HomeMy WebLinkAboutWPO201600021 Review Comments WPO VSMP 2016-09-14 Sow' soire
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: Woodlawn Subdivision—VSMP
Project Number: WP0201600021
Plat/Plan preparer: Craig Kotarski,Clint Shifflett,Timmons Group
608 Preston Ave.#200,Charlottesville,VA 22903 craig.kotarskiga,timmons.com
Owner: Marjorie M.Paul/2163 Bonaventura Drive,Vienna,VA 22181
Applicant/Developer: Woodlawn Development,LLC/2180 Owensville Rd,Charlottesville,VA 22901
Plan received date: 28 Mar 2016
(Rev. 1) 13 Jun 2016
(Rev.2) 19 July 2016
Date of comments: 16 May 2016
(Rev. 1) 18 Jun 2016
(Rev.2) 5 Aug 2016
14 Sept 2016
Reviewer: John Anderson(on behalf of Engineering)
(Rev.2) Matt Wentland
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 approved. The rationale is given in
the comments below.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.
1. Provide SWPPP,as with past projects. Template Attached. (Rev. 1)Partially Addressed.(Rev.2)
Addressed As follow-up:
a. Sec. 9—Sign Certification. Given recent difficulty(3-month delay)acquiring signed SWPPP
certification from this developer(Milestone Partners),additional review is contingent upon
response to these comments—please address all comments with next plan submittal.
b. Sec. 8—TBD'is unacceptable. Timmons personnel may be listed as placeholder qualified
personnel. Qualified personnel will need to be listed before the first inspection.
(Concrete washout,mortar mixing station,aboveground fuel
container)are shown as rectangles without provision for containment. All locations discharge to
graded slope/silt fence. This Exhibit requires care and improvement. All PPP measures should
provide containment(barrier)limiting pollutant transport. PPP exhibit design should prevent
runoff passing through or mixing with material/s in concrete washout,mortar mixing,or fuel
storage locations. Engineering recommends meeting to discuss. Please contact County Engineer
to arrange review meeting(J. Anderson unlikely to participate).
d. Title SWPPP Exhibit PPP Exhibit.
e. Show location of solid(non-hazardous)waste collection/dumpster on Exhibit.
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Engineering Review Comments
Page 2 of 6
f. Show stockpile and spoils areas on Exhibit. Expand LOD,if necessary.
g. Show staging area on Exhibit.
B. VSMP: SWPPP: Stormwater Management Plan(WPO201600021)
VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a SWMP. This plan is
approved for reasons provided in comments below.The stormwater management plan content requirements can be
found in County Code section 17-403
1. Title sheet:Revise index C5.0,C5.1 Site Plan to read Site Layout. VSMP approval does not approve a Site
Plan. (Rev.1)Addressed.
2. C1.0—Show stream buffer. (Rev. 1)Addressed.
3. C4.0—Critical Erosion Areas Note: Please include ref.to ACDSM, 8.A.2.: requirement for permanent
stabilization hardier than grass for slopes steeper than 3:1. If label or plan note overlooked,disregard.
(Rev. 1)Partially Addressed. Response misses intent of ACDSM, 8.A.2.,which stipulates ground cover
hardier than grass,which will not require mowing. Compare requirements at ACDSM with VESCII. Select
and provide non-turf species hardier than grass which will not require mowing for slopes steeper than 3:1.
ACDSM, 8.A.2:
2. For grass stabilization on constructed slopes,the maximum steepness is 3:1. Slopes
steeper than 3:1 must be permanently stabilized with landscaping vegetation hardier than
grass,which will not require mowing.
VF.SCH.`Table 3.32-D
Low Maintenance Slope (Steeper than 3:1)
- Kentucky 31 Tall Fescue
- Common Bermudagrass **
- Red Top Grass
- Seasonal Nurse Crop *
- Sericea Lespedeza **
(Rev.2)Addressed.
4. C4.0—Stor,nwaier Runoff Consideration Note: Include ref.to Level I Extended Detention Facility,since
VRRM .xls indicates Level I design. (Rev.1)Addressed.
5. C4.0 -Sequence of Installation Note#9: Revise to read: "Once upslope areas are permanently stabilized,
and with county inspector approval,remove culvert inlet protection,dewater sediment basin 1,remove
saturated sediment basin floor material,and convert to SWM-1, Level I Extended Detention Facility."
(Rev. 1)Addressed.
