The effects of hydraulic/pneumatic fracturing-enhanced remediation (FRAC-IN) at a site contaminated by chlorinated ethenes: A case study

• Published in: Journal of hazardous materials 2021-09, Vol.417, p.125883-125883, Article 125883
• Main Authors: Lhotský, Ondřej, Kukačka, Jan, Slunský, Jan, Marková, Kristýna, Němeček, Jan, Knytl, Vladislav, Cajthaml, Tomáš
• Format: Article
• Language: English
• Subjects: Chlorinated ethenes; Enhanced reductive dechlorination; Fracturing; Low permeability; Remediation; Zero valent iron
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2021.125883

A low-permeability locality with heterogeneous geology contaminated primarily by tetrachloroethene (PCE) present partially in the free phase in the unsaturated zone was treated on a pilot scale via direct push pneumatic fracturing combined with the hydraulic delivery of a remediation suspension consisting of milled iron, sulphidated nanosized zerovalent iron and sand in guar gum solution. Afterwards, a whey solution was injected into the fractures as a carbon source for bacteria. The unsaturated and saturated zones were treated. Long-term monitoring of the groundwater revealed that the abiotic reduction of PCE and trichloroethene was the dominant remediation processes for several months after the injections. A complex microbial consortium was developed that was capable of effective, long-term chlorinated ethenes (ClE) dechlorination. The consortium consisted mainly of Dehalococcoides but also of other anaerobic bacterial strains capable of partial dechlorination of ClE, including the sulphate-reducing bacteria; Geobacter and Desulfitobacterium. The average chlorine number in the groundwater decreased from 3.65 to 1.38 within 2.5 years after the injections, while the average ClE concentration increased from 13.5 to 31.5 mgL-1 because of the substantial acceleration of the ClE mass-transfer to the groundwater caused by the treatment. The remediation processes remained fully active for 2.5 years. [Display omitted] •Low-permeable locality contaminated by tetrachloroethene successfully remediated.•Direct pneumatic/hydraulic fracturing enhanced chemical and biological reduction.•Microbial consortium capable of long-term contaminant dechlorination developed.•Substantial acceleration of contaminant mass-transfer and degradation documented.•Chlorine number in groundwater decreased from 3.65 to 1.38 within 2.5 years.