Investigation of on-line water quality analyzers for use by Seattle Public Utilities

摘要

Seattle Public Utilities is investigating the use of three online water quality monitors foruse throughout its distribution system. The GuardianBlue (Hach) is a multi-parameterinstrument that measures pH, specific conductance, turbidity, chlorine, total organiccarbon, and temperature. Sensor values are displayed on the screen of a computer thatanalyzes the data for deviations from normal trends. When these deviations are observed,a variety of alarms can be triggered, indicating that events of varying levels of severitymay have occurred. These events range from plant events (deviations pre-defined by theuser that are associated with, for example, a shift from a surface water source to a wellwater source) to agent events (deviations identified by the manufacturer that indicatecontamination by a chemical whose “fingerprint” has been identified in testing labs). ThePipeSonde (Hach) measures pH, specific conductance, turbidity, dissolved oxygen, andoxidation-reduction potential and displays these signals on an on-site monitor. The WaterPanel (Hach) detects pH, specific conductance, turbidity, chlorine, and temperature anddisplays these values on a monitor onsite. Each of these instruments can also beconnected to SCADA.One of each of these instruments was installed in the distribution system served bySeattle Public Utilities in 2007 or 2008. Upon deployment, the instruments weresubjected to a several-month evaluation that assessed each instrument’s accuracy, as wellas calibration and maintenance requirements. Issues related to incorporating the on-linewater quality monitors into SPU’s broader water security program were also considered,as well as nuances associated with coordination with SCADA.