PROBLEMS - Hydrogeology: Objectives, Methods, Applications - page 326

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Figure 3 a) Cross-section of the Fourbanne system. b) Magnesium concentrations. c) Nitrate
concentrations.
Answer: Verne and Fontenotte show the same concentrations for both ions,
showing the absence of mixing of other water with the water from the swallow
holes (pinpoint infi ltration), between the swallow holes and the underground
river. At the Fourbanne spring, on the other hand, this localized infi ltrated
water is mixed with water of different composition (diffuse infi ltration and/
or saturated zone), with a higher magnesium concentration (longer residence
time in the same limestone) (Figure 3b) and a lower nitrate concentration
(less infl uenced by leaching from agricultural land) (Figure 3c).
Problem #4—Piezometry of an aquifer
The Pontarlier alluvial plain aquifer sits in the superfi cial portion of a
heterogeneous fl uvio-glacial evacuation cone (Gaubi, 1993).
Several boreholes and piezometers (Figure 4) enable the measurement
of the water table head. During a low water survey, the measured elevations
a.s.l. are those of Table 4: