  We report observations from the Hubble Space Telescope (HST) and the VLA on
the galactic environment, metallicity, and D/H in strong low-redshift Lya
absorption systems toward the bright BL Lac object PKS 2155-304. GHRS/G160M
spectra at 20 km/s resolution show 14 Lya absorbers, 6 clustered at cz =
16,100-18,500 km/s. ORFEUS claimed LyC absorption at z = 0.056 with N(HI) =
(2-5)x10^16 cm^-2, while our Lya data suggest N(HI) = (3-10)x10^14 cm^-2.
Higher columns are possible if the Lya line core at 17,000 +/- 50 km/s contains
narrow HI components. We identify the Lya cluster with a group of five HI
galaxies offset by 400-800 kpc from the sightline. The two strongest absorption
features cover the same velocity range as the HI emission in the two galaxies
closest to the line of sight. If the Lya is associated with these galaxies,
they must have huge halos of highly turbulent, mostly ionized gas. The Lya
absorption could also arise from an extended sheet of intragroup gas, or from
smaller primordial clouds and halos of dwarf galaxies. We see no absorption
from SiIII 1206, CIV 1548, or DI Lya. Photoionization models yield limits of
(Si/H) < 0.003 solar, (C/H) < 0.005 solar, (D/H) < 2.8x10^-4 (4 sigma) if N(HI)
= 2x10^16 cm^-2. The limits increase to 0.023 solar and D/H < 2.8x10^-3 if
N(HI) = 2x10^15 cm^-2. The data suggest that the IGM in this group has not been
enriched to the levels suggested by X-ray studies of intracluster gas and that
these absorbers could be primordial gas clouds.
