July 4, 2018


Kristin Russo, Bureau of Aquaculture

In order to best classify shellfish growing areas and determine closure areas, the Department of Agriculture (DoAg)ís, 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 pipeóultimately 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.