Installation of Deep Reactive Walls at MMR using a Granular Iron-Guar Slurry
By David W. Hubble and Robert W. Gillham
ABSTRACT
The primary contaminant in the CS-10 plume at a military base on Cape Cod
is tetrachloroethene (PCE) and site groundwater has been shown to be treatable
using granular zero-valent iron. The plume, which extends over a depth interval
of 24 to 37 m near its source, is considered to be deep (i.e. > 15 m below
the ground surface) and not accessible for conventional means of installing
granular iron. Thus, a novel method of vertical reactive wall installation
was selected for a 15 m long, full depth, trial wall at the CS-10 plume. The
method (hydraulic fracturing) uses special tools to mix granular iron in a
guar-based biodegradable polymer and then inject it into a hydraulically created
vertical fracture. Geotechnical and geophysical test results show that iron
was successfully installed in a wall having an average thickness of 80 mm
and between 24 and 37 m depth. The CS-10 demonstration is thus the deepest
installation of any reactive material in a wall to date. Monitoring of inorganic
and organic groundwater parameters has shown the effects of 1) wall installation,
2) a delayed break of the bio-polymer cross-link and 3) an amendment injected
to hasten guar breakdown.