HAZARD RANKING SYSTEM (HRS) DOCUMENTATION RECORD—REVIEW

COVER SHEET

Name of Site: AFTERTHOUGHT MINE

Contact Person: Leslie Ramirez, EPA Region 9 (415) 972-3978

Site Investigation: Leslie Ramirez, EPA Region 9 (415) 972-3978

Documentation Record: Christina Marquis, Weston Solutions, Inc.
christina.marquis@westonsolutions.com

Pathways, Components, or Threats Not Scored

The ground water, soil exposure and subsurface intrusion, and air pathways were not scored. There
are no known active drinking water wells within the Target Distance Limit (TDL) (Ref. 4, p. 17).
There are no residents on or near the site sources (Ref. 3; Ref. 4, p. 19). Therefore, the listing
decision is not significantly affected by those pathways. The site score is sufficient to qualify the
site for the NPL on the surface water pathway score.


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AFTERTHOUGHT MINE

Table of Contents

HRS DOCUMENTATION RECORD	1

HAZARD RANKING SYSTEM SUMMARY SCORESHEETS	2

HRS TABLE 4-1	3

REFERENCES	5

ACRONYM LIST	8

NOTES TO THE READER	9

SITE DESCRIPTION	16

SITE SOURCES	19

2.2 SOURCE 1 SOURCE CHARACTERIZATION	20

2.2.1	SOURCE IDENTIFICATION	20

2.2.2	HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE	20

2.2.3	HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY	23

2.4.2. HAZARDOUS WASTE QUANTITY	24

2.2 SOURCE 2 SOURCE CHARACTERIZATION	26

2.2.1	SOURCE IDENTIFICATION	26

2.2.2	HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE	26

2.2.3	HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY	28

2.4.2. HAZARDOUS WASTE QUANTITY	29

2.2 SOURCE 3 SOURCE CHARACTERIZATION	31

2.2.1	SOURCE IDENTIFICATION	31

2.2.2	HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE	31

2.2.3	HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY	33

2.4.2. HAZARDOUS WASTE QUANTITY	34

2.2 SOURCE 4 SOURCE CHARACTERIZATION	36

2.2.1	SOURCE IDENTIFICATION	36

2.2.2	HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE	36

2.2.3	HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY	38

2.4.2. HAZARDOUS WASTE QUANTITY	39

2.2 SOURCE 5 SOURCE CHARACTERIZATION	41

2.2.1	SOURCE IDENTIFICATION	41

2.2.2	HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE	41

2.2.3	HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY	44

2.4.2. HAZARDOUS WASTE QUANTITY	45

2.2 SOURCE 6 SOURCE CHARACTERIZATION	47

2.2.1	SOURCE IDENTIFICATION	47

2.2.2	HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE	47

2.2.3	HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY	50

2.4.2. HAZARDOUS WASTE QUANTITY	51

4.0 SURFACE WATER MIGRATION PATHWAY	55

4.1 OVERLAND/FLOOD MIGRATION COMPONENT (Figures A-4 and A-5)	55

4.1.1 GENERAL CONSIDERATIONS	55

4.1.1.1	Definition of Hazardous Substance Migration Path for Overland/flood Component	55

4.1.1.2	Target Distance Limit	56

4.1.2.1 Likelihood of Release	57

4.1.2.1.1	Observed Release	57

4.1.2.1.2	Potential to Release	68


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AFTERTHOUGHT MINE

4.1.2 Drinking Water Threat	69

4.1.3.2	Human Food Chain Threat Waste Characteristics	70

4.1.3.2.1	Toxicity/Persistence/Bioaccumulation	70

4.1.3.2.2	Hazardous Waste Quantity	71

4.1.3.2.3	Waste Characteristics Factor Category Value	71

4.1.3.3	Human Food Chain Threat Targets	72

4.1.3.3.1	Food Chain Individual	72

4.1.3.3.2	Population	72

4.1.3.3.2.1	Level I Concentrations	72

4.1.3.3.2.2	Level II Concentrations	72

4.1.3.3.2.3	Potential Human Food Chain Contamination	73

4.1.4.2	Environmental Threat Waste Characteristics	74

4.1.4.2.1	Ecosystem Toxicity/Persistence/Bioaccumulation	74

4.1.2.2.2	Hazardous Waste Quantity	75

4.1.2.2.3	Waste Characteristics Factor Category Value	75

4.1.4.3	Environmental Threat Targets	76

4.1.4.3.1 Sensitive Environments	76

4.1.4.3.1.1 Level I Concentrations	76

4.1.4.3.1.2. Level II Concentrations	76

Figures

Figure A-l: Site Location Map
Figure A-2: Site Vicinity Map

Figure A-3: Afterthought Mine Source Sampling Map
Figure A-4: Afterthought Mine Probable Point of Entry Map
Figure A-5: 15-Mile Surface Water Target Distance Limit
Figure A-6: Afterthought Mine Stream Sample Location Map


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AFTERTHOUGHT MINE

Name of Site:
EPA ID#:

EPA Region:

Date Prepared:

Street Address of Site:
City, County and State:
Topographic Map:

HRS DOCUMENTATION RECORD

AFTERTHOUGHT MINE

CAN000908808
9

March 2024

25 miles northeast of Redding on Highway 299
Bella Vista, Shasta County, California 96008
Oak Run, CA USGS 7.5-Minute Quadrangle (Ref. 3)

Latitude: 40° 44' 4.3692" North Longitude: 122° 4' 20.6256" West (Ref. 3; Ref. 4, p. 44)

Latitude/Longitude Reference Point: The latitude and longitude correspond to Portal 1 (Source 1)
sampling location AC-03 (Ref. 4, p. 44).

SCORES

Air Pathway

=

Not scored

Ground Water1 Pathway

=

Not scored

Soil Exposure and
Subsurface Intrusion
Pathway

'

Not scored

Surface Water Pathway

=

100.00

HRS SITE SCORE

=

50.00

*The street address, coordinates, and contaminant locations presented in this HRS documentation record identify the
general area where the site is located. They represent one or more locations the United States Environmental Protection
Agency (EPA) considers to 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 precisely 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 determination that a certain area may need to be
addressed under the Comprehensive Environmental Response, Compensation & Liability Act (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 contamination has come to be located.

1 "Ground water" and "groundwater" are synonymous; the spelling is different due to "ground water" being codified
as part of the HRS, while "groundwater" is the modern spelling.

1


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AFTERTHOUGHT MINE
HAZARD RANKING SYSTEM SUMMARY SCORESHEETS

SITE NAME: AFTERTHOUGHT MINE
CITY/COUNTY/STATE: Bella Vista. Shasta County. California
EPA ID #: CAN000908808

EVALUATOR: Christina Marquis DATE: March 2024
LATITUDE: 40° 44' 4.3692" N LONGITUDE: 122° 4' 20.6256" W



s

s2

Ground Water Migration Pathway Score (Sgw)

Not scored

Not scored

Surface Water Migration Pathway Score (Ssw)

100

10,000

Soil Exposure and Subsurface Intrusion Pathway

Score (Ssessi)

Not scored

Not scored

Air Migration Pathway Score (Sa)

Not scored

Not scored

Sgw2 +Ssw2 + Ssessi2 + Sa2

xxxxxxx

10,000

(Sgw2 +Ssw2 + Ssessi2 + Sa2) / 4

xxxxxxx

2,500

SQRT ((Sgw2 +Ssw2 + Ssessi2 + Sa2) / 4)

xxxxxxx

50.00

2


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AFTERTHOUGHT MINE

HRS TABLE 4-1

Surface Water Overland/Flood Migration Component Scoresheet

Factor Categories and Factors

Maximum
Value

Value
Assigned

Drinking Water Threat





Likelihood of Release:





1. Observed Release

550

550

2. Potential to Release by Overland Flow:





2a. Containment

10



2b. Runoff

25



2c. Distance to Surface Water

25



2d. Potential to Release by Overland Flow (lines 2a x [2b + 2c])

500



3. Potential to Release by Flood:





3 a. Containment (Flood)

10



3b. Flood Frequency

50



3c. Potential to Release by Flood (lines 3a x 3b)

500



4. Potential to Release (lines 2d + 3c, subject to a maximum of 500)

500

Not scored

5. Likelihood of Release (higher of lines 1 and 4)

550

550

Waste Characteristics:





6. Toxicity/Persistence

(a)

Not scored

7. Hazardous Waste Quantity

(a)

Not scored

8. Waste Characteristics

100

Not scored

Targets:





9. Nearest Intake

50

Not scored

10. Population:





10a. Level I Concentrations

(b)

Not scored

10b. Level II Concentrations

(b)

Not scored

10c. Potential Contamination

(b)

Not scored

lOd. Population (lines 10a + 10b + 10c)

(b)

Not scored

11. Resources

5

Not scored

12. Targets (lines 9 + lOd +11)

(b)

Not scored

Drinking Water Threat Score:





13. Drinking Water Threat Score

([lines 5 x 8 x 12]/82,500, subject to a maximum of 100)

100

Not scored

Human Food Chain Threat





Likelihood of Release:





14. Likelihood of Release (same value as line 5)

550

550

Waste Characteristics:





15. Toxicity/Persistence/Bioaccumulation

(a)

500,000,000

16. Hazardous Waste Quantity

(a)

10,000

17. Waste Characteristics

1,000

1,000

3


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AFTERTHOUGHT MINE

HRS Table 4-1 - Surface Water Overland/Flood Migration Component Scoresheet (cont'd)

Factor Categories and Factors

Maximum
Value

Value
Assigned

Targets:





18. Food Chain Individual

50

20

19. Population:





19a. Level I Concentrations

(b)

0

19b. Level II Concentrations

(b)

0

19c. Potential Human Food Chain Contamination

(b)

0.00003

19d. Population (lines 19a + 19b + 19c)

(b)

0.00003

20. Targets (lines 18 + 19d)

(b)

20.00003

Human Food Chain Threat Score:





21. Human Food Chain Threat Score

100

100.00

([lines 14 x 17 x 20]/82,500, subject to a maximum of 100)

Environmental Threat





Likelihood of Release:





22. Likelihood of Release (same value as line 5)

550

550

23. Ecosystem Toxicity/Persistence/Bioaccumulation

(a)

500,000,000

24. Hazardous Waste Quantity

(a)

10,000

25. Waste Characteristics

1,000

1,000

Targets:





26. Sensitive Environments:





26a. Level I Concentrations

(b)

0

26b. Level II Concentrations

(b)

25

26c. Potential Contamination

(b)

0.175

26d. Sensitive Environments (lines 26a + 26b + 26c)

(b)

25.175

27. Targets (value from 26d)

(b)

25.175

Environmental Threat Score:





28. Environmental Threat Score

60

60

([lines 22 x 25 x 27]/82,500, subject to a maximum of 60)

Surface Water Overland/Flood Migration Component Score for





a Watershed





29. Watershed Scorec

100

100.00

(lines 13 + 21 + 28, subject to a maximum of 100)

Surface Water Overland/Flood Migration Component Score





30. Component Score (S0f), (highest score from line 29 for all
watersheds evaluated, subject to a maximum of 100) (c)

100

100.00

(a)	Maximum value applies to waste characteristics category.

(b)	Maximum value not applicable.

(c)	Do not round to nearest integer.

4


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AFTERTHOUGHT MINE

REFERENCES

Reference
Number

Description of the Reference

1

U.S. Environmental Protection Agency (EPA). Hazard Ranking System
(HRS), Title 40 Code of Federal Regulations (CFR) Part 300, Appendix A
(55 Federal Register [FR] 51583, December 14, 1990, as amended at 82 FR
2779, Jan. 9, 2017; 83 FR 38037, Aug. 3, 2018), as published in the CFR on
July 1, 2019, with two attachments—Attachment A: FR Vol. 55, No. 241.
December 14, 1990. HRS Preamble. Attachment B: FR Vol. 82, No. 5,
January 9, 2017. Addition of a Subsurface Intrusion Component to the
Hazard Ranking System Preamble. 197 Pages. Available on-line at:
https://semspub.epa.gov/work/HO/174028.pdf and
httDs://www.regulations. gov/document?D=EP A-HO-SFUND-2010-1086-



0104.

2

EPA, Superfund Chemical Data Matrix (SCDM) Query, Accessed January
24, 2024, 18 pages. Available online at:

httD ://www. eoa. gov/ suoerfund/ suDerfund-chemical-data-matrix-scdm.

3

U.S. Geological Survey, 7.5 Minute Topographic Map of Oak Run,
California, 2018, 1 sheet.

4

Weston Solutions, Inc., Site Inspection Report Afterthought Mine, prepared
for EPA, May 2023, 62 pages.

5

Weston Solutions, Inc., Site Inspection Report Afterthought Smelter,
prepared for EPA, May 2023, 52 pages.

6

Ned Black, EPA, contact report with Leslie Ramirez, re: Fishing in Little
Cow Creek, with attached California Department of Fish and Wildlife
Fishing Guide and Article of 34 Best Fishing Spots Near Redding and Shasta
County April 21, 2023, 25 pages.

7

Weston Solutions, Inc., Site Inspection Sampling and Analysis Plan,
Afterthought Mine, prepared for EPA, March 2020, 164 pages.

8

Fishbrain.com. Fishing spots, fishing reports and regulations in Little Cow
Creek, data extracted January 28, 2024. 22 pages.

9

Eurofins Burlington, Analytical Report, Job Number: 200-64005-1, SDG
Number: MY0AA0, July 28, 2022, 546 pages.

10

Eurofins Burlington, Analytical Report, Job Number: 200-64005-2, SDG
Number: MY0AC1, July 28, 2022, 876 pages.

11

Eurofins Burlington, Analytical Report, Job Number: 200-64005-3, SDG
Number: MY0AF9, July 29, 2022, 483 pages.

12

Eurofins Burlington, Analytical Report, Job Number: 200-63979-1, SDG
Number: MY0AJ5, July 26, 2022, 2,420 pages.

13

U.S. Fish and Wildlife Service, National Wetlands Inventory,
https://fwsprimarv.wim.usgs.gov/wetlands/apps/wetlands-mapperA data



extracted January 25, 2024, 5 pages.

14

Tuggle, J.M., Exploring Shasta County History, Furnaceville & Ingot: The
Home of the Afterthought Mine. June 23, 2021, 22 pages.

15

EPA, Afterthought Mine Validation Report, October 5, 2022, 399 pages.

16

EPA, Afterthought Mine Validation Report, October 5, 2022, 180 pages.

5


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AFTERTHOUGHT MINE

Reference
Number

Description of the Reference

17

Brown, G.C., California State Mining Bureau, Mines and Mineral Resources
of Shasta County, Siskiyou County, Trinity County. 1915.210 pages.

18

U.S. Fish and Wildlife Service, National Wetlands Inventory,
httDs://fwsDrimarv.wim.usgs.gov/wetlands/aDDs/wetlands-mapperA data

extracted October 3, 2023, 1 page.

19

EPA, Afterthought Smelter Validation ReDort, October 5, 2022, 220 pages.

20

U.S. Department of Commerce, National Oceanic and Atmospheric
Administration, National Marine Fisheries Service, 50 CFR Part 226,
Endangered and Threatened Species; Designation of Critical Habitat for
Seven Evolutionarily Significant Units of Pacific Salmon and Steelhead in
California, (70 FR 52488) September 2, 2005, 140 pages.

21

Albers, J., State of California Division of Mines, Special Report 29, Geology
and Ore Deposits of the Afterthought Mine, Shasta County, California,
February 1953, 30 pages.

22

State of California Department of Natural Resources, California Journal of
Mines and Geology, Volume 50, Number 1, January 1954, 282 pages.

23

State of California Department of Natural Resources, California Journal of
Mines and Geology, Volume 53, Nos. 3 & 4, July-October 1957, 395 pages.

24

California State Mining Bureau, Mining in California, January 1923, 50
pages.

25

California State Mining Bureau, Mining in California, April 1926, 112 pages.

26

State of California, The Resources Agency, Department of Water Resources,
The Greenhorn and Afterthought Mines - a Plan for the Control and
Abatement of Acid and Heavy Metal Pollution, Shasta County, California,
July 1985, 97 pages.

27

Ecology & Environment, Inc., Preliminary Assessment, Afterthought Mine,
August 24, 1987, 118 pages.

28

Hook & Bullet, Little Cow Creek Fishing near Palo Cedro, California,
hookandbullet.com, July 24, 2019, 5 pages.

29

Heiman, Dennis, Associate Land and Water Use Analyst, Memorandum to
File, Survey of Afterthought Mine and Little Cow Creek, May 11, 1982, 3
pages.

30

Mining and Scientific Press, Shasta County as a Smelting Centre, October
24, 1908, 2 pages.

31

Lewis, Robert H., Office Memorandum, Afterthought Mine, 205(j) Project,
Second Quarterly Sampling Results, September 5, 1984, 4 pages.

32

California Regional Water Quality Control Board, Central Valley Region,
Order No. 97-097, NPDES No. CA0084166, Waste Discharge Requirements
for Agricultural Management and Production Company, Inc., Afterthought
Mine, Shasta County, June 20, 1997, 7 pages.

33

California Regional Water Quality Control Board, Central Valley Region,
Order No. Administrative Civil Liability in the Matter of Agricultural
Management and Production Company, Inc., Afterthought Mine, Shasta
County, September 17, 1999, 8 pages.

6


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AFTERTHOUGHT MINE

Reference
Number

Description of the Reference

34

Rossi, Jeri, ICF, ESAT Region 9, Memorandum, Review of Analytical Data,
Tier 3, Afterthought Mine SDGNo. MY0AF9, September 30, 2022, 34
pages.

35

Andrews, John, SHN Consulting Engineers & Geologists, Letter with
Attachments, Base Maps, Cease and Desist Order 97-098, Afterthought
Mine, Shasta County, California, October 24, 1997, 7 pages.

36

SHN Consulting Engineers & Geologists, Remedial Action Plan,
Afterthought Mine, Shasta County, California, August 31, 1998, 58 pages.

37

SHN Consulting Engineers & Geologists, Cow Creek Watershed
Assessment, November 2001, 370 pages.

38

California State Water Resources Control Board, Final California 2012
Integrated Report (303(d) List/305(b) Report), Little Cow Creek
(downstream from Afterthought Mine),

https://www.waterboards.ca.gov/water issues/programs/tmdl/integrated2012.
shtml?wbid=CAR5073301019990126112551, data extracted July 22, 2019, 7
pages.

