United States 

Environmental Protection 

Agency 1200 Pennsylvania Avenue, N.W. 

Washington, D.C. 20460 

March 

2011 

Office of Solid Waste and Emergency Response 

Support Document for the 

Revised National Priorities List 

Final Rule – ACM Smelter & Refinery
Support Document for the 

Revised National Priorities List 

Final Rule 

ACM Smelter and Refinery 

March 2011 

Site Assessment and Remedy Decisions Branch 

Office of Superfund Remediation and Technology Innovation 

Office of Solid Waste and Emergency Response 

U.S. Environmental Protection Agency 

Washington, DC 20460
Table of Contents

Executive Summary ....................................................................................................................................v

Introduction................................................................................................................................................vi

Background of the NPL.........................................................................................................................vi

Development of the NPL.......................................................................................................................vii

Hazard Ranking System.......................................................................................................................vii

Other Mechanisms for Listing ............................................................................................................viii

Organization of this Document.............................................................................................................ix

Glossary ..................................................................................................................................................ix

1. List of Commenters and Correspondence ........................................................................................1

2. Site Description ...................................................................................................................................3

3. Summary of Comments......................................................................................................................4

3.1 Need for Listing...........................................................................................................................5

3.2 Purpose of NPL ...........................................................................................................................6

3.3 Impacts of Listing .......................................................................................................................7

3.4 Previous NPL Decision (Rationale for Listing) ........................................................................7

3.5 Liability........................................................................................................................................8

3.6 Risk Associated with Site............................................................................................................9

3.7 Permitted Releases and Regulatory Limits.............................................................................12

3.8 Adequacy of Site Description...................................................................................................12

3.9 Extent of Site .............................................................................................................................13

3.10 Comments on HRS....................................................................................................................14

3.11 Scoring Other Pathways...........................................................................................................15

3.12 Consideration of Response Actions / Current Conditions.....................................................16

Sources Identified at Proposal .............................................................................................................17

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

3.13 Additional Sources....................................................................................................................17

Source 4 – Slag Waste ........................................................................................................................18

3.14 Source 1......................................................................................................................................19

3.14.1 Hazardous Substances Associated with Source 1 ...............................................................19

3.14.2 Source 1 Delineation/Inference of Contamination..............................................................21

3.14.3 Sampling Procedures...........................................................................................................23

3.14.4 Other Sampling/Current Conditions ...................................................................................24

3.14.5 Source 1 Hazardous Waste Quantity...................................................................................26

3.14.6 Source 1 Containment.........................................................................................................28

3.15 Source 2......................................................................................................................................29

3.15.1 Source 2 Eligibility and Consideration of Response Activities..........................................29

3.15.2 Association of Hazardous Substances with Source 2 .........................................................32

3.15.3 Source 2 Hazardous Waste Quantity...................................................................................33

3.15.4 Source 2 Containment.........................................................................................................35

3.16 Other Possible On-site Sources................................................................................................37

Surface Water Scoring at Proposal .....................................................................................................38

3.17 Evaluation of the Surface Water Pathway..............................................................................38

3.18 Description of Pathway.............................................................................................................41

Likelihood of Release ............................................................................................................................44

3.19 Likelihood of Release - Observed Release by Direct Observation........................................44

3.19.1 Documentation of Observed Release by Direct Observation..............................................45

3.19.2 Quantity of Slag Dumped into the Missouri River .............................................................46

3.20 Surface Water Likelihood of Release - Observed Release by Chemical Analysis...............48

3.20.1 Surface Water Observed Release - Significant Increase.....................................................51

3.20.1.1 Contamination Levels below Regulatory Limits ..............................................................52

3.20.1.2 Releases in Other Aquatic Media......................................................................................53

3.20.1.3 Bias of Conclusions/Current Conditions...........................................................................54

3.20.1.4 Downstream Contaminant Levels.....................................................................................56

3.20.2 Surface Water Observed Release - Attribution...................................................................58

3.20.2.1 Attribution of Releases to On-Site Sources ......................................................................61

3.20.2.2 Other Possible Off-Site Sources........................................................................................63

3.20.2.3 Permitted Storm Water Discharges...................................................................................65

3.20.3 Surface Water Observed Release - Adequacy of Background............................................65

3.21 Potential to Release ...................................................................................................................66

Surface Water – Drinking Water Threat............................................................................................67

3.22 Surface Water - Drinking Water Threat ................................................................................67

Surface Water – Human Food Chain Threat.....................................................................................68

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

3.23 Surface Water - Human Food Chain Threat Waste Characteristics...................................69

3.23.1 Toxicity/Persistence/Bioaccumulation................................................................................69

3.23.2 Human Food Chain Threat Waste Quantity........................................................................71

3.23.3 Human Food Chain Threat Waste Characteristics..............................................................72

3.24 Surface Water - Human Food Chain Threat Targets............................................................73

3.24.1 Targets Subject to Actual Contamination ...........................................................................76

3.24.2 Consideration of Existing Fish Tissue Data........................................................................77

3.25 Surface Water - Human Food Chain Threat Total Score .....................................................79

Surface Water – Environmental Threat .............................................................................................80

3.26 Surface Water - Environmental Threat Waste Characteristics ...........................................80

3.26.1 Environmental Threat Waste Quantity................................................................................80

3.26.2 Environmental Threat Waste Characteristics......................................................................81

3.27 Surface Water - Environmental Threat Targets....................................................................82

3.27.1 Actual Contamination .........................................................................................................82

3.27.2 Aquatic Biota Targets .........................................................................................................84

3.28 Surface Water - Environmental Threat Total Score .............................................................85

3.29 Surface Water Overland/Flood Migration Component Score..............................................86

Soil Exposure.........................................................................................................................................87

3.30 Soil Exposure/Area of Observed Contamination...................................................................87

3.30.1 AOC Sampling Method ......................................................................................................87

3.30.2 Significant Increase of Hazardous Substances....................................................................90

3.30.3 AOC Delineation/Inference ................................................................................................94

3.30.4 Hazardous Substance Deposition/Attribution.....................................................................95

3.30.4.1 Aerial Deposition ..............................................................................................................95

3.30.4.2 Evaluation of Lead............................................................................................................99

3.30.5 Contamination below Cleanup Criteria.............................................................................101

3.31 Soil Exposure Pathway Waste Characteristics.....................................................................101

3.31.1 Soil Exposure Hazardous Waste Quantity ........................................................................101

3.31.1 Calculation of Soil Exposure Pathway Waste Characteristics..........................................103

3.32 Soil Exposure Targets.............................................................................................................104

3.32.1 Identification of Actually Contaminated Targets..............................................................104

3.32.2 Count of Level II Targets..................................................................................................106

3.32.3 Targets Not Scored............................................................................................................107

3.33 Soil Exposure Pathway – Resident Population Threat Total Score ...................................108

3.34 Soil Exposure Pathway – Total Score ...................................................................................109

3.35 Alternate HRS Score...............................................................................................................110

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4.0 Conclusion .........................................................................................................................................116
ACM Smelter & Refinery NPL Listing Support Document March 2011 

Executive Summary 

Section 105(a)(8)(B) of CERCLA, as amended by SARA, requires that the EPA prepare a list of national 

priorities among the known releases or threatened releases of hazardous substances, pollutants, or 

contaminants throughout the United States. An original National Priorities List (NPL) was promulgated 

on September 8, 1983 (48 FR 40658). CERCLA requires that EPA update the list at least annually. 

This document provides responses to public comments received on the ACM Smelter and Refinery site, 

proposed on March 4, 2010 (75 FR 9843). This site is being added to the NPL based on an evaluation 

under EPA’s Hazard Ranking System (HRS) in a final rule published in the Federal Register in March 

2011. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Introduction 

This document explains the rationale for adding the ACM Smelter and Refinery site in Black Eagle, 

Montana, to the National Priorities List (NPL) of uncontrolled hazardous waste sites and provides 

responses to public comments received on this site listing proposal. EPA proposed this site to the NPL on 

March 4, 2010 (75 FR 9843). This site is being added to the NPL based on an evaluation under the 

Hazard Ranking System (HRS) in a final rule published in the Federal Register in March 2011. 

Background of the NPL 

In 1980, Congress enacted the Comprehensive Environmental Response, Compensation, and Liability Act 

(CERCLA), 42 U.S.C. Sections 9601 et seq. in response to the dangers of uncontrolled hazardous waste 

sites. CERCLA was amended on October 17, 1986, by the Superfund Amendments and Reauthorization 

Act (SARA), Public Law No. 99-499, stat., 1613 et seq. To implement CERCLA, EPA promulgated the 

revised National Oil and Hazardous Substances Pollution Contingency Plan (NCP), 40 CFR Part 300, on 

July 16, 1982 (47 FR 31180), pursuant to CERCLA Section 105 and Executive Order 12316 (46 FR 

42237, August 20, 1981). The NCP, further revised by EPA on September 16, 1985 (50 FR 37624) and 

November 20, 1985 (50 FR 47912), sets forth guidelines and procedures needed to respond under 

CERCLA to releases and threatened releases of hazardous substances, pollutants, or contaminants. On 

March 8, 1990 (55 FR 8666), EPA further revised the NCP in response to SARA. 

Section 105(a)(8)(A) of CERCLA, as amended by SARA, requires that the NCP include 

criteria for determining priorities among releases or threatened releases throughout the 

United States for the purpose of taking remedial action and, to the extent practicable, take 

into account the potential urgency of such action, for the purpose of taking removal 

action. 

Removal action involves cleanup or other actions that are taken in response to emergency conditions or 

on a short-term or temporary basis (CERCLA Section 101). Remedial action is generally long-term in 

nature and involves response actions that are consistent with a permanent remedy for a release (CERCLA 

Section 101). Criteria for placing sites on the NPL, which makes them eligible for remedial actions 

financed by the Trust Fund established under CERCLA, were included in the HRS. EPA promulgated the 

HRS as Appendix A of the NCP (47 FR 31219, July 16, 1982). On December 14, 1990 (56 FR 51532), 

EPA promulgated revisions to the HRS in response to SARA, and established the effective date for the 

HRS revisions as March 15, 1991. 

Section 105(a)(8)(B) of CERCLA, as amended, requires that the statutory criteria provided by the HRS be 

used to prepare a list of national priorities among the known releases or threatened releases of hazardous 

substances, pollutants, or contaminants throughout the United States. The list, which is Appendix B of 

the NCP, is the NPL. 

An original NPL of 406 sites was promulgated on September 8, 1983 (48 FR 40658). At that time, an 

HRS score of 28.5 was established as the cutoff for listing because it yielded an initial NPL of at least 400 

sites, as suggested by CERCLA. The NPL has been expanded several times since then, most recently on 

September 29, 2010 (75 FR 59975). The Agency also has published a number of proposed rulemakings 

to add sites to the NPL. The most recent proposal was on October 21, 2010 (75 FR 64976). 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Development of the NPL 

The primary purpose of the NPL is stated in the legislative history of CERCLA (Report of the Committee 

on Environment and Public Works, Senate Report No. 96-848, 96th Cong., 2d Sess. 60 [1980]). 

The priority list serves primarily informational purposes, identifying for the States and 

the public those facilities and sites or other releases which appear to warrant remedial 

actions. Inclusion of a facility or site on the list does not in itself reflect a judgment of the 

activities of its owner or operator, it does not require those persons to undertake any 

action, nor does it assign liability to any person. Subsequent government actions will be 

necessary in order to do so, and these actions will be attended by all appropriate 

procedural safeguards. 

The NPL, therefore, is primarily an informational and management tool. The identification of a site for 

the NPL is intended primarily to guide EPA in determining which sites warrant further investigation to 

assess the nature and extent of the human health and environmental risks associated with the site and to 

determine what CERCLA-financed remedial action(s), if any, may be appropriate. The NPL also serves 

to notify the public of sites EPA believes warrant further investigation. Finally, listing a site may, to the 

extent potentially responsible parties are identifiable at the time of listing, serve as notice to such parties 

that the Agency may initiate CERCLA-financed remedial action. 

CERCLA Section 105(a)(8)(B) directs EPA to list priority sites among the known releases or threatened 

release of hazardous substances, pollutants, or contaminants, and Section 105(a)(8)(A) directs EPA to 

consider certain enumerated and other appropriate factors in doing so. Thus, as a matter of policy, EPA 

has the discretion not to use CERCLA to respond to certain types of releases. Where other authorities 

exist, placing sites on the NPL for possible remedial action under CERCLA may not be appropriate. 

Therefore, EPA has chosen not to place certain types of sites on the NPL even though CERCLA does not 

exclude such action. If, however, the Agency later determines that sites not listed as a matter of policy 

are not being properly responded to, the Agency may consider placing them on the NPL. 

Hazard Ranking System 

The HRS is the principle mechanism EPA uses to place uncontrolled waste sites on the NPL. It is a 

numerically based screening system that uses information from initial, limited investigations -- the 

preliminary assessment and site inspection -- to assess the relative potential of sites to pose a threat to 

human health or the environment. HRS scores, however, do not determine the sequence in which EPA 

funds remedial response actions, because the information collected to develop HRS scores is not 

sufficient in itself to determine either the extent of contamination or the appropriate response for a 

particular site. Moreover, the sites with the highest scores do not necessarily come to the Agency's 

attention first, so that addressing sites strictly on the basis of ranking would in some cases require 

stopping work at sites where it was already underway. Thus, EPA relies on further, more detailed studies 

in the remedial investigation/feasibility study that typically follows listing. 

The HRS uses a structured value analysis approach to scoring sites. This approach assigns numerical 

values to factors that relate to or indicate risk, based on conditions at the site. The factors are grouped 

into three categories. Each category has a maximum value. The categories are: 

• likelihood that a site has released or has the potential to release hazardous substances into the 

environment; 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

• characteristics of the waste (toxicity and waste quantity); and 

• people or sensitive environments (targets) affected by the release. 

Under the HRS, four pathways can be scored for one or more threats as identified below: 

• Ground Water Migration (Sgw) 

- drinking water 

• Surface Water Migration (Ssw) 

The following threats are evaluated for two separate migration components, overland/flood 

migration and ground water to surface water. 

- drinking water 

- human food chain 

- sensitive environments 

• Soil Exposure (Ss) 

- resident population 

- nearby population 

- sensitive environments 

• Air Migration (Sa) 

- population 

- sensitive environments 

After scores are calculated for one or more pathways according to prescribed guidelines, they are 

combined using the following root-mean-square equation to determine the overall site score (S), which 

ranges from 0 to 100: 

4

S + S + S + S = S

2

a

2

s

2

sw

2

gw

If all pathway scores are low, the HRS score is low. However, the HRS score can be relatively high even 

if only one pathway score is high. This is an important requirement for HRS scoring because some 

extremely dangerous sites pose threats through only one pathway. For example, buried leaking drums of 

hazardous substances can contaminate drinking water wells, but -- if the drums are buried deep enough 

and the substances not very volatile -- not surface water or air. 

Other Mechanisms for Listing 

There are two mechanisms other than the HRS by which sites can be placed on the NPL. The first of 

these mechanisms, authorized by the NCP at 40 CFR 300.425(c)(2), allows each State and Territory to 

designate one site as its highest priority regardless of score. The last mechanism, authorized by the NCP 

at 40 CFR 300.425(c)(3), allows listing a site if it meets the following three requirements: 

• Agency for Toxic Substances and Disease Registry (ATSDR) of the U.S. Public Health Service 

has issued a health advisory that recommends dissociation of individuals from the release; 

• EPA determines the site poses a significant threat to public health; and 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

• EPA anticipates it will be more cost-effective to use its remedial authority than to use its 

emergency removal authority to respond to the site. 

Organization of this Document 

The following section contains EPA responses to site-specific public comments received on the proposal 

of the ACM Smelter and Refinery site on March 4, 2010 (75 FR 9843). The site discussion begins with a 

list of commenters, followed by a site description, a summary of comments, and Agency responses to 

each comment. A concluding statement indicates the effect of the comments on the HRS score for the 

site. 

Glossary 

The following acronyms and abbreviations are used throughout the text: 

ACM ACM Smelter and Refinery

Agency U.S. Environmental Protection Agency 

AOC Area of observed contamination 

ARCO Atlantic Richfield Company 

ATSDR Agency for Toxic Substances and Disease Registry 

bgs Below ground surface 

BNSF Burlington Northern Santa Fe 

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act of 

1980, 42 U.S.C. Sections 9601 et seq., also known as Superfund 

CFR Code of Federal Regulations 

CLP Contract Laboratory Program 

CRDL Contract required detection limit 

CRQL Contract required quantitation limit 

EPA U.S. Environmental Protection Agency 

ESI Expanded site investigation 

FR Federal Register

GFR Great Falls Refinery 

HRS Hazard Ranking System, Appendix A of the NCP 

HRS score Overall site score calculated using the HRS; ranges from 0 to 100 

MDEQ Montana Department of Environmental Quality 

MDFWP Montana Department of Fish, Wildlife and Parks 

MDL Method detection limit 

mg/kg Milligram per kilogram 

NCP National Oil and Hazardous Substances Pollution Contingency Plan, 40 C.F.R. 

Part 300 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

 x 

NPL National Priorities List, Appendix B of the NCP 

PPE Probable point of entry 

PRP Potentially responsible party 

RCRA Resource Conservation and Recovery Act 

RI/FS Remedial investigation and feasibility study 

SARA Superfund Amendments and Reauthorization Act 

SCDM Superfund Chemical Data Matrix 

SQL Sample quantitation limit 

TAL Target analyte list 

TDL Target distance limit 
ACM Smelter & Refinery NPL Listing Support Document March 2011 

1. List of Commenters and Correspondence 

EPA-HQ-SFUND-2010-0072-0004 Correspondence, dated March 04, 2010, from Brian 

Schweitzer, Governor, State of Montana, Office of the 

Governor, letter requesting placement of the Newtown 

Creek site on the National Priorities List (NPL) 

EPA-HQ-SFUND-2010-0072-0005 Correspondence, dated April 09, 2010, from Terry Jeng, 

memorandum authorizing extension of the comment 

period without an FR Notice for EPA-HQ-SFUND2010-0072 

EPA-HQ-SFUND-2010-0072-0006 Comment, dated April 12, 2010, from William Duffy, 

Davis Graham & Stubbs LLP on behalf of Atlantic 

Richfield Company, re: Extension Request 

EPA-HQ-SFUND-2010-0072-0007 Comment, dated April 12, 2010, from Douglas Ammon 

OSWER, USEPA, re: Response to Extension Request 

EPA-HQ-SFUND-2010-0072-0008 Comment, dated April 23, 2010, from Gwenette R. 

Christiansen, NPL Coordinator, Site Assessment and 

Brownfields Program, Region 8, USEPA, re: ACM 

Smelter and Refinery Information Request 

EPA-HQ-SFUND-2010-0072-0009 Comment, dated May 11, 2010, from S. Peck, Public 

Commenter 

EPA-HQ-SFUND-2010-0072-0010 Comment, dated May 11, 2010, from Graham and Maria 

Taylor, Public Commenter’s 

EPA-HQ-SFUND-2010-0072-0011 Comment, dated May 14, 2010, from Andrew Finch, 

Senior Planner on behalf of Gregory T. Doyon, City 

Manager, City of Great Falls, Montana 

EPA-HQ-SFUND-2010-0072-0011.1 Comment attachment, dated May 14, 2010, from 

Andrew Finch, Senior Planner on behalf of Gregory T. 

Doyon, City Manager, City of Great Falls, Montana 

EPA-HQ-SFUND-2010-0072-0012 Comment, dated May 14, 2010, from Phil Partain, Public 

Commenter 

EPA-HQ-SFUND-2010-0072-0013 Comment, dated May 14, 2010, from Stuart Lewin, 

Member of Board of Directors, Missouri River Citizens, 

Inc. 

EPA-HQ-SFUND-2010-0072-0013.1 Comment attachment, dated May 14, 2010, from Stuart 

Lewin, Member of Board of Directors, Missouri River 

Citizens, Inc. 

EPA-HQ-SFUND-2010-0072-0013.2 Comment attachment, dated May 14, 2010, from Stuart 

Lewin, Member of Board of Directors, Missouri River 

Citizens, Inc. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

EPA-HQ-SFUND-2010-0072-0013.3 Comment attachment, dated May 14, 2010, from Stuart 

Lewin, Member of Board of Directors, Missouri River 

Citizens, Inc. 

EPA-HQ-SFUND-2010-0072-0014 Comment, dated May 14, 2010, from Gerry and Chuck 

Jennings, Public Commenter’s 

EPA-HQ-SFUND-2010-0072-0015 Comment, dated May 17, 2010, from Stuart Lewin, 

Member of Board of Directors, Missouri River Citizens, 

Inc. 

EPA-HQ-SFUND-2010-0072-0015.1 Comment attachment, dated May 17, 2010, from Stuart 

Lewin, Member of Board of Directors, Missouri River 

Citizens, Inc. 

EPA-HQ-SFUND-2010-0072-0015.2 Comment attachment, dated May 17, 2010, from Stuart 

Lewin, Member of Board of Directors, Missouri River 

Citizens, Inc. 

EPA-HQ-SFUND-2010-0072-0015.3 Comment attachment, dated May 17, 2010, from Stuart 

Lewin, Member of Board of Directors, Missouri River 

Citizens, Inc. 

EPA-HQ-SFUND-2010-0072-0016 Comment, dated May 18, 2010, from Robin Bullock, BP 

Remediation Management, Atlantic Richfield Company 

(Atlantic Richfield) 

EPA-HQ-SFUND-2010-0072-0016.1 Comment attachment, dated May 18, 2010, from Robin 

Bullock, BP Remediation Management, Atlantic 

Richfield Company (Atlantic Richfield) 

EPA-HQ-SFUND-2010-0072-0016.2 Comment attachment, dated May 18, 2010, from Robin 

Bullock, BP Remediation Management, Atlantic 

Richfield Company (Atlantic Richfield) 

EPA-HQ-SFUND-2010-0072-0016.3 Comment attachment, dated May 18, 2010, from Robin 

Bullock, BP Remediation Management, Atlantic 

Richfield Company (Atlantic Richfield) 

EPA-HQ-SFUND-2010-0072-0016.4 Comment attachment, dated May 18, 2010, from Robin 

Bullock, BP Remediation Management, Atlantic 

Richfield Company (Atlantic Richfield) 

EPA-HQ-SFUND-2010-0072-0017 Comment, dated May 21, 2010, from Jack Gannon, 

Public Commenter 

EPA-HQ-SFUND-2010-0072-0017.1 Comment attachment, dated May 21, 2010, from Jack 

Gannon, Public Commenter 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

2. Site Description 

The ACM Smelter and Refinery (ACM) site, situated in the vicinity of Black Eagle and Great Falls area 

of the State of Montana, consists of sources contaminated with metals, an observed release of metals to 

the Missouri River affecting fisheries and sensitive environments, and metals-contaminated soil located 

on residential property. 

In 1893, the Boston and Montana Consolidated Copper and Silver Mining Company built a smelter 

adjoining the Missouri River to treat and process ore mostly generated from mines in Butte, Montana. 

The Missouri River was used to generate electricity for an electrolytic refining process. By 1980, all 

process operations at the facility ceased and demolition of the facility structures took place from 1980 

through 1986. Other closure activities continued through 1999, including: basement substructure 

backfilling; salvaging; on-site burial of flue dust, granulated slag, asbestos-containing material, 

demolition debris, and other wastes; and covering of wastes with soil. Other reclamation activities 

followed, and maintenance of reclaimed areas continues at present. 

As a result of various operations at the facility, large quantities of granulated slag and tailings were 

documented as dumped into the Missouri River. The Montana Department of Environmental Quality 

estimated that millions of cubic yards of waste were dumped into the Missouri River between 1893 and 

1915, and that dumping of waste into the Missouri River continued at a reduced rate after 1915 until the 

facility closed. 

An operating smoke stack for the plant, known as "the Big Stack," was built to a total length of 506 feet 

and operated from 1909 through 1972. The wind in the Great Falls area primarily blows from the 

southwest to the east-northeast, although it is documented to blow from the northeast or east toward Black 

Eagle more than 20 percent of the time. The Big Stack was designed to eject a volume of 1,575,000 cubic 

feet of air per minute at a velocity of 450 feet per minute, and metals are documented to have been 

associated with the air emissions. An internal Anaconda Copper Mining Company memorandum from 

1951 stated that approximately 15.04 pounds of arsenic passed out of the stack every 24 hours. 

The EPA conducted an Expanded Site Inspection of the ACM Smelter and Refinery facility in April 2003 

which found elevated concentrations of arsenic, cadmium, copper, lead, manganese, mercury, silver, and 

zinc in sediment or soil samples. A 2007 Site Assessment and 2008 Expanded Site Inspection of the 

residential soils in the community of Black Eagle, adjacent to the west of the site, identified a large area 

of elevated concentrations of arsenic, cadmium, and lead in the residential soils. 

The EPA also conducted an Expanded Site Inspection of the sediments in the Missouri River adjacent to 

and downstream of the ACM Smelter and Refinery property in July 2009. This investigation identified a 

stream segment with elevated concentrations of cadmium, copper, lead, and zinc, as compared to 

background. This segment of the Missouri River includes widely used fishing areas, along with a number 

of wetland areas. 

An observed release by chemical analysis and an observed release by direct observation to the surface 

water pathway were established in the HRS documentation record at proposal. The observed release by 

chemical analysis included sediment samples adjacent to and downstream of the ACM property that 

contained levels of cadmium and/or lead at levels greater than three times over the respective background 

levels. For the observed release by direct observation, the direct disposal of slag and tailings from the 

facility into the Missouri River was established. A fishery subject to actual contamination from the site 

was established and is documented to be fished for human consumption. In addition, greater than 0.1 

miles of wetland frontage was identified along the Missouri River within the area encompassed by the 

observed release. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

For the soil exposure pathway, an area of observed contamination was scored, encompassing soil 

contaminated with metals at levels 3 times or greater above background. The HRS documentation record 

at proposal counted 8 samples associated with residential properties subject to Level I soil contamination 

and 178 residences as subject to Level II contamination within the area of observed contamination 

attributable to the ACM site. 

3. Summary of Comments 

Several public commenters submitted comments regarding the proposed NPL listing of the ACM Smelter 

and Refinery site (hereinafter referred to as ACM site). Most of the commenters indicated unconditional 

support for the NPL designation. Atlantic Richfield Company (herein referred to as ARCO) submitted 

extensive technical and policy comments, summarized below. 

ARCO asserted that NPL listing of the ACM site is not necessary for several reasons. ARCO asserted 

that further response actions at the site should be completed using the “proven and expeditious model of 

company-Agency cooperation,” rather than utilizing the Superfund process and that listing the ACM site 

would have unnecessary negative impacts. It asserted that listing the site would slow the pace of further 

cleanup efforts and would consume federal and State resources. It contended that areas identified at the 

site have been reclaimed or are subject to ongoing operation and maintenance activities. 

ARCO asserted that the site does not pose an unacceptable risk to human health and the environment, and 

that releases to the surface water migration pathway and the contaminants associated with the soil 

exposure pathway are within applicable regulatory or otherwise acceptable limits. ARCO asserted that 

conditions within both the community of Black Eagle, and the Missouri River have been thoroughly 

investigated by EPA, the Montana Department of Environmental Quality (MDEQ), and ARCO and that 

the HRS does not reflect the presence of unacceptable risk. 

ARCO submitted extensive comments challenging the scoring of the soil exposure pathway and the 

establishment of the area of observed contamination (AOC) in the Black Eagle community. ARCO stated 

that the residential properties sampled by EPA incorrectly included multiple residences that did not have 

concentrations of hazardous substances at concentrations greater than three times background 

concentrations. Thus, ARCO alleged, both the hazardous waste quantity and the number of affected 

targets in the soil exposure pathway scoring were exaggerated, resulting in an inflated scoring of the 

pathway. Challenging the attribution of the hazardous substances detected in the AOC, ARCO asserted 

that the substances found in Black Eagle residential soils are not necessarily the result of emissions from 

the smelter facility and that lead contamination of residential properties could be the result of 

deteriorating lead-based paint, other consumer products, or from other possible off-site sources. 

Additionally, ARCO commented that the HRS scoring of the surface water migration pathway was 

incorrect – challenging the establishment of the observed release by direct observation and the observed 

release by chemical analysis. 

ARCO argued that the evaluation of the observed release by direct observation does not identify a source 

material for the slag in the Missouri River and that the documentation of the disposal of slag into the 

Missouri River was inadequate. Regarding the observed release by chemical analysis, ARCO stated that 

the comparison of upstream background samples to downstream release samples was flawed due to the 

locations of probable points of entry to the Missouri River from site sources, and a lack of consideration 

of other off-site contributors of contamination to the river. Further, ARCO asserted that other studies 

show that sediment, surface water, and fish tissues in the Missouri River were generally comparable to 

upstream background concentrations. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

ARCO disputed the scoring of actually contaminated targets in the human food chain threat and the 

environmental threats of the surface water migration pathway scoring on the basis that no observed 

release was established to the Missouri River. It stated that both human food chain threat targets and 

environmental threat targets could not be evaluated as subject to Level II contamination and that only 

targets subject to potential contamination should have been scored. 

3.1 Need for Listing 

Comment: Atlantic Richfield Company (ARCO) challenged whether NPL listing of the ACM Smelter & 

Refinery site (hereinafter, ACM site) is necessary to protect the Black Eagle community or the 

environment. 

ARCO asserted that further response actions at the site should be completed using the “proven and 

expeditious model of company-Agency cooperation,” rather than utilizing the Superfund process. ARCO 

stated: 

Listing the Site at this juncture will only serve to slow the pace of further cleanup efforts 

(if needed) and will consume federal and State resources that could better be directed to 

sites that pose greater risks to human health and the environment. 

ARCO asserted that it has successfully worked with EPA and the State of Montana to address potential 

risks that may reasonably be traced to the former facility operations, and that it is committed to 

completing appropriate further response actions. ARCO highlighted the previous cleanup work it had 

completed and contended that additional cleanup can and should be completed without NPL listing. 

ARCO stated that it has committed to continue site-related investigation and reclamation activities and 

has offered to work with the appropriate agencies to determine what remedial actions, if any, are 

appropriate to reduce unacceptable risk. ARCO continued that agency cooperation with ARCO will more 

effectively utilize resources and result in a more efficient investigation and remediation process. 

Furthermore, ARCO asserted that based on the available data, existing institutional controls that are in 

place, prior EPA findings, and ARCO’s commitment to perform future work at the former refinery 

operations, NPL designation is not warranted. 

Response: The ACM Smelter & Refinery site qualifies for listing on the NPL. This site has received an 

HRS score of greater than 28.50 and has met all CERCLA and NCP listing criteria. Furthermore, the 

State concurred with the listing, citing the long-term risk to the health of Montanans in the area as a result 

of the site. 

That the commenter asserted it is committed to completing response actions at the site outside of NPL 

listing does not prohibit or encumber listing the site on the NPL. The willingness of a potentially 

responsible party (PRP) to complete various response or investigation activities at a site is not a factor 

considered under the HRS. However, PRPs may affect remedy selection, as can any other member of the 

public, through the public comment process during rulemaking. PRPs may undertake the RI/FS and/or 

remedial design/remedial action stages under EPA supervision and pursuant to appropriate agreements 

with governmental authorities (under enforcement authorities of CERCLA or those of other statutes). 

The listing process does not preclude PRPs from entering into these agreements. 

This comment has no effect on the site score or the decision to place the site on the NPL. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

3.2 Purpose of NPL 

Comment: ARCO stated that the intended use of the NPL is not properly applied to the ACM site. 

ARCO stated: 

The NPL is reserved for the worst sites, where the available data supports the Agency's 

belief that there is a potential risk to human health or the environment. . . .NPL 

designation provides a mechanism to direct federal funding to site investigations and 

studies to investigate and assess site conditions and determine whether unacceptable risk 

is present under the procedures set forth in the National Contingency Plan ("NCP"), 40 

CFR Part 300. 

ARCO asserted that there is no risk to human health or the environment at this site to support NPL 

designation as conditions at the “Former GFR Site” [former Great Falls Refinery facility property], Black 

Eagle, and the Missouri River have been thoroughly investigated by EPA, MDEQ, and ARCO. 

ARCO contended that NPL designation is most appropriate at “orphan” sites, where, it stated: 

...the parties that caused the contamination are bankrupt or otherwise unable to perform 

the work, or at those sites where the responsible parties are solvent, but recalcitrant and 

unwilling to investigate or remediate the site. In those cases, EPA may utilize NPL 

listing to obtain federal funding to address contamination. The Former GFR Site is not 

an "orphan" site as Atlantic Richfield and other viable entities have voluntarily financed 

and performed investigations and reclamation to date. 

ARCO asserted that EPA is not obligated to list all potential NPL sites. It stated that an HRS score above 

28.5 only indicates that there is a potential risk to public health or the environment that merits further 

investigation, and that EPA has the authority to require further investigations and cleanup without NPL 

designation. 

Response: Listing the ACM Smelter & Refinery site on the NPL is consistent with the purpose of the 

NPL. 

The primary purpose of the NPL is stated in the legislative history of CERCLA (Report of the Committee 

on Environment and Public Works, Senate Report No. 96-848, 96th Cong., 2d Sess. 60 [1980]), as 

follows: 

The priority list serves primarily informational purposes, identifying for the States and

the public those facilities and sites or other releases which appear to warrant remedial 

actions. Inclusion of a facility or site on the list does not in itself reflect a judgment of 

the activities of its owner or operator, it does not require those persons to undertake any 

action, nor does it assign liability to any person. Subsequent government actions will be

necessary in order to do so, and these actions will be attended by all appropriate 

procedural safeguards. 

Thus, the identification of a site for the NPL is intended primarily to guide EPA in determining which 

sites warrant further investigation to assess the nature and extent of the human health and environmental 

risks associated with the site, and to determine what CERCLA-financed remedial action(s), if any, may be 

appropriate. The NPL also serves to notify the public of sites that warrant further investigation. 

Listing a site may, to the extent PRPs are identifiable at the time of listing, serve as notice to such parties 

that the Agency may initiate CERCLA-financed remedial action. However, CERCLA contains no 

restriction that limits its application to orphan sites or insolvent or recalcitrant parties. Therefore, whether 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

or not a site is associated with a PRP that is able to perform investigative or remedial work at the site has 

no bearing on the eligibility of a site for the NPL. 

This comment has no effect on the site score or on the decision to place the site on the NPL. 

3.3 Impacts of Listing 

Comment: ARCO contended that listing the ACM site would have unnecessary negative impacts. 

ARCO asserted that listing the site would slow the pace of further cleanup efforts and would consume 

federal and State resources, which it stated “could better be directed to sites that pose greater risks to 

human health and the environment.” 

ARCO asserted that NPL listing would last for many years and that developers and prospective future 

purchasers of the many private properties encompassed by the site as proposed would “look elsewhere for 

economic development opportunities.” 

Response: Potential negative impacts such as those raised by the commenter are not considered in the 

assessment of whether a site belongs on the NPL. Inclusion of a site or facility on the list does not in 

itself reflect a judgment on the activities of the owner(s) or operator(s), but rather reflects the Agency’s 

judgment that a significant release or threat of release has occurred and that the site is a priority for 

further investigation under CERCLA. 

The Agency notes that there are both costs and benefits that can be associated with listing a site. Among 

the benefits associated with listing a site on the NPL are increased health and environmental protection as 

a result of increased public awareness of potential hazards. In addition to the potential for federally 

financed remedial actions, the addition of a site to the NPL could accelerate privately financed, voluntary 

cleanup efforts. Listing sites as national priority sites also may give States increased support for funding 

responses at particular sites. As a result of the additional CERCLA remedies, there will be lower human 

exposure to high-risk chemicals and higher quality surface water, ground water, soil, and air. 

Therefore, it is possible that any perceived or actual negative fluctuations in property values or 

development opportunities that may result from contamination may be countered by positive fluctuations 

when a CERCLA investigation and any necessary cleanup are completed. 

Further, NPL listing does not necessarily hinder further cleanup efforts at a site, as discussed in Section 

3.1, Need for Listing, of this support document. PRPs may undertake the RI/FS and/or remedial actions 

at a site, which is not precluded by placing a site on the NPL. Results of work undertaken will be taken 

into account during the evaluation of the need for remedial actions at the site. 

3.4 Previous NPL Decision (Rationale for Listing) 

Comment: In challenging the proposal to list the ACM site, ARCO commented that EPA had initially 

scored the “Former GFR Site” [former Great Falls Refinery facility property] in 1982 and did not 

calculate an HRS score greater than 28.50. ARCO asserted that: 

the potential contribution of the multitude of sources that release contaminants to surface 

waters tributary to the Missouri River in the Great Falls area was a factor in EPA's 

decision not to propose NPL designation in 1983. See Action Memorandum dated 

September 2, 1983 (This site is not on the National Priorities List (NPL). It did not score 

above 28.5 on the NPL because its location is downstream of a major metropolitan area). 

(AR Reference #42) 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Response: A previous EPA decision regarding the “GFR” site based on the information available at the 

time and using the original HRS evaluation process does not mean that the present ACM site does not 

warrant listing based on more recent information and on the present HRS which was revised in 1990. 

That the site was evaluated by EPA as not qualifying for the NPL based on the original HRS, is not 

relevant to the listing decision for three reasons. First, the site previously evaluated is not necessarily the 

same site as evaluated at this proposal. The extent of the ACM Smelter & Refinery site at this proposal is 

not the same as the “site” evaluated under the 1982 evaluation described by the commenter. The site at 

this proposal includes sources and releases of hazardous substances to the Missouri River, and an area of 

observed contamination in the Black Eagle residential area, that was not included in the previous 

evaluation. 

Second, a significant amount of information has been obtained at the site at this proposal since the 

previous NPL decision regarding the ACM site. This information has further contributed to the 

understanding of the nature and extent of the site. Information used in the scoring of the ACM site has 

been gathered after 1982 (including but not limited to a 2003 Expanded Site Inspection, a 2007 Site 

Assessment and 2008 Expanded Site Inspection of residential soils in Black Eagle, and a 2009 Expanded 

Site Inspection of Missouri River sediments adjacent to and downstream of the site). 

Third, the 1982 HRS evaluation of the site was developed under a prior version of the HRS. The HRS as 

revised in December of 1990 (55 FR 51532), included several modifications. Notably in this case, the 

soil exposure pathway was added to the revised HRS, which was not accounted for under the original 

HRS, and has been scored in this HRS evaluation. Also, significant changes to the evaluation of releases 

or threatened releases to surface water were included in the revised HRS, such as the evaluation of threats 

to human health via the aquatic food chain (human food chain threat), and the evaluation of actually 

contaminated fisheries and the associated use of bioaccumulation potential factor values. In establishing 

an observed release by chemical analysis, the revised HRS included wording allowing for partial 

attribution of the significant increase of an observed release, which was not considered in the original 

HRS. 

Therefore, a previous decision on the eligibility of this site to be placed on the NPL does not discredit 

current HRS evaluation and scoring. This comment has no effect on the HRS site score or on the decision 

to place the site on the NPL. 

3.5 Liability 

Comment: ARCO stated that other sources, facilities, and private parties within the Great Falls area are 

liable for contamination at the ACM site. ARCO commented that other sources are implicated and 

discussed in the HRS documentation record and that 

a broad site description advanced by the EPA in the HRS Record generally attributes 

contamination in soils, sediment, and surface water to the Former GFR Site and fails to 

describe other potential sources of contamination located both upstream and downstream 

of the site. Numerous industrial facilities operated in the greater Great Falls area over the 

past century, each a potential source of air emissions and water discharges that could 

impact soils, surface water and sediments in the Missouri River. 

ARCO asserted that all of the private parties that contributed contamination to the region share 

responsibility for cleanup. ARCO noted that Burlington Northern Santa Fe (BNSF), formerly Great 

Northern Railway, was involved in operations at the former refinery at the site starting in the late 1800s, 

and that BNSF owns track that served the refinery. ARCO contended that PPL Montana owns and 

operates hydroelectric facilities on the Missouri River in the Great Falls area “which have influenced the 

distribution of potentially contaminated sediments,” and that Northwestern Energy and Pacific Steel and 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Recycling each owns land included in the site description of the HRS documentation record at proposal. 

Further, ARCO stated that “numerous other industrial and commercial operators, such as Montana 

Refining Company, a documented source of metals and arsenic in air emissions,” are contributors of 

contaminants to soil, water, and sediment. 

ARCO asserted that the City of Great Falls and Cascade County are also liable for contamination. ARCO 

commented that storm sewer systems that carry urban runoff from Great Falls and Black Eagle empty into 

the Missouri River. ARCO stated that: 

Cascade County, as the owner of the former Montana Silver Smelter property, owns 

lands that are known to be contaminated and a contributing source to the Missouri River. 

. . . This smelter could have impacted soils in Black Eagle, as well as river sediments, 

during its period of operation in the late 1800's and during the century that followed when 

the site was left unattended. 

Further, ARCO stated that as an owner, the State of Montana shares responsibility for any contamination 

found in the Missouri River, and that 

for more than a century, the State encouraged and profited from businesses, including the 

historic smelter operators, that utilized the Missouri River for waste disposal. As a result, 

the State shares responsibility for any investigation and cleanup of river sediments, 

including a substantial share of the orphan costs. 

Response: Liability is not considered in evaluating a site under the HRS. EPA neither confirms nor 

denies the accuracy of the commenter’s statements as to who was liable for the contamination at and 

released from this site. The NPL serves primarily as an informational tool for use by the Agency in 

identifying those sites that appear to present a significant risk to public health or the environment. It does 

not reflect a judgment on the activities of the owner(s) or operator(s) of a site. It does not require those 

persons to undertake any action, nor does it assign any liability to any person. This position, stated in the 

legislative history of CERCLA, has been explained more fully in the Federal Register (48 FR 40759, 

September 8, 1983 and 53 FR 23988, June 24, 1988). See Kent County v. EPA, 963 F.2d 391 (D.C. Cir. 

1992). 

3.6 Risk Associated with Site 

Comment: ARCO asserted that the ACM site, as proposed, does not pose an unacceptable risk to 

human health and the environment. 

ARCO stated that the completed mitigation measures at the “Former GFR Site,” such as the completion 

of demolition and removal actions, containment of remaining site-related debris, and improvement of 

storm water runoff structures have reduced the potential for transport of residual metals from the “Former 

GFR Site” to surface water and groundwater, and have resulted in no complete exposure pathways at the 

“Former GFR Site.” ARCO stated that EPA has not provided documentation that the community of 

Black Eagle, or fisheries and sensitive environments of the Missouri River have been negatively 

impacted. 

ARCO stated that under the Superfund program, no further action is generally granted at sites where 

contaminant concentrations fall below “screening levels,” and that these screening levels for contaminants 

in the Black Eagle residential soils are generally not exceeded. ARCO asserted that concentrations of 

arsenic, cadmium, and lead in the Black Eagle residential soils are generally below established screening 

criteria or levels to be protective of human health. Specifically, ARCO stated that: 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

None of the arsenic concentrations exceed a safe level established by EPA for Anaconda, 

Montana, a nearby similar site. Only one of the cadmium concentrations exceeds EPA's 

conservative soil screening level for cadmium. Eleven of the lead concentrations exceed 

EPA's conservative soil screening level for lead, but the pattern shown in the data is 

consistent with lead paint deterioration. These soil screening levels are considered by 

EPA to be protective of humans (including sensitive populations) over a lifetime. Further, 

many of these exceedances occur in subsurface soils where regular exposure to humans 

would not occur. 

ARCO stated that the quality of the Missouri River adjacent to the site is not significantly impacted by 

releases of hazardous substances; that fisheries at the site do not pose a risk to human health; and, that 

there are no obvious increases of hazardous substances in fish tissues from the site. ARCO claimed that 

results from the Parametrix1

 investigation show concentrations of chemicals in sediment, surface water, 

and fish tissue are generally comparable to background, and that an EPA toxicologist determined that the 

risks from these media would be minimal. ARCO stated that EPA and the State reviewed the findings of 

the Parametrix report and concluded that existing conditions in the river did not pose a threat, or require 

remediation to protect aquatic life or human health. 

Further, ARCO asserted that the risks associated with soil exposure at residential properties of Black 

Eagle are not expected to be significant. ARCO stated that the soil contaminant concentrations of these 

residences are sporadic and non-uniform, and that many of the higher concentrations are found at depths 

below the surface, where ARCO asserted, “ongoing, chronic exposures by residents are likely to be 

limited.” 

ARCO stated that the NPL is reserved for the worst sites, “where the available data supports the Agency's 

belief that there is a potential risk to human health or the environment.” ARCO stated that NPL 

designation: 

provides a mechanism to direct federal funding to site investigations and studies to 

investigate and assess site conditions and determine whether unacceptable risk is present 

under the procedures set forth in the National Contingency Plan ("NCP"), 40 CFR Part 

300. 

ARCO asserted that the circumstances cited above are not present to support NPL designation of the site. 

It stated that conditions at the site have been thoroughly investigated and that risks from the “Former GFR 

Site” itself are expected to be negligible due to measures that have been undertaken to prevent contact 

with site-related contaminants within the boundaries of the “Former GFR Site.” ARCO stated that EPA 

ignored relevant risk-assessment work from other related NPL sites that could provide context for the 

evaluation of risk at the ACM Smelter & Refinery Site. 

Response: The HRS is a numerically-based screening tool that the Agency uses to assess the relative 

degree of risk to human health and the environment posed by a site compared to other sites subject to 

review. The HRS score is used to determine whether a site is eligible for placement on the NPL. The 

NPL is intended primarily to guide EPA in determining which sites warrant further investigation to assess 

the nature and extent of public health and environmental risks associated with a release of hazardous 

substances, pollutants or contaminants. See 75 FR 9844 (Proposed Rule, ACM Smelter and Refinery Site, 

March 4, 2010); see also 55 FR 51532 (Final Rule, Hazard Ranking System, December 14, 1990). 

 

1

 The Parametrix investigation, as discussed throughout this support document, was a 2004 investigation performed 

by Parametrix for ARCO to assess the Missouri River in the proximity of the former ACM facility to determine 

whether sediment, surface water, and/or fish tissue may have been negatively impacted by the former smelter 

operations at the site. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

CERCLA § 105(a)(8)(a) requires EPA to determine NPL priorities based on the “relative risk or danger to 

public health or welfare, or the environment.” The criteria EPA applies to determine this relative risk or 

danger is codified in the HRS, and is the Agency’s primary tool for deriving a site score based on the 

factors identified in CERCLA. In this case, the HRS evaluation and score above 28.50 represents EPA’s 

determination that the site may pose a relative risk or danger to human health and the environment and 

warrants further investigation under CERCLA. 

In the preamble to the HRS, EPA stated: 

The Agency stresses that the limited data generated at the SI stage are designed to 

support site screening, and are not intended to provide support for a quantitative risk 

assessment (55 FR 51541, December 14, 1990). 

EPA performs a comprehensive risk assessment for the site as part of further investigations that typically 

follow listing. The results of risk assessment activities will be considered during the evaluation of the 

need for remedial actions at the site. At that time, EPA will consider relevant information provided by 

ARCO. 

The Parametrix investigation of the surface water, sediment, and fish tissue of the Missouri River and 

subsequent review thereof by an EPA ecotoxicologist, does not establish that the contamination in the 

Missouri River adjacent to the site poses no risk. In reviewing the Parametrix investigation, the EPA 

ecotoxicologist concluded that metals results in surface water or sediment generally did not exceed 

applicable media-specific benchmark criteria2

. (As explained in section 3.7, Permitted Releases and 

Regulatory Limits, of this support document, whether or not a releases is within applicable regulatory or 

otherwise acceptable limits does not eliminate those hazardous substances or their releases from 

consideration when evaluating a site using the HRS.) In noting the locations of sediment water quality 

exceedances, the ecotoxicologist stated, however, that “[m]etals concentrations in the other two north 

shore sediment locations. . . were much higher than any others perhaps indicating a pattern of 

contamination emanating from the site downstream.” Thus, in analyzing the sediment data from the 

Parametrix investigation, the EPA ecotoxicologist identified that sediment samples taken from closer to 

the north side of the Missouri River (closer to the ACM facility) were contaminated at higher levels than 

other locations. This analysis by the EPA toxicologist calls into question the comprehensiveness of the 

Parametrix investigation, and conclusions about site risk from the Parametrix investigation is therefore 

inherently limited. 

Furthermore, ARCO has not shown that reclamation activities or other measures have mitigated all risk at 

the site. ARCO has not demonstrated that measures taken at the “Former GFR Site,” such as the 

completion of demolition and removal actions, capping activities, and construction of storm water runoff 

structures have eliminated the risk to human health or the environment. Refer to section 3.12, 

Consideration of Response Actions / Current Conditions, of this support document for further discussion 

on the topic of consideration of reclamation activities at the site. 

 

2

 In reviewing the Parametrix investigation, EPA Ecotoxicologist Dale J. Huff concluded that “[n]one of the 

concentrations of metals/metalloids in surface water samples taken from this sampling event exceed National 

Ambient Water Quality Criteria,” and that with the exception of a few sample locations for bulk sediment metal 

concentrations “none of the metals exceed conservative ecotoxicological benchmark screening values . . . . for Cd, 

Cu, Pb and Zn,” See Reference 20 of the HRS documentation record at proposal. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

3.7 Permitted Releases and Regulatory Limits 

Comment: ARCO asserted that the releases to the surface water migration pathway, and the contaminants 

associated with the soil exposure pathway as presented in the HRS documentation record at proposal, are 

within applicable regulatory or otherwise acceptable limits. 

ARCO stated that surface water discharge into the Missouri River from the site is permitted at two 

discharge locations. It stated that EPA’s toxicologist concluded that “none of the water quality data 

exceeded applicable National Ambient Water Quality Criteria,” and that “metals concentrations in fish 

tissue are substantially less than concentrations anticipated to impact survival, growth or fish 

reproduction.” 

Response: That releases to the surface water migration pathway, or contaminant levels associated with 

the soil exposure pathway are within applicable regulatory or otherwise acceptable limits does not 

eliminate those hazardous substances or their releases from consideration when evaluating a site using the 

HRS. 

CERCLA Section 105(a)(8)(B) directs EPA to list on the NPL “releases” of hazardous substances, 

pollutants, and contaminants according to specific criteria set out in CERCLA Section 105(a)(8)(A). The 

definition of “release” in CERCLA Section 101(22) exempts certain releases from its scope, but it does 

not exempt releases below regulatory limits. CERCLA exempts Federally-permitted releases only from 

the notification (Section 103(a)) and cost-recovery (107(j)) sections of the statute); such releases remain 

subject to the listing requirements set out in CERCLA section 105. 

As the Agency explained regarding observed releases specifically, on July 16, 1982, when responding to 

public comments on the proposed (original) HRS (47 FR 31188), and again on September 8, 1983 (48 FR 

40665), the idea that releases within regulatory limits should not be considered “observed releases” 

specifically, and not used in general in scoring a site, was rejected. As the Agency noted in 1982: 

[e]mission or effluent limits do not necessarily represent levels which cause no harm to 

public health or the environment. These limitations are frequently established on the 

basis of economic impacts or achievability. 

The relative hazard of the site is approximated by the total HRS score, which incorporates the observed 

release factors with other factors such as waste characteristics (including waste quantity, toxicity, and 

persistence) and targets. This total HRS score reflects the hazard of the site relative only to the other sites 

that have been scored. The actual degree of contamination and its effects are more fully determined 

during the Remedial Investigation. Refer to section 3.6, Risk Associated with the Site, for further 

discussion on the evaluation of risk. 

3.8 Adequacy of Site Description 

Comment: ARCO challenged the description of the site as presented in the HRS documentation record at 

proposal. It asserted that EPA arbitrarily selected non-representative data to score and bias the HRS 

evaluation of the site. 

ARCO asserted that “selective use of data” and the “arbitrary exclusion of relevant information” 

regarding site activities is evident throughout the HRS evaluation of the site. ARCO stated that EPA 

ignored reports of reclamation activities and other investigations, and incorrectly represented the “former 

Great Falls Refinery operations” as the significant source of hazardous substances contributing to soil, 

water, and sediment impacts over a broad area. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Response: The description of the site presented in the HRS documentation record at proposal was 

sufficient to allow the public to review the HRS evaluation of the site. The purpose of the site description 

is to inform the public of information that is relevant to the sources, releases, and targets used in the site 

evaluation. Any information gaps or incorrect statements pointed out by the public during the comment 

period are addressed in this support document and the HRS documentation package has been revised 

accordingly and made available to the public at promulgation of the site. 

The Site History and Description on pages 12 through 14 of the HRS documentation record at proposal 

presents information pertinent for the reader’s general comprehension of the site, including description of 

investigations that have taken place at the site. The commenter is incorrect in its assertion that EPA 

arbitrarily excluded relevant information in describing the site, as significant information regarding the 

site has been obtained from various studies and appropriately presented within the HRS documentation 

record at promulgation to support the HRS score for the site. Sections 3.13 through 3.31 of this support 

document discuss in detail any and all scoring modifications of the HRS evaluation of this site, and 

section 3.35, Alternate HRS Score, of this support document presents the revised scoring scenario of the 

HRS documentation record at promulgation. 

3.9 Extent of Site 

Comment: ARCO challenged the extent of the ACM site as established in the HRS documentation record 

at proposal, questioning whether the soil contamination and surface water contamination was a result of 

releases from this site. ARCO referred to the site name as the “Former Great Falls Refinery” (GFR) site. 

ARCO argued that the soil contamination detected in the Black Eagle residential area is not part of the 

site and that the contamination in the residential properties was not part of the “Former GFR site,” nor 

was the contamination caused by the former operations at the site. Also, ARCO contended that the 

contaminated residential properties do not contribute to surface water releases associated with the site. 

Furthermore, ARCO argued that the extent of the area of observed contamination (AOC) was much 

smaller in size than established in the HRS documentation record at proposal. 

Response: The ACM Smelter & Refinery site, as established at promulgation, consists of sources and 

areas that have become contaminated due to releases from the site sources. 

The full extent of the ACM Smelter & Refinery site is not conclusively determined upon NPL listing. 

Placing a site on the NPL is based on an evaluation, in accordance with the HRS, of a release or 

threatened release of hazardous substances, pollutants, or contaminants. However, the fact that EPA 

initially identifies and lists the release based on a review of contamination at a certain parcel of property 

does not necessarily mean that the site boundaries are limited to that parcel. 

CERCLA Section 105(a)(8)(A) requires EPA to list national priorities among the known "releases or 

threatened releases" of hazardous substances; thus, the focus is on the release, not precisely delineated 

boundaries. Further, CERCLA Section 101(a) defines a "facility" as the "site" where a hazardous 

substance has been "deposited, stored, placed, or otherwise come to be located." The "come to be 

located" language gives EPA broad authority to clean up contamination when it has spread from the 

original source. On March 31, 1989 (54 FR 13298), EPA stated: 

HRS scoring and the subsequent listing of a release merely represent the initial 

determination that a certain area may need to be addressed under CERCLA. 

Accordingly, EPA contemplates that the preliminary description of facility boundaries at 

the time of scoring will need to be refined and improved as more information is 

developed as to where the contamination has come to be located; this refining step 

generally comes during the RI/FS stage. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

The revised HRS (55 FR 51587, December 14, 1990) elaborates on the "come to be located" language, 

defining "site" as: 

area(s) where a hazardous substance has been deposited, stored, disposed, or placed, or 

has otherwise come to be located. Such areas may include multiple sources, and may 

include the area between the sources. 

Until the site investigation process has been completed and a remedial action (if any) selected, EPA can 

neither estimate the extent of contamination at the site, nor describe the ultimate dimensions of the NPL 

site. Even during a remedial action, such as removing contaminated soils, EPA may find that the 

contamination has spread further than previously estimated, and the site definition may be 

correspondingly expanded. In addition, if another, unrelated area of contamination is discovered 

elsewhere on the property, EPA may decide to evaluate that release for the NPL. 

Regarding the commenter’s assertions that the “Former Great Falls Refinery (GFR) site” does not include 

the contaminated soil detected in the Black Eagle residential area, the commenter is highlighting the 

“former GFR” facility property – not the ACM Smelter & Refinery site as established under the HRS. 

The HRS definition of “site,” as cited above is not bounded by facility or property boundaries – only 

where hazardous substances have come to be located. Properties within the Black Eagle residential area 

have been documented to contain hazardous substances and are considered a part of this site. 

Upon consideration of the comments relating to the area of observed contamination in the Black Eagle 

Residential area, the area of observed contamination of the Black Eagle residential area has been revised 

in the HRS documentation record at promulgation (refer to section 3.29.1, Area of Observed 

Contamination, of this support document for a full discussion on this topic). However, at least some of 

the Black Eagle residential properties are still documented as contaminated and are included as part of the 

site. 

3.10 Comments on HRS 

Comment: ARCO submitted comments challenging the adequacy of the HRS to identify sites for the 

NPL on the basis that it does not identify unacceptable site-specific risk. Specifically, ARCO challenged 

whether the HRS procedures for establishing observed release, observed contamination, and determining 

the level of contamination, establish the presence of unacceptable risk. ARCO asserted that the 

evaluation of a significant increase of a hazardous substance in a sample medium compared to 

background concentrations, and the evaluation of SCDM benchmarks in the determination of level of 

contamination, does not confirm the presence of an unacceptable risk posed by the presence of the 

hazardous substance in a sampled medium. 

Regarding the HRS procedure for establishing an observed release to surface water, ARCO challenged 

the scoring of an observed release to surface water based on a single release sample, stating that: 

[t]he only evidence EPA relies on to justify scoring potential adverse effects to the River 

consists of one sediment sample with a weakly elevated cadmium concentration collected 

above Rainbow Falls dam and sediment samples with weakly elevated metals 

concentrations that were collected from locations far downstream of the Site. Evidence 

of wide-spread or significant contamination is not documented by EPA for scoring or by 

any of the many studies that have been completed. 

Response: The HRS was promulgated on December 14, 1990 (55 FR 51569), and comments on the HRS 

itself are not relevant to the proposal to place the ACM Smelter & Refinery site on the NPL and are 

outside the scope of this rulemaking. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

The HRS is intended to be a "rough list" of prioritized hazardous sites; a "first step in a process--nothing 

more, nothing less" Eagle Picher Indus. v. EPA, 759 F.2d 922, 932 (D.C. Cir. 1985) (Eagle Picher II). 

EPA would like to investigate each possible site completely and thoroughly prior to evaluating them for 

proposal for NPL, but it must reconcile the need for certainty before action with the need for inexpensive, 

expeditious procedures to identify potentially hazardous sites. The courts have found EPA's approach to 

solving this conundrum to be "reasonable and fully in accord with Congressional intent.” (Eagle Picher 

Industries, Inc. v. EPA, (759 F.2d 905 (D.C. Cir. 1985) Eagle Picher I)). 

This comment has no effect on the HRS site score or on the decision to place the site on the NPL. 

3.11 Scoring Other Pathways 

Comment: ARCO stated that it agrees with EPA's decision not to score the ground water and air 

migration pathways. It asserted that there are no active sources at the site that would contribute to 

releases by the air pathway, and that geologic formations underlying the site limit the downward 

migration of contaminants to underlying aquifers. 

Response: That the air and ground water migration pathways were not scored in the HRS evaluation of 

the ACM Smelter & Refinery site does not represent a decision that there is no risk associated with these 

pathways or that EPA does not intend to investigate these pathways during further investigations at the 

site. 

Regarding the scoring of the ground water migration pathway, the cover page of the HRS documentation 

record at proposal stated: 

based on lack of analytical data supporting a release to the aquifers and on the fact that 

the ground water is not used as a drinking water source, the ground water pathway will 

not be scored as part of this Hazard Ranking System (HRS) package. 

However, this does not mean that the Agency is not concerned that there may be ground water 

contamination under the facility that may be reaching targets such as by migration of ground water to 

surface water. In fact, future investigations at the site may document that ground water contamination at 

the site needs to be addressed. 

Further, regarding the air migration pathway, the cover page of the HRS documentation record at 

proposal stated: 

Documentation of investigations from over 100 years ago conducted by the Boston and 

Montana Consolidated Copper and Silver Mining Company (Boston & Montana) and 

later by Anaconda Copper Mining Company (ACM) indicates that the operators of the 

smelter and refinery were aware that a significant amount of contamination was being 

emitted by the stack. Topsoil samples were collected and analyzed by the Boston & 

Montana laboratory in 1904 and 1905. Company chemists concluded that over 40 pounds 

of arsenic trioxide (As203) had been deposited per acre up to a distance of 6.24 miles to 

the northeast of the stack (Ref.32, p. 2). Samples collected from different locations in 

1905 confirmed the aerial deposition of contaminates [sic] from the stack (Ref. 47, p. 2). 

Internal ACM company correspondence from November 1951 indicated that the amount 

of arsenic leaving the stack per twenty-four hours in the early 1950s was approximately 

15.04 pounds (Ref. 33). 

The EPA chooses not to score the Air Migration Pathway at this time; however the EPA 

is interested in this potential pathway and may choose to pursue it further at a later date. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

The air migration pathway was not used in developing the HRS score, however emissions from the 

smelter facility at the site have been documented and are thought to be a source of contamination in soils 

surrounding the ACM facility and the risk associated with these emissions will be considered during 

further investigation of the site. 

The HRS does not require scoring all four pathways if scoring those pathways does not change the listing 

decision. For some sites, data for scoring a pathway are unavailable, and obtaining these data would be 

time-consuming or costly. In other cases, data for scoring some pathways are available, but will only 

have a minimal effect on the site score. In still other cases, data on other pathways could substantially 

add to a site score, but would not affect the listing decision. The HRS is a screening model that uses 

limited resources to determine whether a site should be placed on the NPL for possible Superfund 

response. A subsequent stage of the Superfund process, the RI, characterizes conditions and hazards at 

the site more comprehensively. 

In general, if reliable information shows that the site scores 28.50 or above, EPA will not seek more 

information to increase the HRS score. In these cases, such as at this site, the HRS documentation record 

may include a brief qualitative discussion to present a more complete picture of the conditions and 

hazards at the site, and to identify areas that may require further investigation at subsequent stages in the 

Superfund process. 

3.12 Consideration of Response Actions / Current Conditions 

Comment: ARCO alleged that EPA did not present the current conditions of the site in the HRS 

evaluation nor consider the various mitigation/improvement measures that have taken place at the site. 

ARCO stated that the completed mitigation measures at the “Former GFR Site,” such as the completion 

of demolition and removal actions, containment of remaining site-related debris, revegetation actions, 

structure void filling, and improvement of storm water runoff structures have removed potential exposure 

pathways at the “Former GFR Site.” In asserting that current conditions were not properly evaluated in 

the HRS evaluation, ARCO presented photographs of the site from April 2010, and maintenance activity 

reports summarizing reclamation activities that have taken place at the site. 

ARCO stated that the water quality exceedances reported in the 2003 Expanded Site Inspection, were not 

confirmed by the Parametrix investigation. 

Response: ARCO has not shown that reclamation or other activities performed after the information used 

in the HRS evaluation resulted in changes to the HRS evaluation or to the listing decision. 

EPA has reviewed the reclamation activity reports and site photographs taken of the site, and agrees that 

vegetation activities, surface stabilization, and soil capping activities have taken place at the ACM 

Smelter & Refinery site. In fact, EPA agrees that the sampling information used to establish hazardous 

substances associated with Source 2 was from 2003 and that reclamation activities presented by the 

commenter have taken place since this information was gathered. However, ARCO has not presented 

information establishing that any of these activities have completely removed any sources from the site, 

or mitigated hazardous substances releases from these sources that are occurring or have occurred from 

the site. To lower the HRS site score, information regarding the current conditions at the site would need 

to demonstrate that hazardous substances associated with the site have been completely contained, or that 

any site source and any associated releases from the site have been addressed so as to no longer pose a 

risk. Such information was not supplied by ARCO. While the reclamation activities may have limited 

further migration from the site via runoff, none of the actions identified by ARCO have addressed past 

releases from the site. See Section 3.15.1, Source 2 Characterization and Consideration of Response 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Activities, of this support document for further discussion on the consideration of response activities 

specifically associated with Source 2. 

Information used in establishing observed release was collected from the 2009 Site Assessment Expanded 

Site Inspection of the Missouri River sediments, and the current conditions of the Missouri River are 

represented in the HRS evaluation. Refer to section 3.20.1.3, Bias of Conclusions/Current Conditions, of 

this support document for a discussion on ARCO’s assertion that the water quality exceedances reported 

in the 2003 ESI were not confirmed by the 2004 Parametrix investigation. 

Sources Identified at Proposal 

The HRS documentation record at proposal identified two sources at the site. Source 1 consisted of 

contaminated residential soil in the Black Eagle community located adjacent to the former smelter facility 

on the north bank of the Missouri River across from Great Falls, Montana. Arsenic, cadmium and lead 

have been detected in multiple soil samples throughout the community area. Based on these samples, a 

contaminated area of approximately 1,926,569 square feet was delineated. Contaminants in Source 1are 

considered available to migrate to surface water. The contaminated soil area is also identified as an area 

of observed contamination for the soil exposure pathway. Pages 15-30 of the HRS documentation record 

at proposal present information used in establishing Source 1. 

Source 2 was identified as the East Ditch Dump located on a ridge above the Missouri River 

approximately 400 feet north of the River and approximately 3,500 feet east of the former smelter facility 

stack, and was observed to contain building/construction debris, stained soils, blister copper, and slag. A 

waste sample from this area was found to contain arsenic, cadmium, lead, manganese and zinc. 

Contaminants in this source are considered available to migrate to surface water. Pages 31-35 of the HRS 

documentation record at proposal present information used in establishing Source 2 (See Figure 1 of this 

support document). 

3.13 Additional Sources 

Comment: ARCO argued that the evaluation of the ACM site does not appropriately identify the source 

of hazardous substances found in Black Eagle residential soils or a source material for the slag in the 

Missouri River. 

Response: After review of ARCO’s comments and the HRS documentation record at proposal, two 

sources have been added to the HRS documentation record at promulgation. Source 3, facility air 

emissions (including stack emissions), has been added to the HRS documentation record at promulgation 

to more clearly show that hazardous substances documented in the Black Eagle residential soils came to 

be located due to migration from a site source. Source 4, the slag waste, has been added to the HRS 

documentation record at promulgation to link the slag generated at the site with the slag found in the 

Missouri River. Refer to Figure 1 of this support document for source locations. 

HRS Section 1.1, Definitions, defines “source” as: 

Any area where a hazardous substance has been deposited, stored, disposed, or placed, 

plus those soils that have become contaminated from migration of a hazardous substance. 

Sources do not include those volumes of air, ground water, surface water, or surface 

water sediments that have become contaminated by migration, except: in the case of 

either a ground water plume with no identified source or contaminated surface water 

sediments with no identified source, the plume or contaminated sediments may be 

considered a source. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Sources 3 and 4, added to the HRS documentation record at promulgation, meet the above HRS 

definition of a source. 

Source 3 – Facility Air Emissions 

Although the HRS documentation record at proposal did not designate the former stack at the ACM site 

as a source, facility air emissions, were discussed on page 12 of the HRS documentation record at 

proposal: 

The Big Stack was constructed in 1908 to a length of 506 feet and a total height of 751 

feet above the smelter’s blast furnace (Ref. 8 p. 7A). The Big Stack went into service on 

June 12, 1909 and continued belching smoke until August 06, 1972 (Ref. 9, p. 15). The 

Big Stack was designed to eject a volume of 1,575,000 cubic feet of air per minute at a 

velocity of 450 feet per minute, a sufficient volume and rate to entrain and remove from 

the smelter all the gases and dust generated during the smelting process (Ref. 9, p. 20) . 

An internal Anaconda Copper Mining Company Memorandum from 1951 stated that 

approximately 15.04 pounds of arsenic passed out of the stack every 24 hours (Ref. 33, p. 

1). 

The HRS documentation record at proposal explained that “aerial deposition of contaminants emanating 

from the smelter smoke stacks between 1893 and 1972 is the most likely mechanism of contaminants 

transport to the residential soils in the community of Black Eagle” (Page 12 of the HRS documentation 

record at proposal). Thus, the addition of Source 3 at promulgation is consistent with the information 

presented in the HRS documentation record at proposal, and did not require the addition of information 

not already included in the HRS documentation package at proposal. Nor does the addition of this source 

change the site score. Addition of this source demonstrates that the contamination in Source 1, the Black 

Eagle residential area, is at least partially due to a source at the site. That is, the hazardous substances 

associated with Source 3, facility air emissions, migrated toward and deposited at the Black Eagle 

residential area. 

Arsenic, antimony, cadmium, chromium, copper, lead, mercury, selenium and zinc are associated with 

Source 3 through flue dust samples taken from former smelter stack operation. As discussed on page 40 

of the HRS documentation record at promulgation, Source 3 is documented to have a containment value 

of greater than 0, as evidence of migration of hazardous substances from this source has been 

documented. Also, as hazardous substances are associated with the source yet the hazardous waste 

quantity is undetermined, Source 3 is assigned a source hazardous waste quantity value of greater than 0. 

Although emissions from this source may reasonably be expected to have also directly deposited into the 

Missouri River, this source is not included in the waste quantity evaluation for the surface water pathway 

because addition of this source would not affect the surface water pathway score which was already at the 

maximum score of 100. 

Source 4 – Slag Waste 

Source 4, slag waste, consists of the slag produced from the operations at the ACM facility and the 

resultant dump areas associated with the slag production. In the HRS documentation record at proposal, 

slag was documented as generated from operations at the site (see Reference 14, p. 1 of the HRS 

documentation record at proposal). A slag dump was identified and sampled during a 1983 screening 

study and was documented to contain the hazardous substances arsenic, cadmium, chromium, copper, 

lead, nickel and zinc (see Reference 58 of the HRS documentation record at proposal, Table 4-5, results 

for slag dump “Fill Mtrl” samples). 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

As discussed on page 44 of the HRS documentation record at promulgation, this source (slag waste) is 

documented to have a containment value of greater than 0, as evidence of migration of hazardous 

substances from this source has been documented. Also, as hazardous substances are associated with this 

source yet the hazardous waste quantity is undetermined, this source is assigned a hazardous waste 

quantity value of greater than 0. Overland drainage from this source enters the surface water of the 

Missouri River at PPE #7 (Figure 1 of this support document). 

This comment has no effect on the HRS site score or the decision to place the site on the NPL. 

3.14 Source 1 

Comment: ARCO asserted that the HRS documentation record at proposal incorrectly characterizes 

Source 1, contaminated soils in the Black Eagle residential area, including the area of observed 

contamination associated with it, the evaluation of hazardous substances, and the calculation of source 

hazardous waste quantity. 

Response: The following subsections of this support document address specific assertions regarding the 

evaluation of Source 1: 

• 3.14.1 Hazardous Substances Associated with Source 1 

• 3.14.2 Source 1 Delineation/Inference of Contamination 

• 3.14.3 Sampling Procedures 

• 3.14.4 Other Sampling/Current Conditions 

• 3.14.5 Source 1 Hazardous Waste Quantity 

• 3.14.6 Source 1 Containment 

3.14.1 Hazardous Substances Associated with Source 1 

Comment: ARCO submitted comments that challenged the association of hazardous substances with 

Source 1, the contaminated soils in the Black Eagle residential area (and the area of observed 

contamination associated with the source). In contesting the “attribution” of the arsenic, cadmium and 

lead in the area of contamination to the site based in part on their presence in this soil source, ARCO 

challenged the association of arsenic, cadmium, and lead in this source. 

Also, ARCO stated that none of the soil samples collected from residential areas in Black Eagle contained 

concentrations of antimony greater than three times background; therefore antimony cannot be regarded 

as elevated. 

Response: Arsenic, cadmium, and lead were appropriately associated with Source 1 in the HRS 

documentation record because the soil in this source was shown to have come to be contaminated by 

these substances. Antimony has been dropped from the source discussion in the HRS documentation 

record at promulgation. For establishing sources, the HRS does not require “attribution” to be established 

to associate a substance with a source. (See section 3.30.4, Hazardous Substance Deposition/Attribution, 

of this support document regarding attributing contamination in the corresponding area of observed 

contamination to the site.) 

HRS Section 1.1, Definitions, defines source, in relevant part, as: 

Any area where a hazardous substance has been deposited, stored, disposed, or placed, 

plus those soils that have become contaminated from migration of a hazardous substance. 

Thus, contaminated soil is an eligible source if the soil came to be contaminated due to migration. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

HRS Section 2.2.2, Identify hazardous substances associated with a source, explains what substances can 

be associated with a source. It states in relevant part: 

For each of the three migration pathways, consider those hazardous substances 

documented in a source (for example, by sampling, labels, manifests, oral or written 

statements) to be associated with that source when evaluating each pathway. . . . 

The HRS documentation record at proposal demonstrated that hazardous substances were associated with 

Source 1 through sampling. Page 15 of the HRS documentation record at proposal stated: 

The 2007 EPA CERCLA Site Assessment sampled residences on both the north and 

south sides of the Missouri River adjacent to the Anaconda Minerals Co, Great Falls 

Refinery (Ref. 21, p. 11). Of the eleven residences sampled in Great Falls on the south 

side of the Missouri River in August of 2007 only one residence had an elevated 

concentration of arsenic (Ref. 21, p. 13). The results of the 2007 investigation of the 

residential soil in the community of Black Eagle identified an area of arsenic, cadmium, 

and lead concentrations greater than three times background centered on eastern and 

central Black Eagle (Ref. 21, p. 13-14, 18). 

The 2008 EPA CERCLA Expanded Site Investigation was focused in the unincorporated 

community of Black Eagle, Montana. The residential soil at fifty nine residential 

properties in Black Eagle was sampled in July 2008 to a depth of one foot (Ref. 5, p. 1). 

Concentrations of arsenic, cadmium, and lead elevated three times background were 

detected in the residential soil in Black Eagle centered on the central and southwestern 

area of Black Eagle (Ref. 5, p. 13; Ref. 22, pp. 1-2). 

To document that the soils came to be contaminated by migration of arsenic, cadmium, and/or lead, as 

discussed above, it was documented that the levels of these hazardous substances are in the soil source at 

levels significantly greater than background using the HRS criteria necessary to establish a release has 

occurred to other media. Samples collected from Source 1 were documented to contain arsenic, cadmium 

and lead at concentrations significantly greater than the highest background levels. The highest 

background level results of arsenic, cadmium and lead are presented on page 17 of the HRS 

documentation record at proposal. Section 2.2.1.2, Hazardous substances associated with the source, of 

the HRS documentation record at proposal, presents those Source 1 samples that were documented to 

contain arsenic, cadmium, and/or lead significantly above background levels. These results show that the 

soils at Source 1 came to be contaminated due to migration of hazardous substances, as the hazardous 

substances detected in Source 1 are documented as significantly greater than background concentrations. 

Therefore, as the hazardous substances arsenic, cadmium and lead were documented in Source 1 through 

sampling at levels significantly above background, each hazardous substance was properly associated 

with the source in the evaluation of the surface water migration pathway. Although antimony and other 

hazardous substances were discussed as detected in Black Eagle residential soils, they are not included in 

the evaluation of hazardous substances associated with the source, and are not included in the HRS 

documentation record at promulgation. The removal of antimony from the Source 1 discussion of the 

HRS documentation record at promulgation has no impact on the scoring of the site, as it was never 

included in the HRS evaluation. 

Regarding the commenter’s assertion that the distribution patterns of hazardous substances used in 

defining Source 1 were not adequately evaluated; the HRS does not require evaluation of hazardous 

substance distribution patterns as part of the HRS evaluation. As cited above, the HRS requires that a 

hazardous substance be associated with a source, which in this case was determined through sampling of 

soils at the site. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

This comment has no effect on the HRS site score or the decision to place the site on the NPL. 

3.14.2 Source 1 Delineation/Inference of Contamination 

Comment: In challenging the area associated with the contamination in the Black Eagle residential area, 

ARCO equated the extent of Source 1 with the extent of the area of observed contamination and 

challenged how this area was delineated. ARCO alleged that EPA’s inference of contamination between 

sample locations used to delineate the AOC is incorrect according to the HRS, and that as a result EPA 

significantly overestimated the dimensions of Source 1. 

ARCO stated, citing from the HRS Guidance Manual (HRS Guidance Manual, Interim Final Draft), that 

“for contaminated soil, consider the sampling locations that indicate observed contamination and the area 

lying between such locations to be an area of observed contamination, unless information indicates 

otherwise.” 

ARCO stated: 

EPA states that arsenic and cadmium results delineate an area of contaminated soil of 

approximately 1,926,569 ft2

 (AR Reference #53); however the area delineated is based on 

a few widely-distributed sample locations exhibiting weakly elevated arsenic and/or 

cadmium concentrations with a broad area with no elevated arsenic or cadmium 

concentrations in between. In accordance with the EPA HRS Guidance Manual, a 

property can be inferred to have observed contamination if the property lies between 

points of observed contamination unless information indicates otherwise (AR Reference 

#46, p. 369). Atlantic Richfield has delineated two smaller areas of observed 

contamination in soil based on "elevated" concentrations of arsenic and cadmium that 

have a combined area of 153,000 ft2

 (see Figure A). 

ARCO stated that the delineation established in the HRS documentation record at proposal “ignores 

dozens of included residences that do not have elevated arsenic or cadmium concentrations based on 

EPA's own data.” ARCO continued that: 

Consideration of the 2009 data [collected by Atlantic Richfield] in combination with soil 

data from the 2007 and 2008 EPA investigations yields a large dataset inclusive of 790 xray fluorescence (XRF) soil samples for the community and covering 122 residential 

yards plus a public ball field and playground. 

ARCO discussed a soil investigation it completed in 2009 and asserted that data gathered in this study 

indicates that the distribution of arsenic and cadmium in the residential soils is not uniform across Black 

Eagle residential properties. It stated: 

Data from the 2009 residential soils investigation indicate that concentrations of lead and 

arsenic are not uniformly elevated across all properties sampled despite the biased 

selection of these properties based on the highest arsenic and lead concentrations from 

the 2007 and 2008 EPA sampling investigations. Concentrations vary by property, depth, 

and sample type (e.g., drip line versus yard) for both arsenic and lead. 

ARCO continued that: 

[a]lthough sporadically higher concentrations of arsenic and lead have been identified at 

various locations throughout Black Eagle, these occurrences are more indicative of 

random hot spots than a pervasively elevated soil exposure medium. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

ARCO stated that after review of all available data, the HRS evaluation of this source and its 

corresponding AOC should be changed using its revised area of observed contamination in soil for the 

Black Eagle residential area. 

Response: Upon a comprehensive review of all available sampling data taken from the Black Eagle 

residential area, the delineation of Source 1 and the associated AOC has been revised at promulgation. 

Specifically, after review of ARCO’s comments, the extent of source 1 at promulgation has been revised 

to only include those locations where samples show contaminated soils came to be located as being part 

of Source 1. The areas between those locations are no longer evaluated as part of the source (Figure 2 of 

this support document). 

The HRS does not give explicit directions on how to delineate a contaminated soil source; however the 

Agency finds it reasonable to consider the Source 1 soils that have come to be contaminated as the 

location of the source. That is, Source 1 is composed of the locations from which samples showing 

hazardous substances significantly greater than background were taken. At proposal, the area of Source 1 

was delineated in the same manner as the delineation of the AOC associated with it. Page 15 of the HRS 

documentation record at proposal states: 

The 2007 EPA CERCLA Site Assessment sampled residences on both the north and 

south sides of the Missouri River adjacent to the Anaconda Minerals Co, Great Falls 

Refinery (Ref. 21, p. 11). Of the eleven residences sampled in Great Falls on the south 

side of the Missouri River in August of 2007 only one residence had an elevated 

concentration of arsenic (Ref. 21, p. 13). The results of the 2007 investigation of the 

residential soil in the community of Black Eagle identified an area of arsenic, cadmium, 

and lead concentrations greater than three times background centered on eastern and 

central Black Eagle (Ref. 21, p. 13-14, 18). 

The 2008 EPA CERCLA Expanded Site Investigation was focused in the unincorporated 

community of Black Eagle, Montana. The residential soil at fifty nine residential 

properties in Black Eagle was sampled in July 2008 to a depth of one foot (Ref. 5, p. 1). 

Concentrations of arsenic, cadmium, and lead elevated three times background were 

detected in the residential soil in Black Eagle centered on the central and southwestern 

area of Black Eagle (Ref. 5, p. 13; Ref. 22, pp. 1-2). 

Those samples collected from the Black Eagle residential area, as cited above, were appropriately used in 

defining Source 1 and are the same samples used at promulgation as those at proposal to identify the 

presence of the source (see section 2.2.1.2 of the HRS documentation record at proposal and section 

2.2.1.2 of the HRS documentation record at promulgation). However, at promulgation, the assumption 

that there is contamination between the 53 sample locations is no longer made. Information indicates that 

contaminant levels at certain sampling locations between the53sample locations may not be significantly 

above background levels. This indicates that soil between source sample points may not have come to be 

contaminated due to migration based on a significant increase of hazardous substances above background 

concentrations (Figure 2 of this support document). 

However, all 53 samples used at the time of proposal to delineate this source are locations where the 

contaminant levels are significantly greater than background and thus are appropriately used to identify a 

soil source composed of the individual sample locations, considering the proximity and type of the source 

samples, similarity of hazardous substances in each sample, similarity of containment considerations of 

each source sample, and increase in contaminant levels. These changes are consistent with the 

recommendations in the HRS Guidance Manual and in the HRS in that the inference of contamination 

between sample locations has been dropped given information suggesting otherwise. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

These changes to the evaluation of the delineation of Source 1 and the associated AOC impact the 

calculation of Source 1 hazardous waste quantity and, as explained later in this support document, the 

evaluation of the soil exposure pathway. Refer to section, 3.14.5, Source Hazardous Waste Quantity; 

3.29, Soil Exposure Pathway; 3.30, Soil Exposure Waste Characteristics; and 3.31, Soil Exposure 

Targets, of this support document for a discussion on how these evaluations have changed at 

promulgation. 

This comment has no effect on the decision to place the site on the NPL. 

3.14.3 Sampling Procedures 

Comment: ARCO asserted that the sampling procedures employed to collect the soil samples used in the 

Source 1 evaluation were flawed. It contended that all samples collected by EPA for the 2007 and 2008 

site investigations were “random grab samples rather than systematic composite samples” and were not 

representative of actual site conditions. ARCO asserted that the sampling it completed in 2009 utilized a 

composite sampling method. It stated 

Many of these residences were resampled in 2009 by Atlantic Richfield (AR Reference 

#14) using systematic composite sampling methods outlined in EPA's Superfund LeadContaminated Residential Sites Handbook (AR Reference #15). . . . In general, the 

composite sampling did not confirm the highest concentrations reported by EPA. 

Response: The sampling methods used in establishing Source 1were appropriate for HRS purposes. 

HRS Section 1.1, Definitions, defines a source, in relevant part, as: “Any area where a hazardous 

substance has been deposited, stored, disposed, or placed, plus those soils that have become contaminated 

from migration of a hazardous substance.” 

HRS Section 2.2.2, Identify hazardous substances associated with a source, states: 

For each of the three migration pathways, consider those hazardous substances 

documented in a source (for example, by sampling, labels, manifests, oral or written 

statements) to be associated with that source when evaluating each pathway. In some 

instances, a hazardous substance can be documented as being present at a site (for 

example, by labels, manifests, oral or written statements), but the specific source(s) 

containing that hazardous substance cannot be documented. For the three migration 

pathways, in those instances when the specific source(s) cannot be documented for a 

hazardous substance, consider the hazardous substance to be present in each source at the 

site, except sources for which definitive information indicates that the hazardous 

substance was not or could not be present. 

For an area of observed contamination in the soil exposure pathway, consider only those 

hazardous substances that meet the criteria for observed contamination for that area (see 

section 5.0.1) to be associated with that area when evaluating the pathway. 

Page 16 of the HRS documentation record at proposal summarized how the samples establishing Source 1 

were collected: 

All samples were collected as grab samples following the guidelines of the UOS TSOPs 

using stainless steel spoons, bowls, and hand augers to collect the soil into 12X12 inch 

seal top poly bags. The 0-2 inch horizon was collected directly into the plastic zip lock 

bag using a stainless steel spoon, and the 6-12 inch horizon was collected using a hand 

auger into a stainless steel bowl where the soil was lightly homogenized by stirring 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

before a sample was collected into 12X12 inch seal top poly bags (Ref. 5, p. 11; Ref. 21, 

pp. 11-12). All of the background samples were collected from the area north of the 

Missouri River, west of the site, in soils developed on the Kootenai Formation which also 

underlies the community of Black Eagle (Ref. 5, p. 5; Ref. 10. 1 sheet; Ref. 21, p. 4). 

The soil was moist, fine-grained well sorted silty sand at the locations (Ref. 52, pp. 15-16 

& 28). All soil samples collected were analyzed in the field using an x-ray fluorescence 

(XRF) unit (Ref. 5, p. 12; Ref. 21, p. 12). All samples for fixed laboratory analyses were 

analyzed through the EPA’s Contract Laboratory Program (CLP), Routine Analytical 

Services (RAS). The samples collected in 2007 were analyzed by A4 Scientific, Inc. of 

The Woodlands, Texas by EPA CLP method ILM05.4 (Ref. 60, p. 1; Ref. 61, p. 1; Ref. 

62, p. 1). The samples collected in 2008 were analyzed by Chemtech Consulting Group, 

Mountainside, New Jersey by EPA CLP method ILM05.4 (Ref. 63. p. 1; Ref. 64, p. 1). 

These grab samples from the 2007 and 2008 sampling events were documented to contain hazardous 

substances, and thus meet the provisions of HRS Section 2.2.2 cited above. The HRS does not exclude 

grab samples in establishing a source or an area of observed contamination. As stated in the HRS, the 

scorer need only document that hazardous substances are associated with a source. Composite sampling 

methodology, as presented by the commenter, averages the level of contamination over a collection area. 

Grab sampling methodology, which entails collection of one sample from a specific location, is used to 

determine the existence of hazardous substances at that given sample location, which is appropriate for 

HRS purposes. The HRS is a screening tool and is based on screening sampling. More comprehensive 

sampling and sampling methodologies may be employed as part of the RI/FS, which is separate from the 

listing process. 

The handbook cited by the commenter, the Superfund Lead-Contaminated Residential Sites Handbook

was written by the EPA’s Lead Sites Workgroup (2003) to promote a nationally consistent decisionmaking process for assessing and managing risks associated with lead-contaminated residential sites 

across the country. As stated on page 1 of this handbook “[t]he primary audience for this risk 

management document is Superfund project managers working on the characterization and cleanup of 

lead-contaminated residential site” [emphasis added]. This handbook is intended for response selection, 

not for HRS purposes. Sampling for the purpose of establishing a source or an area of observed 

contamination during an HRS evaluation is not intended for the determination of risk, but rather, to 

determine the existence of contamination at a sampling location. Establishing the existence of 

contamination at this site was conducted in accordance with the HRS. Refer to section 3.6, Risk 

Associated with the Site, of this support document for further discussion on the evaluation of risk at this 

site. 

This comment has no effect on the HRS site score or the decision to place the site on the NPL. 

3.14.4 Other Sampling/Current Conditions 

Comment: ARCO asserted that previous sampling of the Black Eagle residential soils by EPA and more 

current sampling performed by ARCO do not show the same extent or levels of contamination as 

established in the HRS documentation record at proposal. ARCO stated that its 2009 investigation of the 

Black Eagle residential soils “did not confirm the highest concentrations reported by EPA,” and submitted 

results from the Parametrix 2009 investigation performed for ARCO. 

Response: ARCO has not shown that any of the sampling results used in establishing Source 1 were 

inappropriate in establishing Source 1 according to the HRS; sampling information presented by ARCO 

supports the conclusion that hazardous substances are appropriately associated with Source 1. More 

recent sampling performed by ARCO and the previous 2003 sampling completed by EPA do not indicate 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

an error in the sampling results used in establishing the extent of Source 1 nor document that there is not 

contamination present. 

HRS Section 2.2, Characterize sources, states that source characterization includes: the identification of 

sources, hazardous substances associated with the sources, and pathways potentially threatened by the 

hazardous substances. There is no reason to expect two nearby samples within the soil matrix at the 

Black Eagle residential area to yield exactly the same results, considering that residential yards may have 

been subject to modification or soil mixing by the resident. 

The 2003 ESI performed by EPA involved the collection of multiple samples from the ACM site, only 

three of which were collected from residential properties in Black Eagle. The sampling data used in 

establishing Source 1 came from the more comprehensive investigations of the Black Eagle residential 

properties - the 2007 Site Assessment and 2008 Expanded Site Inspection, which involved the collection 

of multiple samples from this area. 

Under the heading Description and Location of the source, page 15 of the HRS documentation record at 

proposal states: 

The 2007 EPA CERCLA Site Assessment sampled residences on both the north and 

south sides of the Missouri River adjacent to the Anaconda Minerals Co, Great Falls 

Refinery (Ref. 21, p. 11). Of the eleven residences sampled in Great Falls on the south 

side of the Missouri River in August of 2007 only one residence had an elevated 

concentration of arsenic (Ref. 21, p. 13). The results of the 2007 investigation of the 

residential soil in the community of Black Eagle identified an area of arsenic, cadmium, 

and lead concentrations greater than three times background centered on eastern and 

central Black Eagle (Ref. 21, p. 13-14, 18). 

The 2008 EPA CERCLA Expanded Site Investigation was focused in the unincorporated 

community of Black Eagle, Montana. The residential soil at fifty nine residential 

properties in Black Eagle was sampled in July 2008 to a depth of one foot (Ref. 5, p. 1). 

Concentrations of arsenic, cadmium, and lead elevated three times background were 

detected in the residential soil in Black Eagle centered on the central and southwestern 

area of Black Eagle (Ref. 5, p. 13; Ref. 22, pp. 1-2). 

Thus, multiple residential properties were sampled and documented to contain hazardous substances that 

met observed contamination criteria during the 2007 and 2008 investigations. That three residential 

properties sampled during the 2003 study were not documented to contain hazardous substances that met 

observed contamination criteria does not discredit findings of contamination on the same properties based 

on data from the 2007 and 2008 investigations that were used in establishing Source 1. In addition, 

ARCO presented no rationale for rejecting the results from the 2007 and 2008 sampling events. 

The analytical results from the 2009 sampling performed by ARCO, as presented in its comments, 

support that elevated levels of metals have been detected at several Black Eagle residential properties. 

Every property sampled by ARCO contained levels of lead significantly greater than background 

concentrations and 10 of these properties contained levels of arsenic significantly greater than background 

concentrations. Thus, ARCO’s 2009 investigation of the Black Eagle residential properties presents data 

showing elevated levels of hazardous substances in parts of the Black Eagle residential area and does not 

preclude, or otherwise discredit, the data used to establish Source 1 in the HRS documentation record at 

promulgation. 

This comment has no effect on the HRS site score or the decision to place the site on the NPL. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

3.14.5 Source 1 Hazardous Waste Quantity 

Comment: ARCO stated that the estimated source hazardous waste quantity for Source 1 is overstated. 

ARCO asserted that the estimated source hazardous waste quantity value based on ARCO’s calculated 

area of contaminated soil would be 4.5 - instead of the 56.66 estimated in the HRS documentation record 

at proposal. In addition, ARCO asserted that the hazardous constituent quantity for Source 1 is 

adequately determined, not incomplete as the HRS documentation record at proposal indicates. [This 

estimate could then have been used to estimate the source waste quantity instead of the estimate based on 

area.] 

Response: The source hazardous waste quantity has been revised at promulgation to reflect the redelineation of Source 1. 

The source hazardous waste quantity for Source 1 based on the area of the source is appropriately 

evaluated as “greater than 0.” 

HRS Section 2.4.2, Hazardous waste quantity, states: 

Evaluate the hazardous waste quantity factor by first assigning each source (or area of 

observed contamination) a source hazardous waste quantity value as specified below. 

Sum these values to obtain the hazardous waste quantity factor value for the pathway 

being evaluated. 

In evaluating the hazardous waste quantity factor for the three migration pathways, 

allocate hazardous substances and hazardous wastestreams to specific sources in the 

manner specified in section 2.2.2. . . . 

HRS Section 2.4.2.1, Source hazardous waste quantity, states: 

For each of the three migration pathways, assign a source hazardous waste quantity value 

to each source (including the unallocated source) having a containment factor value 

greater than 0 for the pathway being evaluated. . . . 

For all pathways, evaluate source hazardous waste quantity using the following four 

measures in the following hierarchy: 

• Hazardous constituent quantity. 

• Hazardous wastestream quantity. 

• Volume. 

• Area. 

HRS Section 2.4.2.1.1, Hazardous constituent quantity, states: 

Evaluate hazardous constituent quantity for the source (or area of observed 

contamination) based solely on the mass of CERCLA hazardous substances (as defined in 

CERCLA section 101(14), as amended) allocated to the source (or area of observed 

contamination) 

. . . . 

If the hazardous constituent quantity for the source (or area of observed contamination) is 

adequately determined (that is, the total mass of all CERCLA hazardous substances in the 

source and releases from the source [or in the area of observed contamination] is known 

or is estimated with reasonable confidence), do not evaluate the other three measures 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

discussed below. Instead assign these other three measures a value of 0 for the source (or 

area of observed contamination) and proceed to section 2.4.2.1.5. 

The hazardous constituent quantity was not adequately determined for Source 1 because the total mass of 

all CERCLA hazardous substances within the source was not known or able to be estimated with 

reasonable confidence. Only the Area tier of the source hazardous waste quantity evaluation was 

estimated for Source 1 because information was not available to adequately score the other tiers. 

HRS Section 2.4.2.1.4, Area, states: 

Evaluate the area measure using the area of the source (or the area of the area of observed 

contamination). Based on this area, designated as A, assign a value to the area measure 

as follows: 

• For the migration pathways, assign the source a value for area using the 

appropriate Tier D equation of Table 2-5. 

Section 2.2.2.4.4, Area, of the HRS documentation record at promulgation presents the evaluation of the 

Tier D, Area measure of the source hazardous waste quantity evaluation. As hazardous substances were 

detected in all 53 source samples and the full extent of the area of contaminated soil source is not 

determined, the source hazardous waste quantity value of “greater than 0” was estimated (see page 32 of 

the HRS documentation record at promulgation). 

As described in section 3.14.2, Source 1 Delineation/Inference of Contamination, of this support 

document, contamination is no longer inferred between the 53 source sample locations at promulgation, 

and thus only the individual sample locations are considered part of this source (Figure 2 of this support 

document). As such, a specific total area for Source 1 in the Tier D, Area evaluation reflecting the area of 

the sample locations was not estimated, but is clearly greater than zero. Thus, a source area of “greater 

than 0” was assigned to the hazardous waste quantity evaluation of Source 1. 

Further, even if the source hazardous waste quantity value of 4.5 based on area as presented by ARCO 

was considered adequately determined and the value was used in evaluating Source 1 hazardous waste 

quantity, or if a hazardous constituent quantity was estimated at an even lower value, it would not impact 

the evaluation of the respective pathway hazardous waste quantity evaluations and would have no impact 

on the site score. That is, according to HRS Table 2-6, the source hazardous waste quantity value of 4.5 

corresponds to a hazardous waste quantity factor value of 1. However, Footnote B of Table 2-6 of the 

HRS states that “if the hazardous constituent quantity is not adequately determined, assign a value as 

specified in the text; do not assign the value of 1.” Given that the hazardous constituent quantity for this 

source was not adequately determined, as explained above, HRS Section 2.4.2.2, Calculation of 

hazardous waste quantity factor value, states in relevant part: 

If the hazardous constituent quantity is not adequately determined for one or more 

sources. . . . assign a factor value as follows: 

If any target for that migration pathway is subject to Level I or Level II 

concentrations (see section 2.5), assign either the value from Table 2-6 or a value 

of 100, whichever is greater, as the hazardous waste quantity factor value for 

that pathway. [emphasis added] 

Thus, as targets in the scored pathways are subject to Level II contamination (or greater), the hazardous 

waste quantity factor value of 100 would be assigned to the scored pathway. Therefore, the source area of 

4.5 presented by the commenter would not impact the scoring of the respective pathway hazardous waste 

quantity evaluations and would have no impact on the site score. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Even though the Source 1 area estimate has been reduced at promulgation, this change does not impact 

the pathway hazardous waste quantity, nor the scoring of the waste characteristics factor values for the 

surface water migration pathway or the soil exposure pathways. 

This comment has no effect on the decision to place the site on the NPL. 

3.14.6 Source 1 Containment 

Comment: ARCO alleged that EPA ignored “the concept of sediment mobilization and transport,” with 

respect to Source 1, i.e., lack of mobility of the Black Eagle residential soil to be transported via surface 

water runoff, when it identified Source 1 as eligible for the surface water pathway. ARCO also claimed 

that since "subsurface soils in flat, vegetated areas" are not likely to be eroded and transported to the 

Missouri River, this would be an additional argument against the Black Eagle soils as a source for the 

surface water pathway. 

Response: The Source 1 containment evaluation was conducted in accordance with HRS requirements. 

HRS Section 2.2.3, Identify hazardous substances available to a pathway, states that: 

In evaluating each migration pathway, consider the following hazardous substances 

available to migrate from the sources at the site to the pathway: 

• Surface water migration—overland/flood component. 

- Hazardous substances that meet the criteria for an observed release to 

surface water in the watershed being evaluated. 

- All hazardous substances associated with a source with a surface water 

containment factor value greater than 0 for the watershed (see sections 

4.1.2.1.2.1.1 and 4.1.2.1.2.2.1). 

Hazardous substances associated with Source 1 may be available to migrate to the surface water pathway 

if the HRS containment value assigned for that source is greater than 0. 

HRS Section 4.1.2.1.2.1.1, Containment, directs the user to “assign a containment factor value from Table 

4–2 to each source at the site that can potentially release hazardous substances to the hazardous substance 

migration path for this watershed.” 

Table 4-2, Containment Factor Values for Surface Water Migration Pathway, of the HRS directs that 

when evidence of hazardous substance migration from a source area is not established, a containment 

value of 10 is assigned to the source when neither a maintained engineered cover is present, nor a 

functioning and maintained run-on control system/runoff management system is present. 

Page 29 of the HRS documentation record at proposal presents the rationale for why the Source 1 

containment value was evaluated as 10: 

There is no documentation of a maintained engineered cover or and [sic] functioning and 

maintained run-on control system and runoff management system. Building pads, streets, 

sidewalks, etc. cover less than half of the area, but are not engineered containment 

features. Surface water runoff flows directly to the Missouri River through a series of 

culverts. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Thus, as no maintained engineered cover or functioning and maintained run-on control system/runoff 

management system was documented to be in place at Source 1, the containment value of 10 was 

appropriately applied to Source 1. 

ARCO’s undocumented assertion that Source 1 samples are from areas that are not likely to be eroded 

and transported to the Missouri River does not establish that Source 1 is contained. Whether or not the 

Source 1 samples were located on flat or vegetated areas or were otherwise perceived as not likely to be 

eroded and transported to the Missouri River are not factors considered in the HRS evaluation of 

containment. 

This comment has no effect on the HRS site score or the decision to place the site on the NPL. 

3.15 Source 2 

Comment: ARCO asserted that the HRS documentation record at proposal incorrectly characterizes 

Source 2, the East Ditch Dump. The following subsections of this support document address specific 

assertions regarding the evaluation of Source 2: 

• 3.15.1 Source 2 Eligibility and Consideration of Response Activities 

• 3.15.2 Association of Hazardous Substances with Source 2 

• 3.15.3 Source 2 Hazardous Waste Quantity 

• 3.15.4 Source 2 Containment 

3.15.1 Source 2 Eligibility and Consideration of Response Activities 

Comment: ARCO asserted that Source 2 (East Ditch Dump) was inaccurately depicted in the HRS 

documentation record at proposal. ARCO contended that only a small portion of the East Ditch Dump is 

located in the “natural draw” near the Missouri River, and that EPA’s use of a single soil sample to 

characterize Source 2 does not accurately portray the full extent of the East Ditch Dump and reclamation 

activities that have taken place there. 

ARCO asserted that significant work at Source 2 has minimized or eliminated the exposure of potential 

hazardous substances to surface water transport, citing various response activities that have taken place 

(i.e., the moving equipment and debris, construction of erosion cover and run-on control channels, 

revegetation actions, capping activities, etc.). 

ARCO asserted that storm water monitoring reports indicate that spring/seep flows on-site “have been 

essentially eliminated since the establishment of a good grass cover following Site reclamation.” ARCO 

contended that “minor bare areas” that are present on the surface of the East Ditch Dump are scattered 

and consist of clean cover soil and that the area is managed by surface water control systems and a 

retention pond. 

Response: Source 2 was appropriately evaluated as a source according to the HRS. ARCO has not 

shown that reclamation and surface water management activities in the vicinity of Source 2 are adequate 

to justify removing this source from consideration in the HRS evaluation. 

HRS Section 1.1, Definitions, defines source, in relevant part, as: 

Any area where a hazardous substance has been deposited, stored, disposed, or placed, 

plus those soils that have become contaminated from migration of a hazardous substance. 

HRS Section 2.2.1, Identify sources, states, “[f]or the three migration pathways, identify the sources at the 

site that contain hazardous substances. Identify the migration pathway(s) to which each source applies.” 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

HRS Section 2.2.2, Identify hazardous substances associated with a source, states in relevant part: 

For each of the three migration pathways, consider those hazardous substances 

documented in a source (for example, by sampling, labels, manifests, oral or written 

statements) to be associated with that source when evaluating each pathway. 

HRS Section 2.2.3, Identify hazardous substances available to a pathway, states: 

In evaluating each migration pathway, consider the following hazardous substances 

available to migrate from the sources at the site to the pathway: 

• Surface water migration—overland/flood component. 

-Hazardous substances that meet the criteria for an observed release to surface 

water in the watershed being evaluated. 

-All hazardous substances associated with a source with a surface water 

containment factor value greater than 0 for the watershed (see sections 

4.1.2.1.2.1.1 and 4.1.2.1.2.2.1). 

Page 31 of the HRS documentation record at proposal presented the information used in establishing 

Source 2, the East Ditch Dump. It stated that the: 

East ditch dump is on a ridge above the Missouri River approximately 400 feet north of 

the River and approximately 3,500 feet east of the former stack (Ref. 18, Figure 2; Ref. 

58, Appendix I). No continuous cap or soil cover is documented to be in place over the 

east ditch dump. Building/construction debris, stained soils, blister copper, and slag were 

observed on the surface and mixed in the soil throughout the landfill area during the 2003 

EPA site inspection (Ref. 18, pp. 17, 22, and 32; Ref. 53, 1 page). 

The table displayed in section 2.2.2 of the HRS documentation record at proposal presents those 

hazardous substances detected in samples collected from the East Ditch Dump, and is reproduced below. 

Evidence (total metals) Hazardous 

Substance Sample No. / 

CLP No. 

Concentration 

(mg/kg) Background 

References 

Arsenic AM-SO-03 / 

MX0XH0 377 23.1 

Cadmium AM-SO-03 / 

MX0XH0 89.8 1.2 J+ 

Lead AM-SO-03 / 

MX0XH0 4270 30.1 

Manganese AM-SO-03 / 

MX0XH0 899 - 

Zinc AM-SO-03 / 

MX0XH0 4060 - 

Ref. 18, p. 94; Ref. 21, 

p. 29-32; Ref. 51, pp. 2, 

5, 9, 16, 17, 117, 120, 

124, 138; Ref. 52. pp. 

15-16, 28; Ref. 60, pp. 

1, 3, 6, 8, 18, 78, 363-

365, 594, 599, 604; 

Ref. 61, pp. 1, 3, 5, 8, 

9, 13-14, 219-224 

Page 31 of the HRS documentation record at proposal, under the subheading Source Sample Information, 

presented information regarding the source samples: 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

The source sample listed above was collected in April 2003 during the Expanded Site 

Inspection conducted by Tetra Tech EM Inc. for EPA. All samples were analyzed 

through the EPA CLP, RAS for total metals. Soil samples for inorganic analysis were 

delivered to Sentinal Inc, of Huntsville, Alabama (Ref. 18, p. 3). The analytical data was 

validated by Tetra Tech, EM, Inc, of Chicago, IL on July 30, 2003 (Ref. 18, p. 56). 

Analytical results from the sample indicate the presence of arsenic, cadmium, copper, 

lead, manganese, silver, and zinc in the East Ditch Dump (Ref. 18, p. 94). 

As materials were clearly dumped at the East Ditch Dump and it is evaluated as source type landfill, a 

comparison to background was not necessary to establish the existence of hazardous substances within 

Source 2. However, several hazardous substances in Source 2 were compared to background in the HRS 

documentation record at proposal. Page 31 of the HRS documentation record at proposal, under the 

subheading Background Sample Information, presented information regarding the background samples 

used in source samples: 

The sample collected from the East Ditch Dump is compared to soil samples collected 

during the 2007 EPA Site Inspection. The East Ditch Dump sample was collected from 

the 0 to 24 inch horizon using a macrocore (Ref. 57, 1 page). The 0-2 inch horizon 

background soil sample was collected directly into a plastic seal top bag using a stainless 

steel spoon and the 6-12 inch horizon was collected with a hand auger into a stainless 

steel bowl where the soil was lightly homogenized by stirring before a sample was 

collected into 12X12 inch seal top poly bags (Ref. 5, p. 11; Ref. 21, pp. 11-12). The 

background samples were collected from the area north of the Missouri River, west of the 

site, in soils developed on the Kootenai Formation (Ref. 10. 1 sheet). The soil was moist, 

fine-grained well sorted silty sand at the locations (Ref. 52, pp. 15-16 & 28). 

The highest background sample values available for the surface soil are 23.1 mg/kg 

arsenic, 1.2 J+ mg/kg for cadmium, and 30.1 mg/kg for lead. 

Thus, a sample (AM-SO-03) collected from Source 2 was documented to contain hazardous substances. 

Moreover, Source 2 was identified as eligible for evaluation in the surface water pathway. Section 2.2.3, 

Hazardous Substances Available to a Pathway, on page 34 of the HRS documentation record at proposal 

documents that the containment value for Source 2 was greater than 0. The table presented on page 34 of 

the HRS documentation record at proposal states: 

No continuous maintained engineered cover, cap or soil cover is documented to be in 

place over the east ditch dump and waste was observed in the upper two feet of soil at the 

site in 2003. There is no documentation of a run-on control system and run-off is allowed 

to flow unchecked to concrete channels which direct run-off southward to the Missouri 

River. 

Thus, hazardous substances were associated with Source 2 through sampling and the containment 

value for the source was documented as greater than 0. 

Regarding the reclamation activities cited by ARCO, such activities do not impact the eligibility 

of this area to be identified as a source. ARCO’s assertions that the reclamation activities (such 

as revegetation efforts, construction of erosion cover and run-on control channels, and capping 

actions) have minimized or eliminated the potential migration of hazardous substances from 

Source 2 to the surface water migration pathway do not alter the identification of it as a source. 

Although the commenter presented and discussed revegetation activities at the source and that 

bare soil areas at the East Ditch Dump are composed of clean cover soils, the commenter has not 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

supplied documentation establishing that a continuous, maintained engineered cover, cap or soil 

cover is present at the East Ditch Dump. In fact, the commenter conceded that bare areas present 

on the surface of the East Ditch Dump are composed only “in most instances” of clean cover soil. 

Because ARCO has not demonstrated that the HRS containment value should be zero, Source 2 is 

an eligible source for the surface water migration pathway. 

Additionally, despite ARCO asserting that surface water is managed at Source 2 with the use of 

run-on and runoff control systems, ARCO does not establish that hazardous substances have not 

been released from the source, or are not available to release to the surface water migration 

pathway. The HRS documentation record at proposal acknowledges that concrete channels in the 

vicinity of Source 2 direct surface water southward from the source area toward the Missouri 

River. The commenter has not shown that Source 2 does not contribute hazardous substances to 

these storm water conveyances. Thus, ARCO has not demonstrated that the HRS containment 

value should be zero, and Source 2 is therefore an eligible source for the surface water migration 

pathway. See also section 3.15.4, Source 2 Containment, of this support document. 

Regarding ARCO’s assertion that only a portion of the East Ditch Dump is located within the “natural 

draw” of the Missouri River, only one sample was taken from this source and the entire East Ditch Dump 

was not fully evaluated. Whether or not a portion of the East Ditch Dump is within the “natural draw” of 

the Missouri River does not establish that hazardous substances are not available to migrate from Source 

2 to surface water, and this assertion does not discredit the determination that overland flow from Source 

2 enters the surface water pathway. Section 3.18, Description of Pathway, of this support document 

further discusses the description of the surface water pathway. 

This comment has no effect on the HRS site score or the decision to place the site on the NPL. 

3.15.2 Association of Hazardous Substances with Source 2 

Comment: ARCO challenged the evaluation of hazardous substances associated with Source 2. 

Specifically, ARCO asserted that manganese should not have been used to score the site as its 

concentration within the Source 2 soil sample was less than three times background. Also, ARCO 

contended that silver was not detected above the Contract Required Detection Limit (CRDL) in either the 

soil sample from the East Ditch Dump or in any of the background samples, yet is listed as associated 

with Source 2 in the HRS documentation record at proposal. 

ARCO asserted that only five metals (arsenic, cadmium, copper, lead and zinc) were detected at 

concentrations “greater than three times background in the one grab sample collected from this possible 

source area.” 

Response: Hazardous substances were appropriately associated with Source 2 as the hazardous 

substances were detected in Source 2 through sampling. HRS Section 2.2.2, Identify hazardous 

substances associated with a source, states in part: 

 For each of the three migration pathways, consider those hazardous substances 

documented in a source (for example, by sampling, labels, manifests, oral or written 

statements) to be associated with that source when evaluating each pathway. 

The HRS documentation record at proposal presents the hazardous substances associated with a source 

sample (AM-SO-03) taken from the East Ditch Dump. The table under the heading Hazardous 

Substances Associated with the Source on Page 31 of the HRS documentation record at proposal, presents 

that sample AM-SO-03 contained the CERCLA hazardous substances: arsenic, cadmium, lead, 

manganese, and zinc. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Although silver was discussed in the text of the HRS documentation record at proposal as detected in the 

Source 2 sample, it was not listed as a hazardous substance associated with Source 2 as no analytical data 

was presented to support this claim. The discussion of the hazardous substances associated with Source 2 

has been revised in HRS documentation record at promulgation and silver has been dropped from the 

discussion. Only those substances displayed on the table on page 31 of the HRS documentation record at 

promulgation are associated with Source 2 and were included in the HRS evaluation. 

Regarding ARCO’s assertion that manganese cannot be associated with the source because it did not 

exceed three times the background concentration, there is no HRS provision for a source (with source 

type landfill) to have substances present above background levels. 

HRS Section 1.1, Definitions, defines source as: 

Any area where a hazardous substance has been deposited, stored, disposed, or placed, 

plus those soils that have become contaminated from migration of a hazardous substance. 

Sources do not include those volumes of air, ground water, surface water, or surface 

water sediments that have become contaminated by migration, except: in the case of 

either a ground water plume with no identified source or contaminated surface water 

sediments with no identified source, the plume or contaminated sediments may be 

considered a source. 

This definition only restricts soils to be considered a source if the soil came to be contaminated due to 

migration, (which is often demonstrated by showing the contaminant levels are significantly greater than 

in background soils). It has no such restriction for other source types. However, several hazardous 

substances in Source 2 were compared to background in the HRS documentation record at proposal 

simply to illustrate the high concentrations of hazardous substances found within Source 2. 

This comment has no effect on the HRS site score or the decision to place the site on the NPL. 

3.15.3 Source 2 Hazardous Waste Quantity 

Comment: ARCO challenged the evaluation of the Source 2 hazardous waste quantity. ARCO stated 

that, using the area of the location where the source sample was collected, the estimated source hazardous 

waste quantity value should have been 0.44, instead of “> 0.” 

Additionally, ARCO contended that Tier A, hazardous constituent quantity, is adequately determined, not 

incomplete as presented in the HRS documentation record at proposal. 

Response: The source hazardous waste quantity was appropriately evaluated for Source 2 as “greater 

than 0.” The exact boundaries of the East Ditch Dump have not been established with any certainty and 

the estimate provided by ARCO is itself only a portion of the East Ditch Dump area. Even if the source 

hazardous waste quantity value of 0.44 suggested by ARCO was used in evaluating Source 2 hazardous 

waste quantity, it would not impact the evaluation of the respective pathway hazardous waste quantity 

evaluations and would not change the site score. 

HRS Section 2.4.2, Hazardous waste quantity, states: 

Evaluate the hazardous waste quantity factor by first assigning each source (or area of 

observed contamination) a source hazardous waste quantity value as specified below. 

Sum these values to obtain the hazardous waste quantity factor value for the pathway 

being evaluated. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

In evaluating the hazardous waste quantity factor for the three migration pathways, 

allocate hazardous substances and hazardous wastestreams to specific sources in the 

manner specified in section 2.2.2. . . . 

HRS Section 2.4.2.1, Source hazardous waste quantity, states: 

For each of the three migration pathways, assign a source hazardous waste quantity value 

to each source (including the unallocated source) having a containment factor value 

greater than 0 for the pathway being evaluated. . . . 

For all pathways, evaluate source hazardous waste quantity using the following four 

measures in the following hierarchy: 

• Hazardous constituent quantity. 

• Hazardous wastestream quantity. 

• Volume. 

• Area. 

For evaluating the hazardous constituent quantity, HRS Section 2.4.2.1.1 Hazardous constituent 

quantity, states: 

Evaluate hazardous constituent quantity for the source (or area of observed 

contamination) based solely on the mass of CERCLA hazardous substances (as defined in 

CERCLA section 101(14), as amended) allocated to the source (or area of observed 

contamination). . . . 

If the hazardous constituent quantity for the source (or area of observed contamination) is 

adequately determined (that is, the total mass of all CERCLA hazardous substances in the 

source and releases from the source [or in the area of observed contamination] is known 

or is estimated with reasonable confidence), do not evaluate the other three measures 

discussed below. Instead assign these other three measures a value of 0 for the source (or 

area of observed contamination) and proceed to section 2.4.2.1.5. 

If the hazardous constituent quantity is not adequately determined, assign the source (or 

area of observed contamination) a value for hazardous constituent quantity based on the 

available data and proceed to section 2.4.2.1.2. 

The HRS documentation record at proposal stated in section 2.4.2.1.1, Hazardous Constituent Quantity: 

There are no Hazardous Constituent Quantity data available for the East Ditch Dump to 

calculate a Hazardous Constituent Quantity value. 

As stated above, the hazardous constituent quantity (Tier A) is evaluated based on the mass of CERCLA 

hazardous substances in the source, and is properly established if this total mass is known or estimated 

with reasonable confidence. Since only one sample has been taken from Source 2, clearly the total mass 

of CERCLA hazardous substances could not have been determined or estimated with reasonable 

confidence. Thus, hazardous constituent quantity (Tier A) could not be determined in the source 

hazardous waste quantity evaluation. 

Page 30 of the HRS documentation record at proposal discussed that both Tier B (Hazardous wastestream 

quantity) and Tier C (Volume) were not adequately determined. As such, Tier D, Area, was evaluated 

according to the HRS in the source hazardous waste quantity evaluation. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

HRS Section 2.4.2.1.4, Area, states: 

Evaluate the area measure using the area of the source (or the area of the area of observed 

contamination). Based on this area, designated as A, assign a value to the area measure 

as follows: 

• For the migration pathways, assign the source a value for area using the 

appropriate Tier D equation of Table 2-5. 

Section 2.2.2.4.4, Area, of the HRS documentation record at proposal, stated: 

The area covered by the East Ditch Dump is currently not quantifiable; however as 

contamination has been documented at the source can be said to be unknown but greater 

than zero 

Because the exact boundary of the East Ditch Dump remains unknown, assigning Source 2 a hazardous 

waste quantity value of “greater than 0” was consistent with the HRS. 

Furthermore, even if the source hazardous waste quantity value of 0.44 based on an area of source 

estimate presented by ARCO was used in evaluating Source 2 hazardous waste quantity, it would not 

impact the evaluation of the respective pathway hazardous waste quantity evaluations and would have no 

impact on the site score. That is, according to HRS Table 2-6, the source hazardous waste quantity value 

of 0.44 corresponds to a hazardous waste quantity factor value of 1. Footnote B of Table 2-6 of the HRS 

states that “if the hazardous constituent quantity is not adequately determined, assign a value as specified 

in the text; do not assign the value of 1.” As the hazardous constituent quantity for this source was not 

adequately determined nor did ARCO suggest it could be, HRS Section 2.4.2.2, Calculation of hazardous 

waste quantity factor value, states in relevant part: 

If the hazardous constituent quantity is not adequately determined for one or more 

sources. . . . assign a factor value as follows: 

If any target for that migration pathway is subject to Level I or Level II 

concentrations (see section 2.5), assign either the value from Table 2-6 or a value 

of 100, whichever is greater, as the hazardous waste quantity factor value for 

that pathway. [emphasis added] 

Thus, as targets in the scored pathways are subject to Level II contamination (see section 3.27.1, Actual 

Contamination, of this support document), the hazardous waste quantity factor value of 100 would be 

assigned to the scored pathway. Therefore, the source hazardous waste quantity value of 0.44 presented 

by the commenter would not impact the scoring of the respective pathway hazardous waste quantity 

evaluations and would have no impact on the site score. 

This comment has no effect on the HRS site score or the decision to list the site on the NPL. 

3.15.4 Source 2 Containment 

Comment: ARCO alleged that the containment value of 10 assigned to Source 2 is incorrect as it does not 

account for the reclamation and stabilization work that has taken place. ARCO stated that the 

containment value of 9 should have been assigned to Source 2 as there is no evidence of hazardous 

substance migration from Source 2, and that a functional run-on control and runoff management system is 

in place at the site. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Response: The Source 2 containment evaluation is correct and is consistent with the HRS criteria for 

assigning a containment value to a source. 

In part, HRS Section 4.1.2.1.2.1.1, Containment, directs that for all source types: 

Determine the containment factor value for the watershed as follows: 

. . . . 

-If none of the sources is located in surface water in the watershed, assign a 

containment factor value from table 4–2 to each source at the site that can 

potentially release hazardous substances to the hazardous substance migration path 

for this watershed. 

Table 4-2, Containment Factor Values for Surface Water Migration Pathway, of the HRS directs the 

scorer to assign a containment value of 10 to all sources (except surface impoundments, land treatment, 

containers, and tanks) when there is evidence of hazardous substance migration from a source area. 

When evidence of hazardous substance migration from a source area is not established, HRS Table 4-2 

directs the scorer to assign a containment value of 10 to the source area for all source types (except 

surface impoundments, land treatment, containers, and tanks) when there is neither a maintained 

engineered cover nor a functioning and maintained run-on control system/runoff management system 

present. 

Page 34 of the HRS documentation record at proposal stated: 

No continuous maintained engineered cover, cap or soil cover is documented to be in 

place over the east ditch dump and waste was observed in the upper two feet of soil at the 

site in 2003. There is no documentation of a run-on control system and run-off is 

allowed to flow unchecked to concrete channels which direct run-off southward to the 

Missouri River. 

Thus, as no documented maintained engineered cover or functioning and maintained run-on control 

system/runoff management system were documented to be in place at Source 2, the containment value of 

10 was appropriately applied to Source 2. As noted in section 3.15.1, Source 2 Eligibility and 

Consideration of Response Activities, of this support document, although ARCO presented information 

on capping and revegetation activities in the vicinity of Source 2, the commenter has not supplied 

documentation establishing that a continuous, maintained engineered cover, cap or soil cover is present at 

the source. 

Moreover, the HRS documentation record at proposal identified that concrete channels in the vicinity of 

Source 2 direct surface water southward from the source area toward the Missouri River. ARCO’s 

assertions that surface water is managed at Source 2 with the use of run-on and runoff control systems, 

does not establish that hazardous substances have not released from the source, or are not available to 

release to the surface water migration pathway. Water in the concrete channels reaches the river more 

rapidly than if the channels were not in place; the channels do not in any way restrict the contamination in 

the runoff from reaching the river. 

Further, even if a maintained engineered cover and a functioning and maintained run-on control 

system/runoff management system as described in HRS Table 4-2 were present at Source 2, this condition 

would not result in a containment factor value of 0 for Source 2. That is, according to HRS Table 4-2, a 

containment value of 0 is assigned for all sources (except surface impoundments, land treatment, 

containers, and tanks) when the source is documented to be: 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

under maintained intact structure that provides protection from precipitation so that 

neither runoff nor leachate is generated, liquids or materials containing free liquids not 

deposited in source area, and functioning and maintained run-on control present. 

ARCO has not demonstrated that the above considerations have been met and therefore a containment 

factor value of 0 does not apply to Source 2. 

This comment has no effect on the HRS site score or the decision to place the site on the NPL. 

3.16 Other Possible On-site Sources 

Comment: ARCO asserted that the other possible source areas identified in the HRS documentation 

record at proposal are not correctly evaluated as possible sources. ARCO contended that the areas 

identified have been reclaimed or are subject to ongoing operation and maintenance activities. 

Also, ARCO alleged that only those hazardous substances that are evaluated as "elevated" within each 

possible source area need be associated with each identified other possible source, and that hazardous 

substances detected below the CRDL3

 should be excluded. 

Response: The other possible sources identified in the HRS documentation record at proposal were 

appropriately described at proposal. 

HRS Section 1.1, Definitions, defines source, in part, as: 

Any area where a hazardous substance has been deposited, stored, disposed, or placed, 

plus those soils that have become contaminated from migration of a hazardous substance. 

HRS Section 2.2.1, Identify sources, states, “[f]or the three migration pathways, identify the sources at the 

site that contain hazardous substances. Identify the migration pathway(s) to which each source applies.” 

HRS Section 2.2.2, Identify hazardous substances associated with a source, states in part: 

For each of the three migration pathways, consider those hazardous substances 

documented in a source (for example, by sampling, labels, manifests, oral or written 

statements) to be associated with that source when evaluating each pathway. 

Pages 35 and 36 of the HRS documentation record at proposal present 14 other possible source areas that 

were sampled at the ACM site and were determined to contain hazardous substances. The discussion of 

these other possible sources in the HRS documentation record identifies that EPA may further investigate 

these sources during the Remedial Investigation for the site and, if possible, determine whether releases 

from these other possible sources pose a sufficient risk and warrant remediation. 

Also, hazardous substances need not be “elevated,” or significantly above background to be considered 

associated with a potential source area. As quoted above, the HRS identifies that sampling can be used to 

associate hazardous substances with a source. The HRS does not require that the levels of a hazardous 

substance be significantly greater than background levels or that the sampling result be greater than a 

CRDL for consideration. The substance only needs to be present in the source. This can be documented 

 

3

 The Contract Required Detection Limit, as defined on page 51585 of the HRS, is a term equivalent to the Contract 

Required Quantitation Limit (CRQL). The HRS states that the CRQL is the “[s]ubstance-specific level that a CLP 

laboratory must be able to routinely and reliably detect in specific sample matrices. It is not the lowest detectable 

level achievable, but rather the level that a CLP laboratory should reasonably quantify. The CRQL may or may not 

be equal to the quantitation limit of a given substance in a given sample. For HRS purposes, the term CRQL refers 

to both the contract-required quantitation limit and the contract-required detection limit.” 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

by showing the substance is present above the detection limit of the analytical method employed. The 

CRDL is not the lowest detectable level achievable for a sample analysis; and detections below a CRDL 

can still exceed a detection limit specific to the analytical method, and thus still be documented in a 

source. Thus, hazardous substances were appropriately associated with other possible on-site source 

areas as these substances were detected in samples taken from the other possible on-site source areas. 

This comment has no effect on the HRS site score or the decision to place the site on the NPL. 

Surface Water Scoring at Proposal 

The HRS documentation record at proposal evaluated observed releases of hazardous materials to the 

Missouri River adjacent to Source 1 (contaminated soil in the Black Eagle community) and Source 2 

(East Ditch Dump, located east of the former stack on a ridge above the river). Five probable points of 

entry (PPEs) were identified where contaminant-carrying runoff may drain from Source 1 to the Missouri 

River via outfalls. A sixth PPE was identified as a gully through which runoff from the Source 2 area 

may enter the Missouri River. Observed releases of hazardous substances were established both by direct 

observation of slag dumped into the river and chemical analysis of metal levels in river sediment samples. 

The locations of the PPEs and the samples used in the characterization of the observed release are 

displayed on Figure 1 of this support document which follows. The targets scored for this pathway 

include a human food chain fishery and wetland sensitive environments subject to actual contamination. 

The scoring of the surface water migration pathway was presented on pages 37-49 of the HRS 

documentation record at proposal. 

3.17 Evaluation of the Surface Water Pathway 

Comment: ARCO argued that it would be appropriate to not score the surface water pathway, stating that 

HRS guidance indicates this as the course of action when no observed release is established from the 

scored sources at a site. ARCO contended that the entire pathway should be deleted, as it was based on 

faulty assumptions arising from the use of data not reflecting current conditions. ARCO stated that it had 

developed an alternative score for the surface water migration pathway in which it scored potential to 

release for Source 1 and Source 2 separately, with Source 2 yielding the slightly higher potential to 

release score. 

Response: The surface water pathway was scored because it poses a threat to human health and the 

environment. That a threat exists is shown in the identification of observed releases to surface water 

within a human food chain fishery and the presence of wetlands subject to contamination, in accordance 

with the HRS (and consistent with the HRS Guidance Manual). The likelihood of release for the surface 

water pathway has been correctly scored based on the identification of observed releases to the Missouri 

River. The potential to release was not scored in evaluation of likelihood of release, consistent with the 

HRS, as an observed release to surface water was established. 

HRS Section 2.3, Likelihood of release, states: 

Likelihood of release is a measure of the likelihood that a waste has been or will be 

released to the environment. The likelihood of release factor category is assigned the 

maximum value of 550 for a migration pathway whenever the criteria for an observed 

release are met for that pathway. If the criteria for an observed release are met, do not 

evaluate potential to release for that pathway. 

Establish an observed release either by direct observation of the release of a hazardous 

substance into the media being evaluated (for example, surface water) or by chemical 

analysis of samples appropriate to the pathway being evaluated (see sections 3, 4, and 6). 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

 39 

The minimum standard to establish an observed release by chemical analysis is analytical 

evidence of a hazardous substance in the media significantly above the background level. 

Further, some portion of the release must be attributable to the site. Use the criteria in 

table 2–3 as the standard for determining analytical significance. 

HRS Section 4.1.2.1.1, Observed release, states in relevant part: 

If an observed release can be established for a watershed, assign an observed release 

factor value of 550 to that watershed, enter this value in Table 4-1, and proceed to section 

4.1.2.1.3. If no observed release can be established for the watershed, assign an observed 

release factor value of 0 to that watershed, enter this value in Table 4-1, and proceed to 

section 4.1.2.1.2. 

The HRS documentation record at proposal, on page 39, stated: 

According to the HRS, if an observed release can be established, a value of 550 is 

assigned for Likelihood of Release (Ref. 1, Section 4.1.2.1.1, p. 51609). 

As established in sections 3.19, Likelihood of Release - Observed Release by Direct Observation, and 

3.20, Surface Water Likelihood of Release - Observed Release by Chemical Analysis, of this support 

document, an observed release by direct observation and an observed release by chemical analysis have 

been established. The evaluation of the entire surface water migration pathway should not be deleted in 

the HRS evaluation, as asserted by ARCO in its interpretation of the HRS guidance, because the observed 

releases have been properly established according to the HRS and there is no need to score potential to 

release. 

Regarding the use of data not reflecting current conditions, ARCO appears to be implying, though does 

not clearly state, that the site’s current threats are less than in the past. However the HRS evaluates the 

threat posed both by past and current releases. For example, the HRS specifies in Section 4.1.2.1.1 that 

the user is to “[e]stablish an observed release to surface water for a watershed by demonstrating that the 

site has released a hazardous substance to the surface water in the watershed [emphasis added].” The 

HRS does not require that the release be ongoing, just that it has occurred, and the HRS evaluation shows 

that this release poses sufficient threat relative to other sites to warrant listing and further investigation. 

This topic is discussed in further detail in section 3.20.1.3, Bias of Conclusions/Current Conditions, of 

this support document. Furthermore, as discussed in section 3.6, Risk Associated with the Site, of this 

support document, contrary to ARCO’s statements ARCO has not shown that no unacceptable risk is 

associated with releases from the site. 

These comments have no effect on the site score or the decision to list the site on the NPL. 
ACM Smelter & Refinery NPL listing Support Document 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

3.18 Description of Pathway 

Comment: ARCO challenged the description of the overland flow/flood component of the surface water 

pathway. 

ARCO stated that the HRS documentation record at proposal documented that the outfalls draining the 

contaminated soil in the Black Eagle residential area enter the Missouri River at PPE #s 1 through 5. 

ARCO commented that the background sediment sample was collected in the vicinity of the most 

upstream outfall, PPE #1, and that, on this basis, the area drained by that outfall should be removed from 

consideration in the surface water pathway. ARCO further alleged that, if the sediment sample under 

consideration were not considered a background sample, then its results do not indicate contaminant 

transport from the Black Eagle residential area into the River. 

ARCO noted that, while the PPE for Source 2 is indicated as being PPE #6, the two sediment samples 

with the highest contaminant concentrations in the 2009 Expanded Site Investigation (ESI) (AGFSED-2 

and AGFSED-3) were collected upstream from this PPE. On this basis, ARCO concludes that Source 2 

cannot be the source of sediment contamination for this reach of the river. 

Response: The surface water pathway for the overland/flood migration component was appropriately 

characterized in accordance with the HRS requirements. These requirements are presented in HRS 

Section 4.1.1.1, Definition of hazardous substance migration path for overland/flood migration 

component, which specifies the following: 

The hazardous substance migration path includes both the overland segment and the inwater segment that hazardous substances would take as they migrate away from sources 

at the site: 

• Begin the overland segment at a source and proceed downgradient to the 

probable point of entry to surface water. 

• Begin the in-water segment at this probable point of entry. 

- For rivers, continue the in-water segment in the direction of flow (including 

any tidal flows) for the distance established by the target distance limit (see 

section 4.1.1.2). 

- For lakes, oceans, coastal tidal waters, or Great Lakes, do not consider flow 

direction. Instead apply the target distance limit as an arc. 

- If the in-water segment includes both rivers and lakes (or oceans, coastal 

tidal waters, or Great Lakes), apply the target distance limit to their 

combined in-water segments. 

Further, HRS Section 4.1.1.2, Target distance limit, continues the description of the in-water segment of 

the migration pathway, as follows: 

The target distance limit defines the maximum distance over which targets are considered 

in evaluating the site. Determine a separate target distance limit for each watershed as 

follows: 

• If there is no observed release to surface water in the watershed or if there is an 

observed release only by direct observation (see section 4.1.2.1.1), begin 

measuring the target distance limit for the watershed at the probable point of 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

entry to surface water and extend it for 15 miles along the surface water from that 

point. 

• If there is an observed release from the site to the surface water in the watershed 

that is based on sampling, begin measuring the target distance limit for the 

watershed at the probable point of entry; extend the target distance limit either 

for 15 miles along the surface water or to the most distant sample point that 

meets the criteria for an observed release to that watershed, whichever is greater. 

In accordance with the requirements specified above, the HRS documentation record at proposal 

described the surface water migration pathway for Sources 1 and 2 in Section 4.1.1.1, beginning on page 

37, as follows: 

Two sources have been evaluated at the ACM Smelter and Refinery site. The first 

source, Source 1, the contaminated soil in the community of Black Eagle (Ref. 22, p. 2) 

would enter the surface water pathway of the Missouri River via a series of culverts 

draining surface water runoff from the community into the Missouri River. All outfall 

culvert locations are on the north bank of the Missouri River and are identified from 

information provided by the Cascade County Public Works Department (Ref. 55, 12 

pages; Ref. 59, pp. 1-2). The five of the outfall locations are listed in the following table. 

A map showing the locations is also provided (Ref. 50, 1 page). 

Outfalls draining from Contaminated Residential Soil to the Missouri River 

(Ref. 50, p. 2; Ref. 55, 11 pages; Ref. 59, pp. 1-2) 

Outlet Name Outfall 

Location 

Outfall 

Description 

Drainage Area Responsible 

Party 

PPE#1, North River 

Road 9th to 15th 

Street-No. 2 

630 feet east of 

10th Street 

Bridge 

24-inch diameter 

corrugated steel 

pipe 

37 acres 

Western Black 

Eagle 

Cascade 

County 

PPE#2, North River 

Road 9th to 15th 

Street-No. 3 

1,400 feet east 

of 10th Street 

Bridge 

24-inch diameter 

corrugated steel 

pipe 

8 acres 

Western Black 

Eagle along 

Missouri River 

Cascade 

County 

PPE#3, 15th Street 

Bridge North 

60 feet west of 

15th Street 

Bridge 

30-inch diameter 

corrugated 

132 acres 

Central Black 

Eagle 

MDT and 

Cascade 

County 

PPE#4, Black Eagle 

South East 

East of 15th 

Street Bridge 

under North 

River Rd. 

20-inch diameter 

corrugated steel 

pipe 

22 acres 

South central 

Black Eagle 

Cascade 

County 

PPE#5, Anaconda 

Hills West 

(Coulee) 

380 feet west of 

Black Eagle 

Dam 

Twin 36-inch 

diameter 

corrugated steel 

pipes 

188 acres Cascade 

Eastern Black County 

Eagle, Moose 

Lodge, and golf 

course 

The most upstream outfall for surface water runoff from the contaminated soil identified 

in the unincorporated community of Black Eagle would be outfall North River Road 9th to 

15th Street No. 2 (PPE # 1) with a drainage area of approximately 37 acres (Ref 50, 1 

page; Ref. 55, p. 7; Ref. 59, pp. 1-2). This outlet captures runoff from western edge of 

the community of Black Eagle and delivers the runoff through the outfall to the Missouri 

River (Ref. 50; Ref. 59, pp. 1-2). PPE # 2 delivers runoff from approximately 8 acres in 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

western Black Eagle along the Missouri River to the river at the outfall named North 

River Road 9th to 15th Street. PPE # 3 drains approximately 132 acres in central Black 

Eagle to the Missouri River at the outfall named 15th Street Bridge North. PPE # 4 drains 

approximately 22 acres in south central Black Eagle at the outfall named Black Eagle 

South East. The eastern area of Black Eagle, approximately 188 acres including the 

Moose Lodge and the northeast quadrant of the golf course, drains through PPE # 5 into 

the Missouri River (Ref. 55, pp. 1-11; Ref. 50, 1 page; Ref. 59, pp.1-2). The surface 

water pathway for source 1-residential soil, would continue through Black Eagle Dam, 

past the sample collection locations of the 2003 and 2009 EPA investigations, through 

Rainbow Dam and Morony Dam to the 15-mile target distance limit (TDL) (Ref. 50, 1 

page). 

The probable point of entry (PPE #6) for wastes associated with source 2-the East Ditch 

Dump on the ACM Smelter and Refinery property is shown on the surface water pathway 

map (Ref. 18, p. 38; Ref. 50; Ref. 58, Appendix I). The overland flow route from the 

East Ditch Dump to the Missouri River is south off the ridge to the river through a gully 

for approximately 400 feet to the Missouri River (Ref. 4, map 1; Ref. 50; Ref. 58, 

Appendix I). However, other sources at the facility likely also have potential to release 

by overland flow due to lack of cover, the natural slope of the land toward the Missouri 

River, and culverts that drain surface water directly into the Missouri River (Ref. 18, p. 

19, 20, 22, 32, & 38; Ref. 23, p. 31). The surface water pathway from PPE#6 would 

continue past the sample collection locations of the 2003 and 2009 EPA investigations, 

through Rainbow Dam and Morony Dam to the 15-mile target distance limit (TDL) (Ref. 

50, 1 page). 

As such, the overland segment of the hazardous substance migration path from each source has been 

appropriately described, as the migration path from each source and associated downgradient probable 

point of entry to surface water was detailed according to the HRS (see Figure 1 of this support document 

for site map presenting sources and PPEs). Also, the in-water segment and target distance limit (TDL) for 

the watershed were appropriately established as the TDL was defined as 15 miles downstream of PPE#6 

within the Missouri River. 

ARCO is incorrect in its assertion that the drainage area associated with PPE #1 should be removed from 

the surface water pathway evaluation because it is upstream of the most upstream background sample 

(AGFSED1). The HRS does not require that each individual PPE have an observed release associated 

specifically with it. PPE #1 was established following the directions cited above from HRS Section 

4.1.1.1, which contains no requirement that a PPE be ignored if it is upstream of a sample used to 

establish an observed release. 

Sample AGFSED1 was selected to establish a background level and thus used to illustrate a significant 

increase in observed release samples. Even though this sample is located downstream of PPE #1, this 

does not mean that some contamination is not still migrating from Source 1 through PPE #1 to the 

Missouri River. In fact, as shown in Section 3.20, Surface Water Likelihood of Release - Observed 

Release by Chemical Analysis, of this support document, this sample does contain detectable levels of 

hazardous substances associated with Source 1. 

Additionally, the possibility that this background sample may be affected by site contamination does not 

diminish its ability to fulfill the purpose of a background sample: to establish a background level in the 

medium of concern for the site to determine whether or not a significant increase in contaminant levels 

from the site has occurred. As established in section 3.20, Surface Water Likelihood of Release - 

Observed Release by Chemical Analysis, of this support document, the downstream observed release 

levels are clearly three times greater than the background levels. Therefore, there is no reason to remove 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

the area drained by PPE #1 from consideration in the surface water pathway, and no reason to question 

the validity of the background levels established by sample AGFSED1. 

ARCO is also incorrect in its assertion that higher levels of contaminants found upstream of Source 2's 

probable point of entry (PPE #6) means Source 2 is not a source of contamination to the surface water 

pathway. Just because the two sediment samples with the highest contaminant concentrations in the 2009 

ESI (AGFSED-2 and AGFSED-3) are upstream of Source 2, it does not mean that Source 2 is not 

contributing hazardous substances to surface water. Further, observed release samples AGFSED-5 and 

AGFSED-6 are downstream of Source 2, and while they could be affected by contamination migrating 

from Source 1, they also could be affected by contaminants migrating from Source 2. The information 

available is insufficient to demonstrate that Source 1 is the only contributor to the contamination found in 

samples AGFSED-5 and AGFSED-6. 

Regarding ARCO’s assertion that a portion of Source 1 should not be included in the site simply because 

it has not been definitively shown to be releasing to surface water, the HRS has no such requirement. 

HRS Section 2.2.3, Identify hazardous substances available to a pathway, specifies that the surface water 

containment factor value need be greater than zero to consider hazardous substances identified in the 

source to be available to migrate to the surface water pathway. In addition, the HRS does not require that 

an observed release need be attributed to specific sources. HRS Section 4.1.2.1.1, Observed release, 

specifies that the observed release concentration must be significantly above background and some 

portion of that significant increase must be attributable to the site (not specifically to an individual source) 

in order to establish an observed release in a watershed (see Section 3.20, Surface Water Likelihood of 

Release - Observed Release by Chemical Analysis, of this support document). 

These comments have no impact on the site score or the decision to list the site on the NPL. 

Likelihood of Release 

The HRS documentation record at proposal established observed releases of hazardous substances to the 

Missouri River both by direct observation of slag dumped into the river and by chemical analysis of 

metals levels in river sediment samples. Historical evidence was presented to document extensive 

dumping of slag from the former facility into the river over the course of several decades, and showing 

that slag contained substantial concentrations of copper (see pages 38-39 of the HRS documentation 

record at proposal). Four contaminated sediment samples and one background sediment sample were 

described to show that concentrations of cadmium and lead significantly above background levels were 

present in river sediments; these samples established observed releases of hazardous substances 

attributable to the site and meet the HRS criteria to establish observed release by chemical analysis (see 

pages 39-40 of the HRS documentation record at proposal). 

3.19 Likelihood of Release - Observed Release by Direct Observation 

Comment: ARCO made a number of comments in opposition to EPA's scoring of an observed release to 

surface water by direct observation, including objections to the use of alleged “anecdotal evidence,” 

objections to references, and objections to source association. 

Responses to specific comments are presented in the following subsections of this support document: 

• 3.19.1 Documentation of Observed Release by Direct Observation 

• 3.19.2 Quantity of Slag Dumped into the Missouri River 

• 3.19.3 Source of Slag Material 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

3.19.1 Documentation of Observed Release by Direct Observation 

Comment: ARCO challenged the observed release by direct observation by alleging that EPA uses 

“anecdotal evidence from almost 100 years ago” of tailings and slag disposal in the Missouri River to 

establish the observed release by direct observation to the river. ARCO acknowledges that “the historical 

record reports some volume of tailings and slag were disposed in the River nearly a century ago,” and that 

“this standard practice at the time was followed.” 

ARCO also states that, in the Observed Release by Direct Observation section of the HRS documentation 

record at proposal, EPA states that cindery slag material was observed in the sediments during 2009 

sampling; “however, three of the four references cited make no mention of slag in the Missouri River 

sediment.” 

Response: The observed release by direct observation has been correctly documented and scored in 

accordance with the HRS. Furthermore, as quoted above, ARCO acknowledges the historical record of 

the disposal of slag and tailings into the river. 

HRS Section 4.1.2.1.1, Observed Release, contains the requirements for establishing an observed release 

by direct observation: 

Establish an observed release to surface water by demonstrating that the site has released

a hazardous substance to the surface water in the watershed. (Emphasis added.) 

HRS Section 4.1.2.1.1 provides that an observed release by direct observation can be based on any one of 

three criteria: 

- A material that contains one or more hazardous substances has been seen entering surface 

water through migration or is known to have entered surface water through direct 

deposition, or 

- A source area has been flooded at a time that hazardous substances were present, and one 

or more hazardous substances were in contact with the flood waters, or 

- When evidence supports the inference of a release of a material that contains one or more 

hazardous substances by the site to surface water, demonstrated adverse effects 

associated with that release may also be used to establish an observed release. 

The first of these criteria has been satisfied in the HRS documentation record at proposal, which stated the 

following on pages 38 and 39: 

The Boston and Montana smelter routinely dumped large quantities of granulated slag 

and tailings into the Missouri River (Ref. 6, p. 42; Ref. 15, p. 1). In 1907, the Boston and 

Montana Consolidated Copper and Silver Mining Company estimated that the facility 

could receive up to 4800 tons a day of ore and changing the disposal of slag to railcar 

would significantly increase rail traffic (Ref. 14, p. 1). The Montana Department of 

Environmental Quality (Montana DEQ) estimates that between 27,500,000 and 

31,000,000 cubic yards of waste were dumped into the Missouri River between 1893 and 

1915 until onsite containment was instituted in 1915. Montana DEQ also reports that it is 

possible that dumping of waste into the Missouri River continued at a reduced rate after 

1915 until the facility closed in the 1970s (Ref. 16, p. 1). So much smelter waste was 

dumped into the Missouri River between 1893 and 1915 that the management and legal 

department of the Boston and Montana Company were concerned that the Federal 

Government would intervene and enjoin the deposition of tailings into the Missouri River 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

by virtue of the constitutional provisions requiring the federal government to maintain 

navigable streams (Ref. 15, pp. 1 and 2). In 1884 Judge Lorenzo Sawyer of the United 

States Circuit Court in San Francisco had granted a perpetual injunction against hydraulic 

mining in California’s American River on these very grounds (Ref. 6, p. 38). 

Numerous complaints were filed by property owners and communities along the Missouri 

River downstream of the ACM Smelter and Refinery of water quality issues and slag and 

smelter waste clogging the Missouri River (Ref. 6, p. 42; Ref. 29, p. 8A). These 

complaints increased after the 1908 flood of the Missouri River inundated the community 

of Fort Benton, 40 miles downstream of the Boston and Montana Smelter with smelter 

waste (Ref. 6, p. 38; Ref. 29, p. 8A). A company analysis of slime (very fine grained slag 

and tailings, which tended to float in the Missouri River) taken above Rainbow Falls 

Dam in 1914 indicated that the slime contained between .55 and 1.1 percent copper (Ref. 

17, p. 1). The Boston and Montana Company sought to buy off disgruntled property 

owners and placate communities by providing alternate domestic water sources (Ref. 6, 

pp. 49-51). 

Cindery slag material was also currently observed to be in the sediments of the Missouri 

River adjacent to the ACM Smelter and Refinery facility (Ref. 23, p. 57 and 202, Ref, 53 

p. 1; Ref. 54, p. 1). 

That a hazardous substance was associated with the slag is shown above by the documentation of the 

analysis of fine-grained slag and tailings (referred to as “slime”) that resulted from the slag deposition 

into the river, which contained between 0.55 and 1.1 percent copper. 

In addition, the presence of other hazardous substances has been documented in the slag through 

sampling. As discussed in section 3.13, Additional Sources, of this support document, a slag source 

(Source 4) has been added to the HRS evaluation at promulgation. A sample of this slag is described in 

section 2.2.2, Source 4, of the HRS documentation record at promulgation, and reveals the presence of the 

hazardous substances arsenic, cadmium, copper, lead, manganese, and zinc. These substances are also 

added to the discussion in the Observed Release by Direct Observation section of the HRS documentation 

record at promulgation (see pages 49-50 of the HRS documentation record at promulgation). 

While ARCO objected to the timeframe in which the documentation of slag disposal in the Missouri 

River originated, ARCO does not dispute the disposal of the slag, and in fact, actually acknowledges in its 

comments that the facility historically followed the standard practice of disposing tailings and slag in the 

Missouri River (see the second paragraph on [bottom] page number 6 of ARCO’s Comment Section B: 

Atlantic Richfield's General Comments on the HRS Documentation Record Former Great Falls Refinery 

Site, docket ID EPA-HQ-SFUND-2010-0072-0016.2). Regardless of when the slag dumping in the 

Missouri River occurred, the establishment of an observed release is based on whether or not a release 

“has occurred” – the HRS does not direct the scorer to determine a specific timeframe of a release. 

Thus, the available documentation clearly shows that slag, demonstrated to contain hazardous substances, 

was documented in the Missouri River by visual observation of sediments and was documented through 

facility records and ARCO statements as being dumped into the Missouri River. 

These comments have no effect on the site score or the decision to list the site on the NPL.

3.19.2 Quantity of Slag Dumped into the Missouri River 

Comment: ARCO discounted the quantity of slag that was documented to have been dumped by the 

Anaconda Mining Company at the site, commenting that there was no reference in the [MDEQ] site 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

investigation report to document how MDEQ arrived at its estimate of 27,500,000-31,000,000 cubic yards 

of waste [slag] dumped in the Missouri River between 1893 and 1915. ARCO also dismissed as "pure 

speculation" MDEQ's statement that “it is possible that dumping of waste into the Missouri River 

continued at a reduced rate after 1915 until the facility closed in the 1970's.” In addition, ARCO 

commented on the ambiguity of a reference describing a possible increase in the amount of ore received 

by the facility. 

Response: The observed release by direct observation was appropriately established, regardless of the 

quantity of slag disposed into the Missouri River. The quantity of slag that has entered the Missouri 

River as a result of facility operations is not considered in the establishment of an observed release by 

direct observation nor was the quantity used in the HRS scoring to assign any scoring factor. 

As discussed in subsection 3.19.1, Documentation of Observed Release by Direct Observation, of this 

support document, in establishing an observed release by direct observation, HRS Section 4.1.2.1.1 

requires that: 

A material that contains one or more hazardous substances has been seen entering surface 

water through migration or is known to have entered surface water through direct 

deposition. 

The HRS documentation record at proposal, on pages 38 and 39, fulfills these requirements by 

documenting, in relevant part: 

The Boston and Montana smelter routinely dumped large quantities of granulated slag 

and tailings into the Missouri River (Ref. 6, p. 42; Ref. 15, p. 1). . . So much smelter 

waste was dumped into the Missouri River between 1893 and 1915 that the management 

and legal department of the Boston and Montana Company were concerned that the 

Federal Government would intervene and enjoin the deposition of tailings into the 

Missouri River by virtue of the constitutional provisions requiring the federal government 

to maintain navigable streams (Ref 15, pp. 1 and 2). 

Cindery slag material was also currently observed to be in the sediments of the Missouri 

River adjacent to the ACM Smelter and Refinery facility (Ref. 23, p. 57 and 202, Ref. 53, 

p. 1; Ref. 54, p. 1). 

The HRS does not require that an exact amount of the material containing hazardous substances that 

entered the surface water be known to score an observed release by direct observation. Therefore, the 

amount of slag waste dumped into the river was not considered in establishing the observed release by 

direct observation, nor was the amount of waste slag considered in the hazardous waste quantity 

evaluation for the surface water pathway. Therefore, the MDEQ estimate of the quantity of slag dumped 

into the Missouri River, and whether slag waste was dumped into the Missouri River after 1915 have no 

bearing on the establishment of an observed release by direct observation in the HRS evaluation. Also, 

the amount of slag dumped into the river is not used in estimating the waste quantity of the new Source 4 

(slag waste) added in the HRS documentation at promulgation. 

These comments have no effect on the site score or the decision to list the site on the NPL. 

3.19.3 Source of Slag Material 

Comment: In its specific comments objecting to the observed release by direct observation, ARCO 

contended that “no observed release has been established for Source 1 or Source 2,” and that slag is not 

related to these sources. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Response: An observed release by direct observation has been appropriately established from the site, in 

accordance with the provisions of the HRS, and an additional origin (source) of slag material has been 

associated with the site at promulgation. Source 4, slag waste, has been added to the HRS documentation 

record at promulgation as discussed in section 3.13, Additional Sources, of this support document. Slag 

from this source was sampled and documented as containing hazardous substances as described in the 

HRS documentation record at proposal. 

HRS Section 4.1.2.1.1, Observed release, directs the user to: 

Establish an observed release to surface water for a watershed by demonstrating that the 

site [emphasis added] has released a hazardous substance to the surface water in the 

watershed. 

The HRS specifies that the observed release has to have come from the site, not that it has to have come 

from individual sources at the site. 

The HRS documentation record at proposal, while not associating the slag in the observed release by 

direct observation with Source 1, the Black Eagle soils, or Source 2, the East Ditch Dump, clearly 

associates it with the site, as specified by the HRS. This is shown on page 38 of the HRS documentation 

record at proposal, excerpted in relevant part as follows: 

The Boston and Montana smelter routinely dumped large quantities of granulated slag 

and tailings into the Missouri River (Ref. 6, p. 42; Ref. 15, p. 1). . . So much smelter 

waste was dumped into the Missouri River between 1893 and 1915 that the management 

and legal department of the Boston and Montana Company were concerned that the 

Federal Government would intervene and enjoin the deposition of tailings into the 

Missouri River by virtue of the constitutional provisions requiring the federal government 

to maintain navigable streams (Ref 15, pp. 1 and 2). 

In addition, as discussed in section 3.13, Additional Sources, of this support document, two sources have 

been added to the HRS documentation record at promulgation, one of which (Source 4) represents onsite 

disposal of slag waste. This source is described in detail in section 3.13 of this support document. Its 

addition clarifies that the slag wastestream generated on site is part of the site as scored. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.20 Surface Water Likelihood of Release - Observed Release by Chemical 

Analysis 

Comment: ARCO provided a number of comments contesting the observed release by chemical analysis 

to the Missouri River. ARCO referred to the sediment samples meeting observed release criteria as 

having "weakly elevated metals concentrations," and pointed out that they were also located downstream 

of urban and industrial areas. ARCO also argued against the adequacy of the background sediment 

sample. 

Response: The observed release by chemical analysis was appropriate, adequate, and established in 

accordance with HRS requirements. Four sediment sample locations were documented as meeting 

observed release criteria in the HRS documentation record at proposal (see Figure 1 in section 3.17, 

Description of Pathway, of this support document for sample locations). These requirements are 

presented in HRS Section 4.1.2.1.1, Observed release, which directs the user to: 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Establish an observed release to surface water for a watershed by demonstrating that the 

site has released a hazardous substance to the surface water in the watershed. Base this 

demonstration on either: 

• Direct observation: 

. . . . [or] 

• Chemical analysis: 

- Analysis of surface water, benthic, or sediment samples indicates that the 

concentration of hazardous substance(s) has increased significantly 

above the background concentration for the site for that type of sample 

(see section 2.3). 

– Limit comparisons to similar types of samples and background 

concentrations - for example, compare surface water samples to 

surface water background concentrations. 

– For benthic samples, limit comparisons to essentially sessile 

organisms. 

- Some portion of the significant increase must be attributable to the site to 

establish the observed release, except: when the site itself consists of 

contaminated sediments with no identified source, no separate attribution 

is required. 

- If an observed release can be established for a watershed, assign an 

observed release factor value of 550 to that watershed, enter this value in 

Table 4-1, and proceed to section 4.1.2.1.3. 

In addition, HRS Section 2.3, Likelihood of Release, specifies that the scorer “[u]se the criteria in Table 2-

3 as the standard for determining analytical significance.” HRS Table 2-3 states that, if a sample 

measurement is greater than or equal to the SQL, an observed release is established: 

• If the background concentration is not detected (or is less than the detection 

limit), an observed release is established when the sample measurement equals or 

exceeds the sample quantitation limit. 

• If the background concentration equals or exceeds the detection limit, an 

observed release is established when the sample measurement is 3 times or more 

above the background concentration. 

In accordance with these requirements, the HRS documentation record at proposal, beginning on page 39, 

presents the rationale and cites the supporting documentation for the observed release by chemical 

analysis by describing sediment sample collection and analysis from two investigations conducted in the 

Missouri River adjacent to and downstream of the site. The discussion of the April 2003 field 

investigation, in relevant part, stated: 

Eight sediment samples from the Missouri River were collected by Tetra Tech EM, Inc 

for the EPA’s Expanded Site Inspection in April 2003. These samples were collected 

from the north bank of the Missouri River and consisted of medium to medium fine 

grained tan particles (Ref. 54, 1 page). All samples were analyzed through the EPA CLP, 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

RAS for TAL total metals. Soil samples for inorganic analysis were delivered to Sentinal 

Inc, of Huntsville, Alabama (Ref. 18, p. 3). The analytical data was validated by Tetra 

Tech, EM, Inc, of Chicago, IL on July 30, 2003 (Ref. 18, p. 56) . . . 

Analyses of sediment samples collected during the April 2003 sampling event indicate 

that concentrations of arsenic, cadmium, copper, lead, manganese, and zinc are 

significantly above background concentrations in the Missouri River for a distance of 

2.39 miles downstream of the probable point of entry (PPE) at the Black Eagle Dam (Ref. 

18, p. 39, Figure 3). 

The discussion of the 2009 sampling investigation, the primary support for the observed release to surface 

water by chemical analysis, was presented at proposal in both text and table formats. The text portion of 

this description, on page 39 of the HRS documentation record at proposal, is as follows: 

Seven release sediment samples were collected by START for the EPA Region 8 on July 

14, 2009. All release samples were collected by boat from the north side of the Missouri 

River from beneath the water. A background sample (AGFSED1) was collected from the 

north bank of the Missouri River, downstream of the Montana Refining Company facility 

and upstream of the outfall North River Road 9th to 15th Street No. 3 (PPE#1) and the 

community of Black Eagle (Ref. 50, 1 page). The samples were analyzed by Compuchem 

Laboratory in Cary, North Carolina, for total Target Analyte List (TAL) metals analysis 

with a supporting Level 4 data package (Ref. 23, pp 6, 15, & 21). The data package was 

validated by a START chemist who determined that the background cadmium result was 

biased high as well as two downstream results (Ref. 23, pp. 77-198). The analytical data 

was revised in accordance with the EPA guidelines for using qualified data, which 

resulted in the high bias for the background sample being retained while the two 

downstream, analytical results were revised downward (Ref. 43, pp. 1-9, 18). The 

following table provides analytical data to document the observed release by chemical 

analysis. 

Analyses of sediment samples collected during the July 2009 sampling event indicate that 

concentrations of lead are above background concentrations in the Missouri River for a 

distance of 2.39 miles downstream of the probable point of entry (PPE) at the Black 

Eagle Dam (Ref. 24, p. 28, Table 3; Ref. 50). According to the HRS, if an observed 

release can be established, a value of 550 is assigned for Likelihood of Release (Ref. 1, 

Section 4.1.2.1.1, p. 51609). 

The observed release samples were presented on page 40 of the HRS documentation record at proposal, 

and are shown in the following table. 

Sediment Samples Collected from the Missouri River adjacent and downstream of the ACM Smelter and 

Refinery, July 2009 

Sample ID Sample 

Location 

Sample 

Date 

Cadmium 

(Cd) 

mg/kg 

Lead 

(Pb) 

mg/kg 

CRQL HRS Documentation Record 

at Proposal Reference 

AGFSED1 

0907118-01 

Background 

Sample at 

11th Street 

07/14/09 0.36 J+ 12.3 Cd :0.06 

Pb: 0.21- 

Ref. 2, p. BII-2, BII-8; Ref. 23, 

pp. 28, 30, 37, 40, 46, 69, 70, 

85, 174-176, 177, 179, 182, 

183, 190, 204. 

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Sediment Samples Collected from the Missouri River adjacent and downstream of the ACM Smelter and 

Refinery, July 2009 

Cadmium Lead Sample Sample Sample ID CRQL Location Date (Cd) (Pb) 

mg/kg mg/kg 

HRS Documentation Record 

at Proposal Reference 

AGFSED2 

0907118-02 

1.89 miles 

downstream 

of PPE No. 1 

07/14/09 (11.7 J+) 

8.3 168 Cd: 0.06 Pb: 0.21- 

Ref. 2, p. BII-2, BII-8; Ref. 23, 

pp. 28, 30, 37, 40, 47, 69, 70, 

85, 174-176., 177, 179, 182, 

183, 191, 202. 

AGFSED3 

0907118-03 

1.95 miles 

downstream 

of PPE No. 1 

07/14/09 11.8 78.4 Cd: 0.06 

Pb: 0.21 

Ref. 2, p. BII-2, BII-8; Ref. 23, 

pp. 28, 31, 37, 40, 48, 69, 70, 

85, 174-176, 177, 182, 192, 

202. 

AGFSED4 

0907118-04 

2.06 miles 

downstream 

of PPE No. 1 

07/14/09 3.9 18.9 Cd: 0.06 

Pb: 0.21 

Ref. 2, p. BII-2, BII-8; Ref. 23, 

pp. 28, 31, 37, 40, 49, 69, 70, 

85, 174-176, 177, 182, 193, 

202. 

AGFSED5 

0907118-05 

2.39 miles 

downstream 

of PPE No. 1 

07/14/09 (4.2 J+) 

2.9 49.9 Cd: 0.06 

Ref. 2, p. BII-2, BII-8; Ref. 23, 

pp. 28, 32, 37, 40, 50, 69, 70, 

85, 174-176, 177, 179, 182, 

183, 194, 202-203. 

Pb: 0.21 

These samples (AGFSED2, AGFSED3, AGFSED4, AGFSED5) illustrate that concentrations of cadmium 

or lead in sediments are present in levels greater that three times the levels found in the background 

sample (AGFSED1), meeting the criteria in HRS Section 2.3, Likelihood of Release, cited above. 

As further detailed in section 3.20.2 of this support document, Surface Water Observed Release – 

Attribution, the HRS documentation record at proposal documents that the released substances are 

associated with the ACM site as they are in on-site sources and at least part of the contamination in the 

river came from the site based on direct observation of slag being dumped into the river. Therefore, the 

significant increase in contaminant levels has been appropriately attributed at least in part to the ACM 

site. In addition ARCO only alleged contributions from other off site sources; it did not document actual 

contribution. 

Thus, an observed release by chemical analysis has been appropriately established according to the HRS 

requirements, as the presence of hazardous substances attributable to the site were found in release 

samples adjacent to and downstream of the site at levels significantly above background concentrations. 

Specific issues related to ARCO's objections to the observed release to chemical analysis are addressed in 

the following subsections of this support document: 

• 3.20.1 Surface Water Observed Release - Significant Increase 

• 3.20.2 Surface Water Observed Release - Attribution 

• 3.20.3 Surface Water Observed Release - Adequacy of Background 

3.20.1 Surface Water Observed Release - Significant Increase 

Comment: ARCO made a number of comments arguing that the contamination used to score the 

significant increase for the surface water observed release was not sufficient. These arguments were that: 

• the contamination levels did not exceed regulatory criteria, 

• recent data do not indicate contamination of the water column, 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

• EPA's conclusions regarding the contamination are biased, and 

• the contamination levels are not indicative of release. 

Specific comments are addressed in the following subsections of this support document: 

• 3.20.1.1 Contamination Levels Below Regulatory Limits 

• 3.20.1.2 Releases in Other Aquatic Media 

• 3.20.1.3 Bias of Conclusions/Current Conditions 

• 3.20.1.4 Downstream Contaminant Levels 

 

3.20.1.1 Contamination Levels below Regulatory Limits 

Comment: In challenging the sufficiency of the significant increase in the observed release, ARCO 

stated that “[a] recent and multiple sampling station comparison of Missouri River water quality 

upstream and downstream of the Site indicates that, while a few statistically significant differences in 

concentrations were noted, none of the reported total or dissolved concentrations exceeded applicable 

aquatic life water quality standards at any sampling station.” ARCO also maintained that only a few 

concentrations from similar sampling “exceeded relevant sediment quality biological effect threshold 

concentrations.” 

 

Response: Whether or not the contaminant levels documented that the Missouri River exceeded various 

regulatory limits does not discredit that an observed release by chemical analysis was appropriately 

evaluated. As identified in section 3.20, Surface Water Likelihood of Release - Observed Release by 

Chemical Analysis, of this support document, the analytical data provided for the observed release by 

chemical analysis in the HRS documentation record at proposal meet the HRS criteria for an observed 

release by chemical analysis. 

As discussed in more detail in section 3.20, Surface Water Likelihood of Release - Observed Release by 

Chemical Analysis, of this support document, in establishing an observed release by chemical analysis, 

HRS Section 4.1.2.1.1, Observed release, states: 

• Chemical analysis: 

- Analysis of surface water, benthic, or sediment samples indicates that the 

concentration of hazardous substance(s) has increased significantly above the 

background concentration for the site for that type of sample (see section 2.3). 

. . . . . 

- Some portion of the significant increase must be attributable to the site to 

establish the observed release, except: when the site itself consists of 

contaminated sediments with no identified source, no separate attribution is 

required. 

- If an observed release can be established for a watershed, assign an observed 

release factor value of 550 to that watershed, enter this value in Table 4-1, and 

proceed to section 4.1.2.1.3. 

HRS Section 2.3, Likelihood of Release, specifies that the user is to “[u]se the criteria in Table 2-3 as the 

standard for determining analytical significance.” HRS Table 2-3 states the following: 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

An observed release is established as follows: 

• If the background concentration is not detected (or is less than the detection 

limit), an observed release is established when the sample measurement equals or 

exceeds the sample quantitation limit. 

• If the background concentration equals or exceeds the detection limit, an 

observed release is established when the sample measurement is 3 times or more 

above the background concentration. 

Because cadmium and lead were found at detectable levels in the background sample as presented in 

section 3.20, Surface Water Likelihood of Release - Observed Release by Chemical Analysis, of this 

support document, the HRS requires that, to meet the criteria for analytical significance, these 

contaminants be present in a release sample at levels three times or greater than the respective background 

concentrations. As shown in section 3.20 of this support document, the background level for cadmium 

was 0.36 mg/kg and the release sample results for cadmium ranged from 2.9 to 11.8 mg/kg. Not only do 

the release sample concentrations exceed the background level by more than 3 times, all but one of the 

release sample concentrations exceed the background by more than 10 times. For lead, the background 

level was 12.3 mg/kg and the release samples ranged from 18.9 to 168 mg/kg; three of four release 

sample concentrations clearly exceed the background level by more than 3 times. 

In addition, although not included in the HRS evaluation, other metals were also detected in release 

samples at levels that meet the criteria for significant increase in downstream sediment samples. In 

downstream sediment sample AGFSED2, copper and zinc were detected at concentrations of 472 and 

2370 mg/kg, respectively. In sample AGFSED3, copper and zinc were detected at 129 and 1,060 mg/kg, 

respectively. These concentrations are more than three times greater than their related concentrations in 

the background sample AGFSED1—41 mg/kg copper and 99.2 mg/kg zinc (see HRS Reference 23, pages 

190-192). 

Regarding exceedances of water quality standards or sediment quality threshold concentrations, the HRS 

does not require that any standards or benchmarks be exceeded to document an observed release, as 

shown by HRS Sections 4.1.2.1.1 and 2.3, above. Section 3.7, Permitted Releases and Regulatory Limits, 

of this support document, addresses this topic in further detail. On this basis, the cadmium and lead 

concentrations presented on pages 39 and 40 of the HRS documentation record at proposal meet the HRS 

criteria for significant increase and are therefore sufficient to identify an observed release by chemical 

analysis. 

This comment has no effect on the HRS site score or the decision to list the site on the NPL. 

3.20.1.2 Releases in Other Aquatic Media 

Comment: ARCO asserted that both surface water and fish tissue data collected from the Missouri River 

in the vicinity of the site do not support the establishment of an observed release. ARCO stated that the 

majority of the site-specific water quality data from sampling locations in the vicinity of the ACM facility 

do not indicate contamination of the water column. ARCO also stated that the Montana Department of 

Fish, Wildlife and Parks (MDFWP) Pollution Control Biologist, upon review of the 2004 Parametrix 

investigation, concluded that “the results indicate no obvious increase in metals in fish between the Black 

Eagle and Rainbow Dams.” 

Response: Sediment samples were appropriately used in the documentation of an observed release by 

chemical analysis; other aquatic media, such as surface water and fish tissue samples, were not used in 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

establishing the observed release nor are they required. Furthermore, other sampling results not 

establishing observed releases do not negate that other observed releases were found. 

In establishing an observed release by chemical analysis, HRS Section 4.1.2.1.1, Observed release, states: 

• Chemical analysis: 

- Analysis of surface water, benthic, or sediment samples indicates that 

the concentration of hazardous substance(s) has increased significantly 

above the background concentration for the site for that type of sample

(see section 2.3). [emphasis added] 

. . . . . 

- Some portion of the significant increase must be attributable to the site to 

establish the observed release, except: when the site itself consists of 

contaminated sediments with no identified source, no separate attribution 

is required. 

- If an observed release can be established for a watershed, assign an 

observed release factor value of 550 to that watershed, enter this value in 

Table 4-1, and proceed to section 4.1.2.1.3. 

As detailed further in section 3.20, Surface Water Likelihood of Release - Observed Release by Chemical 

Analysis, of this support document, pages 39-40 of the HRS documentation record at proposal correctly 

established an observed release of hazardous substances in Missouri River sediments. As stated in HRS 

Section 4.1.2.1.1, Observed Release, an observed release by chemical analysis is established in either 

surface water, benthic, or sediment samples; there is no requirement that an observed release be 

established in all three media. Thus, the HRS allows for an observed release to surface water to be 

documented by sediment samples alone. 

This comment has no effect on the HRS site score or the decision to list the site on the NPL. 

3.20.1.3 Bias of Conclusions/Current Conditions 

Comment: ARCO stated that EPA's conclusions regarding metals concentrations in Missouri River 

sediment are biased to support the HRS score, and do not reflect data that describe current conditions. 

ARCO stated: 

The water quality exceedances reported in Tetra Tech (AR Reference #10), from that 

limited distribution of sampling stations adjacent to or within the Site boundaries, were 

not confirmed by the more recent and far more widely distributed sampling transects and 

stations proximate to the Former GFR Site and reported in Parametrix (AR Reference 

#16). 

Response: ARCO has not presented data that refute EPA’s identification of an observed release by 

chemical analysis. Further ARCO has not documented any improper bias in the data or in how the data 

were used by the Agency to perform the HRS evaluation. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

In establishing an observed release by chemical analysis, HRS Section 4.1.2.1.1, Observed release, states: 

• Chemical analysis: 

- Analysis of surface water, benthic, or sediment samples indicates that the 

concentration of hazardous substance(s) has increased significantly 

above the background concentration for the site for that type of sample 

(see section 2.3). 

. . . . . 

- Some portion of the significant increase must be attributable to the site to 

establish the observed release, except: when the site itself consists of 

contaminated sediments with no identified source, no separate attribution 

is required. 

- If an observed release can be established for a watershed, assign an 

observed release factor value of 550 to that watershed, enter this value in 

Table 4-1, and proceed to section 4.1.2.1.3. 

The HRS documentation record at proposal stated on page 39: 

Eight sediment samples from the Missouri River were collected by Tetra Tech EM, Inc 

for the EPA’s Expanded Site Inspection in April 2003. . . .Analyses of sediment samples 

collected during the April 2003 sampling event indicate that concentrations of arsenic, 

cadmium, copper, lead, manganese, and zinc are significantly above background 

concentrations in the Missouri River for a distance of 2.39 miles downstream of the 

probable point of entry (PPE) at the Black Eagle Dam (Ref. 18, p. 39, Figure 3). . . . 

Seven release sediment samples were collected by START for the EPA Region 8 on July 

14, 2009. All release samples were collected by boat from the north side of the Missouri 

River from beneath the water. A background sample (AGFSED1) was collected from the 

north bank of the Missouri River, downstream of the Montana Refining Company facility 

and upstream of the outfall North River Road 9th to 15th Street No. 3 (PPE#1) and the 

community of Black Eagle (Ref. 50, 1 page). 

Data from the 2009 Site Assessment Expanded Site Inspection of the Missouri River sediments were used 

in the documentation of an observed release by chemical analysis. Thus, the more recent 2009 

investigation (compared to the 2004 Parametrix investigation cited by ARCO) of the Missouri River 

sediments was utilized in establishing the observed release by chemical analysis. 

Although the 2003 Expanded Site Inspection performed by Tetra Tech found concentrations of various 

metals in Missouri River sediments, data from this study was not used in establishing the observed release 

by chemical analysis. Furthermore, HRS Section 4.1.2.1.1, Observed Release, states in part: “Establish 

an observed release to surface water for a watershed by demonstrating that the site has released a 

hazardous substance to the surface water in the watershed” [emphasis added]. As discussed in Section 

3.20, Surface Water Likelihood of Release - Observed Release by Chemical Analysis, of this support 

document, an observed release was established by demonstration that hazardous substances detected 

within release samples was significantly greater than background levels. There is no requirement that the 

release is ongoing, nor is there specification of any timeframe at all. ARCO’s assertion that the “water 

quality exceedances” reported in the 2003 Tetra Tech investigation were not confirmed by the more 

recent Parametrix investigation does not negate the sediment concentrations detected in the more recent 

2009 investigation used in establishing the observed release by chemical analysis. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

To the extent ARCO has asserted that EPA was biased in its conclusions regarding sediment metals 

concentrations, as shown above, EPA used the most recent data available in establishing observed 

releases at this site in a manner consistent with HRS requirements. If ARCO is alleging that the data used 

by EPA was not as comprehensive as that in other studies, the HRS evaluation is a screening tool based 

on limited sampling and only indicates further investigation is necessary—further sampling is performed 

at the remedial investigation phase of the Superfund process (see section 3.6, Risk Associated with Site, 

of this support document). 

This comment has no effect on the HRS site score or the decision to list the site on the NPL. 

3.20.1.4 Downstream Contaminant Levels 

Comment: ARCO stated that in 2004 it retained Parametrix to conduct an investigation, which concluded 

that metals concentrations in sediment, surface water, and fish tissues at the ACM facility were generally 

comparable to upstream (background) concentrations. 

ARCO stated that results of an MDEQ river sampling event conducted approximately 32 miles 

downstream from the ACM facility caused MDEQ to speculate that “both upriver and downriver soils and 

sediments may contain elevated metals levels.” ARCO stated that “the investigators specifically focused 

on....slag particles mixed with natural river sands,” and that MDEQ's speculations were “[b]ased on these 

limited data.” 

Response: The HRS evaluation of the observed release by chemical analysis appropriately compared an 

upgradient background sample to downgradient release samples. The Parametrix study, as presented in 

Reference 16 of ARCO’s comments, does not indicate any flaw in the evaluation of the analytical results 

used in the establishment of observed releases by chemical analysis. 

In establishing an observed release by chemical analysis, HRS Section 4.1.2.1.1, Observed release, states: 

• Chemical analysis: 

- Analysis of surface water, benthic, or sediment samples indicates that the 

concentration of hazardous substance(s) has increased significantly above the 

background concentration for the site for that type of sample (see section 2.3). 

. . . . . 

- Some portion of the significant increase must be attributable to the site to 

establish the observed release, except: when the site itself consists of 

contaminated sediments with no identified source, no separate attribution is 

required. 

- If an observed release can be established for a watershed, assign an observed 

release factor value of 550 to that watershed, enter this value in Table 4-1, and 

proceed to section 4.1.2.1.3. 

HRS Section 2.3, Likelihood of Release, specifies that the scorer "[u]se the criteria in Table 2-3 as the 

standard for determining analytical significance." HRS Table 2-3 states the following: 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

An observed release is established as follows: 

• If the background concentration is not detected (or is less than the detection 

limit), an observed release is established when the sample measurement equals or 

exceeds the sample quantitation limit. 

• If the background concentration equals or exceeds the detection limit, an 

observed release is established when the sample measurement is 3 times or more 

above the background concentration. 

As presented in section 3.20, Surface Water Likelihood of Release - Observed Release by Chemical 

Analysis, of this support document, an observed release of hazardous substances was established in 

Missouri River sediments. The background sample (AGFSED1) was compared to the downstream 

release samples (AGFSED2, AGFSED3, AGFSED4, and AGFSED5). Concentrations of lead and/or 

cadmium were detected in the downstream release samples at levels greater than 3 times the detected 

levels of lead and cadmium in the upstream background sample. 

ARCO’s assertion that the Parametrix investigation conclusion that metals concentrations in sediment, 

surface water, and fish tissues at the ACM facility were generally comparable to upstream (background) 

concentrations, does not establish that the HRS evaluation improperly compared release samples to 

background samples. In fact, upon a comprehensive review of the Parametrix report, data gaps and 

inconsistencies have been identified in the Parametrix report that may be the cause of the differences in 

results between that report and the 2009 ESI data used to establish an observed release by chemical 

analysis in this HRS evaluation. 

For example, “background” sampling locations within the Parametrix evaluation were collected from 

areas that are not representative of background conditions for the site. As shown in ARCO Ref. 16, 

Figure 2-1, the two Parametrix “background” locations, identified as Area C and Area D, are located 

downstream of four of the five PPEs associated with Source 1 (see HRS documentation record Reference 

50), indicating that these areas are influenced by contaminated runoff from Source 1. If the background 

locations presented in the Parametrix investigation are actually subject to contamination from the site, this 

could explain why the adjacent and downstream sample locations are not significantly elevated above 

their background. 

Further, with respect to Parametrix' sampling Area A, the long stretch of river designated as being 

adjacent to the facility property, 4 of the 7 samples collected from this area were from the opposite bank 

(south) of the river (ARCO Ref. 16, Figure 2-1). Of the remaining 3 samples, 2 were collected south of 

midstream, and only 1 sample of the 7 was collected from the north bank. This configuration of samples 

is not likely to be representative of the sources’ influence on the river, whereas samples collected nearer 

to or directly from the north bank would be more likely to be representative of the release from the ACM 

facility because of its proximity to the north shore. This conclusion is supported by the fact that the 

Parametrix investigation Area A north bank sediment sample (A41) has, in general, much higher 

concentrations of metals than the other Area A samples (ARCO Ref. 16, Table 3-2). This lack of 

sampling near the more highly contaminated north shore was also highlighted by an EPA toxicologist in 

his assessment of the Parametrix report, as further discussed in section 3.6, Risk Associated with the Site, 

of this support document. 

Based on these considerations, nothing in the Parametrix study results is found to cast doubt upon the 

analytical results used to support the HRS evaluation or the finding of an observed release by chemical 

analysis from the site. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Regarding the MDEQ river sampling event cited by ARCO (ARCO Ref. 9), the event was conducted to 

obtain analytical data to determine the contaminant impact of slag waste transported downriver from the 

ACM site in a historic flood to an area including property known as the Witt ranch. A few years 

subsequent to the flood, the Witt ranch property was purchased by the then-owners of the ACM property. 

MDEQ's statement that it was possible that elevated metals levels in sediments would be found upstream 

referred to the area on the Missouri River between the Witt ranch and the ACM site. In fact, the 

analytical data used in support of the HRS evaluation does document elevated levels of metals in 

sediments along a portion of that stretch of the river, by meeting the significant increase requirements 

found in HRS Section 2.3, as demonstrated in section 3.20 of this support document, Surface Water 

Likelihood of Release - Observed Release by Chemical Analysis. 

These comments have no effect on the site score or the decision to list the site on the NPL. 

3.20.2 Surface Water Observed Release - Attribution 

Comment: ARCO made several comments challenging the attribution of the releases in the Missouri 

River to the ACM site. ARCO’s comments on attribution dealt the following topics: 

• Attribution of Releases to On-Site Sources 

• Other Possible Off-Site Sources 

• Permitted Storm Water Discharges 

Response: An observed release has been appropriately attributed at least in part to the ACM site, as the 

observed releases are associated with on-site sources containing hazardous substances at the site, and the 

significant increase of hazardous substances in the observed releases is documented as not caused in total 

by off-site sources. 

HRS Section 2.3, Likelihood of release, states: 

Likelihood of release is a measure of the likelihood that a waste has been or will be 

released to the environment. The likelihood of release factor category is assigned the 

maximum value of 550 for a migration pathway whenever the criteria for an observed 

release are met for that pathway. If the criteria for an observed release are met, do not 

evaluate potential to release for that pathway. When the criteria for an observed release 

are not met, evaluate potential to release for that pathway, with a maximum value of 500. 

The evaluation of potential to release varies by migration pathway (see sections 3, 4 and 

6). 

Establish an observed release either by direct observation of the release of a hazardous 

substance into the media being evaluated (for example, surface water) or by chemical 

analysis of samples appropriate to the pathway being evaluated (see sections 3, 4, and 6). 

The minimum standard to establish an observed release by chemical analysis is analytical 

evidence of a hazardous substance in the media significantly above the background level. 

Further, some portion of the release must be attributable to the site. [emphasis 

added] 

HRS Section 4.1.2.1.1, Observed Release, specifies the following concerning attribution as it discusses 

documenting an observed release by chemical analysis: 

Some portion of the significant increase must be attributable to the site to establish the 

observed release, except: when the site itself consists of contaminated sediments with no 

identified source, no separate attribution is required. 

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The HRS does not expressly contain specific instruction regarding the methodology for establishing 

attribution. However, consistent with the HRS Guidance Manual, the Agency considers it is appropriate 

to establish attribution by first documenting that hazardous substances are present at the site by showing 

that the contaminants are associated with the sources, and second, by documenting that not all of the 

increase in contaminant concentrations could have come from off-site sources. This is established by 

demonstrating that the site at least partially contributes to the significant increase of hazardous substances 

in the release. 

The Attribution section of the HRS documentation record at proposal, beginning on page 41, discussed 

the hazardous substances detected in Source 1 and Source 2 areas during 2003, 2007, and 2008 

investigations. It stated that in Black Eagle soils: 

• The 2003 investigation found “elevated concentrations of antimony, arsenic, cadmium, 

chromium, cobalt, copper, iron, lead, manganese, mercury, nickel, silver, sodium, and zinc” in 

one or more samples 

• The 2007 investigation found “an area of arsenic, cadmium, and lead concentrations greater than 

three times background centered on eastern and central Black Eagle” 

• The 2008 investigation found “[c]oncentrations of arsenic, cadmium, and lead elevated three 

times background . . . centered on the central and southwestern area of Black Eagle.” 

Page 41 of the HRS documentation record at proposal (Attribution section) also indicated that the soil 

contamination is localized in noting that during the 2007 investigation residences on both the north and 

south sides of the Missouri River adjacent to the site were sampled and “[o]f the eleven residences 

sampled in Great Falls on the south side of the Missouri River in August of 2007 only one residence had 

an elevated concentration of arsenic.” 

The Attribution section continues to state that the 2003 investigation sampled several sources on the 

facility property, finding contaminants including antimony, arsenic, cadmium, chromium, cobalt, copper, 

iron, lead, manganese, mercury, nickel, selenium, silver, and zinc. This investigation also noted a lack of 

containment in the area, and identified culverts that drain local surface water into the Missouri River. 

The HRS documentation record at proposal, on page 41, added that two of these source contaminants—

cadmium and lead—were detected in downstream river sediments: 

Sediment samples from the north bank of the Missouri River were collected by boat on July 14, 

2009 (Ref. 23, p. 16). . . . Cadmium and lead elevated three times background was detected for a 

total distance of 2.39 miles downstream of PPE #1 (Ref. 23, p. 23; Ref. 50). 

The Attribution section on page 41 of the HRS documentation record at proposal proceeded by referring 

to the observed release by direct observation, as further proof that the contaminants in the observed 

release by chemical analysis are attributable to the site. 

The Boston and Montana smelter [former owner/operator of the facility at the ACM site] 

routinely dumped large quantities of granulated slag and tailings into the Missouri River 

(Ref. 6, p. 42; Ref. 15, p. 1). In 1907, the Boston and Montana Consolidated Copper and 

Silver Mining Company estimated that the facility could receive up to 4800 tons a day of 

ore and changing the disposal of slag to railcar would significantly increase rail traffic 

(Ref. 14, p. 1). The Montana Department of Environmental Quality (Montana DEQ) 

estimates that between 27,500,000 and 31,000,000 cubic yards of waste were dumped 

into the Missouri River between 1893 and 1915 until onsite containment was instituted in 

1915. Montana DEQ also reports that it is possible that dumping of waste into the 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Missouri River continued at a reduced rate after 1915 until the facility closed in the 1970s 

(Ref. 16, p. 1). So much smelter waste was dumped into the Missouri River between 

1893 and 1915 that the management and legal department of the Boston and Montana 

Company were concerned that the Federal Government would intervene and enjoin the 

deposition of tailings into the Missouri River by virtue of the constitutional provisions 

requiring the federal government to maintain navigable streams (Ref. 15, pp. 1 and 2). In 

1884 Judge Lorenzo Sawyer of the United States Circuit Court in San Francisco had 

granted a perpetual injunction against hydraulic mining in California’s American River 

on these very grounds (Ref. 6, p. 38). 

Numerous complaints were filed by property owners and communities along the Missouri 

River downstream of the ACM Smelter and Refinery of water quality issues and slag and 

smelter waste clogging the Missouri River (Ref. 6, p. 42; Ref. 29, p. 8A). These 

complaints increased after the 1908 flood of the Missouri River inundated the community 

of Fort Benton, 40 miles downstream of the Boston and Montana Smelter with smelter 

waste (Ref. 6, p. 38; Ref. 29, p. 8A). A company analysis of slime (very fine grained slag 

and tailings, which tended to float in the Missouri River) taken above Rainbow Falls 

Dam in 1914 indicated that the slime contained between .55 and 1.1 percent copper (Ref. 

17, p. 1). The Boston and Montana Company sought to buy off disgruntled property 

owners and placate communities by providing alternate domestic water sources (Ref. 6, 

pp. 49-51). 

Cindery slag material was also currently observed to be in the sediments of the Missouri 

River adjacent to the ACM Smelter and Refinery facility (Ref. 23, p. 57 and 202, Ref, 53 

p. 1; Ref. 54, p. 1). 

Finally, the HRS documentation record at proposal identified a nearby facility as another potential 

contributor to the contamination in the Missouri River, and concluded that the contamination is still at 

least partially attributable to the ACM site: 

The former Montana Silver Smelter site is located on the south bank of the Missouri 

River in Giant Springs State Park, approximately 2.85 miles east-northeast of the 15th 

Street Bridge (Ref. 4, 2 pages; Ref. 50, p. 1). The Montana Silver Smelter was 

constructed in 1888 by Great Falls city father, Paris Gibson (Ref. 56, p. 2). The smelter 

had two small stacks. Many of the structures at Giant Springs State Park and Giant 

Springs State Fish Hatchery were built on mineral processing wastes that contained 

extremely high levels of arsenic and lead. This property was cleaned up by the Montana 

Mine Waste Cleanup Bureau’s Abandoned Mine Lands Program in 2004 (Ref. 57, pp. 9-

11). The Montana Refining Company facility is located upstream of the unincorporated 

community of Black Eagle on the north bank of the Missouri River (Ref. 50, 1 map). The 

Montana Refining Company produces various grades of gasoline, diesel, jet fuel, 

distillates, and high grade asphalt products (Ref. 65, 1 page.). The facility has an 

operable capacity of 9,500 barrels per calendar day ranking the facility as number 132 of 

the 143 U.S. Refineries (Ref. 66, p. 4). 

Both of the operations could potentially have contributed to the contamination 

documented in the Missouri River; however, the contamination found in the Missouri 

River sediments is at least partially attributable to the sources found on the ACM Smelter 

and Refinery property because of the evidence presented above. 

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Thus, the HRS documentation record at proposal documents that the released substances are associated 

with the ACM site as they are in and associated with on-site sources and at least part of the contamination 

in the river came from the site based on direct observation of slag being dumped into the river. Thus, the 

significant increase in contaminant levels has been appropriately attributed at least in part to the ACM 

site. 

ARCO’s specific comments on this subject are addressed in the following subsections of this support 

document: 

• 3.20.2.1 Attribution of Releases to On-Site Sources 

• 3.20.2.2 Other Possible Off-Site Sources 

• 3.20.2.3 Permitted Storm Water Discharges 

3.20.2.1 Attribution of Releases to On-Site Sources 

Comment: ARCO challenged the attribution of the significant increase in contaminant levels to the site 

sources because the observed release substances were not shown to be migrating from the scored sources. 

ARCO maintained that EPA provided no information, such as analysis of metals concentrations in runoff 

from Sources 1 and 2, to support attribution of metals concentrations in sediment to the sources. 

ARCO, quoting from the HRS Guidance Manual, stated: 

An observed release is established for the . . . surface water pathway. . . either by 

chemical analysis or by direct observation. The minimum requirements for establishing 

an observed release by chemical analysis are analytical data demonstrating the presence 

of a hazardous substance in the medium significantly above background level, and 

information that some portion of that increase is attributable to the site. The minimum 

criterion for establishing an observed release by direct observation is evidence that the 

hazardous substance was placed into or has been seen entering the medium. [emphasis in 

comment] 

ARCO also stated that EPA had “no information whatsoever” to document that some portion of the 

significant increase was attributable to the sources at the facility (Source 1 or Source 2). ARCO 

concluded that no observed release by chemical analysis had been established, and that the pathway 

should therefore be scored on potential to release. 

ARCO noted that storm water from Black Eagle is conveyed to the Missouri River by approximately five 

culverts and stated that there are no known water quality sample results for any of these culverts. 

ARCO also pointed to a sample identified as representative of background but downgradient of one of the 

five culverts associated with Source 1 (Black Eagle soils) and argued that, if this sample (AGFSED-1) is 

background, then the PPE and associated drainage area should be removed from consideration in the 

surface water pathway. ARCO also maintained that, if AGFSED-1 is not background, then the results of 

the sample “show that metals are not transported from soil underlying the Black Eagle residential area 

into the Missouri River.” 

Further, ARCO asserted that samples AGFSED-2 and AGFSED-3, containing the highest relative 

concentrations of metals detected in the release sediment samples, were collected from locations that are 

upstream of the East Ditch Dump (Source 2) and PPE #6, and concluded that “the East Ditch Dump 

cannot be the source of contamination for the surface water migration pathway EPA describes for this 

reach of the Missouri River.” 

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Response: The HRS documentation record at proposal presented and documented adequate rationale for 

documenting that at least part of the significant increase in contaminant concentrations is due to release 

from the ACM site. Nothing in ARCO’s comments demonstrates this not to be the case. 

As excerpted in section 3.20.2, Surface Water Observed Release - Attribution, of this support document, 

HRS Section 4.1.2.1.1 specifies that “Some portion of the significant increase must be attributable to the 

site. . .” [Emphasis added]. As such, attribution focuses on the site, as opposed to individual sources. 

Notwithstanding, to clarify the extent of the site, two new sources have been added to the HRS 

documentation record at promulgation, and the Attribution discussion has been revised to demonstrate 

how the hazardous substances in the observed release to surface water are associated with these new 

sources. Specifically, section 3.13, Additional Sources, of this support document discusses that sampling 

has revealed arsenic, cadmium, copper, lead, and zinc in flue dust at the former stack and also in Source 

4, slag waste. As such, the contaminants meeting the significant increase criteria (as demonstrated in 

section 3.20.1.1, Contaminant Levels Below Regulatory Limits, of this support document) are associated 

with these two sources. 

Further, as cited in section 3.20.2, Surface Water Observed Release - Attribution, of this support 

document, the HRS documentation record at proposal documented an observed release by direct 

observation. This is discussed in further detail in section 3.19.1, Documentation of Observed Release by 

Direct Observation, of this support document. Documenting the direct deposition of site-related waste 

into surface water demonstrates that the site contributed to the significant increase in the contamination in 

the river. This is sufficient to conclusively show attribution at least in part to the site. 

It is significant to note that, as shown above by the citation of HRS Sections 2.3 and 4.1.2.1.1 in section 

3.20.2, Surface Water Observed Release – Attribution, of this support document, the HRS does not 

require documenting the observation of migration of contaminants from the sources overland and into 

surface water to establish an observed release by chemical analysis; therefore, it is not necessary to 

establish contaminant results in the runoff as suggested by ARCO's comments. 

Regarding ARCO's assertion that the PPE (PPE#1) and associated drainage area upstream of the sediment 

background sample should be removed from consideration in the surface water pathway, the results of the 

background sample do not demonstrate that the most upstream outfall is an invalid probable point of entry 

or that hazardous substances are not being conveyed through PPE#1. Because hazardous substances were 

lower in the background sample than those found in the release samples, this does not establish that 

hazardous substances are not conveyed through PPE#1 to surface water. The background sediment 

sample, while downstream of PPE#1, is still upstream of the other four outfalls from Source 1. Thus, 

sample AGFSED1 still acts as an appropriate sediment background in establishing an observed release. 

See section 3.20.3, Adequacy of Background, of this response document, for further discussion on the 

adequacy of background used in establishing an observed release. 

EPA concurs that sediment samples AGFSED-2 and AGFSED-3 are upstream of Source 2 and PPE #6; 

however, these samples are downstream of four PPEs from Source 1, as well as being downstream of the 

newly added sources (Source 3, facility air emissions, and Source 4, the slag waste). Therefore, these two 

sediment sample locations are expected to be impacted by three sources (Sources 1, 3, and 4). And, as 

explained in section 3.18, Description of Pathway, of this support document, observed release sample 

AGFSED5 is downstream of PPE #6 and, while it may be affected by contamination migrating from 

Source 1, it is also likely to be affected by contaminants migrating from Source 2. 

Thus, as explained in section 3.20.2, Surface Water Observed Release – Attribution, of this support 

document, the significant increases in contaminants in sediment in the Missouri River were reasonably 

attributed to the site in accordance with the HRS at proposal. And, two additional sources (Source 3, 

facility air emissions, and Source 4, slag waste) added to the site at promulgation further clarify the 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

association between observed release sample hazardous substances and the site. This rationale is 

consistent with the suggestions in the HRS Guidance Manual cited by ARCO. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.20.2.2 Other Possible Off-Site Sources 

Comment: ARCO challenged the attribution of the observed release to the site on the basis that many 

other sources of contamination existed upstream and downstream of the site. ARCO argued that 

discharges reaching the river from Black Eagle and Great Falls may contain metals in concentrations 

typical of urban and industrial areas, and that there are numerous storm water and industrial discharge 

sources both upstream and downstream of the site. ARCO asserted that EPA omitted or did not 

adequately describe these sources and their respective contributions of hazardous substances to the 

Missouri River. 

ARCO named a number of potential contributors, via discharge and/or runoff, to the contamination in the 

Missouri River: Northwestern Energy, Pacific Steel and Recycling, Montana Refining Company, the 

City of Great Falls, and Cascade County. 

ARCO also noted that besides storm water and industrial discharge sources, other human uses of the river 

including recreational and agricultural use contributed to water quality problems in the Missouri River, 

such as “sedimentation/siltation and nutrient enrichment...and occasional metal/metalloid listings.” 

ARCO presented a table providing Missouri River reaches (downgradient or in the vicinity of the ACM 

facility) that were documented with exceedances of specific Clean Water Act Section provisions (such as 

metals, nitrates, sedimentation, etc.) This table is shown below: 

Missouri River Regulated Reach Description Listed Parameter(s) 

Headwaters to Toston Arsenic, total nitrogen, sedimentation/siltation 

Toston Dam to Canyon Ferry Reservoir Cadmium, copper, lead, sedimentation/siltation 

Canyon Ferry Reservoir Dam to Hauser Lake Nitrogen (nitrate), dissolved oxygen, total phosphorus 

Total phosphorus, total Kjehldahl nitrogen, 

sedimentation/siltation 

Holter Dam to Little Prickly Pear Creek 

Sun River to Rainbow Dam (includes Former GFR 

Site at Great Falls) 

Total chromium, mercury, pentachlorobenzene, selenium, 

sedimentation/siltation, suspended and bedload solids, 

turbidity 

Rainbow Dam to Morony Dam Arsenic, copper, pentachlorobenzene, 

sedimentation/siltation, water temperature, turbidity 

Response: An observed release has been appropriately attributed to the ACM site, and at least part of the 

significant increase of hazardous substances in the observed releases is documented as not caused by offsite sources. 

As stated in HRS Section 4.1.2.1.1, Observed Release, “[s]ome portion of the significant increase must be 

attributable to the site to establish the observed release.” 

As presented on page 40 of the HRS documentation record at proposal, an observed release by chemical 

analysis was documented that included the comparison of an upgradient background sample to 

downgradient release samples. Potential off-site upstream sources of contamination have been screened 

out by this background sample because it would be affected by these sources in the same way that 

observed release samples would. A significant increase of lead and cadmium was detected in the 

downstream release samples at levels greater than three times the levels of lead and cadmium detected in 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

the upstream background sample. Thus, samples taken in the Missouri River adjacent to and 

downgradient of the ACM site show contaminant levels significantly higher than the levels established 

upstream. Thus, the contributions of upstream off-site sources to the surface water migration pathway 

have been documented as not contributing to the significant increase of hazardous substances documented 

in the observed release. 

Regarding the table of water quality exceedances presented by ARCO (see Reference 68 of the HRS 

documentation record at promulgation): 

• The segment of the Missouri River that includes the ACM site (Sun River to Rainbow Dam), 

includes portions of the river upstream of the site and includes exceedances for some metals 

(chromium, mercury, and selenium). However, these metals are not associated with any source or 

observed release at the site, and would have no affect on the observed releases scored or on their 

attribution to the site. (See Section 2.2.1, Source Identification, and Section 4.1.2.1, Likelihood of 

Release, of the HRS documentation record at promulgation for a discussion of the hazardous 

substances associated with site sources and the observed releases.) 

• The segment of the Missouri River downstream of the ACM site (Rainbow Dam to Morony Dam) 

includes exceedances of arsenic and copper—two site-related hazardous substances (arsenic was 

detected in Source 1 and Source 2; copper was associated with the observed release by direct 

observation). These may have resulted from site-related releases. Releases in this area were not 

scored in the HRS evaluation. 

• In the segments of the Missouri River upstream of the ACM site there are detections of some 

metals which are also scored at this site (arsenic, cadmium, copper, and lead). However, these 

exceedances are located in the two most upstream segments (Headwaters to Toston and Toston 

Dam to Canyon Ferry Reservoir). Two more river segments exist between those and the site in 

which no metals exceedances are noted (Canyon Ferry Reservoir Dam to Hauser Lake and Holter 

Dam to Little Prickly Pear Creek). There are well over 100 miles between Canyon Ferry 

Reservoir and the ACM site in which no metals exceedances are shown; it is therefore highly 

unlikely that the detected metals in the extreme upstream areas of the river have any effect on the 

sediments at this site or on the observed releases established and attribution to the site. And, even 

if these distant upstream contaminants could affect the ACM site, as discussed above, the 

background sample used in establishing the observed release (located downstream of these 

locations ) would screen out their effects, as any contamination coming from upstream would 

have impacted the background sample. 

Therefore, there is no indication that off-site sources affect the attribution of observed releases to the site. 

ARCO’s assertion that EPA did not adequately address off-site sources is unfounded. As quoted above in 

section 3.20.2, Surface Water Observed Release – Attribution, of this support document, the HRS 

documentation record at proposal identifies and discusses other possible off-site contributors of hazardous 

substances that could have reasonably affected the ACM site (Montana Silver Smelter and Montana 

Refining Company). At least part of the contamination in the river is documented to have come from the 

ACM site, and the significant increase in contaminant levels has been appropriately attributed at least in 

part to the site. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

3.20.2.3 Permitted Storm Water Discharges 

Comment: ARCO argued against attribution of the observed release to any recent runoff conditions on 

the basis that ARCO’s current storm water discharges are permitted. ARCO maintained that it has 

expended considerable effort to keep storm water from running across reclaimed areas. ARCO stated that 

its storm water control system was designed to direct storm water to the Missouri River at two existing, 

permitted discharge locations. ARCO also stated that, after the completion of its capping and 

revegetation activities, with the exception of copper and zinc, storm water sampling and reporting 

continued to comply with the general storm water discharge permit. 

Response: An observed release has been appropriately attributed to the ACM site, and whether or not 

hazardous substances in the observed releases are associated with permitted discharges is not considered 

in the HRS evaluation. As discussed in section 3.6, Permitted Releases and Regulatory Limits, of this 

support document, emission or effluent limits do not necessarily represent levels which cause no harm to 

public health or the environment, and are not considered in the HRS scoring process. 

Further, over the multiple decades of operations at the site, unpermitted discharges to surface water prior 

to regulatory oversight would not be addressed in later permits. ARCO’s efforts do not address the 

releases that have occurred during the long operational history at the site. 

This comment has no effect on the HRS site score or the decision to list the site on the NPL. 

3.20.3 Surface Water Observed Release - Adequacy of Background 

Comment: ARCO argued against the adequacy of the background sediment sample, challenging that its 

location was downstream of PPE #1 associated with the Black Eagle community. ARCO alleged that, if 

the sample were not considered a background on this basis, then its results do not indicate contaminant 

transport from the Black Eagle residential area into the river. 

Response: Background sample AGFSED1, although collected a short distance downstream of PPE#1, 

provides an adequate background level for comparison to the downstream sediment samples collected 

from the Missouri River. 

The HRS does not identify requirements or define conditions for establishing background levels of 

contaminants. The HRS addresses background only in the context of identifying an observed release of a 

hazardous substance to the environment by chemical analysis. HRS Section 4.1.2.1.1, Observed release, 

states in relevant part: 

Establish an observed release to surface water for a watershed by demonstrating that the 

site has release a hazardous substance to the surface water in the watershed. Base this 

demonstration on either: 

• Direct observation: . . . 

• Chemical analysis: 

- Analysis of surface water, benthic, or sediment samples indicates that the 

concentration of hazardous substance(s) has increased significantly 

above the background concentration for the site for that type of sample 

(see section 2.3) 

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- Limit comparisons to similar types of samples and background 

concentrations—for example compare surface water samples to 

surface water background concentrations. 

The background sample (AGFSED1) is used as a reference point in the HRS evaluation to establish that a 

significant increase in contaminant levels in the release samples has occurred, and to screen out 

upgradient sources of contamination. Page 39 of the HRS documentation record at proposal documents 

that all samples collected during the 2003 Expanded Site Inspection were collected from the north side of 

the Missouri River, which consisted of “medium to medium fine grained tan particles.” A significant 

increase of hazardous substances between the background and release samples was documented. The 

release samples collected during the 2009 sampling event, upon which the observed release by chemical 

analysis was documented in this HRS evaluation, were collected from the same area at the north side of 

the Missouri River and showed significant increase of hazardous substances between background and 

release samples. 

The background sample AGFSED1 was located not only upstream of the majority of Source 1's influence 

(the other four outfalls), but also upstream of the influence of Source 2 (East Ditch Dump) and Source 4 

(slag waste), as shown in Reference 18, pages 38-39, and Reference 50 of the HRS documentation record 

at proposal. 

While levels of some metals in the background sample may be a result of runoff from PPE #1, a 

significant increase of hazardous substances is still documented between the upstream background sample 

and the downstream release samples. The concentrations of source-related metals in the downstream 

(observed release) samples still clearly meet the HRS significant increase criteria for observed release by 

chemical analysis (i.e., more than 3 times greater than the background levels), as discussed in section 

3.20.1.1, Contamination Levels Below Regulatory Limits, of this support document. 

Therefore, sample AGFSED1 is a valid background sample, and its location acts as a reference point to 

establish significant increases in downstream observed release samples and to screen out upgradient 

sources of contamination. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.21 Potential to Release 

Comment: ARCO maintained that, since (as it previously argued) no observed release had been 

established, the surface water pathway should be scored based on "likelihood of a release," or potential to 

release, as specified by the HRS. ARCO suggested potential to release scores from both sources 

identified in the HRS documentation record at proposal. 

Response: The potential to release was not scored in evaluation of likelihood of release, as an observed 

release was appropriately evaluated from the site to the surface water pathway according to HRS 

requirements. 

HRS Section 2.3, Likelihood of release, states: 

Likelihood of release is a measure of the likelihood that a waste has been or will be 

released to the environment. The likelihood of release factor category is assigned the 

maximum value of 550 for a migration pathway whenever the criteria for an observed 

release are met for that pathway. If the criteria for an observed release are met, do 

not evaluate potential to release for that pathway. [emphasis added] 

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The HRS documentation record at proposal section 4.1.2.1.2, Potential to Release, stated that “Potential 

to Release by overland flow was not evaluated because an observed release was established.” 

As established in sections 3.19, Observed Release by Direct Observation, and 3.20, Observed Release by 

Chemical Analysis, of this support document, an observed release by direct observation and an observed 

release by chemical analysis have been established. As such, and according to the HRS directions stating 

to not evaluate potential to release for that pathway if an observed release is established, the potential to 

release was not evaluated for the surface water migration pathway. 

This comment has no effect on the HRS score or the decision to list the site on the NPL. 

Surface Water – Drinking Water Threat 

The surface water drinking water threat was not included in the scoring of the surface water migration 

pathway because, as stated on page 38 of the HRS documentation record at proposal, “[n]o information 

was found regarding existing surface water intakes on the 15-mile downstream segment.” 

3.22 Surface Water - Drinking Water Threat 

Comment: ARCO commented that, while the HRS documentation record at proposal stated that no 

information was found regarding existing surface water intakes on the 15-mile downstream segment, the 

2009 ESI report states that there are two surface water intakes located upstream of the site supplying the 

city of Great Falls (and Black Eagle, which purchases its water from Great Falls). 

Response: The surface water drinking water threat was not scored in the HRS evaluation of the site, and 

thus the consideration of intakes was not included in any scoring. 

HRS Section 4.2.2, Drinking water threat, provides instruction on scoring the drinking water threat in the 

surface water migration pathway. HRS Section 4.1.2.3, Drinking water threat-targets, states to: 

[e]valuate the targets factor category for each watershed based on three factors: nearest 

intake, population, and resources. 

To evaluate the nearest intake and population factors, determine whether the target 

surface water intakes are subject to actual or potential contamination as specified in 

section 4.1.1.2. Use either an observed release based on direct observation at the intake 

or the exposure concentrations from samples (or comparable samples) taken at or beyond 

the intake to make this determination (see section 4.1.2.1.1). The exposure 

concentrations for a sample (that is, surface water, benthic, or sediment sample) consist 

of the concentrations of those hazardous substances present that are significantly above 

background levels and attributable at least in part to the site (that is, those hazardous 

substance concentrations that meet the criteria for an observed release). 

HRS Section 4.1.1.2, Target distance limit, states that: 

The target distance limit defines the maximum distance over which targets are considered 

in evaluating the site. Determine a separate target distance limit for each watershed as 

follows: 

. . . 

• If there is an observed release from the site to the surface water in the watershed 

that is based on sampling, begin measuring the target distance limit for the 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

watershed at the probable point of entry; extend the target distance limit either 

for 15 miles along the surface water or to the most distant sample point that 

meets the criteria for an observed release to that watershed, whichever is greater. 

[i]n evaluating the site, include only surface water targets (for example, intakes, 

fisheries, sensitive environments) that are within or contiguous to the hazardous 

substance migration path and located, partially or wholly, at or between the 

probable point of entry and the target distance limit applicable to the watershed. 

[emphasis added] 

Also, HRS Section 4.1.1.1, Definition of hazardous substance migration path for overland/flood 

migration component, states the following: 

The hazardous substance migration path includes both the overland segment and the inwater segment that hazardous substances would take as they migrate away from sources 

at the site: 

• Begin the overland segment at a source and proceed downgradient to the 

probable point of entry to surface water. 

• Begin the in-water segment at this probable point of entry. 

- For rivers, continue the in-water segment in the direction of flow (including 

any tidal flows) for the distance established by the target distance limit (see 

section 4.1.1.2). [emphasis added] 

Therefore, in a river, only intakes downstream of the probable point of entry and within the target 

distance limit are evaluated in the drinking water threat of the surface water migration pathway. 

The HRS documentation record at proposal stated on page 38 that “[n]o information was found regarding 

existing surface water intakes on the 15-mile downstream segment.” The intakes discussed by the 

commenter are upstream of the site and not located within the target distance limit and would not be 

available for evaluation if the drinking water threat were scored. 

If, during the course of subsequent investigations it is determined that hazardous substances released from 

the ACM site are impacting surface water drinking water supplies, that threat will be evaluated during a 

separate stage of the Superfund process. Furthermore, as discussed in section 3.11, Scoring Other 

Pathways, of this support document, EPA need not score all pathways in an HRS evaluation if the site 

score is above 28.50 based on those pathways already evaluated. 

This comment has no effect on the HRS score or the decision to list the site on the NPL.

Surface Water – Human Food Chain Threat 

The HRS documentation record at proposal identified an active fishery within the zone of actual 

contamination in the Missouri river established by the observed releases in sediment samples. Based on 

hazardous substances—arsenic, cadmium, lead, manganese, and zinc—available to migrate to surface 

water from Sources 1 and 2, this fishery was determined to be subject to Level II concentrations, due to a 

release of a contaminant (cadmium) with a bioconcentration factor of greater than or equal to 500. The 

food chain individual, level II concentrations, and potential human food chain contamination targets were 

scored as described in pages 43-46 of the HRS documentation record at proposal. 

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3.23 Surface Water - Human Food Chain Threat Waste Characteristics 

Comment: ARCO commented on EPA's assigned values for both the toxicity/persistence/ 

bioaccumulation factor and the hazardous waste quantity value, and as part of its comments assigned 

alternative, lower values than those in the HRS documentation record at proposal. 

Specific comments are addressed in the following subsections of this support document: 

• 3.23.1 Toxicity/Persistence/Bioaccumulation 

• 3.23.2 Human Food Chain Threat Waste Quantity 

• 3.23.3 Human Food Chain Threat Waste Characteristics 

3.23.1 Toxicity/Persistence/Bioaccumulation 

Comment: ARCO challenged EPA's use of manganese to assign the toxicity/persistence/bioaccumulation 

values for the human food chain threat, citing to the HRS Guidance as its reason, ARCO stated the 

substance(s) used should be present at concentrations greater than three times background. ARCO 

instead assigned the value for cadmium, which has a lower toxicity/persistence/bioaccumulation value for 

the human food chain threat than assigned in the EPA HRS scoring. 

Response: The toxicity/persistence/bioaccumulation values for the human food chain threat were 

correctly assigned in the HRS documentation record at proposal. The HRS does not require that the 

hazardous substance used to determine the surface water pathway toxicity/persistence/bioaccumulation 

factor value meet the criteria for an observed release by chemical analysis. Rather, it specifies the 

evaluation of toxicity/persistence/bioaccumulation factor values for any hazardous substance meeting 

observed release criteria and any hazardous substance associated with a source whose containment value 

is greater than zero. Furthermore, as explained below and in section 3.15.2, Association of Hazardous 

Substances with Source 2, of this support document, the HRS does not require the substance be present at 

concentrations significantly above background (e.g., three times) to be associated with a non-soil source, 

to be used in this calculation if it is otherwise associated with a source, nor does the HRS Guidance 

Manual suggest that this be demonstrated. In this case the manganese is associated with Source 2, a 

landfill. 

HRS Section 4.1.3.2, Human food chain threat-waste characteristics, states: 

Evaluate the waste characteristics factor category for each watershed based on two 

factors: toxicity/persistence/bioaccumulation and hazardous waste quantity. 

HRS Section 4.1.3.2.1, Toxicity/persistence/bioaccumulation, then directs to: 

Evaluate all those hazardous substances eligible to be evaluated for toxicity/persistence in 

the drinking water threat for the watershed (see section 4.1.2.2). 

The HRS sets forth the procedures for each factor in Section 4.1.2.2, Drinking water threat-waste 

characteristics, which states: 

Evaluate the waste characteristics factor category for each watershed based on two 

factors: toxicity/persistence and hazardous waste quantity. Evaluate only those 

hazardous substances that are available to migrate from the sources at the site to surface 

water in the watershed via the overland/flood hazardous substance migration path for the 

watershed (see section 4.1.1.1). Such hazardous substances include: 

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• Hazardous substances that meet the criteria for an observed release to surface water 

in the watershed 

• All hazardous substances associated with the source that has a surface water 

containment factor value greater than 0 for the watershed... 

Regarding bioaccumulation, HRS Section 4.1.3.2.1.3, Bioaccumulation potential, states to: 

Use the following data hierarchy to assign a bioaccumulation potential factor value to 

each hazardous substance: 

• Bioconcentration factor (BCF) data. 

• Logarithm of the n-octanol-water partition coefficient (log Kow) data. 

• Water solubility data. 

Assign a bioaccumulation potential factor value to each hazardous substance from table 

4–15. 

If BCF data are available for any aquatic human food chain organism for the substance 

being evaluated, assign the bioaccumulation potential factor value to the hazardous 

substance as follows: 

• If BCF data are available for both fresh water and salt water for the hazardous 

substance, use the BCF data that correspond to the type of water body (that is, 

fresh water or salt water) in which the fisheries are located to assign the 

bioaccumulation potential factor value to the hazardous substance. 

• If, however, some of the fisheries being evaluated are in fresh water and some are 

in salt water, or if any are in brackish water, use the BCF data that yield the 

higher factor value to assign the bioaccumulation potential factor value to the 

hazardous substance. 

• If BCF data are available for either fresh water or salt water, but not for both, use 

the available BCF data to assign the bioaccumulation potential factor value to the 

hazardous substance. 

If BCF data are not available for the hazardous substance, use log Kow data to assign a 

bioaccumulation potential factor value to organic substances, but not to inorganic 

substances. If BCF data are not available, and if either log Kow data are not available, the 

log Kow is available but exceeds 6.0, or the substance is an inorganic substance, use water 

solubility data to assign a bioaccumulation potential factor value. 

To determine the toxicity/persistence/bioaccumulation factor value, HRS Section 4.1.3.2.1.4, Calculation 

of toxicity/persistence/bioaccumulation factor value, states: 

Assign each hazardous substance a toxicity/persistence factor value from Table 4-12, 

based on the values assigned to the hazardous substance for the toxicity and persistence 

factors. Then assign each hazardous substance a toxicity/persistence/bioaccumulation 

factor value from Table 4-16, based on the values assigned for the toxicity/persistence 

and bioaccumulation potential factors. Use the hazardous substance with the highest 

toxicity/persistence/bioaccumulation factor value for the watershed to assign the value to 

this factor. 

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Page 15 of the HRS documentation record at proposal states that according to a 2003 Expanded Site 

Inspection for Source 1, “elevated concentrations of antimony, arsenic, cadmium, chromium, cobalt, 

copper, iron, lead, manganese, mercury, nickel, silver, sodium, and zinc were found in one or more 

samples.” Also, Section 2.2.2, Hazardous substances associated with the source, of the HRS 

documentation record at proposal identifies arsenic, cadmium, lead, manganese, and zinc associated with 

Source 2. Sections 2.2.1.3 and 2.2.3, Hazardous substances available to a pathway, of the HRS 

documentation record at proposal, state that Sources 1 and 2 were assigned a containment factor value of 

10 for the release via overland migration and/or flood to the surface water pathway. Therefore, 

manganese was appropriately evaluated as a hazardous substance for the human food chain threat in the 

surface water pathway. 

Section 4.1.3.2.1, Toxicity/Persistence/Bioaccumulation, of the HRS documentation record at proposal 

listed the toxicity/persistence/bioaccumulation values for manganese and other eligible hazardous 

substances for the human food chain threat in the surface water pathway, and provides the citation to the 

source of the assigned values. In accordance with HRS Section 4.1.3.2.1.4, Calculation of 

toxicity/persistence/bioaccumulation factor value, the highest toxicity/persistence/bioaccumulation factor 

value of 5 x 108

 was selected - that for manganese. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.23.2 Human Food Chain Threat Waste Quantity 

Comment: ARCO disputed the Human Food Chain threat hazardous waste quantity value. Specifically, 

it included in its evaluation of this category value only the East Ditch Dump source (Source 2). ARCO 

stated that the source waste quantity value for the East Ditch Dump should be 0.44, yielding an assigned 

food chain threat waste quantity of 1. 

Response: The human food chain threat pathway waste quantity value was calculated correctly. The 

source hazardous waste quantity values for Source 2 (East Ditch Dump), Source 1 (Black Eagle 

residential soil), and Source 4 (slag waste) are each assigned a value of “> 0”, as detailed in sections 

3.15.3, Source 2, 3.14.5, Source 1, and 3.13, Addition of Sources, respectively, of this support document. 

However, as explained below, the human food chain threat hazardous waste quantity factor value remains 

100 as it was assigned in the HRS documentation record at proposal. Note that as discussed in section 

3.13, Additional Sources, of this support document, Source 3 (facility air emissions) is not included in the 

waste quantity evaluation of the surface water pathway. 

HRS Section 2.4.2.1, Source hazardous waste quantity, states: 

For each of the three migration pathways, assign a source hazardous waste quantity value 

to each source (including the unallocated source) having a containment factor value 

greater than 0 for the pathway being evaluated. 

As established in section 2.2.2 of the HRS documentation record at promulgation, Sources 1, 2, and 4 all 

have surface water containment factor values “greater than 0”, and are therefore applicable to the waste 

quantity evaluation for the surface water migration pathway. 

HRS Section 2.4.2.2, Calculation of hazardous waste quantity factor value, states: 

Sum the source hazardous waste quantity values assigned to all sources (including the 

unallocated source) or areas of observed contamination for the pathway being evaluated 

and round this sum to the nearest integer, except: if the sum is greater than 0, but less 

than 1, round it to 1. Based on this value, select a hazardous waste quantity factor value 

for the pathway from table 2–6. 

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For a migration pathway, if the hazardous constituent quantity is adequately determined 

(see section 2.4.2.1.1) for all sources (or all portions of sources and releases remaining 

after a removal action), assign the value from table 2–6 as the hazardous waste quantity 

factor value for the pathway. If the hazardous constituent quantity is not adequately 

determined for one or more sources (or one or more portions of sources or releases 

remaining after a removal action) assign a factor value as follows: 

• If any target for that migration pathway is subject to Level I or Level II 

concentrations (see section 2.5), assign either the value from table 2–6 or a value 

of 100, whichever is greater, as the hazardous waste quantity factor value for that 

pathway. 

Therefore, the source hazardous waste quantity values are added together to obtain the pathway waste 

quantity. Footnote B of Table 2-6 of the HRS states that “[f]or the pathway, if hazardous constituent 

quantity is not adequately determined, assign a value as specified in the text; do not assign the value of 

1.” 

As discussed in sections 3.14.5, Source 1 Hazardous Waste Quantity, and 3.15.4, Source 2 Hazardous 

Waste Quantity, of this support document, Sources 1 and 2 were both assigned a hazardous waste quantity 

value of “greater than 0” at promulgation. Additionally, the hazardous waste quantity value for Source 4 

was appropriately evaluated as “greater than 0,” as discussed on pages 44-45 of the HRS documentation 

record at promulgation and as explained in section 3.13, Additional Sources, of this support document. 

As the hazardous constituent quantity was not adequately determined for any site source, a value was 

assigned to the pathway hazardous waste quantity as directed from the text of HRS Section 2.4.2.2, which 

directs the scorer to assign a value for the pathway hazardous waste quantity from Table 2–6 of the HRS, 

or a value of 100, whichever is greater, if any target for that migration pathway is subject to Level I or 

Level II concentrations. Because the presence of Level II targets has been appropriately identified (see 

section 3.24.1, Actual Contamination, of this support document), the assigned hazardous waste quantity 

value at promulgation remains 100—the same as that assigned at proposal. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.23.3 Human Food Chain Threat Waste Characteristics 

Comment: ARCO claimed that the HRS assigned “human food chain threat waste characteristics 

product” was incorrect, based on its allegation that the toxicity/persistence/bioaccumulation values should 

have been derived from cadmium instead of manganese, and that a lesser human food chain threat 

hazardous waste quantity factor value should have been assigned. 

Response: The waste characteristics category value [ i.e., the product] of the human food chain threat was 

correctly determined at proposal. The human food chain threat waste characteristics factor category 

value remains 320 in the HRS documentation record at promulgation, unchanged from that assigned at 

proposal, despite the change of the Source 1 hazardous waste quantity to > 0, and the addition of Source 

4. 

As described in section 3.23.1, Toxicity/Persistence/Bioaccumulation, of this support document, in 

accordance with HRS Section 4.1.3.2.1.4, the greatest toxicity/persistence/bioaccumulation factor value 

of 5 x 108

 based on manganese was correctly assigned in the HRS documentation record at proposal. 

Also, as detailed in section 3.23.2, Human Food Chain Threat Waste Quantity, of this support document, 

the human food chain threat hazardous waste quantity factor value was correctly scored as 100 in the 

HRS documentation record at proposal and remains so at promulgation. 

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HRS Section 2.4.3.2, Factor category value, considering bioaccumulation potential, states: 

For the surface water-human food chain threat and the surface water environmental 

threat, multiply the toxicity or combined factor value, as appropriate, from section 2.4.1.2 

and the hazardous waste quantity factor value from section 2.4.2.2, subject to: 

• A maximum product of 1×1012 , and 

• A maximum product exclusive of the bioaccumulation (or ecosystem 

bioaccumulation) potential factor of 1×108

 . 

Based on the total waste characteristics product, assign a waste characteristics factor 

category value to these threats from table 2–7. 

The greatest toxicity/persistence/bioaccumulation factor value of 5 x 108

 (that for manganese, as shown 

on page 43 of the documentation record at proposal) was assigned. This value multiplied by the pathway 

hazardous waste quantity factor value of 100 produces a value of 5x1010. According to HRS Table 2-7, 

the value of 5x1010 corresponds to a waste characteristics factor category value of 320. 

Thus, the human food chain threat waste characteristics factor category value at promulgation has not 

changed from that assigned at proposal. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.24 Surface Water - Human Food Chain Threat Targets 

Comment: In its comments on the human food chain threat targets scoring, ARCO presented arguments 

against scoring an actually contaminated fishery, concluding that an observed release was not established, 

and that fish tissue data indicated no risk to fish or humans. 

Response: The scoring of human food chain targets correctly identified actually contaminated targets 

within the zone of contamination, and potentially contaminated targets within the TDL. 

In establishing the TDL, HRS Section 4.1.1.2, Target distance limit, states that: 

[t]he target distance limit defines the maximum distance over which targets are 

considered in evaluating the site. Determine a separate target distance limit for each 

watershed as follows: 

. . . 

• If there is an observed release from the site to the surface water in the watershed that 

is based on sampling, begin measuring the target distance limit for the watershed at 

the probable point of entry; extend the target distance limit either for 15 miles along 

the surface water or to the most distant sample point that meets the criteria for an 

observed release to that watershed, whichever is greater. 

In evaluating the site, include only surface water targets (for example, intakes, fisheries, 

sensitive environments) that are within or contiguous to the hazardous substance 

migration path and located, partially or wholly, at or between the probable point of entry 

and the target distance limit applicable to the watershed: 

. . . 

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• Determine whether targets within or contiguous to the hazardous substance migration 

path are subject to actual or potential contamination as follows: 

- If a target is located, partially or wholly, either at or between the probable point 

of entry and any sampling point that meets the criteria for an observed release to 

the watershed or at a point that meets the criteria for an observed release by 

direct observation, evaluate that target as subject to actual contamination, except 

as otherwise specified for fisheries in section 4.1.3.3 and for wetlands in section 

4.1.4.3.1.1. If the actual contamination is based on direct observation, assign 

Level II to the actual contamination. However, if the actual contamination is 

based on samples, determine whether the actual contamination is at Level I or 

Level II concentrations as specified in sections 4.1.2.3, 4.1.3.3, and 4.1.4.3.1. 

- If a target is located, partially or wholly, within the target distance limit for the 

watershed, but not at or between the probable point of entry and any sampling 

point that meets the criteria for an observed release to the watershed, nor at a 

point that meets the criteria for an observed release by direct observation, 

evaluate it as subject to potential contamination. 

Thus, the HRS instructs the scorer to consider that targets are subject to actual contamination if they are 

between the PPE and the furthest downstream sample that meets observed release criteria. HRS Section 

4.1.3.3, Human food chain threat-targets, identifies further requirements for determining a human food 

chain fishery within the zone of contamination: 

Evaluate two target factors for each watershed: food chain individual and population. 

For both factors, determine whether the target fisheries are subject to actual or potential 

human food chain contamination. 

Consider a fishery (or portion of a fishery) within the target distance limit of the 

watershed to be subject to actual human food chain contamination if any of the 

following apply: 

• A hazardous substance having a bioaccumulation potential factor value of 500 

or greater is present either in an observed release by direct observation to the 

watershed or in a surface water or sediment sample from the watershed at a level 

that meets the criteria for an observed release to the watershed from the site, and 

at least a portion of the fishery is within the boundaries of the observed release 

(that is, it is located either at the point of direct observation or at or between the 

probable point of entry and the most distant sampling point establishing the 

observed release). 

• The fishery is closed, and a hazardous substance for which the fishery has been 

closed has been documented in an observed release to the watershed from the 

site, and at least a portion of the fishery is within the boundaries of the observed 

release. 

• A hazardous substance is present in a tissue sample from an essentially sessile, 

benthic, human food chain organism from the watershed at a level that meets the 

criteria for an observed release to the watershed from the site, and at least a 

portion of the fishery is within the boundaries of the observed release. 

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For a fishery that meets any of these three criteria, but that is not wholly within the 

boundaries of the observed release, consider only the portion of the fishery that is within 

the boundaries of the observed release to be subject to actual human food chain 

contamination. Consider the remainder of the fishery within the target distance limit to be 

subject to potential food chain contamination. 

In addition, consider all other fisheries that are partially or wholly within the target 

distance limit for the watershed, including fisheries partially or wholly within the 

boundaries of an observed release for the watershed that do not meet any of the three 

criteria listed above, to be subject to potential human food chain contamination. If only a 

portion of the fishery is within the target distance limit for the watershed, include only 

that portion in evaluating the targets factor category. 

When a fishery (or portion of a fishery) is subject to actual food chain contamination, 

determine the part of the fishery subject to Level I concentrations and the part subject to 

Level II concentrations. If the actual food chain contamination is based on direct 

observation, evaluate it using Level II concentrations. However, if the actual food chain 

contamination is based on samples from the watershed, use these samples and, if 

available, additional tissue samples from aquatic human food chain organisms as 

specified below, to determine the part subject to Level I concentrations and the part 

subject to Level II concentrations. . . . 

As established in sections 3.19, Likelihood of Release - Observed Release by Direct Observation, and 

3.20, Surface Water Likelihood of Release - Observed Release by Chemical Analysis, of this support 

document, an observed release by direct observation and an observed release by chemical analysis have 

been established at this site in accordance with the HRS. Regarding the zone of contamination, page 44 

of the HRS documentation record at proposal documents that the farthest downstream Level II observed 

release sediment sample (AGFSED5) is located 2.39 miles downstream of the most upstream PPE 

(PPE#1). Page 45 of the HRS documentation record at proposal stated: 

The extent of the Level II contamination of the Missouri River fishery is 2.39 miles 

(distance from the most upstream PPE (PPE #1) in Missouri River at 11th Street in Black 

Eagle, Montana to Sample AGFSED5 (Ref. 23, p. 28; Ref. 50). 

Targets subject to actual contamination within this zone include the Missouri River fishery. Page 45 of 

the HRS documentation record at proposal stated: 

Actual contamination of the Missouri River fishery was documented by Level II 

concentrations in sediment sample AGFSED5 (0907118-05). The stretch of the Missouri 

River between Black Eagle Dam and Rainbow Dam is an active fishery. 

Therefore, the establishment of the zone of contamination and consideration of targets within the zone of 

contamination to be subject to actual contamination was consistent with the HRS. The Missouri River 

fishery was considered for scoring as a human food chain fishery as it was identified as subject to actual 

human food chain contamination, as samples collected within this zone were documented to contain 

hazardous substances with a bioaccumulation concentration factor of greater than 500 (cadmium in 

sample AGFSED5). 

Responses to specific comments on the evaluation of human food chain targets are presented in the 

following subsections of this support document: 

• 3.24.1 Targets Subject to Actual Contamination 

• 3.24.2 Contaminants in Fish Tissue 

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3.24.1 Targets Subject to Actual Contamination 

Comment: ARCO commented that, since it asserted that an observed release to surface water was not 

established, the presence of an actually contaminated fishery was not documented, and that the Missouri 

River fishery should be scored based on potential human food chain contamination (not actual 

contamination). ARCO challenged the value of 45 for the Food Chain Individual factor in the Human 

Food Chain Threat, stating that since no observed release is established, the factor value should be based 

on the dilution weight of the Missouri River. 

Response: An actually contaminated fishery was correctly established based on a zone of contamination 

in the Missouri river and correctly delineated using observed release samples; the food chain individual 

factor value of 45 was appropriately assigned at proposal in accordance with the HRS. 

As explained in section 3.24, Surface Water - Human Food Chain Threat Targets, of this support 

document, the portion of the Missouri River within the zone of contamination (from PPE#1 downstream 

to observed release sample AGFSED5) was documented as an actually contaminated fishery according to 

the HRS. 

HRS Section 4.1.3.3.1, Food chain individual, directs the scorer how to establish the scoring of the food 

chain individual as follows: 

Evaluate the food chain individual factor based on the fisheries (or portions of fisheries) 

within the target distance limit for the watershed. Assign this factor a value as follows: 

• If any fishery (or portion of a fishery) is subject to Level I concentrations, 

assign a value of 50. 

• If not, but if any fishery (or portion of a fishery) is subject to Level II 

concentrations, assign a value of 45. 

Page 45 of the HRS documentation record at proposal presented how food chain individual was scored. It 

stated: 

Actual contamination of the Missouri River fishery was documented by Level II 

concentrations in sediment sample AGFSED5 (0907118-05). The stretch of the Missouri 

River between Black Eagle Dam and Rainbow Dam is an active fishery. Fishing was 

observed and photo documented by the sampling team during the 2009 Expanded Site 

Inspection at the Rainbow Boat Ramp. Photo documentation of fishing and a statement 

attesting to the consumption of fish caught in that reach of the Missouri River at the 

Rainbow Boat Ramp is documented (Ref. 23, pp. 27, 28, 33; Ref. 44, 1 page; Ref. 45; 

Ref. 46, 1 page). The Montana Department of Fish, Wildlife and Parks estimates that a 

population of 1,292 rainbow trout and 302 brown trout are found in the 1.5 mile stretch 

between Black Eagle Dam and Giant Springs State Park (Ref. 34, p. 1). The fish that are 

caught along this stretch of the river are eaten by the anglers and their families (Ref. 44, 1 

page; Ref. 46, 1 page). This fishery is subject to Level II concentrations, due to a release 

of a contaminant with a BCF of greater than or equal to 500; a value of 45 is assigned to 

the Human Food Chain Individual Factor Value (Ref. 1, Sec. 4.1.3.3.1 and Sec. 4.1.3.3). 

ARCO is incorrect in its assertion that all of (or “the entire”) Missouri River fishery within the TDL for 

the site is subject to potential contamination. As documented on page 45 of the HRS documentation 

record at proposal, the Missouri River downstream of sample location AGFSED05 to the 15-mile TDL 

was considered subject to potential contamination, and dilution values were appropriately considered in 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

the assessment of this segment of the Missouri River fishery. However, a fishery subject to actual 

contamination was correctly established within the zone of contamination, and it was appropriate to 

assign the resulting food chain individual score of 45. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.24.2 Consideration of Existing Fish Tissue Data 

Comment: ARCO asserted that fish tissue data were available and should have been recognized in the 

HRS evaluation of the human food chain threat. ARCO also claimed that language on page 44, Section 

4.1.3.3 Human Food Chain Threat Targets, Fish Tissue, of the HRS documentation record at proposal 

“arbitrarily portrays the sediment data as deleterious to fish in the Missouri River when the contrary 

conclusion has previously been documented and accepted in the course of prior investigations.” In 

support of this statement, ARCO referred to a MDFWP biologist review of the Parametrix study (AR 

Reference #16 of the ARCO comments) data and stated that the review concluded that there is “no health 

risk to people from eating fish from this area and there is no risk to the fish themselves.” 

Response: Fish tissue contaminant data were not used in the HRS evaluation of the human food chain 

threat, and are not required to be used in any threat or factor value evaluation. While fish tissue data, if 

available, can be used to establish an observed release, to identify actually contaminated fisheries, and to 

assign the level of actual contamination of the fisheries, in none of these cases is the use of fish tissue 

samples required. 

HRS Section 4.1.2.1.1, Observed release, states in part that an observed release to surface water is 

established if: 

Analysis of surface water, benthic, or sediment samples indicates that the 

concentration of hazardous substance(s) has increased significantly above the background 

concentration for the site for that type of sample. . . . [emphasis added] 

As shown in section 3.20, Surface Water Likelihood of Release - Observed Release by Chemical 

Analysis, of this support document, an observed release by chemical analysis has been established 

because hazardous substances significantly greater than background concentrations were documented in 

sediments within the Missouri River. Since the analysis of either surface water, benthic, or sediment 

samples can be used to establish an observed release to surface water through chemical analysis, only the 

sediment sample contaminant data was necessary to establish an observed release. 

HRS Section 4.1.3.3, Human food chain threat – targets, provides for establishing actual contamination 

of a fishery using surface water, sediment or fish tissue samples from essentially sessile, benthic food 

chain organisms. It states: 

Consider a fishery (or portion of a fishery) within the target distance limit of the 

watershed to be subject to actual human food chain contamination if any [emphasis 

added] of the following apply: 

• A hazardous substance having a bioaccumulation potential factor value of 500 or 

greater is present in an observed release by direct observation to the watershed or 

in a surface water or [emphasis added] sediment sample from the watershed at a 

level that meets the criteria for an observed release to the watershed from the site, 

. . . 

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• A hazardous substance is present in a tissue sample from an essentially sessile, 

benthic human food chain organism from the watershed at a level that meets the 

criteria for an observed release from the site, . . . 

The identification of an actually contaminated fishery was established by demonstrating that sediment 

samples from a human food chain fishery that meet the observed release criteria contain one or more 

hazardous substances that have a bioaccumulation potential factor value of 500 or greater. Page 45 of the 

HRS documentation record at proposal, under section 4.1.3.3.1, Food Chain Individual, stated: 

Actual contamination of the Missouri River fishery was documented by Level II 

concentrations in sediment sample AGFSED5 (0907118-05). The stretch of the Missouri 

River between Black Eagle Dam and Rainbow Dam is an active fishery. Fishing was 

observed and photo documented by the sampling team during the 2009 Expanded Site 

Inspection at the Rainbow Boat Ramp. Photo documentation of fishing and a statement 

attesting to the consumption of fish caught in that reach of the Missouri River at the 

Rainbow Boat Ramp is documented . . . The Montana Department of Fish, Wildlife and 

Parks estimates that a population of 1,292 rainbow trout and 302 brown trout are found in 

the 1.5 mile stretch between Black Eagle Dam and Giant Springs State Park . . . The fish 

that are caught along this stretch of the river are eaten by the anglers and their families . . 

. This fishery is subject to Level II concentrations, due to a release of a contaminant with 

a BCF of greater than or equal to 500; a value of 45 is assigned to the Human Food Chain 

Individual Factor Value. 

As cited in the HRS above, since either surface water, sediment, or fish tissue samples can be used for 

establishing actual contamination of a fishery, sediment samples were sufficient for use in this evaluation. 

In general, fish tissue samples can also be used to identify Level I fishery targets. HRS Section 4.1.3.3, 

Human food chain threat—targets, states: 

When a fishery (or portion of a fishery) is subject to actual food chain contamination, 

determine the part of the fishery subject to Level I concentrations and the part subject to 

Level II concentrations. If the actual food chain contamination is based on direct 

observation, evaluate it using Level II concentrations. However, if the actual food chain 

contamination is based on samples from the watershed, use these samples and if 

available, additional tissue samples from aquatic human food chain organisms as 

specified below, to determine the part subject to Level I concentrations and the part 

subject to Level II concentrations. 

In this evaluation, Level II concentrations were determined within the fishery from sediment 

contamination data; therefore, by the HRS mechanism described above, if contaminant levels within fish 

tissue were great enough, the addition of fish tissue data to this analysis would only be used to raise the 

level of contamination from Level II to Level I. 

Regarding the claim that the HRS documentation record at proposal incorrectly “portrays the sediment 

data as deleterious to fish in the Missouri River”, the commenter is incorrect. The language on page 44 of 

the HRS documentation record at proposal, section 4.1.3.3, Human Food Chain Threat Targets, Fish 

Tissue, stated: 

Fish tissue samples were collected by ARCO’s contractor Paramatrix in 2004. 

Paramatrix concluded that the concentrations in tissue were largely comparable between 

upstream (background) and downstream (site) areas. A statistical analysis of the 

analytical data was not performed . . . A review of the report by the EPA’s Regional 

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Ecological toxicologist noted that at three sample locations ecotoxicological benchmarks 

were exceeded in soil samples, and it is likely that higher concentrations of metals in all 

samples could have been obtained by taking samples on the north side of the Missouri 

River, which is the same side as the facility rather than across from the facility on the 

south bank of the Missouri River (Ref. 20, p. 1, 2). 

The text above simply repeats a fact stated by the EPA toxicologist—that the metals concentrations in 3 

sediment samples were greater than the ecotoxicological benchmarks that the toxicologist used in his 

evaluation. This statement does not draw any final conclusions on the actual risk posed by the related 

contamination. Additionally, a biologist from the MDFWP also referred to by ARCO stated that his 

search for relevant risk-based levels was “cursory” and his conclusions were based on “crude risk 

calculations.” 

Finally, as noted in section 3.6, Risk Associated with Site, of this support document, EPA performs a 

comprehensive risk assessment for the site as part of further investigations that typically follow listing. 

As further discussed in section 3.6 of this support document, the Parametrix study upon which 

conclusions about site risk were based is limited and is not considered sufficient to draw a comprehensive 

conclusion on risk at the site. 

This comment has no effect on the HRS site score or the decision to list the site on the NPL. 

3.25 Surface Water - Human Food Chain Threat Total Score 

Comment: ARCO attempted to rescore the entire human food chain threat of the surface water pathway, 

and in doing so claimed that it "refined" the components of all of the major factor categories of likelihood 

of release, waste characteristics, and targets, as well as the resultant human food chain threat score. 

ARCO summarized the Human Food Chain Threat scoring by alleging that, since EPA had not 

established an observed release to surface water, there was no actual contamination in a fishery. ARCO 

asserted that the score for the surface water human food chain threat should be calculated as follows: (259 

x 56 x 1.000003)/82,500 = 0.18. 

Response: The human food chain threat remains the same at promulgation as that assigned in the HRS 

documentation record at proposal, and was performed correctly and appropriately per the HRS, thus the 

revised scoring provided by ARCO is not appropriate. 

Sections 3.19.1, Documentation of Observed Release by Direct Observation, and 3.20, Surface Water 

Likelihood of Release - Observed Release by Chemical Analysis, of this support document, demonstrate 

that an observed release by direct observation and an observed release by chemical analysis were 

correctly documented and scored in accordance with the HRS. 

Section 3.23.3, Food Chain Threat Waste Characteristics, of this support document, demonstrates that the 

human food chain threat waste characteristics factor category value of 320 assigned at proposal remains 

the same in the HRS documentation record at promulgation. 

Finally, section 3.24, Surface Water - Human Food Chain Threat-Targets, of this support document, 

makes clear that a fishery subject to actual contamination was correctly established. Therefore, the 

human food chain threat score remains the same at promulgation as that assigned at proposal, and the 

revised scoring scenario provided by ARCO is not appropriate. 

This comment has no effect on the HRS site score or on the decision to list the site on the NPL. 

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Surface Water – Environmental Threat 

Pages 47-49 of the HRS documentation record at proposal identified wetlands within the zone of actual 

contamination. These wetlands were determined to be subject to Level II contamination due to releases 

from the site. See Figure 1 of this support document for the locations of these wetlands in relation to the 

observed release locations. 

3.26 Surface Water - Environmental Threat Waste Characteristics 

Comment: ARCO commented on EPA's assigned values for the hazardous waste quantity value and the 

resulting waste characteristics factor category value, and as part of its comments assigned alternative, 

lower values than those in the HRS documentation record at proposal. 

Specific comments are addressed in the following subsections of this support document: 

• 3.26.1 Environmental Threat Waste Quantity 

• 3.26.2 Environmental Threat Waste Characteristics 

3.26.1 Environmental Threat Waste Quantity 

Comment: ARCO stated that EPA's assigned value for the hazardous waste quantity value was incorrect, 

and assigned an alternative, lower value for this category. ARCO disputed the hazardous waste quantity 

values EPA assigned for both sources at the site, and stated it had assigned alternative lower values in its 

own scoring scenario, which used only the waste quantity for the East Ditch Dump (Source 2). ARCO 

stated that the source waste quantity value for the East Ditch Dump should be 0.44, yielding an assigned 

the hazardous waste quantity value for the site of 1, as opposed to the hazardous waste quantity value of 

100 established in the HRS documentation record at proposal. 

Response: After consideration of ARCO’s comments on the site sources, while the source waste quantity 

for source 1 has been revised, the environmental threat hazardous waste quantity value remains 100, the 

same as that assigned at proposal. This, as explained below, reflects the waste quantity for Sources 1, 2, 

and 4. Note that as discussed in section 3.13, Additional Sources, of this support document, Source 

3(facility air emissions) is not included in the waste quantity evaluation of the surface water pathway. 

HRS Section 4.1.4.2, Environmental threat-waste characteristics, states: 

Evaluate the waste characteristics factor category for each watershed based on two 

factors: ecosystem toxicity/persistence/bioaccumulation and hazardous waste quantity. 

HRS Section 4.1.4.2.2, Hazardous waste quantity, directs the scorer to “[a]ssign the same factor value for 

hazardous waste quantity for the watershed as would be assigned in section 4.1.2.2.2 for the drinking 

water threat.” 

HRS Section 4.1.2.2.2, Hazardous waste quantity, directs the scorer to “[a]ssign a hazardous waste 

quantity factor value for the watershed as specified in section 2.4.2.” 

HRS Section 2.4.2.1, Source hazardous waste quantity, states: 

For each of the three migration pathways, assign a source hazardous waste quantity value to each 

source (including the unallocated source) having a containment factor value greater than 0 for the 

pathway being evaluated. 

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As established in section 2.2.2, Hazardous Substances Associated with Source, of the HRS documentation 

record at promulgation, Sources 1, 2, and 4 all have surface water containment factor values of “greater 

than 0”, and are therefore included in the waste quantity evaluation for the surface water migration 

pathway. 

HRS Section 2.4.2.2, Calculation of hazardous waste quantity factor value, states: 

Sum the source hazardous waste quantity values assigned to all sources (including the 

unallocated source) or areas of observed contamination for the pathway being evaluated 

and round this sum to the nearest integer, except: if the sum is greater than 0, but less 

than 1, round it to 1. Based on this value, select a hazardous waste quantity factor value 

for the pathway from table 2–6. 

For a migration pathway, if the hazardous constituent quantity is adequately determined 

(see section 2.4.2.1.1) for all sources (or all portions of sources and releases remaining 

after a removal action), assign the value from table 2–6 as the hazardous waste quantity 

factor value for the pathway. If the hazardous constituent quantity is not adequately 

determined for one or more sources (or one or more portions of sources or releases 

remaining after a removal action) assign a factor value as follows: 

• If any target for that migration pathway is subject to Level I or Level II 

concentrations (see section 2.5), assign either the value from table 2–6 or a value 

of 100, whichever is greater, as the hazardous waste quantity factor value for that 

pathway. 

Therefore, the source hazardous waste quantity values are added together to obtain the pathway waste 

quantity. Footnote B of HRS Table 2-6 states that “[f]or the pathway, if hazardous constituent quantity is 

not adequately determined, assign a value as specified in the text; do not assign the value of 1.” 

As discussed in sections 3.14.5, Source 1 Hazardous Waste Quantity, and 3.15.4, Source 2 Hazardous 

Waste Quantity, of this support document, Sources 1 and 2 were both assigned a hazardous waste quantity 

value of “greater than 0” at promulgation. Additionally, the hazardous waste quantity value for Source 4 

was appropriately evaluated as “greater than 0,” as discussed on pages 44-45 of the HRS documentation 

record at promulgation, and as explained in section 3.13, Additional Sources, of this support document. 

As the hazardous constituent quantity was not adequately determined for any site source, a value was 

assigned to the pathway hazardous waste quantity as directed by HRS Section 2.4.2.2, which instructs the 

scorer to assign a value for the pathway hazardous waste quantity from Table 2–6 of the HRS, or a value 

of 100, whichever is greater, if any target for that migration pathway is subject to Level I or Level II 

concentrations. Because the presence of Level II targets has been appropriately identified (see section 

3.27.1, Actual Contamination, of this support document), the assigned hazardous waste quantity value at 

promulgation remains 100—the same as that assigned at proposal. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.26.2 Environmental Threat Waste Characteristics 

Comment: ARCO claimed that the environmental threat waste characteristics factor category was 

incorrect, based on its allegation that a lesser human food chain threat hazardous waste quantity factor 

value should have been assigned. 

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Response: The human food chain threat waste characteristics factor category value remains 320 in the 

HRS documentation record at promulgation, unchanged from that assigned at proposal, despite the 

change of the Source 1 hazardous waste quantity to ”greater than 0,” and the addition of Source 4. 

HRS Section 4.1.4.2.3, Calculation of environmental threat-waste characteristics factor category value, 

states: 

For the hazardous substance selected for the watershed in section 4.1.4.2.1.4, use its 

ecosystem toxicity/persistence factor value and ecosystem bioaccumulation potential 

factor value as follows to assign a value to the waste characteristics factor category. 

First, multiply the ecosystem toxicity/persistence factor value and the hazardous waste 

quantity factor value for the watershed, subject to a maximum product of 1×108

. Then 

multiply this product by the ecosystem bioaccumulation potential factor value for this 

hazardous substance, subject to a maximum product of 1×1012. Based on this second 

product, assign a value from Table 2–7 (section 2.4.3.1) to the environmental threatwaste characteristics factor category for the watershed. 

Pages 47-48 of the HRS documentation record at proposal assigned an ecosystem toxicity/persistence/ 

bioaccumulation factor value of 5 x 108

, an ecosystem toxicity/persistence factor value of 10,000, and an 

ecosystem bioaccumulation potential factor value of 50,000 based on cadmium; these values were not 

challenged by ARCO. As described in section 3.26.1, Environmental Threat Waste Quantity, of this 

support document, a hazardous waste quantity value of 100 was correctly assigned at proposal and 

remains at promulgation. Therefore, because the product of the ecosystem toxicity/persistence factor 

value and the waste quantity factor value remains 5 x 1010, the resulting environmental threat waste 

characteristics factor category value assigned from HRS Table 2-7 at promulgation is still 320, as 

assigned at proposal. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.27 Surface Water - Environmental Threat Targets 

Comment: In its comments on the surface water pathway environmental threat, ARCO maintained that 

the targets scoring should be based on potential contamination rather than actual contamination, that there 

was no risk to the aquatic biota (i.e., fish in the Missouri River) from the site, and that the target score 

should be substantially reduced. 

Responses to specific comments are presented in the following subsections of this support document: 

• 3.27.1 Actual Contamination 

• 3.27.2 Aquatic Biota Targets 

3.27.1 Actual Contamination 

Comment: ARCO disputed the scoring of actual contamination in the environmental threat on the basis 

that no observed release was established. ARCO specifically commented that Level I and II 

concentrations were not applicable, and that the scoring should instead be determined solely from 

potential contamination to wetlands, incorporating the dilution weight of the river. Based on this 

argument ARCO asserted that the environmental threat-target factor category value should be 0.025 

instead of 25 as assigned in the HRS documentation record at proposal. 

Response: Environmental targets subject to actual contamination were appropriately identified and were 

correctly assigned a Level II target value of 25 because wetlands subject to actual contamination were 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

properly established in the HRS documentation record at proposal. ARCO is incorrect in its assertion that 

no observed releases were correctly identified in the HRS documentation record at proposal. 

As established in sections 3.19, Likelihood of Release - Observed Release by Direct Observation, and 

3.20, Surface Water Likelihood of Release - Observed Release by Chemical Analysis, of this support 

document, observed releases were properly established for the surface water pathway by chemical 

analysis as well as by direct observation. See Figure 1 of this support document for the locations of the 

wetlands in relation to the observed release locations. 

HRS Section 2.5, Targets, explains how to determine the level of contamination and the associated factor 

values associated with environmental targets: 

The factor values that may be assigned to each type of target have the same range for 

each pathway for which that type of target is evaluated. The factor value for most types 

of targets depends on whether the target is subject to actual or potential contamination for 

the pathway and whether the actual contamination is Level I or Level II: 

• Actual contamination: Target is associated either with a sampling location that 

meets the criteria for an observed release (or observed contamination) for the 

pathway or with an observed release based on direct observation for the pathway 

(additional criteria apply for establishing actual contamination for the human 

food chain threat in the surface water migration pathway, see sections 4.1.3.3 and 

4.2.3.3). Sections 3 through 6 specify how to determine the targets associated 

with a sampling location or with an observed release based on direct observation. 

HRS Section 4.1.4.3.1, Sensitive environments, states: 

Evaluate sensitive environments along the hazardous substance migration path for the 

watershed based on three factors: Level I concentrations, Level II concentrations, and 

potential contamination. 

Determine which factor applies to each sensitive environment as specified in section 

4.1.2.3, except: use ecological-based benchmarks (Table 4–22) rather than health-based 

benchmarks (Table 3–10) in determining the level of contamination from samples. In 

determining the level of actual contamination, use a point of direct observation anywhere 

within the sensitive environment or samples (that is, surface water, benthic, or sediment 

samples) taken anywhere within or beyond the sensitive environment (or anywhere 

adjacent to or beyond the sensitive environment if it is contiguous to the migration path). 

HRS Section 4.1.4.3.1.2, Level II concentrations, states: 

Assign value(s) from table 4–23 to each sensitive environment subject to Level II 

concentrations. Do not include sensitive environments already counted for table 4–23 

under the Level I concentrations factor for this watershed. 

For those sensitive environments that are wetlands, assign an additional value from table 

4–24. In assigning a value from table 4–24, include only those portions of wetlands 

located along the hazardous substance migration path in the area of Level II 

concentrations, as specified in section 4.1.4.3.1.1. 

Estimate the total length of wetlands along the hazardous substance migration path (that 

is, wetland frontage) in the area of Level II concentrations and assign a value from table 

4–24 based on this total length. Estimate this length as specified in section 4.1.4.3.1.1, 

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except: for an isolated wetland or for a wetland where the probable point of entry to 

surface water is in the wetland, use the perimeter of that portion of the wetland subject to 

Level II (not Level I) concentrations as the length. 

Section 4.1.4.3, Environmental Threat – Targets, of the HRS documentation record at proposal explained 

the assignment of the environmental targets factor values specifically at this site as follows: 

Wetlands along the banks of the Missouri River and on Black Eagle Island and 

Steamboat Island in the Missouri River are identified by the U.S. Fish and Wildlife 

Service as part of the National Wetlands Inventory . . . Most of the wetlands immediately 

below Black Eagle Dam are classified as Riverine Perennial wetlands, and Palustrine 

Emergent wetlands are identified further downstream of the Black Eagle Dam within the 

zone of documented contamination . . . Most of the wetlands identified on the U.S. Fish 

and Wildlife Service National Wetlands Inventory Map for Northeast and Northwest 

Great Falls Montana within the zone of actual contamination qualify as eligible wetlands 

defined in 40 CFR Sec 230.2 because most of these wetland types are likely to contain a 

prevalence of wetland plant species based on their classification such as the palustrine 

emergent wetlands mentioned above. 

Section 4.1.4.3.1.2, Level II Concentrations, of the HRS documentation record at proposal stated that 

“[a]t least 0.1 mile of wetland frontage occurs within the zone of actual contamination and is subject to 

Level II contamination using sediment samples alone (Ref. 1, Table 4-24).” Citing to HRS Table 4–24, 

Wetlands Rating Values for Surface Water Migration Pathway, the HRS documentation record at 

proposal assigned the appropriate Level II concentrations factor value of 25 for a wetland frontage within 

the 0.1 to 1 mile category. See Figure 1 of this support document for the locations of the wetlands in 

relation to the observed release locations. 

Thus, wetlands subject to actual contamination at level II contaminations were appropriately established. 

Therefore, the commenter’s assertion that the environmental threat-target factor category value should 

have been based only on potential contamination is incorrect, and the score at proposal was correctly 

calculated in accordance with the HRS instructions. 

Regarding dilution weight, this parameter is only used in the environmental threat of the surface water 

pathway in calculating the potential contamination factor value (HRS Section 4.1.4.3.1.3, Potential 

contamination, describes this calculation). Because, as described above, wetlands were correctly scored 

as subject to actual Level II contamination and not potential contamination, this parameter does not apply. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.27.2 Aquatic Biota Targets 

Comment: ARCO asserted that no environmental impact to fish species was shown. 

Response: The HRS documentation record at proposal did not evaluate environmental impacts to a 

specific species as part of the environmental threat evaluation. The environmental threat-targets 

evaluated at this site only included HRS eligible wetlands as sensitive environments. 

HRS Section 4.1.4.3.1, Sensitive environments, states: 

Evaluate sensitive environments along the hazardous substance migration path for the 

watershed based on three factors: Level I concentrations, Level II concentrations, and 

potential contamination. 

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Determine which factor applies to each sensitive environment as specified in section 

4.1.2.3, except: use ecological-based benchmarks (Table 4–22) rather than health-based 

benchmarks (Table 3–10) in determining the level of contamination from samples. In 

determining the level of actual contamination, use a point of direct observation anywhere 

within the sensitive environment or samples (that is, surface water, benthic, or sediment 

samples) taken anywhere within or beyond the sensitive environment (or anywhere 

adjacent to or beyond the sensitive environment if it is contiguous to the migration path). 

HRS Section 4.1.4.3.1.2, Level II concentrations, directs the assignment of values from HRS Table 4-23 

for each sensitive environment subject to Level II contamination or from HRS Table 4-24 for wetlands: 

Assign value(s) from table 4–23 to each sensitive environment subject to Level II 

concentrations. . . . For those sensitive environments that are wetlands, assign an 

additional value from table 4–24. In assigning a value from table 4–24, include only 

those portions of wetlands located along the hazardous substance migration path in the 

area of Level II concentrations, as specified in section 4.1.4.3.1.1. 

HRS Table 4-23, Sensitive Environments Rating Values, provides a list of sensitive environments and 

related values eligible for scoring in the HRS surface water migration pathway. 

Section 4.1.4.3, Environmental Threat – Targets, of the HRS documentation record at proposal, on page 

48 stated: 

Wetlands along the banks of the Missouri River and on Black Eagle Island and 

Steamboat Island in the Missouri River are identified by the U.S. Fish and Wildlife 

Service as part of the National Wetlands Inventory (Ref. 35, pp 1-3). Most of the 

wetlands immediately below Black Eagle Dam are classified as Riverine Perennial 

wetlands, and Palustrine Emergent wetlands are identified further downstream of the 

Black Eagle Dam within the zone of documented contamination (Ref. 35, pp 1-3). Most 

of the wetlands identified on the U.S. Fish and Wildlife Service National Wetlands 

Inventory Map for Northeast and Northwest Great Falls Montana within the zone of 

actual contamination qualify as eligible wetlands defined in 40 CFR Sec 230.2 because 

most of these wetland types are likely to contain a prevalence of wetland plant species 

based on their classification such as the palustrine emergent wetlands mentioned above. 

As explained above, HRS Table 4-23 identifies the sensitive environments which are eligible for 

evaluation within the surface water pathway; while this includes contamination of certain state and federal 

threatened, endangered, or otherwise protected aquatic biota, none of these aquatic biota were identified 

as present within the TDL for this site. See section 3.6, Risk Associated with Site, of this support 

document for other information regarding risk to aquatic biota at the site. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.28 Surface Water - Environmental Threat Total Score 

Comment: ARCO stated that it had rescored the entire environmental threat of the surface water 

pathway, and in doing so had “refined” the components of all of the major factor categories of likelihood 

of release, waste characteristics, and targets, as well as the resultant environmental threat score. ARCO 

asserted that the score for the environmental threat should be 0.0078, instead of 53.33. 

Response: The environmental threat score was correctly assigned as 53.33 at proposal and remains the 

same at promulgation. 

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Sections 3.19.1, Documentation of Observed Release by Direct Observation, and 3.20, Surface Water 

Likelihood of Release - Observed Release by Chemical Analysis, of this support document, demonstrate 

that an observed release by direct observation and an observed release by chemical analysis were 

correctly documented and scored in accordance with the HRS. 

Section 3.26, Surface Water - Environmental Threat Waste Characteristics, of this support document, 

shows that the environmental threat waste characteristics factor category value of 320 remains unchanged 

from proposal. 

Finally, section 3.27.1, Actual Contamination, of this support document, makes clear that sensitive 

environments subject to actual contamination were correctly established. Therefore, the environmental 

threat score remains the same at promulgation as that assigned at proposal, and the revised scoring 

scenario provided by ARCO is not appropriate. 

This comment has no effect on the HRS site score or the decision to list the site on the NPL. 

3.29 Surface Water Overland/Flood Migration Component Score 

Comment: ARCO stated that it had rescored the entire surface water migration pathway. ARCO asserted 

that the score for the surface water overland/flood migration pathway should be 0.18, instead of 100 as 

assigned in the HRS documentation record at proposal. 

Response: Although the assignment of certain HRS factor values were revised at promulgation, the 

surface water overland/flood migration pathway component score remains the same at promulgation as 

that assigned in the HRS documentation record at proposal. 

HRS Section 4.1.5, Calculation of overland/flood migration component score for a watershed, states to: 

[s]um the scores for the three threats for the watershed (that is, drinking water, human 

food chain, and environmental threats). Assign the resulting score, subject to a maximum 

value of 100, as the surface water overland/flood migration component score for the 

watershed. 

HRS Section 4.1.6, Calculation of overland/flood migration component score, states to: 

[s]elect the highest surface water overland/flood migration component score from the 

watersheds evaluated. Assign this score as the surface water overland/flood migration 

component score for the site, subject to a maximum score of 100. 

As explained in section 3.22, Surface Water - Drinking Water Threat, of this support document, the 

drinking water threat was not scored in the HRS evaluation of the site. 

Section 3.25, Surface Water - Human Food Chain Threat Total Score, of this support document, 

establishes that the human food chain threat score of 96.06 assigned at proposal remains the same at 

promulgation. 

Section 3.28, Surface Water - Environmental Threat Total Score, of this support document, establishes 

that the environmental threat score of 53.33 assigned at proposal remains the same at promulgation. 

Therefore, the component score, generated by the sum of these threats and subject to a maximum of 100, 

remains 100 at promulgation. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

 87 

Soil Exposure 

The HRS documentation record at proposal identified an area of observed contamination based on 

contaminated residential soil samples in Black Eagle. Background and contaminated soil samples utilized 

in the record at proposal were taken from a 2007 investigation and a 2008 investigation, and were 

collected from a 0-2 inch horizon and a 6-12 inch horizon. Levels of metals meeting HRS criteria for 

establishing observed contamination (including arsenic, cadmium, and lead) were detected in 53 samples 

taken from 53 different residences (see Figure 2 of this support document which follows). Of the 53 

sampled residences, 8 exhibited Level I concentrations. The remainder of the residences and their 

associated population within the area of contamination were scored as targets subject to Level II 

contamination. 

3.30 Soil Exposure/Area of Observed Contamination 

Comment: ARCO alleged that the establishment of the AOC associated with Source 1 was flawed, and 

the soil exposure pathway score as presented in the HRS documentation record at proposal is incorrect. 

The following subsections of this support document address specific comments on this topic raised by 

ARCO. 

• 3.30.1 AOC Sampling Method 

• 3.30.2 Significant Increase of Hazardous Substances 

• 3.30.3 AOC Delineation/Inference 

• 3.30.4 Hazardous Substance Deposition/Attribution 

• 3.30.5 Contamination Below Cleanup Criteria 

3.30.1 AOC Sampling Method 

Comment: ARCO asserted that the sampling procedures employed to collect the soil samples used in the 

AOC evaluation were flawed. ARCO contended that all samples collected by EPA for the 2007 and 2008 

site investigations were “random grab samples rather than systematic composite samples” and were not 

representative of actual site conditions. In addition, ARCO asserted that the sampling it completed in 

2009 utilized a composite sampling method. It stated: 

Many of these residences were resampled in 2009 by Atlantic Richfield (AR Reference 

#14) using systematic composite sampling methods outlined in EPA's Superfund LeadContaminated Residential Sites Handbook (AR Reference #15). . . . In general, the 

composite sampling did not confirm the highest concentrations reported by EPA. 

Response: The sampling methods used to collect the necessary data in the evaluation of the area of 

observed contamination at the ACM site were appropriate. Grab samples are sufficient to collect the data 

necessary to identify the presence of contamination in establishing an area of contamination. Additional 

sampling is conducted in a later stage of the Superfund process when a site-specific risk assessment is 

performed. 

HRS Section 5.0.1, General considerations, states: 

 Evaluate the soil exposure pathway based on areas of observed contamination: 

• Consider observed contamination to be present at sampling locations where analytic 

evidence indicates that: 
ACM Smelter & Refinery NPL Listing Support Document 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

–A hazardous substance attributable to the site is present at a concentration 

significantly above background levels for the site (see table 2–3 in section 2.3 for 

the criteria for determining analytical significance), and 

–This hazardous substance, if not present at the surface, is covered by 2 feet or 

less of cover material (for example, soil). 

• Establish areas of observed contamination based on sampling locations at which there is 

observed contamination as follows: 

–For all sources except contaminated soil, if observed contamination from the 

site is present at any sampling location within the source, consider that entire 

source to be an area of observed contamination. 

–For contaminated soil, consider both the sampling location(s) with observed 

contamination from the site and the area lying between such locations to be an 

area of observed contamination, unless available information indicates otherwise. 

• If an area of observed contamination (or portion of such an area) is covered by a 

permanent, or otherwise maintained, essentially impenetrable material (for example, 

asphalt) that is not more than 2 feet thick, exclude that area (or portion of the area) in 

evaluating the soil exposure pathway. 

• For an area of observed contamination, consider only those hazardous substances that 

meet the criteria for observed contamination for that area to be associated with that area 

in evaluating the soil exposure pathway (see section 2.2.2). 

The HRS does not give explicit direction on what sampling methodology to use in establishing an area of 

contamination. However, the HRS directs the scorer, as cited above, to consider observed contamination 

to be present at sampling locations where analytic evidence indicates that a hazardous substance 

attributable to the site is present at a concentration significantly above background levels for the site. 

Page 50 of the HRS documentation record at proposal documented the collection of samples used 

in establishing the area of contamination: 

The 2007 EPA CERCLA Site Assessment sampled residences on both the north and 

south sides of the Missouri River adjacent to the Anaconda Minerals Co, Great Falls 

Refinery (Ref. 21, p. 11). Of the eleven residences sampled in Great Falls on the south 

side of the Missouri River in August of 2007 only one residence had a elevated 

concentration of arsenic (Ref. 21, p. 13). Thirty-three residences were sampled for CLP 

analysis north of the Missouri River in Black Eagle in August of 2007, and arsenic and 

lead concentrations greater than three times background were identified in central and 

eastern Black Eagle from the results of the 2007 investigation (Ref. 21, pp. 13-14, 18). 

All soil samples collected were analyzed in the field using a portable XRF device (Ref. 5, 

p. 12; Ref. 21., p. 12). All samples for fixed laboratory analyses were analyzed through 

the EPA’s CLP, RAS. The samples collected in 2007 were analyzed by A4 Scientific, 

Inc. of The Woodlands, Texas by EPA CLP method ILM05.4 (Ref. 60, p. 1; Ref. 61., p. 

1; Ref. 62, p. 1). 

The 2008 EPA CERCLA Expanded Site Investigation was focused in the community of 

Black Eagle, Montana. The residential soil at fifty-nine residential properties in Black 

Eagle was sampled in July 2008 to a depth of one foot (Ref. 5, p. 1). Concentrations of 

arsenic, cadmium, lead and zinc elevated three times background were detected in the 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

residential soil in Black Eagle (Ref. 5, pp. 13-14; Ref. 18, pp. 28-30; Ref. 21, pp. 13-14). 

Elevated arsenic and cadmium results delineated an area of contamination centered on 

southwestern and central Black Eagle (Ref. 5, pp. 13-14, 23-24). 

All 2008 soil samples collected were analyzed in the field using a portable XRF device 

(Ref. 5, p. 12; Ref. 21., p. 12). All samples for fixed laboratory analyses were analyzed 

through the EPA’s Contract Laboratory Program (CLP), Routine Analytical Services. 

The samples collected in 2008 were analyzed by Chemtech Consulting Group, 

Mountainside, New Jersey by EPA CLP method ILM05.4 (Ref. 63. p. 1; Ref. 64, p. 1). 

The collection of the 2007 and 2008 samples described above, resulted in the collection of data meeting 

the HRS provisions for establishing an AOC. This method resulted in the determination that the soil at 

the sampling locations was contaminated at levels meeting observed release criteria. 

While the HRS does not give explicit direction on the sampling methodology necessary to establish the 

concentrations of a hazardous substance at a particular location, page 51532 of the HRS, under Section I, 

Background, states: 

In 1986, Congress enacted the Superfund Amendments and Reauthorization Act of 1986 

(SARA). . . .requiring EPA to amend the HRS to assure ‘to the maximum extent feasible, 

that the hazard ranking system accurately assesses the relative degree of risk to human 

health and the environment posed by sites and facilities subject to review.’ Congress, in 

its Conference Report on SARA, stated that substantive standard against which HRS 

revisions could be assessed: 

This standard is to be applied within the context of the purpose for the National Priorities 

List; i.e., identifying for the States and the public those facilities and sites which appear 

to warrant remedial actions....This standard does not, however, require the Hazard 

Ranking System to be equivalent to detailed risk assessments, quantitative or qualitative, 

such as might be performed as part of remedial actions. The standard requires the Hazard 

Ranking System to rank sites as accurately as the Agency believes is feasible using 

information from preliminary assessments and site inspections. 

The sample results used in establishing the area of contamination at the ACM site were collected from 

site inspections of the Black Eagle residential area which were specifically performed to collect data 

necessary to evaluate the site. As described in section 3.14.3, Sampling Procedures, of this support 

document, the collection of grab samples documented the level of hazardous substances at each sampling 

location to determine that observed contamination was present each sampling location. That hazardous 

substances within the area of contamination were detected significantly above background levels is 

discussed in section 3.29.2, Significant Increase of Hazardous Substances, of this support document. 

Regarding the Superfund Lead-Contaminated Residential Sites Handbook, nothing in this guidance 

document precludes the use of grab samples for an HRS evaluation. This document is directed toward a 

detailed site characterization and the remedy section for the site; this occurs during a later stage of the 

Superfund process, not during a screening HRS investigation. 

This comment has no effect on the HRS site score or the decision to list the site on the NPL. 

3.30.2 Significant Increase of Hazardous Substances 

Comment: In its comments challenging the establishment of the AOC, ARCO challenged the significant 

increase of various hazardous substances in samples used to determine the AOC. ARCO specifically 

stated that the residential properties sampled by EPA incorrectly included 114 residences that did not 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

have concentrations of arsenic and cadmium greater than three times background concentrations and their 

respective SCDM4

 benchmarks . 

In addition, ARCO stated that none of the soil samples collected from residential areas in Black Eagle 

contained concentrations of antimony greater than three times background, therefore antimony cannot be 

regarded as elevated. 

Response: A significant increase (i.e, three times background) of arsenic, cadmium, and lead in samples 

from the AOC were correctly identified in accordance with the HRS. The number of residences included 

the AOC evaluation has been reduced at promulgation (see section 3.32, Soil Exposure Targets, of this 

support document). Antimony has been removed from the HRS evaluation at promulgation. 

HRS Section 5.0.1, General considerations, states: 

Evaluate the soil exposure pathway based on areas of observed contamination: 

• Consider observed contamination to be present at sampling locations where analytic 

evidence indicates that: 

–A hazardous substance attributable to the site is present at a concentration 

significantly above background levels for the site (see table 2–3 in section 2.3 for 

the criteria for determining analytical significance), and 

–This hazardous substance, if not present at the surface, is covered by 2 feet or 

less of cover material (for example, soil). 

Establish areas of observed contamination based on sampling locations at which there is 

observed contamination as follows: 

–For all sources except contaminated soil, if observed contamination from the 

site is present at any sampling location within the source, consider that entire 

source to be an area of observed contamination. 

–For contaminated soil, consider both the sampling location(s) with observed 

contamination from the site and the area lying between such locations to be an 

area of observed contamination, unless available information indicates otherwise. 

• If an area of observed contamination (or portion of such an area) is covered by a 

permanent, or otherwise maintained, essentially impenetrable material (for example, 

asphalt) that is not more than 2 feet thick, exclude that area (or portion of the area) in 

evaluating the soil exposure pathway. 

• For an area of observed contamination, consider only those hazardous substances that 

meet the criteria for observed contamination for that area to be associated with that area 

in evaluating the soil exposure pathway (see section 2.2.2). 

The portions of HRS Table 2-3 used to establish observed contamination and the AOC are cited as 

follows: 

 

4

 Superfund Chemical Data Matrix. EPA assumes that ARCO’s reference to the SCDM benchmarks is referring to the 

benchmarks cited in the HRS (HRS Section 5.1.3.2) as to be used for establishing Level I contamination. SCDM repeats the list 

of those HRS benchmarks and presents the contaminant levels currently associated with the benchmarks. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

An observed release is established as follows: 

• If the background concentration is not detected (or is less than the detection 

limit), an observed release is established when the sample measurement equals or 

exceeds the sample quantitation limit. 

• If the background concentration equals or exceeds the detection limit, an 

observed release is established when the sample measurement is 3 times or more 

above the background concentration. 

Pages 50-51 of the HRS documentation record at proposal document that samples taken from the Black 

Eagle residential area contained hazardous substances elevated significantly above background levels: 

The 2007 EPA CERCLA Site Assessment sampled residences on both the north and 

south sides of the Missouri River adjacent to the Anaconda Minerals Co, Great Falls 

Refinery (Ref. 21, p. 11). Of the eleven residences sampled in Great Falls on the south 

side of the Missouri River in August of 2007 only one residence had an elevated 

concentration of arsenic (Ref. 21, p. 13). Thirty-three residences were sampled for CLP 

analysis north of the Missouri River in Black Eagle in August of 2007, and arsenic and 

lead concentrations greater than three times background were identified in central and 

eastern Black Eagle from the results of the 2007 investigation (Ref. 21, pp. 13-14, 18). . . 

The 2008 EPA CERCLA Expanded Site Investigation was focused in the community of 

Black Eagle, Montana. The residential soil at fifty-nine residential properties in Black 

Eagle was sampled in July 2008 to a depth of one foot (Ref. 5, p. 1). Concentrations of 

arsenic, cadmium, lead and zinc elevated three times background were detected in the 

residential soil in Black Eagle (Ref. 5, pp. 13-14; Ref. 18, pp. 28-30; Ref. 21, pp. 13-14). 

Elevated arsenic and cadmium results delineated an area of contamination centered on 

southwestern and central Black Eagle (Ref. 5, pp. 13-14, 23-24). 

All 2008 soil samples collected were analyzed in the field using a portable XRF device 

(Ref. 5, p. 12; Ref. 21., p. 12). All samples for fixed laboratory analyses were analyzed 

through the EPA’s Contract Laboratory Program (CLP), Routine Analytical Services. 

The samples collected in 2008 were analyzed by Chemtech Consulting Group, 

Mountainside, New Jersey by EPA CLP method ILM05.4 (Ref. 63. p. 1; Ref. 64, p. 1). 

Page 52 of the HRS documentation record at proposal presented the background soil samples to which the 

samples taken from the area of observed contamination were compared. A background level was 

developed for arsenic, cadmium, and lead from two horizons of soil – the 0-2 and the 6-12 horizons. The 

following tables present the highest background levels established from each horizon in the evaluation of 

the area of observed contamination. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

ACM Smelter and Refinery – Background Samples 0-2 inch horizon collected in 2007 and 2008* 

(mg/kg)

Analyte 

CRDL/ 

MDL 

(2007/2008) 

SCDM 

Benchmark 

RDSC 

Jaycee Park 

R04ST2400F102 

CLP - MHIH26 

Sampled 

8/10/2007 

North Middle 

School 

R08ST2601F102 

CLP - MH1H34 

Sampled 8/8/2007 

724 25th Ave. 

R25AV0724FY02 

CLP - MH26P6 

Sampled 

7/11/2008 

737 25th Ave. 

R25AV0737SY02 

CLP - MH26P7 

Sampled 

7/11/2008 

Arsenic 1/(0.49/ 

0.37) 

0.43 13.3 (10.4 J) 18.1 6.3 16.1 

Cadmium 0.5/(0.20/ 

0.040) 

39 1.2 J+ 0.82 J+ 0.53 (0.34 J) 0.48 

Lead 1/(0.49/ 

0.25) 

- 30.1 (17.5 J) 25.2 25.3 20.6 

Note: 

* Sample IDs ending in 02 represent samples collected from 0-2 inches (Ref. 5, p. 10; Ref. 21, p. 11). 

Bold Indicates background value selected for this document / mg/kg 

CRSC Cancer Risk Screening Concentration 

RDSC Reference Dose Screening Concentration 

J The associated numerical value is an estimated quantity and is the approximate concentration of the analyte in the sample.

J+ The associated numerical value is an estimated quantity, but the result may be biased high. 

( ) Validated value prior to adjustment as per EPA Fact Sheet “Using Qualified Data to Document an Observed Release and 

Observed Contamination” (Ref. 43, 18 pages). 

mg/kg milligrams per kilogram 

ACM Smelter and Refinery – Background Samples 6-12 inch horizon collected in 2007** 

(mg/kg)

Analyte CRDL/ 

MDL(2007) 

SCDM 

Benchmark 

RDSC 

Jaycee Park 

R04ST2400F112 

CLP - MHIH27 

Sampled 8/10/2007 

North Middle 

School 

R08ST2601F112 

CLP - MH1H35 

Sampled 8/8/2007 

724 25th Ave. 

6-12 inch 

sample not 

collected in 

2008 

737 25th Ave. 

6-12 inch 

sample not 

collected in 

2008 

Arsenic 1/0.49 0.43 17.2 (13.3 J) 23.1 - - 

Cadmium 0.5/0.20 39 0.43 J+ 0.67 J+ - - 

Lead 1/0.49 - 10.6 (12.9 J)18.6 - - 

Note: 

** Sample IDs ending in 12 represent samples collected from 6-12 inches 

Bold Indicates background value selected for this document / 

mg/kg Milligrams per kilogram 

CRSC Cancer Risk Screening Concentration 

RDSC Reference Dose Screening Concentration 

As identified above , pages 54-63 of the HRS documentation record at proposal presented multiple 

samples taken from the Black Eagle residential area that were documented to contain arsenic, cadmium, 

or lead at a concentration greater than 3 times the highest background level of each respective horizon. 

As arsenic, cadmium, and lead were all detected in the background samples, according to HRS Table 2-3, 

a significant increase is shown when the hazardous substance detected in the release sample (observed 

contamination sample) is greater than 3 times the highest detected background. Each of the 53 sampling 

locations presented on pages 54-63 of the HRS documentation record at proposal contained either lead, 

cadmium, or arsenic at levels greater than 3 times detected background concentrations, thus satisfying 

HRS Table 2-3 requirements. These hazardous substances were associated with the AOC, as 

contamination associated with Source 3 was documented as present at sampling locations within the AOC 

within 2 feet of the surface. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

The commenter is incorrect in its assertion that a hazardous substance need be greater than 3 times 

background and above an HRS benchmark [referred to by ARCO as “SCDM benchmarks”] (in this case, 

an HRS health-based benchmark for hazardous substances in soils) to identify residences as within the 

AOC. As stated above, there is no requirement that a substance be above a benchmark to use it in 

identifying an AOC or identifying residences with the AOC (EPA notes that it does impact whether the 

residences are considered exposed to Level I or Level II exposure. See section 3.32, Soil Exposure 

Targets, of this support document.) 

Regarding antimony, it was not included in the evaluation of the AOC (or the corresponding source 1) at 

proposal. The discussion of antimony has been removed in the HRS documentation record at 

promulgation, and because this substance was not scored in the HRS documentation record at proposal, 

its removal has no impact on the scoring of the site. The removal of this substance has no effect on the 

identification of residences exposed to arsenic, cadmium or lead. 

This comment has no effect on the HRS site score or the decision to list the site on the NPL. 

3.30.3 AOC Delineation/Inference 

Comment: ARCO alleged that the inference of contamination between sample locations in the Black 

Eagle residential soil AOC delineation is incorrect according to the HRS, and as a result EPA has 

significantly overestimated the AOC. ARCO asserted that AOC evaluation at proposal “ignores dozens 

of included residences that do not have elevated arsenic or cadmium concentrations based on EPA's own 

data.” 

Response: The evaluation of the AOC delineation at promulgation has been revised. As stated in section 

3.14.2, Source 1 Delineation/Inference of Contamination, contamination is no longer inferred between 

sample locations in the evaluation of the AOC in the HRS evaluation at promulgation (see Figure 2 of this 

support document for a presentation of the sample locations used in establishing the AOC). 

HRS Section 5.0.1, General considerations, states: 

Establish areas of observed contamination based on sampling locations at which there is 

observed contamination as follows: 

. . . . 

–For contaminated soil, consider both the sampling location(s) with observed 

contamination from the site and the area lying between such locations to be an 

area of observed contamination, unless available information indicates otherwise. 

The samples used in defining the AOC remain the same at promulgation as defined at proposal (see pages 

54-63 of the HRS documentation record at proposal); however, the area between the sample locations is 

no longer considered part of the AOC. As discussed in section 3.30.2, Significant Increase of Hazardous 

Substances, of this support document, 53 samples within the Black Eagle residential area were 

documented as meeting the HRS criteria for observed contamination. 

However, as noted by ARCO, certain information collected from various investigations of the Black 

Eagle residential area indicates that sampling locations between the 53 AOC samples exhibit levels of 

arsenic, cadmium, or lead not significantly greater than background levels. For example, during the 2008 

ESI of the Black Eagle residential area, field sample location RMTAV1721F12, collected between AOC 

sample locations, did not show levels of arsenic, lead, and/or cadmium at levels significantly greater than 

background. Therefore, no contamination was inferred between the 53 AOC sample locations at 

promulgation (See Figure 2 of this support document). 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

Changes to the evaluation of the soil exposure pathway waste characteristics and targets have been made 

at promulgation in association with the change to no longer infer contamination in areas lying between the 

AOC sampling locations. Specifically, the soil exposure pathway hazardous waste quantity area 

evaluation at promulgation has been reduced from the defined area at proposal to “greater than 0”. Also, 

the count of soil exposure targets subject to Level II concentrations has been reduced at promulgation. 

Refer to section 3.31, Soil Exposure Pathway Waste Characteristics, and section 3.31.2, Count of Level II 

Targets, of this support document for a discussion on the scoring of the soil exposure pathway waste 

characteristics and targets at promulgation. How this change impacts the overall site score is discussed in 

the corresponding sections described above. 

3.30.4 Hazardous Substance Deposition/Attribution 

Comment: ARCO submitted comments challenging the attribution of hazardous substances in the 

observed contamination samples at the site. ARCO asserted that the concentrations of arsenic, cadmium, 

and lead in the samples show a sporadic and variable distribution that is not consistent with aerial 

deposition from a single dominant source and that the prevailing wind direction at the site is not toward 

the Black Eagle residential properties associated with the AOC. Additionally, ARCO asserted that 

concentrations of lead in residential soils are consistent with degradation of lead-based paint and other 

consumer products. ARCO submitted sampling data to support its assertion (see pages 88-112 of 

ARCO’s comments at Docket ID: EPA-HQ-SFUND-2010-0072-0016.1).

The following subsections of this support document address specific assertions regarding the evaluation 

of the hazardous substance attribution with the AOC: 

• 3.30.4.1 Aerial Deposition 

• 3.30.4.2 Evaluation of Lead 

3.30.4.1 Aerial Deposition 

Comment: ARCO challenged the attribution of hazardous substances in the AOC to an aerial deposition 

source, stating that “the data collected by EPA demonstrates that concentrations of arsenic, cadmium, and 

lead in the residential soil throughout Black Eagle do not exhibit a spatial distribution that is consistent 

with aerial deposition.” 

ARCO asserted that the HRS criteria for determining impacts from an aerial source are “quite simple,” 

and that: 

a more relevant consideration of potential impacts related to an aerial deposition source 

would consider not only the presence of potentially source-related contaminants, but also 

the spatial distribution of contaminant concentrations relative to the source. 

ARCO stated that a more relevant consideration of an aerial deposition source would consider more 

factors than just the presence of site-related hazardous substances. ARCO argued that other factors 

should have been evaluated, such as the distribution of contaminant concentrations in the soils in relation 

to the source (both horizontally and vertically), whether the distribution corresponds with prevailing wind 

direction and distance from the source, and the consideration of other potential sources, such as 

commercial operators, such as Montana Refining Company, “a documented source of metals and arsenic 

in air emissions.” ARCO cited to a Montana Department of Environmental Quality (MDEQ) database in 

support of this assertion. Further, ARCO asserted: 

The data collected by EPA demonstrate that concentrations of arsenic, cadmium, and lead 

in the residential soil throughout Black Eagle do not exhibit a spatial distribution that is 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

consistent with aerial deposition from the Former GFR Site. If aerial emissions were the 

primary source of arsenic, cadmium, and lead in Black Eagle soil, the concentrations of 

these metals should be higher at locations that are closer to the former stack location, and 

decrease with distance from the former stack location. In fact, the few higher 

concentration locations for arsenic and cadmium are located in the southwestern portion 

of Black Eagle, distant from the former smoke stack location and the higher 

concentrations often occurred in the deeper (6-12 inch bgs) soil horizon. The spatial 

distribution of arsenic, cadmium, and lead, as shown on Figures 5-3, 5-4, and 5-5, do not 

exhibit any sort of gradient that could be linked to emissions from the former smoke 

stack. Instead, and as detailed above, the concentrations of these metals in the residential 

yards show a sporadic and variable distribution throughout Black Eagle and also within 

individual properties that is not indicative of a single dominant source. “ 

ARCO stated that its 2009 residential soil investigation showed a variability of arsenic and lead 

concentrations by sample location and depth, as well as a lack of discernible pattern in the distribution of 

arsenic relative to lead. ARCO stated that arsenic concentrations were generally higher in deeper depth 

horizons (6-18 inches bgs) than in upper depth horizons (0-6 inches bgs), whereas lead concentrations 

were generally higher in the more shallow (0-6 inches bgs) depth intervals. 

Also, ARCO noted that the distribution of lead and arsenic concentrations in their sampling across 

different properties is relatively consistent between front and back yard samples, whereas the distribution 

of concentrations in garden, driveway, and dripline samples was less consistent between properties, which 

it asserted may be the result of differences in structures between individual properties that could influence 

dripline lead concentrations or soil mixing in gardens and during driveway construction. 

Response: The HRS documentation record has been revised at promulgation to better explain the 

attribution of the hazardous substances in the AOC to emissions to the site and specifically to Source 3, 

the facility air emissions. 

HRS Section 5.0.1, General considerations, states: 

Evaluate the soil exposure pathway based on areas of observed contamination: 

• Consider observed contamination to be present at sampling locations where analytic 

evidence indicates that: 

–A hazardous substance attributable to the site [emphasis added] is present at a 

concentration significantly above background levels for the site (see table 2–3 in 

section 2.3 for the criteria for determining analytical significance), and 

–This hazardous substance, if not present at the surface, is covered by 2 feet or 

less of cover material (for example, soil). 

Establish areas of observed contamination based on sampling locations at which there is 

observed contamination as follows: 

. . . . 

–For contaminated soil, consider both the sampling location(s) with observed 

contamination from the site and the area lying between such locations to be an 

area of observed contamination, unless available information indicates otherwise. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

• If an area of observed contamination (or portion of such an area) is covered by a 

permanent, or otherwise maintained, essentially impenetrable material (for example, 

asphalt) that is not more than 2 feet thick, exclude that area (or portion of the area) in 

evaluating the soil exposure pathway. 

• For an area of observed contamination, consider only those hazardous substances that 

meet the criteria for observed contamination for that area to be associated with that area 

in evaluating the soil exposure pathway (see section 2.2.2). 

As described in section 3.13, Additional Sources, of this support document, although the HRS 

documentation record at proposal did not designate the former stack at the ACM site as a source, 

emissions from the stack were discussed on page 12 of the HRS documentation record at proposal: 

The Big Stack was constructed in 1908 to a length of 506 feet and a total height of 751 

feet above the smelter’s blast furnace (Ref. 8 p. 7A). The Big Stack went into service on 

June 12, 1909 and continued belching smoke until August 06, 1972 (Ref. 9, p. 15). The 

Big Stack was designed to eject a volume of 1,575,000 cubic feet of air per minute at a 

velocity of 450 feet per minute, a sufficient volume and rate to entrain and remove from 

the smelter all the gases and dust generated during the smelting process (Ref. 9, p. 20). . . 

. An internal Anaconda Copper Mining Company Memorandum from 1951 stated that 

approximately 15.04 pounds of arsenic passed out of the stack every 24 hours (Ref. 33, p. 

1). 

The HRS documentation record at proposal on page 12 explained that “aerial deposition of contaminants 

emanating from the smelter smoke stacks between 1893 and 1972 is the most likely mechanism of 

contaminants transport to the residential soils in the community of Black Eagle.” The addition of Source 

3 at promulgation provides for a clear link between the hazardous substances associated with the former 

stack emissions, and the hazardous substances detected in the AOC – as lead, cadmium, and arsenic were 

associated with both the AOC and with the former stack emissions. 

As presented on pages 38-39 of the HRS documentation record at promulgation and references cited 

therein, arsenic was detected in emissions from Source 3 and samples taken from flue dust associated 

with smelter emissions. Large quantities of flue dust, a by-product of smelting operation emissions, were 

accumulated at the former stack. This flue dust was documented as containing arsenic, lead, and 

cadmium. These hazardous substances were also detected in the AOC located in the Black Eagle 

residential area as described in section 3.30.2, Significant Increase of Hazardous Substances, of this 

support document. 

Regarding ARCO’s assertion that other sources of metals in air emissions, such as the nearby Montana 

Refining Company facility, could have caused the significant increase of hazardous substances within the 

AOC, no information from this facility or any other nearby facilities documents that air emissions of 

arsenic, cadmium, and lead have occurred that could have caused the significant increase of hazardous 

substances found within the AOC. Although ARCO alluded that the Montana Refining Company emitted 

metals to the air, the information provided by ARCO does not support such an assertion. The MDEQ 

database cited by the ARCO to support this assertion only notes the cleanup and maintenance of solid 

wastes at that facility, and no information regarding air emission of metals. 

Thus, it is reasonable to conclude that the emissions from Source 3, facility air emissions, which are 

documented to contain arsenic, cadmium, and lead resulting from operations at the site, have caused the 

significant increase of hazardous substances in the AOC. 

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Evaluation of Wind Direction 

Regarding ARCO’s questioning of whether the hazardous substance distribution in the AOC corresponds 

with established wind direction data at the site, evidence of the wind blowing from the former stack, 

southwest toward the Black Eagle residential area has been established (see Figure 1 of this support 

document for locational information regarding the former stack in relation to the Black Eagle residential 

area). Page 64 of the HRS documentation record at proposal, under the subheading Attribution, states: 

The wind direction in the Great Falls, Montana area is usually from the southwest, 

particularly in the months of October through March. Wind data collected at the Great 

Falls International Airport, approximately 5 miles southwest of the community of Black 

Eagle shows that during March, April, and May the winds can blow from the northwest 

or northeast more than twenty percent of the time and that in the summer months of June, 

July, and August wind direction over Black Eagle is from the northeast or east more than 

20 percent of the time (Ref. 30, pp. 2-13). A south facing aerial photo published by the 

Great Falls Tribune in 2002 shows smoke from the 506 foot tall stack wafting westward 

across the community of Black Eagle (Ref. 29, p. 8A). 

Thus, the wind is documented to blow at least part of the time from the former stack location toward the 

Black Eagle residential area and the AOC, allowing for the transport of hazardous substances from the 

former stack to the AOC. 

Regarding ARCO’s assertion that concentrations of hazardous substances detected in the Black Eagle 

residential area did not display a specific pattern, such as a gradient dissipating to lesser concentrations 

farther from the former stack location, this information does not negate the fact that hazardous substances 

came to be located in the Black Eagle residential area from the smelter emissions. The HRS 

documentation record at promulgation does not conclude that a predictable pattern by which hazardous 

substances were deposited in the Black Eagle residential area was determined, nor does the HRS require 

this analysis be performed. As explained above, the HRS only requires that at least part of the significant 

increase be due to releases from the ACM site, and this requirement was met. 

Furthermore, the deposition of airborne hazardous substances into a predictable pattern, as asserted by 

ARCO, could not have been adequately determined without the use of extensive modeling, and does not 

consider the multiple dynamic factors at play (i.e., stack height, discharge temperatures, variability in 

wind direction). Also, as documented on page 12 of the HRS documentation record at proposal, 

operations at the facility changed over the long history from the late 1800’s and into the 1970’s, such as 

the 1916 addition of electrolytic zinc and copper operations, and the closure of zinc refining operations in 

1972. It is reasonable to conclude that stack emission composition and rates varied during these 

operational time periods and that the potential influence on the deposition patterns of emitted substances 

would vary. 

Further, residential soils can be disturbed by a variety of factors, such as gardening, landscaping, paving, 

and work on public utilities. Even if reasonably precise air modeling from the former stack were 

completed, deposition patterns of hazardous substances within the soil of the Black Eagle residential area 

would still be influenced by these factors. 

