HomeMy WebLinkAboutWPO201900052 Correspondence 2020-02-18TIMMONS GROUP
YOUR VISION ACHIEVED THROUGH OURS.
February 07, 2020
David James
County of Albemarle
Dept. of Community Development
401 McIntire Road, North Wing
Charlottesville, VA 22902-4596
RE: WP0201900052 Berkmar Drive Apartments
Mr. James:
1001 Boulders Parkway
Suite 300
Richmond, VA 23225
P 804.200.6500
F 804.560.1016
www.timmons.com
On behalf of our client, Berkmar Apartments, LLC, we are pleased to resubmit for Albemarle County's review
the WPO plan for Berkmar Drive Apartments, revised per comments provided by county Staff. Please find
attached to this letter 2 full size sets (24"06") of the revised plans and a copy of the calculation binder.
Below is the latest edition of the County's review comments, followed by the response in bold italics:
A. Stormwater Pollution Prevention Plan (SWPPP)
1. Submit the SWPPP.
Response: Two revised copies of the SWPPP have been included in this plan submission.
2. Provide PPP site exhibit sheet.
Response: The PPP site exhibit has been added to the plan set and the SWPPP binders.
4. Please complete the VSMP application form with every submission.
Response: A VSMP application has been included in this submission.
5. Please have the operator/permittee sign page 4 of the Registration Statement
Response: Signed copies of the Registration Statement have been included in the SWPPP.
6. Please provide reduced size copies (l lxl7) of the E&SC and SWM plans for the SWPPP
Response: Reduced size copies of the ESC and SWMplans have been included in the SWPPP
binders
7. Complete Section 8: Qualified Personal, Section 9: Signed Certification, Section 10: Delegation
of Authority.
Response: All applicable sections have been completed in the SWPPP.
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YOUR VISION ACHIEVED THROUGH OURS.
B. Pollution Prevention Plan (PPP)
1001 Boulders Parkway
Suite 300
Richmond, VA 23225
P 804.200.6500
F 804.560.1016
www.timmons.com
1. Show any proposed clearing/grading activities, paving operations, landscaping operations, E&S
controls, staging, stockpile, borrow, fueling, waste disposal, vehicle/equipment washing,
concrete washout locations on the PPP. Also, show locations where concentrated stormwater
discharges.
Response: PPP has been added to the plans as sheets C3.5 and C3.6.
C. Stormwater Management Plan (SWMP)
6. 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):
a. Calculate the treatment volume to the device (TvBMP). The calculated TvBMPcan be
obtained from the Virginia Runoff Reduction Method (VRRM) spreadsheets.
Response: The treatment volume to the proposed Hydrodynamic Separator has been
calculated via the VRRM spreadsheet. Refer to provided VRRM and sheet C7.4
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.
Response: The peak discharge for the calculated treatment volume has been
calculated based on the DEQ recommended method. A copy of this calculation has
been added to sheet C7.4 and provided in the submitted calculation binder.
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).
Response: Documentation has been obtained from the vendor showing that the
proposed system size can accommodate the calculated treatment flow rate (7.76 cfs).
Per the vendor's documentation, the proposed CS-10 system can accommodate
treatment flows of up to 11.3 cfs.
8. Label ditches & channels. Provide design calcs. Show geometry and adequate lining
information.
Response: The drainage concept at the southern end of the site has been revised so that
substantial drainage ditches are no longer proposed. With the sidewalk being removed behind
buildings 6, 7, and 8, all yard drains have been shifted away from the buildings and are now
spaced regularly (50' or less) along the line where the longer ditches were formerly proposed.
The grades have been revised to sheet flow from the buildings and the property line to these
yard drains, much like the yard drainage concept for the rest of the buildings. Therefore,
ditches are no longer being proposed and calculations are no longer necessary. The
stormwater capacity calculations account for the sheet flow to each individual yard drain.
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1001 Boulders Parkway P 804.200.6500
T I M M O N S GROUP Suite 300 F 804.560.1016
YOUR VISION ACHIEVED THROUGH OURS. Richmond, VA 23225 www.timmons.com
9. Provide the DA to each ditch; Catchment area to each inlet. Provide assumed values for inlet
design (refer to LD-204).
