  We study of the properties of a new class of circumgalactic medium absorbers
identified in the Lyman-$\alpha$ forest: "Strong, Blended Lyman-$\alpha$" (or
SBLA) absorption systems. We study SBLAs at $2.4<z<3.1$ in SDSS-IV/eBOSS
spectra by their strong extended Lyman-$\alpha$ absorption complexes covering
138 $\,\,{\rm km}\,{\rm s}^{-1}$ with an integrated $\log (N_{HI}/$cm$^{-2})
=16.04\substack{+0.05 \\ -0.06}$ and Doppler parameter $b=18.1 \substack{+0.7
\\ -0.4}\,\,{\rm km}\,{\rm s}^{-1}$. Clustering with the Lyman-$\alpha$ forest
provides a large-scale structure bias of $b = 2.34\pm0.06$ and halo mass
estimate of $M_h \approx 10^{12}{\rm h^{-1}M_{sol}}$ for our SBLA sample. We
measure the ensemble mean column densities of 22 metal features in the SBLA
composite spectrum and find that no single-population multiphase model for them
is viable. We therefore explore the underlying SBLA population by forward
modelling the SBLA absorption distribution. Based on covariance measurements
and favoured populations we find that $\approx 25$\% of our SBLAs have stronger
metals. Using silicon only we find that our strong metal SBLAs trace gas with a
$\log(n_H / $cm$^{-3}) > -2.40$ for $T=10^{3.5}$K and show gas clumping on
$<210$ parsec scales. We fit multiphase models to this strong sub-population
and find a low ionization phase with $n_H=1$cm$^{-3}$, $T=10^{3.5}$K and
$[X/H]=0.8$, an intermediate ionization phase with $\log(n_H / $cm$^{-3}) =
-3.05$, $T=10^{3.5}$K and $[X/H]=-0.8$, and a poorly constrained higher
ionization phase. We find that the low ionization phase favours cold, dense
super-solar metallicity gas with a clumping scale of just 0.009 parsecs.
