December 2003 

03/12/WQPC-WWF 

EPA/600/R-04/035 

Environmental Technology

Verification Report 

Wet Weather Flow Monitoring 

Equipment 

ADS Environmental Model 3600 

Open Channel Flow Monitor 

Part II – Field Test Results 

Prepared by 

NSF International 

Under a Cooperative Agreement with 

U.S. Environmental Protection Agency 
THE ENVIRONMENTAL TECHNOLOGY VERIFICATION 

PROGRAM 

U.S. Environmental NSF International 

Protection Agency 

ETV Joint Verification Statement 

TECHNOLOGY TYPE: AREA/VELOCITY FLOW METERS 

APPLICATION: FLOW METERING IN SMALL- AND MEDIUM-SIZED 

(10- to 42-inch) SEWERS 

TECHNOLOGY NAME: ADS ENVIRONMENTAL SERVICES MODEL 3600 OPEN 

CHANNEL FLOW METER 

TEST LOCATION: QUEBEC CITY, QUEBEC, CANADA, AND LOGAN, UTAH 

COMPANY: ADS ENVIRONMENTAL SERVICES 

ADDRESS: 5030 BRADFORD DRIVE PHONE: (800) 633-7246 

BUILDING 1, SUITE 210 FAX: (256) 430-6633 

HUNTSVILLE, AL 35805 

WEB SITE: http:\\www.adsenv.com 

EMAIL: info@adsenv.com 

NSF International (NSF) manages the Water Quality Protection Center (WQPC) under the U.S. 

Environmental Protection Agency’s (EPA) Environmental Technology Verification (ETV) Program. 

NSF evaluated the performance of the Model 3600 Open Channel Flow Meter manufactured by ADS 

Environmental Services. Utah Water Research Laboratory (UWRL) in Logan, Utah, and BPR of Quebec 

City, Canada, both NSF-qualified testing organizations, performed the laboratory and field verification 

testing, respectively. 

EPA created the ETV Program to facilitate the deployment of innovative or improved environmental 

technologies through performance verification and dissemination of information. The goal of the ETV 

program is to further environmental protection by accelerating the acceptance and use of improved and 

cost-effective technologies. ETV seeks to achieve this goal by providing high-quality, peer-reviewed data 

on technology performance to those involved in the design, distribution, permitting, purchase, and use of 

environmental technologies. 

ETV works in partnership with recognized standards and testing organizations; stakeholder groups 

consisting of buyers, vendor organizations, and permitters; and with the full participation of individual 

technology developers. The program evaluates the performance of innovative technologies by developing 

test plans that are responsive to the needs of stakeholders, conducting field or laboratory tests (as 

appropriate), collecting and analyzing data, and preparing peer reviewed reports. All evaluations are 

conducted in accordance with rigorous quality assurance protocols to ensure that data of known and 

adequate quality are generated, and that the results are defensible. 

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VS-i 
TECHNOLOGY DESCRIPTION 

The following technology description is provided by the vendor and does not represent verified 

information. 

Area/velocity flow meters are commonly used in wastewater collection, storm sewer, and combined 

sewer systems. The ADS 3600 flow meter utilizes a quad-redundant ultrasonic sensor that measures the 

time required for an ultrasonic pulse to travel from the sensor face to the surface of the water and back to 

the sensor. The meter converts the travel time to distance by calculating the speed of sound through air 

and adjusting for temperature, which is measured by two sensors inside the ultrasonic sensor head. The 

depth of the flow is then calculated using the pipe diameter and the range measured by the ultrasonic 

sensor. A pressure-depth sensor is also installed at the bottom of the pipe to measure surcharge levels and 

to provide a redundant depth reading when used with the ultrasonic level sensor. Doppler velocity 

measurements are made by transmitting an ultrasonic signal upstream using a submerged velocity sensor 

and measuring the frequency shift in the sound waves reflected by the moving particles in the water. The 

depth and velocity sensor readings are stored in the flow meter’s memory until the data can be 

downloaded to a computer through either a voice-grade telephone line or a cellular network. The 

computer software calculates flow rates using the depth and velocity readings. 

The ADS 3600 flow meter system includes the flow meter unit, sensors, and installation hardware. The 

flow meter unit is housed in a waterproof, marine-grade aluminum housing. The submersible pressure 

sensor, ultrasonic level sensor, and velocity sensor are attached to a circular stainless steel band installed 

around the inner circumference of the sewer pipe. Waterproof cables with sealed connectors convey 

power and signals between the flow meter unit and the sensors. The system is battery-powered, and can 

power the unit for about one year at a standard 15-minute measurement interval. The unit is intrinsically 

safe. According to vendor claims, after the unit is installed, minimal operation and maintenance (O&M) 

or unit calibration is required; the most common O&M procedure is cleaning the sensors. 

VERIFICATION TESTING DESCRIPTION 

Laboratory Test Site 

The laboratory testing was completed at the Utah Water Research Laboratory (UWRL), at Utah State 

University in Logan, Utah. The flow meter was installed in three nominal pipe sizes: 10-inch, 20-inch, 

and 42-inch. The straight lengths were sized so they were at least 40 times the pipe diameter for the 10- 

and 20-inch pipes and at least 22 times for the 42-inch pipes. Pipe slopes were adjustable to allow the 

flow meter to be evaluated under different slope conditions. Sluice gates at both ends of the pipes were 

used to regulate appropriate flow, head, and obstruction during testing. Reference devices were directly 

traceable to the National Institute of Standards and Technology (NIST), and were regularly calibrated. 

Uncertainty for the reference devices was less than 0.25 percent. 

Field Test Site 

Field verification testing was conducted in a section of the Quebec Urban Community’s sewer network, 

located in the City of Sainte-Foy, Quebec, Canada. The ADS flow meter and reference meters were 

installed in a 41.7-inch diameter interceptor pipe, near the downstream end of a straight run of pipe that 

had a mean slope of 0.169 percent. The reference devices, which consisted of a bubbler for reference level 

measurement, a reference flow monitor, and an Accusonic 4-path flow monitor, were installed 

downstream of the ADS flow meter. Upstream and downstream sluice gates were used to create the 

required flow conditions. 

Validation of the reference flow monitor and bubbler were performed by lithium tracer dye tests. Flow 

rates under the upstream and downstream gates were calculated using standard hydraulic equations for a 

redundant check of flow data. 

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Methods and Procedures 

Laboratory evaluation of the flow meters consisted of collecting depth, velocity, and flow data from the 

ADS meter and comparing it to the depth, velocity, and flow data from the reference devices. These tests 

were performed under normal operating conditions of uniform flow, backwater flow, full pipe (manhole 

surcharged), and simulated silt. Water transmission through the pipes, as a ratio of flow depth versus the 

pipe diameter (d/D), ranged from 10 to 250 percent (surcharged conditions). Tests were also performed 

under the abnormal operating conditions of reverse flow and grease accumulation. 

Field evaluation of the ADS flow meter at the Quebec site consisted of a general evaluation of the flow 

meter (Test A) and the performance of the meter under varying flow conditions. Testing consisted of 

collecting depth, velocity, and flow data at regular time intervals and comparing the data to the 

corresponding depth, velocity, and flow data from the reference devices. Four test scenarios were used: 

1. Test B—accuracy under low weather flow (approximately 1.71 million gallons per day [MGD]), with 

back-flow conditions; 

2. Test C—accuracy under wet weather flow (1.71–29.7 MGD), without back-flow conditions; 

3. Test D—accuracy under wet weather flow (1.71–29.7 MGD), with back flow-conditions; and, 

4. Test E—accuracy under short-term (26-day) continuous operation, with various flow rates. 

Three conditions were identified during testing that created an unintended challenge to the ADS flow 

meter: 

1. The water used in the testing at UWRL did not contain the particulate concentrations of normal 

sewage, so small quantities of coffee creamer were added to the water on some test runs. The 

operating principle utilized by the ADS flow meter requires particles in the water to serve as 

reflectors for sound waves. The vendor maintained that the coffee creamer additive provided a level 

of reflectivity, but the particulate concentration in the test water did not approach that of sewage and 

could be a source of measurement error. 

2. During each field test, a portion of the ADS flow meter data collected at one-minute intervals was not 

recorded. ADS personnel indicated that this happened because the flow meter was configured for 

maximum error checking and sensor refiring. They further indicate that the ADS 3600 flow meter can 

be reconfigured to collect data at one-minute intervals by reducing the level of real-time error 

checking. 

3. The field testing results include data in which it appears that standing waves and troughs were present 

beneath the ADS 3600 flow meter’s ultrasonic depth sensor. During portions of the testing, the depth 

sensor was likely affected by standing waves and troughs up to +5 inches. The ADS flow meter 

measures depth with a downward-looking, narrow-beam ultrasonic sensor mounted on the top of the 

pipe, so depth measurements would be susceptible to influence by waves. Based on a review of the 

field data, it appears that waves were most prevalent at higher depths and flow rates. 

No editing was allowed on the metered data during field or laboratory testing. In actual applications, the 

flow monitoring service provider may implement post-monitoring quality control measures to attempt to 

improve the accuracy of final data. According to ADS, the company typically bundles flow meter sales 

with post-monitoring quality control and reporting services. 

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VS-iii 
VERIFICATION OF PERFORMANCE 

System Operation 

The testing organizations found the equipment durable and easy to use, and that it required minimal 

maintenance. The flow meter operation and data retrieval software programs were easy to learn. The 

ultrasonic sensors and stainless steel band did not promote accumulation of debris during testing. 

Laboratory Testing Results 

The mean deviations and the 95-percent confidence intervals under normal operating conditions (i.e., all 

test conditions except grease tests and reverse flow) are presented in Table 1. The width of the 95-percent 

confidence interval is a function of the variation in instrument deviation, and the number of test runs in 

each reported category. Categories with a fewer number of runs show wider confidence intervals. The 

calculations exclude “abnormal condition” tests, where grease was applied to the sensors or where 

reverse-flow conditions were created. The mean deviation for the abnormal operating conditions was 1.9 

percent for the 0.5-mm grease tests, -100.0 percent for the 2.0-mm grease tests, and –72.7 percent for the 

reverse-flow tests. 

Table 1. Deviation and 95-Percent Confidence Interval by Test Configuration for Lab Testing 

Deviation 95-percent 

Pipe size (inches) (percent) confidence interval 

10 2.8 0.2 – 5.4 

20 7.2 2.4 – 12.0 

42 1.6 -1.8 – 5.0 

Pipe slope (percent) 

0.1 4.9 -1.4 – 11.2 

0.2 1.6 -1.8 – 5.0 

0.5 5.6 1.6 – 9.6 

1.25 4.2 -1.6 – 9.9 

2.0 6.1 -3.8 – 16.1 

 Percent full (d/D, percent) 

10 3.6 -9.4 – 16.6 

30 11.1 6.5 – 15.7 

50 3.4 0.2 – 6.7 

80 1.3 -3.1 – 5.6 

150 0.9 0.9 – 2.8 

250 4.8 -5.0 – 14.6 

Condition 

Free-flow 2.6 -1.4 – 6.7 

Back-flow 5.8 2.9 – 8.7 

All conditions 4.5 2.1 – 6.9 

The overall accuracy of the ADS flow meter under normal operating conditions is shown in Figure 1. The 

meter deviation is segregated into two components—bias and precision. Overall bias was 1.6 percent, as 

calculated by the slope of the best-fit line. Precision, as calculated with the correlation coefficient (r2), 

was 0.45 percent. 

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VS-iv 
Figure 1. Laboratory metered flow rate versus reference. 

Field Testing Results 

Table 2 summarizes the field testing results in two categories: mean deviation and trimmed mean 

deviation. The mean deviation is the arithmetic mean of all of the one-minute–interval data. The trimmed 

mean deviation is calculated by eliminating values greater than ±99 percent, making it less susceptible to 

skewing from large outliers, such as those produced when the ADS flow meter recorded zero velocity. 

Table 2. Deviation from Reference Flow: Tests B, C, and D 

Mean deviation Trimmed mean deviation 

Flow regime (percent) (percent) 

Test B -29.7 2.4 

Test C 5.0 5.0 

Test D -1.0 4.7 

Test B-D combined -5.7 2.1 

Simulated low flow -7.6 12.2 

Simulated high flow -4.3 -4.1 

Combined flows -5.7 2.1 

Analysis of the data collected during Test B (low flow) revealed that the deviation was –100 percent in 

nearly one-third of the samples. This occurred most frequently during back-flow conditions when the 

ADS 3600 recorded zero velocity and calculated zero flow. The data collected during Tests C and D 

showed a much lower occurrence of data with deviations exceeding ±99 percent. 

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Test E (not included in Table 2) evaluated the performance of the flow meter over an extended (26-day) 

time period. Generally, the data collected during Test E closely correlated with the reference flow monitor 

data. Spikes were noted in water level measurements collected toward the end of the test, which may have 

been the result of accumulated condensation on the ultrasonic depth probe. No debris accumulation was 

observed on the equipment, and, aside from a thin film of grease on the probes, the equipment was in 

good condition and did not require maintenance. 

QUALITY ASSURANCE/QUALITY CONTROL 

A complete description of the quality assurance/quality control procedures and findings are included in 

the verification reports. Calibration records were maintained by the testing organizations and validation of 

the reference flow devices fell within control limits. NSF completed a data quality audit of at least 10 

percent of the test data to ensure that the reported data represented the data generated during testing. 

Audits of the field and laboratory testing were conducted by NSF with no significant issues noted. 

Original Signed by Original Signed by 

Lee A. Mulkey March 31, 2004 Gordon Bellen April 26, 2004 

Lee A. Mulkey Date Gordon Bellen Date 

Acting Director Vice President 

National Risk Management Laboratory Research 

Office of Research and Development NSF International 

United States Environmental Protection Agency 

NOTICE: Verifications are based on an evaluation of technology performance under specific, 

predetermined criteria and the appropriate quality assurance procedures. EPA and NSF make no expressed 

or implied warranties as to the performance of the technology, and do not certify that a technology will 

always operate as verified. The end user is solely responsible for complying with any and all applicable 

federal, state, and local requirements. Mention of corporate names, trade names, or commercial products 

does not constitute endorsement or recommendation for use of specific products. This report is not an NSF 

Certification of the specific product mentioned herein. 

Availability of Supporting Documents 

Copies of the Draft 4.0 – Generic Verification Protocol, Flow Monitors for Wet Weather Flows 

Applications in Small- and Medium-Sized Sewers, September, 2000, the verification statement, and 

the verification report (NSF Report #03/12/WQPC-WWF) are available from: 

ETV Water Quality Protection Center Program Manager (order hard copy) 

 NSF International 

 P.O. Box 130140 

Ann Arbor, Michigan 48113-0140 

NSF web site: http://www.nsf.org/etv (electronic copy) 

EPA web site: http://www.epa.gov/etv (electronic copy) 

(NOTE: Appendices are not included in the verification report. Appendices are available upon 

request from NSF.) 

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VS-vi 
Environmental Technology Verification Report 

WET WEATHER FLOW MONITORING EQUIPMENT VERIFICATION 

ADS ENVIRONMENTAL MODEL 3600 

OPEN CHANNEL FLOW MONITOR 

PART II: FIELD TEST RESULTS 

QUEBEC URBAN COMMUNITY TEST SITE 

Prepared for: 

NSF International 

Ann Arbor, Michigan 

Prepared by: 

BPR 

Quebec City, Quebec, Canada 

December 2003 

Under a cooperative agreement with the U.S. Environmental Protection Agency 

Raymond Frederick, Project Officer 

National Risk Management Research Laboratory 

U.S. Environmental Protection Agency 

Edison, NJ 08837 
Notice 

The U.S. Environmental Protection Agency (EPA) through its Office of Research and 

Development has financially supported and collaborated with NSF International (NSF) under a 

cooperative agreement. This verification effort was supported by the Water Quality Protection 

Center operating under the Environmental Technology Verification (ETV) Program. This 

document has been peer reviewed and reviewed by NSF and EPA and recommended for public 

release. 

i 
Foreword 

The following is the final report on an Environmental Technology Verification (ETV) test 

performed for NSF International (NSF) and the United States Environmental Protection Agency 

(EPA) by BPR-CSO, in cooperation with ADS Environmental Services for the Model 3600 Open 

Channel Flow Monitor. The test protocol for flow monitors requires both laboratory and field 

testing. The final report for this verification is divided into two parts to address both portions of 

testing. 

This part of the report (Part II) describes the testing and summarizes the data from the field 

testing. Part I: Laboratory Test Results, describes the testing and summarizes the data of the 

laboratory testing. Both parts of the report are available on the NSF and EPA websites. 

The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the 

Nation’s land, air, and water resources. Under a mandate of national environmental laws, the 

Agency strives to formulate and implement actions leading to a compatible balance between 

human activities and the ability of natural systems to support and nurture life. To meet this 

mandate, EPA’s research program is providing data and technical support for solving 

environmental problems today and building a science knowledge base necessary to manage our 

ecological resources wisely, understand how pollutants affect our health, and prevent or reduce 

environmental risks in the future. 

The National Risk Management Research Laboratory (NRMRL) is the Agency’s center for 

investigation of technological and management approaches for preventing and reducing risks 

from pollution that threaten human health and the environment. The focus of the Laboratory’s 

research program is on methods and their cost-effectiveness for prevention and control of 

pollution to air, land, water, and subsurface resources; protection of water quality in public water 

systems; remediation of contaminated sites, sediments and ground water; prevention and control 

of indoor air pollution; and restoration of ecosystems. NRMRL collaborates with both public and 

private sector partners to foster technologies that reduce the cost of compliance and to anticipate 

emerging problems. NRMRL’s research provides solutions to environmental problems by: 

developing and promoting technologies that protect and improve the environment; advancing 

scientific and engineering information to support regulatory and policy decisions; and providing 

the technical support and information transfer to ensure implementation of environmental 

regulations and strategies at the national, state, and community levels. 

This publication has been produced as part of the Laboratory’s strategic long-term research plan. 

It is published and made available by EPA’s Office of Research and Development to assist the 

user community and to link researchers with their clients. 

ii 
Contents 

Verification Statement ...............................................................................................................VS-i 

Notice............................................................................................................................................... i 

Foreword......................................................................................................................................... ii 

Contents .........................................................................................................................................iii 

Tables............................................................................................................................................. vi 

Figures............................................................................................................................................ vi 

Acronyms and Abbreviations ....................................................................................................... vii 

Chapter 4 Field Report.................................................................................................................... 1 

4.1 Description of Test Site ...................................................................................................... 1 

4.1.1 Test Site Infrastructure Description............................................................................ 1 

4.1.2 Pipe Configuration...................................................................................................... 4

4.1.3 Waves in the Test Pipe................................................................................................ 6 

4.2 Description of Test Equipment ......................................................................................... 11 

4.2.1 Downstream Gate Site .............................................................................................. 11 

4.2.1.1 ADS 3600 Flow Meter.......................................................................................... 11 

4.2.1.2 Transit-Time Reference Flow Meter .................................................................... 13 

4.2.1.3 Reference Flow Meter Bubbler............................................................................. 13 

4.2.1.4 Ultrasonic Reference Level Meter........................................................................ 13 

4.2.1.5 Downstream Gate.................................................................................................. 14 

4.2.2 Upstream Gate Site ................................................................................................... 14 

4.2.2.1 Electrical Control Room ....................................................................................... 14 

4.2.2.2 Upstream Gate ...................................................................................................... 14 

4.3 Description of Reference Methods ................................................................................... 15 

4.3.1 Reference Depth Measurements ............................................................................... 15 

4.3.1.1 Manual Depth Measurement................................................................................. 15 

4.3.1.2 Reference Depth Meters ....................................................................................... 15 

4.3.2 Reference Velocity Measurements ........................................................................... 16 

4.3.2.1 Reference Velocity Computed from Tracer Dilution ........................................... 16 

4.3.2.2 Reference Velocity Meter..................................................................................... 16 

4.3.3 Reference Flow Measurement .................................................................................. 16 

4.3.3.1 Tracer Dilution Method ........................................................................................ 16 

4.3.3.1.1 At the Injection Site ........................................................................................ 17 

4.3.3.1.2 At the Sampling Site ....................................................................................... 19 

4.3.3.2 Reference Flow Meter........................................................................................... 19 

4.3.3.2.1 Flow Under the Gate....................................................................................... 19 

4.3.3.2.2 Upstream Gate ................................................................................................ 20 

4.3.3.2.3 Downstream Gate............................................................................................ 20 

4.4 Experimental Procedures .................................................................................................. 20

4.4.1 General Evaluation (Test A: Flow Meter Software)................................................ 21 

4.4.1.1 Procedures............................................................................................................. 21 

4.4.1.2 Measurements ....................................................................................................... 21 

4.4.2 Performance Evaluation............................................................................................ 22 

4.4.2.1 Test B: Accuracy under Dry Weather Flow with Back-Flow Conditions............ 22 

4.4.2.1.1 Procedures....................................................................................................... 22 

iii 
4.4.2.1.2 Measurements ................................................................................................. 23 

4.4.2.2 Test C: Accuracy Under Wet Weather Flow Without Back Flow Conditions.... 23 

4.4.2.2.1 Procedure ........................................................................................................ 23 

4.4.2.2.2 Measurements ................................................................................................. 25 

4.4.2.3 Test D: Accuracy Under Wet weather flow With Back flow Conditions............ 25 

4.4.2.3.1 Procedure ........................................................................................................ 25 

4.4.2.3.2 Measurements ................................................................................................. 26 

4.4.2.4 Test E: Accuracy Under Short-Term Continuous Operation................................ 26 

4.4.2.4.1 Procedures....................................................................................................... 26 

4.4.2.4.2 Measurements ................................................................................................. 27 

4.5 ADS 3600 Evaluation Results .......................................................................................... 27 

4.5.1 Software Evaluation.................................................................................................. 27 

4.5.2 Performance Tests..................................................................................................... 29 

4.5.2.1 Scatter Plots .......................................................................................................... 30 

4.5.2.2 Deviation Distribution Plots ................................................................................. 33 

4.5.2.2.1 Test B.............................................................................................................. 38 

4.5.2.2.2 Test C.............................................................................................................. 40 

4.5.2.2.3 Test D.............................................................................................................. 44 

4.5.2.2.4 Test E .............................................................................................................. 46 

4.5.2.3 General Verification Tests .................................................................................... 49 

4.5.2.3.1 Installation, Configuration, and Calibration ................................................... 49 

4.5.2.3.2 Operation......................................................................................................... 51 

4.5.2.3.3 Time for Data Retrieval .................................................................................. 52 

4.5.2.3.4 Dismantling..................................................................................................... 52 

4.5.2.3.5 General Characteristics of the ADS 3600....................................................... 52 

4.6 Reference Meters .............................................................................................................. 53 

4.6.1 Scatter Plots .............................................................................................................. 53 

4.6.2 Deviation Distribution Plots ..................................................................................... 54 

4.6.2.1 Tests B, C, and D .................................................................................................. 55 

Chapter 5 Quality Assurance/Quality Control.............................................................................. 57 

5.1 Audits................................................................................................................................ 57 

5.1.1 Field Audits............................................................................................................... 58 

5.1.2 Report Audit.............................................................................................................. 59 

5.2 Validation of the Lithium Tracer Methods ....................................................................... 61 

5.2.1 Sample and Data Handling ....................................................................................... 62 

5.2.2 Methods Used to Validate Lithium Concentrations.................................................. 62 

5.2.2.1 Concentrated Samples........................................................................................... 62 

5.2.2.2 Blank and Diluted Samples................................................................................... 63 

5.2.3 Validation Results for Test C0.................................................................................. 65 

5.2.4 Validation Results for Test C3.................................................................................. 66 

5.2.5 Conclusion ................................................................................................................ 68 

5.3 Validation of the Reference Flow Meter .......................................................................... 68 

5.3.1 Validation Methods................................................................................................... 68 

