Has been studied in the environmental herbicide terbuthylazine, terbacil, molinate and tiobencarb. The results indicate that terbuthylazine and terbacil is strongly absorbed in the first few centimeters of the soil profile, remaining without significant leaching despite its high persistence. The best way to incorporate the herbicide terbuthylazine was herbigación through or on damp soil previously been observed for this product can blow at the time of application. Molinate herbicides, a high vapor pressure, are easily volatilised tiobencarb and is strongly fixed to the ground. It has been used two mathematical models simulating the behavior and distribution of pesticides in soil. VARLEACH and LEACHP in order to assess their validity in predicting the behavior and distribution in the soil of terbiutilazina and terbacil. Both models behaved similarly giving acceptable predictions of the amount of waste in the profile, when compared with data observed in the field, especially in the case of terbacil. But this only occurred when herbicides have high absorption coefficients, since with low ratios, the different way that has both models simulate the flow of water through the soil influences the transport and distribution of solutes in the soil profile. Both for its simplicity and by the characteristics of water management and climate of Valencia is the use of model VARLEACH.