October 2005
Environmental Technology
Verification Report
CLARION SENSING SYSTEMS, INC,
SENTINAL™ 500 SERIES
CONTINUOUS MULTI-PARAMETER
WATER QUALITY MONITOR
Prepared by
Battelle
Baireiie
Ira Business erf Innovation
Under a cooperative agreement with
U.S. Environmental Protection Agency
ET1/ET1/ET1/
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THE ENVIRONMENTAL TECHNOLOGY VERIFICATION
PROGRAM
EPA
U.S. Environmental Protection Agency
ET/
Bairene
The Business of Innovation
ETV Joint Verification Statement
TECHNOLOGY TYPE: MULTI-PARAMETER WATER MONITORS FOR
DISTRIBUTION SYSTEMS
APPLICATION: MONITORING DRINKING WATER QUALITY
TECHNOLOGY NAME: Sentinal™ 500 Series
COMPANY: Clarion Sensing Systems, Inc.
ADDRESS: 3901 West 30th Street PHONE: 317-295-1433
Indianapolis, Indiana 46222 FAX: 317-295-1436
WEB SITE: www.clarionsensing.com
E-MAIL: clarionsystems@earthlink.net
The U.S. Environmental Protection Agency (EPA) supports the Environmental Technology Verification (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, financing, permitting, purchase, and use of environmental technologies. Information and ETV
documents are available at www.epa.gov/etv.
ETV works in partnership with recognized standards and testing organizations, with stakeholder groups
(consisting of buyers, vendor organizations, and permitters), and with 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 pre-
paring peer-reviewed reports. All evaluations are conducted in accordance with rigorous quality assurance (QA)
protocols to ensure that data of known and adequate quality are generated and that the results are defensible.
The Advanced Monitoring Systems (AMS) Center, one of six technology areas under ETV, is operated by Battelle
in cooperation with EPA's National Exposure Research Laboratory. The AMS Center evaluated the performance
of the Clarion Sensing Systems, Inc., Sentinal™ 500 Series in continuously measuring free chlorine, temperature,
conductivity, pH, and oxidation-reduction potential (ORP) in drinking water. This verification statement provides
a summary of the test results.
VERIFICATION TEST DESCRIPTION
The performance of the Sentinal™ 500 was assessed in terms of its accuracy, response to injected contaminants,
inter-unit reproducibility, ease of use, and data acquisition. The verification test was conducted between August 9
and October 28, 2004, and consisted of three stages, each designed to evaluate a particular performance
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characteristic of the Sentinal™ 500. All three stages of the test were conducted using a recirculating pipe loop at
the U.S. EPA's Test and Evaluation (T&E) Facility in Cincinnati, Ohio.
In the first stage of this verification test, the accuracy of the measurements made by the Sentinal™ 500 units was
evaluated during nine, 4-hour periods of stable water quality conditions by comparing each Sentinal™ 500 unit
measurement to a grab sample result generated each hour using a standard laboratory reference method and then
calculating the percent difference (%D). The second stage of the verification test involved evaluating the response
of the Sentinal™ 500 units to changes in water quality parameters by injecting contaminants (nicotine, arsenic
trioxide, and aldicarb) into the pipe loop. Two injections of three contaminants were made into the recirculating
pipe loop containing finished Cincinnati drinking water. The response of each water quality parameter, whether it
was an increase, decrease, or no change, was documented and is reported here. In the first phase of Stage 3 of the
verification test, the performance of the Sentinal™ 500 units was evaluated during 52 days of continuous
operation, throughout which references samples were collected once daily. The final phase of Stage 3 (which
immediately followed the first phase of Stage 3 and lasted approximately one week) consisted of a two-step
evaluation of the Sentinal™ 500 performance to determine whether this length of operation would negatively
impact the results from the Sentinal™ 500. First, as during Stage 1, a reference grab sample was collected every
hour during a 4-hour analysis period and analyzed using the standard reference methods. Again, this was done to
define a formal time period of stable water quality conditions over which the accuracy of the Sentinal™ 500 could
be evaluated. Second, to evaluate the response of the Sentinal™ 500 to contaminant injection after the extended
deployment, the duplicate injection of aldicarb, which was also included in the Stage 2 testing, was repeated. In
addition, a pure E. coli culture, including the E. coli and the growth medium, was included as a second injected
contaminant during Stage 3. Inter-unit reproducibility was assessed by comparing the results of two identical units
operating simultaneously. Ease of use was documented by technicians who operated and maintained the units, as
well as the Battelle Verification Test Coordinator.
QA oversight of verification testing was provided by Battelle and EPA. Battelle QA staff conducted a technical
systems audit, a performance evaluation audit, and a data quality audit of 10% of the test data.
This verification statement, the full report on which it is based, and the test/QA plan for this verification test are
all available at www.epa.gov/etv/centers/centerl.html.
TECHNOLOGY DESCRIPTION
The following description of the Sentinal™ 500 unit was provided by the vendor and does not represent verified
information.
The Sentinal™ 500 is designed to remotely monitor and report drinking water quality. The Sentinal™ 500 uses a
sensor array to acquire information about drinking water quality on site in near-real time by analyzing the water
quality and comparing it to its normal baseline values and notifies utility/security personnel if water quality
changes significantly from its baseline. The Sentinal™ 500 used in this verification test measured free chlorine,
temperature, conductivity, pH, and GKP in drinking water. The sensors measured these parameters by
potentiometric, amperometric, and conductance methods.
The Sentinal™ 500 consists of sensors and their respective meters with digital displays; a data acquisition,
analysis, and management microprocessor; a communications link such as radio, cellular networks, satellite
networks, wireless Ethernet or LANs (as configured during this test), and a receiving station where the data are
presented and alarms are distributed. The systems can serve up their own Web pages to the network, and other
monitoring sites can be accessed through each site. The system could be configured to actuate valves and pumps
to shut off or divert water for on-site treatment.
For this verification test, the continuous data were stored on the on-board computer and downloaded daily by
plugging an Ethernet cable into a laptop and entering an IP address into Microsoft Explorer. A Web page was
called up, and the data could be easily downloaded as an Excel spreadsheet. System software (the Sentinal™ Data
Acquisition and Management Device) could be configured to average all of the data over time to determine site-
specific normal baselines. The software also can be programmed to recognize when deviations (threshold set by
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the user) from the baseline occur and either triggers "alerts" or "alarms," depending on the degree of deviation.
All aspects of the data acquisition could be configured for remote observation and data collection.
The Sentinal™ 500 is 30 inches by 36 inches and weighs about 30 pounds. Prices for Sentinal™ systems range
from $12,600 to $24,500. The cost of the system as configured for the verification test is $17,000. Other costs
include $800 annually for replacement chlorine sensor gel caps and electrolyte gel and a one-time purchase of a
calibration kit for $540.
VERIFICATION OF PERFORMANCE
Evaluation Parameter
Stage 1—
Accuracy
Stage 2—
Response to
Injected
Contaminants
Stage 3—
Accuracy During
Extended
Deployment
Stage 3 —
Accuracy After
Extended
Deployment
Stage 3 —
Response to
Injected
Contaminants
Injection
Summary
Inter-unit
Reproducibility
(Unit 2 vs. Unit 1)
Ease of Use
and Data
Acquisition
Units 1 and 2,
range of %D (median)
Nicotine
Arsenic
trioxide
Aldicarb
Reference
Sentinal™ 500
Reference
Sentinal™ 500
Reference
Sentinal™ 500
Units 1 and 2,
range of %D (median)
Unit 1, %D
Unit 2, %D
E. colt
Aldicarb
Reference
Sentinal™ 500
Reference
Sentinal™ 500
Free Chlorine
3.4 to 117.1
(26.2)
-
-
-
-
-
-
-54.8 to 50.0
(-21.5)
-10.9
-18.5
-
-
-
-
Temperature
-18.4 to 2.7
(-3.7)
NC
NC
NC
NC
NC
NC
-7.8 to 2.7
(-2.7)
-0.5
-3.1
NC
NC
NC
NC
Conductivity
-26.8 to -22.4
(-24.6)
NC
NC
+
+
NC
NC
-0.8 to 5.5
(2.1)
2.5
0.3
+
+
NC
NC
pH
-6.1 to 0.5
(-1.9)
NC
NC
+
+
NC
NC
-7.2 to 1.6
(0.3)
0.0
1.2
-
-
-
-
ORP
(a)
-
-
-
-
-
-
(a)
(a)
(a)
-
-
-
-
For a reason that is not clear, aldicarb altered the pH, as measured by the reference method, during the
Stage 3 injections, but not during the Stage 2 injections.
Slope (intercept)
9
r
p-value
0.86(0.10)
0.87
0.92
0.98 (-0.04)
1.00
0.23
1.01 (-4.13)
0.98
0.74
1.05 (-0.3)
0.95
0.17
0.89 (72)
0.98
0.87
All sensors generated results that were similar according to the results of the t-test. However, the slopes
of the ORP and free chlorine sensor data plotted against one another suggest that the results from each
unit were somewhat different from one another.
Based on the performance of the free chlorine sensors, they may have to be adjusted periodically to
maintain the accuracy of the measurements. The memory module in Unit 1 had to be replaced and,
twice, each unit had to be rebooted before data could be downloaded.
