PB95-963114
EPA/ESD/R08-91/091
March 1995
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
Silver Bow Creek/Butte Area,
(Warm Springs Ponds O.U.)
Silver Bow/Deer Lodge, MT
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EXPLANATION OF SIGNIFICANT DIFFERENCES
Silver Bow Creek/Butte Area NP.L .Site (original portion)
Warm Springs Ponds Operable Unit
Upper Clark Fork River Basin, Montana
United States Environmental Protection Agency
June 1991
I. INTRODUCTION
•/
This Explanation of Significant Differences modifies certain
elements of the Warm Springs Ponds remedy, as described in the
Warm Springs Ponds Record of Decision (September 1990).
The most significant aspect of this decision involves Pond 1
and the area below Pond 1. The Record of Decision specified that
Pond 1 would ba dry-closed, but a decision regarding the area
below Pond 1 was deferred for one year. While evaluating
alternatives for the area below Pond 1, the EPA has determined
that these alternatives may also have important implications on
Pond 1 itself. Because these areas have no role in the treatment
of water entering the pond system from Silver Bow Creek, the
decision has been made to separate them from the active portions
(Ponds 2 and 3). Pond 1 and the area below will be the subject
of a second and separate proposed plan, public review, and Record
of Decision.
This change, together with other minor and ancillary changes
to the Warm Springs Ponds remedy, are described in detail in the
following sections. The changes enable the EPA to proceed with
necessary work on the active portions of the pond system (Ponds 2
and 3), either through an enforcement action against ARCO or
through use of Superfund money. At the same time, these changes
allow the EPA to conduct a more thorough evaluation of various
alternatives for closing the inactive portions of the pond system
(Pond 1 and below).
The EPA intends to offer a preferred remedy for the
inactive areas, before the end .of September 1991, followed by a
full public review of the preferred remedy, as well as other
alternatives evaluated. The EPA will then select a remedy for
the inactive portions.
II. BACKGROUND AND PURPOSE
On September 28, 1990, the U. S. Environmental Protection
Agency signed and issued the Record of Decision for the Warm
Springs Ponds, which are part of the Silver Bow Creek/Butte Area
"Superfund" Site in the upper Clark Fork River Basin of Montana.
This Record of Decision presented and described a remedy selected
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by the EPA for controllin~ the highly contaminated tailings,
sediments, and water contained within the ponds and for
-preventing these contaminated materials and water from entering
the Clark Fork River.
Figure 1 of the Record of Decision shows the location of the
Warm Springs Ponds in relation to the four tributaries that
combine to form the Clark Fork River below the ponds and it
summarizes the remedy. The Warm Springs Ponds cover an area
approximately four miles long and one mile wide. Key features
include three settling ponds, three wildlife ponds, extensive
wetlands areas ~nd the Mill-Willow Bypass.
. This Explanation of Significant Differences, or ESD,
de{scribes and documents the changes made by the EPA for the Warm
Springs Ponds remedy. . .
In accordance with federal regulations regarding Superfund
activities, specifically Sections 117(c) and 121 of the
Comprehensive Environmental Response, Compensation~ and Liability
Act of 1980 (CERCLA), as amended, 42 U.S.C. Sec. 9601, et sea.,
and 40 CFR Section 300.43S(c)(2)(i) of the National Contingency
Plan (NCP), 40 CFR Part 300, this Explanation of Significant
Differences has been prepared for the following reasons:
. a~
b.
c.
to provide the public with. an. explanati9n of the nature
of the changes;
to summarize the information that led to the changes;
and
to affirm that the revised remedy complies with all
statutory requirements.
The Montana Department of Health and Environmental Sciences
(MDHES), which conducted the remedial investigation and
feasibility study for the Warm Springs Ponds, participated in the
deliberations that led to, the. selection of the remedy described .'
in the September 1990 Record of Decision and the changes
described in this Explanation of Significant Differences.
III.
REMEDY DESCRIBED IN THE RECORD OF DECISION
The remedy selected by the EPA and specified in the Record
of Decision was summarized as follows:
. 1 .
2.
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Allow the ponds to remain in place; Ponds 2 and. 3 will
continue to function as treatment ponds until upstream
sources of contamination are cleaned up;
Raise and strengthen all pond berms according to
specified criteria, which will protect against dam
failure in the event of major earthquakes or floods,
and increase the storage capacity of Pond 3 to receive
and treat flows up to 100-year flood;
2.
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3.
4.
-5.
6.
10.
11.
12.
Construct new inlet and hydraulic structures to prevent
debris from plugging the Pond 3 inlet and to safely
route flows in excess of the 100-year flood around the
ponds;
Comprehensively upgrade the treatment capability of
Ponds 2 and 3 to fully treat all flows up to 3,300 cfs
(100-year peak discharge) and construct spillways for
routing excess flood water into the bypass channel;
Remove all remaining tailings and contaminated soils
from the Mill-Willow Bypass, consolidate them over
existing dry tailings and contaminated soils within the
-Pond 1 and Pond 3 berms and provide adequate cover
material which will be revegetated;
7.