5.3.1.1 Qualitative Analysis.............................................................................................. 68 

5.3.1.2 Statistical Analysis................................................................................................ 69 

5.3.1.3 Reference Flow Deviation Distribution Analysis................................................. 69 

iv 
5.3.2 Test C0 Results ......................................................................................................... 70 

5.3.2.1 Qualitative Analysis.............................................................................................. 70 

5.3.2.2 Statistical Analysis................................................................................................ 70 

5.3.2.3 Reference Flow Deviation Distribution................................................................ 71 

5.3.3 Test C3 Results ......................................................................................................... 71 

5.3.3.1 Qualitative Analysis.............................................................................................. 71 

5.3.3.2 Statistical Analysis................................................................................................ 72 

5.3.3.3 Reference Flow Deviation Distribution................................................................ 72 

5.3.4 Test B and D Results................................................................................................. 73 

5.3.5 Conclusion ................................................................................................................ 73 

5.4 Validation of the Reference Depth Meter (Bubbler) ........................................................ 74 

5.4.1 Validation Methods................................................................................................... 74 

5.4.1.1 Qualitative Analysis.............................................................................................. 74 

5.4.1.2 Statistical Analysis................................................................................................ 74 

5.4.1.3 Reference Depth Deviation Distribution .............................................................. 74 

5.4.2 Test B Results ........................................................................................................... 75 

5.4.2.1 Qualitative Analysis.............................................................................................. 75 

5.4.2.2 Statistical Analysis................................................................................................ 76 

5.4.2.3 Reference Depth Deviation Distribution Analysis ............................................... 76 

5.4.3 Test C Results ........................................................................................................... 76 

5.4.3.1 Qualitative Analysis.............................................................................................. 76 

5.4.3.2 Statistical Analysis................................................................................................ 77 

5.4.3.3 Reference Depth Deviation Distribution Analysis ............................................... 77 

5.4.4 Test D Results........................................................................................................... 77 

5.4.4.1 Qualitative Analysis.............................................................................................. 77 

5.4.4.2 Statistical Analysis................................................................................................ 78 

5.4.4.3 Reference Depth Deviation Distribution Analysis ............................................... 78 

5.4.5 Tests B, C, and D Combined .................................................................................... 78 

5.4.5.1 Qualitative Analysis.............................................................................................. 78 

5.4.5.2 Reference Depth Deviation Distribution Analysis ............................................... 78 

5.4.6 Conclusion ................................................................................................................ 78 

Appendices.................................................................................................................................... 80 

A Complementary Test Site and Reference Meters Information................................................. 80 

B Experiment Procedures ............................................................................................................ 80 

C Detailed Experimentation Results............................................................................................ 80 

D Quality Assurance Project Plan: Complementary Information................................................ 80 

E Field Verification: Reports Generated during Tests................................................................. 80 

F ADS 3600 Flow Meter: Configuration..................................................................................... 80 

G ADS 3600 Flow Meter Software Functionality/Flexibility Summary..................................... 80 

H Flow Test Data Figure Summaries........................................................................................... 80

Glossary ........................................................................................................................................ 81 

v 
Tables 

Table 4-1. Flow Meter Verification Test Overview ..........................................................................21 

Table 4-2. Personal Computers Used in Flow Meter Software Evaluation.......................................22 

Table 4-3. Deviation from Reference Flow—Tests B, C, and D.......................................................30 

Table 4-4. Flow Rate Comparison of Data Point Samples for the Three Replicas of Test B............39 

Table 4-5. Water Level Comparison of Data Point Samples for Three Replicas of Test B ..............40 

Table 4-6. Flow Rate Comparison of Data Point Samples for Three Replicas of Test C .................42 

Table 4-7. Water Level Comparison of Data Point Samples for Three Replicas of Test C ..............43 

Table 4-8. Flow Rate Comparison of Data Point Samples for Three Replicas of Test D .................45 

Table 4-9. Water Level Comparison of Data Point Samples for Three Replicas of Test D..............46 

Table 4-10. Daily Manual Level Measurement – ADS 3600 ............................................................47 

Table 4-11. Time Estimate Required to Install, Operate and Service Flow Meter............................50 

Table 5-1. Concentrated Samples Validation Chart ..........................................................................63 

Table 5-2. Validation Chart for the Blank and Diluted Samples.......................................................65 

Table 5-3. Validation Chart for Test C0 ............................................................................................66 

Table 5-4. Validation Chart for Test C3 ............................................................................................67 

Figures 

Figure 4-1. Test site plan view...........................................................................................................2 

Figure 4-3. Test site profile view of downstream gate site................................................................4 

Figure 4-4. Test site pipe invert profile. ............................................................................................5 

Figure 4-5. Pipe joint conditions in test system.................................................................................6 

Figure 4-6. Waves in test pipe. ..........................................................................................................7 

Figure 4-7. Scatter-plot showing possible standing wave and trough influence. ..............................9 

Figure 4-8. Flow graph with possible wave and trough influences shown........................................10 

Figure 4-9. Tri-nodal nature of deviation pattern is consistent with presence of waves. ..................10 

Figure 4-10. General view of the downstream test site. ....................................................................11 

Figure 4-11. ADS 3600 flow meter components...............................................................................12 

Figure 4-12. ADS 3600 flow meter installed in pipe.........................................................................12 

Figure 4-13. Reference flow devices installed in the test pipe. .........................................................13 

Figure 4-14. Upstream gate site arrangements. .................................................................................14 

Figure 4-15. Tracer injection diagram. ..............................................................................................17 

Figure 4-16. Lithium injection system...............................................................................................18 

Figure 4-17. Blank sample collection. ...............................................................................................19 

Figure 4-18. ADS 3600 system behavior, Test C. .............................................................................31 

Figure 4-19. Reference meter system behavior. ................................................................................32

Figure 4-20. ADS 3600 flow vs. reference flow, Tests B, C and D. .................................................33 

Figure 4-21. Flow deviation distribution—Test B.............................................................................34 

Figure 4-22. Flow deviation distribution—Test C.............................................................................35 

Figure 4-23. Flow deviation distribution—Test D. ...........................................................................36 

Figure 4-24. Flow deviation distribution—Tests B, C and D............................................................37 

Figure 4-25. Flow deviation distribution—simulated low flow conditions.......................................37 

Figure 4-26. Flow deviation distribution—simulated wet flow conditions.......................................38 

vi 
Acronyms and Abbreviations 

ADS ADS Environmental Services, a division of ADS Corporation 

avg Average 

BPR BPR, Quebec, Canada 

cfs Cubic feet per second 

CSO Combined sewer overflow 

EPA United States Environmental Protection Agency 

ETV Environmental Technology Verification 

ft Foot or feet 

gpm Gallons per minute 

in. Inch 

kPa Kilopascal 

Lb Pound 

LCQ Laboratoire de l’environnement LCQ Inc. 

TO testing organization 

mA milliamps 

MGD Million gallons per day 

mg/L Milligrams per liter 

m Meter 

mm Millimeter 

NIST National Institute of Standards and Technology 

NSF NSF International (formerly National Sanitation Foundation) 

PC Personal computer 

PLC Programmable logic controller 

psi Pounds per square inch 

QA Quality assurance 

QAPP Quality Assurance Project Plan 

QUC Quebec Urban Community 

SD Standard deviation 

sec Second 

TO Testing organization 

UWRL Utah Water Research Laboratory 

VTP Verification test plan 

WWF Wet Weather Flow 

WWTP Wastewater treatment plant 

vii 
Chapter 4

Field Report 

4.1 Description of Test Site 

The test site for the field testing component of the verification of the ADS Model 3600 Open 

Channel Flow Monitor (ADS Model 3600) was a section of the Quebec Urban Community’s 

(QUC) sewer network. The site is located in the City of Sainte-Foy, along the east side of the 

Chaudière Blvd, approximately between the Bombardier and Mendel Streets. Figures 4-1(a) 

through 4-1(c) present a schematic layout of the complete test site and Figure 4-2 presents details 

about the portion of the sewer where the ADS Model 3600 was installed and tested. 

4.1.1 Test Site Infrastructure Description 

The test site was defined on the upstream side (north) by the Versant-Sud tunnel, which was 

controlled at its downstream end by a regulation chamber (Station #100) equipped with a sluice 

gate. This gate was referred as the “upstream gate” of the test site. The sluice gate was used to 

control the flow under the gate and the volume of wastewater in the Versant-Sud tunnel when 

performing tests under high flows. A retention volume of 2.9 million gallons (11,000 m3) was 

available from this 96-inch (in.) (2,466 millimeters [mm]) nominal diameter tunnel. 

The test site was defined on the downstream side (south) by the west junction chamber 

(Station #80A), which was the last chamber before the effluent tunnel that leads to QUC’s West 

Wastewater Treatment Plant (WWTP). The test site’s “downstream gate” was located just 

upstream of the west junction chamber. 

As shown in Figures 4-1(a) to (c), the test site was an interceptor pipe 41.7 in. (1,059 mm) in 

diameter. There was approximately 3,620 feet (ft) (1,103 meters (m)) between the downstream 

gate near which the ADS flow meter was installed and the upstream gate where the flow was 

controlled. The interceptor pipe between manholes S-1 to S-2 is 279.1 ft (85.1 m) long on an 

average slope of 0.169 percent. The pipe between manholes S-2 and S-3 is 559.9 ft (170.7 m) 

long on an average slope of 0.181 percent. The pipe changes direction by 20 degrees at the S-2 

manhole and by 15 degrees at the S-1 manhole. Downstream from the S-1 manhole, the pipe 

sloped 10.6 percent over a distance of 82 ft (25 m) before reaching Station #80A. 

As shown in Figure 4-1(b), the Craig Collector coming from the southeast joined the interceptor 

pipe at manhole S-5B, approximately 1,968 ft (600 m) upstream of manhole S-1. Manhole S-5B 

was the injection site for the lithium dilution tests. The last section of pipe of the Craig Collector 

had a 36 in. (910 mm) nominal diameter and was 421 ft (128.4 m) long, with an average slope of 

0.417 percent. The Craig Collector was a small pseudo-sanitary uncontrolled flow collector, in 

which a bubbler level meter was installed 8.6 ft (2.6 m) upstream of manhole S-5B. The 

electrical panel for this instrument is located nearby on Chaudière Boulevard and the 

measurements were transmitted to Station #100 by a radio link to take into account the 

uncontrolled flow in the upstream flow management. 

1 
(a) 

(b) 

Figure 4-1. Test site plan view. 

2 
(c) 

Figure 4.1 (cont’d). Test site plan view. 

As shown on Figure 4-2, the reference bubbler and ultrasonic level meters were installed 4.0 ft 

(1.24 m) and 7.52 ft (2.30 m) upstream of the S-1 manhole, respectively, and the reference flow 

meter was installed in a pipe section from 5.4 ft (1.65 m) to 9.2 ft (2.80 m) upstream of the S-1 

manhole. This manhole is made of concrete with a nominal diameter of 6.8 ft (2.1 m). It was 

covered with a concrete roof with two circular 28.5-in. (724-mm) diameter access covers. One 

access was downstream from the control gate. The other access was just upstream and was 

equipped with a trap to facilitate the access to the sewer for meter installation and operation. 

3 
Figure 4-2. Test site profile view of downstream gate site. 

There was an electrical room adjacent to the west junction chamber where the transmitters of the 

reference flow meter and the reference bubbler level meter were located. The transmitter for the 

reference ultrasonic level meter was hung in manhole S-1. This manhole was also the sampling 

site for the lithium dilution tests and was the nearest access to the flow meters under test, the 

reference meters, and the downstream gate. 

Construction of the main interceptor pipe was completed around 1991, with the remainder of the 

site constructed between November 1998 and June 2000. The newest parts of the system are the 

control gate downstream from manhole S-1 and the ultrasonic level meter at the reference flow 

meter site. 

4.1.2 Pipe Configuration 

The normal flow condition in the interceptor pipe was free surface flow. Neither accumulation of 

solids nor surface foam was observed in the pipe. The flow delay between the test site’s 

upstream and downstream control gates was 12 to 15 minutes. Figure 4-3 shows the profile of 

the last 13 pipe sections. All sections were 8 ft (2.44 m) long, except the last section, which was 

3.7 ft (1.15 m) long. A survey of the invert pipe profile was performed with a 100 ft (30.5 m) 

long by 0.5 in. (13 mm) diameter water hose and rulers graduated every 0.039 in. (1 mm). This 

method provided an accuracy of approximately ±0.079 in. (±2 mm). As in all sewers, the slope 

4 
of every pipe section was slightly different. Four major elements had a hydraulic impact on the 

test site: 

• There was a 2.2 in. (55 mm) bump at the end of the last pipe section due to an excess of 

concrete at the bottom of manhole S-1. The consequence of this bump, although not the 

purpose, was that the lowest path of the reference flow meter was always submerged. 

• The last pipe section had a negative slope of approximately 1.2 in. (31 mm). 

• The coupling of the last two pipe sections was not very good and the last pipe has a 

negative elevation of approximately 0.55 in. (14 mm). 

• The large cross-section of the downstream manhole S-1 and its sluice gate could create 

slower wastewater velocity and an upstream surge. The impact of these elements was 

reduced since the velocity increased in the manhole due to the steep slope (10.6 percent) 

in the downstream pipe. 

Figure 4-3. Test site pipe invert profile. 

The difference in elevation between the invert elevation at the ADS 3600 testing site and at the 

reference level meter (bubbler) was approximately +1.97 in. (50.0 mm). Since there is a slope of 

-3.97 in. (-101 mm) between the invert at the bubbler and the bump described earlier, the back 

flow caused by the bump had a hydraulic impact up to approximately 23 ft (7 m) upstream of the 

ADS 3600 testing site. For this reason, the hydraulic profile was not exactly the same at the 

5 
reference meters location and at the ADS 3600 location. The water level was lower and the 

velocity was higher at the ADS 3600 location than at the reference meters location. 

No back flow could occur downstream of the downstream gate, because the maximum level over 

the overflow weir in the downstream west junction chamber is approximately 20 in. (500 mm) 

under the invert of manhole S-1. When required during a test, it was possible to create back-flow 

conditions by closing the test site’s downstream gate. The water level could then be raised up to 

14 in. (350 mm) over the crown of the pipe at the reference level meter location. 

4.1.3 Waves in the Test Pipe 

Waves in sewer pipes are common, and result from a variety of different factors (Figure 4.4). 

Waves are commonly caused by the roughness of the pipe walls, poor coupling of the pipe 

sections, or surge caused by a change of direction, slope, cross-section or velocity. Because of 

these waves, the measurement of the water level in sewers is not easy, even for a technician 

measuring with a ruler. The following were some of the conditions that make level 

measurements difficult: 

• High flows (sometimes present on this test site); 

• High energy slopes (sometimes present on this test site); 

• Location near a change of direction (not significant on this test site); 

• Location near a change of slope (present at some places on this test site); 

• When pipe couplings are not very good, resulting in open junctions, steps, uncoupled 

junctions, etc. (present at some places on this test site). 

Opening of 1 

inch (25 mm) 

that can create 

waves. 

Pipe 

junction 

completely 

closed. 

(a) Open joint. (b) Closed joint. 

Figure 4-4. Pipe joint conditions in test system. 

There were different sizes and kinds of waves on the water surface. Depending on the water level 

and flow rate, waves have different behaviors. Three kinds of waves were observed at the test 

site (surface disturbances caused by surges are considered waves): 

6 
1. Short, local dynamic waves: Small waves with lengths of 1 to 3 in. (25 to 75 mm) that 

created small ripples in all directions on the water surface, as on any river or lake. These 

waves were present everywhere. Their amplitude, approximately 0.5 to 1 in. (13 to 

25 mm), is a function of the flow rate and water level (Figure 4-5). They were visual 

signs of surface turbulence. 

2. Short, local standing waves: Small waves with lengths 3 to 6 in. (75 to 150 mm) that 

stood at a specific location on the water surface, without moving forward or upward. 

Their amplitude, approximately 1 to 3 in. (25 to 75 mm), was also a function of the flow 

rate and water level. These waves were rare (two or less per pipe section) and were 

mostly asymmetric in the pipe (Figure 4-5). They were visual signs of surge. At the test 

site, the negative slope, the downstream manhole, or the reference flow meter probes 

could have caused short local standing waves. 

3. Long, standing waves: Long waves with lengths of several feet. Their number and 

amplitude (>2 in. [>50 mm]) were a function of the flow rate, water level and wave 

length. Most of these waves were symmetric in the pipe. 

Small ripples 

Standing wave 

Figure 4-5. Waves in test pipe. 

On June 27, 2001 ADS reviewed data recorded during a high-flow trial the previous day and 

noticed a large and unexpected aberration in the depth-velocity flow relationship in the pipe. 

Analysis in the field conducted by ADS suggested that a hydraulic jump or large waves were the 

7 
likely cause of the aberration. Both BPR and NSF were notified of the concern and a request was 

made to re-run the high-flow trial to verify if large waves were present. 

The high-flow trial was re-run and an ADS field person with a camera was suspended over the 

flow at the access manhole. Figure 4-5 was taken during the high-flow trial and it captures an 

asymmetrical standing wave in the reference meter section just upstream of the access manhole. 

Although not visible in Figure 4-5, the photographer reported seeing several similar waves 

farther upstream. 

Area and velocity flow meters are designed to function in sewers with uniform flow conditions 

such that depth and velocity are constant as flow passes through the metering area. The ADS 

flow meter measures depth with a downward-looking, narrow beam ultrasonic sensor installed 

on top of the pipe. Based on this configuration, it was expected that depth measurements were 

more susceptible to influence by waves. Local wave peaks and troughs would affect the depth 

measurement by the narrow-beam depth sensor when they occurred immediately below the 

sensor. Therefore an important consideration in selecting a site in which an area and velocity 

flow meter is to be installed is to identify a location where the adverse effects of standing waves 

are minimized or eliminated. 

Determining if standing waves were present at the ADS meter location was difficult without 

visual confirmation of the waves. During high flow conditions, it was extremely difficult to 

safely access the test site to make a visual determination of the presence of standing waves. 

Based on the specific characteristics of the test pipe and the photographic documentation of the 

standing wave, there exists the potential for standing waves under certain flow conditions in the 

test pipe area. 

If there was a standing wave below the flow meter’s ultrasonic depth sensor and the flow meter 

was working properly, the depth readings would be influenced by the presence of the wave. A 

comparison of the flow meter data with the reference data would show a larger than normal 

deviation between the flow meter depth readings and the reference depth readings. 

Figure 4-6 presents a scatter plot of the velocity deviation (the difference in velocity readings 

between the test and reference meters) versus depth deviation (the difference in depth readings 

between the test and reference meters). These observations are for the period June 28 through 

July 4, though the apparent wave conditions were observed throughout the testing period. Three 

distinct clusters of observations were apparent. The clustering suggests that for certain flow 

conditions the difference in velocities are relatively constant (2 ft/sec) while the difference in 

depth changes up to 5 in. (-3 to -8 in.). This clustering was repeatable throughout the test, which 

suggests the effect was due to standing waves. The cluster of data points on the right side of the 

plot appears to be generated when wave peaks influenced the depth measurement, while the 

cluster of data points on the left side of the plot appears to be generated when wave troughs 

influenced the depth measurement. 

8 
Low depths relative to 

reference at +2 fps. High depths relative to 

reference at +2 fps. 

Figure 4-6. Scatter-plot showing possible standing wave and trough influence. 

The presence of local wave peaks under the depth sensor would result in incorrectly high 

measurements and correspondingly high flow rate calculations. Conversely, the presence of a 

local trough under the depth sensor would result in incorrectly low depth measurements and low 

flow rate calculations. Figure 4-7 shows that deviations from reference flow rates appear to 

correlate with the influence of waves. 

Consistent with the protocol for this field test, accuracy for each of the several flow conditions is 

reported as a single value. The reader should be aware that this single value might contain large 

deviations resulting from waves. Figure 4-8 displays the deviation distribution of data from June 

28 to July 4 and the tri-modal nature of the error pattern is apparent. The bars clustered to the 

right of the center cluster represent data under the influence of wave peaks, while the cluster of 

bars left of the center cluster represent data under the influence of wave troughs. Together the 

waves appear to widen the range of deviation. Because of the uncertainty associated with these 

conditions, ADS recommends against installing flow meters in locations with large standing 

waves. 

9 
Figure 4-7. Flow graph with possible wave and trough influences shown. 

Wave 

Wave Peaks

Troughs 

Figure 4-8. Tri-nodal nature of deviation pattern is consistent with presence of waves. 

10 
4.2 Description of Test Equipment 

4.2.1 Downstream Gate Site 

The downstream gate site was the primary site for the verification of the flow meters. The 

ADS 3600 and the reference meters were installed at this site. This is also where the level of 

back flow was controlled using the downstream gate, where the diluted tracer samples were 

collected and the manual level readings taken. Figure 4-9 shows the downstream gate site during 

a tracer dilution test, while one technician was taking manual level readings and another was 

collecting diluted samples. 

Sluice gate 

hand wheel 

Gate displacement 

Manual level measurement Sewer access 

tape 

Figure 4-9. General view of the downstream test site. 

4.2.1.1 ADS 3600 Flow Meter 

As shown in Figure 4-2, the ADS 3600 flow meter was installed 24.1 ft (7.4 m) upstream of 

manhole S-1. The flow meter is composed of a transmitter and a pressure level probe, an 

ultrasonic level probe, and a velocity probe, as shown in Figure 4-10. All probes were preinstalled on a stainless steel band, which was installed in the sewer using a bender that extends 

the diameter of the band to squeeze it on the pipe wall, as shown in Figure 4-11. The transmitter 

was hung on the ladder in the manhole. The submersible pressure probe was at the bottom of the 

pipe and the velocity probe was close to it, slightly off-center. Wires for the submerged probes 

were attached using tie-wraps on the downstream side of the stainless steel band. The probes 

were small and had a good hydrodynamic profile, causing no discernable disturbance to the flow 

pattern. The bender did not accumulate debris, since it was pressed on the pipe wall. 

11 
ADS 3600 

transmitter 

Submersible 

pressure probe 

Velocity probe 

Ultrasonic 

level probe 

Stainless steel band Bender

Figure 4-10. ADS 3600 flow meter components. 

Figure 4-11. ADS 3600 flow meter installed in pipe. 

12 
4.2.1.2 Transit-Time Reference Flow Meter 

The reference flow meter transducers (probes) were installed in a pipe section from 5.4 ft 

(1.65 m) to 9.2 ft (2.80 m) upstream of manhole S-1 (Figure 4-12(a)). The transmitter was 

located in the electrical room of Station #80A approximately 130 ft (40 m) from manhole S-1. 

The reference bubbler level meter described in Section 4.2.1.3 provided the level measurement 

necessary to calculate the flow rate. A description of the operating principle for the reference 

flow meter is provided in Appendix A, along with details of its configuration and installation 

drawings. 

4.2.1.3 Reference Flow Meter Bubbler 

The injection pipe for the bubbler level meter was located 16.1 in. (410 mm) downstream from 

the reference flow meter transducers described in Section 4.2.1.2. To avoid a venturi effect due 

to high velocities at the outlet of the injection pipe, a deflector plate was installed at the end of 

the pipe, as shown in Figure 4-12. This instrument transmitted the water level measurements via 

the local programmable logic controller (PLC) to the reference flow meter. A periodic, 100 

pound per square inch (psi) air purge lasting three seconds was automatically triggered to keep 

the end of the pipe clear. Specifications for the bubbler system are included in Appendix A. 

Second path, 

13” over the 

invert 

First path 

submerged, 4” 

over the invert 

Reference 

ultrasonic 

level probe 

ADS 3600 

flow meter 

Deflector 

installed over 

the outlet of the 

bubbler tube 

Bubble injection tube 

Reference 

flow meter 

probe 

(a) Reference flow meter. (b) Bubbler installation. 

