CONSIDERATII IZOTOPICE ASUPRA ZACAMNTULUI HIPOTERMAL GEOAGIU BAI

1
National Institute of Hydrology and Water
Management Bucharest, Romania
ISOTOPIC CONSIDERATIONS ON THE GEOAGIU BAI
THERMAL HYDROSTRUCTURE
Augustin TENU, Florin DAVIDESCU, Gabriela
STANESCU
BALWOIS 2006
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ISOTOPIC CONSIDERATIONS ON THE GEOAGIU BAI
THERMAL HYDROSTRUCTURE

• From antiquity, Geoagiu Bai Spa it was known
  for
• its hypothermal waters with curative effect
• The hydrogeological model is already known
• the main recharge is made through a major
• hydrostructure (the Rapolt Geoagiu anticlinal)
• the secondary recharge is made through direct
• infiltrations from the meteoric waters
• Objectiv of the study
• the necessity of confirming or amend the already
• elaborated hydrogeological model
• to elucidate the aspects of the origin of the
• thermal waters, its residence times and the
  mixing
• degree with superficial waters

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ISOTOPIC CONSIDERATIONS ON THE GEOAGIU BAI
THERMAL HYDROSTRUCTURE
Geological - Structural Conditions
Basement - crystalline limestones, genetically
surrounded in the epi-methamorfic Rapolt
series, appearing at 40 m depth in the drills
Cenomanian - a basal grezous complex, a superior
complex, predominantly marlous it appears
at depths greater than 26 m
Quaternary - calcareous greenstone, delluvial
deposits, agester and alluvia deposits
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ISOTOPIC CONSIDERATIONS ON THE GEOAGIU BAI
THERMAL HYDROSTRUCTURE
Tectonic conditions
Regionally, the crystalline limestone is
framed to an anticlinal developed westward of
Geoagiu, while the sedimentary cover is disposed
as a vast monocline Geoagiu fault is an
important tectonic accident developed VSV ENE,
which determines around the spa a drop of 30 m
of the North compartment and affects axially the
anticlinal of crystalline limestone of
the basement
Geoagiu fault
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ISOTOPIC CONSIDERATIONS ON THE GEOAGIU BAI
THERMAL HYDROSTRUCTURE
Hydrogeological Elements

• The thermo-mineral water from Geoagiu is
  exploited by 6 springs and 7 wells
• Main thermal aquifer horizon crystalline
  limestones exploited by 5 drills,
• T 23-30 0C, Q 1- 4 l/s
• The 2-nd aquifer horizon cenomanian basal
  complex exploited by 1 drill,
• T 330C, Q 22 l/s
• The 3-rd aquifer horizon - calcareous greenstone
  and travertines exploited
• by 2 drills, T 26 -280C,Q 2 - 4 l/s

• Recharge mainly made through regional
  hydrostructure Rapolt Geoagiu
• anticlinal and secondarily by direct
  infiltrations of meteoric waters where the
• crystalline limestones and cretacic deposits
  outcrop

• Hydrochemical, the waters of all sources are
  almost identical, having a
• mineralization in the oligomineral and mineral
  domain limit (total mineralization, around 1.1
  g/l) the hydrochemical type is bicarbonate
  calcium - magnesium.

• The conductivity differs neatly the cold carstic
  waters, with 300 µScm-1 from thermal waters with
  916 - 956 µScm-1

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ISOTOPIC CONSIDERATIONS ON THE GEOAGIU BAI
THERMAL HYDROSTRUCTURE
Isotopic Results
Were sampled 14 water points and later analyzed
in the lab for T, D, 14C, 18O
Stable isotopes - warm waters and cold karstic
waters have almost identical 18O and D contents,
fact that suggests common or identical genesis
condition of recharge waters
(cold season or high
altitudes) - the surface
water, sampled in the
same area it is sensibly different
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Tritium characterize clearly recent waters
(surface, shallow and cold karstic waters) with
35 - 55 TU from warm waters, older, with contents
of 5 - 8 TU.
ISOTOPIC CONSIDERATIONS ON THE GEOAGIU BAI
THERMAL HYDROSTRUCTURE
For warm waters, the ages obtained by usual
modeling lead to results beyond the theoretical
possibilities of the method. For cold karstic
waters, by using MULTIS model (AIEA model,
exponential 75 connected in series with piston
flow) and input specific function H3rom leads to
a MRT 5 ani.
Output functions" modelling for different
residence times (MRT) of groundwater (red point
cold karstic water)
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Radiocarbon emphasizes three elements with
hydrogeological signification
ISOTOPIC CONSIDERATIONS ON THE GEOAGIU BAI
THERMAL HYDROSTRUCTURE

• The evaluatiom of an average age of max. 13000
  years for sampled warm
• waters, which explain the transit time of a min.
  1300 years
• The obvious difference between the two types of
  karstic waters cold karstic
• waters with actual ages and warm waters having
  1300 to 13000 years
• The exceptionally good grouping of the pMC
  values for warm waters, which
• indicates an unitary supply

1) calculated by T1/2 5730 years for the
Vogel approximation (A0 90 pMC)
Average isotopic values by water types
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ISOTOPIC CONSIDERATIONS ON THE GEOAGIU BAI
THERMAL HYDROSTRUCTURE
Conclusions

• Our results confirmed to a great extent the
  anterior conceptual model and bring also new
  elements for genetic image (genesis, degree and
  proportion of mixing with superficial waters,
  underground transit times).
• The hydrodynamic and genetic synthesis for
  Geoagiu Bai thermal hydrostructure may be the
  following
• - Recharge by meteoric waters formed in
  climatic and altitude conditions of high plateau
  and in the cold season of the year.
• - The average estimated ages by tritium and
  radiocarbon are 5 years for cold karstic water
  and min. 1300 years for warm water.
• - The thermal water from Rapolt - Geoagiu
  anticlinal is lead through the Geoagiu Fault in
  the spa area where is mixed with a recent,
  meteoric, component.
• - It is estimated that the mixing ratio is 1/5
  recent water for the sprigs having more than 10
  TU and its practically zero for those having 5
  TU.

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ISOTOPIC CONSIDERATIONS ON THE GEOAGIU BAI
THERMAL HYDROSTRUCTURE
THANK YOU VERY MUCH FOR YOUR ATTENTION
BALWOIS 2006