### HRS DOCUMENTATION RECORD (HRS)

— REVIEW COVER SHEET

Name of Site: ARGONAUT MINE

Contact Person: Sharon Murray, EPA Region 9 (415) 972-4250

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

Documentation Record: Christina Marquis, Weston Solutions, Inc. (818) 350-7308

Pathways, Components, or Threats Not Scored

Ground Water Pathway

Ground water in most of Amador County is not well defined. The majority of available ground water is transient and found in fractured rock (Ref. 7, p. 26). There are no known drinking water wells within the target distance limit from Argonaut Mine sources (Ref. 30 , p. 1). Therefore, scoring this pathway does not contribute significantly to the listing decision for the site

.

Surface Water Pathway – Ground Water to Surface Water

Ground w ater within the Tailings Area Tailings Impoundment flows through cracks in the base of the

dam (Ref. 6, p. 10) to an unnamed intermittent stream that flows to North Fork Jackson Creek (see

Attachment A

- 1). However, North Fork Jackson Creek is an intermittent stream, and average annual precipitation in the site vicinity exceeds 20 inches (Ref. 3 ; Ref. 4, p. 45; Ref. 7, pp. 25

- 26; Ref. 33 ). Therefore, as the threat to surface water via overland flow is sufficient to qualify the site for listing, scoring th e ground water to surface water component of the surface water pathway would not contribute significantly to the listing decision for the site.

Air Migration Pathway The air pathway was not scored because there is no documented obse rved release to the atmosphere , and scoring the potential to release to air would not contribute significantly to the listing decision for the site.

Soil Exposure Pathway – Nearby Population Threat The Argonaut Mining Company historically owned approximately 330 acres of land northwes t of downtown Jackson. The property was sold after the mine closed, and approximately 90 acres of the 330

acres of the former property have been developed as residential neighborhoods (Ref. 4, pp. 7, 64; Ref. 28, p. 8). The threat posed by the mining waste to nearby population s may be considered at a later point. However, because the Resident Population Threat score is sufficient to identify the threat to residential

pop ulations is significant

, it was not necessary to evaluate the Nearby Population Threat t o support the listing decision for the site.1 

### HRS DOCUMENTATION RECORD

Name of Site: ARGONAUT MINE

EPA ID#: CAD983650011 EPA Region: 9 Date Prepared: April 2016

Street Address of Site: Argonaut Lane City, County and State: Jackson, Amador County, California 95642 Topographic Map: Jackson, California USGS 7.5 -Minute Quadrangle (Ref. 3)

Latitude: 38° 21' 12.0" North, Longitude: 120° 47' 8.7" West (Ref. 3; Ref. 4, pp. 39, 41)

Lati tude/Longitude Reference Point: The latitude a nd longitude is the location of sample ATS -01, collected within Source 1 during the 2014 Site Inspection (SI) (Ref. 3; Ref. 4, pp. 39, 41 ).

SCORES

Air Pathway = Not S cored

Ground Water Pathway = Not S cored

Soil Exposure Pathway = 100

Surface Water Pathway = 60

HRS SITE SCORE = 58.31

*The street address, coordinates, and contaminant locations presented in this HRS documentation record identify the general area the site is located. They represent one or more locations 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 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 contamina tion has come to be located.

### WORKSHEET FOR COMPUTING HRS SITE SCORE

S S 2



### 1. Ground Water Migration Pathway Score (S gw 

### ) NS NS

2a. Surface Water Overland/Flood Migration Component (from Table 4 -1, line 30) 60 3,600

2b.

2c. Ground Water to Surface Water Migration Component (from Table 4 -25, line 28)

Surface Water Migration Pathway Score (S

sw 

### )

Enter the larger of lines 2a and 2b as the pathway score. NS

60 NS

3,600

3. Soil Exposure Pathway Score (S

s 

### ) (from Table 5 -1, line 22) 100 10,000

4.

5. Air Migration Pathway Score (S

a 

### ) (from Table 6 -1, line 12)

Total of S gw 2 

### + S

sw 2 

### + S

s 2 

### + S

a 2 

### NS NS

13,600

6. HRS Site Score Divide the value on line 5 by 4 and take the square root 58.31

2HRS 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:

3a. 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

5. Likelihood of Release (higher of lines 1 and 4) 550 550

Waste Characteristics:

6. Toxicity/Persistence ( a ) NS

7. Hazardous Waste Quantity ( a ) NS

8. Waste Characteristics 100 NS Targets:

9. Nearest Intake 50

10. Population:

10a. Level I Concentrations ( b )

10b. Level II Concentrations ( b )

10c. Potential Contamination ( b )

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

11. Resources 5

12. Targets (lines 9 + 10d + 11) ( b ) NS Drinking Water Threat Score:

13. Drinking Water Threat Score ([lines 5 x 8 x 12]/82,500, subject to a maximum of 100) 100 NS

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 )

16. Hazardous Waste Quantity ( a )

17. Waste Characteristics 1,000 NS Targets:

18. Food Chain Individual 50

19. Population:

19a. Level I Concentrations ( b )

19b. Level II Concentrations ( b )

1 9c. Potential Human Food Chain Contamination ( b )

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

20. Targets (lines 18 + 19d) ( b ) NS

34 Factor Categories and Factors Maximum

Value Value Assigned

Human Food Chain Threat Score:

21. subject Human Food Chain to a maximum of 100) Threat Score ([lines 14 x 17 x 20]/82,500, 100 NS

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 )

26b. Level II Concentrations ( b ) 25

26c. Potential Contamination ( b )

26d. Sensitive Environments (lines 26a + 26b + 26c) ( b ) 25

27. Targets (value from 26d) ( b ) 25

Environmental Threat Score:

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

Surface Water

Watershed Overland/Flood Migration Component Score For A

29. c Watershed Score (lines 13 + 21 + 28, subject to a maximum of 100) 100 60

Surface Water Overland/Flood Migration Component Score Component Score (S of ) c , (highest score evaluated, subject to a maximum of 100) from line 29 for all watersheds 100 60 28.

30.

a Maximum value applies to waste characteristics category.

b Maximum value not applicable.

c Do not round to nearest integer.5 HRS Table 5-1 Soil Exposure Pathway Scoresheet

Factor Categories and Factors Maximum

Value Value Assigned

Resident Population Threat Likelihood of Exposure:

1. Likelihood of Exposure 550 550

Waste Characteristics:

2. Toxicity ( a ) 10,000

3. Hazardous Waste Quantity ( a ) 10,000

4. Waste Characteristics 100 100 Targets:

5. Resident Individual 50 50

6. Resident Population:

6a. Level I Concentrations ( b ) 4,547.2

6b. Level II Concentrations ( b ) 4.64

6c. Resident Population (lines 6a + 6b) ( b ) 4551.84

7. Workers 15 5

8. Resources 5 0

9. Terrestrial Sensitive Environments ( c ) 0

10. Targets (lines 5 + 6c + 7 + 8 + 9) ( b ) 460 6 .84

Resident Population Threat Score:

11. Resident Population Threat (lines 1 x 4 x 10) ( b ) 253

, 376

, 200 Nearby Population Threat Likelihood of Exposure:

12. Attractiveness/Accessibility 100

13. Area of Contamination 100

14. Likelihood of Exposure 500 NS

Waste Characteristics:

15. Toxicity ( a )

16. Hazardous Waste Quantity ( a )

17. Waste Characteristics 100 NS Targets:

18. Nearby Individual 1

19. Population Within 1 Mile ( b )

20. Targets (lines 18 + 19) ( b ) NS Nearby Population Threat Score:

21. Nearby Population Threat (lines 14 x 17 x 20) ( b ) NS Soil Exposure Pathway Score

22. subject Soil Exposure Pathway to a maximum of 100) d Score (S

s ), (lines [11 + 21]/82,500, 100 100

a Maximum value applies to waste characteristics category.

b Maximum value not applicable.

c No specific maximum value applies to factor. However, pathway score based solely on terrestrial sensitive

environments is limited to maximum of 60.

d Do not round to nearest integer.6 

### ACRONYM LIST

bgs below ground surface CRQL EPA Contract Laboratory Program Contract Required Quantitation Limit

DU Decision Unit

EMAD Eastwood Multiple Arch Dam

EPA United States Environmental Protection Agency

HRS Hazard Ranking System mg/kg milligrams per kilogram

SAP Sampling and Analysis Plan

SI Site Inspection SQL Sample Quantitation Limit

START Superfund Technical Assessment and Response Team

XRF X- Ray Fluorescence

NOTES TO THE 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.

Attachment A contains the following documents:

• Attachment A Data Citations

• Attachment A-1: Argonaut Mine Layout

• Attachment A -2: Argonaut Site Sources

• Attachment A -3: Source 1 Sampling Locations

• Attachment A

- 4: Residential Parcels on the Historical Aerial

• Attachment A

- 5: Residential Soil Sampling Locations

• Attachment A

- 6: Ob served Contamination Areas

• Attachment A -7: Jackson Junior High School Sampling and Removal Locations

• Attachment A -8: Source 1 Wetland7 

### REFERENCE LIST

Reference

Number Description of the Reference

1 40 CFR Part 300, Hazard Ranking System; Final Rule, 14 December 1990, Vol. 55, No. 241, 138 pages.

Available online: semspub.epa.gov/src/document/HQ/174028

2 U.S. Environmental Protection Agency (EPA), Superfund Chemical Data Matrix (SCDM) Methodology, Accessed February 29, 2016, 13 pages. Available online : http://www.epa.gov/superfund/superfund- chemical

- data

- matrix

- scdm

3 U.S. Geological Survey, 7.5 Minute Topographic Map of Jackson, California, 1962, Photoinspected 1973, 1 sheet.

4 Weston Solutions, Inc., Site Inspection Report, Argonaut Mine

, Jackson, Amador County, California, July 2015 , 1946 pages.

5 Ecology & Environment, Inc., Removal Assessment Addendum Report; Argonaut Mine Tailings Pile

, AOCs 1, 2, 4, and 6; Jackson, Amador County, California, February 21, 2014, 63 pages.

6 Ecology & Environment, Inc., Argonaut Mine Tailings Pile

, Removal Assessment Report, Jackson, California, December 2013, 59 pages.

7 Amador County, Hydrology and Water Quality General Plan Update Working Paper, May 2007, 44 pages.

8 Amador County Environmental Health Department

, Letter to Megan Cambridge from Margaret Blood and Michae l Israel concerning soil cap mitigation, January 21, 1994 , 5

pages.

9 U.S. Environmental Protection Agency, Solid Waste and Emergency Response, Using Qualified Data to Document an Observed Release and Observed Contamination, November 1996, 18 pages.

10 U.S. Environmental Protection Agency, Center of Environmental Computing

, Office of Technology Operations & Planning

, Office of Environmental Information Aerial Photographic Analysis of Argonaut Mine Site, June 2014, 70 pages.

11 Weston Solutions, Inc., Argonaut Mine Residential Removal Assessment Sampling with

attachments , October 29, 2015, 122 pages

.

12 Anthropological Studies Center, Sonoma State University, A Cultural Resources Inventory and Evaluation of the Argonaut Mine Cyanide Plant and Tailings Site, Jackson, Amador County, California, April 29, 2014, 166 pages.

13 Aguilera, Rachel, Amador County Schools, telephone conversation recorded on contact report by Christina Marquis, Weston Solutions, Inc., February 5, 2016

, signed February8 

### REFERENCE LIST

Reference

Number Description of the Reference

17, 2016. 1 page.

14 U.S. Environmental Protection Agency

, Releasable Chronology of the Argonaut Mine Site Ownership & Operation Memorandum, January 28, 2013, 22 pages.

15 Weston Solutions, Inc., Residential Sample Address Codes, February 5, 2016, 1 page.

To protect the privacy of individual residents, this reference is not included. The full reference may be made available upon request.

