HomeMy WebLinkAboutWPO201900062 Correspondence 2020-09-10f•�eas
608 Preston Avenue
P 434.295.5624
Suite Zoo IF434.295.1800
T I M M O N S GROUP
Charlottesville, VA 22903 www.timmons.com
September 10, 2020
Matt Wentland
Albemarle County Community Dev.
401 McIntire Rd, Rm. 227
Charlottesville, VA 22902
RE: Southwood Redevelopment — Village 1- VSMP Permit Plan Review— WP0201900062 —
Rev. 2 Comment Response Letter
Dear Mr. Wentland:
We have reviewed all of your comments from Rev. 2 dated July 1, 2020 and made the
necessary revisions. Please find our responses to the comments below in bold lettering.
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. Provide a signed Registration Form.
A signed Registration Form has been included in the SWPPP.
Rev. 1 Comment addressed.
2. Provide a signed Certification.
A signed Certification has been included in the SWPPP.
Rev. 1 Comment addressed.
3. Include the information on impaired waters in Section 7.
The TMDL Report for Moores Creek has been included in the SWPPP.
Rev. 1 Comment addressed.
Revision 1 comments:
4. The proposed area of disturbance is listed differently throughout the SWPPP and plans
(12.88 ac. On the Registration Statement, 15.58 ac. In the Nature of Activity, 15.04 ac. In
the VRRM not including forest and open space). Please revise to have the same acreage.
The proposed area of disturbance has been revised on the plans and throughout the SWPPP.
Rev. 2 Comment addressed.
ENGINEERING I DESIGN I TECHNOLOGY
B. Pollution Prevention Plan (PPP)
The PPP content requirements can be found in County Code Section 17-404.
1. The PPP is acceptable at this time.
Acknowledged.
C. 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. A FDP permit application and a Flood Study will need to be submitted and approved
[18.30.3.12, 18.30.3.131.
Acknowledged. A flood plain permit will be submitted/approved prior to the VSMP and final
plat approval.
Rev. 1 Comment not addressed.
A draft of a Flood Study has been attached. However, this outfall has been recently revised. A
final Flood Study for the proposed outfall shall be submitted prior to plan approval.
Rev. 2 Comment not addressed, response noted.
The Flood Study was submitted on July 23.
2. This plan cannot be approved until the 1.84 Ib/yr of nutrient credits have been
purchased. Please contact Ana Kilmer prior to purchasing credits.
Acknowledged. We have reached out to Ana Kilmer in regard to purchasing nutrient credits.
Note that with the revised routing, 1.38 Ib/yr of nutrient credits is required.
Rev. 1 Comment not addressed.
We have reached out to Ana Kilmer in regard to purchasing nutrient credits.
Rev. 2 Comment not addressed, response noted.
An affadavit has been sent to Ana Kilmer for the nutrient credits to be purchased.
3. Please contact Ana Kilmer to complete a Stormwater Management Facilities
Maintenance agreement.
We have reached out to Ana Kilmer to complete a Stormwater Management Facilities
Maintenance agreement.
Rev. 1 Comment addressed, the agreement will need to be recorded prior to approval.
We have reached out to Ana Kilmer to complete a Stormwater Management Facilities
Maintenance Agreement.
Rev. 2 Response noted.
We have sent Ana Kilmer an Attorney Letter in order to submit a Stormwater Management
Facilities Maintenance Agreement.
4. The Forest and Open Space Easement, SWM Facility easements and Mitigation
easement will need to be shown on the Final Plat and a Deed of Dedication will need to
be signed and recorded for this easement. The Deed will be filled out by the County and
forwarded to the applicant when the plat is nearing approval.
Acknowledged.
Rev. 1 Response noted.
5. Show and label all proposed easements on the plans, including facility and access
easements.
All easements have been shown and labeled on the Grading and Drainage Plan on sheets
C4.05-C4.08.
