HomeMy WebLinkAboutWPO202200020 Review Comments WPO VSMP 2023-02-07�q oe nt 401 McIntire Road, North Wing
Charlottesville,VA22902-4579
County of Albemarle Telephone:434-296-5832
COMMUNITY DEVELOPMENT DEPARTMENT WWW.ALBEMARLE.ORG
VSMP Permit Plan Review
Project title:
SOUTH PANTOPS DRIVE PARCEL 20R
Project file number:
WPO202200020
Plan preparer:
Justin Shimp [Justin@shimp-engineering.com]
Owner or rep.:
South Pantops II Land Trust c/o Charlie Hurt, Shirley Fisher
[provide email]
Plan received date:
May 6, 2022
(Rev. 1)
13 Jan 2023
Date of comments:
June 8, 2022
(Rev. 1)
7 Feb 2023
Reviewer:
David James [djames2@albemarle.org]
John Anderson, PE, Rev. 1
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/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. Registration Statement
a. Sec.l B. - Check box (Rev. 1) Addressed.
b. Sec.11 F. - Change to Albemarle County (Rev. 1) Addressed.
c. Sec.11 H. - Check box (Rev. 1) Addressed.
d. Sec. III - Complete prior to permit issuance (Rev. 1) Persists. Information required
prior to Grading Permit issuance.
e. Sec. V - Sign & date (Rev. 1) Addressed.
2. Complete Section 9. Signed Certification prior to plan approval. (Rev. 1) Addressed.
3. Complete other sections prior to pre -con. (Rev. 1) Persists. Sec. 6.E. /Sec. 8, require named
individual be listed: an individual responsible for PPP (6.E.) and for compliance inspections
(Sec. 8) prior to state VAR10 permit registration, or Grading Permit issuance.
4. (Rev. 1) New. Revise Sec. 4/5, once ESC and SWM plan sheets revised, reviewed, and
approved.
B. Pollution Prevention Plan (PPP)
The PPP content requirements can be found in County Code section 17-404.
1. Appears complete; revise as needed. (Rev. 1) May persist.
C. Stormwater Management Plan (SWMP)
VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a SWMP.
This plan is denied, and the reasons are provided in the comments below. The stormwater
management plan content requirements can be found in County Code section 17-403.
1. Show the Forest & Open Space easement(s) areas to be protected. According to VRRM
Engineering Review Comments
Page 2 of 7
4.13ac F/OS protected. (Rev. 1) Partially addressed. Pls. see item 4.g.i.3., below.
2. A swm narrative will need to be included on the plans. (Rev. 1) Partially addressed. As follow-
Once calculations revised, revise narrative as needed.
3. 1 would prefer that information on the type and location of stormwater discharges,
predevelopment and postdevelopment drainage areas be shown on the plans rather than
separately in calc. packet. (Rev. 1) Addressed.
4. Calculations packet:
a. Pg. 16 - Revise title of map to 'POSTDEV...". (Rev. 1) Addressed.
b. Your pre- & post- development drainage area totals should match. (Rev. 1)
Addressed. As follow-un, see item 4.e.iii., below.
c. It's not clear from the maps how you are reducing offsite impervious area (1S/8S)
postdevelopment. (Rev. 1) NA given need for design /calc revision. Ref. item 4.e.iii.,
below.
d. Label/show offsite & onsite drainage areas (Rev. 1) Addressed.
e. Pg. 24 -
i. Please cite the page numl_ (Rev. 1) Addressed.
ii. Clarify why you are subtracung iviax uaev i turn use Qpredev? Max Qdev
determined (0.15cfs) is less than the Achieved Reduction (0.89cfs). (Rev. 1)
Withdrawn. Applicant response, SE Letter d. 1/11/23: 'This analysis now
uses the DEQ Offsite run-on EBE analysis, so this comment is no longer
applicable. Note: Limits of Disturbance area has been added, because we got
the new survey topo area. Also note, we have utilized permeable paver
driveways to help achieve compliance with the energy balance equation.' As
follow-ua. See comments elsewhere concerning EB equation (4.e.iii, next
item), and permeable pavers (item 4..i. .
iii. Use the Energy Balance (offsite) equation. Consult the Plan reviewer SWM
participant guide. (Rev. 1) Not addressed. There is fundamental error in
calculation /SWM design strategy:
1. Pg. 22 indicates subcatchment 2S: Post DA onsite (1.100 Ac.) VRRM
runoff=2.23cfs, with Tc =5.0 min.