16 EPA Contract Laboratory Program, File 405780_201158.SS44272.EPW09037.MY9F52, April 15, 2015, 8 pages.

17 EPA Contract Laboratory Program, File 405761_201159.SS44272.EPW09037.MY9F22, April 15, 2015, 8 pages.

18 EPA Contract Laboratory Program, File 406097_201227.SS44272.EPW09037.MY9EX7, April 15, 2015, 9 pages.

19 U.S. Environmental Protection Agency, Contract Laboratory Program, Universal Spreadsheet Data Field Names , October 7, 2015, 1 page.

20 EPA Contract Laboratory Program, File 406087_201229.SS44272.EPW09037.MY9EY0, April 15, 2015, 10 pages.

21 Bonner Analytical Testing Company , Full Inorganics Complete SDG file, Case No. 44272, SDG No. MY9F52 , August 25, 2014, 267 pages.

22 Bonner Analytical Testing Company , Full Inorganics Complete SDG file, Case No. 44272, SDG No. MY9F22 , August 25, 2014, 194 pages.

23 Bonner Analytical Testing Company , Full Inorganics Complete SDG file, Case No. 44272, SDG No. MY9EX7 , August 26, 2014, 206 pages.

24 Bonner Analytical Testing Company , Full Inorganics Complete SDG file, Case No. 44272, SDG No. MY9EYO , August 26, 2014, 228 pages.

25 Bonner Analytical Testing Company , Full Inorganics Complete SDG file, Case No. 44272, SDG No. MY9F74 , August 25, 2014, 186 pages.

26 Amador County Environmental Health Department , Letter to Gary Urzik from Margaret Blood concerning soil cap mitigation, May 25, 1994 and Letter to Dr. McClenahan, Amador County Health Dept. from Paul Accinelli, Central Sierra Builders, Inc., May, 23, 1994, 3 pages.

27 Amador County Environmental Health Department , Re: Proposed Grading and Development, Lots 30 and 31, Argonaut Heig hts, Jackson (APN 044

- 071

- 002, 044

- 071

­9 

### REFERENCE LIST

Reference

Number Description of the Reference

003), January 28, 200 3 , 4 pages

.

28 URS Corporation, Argonaut Mine Tailings Site, Draft Site Investigation Report, March 30, 2009, 109 pages.

29 United States Census Bureau, Quick Facts, Amador County, California, http://www.census.gov/data/data-tools.html , data extracted on February 9, 2015, 3 pages.

30 Weston Solutions, Inc. (Weston), Drinking Water Sources Map, Threatened/Endangered Species and Wetlands Map and Census Block Population and Parcels Map , Argonaut Mine Site, 3 pages. To protect the security of drinking water intake locations, this reference is not included. The full reference may be made available upon request.

31 URS Corporation , Contract Agreement No. 07

- T3375, Draft Final Interim Soil Removal

Action Work Plan, Argonaut Mine Tailings Site, Jackson, California, June 9 , 2011 , 233

pages

.

32 Weston Solutions, Inc., Argonaut Mine Tailings Area Additional Removal Assessment Sampling, Jackson, Amador County, California, February 9, 2015, 41 pages.

33 Western Regional Climate Center

, Camp Pardee, California (041428) Climate Summary, http://www.wrcc.dri.edu/

, data extracted on September 29 , 2015, 1 page.

34 Weston Solutions, Inc., Argonaut Mine Tailings Pile Removal Site, Jackson, Amador County, California, Jackson Junior High School Removal Action Report, February 2, 2016, 618 pages.

35 Mining and Scientific Press, January 27, 1917, Excerpt, 1 page.

36 Department of Commerce, United States Bureau of Mines, Information Circular, Milling Methods and Costs at the Argonaut Mill, Jackson, CA, July 1931, 16 pages

.

37 EPA Contract Laboratory Program, File 405808_201157.SS44272.EPW09037.MY9F74, April 15, 2015, 9 pages.

38 U.S. Fish and Wildlife Service, National Wetlands Inventory, February 5, 2016, 2 pages.

39 Summary of Confirmation Soil Sampling and Removal Activities, Argonaut Mine Tailings Pile, Residential Removal Action, Jackson, California, undated, 148 pages.

To protect the privacy of individual residents, this reference is not included. The full reference may be made available upon request.

40 U.S. Environmental Protection Agency, Pollution/Situation Report, Argonaut Mine Site

Residential Yards Removal Action – Removal Polrep, September 5, 2015, 10 pages.10 

### REFERENCE LIST

Reference

Number Description of the Reference

To protect the privacy of individual residents, this reference is not included. The full reference may be made available upon request.

41 Weston Solutions, Inc., Argonaut Mine Tailings Area Geotechnical Sampling, City of Jackson, Amador County, California, January 23, 2015, 98 pages.

42 Weston Solutions, Inc., Final Removal Action Report for Argonaut Mine Tailings Pile

Removal Site

– Area of Concern 5, Jackson, Amador County, California , September 2015, 49 pages.

43 Bauer, Richard

, U.S. EPA Region 9 Laboratory

, email correspondence with Christina Marquis, Weston Solutions, Inc., February 11, 2016, 2 pages.

44 Bronson, C.E., Mining Engineer and Licensed Surveyor, Contour Map of Argonaut Mill Tailings, February 1955, 1 page.

45 Fortner, Tom, Weston Solutions, Inc., telephone conversation recorded on contact report by Christina Marquis, Weston Solutions, Inc., February 11, 2016, 1 page.

46 Fitzgerald, Tara, Weston Solutions, Inc., teleph one conversation recorded on contact report by Christina Marquis, Weston Solutions, Inc., February 19, 2016, 1 page.

47 U.S. Environmental Protection Agency, Region 9 Laboratory, Analytical Testing Results

– Project R15S53 , SDG: 15092C, April 20, 2015, 406 pages.

48 U.S. Environmental Protection Agency, Region 9 Laboratory, Analytical Testing Results

– Project R15S53 , SDG: 15175D, July 15, 2015, 328 pages.

49 U.S. Environmental Protection Agency, Region 9 Laboratory, Analytical Testing Results

– Project R15S53 , SDG: 15244A, September 17, 2015, 362 pages.

50 Plan of Property of the Argonaut Mining Co and Hoffman Farms Extension, Jackson

– Amador Co, California 122, April 1907, 1 page.11 

### SITE SUMMARY

The Argonaut Mine s ite consists of areas of contamination resulting from the release of hazardous substances from mining operations conducted on the Argonaut Mine property. Six hazardous substance sources are scored as part of the site . Source 1 is a tailings pile containing approximately 1,712,000 tons of processed tailings (Ref. 12, pp. 44 -45 ; Ref. 44 ). Sources 2 through 5 consist of areas of re sidential properties within the former Argonaut Mine property boundary, which were built on imported fill placed over waste rock, tailings, and so ils contaminated by Argonaut Mine operations (Ref. 4, p p. 16, 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2

- 3). Source 6 is the Jackson Junior High School athletic field, which

was constructed on a waste rock and tailings pile ( Ref. 10, pp. 28, 36; Ref. 34 , p. 2). Hazardous substances in the sources include arsenic, lead, and mercury. Targets affected by releases from these

sources include a wetland located on the surface of Source 1 , as well as residents, students, and workers occupying or working within areas of surface contamination in Sources 2 through 6.

The Argonaut Mine, located in the City of Jackson, Amador County, California, operated as a gold mine

from the 1850s until 1942 (Ref. 4, p, 6; Ref. 12, p. 25; Ref. 14, pp. 1, 4 -10 ). The Argonaut Mini ng Company historically owned approximately 330 acres of land northwest of downtown Jackson. The property was sold after the mine closed

, and approximately 90 acres of the former property have been developed as residential neighborhoods (Ref. 4, pp. 7, 64)

. Argonaut Mine operations compri se two principal areas: the Mill Area (mine shafts, buildings, former milling areas, and waste rock piles) and the Tailings Area (unprocessed and semi

- processed ore storage area, cyanide plant, and tailings impoundments) (Ref. 4, pp. 11

- 12, 64; Ref. 14, p. 1). The Argonaut Mine property l ayout is shown on

Attachment A-1.

Subsurface mining at the Argonaut Mine began in the 1850s (Ref 12, p. 26; Ref. 14, p. 1). The Argonaut Mine shaft is located in the northern part of the property, to the west of the current location of State Highway 49 (Ref. 12, p p . 9, 11, 12 ). Raw ore extracted from the shaft was processed at a 40

- stamp mill on the east side of Highway 49 from 1898 until 1916, when it was replaced by a 60

- stamp mill loca ted west of Highway 49 (Ref. 4, p. 9; Ref. 12, pp. 12, 28

- 30, 32; Ref. 36, p. 3). Processed tailings from the

40- stamp mill were deposited on “adjacent, erodible piles” in the Mill Area (Ref. 12, p. 32). Processed tailings from the 60

- stamp mill were trans ported through a flume to the Tailings Area, where they were deposited in the Source 1 tailings pile behind the Eastwood Multiple Arch Dam (EMAD) in a gulch north and west of Jackson Junior High School (Ref. 4, p. 9; Ref. 12, p. 32; Ref. 14, p. 1; Ref. 36, p. 13).12 

### SITE SOURCES

A total of six sources were evaluated for scoring the Argonaut Mine site (see Attachment A

- 2). Detailed information about each source, with reference citations, is available in the following sections. Additional

sources that were not scored are discussed in the Other Possible Sources Not Scored section.

Source 1 is the Tailings Area Tailings Impoundment

, containing approximately 1,712,000 tons of processed tailings. Sources 2 through 5 consist of areas of re siden tial properties within the former Argonaut Mine property boundary, which were built on imported fill placed over waste rock, tailings,

and soils contaminated by Argonaut operations. Source 6 is the Jackson Junior High School athletic field, which was constructed on a pile of waste rock and tailings.

Hazardous substances associated with these sources include arsenic, lead, and/or mercury.

Argonaut Mine Sources

Source

number Source Name Source Type

1 Tai lings Area Tailings Impoundment Pile

2 Argonaut Estates Tailings Pile Pile

3 Argonaut Heights – North Tailings Pile Pile

4 Argonaut Heights – South Contaminated Soil Contaminated Soil

5 Sierra View Estates Contaminated Soil Contaminated Soil

6 Jackson Junior High School Tailings Pile Pile13 Source No: 1



### 2.2 SOURCE CHARACTERIZATION : Source 1, Tailings Area Impoundment

2.2.1 SOURCE IDENTIFICATION

Name of source: Tailings Area Tailings Impoundment

Source Type: Tailings Pile

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

The Tailings Area Tailings Impoundment (EPA AOC

- 3) consists of a Number of source: 1

tailings pile covering approximately 48 acres constructed in a drainage valley (Ref. 4, pp. 8, 13; Ref. 12, p. 9)

. In 1916

, the

EMAD was constructed in the ravine southeast of the Argonaut Mine shaft and mill to impound tailings generated from Argonaut mining and milling operations (Ref. 6, p. 10; Ref. 12, p. 41). The EMAD is roughl y 390 feet wide and 46 feet tall (Ref. 6, p. 10)

. The impoundment was expanded in 1931 and 1940

with two additional dams constructed of tailings (Ref. 12, pp. 41 -42 ; Ref. 41 , p. 9 ). Two wetland s are present on the surface of Source 1 (Ref. 4, pp. 8, 65 ; Ref. 38).

Sediment and tailings have filled the valley behind the EMAD to within a few feet of its top. Standing

water flows over the top of the dam during wet periods. Water also flows through cracks in the base of the dam, suggesting materials behind the dam are saturated (Ref. 6, p. 10).

Soils at the surface of Source 1 are predominantly gr ey tailings. In most areas , veget ation has been

re established and a thin layer of organic material is present, stabilizing the surface . However, large

port ions of Source 1 contain exposed gray tailings that are devoid of vegetation. These soils are easily eroded during large magnitude rain events

, and large gullies and sinkholes have formed. Some of the gullies exceed 20 feet in depth and top- width (Ref. 6, p. 9).