Reconstruct the Mill-Willow Bypass channel and armor
the north-south berms of all ponds to safely route
flows up to 70,000 cubic feet per second (one-half of
the estimated probable maximum flood);
Flood (wet-close) all dry portions of Pond 2f
8.
Construct interception trenches to collect contaminated
groundwater in and below Pond 1 and pump the water to -
Pond 3 for treatment; -.
9.
Dewater wet portions of Pond 1 and cover and revegetate
(dry-close) all areas within the Pond 1 berms;
Establish surface and ground water quality monitoring
systems and perform all other activities necessary to
assure compliance with all applicable or relevant and,
appropriate requirements;
Implement institutional controls to prevent future
residential development, to prevent swimming, and to
prevent consumption of fish by humans; and
Defer, for not more than one year after the effective
date of this document, decisions concerning the
remediation of contaminated soils, tailings, and ground
water in the area below Pond 1, pending evaluation of
various wet- and dry-closure alternatives and public
r~view~ -
The selected remedy for the Warm Springs Ponds is composed
of a series of remedies, or elements. It represented a synthesis
of the State's and EPA's original Alternative 3 (see the -
feasibility study or proposed plan) and ARCO'sAlternative 3A.
This new alternative, Alternative 3 + 3A, was developed and
selected following months of consultation with the public and the
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potentially responsible party, ARCa. It is described in greater
detail in Section 8.4 of the Record of Decision.
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IV.
MODIFICATIONS TO THE REMEDY
As stated in the Introduction, only certain elements of the
overall remedy have been modified. The most significant change
involves Pond 1 and the area below Pond 1, ,or the inactive area
of the Warm Springs Ponds. . Thus, Element Nos. 1-7 and 10 (se~
above) remain essentially unchanged and they either have been or
will be implemented without delay, including operation. and
maintenance activities. . These elem~nts of the remedy involve dam
. safety and flood routing requirements, removal of tailings from'
the Mill-Willow Bypass, and water treatment improvements.
Clar ification of certain aspects of Element Nos. .1-7 and 10 is
provided below. .
Element Nos. 8, 9, 11 and 12 (see above) may be either
slightly or significantly modified, or they .may not be modified
at all, pending the EPA's and MDHES's thorough evaluation of.
various alternatives for Pond 1 and the area belo~. As stated
earlier, the EPA intends to issue a separate proposed plan for
Pond 1 and the area below Pond 1 befQre the end of September 1991
and will subject the proposal to full public review before a
remedy is selected.
Element No. 12, as described in the Record of Decision,'
reads as follows:
Defer, for not more than one year after the effective date
of this document, decisions concerning the remediation of
contaminated soils, tailings, and ground water in the area
below Pond 1, pending evaluation of various wet- and dry-
closure alternatives and a public review.
. In essence, this will not change. The. EPA has already .
received a draft alternatives analysis from ARCO which evaluates
. the various possibilities for wet- or dry-closure of both Pond 1 .
and the area immediately.below Pond 1. While the draft report
has undergone an initial review by the agencies, additional
analysis is needed. Since it is the desire of the EPA to subject
these alternatives to a more thorough evaluation and full public
review, without impeding the progress of those elements of the
remedy involving the active portions of the pond system, it is
logi~al that the remedy should be divided.'
The Warm Springs Ponds operable unit, therefore, has been
divided into two separate actions. The first action involves the
active areas (Ponds 2 and 3, as well as the bypass and berms,
inlet and outlet structures, treatment improvement features and
monitoring systems). The second action involves the inactive
areas (Pond 1 and the area below Pond 1, including the Pond 1
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berms, the old Silver Bow Creek channel, and the lowermost
__portion of the bypass). The second action also involves those
decisions deferred by the September 1990 Record of Decision
concerning the remediation of contaminated'soils and tailings.
v.
OTHER MODIFICATIONS
A number of minor changes have also been made by the EPA to
the remedy described in the September 1990 Warm Springs Ponds
Record of Decision. These changes may be more accurately
characterized as technical and legal corrections; however, they
are modifications and the EPA is obliged to identify them and
briefly discuss the reasons for them.
A. '
Pond 3 Outflow Structures
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Two modifications involve the Pond 3 outflow structures.
