The parametric model Drastic (acronym of Deep water; Recharge, net; Aquifer media; Soil media; Topography; Impact of vadose zone; Conductivity, hydraulic) is applied to the terminal stretch of Tordera River (in the Catalan Region, next to Blanes and Malgrat de Mar) to evaluate the risk of pollution of the underground water. The total area examined, which is covered by a principal aquifer composed of gravel and sands, is divided into more than 700 square cells with a side of 125 m long. It is calculated the vulnerability index PP for each cell, and the whole studied area, on the base of the PP value, is subdivided into 2 classes of risk: a big sector of moderate risk and a small sector of elevated risk