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Open AccessArticle

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

1
Jiangsu Key Laboratory of Urban Underground Engineering & Environmental Safety; Institute of Geotechnical Engineering, Southeast University, Nanjing 210096, China
2
Department of Civil & Materials Engineering, University of Illinois at Chicago, Chicago, IL 60607, USA
3
Department of Civil Engineering, Shanghai University, Shanghai 200072, China
4
School of Materials Science and Engineering, Southeast University, Nanjing 210096, China
*
Author to whom correspondence should be addressed.
Int. J. Environ. Res. Public Health 2020, 17(1), 370; https://doi.org/10.3390/ijerph17010370
Received: 15 November 2019 / Revised: 29 December 2019 / Accepted: 4 January 2020 / Published: 6 January 2020
(This article belongs to the Special Issue Environmental Remediation of Soils and Groundwater)
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. View Full-Text
Keywords: soil-bentonite slurry walls; hydraulic conductivity; sorption; lead contamination; groundwater soil-bentonite slurry walls; hydraulic conductivity; sorption; lead contamination; groundwater
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Yang, Y.-L.; Reddy, K.R.; Zhang, W.-J.; Fan, R.-D.; Du, Y.-J. SHMP-Amended Ca-Bentonite/Sand Backfill Barrier for Containment of Lead Contamination in Groundwater. Int. J. Environ. Res. Public Health 2020, 17, 370.

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