The following are responses to the items raised in your letter and the engineering meeting: A. Stormwater Pollution Prevention Plan(SWPPP) 1. The requested revisions and documents have been included. B. Pollution Prevention Plan(PPP) 1. A PPP similar to that provided for Briarwood has been provided. C. Stormwater Management Plan (WP0201400031) 1. The cover sheet has been revised per the comments. Four copies of the cover sheet have been provided. Three copies of the SWPPP/PPP have been provided. Please contact me if you have any questions or require any additional information in your review of this submission. Sincerely, Scott Collins, PE 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 VSMP Permit plan review Project: Westlake Hills Phase II, III, & IV Plan preparer: Scott Collins; Collins Engineering [200 Garrett St., Suite K, Charlottesville, VA 22902, scott@collins -en ing eering com] Owner or rep.: Lickinghole Creek, LLC [P. O. Box 1467, Charlottesville VA 22902, alan(&riverbenddev. com] Plan received date: 16 April 2014 (Rev. 1) 6 June 2014 (Road Plan/ESC /SWM/Mitigation) (Rev. 2) 28 August 2014 (Road Plan/ESC /SWM /Mitigation) Date of comments: 12 May 2014 (Rev. 1) 18 July 2014 (21 July 2014; SMW Items 15 -20) (Rev. 2) 13 October 2014 (Road Plan/ESC /SWM/Mitigation) Reviewer: John Anderson County Code section 17 -410 and Virginia Code §62.1- 44.15:34 requires the VSMP authority to act on any VSMP permit by issuing a project approval or denial. This project is denied. The rationale is given in the comments below. The application may be resubmitted for approval if all of the items below are satisfactorily addressed. The VSMP application content requirements can be found in County Code section 17 -401. 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. — Furnish SWPPP, similar to WP0201400059, WP0201400030 (Briarwood/Collins Engineering). B. Pollution Prevention Plan (PPP) The PPP content requirements can be found in County Code section 17 -404. — Furnish PPP, similar to WP0201400059, WP0201400030 (Briarwood /Collins Engineering). C. Stormwater Management Plan (WP0201400031) VSMP Regulation 9VAC25- 870 -108 requires the VSMP authority to approve or disapprove a SWMP. This plan is disapproved, and the reasons are provided in the comments below (2 new, minor comments). The stormwater management plan content requirements can be found in County Code section 17 -403. Separate out the WPO plans. They cannot be approved as part of a road plan set. (Rev. 1) Comment partially addressed. Please restore plan sheets 2 (existing conditions), 5, and 5A (grading plan) to WPO plan set, as grading and existing conditions are essential to WPO review /approval. These sheets should remain with the road plan set, as well. (Rev. 2) Comment addressed. 2. Drainage areas are confusing. Drainage divides' upper boundaries should coincide with topographical high points (see post - development, Areas 1A, 4A). Downslope drainage area boundaries are somewhat subjective, but areas included in post - development plans (and runoff calculations) are excluded as undisturbed on ESC sheets 26 and 27. Drainage area divides should coincide with actual existing and proposed finished grades. (Rev. 1) Comment addressed. Engineering Review Comments Page 2 of 7 3. Runoff from Areas IA & 4A should be controlled and treated to the extent practicable. Area 4A is controlled during construction by a sediment trap (ST 1), sediment basin (SB5), and temporary diversions. Area I runoff is diverted to SB1 during construction. These temporary structures are eliminated and not replaced with permanent SWM features. Please consider permanent SWM basin or berm structures located to avoid conflict with allowable use of lots. A berm, for example, on the downslope (western) boundary of drainage area lA may divert runoff to SWM basin 1. Grading Plan (sheet 5A) does not reflect alteration of contours likely to occur with removal of S135. Show grades that result from removing S135 (pre- existing contours will be altered). (Rev. 1) Comment addressed. 4. Use 1 -2% existing impervious area to calculate %RR, for all drainage areas. 8% pre - development impervious area is too high. Proposed SWM Facilities are Extended Detention (2WQV) with phosphorus removal efficiency of 35 %, but %RR for Areas 1, 2, 3, are 47, 40, 46, respectively, so extended detention will not provide minimum water quality pollutant removal. Once %RR is re- calculated for Area 4 using 1- 2% existing impervious area, extended detention may not be suitable as SWM for Area 4, as well. Extended detention is appropriate for a required removal rate of 35 %. (Rev. 1) As follow -up to discussion with Scott Collins and ACCD staff on 18 -Jul, comment withdrawn / Extended detention basins are suitable, except SWM Facility #1; ref. 15 -20, below. Ref short version BMP computations for worksheets 2 — 6. Use yards / cultivated turf = Area X 0.08. Check effect of change (0.08) on V, water quality volume (21- Jul). Also, see comment #14 below, Summary of Watershed tables. please Note:. The County has received a list of projects which have applied for general permit coverage from DEQ. This project (all phases) does not appear on that list. Without a current permit, conditional permit, or permit continuation by DEQ, we cannot approve the stormwater management plan. This project would have to apply for a new permit, and meet the current state requirements. Please provide copies of documents demonstrating current DEQ VSMP general permit coverage, or apply for a new VSMP general permit with the County. (Rev. 2) Comment partially addressed —ref. 9/12/14 Letter; VDEQ to Piedmont Neighborhoods, LP. Also, email, ACCD to Collins, 10/13/2014 2:37 PM, re VAR1017988. Project covered under VAR10F988, but VPDES permit is assigned to Piedmont Neighborhoods, LP, which differs from name of owner on file with ACCD, or, apparently, recorded in County Land Records. 5. The shape of SWM Facility 2 is problematic; the area between sediment forebay and retention basin is so narrow it constricts flow. Floor width at transition from forebay to basin is 4 -11, which is susceptible to sedimentation and obstruction. Please use less narrow configuration for SWM Facility #2. (Rev. 1) Comment addressed — dimensions revised slightly (4 - 6 ft); further revision recommended (not mandated). 6. Plan views of each SWM facility (1,2,3,4) are drawn to scale. Please furnish profile views of each facility drawn to scale. Include entire culvert pipe (outfall). Typical sections do not reflect design heights listed as 6, 2, 8, and 10 -ft for SWM Facilities 1, 2, 3, and 4, respectively. (Rev. 1) Comment addressed. 7. If SWM Facilities #1, 2 appear to be constructed by down - cutting existing terrain. There are wetlands between these two SWM facilities. Soil borings are needed for these proposed SWM facility locations. Groundwater depth is a practical concern at each location. (Rev. 1) Comment addressed. 8. Drainaize: Please ensure the carryover at any on -grade inlet is included in downstream inlet calculations (structure 30, for example, with carryover to structure 2813). Evaluate last on -grade inlet or inlets with carryover located prior to sump inlets, often in cul -de -sacs, to ensure that final roadway grades and drive entrance details allow on -grade inlet carryover to reach a point of entry to stormwater collection system. In the case of structure 30, for example, will carryover reach structure 28B, or will it find lower outlet at drive Engineering Review Comments Page 3 of 7 entrances to Lot 79, 80, or 81 (prefer no carryover at such last on -grade inlets)? (Rev. 1) Comment addressed. 9. Please superimpose critical slopes that appear on sheet 2 on sheets 5 and 5A to facilitate review of proposed development on critical slopes. (Rev. 1) Comment addressed, but show Approved critical slope impact layer (dark shading, as shown on sheet 2, 16 -Apr plans; ref. #1, above). This will guide inspection and New construction, help avoid misunderstandings that easily arise. 10. Please ensure that spread at inlet Str. 84B (San Marcos Way) does not exceed 9 -ft, and at Str. 38 (Westhall Drive) does not exceed 10 -ft. Furnish flanking inlets upslope of structures 20 and 22 on Westhall Drive, since spread at each inlet is > 10.2 -ft. (Rev. 1) Comment addressed. 11. As many as 26 inlets have a calculated required throat length greater than design throat length (sheets 19, 20). Please use engineering judgment to provide design at least equal the calculated required throat length. There are examples of slight mismatch: 12 -ft vs. 12.06 (rate insignificant), and greater disparity: 12 -ft vs. 14.47 -ft, for example. It is cases of greater disparity that will benefit from design that meets calculated requirements. (Rev. 1) Comment addressed. Note- number of inlets fell from 26 to 0 if use 4 "/hr table, to 12 if use 6.5 " /hr table (sheets 19/20, SUB201400067). 5 out of 12 show design v. calculated difference < 0.15'(2"). Thank you. 12. Minor: Titles of computations (tables) on sheet 22 should reference SWM Facility #3 and #4. Also, using a start elevation of 547.5 to model SWM Facility #1 yields negative elevations. Should start elevation for SWM Facility #1 be 542.00 instead? (Rev. 1) Comment addressed. 13. Label PERMANENT DITCH #1 (detail, sheet 6) on sheet 3, where drainage area divide line obscures this new design feature, and on sheet 5 once sheets 5A and 5 are restored to WPO plan set (comment #1, above). (Rev. 2) Comment addressed. 14. Summary of Watershed tables, sheets 3, 4, and 5 — revise to clarify that values are peak flow (cfs) values. Confirm SCS routing compares pre - development peak flow using pre - development DA acreage against post - development peak flow using post - developed DA acreage. Acreage varies: pre -post development. (Rev. 2) Comment addressed. 15. Check revised V, required treatment volume, .xls (cy), against Extended Detention Facility Data, cf, each SWM basin. (SWM Facility #1, 6 -Jun plans: V (.xls) = 281.3 cy = 7595 cf - Extended detention facility data reports = 11,704 cf, for example. Remaining basins: SWM Facility #2, 6 -Jun plans: V (.xls) = 153.9 cy = 4155 cf - Extended detention facility data reports = 2,465 cf. SWM Facility #3, 6 -Jun plans: V (.xls) _ 258.6 cy = 6982 cf - Extended detention facility data reports = 6,233 cf. SWM Facility #4, 6 -Jun plans: V (.xls) = 267.2 cy = 7214 cf - Extended detention facility data reports = 4,188 cf.) Ensure WQV and 2 X WQV required are accurate since basis of SWM basin design. Check SWM facility design against 2 X water quality volume. (Rev. 2) Comment addressed. 16. Revise % RR calc, DA #1, 2, 3, 4A -413: Use'C' = 0.70 only (instead of 0.76, 0.28, 0.44, 0.36. C, pollutant concentration,is not a variable, but a constant, mg /L, phosphorous, New Development in Development Areas. (Rev. 2) Comment addressed. 17. Revise .xls (Short Version BMP Computations): Use post - developed D.A. areas to calculate L ost . ( All pre- and post - development Drainage Areas differ: 1, 2, 3, 4A - 4B ) (Rev. 2) Comment addressed 18. SWM basin #1: Extended Detention for D.A. #1 is not suitable. %RR = 67. Re- evaluate SWM control for DA #1. Sheets 4 -5: Update Notes re. Lickinghole Creek Prorata share (Rev. 2) Comment addressed. Engineering Review Comments Page 4 of 7 19. Revise Runoff Curve Number Table, DA #4A, Developed: revise Woods = 3.36 Acres; Area nezlivible, once lots developed. (Sheet 3, 6- June -2014 plan set) (Rev. 2) Comment addressed. 20. Re -run SCS routing using: revised 1% meadow -woods pre - developed condition (12- May -14, comment #4); L(post) [ revised using post - developed D.A. areas ]; (revised) required 2 x WQV; revised basin geometry (if revised); alternate SWM Facility #1; and higher post - developed CN, DA #4A. Also, see #4, above. (Rev. 2) Comment addressed. 21. Reconcile impervious area, DA #4, post - developed. Runoff Curve Number Table lists as 2.31 Ac; Short Version BMP.xls lists as 3.01 Ac. (Rev. 2) Comment not addressed, but discrepancy inconsequential. New, Rev -2 1. Title p. — INDEX, list mitigation plan as sheet 15. 2. Wherever possible, label proposed public drainage easements beyond public RW as proposed rp ivate drainage easements —sheet 4, for example. D. Erosion Control Plan (WP0201400031) Virginia Code §62.1- 44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This plan is disapproved, and the reasons are provided in the comments below (Minor edit; follow -up). The erosion control plan content requirements can be found in County Code section 17 -402. Separate out the WPO plans. They cannot be approved as part of a road plan set. (Rev. 1) Partially addressed, see item #1, SWM plan, above. Restore sheets. (Rev. 2) Comment addressed. 2. Super silt fence is proposed as single perimeter control at various locations with 160 -200 ft upslope drainage areas. VESCH details design criteria, planning considerations, construction specifications, and conditions where silt fence may be used, and does not recognize super silt fence. Please eliminate reference to super silt fence wherever it occurs (at least 1,600 LF are shown as perimeter controls measures for Drainage Areas 3, 4). Please revise design to include measures consistent with topography, percent grade, length, acreage, and suitability per VESCH. Silt fence should not be installed cross - contour, but on- contour with minimal rise or fall along its length. Diversion dikes and sediment traps (or basins) may be more appropriate in many locations currently shown to be controlled with super silt fence. Request for variance is an option. (Rev. 1) Comment partially addressed. Sheet 9: show IP [VESCH Plate 3.07 -1] at each of 24" yard drain inlets [`A' —`O'; 16 -Apr, sheets 5 -5A]. Pipes between yard drain inlets are 12" DIA. Grading and runoff are significant. Q, from system `N'- `M' -`L' = 3.5cfs, at structure 44. IP required at each inlet, A -0. [Concho Lane: A -D; Lampasas Dr: E,F; Pecos Ct: G,H; Westhall Dr: I, J, K; and Area between San Marcos Way - Westhall Dr: M,N,L] (Rev. 2) Comment addressed. 