HomeMy WebLinkAboutWPO202100041 Correspondence 2021-10-28SHIMP ENGINEERING, P.C.
Design Focused Engineering
October 28, 2021
John Anderson
County of Albemarle
Department of Community Development
401 McIntire Road, North Wing
Charlottesville, Virginia 22902
RE: Response Letter #1 for WPO2021-00041 HTC Area C Townhomes- VSMP
Dear John,
Thank you for your review of the VSMP plan for HTC Area C Townhomes. This letter contains
responses to County comments dated September 8, 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 title of SWPPP to include ref. to WPO202100041
RESPONSE: Title revised as requested.
2. Update ESC-SWM 11"x17" plan sheet inserts, if/when revised.
RESPONSE: The plan sheet inserts revised as requested.
B. Pollution Prevention Plan (PPP)
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. Cl
a. Revise plan and SWPPP title/cover sheet include reference to WPO202100041.
RESPONSE: Cover Sheet Title revised as requested.
b. Replace Stormwater Management Note first sentence with these two sentences: "Per
the approved ZMA200200002 and Approved SWM plans, runoff will be directed to
existing regional stormwater facilities designed for a full buildout of each site.
Reference Engineering file 2301, Hollyntead Town Center, regional SWM1 for block
II SWM facility design (adjacent to Rt. 29), and SWM2 for block III SWM facility
design (west of Laurel Park Lane).
RESPONSE: Cover Sheet Title revised as requested.
c. Despite Stormwater Management Note that states `Both facilities, as well as the
offsite storm pipes which convey runoff into them, were designed for a maximum of
85% impervious cover...' provide LD-229 storm pipe computations and LD-204
storm inlet design data tables that consider total watershed full build -out runoff
912 E. High Sr. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
2. C2
reaching offsite storm pipes. It is unclear that existing storm pipes are designed for
total watershed full build -out. It is important to evaluate effects of routing additional
runoff to existing pipe networks.
i. In the case of Area C, block II, proposed on -site 15" HDPE connects with ex.
18" RCP (C7) at Connor Drive.
RESPONSE: this is now addressed in the SWM plan sheet C20. Specifically,
we analyzed all site outfall points (CI, D2, D1, 130) to demonstrate
compliance with our best estimate of the HTC storm sewer design
parameters. We included a factor of safety for these original estimates by
estimating that the original design for this site was 5% less impervious than
the design of the overall watershed drainage area. Even with this factor of
safety included, we are confident that this development's peak runoff (shown
as C * A) is less than each storm sewers' original design. Due to this we will
proceed with the submittal. Please reference SHEET Sl "SWM & BMP
PLAN" FROM WPO2003-02301 "HOLLYMEAD TOWN CENTER
REGIONAL SERVICE AREA C" included with this submittal.
We will continue to search for the original storm channel designs (LD-229,
for an easy direct comparison, as was done for Block III below), but we are
confident this development design routes runoff into the existing system at
rates that comply with the original design, thus satisfying channel protection
and flood requirements.
ii. In the case of Area C, block III, proposed on -site 15" HDPE connects with
ex. 24" RCP (C8) at Lockwood Drive.
RESPONSE: this is now addressed in the SWM plan sheets. Specifically, we
analyzed the site outfall point (AO) to demonstrate compliance with the
original HTC storm sewer design parameters. It is compliant. See included
"SDP 2005-00019 "ABINGTON PLACE - PHASE 1" (specifically, sheet
S 11) included with this submittal.
a. Label Connor Drive east of Timberwood Blvd.
RESPONSE: The label for Connor Drive is towards the lower corner of block U's
boundary, in front of TMP 32-43. Road names are now bold on this sheet for clarity.
b. Recommend a label to clarify that Area of block C north of Connor Drive and
Timberwood Blvd, east and adjacent to Berkmar Drive Ext. is not included in
WPO202100041.
RESPONSE: The boundary and text linetypetweight has been revised to clarify that
this area (block VII) is not included in WPO202100041.
c. Identify regional SWM facilities as SWMI and SWM2.
RESPONSE: Labels added as requested.
3. C5, C6
a. Revise sheet title to read Site Layout, rather than Site Plan. A WPO plan does not
approve a site plan.
RESPONSE: Sheet titles have been revised accordingly.
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom
4. C7, C8
a. Revise Conner Drive to read Connor Drive.
RESPONSE: This street name has been corrected.
5. C9
6. Cll
a. Name roadway network (streets/Orchid Bend).
RESPONSE: Block 11's road names are included on this sheet.
a. Road profile will be evaluated with HTC Area C Townhomes Road Plan. Please
submit Road Plan at earliest convenience.
RESPONSE: A road plan been reviewed once. We have incorporated relevant road
plan review comment revisions into this plan. second road plan submittal pending.
b. Revise block II road & WL profile captions (since identical).
RESPONSE: Thank you for bringing this to our attention. This has been updated.
c. Check block III structure profile labels (Note: 2 A2 labels); please revise.
RESPONSE: Noted, this has been updated.
d. Check/revise Block 11 storm profile captions, as needed (Profile Al-A7).
RESPONSE: Thank you for bringing this to our attention. This has been updated.
e. F3-A7 profile: provide label/note specifying subgrade compaction for
pipes/structures. Entire pipe -structure network is in fill.
RESPONSE: A note requiring subgrade compaction has been added to this profile.
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.
7. C 14
a. Acquire offsite temporary construction easement to construct stepped retaining walls,
if needed, TMP 32-43.
RESPONSE: Thank you for bringing this to our attention. An offsite temporary
construction easement will not be necessary for the stepped retaining walls as the
walls will be constructed from above.
b. Please remove extraneous linework that may be mistaken as a third (stepped)
retaining wall; this linework crosses DD, proposed grade, and a feature that is
unknown. Eliminate linework unless relevant to ESCP Phase 1. Highlight yellow,
image, below. [Image removed in comment response].
RESPONSE: Noted, this was a drafting item to help draw the ESCP items, it is
extraneous and has been removed.
c. During HTC hotel construction downslope in the same development, a sediment trap
(sized per VESCH) positioned near the edge of the hotel development failed on
several occasions. In that instance, sediment -laden release to neighboring parcels
following storm events proved resistant to remedy. Experience of failed attempts to
912 E. High St. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom
modify a trap with limited offset distance to property line is sufficient basis for
Engineering to request additional volume for ST I, ST2. Any failure of either ST will
result in release of sediment -laden discharge to Connor Drive, existing storm inlets,
and ex. storm network.
Note: proposal to use existing culvert as sediment trap 1 outlet is virtually identical to
proposal at HTC hotel, where this approach failed.
GIS image, below [HTC Area C blocks 11, III] — development, blue circle left; hotel
ST, blue circle right [Image removed in comment response].
RESPONSE: Noted, this is an agreeable request, with the trap location in a developed
and heavy -trafficked area, in an equivalent situation to a location with documented
trap failure. Both STl and ST2 have been oversized by 15% to prevent sediment trap
failure on block H.
If you have any questions or concerns about these revisions, please feel free to contact me at
keane@shimp-en 'ngi eering com or by phone at 434-227-5140.
Regards,
Keane Rucker, Eff
Shimp Engineering, P.C.
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom