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.