HomeMy WebLinkAboutSDP202200061 Correspondence 2023-04-05 (2)Dewberry
Dewberry Engineers Inc. 804.290.7957
4805 Lake Brook Drive, Suite 200 804.290.7928 fax
Glen Allen, VA 23060-9278 I www.dewberry.com
April 4, 2023
County of Albemarle Community Development Department
Attn: David James, Engineering
401 McIntire Road, North Wing
Charlottesville, VA 22902-4579
RE: WPO202100071 ACSA Avon Maintenance Yard
Dear Mr. James,
Please see comment responses below.
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. Please subs the SWPPP review. (Rev.1) Addressed
2. Note: Engineering will append approved plan to SWPPP once approved.
B. Pollution Prevention Plan (PPP)
The PPP content requirements can be found in County Code section 17-404.
1. Please submit PPP exhibit sheet for review. (Rev.1) Addressed.
2. Provide concrete washout detail. (Rev.1) Addressed.
3. Fuel/Chemical areas will need to be covered under a separate permit if discharging
to drainageways that will leave site. Provide locations of any stormwater treatment
and/or separator system to be used. (Rev.1) Not addressed. I didn't find the note.
Dewberry: Note added to Pollution Prevention Plan sheet.
4. (Rev.1) Show paving operations, landscaping operations, CE locations,
staging, stockpile, borrow, fueling, waste disposal, vehicle/equipment washing,
concrete washout locations on the PPP. Also, show locations where
concentrated stormwater discharges.
Dewberry: Addressed.
C. Stormwater Management Plan (SWMP)
VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a
SWMP. This plan is denied, 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. Ditches/Channels —
a. Provide callout/label for each.
b. Show grading and centerline.
c. Show stationing at 50' intervals.
d. Provide cross-section details and determine 2-yr velocity and lining
requirements.
e. Provide ditch design worksheet. See VDOT drainage manual for guidance.
f. Provide profiles in cases where the channel slope varies or connects to a
drainage structure.
(Rev.1) Comments have been addressed for the ditches shown. Please
provide for this additional one.
Dewberry: Ditch 7 profile and cross section provided on sheet C4.17.
2. C3.03-4.12:
a. Show the HGL in the profiles. (Rev.1) Addressed.
Page 1 of 5
Mr. David James
ACSA Avon Maintenance Yard
WP0202100071
April 4, 2023
b. Revise: The minimum pipe size diameter is 8" for STM 13-14-12, STM 19-20.
(Rev.1) Addressed.
c. (Rev.1) Show the profiles & design for structures STM 22-25 (to existing
DI). Initial pipe run can be 12" (min) but the rest will need to be 15"
diameter.
Dewberry: Addressed. Profile provided on sheet C4.11. Calculations
provided on C4.12.
d. (Rev.1) Provide SL-1 for MH structures higher than 12 ft.
Dewberry: Note added to storm profiles on sheets C4.10 and C4.11 to
indicate SL-1 required on manhole structures higher than 12 ft.
e. (Rev.1) Show labels & type of VDOT inlets.
Dewberry: VDOT inlet types labeled on storm profiles on sheets C4.10 and
C4.11.
f. (Rev.1) Provide LD-204 inlet design.
Dewberry: Provided in stormwater comp book appendix E.
3. C6.01 - Your SWM narrative mentions three outfalls. Your Water Quantity only shows
energy balance for A02. What about the other outfalls how do they meet Quantity?
(Rev.1) Acknowledged.
4. C6.06 - Show Tc path for A03; seems low. (Rev.1) Acknowledged.
5. Provide the inlet design for STM 18. Provide half -clogged design per VDOT drainage
manual. Ensure existing drainage system along Founders Place is designed
adequately to handle the additional flow. (Rev.1) Not addressed.
Dewberry: Inlet computations have been added to Stormwater comp book appendix
E. The profile has been added to C4.10 and drainage calculations have been added
to C4.12.
6. Provide half -clogged design for STM 6 & STM 16 per VDOT DM. (Rev.1) Not
addressed.
Dewberry: Half clogged design has been added to the inlet computations in the
stormwater comp book appendix E.
7. Provide letter of availability from offsite nutrient credit provider on the plans. (Rev.1)
Addressed.
8. Include this checklist in the plan set.
http://www. albemarle. org/upload/im ages/forms_center/departments/Community_De
velopment/forms/Engineering_and_W PO_Forms/W PO_VS M P_Construction_Record
_D rawings_Policy_23May2014.pdf. (Rev.1) Addressed.
9. Show the SWM facility and access easement(s). Easements should be recorded with
plat prior to grading permit issuance. (Rev.1) Acknowledged.
10. (Rev.1) C6.01/6.07/SWM report: Energy balance for A01 & A03. Thanks for
providing a summary. Where do you obtain those values shown to solve the
equation so I can verify?
Dewberry: In Appendix C you can find the HydroCAD reports. These HydroCAD
reports contain the drainage areas broken down into land uses and Tc calculations.
On the allowable discharge summary sheet, you can find the weighted CN, area, and
rainfall in step 1 and the Rv values and the flows for existing and forested conditions
in step 2.
Dewberry Page 2 of 5
Mr. David James
ACSA Avon Maintenance Yard
WP0202100071
April 4, 2023
11. (Rev.1) C6.07: Provide detail of SWM2 - mentions a weir wall see sheet C5.06
(Not found).
Dewberry: Note corrected; see detail on sheet C5.02.
12. (Rev.1) Callout the weir wall on the plans to a detail sheet. Show the location of
weir in the ditch profile.
Dewberry: Weir wall added to ditch profile.