3. Please review sediment basin design. Please provide emergency spillway exit channel length calculations or narrative supporting exit channel lengths of 2.4, 4, 4, and 15 -ft. Please explain (narrative is okay) why sediment basin #5 does not have an emergency spillway. Revise anti -seep collar dimensions for all 5 sediment basins (size at least 4 -11 larger than barrel diameter / VSMH, 1999, p. 5 -68). SB1 requires 3 collars given length of barrel in saturated zone = 57.68 -ft. SB 1 upstream face slope must be 2.5:1 (or flatter) given embankment height = 12 -ft. (Rev. 1) Comment addressed. 4. Invert in -out for three sediment basin outfall pipes is identical and does not correspond with invert information on details; please revise invert data for SB1, 2, and 4 (sheet 27), as necessary. (Rev. 1) Partially addressed — please reconcile plan and profile culvert slope and INV information for S134. (Rev. 2) Comment partially addressed — Minor, please edit plan view — revise slope to read 2.51 %. Engineering Review Comments Page 5 of 7 5. Please draw sediment basin profiles to scale. Show actual existing contours with relative scale. Generic section views are furnished. Existing ground is shown no higher than invert of outfall of culverts through embankments, at base of 3:1 slope. Actual slopes are flatter. Embankment heights are given as 6, 2, 8, 12, 6 -ft (SB 1, 2, 3, 4, and 5, respectively). Note: embankment height of S134 and SWM Facility #4 are not identical (SWM #4 embankment height is given as 10 -ft). (Rev. 1) Comment addressed. 6. Show baffles on plan view details for SB4 and SB5. (Rev. 1) Comment addressed. 7. Show soil stockpiles. Show staging areas. Identify any off -site borrow or spoils sites. (Rev. 1) Comment addressed. 8. Minor: Titles of Erosion and Sediment Control Plans Phase I and Phase II are reversed (sheets 26, 27). (Rev. 1) Comment addressed. New 9. Revise line of 24" berm between S132 and SB3, redraw uphill portion. (Rev. 2) Comment addressed. 10. Minor: Sheet 7 —Re -label Temporary Diversion detail to read Temporary 24 " Diversion Berm. If temporary right -of -way diversions are used, show where practice will be used (plan view), else delete detail. It is confusing given second temporary diversion detail. Sheet 8 — please label 100 -yr floodplain and Lickinghole Creek. Sheet 10 —label ESC BASIN 3 profile. (Rev. 2) Comments addressed. 11. Sheet 8 — Restore SF between S132 and S133 (make continuous; ref 16 -Apr, sheet 26). (Rev. 2) Comment addressed. 12. Sheet 8 — S134 — Extend SF east with tree protection line, 80 -100', as initially shown, 16 -Apr. (Rev. 2) Comment addressed. 13. Sheet 8 —Show additional SF north and west of S135, unless existing land cover is woods. (Rev. 2) Comment addressed. 14. Sheet 8 —Label CE paved, plan view. [Ref. Sequence of Construction, Note 4] (Rev. 2) Comment addressed. As follow -up, please include paved wash rack detail with ESC details, sheet 10. 15. Sheet 9 —PS -DC shown; show TS -MU as well. (Rev. 2) Comment addressed. 16. Sheet 9 — Relocate IP symbol and label to yard drain inlet between Concho Lane and Lampasas Drive. (Rev. 2) Comment addressed. C. Road plans (SUB201400067) - 1. Intersection of San Marcos Way and Weshall Drive does not continue the 2% intersected cross grade for a minimum of 20' from the edge of pavement of the intersected street (ref. Sta. 14 +03.17, San Marcos Way). (Rev. 1) Defer to VDOT. 2. Furnish Route Number for Jonna Street (show on plans). (Rev. 1) Comment addressed. 3. ACCD defers to VDOT. All streets are proposed as public roads. (Rev. 1) Comment acknowledged. 4. VDOT approval is required. (Rev. 1) Comment acknowledged. Engineering Review Comments Page 6 of 7 D. Mitigation plans (WP0201400031) 1. 100 -ft. stream buffer (unnamed tributary to Lickinghole Creek) appears to be different on several sheets (4A, 26, and 32). Stream buffers should not shift from one sheet to the next. (Rev. 1) Comment addressed. 2. These sheets do not accurately capture installation impacts required to establish sewer line in the vicinity of MH -11. Sheet 32 does not calculate impact for this sanitary line. These impacts are permanent in that maintenance requires permanent, clear access to sanitary facilities. Calculate and offset impacts to areas of stream buffer impacted by sanitary sewer line installation (see portions of lots 61, 62, 80, and 81; sheet 32). (Rev. 1) Comment addressed. 3. SWM basins #1 and #2 cannot be installed without impact to stream buffers. They may be drawn to show no impact, but final grade lines that touch buffer boundaries cannot be achieved without permanent alteration of landscape within the 100 -ft stream buffer or 100 -year floodplain. Delineate a reasonable zone for construction equipment operation and alteration or loss of vegetative cover during construction or maintenance of downslope embankments. Show reasonable buffer and floodplain impacts on sheet 32. As drawn, design assumes no impact more than 10 -ft downslope of top of embankment of SWM #1, or more than 9 -ft downslope of top of embankment of SWM #2. This is unrealistic. (Rev. 1) Comment addressed. 4. Mitigation area proposed with this plan should increase above 1.04 Acres. (Rev. 1) Comment addressed. New 5. Label PERMANENT DITCH #1 (detail, sheet 6) on sheet 12. (Rev. 2) Comment addressed. The VSMP permit application and all plans may be resubmitted for approval when all comments have been satisfactorily addressed. For re- submittal (assumed final), please provide 4 copies of the complete permit package with a completed application form. Engineering plan review staff are available from 2 -4 PM on Thursdays, should you require a meeting to discuss this review. Process: (Disregard re nce to DEQ, below; Note reference to DEQ, SWM plan comment #4, above) After approval, plans will need 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 need to be completed by the owner and submitted along with cash, certificates or sureties for the amounts specified. The agreements will need to be approved and signed by the County Attorney and County Engineer. This may take 2 -4 weeks to obtain all the correct signatures and forms. Stormwater Management Facilities Maintenance agreements will also need to be completed and recorded. The County's Management Analyst or other staff will prepare the forms and check for ownership and signature information. The completed forms will need to be submitted along with court recording fees. After bonding and agreements are complete, county staff will need to 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 need to be paid directly to the state. For fastest Engineering Review Comments Page 7 of 7 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 will need to 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; hllp://www.albemarle.orgJdeptforms.asp?dei2artinent--cdengno File: WPO201400031-Westlake Hills-Memo- 10 1 314-Rev2 4 shy '4400'i + tee ' COMMONWEALTH of VIRGINIA DEPARTMENT OF ENVIRONMENTAL QUALITY Street address:629 East Main Street,Richmond,Virginia 23219 Molly Joseph Ward Mailing address: P.O.Box 1105,Richmond,Virginia 23218 David K.Baylor Secretary of Natural Resources www.deq.virginia.gov Director (804)698-4020 1-800-592-5482 September 12, 2014 Piedmont Neighborhoods LP 200 Garrett St Ste B Charlottesville,VA 22903 RE: Coverage under the 2014 VPDES Construction General Permit(VAR10) General Permit No.VAR10F988 West Lake Hills Private-Residential Dear Permittee: DEQ has reviewed your Registration Statement received on June 2, 2014 and determined that the proposed land-disturbing activity is covered under the General VPDES Permit for Discharges of Stormwater from Construction Activities (VAR10)_ The effective date of your coverage under this general permit is the date of this letter. A copy of the general permit can be obtained from DEQ's webpage at the following location: http://www.deo_virginia qov/Portals/0/DEQ/Water/Publications/CGP2014.pdf. The general permit contains the applicable Stormwater Pollution Prevention Plan (SWPPP) requirements and other conditions of coverage. Please print the general permit and read it carefully as you will be responsible for compliance with all permit conditions. The general permit requires that you update your SWPPP to incorporate the changes that the Department made for this permit reissuance. Please update the SWPPP as soon as possible but no later than sixty(60)days from the date of this letter. DEQ staff has determined that the proposed land-disturbing activity will discharge to a surface water identified as impaired or for which a TMDL wasteload allocation has been established and approved prior to the term of the general permit for(i) sediment or a sediment-related parameter or (ii) nutrients. Therefore, the following general permit(Part I.B.4)and SWPPP requirements(Part Il.A.5)must be implemented for the land-disturbing activity: • Permanent or temporary soil stabilization shall be applied to denuded areas within seven (7) days after final grade is reached on any portion of the site; • Nutrients (e.g., fertilizers) shall be applied in accordance with manufacturer's recommendations or an approved nutrient management plan and shall not be applied during rainfall events; • Inspections shall be conducted at a frequency of (i) at least once every four(4) business days or(ii) at least once every(5) business days and no later than 48 hours following a measurable storm event. In the event that a measurable storm event occurs when there are more than 48 hours between business days, the inspection shall be conducted on the next business day; and • Representative inspections used by utility line installation, pipeline construction, or other similar linear construction activities shall inspect all outfalls. rayucuic General Permit No AR10F988 '.' ' West Lake Hills The general permit will expire on June 30, 2019. The conditions of the general permit require that you submit a new registration statement at least 90 days prior to that date if you wish to continue coverage under the general permit, unless permission for a later date has been granted by the Board. Permission cannot be granted to submit the registration statement after the expiration date of the general permit. If you have any questions about this permit, please contact the DEQ Office of Stormwater Management at C onstru cti o n G P Card eq.vi rq i n ia.q ov. Sincerely, g Frederick K. Cunningham, Director Office of Water Permits COLLINS 200 biota St._Suite KC.Cliartottewille.VA 222902 434. 93.3719 PH 434.293.2813 FX www °Harm,..oraoano rAn torn August 26,2014 John Anderson Albemarle County Department of Community Development 401 McIntire Road Charlottesville,VA 22902 RE: Westlake Hills Phase II,III, &IV Dear John: Thank you for your comments dated July 21, 2014 on the above-referenced project. The following are responses to the items raised in your letter and the engineering meeting: A. Stormwater Management and Mitigation Plan (WP0201400031) 1. The requested sheets have been added to the WPO set. 2. N/A 3. N/A 4. The post-development yards/cultivated turf value is now multiplied by 0.08. Updated simple method calculations are now provided. 5. The applicant acknowledges this suggestion. 6. N/A 7. N/A 8. N/A 9. The critical slope impacts are now shown on sheet 5 and 5A. 10. N/A 11. N/A 12. N/A 13. The Permanent Ditch#1 label has been added to the requested sheets. 14. The cfs unit of measure has been added to the Summary of Watersheds table. The values are computed with the pre-development drainage areas in the pre-development scenario, and the post-development drainage areas in the post-development scenario. 15. The extended detention facility data now provides an additional column showing the conversion of the volume from of to cy,which matches the basin input data used in the routing. The water quality volume provided exceeds the 2xWQV requirement. 16. C has been revised to read 0.70 in the simple method spreadsheet. 17. Lpost is now calculated with the post-development drainage areas. With all the revisions required to the simple method spreadsheet, a negative%RR is required for SWM 2. Rather than remove this basin, an analysis for the SWM Project Area defined as Pre-DA#1, 2, 3, & 4 and Post-DA#1, 2, 3, 4A, and 4B is provided. The result of this analysis is a removal rate of 35%required for the development as a whole. As 35%removal rate is provided with the extended detention basins,and the Lickinghole Creek Prorata share provides further removal credit ensuring that the project meets the required removal for the SWM Project Area. 18. See response to item 17 above. The Lickinghole Creek Prorata share note has been revised and moved to the pre-development sheet. 19. The 4A runoff curve number has been revised to reduce the wooded area to 2.34 acres,which was calculated by providing a minimum of 40' from the back of the buildable area for each • lot. The developer intends to preserve as many trees as possible on each lot, and the remaining wooded area in drainage area 4A will contribute to the runoff curve number. The pre and post-development flow for 4A have been updated accordingly. 20. The routings have been rerun and basins 3 and 4 redesigned as well. 21. The basins now use the 8%grass imperviousness in their proposed contributing impervious area total for water quality sizing. B. Erosion Control Plan (WP0201400031) 1. The requested sheets have been added to the WPO set. 2. Inlet protection has been placed at each yard drain inlet. 3. N/A 4. The plan and profile have been reconciled for sediment basin 4. 5. N/A 6. N/A 7. N/A 8. N/A 9. The berm has been revised to ensure positive drainage. 