2. Pg. 22 indicates subcatchment 1S: Post DA offsite (51.540 Ac.) runoff
=29.47cfs, Tc =31.2 min.
3. This development cannot combine development discharge with
bypass discharge, and model merged flow as post -developed flow at
the point development runoff exits concrete ditch /flume. The bypass
flow is independent of South Pantops Drive Parcel 20R development.
4. 2/1/23 site photos, calc. packet, and plan indicate post -development
discharge is to an existing concrete flume.
5. At point concrete flume discharges to natural stream, which is at
plunge pool for 48" DIA concrete culvert beneath S. Pantops Drive,
9VAC25-870-B(3) energy balance applies.
6. Calc. packet, p. 22, indicates post-dev Q peakl-yrundetafned,=2.23cfs.
7. Apply Energy balance to 1.10 Ac./2.03 Ac. (Ditch DA), using Rv values
(pre -post) and Q 1 pre, site, = 0.87 cfs, which yields Q 1 post, site, _
0.285cfs.
8. Revise design to meet Energy balance for the 1.10 Ac./2.03 Ac. DA
development at point post-dev. discharge at base of concrete flume
discharges to natural stream, coincident with 48" DIA concrete pipe.
9. Remove reference to 51.540 Ac. off -site DA when calculating EB for
this development) from plan, narrative, and calc. packet.
10. 51.540 Ac. enters flood protection evaluation since at point bypass
and development runoff merge at 48" pipe outfall/natural stream
Engineering Review Comments
Page 3 of 7
plunge pool, site DA has not reached 1% of overall watershed DA
(110 Ac.), but is only 52.640 Ac. at that location. Flood protection
evaluation likely continues to Rivanna River mapped floodplain.
11. In this instance, strategy of meeting EB by offsetting hydrographs is
impermissible. To reiterate, provide channel protection evaluation at
Point Al, top of concrete flume, per 9VAC25-870-66-B(1) /manmade
channel, and per 9VAC25-870-66-B(3)/energy balance, at the bottom,
12. Last: In this case, bypass flow is simply a 'receiving stream.'
Development discharge must meet channel protection at top
(manmade) and bottom (EB) of the concrete ditch (natural stream).
Engineering Review Comments
Page 4 of 7
f. Please clarify: On pg. 24 you state you're meeting flood protection under 66-C(2)b,
but on pg. 3 for flood protection it looks like your trying to meet 66-C(1).
i. You're not showing you meet 66-C(2)b, Qpost>Qpre. (Rev. 1) Partially
addressed. As follow-up. Pg. 29 Calc. packet indicates Q10 postdev /design
=109.50 cfs while Q10pre =Max Q10post=109.16. Qdemgn > QM... Revise
design, review, or clarify if typo. Also, provide cross reference to hydrograph,
by calc. p. #. Note: Calculations require revision, with flood /channel
protection evaluation of site development runoff compliance at top of
concrete flume /ditch, and further channel/flood protection evaluation at
bottom of the flume. At bottom of flume, site development runoff must meet
EB Eq., for channel protection, while below point of plunge pool, where off -
site 51.540 Ac. bypass runoff joins 1.10 Ac. site development runoff (2.03 Ac.
ditch DA), natural channel must be evaluated for flood protection (for areas
prone to flooding, or not prone to flooding, to limit of mapped floodplain).
g. VRRM - Please use New development spreadsheet. The parcel is undeveloped. (Rev
1) Addressed. As follow-un:
i. Engineering notes permeable pavers and forest /open space (FOS) post -
developed land cover are used to comply with storm water quality
requirements. FOS easement must be platted prior to WPO plan approval.
1. Please confirm whether development is to be subdivided; if so, FOS
easement may be platted with subdivision plat, afterWPO plan
approval.
2. If no subdivision, please submit easement plat, via separate plat
application process for review /approval prior to WPO plan approval.