Therefore, because a specific discernible gradient of hazardous substances geographically across the 

Black Eagle residential area in relationship with the smelter emissions was not identified, does not 

discredit that the hazardous substances detected within the AOC are attributable to the site. 

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Vertical Distribution of Hazardous Substances within Soil 

ARCO’s assertion that arsenic was more often detected at concentrations of greater depth in the 2009 

study it completed, and that lead was more often detected at more shallow depths, does not necessarily 

indicate and certainly does not demonstrate or prove that these hazardous substances were not deposited 

from the same aerial emission source. 

Variability in the vertical contaminant distribution within the Black Eagle residential soils was noted in 

ARCO’s 2009 study, as both arsenic and lead were detected in both deep and shallow samples in the 

Black Eagle residential area. 

Again, variations in former facility operations at the site would have influenced which hazardous 

substance and how much of that hazardous substance was emitted at various time periods, and 

disturbances in residential soils may have altered the relative location of hazardous substances within 

Black Eagle residential properties. 

Regardless, HRS Section 5.0.1, General considerations, directs that in evaluating which hazardous 

substances are to be included in the establishment of observed contamination, the hazardous substance “ if 

not present at the surface, is covered by 2 feet or less of cover material (for example, soil).” Pages 53 of 

the HRS documentation record at proposal documents that the samples used in identifying the AOC were 

collected less than 2 feet below ground surface, and that all AOC samples were documented to contain 

either arsenic, cadmium, or lead at levels greater than 3 times background levels. It states: “[a]ll of the 

residential soil samples listed in the table [table beginning on page 54 of the HRS documentation record 

at proposal] were collected as grab samples from either the 0 to 2 or the 6 to 12 horizon...” Thus, it is 

reasonable to conclude that the emissions that are documented to contain arsenic, cadmium, and lead 

resulting from operations at the site have caused the significant increase of hazardous substances in the 

Black Eagle residential area. 

This comment has no effect on the HRS site score or the decision to list the site on the NPL. 

3.30.4.2 Evaluation of Lead 

Comment: ARCO asserted that detections of lead on residential properties within the AOC are indicative 

of deteriorating lead-based paint, varnishes, plumbing, or other consumer products. ARCO asserted that, 

of those concentrations that exceeded soil screening level for lead established by EPA, the pattern shown 

in the data is consistent with lead paint deterioration. ARCO stated that, among the shallower soil 

samples, higher lead concentrations were often associated with dripline sample locations, yet arsenic was 

not. ARCO stated that: 

Given the age of housing stock in Black Eagle (most homes constructed prior to 1920), 

the presence of lead at these locations is not unexpected and generally higher 

concentrations associated with dripline samples is likely due to deteriorating lead-based 

paint. As shown in Table 5-5, paint chips were frequently identified in soil samples from 

the 2009 investigation where lead concentrations exceeded 400 mg/kg.” 

Further, ARCO asserted that the HRS documentation record at proposal attempted to justify the area of 

observed contamination by noting a "pervasive distribution of lead" in the residential soils, yet elevated 

lead concentrations were not used to justify the claim that the area was contaminated. ARCO stated that 

“EPA's decision to use elevated lead concentrations to support the breadth of its ‘area of contamination,’ 

but not the substance of its ‘area of contamination’ is transparent,” and that “EPA's CERCLA authorities 

do not generally support soils remediation to abate risks posed by deteriorating lead based paint.” 

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Response: The significant increase in lead concentrations in samples collected from properties within the 

Black Eagle residential area was appropriately attributed to releases of hazardous substances from the 

site. It is well documented that lead was emitted from the facility and migrated via air toward the 

residential area of Black Eagle. Furthermore, the AOC samples were specifically collected from locations 

unlikely to be contaminated by the lead sources identified by ARCO. 

As discussed in section 3.30.4.1, Aerial Deposition, of this support document, HRS Section 5.0.1, 

General considerations, states: 

Evaluate the soil exposure pathway based on areas of observed contamination: 

• Consider observed contamination to be present at sampling locations where analytic 

evidence indicates that: 

–A hazardous substance attributable to the site [emphasis added] is present at a 

concentration significantly above background levels for the site (see table 2–3 in 

section 2.3 for the criteria for determining analytical significance), and 

–This hazardous substance, if not present at the surface, is covered by 2 feet or 

less of cover material (for example, soil). 

As detailed on pages 38-39 of the HRS documentation record at promulgation, flue dust samples collected 

from Source 3 (facility air emissions) document the presence of lead and several other hazardous 

substances as associated with facility emissions. Analytical data documentation shows that lead was one 

of the most common hazardous substances detected in the stack flue dust (Reference 58, p. 103 of the 

HRS documentation record at proposal). As emissions from the stack are documented to have migrated 

via air toward the Black Eagle residential area, it is reasonable to conclude that the hazardous substances 

migrating from the stack emissions and settling on the Black Eagle residential area would have included 

high amounts of lead. 

Also, the sampling data used in establishing the AOC (the 2007 Site Assessment and 2008 Expanded Site 

Inspection) was collected using a sampling methodology cognizant of the potential influence of 

residential sources of lead. Sample sketches were developed for each AOC sample location detailing the 

spatial relationship between the sample locations and property features of note such as houses, driveways, 

and shed, etc. (Reference 5, pp. 149-208; Reference 21, pp. 98-161 of the HRS documentation record at 

proposal). These sketches demonstrate that the majority of the sample locations were located away from 

buildings and often in the middle of an open area of the residential yards. For example, the sketches 

demonstrate that at least 32 of the AOC samples were collected at a distance of 5 feet or greater from any 

nearby structure on the residential properties - minimizing the potential influence from degrading paint or 

other lead containing materials. 

Further, if lead were not included in the evaluation of the AOC and overall soil exposure pathway, the 

hazardous substances arsenic and cadmium would still establish an AOC and targets would still be subject 

to Level I and Level II contamination for those substances within the AOC. 

EPA also disagrees with ARCO’s unsupported statement that CERCLA authorities “do not generally 

support soils remediation to abate risks posed by deteriorating lead based paint.” CERCLA contains no 

provision precluding releases of lead from lead-based paint from coverage under CERCLA. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

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3.30.5 Contamination below Cleanup Criteria 

Comment: ARCO asserted that hazardous substances detected in samples associated with the AOC were 

below various screening levels and cleanup criteria. ARCO stated that “[n]one of the arsenic 

concentrations exceed a safe level established by EPA for Anaconda, Montana, a nearby similar site,” and 

that only one of the cadmium concentrations exceeds EPA's conservative soil screening level for 

cadmium. 

Response: Hazardous substance levels identified as meeting observed contamination criteria in the AOC 

evaluation were established according to the HRS; there is no HRS requirement that hazardous substance 

levels exceed cleanup or screening levels in order to establish an area of observed contamination. 

As explained in section 3.7, Permitted Releases and Regulatory Limits, of this support document, whether 

or not the level of a hazardous substance in a sample is within applicable regulatory or otherwise 

acceptable limits does not eliminate that hazardous substance from HRS scoring consideration or affect 

the establishment of an AOC. Section 3.30.2, Significant Increase of Hazardous Substances, of this 

support document shows that a significant increase of hazardous substances was identified in the AOC 

according to the HRS. 

Thus, that the levels of hazardous substances within specific soil samples at this site do not exceed 

cleanup or screening levels established at another Superfund site does not preclude the inclusion of those 

hazardous substances in the establishment of an AOC at the site in the HRS evaluation. 

This comment has no effect on the HRS site score or on the decision to list the site on the NPL. 

3.31 Soil Exposure Pathway Waste Characteristics 

Comment: ARCO alleged that the waste characteristics factor category for the soil exposure pathway was 

incorrectly evaluated as the pathway hazardous waste quantity was incorrectly calculated. The following 

subsections of this support document address specific comments on this topic raised by ARCO. 

• 3.31.1 Soil Exposure Pathway Hazardous Waste Quantity 

• 3.31.2 Significant Increase of Hazardous Substances 

3.31.1 Soil Exposure Hazardous Waste Quantity 

Comment: ARCO claimed that its assessment of the AOC resulted in a smaller area from which the 

hazardous waste quantity would be evaluated. ARCO stated that it had: 

calculated a revised area assigned value of 153,000 - 26,010 (17% pavement) = 142,290 

x 69% (open grass/soil) = 98,180 ft. 98,180/34,000 = 2.8876, which is significantly less 

than the 32.5633 used by EPA. 

Response: The evaluation of the soil exposure pathway hazardous waste quantity has been revised at 

promulgation to reflect that areas between soil samples are no longer inferred as part of the AOC. 

However, this revision results in a pathway waste characteristics factor value of 18 at promulgation, the 

same as at proposal. 

As discussed in section 3.30.3, AOC Delineation, of this support document, the delineation of the AOC in 

the Black Eagle residential area has been revised at promulgation. 

In determining the hazardous waste quantity factor value for the AOC in the soil exposure pathway, HRS 

Section 5.1.2.2, Hazardous waste quantity, states: 

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Assign a hazardous waste quantity factor value as specified in section 2.4.2. In 

estimating the hazardous waste quantity, use table 5–2 and: 

• Consider only the first 2 feet of depth of an area of observed contamination, 

except as specified for the volume measure. 

• Use the volume measure (see section 2.4.2.1.3) only for those types of areas of 

observed contamination listed in Tier C of Table 5-2. . . . 

• Use the area measure (see section 2.4.2.1.4), not the volume measure, for all 

other types of areas of observed contamination, even if their volume is known. 

HRS Section 2.4.2.2, Calculation of hazardous waste quantity factor value, states to: 

[s]um the source hazardous waste quantity values assigned to all sources (including the 

unallocated source) or areas of observed contamination for the pathway being evaluated 

and round this sum to the nearest integer, except: if the sum is greater than 0, but less 

than 1, round it to 1. Based on this value, select a hazardous waste quantity factor value 

for the pathway from table 2–6. 

Table 2-6 of the HRS, presented below, displays the criteria used in establishing the hazardous waste 

quantity factor value. 

Hazardous Waste Quantity 

Value 

Assigned Value 

0 0 

1a to 100 1b 

Greater than 100 to 10,000 100 

Greater than 10,000 to 1,000,000 10,000 

Greater than 1,000,000 1,000,000 

a If the hazardous waste quantity value is greater than 0, but less than 1, round it 

to 1 as specified in text 

b For the pathway, if hazardous constituent quantity is not adequately determined, 

assign a value as specified in the text; do not assign the value of 1. 

HRS Section 2.4.2.2, Calculation of hazardous waste quantity factor value, continues: 

For the soil exposure pathway, if the hazardous constituent quantity is adequately 

determined for all areas of observed contamination, assign the value from table 2–6 as the 

hazardous waste quantity factor value. If the hazardous constituent quantity is not 

adequately determined for one or more areas of observed contamination, assign either the 

value from table 2–6 or a value of 10, whichever is greater, as the hazardous waste 

quantity factor value. [emphasis added] 

Page 65 of the HRS documentation record at proposal documented that data were not available to 

evaluate Tier A, hazardous constituent quantity, Tier B, hazardous wastestream quantity, or Tier C, 

volume, in the evaluation of the soil exposure pathway hazardous waste quantity. The HRS 

documentation record at proposal explained that Tier D, area, was evaluated, and that an area assigned 

value was calculated. It stated: 

Arsenic and cadmium results from soil samples collected in the summers of 2007 and 

2008 that are documented to be at Level I concentrations delineate an area of 

approximately 1,926,569 square feet (ft2) (Ref. 1, Sections 2.5.1, 2.5.2, 5.1.3.1; Ref. 22, 

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p. 2). The area covered by streets within the area was calculated to be 322,000 square 

feet (Ref. 25, p. 1). It was calculated that an average of 31 percent of each lot in Black 

Eagle, Montana is covered by a structure or pavement or 69 percent of the average 

property is open soil (Ref. 26, p. 3). 

(1,926,569 ft2

 of contaminated soil) – (322,000 ft2 of pavement) = 1,604,569 ft2. 

(1,604,569 ft2

)(0.69 open soil) = 1,107,152.61ft2 

Thus, according to HRS Table 5-2, the value of 1,107,152.6 ft2

 calculated above for contaminated soil 

was divided by 34,000 (the divisor used for contaminated soil according to HRS Table 5-2) and an area 

assigned value of 32.5633 was calculated at proposal (1,107,152.61(ft2

) / 34,000 = 32.5633). This value 

equated to an assigned value of 1 from HRS Table 2-6. Footnote B of HRS Table 2-6, directs the scorer 

to assign a value as specified in the text, instead of from HRS Table 2-6, if the hazardous constituent 

quantity was not adequately determined. As the hazardous constituent quantity was not adequately 

determined, a value of 10 was assigned as the hazardous waste quantity factor value at proposal, in 

accordance with HRS Section 2.4.2.2 cited above. 

However, as discussed in section 3.30.3, AOC Delineation, of this support document, the delineation of 

the AOC in the Black Eagle residential area has been revised at promulgation to reflect that contamination 

is no longer inferred between the AOC sample locations. At promulgation, as at proposal, no information 

was available to determine the hazardous constituent quantity (Tier A), hazardous wastestream quantity 

(Tier B), and volume (Tier C) measures in evaluating the soil exposure hazardous waste quantity. 

Therefore, because the presence of hazardous substances meeting observed contamination criteria within 

the AOC samples has been established and a defined contiguous area comprising the AOC has not been 

evaluated; the area of the AOC is evaluated as “greater than 0” at promulgation. 

According to HRS Table 2-6, a value of “greater than 0” corresponds to a hazardous waste quantity factor 

value of 1. Footnote B of HRS Table 2-6, states that “if the hazardous constituent quantity is not 

adequately determined, assign a value as specified in the text; do not assign the value of 1.” As the 

hazardous constituent quantity for this AOC was not adequately determined at promulgation, a value of 

10 was assigned as the hazardous waste quantity factor value at promulgation. 

Furthermore, even if ARCO’s revised area value of 2.8876 for the AOC were used, it would not change 

the hazardous waste quantity factor value assigned at proposal. That is, ARCO’s area assigned value for 

the AOC [2.8876] would be subject to HRS Section 2.4.2.2 cited above, which states that in situations 

when the hazardous constituent quantity is not adequately determined—as is the case here—a hazardous 

waste quantity factor less than 10 determined by HRS Table 2-6 is replaced with a value of 10. 

This comment has no effect on the HRS site score or the decision to place the site on the NPL. 

3.31.1 Calculation of Soil Exposure Pathway Waste Characteristics 

Comment: ARCO asserted that a value of 10 should have been assigned to the waste characteristics 

factor category value, instead of the value of 18 assigned at proposal 

Response: The soil exposure pathway waste characteristics factor value of 18 assigned at proposal was 

correct according to the HRS; revisions to the hazardous waste quantity evaluation have not changed this 

value at promulgation. 

The soil exposure pathway waste characteristics value reflects the toxicity and quantity of the hazardous 

substances associated with the AOC. HRS Section 5.1.2 Waste characteristics, states: 

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Evaluate waste characteristics based on two factors: toxicity and hazardous waste 

quantity. Evaluate only those hazardous substances that meet the criteria for observed 

contamination at the site (see section 5.0.1). 

HRS Section 5.1.2.3, Calculation of waste characteristics factor category value, directs the 

scoring of the waste characteristics factor category value. It states: 

Multiply the toxicity and hazardous waste quantity factor values, subject to a maximum 

product of 1×108

. Based on this product, assign a value from table 2–7 (section 2.4.3.1) to 

the waste characteristics factor category. 

Because the hazardous substances scored in the soil exposure pathway in the HRS documentation record 

at proposal are the same as those at promulgation (arsenic, cadmium, and lead), the toxicity factor value 

remains 10,000 as presented in section 5.1.2.1, Toxicity, of the HRS documentation record at 

promulgation. ARCO did not challenge this toxicity factor value in its comments. 

As discussed in section 3.31.1, Soil Exposure Pathway Hazardous Waste Quantity, of this support 

document, the hazardous waste quantity factor value at promulgation is 10. Therefore, in accordance with 

HRS Section 5.1.2.3, Calculation of waste characteristics factor category value, the toxicity value of 

10,000, multiplied by the hazardous waste quantity factor value of 10, results in a product of 100,000, 

which according to HRS Table 2-7 corresponds to a waste characteristics factor category value of 18. 

This waste characteristics factor category value assigned at promulgation remains unchanged from 

proposal. 

This comment has no effect on the HRS site score or the decision to list the site on the NPL. 

3.32 Soil Exposure Targets 

Comment: ARCO submitted comments challenging the establishment of soil exposure targets in the HRS 

documentation record at proposal. The following subsections of this support document address specific 

comments raised by the commenter on this topic. 

• 3.32.1 Identification of Actually Contaminated Targets 

• 3.32.2 Count of Level II Concentrations 

• 3.32.3 Targets Not Scored 

3.32.1 Identification of Actually Contaminated Targets 

Comment: ARCO questioned the establishment of actually contaminated targets in the evaluation of the 

soil exposure pathway. ARCO stated that EPA delineated the AOC using soil samples from two different 

depth intervals (0-2 inches and 6-12 inches below ground surface [bgs]) and that residents would have 

the greatest exposure to contaminants in surface soil (0-2 inches bgs); ARCO noted that many of the 

higher concentrations in residential soils are present at depths greater than 6 inches bgs. 

Response: The number of residences considered actually contaminated based on the presence of 

contamination on the property and within 200 feet of the residence was correctly identified at the time of 

proposal. The HRS establishes AOCs based on contamination documented within 2 feet of the soil 

surface. The exact amount of exposure that results from this contamination is determined at a later stage 

of the Superfund process when a site-specific risk assessment is performed. 

HRS Section 5.0.1, General considerations, states: 

Evaluate the soil exposure pathway based on areas of observed contamination: 

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• Consider observed contamination to be present at sampling locations where analytic 

evidence indicates that: 

–A hazardous substance attributable to the site is present at a concentration 

significantly above background levels for the site (see table 2–3 in section 2.3 for 

the criteria for determining analytical significance), and 

–This hazardous substance, if not present at the surface, is covered by 2 feet or 

less of cover material (for example, soil). 

HRS Section 5.1.3, Targets, states: 

Evaluate the targets factor category for the resident population threat based on five 

factors: resident individual, resident population, workers, resources, and terrestrial 

sensitive environments. 

In evaluating the targets factor category for the resident population threat, count only the 

following as targets: 

• Resident individual—a person living or attending school or day care on a 

property with an area of observed contamination and whose residence, school, or 

day care center, respectively, is on or within 200 feet of the area of observed 

contamination. 

• Worker—a person working on a property with an area of observed 

contamination and whose workplace area is on or within 200 feet of the area of 

observed contamination. 

• Resources located on an area of observed contamination, as specified in section 

5.1. 

• Terrestrial sensitive environments located on an area of observed 

contamination, as specified in section 5.1. 

The HRS documentation record at proposal presented that samples meeting observed contamination 

criteria were taken on or within 200 feet of the residential properties. Section 5.1, Resident Population 

Threat, of the HRS documentation record at proposal stated: 

Observed contamination samples were selected from the Analytical Results Reports for 

the 2007 CERCLA Site Assessment and from the 2008 Expanded Site Investigation to 

establish laboratory verified concentrations of arsenic lead, and cadmium, as well as 

sample ID, street address, property owner, and the date each sample was collected (Ref. 

21, pp. 29-32; Ref. 5, pp. 28-31). All samples listed in Section 5.0.1 of this HRS 

documentation record were collected within 200 feet of the residence (Ref. 21, p. 1; Ref. 

5, pp. 4 and 5). Analysis of sample R12ST0121FY12 (MH26N5) collected on July 11, 

2008, with an arsenic concentration of 215 mg/kg, a cadmium concentration of 13 mg/kg, 

and a lead concentration of 706 mg/kg in surface soils from a collection depth < 2 feet 

bgs documents the resident population threat (Ref. 5, Appendix C, p. 49. Appendix D, 

p.8; Ref. 24, p. 1; Ref. 36, book 3, p. 17; Ref. 63 p. 15) 

Since observed contamination was found to be within 2 feet or less of the surface, the samples at both 0 to 

2 inch and 6 to 12 inch soil horizons were properly used to identify the AOC. Correspondingly, the 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

residences on the property and within 200 feet of the sample locations were appropriately considered 

actually contaminated targets. 

Furthermore, as the HRS allows for the evaluation of observed contamination within 2 feet or less of the 

ground surface; ARCO’s assertions regarding the lack of risk of exposure of deeper contamination are a 

challenge to the HRS itself in the establishment of observed contamination within an AOC. As explained 

in section 3.10, Comments on HRS, of this support document, comments on the HRS rule are not relevant 

to the proposal to place the ACM site on the NPL and are outside the scope of this rulemaking. 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.32.2 Count of Level II Targets 

Comment: ARCO asserted that the evaluation of the number of residences exposed to Level II 

concentrations as presented in the HRS documentation record at proposal is incorrect. ARCO alleged that 

the AOC delineation as proposed incorrectly included soil sample locations that did not have arsenic and 

cadmium concentrations greater than three times background and exceeding their respective SCDM 

benchmarks. 

ARCO presented its own AOC evaluation that excluded these soil samples, and asserted that only 42 

residences are associated with Level II concentrations, as opposed to the 170 residences associated with 

Level II concentrations in the HRS documentation record at proposal. 

Response: The number of targets subject to Level II concentrations has been reduced in the scoring of the 

resident population soil exposure targets in the HRS documentation record at promulgation to reflect the 

decision to no longer infer contamination between AOC samples. However, as discussed in section 

3.30.3, AOC Delineation/Inference, of this support document, the 53 AOC samples are appropriately 

documented as containing hazardous substances meeting observed contamination criteria, and targets 

associated with these individual sampling points are correctly considered exposed to Level II 

concentrations. 

HRS Section 5.1.3, Targets, states: 

Evaluate the targets factor category for the resident population threat based on five 

factors: resident individual, resident population, workers, resources, and terrestrial 

sensitive environments. 

In evaluating the targets factor category for the resident population threat, count only the 

following as targets: 

• Resident individual—a person living or attending school or day care on a 

property with an area of observed contamination and whose residence, school, or 

day care center, respectively, is on or within 200 feet of the area of observed 

contamination. 

HRS Section 5.1.3.2, Resident population, states: 

Evaluate resident population based on two factors: Level I concentrations and Level II 

concentrations. Determine which factor applies as specified in sections 2.5.1 and 2.5.2, 

using the health-based benchmarks from table 5–3. Evaluate populations subject to Level 

I concentrations as specified in section 5.1.3.2.1 and populations subject to Level II 

concentrations as specified in section 5.1.3.2.2. 

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HRS Section 5.1.3.2.2, Level II concentrations, states: 

Sum the number of resident individuals subject to Level II concentrations. Do not include 

those people already counted under the Level I concentrations factor. Assign this sum as 

the value for this factor. Enter this value in table 5–1. 

Pages 68 of the HRS documentation record at proposal presented the evaluation of how targets subject to 

Level II contamination were scored: 

Properties that are wholly or partially included within the zone defined by arsenic and 

cadmium contamination at Level I concentrations include approximately 178 residences 

that are within 200 feet of the zone of contamination (Ref. 22, p. 2; Ref. 37, p. 1). Eight 

of these residences have documented Level I contamination within 200 feet of the 

residence leaving approximately 170 residences exposed to Level II contamination (Ref. 

22. page 2; Ref. 37, p. 1). 170 residences with a county average of 2.41 individuals per 

residence results in 409.7 people being exposed to Level II Concentrations (Ref. 28, p. 1) 

At promulgation, all 53 samples taken from the AOC were determined to be on residential properties, and 

residences are documented within 200 feet of each AOC sample – the same as at proposal (see Figure 2 of 

the HRS documentation record at promulgation). Of the 53 residences within 200 feet of the AOC 

samples, 8 of the residences were already included in the evaluation of Level I concentrations. Because 

no contamination is inferred between the AOC samples, at promulgation 45 residential properties were 

evaluated for Level II concentrations. 

Thus, at promulgation, 108.45 individuals are subject to Level II concentrations, considering the county 

average of 2.41 persons per residence (as directed by HRS Section 5.1.3.2, Resident population) (45 

residences multiplied by 2.41 persons per residence = 108.45 persons). 

This comment has no effect on the site score or the decision to list the site on the NPL. 

3.32.3 Targets Not Scored 

Comment: In its reassessment of the soil exposure pathway score, ARCO made assertions regarding the 

lack of scoring potential of other targets. ARCO stated that workers were not scored in the targets 

evaluation “because the area of contaminated soil was scored for residents.” Also, ARCO asserted that 

the nearby population threat did not warrant scoring because “the data does not support the presence of 

such threat.” 

Response: ARCO incorrectly asserted that both workers and the nearby population threat could not have 

been scored as part of the HRS documentation record at proposal. 

HRS Section 5.1.3, Targets, states: 

Evaluate the targets factor category for the resident population threat based on five 

factors: resident individual, resident population, workers, resources, and terrestrial 

sensitive environments. 

In evaluating the targets factor category for the resident population threat, count only the 

following as targets: 

• Resident individual... 

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• Worker – a person working on a property with an area of observed contamination 

and whose workplace area is on or within 200 feet of the area of observed 

contamination. 

• Resources... 

HRS Section 5.1.3.3, Workers, states: 

Evaluate this factor based on the number of workers that meet the section 5.1.3 criteria. 

Assign a value for these workers using table 5-4. Enter this value in table 5-1. 

HRS Section 5.2, Nearby Population Threat, states: 

Include in the nearby population only those individuals who live or attend school within a 

1-mile travel distance of an area of observed contamination at the site and who do not 

meet the criteria for resident individual as specified in section 5.1.3. 

The HRS documentation record at proposal did not document the presence of workers, or potentially 

affected nearby population targets, that could have been scored in the soil exposure targets evaluation. 

The scoring of workers or nearby population targets would not have significantly added to the HRS site 

score, as a site score of greater than 28.50 was established. 

Note, however, that although page 68 of the HRS documentation record at proposal stated that workers 

were not scored in the targets evaluation of the soil exposure pathway, this statement does not establish 

that workers could not have been scored in the targets evaluation of the soil exposure pathway. For 

instance, a church located within 200 feet of the AOC (located at 2200 Smelter Avenue, Black Eagle; Ref. 

18, pp. 27-30 of the HRS documentation record at proposal) could have been potentially evaluated for 

workers (e.g., the minister) concurrently with resident individuals under the resident population threat 

scoring. 

In addition, further analysis of the nearby population threat could have resulted in the scoring of nearby 

populations, as the AOC is located within a residential area near schools (Ref. 4, Map 1 of the HRS 

documentation record at proposal). 

This comment has not effect on the site score or the decision to list the site on the NPL. 

3.33 Soil Exposure Pathway – Resident Population Threat Total Score 

Comment: In determining an alternate score for the soil exposure hazardous waste quantity and targets, 

ARCO asserted that the resulting score for the soil exposure pathway resident population threat should be 

1,892,110, instead of 6,459,750 assigned in the HRS documentation record at proposal. 

Response: Incorporating the changes made to the waste quantity yields a soil exposure pathway resident 

population threat score of 3,477,375 in the HRS documentation record at promulgation. 

HRS Section 5.1.3.6, Calculation of resident population targets factor category value, states to: 

[s]um the values for the resident individual, resident population, workers, resources, and 

terrestrial sensitive environments factors. Do not round to the nearest integer. Assign this 

sum as the targets factor category value for the resident population threat. 

HRS Section 5.1.3.2.3, Calculation of resident population factor value, states to: 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

[s]um the factor values for Level I concentrations and Level II concentrations. Assign this 

sum as the resident population factor value. 

ARCO’s comments did not challenge the resident individual value of 50 assigned in the HRS 

documentation record at proposal. ARCO also did not challenge the Level I concentrations value of 

192.8 assigned in the HRS documentation record at proposal. These values remain unchanged at 

promulgation. 

Section 3.32.2 Count of Level II Targets, of this support document explains that 108.45 individuals are 

subject to Level II concentrations. 

Therefore, per HRS section 5.1.3.2.3 quoted above, the resident population factor value at promulgation is 

301.25 (192.8 + 108.45). 

Per HRS Section 5.1.3.6 quoted above, the resident population targets factor category value is thus 351.25 

(50 + 301.25). Note that workers, resources, and terrestrial sensitive environments were not scored. 

HRS Section 5.1.4, Calculation of resident population threat score, states to: 

[m]ultiply the values for likelihood of exposure, waste characteristics, and targets for the 

resident population threat, and round the product to the nearest integer. Assign this 

product as the resident population threat score 

The likelihood of exposure factor category value of 550 assigned in the HRS documentation record at 

proposal remains unchanged at promulgation; this value was not challenged by ARCO. 

As explained in section 3.31.1, Calculation of Soil Exposure Pathway Waste Characteristics, of this 

support document, the value of 18 assigned as the soil exposure pathway waste characteristics factor 

value assigned at proposal was correct according to the HRS, and revisions to the hazardous waste 

quantity evaluation have not changed this value at promulgation. 

Per HRS Section 5.1.4 quoted above, the resident population threat score assigned in the HRS 

documentation record at promulgation is 3,477,375 (550 x 18 x 351.25). The effects of the changes to the 

resident population threat score on the soil exposure pathway are detailed in section 3.34, Soil Exposure 

Pathway – Total Score, of this support document; the effects on the total site score are taken into account 

in section 3.35, Alternate HRS Score, of this support document. 

This comment has no effect on the decision to list the site on the NPL. 

3.34 Soil Exposure Pathway – Total Score 

Comment: ARCO stated that it had rescored the soil exposure pathway. ARCO asserted that the score 

for the surface water overland/flood migration pathway should be 22.93, instead of 78.3 as assigned in the 

HRS documentation record at proposal. 

Response: The soil exposure component score assigned in the HRS documentation record at 

promulgation is 42.15. 

HRS section 5.3, Calculation of soil exposure pathway score, states to: 

[s]um the resident population threat score and the nearby population threat score, and 

divide the sum by 82,500. Assign the resulting value, subject to a maximum of 100, as 

the soil exposure pathway score (Ss). 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

As described in section 3.33, Soil Exposure Pathway – Resident Population Threat Total Score, of this 

support document, the resident population threat score assigned in the HRS documentation record at 

promulgation is 3,477,375. 

Section 3.32.3, Targets Not Scored, of this support document explains that the nearby population threat 

was not scored. 

Therefore, the soil exposure pathway score assigned at promulgation is 42.15 (3,477,375 / 82,500). The 

effects of the changes to the soil exposure pathway score on the total site score are taken into account in 

section 3.35, Alternate HRS Score, of this support document. 

This comment has no effect on the decision to list the site on the NPL. 

3.35 Alternate HRS Score 

Comment: ARCO asserted that the Surface Water Migration Pathway Score of 100.00 and the Soil 

Exposure Pathway Score of 78.30 in the HRS documentation record at proposal are “grossly inflated.” 

ARCO presented an alternative HRS site score it considers appropriate for the ACM site. 

ARCO argued that the surface water migration pathway in the HRS documentation record at proposal is 

incorrect. ARCO stated that a more realistic alternative HRS score for the surface water migration 

pathway would only assess the potential to release of hazardous substances from soil in the East Ditch 

Dump (Source 1) and Black Eagle residential soils (Source 2), and would result in a pathway score of 

0.18. ARCO included an attachment with its comments (Attachment 1, DOCKET # EPA-HQ-SFUND2010-0072, Document # 0016) to support its contention that the surface water migration pathway should 

be rescored. 

For the soil exposure pathway, ARCO asserted that “EPA selectively used the available soils data to drive 

the HRS score beyond the threshold required for listing.” ARCO asserted that two smaller areas of 

contamination should have been assessed, rather than the AOC used in scoring. Based on using two 

smaller areas of contamination, ARCO assigned an alternate soil exposure pathway score of 22.93 

(presented in Attachment 1 of ARCO’s comments at Docket # EPA-HQ-SFUND-2010-0072, Document # 

0016). 

ARCO submitted revised HRS scoresheets to illustrate their rescoring of the site, which present ARCO’s 

interpretation of each scoring factor value and score component. 

Thus, ARCO argued that the overall site score should be 11.47, which would be lower than the 28.50 

score threshold for inclusion of a site on the NPL. 

Response: After considering all comments received on the proposed NPL listing of the ACM site, and 

making revisions where appropriate as described throughout this support document, the final ACM site 

score is 54.26. The following HRS worksheet documents the final HRS scoring; this worksheet and 

detailed scoresheets for the surface water overland/flood migration and soil exposure pathways appear on 

pages 2-6 of the HRS documentation record at promulgation. Following the worksheet, are HRS 

scoresheets for the surface water migration and soil exposure pathways that identify the components of 

the site score at promulgation shown alongside the scores at proposal and the scores presented by ARCO 

in its comments. The far right column on the scoresheets cites the section(s) within this support 

document where each scoring factor or component is addressed. The comparison scoresheets are 

provided below to facilitate understanding of the changes made to the score at promulgation. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

WORKSHEET FOR COMPUTING HRS SITE SCORE 

 S S2

 

1. Groundwater Migration Pathway Score (Sgw) NS NS 

(from Table 3-1, line 13) 

2a. Surface Water Overland/Flood Migration Component 100

(from Table 4-1, line 30) 

2b. Groundwater to Surface Water Migration Component NS 

(from Table 4-25, line 28) 

2c. Surface Water Migration Pathway Score (Ssw) 100 10,000.00

Enter the larger of lines 2a and 2b as the pathway score. 

3. Soil Exposure Pathway Score (Ss) 42.15 1,776.62

 (from Table 5-1, line 22) 

4. Air Migration Pathway Score (Sa) 

(from Table 6-1, line 12) NS NS 

5. Total of Sgw

2

 + Ssw2 + Ss

2

 + Sa

2

 11,776.62

6. HRS Site Score Divide the value on line 5 

by 4 and take the square root 54.26

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

SURFACE WATER OVERLAND/FLOOD MIGRATION COMPONENT SCORE SHEET 

Factor Categories and Factors 

Value 

Assigned at 

Proposal 

ARCO 

Provided 

Explanation 

in Section # of 

this Support 

Document* 

Value 

Assigned at 

Value Promulgation 

Drinking Water Threat 

Likelihood of Release: 

1. Observed Release 

2. Potential to Release by Overland Flow: 

2a. Containment 

2b. Runoff 

2c. Distance to Surface Water 

2d. Potential to Release by Overland Flow (lines 

2a[2b+2c]) 

3. Potential to Release by Flood: 

3a. Containment (Flood) 

3b. Flood Frequency 

3c. Potential to Release by Flood (lines 3a×b) 

4. Potential to Release (lines 2d+3c, subject to a 

maximum of 500) 

5. Likelihood of Release (higher of lines 1 and 4) 

550 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

550 

0 

9 

1 

20 

189 

10 

7 

70 

259 

259 

550 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

550 

3.19, 3.20 

3.19, 3.20 

Waste Characteristics: 

6. Toxicity/Persistence 

7. Hazardous Waste Quantity 

8. Waste Characteristics 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

Targets: 

9. Nearest Intake 

10. Population 

10a. Level I Concentrations 

10b. Level II Concentrations 

10c. Potential Contamination 

10d. Population (lines 10a+10b+10c) 

11. Resources 

12. Targets (lines 9+10d+11) 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

NS 

Drinking Water Threat Score: 

13. Drinking Water Threat Score ([lines 

5×8×12]/82,500, subject to a maximum of 100) NS NS NS 

Human Food Chain Threat 

Likelihood of Release: 

14. Likelihood of Release (same value as line 5) 550 259 550 3.19, 3.20 

Waste Characteristics: 

15. Toxicity/Persistence/Bioaccumulation 

16. Hazardous Waste Quantity 

17. Waste Characteristics 

500,000,000 

100 

320 

50,000,000 

1 

56 

500,000,000 

100 

320 

3.23.1 

3.23.2 

3.23.3 

Targets: 

18. Food Chain Individual 

19. Population 

19a. Level I Concentrations 

19b. Level II Concentrations 

19c. Potential Human Food Chain Contamination 

19d. Population (lines 19a+19b+19c) 

20. Targets (lines 18+19d) 

45 

0 

0.03 

0.000003 

0.030003 

45.030003 

1 

0 

0 

0.000003 

0.000003 

1.000003 

45 

0 

0.03 

0.000003 

0.030003 

45.030003 

3.19, 3.20 

3.24.1 

3.24.1, 3.24.2 

3.24.1, 3.24.2 

3.24.1, 3.24.2 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

SURFACE WATER OVERLAND/FLOOD MIGRATION COMPONENT SCORE SHEET 

Explanation 

in Section # of 

this Support 

Document* 

Value ARCO Value 

Assigned at 

Promulgation 

Factor Categories and Factors Assigned at Provided 

Proposal Value 

Human Food Chain Threat Score: 

21. Human Food Chain Threat Score ([lines 

14×17×20]/82,500, subject to a maximum of 100) 96.06 0.18 96.06 3.25 

Environmental Threat 

Likelihood of Release: 

22. Likelihood of Release (same value as line 5) 550 259 550 3.19, 3.20 

Waste Characteristics: 

23. Ecosystem Toxicity/Persistence/Bioaccumulation 

24. Hazardous Waste Quantity 

25. Waste Characteristics 

500,000,000 

100 

320 

500,000,000 

1 

100 

500,000,000 

100 

320 

3.26 

3.26 

Targets: 

26. Sensitive Environments 

26a. Level I Concentrations 

26b. Level II Concentrations 

26c. Potential Contamination 

26d. Sensitive Environments (lines 26a+26b+26c) 

27. Targets (value from line 26d) 

0 

25 

0 

25 

25 

0 

0 

0.025 

0.025 

0.025 

0 

25 

0 

25 

25 

3.27.1, 3.27.2 

Environmental Threat Score: 

28. Environmental Threat Score ( [lines 

22×25×27]/82,500, subject to a maximum of 60) 53.33 0.0078 53.33 3.28 

Surface Water Overland/Flood Migration Component Score for a Watershed 

29. Watershed Score (lines 13+21+28, subject to a 

maximum of 100) 100 0.18 100 3.29 

Surface Water Overland/Flood Migration Component Score 

30. Component Score (Sof)

c

 (highest score from line 

29 for all watersheds evaluated, subject to a 

maximum of 100) 

100 0.18 100 3.29 

NS = Not Scored. 

* = See Table of Contents of this support document. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

SOIL EXPOSURE PATHWAY SCORE SHEET

Factor Categories and Factors Value Assigned 

at Proposal 

Explanation in 

Section # of 

this Support 

Document* 

ARCO 

Provided 

Value 

Value 

Assigned at 

Promulgation 

RESIDENT POPULATION THREAT 

Likelihood of Exposure

1. Likelihood of Exposure 550 550 550 3.30 

Waste Characteristics

2. Toxicity 10,000 10,000 10,000 

3. Hazardous Waste Quantity 10 2.8876 10 3.31.1 

4. Waste Characteristics 18 10 18 3.31 

Targets

5. Resident Individual 50 50 50 

6. Resident Population 

6a. Level I Concentrations 192.8 192.8 192.8 

6b. Level II Concentrations 409.7 101.22 108.45 3.32.2 

6c. Resident Population 

(lines 6a + 6b) 602.5 294.02 301.25 3.32.2, 3.32.3 

7. Workers 0 0 0 

8. Resources 0 0 0 

9. Terrestrial Sensitive Environments 0 0 0 

10. Targets 

(lines 5 + 6c + 7 + 8 + 9) 652.5 344.02 351.25 3.32, 3.33 

Resident Population Threat Score

11. Resident Population Threat 

(lines 1 x 4 x 10) 6,459,750 1,892,110 3,477,375 3.33 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

SOIL EXPOSURE PATHWAY SCORE SHEET

Factor Categories and Factors 

Value 

Assigned at 

Proposal 

ARCO 

Provided 

Value 

Explanation in 

Section # of 

this Support 

Document* 

Value 

Assigned at 

Promulgation 

NEARBY POPULATION THREAT 

Likelihood of Exposure

12. Attractiveness/Accessibility NS NS NS 

13. Area of Contamination NS NS NS 

14. Likelihood of Exposure NS NS NS 

Waste Characteristics

15. Toxicity NS NS NS 

16. Hazardous Waste Quantity NS NS NS 

17. Waste Characteristics NS NS NS 

Targets

18. Nearby Individual NS NS NS 

19. Population Within 1 Mile NS NS NS 

20. Targets (lines 18 + 19) 

Nearby Population Threat Score

21. Nearby Population Threat 

(lines 14 x 17 x 20) NS NS NS 

SOIL EXPOSURE PATHWAY SCORE 

Soil Exposure Pathway Scored

22. (Ss), (lines [11 + 21] ÷ 82,500 

subject to a maximum of 100) 78.3 22.93 42.15 3.31 

* = See Table of Contents of this support document. 

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ACM Smelter & Refinery NPL Listing Support Document March 2011 

 116 

4.0 Conclusion 

The original HRS score for this site was 63.50. Based on the above responses to comments and the

modifications detailed in section 3.35, Alternate HRS Score, of this support document, the HRS score at 

promulgation is 54.26. The final scores for the ACM Smelter and Refinery site are: 

Ground Water Not Scored

Surface Water 100 

Soil Exposure 42.15

Air Not Scored 

HRS Site Score 54.26