10. The temporary diversion detail has been relabeled,the right-of-way diversion detail has been removed,the 100-year floodplain and Lickinghole Creek are labeled on sheet 8, and the ESC Basin 3 is labeled on sheet 10. 11. The silt fence now provides continuous protection between SB2 and SB3 on sheet 8. 12. Silt fence slightly adjusted and provides adequate protection behind SB4. East of SB4 a 24" Diversion Berm is already shown. This is preferable over the April 16th design because it impacts less trees. 13. Existing land cover is woods,no additional silt fence added at SB5. 14. The CE is now labeled as paved. 15. The TS and MU symbols have been added to sheet 9. 16. The IP symbol has been relocated as requested. C. Road Plans(SUB201400067) 1. The applicant acknowledges this comment. 2. N/A 3. N/A 4. N/A D. Mitigation Plans (WP0201400031) 1. N/A 2. N/A 3. N/A 4. N/A 5. The permanent ditch#1 has been added to sheet 12. VDOT 1. The sewer has been located along lots 61 and 62 to reduce the required grading and disturbance and subsequent mitigation within the 100-year floodplain. The sewer has not been relocated. 2. The yard drains are provided to intercept overland flow between the lots,to prevent excessive runoff. This technique has been successful in our previously constructed developments. 3. The missing STR 100-84 and STR 96B-96 profiles have been added to the plans. 4. The Westhall Drive trip value has been revised and increased. 5. The aggregate course thickness has been increased to 6"for each roadway. 6. No parking signs have been added on each street to identify where parking is prohibited, see the site plan sheet. 7. Parking has been delineated to avoid the sight distance easements. 8. The CD-2 has been added to road profiles and Sheet 5, 5A. 9. The CD-1 has been added to road profile and Sheet 5, 5A. 10. The CD-1 has been added to road profile and Sheet 5, 5A. 11. The CD-1 has been added to road profile and Sheet 5, 5A. 12. The CD-1 has been added to road profile and Sheet 5, 5A. 13. The profile has been updated with the correct elevations. 14. Invert out elevations of outfall pipes have been added to the storm sewer profiles. 15. The STR 26B-26 profile label has been fixed. 16. Drainage Description has been corrected to reflect profile information. Please contact me if you have any questions or require any additional information in your review of this submission. Sincerely, Scott Collins, PE �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: Westlake Hills Phase II, 111, & IV Plan preparer: Scott Collins; Collins Engineering [200 Garrett St., Suite K, Charlottesville, VA 22902, scott(cDcollins- enizineering com] Owner or rep.: Lickinghole Creek, LLC [P. O. Box 1467, Charlottesville VA 22902, alan(a)riverbenddev. com] Plan received date: 16 April 2014 (Rev. 1) 6 June 2014 (Road Plan/ESC /SWM/Mitigation) Date of comments: 12 May 2014 (Rev. 1) 18 July 2014 (21 July 2014; SMW Items 15 -20) Reviewer: John Anderson A. Stormwater Management Plan (WP0201400031) 1. Separate out the WPO plans. They cannot be approved as part of a road plan set. (Rev. 1) Comment partially addressed. Please restore plan sheets 2 (existing conditions), 5, and 5A (grading plan) to WPO plan set, as grading and existing conditions are essential to WPO review /approval. These sheets should remain with the road plan set, as well. 2. Drainage areas are confusing. Drainage divides' upper boundaries should coincide with topographical high points (see post - development, Areas 1A, 4A). Downslope drainage area boundaries are somewhat subjective, but areas included in post - development plans (and runoff calculations) are excluded as undisturbed on ESC sheets 26 and 27. Drainage area divides should coincide with actual existing and proposed finished grades. (Rev. 1) Comment addressed. 3. Runoff from Areas I & 4A should be controlled and treated to the extent practicable. Area 4A is controlled during construction by a sediment trap (ST I), sediment basin (S135), and temporary diversions. Area 1 A runoff is diverted to SB 1 during construction. These temporary structures are eliminated and not replaced with permanent SWM features. Please consider permanent SWM basin or berm structures located to avoid conflict with allowable use of lots. A berm, for example, on the downslope (western) boundary of drainage area IA may divert runoff to SWM basin 1. Grading Plan (sheet 5A) does not reflect alteration of contours likely to occur with removal of S135. Show grades that result from removing S135 (pre- existing contours will be altered). (Rev. 1) Comment addressed. Use 1 -2% existing impervious area to calculate %RR, for all drainage areas. 8% pre - development impervious area is too high. Proposed SWM Facilities are Extended Detention (2WQV) with phosphorus removal efficiency of 35 %, but %RR for Areas 1, 2, 3, are 47, 40, 46, respectively, so extended detention will not provide minimum water quality pollutant removal. Once %RR is re- calculated for Area 4 using 1- 2% existing impervious area, extended detention may not be suitable as SWM for Area 4, as well. Extended detention is appropriate for a required removal rate of 35 %. (Rev. 1) As follow -up to discussion with Scott Collins and ACCD staff on 18 -Jul, comment withdrawn / Extended detention basins are suitable, except SWM Facility #1; ref. 15 -20, below. Ref. short version BMP computations for worksheets 2 — 6. Engineering Review Comments Page 2 of 5 Use yards/ cultivated turf= Area X 0.08. Check effect of change (0.08) on V, water quality volume (21- Jul). Also, see comment #14 below, Summary of Watershed tables. please Note:. The County has received a list of projects which have applied for general permit coverage from DEQ. This project (all phases) does not appear on that list. Without a current permit, conditional permit, or permit continuation by DEQ, we cannot approve the stormwater management plan. This project would have to apply for a new permit, and meet the current state requirements. Please provide copies of documents demonstrating current DEQ VSMP general permit coverage, or apply for a new VSMP general permit with the County. 5. The shape of SWM Facility 2 is problematic; the area between sediment forebay and retention basin is so narrow it constricts flow. Floor width at transition from forebay to basin is 4 -ft, which is susceptible to sedimentation and obstruction. Please use less narrow configuration for SWM Facility #2. (Rev. 1) Comment addressed — dimensions revised slightly (4 - 6 ft); further revision recommended (not mandated). 6. Plan views of each SWM facility (1,2,3,4) are drawn to scale. Please furnish profile views of each facility drawn to scale. Include entire culvert pipe (outfall). Typical sections do not reflect design heights listed as 6, 2, 8, and 10 -ft for SWM Facilities 1, 2, 3, and 4, respectively. (Rev. 1) Comment addressed. 7. If SWM Facilities #1, 2 appear to be constructed by down - cutting existing terrain. There are wetlands between these two SWM facilities. Soil borings are needed for these proposed SWM facility locations. Groundwater depth is a practical concern at each location. (Rev. 1) Comment addressed. 8. Drainage: Please ensure the carryover at any on -grade inlet is included in downstream inlet calculations (structure 30, for example, with carryover to structure 2813). Evaluate last on -grade inlet or inlets with carryover located prior to sump inlets, often in cul -de -sacs, to ensure that final roadway grades and drive entrance details allow on -grade inlet carryover to reach a point of entry to stormwater collection system. In the case of structure 30, for example, will carryover reach structure 2813, or will it find lower outlet at drive entrances to Lot 79, 80, or 81 (prefer no carryover at such last on -grade inlets)? (Rev. 1) Comment addressed. 9. Please superimpose critical slopes that appear on sheet 2 on sheets 5 and 5A to facilitate review of proposed development on critical slopes. (Rev. 1) Comment addressed, but show Approved critical slope impact layer (dark shading, as shown on sheet 2, 16 -Apr plans; ref. #1, above). This will guide inspection and construction, help avoid misunderstandings that easily arise. 10. Please ensure that spread at inlet Str. 84B (San Marcos Way) does not exceed 9 -ft, and at Str. 38 (Westhall Drive) does not exceed 10 -ft. Furnish flanking inlets upslope of structures 20 and 22 on Westhall Drive, since spread at each inlet is > 10.2 -ft. (Rev. 1) Comment addressed. 11. As many as 26 inlets have a calculated required throat length greater than design throat length (sheets 19, 20). Please use engineering judgment to provide design at least equal the calculated required throat length. There are examples of slight mismatch: 12 -ft vs. 12.06 (rate insignificant), and greater disparity: 12 -ft vs. 14.47 -ft, for example. It is cases of greater disparity that will benefit from design that meets calculated requirements. (Rev. 1) Comment addressed. Note- number of inlets fell from 26 to 0 if use 4 "/hr table, to 12 if use 6.5 " /hr table (sheets 19/20, SUB201400067). 5 out of 12 show design v. calculated difference < 0.15'(2"). Thank you. New Engineering Review Comments Page 3 of 5 12. Minor: Titles of computations (tables) on sheet 22 should reference SWM Facility #3 and #4. Also, using a start elevation of 547.5 to model SWM Facility #1 yields negative elevations. Should start elevation for SWM Facility #1 be 542.00 instead? (Rev. 1) Comment addressed. 13. Label PERMANENT DITCH #1 (detail, sheet 6) on sheet 3, where drainage area divide line obscures this new design feature, and on sheet 5 once sheets 5A and 5 are restored to WPO plan set (comment #1, above). 14. Summary of Watershed tables, sheets 3, 4, and 5 — revise to clarify that values are peak flow (cfs) values. Confirm SCS routing compares pre - development peak flow using pre - development DA acreage against post - development peak flow using post - developed DA acreage. Acreage varies: pre -post development. 15. Check revised V, required treatment volume, .xls (cy), against Extended Detention Facility Data, cf, each SWM basin. (SWM Facility #1, 6 -Jun plans: V (.xls) = 281.3 cy = 7595 cf - Extended detention facility data reports = 11,704 cf, for example. Remaining basins: SWM Facility #2, 6 -Jun plans: V (.xls) = 153.9 cy = 4155 cf - Extended detention facility data reports = 2,465 cf. SWM Facility #3, 6 -Jun plans: V (.xls) _ 258.6 cy = 6982 cf - Extended detention facility data reports = 6,233 cf. SWM Facility #4, 6 -Jun plans: V (.xls) = 267.2 cy = 7214 cf - Extended detention facility data reports = 4,188 cf.) Ensure WQV and 2 x WQV required are accurate since basis of SWM basin design. Check SWM facility design against 2 x water quality volume. 16. Revise % RR calc, DA 41, 2, 3, 4A -413: Use'C' = 0.70 only (instead of 0.76, 0.28, 0.44, 0.36. C, pollutant concentration,is not a variable, but a constant, mg /L, phosphorous, New Development in Development Areas. 17. Revise .xls (Short Version BMP Computations): Use post - developed D.A. areas to calculate L ost ). ( All pre- and post - development Drainage Areas differ: 1, 2, 3, 4A - 4B ) 18. SWM basin #1: Extended Detention for D.A. #1 is not suitable. %RR = 67. Re- evaluate SWM control for DA #1. Sheets 4 -5: Update Notes re. Lickinghole Creek Prorata share 19. Revise Runoff Curve Number Table, DA #4A, Developed: revise Woods = 3.36 Acres; Area negligible, once lots developed. (Sheet 3, 6 -June -2014 plan set) 20. Re -run SCS routing using: revised 1% meadow -woods pre - developed condition (12- May -14, comment #4); L(post) [ revised using post - developed D.A. areas ]; (revised) required 2 x WQV; revised basin geometry (if revised); alternate SWM Facility 41; and higher post - developed CN, DA 44A. Also, see #4, above. 21. Reconcile impervious area, DA #4, post - developed. Runoff Curve Number Table lists as 2.31 Ac; Short Version BMP.xls lists as 3.01 Ac. B. Erosion Control Plan (WP0201400031) Separate out the WPO plans. They cannot be approved as part of a road plan set. (Rev. 1) Partially addressed, see item #1, SWM plan, above. Restore sheets. 2. Super silt fence is proposed as single perimeter control at various locations with 160 -200 ft upslope drainage areas. VESCH details design criteria, planning considerations, construction specifications, and conditions where silt fence may be used, and does not recognize super silt fence. Please eliminate reference to super silt fence wherever it occurs (at least 1,600 LF are shown as perimeter controls measures for Drainage Areas 3, 4). Please revise design to include measures consistent with topography, percent grade, length, acreage, and suitability per VESCH. Silt fence should not be installed cross - contour, but on- contour with minimal rise or fall along its length. Diversion dikes and sediment traps (or basins) may be more Engineering Review Comments Page 4 of 5 appropriate in many locations currently shown to be controlled with super silt fence. Request for variance is an option. (Rev. 1) Comment partially addressed. Sheet 9: show IP [VESCH Plate 3.07 -1] at each of 24" yard drain inlets [`A' —`O'; 16 -Apr, sheets 5 -5A]. Pipes between yard drain inlets are 12" DIA. Grading and runoff are significant. Q, from system `N'- `M' -`L' = 3.5cfs, at structure 44. IP required at each inlet, A -O. [Concho Lane: A -D; Lampasas Dr: E,F; Pecos Ct: G,H; Westhall Dr: I, J, K; and Area between San Marcos Way - Westhall Dr: M,N,L] 3. Please review sediment basin design. Please provide emergency spillway exit channel length calculations or narrative supporting exit channel lengths of 2.4, 4, 4, and 15 -ft. Please explain (narrative is okay) why sediment basin #5 does not have an emergency spillway. Revise anti -seep collar dimensions for all 5 sediment basins (size at least 4 -ft larger than barrel diameter / VSMH, 1999, p. 5 -68). SB 1 requires 3 collars given length of barrel in saturated zone = 57.68 -ft. SB 1 upstream face slope must be 2.5:1 (or flatter) given embankment height = 12 -ft. (Rev. 1) Comment addressed. 