20110661 Ver 1_Staff Comments_20111020

Lucas, Annette
From: Lucas, Annette
Sent: Thursday, October 20, 2011 2:01 PM
To: Chapman, Amy
Subject: 11-0661 Chastain
Attachments: 11-0661 Chastain II - TAKE 2.docx
Amy,
Some lengthy bullets attached. I have had two conversations with Peter Cnossen about this and he seems agreeable
about seeing if a LS-VFS with flow splitter will work there instead of the huge scour hole that he has proposed.
Thanks,
A
Annette M. Lucas, PE
Environmental Engineer
NCDENR I DWQ I Wetlands and Stormwater Branch
1650 Mail Service Center, Raleigh, NC 27699-1650 (NI' ad)
512 N. Salisbury St, Raleigh, NC 27604 1 91r, Floor 0 tlw?ition t<. P,m ,+,!
Phone: [phone] Fax: [phone] Email: A. Ir- iuor
Website http://portal.ncdenr.org/web/wq/swp/ws/401
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11-0661 Chastain It - TAKE 2
AML comments
October 20, 2011
Please analyze the option of replacing the scour hole with a flow splitting box and level spreader-
engineered filter strip (constructed outside the riparian buffer). This approach would be
compliant with Neuse Buffer diffuse flow requirements. Also, the DWQ believes that splitting
the flow would better protect the buffer from erosion and possibly be less costly than the
proposed scour hole. If you choose this option, then please provide a LS-VFS supplement form
with all required items.
2. If your analysis shows that it is not possible to implement the design suggested under Item (1),
then please provide the following information at the correct scales (or risk a return of
application):
a. Calculations for the peak flow during the one inch/hour and ten-year storms based on the
drainage area size and rational C coefficient.
b. Plans (1" - 50' or larger) of the entire site showing:
° The delineated drainage basin.
The storm drainage system, including all inlets, outlets and conveyances.
Maintenance access.
c. Plan details (1" = 30' or larger) for the scour hole showing:
One foot proposed topo lines between the scour hole and top of stream bank.
Proposed drainage easement.
° Design at ultimate build-out.
d. Section view of the scour hole (I" = 20' or larger) showing:
#57 stone.
° Downslope filter fabric.
e. A construction sequence that shows how the scour hole will be protected from sediment until
the entire drainage area is stabilized.
f. A copy of the signed and notarized operation and maintenance (O&M) agreement.