Evaluation of methods for wellhead protection areas for the State of S o Paulo

The wellhead protection areas play an important role in protecting the groundwater quality exploited by public waterwells. There are some methods that allow to define dimensions and shape of contribution zones, that is, the area wherethe entire surface of the aquifer recharge is captured by well, besides zones based on time traffic, defi ned in time wherea particular contaminant can reach the well. Both zones allow gradual control of land use. This paper has presented acomparative study between three different methods in different aquifers of the State of S o Paulo. The methods include:calculated fixed radius, based on cylindrical volumetric flow equation; analytical model, using the equation of uniformflow; and numerical model, using mathematical models to simulate the flow. The results showed that each method generateddifferent areas, both in the shapes and in the dimensions. The two first methods established contribution zones withsimilar sizes, but with different shapes and on average 200% bigger than the results from the numeric method, for thesame hydrogeological conditions. From the results, it appears that the use of the analytical model is feasible as a first approximation,since the data for that are now available for almost all public wells in the state, and its accuracy is superiorto the calculated fixed radius method. In a later stage, where the definition of the contribution zones is more sensitive,the numerical model would be the natural alternative.