The Record of Decision specified that the two decant structures
within Pond 3 should be raised and modified to provide controlled
releases into Pond 2, not to exceed 200 cfs. It also specified
that an additional outflow structure (in addition to the
emergency spill~ay) would be constructed to avoid exceeding the
'maximum allowable storage volume. in Pond 3 during the lOa-year
flood. In other words, outflows in excess of 200 cfs (via the
'decant structures into Pond 2) were to be routed directly ~nto
the Mill-Willow Bypass'via a large pipe from the w~st decant
structure. The pipe would have been capable of discharging up to
500 cfs. '
Preliminary engineering design work by ARCO has led to
uncertainty concerning the integrity of the existing decant
structures. Therefore, ARCO has proposed to, construct two new
decant structures and decommission the old ones. This decision
necessitates two modifications to the Pond 3 outflow structures.
The first is to con~truct the new decant
to accommodate as much as 300 cfs. 'They will
to decant 200 cfs, or any lesser flow amount,
feasible and desirable to route more than. 200
during floods, once experience is gained from
structures in order
retain the ability
but it may be both
cfs into Pond 2
actual operation.
The second modification is to discard plans for adding a
large pipe to the existing west decant structure. The pipe,
which would have passed through the Pond 3 berm, was feasible
only if the existing decant structures were to be kept intact.
Because new decant structures are necessary, a simpler but more'
reliable additional outflow structure will be constructed in the
northwest corner of Pond 3, separate from either the new or old
decant structures. '
Preliminary design' by ARCO indicates that this bypass
outflowstructure'willbe less likely to create hydraulic
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problems or fail during floods, as compared to the ea,rlier-
proposed outlet pipe. More significantly, the new design offers
-much greater operatiorial flexibility: Control features will
allow outflows up to 1,000 cfs at elevations ranging from 4869.1
ft. to 4876.5 'ft. (The normal operating pool level is expected
to be about elevation 4868 ft. and the emergency spillway
elevation will be at 4876.6 ft.)
Experience gained from actual operation during floods in
the future may prove it desirable under certain conditions to
discharge Pond 3 water directly into the bypass,through this
outflow structure and around Pond 2. Experience may also prove
it desirable under different condition& to discharge more that
200 cfs into Pond 2. These two modifications offer that kind of
flexibility; however, the EPA allowed the modifidations with the
understanding that their design must retain the ability to
operate within the full range of possibilities described above
and, at the same time, assure compliance with all applicable or
relevant and appropriate requirements.
B.
Regulation of Point Source Discharges from the Warm Springs
Ponds
The ROD at pages 1-3 and 2-52 describes the need for
adequate treatment of water, discharged from the ponds, the need,
for ari additional outlet structurefro~ Pond 3, an~ th~ need 'for
ov~rflow spillways. Applicable and relevant and appropriate
requirements for the Pond 2 discharge are identified in the ROD
in Attachment 1 to Part II.
The following additional information will be 'useful in
understanding the future workings of these aspects of the ponds,
and defines required ARARs and use compliance for the various
discharges. . .
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T~e disch,rge from P~nd 3 will also be ~ubje6~.to discharg~
limits and will be used only when necessary.
The ROD does not clearly state that the Pond 3 overflow
discharge will be subject to discharge limits. This ESD
clarifies that the discharge is subject to ARARs limits.
The use of the Pond 3 discharge structure will be evaluated
as experience is gained from the pond system's operation
during below-normal, normal, and above-normal flows. The
.ESD further clarifies theARAR requirements for the Pond 2
discharge. Remedial design do6uments required for this
action will further define the use of this discharge
structure. Overflow spillways, which will be used if flood
waters exceed the 100 year flood, will not be subject to any
discharge requirement.
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Specific bioassays described in the ROD will not' be
required.
The ROD at pages 2-55 and 2-56 identifies specific bioassay'
studies'to be performed at the ponds~ .to determine the
effects of resuspension of bottom sediments. Upon further
consideration, EPA ha~ determined that these specific
bioassays are not necessary. Rather, interim and final ARAR
levels explained below will be required to be met for the
point source discharges at the ponds. Any specific studies
or additional actions necessary to achieve these levels will
be determined during remedial design and remedial action
implementation.
No permit is required for theldischarges, at the time that
the ROD and the ESD are undertaken. .
3.
'In the pas~, the point source discharge from Pond 2 has been
regulated under the State Clean Water Act through a permit
issued by the State Department of Health and, Environmental
Sciences. EPA has continued to examine the effect that
section 121(e)(1) of CERCLA, 42 D.S.C. S 9621(e)(1), has on
this action and the State's ~xisting permit. EPA has.
determined that section 121(e)(1) negates the requirement
that continued or new point source discharges from the pon9s
c into.M~ll-Willow Bypass be regulated under..a State water
quality permit. (See the opinion of the EPA Office of
General Counsel dated March 12, 1991, contained in the
administrative record). However, the discharges must meet
the substantive requirements of the State Clean Water Act
and implementing regulations. Final discharge requirements
are listed in the ARARs list, Attachment 1 to Part II of the
ROD. .
To clarify how the discharges are and will be. regulated, EPA
has d,etermined:
a.
The State's permit will continue to govern the Pond 2
discharge until a consent decree is entered for this
action,. or a unilateral order is issued for this
action, or judicial relief is granted under section 106
of CERCLA for this action, or EPA begins remedial
design at the site using Superfund money.
b.
I
Once a consent decree is entered for this actipn, or. a
unilateral order is issued for this action, or judicial
relief is granted under section 106 of CERCLA for t~is
action, or EPA begins remedial design at the Site,
using Superfund money, interim limits will apply to the
point source discharges until remedial design is
completed and remedial action is implemented. Interim
limits will be protective of human health' and the
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environment, and will be further defined in the consent
decree or unilateral order.
c.
Upon completion of remedial action implementation, ARAR
limits defined in Attachment 1 to Part II of the ROD
and further clarified in this ESD will apply to the
point source discharges. These requirements will be
contained in an attachment to the consent decree or
unilateral order and the limits will be subject to
review during any five-year review performed for the
Site, and in any future decision document for the Site.
Interim and final discharge limits and associated
requirements will be~ully enforceable by EPA and the State
. pursuant to the terrnsof.a consent decree or unilateral order~
C.
ARAR s :
Corrections and Clarification
Section 5.0 of Part II of the ROD, and Attachment 1 to Part
II define ARARs which must be met during and upon completion of
the action. Some of these ARARs were inaccurate, due to
typographical errors. The following are the correct ARARs for
thi.s action, and replace the specific corresponding ARARS listed
in the ROD. Other ARARs listed in the ROD are not changed, and
remain as necessary requ~rements for this Site.
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1.
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ARARs Corrections
a.
Contaminant Specific ARARs for Groundwater
Arsenic should read 0.05 milligrams per liter (mg/l)
instead of 0.02 mg/l, as indicated on page 3, Attachment 1
to Part II of the ROD.
Mercury should read 0.002 mg/l instead of 0.0002 mg/l, as
indicated on page 3,' Attachment 1 to Part II of the ROD. .
b. Contaminant Specific ARARs for Surface Water, Ambient
and Point Source Discharge .
The table given at page 8 of. Attachment 1 to Part II of the
ROD should be revised to read as follows:
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Acute
(mg / I )
"Arsenic(III)
0.36
Arsenic(V)
0.85
Arsenic(Total)
Cadmium
0.0039*
" I
Copper
0.018*
Iron
Lead
0.082*
Mercury
0.0024
Selenium
0.26
Silver
0.0041*
Zinc
0.12*
Chronic Water and
Fish"
" Inqestion
( mg / I) (ng/l)
O. 19.
0.048
2.2
0.0011*
0.012*
1 . 0
0.0032*
0.000012" 144.0
0.035
0.00012
0.11*
This chart reflects minor corrections in arsenic (total),
mercury, and selenium levels, and clarifies which standards are
chronic numbers, and which standards are acute numbers, as well
as indicating that certain of the State's water quality standards
relate to water and fish ingestion.
2.
ARARs Clarification
Attachment 1 to Part II of the ROD lists a number ~f ARARs,
TCEs, and Other Laws for the entire Warm Springs Ponds operable
unit action. This portion of the ESDclarifies which of those
standards and requirements apply to the remedial action
implemented pursuant to the Record of Decision, as modified by
this ESD. "
Contaminant Specific
Air st'anda"rds listed "in Part I. 2. are applicable to this
action as described.
a.
Surface Water standards for point source discharges "listed
in I are applicable to this action as described, as modified
by Section 5(E)(3) of the ESD.
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Ground water standards'listed in Part 1(1), Sections I & J,
are applicable to this action.
As stated in the September 1990 ROD, temporary diversion of
Mill and Willow Creeks into the Ponds may be required in
order to meet ARARs for the Site. 'This issue will continue
to be examined, and EPA may require such action as part of
this action, or as part of the inactive portion action. EPA
will continue to examine possible clean up actions in the
upstream portions of Mill and Willow Creeks.
b.
Location Specific
All location specific standards listed in Part II are
applicable to this action as described, incl~ding
requirements under the Endangered Species Act' and
requirements relating to wetlands, as explained below. The
Endangered Species Act requirements should also include
necessary assessments and actions for protection of
peregrine falcons, which have been sighted recently at the
ponds. .
c.
Action Specific
. Safety standards, incl~ding OSHA safety standards,
.' identified in section 111.1 .A. - C. are 'applicable to this
act~on as described.
Cleanup standards for the Mill-Willow Bypass identified in
section III.2.A. ~ D. are applicable to this action as
described. .
Revegetation standards identified in section III.3.A. - B.
are applicable to the disposal area created in Pond 3, and
to any areas within or around Ponds 2 and 3 and the Mill-
Willow. Bypass .which involve capping waste in place, as
described.