In February 1955, mining engineer and licensed surveyor C.E. Bronson estimated a total of 1,712,000 tons of tailings within Source 1 by comparing the existing tailings surface with an estimated contour of the original ground surface below (Ref. 12, pp. 43-45 ; Ref. 44 ).

2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

Weston Solutions, Inc. 2014 S ite I nspection (SI) Sampling From July 28, 2014 through August 1, 2014, Weston Solutions, Inc. collected soil, sediment and surface water samples as part of a SI of the Argonaut Mine . Samples were collected in accordance with a S ampling and A nalysis P lan (SAP) approved by EPA on March 10, 2014. A total of 90 soil samples

were collected from the surface (0 to 6 inches) and shallow subsurface (up to 2 fe et) a t 47 sampling

locations. The subsurface samples were collected using either a track

- mounted direct push sampling rig

and Macro

- core soil sampler lined with an acetate sleeve, or by hand auger. A total of 27 sediment samples were collected fro m 25 samp ling locations (Ref. 4, p. 22).14 Source No: 1



### S oil and sediment s amples were submitted to Bonner Analytical, located in Hattiesburg, Miss issippi,

under the EPA Contract Laboratory Program for metal analysis by Inorganic Superfund Methods (ISM01.3) and cyanide by EPA Me thod 9010/9012. The metal s analytical data were validated by EPA (Ref. 4, p. 22).

Soil samples were collected from five locations within Source 1 (Ref. 4, p. 27). Two sample locations (ATA

- 01 and ATA

- 02) were gray sands from the upper tailings dam. S ampling location ATA

- 03 was

near the Sierra View Estates residentia l properties off of Detert Lane . S ampling location ATA

- 04 was at

the northern end of the lower tailings dam; near Sierra View Estates . S ampling location ATA

- 05 was near residential properties off of Muldoon Place near Sierra View Estates (Ref. 4, pp. 27 -28 , 65 ). Sediment samples ATS

- 01 and ATS

- 02 were collected from the two wetlands on the surface of Source 1 (Ref. 4, p. 33). Soil and sediment s ampling locations are presented in A ttachment A -3.

2014 SI, Source 1 Tailings Concentrations

Sample ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration

(mg/kg) Sample Adjusted CRQL* (mg/kg) References

ATA

- 01 -0
(MY9F89) 0

- 0.5 7/29/14 Arsenic 54.8 1.0 Ref. 4, pp. 28, 39 , 65, 1812, 1817,

1822 ; Ref. 18, p. 4 ; Ref. 23, pp. 11, 24

ATA

- 02 -0
(MY9F90) 0

- 0.5 7/29/14 Arsenic 49.4 1.1 Ref. 4, pp. 28, 39, 65, 1812, 1817, 1822; Ref. 18, p. 5; Ref. 23, pp. 11, 25 Mercury 0.38 0.10

ATA

- 03 -0
(MY9F91) 0

- 0.5 7/29/14 Arsenic 3,490 15.5 Ref. 4, pp. 28, 39, 65, 1812, 1892 ; Ref. 25, pp. 8, 25; Ref. 37, p. 6 Lead 193 1.0

Mercury 2.5 0.52

ATA

- 03 -2
(MY9F92) 1.5 - 2 7/29/14 Arsenic 502 2.1 Ref. 4, pp. 28, 39, 65, 1812, 1892 ; Ref. 25, pp. 8, 26; Ref. 37, p. 6

ATA

- 04 -0
(MY0F93) 0

- 0.5 7/29/14 Arsenic 362 1.0 Ref. 4, pp. 28, 39, 65, 1812, 1893 ; Ref. 25, pp. 8, 27; Ref. 37, p. 6

ATA

- 05

- 1.5
(MY9F96) 1

- 1.5 7/29/14 Arsenic 237 1.1 Ref. 4, pp. 28, 39, 65, 1812, 1893 ; Ref. 25, pp. 8, 30; Ref. 37, pp. 7-9 Lead 27.9 1.1

Mercury 0.52 0.11

mg/kg: milligrams analyte per kilogram tailings

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit
*: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).15 Source No: 1



### 2014 SI, Source 1 Sediment Concentrations

Sample ID Date Hazardous

Substance Hazardous

Substance

Concentration (mg/kg) Sample Adjusted CRQL* (mg/kg) References

ATS

- 01 -0
(MY9F97) 7/29/14 Arsenic 1,690 1.3 Ref. 4, pp. 41, 65, 75, 1812, 1822 ; Ref. 18, p. 5 ; Ref. 23, pp. 11, 26 Lead 95.8 1.3

Mercury 0.56 0.13

ATS

- 02 -0
(MY9F98) 7/29/14 Arsenic 204 1.3 Ref. 4, pp. 41, 65, 1812, 1823 ; Ref. 18,

pp. 5-6 ; Ref. 23, pp. 11, 27 Lead 38.8 1.3

Mercury 1.5 0.13

mg/kg: milligrams analyte per kilogram sediment

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit
*: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).



### List of Hazardous Substances Associa ted with Source Arsenic, Lead, and Mercury

2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY

Containment Description Containment

Factor Value References

Release via overland migration : L arge portions of Source 1 contain exposed gray tailings that are devoid of vegetation

Sediment and tailings have filled the basin behind the EMAD to within a few feet of its top. Standing water flows over the top of the dam, through cracks in the base of the dam

. There is

n o evide nce of a liner. 10 Ref. 6, pp. 9-1016 Source No: 1

2.4.2 HAZARDOUS WASTE QUANTITY



### Tier A: H azardous Constituent Quantity The total Hazardous Constituent Quantity for Source 1 could not be adequately determined according to the HRS requirements; that is, the total mass of all CERCLA hazardous substances in the source and releases from the source is not known and cannot be estimated with reasonable confidence (Ref. 1, Section 2.4.2.1.1). 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 CERCLA

haz ardous substances in the source and the associated releases from the source. Therefore, there is insufficient information to calculate a total or partial Hazardous Constituent Quantity estimate for

Source 1 with reasonable confidence

. Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

Tier B: Hazardous Wastestream Quantity 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 conf idence (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 pol lutants 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 confiden ce. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section 2.4.2.1.3).

Hazardous Wastestream Quantity Value: NE

Tier C: Volume The Tailings Area Tailings Impoundment was estimated to hold approximately 1,712,000 tons of processed tailin gs based on surface contour levels prior to and after creation of the pile and the boundaries of each of three piles comprising the entirety of the tailings impoundment pile (Ref. 12, p. 45; Ref. 44 ). In accordance with Ref. 1, Table 2

- 5:

1,712,000 tons = 1,712,000 cubic yards 1,712,000 / 2.5 = 684,800

Volume Assigned Value: 684,80017 Source No: 1



### Tier D: Area Because the volume of Source 1 is determined, Tier D: area is not evaluated.

Area Assigned Value: 0

Source Hazardous Waste Quantity Value: 684,80018 Source No: 2



### 2.2.1 SOURCE IDENTIFICATION : Source 2: Argonaut Estates Tailings Pile

Name of source: Argonaut Estates Tailings Pile Number of source: 2

Source Type : Tailings Pile

Description and Location of Source ( see Attachments A -4 through A -6 ):

From 1989 through 2004, the Argonaut Estates, Jackson View Estates, Sierra View Estates, and Argonaut Heights residential developments were reportedly built on areas of known waste rock and mine tailings that were covered with imported fill prior to construction of the homes (see Attachment A

4) (Ref. 4, p p. 16, 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2 -3) . A historical aerial photo review conducted by EPA showed that some residential properties in the Argonaut Estates development were built on the location of a waste rock pile associated with Argonaut operations ( Ref. 4, p. 28; Ref. 10, p p. 13 , 28, 36 ). Sampling conducted at Argonaut Estates properties ARA

- 07 and ARA -08 on Spunn Road showed the presence of elevated concentrations of ars enic , lead, and mercury in soils from 0 to 2 feet below ground surface ( bgs ) ( Attachment A -5) (Ref. 4, pp. 28-29, 66; Ref. 15 ).

Attachment A -4 shows the locations of residential properties ARA

- 07 and ARA

- 08 overlaid on a 1944 aerial photo showing the waste rock pile (Ref. 10, pp. 29, 36). The area of Source 2 is estimated to be approximately 79,500 square feet based on the footprint of the waste rock pile in the 1944 aerial photo, as well as the sampling locations on ARA

- 07 and ARA

- 08 showing elevated concentrations of arsenic (Attachment A -5) . The area includes ARA -33, the property between ARA

- 07 and ARA -08, because the waste rock pile extended across this property as well. The es t imated area of Source 2 is shown on

Attachment A -6.

In August and September 2015, EPA conducted removal actions at 11 residential properties built within

the former Argonaut Mine property ( Ref. 15; Ref. 40 , pp. 1 -2 , 7). However, this removal did not include any actions at the residential properties in Source 2.19 Source No: 2



### 2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

Weston Solutions, Inc. 2014 SI Soil Sampling From July 28, 2014 through August 1, 2014, Weston Solutions, Inc. collected soil, sediment an d surface water samples as part of a SI of the Argonaut Mine. Samples were collected in accordance with a SAP approved by EPA on March 10, 2014

. Samples were submitted to Bonner Analytical, located in Hattiesburg, Miss issippi , under the EPA Contract Laboratory Program for metal s analysis by Inorganic Superfund Methods (ISM01.3) and cyanide by EPA Method 9010/9012. The metal s analytical data were validated by EPA (Re f. 4, p. 22).

Surface soil and shallow subsurface soil samples were collected from 19 residential lots and from Jackson Junior High School to assess whether the properties were impacted by historic al Argonaut Mine operations. S ampling locations ARA

- 07 and ARA -08 were collected from the Argonaut Estates neighborhood developed along the waste rock pile south of the Argonaut Mine Mill Area (Ref. 4, p. 28).

Sampling locations are presented in Attachment A -5. To preserve the privacy of local residents, soil samples are identified by address code only. A ddress codes are defined in a confidential reference (Ref.

15 ).

2014 Site Inspection, Source 2 Concentrations

Address

Code Sample

ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration ** ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

ARA

- 07 ARA

07 -0
(MY9F 56) 0

- 0.5 7/3 1 /14 Arsenic 68.5 J+ 1.1 Ref. 4, pp. 40

, 66, 1811, 1873, 1875, 1944; Ref. 16, p. 2; Ref. 21, pp. 7, 14 Lead 25.6 J 1.1

Mercury 0.14 0.11

ARA

07 -1
(MY9F 57) 1.5 - 2 7/3 1 /14 Arsenic 148 1.1 Ref. 4, pp. 40

, 66, 1811, 1865, 1944; Ref. 17, p. 7; Ref. 22, pp. 10, 32 Lead 21.5 1.1

Mercury 0.16 0.11

ARA

- 08 ARA

08 -0
(MY9F 58) 0

- 0.5 7/3 1 /14 Arsenic 68.3 J+ 1.1 Ref. 4, pp. 40, 66, 1811, 1873, 1876, 1944; Ref. 16, p. 2; Ref. 21, pp. 7, 15 Lead 13.0 1.1

mg/kg: milligrams analyte per kilogram soil CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit *: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

J+: The result is estimated and may be biased high (Ref. 4, p p

. 1867, 1873)

. J: The result is estimated with an unknown bias (Ref. 4, p p

. 1867, 1873). **: Qualified data presented in this table reflect a positive identification of the substance, although the data may be qualified.