6. C4.0—Sequence of Installation Notes:Ref.material required to raise floor elevation of sediment basin 4.5'
to convert to SWM-1 (Level I ED Facility). (Rev. 1)Withdrawn. Redesign eliminates need for comment.
As follow-up: Compare initial SB-1 (C4.1)with revised.SB-1 dewatering structure design. Recommend
restore initial design(perforated riser pipe). Provide SB-1 profile caption:Sediment basin (SB-I). Also,
recommend against proposed 3"orifice at SWM-1 floor(sheet 7.2). Ref. initial design. Restore perforated
riser. Proposed design is prone to immediate obstruction. This skews routing calculations,and undermines
compliance.
(Rev.2)Addressed.
7. C5.0,C7.1 Provide labels that dimension wood timber level spreaders. (Rev. 1)Partially Addressed. As
follow-up: If two(2)stacked timbers are proposed,as appears to be the case,revise label. If re-bar steel
anchoring is proposed,provide dimension labels(DIA/L).
(Rev.2)Addressed.
8. C5.0 Label floor dimensions, SWM-i. (Rev. 1)Addressed.
9. C5.0—Label forebay floor and gabion wa a \1-1. (Rev. 1)Partially Addressed. As follow-
up,C7.2: Provide galvanized steel post gabion basket dimension labels(depth of embedment,DIA,L,etc.)
(Rev.2)Addressed.
10. C5.0,C5.1—Revise sheet title to Site Layout. (Rev. 1)Addressed.
Lid
Engineering Review Comments
Page 3 of 6
11. C5.1 Channel `B' Level Spreader 538.30' and 539.30' elevations do not appear to match LS detail,C7.2.
Please check 0.5' vertical dimension on detail against plan. (Rev. 1)Addressed.
12. C7.0,C7.1 Show/label length of overland flow,shallow concentrated flow,and channel flow. (Rev. 1)
Addressed. Note: Applicant response(9 Jun 2016)that"channel flow was not considered which results in
a more conservative design"is at odds with hydrologic methodology. If t,increases,which occurs if
channel flow is not considered,then intensity(I,see IDF chart)decreases,and Q decreases(Q—CIA);this
is less conservative. Channel flow reduces time of concentration OA increasing intensity(in./hr.)and
runoff,Q—this is a more conservative approach. Please help reviewer overcome any misperception.
(Rev.2)Addressed.
13. C7.1—Provide restrictive covenant for 3.65 Ac.preserved wooded area. County can provide deeded
easement template. (Rev. 1)Applicant:"We would prefer to provide this at the time of final Subdivision,
similar to the approach that was taken at Dunlora V." Engineering has requested County Attorney's
guidance on timing of restrictive covenant,and will work toward a helpful response to Applicant.
(Rev.2)Response Noted.This will not stand in the way of road plan approval,but a grading permit will
not be issued until the easement has been recorded.
14. C7.1 —Post-development L:; 1:. with VRRM values. (Rev. 1)Addressed.
a. Impervious,C7.1 (DA#1,#1A,#lB,#1U)=1.872 Ac.
b. Impervious,VRRM: 1.77 Ac.
c. Turf,C7.1 (DA#1,#1A,#1B,#1U)—24.14.
d. Turf,VRRM: 17.59.
c. If use C7.1 values with VRRM.xls,there appears to be a remaining phosphorus load=0.29 lb/yr±.
C7.2
15. Provide gabion wall detail. (Rev. 1)Partially Addressed. As follow-up,provide galvanized steel post
depth of embedment,post dimensions(DIA,L). (Rev.2)Addressed.
16. Grass channel A calculations: If use VRRM to check,Qa=Rv— rather than 0.23 in. [Please call to
discuss.] (Rev. 1)Although discussed,Not Addressed. Applicant response to"Please refer to the VRRM
summary"does not clarify discrepancy since the only VRRM summaries provided are: Site Data, DA 'A',
DA 'B', and DA 'C'. Further,routing computations do not appear to be source of 0.23 Rv value. A
meeting may prove helpful. Engineering relies on VRRM channel and flood protection tab,and values.
Text image of this tab for Woodlawn Subdivision is shown below. (Rev.2)Addressed.
17. Grass channel B calculations: If use VRRM to check,Qa=Rv=0.544,,rather than 0.31 in. [Please call to
discus, (Rev. 1)Although discussed,Not Addressed. See item#16,above. A meeting niay be helpful.
1Based on the use of Runoff Reduction practices in the selected drainage areas,the spreadsheet calculates en adjusted RVow.we,a and adjusted Curve Number.
