SW3190704_Signed Response Comments Letter_3/12/2020

` AMERICAN
Engineering
March 12, 2020
North Carolina DEQ
Stormwater Permitting
512 N. Salisbury Street
1612 Mail Service Center
Raleigh, NC 27699-1612
RE: Response to Stormwater Management Permit Review Comments for
Request for Additional Information
Stormwater Permit No. SW3190704
Skyland Drive Townhomes — Cabarrus County
Original Comment I - Please provide a boring showing the SHWT in the vicinity of
the proposed sand filter. This is a Minimum Design Criteria. Separation from the
SHWT must be demonstrated, not inferred, especially for an open bottom design.
Please refer to the attached report dated November 25, 2019 from GTA
Associates regarding results of Seasonal High -Water Table.
2. Original Comment 15 - Section IV, 10 indicates that there are 2,318 sf of off -site
impervious area draining to the proposed sand filter whereas the Supplement-EZ
Form Drainage Area Sheet indicates that there are 3,521 sf of off -site impervious
area draining to the proposed sand filter. Please revise for consistency.
Section IV, 10 has been revised to reflect 3,521 sf of off -site impervious
area draining to the sand filter. This impervious area consists of a portion
of Skyland Drive, the new driveway entrance within the RW, and a
portion of proposed sidewalk within the RW.
American Engineering Associates —Southeast, PA
8008 Corporate Center Drive, Suite 110, Charlotte, NC 28226 # 704-375-2438 0 www.American-EA.com

State Proj. No. SW3190704
March 12, 2020
Page 2 of 5
3. Prior Comment 8 —Please correct the following issues with the Supplement-EZ Form:
a. Drainage Areas Sheet:
i. Entire Site Column:
1. Line 5 — This is the total amount of BUA that will exist within the property
boundary (No offsite areas) in proposed conditions. Per the post development
drainage area map provided with the prior submittal, this value should be the
detained, on -site, post -development impervious area (1.271 ac) plus the undetained,
on -site, post -development impervious area (0 ac.), expressed in square feet (1.271 ac.
+ 0 ac. = 1.271 ac. = 55,357 s)).
Line 5 has been revised to reflect the total amount of BUA within the
property boundary of 58,050 sf. There has been a slight increase in total
BUA due to a contingent built into the Deed Restriction. Approximately
163 sf per lot has been allocated for a future walkway or patio. In
addition, the Post Development Drainage Map has been updated to
include the total amount of BUA within the property boundary of 58,050
sf=1.33ac. The design procedure Form 4.8.7 has also been updated to
include the revised total detained area of 2.305ac.
2. Line 6 — This item should be the amount of BUA allocated to the proposed
subdivided lots. Per the deed restriction document provided with the prior submittal,
this value should be 27, 200 sf (1, 700 sf per lot * 16 lots = 27, 200 sf. Please provide
revised deed restriction documents if needed.
Line 6 has been revised to 27,200 sf per the deed restriction document
and reflects the total amount of BUA contained within the subdivided
lots.
The total BUA of 27,200 sf per the deed restriction document for the 16
subdivided lots is as follows: 16 * 1,320 sf of roof area/unit = 21,120 sf,
3,465 sf of proposed driveway area for the 16 units, and 2,615 sf of
contingent BUA (patios, walkways, etc...).
21,120 sf + 3,465 sf + 2,615 sf = 27,200 sf BUA.
3. Line 7 — This item is the remaining B UA that will be located outside of the
proposed subdivided lots. Per the information provided in the prior submittal, this
value should be 28,157 sf (Total proposed BUA located on -site 55, 357 sf. 55, 357 —
27, 200 sf (Line 6) = 28,157 s)).
Line 7 has been revised to reflect 30,850 sf of total BUA located outside of
the subdivided lots. The new total of BUA 58,050 sf — 27,200 sf BUA
contained within the subdivided lots = 30,850 sf remaining BUA.
4. Lines 8 & 9 — There should not be any off -site components to the project site.
American Engineering Associates — Southeast, PA • North Carolina Engineering License C-3881
8008 Corporate Center Drive, Suite 110, Charlotte, NC 28226 e 704-375-2438 # www.American-EA.com

