DERR-2024-008217

EPA/ESD/R08-03/003
2003
EPA Superfund

Explanation of Significant Differences:

KENNECOTT (SOUTH ZONE)
EPA ID: UTD000826404
OU 02
COPPERTON, UT
06/23/2003
EXPLANATION OF SIGNIFICANT DIFFERENCES
KENNECOTT SOUTH ZONE OPERABLE UNIT 2
SOUTHWEST JORDAN RIVER VALLEY GROUND WATER PLUMES
U. S. Environmental Protection Agency, Region VIII
999 18th St. Suite 300.
Denver, Colorado, 80202
BACKGROUND
In December, 2000, EPA and UDEQ signed a Record of Decision which selected a remedy
for the Zone A ground water plumes associated with past mining activity in the Oquirrh Mountains.
During the design phase of the project, Kennecott Utah Copper Corp. (KUCC) conducted treatability
studies to refine flows and treatment parameters and to combine the infrastructure associated with this
project with similar infrastructure needed to manage other contaminated flows at the mine. These new
concepts and study results have led to some minor changes in the selected remedy as chosen by the
Record of Decision. The overall approach to the problem and ability to meet the stated objectives
remain unchanged.
COMPARISON OF SELECTED REMEDY (as given in the Record of Decision) AND THE
REMEDIAL DESIGN (as detailed in the Final Design for Remedial Action)
Remedy in Record of Decision Remedy in Design Phase Differences, if any
Operations and maintenance of
surface source controls
Not specifically mentioned in
the Remedial Design. O+M of
the source controls is
addressed in a State Ground
Water Permit.
Surface source controls not
addressed in Remedial Design
document. This is required in a
State Ground Water Permit.
Integration and use of
Institutional Controls, as
approved by the State Engineer
Restrictions on use of water
from existing wells, restrictions
on installation of new wells,
moratorium on new water rights
will be established through the
State Engineer as needed.
The State Ground Water
Management Plan issued by the
State Engineer in June 2002
addresses issues specific to the
remediation effort and needed
restrictions in the area of the
plumes.
Point of Use Management for
private well owners (in-home
treatment units, bottled water,
deepening of wells,
replacement of wells)
Plan for addressing impacts to
other well owners was
developed. Work with owners
to develop best form of
reparations.
Same
Remedy in Record of Decision Remedy in Design Phase Differences, if any
Plan to deal with consequences
of water level drops (new and
deeper wells, deeper
completions in wells, alternate
water sources, purchase or
exchange of water rights), well
abandonment and
compensation.
Options include reduced
pumping, replacement water,
injection, deeper well
installation
Same
Install a barrier well
containment system at leading
edge of acid plume at points in
path of movement (where
sulfate is less than 1500 ppm).
No water with sulfate
concentrations greater than
1500 ppm should move off
Kennecott property.
Three wells to serve as an initial
barrier well system have
already been installed
Same
Install well or wells in core of
acid plume
Two wells to operate at any
time. Wells moved in response
to plume
Same
Pretreatment of acid water
using nanofiltration
Acid water sent directly to
tailings line without
pretreatment. Neutralization
and metals removal takes place
in the tailings line.
Neutralization by tailings can be
augmented with lime if needed.
Nanofiltration step eliminated in
final design.
Treatment of pretreated acid
waters by RO
Not relevant any more No pretreatment of acid
waters. Treatment of acid
waters occurs in tailings lines,
not by RO plant.
Treatment of water from barrier
wells by RO
Treatment of water from sulfate
barrier wells by RO
Same
Treated waters to municipal
water purveyor
Treated waters from sulfate
wells sent to JVWCD, acid
waters kept by Kennecott for
use in milling processes.
Acid waters are kept by
Kennecott for use in processes,
and are not sent to a water
purveyor.
Remedy in Record of Decision Remedy in Design Phase Differences, if any
Install and maintain a
monitoring system to track
plume movement
Monitoring system plan
presented
Same
Prior to mine closure, dispose
of concentrates in the tailings
line
Acid water and RO
concentrates added to tailings
line
Very similar
Post Closure plan should be
developed during RD/RA
which can be implemented
quickly.
Post Closure Conceptual
design options presented
Same
EXPLANATION OF DIFFERENCES
In the process of designing the remedy, the approach to treating the waters withdrawn from
acid plume was changed. Originally, the waters from the acid plume core were to be pretreated using
nano-filtration technology. The permeate was then to be further treated using reverse osmosis, with the
