LNAPLs do not Always Float: An Example Case of a Viscous LNAPL under Variable Water Table Conditions Page: 1 of 12
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Hydrology Days 2006
LNAPLs do not Always Float: An Example Case of a
Viscous LNAPL under Variable Water Table Conditions
M. Oostrom'
Environmental Technology Division, Pacific Northwest National Laboratory, Richland, Wash-
ington
C. Hofstee
TNO, Geo-Energy Division, Utrecht, The Netherlands
T.W. Wietsma
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory,
Richland, Washington
Abstract. An intermediate-scale experiment was conducted to investigate the
behavior of a viscous LNAPL under variable water table conditions. Two
LNAPL volumes were released from a small source zone on top of the flow
cell into a partly saturated, homogenously packed porous medium. Following a
30-day redistribution period, the water table was increased 0.5 m in 50 min-
utes. After the water table rise, LNAPL behavior was monitored for an addi-
tional 45 days. Fluid saturation scans were obtained periodically with a fully
automated dual-energy gamma radiation system. Results show that both spills
follow similar paths downwards. LNAPL drainage from the unsaturated zone
was relatively slow and a considerable residual LNAPL saturation was ob-
served after 30 days of drainage. Most of the mobile LNAPL moved into the
capillary fringe during this period. After the water table rise, LNAPL moved
up in a delayed fashion. After 45 days, the LNAPL has moved up only ap-
proximately 0.2 m. Since the LNAPL has only moved up a limited amount,
nonwetting fluid entrapment was also limited. The experiment was simulated
using the STOMP multifluid flow simulator. A comparison indicates that the
simulator is able to predict the observed phenomena well, including residual
saturation formation in the vadose zone, and limited upward LNAPL move-
ment after the water table rise. The results of this experiment show that viscous
mobile LNAPL, subject to variable water table conditions, does not necessarily
float on the water table and may not appear in an observation well.
'Hydrology Group
Environmental Technology Division
Pacific Northwest National Laboratory
P.O. Box 999, MS K9-33
Richland, WA 99352
Tel. (509) 375-0737
e-mail: mart.oostrom@pnl.govHydrology Days
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Oostrom, Mart; Hofstee , C & Wietsma, Thomas W. LNAPLs do not Always Float: An Example Case of a Viscous LNAPL under Variable Water Table Conditions, article, March 20, 2006; (https://digital.library.unt.edu/ark:/67531/metadc873651/m1/1/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.