DYE STUDIES PROTECT CONNECTICUT SHELLFISH GROWING AREAS
Kristin Russo, Bureau of Aquaculture
In order to best classify shellfish growing areas and
determine closure areas, the Department of Agriculture (DoAg)’s, Bureau of
Aquaculture collaborates with the Food and Drug Administration (FDA) to conduct
waste-water treatment plant hydrographic dye studies in Connecticut waters. DoAg has performed several hydrographic dye studies on
waste-water treatment plants along the shore to better classify shellfish growing
areas. During the second week of June, DoAg environmental
analyst Kristin Russo had the opportunity to observe and participate in a
waste-water treatment plant hydrographic dye study in Plymouth, MA. Participation in the Plymouth study allowed DoAg staff to
gain hands-on experience to better understand the study process for when the
FDA returns to Connecticut to perform another hydrographic dye study at a plant
in Connecticut. During a hydrographic dye study of a waste-water
treatment plant, dye is injected into the plant, then the effluent is tracked
from the outflow of the plant into the surrounding water. This tool is
essential for classifying shellfish growing areas and determining closure areas
should the waste-water treatment plant have a disruption and release untreated
or partially treated sewage. The FDA has a team of engineers that travel to coastal
states to perform these hydrographic dye studies alongside state environmental
staff. Prior to dye injection, the FDA gathers information about
the waste-water treatment plant and its discharge zone. Some of the information
gathered about the plant includes how often treated effluent is discharged,
level of treatment, distance the effluent must travel to the end of the
discharge pipe, and how much effluent is discharged on average. Engineers also perform a drogue study and collect
background readings of the area surrounding the discharge pipe—ultimately where
the effluent will dissipate when released. A drogue study consists of releasing objects (in this
case, oranges) near the outfall of the treatment plant and observing where the
current/tide takes the drogue. This can help engineers better predict where the
dye will travel when it is released. Taking background measurements allows the engineers to
take accurate readings of the dye concentration when it is released, since each
body of water typically has a different hue. Background readings are taken using a field fluorometer,
which is an instrument that measures the fluorescence of a liquid at a certain
wavelength. Fluorometers were also used to measure the concentration of dye on
tracking days, which are the first day the dye is injected at the plant and the
subsequent three days. Other fluorometers were anchored in oyster cages at 10
stations in the Plymouth harbor to test the concentration of dye at the bottom
of the water column, where shellfish reside and would likely be accumulating
any harmful microorganisms. The fluorometer is attached to a field computer with a
GIS program that draws tracks on a map based on the concentration of dye in the
water, leaving the engineers with a real-time view of where the dye traveled
and at what concentration. With all of this information, engineers can create a
model of where the effluent will travel and concentration of effluent in the
harbor and surrounding waters after a period of time, allowing environmental
analysts to classify shellfish growing areas and determine closure areas.