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NOTICE: ETV verifications are based on an evaluation of technology performance under specific,
predetermined criteria and the appropriate quality assurance procedures. EPA and Battelle 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 commercial product names does not imply endorsement.
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October 2005
Environmental Technology Verification
Report
ETV Advanced Monitoring Systems Center
CLARION SENSING SYSTEMS, INC.
SENTINAL™ 500 SERIES
CONTINUOUS MULTI-PARAMETER
WATER QUALITY MONITOR
by
Ryan James
Amy Dindal
Zachary Willenberg
Karen Riggs
Battelle
Columbus, Ohio 43201
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Notice
The U.S. Environmental Protection Agency (EPA), through its Office of Research and
Development, has financially supported and collaborated in the extramural program described
here. This document has been peer reviewed by the Agency. Mention of trade names or
commercial products does not constitute endorsement or recommendation by the EPA for use.
11
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Foreword
The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the
nation's air, water, and land 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, the EPA's Office of Research and Development provides data and science support that
can be used to solve environmental problems and to build the scientific knowledge base needed
to manage our ecological resources wisely, to understand how pollutants affect our health, and to
prevent or reduce environmental risks.
The Environmental Technology Verification (ETV) Program has been established by the EPA to
verify the performance characteristics of innovative environmental technology across all media
and to report this objective information to permitters, buyers, and users of the technology, thus
accelerating the entrance of new environmental technologies into the marketplace. Verification
organizations oversee and report verification activities based on testing and quality assurance
protocols developed with input from major stakeholders and customer groups associated with the
technology area. ETV consists of six verification centers. Information about each of these
centers can be found on the Internet at http://www.epa.gov/etv/.
Effective verifications of monitoring technologies are needed to assess environmental quality
and to supply cost and performance data to select the most appropriate technology for that
assessment. Under a cooperative agreement, Battelle has received EPA funding to plan,
coordinate, and conduct such verification tests for "Advanced Monitoring Systems for Air,
Water, and Soil" and report the results to the community at large. Information concerning this
specific environmental technology area can be found on the Internet at
http://www.epa.gov/etv/centers/centerl.html.
111
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Acknowledgments
The authors wish to acknowledge the support of all those who helped plan and conduct the
verification test, analyze the data, and prepare this report. We would like to thank Roy Haught
and John Hall of the U.S. Environmental Protection Agency's (EPA's) Test and Evaluation
(T&E) Facility (operated by Shaw Environmental, Inc. [Shaw]) in Cincinnati, Ohio, for hosting
the verification test. The U.S. EPA primary contract to Shaw provided significant support in
interfacing the continuous monitors with the pipe loop, as well as facilitating the experimental
plan. The T&E Facility's contribution included providing the reference analyses and operating
the pipe loop, as well as reviewing the test/quality assurance (QA) plan and the reports. In
addition, we would like to thank Steve Allgeier of EPA's Office of Water, Gary Norris and Alan
Vette of the EPA National Exposure Research Laboratory, Lisa Olsen of the U.S. Geological
Survey, Matthew Steele of the City of Columbus Water Quality Assurance Laboratory, and Ron
Hunsinger of East Bay Municipal Utility District, who also reviewed the test/QA plan and/or the
reports.
IV
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Contents
Page
Notice ii
Foreword iii
Acknowledgments iv
List of Abbreviations viii
1 Background 1
2 Technology Description 2
3 Test Design 4
3.1 Introduction 4
3.2 Test Stages 4
3.2.1 Stage 1, Accuracy 5
3.2.2 Stage 2, Response to Injected Contaminants 5
3.2.3 Stage 3, Extended Deployment 6
3.3 Laboratory Reference and Quality Control Samples 6
3.3.1 Reference Methods 7
3.3.2 Reference Method Quality Control Samples 8
4 Quality Assurance/Quality Control 9
4.1 Audits 9
4.1.1 Performance Evaluation Audit 9
4.1.2 Technical Systems Audit 9
4.1.3 Audit of Data Quality 10
4.2 Quality Assurance/Quality Control Reporting 10
4.3 Data Review 10
5 Statistical Methods 12
5.1 Accuracy 12
5.2 Response to Injected Contaminants 12
5.3 Inter-unit Reproducibility 13
6 Test Results 14
6.1 Accuracy 15
6.2 Response to Injected Contaminants 19
6.3 Extended Deployment 23
6.4 Accuracy and Response to Injected Contaminants After Extended Deployment ... 27
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6.5 Inter-unit Reproducibility 31
6.6 Ease of Use and Data Acquisition 32
7 Performance Summary 33
8 References 34
Figures
Figure 2-1. Clarion Sensing System's Sentinal™ 500 2
Figure 6-1. Stage 2 Contaminant Injection Results for Free Chlorine 20
Figure 6-2. Stage 2 Contaminant Injection Results for ORP 21
Figure 6-3. Stage 2 Contaminant Injection Results for Conductivity 21
Figure 6-4. Stage 2 Contaminant Injection Results for pH 22
Figure 6-5. Extended Deployment Results for Free Chlorine 24
Figure 6-6. Extended Deployment Results for pH 24
Figure 6-7. Extended Deployment Results for ORP 25
Figure 6-8. Extended Deployment Results for Temperature 25
Figure 6-9. Extended Deployment Results for Conductivity 26
Figure 6-10. Stage 3 Contaminant Injection Results for Free Chlorine 29
Figure 6-11. Stage 3 Contaminant Injection Results for ORP 30
Figure 6-12. Stage 3 Contaminant Injection Results for pH 30
Figure 6-13. Stage 3 Contaminant Injection Results for Conductivity 31
VI
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Tables
Table 3-1. Reference Methods 7
Table 3-2. Reference Analyses and Quality Control Samples 8
Table 4-1. Performance Evaluation Audit
and Reference Method Duplicate Analysis Results 10
Table 4-2. Summary of Data Recording Process 11
Table 6-1. Summary of Test Stages and Type of Data Presentation 14
Table 6-2a. Accuracy Evaluation Under Various Conditions—Free Chlorine 15
Table 6-2b. Accuracy Evaluation Under Various Conditions—Temperature 16
Table 6-2c. Accuracy Evaluation Under Various Conditions—Conductivity 17
Table 6-2d. Accuracy Evaluation Under Various Conditions—pH 18
Table 6-3. Effect of Contaminant Injections Prior to Extended Deployment 20
Table 6-4. Accuracy During Extended Deployment 26
Table 6-5. Post-Extended Deployment Results 28
Table 6-6. Effect of Contaminant Injections After Extended Deployment 29
Table 6-7. Inter-unit Reproducibility Evaluation 32
vn
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List of Abbreviations
AMS Advanced Monitoring Systems
°C degree centigrade
DI deionized
EPA U.S. Environmental Protection Agency
ETV Environmental Technology Verification
L liter
|j,S/cm microSiemens per centimeter
mg/L milligram per liter
mV millivolt
NIST National Institute of Standards and Technology
ORP oxidation reduction potential
%D percent difference
PE performance evaluation
PVC polyvinyl chloride
QA quality assurance
QC quality control
QMP quality management plan
SD standard deviation
T&E Test and Evaluation
TSA technical systems audit
Vlll
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Chapter 1
Background
The U.S. Environmental Protection Agency (EPA) supports the Environmental Technology
Verification (ETV) Program to facilitate the deployment of innovative 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, financing, permitting, purchase, and use of environmental technologies.
ETV works in partnership with recognized testing organizations; with 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 (QA) protocols to ensure that data of known and adequate quality are generated and
that the results are defensible.
The EPA's National Exposure Research Laboratory and its verification organization partner,
Battelle, operate the Advanced Monitoring Systems (AMS) Center under ETV. The AMS Center
evaluated the performance of the Clarion Sensing Systems, Inc., Sentinal™ 500 Series water
quality monitor in continuously measuring free chlorine, temperature, conductivity, pH, and
oxidation-reduction potential (ORP) in drinking water. Continuous multi-parameter water
monitors for distribution systems were identified as a priority technology verification category
through the AMS Center stakeholder process.
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Chapter 2
Technology Description
The objective of the ETV AMS Center is to verify the performance characteristics of
environmental monitoring technologies for air, water, and soil. This verification report provides
results for the verification testing of the Sentinal™ 500 Series water quality monitor. Following
is a description of the Sentinal™, based on information provided by the vendor. The information
provided below was not verified in this test.
The Sentinal™ 500 (Figure 2-1) is designed to remotely monitor and report drinking water
quality. The Sentinal™ 500 uses a sensor array to acquire information about drinking water
quality on site in near-real time by analyzing the water quality and comparing it to its normal
baseline values and notifies utility/security personnel if water quality changes significantly from
its baseline. The Sentinal™ 500 used in this verification test measured pH, temperature, free
chlorine, conductivity, and the ORP of
drinking water. The sensors measured these
parameters by potentiometric, ampero-
metric, and conductance methods.
