technical BRIEF
www.epa.gov/nhsrc
Detecting Contamination Events in Water Distribution
Systems, Using Multi-Parameter Sensors
Five water-monitoring sensors evaluated for detecting contamination events
In the past, people in the United States have largely
taken for granted the convenience of potable municipal
water. However, the threat of intentional contamination
of our water supplies is becoming a concern because of
a rise in the number of terrorist acts around the world.
As a result, there is much interest in technologies that
can be used to detect a contamination event either as it
is occurring or immediately after. Such technologies
include multi-parameter water monitors that are
integrated into sensor units.
These sensor units can be deployed at multiple locations
in water distribution systems and collect general water
quality data that can be transmitted to various locations,
including remote locations, thereby giving water utilities access to real-time or near real-time
data from their overall system. These units can also be customized for users' needs to include
various monitoring devices for pH, conductivity, alkalinity, total organic carbon (TOC), oxidation
reduction potential (ORP), temperature, turbidity, and chlorine.
Residual chlorine is particularly important because changes in its concentration can indicate the
presence of low levels of contamination within a distribution system. Chlorination is a very
common form of water treatment used by water utilities.
During 2004, EPA evaluated five multi-parameter water sensors:
•	Q45WQ Series (Analytical Technology, Inc.)
•	Sentinal™500 Series (Clarion Sensing Systems, Inc.)
•	Water Distribution Monitoring Panel (WDMP) and Event Monitor™
Trigger System (Hach Company)
•	TitraSip™SA (Man-Tech Associates Inc.)
•	Model WQS (Rosemount Analytical)
Each unit was evaluated for:
•	Accuracy
•	Response to injected contaminants
•	Inter-unit reproducibility
•	Ease of use
U.S. EPA's Homeland Security Research Program
(HSRP) develops products based on scientific
research and technology evaluations. Our products
and expertise are widely used in preventing, preparing
for, and recovering from public health and
environmental emergencies that arise from terrorist
attacks. Our research and products address
biological, radiological, or chemical contaminants that
could affect indoor areas, outdoor areas, or water
infrastructure. HSRP provides these products,
technical assistance, and expertise to support EPA's
roles and responsibilities under the National
Response Framework, statutory requirements, and
Homeland Security Presidential Directives.
This document does not constitute nor should be construed as an EPA endorsement of any particular product,
service, or technology.

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Chlorine was measured using amperometric, colorimetric, or potentiometric titration methods.
Turbidity was measured by nephelometry, and conductivity, pH, and ORP were measured using
the applicable electrodes/meters. TOC analysis combined chemical and ultraviolet oxidation
techniques and alkalinity was measured using titration. Data were collected from each sensor
unit using a data logger or memory stick. Data were then imported into a database. Some
sensors were equipped with alarms that would signal when a threshold was exceeded.
Test Design
The sensors were evaluated in three stages, using the recirculating pipe loop at the EPA Test
and Evaluation Facility in Cincinnati, OH:
•	Stage 1 tested accuracy.
•	Stage 2 tested responsiveness to water quality changes.
•	Stage 3 tested performance, including inter-unit reproducibility and ease of use.
Stage 1 (Accuracy):
Water quality conditions were simulated by changing pH and temperature variables. Seven four-
hour test periods of unique pH and temperature conditions with reference method sampling and
analysis every hour were used to evaluate the accuracy of the units:
•	pH at approximately 7, 8, and 9, with water temperatures between 21 and 23 °C
•	pH at approximately 7 and 8, with water temperatures between 12 and 14 °C
•	pH at approximately 7 and 8, with water temperatures of approximately 27 °C
Monitor measurements from two sensor units were evaluated by comparing each measurement
to the hourly result from standard laboratory reference methods and then calculating the percent
difference.
Stage 2 (Responsiveness):
Six runs were performed to evaluate responsiveness of each unit's monitors. Specifically,
contaminants (nicotine, arsenic trioxide, and aldicarb) were injected at two separate times into
the recirculating pipe loop. Upon injection, contaminant concentrations within the pipe loop were
approximately 10 milligrams per liter (mg/L).
This concentration level was chosen since it is of sufficient magnitude that it could be detected
by the sensor units. After contaminant injection, the response of each water quality parameter
(increase, decrease, or no change) was then documented
Stage 3 (Performance):
This stage consisted of two phases. The first phase evaluated the performance of the sensor
during an extended deployment of 52 continuous-operation days. References samples were
collected once daily throughout this time period.
The second phase, which lasted approximately one week, consisted of a two-step evaluation: 1)
to determine whether extended operation negatively impacts the accuracy of the sensor unit
and 2) to determine how well the sensor units respond to the injection of a contaminant.
June 2008
E PA/600/S-08/008
This document does not constitute nor should be construed as an EPA endorsement of any particular product,
service, or technology.

