HomeMy WebLinkAboutWPO201800085 Plan - VSMP WPO VSMP 2019-01-18PROJECT MANAGEMENT
SHIMCIVIL ENGINEERING
LAND PLANNING
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January 18t", 2019
Mr. David James
Albemarle County
Department of Community Development
401 McIntire Road
Charlottesville, VA 22902
RE: TMP-18-34F1-G — VSMP Plan Comment Response
Dear Mr. James,
Thank you for your review of the VSMP Plan for the property at TMP-1 8-34F1 -G. We have revised the plan per
your most recent comments dated, December 13th, 2018. Please see below for a detailed response to each of
your comments.
A. Stormwater Pollution Prevention Plan
1. Please complete sections prior to pre -construction meeting. Update reduced plan inserts for SWPPP
when plan is finalized.
The SWPPP has been prepared and updated to reflect the latest revisions.
B. Pollution Prevention Plan (PPP)
1. Show any proposed clearing/grading activities, paving oblations, landscaping operations, E&S
controls, staging, stockiJling, borxbw, fueling, waste disposal, vehicle/equipment washing, concrete
washout locations on the PPP.
The PPP has been prepared and all activities are shown with the latest revisions.
C. Stormwater Management Plan (SWMP)
1. Specify maintenance requirements for the level spreaders and detention basin.
The maintenance requirements for the level spreaders is provided on Sheet C2.
2. Show a SWM facility easement around the level spreaders and detention basins.
A SWM Facility Easement has been provided around each level spreader and detention facility.
3. A conserved open space or vegetated filter strip must be shown downwards from the level spreader to
function as a permanent measure. This management area should extend to the edge of property or
floodplain and be labeled as such.
The level spreaders are not being used for the purpose of reducing Nutrient Credit Requirements.
4. SWM easements to be recorded with a deed & plat prior to VSMP Plan approval.
Acknowledged, the SWM Easements will be recorded prior to VSMP Plan approval.
5. 1 don't believe the detention basins proposed meet any ESC/SWM spec. Show design calcs meet
spec. (i.e. for drainage area, volume, shape, wet pool, drawdown, etc.) Basins should meet the 25-yr
design/spec. The riser structure should have a trash rack.
The detention ponds have been designed to meet the Energy Balance Equation at the outlets.
Calculations for the detention pond and ESC Sediment Traps have been provided with this submittal.
The 25-yr storm has been included in the HydroCAD report. Further, a trash rack has been called out
for each standpipe.
6. Detention Design — It looks like the orifice is located between riser and 15" pipe. No stagnant pools.
The detention design has been revised to have identical invert elevations for the 1-yr orifice and the
15" pipe so as to not have stagnant pools.
7. The level spreader design should follow the SWM design specs. It appears from county GIS that
there's existing forest buffer, so the equation would be 40' length for every cfs. So, level spreader A
would be 1.47*40'. The minimum length is 13' and the max is 130'. The maximum sheet flow length of
either also must be satisfied.
The level spreader is following the ESC design specs as the design is not intended for VRRM
Compliance. The purpose is solely to manage the concentrated flow from the culvert outlet.
8. Show road ditchlines. Provide design calcs.
The road ditchlines have been provided and the design calculations have been included with this
submittal.
D. Erosion and Sediment Control Plan (ESCP)
1. The requirements of 18-4.6.6 Lot Access must be met. (general comment)
Acknowledged.
2. Sheet C3/C4:
a. Show critical slope areas.
There are not critical slope areas on this site.
b. Unknown easement is the WPO buffer of the offsite pond.
Acknowledged, the WPO buffer has been labeled as such.
c. Cannot find private street easement of 5059/405. Please provide plat.
The plat will be provided with a future submittal.
d. What is the source & date of the 2' contours? When was the property last surveyed?
The source & date of the 2' contours is provided on the cover sheet. Survey dated 10/8/2018.
3. Show location of all existing and proposed utilities and easements with deed book references.
The existing and proposed utilities and easements have been provided. Deed book references will be
provided after competition of the plat.
EM
4. Sheet C8:
a. Also show the culvert profiles. Show that the OP apron is flat.
All of the culvert profiles have been provided. OP apron is 0% where required.
b. Show that C7-OP is adequately designed. Doesn't appear to be adequate for the slope.
The C7 Outlet Protection has been designed at a permanent channel, calculations have been
included on the LD-268 table provided in the SWM packet. Outlet protection is provided on a
0% slope at the base of the detention pond.
5. Sheet C9:
a. Show OP symbols where used.
The OP symbol is provided where outlet protection is proposed.
b. Show SB/ST symbol and design computations for the detention. Show a phased plan — ESC1
sheet for perimeter controls, ESC2 sheet for grading and additional controls based upon your
construction sequence.
The ST symbol is provided where sediment traps are proposed. The ST details are provided on
Sheet C10. The detention facility calculations have been included with this submittal in the
SWM packet. An ESC Stage 2 sheet has been provided.
c. Show diversions going to SB/ST.
The diversions have been provided.
d. Show grading (road, etc) show all existing contours.
All of the existing contours and proposed grading is provided.
6. Show proposed grading.
The proposed grading is provided.
7. Show ST/detention calcs showing the design meets spec and provide ST detail.
The ST & Detention facility calculations have been provided with this submittal. The ST detail is
provided on Sheet C10. The detention facility design calculations are included in the HydroCAD
report, provided in the attached SWM Packet.
8. Area draining to C4 is over an acre and a culvert inlet sediment trap will be needed instead (ESC HB,
III-48). Provide design & detail.
An additional sediment trap/ detention pond has been provided for area C4. The design calculations
and details have been provided. The ST details are provided on Sheet C10 and the detention design
calculations are included in the HydroCAD report, provide in the attached SWM Packet.
Page 13
If you have any questions please feel free to contact me via e-mail at michael@shimp-enginee ring. com or
Justin Shimp at Justin @shimp-engi nee ring. com or by telephone at 434-227-5140.
Sincerely,
Michael Chandler
Shimp Engineering, P.C.
TMP-18-34F1-G Residence
Sediment Trap Calculations
TMP-18-34F1-G Residence (5639 Markwood Rd.)
Sediment Trap Calculations
Trap A
D1
D2
z
6jiP,
Incremental
Total Volume
Elevation
Area (sf)
Volume (CY)
(CY)
A 596
310
B 598
3672
147.5
147.5
C 600
5700
347.1
494.6
TMP-18-34F1-G Residence (S639 Markwood Rd.)
Sediment Trap Calculations
Trap B
L
w
o1
a2
Total
Elevation
Area (sf)
Incremental
Volume
Volume {CY)
(CY)
587
590
590
1530
117.8
117.8
592
2215
138.7
256.5
Drainage Area= 0.59 Ac
Wet Volume Required= 39.53 CY Drainage Area= 0.617 Ac
Dry Volume Required= 39.53 CY Wet Volume Required= 41.339 CY
Dry Volume Required= 41,339 CY
TMP-18-34F1-G Residence (5639 Markwood Rd.)
Sediment Trap Calculations
Trao C
L
w
D1
D2
Total
Incremental
Elevation
Area (sf)
Volume
Volume (CY)
(CY)
586
1000
588
1600
96.3
96.3
590
2310
144.8
241.1
Drainage Area= 1.39 Ac
Wet Volume Required= 93.13 CY
Dry Volume Required= 93.13 CY