We present observations and analysis of the massive molecular outflow G331.512-0.103, obtained with ALMA band 7, preliminary presented in Merello et al. (2013a). The lines can be classified into two groups: with narrow velocity emission, tracing the systemic velocity ambient medium and the sub-structures within; and with broad velocity wings, tracing the outflow and shocked gas emission. The physical conditions are calculated. The ambient medium core has a mean density of similar to 5 x 10(6) cm(-3) and a temperature of similar to 70 K. The interpretation of the molecular emission suggest an expanding cavity geometry powered by stellar winds from a new-born UCHII region, alongside a massive and high-velocity molecular outflow. Also, the presence of sub-structures is made evident by the emission of narrow lines such as CH3OH and CH3CCH. This scenario, along with the estimated physical conditions, is modeled through a 3D geometry radiative transfer code: MOLLIE; in the SiO(J= 8 7) molecular line. The main features of the the outflow and the expanding cavity are reproduced by the model.