  We analyze HST and ground based spectra of the brightest BALQSO in the UV:
PG~0946+301. A detailed study of the absorption troughs as a function of
velocity is presented, facilitated by the use of a new algorithm to solve for
the optical depth as a function of velocity for multiplet lines. We find
convincing evidence for saturation in parts of the troughs. This supports our
previous assertion that saturation is common in BALs and therefore cast doubts
on claims for very high metallicity in BAL flows. Due to the importance of BAL
saturation we also discuss its evidence in other objects. In PG~0946+301 large
differences in ionization as a function of velocity are detected and our
findings supports the hypothesis that the line of sight intersects a number of
flow components that combine to give the appearance of the whole trough. Based
on the optical depth profiles, we develop a geometrical-kinematical model for
the flow. We have positively identified 16 ions of 8 elements (H~I, C~III,
C~IV, N~III, N~IV, N~V, O~III, O~IV, O~V, O~VI, Ne~V, Ne~VIII, P~V, Si~IV, S~V,
S~VI) and have a probable identifications of Mg~X and S~IV. Unlike earlier
analysis of IUE data, we find no evidence for BALs arising from excited ionic
states in the HST spectrum of PG~0946+301.
