U.S. patent application number 09/791765 was filed with the patent office on 2002-08-29 for aquifer remediation barrier for removal of inorganic contaminants.
Invention is credited to Davis, James A., Naftz, David L..
Application Number | 20020117434 09/791765 |
Document ID | / |
Family ID | 25154720 |
Filed Date | 2002-08-29 |
United States Patent
Application |
20020117434 |
Kind Code |
A1 |
Naftz, David L. ; et
al. |
August 29, 2002 |
AQUIFER REMEDIATION BARRIER FOR REMOVAL OF INORGANIC
CONTAMINANTS
Abstract
A permeable barrier for decontaminating groundwater having two
distinct components for increasing contaminant removal. Preferably,
the barrier material is a mixture or distinct layers of bone-char
phosphate material and iron oxide pellets. The barrier material can
be incorporated as part of a shallow trenching decontamination
system, or incorporated in a non-pumping well, or array of
non-pumping wells, as part of a deep underground decontamination
system. The system can be used for removing, among other things, a
radionuclide, such as uranium, from water.
Inventors: |
Naftz, David L.; (Park City,
UT) ; Davis, James A.; (Menlo Park, CA) |
Correspondence
Address: |
E. Philip Koltos
Division of General Law, Oiffice of the Solicitor
Department of the Interior
1849 C Street NW, Mail Stop 6530
Washington
DC
20240
US
|
Family ID: |
25154720 |
Appl. No.: |
09/791765 |
Filed: |
February 26, 2001 |
Current U.S.
Class: |
210/170.07 |
Current CPC
Class: |
C02F 1/283 20130101;
B09C 1/002 20130101; C02F 2103/06 20130101; Y10S 210/912 20130101;
C02F 2101/20 20130101; C02F 1/281 20130101 |
Class at
Publication: |
210/170 |
International
Class: |
E02B 001/00 |
Claims
1. A permeable barrier for decontaminating groundwater, said
barrier being disposed in a flow path for groundwater to be
decontaminated and said barrier comprising a bone-char phosphate
and iron oxide pellets.
2. A permeable barrier for decontaminating groundwater according to
claim 1, wherein said phosphate and said pellets are a
substantially uniform admixture.
3. A permeable barrier for decontaminating groundwater according to
claim 1, wherein said phosphate and said pellets are in vertically
alternating layers.
4. A permeable barrier according to claim 1, wherein the barrier is
used for decontaminating a radionuclide from water.
5. A permeable barrier according to claim 4, wherein the
radionuclide is uranium.
6. A system for decontaminating groundwater comprising an array of
non-pumping treatment wells disposed in a flow area for groundwater
to be decontaminated, each of said wells containing a barrier
comprised of bone-char phosphate and iron oxide pellets for
decontaminating groundwater flowing therethrough.
7. A system for decontaminating groundwater according to claim 6,
wherein said phosphate and said pellets are a substantially uniform
admixture.
8. A system for decontaminating groundwater according to claim 6,
wherein said phosphate and said pellets are in vertically
alternating layers.
9. A system for decontaminating groundwater, comprising a trench
disposed in a flow area for groundwater to be decontaminated and a
barrier comprised of bone-char phosphate and iron oxide pellets
disposed within said trench for decontaminating groundwater flowing
therethrough.
10. A permeable barrier for decontaminating groundwater according
to claim 9, wherein said phosphate and said pellets are a
substantially uniform admixture.
11. A permeable barrier for decontaminating groundwater according
to claim 9, wherein said phosphate and said pellets are in
vertically alternating layers.
12. A groundwater decontamination system comp rising a non-pumping
well decontamination unit, a barrier comprised of bone-char
phosphate and iron oxide pellets incorporated within said
decontamination unit, and means for lowering said unit down through
a non-pumping well into an acquifer containing contaminated
water.
13. A permeable barrier for decontaminating groundwater according
to claim 12, wherein said phosphate and said pellets are a
substantially uniform admixture.
14. A permeable barrier for decontaminating groundwater according
to claim 12, wherein said phosphate and said pellets are in
vertically alternating layers.
Description
FIELD OF THE INVENTION
[0001] In general, the present invention relates to the removal of
inorganic contaminants from groundwater. More particularly, this
invention relates to a sandwich barrier for use with either a
passive treatment system employing an array of non-pumping wells or
in a passive treatment trenching system for removal of such
contaminants.
