WQ0039913_Report_20220523

Average Daily Flow Calculations
Stirrup Iron Creek Pump Station
Prepared For:
Durham County
May 2022
:
NC License #F-0102
ADF Calculations
May 2022│Draft
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This document, together with the concepts and designs presented herein, as an instrument of service, is
intended only for the specific purpose and client for which it was prepared. Reuse of and improper
reliance on this document without written authorization and adaptation by Kimley-Horn shall be without
liability to Kimley-Horn.
ADF Calculations
May 2022│Draft
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ABBREVIATIONS
ADF Average Daily Flow
ARV Air Release Valve
AVV Air Vacuum Valve
DIPS Ductile Iron Pipe Size
EPA Environmental Protection Agency
FEMA Federal Emergency Management Agency
GIS Geographic Information System
GPAD Gallons Per Acre Per Day
GPCD Gallons Per Capital Per Day
GPD Gallons Per Day
GPH Gallons Per Hour
GPM Gallons Per Minute
HDPE High Density Polyethylene
HGL Hydraulic Grade Line
HP Horsepower
I/I Inflow and Infiltration
KWH Killo-Watt Hours
LF Linear Feet
MDF Maximum Daily Flow
MFWWTP Mason Farms Wastewater Treatment Plant
MG Million Gallons
MGD Million Gallons Per Day
NCDEQ North Carolina Department of Environmental Quality
NFPA National Fire Protection Association
NPDES National Pollutant Discharge Elimination System
NSF National Sanitation Foundation
NWI National Wetlands Index
O&M Operation and Maintenance
OWASA Orange Water and Sewer Authority
OPCC Opinion of Probable Construction Costs
PHF Peak Hour Flow
PS Pump Station
PVC Polyvinyl Chloride
PWS Public Water System
SCADA Supervisory Control and Data Acquisition
SD-ADF Speed Distribution – Average Daily Flow
SF Square Feet
TDH Total Dynamic Head
USGS United States Geological Survey
VFD Variable Frequency Drive
WWTP Wastewater Treatment Plant
Δ Delta (Change)
ADF Calculations
May 2022│Draft
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1 ADF Flow Calculations
Introduction
1 INTRODUCTION
The Stirrup Iron Creek (SIC) Pump Station is anticipated to have significant growth in the near future and
has limited sewer capacity. The County is planning to build a new sewer pump station on Chin Page
Road that will intercept a portion of the flow tributary to Stirrup Iron Creek. This work will take some time
to complete, and developments are anticipated before the Chin Page Road Pump Station and associated
infrastructure can be constructed. As a result, Durham County retained the services of Kimley-Horn to
study the Stirrup Iron Creek Pump Station to determine its capacity and make recommendations for
increasing capacity. This document summarizes the process in which the existing dry weather ADF
(DWADF) was determined.
Stirrup Iron Creek Pump Station is located in Durham County on Page Road north of the I-40 and I-540
intersection, as shown on Figure 1.1 - Site Location Map. The SIC Pump Station and tributary sewer
shed is in the Stirrup Iron Creek drainage basin, which is part of the Neuse River basin. The SIC tributary
sewer shed is approximately 4,874 acres of largely industrial and residential land. The station delivers
flow to the Triangle Wastewater Treatment Plant in Durham County through a 9,900-LF, 18-inch DIP force
main that discharges into a manhole near the intersection of Hopson Road and Keystone Park Drive.
Figure 1.1 - Site Location Map
The station was constructed circa 1986, and the firm capacity is currently 6.5 MGD. The pump station is
a large, submersible sewage pump station with three existing pumps and both piping and MCCs for a
fourth pump. The wet well is 34.91 feet in diameter. Design operating points include 3,270 GPM at 160
Ft TDH. The pumps are 200 HP, 1750 RPM, 3-phase Yeomans submersible pumps.
2 ADF Flow Calculations
Dry Weather ADF Calculation
2 DRY WEATHER ADF CALCULATION
Verification of flows at the SIC Pump Station required a unique approach because there is no way to
directly measure the inflow or outflow of the station using existing, onsite instrumentation. The pumps
also operate on VFDs at a reduced speed the majority of the time. The SIC pump station has a magnetic
flow meter on the discharge header that does not provide accurate results, so it was ignored for purposes
of this study. There are reliable pump run time meters on each pump’s control circuits, however, the
pumps operate at a reduced speed. This made direct usage of the run time meters to calculate station
output impossible without a detailed analysis of the speeds. The only time the station operates at full
speed is when it is operated in hand, which is only done to confirm operation, or in extenuating
circumstances. The station operates this way intentionally to match flow into the station as much as
possible and to limit the pressure in the force main. Additionally, there is not a flow-based need to
operate the station at full speed under ADF conditions.
For this study, we utilized specialized data loggers, detailed pump performance tests, rainfall data, and
historical run-time data to approximate the ADF over a 12-month period. Each dataset is described
below.
1. Pump Performance Test Data – Pump performance data was obtained by KH on three different
dates utilizing Kimley-Horn’s proprietary Xak-Pack, a pump performance measurement tool.
Pump performance was measured on 7/22/2021, 4/13/2022, and 5/13/2022. A graphical
representation of this data can be found as Exhibit 1 – Pump and System Curves.
2. VFD Speed Data – This data was obtained by KH directly from each pump’s VFD output recorded
in Hertz (Hz) at 22 second intervals from 4/13/2022 to 5/12/2022 (29 days). This data is very high
resolution and recorded to the one hundredth of a Hz precision with similar accuracy. A graph of
this data can be found in Exhibit 2 – VFD Speed Data.
3. Daily Run-Time Data – This data was provided by the County and collected by their SCADA
system from 12/1/2022 to 5/13/2022 (166 days). This data includes the number of pump cycles
and the hours of pump run time for each pump. This data is included in Exhibit 3 – Run-Time
Data.
4. 12-Month Weekly Run-Time Data – This data was provided by the County based on operator logs
spanning from 4/5/2021 to 5/3/2022 (393 days). This data includes the hours of run time for each
pump. This data is in included in Exhibit 3 – Run-Time Data.
5. NOAA Rainfall Data – This data was obtained from the USGS website on daily intervals for the
period of 4/5/2022 to 5/3/2022. This data includes the number of inches of rain measured at the
Third Creek Woodcroft Parkway NR Blands Rain Gauge approximately 5.81 miles from the SIC
Pump Station Basin. This data in included in Exhibit 3 – Run Time Data.
Dry Weather ADF Calculation Method
The general procedure for calculating the DWADF is listed below in the general sequence each step was
completed.
1. Define Pressurized System Hydraulics –A verified system curve was developed (see Exhibit 1 –
Pump and System Curves) based on field testing under multiple hydraulic conditions and
measured pump performance. The system curve was developed based on a wide range of flows
to ensure it fully represents the operating characteristics of the force main. The pump
performance was measured on multiple occasions and under various speeds to determine the
output throughout each pump’s operating range.
3 ADF Flow Calculations
Dry Weather ADF Calculation
2. Monitor Speed –Data loggers were installed to monitor speed directly from the VFDs. Once the
data was collected, KH analyzed it to determine the system response to diurnal curves. Based
on the speed data, this system runs very predictably and responds very uniformly to dry weather
flows. This was the anticipated outcome due to the fixed control levels and VFD PID loop
algorithm.Figure 2.1 - Pump Speed Distribution shows the percent of time each pump runs at
each speed. As shown, the pumps are usually off or running at very low speed.
Figure 2.1 - Pump Speed Distribution
3. Affinity Curves – Pump reduced-speed affinity curves were calculated for both pumps at 1 Hz
intervals and verified through field testing for 50, 55, and 60 Hz.Exhibit 1 – Pump and System
Curves shows the output of the pumps at various speeds. The lower limit of pump operation is
45 Hz and could not be verified at the time of testing due of the high inflow at that time of day.
4. Calculate Total Flow – The VFD speed data was utilized in conjunction with the affinity curves to
calculate the instantaneous flow rates for each speed data point and the total volume pumped
over that period. Most of the speed data included fractional speeds which required straight line
interpolation between the one Hz affinity curves shown on Exhibit 1 – Pump and System
Curves. The flows were totaled for each day and for the 29-day monitoring period.
5. Define Dry Weather – By reviewing the system’s response to rain events, it was determined that
rainfall events less than 0.3 inches had little to no influence on the system for that period of time
in our data. As seen in Exhibit 5 – Pump Testing One Month Summary, any rain events
exceeding 0.3 inches were considered wet weather events and were not included in the DWADF.
0%
10%
20%
30%
40%
50%
60%
70%60-5859-5858-5757-5656-5555-5454-5353-5252-5151-5050-4949-4848-4747-4646-4545-4444-4343-42%0f1-MonthRunTimeSpeed (Hz)
P1 P2
4 ADF Flow Calculations
Dry Weather ADF Calculation
6. Establish DWADF to Run-Time Ratio – A ratio was established to correlate the run-time readings
to dry weather flows during the one month of VFD speed data. This ratio describes the control
systems response to the DWADF. The average DWADF to Run-Time ratio was calculated to be
15.29 Hours per MGD.
7. Calculate the 6-Month ADF – The 6-month ADF was calculated using the run-time ratio. A
summary of both the one-month and six-month data sets is provided in Table 2.1 - ADF
Summary.
Parameter Units One-Month VFD Speed
Data
Six-Month Daily RT
Data
Total ADF MGD 1.185 1.15
Maximum ADF MGD 1.473 1.53
Minimum ADF MGD 0.986 0.83
Avg DW Run Time Hrs 17.78 17.48
Dry Weather ADF MGD 1.163 1.14
Table 2.1 - ADF Summary
5 ADF Flow Calculations
Conclusion
3 CONCLUSION
The DWADF is 1.14 MGD for the last six months. See Exhibit 4 – Dry Weather Average Daily flows for
a graphical representation of all DWADF calculations. Considering this flow calculation method is not a
direct measurement, there is some error involved in the calculations. Accordingly, we are recommending
adding a 5% buffer to account for error. Adding 5% to the One-Month ADF results in an ADF of 1.197
MGD.