Drainage Area A A soils B Soils C Soils D Soils
Forest/Open Space-undisturbedprotected forest/open Area!acres'' 0 09 .. 0 00
space or reforested land CII '3C 70
Managed Turf--disturbedgraded for yards or other turf to be Area(acres) -=_ 0 00 -..
mowed'managed CN -. 03 --
Area!acres) L 33 0.r 3 00 0 CC
Impetuous Corer ON 93 93 98
Wei.hted CR S
0111
1.year storm 2-year storm 10 year storm _
RVu..,ov.a(in)with no Runoff Reduction 0 49 0 80 1 96
RVu...oe.a(in)with Runoff Reduction 0 43 0,5 1 91
Adjusted CR 63 63 63 _.
Drainage Area B A soils B Soils C Soils U Soils
Forest/Open Space-undisturbedprotected forestropen Area!acres: 0 00 0 C: .-. 0 00
space or reforested land Cli 30
Managed Turf--disturbed,graded for yards or other turf to be Arca!acres_ 0 00 4 36 _,_ 0 00
mowed/managed CII 39 E1 80
Impervious Cover Area lasses 0.00 0 82 0 00 0 00
CI! 98 98 98 98
Weighted CN S
6, I 4 93
1.year storm 2-year storm 10yearstorm
RVo,..mpa(in)with no Runoff Reduction 0 80 0 95 2 21
RVawaw.a(in)with Runoff Reduction 0 54 0.89 2.15
Adjusted CN 65 - .-fi-... 66
(Rev. 1)Next 5 comments.Not Addressees. may prove 11,_wiul. (Rev.2)Addressed.
ngineering Review Comments
Page 4 of 6
18. Grass channel A calculations:Revise Q(1-Y R)to read Q(1"). Revise Maximum 1-YR Depth=4"to read
Maximum 1"(runoff event) Det "' (Ref. V^ "' G) Stormwater Design Specification No.3,p. 11).
(Rev. 1)Comment re-stated. (Rev.2)Addressed.
19. Grass channel A calculations: I,. . ; CFS to read—0.52 CFS,consistent with Hydrograph in
calculations booklet. (Rev. 1) Response was to eliminate calculation altogether,and replace with Q2,Qro
calculations,which are less directly relevant. Restore/revise calculation in response to initial comment.
(Rev.2)Addressed.
20. Revise grass channel A design if Q(1") Depth>3",as it appears to be. (Rev. 1)Q(1-inch runoff event)
depth reported—3.7". Max. 1-IN runoff grass channel depth=3". Ref.DEQ Spec.No. 3. Revise design.
(Rev.2)Addressed.
21. Grass channel B calculations:Revise Q(1-YR)to read Q(1"). Revise Maximum 1-YR Depth—4"to read
Maximum 1"(ninoff event)Depth=3". (Rev. 1)Not Addressed;see item#19,above.(Rev.2)
Addressed.
22. Revise grass channel B design if Q(1") Depth>3",as it appears to be. (Rev. 1)Comment re-stated.
Note: County and Timmons have discussed possibility we are relying on different sources. Although DEQ
notified local programs that revised VRRM spreadsheets were released(May 3),and Albemarle shared this
notice with design community,VA DEQ Stormwater Design Specification No. 3-Grass Channels appears
unchanged. Ref. images below. Conunents 18.-22. should be addressed;please provide design response.
We believe a meeting to discuss comments may be helpful.
Additional Follow-Up(New): Design Spec No. 3 requires a Min. of 6"of freeboard;revise design to
provide 10-yr peak flow rate containment within each grass channel,with a Mui. of 6"of freeboard. (Rev.
2)Addressed.
23. Provide VRRM worksheet data that identifies DA routings through specific BMP measures,since not
readily apparent(requires inference). (Rev. 1)Addressed.
24. Energy balance Eq.—Provide Rv pre-D—42,427 cu. f.;Rv post-D=44,832 cu. ft.background calculations.
(Rev. 1)Inadequately Addressed. Despite conversation,values remain perplexing. Ref. Calc.packet,
Sub-catchment 4S,6S (G.C.A,G.C.B); there are no easily traceable values that correspond with Rv values.
Applicant: "Please refer to the 1-year storm hydrographs within the calculation booklet. The volume was
converted from Ac-Ft,to Cu. Ft." Despite reference and best effort,cannot make sense of Rv values. A
meeting may prove helpful. (Rev.2)Addressed.