BACKGROUND OF THE INVENTION
[0002] As interest in environmental issues has increased, so has
interest in improved methods of cleaning the land, air and water.
In this regard, the interest in improved methods of groundwater
cleanup has been acute. Potable ground-water supplies worldwide are
contaminated by, or threatened by, advancing plumes containing
radionuclides and metals. Unlike air, land and above groundwater
cleanups, removal of contaminants from groundwater areas presents
special problems with respect to gaining access to the contaminated
areas which can make these cleanups very difficult.
[0003] Once a contaminant enters a groundwater system, it can be
transported by the groundwater to a great depth. Additionally, such
activities as mining or deep underground storage of radioactive or
toxic materials can create a flow of contaminants through
groundwater hundreds of feet below the surface. Contamination by
uranium and other radioactive materials is particularly troubling
because of the longevity of these materials.
[0004] Conventional methods for treating deep groundwater
contamination are largely unsatisfactory because of cost and other
considerations. Active methods that seek out the undergroundwater
and bring it to the surface for treatment are most commonly used.
The active methods most frequently used are so-called pump and
treat methods, trenching methods, or some mixture of the two.
[0005] In a pumping method, contaminated groundwater is pumped from
the contaminated lower regions to the upper regions where the
groundwater may be treated and returned. The water may be brought
up to the surface using drilled holes, trenches, or other means
that provide the pumping equipment access to the water. Pump and
treat systems suffer from several problems. The power requirements
for a pump and treat operation are very high, and can be
prohibitively expensive. This is particularly true of pump systems
that treat deeper (>100 feet below land surface) groundwater.
Further, these systems are costly and difficult to maintain.
[0006] A trenching system employs a trench dug into the ground down
to the point of contamination. The exposed water is pumped from the
trench or treated on site as the water flows through the trench
area. Trenching systems work well in some instances of shallow
contamination but run into difficulties when applied to
contamination deeper within the ground because of the high cost of
digging the trench, monitoring costs and issues of ground
disturbance and recontouring. Another great disadvantages of
trenching systems is the high cost of pumping the contaminated
water from the trench to the surface for cleanup.
[0007] Because of the high costs of active systems using pump
means, interest has increased in passive systems that can treat
undergroundwater without a need for actual removal of the water.
The use of arrays of non-pumped wells has been proposed as a method
to remediate contaminated groundwater when the installation of
treatment wells is not possible because of technical or financial
constraints, for example, when contaminant streams are >200 feet
below the land surface.
[0008] Prior art of interest include U.S. Pat. Nos. 5,512,702
(Methods for in-situ immobilization of lead in contaminated soils,
wastes, and sediments using solid calcium phosphate materials);
U.S. Pat. No. 5,514,279 (System for treating contaminated
groundwater); and U.S. Pat. No. 5,362,394 (System for treating
contaminated groundwater).
[0009] Important limitations of prior art treatment materials
include the following: the materials are effective only with
respect to a small number of contaminants, and the treatment
materials are difficult to replace.
[0010] It will be evident from the foregoing that there is a need
in this art of contaminated groundwater treatment for a passive,
low cost materials for groundwater treatment that can treat a wide
variety of underground contaminants including radioactive
contaminants, can treat a large amount of water per unit, can be
incorporated into a passive treatment system, and offers simple
retrieval, replacement, and disposal of the reactive material used.
In this regard, an alternative, cost effective approach to
pump-and-treat methods could be widespread applicability to the
treatment of contaminated groundwater associated with abandoned and
active mine sites throughout the United States and other parts of
the world.
SUMMARY OF THE INVENTION
[0011] In accordance with the invention, an improved permeable
barrier is provided for decontaminating groundwater. The barrier
can efficiently treat a wide variety of contaminants as part of a
low-cost passive treatment system, and the barrier is simple and
inexpensive to replace.
[0012] The barrier is disposed in a flow path for groundwater to be
decontaminated and is comprised of a bone-char phosphate and iron
oxide pellets.
[0013] In one embodiment, the phosphate and pellets of the barrier
are a substantially uniform admixture.
[0014] In an alternative embodiment, the barrier comprises
vertically alternating layers of the phosphate and pellets.