39

U.S. Geological Survey, Geological Survey Professional Paper 338, Geology
and Ore Deposits of East Shasta Copper-Zinc District, Shasta County,
California, 1961, 125 pages.

40

U.S. Geological Survey, National Water Information System, USGS
11373300 Little Cow C NR Ingot CA, https://waterdata.usgs.gov/nwis, data
extracted June 5, 2019, 2 pages.

41

Weston Solutions, Inc., Preliminary Assessment Report, Afterthought Mine,
September 2019, 1,982 pages.

42

Weston Solutions, Inc., Preliminary Assessment Report, Afterthought
Smelter, September 2019, 1,842 pages,

43

Rossi, Jeri, ICF, Environmental Services Assistance Team (ESAT) Region 9,
Memorandum, Review of Analytical Data, Tier 3, Afterthought Mine SDG
No. MY0AA0, September 30, 2022, 49 pages.

44

Rossi, Jeri, ICF, ESAT Region 9, Memorandum, Review of Analytical Data,
Tier 3, Afterthought Mine SDGNo. MY0AC1, September 30, 2022, 68
pages.

45

EPA, Afterthought Smelter Validation Report, October 5, 2022, 240 pages.

46

Rossi, Jeri, ICF, ESAT Region 9, Memorandum, Review of Analytical Data,
Tier 3, Afterthought Mine SDGNo. MY0AJ5, October 4, 2022, 53 pages.

47

Weston Solutions, Inc., Attachment 4 Field Logbook. June 2022, 3 pages.

48

EPA. Office of Superfund Remediation and Technology Innovation. Using
Qualified Data to Document an Observed Release and Observed
Contamination. Directive 9285.7-89FS. November 2022. 20 pages.

7


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AFTERTHOUGHT MINE

ACRONYM LIST

Vigfi

micrograms per liter

AMD

acid mine drainage

CERCLA

Comprehensive Environmental Response, Compensation, and Liability Act

cfs

cubic feet per second

CLP

Contract Laboratory Program

CRQL

Contract Required Quantitation Limit

EPA

United States Environmental Protection Agency

gpm

gallons per minute

HRS

Hazard Ranking System

ISM

Inorganic Superfund Method

mg/kg

milligrams per kilogram

ND

not detected at or above the method detection limit

NPL

National Priorities List

NS

Not Scored

PPE

Probable Point of Entry

PRP

Potentially Responsible Party

SAP

Sampling and Analysis Plan

SCDM

Superfund Chemical Data Matrix

SI

Site Inspection

SQL

Sample Quantitation Limit

TDL

Target Distance Limit

USGS

United States Geological Survey

WESTON

Weston Solutions, Inc.

8


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AFTERTHOUGHT MINE

NOTES TO HI! READER

Page numbers have been added to the references in the lower right corner. For reference citations,
please refer to the page numbers in this location.

9


-------
Legend

~ Afterthought Mine Parcels

Other Parcels

References
- Parcel Data from County of Shasta
GIS, August 2023

Afterthought Mine Parcels

jnc -

CALIFORNIA

Site

Location

San
Franci sco

NATIONAL

v

Los AnifSles

The source of this image is ESRI,
used by the EPA with ESRI's permission.



o0?1

The source of this image is ESRI, used by the EPA with ESRI's permission

©

Scale in Miles 0.5
1:24,000

Prepared For:

EPA Region 9
Site Assessment
Program

Prepared By:

Weston Solutions, Inc.
Concord, CA 94520
February 2024



^—^roimr«i:n

FIGURE A-1

SITE LOCATION MAP

Afterthought Mine
HRS Documentation Record
Bella Vista, Shasta County, California

10


-------




!!



The source of this image is ESRI
used by the EPA with ESRI's

Legend

~ Afterthought Mine Parcels
Other Parcels

' • «3?t

Waste Rock/Tailings

Ore Railroad
Stream

References

-Waste Rock/Tailings from References:
#4, page 35; #21, page 21

-	Site Features from Reference:

#21, page 21

-	Ore Railroad from Reference:

#4, page 40

-	Parcel Data from County of Shasta GIS,
August 2023

iHHBH

	

Afterthought Mine Parcels

~ ~

WMWHItI



j-> v?x 1

•' 'TwrnmSfirfr '" m' 1

; Wm_M















v'-



WIS

%

/

H

Ttf

* r.V-.

i«

V ¦

§raBRM®tm^

¦WWi

""		--•*

r •¦Zi&SW -

-

a^JlV

- -

• Tl-fJ v

I

hZZjkIk' * * ¦ t ; >

v '?» *	/ -

V'j ' *' " <•' * ^ ^

» »/

Afterthought Smelter

n

Su„ . f

ftflNrfii

Ji

*v	* ¦



Ttt"

V * V-—X*,"

• J' t • '

• .vJw» •,* r A\

¦ \

; v

Vf -ys 3 , v /'•

K#* "	;

¦ % Nt m -	i

V "	> . ~

Scale in Feet
1:6,000

Prepared For:

EPA Region 9
Site Assessment
Program

Prepared By:

Weston Solutions, Inc.
Concord, CA 94520
February 2024

' v

' ffkl&

^

, / * - s*?.

FIGURE A-2

SITE VICINITY MAP

Afterthought Mine
HRS Documentation Record
Bella Vista, Shasta County, California

Awimw?n


-------
r

wam>i

North Fork
Waste Rock
Source 2

North Shaft

	

.' '*j

	

No. 1 Shaft

Mill Area
Waste Rock
Source 5

_ Portal 1

Source 1

ffifterthougM

Central Waste Rock
Source 3

AM-33
As: 56

East Portal

South Fork
Waste Rock
Source 4

Former Mill and
Tram Terminal

Legend

Source Samples (2022)

Arsenic Results (milligrams/kilogram)

V\feste Rock / Tailings

South Shaft

Ore Railroad

Stream

Tailings Pile
Source 6

69 - 300 (100X Industrial RSL)

As = Arsenic

RSL = EPA Regional Screening Level
Residential RSL = 0.68 milligrams per kilogram
Industrial RSL = 3.0 milligrams per kilogram

300 - 680 (1,000X Residential RSL)

Waste Rock/Tailings from References: #4, page 35; #21, page 21
Site Features from Reference: #21, page 21
Ore Railroad from Reference: #4, page 40
Sample Locations from Reference: #4, page 36
Sample Concentrations from References: #4, page 29; HRS
Documentation Record, Tables 1-7

The source of this image is ESRlIusgtj]
by the EPA with ESRI's permission

Prepared For:

EPA Region 9	fi A \

Site Assessment
Program
Prepared By:

Weston Solutions, Inc.

Concord, CA 94520
February 2024

FIGURE A-3

AFTERTHOUGHT MINE
SOURCE SAMPLING MAP
Afterthought Mine
HRS Documentation Record

Bella Vista, Shasta County, California

12


-------
North Shaft

i



wp.

Adit 4

.is

Source 2
North Fork
Waste Rock

No. 1 Shaft

y rm

Source 5
Mill Area
Waste Rock

L

Glory Hole



Sa 3

East Portal

Source 1
Portal 1

• ¦ y-

• ' *. - -1

m

xsrm



Former Mill and
Tram Terminal

South Shaft I

\

_ Source 6

f—	

\

Tailings Pile

t&CsSl -A-

K- 		

The source of^tnis image is ESRI, used
by the ERA* with ESRI's permission

Scale in Feet 300

1:3,000

%

m

(

C9RUi

Source 3
Central Waste Rock

Source 4
South Fork
Waste Rock

J

J



Legend

* ;	Probable Point of Entry (PPE)

Stream

/ %

OverlandFlow

Ore Railroad
Waste Rock / Tailings

References

| - Waste Rock/Tailings from References: #4,

page 35; #21, page 21
I - Site Features from Reference: #21, page 21
- Ore Railroad from Reference: #4, page 40

Prepared For;

EPA Region 9
Site Assessment
Program
Prepared By:

Weston Solutions, Inc.
Concord, CA 94520
February 2024

FIGURE A-4

AFTERTHOUGHT MINE
PROBABLE POINT of ENTRY MAP

Afterthought Mine
HRS Documentation Record
Bella Vista, Shasta County, California

13


-------
Legend

~ Afterthought Mine Parcels
*	Surface Water Pathway TDL

Wetland

Central Valley Steelhead Distinct Population Segment

TDL = Target Distance Limit
References

-	Wetlands from References: #13, pages 1-5; National

Wetlands Inventory Map Service

-	Central Valley Steelhead Population from Reference:

#20, pages 117 and 121

-	Parcel Data from County of Shasta GIS,

August 2023

ASTA
ION AL
REST





e*

Afterthought Mine Parcels



TDL Beginning Point

V-

SHASTA	J

NATIONAL (J
FOREST



ttle Round



Rodgen £utch

*

Soak Ru*

The source of this image is ESRI
used by the EPA with ESRI's
permission

v

oak f 'm

Scale in Miles

1:54,000

Prepared For:

EPA Region 9
Site Assessment
Program

Prepared By:

Weston Solutions, Inc.
Concord, CA 94520
February 2024

FIGURE A-5

15-MILE SURFACE WATER
TARGET DISTANCE LIMIT

Afterthought Mine
HRS Documentation Record
Bella Vista, Shasta County, California

14


-------
Legend

Q Sediment Sampling Location

Surface Water Sampling Location
Stream

r "\ M probable Point of Entry (PRE)

Wetland

AC = Afterthought Creek

LCC-AM = Little Cow Creek - Afterthought Mine

PPE = Probable Point of Entry

References

-	Sampling Data from Reference: #4, page 44
-Waste Rock/Tailings from References:

#4, page 35; #21, page 21

-	Site Features from Reference:

#21, page 21

-	Wetlands from References: #13, pages 1-2

National Wetlands Inventory Wetlands Map

' '' •. rim? ¦ ¦«
'¦ wim-$$$% Mm?®** * ¦¦ *

• 1 * mre? '• • ,J' . « J

K ¦ ' ' >"

• »¦. ~ i s i.	i ojjvv'7

*j-" Sa ''y*~

'-jfe ' '

II'- ¦., -

• f

«j







,-jf -tji'.S; /•	Vf .'V T





» r • ' » r' K' t JifT

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viiri
Sfc • '•

Ownfli jfcjl

HU

¦









¦

¦



i'1

ft**' S

vrMt#». >

«rv

rit

ftflg I

Scale in Feet

1:6,000

1,000

Prepared For:
EPA Region 9
Site Assessment
Program
Prepared By:

Weston Solutions, Inc.
Concord, CA 94520
February 2024

FIGURE A-6

AFTERTHOUGHT MINE
STREAM SAMPLE LOCATION MAP
Afterthought Mine
HRS Documentation Record
Bella Vista, Shasta County, California

15


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AFTERTHOUGHT MINE

SITE DESCRIPTION

The Afterthought Mine site is located approximately 25 miles northeast of Redding on Highway
299 East, Bella Vista, Shasta County, California (Figure A-l of this HRS documentation record;
Ref. 4, p. 8). For Hazard Ranking System scoring purposes, the site consists of the release of
hazardous substances from former operations associated with mining and ore processing. The
sources of hazardous substances includes waste rock, tailings, and acid mine drainage (AMD)
(Sources 1-6) (Figure A-2 and Figure A-3 of this HRS documentation record; see section 2.2 and
subsections of this HRS documentation record).

Hazardous substances associated with the site sources include arsenic, cadmium, copper, lead,
mercury, and zinc (see Section 2.2, Source Characterization of this HRS documentation record).
An observed release of cadmium, copper, lead, and zinc is documented to Little Cow Creek (see
Section 4.1.2.1.1, Observed Release of this HRS documentation record). Targets affected by the
observed release include the Little Cow Creek fishery (see Section 4.1.3.3 Human Food Chain
Threat Targets of this HRS documentation record). Additional targets include potential
contamination of Critical Habitat for the Federal-listed threatened Steelhead (Oncorhynchus
mykiss), and Level II actual contamination of wetlands (see Section 4.1.4.3 Environmental Threat
Targets of this HRS documentation record).

The Afterthought Mine site is located in a canyon formed by Little Cow Creek, a perennial stream
that flows southwest to Cow Creek. Afterthought Mine is located approximately 3/4 mile upstream
from the town of Ingot. The former Afterthought Smelter is located approximately 1 mile
downstream of Afterthought Mine. A former rail bed that appears to have been constructed from
tailings and/or waste rock connects Afterthought Mine and Afterthought Smelter along the eastern
bank of Little Cow Creek (Figure A-2 of this HRS documentation record; Ref. 4, p. 8; Ref. 14, pp.
9, 22; Ref. 17, pp. 28-29).

The Afterthought Mine dates to 1862, when seven claims of the Copper Hill group were staked.
During the first few years after the mine's discovery, the oxidized ore near the surface was mined
on a small scale for gold and silver. In 1873, M.H. Peck purchased the property, named it the Peck
Mine, and mined copper ore that was shipped to Swansea, Wales, for processing. In 1875, Peck
built a small reverberatory furnace to reduce the sulfide ore, which failed, as did a water-jacketed
furnace built soon afterward. Subsequently, the mine was acquired by Joseph Conland and
Associates, who built a 25-ton water-jacketed blast furnace. Two attempts to treat the ore in this
furnace were made but both were unsuccessful. In 1896, 200 tons of ore were smelted. This yielded
32 tons of copper matte containing 37 percent copper, 45 ounces of silver, and $7 in gold per ton
(Ref. 17, pp. 28-29; Ref. 21, p. 5; Ref. 24, p. 26; Ref. 25, p. 35; Ref. 26, p. 54; Ref. 36, p. 7; Ref.
39, pp. 79, 95-96).

In 1903, the mine was purchased by the Great Western Gold Company. In 1905, the company
constructed a 250-ton water-jacketed blast furnace 1 mile downstream of the site at Afterthought
Smelter. Operation of this furnace continued successfully until 1908. During this period, the
average yearly output was reported to have been $350,000. The copper matte produced in the blast
furnace was shipped to a smelter in Salt Lake City where it was converted into blister copper.
However, the high zinc content of the ore made it extremely refractory, necessitating a large coke
charge and causing the furnace to frequently freeze (Ref. 17, pp. 28-29; Ref. 21, p. 5; Ref. 24, p.
26; Ref. 25, p. 35; Ref. 26, p. 54; Ref. 30; Ref. 36, p. 7; Ref. 39, p. 96).

16


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AFTERTHOUGHT MINE

In 1909, the Afterthought Copper Company acquired Afterthought Mine. A 300-ton oil-flotation
mill and a 300-ton reverberatory furnace were completed in 1919 at Afterthought Smelter, with
the objective of treating the sulfide ore by the Harwood process. In this process, the ore was first
pre-roasted in the reverberatory furnace and then treated by flotation. Operation began in July 1919
and lasted only 8 months, because the zinc and copper sulfides could not be cleanly separated.
Late in 1923, the company lost the mine through foreclosure. In February 1925, the Glidden Paint
Company, under the name California Zinc Company, began mining zinc ore under lease. The ore
was moved by an 8.5-mile aerial tram to the Bully Hill Mill. This tramway was put in operation in
November 1925 and delivered about 75 tons a day to the mill. A drop in the price of copper and
zinc in 1927 closed the operation (Ref. 21, p. 5; Ref. 23, pp. 14, 340; Ref. 24, pp. 16, 26-27; Ref.
25, pp. 35-36, 108-110; Ref. 26, p. 54; Ref. 36, p. 7; Ref. 39, p. 96).

The Coronado Copper & Zinc Co. purchased the mine in 1946, and after new ore bodies had been
located by exploratory drilling, the company constructed a 100-ton selective flotation plant.
Mining started in October 1948 and continued until July 1949, when the operation ceased due to a
drop in the price of metals. In July 1950, the mine reopened and operated continuously until August
1952. During this time, the crude oxide ore was ground to 94% minus 200 mesh, and the
concentrates were made by selective flotation. A copper-lead concentrate was shipped to a smelter
in Tooele, Utah, and a zinc concentrate was shipped to a smelter in Great Falls, Montana (Ref. 21,
p. 5, Ref. 23, p. 340; Ref. 26, p. 56; Ref. 36, p. 7; Ref. 39, pp. 79, 96).

In 1951, Afterthought Mine was reported to be the highest producer of copper, the second highest
producer of zinc, and the third highest producer of lead and silver in California (Ref. 22, pp. 129,
134, 138, 141). From 1900 to 1952, 166,424 tons of ore were mined from Afterthought Mine.
Production included 10,730,580 pounds of copper, 23,635,840 pounds of zinc, 1,738,300 pounds
of lead, 923,653 ounces of silver, and 4,992 ounces of gold (Ref. 39, pp. 80, 96). Afterthought
Mine ceased operations in August 1952 (Ref. 23, p. 340; Ref. 26, p. 56; Ref. 36, pp. 7-8; Ref. 39,
p. 79).

During operations, the mine workings totaled about 19,400 linear feet, including 17,200 feet of
drifts, crosscuts, and stopes and 2,200 feet of raises and shafts, developed to a depth of 729 feet
with 10 levels (Ref. 21, pp. 4, 23; Ref. 24, p. 27; Ref. 26, p. 56; Ref. 39, pp. 95, 97). Remnants of
the mine are still present on the mine property, including waste rock piles, adits/portals, and the
ruins of the mine plant. AMD discharges from mine portals and mine waste rock piles to
Afterthought Creek, which flows into Little Cow Creek adjacent to the mine property (Ref. 4, p.

8).

From the late 1970s to the present, multiple sampling investigations were conducted at the mine
property and in downstream surface water by the EPA, California Regional Water Quality Control
Board, and California Department of Fish and Wildlife (Ref. 4, pp. 11-12; Ref. 26, p. 60; Ref. 27,
pp. 1, 2; Ref. 29; Ref. 31; Ref. 32, p. 1; Ref. 33, p. 4; Ref. 36, p. 7; Ref. 37, pp. 200, 203; Ref. 41,
p. 5; Ref. 42, p. 5). A 1.1-mile portion of Little Cow Creek downstream of Afterthought Mine is
listed as impaired under Section 303 of the Clean Water Act (Ref. 38, p. 1).

In 2022, EPA conducted a Site Inspection (SI) at Afterthought Mine to determine whether the site
was eligible for placement on the National Priorities List (NPL). Based on the June 2022 SI
sampling event, on-site hazardous substance sources have been documented at Afterthought Mine,
including waste rock, tailings, and AMD (Ref. 4, pp. 5-6; Ref. 5, p. 5). Elevated concentrations of
metals, including maximum concentrations of 1,300 milligrams per kilogram (mg/kg) arsenic, 97

17


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AFTERTHOUGHT MINE

mg/kg cadmium, 9,600 mg/kg copper, 11,000 mg/kg lead, 27 mg/kg mercury, and 18,000 mg/kg
zinc, were detected in soil and waste rock samples (Ref. 4, p. 5).

18


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SITE SOURCES

A total of six sources were evaluated for scoring the Afterthought Mine site (see Figure A-3 of this
HRS documentation record). The sources originated as part of the Afterthought Mine operations.
Detailed information about each source, with reference citations, is available in the following
sections.

Hazardous substances associated with these sources include arsenic, cadmium, copper, lead,
mercury, and zinc.

Afterthought Mine Sources

Source
Number

Source Name

Source Type

1

Portal 1

Other

2

North Fork Waste Rock

Pile

3

Central Waste Rock

Pile

4

South Fork Waste Rock

Pile

5

Mill Area Waste Rock

Pile

6

Tailings Pile

Pile

19

Source 1 Characterization


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2.2 SOURCE 1 SOURCE CHARACTERIZATION

2.2.1	SOURCE IDENTIFICATION

Name of Source: Portal 1 Number of Source: 1
Source Type: Other

Description and Location of Source (see Figure A-3 of this HRS documentation record):

Source 1 consists of AMD discharge from Portal 1, located in the lower portion of the mine
property adjacent to Afterthought Creek (Ref. 4, p. 36). Portal 1 is also referred to as the main
portal in some historical documentation (Ref. 21, p. 4; Ref. 26, p. 16; Ref. 31, pp. 1-2; Ref. 35, p.
7). During mining operations, Portal 1 was the only known portal for the lower levels of the mine
and accessed over 3,000 feet of tunnels. Portal 1 has since collapsed (Ref. 26, p. 56).

AMD from Portal 1 flows into Afterthought Creek from the south, depositing a bright orange and
green slime on waste rock between the portal and the creek (Ref. 4, pp. 8, 50, 55; Ref. 41, pp. 33,
38-39). Flow from the portal was estimated at 10-20 gallons per minute (gpm) on April 23, 1982
(Ref. 29, p. 2). In 1984, average flow for Portal 1 was estimated at 20 acre-feet per year (Ref. 26,
p. 60). When Afterthought Creek is flowing, discharge from Portal 1 has been observed flowing
to Afterthought Creek and into Little Cow Creek causing a plume of mine drainage downstream
on the south bank (Ref. 26, pp. 60, 62; Ref. 29, p. 2; Ref. 41, pp. 33, 39). Surveys conducted in
1984 estimated that over 90% of the Afterthought Mine-related AMD emanated from Portal 1
(Ref. 26, pp. 60-61; Ref. 31, p. 1).

2.2.2	HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE
2022 EPA SI Sampling

From June 21, 2022 through June 24, 2022, Weston Solutions, Inc. collected soil, sediment, and
surface water samples as part of the SI for Afterthought Mine (Ref. 4, pp. 50-51). Samples were
collected in accordance with Sampling and Analysis Plan (SAP) approved by EPA on May 29,
2020 (Ref. 4, p. 13; Ref. 7, p. 2). Sediment samples were submitted to Eurofins Burlington under
the EPA Contract Laboratory Program (CLP) for metals analysis by Inorganic Superfund Method
(ISM) 02.4 ICP-AES. Surface water samples were submitted for metals analysis by ISM 0.24 ICP-
AES and ICP-MS (Ref. 4, p. 14; Ref. 5, p. 11). Validation of analytical data was contracted by
EPA in accordance with ISM 02.4 (Ref. 4, p. 13; Ref. 7, pp. 44-45; Ref. 34, pp. 1-3; Ref. 46, pp.
1, 2, 4).

Water and sediment samples were collected as it flows from the Portal 1 opening (AC-03). The
surface water had a pH of 2.77 and conductivity of 2,898 [j,S/cm (Ref. 4, pp. 50, 55). Sediment
samples were collected using a sample-dedicated plastic disposable scoop and transferred to a 4-
oz. wide-mouth glass jar. Water was removed from sediment samples by allowing the solids to
settle in the sample container and decanting the water after the water clarified sufficiently (Ref. 4,
pp. 13, 14; Ref. 7, p. 36). Surface water was collected by submerging the sample container in a
location where the bottle could be submerged beneath the surface such that it could be filled and
capped without entraining surface scum or bottom sediment. Two sets of surface water samples
were collected. The first set was unfiltered and preserved with nitric acid to a pH of less than 2;
the second set was filtered with a 0.45-micrometer, disposable filter and preserved with nitric acid

20

Source 1 Characterization


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to a pH of less than 2. A peristaltic pump with disposable plastic tubing was used to draw the water
through the disposable filter. (Ref. 4, p. 13; Ref. 7, pp. 36-37). Portal sediment samples are
compared to a background sample to show the relative increase in hazardous substances over
background levels. One background sediment sample was collected from South Fork Afterthought
Creek upstream of areas impacted by mining activities. Background surface water samples were
not collected as there was no surface water in Afterthought Creek upstream of mine property
sources (Ref. 4, pp. 14, 15, 51). Background samples were collected using the same methods as
the Source samples (Ref. 4, p. 14). Sampling locations are presented in Figure A-3 of this HRS
documentation record.

Table 1: 2022 SI, Source 1 Portal 1 Discharge Concentrations

Station
Location

CLP
Sample
ID

Filtered/
Unfiltered

Sampling
Date

Hazardous
Substance

Concentration
(HS/L)

Sample
Adjusted
CRQL*
(Hg/L)

References

ICP-MS Results

AC-03-
W-T

MY0AJ8

Unfiltered

6/23/2022

Arsenic

11

1.0

Ref. 4, pp. 31,44, 50,
55; Ref. 12, pp. 3, 676;
Ref. 15, pp. 64-66, 73,
85-87, 94; Ref. 46, p.
20; Ref. 47, p. 2

Cadmium

490

1.0

Copper

16,000

10

Lead

81

1.0

Zinc

120,000

150

AC-03-
W-F

MY0AJ7

Filtered

6/23/2022

Arsenic

3.6

1.0

Ref. 4, pp. 31,44, 50,
55; Ref. 12, pp. 3, 675;
Ref. 15, pp. 43-45, 52,
64-66, 73; Ref. 46, p.
17; Ref. 47, p. 2

Cadmium

470

1.0

Copper

16,000

10

Lead

78

1.0

Zinc

110,000

150

ICP-AES Results

AC-03-
W-T

MY0AJ8

Unfiltered

6/23/2022

Arsenic

15

10

Ref. 4, pp. 44, 50, 55;
Ref. 12, pp. 3, 18; Ref.
15, pp. 64-66, 73, 85-
87, 94; Ref. 46, p. 19;
Ref. 47, p. 2

Cadmium

460

5.0

Copper

15,000

50

Lead

83

10

Zinc

110,000

600

AC-03-
W-F

MY0AJ7

Filtered

6/23/2022

Cadmium

460

5.0

Ref. 4, pp. 44, 50, 55;
Ref. 12, pp. 3, 17; Ref.
15, pp. 43-45, 52, 64-
66, 73; Ref. 46, p. 16;
Ref. 47, p. 2

Copper

15000

50

Lead

80

10

Zinc

110,000

600

CLP: Contract Laboratory Program

|ig/L: micrograms analyte per liter adit discharge

ng/L nanograms mercury per liter adit discharge

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*: Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as defined
by the HRS (Ref. 1, Sections 1.1 and 2.3).

21

Source 1 Characterization


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Table 2: 2<

)22 SI, Source 1 Portal

Sediment Concentrations

Station
Location

CLP Sample
ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References

Background Sediment Sample

AC-BG-02-S

MYOAJO

6/24/2022

Arsenic

26

0.98

Ref. 4, pp. 31,44,
51; Ref. 11, pp. 4,
27, 413, 435; Ref.
16, pp. 101-103,
110, 121-123, 130;
Ref. 34, pp. 33-34;
Ref. 47, p. 3; Ref.
48, pp. 8, 20

Cadmium

1.9

0.49

Copper

53

2.5

Lead

32 J
(46.08)

0.98

Mercury

0.11 J-
(0.2013)

0.097

Zinc

370

5.9

Source 1 Portal 1 Sample

AC-03-S

MY0AH2

6/23/2022

Arsenic

800

4.8

Ref. 4, pp. 31,44,
50, 55; Ref. 11, pp.
3, 21, 413, 429; Ref.
16, pp. 61-63,70;
Ref. 34, pp. 21-22;
Ref. 47, p. 2; Ref.
48, pp. 8, 20

Cadmium

17

2.4

Copper

370

2.4

CLP: Contract Laboratory Program

mg/kg: milligrams analyte per kilogram sediment

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*: Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as

defined by the HRS (Ref. 1, Sections 1.1 and 2.3).

J-: The sample concentration is an estimated quantity, but the result may be biased low (Ref. 34, pp. 4, 8).
J: The result is an estimated quantity because the laboratory duplicate results were outside the method limit (Ref.
34, pp. 5, 8).

22

Source 1 Characterization


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2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY

All hazardous substances associated with Source 1 are available to the surface water pathway based
on a containment factor value of greater than zero (Ref 1, Section 2.2.3).

Containment Description

Containment
Factor
Value

References

Release to surface water:

When Afterthought Creek is flowing,
discharge from Portal 1 has been observed
flowing into Afterthought Creek and into
Little Cow Creek causing a plume of mine
drainage downstream on the south bank. A
containment factor of 10 is assigned.

10

Ref. 26, pp. 60, 62; Ref. 29, p.
2; Ref. 41, pp. 33, 39

23

Source 1 Characterization


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2.4.2. HAZARDOUS WASTE QUANTITY

2.4.2.1.1	Hazardous Constituent Quantity (Tier A)

The hazardous constituent quantity for Source 1 could not be adequately determined according to
the HRS requirements; that is, the total mass of all Comprehensive Environmental Response,
Compensation, and Liability Act of 1980 (CERCLA) hazardous substances in the source and
releases from the source is not known and cannot be estimated with reasonable confidence (Ref.
1, Section 2.4.2.1.1). There are insufficient historical and current data (manifests, potentially
responsible party [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 confidence. Scoring proceeds to the evaluation of Tier B, hazardous wastestream
quantity (Ref. 1, Section 2.4.2.1.1).

Hazardous Constituent Quantity Value: NS

2.4.2.1.2	Hazardous Wastestream Quantity (Tier B)

The total Hazardous Wastestream Quantity for Source 1 could not be adequately determined
according to the HRS requirements; that is, the total mass, or a partial estimate, of all hazardous
wastestreams and CERCLA pollutants and contaminants for the source and releases from the
source is not known and cannot be estimated with reasonable confidence (Ref. 1, Section
2.4.2.1.2). Insufficient historical and current data (permits, waste concentration data, annual
reports, etc.) are available to adequately calculate the total mass, or a partial estimate, of all
hazardous wastestreams and CERCLA pollutants and contaminants for the source and the
associated releases from the source. Therefore, there is insufficient information to adequately
calculate or extrapolate a total or partial Hazardous Wastestream Quantity for Source 1 with
reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section
2.4.2.1.2).

Hazardous Wastestream Quantity Value: NS

2.4.2.1.3	Volume (Tier C)

The exact volume for Source 1 could not be adequately determined with reasonable confidence.
Flow from the portal was estimated at 10-20 gpm on April 23, 1982 (Ref. 29, p. 2). In 1984,
average flow for Portal 1 was estimated at 20 acre-feet per year (Ref. 26, p. 60). However, as these
were not continuous observations and estimates, there is insufficient information to calculate the
volume for Source 1 with reasonable confidence. Therefore, based on the presence of hazardous
substances in the Portal 1 discharge, the volume of the source is greater than 0 but the total volume
is unknown (Ref. 1, Section 2.4.2.1.3).

Volume Assigned Value: >0

2.4.2.1.4	Area (Tier D)

Area is not evaluated for source type "other" (Ref. 1, Section 2.4.2.1.4).

Area Assigned Value: 0

24

Source 1 Characterization


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Source Hazardous Waste Quantity Value

According to the HRS, the highest of the values assigned to the source for hazardous constituent
quantity (Tier A), hazardous wastestream quantity (Tier B), Volume (Tier C), and Area (Tier D)
is assigned as the source hazardous waste quantity value (Ref. 1, Section 2.4.2.1.5).

Tier Evaluated

Source 1 Values

A

NS

B

NS

C

>0

D

0

Source 1 Hazardous Waste Quantity Value: >0

25

Source 1 Characterization


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2.2 SOURCE 2 SOURCE CHARACTERIZATION

2.2.1	SOURCE IDENTIFICATION

Name of Source: North Fork Waste Rock Number of Source: 2
Source Type: Pile

Description and Location of Source (see Figure A-3 of this HRS documentation record):

Source 2 consists of the waste rock pile along North Fork Afterthought Creek (Ref. 4, p. 35; Ref.
21, p. 21; Ref. 36, pp. 16-18). This waste rock pile is located in the upper portion of the mine
property and consists of waste rock from the No. 1 Shaft and Adit 4. Intermittent surface water in
the North Fork Afterthought Creek flows through the waste rock pile (Ref. 4, p. 8; Ref. 36, pp. 16-
18; Ref. 41, pp. 33, 36-37). A mine dump was mapped at this location in 1921 (Ref. 21, p. 21).
The area of the Source 2 waste rock pile is approximately 42,672.58 square feet. The area was
measured based on the aerial photo presented in Figure A-3 of this HRS documentation record and
on field observations during the 2019 PA and the 2022 SI correlating the unvegetated area with
the boundaries of the waste rock pile (Ref. 4, pp. 35, 51, 53-54; Ref. 41, pp. 33, 36-37).

2.2.2	HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE
2022 EPA SI Sampling

From June 21, 2022 through June 24, 2022, Weston Solutions, Inc. collected soil, sediment, and
surface water samples as part of the SI for Afterthought Mine (Ref. 4, pp. 50-51). Samples were
collected in accordance with the SAP approved by EPA on May 29, 2020 (Ref. 4, p. 13; Ref. 7, p.
2). Soil samples were submitted to Eurofins Burlington under the EPA CLP for metals analysis by
ISM 02.4 ICP-AES (Ref. 4, p. 14). Validation of analytical data was contracted by EPA in
accordance with ISM 02.4 (Ref. 7, pp. 44-45; Ref. 43, pp. 1, 2, 4; Ref. 44, pp. 1, 2, 4).

Waste rock samples were collected from one location within Source 2 (AM-25) (Ref. 4, p. 36).
Waste rock samples were collected using a sample-dedicated plastic disposable scoop and
transferred to a 4-oz. wide-mouth glass jar (Ref. 4, p. 13; Ref. 7, p. 36). Pile source samples were
compared to a background sample to show the relative increase in hazardous substances over
background soil levels. A background soil sample was collected from native soils north of the mine
property in an area that was not observed to be impacted by mining activities (Ref. 4, pp. 13-14,
50). Background samples were collected using the same methods as the Source samples (Ref. 4,
pp. 13, 14). Source sampling locations are presented in Figure A-3 of this HRS documentation
record.

26

Source 2 Characterization


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Table 3: 2(

)22 SI, Source 2 North Fork Waste Rock

Station
Location

CLP
Sample
ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References

Background Soil Samples

AM-BG-1

MY0AA0

6/22/2022

Arsenic

23

1.0

Ref. 4, pp. 29, 50;
Ref. 9, pp. 2-3, 12,
14, 470; Ref. 19, pp.
1-3, 10; Ref. 43, pp.
10-11; Ref. 47, p. 2;
Ref. 48, pp. 8, 20

Cadmium

1.7

0.51

Copper

77

2.5

Lead

100

1.0

Mercury

0.20 J-
(0.366)

0.10

Zinc

310

6.1

Source 2 North Fork Waste Rock Sample

AM-25

MY0AC6

6/24/2022

Arsenic

290

1.7

Ref. 4, pp. 29,51;
Ref. 10, pp. 3, 13, 18,
764, 786; Ref. 44, pp.
18-19; Ref. 45, pp.
41-43, 50; Ref. 47, p.
3; Ref. 48, pp. 8, 20

Cadmium

9.5

0.86

Copper

780

2.2

Lead

1,800

1.7

Mercury

2.9 J-

0.20

Zinc

1,400

10

CLP: Contract Laboratory Program
mg/kg: milligrams analyte per kilogram tailings

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*: Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as

defined by the HRS (Ref. 1, Sections 1.1 and 2.3).

J-: The result is an estimated quantity, but the result may be biased low (Ref. 43, pp. 5, 9; Ref. 44, pp. 5, 10).

27

Source 2 Characterization


-------
2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY

All hazardous substances associated with Source 2 are available to the surface water pathway based
on a containment factor value of greater than zero (Ref 1, Section 2.2.3).

Containment Description

Containment
Factor
Value

References

Release to surface water:

There is no known maintained engineered
cover or functioning and maintained run-on
control system and runoff management
system. Surface water in the intermittent
North Fork Afterthought Creek flows
through the waste rock pile.

10

Ref. 4, p. 8; Ref. 41, pp. 33, 36-
37

28

Source 2 Characterization


-------
2.4.2. HAZARDOUS WASTE QUANTITY

2.4.2.1.1	Hazardous Constituent Quantity (Tier A)

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
and releases from the source is not known and cannot be estimated with reasonable confidence
(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 2 with reasonable
confidence. Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1,
Section 2.4.2.1.1).

Hazardous Constituent Quantity Value: Not Scored (NS)

2.4.2.1.2	Hazardous Wastestream Quantity (Tier B)

The total Hazardous Wastestream Quantity for Source 2 could not be adequately determined
according to the HRS requirements; that is, the total mass, or a partial estimate, of all hazardous
wastestreams and CERCLA pollutants and contaminants for the source and releases from the
source is not known and cannot be estimated with reasonable confidence (Ref. 1, Section
2.4.2.1.2). Insufficient historical and current data (permits, waste concentration data, annual
reports, etc.) are available to adequately calculate the total mass, or a partial estimate, of all
hazardous wastestreams and CERCLA pollutants and contaminants for the source and the
associated releases from the source. Therefore, there is insufficient information to adequately
calculate or extrapolate a total or partial Hazardous Wastestream Quantity for Source 2 with
reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section

2.4.2.1.2).

Hazardous Wastestream Quantity Value: NS

2.4.2.1.3	Volume (Tier C)

The volume for Source 2 could not be adequately determined with reasonable confidence The
depth of Source 2 is unknown. Scoring proceeds to the evaluation of Tier D, area (Ref. 1, Section

2.4.2.1.3).

Volume Assigned Value: 0

2.4.2.1.4	Area (Tier D)

The area of the Source 2 waste rock pile is approximately 42,672.58 square feet. The area was
measured based on the aerial photo presented in Figure A-3 of this documentation record and on
field observations during the 2019 PA and the 2022 SI correlating the unvegetated area with the
boundaries of the waste rock pile (Figure A-3 of this documentation record; Ref. 4, pp. 51, 53-54;
Ref. 41, pp. 33, 36-37). In accordance with Ref. 1, Table 2-5, the equation for assigning a value
for a pile is the area in square feet divided by 13:

42,672.58/ 13 = 3,282.51

Area Assigned Value: 3,282.51

29

Source 2 Characterization


-------
Source Hazardous Waste Quantity Value

According to the HRS, the highest of the values assigned to the source for hazardous constituent
quantity (Tier A), hazardous wastestream quantity (Tier B), Volume (Tier C), and Area (Tier D)
is assigned as the source hazardous waste quantity value (Ref. 1, Section 2.4.2.1.5).

Tier Evaluated

Source 2 Values

A

NS

B

NS

C

0

D

3,282.51

Source Hazardous Waste Quantity Value: 3,282.51

30

Source 2 Characterization


-------
2.2 SOURCE 3 SOURCE CHARACTERIZATION

2.2.1	SOURCE IDENTIFICATION

Name of Source: Central Waste Rock Pile Number of Source: 3
Source Type: Pile

Description and Location of Source (see Figure A-3 of this HRS documentation record):

Source 3 consists of the waste rock pile between North Fork and South Fork Afterthought Creek
in the upper portion of the mine property (Figure A-3 of this HRS documentation record; Ref. 4,
pp. 35, 51, 53; Ref. 36, pp. 17-18). A mine dump was mapped at this location in 1921 (Ref. 21, p.
21). The area of the Source 3 waste rock pile is approximately 14,809.81 square feet. The area was
measured based on the aerial photo presented in Figure A-3 of this documentation record and on
field observations during the 2022 SI correlating the unvegetated area with the boundaries of the
waste rock pile (Figure A-3 of this documentation record; Ref. 4, pp. 35, 51, 53).

2.2.2	HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE
2022 EPA SI Sampling

From June 21, 2022 through June 24, 2022, Weston Solutions, Inc. collected soil, sediment, and
surface water samples as part of the SI for Afterthought Mine (Ref. 4, pp. 50-51). Samples were
collected in accordance with the SAP approved by EPA on May 29, 2020 (Ref. 4, p. 13; Ref. 7, p.
2). Soil samples were submitted to Eurofins Burlington under the EPA CLP for metals analysis by
ISM 02.4 ICP-AES (Ref. 4, p. 14). Validation of analytical data was contracted by EPA in
accordance with ISM 02.4 (Ref. 7, pp. 44-45; Ref. 43, pp. 1, 2, 4; Ref. 44, p. 1, 2, 4).

Waste rock samples were collected from three locations within Source 3 (AM-35 through AM-37)
(Ref. 4, pp. 36, 51, 53). Waste rock samples were collected using a sample-dedicated plastic
disposable scoop and transferred to a 4-oz. wide-mouth glass jar (Ref. 4, p. 13; Ref. 7, p. 36). Pile
source samples were compared to a background soil sample to show the relative increase in
hazardous substances over background soil levels. A background soil sample was collected from
native soils north of the mine property in an area that was not observed to be impacted by mining
activities (Ref. 4, pp. 13-14, 50). Background samples were collected using the same methods as
the Source samples (Ref. 4, pp. 13, 14). Source sampling locations are presented in Figure A-3 of
this HRS documentation record.

31

Source 3 Characterization


-------
Table 4: 2C

122 SI, Source 3 Central Waste Rock Pile

Station
Location

CLP
Sample
ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References

Background Soil Samples

AM-BG-1

MY0AA0

6/22/2022

Arsenic

23

1.0

Ref. 4, pp. 29, 50;
Ref. 9, pp. 2-3, 12,
14, 470; Ref. 19, pp.
1-3, 10; Ref. 43, pp.
10-11; Ref. 47, p. 2;
Ref. 48, pp. 8, 20

Cadmium

1.7

0.51

Copper

77

2.5

Lead

100

1.0

Mercury

0.20 J-
(0.366)

0.10

Zinc

310

6.1

Source 3 Central Waste Rock Pile Samples

AM-35

MY0AD8

6/24/2022

Arsenic

440

2.4

Ref. 4, pp. 29,51,53;
Ref. 10, pp. 3, 13,21,
764, 789; Ref. 44, pp.
30-31; Ref. 45, pp.
61-63, 70; Ref. 47, p.
3; Ref. 48, pp. 8, 20

Cadmium

21

1.6

Copper

2,400

6.1

Lead

8,700

12

Mercury

16 J-

0.87

Zinc

3,200

19

AM-36

MY0AD9

6/24/2022

Arsenic

470

3.7

Ref. 4, pp. 29,51,53;
Ref. 10, pp. 3, 13, 22,
764, 790; Ref. 44, pp.
32-33; Ref. 45, pp.
61-63, 70, 81-83, 90;
Ref. 47, p. 3; Ref. 48,
pp. 8, 20

Cadmium

34

1.9

Copper

3,000

9.4

Lead

8,500

9.4

Mercury

12 J-

0.95

Zinc

4,200

22

AM-37

MY0AE0

6/24/2022

Arsenic

300

2.0

Ref. 4, pp. 29,51,53;
Ref. 10, pp. 3, 13, 23,
764, 791; Ref. 44, pp.
34-35; Ref. 45, pp.
81-83, 90; Ref. 47, p.
3; Ref. 48, pp. 8, 20

Cadmium

6.5

0.98

Copper

1,200

2.5

Lead

3,100

3.9

Mercury

5.0 J-

0.37

CLP: Contract Laboratory Program
mg/kg: milligrams analyte per kilogram tailings

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*: Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as

defined by the HRS (Ref. 1, Sections 1.1 and 2.3).

J-: The result is an estimated quantity, but the result may be biased low (Ref. 43, pp. 5, 9; Ref. 44, pp. 5, 10).

32

Source 3 Characterization


-------
2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY

All hazardous substances associated with Source 3 are available to the surface water pathway based
on a containment factor value of greater than zero (Ref 1, Section 2.2.3).

Containment Description

Containment
Factor
Value

References

Release to surface water:

There is no evidence of a maintained
engineered cover or functioning and
maintained run-on control system and
runoff management system.

10

Ref. 4, pp. 35, 51, 53; Ref. 21,
p. 21

33

Source 3 Characterization


-------
2.4.2. HAZARDOUS WASTE QUANTITY

2.4.2.1.1	Hazardous Constituent Quantity (Tier A)

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
and releases from the source is not known and cannot be estimated with reasonable confidence
(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
confidence. Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1,
Section 2.4.2.1.1).

Hazardous Constituent Quantity Value: NS

2.4.2.1.2	Hazardous Wastestream Quantity (Tier B)

The total Hazardous Wastestream Quantity for Source 3 could not be adequately determined
according to the HRS requirements; that is, the total mass, or a partial estimate, of all hazardous
wastestreams and CERCLA pollutants and contaminants for the source and releases from the
source is not known and cannot be estimated with reasonable confidence (Ref. 1, Section
2.4.2.1.2). Insufficient historical and current data (permits, waste concentration data, annual
reports, etc.) are available to adequately calculate the total mass, or a partial estimate, of all
hazardous wastestreams and CERCLA pollutants and contaminants for the source and the
associated releases from the source. Therefore, there is insufficient information to adequately
calculate or extrapolate a total or partial Hazardous Wastestream Quantity for Source 3 with
reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section
2.4.2.1.2).

Hazardous Wastestream Quantity Value: NS

2.4.2.1.3	Volume (Tier C)

The volume for Source 3 could not be adequately determined in accordance with HRS
requirements. The depth of Source 3 is unknown. Scoring proceeds to the evaluation of Tier D,
area (Ref. 1, Section 2.4.2.1.3).

Volume Assigned Value: 0

2.4.2.1.4	Area (Tier D)

The area of the Source 3 waste rock pile is approximately 14,809.81 square feet. The area was
measured based on the aerial photo presented in Figure A-3 of this documentation record and on
field observations during the 2022 SI correlating the unvegetated area with the boundaries of the
waste rock pile (Figure A-3 of this documentation record; Ref. 4, pp. 35, 51, 53). In accordance
with Ref. 1, Table 2-5, the equation for assigning a value for a pile is the area in square feet divided
by 13:

14,809.81 / 13 = 1,139.22

Area Assigned Value: 1,139.22

34

Source 3 Characterization


-------
Source Hazardous Waste Quantity Value

According to the HRS, the highest of the values assigned to the source for hazardous constituent
quantity (Tier A), hazardous wastestream quantity (Tier B), Volume (Tier C), and Area (Tier D)
is assigned as the source hazardous waste quantity value (Ref. 1, Section 2.4.2.1.5).

Tier Evaluated

Source 3 Values

A

NS

B

NS

C

0

D

1,139.22

Source Hazardous Waste Quantity Value: 1,139.22

35

Source 3 Characterization


-------
2.2 SOURCE 4 SOURCE CHARACTERIZATION

2.2.1	SOURCE IDENTIFICATION

Name of Source: South Fork Waste Rock Number of Source: 4
Source Type: Pile

Description and Location of Source (see Figure A-3 of this HRS documentation record):

Source 4 consists of the waste rock pile along South Fork Afterthought Creek (Figure A-3 of this
HRS documentation record; Ref. 4, p. 35; Ref. 21, p. 21; Ref. 36, pp. 16-18). This waste rock pile
is located in the upper portion of the mine property and is associated with Adit 3, also known as
Portal 3 (Ref. 4, pp. 8, 35, Ref. 36, pp. 16-18; Ref. 41, pp. 22, 33) A mine dump was mapped at
this location in 1921 (Ref. 21, p. 21). Water in the South Fork Afterthought Creek flows through
the waste rock pile (Figure A-3 of this HRS documentation record; Ref. 4, p. 8; Ref. 36, p. 17; Ref.
41, pp. 33, 36-37). The area of the Source 4 waste rock pile is approximately 10,136 square feet,
based on the historical boundaries of the mine dump (Figure A-3 of this HRS documentation
record; Ref. 4, p. 35; Ref. 21, p. 21; Ref. 36, pp. 17-18; Ref. 41, p. 22).

2.2.2	HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE
2022 EPA SI Sampling

From June 21, 2022 through June 24, 2022, Weston Solutions, Inc. collected soil, sediment, and
surface water samples as part of the SI for Afterthought Mine (Ref. 4, pp. 50-51). Samples were
collected in accordance with the SAP approved by EPA on May 29, 2020 (Ref. 4, p. 13; Ref. 7, p.
2). Soil samples were submitted to Eurofins Burlington under the EPA CLP for metals analysis by
ISM 02.4 ICP-AES (Ref. 4, p. 14). Validation of analytical data was contracted by EPA in
accordance with ISM 02.4 (Ref. 7, pp. 44-45; Ref. 43, pp. 1, 2, 4; Ref. 44, pp. 1, 2, 4).

Waste rock samples were collected from two locations within Source 4 (AM-32 and AM-33) (Ref.
4, pp. 36, 51). Waste rock samples were collected using a sample-dedicated plastic disposable
scoop and transferred to a 4-oz. wide-mouth glass jar (Ref. 4, p. 13; Ref. 7, p. 36). Pile source
samples were compared to a background soil sample to show the relative increase in hazardous
substances over background soil levels. A background soil sample was collected from native soils
north of the mine property in an area that was not observed to be impacted by mining activities
(Ref. 4, pp. 13-14, 50). Background samples were collected using the same methods as the Source
samples (Ref. 4, pp. 13, 14). Source sampling locations are presented in Figure A-3 of this HRS
documentation record.

36

Source 4 Characterization


-------
Table 5: 2(

)22 SI, Source <¦

South Fork Waste Rock

Station
Location

CLP
Sample
ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References

Background Soil Samples

AM-BG-1

MY0AA0

6/22/2022

Arsenic

23

1.0

Ref. 4, pp. 29, 50;
Ref. 9, pp. 2-3, 12,
14, 470; Ref. 19, pp.
1-3, 10; Ref. 43, pp.
10-11; Ref. 47, p. 2;
Ref. 48, pp. 8, 20

Cadmium

1.7

0.51

Copper

77

2.5

Lead

100

1.0

Mercury

0.20 J-
(0.366)

0.10

Zinc

310

6.1

Source 4 South Fork Waste Rock Pile Samples

AM-32

MY0AD5

6/24/2022

Arsenic

560

4.0

Ref. 4, pp. 29,51;
Ref. 10, pp. 3, 13, 19,
764, 787; Ref. 44, pp.
20-21; Ref. 45, pp.
41-43, 50; Ref. 47, p.
3; Ref. 48, pp. 8, 20

Cadmium

13 J+
(9.219)

2.0

Copper

790

2.5

Lead

1,300

2.0

Mercury

4.2 J-

0.41

AM-33

MY0AD6

6/24/2022

Copper

260

2.2

Ref. 4, pp. 29,51;
Ref. 10, pp. 3, 13, 20,
764, 788; Ref. 44, pp.
28-29; Ref. 45, pp.
41-43, 50, 61-63, 70;
Ref. 47, p. 3; Ref. 48,
pp. 8, 20

CLP: Contract Laboratory Program
mg/kg: milligrams analyte per kilogram tailings

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*: Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as

defined by the HRS (Ref. 1, Sections 1.1 and 2.3).

J-: The result is an estimated quantity, but the result may be biased low (Ref. 43, pp. 5, 9; Ref. 44, pp. 5, 10).
J+: The result is an estimated quantity, but the result may be biased high (Ref. 44, pp. 6, 10)

J:	Result is considered qualitatively uncertain because serial dilution analysis does not meet analysis

criteria (Ref. 44, pp. 6-7).

37

Source 4 Characterization


-------
2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY

All hazardous substances associated with Source 4 are available to the surface water pathway based
on a containment factor value of greater than zero (Ref 1, Section 2.2.3).

Containment Description

Containment
Factor
Value

References

Release to surface water:

There is no evidence of a maintained
engineered cover or functioning and
maintained run-on control system and
runoff management system. Surface water
in the South Fork Afterthought Creek flows
intermittently through the waste rock pile.

10

Ref. 4, pp. 8, 35, Ref. 21, p. 21;
Ref. 41, pp. 22, 33, 36-37

38

Source 4 Characterization


-------
2.4.2. HAZARDOUS WASTE QUANTITY

2.4.2.1.1	Hazardous Constituent Quantity (Tier A)

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
and releases from the source is not known and cannot be estimated with reasonable confidence
(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 4 with reasonable
confidence. Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1,
Section 2.4.2.1.1).

Hazardous Constituent Quantity Value: NS

2.4.2.1.2	Hazardous Wastestream Quantity (Tier B)

The total Hazardous Wastestream Quantity for Source 4 could not be adequately determined
according to the HRS requirements; that is, the total mass, or a partial estimate, of all hazardous
wastestreams and CERCLA pollutants and contaminants for the source and releases from the
source is not known and cannot be estimated with reasonable confidence (Ref. 1, Section
2.4.2.1.2). Insufficient historical and current data (permits, waste concentration data, annual
reports, etc.) are available to adequately calculate the total mass, or a partial estimate, of all
hazardous wastestreams and CERCLA pollutants and contaminants for the source and the
associated releases from the source. Therefore, there is insufficient information to adequately
calculate or extrapolate a total or partial Hazardous Wastestream Quantity for Source 4 with
reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section

2.4.2.1.2).

Hazardous Wastestream Quantity Value: NS

2.4.2.1.3	Volume (Tier C)

The volume for Source 4 could not be adequately determined with reasonable confidence. The
depth of Source 3 is unknown. Scoring proceeds to the evaluation of Tier D, area (Ref. 1, Section

2.4.2.1.3).

Volume Assigned Value: NS

2.4.2.1.4	Area (Tier D)

The area of the Source 4 waste rock pile is approximately 10,136 square feet, based on the
historical boundaries of the mine dump (Figure A-3 of this HRS documentation record; Ref. 4, p.
35; Ref. 21, p. 21; Ref. 36, pp. 17-18; Ref. 41, p. 22). In accordance with Ref. 1, Table 2-5, the
equation for assigning a value for a pile is the area in square feet divided by 13:

10,136/ 13 =779.69

Area Assigned Value: 779.69

39

Source 4 Characterization


-------
Source Hazardous Waste Quantity Value

According to the HRS, the highest of the values assigned to the source for hazardous constituent
quantity (Tier A), hazardous wastestream quantity (Tier B), Volume (Tier C), and Area (Tier D)
is assigned as the source hazardous waste quantity value (Ref. 1, Section 2.4.2.1.5).

Tier Evaluated

Source 4 Values

A

NS

B

NS

C

0

D

779.69

Source Hazardous Waste Quantity Value: 779.69

40

Source 4 Characterization


-------
2.2 SOURCE 5 SOURCE CHARACTERIZATION

2.2.1	SOURCE IDENTIFICATION

Name of Source: Mill Area Waste Rock Number of Source: 5
Source Type: Pile

Description and Location of Source (see Figure A-3 of this HRS documentation record):

Source 5 consists of the waste rock pile along Afterthought Creek and Little Cow Creek in the
lower portion of the mine in the vicinity of the former mill (Figure A-3 of this HRS documentation
record; Ref. 4, pp. 35, 51; Ref. 21, p. 21; Ref. 36, pp. 18-19; Ref. 41, pp. 33, 40). Afterthought
Creek flows through this waste rock pile to Little Cow Creek (Ref. 4, p. 52; Ref. 36, pp. 17-18;
Ref. 41, p. 40). Amine dump was mapped at this location in 1921, forming the flat surface beneath
the former mill building (Ref. 21, p. 21).

Source 5 is located along the eastern bank of Little Cow Creek and has been observed to be in
contact with Little Cow Creek surface water (Figure A-3 of this HRS documentation record; Ref.
4, pp. 8, 50-52, 58; Ref. 41, pp. 7, 33, 39-40). The area of the Source 5 waste rock pile is
approximately 32,726 square feet. The area was measured based on the aerial photo presented in
Figure A-3 of this documentation record and on field observations during the 2019 PA and the
2022 SI correlating the unvegetated area with the boundaries of the waste rock pile (Figure A-3 of
this HRS documentation record; Ref. 4, pp. 51-52, 58; Ref. 41, pp. 33, 40).

2.2.2	HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE
2022 EPA SI Sampling

From June 21, 2022 through June 24, 2022, Weston Solutions, Inc. collected soil, sediment, and
surface water samples as part of the SI for Afterthought Mine (Ref. 4, pp. 50-51). Samples were
collected in accordance with the SAP approved by EPA on May 29, 2020 (Ref. 4, p. 13; Ref. 7, p.
2). Soil samples were submitted to Eurofins Burlington under the EPA CLP for metals analysis by
ISM 02.4 ICP-AES (Ref. 4, p. 14). Validation of analytical data was contracted by EPA in
accordance with ISM 02.4 (Ref. 7, pp. 44-45; Ref. 43, pp. 1, 2, 4).

Waste rock samples were collected from seven locations within Source 5 (AM-05 through AM-09
and AM-11 through AM-12) (Figure A-3 of this documentation record; Ref. 4, pp. 36, 51, 58).
Waste rock samples were collected using a sample-dedicated plastic disposable scoop and
transferred to a 4-oz. wide-mouth glass jar (Ref. 4, p. 13; Ref. 7, p. 36). Pile source samples were
compared to a background soil sample to show the relative increase in hazardous substances over
background soil levels. A background soil sample was collected from native soils north of the mine
property in an area that was not observed to be impacted by mining activities (Ref. 4, pp. 13-14,
50). Background samples were collected using the same methods as the Source samples (Ref. 4,
p. 14). Source sampling locations are presented in Figure A-3 of this HRS documentation record.

41

Source 5 Characterization


-------
Table 6: 2022 SI, Source 5 Mill Area Waste Rock

Station
Location

CLP
Sample
ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References

Background Soil Samples

AM-BG-1

MY0AA0

6/22/2022

Arsenic

23

1.0

Ref. 4, pp. 29, 50;
Ref. 9, pp. 2-3, 12,
14, 470; Ref. 19, pp.
1-3, 10; Ref. 43, pp.
10-11; Ref. 47, p. 2;
Ref. 48, pp. 8, 20

Cadmium

1.7

0.51

Copper

77

2.5

Lead

100

1.0

Mercury

0.20 J-
(0.366)

0.10

Zinc

310

6.1

Source 5 Mill Area Waste Rock Samples

AM-05

MY0AA6

6/23/2022

Arsenic

240

1.7

Ref. 4, pp. 29,51;
Ref 9, pp. 2-3,5, 12,
19, 460, 475; Ref. 19,
pp. 41-43, 50, 61-63,
70; Ref. 43, pp. 20-
21; Ref. 47, p. 2; Ref.
48, pp. 8, 20

Cadmium

39

0.84

Copper

1,300

4.2

Lead

2,500

2.5

Mercury

1.7 J-

0.10

Zinc

8,700

50

AM-06

MY0AA7

6/23/2022

Arsenic

500

3.8

Ref. 4, pp. 29,51;
Ref 9, pp. 2-3,5, 12,
20, 460, 476; Ref. 19,
pp. 61-63, 70; Ref.
43, pp. 22-23; Ref.
47, p. 2; Ref. 48, pp.
8, 20

Cadmium

20

1.9

Copper

640

1.9

Lead

2,100

2.3

Mercury

2.9 J-

0.20

Zinc

3,100

23

AM-07

MY0AA8

6/23/2022

Arsenic

720

3.9

Ref. 4, pp. 29,51;
Ref 9, pp. 2-3,5, 12,
21,460, 477; Ref. 19,
pp. 61-63, 70; Ref.
43, pp. 24-25; Ref.
47, p. 2; Ref. 48, pp.
8, 20

Cadmium

16

3.9

Copper

1,400

3.9

Lead

5,700

7.9

Mercury

6.5 J-

0.58

Zinc

1,500

9.4

AM-08

MY0AA9

6/23/2022

Arsenic

620

4.1

Ref. 4, pp. 29,51;
Ref 9, pp. 2-3,5, 12,
22, 460, 478; Ref. 19,
pp. 61-63, 70, 81-83,
90; Ref. 43, pp. 26-
27; Ref. 47, p. 3; Ref.
48, pp. 8, 20

Cadmium

28

2.0

Copper

790

2.0

Lead

1,900

1.6

Mercury

5.2 J-

0.48

Zinc

4,200

24

AM-09

MY0AB0

6/23/2022

Arsenic

630

4.0

Ref. 4, pp. 29,51;
Ref 9, pp. 2-3,5, 12,
23, 460, 479; Ref. 19,
pp. 81-83, 90; Ref.
43, pp. 28-29; Ref.
47, p. 3; Ref. 48, pp.
8, 20

Cadmium

19

2.0

Copper

600

2.0

Lead

1,700

1.6

Mercury

3.3 J-

0.21

Zinc

2,200

14

AM-11

MY0AB2

6/23/2022

Arsenic

810

5.4

Ref. 4, pp. 29,51;
Ref 9, pp. 2, 4, 5, 12,
25,460, 481; Ref. 19,

Cadmium

63

2.7

Copper

2,100

5.4

42

Source 5 Characterization


-------
Table 6: 2022 SI, Source 5 Mill Area Waste Rock

Station
Location

CLP
Sample
ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References







Lead

4,800

5.4

pp. 121-123, 130;
Ref. 43, pp. 32-33;
Ref. 47, p. 3; Ref. 48,
pp. 8, 20

Mercury

11 J-

1.0

Zinc

11,000

64

AM-12

MY0AB3

6/23/2022

Arsenic

120

0.87

Ref. 4, pp. 29,51;
Ref 9, pp. 2, 4, 5, 12,
26, 460, 482; Ref. 19,
pp. 121-123, 130;
Ref. 43, pp. 34-35;
Ref. 47, p. 3; Ref. 48,
pp. 8, 20

Cadmium

26

0.44

Copper

2,000

6.5

Lead

2,300

2.6

Mercury

3.5 J-

0.19

Zinc

7,700

78

CLP: Contract Laboratory Program
mg/kg: milligrams analyte per kilogram tailings

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*: Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as

defined by the HRS (Ref. 1, Sections 1.1 and 2.3).

J-: The result is an estimated quantity, but the result may be biased low (Ref. 43, pp. 5, 9).

43

Source 5 Characterization


-------
2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY

All hazardous substances associated with Source 5 are available to the surface water pathway based
on a containment factor value of greater than zero (Ref 1, Section 2.2.3).

Containment Description

Containment
Factor
Value

References

Release to surface water:

There is no known maintained engineered
cover or functioning and maintained run-on
control system and runoff management
system. Afterthought Creek runs through
this waste rock pile to Little Cow Creek.
Source 5 is located along the eastern bank
of Little Cow Creek and has been observed
to be in contact with Little Cow Creek
surface water.

10

Figure A-3 of this HRS
documentation record; Ref. 4,
pp.35, 50-52, 58; Ref. 21, p. 21;
Ref. 41, pp. 7, 33, 39-40

44

Source 5 Characterization


-------
2.4.2. HAZARDOUS WASTE QUANTITY

2.4.2.1.1	Hazardous Constituent Quantity (Tier A)

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
and releases from the source is not known and cannot be estimated with reasonable confidence
(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 5 with reasonable
confidence. Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1,
Section 2.4.2.1.1).

Hazardous Constituent Quantity Value: NS

2.4.2.1.2	Hazardous Wastestream Quantity (Tier B)

The total Hazardous Wastestream Quantity for Source 5 could not be adequately determined
according to the HRS requirements; that is, the total mass, or a partial estimate, of all hazardous
wastestreams and CERCLA pollutants and contaminants for the source and releases from the
source is not known and cannot be estimated with reasonable confidence (Ref. 1, Section
2.4.2.1.2). Insufficient historical and current data (permits, waste concentration data, annual
reports, etc.) are available to adequately calculate the total mass, or a partial estimate, of all
hazardous wastestreams and CERCLA pollutants and contaminants for the source and the
associated releases from the source. Therefore, there is insufficient information to adequately
calculate or extrapolate a total or partial Hazardous Wastestream Quantity for Source 4 with
reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section

2.4.2.1.2).

Hazardous Wastestream Quantity Value: NS

2.4.2.1.3	Volume (Tier C)

The volume for Source 5 could not be adequately determined with reasonable confidence. The
depth of Source 5 is unknown. Scoring proceeds to the evaluation of Tier D, area (Ref. 1, Section

2.4.2.1.3).

Volume Assigned Value: 0

2.4.2.1.4	Area (Tier D)

The area of the Source 5 waste rock pile is approximately 32,726 square feet. The area was
measured based on the aerial photo presented in Figure A-3 of this documentation record and on
field observations during the 2019 PA and the 2022 SI correlating the unvegetated area with the
boundaries of the waste rock pile (Figure A-3 of this HRS documentation record; Ref. 4, pp. 51-
52, 58; Ref. 41, pp. 33, 40). In accordance with Ref. 1, Table 2-5, the equation for assigning a
value for a pile is the area in square feet divided by 13:

32,726/ 13 =2,517.38

Area Assigned Value: 2,517.38

45

Source 5 Characterization


-------
Source Hazardous Waste Quantity Value

According to the HRS, the highest of the values assigned to the source for hazardous constituent
quantity (Tier A), hazardous wastestream quantity (Tier B), Volume (Tier C), and Area (Tier D)
is assigned as the source hazardous waste quantity value (Ref. 1, Section 2.4.2.1.5).

Tier Evaluated

Source 5 Values

A

NS

B

NS

C

0

D

2,517.38

Source Hazardous Waste Quantity Value: 2,517.38

46

Source 5 Characterization


-------
2.2 SOURCE 6 SOURCE CHARACTERIZATION

2.2.1	SOURCE IDENTIFICATION

Name of Source: Tailings Pile Number of Source: 6
Source Type: Pile

Description and Location of Source (see Figure A-2 and A-3):

Source 6 consists of the tailings pile along Little Cow Creek in the lower portion of the mine
property (Figure A-3 of this HRS documentation record; Ref. 4, pp. 35, 51; Ref. 21, p. 21; Ref.
36, pp. 17-18; Ref. 41, pp. 33, 40). Amine dump was mapped at this location in 1921, forming the
flat surface and road base along the eastern bank of Little Cow Creek (Ref. 21, p. 21). Tailings and
waste rock appear to have been used to construct a rail bed between Afterthought Mine and
Afterthought Smelter located approximately 1 mile downstream of the mine. The tailings pile was
observed to be in direct contact with surface water in Little Cow Creek (Ref. 4, pp. 50-52, 59-60;
Ref. 14, pp. 9, 22; Ref. 17, pp. 28-29; Ref. 41, pp. 33, 41). During the SI sampling event, acidic
water was observed emerging from the tailings on Little Cow Creek bank and flowing into Little
Cow Creek (Ref. 4, pp. 57-58).

The area of the Source 6 tailings pile is approximately 63,883 square feet. The area was measured
based on the aerial photo presented in Figure A-3 of this documentation record and on field
observations during the 2019 PA and the 2022 SI correlating the unvegetated area with the
boundaries of the tailings pile (Figure A-3 of this HRS documentation record; Ref. 4, pp. 35, 50-
52, 59; Ref. 41, p. 33).

2.2.2	HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE
2022 EPA SI Sampling

From June 21, 2022 through June 24, 2022, Weston Solutions, Inc. collected soil, sediment, and
surface water samples as part of the SI for Afterthought Mine (Ref. 4, pp. 50-51). Samples were
collected in accordance with the SAP approved by EPA on May 29, 2020 (Ref. 4, p. 13; Ref. 7, p.
2). Soil samples were submitted to Eurofins Burlington under the EPA CLP for metals analysis by
ISM 02.4 ICP-AES (Ref. 4, p. 14). Validation of analytical data was contracted by EPA in
accordance with ISM 02.4 (Ref. 7, pp. 44-45; Ref. 43, pp. 1, 2, 4; Ref. 44, pp. 1, 2, 4).

Tailings samples were collected from eight locations within Source 6 (AM-13 through AM-15
and AM-17 through AM-21) (Figure A-3 of this documentation record; Ref. 4, p. 36). Tailings
samples were collected using a sample-dedicated plastic disposable scoop and transferred to a 4-
oz. wide-mouth glass jar (Ref. 4, p. 13; Ref. 7, p. 36). Pile source samples were compared to a
background soil sample to show the relative increase in hazardous substances over background
soil levels. A background soil sample was collected from native soils north of the mine property
in an area that was not observed to be impacted by mining activities (Ref. 4, pp. 13-14, 50).
Background samples were collected using the same methods as the Source samples (Ref. 4, p. 14).
Source sampling locations are presented in Figure A-3 of this HRS documentation record.

47

Source 6 Characterization


-------
Table 7: 2022 SI, Source 6 Tailings Pile

Station
Location

CLP
Sample
ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References

Background Soil Samples

AM-BG-1

MY0AA0

6/22/2022

Arsenic

23

1.0

Ref. 4, pp. 29, 50;
Ref. 9, pp. 2-3, 12,
14, 470; Ref. 19, pp.
1-3, 10; Ref. 43, pp.
10-11; Ref. 47, p. 2;
Ref. 48, pp. 8, 20

Cadmium

1.7

0.51

Copper

77

2.5

Lead

100

1.0

Mercury

0.20 J-
(0.366)

0.10

Zinc

310

6.1

Source 6 Tailings Pile Samples

AM-13

MY0AB4

6/23/2022

Arsenic

480

2.5

Ref. 4, pp. 29,51;
Ref. 9, pp. 2, 4, 12,
27, 460, 483; Ref. 19,
pp. 121-123, 130,
141-143, 150; Ref.
43, pp. 36-37; Ref.
47, p. 3; Ref. 48, pp.
8, 20

Cadmium

59

1.7

Copper

2,100

6.2

Lead

3,000

2.5

Mercury

8.6 J-

0.46

Zinc

13,000

75

AM-14

MY0AB5

6/23/2022

Arsenic

1,300

9.6

Ref. 4, pp. 29,51;
Ref. 9, pp. 2, 4, 12,
28, 460, 484; Ref. 19,
pp. 141-143, 150;
Ref. 43, pp. 38-39;
Ref. 47, p. 3; Ref. 48,
pp. 8, 20

Cadmium

38

4.8

Copper

590

2.4

Lead

2,200

2.9

Mercury

6.9 J-

0.49

Zinc

3,600

17

AM-15

MY0AB6

6/23/2022

Arsenic

490

3.0

Ref. 4, pp. 29,51;
Ref. 9, pp. 2, 4, 12,
29, 460, 485; Ref. 19
pp. 141-143, 150,
161-163, 170; Ref.
43, pp. 40-41; Ref.
47, p. 3; Ref. 48, pp.
8, 20

Cadmium

25

1.5

Copper

480

2.5

Lead

2,900

3.0

Mercury

7.1 J-

0.46

Zinc

4,100

24

AM-17

MY0AB8

6/23/2022

Arsenic

140

0.98

Ref. 4, pp. 29,51;
Ref. 9, pp. 2, 4, 12,
31, 461, 487; Ref. 19,
pp. 161-163, 170,
181-183, 190; Ref.
43, pp. 44-45; Ref.
47, p. 3; Ref. 48, pp.
8, 20

Cadmium

31

0.49

Copper

2,400

4.9

Lead

2,000

2.0

Mercury

3.5 J-

0.19

Zinc

7,500

59

AM-18

MY0AB9

6/23/2022

Arsenic

250

1.6

Ref. 4, pp. 29,51;
Ref. 9, pp. 2, 4, 12,
32, 461, 488; Ref. 19,
pp. 181-183, 190;
Ref. 43, pp. 46-47;
Ref. 47, p. 3; Ref. 48,
pp. 8, 20

Cadmium

24

0.79

Copper

3,800

9.8

Lead

6,900

7.9

Mercury

3.8 J-

0.20

Zinc

4,300

24

AM-19

MY0AC0

6/23/2022

Arsenic

520

3.1



48

Source 6 Characterization


-------
Table 7: 2022 SI, Source 6 Tailings Pile

Station
Location

CLP
Sample
ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References







Cadmium

43

1.5

Ref. 4, pp. 29,51;
Ref. 9, pp. 2, 4, 12,
33, 461, 489; Ref. 19,
pp. 181-183, 190,
201-203, 210; Ref.
43, pp. 48-49; Ref.
47, p. 3; Ref. 48, pp.
8, 20

Copper

6,100

26

Lead

6,200

10

Mercury

18 J-

0.94

Zinc

10,000

62

AM-20

MY0AC1

6/23/2022

Arsenic

1,000

9.7

Ref. 4, pp. 29,51;
Ref. 10, pp. 3, 13, 15,
764, 783; Ref. 44, pp.
12-13; Ref. 45, pp. 1-
3, 10, 21-23, 30; Ref.
47, p. 3; Ref. 48, pp.
8, 20

Cadmium

97

4.8

Copper

9,200

24

Lead

11,000

9.7

Mercury

27 J-

1.8

Zinc

18,000

87

AM-21

MY0AC2

6/23/2022

Arsenic

230

1.4

Ref. 4, pp. 29,51;
Ref. 10, pp. 3, 13, 16,
764, 784; Ref. 44, pp.
14-15; Ref. 45, pp.
21-23, 30; Ref. 47, p.
3; Ref. 48, pp. 8, 20

Cadmium

34

0.72

Copper

4,200

9.0

Lead

4,300

3.6

Mercury

19 J-

0.99

Zinc

8,300

43

CLP: Contract Laboratory Program
mg/kg: milligrams analyte per kilogram tailings

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*: Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as

defined by the HRS (Ref. 1, Sections 1.1 and 2.3).

J-: The result is an estimated quantity, but the result may be biased low (Ref. 43, pp. 5, 9; Ref. 44, pp. 4-5, 10).

49

Source 6 Characterization


-------
2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY

All hazardous substances associated with Source 6 are available to the surface water pathway based
on a containment factor value of greater than zero (Ref 1, Section 2.2.3).

Containment Description

Containment
Factor
Value

References

Release to surface water:

There is no maintained engineered cover or
functioning and maintained run-on control
system and runoff management system. The
tailings pile was observed to be in direct
contact with surface water in Little Cow
Creek. During the SI sampling event, acidic
water was observed emerging from the
tailings on Little Cow Creek bank and
flowing into Little Cow Creek.

10

Figure A-3 of this HRS
documentation record; Ref. 4,
pp. 35, 50-52, 57-59; Ref. 14,
pp. 9, 22; Ref. 17, pp. 28-29;
Ref. 21, p. 21; Ref. 41, pp. 33,
40

50

Source 6 Characterization


-------
2.4.2. HAZARDOUS WASTE QUANTITY

2.4.2.1.1	Hazardous Constituent Quantity (Tier A)

The hazardous constituent quantity for Source 6 could not be adequately determined according to
the HRS requirements; that is, the total mass of all CERCLA hazardous substances in the source
and releases from the source is not known and cannot be estimated with reasonable confidence
(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 6 with reasonable
confidence. Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1,
Section 2.4.2.1.1).

Hazardous Constituent Quantity Value: NS

2.4.2.1.2	Hazardous Wastestream Quantity (Tier B)

The total Hazardous Wastestream Quantity for Source 6 could not be adequately determined
according to the HRS requirements; that is, the total mass, or a partial estimate, of all hazardous
wastestreams and CERCLA pollutants and contaminants for the source and releases from the
source is not known and cannot be estimated with reasonable confidence (Ref. 1, Section
2.4.2.1.2). Insufficient historical and current data (permits, waste concentration data, annual
reports, etc.) are available to adequately calculate the total mass, or a partial estimate, of all
hazardous wastestreams and CERCLA pollutants and contaminants for the source and the
associated releases from the source. Therefore, there is insufficient information to adequately
calculate or extrapolate a total or partial Hazardous Wastestream Quantity for Source 6 with
reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section

2.4.2.1.2).

Hazardous Wastestream Quantity Value: NS

2.4.2.1.3	Volume (Tier C)

The volume for Source 6 could not be adequately determined with reasonable confidence. The
depth of Source 6 is unknown. Scoring proceeds to the evaluation of Tier D, area (Ref. 1, Section

2.4.2.1.3).

Volume Assigned Value: NS

2.4.2.1.4	Area (Tier D)

The area of the Source 6 tailings pile is approximately 63,883 square feet. The area was measured
based on the aerial photo presented in Figure A-3 of this documentation record and on field
observations during the 2019 PA and the 2022 SI correlating the unvegetated area with the
boundaries of the tailings pile (Figure A-3 of this HRS documentation record; Ref. 4, pp. 35, 50-
52, 59-60; Ref. 41, pp. 33, 40). In accordance with Ref. 1, Table 2-5, the equation for assigning a
value for a pile is the area in square feet divided by 13:

63,883 / 13 =4,914.08

Area Assigned Value: 4,914.08

51

Source 6 Characterization


-------
Source Hazardous Waste Quantity Value

According to the HRS, the highest of the values assigned to the source for hazardous constituent
quantity (Tier A), hazardous wastestream quantity (Tier B), Volume (Tier C), and Area (Tier D)
is assigned as the source hazardous waste quantity value (Ref. 1, Section 2.4.2.1.5).

Tier Evaluated

Source 6 Values

A

NS

B

NS

C

0

D

4,914.08

Source Hazardous Waste Quantity Value: 4,914.08

52

Source 6 Characterization


-------
SITE SUMMARY OF SOURCE DESCRIPTIONS

Source No.

Source Hazardous Waste
Quantity Value
(see Section 2.4.2)

Containment

Ground
Water

Surface
Water

Gas

Air
Particulate

1

>0

NE

10

NE

NE

2

3,282.51

NE

10

NE

NE

3

1,139.22

NE

10

NE

NE

4

779.69

NE

10

NE

NE

5

2,517.38

NE

10

NE

NE

6

4,914.08

NE

10

NE

NE

TOTAL

>12,632.88









Notes:

NE = Not Evaluated.

Other Possible Sources Not Scored

Afterthought Smelter

Afterthought Smelter is located approximately 1 mile downstream of Afterthought Mine on the
east bank of Little Cow Creek. In 1905, a 250-ton water-jacketed blast furnace was constructed at
Afterthought Smelter to process ore from Afterthought Mine. Operation of this furnace continued
successfully until 1908. A 300-ton oil-flotation mill and a 300-ton reverberatory furnace were
completed in 1919 at Afterthought Smelter. Operation began in July 1919 and lasted only 8
months, because the zinc and copper sulfides could not be cleanly separated. (Ref. 21, p. 5; Ref.
23, p. 340; Ref. 24, pp. 16, 26-27; Ref. 25, pp. 35-36, 108-110; Ref. 26, p. 54; Ref. 36, p. 7; Ref.
39, p. 96).

Afterthought Smelter was terraced with waste rock and included tailings ponds and a tailings
impoundment, which are still present on the smelter property (Ref. 5, p. 8). During the 2022 SI
sampling event, the soil berm at the south end of the tailings ponds was observed to be breached,
with a drainage channel to Little Cow Creek (Ref. 5, pp. 39-40, 47-50). A tailings impoundment
located at the southern end of the smelter property in a ravine was observed to have failed, and
tailings were deeply eroded from seasonal surface water drainage (Ref. 5, pp. 39, 46). Waste rock
and tailings on the smelter property contained elevated concentrations of metals, including up to
2,600 mg/kg arsenic, 650 mg/kg cadmium, 54,000 mg/kg copper, 41,000 mg/kg lead, 73 J mg/kg
mercury, and 160,000 mg/kg zinc (Ref. 5, p. 5). Sources at Afterthought Smelter were not scored
as part of this HRS documentation record due to the distance from the sources at Afterthought
Mine.

Rail Bed

A rail bed that appears to have been constructed from tailings and/or waste rock connects
Afterthought Mine and Afterthought Smelter along the eastern bank of Little Cow Creek (Figures
A-2 and Figure A-4 of this HRS documentation record; Ref. 4, p. 8; Ref. 14, pp. 9, 22; Ref. 17,
pp. 28-29). Based on the SI sampling results presented in Section 4.1.2.1.1 Observed Release,
Attribution of this HRS documentation record, elevated concentrations of arsenic, cadmium,

53

Source Characterization


-------
copper, lead, mercury, and zinc are present in the rail bed materials. The rail bed was not scored
as a source due to lack of information regarding the history and construction.

Other Areas of Concern

Afterthought Mine

Additional adits, portals, and waste rock piles are located on the mining property (Figure A-3 of
this HRS documentation record; Ref. 21, pp. 21-23; Ref. 26, p. 56; Ref. 35, p. 5; Ref. 36, pp. 17-
18). These possible sources are not scored as they were not sampled during the SI. Sampling was
not conducted due to lack of field access, or lack of available surface water to sample (Ref. 4, p.
15).

54

Source Characterization


-------
4.0 SURFACE WATER MIGRATION PATHWAY

Little Cow Creek is a perennial stream that flows south adjacent to the Afterthought Mine site.
The six site sources drain to Little Cow Creek. Little Cow Creek discharges into Cow Creek, which
is a tributary to the Sacramento River. The Little Cow Creek confluence with Cow Creek is beyond
the 15-mile target distance limit (TDL) from the site (Figure A-5 of this HRS documentation
record; Ref. 3; Ref. 37, p. 149).

Little Cow Creek within the TDL is a fishery (Ref. 4, p. 18; Ref. 6, p. 1; Ref. 8, pp. 11-20; Ref.
28; Ref. 37, pp. 300, 305, 315-316, 320-321). Little Cow Creek within the TDL is designated
critical habitat for steelhead trout (Oncorhynchus mykiss) (Ref. 20, pp. 117, 121). Approximately
2.31 miles of wetlands are located within the TDL (Figure A-6 of this HRS documentation record;
Ref. 13, pp. 1-5; Ref. 18).

4.1 OVERLAND/FLOOD MIGRATION COMPONENT (Figures A-4 and A-5)

The overland/flood migration component evaluates surface water threats that result from overland
migration of hazardous substances from a source at the site to surface water. Three types of threats
are evaluated for this component: drinking water threat, human food chain threat, and
environmental threat (Ref. 1, Section 4.1).

4.1.1 GENERAL CONSIDERATIONS

4.1.1.1 Definition of Hazardous Substance Migration Path for Overland/flood Component

The hazardous substance migration path includes both the overland segment and the in-water
segment that hazardous substances would take as they migrate away from sources at the site. The
overland segment begins at a source and proceeds downgradient to the probable point of entry
(PPE) to the surface water. The in-water segment begins at this PPE. For rivers, the in-water
segment continues in the direction of flow for the distance established by the TDL (Ref. 1, Section
4.1.1.1).

As shown in Figure A-4 of this HRS documentation record, most of Afterthought Mine, including
Sources 1 through 5, is drained by the intermittent Afterthought Creek and its tributaries to Little
Cow Creek. Sources 5 and 6 also drain directly into the perennial Little Cow Creek. Multiple mine
adits/portals and waste rock piles are located throughout Afterthought Mine. In the upper portion
of the mine, intermittent surface water in the North Fork Afterthought Creek flows through waste
rock (Source 2) associated with the No. 1 Shaft and Adit 4. The overland drainage path from
Source 2 waste rock to its PPE in Little Cow Creek is approximately 1,320 feet and consists of the
North Fork Afterthought Creek and Afterthought Creek (Figure A-4 of this HRS documentation
record). Intermittent surface water in the South Fork Afterthought Creek is fed in part by drainage
emitting from Adit 3. The intermittent South Fork Afterthought Creek drains the South Fork Waste
Rock pile (Source 4), and overland drainage flows from the Central Waste Rock pile (Source 3) to
the South Fork Afterthought Creek before reaching the intermittent Afterthought Creek, which
then drains into Little Cow Creek. The overland drainage paths from Sources 3 and 4 to their PPE
in Little Cow Creek are approximately 1,690 feet and 1,162 feet, respectively (Figure A-4 of this
HRS documentation record). The North Fork and South Fork Afterthought Creek join to flow
downhill through the lower portion of the mine property. In the lower portion of the mine, near
Little Cow Creek, AMD from Portal 1 (Source 1) flows into the intermittent Afterthought Creek

55

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from the south, depositing a bright orange and green slime on waste rock between the portal and
the creek. The overland drainage path from Source 1 to Little Cow Creek is approximately 528
feet (Figure A-4 of this HRS documentation record). In April 2019, Afterthought Creek was
observed to flow into Little Cow Creek, causing the water in Little Cow Creek to be cloudy for
some distance downstream. During the June 2022 SI sampling, surface water in Afterthought
Creek infiltrated into the ground downstream of the confluence with the Portal 1 AMD before
reaching Little Cow Creek. The point where Afterthought Creek flows into Little Cow Creek is
designated as PPE 2 (Figure A-4 of this HRS documentation record; Ref. 4, pp. 8, 50-55; Ref. 36,
pp. 17-18; Ref. 41, pp. 15, 33, 35-36, 39).

In addition to the flow from Afterthought Creek, Source 5 and Source 6 are located along the
eastern bank of Little Cow Creek and have been observed to be in contact with Little Cow Creek
surface water. PPE 1 is the length of approximately 250 feet where Source 5 is in contact with
Little Cow Creek. PPE 3 is the length of approximately 500 feet where Source 6 in contact with
Little Cow Creek (Figure A-4 of this HRS documentation record; Ref. 4, pp. 8, 50-55; Ref. 41, pp.
15, 33, 39).

Distance from Sources to Surface Water

Source

Approximate Distance from Source to PPE

(Figure A-4 of this HRS documentation record)

PPE

Source 1 - Portal 1

528 ft

2

Source 2 - North Fork Waste Rock

1,320 ft

2

Source 3 - Central Waste Rock Pile

1,690 ft

2

Source 4 - South Fork Waste Rock

1,162 ft

2

Source 5 - Mill Area Waste Rock

Oft

1

Source 6 - Tailings Pile

Oft

3

4.1.1.2 Target Distance Limit

The TDL defines the maximum distance over which targets are considered in evaluating the site.
The TDL begins at the farthest upstream PPE (PPE 1). The TDL ending is measured from the
furthest downstream PPE (PPE 3) and extends for 15 miles along the surface water from that point
(Ref. 1, Section 4.1.1.2). The TDL is shown on Figure A-5 of this HRS documentation record.

Little Cow Creek is a perennial stream that flows south adjacent to the Afterthought Mine site.
The six site sources drain to Little Cow Creek. Little Cow Creek discharges into Cow Creek, which
is tributary to the Sacramento River. The Little Cow Creek confluence with Cow Creek is beyond
the 15-mile TDL from the site (Figure A-l and Figure A-5 of this HRS documentation record; Ref.
3; Ref. 37, p. 149).

The drainage basin of Little Cow Creek above Afterthought Mine comprises about 60 square miles.
Mean flow in Little Cow Creek was measured at upstream USGS stream gage 11373300 from
1957-1965 at 51.1 to 252.0 cubic feet per second (cfs), or 62,657 gpm. Flows in Little Cow Creek
were measured approximately 200 feet upstream from Afterthought Creek from August 1997 to
May 1998 at an average flow rate of 211,509 gpm, or 565.9 cfs (Ref. 26, pp. 10, 61; Ref. 36, pp.
20, 22; Ref. 40).

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AFTERTHOUGHT MINE

4.1.2.1 Likelihood of Release
4.1.2.1.1 Observed Release
Observed Release by Direct Observation

An observed release to surface water may be established when a material that contains one or more
hazardous substances has been seen entering surface water through migration or is known to have
entered surface water through direct deposition (Ref. 1, Section 4.1.2.1.1).

Basis for Direct Observation:

Source 5 and Source 6 at the Afterthought Mine property are located along the bank of Little Cow
Creek and have been observed to be in contact with surface water (PPE 1 and PPE 3) (Figure A-4
of this HRS documentation record; Ref. 3; Ref. 4, p. 8; Ref. 41, pp. 33, 41). Source 5 and Source
6 border Little Cow Creek for approximately 750 feet (Figure A-4 of this HRS documentation
record).

Analytical data documenting the presence of hazardous substances in Source 5 and Source 6 is
presented in Section 2.2.2 Hazardous Substances Associated with the Source of this HRS
documentation record.

Hazardous Substances in Release:

Hazardous substances documented in Source 5 and Source 6 include arsenic, cadmium, copper,
lead, mercury, and zinc (see Section 2.2.2, Hazardous Substances Associated with the Source of
this HRS documentation record).

Observed Release by Chemical Analysis

The minimum standard to establish an observed release by chemical analysis is analytical evidence
of a hazardous substance significantly above the background level and some portion of the
significant increase above the background level is attributable to the site. In accordance with HRS
Table 2-3, if the background concentration is not detected, a significant increase is established
when the sample measurement equals or exceeds the sample quantitation limit (SQL). If the
background concentration equals or exceeds the detection limit, a significant increase is
established when the sample measurement is three times or more above the background
concentration. If the sample analysis was performed under the EPA CLP, the EPA Contract
Required Quantitation Limit (CRQL) can be used in place of the SQL if the SQL is not available
(Ref. 1, Section 2.3). Attribution will be discussed later in this Section.

2022 EPA SI Sampling

EPA tasked Weston Solutions, Inc. to conduct an SI at the Afterthought Mine site (Ref. 4, p. 13).
From June 21, 2022 through June 24, 2022, Weston Solutions, Inc. collected soil, sediment, and
surface water samples as part of the SI for Afterthought Mine (Ref. 4, pp. 50-51). Samples were
collected in accordance with the SAP approved by EPA on May 29, 2020 (Ref. 4, p. 13; Ref. 7, p.
2). Sediment samples were submitted to Eurofins Burlington under the EPA CLP for metals
analysis by ISM 02.4 ICP-AES. Surface water samples were submitted for metals analysis by ISM
0.24 ICP-AES and ICP-MS (Ref. 4, p. 14; Ref. 5, p. 11). Validation of analytical data was
contracted by EPA in accordance with ISM 02.4 (Ref. 4, p. 13; Ref. 7, pp. 44-45; Ref. 46, p. 1).

57

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AFTERTHOUGHT MINE

To document an observed release, surface water and sediment samples were collected from Little
Cow Creek upstream and downstream of site sources. Background sample LCC-AM-02 was
collected upstream of all sources at Afterthought Mine (Ref. 4, pp. 44, 50, 57). Sample LCC-AM-
04 was collected immediately downstream of the confluence with Afterthought Creek (PPE 2)
(Ref. 4, pp. 44, 50, 56). Sample LCC-AM-05 was collected approximately 140 feet downstream
of the confluence with Afterthought Creek (Ref. 4, pp. 44, 50-51, 57). Sample LCC-AM-10 was
collected approximately 0.9 mile downstream of Afterthought Creek and upstream of Afterthought
Smelter (Figure A-6 of this HRS documentation record; Ref. 5, pp. 33, 39, 49-50).

Each surface water sample included one filtered sample for dissolved metals and one unfiltered
sample for total metals analyses. Sediment samples were analyzed for metals via EPA CLP ISM
02.4 ICP-AES. Filtered and unfiltered surface water samples were analyzed for metals via both
EPA CLP ISM 02.4 ICP-AES and EPA CLP ISM 02.4 ICPMS. Water samples were also screened
for pH in the field, using a YSI 650 Water Quality Meter (Ref. 4, p. 14; Ref. 5, p. 11). No other
mining or smelting operations are known to be present downstream of Site sources and upstream
of surface water and sediment samples documenting an observed release (Figure A-6 of this HRS
documentation record; Ref. 3; Ref. 26, p. 11; Ref. 36, p. 6; Ref. 37, p. 198).

58

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AFTERTHOUGHT MINE

-Background Little Cow Creek

Background location LCC-AM-02 was sampled for surface water and sediments during the same
sampling event using the same sampling methods and laboratories as the downstream
contaminated Little Cow Creek surface water and sediment samples (Ref. 4, p. 14). An observed
release is established based on Little Cow Creek surface water and sediment sampling.

Table 8: 2022 SI, Little Cow Creek Background Surface Water Concentrations

Station
Location

CLP
Sample
ID

Filtered/
Unfiltered

Sampling
Date

Hazardous
Substance

Concentration
(HS/L)

Sample
Adjusted
CRQL*
(Hg/L)

References

ICP-MS Results

LCC-
AM-02-
W-T

MY0AM6

Unfiltered

6/23/22

Cadmium

1.0U

1.0

Ref. 4, pp. 32, 50, 57;
Ref. 12, pp. 4, 24, 682;
Ref. 15, pp. 190-192,
199, 211-213, 220; Ref.
46, p. 38; Ref. 47, p. 2

Copper

2.0U

2.0

Lead

1.0U

1.0

Zinc

5.0U

5.0

LCC-
AM-02-
W-F

MY0AM5

Filtered

6/23/22

Cadmium

1.0U

1.0

Ref. 4, pp. 32, 50, 57;
Ref. 12, pp. 4, 23,681;
Ref. 15, pp. 169-171,
178, 190-192, 199; Ref.
46, p. 35; Ref. 47, p. 2

Copper

2.0U

2.0

Lead

LOU

1.0

Zinc

5.0U

5.0

ICP-AES Results

LCC-
AM-02-
W-T

MY0AM6

Unfiltered

6/23/22

Cadmium

5.0U

5.0

Ref. 4, pp. 32, 50, 57;
Ref. 12, pp. 4, 24; Ref.
15, pp. 190-192, 199,
211-213, 220; Ref. 46,
p. 37; Ref. 47, p. 2

Copper

25U

25

Lead

10U

10

Zinc

60U

60

LCC-
AM-02-
W-F

MY0AM5

Filtered

6/23/22

Cadmium

5.0U

5.0

Ref. 4, pp. 32, 50, 57;
Ref. 12, pp. 4, 23; Ref.
15, pp. 169-171, 178,
190-192, 199; Ref. 46,
p. 34; Ref. 47, p. 2

Copper

25U

25

Lead

10U

10

Zinc

60U

60

CLP: Contract Laboratory Program

|ig/L: micrograms analyte per liter surface water

U: Not detected above the level of the reported CRQL (Ref. 46, p. 8)

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*: Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as defined
by the HRS (Ref. 1, Sections 1.1 and 2.3).

59

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AFTERTHOUGHT MINE



"able 9: 2022 SI, Little Cow Creek Background Sediment Concentrations

Station
Location

CLP
Sample
ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References

LCC-AM-
02-S

MY0AF9

6/23/22

Cadmium

0.35 J

0.65

Ref. 4, pp. 32, 50, 57;
Ref. 11, pp. 3, 13, 15;
Ref. 16, pp. 1-3, 10,
21-23, 30; Ref. 34, p.
10; Ref. 47, p. 2; Ref.
48, pp. 8, 20

Copper

21

3.3

Zinc

51

7.8

CLP:	Contract Laboratory Program

mg/kg	milligrams analyte per kilogram sediment

ND:	Not Detected above the method detection limit

CRQL:	EPA Contract Laboratory Program Contract Required Quantitation Limit

*:	Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as

defined by the HRS (Ref. 1, Sections 1.1 and 2.3).

J:	Result is above the MDL but below the CRQL (Ref. 16, p. 1; Ref. 34, p. 4).

Table 10: Background Levels to Establish an Observed Release to Little Cow Creek

Sample Type

Hazardous
Substance

Maximum
Background
Concentration
2022 SI Sampling
Results (jig/L)

HRS Table 2-3
Minimum Concentration to Document an
Observed Release by Chemical Analysis
(Hg/L)

Unfiltered Surface
Water (|ig/L)

ICP-MS and ICP-AES
Results

Cadmium

ND

sample CRQL

Copper

ND

sample CRQL

Lead

ND

sample CRQL

Zinc

ND

sample CRQL

Filtered Surface Water
(lig/L)

ICP-MS and ICP-AES
Results

Cadmium

ND

sample CRQL

Copper

ND

sample CRQL

Lead

ND

sample CRQL

Zinc

ND

sample CRQL

Sediment (mg/kg)

Cadmium

0.35 J, CRQL = 0.65*

1.95

Copper

21

63

|ig/L: micrograms analyte per liter surface water
ng/L: nanograms mercury per liter surface water

J: Result is above the MDL but below the CRQL (Ref. 11, p. 15; Ref. 16, p. 1).

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit
ND: Not detected above the method detection limit

*: Detection below the CRQL is treated as non-quantifiable for HRS purposes, and adjustment factors are not
applied. For a conservative background level, the sample adjusted CRQL of cadmium in sample LCC-AM-02-S is
used here as a maximum background concentration (Ref. 12, p. 6; Ref. 16, p. 1; Ref. 34, p. 4).

- Little Cow Creek Samples Establishing an Observed Release

Surface water and sediment samples establishing an observed release are shown on Figure A-6 of
this HRS documentation record. These samples contained cadmium, copper, lead, and/or zinc at
concentrations exceeding the background levels specified above.

60

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AFTERTHOUGHT MINE

Table 11: 2C

122 SI, Little Cow Creek Contaminated Surface Water Concentrations

Station
Location

CLP
Sample
ID

Filtered/
Unfiltered

Sampling
Date

Hazardous
Substance

Concentration

(Mg/L)

Sample
Adjusted
CRQL*
(Hg/L)

References

ICP-MS Results

LCC-
AM-05-
W-T

MY0AN2

Unfiltered

6/23/22

Cadmium

410

1.0

Ref. 4, p. 32; Ref. 12,
pp. 4, 684; Ref. 15,
pp. 253-255, 262,
274-276, 283; Ref.
46, p. 44; Ref. 47, p.

2

Copper

13,000

8.0

Zinc

98,000

130

LCC-
AM-05-
W-F

MY0AN1

Filtered

6/23/22

Cadmium

410

1.0

Ref. 4, p. 32; Ref. 12,
pp. 4, 683; Ref. 15,
pp. 211-213,220;
Ref. 46, p. 41; Ref.
47, p. 2

Copper

13,000

8.0

Zinc

98,000

130

LCC-
AM-10-

W-T

MY0AP2

Unfiltered

6/23/22

Copper

15

2.0

Ref. 4, p. 32; Ref. 12,
pp. 4, 686; Ref. 15,
pp. 337-339, 346;
Ref. 46, p. 50; Ref.
47, p. 3

LCC-
AM-10-

W-F

MY0AP1

Filtered

6/23/22

Copper

12

2.0

Ref. 4, p. 32; Ref. 12,
pp. 4, 685; Ref. 15,
pp. 316-318,325;
Ref. 46, p. 47; Ref.
47, p. 3

ICP-AES Results

LCC-
AM-05-
W-T

MY0AN2

Unfiltered

6/23/22

Cadmium

380

5.0

Ref. 4, p. 32; Ref. 12,
pp. 4, 26; Ref. 15,
pp. 253-255, 262,
274-276, 283; Ref.
46, p. 43; Ref. 47, p.

2

Copper

12,000

25

Lead

92

10

LCC-
AM-05-
W-F

MY0AN1

Filtered

6/23/22

Cadmium

380

5.0

Ref. 4, p. 32; Ref. 12,
pp. 4, 25; Ref. 15,
pp. 211-213,220;
Ref. 46, p. 40; Ref.
47, p. 2

Copper

12,000

25

Lead

92

10

Zinc

89,000

600

CLP: Contract Laboratory Program

|ig/L: micrograms analyte per liter surface water

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*: Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as defined
by the HRS (Ref. 1, Sections 1.1 and 2.3).

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Table 12: 2022 SI, Litt

e Cow Creek Contaminated Sediment Concentrations

Station
Location

CLP
Sample
ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References

LCC-AM-
04-S

MY0AG1

6/23/22

Cadmium

4.6

0.47

Ref. 11, pp. 3, 13. 16;
Ref. 16, pp. 21-23, 30;
Ref. 34, p. 12; Ref. 47,
p. 2

Copper

200

2.4

LCC-AM-
05-S

MY0AG2

6/23/22

Cadmium

4.7

0.52

Ref. 11, pp. 3, 13, 17;
Ref. 16, pp. 21-23, 30;
Ref. 34, p. 14; Ref. 47,
p. 2

Copper

130

2.6

CLP: Contract Laboratory Program

mg/kg: milligrams analyte per kilogram sediment

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*: Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as
defined by the HRS (Ref. 1, Sections 1.1 and 2.3).

Attribution

Operations at the Afterthought Mine began in 1862. The mine operated over a span of 90 years
under various owners until activities ceased in August 1952 (Ref. 23, p. 340; Ref. 26, p. 56; Ref.
36, pp. 7-8; Ref. 39, p. 79). During operations, Afterthought Mine was mined for gold, silver,
copper, and/or zinc (see the Site Description section of this HRS documentation record).

Remnants of the mine, including waste rock piles, adits/portals, and the ruins of the mine plant,
are still present on the property. AMD still discharges from mine portals, including Portal 1
(Source 1), to the intermittent Afterthought Creek, and runoff from mine waste rock piles,
including Sources 2 through 5, drains into the creek. Afterthought Creek then flows into Little
Cow Creek adjacent to the mine property (Figure A-4 of this HRS documentation record; Ref. 4,
p. 8).

Where AMD from Portal 1 (Source 1) flows into Afterthought Creek, it has deposited a bright
orange and green slime on waste rock. In April 2019, Afterthought Creek was observed to flow
into Little Cow Creek, causing the water in Little Cow Creek to be cloudy for some distance
downstream (Ref. 4, pp. 8, 50-55; Ref. 41, pp. 15, 33, 35-36, 39). Water collected from Portal 1
had a pH of 2.77 during the 2022 SI (Ref. 4, pp. 50). The waste rock and tailings piles scored as
sources in this HRS documentation record (Sources 2 through 6) and that drain to Little Cow Creek
cover a combined area of about 164,227.39 square feet (Section 2.4.2 in this HRS documentation
record for each source scored).

Little Cow Creek is a perennial stream that flows south adjacent to the Afterthought Mine site.
The six site sources scored in this HRS documentation record all drain into Little Cow Creek at
PPEs 1 through 3. Little Cow Creek discharges into Cow Creek beyond the site TDL (Figure A-5
of this HRS documentation record; Ref. 3; Ref. 37, p. 149).

Source 5 and Source 6 at the site are located along the bank of Little Cow Creek and have been
observed to be in contact with surface water (PPE 1 and PPE 3) (Figure A-4 and Section 4.1.1.1
of this HRS documentation record; Ref. 3; Ref. 4, p. 8; Ref. 41, pp. 33, 41). Sources 1 through 4,
as well as additional possible sources not scored at the mine property, drain to the intermittent

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AFTERTHOUGHT MINE

Afterthought Creek, which flows into Little Cow Creek (PPE 2) (Figure A-4 of this HRS
documentation record; Ref. 4, pp. 8, 50-55; Ref. 41, pp. 15, 33, 35-36, 39).

Surface water and sediment samples were collected from the intermittent Afterthought Creek
downstream of Sources 1 through 5 during the 2022 SI to show migration of hazardous substances
from the sources to Little Cow Creek (Ref. 4, p. 13). A background sediment sample was collected
from the intermittent South Fork Afterthought Creek upstream of site sources. Background surface
water samples were not collected as surface water was not present in Afterthought Creek upstream
of the site sources. (Ref. 4, pp. 14, 15, 50-51). Arsenic, cadmium, copper, lead, and zinc were
present at detectable levels in surface water samples downstream of the Afterthought Mine
sources. Arsenic, cadmium, copper, lead, mercury, and zinc were present at elevated
concentrations in sediment samples (as compared to background levels) in Afterthought Creek
downstream of Afterthought Mine sources, and they show the impact of the sources on
Afterthought Creek sediments to its confluence with Little Cow Creek at PPE 2. Afterthought
Creek water and sediment sample data are shown below in Table 13 and Table 14 of this HRS
documentation record. Also shown below in Table 15 are the results of surface soil samples
collected from the former rail bed during the SI, as it appeared to be constructed of waste rock
from the Afterthought Mine operations (Ref. 4, pp. 29-30, 40, 50). This former rail bed runs south
along Little Cow Creek through Source 6 and towards the Afterthought Smelter property (Figure
A-2 and Figure A-4 of this HRS documentation record).

Surface water and sediment samples were collected from Little Cow Creek during the 2022 SI to
determine if a release to the creek has occurred (Ref. 4, pp. 44, 50, 57). Cadmium, copper, lead,
and zinc were detected at concentrations significantly above background levels in surface water
samples collected from Little Cow Creek downstream of one or more PPEs from Sources 1 through
6. Cadmium and copper were detected at concentrations significantly above background levels in
sediment samples collected from Little Cow Creek at or downstream of one or more PPEs from
Sources 1 through 6 (Table 8 through Table 12 of this HRS documentation record).

As explained above, the hazardous substances in the observed release by chemical analysis to
Little Cow Creek (cadmium, copper, lead, and zinc) at and downstream of the site PPEs were also
detected in the reach of Afterthought Creek that drains Sources 1 through 4 and a portion of Source
5, in Sources 5 and 6 that border Little Cow Creek, and in each of the other four sources scored.
No other non-site-related sources of the hazardous substances in the observed release have been
identified in the immediate vicinity of the site or in between the site PPEs and the upgradient
background samples. (See Figures A-l and A-6 of this HRS documentation record).

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Table 13: 2022 SI, Afterthought Creek Sediment Attribution Sampling

Station Location

CLP
Sample
ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References

Background Sediment Sample

AC-BG-02-S
(South Fork
Afterthought
Creek upstream of
site sources)

MY0AJ0

6/24/2022

Arsenic

26

0.98

Ref. 4, pp. 31,44, 51;
Ref. 11, pp. 4, 13,27,
413, 435; Ref. 16, pp.
101-103, 110-113,
121-123, 130; Ref.
34, pp. 33-34; Ref.
47, p. 3

Cadmium

1.9

0.49

Copper

53

2.5

Lead

32 J1

0.98

Mercury

0.11 J-

0.097

Zinc

370

5.9

Afterthought Creek Attribution Samples

AC-07-S
(South Fork
Afterthought
Creek downstream
of Adit 3)

MY0AH6

6/24/2022

Arsenic

920

5.3

Ref. 4, pp. 31,44, 51;
Ref. 11, pp. 3, 13,24,
413, 432; Ref. 16, pp.
81-83, 90, 101-103,
110; Ref. 34, pp. 27-
28; Ref. 47, p. 3

Cadmium

21

2.6

Copper

850

2.6

Lead

1,600J

2.1

Mercury

3.5 J-

0.18

Zinc

1,200

13

AC-05-S
(North Fork
Afterthought
Creek downstream
of Adit 4)

MY0AH4

6/24/2022

Arsenic

140

0.98

Ref. 4, pp. 31,44, 51;
Ref. 11, pp. 3, 13,23,
413, 431; Ref. 16, pp.
81-83, 90; Ref. 34,
pp. 25-26; Ref. 47, p.
3

Cadmium

11

0.49

Copper

1,200

2.5

Lead

1,200 J

0.98

Mercury

2.1 J-

0.18

Zinc

2,000

12

AC-04-S
(Afterthought
Creek downstream
of East Portal)

MY0AH3

6/24/2022

Arsenic

260

1.9

Ref. 4, pp. 31,44, 51;
Ref. 11, pp. 3, 13,22,
413, 430; Ref. 16, pp.
61-63, 70, 81-83, 90;
Ref. 34, pp. 23-24;
Ref. 47, p. 3

Cadmium

11

0.96

Copper

950

2.4

Lead

1,800 J

1.9

Mercury

4.0 J-

0.40

Zinc

1,500

12

AC-02-S
(Afterthought
Creek downstream
of Portal 1)

MY0AH1

6/24/2022

Arsenic

490

3.5

Ref. 4, pp. 31,44, 50,
51; Ref. 11, pp. 3, 13,
20, 413, 428; Ref. 16,
pp. 61-63, 70; Ref.
34, pp. 19-20; Ref.
47, p. 3

Cadmium

14

1.8

Copper

480

2.9

Lead

1,000 J

1.2

Mercury

5.7 J-

0.46

Zinc

1,200

7.0

AC-01-S
(Afterthought
Creek immediately
upstream of
confluence with
Little Cow Creek)

MY0AH0

6/24/2022

Arsenic

220

2.0

Ref. 4, pp. 31,44, 50,
51; Ref. 11, pp. 3, 13,
19, 413, 427; Ref. 16,
pp. 41-43, 50; Ref.
34, pp. 17-18; Ref.
47, p. 3

Cadmium

9.2

1.0

Copper

420

2.5

Lead

670 J

1.0

Mercury

3.6 J

0.19

Zinc

1,300 J1

12

64

SWOF-Likelihood of Release


-------
AFTERTHOUGHT MINE

CLP:	Contract Laboratory Program

mg/kg:	milligrams analyte per kilogram tailings

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*:	Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as

defined by the HRS (Ref. 1, Sections 1.1 and 2.3).

J-:	The result is an estimated quantity, but the result may be biased low (Ref. 34, pp. 4, 8).

J:	Result is an estimated quantity because laboratory duplicate results are outside method limit (Ref. 34, pp. 5, 8)

Table 14: 2022 SI, Afl

erthought Creek Surface Water Attri

jution Sampling

Station
Location

CLP
Sample
ID

Filtered/
Unfiltered

Sampling
Date

Hazardous
Substance

Concentration

(Mg/L)

Sample
Adjusted
CRQL*
(Ug/L)

References

ICP-MS Results

AC-04-W-T
(downstream
of East Portal)

MY0AK0

Unfiltered

6/24/2022

Arsenic

2.2

1.0

Ref. 4, pp. 31,44, 50-
51, 55; Ref. 12, pp. 3,
678; Ref. 15, pp. 106-
108, 115, 127-129,
136; Ref. 46, p. 26;
Ref. 47, p. 3

Cadmium

13

1.0

Copper

2,700

2.0

Lead

29

1.0

Zinc

2,800

5.0

AC-04-W-F
(downstream
of East Portal)

MY0AJ9

Filtered

6/24/2022

Cadmium

3.7

1.0

Ref. 4, pp. 31,44, 50-
51, 55; Ref. 12, pp. 3,
677; Ref. 15, pp. 85-
87, 94, 106-108, 115;
Ref. 46, p. 23; Ref.
47, p. 3

Copper

18

2.0

Zinc

340

5.0

ICP-AES Results

AC-04-W-T
(downstream
of East Portal)

MY0AK0

Unfiltered

6/24/2022

Cadmium

13

5.0

Ref. 4, pp. 31,44, 50-
51, 55; Ref. 12, pp. 3,
20; Ref. 15, pp. 106-
108, 115, 127-129,
136; Ref. 46, p. 25;
Ref. 47, p. 3

Copper

2,400

25

Lead

29

10

Zinc

2,800

60

AC-04-W-F
(downstream
of East Portal)

MY0AJ9

Filtered

6/24/2022

Cadmium

3.6 J

5.0

Ref. 4, pp. 31,44, 50-
51, 55; Ref. 12, pp. 3
19, Ref. 15, pp. 85-87,
94, 106-108, 115; Ref.
46, p. 22; Ref. 47, p. 3

Copper

19 J

25

Zinc

360

60

CLP: Contract Laboratory Program

|ig/L: micrograms analyte per liter adit discharge

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*: Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as defined by

the HRS (Ref. 1, Sections 1.1 and 2.3).

J: Result is an estimated quantity. Result is above the MDL but below the CRQL (Ref. 15, p. 85; Ref. 46, pp. 5, 8).

