Leak Detection, ground water tracing, measurement of flow rates, measurement of tank residence times, dispersion studies… The list of dye tracing applications is long and continually growing due to the flexibility and accuracy of this powerful fluorescence-based technology. In basic terms, fluorescent dyes are injected into natural or man-made fluid transport and containing systems, a fluorometer can then be used to measure the concentration of the dye at any point in the system. The possibilities are limitless - click here for some examples.

The use of fluorometers enables quantitative data to be collected in almost any fluid environment. Further, because of the sensitivity of fluorometers, dyes can be used in very low concentration (sub parts per billion) so that natural water systems are not disturbed and the volume of dye required is minimized. Also, the relative low cost and stability of dyes and the decreasing price tag and rental programs for instrumentation make dye studies a realistic and accessible technology for practically all investigations.

Have a look at the articles below to discover how dye tracing may be of value to you and please do not hesitate to contact us if you have any questions or ideas related to dye tracing. We are always interested in hearing from our existing or prospective customers.

Yours truly,
Rob Ellison
Director of Sales and Marketing

In The Spotlight - SCUFA Submersible Fluorometer

The SCUFA (Self-Contained Underwater Fluorescence Apparatus) is an accurate, simple-to-use and versatile submersible fluorometer for chlorophyll and dye tracing applications. The SCUFA has been designed to operate in a wide range of concentrations and environmental conditions. The capability to program sampling intervals via the Windows Interface Software and the automatic range control enable the user to configure the SCUFA for any type of profiling or moored deployment.

Simplicity

• The SCUFA's menu-driven software provides the interface for instrument configurations and data analysis. The software walks the user through easy-to-follow steps for functions such as calibration and data collection.
• The Auto-Ranging capability provides an extremely wide dynamic range, allowing the SCUFA to be used in dramatically different environments without manually changing gain settings or going over range.
• The SCUFA's solid secondary standard allows the user to verify instrument calibration quickly and easily and to re-calibrate if necessary.
• The optional Copper Anti-Fouling Screens enable unattended deployment for extended periods without the performance suffering from the effects of biofouling.

Versatility

• 0-5V and RS-232 signal outputs are standard features, so the SCUFA can be mated to a variety of CTDs and data collection devices.
• Open optics eliminates the need for a pump, but with the optional flow-through cap, a pump can be used.
• The SCUFA can be programmed for user-defined sampling rates and times with the purchase of the Internal Data Logging (IDL) Package. IDL also reduces power consumption through the use of Sleep Mode between sampling intervals.

Accuracy

• Typical temperature fluctuations in natural waters can result in significant changes in fluorescence values. The SCUFA, with its integrated temperature probe and software, automatically corrects fluorescence data of temperature effects.
• Turbidity can also cause errors in fluorescent readings. The SCUFA II, and III utilize a dedicated secondary channel for turbidity measurement that provides valuable data for potential correlation and correction.
• User-selectable 0V and 5V values result in optimal range selection and improved resolution of analog data.
• Superior ambient light rejection eliminates the effects of sunlight and allows the SCUFA to be used in surface waters without the need for external pumps or light shields.

Question:
If we encounter high Rhodamine dye concentrations above 100 ppb, can we accurately measure these levels?

Answer:
Fluorescence readings are impacted by "absorbance quenching" at high concentrations. If you are using a 25 mm diameter sample cell, then 100 ppb of Rhodamine dye (active ingredient) is the upper point of linearity. For concentrations up to 500 ppb of dye, you can manually construct a calibration curve to apply corrections to these high readings or if you are using the Model TD 700, you can use the "multi-point" calibration mode . For concentrations above 500 ppb, you must dilute the sample down to the linear range and then correct the reading by the dilution factor.

Turner Designs has selected distributors in the following countries to provide local sales support and ordering convenience for our international customers. Please contact them for further information on our SCUFA and our range of fluorometers.

If your country is not listed, please contact Turner Designs directly.

Groundwater Tracing in a Density-Stratified Aquifer using a SCUFA Submersible Fluorometer

Cave-diving scientists from the Exploration Research Institute (ERI) have conducted annual research projects to study complex groundwater flows in Mexico's Yucatan peninsula. Recently, ERI utilized the unique capabilities of the Turner Designs SCUFA submersible fluorometer to aid in this study.

Along the eastern Caribbean coast of the Yucatan Peninsula, nearly all freshwater discharges to the sea through extensive cave networks and springs rather than by surface streams. This karst region is underlain by an extensive network of cave passages that carry fresh groundwater from the peninsula's interior to springs along the coast. The fresh groundwater "floats" atop deeper saline groundwater. Within 10 km of the coast, the seaward-flowing freshwater and underlying saline water begin to mix. The mixing of fresh and saline waters creates a complex "mixing zone" of brackish water. The mixing zone is often sharply stratified by the formation of haloclines and thermoclines that segregate water masses of various densities.