4. Invert in -out for three sediment basin outfall pipes is identical and does not correspond with invert information on details; please revise invert data for S13 1, 2, and 4 (sheet 27), as necessary. (Rev. 1) Partially addressed — please reconcile plan and profile culvert slope and INV information for S134. 5. Please draw sediment basin profiles to scale. Show actual existing contours with relative scale. Generic section views are furnished. Existing ground is shown no higher than invert of outfall of culverts through embankments, at base of 3:1 slope. Actual slopes are flatter. Embankment heights are given as 6, 2, 8, 12, 6 -ft (SB 1, 2, 3, 4, and 5, respectively). Note: embankment height of SB4 and SWM Facility #4 are not identical (SWM #4 embankment height is given as 10 -ft). (Rev. 1) Comment addressed. 6. Show baffles on plan view details for S134 and S135. (Rev. 1) Comment addressed. 7. Show soil stockpiles. Show staging areas. Identify any off -site borrow or spoils sites. (Rev. 1) Comment addressed. 8. Minor: Titles of Erosion and Sediment Control Plans Phase I and Phase II are reversed (sheets 26, 27). (Rev. 1) Comment addressed. New 9. Revise line of 24" berm between S132 and S133, redraw uphill portion. 10. Minor: Sheet 7 —Re -label Temporary Diversion detail to read Temporary 24 "Diversion Berm. If temporary right -of -way diversions are used, show where practice will be used (plan view), else delete detail. It is confusing given second temporary diversion detail. Sheet 8 — please label 100 -yr floodplain and Lickinghole Creek. Sheet 10 —label ESC BASIN 3 profile. 11. Sheet 8 — Restore SF between S132 and S133 (make continuous; ref 16 -Apr, sheet 26). 12. Sheet 8 — S134 — Extend SF east with tree protection line, 80 -100', as initially shown, 16 -Apr. 13. Sheet 8 —Show additional SF north and west of S135, unless existing land cover is woods. 14. Sheet 8 —Label CE paved, plan view. [Ref. Sequence of Construction, Note 4] 15. Sheet 9 —PS -DC shown; show TS -MU as well. Engineering Review Comments Page 5 of 5 16. Sheet 9 — Relocate IP symbol and label to yard drain inlet between Concho Lane and Lampasas Drive. C. Road plans (SUB201400067) 1. Intersection of San Marcos Way and Weshall Drive does not continue the 2% intersected cross grade for a minimum of 20' from the edge of pavement of the intersected street (ref. Sta. 14 +03.17, San Marcos Way). (Rev. 1) Defer to VDOT. 2. Furnish Route Number for Jonna Street (show on plans). (Rev. 1) Comment addressed. 3. ACCD defers to VDOT. All streets are proposed as public roads. (Rev. 1) Comment acknowledged. 4. VDOT approval is required. (Rev. 1) Comment acknowledged. D. Mitigation plans (WP0201400031) 1. 100 -ft. stream buffer (unnamed tributary to Lickinghole Creek) appears to be different on several sheets (4A, 26, and 32). Stream buffers should not shift from one sheet to the next. (Rev. 1) Comment addressed. 2. These sheets do not accurately capture installation impacts required to establish sewer line in the vicinity of MH -11. Sheet 32 does not calculate impact for this sanitary line. These impacts are permanent in that maintenance requires permanent, clear access to sanitary facilities. Calculate and offset impacts to areas of stream buffer impacted by sanitary sewer line installation (see portions of lots 61, 62, 80, and 81; sheet 32). (Rev. 1) Comment addressed. SWM basins #1 and #2 cannot be installed without impact to stream buffers. They may be drawn to show no impact, but final grade lines that touch buffer boundaries cannot be achieved without permanent alteration of landscape within the 100 -ft stream buffer or 100 -year floodplain. Delineate a reasonable zone for construction equipment operation and alteration or loss of vegetative cover during construction or maintenance of downslope embankments. Show reasonable buffer and floodplain impacts on sheet 32. As drawn, design assumes no impact more than 10 -ft downslope of top of embankment of SWM #1, or more than 9 -11 downslope of top of embankment of SWM #2. This is unrealistic. (Rev. 1) Comment addressed. 4. Mitigation area proposed with this plan should increase above 1.04 Acres. (Rev. 1) Comment addressed. New 5. Label PERMANENT DITCH #I (detail, sheet 6) on sheet 12. File: WP020140003 I -Westlake Hills - Memo - 072114 -Revl C O C L I N N :: =5..: 20 C.,„,.,tt St..Suite K.Charlottenille.VA 22.902 434.293.3719 PH 434.2932813 FX VitVe . a),il >e.,11$)il§,o oP grofj cA.10T, May 28,2014 John Anderson Albemarle County Department of Community Development 401 McIntire Road Charlottesville,VA 22902 RE: Westlake Hills Phase II,III, &IV Dear John: Thank you for your comments dated May 12,2014 on the above-referenced project. The following are responses to the items raised in your letter and the engineering meeting: A. Stormwater Management and Mitigation Plan(WP0201400031) 1. The WPO plans have been submitted in a standalone set. 2. The SWM drainage upper boundaries have been revised to coincide with topographical high points. The 4A upper drainage area accounts for collection of the front of the lots and homes draining to Westhall Drive. The limits of disturbance are consistent between SWM and ESC. 3. A permanent ditch has been designed to divert more of the site area to SWM Basin#1. Drainage area 4(4A and 4B)is controlled to the maximum extent practicable with SWM Basin 4. Only the back half of the eleven homes will be released untreated. Efforts to capture and divert runoff behind these lots and outside of the buildable area would cause significant disturbance within the existing treeline and heavily wooded area behind the homes. SWM Basin 4 provides a removal rate in excess of that required for the entire drainage area 4,and provides post-development flows less than the pre-development flow for the entire area. 4. The grass imperviousness has been reduced to 1%. SWM Basins#1 and#3 require 40%and 39%removal rates,respectively. These extended detention basins will provide 35%removal, with the additional 5%and 4%removal provided with the Lickinghole Basin pro-rata share. 5. SWM Basin#2 has been revised to include a wider basin floor. 6. Profile views of each SWM Basin are now provided. 7. The applicant shall obtain soil borings in the location of SWM facilities#1 and#2. 8. The on-grade inlets have been upsized to provide improved inlet efficiency. Inlet carryover has been eliminated prior to sump inlets. 9. The existing critical slopes are now shown on sheets 5 and 5A. 10. The spread at STR 84B, STR 20, and STR 22 meets requirements. Please reference the 4 in/hr intensity storm table for spread,not the 6.5 in/hr storm table which is used to evaluate capacity and depth only. 11. The on-grade inlets have been upsized to provide improved inlet efficiency. 12. The table titles have been corrected. The SWM Facility#1 routing has been revised. B. Erosion Control Plan(WP0201400031) 1. The WPO plans have been submitted in a standalone set. a 2. The super silt fence has been removed from the plans. Silt fence has been placed along contours in areas of less than 0.25 acre upland area per 1001f fencing. A diversion berm conveying runoff to sediment basin 3 has been included. 3. The sediment basins have been redesigned,with updated calculations. Sediment basin#5 does not have an emergency spillway given the temporary nature of this basin. The basin takes only 4.05 acres in Phase I, and once the roadway is installed in Phase II,the drainage area is reduced to only 1.30 acres. 4. The sediment basin details have been revised. 5. The sediment basin details have been revised and are now shown as profiles to scale. 6. Baffles are now shown in plan view on SB4 and SB5. 7. Soil stockpiles and a staging area are now shown. There is no off-site borrow or spoil site proposed. 8. The titles of the ESC plans have been corrected. C. Road Plans(SUB201400067) 1. The Westhall Drive 2%cross grade is continued 16' from the centerline of the roadway along San Marcos Way. A PVI is set 5' from the edge of pavement(21' from the centerline of the intersecting roadway)with a vertical curve 10' length. A 40' landing with a change in slope less than 4%is provided. This intersection design technique has been approved by VDOT to transition roadway grades at stopping conditions. 2. Jonna Street is now labeled as Route 1902 on the plans. 3. The applicant acknowledges this comment. 4. The applicant acknowledges this comment. D. Mitigation Plans(WPO201400031) 1. The correct 100-ft. stream buffer is now provided consistently on all sheets. The discrepancy has been revised in the plans and additional mitigation is provided. 2. The limits of disturbance have been revised to include all impact. The mitigation has been revised. 3. The stream buffer impacts adjacent to SWM basin#1 and#2 have been enlarged. 4. The mitigation area has increased for the increases in the LOD. Please contact me if you have any questions or require any additional information in your review of this submission. Sincerely, Scott Collins,PE �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: Westlake Hills Phase 11,111, & IV Plan preparer: Scott Collins; Collins Engineering [200 Garrett St., Suite K, Charlottesville, VA 22902, scott(&collins -en in�g com] Owner or rep.: Lickinghole Creek, LLC [P. O. Box 1467, Charlottesville VA 22902, alan(&riverbenddev.com] Plan received date: 16 April 2014 Date of comments: 12 May 2014 Reviewer: John Anderson A. Stormwater Management and Mitigation Plan (WP0201400031) 1. Separate out the WPO plans. They cannot be approved as part of a road plan set. 2. Drainage areas are confusing. Drainage divides' upper boundaries should coincide with topographical high points (see post - development, Areas IA, 4A). Downslope drainage area boundaries are somewhat subjective, but areas included in post - development plans (and runoff calculations) are excluded as undisturbed on ESC sheets 26 and 27. Drainage area divides should coincide with actual existing and proposed finished grades. Runoff from Areas I & 4A should be controlled and treated to the extent practicable. Area 4A is controlled during construction by a sediment trap (ST I), sediment basin (SB5), and temporary diversions. Area 1 runoff is diverted to SB1 during construction. These temporary structures are eliminated and not replaced with permanent SWM features. Please consider permanent SWM basin or berm structures located to avoid conflict with allowable use of lots. A berm, for example, on the downslope (western) boundary of drainage area I may divert runoff to SWM basin 1. Grading Plan (sheet 5A) does not reflect alteration of contours likely to occur with removal of SB5. Show grades that result from removing SB5 (pre- existing contours will be altered). 4. Use 1 -2% existing impervious area to calculate %RR, for all drainage areas. 8% pre - development impervious area is too high. Proposed SWM Facilities are Extended Detention (2WQV) with phosphorus removal efficiency of 35 %, but %RR for Areas 1, 2, 3, are 47, 40, 46, respectively, so extended detention will not provide minimum water quality pollutant removal. Once %RR is re- calculated for Area 4 using 1 -2% existing impervious area, extended detention may not be suitable as SWM for Area 4, as well. Extended detention is appropriate for a required removal rate of 35 %. 5. The shape of SWM Facility 2 is problematic; the area between sediment forebay and retention basin is so narrow it constricts flow. Floor width at transition from forebay to basin is 4 -ft, which Engineering Review Comments Page 2 of 4 is susceptible to sedimentation and obstruction. Please use less narrow configuration for SWM Facility #2. 6. Plan views of each SWM facility (1,2,3,4) are drawn to scale. Please furnish profile views of each facility drawn to scale. Include entire culvert pipe (outfall). Typical sections do not reflect design heights listed as 6, 2, 8, and 10 -ft for SWM Facilities 1, 2, 3, and 4, respectively. 7. If SWM Facilities #1, 2 appear to be constructed by down - cutting existing terrain. There are wetlands between these two SWM facilities. Soil borings are needed for these proposed SWM facility locations. Groundwater depth is a practical concern at each location. 8. Drainage: Please ensure the carryover at any on -grade inlet is included in downstream inlet calculations (structure 30, for example, with carryover to structure 2813). Evaluate last on -grade inlet or inlets with carryover located prior to sump inlets, often in cul -de -sacs, to ensure that final roadway grades and drive entrance details allow on -grade inlet carryover to reach a point of entry to stormwater collection system. In the case of structure 30, for example, will carryover reach structure 28B, or will it find lower outlet at drive entrances to Lot 79, 80, or 81 (prefer no carryover at such last on -grade inlets)? 9. Please superimpose critical slopes that appear on sheet 2 on sheets 5 and 5A to facilitate review of proposed development on critical slopes. 10. Please ensure that spread at inlet Str. 84B (San Marcos Way) does not exceed 9 -ft, and at Str. 38 (Westhall Drive) does not exceed 10 -ft. Furnish flanking inlets upslope of structures 20 and 22 on Westhall Drive, since spread at each inlet is > 10.2 -ft. 11. As many as 26 inlets have a calculated required throat length greater than design throat length (sheets 19, 20). Please use engineering judgment to provide design at least equal the calculated required throat length. There are examples of slight mismatch: 12 -ft vs. 12.06 (rate insignificant), and greater disparity: 12 -ft vs. 14.47 -ft, for example. It is cases of greater disparity that will benefit from design that meets calculated requirements. 