Figure 4-12. Reference flow devices installed in the test pipe. 

4.2.1.4 Ultrasonic Reference Level Meter 

This meter provided redundancy of the level measurement of the reference bubbler level meter. 

The meter’s probe was located in the 42 in. pipe, 7.52 ft (2.3 m) upstream of manhole S-1, above 

all the paths of the reference flow meter. Mounted on the crown of the pipe, the probe had an 

intrinsic dead band of approximately two in. (50.8 mm), allowing the meter to measure from 

approximately 0 to 40 in. The transmitter was hung in manhole S-1. Additional information 

about the meter is provided in Appendix A. 

13 
4.2.1.5 Downstream Gate 

Manhole S-1 is equipped with a manual sluice gate to control the water level in the pipe where 

the reference flow meter and the ADS 3600 flow meter were installed. The gate could be closed 

to create back-flow conditions in the upstream pipe, but the pipe would return to free surface 

flow when the gate was fully opened (Figure 4-2). The manual actuator for the gate permitted 

vertical movement of one inch (25 mm) for four turns of crankshaft. The vertical displacement of 

the downstream gate was measured manually using a fixed aluminum ruler graduated every 

1/16 in. (2 mm). The ruler was attached vertically to the top of the gate and passed through the 

roof of the chamber in a standard floor valve box. The displacement was measured using a fixed 

point on the side of the floor valve box. 

4.2.2 Upstream Gate Site 

4.2.2.1 Electrical Control Room 

The tests were directed from the electrical control room of the upstream gate. The technician at 

that site logged all information and measurements taken during the test into the computer (Figure 

4-13(a). The technician at the upstream gate site was in continuous telephone communication 

with the technician at the downstream gate and used radio communication with the technician at 

the injection site during tracer dilution. 

Gate opening 

measurement 

ruler 

Reading on the 

ruler at the top 

of the screw rod 

Radio 

Laptop with 

the test report 

spreadsheet 

Telephone 

and 

headset 

(a) Test operator entering data. (b) Upstream gate actuator. 

Figure 4-13. Upstream gate site arrangements. 

4.2.2.2 Upstream Gate 

The upstream control gate at Station #100 permitted water retention in the Versant-Sud tunnel to 

control flows during rainfall events. It was used during the tests to simulate of a wide range of 

flow conditions. When fully closed, only flow from the Craig Collector would remain in the pipe 

at the flow meter location. 

14 
The gate was equipped with an electrical actuator, but most gate movements were done with the 

hand wheel (Figure 4-13(b)). Flow control was made using a mathematical model of the flow 

under the gate that used the downstream bubbler level meter reading, the average value of the 

two upstream ultrasonic level meter readings, and the gate opening reading made directly on a 

ruler on the gate actuator. 

4.3 Description of Reference Methods 

Area-velocity flow meters have two measurable components, depth and velocity, which are 

evaluated independently. Reference measurements were required to evaluate the accuracy of 

depth and velocity readings from the flow meter under test. The flow rates for the flows under 

the upstream and downstream gates were also used to verify the accuracy of the reference flow 

meter. A reference instrument that recorded depth, velocity, or flow in the same interval as the 

ADS meter was preferred over manual measurements, since the test and reference data sets were 

then comparable in size. 

4.3.1 Reference Depth Measurements 

4.3.1.1 Manual Depth Measurement 

Manual measurements of the water depth were made using a standard Solinst level meter tape 

with a stainless steel probe at the location specified in Figure 4-2. The probe was modified to 

ensure that both contacts touched the water surface at the same time to avoid dragging the tape, 

which would result in a higher water level reading. A metallic tape, graduated in millimeters, 

was attached to the plastic tape since plastic bends more easily than metal. 

During the challenge tests (tests B, C, and D), three manual measurements were taken at the site 

of the reference depth meter, roughly every five minutes. The first measurement was taken 30 

seconds before the target time, the second 15 seconds before the target time, and the third at the 

target time. During the passive test (test E), five consecutive manual measurements were made 

on most weekdays at 60-second intervals. 

4.3.1.2 Reference Depth Meters 

Two reference instruments were used to record depths. The bubbler on the Accusonic meter was 

the primary reference meter. The secondary depth meter was the ultrasonic depth meter. Depth 

readings from the ADS Model 3600 were compared with depth measurements obtained from the 

Accusonic bubbler. The ultrasonic depth meter and the manual depth readings provided 

calibration data for the bubbler. Depth measurements from both instruments were logged at oneminute intervals, whereas manual readings were taken approximately every five minutes during 

challenge tests. The reference depth meters were calibrated prior to initiation of the verification 

testing to ensure their accuracy. 

15 
4.3.2 Reference Velocity Measurements 

4.3.2.1 Reference Velocity Computed from Tracer Dilution 

Whenever possible, reference velocities were compared to calculated velocities based on the 

tracer dilution flow rates and on the flow sections computed from the bubbler depth readings. 

4.3.2.2 Reference Velocity Meter 

The reference flow meter used during verification was a 4-path Accusonic flow meter. Because 

this instrument did not provide the average velocity on the modbus signal (a serial link to output 

data), reference velocities were computed from the reference flow rates divided by the flow 

sections. The flow sections were computed from the bubbler depth readings. To demonstrate 

their accuracy and the fact that they exhibit no bias, the reference flow meter and depth meter 

were tested prior to ADS verification testing. 

4.3.3 Reference Flow Measurement 

Three reference flow measurement methods were used for testing and evaluation of the test data: 

1. Tracer dilution was used during two of the three replicas of Test C. 

2. A reference flow meter (Accusonic) was used continuously for all tests. 

3. The flow rate under the downstream gate was calculated during tests B and D, when 

back-flow conditions were present, and the flow rate under the upstream gate was 

calculated during tests C0 and C3 (to verify accuracy of reference meters). 

4.3.3.1 Tracer Dilution Method 

Tracer dilutions performed during the verification were based on the guidelines presented in the 

protocol. The major elements were: 

• Due to the variation in suspended solids concentrations in combined sewers, lithium 

chloride was used for the tracer dilution tests. 

• For two of the replicates of Test C, tracer dilution was performed to verify the accuracy 

of the reference meter. The first tracer dilution was done before the first replicate and the 

second was performed during the third replicate, near the end of the challenge tests. 

• No dilution was performed on the day before a non-working day to ensure faster analysis 

of samples. Samples were brought to the laboratories at the end of the day. Samples from 

the dilution performed Sunday, July 15, 2001 were put in a cooler with ice packs and 

brought to the laboratories the following morning. 

• Samples were analyzed for lithium content by an accredited laboratory in accordance 

with Method SM-3111B, from Standard Methods for the Examination of Water and 

Wastewater (American Public Health and Association, 20th Edition, 1998) and MA 200-

Method 1.0, from Quebec Environment Ministry–Laboratory Expertise Center. 

16 
• To increase the accuracy of the analysis of the concentrated samples, each sample was 

analyzed five times by the laboratories (five separate dilutions) and the laboratories 

provided the results for each analysis. 

While laboratories may have good in-house accuracy and low variability results (±3 percent for 

diluted samples and ±2 percent for averaged concentrated samples), deviations of more than ±10 

percent between laboratories may occur. This is not a problem as long as the difference for both 

laboratories remains constant considering the calculation of the tracer dilution flow rate. 

4.3.3.1.1 At the Injection Site 

A leveled table with the flow injection control system was installed at the injection site. The flow 

injection control system consisted of two cylinders for flow injection control, two metering 

pumps and a set of pipes and valves (Figures 4-14 and 4-15). The cylinders were used one at a 

time, with one in use while the other was refilled and prepared for the next flow injection 

control. Three quarters of a cylinder was injected over a period of 15 minutes, then the technician 

switched to the other cylinder. One metering pump was used, with the second being available in 

case of failure. Specifications of the equipment used in the injection control system are provided 

in Appendix A. 

Craig collector 

Tracer injection line 

S-5A Manhole 

S-5B Manhole 

Metering pumps 

TRACER INJECTION SET UP DIAGRAM

 (no scale) 

Continuous flow 

measurement 

Cylinders and valves 

Boulevard Chaudière interceptor 

Water sampling point 

(without tracer) Outside control 

panel with 110 

volts available 

S-5C Manhole 

Flow direction 

105 gallons tracer 

solution tank with 

mixer High concentration 

tracer samples 

A 

B 

Injection point 

8' inside of pipe 

Figure 4-14. Tracer injection diagram. 

17 
Metering pump 

Control cylinder 

Volume control 

ruler 

(a) Lithium injection control system. 

Lithium 

tank 

agitator 

Lithium 

transfer 

pump 

Lithium 

injection 

point – 8 ft 

in the pipe 

Debris 

(b) Mobile unit. (c) Injection point inside pipe. 

Figure 4-15. Lithium injection system. 

The tank containing the concentrated lithium solution was located in the injection mobile unit. 

The solution was prepared a few days before the test and agitated continuously during the test 

(Figure 4-15(b)). The concentrated lithium was injected eight feet (2.4 m) downstream of 

manhole S-5B through a 0.5 in. (13 mm) diameter pipe installed along the crown of the pipe 

(Figure 4-15(c)). The injection pipe had a counter-pressure foot valve to minimize the variation 

in the injection flow rate under surcharge flow conditions. 

18 
Blank samples were collected every 30 minutes, with one additional blank collected at the end of 

the test. A sample of the concentrated lithium solution was taken every two hours, and at the end 

of the test. The concentrated samples were collected with the peristaltic pump from the automatic 

water sampler used to refill the cylinders. Blank samples were taken using a sampling rod 

(Figure 4-16) on which the bottles were installed. After sampling, preprinted labels were applied 

to the bottles. 

Sampling rod 

Watertight bag 

to avoid bottle 

contamination 

Figure 4-16. Blank sample collection. 

4.3.3.1.2 At the Sampling Site 

Diluted samples were taken every five minutes at the downstream gate sampling site. Samples 

were placed into the cooler in a plastic bag to separate them from the blanks and concentrated 

samples that were collected at the injection site. 

4.3.3.2 Reference Flow Meter 

Reference flow measurements were logged at one-minute intervals. 

4.3.3.2.1 Flow Under the Gate 

The flow rates under the upstream and downstream gates were calculated from a standard 

hydraulic equation and were used as a redundant method to verify the accuracy of the reference 

meter. The calculation depended on depths upstream and downstream of the gate and the height 

of the gate opening. The downstream gate was never submerged because of a steep slope, so the 

depth downstream of the gate was not required for the computation. The following two sections 

describe particularities of the application for both gates. 

19 
4.3.3.2.2 Upstream Gate 

The flow rate under the upstream gate was calculated for tests C0 and C3, to provide an 

estimation of the flow rate measurement at the downstream gate. Graphs showing the flow rate 

measurements for these tests are included in Appendix H. The calculation depends on the 

upstream and downstream depths, the gate opening, the flow rate of the Craig Collector, and the 

transit time from the upstream gate to the downstream gate. An estimation of the flow rate at the 

downstream gate was computed by delaying the summation of the flow rate at the upstream gate 

and the flow rate of the Craig Collector by 15 minutes because of the distance between the gates. 

The flow rate of the Craig Collector was generally inconsequential and therefore not measured. 

The dry weather flow rate curve was used as the flow rate control during active tests. Based on 

the observations made during these last tests, the precision on this flow rate is estimated to ±0.23 

MGD (±10 L/sec). 

The equation of the flow rate under the upstream gate was calibrated for this site during the 

installation of the real-time control system of the QUC. The methods used for these 

measurements are discussed in Section 4.2.1. 

4.3.3.2.3 Downstream Gate 

The downstream gate was used to create back flow conditions in the section of pipe used for the 

verification testing. Prior to the testing, preliminary calculations were completed by the TO to 

estimate the approximate gate positions needed to achieve different back flow conditions in the 

pipe. Because there is a steep slope downstream of the gate, the calculation depends only on the 

upstream depth and the gate opening. 

4.4 Experimental Procedures 

This section describes the tests conducted as part of the flow meter verification. The tests can be 

classified as either general evaluations or performance evaluations, and are summarized in 

Table 4-1. The general evaluation of the flow meter included: 

• Software evaluation (Test A); 

• Ease of operation and maintenance (Test E); 

• Potential for debris accumulation (Test E); and 

• Data retrieval (Test E). 

The performance evaluation for accuracy of depth and velocity measurements and accuracy of 

the flow calculation included tests: 

• Under a controlled range of flow conditions (Tests B, C, and D); 

• During simulated rainfall events (Tests C and D); and 

• Under short-term continuous operation (Test E). 

20 
Test F, operation and maintenance under extended operations, was not performed, as noted in the 

verification test plan (VTP). 

Table 4-1. Flow Meter Verification Test Overview 

Evaluation Test Objectives General Performance 

Flow meter software User-friendliness, functionality, and 

flexibility A -

Accuracy under dry Accuracy of depth and velocity measurements 

weather flow with and accuracy of the flow calculation under - B 

back-flow conditions controlled range of flow conditions 

Accuracy under wet Accuracy of depth and velocity measurements 

weather flow and accuracy of the flow calculation under - C 

controlled range of flow conditions 

Accuracy under wet Accuracy of depth and velocity measurements 

weather flow with and accuracy of the flow calculation under - D 

back-flow conditions controlled range of flow conditions 

Accuracy under - Ease of operation and maintenance 

short-term - Potential for debris accumulation 

continuous operation - Data retrieval E E 

- Accuracy of the flow calculation under 

controlled range of flow conditions 

4.4.1 General Evaluation (Test A: Flow Meter Software) 

The objective of this test was to evaluate the software provided by the flow meter manufacturer 

for user-friendliness, functionality, innovation and compatibility. 

4.4.1.1 Procedures 

This was a qualitative evaluation, parts of which were performed in the field during 

configuration, calibration and data collection. Other parts were completed in the TO’s office 

after the flow meter was removed from the sewer. 

The two flow meter software programs were installed on a PC provided by the testing 

organization and on a PC provided by ADS. The specifications for the PCs used for this 

evaluation are included in Table 4-2. 

4.4.1.2 Measurements 

All of the elements that the vendor had indicated were available at the beginning of the 

verification were tested. The elements were rated as “possible” or “not possible,” according to 

21 
the ability of the flow meter software to process them. Relevant comments concerning the 

evaluated elements were noted by the TO. 

Table 4-2. Personal Computers Used in Flow Meter Software Evaluation 

Testing Organization PC ADS PC 

Manufacturer Toshiba Dell 

Processor Pentium 2-400 MHz Pentium 

Hard Disk 6.4 GB, > 1 GB disk free > 1 GB disk free 

Disk Drives CD ROM CD ROM, 3.5 in. floppy 

Operating System Windows 95 Windows 95 

4.4.2 Performance Evaluation 

In the following procedures, the waiting period to reach steady flow and tracer concentration 

conditions was established by experimentation. 

4.4.2.1 Test B: Accuracy under Dry Weather Flow with Back-Flow Conditions 

Test B verified the accuracy of depth and velocity measurements and flow calculations during 

field-simulated dry weather flow conditions (low flow), and when subjected to back-flow 

conditions caused by a downstream obstruction. This test was run three times. 

4.4.2.1.1 Procedures 

For every trial of Test B, the following procedure was applied: 

1. Adjust the upstream gate to a position corresponding to a flow of approximately 

1.71 MGD (75 L/sec) at the flow meter location. 

2. Initiate the reference flow, velocity and depth measurements; manually verify the 

reference depth measurements. 

3. Wait 45 minutes to establish a steady flow at the flow meter location and maintain this 

steady flow condition for 30 minutes. 

4. Close the downstream gate as necessary to establish a flow of approximately 0.86 MGD 

(37.5 L/sec); hold the flow for about five minutes to accumulate a head of water equal to 

18 ± 2 in. at the flow meter location. 

5. Open the downstream gate as necessary to establish a steady flow of 1.71 MGD 

(75 L/sec) and a head of water equal to 18 ± 2 in. at the flow meter location. A steady 

22 
flow and depth was established at the flow meter location approximate 60 minutes after 

step 4; maintain this flow rate for 60 minutes. 

6. Close the downstream gate for about 25 minutes to accumulate a head of water equal to 

36 ± 4 in. at the flow meter location. 

7. When a head of 36 in. is reached, open the downstream gate to establish a steady flow of 

1.71 MGD (75 L/sec) and a head of water equal to 36 ± 4 in. at the flow meter location. 

A steady flow and depth was established at the flow meter location approximately 90 

minutes after the beginning of step 6; maintain this flow rate for 60 minutes. 

8. Collect data from the ADS 3600 and reference meters. 

4.4.2.1.2 Measurements 

During the testing under Test B, measurements were taken in the following manner: 

1. Log the depth, velocity and flow of the ADS 3600 and the reference meters each minute. 

2. Log every gate manipulation, with the corresponding time and the depths upstream and 

downstream of the gate, for the upstream gate. 

3. Log every gate manipulation for the downstream gate, with the corresponding time and 

depth upstream of the gate. 

4. Record noteworthy events and the corresponding times. 

5. Take manual depth measurements at five minute intervals for comparison with values 

recorded by the reference depth meter. Each time measurements are taken, measure the 

depth three times at 15-second intervals, the third measurement to be taken at the exact 

time that the data is reported. For example: the first reading at 10:19:30, the second at 

10:19:45, and the third at 10:20:00, the mean value of the three readings to be reported at 

10:20:00. 

4.4.2.2 Test C: Accuracy Under Wet Weather Flow Without Back Flow Conditions 

Test C verified the accuracy of depth and velocity measurements and flow calculations during 

field-simulated wet weather flow conditions (normal and high flow). This test was run three 

times. 

4.4.2.2.1 Procedure 

For every trial of Test C, the following procedure was applied: 

23 
1. Adjust the upstream gate to a position corresponding to a flow of approximately 

1.71 MGD (75 L/sec) at the flow meter location. Start the tracer injection when 

applicable. 

2. Initiate reference flow, velocity, and depth measurements; manually verify reference 

depth measurements. 

3. Wait 45 minutes to establish a steady flow (and tracer concentration when applicable) at 

the flow meter location and maintain flow (and concentration when applicable) 

conditions for 30 minutes. 

4. Progressively open the upstream gate during a 10-minute period to establish a flow equal 

to 17.1 MGD (750 L/sec) ± 1.14 MGD (50 L/sec) at the flow meter location. A steady 

flow (and tracer concentration, when applicable) was established at the flow meter 

location approximately 45 minutes after beginning this step. Maintain this flow rate for 

30 minutes. 

5. Close the upstream gate during a five-minute period to establish a flow equal to 

8.56 MGD (375 L/sec) ± 1.14 MGD (50 L/sec) at the flow meter location. A steady flow 

(and tracer concentration, when applicable) was established at the flow meter location 

approximately 45 minutest after beginning this step. Maintain the flow rate for 30 

minutes. 

6. Open the upstream gate during a ten-minute period to establish a flow equal to 29.7 MGD 

(1,300 L/sec) ± 1.71 MGD (75 L/sec) at the flow meter location. A steady flow (and 

tracer concentration, when applicable) was established at the flow meter location 

approximately 45 minutes after beginning this step. Maintained the flow rate for 30 

minutes. 

7. Close the upstream gate during a ten-minute period to establish a flow equal to 

8.56 MGD (375 L/sec) ± 1.14 MGD (50 L/sec) at the flow meter location. A steady flow 

(and tracer concentration, when applicable) was established at the flow meter location 

approximately 45 minutes after beginning this step. Maintain the flow rate for 30 

minutes. 

8. Close the upstream gate during a five-minute period to establish a flow of 1.71 MGD 

(75 L/sec) at the flow meter location. A steady flow (and tracer concentration, when 

applicable) was established at the flow meter location approximately 45 minutes after 

beginning this step. Maintain the flow rate for 30 minutes. 

9. Stop the tracer injection, when applicable. 

10. Collect data from the ADS 3600 and the reference meters. 

24 
4.4.2.2.2 Measurements 

Measurements made during testing under Test C were taken in the same manner as for Test B. 

Refer to Section 4.4.2.1.2 for more detail. 

4.4.2.3 Test D: Accuracy Under Wet weather flow With Back flow Conditions 

Test D verified the accuracy of depth and velocity measurements and flow calculations during 

simulated wet weather flow (high flow) when subjected to back-flow conditions caused by a 

downstream obstruction. This test was run three times. 

4.4.2.3.1 Procedure 

For every trial of Test D, the following procedure was applied: 

1. Adjust the upstream gate to a position corresponding to a flow of approximately 

1.71 MGD (75 L/sec) at the flow meter location, according to the calibrated upstream 

gate equation. 

2. Initiate reference flow, velocity, and depth measurements; manually verify reference 

depth measurements. 

3. Wait 45 minutes to establish a steady flow at the flow meter location and maintain this 

steady flow condition for 30 minutes. 

4. Open the upstream gate during a five-minute period to establish a flow equal to 8.56 

MGD (375 L/sec) ± 1.14 MGD (50 L/sec) at the flow meter location, according to the 

calibrated upstream gate equation. A steady flow was established at the flow meter 

location approximately 45 minutes after beginning this step. Maintain the flow rate for 30 

minutes. 

5. Open the upstream gate to establish a flow of approximately 11.4 MGD (500 L/sec) at the 

upstream gate to accumulate a head of water equal to 54 ± 4 in. at the flow meter 

location. 

6. Position the downstream gate at 23⁄8 in. (60 mm) to establish a head of water equal to 54 

± 4 in. at the flow meter location. When the depth of water is close to 54 ± 4 in., operate 

the downstream gate to maintain a head of water equal to 54 ± 4 in. at the flow meter 

location. 

7. Three minutes after the beginning of step 5, close the upstream gate as necessary to 

establish a flow equal to 8.56 MGD (375 L/sec) ± 1.14 MGD (50 L/sec) at the flow meter 

location, according to the calibrated upstream gate equation. A steady flow and depth was 

established at the flow meter location approximately 60 minutes after the beginning of 

step 5. Maintain this flow rate for 30 minutes. 

25 
8. Open the upstream gate during a five-minute period to establish a flow equal to 

17.1 MGD (750 L/sec) ± 1.14 MGD (50 L/sec) at the flow meter location, while 

adjusting the downstream gate to maintain a head of water equal to 54 ± 4 in. at the flow 

meter location. A steady flow and depth was established at the flow meter location 

approximately 60 minutes after beginning this step. Maintain this flow rate for 30 

minutes. 

9. Open the upstream gate as necessary during a ten-minute period to establish a flow equal 

to 29.7 MGD (1,300 L/sec) ± 1.71 MGD (75 L/sec) at the flow meter location, while 

adjusting the downstream gate to maintain a head of water equal to 54 ± 4 in. at the flow 

meter location. A steady flow and depth was established at the flow meter location 

approximately 60 minutes after beginning this step. Maintain the flow and depth for 30 

minutes. 

10. Maintain the downstream gate position. Progressively close the upstream gate as 

necessary during a 10-minute period to establish a flow equal to 1.71 MGD (75 L/sec) at 

the flow meter location, according to the calibrated upstream gate equation. A steady 

flow was established at the flow meter location approximately 60 minutes after beginning 

this step. Maintain the flow and depth for 30 minutes. 

11. Collect data from the ADS 3600 and the reference meters. 

4.4.2.3.2 Measurements 

Measurements made during testing under Test D were taken in the same manner as for Test B. 

Refer to Section 4.4.2.1.2 for more detail. 

4.4.2.4 Test E: Accuracy Under Short-Term Continuous Operation 

Test E verified the accuracy of depth and velocity measurements and flow calculations over a 

21-day period of continuous operation. 

4.4.2.4.1 Procedures 

1. There was one period following completion of tests B, C, and D, during which flow data 

were not retrieved during seven consecutive days of data collection. 

