PROBLEMS - Hydrogeology: Objectives, Methods, Applications - page 347

Problem #13—Emptying test on a well in a karst aquifer
In the area around Nice (Alpes-Maritimes), a drinking water supply well
draws on the karst Jurassic reservoir after having passed through its cover
of Cenomanian marl, beneath which the aquifer is confi ned.
In order to estimate the productivity of the well and the recharge
conditions of the aquifer, an emptying test by pumping was undertaken
over a period of 5 months, spanning the summer dry period and the
autumnal rains.
During this test, the volume of extracted water and the level of the
aquifer calibrated to elevations a. s. l. were the subject of daily monitoring
(Table 13).
Question 1: Establish the graphical relationship at the well location between
the piezometric evolution of the aquifer and the volume of water extracted
during the emptying test; complete the curve with characteristic values
(instantaneous drawdown, slow emptying, natural recharge, instantaneous
rise), and explain its evolution.
Question 2: Calculate the following characteristics of the pumping well:
• the values of the initial instantaneous drawdown of the aquifer and
that of its fi nal instantaneous rise;
• the value of the specifi c volume V of the aquifer;
• the value of the natural recharge observed during the test, knowing
that rainfall remained minimal during the fi rst two months (10 mm in
July and 20 mm in August) but were abundant afterwards (261 mm in
September, 128 mm in October, 194 mm in November), and dropped
off in the last month (13 mm in December).