20050949 Ver 2_Staff Comments_20081010

05-0949v2 Partners Equity Group
Subject: 05-0949v2 Partners Equity Group
From: Annette Lucas <[e-mail]>
Date: Fri, 10 Oct 2008 11:24:30 -0400
To: Ian McMillan <[e-mail]>
CC: Cyndi Karoly <[e-mail]>, Annette Lucas <[e-mail]>
Ian,
I have reviewed the Stormwater Management Plan for this project and I approve it.
Annette
1 of 1 10/10/2008 11:24 AM
05-0949v2 Partners Equity SD
AML Comments
August 18, 2008
Please provide the appropriate Wet Detention Pond Supplement Form with all
the required items at the appropriate scales (including a section view of the entire
device and details of the inlet and outlet structures). The form that was provided
pertains to stormwater wetlands.
2. The pond as it is currently proposed has a number of design issues:
a. It is undersized for the amount of stormwater that is proposed to be directed to
it. The depth and surface area need to reflect an appropriate SA/DA ratio for
the site (minimum 2.88 for a 70 percent impervious drainage area with three
foot average depth). If the pond cannot be retrofitted such that it is sufficient
to handle the additional stormwater volumes, then additional stormwater will
need to be provided elsewhere on the site.
b. The surface area of the device appears to be overstated in the supplement
form.
c. This pond should be a minimum of three feet in average depth with an
additional foot of depth provided for sediment storage.
d. The outlet orifice appears to be oversized.
e. The forebays (both of them together) should comprise approximately 20
percent of the permanent pool volume. They appear to be undersized.
f. The planting plan must show the planting locations.
In order to obtain pollutant removal credit, the swales must be retrofitted to meet
current design standards for pollutant removal swales per the BMP Manual. This
includes a requirement for 5:1 side slopes and a velocity of 1 foot per second or
less during the 10-year storm. The DWQ is also willing to consider a "wet swale"
design. If you prefer to consider this alternative, then please provide the design
standards (planting, geometry, soils, slopes, water table levels, etc.) to which
these devices are constructed as well as the plan details to demonstrate that the
proposed wet swales have been designed to meet the design standards. An
operation and maintenance agreement is required for swales.
RE: Your message
Subject: RE: Your message
From: "[e-mail]" <annette. lucas@ncmail. net>
Date: Thu, 11 Sep 2008 15:30:20 -0400 (EDT)
To: <[e-mail]>
CC: [e-mail]
Jonathan,
There is no official policy regarding additional TN removal from a
pond sized for 90% TSS removal. However, I am willing to award you the
30% credit if the pond is designed for 90% TSS removal and stringently
adheres to all of the BMP Manual standards for wet detention pond
design.
I am not familiar with the design point method of determining
pollutant removal. It sounds interesting. If a BMP is designed in
accordance with the NC BMP Manual, however, it will received the
pollutant removal rate stated in the NC BMP Manual.
Annette
1 of 1 9/11/2008 3:31 PM