SHMP-Amended Ca-Bentonite/Sand Backfill Barrier for Containment of Lead Contamination in Groundwater

Abstract

This study investigated the feasibility of using sodium hexametaphosphate (SHMP)- amended calcium (Ca) bentonite in backfills for slurry trench cutoff walls for the containment of lead (Pb) contamination in groundwater. Backfills composed of 80 wt% sand and 20 wt% either Ca-bentonite or SHMP-amended Ca-bentonite were tested for hydraulic conductivity and sorption properties by conducting laboratory flexible-wall hydraulic conductivity tests and batch isothermal sorption experiments, respectively. The results showed that the SHMP amendment causes a one order of magnitude decrease in hydraulic conductivity of the backfill using tap water (1.9 to 3.0 × 10−10 m/s). Testing using 1000 mg/L Pb solution resulted insignificant variation in hydraulic conductivity of the amended backfill. Moreover, SHMP-amendment induced favorable conditions for increased sorption capacity of the backfill, with 1.5 times higher retardation factor relative to the unamended backfill. The Pb transport modeling through an hypothetical 1-m-thick slurry wall composed of amended backfill revealed 12 to 24 times of longer breakthrough time for Pb migration as compared to results obtained for the same thickness slurry wall with unamended backfill, which is attributed to decrease in seepage velocity combined with increase in retardation factor of the backfill with SHMP amendment. Overall, SHMP is shown to be a promising Ca-bentontie modifier for use in backfill for slurry trench cutoff wall for effective containment of Pb-contaminated groundwater.

Index Properties, Hydraulic Conductivity and Contaminant-Compatibility of CMC-Treated Sodium Activated Calcium Bentonite

“…It is noted that analyses of contaminant transport and long-term performance are important in the design of engineered barriers. Therefore, further studies are warranted to investigate contaminant transport parameters (e.g., effective diffusion coefficient and retardation factor) and long-term performance in terms of long-term hydraulic conductivity, potential elution of CMC, mechanical properties, and wet-dry cycle durability [47][48][49][50][51][52][53][54][55][56][57][58][59]. In addition, X-ray diffraction, Zeta potential, and Fourier transform infrared spectroscopy analyses are recommended in the further studies.…”

Experimental Investigation of the Effect of Groundwater on the Relative Permeability of Coal Bodies around Gas Extraction Boreholes

“…The amount of gas extracted from the surface is only 0.45 × 10 10 m 3 , while the amount of gas extracted from underground boreholes reaches 1.23 × 10 10 m 3 , accounting for 73.2% of the total amount of gas extracted [ 4 ]. In order to improve the extraction efficiency of gas energy, borehole gas pre-pumping has become an important means of gas management in high-gas mines, and gas control in high-gas mines is also an important part of ensuring safe production in coal mines [ 5 ]. However, as the mining depth increases, the hydrogeological conditions of the mine become more and more complex.…”

Heterogeneity-controlled uncertain optimization of pump-and-treat systems explained through geological entropy

“…From a physical perspective, P&T hydraulic barriers can be combined with physical barriers, such as low-permeable cutoff walls or diaphragms (e.g. Dominijanni et al, 2017;Pedretti et al, 2017;Yang et al, 2020). Compared to "conventional" (i.e., physical-barrierfree) P&T systems, a "combined" P&T system is expected to decrease Q, as the physical barrier reduces the seepage flow between the solute plume source and the hydraulic barriers, while funneling the contaminant plume towards the extraction wells (e.g.…”