C. VSMP: SWPPP: Erosion Control Plan(WPO201600021)
Virginia Code§62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This ESC plan is
approved.
1. C4.1 Sediment Basin#1 design data: dry storage provided at principal spillway crest listed as 300 cy
(<761.1 cy dry storage required). Misprint? (Rev. 1)Addressed.
2. C4.1 —Sediment Basin#1 design data: depth of water at(emergency)spillway crest listed as 8.2',but using
crest and bottom of basin elevations. depth appears=9.2'. (Rev. 1)Addressed via sediment basin redesign.
C4.2
3. Label floor dimensions,SB-1 (Rev. 1) Addressed.
4. Provide dimensions for stilling (Rev. 1) Addressed.
5. Provide dimensions for culvert A,B outlet pi, .,rent from stilling basin dimensions. (Rev. 1)
Addressed. "The outlet protection dimensions are the same as the stilling basin dimensions."
6. Limits of disturbance appear impractical as drawn. Expand LOD to accommodate typical construction
equipment,especially on individual Lots(dwellings,septic field,driveways). Equipment operators will
likely not consult plan,and if they do,may inadvertently or unwillingly be unable to perform fine grading,
or grading required to level site,or construct driveways/septic fields. Expanding LOD somewhat(up to
9.99 Ac.)has no effect on permit application or VSMP plan review fees,although increased.LOD may
increase annual permit maintenance fee($100/Ac.). (Rev. 1)Addressed. As follow-up: Recommend
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Engineering Review Comments
Page 5 of 6
consider stockpile/spoils/staging area requirements,and revise LOD,as necessary. Also,see SWPPP
comments,above.
7. Recommend Notes and labels to prevent equipment or construction activity impacts to Areas to be used for
SWM BMP grass channels A.B. (Rev.1)Addressed.
8. Recommend include Sequence of Installation Note(C4.0)that reflects C4.2 Note: `Finalize grass channel
grading and groundcover only after contributing drainage area is stabilized.' (Rev. 1)Addressed.
9. No ESC measures appear to be provided on individual Lots. It is unclear if driveways and home sites are to
be built with this WPO. If not,please label build sites `for illustration only,with ESC measures(each Lot)
to be provided by builder/others.' If build sites,driveways,and septic fields are to be addressed under this
WPO Plan, then provide required ESC measures required to grade Lots. Provide SF,check dams,etc.
(Rev. 1)Addressed.
10. Recommend check dams along west side Woodlawn Rd.given 24' vertical interval between Lot 1 driveway
and culvert B INV IN. (Rev. 1)Addressed.
11. Estimate stream buffer impact(SF);prepare/submit Mitigation Plan. (Rev. 1)Addressed.
12. Eliminate SWM-1 proposed contours. (Rev. 1)Addressed.
13. Provide SF.east side Woodlawn Rd. (Rev. 1)Addressed.
C4.3
14. Lot 6-Provide ES for 15" DIA driveway culvert pipe. (Rev. 1)Addressed.
15. Provide individual Lot ESC measures. Also,item#9,above. (Rev. 1)Addressed.
16. Provide check dams,Lot 5 and 6 driveways. (Rev.1)Addressed.
17. C5.1 —Coordinate Lot 6 driveway design with ACF&R. With opposing 12.6 and 9.4%grades,newer fire
engine units with 13- 1/8"clearance from tow hook to ground may have limited access to this Lot. This
may require driveway profile. (Rev. 1)Addressed. Ref.ACF&R email to Applicant: 6/16/2016 10:43
AM;no concerns expressed. No portion of Lot 6 driveway exceeds 16%.
Engineering plan review staff are available from 2-4 PM on Thursdays,should you require a meeting to discuss this
review. Plan review staff is available at 434-296-5832 should you have any questions—request Engineering.
Process:
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 request a pre-construction conference by completing a form,and pay the remainder of the application
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ngineering Review Comments
Page 6 of 6
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/deptforms.asp?department=cdengwpo
Thank you
(Please contact Frank Pohl,County Engineer,to schedule plan review meeting—434.296-5832—x7914)
W PO201600021_W oodlawn_V SM P_080516rev3
. L �
'sloe 'told
July 18`h, 2016
County of Albemarle
John Anderson, P.E.
Community Development
401 McIntire Road, Room 227
Charlottesville,Va. 22902
RE: WPO20160002 I —Woodlawn Subdivision
Dear Mr.Anderson:
We have reviewed all of your comments from June I8`h, 2016 and made the necessary
revisions. Please find our responses to the comments below in bold lettering.