Response: Please see response above referring to areas where ditches were formerly
proposed. All drainage areas are to yard drains are accounted for in the stormwater capacity
calculations, with an assumed C factor of 0.85 for each DA and a time -of -concentration of 5
minutes for the upstream end of each pipe run.
10. Show pipe runs: Label slope for 3 to 1
Response: Slope label for pipe 2 (structure 3 to structure 1) has been added to the storm
sewer profiles on sheet C6.5
15. Provide that channel protection is met for the runoff to your limits of analysis (2-yr for any
receiving channel/10-yr for pipe), or that Energy Balance was meet if entering a natural
channel. You must discharge to natural stormwater conveyance system. Extend pipe outlet
protection to edge of stormwater conveyance. [9VAC25-870-66.3] Confirm Analysis point B
inlet exists.
Response: The wet pond currently discharges at the limits of the existing wetlands, which the
project considers part of the flood prone area adjacent to the main channel of the stream and
therefore part of the "Natural Stormwater Conveyance System "per VSMP definitions.
The location of the inlet for analysis point B has been verified and does exist.
17. Show that design criteria are met for the level 1 Wet Pond & forebay (VADEQ BMP Design
Spec. 14). Show plan & profile views of design (Refer to Section 4: Typical Details).
d. Show planting plan, turf provided.
Response: Landscape plan for the aquatic shelf has been added to the plans as sheet
L5.1
e. Provide safety fence for vertical wall of pond & warning signs.
Response: A 6' fence has been proposed for the length of all retaining walls,
including the pond wall. Please refer to the Layout Plan (C4.0-C4.2) in the associated
FSP. Callouts for the warning signage have been added to C4.1 on the FSP.
f. Conduct soil tests to determine suitability for use as structural fill or spoil,
compaction/composition needs for embankment, need for liner (A&B soils), or depth to
ground water or bedrock (see section 6.3 of specs). Engineering recommends a
geotechnical review/analysis of the site & design of embankment due to size and
proximity to wetlands.
Response: The applicant acknowledges and appreciates the recommendation. A
geotechnical analysis and report has been conducted for the site.
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1001 Boulders Parkway P 804.200.6500
T I M M O N S GROUP Suite 300 F 804.560.1016
YOUR VISION ACHIEVED THROUGH OURS. Richmond, VA 23225 www.timmons.com
g. Design the low -flow orifice to minimize clogging. Install anti -clogging device; provide
note and show in detail. Engineering recommends increasing hole size.
Response: An anti -clogging device has been called out and detailed on sheet C7.5.
The low flow orifice has been increased to 2.5" diameter, which is the largest sized
orifice that can still release stormwater discharge at a rate that meets energy balance
requirements based on the pond routing.
h. Ensure adequate outfall protection (see section 6.5). Use of rip -rap channel design may
be used to get to natural channel.
Response: Appropriately sized outlet protection has been provided at the discharge
point of the barrel from the wet pond and into the existing wetland system.
j. The embankment is about 22' high, therefore the top width should be 12'. (...height is
the vertical distance between the lowest elevation, measured at the outside limit of the
embankment, and the top of the embankment.) [VADEQ BMP Design Spec, Appx. A]
Response: The embankment design has been revised to provide a 12' top width.
k. Show that emergency spillway is adequately designed and will not overtop or undercut
bank anywhere. Provide profile/cross-section. Show that discharge is going to a defined
& adequate receiving channel at a non -erosive velocity. [VADEQ BMP Design Spec,
Appx. Cl
Response: The emergency spillway has been profiled and detailed on sheet C6.5 and
C7.5 and has been designed to not overtop or undercut the embankment (100 year
storm contained within pond embankment with I' freeboard) while discharging to the
wetlands at a non -erosive velocity.
1. Provide Tv calculation for the pond. Show Rv value used.
Response: Tv calculations for the wetpond have been added to sheet C7.4 and
included in the calculations binder.
m. What is the velocity at the outlet of barrel? The outlet velocity should be 10 fps or less.
