HomeMy WebLinkAboutWPO201500047 Correspondence 2015-09-16 PROJECT MANAGEMENT
SHIMP CIVIL ENGINEERING
LAND PLANNING
ENGINEERING 'oj.;
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September 16, 2015
John Anderson
Albemarle County
Department of Community Development
Regarding: WPO 2015 00047 -The Pants Project
Dear Mr. Anderson,
We have submitted revisions to the VSMP Plans for Chesterfield Landing. Your comments for the first submittal and
the changes we have made in response are below.
A. Stormwater Pollution Prevention Plan (SWPPP)
1. Coordinate single-family residence SWPPP (22-Apr-2015) with Geoff Elsie, Engineering
Inspector(434.270-3471)
We have called Geoff Elsie and are waiting to hear back.We will submit any revisions he requires as soon as
possible.
B. VSMP: SWPPP: Stormwater Management Plan
1. Energy balance, can't follow—variables, where from?? Tie Eq. variables to plan, or provide
narrative and direct calculations that explain.
Notes have been added to the energy balance computation identifying the sources of the variables.A
computation totaling the runoff volumes from the post-development HydroCAD report has also been added.
2. 36" HDPE PIPE OUT, INV =674
Thanks for catching this error; it is now corrected.
3. Label principal spillway barrel (36" HDPE) length (100').
The principal spillway barrel is now labelled with material, length, and slope.
4. Provide Emergency spillway dimensions, profile view.
The emergency spillway dimensions are now shown on the profile view.
5. Show Emergency spillway contours, plan view.
The emergency spillway is now shown and dimensioned on the plan view.
6. Locate Emergency spillway in cut, not fill.
The emergency spillway is now shown in cut.
8. Dimension culvert#3/#4 outfall protection (riprap), plan view.
The outlet protection for culverts 3 and 4 is dimensioned in detail 2105.
9. Provide VDOT End Section, Wet Pond outfall pipe, profile view.
A VDOT End Section is now specified for the wet pond outfall pipe in the profile view.
10. Show and dimension Wet Pond outfall pipe OP (riprap), plan view.
Outlet protection is now shown and dimensioned for the wet pond outfall on sheet C7.
11. Provide culvert#3-wet pond cross section, similar to culvert#4-wet pond cross-section.
A cross-section for culvert#3 has been added to sheet C7.
12. Estimate stream buffer impact. Provide narrative analysis and details re. Mitigation. (please call if
questions)
All on-site areas that are outside of the proposed pond area are already densely wooded.A narrative listing the
relevant areas has been added to the plan, and photos are attached to this submittal.
13. With 6' of riser submerged, provide buoyancy calculations.
Buoyancy calculations are now shown on sheet C7.
14. Provide concrete base/ embedment detail for riser, Also, 4. Above.
A detail for the concrete base has been added to C7.
15. Specify 48" DIA riser material.
The 48" DIA riser is now specified to be concrete.
16. Provide detail for riser/barrel, suitable to guide construction.
A riser detail is now provided on sheet C7.
17. Although listed elsewhere, include Area of disturbance =4.47 Ac. on C3.
A label stating the area of disturbance has been added to C3.
19. 6' x 6' weir, can't follow-12.0' top of dam.
The emergency spillway dimension is now listed accurately in the HydroCAD report.
20. Provide emergency spillway elevation.
The elevation of the emergency spillway is now provided in the plan and profile views.
21. Provide trash rack, 8" Vert. Orifice/Grate.
A wire trash rack is now specified for the 8"vertical orifice.
22. Provide trash rack, riser crest: Hanson or Alt—for example [images]:
The standard trash rack detail from VDOT's Road and Bridge Standards is now provided on sheet C7.
23. Sum DA 2,3,4,5 =32.21 Ac. Compare with [report excerpt]:
It looks like the label for the drainage area that flows directly to the pond, not through a culvert, got moved
off to the side of the drainage area map. I have moved it on top of the pond. I double-checked all the
numbers, and this should resolve the discrepancy.
24. Impervious Area to pond =0.43 Ac., compare with image above.
One of the quirks of the HydroCAD program that was used to generate the stormwater computations is that it
computes curve numbers separately from impervious areas. Most of the impervious area on the site is gravel
driveway,and the runoff volumes and peak rates are computed with a curve number appropriate for gravel,
but the gravel is not included in the impervious percentage computation. Similarly,we have found that
labelling impervious areas with any other descriptor, such as "rooftops" or"parking lot",while using the 98
curve number, still results in the program omitting these areas from the impervious area percentage
reported. However, the computations for discharge and volume are correct.