3. Show linework /boundary of 3.26 Ac. FOS easement on plan sheet C4
(shown on C9, but please show portions visible on C4 as well).
4. Provide public SWM facility easement for permeable pavers:
a. Permeable pavers constitute material surface type of each of
13 townhouse driveways.
b. Acknowledge that individual owners of each townhouse will in
effect be responsible for SWM facility maintenance of
permeable pavers, in perpetuity.
c. This means, pavers are the only permissible driveway surface
material, and may not be removed unless water quality
phosphorus reduction provided by pavers is offset via
alternative SWM BMP, or nutrient purchase that provides
equivalent phosphorus reduction.
d. Were credits purchased instead of driveway permeable
pavers, Engineering estimates expense to purchase 0.32 lb.
credits would be approximately $4,000.
e. While Engineering cannot prohibit this design strategy, i.e.,
perpetual maintenance of permeable paver driveways by 13
individual townhouse owners, we wish to point out the
strained logic of developer avoidance of relatively modest
$4000 expense, transferring maintenance of SWM facilities
located on everytownhouse (lot?) to 13 individual townhouse
owners that will likely take exception to this design, perpetual
maintenance responsibility, and maintenance expense.
f. Engineering recommends developer instead purchase 0.27 lb.
credits since this practice along with 3.26 Ac. FOS easement
net a 0.05 lb. credit, meaning, 0.27 lb. purchase (with FOS)
would meet site phosphorus reduction requirement.
Engineering Review Comments
Page 5 of 7
g. Engineering would not object to permeable pavers placed
within private access if CCR assigns SWM facility maintenance
expense to HCA, but finds permeable driveways problematic
in the extreme.
h. Note: Under proposed design, eachdrivewav requires
independentSWM facility easement (metes /bounds) since
driveways are discontinuous, with sanitary laterals between.
i. Each driveway /SWM facility will be owned and maintained
separately, by a private individual /townhouse owner.
j. C4 shows permeable paver underdrains; west rear corner of
each townhouse spills to permeable pavement.
i. C3-C4 show permeable paver common UD connecting
with individual UDs beneath pavers at each driveway.
The common UD collects individual UD runoff, once
surface runoff passes through permeable pavers.
ii. The two common UDs serve 5 lots, and 8 lots. A
common UD that spans multiple privately -owned
SWM facilities (permeable paver driveways) poses
obstacle; which, for example, of thirteen townhouse
owners is responsible for investigating or repairing an
issue affecting common underdrains?
iii. Remove common underdrains from driveways.
k. Advantages of 0.27 lb. nutrient purchase to meet SW quality
requirements are practical, and multiple, for future owners,
and current developer.
i. Expense of SWM facility easement plat and
underdrain redesign may exceed expense of 0.27 lb.
nutrient purchase, while individual townhouse owners
would likely far prefer piped collection /conveyance of
rear roof runoff to an UG detention system placed
beneath rear driveway private access.
ii. It is important to note that a detention system appears
unavoidable to meet energy balance for 2.03 Ac. ditch
DA at bottom of the concrete ditch /flume.
iii. It seems expedient to route rear roof runoff to such a
dedicated underground detention system as opposed
to 13 individual SWM facilities that are, at the same
time, privately -owned driveways.
Provide inlet drainage area map and assumed values to match calc. table. (Rev. 1)
May persist: C9 shows ditch and inlet drainage map. As noted elsewhere, calculations
must be revisited.
Provide channel adequacy/protection is met from the Al discharge point to outfall
natural channel (i.e. portion of ex. manmade channel). 66-B(1)a (Rev. 1) Persists.
Applicant response, letter d. 1/11/23: 'LD-268 table has been used to demonstrate
that 2-yr velocity and 10-yr depth at the concrete channel is adequate up to the
outfall point. See table on sheet C9.' As follow-uy. 66-B(1)a, channel protection for
manmade system requires Q Peak 2-yr PcGt dev not cause erosion of manmade channel
from Al to outfall to natural channel. Modified LID-268, p. 34, Calc. packet, lists
Allowable velocity=10.Ofps and 2-yr velocity=17.25fps, 72% higher than Vmax.