The Sentinal™ 500 consists of sensors and
their respective meters with digital displays;
a data acquisition, analysis, and manage-
ment microprocessor; a communications
link such as radio, cellular networks,
satellite networks, wireless Ethernet or
LANs (as configured during this test), and a
receiving station where the data are
presented and alarms are distributed. The
systems can serve up their own Web pages
to the network, and other monitoring sites
can be accessed through each site. The
system could be configured to actuate
valves and pumps to shut off or divert water
for on-site treatment. No reagents were
required.
For this verification test, the data were
stored on the on-board computer and
downloaded daily by plugging an Ethernet
cable into a laptop and entering an IP
SEKTJN
SERIES 3QO
Figure 2-1. Clarion Sensing System's
Sentinal™ 500
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address into Microsoft Explorer. An Internet Web page was called up, and the data could be
easily downloaded as an Excel spreadsheet. System software (the Sentinal™ Data Acquisition
and Management Device) could be configured to average all of the data over time to determine
site-specific normal baselines. The software also can be programmed to recognize when
deviations (threshold set by the user) from the baseline occur and either triggers "alerts" or
"alarms," depending on the degree of deviation. All aspects of the data acquisition could be
configured for remote observation and data collection.
The Sentinal™ 500 is 30 inches by 36 inches and weighs about 30 pounds. Prices for Sentinal™
systems range from $12,600 to $24,500. The cost of the system as configured for the verification
test is $17,000. Other costs include $800 annually for replacement chlorine sensor gel caps and
electrolyte gel and a one-time purchase of a calibration kit for $540.
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Chapter 3
Test Design
3.1 Introduction
The multi-parameter water monitors tested consisted of instrument packages that connect to or
are inserted in distribution system pipes for continuous monitoring. Also included in this
technology category were technologies that can be programmed to automatically sample and
analyze distribution system water at regular intervals. The minimum requirement for
participation in this verification test was that the water monitors were able to measure residual
chlorine, as well as at least one other water quality parameter. Residual chlorine is a particularly
important water quality parameter because changes in its concentration can indicate the presence
of contamination within a distribution system, and chlorination is a very common form of water
treatment used by water utilities in the United States.
This verification test was conducted according to procedures specified in the Test/QA Plan for
Verification of Multi-Parameter Water Monitors for Distribution Systems^ and assessed the
performance of the Sentinal™ 500 units in continuously monitoring pH, conductivity, free
chlorine, ORP, and temperature in terms of the following:
• Accuracy
• Response to injected contaminant
• Inter-unit reproducibility
• Ease of use and data acquisition.
Accuracy was quantitatively evaluated by comparing the results generated by two
Sentinal™ 500 units to grab sample results generated by a standard laboratory reference method.
Response to injected contaminants was evaluated qualitatively by observing whether the
measured water quality parameters were affected by the injection of several contaminants. Inter-
unit reproducibility was assessed by comparing the results of two identical units operating
simultaneously. Ease of use was documented by technicians who operated and maintained the
units, as well as the Battelle Verification Test Coordinator.
3.2 Test Stages
This verification test was conducted between August 9 and October 28, 2004, and consisted of
three stages, each designed to evaluate a particular performance characteristic of the Sentinal™
500. All three stages of the test were conducted using a recirculating pipe loop at the U.S. EPA's
Test and Evaluation (T&E) Facility in Cincinnati, Ohio. The recirculating pipe loop consisted of
ductile iron pipe, 6 inches in diameter and 100 feet long, which contained approximately
240 gallons of Cincinnati drinking water with a flow rate of approximately 1 foot/second. The
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water within the pipe loop had a residence time of approximately 24 hours. Water from the pipe
loop was plumbed to two Sentinal™ 500 units by a section of 2-inch polyvinyl chloride (PVC)
pipe in series with a shut-off valve with a ribbed nozzle that was connected to the Sentinal™ 500
units with a 1/2-inch PVC hose and a hose clamp. Reference samples of approximately 1 liter
(L) (enough volume to perform all the required analyses) to be analyzed by each standard
laboratory reference method were collected from the reference sample collection valve located
approximately 11 feet from the Sentinal™ 500 units on the PVC pipe.
3.2.1 Stage 1, Accuracy
During the first stage of this verification test, the accuracy of the measurements made by both
Sentinal™ 500 units was evaluated by comparing the results from each unit to the result
generated by a standard laboratory reference method. Stage 1 testing simulated the
characteristics of a variety of water quality conditions by changing two variables: pH and
temperature. Using nine sets of pH and temperature conditions, this evaluation consisted of
separate four-hour testing periods of continuous analysis, with reference method sampling and
analysis every hour. Four sets of conditions involved varying only the pH by injecting the pipe
loop with a steady stream of sodium bisulfate. Those sets consisted of pHs of approximately 7, 8,
and 9 pH units (ambient pH at the T&E Facility was between 8 and 9) and a temperature
between 21 and 23 degrees centigrade (°C) (T&E Facility ambient during the time of testing).
Two other sets included changing the water temperature to between 13 and 14°C and testing at
pHs of approximately 7 and 8; and two sets at approximately these pHs, but at a temperature of
approximately 27°C. One set (Set 2) was repeated as Set 3. The pipe loop ambient conditions
were analyzed at the start and end of this stage. Prior to each testing period with unique
conditions, the water in the pipe loop was allowed to equilibrate until the pH and temperature
were at the desired level, as determined by the standard reference methods. This equilibration
step took approximately 12 hours from the time the sodium bisulfate was added (to decrease pH)
or the temperature was adjusted.
3.2.2 Stage 2, Response to Injected Contaminants
The second stage of the verification test involved testing the response of the Sentinal™ 500 units
to changes in water quality parameters by injecting contaminants into the pipe loop. Two
separate injections of three contaminants were made into the recirculating pipe loop containing
finished Cincinnati drinking water. Each injection was made over a period of approximately
15 seconds by connecting the injection tank to the pipe loop's recirculating pump. The three
contaminants were nicotine, arsenic trioxide (adjusted to pH 12 to get it into solution), and
aldicarb. With the exception of the first nicotine injection, each of these contaminants was
dissolved in approximately 5 gallons of pipe loop water that had been dechlorinated using
granular carbon filtration to prevent degradation of the contaminant prior to injection. Upon
injection, concentrations of these contaminants within the pipe loop were approximately
10 milligrams per liter (mg/L). For the first nicotine injection, however, not enough nicotine to
attain this concentration was available so the available nicotine was dissolved into 2 gallons of
the dechlorinated pipe loop water and injected. The resulting nicotine concentration in the pipe
loop was approximately 6 mg/L. Because the qualitative change in water quality parameters was
similar for both nicotine injections despite the concentration difference, it was not necessary to
repeat the 10 mg/L injection of nicotine. For all three sets of injections, a reference sample was
collected prior to the injection and again at 3, 15, and 60 minutes after the injection. The
5
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difference between reference method results occurring before and then again after injection
indicated the directional change in water quality caused by the injected contaminant. For each
injected contaminant, the results from the Sentinal™ 500 units were evaluated based on how
well their directional change matched that of the reference method result. After each injection,
the pipe loop was allowed to re-equilibrate for approximately 12 hours so that each
Sentinal™ 500 unit returned to a steady baseline. Injected contaminants were obtained from
Sigma-Aldrich (St. Louis, Missouri) or ChemService (West Chester, Pennsylvania) and were
accompanied by a certificate of analysis provided by the supplier. Battelle QA staff audited the
gravimetric preparation of these solutions.
3.2.3 Stage 3, Extended Deployment
In the first phase of Stage 3 of the verification test, the performance of the Sentinal™ 500 units
was evaluated during 52 days of continuous operation. The Sentinal™ 500 required no regularly
scheduled maintenance during this deployment. To track the performance of the Sentinal™ 500
with respect to the reference results, reference samples were collected and analyzed for the
selected parameters at least once per day (excluding weekends and holidays) for the duration of
Stage 3. All continuously measured data were graphed, along with the results from the reference
measurements, to provide a qualitative evaluation of the data. Throughout the duration of the
deployment, the average percent difference (%D), as defined in Section 5.1, between the results
from the Sentinal™ 500 units and those from the reference methods was evaluated.
The final phase of Stage 3 (which immediately followed the first phase of Stage 3 and lasted
approximately one week) consisted of a two-step evaluation of the Sentinal™ 500 performance
after the 52-day extended deployment to determine whether this length of operation would
negatively affect the results from the Sentinal™ 500. First, while the Sentinal™ 500s were
continuously operating, a reference sample was collected every hour during a 4-hour analysis
period and analyzed using the standard reference methods. This was done to define a formal time
period of stable water quality conditions for the accuracy of the Sentinal™ 500 to be evaluated.
Second, to evaluate the response of the Sentinal™ 500 to contaminant injection after the
extended deployment, the duplicate injection of aldicarb, which was also included in the Stage 2
testing, was repeated. In addition, a pure E. coli culture, including the E. coli and the growth
medium, was included as a second injected contaminant during Stage 3. E. coli was intended as
an injected contaminant during Stage 2, but was not available until later in the test. During this
contaminant injection component of Stage 3, reference samples were collected as they were
during Stage 2.
3.3 Laboratory Reference and Quality Control Samples
The Sentinal™ 500 units were evaluated by comparing their results with laboratory reference
measurements. The following sections provide an overview of the applicable procedures,
analyses, and methods.