12. Minor: Titles of computations (tables) on sheet 22 should reference SWM Facility #3 and #4. Also, using a start elevation of 547.5 to model SWM Facility #1 yields negative elevations. Should start elevation for SWM Facility #1 be 542.00 instead? B. Erosion Control Plan (WP0201400031) 1. Separate out the WPO plans. They cannot be approved as part of a road plan set. 2. Super silt fence is proposed as single perimeter control at various locations with 160 -200 ft upslope drainage areas. VESCH details design criteria, planning considerations, construction specifications, and conditions where silt fence may be used, and does not recognize super silt fence. Please eliminate reference to super silt fence wherever it occurs (at least 1,600 LF are shown as perimeter controls measures for Drainage Areas 3, 4). Please revise design to include measures consistent with topography, percent grade, length, acreage, and suitability per VESCH. Silt fence should not be installed cross - contour, but on- contour with minimal rise or fall along its Engineering Review Comments Page 3 of 4 length. Diversion dikes and sediment traps (or basins) may be more appropriate in many locations currently shown to be controlled with super silt fence. Request for variance is an option. 3. Please review sediment basin design. Please provide emergency spillway exit channel length calculations or narrative supporting exit channel lengths of 2.4, 4, 4, and 15 -ft. Please explain (narrative is okay) why sediment basin #5 does not have an emergency spillway. Revise anti -seep collar dimensions for all 5 sediment basins (size at least 4 -ft larger than barrel diameter / VSMH, 1999, p. 5 -68). SB 1 requires 3 collars given length of barrel in saturated zone = 57.68 -ft. SB 1 upstream face slope must be 2.5:1 (or flatter) given embankment height = 12 -ft. 4. Invert in -out for three sediment basin outfall pipes is identical and does not correspond with invert information on details; please revise invert data for SB1, 2, and 4 (sheet 27), as necessary. 5. Please draw sediment basin profiles to scale. Show actual existing contours with relative scale. Generic section views are furnished. Existing ground is shown no higher than invert of outfall of culverts through embankments, at base of 3:1 slope. Actual slopes are flatter. Embankment heights are given as 6, 2, 8, 12, 6 -ft (SB 1, 2, 3, 4, and 5, respectively). Note: embankment height of SB4 and SWM Facility #4 are not identical (SWM #4 embankment height is given as 10 -ft). 6. Show baffles on plan view details for SB4 and SB5. 7. Show soil stockpiles. Show staging areas. Identify any off -site borrow or spoils sites. 8. Minor: Titles of Erosion and Sediment Control Plans Phase I and Phase I1 are reversed (sheets 26, 27). C. Road plans (SUB201400067) 1. Intersection of San Marcos Way and Weshall Drive does not continue the 2% intersected cross grade for a minimum of 20' from the edge of pavement of the intersected street (ref. Sta. 14 +03.17, San Marcos Way). 2. Furnish Route Number for Jonna Street (show on plans). 3. ACCD defers to VDOT. All streets are proposed as public roads. 4. VDOT approval is required. D. Mitigation plans (WP0201400031) 100 -ft. stream buffer (unnamed tributary to Lickinghole Creek) appears to be different on several sheets (4A, 26, and 32). Stream buffers should not shift from one sheet to the next. 2. These sheets do not accurately capture installation impacts required to establish sewer line in the vicinity of MH -11. Sheet 32 does not calculate impact for this sanitary line. These impacts are permanent in that maintenance requires permanent, clear access to sanitary facilities. Calculate and offset impacts to areas of stream buffer impacted by sanitary sewer line installation (see portions of lots 61, 62, 80, and 81; sheet 32). 3. SWM basins #1 and #2 cannot be installed without impact to stream buffers. They may be drawn to show no impact, but final grade lines that touch buffer boundaries cannot be Engineering Review Comments Page 4 of 4 achieved without permanent alteration of landscape within the 100 -ft stream buffer or 100 -year floodplain. Delineate a reasonable zone for construction equipment operation and alteration or loss of vegetative cover during construction or maintenance of downslope embankments. Show reasonable buffer and floodplain impacts on sheet 32. As drawn, design assumes no impact more than 10 -ft downslope of top of embankment of SWM #1, or more than 9 -ft downslope of top of embankment of SWM #2. This is unrealistic. 4. Mitigation area proposed with this plan should increase above 1.04 Acres. E. Final Plat None Received File: WPO201400031-Westlake Hills- Memo - 051214 �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: Westlake Hills Phase II, 111, & IV Plan preparer: Scott Collins; Collins Engineering [200 Garrett St., Suite K, Charlottesville, VA 22902, scott(cDcollins- enizineering com] Owner or rep.: Lickinghole Creek, LLC [P. O. Box 1467, Charlottesville VA 22902, alan(a)riverbenddev. com] Plan received date: 16 April 2014 (Rev. 1) 6 June 2014 (Road Plan/ESC /SWM/Mitigation) Date of comments: 12 May 2014 (Rev. 1) 18 July 2014 (21 July 2014; SMW Items 15 -20) Reviewer: John Anderson A. Stormwater Management Plan (WP0201400031) 1. Separate out the WPO plans. They cannot be approved as part of a road plan set. (Rev. 1) Comment partially addressed. Please restore plan sheets 2 (existing conditions), 5, and 5A (grading plan) to WPO plan set, as grading and existing conditions are essential to WPO review /approval. These sheets should remain with the road plan set, as well. 2. Drainage areas are confusing. Drainage divides' upper boundaries should coincide with topographical high points (see post - development, Areas 1A, 4A). Downslope drainage area boundaries are somewhat subjective, but areas included in post - development plans (and runoff calculations) are excluded as undisturbed on ESC sheets 26 and 27. Drainage area divides should coincide with actual existing and proposed finished grades. (Rev. 1) Comment addressed. 3. Runoff from Areas I & 4A should be controlled and treated to the extent practicable. Area 4A is controlled during construction by a sediment trap (ST I), sediment basin (S135), and temporary diversions. Area 1 A runoff is diverted to SB 1 during construction. These temporary structures are eliminated and not replaced with permanent SWM features. Please consider permanent SWM basin or berm structures located to avoid conflict with allowable use of lots. A berm, for example, on the downslope (western) boundary of drainage area IA may divert runoff to SWM basin 1. Grading Plan (sheet 5A) does not reflect alteration of contours likely to occur with removal of S135. Show grades that result from removing S135 (pre- existing contours will be altered). (Rev. 1) Comment addressed. Use 1 -2% existing impervious area to calculate %RR, for all drainage areas. 8% pre - development impervious area is too high. Proposed SWM Facilities are Extended Detention (2WQV) with phosphorus removal efficiency of 35 %, but %RR for Areas 1, 2, 3, are 47, 40, 46, respectively, so extended detention will not provide minimum water quality pollutant removal. Once %RR is re- calculated for Area 4 using 1- 2% existing impervious area, extended detention may not be suitable as SWM for Area 4, as well. Extended detention is appropriate for a required removal rate of 35 %. (Rev. 1) As follow -up to discussion with Scott Collins and ACCD staff on 18 -Jul, comment withdrawn / Extended detention basins are suitable, except SWM Facility #1; ref. 15 -20, below. Ref. short version BMP computations for worksheets 2 — 6. Engineering Review Comments Page 2 of 5 Use yards/ cultivated turf= Area X 0.08. Check effect of change (0.08) on V, water quality volume (21- Jul). Also, see comment #14 below, Summary of Watershed tables. please Note:. The County has received a list of projects which have applied for general permit coverage from DEQ. This project (all phases) does not appear on that list. Without a current permit, conditional permit, or permit continuation by DEQ, we cannot approve the stormwater management plan. This project would have to apply for a new permit, and meet the current state requirements. Please provide copies of documents demonstrating current DEQ VSMP general permit coverage, or apply for a new VSMP general permit with the County. 5. The shape of SWM Facility 2 is problematic; the area between sediment forebay and retention basin is so narrow it constricts flow. Floor width at transition from forebay to basin is 4 -ft, which is susceptible to sedimentation and obstruction. Please use less narrow configuration for SWM Facility #2. (Rev. 1) Comment addressed — dimensions revised slightly (4 - 6 ft); further revision recommended (not mandated). 6. Plan views of each SWM facility (1,2,3,4) are drawn to scale. Please furnish profile views of each facility drawn to scale. Include entire culvert pipe (outfall). Typical sections do not reflect design heights listed as 6, 2, 8, and 10 -ft for SWM Facilities 1, 2, 3, and 4, respectively. (Rev. 1) Comment addressed. 7. If SWM Facilities #1, 2 appear to be constructed by down - cutting existing terrain. There are wetlands between these two SWM facilities. Soil borings are needed for these proposed SWM facility locations. Groundwater depth is a practical concern at each location. (Rev. 1) Comment addressed. 8. Drainage: Please ensure the carryover at any on -grade inlet is included in downstream inlet calculations (structure 30, for example, with carryover to structure 2813). Evaluate last on -grade inlet or inlets with carryover located prior to sump inlets, often in cul -de -sacs, to ensure that final roadway grades and drive entrance details allow on -grade inlet carryover to reach a point of entry to stormwater collection system. In the case of structure 30, for example, will carryover reach structure 2813, or will it find lower outlet at drive entrances to Lot 79, 80, or 81 (prefer no carryover at such last on -grade inlets)? (Rev. 1) Comment addressed. 9. Please superimpose critical slopes that appear on sheet 2 on sheets 5 and 5A to facilitate review of proposed development on critical slopes. (Rev. 1) Comment addressed, but show Approved critical slope impact layer (dark shading, as shown on sheet 2, 16 -Apr plans; ref. #1, above). This will guide inspection and construction, help avoid misunderstandings that easily arise. 10. Please ensure that spread at inlet Str. 84B (San Marcos Way) does not exceed 9 -ft, and at Str. 38 (Westhall Drive) does not exceed 10 -ft. Furnish flanking inlets upslope of structures 20 and 22 on Westhall Drive, since spread at each inlet is > 10.2 -ft. (Rev. 1) Comment addressed. 11. As many as 26 inlets have a calculated required throat length greater than design throat length (sheets 19, 20). Please use engineering judgment to provide design at least equal the calculated required throat length. There are examples of slight mismatch: 12 -ft vs. 12.06 (rate insignificant), and greater disparity: 12 -ft vs. 14.47 -ft, for example. It is cases of greater disparity that will benefit from design that meets calculated requirements. (Rev. 1) Comment addressed. Note- number of inlets fell from 26 to 0 if use 4 "/hr table, to 12 if use 6.5 " /hr table (sheets 19/20, SUB201400067). 5 out of 12 show design v. calculated difference < 0.15'(2"). Thank you. New Engineering Review Comments Page 3 of 5 12. Minor: Titles of computations (tables) on sheet 22 should reference SWM Facility #3 and #4. Also, using a start elevation of 547.5 to model SWM Facility #1 yields negative elevations. Should start elevation for SWM Facility #1 be 542.00 instead? (Rev. 1) Comment addressed. 13. Label PERMANENT DITCH #1 (detail, sheet 6) on sheet 3, where drainage area divide line obscures this new design feature, and on sheet 5 once sheets 5A and 5 are restored to WPO plan set (comment #1, above). 14. Summary of Watershed tables, sheets 3, 4, and 5 — revise to clarify that values are peak flow (cfs) values. Confirm SCS routing compares pre - development peak flow using pre - development DA acreage against post - development peak flow using post - developed DA acreage. Acreage varies: pre -post development. 15. Check revised V, required treatment volume, .xls (cy), against Extended Detention Facility Data, cf, each SWM basin. (SWM Facility #1, 6 -Jun plans: V (.xls) = 281.3 cy = 7595 cf - Extended detention facility data reports = 11,704 cf, for example. Remaining basins: SWM Facility #2, 6 -Jun plans: V (.xls) = 153.9 cy = 4155 cf - Extended detention facility data reports = 2,465 cf. SWM Facility #3, 6 -Jun plans: V (.xls) _ 258.6 cy = 6982 cf - Extended detention facility data reports = 6,233 cf. SWM Facility #4, 6 -Jun plans: V (.xls) = 267.2 cy = 7214 cf - Extended detention facility data reports = 4,188 cf.) Ensure WQV and 2 x WQV required are accurate since basis of SWM basin design. Check SWM facility design against 2 x water quality volume. 16. Revise % RR calc, DA 41, 2, 3, 4A -413: Use'C' = 0.70 only (instead of 0.76, 0.28, 0.44, 0.36. C, pollutant concentration,is not a variable, but a constant, mg /L, phosphorous, New Development in Development Areas. 17. Revise .xls (Short Version BMP Computations): Use post - developed D.A. areas to calculate L ost ). ( All pre- and post - development Drainage Areas differ: 1, 2, 3, 4A - 4B ) 18. SWM basin #1: Extended Detention for D.A. #1 is not suitable. %RR = 67. Re- evaluate SWM control for DA #1. Sheets 4 -5: Update Notes re. Lickinghole Creek Prorata share 19. Revise Runoff Curve Number Table, DA #4A, Developed: revise Woods = 3.36 Acres; Area negligible, once lots developed. (Sheet 3, 6 -June -2014 plan set) 20. Re -run SCS routing using: revised 1% meadow -woods pre - developed condition (12- May -14, comment #4); L(post) [ revised using post - developed D.A. areas ]; (revised) required 2 x WQV; revised basin geometry (if revised); alternate SWM Facility 41; and higher post - developed CN, DA 44A. Also, see #4, above. 