13. (Rev.1) Provide WSE for design storm if the weir wall orifice is half -clogged.
Dewberry: Design storms for half -clogged orifices have been added to C5.02, and
C6.09. Calculations have been added to the Stormwater Comp. book appendix B.1.
14. (Rev.1) C6.09: The county would prefer 3" min. orifice size due to
clogging/increased maintenance. Provide half -clogged design for less than 3".
Dewberry: Design storms for half -clogged orifices have been added to C5.02, and
C6.09. Calculations have been added to the Stormwater Comp. book appendix B.1.
A Trash rack is called out for the orifice on sheet C6.09.
15. (Rev.1) SWM report:
a. Show the pre- & post- land cover and drainage area maps (to go along
with the routing).
Dewberry: Sheets added to Stormwater Comp. Book
b. Provide summary routing report for the design storms.
Dewberry: All design storms have been added to Appendix B of the
stormwater comp. book
16. (Rev.1) Update SWM report and have PE stamp seal them.
Dewberry: Acknowledged.
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, 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. Sheets C5.01. 5.03-5.06 can be removed from the WPO plan set. (Rev.1)
Addressed.
2. Cover: Please add the WPO# under title. (Rev.1) Addressed.
3. C1.01-.03: Show all existing utilities and easements with deed book references.
(Rev.1) Addressed.
4. Please correct grading here to be 2:1 or less. (Rev.1) Revise slope to be 2:1 or
less.
Dewberry: Grading revised to be 2:1.
5. C2.04: Provide TS, B/M on back of sed. basin slope. Where grade is 3:1 and over,
use B/M. [VADEQ ESC HB, Spec. 3.31, 3.35, 3.36] (Rev.1) Addressed.
6. C2.04/2.04: Show location of sediment trapping device at CEs. (Rev.1) Addressed.
7. C2.05/2.06:
a. Provide CRS for the access roads. [VADEQ ESC HB, Spec. 3.03] (Rev.1)
Addressed.
b. Provide MU/PS on slopes. Where slopes are 3:1 and greater use B/M.
[VADEQ ESC HB, Spec. 3.31, 3.35, 3.36] (Rev.1) Addressed.
c. Provide mix or type of low -maintenance ground cover (not grass) to be used
on slopes 3:1 and greater. (Rev.1) Addressed.
19 Dewberry® Page 3 of 5
Mr. David James
ACSA Avon Maintenance Yard
WP0202100071
April 4, 2023
d. (Rev.1) C2.06 —Show proposed grading. Layer turned off?
Dewberry: Acknowledged. Layer fixed.
8. C2.06: Provide callout to a detail of type of IP to be provided here. [VADEQ ESC HB,
Spec. 3.07] (Rev.1) Not addressed.
Dewberry: Callout added.
9. C6.09:
a. Show anti -seep collar placement along barrel. (Rev.1) Addressed.
b. Show the 4' min. depth cut-off trench placement under embankment. (Rev.1)
Show cut-off trench in profile.
Dewberry: Cut off trench added to the profiles on sheet C6.09.
10. Revise: STM 3 exceeds 1-acre minimum drainage area. [VADEQ ESC HB, Spec.
3.07] (Rev.1) Not currently addressed. Suggest adding SF, SF/CD to filter out
sediment prior to IP.
Dewberry: Check dams are present in the ditch. Additional silt fence added.
11. Need to show the length of OP along with the OP calcs to determine minimum length
and also show the graded receiving channel from OP. (Rev.1) Addressed.
12. Show graded receiving channel from barrel. What is the velocity out of barrel? 90
degrees is the minimum skew angle to receiving channel consider adjusting angle or
depending on velocity provide solution to prevent scour. (Rev.1) Addressed.
13. Revise: Concentrated discharge must be contained and not cut down slope, i.e., STM
21. [MS-8] (Rev.1) Addressed.
14. Constructed channels/ditches on slopes. Unless these channels are properly
designed it might be best to consider Temp. Slope Drains (TSD). [VADEQ ESC HB,
Spec. 3.151 (Rev.1) Acknowledged; Show the proper grading for the concrete
channel.
Dewberry: A manhole (STM 26) has been added to the stormsewer system, and STM
26 outfalls at the embankment and the flow path to the forebay is protected with
riprap.
15. Provide conversion details for the sed. basin to permanent facility.
a. Notify/Coordinate with ESC inspector on the start of embankment
construction. A geotech engineer should be present during and after
construction to monitor, report and verify stability and compaction of dam.
(Rev.1) Addresses'
16. (Rev.1) C6.08/9: Revise design: The basin should have endwall at barrel end
called out and the `toe of dam' appears to be at 518' in profile.
Dewberry: Design revised to an endwall.
17. (Rev.1) C6.09: STM 8 pipe should not outfall on 2:1 slop. Scout at channel bend
is a concern. Consider outletting pipe at bench or forebay, eliminating channel
bend, adding scour protection, adding energy dissipator.
Dewberry: A manhole (STM 26) has been added to the stormsewer system, and STM
26 outfalls at the embankment and the flow path to the forebay is protected with
riprap.
18. (Rev.1) Tie-in grade
Dewberry: Proposed grading has been updated and fixed to tie properly.
19. (Rev.1) Note: VDOT entrance permit required prior to start of construction.
Dewberry® Page 4 of 5
Mr. David James
ACSA Avon Maintenance Yard
WPO202100071
April 4, 2023
Dewberry: Acknowledged.
Sincerely,
f 4 P
Kevin Pennock
Senior Associate, Senior Project Manager
10 Dewberry Page 5 of 5