NC0024911_Authorization to Construct_20160617

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Metropolitan Sewerage District
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OF BUNCOMBE COUNTY, NORTH CAROLINA
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Mr.Ron Berry, Engineer June 17, 2016
Division of Water Resources/Complex Permitting
North Carolina Department of Environmental Quality
512 N.Salisbury Street
1617 Mail Service Center RECEIVEDINCDEQJNIR
Raleigh,NC 27699-1617 JUN 2 3 2016
Water Quality
Re: Authorization to Construct Application Permitting Section
Metropolitan Sewerage District of Buncombe County
NC0024911
Mr. Berry,
Thank you for your letter of June 10, 2016 regarding the above-referenced application.
The Metropolitan Sewerage District of Buncombe County (MSD) still believes that you have
inappropriately applied peaking factors which result in a drastic overestimation of potential peak
flows to be realized at the treatment facility.The resultant oversizing does not provide any
environmental benefit,adds millions of dollars to construction of the treatment system, and sets both
an unnecessary precedent that all future plant upgrades will likely have to be designed to meet.
Please find the attached memorandum from HDR engineers with actual performance data and
pertinent information conveying system dynamics.
As conveyed in my letter of May 31, 2016, MSD respectfully requests a meeting with you and your
supervisors along with our Engineer of Record and HDR Engineering at your earliest convenience.
Please respond with some dates and times that you may be available to speak on these important and
impactful matters.
Sincerely, cc
Gr �
Thomas E. Hartye,P.E., eneral Manager
Cc: Tom Belnick, NCDEQ
Jeff Poupart, NCDEQ
Jay Zimmerman, NCDEQ
Landon Davidson, NCDEQ Supervisor Regional Operations
Forrest Westall, McGill Associates
Erika Bailey, HDR Engineering
Brian Thorsvold, HDR Engineering
Protecting Our Natural Resources-
2028 Riverside Drive,Asheville,North Carolina 28804 Telephone:[phone] Website:www.msdbc.org

Memo
Date: Friday, June 17, 2016
Project: Metropolitan Sewerage District of Buncombe County (MSD) Plant Headworks Improvements
To: Tom Hartye, P.E., MSD
From: Erika L. Bailey, P.E., HDR RECEIVEDINCDEQIDWR
Subject: MSD WRF Peak Flow Evaluation JUN 2 3 2016
Water Quality
Permitting Section
HDR developed basis for design flows for the Metropolitan Sewerage District of Buncombe
County (MSD)'s Water Reclamation Facility (WRF) as part of the 2015 Facility Plan Update.
Table 1 summarizes projected wastewater flows at the maximum monthly average flow of 40
mgd, which serves as the basis for design for the MSD WRF fine screen and grit removal
improvements. The design flows were developed based on review of historical flow trends at
MSD WRF between 2008 and 2013 and utilized the historical flow trends to establish historical
peaking factors and project corresponding flows at 40 mgd maximum monthly average
permitted flow condition. The peak hourly flow design criterion is 80 mgd. The peak flow
design criteria is supported by flow trends observed at the plant and takes into account an
observed downward trend between peak hourly flow peaking factors and monthly average
flows, as described further in the summary bullets below.
Table 1: Summary of Wastewater Flows at 40 mgd permitted Capacity (Year 2042)
Parameter Average Max Month Peak Week Max Day Peak Hour
Annual
Flow (mgd) 25.4 40 65.0 75 80
HDR reviewed the North Carolina Department of Environmental Quality (DEQ), Division of
Water Resources' (DWR) proposed revised peak hourly peaking factor summarized in Ron
Berry's June 10, 2016 letter to the Metropolitan Sewerage District of Buncombe County (MSD).
The proposed revised peak hourly peaking factor equates to a 2.64 peak hourly/ maximum
monthly flow peaking factor at the monthly average permitted flow of 40 mgd. This results in a
peak hourly flow design criterion of 105.6 mgd, which we do not feel is appropriate for design.
Attached for reference is an updated effluent flow data summary evaluation for MSD WRF for
data between 2006 and 2015. Below is a summary of key points from the analysis:
• While we acknowledge that DWR's updated evaluation results in the reduction in the
peaking factor provided in DWR's initial letter dated May 27, 2016, we contend there is
strong justification for a lower peaking factor based on historical flow trends. Figure 1
compares historical daily average and maximum flows for MSD WRF to the DEQ
hdrinc.com 555 Fayetteville Street,Suite 900,Raleigh,NC 27601-3034
919.232.6600
1

suggested original and revised design peak hourly flows of 120 and 105.6 mgd
respectively which illustrates how much higher the suggested design peak hourly flow is
in comparison to observed maximum flows, even in 2013 when the maximum monthly
average flow reached 37.5 mgd. The peak flow design criterion of 80 mgd is supported
by flow trends observed at the plant between 2006 and 2015.
• The MSD WRF historical flow data illustrates a downward trend between peak hourly
flow peaking factors and monthly average flows(see Figure 2). The attached data
evaluation for the 2006 to 2015 data set is evidence that a 2.64 peak hourly flow/monthly
average peaking factor is not appropriate. Clearly, during wet weather periods, when
the highest monthly average flows have been observed, peak flow estimates using a
2.64 peaking factor results in an overestimation of the peak hourly flow when compared
to actual observations.
• It would be helpful to understand how DWR is arriving at the 2.2 max daily/monthly
average peaking factor. It is noted that in the two highest calendar monthly average
flows (35.1 mgd in 2004 and 37.5 mgd in 2013), the actual observed maximum
day/monthly average peaking factors during these months were 1.9 and 2.0.
• HDR has concerns with DWR's approach of applying a dry weather diurnal peaking
factor to the maximum day/monthly average peaking factor. Our concern is that applying
the dry weather diurnal peaking factor during a wet weather monthly average flow period
will result in an overly conservative estimate of the diurnal peak that would occur during
a wet weather period. For example, the highest observed daily flow was 74.6 mgd,which
occurred on July 4th, 2013;the reported maximum flow on this day was 78 mgd
according to the calendar year flow and slightly higher at 79 mgd based on the 15
minute SCADA data. The resulting peak hour/max day peaking factor for this day was
1.05 to 1.06 (so less than 1.15 for typical diurnal dry weather period).
• Utilization of the higher peaking factor results in design changes requiring hydraulic
modifications that provide no additional ability to pass expected peak flows. It is difficult
to envision how this higher flow will provide any overall benefit to either the operational
integrity of the WRF during high flows or the environment.
• Establishing a peak flow based on the higher peaking factor at this stage of MSD's
capital improvement program will have significant implications to cost of future facility
upgrades. MSD is engaged in a large upgrade program that will continue for several
years. The peak flow determination is critical to the design and cost of these
improvements.
HDR suggests meeting with the DWR to explain our analysis of this data and discuss
determining a peaking factor that satisfies the requirements of protecting water quality without
being overly conservative to the point of adding cost to this project without adding value in the
way of additional protections.
hdrinc.com 555 Fayetteville Street,Suite 900,Raleigh,NC 27601-3030
919.232.6600
2

Figure 1. MSD WRF Effluent Flow Summary
140
120
100 —Projected Max Flow Using Original Suggested DWR PF
—Projected Max Flow Using Revised DWR Suggested PF
a —Effluent Flow Max
Eao
—Effluent Flow
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2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016
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Figure 2. MSD WRF - 2006 to 2015 Peak Hour/MM Flow PF vs MM Flow
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MSD WRF Flow Data Evaluation Summary •
Historical Flow Data Analysis DEQ Suggested Calculations
Annual
Average Max Monthly Peak Calendar Max Max Day Flow Peak Hr During ;'ax Day/Calendar Pk Hrty Pea Calculated Hourly
Flow Flow(30-Day Hourly Max Day Monthly during Max Max Monthly ax Month Peak Dry Weather Pk Factor ' Peak at Max Monthly
Year (mgd) Rolling Avg) Flow Flow Flow Monthly Flow Flow Factor Hrty/Ave PF** Calculat'. Flow
(mgd) (mgd) (mgd) (mgd) (mgd) (mgd) (mgd) (mgd)
2006 19.2 22.9 60 51 22.2 51.0 60.0 2.30 1.15 2.65 58.7
2007 16.7 22.1 60 47.9 22.0 47.9 60.0 !. 2.18 1.15 2.51 ' 55.1
2008 15.8 19.5 60 40.2 19.3 33.1 60.0 2.09 1.15 2.40 '" 46.2
2009 19.1 26.6 70 66.25 26.3 57.4 60.0 2.52 1.15 2.89 76.2
2010 19.5 30.5 70 57.8 27.4 54.8 65.0 :.2.11 1.15 2.42 66.5
2011 18.3 22.8 63 56.8 22.3 49.8 63.0 ' 2.55 1.15 2.93 i, 65.3
2012 19.2 22.2 70 50.2 22.1 50.2 60.0 2.27 1.15 2.61 57.7
2013 24.6 37.9 78 74.6 37.5 74.6 78.01.99 1.15 2.29 85.8
2014 20.3 24.7 70 58.32 24.0 58.3 70.0 ;2.43 1.15 2.79 '< 67.1
2015 20.2 30.7 77 67.10 30.7 67.1 77.0 , 2.18 1.15 2.51 77.2
Averages 19.3 26.0 67.8 57.0 25.4 54.4 65.3 2.26 1.15 2.60 ". 65.6
At Design Flow 2.26 1.15 2.60 IIIIIIIIIIIIIIIIIIII
**Typical Dry Weather Diurnal PF based on hourly scada flow data during a dry weather period in 2009 and 2010;note that this is lower during wet-weather event
6/17/2016