21. Reconcile impervious area, DA #4, post - developed. Runoff Curve Number Table lists as 2.31 Ac; Short Version BMP.xls lists as 3.01 Ac. B. Erosion Control Plan (WP0201400031) Separate out the WPO plans. They cannot be approved as part of a road plan set. (Rev. 1) Partially addressed, see item #1, SWM plan, above. Restore sheets. 2. Super silt fence is proposed as single perimeter control at various locations with 160 -200 ft upslope drainage areas. VESCH details design criteria, planning considerations, construction specifications, and conditions where silt fence may be used, and does not recognize super silt fence. Please eliminate reference to super silt fence wherever it occurs (at least 1,600 LF are shown as perimeter controls measures for Drainage Areas 3, 4). Please revise design to include measures consistent with topography, percent grade, length, acreage, and suitability per VESCH. Silt fence should not be installed cross - contour, but on- contour with minimal rise or fall along its length. Diversion dikes and sediment traps (or basins) may be more Engineering Review Comments Page 4 of 5 appropriate in many locations currently shown to be controlled with super silt fence. Request for variance is an option. (Rev. 1) Comment partially addressed. Sheet 9: show IP [VESCH Plate 3.07 -1] at each of 24" yard drain inlets [`A' —`O'; 16 -Apr, sheets 5 -5A]. Pipes between yard drain inlets are 12" DIA. Grading and runoff are significant. Q, from system `N'- `M' -`L' = 3.5cfs, at structure 44. IP required at each inlet, A -O. [Concho Lane: A -D; Lampasas Dr: E,F; Pecos Ct: G,H; Westhall Dr: I, J, K; and Area between San Marcos Way - Westhall Dr: M,N,L] 3. Please review sediment basin design. Please provide emergency spillway exit channel length calculations or narrative supporting exit channel lengths of 2.4, 4, 4, and 15 -ft. Please explain (narrative is okay) why sediment basin #5 does not have an emergency spillway. Revise anti -seep collar dimensions for all 5 sediment basins (size at least 4 -ft larger than barrel diameter / VSMH, 1999, p. 5 -68). SB 1 requires 3 collars given length of barrel in saturated zone = 57.68 -ft. SB 1 upstream face slope must be 2.5:1 (or flatter) given embankment height = 12 -ft. (Rev. 1) Comment addressed. 4. Invert in -out for three sediment basin outfall pipes is identical and does not correspond with invert information on details; please revise invert data for S13 1, 2, and 4 (sheet 27), as necessary. (Rev. 1) Partially addressed — please reconcile plan and profile culvert slope and INV information for S134. 5. Please draw sediment basin profiles to scale. Show actual existing contours with relative scale. Generic section views are furnished. Existing ground is shown no higher than invert of outfall of culverts through embankments, at base of 3:1 slope. Actual slopes are flatter. Embankment heights are given as 6, 2, 8, 12, 6 -ft (SB 1, 2, 3, 4, and 5, respectively). Note: embankment height of SB4 and SWM Facility #4 are not identical (SWM #4 embankment height is given as 10 -ft). (Rev. 1) Comment addressed. 6. Show baffles on plan view details for S134 and S135. (Rev. 1) Comment addressed. 7. Show soil stockpiles. Show staging areas. Identify any off -site borrow or spoils sites. (Rev. 1) Comment addressed. 8. Minor: Titles of Erosion and Sediment Control Plans Phase I and Phase II are reversed (sheets 26, 27). (Rev. 1) Comment addressed. New 9. Revise line of 24" berm between S132 and S133, redraw uphill portion. 10. Minor: Sheet 7 —Re -label Temporary Diversion detail to read Temporary 24 "Diversion Berm. If temporary right -of -way diversions are used, show where practice will be used (plan view), else delete detail. It is confusing given second temporary diversion detail. Sheet 8 — please label 100 -yr floodplain and Lickinghole Creek. Sheet 10 —label ESC BASIN 3 profile. 11. Sheet 8 — Restore SF between S132 and S133 (make continuous; ref 16 -Apr, sheet 26). 12. Sheet 8 — S134 — Extend SF east with tree protection line, 80 -100', as initially shown, 16 -Apr. 13. Sheet 8 —Show additional SF north and west of S135, unless existing land cover is woods. 14. Sheet 8 —Label CE paved, plan view. [Ref. Sequence of Construction, Note 4] 15. Sheet 9 —PS -DC shown; show TS -MU as well. Engineering Review Comments Page 5 of 5 16. Sheet 9 — Relocate IP symbol and label to yard drain inlet between Concho Lane and Lampasas Drive. C. Road plans (SUB201400067) 1. Intersection of San Marcos Way and Weshall Drive does not continue the 2% intersected cross grade for a minimum of 20' from the edge of pavement of the intersected street (ref. Sta. 14 +03.17, San Marcos Way). (Rev. 1) Defer to VDOT. 2. Furnish Route Number for Jonna Street (show on plans). (Rev. 1) Comment addressed. 3. ACCD defers to VDOT. All streets are proposed as public roads. (Rev. 1) Comment acknowledged. 4. VDOT approval is required. (Rev. 1) Comment acknowledged. D. Mitigation plans (WP0201400031) 1. 100 -ft. stream buffer (unnamed tributary to Lickinghole Creek) appears to be different on several sheets (4A, 26, and 32). Stream buffers should not shift from one sheet to the next. (Rev. 1) Comment addressed. 2. These sheets do not accurately capture installation impacts required to establish sewer line in the vicinity of MH -11. Sheet 32 does not calculate impact for this sanitary line. These impacts are permanent in that maintenance requires permanent, clear access to sanitary facilities. Calculate and offset impacts to areas of stream buffer impacted by sanitary sewer line installation (see portions of lots 61, 62, 80, and 81; sheet 32). (Rev. 1) Comment addressed. SWM basins #1 and #2 cannot be installed without impact to stream buffers. They may be drawn to show no impact, but final grade lines that touch buffer boundaries cannot be achieved without permanent alteration of landscape within the 100 -ft stream buffer or 100 -year floodplain. Delineate a reasonable zone for construction equipment operation and alteration or loss of vegetative cover during construction or maintenance of downslope embankments. Show reasonable buffer and floodplain impacts on sheet 32. As drawn, design assumes no impact more than 10 -ft downslope of top of embankment of SWM #1, or more than 9 -11 downslope of top of embankment of SWM #2. This is unrealistic. (Rev. 1) Comment addressed. 4. Mitigation area proposed with this plan should increase above 1.04 Acres. (Rev. 1) Comment addressed. New 5. Label PERMANENT DITCH #I (detail, sheet 6) on sheet 12. File: WP020140003 I -Westlake Hills - Memo - 072114 -Revl �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: Westlake Hills Phase 11,111, & IV Plan preparer: Scott Collins; Collins Engineering [200 Garrett St., Suite K, Charlottesville, VA 22902, scott(&collins -en in�g com] Owner or rep.: Lickinghole Creek, LLC [P. O. Box 1467, Charlottesville VA 22902, alan(&riverbenddev.com] Plan received date: 16 April 2014 Date of comments: 12 May 2014 Reviewer: John Anderson A. Stormwater Management and Mitigation Plan (WP0201400031) 1. Separate out the WPO plans. They cannot be approved as part of a road plan set. 2. Drainage areas are confusing. Drainage divides' upper boundaries should coincide with topographical high points (see post - development, Areas IA, 4A). Downslope drainage area boundaries are somewhat subjective, but areas included in post - development plans (and runoff calculations) are excluded as undisturbed on ESC sheets 26 and 27. Drainage area divides should coincide with actual existing and proposed finished grades. Runoff from Areas I & 4A should be controlled and treated to the extent practicable. Area 4A is controlled during construction by a sediment trap (ST I), sediment basin (SB5), and temporary diversions. Area 1 runoff is diverted to SB1 during construction. These temporary structures are eliminated and not replaced with permanent SWM features. Please consider permanent SWM basin or berm structures located to avoid conflict with allowable use of lots. A berm, for example, on the downslope (western) boundary of drainage area I may divert runoff to SWM basin 1. Grading Plan (sheet 5A) does not reflect alteration of contours likely to occur with removal of SB5. Show grades that result from removing SB5 (pre- existing contours will be altered). 4. Use 1 -2% existing impervious area to calculate %RR, for all drainage areas. 8% pre - development impervious area is too high. Proposed SWM Facilities are Extended Detention (2WQV) with phosphorus removal efficiency of 35 %, but %RR for Areas 1, 2, 3, are 47, 40, 46, respectively, so extended detention will not provide minimum water quality pollutant removal. Once %RR is re- calculated for Area 4 using 1 -2% existing impervious area, extended detention may not be suitable as SWM for Area 4, as well. Extended detention is appropriate for a required removal rate of 35 %. 5. The shape of SWM Facility 2 is problematic; the area between sediment forebay and retention basin is so narrow it constricts flow. Floor width at transition from forebay to basin is 4 -ft, which Engineering Review Comments Page 2 of 4 is susceptible to sedimentation and obstruction. Please use less narrow configuration for SWM Facility #2. 6. Plan views of each SWM facility (1,2,3,4) are drawn to scale. Please furnish profile views of each facility drawn to scale. Include entire culvert pipe (outfall). Typical sections do not reflect design heights listed as 6, 2, 8, and 10 -ft for SWM Facilities 1, 2, 3, and 4, respectively. 7. If SWM Facilities #1, 2 appear to be constructed by down - cutting existing terrain. There are wetlands between these two SWM facilities. Soil borings are needed for these proposed SWM facility locations. Groundwater depth is a practical concern at each location. 8. Drainage: Please ensure the carryover at any on -grade inlet is included in downstream inlet calculations (structure 30, for example, with carryover to structure 2813). Evaluate last on -grade inlet or inlets with carryover located prior to sump inlets, often in cul -de -sacs, to ensure that final roadway grades and drive entrance details allow on -grade inlet carryover to reach a point of entry to stormwater collection system. In the case of structure 30, for example, will carryover reach structure 28B, or will it find lower outlet at drive entrances to Lot 79, 80, or 81 (prefer no carryover at such last on -grade inlets)? 9. Please superimpose critical slopes that appear on sheet 2 on sheets 5 and 5A to facilitate review of proposed development on critical slopes. 10. Please ensure that spread at inlet Str. 84B (San Marcos Way) does not exceed 9 -ft, and at Str. 38 (Westhall Drive) does not exceed 10 -ft. Furnish flanking inlets upslope of structures 20 and 22 on Westhall Drive, since spread at each inlet is > 10.2 -ft. 11. As many as 26 inlets have a calculated required throat length greater than design throat length (sheets 19, 20). Please use engineering judgment to provide design at least equal the calculated required throat length. There are examples of slight mismatch: 12 -ft vs. 12.06 (rate insignificant), and greater disparity: 12 -ft vs. 14.47 -ft, for example. It is cases of greater disparity that will benefit from design that meets calculated requirements. 12. Minor: Titles of computations (tables) on sheet 22 should reference SWM Facility #3 and #4. Also, using a start elevation of 547.5 to model SWM Facility #1 yields negative elevations. Should start elevation for SWM Facility #1 be 542.00 instead? B. Erosion Control Plan (WP0201400031) 1. Separate out the WPO plans. They cannot be approved as part of a road plan set. 2. Super silt fence is proposed as single perimeter control at various locations with 160 -200 ft upslope drainage areas. VESCH details design criteria, planning considerations, construction specifications, and conditions where silt fence may be used, and does not recognize super silt fence. Please eliminate reference to super silt fence wherever it occurs (at least 1,600 LF are shown as perimeter controls measures for Drainage Areas 3, 4). Please revise design to include measures consistent with topography, percent grade, length, acreage, and suitability per VESCH. Silt fence should not be installed cross - contour, but on- contour with minimal rise or fall along its Engineering Review Comments Page 3 of 4 length. Diversion dikes and sediment traps (or basins) may be more appropriate in many locations currently shown to be controlled with super silt fence. Request for variance is an option. 3. Please review sediment basin design. Please provide emergency spillway exit channel length calculations or narrative supporting exit channel lengths of 2.4, 4, 4, and 15 -ft. Please explain (narrative is okay) why sediment basin #5 does not have an emergency spillway. Revise anti -seep collar dimensions for all 5 sediment basins (size at least 4 -ft larger than barrel diameter / VSMH, 1999, p. 5 -68). SB 1 requires 3 collars given length of barrel in saturated zone = 57.68 -ft. SB 1 upstream face slope must be 2.5:1 (or flatter) given embankment height = 12 -ft. 4. Invert in -out for three sediment basin outfall pipes is identical and does not correspond with invert information on details; please revise invert data for SB1, 2, and 4 (sheet 27), as necessary. 5. Please draw sediment basin profiles to scale. Show actual existing contours with relative scale. Generic section views are furnished. Existing ground is shown no higher than invert of outfall of culverts through embankments, at base of 3:1 slope. Actual slopes are flatter. Embankment heights are given as 6, 2, 8, 12, 6 -ft (SB 1, 2, 3, 4, and 5, respectively). Note: embankment height of SB4 and SWM Facility #4 are not identical (SWM #4 embankment height is given as 10 -ft). 