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For the second phase of Stage 3, a reference grab sample was collected every hour during a 4-
hour time period. The sample results from the sensor unit monitors were then compared to
results from the standard laboratory reference method. Next, aldicarb and E. coli were injected
at two different times (duplicates for each contaminant) into the recirculating pipe loop to
evaluate the sensor's response to contaminant injections after extended deployment. In most
cases, the differences between the results before and after extended deployment were nominal.
In addition to analysis of the accuracy and contaminant injection data, inter-unit reproducibility
was assessed by comparing the results of two identical sensor units operating simultaneously.
Overall ease of the sensor unit use was also documented by the technicians who operated and
maintained them.
The multi-parameter water monitoring sensor (Hach WDMP), equipped with event detection and
contaminant identification software, was separately evaluated from the other units.
An additional stage (Stage 4) was included as part of this unit's testing to determine:
1)	whether the software detected the injection of selected contaminants
2)	whether it correctly identified each contaminant.
Testing involved two separate injections of 13 contaminants (aldicarb, arsenic trioxide,
colchicine, dichlorvos, dicamba, E. coli, bacteria, glyphosate, lead nitrate, mercuric chloride,
methanol, nicotine, potassium ferricyanide, and sodium fluoroacetate).
Performance and Results
Table 1 provides the sensor units' range of percent differences and median percent differences
for various water quality parameters.
Table 1. Stage 1- Accuracy Evaluation Range of % Difference (Median % Difference)
Sensor
Unit
Free
Chlorine
Turbidity
Conductivity
pH
TOC
Alkalinity
Q45WQ
Series
-41.5 to 54.3
(-15.7)
-47.2 to-16.9
(-24.9)
-19.7 to -2.6
(-12.7)
-11.8 to -0.9
(-5.0)
NM
NM
WQS
-11.1 to 96.7
(14.5)
NM
2.9 to 5.3
(4.2)
-7.4 to-1.1
(-3.0)
NM
NM
Sentinal "
500
3.4 to 117.1
(26.2)
NM
-26.8 to -22.4
(-24.6)
-6.1 to 0.5
(-1.9)
NM
NM
TitraSip "
-13.2 to 20.6
(7.5)
-65.2 to 0.6
(-45.2)
37.9 to 94.3
(57.5)
-2.2 to 5.4
(0.6)
NM
3.2 to 30.4
(11.5)
WDMP
-47.4 to 4.5
(-3.9)
-53.9 to-1.3
(-34.1)
-15.5 to 8.1
(2.2)
-6.6 to 3.1
(0.9)
-64.7 to 147.5
(-14.8)
NM
NM = Parameter was not measured by this sensor unit.
The ranges of percent difference for free and total chlorine, turbidity, and TOC were large, which
indicates the sensors were not very accurate for these water quality parameters.
The ranges of percent difference for conductivity, pH and alkalinity were generally within ±30%
difference from the reference results, which indicates the sensors were more accurate for these
water quality parameters.
June 2008
EPA/600/S-08/008
This document does not constitute nor should be construed as an EPA endorsement of any particular product,
service, or technology.

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The median percent difference (in parentheses in Table 1) identifies the central value across all
measurements for the water quality parameter of interest. This evaluation for accuracy
was repeated after extended deployment, and the results were very similar.
Table 2 summarizes the responses to injected contaminants. Results are reported as either no
change (NC), not measured (NM), an increase (+), or a decrease (-).
Table 2. Stage 2- Response to Injected Contaminants
Contaminant
Sensor
Unit
Free &
Total
Chlorine
Turbidity
Conductivity
pH
ORP
TOC
Alkalinity

Q45WQ
-
+
NC
NC
-
NM
NM

WQS
-
NM
NC
NC
-
NM
NM
Nicotine
Sentinal™
500
-
NM
NC
NC
-
NM
NM

TitraSip
-
(a)
NC
NC
NM
NM
NC

WDMP
-
+
NC
NC
NM
+
NM

Q45WQ
-
+
+
+
-
NM
NM

WQS
o»>
NM
+
+
-
NM
NM
Arsenic trioxide
Sentinal™
500
-
NM
+
+
-
NM
NM

TitraSip""
-
(a)
+(W
+
NM
NM
+

WDMP
-
+
+
+
NM
NC
NM

Q45WQ
-
+
NC
NC
-
NM
NM

WQS
-
NM
NC
NC
-
NM
NM
Aldicarb
Sentinal™
500
-
NM
NC
NC
-
NM
NM

TitraSip™
-
(b)
NC
NC
NM
NM
NC

WDMP
-
+
NC
NC
NM
+
iNM
w =Relatively large uncertainties occurred in the reference and continuous measurements that made it
difficult to determine a significant change,
to = Duplicate injection results did not agree.
+ or - = Parameter measurement increased or decreased, respectively, upon injection.
NC = No obvious change was noted through visual inspection of the data.
NM = Parameter was not measured by this sensor unit.
The following can be concluded regarding the injection of the three contaminants (nicotine,
arsenic trioxide, and aldicarb):
•	All sensor units showed decreases in free chlorine concentrations after the three
contaminants were injected.
•	All sensor units showed decreases in ORP measurements concentrations after
the three contaminants were injected.
•	No sensor unit showed a change in pH and conductivity readings when nicotine and
aldicarb were injected; however, they showed an increase in pH and conductivity readings
after arsenic trioxide was injected.
This evaluation was repeated after the extended deployment using aldicarb and E. coli.:
•	Injection of aldicarb yielded similar results to those in Table 2.
June 2008
EPA/600/S-08/008
This document does not constitute nor should be construed as an EPA endorsement of any particular product,
service, or technology.

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•	Injection of E. coli. showed decreases in free chlorine and increases in ORP,
alkalinity, and conductivity.
For the Stage 4 testing of the Hach WDMP:
•	All contaminant events (22 contaminant events - two separate injections of 13
contaminants) were identified as they occurred.
•	Eleven of the 13 contaminants injected were correctly identified during the testing.
•	Two of the 13 contaminants injected (potassium ferricyanide and lead nitrate) were
correctly identified during the entire testing (i.e., injection) time period.
CONTACT INFORMATION
For more information, visit the EPA Web site at www.epa.gov/nhsrc.
Technical Contact: Eric Koglin (koglin.eric@epa.gov)
General Feedback/Questions: Kathy Nickel (nickel.kathy@epa.gov)
June 2008
E PA/600/S-08/008
This document does not constitute nor should be construed as an EPA endorsement of any particular product,
service, or technology.

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