HomeMy WebLinkAboutWPO201900039 Correspondence 2020-09-010*0 4oltteverde
9/1/2020
Seth Roderick
Monteverde Engineering & Design Studio
250 E Elizabeth St, Suite 114
Harrisonburg, VA 22801
Albemarle County Community Development Department
Attn: John Anderson
401 McIntire Road
North Wing
Charlottesville, VA 22902
RE: Hillcrest Vineyard Tasting & Venue WPO 2019-00039
Mr. Anderson,
The plans that accompany this letter have been revised per the review comments dated June 23, 2020
and June 24, 2020, both transmitted by email. The comments have been addressed as follows:
1. Mitigation plan sheet does not appear in Amendment plan sheet index —please restore.
Response: Stream buffer impact eliminated from project. C6.05 Stream Buffer Mitigation Plan has
been added to sheet index on CO.01 and crossed out. See note below sheet index on CO.01.
2. Detention basin #2
a. Access (longitudinal) slope limited to 20%, but since no scale, cannot evaluate.
Provide detention basin #2 scaled schematics, both plan /profile (revise C-6.042).
Ref. pg. 12, Alb. Co. Design Standards Manual (ACDSM), best management practices for
SWM. Link to ACDSM: hqs://www.albemarle.org/liome/ShowDocument?id=270.
Best Management Practica for Stormwater Management: All practices must have
adequate vehicle access; 10' width graded at less than 200/a. Anything over 20% must be
surfaced with gravel or pavement. Access must be to all structures and forebay cicanout
areas. Easements must be provided over all access and facilities. to accompany deeds and
agreements as available on the county e•cbsite;
tt ://NMM albcmarlaore dcptforms.asn''dcnanmcnt cdcn gam)
Response: Basin #2 access path and slope noted on sheet C6.042R. Access is @ 12.5% slope (note
added sheet C6.042R). Access is not required to be surfaced. Inset plan is at 1 "=30' scale.
Stormwater easements not required. Profile above plan is NTS.
b. Confirm detention basin #2 access meets ACDSM standard.
Response: See above.
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RE: Hillcrest Vineyard Tasting & Venue WPO 2019-00039, Albemarle County, Va. July 1, 2020
d. SWM facility access: show proposed grading required to construct detention #2 basin access
Specifically, propose access contours that ensure vehicle stability, side -to -side.
As it is, vehicles may cant as they traverse existing ungraded terrain (existing contours).
Response: Access route modified and shown on sheet C6.042R with minor grading shown for vehicle
stability.
e. Revise /amend WP0201900039 recently -amended ESC Plan to reflect measures required to
construct detention basin Q.
Response: ESC plan modified to include area disturbed for basin #2. Basin is in an existing drainage
path, silt fence and check dams were added for sediment control.
f. Label basin floor dimensions.
Response: Basin floor dimensions added Sheets C6.041R & C6.042R.
g. Label riprap outlet protection (similar to detention basin #1); L x W x D.
[ image below from ESC Plan Amendment, approved 7/2/201
Response: Riprap outlet protection dimensions shown in profile view and added to plan notes.
h. Provide label similar to basin riser label that explains if sediment basin pipe will be used as
permanent detention basin #1 pipe, which appears to be the case [ image, above].
Response: Basin #2 is new construction and not part of the ESC plan. Note for basin #1 revised to
read "Existing sediment basin riser and barrel to be reused for detention basin "
i. If sediment basin (SB) outfall pipe will serve detention basin # 1 and if SB barrel has collars,
include collars in detention basin outfall pipe.
Response: Per VESCH Standards and Specs 3.14 Temporary Sediment Basin anti seep collars are not
required for this embankment; the embankment is less than 10' in height.
Wavide details as needed faF SB/basin 4 1 plunge pool to ehange difeetion of flaA, designed
spillway elev.). Albemade needs to eheek and enstwe that design limits sediment tFaRspOF4,
,...t:....,, tw_.. the pit.fige P001 OF tO ,._,.a,.. 001 affflOf ,.....OSit. the pipe, a iall high,...
.el via Ditel n
fir.
(8/26/20) Provide manhole to redirect discharge from basin #L Include VDOT inlet shaoin¢
detail on plans. C-6.041R [image, below; provide MH at blue circle. ]
Label basin # 1, #2 embankment side -slopes (item not discussed with Frank) for comparison
with Appendix A, Earthen Embankments, p. 10 of 19, Maintenance and Safety [ image,
below].
Also not discussed, recommend check basin # 1 /#2 design against BMP Clearinghouse 2013
Draft VA Stormwater Management Handbook ( link/s, below):
these are relevant
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RE: Hillcrest Vineyard Tasting & Venue WPO 2019-00039, Albemarle County, Va. July 1, 2020
2013 Draft VA SWMH, https://www.swbmp.vwrrc.vt.edu/references-tools/2013-draft-
handbook/
• Appendix 8-A, specifically, 8-A.16.0 , Extended Detention Ponds, design checklist,
beginnings 113 (on-line .PDF): http://www.swbmp.vvTrc.vt.edu/n-
contenUuploads/32_Chap-8-8 App-8-A_Example-BMP-Design-Checklists.pddf
• Appendix A, Earthen Embankments, b—qs://www.swbmp.vwrrc.vt.edu/n-
contenUuploads/2017/11/lntroduction App-A Earthen-Embankments_03012011.pddf
• Appendix C, Vegetated Emergency Spillway, b—qs://www.swbmp.vwrrc.vt.edu/W-
content/uploads/2017/1 I/Introduction App-C Vegetated -Emergency -
Spillways 03012011.pddf
Note: Frank checked top of embankment /100-yr elevations against 1.0' Min. freeboard
requirement; both basins obtain min. freeboard. Thank you
Maintenance and Splety
Emban :n , s opts should be no steeper than 3H:1 V if possible, with a maximum combined
upstream and downstream slope of 5:1 (3:1 downstream face and 2:1 upstream face). For
embankments exceeding 15 feet in height, a 6 to 10 foot wide bench should be provided at
intervals of 10 to 15 fat of height, particularly if slopes are steeper than 3H:1 V.
Response:
Basin #1 embankment slopes are 3:1 on both the upstream and down stream faces. As noted
on sheets C6.041R & C6.042R.
Embankments and emergency spillways were designed to meet Appendix A and Appendix C
requirements.
Basin 0outlet has been redesigned to discharge into a 6' dia. concrete weir structure to
direct outflows to ditch A. Weir has been sized to accommodate IOyr storm from basin 0.
3. It appears project limits expand with detention basin Q. If LOD changes, VRRM.xIs table /data entry
values change. Please revise VRRM.xIs, as needed. Note: post -development VRRM.xIs land cover
values presented with 8/7/20 SWM (Amendment) talc packet (p. 74) are identical with SWPPP,
approved 4/8/20, p. 76 VRMM.xIs land use cover values: 26.00 Ac. forest. 5.20 Ac. turf, 4.86 Ac.
impervious. With this Amendment, they are not identical; one change is additional LOD with
additional basin #2 /access.
Response: VRRMSpreadsheet land cover values revised.
4. C-6.041R
a. Access: Similar to comments above; please provide:
i. Traversable grade for vehicles to exit Venue paved parking and access the SWM
facility. Access to basins is typically to basin embankment, often designed to allow
vehicles to approach riser structures.
Maintenance assumes a need to access SWM facility structures. Provide
conventional SWM facility access that meets ACDSM standards, p. 14.
Response: Note added to sheet C6.0421? "Accessible path is available around the north east side of
the pond across the emergency spillway to embankment and riser structure. "
ii. Revise easement to inelude weess that a4 least with eopmeets with FeeeFded S"
r edit. ,.,.,,,....ent, plat F,.,.,._ ed at deed tit, pg. 5301 64 o
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RE: Hillcrest Vineyard Tasting & Venue WPO 2019-00039, Albemarle County, Va. July 1, 2020
iv. Dimension detention basin #1 floor (L x W).
Response: Basin,/loor dimensions added Sheets C6.041R & C6.042R.
v. W....:.Je p blie dFai.age ,.....,.meat eyef 4geL A May .hew -with ...... CAI Art f ..:I:�..
easefnepAs on a single plat ( detention basins 4 1, 42).
5. Provide existing permanent fill diversion cross -sectional detail. Confirm it is constructed /i.e.
existing, stabilized, permanent.
Response: Permanent fill diversion installed and observed site visit 612712020. Detail added sheet
C6.03R.
Although satellite image below is dated early summer (6/3/20) and provides limited resolution, only
SF is clearly visible in this image.
6.
Open
aspS..aee Easement. Engi.eeFi....needs to ,,sets., this inte_. ally Withdrawn; covered by 7, 8,
below; 8/26/20
7. C6.03IL image above right, includes three Ditch C section labels. Transfer relevant data (x-section
/graphic; Qlo-n, pre- /post; V2-y, pre- /post) for each ditch section from Cale. packet (p. 97-102) to
C6.03R.
G. (8/26/20) Include V2-year pre -/post -development in Calculation report, and on plans.
Response: Table summarizing Ditch C 2yrp 1p.., &10yrp,O., velocities added to sheet C6.03R
8. Revise Stormwater Calculation (report) to include narrative and table summaries to provide context
/demonstrate compliance for PDA A, and POA B. With narrative and tables, please include:
a. pre- /post -development QI-yr, Qlayr values
b energy balance, incl. Qwilo ble
Albemarle requests summary information
As it is, reviewer must construct understanding of compliance using hydrographs, drainage maps,
channel /culvert reports.
