Protection of Aquifers - Hydrogeology: Objectives, Methods, Applications - page 201

Figure 105 Satellite immediate zones around the Arcier catchment supplying Besançon.
ponor in Creux-sous-Roche), and one of which encompasses an active
collapse zone located above subterranean circulations. The close zones are
totally disconnected from the spring, but they protect the drainage basins
of the streams disappearing into the ponors, which water reaches Arcier's
catchment within few hours.
5 THE PROBLEM OF NITRATES
Nitrates are the common oxidized form of nitrogen gas. Naturally present
in the water cycle due to the mineralization of nitrogenous organic material
in the soil, their natural background level does not exceed 5 mg·L -1 in our
climate.