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
         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


          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
                               Online Water Quality Monitoring Station

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
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