^: Page 2 of Reference 16 presents a J

- qualifier for qualified arsenic samples, p age s 1875 and 1876 of Reference 4 present arsenic concentrations without qualifiers , and Reference 4 page 1873 indicates that the qualified arsenic samples are biased high. Regardless of the qualifier assigned, the substance can still be associated with the source.20 Source No: 2



### List of Hazardous Substances Associated with Source Arsenic, Lead, and Mercury

2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY The migration pathways are not scored for Source 2.21 Source No: 2



### 2.4.2. Hazardous Waste Quantity

Tier A: Hazardous Constituent Quantity The total Hazardous Constituent Quantity for Source 2 co uld 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 ). 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 CERCLA

hazardous substances in the source and the associated relea ses from the source. Therefore, there is insufficient information to calculate a total or partial Hazardous Constituent Quantity estimate for

Source 2 with reasonable confidence. Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

Tier B: Hazardous Wastestream Quantity 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 haza rdous 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 2.4.2.1.3).

Hazardous Wastestream Quantity Value: NE

Tier C: Volume The information available is not sufficient to meaningfully evaluate Tier C: volume, because the depth and total extent of the waste rock pile across Source 2 is unknown. Therefore it is not possible to adequately determine a volume for Source 2 (Ref. 1, Section 2.4.2.1.3). Scoring proceeds to the evaluation of Tier D, area (Ref. 1, Section 2.4.2.1.4).

Volume Assigned Value: 022 Source No: 2



### Tier D: Area

The area of Source 2 is estimated to be approximately 79,500 square feet based on the footprint of the

waste roc k pile in the 1944 aerial photo, as well as the sampling locations on ARA

- 07 and ARA -08 showing elevated concentrations of arsenic (see Attachment A -5). In accordance with Ref. 1, Table 2-5:

79,500 / 13 = 6,115.4

Area Assigned Value: 6,115.4

Source Hazardous Waste Quantity Value: 6,115.423 Source No: 3



### 2.2.1 SOURCE IDENTIFICATION : Source 3 Argonaut Heights North Tailing Pile

Name of source: Argonaut Heights – North Tailings Pile Number of source: 3

Source Type : Tailings Pile

Description and Location of Source (s ee Attachments A -4 through A-6 ):

From 1989 through 2004, the Argonaut Estates, Jackson View Estates, Sierra View Estates, and Argonaut Heights residential developments were reportedly built on areas of known waste rock and mine tailings that were covered with imported fill prior to construction of the homes (see Attachment A

4) (Ref. 4, p p. 16, 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2 -3 ). A historical aerial photo review conducted by EPA showed trenches, pits, and berms for tailings disposal in the northern portion of the Argonaut Heights development near Pioneer Street and Argonaut Lane (Ref. 10 , pp. 2 9-30, 36 ; Ref. 42,

p. 7 ). Sampling conducted at these properties showed the presence of elevated concentrations of arsenic, lead, and mercury in soils from 0 to 2 feet bgs ( Attachment A -5 ) ( Ref. 4, pp. 28-29, 66; Ref. 15 ).

Attachment A -4 shows the locations of residential properties overlaid on a 1944 aerial photo of the Argonaut Mine property (Ref. 10, p. 36). In March 2015, EPA conducted a removal action of the vacant parcel located at the northeast corner of Pioneer Street and Argonaut Lane (EPA AOC

- 5) ( Attachment

A-1 ) (Ref. 42, p. 5). During the removal, mine tailings and wastes were observed to extend beyond the boundaries of AOC-5 into the neighboring residential proper ties of Source 3 (Ref. 42, pp. 10, 12, 45).

In August and September 2015, EPA conducted removal actions at 11 residential properties built within

the former Argonaut Mine property , including four of the 12 residential properties in Source 3 ( Ref. 40

, pp. 1

- 2, 4 -5 , 7; Ref. 15 ). Based on samples collected pre

- and post -removal, as well as samples collected during the 2014 SI, the area of Source 5 is estimated to be approximately 97,350 square feet (see

Attachment A -6 ). The August 2015 removal action did not change the calculated area of Source 3, because soils exceeding 100 mg/kg arsenic were only removed to 12 inches bgs, and confirmation sampling showed that soils with elevated concentrations o f arsenic were still present beneath the excavations (Ref. 39, pp. 7-10; Ref. 40, pp. 2, 4).

During the August 2015 removal, the following actions were taken at each of the residential properties

within Source 3 ( Ref. 40 , pp. 2, 4 -5) . Properties are identified by address code to preserve the privacy of the residents (Ref. 15).24 Source No: 3



### Address Code Action

ARA

- 09 No action

.

ARA -10 Soil s exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and

b ackfilled with clean topsoil. Removed soils covered an area of 1,223 square feet ( Ref. 39, p. 8; Ref. 40 , pp. 2, 5).

ARA -11 Soils exceeding 100 mg/kg arsenic removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 1,275 square feet ( Ref. 39, p. 9; Ref. 40 , pp. 2, 5 )

. ARA

- 12 No action

.

ARA -13 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 2,846 square feet ( Ref. 39, p. 7; Ref. 40 , pp. 2, 5 )

. ARA

- 23 No action.

ARA

- 25 No action.

ARA

- 26 No action.

ARA

- 27 No action.

ARA -28 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 1,025 square feet ( Ref. 39, p. 10; Ref. 40 , pp. 2, 5 ).

ARA

- 31 No action.

ARA

- 32 No action.

2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

Weston Solutions, Inc. 2014 SI Soil Sampling From July 28, 2014 through August 1, 2014, Weston Solutions, Inc. collected soil, sediment an d surface water samples as part of a SI of the Argonaut Mine. Samples were collected in accordance with a SAP approved by EPA on March 10, 2014

. Samples were submitted to Bonner Analytical, located in Hattiesburg, Mis sissippi , u nder the EPA Contract Laboratory Program for metals analysis by Inorganic Superfund Methods (ISM01.3) and cyanide by EPA Method 9010/9012. The metals analytical data were validated by EPA (Ref. 4, p. 22).

Surface soil and shallow subsurface soil samples were collected from 19 residential lots and from Jackson Junior High School to assess whether the properties were impacted by historic al Argonaut Mine operations. Five sampling locations (ARA

- 09 through ARA

- 13) were collected from residential properties in Source 3 (Ref. 4, p. 28 ; see Attachment A -6 ). Laboratory results are reported below. Analytical results from soils that were later removed during the August 2015 Removal Action are not reported

.

Sampling locations are presented in Attachment A -5. To preserve the privacy of local residents, sample

location s are identified by address code only. A ddress codes are defined in a confidential reference (Ref.

15 ).25 Source No: 3



### 2014 Site Inspection, Source 3 Concentrations

Address

Code Sample

ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration ** (mg/kg) Sample Adjusted CRQL* (mg/kg) References

ARA

- 09 ARA

09 -0
(MY9F 60) 0

- 0.5 7/31/14 Arsenic 1,380 J+ 5.2 Ref. 4, pp. 40, 66

, 1811, 1873, 1876, 1945; Ref. 16, p. 3; Ref. 21, pp. 7, 17 Lead 226 1.0

Mercury 1.4 0.21

ARA

09 -2
(MY9F 62) 1.5 - 2 7/31/14 Arsenic 39,900 J+ 123 Ref. 4, pp. 40, 66, 1811, 1873, 1876

, 1945; Ref. 16, p. 3; Ref. 21, pp. 7, 18 Lead 3,220 9.9

Mercury 193 24.6

ARA

- 10 ARA

10 -2
(MY9F 63) 1.5 - 2 7/31/14 Arsenic 655 J+ 1.1 Ref. 4, pp. 40, 66, 1811, 1873, 1877

, 1944; Ref. 16,

pp . 3 -4 ; Ref. 21, pp. 7, 20 Lead 50.5 1.1

Mercury 0.30 0.11

ARA

- 12 ARA

12 -2 (MY9F 63) 1.5 - 2 7/31/14 Arsenic 58.6 J+ 1.1 Ref. 4, pp. 40

, 66, 1811,

1 873, 1878, 1945; Ref. 16, p. 5; Ref. 21, pp. 7, 24 Lead 19.2 J 1.1

Mercury 0.44 0.11

ARA

- 13 ARA

13 -1
(MY9F 69) 1.5 - 2 7/31/14 Arsenic 1,200 J+ 4.4 Ref. 4, pp. 40, 66, 1811, 1873, 1878

, 1945; Ref. 16, pp. 5

- 6; Ref. 21, pp. 7, 26 Lead 225 1.1

Mercury 1.8 0.33

mg/kg: milligrams analyte per kilogram soil CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit *: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

J+: The result is estimated and may be biased high (Ref. 4, p. 1873).

J: The result is estimated with an unknown bias (Ref. 4, p. 1873). **: Qualified data presented in this table reflect a positive identification of the substance, although the data may be qualified.26 Source No: 3



### March 2015 Superfund Technical Assessment and Response Team ( START ) Removal Assessment

In March 2015, START conducted a removal assessment of 20 residential properties in the Argonaut Heights and Sierra View Estates neighborhoods (Re f. 4, p. 14; Ref. 11, p. 2)

. The residential properties were divided into two to six decision units (DUs) composed of roughly equal areas at a maximum of 1,250 square feet each to cover unpaved areas of the property. A 5

- point composite sample was

collecte d from each DU at sampling intervals of 0 to 2 inches and 12 to 18 inches bgs using a trowel or hand auger and disposable scoops . Discrete samples were collected from some of the residences at the locations of play areas and gardens (Ref. 11, p. 2 ).

Samples were analyzed for lead and arsenic via X- Ray Fluorescence ( XRF ) , with at least one sample from each property submitted to a laboratory for confirmation . Confirmation samples were submitted to the EPA Region 9 Laboratory for analysis of arsenic and lead by EPA SW

- 846 Method 6010C (Ref. 11, pp. 3-4 ). Sampling locations are presented on Attachment A -5.27 Source No: 3



### 2015 EPA Removal Assessment, Source 3 Concentrations

Address

Code Sample

ID Sample Depth (inches) Date Hazardous

Substance Hazardous

Substance

Concentration

( mg/kg ) QL (mg/kg) References

ARA

- 09 R- 12

- 03

­ C- 12 12 to 14 3/25/15 Arsenic 680 10 Ref. 11 , pp. 86, 91, 97 ; Ref. 15 ; Ref. 39, p p . 16 , 17 ; Ref. 47, pp. 4, 29, 32, 42 Lead 130 3

ARA

10 (1) R- 14

- 01

­ C- 12 12 to 14 3/25/15 Arsenic 220 2 Ref. 11 , pp. 86, 91, 97 ; Ref. 15 ; Ref. 39, p. 17; Ref. 47, pp. 4, 30, 33, 42 Lead 35 3

ARA

11 (1) R- 13

- 01

­ C- 12 12 to 14 3/25/15 Arsenic 590 10 Ref. 11 , pp. 86, 91, 97 ; Ref. 15 ; Ref. 39, p p . 16 , 17 ; Ref. 47, pp.

