HomeMy WebLinkAboutWPO202100042 Correspondence 2021-10-13SHIMP ENGINEERING, P.C.
Design Focused Engineering
October 13, 2021
John Anderson
County of Albemarle
Department of Community Development
401 McIntire Road, North Wing
Charlottesville, Virginia 22902
RE: Response Letter #1 for WP02021-42 Bamboo Grove
Dear John,
Thank you for your review of the VSMP plan for Bamboo Grove. This letter contains responses to
County comments dated September 17, 2021. Our responses are as follows:
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. Revise SWPPP title page to include correct TMPs (05500-00-00-068C0; 05500-00-00-
068D0) and Project Name (Bamboo Grove VSMP).
RESPONSE: This information added to the revised SWPPP.
2. Include ref. to WP0202100042 in SWPPP title.
RESPONSE: This project number has been included in the title.
3. Revise Owner to Bamboo Grove, LLC, consistent with Sec. 9 Certification Statement.
RESPONSE: "Prepared For _" name revised to Bamboo Grove, LLC. Also added to
plan cover sheet as the developer.
4. Sec. 1 — Registration Statement Statement
a. Sec. I.A. — Please revise Operator Name to Bamboo Grove, LLC, consistent with
Sec. 9.
RESPONSE: Operator name revised.
b. Sec. II.F. — Leave blank since parcels are not located within Albemarle County
MS4.
RESPONSE: "Albemarle County MS4" This has been removed.
5. Sec. 4, 5 — Update to reflect ESC/SWM plan revisions.
RESPONSE: SWPPP updated with ESC & SWM plan revisions.
6. Sec. 5: Please remove HydroCAD routings from SWPPP. Routings in Calc. booklet are
sufficient.
RESPONSE: Noted, HydroCAD routings removed from SWPPP.
7. Sec. 6.A. /Exhibit: Locate rain gauge within parcel boundaries, outside public RW.
RESPONSE: rain gage, SWPPP mailbox moved inside parcel boundary.
912 E. High Sr. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
8. Sec 6.E.: Person responsible for PPP must be identified prior to pre -construction, but not
for WPO plan approval.
RESPONSE: noted, since this is not known yet, it will be updated once a contractor is
selected before Precon. meeting.
B. Pollution Prevention Plan (PPP) — see SWPPP item 7 above
The PPP content requirements can be found in County Code section 17-404.
C. Stormwater Management Plan (SWMP)
VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a SWMP.
This plan is disapproved for reasons listed below. The stormwater management plan content requirements
can be found in County Code section 17-403.
1. C13
a. Note: Project proposes to meet water quality requirements with combination of
forest -open space easement and 0.51 lb. nutrient credit purchase. Forest -open
space easement must be recorded prior to plan approval and requires separate plat
application and review/approval process. Nutrient credit purchase is not required
for plan approval but is required to receive a Grading Permit. Please coordinate
nutrient credit purchase with Ana Kilmer prior to finalizing purchase, as both bill
of sale and affidavit must list project specific information (WPO#, project name,
project HUC, 0.51 lb. of credits, etc.). Please coordinate with Ms. Kilmer at
earliest convenience (434-296-5832 x 3246, akilmer@albemarle.ore). Please find
easement plat application at:
https://www. albemarle.org/home/showpublisheddocument/ 1052/6376240893141
00000.
RESPONSE: Noted. After coordinating with the client, they prefer to expedite
the timeline by removing the Forest -Open Space Easement (thus removing the
requirement for an approved plat pre -approval) and plan to only purchase
nutrient credits. As such, the VRRM spreadsheet has been revised to only include
the limits of disturbance. To satisfy updated VRRM requirements, an additional
0.081bs must be purchased, for a total of 0.591b/yr.
b.Include (image of) Construction Record Drawings (As -built) for VSMP on the
plans; link:
https:/%www.albemarle.orwhome/showpublisheddocument/3381/6373275105367
00000.
RESPONSE: This document is now provided on C6.
c. Provide reference to dry detention pond design criteria.
RESPONSE: reference added below profile on C6. No additional DEQ BMP
criteria apply to this pond.
d.Label dry detention pond floor dimensions L x W.
RESPONSE: dimensions added to plan sheets
e. Provide detailed profile for pond structures.
i. Riser Added to profile
ii. Riser base elevation Added to profile
iii. Existing/proposed grade Added to profile
iv. Pond floor Added to profile
V. Pond structures /see hydroCAD routings Added to profile
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom
2. C14
1. 18" culvert (primary spillway) Added to profile
2. 8" orifice Added to profile
3. 5' DIA riser Added to profile, added as detail (Revised to 48")
4. Emergency spillway (dimensions/material) Added to profile,
added as detail
RESPONSE: These details were added to the profile on Sheet C6. Riser Detail
added to C6. Emergency Spillway detail added to C6.
f. Plan view of dry detention pond is missing linework, labels, leaders, etc. Provide
complete plan view design with level of detail required to evaluate design,
estimate bond amount, construct, inspect, and operate this facility.
