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Fluorescent Tracer Studies
An Overview
 Tracers
are compounds, usually dyes or salts, used for measuring, mapping, and
monitoring water systems. Tracers are used for measuring water flows,
studying and modeling surface and ground water systems, tracing contaminants
in emergency response situations, detecting leaks, and measuring tank
retention times.
Fluorescent tracers are chosen because
they are cost-effective and easily and accurately measured on-site with
a portable, field-ready fluorometer.
The ideal tracer is nontoxic, usable in
small quantities, cost-effective, easy to measure at very low concentrations,
and stable during the course of the study. Rhodamine WT, the fluorescent
tracer of choice, meets all of these requirements and is approved for
use by the Environmental Protection Agency.(1)
1. Cortuvo, J.A., RHODAMINE WT AND B, Memo
to J. Warnquist, dated Aug 2, 1988
Applications Include:
- Measuring Effluent Discharge Rates
- Localizing Sewer Infiltration
- Mapping Discharge Dilution in Receiving
Water Systems
- Calculating Time of Travel & Identifying
Dispersion Patterns
- Identifying Mixing Zones
- Determining Sewer Flows to Verify Hydraulic
Limits
- Determining Sewer Flows to Settle Billing
Disputes
- Calibrating Installed Flowmeters
- Measuring Pump Performance
- Determining Contact Chamber and Settling
Tank Efficiency
- Tracking Pesticide Spills
- Mapping Glaciers
How it works...
Rhodamine WT is a highly fluorescent material
with the unique ability to absorb green light and emit red light. Very
few compounds have this property, so interferences from other substances
are very rare. This makes Rhodamine WT a highly specific tracer. The Turner
Designs fluorometer is easily configured to shine green light on the sample
and detect the red light emitted. The amount of red light emitted is directly
proportional to the concentration of the dye, up to 100 parts per billion
(100 µg/L). Relative fluorescence readings, dye concentrations, dilution
factors, dye travel time, and other parameters provide valuable data used
to draw conclusions regarding the water system being studied.
An Excellent Tracer
System... Selective, Portable, Durable, Cost-Effective, and Convenient
The Turner Designs 10-AU Fluorometer and
Rhodamine WT combine to form a near perfect tracer system. The fluorometer
can be configured to selectively measure Rhodamine WT with minimal interference
from background materials. The instrument's portable, rugged, and waterproof
design allows on-site measurement, even in the most remote locations.
The 10-AU Fluorometer will directly measure discrete or continuous flow
samples in the field, eliminating the need for expensive laboratory analysis.
The hermetically-sealed sample cell, automatic range changing, dual beam
design, and temperature compensation features make the 10-AU the instrument
of choice for fluorescent tracer studies. In addition, the 10-AU can detect
as low as 10 parts per trillion (0.01µg/L) of Rhodamine WT in potable
water, and 100 parts per trillion (0.1µg/L) in industrial and sanitary
sewage. This low detectability minimizes the dye required, making this
tracer system both economical and convenient.
Flow Measurement
Flow measurement by dye dilution is chosen
for its superior accuracy (+/- 2%). This flow measurement technique can
accurately measure flows as low as 1 gallon per minute and as high as
1 billion gallons per day. It is the method of choice in cases of turbulent,
large volume, and rapidly changing flows. It is also commonly used to
measure difficult-to-access flows and flows in large diameter pipes. In
these situations, other methods are significantly more expensive, highly
inaccurate, or impractical to implement.
To measure water flow, inject the dye at
a constant rate and use the fluorometer to determine how much the water
stream dilutes it. Multiply the dye injection rate by the dilution ratio
to get the flow rate. These highly accurate flow measurements are used
to:
Calibrate Flowmeters: Flow
metering devices typically have measurement errors of +/- 20% when installed
in the field. Flow measurement by dye dilution is an excellent way to
routinely check the accuracy of these devices.
Verify Flow Capacity: Wastewater
treatment plants use flow measurement by dye dilution to determine if
they are operating at their hydraulic limit. Discovering an additional
25% capacity through accurate flow measurement has prevented treatment
plants from spending millions of dollars to increase capacity.
Settle Billing Disputes:
Municipalities often use flow measurement by dye dilution to settle billing
disputes by verifying wastewater flows into treatment facilities. Resolution
of a 3% billing error can result in significant savings for the wronged
party.
Localize Infiltration: Flow
measurement from manhole to manhole is used to determine groundwater infiltration
or surface water inflow into a sanitary sewer. Differing flow rates between
two points may indicate a leak in the sewer line. Using a dye tracer study
to localize infiltration reduces field study time and eliminates the expense
of personnel or camera equipment to monitor a sewer line.
Determine Discharge Rates:
Flow measurement by dye dilution is used to accurately determine the discharge
rate of chemically treated or heated water into natural systems. Accurate
flow measurements are required in order to grant discharge permits or
to confirm that facilities are in compliance with their discharge permits.
Measure Pump Performance:
Power plants and wastewater treatment facilities use dye tracer systems
to accurately measure flow in and out of pumps, turbines, condensers,
and other flow system equipment; and to troubleshoot, check the performance
of, and measure the efficiency of such equipment.
Time of Travel and
Dispersion Studies
Time-of-travel and dispersion studies are
used to better understand the behavior of a surface or ground water system.
In these studies the travel time and distribution of the tracer is of
interest. A fluorescent dye tracer system provides the accuracy and ease
of on-site measurement critical to successful dispersion and time-of-travel
determinations. One example is the use of time-of-travel studies for glacier
mapping. Time-of-travel and dispersion studies are often used to map out
zones and dilution patterns near sewage and wastewater discharge. This
type of zoning is critical when establishing fish harvesting regions and
recreational areas.
Mixing Zone Studies
Engineering consulting firms use fluorescent
tracers to determine how quickly a wastewater stream mixes with another
body of water. The tracer mimics the behavior of the discharged wastewater.
Mixing zone studies are conducted when new plants are built and discharge
permits are granted.
Emergency Response
Fluorescent tracers are used to track contaminant
spills. Emergency response crews inject Rhodamine WT at the spill site
and use the Turner Designs fluorometer to trace the path of the contaminant.
Rhodamine WT's physical and chemical properties make it an ideal tracer
for pesticide tracking.
Leak Detection
Fluorescent tracers are used to detect
leaks in sewers, discharge lines, underground tunnel and cooling systems,
and landfills. Leaks as small as 1 gallon per minute can be detected using
the 10-AU Fluorometer and Rhodamine WT dye.
Tank Retention Time
Tracers are used to measure the time that
a given volume of water is retained in a tank. This study is conducted
by wastewater treatment plants in order to determine the efficiency of
settling tanks and chlorine contact chambers.
Fluorescent Tracer
Monographs
- A Practical Guide to Flow Measurement
(998-5000)
- Using the Turner Designs Model 10-AU
Fluorometer to Perform Flow Measurements in Sanitary Sewers by Dye Dilution
(998-5001)
- Fluorometry in the Water Pollution Control
Plant (998-5102)
- Fluorescein (998-5103)
- Fluorescent Tracer Dyes (998-5104)
- Circulation, Dispersion and Plume Studies
(998-5106)
- Flow Measurements in Sanitary Sewers
by Dye Dilution (998-5107)
- Preparation of Standards for Dye Studies
Using Rhodamine WT (998-5111)
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