4 , 29 , 32, 42 Lead 120 3

ARA

- 12 R- 04

- 02

­ D-4 4 to 8 3/24 /15 Arsenic 430 2 Ref. 11 , pp. 84

, 91, 96 ; Ref. 15 ; Ref. 39, p p . 14 , 15 ; Ref. 47, pp. 3, 28, 32, 41 Lead 41 3

ARA

13 (1) R- 10

- 06

­ C- 16 16 to 18 3/25/15 Arsenic 5,100 100 Ref. 11 , pp. 8 5

, 91, 97 ; Ref. 15 ; Ref. 39, p p

. 15, 16 ; Ref. 47, pp. 4, 29, 32, 41 Lead 1,900 3

ARA

- 23 R- 01

- 02

­ C- 12 12 to 14 3/23/15 Arsenic 140 2 Ref. 11 , pp. 8 4

, 91, 96 ; Ref. 15 ; Ref. 39, p p . 12 , 13 ; Ref. 47, pp. 3, 28, 32, 41 Lead 7.8 3

ARA

- 25 R- 03

- 02

­ C-0 0 to 2 3/23/15 Arsenic 270 2 Ref. 11

, pp. 84, 91, 96; Ref. 15; Ref. 39, p. 13; Ref. 47, pp. 3, 28, 32, 41 Lead 28 3

ARA

- 26 R- 05

- 02

­ C-0 0 to 2 3/24/15 Arsenic 40 2 Ref. 11 , pp. 86, 91, 96; Ref. 15 ; Ref. 39, p. 14; Ref. 47, pp. 3, 28, 32, 41 Lead 83 3

ARA

- 27 R- 06

- 03

­ D- 16 16 to 18 3/24/15 Arsenic 1,000 10 Ref. 11 , pp. 86, 91, 96; Ref. 15 ; Ref. 39, p. 14; Ref. 47, pp. 3, 28, 32, 41 Lead 110 3

ARA

28 (1) R- 07

- 01

­ C- 12 12 to 14 3/24/15 Arsenic 40 2 Ref. 11 , pp. 86, 91, 96; Ref. 15 ; Ref. 39, p p . 14 , 15 ; Ref. 47, pp. 3, 29, 32, 41 Lead 12 3

ARA

- 31 R- 18

- 01

­ C-0 0 to 2 3/2 5 /15 Arsenic 62 2 Ref. 11 , pp. 86, 91, 97; Ref. 15 ; Ref. 39, p p

. 17, 18 ; Ref. 47, pp. 4, 30, 33, 42 Lead 26 3

mg/kg: milligrams analyte per kilogram soil

QL : Quantitation Limit . EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).

(1) : Although a removal was conducted on this property, soils were not excavated to this depth (14

- 18 inches, as applicable for the samples presented above.) ( Ref. 15; Ref. 4 0 , p. 2 ). Therefore, these contaminated soils are still present on the property.28 Source No: 3



### EPA August 2015 Removal Action In August 2015, EPA conducted removal actions at 11 residential properties built with in the former Argonaut Mine property , including four of the 12 residential properties in Source 3 (Ref. 15; Ref. 40 , pp. 1- 2, 4

- 5). Soils exceeding the action level of 100 mg/kg for arsenic were removed to 12 inches bgs and backfilled with clean topsoil ( Ref. 40, p. 2). Confirmation samples were collected from 12 to 14 inches bgs within the excavations (Ref. 39, p. 1). Samples were analyzed for lead and arsenic via XRF, with at least one sample from each property submitted to a laboratory for confirmation. Confirmation samples

were submitted to the EPA Region 9 Laboratory for analysis of arsenic and lead by EPA SW -846 Method 6010C ( Ref. 11 , pp. 3, 4, 120-121 ). Laboratory results are presented below. Sampling locations are presented on Attachment A -5.

2015 EPA Removal Action , Source 3 Concent rations

Address

Code Sample ID Sample Depth (inches) Date Hazardous

Substance Hazardous

Substance

Concentration ( mg/kg ) QL (mg/kg) References

ARA

- 10 R- 14

- 01 -C12

- 082715 12 to 14 8/27/15 Arsenic 1,500 2 Ref. 11, p. 121; Ref. 39

, pp. 1, 75; Ref. 49, pp. 4,

22

- 23, 27 Lead 320 3

ARA

- 13 R- 10

- 06 -C12

- 082115 12 to 14 8/21/15 Arsenic 5,300 4 Ref. 11, p p

. 90

- 92, 120;

Ref. 39 , p p . 1, 77 ; Ref. 49, pp. 3, 22

- 23, 27 Lead 1,600 3

ARA

- 28 R- 07

- 01 -C12

- 082615 12 to 14 8/26/15 Arsenic 25 2 Ref. 11, p. 120; Ref. 39

, pp . 1, 73 ; Ref. 49, pp. 3,

22

- 23, 27 Lead 15 3

mg/kg: milligrams analyte per kilogram soil

QL : Quantitation Limit. EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).



### List of Hazardous Substances Associated with Source Arsenic, Lead, and Mercury

2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY The migration pathways are not scored for Source 3.29 Source No: 3



### 2.4.2. Hazardous Waste Quantity

Tier A: Hazardous Constituent Quantity The total 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). Insufficient historical and current data (permits, waste concentration data, annual reports, etc.) are available to adequately calculate the total mass, or a part ial estimate, of all CERCLA hazardous substances in the source and the associated releases from the source. Therefore, there is insufficient information to calculate a total or partial Hazardous Constituent Quantity estimate for

Source 3 with reasonable co nfidence . Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

Tier B: Hazardous Wastestream Quantity The total Hazardous Wastestream Quantity for Source 3 c ould 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 hazard ous 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

So urce 3 with reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section 2.4.2.1.3).

Hazardous Wastestream Quantity Value: NE

Tier C: Volume The information available is not sufficient to meaningfully evaluate Tier C: volume, because the depth and total extent of the tailings and waste rock pile across Source 3 is unknown. Therefore

, it is not possible to adequately determine a volume for Sourc e 3 (Ref. 1, Section 2.4.2.1.3). Scoring proceeds to

the evaluatio n of Tier D: area (Ref. 1, Section 2.4.2.1.4).

Volume Assigned Value: 030 Source No: 3



### Tier D: Area Based on pre

- and post

- removal samples collected in 2015 , as well as samples collected during the 2014 SI, the area of Source 3 is estimated to be approximately 97,350 square feet (see Attachment A -6 ). Soil areas that were removed during the August 2015 removal action were not included in the area estimate. In accordance with Ref. 1, Table 2 -5:

97,350 / 13 = 7,488.5

Area Assigned Value: 7,488.5

Source Hazardous Waste Quantity Value: 7,488.531 Source No: 4



### 2.2.1 SOURCE IDENTIFICATION : Source 4, Argonaut Heights – South Contaminated Soil

Name of source: Argonaut Heights – South Contaminated Soil Number of source: 4

Source Type : Contaminated Soil

Description and Location of Source ( see Attachment A -4 through A-6 ):

From 1989 through 2004, the Argonaut Estates, Jackson View Estates, Sierra View Estates, and Argonaut Heights residential developments were reportedly built on areas of known waste rock and mine tailings that were covered with imported fill prior to construction of the homes (see Attachment A

4) (Ref. 4, p p. 16, 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2 -3 ). Elev ated concentrations of arsenic, lead, and mercury have been detected in surface soils collected from five residential properties on Buena

Vista Drive and Amador Street adjacent to the former cyanide plant located within EPA AOC -2 ( Ref. 4, pp. 28, 48 , 66; R ef. 15; Ref. 11, p. 86; Ref. 3 9 , p. 1 ; see Attachment A -6 ). A historical aerial photo review conducted by EPA showed that the cyanide plant was accessed by a dirt road and dirt trail through these residential properties. A former flume was also observed extending across all 5 properties (see Attachment A -4) (Ref. 10, pp. 31, 36 ). During sampling conducted in 2014, distinct tailings or waste rock were not visually identified in Source 4; therefore, the source type is evaluated as Contaminated Soil ( Ref. 46 ).

In August and September 2015, EPA conducted removal actions at 11 residential properties built within the former Argonaut Mine property, including four of the five properties in Source 4 ( Ref. 40, pp. 1

- 2, 4-5). Based on samples collected pre- and post-removal, as well as samples collected during the 2014 SI,

the area of Source 4 is estimated to be approximately 72,511 square feet (see Attachment A -6). The August 2015 removal action did not change the calculated area of Source 4 , because soils exceeding 100 mg/kg arsenic were only removed to 12 inches bgs, and confirmation sampling showed that soils with

elevated concentrations of arsenic were still present beneath the excavations (Ref. 39, pp. 3 -6 ; Ref. 40, pp. 2, 4).

During the August 2015 removal, th e following actions were taken at each of the residential properties

within Source 4 ( Ref. 40 , pp. 2, 4

- 5). Properties are identified by address code to preserve the privacy of the residents (Ref. 15).32 Source No: 4



### Address Code Action

ARA -15 Soil s exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 2,846 square feet ( Ref. 39, p. 5; Ref. 40 , pp. 2, 4 ).

ARA -16 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 1,798 square feet ( Ref. 39, p. 6; Ref. 40 , pp. 2, 5 ).

ARA -17 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 1,275 square feet ( Ref. 39, p. 4; Ref. 40 , pp. 2, 4 ).

ARA

- 24 No action.

ARA -30 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 7,297 square feet ( Ref. 39, p. 3; Ref. 40 , pp. 2, 4 ).

2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

Weston Solutions, Inc. 2014 SI Soil Sampling From July 28, 2014 through August 1, 2014, Weston Solutions, Inc. collected soil, sediment an d surface water samples as part of a SI of the Argonaut Mine. Samples were collected in accordance with a SAP approved by EPA on March 10, 2014

. Samples were submitted to Bonner Analytical, located in Hattiesburg, Miss issippi , under the EPA Contract Laboratory Program for metals analysis by Inorganic Superfund Methods (ISM01.3) and cyanide by EPA Method 9010/9012. The metals analytical data were validated by EPA (Ref. 4, p. 22).33 Source No: 4



### - Background Concentrations: Background soil samples were collected from location AB

- 01 in pasture land located northwest of the

Source 1 Tailings Impoundment and location AB

- 02 in pasture land located southwest of the Source 1 Tailings Impoundment (Ref. 4, p. 24 ; see Attachment A -3 ). Background sampling locations are shown

in Attachment A -3.

Residential properties built within the former Argonaut Mine property boundary were built on imported fill placed over waste rock, tailings, and soils contaminated by Argonaut Mine operations ( Re f. 4, pp. 16 , 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2 -3). Prior to the construction of the Source 1 Tailings Impoundment and the AOC -2 Cyanide Plant, a portion of the property was farmland (Ref. 12, p. 28 ; Ref. 50 ). Therefore, background samples were collected from nearby pasture lands to be representative

of local conditions without the Argonaut Mine. Sample depths of the background and release samples

are all from the upper 2 feet, though depths are not directly com parable as the background locations are native soil while soils from the residential properties include tailings and waste rock generated by mining activities, as well as imported fill.

Source 4 Background Soil Concentrations

Sample ID Sample Depth (feet ) Date Hazardous

Substance Hazardous

Substance

Concentration ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

AB

- 01 -0
(MY9EX7) 0

- 0.5 7/31/14 Arsenic 8.9 1.0 Ref. 4, pp. 25, 39

- 40, 66, 76, 1808,

1818

- 1820, 1944; Ref. 18, p. 1; Ref. 23, pp. 7, 15 Lead 14.8 J 1.0

Mercury 0.15 0.10

AB

- 01

- 1.5
(MY9EY0) 1.0

- 1.5 7/31/14 Arsenic 2 .0 J

­ 1.1 Ref. 4, pp. 25 39

- 40, 66, 76, 1808,

1830

- 1832, 1834, 1944; Ref. 20, p. 1; Ref. 24, pp. 6, 10 Lead 9 .0 J 1.1

Mercury <0.11 0.11

AB

- 02 -0
(MY9EY1) 0

- 0.5 7/28/14 Arsenic 3.1 J

­ 1.0 Ref. 4, pp. 25, 39

- 40, 65, 1808, 1830

­ 1832, 1834, 1941; Ref. 20, p. 1; Ref. 24, pp. 6, 11 Lead 11.2 J 1.0

Mercury <0.10 0.10

AB

- 02

- 1.5
(MY9EY2) 1.0

- 1.5 7/28/14 Arsenic 1.2 J

­ 1.1 Ref. 4, pp. 25, 39

- 40, 65, 1808, 1830

­ 1832, 1834, 1941; Ref. 20, pp. 1

- 2; Ref. 24, pp. 6, 12 Lead 7.1 J 1.1

Mercury <0.11 0.11
mg/kg: milligrams analyte per kilogram soil CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit *: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

J: The result is an estimated quantity, with an unknown bias (Ref. 4, pp. 1818, 1830

- 1832 , 1867 ).