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.
1. Provide SWPPP, as with past projects. Template Attached. (Rev. 1)Partially Addressed.As
follow up:
a. Sec.9-Sign Certification. Given recent difficulty(3-month delay)acquiring signed SWPPP
certification from this developer(Milestone Partners),additional review is contingent upon
response to these comments-please address all comments with the next plan submittal.
b. Sec.8-`TBD' is unacceptable. Timmons personnel may be listed as placeholder qualified
personnel.
c. Sec.6-Critical PPP measures. (Concrete washout,mortar mixing station,aboveground fuel
container)are shown as rectangles without provision for containment,all locations
discharge to graded slope/slit fence. This Exhibit requires care and improvement. All PPP
measures should provide containment(barrier)limiting pollutant transport.PPP exhibit
design should prevent runoff passing through or mixing with material/s in concrete
washout,mortar mixing,or fuel storage locations.Engineering recommends meeting to
discuss. Please contact County Engineer to arrange review meeting(J. Anderson unlikely to
participate).
d. Title SWPPP Exhibit PPP Exhibit.
e. Show location of solid(non-hazardous)waste collection/dumpster on Exhibit
f. Show stockpile and spoils areas on Exhibit.Expand LOD,if necessary.
g. Show staging gage on Exhibit.
A revised SWPPP has been provided with this submittal, and includes all of the required
signatures listed above, as well as revisions to the PPP Plan.
B. VSMP: SWPPP: Stormwater Management Plan(WP0201600021)
VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a SWMP.This
plan is disapproved for reasons provided in comments below.The stormwater management plan content
requirements can be found in County Code section 17-403
1. Title sheet: Revise index C5.0,C5.1 Site Plan to read Site Layout. VSMP approval does not approve
a Site Plan. (Rev.1)Addressed.
2. C1.0—Show stream buffer. (Rev.1)Addressed.
3. C4.0—Critical Erosion Areas Note: Please include ref. to ACDSM, 8.A.2.:requirement for
permanent stabilization hardier than grass for slopes steeper than 3:1. If label or plan note
overlooked,disregard. (Rev.1)Partially Addressed.Responses misses intent of ACDSM, 8.A.2./
which stipulates ground cover hardier than grass,which will not require mowing. Compare
*441,00" July 18, 2016
Page 2 of 5
requirements at ACDSM with VESCH. Select and provide non-turf species hardier than grass which
will not require mowing for slopes steeper than 3:1.
ACDSM 8. A.2:
2.)For grass stabilization on constructed slopes, the maximum steepness is 3:1. Slopes
steeper than 3:1 must be permanently stabilized with landscaping with landscaping
vegetation hardier than grass,with will not require mowing.
VESCH. Table 3.32-D
Low Maintenance Slope(Steeper than 3:1)
- Kentucky 3 I Tall Fescue
- Common Bermudagrass
- Red Top Grass
- Seasonal Nurse Crop*
- Sericea Lespedeza**
4. C4.0-Stormwater Runoff Consideration Note: Include ref.to Level I Extended Detention Facility,
since VRRM.xis indicates Level I design. (Rev.1)Addressed.
5. C4.0-Sequence of Installation Note#9:Revise to read:"Once upslope areas are permanently
stabilized,and with county inspector approval,remove culvert inlet protection,dewater sediment
basin 1,remove saturated sediment basin floor material,and convert to SWM-1,Level I Extended
Detention Facility."(Rev.1)Addressed.
6. C4.0-Sequence ofInstallation Notes:Ref material required to raise floor elevation of sediment
basin 4.5'to convert to SWM-1 (Level I ED Facility). (Rev.1)Withdrawn. Redesign eliminates
need for comment. As follow-up: Compare initially SB-1 (c4.1)with revised SB-1 dewatering
structure design. Recommend restore initial design(perforated riser pipe).Provide SB-i profile
caption:Sediment basin(SB-1)/. Also, recommend against proposed 3'orifice at SWM-floor(sheet
7.2). Ref initial design.Restore perforated riser.Proposed design is prone to immediate obstruction.
This skews routing calculation,and undermines compliance.
7. C5.0,C7.1-Provide labels that dimension wood timber level spreaders. (Rev.1)Partially
Addressed.As follow-up: If two(2)stacked timbers are proposed, as appears to be the case,revise
label. Id re-bar steel anchoring is proposed,provide dimension label(DIA/L).
Re-bar specifications have been added and(2)timbers have been indicated.
8. C5.0-Label floor dimensions, SWM-i. (Rev. 1)Addressed
9. C5.0-Label forebay floor and gabion wall dimensions, SWM-1. (Rev.1)Partially Addressed.As
follow-up: C7.2: Provide galvanized steel post gabion basket dimensions labels(depth of
embankment,DIA,L,etc.)
The gabion wall detail on sheet C7.2 has been revised to specify the steel post material
and length as well as the depth of embedment.
10. C5.0.C5.1-Revise sheet title to Site Layout. (Rev. 1)Addressed
11. C5.1-Channel `B'Level Spreader 538.30'and 539.30'elevations do not appear to match LS detail,
C7.2. Please check 0.5'vertical dimension on detail against plan. (Rev. 1)Addressed
12. C7.0,C7.1-Show/label Length of overland flow, shallow concentrated flow,and channel flow.
(Rev. 1)Addressed.Note: Applicant response(9 Jun 2016)that"channel flow was not considered
which results in a more conservative design"is at odds with hydrology methodology. If t.increases,
which occurs if channel flow is not considered,then intensity(I, see IDF Chart)decreases, and Q
decreases(Q=CIA);this is less conservative. Channel flow reduces time of concentration(tc),
increasing intensity(in./hr)and runoff,Q-this is a more conservative approach.Please help reviewer
overcome and misconception.
July 18, 2016
Page 3 of 5
Time of concentration flow paths have been provided and labeled. Please note, channel
flow was not considered which results in a lower Tc, thus higher Q for a more
conservative design.
13. C7.1—Provide restrictive covenant for 3.65 Ac.preserved wooded area. County can provide deeded
easement template.(Rev.1)Applicant:"We would prefer to provide this at this time of final
Subdivision similar to the approach that was taken at Dunlora V.
We would prefer to provide this at the time of Final Subdivision, similar to the approach
that was taken at Dunlora V. However, per our discussion in the engineering meeting, it
appears that this approach is no longer an option. The developer currently has a copy of
the County's deeded easement template and intends to provide the signed document/
plat as necessary. If this stands in the way of final Road Plan approval, we would like to
seek "conditional approval" at this time, and submit the required restrictions document
shortly. i7� °� i �;S " ,t1 %AL t' (Loo a:: „ . C1C(''`.,(
1 rtC two Q� re...) /1 t �
14. C7.1—Post-development DA is inconsistent with VRRM values. (Rev. 1)Addressed
a. Impervious, C7.1 (DA#1,#1A,#1B,#1U)=1.872 Ac.
b. Impervious, VRRM: 1.77 Ac.
c. Turf, C7.1 (DA#1,#1A,#1B,#1U)=24.14.
d. Turf,VRRM: 17.59.
e. If use C7.1 values with VRRM.xis,there appears to be a remaining phosphorus load=0.29
lb/yr±. Addressed
C7.2
15. Provide gabion wall detail.(Rev. 1)Partially Addressed.As follow-up,provide galvanized steel
post depth of embedment,post dimensions(DIA,L).
Steel post specifications have been added to the detail on sheet C7.2.
16. Grass channel A calculations: If use VRRM to check,Qa=Rv=0.43 in,rather than 0.23 in. [Please
call to discuss.](Rev.1)Although discussed,Not Addressed. Applicant response to"Please refer to
VRRM summary”does not clarify discrepancy since the only VRRM summaries provided are: Site
Data,DA 'A',DA`B'. and DA 'C'.Further,routing computations do not appear to be source of
0.23 Rv value. A meeting may prove helpful.Engineering relies on VRRM channel and flood
protection tsb,and values.Text image of this tab for Woodlawn Subdivision is shown below.
17. Grass channel B calculations:If use VRRM to check,Qa=Rv=0.54 in,rather than 0.31 in. [Please
call to discuss.] (Rev.1)Although discussed, Not Addressed. See item#16,above. A meeting may
be helpful.
Based on the use of Runoff Reduction practices in the selected drainage areas.the spreadsheet calculates an adjusted RVrr,.h.n.,,and adjusted Curve Number.
