| Using Advanced Chemometrics for Continuous Monitoring
of Source Water
By Dan Kroll
There are a number of potential problems with implementing a monitoring
system for source water. There is the problem of diurnal (night and day) as
well as seasonal shifts in water quality due to a variety of factors such as
aquatic plant respiration and decaying vegetation from autumn leaf falls.
Varying amounts of sediments, turbidity and dissolved solids due to
precipitation events and spring run-off fluctuations may be problematic. Due
to the transient and unexpected nature of the events we are trying to
detect, the monitoring systems also need to be on-line and continuous
because if we knew when we needed to monitor, we wouldn't need to monitor.
The basic concept here is to actively and continuously monitor a variety of
basic water quality parameters and look for significant changes that may be
indicative of an event. There are a variety of source water parameters that
may find application for this sort of system. Various manufacturers in the
environmental market have for many years combined a variety of this sort of
instrumentation into self contained data collection bundles that can feed
data back to a central location via wireless telemetry or hard wired
packages. There are a number of parameters currently available for on-line
monitoring. The relative low cost of these instrumentation packages allows
monitoring at a variety of sites. The major drawback is the huge amount of
data that must be analyzed and correlated to determine if a change is
significant or the result of natural variation.
The use of advanced chemometrics techniques have been proven to be effective
in recognizing and classifying events in the complex matrix of the drinking
water distribution system as demonstrated by the Hach Event Monitor and
GaurdianBlue® systems. The use of these same algorithms with a different
sensor set to monitor source water is now available for source water
deployments. In the system as it is designed, signals from a number of
separate orthogonal measurements of water quality contained in the Hach
Source Water Panel are processed from a multi-parameter measure into a
single scalar trigger signal in an Event Monitor computer system that
contains the algorithms modified for source water. The signal then goes
through a crucial proprietary baseline estimator. A deviation of the signal
from the established baseline is then derived. Then a gain matrix is applied
that weights the various parameters based on empirical data. The magnitude
of the deviation signal is then compared to a preset threshold level. If the
signal exceeds the threshold, the trigger is activated.
The algorithms include an adaptive tuning section that adjusts the "Slow"
constants to values that reduce the sensitivity of the Trigger Algorithm to
the background noise commonly found at the site. This is done to reduce
nuisance triggers. Note that the slow values calculated are not permitted to
de-sensitize the algorithm to the point where it cannot recognize serious
events. This allows for a simplified method to handle the vast data streams
involved in continuous monitoring and provide a simple and
easy-to-understand alarm system.
About the Author: Dan Kroll is chief scientist at Hach Company's Homeland
Security Technologies division, in Loveland, CO. He has been the lead
researcher on a variety of method development projects for the physical,
chemical and microbiological quality of water and soils for which he holds
several patents.
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