J- : The result is an estimated quantity, with a low bias (Ref. 4, pp. 1818, 1830

- 1832, 1867). <: The analyte was not detected. ^: Page 1831of Reference 4 present s a J qualifier for arsenic concentrations , and Reference 4 pages 1830 and 1834 indicate that the reported results may be biased low

.34 Source No: 4



### - Source Samples: Surface soil and shallow subsurface soil samples were collected from 19 residential lots and from Jackson Junior High School to assess whether the properties were impacted by historical Argonaut Mine operations. Three sampling locations (ARA -15 through ARA -17 ) were collected from the Argonaut Heights neighborhood adjacent to the AOC -2 cyanide plant (Ref. 4, p. 28). Analytical results from soils

that were later removed during the 2015 Removal Action are not reported

.

Sampling locations are presented in Attachment A -5. To preserve the privacy of local residents, samples are identified by address code only. Sample address codes are defined in a confidential reference (Ref.

15 ).

2014 Site Inspection, Source 4 Concentrat ions

Address

Code Sample

ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration ** ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

ARA

- 15 ARA

15 -1
(MY9F 73) 1.5 - 2 7/31/14 Arsenic 269 J+ 1.1 Ref. 4, pp. 40, 1873, 1879

, 1944; Ref. 16, p. 7; Ref. 21, pp. 8, 30 Lead 286 1.1

Mercury 3.3 0.53

ARA

- 16 ARA

16 -1
(MY9F 75) 0.5 - 1 7/31/14 Arsenic 147 1.1 Ref. 4, pp. 40, 66

, 1889, 1944; Ref. 21, p. 8; Ref. 25, pp. 7, 12; Ref. 37, p. 1 Lead 121 1.1

Mercury 0.85 0.11

ARA

- 17 ARA

17 -2
(MY9F 77) 1.5 - 2 7/31/14 Arsenic 123 1.1 Ref. 4, pp. 40, 66

, 1812,

1888

- 1889, 1944; Ref. 21, p. 8; Ref. 25, pp. 7, 14; Ref. 37, p. 2 Lead 30.0 J 1.1

mg/kg: milligrams analyte per kilogram soil

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit
*: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

J+: The result is an estimated quantity, but the result may be biased high (Ref. 4, p p

. 1867, 1873).

J: The result is an estimated quantity with an unknown bias (Ref. 4, p p

. 1867, 1873, 1888 ).
**: Qualified data presented in this table reflect a positive identification of the substance, although the data may be quali fied.

^: Page 7 of Reference 16 presents a J

- qualifier for qualified samples, page s 1875 and 1876 of Reference 4 present arsenic concentrations without qualifiers, and Reference 4 page 1873 indicates that the qualified arsenic samples are biased high. Regardless of the qualifier assigned, the substance can still be associated with the source.



### EPA March 2015 Removal Assessment

In March 2015, EPA conducted a removal assessment of 20 residential properties in the Argonaut Heights and Sierra View Estates neighborhoods (Ref. 4, p. 14; Ref. 11, p. 2)

. The residential properties were divided into two to six DUs composed of roughly equal areas at a maximum of 1,250 square feet35 Source No: 4



### each to cover unpaved areas of the property. A 5

- point composite sample was collected from each DU at

s ampling intervals of 0 to 2 inches and 12 to 18 inches bgs using a trowel or hand auger and disposable scoops. Discrete samples were collected from some of the residences at the locations of play areas and gardens (Ref. 11, p. 2 ). Samples were analyzed for lead and arsenic via XRF, with at least one sample from each property submitted to a laboratory for confirmation. Confirmation samples were submitted to the EPA Region 9 Laboratory for analysis of arsenic and lead by EPA SW

- 846 Method 6010C (Ref. 11, pp. 3-4).

Sampling locations are presented in Attachment A -5. Analytical results from soils that were later removed during the August 2015 EPA Removal Action are not reported

. Background sampling was not conducted during this sampling event; therefore, samples are compared to background concentrations from the 2014 SI sampling event.

2015 EPA Removal Assessment, Source 4 Concentrations

Address

Code Sample

ID Sample Depth (inc hes) Date Hazardous

Substance Hazardous

Substance

Concentration ( mg/kg ) QL (mg/kg) References

ARA

15 (1) R- 08

- 04

­ C- 12 12 to 14 3/24/15 Arsenic 340 2 Ref. 11, pp. 85, 96 ; Ref. 15 ; Ref. 39, p p . 14 , 15 ; Ref. 47, pp. 3, 29, 32, 41 Lead 280 3

ARA

16 (1) R- 09

- 03

­ C- 12 12 to 14 3/24/15 Arsenic 350 2 Ref. 11, pp. 85, 90

- 92, 96 ; Ref. 15 ; Ref. 39, p p

. 15, 16 ; Ref. 47, pp. 3, 29, 32, 41 Lead 500 3

ARA

- 17 R- 19

- 02

­ C- 12 (1) 12 to 14 3/27/15 Arsenic 130 2 Ref. 11, pp. 87, 105 ; Ref. 15; Ref. 39, p. 18; Ref. 47, pp. 9, 31, 33, 44 Lead 49 3

R- 19

- 04

­ C-0 (2) 0 to 2 6/23/15 Arsenic 92 2.1 Ref. 11, pp. 87, 115; Ref. 15; Ref. 39, p. 4; Ref. 48, pp. 4, 25

- 26, 30 Lead 25 3.2

ARA

- 24 R- 02

- 02

­ C-0 0 to 2 3/23/15 Arsenic 69 2 Ref. 11, pp. 8 4 , 96 ; Ref. 15; Ref. 39, p. 13; Ref. 47, pp. 3, 28, 32, 41 Lead 56 3

mg/kg: milligrams analyte per kilogram soil

QL : Quantitation Limit. EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).

(1) : Although a removal was conducted on this property, soils were not excavated to this depth (Ref. 15; Ref. 40, p.2 ). Therefore, these soils are still present on the property.

(2) : Although a removal was conducted on this property, soils were not excavate d at this location because the arsenic

concentration was below the removal action level of 100 mg/kg (Ref. 39, p. 4; Ref. 40, p. 2 ).36 Source No: 4



### EPA August 2015 Removal Action In August 2015, EPA conducted removal actions at 11 residential properties built in the area of former Argonaut Mine operations, including four of the five properties in Source 4 (Ref. 15; Ref. 40, pp. 1

- 2, 4

­ 5). Soils exceeding the action level of 100 mg/kg for arsenic were removed to 12 inches bgs and

ba ckfilled with clean topsoil ( Ref. 40, p. 2). Confirmation samples were collected from 12 to 14 inches bgs within the excavations (Ref. 39, p. 1). Samples were analyzed for lead and arsenic via XRF, with at least one sample from each property submitted to a laboratory for confirmation. Confirmation samples were submitted to the EPA Region 9 Laboratory for analysis of arsenic and lead by EPA SW -846 Method 6010C ( Ref. 11 , pp. 120-121 ). Sampling locations are presented on Attachment A -5. Background sampling was not conducted during this sampling event; therefore, samples are compared to background concentrations from the 2014 SI sampling event.

2015 EPA Removal Action , Source 4 Concentrations

Address

Code Sample ID Sample Depth (inches) Date Hazardous

Substanc e Hazardous

Substance

Concentration ( mg/kg ) QL (mg/kg) References

ARA

- 16 R- 09

- 03 -C12

- 082415 12 to 14 8/24/15 Arsenic 580 2 Ref. 11, p. 120; Ref. 15;

Ref. 39

, pp. 1, 7 1 ; Ref. 49, pp. 3, 22

- 23, 27 Lead 570 3

ARA

- 30 R- 17

- 02E

C- 12

­ 081815 12 to 14 8/18/15 Arsenic 120 2 Ref. 11, p. 120; Ref. 15;

Ref. 39 , p p . 1, 6 6 ; Ref. 49, pp. 3, 22

- 23, 27 Lead 8 .4 3

mg/kg: milligrams analyte per kilogram soil

QL : Quantitation Limit. EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).



### List of Hazardous Substances Associated with Source Arsenic, Lead, and Mercury

2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY The migration pathways are not scored for Source 4.37 Source No: 4



### 2.4.2. Hazardous Waste Quantity

Tier A: Hazardous Constituent Quantity The total 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). 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 CERCLA hazardous substances in the source and the associated releases from the source. Therefore, there is insufficient information to calculate a total or partial Hazardous Constituent Quantity estimate for

Source 4 with reasonable confidence. Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

Tier B: Hazardous Wastestream Quantity

The total Haz ardous 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 par tial Hazardous Wastestream Quantity for

Source 4 with reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section 2.4.2.1.3).

Hazardous Wastestream Quantity Value: NE

Tier C: Volume

The information available is not suf ficient to meaningfully evaluate Tier C: volume, because the depth

and total extent of the contaminated soil across Source 4 is unknown. Therefore it is not possible to adequately determine a volume for Source 4 (Ref. 1, Section 2.4.2.1.3). Scoring proce ed s to the evaluation of Tier D: area (Ref. 1, Section 2.4.2.1.4).

Volume Assigned Value: 038 Source No: 4



### Tier D: Area Based on samples collected pre

- and post

- removal, as well as samples collected during the 2014 SI, the

area of Source 4 is estimated to be approximately 72,511 square feet (see Attachment A -6 ). In accordance with Ref. 1, Table 2 -5:

72,511 / 34,000 = 2.1

Area Assigned Value: 2.1

Source Hazardous Waste Quantity Value: 2.139 Source No: 5



### 2.2.1 SOURCE IDENTIFICATION : Source 5, Sierra View Estates Contaminated Soil

Name of source: Sierra View Estates Contaminated Soil Number of source: 5

Source Type : Contaminated Soil

Description and Location of Source ( see Attachment A -4 through A-6 ):

From 1989 through 2004, the Argonaut Estates, Jackson View Estates, Sierra View Estates, and Argonaut Heights residential developments were reportedly built on areas of known waste rock and mine tailings that were covered with imported fill prior to construction of the homes (see Att achment A

4) (Ref. 4, p p. 16, 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2 -3 ). Elevated concentrations of arsenic, lead, and mercury have been detected in surface soils collected from three residential properties on

Detert Lan e adjacent to the Source 1 Tailings Impoundment ( Ref. 4, pp. 23, 48, 66; Ref. 15 ; See

Attachment A -2 ). A historical aerial photo review conducted by EPA showed a former flume across this area (see Attachment A -4) (Ref. 10 , pp. 23, 28, 32, 36). During sampling conducted in 2014, dist inct tailings or waste rock were not visually identified in Source 5; therefore, the source type is evaluated as Contaminated Soil ( Ref. 46 ).

In August and September 2015, EPA conducted removal actions at 11 residential properties built with in

the former Argonaut Mine property , including two properties in Source 5 ( Ref. 40, pp. 1

- 2, 4 -5 , 7 ; Ref 15; see Attachment A -6 ; see table below). Based on samples collected pre

- and post

- removal, as well as samples collected during the 2014 SI, the area of Source 5 is estimated to be approximately 40,341 square feet (see Attachment A -6 ). The removal action did not change the calculated area of Source 5,

because soils with arsenic exceeding 100 mg/kg were only removed to 12 inches bgs, or were left in place and covered with wood chips and rock. Confirmation sampling showed that soils with elevated concentrations of arsenic were still present beneath the excavation (Ref. 39, p. 2; Ref. 40, pp. 2, 4).

During the August 2015 removal, the following actions were taken at each of the residential properties

within Source 5 ( Ref. 40 , pp. 2, 4

- 5). Properties are identified by address code to preserve the privacy of the residents (Ref. 15).

Address Code Action

ARA -18 No soils were removed

. A n area of 5,324 square feet was covered with wood chips and rock ( Ref. 40 , pp. 2, 4).

ARA

- 19 No action.

