Environmental Engineering Reference
In-Depth Information
• High-temperature method (between 680 and 950°C or higher in a
few special cases, best possible oxidation), 1 mg/L carbon
• Low-temperature method (below 100°C, limited oxidation poten-
tial), 0.2 mg/L carbon
The response time of a TOC analyzer may vary depending on the manufac-
turer's specifications, but it usually takes from 5 to 15 minutes to get a stable,
accurate reading.
Chlorine Measurement Systems
Residual chlorine is one of the most sensitive and useful indicator param-
eters in water distribution system monitoring. All water distribution systems
monitor for residual chlorine concentrations as part of their Safe Drinking
Water Act requirements, and procedures for monitoring chlorine concentra-
tions are well established and accurate. Chlorine monitoring ensures proper
residual chlorine levels at all points in the system, helps pace rechlorination
when required, and quickly and reliably signals any unexpected increase in
disinfectant demand. A significant decline or loss of residual chlorine could
be an indication of potential threats to the system. Several key points regard-
ing residual chlorine monitoring for security purposes are provided below:
• Residual chlorine can be measured using continuous online moni-
tors at fixed points in the system or by taking grab samples at any
point in the system and using chlorine test kits or portable sensors
to determine chlorine concentrations.
• Correct placement of residual chlorine monitoring points within a
system is crucial to early detection of potential threats. Although
dead ends and low-pressure zones are common trouble spots that
can show low residual chlorine concentrations, these zones are gen-
erally not of great concern for water security purposes because sys-
tem hydraulics will limit the circulation of any contaminants present
in these areas of the system.
• Monitoring points and monitoring procedures for SDWA compli-
ance vs. system security purposes may be different, and utilities
must determine the best use of online, fixed monitoring systems vs.
portable sensors or test kits to balance their SDWA compliance and
security needs.
Various portable and online chlorine monitors are commercially avail-
able. These range from sophisticated online chlorine monitoring systems to
portable electrode sensors to colorimetric test kits. Online systems can be
equipped with control, signal, and alarm systems that notify the operator of
low chlorine concentrations, and some may be tied into feedback loops that