Response: Velocity at the outlet of the wet pond barrel is 8.5 fps.
18. Show embankment cross-section/profile — Show geometry (height, width, slope), cutoff trench,
fill material, foundation material, internal drainage (as necessary), Riser & barrel (type, length,
slope). Provide dimensioned cross section of pond's embankment design.
Response: Cross-section, profiles, details, and dimensions of the pond embankment are
provided on Sheets C6.5 and C7.5.
20. Provide Mitigation Plan for the impacts to 100' buffer area around wetlands. There should be a
100' buffer from the edge of the wetland.
Response: The 100' buffer from the wetlands adjacent to the portion of the existing stream
deemed perennial is shown on the plans. The remaining wetlands are adjacent to a portion of
the stream that is deemed intermittent and therefore do not have the associated 100' buffer.
No impacts into the 100' buffer are proposed with this project.
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1001 Boulders Parkway P 804.200.6500
T I M M O N S GROUP Suite 300 F 804.560.1016
YOUR VISION ACHIEVED THROUGH OURS. Richmond, VA 23225 www.timmons.com
21. Provide VRRM file (email is fine).
Response: A full copy of the VRRMfile has been entailed to Engineering for review.
22. Contact Ana Kilmer regarding nutrient credit purchase & agreement requirements. Currently
3.38 TP load credits required. Nutrient credit agreement required prior to plan approval.
Response: Per discussion with Ana Kilmer, the nutrient credit purchase cannot be executed
until the plans are approvable. The applicant is prepared to purchase the required nutrient
credits from an applicable bank once Engineering is satisfied with SWMplans and nutrient
requirement. Nutrient availability has been confirmed with the bank.
23. A recorded SWM facility easement & deed required prior to permit issuance. Also, forest/open
space easements need to be recorded.
Response: Plats for A SWM easement and forest/open space easements have been prepared
and are currently under review by the County.
24. Record the SWM maintenance agreement.
Response: The SWM maintenance agreement is being executed by the owner and will be sent
to the County for recordation.
25. Please sign and seal the Stormwater Calculations Packet.
Response: Hard copies of the Stormwater Calculations binder will be sealed and signed.
26. Show easement over areas of Forest/Open Space. Also, show some form of barrier or fencing
for these areas during construction, and signage. Currently, 2.75 ac are to be protected post -
development according to VRRM spreadsheet.
Response: The area of the Forestl0pen Space easements have been called out on the E&S
plans, and the easements have been added to sheet C7.0. Tree protection has been provided
on the E&S plans for protection of these area during construction. Plats for forest/open space
easements have been prepared and are currently under review by the County. The area of
easements has been revised to 2.61 ac, which is reflected in the revised VRRMfile.
27. Please add note on the cover sheet: "The SWM Forest and Open Space Easement is subject to
the guidance set forth by DEQ in the Virginia Stormwater Management Program. The areas will
remain undisturbed in a natural, vegetated state, except for activities as approved by the local
program authority, such as forest management, control of invasive species, replanting and
revegetating, passive recreation (e.g., trails), and limited bush hogging to maintain desired
vegetative community (but no more than four times a year)."
Response: The above note has been added to the cover sheet (CO.0).
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1001 Boulders Parkway P 804.200.6500
T I M M O N S GROUP Suite 300 F 804.560.1016
YOUR VISION ACHIEVED THROUGH OURS. Richmond, VA 23225 www.timmons.com
D. Erosion and Sediment Control Plan (ESCP)
2. Provide OP shape & stone size calcs (see VADEQ ESC HB Spec. 3.18). Add OP at pipe 1
outlet.
Response: Outlet protection and sizing has been added at structure I (C3.1, C3.3).
3. Show low maintenance measures as final stabilization measure of the E&SC plan. Low
maintenance (not grass) ground cover shall be specified on the plans where grades are steeper
than 3:1. {DSM, Sect 8A} Please indicate slopes 3:1 and steeper. Mulch (MU) should be
applied after seeding. B/M — Treatment 2 (EC-3) should be used for slopes 3:1 or greater.
