Evaluation of methods for wellhead protection areas for the State of São Paulo

Abstract

The wellhead protection areas play an important role in protecting the groundwater quality exploited by public water wells. There are some methods that allow to define dimensions and shape of contribution zones, that is, the area where the entire surface of the aquifer recharge is captured by well, besides zones based on time traffic, defined in time where a particular contaminant can reach the well. Both zones allow gradual control of land use. This paper has presented a comparative study between three different methods in different aquifers of the State of São Paulo. The methods include: calculated fixed radius, based on cylindrical volumetric flow equation; analytical model, using the equation of uniform flow; and numerical model, using mathematical models to simulate the flow. The results showed that each method generated different areas, both in the shapes and in the dimensions. The two first methods established contribution zones with similar sizes, but with different shapes and on average 200% bigger than the results from the numeric method, for the same 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 superior to 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.