concentrate recycled to the waste rock dumps for use in active leaching of the waste rock. However,
since this approach was studied and advocated, Kennecott discontinued the active leaching of waste
rock. This makes the concept of re-use of the concentrate for leaching no longer available. With the
cessation of active leaching, Kennecott began experimentation on treatment of the residual leachate and
leachates produced with precipitation falls on the dump areas. A study during the design phase
indicated that insertion of the acid waters into the tailings pipeline was feasible. The tailings, which
contain carbonates, were able to neutralize the acids. The tailings line, therefore, serves as a 13-mile
long acid neutralizing facility. The neutralization capacity is required in the tailings line whether the nano-
filtration concentrate waters are neutralized or the acid plume waters themselves are neutralized. Further
studies revealed that the neutralization process was actually completed in the first few hundred yards of
the pipeline. The experiments further proved that both waste streams, the residual leachate water from
the dumps and the acid waters removed from the aquifer, could be treated effectively in this manner.
The resulting water with its soluble components is not of drinking water quality and therefore will not be
provided to the municipalities. Instead, it would be recycled and used in Kennecott’s processing,
especially at the Copperton Concentrator. One of the principles in the National Contingency Plan
(NCP) indicates that water generated by treatment of contaminated aquifers should be put to beneficial
uses. Although the water will not go to municipal culinary use, it will have a beneficial use as industrial
water.
Calculations have also revealed that treatment of the acid plume is not cost-effective because
the acid plume is of such poor quality. Although such a scheme was proposed in the RI/FS and agreed
to in the ROD, only 24% of the acid plume waters would actually go to drinking water and the rest
would end up in the tailings pipeline (and then for industrial use). For this small volume of drinking
water product, the cost would be about $6-7/1000 gals. Treatment of the less contaminated waters at
the barrier wells is much more cost-effective and can be done with less waste of the water. The cost of
treatment of barrier well water is $0.70/1000 gals.
In terms of operations of the barrier well reverse osmosis treatment plant in Zone A, Kennecott
will construct and operate the plant for the first 5 years at least, perhaps longer. This is to allow time
for Kennecott to develop the operational parameters and costs so that long-term management
negotiations can proceed. Kennecott may choose to operate the plant indefinitely so that the facility
can be expanded and integrated with Kennecott’s industrial water management system. As is the
original plan, the treated water from the reverse osmosis plant will go to JVWCD and the treatment
concentrate to the tailings line.
Scientists agreed very early that effectiveness of source control infrastructure was extremely
critical in cleaning up the aquifer. The cut-off walls and pipelines associated with these source control
measures were constructed and are now maintained through provisions of a state groundwater
protection permit. Because of its importance to the cleanup program, maintenance of these source
controls was listed as an element of the ROD of December, 2000. The source control maintenance is
not described in the remedial design because this is already included in the groundwater permit. The
parties remain committed to this part of the remedy. Maintenance of the source control facilities will
continue either under the auspices of the groundwater permit or under terms of the federal RD/RA
Consent Decree.
CONCLUSIONS
Although some of the treatment details presented in the Remedial Design are different than
detailed in the ROD, the overall approach remains unchanged. Unchanged is the concept of barrier
wells which prevent spread of the contamination. Unchanged is the withdrawal of the heavily
contaminated waters from the core of the acid plume so that the plume diminishes in size over time.
Unchanged is the approach for beneficial use of the waters withdrawn from the plume, a concept which
works for both the waters treated in the reverse osmosis plant and in the tailings pipeline.
APPROVED:
_________________________________________
Max H. Dodson Date
Assistant Regional Administrator
Office of Ecosystems Protection and Remediation
U. S. Environmental Protection Agency, Region VIII
_________________________________________
Dianne R. Nielson, Ph.D.Date
Executive Director
Utah Department of Environmental Quality