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3.3.1 Reference Methods
To eliminate the possibility of using stagnant water residing in the reference sample collection
valve (dead volume) as the reference samples, the first step in the reference sample collection
procedure included collecting and discarding approximately 1 L of water, which was estimated
to be approximately 10 times the dead volume of the reference sample collection valve. Then,
from the same valve, approximately 1 L of water was collected in a glass beaker and carried
directly to a technician, who immediately began the reference analyses. All the analyses were
performed within minutes of sample collection. The standard laboratory methods used for the
reference analyses are shown in Table 3-1. Also included in the table are method detection limits
and quality control (QC) measurement differences. Battelle technical staff collected the
reference samples, and technical staff at the T&E Facility performed the analyses. The T&E
Facility provided calibrated instrumentation, performed all method QA/QC, and provided
calibration records for all instrumentation. The T&E Facility provided reference sample results
upon the analysis of the reference samples (within one day). Because previous work at the T&E
facility(2) showed that the laboratory reference method for ORP using a grab sample is not
directly comparable to a continuous measurement in a flowing pipe, accuracy results were not
included for ORP. ORP reference and continuous measurement results were, however, included
for the purpose of a qualitative accuracy evaluation in figures showing the continuous data and
reference method results. Although the ORP reference value may not be equivalent to the
continuous measurement, changes in the continuous measurements were evaluated with the
reference results to determine whether the sensor was identifying increases and decreases
correctly and whether both units were producing similar results.
Table 3-1. Reference Methods
Method Detection
Acceptable
Differences for QC
Parameter
PH
Conductivity
Method
EPA150.1(3)
SM2510(4)
Reference Instruments
Corning 320 pH meter
YSI 556 multi-parameter
Limit
NA
2 microSiemens/
Measurements
±0.3 pH units
±25 %D
water monitor
centimeter
(|iS/cm)
Free chlorine
ORP(a)
Temperature
SM 4500-G(5)
SM 2580-B(6)
EPA170.1(7)
Hach 2400 portable
spectrophotometer
YSI 556 multi-parameter
water monitor
YSI 556 multi-parameter
water monitor
0.01mg/LasCl2
NA
NA
±25 %D
±25 %D
±1°C
(a) The reference method for measuring ORP is not directly comparable because of the difference in potential in a
flowing pipe compared to that measured in a grab sample.
NA = not applicable.
-------
3.3.2 Reference Method Quality Control Samples
As shown in Table 3-2, duplicate reference samples were collected and analyzed once daily
during Stages 1 and 2 and weekly during Stage 3. Also, laboratory blanks consisting of
American Society for Testing and Materials Type n deionized (DI) water were analyzed with the
same frequency. These blank samples were most important for chlorine because it was the only
parameter that needed confirmation of the lack of contamination. For the other parameters, the
performance evaluation (PE) audit confirmed the accuracy of the method and the absence of
contamination. Duplicate measurements had to be within the acceptable differences provided in
Table 3-1.
Table 3-2. Reference Analyses and Quality Control Samples
1:
Stage
Accuracy
Sampling
Periods (length)
9 (4 hours)
Reference
Sample
Frequency
One at start, one
every hour
thereafter
Reference
Samples per
Period
5
QC Samples per
Period
One duplicate and
one DI water blank
daily
Total QC
Samples
18
2: Response to
injected
contaminants
One pre-
injection;
6 (one injection) one at 3, 15, and
60 minutes post-
injection
One duplicate and
one DI water blank
daily
12
3: Extended
deployment
1 (52 days)
Once each
weekday
37
One duplicate and
one DI water blank
each week
16
3: Post-extended
deployment 1 (4 hours) Same as Stage 1
accuracy
Same as Stage 1
3: Response to
injected 4 (one injection) Same as Stage 2
contaminants
Same as Stage 2
-------
Chapter 4
Quality Assurance/Quality Control
QA/QC procedures were performed in accordance with the quality management plan (QMP) for
the AMS Center(8) and the test/QA plan (1) for this verification test.
4.1 Audits
4.1.1 Performance Evaluation Audit
A PE audit was conducted to assess the quality of the reference measurements made in this
verification test. With the exception of temperature, each type of reference measurement was
compared with a National Institute of Standards and Technology (NIST)-traceable standard
reference water sample. The standard reference water samples had certified values of each water
quality parameter that were unknown to the analyst. These samples were analyzed in the same
manner as the rest of the reference analyses to independently confirm the accuracy of the
reference measurements. The temperature PE audit was performed by comparing two
independent thermometer results. As Table 4-1 shows, all PE audit results were within the
acceptable differences provided in Table 3-1. The %D was calculated using the following
equation:
C - C
%D= R N xlOO%
where CR is the reference method result and CN is the NIST value for each respective water
quality parameter (or, for temperature, data from the second thermometer). Other QC data
collected during this verification test were reference method duplicate analysis results, which are
also shown in Table 4-1. All parameters were always within the differences defined in Table 3-1.
Because pH units are measured on a logarithmic, rather than linear, scale, and the measurement
of temperature is extremely precise; the quality control metrics for those two parameters were
the absolute units rather than percent difference.
4.1.2 Technical Systems Audit
The Battelle Quality Manager performed a technical systems audit (TSA) to ensure that the
verification test was performed in accordance with the AMS Center QMP,(8) the test/QA plan,(1)
published reference methods, and any standard operating procedures used by the T&E Facility.
The TSA noted no adverse findings. A TSA report was prepared, and a copy was distributed to
the EPA AMS Center Quality Manager.
-------
Table 4-1. Performance Evaluation Audit and Reference Method Duplicate Analysis
Results
Parameter
pH
Conductivity (|iS/cin)
Free chlorine (mg/L)
Temperature (°C)
NIST
Standard
Value
9.26
1,920
4.19
23.0(a)
PE Audit
Reference
Method Result
9.18
1,706
3.62
23.80
Difference
-0.08 pH units
-11.15%
-13.6%
0.00°C
Duplicate Analysis
Average of
Absolute Values Range of
of Difference Difference
0.04 pH units 0.0 to 0.13 pH units
0.25% -1.9 to 0.7%
2.62% -7.3 to 2.1%
0.02 °C -0.18to0.29°C
-------
Table 4-2. Summary of Data Recording Process
Data to Be
Recorded
Dates, times, and
details of test
events
Calibration
information
(Sentinal™ 500
units and reference
methods)
Sentinal™ 500
units results
Where Recorded
ETV data sheets
and testing
notebook
ETV data sheets
and testing
notebook
Recorded
electronically by
How Often
Recorded
Start/end of test and
at each change of a
test parameter
Upon each
calibration
Recorded
continuously
By
Whom
Battelle
and T&E
Facility
Battelle
and T&E
Facility
Battelle
Disposition of
Data
Used to
organize/check test
results; manually
incorporated in
data spreadsheets
as necessary
Manually
incorporated in
data spreadsheets
as necessary
Excel files
Reference method
procedures
each monitor and
then downloaded to
computer daily
ETV laboratory
record books or
data recording
forms
Throughout sample T&E
analysis process Facility
Transferred to
spreadsheets or
laboratory record
book
11
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Chapter 5
Statistical Methods
The statistical methods presented in this chapter were used to verify the Sentinal™ 500 units'
accuracy, response to injected contaminants, and inter-unit reproducibility.
5.1 Accuracy
Throughout this verification test, results from the Sentinal™ 500 units were compared to the
results obtained from analysis of a grab sample by the reference methods. During Stage 1, the
percent difference (%D) between these two results was calculated using the following equation:
%D= ~
where CR is the result determined by the reference method and Cm is the result from a
Sentinal™ 500 unit; the Sentinal™ 500 unit results were recorded every 30 seconds, whereas
collecting the reference samples took only a few seconds. Therefore, Cm was the measurement
recorded closest to the time the reference sample was collected. Water quality stability, as well
as the stability of each sensor, was evaluated during the four-hour time period when reference
samples were analyzed every hour for each of the parameters. Ideally, if the result from a
Sentinal™ 500 unit and a reference method measurements were the same, there would be a
percent difference of zero. During Stages 2 and 3, the continuous data, graphed with the
reference method results, were visually examined to evaluate the response of the Sentinal™ 500
units to the injection of contaminants and their stability over an extended deployment. During
the accuracy and contaminant injection components of Stage 3, the data were evaluated as they
were for Stages 1 and 2, respectively.
5.2 Response to Injected Contaminants
To evaluate the response (i.e., the increase or decrease of water quality parameter measured by
the of the Sentinal™ 500 units) to contaminant injections, the pre- and post-injection reference
samples were graphed as individual data points, along with the continuous measurements. The
reference results showed the effect of each injection on the chemistry of the water in the pipe
loop, and the continuous results from the Sentinal™ 500 unit highlighted its response to such
changes.
