Development and Operation of a Passive-Flow Treatment System for (Sup 90)Sr-Contaminated Groundwater Page: 4 of 12
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Development and Operation of a Passive-Flow Treatment System
For 9'Sr-Contaminated Groundwater
P. A. Taylor and P. S. Kirkham
ABSTRACT
Seep C was a free-flowing stream of groundwater that emerged in a narrow valley below the old
low-level waste (LLW) disposal trenches in Solid Waste Storage Area 5 (SWSA 5) at Oak Ridge
National Laboratory (ORNL). The flow rate of the seep water was strongly influenced by rainfall, and
typically ranged from 0.5 to 8 L/min. The seep water entered Melton Branch, a small stream that joins
White Oak Creek before exiting the ORNL boundary. The seep water contained high concentrations of
90Sr (10,000 to 20,000 Bq/L) and, before the full-scale treatment system was installed, contributed about
25% of all the 90Sr leaving ORNL. Seep C was identified as a primary source of off-site contaminant
transport and was designated for an early removal action under the Comprehensive Environmental
Response and Liability Act (CERCLA). A passive flow treatment system was chosen as the most cost-
effective method for treating the water.
In order to provide design and operating data for the full-scale system, a pilot-scale treatment
system consisting of a 5-gal bucket filled with 16 L of chabazite zeolite, was used to treat the seep water.
The test was started on 3/17/94 and concluded on 6/15/94. The system treated 63,470 L (3967 bed
volumes) of water and removed 22.7 mCi of 90Sr from the seep water. The system removed more than
99.5% of the 90Sr from the incoming water for the first 43,000 L of water treated. Then the removal
efficiency slowly decreased, as the zeolite became loaded, until it reached 84% removal for the final
sample. The passive system performed at least as well as comparable pumped zeolite systems in terms
of 90Sr removal efficiency and zeolite utilization. The test was terminated just before the construction
crew mobilized at Seep C to build the full-scale system.
The full-scale system consists of a french drain to collect the water and eight 55-gal drums of
zeolite (Norit Americas, Atlanta, GA), located in an underground vault, to provide treatment. The zeolite
drums are arranged in a lead-lag configuration, with the four lead drums connected to a common header
and the four lag drums supplied from a common header on the exit of the lead drums. There is an
elevation drop of about 1.5 m from the french drain to the zeolite drums, which pushes the water
successively through the zeolite, an air lock, and finally into Melton Branch.
The treatment system typically removes over 99.9% of the 90Sr from the water passing through
the drums of zeolite. The system has treated more than 3.3 X 106 liters of water since startup, and has
removed over 1.6 Ci of 90Sr. The iron hydroxide present in the seep water, which can plug the zeolite
and restrict flow through the treatment drums, has been a continuing problem, and has resulted in
additional costs of at least $50,000. Nitrogen gas, which is being added to the french drain at a flow rate
of about 10 L/min, has reduced, but not eliminated, the iron hydroxide problem.
Pilot-scale filtration tests have been conducted at the site to determine whether it would be
feasible to pump water from the french drain, through a pressure-filtration system, and then at low
pressure through the existing zeolite drums. The tests showed that removal of the very small iron
hydroxide particles required a 0.5 pm pore-size filter, which plugged very quickly. It does not appear
feasible to use a filtration system on the seep water.
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Kirkham, P. S. & Taylor, P. A. Development and Operation of a Passive-Flow Treatment System for (Sup 90)Sr-Contaminated Groundwater, article, February 28, 1999; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc685447/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.