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Funnel
& Gate System
The Need
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To clean the contaminated soil
and groundwater more efficiently, reactive barriers can be used to treat a variety of
organic compounds and heavy metal contamination using specialty engineered media or
bio-organisms. But, the limited success and high cost of traditional 'active'
ground-water-contaminant plume management efforts (i.e., pump-and-treat systems) has
stimulated a search for less expensive 'passive' plume interception and in-situ treatment
technologies. The 'funnel and gate system,' which uses heterogeneous (surface-mediated)
reactions on porous media to degrade dissolved contaminants, is one passive technology
under consideration. |
The Technology
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A funnel and gate system is a
passive remediation method which utilizes cutoff walls (the funnel) to modify flow
patterns so that ground water flows primarily through high conductivity gaps (the gates). |
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Remediation
System of the Funnel and Gate system |
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The system would have to expend to
depths of 60 to 70 feet, with at least 25 feet of this depth in the very dense weathered
rock zone. And it can be installed at the front of plumes to prevent further plume growth,
or immediately down gradient of contaminant source zones to prevent contaminants from
moving into plumes. |
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The non-permeable funnel serves to lead the
contaminated groundwater to the highly permeable gate which contains a reactive agent
(e.g., iron granules), and as groundwater flows through (in the absence of oxygen), the
chlorinated solvents are transformed into innocuous components. With these a biotic,
biological and/or physic-chemical processes, contaminants are destroyed or degraded
resulting in non-toxic chloride and simple hydrocarbons, which are further reduced by
naturally occurring bacteria (see above figure). The groundwater leaving the gate is
decontaminated. |
Funnel and Gate system
excavation |
The Benefits
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The significant advantage of the funnel and
gate system is that they can be effective without pumping, mass excavation of contaminated
soil, above-ground treatment facilities or off site disposal. And contaminated groundwater
can be steered, under the influence of the current natural groundwater flow and isolation
walls (funnel), through a controlled reactive zone in the soil (gate). The ongoing
operation and maintenance costs are comparatively low than other alternatives
‘pump-and-treat’ Over the long term, funnel-and-gate technology costs about 50%
less, depending upon the site-specific variables with little or no maintenance for long
periods. In addition, the system does not require aboveground structures, so use of the
property is not restricted. |
Status
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A reactive zone can be considered as a
compact, permeable in-situ 'reactor', in which the collected groundwater is remediated in
various ways. Since biological as well as chemical and electro-kinetic remediation
techniques can be applied, if required in combination, the concept is widely applicable
for a wide range of contamination. The funnel and gate installations often use slurry
cutoff walls as wingwalls to funnel groundwater into a permeable reactive barrier or gate.
Slurry cutoff walls can also be used to encircle contamination and permit a single vessel
of permeable reactive media inside the containment to economically treat a controlled
volume of groundwater. Special bacteria or high carbon fly ash can be added to the
soil-bentonite slurry cutoff wall to create an impermeable reactive barrier. As the first
commercial permeable reactive barrier, the funnel and gate used cement bentonite and soil
cement bentonite slurry walls to funnel ground water through an iron filing gate was
installed in 1994 on a congested industrial site in California. Subsequent to the
installation of the optimized Funnel and Gate system, the various remediation techniques
will be tested and assessed. |
Barriers
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Comparing the traditional technologies such as
pump-and-treat, the funnel-and-gate system is more expensive to install. Though the
ongoing operation and maintenance costs for other alternative are comparatively high, the
cost saving of the funnel-and-gate system should be verified. The efficiency of reactive
barrier installations significantly depends on controlling the flow of groundwater through
the media. |
Points of Contact
- Michael J. Wyatt, Marcor Corporate Headquarters, National
Remediation Group, 246 Cockeysville Road, Hunt Valley, MD 21030-6043, Phone: 800-547-0128, Fax: 410-771-0348, E-mail: info@marcor.com
References
- Burris, David R. Hatfield, Kirk. Wolfe, N L. Laboratory
experiments with heterogeneous reactions in mixed porous media Journal of Environmental
Engineering. v 122 n 8 Aug 1996. p 685-691
- Howard, Lonnie V. Hatfield, Kirk. Christensen, B A. Minimum
cost design of a funnel-and-gate system International Symposium on
Groundwater Management - Proceedings 1995. ASCE, New York, NY, USA. p 259-264
- Peter Werner, Technical University of Dresden, Germany, The State of the Art of
Operational Remediation Technologies, 1997, 20th World Gas Conference,
Copenhagen Denmark
- MARCOR Remediation, Inc. News Letter – Project, 1997,
<http://www.marcor.com/newsletter/index.htm>
- NOBIS, Dutch Research Program Biotechnological In Situ Remediation, project: 97-1-13 -
In-situ bioremediation of contaminated groundwater by Funnel and Gate, 1997
- INQUIP Associates, Inc, Reactive Barriers : Funnel & Gate, 1997, <http:/www.inquip.com/>
- Advanced Geo-Services corporation, GEOTECHNICAL PROJECTS: Representative Projects -
FUNNEL AND GATE SYSTEM, Geotechnical Investigation Feasibility/Constructability Studies,
<http://www.zigzag.net/clients/agc/index2.html
>
Disclaimer Statement
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Neither the Construction
Industry Institute nor Purdue University in any way endorses this
technology or represents
that the information presented can be relied upon without further investigation. |
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