RESPONSE: Additional plan view detail (and additional reference plan view,
located on C6) added to plans.
g. Provide dry detention pond installation steps on the plan.
RESPONSE: Installation notes added to C6.
h. Provide periodic dry detention pond inspection guidelines on the plan.
RESPONSE: Inspection guidelines added to C6.
i. Include notes/guidelines to convert sediment trap to dry detention pond.
RESPONSE: Conversion notes added to C6.
a. Pre -/post -developed offsite overland sheet flow is intuitively an identical longest
path. This may be a misconception, but whatever sheet flow path is shown for
upslope offsite runoff, it is a single path perpendicular to existing contours, and is
unaffected by on -site downgradient development, or change to on -site contours.
When offsite sheet flow encounters altered site grading, that would appear to be
the point pre-/post-dev storm runoff may diverge in pre -/post -condition (sheet,
shallow concentrated, concentrated). Please identify longest off -site sheet/SC
flow paths and represent these as pre-/post-dev runoff condition, and revise
graphics/calculations, as needed. Else, correct misconception.
RESPONSE: Noted, that makes sense. After further analysis, it appears that the
flow path used in the post -development TOC is a better representation of both the
pre- and post -development offsite TOC, and this flow path is therefore used for
both "pre-dev offsite" TOC and "post-dev offsite to dry pond" TOC. These both
share the same offsite flow path characteristics. Associated graphics/calculations
updated.
b. Please update 1-yr, 10-yr page references to Calculation booklet; pp. 16, 22, 36,
55 appear inaccurate.
RESPONSE: You are correct, the references to the calc. booklet have been
updated to include correct page numbers.
c. Check 1-yr, 10-yr values against Calculation booklet; for example: Calc. booklet
reports 24-hr 1-yr Qpo,= 3.48 cfs, while plan lists 3.74 cfs. Calc. booklet reports
24-hr 10-yr Qpr = 13.64 cfs, while plan list 14.35 cfs. Please check plan v.
calculation booklet values for consistency. Revise energy balance equation and
plan table values, as needed to correspond with booklet HydroCAD routing
values.
912 E. High St. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom
RESPONSE: You are correct, the values did not match (this happened because
we had changed our dry pond design after printing the Energy Balance Equation
table). Strategy has been optimized and updated, all values are now internally
consistent.
d.3-A7 profile: provide label/note specifying subgrade compaction for
pipes/structures. Entire pipe -structure network is in fill.
RESPONSE: This is provided for Pipe C, which is the only pipe in fill. Other
pipes are not in fill.
3. Cl: Tax map parcels appear to correspond with HTC development; please revise.
RESPONSE: The tax map parcel numbers on the cover sheet have been corrected.
D. Erosion and Sediment Control Plan (ESCP)
Virginia Code §62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This plan
is disapproved for reasons listed, below. The erosion control plan content requirements can be found in
County Code section 17-402.
1. C9
a. Revise CE label to PCE (paved construction entrance); provide ACDSM paved
wash rack detail on sheet C12 (p. 8/ACDSM).
RESPONSE: Comment received. Label has been revised, with accompanying
detail.
b.CWD appears to concentrate sheet flow (offsite clean runoff) and divert it toward
Orchard Drive; design relies on slight Swale to route it beneath (paved)
construction entrance. Provide barrier to prevent higher -than -anticipated
concentrated/channelized diverted flow from causing flooding in Orchard Drive
(provide an earth berm, more pronounced grade, etc.).
RESPONSE: This ditch has now been analysed for increased temporary
cleanwater construction runoff. The ditch has a 7:1 side slope, and a 9" depth.
The ditch is adequate to convey the increased 10-yr runoff from the cleanwater
diversion.
c. Project proposes ESC measures within public right of way and a diversion
immediately adjacent to edge of pavement. VDOT land use permit is required.
RESPONSE: Noted, this is noted in General Construction Notes #1 on the cover
sheet. (also required for entrance construction)
Cl. Provide construction entrance culvert IP.
RESPONSE: CE culvert IP added. Added as permanent feature also.
e. Provide grade required to install construction entrance culvert in ESCP Phase 1.
RESPONSE: Note added to C9. "INSTALL CULVERT Al-A2 PER
PERMANENT SETUP. SEE SHEET C6." Grade is the same as that profile.
f. Label trap outfall/weir riprap L x W dimensions.
RESPONSE: Trap Weir LxW added to C9
g.Label sediment trap.
RESPONSE: Sediment trap is now labeled with symbol STl.
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineering.rom
If you have any questions or concerns about these revisions, please feel free to contact me at
keane@shimp-en ing eering com or by phone at 434-299-9843.
Regards,
Keane Rucker, Err
Shimp Engineering, P.C.
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom