HRS DOCUMENTATION RECORD COVER SHEET

Name of Site: Anaconda Aluminum Co Columbia Falls Reduction Plant EPA ID No.: MTD057561763

Contact Person Site Investigation and Documentation Record: Sabrina Forrest (303) 312-6484 NPL Coordinator U.S. Environmental Protection Agency, Region 8 1595 Wynkoop Street, Mail Code: 8EPR-B Denver, Colorado 80202-1129

Pathways, Components, or Threats Not Scored

Soil Exposure Pathway

Although several contaminants are present at elevated concentrations in soils, the distance to nearby residents or other targets, the size

, and the relative inaccessibility of the former facility precludes easy

access to all the source area s. Therefore, th e pathway score is unlikely to impact the listing decision.

Air Migration Pathway

There are no data to satisfy HRS requirements for establishing an observed release and no evidence to suggest a significant release to the air at the Anaconda Aluminum Co Columbia Falls Reduction Plant

. As such, the air migration pathway will not be scored as part of this HRS package.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763HRS DOCUMENTATION RECORD

Name of Site: Anaconda Aluminum Co Columbia Falls Date Prepared: March 2015 Reduction Plant

EPA Region: 8

Street Address of Site: Eastern end of Aluminum Drive

City, County, State: Columbia Falls, Flathead County, Montana 59912

General Location in the State: Ap proximately 1 .5 miles north east of downtown Columbia Falls . The site is just north of the Flathead River (Figure 1)

.

Latitude: 4 8 ° 23 ' 16.35 " North Longitude: 11 4 ° 07 ' 49.07 " West for the easternmost southern percolation pond (Figure 2).

* The street address, coordinates, and contaminant locations presented in this HRS documentation record identify the general area the site is located. They represent one or more locations the United States Environmental Protection Agency ( EPA ) considers t o be part of the site based on the screening information EPA used to evaluate the site for NPL listing. EPA lists national priorities among the known "releases or threatened releases" of hazardous substances; thus, the focus is on the release, not precisel y delineated boundaries. A site is defined as where a hazardous substance has been "deposited, stored, disposed, or placed, or has otherwise come to be located." Generally, HRS scoring and the subsequent listing of a release merely represent the initial de termination 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 be refined as more information is developed as to where the contaminati on has come to be located.

Scores

Air Migration Pathway NS Ground Water Migration Pathway 93.33 Soil Exposure Migration Pathway NS Surface Water Migration Pathway 100.00

HRS Site Score 68.39

NS

– Not Scored

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 1WORKSHEET FOR COMPUTING HRS SITE SCORE

S S 2

1. Ground Water Migration Pathway Score (S gw ) 93.33 8710.48 (from Table 3-1, line 13)

2a. Surface Water Overland/Flood Migration Component NS NS (from Table 4-1, line 30)

2b. Ground water to Surface Water Migration Component 100.00 10,000 (from Table 4- 25, line 28)

2c. Surface Water Migration Pathway Score (S
sw ) 100.00 10,000 Ent er the larger of lines 2a and 2b as the pathway score.

3. Soil Exposure Pathway Score (S
s ) NS NS (from Table 5-1, line 22)

4. Air Migration Pathway Score (S
a ) NS NS (from Table 6-1, line 12)

5. Total of S 2 gw + S 2

sw + S 2

s + S 2

a 18710.48

6. HRS Site Score Divide the value on line 5 by 4 and take the square root 68.39

NS = Not Scored

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 2TABLE 3 -1 GROUND WATER MIGRATION PATHWAY SCORESHEET

Factor Categories and Factors Maximum Value Value Assigned Likelihood of Release to an Aquifer

1. Observed Release 550 550

2. Potential to Release:

2a. Containment 10 NS 2b. Net Precipitation 10 NS 2c. Depth to Aquifer 5 NS

2d. Travel Time 35 NS
2e. Potential to Release [lines 2a(2b+2c+2d)] 500 NS

3. Likelihood of Release (higher of lines 1 and 2e) 550 550

Waste Characteristics

4. Toxicity/Mobility a 10,000

5. Hazardo us Waste Quantity a 10,000

6. Waste Characteristics 100 100 Targets

7. Nearest Well 50 50 8. Population

8a. Level I Concentrations b 90

8b. Level II Concentrations b 0

8c. Potential Contamination b 0
8d. Populat ion (lines 8a + 8b + 8c) b 90

9. Resources 5 0

10. Wellhead Protection Area 20 0 11. Targets (lines 7 + 8d + 9 + 10) b 140 Ground Water Migration Score for an Aquifer

12. Aquifer Score [(lines 3 x 6 x 11)/82,500] c 100.00 93.33

Ground Water Migration Pathway Score

13. Pathway Score (SW
sw ), (highest value from line 12 for all aquifers evaluated) c 100.00 93.33

a Ma ximum value applies to waste characteristics category b Maximum value not applicable

c Do not round to the neare st integer NS Not scored

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 3(continued) TABLE 4 -25 GROUND WATER TO SURFACE WATER MIGRATION COMPONENT SCORE SHEET

Factor Categories and Factors Maximum Value Value Assigned

Drinking Water Threat

Likelihood of Release :

1. Observed Release 2. Potential to Release : 2a. Containment 2b. Net Precipitation 2c. Depth to Aquifer 2d. Travel Time 2e. Potential to Release (line 2a[2b+2c+2d]) 3. Likelihood of Release (higher of lines 1 and 4) 550

10 10 5 35 500 550 550

NS NS NS NS NS 550

Waste Characteristics :

4. Toxicity/ Mobility/Persistence 5. Hazardous Waste Quantity
6. Waste Characteristics (a) (a) 100 NS NS NS

Targets :

7. Nearest Intake 8. Population 8a. Level I Concentrations 8b. Level II Concentrations 8c. Potential Contamination 8d. Population (lines 8a+8b+18c) 9. Resources 10. Targets (lines 7+18d+19) 50

(b) (b) (b) (b) 5 (b) NS

NS NS NS NS NS NS

Drinking Water Threat Score :

11. Drink ing Water Threat Score ([lines 3 × 6 × 10 ]/82,500, subject to a maximum of 100) 100 NS

Human Food Chain Threat

Likelihood of Release :

12. Likelihood of Release (same value as line 3 ) 550 550

Waste Characteristics :

13. Toxicity/Mobility/ Persistence/Bioaccumulation 14. Hazardous Waste Quantity 15. Waste Characteristics (a) (a) 1,000 5 x 10 6 10,000

320

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 4(continued) TABLE 4 -25 GROUND WATER TO SURFACE WATER MIGRATION COMPONENT SCORE SHEET

Factor Categories and Factors Maximum Value Value Assigned Targets :

16. Food Chain Individual 17. Population 17a. Level I Concentrations 17b. Level II Concentrations 17c. Potential Human Food Chain Contamination 17d. Population (lines 19a+19b+19c) 18. Targets (lines 16+17d) 50

(b) (b) (b) (b) (b) 45

0 0.03

0 0.03 45.03

Human Food Chain Threat Score :

19. Human Food Chain Threat Score ([lines 1 2 × 15 × 18 ]/82,500, subject to a maximum of 100) 100 96

Environmental Threat

Likelihood of Release :

20. Likelihood o f Release (same value as line 5) 550 550

Waste Characteristics :

21. Ecosystem Toxicity/ Mobility/Persistence/Bioaccumulation 22. Hazardous Waste Quantity 23. Waste Characteristics (a) (a) 1,000 5 x 10 6 10,000

320

Targets :

24. Sensitive E nvironments 24a. Level I Concentrations 24b. Level II Concentrations 24c. Potential Contamination 24d. Sensitive Environments (lines 26a+26b+26c) 25. Targets (value from line 24d) (b) (b) (b) (b) (b) 0 150

0 150 150

Environmental Threat Score :

26. Environmental Threat Score ( [lines 20 × 23 × 25]/82,500, subject to a maximum of 60) 60 60

Surface Water Overland/Flood Migration Component Score for a Watershed

27. Watershed Score c (lines 11+19+26, subject to a maximum of 100) 100 100

Surface Water Overland/Flood Migration Component Score

27. Component Score (S of ) c (highest score from line 27 for all watersheds evaluated, subject to a maximum of 100) 100 100

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 5NS = Not Scored. (a) = Maximum value applies to waste characteristics category (b) = Maximum value not applicable (c) = Do not round to the nearest integer

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 6REFERENCES

Ref. No. Description of the Reference

1. U.S. Environmental Protection Agency (EPA), Hazard Ranking System (HRS). December 14, 1990. Excerpt. Cover page only. A complete copy is available

at: http://www.epa.gov/supe rfund/sites/npl/hrsres/rule/hrsrule.pdf and in the Region 8 Docket.

2. EPA. Superfund Chemical Data Matrix (SCDM). J une 2014. Excerpt. 42 pages. A complete copy of SCDM is available at: http://epa.gov/superfund/sites/npl/hrsres/tools/scdm.htm

.

3. Weston Solutions, Inc

. 20 1 4

. Site Reassessment for Columbia Falls Aluminum Company, Aluminum Smelter Facility, Columbia Falls, Flathead County, Montana. April 4, 2014. 355 p ages.

3a. Weston Solutions, Inc

. 20 1 4

. Appendix F, Sections 1 through 7. Site Reassessment for Columbia Falls Aluminum Company, Aluminum Smelter Facility, Columbia Falls, Flathead County, Montana. April 4, 2014. Sections 1 thr ough 6, 1517 pages each, Section 7, 151 1 pages

.

4 . U.S. Census Bureau , 2010 . Flathead County Quickfacts. July 8, 2014. Available from: http://quickfacts.census.gov/qfd/states/30/30029.html

. Accessed October 16, 2014. 2 pages.

5 . Ecology and Environment, Inc., 1988. Draft Report of Sampling Activities, Columbia Falls Aluminum Company, Columbia Falls, Montana. July 15, 1988. 71 pages.

6. Columbia Fall s Aluminum Company (CFAC), 1994. Storm Water Pollution Prevention Pla n (SWPPP)

, CFAC, October 1994 . 32 pages.

7 . MT D epartment of E nvironmental Q uality (DEQ) , 1999. Major Industrial No Bio

- monitoring Permit No: MT0030066. Authorization to Discharge under the Montana Pollutant Discharge Elimination System. January 4, 1999. 26 pages.

8. Ecol ogy and Environment, Inc., 1988

. Draft Analytical Results Report, Columbia Falls Aluminum Company, Columbia Falls, Montana . November 11, 1988. 294 pages.

9

. CFAC , 1998. Letter with attachment. MPDES Permit Renewal and Mixing Zone Applica tion, CFAC. July 31, 1998 . 41 pages.

10

. Reference Number Reserved.

11

. EPA, 1984. Aerial Photographic Analysis of Waste Study Sites, Montana . EPA Region 8. November, 1984. 59 pages.

1 2. Reference Number Reserved.

13

. Reference Number Reserved.

14

. Reference Number Reserved.

15 . Olympus Environmental, Inc., 1992. Remedial Activities Report for Transformer Oil Spill at Columbia Falls Aluminum Company, Columbia Falls, Montana. April 14, 1992. 6 pages.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 716. Reference Number Reserved.

1 7 . EPA, 1996. Using Qualified Data to Document and Observed Release and Observed Contamination. Office of Solid Waste and Emergency Response (OSWER). November 1996. 18 pages.

18 . Hydrometrics, 1985. Hydrogeologic Evaluation, Columbia Falls Aluminum Company , Columbia Falls, Montana. September 16, 1985. 177 pages.

19. CFAC, 20 1 3

. CFAC EPA Presentation. June 3, 20 1 3. 3 7 pages.

2 0. Konizeski, R.L., Brietkrietz, A., and McMurtrey, G.G

., 1968. Geology and Ground Water Resources of the Kalispell Valley, Northwestern Montana

, Bulletin No. 68 . Montana Bureau of Mines and Geology. July, 1968. 46 pages.

21. Reference Number Reserved.

22

. Reference Number Reserved.

2 3

. Reference Number Reserved.

24. Parker, Robert, 2013. Site Assessment Manager, EPA Regi on 8. Email communication with Natalie Quiet , September 30 , 2013. 1 page.

25. US Geological Survey, 201 4

. National Water Information System, USGS Surface

- Water Annual Statistic for the Nation, USGS 12363000 Flathead River at Columbia Falls
MT

. http://waterda ta.usgs.gov/nwis/annual/?referred_module=sw&site_no=12363000&por_12363000_5= 66275,00060,5,1922,2014&year_type=W&format=html_table&date_format=YYYY

- MM

DD&rdb_compression=file&submitted_form=parameter_selection_list . Accessed January 22, 2014. 4

pages.

26. US Fish and Wildlife Service (USFWS), 2014. Information, Planning, and Conservation System (IPaC)

. Trust Resources List. http://ecos.fws.gov/ipac/

. October 17, 2014. 8 pages.

27. Montana State Parks (MSP). Montana Fish, Wildlife & Parks, Montana Fisheries Information System (MFish)

. Waterbody Report. http://fwp.mt.gov/fishing/mFish/ . Accessed October 15, 2014. 50 pages.

28

. Deleray, Mark, 2014

. Email Communication with Natalie Quiet, Weston. Fishery information on Cedar Creek. March 19

- 21 , 2014. 1 page

.

29. U.S. Fish and Wildlife Service

. National Wetlands Inventory

. Accessed February 26 , 201 5

. 6 page s

.

30. Wessling, Elizabeth , 201 5

. Senior Vice President

, MECx

, Aurora , CO . Email Communication with Natalie Quiet , February 1 8, 2015. 1 page

.

31. Quiet, Natalie, 2014. Weston Solutions. Email Communication , Areas of Various Sources for CFAC. December 3, 2014

- December 18, 2014. 4 pages.

32. Weston Solutions, Inc

. , 2013. Sampling and Analysis Plan for the Columbia Falls Aluminum Company, Aluminum Smelter Facility, Columbia Falls, Flathead County, Montana. September, 2013. 140 Pages.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 833. ArcGIS, 2013

. Bing Maps Aerial, Layer Package by esri. Last modified on November 25, 2013. 2

pages.

34. Federal Emergency Management Agency (FEMA). 1988. Flood Insurance Rate Map, Flathead County, Montana and Incorporated Areas. Panel 1120G and 1140G of 3525. Map Num ber 30029C1120G. Dated September 28, 2007. 2 pages, includes 1 map sheet.

35. Deleray, Mark, 201 5 . Email Communication, January 23, 2015 . 1 p age.

36. MT DEQ

, 1998 . Letter Communications between Steve Wright, Environmental Manager , CFAC , and Montana Depar tment of Environmental Quality, February 13 through October 14, 1998

. 8 pages.

37

. Quiet, Natalie, 2014. Weston Solutions. Email Communication with John Lucotch . December 18, 2014. 1 page.

38

. City of Columbia Falls, 2013. PUBLIC NOTICE

, 2013 Annual Drinking Water Quality Report . 4

pages.

39

. EPA , 2015

. EnviroMapper

. Available from: http://www.epa.gov/myem/efmap/index.html

. Accessed February 11, 2015. 1 page.

40. MSP, 2014. Montana Fish, Wildlife, and Parks. Bull Trout. http://fwp.mt.gov/fishAndWildlife/species/threatened/bullTrout/

. Accessed February 1 4 , 2015. 1 page

.

41. Quiet, Natalie, 2015. Weston Solutions. Memorandum with attachment : Reference 41

– Methodology and Source D a ta Used to C reate Figure 1 . March 18, 2015. 1374 pages.

42. Montana Natural Heritage Program , 201 4 . Animal Species of Concern Report. http://mtnhp.org/SpeciesOfConcern/?AorP=a

. Updated April 21, 2014. 16 pages.

43. Parker, Rob, 2015. U. S. EPA Region 8. Memorandum: Number of residences and residents supplied by Pump One Association well. February 25, 2015. 1 page.

44. Sandusky, Eric, Weston Solutions. 2015. Memorandum. February 25, 2015. 1 page.

45. U.S. Fish and Wildlife Service. Critical Habitat for Bull Trout (Salvelinus confluentus) Unit: 31, Sub

Unit Flathead Lake North Flathead Ri ver . 1 page.

46. Department of the Interior. 2010. Fish and Wildlife Service. 50 CFR Part 17. Endangered and Threatened Wildlife and Plants; Revised Designation of Critical Habitat for Bull Trout in the Conterminous United States; Final Rule. October 18, 2010. 174 pages.

47. Quiet, Natalie, Weston Solutions. 2015. Memorandum: Wetland Calculations in Actual Contamination Area. February 27, 2015. 1 page.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 9FIGURE 1 SITE LOCATION MAP

COLUMBIA FALLS ALUMINUM COMPANY COLUMBIA FALLS, MONTANA

Date: 3/14/2014 

## Legend

Property Boundary

0 0.275 0.55 1.1 M iles Prepared for: U.S. EPA Region 8

Contract No.: EP-S8-13-01

TDD: 1305-04

DCN: W0004.1A.00115 Prepared By: Weston Solutions, Inc. START IV

Suite 100 1435 Garrison Street Lakewood, CO 80215 Montana

Utah Idaho

Nevada Wyoming

Colorado

California Oregon

Arizona New Mexico Washington



# ± ! (RIV-M RIV-2

RIV-1 W10-TW22

W8-TW2

W1-PW7 W7-TW19

W9-PW5 W3-TW20 W11-TW17

W5-TW15

TW11 TW23

TW12

TW16 TW1

PW6 PW3

PW4 TW9 TW3

TW10 TW14

TW8

W0-CFMW2

FIGURE 2 FEATURES MAP ANACONDA ALUMINUM

CO COL FLS RED PL COLUMBIA FALLS, MONTANA

Date: 2/17/2015 Legend

Groundwater Monitoring Wells
MPDES Permit Surface Water Monitoring Locations
MPDES Permit Groundwater Monitoring Wells

Cross Section
Streams and Drainages

Feature Boundary

0 0.15 0.3 0.6 Miles Prepared for: U.S. EPA Region 8

Contract No.: EP-S8-13-01

TDD: 1407-05

DCN: W0  .1A.00  

# ± Prepared By: Weston Solutions, Inc. START IV

Suite 100 1435 Garrison Street Lakewood, CO 80215 Cedar Creek Reservoir Overflow Drainage W2-CFMW1

Cedar Creek Industrial Landfill

Asbestos Landfill West Landfill Sanitary Landfill

B Wet Scrubber Sludge Pond

A North Leachate Pond

Center Landfill

East Landfill

South Leachate Pond

Asbestos Landfill

Industrial By-products

North Percolation Pond North Percolation Pond

West Percolation Pond

A'

South Percolation Ponds ! (

Flathead River B'

Montana

Utah Idaho

Nevada Wyoming

Colorado

California Oregon

Arizona New Mexico WashingtonFIGURE 3 POTENTIOMETRIC

CONTOUR MAP COLUMBIA FALLS ALUMINUM COMPANY COLUMBIA FALLS, MONTANA

Date: 3/14/2014 Legend

Groundwater Monitoring Wells

MPDES Permit Surface Water Monitoring Locations

MPDES Permit Groundwater Monitoring Wells

3080 Potentiometric Surface Contour (Dashed where Inferred)

Note: Survey data not available; elevations are estimated

0 0.15 0 .3 0.6 Miles Prepared for: U.S. EPA Region 8

Contract No.: EP-S8-13-01

TDD: 1305-04

DCN: W0004.1A.00115 Prepared By: Weston Solutions, Inc. START IV

Suite 100 1435 Garrison Street Lakewood, CO 80215 3040.55 3085.16

3026.97

3025.14

3056.05 3083.19
3058.21 3072.29 3059.28

3013.72 3024 RIV-M RIV-2

RIV-1 W10-TW22

W8-TW2

W1-PW7 W7-TW19

W9-PW5 W3-TW20 W11-TW17

W6-TW18 W5-TW15 W2-CFMW1

TW11 TW23

TW12

TW16 TW1

PW6 PW3 PW4 TW9 TW3

TW10 TW14

TW8

W0-CFMW2

3014.55 3144.33

3058.31 W4-TW21 3058.03 3073.15

3058.88 3060.01

3055.85

3021.27 NM

NM

NM

NM NM NM



# ± 3013 3012

3010 3080

3070

3060

3050

3040

3030

3020 3140

3130
3120

3110

3090 3100 3140 3130

3120 3110 3100 3090

3080

3070 3060

3050

3040

3030

3020

3010FIGURE 4 SAMPLE LOCATIONS MAP

ANACONDA ALUMINUM

CO COL FLS RED PL COLUMBIA FALLS, MONTANA

Date: 2/17/2015 0 0.3 0 .6 1.2
Miles 

### Legend

Feature Boundary

! ( Groundwater Sampling Location

! ( Surface Water & Waste Source Sampling Location

! ( Surface Soil Sample Locations ! ( Surface Water & Sediment Sampling Location Prepared for: U.S. EPA Region 8

Contract No.: EP-S8-13-01

TDD: 1407-05

DCN: W0 157 .1A.00 381 

# ± Prepared By: Weston Solutions, Inc. START IV

Suite 100 1435 Garrison Street Lakewood, CO 80215 ! ( ! ( ! (

! (

! ( ! ( ! (

! (

! ( ! (

! (

! (

! ( ! ( ! (

! ( ! ( ! ( ! (

! (

! ( ! (

! ( ! ( ! ( ! ( ! ( ! ( ! (

! ( ! ( !

( ! ( ! (

! ( ! ( ! ( ! (

! (

! ( ! ( ! (

! ( ! (

CF-SD-04 CF-SS-07 CF-SS-06

CF-SW-07 CF-SD-07

CF-SD-08 CF-SW-09

CF-SD-09 CF-SD-OP-01

CF-SS-05

CF-GW-MW-14 CF-GW-MW-01

CF-GW-MW-08

CF-GW-MW-09

CF-GW-MW-10 CF-GW-MW-07 CF-GW-MW-02

CF-GW-MW-04 CF-GW-MW-03

CF-GW-MW-11

CF-SW-05 CF-SD-05 CF-SD-06

CF-SS-04 CF-SS-08 CF-SS-03

CF-SS-01 CF-SS-02 CF-SD-02 CF-SD-01

CF-SD-03 CF-SW-19

CF-SW-22 CF-GW-OP-02 CF-SW-21 CF-GW-MW-12

CF-SD-14

CF-SD-13 CF-GW-MW-13 CF-SD-15

CF-SD-16 CF-GW-MW-15

CF-WS-17

CF-WS-18

CF-SW-03 CF-WS-20 CF-WS-19

CF-WS-21

CF-SW-08 CF-SW-13 CF-SW-14

CF-SW-16 CF-SW-15 CF-GW-MW-06 CF-SW-20 CF-GW-MW-05

CF-WS-22 CF-SW-01

CF-SW-06FIGURE 5 GROUNDWATER SAMPLE LOCATION MAP ANACONDA ALUMINUM CO COL FLS PLT COLUMBIA FALLS, MONTANA

Date: 2/16/2015 

### Legend

! Columbia Falls Municipal Wells

! ( Groundwater Sampling Location

Feature Boundary

0 0.5 1
Miles Prepared for: U.S. EPA Region 8

Contract No.: EP-S8-13-01

TDD: 1407-05

DCN: W0 157 .1A.00 381 Prepared By: Weston Solutions, Inc. START IV

Suite 100 1435 Garrison Street Lakewood, CO 80215FIGURE 6 SURFACE WATER/SEDIMENT AND SURFACE WATER/WASTE SOURCE SAMPLE LOCATION MAP ANACONDA ALUMINUM CO COL FLS RED PLT. COLUMBIA FALLS, MONTANA

Date: 2/27/2015 

### Legend

( Surface Water & Sediment Sampling Location

! ( Surface Water & Waste Source Sampling Location

Wetlands (source: NWI)

0 0.25 0.5 1
Miles Prepared for: U.S. EPA Region 8

Contract No.: EP-S8-13-01

TDD: 1407-05

DCN: W0157.1A.00381 

# ± Prepared By: Weston Solutions, Inc. START IV

Suite 100 1435 Garrison Street Lakewood, CO 80215 CF-WS-17

CF-WS-18

CF-SW-03

CF-WS-20 CF-WS-19

CF-WS-21

CF-SW-08

CF-SW-13 CF-SW-14

CF-SW-16 CF-SW-15 CF-SW-20

CF-WS-22 CF-SW-01

CF-SW-06 CF-SD-01

CF-SD-02

CF-SD-OP-01

CF-SW-19 CF-SD-03

CF-SW-05
CF-SD-05 CF-SD-06 CF-SW-07 CF-SD-07 CF-SW-21

CF-SD-08 CF-SW-22

CF-SW-09
CF-SD-09 CF-SD-04

CF-SD-13 CF-SD-14 CF-SD-15

CF-SD-16

! Actual Contamination Actual Contamination Uppermost PPE Uppermost PPE

PPE PPE

Source 1 Source 1 PPE PPE

Source 4 Source 4 PPE PPE

Source 3 Source 3 PPE PPE

Source 2 Source 2GROUNDWATER ELEVATION

GC = GRAVEL-SAND-CLAY MIXTURE

GM = GRAVEL-SAND-SILT MIXTURE

GP = GRAVEL-SAND MIXTURE (WELL SORTED)

SM = SAND-SILT MIXTURE

ROCK = BEDROCK

2800 2900 3000 3100 3200

2800 2900 3000 3100 3200 HORIZONTAL DISTANCE

TW16

TW1 W8-TW2 W11-TW17 TW9

TD=100FT

SM

TD=240FT GC

TD=60FT GP

TD=90FT

GP GC

TD=195FT

GM GC ROCK 

### A' A

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500

SM

HORIZONTAL

VERTICAL 0 350' 700'

0 70' 140'2800 2900 3000 3100 3200

2800 2900 3000 3100 3200 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500

HORIZONTAL DISTANCE

TW11 W10-TW22 W11-TW17 TW9

TD=300FT

TD=60FT GP

TD=90FT
GP GC

TD=195FT GC ROCK 

### B' B

CF-GW-OP-02

TD=169FT GC

GW GW
GM

GM

GW SM SW SW SW

GP

SC GC

SW
GW

GW GROUNDWATER ELEVATION

GC = GRAVEL-SAND-CLAY MIXTURE

GM = GRAVEL-SAND-SILT MIXTURE

GP = GRAVEL-SAND MIXTURE (WELL SORTED)

GW = GRAVEL-SAND MIXTURE (POORLY SORTED)

SM = SAND-SILT MIXTURE

SW = WELL – GRADED GRAVELLY SANDS

ROCK = BEDROCK

HORIZONTAL

VERTICAL 0 550' 1100'

0 110' 220'Figure 9

- 15

- Mile Target Distance Limit Map for Anaconda Aluminum Co Co lumbia Falls Reduction
Plant

This document can be viewed at the USEPA Docket Center, Public Reading Room. Address: USEPA West 1301 Constitution Ave, NW Room 3334

, Washington, DC 20004

. Telephone: 202

- 566

- 1744

. Fax:
566

- 9744

. Email: docket

- customerservice@epa.gov

.Figure References

Figure 1 – Refs. 33; 41

Figure 2 – Refs. 3, Appendix A, pp. 111-156, Appendix C, pp. 187 and 189; 8, p. 37; 33

Figure 3 - Refs. 3, Appendix A, pp. 111-156, Appendix C, pp. 187 and 189; 33; p. 55 of this HRS Documentation Record

Figure 4 – Refs. 3, Appendix A, pp. 111-156, Appendix C, pp. 187 and 189; 8, p. 37; 33; p. 55 of this HRS Documentation Record

Figure 5 - Refs. 3, Appendix A, pp. 111-156, Appendix C, pp. 187 and 189; 24; 8, p. 37; 33; 38; p. 55 of this HRS Documentation Record

Figure 6 - Refs. 3, Appendix C, p. 187; 29; 33; Figure 2 of this HRS Documentation Record

Figure 7 - Refs. 3, Appendix A, pp. 111, 112, 115, 127, 128, 130, Appendix C, pp. 187 and 189, Appendix D, p. 195; 33; p. 55 of this HRS Documentation Record

Figure 8 - Refs. 3, Appendix A, pp. 115, 130, 119-121, 153-156, Appendix C, pp. 187 and 189, Appendix D, p. 195; 33; p. 55 of this HRS Documentation Record

Figure 9 - Refs. 3, Appendix C, pp. 187; 33; Figures 2 and 6 of this HRS Documentation RecordSITE DESCRIPTION

The Anaconda Aluminum Co Columbia Falls Reduction Plant site includes the release from an aluminum production facil ity locat ed in Flathead County, Montana. EPA is evaluating the Ground Water and Surface Water Migration Pathway s for the Anaconda Aluminum Co Columbia Falls Reduction Plant site

. For HRS scoring purposes, the site consists of five source areas that have been documented through chemical analysis to contain hazardous substances and releases to ground and surface water . Source No. 1 comprises the Eastern North Percolation Pond ; Source No. 2 is the Western North Percolation Pond: Source No. 3 is the Western South Percolation Pond: Source No. 4 is the Eastern South Percol ation Pond: and Source No. 5 is the West Landfill (Ref

. 3, pp. 8

- 12 and Figure 2 of this HRS documentation record). Source No. 1 is considered as source type “surface impoundment”; Sources No. 2 through 4 are consid ered as source type “ pile”, while Source No. 5 is considered to be source type “landfill” under the HRS (Ref. 1, pp. 51587, 51591). Additional possible sources of various hazardous substances at the property that have not been characterized to date include six additional landfill areas, three add itional ponds

, storage tanks, a waste pile area, and the cathode pits (Ref s

. 3

, p p. 20

- 24 ; 19, pp. 14

- 17; Figure 2 of this HRS documentation record).

The hazardous substances that have been detected in at least one of the sources listed above include, but are not limited to: Aroclor 1254; and the metals arsenic, cadmium, chromium, cyanide , manganese , and zinc (Ref. 3, pp. 46

- 49; S ection 2.2.1 of this HRS documentation record for Sources 1, 2, 3 , 4, and 5 ). Samples collected from the Eastern North Percolat ion Pond (co

- located aqueous and solid samples: CF

SW

- 19 and CF

- S D

- 19, and CF

- SW

- 20 and CF

- S D

- 20) were located near the inflow point or depositional area of discharge from the Paste Plant Briquette Quench system, Paste Plant Ball Mill Bearing Cooling syst em, Wet Scrubber Blowdown, Air Compressor Cooling, Air Compressor Condensate Blowdown, Masonry Shop, and Battery Shop. Samples for the Western North Percolation Pond ( CF

- SW

- 17 and CF

S D

- 17, and CF

- SW

- 18 and CF

- S D

- 18) were collected near the inflow point or depositional area of discharge from the Eastern North Percolation Pond (Ref. 32, p. 37; Figures 4 and 6 of this HRS d ocumentation r ecord)

.
Samples for the Central South Percolations Pond (co

- located aqueous and solid samples: CF

- SW

- 21 and CF

- SD

- 21 )

, were located at the inflow point from the western pond, and samples for the Eastern South Percolation Pond ( CF

- SW

- 22 and CF

- S D

- 22 ) we re located at the center of the pond (Ref. 32, p. 37; Figures 4 and 6 of this HRS d ocumentation r ecord)

.

Some of these hazardous substances have been released into ground water beneath the property, as well as the Flathead River (located directly adjacent to the property), at concentrations elevated above background (Section 2.2.2 [Source 5], and Sections 3.1 .1 and 4.2.1 of this HRS documentation record). According to the MDEQ Pollutant Discharge Elimination System Permit, ground water at the facility, which receives process wastewaters, discharge to the surface water of the Flathead River along the southwest ern portion of the property (Refs. 7, p. 5; 19, pp. 18, 19).

Given the interconnected nature of the waste streams at the facility and the hazardous substances already identified within the percolation ponds and the west landfill (Sources 1, 2 , 3, 4, and 5 )

, it is possible that the other possible sources listed below would have similar types and concentrations of hazardous substances to those identified in the s ources evaluated for this documentation record through chemical analysis. The west percolation pon d, the wet scrubber sludge pond, the north and south leachate ponds, the i ndustrial b y

- products a rea , and the cathode soaking pits were not directly evaluated during the 2013 sampling event and therefore chemical analytical data are not available for those potential sources. In addition, none of the landfills listed were sampled during the 2013 sampling event. Given the age of the plant, fashion in which contaminants present onsite were handled, that some of the landfills were only covered (not capped), and the connectivity of ground water with surface water in the area, these other

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 20possible sources may need to be characterized during the Remedial Investig ation/Feasibility Study (Refs. 3 , p p

. 21

- 24).

Targets evaluated for this HRS documentation record were ground water users, fisheries, wetlands and sensitive environments. Ground water in the area is used for drinking by both municipal and private residents. The nearest private well is located approximately one mile to the west and the city of Columbia Falls operates two municipal wells between three and four miles to the west (Refs. , 24 , 38 ). The Flathead River watershed was evaluated for this HRS documentation record . The Flathead River is a fishery that supports a variety of finfish that are harvest ed for human consumption

, as well as supporting the federally designated threatened bull trout (Refs. 27, pp. 33

- 34, 48, 49 28 ). Significant areas of wetlands are present along the Flathead River, in areas adjacent to and downstream of the facility (Ref

. 29 ).

The facility is located within the boundaries of Township 30N, Range 20W, Section 3 at 48.3931351074135 latitude and

- 114.1341 58794466 longitude (Figure 1). It is approximately 2.0 miles northeast from the population center of Columbia Falls, Flathead County, Montana, at 2000 Aluminum Drive (Ref. 3, p. 14) . The closest residences are approximately 1 mile north, southeast, and west of the facility (Ref. 3, p. 20)

. According to the 2010 Census , the total population of Flathead County is 90,928 (Ref. 4). The elevation at the facility is approximately 3,100 feet above mean sea level (amsl). Topography at the facility is generally flat with a southern slope at approximately 3° to 4° with the area north of the Facility slightly steeper at approximately 5° to 6° ( Ref. 5, pp. 2, 3).

The total area of the property owned by Anaconda Aluminum Co Columbia Falls Reduction Plant is approximately 3,196 acres (Figure 1). For the purposes of this investigation site is d efined as the areas where hazardous substances have been deposited, stored, disposed, placed, or have otherwise come to be located. (Figure 1 , Ref. 3, p. 14) . The facility is bordered to the north by Cedar Creek Reservoir, to the east by Teakettle Mountain, to the s outh by the Flathead River, to the west by Cedar Creek , and sits within the Flathead River

- Columbia Falls watershed . Current Facility use is primarily for minimal plant maintenance activities, wildlife corridors, and local specially permitted hunting limit ed to the west and north sides of the Facility in the fall. Access to the Facility is available via Aluminum Drive and through private land from the north. The closest residence is adjacent to the western CFAC property boundary and is approximately 0.92 mi le from the plant (Ref. 3, p. 14)

.
The Anaconda Copper Mining Company built the Anaconda Aluminum Reduction Facility and began production in 1955. The Atlantic Richfield Company (ARCO) purchased the plant in 1978 and operated it until 1985 when it was sol d to the Montana Aluminum Investor’s Corporation and began operations under Anaconda Aluminum Co Columbia Falls Reduction Plant . In 1999, Glencore acquired the company and operated until 2009 when production was curtailed due to poor economic conditions fo r aluminum production. The plant is a Vertical Stud Soderberg aluminum reduction facility that uses the Hall Heroult process of producing aluminum in carbon

– lined “pots” heated to 960 degrees Celsius (°C). Aluminum oxide is dissolved in a molten cryolite b ath and aluminum oxide is reduced to aluminum metal by electrons from direct current through the pot. The molten aluminum is then tapped from the pot and cast into ingots. This process uses 350 megawatts, and 600 pots at 100% production. There are currentl y 451 pots in place; however the facility has not operated since October 31, 2009 (Refs. 3, p. 20; 19, pp. 6

- 8)

.
Aluminum smelting operations are not currently active on

- site; however, the plant features identified and included in this investigation consi st of numerous buildings and industrial operating facilities such as offices, warehouses, mechanical shops, laboratory, washhouse, paste plant, coal tar pitch tanks, pump houses, and the main pot line facility. Features on the facility property include per colation ponds, leachate ponds, sludge ponds, sewage treatment ponds, cathode soaking pits, closed and operational landfills (Figure 2). Current Facility conditions are based on observations made during the September 23, 2013

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 21through October 1, 2013 sampling event. Facility features (Figure 2) observed during the 2013 sampling event are described in the table below (Ref. 3, p. 20).



### Feature (Reference) Description

East Landfill (Refs. 3, p. 21; 19, pp. 15

- 16) The Spent Potliner Landfill, also known as the East Landfill, operated from approximately 1980

- 1990 and is a clay

- lined landfill used to dispose of spent potliners prior to their declaration as a hazardous waste. The landfill was capped with a synthetic ca p and revegetated in 1990 . MT DEQ was aware of the landfill closure plan (October 12, 1989 letter from John Arrigo, MT DEQ Water Quality Bureau, to Don Ryan, Anaconda Aluminum Co Columbia Falls Reduction Plant ). This area was observed to be closed and cove red with grass during the field sampling activities. West Landfill (Refs. 3, p. 21; 8, p. 9; 19, p. 16.) Anaconda Aluminum Co Columbia Falls Reduction Plant operated an unlined solid waste landfill, also known as the West Landfill, from 1955

- 1981 for which they disposed of general garbage including, paper, scrap from the shops, strapping, steel scrap and scrap wood, and spent potliner (1955

- 1970). Spent potliner wasn’t listed by the EPA as hazardous waste until 1991. As a result, ground water monitoring around the landfill had detected elevated concentrations of cyanide, a byproduct of the carbon product pot life. The landfill was capped with a clay cap in approximately 1992 / synthetic cap in 1994 (EPA Presentation) as a special permit condition under the MPDES Permit No. MT0030066. Solvents and hazardous wastes are known to have been buried on

- site in the closed landfills (West, Center and Sanitary). This area was observed to be closed and covered with grass during the field sampling activities. Wet S crubber Sludge Pond Landfill (Refs. 3, p. 21; 9, p. 13; 19, p. 15. Identified by Steve Wright, CFAC, during June 2013 facility visit.) Wet Scrubber Sludge Pond Landfill was closed in approximately 1980 and contained sludge waste generated from the Wet Scru bber System and for a period from approximately 1994

- 1998 contained spent potliner material. The landfill was recontoured, covered with native soil and revegetated with native grasses. This area was observed to be closed and covered with grass during the f ield sampling activities.

Center Landfill (Refs. 3, p. 21; 8, p. 9; 19, p. 16.) The Center Landfill, also known as the Carbon Pile, is an unlined landfill operated from approximately 1970 - 1980. Solvents and hazardous wastes are known to have been buried on

- site in the closed landfills (West, Center and Sanitary). This area was observed to be closed and covered with grass during the field sampling activities. Sanitary Landfill (Refs. 3, p. 22; 19, p. 15.) The Sanitary Landfill is a clay

- lined historic lan dfill used for plant garbage. The landfill was covered with soil and re

- vegetated. Years of operation unknown. Solvents and hazardous wastes are known to have been buried on

- site in the closed landfill (West, Center and Sanitary). This area was observed to be closed and covered with grass during the field sampling activities. Asbestos Landfill (Location identified by Steve Wright, CFAC, during June 2013 facility visit.) Based on a review of aerial photography the Asbestos Landfill began operation in

approx imately the early 2000's; date last used is unknown. This area was observed to be closed and covered with grass during the field sampling activities.

Industrial Landfill (Location identified by Steve Wright, CFAC during June 2013 facility visit. 19.) The Industrial Landfill is an active landfill that receives non

- hazardous waste and debris. This area was observed to be active and disturbed. The area was covered with gravelly soil during the field sampling activities.

North and South Leachate Ponds (Refs. 3, p. 22; 6, p. 11) Two hypalon

- lined leachate ponds were constructed on opposite ends of the East Landfill in 1980, one on the north side of the landfill (North Leachate Pond) and one on the south side of the landfill (South leachate Pond). The ponds wer e used to collect runoff water from the East Landfill containing the spent potliner material and aerated during the summer months to reduce water volume and utilize ultraviolet light to break down the cyanide. According to a letter from Donald F. Ryan, Lab oratory Manager at

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 22

### Feature (Reference) Description

Anaconda Aluminum Co Columbia Falls Reduction Plant , to MT DEQ dated January 5, 1990, approximately 150,000 gallons of leachate water containing fluoride and approximately 3 mg/L of cyanide was drained from the South Leachate Pond into t he Wet Scrubber Sludge Pond Landfill. This transfer of leachate was approved by MT DEQ (October 12, 1989 letter from John Arrigo, MT DEQ Water Quality Bureau, to Don Ryan, Anaconda Aluminum Co Columbia Falls Reduction Plant ). The South leachate Pond was dr ied, capped, and subsequently closed in 1993. An underground pipe leads from the North Leachate Pond to the Wet Scrubber Sludge Pond. The North Leachate Pond held cyanide

- free water containing fluoride and was subsequently drained into the Wet Scrubber Slu dge Pond Landfill. The North Leachate Pond was capped and then closed in 1994. These areas were observed to be closed and covered with grass during the field sampling activities. North Percolation Ponds (Refs. 3, p. 23; 6, pp. 4, 5,
7

- 9, 12

- 15; 7, p. 4; 9 , p. 4) The North Percolation Ponds (smaller eastern pond receives direct discharge, larger western pond is overflow) historically received wastewaters from the Paste Plant Briquette Quench system, Paste Plant Ball Mill Bearing Cooling system, Wet Scrubber Blowdown (until approximately 1999), Air Compressor Cooling, Air Compressor Condensate Blowdown, Masonry Shop, and Battery Shop. Prior to 1978 the waste effluent from the soaking of the carbon cathodes was piped to the North Percolation Pond, also known a s the Boiler Blowdown Pond (smaller pond). In addition to the aforementioned, the ponds currently receive garage waste water, steam cleaning and pin crane sumps waters, lab boiler blowdown water, equipment non

- contact cooling water, and process area storm water. Both ponds contained dark gray/black process material and were sparsely vegetated with grasses, shrubs, and trees. No water was present in the western pond during the field sampling activities. The smaller eastern pond contained water of an unknown depth. West Percolation Pond (Refs. 3, p. 23) The West Percolation Pond receives wastewater from the boiler blowdown (Fabrication Shop, Warehouse, and Change House) and storm water from the parking lots. The pond was not visited during the field sampling activities. South Percolation Ponds (Refs. 3, p. 23; 6, p. 5, 9, 10; 7. pp. 4, 5; 9, p. 4) The South Percolation Ponds receive wastewaters from the Rectifier Oil Separator Sump, Facility Production Area storm water, non

- contact equipment cooling water, S ewage Treatment Plant, Restrooms and Change House sinks, Laboratory Sinks, laboratory non

- contact cooling water, laboratory non

- solvent waste water, plant wide lavatories and sinks, Rectifier non

- contact cooling water, casting mold cleaning water, casting mold steam cleaning, contact cooling water from direct chill casting of aluminum ingots, and Fabrication Shop Steam Cleaning Bay. The south percolation ponds were predominantly dry with minimal amounts of water in the ponds during the field sampling event. Both were vegetated with grasses, shrubs, and trees Industrial By

- products Area (Refs. 3, p. 24; 11, pp. 27

- 29.) The Industrial by

- products area and numerous waste piles have been identified in various locations throughout the Facility. This area was observed during the field activities to be disturbed with some grass cover.

Cathode Soaking Pits (Refs. 3, p. 24; ) Carbon cathode soaking pits contained water and ammonia to expedite the carbon removal process. The pits were not observed during the sam pling activities.

Cleanup a ctivities that have occurred on the Facility include addressing a transformer fire in the rectifier yard that occurred on September 10, 1991. The transformer held approximately 10,000 gallons of dielectric fluid that contain approximately 207 parts per million (ppm) polychlorinated biphenyls (PCBs). Approximately 4,000 gallons spilled into the containment basin and the explosion resulted in the contamination of an approximate 4,000 to 5,000 square

- foot area. According to the R emedial Activities Report by Olympus Environmental, Inc. the spill area soils and structures were remediated to less than 10 ug/100 cm 3 and no further cleanup was recommended to the MDEQ (Refs. 15, pp. 3, 4, 6; 6, pp. 1, 11 )

.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 23In 1994 two capacitors in the West Rectifier Yard Capacitor Bank exploded contaminating steel holding frames and soil with 3 to 4 gallons of pure PCBs. According to Anaconda Aluminum Co Columbia Falls Reduction Plant ’s October, 1994 SWPPP the surrounding capacitors, framing, and soils were removed and disposed of in a certified Toxic Substances Control Act (TSCA) landfill, and the area cleared for operational use . It is unknown what regulatory agency approved this action ( Ref. 6, pp. 1, 11 )

.
In February 1998, The State of Montana’s P ermitting and Compliance Division of the Air & Water Management Bureau requested that Anaconda Aluminum Co Columbia Falls Reduction Plant remove all of the spent potliner material (EPA hazardous waste number K088) present in the Wet Scrubber Sludge Pond La ndfill due to improper disposal of a hazardous waste. Post removal, on July 28, 1998 Anaconda Aluminum Co Columbia Falls Reduction Plant sampled the pot diggings material from the Wet Scrubber Sludge Pond Landfill to determine if carbon in the Wet Scrubber Sludge Pond Landfill had been adequately removed. Results of the sampling indicated that cyanide was detected in all of the pot diggings material samples collected (highest concentration 2.1 ppm) and half of the soil samples collected from under the waste pile. EPA Region III Residential Risk

- Based Criteria was 1600 ppm and thus, in October 1998, the State declared no further clean

- up action required for the pot diggings material or soil under the pile (Refs. 19, p p

. 12, 30; 36, p. 5)

.

Anaconda Aluminum Co Columbia Falls Reduction Plant conducted sampling on September 25, 2001 during suspended plant operations in response to inquiries by the Montana Department of Environmental Quality Air and Waste Management Bureau as to the determination if waste in acc umulation is hazardous

waste. Materials sampled were anode briquettes, cryolite bath, coal tar pitch, anode dust control bags and potline s sweepings bags. The analytical results indicated that one of the sampled materials were classified as hazardous waste under RCRA regulation but may be eligible substances under CERCLA ( Ref. 19, p. 31

- 34)

.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 24

## 2.2 SOURCE CHARACTERIZATION

Although there are many possible sources contributing to ground water and surface water contamination associated with this site, this d ocumentation r ecord is focused on the following five sources, due to the relatively recent sampling event that has provided the data regarding the northern percolation ponds, the southern percolation ponds, and the west landfill.



## 2.2.1 SOURCE IDENTIFICATIO N

Source Number : 1

Name of source: Eastern North Percolation Pond

Source Type : Surface Impoundment

Description and Location of Source (with reference to a map of the facility ):

The Eastern North Percolation Pon d (also known as the boiler blowdown pond [Figure 2]) receive d direct discharge of the Paste Plant Briquette Quench system, Paste Plant Ball Mill Bearing Cooling system, Wet Scrubber Blowdown (until approximately 1999), Air Compressor Cooling, Air Compresso r Condensate Blowdown, Masonry shop, and Battery s hop. Prior to 1978

, the waste effluent from the soaking of the carbon cathodes was piped to th is pond. In addition to the aforementioned, the pond was receiv ing garage waste water, steam cleaning and pin cr ane sumps waters, lab boiler blowdown water

, equipment non

contact cooling water, and process area s torm water. Because the primary wastestream generated onsite was spent potliner (i.e., RCRA listed waste K088 for cyanide) and this source received effluent containing anode material as well as discharge from several shops, metals, cyanide, and miscellaneous organic contaminants would be found in this source (Refs. 6, pp. 4, 5, 7, 8, 11

- 15; 7, pp. 5, 6 , 26 ; 19, pp. 12, 17).

The pond covered approximately 1.1 acres in the center of the facility as determined using GIS (Ref. 3 1, p. 1; 33)

. Overflow from this pond flowed via channel into the Western North Percolation Pond (i.e., Source 2; see below) (Ref. 7, pp. 4, 5). A total of three (including one duplicat e) source surface water samples (CF

- S W

- 19, CF

- S W

- 20 and CF

- S W

- 25 [duplicate of CF

- SW

- 19] ) were collected from the
Eastern North Percolation Pond. Concentratio ns of SVOCs and metals were detected above the reporting limit in surface water samples collected from the Eastern North Percolation Pond (Ref. 3, pp. 73, 74 ; Figure 6 ).



## 2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

Source Samples:

All source sampling was done in accordance with EPA Environmental Response Team (ERT) SOPs 2012, 2013, 2016, a nd 2017 (Ref. 32, p. 47 ). For example, at each location

, the aqueous sample was collected before the solid

- matrix sample, and a new disposable plastic scoop was used to collect each solid

- matrix sample to ensure that the aqueous sample didn’t include any s olids disturbed by the sampling

process . All samples were collected during the same September/ October 201 3 sampling event, over a period of nine days ( September 23 to October 1 ) (Ref. 3 , p p. 27, 37 )

The analytical results of the sludge waste (solid

- matrix) source samples (C F

- SD

- 19, CF

- SD

- 20 and CF

SD

- 25 (duplicate for CF

- SD

- 19) [Figure 6] ) ) from the Eastern North Percolation Pond are presented in

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 25Tables E17

- E23, Appendix E of the Site Reassessment Report (SRR) (Ref. 3, pp. 176, 263 -275). Labo ratory data and validation reports are presented in Appendix F of the same document (R ef . 3a , App. F, Section 7, pp. 1431 -1516) . Contaminant concentrations in the solid

- matrix waste source samples were considered detections when the result was greater than the analytical reporting limit. Although several TAL metals contaminants were detected in waste source samples collected from the Eastern North Percolation Pond that were consistent with wastes expected to be found, only the following are evaluated based on their impact in scoring :

Hazardous Substance Evidence References Sample

No. RL (mg/kg) Concentration (mg/kg)

Arsenic CF

- SD -19 (MH0063)

1 43.3 Ref s . 3, p p . 4 7

- 49 , App. B, p. 17 6 ; App. D, p. 205; App E, Table E22, pp. 273; 3a, App. F Section 5, pp. 392, 398, Section 7, pp. 1431, 14 41, 1442

CF

- SD -20 (MH0064) 10.5 Ref s . 3, p p . 4 7

- 49 , App. B, p. 17 7 ; App. D, p p

. 205, 206 ; App E, Table E22, pp. 273; 3a App. F, Section 5, pp. 392, 399, Section 7, pp. 1431, 1442

CF

- SD -25 (MH00 69) 15.3 Ref s . 3, p p. 4 7

- 49 ; App. D, p. 205; App E, Table E22, pp. 273 ; 3a App. F, Section 5, pp.

393, 402, Section 7, pp. 143 1 , 144 4 , 1445

Cadmium CF

- SD -19 (MH0063)

0.5 14 Ref s . 3, pp. 47

- 49, App. B, p. 176; App. D, p. 205; App E, Table E22, pp. 273 ; 3a, App. F Section 5, pp. 392, 398, Section 7, pp. 1431, 1441, 1442

CF

- SD -20 (MH0064) 4 Ref s . 3, pp. 47

- 49, App. B, p. 177; App. D, p p

. 205, 206 ; App E, Table E22, pp. 273; 3a

, App. F, Section 5, pp. 392, 399, Section 7, pp. 1431, 1442

CF

- SD -25 (MH0069) 3.8 Ref s . 3, pp. 47

- 49 ; App. D, p. 205; App E, Table E22, pp. 273 ; 3a , App. F, Section 5, pp. 393, 402, Section 7, pp.1431, 1444, 1445

Chromium CF

- SD -19 (MH0063)

1 36.1 Ref s . 3, pp. 47

- 49, App. B, p. 176; App. D, p. 205; App E, Table E22, pp. 273 ; 3a , App. F Section 5, pp. 392, 398, Section 7, pp. 1431, 1441, 1442

CF

- SD -20 (MH0064) 21.1 Ref s . 3, pp. 47

- 49, App. B, p. 177; App. D, p p

. 205, 206 ; App E, Table E22, pp. 273; 3a

, App. F, Section 5, pp. 392, 399, Section 7, pp. 1431, 1442

CF

- SD -25 (MH0069) 21.5 Ref s . 3, pp. 47

- 49 ; App. D, p. 205; App E, Table E22, pp. 273 ; 3a , App. F, Section 5, pp.

393, 402, Section 7, pp. 1431, 1444, 1445

Cyanide CF

- SD -19 (MH0063) 0.5 172 Ref s . 3, pp. 47

- 49, App. B, p. 176; App. D, p. 205; App E, Table E22, pp. 273 ; 3a , App. F Section 5, pp. 392, 398, Section 7, pp. 1431, 1438
CF

- SD

- 20 (MH0064) 2.9 Ref s . 3, pp. 47

- 49, App. B, p. 177; App. D, p p

. 205 , 206 ; App E, Table E22, pp. 273 ; 3a

, App.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 26Hazardous Substance Evidence References Sample

No. RL (mg/kg) Concentration (mg/kg) F, Section 5, pp. 392, 399, Section 7, pp. 1431, 1438

CF

- SD

- 25 (MH0069) 106 Ref s . 3, pp. 47

- 49 ; App. D, p. 205; App E, Table E22, pp. 273 ; 3a

, App. F, Section 5, pp. 393, 402, Section 7, pp.1431, 1439

Manganese CF

- SD

- 19 (MH0063)

1.5 106 Ref s . 3, pp. 47

- 49, App. B, p. 176; App. D, p. 205; App E, Table E22, pp. 273 ; 3a

, App. F Section 5, pp. 392, 398, Section 7, pp. 1431, 1438, 1440

CF

- SD

- 20 (MH0064) 29.3 Ref s . 3, pp. 47

- 49, App. B, p. 177; App. D, p p

. 205 , 206 ; App E, Table E22, pp. 273 ; 3a

, App. F, Section 5, pp. 392, 399, Section 7, pp. 1431, 1442

CF

- SD

- 25 (MH0069) 61.4 Ref s . 3, pp. 47

- 49 ; App. D, p. 205; App E, Table E22, pp. 273 ; 3a

, App. F, Section 5, pp. 393, 402, Section 7, pp.1431, 1444, 1445

Zinc CF

- SD

- 19 (MH0063)

6 565 Ref s . 3, pp. 47

- 49, App. B, p. 176; App. D, p. 205; App E, Table E22, pp. 273 ; 3a

, App. F Section 5, pp. 392, 398, Section 7, pp. 1431, 1438, 1440

CF

- SD

- 20 (MH0064) 431 Ref s . 3, pp. 47

- 49, App. B, p. 177; App. D, p p

. 205 , 206 ; App E, Table E22, pp. 273 ; 3a

, App. F, Section 5, pp. 392, 399, Section 7, pp. 1431, 1442

CF

- SD

- 25 (MH0069) 235 Ref s . 3, pp. 47

- 49 ; App. D, p. 205; App E, Table E22, pp. 273 ; 3a

, App. F, Section 5, pp. 393, 402, Section 7, pp.1431, 1444, 1445

Notes: mg/kg milligrams per kilogram
J The associated value is an estimated quantity . The value is well above the reporting limit, and a s such useable for characterization.
RL The value shown is the sample specific Contract Required Quantitation Limit (Ref. 30)

.
Source Sample Information

The source samples listed above were collected during the 201 3 sampling effort conducted by START for the EPA. Samples were analyzed using the Contract Laboratory Program Statement of Work for
I norganic Superfund Methods, ISM01.3

— Metals, Mercury and Cyanide (Ref s

. 3, pp. 34 ; 3a , App. F, Section 7, pp. 1350, 1355 ). Laboratory samples were analyzed by the CLP laborator y ALS Laboratory Group in Salt Lake City, Utah (Ref. 3

, p. 46 ; 3a, App. F, p. 1431 ).



## 2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY (Ref. 1, p. 51588)

START did not observe a maintained and engine ered cover, a liner, or a functioning, run

- on/run

- off control system during the 201 3 field sampling event. Further, since this source is designed to allow water to percolate into the aquifer below the plant it can’t have a liner of any low transmissivity (Refs. 3 , p. 23; 6, p. 5; 7, pp. 4, 5, 26; 19, p. 17 ).

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 27Containment Description Containment Value References

Gas release to air: NS

Particulate release to air: NS

Release to ground water: No liner present 10 Ref s. 1, Table 3 -2; 3, p. 23; 6, p. 5; 7, pp. 4, 5, 26; 19, p. 17

Release to Surface Water vi a overland migration: NS

Notes: NS = Not Scored



## 2.4.2 HAZARDOUS WASTE QUANTITY (Ref. 1, p. 51590)

2.4.2.1.1 Hazardous Constituent Quantity (Tier A) (Ref. 1, pp. 51590, 51591)

Description The hazardous constituent quantity for Source 1 could not be adequately determined according to the HRS requirements; that is, the total mass of all CERCLA hazardous substances in the source is not known and cannot be estimated with reasonable co nf idence (Ref. 1, Section 2.4.2.1.1). There are insufficient historical and current data (Manifests, PRP records, State records, Permits, Waste concentration data, etc.) available to adequately calculate the total or partial mass of all CERCLA hazardous substances in the source and the associated releases from the source. Therefore, there is insufficient information to evaluate the associated releases from the source to calculate the hazardous constituent quantity for Source 1 with reasonable co nf idence. Scoring therefore proceeds to the evaluation of Tier B, hazardous wastestream quantity. Hazardous Constituent Quantity Assigned Value: Not Scored

2.4.2.1.2 Hazardous Waste s tream Quantity (Tier B) (Ref. 1, p. 51591)

Description The hazardous wastestream quantity for Source 1 could not be adequately determined according to the HRS requirements; that is, the total mass of all hazardous wastestreams and CERCLA pollutants and contaminants in the source is not known and cannot be estimated with reasonable confidence [Ref. 1, pp. 51591 (Section 2.4.2.1.2)]. There are insufficient historical and current data (Manifests, PRP records, State records, permits, etc.) available to adequately calculate the total or partial mass of all CERCLA hazardous

wastestream and CERCLA pollutants and contaminants in the source and the associated releases from the source. Therefore, there is insufficient information to evaluate the associated releases from the source to calculate the hazardous wastestream quantity for Sour ce 1 with reasonable co nfidence.

Sum (pounds): NA Sum of Wastestre am Quantity/5,000 (Table 2-5): NA

Hazardous Waste s trea m Quantity Assigned Value (W): Not Scored

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 282.4.2.1.3 Volume (Tier C) (Ref. 1, p. 51591)

Description

Because the horizontal and vertical extent of the source has not been fully characterized, it is not possible to adequately determine the volume of this source. As a volume cannot be determined, a value of zero is assigned. (Ref. 1, Table 2

- 5

, p. 51591 ).

Volume Assigned Value (V): 0

2.4.2.1.4 Area (Tier D) (Ref. 1, p. 51591)

Description

Source 1 is evaluated as a surface impoundment covering roughly 1.1 acres as calculated using GIS to determine the area of a provided polygon by the START project manag er (Ref . 1, Table 2

- 5

- p. 51591; Figure 2; 31, p.1; 33)

. There are 43,560 square feet in each acre, so the total number of square feet for this source area is 47,916.

Since the equation for a ssigning v alue (Ref. 1, Table 2

- 5) is the area divided by 13, t he HWQ value is equal to 47,916 ft 2 / 13 = 3,685.8

Area Assigned Value (A): 3,685.8

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 29

## 2.2.1 SOURCE IDENTIFICATION

Source Number : 2

Name of source: Western North Percolation Pond

Source Type : Pile

Description and Location of Source (with reference to a map of the facility ):

The Western N orth P ercolation P ond ( the larger western pond [Figure 2]) receive d overflow and high flow events from the smaller Eastern North Percolation Pond (i.e., Source 1)

, which had become partial ly sealed due to s ettling out of finer particles. In other words, process waters that went to the eastern pond flowed to the western pond via a connecting ditch d uring production operations (Ref. 3, App. B, pp. 175

- 177). Because the western pond was still functioning fully as a percolation pond (allowing for the transmission of liquids to migrate to the shallow ground water onsite), this source has been evaluate d as a pile (Ref. 7, pp. 4, 5)

. Because the primary wastestream generated onsite consisted of spent potliner (RCRA listed waste K088 for cyanide) and this source received effluent containing anode material as well as discharge from several shops, metals, cyanide, and miscellaneous orga nic contaminants would be found in this source (Refs. 7, pp. 5, 6; 19, pp. 12, 17).

The Western North Percolation Pond covers approximately 7.6 acres in the center of the facility as determined using GIS to determine the area of a provided polygon by the START project manager (Ref. 31, p. 1; 3 3 ). A total of two dried, settled solid waste source samples (CF

- SD

- 17 and CF

- SD

- 18 ) were collected from the Western North Percolation Pond

. Concentrations of SVOCs, and metals were detected above the reporting limi t in waste source samples collected from the Western North Percolation Pond . No water was present in the Western North Percolation Pond during the 2013 sampling event . Sample locations are shown in Figure 6 (Ref. 3, pp. 73, 74 ; Figure 6 ).



## 2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

Source Samples:

All source sampling was done in accordance with EPA ERT SOPs 2012, 2013, 2016, and 2017 (Ref. 32,

p. 47 ). For example, at each location

, the aqueous sample was collected before the solid

- matrix sample to ensure that the aqueous sample didn’t include any solids disturbed by the sampling process

. A new disposable plastic scoop was used to collect each solid

- matrix sample from a depth of approximately 0

- 6 inches below the water surface. All samples were collected during the same September/ October 201 3 sampling event, over a period of nine days ( September 23 to October 1 ) (Ref. 3 , p p. 27, 37 )

.
The analytical results of the dried, settled solids waste source samples (C F

- SD

- 17 and CF

- S D

- 18 [Figure 6] ) from the Western North Percolation Pond are presented in Tables E17

- E23, Appendix E of the SRR. Laboratory data and validation reports are presented in Appendix F of the same document (R ef

. 3 , Section 7, pp. 1431

- 1 441 ) . Contaminant concentrations in waste source samples were considered detections when the result was greater than the analytical reporting limit. Although several TAL metals contaminants were detected in waste source samples collected from the Western North Percolation Pond that were cons istent with wastes expected to be found, only the following are evaluated based on their impact in scoring :

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 30Hazardous Substance Evidence References Sample No. RL (mg/kg) Concentration (mg/kg)

Arsenic CF

- SD -17 (MH0061)

1 17.8 Ref s . 3, pp. 47

- 49, App. B, p. 17 5 ; App. D, p. 206 ; App E, Table E22, pp. 273 ; 3a , App. F Section 5, pp. 392, 396, Section 7, pp. 1431, 1440

CF

- SD -18 (MH0062) 5.8 Ref s . 3, pp. 47

- 49, App. B, p. 176; App. D, p. 206 ; App E, Table E22, pp. 273 ; 3a , App. F Section 5, pp. 392, 397, Section 7, pp. 1431, 1440, 1441

Cadmium CF

- SD -17 (MH0061)

0.5 5.8 Ref s . 3, pp. 47

- 49, App. B, p. 175; App. D, p. 206 ; App E, Table E22, pp. 273 ; 3a , App. F Section 5, pp. 392, 396, Section 7, pp. 1431, 1440

CF

- SD -18 (MH0062) 1.2 Ref s . 3, pp. 47

- 49, App. B, p. 176; App. D, p. 206 ; App E, Table E22, pp. 273; 3a

, App. F Section 5, pp. 392, 397, Section 7, pp. 1431, 1440, 1441

Chromium CF

- SD -17 (MH0061)
1 43.6 Ref s . 3, pp. 47

- 49, App. B, p. 175; App. D, p. 206 ; App E, Table E22, pp. 273; 3a

, App. F Section 5, pp. 392, 396, Section 7, pp. 1431, 1440

CF

- SD -18 (MH0062) 34.8 Ref s . 3, pp. 47

- 49, App. B, p. 176; App. D, p. 206 ; App E, Table E22, pp. 273; 3a

, App. F Section 5, pp. 392, 397, Section 7, pp. 1431, 1440, 1441

Cyanide CF

- SD -17 (MH0061) 0.5 5.1 Ref s . 3, pp. 47

- 49, App. B, p. 175; App. D, p. 206 ; App E, Table E22, pp. 273; 3a

, App. F Section 5, pp. 392, 396, Section 7, pp. 1431, 1438

Manganese CF

- SD -17 (MH0061)

1.5 97.5 Ref s . 3, pp. 47

- 49, App. B, p. 175; App. D, p. 206 ; App E, Table E22, pp. 273; 3a

, App. F Section 5, pp. 392, 396, Section 7, pp. 1431, 1440

CF

- SD -18 (MH0062) 63.3 Ref s . 3, pp. 47

- 49, App. B, p. 176; App. D, p. 206 ; App E, Table E22, pp. 273; 3a

, App. F Section 5, pp. 392, 397, Section 7, pp. 1431, 1440, 1441

Zinc CF

- SD -17 (MH0061)

6 814 Ref s . 3, pp. 47

- 49, App. B, p. 175; App. D, p. 206 ; App E, Table E22, pp. 273; 3a

, App. F Section 5, pp. 392, 396, Section 7, pp. 1431, 1440

CF

- SD -18 (MH0062) 128 Ref s . 3, pp. 47

- 49, App. B, p. 176; App. D, p. 206 ; App E, Table E22, pp. 273; 3a

, App. F Section 5, pp. 392, 397, Section 7, pp. 1431, 1440, 1441

Notes: mg/kg milligrams per kilogram J The associated value is an estimated quantity. The value is well above the reporting limit, and as such its presence is not in question

. RL The value shown is the sample specific Contract Required Quantitation Limit (Ref. 30).

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 31Source Sample Information

The source samples listed above were collected during the 201 3 sampling effort conducted by START for the EPA. Samples were analyzed using the Contract Laboratory Program Statement of Work for
I norganic Superfund Methods, ISM01.3

— Metals, Mercury and Cyanide (Ref s. 3, pp. 34; 3a, App. F, Section 7, pp. 1350, 1355 ). Laboratory samples were analyzed by the CLP laborator y ALS La boratory Group in Salt Lake City, Utah (Ref. 3, p. 46).



## 2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY (Ref. 1, p. 51588)

START did not observe a maintained and engineered cover, a liner, or a functioning, run -on/run- off control system during the 2013 field sampling event. Further, since this source is designed to allow water to percolate into the aquifer below the plant it can’t have a liner of any low transmissivity (Refs. 3 , p. 23; 6, p. 5; 7, pp. 4, 5, 26; 19, p. 17 ).

Containment Description Containment Value References

Gas release to air: NS

Particulate release to air: NS

Release to ground water: No liner present 10 Ref s. 1, Table 5; 7, pp. 4, 5, 3 -2; 3, p. 23; 6, p. 26; 19, p. 17

Release vi a overland migration NS

Notes: NS = Not Scored


## 2.4.2 HAZARDOUS WASTE QUANTITY (Ref. 1, p. 51590)

2.4.2.1.1 Hazardous Constituent Quantity (Tier A) (Ref. 1, pp. 51590, 51591)

Description The hazardous constituent quantity for Source 2 could not be adequately determined according to the HRS requirements; that is, the total mass of all CERCLA hazardous substances in the source is not known and cannot be estimated with reasonable co nf idence ( Ref. 1, Section 2.4.2.1.1). There are insufficient historical and current data (Manifests, PRP records, State records, Permits, Waste concentration data, etc.) available to adequately calculate the total or partial mass of all CERCLA hazardous substances i n the source and the associated releases from the source. Therefore, there is insufficient information to evaluate the associated releases from the source to calculate the hazardous constituent quantity for Source 2 with reasonable co nf idence. Scoring ther efore proceeds to the evaluation of Tier B, hazardous wastestream quantity.

Hazardous Constituent Quantity Assigned Value: Not Scored

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 322.4.2.1.2 Hazardous Waste s tream Quantity (Tier B) (Ref. 1, p. 51591)

Description The hazardous wastestream quantity for Source 2 could not be adequately determined according to the HRS requirements; that is, the tot al mass of all hazardous wastes treams and CERCLA pollutants and contaminants in the source is not known and cannot be estimated with reasonable conf idence [Ref. 1, pp. 51591 (Section 2.4.2.1.2)]. There are insufficient historical and current data (Manifests, PRP records, State records, permits, etc.) available to adequately calculate the total or partial mass of all CERCLA hazardous wastestream and CE RCLA pollutants and contaminants in the source and the associated releases from the source. Therefore, there is insufficient information to evaluate the associated releases from the source to calculate the hazardous wastestream quantity for Source 2 with r easonable co nf idence.

Sum (pounds): NA Sum of Wastestream Quantity/5,000 (Table 2

- 5): NA Hazardous Waste s tream Quantity Assigned Value (W): Not Scored

2.4.2.1.3 Volume (Tier C) (Ref. 1, p. 51591)

Description

Because the horizontal and vertical ex tent of the source has not been fully characterized, it is not possible to adequately determine the volume of this source. As an area has been calculated, volume is assigned a value of 0. (Ref. 1, Table 2

- 5).

Volume Assigned Value (V): 0

2.4.2.1.4 Area (Tier D) (Ref. 1, p. 51591)

Description

Source 2 is evaluated as a pile covering roughly 7.6 acres as calculated using GIS to determine the area of a provided polygon by the START project manager (Ref . 1, Table 2

- 5, p. 51591; Figure 2; 31, p. 1; 33)

. There are 43,560 square feet in each acre, so the total number of square feet for this source area is 331,056.

Since the equation for a ssigning v alue (Ref. 1, Table 2

- 5) is the area divided by 13, t he HWQ value is equal to 331,056 ft 2 / 13 = 25,465.8 Area Assigned Value (A): 25,465.8

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 33

## 2.2.1 SOURCE IDENTIFICATION

Source Number : 3

Name of source: Western South Percolation Pond

Source Type : Pile

Description and Location of Source (with reference to a map of the facility ):

The Western South Percolation Pond cover s approximately 1.7 acres (Figure 2, Refs. 3, App. B, p. 177; 37 p. 1 ; 33) and receive d piped wastewaters from the Rectifier Oil Separator Sump, Facility Production Area storm water, non

- contact equipment cooling water, Sewage Treatme nt Plant, Restrooms and Change House sinks, Laboratory Sinks, laboratory non

- contact cooling water, laboratory non

- solvent waste water, plant wide lavatories and sinks, Rectifier non

- contact cooling water, casting mold cleaning water, casting mold steam cl eaning, contact cooling water from direct chill casting of aluminum ingots, and Fabr ication Shop Steam Clea ning Bay (Refs. 7, pp. 4, 5, 26 ). Process water that overflows from the Western South Percolation Pond flows into the west central, central, and eastern ponds, providing additional surface area for percolation as needed. The south percolation ponds are all interconnected, with the initi al plant outfalls (004 and 005) piped into the westernmost p ond (Ref. 3, photo 38, p. 177). Because the western pond was still functioning fully as a percolation pond (allowing for the transmission of liquids to migrate to the shallow ground water onsite), this source has been evaluated as a pile (Ref. 7, p p

. 4 , 5 ). Because this source received effluent containing anode material as well as discharge from several shops, and storm water runoff, Source 3 was found to contain metals and miscellaneous organic co ntaminants (including PCBs from the transformer fire in the early 1990’s) (Refs. 7, pp. 5, 6, 25; 19, pp. 12, 17, 22).

C o

- located source liquid and solid samples (C F

- SW/ S D

- 21 ) were collected from within the area delineated as the Western South Percolatio n Pond (Figure 6) (Ref. 3, pp. 48, 49, photo 38, p. 177)

. Concentrations of SVOCs and metals were detected above the reporting limit in liquid source samples collected from the Central South Percolation Pond. SVOCs, pesticides and metals were detected in w aste

source samples at concentrations above the reporting limits in waste source samples collected from the Central South Percolation Pond.



## 2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

Source Samples:

All source sampling was done in accordance with EPA ERT SOPs 2012, 2013, 2016, and 2017 (Ref. 32,

p. 47 ). For example, at each location

, the aqueous sample was collected before the solid

- matrix sample to ensure that the aqueous sample didn’t include any solids distu rbed by the sampling process

. A new disposable plastic scoop was used to collect each solid

- matrix sample from a depth of approximately 0

- 6 inches below the water surface. All samples were collected during the same September/ October 201 3 sampling event, ov er a period of nine days ( September 23 to October 1 ) (Ref. 3 , p p. 27, 37 )

.

Source Sediment Sample :

The analytical results of the soil waste mix source sample (CF

- S D

- 21 [Figure 6]) from the Western South Percolation Pond are presented in Tables E17

- E23, A ppendix E of the SRR (Ref. 3, Tables E17

- E23). Laboratory data and validation reports are presented in Appendix F of the same document (R ef

. 3 a ,

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 34HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 35 Section 7, pp. 1431 -1443) . Contaminant concentrations in the waste source samples were considered detections when the result was greater than the analytical reporting limit. S everal TAL metals contaminants were detected in waste source samples collected from the South Percolation Ponds that were consistent with wastes expected to be fo und:

Hazardous Substance Evidence References Sample

No. RL (mg/kg) Concentration (mg/kg) Arsenic 1 7.5 Ref s . 3, pp. 47

- 49, App. B, p. 177; App. D, p. 205; App E, Table E22, pp. 273; 3a

, App. F, Section 5, pp. 393, 40 0 , Section 7, pp. 1431, 1443 Cadmium 0.5 2.4

Chromium 1 18.5

Cyanide CF

- SD -21 (MH0065) 0.5 6 Ref s . 3, pp. 47

- 49, App. B, p. 177; App. D, p. 205; App E, Table E22, pp. 273; 3a

, App. F, Section 5, pp. 393, 40 0 , Section 7, pp. 1431, 1438 Manganese 1.5 57.5 Ref s . 3, pp. 47

- 49, App. B, p. 177; App. D, p. 205; App E, Table E22, pp. 273; 3a

, App. F, Section 5, pp. 393, 40 0 , Section 7, pp. 1431, 1443 Zinc 6 982

Notes: mg/kg milligrams per kilogram
J The associated value is an estimated quantity. The value is well above the reporting limit, and as such its presence is not in question

. RL The value shown is the sample specific Contract Required Quantitation Limit (Ref. 30)

.

Source S ediment Sample Information

The source samples listed above were collected during the 201 3 sampling effort conducted by START for the EPA. Samples were analyzed using the Contract Laboratory Program Statement of Work for
I norganic Superfund Methods, ISM01.3

— Metals, Merc ury and Cyanide (Ref s

. 3, pp. 34; 3a, App. F, Section 7, pp. 1350, 1355 ). Laboratory samples were analyzed by the CLP laborator y ALS Laboratory Group in Salt Lake City, Utah (Ref. 3, p. 46).

Source Aqueous Samples:

The analytical results of the aqueous waste source sample ( CF

- SW -21 [Figure 6]) from the Central South Percolation Pond are presented in Tables E 9-E15 , Appendix E of the SRR (Ref. 3, Tables E9

- E15, pp. 247-261). Laboratory data and validation reports are presented in Appendix F of the same document (R ef

. 3a , App. F, Section 7, pp. 1350, 1360, 1368, 1369 ) . Contaminant concentrations in the source aqueous sample were considered detections when the result was greater than the analytical reporting limit. S everal TAL metals contamina nts were detected in waste aqueous sample collected from the Central South Percolation Pond that were consistent with wastes expected to be found:HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 36 Hazardous Substance Evidence References Sample

No. RL ( μg/L ) Concentration ( μg/L )

Cyanide CF

- SW -21 10 70.8 Ref s . 3, App. D, p. 208; App E, Table E14, p. 257 ; 3a , App. F, Section 5, p. 660, 671, Section 7, pp. 1350, 1360

Zinc (MH0039)
2 39 Ref s . 3, App. D, p. 208; App E, Table E14, p. 257 ; 3a , App. F, Section 5, p. 660, 671, Section 7, pp. 1350, 1368, 1369

Notes: μg/L micrograms per liter
RL The value shown is the sample specific Contract Required Quantitation Limit (Ref. 30)

.
Source Sample Information

The source samples listed above were collected during the 201 3 sampling effort conducted by START for the EPA. Samples were analyzed using the Contract Laboratory Program Statement of Work for
I norganic Superfund Methods, ISM01.3

— Metals, Mercury and Cyanide (Ref s

. 3, pp. 34; 3a, App. F, Section 7, pp. 1350, 1355 ). Laboratory samples were analyzed by the CLP laborator y ALS Laboratory Group in Salt Lake City, Utah (Ref. 3, p. 46).



## 2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY (Ref. 1, p. 51588)

START did not observe a maintained and engineered cover, a liner, or a functioning, run -on/run- off control system during the 2013 field sampling event. Further, since this source is designed to allow water to percolate into the aquifer below the plant it can’t have a liner of any low transmissivity (Refs. 3 , p. 23; 6, p. 5; 7, pp. 4, 5, 26; 19, p. 17 ).

Containment Description Containment Value References

Gas release to air: NS

Particulate release to air: NS

Release to Ground water; No liner present 10 Ref s. 1, Table 3 -2; 3, p. 23; 6, p. 5; 7, pp. 4, 5, 26; 19, p. 17

Release vi a overland migration: NS

Notes: NS = Not Scored



## 2.4.2 HAZARDOUS WASTE QUANTITY (Ref. 1, p. 51590)

2.4.2.1.1 Hazardous Constituent Quantity (Tier A) (Ref. 1, pp. 51590, 51591)

Description The hazardous constituent quantity for Source 3 could not be adequately determined according to the HRS requirements; that is, the total mass of all CERCLA hazardous substances in the source is not known and cannot be estimated with reasonable co nf idence (Ref. 1, Section 2.4.2.1.1). There are insufficient historical and current data (Manifests, PRP records, State records, Permits, Waste concentration data, etc.)available to adequately calculate the total or partial mass of all CERCLA hazardous substances in the source and the associated releases from the source. Therefore, there is insufficient information to evaluate the associated releases from the source to calculate the hazardous constituent quantity for Source 3 with reasonable co nf idence. Scoring therefore proceeds to the evaluation of Tier B, hazardous wastestream quantity. Hazardous Constituent Quantity Assigned Value: Not Scored

2.4.2.1.2 Hazardous Waste s tream Quantity (Tier B) (Ref. 1, p. 51591)

Description The hazardous wastestream quantity for Source 3 could not be adequately determined according to the HRS requirements; that is, the total mass of all hazardous wastestreams and CERCLA pollutants and contaminants in the source is not known and cannot be estimated with rea sonable confidence [Ref. 1, pp. 51591 (Section 2.4.2.1.2)]. There are insufficient historical and current data (Manifests, PRP records, State records, permits, etc.) available to adequately calculate the total or partial mass of all CERCLA hazardous wastestream and CERCLA pollutants and contaminants in the source and the associated releases from the source. Therefore, there is insufficient information to evaluate the associated releases from the source to calculate the haz ardous wastestream quantity for Source 3 with reasonable co nf idence. Sum (pounds): NA Sum of Wastestream Quantity/5,000 (Table 2

- 5): NA

Hazardous Waste s tream Quantity Assigned Value (W): Not Scored

2.4.2.1.3 Volume (Tier C) (Ref. 1, p. 51591)

Desc ription

Because the horizontal and vertical extent of the source has not been fully characterized, it is not possible to adequately determine the volume of this source. As a volume cannot be determined, a value of zero is assigned. (Ref. 1, Table 2

- 5 , p. 51591 ).

Volume Assigned Value (V): 0

2.4.2.1.4 Area (Tier D) (Ref. 1, p. 51591)

Description

Source 3 is evaluated as an pile and covers roughly 1.7 4 acre as estimated by the sampling team and shown in photo 38 (Ref. 3, p. 177) (Ref . 1, Table 2

- 5, p. 51591; Figure 2; 3, p. 177; 33 ; 37 )

. There are 43,560 square feet in one acre, yielding 75794.4 sq. ft. in 1.74 acre s

.
Since the equation for a ssigning v alue (Ref. 1, Table 2

- 5) is the area divided by 13, t he HWQ value is equal to 75794.4 ft 2 / 13 = 5830.3 Area Assigned Value (A) : 5830.3

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 37

## 2.2.1 SOURCE IDENTIFICATION

Source Number : 4

Name of source: Eastern South Percolation Pond

Source Type : Pile

Description and Location of Source (with reference to a map of the facility ):

The Eastern South Percolation Pond cover s approximately 3.98 acres (Figure 2, Ref. 36, p. 1; 33), and receive d wastewaters from the Rectifier Oil Separator Sump, Facility Production Area storm water, non

contact equipment cooling water, Sewage Treatment Plant, Restroo ms and Change House sinks, Laboratory Sinks, laboratory non

- contact cooling water, laboratory non

- solvent waste water, plant wide lavatories and sinks, Rectifier yard storm water and non

- contact cooling water, casting mold cleaning water, casting mold stea m cleaning, contact cooling water from direct chill casting of aluminum ingots, and Fabr ication Shop Steam Cleaning Bay (Ref. 7, pp. 4, 5 ). Process water that overflows from the Central South Percolation Pond (i.e., Source 3) flows into the eastern pond, p roviding additional surface area for percolation as needed. The south percolation ponds are all interconnected, with the initial plant outfalls (004 and 005) piped into the weste rnmost pond (photo 38, p. 178). Because the western pond was still functioning fully as a percolation pond (allowing for the transmission of liquids to migrate to the shallow ground water onsite), this source has been evalua ted as a pile (Ref. 7, p. 5). Because this source received effluent containing anode material as well as disch arge from several shops, and storm water runoff, the 2014 SRR found it to contain metals (Refs. 7, pp. 5, 6, 25; 19, pp. 12, 17, 22).

C o

- located source liquid and solid samples ( CF

- SW/SD

- 22) were collected from within the area delineated as the Eastern South Percolation Pond (Figure 6) (Ref. 3, pp. 48, 49) . Concentration s of SVOCs and metals were detected above the reporting limit in liquid source samples collected from the Eastern South Percolation P ond . SVOCs, pesticides, and metals were detected at co ncentrations above the reporting limits in the solid

- matrix waste source sample collected from the eastern South Percolation Ponds.



## 2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

Source Samples:

All source sampling was done in accordance with EPA ERT SOPs 2012, 2013, 2016, and 2017 (Ref. 32,

p. 47 ). For example, at each location

, the aqueous sample was collected before the solid

- matrix sample to ensure that the aqueous sample didn’t include any solids disturbed by the sampling process

. A new di sposable plastic scoop was used to collect each solid

- matrix sample from a depth of approximately 0

- 6 inches below the water surface. All samples were collected during the same September/ October 201 3 sampling event, over a period of nine days ( September 23 to October 1 ) (Ref. 3 , p p. 27, 37 ).

Source Sediment Samples:

The analytical results of the soil waste mix source sample ( CF

- SD

- 22 [Figure 6]) from the eastern South Percolation Pond are presented in Tables E17

- E23, Appendix E of the SRR (Ref. 3, Tables E17

- E23, pp. 263

- 275). Laboratory data and validation reports are presented in Appendix F of the same document (R ef

. 3 a , App. F, Section 7, pp. 1431 , 1443, 1444 ) . Contaminant concentrations in source sediment were

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 38HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 39 considered det ections when the result was greater than the analytical reporting limit. S everal TAL metals contaminants were detected in waste source samples collected from the Eastern South Percolation Pond that were consistent with wastes expected to be found:

Hazardo us Substance Evidence References Sample No. RL (mg/kg) Concentration (mg/kg) Arsenic 1 2.3 Ref s . 3, pp. 47

- 49, App. B, p. 178 ; App. D, p p . 205, 207 ; App E, Table E22, pp. 273 ; 3a , App. F, Section 5, pp. 393, 401

, Section 7, pp. 1431, 1443 , 1444 Chromium CF

- SD -22 1 9.1 Manganese (MH0066) 1.5 83.4

Zinc 6 45.4

Notes: mg/kg milligrams per kilogram
RL The value shown is the sample specific Contract Required Quantitation Limit (Ref. 30)

.
Source Sample Information

The source samples listed above were collected during the 201 3 sampling effort conducted by START for the EPA. Samples were analyzed using the Contract Laboratory Program Statement of Work for
I norganic Superfund Methods, ISM01.3

— Metals, Mercury and Cyanide (Ref s

. 3, pp. 34; 3a, App. F, Section 7, pp. 1350, 1355 ). Laboratory samples were analyzed by the CLP laborator y ALS Laboratory Group in Salt Lake City, Utah (Ref. 3, p. 46 , 3a, App. F, Section 7, p. 1431 ).

Source Aqueous Samples:

The analytical results of the aqueous waste source sample ( CF

- SW

- 22 [Figure 6]) from the eastern South Percolation Pond are presented in Tables E 9-E15 , Appendix E of the SRR (Ref. 3, Tables E9

- E15, pp. 247-261). Laboratory data and validation reports are presented in Appendix F of the same document (R ef

. 3a , App. F, Section 7, pp. 1431 -1516) . Contaminant concentrations in the source aqueous sample were considered detections when the result was greater than the analytical reporting limit. S everal TAL metals contaminants were dete cted in waste aqueous sample collected from the Eastern South Percolation Pond that were consistent with wastes expected to be found:

Hazardous Substance Evidence References Sample No. RL ( μg/L ) Concentration ( μg/L )
Arsenic 1 1.6 Ref s . 3, App. D, p. 20 7 ; App E, Table E14, p. 257 ; 3a , App. F, Section 5, p. 661, 672, Section 7, pp. 1350, 1369 Chromium 2 8.4

Cyanide CF

- SW -22 (MH0040) 10 24.8 Ref s . 3, App. D, p. 20 7 ; App E, Table E14, p. 257 ; 3a , App. F, Section 5, p. 661, 672, Section 7, pp. 1350, 1360 Manganese 1 92.1 Ref s . 3, App. D, p. 20 7 ; App E, Table E14, p. 257 ; 3a , App. F, Section 5, p. 661, 672, Section 7, pp. 1350, 1369 Zinc 2 49.3

Notes μg/L micrograms per liter
RL Reporting Limit. The value shown is the sample specific Contract Required Quantitation Limit (Ref. 30)

.HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 40 Source Sample Information

The source samples listed above were collected during the 201 3 sampling effort conducted by START for the EPA. Samples were analyzed using the Contract Laboratory Program Statement of Work for
I norganic Superfund Methods, ISM01.3

— Metals, Mercury and Cyanide (Ref s

. 3, pp. 34; 3a, App. F, Section 7, pp. 1350, 1355 ). Laboratory samples were analyzed by the CLP laborator y ALS Laboratory Group in Salt Lake City, Utah (Ref. 3, p. 46).



## 2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY (Ref. 1, p. 51588)

START did not observe a maintained and engineered cover, a liner, or a functioning, run -on/run- off control system during the 2013 field sampling event

. Further, since this source is designed to allow water to percolate into the aquifer below the plant it can’t have a liner of any low transmissivity (Refs. 3 , p. 23; 6, p. 5; 7, pp. 4, 5, 26; 19, p. 17 ).

Containment Description Containment Value References

Gas release to air: NS

Particulate release to air: NS

Release to Ground water: No liner present 10 Ref s. 1, Table 3 -2; 3, p. 23; 6, p. 5; 7, pp. 4, 5, 26; 19, p. 17

Release vi a overland migration: NS

Notes: NS = Not Scored



## 2.4.2 HAZARDOUS WASTE QUANTITY (Ref. 1, p. 51590)

2.4.2.1.1 Hazardous Constituent Quantity (Tier A) (Ref. 1, pp. 51590, 51591)

Description

The hazardous constituent quantity for Source 4 could not be adequately determined according to the HRS requirements; that is, the total mass of all CERCLA hazardous substances in the source is not known and cannot be estimated with reasonable co nf idence (Ref. 1, Section 2.4.2.1.1). There are insufficient historical and current data (Manifests, PRP records, State records, Permits, Waste concentration data, etc.) available to adequately calculate the total or partial mass of all CERCLA hazardous substances in the source and the associated releases from the source. Therefore, there is insufficient information t o evaluate the associated releases from the source to calculate the hazardous constituent quantity for Source 4 with reasonable co nf idence.

Scoring therefore proceeds to the evaluation of Tier B, hazardous wastestream quantity. Hazardous Constituent Quantity Assigned Value: Not Scored2.4.2.1.2 Hazardous Waste s tream Quantity (Tier B) (Ref. 1, p. 51591)

Description

The hazardous wastestream quantity for Source 4 could not be adequately determined according to the HRS requirements; that is, the total mass of all hazardous wastestreams and CERCLA pollutants and contaminants in the source is not known and cannot be estimated with reasonable confidence [Ref. 1, pp. 51591 (Section 2.4.2.1.2)]. There are insufficient historic al and current data (Manifests, PRP records, State records, permits, etc.) available to adequately calculate the total or partial mass of all CERCLA hazardous wastestream and CERCLA pollutants and contaminants in the source and the associated releases from the source. Therefore, there is insufficient information to evaluate the associated releases from the source to calculate the hazardous wastestream quantity for Source 4 with reasonable confidence.

Sum (pounds): NA Sum of Wastestream Quantity/5,000 (Ta ble 2

- 5): NA

Hazardous Waste s tream Quantity Assigned Value (W): Not Scored

2.4.2.1.3 Volume (Tier C ) (Ref. 1, p. 51591)

Description

Because the horizontal and vertical extent of the source has not been fully characterized, it is not possible

to adequately determine the volume of this source

. As a volume cannot be determined, a value of zero is assigned. (Ref. 1, Table 2

- 5 , p. 51591)

.
Volume Assigned Value (V): 0

2.4.2.1.4 Area (Tier D ) (Ref. 1, p. 51591)

Description

Source 4 is evaluated as a pile and covers roughly 3.98 acres as calculated using GIS to determine the area of a provided polygon by the START project manager (Ref. 1, Table 2

- 5

- p. 51591; 3, pp. 47

- 48, Figure 2; 36 , p. 1; 33). There are 43,560 square feet in one acre, yielding 173, 368.8 sq. ft. in 3.98 acres.

Since the equation for a ssigning v alue (Ref. 1, Table 2

- 5) is the area divided by 13, t he HWQ value is equal to 173, 368.8 ft 2 / 13 = 13, 336. 06

Area Assigned Value (A) : 13,336. 06

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 41

## 2.2.1 SOURCE IDENTIFICATION

Source Number : 5

Name of source: West Landfill

Source Type : Landfill

Description and Location of Source (with reference to a map of the facility ):

The W est L andfill operated as an unlined solid waste landfill from 1955

- 1981 (Figure 2)

. The facility disposed of general garbage

, including paper, scrap from the shops, strapping, steel scrap and scrap wood, and spent potliner ( from 1955

- 1970). Spent potliner wasn’t listed by the EPA as hazardous waste until 1991. State required semi

- annual ground water monitoring around the landfill had detected elevated concentrations of cyanide, a byproduct of aluminum production found in the c arbon anode potliner (a RCRA hazardous waste) . The landfill was capped with a clay cap in approximately 1992 and a synthetic

ca p in 1994 ( Refs. 3, p. 21; 19, pp. 12, 15, 16; 19, p. 13 ) . The landfill covers approximately 7.8 acres a s determined using GIS (Ref s . 3, pp. 48, 49 ; 31, p. 1; 33 ).

A total of four monitoring well locations were sampled for contaminants associated with th is source. Two background locations CF

- GW

- MW

- 01 (and duplicate CF

- GW

- MW

- 18) located approximately 0.5 miles upgradient of the landfill and monitoring well CF

- GW

- MW

- 02 located approximately 300 feet upgradient of the landfill ( Figures 3 and 5). Four wells located immediately downgradient of the landfill (CF

- MW

03, CF

- MW

- 04, CF

- MW

- 05, and CF

- MW

- 06) (Figure 5 ) were sampled ( Figure 3; Ref. 3, pp. 33, 35, 36, 51

- 55 ). Concentrations of metals were detected above the reporting limit in ground water samples collected from the downgradient wells and will be used to characterize this source (Ref s . 3, pp. 51

- 55, 103, 241, 242, 287, Table E 29; 3a, App. F, Section 7, pp. 1458, 1469, 1470, 1471, 1472, 1473, 1482, 1486, 1497

- 1499, 1505, 1506, 1507; Figure 5)



## 2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

Background Samples:

All source sampling was done in accordance with EPA ERT SOPs 2012, 2013, 2016, and 2017 (Ref. 32,

p. 47 ) . All samples were collected during the same September/ October 201 3 sampl ing event, over a period of nine days ( September 23 to October 1) (Ref. 3, p. 27). The monitoring wells downgradient of the West landfill will be compared to the site monitoring well located to the north of the facility area (CF

GW

- MW

- 01), as well as to the monitoring well immediately upgradient of the landfill (02), to ensure comparability (Figure 3, Section 3.1 Table, p.50).

Because the landfill was capped in the early 1990’s (Ref s

. 3, p. 21; 19, p. 1 6 ), the source was characterized by sampling upgradient and downgradient from the monitoring wells installed by the facility, rather than collect samples dir ectly from th e capped landfill. The analytical results of the background sample being evaluated based on their impact in scoring are shown below (Refs. 3, pp. 21, 241, Table E 6). Results flagged with a J and above the reporting limit , were applied a matrix factor as de scribed in EPA guidance Using Qualified Data to Document an Observed Release and Observed Contamination to determine if the calculated result was above the analytical reporting limit , and therefore useable for HRS purposes ( Refs. 3, p. 48; 17, pp. 1

- 5 ). ST ART took this approach to characterize the source in the absence of actual source samples, and erred on the side of caution using the Directive to establish the observed release.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 42

### Hazardous Substance Location Concentration (μg/L) RL (μg/L) References

Total Arsenic (dissolved) CF

- GW

MW

- 01 (MH5099) 1.0U 1.0 Refs. 3, Table E30, p. 289, App. D, pp. 218; 3a, App. F Section 5, pp. 1135, Section 7. pp. 1,458, 1,482 ; 44

CF

- GW

MW

- 02 (MH5002) 1.0U 1.0 Refs. 3, Table E30, p. 243, App. D, pp. 216; 3a, App. F Section 5, pp. 1135,

1429, Section 7. pp. 1,458, 1,469, 1,470 ; 44

Total Chromium (dissolved) CF

- GW

MW

- 01 (MH5099) 2.0U 2.0 Refs. 3, Table E30, p. 289, App. D, pp. 218; 3a, App. F Section 5, pp. 1135, Section 7. pp. 1,458, 1,482 ; 44

CF

- GW

MW

- 02 (MH5002) 2.0U 2.0 Refs. 3, Table E30, p. 243, App. D, pp. 216; 3a, App. F Section 5, pp. 1135,

1429, Section 7. pp. 1,458, 1,469, 1,470 ; 44

Cyanide (Total) CF

- GW

MW

- 01 (MH0099) 5.7J

- [7.752 ] 10 Refs. 3, Table E29, p. 287, App. D, p. 218; 3a, App. F Section 5, pp. 1134, 1157, Section 7, pp. 463, 1,374, 1385 ; 44

Manganese (Dissolved) CF

- GW

MW

- 01 (MH5099) 10.9 1.0 Refs. 3, Table E30, p. 289, App. D, pp. 218; 3a, App. F Section 5, pp. 1135, Section 7. pp. 1,458, 1,482 ; 44

CF

- GW

MW

- 02 (MH5002) 6.4 1.0 Refs. 3, Table E30, p. 289, App. D, pp. 216; 3a, App. F Section 5, pp. 1135,

1429, Section 7. pp. 1,458, 1,469, 1,470 ; 44

Notes: μg/L micrograms per liter.
U The material was analyzed for, but was not detected above the level of the associated value. UJ The analyte was not deemed above the reported sample quantitation limit. However, the reported quantitation limit is approximate and may or may not represent the actual limit of quantitation necessary to accurately and precisely measure the analyte in the sample.
J

- The associated value is an estimated quantity, biased low. ( ) CLP Laboratory number [ ] The associated value is adjusted according to the EPA guidance Using Qualified Data to Document an Observed Release and Observed Contamination (Ref. 17)
RL The value shown is the sample specific Contract Required Quantitation Limit (Ref. 30).

Source Sample Information

The source samples listed above were collected during the 201 3 sampling effort conducted by START for the EPA. Sa mples were analyzed using the Contract Laboratory Program Statement of Work for
I norganic Superfund Methods, ISM01.3

— Metals, Mercury and Cyanide (Ref s

. 3, pp. 34; 3a, App. F, Section 7, pp. 1350, 1355 ). Laboratory samples were analyzed by the CLP laborator y ALS Laboratory Group in Salt Lake City, Utah (Ref. 3

, p. 46).

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 43Ground Water Samples:

The analytical results of the monitoring well samples ( CF

- MW

- 03 to CF

- MW

- 06 [Figure 6]) downgradient of the West Landfill are presented in Tables E 1

- E 8

, Appendix E of the SRR (Ref. 3, pp. 231

- 245). Laboratory data and validation reports are presented in Appendix F of the same document (R ef

. 3 a , p. 10532

- 10617) . Contaminant concentrations in the ground water samples used to characterize the

source were cons idered detections when the result was greater than the analytical reporting limit. Results flagged with a J and above the reporting limit , were applied a matrix factor as described in EPA guidance Using Qualified Data to Document an Observed Release and Ob served Contamination to determine if the calculated result was above the analytical reporting limit

, and therefore useable for HRS purposes ( Refs. 3, p. 48; 17, pp. 1

- 5, 13 ). The following TAL metals co ntaminant s were detected in ground water that are both associated with wastes deposited and exceed background levels collected :



### Hazardous Substance Location Highest Background Concentration (μg/L) Concentration (μg/L) RL (μg/L) References

Total Arsenic (dissolved) CF

- GW

MW

- 03 (MH5003) 1.0U 344 1.0 Refs. 3, Table E7, p. 243, App. D, p. 221; 3a,

App. F Section 5, pp. 1,425, 1,430, Section 7,

pp.1,458, 1,470 ; 44

Total Chromium (dissolved) 2.0U 10.3 2.0 Refs. 3, Table E7, p. 243, App. D, p. 221; 3a,

App. F Section 5, pp. 1,425, 1,430, Section 7,

pp.1,458, 1,470 ; 44

Total cyanide CF

- GW

OP

- 02 (MH00C7)

5.7J

- [7.752] 111 0.5 Refs. 3, Table E29, p. 287, App. D, p. 208; 3a,

App. F Section 5, p. 661, 675, Section 7, pp. 1,350, 1,36 0

CF

- GW

MW

- 03 (MH003) 769 10 Refs. 3, Table E6, p. 241, App. D, p. 221; 3a,

App. F Section 5, p. 659, 663, Section 7, p. 1,350, 1,359 ; 44

CF

- GW

MW

- 04 (MH004) 1040J

- 0.5 Refs. 3, Table E6, p. 241, App. D, p. 217; 3a,

App. F Section 7, pp. 462, 466, 1,332, 1,341; 17, pp. 1

- 18 ; 44

Manganese (dissolved) CF

- GW

MW

- 08 (MH5008) 10.9 109 1 Refs. 3, Table E30, p. 289, App. D, p. 215; 3a,

App. F Section 6, pp. 225, 235, Section 7. pp. 1,485, 1,499, 1,500

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 44

### Highest Hazardous Substance Location Background Concentration Concentration (μg/L) RL (μg/L) References
(μg/L) Refs. 3, Table E30, p. CF

- GW

- 289, App. D, p. 215; 3a,
MW -09 181 1 App. F Section 6, p. (MH5009) 225, 236, Section 7. pp. 1,485, 1,500

Notes: μg/L - micrograms per liter. U The material was analyzed for, but was not detected above the level of the associated value. The associated value is the reporting limit.
J- The associated value is an estimated quantity, biased low. ( ) CLP Sample ID [ ] The associated value is adjusted according to the EPA guidance Using Qualified Data to Document an Observed Release and Observed Contamination (Ref. 17)

. RL The value shown is the sample specific Contract Required Quantitation Limit (Ref. 30).

Source Sample Information

The source samples listed above were collected during the 201 3 sampling effort conducted by START for the EPA. Samples were analyzed using the Contract Laboratory Program Statement of Work for
I norganic Superfund Methods, ISM01.3— Metals, Mercury and Cyanide (Ref s

. 3, pp. 34; 3a, App. F, Section 7, pp. 1350, 1355 ). Laboratory samples were analyzed by the CLP laborator y ALS Laboratory Group in Salt Lake City, Utah (Ref. 3, p. 46).



## 2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY (Ref. 1, p. 51588)

Neither a liner

, nor a functioning, run -on/run- off control system were documented during the 201 3 field sampling event: there is an engineered clay cap in pla ce. The absence of a liner was provided by the facility in their Powerpoint presentation (Refs. 3; 9, p. 16 ).

Containment Description Containment Value References

Gas release to air: NS

Particulate release to air: NS

Release to Ground water: No liner present 10 Ref s. 1, Table 3 -2; 3, pp. 51-57; 6, p. 5
Release via overland migration: NS

. NS

Notes: NS = Not Scored

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 45

## 2.4.2 HAZARDOUS WASTE QUANTITY (Ref. 1, p. 51590)

2.4.2.1.1 Hazardous Constituent Quantity (Tier A) (Ref. 1, pp. 51590, 51591)

Description

The hazardous constituent quantity for Source 5 could not be adequately determined according to the HRS requirements ; that is, the total mass of all CERCLA hazardous substances in the source is not known and cannot be estimated with reasonable co nf idence (Ref. 1, Section 2.4.2.1.1). There a re insufficient historical and current data (Manifests, PRP records, State records, Permits, Waste concentration data, etc.) available to adequately calculate the total or partial mass of all CERCLA hazardous substances in the source and the associated rel eases from the source. Therefore, there is insufficient information to evaluate the associated releases from the source to calculate the hazardous constituent quantity for Source 5 with reasonable co nf idence. Scoring therefore proceeds to the evaluation of Tier B, hazardous wastestream quantity. Hazardous Constituent Quantity Assigned Value: Not Scored

2.4.2.1.2 Hazardous Waste s tream Quantity (Tier B) (Ref. 1, p. 51591)

Description

The hazardous wastest ream quantity for Source 5 could not be adequately determined according to the HRS requirements; that is, the total mass of all hazardous wastestreams and CERCLA pollutants and contaminants in the source is not known and cannot be estimated with reasonable confidence [Ref. 1, pp. 51591 (Section 2.4.2.1.2)]. There are insufficient historical and current data (Manifests, PRP records, State records, permits, etc.) available to adequately calculate the total or partial mass of all CERCLA hazardous

wastestream an d CERCLA pollutants and contaminants in the source and the associated releases from the source. Therefore, there is insufficient information to evaluate the associated releases from the source to calculate the hazardous wastestream quantity for Source 5 wi th reasonable co nf idence. Sum (pounds): NA Sum of Wastestream Quantity/5,000 (Table 2

- 5): NA

Hazardous Waste s tream Quantity Assigned Value (W): Not Scored

2.4.2.1.3 Volume (Tier C ) (Ref. 1, p. 51591)

Description

Because the horizontal and vertical extent of the source has not been fully characterized, it is not possible to adequately determine the volume of this source. As a volume cannot be determined, a value of zero is assigned. (Ref. 1, Table 2

- 5 , p. 51591 ).

Volume Assigned Value (V): 0

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 462.4.2.1.4 Area (Tier D ) (Ref. 1, p. 51591)

Description

Source 5 is evaluated as a landfill covering roughly 7.8 acres as calculated using GIS to determine the area of a provided polygon by the START project manager (Ref . 1, Table 2

- 5

- p. 51591; Figure 2; 31, p. 1; 33)

. There are 43,560 square feet in one acre, yielding 339,768 sq. ft. in 7.8 acres.

The HWQ value per Table 2

- 5 (Ref. 1) 339,768 ft 2 / 3,400 = 99.93

Area Assigned Value (A) : 99.93

SUMMARY OF SOURC E DESCRIPTIONS

Source

No. Source Hazardous Waste Quantity

Value Source Hazardous Constituent

Quantity Complete? (Y/N) Available to Pathway (X)

Ground

water (GW) Surface Water (SW) Air

Overland/ flood GW to SW Gas Particulate

1 3,685.8 N X NS X NS NS

2 25,465.8 N X NS X NS NS

3 5

, 830.3 N X NS X NS NS

4 13,336. 06 N X NS X NS NS

5 99.93 N X X NS NS NS

Total 48,417.89

Description of Other Possible Sources not Evaluated

Given the interconnected nature of the waste streams at the facility and the hazardous substances already identified within the percolation ponds and the west landfill (Sources 1, 2 , 3, 4, and 5 ); it is possible that the other possible sources listed below would have similar types and concentrations of hazardous substances to those identified in the s ources evaluated for this HRS documentation record through chemical analysis (Refs. 7, pp. 4, 5; 9, p. 4; 19, p. 17)

. Given the age of the plant, fashion in which contaminants present onsite were handled, the fact that some of the landfills were only covered (not capped), and the connectivity of ground water with surface water in the area, these other possible sources may need to be characterized during the Remedial Investig ation/Feasibility Study (Refs. 3 , p p

. 21

- 24).

Current facility conditions are based on observations made during the September 23, 2013 through October 1, 2013 sampling event. Other possible sources observed during the 2013 sampling event , for whi ch there are no chemical analytical data or other direct evidence of hazardous substances, are listed in the table below and are shown in Figure 2 (Ref. 3, p p . 20

- 24 ). The HRS defines sources as “ Any area where a hazardous substance has been deposited, sto red, disposed, or placed, plus those soils that may have become contaminated from hazardous substance migration. In general, however, the volumes of air, ground water, surface water, and surface water sediments that may have become contaminated through

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 47mig ration are not considered sources.” ( Re f. 1, p. 51587). All of the features described below meet this definition.



### Feature (Reference) Description

East Landfill (Refs. 3, p. 21; 19, pp. 15

- 16) The Spent Potliner Landfill, also known as the East Landfill, operated from approximately 1980

- 1990 and is a clay

- lined landfill used to dispose of spent potliners prior to their declaration as a hazardous waste. The landfill was capped with a synthetic ca p and revegetated in 1990. Wet Scrubber Sludge Pond Landfill (Refs. 3, p. 21; 6, p. 3; 9, p. 13; 19, p. 15. Identified by Steve Wright, CFAC, during June 2013 facility visit.) Wet Scrubber Sludge Pond Landfill was closed in approximately 1980 and contained sludge waste generated from the Wet Scrubber System and for a period from approximately 1994

- 1998 contained spent potliner material.

Center Landfill (Refs. 3, p. 21; 8, p. 9 ; 19, p. 16.) The Center Landfill, also known as the Carbon Pile, is an unlined landfill operated from approximately 1970

- 1980. Solvents and hazardous wastes are known to have been buried on

- site in the closed landfills (West, Center and Sanitary). Sani tary Landfill (Refs. 3, p. 22; 19, p. 15.) The Sanitary Landfill is a clay

- lined historic landfill used for plant garbage. The landfill was covered with soil and re

- vegetated. Years of operation unknown. Solvents and hazardous wastes are known to have been buried on

- site in the closed landfill (Wes t, Center and Sanitary). Asbestos Landfill (Location identified by Steve Wright, CFAC, during June 2013 facility visit.) Based on a review of aerial photography the Asbestos Landfill began operation in approximately the early 2000's; date last used is un known.

North and South Leachate Ponds (Refs. 3, p. 22; 6, p. 11) Two hypalon

- lined leachate ponds were constructed on opposite ends of the East Landfill in 1980, one on the north side of the landfill (North Leachate Pond) and one on the south side of th e landfill (South leachate Pond). The ponds were used to collect runoff water from the East Landfill containing the spent potliner material and aerated during the summer months to reduce water volume and utilize ultraviolet light to break down the cyanide. According to a letter from Donald F. Ryan, Laboratory Manager at Anaconda Aluminum Co Columbia Falls Reduction Plant , to MT DEQ dated January 5, 1990, approximately 150,000 gallons of leachate water containing fluoride and approximately 3 mg/L of cyanide was drained from the South Leachate Pond into the Wet Scrubber Sludge Pond Landfill. This transfer of leachate was approved by MT DEQ (October 12, 1989 letter from John Arrigo, MT DEQ Water Quality Bureau, to Don Ryan, Anaconda Aluminum Co Columbia Falls R eduction Plant ). The South leachate Pond was dried, capped, and subsequently closed in 1993. An underground pipe leads from the North Leachate Pond to the Wet Scrubber Sludge Pond. The North Leachate Pond held cyanide

- free water containing fluoride and was subsequently drained into the Wet Scrubber Sludge Pond Landfill. The North Leachate Pond was capped and then closed in 1994. These areas were observed to be closed and covered with grass during the field sampling activities. Cathode Soaking Pits (Refs. 3 , p. 24; 13) Carbon cathode soaking pits contained water and ammonia to expedite the carbon removal process.

Other areas on the facility may also qualify as sources ; however

, sampling to date does not document association of hazardous substances with these areas

.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 48

## 3.0 GROUND WATER MIGRATION PATHWAY

3.0.1 GENERAL CONSIDERATIONS

Ground Water Migration Pathway Description

Description :

The facility is located adjacent to the west side of the Teakettle Mountain, a part of the Whitefish Range. The aquifer being evaluated consists of the unconsolidated alluvial deposits that are found in the Flathead River valley bottoms, and the smaller, localized gl acial outwash lenses that have intermingled and mixed along the margins of the mountain/valleys with the river alluvium (Ref. 20, p. 20

, F igure 18 ). In some places, the glacial outwash extends to depths of up to 94 below ground surface [bgs], and the allu vium ranges from 70 to 300 feet in thickne s s of glacial, glac i o

- lustrine, and glacial

- alluvial sed i ments. These

are u nderlain by several hundred feet of relatively impermeable till (Ref s

. 18, p.41; 20, pp. 20, 38, 40). This interbedded aquifer is hereinaf ter referred to as the Alluvial/Glacial aquifer, is the most permeable aquifer in the Kalispell Valley consisting of various water bearing gravel strata that were laid down by glaciation or the Flathead River and are interconnected above the till layer con fining the Pleistocene artesian aquifer. These deposits consist of heterogeneous mixtures of gravels, sands, silts and clays (Ref 18, p. 12 ; Figure 7 and Figure 8 of this HRS documentation record ). The thickness of the sediments at the site is known to be at least 300 feet as measured at Well TW

- 11 (Figure 7 and Figure 8 of this HRS documentation record ).

Due to the variability in topography, depth to water across the plant property ranges from less than 20 feet bgs to over 100 feet bgs (Ref 3, Table C2, p. 189 ; the Well Table in Section 3.1.1 ). While the monitoring wells on site are screened at varying depth ranges, the ground water levels measured in 2013 (Ref 3, Table C2, p. 189) and historically in 1983 and 1984 (Ref 18, p. 23) indicate hydraulic interconnectivity across the site, with ground water flow at the plant property generally south to southwest (Ref 3, Figure 3, p.99) towards the Flathead River. Drinking water wells alon g the Flathead River and downstream of the site withdraw water from the interconnected deposits that make up the Alluvial/Glacial aquifer, and there is no evidence of aquifer discontinuities between the site and the target wells along the river valley (Ref s. 18, pp. 30, 31; 20, pp. 40, 41; 8, p. 38; Figures 5, 7, and 8 of this HRS d ocumentation r ecord).

A detailed study of Site geology was conducted in the early 1980s by Hydrometrics, Inc

. (Ref 18). This study provided information on local and regional cl imate, geology, soils and hydrology. Key portions of the study are provided below.

Regional Geology:

The u pper portion of the Flathead Valley basin

, up to the Columbia Falls area, is a major structural feature formed by down dropping of a huge block of the earth's crust (Ref. 18, p. 14) . A major system of faults is assumed to exist along the contact between the valley and mountains that bound the valley on both the east and west sides to the south of Columbia Falls . This major block faulting is outside t he four mile radius of the site. The site is located in the northeast portion of the upper Flathead Valley basin, west of Teakettle Mountain (Refs. 18; p. 14; 20, p. 16)

.

The Flathead Valley basin is underlain at depth by a thick sequence of partially me tamorphosed Precambrian rocks having a total thi ckness of several tens of thousands of feet. These rocks are

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 49predominantly vari

- colored argillite, quartzite, and carbonate of the Belt Series. The rocks are tightly compacted and have very low porosity and p ermeability (Ref s . 18; p. 15; 20, pp. 13, 14 ).

Less than 0.2 miles east of the West landfill at the Anaconda Aluminum Co Columbia Falls Reduction Plant facility is Teakettle Mountain, part of the Whitefish Mountain Range. The range consists primarily of P recambrian undifferentiated sedimentary rocks of the Ravalli Group, overlain by gray, silty, dolomites of the Piegan Group. The Whitefish Range is separated from the adjacent Flathead Valley to the west by a buried north

- south trending normal fault located over eight miles to the west of the site . The downthrown western block underlies the upper Flathead River drainage, while the eastern block largely comprises the mountains. (Refs. 18, p. 16 ; 20, p p . 12 , 16 ).

Stratigraphy in the Anaconda Aluminum Co Colum bia Falls Reduction Plant area is the result of three former coalescing ice streams. Similarly, the topography, surficial geology, and near

- surface sedimentology are largely due to Pleistocene and Recent glaciation, and by post

- glacial fluvial erosion and deposition. Konizeski, mapped the area about Columbia Falls and the aluminum plant as being, “ice contact, drumlin

- forming clay and boulder till; locally overlain by glaciolacustrine deposits". (Refs. 18, p. 21 ; 20; p. 1 6; 8, p. 38 ).

Superimposed upon the glacial stratigraphy is the depositional result of late Pleistocene and Recent glaciofluvial outwash from the Flathead River which flows westerly across the southern border of the site

, and less so from Cedar Creek, which descends to the west of the Anaconda Aluminum Co Columbia Falls Reduction Plant area from the Whitefish Mountain Range to the north. The Flathead River and Cedar Creek flow primarily through the recent continuous alluvium consisting dominantly of silts and sands comprising the modern flood plains (Ref. 18; p. 17; 20, pp. 41, 43; 8, p. 38 ).

Ground water is widely used in the Flathead River drainage primarily for domestic and stock use and to a lesser extent for irr igation, industry and public water supply. The majority of wells are located in the basin's large intermountain river valleys , such as Columbia Falls’ two municipal wells (Ref s

. 24; 38; Figure 5) . The occurrence, distribution and quality of ground water is closely related to the geology of the basin. The ground water resources are greatly influenced by three geological units. These are Precambrian bedrock, Pleistocene glacial deposits and recent alluvial deposits (Ref. 18; p p . 2 0, 21 ).

The entire Flathead Valley basin is underlain by a thick sequence of rocks of Precambrian age ( over 600 million years old). Due to their low permeability, very little water is found in these rocks. If fractured and broken zones are encountered, the rocks can yield small amoun ts of fair to good quality water to wells (Ref. 18; p. 2 1 ) . This Precambrian layer is located below the alluvial/glacial aquifer present within the Anaconda Aluminum Co Columbia Falls Reduction Plant area as well as the wells used to document an observed release (Ref. 20, p. 20 , Figure 18 ).

Glacial o utwash channels and layers of lenses of sand and gravel also occur in these mountain areas and are the principa l water

- yie l ding materials where the alluvial d eposits are not present . Thickness of glacial deposits varies from thin veneer a few feet thick, to as much as several hundred feet. Wells drilled into glacial deposits vary widely in yield. Some wells yield little water, whereas other wells yield over 1,0 00 gallons per minute. Ground water is recharged in the glacial deposits by infiltration of water from irrigated land; from numerous reservoirs, streams and lakes in the area and from precipitation. Glacial deposits are exposed or underlie almost all of th e intermountain valley a reas in the basin (Ref. 18; p. 2 2 ).

Alluvial flood plain deposits of unknown thickness are present along major streams in the basin. These sediments are Pleistocene and r ecent in age

, and are derived from the surrounding bedrock an d glacial debris. In the Flathead Valley

, alluvium underlies the flood plain of the Flathead river and constitutes an extensive aquifer which is about 30 feet thick and supplies water to a large number of wells in the valley

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 50bottom . The aquifer is recharge d by precipitation and irrigation water; is very permeable and can yield large quantities of good quality water to wells. In other areas, recent alluvial deposits supply small to moderate quantities of water to wells. Although the quality of water in recen t alluvial deposits generally is good, there are some localized areas where it is fair to poor (Ref. 18; p p

. 22, 2 4 ).

Site Specific Geology and Hydrogeology:

The Anaconda Aluminum Co Columbia Falls Reduction Plant is located on the eastern margin of the upper Flathead Valley, approximately one

- half mile northwest of where the Flathead River leaves the mountains through Badrock Canyon. The Flathead Valley is a southern extension of the structural depression termed t he Rocky Mountain Trench. The major axis of the valley is generally north east /southwest. Surface drainage of the property is to the south (Ref. 18

, p. 15 ).

A series of nine piezometer placements made by Hydrometrics in July 1980 provided stratigraphic

ev idence to substantiate glacial and glaciofluvial deposition. All nine sites showed a succession of till and small patches of glaciolacustrine clays, capped by from one foot to greater than twelve feet of imbricated glaciofluvial and alluvial sands, gravels and cobbles. This capping unit appeared to be more extensive and thicker north and west of the plant complex than it was to the northeast (Ref. 18; p. 37 ).

Driller's logs from production and hydrologic test wells in the vicinity of the plant provide more evidence of successive depositional modes. Examination of these logs indicate that from 70 to greater than 300 feet of interbedded glacial, glaciolacustrine, and glaciofluvial sediments underlie the surface of the site with minor occurrences of well

- sorte d, permeable gravels and cobbles. Hydrologic testing indicates a zone of highly transmissive cobbles and gravels at depths greater than approximately 100 feet along the southern edge of the plant property . This zone probably r epresents buried glacial outwa sh associated with advancing or retracting phases of the Flathead Glacier which entered the valley through Badrock Canyon

, as well as high transmissivity gravels associated with the reworking of glacial debris by the ancestral Flathead River (Ref. 18; pp. 37, 38).

- Aquifer Interconnections/Distance from Source

Description

Ground water is present in the glacial (where present) and alluvial deposits beneath the plant property. The occurrence, distribution and abundance of ground water is closely related to subsurface geological conditions. As described above, this area was influenced by several glacial events and hydrogeology of the area is complex (Ref. 18

, pp. 38, 39, 42, 43). The glacial and alluvial aquifers are considered to be inte rconnected at the site and within two miles of the sources along the river valley due to the absence of any confining layers or aquatards separating the glacial outwash hydrologic unit from the alluvial unit as shown in the cross

- sections (Figures 7 and 8)

. Further, the presence of site contaminants in ground water on site as well as in a Level I actual contamination well demonstrate an interconnection and absence of discontinuities between the sources and the target well (Section 3.3.2 of this HRS do cument ation r ecord). In addition

, all the layers appear to have hydraul ic conductivitie s within two orders of magnitude ( Ref. 1, Table 3

- 6)

. The alluvial/glacial aquifer extends downstream at least to the location of the community well CF

- GW

- OP

- 02 and constitutes a single hydrogeologic unit, i.e., the Alluvial/Glacial aquifer (Refs. 8, p. 38; 18, pp. 37, 38; 20, pp. 20, 38, 40).

Geology of Anaconda Aluminum Co Columbia Falls Reduction Plant area, including the community well (CF

- GW

- OP

- 02), are sho wn in Figures 7 and 8 of this HRS d ocumentation r ecord. The cross section locations are shown in Figure 2. The cross sections show the absence of any confining layer between the

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 51prevalent alluvial/gravel water bearing strata and the glacial outwash that overlaps the alluvial along the valley sides.

- Aquifer Discontinuities within Target Distance Limit

Description

In the vicinity of the Anaconda Aluminum Co Columbia Falls Reduction Plant site

, the alluvial aquifer is hydraulically connected with layers/lenses of the glacial aquifer that contain significant supplies of ground water and are in direct contact with the alluvial aquifer. T he alluvial /glacial aquifer is present in valley

- fill alluvium that is continuous between the areas of the sources and the Flathead River (Ref s. 18, pp. 37, 38; 20, pp. 8, 10). There is no evidence that any geologic (e.g., major faults, intrusive formations such as dikes or sills), topographic, or other structure or feature (e.g., erosional channels and large bodies of water), that entirely transects the alluvial aquifer and that creates a continuous boundary to ground water flow, exists anywhere between the sources and the Flathead River (Ref s. 18, pp. 37, 38 ; 20, pp. 8, 10, 16 ; Figure s 7 and 8 of this HRS documentation record ). The interconnected aquifers are found in the river valley that extends southward to the Swan Range, south of the Flathead River. The mountain ranges of the study area are shown in Refe rence 20, p. 16, Figure 14; 5, p. 31. The Teakettle Mountain acts as an aquifer boundary ( discontinuity) for HRS purposes (Ref. 20, p. 16 , Figure 18). Furthermore the Flathead
R iver does not entirel y transec t the combined aquifer as described in section 4.2.1.1 of this HRS documentation record

.

Evidence that there are no discontinuities between the source areas and target wells includes that all seepage water from the percolation ponds that had entered the alluvial aquifer eventually reached the river (R ef. 7, pp. 4, 5). Further, the presence of site contaminants in ground water on site as well as in a Level I actual contamination well demonstrate an absence of discontinuities between the sources and target well (Section 3.3.2 of this HRS d ocumentation r ecord).

Aquifer

Name Is Aquifer Interconnected within 2 miles? (Yes/No) Is Aquifer Continuous within 4

- Mile TDL? (Yes/No) Is Aquifer Karst? (Yes/No) References

Alluvial Aquifer Yes Yes, within the Flathead River valley/west of Teakettle Mountain No Refs. 3, pp.16, 17; 5, pp. 9

- 11; 18, pp. 20-22, 24, 37-38, 51; 20, p. 16, 20, 38, 40

Glacial Aquifer Yes Yes No Refs. 3, pp.16, 17; 5, pp. 9

- 11; 18, pp. 20-22, 24, 37-38, 51; 20, p. 16, 20, 38, 40



## 3.1 LIKELIHOOD OF RELEASE (Ref. 1, p. 51595)

3.1.1 OBSERVED RELEASE (Ref. 1, p. 51595)

Aquifer Being Evaluated: Alluvial /Glacial Combined Aquifer

Chemical Analysis

Prior to ground water sample collection, ground water was field screened with a Horiba U -50 Series Multi

- Parameter water quality meter to determine water quality parameters and results recorded in the

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 52field logbook for temperature, conductivity, pH, dissolved oxygen, and oxygen reduction potential. After three well volumes were purged, ground water was collected from each well into a 5

- gallon bucket and the water quality meter probe placed in the bucket and allowed to sit until the readings stabilized. The readings were then recorded in the field logbook (Ref s

. 3, p. 35; 32, p. 47)

.
Decontamination of the meter was conducted by spr aying the meter with a non

- phosphate detergent solution followed by a deionized water rinse in conformance with the SOP presented in the approved SAP ( Ref. 32, p. 47 ).

Ground water samples were collected from a total of 16 locations on and offsite. Prior to sample collection activities, three well volume casings were purged from each on plan t property well . Collection of onsite ground water samples was accomplished using the dedicated pumps installed in the wells with the exception of CF

- GWMW

- 01, CF

- GM

- MW

- 03, CF

- GM

- MW

- 06, and CF

- GM

- MW

- 07. CF

- GW

- MW

01 did not have a dedicated pump installed in the well and CF

- GM

- MW

- 03, CF

- GM

- MW

- 06 and CF

GM

- MW

- 07’s dedicated pumps were not operational during the sampling event

. Wells that had dedicated

pumps were conne cted to a Coleman Powermate 6250 generator and the pump turned on. The samples were then collected from the sample port or spigot on the well. For the wells that did not have dedicated pumps installed, a Grundfos Redi

- Flow 2 submersible pump was used. The pump was lowered into the well until it reached the bottom of the well. The pump was then extracted approximately 2 feet above the total depth to avoid intake of sediments. The pump was connected to a Lincoln Electric Ranger generator, the pump turned on a nd the samples collected directly from the pump tubing (Refs. 3, p. 35; 32, p. 47).

Decontamination of the pump and tubing was conducted by submersing the pump and tubing into a bin of tap water and pumping the rinse water through the pump. This was follo wed by submersion and pumping with a non

- phosphate detergent solution, followed by a rinse with deionized water in conformance with the SOP presented in the approved SAP ( Ref s

. 3, pp. 35, 36; 32, p. 47 ).

Analysis of the samples collected during 2013 sampling event were performed according to the United States Environmental Protection Agency Contract Laboratory Program Statement of Work for Inorganic Superfund Methods, ISM01.3 (5/2005) (Ref. 3 a , App. F section 7, p. 1355).

Background Ground Water Samples:

Field measurements were collected from the background wells CF

- GM

- MW

- 01 and CF

- GM

- MW

- 0 2. CF

- GM

- MW

- 01 was measured within the interconnected alluvial aquifer to a total depth of approximately 15 3.15 feet bgs (3,013 feet amsl) and static ground water was measured at 9 6.85 feet b g s (3,073 feet amsl) prior to sampling (Ref. 3, App. D, p. 195 ) . The screened interval was not noted in the boring log (Ref. 8, pp. 264, 265). CF

- GM

- MW

- 0 2 was measured within the interconnected alluvial aquifer to a total depth of 69.24 feet bgs (3, 134 feet amsl) and static ground water was measured at 60.17 feet b g s (3,144 feet amsl) prior to sampling (Ref. 3, App. D, p. 195 ; the Well Table in Section 3.1.1 ). The well is not screened (Ref. 3, p.115).

A site background sa mple (CF

- GM

- MW

- 01) w as collected from a ground water monitoring well located north and up gradient of the Site features, but within the Facility boundary (Figure 5) (Ref s . 3, pp. 51; App . D, pp. 218 ; 3a

, App. F Section 5, pp. 1130, 1135, Section 7, p p

. 460, 463, 1, 402, 1,458, 1,470, 1,482 ). An additional monitoring well (CF

- GW

- MW

- 02) was selected immediately upgradient of the West Landfill to provide another background in a more similar regime to the monitoring wells used to document the observed release (Figure 5) (Ref s . 3, pp. 241, 243, App. D, p. 216 ; 3a

, App. F Section 5, p. 1130, Section 7, p p. 463, 1, 332, 1,343, 1,458, 1,470 ) ; however, the higher sample result from either background was used to document an observed release to err on the side of caut ion

.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 53The background samples listed below were collected during the 201 3 sampling effort conducted by START for the EPA. Samples were analyzed using the Contract Laboratory Program Statement of Work for I norganic Superfund Methods, ISM01.3

— Metals, Mercur y and Cyanide (Ref s. 3, pp. 34; 3a, App. F, Section 7, pp. 1350, 1355 ). Laboratory samples were analyzed by the CLP laborator y ALS Laboratory Group in Salt Lake City, Utah (Ref. 3, p. 46).



### Hazardous Substance Location Concentration (μg/L) RL (μg/L) References

Arsenic

Total (dissolved) CF

- GW

MW -01 (MH5099) 1.0U 1.0 Refs. 3, Table E30, p. 289, App. D, pp. 218; 3a, App. F Section 5, pp. 1135, Section 7. pp. 1,458, 1,482 ; 44

CF

- GW

MW -02 (MH5002) 1.0U 1.0 Refs. 3, Table E30, p. 243, App. D, pp. 216; 3a, App. F Section 5, pp. 1135,

1429, Section 7. pp. 1,458, 1,469, 1,470 ; 44

Chromium Total (dissolved) CF

- GW

MW -01 (MH5099) 2.0U 2.0 Refs. 3, Table E30, p. 289, App. D, pp. 218; 3a, App. F Section 5, pp. 1135, Section 7. pp. 1,458, 1,482 ; 44

CF

- GW

MW -02 (MH5002) 2.0U 2.0 Refs. 3, Table E30, p. 243, App. D, pp. 216; 3a, App. F Section 5, pp. 1135,

1429, Section 7. pp. 1,458, 1,469, 1,470 ; 44

Cyanide (Total) CF

- GW

MW -01 (MH0099) 5.7J- [7.752] 10 Refs. 3, Table E29, p. 287, App. D, p. 218; 3a, App. F Section 5, pp. 1134, 1157, Section 7, pp. 463, 1,374, 1385 ; 44

Manganese (Dissolved) CF

- GW

MW -01 (MH5099) 10.9 1.0 Refs. 3, Table E30, p. 289, App. D, pp. 218; 3a, App. F Section 5, pp. 1135, Section 7. pp. 1,458, 1,482 ; 44

CF

- GW

MW -02 (MH5002) 6.4 1.0 Refs. 3, Table E30, p. 289, App. D, pp. 216; 3a, App. F Section 5, pp. 1135,

1429, Section 7. pp. 1,458, 1,469, 1,470 ; 44

Notes: μg/L micrograms per liter.
U The material was analyzed for, but was not detected above the level of the associated value.
UJ The analyte was not deemed above the reported sample quantitation limit. However, the reported quantitation limit is approximate and may or may not represent the actual limit of quantitation necessary to accurately and precisely measure the analyte in the sample.
J- The associated value is an estimated quantity, biased low. ( ) CLP Laboratory number [ ] The associated value is adjusted according to the EPA guidance Using Qualified Data to Document an Observed Release and Observed Contamination (Ref. 17)

. RL The value shown is the sample specific Contract Required Quantitation Limit (Ref. 30).

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 54Contaminated Ground Water Samples :

Field measurements were collected from the contaminated wells. Sample CF

- GW

- MW

- 03 was collected from monitoring well TW17 which is completed within the Alluvial/Glacial aquifer to a depth of 90 feet bgs (3

, 047 feet amsl) screened between 70 and 85 feet bgs; ground water was static at 6 3.3 feet bgs after completion (Re f. 3, p . 130 ; the Well Table in Section 3.1.1 ). Sample CF

- GW

- MW

- 04 was collected from monitoring well TW2 1 which had a field measured total depth of 94.74 feet bgs ; ground water elevation

was measured at 3058.88 feet bgs ( Ref. 3, App. C, p. 189 ). Sample CF

- GW

- MW

- 09 was collected from monitoring well W8

- TW2 which had a field measured total depth of 54.29 feet bgs ; ground water elevation was measured at 3055.85 feet bgs ( Ref. 3, p. 112; App. C, p. 189 ). Sample CF

- GW

- OP

- 02 was collected from a privately owned well currently supplying five homes west of the site and completed to a depth of 169 feet bgs (Ref. 3, pp. 15 3

- 155, Appendix D, p. 208 ; 43, p. 1 ). A compilation of the well information obtained for the wells sampled during the 2013 event is found in the table below.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 55Sample ID 1 Well ID 2 Geographical Coordinates UTM Zone 11 (NAD83) 3 Top of Casing Elevation (ft amsl) * 4 Ground Surface Elevation (ft ams l ) * 4 Field Measured Depth to Ground
water (ft btoc) 5 Ground
water Elevation* (ft amsl) 6 Boring Log Static

Water Level from TOC (ft) 7 Boring TD / Well TD (ft bgs) 7 Screen Interval (ft bgs) 7 Field Measured TD (ft btoc) 5 Latitude Longitude

CF

- GW

- MW

- 01 W2

- CFMW1 48.4077268600

- 114.141032691 3170 3168 96.85 3073 96.79

-- -- 153. 15

CF

- GW

- MW

- 02 TW9 48.4008761600

- 114.132919717 3205 3203 60.17 3144 Dry 8 195 / 163 None 69.24

CF

- GW

- MW

- 03 W11

- TW17 48.3993389588

- 114.136443294 3139 3137 79.52 3059 63.3 90 / 90 70

- 85 82.1

CF

- GW

- MW

- 04 W4

- TW21 48.3984139600

- 114.137148400 3137 3135 78.12 3059

-- -- -- 94.74

CF

- GW

- MW

- 05 W5

- TW15 48.3979853801

- 114.135871277 3136 3134 75.79 3060 70 105 / 96 78

- 88 92.44

CF

- GW

- MW

- 06 W6

- TW18 48.3975817909

- 114.134063729 3134 3132 76.11 3058 62.79 90 / 90 70

- 85 90.17

CF

- GW

- MW

- 08 W10

- TW22 48.3967190870

- 114.145543852 3108 3106 35.61 3072 29.45 60 / 60 45

- 60 51.31

CF

- GW

- MW

- 09 W8

- TW2 48.3937082010

- 114.141720973 3106 3104 50.15 3056

-- Cased from 2

- 53 Open Bottom 54.29

CF

- GW

- OP

- 02 Not Applicable 48.388222000 114.159917000

-- -- -- -- 169 169 / 169 None NM

N otes: * Survey data n ot avai lable; eleva tions ar e estimated

-- Unknown ft amsl - feet above mean sea lev el ft bgs - feet below ground surface ft btoc
– feet below top of casing
NM
– Not Measured
TD
– Total Depth

References: 1 Ref. 3, p. 103; Figure 5 of this HRS documentation record 2 Ref. 3, p. 97; Figure 2 of this HRS documentation record 3 Ref. 3, pp. 187, 189 4 Ref. 33 5 Ref. 3, p. 195 6 Ground water Elevation = Top of Casing Elevation
– Depth to Ground water 7 Ref. 8, pp. 264, 265; 3, pp. 112, 115, 130, 134, 135, 153

- 156 8 TW9 ran dry following purging and initial sample collection (Ref. 3, p p. 39, 40)

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 56Analytical results from the 2013 sampling event were performed according to the United States Environmental Protection Agency Contract Laboratory Program Statement of Work for Inorganic Superfund Methods, ISM01.3 (5/2005) (Ref. 3 a , App. F section 7, p. 1355). The source samples listed below were collected during the 201 3 sampling effort conducted by START for the EPA. Samples were analyzed using the Contract Laboratory Program Statement of Work for I norganic Superfund Methods, IS M01.3— Metals, Mercury and Cyanide (Ref s

. 3, pp. 34; 3a, App. F, Section 7, pp. 1350, 1355 ). Laboratory samples were analyzed by the CLP laborator y ALS Laboratory Group in Salt Lake City, Utah (Ref. 3, p. 46).

Water quality parameters collected during the 2013 sampling event were similar for all ground water monitoring well samples in the site area and CF

- GW

- MW

- 01 and CF

- GW

- OP

- 02 also had similar chemical properties to each other, demonstrating sample similarity for comparison purposes (Ref. 3, Table C1, p. 187). The analytical results indicate the presence of several contaminants in ground water under and near the facility. Samples collected from both down gradient on facility monitoring wells and a down gradient off facility drinking water well show the presence of total arsenic, total chromium

, total cyanide and dissolved manganese in the alluvial aquifer that meet the observed release criteria as stated in HRS Section 2.3 (Ref s . 3, pp. 241, 243, 287, Tables E6, E7, E29; 3a, App. F Section 7, pp. 1332, 1,341, 1,350, 1,360, 1,350, 1359, 1360, 1,362, 1,363, 1374, 1,389, 1,390).



### Hazardous Substance Location Highest Background Concentration (μg/L) Concentration (μg/L) RL (μg/L) References

Total Arsenic (dissolved) CF

- GW

MW -03 (MH5003) 1.0U 344 1.0 Refs. 3, Table E7, p. 243, App. D, p. 221; 3a, App. F Section 5,

pp. 1,425, 1,430, Section 7, pp.1,458, 1,470 ; 44

Total Chromium (dissolved) 2.0U 10.3 2.0 Refs. 3, Table E7, p. 243, App. D, p. 221; 3a, App. F Section 5,

pp. 1,425, 1,430, Section 7, pp.1,458, 1,470 ; 44

Total cyanide CF

- GW

OP -02 (MH00C7)

5.7J- [7.752] 111 0.5 Refs. 3, Table E29, p. 287, App. D, p. 208; 3a, App. F Section 5, p. 661, 675, Section 7,

pp. 1,350, 1,36 0 ; 44

CF

- GW

MW -03 (MH003) 769 10 Refs. 3, Table E6, p. 241, App. D, p. 221; 3a, App. F Section 5, p. 659, 663, Section 7,

p. 1,350, 1,359 ; 44 CF

- GW

MW -04 (MH004) 1040J- 0.5 Refs. 3, Table E6, p. 241, App. D, p. 217; 3a, App. F Section 7,

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 57

### Hazardous Substance Location Highest Background Concentration (μg/L) Concentration (μg/L) RL (μg/L) References

pp. 462, 466, 1,332, 1,341; 17, pp. 1

- 18 ; 44

Manganese (dissolved) CF

- GW

MW -08 (MH5008)

10.9 109 1 Refs. 3, Table E30, p. 289, App. D, p. 215; 3a, App. F Section 6, pp. 225, 235, Section

7. pp. 1,485, 1,499, 1,500 ; 44

CF

- GW

MW -09 (MH5009) 181 1 Refs. 3, Table E30, p. 289, App. D, p. 215; 3a, App. F Section 6, p. 225, 236, Section 7.

pp. 1,485, 1,500 ; 44

Notes: μg/L - micrograms per liter.
U The material was analyzed for, but was not detected above the level of the associated value. The associated value is the reporting limit.
J- The associated value is an estimated quantity, biased low. ( ) CLP Sample ID [ ] The associated value is adjusted according to the EPA guidance Using Qualified Data to Document an Observed Release and Observed Contamination (Ref. 17)

. RL The value shown is the sample specific Contract Required Quantitation Limit (Ref. 30).

Attribution

It has been documented that arsenic, total chromium

, total cyanide and manganese have all been found in sources onsite. Chromium is used in making aluminum alloys and total cyanide is found in spent potliner material that has been disposed of onsite (Ref s. 9, p. 7; 19, p. 12). Total cyanide has been previously documented in a release to both ground water and surface water (Ref. 3, p. 25). Cadmium, total chromium and iron are common in aluminum ores. Further, these substances have been documented in onsite sources evaluated for this site. There are no other potential sources for these contaminants located either

up- gradient or in the immediate area (Ref. 39).

Hazardous Substances Released : Arsenic, total chromium

, total cyanide , and Manganese

.

Ground W ater Observed Release Factor Value: 550



## 3.2 WASTE CHARACTERISTICS

3.2.1 TOXICITY/MOBILITY

Hazardous Substance Source No. Toxicity Factor Value * Mobility Factor Value * Tox /Mobility (Table 3

- 9) References

Arsenic 1,2,3,4,5 10,000 1* 10,000 2, p. BI

- 1

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 58Hazardous Substance Source No. Toxicity Factor Value * Mobility Factor Value * Tox /Mobility (Table 3

- 9) References

Cadmium 1,2,3 10,000 1x10 - 2 100 2, p. BI

- 2 Chromium (total) 1,2,3,4,5 10,000 1 10,000 2, p. BI

- 3
C yanide 1,2,3,5 10,000 1 10,000 2, p. BI

- 3 Manganese 1,2,3,4, 10,000 1 10

, 0 00 2, p. BI

- 7 Zinc 1,2,3,4,5 10 1 10 2, p. BI

- 10 *According to HRS section 3.2.1.2, for any hazardous substance that meets the criteria for an observed release by chemical analysis to one or more aquifers underlying the sources at the site, regardless of the aquifer being evaluated, assign a mobility factor value of 1. Arsenic, total chromium, total cyanide, and zinc have all been detected at elevated levels in grou nd water. The hazardous substances are arsenic, total chromium, and total cyanide.

Toxicity/Mobility Factor Value: 10,000 (Ref. 1, Section 3.2.1.3)

3.2.2 HAZARDOUS WASTE QUANTITY

Source Number Source Hazardous Waste Quantity Value (Section 2.4.2.1.5) Is source hazardous constituent quantity data complete? (yes/no)
1 3,685.8 No
2 25,465.8 No 3 5,830.3 No
4 13,336. 06 No 5 99.9 3 No Total 48,417.89

According to Section 2.4.2.2 of the HRS (Ref. 1, p p. 51591, 51592), if any target for the migration pathway under consideration is subject to Level I (or Level II) concentrations, assign either the value from Table 2

- 6 (Ref. 1, p. 51591) or a value of 100, whichever is greater, as the hazardous waste quantity facto r value for that pathway.

Hazardous Waste Quantity Factor Value: 10,000 (Ref. 1, Table 2 -6, p. 51591)

3.2.3 WASTE CHARACTERISTICS FACTOR CATEGORY VALUE

Toxicity/Mobility Factor Value: 10,000 Hazardous Waste Quantity Factor Value: 10,000

Toxicity/Mobility Factor Value X Hazardous Waste Quantity Factor Value: 1 x 10 8 (per HRS Section 3.2.3, the Hazardous Waste Quantity Factor Category Value is capped at 1 x 10 8 )

Waste Characteristics Factor Category Value: 100 ( Ref. 1, Table 2 -7)

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 59

## 3.3 TARGETS (Ref. 1, p. 51602)

The City of Columbia Falls utilizes two municipal ground water wells as a primary potable water supply for 1,040 connections (Refs. 24; 32 ). The two municipal wells (Louisiana Pacific Well and Clare Park Well) are located within the Columbia Falls city limits ( Refs. 24; 38; Figure 5 ). The Clare Park Well is located approximately 0.5 mile west of the Flathead River and approximately 3.22 miles down gradient of the Site and is 304 feet deep (Refs. 24; 38; Figure 5 ). The second well (Louisiana Pacific Well) is located approximately 1.8 miles west of the Flathead River and approximately 3.4 miles down gradient of the Site and is 231 feet deep ( Refs . 24; 38; Figure 5 ). The average number of persons per household in Flathead County, Montana, is 2.43 (Ref. 4, p. 1). There are also multiple private wells within the four mile ground water target distance limit of the site. However, because it is not clea rly been demonstrated that the alluvial aquifer is continuous from the facility to these wells, they have not been included in the site scoring. However, the se wells are of concern to EPA.

3.3.1 NEAREST WELL (Ref. 1, pp. 51602, 51603)

Well CF

- GW

- OP -02 provides potable water to five residences and c oncentrations of total cyanide in CF

GW

- OP

- 02 meet the observed release criteria found in HRS Table 2 -3 (Refs. 1, p. 51603 ; 3 , Table E29, p. 287 ). The total cyanide concentration recorded in this well is 111 μg/L (Ref s. 3, Table E29, p. 287 ; 3a

, App. F, Section 7, pp. 1,351, 1,361 ). As this is above the applicable health

- based benchmark for drinking water (the Reference Dose Screening Concentration [RDSC], which is 9.0 μg/L), this well is considered to be subj ect to Level I concentrations (Ref. 1, p.51592) and is considered the nearest well

. The well is 169 feet in depth with an open bottom and cased but not screened, although it is capped. (Ref. 3, pp. 153, 155).

In accordance with Table 3

- 10 and 3

- 11 within Section 3.3.1 of the HRS, a Nearest Well Factor Value of 50 has been assigned (Ref. 1, pp. 51602, 51603).

Well ID: CF

- GW

- OP -02 Level of Contamination (I, II, or potential): I If potential contamination, distance from source in miles: Not applicable

Nearest Well Factor Value: 50 (Refs. 1, pp. 51602, 51603 Table 3 -11)

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 603.3.2 POPULATION

3.3.2.1 Level of Contamination

3.3.2.2 Level I Concentrations

Level I Samples

Hazardous Substance Sample ID (Description) Hazardous Substance Conc. (μg/L) Benchmark Concentration (μg/L) Bench

mark References

Total Cyanide GW

- OP -02 : private well supplying 5 residences 111 9 RDSC 2, p. BII-4: 3, pp. 36, App. D, p. 208 ; 3a , App. F,

Section 5, pp. 661, Section 7, pp. 1,350, 1,362 ; 43, p. 1

RDSC Reference Dose Screening Concentration

Level I Well Population References

CF

- GW

- OP -02 9 3, pp. 35, 36, App E, Table E29, pp. 287 ; 3a , App F, Section 7, p. 1361; 4; 43, p.1

P opulation served by Level I Wells: 9 Population served by Level I Wells x 10: 90 Level I Concentration Factor Value: 90

3.3.2.3 Level II Concentrations

Not applicable as no Level II concentrations have been identified. Total Population Served by Level II Wells: 0 Level I I Concentrations Factor Value: 0

3.3.2.4 Potential Contamination

Domestic and municipal wells are present within the 4

- mile target distance limit. However, as a sufficient site score is achieved using actual contamination, potential contamination is not evaluated in this HRS documentation record. However

, the threat of contamination m i gr a ting to these wells is of concern to EPA.

Potential Contamination Factor Value: 0

3.3.3 RESOURCES

It is not known if any well within the four

- mile radius is used for irrigation of commercia l food or forage crops, or if any well may otherwise be considered a resource for scoring purposes. Resources Factor Value: 0

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 613.3.4 WELLHEAD PROTECTION AREA

Wellhead Protection Areas (WPAs) were not identified within 4 miles of the sources and as such, were assigned a value of 0 (Refs. 1, p. 51604; Figure s 1

- 6 ).

As per Section 3.3.4 of the HRS, a Wellhead Protection Area Factor Value of 0 has been assigned for the principal aquifer (Ref. 1, p. 51604). Wellhead Protection Area Factor Value: 0

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 62

## 4.0 SURFACE WATER MIGRATION PATHWAY

4.0.1 Migration Components

The surface water migration pathway score for the Anaconda Aluminum Co Columbia Falls Reduction Plant is based on the ground water to surface water migration component, as described in Section 4.2 below (Ref. 1, pp. 51604

- 51605, Section 4.0.1). The ground water t o surface water migration component is used to evaluate surface water threats that result from migration of hazardous substances from source(s) to surface water via ground water , as has occ urred at t he Anaconda Aluminum Co Columbia Falls Reduction Plant

. As per the HRS, three possible threats exist for the surface water migration pathway through the ground water to surface water migration component: the drinking water threat, human food chain threat

, and environmental threat (Ref. 1, pp. 51604

- 51605, Sec. 4.0.1). For the Anaconda Aluminum Co Columbia Falls Reduction Plant site, the human food chain and environmental threats are scored for the ground water to surface water migration compon ent of the surface water migration pathway. These threats are discussed within Sections 4.2.3 and 4.2.4 of this HRS documentation record.

The overland/flood migration component was not scored because the ground water to surface water component scores suff iciently to place the site on the NPL. Given that the south percolation ponds of the site (Sources 3 and 4) lie within the 100

- year flood plain for the Flathead River

, the overland/flood migration to surface water component is likely complete at this site (Ref. 3 4 ; Figure 2 of this HRS documentation record). In addition, for many years the Anaconda Aluminum Co Columbia Falls Reduction Plant discharged wastewater to the Flathead River through O utfall D 006

, a reach extending from Latitude 48° North, 23' 18", Longitude 144° East, 7' 19" to Latitude 48° North, 3' 13 ", Longitude 144° East, 9' 04" (Ref. 7, pp. 5, 24, 25). The outfall is considered a probable point of entry (PPE) for the entry of hazardous substances from possibly four identified sources (Sources 1 through 4) into the river, as well as from the other possible sources identified within the S ummary of Source Descriptions S ection of this HRS documentation record, for the overland/flood migration component. The Cedar Creek watershed is located to the w est of the westernmost source (Source No. 2), there is no overland runoff pathway from any sources reaching the Creek, and the bottom of the Creek at the westernmost (lowest) sample point (CF

- SW/SD

- 06) is approximately 44 feet above the aquifer (Figures 3, 5, 6, 7, and 8 of this HRS d ocumentation r ecord). Therefore, t he overland flow pathway is not used for scoring the ground

water to surface water migration component.



## 4.2 GROUND WATER TO SURFACE WATER MIGRATION COMPONENT

4.2.1 General Considerations

4.2.1.1 Eligible Surface Waters

According to the HRS, surface waters eligible to be scored under the ground water to surface water migration component must meet certain conditions. The Flathead River is documented to be an eligible surface water for the g round water to surface water migration component, as described below (Ref. 1, p. 51626, Section 4.2.1.1).

Condition 1: A portion of the surface water is located within 1 mile of one or more sources at the site having a containment value greater than 0:

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 63Although two watersheds are present in the study area, only the Flathead River is being evaluated for this pathway. The Cedar Creek watershed is located to the west of the westernmost source (Source No. 2 ), there is no overland runoff pathway from any sources reaching the Creek

, and the bottom of the Creek at the westernmost (lowest) sample point ( CF

- SW /SD

- 06) is approximately 44 feet above the aquifer (Figures 3, 5, 6, 7, and 8 of this HRS d ocumentation r ecord)

. The Flathead River is l ocated approximately 5,000 feet in straight

- line as measured from the east edge of Source No. 1, approximate ly 3,700 feet in straight

- line from the east edge of Source No. 2, approximately 600 feet in straight

- line from the east edge of Source No. 3, and a pproximately 200 feet in straight

- line from the east edge of Source No. 4 (Ref. 33; Figure 6 of this HRS documentation record)

. All f our of these sources have a containment value of 10 for the ground water migration pathway (Refs. 3, p. 23; 6, p. 5; 7, pp. 4, 5, 26; 19, p. 17 ; Section 2.2.3 for Sources 1, 2, 3 and 4, and Figure 2 of this HRS documentation record)

.

Condition 2: The top of the uppermost aquifer is at or above the bottom of the surface water body:

A detailed description of the geology and hydrogeology of the site is found within section 4.2.1.2 (Definition of Hazardous Substance Migration Path for Ground Water to Surface Water Component) below. The pertinent information from section 4.2.1.2 is summarized here.

The uppermost aquifer beneath the Anaconda Aluminum Co Columbia Falls Reduction Plant property is the alluvial / glacial aquifer that exists throughout the site vicinity (Ref s

. 18, pp. 43, 44, 46; 20 p. 20). Ground water elevations were measured within existing facility monitoring wells completed in the alluvial / glacial aquifer during the 2013 field investigation (as demonstrated by the well logs) (Refs. 3 , p. 189, App. A pp. 111

- 150 ; Figures 7 and 8 and Section 3.1.1 of this HRS d ocumentation r ecord ). Two representative wells, CF

- GW

- MW

- 0 2 and CF

- GW

- MW

- 09 , have been selected to demonstrate the elevation of the top of the uppermost aquifer. These wells have been chosen as they are in line with the general ground water flow direction within the aquifer ( T able in Section 3.1.1, Figures 8 and 9 of this HRS d ocumentation r ecord ).

The elevation measured for the bottom of the Flathead River (i.e. its deepest point) was 2,977.67 feet amsl, measured at the USGS gauging station in Columbia F alls located at the highway 2 bridge over the Flathead River (Ref. 25, pp. 1

- 3 ) . This elevation is 79 feet lower than the ground water elevation measured in CF

- GW

- MW

- 0 9 (3,0 56 feet amsl ), and 127 feet lower than the ground water elevation measured in CF

- GW

- MW

- 0 2 (3, 1 0 4 feet amsl ) (Refs. 3, p. 97, 103, 1 89

, 195, 112, 115, 130, 134, 135, 153

- 156 ; 8 , pp. 264, 265 ). Historic ally, ground water elevations measured in these wells are also higher than the elevation of the bottom of the river (Ref. 1 8

, p p. 49, 50 ). Therefore, the condition that the top of the uppermost aquifer is at or above the bottom of the surface water body is met.

Condition 3: No aquifer discontinuity is established between the source and the portion of the Flathead River within 1 mile of any o f the sources:

In the vicinity of the Anaconda Aluminum Co Columbia Falls Reduction Plant site, the uppermost aquifer is present in valley

- fill glacial/ alluvium that is continuous between the areas of the sources , target wells, and the Flathead River (Ref s

. 8, p. 38; 20, p. 20 Figure 18; Figures 7 and 8, and the well log table in Section 3.1.1 of this HRS d ocumentation r ecord ). There is no evidence that any geologic, topographic, or other structure or feature, that entirely transects the aquifer or that cr eates a continuous boundary to ground water flow, exists anywhere between the sources ( i.e ., ponds and landfill) and the Flathead River (Figures 7 and 8) . Evidence that there are no discontinuities between the source areas and the river includes that seepage water from the ponds that entered the uppermost aquifer eventually reached the river as documented by the MPDES permit ( Ref. 7, pp. 1, 5, 25, 26)

.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 644.2.1.2 Definition of Hazardous Substance Migration Path for Ground Water to Surface Wa ter Migration Component

Ground Water Migration Pathway Description :

The hazardous substance migration path includes both the ground water segment and the surface water in

water segment that hazardous substances would take as they migrate away from sources at the site (Ref. 1, p. 51626).

The ground water segment of the hazardous substance migration path begins at each source and extends to the PPE through the uppermost aquifer ( i.e., the alluvial /glacial aquifer) to the surface water (Figure s 6 and 9 of this HRS documentation record). The PPE is defined as the point at the surface water that results from the shortest straight

- line distance through the uppermost aquifer beneath th e sources with a containment factor greater than zero to the surface water (Ref. 1, p. 51626, Section 4.2.1.2). There are five sources identified for the site, four within 1 mile and having a PPE into the Flathead River (Figure s 2 and 6 of this HRS documen tation record). The ground water segment is restricted to migration via the uppermost aquifer between a source and the surface water (Ref. 1, p. 51626). A description of the geology and hydrogeology (both regional and site specific) is therefore necessary to evaluate this migration pathway.



### Site Specific Geology and Hydrogeology:

The Anaconda Aluminum Co Columbia Falls Reduction Plant is located on the eastern margin of the upper Flathead Valley, approximately one

- half mile northwest of where the Flathead River leaves the mountains through Badrock Canyon. The Flathead Valley is a southern extension of the structural depression termed th e Rocky Mountain Trench. The major axis of the valley is generally northeast/southwest. Surface drainage of the property is to the south (Ref. 18, p. 15).

A series of nine piezometer placements made by Hydrometrics in July 1980 provided stratigraphic evi dence to substantiate glacial and glaciofluvial deposition. All nine sites showed a succession of till and small patches of glaciolacustrine clays, capped by from one foot to greater than twelve feet of imbricated glaciofluvial and alluvial sands, gravels and cobbles. This capping unit appeared to be more extensive and thicker north and west of the plant complex than it was to the northeast (Ref. 18; p. 37).

Driller's logs from production and hydrologic test wells in the vicinity of the plant provide more evidence of successive depositional modes. Examination of these logs indicate that from 70 to greater than 300 feet of interbedded glacial, glaciolacustrine, and glaciofluvial sediments underlie the surface of the site with minor occurrences of well

- sorted , permeable gravels and cobbles. Hydrologic testing indicates a zone of highly transmissive cobbles and gravels at depths greater than approximately 100 feet along the southern edge of the plant property. This zone probably represents buried glacial outwas h associated with advancing or retracting phases of the Flathead Glacier which entered the valley through Badrock Canyon, as well as high transmissivity gravels associated with the reworking of glacial debris by the ancestral Flathead River (Ref. 18; pp. 3 7, 38).

- Aquifer Interconnections Between Sources and the Flathead River /Distance from Source

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 65Description

Ground water is present in the glacial (where present) and underlying alluvial deposits beneath the plant property. The occurrence, distribution and abundance of ground water is closely related to subsurface geological conditions. As described above, this area was influenced by several glacial events and hydrogeology of the area is complex (Ref. 18; pp. 20, 21 ). The glacial and alluvi al aquifers are considered to be interconnected at the site and within two miles of the sources along the river valley due to the absence of any confining layers or aquatards separating the glacial outwash hydrologic unit from the alluvial unit as shown in the cross sections (Figures 7 and 8). In addition, all the layers appear to have hydraulic conductivities within two orders of magnitude (Ref. 1, Table 3

- 6). Further, the presence of site contaminants in ground water on site as well as in a Level I actual contamination well demonstrate an interconnection and absence of discontinuities ( Ref.1, Sections 3.0.1.2.1 and 3.0.1.2.2 and Section 3.3.2 of this HRS documentation record) between site sources and this target well . The alluvial/glacial aquifer extends d ownstream past Columbia Falls and constitutes a single hydrogeologic unit (due to similar hydraulic conductivities and a lack of any confining layers), i.e., the Alluvial/Glacial aquifer (Refs. 8, p. 38; 18, pp. 37, 38; 20, pp. 20, 38, 40).

Geology of Ana conda Aluminum Co Columbia Falls Reduction Plant area, including the community well (CF

- GW

- OP

- 02), are shown in Figures 7 and 8 of this HRS documentation record . The cross section locations are shown in Figure 2. The cross sections show the absence of any confining layer between the prevalent alluvial/gravel water bearing strata and the glacial outwash that overlaps the alluvial along the valley sides.

- Aquifer Discontinuities between the Plant Ground water and the Flathead River

Description

In the v icinity of the Anaconda Aluminum Co Columbia Falls Reduction Plant site, the alluvial/glacial aquifer is present in valley

- fill alluvium that is continuous between the areas of the sources and the Flathead River (Refs. 18, pp. 37, 38; 20, pp. 8, 10, 16). T here is no evidence that any geologic (e.g., major faults, intrusive formations such as dikes or sills), topographic, or other structure or feature (e.g., erosional channels and large bodies of water), that entirely transects the surficial alluvial aquifer and that creates a continuous boundary to ground water flow, exists anywhere between the sources and the Flathead River (Refs. 18, pp. 37, 38; 20, pp. 8, 10, 16; Figures 7 and 8 of this HRS documentation record).

Evidence that there are no discontinuitie s between the source areas and target wells includes that all seepage water from the percolation ponds that had entered the alluvial aquifer eventually reached the river (Ref. 7, pp. 4, 5). Further, the presence of site contaminants in ground water on site as well as in a Level I actual contamination well demonstrate an absence of discontinuities between the sources and target well (Section 3.3.2 of this HRS documentation record ).

Elevation of Top of Aquifer (mean sea level):

The elevation measured for t he bottom of the Flathead River (i.e. its deepest point) was 2,977.67 feet amsl, measured at the USGS gauging station in Columbia falls (Ref. 25, pp. 1

- 3 ) . Historic ground water elevations measured in CF

- GW

- MW

- 02 (TW9), and CF

- GW

- MW

- 09 (TW2) are also higher than the elevation of the bottom of the river ( Refs. 3, p. 189; the Well Table in Section 3.1.1, and Figures 7 and 8 of this HRS documentation record ). The average gradient of the Flathead River valley above Kalispell is six feet per mile (Ref. 20, p. 10).

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 66Elevation of Bottom of Surface Water Body (mean sea level):

The elevation measured for the bottom of the Flathead River (i.e. its deepest point) was 2,977.67 feet amsl, measured at the USGS gauging station in Columbia falls (Ref. 25, pp . 1

- 3 ) . Historic ground water elevations measured in CF

- GW

- MW

- 02 ( TW9) and CF

- GW

- MW

- 09 (TW2) are also higher than the elevation of the bottom of the river ( Refs. 3, p. 189; the Well Table in Section 3.1.1, and Figures 7 and 8 of this HRS documentation record; 18, pp. 4 7

- 51 ).

Surface Water Probable Point of Entry and In

- Water Segment Description:

The hazardous substance migration path includes both the ground water segment and the surface water in

water segment that hazardous substances would take as they migrate away from sources at the site (Ref. 1, p. 51626, Section 4.2.1.2). The hazardous substance migration path for the Anaconda Aluminum Co Columbia Falls Reduction Plant site begins at Source No. 4 (eastern south percolation pond), the source with the most upstream PPE to the Flathead River (Figure 2 of this HRS documentation record). As the south percolation pond is directly adjacent to the Flathead River, the ground wate r segment of the hazardous substance migration path is approximately 200 feet (Figure 2 of this HRS documentation record).

The location where this PPE enters the Flathead River marks the beginning of the surface water in

- water segment of the hazardous sub stance migration path for the ground water to surface water migration component (Ref. 1, p. 51626; Figure 5 of this HRS documentation record). From this point, the Flathead River flows generally west along the southern edge of the Anaconda Aluminum Co Colu mbia Falls Reduction Plant property, passing the ground water to surface water PPEs from source No. 3, then source
No. 1, and finally source No. 2 (Figure 2 of this HRS documentation record). The PPE for Source No. 2 is the lowest (most downstream) PPE for the site and is located approximately 1.5 miles downstream of the PPE for Source No. 3 (Figure 2 of this HRS documentation record). From this lowest PPE, the Flathead River (and therefore the migration pathway) then continues generally west, then south to the end of the target distance limit (TDL) (Figure 5 of this HRS documentation record). The total distance from the highest PPE (most upstream) to the end of the TDL is approximately 16.5 miles (Ref. 1, p. 51626, Section 4.2.1.4; Figure 2 of this HRS docu mentation record).

The surface water body being scored for this HRS documentation record is the Flathead River (a large river). The in

- water segment for HRS purposes begins at the highest upstream ground water to surface water PPE on the Flathead River an d ends 15 miles downstream of the PPE from Source No. 2, a total distance of approximately 16.25 miles (as described above) (Figure 9 of this HRS documentation record).

Dilution Weight Adjustment for In

- Water Segment :

A dilution weight adjustment is not calculated because the inclusion of potential contamination in the human food chain and environmental threats of the ground water to surface water migration component of the surface water migration pathway does not likel y contribute significantly to the overall site score.

The mean annual flow rate for the Flathead River

, as measured from a USGS gauging station located south and adjacent to Columbia Falls, Montana located approximately 1.7 miles downstream from the site (USGS station # 12363000)

, from the years 1952 through 2013 is 9,777 cfs. (Ref. 25). The river is, therefore, described as a large stream or river under the HRS (Ref. 1, Table 4

- 13, p. 51613) . However, the 2013 annual average of 10,2 1 0 will be used to err on the side of caution, due to the nearness of the 10,000 cfs category change (Ref s . 1, Table 4

- 13, p. 51613 ; 25, p. 3 ). It is shown as a perennial river on the GIS software package used for this site (Refs. 3; Figures 1

- 6 of this HRS documentation record ; 33).

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 67Because the gauging station is so close to the site, the overall flow rate was evaluated as greater than 10,000 cfs and less than 100,000 cfs for the TDL

.
Information regarding threatened, endangered, or sensitive species is available for Flathead County but not currently available on a site specific basis. A search of the U.S. Fish & Wildlife Service (USFWS) Environmental Conservation Online System (ECOS), available online at http://www.fws.gov/endangered/ the Montana Fish, Wildlife & Parks (FWP) T hreatened Species list, available online at http://fwp.mt.gov, and the and the Montana National Heritage Program (MNHP) Species of Concern report, available online at http://mtnhp.org indicates 3 different species (two fish and one insect) to be present in Flathead County along the TDL that are considered federal or state listed threatened, endangered, or sensitive species and are associated with the study area (Refs, 26; 27; 40; 42) :

• Bull Trout (Salvelinus confluentus);

• Westslope Cutthroat Trout (Oncorhyn chus clarkii lewisi);

• Meltwater Lednian stonefly (Lednia tumana).

A site specific biological assessment has not been performed; however, according to a query of the FWP Montana Fisheries Information System database (MFISH), along the Anaconda Aluminum Co Columbia Falls Reduction Plant southern property boundary, the Westslope Cutthroat Trout is found in the Flathead River (Ref s . 27, pp. 17

- 3 3 ; 42 ). The ECOS and MFISH identified habitat for the Bull Trout (federally threatened) and Westslope Cutthroat Trout (federally sensitive) in the Flathead River (Refs. 26; 27, pp. 17

- 3 3 ; 42 ). Fish surveys conducted by FWP have confirmed the presence of both species in the Flathead River adjacent to the Site and the presence of Westslope Cutthroat Trout i n Cedar Creek (Ref. 27, pp. 17

- 3 3 ; 28 ; 42 ) . Creel surveys performed by FWP show that fish are caught

, and consum ption of fish caught along the Flathead River from well upstream of the facility down to Kalispell occurs (Refs. 27, pp. 17

- 3 3

, 47

- 49 ; 28; 35 ).

A ccording to the MNHP Map Viewer

- Wetland and Riparian Mapping database, approximately 15.53 miles (on both sides of the river) of streamside wetlands are present from the site along the Flathead River downstream 15 miles (Refs. 29; 33) . The dominant vegetation is freshwater palustrine scrub shrub and emergent wetlands. These wetland types meet the HRS definition of a wetland, 40 CFR 230.3, and are considered eligible for HRS scoring (Refs. 1, Table 4

- 24, p. 51625; 29).

4.2.1. 3 Observed Release

Alluvi al/glacial Aquifer:

According to the HRS, in order to establish an observed release of an individual hazardous substance to surface water under the ground water to surface water migration component of the surface water pathway, an observed release to both ground water and an observed release by chemical analysis to surface water must be documented (Ref. 1, p. 51626, Section 4.2.1.3). Please refer to section 3.1.1 of this HRS documentation record to see the necessary information to support the observed release conditions present in the aquifer beneath Anaconda Aluminum Co Columbia Falls Reduction Plant ( a lluvial / g lacial Aquifer).

Surface Water: Flathead River

All surface water sampling was done in accordanc e with EPA ERT SOP 2013 (Ref. 32, p. 47 ). All samples were collected during the same 2013 sampling event, over a period of nine days (September 23 through October 1) (Ref. 3, pp. 27, 198 , 219, 220 ) . All samples adjacent to the Site were collected from the north bank of the Flathead River, the side closest to the site ( Figure 6 ) . Surface water quality parameters, such as pH, temperature, and conductivity, were measured at each sampling location and the

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 68results were similar at each (Ref. 3, p. 187). The speci fic areas sampled were backwater locations that acted as sediment traps for the finer

- grained material (sands and silts) that were targeted for sampling (Figure 6 of this HRS documentation record) . All surface water samples were collected from 0 to 1 foot depth, and were collected before the sediment samples (Ref. 32, p. 27)

.
Samples were analyzed using the Contract Laboratory Program Statement of W ork for Inorganic Superfund Methods, ISM01.3

— Metals, Mercury and Cyanide (Ref. 3, pp. 34, 3a, App. F, Section 7, pp. 1458, 1463 ). Laboratory samples were analyzed by the CLP laboratory ALS Laboratory Group in Salt Lake City, Utah (Ref. 3, p. 46 ; 3a, App. F. Section 7, p. 1458 ).

Surface Water Background Concentrations:

The bac kground concentration for each analyte was selected from the highest detected laboratory result of the evaluated surface water background samples collected from SW

- 13, SW

- 14, SW

- 15, SW

- 16 (CF

- SW

13, CF

- SW

- 14, CF

- SW

- 15, CF

- SW

- 16 [Figure 6] ) (Ref. 3, Tables E32

- E39 , 293

- 307 ). Laboratory data and validation reports are presented in Appendi ces of the SRR (Ref. 3, App. D, pp. 219, 220 ; 3a, App. F

, Section 5, p. 1136, App. F, Section 7, pp. 1474

- 1476; Figure 6 of this HRS documentation record ). The background samples were all collected September 27, 2013 : locations are shown on figure 5 of this HRS documentation record (Ref. 3 a , App. F

, Section 5, p. 1136)

.
Background Surface Water Samples

Sample ID CLP ID Date Sampled Hazardous Substance Concentration ( μ g/L) References

CF

- SW

- 13 MH 5 031 9/27/13

Manganese (dissolved) 2.2 (1. 0 ) Ref. 3, p. 219, Table E3 8

, p. 30 5 ; 3a, App. F, Section 5, pp. 1136, 1435; Section 7, p. 1474 ; 44

CF

- SW

- 14 MH 5 032 9/27/13 1

. 2 (1. 0 ) Ref. 3, p. 219, Table E3 8

, p. 30 5 ; 3a, App. F, Section 5, pp. 1136, 1436; Section 7, pp. 1474, 1475 ; 44

CF

- SW

- 15 MH 5 033 9/27/13 1. 0 U (1.0) Ref. 3, p. 220, Table E3 8

, p. 30 5 ; 3a, App. F, Section 5, pp. 1136, 1437; Section 7, pp. 1475 , 1476 ; 44

CF

- SW

- 16 MH 5 034 9/27/13 1.0 U (1. 0 ) Ref. 3, p. 220, Table E3 8

, p. 30 5 ; 3a, App. F, Section 5, pp. 1136, 1438; Section 7, pp. 1476 ; 44

Notes: μ g/L micrograms per Liter
U The material was analyzed for, but was not detected above the sample specific Contract Required Quantitation Limit

. ( ) The value shown is the sample specific Contract Required Quantitation Limit (Ref. 30).

