20191303 Ver 1_Email_20191108

Carpenter,Kristi
From: Doug Keller <[e-mail]>
Sent: Thursday, November 07, 2019 3:53 PM
To: Ridings, Rob
Subject: [External] Re: City of Durham: Bradford Circle (DWR#20191303)
Attachments: Bradford Drawdown Split.pdf
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Rob,
Robert is correct -we have 3 separate reservoirs with 3 separate outlets. The permeable pavement will be
subject to heavy vehicle loading, so we minimized the storage depth beneath the surface. We also want to
avoid a condition where the subgrade is regularly saturated.
The relatively small volume collected will be difficult to drawdown over 2+days. However, this is a test case to
be monitored by the City and NCSU as of now. Infiltration may be tested by blocking orifice and utilizing an
upturned elbow. Please see the attached drawdown calculations for the 3 reservoirs conditions as designed.
We feel we are designing to the maximum extent practicable in this instance. Please let me know how this
affects the permit app.
Thank you,
Doug
DOUG KELLER, P.E., LEED AP
Project Manager
900 Ridgefield Drive,Suite 350
Raleigh, NC 27609
919.878.9560 P 1919.653.7375 D 1919.946.4575 C
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From: Ridings, Rob<[e-mail]>
Sent:Thursday, November 7, 2019 12:47 PM
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To: Doug Keller<[e-mail]>
Subject: City of Durham: Bradford Circle (DWR#20191303)
Doug,
I was reviewing your application for city of Durham's project to pave Bradford Circle with permeable pavement. The
401/Buffer part was self-explanatory. However due to my own lack of expertise in alternative stormwater treatment, I
had our in-house stormwater engineer, Robert Paterson, review the calcs and design of the permeable pavement
treatment.
He had a question I wanted to quickly bounce to you before final review---
He asked about the drawdown calculation being 0.87 days even though minimum recommendation is 2 days, and was
wondering the reason or justification for that deviation. He was wondering that if there are three separate reservoirs, if
the drawdown would be reflected differently if calculated for each one?
Rob Ridings
Environmental Specialist
401/Buffer Transportation Permitting (DOT Divisions 4-5)
Division of Water Resources, NC Department of Environmental Quality
919-707-3873 office
[e-mail]
512 North Salisbury Street, 12th Floor
1617 Mail Service Center
Raleigh, NC 27699
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