Due to low hydraulic conductivity and cost-effectiveness, the soil-bentonite (SB) slurry trench cutoff walls have been widely adopted in the US, Canada and Japan to control transport of contaminated groundwater at landfill and industrial sites. Traditional SB backfill is consisted of trench spoils or proper imported soils, water, and sodium bentonite (Na-bentonite) with bentonite content ranging from ~1% to about 6%. However, using low swelling calcium bentonite (Ca-bentonite) is extremely meaningful for countries where high-quality Na-bentonite is scarce while Ca-bentonite is plentiful. Sodium hexametaphosphate (SHMP) has been manifested as an effective amendment for improving workability and hydraulic performances of the Ca-bentonite in SB backfill. However, by date the hydraulic conductivity response of the SB backfill containing SHMP-amended Ca-bentonite to aggressive chemical solutions has not been addressed. This study presented lab-scale investigation of hydraulic conductivity of SB backfill composed of 80% sand and 20% SHMP-amended Ca-bentonite (dry weight basis) in potassium dichromate (K₂Cr₂O₇) solution with 19.2 mM (1000 mg/L) Cr(VI) concentration. Duplicated flexible-wall hydraulic conductivity tests were conducted using tap water first and followed by the Cr(VI) solution. The volume, pH and electrical conductivity of the inflow and outflow liquids were monitored, and Cr(VI) concentrations in the outflow liquid were measured. The variation in hydraulic conductivity with the pore volume of flow of permeant liquid was assessed. The results show that the hydraulic conductivity maintained a value lower than the commonly used value of 10^-9 m/s regardless of the type of permeant liquid, indicating that Cr(VI) solution had insignificant adverse effects during the tested period. Overall, the results obtained in this study can facilitate the application of SHMP-amended sand/Ca-bentonite backfills for containment of Cr(VI) impacted groundwater.