Contaminated Surface Water Concentrations:

The analytical results of the Flathead River surface water samples (CF

- SW

- 05 through CF

- SW

- 12 [Fi gure 6]) were compared to three times background concentration for surface water to further ensure that contaminants attributed to site activities were not also naturally occurring at similar concentrations and meeting observed release criteria. The three times background concentration was calculated for each

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 69analyte using the highest detected laboratory result of the evaluated Flathead River surface water background samples (CF

- SW

- 13, CF

- SW

- 14, CF

- SW

- 15, CF

- SW

- 16, CF

- SW

- 24 [duplicate] [Tables E32

- E39, App endix E]) ( Ref. 3, pp. 293

- 307 ; 3a, App. F, Section 7, pp. 1458, 1474

- 1476 ). If the background results are non

- detect for a specific analyte, then a detection in a release sample above the reporting limit for the Flathead River background sample for the associated analyte is considered an exceedance of the background concentration

. (Ref. 1 , Section 2.3, p. 51589 ).

Contaminated Surface Water Samples

Sample ID Sample Location Distance from Upper PPE Depth Date References

CF

- SW

- 07 Flathead River 0.8 miles 0

- 12 ” 9/25/13 Refs. 3, Figure 4; Table E3 8 , p. 30 5 , App. D, p. 198 ; 3a, App. F Section 6, pp. 226, 247, Section 7, pp. 1485, 1508, 1509 ; 32, p. 27

Sample ID CLP ID Hazardous Substance Concentration ( μg/L ) R L ( μg/L ) References

CF

- SW

- 07 MH5025 Manganese (dissolved) 31.4 1 .0 Ref. 3, Table E3 8 , p. 30 5

, Appendix D, p. 198; 3a, App. F, Section 5, pp. 1131,1132, Section 6, pp. 225, 226 , 247 ; Section 7, pp. 1485, 1508, 1509 Notes: mg/ k g milligrams per kilogram
RL The value shown is the sample specific Contract Required Quantitation Limit (Ref. 30)

.

Attribution

Manganese is an analyte associated with the Anaconda Aluminum Co Columbia Falls Reduction Plant sources listed in Section 2.2.1. No sources were found to be fully contained and the southern ponds are located adjacent to the surface water (Ref. 3, p. 23; 6, p. 5; 7, pp. 4, 5, 26; 19, p. 17 ; Figure 2 of this HRS documentation record ). There are no other potential sources for these contaminants located either up

gradient or in the immediate area (Ref. 39).

Hazardous Substances Released

Analyses of surface water samples collected during the 2013 sampling event indicate that concentr ations of manganese are significantly above background concentrations in the Flathead River (Ref. 3, Figure 4, Ref. 3, p. 48, App E, Table E 38 , pp. 305 , Table E22, pp. 273, Table E45, p.319). According to the HRS, if an observed release can be established for the watershed, an observed release factor value of 550 is assigned (Ref. 1, Section 4.1.2.1.1, p. 51609).

Surface Water Observed Release Factor Value: 550

4.2.2 Drinking Water Threat

No drinking water intakes are located on the Flathead River within the downstream Target Distance Limit (Figure 5 of this HRS documentation record). As such, the drinking water threat was not scored because it is not expected to contribute significantly to the overall site score.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 704.2. 3 Human Food Chain Threat

4.2. 3 .1 Human Food Chain Threat Likelihood of Release

As was shown above in Section 4.2.1.3 of this HRS documentation record, an observed release of site attributable contaminants is established for both the alluvial/glacial aquifer as well as the Flathead River. Therefore, an observed release factor value of 550 is assigned for the watershed (Ref. 1, pp. 51629, 51638, Sections 4.2.2.1.1 and 4.2. 3 .1). Surface Water Observed Release Factor Value: 550

4.2.3.2 Human Food Chain Threat Waste Characte ristics

4.2.3.2.1 Toxicity/Mobility/Persistence/Bioaccumulation

Hazardous Substance Source No. Toxicity Factor Value Mobility Factor Value Persistence Factor Value* Bioaccu

mulation Value** Toxicity/Mobility/ Persistence/ Bioaccumulation

Factor Value (Table 4

- 16) Reference

Arsenic 1,2,3,4 10,000 1 1.0 5 50,000 2, p. B I

- 1 Cadmium 1,2,3 10,000 1 x 10 - 2 1.0 50,000 5 x 10 6 2, p. B I

- 2 Chromium 1,2 ,3,4 10,000 1 1 5 50,000 2, p. B I

- 3

Cyanide 1,2,3 , 4 10,000 1 0.4 0.5 2 ,000 2, p. B I

- 3 Manganese 1,2,3,4 10,000 1 1.0 500 5 x 10 6 2, p. B I

- 7

Zinc 1,2,3,4 10 1 1.0 500 5,000 2, p. B I

10
Notes:

* Persistence value for Rivers

** Bioaccumulation factor value for Freshwater

The hazardous substance with the highest Toxicity/Mobility/Persistence/Bioaccumulation Factor Value is cadmium with a value of 5 x 10 6 (Ref. 1, Section 4.2.3.2.1. 5 , Table 4

- 16; Ref. 2, pp. BI

- 2 ).

Tox icity/Persistence/Bioaccumulation Factor Value: 5 x 10 6 4.2.3.2.2 Hazardous Waste Quantity

Source No. Source Type Source Hazardous Waste Quantity

1 Surface impoundm ent 3,685.8
2 P ile 25,465.8
3 P ile 5,830.3
4 P ile 13,336. 06
Total 48,317.96

Hazardous Waste Quantity Factor Value: 10,000 (Ref. 1, Sec 2.4.2.2)

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 714.2.3.2.3 Waste Characteristics Factor Category Value

The hazardous substance cadmium associated with four of the waste sources (which all have surface water pathway containment factors of greater than 0 for the watershed) corresponds to a toxicity/ mobility/persistence factor of 100 and a bioaccumulation potential factor value of 50,000 (Ref. 1, Tables 3

- 9, 4

- 26 ; 2, p. BI

- 2 ).

Toxicity/Mobility/Persistence/ Hazardous Waste Quantity Factor Value: 1 x 10 6
Bioaccumulation Factor Value: 5 x 10 4

Waste Characteristics Factor Category Value: 320 (Ref. 1, Table 2

- 7) 4.2.3.3 Human Food Chain Threat Targets

Actual Human Food Chain Contamination

Fish are caught and consumed from within the zone of actual contamination (Refs. 35; Figure 6 of this HRS documentation record) . The zone of contamination begins at the uppermost PPE (for the eastern south percolation pond) and continues a distance of 0.8 miles downstream to the furthest downstream observed release sample (CF

- SW

- 07) containing a hazardous substance with a bioaccumulation potential factor value of 500 or g reater (Refs. 1, Sec. 4.2.3.3; 3 a , App. F Section 7, pp. 1485, 1508, 1509 ; 35; Figure 6 of this HRS documentation record ). Level II concentrations of manganese were detected in surface water samples within the zone of contamination. The Table below represe nts the zone of actual contamination in the Flathead River.

Sample ID Sample Medium Distance from uppermost PPE Hazardous Substance Bio

accumulation Factor Value References

CF

- SW

- 07 Surface

water 0.8 miles Manganese (dissolved) 500 Refs. 2, pp . BI

- 7 ; 3, Table E3 8

, p. 30 5 , Appendix D, p. 198; 3a, App. F, Section 5, pp. 1131,1132, Section 6, pp. 225, 226; Section 7, pp. 1485, 1508, 1509

- Closed Fisheries:

According to the 

### MFW&P , the Flathead River is a producing fishery with fish harvested for consumption, with no portion of the TDL closed. (Refs. 27 ; 28 ; 35 ).

Level I Fisheries

Without finfish tissue samples, Level I actual contamination cannot be documented. As such, no Level I fisheries will be evaluated. (Ref. 1, p. 51620).

Most Distant Level II Sample

The most distant Level II observed release s urface water sample, CF

- SW

- 07, was collected from the Flathead River approximately 1,000 feet down stream of the facility’s NPDES discharge location , a reach extending from Latitude 48° North, 23' 18"

, Longitude 144° East, 7' 1 9" to Latitude 48 ° North

, 3' 13 ",

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 72Longitude 144 ° East, 9' 04" (Ref. 7, p. 5)

. The sample qualifies as an observed release because the concentration of dissolved manganese in sample CF

- SW

- 07 is greater than thre e times the highest background concentration (Section 4.2.1.3 of this HRS documentation record)

. This area of Level II actual contamination is approximately 0.8 miles downstream of the uppermost Anaconda Aluminum Co Columbia Falls Reduction Plant PPE (at the eastern end of the southern percolation ponds) (Figure 6 of this HRS documentation record ).

Level II Fisheries

Identity of

Fishery Extent of Level II Fishery (Relative to PPE) Refs.

Flathead River 0.8 miles Figure 6 , Figure 9 ; Ref s . 3, Table E3 8 , p. 30 5

, Appendix D, p. 198; 3a, App. F, Section 5, pp. 1131,1132, Section 6, pp. 225, 226; Section 7, 1485, 1508, 1509 ; 27; 28; 35

4.2.3.3.1 Food Chain Individual

As noted previously, an observed release of the hazardous substanc e manganese, which ha s a bioaccumulation factor value of 500 or greater, is documented in a perennial surface water body that is a fishery (the Flathead River)

, thus documenting L evel II actual contam ination for the human food chain portion of the surface w ater pathway (see Section 4.2.3.2.1 of this HRS documentation record). The Flathead River is a cold water fishery and is used by anglers (Refs. 27 ; 35 ). According to the MFWP the portion of the Flathead River adjacent to the Anaconda Aluminum Co Columbia F alls Reduction Plant property is fished and the fish are kept and consumed (Refs. 27; 35 ; Figure 6 of this HRS documentation record).

As a portion of the Flathead River where fish are taken and consumed is subject to Level II contamination, this portion of the river is assigned a food chain individual factor value of 45 (Ref. 1, p. 51638, and Section 4.2.3.3.1). Food Chain Individual Factor Value: 45

4.2.3.3.2 Population

4.2.3.3.2.1 Level I Concentrations

No Level I concentrations have been documented Level I Concentrations Factor Value: 0

4.2.3.3.2.2 Level II Concentrations

The extent of the Level II contamination of the Flathead River fishery is 0.8 mil es (distance from the upper most PPE (Source 4) ) to the sample CF

- SW

- 07 (Refs. 3, Figure 4, pp. 59 , 60 , Table E 38 , p. 30 5 ; 30). Values for the amount of human food chain organisms produced annually from this fishery has been estimated at greater than 0 since actual production is not documented. For an annual production of greater than 0 to 100 pounds per year, a Human Food Chain Population Value of 0.03 is assigned for the fishery (Ref. 1, Section 4.2.3.3.2.2, Table 4

- 18).

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 73Identity of Fishery Annual Production

(pounds) References Human Food Chain Population Value (Table 4- 18)

Flathead River fishery >0 Ref. 1, pp. 51621, 51638; 3, Table E3 8, p. 305, Appendix D, p. 198; 3a, App. F, Section 5, pp. 1131,1132, Section 6, pp. 225, 226; Section 7, 1485, 1508, 1509 ; 27; 35 0.03

Sum of Level II Human Food Chain Population Values: 0.03

Level II Concentrations Factor Value: 0.03 4.2.3.3.2.3 Potential Human Food Chain Contamination

A s the actual contamination score is sufficient to score the Human Food Chain threat , potential contamination is not scored

. However , the EPA is concerned with the threat posed to fisheries downstream of the zone of contamination.

4.2.3.3.2.4 Calculation of Population Factor Value

The population factor value is calculated by summing the value of Level I concentration (0), Level II concentration (0.03) and potential human food chain contamination factors for the watershed (0). The resulting value is assigned the population factor value for the watershed (Ref. 1, Section 4. 2.3.3.2.4).

Calculations:

0 + 0.03 + 0= 0.03

4.2.3.3.3 Calculation of a Human Food Chain Threat - Target Factor Category Value

The Human Food Chain Threat

- Target Factor Category Value is calculated by summing the Food Chain Individual (45) and Population Factor Value of the watershed (0.03). The resulting value, 45.03, is assigned as the Human Food Chain Threat -Target Score (Ref. 1, Sec. 4.2.3.3).

Food Chain Target Factor Category Value: 45.03

4.2.3.4. Calculation of a Human Food Chain Threat Score for a Watershed

The Human Food Chain Threat is calculated by multiplying the Human Food Chain Threat Factor Category Value for likelihood of release (550), Waste Characteristics (320) and Targets for a Watershed (45.03). The product is rounded to the nearest in teger and divided by 82,500. The resulting value, of 96 , is assigned as the Human Food Chain Threat Score for the watershed (Ref. 1, Sec. 4.2.3.4).

Calculations: (550 x 320 x 45.03) ÷ 82,500 = 96, capped to 100

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 744.2.4 Environmental Threat

4.2.4.1 Environmental Threat Likelihood of Release

As was shown above in Section 4.2.1.3 of this HRS documentation record, an observed released of site attributable contaminants is established for both the alluvial/glacial aquifer as well as the Flathead River. Therefore, an observed release factor value of 550 is assigned for the watershed (Ref. 1, pp. 51629, 51638, Sections 4.2.2.1.1 and 4.2.4.1). Surface Water Observed Release Factor Value: 550

4.2.4.2 Environmental Threat Waste Characteristics

4.2.4.2.1 Ecosystem Toxicity/Mobility/Persistence/Bioaccumulation

The table below summarizes the ecosystem toxicity, mobility, persistence, and bioaccumulation potential factor values for each hazardous substance for which an observed release into the alluvial/glac ial aquifer has been established (Ref. 1, p. 51638, Section 4.2.4.2.1). As per Section 4.2.4.2.1.5 of the HRS, the substance with the highest ecosystem toxicity/ mobility/ persistence/ bioaccumulation potential factor value is used to assign the ecosystem tox icity/ mobility/ persistence/ bioaccumulation potential factor value for the watershed (Ref. 1, p. 51638, Section 4.2.4.2.1.5). M anganese and total c hromium ha ve the highest ecosystem toxicity/mobility/ persistence/ bioaccumulation potential factor value o f 5 x 10 6

.
Toxicity/Persistence/Bioaccumulation Factor Value: 5 x 10 6

Hazardous Substance Source No. Eco

Toxicity Factor Value Mobility Factor Value Persistence Factor Value* Bioaccu mulation Value** Toxicity/Mobility/ Persistence/ Bioaccumulation

Fa ctor Value (Table 4

- 16) Reference

Arsenic 1,2,3, 4 10 1 1.0 50,000 5 x 10 5 2, p. BI-1

Chromium (total) 1,2 ,3, 4 10,000 1 1.0 500 5 x 10 6 2, p. BI-3

Cyanide 1,2,3

, 4 1,000 1 0.4 0.5 200 2, p. BI-3

Manganese 1,2,3, 4 100 1 1.0 50,000 5 x 10 6 2, p. BI-7

Zinc 1,2,3, 4 10 1 1.0 50,000 5 x 10 5 2, p. B I

10
Notes: * Persistence value for Rivers ** Environmental Bioaccumulation factor value for Freshwater

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 754.2.4.2.2 Hazardous Waste Quantity

Source No. Source Type Source Hazardous Waste Quantity

1 Surface impoundm ent 3,685.8
2 P ile 25,465.8
3 P ile 5,830.3
4 P ile 13,336.06
Total 48,317.96

The sum of the hazardous waste quantity values for Sources 1, 2, 3 and 4 corresponds to a hazardous waste quantity factor value of 10,000 in Table 2

- 6 of the HRS (Ref. 1, p. 51591). Therefore, a hazardous waste quantity factor value of 10,000 is assigned for the ground water to surface water migration component of the surfac e water migration pathway (Ref. 1, Sections 2.4.2.2 and 4.2.4.2.2, pp. 51591, 51592, 51644). Hazardous Waste Quantity Factor Value: 10,000 (Ref. 1, Sec 2.4.2.2)

4.2.4.2.3 Waste Characteristics Factor Category Value

The hazardous substance manganese, associated with percolation pond sources 1, 2, 3 and 4, and chromium (total) associated with percolation pond sources 1 and 2 (all ponds have a ground water pathway containment factor of greater than 0 for the watershed) corresponds to an ecosy stem toxicity/ mobility/persistence factor of 100 and 1 0 ,000 and a bioaccumulation potential factor of 50,000 and 5 00 respectively (Ref. 1, Tables 3

- 9 and 4

- 29; Ref. 2, p p

. BI

- 3, BI

- 7 ; Table 6 of this HRS documentation record).

Toxicity/Mobility/Persisten ce/ Hazardous Waste Quantity Factor Value: 1 x 10 8
Bioaccumulation Factor Value: 5 x 10 2

Waste Characteristics Factor Category Value: 320 (Ref. 1, Table 2

- 7) 4.2.4.3 Environmental Threat Targets

4.2.4.3.1. Sensitive Environments

4.2.4.3.1.1 Level I Sensitive Environments

No level I sensitive environments have been documented for this site.

4.2.4.3.1.2 Level II Sensitive Environments

Actual Environmental Threat Contamination

Targets are documented within the zone of actual contamination. The zone of contamination begins at the uppermost PPE (for the eastern south percolation pond) and continues a distance of 0.8 miles downstream to the furthest downstream observed release sample (CF

- SW

- 07) containing a hazardous substance with a bioaccumulation po tential factor value of 500 or greater (Refs. 1, Sec. 4.2.3.3; 3 a , App. F

, Section 7, pp. 1485, 1508, 1509 ; Figure 6 of this HRS documentation record ). Level II concentrations of dissolved manganese were detected in surface water samples within the zone of contamination. The Table below represents the zone of actual contamination in the Flathead River.

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 76Sample ID Sample Medium Distance from uppermost PPE Hazardous Substance Bio

accumulation Factor Value References

CF

- SW

- 07 Surface

water 0.8 miles Manganese (diss olved ) 500 Refs. 2, p. BI

- 7 ; Ref. 3, Table E3 8 , p. 30 5 , Appendix D, p. 198; 3a, App. F, Section 5, pp. 1131,1132,

Section 6, pp. 225, 226; Section 7, pp. 1485, 1508, 1509

Most Distant Level II Sample

The most distant Level II observed release surface water sample, CF

- SW

- 07, was collected from the Flathead River below the historical discharge location Outfall D006, approximately 0.8 miles downstream of the uppermost Anaconda Alu minum Co Columbia Falls Reduction Plant PPE ( Ref. 3, pp. 76, 77 , Table E4 8 , p. 30 5 ; 3a, App. F, Section 5, pp. 1131,1132, Section 6, pp. 225, 226; Section 7, pp. 1485, 1509; 7, p. 5; Figures 4, 5, 6, and 9 of this HRS documentation record ).

Sensitive Environment Assigned Value Extent of Sensitive Environment (Relative to PPE) Refs.

Critical Habitat for the Bull Trout 100 0.8 miles Ref. 3, Table E3 8 , p. 30 5 , Appendix D, p. 198; 3a, App. F, Section 5, pp. 1131,1132, Section 6, pp. 225, 226, Section 7, pp. 1485, 1508, 1509 ; 26, p. 2; 27, pp. 33

- 34, 47

- 49; 33; 42; 45; 46 ; Figures 6 and 9 of this HRS documentation record

Wetlands 50 1. 45 miles Ref. 3, Table E3 8 , p. 30 5 , Appendix D, p. 198; 3a, App. F, Section 5, pp. 1131,1132, Section 6, pp. 225, 226, Section 7, pp. 1485, 1508, 1509 ; 29 ; 33; 47; Figures 6 and 9 of this HRS documentation record

The ECOS and MFISH identified habitat for the Bull Trout (fede rally threatened) and Westslope Cutthroat Trout (federally sensitive) in the Flathead River (Refs. 26; 27, pp. 17

- 32; 42 ; 45; 46 ). Fish surveys conducted by FWP have confirmed the presence of both species in the Flathead River adjacent to the Site and the presence of Westslope Cutthroat Trout in Cedar Creek (Ref. 27, pp. 32

- 35 ; 28; 42). In addition to fish surveys identifying the Bull Trout and the Westslope Cutthroat Trout in the zone of actual contamination, the Flathead River in this zone is designated as critical habitat for the Bull Trout by the US Fish and Wildlife Service pursuant to 50 CFR 424.02 ( Ref. 45, p. 1; 46, pp. 1

- 174 ). Further, river bottom in the areas of CF

- SW

- 09, CF

- SW08, and CF

- SW

- 07 demonstrate the conditions necessary to construct the clean cobble and low silt substrates necessary for the species to construct their redds (Ref. 3, App. B, pp. 171

- 172).

According to the US Fish and Wildlife Service National Wetlands Inventory Wetlands mapper, approximately 15.53 miles (on both sides of the river) of streamside wetlands were digitally measured along the length of the wetland in the riverbed, and are present from the site along the Flathead River

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 77downstream 15 miles to the Target Distance Limit. These wetland types meet the HRS definition of a wetland, 40 CFR 230.3, and are considered eligible for HRS scoring (Refs. 1, Table 4

- 24, p. 51625; 29). Wetlands within the area of actual contamination were digitally measured at 1.45 miles in length by drawing a polygon around the portions of the we tlands that are in contact with the river at any time during the year (Refs. 29; 33; 47 ; Figure 6 of this documentation record). The dominant vegetation is freshwater palustrine scrub shrub and emergent wetlands, although they are defined as “Freshwater em ergent wetlands” and “freshwater forest/shrub wetlands” in Wetlands Mapper.

Actual contamination of sensitive environments in the Flathead River was documented by the Level II concentrations in surface water sample CF

- SW

- 07 (Refs. 3, Figure 4, p. 6 0

, Table E 38 , p. 30 5 ; 3a, App. F, Section 5, pp. 1131 , 1132 , Section 6, pp. 225, 226, Section 7, pp. 1485, 1509 ). Both the federally threatened Bull Trout and 1. 2 miles of wetlands are subject to Level II concentrations; therefore, a value of 125 is assigne d to the Environmental Threat Level II Concentration Factor Value (Ref. 1, Sec. 4.2.4.3.1.2). Level II Concentration Factor Value: 1 50

4.2.4.3.1.3 Potential Contamination

There are targets subject to potential contamination associated with the surface water bodies downstream of the zone of contamination and within the TDL, including additional bull trout habitat and wetlands; however, as the actual contamination score is su fficient to score the environmental threat, potential contamination is not scored (Refs. 1, Section 4.2.4.3.1.3; 26; 27; 29 ; 40 ). However

, the EPA is concerned with the threat to these sensitive environments

.

Environmental Potential Contamination Factor Value: 0

4.2.4.3.1.4 Calculation of an Environmental Threat

- Target Factor Category Value

The Environmental Threat

- Target Factor Category Value is calculated by summing the Level I concentrations (0), the Le vel II concentrations (1 50 ), and the potential contamination (NS). The resulting value, 125, is assigned as the Environmental Threat

- Target Sc ore (Ref. 1, Sec. 4.1.4.3.2.1.4 )

.

Calculations: 0 + 1 50 + 0 = 1 50

Environmental Target Factor Category Value: 1 50

4.2.4.4 Calculation of an Environmental Threat Score for a Watershed

The Environmental Threat is calculated by multiplying the Environmental Threat Factor Category Value for likelihood of release (550), Waste Characteristics ( 320 ) and Target s for a Watershed (150 ). The product is rounded to the nearest integer and divided by 82,500. The resulting value, subject to a maximum of 60, is assigned as the Environmental Threat Score for the watershed (Ref. 1, Sec. 4. 2 .4.4).

Calculations:

(550 x 320 x 150 ) ÷ 82,500 = 320 , capped at 60

HRS Documentation Record Anaconda Aluminum Co Columbia Falls Reduction Plant MTD057561763 78