ARA -29 Soil exceeding 100 mg/kg arsenic was removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 1,275 square feet ( Ref. 39, p. 2; Ref. 40 , pp. 2, 4).40 Source No: 5



### 2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

Weston Solutions, Inc. 2014 SI Soil Sampling From July 28, 2014 through August 1, 2014, Weston Solutions, Inc. collected soil, sediment an d surface water samples as part of a SI of the Argonaut Mine (Ref. 4, pp. 6, 22) . Samples were collected in

accordance with a SAP approved by EPA on March 10, 2014 (Ref. 4, p. 22)

. Samples were submitted to Bonner Analytical, located in Hattiesburg, Miss issippi , under the EPA Contract Laboratory Program for metals analysis by Inorganic Superfund Methods (ISM01.3) and cyanide by EPA Method 9010/9012 (Ref. 4, p. 22) . The metals analytical data were validated by EPA (Ref. 4, p. 22 ).

- Background Concentrations: Background soil samples were collected from location AB

- 01 in pasture land located northwest of the Tailings Area and location AB

- 02 in pasture land located southwest of the Tailings Area (Ref. 4, p. 24). Background sampling locations are shown in Attachment A -3.

Residential properties built within the former Argonaut Mine property boundary were built on imported fill placed over waste rock, tailings, and soils c ontaminated by Argonaut Mine operations (Ref. 4, pp. 16 , 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2

- 3). Prior to the construction of the Source 1 Tailings Impoundment and the AOC

- 2 Cyanide Plant

, part of the property was farmland (Ref. 12, p. 28; Ref. 50 ). Therefore, background samples were collected from nearb y pasture lands to be representative of local conditions without the Argonaut Mine. Sample depths of the background and release samples are all from the upper 2 feet, al though the background locations are native soil while soils from the residential

proper ties include tailings and waste rock generated by mining activities, as well as imported fill (See Source 5 Background Soil Concentrations below).41 Source No: 5



### Source 5 Background Soil Concentrations

Sample ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration ** ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

AB

- 01 -0
(MY9EX7) 0

- 0.5 7/31/14 Arsenic 8.9 1.0 Ref. 4, pp. 39

- 40, 66, 76, 1808, 1818

­ 1820, 1944; Ref. 18, p. 1; Ref. 23, pp. 7, 15 Lead 14.8 J 1.0

Mercury 0.15 0.10

AB

- 01

- 1.5
(MY9EY0) 1.0

- 1.5 7/31/14 Arsenic 2 .0 J

­ 1.1 Ref. 4, pp. 39

- 40, 66, 76, 1808, 1830

­ 1832, 1834, 1944; Ref. 20, p. 1; Ref. 24, pp. 6, 10 Lead 9 .0 J 1.1

Mercury <0.11 0.11

AB

- 02 -0
(MY9EY1) 0

- 0.5 7/28/14 Arsenic 3.1 J

­ 1.0 Ref. 4, pp. 39

- 40, 65, 1808, 1830

­ 1832, 1834, 1941; Ref. 20, p. 1; Ref. 24, pp. 6, 11 Lead 11.2 J 1.0

Mercury <0.10 0.10

AB

- 02

- 1.5
(MY9EY2) 1.0

- 1.5 7/28/14 Arsenic 1.2 J

­ 1.1 Ref. 4, pp. 39

- 40, 65, 1808, 1830

­ 1832, 1834, 1941; Ref. 20, pp. 1

- 2; Ref. 24, pp. 6, 12 Lead 7.1 J 1.1

Mercury <0.11 0.11
mg/kg: milligrams analyte per kilogram soil CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit *: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

J: The result is an estimated quantity, with an unknown bias (Ref. 4, pp. 1818, 1830

- 1832 , 1867 ).

J- : The result is an estimated quantity, with a low bias (Ref. 4, pp. 1818, 1830

- 1832, 1867). <: The analyte was not detected. **: Qualified data presented in this table reflect a positive identification of the substance, although the data may be quali fied. ^: Page 1831of Reference 4 present s a J qualifier for arsenic, and Reference 4 pages 1830 and 1834 indicate that the reported results may be biased low.



### - Source Samples: Surface soil and shallow subsurface soil samples were collected from 19 residential lots and from Jackson Junior High School to assess whether the properties were impacted by historic al Argonaut Mine operations (Ref. 4, p. 28)

. Two sampling locations (ARA

- 18 and ARA -19 ) were collected from the

Sierra View Estates neighborhood adjacent to the Source 1 Tailings Impoundment (Ref. 4, p. 28). No soils were removed from these properties during the Augus t 2015 Removal Action (Ref. 40, pp.4- 5)

.

Sampling locations are presented in Attachment A -5. To preserve the privacy of local residents, sample

location s are identified by address code only. A ddress codes are defined in a confidential reference (Ref.

15 ).42 Source No: 5



### 2014 Site Inspection, Source 5 Concentrations

Address

Code Sample

ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration (mg/kg) Sample Adjusted CRQL* (mg/kg) References

ARA

- 18 ARA

18 -0
(MY9F 78) 0

- 0.5 7/31/14 Arsenic 310 1.0 Ref. 4, pp. 40, 66

, 1812, 1890, 1944; Ref. 25, pp. 7, 15; Ref. 37, p. 2 Lead 46.0 1.0

Mercury 0.63 0.10

ARA

18

- 1.5
(MY9F 79) 1

- 1.5 7/31/14 Arsenic 423 1.1 Ref. 4, pp. 40, 66

, 1812, 1890, 1944; Ref. 25, pp. 7, 16; Ref. 37, pp. 2 -3 Lead 115 1.1

Mercury 1.4 0.21

ARA

- 19 ARA

19 -0 (MY9F 81) 0

- 0.5 7/31/14 Arsenic 55.3 1.1 Ref. 4, pp. 40, 66

, 1812, 1888, 1890, 1944; Ref. 25, pp. 7, 17; Ref. 37, p. 3

ARA

19 -1
(MY9F 82) 1.5 - 2 7/31/14 Arsenic 122 1.1 Ref. 4, pp. 40, 66

, 1812, 1888, 1890, 1944; Ref. 25, pp. 7, 18; Ref. 37, p. 3

mg/kg: milligrams analyte per kilogram soil

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit
*: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).



### EPA March 2015 Removal Assessment

In March 2015, EPA conducted a removal assessment of 20 residential properties in the Argonaut Heights and Sierra View Estates neighborhoods (Ref. 4, p. 14; Ref. 11, p p . 2, 6 ). The residential properties were divided into two to six DUs composed of roughly equal areas at a maximum of 1,250 square feet each to cover unpaved areas of the property (Ref. 11, p. 2) . A 5

- point composite sample was collected from each DU at sampling in tervals of 0 to 2 inches and 12 to 18 inches bgs using a trowel or hand auger and disposable scoops (Ref. 11, p. 2) . Discrete samples were collected from some of the residences at the locations of play areas and gardens (Ref. 11, p. 2 ). Samples were analyz ed for lead and arsenic via XRF, with at least one sample from each property submitted to a laboratory for confirmation. Confirmation samples were submitted to the EPA Region 9 Laboratory for analysis of arsenic and lead by EPA SW -846 Method 6010C (Ref. 11, pp. 3-4).

Sampling locations are presented in Attachment A -5. Background sampling was not conducted during this sampling event; therefore, samples are compared to background concentrations from the 2014 SI sampling event.43 Source No: 5



### 2015 EPA Removal Assessmen t, Source 5 Concentrations

Address

Code Sample ID Sample Depth (inches) Date Hazardous

Substance Hazardous

Substance

Concentration

( mg/kg ) QL (mg/kg) References

ARA

18 (2) R- 16

- 01

­ C-0 0 to 2 3/26/15 Arsenic 210 2 Ref. 11 , pp. 86, 91, 97; Ref. 39, p. 18; Ref. 47, pp. 4, 30, 33, 39 Lead 32 3

R- 16

- 04

­ C-0 0 to 2 6/23/15 Arsenic 100 2 Ref. 11 , pp. 8 6 , 107, 115; Ref. 48, pp. 4, 24, 26, 30,

32 Lead 23 3.1

ARA

29 (1) R- 15

- 02

­ C- 12 12 to 14 3/26/15 Arsenic 910 10 Ref. 11 , pp. 86, 91, 97; Ref. 39, p. 18; Ref. 47, pp. 4, 30, 33, 39 Lead 66 3

mg/kg: milligrams analyte per kilogram soil

QL : Quantitation Limit. EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).

(1) : Although a removal was conducted on this property, soils were not excavated to this depth (Ref. 15; Ref. 4 0 , p. 2).

(2) : Although a removal was conducted on this property, no soils were excavated. Soils exceeding the action level were covered with wood chips and rock ( Ref. 40

, pp. 2, 4 ).



### List of Hazardous Substances Associated with Source Arsenic, Lead, and Mercury

2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY The migration pathways are not scored for Source 5.44 Source No: 5



### 2.4.2. Hazardous Waste Quantity

Tier A: Hazardous Constituent Quantity The total 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

releas es from the source is not known and cannot be estimated with reasonable confidence (Ref. 1, Section 2.4.2.1.1). 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 CERCLA hazardous substances in the source and the associated releases from the source. Therefore, there is insufficient information to calculate a total or partial Hazardous Constituent Quantity estimate for

Source 5 with reasonable confidence. Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

Tier B: Hazardous Wastestream Quantity 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 adequate ly 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 ext rapolate a total or partial Hazardous Wastestream Quantity for

Source 5 with reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section 2.4.2.1.3).

Hazardous Wastestream Quantity Value: NE

Tier C: Volume The information available is not sufficient to meaningfully evaluate Tier C: volume, because the depth

and total extent of the contaminated soil across Source 5 is unknown. Therefore it is not possible to adequately determine a volume for Source 5 (Ref. 1, Section 2.4.2.1.3). Scoring proceeds to the evaluation of Tier D: area (Ref. 1, Section 2.4.2.1.4).

Volume Assigned Value: 0

Tier D: Area Based on samples collected pre

- and post

- removal, as well as samples collected during the 2014 SI, the

area of Source 5 is es timated to be approximately 40,341 square feet (see Attachment A -6 ). In accordance with Ref. 1, Table 2 -5:

40,341 / 34,000 = 1.2Source No: 5



### Area Assigned Value: 1.2

Source Hazardous Waste Quantity Value: 1.2

4546 Source No: 6



### 2.2.1 SOURCE IDENTIFICATION : Source 6 Jackson Junior High School Tailings Pile

Name of source: Jackson Junior High School Tailing Pile Number of source: 6

Source Type : Tailings Pile

Description and Location of Source (See Attachment A-7 ):

Exposed fill material resembling processe d tailings was observed in the east

- facing slope of the athletic field embankment of Jackson Junior High School (Ref. 4, pp. 28, 77 ; Ref. 34 , p p. 2, 609, 611 -612 ). The upper athletic field playing area may have been constructed using mine tailings imported from the Argonaut Mine (Ref. 10, p. 36; Ref. 34 , p p. 2, 4, 609, 611 -612 ). It appears the tailings were subsequently covered with imported s oil to establish a grass field (Ref. 10, pp. 28, 36; Ref. 34, p. 2). The extent of mine tailings and soil cover at the athletic field is unknown. At several locations, a mound of black tailings was observed adjacent to a ground squirrel burrow, suggesting that ground squirrels are bringing tailings to the surface of the playing field (Ref. 34, pp. 2, 609, 610).

Elev ated concentrations of arsenic, lead, and mercury were detected in samples collected from the athletic field embankment, as well as from the outdoor lunch area above the embankment (Ref. 4, pp. 28, 31, 40; Ref. 11, pp. 5, 88, Ref. 34, pp. 2-3).

