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Field Tracer Test for the Design of LNAPL Source Zone Surfactant Flushing
Author(s) -
Robert Thomas,
Martel Richard,
Lefebvre René,
Lauzon JeanMarc,
Morin Annie
Publication year - 2016
Publication title -
groundwater monitoring and remediation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 47
eISSN - 1745-6592
pISSN - 1069-3629
DOI - 10.1111/gwmr.12164
Subject(s) - tracer , capillary action , viscosity , aquifer , extraction (chemistry) , volumetric flow rate , flushing , pulmonary surfactant , chemistry , flow (mathematics) , porous medium , slug test , mechanics , geotechnical engineering , soil science , analytical chemistry (journal) , geology , chromatography , materials science , porosity , groundwater , composite material , medicine , biochemistry , physics , endocrinology , nuclear physics
A field tracer test was carried out in a light nonaqueous phase liquid ( LNAPL ) source zone using a well pattern consisting of one injection well surrounded by four extraction wells (5‐spot well pattern). Multilevel sampling was carried out in two observation wells located inside the test cell characterized by heterogeneous lithology. Tracer breakthrough curves showed relatively uniform flow within soil layers. A numerical flow and solute transport model was calibrated on hydraulic heads and tracer breakthrough curves. The model was used to estimate an average accessible porosity of 0.115 for the swept zone and an average longitudinal dispersivity of 0.55 m. The model was further used to optimize the relative effects of viscous forces versus capillary forces under realistic imposed hydraulic gradients and to establish optimal surfactant solution properties. Maximum capillary number ( N Ca ) values between injection and extraction wells were obtained for an injection flow rate of 16 L/min, a total extraction flow rate of 20 L/min, and a surfactant solution with a viscosity of 0.005 Pa⋅s. The unconfined nature of the aquifer limited further flow rate or viscosity increases that would have led to unrealistic hydraulic gradients. An N Ca range of 3.8 × 10 −4 to 7.6 × 10 −3 was obtained depending on the magnitude of the simulated LNAPL ‐water interfacial tension reduction. Finally, surfactant and chase water slug sizing was optimized with a radial form of the simplified Ogata‐Banks analytical solution (Ogata and Banks 1961) so that injected concentrations could be maintained in the entire 5‐spot cell.