2. The TO was responsible for the proper operation and maintenance of the flow meter in 

accordance with the operating instructions. Any intervention required to maintain the 

flow meter in good operating order was authorized and done by the vendor. The TO 

recorded the nature and frequency of any operation and maintenance procedures required 

during a 21-day period of continuous operation. 

3. The TO performed the procedures listed in Section 4.4.2.4.2 as well as other specific 

procedures specified in the ADS 3600 operating manual. 

26 
4. The personnel required for operation and maintenance procedures were also classified 

according to their qualifications as engineer, technician or general laborer. 

5. The TO noted whether any specialized tool or equipment was required, and whether the 

need for such tools or equipment was indicated by the operation and maintenance 

instructions. 

4.4.2.4.2 Measurements 

The nature and frequency of operation and maintenance procedures required during a 21-day 

period of continuous operation were noted by the TO, and are reported in Section 4.5.2.3. 

Specifically, the TO completed the following measurements: 

1. The numbers of hours (rounded to nearest whole hour) for each personnel classification 

were recorded for any field intervention to maintain the flow meter in operating order, in 

accordance with the operation manual or the procedures recommended by the flow meter 

manufacturer. 

2. The time, depth, velocity, and flow were recorded by the flow meter under test and the 

reference meters during all periods of normal operation, including the periods covered 

under tests B, C, and D. 

3. Manual depth measurements were taken at least once a day at the flow meter under test 

for comparison with values recorded by the verified depth meter. For each measurement 

time, the depths were measured five times at intervals of 60 seconds. During this visit, the 

depth and velocity probes were inspected to observe debris accumulation or other 

problems. The presence of accumulated debris on the probes was noted and documented 

by photographs. 

4. After dismantling, the flow meter and probes were inspected for infiltration, broken, 

cracked, or scratched components. The extent and nature of the damage was described. 

Evidence of water infiltration or broken components was noted and documented with 

photographs. 

5. Any unusual event occurring during the test was noted with its corresponding time. 

4.5 ADS 3600 Evaluation Results 

4.5.1 Software Evaluation 

The ADS 3600 flow meter required two different software programs: FieldscanTM V.3.1, released 

on March 28, 2001, and Profile V.1.4.1, released on April 6, 2001. ADS provided the TO with a 

portable computer using a Microsoft Windows 95TM operating system with the two software 

programs installed. The TO tested the installation and start-up procedures, along with the usual 

applications of the software as used during the flow meter testing period. 

27 
TO personnel received training on the flow meter software at the beginning of the test. This sixhour training, combined with the software user guide, allowed TO personnel to become familiar 

with the flow meter software and to accomplish the required tasks for the flow meter verification. 

Some complex operations performed afterward with the flow meter software required the help of 

the ADS analysts. 

FieldscanTM was used to set the parameters for the on-site installation as well as for the 

configuration and calibration of the flow meter. It can also collect data from the flow meter and 

allow real-time viewing of the monitor status and data. 

When the FieldscanTM installation was completed, the Profile software was used to collect data 

from the monitor, store it in a database, and view, analyze and export it. The Profile software 

cannot be used to modify set-up parameters on the flow meter. FieldscanTM must be used to 

perform these tasks. 

FieldscanTM stores parameters and data in files while Profile uses a Microsoft Access database. 

FieldscanTM data and parameters can be imported into the Profile database but not vice-versa. 

Both programs must be used during normal operation, but since they do not use the same source 

files, the user has to keep both sources of information updated. 

The manufacturer first completed a checklist of available features and the TO verified their 

availability. A detailed evaluation of the features of both programs is presented in Appendix G. 

Both programs were easy to learn, and quick and easy to use. Profile was a powerful analysis 

tool with a large variety of features. The procedure to collect data was simple and efficient, 

taking about 1.5 minutes to record data collected at one-minute intervals. A few additional 

minutes were required to view data on graphs and to make sure that the collection was complete. 

Considering that this task had to be performed frequently under difficult conditions, the features 

of Profile were a significant advantage. 

The use of a database to store data was also a significant advantage. It allowed users to easily 

access data from several monitoring points and for any time period. It could also easily export 

data in ASCII or Microsoft Excel files for other uses. A disadvantage was that two software 

programs are needed to perform the required operations. The user had to learn both programs and 

keep both sources of information individually updated, which could become a source of 

problems. 

One software issue was identified during testing. As tests commenced, the TO noted the program 

implemented in the flow meter would occasionally fail to store data points in its memory. The 

protocol required the flow meter to electronically collect mean velocity, ultrasonic depth, and 

pressure depth data, and compute flow rate at one-minute intervals. The ADS flow meter and 

laptop computer, as supplied and set up during testing, was not capable of retrieving, computing 

and storing all the data within the one-minute interval; it would respond by not storing any of the 

data at the particular time interval. The missing data points would typically be spread randomly 

throughout the dataset, with at most four or five consecutive missing data points. 

28 
True zero readings were represented on the graphs generated by the program while missing data 

were not. Data points around the missing data were simply connected. ADS personnel indicated 

the program settings could be modified to provide the one-minute readings. The quantity of data 

points retrieved was sufficient to provide verification of flow meter effectiveness. 

The number of missing data points for each test was noted. The minimum number of missing 

data during a 24-hour period was 41, the maximum was 455 and the mean was 184 out of 1,440 

data points. This represents 3 percent, 32 percent, and 13 percent of the daily data collection, 

respectively. 

A complementary test was conducted by the TO on July 24 and 25, 2001 to further investigate 

the issue. During this test, data was logged at two-minute intervals instead of one-minute 

intervals for approximately 24 hours. During this test, no data points were missing from the time 

series. It was hypothesized that the root of the problem was the flow meter processor, and that 

the program implemented in the flow meter was not able to process and store the volume and 

frequency of data being provided by the ADS flow meter probes (one pressure probe, four 

ultrasonic probes and one velocity probe) or to calculate the flow rate. 

The Utah Water Research Laboratory (UWRL) conducted laboratory testing with the same ADS 

flow meter equipment. They collected data at one-minute intervals, but did not have the problem 

with data collection and storage experienced at the field testing site. 

4.5.2 Performance Tests 

The performance tests were completed between June 28 and July 24, 2001 according to the 

procedures outlined in the VTP. Tests were performed on days without precipitation (morning, 

afternoon or evening), in no particular sequence except that the first and second to last tests were 

two of the three replicates of Test C, for which dilution tests were done. No data were collected 

for seven consecutive days (July 17 to 24) as specified in the protocol. The results from tests B, 

C, and D are summarized in Table 4-3. 

Results of all performance tests are presented in graphical form with one-minute data for all 

instruments (Accusonic, bubbler, ADS 3600). Clocks from all instruments were synchronized 

and no more than a two-minute difference was observed for the duration of the tests. 

29 
Table 4-3. Deviation from Reference Flow—Tests B, C, and D 

Flow regime Average deviation 

(percent) 

Trimmed average deviation 

(percent)a 

Test B -29.7b

 2.4 

Test C 5.0 5.0 

Test D -1.0 4.7 

Test B-D combined -5.7 2.1 

Simulated dry flow -7.6b 12.2 

Simulated wet flow -4.3 -4.1 

Combined flows -5.7 2.1 

a

 The trimmed average deviation removes the deviations greater than 99 percent or less than –99 percent from 

the average deviation, and then averages the remaining values. This computation mitigates the skewing 

caused by large outliers. 

b

 The ADS 3600 flow meter read zero velocity during low-flow testing, resulting in a deviation of –100 percent 

and a skewing of the data. 

The hydraulic conditions at the test site created a condition where water depths at the reference 

site (bubbler) and at the ADS 3600 flow meter were different. These two measuring sites were 

approximately 20.2 ft (6.2 m) apart, on a theoretical slope of 0.169 percent (a calculated 

elevation difference of 0.4 in., or 10.4 mm). The three pipe sections involved were on slightly 

different slopes, resulting in a measured elevation difference of 1.97 in. (50 mm). Furthermore, 

there was a 2.17-in. (55 mm) high concrete bump approximately four feet (1.2 m) downstream 

from the bubbler, which caused a permanent back flow over both the bubbler and the ADS 3600 

sites. 

4.5.2.1 Scatter Plots 

Two types of scatter plots are presented in this report: a system behavior (velocity versus depth) 

plot and a flow rate comparison plot. The system behavior scatter plot is shown in Figure 4-17. 

The figure presents the hydraulic conditions at the ADS 3600 testing site during the three 

replicas of Test C, when there was no back flow. There are 1,272 data points on this figure, 

which includes data for all three replicas. The data is segregated into three water profile groups: 

stable (943 data points), ebbing (234) and rising (95). There are 81 missing data points compared 

to the reference data set. There are fewer data points for the rising water profiles because the 

transition was more rapid under this condition. 

30 
Velocity (ft/s) 

10 

Stable 

9 

Ebbing 8 

Rising 7 

6 

5 

4 

3 

2 

1 

0 

0 5 10 15 20 25 30 35 

Level (inches) 

Figure 4-17. ADS 3600 system behavior, Test C. 

Figure 4-18 presents the same scatter plot for the reference flow meter. Three observations can

be made from the figure: 

1. The four stable water profiles of Test C, obtained at flow rates of 1.71, 8.56, 17.1 and 29.7 

MGD (75, 375, 750 and 1,300 L/sec) are clearly defined; 

2. The ebbing water profiles data points are generally above the best-fit curve drawn from

stable conditions data points; and

3. The rising water profiles data points are generally below the best-fit curve. 

These conditions are not observed on Figure 4-17 for the ADS 3600. 

31 
Velocity (ft/s) 

10 

Stable 

9 

Ebbing 

8 Rising 

Best fit curve of stable conditions 7 

y = -0.0016x2 + 0.2987x - 1.6057 6 

R2

 = 0.9938 

5 

4 

3 

2 

1 

0 

0 5 10 15 20 25 30 35 

Level (inches) 

Figure 4-18. Reference meter system behavior.

Figure 4-19 presents a flow rate comparison plot between the ADS 3600 and the reference flow

meter for all data from tests B, C, and D. The line on the figure represents a perfect fit between 

the two flow meters. The reference flow meter recorded 3,924 data points (five true zero 

readings and five negative values) during those tests while the ADS 3600 recorded 3,600 data

points (324 missing data points). The zero readings and negative values of the reference flow 

meter were recorded during a transition period during Test B just after the gate was closed and

there was some counter-flow. 

32 
ADS 3600 flow rate (MGD) 30 

Free flow 25 Backflow 

y = x 

20 

15 

10 

5 

0 

0 5 10 15 20 25 30 

Reference flow rate (MGD) 

Figure 4-19. ADS 3600 flow vs. reference flow, Tests B, C and D. 

Of the 3,600 matching data points between the ADS 3600 and the reference flow meter, the ADS 

3600 had 280 true zero readings and no negative values, while the reference flow meter had two 

true zero readings and two negative values. Most (272) of the 280 true zero readings of the ADS 

3600 were recorded during Test B (low flow) with 36-inch back fl, while the reference flow 

meter was recording flows in the range of 1.37 to 2.05 MGD (60 to 90 L/sec). Under these 

conditions, velocities were in the range of 0.33 ft/sec (0.1 m/sec). The resolution of the velocity 

meter on the ADS 3600 was 0.0394 ft/sec (0.012 m/sec). 

4.5.2.2 Deviation Distribution Plots 

Figures 4-20 to 4-25 present the ADS 3600 flow deviation distributions. For all these plots, the 

+100 percent deviation bar groups all data equal or greater than 100 percent, whereas the -100 

percent deviation bar groups all data points equal to zero (the ADS 3600 does not output 

negative flow rates). The deviation is presented in two-percent increments. Indicated on the 

figures are the: 

• Margin of deviation (±X percent) that contains 95 percent of all measurements (i.e. 

standard ±2σ); 

• Percentage of measurements within a margin of deviation of ±20 percent; 

• Percentage of measurements within a margin of deviation of ±10 percent; 

• Mean deviation of all measurements (influenced by very large positive deviations); 

33 
100% 

-100% 

-90% 

-80% -70% 

-60% -50% 

-40% -30% -20% 

-10% 

0% 

10% 20% 30% 

40% 50% 60% 70% 80% 

90% 

100% 

• Mean deviation of measurements within a margin of deviation of ±99 percent (to exclude 

very large deviations); and 

• Median deviation (gives an indication of the spread). 

Figure 4-20 presents the deviation distribution for Test B. It is roughly a widely spread, centered 

bell-shaped curve. The high frequency (32 percent) of data points with a deviation of -100 

percent arises because the ADS 3600 flow rate equaled zero when the velocity meter recorded 

velocities of zero (refer to Section 4.5.2.2.1). One percent of measurements (eight data points) 

had a deviation greater than 100 percent. These had a large impact on the mean deviation (-29.7 

percent) compared to the median deviation (-4.6 percent). 

35% 

30% 

25% 

20% 

15% 

10% 

5% 

0% 

60.1% 

95% of measurements within a margin of deviation of ± Mean deviation: -29.7%

of measurements within a margin of deviation of ± 20% 

38.7% of measurements within a margin of deviation of ± 10% 

Mean of data within ± 99% of deviation: 

Median deviation: -4.6% 

2.4% 

Frequency (%) 

Deviation (%) 

Figure 4-20. Flow deviation distribution—Test B. 

Figure 4-21 presents the deviation distribution for Test C. It is a bell-shaped curve decentered on 

the negative side. Deviations are less spread than for Test B: 95 percent of measurements are 

within a margin of deviation of ±31 percent compared to ±100 percent for Test B. 

34 
-100% 

-90% 

-80% -70% -60% -50% -40% 

-30% -20% -10% 

0% 

10% 20% 

30% 40% 50% 60% 70% 80% 90% 

100% 

10% 

9% 

8% 

7% 

6% 

5% 

4% 

3% 

2% 

1% 

0% 

74.8% 

95% Mean deviation: 5.0% of measurements within a margin of deviation of 

of measurements within a margin of error of ± 20% 

43.8% of measurements within a margin of error of ± 10% 

Mean of data within ± 99% of deviation: 

Median deviation: 3.4% 

5.0% 

31% 

Frequency (%) 

Deviation (%) 

Figure 4-21. Flow deviation distribution—Test C. 

Figure 4-22 presents the deviation distribution for Test D. It is a two-peak bell-shaped curve 

decentered on the negative side. Deviations are spread similar to Test C: 95 percent of 

measurements are within a margin of deviation of ±36 percent compared to ±31 percent for 

Test C. 

35 
-100% 

-90% -80% -70% 

-60% -50% -40% 

-30% -20% -10% 

0% 

10% 20% 30% 40% 50% 60% 

70% 

80% 90% 

100% 

20% 

18% 

16% 

14% 

12% 

10% 

8% 

6% 

4% 

2% 

0% 

36% 

76.4% 

95% of measurements within a margin of deviation of Mean deviation: -1.0%

of measurements within a margin of deviation of ± 20% 

30.3% of measurements within a margin of deviation of ± 10% 

Mean of data within ± 99% of deviation: 

Median deviation: -8.0% 

4.7% 

Frequency (%) 

Deviation (%) 

Figure 4-22. Flow deviation distribution—Test D. 

Figure 4-23 presents the deviation distribution for tests B, C, and D combined. It is roughly a 

two-peak bell-shaped curve decentered on the negative side. Data points with a deviation of -100 

percent are due to the zero flows of Test B. The large mean deviation (-5.7 percent) is also due to 

the large deviations from Test B, discussed above. Figure 4-24 presents the deviation distribution 

for dry weather conditions and Figure 4-25 for wet weather conditions. The criterion for wet 

weather flow was for a flow greater than 1.5 times maximal dry-weather flow (1.71 MGD; 75 

L/sec), or 2.57 MGD (112.5 L/sec). As expected, the dry weather deviation distribution plot is a 

centered bell-shaped curve on a positive value while the wet weather flow plot is a two-peak 

bell-shaped curve decentered on the negative side, the right peak being associated with the lower 

flows 8.56 MGD (375 L/sec). 

36 
-100% 

-90% -80% -70% -60% -50% -40% -30% -20% -10% 

0% 

10% 

20% 30% 

40% 50% 60% 70% 80% 90% 

100% 

-100% 

-90% -80% -70% -60% -50% -40% -30% -20% -10% 

0% 

10% 20% 

30% 40% 50% 60% 70% 80% 

90% 

100% 

0% 

2% 

4% 

6% 

8% 

10 % 

12 % 

14 % 

Frequency (%) 

100% 

72.0% 

Mean deviation: 95% of measurements within a margin of deviation of ± -5.7% 

of measurements within a margin of deviation of ± 20% 

37.0% of measurements within a margin of deviation of ± 10% 

Mean of data within ± 99% of deviation: 

Median deviation: -2.5% 

2.1% 

Deviation (%) 

Figure 4-23. Flow deviation distribution—Tests B, C and D. 

20% 

18% 

16% 

14% 

12% 

10% 

8% 

6% 

4% 

2% 

0% 

95% Mean deviation: of measurements within a margin of deviation of ± 

of measurements within a margin of deviation of ± 20% 

28.9% of measurements within a margin of deviation of ± 10% 

Mean of data within ± 99% of deviation: 

Median deviation: 16.9% 

12.2% 

100.0% 

59.1% 

-7.6% 

Frequency (%) 

Deviation (%) 

Figure 4-24. Flow deviation distribution—simulated low flow conditions. 

37 
-100% 

-90% -80% 

-70% 

-60% -50% -40% -30% -20% -10% 

0% 

10% 20% 30% 40% 50% 60% 70% 80% 

90% 

100% 

20% 

18% 

16% 

14% 

12% 

10% 

8% 

6% 

4% 

2% 

0% 

32.3% 

81.4% 

95% of measurements within a margin of deviation of ± Mean deviation: -4.3%

of measurements within a margin of deviation of ± 20% 

43.0% of measurements within a margin of deviation of ± 10% 

Mean of data within ± 99% of deviation: 

Median deviation: -8.6% 

-4.1% 

Frequency (%) 

Deviation (%) 

Figure 4-25. Flow deviation distribution—simulated wet flow conditions. 

For tests B, C, D, and E, figures are presented in Appendix H in the following order: (1) flow 

rates; (2) water depths; and (3) velocities. While flow rates measured by the verified flow meter 

and the reference flow meter can be compared directly, water depths and velocities cannot, 

because the flow meters were not installed at the same location in the pipe. Since the pipe profile 

was known, it was possible to have a good appreciation of the quality of the water depth 

readings. It was much more difficult to evaluate the velocity readings on their own. 

4.5.2.2.1 Test B 

After flushing of the sewer line, this test was conducted at maximal dry-weather flow 

(1.71 MGD; 75 L/sec) with three consecutive hydraulic conditions: 

1. No back flow; 

2. With a back flow of 18 in.; and 

3. With a back flow of 36 in 

Figures H-1 through H-3 (Appendix H) present flow rates measured by the ADS 3600 and by the 

reference flow meter for each replica of Test B. Flow rates measured by both meters were close 

except with a back flow of 36 in. when the ADS 3600 recorded velocities of zero. Table 4-4 

provides an appreciation of the difference between the flow rates (reference/ADS 3600) for 

samples of data points taken during stable periods (delimited by the indicated start and end 

times) for each replica and for the three hydraulic conditions of this test. Also shown in this table 

38 
are the average reference flow rates, the standard deviations of the flow rate differences, and the 

differences represent in comparison with the reference flow rates. Without back flow, flow rates 

are overestimated by roughly 15 percent. Under an 18 in. back flow, flow rates are within five 

percent. 

Table 4-4. Flow Rate Comparison of Data Point Samples for the Three Replicas of Test B 

Hydraulic Replica Average 

conditions B1 B2 B3 (L/sec) 

Start time 9:40 9:40 19:40 

End time 10:15 10:15 20:15 

Flow rate: 75 L/sec Mean reference flow rate (L/sec) 79.6 64.9 71.1 71.9 

Back flow: None Mean difference (L/sec) -5.5 -8.3 -12.6 -8.8 

Standard deviation of differences 4.3 3.3 7.0 

Difference/reference (percent) -7 -13 -18 

Start time 10:30 10:30 20:30 

End time 12:15 12:15 22:15 

Flow rate: 75 L/sec Mean reference flow rate (L/sec) 74.0 68.1 89.1 77.1 

Back flow: 18 in. Mean difference (L/sec) -0.9 -3.6 3.5 -0.3 

Standard deviation of differences 5.3 6.6 9.3 

Difference/reference (percent) -1 -5 4 

Start time 12:45 12:45 22:45 

End time 14:45 14:45 0:45 

Flow rate: 75 L/sec Mean reference flow rate (L/sec) 78.2 77.7 83.6 79.9 

Back flow: 36 in. Mean difference (L/sec) - - - -

Standard deviation of differences - - -

Difference/reference (percent) - - -

Figures H-4 through H-6 present water depths measured by the ADS 3600 and by the reference 

depth meter (bubbler) for each replica of Test B. Considering the profile of the test site, a 1.97­

inch (50.0-mm) difference in water depth was expected between the two sites under back flow 

conditions, with the ADS 3600 water depths always being lower. The ADS 3600 water depths 

are always lower with an average of 1.83 in. (46.4 mm, see Table C-4). Table 4-5 gives an 

appreciation of the difference between the two water depth readings (reference/ADS 3600) for 

data points taken during stable periods (delimited by the indicated start and end times) for each 

replica and for the three hydraulic conditions of this test. Also shown in this table are the average 

reference water depths and the standard deviations of the water depth differences. The 

differences in water depth vary between 1.73 in. and 2.31 in. (44.0 and 58.7 mm) under back 

flow conditions. Since there is very low disturbance due to velocity under these conditions, these 

values match the difference in slope, as expected. 

39 
Table 4-5. Water Level Comparison of Data Point Samples for Three Replicas of Test B 

Hydraulic Replica Average 

condition B1 B2 B3 (mm) 

Start time 9:40 9:40 19:40 

Flow rate: 75 L/sec 

Back flow: None 

End time 

Mean reference level (mm) 

Mean difference (mm) 

10:15 

273.1 

62.0 

10:15 

259.6 

61.5 

20:15 

267.5 

57.5 

266.8 

60.3 

Standard deviation of differences 1.6 2.4 3.0 

Start time 10:30 10:30 20:30 

Flow rate: 75 L/sec 

Back flow: 18 in. 

End time 

Mean reference level (mm) 

Mean difference (mm) 

12:15 

445.4 

58.7 

12:15 

464.2 

51.0 

22:15 

513.5 

50.4 

474.4 

53.4 

Standard deviation of differences 3.3 4.7 2.5 

Start time 12:45 12:45 22:45 

Flow rate: 75 L/sec 

Back flow: 36 in. 

End time 

Mean reference level (mm) 

Mean difference (mm) 

14:45 

908.2 

49.5 

14:45 

926.5 

44.9 

0:45 

919.9 

44.0 

918.2 

46.1 

Standard deviation of differences 2.5 4.0 2.5 

Figures H-7 through H-9 present velocities measured by the ADS 3600 and by the reference flow 

meter for each replica of Test B. Considering the difference in water depth, velocities measured 

by the ADS 3600 are expected to be higher than those measured by the reference meter. Since 

Test B was conducted at low flow rates with back flow, velocities are expected to be low. Under 

the 18 in. back flow condition, velocities are in the vicinity of 0.66 to 0.98 ft/sec (0.2 to 0.3 

m/sec), with ADS velocities being slightly higher than those measured by the reference meter. 

Under back flow of 36 in., velocities fall under 0.49 ft/sec (0.15 m/sec) and were not recorded by 

the ADS 3600 for all three replicas although the velocity meter had a resolution of 0.0394 ft/sec 

(0.012 m/sec). The signal of the ADS 3600 velocity meter had more noise than the reference 

meter. 