12
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5.3 Inter-unit Reproducibility
The results obtained from two identical Sentinal™ 500 units were compared to assess inter-unit
reproducibility. Each time a reference sample was collected and analyzed (approximately
127 times throughout this verification test), the results from each Sentinal™ 500 unit were
compared to evaluate whether the two units were generating similar results. This was done in
two ways. First, the results from one unit were graphed against the results of the other unit. In
this evaluation, a slope of unity and a coefficient of determination (r2) of 1.0 would indicate ideal
inter-unit reproducibility. Slopes above 1.0 may indicate a high bias from Unit 2 (graphed on the
y-axis) or a low bias for Unit 1 with respect to each other. Similarly, slopes below 1.0 may
indicate a low bias for Unit 2 or a high bias for Unit 1, again with respect to each other. Second,
the data from each unit were included in a paired t-test, with the assumption that the data from
each unit had equal variances. The t-test calculated the probability of obtaining the subject
results from the two units if there was no significant difference between their results. Therefore,
probability values (p-values) of less than 0.05 (i.e., less than a 5% probability that this data set
would be generated if there actually was no difference between the two units) indicated a
significant difference between the two units. In addition, the results from both units were
graphed together for the Stages 2 and 3 results, allowing a visual comparison.
13
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Chapter 6
Test Results
As mentioned previously, this verification test was conducted in three stages that focused on
three different aspects of multi-parameter water monitors for distribution systems. The three
stages are summarized in Table 6-1. The first stage consisted of an evaluation (with varied pHs
and temperatures) of the accuracy of each sensor: free chlorine, temperature, conductivity, and
pH. ORP also was measured; but, because a laboratory reference measurement equivalent to the
on-line continuous measurement was not available, ORP was not included in the accuracy
evaluation. The second stage of the verification test consisted of an evaluation of the response of
the Sentinal™ 500 units to the injection of several contaminants into the pipe loop. The third
stage consisted of deploying the Sentinal™ 500 units for 52 consecutive days with minimal
intervention for maintenance. In addition, contaminant injections were performed at the close of
Stage 3 to confirm that the Sentinal™ 500 units were still responsive to contaminant injection
after the extended deployment. Two Sentinal™ 500 units were tested to evaluate inter-unit
reproducibility. In addition, required maintenance and operational characteristics were
documented throughout the verification test. This chapter provides the results of the three testing
stages, the inter-unit reproducibility data, and ease of use information.
Table 6-1. Summary of Test Stages and Type of Data Presentation
Stage Summary
Data Presentation
1 Accuracy when pH and temperature
were varied
Table of percent differences between
Sentinal™ 500 units and reference
measurements
Response to contaminant injection
Graphs of Sentinal™ 500 unit
measurements and reference measurements,
table showing the effect of injections on
both reference and Sentinal™ 500
measurements
Extended deployment with minimal
maintenance along with post-extended
deployment accuracy and response to
contaminant injections
Graphs of Sentinal™ 500 unit
measurements with reference measurements,
table showing average percent differences
throughout extended deployment, table
showing the effect of injections on both
reference and Sentinal™ 500 measurements
14
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6.1 Accuracy
Tables 6-2a-d list the data from the accuracy evaluation performed during the first stage of the
verification test. During four-hour periods, the water quality conditions were held stable, and
reference samples were collected and analyzed five times, once at the start of the designated test
period and four times at one-hour increments thereafter. Because reference sample collection
took just a few seconds and the results from the Sentinal™ 500 units were recorded every
30 seconds, the water quality parameter measurement at the time closest to reference sample
collection was compared to the reference sample. For each unit, this approach resulted in five
paired Sentinal™ 500 and reference results for each of nine sets of water conditions used to
simulate pH and temperature variations at a water utility. The average and standard deviations of
these five results are shown in the tables below, as well as the percent differences between the
average results from both Sentinal™ 500 units and the average of the reference results.
Table 6-2a. Accuracy Evaluation Under Various Conditions—Free Chlorine
Set
1
2
3
4
5
6
7
8
9
Conditions
ambient pH,
ambient temperature
decreased pH, ambient
temperature
decreased pH, ambient
temperature
decreased pH, ambient
temperature
ambient pH, decreased
temperature
decreased pH, decreased
temperature
ambient pH, increased
temperature
decreased pH, increased
temperature
ambient pH, ambient
temperature
Reference
Average (SD)
[mg/L]
0.91 (0.08)
0.78 (0.02)
0.65 (0.01)
0.29 (0.02)
0.41 (0.08)
1.47 (0.06)
0.60 (0.04)
0.54 (0.05)
0.91 (0.03)
Unitl
Average (SD)
[mg/L]
1.00(0.00)
0.86 (0.05)
0.82 (0.00)
0.34 (0.01)
0.83 (0.05)
1.86(0.07)
0.96 (0.03)
0.72 (0.07)
1.20(0.02)
%D
9.9
10.3
26.2
17.2
102.4
26.5
60.0
33.3
31.9
Unit 2
Average (SD)
[mg/L]
0.97 (0.00)
1.05 (0.08)
0.82 (0.00)
0.34 (0.01)
0.89 (0.05)
1.52(0.02)
1.05 (0.02)
0.67 (0.05)
1.08(0.02)
%D
6.6
34.6
26.2
17.2
117.1
3.4
75.0
24.1
18.7
15
-------
Table 6-2b. Accuracy Evaluation Under Various Conditions—Temperature
Reference
Unit 1 Unit 2
Average (SD) Average (SD) Average (SD)
Set Conditions [°C] [°C] %D [°C] %D
1
2
3
4
5
6
7
8
9
ambient pH,
ambient temperature
decreased pH, ambient
temperature
decreased pH, ambient
temperature
decreased pH, ambient
temperature
ambient pH, decreased
temperature
decreased pH,
decreased temperature
ambient pH, increased
temperature
decreased pH, increased
temperature
ambient pH, ambient
22.66 (0.33)
22.73 (0.23)
21.61 (0.16)
21.93(0.15)
13.82 (0.44)
12.63 (0.26)
26.60 (0.27)
26.69 (0.23)
22.79 (0.21)
21.80(0.11)
21.89(0.07)
21.05 (0.07)
21.72(0.04)
11.98(0.19)
10.52 (0.25)
27.31 (0.05)
27.34 (0.07)
22.41 (0.29)
-3.8
-3.7
-2.6
-1.0
-13.3
-16.7
2.7
2.4
-1.7
21.40(0.14)
21.46 (0.12)
21.05 (0.07)
21.11 (0.05)
11.64(0.22)
10.31 (0.21)
26.82 (0.02)
26.76 (0.06)
21.86(0.31)
-5.6
-5.6
-2.6
-3.7
-15.8
-18.4
0.8
0.3
-4.1
temperature
16
-------
Table 6-2c. Accuracy Evaluation Under Various Conditions—Conductivity
Reference
Unitl
Unit 2
Set
Conditions
Average (SD) Average (SD)
[US/cm]
Average (SD)
%D
%D
ambient pH, 451(1)
ambient temperature
decreased pH, ambient 484 (10)
temperature
decreased pH, ambient 503 (6)
temperature
decreased pH, ambient 694 (12)
temperature
ambient pH, decreased 412(1)
temperature
decreased pH, 501 (10)
decreased temperature
ambient pH, increased 447 (1)
temperature
decreased pH, increased 529 (2)
temperature
ambient pH, ambient 442(1)
temperature
334 (2)
360 (8)
380 (4)
515(8)
318(1)
380(10)
327 (2)
391 (4)
329(1)
-25.9
-25.6
-24.5
-25.8
-22.8
-24.2
-26.8
-26.1
-25.6
341 (1) .24.4
365 (8) -24.6
380 (4) -24.5
517(8)
319(1)
389 (9)
337 (1)
397 (2)
336 (0)
-25.5
-22.6
-22.4
-24.6
-25.0
-24.0
17
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Table 6-2d. Accuracy Evaluation Under Various Conditions—pH
Set
1
2
3
4
5
6
7
8
9
Conditions
ambient pH,
ambient temperature
decreased pH, ambient
temperature
decreased pH, ambient
temperature
decreased pH, ambient
temperature
ambient pH, decreased
temperature
decreased pH, decreased
temperature
ambient pH, increased
temperature
decreased pH, increased
temperature
ambient pH, ambient
temperature
Reference
Average (SD)
[pH unit]
8.76 (0.02)
7.89 (0.09)
7.52 (0.04)
6.73 (0.12)
8.48 (0.02)
7.31 (0.08)
8.37 (0.05)
7.60 (0.06)
8.74 (0.01)
Unitl
Average (SD)
[pH unit]
8.62 (0.00)
7.72 (0.14)
7.32 (0.04)
6.38 (0.07)
8.52 (0.02)
7.06 (0.09)
8.30 (0.04)
7.32 (0.02)
8.65 (0.01)
Unit 2
%D
-1.6
-2.2
-2.7
-5.2
0.5
-3.4
-0.8
-3.7
-1.0
Average
(SD)
[pH unit]
8.80 (0.00)
7.77 (0.16)
7.32 (0.04)
6.32 (0.06)
8.51 (0.01)
7.09 (0.10)
8.34 (0.03)
7.27 (0.01)
8.67 (0.02)
%D
0.5
-1.5
-2.7
-6.1
0.4
-3.0
-0.4
-4.3
-0.8
Of the parameters that were evaluated for accuracy, the free chlorine sensor generated the largest
range of percent differences compared to the reference method (with the median shown in
parentheses): from 3.4 to 117.1 (26.2); for temperature, -18.4 to 2.7 (-3.7); for conductivity
-26.8 to -22.4 (-24.6); and for pH, -6.1 to 0.5 (-1.9).1 The chlorine sensor was calibrated by the
vendor before the verification test, but was not recalibrated throughout Stage 1. The tendency
evidenced by the range and median was for the sensor to drift high. As discussed in Section 6.2,
calibration of the free chlorine sensor was required to maintain accurate free chlorine measure-
ments. The temperature sensors generated very small percent differences (between -6% and 0%)
with respect to the reference method at ambient temperatures, larger negative percent differences
(between -13% and -18%) when the temperature of the water in the pipe loop was decreased, and
small positive percent differences (between 0% and 3%) when the temperature of the pipe loop
water was increased. This trend in percent differences is thought to be chiefly a result of the
reference sample collection and analysis procedure. Reference samples were carried to a
laboratory bench approximately 25 feet from the reference sample collection valve. Therefore,
upon sample collection, the reference sample immediately began equilibrating with the ambient
1 Throughout this report, median values are provided when a range of values is presented. The median of a set of
positive and negative numbers provides a good indicator of the overall direction of the percent differences in the
data set (i.e., whether most values were positive or negative). The disadvantage is that, unless the signs of all the
data are the same, information about the magnitude of change is not available from the median. In summary, the
medians in this report provide the direction, not magnitude, of difference information.
