HomeMy WebLinkAboutWPO202000017 Correspondence 2020-07-20 (2)SHIMP ENGINEERING, P.C.
Design Focused Engineering
July 17, 2020
David James
County of Albemarle
Department of Community Development
401 McIntire Road, North Wing
Charlottesville, Virginia 22902
RE: Response Letter #1 for WPO202000017 — Proffrt Road Townhomes South
Dear David,
Thank you for your review of the VSMP request for Proffit Road Townhomes South. This letter contains
responses to County comments dated May 71, 2020. Our responses are as follows:
A. General
Cover — Add WPO202000017 under title.
Acknowledged, the WPO202000017 has been added to Sheet C1 under the title.
B. 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 ESOP, (3) a SWMP, and (4) any TMDL measures necessary.
Registration Statement:
a. Update the Start & End dates under Section IV.
Acknowledged, the start and end dates have been updated in the registration statement.
b. Add `County of Albemarle' for Section IV._
Acknowledged, "County of Albemarle" has been added to Section IV.E in the
registration statement.
2. Complete Sect. 9 — Signed Certification
Acknowledged, we will send the signed Sec. 9 and Sec. 10 in an email upon receiving them
from the owner.
C. Pollution Prevention Plan (PPP)
The PPP content requirements can be found in County Code section 17-404.
1. Submit a PPP exhibit sheet.
Acknowledged, the PPP is included with this submission in the SWPPP document and as a
separate attachment.
D. Stormwater Management Plan (SWMP)
VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a
SWMP.
This plan is disapproved, 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. Provide LD-347 or equivalent Cates & show HGL in the storm sewer profiles.
912 E. High Sr. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
Acknowledged, the LD-347 is provided with this submission, and the HGL is shown on the
storm sewer profiles.
2. Show drainage area for the entrance and show that the entrance will be free of
flooding during the 25-yr storm.
The entrance is at a high point of the road and therefore, the water is flowing away from
it.
3. Provide curb to keep stormwater on -site:
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Water is flowing into the site such that very small drainage area from off site would flow
into the site and we've accounted for that in our Stormwater calculations.
4. Provide ditch or berm:
Win needed_
here-tO-dir6C�w2terf w—••,—°"—°"—'°-
inlet(s) on -site
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3a
I� � [ FFLCr 3F &. 53
Acknowledged, the water is flowing away from the back of the site; thus, a berm is not
needed.
5. Provide proposed inlet drainage area map.
Acknowledged, Inlets Drainage area map is provided with this submission.
912 E. High St. Charlottesville, VA 22902 1434,227,5140 1 shimp-engineeringcom
6. You will need to confirm that the off -site Biofilter' facility's will handle this site's drainage
area since you are diverting stormwater directly to it.
The offsite "biofilter" will not be affected because the stormwater is already being
filtered on our site and is out -letting into a channel not the bio£dter.
7. Show WSE on the weir elate iii str A4
Acknowledged, the WSE are now shown on the weir plate in str. A4. See detail 6 on
Sheet C9.
8.Sheet 9—IIUiIUc L„_11
Acknowledged, Al to A2 profile is now provided. Please see detail 9 on Sheet C9.
9. I was unable to find this Stormtech MC-4500 system listed on DEQs approved list posted on
the BMP Clearinghouse website.
Acknowledged, the certificate is provided with this submission. Please see attacked.
10. VRRM — Please verify (with DEQ) the pollutant removal eff /o of this Stormtech system.
Acknowledged, the pollutant removal eff is 40% based on TP performance data, you can
find this information in the Stormtech MC-4500 system certificate provided for comment
9.
11. Show that the MTD is sized for the project
(https://www.swbmp.vwrrc.vt.edu/bmps/hydrodynamic-devices/ - VADEQ Practice 16:
Hydrodynamic Devices, Sizing information):
Note: Our proposal actually falls into Practice 17: Filtering Devices not Practice 16:
Hydrodynamic Devices,
a. Calculate the treatment volume to the device (TvBMP). The calculated TvBMP can be
obtained from the Virginia Runoff Reduction Method (VRRM) spreadsheets.
Acknowledged, TvBMP is 7,053 Fe. Please see the VRRM sheets included in the
SWM Packet.
b. Calculate the peak discharge of the obtained treatment volume (gpTv). DEQ's preferred
method to calculate the peak discharge for a BMP drainage area is described here.
Acknowledged, gpTv = 2.86 cfs
c. Work with the MTD vendor to ensure that the obtained peak discharge to the device (gpTv)
is less than or equal to the maximum treatment flow rate (MTFR) of the device (gpTv <
MTFR).
Acknowledged, the MTFT = 3.2 CFS > 2.86. Therefore, requirement met.
12. Show TvBMP area of the Stormtech.
Acknowledged, the TvBMP area is now shown on the Post Dev map. A legend was
provided to eliminate any confusion.
Note: On the drawing, the term "Onsite Drainage Area" means the TvBMP drainage
area.
13. Sheet 12 - Show these post-dev areas of runoff on the map.
912 E. High St. Charlohesville, VA 22902 1434.227.5140 1 shimp-engineering.com
Acknowledged, the post-dev areas are now shown on sheet C12. A legend was provided
to eliminate any confusion.
14. Show/label `SWM facilir Isements for the underground detention and Stormtech system.
Acknowledged, the SWM Facility easement for the underground detention and
Stormtech is shown on Sheet C4, C7, & C12, as well as on the Post Dev DA map.
15. Provide minimum easement width for the SWM pipes to follow sizing, [ACDSM, p.15].
EASENU.\T WIDTH. DLOtETER . S' . 21H-5'I *IV 19M NEM.1
Below are the easement calculations based on the formula provided:
Al to A2:
A2 to A3:
A3 to A4:
A4 to A5:
A5 to A6:
A7 to A8:
A8 to A9:
A9 to A10:
2+2+2*(4.10-5) +10 =12.2 ft
2 + 2 +2*(3.23-5) +10 =10.46 ft
2 +2 +2*(7.74-5) +10 =19.48 ft
3+2+2*(6.76-5) +10=18.52ft
3+2+2*(7.07-5)+10=19.4ft
L25 + 2 +2*(4.12-5) + 10 =11.49 ft
L25 +2 +2*(6.27--5) +10 =15.79 ft
z25 + 2 +2*(4.25-5) +10 =11.75 ft
Since all the results of the calculations are less than 20 ft, the easements are kept as 20ft
easement.
16. Record the SWM maintenance agreement prior to approval. [Sec. 17-415]
Acknowledged.
17. A recorded SWM facility easement plat & deed prior to permit issuance.
Acknowledged.
18. Provide letter of availability from the off -site nutrient bank provider. Currently 1.16 TP load
credits required. [Sec. 17-403 A.9]
Acknowledged, we will send this via email upon receiving it from the owner.
19. Provide list of materials auu P1,oc Icl tiIo �IDlmlcLit MC-4500 s) stciii wi uIo DOW est.
Acknowledged, please see the document provided with this submission that has the MC-
4500 Site Calculator.
E. Erosion and Sediment Control Plan (ESCP)
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
Virginia Code §62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESOP.
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 — Visually field verify topography & existing site show on sheet 3 and provide date of
field verification.
Acknowledged, Justin Shimp, P.E. has field verified the site on June 4' 2020. A note was
also added to Sheet C1 under Source of Boundary and Topography.
2. Show location of all existing utilities and easements with deed book references.
Acknowledged, all existing easements are shown on Sheet C3, C4, C5, C6, C7, & C11 and
the text of the easements is shown on Sheet C2, C3, C4, C5, & CIL
3. Provide offsite easement for proposed drainage connection to offsite SWM facility. A letter
from off -site property owner is enough for this plan review, but any legal easements will need
to be signed by the property owners. [ACDSM, p.22]
Acknowledged, the offsite easement is provided, it is located right on the limits of
disturbance, therefore, it is not showing clearly. However, it is labeled as "20' Drainage
Easement" and this is shown on Sheet C4, and C12 as well as on the Post DA Map.
4. Sheet 4 —Please show all grading elevation labels (a few missing).
Acknowledged, more grading elevations were added.
5. Sheet 6 —
a. Provide CRS (3.03) for the road.
Acknowledged. Please see #4 of sequence of construction notes on Sheet C6. The road
will be stabilized with 1.5-inch stone.
b. Provide SCC (3.17) instead of DV & CIP. That way you have both outlet & inlet protection.
DV not meant to receive concentrated flow. under title.
Acknowledged. The DV have been replaced with SCC. The CH' is still necessary
because the SCC is proposed with only the filter cloth without stone. Please see Sheet
C6.
If you have any questions or concerns about these revisions, please feel free to contact me at
Stephaniekshimp-en ing eering com or by phone at 434-227-5140.
Regards,
Stephanie Paul
Shimp Engineering, P.C.
912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com