SW3201202_Responce to Comments_20210401

Y
CDM,,,,
Sith
4600 Park Rd, Suite 240
Charlotte, North Carolina 27209
tel: [phone]
Apri11, 2021
Mr. Jim Farkas
Environmental Engineer
North Carolina Department of Environmental Quality
Division of Energy, Mineral & Land Resources Stormwater Program
512 N. Salisbury Street
Raleigh, NC 27699-1612
Subject: Union County Public Works - Yadkin Regional Water Treatment Plant
Post -Construction Stormwater Permit Application
State Project Number SW3201202
Dear Mr. Farkas:
We received your email dated March 24, 2021 with comments related to the subject permit submittal
for Union County Public Works (UCPW) and the new Yadkin Regional Water Treatment Plant (WTP).
Please find below a summary of your comments and our responses:
1. Please provide the original signed copy of the Supplement-EZ Form and O&M Agreement
Form. If it is not possible/practical to provide the original signed hard copies (due to the
ongoing Covid pandemic) we will accept the provided copies with electronic signatures.
Response: Original signed copies of the Supplement-EZ Form and 0&M Agreement are
included with this letter.
2. Supplement-EZForm, Low -Density Page:
a. Please show the slope of the swales as a percentage (%), not as a slope (ft/ft).
Response: The requested change has been made.
b. Please clarify the fact that some of these swales flow into other swales and only the
portion of the drainage area that flows directly to the Swale (not the upstream swales)
is shown in the Swale table. For example, the total drainage area to Swale 3 should be
about 6 acres (Area A + B + D + F) whereas only drainage area 'B" is shown (You can
add a note stating that "Swale 2 flows into Swale 4 and Swales 1 & 4 flow into Swale 3
(The drainage areas below show the portion of the drainage area that flows directly to
the Swale and the flow takes the entire drainage area into account. Please refer to the
calculations for more information" or something along those lines) or adjust the
drainage area information in the table so that the total drainage area to the Swale is
shown).
Response: The requested change has been made in the Additional Information section
of the Supplement-EZ Form.

Y
CDM,,,,
Sith
Mr. Jim Farkas
Apri11, 2021
Page 2
3. Swale 4: Per 15A NCAC 02H .1003(2)(c)(i), the maximum allowable side slope of a vegetated
conveyance is 3:1. Ifyou would like to use a steeper side slope, you must provide calculations
and an on -site soil investigation showing that the soils and vegetation will remain stable.
Response: The swale size was designed using the NCDEQ Erosion and Sediment Control
Planning and Design Manual (i.e., permissible velocity procedure for vegetated channels)
as a guide. Please see the attached calculations for sizing of Swale 4. Note that the swale
dimensions were modified post -submission for the Post -Construction Stormwater Permit
Application, and the side slope at this location has been modified to 1.5:1. Per Detail F,
Sheet CD-1, Turf Reinforcement Matting is required to aid slope stability at this swale. In
addition, the permanent swale will be installed in an area of fill, where the fill thickness is
up to 10 ft. The depth of the swale will only be 1.5 feet where the bottom width is 4 feet,
and top width is about 8 feet Based on analysis by our geotechnical engineer, due to
following factors, slope/soil stability is not considered to be an issue:
1) Swale is shallow
2) Swale bottom width is narrow
3) Swale will be in a fill area where material will be compacted in a controlled manner
with high strength
4) Turf Reinforcement Matting will be provided to aid instability.
Enclosed are the original signed hard copies of the revised Supplement-EZ Form and 0&M
Agreement Form, two copies of the revised plan sheets, and one copy of the swale calculations.
Electronic copies have been uploaded to the edocs website.
If you have any questions or require anything further, please do not hesitate to contact me at (704)
342-4546 or at [e-mail].
Sincerely,
.f
athan S. Lapsley, P. ., P P
ice President
CDM Smith Inc.
cc (email): John Shutak, UCPW Tracy Randazzo, HDR
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WTP - Stormwater Comments Response Cover Letter_032621