Groundwater Chlorophyll monitoring within Karst Compartments

A great deal of drinking water is supplied by karst springs that could be close to rivers, lakes or even salt water and the relationship between a restitution karst and associated surface water is a key element in the management of the water catchment area.  Depending on the relative water levels, the circulation of water within the karst can be reversed, a phenomenon known as “estavelle” or “inversac”, resulting in water returning to the karst compartments having spent time outside in the open.

Estavelle events represent a major risk of contamination; they must be identified and qualified in order to manage the drinking water supply.  The different chemical characteristics of surface water and groundwater can be used to identify estavelle events through hydrochemical analysis. However, surface water and groundwater often have similar characteristics, which requires the use of other parameters to differentiate them.

In order to characterise these types of mass transfer, CPGF Horizon has developed, over many years, a new approach based on the study of chlorophyll.  As a natural parameter presenting a characteristic signal for one of the water masses, surface water, and almost zero background noise for the other, groundwater, it is an environmentally and scientifically sound parameter to characterise.  Algae, which contain chlorophyll-a, live only in surface water exposed to sunlight. Chlorophyll-a, therefore, represents a natural biological tracer which makes it possible to distinguish surface water from groundwater, where no algae can survive.