Requirements and standards governing 'continued operation of
Ponds 2 and 3, .identified In Section 111.4., are applicable
to this action as described.
Requirements and standards governing berm strength,
identified in section 111.5., are applicable to this action,'
as described. .
Closure and post closure care requirements and standards,
identified in section III.6.A. - F., are applicable to the
Pond 3 disposal area, which is part of this action.
Requirements and standards for point source discharges,
identified in section III.S.A. - C., are applicable to Pond
2 and Pond 3 point source discharges, as described in the.
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Attachment and further clarified above.
All TBCs and Other Potentially Relevant Laws identified in
the Attachment are applicable ~r may affect this action, as
. described.
D.
Institutional Controls
The ROD at pag~ 1-4 describes the need for the
implementation of institutional controls at the Site, and lists
examples of institutional controls which may be necessa~y. This
requirement was made part of the ROD to prevent residential
development of the area, and to prevent unnecessary exposure to
contaminants in the area. Since the publication of the ROD, EPA.
has examined specific institutional controls which should be
.' . implemented at the: site. For purposes of clarification, the.
. following specific institutional controls shall be initiated in
cooperation with local governments at the site:
1 .
Renewal of the lease agreement
State of Montana Department of
Parks, for continuation of use
area as a wildlife refuge.
between ARCO and the
Fish, Wildlife, and
of major portions of the
2.
Implementation of a conservation easement with
. restrictive covenants by ARCO for .the Site, to ensure
that. futur.e development. will not. include residential.
use, and will not cause disruption of disposal areas or
waste ponds.
3.
Implementation of a permit development system, in
cooperation with Anaconda and Deer Lodge Counties and
ARCO, which will prevent residential development at the
Site. The permit system includes the development of a
master plan, which will designate the ponds as a
wildlife refuge. '.
4.
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Implementation of a water well ban'in the area~ 'The
well ban shall prohibit water wells within the.waste
ponds at the Site permanently, and shall temporarily
prohibit water wells within the Site in areas Qutside
of the waste ponds, until such time as ARARs are
achieved for the ground water at the Site.
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5 .
Implementation of a ban on swimming in the Ponds at the
Site, to be accomplished through the pos~ing of
appropriate signs at the Site.. . .
The ROD describes institutional controls which would ban
fish consumption at the Site. EPA has considered this issue
further, in consultation with the State Department of Fish,
Wildlife, and Parks, and has determined that the ban on taking
fish for consumption may. not. be appropriate for the Site. EPA
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will continue to evaluate this issue, and may require such action'
at a later time, if data indicates such a ban is appropriate.
~he Montana Department of Fish, Wildlife and Parks retains the
ability to implement catch and release policies in order to
manage the fishery most effectively.
E.
Technical Corrections
This Explanation of Significant Differences offers the EPA .
an opportunity to correct or clarify certain technical aspects of
the Record of Decision. These corrections or clarifications
address technical details regarding the construction of treatment
improvements and the operation of the pond system. Discussions.
with the public, the potentially responsible party (ARCO), and
other state and federal agencies indicated a need for the
following technical corrections:
'{
1 .
Page 2-51 of the Decision Summary, last full paragraph,
states that storage of flood flows up to the 100-year
. event is one of the primary purposes of Alternative 3~+
3A. The term "storage" ~as used elsewhere in the
document, as well. Use of the term "storage" was ~ot
done with the intent of requiring the complete.
retention of 100-year flood flows in the same manner
that a larger, multi-purpose dam would store flood
. flows~ Rather, the intent was to.ensurethat Pond 3
(and to the extent practicable, Pond 2) could safely
receive and treat those 100-year flood flows, but
release water as rapidly as possible to balance
treatment needs and dam safety -requirements.
Additionally, water rights are a consideration, and the
ponds system must be operated in a manner which will
not interfere with downstream water users' rights.
2.
Page 2-52 of the Decision Summary, first sentence,
requires some clarification and correction. As.
explained above, "storage" should not be misc6nstrued~
Additionally, however, the figure 13,000 acre-feet
should have been 12,500 acre-feet. The crest of the
emergency spillway, as designed for dam safety
requirements in effect for a flood of one-half the
estimated probable maximum flood, will allow no more
than 12,500 acre-feet to be contained by Pond 3. It
should be understood that under normal operating
conditions (before a flood), Pond 3 will alre~dy
cbntain approximately 4,800 acre-feet of water. In the
event of a flood, Pond 3 will effectively receive and
treat all flows up to the 100-year event (3,300 cfs).
The difference between 4,800 acre-feet and 12,500 acre-
feet is 7,700 acre-feet, and the 100-year design flood
for sizing and design, as determined by flood modeling
studies conducted by the State of Montana, is .
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approximately 13,000~13,500 acre-feet.
has no effect on treatment capability.
