General studies : November, 1967 / by John C. Ayers, Joseph C. K. Huang.

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and work along it under the prevailing winds of summer and winter.
They further suggest that if the plant's water intake is at
distance and at depth comparable to those of the direct-withdrawal
water treatment plants of the region there should be limited
chance that the effluent could reach the intake.
Local Natural Dilution
Our in situ studies of natural dilution rate in the alongshore
water off the plant site used the red fluorescent dye, Rhodamine B,
in the technique of Pritchard and Carpenter (1960). Stock dye in
a 40% solution in acetic acid was used. It has a small negative
buoyancy and requires dilution with an alcohol to become neutrally
buoyant. Our dye sets consisted of one quart of the dye stock
diluted with six quarts of methanol antifreeze. Dilutions were
made in a plastic garbage can and introduced by gently lowering
the can into the water until the dye floated out. After an
interval to allow surface tension effects caused by the alcohol
to die away, the initial measurement of dye concentration was
made by slowly coasting the boat through the visibly-heaviest part
of the dye patch. Slow coasting with the screw stopped allowed
the boat to pass through the dye with little if any artificial
mixing.
Measurements of dye concentration were made with the ultraviolet fluorometer of Noble and Ayers (1961). In this instrument
the fluorescence of the dye under ultraviolet light is measured
photoelectrically and converted by calibration curve to concentration of dye. Colored water of the dye patch was pumped continuously
through the fluorometer during each pass through the patch. Only