65

SWOF-Likelihood of Release


-------
AFTERTHOUGHT MINE

Table 15: 2022 SI, Rail E

»ed Attribution Sampling

Station
Location

CLP
Sample ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References

AR-01

MY0AE9

6/22/2022

Arsenic

38

0.98

Ref. 4, pp. 29-30, 40,
50; Ref. 10, pp. 4, 13,
26, 764, 794; Ref. 44,
pp. 40-41; Ref. 45, pp.
101-103, 110; Ref. 47,
p. 2

Cadmium

2.8

0.49

Copper

410

2.5

Lead

190

2.0

Mercury

0.40 J-

0.11

Zinc

500

12

AR-02

MY0AF0

6/22/2022

Arsenic

14

0.96

Ref. 4, pp. 29-30, 40,
50, 60; Ref. 10, pp. 4,
13, 27, 764, 795; Ref.
44, pp. 48-49; Ref. 45,
pp. 101-103, 110, 121-
123, 130; Ref. 47, p. 2

Cadmium

2.1

0.48

Copper

30

2.4

Lead

540

0.96

Mercury

4.0 J-

0.38

Zinc

450

5.7

AR-03

MY0AF1

6/22/2022

Arsenic

210

1.8

Ref. 4, pp. 29-30, 40,
50; Ref. 10, pp. 4, 13,
28, 764, 796; Ref. 44,
pp. 50-51; Ref. 45, pp.
121-123, 130; Ref. 47,
p. 2

Cadmium

3.9

0.89

Copper

620

2.2

Lead

250

1.8

Mercury

1.2 J-

0.096

Zinc

170

11

AR-04

MY0AF2

6/22/2022

Arsenic

300

2.1

Ref. 4, pp. 29-30, 40,
50; Ref. 10, pp. 4, 13,
29, 764, 797; Ref. 44,
pp. 52-53; Ref. 45, pp.
121-123, 130, 141-
143, 150; Ref. 47, p. 2

Cadmium

14

1.0

Copper

2,000

5.2

Lead

2,100

2.1

Mercury

6.0 J-

0.48

Zinc

2,200

13

AR-05

MY0AF3

6/22/2022

Arsenic

770

4.8

Ref. 4, pp. 29-30, 40,
50; Ref. 10, pp. 4, 13,
30, 765, 798; Ref. 44,
pp. 54-55; Ref. 45, pp.
141-143, 150; Ref. 47,
p. 2

Cadmium

33

2.4

Copper

780

2.4

Lead

320

0.96

Mercury

2.3 J-

0.19

Zinc

5,200

29

AR-06

MY0AF4

6/22/2022

Arsenic

370

2.9

Ref. 4, pp. 29-30, 40,
50; Ref. 10, pp. 4, 13,
31, 765, 799; Ref. 44,
pp. 56-57; Ref. 45, pp.
141-143, 150, 161-
163, 170; Ref. 47, p. 2

Cadmium

7.6

1.5

Copper

370

2.4

Lead

570

0.98

Mercury

10 J-

0.97

Zinc

340

5.9

AR-07

MY0AF5

6/22/2022

Arsenic

430

2.9

Ref. 4, pp. 29-30, 40,
50; Ref. 10, pp. 4, 13,
32, 765, 800; Ref. 44,
pp. 58-59; Ref. 45, pp.
161-163, 170; Ref. 47,
p. 2

Cadmium

18

1.5

Copper

250

2.4

Lead

650

0.97

Mercury

3.2 J-

0.19

66

SWOF-Likelihood of Release


-------
AFTERTHOUGHT MINE

Table 15: 2022 SI, Rail E

»ed Attribution Sampling

Station
Location

CLP
Sample ID

Sampling
Date

Hazardous
Substance

Concentration

(mg/kg)

Sample
Adjusted
CRQL*
(mg/kg)

References







Zinc

2,200

12



AR-08

MY0AF6

6/22/2022

Arsenic

220

1.7

Ref. 4, pp. 29-30, 40,
50, 60; Ref. 10, pp. 4,
13, 33,765, 801; Ref.
44, pp. 60-61; Ref. 45,
pp. 161-163, 170; Ref.
47, p. 2

Cadmium

34

0.87

Copper

2,400

6.5

Lead

2,500

2.6

Mercury

3.2 J-

0.17

Zinc

8,700

78

AR-08

MY0AF7

6/22/2022

Arsenic

230

1.9

Ref. 4, pp. 29-30, 40,
50; Ref. 10, pp. 4, 13,
34, 765, 802; Ref. 44,
pp. 62-63; Ref. 45, pp.
161-163, 170, 181-
183, 190; Ref. 47, p. 2

Cadmium

34

0.96

Copper

2,300

4.8

Lead

2,100

1.9

Mercury

4.9 J-

0.35

Zinc

9,000

58

CLP: Contract Laboratory Program
mg/kg: milligrams analyte per kilogram tailings

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit

*: Since the samples were analyzed through the CLP, the CRQLs presented above are equivalent to the CRQL as

defined by the HRS (Ref. 1, Sections 1.1 and 2.3).

J-: The result is an estimated quantity, but the result may be biased low (Ref. 44, pp. 4, 10).

Hazardous Substances Released

An observed release of cadmium, copper, lead, and zinc to surface water is documented by
chemical analysis.

Surface Water Observed Release Factor Value: 550

67

SWOF-Likelihood of Release


-------
AFTERTHOUGHT MINE

4.1.2.1.2 Potential to Release

Potential to Release was not scored, because an Observed Release was established.

68

SWOF-Likelihood of Release


-------
4.1.2 Drinking Water Threat

No drinking water intakes are located within 15 miles downstream of the PPEs. Therefore, the
listing decision is not significantly affected by the drinking water threat to the surface water
pathway.

69

SWOF/DW-Targets


-------
4.1.3.2	Human Food Chain Threat Waste Characteristics

The human food chain threat waste characteristics factor category value is based on hazardous
waste quantity, toxicity, surface water persistence, and bioaccumulation potential for the
hazardous substances documented in the site source in the release to surface water.

4.1.3.2.1 Toxicity/Persistence/Bioaccumulation

HRS Toxicity, Persistence, and Bioaccumulation Potential Factor Values are presented below for
the hazardous substances documented in Sources 1 through 6. Factor Values are provided in the
Superfund Chemical Data Matrix (Ref. 2).

Table 16: Toxicity/Persistence/Bioaccumulation

Hazardous
Substance

Source
No.

Toxicity
Factor
Value

Persistence
Factor
Value*

Bioaccumulation
Potential Factor
Value**

Toxicity/
Persistence/
Bioaccumulation

Factor Value
(Ref. 1, Table 4-
16)

Reference

Arsenic

1-6, OR

10,000

1

5

50,000

Ref. 2, p. 2

Cadmium

1-6, OR

10,000

1

50,000

500,000,000

Ref. 2, p. 5

Copper

1-6, OR

100

1

50,000

5,000,000

Ref. 2, p. 8

Lead

1-6, OR

10,000

1

5,000

50,000,000

Ref. 2, p. 11

Mercury

2-6, OR

10,000

1

50,000

500,000,000

Ref. 2, p. 14

Zinc

1-3,5,
6, OR

10

1

500

5,000

Ref. 2, p. 17

Notes:

*	Persistence factor value for Rivers

*	* Bioaccumulation factor value for Freshwater
OR = Observed Release

Toxicity/Persistence/Bioaccumulation Factor Value: 500,000,000

(Ref 1, Table 4-16)

70

SWOF/HFC-Waste Characteristics


-------
4.1.3.2.2 Hazardous Waste Quantity

The calculations for hazardous waste quantities for Sources 1 through 6 are presented in Section
2.4.2.

Table 17: Hazardous Waste Quantity

Source No.

Source Type

Source Hazardous Waste Quantity

1

Other

>0

2

Pile

3,282.51

3

Pile

1,139.22

4

Pile

779.69

5

Pile

2,517.38

6

Pile

4,914.08

sum:

>12,632.88

Hazardous Waste Quantity Factor Value: 10,000

(Ref. 1, Table 2-6, Section 2.4.2.2)

4.1.3.2.3 Waste Characteristics Factor Category Value

Toxicity/Persistence/Bioaccumulation Factor Value: 500,000,000
Hazardous Waste Quantity Factor Value: 10,000

Toxicity/Persistence/Bioaccumulation Factor Value X
Hazardous Waste Quantity Factor Value: 5,000,000,000,000

Waste Characteristics Factor Category Value: 1,000

(Ref. 1, Table 2-7)

71

SWOF/HFC-Waste Characteristics


-------
4.1.3.3 Human Food Chain Threat Targets

Fall-run chinook salmon migrate upstream into Cow Creek, including Little Cow Creek, during
the fall (late September through December) after the first autumn rains have increased stream flow.
Little Cow Creek provides habitat for fish, including rainbow trout, steelhead trout, Sacramento
sucker, and California roach. Fish reported caught in Little Cow Creek downstream of the site
include largemouth bass, smallmouth bass, spotted bass, steelhead trout, carp, Chinook salmon,
brown trout, bream/bluegill, brook trout, and rainbow trout (Ref. 4, p. 18; Ref. 8, pp. 11-22; Ref.
28; Ref. 37, pp. 300, 305, 315-316, 320-321).

Rainbow trout, Sacramento sucker, and California roach have been observed in Little Cow Creek
downstream from the mine property, as well as upstream and in the vicinity of the smelter property
(Ref. 26, pp. 62-63). Multiple documented fish catches on Little Cow Creek (Ref. 8, pp. 12-20).
While most fish catches on Little Cow Creek did not log exact locations, at least one was logged
within the TDL in 2019 (Ref. 8, p. 16).

The California Department of Fish and Wildlife refers to Little Cow Creek as North Cow Creek
in some documents (Ref. 6, p. 1; Ref. 37, p. 154). North Cow Creek is identified as a fishery and
has been stocked with trout in the past. Discarded fishing tackle has been observed all along Little
Cow Creek, including within the zone of actual contamination and the TDL (Ref. 6, p. 1).

4.1.3.3.1	Food Chain Individual

Little Cow Creek within the TDL is a fishery and fish are caught for human consumption (see
Section 4.1.3.3 of this HRS documentation record). An observed release of cadmium, copper, lead,
and zinc from the site to surface water is documented by chemical analysis and by direct
observation (see Section 4.1.2.1.1 of this HRS documentation record).

Food Chain Individual Factor Value: 20

4.1.3.3.2	Population

4.1.3.3.2.1	Level I Concentrations

Level I actual contamination is not documented.

Level I Concentrations Factor Value: 0

4.1.3.3.2.2	Level II Concentrations

Level II actual contamination is not documented

Level II Concentrations Factor Value: 0

72

SWOF/HFC-Targets


-------
4.1.3.3.2.3 Potential Human Food Chain Contamination
Potential Population Targets

Table 18: Potential Population Targets

Identity of
Fishery

Annual
Production
(pounds)

Type of Surface
Water Body

Average
Annual
Flow
(cfs)

Reference

Population
Value (Pi)
(Ref. 1,
Table 4-18)

Dilution
Weight (Di)

(Ref. 1,
Table 4-13)

Pi x Di

Little Cow
Creek within
the TDL

>0

moderate to
large stream

51.1 to
252.1

Ref. 8, p.
16; Ref.
40, p.l

0.03

0.01

0.0003

Sum of P; xD;: 0.0003
(Sum of Pi x D;)/10: 0.00003

Potential Human Food Chain Contamination Factor Value: 0.00003

73

SWOF/HFC-Targets


-------
4.1.4.2 Environmental Threat Waste Characteristics

The environmental threat waste characteristics factor category value is based on hazardous waste
quantity, ecosystem toxicity, surface water persistence, and ecosystem bioaccumulation potential
for the hazardous substances documented in the site source in the release to surface water.

4.1.4.2.1 Ecosystem Toxicity/Persistence/Bioaccumulation

HRS Ecosystem toxicity, Persistence, and Environmental Bioaccumulation Factor Values are
presented below for the hazardous substances documented in Sources 1 through 6. Factor Values
are provided in the Superfund Chemical Data Matrix (Ref. 2).

Table 19: Ecosystem Toxicity/Persistence/Environmental Bioaccumulation

Hazardous
Substance

Source
No.

Ecosystem
Toxicity
Factor
Value

Persistence
Factor
Value*

Environmental
Bioaccumulation
Factor Value**

Ecosystem
Toxicity/
Persistence/
Environmental
Bioaccumulation
Factor Value (Ref.
1, Table 4-21)

Reference

Arsenic

1-6, OR

10

1

50,000

500,000

Ref. 2, p. 2

Cadmium

1-6, OR

10,000

1

50,000

500,000,000

Ref. 2, p. 5

Copper

1-6, OR

1,000

1

50,000

50,000,000

Ref. 2, p. 8

Lead

1-6, OR

1,000

1

50,000

50,000,000

Ref. 2, p. 11

Mercury

2-6, OR

10,000

1

50,000

500,000,000

Ref. 2, p. 14

Zinc

1-3,5,
6, OR

10

1

50,000

500,000

Ref. 2, p. 17

Notes:

*	Persistence factor value for Rivers

*	* Bioaccumulation factor value for Freshwater
OR = Observed Release

Toxicity/Persistence/Bioaccumulation Factor Value: 500,000,000

(Ref 1, Table 4-21)

74

SWOF/ENV-Waste Characteristics


-------
4.1.2.2.2 Hazardous Waste Quantity

The calculations for hazardous waste quantities for Sources 1 through 6 are presented in Section
2.4.2.

Table 20: Hazardous Waste Quantity

Source No.

Source Type

Source Hazardous Waste Quantity

1

Other

>0

2

Pile

3,282.51

3

Pile

1,139.22

4

Pile

779.69

5

Pile

2,517.38

6

Pile

4,914.08

sum:

>12,632.88

Hazardous Waste Quantity Factor Value: 10,000

(Ref. 1, Table 2-6, Section 2.4.2.2)

4.1.2.2.3 Waste Characteristics Factor Category Value

Toxicity/Persistence/Bioaccumulation Factor Value: 500,000,000
Hazardous Waste Quantity Factor Value: 10,000

Toxicity/Persistence/Bioaccumulation Factor Value X
Hazardous Waste Quantity Factor Value: 50,000,000,000

Waste Characteristics Factor Category Value: 1,000

(Ref. 1, Table 2-7)

75

SWOF/ENV-Waste Characteristics


-------
4.1.4.3 Environmental Threat Targets

Most Distant Level II Sample

Sample ID: LCC-AM-10-W-F and LCC-AM-10-W-T

Distance from the probable point of entry: Approximately 4,075 feet downstream of the
downstream end of PPE 3

Reference: Figure A-6 of this HRS documentation record; Ref. 4, p. 32; Ref. 12, pp. 4, 27-28; Ref.
15, pp. 316-318, 325, 337-339, 346; Ref. 46, pp. 47, 50

4.1.4.3.1 Sensitive Environments

Little Cow Creek within the TDL provides Critical Habitat for the Federal-listed threatened
Steelhead (Oncorhynchus mykiss) (Figure A-5 of this HRS documentation record; Ref. 20, pp.
117, 121).

Approximately 0.15 mile of wetlands frontage are located along Little Cow Creek between the
most upstream point of PPE 1 and sample location LCC-AM-10. Approximately 2.15 miles of
wetlands are located along Little Cow Creek downstream of sample location LCC-AM-10 within
the TDL (Figure A-6 of this HRS documentation record; Ref. 13, pp. 1-5; Ref. 18).

4.1.4.3.1.1 Level I Concentrations

Level I actual contamination is not documented.

Level I Concentrations Factor Value: 0

4.1.4.3.1.2. Level II Concentrations

Level II Sensitive Environment Targets

Table 21: Level II Sensitive Environment Targets

Total Length of
Wetlands Frontage

Surface Water
Body

Distance from
PPE 1 to
Nearest
Sensitive
Environment

References

Sensitive
Environment

Value
(Ref. 1, Table
4-24)

0.15 mile

Little Cow
Creek

0 miles

Figure A-6 of this
HRS documentation
record; Ref. 13, p. 1

25

Sum of Level II Sensitive Environments Value: 25

Level II Concentrations Factor Value: 25

76

SWOF/ENV-Targets


-------
4.1.4.3.1.3

Potential Contamination

Little Cow Creek within the TDL provides Critical Habitat for the Federal-listed threatened
Steelhead (Oncorhynchus mykiss) (Figure A-5 of this HRS documentation record; Ref. 20, pp.
117, 121). Approximately 2.34 miles of wetlands are located along Little Cow Creek downstream
of sample location LCC-AM-10 within the TDL (Figure A-6 of this HRS documentation record;
Ref. 13, pp. 1-5; Ref. 18). Mean flow in Little Cow Creek was measured at upstream USGS stream
gage 11373300 from 1957-1965 at 51.1 to 252.0 cubic feet per second (cfs). Flows in Little Cow
Creek were measured approximately 200 feet upstream from Afterthought Creek from August
1997 to May 1998 at an average flow rate of 211,509 gpm (Ref. 26, pp. 10, 61; Ref. 36, pp. 18,
20, 22; Ref. 40). In accordance with Ref. 1, Table 4-13, Little Cow Creek within the TDL is
described as a moderate to large stream.

Table 22: Potential Sensitive Environment Targets

Type of Surface
Water Body
(Ref. 1, Table 4-13)

Sensitive Environment

References

Sensitive
Environment
Value
(Ref. 1, Table 4-23)

Moderate to large
stream

Designated critical habitat for
steelhead trout (Oncorhynchus
mykiss)

Ref. 20, pp. 1,
117, 121

100

Table 23: Potential Wetland Frontages

Type of Surface
Water Body
(Ref. 1, Table 4-13)

Total Length of Wetlands

References

Sensitive
Environment
Value
(Ref. 1, Table 4-23)

Moderate to large
stream

2.15 miles

Figure A-6 of this
HRS documentation
record; Ref. 13, pp.
2-5; Ref. 18

75

Table 24: Potential Contamination

Type of Surface
Water Body

Sum of Sensitive
Environments
Values (Sj)

Wetland
Frontage
Value (Wj)

Dilution
Weight (Dj)
(Ref. 1, Table 4-13)

Dj(Wj + Sj)

Moderate to large
stream

100

75

0.01

1.75

Sum of Dj(Wj + Sj): 1.75
(Sum of Dj(Wj + Sj))/10: 0.175

Potential Contamination Factor Value: 0.175

77

SWOF/ENV-Targets


-------