Journal
SCIENCE OF THE TOTAL ENVIRONMENT
Volume 622, Issue -, Pages 164-171Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.scitotenv.2017.11.347
Keywords
Secondary source; Persistence contamination; Molecular diffusion; Pumping technology; Remediation time
Categories
Funding
- Hydraulic and Enviromental Engineering PhD course, La Sapienza
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Low-permeability lenses represent potential sources of long-term release when filled from contaminant solute through direct contact with dissolved plumes. The redistribution of contaminant from low to high permeability aquifer zones (Back-Diffusion) was studied. Redistribution causes a long plume tail, commonly regarded as one of the main obstacles to effective groundwater remediation. Laboratory tests were performed to reproduce the redistribution process and to investigate the effect of pumping water on the remediation time of these contaminated low-permeability lenses. The test section used is representative of clay/silt lenses (k approximate to 1*10(-10) m/s/k approximate to 1*10(-7) m/s) in a sand aquifer (k approximate to 1*10(-3) m/s). Hence, an image analysis procedure was used to estimate the diffusive flux of contaminant released by these low-permeability zones. The proposed technique was validated performing a mass balance of a lens saturated by a known quantity of tracer. For each test, performed using a different groundwater velocity, the diffusive fluxes of contaminant released by lenses were compared and the remediation times of the low- permeability zones calculated. For each lens, the obtained remediation timeframes were used to define an analytical relation vs groundwater velocity and the coefficients of these relations were matched to grain size of the low- permeability lenses. Results show that an increase of the velocity field is not useful to diminish the total depletion times as the process mainly diffusive. This is significant when the remediation approach relies on pumping technology. (c) 2017 Elsevier B.V. All rights reserved.
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