20001195 Ver 12_Staff Comments_20111223

Patterson, Robert
From Patterson Robert
Sent Friday December 23 2011 9 17 AM
To Lucas Annette
Subject 00 1195 CDIA West Blvd Additional Information Request
Attachments 00 1195V12 Comments 23Dec2011 docx
Annette
This one was a little hard since I don t know what was previously approved I wasn t sure if the swales along Wallace
Neel Rd needed to be reviewed as part of this mod or not If they are no supporting calcs or supplements were
provided for them The DAs for the bioretention cells were really hard to follow For cell #1 it appears as though they
could bypass a huge area of pervious area around the cell Seems silly to route this area to the cell unless it includes
impervious area that I m not seeing
Robert D Patterson PE
Environmental Engineer
NCDENR I DWQ I Stormwater Permitting
1617 Mail Service Center Raleigh NC 27699 1617 Mail 1 512 N Salisbury St Raleigh NC 27604 1 9 h Floor Location & 1 arcelti
[phone] Phone [phone] arc I Robert Pattersonacncdenr gov l mail I http / /portal ncdenrorg /web /wq /ws /su W bsite
.A Before pnnun this email please consider your budget 'ind the environment
E mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may be disclosed to third parties unless the content is
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1

ti
00 1195 — CDIA West Blvd Mecklenburg Co
RDP Comments
23 December 2011
Bioretention Cell #I
-
I Does the drainage received by the pipe under West Blvd contain runoff from any
impervious area9 If not it may be better to bypass that runoff around the cell
Bioretention cells work best treating runoff from impervious areas
2 The plans and supplement show the temporary pool at 711 but it should be at the
overflow weir at 710 5
3 The supplement states the planting elevation is at 708 75 but the plans show
708 to 709 5 Bioretention cells must be flat throughout their section to function
properly
4 The supplement shows the bottom of the media at 708 58 but it should be the
planting elevation minus the 3 of planting media
5 The supplement shows the depth of sand as an elevation This should be shown
as the depth (thickness) of the sand layer in feet
Bioretention Cell #2
1 On sheet 14B a spot elevation is needed at the overflow to show that it is to be
built to elevation 704 (as done on sheet 14A)
2 The supplement states the planting elevation is at 702 35 but the plans show
702 7 to 703 Bioretention cells must be flat throughout their section to function
properly
3 The depth of sand on the supplement should be shown in feet not inches
4 The supplement shows the top of the upturned elbow at 700 03 but the plans
show it at 699 7 Please make it consistent
Both Bioretention Cells
1 Please be sure that any changes are consistently reflected on all documents (plans
calcs supplement forms O &M forms etc )

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2 Plans and calculations must sealed signed and dated by an appropriate NC
licensed design professional
3 Please verify the drainage area delineations for the BMPs They do not appear to
follow the contours
4 The surface of the cells are sloped Bioretention cells must be flat not sloped
Please revise
5 The plans show pondmg over 12 Pondmg shall not be greater than 12 Please
revise
6 An original signed O &M Agreement form must be submitted None were
submitted It can be downloaded from
hW2 / /portal ncdenr org /web /wq /ws /su /bmp ch12
7 The SHWT elevation was left blank on the supplements Also a soils report must
be provided that states what the SHWT is based on a boring within the footprint
of each of the proposed cells
8 The type of grass sod must be specified Also it should be specified that the sod
shall not be from a farm grown in tight clay soil that would restrict flow through
9 Both supplements state that a vegetated filter strip (VFS) is provided but there are
not any Note however that a properly designed VFS per chapter 8 of the BMP
Manual is not required for bioretention cells
10 Please provide supporting calculations for the drawdown and underdram sizing
for each cell