25. '100.00%Pervious Area' descriptor, DA 2,3,4,5/report—a value carried to the hundredths, is
inaccurate. Explain or revise.
This is another aspect of the software quirk described above. The program automatically computes and lists
the impervious percentage in a way that is difficult to predict or control,without actually influencing the
computation,which is based on the curve number. If it is preferred,these notes can be expunged from the
report.
26. Is forebay =684' a WSE? Will this Elev. equalize with wet pond 682' WSE?
The 684' label was included to indicate the top of the forebay volume, not the water surface elevation.This
has been clarified in the plans.
27. Please confirm that 24" DIA culvert#3 and 36" DIA culvert#4 will convey the 25-yr storm event
without overtopping driveway.
The HydroCAD report has been expanded to include computations showing that culverts#3 and#4 will
convey the 25-yr storm.
28. Please explain 4.35 Ac. site data Land Cover vs. 4.47 Ac. disturbance. VaRRM .xls site data must
at least=Area of disturbance.
This error was an oversight from a revision of the plan. It has now been resolved; thank you for finding it.
29. Provide SWM Facility single-vehicle parking (Access) for Alb. County periodic inspection.
A parking spot is now provided on the grass next to the SWM facility.
30. Provide SWM Facility Easements.
SWM easements are now provided, encompassing the wet pond and the parking spot.
31. Discuss SWM in project description, C2.
A section of the narrative has been added for stormwater management.
32. Provide Narrative, description,Notes, and sequence that correlate wet pond construction with
project development generally, and sheet C2 ESC sequence, specifically.
The sequence of construction and other notes on sheet C2 have been updated to include discussion of the
Wet Pond.
33. Provide ESC perimeter measures to limit offsite impacts during wet pond construction.
Erosion and sediment control measures are now specified for the wet pond construction.
34. Provide wetland plant species quantities as supplement to Design Specification No. 13 Tables
13.4/13.3, C7 (aid bonding).
The wetland species table has been expanded to show species quantities.
35. Provide L x W plan view dimension for each forebay and wet pond to aid construction and
earthwork estimate (bonding).
Dimensions are now shown for each forebay and the wet pond.
36. Provide anti-seep collar design for principal spillway (100' L pipe outfall).
Anti-seep collars are now specified for the principal spillway.
37. From Table 2.2, Filter strip design criteria VA DEQ Stormwater Design Specification No. 2:
Revise ELS design. Compare design criteria with Darken residence Modified LD-268 values, p.
30, 9-Jul SWM report.
The engineered level spreaders for this project are not based on the VA DEQ Stormwater Design
Specification No. 2, as they are not being applied to water quality. They are designed per the specifications of
the Virginia Erosion and Sediment Control Handbook, No. 3.21,which only calls for a length of 10'for level
spreaders receiving a 10-year peak flow less than 10 cfs.
C. VSMP: SWPPP: Erosion Control Plan
1. C3 —Label ditch sections to correspond with Stormwater Management Report Modified LD-268
ditch labeling convention.
Labels have been added to clarify which ditch sections correspond to which entries on the Modified LD-268.
2. LD-268 table—Add note to make protective lining design intent clear.
A note has been added to the LD-268 table to clarify that EC-2 matting is required on all sections of the
stormwater conveyance channel.
3. C4—Provide stockpile silt fence.
Silt fence is now specified around the topsoil stockpile.
If you have any questions, please do not hesitate to contact me at your earliest opportunity. I may be reached at:
Justinshimp-enqineering.com or by phone at 434-953-6116.
Best Regards,
Justin Shimp, P.E.
Shimp Engineering, P.C.
lope' fteur
Johnathan Newberry
From: Seale, Dennis L. (VDOT) <Dennis.Seale@VDOT.Virginia.gov>
Sent: Monday, September 21, 2015 3:05 PM
To: Johnathan Newberry
Subject: Herman and Stella Morris Property Route 643 Albemarle County SUB-201500103
Good Afternoon J.T.,
I have reviewed the plat drawn up by Old Albemarle Surveying that will serve these two parcels with a shared use
private entrance and find this to be an approved location.A permit has been issued for this new access as requested
from the landowner. If you should have any questions or concerns please let me know.
Thanks,
Dennis Seale
Engineering Specialist
VDOT
Charlottesville Residency
434-531-2877
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