4.5.2.2.2 Test C 

After flushing of the sewer line, this test was conducted at six consecutive flow rates with no 

back flow: 

• 1.71 MGD (75 L/sec); 

• Up to 17.1 MGD (750 L/sec); 

• Down to 8.56 MGD (375 L/sec); 

• Up to 29.7 MGD (1300 L/sec); 

• Back down to 8.56 MGD (375 L/sec); and 

• Back to the maximal dry-weather flow rate of 1.71 MGD (75 L/sec). 

40 
Figures H-10 through H-12 present flow rates measured by the ADS 3600 and by the reference 

flow meter for each replica of Test C. Flow rates were in turn overestimated and underestimated. 

Table 4-6 shows the difference between the flow rates (reference/ADS 3600) for data points 

taken during stable periods (delimited by the indicated start and end times) for each replica and 

for the six hydraulic conditions of this test. Also shown in this table are the average reference 

flow rates, the standard deviations of the flow rate differences and the percentage these 

differences represent in comparison with the reference flow rates. Both sets of maximal dry 

weather flow (1.71 MGD; 75 L/sec) data points are overestimated by roughly 15 percent. The 

three performances with the largest deviations were obtained at 8.56 MGD (375 L/sec) 

(29 percent, 24 percent, and 24 percent). The best performances were obtained in replica 

Test C3. 

Figures H-13 through H-15 present water depths measured by the ADS 3600 and by the 

reference depth meter (bubbler) for each replica of Test C. Due to the profile of the test site, the 

ADS 3600 water depths are expected to always be lower than the reference depths, which they 

are. Table 4-7 shows the difference between the two water depth readings (reference/ADS 3600) 

for data points taken during stable periods (delimited by the indicated start and end times) for 

each replica and for the six hydraulic conditions of this test. Also shown in this table are the 

average reference water depths and the standard deviations of the water depth differences. Water 

depth differences at 1.71 MGD (75 L/sec), 2.28 in. and 2.36 in. (57.9 mm and 60.0 mm), are 

close to those of Test B under the same conditions (no back flow - 2.37 in. [60.3 mm]). The 

biggest difference in water depth is found at 17.1 MGD (750 L/sec), with an average depth of 

5.82 in. (147.9 mm), not at 29.7 MGD (1,300 L/sec) where the average depth was 4.30 in. 

(109.3 mm). 

Figures H-16 through H-18 present velocities measured by the ADS 3600 and by the reference 

flow meter for each replica of Test C. Velocities measured by the ADS 3600 are higher than 

those measured by the reference meter, as expected. Reference velocities are mostly in the range 

of 0.98 to 5.91 ft/sec (0.3 to 1.8 m/sec). Excluding data points at 1.71 MGD (75 L/sec), the span 

of reference velocities of 3.28 to 5.91 ft/sec (1.0 to 1.8 m/sec) is greater than for the ADS 3600 

recorded velocities of 4.59 to 6.56 ft/sec (1.4 to 2.0 m/sec). 

41 
Table 4-6. Flow Rate Comparison of Data Point Samples for Three Replicas of Test C 

Replica Average Hydraulic condition C1 C2 C3 (L/sec) 

Start time 8:40 15:40 7:40 

End time 9:30 16:30 8:30 

Flow rate: 75 L/sec Mean reference flow rate (L/sec) 70.2 82.8 41.4 64.8 

Back flow: None Mean difference (L/sec) -9.7 -15.1 -4.4 -9.7 

Standard deviation on differences 4.7 6.0 4.8 

Difference/reference (percent) -14 -18 -11 

Start time 9:45 16:45 8:45 

End time 10:30 17:30 9:30 

Flow rate: 750L/sec Mean reference flow rate (L/sec) 700.0 704.7 687.6 697.4 

Back flow: None Mean difference (L/sec) 61.9 49.0 22.0 44.3 

Standard deviation on differences 13.2 10.3 23.3 

Difference/reference (percent) 9 7 3 

Start time 10:45 17:45 9:45 

End time 11:45 18:45 10:45 

Flow rate: 375 L/sec Mean reference flow rate (L/sec) 395.9 404.8 411.2 404.0 

Back flow: None Mean difference (L/sec) -93.3 -117.6 -8.7 -73.2 

Standard deviation on differences 15.3 13.6 9.5 

Difference/reference (percent) -24 -29 -2 

Start time 12:00 19:00 11:00 

End time 13:0 20:00 12:00 

Flow rate: 1,300 L/sec Mean reference flow rate (L/sec) 1224.6 1213.3 1213.9 1,217.3 

Back flow: None Mean difference (L/sec) 121.7 151.7 120.4 131.3 

Standard deviation on differences 28.2 29.7 27.0 

Difference/reference (percent) 10 13 10 

Start time 13:30 20:30 12:30 

End time 14:30 21:30 13:30 

Flow rate: 375 L/sec Mean reference flow rate (L/sec) 379.9 401.0 389.1 390.0 

Back flow: None Mean difference (L/sec) -90.5 -26.2 -21.0 -45.9 

Standard deviation on differences 13.7 23.1 13.3 

Difference/reference (percent) -24 -7 -5 

Start time 15:00 22:00 14:00 

End time 14:45 22:45 14:45 

Flow rate: 75 L/sec Mean reference flow rate (L/sec) 101.7 88.9 91.3 94.0 

Back flow: None Mean difference (L/sec) -15.7 -13.8 -13.8 -14.4 

Standard deviation on differences 6.7 7.1 6.5 

Difference/reference (percent) -15 -16 -15 

42 
Table 4-7. Water Level Comparison of Data Point Samples for Three Replicas of Test C 

Hydraulic condition C1 

Replica 

C2 C3 

Average 

(mm) 

Start time 8:40 15:40 7:40 

Flow rate: 75 L/sec 

Back flow: None 

End time 

Mean reference level (mm) 

Mean difference (mm) 

9:30 

262.2 

55.4 

16:30 

279.6 

59.1 

8:30 

228.5 

59.1 

256.8 

57.9 

Standard deviation on differences 1.8 1.9 2.4 

Start time 9:45 16:45 8:45 

Flow rate: 50L/sec 

Back flow: None 

End time 

Mean reference level (mm) 

Mean difference (mm) 

10:30 

582.7 

177.4 

17:30 

585.5 

165.9 

9:30 

591.3 

100.3 

586.5 

147.9 

Standard deviation on differences 2.4 2.4 8.7 

Start time 10:45 17:45 9:45 

Flow rate: 375 L/sec 

Back flow: None 

End time 

Mean reference level (mm) 

Mean difference (mm) 

11:45 

475.2 

92.2 

18:45 

480.4 

66.2 

10:45 

485.2 

115.7 

480.3 

91.4 

Standard deviation on differences 9.1 4.2 5.4 

Start time 12:00 19:00 11:00 

Flow rate: 1,300 L/sec 

Back flow: None 

End time 

Mean reference level (mm) 

Mean difference (mm) 

13:00 

778.6 

98.5 

20:00 

761.8 

111.4 

12:00 

759.9 

118.0 

766.8 

109.3 

Standard deviation on differences 7.1 4.6 3.2 

Start time 13:30 20:30 12:30 

Flow rate: 375 L/sec 

Back flow: None 

End time 

Mean reference level (mm) 

Mean difference (mm) 

14:30 

468.0 

93.8 

21:30 

481.5 

93.9 

13:30 

476.0 

102.3 

475.2 

96.7 

Standard deviation on differences 7.6 8.9 9.9 

Start time 15:00 22:00 14:00 

Flow rate: 75 L/sec 

Back flow: None 

End time 

Mean reference level (mm) 

Mean difference (mm) 

15:45 

291.1 

56.3 

22:45 

285.6 

61.9 

14:45 

288.9 

61.7 

288.5 

60.0 

Standard deviation on differences 2.3 2.8 3.5 

43 
4.5.2.2.3 Test D 

Test D was completed with varying flow rates and back flow conditions, as described in Section 

4.4.2.3. In summary, the six hydraulic conditions used during the test included: 

• 1.71 MGD (75 L/sec) with no back flow; 

• 8.56 MGD (375 L/sec) with no back flow; 

• 8.56 MGD (375 L/sec) with a back flow of 54 in.; 

• 17.1 MGD (750 L/sec) with a back flow of 54 in.; 

• 29.7 MGD (1300 L/sec) with a back flow of 54 in.; and 

• 1.71 MGD (75 L/sec) with no back flow. 

Figures H-19 through H-21 present flow rates measured by the ADS 3600 and by the reference 

flow meter for each replica of Test D. Table 4-8 shows the difference between the flow rates 

(reference/ADS 3600) for data points taken during stable periods (delimited by the indicated start 

and end times) for each replica and for the six hydraulic conditions of this test. Also shown in the 

table are the average reference flow rates, the standard deviations of the flow rate differences, 

and the percentage these differences represent in comparison with the reference flow rates. 

Differences in flow rates at maximal dry weather flow are higher than in tests B and C (23 

percent and 17 percent, compared to roughly 15 percent in this test). Under back flow conditions, 

flow rates are underestimated by 10 to 15 percent for the three flow rates. 

Figures H-22 through H-24 present water depths measured by the ADS 3600 and by the 

reference depth meter (bubbler) for each replica of Test C. Considering the profile of the test site 

(Figure 4-3), a 1.97-inch (50.0-mm) difference in water depth is expected between the two sites 

under back flow conditions, with the ADS 3600 water depths always being lower. The ADS 

3600 water depths are always lower. Table 4-9 shows the difference between the two water depth 

readings (reference/ADS 3600) for data points taken during stable periods (delimited by the 

indicated start and end times) for each replica and for the six hydraulic conditions of this test. 

Also shown in this table are the average reference water depths and the standard deviations of the 

water depth differences. Water depth differences at 1.71 MGD (75 L/sec) of 2.42 in. and 2.46 in. 

(61.5 and 62.6 mm) are close to those of tests C and B under the same conditions. Under back 

flow conditions, the water depth difference of 2.32 in. (59.0 mm) approaches the difference in 

slope, as expected. 

Figures H-25 through H-27 present velocities measured by the ADS 3600 and by the reference 

flow meter for each replica of Test D. As expected, velocities measured by the ADS 3600 are 

higher than those measured by the reference meter for all conditions without back flow. Under 

back flow, ADS 3600 velocities are always below the reference ones, which would lead to 

underestimation of the flow rates. 

44 
Table 4-8. Flow Rate Comparison of Data Point Samples for Three Replicas of Test D 

Hydraulic condition D1 

Replica 

D2 D3 

Average 

(L/sec) 

Start time 8:45 8:45 19:45 

End time 9:30 9:30 20:30 

Flow rate: 75 L/sec Mean reference flow rate (L/sec) 63.2 68.2 66.7 66.0 

Back flow: None Mean difference (L/sec) -12.1 -14.7 -18.7 -15.2 

Standard deviation on differences 4.7 5.6 4.9 

Difference/reference (percent) -19 -22 -28 

Start time 9:45 9:45 20:45 

End time 10:30 10:30 21:30 

Flow rate: 375 L/sec Mean reference flow rate (L/sec) 379.2 382.8 387.4 383.1 

Back flow: None Mean difference (L/sec) -14.1 -24.2 -11.8 -16.7 

Standard deviation on differences 13.6 16.6 11.8 

Difference/reference (percent) -4 -6 -3 

Start time 10:45 10:45 21:45 

Flow rate: 375 L/sec 

Back flow: 36 in. 

End time 

Mean reference flow rate (L/sec) 

Mean difference (L/sec) 

12:00 

400.1 

50.1 

12:00 

413.2 

70.6 

23:00 

414.4 

66.3 

409.2 

62.3 

Standard deviation on differences 15.6 23.9 19.7 

Difference/reference (percent) 13 17 16 

Start time 12:15 12:15 23:15 

Flow rate: 750 L/sec 

Back flow: 36 in. 

End time 

Mean reference flow rate (L/sec) 

Mean difference (L/sec) 

13:30 

711.8 

75.3 

13:30 

710.7 

77.6 

00:30 

696.7 

75.2 

706.4 

76.0 

Standard deviation on differences 16.3 21.6 21.1 

Difference/reference (percent) 11 11 11 

Start time 14:00 14:00 01:00 

End time 15:00 15:00 02:00 

Flow rate: 1,300 L/sec Mean reference flow rate (L/sec) 1285.3 1272.5 1262.5 1,273.4 

Back flow: 36 in. Mean difference (L/sec) 135.2 131.0 148.0 138.1 

Standard deviation on differences 27.4 22.8 26.3 

Difference/reference (percent) 11 10 12 

Start time 15:45 15:45 02:45 

End time 16:00 16:00 03:30 

Flow rate: 75 L/sec Mean reference flow rate (L/sec) 86.9 93.8 66.2 82.3 

Back flow: None Mean difference (L/sec) -14.6 -13.5 -14.9 -14.3 

Standard deviation on differences 5.6 5.7 4.8 

Difference/reference (percent) -17 -14 -23 

45 
Table 4-9. Water Level Comparison of Data Point Samples for Three Replicas of Test D 

Hydraulic condition D1 

Replica 

D2 D3 

Average 

(mm) 

Start time 8:45 8:45 19:45 

Flow rate: 75 L/sec 

Back flow: None 

End time 

Mean reference level (mm) 

Mean difference (mm) 

9:30 

262.7 

61.9 

9:30 

269.5 

61.4 

20:30 

270.0 

61.2 

267.4 

61.5 

Standard deviation of differences 1.5 3.4 2.9 

Start time 9:45 9:45 20:45 

Flow rate: 375 L/sec 

Back flow: None 

End time 

Mean reference level (mm) 

Mean difference (mm) 

10:30 

471.4 

106.5 

10:30 

477.1 

106.5 

21:30 

475.5 

113.3 

474.7 

108.8 

Standard deviation of differences 8.7 11.4 2.5 

Flow rates: 375 L/sec 

750 L/sec 

1,300 L/sec 

Back flow: 54 in. 

Start time 

End time 

Mean reference level (mm) 

Mean difference (mm) 

Standard deviation of differences 

11:00 

15:00 

1458.5 

56.8 

15.0 

11:00 

15:00 

1440.2 

57.3 

11.1 

22:00 

02:00 

1420.0 

62.9 

9.7 

1429.6 

59.0 

Start time 15:45 15:45 02:45 

Flow rate: 75 L/sec 

Back flow: None 

End time 

Mean reference level (mm) 

Mean difference (mm) 

16:30 

280.3 

60.4 

16:30 

298.8 

66.0 

03:30 

264.9 

61.3 

281.3 

62.6 

Standard deviation of differences 2.7 3.3 3.1 

4.5.2.2.4 Test E 

This test was conducted once over a minimum of 21 days, including a period of seven days 

without data collection. It comprises results obtained from the three replicas of tests B, C, and D. 

Test E was conducted over 26 days (June 28 to July 24, 2001), with no data collection from July 

18 to 24, 2001. Flow rates outside periods of active testing do not vary much and are generally 

between 6.85 to 15.98 MGD (300 to 700 L/sec). Continuous operation was useful to identify 

shifts in the depth and/or velocity measurements. 

Figures H-28 through H-54 (Appendix H) present flow rates measured by the ADS 3600 and by 

the reference flow meter for each 24-hour period of Test E. Flow rates measured by the ADS 

3600 were generally larger than the reference flows during low flow conditions and smaller than 

the reference flows during high flow conditions. Spikes and shifts (up and down) in the ADS 

3600 signal can be linked to the water depth measurements. Flow rates of zero are due to the 

zero velocities. 

Figures H-55 through H-81 present water depths measured by the ADS 3600 and by the 

reference depth meter (bubbler) for each 24-hour period of Test E. As expected, considering the 

configuration of the test site, ADS 3600 water depths were lower than the reference depths. It is 

46 
only periodically that the ADS 3600 depths were higher. Manual readings at the verified flow 

meter location are presented on the figures. Since these data points are difficult to decipher, 

Table 4-10 presents all the manual readings taken during the tests. 

Table 4-10. Daily Manual Level Measurement – ADS 3600 

Verification of level measurement 

Site and location Time Meter 

reading 

Manual 

reading Gap Site and location Time Meter 

reading 

Manual 

reading Gap 

(hh:mm) (mm) (mm) ( percent) (hh:mm) (mm) (mm) ( percent) 

Date : 2001/06/28 Date : 2001/07/09 

Reading #1 7:04:10 221 226 -2.0 Reading #1 7:03:00 195 192 1.5 

Reading #2 7:05:10 222 224 -0.7 Reading #2 7:04:00 198 195 1.4 

Reading #3 7:06:10 222 228 -2.8 Reading #3 7:05:00 200 

Reading #4 7:07:10 221 224 -1.5 Reading #4 7:06:00 199 200 -0.5 

Reading #5 7:08:10 224 224 -0.1 Reading #5 7:07:00 203 

Extra reading Extra reading 

Average reading : 222 225 -1.4 Average reading : 197 198 -0.4 

Comments Condensation on Ultrasonic probe, 

paper on the ring bender 

Comments Condensation on Ultrasonic probe. 

Everything seems ok 

Date : 2001/06/29 Date : 2001/07/10 

Reading #1 7:28:00 275 Reading #1 18:34:00 336 350 -4.0 

Reading #2 7:29:00 303 310 -2.1 Reading #2 18:35:00 327 340 -3.7 

Reading #3 7:30:00 309 310 -0.3 Reading #3 18:36:00 325 330 -1.4 

Reading #4 7:31:00 313 315 -0.8 Reading #4 18:37:00 321 328 -2.2 

Reading #5 7:32:00 270 315 -14.4 Reading #5 18:38:00 315 324 -2.8 

Extra reading Extra reading 

Average reading : 299 305 -2.1 Average reading : 325 334 -2.9 

Comments Comments Little condensation on Ultrasonic probe 

(less than usual). Everything seems ok 

Date : 2001/07/03 Date : 2001/07/13 

Reading #1 7:42:00 243 248 -2.1 Reading #1 7:44:00 360 352 2.4 

Reading #2 7:43:00 243 245 -0.7 Reading #2 7:45:00 367 360 1.8 

Reading #3 7:44:00 244 248 -1.8 Reading #3 7:46:00 368 

Reading #4 7:45:00 244 248 -1.6 Reading #4 7:47:00 378 375 0.8 

Reading #5 7:46:00 220 250 -11.8 Reading #5 7:48:00 385 380 1.4 

Extra reading Extra reading 

Average reading : 239 248 -3.6 Average reading : 373 367 1.5 

Comments There is condensation on the back 

part of the Ultrasonic probe. 

Everything seems ok 

Comments Condensation on Ultrasonic probe. 

Everything seems ok 

Date : 2001/07/05 Date : 2001/07/15 

Reading #1 7:51:00 245 Reading #1 5:52:00 206 213 -3.3 

Reading #2 7:52:00 245 247 -1.0 Reading #2 5:53:00 206 210 -1.8 

Reading #3 7:53:00 244 247 -1.2 Reading #3 5:54:00 205 210 -2.5 

Reading #4 7:54:00 245 250 -2.1 Reading #4 5:55:00 185 210 -11.8 

Reading #5 7:55:00 244 250 -2.6 Reading #5 5:56:00 173 208 -16.9 

Extra reading Extra reading 

Average reading : 244 248 -1.4 Average reading : 195 210 -7.2 

Comments Everything seems ok. We took photo. Comments A few drops under the ultrasonic probes 

47 
Table 4-10. (cont’d) 

Verification of level measurement 

Site and location Time Meter 

reading 

Manual 

reading Gap Site and location Time Meter 

reading 

Manual 

reading Gap 

(hh:mm) (mm) (mm) ( percent) (hh:mm) (mm) (mm) ( percent) 

Date : 2001/07/16 Date : 2001/07/22 

Reading #1 7:07:00 308 303 1.5 Reading #1 6:44:00 185 193 -4.1 

Reading #2 7:08:00 311 305 1.9 Reading #2 6:45:00 188 190 -1.2 

Reading #3 7:09:00 313 310 0.9 Reading #3 6:46:00 193 190 1.7 

Reading #4 7:10:00 316 314 0.7 Reading #4 6:47:00 167 192 -12.9 

Reading #5 7:11:00 313 315 -0.5 Reading #5 6:48:00 161 197 -18.4 

Extra reading Extra reading 

Average reading : 312 309 0.9 Average reading : 179 192 -7.1 

Comments Condensation on Ultrasonic probe. 

Debris accumulated on the bender. 

Everything seems ok 

Comments No accumulation on the bender. 

Date : 2001/07/18 Date : 2001/07/23 

Reading #1 20:06:00 356 392 -9.1 Reading #1 6:46:00 207.19 213 -2.7 

Reading #2 20:07:00 338 375 -9.8 Reading #2 6:47:00 206.73 215 -3.8 

Reading #3 20:08:00 319 362 -11.9 Reading #3 6:48:00 215 

Reading #4 20:09:00 285 340 -16.2 Reading #4 6:49:00 187.17 213 -12.1 

Reading #5 20:10:00 261 322 -18.9 Reading #5 6:50:00 177.85 218 -18.4 

Extra reading Extra reading 

Average reading : 312 358 -12.9 Average reading : 195 215 -9.3 

Comments Comments Condensation on the ultrasonic 

probe. 

Date : 2001/07/20 Date : 2001/07/24 

Reading #1 7:57:00 569 565 0.8 Reading #1 7:27:00 227 228 -0.6 

Reading #2 7:58:00 576 Reading #2 7:28:00 229 232 -1.3 

Reading #3 7:59:00 597 590 1.2 Reading #3 7:29:00 230 232 -1.0 

Reading #4 8:00:00 559 603 -7.3 Reading #4 7:30:00 205 235 -12.7 

Reading #5 8:01:00 617 Reading #5 7:31:00 198 237 -16.6 

Extra reading Extra reading 

Average reading : 575 590 -2.5 Average reading : 218 233 -6.5 

Comments 2 fist photo. Condensation on the 

ultrasonic probe 

Comments 

Date : 2001/0721 Date : 

Reading #1 7:51:00 224 233 -4.1 Reading #1 

Reading #2 7:52:00 220 230 -4.6 Reading #2 

Reading #3 7:53:00 219 228 -4.0 Reading #3 

Reading #4 7:54:00 190 228 -16.5 Reading #4 

Reading #5 7:55:00 181 225 -19.4 Reading #5 

Extra reading Extra reading 

Average reading : 207 229 -9.6 Average reading : 

Comments Condensation on Ultrasonic probe Comments 

48 
The periodic air purges to flush debris at the end of the bubbler injection tube can be observed in 

the data. Downward spikes around 5:00, 9:00, and 21:00 on June 30 represent air purges, which 

have no impact on the flow rate. Spikes (amplitude of roughly five to ten inches) and/or shifts 

(up and down) can be observed almost daily in the ADS 3600 signal. Spikes become very 

frequent from July 20 on. According to ADS staff, this is due to condensation under the 

ultrasonic probe. It should be noted that sewers typically have a humidity of 100 percent, and 

condensation is likely to occur. 

Figures H-82 through H-108 present velocities measured by the ADS 3600 and by the reference 

flow meter for each 24-hour period of Test E. There are a few zero readings of the ADS 3600 

velocity meter. When the reference velocities fall below 0.49 ft/sec (0.15 m/sec), the ADS 3600 

velocity meter records zero. 

Figures H-109 through H-117 present comparisons between water depth output by the reference 

depth meter (bubbler) and three water depth readings output by the ADS 3600: the pressure 

depth, average ultrasonic depth and final depth. The final depth is either the pressure depth or the 

average ultrasonic depth. A built-in proprietary algorithm selects the reading to be used, so it is 

always superimposed on either curve. The decision is not always a good one, as shown in Figure 

H-112, where the pressure depth is more stable than the average ultrasonic depth but the final 

depth is mostly the average ultrasonic reading. 

4.5.2.3 General Verification Tests 

Test E was composed of two parts: the performance evaluation and the general evaluation. 

Appendix C presents a day-to-day description of the tests. 

