Application of the Back-Tracking Method to the Definition of Sanitary Zones of Catchwork Protection for Drinking Water Supply

The implementation of sanitary zones of catchwork protection for drinking water supply has become a requirement stated by the legislator for years. However, this is a complex and technical issue which has often led to inadequate or questionable-and questioned-recommendations or implementations of sanitary zones. Sometimes, their implementations were even delayed.However, new systems of mathematical groundwater flow modeling allow to determine these sanitary zones, at reasonable cost and in any case objectively, while referring to widely recognized normative criteria. This is particularly true for travel times to the catchwork — from the boundaries of the sanitary zone — that most of European laws laid down at 50 days.This paper presents a method to calculate time contours around a catchwork by backtracking pathways. This method, known as the back tracking method can easily adapt to all kinds of flow mathematical models. Thereafter, we analyze and discuss examples of results obtained in real situations.