Rev. 1 Comment partially addressed. Revise the easement linetype so it shows up
clearer. Show easements on the entrance culvert, structure 600 on the entrance road,
and on the structures/pipes in the parking lots of the proposed apartment buildings
(others may not be listed).
Easements have been added at structure 600 and through parking lots at condo buildings.
Rev. 2 Comment addressed.
6. Clearly shown and label how the bioretention will be accessed for maintenance.
An access easement has been added in the vicinity of pipe 201.
Rev. 1 Comment partially addressed. The maximum slope for a grassed access is 20%,
please revise. [Design Standards Manual].
Grading has been revised to 20% maximum for 10' wide access path.
Rev. 2 Comment not addressed, scaling the contours shows a 25% slope.
Grading has been revised to 20% maximum slope.
7. Include the bioretention maintenance and inspection schedules from DEQ BMP Spec. 9
on the plans.
DEQ BMP Spec. 9 maintenance and inspection schedules have been added to the Stormwater
Summary on sheet C6.01.
Rev. 1 Comment addressed.
8. Include the planting plans for the bioretention.
A planting plan has been added for the bioretention. See sheet L1.01 and L1.02.
Rev. 1 Comment partially addressed. Only one biofilter shows any plantings on the
landscape plan. Provide separate details/tables for the biofilter plantings following the
requirements in DEQ BMP Spec. 9 sections 6.8 and 6.9.
Plantings for both biofilters have been shown on sheets L1.01 and L1.02.
Rev. 2 Comment not addressed, separate biofilter requirements and proposed landscaping
were not found on the landscape sheets. Biofilter 1 does not show up fully on the sheets.
Biofilter landscape has been shown on sheet U.N.
9. Provide the routing calculations for the bioretention.
Bioretention routing calculations have been included in the calculation book.
Rev. 1 Comment addressed.
10. Show and label the pre-treatment requirements for the level 2 bioretention on the
plans.
Gabion basket forebay wall details have been added to sheet C6.00.
Rev. 1 Comment partially addressed. Show and label both of the two required pre -
treatments for each Level 2 biofilter. Include the size of the pre-treatment cells. [DEQ
BMP Spec. 9, Table 9.3 and Section 6.4]
Per Table 9.4, pre-treatment cell and gravel diaphragm have been provided at each
bioretention basin. Riprap-lined pre-treatment cell has been added to detail for additional
clarity.
Rev. 2 Comment partially addressed, I did not see the size of the cells on the plans.
The size of the pre-treatment cells has been added to C6.01 Bioretention Facility Details.
11. 'rovide more detail on the path through bioretention 2.
Bioretention 2 has been relocated and revised.
Rev. 1 Comment addressed.
12. Include the County As -built requirements on the plans.
The As -built Road Plan policy has been added to the Notes and Details on Sheet C3.00.
Rev. 1 Comment not addressed. Include the VSMP As -built requirements.
The VSMP As -Built requirements have been added to sheet C1.00.
Rev. 2 Comment addressed.
13. On Sheet C6.0, include a breakdown of the proposed and conceptual impervious areas
in each biofilter drainage area.
The proposed and conceptual impervious areas have been labeled for each drainage area on
sheet C6.00.
Rev. 1 Comment addressed.
14. Show more detail for the outfall into the stream. Include the stream banks, as it will
need to outfall directly in the stream to not use energy balance. Include a drainage area
map for the stream to show the 1% is being met.
Outfall location has been revised. 1% drainage area map has been added to plans on sheet
C6.02.
Rev. 1 The provided DA map appears to be incorrect. Areas are included that enter the
stream below the proposed outfall and areas that drain to the other side of the
Interstate. I've attached a printout from County GIS showing the drainage area at the
pipe outfall.
Stormwater management approach has been revised to include an oversized storage pipe to
meet energy balance requirements. See sheet C6.00 for additional information.
Rev. 2 See comments below.
Acknowledged.
15. Contact the Army Corp and provide correspondence allowing the outfall into the
stream.
