HomeMy WebLinkAboutWPO201500033 Review Comments 2015-08-21 42.
;I PROJECT MANAGEMENT
sHimpf�'� CIVIL ENGINEERING
t'� LAND PLANNING
ENGINEERINGL
August 21, 2015
Justin Deel
Regarding: WPO-2015-00033 Hillbrook
VSMP Plans
Dear Mr. Deel,
I have attached four copies of the VSMP Plans for Hillbrook.Your comments.for the second submittal and the
changes we have made in response are below. Please forward two copies of the plans to VDOT per the request of
Troy Austin.
C. Stormwater Management Plan (SWMP)
1. Please ensure that the entire 1 year storm event will reach the biofilter. Your invert out elevation at
structure 4 is shown at about 497' (labeled as 496.1,please check) while the 1 year storm elevation
is 497.36.
Thank you for calling attention to structure 4.The labels had been switched, and the invert out was too low.
The invert out has been raised to 496.45.
4. Please provide a larger more clear detail of your vault system. Are you accounting for the stone in
your calculations? Is it necessary for a self-cleaning pipe system? If the stone stays in place, it will
most likely clog; if not, it will wash away,probably down the pipe. Please explore an alternative to
the gravel inlet protection at the weir orifice. This also applies to the proposed stone in the
detention system.
Per our phone conversation,the gravel inlet protection has been replaced with a wire mesh screen.
Revision 1 Comments:
10. Please check invert elevations and pipe slopes on storm sewer profile, specifically structure 4.
Structure 4 has been checked and revised to properly show the design.
11. Please elaborate on the self-cleaning velocity table values from structure 5 to 6. I'd like to see
those computations, as it just meets the minimum 3.0 ft/s.
The self-cleaning velocity table was created by copying certain values from the LD-229, computing the flow at
different intensities using the rational equation,and reporting the intensity which resulted in the minimum
velocity being met. During a meeting with County engineers, it was established that self-cleaning velocities
were required for the 2-year storm,which,for this project, has an intensity of 5.2 in/hr.All of the intensities
listed in the table are well below this threshold, meaning that self-cleaning velocities occur much more
frequently than every 2 years.
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12. Please provide a larger clearer cross-section of the biofilter. It impossible both to see where the
leaders are pointing and to differentiate the layers. Please specify filter media depth.
A larger cross-section of the biofilter is now provided and filter media depth is now specified.
13. I realize that the sequence of construction detail in Specification No. 9 is barely legible, but at this
scale on your plan it is completely illegible. Please try to clear this up.
We have re-drawn Specification No. 9 to make it clearly legible.
If you have any questions, please do not hesitate to contact me at your earliest opportunity. I may be reached at:
Justin a(�shimp-engineerinq.com or by phone at 434 953-6116.
Best : ds,
Justin Shimp, P.E.
Shimp Engineering, P.C.
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