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
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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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
SWOF-General
-------
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).
56
SWOF-General
-------
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
SWOF-Likelihood of Release
-------
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
SWOF-Likelihood of Release
-------
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
SWOF-Likelihood of Release
-------
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
SWOF-Likelihood of Release
-------
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).
61
SWOF-Likelihood of Release
-------
AFTERTHOUGHT MINE
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
62
SWOF-Likelihood of Release
-------
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).
63
SWOF-Likelihood of Release
-------
AFTERTHOUGHT MINE
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
------- |