We have reached out to the Army Corp pertaining to the outfall into the stream.
Rev. 1 Comment not addressed, response noted.
We are in communication with the Army Corp on the revised outfall and will provide
correspondence in future submittals.
Rev. 2 Comment not addressed, response noted.
We have emailed with Vinny Pero at the Army Corps of Engineers. He has stated that this
project qualifies for a non -reporting Nationwide Permit No. 18.
Revision 2 comments:
16. The 1-yr flows on the table on sheet C6.00 do not add up to what is shown for the total
(it looks like the 0.32 should be 0.23).
Calculations on sheet C6.00 have been verified to match HydroCAD calculations. Due to
routing formulas, combined flows occasionally differ from simple addition. Refer to
calculation book for additional details.
17. Provide the 10-yr routing for the storage pipe and for the whole system.
The 10-yr routing has been provided in the Design Calculations and Narrative.
18. Provide more detail on the storage pipe, such as a detail of the weir wall. Ensure
maintenance access to both sides of the weir wall, at the weir wall.
A storage pipe weir wall detail has been added to sheet C6.01.
19. The storage pipe easement may need to be greater than 20' Use the calculation from
the Design Standards Manual to determine the easement width (Width = Pipe Diameter
+ 2' (Depth to bottom of pipe — 5') + 10'). The easement over the pipe should also be
labelled as a Stormwater Facility Easement, as it's addressing the DEQ quantity
requirement.
The storage pipe easement has been revised to be 32.5' and 42.5' wide dependent on depth.
The easement has been called out as a Stormwater Facility Easement. See sheet C4.09.
20. After considering the larger than usual drainage area to Bioretention #1, provide a flow
splitter prior to the outlet to allow only the Treatment Volume to enter the facility (and
any additional amount in order to meet Energy Balance). [DEQ BM Spec. 9, Section
6.5].
The BMP clearinghouse includes a recommendation for a 2.5 acre maximum drainage area
and allows up to 5 acres. Bioretention Facility #1 currently captures 4.39 acres of runoff,
although only 2.55 acres of that is impervious land cover. Bioretention Facility #2 captures
1.69 acres of runoff. The facilities are currently designed to capture the amount of runoff
necessary to meet the energy balance equation. Any reduction in runoff sent to the facilities
would result in a site outflow that would not meet the energy balance equation. Bioretention
Facility #1 has maximized the area available and providing two bioretention facilities in this
area is not feasible due to site constraints and the proximity of the floodplain. Please also
note, stone rip -rap and a forebay with gabion basket weir structure have been provided to
mitigate the larger flow.
21. Provide more separation between Pipe 201 and Pipe 105/Structure 104. 10' is
preferred.
10' separation has been provided between Pipe 201 and Pipe 105/Structure 104. See Sheet
C4.10.
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 approved, and the reasons are provided in the comments below. The erosion
control plan content requirements can be found in County Code Section 17-402.
Acknowledged.
Revision 1 Comments:
2. Provide a sediment trap for the grading on the northeast side of the entrance. The final
grading should also be revised to direct the runoff to the culvert instead of having
channelized runoff flowing into the road.
Sediment Trap #3 has been added. Ditch has been added in the proposed condition to
direct runoff to culvert. Note that storm pipes along Road 1 have been sized for future
development by others on this parcel with approximately 80% impervious surface.
(Rev. 2) Comment addressed.
Revision 2 Comments:
3. It appears the outlet pipe for Sediment Basin 1 is shown going under Old Lynchburg
Road. Please revise to stay out of the public road and show the existing road more
clearly on the plans.
Sediment Basin 1 outlet pipe has been revised. Old Lynchburg Road has been labeled close to
the Sediment Basin 1 outlet pipe in order to clarify the location of the existing road.
We have included PDF copies of the plans and calculations for your review. If you have any
questions or comments, please feel free to email me at clint.shifflettPtimmons.com .
Sincerely,
Clint Shifflett, PE
Project Manager