[0015] Preferably, the barrier is used for decontaminating a
radionuclide from water. The radionulide decontaminated from water
is preferably uranium.
[0016] In another aspect of the invention, a system is provided for
decontaminating groundwater, the system comprising an array of
non-pumping treatment wells disposed in a flow area for groundwater
to be decontaminated, each of the wells containing a barrier
comprised of bone-char phosphate and iron oxide pellets for
decontaminating groundwater flowing therethrough.
[0017] In yet another aspect of the invention, a system is provided
for decontaminating groundwater, the system comprising a trench
disposed in a flow area for groundwater to be decontaminated and a
barrier comprised of bone-char phosphate and iron oxide pellets
disposed within the trench for decontaminating groundwater flowing
therethrough.
[0018] In still another aspect of the invention, a groundwater
decontamination system is provided, the system comprising a
non-pumping well decontamination unit, a barrier comprised of
bone-char phosphate and iron oxide pellets incorporated within the
decontamination unit, and means for lowering the unit down through
a non-pumping well into an acquifer containing contaminated
water.
[0019] Further features and advantages of the present invention
will be set forth in, or will be apparent from, the detailed
description of a preferred thereof which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a side elevational view of the reactive barrier
being deployed as part of a decontamination unit in a non-pumping
well water treatment system.
[0021] FIG. 2 is a top plan view of the reactive barrier
incorporated within the decontamination unit.
[0022] FIG. 3 is a perspective view of the barrier incorporated in
an array of non-pumping decontamination wells.
[0023] FIG. 4 is a perspective view of the barrier incorporated in
a trenching system.
[0024] FIGS. 5a and 5b are two graphs showing the change in uranium
concentrations in water samples taken along the perimeter of
barrier deployment tubes in a non-pumping well treatment system in
two different locations.
DESCRIPTION OF A PREFERRED EMBODIMENT
[0025] Referring to the drawings and, in particular to, FIG. 1,
there is shown a permeable reactive barrier 10 incorporated within
a deep aquifer remediation tool (referred to by the acronym DART)
for decontaminating deep groundwater. The barrier 10 is
incorporated in a permanent, semi-permanent, or replaceable unit
that contains a zone of reactive material that acts as a passive
in-situ treatment zone.
[0026] This in-situ treatment zone degrades or immobilizes
contaminants, such as radionuclides and other trace elements, as
the groundwater flows therethrough. Operational and maintenance
costs are lower because water flow across the barrier 10 is driven
by the natural hydraulic gradient between the well and aquifer, and
the treatment system does not require operational maintenance.
Reactions within the barrier either degrade contaminants to
non-toxic forms or transfer the contaminants to an immobile
phase.
[0027] In accordance with the invention, the barrier 10 contains a
barrier material comprising a mixture of iron pellets and bone char
phosphate. Such a mixture increases the efficiency of removing
contaminants such as uranium from groundwater. The removal of
uranium by this mixture of iron and bone-char phosphate occurs
because the phosphate that dissolves from the bone-char pellets is
strongly adsorbed by the iron oxides in the mixture. The adsorbed
phosphate on the iron source reacts with uranium in the groundwater
to form a low solubility metal phosphate, hence removing the
uranium from the groundwater. The barrier of the invention
increases the treatment capacity and allows for longer treatment
periods before material replacement. This results in a more cost
effective groundwater treatment program.
[0028] In one embodiment of the invention, the overall tool or
system includes a plurality of non-pumping wells, one of which is
indicated at 22 in FIG. 1. In FIG. 3, three non-pumping wells 22
are located downstream of contaminant groundwater 18 which flows,
as indicated by the "flow" arrow, into an acquifer 20. Referring to
FIG. 1, a decontamination unit 12 is shown as being disposed in
aquifer 20 having been lowered down by a cable 15 through a
non-pumping well 22 into the aquifer 20 through which the
contaminated groundwater flows. As water flows past the lowered
unit 12, the water is passively treated by contact by the barrier
10.