18
-------
air, causing the trends in percent differences with respect to the reference method. The
conductivity results generated a consistently negative percent difference throughout Stage 1, but
one recalibration of the conductivity sensor to match the reference result corrected the negative
percent difference. Stages 2 and 3 exhibited very small conductivity percent differences.
The standard deviations of the reference and continuous measurements collected during each test
period were, with few exceptions, very small with respect to the average result. In only a few
instances was the standard deviation greater than 5% of the average result. This shows both that
the water conditions during these test periods were very stable and that there was very little
variability in the sensors themselves.
6.2 Response to Injected Contaminants
Six injections of contaminants were performed during the second stage of this verification test;
i.e., duplicate injections of nicotine, arsenic trioxide, and aldicarb. Table 6-3 shows the
directional change of each reference and Sentinal™ 500 measurement in response to the
contaminant injections. In general, free chlorine and ORP were the only parameters clearly
affected (for both the reference and continuous measurements) by all six injections. Figures 6-1
through 6-4 show the responses of free chlorine, ORP, conductivity, and pH. The blue and
yellow lines on the graphs represent the measurements made by each Sentinal™ 500 unit, and
the magenta data points represent the results from the laboratory reference method. Because
accuracy was the focus of the first stage of verification testing, percent differences between the
Sentinal™ 500 units and the reference method results are not presented here; however, the
reference method results are included in these figures to confirm that the fluctuations in the
continuous results are due to changes in water chemistry as the result of the injected
contaminants. The figures are divided with vertical lines that define the approximate time period
for each injection. Each injection time period defined on the figures is approximately 24 hours,
but the times vary somewhat depending on when chlorine was added to restore the system to pre-
injection conditions. The contaminant that was injected and whether it was the first or second
replicate are shown at the top of each section of the figures. For each injection, at least four
reference sample results were collected and are included in these figures. The first occurred
within approximately one hour prior to contaminant injection during a period of stable water
quality conditions. The next three reference data points were from samples collected 3, 15, and
60 minutes after contaminant injection. For some of the injections, another reference sample was
collected the following day to show that the pipe loop system had recovered or was in the
process of recovering after the injection. This final reference data point also served as the first
reference sample collected for some of the injections, representing the stable baseline just prior
to injection.
19
-------
Table 6-3. Effect of Contaminant Injections Prior to Extended Deployment
Parameter
Free chlorine
Temperature
Conductivity
pH
ORP
Nicotine
Reference Sentinal™ 500
-
NC
NC
NC
-
NC
NC
NC
Arsenic
Trioxide
Reference Sentinal™ 500
-
NC
+
+
..
-
NC
+
+
Aldicarb
Reference Sentinal™ 500
-
NC
NC
NC
-
NC
NC
NC
+/- = Parameter measurement increased/decreased upon injection.
NC = No change in response to the contaminant injection.
2.5
Nicotne " Nicotine 2 Arsenic 1 Arsenic 2 Aldicart 1 Aldicarb 2
—Unitl
* Reference
Unit 2
Each section (separated by vertical lines) represents approximately 24 hours.
Figure 6-1. Stage Contaminant Injection Results for Free Chlorine
20
-------
5UU
800 -
700 -
600 -
500 -
400 -
300 -
200 -
100 -
n
Nicotine 1
^
1
. /
M ' *
*^
*
Nicotine 2
^ \
*
i /
/
i /
y
Arsenic 1
* /
|
I
4
Arsenic 2
'
••
|
^
c
'
1
Aldicarb 1
1
Aldicarb 2
1 f T
i
4
i
\
1
I
1
1
1 "
— Unitl
• Reference
Unit 2
Eacli section (separated by vertical lines) represents approximately 24 hoLirs.
Figure 6-2. Stage 2 Contaminant Injection Results for ORP
460
Nicotirp 2 Arsenic 1 Arsenic 2
400 -"-
Each section (separated by vertical lines) represents approximately 24 hours
Figure 6-3. Stage 2 Contaminant Injection Results for Conductivity
21
-------
Each section (separated by vertical lines) lepresents approximately 24 hours
Figure 6-4. Stage 2 Contaminant Injection Results for pH
Figure 6-1 shows how the measurement of free chlorine was affected by the contaminant
injections. Prior to the injections, the free chlorine level was maintained at approximately 1 mg/L.
At the start of Stage 2, the Sentinal™ 500 unit's measurements had drifted significantly higher
than the reference measurement, a trend that had been observed during Stage 1. Nonetheless, in
each case, within one hour of contaminant injection, the free chlorine level, as measured by the
laboratory reference method, dropped to its low point. As evidenced by the vertical drop in the
line representing the free chlorine concentration, it was clear that the chlorine sensor on the
Sentinal™ 500 units responded to the decrease in free chlorine levels as a result of the presence
of the contaminant. In addition to the high measurements prior to the injections, the Sentinal™
500 units recovered from both nicotine injections to levels higher than for the reference method.
Note that just prior to the first arsenic injection, the chlorine measurements dropped to match the
reference measurement much more closely. At this time, the chlorine sensors were calibrated to
match the reference method measurements. Thereafter, the sensors seemed less prone to
recovering to a result biased high, but Unit 2 appeared to have drifted low after the arsenic
injection. Also, after the first aldicarb injection, Unit 2 recovered to a high measurement and
Unit 1 drifted low. Both sensors were calibrated prior to the final aldicarb injection, which is
evidenced by the convergence of their respective lines. Also, after the second aldicarb injection,
both chlorine sensors recovered to very high measurements, requiring calibration prior to the next
stage of the verification test. For each injection, the drop in free chlorine levels was followed by
the restoration of the pipe loop system to approximately pre-injection conditions through the
addition of sodium hypochlorite. This is shown in Figure 6-1 by the rapidly increasing free
chlorine concentration after the sensor reaches a low point in free chlorine concentration.
The ORP in water is dependent on the occurrence of oxidation-reduction chemical reactions
within the water. Therefore, when free chlorine is reacting with injected contaminants, it can be
expected that the ORP would be affected. Figure 6-2 shows that ORP tracked the concentration of
22
-------
free chlorine upon injection of the contaminants. The free chlorine reacted with the contaminants,
and the concentration dropped, as did the ORP. It is difficult to determine if the change in ORP is
in response to the drop in free chlorine or to the presence of the contaminant itself. Conductivity
and pH were affected (as measured by both the reference and continuous measurement) by the
injection of arsenic trioxide only. However, this may have been due to the pH adjustment required
to get it into solution.
6.3 Extended Deployment
Figures 6-5 through 6-9 show the continuous measurements from both Sentinal™ 500 units
during the 52-day extended deployment stage of the verification test. Those measurements are
represented by the blue and yellow lines, while the results of the reference samples, collected
once daily throughout this deployment, are represented by the magenta symbols. The x-axis on
each figure represents the period of time between September 1, 2004, and October 22, 2004, and
the y-axis gives the results of each water quality measurement. Data points were recorded every
30 seconds during the verification test; but, for the extended deployment figures, only data points
collected approximately every 2 minutes were depicted. This was done so that a standard spread-
sheet could be used to generate these figures. This approach was inconsequential to interpreting
the figures.
