20100549 Ver 1_Staff Comments_20101104

Lucas, Annette
From: Lucas, Annette
Sent: Thursday, November 04, 2010 1:26 PM
To: 'Jesneck, Ken'
Cc: 'John Dempsey; 'Matt. Flynn @TownofCary.org'; Eric. Simpson @townofcary.org; 'Randy King'
Subject: RE: Davis Village DWQ 10-0549
Attachments: image001.gif
Dear Ken:
The DWQ accepts your proposed modification to the diffuse flow plan to discharge the flow entering FES 34 to a scour
hole rather than to the road drainage system. Ordinarily, the DWQ no longer allows scour holes as a means of achieving
diffuse flow, but given the small size and wooded nature of the drainage area and the flat slopes in the riparian buffer,
we will accept your design in this case.
This email will serve as the formal approval of the modification to the diffuse flow plan.
Sincerely,
Annette
Annette Lucas, PE
NC Division of Water Quality - 401 Oversight/Express Unit
2321 Crabtree Boulevard, Suite 250
Raleigh, North Carolina 27604
Phone: [phone]
Fax: [phone]
Email correspondence to and from this address may be subject to the North Carolina Public Records Law and may be
disclosed to third parties.
From: Jesneck, Ken [mailto:KJesneckCa)withersravenel.coml
Sent: Wednesday, November 03, 2010 9:11 AM
To: Lucas, Annette
Cc: 'John Dempsey'; 'Matt. [e-mail]'; [e-mail]
Subject: Davis Village DWQ 10-0549
Annette,
As we discussed yesterday, please find attached the Storm Drainage Plan and supporting calcs for the scour hole plunge
pool.
The storm pipe in question is from FES 34 to FES 35 under Kingston Grove Drive near its intersection with Morrisville
Parkway. The drainage area for this line is the open space between the right of way of Morrisville Parkway and the rear
drainage of the townhomes in Davis Village. The drainage area for FES34 is 0.82 acres, which will result in a 10-year
peak storm flow of 2.0 cfs.
The Town of Cary required that all stormwater from impervious surfaces must be directed to the wet detention pond,
which we have accomplished with this design. Initially, I had FES 34 connected to the junction box serving the storm
drainage system of Morrisville Parkway and then ultimately being discharged through the performed scour hole as shown
on the plans. The design was approved by the Town of Cary Devfelopment Review Committee, but upon approval be the
1
Town of Cary Engineering Department, the amount of flow from FES34 into the Town of Cary system would be in excess
of the maximum flow allowed for a plunge pool for the pipe diameter, which I believe is 10 cfs.
Upon learning of this situation, we met with the Town of Cary to explore options. We discussed several, but two options
seemed the most practical. Option 1 was to skew the pipe to its own scour as shown on this design. Option 2 was to
extend Y133 to the location of FES 34 and capture all the stormwater and pass it through the BMP. Option 2 was selected
for several reasons, one being to avoid having to revised the permit will another point source and the other being the
Town of Cary thought this a better choice, even though this Option included the removal of trees and vegetation for
grading. The invert of Y133 is at a higher elevation that FES 34, and would require grading to direct the stormwater flow
into the inlet structure. The Town of Cary did approved Option 2.
Ultimately, when the clearing and grading of the area was nearing completion, the developer (Pulte Homes) did not want
to remove the trees that were necessary to cosntruction Option 2. So now, we are back at Option 1. 1 have updated
Sheet 5-Storm Drainage Plan to include the new pipe location and the scour hour plunge pool configuration.
Let me know if this is acceptable approach. Thank you for your assistance.
Ken Jesneck, PE, LEED AP
WITHERS RAVENEL
111 MacKenan Drive I Cary, NC 27511
Phone: [phone] Fax: [phone]
Direct: 919.535.5139 1 Mobile: [phone]
kiesneck(a-)withersravenel.com
www,withersravenel.com
,y 1,-•-
'id ' ; v(?r '
2