20090204 Ver 1_Staff Comments_20090527

Lucas, Annette
From: Lucas, Annette
Sent: Wednesday, May 27, 2009 10:35 AM
To: Wiggs, Linda
Cc: '[e-mail]'
Subject: 09-0204 WCU School of Health & Gerontology
Attachments: 09-0204 WCU School of Health & Gerontology.doc
Linda -
At long last, here are my comments on this project. Sorry for the delay. Please let me know if you have questions.
Thanks,
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.
1
09-0204 WCU School of Health & Gerontology
AML comments
May 26, 2009
1. Please address the following issued with the design of the sand filters:
a. Volume in excess of the design volume must bypass the sand filter.
b. These systems require under drains. The under drains should be designed
in accordance with Section 5.7 of the DWQ BMP Manual.
c. Show the boundaries of the recorded drainage easement on the plan sheets.
2. Please address the following issues with the design of the bioretention cell:
a. The drainage area to the bioretention cell is characterized as 14.7 percent
impervious. Since this cell is receiving almost all of its flow from the roof
of the proposed new building, it seems like the percentage of impervious
surface should be much higher for this drainage area. This will affect the
size of the bioretention cell needed to treat the drainage area.
b. Consider organizing the plan sheets so that the information for the
bioretention cell (plans, profiles and planting plan) can be found
conveniently on consecutive plan sheets.
c. Plants should not be backfilled with engineered soil that has been
amended with compost.
d. Imported top soil should not be placed on top of plantings.
e. Provide watering specifications to establish the vegetation.
f. Explain how the berm that conveys flow from the building into the
bioretention cell will be stabilized to prevent erosion (currently the slope
is approximately 20 percent in this swale).
g. Space the underdrains such that they provide more even coverage for the
bottom of the bioretention cell.
h. Show the boundaries of the recorded drainage easement on the plan sheets.