©EPA
www.epa.gov/nhsrc
technical BR
Commonly Used Water Quality Sensors Can Detect
Intentional Drinking Water Contamination
Free chlorine and total organic carbon sensors most successful for detecting
contamination in tests using selected biological and chemical contaminants
Introduction
EPA has released Distribution System Water Quality Monitoring: Sensor Technology Evaluation
Methodology and Results - A Guide for Sensor Manufacturers and Water Utilities, which
summarizes the results of tests with various online (i.e.,
real-time) water quality sensors to see if they could
provide dual use for early warning of intentional
contamination, as well as monitoring general water
quality. Only sensors most commonly used by water
utilities were tested.
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.
Free chlorine and total organic carbon (TOC) sensors
were the most successful in detecting a number of
chemical and biological contaminants.
• Free chlorine levels noticeably dropped in the
presence of various contaminants
• TOC sensors were successful in detecting
carbon containing contaminants or carrier liquids
Background
Water distribution systems are routinely monitored to ensure that drinking water meets
mandated standards and that treatment processes are performing as intended. Online sensors
measure water quality in real-time and have the
potential to serve as an early warning for an
intentional contamination event.
EPA's research on sensors is in support of the
Water Security (WS) initiative, which is
developing contaminant warning systems. The
WSi addresses the risk of intentional
contamination in drinking water distribution
systems. A comprehensive warning system is
being successfully piloted by several water
utilities in major cities throughout the United
States.
Online Water Quality Monitoring Station
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Conclusions
Free chlorine and total organic carbon were the most responsive trigger parameters
• Free chlorine and TOC were the most responsive parameters in chlorinated systems
• Total chlorine was not an effective trigger parameter in chloraminated systems over the
four hour time-frame of the study
• TOC levels were effective in detecting organic compound contamination (e.g., solvents,
pesticides, petrochemicals) in both chlorinated and chloraminated systems
• Additional water quality parameters' responses to the presence of contamination are
summarized in the report
Online water quality sensors alarms were a reliable indicator of a contamination event
• Online water quality sensors can generate reproducible data at various contaminant
concentration levels
• Stable or predictable baseline water quality levels are needed to capture normal water
quality variability for each location
• Background value variations need to be considered when locating online sensors and
interpreting response data
Operational and maintenance costs for online water quality monitoring systems can be
managed
The report also summarizes lessons learned and estimated operation and maintenance costs
for each sensor tested by EPA.
Best practice recommendations for online sensor contaminant warning systems are
provided for the following topics.
• Instrument Setup and Data Acquisition (Section 3)
• Testing Procedures and Safety Precautions (Section 4)
• Data Analysis (Section 5)
• Operation, Maintenance and Calibration of Online Instrumentation (Section 6)
For more information, visit the EPA Web site at www.epa.gov/nhsrc.
Technical Contacts: John Hall (hall.john@epa.gov)
Jeff Szabo (szabo.jeff@epa.gov)
General Feedback/Questions: Kathy Nickel (nickel.kathy@epa.gov)
September 2009
EPA/600/S-06/038A
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