The objective of this stage of the verification test was to evaluate the performance of the
Sentinal™ 500 unit over an extended period of time with minimal intervention to simulate a
situation in which the units may be deployed at a remote location. The continuous trace was
visually evaluated to see whether any aspects of the data were noteworthy. A second, more
quantitative, evaluation was then performed to get an indication of the accuracy of the extended
deployment measurements. This evaluation, much like the accuracy evaluation conducted during
the first stage of testing, included calculating the percent differences between the average
continuous measurements and average reference sample results throughout the extended
deployment, as well as the standard deviation of each of those measurements. The standard
deviation of the results provided a means to evaluate the stability of the water conditions during
Stage 3, as well as how the standard deviations of the continuous measurements differed from the
standard deviations of the reference measurements. Similar relative standard deviations between
the continuous and reference measurements indicate that variability was mostly dependent on the
water conditions and not due to systematic variability in the Sentinal™ 500 unit results. (Note
that the reference results were only generated during business hours, so any fluctuations occurring
during off hours were not reflected in the standard deviation of the reference results. Because of
this, free chlorine, a parameter that varied at times during weekends when the supply of chlorine
ran low, might have been expected to have a larger variability than other more stable parameters.)
Table 6-4 lists the percent differences, along with the average and standard deviations of the
reference and continuous results during the extended deployment. The range and median (see the
footnote in Section 6.1 for direction on interpreting the median) percent difference for each water
quality parameter, as measured for each reference sample analyzed during the extended
deployment, are also given.
For free chlorine, visual inspection of the data in Figure 6-5 revealed that, at the start of Stage 3,
the Sentinal™ 500 units' measurements were dropping from the high reading to which they had
23
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2.5
1.5
B)
E
0.5
— Unitl
» Reference
Unit 2
Event
#3
Duration of Stage 3: 52 clays
Figure 6-5. Extended Deployment Results for Free Chlorine
12
11
10 -
9H
8 -
7 -
•Unitl
Reference
Unit 2
Duration of Stage 3: 52 days
Figure 6-6. Extended Deployment Results for pH
Event
#4
24
-------
800
700 -
600 -
500 -
400
300 -
200-
100-
0
— Unitl
» Reference
Unit 2
Duration of Stage 3: 52 days
Figure 6-7. Extended Deployment Results for ORP
— Unitl
1 Reference
Unit 2
Duration of Stage 3: 52 clays
Figure 6-8. Extended Deployment Results for Temperature
25
-------
500
450
E 400 -1
~
Q)
| 350 ^
iw
2
E 300 4
250 -
200
— Unitl
* Reference
Unit 2
Duration of Stage 3: 52 days
Figure 6-9. Extended Deployment Results for Conductivity
Table 6-4. Accuracy During Extended Deployment
Parameter
Free chlorine
Temperature
Conductivity
PH
Reference
average
(SD)(a)
0.95 (0.09)
22.83 (0.36)
333 (57)
8.72 (0.07)
Unitl
Average (SD)(a)
0.74 (0.22)
22.58 (0.08)
345 (55)
8.60 (0.27)
%D
-22.1
-1.1
3.6
-1.4
Unit 2
Average (SD)(a)
0.76 (0.22)
21.95 (0.08)
335 (54)
8.78 (0.08)
%D
-20.0
-3.9
0.6
0.7
Both Units
%D Range
(median)
-54.8 to 50.0 (-21.5)
-7.8 to 2.7 (-2.7)
-0.8 to 5.5 (2.1)
-7.2 to 1.6 (0.3)
(a) Free chlorine, mg/L; temperature, °C; conductivity, |_iS/cm; pH, pH units.
recovered after Stage 2. This drop was caused by the calibration of the sensors to match the
reference result. It is not clear why the sensors did not track the reference measurements better
thereafter; but, for the first approximately one-third of the extended deployment, the free chlorine
measurements were approximately 0.5 mg/L (with some variation) for both Sentinal™ 500 units,
while the reference method measurement was approximately 1 mg/L. At that point, Clarion
directed the verification staff to recalibrate the chlorine and pH sensors based on the reference
method result (free chlorine Event #1 in Figure 6-5). When this was done, both Sentinal™ 500
units tracked the free chlorine reference measurements rather well for several days until the
measured chlorine concentrations drifted high (to nearly 2 mg/L) for a three-day period (free
chlorine Event #2). The sensors recovered without recalibration and, with a few exceptions,
tracked the reference method results fairly well until the supply of sodium hypochlorite (used to
26
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maintain the chlorine concentrations in the pipe loop) ran low after a weekend and the chlorine
level dropped to less than 0.5 mg/L. After this drop, both chlorine sensors recovered to a
measurement somewhat lower than the reference method (free chlorine Event #3). This continued
until near the end of the extended deployment when the results from the two Sentinal™ 500 units
abruptly converged to a measurement very similar to that of the reference measurement. This
marked the time that Clarion again directed the verification staff to calibrate the chlorine sensors
to match the reference method result (free chlorine Event #4). During the extended deployment,
the percent differences for both Sentinal™ 500 units ranged from -54.8 to 50.0, with a median of
-21.5. The average free chlorine concentration, as measured by the reference method, was 0.95 ±
0.09 mg/L.
The pH results are presented in Figure 6-6. For the first approximately one-third of the extended
deployment, Unit 2 and the reference method were measuring the pH as approximately 8.8, while
Unit 1 was measuring it as approximately 8.0. The start of Stage 3 corresponded with a data
logging memory problem in Unit 1. The Clarion representative removed the memory module, had
it repaired, and replaced it a couple of days later. The large difference between Units 1 and 2
began the same day the memory module was reinstalled in Unit 1 (pH Event #1 in Figure 6-6).
For a reason that is not known, the pH sensor was either improperly calibrated or not calibrated
that day. Both pH sensors were calibrated several days later (at the direction of Clarion), which is
shown by the convergence of pH measurements for both units with the reference measurements
(pH Event #2). After that, both pH sensors maintained the accuracy of the results rather well. The
average pH, as measured by the reference method, was 8.72 ± 0.07, and the average pH
measurements for Units 1 and 2, respectively, were 8.60 ± 0.27 and 8.78 ± 0.08. Overall, during
the extended deployment, the percent difference for the pH sensor ranged from -7.2 to 1.6, with a
median of 0.3.
The other three water quality parameters were not affected by the pH adjustment. The ORP,
temperature, and conductivity sensors were allowed to operate without intervention throughout
the extended deployment. The measurements from these three sensors are shown in Figures 6-7
through 6-9. In Figure 6-7, the ORP results are shown along with a laboratory reference method
result. The reference method is not an accurate representation of water in a flowing pipe, but it
can be used to evaluate a trend in the decrease and increase in the ORP, as it was in the previous
section for the contaminant injections.
The Unit 1 and 2 conductivity results tracked the reference method results throughout the
extended deployment. The temperature results from both Units 1 and 2 had regular variability
because the test was conducted in a facility where the water temperature was heavily affected by
the outdoor temperature; therefore, the water temperature changed as a function of the high and
low for the day. Also, Unit 2 temperature results appeared to be biased low with respect to Unit 1
and the reference method.
6.4 Accuracy and Response to Injected Contaminants After Extended Deployment
After the 52-day deployment of the Sentinal™ 500 units with minimal intervention, their
performance was evaluated during a 4-hour period of ambient pH and temperature during which
reference samples were collected hourly. The results of this evaluation are given in Table 6-5.
The percent differences determined after the extended deployment for free chlorine, conductivity,
27
-------
and pH were considerably different from those determined during Stage 1. This is due to the fact
that each of these sensors was calibrated (as previously discussed) at least once between Stage 2
and Stage 3. In all three cases, the percent differences were closer to zero in the post-extended
deployment accuracy evaluation.
Table 6-5. Post-Extended Deployment Results
Parameter
Free chlorine
Temperature
Conductivity
PH
Reference
average (SD)(a)
0.92 (0.02)
22.66 (0.16)
356(1)
8.59 (0.01)
Unitl
average (SD)(a)
0.82 (0.05)
22.55 (0.01)
365 (2)
8.59 (0.00)
Unit 1 %D
-10.9
-0.5
2.5
0.0
Unit 2
average (SD)(a)
0.75 (0.10)
21.95 (0.05)
357 (1)
8.69 (0.01)
Unit 2 %D
-18.5
-3.1
0.3
1.2
(a) Free chlorine, mg/L; temperature, °C; conductivity, |_iS/cm; pH, pH units.
A second evaluation of the response to injected contaminants after the extended deployment used
four contaminants. Two were a repeat of the aldicarb injections performed during Stage 2 and two
were injections of E. coli, which was not available for injection during the earlier stage of the test.
Table 6-6 gives the directional change of each reference measurement and Sentinal™ 500
measurement in response to the contaminant injections. In general, free chlorine, ORP, and pH
were the three parameters that were affected (for both the reference and continuous measure-
ments) by all four injections. These parameters are shown in Figures 6-10 through 6-12. Conduc-
tivity is shown in Figure 6-13. The response of the chlorine sensor was consistent for all four
injections. The recovery of the chlorine sensors was not as consistent. After the first injection, the
recovery was difficult to evaluate because of a chlorine concentration increase resulting from
occurrences in the Cincinnati water system that could not be controlled. After the second and
third injections, the sensors both recovered to a concentration less than the reference method.
Therefore, the sensors were recalibrated prior to the final injection. After the final injection, the
chlorine sensors recovered fully. As during Stage 2, the ORP sensor tracked the chlorine response
for each injection. Again, it is difficult to determine whether the ORP change is due to the
reaction of chlorine or the presence of the contaminant itself. For pH, the reference results
indicated a decrease in response to all of the contaminant injections; this result was unexpected.
