20081810 Ver 1_Staff Comments_20100902

Lucas, Annette
From: Blumenfeld, Byron [[e-mail]]
Sent: Thursday, September 02, 2010 11:26 AM
To: [e-mail]
Cc: Lucas, Annette
Subject: FW: 08-1810 Village on the Lake II
Allison,
Please note that "grassy" bottoms on bio-retention ponds is now authorized, so you can remove the trees and shrubs
from the design and replace them with centipede... only requirement is that the maintenance plan ensures that the bio's
are not fertilized along with the other lawn areas ...this also makes the two foot media depth correct O
Item two references soil testing ...I remember that we discussed this during the original design (about two years ago) and
that you provided me with data showing adequate separation between the bio bottoms and the average high water
table... if you still have that data, could you include it with your reply.
Finally I know we discussed the low "P" rating for the media mix...even though we are not in a "impaired" watershed,
the design manual requirements still apply...be sure to check the current mix in the NCBMP Manual / Bio Retention
chapter and ensure the contractor adheres to that during final construction.
Thanks
Byron
From: Lucas, Annette [mailto:[e-mail]]
Sent: Wednesday, April 28, 2010 1:29 PM
To: Blumenfeld, Byron
Cc: Lucas, Annette
Subject: 08-1810 Village on the Lake II
Dear Mr. Blumenfeld:
I have received a copy of the stormwater management plan that you approved on behalf of the Town of Spring Lake for
the above project. The DWQ Stormwater Unit will accept this as meeting the stormwater requirements of the 401
Water Quality Certification program. However, I do have the following concerns with the design that was approved:
For a bioretention cell that is planted with trees and shrubs, the depth of the soil media is required to be three
feet, not two feet as shown on Plan Sheet C-6.
The designer should have provided a soils test that documents the level of the Seasonal High Water Table
(SHWT) and the permeability of the in-situ soils. The plan sheet shows that there is a two-foot separation
between the invert of the bioretention cell and the SHWT, but this needs to be documented with a soil boring
within the footprint of each proposed bioretention cell. If the SHWT were found to be less than two feet below
the invert of the bioretention cell, then another BMP would need to be selected for that location. If the soil
permeability were found to be less than 0.5 in/hr per the soils test, then an underdrain would have to be
provided at the bottom of the soil media.
The P-value for the soil media should be specified as 10-30.
I just wanted to make you aware of these deficiencies I observed in order to assist you with future plan reviews. Please
let me know if you have any questions.
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.