In 2003, ERI scientists worked in conjunction with the Grupo de Exploration de Ox Bel Ha (GEO) to begin testing advanced instrumentation that can quantify aquifer processes. Two applications for the SCUFA Submersible Fluorometer were evaluated during this project: (i) quantification of the rate of groundwater flow through a cave conduit, and (ii) a dispersion study in a very slowly flowing density strata.

Quantifying Flow Rate in a Cave Conduit
ERI deployed the SCUFA in conjunction with an acoustic Doppler current profiler instrument. The current profiler was placed at numerous points along a network of cave passages to quantify flow velocities at individual points in the conduits. However, as conduit cross-sections may change significantly over any distance, the flow velocities recorded by the current profiler only represent isolated "point velocities" and may not be representative of average flow rates on a more regional scale. For this reason, the SCUFA was utilized to quantify flow rates over longer distances.

In the field ERI programmed the SCUFA with a laptop computer prior to each dive. Once set up, the SCUFA was handed over to a project diver for transport into the cave system. The divers worked in teams of three to measure flow rates with the SCUFA. The procedure included the following steps: (i) deployment of the SCUFA, (ii) measurement of the distance between the SCUFA and the upstream dye release point, (iii) release of a slug of Rhodamine WT dye, and (iv) recording the time of dye release using a watch that was synchronized to the SCUFA during programming.

After release, the Rhodamine WT slug was carried by groundwater flow to the SCUFA, where it was recorded as a break-through type curve. Later, the SCUFA was recovered and the data downloaded on the surface. Flow rates were calculated according to Equation 1.

Dispersion Test in Very Slowly Flowing Water
ERI divers noted that certain saline water masses in the Yucatan study area do not appear to have visible flow. In order to determine if this was true, a simple test was devised using the SCUFA® and a slug of Rhodamine WT dye.

The SCUFA was programmed to log at 10 second intervals and was then taken into the cave system. Divers swam into the cave system in a slightly flowing brackish strata above the seemingly stagnant saline water strata. When at the study location, a diver reached through a halocline to place the SCUFA on the cave conduit floor and into the saline water body. The diver then injected a slug of Rhodamine WT dye under the halocline and dive team exited the cave system. Thirty one hours later the SCUFA was retrieved. The divers noted that the dye slug was dispersed, but did not appear to have moved significantly. When the SCUFA data was downloaded and subsequently reviewed it was obvious that the dye slug had moved.

Based on the SCUFA data, ERI researchers concluded that (i) the saline water body flows, (ii) the flow is oscillatory with periods of near stagnation punctuated by relatively rapid flow, (iii) flow is related to tide stage, and (iv) the periods of rapid flow cause significant mixing within the saline water body.

(pictures taken by Steve Auer)

Technically Speaking, It All Adds Up...
is a series of articles for people who want to obtain the best possible results from their fluorometer. Last month Technically Speaking described how light effects fluorescence readings. This month's article will discuss performing flow measurements using a fluorometer and Rhodamine Dye. The accuracy is such that that the procedure can be used for calibrating conventional flow meters.

Performing Flow Measurements using Fluorometers and Rhodamine Dye
Flow measurements can be made to an accuracy of ±1% using fluorescent dye dilution techniques when calibrated correctly with a tracer standard.

For best possible accuracy, it has been found that the Constant-Rate Injection (Steady State) technique is the preferred method. This technique uses a precise metering pump to discharge the dye at a consistent rate. Since the accuracy of traditional flow meters is in the order of ±20%, the fluorometer method provides increased flow measurement accuracy which enables the calibration of flow meters.

The EPA approved tracer for measuring, mapping and monitoring water systems is Rhodamine WT. As a Calibration Standard, it offers the following key advantages: useable in small quantities; cost effective; and excellent stability.

In many cases, the fluorometer will be used to measure the dilution of the tracer. Therefore, the fluorometer will be calibrated with a known dilution of the dye. (Note, this means it is not necessary to know the what the actual concentration is of the Rhodamine dye).

Best Accuracy Requires 3 Standards
As described in the Turner Designs Application Note on "Using the 10-AU Fluorometer to Perform Flow Measurements in Sanitary Sewers by Dye Dilution", the process requires producing 3 standards to achieve the ±1% accuracy stated above. Turner Designs supplies the Rhodamine Dye, to produce the required standards, as well as a range of Fluorometers and associated accessories for making accurate flow measurements. To get your copy of the Flow Measurements by Dye Dilution Application Note, go to:

http://www.turnerdesigns.com/t2/doc/appnotes/998_5001.html

We look forward to meeting our customers at the ERF Conference September 15-17, 2003. We will be featuring our SCUFA submersible fluorometer, our AlgaeWatch on-line fluorometer and Aquafluor handheld fluorometer, plus other products from Turner Designs. Complete a survey, and receive a Turner Designs coffee mug. Also, be sure to request a copy of our e-support for chlorophyll measurements CD. We look forward to your visit.

ERF Conference
September 15-17, 2003
Seattle, WA
Booth #26