An application of fluorescent tracer to groundwater tracking-EXPLAINED
V. Cidzinkiene, V. Maseliene, R. Girgzdiene, R. Goranina (2014)
(Open Chemistry)
About the study
Location of the study: Lithuania
Problem statement: To track the groundwater using Sodium
Fluorescein.
Procedure adopted: Sodium
fluorescein is used as a tracer for 2 systems to determine the groundwater flow
direction.
Methodology
Sodium
fluorescein (C20H10Na2O5) is used.
• The
monitoring well network consists of two subsystems.
• System I in
the north-western part of the site consists of 8 wells: 7 observation (S1-1,
S1-2, S1-3, S1-4, S1-5, S1-6, S1-7), and one injection.
• This well
set examines the semi-confined aquifer 10 to 19 m deep.
• Sandy clay
occurs at 4.7–6.7 m.
• The aquifer
of medium-grained sand is below. Borehole S1-7 is installed 4 m deep in an
aquifer of technogenic soil (sandy clay dust, sand, traces of organic, etc.).
• The top
layer consists of technogenic soil from 2.3 to 2.7 m, then peat (4.2–4.3 m).
• A sandy
layer pad was detected at 8.7 min wells S2-5 and S2-10. The pad was not reached
by the other wells.
• System II (
S2-1, S2-2, S2-3, S2-4, S2-5, S2-6, S2-7, S2-8, S2-9, and S2-10) is placed in the
unconfined aquifer at4.5–9 m.
• The tracer
mass required (M) was estimated:
M=10.CB.VW
• Where Vw is
the water volume and CB is the apparent background fluorescein
concentration
CB=0.01.a
• Sodium
fluorescein (500 mg) was dissolved in pure water and injected in the injection
well.
Results
System 1:
• Appearance
was expected 8 hours after injection but no fluorescence was then detected.
• However,
the maximum intensity occurred after 10 hours, the groundwater velocity is
higher than expected.
• The highest
intensity was in well S1-1 showing flow is towards the northwest.
System 2:
• The highest
fluorescence was detected in S2-1 and S2-3, suggesting water flow is toward the northwest.
• The same direction was found in the first system confirming the main flow across the
site.
• The maximum
fluorescence was observed after 350 hours in all wells, the highest in S2-6.
• Which
confirmed the direction of water flow in the NW direction towards Lake Druksiai.
Conclusions
• The results
indicate a great hydraulic connection between injection and observation wells.
• Higher
fluorescence intensity was detected in the wells that sampled closest to the
surface.
• The average
groundwater migration velocity in the deep aquifers is 10 m per day and 6 m per
day in the shallow one.
Reference
• Cidzikienė, V., Jakimavičiūtė-Maselienė, V., Girgždienė, R., & Ivanec-Goranina, R. (2014). An application of fluorescent tracer to groundwater tracking. Open Chemistry, 13(1), 497-501.
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