  We present optical spectra of QSO HS~1946+7658 with either high resolution
(FWHM=10 km/s) or high signal to noise ratio (SNR=40-100). We find 113 Lyman
alpha and six metal line systems. The metal systems at Zabs=2.844 and 3.050
have complex velocity structures. We find that the system at 2.844 is a damped
Ly-a absorption system, with neutral hydrogen column density of
logN(HI)=20.2+/-0.4, and it is the cause of the Lyman limit break at 3520\AA.
The metal abundance in the gas phase of the system is [M/H]=-2.6+/-0.3, with a
best estimate of [M/H]= -2.8, with ionization parameter Gamma=-2.75, from a
photoionization model. We show that the abundance ratios rule out appreciable
dust in this DLA system. We do not see the enhancement of O over C reported in
Nature by Reimers last years. We see CII*(1335) offset by 15 km/s with respect
to CII(1334), presumably because the gas density varies from 2 - 8 cm(-3) with
changing velocity in the DLA system. These densities imply that the damped
component is 6 - 25 pc thick, which is reasonable for a single cloud in a cold
spiral disk. We see a 2.6sigma lack of Ly-a forest lines well away from the QSO
redshift, which may be a chance fluctuation. We also see a correlation between
column density N(HI) and Doppler parameter b for 96 unsaturated Ly-a forest
absorption lines, and although this correlation persists in the 36 Ly-a lines
which lie in regions where SNR=8-16, we agree with Rauch etal (1993) that it is
probably a bogus effect of low SNR. We show that there are few low-b Ly-a
forest lines in moderate SNR data.