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This corr.ection
3.
Page 2-52 of the Decision Summary, second sentence,
requires some clarification. The normal operating,
volume of Pond 2 will be approximately 1,600 acre-feet.
The figure 2,200 acre-feet used in the ROD is roughly
the expected volrime at 'high pool" or during floods.
4.
Page 2-52 of the Decision Summary, last sentence of
second paragraph, requires some clarification. The
figure 4,000 cfs was a preliminary design estimate of
the intake structure's ability to pass flows during a'
"PMF-type" of flood. ARCO's design estimate is now
approximately 4,600 cfs, and,this is acceptible. It '
'should ~e understood that during a'more mod~rate flood,
such as a 100-year event, a maximum of 3,300 cfs will
enter the Pond 3 inlet.
5.
, .
Page 2-54 of the Decision Summary, first'sentence,
requires some clarification. The figure of 8,500 cfs
is a preliminary estimate that may be adjusted, either
upward or downward, in final design.
Wetlands and Endangered Species
Two principal sections of the Record of Decision~ Section
5.0 and Attachment to Part II, identify and analyze the
applicable or relevant and appropriate requirements (ARARs)
associated with the Warm Springs Ponds remedy. While certain
laws, regulations, and requirements pertaining to the protection
of wetlands and ~ndangered species are identified in those
sections, their mention in this Explanation of Significant
Differences is to reemphasize their importance and specify that
ARCO has initiated a wetlands delineation and cla~sification
study for the Warm Springs Ponds. The study will iQentify and
measure the areas already considered to be wetlands. As the
remedies for the two separate portions of the pond system are
implemented, provisions will be necessary to assure that legal
requirements related to the ARARs will be met, and that there is
no net loss of wetlands. '
This may become an important consideration in evaluating
alternatives for Pond 1 and the lower area. Completedry-closure
of Pond 1, which would h,ave occurred under. the provisions of the
, September 1990 Record 'of Decision, and still'may occur pending
reevaluation and public review, would result in the loss of a
portion of those wetlands within the eastern portion of Pond 1.
If that decision is made, then it will be necessary to create new
wetlands of equal habitat value elsewhere in the pond system.
The extent of the increase in wetlands area that is expected to
occur wh~n the Pond 2 pool area is increased, in order to improve
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water treatment capability, will not be fully known until the
_wetlands delineation study is finalized and the remedy has begun.
In all instances, and in respect to both remedies,
compliance with all ARARswill be required, including the
provisions for no net loss of wetlands.' .. .'
Additionally, a biological inventory of the area will be
required. The U.S. Department of the Interior (USDI) has
determined that two endangered bird species inhabit the ponds.
They are the bald eagle and peregrine falcon. The results of a
biological inventory may lead to the need for followup measures.
In any case, the presence of threatened or endangered species
already calls for close coordination with USDI, and the .
likelihood of protective or mitigative ~easures becoming
necessary during the remedial design and remedial action phases
of cleanup is great. .
VI.
ADMINISTRATIVE RECORD
. This Explanation of Significant Differences has been
incorporated into the Administrative Record File for the Silver
Bow Creek/Butte Area NPL Site, which is available for public
review and can be seen between 8:00 a.m and 4:30 p.m., Monday
through Friday, at the EPA's Offices, Federal Building~ 301 South
'Park, Helena, Montana. . . .
VII. APPROVAL
Date: . ~..2.v. rf9r
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ERRATA SHEET
Silver Bow Creek/Butte Area Superfund Site (original portion)
Warm Springs Ponds Active Area Operable Unit
Upper Clark Fork River Basin, Montana
United States Environmental Protection Agency
September 1991
I.
BACKGROUND
. .
Section 121(d) of CERCLA requires Superfund cleanups to
comply with applicable or relevant and appropriate requirements
(ARARs). ARARs are requirements, standards, criteria, or
limitations established under federal environmental or state
environmental. or facility siting laws. The Environmental
Protection 'Agency (EPA) issued a Record of Decision (ROD) for the
Warm Springs Ponds operable unit in September, 1990, and issued
an Explanation of Significant Differences (ESD) in June, 1991.
The ESD indicated EPA's intention to go forward with the active
area. portion of the'September, 1990 ROD, and.corrected or changed
c~rt~in details of the active area remedial decision. . A fuil '
list of ARARs for the Warm Springs Ponds cleanup was presented in
the September, 1990 ROD. The June, 1991 ESD also stated which of
these ARARs were within the scope of. the active area cleanup, and
included some corrections and changes to the ARARs list.
The State of Montana and other commentors have raised 'some
issues regarding the ARARs list. The commentors have noted
additional citation errors in the ROD list ofARARs which were
not corrected ihthe ESD, as well as inadvertent omissions from
the explanation of basis forARARs given in the September 1990
ROD or in the June 1991 ESD. The commentors have also noted that.
a variation in one ARAR standard is necessary for proper
operation of the treatment system at the WSP active area operable
unit. .
Accordingly, this errata document corrects citation errors
and states the appropriate basis for certain ARARs, and grants a
wa.;ver of. the ARAR standard for pH to a slightly higher standard. -
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II.
CORRECTIONS
"'"References to page numbers are to the Attachment to Part II of
the September, 1990 ROD.
1. Page 5, Contaminant Specific I.2.A. Reference should be to
ARM S 16.8.815 rather than ARM S 16.8.818.
2. Page 8 - 9, Contaminant Specific I.3.L.- S. This section
lists ARAR standards for in-stream values which receive point
source discharges. This section was inadvertently not included
in the list of ARARs which were carried over to the ESD from th~
ROD. The standards are hereby included and are ARARs for the
Warm Springs Ponds active area remediation.
. As explained below in #3, these standards derive' from the
B-1 classification for Mill and, Willow Creeks, which are the
receiving waters for the Warm Springs Ponds point source
discharges, as well as from.the C-2 standards applicable to the
nearby upper Clark Fork River. See ARM 8 16.20.618(2).
Accordingly~ I.3..L. should reference a 7.0 milligrams per liter
standard for dissolved oxygen, at all times; I.3.M should also
referenc~ an upper range for induced variation of pH as 8.5, the
B-1 standard, in addition to the 9~O upper range from the C-2
standards; and I.3.N. shopld reference a standard of 5
nephelometric turbidity' units, the B-1 standard, in addition. to
the 10 nephelometric turbidity unit, the C-2 standard.
3. Page 10 - 11, Contaminant Specific I.4.A. Specific water'
quality standards are listed at pages 8 through 10. These
standards are made a requirement for point source discharges at
pages 10 to 11. 'The basis for selecting the standards is given
as ARM 9 16.20.622(2), the C-2 water quality standard regulations
promulgated under State law, because the Clark Fork River near
the Ponds is classified as a C-2 river. The basis' should also
. include ARM .8 16.20.618(2'), the B-1 water quality standard'
regulations. Mill and Willow Creeks run through the Mill-Willow
Bypass, and point source discharges flowing into these creeks,
such as the point source discharges from the Ponds, must comply
with the B-1 standards upon completion of remedial action. Mill
and Willow Creeks are designated as B-1 creeks in
ARM 8 16.20.604(1). In accordance with the opinion of the Water
Quality Bureau of the Montana Department of Health and
Environmental Scie~ces (see the administrative record), the
'standards cited at pages. 8 through 12,' as corrected by the ESD .
and this document, are the correct and legally required standards
for point source discharges from the Warm Springs Ponds.
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4. Page 11, Contaminant Specific I.4.B. An upper range of 9.5
for pH is identified .as the applicable requirement, pursuant to
~M 9 16.20.622. The correct upper range number established in
ARM. 9 16.20.622 for pH for the C-2 classification (Clark Fork
River discharges) is 9.0. The upper range for pH for the B-1
classification (Mill and Willow Creeks discharges), established
in ARM i 16.20.618, is 8.5.
EPA invokes the waiver of ARARs authorities granted it in
sections 121(d)(4)(B) and (C) of CERCLA regarding greater risk
and technically impracticability, to allow a slight deviation
from the State pH standards of 8.5. and 9.0 to a pH of 9.5. The
9.5 final limit is necessary for the treatment system to function
properly .and eliminate the metals and other contaminants to the
extent necessary and appropriate, .and is technically feasible .for
the Pond Treatment system. EPA believes tpat the slightly higher
standards will not harm aquatic habitat in the area. EPA will
continue to monitor the situation as the cleanup progresses.
5. Page 11, Contaminant Specific I.4.C. Monitoring and best
management practices required for the Warm Springs Pond Treatment
system must comply with 40 CFR S 122.44(i), which references
monitoring requirements of 40 CFR Part 136, and 40 CFR i 440.148,
which requires certain management practices, rather than
40 CFR S 440.104, which is stated in the ROD.
6. Page 11, Location Specific 11.1. Reference should be to
MCA 9 76-5-402 rather than MCA S 75-5-402.
7. Page 11, Location Specific 11.2. Reference should be to .
MCA 99 76-5-1101 and 1102, rather than MCA is 75-5-1101 and 1102.
8. Page 12 - 13, Location Specific 11.6. Reference should be to
36 CFR Part 800, rather than 40 CFR Part 800.
. .9~, Page 13, Location Specific 1.1.8. Reference shou.ld be to
40 CFR 9 6.302(h), rather than 40 CFR 9 302(h).
10. Page 15, Action Specific III.l.A. The reference should be
to 29 CFR 99 1910.120 and .132, rather than
20 CFR 99 1910.120 and .132.
11. Page 15, Action Specific III.l.C. The reference should be
to MCA 9 50-78-305, rather than MCA 9 50-78-307.
