220
A. Krawiec
10.4 Chloride Anomalies in the Groundwaters
of the Polish Baltic Coast
The paper presents results of the origin of chloride anomalies in the groundwaters of
the Polish Baltic coast. In the selected exploratory boreholes and wells, water samples
were collected for detailed physicochemical analysis, isotope determination (
3 H,
14 C
18 O,
2 H) and concentrations of noble gases (
4 He,
40 Ar, and
21 Ne). In order to determine the extent of ingression and ascension of saline and brine waters, geophysical
surveys were carried out with the use of electrical resistivity tomography—Fig. 10.5.
The paper presents comprehensive results of the hydrogeochemical and isotope
analysis of waters in terms of their genesis and “ages.” The water exchange rate was
determined in each aquifer systems within the study areas on the basis of the results
of isotope analysis, the concentrations of
4 He and
3 H (see Table 10.1).
Frequent discontinuities in the substratum of Cainozoic deposits affect the groundwater circulation system and are often the cause of merging among different aquifers.
Such connections, particularly between saline waters occurring in the Jurassic or
Cretaceous strata and waters from the Quaternary beds, may result in chloride
anomalies in shallower strata.
Mostly chloride anomalies were found on the Polish Baltic coast. The processes
of ascension and ingression of saline and brackish waters are the main reasons for
their development. Several factors determining the occurrence of chloride anomalies
in the study area were identified (circulation systems, hydrogeological evolution,
water storage capacity of strata).
Groundwater circulation systems are largely dependent on the geological structure, morphology of the coast and tectonics—dislocation zones. Waters from the
Mesozoic strata usually have higher hydraulic heads compared to waters from the
Quaternary strata, which contributes to ascension of saline waters into shallower
aquifers. In the western part of the coast, there are no Neogene and Paleogene
impermeable clay deposits—aquiclude, which greatly facilitates the flow of saline
waters from the Mesozoic substratum to the Quaternary beds (Fig. 10.6). On the
coastal lowlands, islands, and sandspits, low hydraulic heads in the exploited aquifers
(frequently induced by excessive exploitation) are the cause of seawater ingression
and ascension of brine/saline water from the Mesozoic substratum [11, 15, 16].
The fastest changes in the water chemical composition occur in aquifers of low
thickness. Intensive water extraction from an aquifer with a low thickness in adverse
conditions may be followed by fast degradation of its resources through the inflow of
saline waters from the substratum or the shoreline. If the aquifer or the aquifer system
is thick (high water capacity), and hence is abundant in groundwater resources, all
the changes are much slower. The total thickness of the Cainozoic aquifers in the
eastern part of the Polish Baltic coast is usually 2–3 times larger compared to the
western part.
Hydrogeological evolution of the study area, particularly in the late Pleistocene
and the early Holocene had a major effect on the formation of chemical composition and genesis of groundwater. During the glaciation, in places where the ground
A. Krawiec
10.4 Chloride Anomalies in the Groundwaters
of the Polish Baltic Coast
The paper presents results of the origin of chloride anomalies in the groundwaters of
the Polish Baltic coast. In the selected exploratory boreholes and wells, water samples
were collected for detailed physicochemical analysis, isotope determination (
3 H,
14 C
18 O,
2 H) and concentrations of noble gases (
4 He,
40 Ar, and
21 Ne). In order to determine the extent of ingression and ascension of saline and brine waters, geophysical
surveys were carried out with the use of electrical resistivity tomography—Fig. 10.5.
The paper presents comprehensive results of the hydrogeochemical and isotope
analysis of waters in terms of their genesis and “ages.” The water exchange rate was
determined in each aquifer systems within the study areas on the basis of the results
of isotope analysis, the concentrations of
4 He and
3 H (see Table 10.1).
Frequent discontinuities in the substratum of Cainozoic deposits affect the groundwater circulation system and are often the cause of merging among different aquifers.
Such connections, particularly between saline waters occurring in the Jurassic or
Cretaceous strata and waters from the Quaternary beds, may result in chloride
anomalies in shallower strata.
Mostly chloride anomalies were found on the Polish Baltic coast. The processes
of ascension and ingression of saline and brackish waters are the main reasons for
their development. Several factors determining the occurrence of chloride anomalies
in the study area were identified (circulation systems, hydrogeological evolution,
water storage capacity of strata).
Groundwater circulation systems are largely dependent on the geological structure, morphology of the coast and tectonics—dislocation zones. Waters from the
Mesozoic strata usually have higher hydraulic heads compared to waters from the
Quaternary strata, which contributes to ascension of saline waters into shallower
aquifers. In the western part of the coast, there are no Neogene and Paleogene
impermeable clay deposits—aquiclude, which greatly facilitates the flow of saline
waters from the Mesozoic substratum to the Quaternary beds (Fig. 10.6). On the
coastal lowlands, islands, and sandspits, low hydraulic heads in the exploited aquifers
(frequently induced by excessive exploitation) are the cause of seawater ingression
and ascension of brine/saline water from the Mesozoic substratum [11, 15, 16].
The fastest changes in the water chemical composition occur in aquifers of low
thickness. Intensive water extraction from an aquifer with a low thickness in adverse
conditions may be followed by fast degradation of its resources through the inflow of
saline waters from the substratum or the shoreline. If the aquifer or the aquifer system
is thick (high water capacity), and hence is abundant in groundwater resources, all
the changes are much slower. The total thickness of the Cainozoic aquifers in the
eastern part of the Polish Baltic coast is usually 2–3 times larger compared to the
western part.
Hydrogeological evolution of the study area, particularly in the late Pleistocene
and the early Holocene had a major effect on the formation of chemical composition and genesis of groundwater. During the glaciation, in places where the ground