Clarify; reconcile 2-yr design velocity that appears to exceed Vmax; ensure ditch
velocity (Al to outfall), V2-yr, is non -erosive, and will also be non -erosive to plunge
pool at point of discharge to natural receiving stream.
Engineering Review Comments
Page 6 of 7
j I pst.-. aFn dote ntie n seems neeessary based upen iFApervieus ...-..- pest .J......IepffleHt
, tet-there
5. New. Provide Construction Record Drawing (As -built for VSMP on the plan.
6. New. Provide construction, installation, inspection, and periodic maintenance for permeable
pavers on the plan; ref. BMP Clearinghouse VA DEQ Stormwater Design Specification No. 7.
D. Erosion and Sediment Control Plan (ESCP)
Virginia Code §62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This
plan is disapproved, and the reasons are provided in the comments below. The erosion control plan
content requirements can be found in County Code section 17-402.
1. Cover - (Rev. 1) Addressed.
a. Provide date(s) of LIDAR data.
b. Provide date of field verification of topography & existine conditions.
2. Please show LOD on the existing conditions sheet. (Rev. 1) Addressed.
3. Show demolition operations. (Rev. 1) Addressed.
4. Show existing treeline. (Rev. 1) Addressed.
5. Show accurate horizontal depth (batter) of retaining wal (Rev. 1) Addressed.
6. Show geogrid extent of retaining wall. (Rev. 1) Addressed.
7. Label TW/BW elevations at each bend and wall ends. (Rev. 1) Addressed.
8. Tie contour lines along new road to the retaining wall. (Rev. 1) Addressed. Asfollow-up: Tie
east end of retaining wall to existing contours. (TW =417; BW=412.50, but no proposed
contours are shown.)
9. Note: Please submit retaining wall design & computations with the site plan. Separate building
permit required. (Rev. 1) Persists. Applicant: 'Comment noted. We have this in progress we
will submit it separately.'
10. Show all proposed contours at 2' intervals. (Rev. 1) Addressed.
11. Reduce grade to 2:1 or less adjacent to lot 1. (Rev. 1) Addressed.
12. Provide B/M (VAESC H B, 3.36) between lots 5 & 6, and adjacent to lot 1. (Rev. 1) Addressed.
13. Where grade over 3:1 provide low -maintenance (not grass) groundcover. (Rev. 1) Addressed.
14. Show a staging and stockpile area. Show SF around stockpile. (Rev. 1) Addressed.
15. Show temporary construction easement for offsite improvements. (Rev. 1) Addressed.
16. Provide letter of permission from VDOT for work in the ROW prior to disturbance. (Rev. 1)
Addressed. (Not required for WPO plan approval; required for any activity within VDOT RW.
Slight correction: VDOT Approval will take form of a Land Use Permit.) Applicant: 'Letter
should be provided from the contractor.'
17. Provide volume estimate of cut & fill balances. (Rev. 1) Addressed.
The VSMP permit application and all plans may be resubmitted for approval when all comments have
been satisfactorily addressed.
Engineering plan review staff are available from 2-4 PM on Thursdays, should you require a meeting
to discuss this review.
Process:
Engineering Review Comments
Page 7 of 7
After approval, erosion and sediment control and stormwater management improvements must be
bonded. The bonding process begins when the plan is approved, and the applicant submits a bond
estimate request form and fee to the Department of Community Development. A plan reviewer 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 to the County,
who will record the agreement.
After bonding and agreements are complete, county staff enters project information in a DEQ
database for state application processing, if a DEQ permit is required. DEQ reviews 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, which must be
posted at the construction site.
After DEQ coverage is issued, via the coverage letter, the County can hold a pre -construction
conference. Applicants must complete the request for a pre -construction conference form and pay
the remainder of the application fee. The form identifies the contractor and responsible land
disturber, and the fee remaining to be paid. This will be checked by county staff, and upon approval, a
pre -construction conference will be scheduled with the County inspector. At the pre -construction
conference, should everything proceed satisfactorily, a joint VSMP and grading permit will be issued
by the County so that work may begin.
County forms can be found on the county website forms center under engineering;
https://www.albema rle.org/government/commun ity-development/a pply-for/engi neering-
applications
WPO202200020_SOUTH PANTOPS DRIVE PARCEL 20R_020723-ja_revl.docx