12. Page 17, Action Specif~c III.3~B. Standards for
revegetation of the disposal. area, excavated areas, and covered -
contaminated areas should not include ARM SS 26.4.727 and
26.4.729, as they were repealed prior to the ROD and ESD
signature dates.
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13. Page 18, Action Specific III.4.A. Standards for structural
integrity should reference ARM SS 16.44.701 - 703, rather than
-ARM !S 161.44.701 - .703.
14. Page 20, Action Specific III.6.C. Standards for the cap for
the disposal facility should reference portions of
ARM! 16.44.702, as it incorporates
40 CFR S 264.228(a)(2)(iii)(B), (C), and (D), rather than
40 ~FR S 264.228(b)(c)(d).
15. Page 21, Action Specific III.6.F. Waiver. The waiver
discussion uses the phrase "a waiver of this ARAR is appropriate.
. . .". That phrase is meant to waive only
.ARM S 16.14.505 ( 1 ) (c), which prohibits disposal
. wi thin the 1 00 year" flood plain. The remaining
ih III.6.F. are ARAR standards for the disposal
and are not waived.
of solid waste
provisions listed
units .~t.th~ Site
16. Page 21, Action Specific III.7. This section was
inadvertently not included in the list of ARARs which were
carried over to the ESD from the ROD. It is hereby included and
is an ARAR for ground water monitoring activities which will be
conducted as part of the Warm Springs Ponds active area
remediation.
17. Page 22, Action Specific.III.8.A.. andB. This .section .
describes monitoring and best management practices for the Pond
Treatment system. It references ARM S 26.20.904 and
40 CFR S 122.41 and 40 CFR.S 125.100. The references should be
to ARM S 16.20.1321(12)(f) and 40 CPR B 122.44(i) (for
monitoring) and ARM S 16.20.1310(15)(6) and 40 CFR B 125.102 (for
best management practices).
18. Page 22, Action Specific III.8.C. This section describes
operation and maintenance requirements for th~ Ponds Treatment
system~ . It should.reference ARMS. 16.20.633 and
MCA !! 75-6-112(2) and 75-5-605, rather than ARM! 16.20.633 and
75-6~112(2) and 75-5-605.
19.
Page.25, To Be Considered Standards (TBCs).
- Reference should be to MCA ! 85-15-210, rather than
. MCA S 85-15-310;
Reference should be to MCA ! 82-4-222, rather than
MCA S 84-4-222;
- Reference should be to ARM ! 36.14.304, in addition to
ARM S 36.14.305, which is listed twice;
- The reference to ARM ! 36.15.801 should. be deleted,
because that standard is listed as an ARAR;
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- ARM 99 26.4.307 and .309 should be deleted, as they were
repealed prior to the date of signature on the ROD and
ESD;
- MCA 9 82-14-237 does not exist, and should not be listed.
20. Page 16, Action Specific III.2. This section includes by
reference the ARARs list for the Mill-Willow Bypass removal
action, attached to Administrative Order on Consent Docket No.
CERCLA-08-90-15. That list contains the following citation
errors' (references to page numbers are to the page numbers of the
attachment to the Administrative Order):
- Page 2, Contaminant Specific 2.A.a. The reference should
. . be to ARM 9 16.8.815,rather than ARM 9 16.8.818;
- Page 3, Contaminant Specific 2.A.f. The reference should
be to ARM 9i 16.42.101 and .102, rather. than
ARM 9 16.42.101 only;
- Page 4, Location Specific .2.B. Reference should be to
16 U.S.C.9 469, rather than 42 U.S.C. 9 469;
. ,
Page 4, Location' Specific 2..C.' Refe.rence should be to
4D CFR 9 6.302(h), rather than 40 CFRPart 302;'
- Page 5, Location Specific 2.E. Reference should be to
MCA 76-5:"'101 et seq., rather than MCA 75-5-101 et sea.;
- Page .6, Action Specific 2.B.a. Reference should be to ARM
ii 16.44.701 - .703, rather than ARM is 16.44.701 - .
735;
_. Page 6, Action Specific 2.B.c.. References should be to'
30 U.S.C. ii 1201 -1328, rather than .30 U.S.C. ii 1201
- 1326; .
Page 7, General C.d. Reference should be to
, 29 CFR ii 1910.120 and 1910.132, rather than
20 CFR ii 1910.120 and 1910.132;
- Page 7, General 2.C.d. Reference should be to
MCA~ 50-78-305, rather than MCA S 50-78-307.
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III. APPROVAL
- /kŁ!/;JI ~~/ /J~
J~ES J. SCHERER tI
R~gional Administrator ..
U.S. EPA Region 8
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~-~ ~O ~.-.
DATE
6 .
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