[0029] Turning to FIG. 2, the decontamination unit 12 has a porous
outer tube 16 with openings, and a porous inner tube 14 filled with
barrier material forming barrier 10. As contaminated water 18 flows
by the unit 12, a portion of the water moves into openings in the
outer tube 16 to the interior of the unit 14. The water 18 comes
into contact with a porous inner tube 14 that also has a plurality
of openings. The water 18 moves through the openings of the inner
tube 14 into the interior of the inner tube 14 and the barrier 10
therein. The water entering the inner tube 14 comes into contact
with the barrier 10 which removes contaminants from inflowing water
on contact. Since the barrier materials within the treatment tools
can be deployed through wells, passive treatment of deeper
contaminant streams (deeper than 100 feet) that could not be
treated with trenching techniques is now possible.
[0030] Referring to FIG. 4, the contaminant barrier of bone-char
phosphate and iron oxide pellets can be used in other contaminant
removal systems such as the trench deployment illustrated
schematically in FIG. 4. The barrier 10 is located at the bottom of
a trench 24 in the flow path.
[0031] The barrier can also work as part of a greater
decontamination system to clean a large underground area such as a
trench system or an array of non pumping wells. An array of
non-pumping wells 22 are drilled at a fixed distance from each
other, or trenches are dug where needed to effect
decontamination.
EXAMPLES
[0032] The barrier was tested using three barriers at an abandoned
uranium upgrader. The shallow groundwater in the colluvial aquifer
is contaminated with elevated concentrations of uranium that can
exceed 20,000 micrograms per liter (.mu.g/L). Two different iron
sources (natural red sand and manufactured iron oxide pellets)
mixed with bone char phosphate were utilized. Initial results
indicate that iron oxide pellets are a superior iron source.
[0033] Installation and Operation
[0034] As shown in FIG. 3, an array of barrier deployment tubes 12
containing different proportions of bone char phosphate and foamed
iron oxide pellets 10 were placed in 6-inch diameter wells 22 using
a cable tool drilling rig (not shown). Use of arrays of non-pumping
wells has been proposed as a method to remediate contaminated
groundwater when the installation of treatment walls is not
possible because of technical or financial constraints.
[0035] Under natural flow conditions at the site, groundwater
converges to the non-pumping array of wells 22 and the associated
barrier deployment tubes 12 in response to the difference in
hydraulic conductivity between the well 22 and aquifer 20.
Numerical simulations of groundwater movement through the
non-pumping well array indicate that each well intercepts
groundwater in a portion of the upgradient aquifer approximately
twice the inside diameter of the well.
[0036] Different proportions of bone char phosphate and iron oxide
pellets were used to facilitate increased uranium removal from
groundwater. The iron oxide pellets strongly adsorb the phosphate
released form the phosphate pellets. The adsorbed phosphate can
then react with the uranium in the groundwater to facilitate
formation of insoluble uranyl phosphate compounds. The mechanism of
uranium removal is a function of the type of barrier material. The
PO.sub.4 barrier material of pelletized bone charcoal used as a
phosphate source facilitates formation of insoluble uranyl
phosphate compounds.
[0037] The following proportions of bone char phosphate:iron oxide
pellets (volume ratio) were used in testing, the results of which
are shown in FIGS. 5a and 5b: (1) 50:50 (intermixed); (2) 25:75
(intermixed); and (3) 50:50 (layered vertically). The layers of
sample (3) are denoted 10a and 10b in FIG. 3. Each barrier package
had five monitoring points for the collection of water samples.
[0038] Results
[0039] Percent uranium removal was calculated using the following
formula:
U.sub.removed=100(U.sub.ban/U.sub.input) (1)
[0040] Where
[0041] U.sub.removed is the percent of uranium
[0042] U.sub.ban is the concentration of uranium in groundwater 1.5
feet from the poa gravel/barrier interface
[0043] U.sub.input is the concentration of uranium in groundwater
prior to entering the barrier.
[0044] Three months of uranium-concentration data were collected
from three barrier deployment tubes that were installed in the
non-pumping well array The results are as shown in FIGS. 5a and 5b.
During the first three months of operation, the barrier material
removed 95% of the uranium. Excellent results were also obtained
using the barrier as part of a trench system (shown in FIG. 4).
During the first year of operation the barrier removed an average
of 94 percent of the input uranium from the groundwater after
traveling 1.5 feet into the trench barrier.
[0045] Although the invention has been described above in relation
to a preferred embodiment thereof, it will be understood by those
skilled in the art that variations and modifications can be
effected without departing from the scope and spirit of the
invention.
* * * * *