The SIC Pump Station Wet Well is 34.91-Ft in diameter resulting in a very large amount of storage
relative to the inflow rate. Between the pump off and the invert in there is approximately 80,000 gallons
or 1.62 hours of storage before the system begins to surcharge. As a result, there is ample peaking
factor and storage to account for any short-term spikes in flow.
Exhibit 1
Pump and System Curves
59
5755
53
51
49
47
45
0
20
40
60
80
100
120
140
160
180
200
220
240
010020030040050060070080090010001100120013001400150016001700180019002000210022002300240025002600270028002900300031003200330034003500360037003800Head(Ft)Flow (GPM)
60 Hz 59 58 57 56 55
54 53 52 51 50 49
48 47 46 45 System Curve
Exhibit 2
VFD Speed Data
40
42
44
46
48
50
52
54
56
58
60
4/9/220:004/14/220:004/19/220:004/24/220:004/29/220:005/4/220:005/9/220:005/14/220:00Speed(Hz)Pump 1 Pump 2
Exhibit - 3
Run Time Data
0
0.5
1
1.5
2
2.5
3
0
5
10
15
20
25
30
2/23/2021 4/14/2021 6/3/2021 7/23/2021 9/11/2021 10/31/2021 12/20/2021 2/8/2022 3/30/2022 5/19/2022 7/8/2022 Rainfall(in./day)RunTime(hrs.)1 Month Run Time 6 Month Run Time 12 Month Run Time 12 Month Rainfall
Exhibit - 4
Dry Weather Average Daily Flows
0
0.5
1
1.5
2
2.5
3
0.00
0.25
0.50
0.75
1.00
1.25
1.50
11/20/2021 12/10/2021 12/30/2021 1/19/2022 2/8/2022 2/28/2022 3/20/2022 4/9/2022 4/29/2022 5/19/2022 6/8/2022 Rainfall(in./day)ADF(MGD)1 Month Dry Weather ADF 6 Month Dry Weather ADF Rainfall
Exhibit - 5
Pump Testing One Month Summary
Date Pump 1 Pump 2 ADF Runtime Dry ADF/RT Ratio Rainfall Summary Values
MGD MGD MGD Hours Inches 1.185
4/13/2022 0.000 0.271 0.272 5.08 18.72 0 1.473
4/14/2022 0.896 0.281 1.177 18.53 15.75 0 0.986
4/15/2022 0.864 0.335 1.199 17.99 15.00 0 1.163
4/16/2022 0.844 0.331 1.175 17.47 14.86 0 17.78
4/17/2022 0.602 0.554 1.157 18.07 15.62 0 15.29 Dry Weather ADF/RT Ratio
4/18/2022 0.195 1.278 1.473 19.20 13.03 1.29
4/19/2022 1.145 0.232 1.377 19.43 14.11 0
4/20/2022 0.919 0.346 1.264 18.88 14.93 0.1
4/21/2022 0.704 0.282 0.986 13.48 13.67 0
4/22/2022 0.680 0.444 1.124 18.27 16.26 0
4/23/2022 0.796 0.392 1.188 17.04 14.35 0
4/24/2022 0.877 0.284 1.161 18.17 15.66 0
4/25/2022 0.964 0.237 1.201 18.99 15.82 0
4/26/2022 0.962 0.185 1.147 18.53 16.15 0.23
4/27/2022 0.678 0.526 1.204 17.94 14.90 0.01
4/28/2022 0.703 0.421 1.124 18.06 16.06 0
4/29/2022 0.584 0.531 1.115 17.45 15.64 0
4/30/2022 0.759 0.453 1.212 15.81 13.04 0
5/1/2022 0.535 0.622 1.158 17.47 15.09 0.13
5/2/2022 0.979 0.258 1.237 18.93 15.30 0.01
5/3/2022 0.959 0.178 1.138 19.54 17.18 0
5/4/2022 0.675 0.480 1.155 17.69 15.31 0
5/5/2022 0.866 0.312 1.178 18.43 15.65 0
5/6/2022 0.930 0.290 1.220 18.79 15.39 0.2
5/7/2022 0.786 0.444 1.230 16.95 13.79 0.58
5/8/2022 0.770 0.408 1.178 17.00 14.43 0
5/9/2022 0.937 0.238 1.175 18.50 15.75 0 *Excludes start and end dates
5/10/2022 0.631 0.500 1.131 17.35 15.34 0
5/11/2022 0.822 0.350 1.172 17.37 14.82 0
5/12/2022 0.412 0.523 0.935 13.95 14.92 0.07
ADF
Max ADF
Min ADF*
Dry Weather ADF
Included in Dry ADF/RT ratio
Data collection/set-up days
Avg. Dry Weather Run Time (RT)