It is proved by experiments that the problem of decreasing in mass is very notable in transport and transformation from N_(NH_4~+)→N_(NO_2~-)→N_(NO_3~-). Thus, it is unreliable to predict groundwater pollution with dynamical coupling numerical model of their transformation. It is better to predict groundwater pollution by means of selecting NH_4~+ or NO_3~- dispersion-absorption transport model and NH_4~+→NO_3~- transformation model.