The new Cyclops-7 Logger, designed by Precision Measurement Engineering, Inc. (PME) was recently deployed near Clear Lakes, Idaho as part of a dye trace study. The PME logger is a self-contained submersible logger that auto ranges and records up to 28,000 data points on a removable SD memory card. After it was deployed at the site below (green arrow head), the logger system first indicated the detection of the Fluorescein dye about 18 hours after injection over a linear distance of about 2,150 feet for a maximum velocity of 119 feet/hour or 2,867 feet/day or 0.54 miles per day.
One pound of dye mixed with 4 gallons of water was injected into the bottom of a well (149 feet below land surface) on Jan. 31 at 12:30 pm. A small pump and tank were used for the dye mixture and polytubing was guided down the well to about 147 feet depth or 2 feet above the bottom of the well to release the dye. The geology is all basalt related rock types and fairly massive with few fractures until the base of the well where there is a cavern.
This image shows the fluorescein dye as it is injected into the well.
The Cyclops-7 Logger was calibrated using a blank and a 10 ppb calibration standard of fluorescein (Turner Designs P/N 10-508). After calibration the logger was secured to a Turner Designs C3 encased in a protective PVC housing and prepared for deployment. The sample interval for the logger was set at thirty minutes.
The dominant flow velocity based on the peak of the dye breakthrough curve occurred at 32.5 hours after injection for a velocity of 66 feet/hour or 1,587.7 feet per day or 0.3 miles/day. These velocities are consistent with a different dye tracing area to the north about 10 miles named the Malad Gorge which also contains basalt rock types.
Data retrieved from the logger and plotted are illustrated on the image above showing the peak fluorescein concentration at approximately 2.6 ppb which was corroborated with grab samples measured on a TD-700 Laboratory Fluorometer. In addition to the concentration of the dye, the image also illustrates the gain change operation that occurs at 12:00 local time, when the Cyclops measurement range changed from x100 (Low) to x10 (Med) due to an increase in fluorescein concentration. The PME Logger also logs temperature, which is helpful for determining corrections based on fluorophore coefficients.
Precision Measurement Engineering is located in Vista California and more information about the Cyclops-7 Logger can be found at www.pme.com. Turner Designs would like to thank Neal Farmer of the Idaho Department of Water Resources for contributing to this article.
Author: Neal Farmer
Institution: Idaho Department of Water Resources, Idaho, USA