Aldicarb had not altered the pH during the Stage 2 injections. In addition, the conductivity
increased (in both the reference and continuous measurements) very slightly upon injection of the
E. coli.
28
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Table 6-6. Effect of Contaminant Injections After Extended Deployment
Parameter
Free chlorine
Temperature
Conductivity
pH
ORP
E. coli
Reference Sentinal™ 500 Reference
_ _ _
NC NC NC
+ + NC
- -
- - -
Aldicarb
Sentinal™ 500
-
NC
NC
-
-
+/- = Parameter measurement increased/decreased upon injection.
NC = No change in response to the contaminant injection.
z.u
2
1^
.5 -
J
Bi
E
1 -
0.5 -
n
E.coli 1
*
^s
E.coli 2
^
^
i
J
, r
I
j
Aldicarb 3
4
i
I
t
Aldicarb 4
|
iX/*"
i
I
J
*
— Unitl
Reference
Unit 2
^"**
i
Each section (separated by vertical lines) represents approximately 24 hours.
Figure 6-10. Stage 3 Contaminant Injection Results for Free Chlorine
29
-------
Each section (separated by vertical lines) represents approximately 24 hours.
Figure 6-11. Stage 3 Contaminant Injection Results for ORP
7.8 -L
Each section (separated by vertical lines) represents approximately 24 hours.
Figure 6-12. Stage 3 Contaminant Injection Results for pH
30
-------
420
410
340
Each section (separated by vertical lines.) lepresents approximately 24 hours.
Figure 6-13. Stage 3 Contaminant Injection Results for Conductivity
6.5 Inter-unit Reproducibility
Two Sentinal™ 500 units were compared throughout the verification test to determine whether
they generated results that were similar to one another. This was done using the Sentinal™ 500
data collected whenever a reference sample was collected throughout the verification test. Two
evaluations were performed to make this comparison. First, the results from Unit 2 were graphed
on the y-axis; those from Unit 1 were graphed on the x-axis; a line was fitted to the data; and the
slope, intercept, and coefficient of determination (r2) of this line were determined. Second, a t-test
assuming equal variances was performed on those same data. For the linear regression analysis, if
both Sentinal™ 500 units reported the identical result, the slope of such a regression would be
unity (1), the intercept zero (0), and the coefficients of determination (r2) 1.0. The slope can
indicate whether the results are biased in one direction or the other, while the coefficients of
determination provide a measure of the variability of the results. The t-test shows whether the
sensors generated statistically similar data. Small p-values (<0.05 at a 5% confidence level)
would suggest that the results from the two Sentinal™ 500 units are significantly different from
one another. Table 6-7 gives the slope, intercept, and coefficients of determination for the
inter-unit reproducibility evaluation and the p-value for the t-test performed for each sensor.
The temperature, conductivity, and pH sensors had coefficients of determination greater than 0.95
and slopes within 5% of unity, indicating that their results were very similar and repeatable.
Confirming that evaluation, the t-test p-value for those sensors was 0.23, 0.74, and 0.17,
respectively.
31
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Table 6-7. Inter-unit Reproducibility Evaluation
Parameter
Free chlorine
Temperature
Conductivity
pH
ORP
Slope
0.86
0.98
1.01
1.05
0.89
Intercept
0.10
-0.04
-4.13
-0.3
72
r2
0.87
1.00
0.98
0.95
0.98
t-test p-value
0.92
0.23
0.74
0.17
0.87
As can be seen from Table 6-7, the ORP sensors had a coefficient of determination of 0.98,
indicating that they were highly correlated with one another; but the slopes were approximately
11% less than unity, indicating that Unit 2 measurements were lower than Unit 1. This evaluation
was supported by the figures throughout Chapter 6, which show that Unit 2 measurements were
slightly less than Unit 1. However, based on the t-test, this difference was not significant.
The free chlorine sensor had a lower coefficient of determination and a slope that deviated from
unity by more than 10%. This lower correlation was observed in the figures for the extended
deployment when the Sentinal™ 500 units drifted by varying degrees. In addition, calibrating the
chlorine sensor several times during the verification test increased the degree of variability in the
free chlorine results. Because of this, the t-test indicated that the results from the free chlorine
sensors were statistically the same.
6.6 Ease of Use and Data Acquisition
Throughout the duration of the verification test, the verification staff was not required to perform
any routine maintenance. However, on several occasions, Clarion or verification test staff (at the
request of Clarion) adjusted the chlorine sensor reading to match the reference sample measure-
ment. Therefore, the accuracy of the free chlorine measurement was directly affected by this
adjustment. Based on the performance of the free chlorine sensors, they may have to be adjusted
periodically to maintain the accuracy of measurements. This would require a means of measuring
the chlorine content of the water, as well as a site visit, to make the adjustment. No other
maintenance was necessary during the test.
Data were saved onto memory modules mounted onto the Sentinal™ 500 units. With a 30-second
data collection frequency, the storage capacity of the modules was not reached during the three-
month test. One of the modules had to be removed for repair during the verification test. Also, in
two instances, the Sentinal™ 500 units failed to download properly. Both units were rebooted,
and the problem was resolved. This system may need to be reset periodically if the units are
deployed remotely.
32
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Chapter 7
Performance Summary
Evaluation Parameter
Stage 1—
Accuracy
Stage 2 — Response
to Injected
Contaminants
Stage 3 —
Accuracy During
Extended
Deployment
Stage 3 — Accuracy
After Extended
Deployment
Stage 3 — Response
to Injected
Contaminants
Injection Summary
Inter-unit
Reproducibility
(Unit 2 vs. Unit 1)
Ease of Use
and Data
Acquisition
Units 1 and 2, range of
%D (median)
Nicotine
Arsenic
trioxide
Aldicarb
Reference
Sentinal™ 500
Reference
Sentinal™ 500
Reference
Sentinal™ 500
Units 1 and 2, range of
%D (median)
Unit 1, %D
Unit 2, %D
E. colt
Aldicarb
Reference
Sentinal™ 500
Reference
Sentinal™ 500
Free
Chlorine
3.4 to 117.1
(26.2)
-
-
-
-
-
-
-54.8 to 50.0
(-21.5)
-10.9
-18.5
-
-
-
-
Tem-
perature
-18.4 to 2.7
(-3.7)
NC
NC
NC
NC
NC
NC
-7.8 to 2.7
(-2.7)
-0.5
-3.1
NC
NC
NC
NC
Conductivity
-26.8 to -22.4
(-24.6)
NC
NC
+
+
NC
NC
-0.8 to 5.5
(2.1)
2.5
0.3
+
+
NC
NC
pH
-6.1 to 0.5
(-1.9)
NC
NC
+
+
NC
NC
-7.2 to 1.6
(0.3)
0.0
1.2
-
-
-
-
ORP
(a)
-
-
-
-
-
-
(a)
(a)
(a)
-
-
-
-
For a reason that is not clear, aldicarb altered the pH, as measured by the reference method,
during the Stage 3 injections, but not during the Stage 2 injections.
Slope (intercept)
r2
p-value
0.86(0.10)
0.87
0.92
0.98 (-0.04)
1.00
0.23
1.01 (-4.13)
0.98
0.74
1.05 (-0.3)
0.95
0.17
0.89 (72)
0.98
0.87
All sensors generated results that were similar according to the results of the t-test. However,
the slopes of the ORP and free chlorine sensor data plotted against one another suggest that
the results from each unit were somewhat different from one another.
Based on the performance of the free chlorine sensors, they may have to be adjusted
periodically to maintain the accuracy of the measurements. The memory module in Unit 1 had
to be replaced and, twice, each unit had to be rebooted before data could be downloaded.
(a) ORP was not included in the accuracy evaluation because of the lack of an appropriate reference method.
+/- = Parameter measurement increased/decreased upon injection.
NC = No obvious change was noted through a visual inspection of the data.
33
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Chapter 8
References
1. Test/QA Plan for Verification of Multi-Parameter Water Monitors for Distribution Systems,
Battelle, Columbus, Ohio, August 2004.
2. Personal communication with John Hall, U.S. EPA, July 23, 2004.
3. U.S. EPA, EPA Method 150.1, pH, in Methods for Chemical Analysis of Water and Wastes,
EPA/600/4-79/020, March 1983.
4. American Public Health Association, et al, SM 2510, Conductivity, in Standard Methods for
the Examination of Water and Wastewater, 19th Edition, Washington, D.C., 1997.
5. American Public Health Association, et al., SM 4500-G, Residual Chlorine, in Standard
Methods for the Examination of Water and Wastewater, 19th Edition, Washington, D.C., 1997.
6. American Public Health Association, et al., SM 2580-B, Electrochemical Potential, in
Standard Methods for the Examination of Water and Wastewater. 19th Edition, Washington,
D.C., 1997.
7. U.S. EPA, EPAMethod 170.1, Temperature, inMethodsfor Chemical Analysis of Water and
Wastes, EPA/600/4-79/020, March 1983.
8. Quality Management Plan (QMP)for the ETV Advanced Monitoring Systems Center,
Version 5.0, U.S. EPA Environmental Technology Verification Program, Battelle, Columbus,
Ohio, March 2004.
34
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