HomeMy WebLinkAboutWPO200900013 Review Comments Stormwater Management Plan 2009-09-21OF AL
O
,. vIRGI1`IZP
COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project:
Plan preparer:
Owner /Applicant:
Plan received date:
Rev. 1:
Rev. 2:
Date of comments:
Rev. 1:
Rev. 2:
Reviewer:
Van Dine Plaza [SDP200900024 & WP0200900013]
Justin Shimp, PE; Dominion Development Resources
[email: j shimp @ ddrva.com]
Auto LLC
9 April 2009
1 June 2009
7 August 2009
30 April 2009
26 June 2009
21 September 2009
John P. Diez — Engineering Technician
A. Final Site Plan
1. Please provide source and date of topographic verification. [ 18- 32.6.6]
(Rev. 1) Comment has been addressed.
2. Some of the grading in the parking areas exceeds 5% slopes. [18- 4.12.15C]
(Rev. 1) Comment has been addressed.
3. Some of the grading in the travelways adjacent to the parking lots exceeds 10% slopes.
[18- 4.12.17A]
(Rev. 1) Comment has been addressed.
4. Please adjust the loading space to meet 12'X25' requirement on the northwest part of the site.
(Rev. 1) Comment has been addressed.
5. All travelways without parking must be 20' wide measured from curb faces.
(Rev. 1) Comment has been addressed.
6. Sidewalks abutting parking must be 6' wide, or bumper blocks are provided.
(Rev. 1) Comment has been addressed.
7. Please provide guardrails with VDOT designations shown for retaining walls next to parking or
travelways. [18- 32.7.2]
(Rev. 1) Comment has been addressed.
8. Safety railings must be shown for retaining walls over 4' high.
(Rev. 1) Comment has been addressed.
9. Please provide a retaining wall detail.
(Rev. 1) Comment has been addressed.
B. Stormwater Management Plan
10. Please proviae routing models for the stormwater detention facilities.
(Rev. 1) Comment has been addressed.
11. Please provide impervious area and removal rate calculations.
(Rev. 1) Comment has been addressed. However, the areas on the newly submitted simple method
spreadsheet do not match the areas on the plans.
Albemarle County Community Development
Engineering Review Comments
Page 2 of 3
(Rev. 2) Please update the spreadsheet so the pre and post development acreage equals the
drainage area of the detention facility. The percent impervious for pre and post should also be
updated accordingly.
12. Please provide Albemarle County general stormwater notes.
(Rev. 1) Comment has been addressed.
13. A completed copy of the Standard Stormwater Management Maintenance Agreement and fee for
recordation for the stormwater facilities on TMP 45 -100 required prior to final approval.
[17 -304E] The forms and instructions can be found on the Community Development Department
website on www.albemarle.org.
(Rev. 1) Comment has been noted.
(Rev. 2) Comment has been addressed.
14. Please provide adequate channel analysis (MS -19) for the proposed outfall.
(Rev. 1) Comment has not been addressed.
(Rev. 2) The adequate channel analysis has been reviewed. The following modifications are
required before approval can be given:
a. Adequate channel analyses must be evaluated using the 24 hour storm (SCS). This
would mean that the 24 -hour storm must be routed through the detention facility.
b. Each segment of the channel cross - section must have a specific n- value, permissible
velocity, and calculated velocity. For instance, in cross section A, the side slopes is
vegetated and not lined with coarse gravel. For other sections of the stream, the side
slopes are exposed earth.
c. Current Erosion and Sediment Control law requires that the adequate channel analysis
be performed to the point where the developed area is equal 1% of the watershed of the
channel. However, for county approval, the analysis only needs to be performed to
within 100ft of the structure at the VDOT ROW. There are several channel cross -
sections through this section of the stream that appear to be exhibiting erosion and
these sections should be analyzed.
d. Because of the severe angle of the release from the detention facility, riprap into the
stream channel to the opposite bank will be necessary to protect the stream from scour.
Approval from the Army Corps of Engineers will be needed for this work.
Revisions to the adequate channel calculations (a, b, and c) will not be needed if the applicant
provides one of the following:
- Provide extra storage and a smaller orifice size in the detention facility to reduce the 2 and
IO year discharges to I cfs and 2 cfs.
- Obtain the necessary offsite easements and provide additional riprap on all sideslopes that
are currently exposed soil. Some sides would need to be modified so that the slope is not
steeper than the maximum grade allowed for riprap (1 -112 : 1). Work within the existing
stream will need to be approved by the Army Corps of Engineers.
15. Please provide calculations for the existing 24" culvert at the north side of the site.
(Rev. 1) Comment has been addressed.
16. Please provide a Detention Compliance Table.
(Rev. 1) Comment has been addressed.
17. Post - Development drainage areas do not match inlet drainage areas.
(Rev. 1) Comment has been addressed.
18. Please provide a blow up plan view of the riser including invert shaping, if applicable.
(Rev. 1) Comment has been addressed.
C. Erosion and Sediment Control Plan
Albemarle County Community Development
Engineering Review Comments
Page 3 of 3
19. Please extend the diversion dike on the northwest side of the property up to contour 526.
(Rev. I) Comment has been addressed.
20. Please provide a stockpile location.
(Rev. I) Comment has been addressed.
21. Please provide staging or parking area.
(Rev. I) Comment has been addressed.
22. Please show the outlet protection for the Sediment Trap on sheet E -3.
(Rev. I) Comment has been addressed.
Once these comments have been addressed, please submit two (2) copies of the revised plans, calculations,
and narratives to Current Development Engineering.
Current Development Engineering is available from 2:30pm — 4:OOpm on Thursdays to discuss these
review comments. Please contact Amy Pflaum at 434 - 296 -5832 or apflaum @albemarle.org to schedule an
appointment.
CDE3_fsp_esc_smw_JPD_Van Dine Plaza_PHIL.doc