HomeMy WebLinkAboutWPO200800053 Review Comments Stormwater Management Plan 2008-10-10ALg�,��
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COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project:
WPO- 2008 - 00053, Vault ESC Plan
SDP - 2008 - 00080, Minor Amendment
Plan preparer:
Delta Airport Consultants, Inc. fax 804.275.8371
Owner or rep.:
Barbara Hutchinson, Executive Director fax 434.974.7476
Date received:
16 May 2008
(Rev. 2) 3 September 2008
Date of Comment:
27 June 2008
(Rev. 2) 10 October 2008
Engineer:
Phil Custer
(Rev. 1) Andy Lowe
(Rev. 2) Phil Custer
The ESC, SWM, and the minor amendment for the electrical upgrade work at the Charlottesville Airport,
received on 3 September 2008, have been reviewed. This letter comments on the third submittal made to
the County. The second submittal was reviewed under an alternative review procedure with just a
checklist. All comments that were addressed with the second submittal are stated as so. To maintain the
same layout in the applicant's response letter, many of the comments appear twice in the list below. The
plans can be approved after the remaining comments have been addressed.
When the plan is resubmitted, please include a new, complete calculations packet.
A. General Review Comments
1. Please accurately show all stream buffers.
Comment was addressed with the second submittal.
2. A SWM plan will be required for the electrical vault area.
(Rev. 2) A plan has been submitted. Please see the comments below.
3. Please show the treeline on the plan. [DM]
Comment was addressed with the second submittal.
4. It is unclear what the gravel drive to the vault is coming off from. Nothing is labeled on the
plan.
Comment was addre- -' = second submittal.
B. WPO- 2008 -00053 ESC Plan Review Comments:
1. Please show on an ovcivicw piau ut Luc airport where all earth disturbing activity, including
utility line replacement, will be taking place with appropriate limits of disturbance. Please
specify which work will be done in pavement and in soil. ESC measures may be required for
some of the other work on this plan than just the electrical vault. [VESCH]
Comment was addressed with the second submittal.
2. The limits of disturbance line for the electrical vault construction does not appear to close.
Does work continue towards the runway area? If so, please make sure the limits of
disturbance reflect this.
Comment was addressed with the second submittal.
3. Considering ESC comments 1 and 2, it appears an addition to the WPO fee will be necessary.
Comment was addressed with the second submittal.
4. It is understood from previous conversations with the applicant that wet storage in the
sediment trap violates airport regulations. Please provide a letter requesting a variance from
this state standard and how erosion control standards are met or exceeded with a proposed
alternative.
(Rev. 2) Please clearly show the depth of the stone in the sediment trap. It appears the
underdrain pipe is placed in the in -situ soil.
5. Please state on the plan all applicable VESCH minimum standards.
(Rev. 2) Comment not addressed. The applicable minimum standards from Chapter 8 of the
VESCH need to be listed on the sheet set.
6. It appears that the plan needs the standard symbols for permanent seeding, temporary seeding,
construction entrance, and a diversion dike.
(Rev. 2) Comment has been addressed.
7. Please provide dust control on the plan.
(Rev. 2) Comment has been addressed.
8. Please show the grading for the sediment trap on sheet 22.
(Rev. 2) Grading was shown but the review of the sediment trap was difficult because the
contour lines are unclear. In plan view, it is hard to determine what the bottom, wet, weir,
and embankment elevations are supposed to be and how it matches the calculations. Please
clarify. It does not appear that the embankment grading is shown correctly.
9. The diversion dike appears to travel uphill on the plan.
(Rev. 2) Comment has been addressed.
10. Engineering review is concerned with a lack of an adequate channel. Please address.
(Rev. 2) Comment not addressed. The calculations appear to analyze the newly constructed
channel at the outlet of the 8" culvert. The adequate channel that must be proven is at the
outfall of the biofilter.
11. Please provide on the plan the standard county notes for General Construction and General
Notes for Erosion and Sediment Control found in the latest version of the county design
manual available online.
Comment was addressed with the second submittal.
12. Please show outlet protection on both culverts.
(Rev. 2) Comment has not been addressed. Outlet protection is required for all culverts.
13. A bond will be computed once all comments are addressed.
(Rev. 2) The ESC portion of the WPO bond will be computed once the plan is approved.
C. SDP - 2008 -00080 Minor Amendment Plan Review Comments:
1. The minor amendment should not be approved until the SWM plan is.
(Rev. 2) Comment remains unchanged.
D. WPO- 2008 -00053 Plan Review Comments from the checklist review:
1. Provide an existing drainage area map showing existing conditions for on -site and off -site
areas draining to proposed stormwater facilities.
(Rev. 2) Comment has been addressed.
2. Proivde a proposed drainage area map showing proposed conditions for the site and any off -
site areas draining to proposed stormwater facilities.
(Rev. 2) Comment has been addressed.
3. Provide Plan view and details for all stormwater facilities and site layout as shown on the site
plan sheets, preferably at a scale of 1 " =30' or F =20'.
(Rev. 2) The contours of the biofilter are difficult to make out. It is unclear what the
elevations of the top of embankment, weir, and biofilter bed are in this drawing. It appears
that the grading needed to construct the fill for the embankment is also not shown.
4. Provide cross - section details for each facility embankment.
(Rev. 2) Please see comment 11 and 20.
5. Provide cross - section details for each facility principle spillway.
(Rev. 2) Comment has been addressed.
6. Provide cross - section details for each biofilter with minimum floor dimensions lableled.
(Rev. 2) The cross - section has been provided. Please see comments 11 and 20.
7. Provide vehicle access roads to all stormwater facilities.
(Rev. 2) Comment has been addressed.
8. Minimum pipe sizes into and out of the facility require 15" diameter for maintenance.
(Rev. 2) Comment has been withdrawn. These culverts are private lines and will not be
maintained by the public.
9. Provide water quality removal rate computation summary for each facility in the county
worksheet format.
(Rev. 2) The computation summary table appears to be incorrect. Engineering review
agrees that the biofilter facility should be sized to achieve a 50% removal rate. However,
the water quality volumes (both required and provided) appear to be incorrect. Given the
impervious area you provided ( %5 of 2.67 acres), the required WQv is 242cf (9cy). The
biofilter as designed will likely have a provided WQv of 42cy (not 134) if the maximum
ponding depth of Ift was used. Please correct the computation table.
10. Provide detention computation summary for each facility in the county worksheet format.
(Rev. 2) Detention will not be required in the biofilter if an adequate channel is proved by
the calculations.
11. A SWM plan is required in addition to the Stormwater Management Plan submitted.
(Rev. 2) It is difficult to review the geometry of the biofilter because none of the contours
are labeled. The plan also appears to have intermediate contours leftover from the erosion
and sediment control plan. Additionally, it appears the "temporary slope drain" is designed
to be a permanent feature with this plan. The use of the temporary slope drain as the
permanent outfall from the biofilter is not acceptable. Please provide a riser or a spillway
and channel down the slope.
12. Please state on the plan all applicable VESCH minimum standards.
(Rev. 2) Comment not addressed. The applicable minimum standards from Chapter 8 of the
VESCH need to be listed on the sheet set.
13. The plan needs additional standard symbols for permanent seeding, temporary seeding,
construction entrance, and a diversion dike in addition to the specifications submitted.
(Rev. 2) Comment has been addressed.
14. Specify DC for dust control on the plan.
(Rev. 2) Comment has been addressed.
15. A diversion dike appears to travel uphill on the plan.
(Rev. 2) Comment has been addressed.
16. Engineering review is concerned with a lack of adequate channel. Please address and include
cross - sections.
(Rev. 2) Comment not addressed. The calculations appear to analyze just the newly
constructed channel at the outlet of the 8" culvert. The adequate channel that must be
proven is at the outfall of the biofilter.
17. Please show outlet protection on both culverts.
(Rev. 2) Comment has not been addressed. Outlet protection will be required because the
channels will not be established with grass at the time of construction. The permissible
velocity for exposed earth is much lower than that of Bermuda grass.
18. (Sheet 6 of 30) Provide all applicable VESCH minimum standards.
(Rev. 2) Comment not addressed. The applicable minimum standards from Chapter 8 of the
VESCH need to be listed on the sheet set.
19. (Sheet 6 of 30) Provide a biofilter planting design.
(Rev. 2) Comment has been addressed.
20. (Sheet 7 of 30) Provide a detail of the proposed biofilter.
(Rev. 2) The details on sheet 7A are not yet approvable. Please correct the following:
a. The soil mix must be at least 2.5ft. [DM/
b. The elevations of the bed mix, bottom of weir, and embankment must be clear. It
appears the outlet of the sediment trap would need to be retrofitted. The use of
sediment trap weirs in the permanent condition does not work because the water
escapes through the stone before it gets the opportunity to drain through the soil
MIX.
c. The weir should be at an elevation of 6" or ]'above the bed elevation.
d. From reading the contours in plan view, it appears the top of the embankment is
615 rather than 617.
21. (Sheet 7 of 30) Add detail plate 3.13 -1 to the Erosion and Sediment Control Details.
(Rev. 2) Comment has been addressed.
22. (Sheet 7 of 30) Provide a biofilter planting detail.
(Rev. 2) Comment has been addressed.
23. (Sheet 22 of 30) Provide a stormwater management plan similar to Vault Site Grading Plan.
(Rev. 2) See comment 11.
24. (Sheet 22 of 30) Provide standard symbols for seeding and dust control.
(Rev. 2) Comment has been addressed.
25. (Sheet 22 of 30) Provide a construction entrance at the existing perimeter access road.
(Rev. 2) Comment not addressed. The applicant has implied that a construction entrance is
not required for the site because vehicles leaving the site must travel on the existing internal
roads before entering onto a public street. This would be allowable if these roads drained
to an existing sediment basin or trap. However, all sediment deposited on these internal
roads will drain to SWM facilities and county waterways without ESC measures.
26. (Sheet 22 of 30) Provide Water Protection Ordinance buffers along the length of each
protected watercourse.
(Rev. 2) Comment has been addressed.
27. (Rev. 2) The applicant has removed the county's standard SWM and ESC notes from the
set. These need to be included before the plan can be approved.
28. (Rev. 2) The applicant must submit a Stormwater Management Facility Agreement and fee.
Please submit this document with fee directly to Pam Shifflett after consulting the
guidelines available on the county website.
29. (Rev. 2) The SWM portion of the WPO bond will be computed once the plan is approved.
Please contact me at (434)296 -5832 ext. 3072 should you have any questions.
File: E3_esc_swm _ mia_PBC_08- 00053_08 -00080 Airport Electrical vault.doc