6. Show baffles on plan view details for SB4 and SB5. 7. Show soil stockpiles. Show staging areas. Identify any off -site borrow or spoils sites. 8. Minor: Titles of Erosion and Sediment Control Plans Phase I and Phase I1 are reversed (sheets 26, 27). C. Road plans (SUB201400067) 1. Intersection of San Marcos Way and Weshall Drive does not continue the 2% intersected cross grade for a minimum of 20' from the edge of pavement of the intersected street (ref. Sta. 14 +03.17, San Marcos Way). 2. Furnish Route Number for Jonna Street (show on plans). 3. ACCD defers to VDOT. All streets are proposed as public roads. 4. VDOT approval is required. D. Mitigation plans (WP0201400031) 100 -ft. stream buffer (unnamed tributary to Lickinghole Creek) appears to be different on several sheets (4A, 26, and 32). Stream buffers should not shift from one sheet to the next. 2. These sheets do not accurately capture installation impacts required to establish sewer line in the vicinity of MH -11. Sheet 32 does not calculate impact for this sanitary line. These impacts are permanent in that maintenance requires permanent, clear access to sanitary facilities. Calculate and offset impacts to areas of stream buffer impacted by sanitary sewer line installation (see portions of lots 61, 62, 80, and 81; sheet 32). 3. SWM basins #1 and #2 cannot be installed without impact to stream buffers. They may be drawn to show no impact, but final grade lines that touch buffer boundaries cannot be Engineering Review Comments Page 4 of 4 achieved without permanent alteration of landscape within the 100 -ft stream buffer or 100 -year floodplain. Delineate a reasonable zone for construction equipment operation and alteration or loss of vegetative cover during construction or maintenance of downslope embankments. Show reasonable buffer and floodplain impacts on sheet 32. As drawn, design assumes no impact more than 10 -ft downslope of top of embankment of SWM #1, or more than 9 -ft downslope of top of embankment of SWM #2. This is unrealistic. 4. Mitigation area proposed with this plan should increase above 1.04 Acres. E. Final Plat None Received File: WPO201400031-Westlake Hills- Memo - 051214 �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: Westlake Hills Phase II, 111, & IV Plan preparer: Scott Collins; Collins Engineering [200 Garrett St., Suite K, Charlottesville, VA 22902, scott(cDcollins- enizineering com] Owner or rep.: Lickinghole Creek, LLC [P. O. Box 1467, Charlottesville VA 22902, alan(a)riverbenddev. com] Plan received date: 16 April 2014 (Rev. 1) 6 June 2014 (Road Plan/ESC /SWM/Mitigation) Date of comments: 12 May 2014 (Rev. 1) 18 July 2014 (21 July 2014; SMW Items 15 -20) Reviewer: John Anderson A. Stormwater Management Plan (WP0201400031) 1. Separate out the WPO plans. They cannot be approved as part of a road plan set. (Rev. 1) Comment partially addressed. Please restore plan sheets 2 (existing conditions), 5, and 5A (grading plan) to WPO plan set, as grading and existing conditions are essential to WPO review /approval. These sheets should remain with the road plan set, as well. 2. Drainage areas are confusing. Drainage divides' upper boundaries should coincide with topographical high points (see post - development, Areas 1A, 4A). Downslope drainage area boundaries are somewhat subjective, but areas included in post - development plans (and runoff calculations) are excluded as undisturbed on ESC sheets 26 and 27. Drainage area divides should coincide with actual existing and proposed finished grades. (Rev. 1) Comment addressed. 3. Runoff from Areas I & 4A should be controlled and treated to the extent practicable. Area 4A is controlled during construction by a sediment trap (ST I), sediment basin (S135), and temporary diversions. Area 1 A runoff is diverted to SB 1 during construction. These temporary structures are eliminated and not replaced with permanent SWM features. Please consider permanent SWM basin or berm structures located to avoid conflict with allowable use of lots. A berm, for example, on the downslope (western) boundary of drainage area IA may divert runoff to SWM basin 1. Grading Plan (sheet 5A) does not reflect alteration of contours likely to occur with removal of S135. Show grades that result from removing S135 (pre- existing contours will be altered). (Rev. 1) Comment addressed. Use 1 -2% existing impervious area to calculate %RR, for all drainage areas. 8% pre - development impervious area is too high. Proposed SWM Facilities are Extended Detention (2WQV) with phosphorus removal efficiency of 35 %, but %RR for Areas 1, 2, 3, are 47, 40, 46, respectively, so extended detention will not provide minimum water quality pollutant removal. Once %RR is re- calculated for Area 4 using 1- 2% existing impervious area, extended detention may not be suitable as SWM for Area 4, as well. Extended detention is appropriate for a required removal rate of 35 %. (Rev. 1) As follow -up to discussion with Scott Collins and ACCD staff on 18 -Jul, comment withdrawn / Extended detention basins are suitable, except SWM Facility #1; ref. 15 -20, below. Ref. short version BMP computations for worksheets 2 — 6. Engineering Review Comments Page 2 of 5 Use yards/ cultivated turf= Area X 0.08. Check effect of change (0.08) on V, water quality volume (21- Jul). Also, see comment #14 below, Summary of Watershed tables. please Note:. The County has received a list of projects which have applied for general permit coverage from DEQ. This project (all phases) does not appear on that list. Without a current permit, conditional permit, or permit continuation by DEQ, we cannot approve the stormwater management plan. This project would have to apply for a new permit, and meet the current state requirements. Please provide copies of documents demonstrating current DEQ VSMP general permit coverage, or apply for a new VSMP general permit with the County. 5. The shape of SWM Facility 2 is problematic; the area between sediment forebay and retention basin is so narrow it constricts flow. Floor width at transition from forebay to basin is 4 -ft, which is susceptible to sedimentation and obstruction. Please use less narrow configuration for SWM Facility #2. (Rev. 1) Comment addressed — dimensions revised slightly (4 - 6 ft); further revision recommended (not mandated). 6. Plan views of each SWM facility (1,2,3,4) are drawn to scale. Please furnish profile views of each facility drawn to scale. Include entire culvert pipe (outfall). Typical sections do not reflect design heights listed as 6, 2, 8, and 10 -ft for SWM Facilities 1, 2, 3, and 4, respectively. (Rev. 1) Comment addressed. 7. If SWM Facilities #1, 2 appear to be constructed by down - cutting existing terrain. There are wetlands between these two SWM facilities. Soil borings are needed for these proposed SWM facility locations. Groundwater depth is a practical concern at each location. (Rev. 1) Comment addressed. 8. Drainage: Please ensure the carryover at any on -grade inlet is included in downstream inlet calculations (structure 30, for example, with carryover to structure 2813). Evaluate last on -grade inlet or inlets with carryover located prior to sump inlets, often in cul -de -sacs, to ensure that final roadway grades and drive entrance details allow on -grade inlet carryover to reach a point of entry to stormwater collection system. In the case of structure 30, for example, will carryover reach structure 2813, or will it find lower outlet at drive entrances to Lot 79, 80, or 81 (prefer no carryover at such last on -grade inlets)? (Rev. 1) Comment addressed. 9. Please superimpose critical slopes that appear on sheet 2 on sheets 5 and 5A to facilitate review of proposed development on critical slopes. (Rev. 1) Comment addressed, but show Approved critical slope impact layer (dark shading, as shown on sheet 2, 16 -Apr plans; ref. #1, above). This will guide inspection and construction, help avoid misunderstandings that easily arise. 10. Please ensure that spread at inlet Str. 84B (San Marcos Way) does not exceed 9 -ft, and at Str. 38 (Westhall Drive) does not exceed 10 -ft. Furnish flanking inlets upslope of structures 20 and 22 on Westhall Drive, since spread at each inlet is > 10.2 -ft. (Rev. 1) Comment addressed. 11. As many as 26 inlets have a calculated required throat length greater than design throat length (sheets 19, 20). Please use engineering judgment to provide design at least equal the calculated required throat length. There are examples of slight mismatch: 12 -ft vs. 12.06 (rate insignificant), and greater disparity: 12 -ft vs. 14.47 -ft, for example. It is cases of greater disparity that will benefit from design that meets calculated requirements. (Rev. 1) Comment addressed. Note- number of inlets fell from 26 to 0 if use 4 "/hr table, to 12 if use 6.5 " /hr table (sheets 19/20, SUB201400067). 5 out of 12 show design v. calculated difference < 0.15'(2"). Thank you. New Engineering Review Comments Page 3 of 5 12. Minor: Titles of computations (tables) on sheet 22 should reference SWM Facility #3 and #4. Also, using a start elevation of 547.5 to model SWM Facility #1 yields negative elevations. Should start elevation for SWM Facility #1 be 542.00 instead? (Rev. 1) Comment addressed. 13. Label PERMANENT DITCH #1 (detail, sheet 6) on sheet 3, where drainage area divide line obscures this new design feature, and on sheet 5 once sheets 5A and 5 are restored to WPO plan set (comment #1, above). 14. Summary of Watershed tables, sheets 3, 4, and 5 — revise to clarify that values are peak flow (cfs) values. Confirm SCS routing compares pre - development peak flow using pre - development DA acreage against post - development peak flow using post - developed DA acreage. Acreage varies: pre -post development. 15. Check revised V, required treatment volume, .xls (cy), against Extended Detention Facility Data, cf, each SWM basin. (SWM Facility #1, 6 -Jun plans: V (.xls) = 281.3 cy = 7595 cf - Extended detention facility data reports = 11,704 cf, for example. Remaining basins: SWM Facility #2, 6 -Jun plans: V (.xls) = 153.9 cy = 4155 cf - Extended detention facility data reports = 2,465 cf. SWM Facility #3, 6 -Jun plans: V (.xls) _ 258.6 cy = 6982 cf - Extended detention facility data reports = 6,233 cf. SWM Facility #4, 6 -Jun plans: V (.xls) = 267.2 cy = 7214 cf - Extended detention facility data reports = 4,188 cf.) Ensure WQV and 2 x WQV required are accurate since basis of SWM basin design. Check SWM facility design against 2 x water quality volume. 16. Revise % RR calc, DA 41, 2, 3, 4A -413: Use'C' = 0.70 only (instead of 0.76, 0.28, 0.44, 0.36. C, pollutant concentration,is not a variable, but a constant, mg /L, phosphorous, New Development in Development Areas. 17. Revise .xls (Short Version BMP Computations): Use post - developed D.A. areas to calculate L ost ). ( All pre- and post - development Drainage Areas differ: 1, 2, 3, 4A - 4B ) 18. SWM basin #1: Extended Detention for D.A. #1 is not suitable. %RR = 67. Re- evaluate SWM control for DA #1. Sheets 4 -5: Update Notes re. Lickinghole Creek Prorata share 19. Revise Runoff Curve Number Table, DA #4A, Developed: revise Woods = 3.36 Acres; Area negligible, once lots developed. (Sheet 3, 6 -June -2014 plan set) 20. Re -run SCS routing using: revised 1% meadow -woods pre - developed condition (12- May -14, comment #4); L(post) [ revised using post - developed D.A. areas ]; (revised) required 2 x WQV; revised basin geometry (if revised); alternate SWM Facility 41; and higher post - developed CN, DA 44A. Also, see #4, above. 21. Reconcile impervious area, DA #4, post - developed. Runoff Curve Number Table lists as 2.31 Ac; Short Version BMP.xls lists as 3.01 Ac. B. Erosion Control Plan (WP0201400031) Separate out the WPO plans. They cannot be approved as part of a road plan set. (Rev. 1) Partially addressed, see item #1, SWM plan, above. Restore sheets. 2. Super silt fence is proposed as single perimeter control at various locations with 160 -200 ft upslope drainage areas. VESCH details design criteria, planning considerations, construction specifications, and conditions where silt fence may be used, and does not recognize super silt fence. Please eliminate reference to super silt fence wherever it occurs (at least 1,600 LF are shown as perimeter controls measures for Drainage Areas 3, 4). Please revise design to include measures consistent with topography, percent grade, length, acreage, and suitability per VESCH. Silt fence should not be installed cross - contour, but on- contour with minimal rise or fall along its length. Diversion dikes and sediment traps (or basins) may be more Engineering Review Comments Page 4 of 5 appropriate in many locations currently shown to be controlled with super silt fence. Request for variance is an option. (Rev. 1) Comment partially addressed. Sheet 9: show IP [VESCH Plate 3.07 -1] at each of 24" yard drain inlets [`A' —`O'; 16 -Apr, sheets 5 -5A]. Pipes between yard drain inlets are 12" DIA. Grading and runoff are significant. Q, from system `N'- `M' -`L' = 3.5cfs, at structure 44. IP required at each inlet, A -O. [Concho Lane: A -D; Lampasas Dr: E,F; Pecos Ct: G,H; Westhall Dr: I, J, K; and Area between San Marcos Way - Westhall Dr: M,N,L] 3. Please review sediment basin design. Please provide emergency spillway exit channel length calculations or narrative supporting exit channel lengths of 2.4, 4, 4, and 15 -ft. Please explain (narrative is okay) why sediment basin #5 does not have an emergency spillway. Revise anti -seep collar dimensions for all 5 sediment basins (size at least 4 -ft larger than barrel diameter / VSMH, 1999, p. 5 -68). SB 1 requires 3 collars given length of barrel in saturated zone = 57.68 -ft. SB 1 upstream face slope must be 2.5:1 (or flatter) given embankment height = 12 -ft. (Rev. 1) Comment addressed. 4. Invert in -out for three sediment basin outfall pipes is identical and does not correspond with invert information on details; please revise invert data for S13 1, 2, and 4 (sheet 27), as necessary. (Rev. 1) Partially addressed — please reconcile plan and profile culvert slope and INV information for S134. 5. Please draw sediment basin profiles to scale. Show actual existing contours with relative scale. Generic section views are furnished. Existing ground is shown no higher than invert of outfall of culverts through embankments, at base of 3:1 slope. Actual slopes are flatter. Embankment heights are given as 6, 2, 8, 12, 6 -ft (SB 1, 2, 3, 4, and 5, respectively). Note: embankment height of SB4 and SWM Facility #4 are not identical (SWM #4 embankment height is given as 10 -ft). (Rev. 1) Comment addressed. 6. Show baffles on plan view details for S134 and S135. (Rev. 1) Comment addressed. 7. Show soil stockpiles. Show staging areas. Identify any off -site borrow or spoils sites. (Rev. 1) Comment addressed. 8. Minor: Titles of Erosion and Sediment Control Plans Phase I and Phase II are reversed (sheets 26, 27). (Rev. 1) Comment addressed. New 9. Revise line of 24" berm between S132 and S133, redraw uphill portion. 10. Minor: Sheet 7 —Re -label Temporary Diversion detail to read Temporary 24 "Diversion Berm. If temporary right -of -way diversions are used, show where practice will be used (plan view), else delete detail. It is confusing given second temporary diversion detail. Sheet 8 — please label 100 -yr floodplain and Lickinghole Creek. Sheet 10 —label ESC BASIN 3 profile. 11. Sheet 8 — Restore SF between S132 and S133 (make continuous; ref 16 -Apr, sheet 26). 12. Sheet 8 — S134 — Extend SF east with tree protection line, 80 -100', as initially shown, 16 -Apr. 13. Sheet 8 —Show additional SF north and west of S135, unless existing land cover is woods. 14. Sheet 8 —Label CE paved, plan view. [Ref. Sequence of Construction, Note 4] 15. Sheet 9 —PS -DC shown; show TS -MU as well. Engineering Review Comments Page 5 of 5 16. Sheet 9 — Relocate IP symbol and label to yard drain inlet between Concho Lane and Lampasas Drive. C. Road plans (SUB201400067) 1. Intersection of San Marcos Way and Weshall Drive does not continue the 2% intersected cross grade for a minimum of 20' from the edge of pavement of the intersected street (ref. Sta. 14 +03.17, San Marcos Way). (Rev. 1) Defer to VDOT. 2. Furnish Route Number for Jonna Street (show on plans). (Rev. 1) Comment addressed. 3. ACCD defers to VDOT. All streets are proposed as public roads. (Rev. 1) Comment acknowledged. 4. VDOT approval is required. (Rev. 1) Comment acknowledged. D. Mitigation plans (WP0201400031) 1. 100 -ft. stream buffer (unnamed tributary to Lickinghole Creek) appears to be different on several sheets (4A, 26, and 32). Stream buffers should not shift from one sheet to the next. (Rev. 1) Comment addressed. 2. These sheets do not accurately capture installation impacts required to establish sewer line in the vicinity of MH -11. Sheet 32 does not calculate impact for this sanitary line. These impacts are permanent in that maintenance requires permanent, clear access to sanitary facilities. Calculate and offset impacts to areas of stream buffer impacted by sanitary sewer line installation (see portions of lots 61, 62, 80, and 81; sheet 32). (Rev. 1) Comment addressed. SWM basins #1 and #2 cannot be installed without impact to stream buffers. They may be drawn to show no impact, but final grade lines that touch buffer boundaries cannot be achieved without permanent alteration of landscape within the 100 -ft stream buffer or 100 -year floodplain. Delineate a reasonable zone for construction equipment operation and alteration or loss of vegetative cover during construction or maintenance of downslope embankments. Show reasonable buffer and floodplain impacts on sheet 32. As drawn, design assumes no impact more than 10 -ft downslope of top of embankment of SWM #1, or more than 9 -11 downslope of top of embankment of SWM #2. This is unrealistic. (Rev. 1) Comment addressed. 4. Mitigation area proposed with this plan should increase above 1.04 Acres. (Rev. 1) Comment addressed. New 5. Label PERMANENT DITCH #I (detail, sheet 6) on sheet 12. File: WP020140003 I -Westlake Hills - Memo - 072114 -Revl �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: Westlake Hills Phase 11,111, & IV Plan preparer: Scott Collins; Collins Engineering [200 Garrett St., Suite K, Charlottesville, VA 22902, scott(&collins -en in�g com] Owner or rep.: Lickinghole Creek, LLC [P. O. Box 1467, Charlottesville VA 22902, alan(&riverbenddev.com] Plan received date: 16 April 2014 Date of comments: 12 May 2014 Reviewer: John Anderson A. Stormwater Management and Mitigation Plan (WP0201400031) 1. Separate out the WPO plans. They cannot be approved as part of a road plan set. 2. Drainage areas are confusing. Drainage divides' upper boundaries should coincide with topographical high points (see post - development, Areas IA, 4A). Downslope drainage area boundaries are somewhat subjective, but areas included in post - development plans (and runoff calculations) are excluded as undisturbed on ESC sheets 26 and 27. Drainage area divides should coincide with actual existing and proposed finished grades. Runoff from Areas I & 4A should be controlled and treated to the extent practicable. Area 4A is controlled during construction by a sediment trap (ST I), sediment basin (SB5), and temporary diversions. Area 1 runoff is diverted to SB1 during construction. These temporary structures are eliminated and not replaced with permanent SWM features. Please consider permanent SWM basin or berm structures located to avoid conflict with allowable use of lots. A berm, for example, on the downslope (western) boundary of drainage area I may divert runoff to SWM basin 1. Grading Plan (sheet 5A) does not reflect alteration of contours likely to occur with removal of SB5. Show grades that result from removing SB5 (pre- existing contours will be altered). 4. Use 1 -2% existing impervious area to calculate %RR, for all drainage areas. 8% pre - development impervious area is too high. Proposed SWM Facilities are Extended Detention (2WQV) with phosphorus removal efficiency of 35 %, but %RR for Areas 1, 2, 3, are 47, 40, 46, respectively, so extended detention will not provide minimum water quality pollutant removal. Once %RR is re- calculated for Area 4 using 1 -2% existing impervious area, extended detention may not be suitable as SWM for Area 4, as well. Extended detention is appropriate for a required removal rate of 35 %. 5. The shape of SWM Facility 2 is problematic; the area between sediment forebay and retention basin is so narrow it constricts flow. Floor width at transition from forebay to basin is 4 -ft, which Engineering Review Comments Page 2 of 4 is susceptible to sedimentation and obstruction. Please use less narrow configuration for SWM Facility #2. 6. Plan views of each SWM facility (1,2,3,4) are drawn to scale. Please furnish profile views of each facility drawn to scale. Include entire culvert pipe (outfall). Typical sections do not reflect design heights listed as 6, 2, 8, and 10 -ft for SWM Facilities 1, 2, 3, and 4, respectively. 7. If SWM Facilities #1, 2 appear to be constructed by down - cutting existing terrain. There are wetlands between these two SWM facilities. Soil borings are needed for these proposed SWM facility locations. Groundwater depth is a practical concern at each location. 8. Drainage: Please ensure the carryover at any on -grade inlet is included in downstream inlet calculations (structure 30, for example, with carryover to structure 2813). Evaluate last on -grade inlet or inlets with carryover located prior to sump inlets, often in cul -de -sacs, to ensure that final roadway grades and drive entrance details allow on -grade inlet carryover to reach a point of entry to stormwater collection system. In the case of structure 30, for example, will carryover reach structure 28B, or will it find lower outlet at drive entrances to Lot 79, 80, or 81 (prefer no carryover at such last on -grade inlets)? 9. Please superimpose critical slopes that appear on sheet 2 on sheets 5 and 5A to facilitate review of proposed development on critical slopes. 10. Please ensure that spread at inlet Str. 84B (San Marcos Way) does not exceed 9 -ft, and at Str. 38 (Westhall Drive) does not exceed 10 -ft. Furnish flanking inlets upslope of structures 20 and 22 on Westhall Drive, since spread at each inlet is > 10.2 -ft. 11. As many as 26 inlets have a calculated required throat length greater than design throat length (sheets 19, 20). Please use engineering judgment to provide design at least equal the calculated required throat length. There are examples of slight mismatch: 12 -ft vs. 12.06 (rate insignificant), and greater disparity: 12 -ft vs. 14.47 -ft, for example. It is cases of greater disparity that will benefit from design that meets calculated requirements. 12. Minor: Titles of computations (tables) on sheet 22 should reference SWM Facility #3 and #4. Also, using a start elevation of 547.5 to model SWM Facility #1 yields negative elevations. Should start elevation for SWM Facility #1 be 542.00 instead? B. Erosion Control Plan (WP0201400031) 1. Separate out the WPO plans. They cannot be approved as part of a road plan set. 2. Super silt fence is proposed as single perimeter control at various locations with 160 -200 ft upslope drainage areas. VESCH details design criteria, planning considerations, construction specifications, and conditions where silt fence may be used, and does not recognize super silt fence. Please eliminate reference to super silt fence wherever it occurs (at least 1,600 LF are shown as perimeter controls measures for Drainage Areas 3, 4). Please revise design to include measures consistent with topography, percent grade, length, acreage, and suitability per VESCH. Silt fence should not be installed cross - contour, but on- contour with minimal rise or fall along its Engineering Review Comments Page 3 of 4 length. Diversion dikes and sediment traps (or basins) may be more appropriate in many locations currently shown to be controlled with super silt fence. Request for variance is an option. 3. Please review sediment basin design. Please provide emergency spillway exit channel length calculations or narrative supporting exit channel lengths of 2.4, 4, 4, and 15 -ft. Please explain (narrative is okay) why sediment basin #5 does not have an emergency spillway. Revise anti -seep collar dimensions for all 5 sediment basins (size at least 4 -ft larger than barrel diameter / VSMH, 1999, p. 5 -68). SB 1 requires 3 collars given length of barrel in saturated zone = 57.68 -ft. SB 1 upstream face slope must be 2.5:1 (or flatter) given embankment height = 12 -ft. 4. Invert in -out for three sediment basin outfall pipes is identical and does not correspond with invert information on details; please revise invert data for SB1, 2, and 4 (sheet 27), as necessary. 5. Please draw sediment basin profiles to scale. Show actual existing contours with relative scale. Generic section views are furnished. Existing ground is shown no higher than invert of outfall of culverts through embankments, at base of 3:1 slope. Actual slopes are flatter. Embankment heights are given as 6, 2, 8, 12, 6 -ft (SB 1, 2, 3, 4, and 5, respectively). Note: embankment height of SB4 and SWM Facility #4 are not identical (SWM #4 embankment height is given as 10 -ft). 6. Show baffles on plan view details for SB4 and SB5. 7. Show soil stockpiles. Show staging areas. Identify any off -site borrow or spoils sites. 8. Minor: Titles of Erosion and Sediment Control Plans Phase I and Phase I1 are reversed (sheets 26, 27). C. Road plans (SUB201400067) 1. Intersection of San Marcos Way and Weshall Drive does not continue the 2% intersected cross grade for a minimum of 20' from the edge of pavement of the intersected street (ref. Sta. 14 +03.17, San Marcos Way). 2. Furnish Route Number for Jonna Street (show on plans). 3. ACCD defers to VDOT. All streets are proposed as public roads. 4. VDOT approval is required. D. Mitigation plans (WP0201400031) 100 -ft. stream buffer (unnamed tributary to Lickinghole Creek) appears to be different on several sheets (4A, 26, and 32). Stream buffers should not shift from one sheet to the next. 2. These sheets do not accurately capture installation impacts required to establish sewer line in the vicinity of MH -11. Sheet 32 does not calculate impact for this sanitary line. These impacts are permanent in that maintenance requires permanent, clear access to sanitary facilities. Calculate and offset impacts to areas of stream buffer impacted by sanitary sewer line installation (see portions of lots 61, 62, 80, and 81; sheet 32). 3. SWM basins #1 and #2 cannot be installed without impact to stream buffers. They may be drawn to show no impact, but final grade lines that touch buffer boundaries cannot be Engineering Review Comments Page 4 of 4 achieved without permanent alteration of landscape within the 100 -ft stream buffer or 100 -year floodplain. Delineate a reasonable zone for construction equipment operation and alteration or loss of vegetative cover during construction or maintenance of downslope embankments. Show reasonable buffer and floodplain impacts on sheet 32. As drawn, design assumes no impact more than 10 -ft downslope of top of embankment of SWM #1, or more than 9 -ft downslope of top of embankment of SWM #2. This is unrealistic. 4. Mitigation area proposed with this plan should increase above 1.04 Acres. E. Final Plat None Received File: WPO201400031-Westlake Hills- Memo - 051214