4.5.2.3.1 Installation, Configuration, and Calibration 

ADS staff, composed of a project manager, a field manager, a field technician, and an analyst, 

completed field installation of the ADS 3600. The TO helped the ADS field manager with the 

underground installation and supervised all activities of ADS during configuration and 

calibration. The ADS team performed almost all the fieldwork. A complete crew (except the 

project manager) was on-site from June 18 to July 7, 2001; the field analyst who could perform 

any sewer intervention stayed on-site July 7 - 17, 2001. 

The installation activities of ADS were completed as follows: 

• The analyst beside the manhole linked a laptop computer to the ADS 4000 transmitter. 

• The project manager beside the manhole managed the safety harness. 

• One ADS technician entered the pipe, supervised by TO personnel, and installed the 

equipment. 

• A second technician entered the manhole to assist the technician already in the pipe. 

The time spent by the TO staff was not accounted in the observed number of person-hours 

required to install the flow meter shown in Table 4-11. Four individuals could have performed 

the same job in the same amount of time during a normal installation. 

49 
Table 4-11. Time Estimate Required to Install, Operate and Service Flow Meter 

Estimate by Observed by Frequency Activities Work class* ADS tester team 

(person-hours) (person-hours) (if applicable) 

Installation, Configuration and Calibration 

Physical installation 

Configuration of the 

transmitter 

Initialization of the velocity 

measurement 

Initialization of the level 

measurement (Zeroing of 

the level probe) 

Start-up and trouble 

shooting 

Replacement of a level 

probe 

Field Service 

Personnel 

Field Service 

Personnel 

Field Service 

Personnel 

2 

1 

1 

6 

3 

3 

1 

1 

1 

Field Service 

Personnel 1 2 1 

Field Service 

Personnel 

Field Service 

Personnel 

 Total*

1 

1

 7 

48 hours 

3 

65 

1 

Every 2-3 yrs 

N/A 

Operation, Maintenance and Service 

Replacement of desiccant 

(SENSOR) 

Field Service 

Personnel .25 Twice a year 

Replacement of on-board 

memory battery 

Field Service 

Personnel N/A Once a year 

Replacement of the input 

board in the transmitter 

Completed in the 

office by technician; 

not done in the field. 

N/A Several 

Years apart 

Replacement of the output 

board in the transmitter 

Completed in the 

office by technician; 

not done in the field. 

N/A Several 

Years apart 

Replacement of the main 

board in the transmitter 

Completed in the 

office by technician; 

not done in the field. 

N/A Several 

Years apart 

Probes maintenance 

recommended by the 

manufacturer 

Field Service 

Personnel 1 4 

* The work class: project manager, field manager, field technician, data analyst 

The installation, configuration and calibration took approximately 16 person-hours (four people a 

half day). No problems occurred during the installation. However, attention should be paid to the 

bender when installing the band. When screwing it down, the bender must push toward the pipe 

wall. If it does not, it will not squeeze the band tightly and debris could accumulate. 

The installation took approximately eight person-hours. Configuration and calibration required 

another eight person-hours and involved four steps (Appendix F): 

50 
1. Configuration and calibration of the ultrasonic depth meter; 

2. Configuration and calibration of the pressure depth meter; 

3. Configuration and calibration of the Doppler velocity probe; and 

4. Configuration and calibration of flow computation options, such as: 

o Depth measurement used; 

o Calibration or the pressure depth probe with the ultrasonic depth probe; and 

o Range of velocity expected (fast or slow). 

The calibration of the reference flow meter required one specialized tool. A Marsh-McBirney 

Model 2000 portable velocity meter was used to measure the peak velocity in the pipe section. 

This value was required to calibrate the gain of the Doppler velocity probe. 

After calibration with a maximal dry weather flow of 1.71 MGD (75 L/sec), the official test 

began June 20 with the test first replica of Test C. It was discovered after this test that the 

ultrasonic depth sensor was not measuring properly. It was decided to replace the sensor and 

restart the verification. Since tracer dilution was performed to verify the performance of the 

reference meters, the test was considered valid for the reference meters and renamed C0 instead 

of C1. 

The ultrasonic depth probe was replaced and verification of the transmitter and probes was done 

to understand the behavior of the flow meter and try to find a better tuning. This was completed 

while waiting for the arrival of a spare component required for the other flow meter verified at 

the same time. The verification officially began on June 28, 2001. 

4.5.2.3.2 Operation 

The ADS 3600 operation and maintenance manual includes a chapter about unit maintenance. 

ADS recommends a local check at installation, during a monitor site visit and every four months 

or during battery replacement. In summary, the following elements have to be observed: 

• Status of the casing; 

• Status of the battery pack; 

• Verification of the desiccant’s color (for pressure probe); 

• Verification of the stainless steel ring installation; 

• Verification of grease or scum on the face of probes; 

• Wiping the ultrasonic depth sensor with a clean moist cloth; 

• Verification of the ultrasonic probe with a carpenter’s level; 

• Verification of debris accumulation on the ring or probes; and 

• Verification of debris accumulation on cable. 

The flow meter was inspected 16 times from June 28 to July 24, and no debris accumulation was 

observed. Since the probes are thin and have a good hydraulic profile, they did not have a 

tendency to accumulate debris. 

Except for a thin film of grease, the probes were clean at the end of the test. During verification 

in the sewer, drops of condensation were observed on the underside of the ultrasonic depth 

51 
probe. Since there is always some condensation in sewers, the ultrasonic probe was not be wiped 

during verification. 

4.5.2.3.3 Time for Data Retrieval 

There was one period following completion of tests B, C, and D, during which data were not 

retrieved for seven consecutive days. The objective was to verify the time required to retrieve 

data during a normal data retrieval period. 

For the period of seven days, it took approximately 1.3 minutes per day to log the one-minute 

data. This delay was reasonable for a seven-day period, but it may become restrictive for longer 

data collection intervals. 

For retrieval of two to four days of data, the transmitter took approximately two to three minutes 

per day of one-minute data logging. This is probably due to the time required to establish 

communication with the transmitter (see Appendix C, Table C-3 for detailed results). 

4.5.2.3.4 Dismantling 

The probes and the transmitter were dismantled, cleaned, and photographed on July 25, 2001. 

None of the components had been damaged or altered during the tests. 

4.5.2.3.5 General Characteristics of the ADS 3600 

As discussed in Section 4.2.1.1, the probes have a good hydrodynamic profile. The stainless steel 

band holding the probes in place is well designed. It is thin enough to fit the exact shape of the 

pipe and thick enough to have good strength. However, the bender must be pushed onto the pipe 

wall while securing its position. 

The transmitter is well designed for sewers and is easy to hang in the manhole. It has a handle on 

the top to facilitate manipulation and protect connectors. It is waterproof and protected against 

infiltration by a pressurized casing, which is put under approximately 12 psi (82.7 kPa) of air 

pressure. A special internal battery supplied by ADS powers the unit and provides complete 

intrinsically safe protection. There is no connector on the casing for external powering. The 

internal battery is not rechargeable, and it is expensive. The vendor indicates that this battery can 

last up to one year while collecting 15-minute data. Such a long logging period is not useful in 

many combined sewer overflow (CSO) applications, such as modeling and diagnostic, which 

generally require a five-minute period. For data validation purposes, it may become useful to 

perform monitoring at a higher frequency to eliminate spikes caused by temporary local 

disturbances. When a long data-logging period is used, short local disturbances like standing 

waves, surge, or backwash can result in two logging intervals without valid measurements. These 

local disturbances are more frequent during the high flows of a storm event compared to dry 

weather flows. 

The ultrasonic depth probe has a specially designed sliding support to facilitate its installation 

and adjustment. Its low dead band (0.5 inch, 13 mm), low depth profile (0.875 inch, 22 mm), and 

52 
four probes incorporated in the same casing are characteristics that made this probe particularly 

well adapted to sewer pipes. This probe is, however, more affected by local waves than the 

pressure probe, which performs an integration of the various depths above the probe. 

The configuration of the transmitter has various options. For example, it is possible to compute 

the flow using the depth from the ultrasonic depth probe, the pressure probe, or the better of the 

two results according to an algorithm programmed into the flow meter. The ADS 3600 used 

during testing was configured using this last configuration. 

ADS expressed concern about using a cable longer than that typically supplied with the Model 

3600 (25 ft [7.6 m]) because of possible noise in the longer cable. The cable used during 

verification was the standard 25 ft length. This should be a consideration for permanent 

installations. It might be more convenient to install the transmitter in a control cabinet close to 

the street or in a service building. The length of the cable’s probes, the data acquisition 

frequency, the powering options, and the packaging option are not well adapted to CSO real-time 

control applications. 

The transmitter is available with a telephone modem option. With the modem and related 

software, the logging of many transmitters can be performed using a standard telephone line, 

instead of going on-site. The ADS 3600 also provides flexibility to connect a rain gauge and an 

automatic sampler for sampling proportional to the recorded transmitter flow. 

4.6 Reference Meters 

4.6.1 Scatter Plots 

As with the presentation for the ADS 3600, three types of scatter plots are presented for the 

reference meter data: a system behavior (velocity versus depth) plot, flow rate comparison plots, 

and water depth comparison plots. These plots, showing the data collected for all of the reference 

meter runs, are presented in Appendix H. 

The system behavior scatter plot was presented in Figure 4-18, showing the hydraulic conditions 

at the reference flow meter testing site during Test C (no back flow). There are 1,353 data points 

on this figure, segregated in three groups: stable (984 data points), ebbing (261) and rising (108) 

water profiles. There are fewer data points for the rising water profiles because the transition is 

more rapid under this condition. Apart from the stable water profiles, there is no single 

relationship between velocity and water depth. The best-fit curve polynomial equation drawn 

from stable conditions data points is indicated on the figure, along with its coefficient of 

determination (R2

 = 0.9938). 

Figure H-118 presents a flow rate comparison plot between the reference flow meter and tracer 

dilution for all data from replicas C0 and C3. The first replica of Test C with tracer dilution was 

renamed C0 (instead of C1) after a failure and subsequent replacement of the pressure depth 

probe of the ADS 3600. There are 164 data points on this figure, segregated in two groups: stable 

conditions (139 data points) and transition periods (25 data points). Transition data points are 

slightly more scattered around the perfect fit line than the stable data points. Also presented on 

53 
this figure are the correlation coefficients (r) between the stable data points and the perfect fit 

line (r = 0.998) and between all data and the perfect fit line (r = 0.997). Figures H-119 and H-120 

present the same data for C0 and C3 separately. 

Figures H-121 to H-124 present water depth comparison plots between the reference depth meter 

(bubbler) and manual readings for tests B, C, and D respectively, and these three tests combined, 

along with the perfect fit line. 

4.6.2 Deviation Distribution Plots 

Figures H-125 to H-130 present the flow rate deviation distributions (reference flow meter 

compared to the flow rate calculated from the tracer dilutions) for all data of replicas C0 and C3. 

The deviation is presented in two-percent increments. Indicated on the figures are the: 

• Margin of deviation (±X percent) that contains 95 percent of all measurements (i.e. 

standard ±2σ); 

• Percentage of measurements within a margin of deviation of ±8.7 percent (wet-weather 

racer dilution error); 

• Mean deviation of all measurements; and 

• Median deviation (provides an indication of the spread). 

Figure H-125 presents the flow error distribution for replicas C0 and C3. It is a bell-shaped curve 

centered on -0.9 percent. The largest negative error is -45.8 percent and the largest positive error 

is 20.5 percent, both of which occurred during dry-weather conditions (during replica C3 at 8:30 

and 7:45, respectively). Replica C3 was performed on July 15, starting in the early morning 

when the flow rate was roughly 0.80 to 1.03 MGD (35 to 45 L/sec). At such low flow rates, the 

relative error tends to be larger since the flow meter resolution is 0.023 MGD (1 L/sec). 

Excluding these low flows, the largest negative error is -9.5 percent and the largest positive error 

is 19.7 percent. Both data points are during transition periods (during C3 at 10:55 and, C0 at 

14:30 respectively). Of the measurements, 84.1 percent are within the margin of error of 8.7 

percent, which is the tracer dilution error for wet-weather conditions, as indicated in the Protocol 

for Flowmeters for Wet Weather Flow Applications in Small- and Medium-Sized Sewers (Draft 

4.0, September 2000) (protocol). The protocol referred to the fact that 95 percent of 

measurements should be within this margin of error. Figures H-126 and H-127 present the same 

data for C0 and C3 separately (used for the QAPP). Figures H-128 to H-130 present the same set 

of three figures but for stable condition data points only. 

Figures H-131 to 4-133 present the water depth error distributions (reference depth meter 

compared to manual readings) for tests B, C, and D, respectively, while Figure H-134 presents 

all data from tests B, C, and D combined. These error distributions are presented in inches (mm) 

since the protocol referred to an acceptable error of two percent of full scale (full scale is 62.5 in. 

[1,586 mm]), which represents 1.25 in. (31.7 mm). The error is presented in 0.25 in. (6.4 mm) 

increments. Indicated on the figures are the: 

• Margin of error (±X percent) that contains 95 percent of all measurements (i.e. standard 

±2σ); 

54 
• Percentage of measurements within a margin of error of ±2 percent full-scale; 

• Mean error of all measurements; and 

• Median error (provides an indication of the spread). 

Figure H-134 presents the water depth error distribution for all data of tests B, C, and D 

combined. It is a bell-shaped curve with a mean error of 0.13 in. The largest negative error is 

-3.74 in. recorded during replica D3 in the transition period of between 29.7 MGD (1,300 L/sec) 

with a 54-inch back flow to 1.71 MGD (75 L/sec) with no back flow (at 2:20). The largest 

positive error is +4.00 in. recorded during replica C1 in the transition period of between 

17.1 MGD (375 L/sec) to 29.7 MGD (1300 L/sec) (at 12:00). The large positive and negative 

errors are due to waves at high flows (17.1 and 29.7 MGD [750 and 1,300 L/sec], respectively) 

since the manual readings are more affected by waves than is the bubbler. 

Figure H-135 presents the water depth error distribution (reference bubbler depth meter 

compared to the reference ultrasonic depth meter) for all data from tests B, C, and D. It is 

roughly a centered bell-shaped curve. There are 12 data points outside ±5.0 in. The larger 

positive errors are during transition periods from 1.71 to 17.1 MGD (75 to 750 L/sec) and from 

8.56 to 29.7 MGD (375 to 1,300 L/sec) while the larger negative errors are during the transition 

period between 29.7 to 8.56 MGD (1,300 to 375 L/sec). The overestimation at 29.7 MGD (1,300 

L/sec) (all replicas) and underestimation at 17.1 MGD (750 L/sec) (replicas C0, C1 and C3) are 

due to the ultrasonic depth meter being more affected than the bubbler by waves caused by the 

high flows. 

Figure H-136 presents the velocity error distribution (velocity calculated from the reference flow 

rate and water depth compared to velocity calculated from tracer dilutions) for replicas C0 and 

C3. The largest negative error is –45.8 percent and the largest positive error is 20.5 percent, both 

from replica C3 (at 8:30 and 7:45, respectively). Errors are largest at low flows and during 

transition periods. The error made on the velocity is the summation of the error made on flow 

rate and the one on water depth since it is the result of a calculation (velocity equals flow rate 

divided by area). 

4.6.2.1 Tests B, C, and D 

Only figures that supply new information are presented in this section since the bulk of the 

reference data is presented with the ADS 3600 flow meter data in Figures H-1 to H-108. 

Figures H-137 through H-139 present flow rates from the reference flow meter and from the 

flow under the downstream gate equation for the three replicas of Test B, while Figures H-142 

through H-144 present the same information for the three replicas of Test D. Figures H-140 and 

H-141 present flow rates from the reference flow meter, from tracer dilutions, and from the flow 

under the upstream gate with the Craig Collector flow rate added for replicas C0 and C3, 

respectively. On both figures, the largest differences between the reference flow meter and tracer 

dilutions are in the transition zones indicated by the square markers (rising and ebbing water 

profiles). As mentioned, replica C3 (Figure H-141) was performed on a Sunday, with a very low 

early-morning flow. From 11:30, there was not enough water in the Versant-Sud tunnel to 

maintain a stable flow rate of 29.7 MGD (1,300 L/sec) for the prescribed time. 

55 
Figures H-145 through H-154 present water depths from the reference depth meter (bubbler), 

manual readings and reference ultrasonic depth meter for the three replicas of Test B, four 

replicas of Test C, and three replicas of Test D, respectively. Water depths from all three 

instruments for the three replicas of both tests B and D (Figures H-145 through H-147, and 

H-152 through H-154) are practically identical. Water depths of the four replicas of Test C 

(Figures H-148 through H-151) vary more, principally due to the presence of waves during these 

tests. Replicas C0, C1, and C3 present the same pattern: manual readings are higher than the 

bubbler and the ultrasonic depths are lower during the 17.1 MGD (750 L/sec) stable period while 

the opposite is found in the 29.7 MGD (1,300 L/sec) stable period. Both manual readings and 

ultrasonic depths are affected by waves whereas the bubbler buffers the information over a larger 

volume of water. It should be noted that the manual readings are taken very close to the bubbler 

site. 

Figures H-155 and H-156 present velocities calculated from the reference flow meter data and 

tracer dilution data for replicas C0 and C3, respectively. Since these velocities are calculated 

with the same water depths but different flow rates and because the errors on the water depths 

and flow rates are summed, there is simply more noise in the signal. 

56 
Chapter 5

Quality Assurance/Quality Control 

The assessment of the accuracy, precision, and completeness of the flow meters undergoing 

testing requires the existence of reference data for comparison and validation. At the beginning 

of the project, it was decided that the reference flow rates would be produced using a 4-path 

Accusonic flow meter and reference water depths from a bubbler. The choice of a flow meter to 

assess the performance of other flow meters was not obvious. However, considering that a 4-path 

Accusonic flow meter has a theoretical uncertainty of ±4 percent for flows in open channel 

systems (this is smaller than the uncertainty associated with tracer dilution; refer to Appendix 

D-3) and that flow rates can be measured continuously in real time at a low cost, the choice of a 

4-path Accusonic flow meter to generate the reference flow rates was justified. 

Two reference depth meters were used: the bubbler and the ultrasonic. The bubbler was preferred 

as the primary reference for the following reasons. 

• It exhibits no significant bias when properly installed and operated. 

• It provides measurements for a large flow range. 

• It is more reliable. 

• It is the depth measurement linked with the reference flow meter. 

The first step toward the use of the Accusonic flow meter as the reference flow meter was the 

validation of its measured flow rates. Lithium tracer dilutions were used to verify that the flow 

rates measured by the reference flow meter were accurate. 

Validation of the data provided by the reference flow meter and the reference water depth meter 

was performed as rigorously as possible. Tight review of all the procedures used to collect and 

handle data was performed, and is described in the following sections. Such reviews are essential 

to assure that data quality conforms to protocol specifications. After the validation of the data 

collected in the field, described in Section 5.1, the Quality Assurance Project Plan (QAPP) was 

designed to verify the representativeness of the lithium concentrations measured by the standard 

laboratory. These concentrations were used to validate the flow rates measured by the reference 

flow meter. The final objective of the QAPP consisted of verifying that the measurements made 

by the reference devices, a reference flow meter and a bubbler depth meter, were representative 

of the true values considering the uncertainty margins associated with each measurement device. 

These validations are described in Sections 5.2 through 5.4. 

5.1 Audits 

Audits of the field testing and the reporting used in the testing were completed several times over 

the course of the verification testing. 

57 
5.1.1 Field Audits 

During the course of the project, the QAPP representative visited the field several times. These 

visits were conducted without prior notice and included the injection site, the sampling site, and 

the control gate. The objectives of these visits were to ensure the conformity of the sites with 

respect to protocol specifications; and quality measurement procedures. 

At each visit, the QAPP representative verified the measurement procedures followed by the 

field crew. In particular, the synchronization and frequency of measurements, the configuration 

of the measurement sites, the handling of the sampling bottles, and the injection procedure of the 

concentrated lithium were verified. 

Observations made during field visits permitted observation of the methods used by the field 

crewmembers. It was observed that the steps required assuring good quality data were 

meticulously followed according to the VTP. All members knew exactly the tasks at hand, when 

to perform them and how to execute them. The following items were specifically observed: 

• Crewmembers had a thorough knowledge of the hydraulics of the system. They were able 

to assess flow rates under the gates and had a good understanding of the flow delays 

between the injection and the sampling sites. Therefore, they could accurately control the 

flows in the sewer network and evaluate the time required to reach a steady-state flow. 

• The existing communication procedure between the crewmembers was efficient, no 

matter where they were located. This guaranteed all members had real-time access to the 

available information. All collected data were quickly saved at a centralized location 

notwithstanding the fact that some were collected manually. 

• The data collected were well synchronized. This validated the right to use paired sample 

data to assess the accuracy of time-varying measurements provided by different 

measurement devices or different laboratories. 

• The measurement devices were properly configured and installed to provide 

measurements that were as accurate as possible. For example, manual water depth 

measurements were made using a homemade device designed to reduce variations that 

could be introduced by the flow turbulence observed at the sampling site during the wet 

weather flows of Test D. 

• The procedure followed to label the sampling bottles helped ensure that no error could be 

made on location or on the time when samples were collected. 

Field report check-ups conducted in conjunction with field visits verified that the procedures 

followed by the field crewmembers when collecting and handling data met the requirements of 

the QAPP. The field crewmembers were very careful and attentive to details to assure high 

quality data. 

58 
The field reports were completed with accuracy and included pertinent comments. The nonconformities noted were minor, mainly dealing with non-recorded departure times and the names 

of technicians. The collected data was appropriately handled, and the data in the spreadsheets 

used for validation and flow computations was found representative of the measurements made 

in the field. 

The only negative observation concerned the handling of the sample bottles at the tracer injection 

site. The same individual collected the blank and the concentrated samples. This person took 

precautions to isolate the blank samples from the concentrated ones (e.g., changing gloves when 

manipulating new bottles, storing blank bottles in watertight bags). Nonetheless, the risk of 

contaminating the blank samples was not completely eliminated. It would have been safer to 

have a sampling site for the blanks that was geographically distant from the injection site. 

5.1.2 Report Audit 

The data collected in the field were transcribed according to the VTP in different field reports. 

One of the objectives of the audit was to verify if all required reports had been filled out and that 

no data was missing. To verify the completeness of the information gathered in the field, 

verification sheets were specially developed for the QAPP. A verification sheet was filled out for 

each report produced during the field tests. These verification sheets included: 

Preliminary Tasks 

• Instruments Calibration Report Verification 

• Laboratory Report Verification 

Test Tasks 

• General Report Verification 

• Test Report Verification: Daily General Verification 

• Test Report Verification: Monthly General Verification 

• Test Report Verification: Control Table of Test 

• Injection Site Report Verification 

• Sampling Site Report Verification 

• Sampling Site Measurement Verification 

• Tracing Sheet for Injection Site Verification 

• Tracing Sheet for Sampling Site Verification 

• Laboratory Results Verification 

• Flow Meter Configuration and Calibration Verification 

• Flow Meter Operation and Maintenance Verification 

• Flow Meter Software Checklist Verification: Ease of Use 

• Flow Meter Software Checklist Verification: Functionality and Flexibility 

• Flow Meter Installation Report Verification 

• Flow Meter Dismantling Report Verification 

59 
These verification sheets were designed to quickly assess whether the information contained in 

the field or laboratory reports was complete, as specified in the VTP. These sheets were designed 

to follow the data collection and handling sequences in chronological order and were divided 

into three sections: 

Section 1 – General Information 

The first section contained information such as the name of the test, the names of the technicians 

present during the test, the names of visitors, and the time of their visits. 