Copy identical narrative /tabular information from Calc. report to the SWM Plan Amendment.
Not all values reside only in a report, especially those that inform compliance review.
On SWM Plan Amendment and in the Calc. packet, print allowable values, and demonstrate
compliance with applicable requirements.
(8/26/20) Shift points of analysis to end of outfall channel prior to release to natural drainage feature
(detention basin # 1), to end of riprap apron prior to release to natural drainage feature (detention basin
ll)
There are two site discharge points (apart from sheet flow); both release to natural stormwater
conveyance (9VAC25-870-66.B.3.); compliance with energy balance is required at these points. [
And, per DEQ policy.]
No additional (downstream) stormwater quantity analysis is required, provided QI-yr meets energy
balance at these two site discharge points. C-6.02R [ image, below ]
Response:
• Stormwater compliance table added to stormwater calculations report.
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RE: Hillcrest Vineyard Tasting & Venue WPO 2019-00039, Albemarle County, Va. July 1, 2020
• Stormwater compliance table added to sheet C6.03R
• Point of analysis basin #1 shifted to end of Ditch A. Point of analysis moved to end of riprap
outlet for basin #2.
9. Below ELS, permanent earthen furrows /berms between rows of vineyard plantings that serve a SWM
(not agricultural) purpose; space berms with contours, as needed.
This is to provide downslope barriers parallel with terrain contours below basin # 1 discharge, a series
of `stepped' structures to limit tendency of sheet flow (on steep slopes) to re -concentrate, and cause
erosion.
Resvonse: Upon further evaluation and conversation with Frank Pohl on 9-1-20, a decision was made
not to include furrows/berms in the project at this time.
10. Provide detail (notes, labels, narrative, etc.) of permanent earthen berms /furrows spaced downslope
on contours, whether a vineyard is planted or not. Please see attached photos; there are no vineyard
plantings below the sediment basin /detention basin #1, as of this date.
Note: Slopes below discharge from detention basin # 1 exceed VA DEQ Stormwater Design
Specification No. 2, table 2.2 ( 8% Max.), and without additional permanent measures, an ELS cannot
rely on agricultural practice that may or may not be discontinued, or vineyard that may or may not
persist.
Albemarle County Engineering Division experience is that sheet flow traversing downgradient slopes
>8% re -concentrates, and inevitably can cause erosion, a circumstance that 9VAC25-870-66.D.
requires plan review to consider.
Resvonse: Upon further evaluation and conversation with Frank Pohl on 9-1-20, a decision was made
not to include furrows/berms in the project at this time.
11. VA DEQ Design Specification No. 2 detail, Fig. 2.3• below. Please revise plans to provide:
• Flow bypass structure
• Reinforced swale (similar to proposed Ditch A) that continues straight-line flow of excess
basin # 1 discharge that may occur from events less -frequent than the 10-yr design event.
• Reinforced swale designed to accommodate Q10-yr.
• Geometry that ensures excess /bypass discharge is straight-line, as shown in Fig. 2.3.
• Preliminary e-review comment 2.j. (email, 8/26/2020 9:53 AM) touches on straight-line
objective.
• A single section of MH w/o frame and lid, discussed 8/26 (Teams telecon) with inlet shaping
in floor of MH may effect straight-line objective.
Resvonse:
• Flow bypass structure added to oufall of detention basin #1. Detailed sheets C6.03R &
C6.041R
• Ditch A' alignment is driven by the need to prevent the level spreader sheet flow from
entering the ditch. The 15"pipe exiting the flow bypass structure to the level spreader will
limit the flowrate to the level spreader to the 10yr storm. Excess flows from storms less
frequent than IOyr design event will be diverted over a weir to the grass bypass channel.
• Ditch A' analysis shows IOyr sheet flow to the ditch will be non erosive.
• Concrete structurefweir is sized and shaped to divert flows in excess of the IOyr storm to the
bypass channel.
12. Design ELS based on 10-yr event; ref. p. 14• VA DEQ Design Spec. No. 2, image, below.
Resvonse: 56' Engineered level spreader designed and shown on sheet C6.03R & C6.041 R.
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RE: Hillcrest Vineyard Tasting & Venue WPO 2019-00039, Albemarle County, Va. July 1, 2020
It is my hope that these revisions accurately and adequately address your comments. Should you have
any follow-up questions upon review of this re -submittal, please contact me at your earliest
convenience.
Thank you,
Seth Roderick
K____
Managing Partner
Monteverde Engineering and Design Studio
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