[VADEQ ESC HB, Spec. 3.35,3.36]
Response: Treatment 2 matting (EC-3) has been specified for all slopes greater than 3:1.
Refer to E&S legend on C3.0 and C3.1 and detail on C3.4. Notes have been added to the
plans calling for low maintenance vegetation in areas greater than 3:1. Refer to E&S
Sequence on C3.4.
9. A temporary grading/construction easement should be shown where grading/disturbance occurs
on neighboring property. Bonds will need to be signed by the owners of all properties on which
construction takes place, or legal easements will be needed. [DSM, pg. 22]
Response: Applicant acknowledges the above comment
12. Show Stockpile area, Laydown-Staging area, Concrete -Chemical wash area, and Fueling
location on the Erosion and Sediment Control sheets.
Response: Stockpiles, laydown areas, staging area, wash areas, and vehicle parking and
fueling areas have been identified on the erosion control plans (C3.0-C3.1, C3.6).
13. Show sediment trapping device at Construction Entrance, all waste water from vehicle tire
washing must be directed into a trapping facility. Indicate on plans where waste water will be
directed to.
Response: The location where waste water from tire washing will discharge to has been
indicated on the E&S plans and PPP exhibit (C3.0-0.1, C3.6).
17. Show detail for Outlet protection on sheet C3.2 for Sediment Basin 1. Outlet protection should
be installed with a 0% grade. Add note to grade bottom length flat.
Response: A note has been added to the detail on C3.3 indicating the bottom grade of the
outlet protection is to be flat.
18. Show Blanket Matting on all slopes greater than 3:1. B/M — Treatment 2 (EC-3) should be used
for slopes 3:1 or greater. [VADEQ ESC HB, Spec. 3.36]
Response: Treatment 2 (EC-3) matting has been specified for all areas of erosion control
blanket/matting, and the VDOT standard detail has been added to the plans (C3.1, C3.4).
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1001 Boulders Parkway P 804.200.6500
T I M M O N S GROUP Suite 300 F 804.560.1016
YOUR VISION ACHIEVED THROUGH OURS. Richmond, VA 23225 www.timmons.com
19. Show Sediment Basin 1 conversion details. Detail the gabion baskets if that is what is being
used, also the outlet detail at zero grade into the converted basin.
Response: A Narrative for conversion from sediment basin to wet pond has been provided in
the E&S Sequence on sheet C3.4. Details and elevations for the gabion baskets have been
provided on C6.5 and C7.5.
20. Add note that all slopes greater than 3:1 must have low maintenance vegetative ground cover.
Response: Notes have been added to the plans calling for low maintenance vegetation in
areas greater than 3:1. See E&S sequence on C3.4.
21. Show Culvert and headwall details for culvert and headwalls as shown on sheet C3.1.
Response: Culvert and headwall details have been added to C6.4.
26. Sediment Basin - The maximum embankment height allowed is 15'. I calculate 22' height =
448' (top) — 426' (toe).
Response: Since the sediment basin is to be converted into the permanent wet pond, it seems
best practice to construct the embankment for the basin to match that of the final pond,
including size, clay core, outfall structure, barrel, and emergency spillway. This will mitigate
the danger of additional sedimentation on the downstream wetlands and stream by limiting
the embankment construction to one phase, while allowing a more streamline conversion
from sediment basin to permanent pond. Therefore, the applicant requests to keep the
sediment basin embankment at the proposed height, keeping in mind that the extra freeboard
from the higher embankment is not needed to provide the required sediment basin storage,
but will provide a more efficient and environmentally safe construction sequence.
On behalf of our client and Timmons Group, we appreciate the opportunity to continue working with the County
of Albemarle staff on the development of this multifamily product. If there are any questions or comments,
please feel free to contact me at mitchell.bowser@timmons.com or (804) 200-6543.
Respectfully submitted,
Cameron Morgan, PE U
Project Engineer
Timmons Group
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