Section 2 – Field Data 

A part of this section was designed to check on the lithium tracer sampling frequencies, (i.e., 

blanks, concentrated and diluted samples for both the standard and control laboratories) and on 

the lithium concentration measured by the laboratories. The chronological sequence of the sheets 

enabled one to track all the sampling bottles collected during the tracer dilution tests (tests C0 

and C3) from the collection sites to the laboratories. The injection and sampling sites verification 

sheets enabled one to verify if all lithium samples had been properly collected and labeled. The 

tracking sheets for injection and sampling sites confirmed that the standard and control 

laboratories received all samples. Finally, the laboratory results verification sheets guaranteed 

that all samples sent to the laboratories were analyzed and the results sent back to the TO for 

validation and flow computation. 

This section was used to quickly verify that flow rates, velocities and water depths had been 

measured using the frequencies and the accuracy specified in the VTP. Particular attention was 

paid to the synchronization of the data saved in the data report spreadsheet since the data 

originated from several sources. Data on the sampling site measurement verification sheets 

included: 

• Bubbler measurements (data transferred from the PLC to an industrial PC using software 

developed by the TO and then to a spreadsheet); 

• Ultrasonic depth measurements (data transferred from the ADS data logger to a 

spreadsheet); 

• Manual measurements (data directly recorded in a spreadsheet); 

• Reference flow rates and velocity measurements (data transferred from the PLC to an 

industrial PC using a software developed by the TO and then to a spreadsheet); and 

• ADS 3600 flow rate and water depth measurements (data transferred from the ADS data 

logger to a spreadsheet). 

Time series related to flow computations under the upstream and downstream gates, including 

water depths and gate positions, were verified on the test report verification sheet, Control Table 

of Test. 

Due to the large amount of collected data and its various sources, only a fraction of the data 

reported in the spreadsheet used for flow, water depth, and velocity validation were audited. 

These random audits indicated proper handling of the field data. For all testing, the data saved in 

60 
the spreadsheets was identical to the raw measurements and was associated to the exact time 

collected. Moreover, the set of data saved in the spreadsheet was complete and respected the 

sampling frequency reported in the VTP. 

The field data section allowed assessment of the completeness of the information related to the 

measurement devices. The information contained in the flow meter configuration and calibration 

verification sheet, the flow meter operation and maintenance verification sheet, the flow meter 

software checklist verification sheet, the flow meter installation verification sheet, and the flow 

meter dismantling verification sheet, verified that all reports related to flow measurement devices 

had been properly completed. 

Section 3 – Non-Conformity Follow-Up 

This section included questions required to complete the general information and the field data 

sections. Answers provided by the project manager or the crewmembers are also reported. This 

permitted good communication between the QAPP representative and the project manager in 

order to complete the field reports or to explain observations that were not in conformity with the 

VTP. 

It was during the question-and-answer dialogue that the explanation of the existence of the C0 

test was reported (this test was not planned in the original VTP). For this particular nonconformity, during the course of the original Test C1, the ADS 3600 flow meter did not work 

properly. Since this test was done in conjunction with a tracer dilution test, it was decided to 

keep the dilution results, but to rename the Test C0 for the validation of the reference flow meter. 

Thereafter, Test C1 was repeated without dilution to get proper measurements with the ADS 

3600 flow meter. 

5.2 Validation of the Lithium Tracer Methods 

Lithium dilution tests were used to validate the reference flow meter. Before using the tracer for 

the meter validation, the lithium concentrations provided by the standard laboratory needed to be 

validated. Validation of the results provided by the standard laboratory (Laboratoire de 

l’environnement LCQ Inc.) consisted of comparing the standard lithium concentrations with 

those measured by another laboratory, referred to as the control laboratory (Laboratoire de la 

qualité du milieu, Centre d’expertise en analyse environnementale du Québec). This process was 

conducted during the validation of the reference flow meter. Results showed that the 

concentrations measured by the standard laboratory were statistically equivalent to those 

measured by the control laboratory. Since the probability that the two laboratories measured the 

wrong concentrations is very low, it was concluded that the standard laboratory was providing 

concentrations that had the level of accuracy needed to validate the reference flow meter. 

To analyze the performance of the verified flow meters, it was necessary to confirm the 

validation of the standard laboratory analyses previously conducted during the course of the 

validation of the reference flow meter. Two new lithium dilution tests were conducted to verify, 

using the same analysis tools, whether the standard laboratory was still providing concentration 

results representative of the real concentrations in the samples. 

61 
5.2.1 Sample and Data Handling 

Before comparing the concentration results provided by the two laboratories, proper handling of 

the samples had to be guaranteed. Therefore, it was verified that all samples were properly 

collected and identified, they had been sent to the laboratories for analysis, and were returned 

with the concentration results. 

The concentrations measured by the two laboratories were recorded in a spreadsheet for 

statistical analysis. In order to guarantee that the results used for the statistical analysis were 

valid, all the lithium concentrations recorded in the spreadsheet were crosschecked with the 

concentration results sent by the laboratories. Moreover, all the equations programmed into the 

spreadsheets (analysis results from standard and control laboratories) were validated according to 

the theory presented in Appendices D-1 and D-2. 

5.2.2 Methods Used to Validate Lithium Concentrations 

The lithium concentrations collected in the field and needed to compute the flow rates in the 

vicinity of the reference flow meter originate from three sources: 

1. The concentrated samples collected in the injection cylinder. The concentrations at this 

site should match the lithium concentration of the prepared lithium mixture. For the 

duration of a given test, this concentration was assumed to be constant for the purpose of 

flow computation. The statistical analysis made for the validation of the concentrations 

measured by the standard laboratory would reflect this assumption. 

2. Blank samples collected upstream of the lithium injection point. They were used to verify 

that lithium was conveyed in the QUC sewer network and to compute flow rates near the 

reference flow meter. These concentrations were assumed to be time varying and were 

treated as such when performing the statistical analyses. 

3. Diluted samples collected near the reference flow meter, which were treated the same as 

the blank samples when performing hypothesis testing on the lithium concentrations. 

5.2.2.1 Concentrated Samples 

Two tests were used to validate the accuracy of the concentrated samples. The first test was a 

standard statistical test to compare the means of two normally distributed populations. In the 

literature, the test is referred to as a “Two-population test of population means for normal 

populations with the same variance” (Appendix D-1). This test compared the means of the 

concentrated samples, as measured by the standard and control laboratories, and verified whether 

their means differed significantly. A null hypothesis (the mean of the two populations are 

identical) and an alternate hypothesis (the mean of the two populations are different) were 

established, and a variable called the “test statistic” was computed using the null hypothesis. The 

probability of the test statistic being outside the acceptance range was given by the level of 

significance chosen. For this project, a level of significance of 0.05 was chosen to indicate the 

62 
likelihood that the test statistic was outside the acceptance range was low (less than five percent). 

If the test statistic was outside the acceptance range, the alternate hypothesis was accepted. 

Conversely, if the test statistic was inside the acceptance range, the null hypothesis was accepted. 

Accepting the alternate hypothesis means that there was a strong presumption that the two 

laboratories did not measure the same mean concentrations. However, it does not mean that the 

mean concentration measured by the standard laboratory was not suited to compute flow rates at 

the sampling point. If the mean concentrations measured by the two laboratories were inside the 

accuracy margins specified by the standard laboratory, there was no reason not to use the mean 

concentration of the standard laboratory. 

For the concentrated samples, the accuracy observed for the average concentration under normal 

conditions was ±0.02. The validation variable was defined as: 

2(Csl −Ccl ) x = (5-1) v (Csl +Ccl ) 

Where: Csl is the mean concentration of the standard laboratory; and 

Ccl is the mean concentration of the control laboratory. 

xv should be between ±0.04, assuming that the accuracy of the concentrations measured by the 

standard laboratory satisfied the expected accuracy (Appendix D-4). The validation chart of the 

concentrated samples is summarized in Table 5-1. 

Table 5-1. Concentrated Samples Validation Chart 

Result of accuracy test Result of hypothesis test -4% < xv > 4% -4% > xv < 4% 

Null hypothesis accepted Validation of the Validation of the 

concentrated samples concentrated samples 

Alternate hypothesis accepted Validation of the 

concentrated samples 

Rejection of the 

concentrated samples 

If the concentrated samples are rejected for the two tests, the lithium test was not used to 

compute the flow rates needed to validate the performance of the reference flow meter. 

5.2.2.2 Blank and Diluted Samples 

For the concentrated samples, two validation tests were used to assess the accuracy of the blank 

and diluted samples measured by the standard laboratory. The first was a standard statistical 

called “test on paired-sample data” (Appendix D-2). Each number of a data set was associated 

63 
with only one number in the other set. When the differences between the numbers in the pairs 

were the meaningful data, the two samples are called paired samples. The idea consists in 

verifying if the mean of the paired samples is significantly different from zero with a given level 

of significance assuming that the paired data population has a zero mean (the null hypothesis). 

The probability of the test statistic being outside the acceptance range is given by the level of 

significance chosen. As for the two-population test statistic, a 0.05 level of significance was 

used. If the test statistic is outside the acceptance range, since the probability of having such a 

result is little (less than five percent), it was concluded that the null hypothesis was wrong and 

the alternate hypothesis was accepted. Conversely, if the test statistic was inside the acceptance 

range, the null hypothesis was accepted and the alternate one was rejected. 

Accepting the alternate hypothesis means that there was a strong presumption that the two 

laboratories are not measuring the same blank or diluted concentrations. However, it does not 

mean that the concentrations measured by the standard laboratory are not suited to compute the 

flow rates at the sampling point. If the mean concentration of the paired samples was very close 

to zero and the alternate hypothesis was accepted because of the small standard deviation of the 

paired samples, there was no reason not to use the blank and diluted concentrations of the 

standard laboratory since they allow the computation of flow rates that are similar to those 

computed using the concentrations measured by the control laboratory. 

For the diluted samples, the accuracy observed for the measured concentrations under normal 

conditions was ±0.03 (value specified by the standard laboratory). The validation variable was 

defined as: 

xv = ∑ 

n 

1 





2 

(C 

(Csli 

+

− 

C

C

cl

cli

)

)





 

/ n (5-2) 

i=  sli i 

Where: Csl is the concentration of the standard laboratory; and 

Ccl is the concentration of the control laboratory.

xv should be between ±0.06, assuming that the accuracy of the concentrations measured by the 

standard and the control laboratories satisfied the expected accuracy (Appendix D-5). 

For the blank samples, the accuracy was given in absolute values and was equal to ±0.01 mg/L 

for the standard laboratory and to ±0.005 mg/L for the control laboratory. The validation 

variable, as the mean difference of concentrations measured by the two laboratories, is defined 

as: 

n 

xv = ∑(Csl −Ccl ) / n (5-3) i i 

i=1 

Where: Csl is the concentration of the standard laboratory; and 

Ccl is the concentration of the control laboratory.

64 
The blank samples validation variable should be between ±0.015 mg/L, assuming that the 

accuracy of the concentrations measured by the standard and the control laboratories satisfied the 

expected accuracy (Appendix D-6). Converse to the concentrated samples, for the bland and 

diluted samples the validation variable was defined as a mean difference. For this reason, the 

acceptance of the measured concentration could not be restricted to the deviation of xv from zero 

but also be related to the standard deviation (SD) observed. The concentration measured by the 

standard laboratory can be validated only when the mean difference of concentration between the 

two laboratories is small and when the hypothesis test is rejected due to a small variance. An 

acceptable value for the standard deviation is 0.05. The validation chart of the blank and diluted 

samples is summarized in Table 5-2. 

Table 5-2. Validation Chart for the Blank and Diluted Samples 

Dilute samples Blank samples 

-0.06 < xv > 0.06 -0.06 > xv < 0.06 -0.015 < xv > 0.015 -0.015 > xv < 0.015 Result and SD < 0.05 or SD > 0.05 and SD. < 0.05 or SD > 0.05 

Null hypothesis Validation Validation Validation Validation accepted 

Alternate hypothesis Validation Rejection Validation Rejection accepted 

If the blank or diluted samples were rejected for the two tests, the lithium test could not be used 

to compute the flow rates needed to validate the performance of the reference flow meter. 

5.2.3 Validation Results for Test C0 

Two lithium dilution tests were conducted during the course of the project. The first was 

performed during Test C0 and the second during Test C3. For Test C0, the standard and control 

laboratories analyzed 25 and five samples, respectively. The 25 samples analyzed by the 

standard laboratory originated from five different bottles, and each bottle was analyzed five 

times. The five samples analyzed by the control laboratory were produced from a single bottle. 

The data from the 30 concentrated samples were used to validate the mean concentration 

computed using the results provided by the standard laboratory. The mean concentrations 

measured by the standard and control laboratories were 45,500 mg/L and 44,900 mg/L, 

respectively. The test statistic (Appendix D-1) gives a value of 1.91 using the two-population 

test, which was inside the acceptance range. Therefore, the concentrated samples measured by 

the standard laboratory were validated for Test C0. 

Both laboratories analyzed two blank samples. For these samples, the standard laboratory results 

were lower than the detection limit of 0.01 mg/L, and the control laboratory results were 

0.008 mg/L and 0.007 mg/L. Assuming that the blank concentrations measured by the standard 

laboratory are null for concentrations lower than 0.01 mg/L (this was the assumption made for 

the computation of flow rates when the concentration measured by the standard laboratory was 

lower to 0.01 mg/L), the hypothesis test on paired samples did not permit the validation of the 

blank concentrations (Table 5-3). However, the test on the mean differences verified the 

65 
accuracy associated with the blank samples. Therefore, the blank concentrations measured by the 

standard laboratory during Test C0 were judged accurate enough to be used to validate the 

reference flow meter. 

For the diluted samples, nine pairs of samples were collected for the validation of the 

concentrations measured by the standard laboratory. Results show that the paired samples did not 

stand up to the hypothesis that they have a zero mean assuming a significance level of five 

percent. However, the test on the mean value and standard deviation of the paired samples 

indicated that the concentrations measured by the two laboratories were within their accuracy 

margins. The mean concentration of the paired samples was equal to 0.06 mg/L with a standard 

deviation lower than 0.05 mg/L. Therefore, the diluted concentrations measured by the standard 

laboratory were considered accurate enough to be used to validate the reference flow meter. 

Table 5-3. Validation Chart for Test C0 

Hypothesis Test (mg/L) Accuracy Test (mg/L) Validation Samples Lower Test Upper 

Limit Statistic Limit Lower Limit Value Upper Limit Result 

Concentrated -2.05 1.91 2.05 -0.04 0.013 0.04 Accepted 

Blank -12.7 -15.0 12.7 -0.015 (Mean) -0.008 

0.001 

Mean 0.015 

SD 0.05 Accepted 

Diluted -2.31 5.52 2.31 -0.06 (Mean) 0.06 

0.032 

Mean 0.06 

SD 0.05 Accepted 

5.2.4 Validation Results for Test C3 

For Test C3, two analyses with the concentrated samples were done. In the first analysis, the 

standard laboratory analyzed 25 samples and the control laboratory analyzed five. The 25 

samples analyzed by the standard laboratory originated from five different bottles, each being 

analyzed five times, while the five samples analyzed by the control laboratory were produced 

from a single sampling bottle. The mean concentration measured by the standard laboratory was 

42,900 mg/L compared to 38,400 mg/L for the control laboratory. 

Considering the significant difference between the mean concentrations measured by the two 

laboratories, a second analysis was conducted. Samples of the five bottles analyzed by the 

standard laboratory were sent to the control laboratory for analysis. From these five bottles, 25 

aliquots were created and analyzed. The new results obtained by the control laboratory produced 

a mean concentration of 44,000 mg/L, and confirmed that the mean concentration initially 

measured was too low. 

66 
Using the lithium concentrations obtained during the second analysis, the test statistic computed 

using the two-population test (Appendix D-1) gave a value slightly outside the acceptance limits 

considering a level of significance of 0.05 (Table 5-4). However, the mean concentration 

validation test gives for the validation variable -0.026, a value within the validation limits. 

Table 5-4. Validation Chart for Test C3 

Sample Hypothesis Test (mg/L) Mean Test (mg/L) Validation Lower Test Upper Lower Limit Value Upper Result Limit Statistic Limit Limit 

Concentrated 

Analysis 1 

-2.05 4.55 2.05 -0.04 0.11 0.04 Rejected 

Concentrated 

Analysis 2 

Blank 

-2.01 

-12.71 

-2.35 

-0.62 

2.01 

12.71 

-0.04 

Mean -0.015 

-0.026 

-0.007 

0.015 

0.04 

Mean 0.015 

SD 0.05 

Accepted 

Accepted 

Diluted -2.37 3.23 2.37 Mean -0.06 0.04 

0.035 

Mean 0.06 

SD 0.05 

Accepted 

Both laboratories analyzed two blank samples. For both samples, the standard laboratory 

measured a lithium concentration greater than 0.01 mg/L. For Test C0, it was possible to validate 

the concentration of the blank samples using a hypothesis test on paired sample data. However, 

the reliability of the test was limited due to the very small number of samples analyzed. For the 

two, paired samples the degree of freedom of the test was one, which implied a large validation 

range for the null hypothesis. Nevertheless, the test statistic was small (-0.62), which indicated 

that the mean concentration of the paired samples is close to zero. 

The validity of the blank samples measured by the standard laboratory was also confirmed by the 

evaluating whether the mean difference concentration was within the mean value validation 

limits. For the blank samples, the mean concentration is –0.007 mg/L, which was inside the 

±0.015 mg/L validation limits. Therefore, considering the results obtained with the two 

validation tests, the blank concentrations measured by the standard laboratory are accepted, 

which means they were accurate enough to validate the reference flow meter. 

For the diluted samples, nine pairs were collected for the validation analysis of the concentration 

measured by the standard laboratory. The first results provided by the control laboratory showed 

a mix-up of three sample concentrations, probably due to a handling deviation during the sample 

labeling. To ensure that the unexpected results were caused by a handling deviation, the standard 

laboratory reanalyzed the three samples, and the samples were sent to the control laboratory for 

another analysis. The results from the second analysis matched. 

Results show that the paired samples do not stand up to the hypothesis that the paired sample 

data have a zero mean assuming a significance level of five percent. However, the test on the 

67 
mean value and standard deviation of the paired samples indicates that the concentrations 

measured by the two laboratories are within the margin of accuracy. The mean concentration of 

the paired samples was equal to 0.04 mg/L with a standard deviation of 0.042 mg/L. Therefore, 

the diluted concentrations measured by the standard laboratory were considered accurate enough 

to be used to validate the reference flow meter. 

5.2.5 Conclusion 

In order to use a lithium dilution test to validate the reference flow meter, all three sources of 

data (i.e. concentrated, blank and diluted) must be accepted according to the validation tests 

described above. If one is not accepted, it is assumed that the flow rates computed using the 

lithium concentrations measured by the standard laboratory did not have the level of accuracy 

necessary to validate the reference flow meter. 

In this application, all three sources of concentrations were accepted for Tests C0 and C3. 

Therefore, all flow rates computed using the lithium concentrations measured by the standard 

laboratory could be used to validate the reference flow meter. 

5.3 Validation of the Reference Flow Meter 

This section presents the methods used and the results obtained to verify and validate the 

reference flow meter data. Two methods were used to verify the accuracy of the reference flow 

meter and to validate the reference flow data: the tracer dilution and the flow under the gate. 

5.3.1 Validation Methods 

To demonstrate that the reference flow meter was accurate and that it exhibited no bias, the 

reference flow data was compared to that obtained with the tracer dilution and the flow under the 

upstream gate for replicas C0 and C3, and compared with flow under the downstream gate for 

Tests B and D. 

5.3.1.1 Qualitative Analysis 

To assess qualitatively the validity of the reference flow data, two types of figures were 

produced: 

1. Reference meter verification: flow rate measurements: These figures present, in the case 

of replicas C0 and C3, the flow rate output by the reference flow meter, the flow rate 

calculated from the tracer dilution and the flow rate estimated from the equation of the 

flow under the upstream gate (energy balance equation). For replicas C0 and C3, the flow 

rate from the gate equation is actually the sum of the flow under the upstream gate and 

the flow from the Craig Collector (which is measured at its downstream end), delayed by 

15 minutes to account for travel time between the gate (and Craig Collector) and the 

reference testing site. Therefore, this flow rate is given as a rough approximation only. In 

the case of the three replicas of Tests B and D, there is no tracer dilution data and the 

68 
flow rate is calculated from the gate equation for the downstream gate without any 

modification. 

2. Reference flow rate comparison: reference meter versus dilution: These figures present 

the flow rate output by the reference flow meter as a function of the flow rate calculated 

from the tracer dilution (replicas C0 and C3). The y = x (or 1:1) line is drawn as an 

indication of a perfect fit between the two data sets. The correlation coefficient r 

(between the flow data and the y = x line) is also presented. A perfect fit would generate 

an r of 1. 

5.3.1.2 Statistical Analysis 

A hypothesis test on paired sample data (replicas C0 and C3) was performed to assess the 

validity of the reference flow meter. In the paired sample hypothesis test, a new data set was 

calculated, consisting of the differences between the flow rates measured by the reference flow 

meter and those computed from tracer dilution. The hypothesis test was then performed as a onepopulation test on the differences. This test validated whether the new population made of paired 

data has a zero mean. The idea consists in validating whether the mean of the paired samples was 

significantly different from zero, with a given level of significance, assuming that the paired data 

population has a zero mean (the null hypothesis). 

5.3.1.3 Reference Flow Deviation Distribution Analysis 

This test consisted in drawing the bar chart of the flow deviation distribution for which the 

deviation is defined as follows: 

∆Q = 

Qdilution −Qreference (5-4)

(Qreference +Qdilution )/ 2 

The reference flow deviation distribution test is the only test described in the protocol for which 

a quantitative assessment is done. In order to validate the measurements produced by the 

reference flow meter, 95 percent of the flow deviation data (∆Q) must be included within the 

acceptance range. According to the protocol, the acceptance limits are ±0.095 during dry weather 

flow and ±0.087 during wet weather flow. These acceptance margins were re-evaluated during 

the course of the project to better account for uncertainties related to the concentrations measured 

by the laboratories. Using the concentration accuracy margins obtained experimentally, the 

lowest acceptance margins were –0.1066 and –0.1288 for dry and wet weather flows, 

respectively. Upper acceptance limits were 0.1074 for dry weather flow and 0.1355 for wet 

weather flow (Appendix D-7). The wet-weather flow of 2.57 MGD (112.5 L/sec) was defined as 

1.5 times the maximum dry-weather flow of 1.71 MGD (75 L/sec). 

The test also included two qualitative assessments. To accept the flow rates measured by the 

reference flow meter, the frequency distribution of ∆Q must resemble a bell-shaped curve and 

the mean deviation must be close to zero. 

69 
The frequency distribution plots are presented with two-percent increments and additional 

information on each figure, including the: 

• Margin of deviation (±X percent) that contains 95 percent of all measurements (i.e. 

standard deviation ±2σ); 

• Percentage of measurements within a margin of deviation of ±8.7 percent (wet weather 

tracer dilution deviation); 

• Percentage of measurements within the re-evaluated margin of deviation of ±13.55 

percent (wet weather tracer dilution deviation); 

• Mean deviation of all measurements; and 

• Median deviation (provides an indication of the spread). 

5.3.2 Test C0 Results 

5.3.2.1 Qualitative Analysis 

Figure H-142 presents flow rates output by the reference flow meter, flow rates calculated from 

the tracer dilution and, as an indication, flow rates estimated from the equation of the flow under 

the gate for the upstream gate (with modifications for the Craig Collector and travel time). Tracer 

dilution data points are presented with two markers: the dark circles are data taken during 

transition periods (rising and ebbing water profiles) and the hollow circles are data taken during 

stable flow conditions. This segregation is used for later analysis. The reference meter and tracer 

dilution data points were very close, with some minor differences at higher flows of 17.1 and 

29.7 MGD (750 and 1,300 L/sec). The estimation of the flow under the gate also followed the 

reference flow meter curve very closely. 

