NC0065587_Response to Comments_20170818

A-11131
Dewberry
August 18, 2017
NCDEQ Water Resources Division
Attn: Trupti Desai
1617 Mail Service Center
Raleigh, NC 27699-1617
RE: RESPONSE TO COMMENTS
ATC Application
Frye Bride WWTF
NPDES No NCoo65587
Dear Trupti,
Dewberry Engineers Inc 919 881 9939
2610 Wycliff Road, Suite 410 919 881 9923 fax
Raleigh, NC 27607 www dewberry com
RECEIVED/NCDEQ/DWR
AUG 2 9 2017
Water Quality
Permitting Section
On behalf of Aqua North Carolina (Aqua), Dewberry Engineering (Dewberry) is pleased to provide the
following response to your comments received via email on August 9, 2017 for the above mentioned
project. The following paragraphs identify each comment and provide our response.
Comment is DEQ reviewed the facility's flow history and found that the flow exceeds the maximum
predicted hourly flow of 2.5 times the average daily flow. Our best estimate shows an hourly peaking
factor of 3 0. Since peaking factor impacts the hydraulic profile and design of new and existing treatment
units, please demonstrate that the proposed manual bar screen, equalization/aeration tank and pumps
will be able to handle high flow situation when peaking factor is 3.0 Please confirm that the freeboard of
12 inches is maintained in all treatment units with the higher peak flow. Please note that you will need to
submit corrected supporting documents including drawings to show this change.
Response is The system hydraulics in the proposed aeration basin ultimately dependent on the
head over the existing broad crest weir located at the clarifier effluent. Using a peaking factor of
three (3) times the average daily flow (ADF) or o 81 MGD, the resultant head over the weir is o 21
inches, which equates to EL 737 26. The calculated hydraulic losses through the proposed 6"
diameter aeration basin effluent pipe to the existing clarifier influent are negligible Thus, the
calculated water level in the proposed aeration basin is equal to the clarifier water level over the
effluent weir The proposed aeration tank has a top elevation of 738.56 FT, which results in a
calculated freeboard of 15.6 inches This is greater than the required 12".
Furthermore, at a peaking factor of 3, the peak flow is 56 gpm and calculated total dynamic head
ranges from 4.7 to 11.7ft depding on basin water level. The attached pump curve provided in the
ATC application cites a pump capable of 6o gpm at 115 ft TDH with increasing flow rates as head
decreases Therefore the identified pump is adequate for the increased peaking factor. Also, the
proposed manual bar screen is adequately sized for the peak flow.
The following supporting documents are attached
• Revised Table 1: Hydraulic Profile Calculations
Page 1 of 2

Response to Comments
ATC Application
Frye Bridge WWTP
NPIDES No NCO065587
August 18, 2017
Revised Sheet C -o6: Hydraulic Profile and Process Flow Diagram
Comment 2: Second box in Section 3 - A. Cover Letter (Page 3) is checked in both permit applications
but the list is not included in the cover letter. Please confirm.
Response 2: There are no variances from any of the requirements listed in Section 3 Part A of
the ATC application.
Comment 3: Please clarify that the quantity of sludge will not increase after installing the new aeration
basin. You will need to submit a sludge management plan if the quantity of sludge will change from the
existing situation.
Response 3: The quantity of sludge will not increase. The proposed project is a maintenance
activity that provides in-kind replacement of the existing aeration basin.
Comment 4: What is the volume capacity of the existing aeration basin?
Response 4: Historical records of the existing aeration tank were not located. Data collected
form the surveyor and owner indicate a total length, width, and height of 50 ft, 7.5 ft, and io ft
respectively. It is estimated the existing tank volume is approximately 28,000 gallons.
Comment 5: Does the backup power generator have the capacity to run all the demand in the plant
including the two new EQ pumps?
Response 5: Yes, please refer to electrical sheet E-4 detail 2 and panel schedule. According to
this, the identified iso amp generator connection is sufficient to run the proposed and existing
plant equipment. Note that the proposed auxiliary power plan for the facility is not being
modified per this ATC request
Dewberry and Aqua look forward to your concurrence on the proposed facility improvements. If you
should have any additional questions or comments, please do not hesitate to contact me via phone and
email at (984)-255-7056 or mpouhos@dewberry com
Sincerely,
-it
Michael Pouhos, PE
Project Manager
Cc: Moses Thompson, Aqua America, Inc.
g" Dewberry
Page 2 of 2

AQUA NORTH CAROLINA, INC.
202 MACKENAN COURT,
CARY, NC 27513
HYDRAULIC PROFILE CALCULATIONS REV. 1.0
FOR
FRYE BRIDGE WWTP
AERATION BASIN REPLACEMENT
DEWBERRY PROJECT NO. 50087184
AUGUST 18, 2017
Prepared by.
S.
AV
A
013093
�Dewberry
Dewberry Engineers, Inc
2610 Wychff Road, Suite 410
Raleigh, NC 27607
Phone [phone]
Fax: [phone]
www dewbeLa.com

