A FIELD INVESTIGATION OF HUMAN DETECT ABILITY OF
SURFACE WATER COLOR CHANGES
INDUCED BY PULPMILL EFFLUENT DISCHARGE
Raymond C. Whittemore, Research Engineer
James J. McKeown, Regional Manager
National Council of the Paper Industry for
Air and Stream Improvement, Inc.
Tufts University
Medford, Massachusetts 02155
INTRODUCTION
Pulpmill effluent color has been chosen by EPA as one of the effluent characteristics
to be controlled at all new kraft and NSSC mills, and at existing mills by 1983. Selection of this effluent characteristic for inclusion in the list of effluent components to be
controlled is based on the judgment at EPA that a control technology is available for
decolorization and should therefore be used. There is, however, no evidence that the
wide range of color introduced to receiving waters is detrimental to aquatic productivity.
Neither has there been any evidence presented in support of the judgment that: (a)
universal application of color reduction technology would bring about any observable
difference in receiving water color at a significant number of existing mill sites; (b)
there was a defined need for application of color reduction technology at all new mills
without regard for the receiving water background color or dilution afforded; or (c) the
color reduction technology is adequate to cope with those situations where receiving
water is highly discolored from the presence of pulpmill effluents, in those cases where
dilution flows are severely limited.
An extensive literature review conducted prior to this study failed to uncover any
work which described the ability of people to observe color changes in natural waters.
The closest work involved studies related to underwater camouflage of solid objects and,
conversely, studies on outstanding colors related to rescue at sea and more recently for
the acceptability of drinking waters.
Since it is likely that under certain conditions receiving water quality judgments may
be based on subjective observations, and since biologically treated pulpmill effluents
are colored, NCASI has undertaken to determine the ability of observers to perceive
color changes in a variety of receiving waters.
The specific objective of this research was to determine what receiving water color
concentration changes the human observer could see and what factors affected this perception. These factors included the magnitude and direction of the color change, receiving water turbidity, and visibility, sunlight intensity, observer placement, and
individual observer memory differences.
SITE AND OBSERVER SELECTION
Six different sites in the Southeast United States were located which provided a variety of water quality and viewing conditions. Six sites were located downstream from Kraft
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