Figure H-120 presents flow rates output by the reference flow meter as a function of flow rates 

calculated from the tracer dilution. Again, two markers were used to segregate data points taken 

during transition and stable periods. The larger deviations from the y = x (or 1:1) line were the 

data points during transition periods and during higher flows. The correlation coefficients (r) 

calculated from all data points and from stable conditions only were very close to 1. 

Qualitatively, these two figures show that the flow rates output by the reference flow meter were 

very close to those calculated from tracer dilution (and from those estimated from the flow under 

the gate). There were no indications that the reference meter was poorly calibrated or 

malfunctioning. 

5.3.2.2 Statistical Analysis 

The hypothesis test on paired samples validates whether the new population made of paired flow 

data has a zero mean (null hypothesis test). Since the value of the test statistic (-0.528) is within 

the lower and upper limits (±1.990) of the validation range for the given level of significance 

(5 percent), the null hypothesis is accepted. This result indicates a strong probability for the 

paired flow data to belong to a zero mean population. 

70 
5.3.2.3 Reference Flow Deviation Distribution 

Figure H-127 presents the reference flow deviation distribution for replica C0. Two of three 

conditions for the test to be satisfied are met: the frequency distribution approaches a normal 

curve and the mean deviation is close to 0 (0.3 percent). The median deviation (-0.1 percent) 

provides an indication of the spread of the data set. The condition that was not met is the fraction 

of deviation data included in the acceptance margins. Since most of Test C0 is conducted under 

wet weather conditions, the acceptable margin of deviation for 95 percent of measurements is 

±8.7 percent according to the protocol. Only 87.8 percent of measurements are within the ±8.7 

percent margin of deviation. However, as indicated in Figure H-127, 97.6 percent of 

measurements are within the reevaluated ±13.5 percent margin of deviation. 

The largest positive deviation was 19.7 percent (at 14:30), and occurred during the transition 

from 8.56 to 1.71 MGD (375 to 75 L/sec). The largest negative deviation was –13.4 percent (at 

15:25) and is observed at the very end of the test during maximum dry weather flow (1.71 MGD; 

75 L/sec). All negative deviations larger (in absolute value) than –10.0 percent occurred during 

maximum dry weather flow while all positive deviations larger than +10.0 percent occurred 

during transition periods. 

Figure H-128 presents the reference flow deviation distribution for all data points during stable 

conditions and those during stable conditions but without maximal dry weather flow. In both 

cases, the frequency distribution approaches a normal curve and the mean deviation is close to 

zero (-0.6 percent and -0.1 percent, respectively). The acceptable margin of deviation of ±8.7 

percent for 95 percent of the measurements is met for data points during stable conditions 

without maximal dry weather flow (with 100 percent of measurements within this margin) and 

barely missed for all data points during stable conditions (with 94.4 percent of measurements 

within this margin). 

5.3.3 Test C3 Results 

5.3.3.1 Qualitative Analysis 

Figure H-143 presents flow rates output by the reference flow meter, flow rates calculated from 

the tracer dilution and, as an indication, flow rates estimated from the equation of the flow under 

the gate for the upstream gate (with modifications for the Craig Collector and travel time). Tracer 

dilution data points are presented with two markers: the dark circles are data taken during 

transition periods (rising and ebbing water profiles) and the hollow circles are data taken during 

stable flow conditions. This segregation is used for later analysis. The reference meter and tracer 

dilution data points are very close at maximum dry weather flow of 1.71 MGD (75 L/sec) while 

the reference flow rates are always larger for the two intermediate flow rates of 8.56 and 17.1 

MGD (375 and 750 L/sec), and always smaller for the highest flow rate of 29.7 MGD 

(1,300 L/sec). 

The higher the flow rate, the lower the lithium concentration. At 29.7 MGD (1,300 L/sec), the 

lithium concentration is roughly 0.273 mg/L. A small deviation on the blank samples would 

result in a large deviation in flow rate estimation for the higher flows. Since blank samples were 

71 
taken every 30 minutes, the in-between concentrations were interpolated from the two known 

values. This might explain the mismatch between the reference and dilution data sets. The curve 

of the flow under the gate is in the same vicinity as the reference flow meter curve. 

Figure H-121 presents flow rates output by the reference flow meter as a function of flow rates 

calculated from the tracer dilution. Again, two markers are used to segregate data points taken 

during transition and stable periods. The larger deviations from the y = x (or 1:1) line are the data 

points during transition periods and during higher flows. The correlation coefficients (r) 

calculated from all data points and from stable conditions data points only are very close to one. 

Qualitatively, these two figures show that the flow rates output by the reference flow meter are 

close to those calculated from tracer dilution (and from the ones estimated from the flow under 

the gate). There are no indications that the reference meter is poorly calibrated or 

malfunctioning. 

5.3.3.2 Statistical Analysis 

The hypothesis test on paired samples validates whether the new population made of paired flow 

data has a zero mean (null hypothesis of the test). Since the value of the test statistic (0.700) is 

within the lower and upper limits (±1.990) of the validation range for the given level of 

significance (5 percent), the null hypothesis is accepted. This result indicates that there exists a 

strong probability for the paired flow data belongs to a zero mean population. 

5.3.3.3 Reference Flow Deviation Distribution 

Figure H-128 presents the reference flow deviation distribution for replica C3. None of the three 

conditions for the test to be satisfied are met. The frequency distribution does not resemble a 

normal curve (two peaks), the mean deviation is decentered negatively (-2.0 percent) and only 

80.5 percent of measurements are within a margin of deviation of ±8.7 percent (as indicated in 

the protocol for wet weather). The median deviation (-3.8 percent) is even more negatively 

decentered. However, as indicated on Figure H-128, 95 percent of measurements are within the 

reevaluated ±13.5 percent margin of deviation. 

The largest positive deviation is 20.5 percent (at 7:45) and the largest negative deviation is -45.8 

percent (at 8:30). Both occurred at the very beginning of the test during the maximum dry 

weather flow of 1.71 MGD (75 L/sec). All negative and positive deviations larger than ±10.0 

percent (in absolute value) occurred during maximum dry weather flow. Negative deviations are 

mostly due to the intermediate flows of 8.56 and 17.1 MGD (375 and 750 L/sec) and positive 

deviations to the highest flow of 29.7 MGD (1,300 L/sec). Since there are more data points at 

intermediate flows, the curve is decentered negatively. 

Figure H-131 presents the reference flow deviation distribution for all data points during stable 

conditions and those during stable conditions but without maximum dry weather flow for replica 

C3. In both cases, as for Figure H-128, none of the three conditions for the test to be satisfied are 

met. Only data under stable conditions without maximal dry weather flow meet the recalculated 

criteria of 95 percent of measurements within a margin of deviation of ±13.5 percent. 

72 
5.3.4 Test B and D Results 

Figures H-138 through H-140 present flow rates from the reference flow meter and from the 

flow under the downstream gate equation for the three replicas of Test B, while Figures H-143 

through H-145 present the same information for the three replicas of Test D. The flow under the 

downstream gate comes from a standard hydraulic equation. At low flows (Test B and beginning 

and end of Test D), the reference flow meter and gate equation curves are nearly superimposed. 

As the flow rate increases (Test D), the gap between the two curves also increases, with the gate 

equation curve always being higher. This is true for all three replicas of Test D. Therefore, the 

reference flow meter reacted in the same fashion each time (not a punctual malfunction). 

5.3.5 Conclusion 

Except for Test C3, the qualitative validation analyses show that the reference flow meter 

provides results representative of the flows computed using tracer dilution tests and an energy 

balance equation in the vicinity of sluice gates. The figures show the flow rates output by the 

reference flow meter, the tracer dilution, and the energy balance equation show a good match 

between the three time series data sets. The general behavior can be summarized as follows: 

• For the highest flow rates, the measured reference flows follow closely the flows 

computed by the energy balance equation, but are slightly below the flows computed 

using tracer dilution. This observation is particularly visible for Test C3. This 

phenomenon could be due to an overestimation of the blank concentrations caused by 

contamination of the sampling bottles. 

• For dry weather flows and low wet weather flows, the reference flow curve is slightly 

above the tracer dilution flow curve. This observation is particularly apparent for Test C3 

and can be explained by the fact that the diluted concentrations of the standard laboratory 

were barely accepted. The diluted concentrations measured by the standard laboratory are 

systematically greater by 6 percent than the concentrations measured by the control 

laboratory. This constant offset can be the reason why the flow rates measured by the 

reference flow meter are systematically above the flow rates computed using tracer 

dilution. 

For Test C3, the reference flow meter does not pass the qualitative and the quantitative validation 

tests for the reference flow deviation distribution. However, it appears that the validation test is 

strongly affected by potential problems related to the measurement of the blank and diluted 

concentrations. Nevertheless, using the acceptable margin of deviation determined using the 

updated accuracy values for lithium concentration measurements, 95 percent of the reference 

flow measurements are within ±13.5 percent. 

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5.4 Validation of the Reference Depth Meter (Bubbler) 

This section presents the methods used and results obtained to validate the reference water-depth 

data. Two methods were used to verify the accuracy of the reference depth meter (bubbler) and 

to validate the reference water-depth data: manual readings and an ultrasonic depth meter. 

5.4.1 Validation Methods 

To demonstrate that the reference depth meter (bubbler) was accurate and exhibited no bias, the 

reference water depth data was compared qualitatively and quantitatively to that obtained with 

manual readings for Tests B, C, and D, and for all these tests combined. A frequency distribution 

analysis was performed with the reference depth meter for Tests B, C, and D combined. 

5.4.1.1 Qualitative Analysis 

To assess qualitatively the validity of the reference water depth data, two types of figures were 

produced: 

1. Reference meters verification: depth measurements: These figures present water depths 

from the reference depth meter (bubbler), from manual readings, and from the ultrasonic 

depth meter for the three replicas of Test B, four replicas of Test C, and three replicas of 

Test D. 

2. Reference depth comparison: reference meter versus manual measurement: These 

figures present water depths output by the reference depth meter as a function of the 

manual measurements for Tests B, C, and D, and for all these tests combined. The y = x 

(or 1:1) line is drawn as an indication of a perfect fit between the two data sets. The 

correlation coefficient (r) between the reference data and the y = x line is also presented. 

A perfect fit would generate an r of one. 

5.4.1.2 Statistical Analysis 

A statistical test (a hypothesis test on paired sample depth data) was performed to assess the 

validity of the reference depth data. In this test, a new data set was calculated, consisting of the 

differences between the depths measured by the reference depth meter and those measured 

manually. The hypothesis test was then performed as a one-population test on the differences. 

This test validates whether the new population made of paired data has a zero mean, and whether 

the mean of the paired samples was significantly different from zero, with a given level of 

significance assuming that the paired data population has a zero mean (the null hypothesis). 

5.4.1.3 Reference Depth Deviation Distribution 

This test consists of drawing the bar chart of the water-depth deviation distribution for which the 

deviation is defined as: 

∆D =Dmanual −Dreference or Dultrasonic − Dreference (5-5) 

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The reference depth deviation distribution test is the only test described in the protocol for which 

a quantitative assessment is done. In order to validate the measurements produced by the 

reference depth meter, 95 percent of the depth deviation data (∆D) must be included in an 

acceptance range. According to the protocol, the acceptance limits are ±1.25 in. (31.7 mm) or 

two percent full-scale. The test also includes two qualitative assessments. To accept the water 

depths measured by the reference depth meter, the frequency distribution of ∆D must resemble a 

bell-shaped curve and the mean deviation must be close to zero. 

The frequency distribution plots are presented with 0.25-in. increments and additional 

information on each figure, including the: 

• Margin of deviation (±X percent) that contains 95 percent of all measurements (i.e., 

standard deviation ±2σ); 

• Percentage of measurements within a margin of deviation of ±1.25 in. (31.7 mm) or two 

percent full scale; 

• Mean deviation of all measurements; and 

• Median deviation (provides an indication of the spread). 

Qualitative and statistical analyses are presented for Test B, C, and D and for these three tests 

combined. 

5.4.2 Test B Results 

5.4.2.1 Qualitative Analysis 

Figures H-146 through H-148 present water depths from the reference depth meter (bubbler), 

manual readings, and reference ultrasonic depth meter for the three replicas of Test B, 

respectively. Generally, all three curves are superimposed except at the very beginning of 

replicas B1 and B2 (at 9:00) and during two purges of the bubbler (at 9:10 and 13:10 during 

replica B2). 

Figure H-122 presents water depths output by the reference depth meter as a function of manual 

measurements. The larger deviations from the y = x (or 1:1) line are the data points during the 

transition period from the 18-in. back flow to the 36-in. back flow. During this transition and 

under the 36-in. back flow, the reference depth meter seems to slightly underestimate the water 

depths compared to the manual readings, although the correlation coefficient (r) is very close to 

one. 

Qualitatively, these four figures show that the water depths output by the reference depth meter 

are very close to the manual readings and those from the ultrasonic depth meter. There are no 

indications that the reference depth meter was poorly calibrated or malfunctioning. 

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5.4.2.2 Statistical Analysis 

The hypothesis test on paired samples validates whether the new population made of paired data 

has a zero mean (null hypothesis of the test). Since the value of the test statistic (16.39) is outside 

the lower and upper limits (±1.972) of the validation range for the given level of significance 

(five percent), the null hypothesis is rejected. This result indicates that there is a strong 

probability that the paired depth data do not belong to a zero mean population. The two sets of 

data come from populations having very small standard deviations. Therefore, even though the 

depth measurements are almost the same, the intersection covered by the distributions of the two 

populations is small, independent of the values measured. The statistical test reveals a 

measurement bias between the bubbler and the manual readings. 

5.4.2.3 Reference Depth Deviation Distribution Analysis 

Figure H-132 presents the reference depth deviation distribution for Test B (bubbler versus 

manual measurements). All conditions for the test to be satisfied are met. The frequency 

distribution approaches a normal curve, the mean deviation is close to the median deviation, 

which is also close to zero (mean deviation 0.39 in.; 9.9 mm); and more than 95 percent of 

measurements are within the acceptable margin of deviation according to the protocol (2 percent 

full-scale: 1.25 in.; 31.7 mm). 

5.4.3 Test C Results 

5.4.3.1 Qualitative Analysis 

Figures H-149 through H-152 present water depths from the reference depth meter (bubbler), 

manual readings, and reference ultrasonic depth meter for the four replicas of Test C. Water 

depths from the three instruments vary more than for Test B, principally due to the presence of 

stationary waves during these tests. Replicas C0, C1, and C3 present the same pattern: reference 

depth measurements are lower than manual readings but higher that the ultrasonic readings 

during the 17.1 MGD (750-L/sec) stable period, while the opposite is found at the 29.7 MGD 

(1,300-L/sec). During the two 8.56 MGD (375-L/sec) stable periods, manual readings were 

usually closer to the ultrasonic data points. Both manual readings and ultrasonic depths were 

affected by stationary waves (may be at the crest or trough), whereas the bubbler buffers the 

information over a larger volume of water. It should be noted that the manual readings were 

taken close to the bubbler site. 

Figure H-123 presents water depths output by the reference depth meter as a function of manual 

measurements. At lower depths, data points are generally on the perfect-fit line and then, as the 

depth gets higher, they oscillate on each side of the line. Despite this fact, the correlation 

coefficient (r) is relatively close to one (0.984). 

Qualitatively, these five figures show that the water depths output by the reference depth meter 

were somewhat different from the manual readings and those from the reference ultrasonic depth 

meter test due to the presence of stationary waves at higher flow rates. As previously mentioned, 

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manual readings and the ultrasonic depth meter data were strongly affected by waves (punctual 

measurement can be at the crest or trough of waves) whereas the bubbler was less affected. 

5.4.3.2 Statistical Analysis 

The hypothesis test on paired samples validates whether the new population made of paired data 

has a zero mean (null hypothesis of the test). Since the value of the test statistic (0.723) was 

within the lower and upper limits (± 1.967) of the validation range for the given level of 

significance (five percent) the null hypothesis was accepted. This indicates that there was a 

strong probability for the paired depth data to belong to a zero mean population. 

5.4.3.3 Reference Depth Deviation Distribution Analysis 

Figure H-133 presents the reference depth deviation distribution for Test C (bubbler versus 

manual measurements). Only one condition for the test to be satisfied was met. The mean 

deviation was very close to zero (0.05 in. (1.3 mm)). The frequency distribution only vaguely 

resembled a normal curve and less than 95 percent of the measurements (77.8 percent) were 

within the acceptable margin of deviation according to the protocol (two percent full-scale, or 

1.25 in. (31.7 mm)). The deviations larger than ±1.25 in. were positive deviations collected 

during the 17.1 MGD (750-L/sec) flow period. Since during this period the reference depth meter 

did not measure the same depth (due to the distance between the two measurement devices and 

the presence of a non-negligible stationary wave), it was legitimate not to consider these data in 

the frequency distribution test. The resulting frequency distribution graph resembles a bellshaped curve and the quantitative frequency distribution test was satisfied. 

5.4.4 Test D Results 

5.4.4.1 Qualitative Analysis 

Figures H-153 through H-155 present water depths from the reference depth meter (bubbler), 

manual readings and reference ultrasonic depth meter for the three replicas of Test D, 

respectively. Generally, all three curves are superimposed except under back-flow conditions, 

when the ultrasonic becomes out of range (maximum reading of 40.2 in. [1,022 mm]). 

Figure H-124 presents water depths output by the reference depth meter as a function of manual 

measurements. Most data points were very close to the y = x (or 1:1) line. The larger deviations 

were recorded during the transition period from back flow conditions to maximum dry weather 

flow without back flow. The correlation coefficient (r) is one. 

Qualitatively, these four figures show that the water depths output by the reference depth meter 

are close to the manual readings and those from the reference ultrasonic depth meter. There are 

no indications that the reference depth meter was poorly calibrated or malfunctioning. 

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5.4.4.2 Statistical Analysis 

The hypothesis test on paired samples validates whether the new population made of paired data 

has a zero mean (null hypothesis of the test). Since the value of the test statistic (1.22) was inside 

the lower and upper limits (±1.968) of the validation range for the given level of significance 

(five percent), the null hypothesis was accepted. This indicates that a strong probability for the 

paired depth data to belong to a zero mean population exists. 

5.4.4.3 Reference Depth Deviation Distribution Analysis 

Figure H-134 presents the reference depth deviation distribution for Test D (bubbler versus 

manual measurements). The three conditions for the test to be satisfied are met: the mean 

deviation was very close to zero (0.04 in.; 1.0 mm), the frequency distribution resembled a 

normal curve and more than 95 percent of the measurements were within the acceptable margin 

of deviation (two percent full-scale) noted in the protocol. 

5.4.5 Tests B, C, and D Combined 

5.4.5.1 Qualitative Analysis 

Figure H-125 presents water depths output by the reference depth meter as a function of manual 

measurements. Most data points were very close to the y = x (or 1:1) line. The larger deviations 

were from Test C. The correlation coefficient (r) was very close to 1. 

5.4.5.2 Reference Depth Deviation Distribution Analysis 

Figure H-135 presents the reference depth deviation distribution for Tests B, C, and D (bubbler 

versus manual measurements). Two of the three conditions for the test to be satisfied were met. 

The frequency distribution resembled a normal curve and the mean deviation was very close to 

zero (0.13 in.; 3.3 mm). Less than 95 percent of the measurements (88.9 percent) were within the 

acceptable margin of deviation according to the protocol (two percent full-scale, or 1.25 in. 

[31.7 mm]). This last observation reflects the measurement differences observed for Test C 

during the presence of stationary waves. 

Figure H-136 presents the reference depth deviation distribution for Tests B, C, and D (bubbler 

versus reference ultrasonic depth meter). Only one of the three conditions for the test to be 

satisfied was met. The mean deviation was very close to zero (-0.20 in.; -5.1 mm). The frequency 

distribution only vaguely resembled a normal curve and less than 95 percent of the 

measurements (79.7 percent) were within the acceptable margin of deviation (two percent fullscale) noted in the protocol. 

5.4.6 Conclusion 

Except for Test C, the qualitative validation analyses showed that the reference depth meter 

provides results that were representative of the manual readings and the depths measured by the 

ultrasonic depth meter. The figures showing the water depths output by the reference depth 

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meter, the manual readings, and the ultrasonic depth meter showed a good match between the 

three time series. The general behavior observed can be summarized as: 

• Under normal conditions, the measured reference depths closely followed the water 

depths obtained by manual readings and by the ultrasonic depth meter. However, during 

replicas B1, B2, and B3, a relatively constant measurement offset was observed and 

detected by the statistical test. This offset was small, however, and could probably be 

eliminated by a slight readjustment to the calibration of the measurement devices. 

• In the presence of stationary waves (Test C), significant depth differences were observed 

for the three measurement devices. However, these differences were not related to bad 

calibration or malfunctioning of the reference depth meter. The distance existing between 

the different depth meters can explain these results. 

From these observations and the qualitative and quantitative results obtained for the different 

validation tests, the reference depth meter appears to be a valuable measurement device that can 

be used to generate reference depth data. 

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Appendices 

A Complementary Test Site and Reference Meters Information 

B Experiment Procedures 

C Detailed Experimentation Results 

D Quality Assurance Project Plan: Complementary Information 

E Field Verification: Reports Generated during Tests 

F ADS 3600 Flow Meter: Configuration 

G ADS 3600 Flow Meter Software Functionality/Flexibility Summary 

H Flow Test Data Figure Summaries 

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Glossary 

Accuracy - a measure of the closeness of an individual measurement or the mean of a number of 

measurements to the true value and includes random error and systematic error. 

Bias - the systematic or persistent distortion of a measurement process that causes errors in one 

direction. 

Comparability – a qualitative term that expresses confidence that two data sets can contribute to 

a common analysis and interpolation. 

Completeness – a qualitative term that expresses confidence that all necessary data have been 

included. 

Precision - a measure of the agreement between replicate measurements of the same property 

made under similar conditions. 

Protocol – a written document that clearly states the objectives, goals, scope, and procedures for 

the study. A protocol shall be used for reference during vendor participation in the verification 

testing program. 

Quality Assurance Project Plan – a written document that describes the implementation of 

quality assurance and quality control activities during the life cycle of the project. 

Representativeness - a measure of the degree to which data accurately and precisely represent a 

characteristic of a population parameter at a sampling point, a process condition, or 

environmental condition. 

Wet Weather Flows Stakeholder Advisory Group - a group of individuals consisting of any or 

all of the following: buyers and users of flow monitoring technologies, developers and vendors, 

consulting engineers, the finance and export communities, and permit writers and regulators. 

Standard Operating Procedure – a written document containing specific procedures and 

protocols to ensure that quality assurance requirements are maintained. 

Technology Panel - a group of individuals with expertise and knowledge of flow monitoring 

technologies. 

Testing Organization – an independent organization qualified by the Verification Organization 

to conduct studies and testing of flow monitoring technologies in accordance with protocols and 

Test Plans. 

Vendor – a business that assembles or sells flow monitoring equipment. 

Verification – to establish evidence on the performance of flow monitoring technologies under 

specific conditions, following a predetermined study protocol(s) and test plan(s). 

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Verification Organization – an organization qualified by EPA to verify environmental 

technologies and to issue verification statements and verification reports. 

Verification Report – a written document containing all raw and analyzed data, all quality 

assurance/quality control (QA/QC) data sheets, descriptions of all collected data, a detailed 

description of all procedures and methods used in the verification testing, and all QA/QC results. 

The test plan(s) shall be included as part of this document. 

Verification Statement – a document that summarizes the Verification Report reviewed and 

approved and signed by EPA and NSF. 

Verification Test Plan – a written document prepared to describe the procedures for conducting 

a test or study according to the verification protocol requirements for the application of flow 

monitoring technology. At a minimum, the test plan shall include detailed instructions for 

sample and data collection, sample handling and preservation, precision, accuracy, goals, and 

QA/QC requirements relevant to the technology and application. 

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