State Proj. No. SW3190704
March 12, 2020
Page 3 of 5
Lines 8 & 9 of the EZ form have been revised to eliminate any off -site
components.
S. Line 10 — This item is a breakdown of the BUA listed on Line 7. Per the
language of the deed restriction document provided with the prior submittal,
everything within the property boundary (buildings, parking, sidewalks, etc...) is
counted towards a lot's BUA. The value of the items listed under Line 10 should add
up to Line 7 and correspond to the values in Section IV, 10 of the application.
The items listed under Line 10 have been revised to reflect the breakdown
of Line 7. The BUA breakdown also corresponds to the components listed
under Section IV, 10.
ii. Drainage Area 1 Column:
L Line 6— See earlier comment.
Line 6 under the Drainage Area 1 Column has been revised to reflect the
BUA of 27,200 sf contained within the subdivided lots per the deed
restriction document.
2. Line 7 — See earlier comment.
Line 7 has been revised to reflect 30,850 sf of total BUA located outside of
the subdivided lots that contributes to the sand filter. The new total of
BUA 61,571 sf — 27,200 sf BUA contained within the subdivided lots, -
3,521 sf of BUA contributing from off -site = 30,850 sf remaining BUA.
3,521 sf has been added to Line 9 as contributing off -site BUA.
3. Line 10 — See earlier comment.
The items listed under Line 10 have been revised to reflect the breakdown
of Line 7. The BUA breakdown also corresponds to the components listed
under Section IV, 10.
iii. General:
1. Line 20 — Include a description of what the future BUA allocation will be used
for.
The future BUA allocation is a 4,988 sf area reserved for future parking.
b. Sand Filter Sheet:
i. Line 43 — Please elaborate on the dewatering method listed on Line 9 (Other).
In case of the need for dewatering, a pump and silt -bag will be utilized.
ii. Line 18 — See earlier comment.
American Engineering Associates — Southeast, PA • North Carolina Engineering License C-3881
8008 Corporate Center Drive, Suite 110, Charlotte, NC28226 •704-375-2438 # www.American-EA.com

State Proj. No. SW3190704
March 12, 2020
Page 4 of 5
Please refer to the attached report dated November 25, 2019 from GTA
Associates regarding results of Seasonal High -Water Table.
iii. Line 27 — The physical depth of the sediment chamber is the distance between
the bottom of the sediment chamber (666 ft) and the bypass elevation (667.7 ft).
Line 27 of the Sand Filter Sheet has been revised to reflect 20.4 inches.
iv. Line 32 — The area of sand filter (as listed on sheet C5.1) is 504 sf. Per the
guidance provided in the Manual (Part C-6 under A4DC6), the entire surface area of
the sand chamber must contain sand. Please revise.
Sheet C5.1 has been revised both graphically and with a note showing the
sand area to be 845 sf.
v. Line 33 — The physical depth of the sand chamber is the distance between the
bottom of the sand chamber (666 ft) and the bypass elevation (667.7 ft).
Line 33 of the Sand Filter Sheet has been revised to reflect 20.4 inches.
vi. Line 39 — The depth of the sand above the underdrain is shown as 2.5 ft on plan
sheet C5.1.
Line 39 has been revised to reflect the 30 inches shown on Sheet C5.1.
4. Please provide 2 full-sized copies of each plan sheet submitted with the prior
(113012020) submission (15A NCAC 02H. 1042(2) (g)).
The following plan sheets are being resubmitted:
C5.1 BMP Plan, Pre -Development Drainage Map, Post -Development Drainage
Map
5. Note: Per Division Policy, the next review of this application will be the final review.
Failure to provide the requested information will result in being returned as
incomplete. The return of the project will necessitate resubmittal of all required items,
including the application fee.
Understood.
American Engineering Associates - Southeast, PA 0 North Carolina Engineering License C-3881
8008 Corporate Center Drive, Suite 110, Charlotte, NC28226 •704-375-2438 . www.American-EA.com

State Proj. No. SW3190704
March 12, 2020
Page 5 of 5
6. Provide pdfs of all revisions, 2 hardcopies of revised plan sheets, and I hardcopy of
other documents. Pdfs must be uploaded using the form at.•
https:Iledocs.deq.nc.gov/Forms/SW Project Submittal
Agreed.
Sincerely,
American Engineering Associates — Southeast, PA
Principal
bfU(2American-EA. com
Attachments:
GTA Results of Seasonal High -Water Table
Revised Stormwater Management Permit Application
Revised Supplemental EZ
Revised Post Development Drainage Map (2 Copies)
Revised 4.8.7 Design Procedure Form: Sand Filter and Sand Filter Stage -Storage and
Stage Discharge Table
Revised BMP Plan Sheet C5.1 (2 Copies)
Pre Development Drainage Map (2 Copies)
American Engineering Associates — Southeast, PA # North Carolina Engineering License C-3881
8008 Corporate Center Drive, Suite 110, Charlotte, NC28226 # 704-375-2438 # www.American-EA.com