Migration of non-aqueous-phase liquids (NAPLs) such as trichloroethylene or
gasoline can be controlled by barrier systems. The research presented in t
his paper aims to form a horizontal layer by injecting gelling liquids and
to test the ability of horizontal barriers to isolate the downward migratio
n of NAPLs in subsurface environments. We developed a methodology in the la
boratory to form a contiguous horizontal barrier by injecting gelling liqui
ds through horizontal and vertical wells. A series of batch, column, and 2D
sandbox experiments were conducted to investigate the gel development and
horizontal barrier formation. Prior to 2D barrier formation experiments, tw
o different methods were employed to measure pre- and postinjection hydraul
ic conductivity in 1D columns to quantify hydraulic conductivity reductions
. After an impervious grout formed, the durability of the grouted porous me
dia in the presence of two NAPL contaminants was investigated. The hydrauli
c conductivity of filter sand treated with colloidal silica was reduced by
100% in 1D column experiments. In 2D experiments, a contiguous horizontal l
ayer was formed by horizontal or vertical injection of the gelling liquid.
The grouted material in 1D columns worked well in controlling the downward
migration of contaminants. Although some penetration of the gelled layer by
the contaminant was observed, the integrity of the horizontal layer was pr
eserved. Finally, based on scaled capillary pressure versus saturation rela
tionships, it was determined that capillary pressures can reduce as much as
50% with gelling of the colloidal silica solutions.