1 Use NPDES Permitted Average Daily Flow 0.027 0.081 MGD
2 Historical 12 -Month Flow 0.008 0.028 MGD, okay 30% NPDES flow.
*Selected a PEAK FLOW of 3X ADF. i
I Diameter of Pipe
8 inch
2 Min. Slope per 100 ft.
0.4 ft per 100 ft
3 Existing Pipe Invert Elevation _
739.22 ft
4 Required Length
50 ft
5 Calculated Min. Invert Elevation
739.02 ft
6 Tank Top Elevation
738.56 ft
7 Tank Bttm Elevation
727.56 ft, assumes 11FT deep tank
8 Pipe Invert Above Tank
0.46 ft
9 Determined Pipe Inv. Elevation
738.60 ft, set pipe on top tank
10 Screen Burn Elevation
737.39 ft, assume 14" screen depth
11 Calculated Max Water Level in AB
737.26 ft, okay screen above.
1W CONTROLBOX WEIR
1 Flow Box Top El.
741.56 ft
2 Flow Box Bttm. EI.
738.56 ft
3 22.5 Degree V -Notch Weir Elevation*
739.56 ft, m_a_nuf_. to verify
v
4 Head Over Weir
0.37
0.58 ft
4.46
6.92 in
5 Calculated Max. Water EI.
739.93
740.14 ft
*Assumes weir crest is 12" above box bttm.
THROUGHSESS DIA. PIPE FROMTO CLARIFIER
1 Diameter of pipe
6 inch
2 length of pipe
29 feet
3 Estimated velocity (Q/A)
0.053
0.160 fps
4 Reynolds Number
2216
6649 assume, turbulent
S Hazen Williams Coefficient
120
120
6 Major Friction Loss
0.00
0.00 ft _
7 Minor Friction Loss
Fitting K -value #
EK Vz 2
EK V' 2
90° Bends 0.9 3
0.00
0.00 ft
Entrance Exits 1 2
0.00
0.00 ft
8 Total Losses
0.00
�^
0.00 ft, insignificant ignore
9 Calculated Max. Water Level in AB
737.15
_
737.26 ft, assume equal to Clarifier
10 Calculated Free Board
16.89
15.55 in, okay greater than 12"
11 Set Effluent Invert Elevation
737.05 ft, set equal to clarifier weir crest
Dewberry Engineers, Inc. Page 1 of 3
Prepared By: Michael Poulios, PE
Date: 8/18/2017
Rev 1.0

I Crest Elevation
737.05
737.05 ft
2 Head over weir
0.0085
0.0177 ft
3 Inf. Invert Pipe Elevation
735.95
735.95 ft
4 Eff. Invert Pipe Elevation
736.57
736.57 ft
5 Calculated Water Level in Clarifier
737.15
737.26 ft
6 Top of Tank
738.55
738.55 _
7 Calculated Free Board
16.78
15.45 in,
1 Diameter of pipe
736.33
ft
2 length of pipe
ft
0.643
0.643
3 Estimated velocity (Q/A)
735.69
735.69
0.053
4 Reynolds Number
0.38
ft
2216
5 Hazen Williams Coefficient
ft
4.81
120
6 Major Friction Loss
0.310
0.00
7 Minor Friction Loss
Fitting
K -value
#
EK VZ 2
90° Bends
0.90
1
0.00
45° Bends
0.42
2
0.00
Entrance Exits
1
2
0.00
8 Total Losses
0.00
1 Top Tank Elevation
2 Influent Pipe Invert Elevation
3 Weir Height
4 60 Degree V -Notch Weir Crest Elevation
5 Head over weir
6 Calculated Maximum Water Level
7 Calculated Free Board
8 Maximum Allowable Flow _
than 12
6 inch
50 feet
0.160 fps
6649 assume, turbulent
120
0.00 ft
0.00 ft
0.00 ft
0.00 ft
0.00 ft, insignificant ignore
736.33
736.33
ft
736.16
ft
0.643
0.643
ft
735.69
735.69
ft
0.24
0.38
ft
735.93
736.06
ft
4.81
3.20
in
0.310
MG
flows less than 0.07
1 Post Aeration Basin. Eff. Pipe Inv. Elevation 733.65 ft
2 Post Aeration Top Tank Elevation 735.82 ft, from survey
3 Outfall, Eff. Pipe Inv. Elevation 731.59 ft _
4 Based on previous calculations, losses through 6" dia. Effluent pipe is negligible.
Dewberry Engineers, Inc. Page 2 of 3
Prepared By: Michael Poulios, PE
Date: 8/18/2017
Rev 1.0

1 Diameter of pipe
3 inch
2 length of pipe
15 feet
3 Required Pumping Rate
_
56 gpm (Peak flow = ADF X 3.0
1
4 Estimated velocity (Q/A)
2.553 fps
5 Reynolds Number
106387 assume, turbulent
6 Hazen Williams Coefficient
120
7 Major Friction Loss
0.006 ft
i
8 Minor Friction Loss
Fitting
K -value
#
EK VZ 2
90° Bends
0.90
2
0.182 ft
Check Valve
2.30
0
0.000
Plug valve
0.2
0
0.000 ft
Entrance Exits
1
2
0.202 ft
1 9 Total Losses _
10 Define Static Head Conditions
a. Top Pump Discharge EI.
b. Min Water Level
c. Max Water Level
i 11 Total Dynamic Head at Max Water EI.
12 Total Dynamic Head at Min. Water EI.
Dewberry Engineers, Inc. Page 3 of 3
0.39 ft
741.56 ft
730.26 ft
737.26 ft
4.69 ft TDH
11.69 ft TDH
Prepared By: Michael Poulios, PE
Date: 8/18/2017
Rev 1.0