Drainage Area A soils 3 Soils . ..,n s 'D Soilr
ForesVOpen Space-undisturbed protected torestopen Area lacresl 2 00 C 30 5 JO
space or reforested land CN
a
Managed Tud-disturbed,graced For yards or other IA to be Area(acres; 3 11
moweo,'rnanaged CN 3-
Area(acres; 0.00 r_1 ,-,
Impervious Cover
CW 3 07
7-year storm ±L.a:,torn 1G-ye.,swan
RVue„ din)with no Runoff Reduction 0 49 0 30 1 94
RV0,wwsw(Irl with Runoff Reduction 043 C 75 1 3'
-_..—
Adjusted CN 63 53 63
Drainage Area B A oil -
- 'J Sod,-- -�
Forest/Open Space-undisturbed protected forestopen. Area'acres l 0 00 _ ,3 JO j Ott
space or reforested land CN
Managed Turf-disturbed.graded'or ards or other turf to be Area(acres)_ 3 00 -1 35 000 j 00
mowed'managed ON 39 - 61,
Impervious Coves Area facies; 3 00 0 00 3 00
ie,gh;ed S
67
1 year storm 7 year storm 10 year storm
RUa,.ecua(in)with no Runoff Redur.,vn 0.60 005 2 2-
RVp,,,, (int with Runoff Reducian 0.54 2 09 2-15
Adjusted rN 65 66 66
'tem? ` July 18, 2016
Page 4 of 5
(Rev.1)Next 5 comments.Not Addressed. A meeting may provide helpful.
18. Grass channel A calculations:Revise Q(1-YR)to read Q(1"). Revise Maximum 1-YR Depth=4"to
read Maximum 1" (runoff event)Depth=3"(Ref. VA DEQ Stormwater Design Specification No. 3,
p. 11). (Rev.1)Comment re-stated.
19. Grass channel A calculations: Revise Q(1")=0.61 CFS to read=0.52 CFS,consistent with
Hydrograph in calculations booklet. (Rev.1)Response was to eliminate calculation altogether,and
replace with Q2,Qio calculations,which are less directly relevant. Restore/revise calculations in
response to initial comment.
20. Revise grass channel A design if Q(1")Depth>3",as it appears to be.(Rev.1)Q(1-inch runoff
event)depth reported=3.7". Max.1-IN runoff grass channel depth=3". Ref. DEQ Spec.No. 3.
Revise design.Maximum 1"(runoff event)Depth 3". Ref. DEQ Spec.No.3. Revise design.
21. Grass channel B calculations:Revise Q(1-YR)to read Q(1"). Revise Maximum 1-YR Depth=4"to
read Maximum 1" (runoff event)Depth=3".". (Rev.1)Not Addressed; see item#19 above.
22. Revise grass channel B design if Q(1")Depth>3",as it appears to be.(Rev.1)Comment re-stated.
Note: County and Timmons have dicussed possibility we are realying on different sources, Although
DEQ notified local programs that revised VRRM spreadsheets were released(May 3), and
Albermarle shared this notice with design community, VA DEQ Strormwater Design Specification
No.3-Grass Channels appears unchanged.Ref. images below. Comments 18.-22 should be
addressed;please provide design response. We believe a meeting to discuss comments may be
helpful.
Additional Follow-Up(New): Design Spec No.3 requires a Min.of 6'freeboard;revise design to
provide 10-yr peak flow rate containment within each grass channel,with a Min. of 6"freeboard.
VA DEQ BMP Specification No.3
• Hydraulic capacity should be verified using Manning's Equation or an accepted equivalent
method, such a erodibility factors and vegetal retardance(NOVA 2007).
o The Flow Depth for peak treatment volume(1-inch rainfall)should be maintained
at 3 inches or less.
o Manning's"n"value for grass channel should be 0.2 for flow depths up to 4
inches,decreasing to 0.03 at a depth of 12 inches(which would apply to the 2-year
and 10-yr storms if an on-line application—NOCA,2007;Haan et. Al. 1994).
o Peak Flow Rates for the 2-year and 10-year frequency storms must be non-erosive,
in accordance with Table 3.3,or subject to a site specific analysis of the channel
lining material and vegetation;and the 10-year peak flow rate must be contained
within the channel banks(with a minimum of 6inches of freeboard). (NOTE: After
the new Virginia Stormwater Management Regulation revisions take effect,the
above requirement will be driven by the SWM Regulation(4-VAC 50-60-66 A 1
and B 1),which will supersede the MS-19 criteria of the Virginia E&S Control
Regulation).
23. Provide VRRM worksheet data that identifies DA routings through specific BMP measures, since
not readily apparent(requires inference). (Rev.!)Addressed
24. Energy balance Eq.—Provide Rv pre-D=42,427 cu.ft.;Rv post-D=44,832 cu. ft.background
calculations. (Rev.1)Inadequately Addressed.Despite conversation,values remain perplexing.
Ref. Calc.packet, Sub-catchment 4S. 6S(G.C.A,G.C.B);there are no easily traceable values that
correspond with Rv values. Applicant: "Please refer to the 1-year storm hydrographs within the
calculation booklet. The volume was converted from Ac-Ft,to Cu. Ft". Despite reference and bets
effort,cannot make sense of Rv values. A meeting may prove helpful
Comments 16-24: As discussed at the engineering meeting on 6/23/16,the calculations
for the Grass Channels have been revised. They now specifically detail the step by step
design process per the Virginia Stormwater BMP Clearinghouse, as well as the
referenced section, 11.5.3,within the Virginia Stormwater Management Handbook.
C. VSMP: SWPPP: Erosion Control Plan(WPO201600021)
r
Nko+'' July 18, 2016
Page 5 of 5
Virginia Code§62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This plan is
disapproved for reasons provided in comments below.The erosion control plan content requirements can be found in
County Code section 17-402.
1. C4.1-Sediment Basin#1 design data: dry storage provided at principal spillway crest listed as 300
cy (<761.1 cy dry storage required). Misprint?(Rev.!)Addressed
2. C4.1-Sediment Basin#1 design data: depth of water at(emergency)spillway crest listed as 8.2',but
using crest and bottom of basin elevations,depth appears=9.2'. (Rev.!)Addressed via sediment
basin redesign.
C4.2
3. Label floor dimensions, SB-1. (Rev.!)Addressed
4. Provide dimensions for stilling basins A,B. (Rev.!)Addressed
5. Provide dimensions for culvert A,B outlet protection,if different from stilling basin dimensions.
(Rev.1)Addressed."The outlet protection dimensions are the same as the stilling basin
dimensions."
6. Limits of disturbance appear impractical as drawn. Expand LOD to accommodate typical
construction equipment,especially on individual Lots(dwellings,septic field,driveways).
Equipment operators will likely not consult plan,and if they do, may inadvertently or unwillingly be
unable to perform fine grading,or grading required to level site,or construct driveways/septic
fields. Expanding LOD somewhat(up to 9.99 Ac.)has no effect on permit application or VSMP
plan review fees,although increased LOD may increase annual permit maintenance fee($100/Ac.).
(Rev.1)Addressed. As follow-up: Recommend consider stockpile/spoils/staging area requirements,
and revise LOD,as necessary. Also, see SWPPP comments,above.
7. Recommend Notes and labels to prevent equipment or construction activity impacts to Areas to be
used for SWM BMP grass channels A,B. (Rev.!)Addressed
8. Recommend include Sequence of Installation Note(C4.0)that reflects C4.2 Note: `Finalize grass
channel grading and groundcover only after contributing drainage area is stabilized.' (Rev.!)
Addressed
9. No ESC measures appear to be provided on individual Lots. It is unclear if driveways and home
sites are to be built with this WPO. If not,please label build sites 'for illustration only,with ESC
measures(each Lot)to be provided by builder/others.' If build sites,driveways,and septic fields
are to be addressed under this WPO Plan,then provide required ESC measures required to grade
Lots. Provide SF,check dams, etc. (Rev.!)Addressed
10. Recommend check dams along west side Woodlawn Rd. given 24'vertical interval between Lot 1
driveway and culvert B INV IN. (Rev.!)Addressed
11. Estimate stream buffer impact(SF);prepare/submit Mitigation Plan. (Rev.!)Addressed
12. Eliminate SWM-1 proposed contours. (Rev.!)Addressed
13. Provide SF,east side Woodlawn Rd. (Rev.!)Addressed
C4.3
14. Lot 6-Provide ES for 15"DIA driveway culvert pipe. (Rev.!)Addressed
15. Provide individual Lot ESC measures. Also, item#9,above. (Rev.!)Addressed
16. Provide check dams,Lot 5 and 6 driveways. (Rev.!)Addressed
17. C5.1-Coordinate Lot 6 driveway design with ACF&R. With opposing 12.6 and 9.4%grades,
newer fire engine units with 13- 1/8"clearance from tow hook to ground may have limited access to
this Lot. This may require driveway profile. (Rev.1)Addressed.Ref. ACF&R email to Applicant:
6/16/2016 10:43AM,no concerns expressed. No portion of Lot 6 driveway exceeds 16%.
We have submitted 4 revised copies of the WPO Plan for your review. If you have any questions
or comments, please feel free to give me a call at 434.327.1690
Sincerely,
Clint Shifflett, PE
Project Engineer