In July 2 015, EPA conducted a removal action at Jackson Junior High School ( Ref. 34 , p p. 1, 3). The eastern portion of the athletic field was divided into 10 DUs (see Attachment A-7) (Ref. 11, pp. 5, 20; Ref. 34, p. 13). DUs 1 through 5 were along the exposed easte rn embankment of the athletic field. DUs 6 through 10 were in the outdoor lunch area above the embankment (Ref. 11, p. 5). DU 6 is adjacent to the snack bar (Ref. 34, p. 612). DUs 1 through 5 were capped with shotcrete and fenced (Ref. 34, pp. 3

­ 5 , 13 ). Ta ilings

- impacted soils were excavated from DU

- 6 and the northern portion of DU

- 7 to a maximum depth of one foot bgs (Ref. 34 , p p . 4, 612 ). The excavations were backfilled with clean fill (Ref. 34, p. 5).

Based on a 1944 aerial photograph, the area of the tailings pile beneath the Jackson Junior High School athletic field is estimated to measure approximately 109,215 square feet (see Attachment A

- 7) (Ref. 10,

p. 36). The July 2015 removal action did not change the ar ea of Source 6, because soils exceeding 100 mg/kg arsenic were capped in place, or were only excavated to a depth of one foot bgs (Ref. 34, pp. 3

­ 5).47 Source No: 6



### 2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

EPA June and July 2015 Removal Assessment

In June and July 2015, EPA conducted a removal assessment of Jackson Junior High School (Ref. 11, p. 2) . A total of 20 composite soil samples (10 surface and 10 subsurface) from 10 DUs were collected from the athletic field for metal analysis (Ref. 11, p. 2)

. A 5

- point composite sample was collected from each DU at sampling intervals of 0 to 2 inches and 12 to 18 inches bgs using a trowel or hand auger and disposable scoops (Ref. 11, p. 2 ). Samples were analyzed for lead and arsenic via XRF (Ref. 11, p. 3)

. La boratory samples were submitted to the EPA Region 9 Laboratory for analysis of arsenic and lead by

EPA SW -846 Method 6010C (Ref. 11, pp. 3-4). DUs are shown on Attachment A-7.48 Source No: 6



### 2015 EPA Removal Assessment, Source 6 Concentrations

DU Sample

ID Sample Depth (inches) Date Hazardous

Substance Hazardous

Substance

Concentration ( mg/kg ) QL (mg/kg) References

DU

- 1 (1) JJHS

- 01

­ 0 0 to 2 6/23/2015 Arsenic 100 2 Ref. 11, p. 88, 114 ; Ref. 39, p. 86; Ref. 48, pp. 3, 23, 26, 30 Lead 17 3

JJHS

- 01

­ 12 6 to 12 6/23/2015 Arsenic 85 2.1 Ref. 11, p. 88, 114; Ref. 39, p. 86; Ref. 48, pp. 3, 23, 26, 30 Lead 17 3.1

DU

- 2 (1) JJHS

- 02

­ 0 0 to 2 6/23/2015 Arsenic 82 2 Ref. 11, p. 88, 114; Ref. 39, p. 86; Ref. 48, pp. 3, 23, 26, 30 Lead 19 3

JJHS

- 02

­ 12 6 to 12 6/23/2015 Arsenic 81 2.1 Ref. 11, p. 88, 114; Ref. 39, p. 86; Ref. 48, pp. 3, 23, 26, 30 Lead 13 3.1

DU

- 3 (1) JJHS

- 03

­ 0 0 to 2 6/23/2015 Arsenic 170 2 Ref. 11, p. 88, 114; Ref. 39, p. 86; Ref. 48, pp. 3, 23, 26, 30 Lead 31 3

JJHS

- 03

­ 12 6 to 12 6/23/2015 Arsenic 290 2.1 Ref. 11, p. 88, 114

- 115 ; Ref. 39, p. 86; Ref. 48, pp. 3

- 4, 24

, 26, 30 Lead 26 3.2

DU

- 4 (1) JJHS

- 04

­ 0 0 to 2 6/23/2015 Arsenic 300 2 Ref. 11, p. 88, 107

- 110, 115 ; Ref. 39, p. 86; Ref. 48, pp. 4,

24 , 26, 30 Lead 20 3

JJHS

- 04

­ 12 6 to 12 6/23/2015 Arsenic 230 2.2 Ref. 11, p. 88, 115 ; Ref. 39, p. 87; Ref. 48, pp. 4, 24 , 26, 30 Lead 11 3.3

DU

- 5 (1) JJHS

- 05

­ 0 0 to 2 6/23/2015 Arsenic 48 2.1 Ref. 11, p. 88, 115 ; Ref. 39, p. 87; Ref. 48, pp. 4 , 2 4 , 26, 30 Lead 13 3.1

JJHS

- 05

­ 12 6 to 12 6/23/2015 Arsenic 57 2.2 Ref. 11, p . 88, 115 ; Ref. 39, p. 87; Ref. 48, pp. 4, 24 , 26, 30 Lead 14 3.3

DU

- 6 (2) JJHS -C02

- 14

­ 072715 12 to 14 7/27/15 Arsenic 290 2 Ref. 11 , p. 88, 120; Ref. 34, pp. 600

- 601; Ref. 39, pp. 20,

22 ; Ref. 49, pp. 3, 21, 23, 27 Lead 15 3

DU

- 7 (2) JJHS -C06

- 14

­ 072715 12 to 14 7/27/15 Arsenic 100 2 Ref. 11 , p. 88, 120; Ref. 34, pp. 600

- 601; Ref. 39, pp. 20,

22 ; Ref. 49, pp. 3, 21, 23, 27 Lead 15 3

DU -9 JJHS -C10 -2­

072715 0 to 2 7/27/15 Arsenic 62 2 Ref. 11 , p. 88, 120; Ref. 39, pp. 21

- 22 ; Ref. 34, pp. 600

­ 601; Ref. 49, pp. 3, 21, 23, 27 Lead 24 3

mg/kg: milligrams analyte per kilogram soil

QL : Quantitation Limit. EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).

(1) : These sampling locations were covered with shotcrete during the July 2015 EPA Removal Action (Ref. 34, pp. 3

- 4, 13

- 14).

(2) : Although a removal was conducted in this DU , soils were not excavated to t his depth ( Ref. 34, p. 4).49 Source No: 6



### EPA July 2015 Removal Action In July 2015, EPA conducted a Removal Action at the Jackson Junior High School athletic field (Ref. 34, pp. 1, 4). Confirmation soil samples were collected from the excavations, and analyzed for lead and arsenic via XRF ( Ref. 34 , pp. 1, 6-7 ). Laboratory samples were submitted to the EPA Region 9 Laboratory for analysis of arsenic and lead by SW

- 846 Method 6010C (Ref. 34, p. 600). The sampling

location is shown on Attachment A-7.

2015 EPA Removal Action , Source 6 Confirmation Sampling Concentrations

DU Sample ID Sample Depth (inches) Date Hazardous

Substance Hazardous

Substance

Concentration
( mg/kg ) QL (mg/kg) References

DU -7 JJHS -C- 17

­ 12

- 080315 12 to 14 8/3/15 Arsenic 79 2 Ref. 34, pp. 19, 600, Ref. 39, p. 34; Ref. 49, pp. 3, 22

- 23,

27 Lead 18 3

mg/kg: milligrams analyte per kilogram soil
QL : Quantitation Limit. EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).



### List of Hazardous Substances Associated with Source

Arsenic and Lead

2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY The migration pathways are not scored for Source 6.50 Source No: 6



### 2.4.2. Hazardous Waste Quantity

Tier A: Hazardous Constituent Quantity The total 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 ). 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 CERCLA

hazardous substances in the source and the associated re leases from the source. Therefore, there is insufficient information to calculate a total or partial Hazardous Constituent Quantity estimate for

Source 6 with reasonable confidence. Scoring proceeds to the evaluation of Tier B, hazardous wastestream quanti ty (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

Tier B: Hazardous Wastestream Quantity The total Hazardous Wastestream Quantity for Source 6 could not be adequately determined according to the HRS requirements; that is, the to tal 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 hist orical 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 assoc iated 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 2.4.2.1.3).

Hazardous Wastestream Quantity Value: NE

Tier C: Volume The information available is not sufficient to meaningfully evaluate Tier C: volume, because the depth

and total extent of the tailings and waste rock pile across Source 6 are unknown. Therefore it is not possible to adequately determine a volume for Source 6 (Ref. 1, Section 2.4.2.1.3). Scoring proceeds to the evaluation of Tier D, area (Ref. 1, Section 2.4.2.1.4).

Volume Assigned Value: 051 Source No: 6



### Tier D: Area

Base d on a 1944 aerial photograph, the area of the tailings pile beneath the Jackson Junior High School athletic field is estimated to measure approximately 109,215 square feet (see Attachment A

- 7) (Ref. 10,

p. 36). In accordance with Ref. 1, Table 2-5:

109,215 / 13 = 8,401.2

Area Assigned Value: 8,401.2

Source Hazardous Waste Quantity Value: 8,401.252 

### SUMMARY OF SOURCE DESCRIPTIONS

Source

No. Source Hazardous Waste Quantity

Value Containment

Surface

Water

1 684,800 10

2 6,115.4 NE

3 7,488.5 NE

4 2.1 NE

5 1.2 NE

6 8,401.2 NE

TOTAL 706,808.4

Notes:

NE = Not Evaluated.53 

### OTHER POSSIBLE SOURCES NOT SCORED

Tailings Pile in AOC

- 1 Ore Storage Area (see Attachment A -1) The approximately 5

- acre AOC

- 1 Ore Storage Area was used for storage of middlings, a type of tailings that are neither clean mineral products nor pure waste (Ref. 4, p. 9; Ref. 12, pp. 9, 46) . Approximately 159,000 tons of tailings are estimated to remain in the AOC

- 1 tailings pile (Ref. 31, p. 16) . Tailings samples collected from this area contained elevated concentrations of arsenic, lead, and mercury (Ref. 5, pp. 13-14; Ref. 6, pp. 33-34).

Tailings Pile in AOC -2 Cyanide Plant Area (see Attachment A

- 1) The approximately 6.5

- acre AOC

- 2 Cyanide Plant Area contains a former cyanide plant and the foundation of a probable mercury amalgamation building (Ref. 4, p. 8; Ref. 6, p. 9; Ref. 12, pp. 9, 59). A tailings pile covers most of the surface of the area (Ref. 6, p. 9). Tailings samples collected from this area contained elevated concentrations of arsenic, lead, and mercury (Ref. 5, pp. 13

- 16; Ref. 6, pp. 33

­ 36; Ref. 32, p. 12 ).

Cyanide Plant in AOC -2 Cyanide Plant Area (see Attachment A -1) Various abandoned cyanide processing tanks a nd vats still remain in the AOC -2 Cyanide Plant Area ( Ref. 4, p. 8 ; Ref. 6, p. 48; Ref. 12, p p

. 9, 56, 59, 64 , 75). Samples collected from some of the tanks and

vats contained elevated concentrations of arsenic, lead, and mercury ( Ref. 5, pp. 15- 16, 23, 27, 45 -46, 59; Ref. 6, p. 48 ).

Mill Area (see Attachment A -1) The Mill Area occupies approximately 80 acres in a residential area of Jackson, north of the Tailings Area. Mine shaft adits and buildings associated with former Argonaut Mine operations in the Mill Area are located on the east and west sides of Highway 49 (Ref. 4, pp. 7, 11, 64). Tailings were stored in the Mill Area until 1917, after which they were transported by flume to the Tailings Area (Ref. 4, p. 9; Ref. 12, pp. 32, 36; Ref. 14, p. 7; Ref. 35; Ref. 36, p. 13 ). Waste rock and tailings piles are present throughout the Mill Area, but the area is overgrown and their sizes and locations are not well characterized (Ref. 4, pp . 7 -8, 11, 25

- 26, 38, 64 , 6 6-67 ). Samples collected from waste rock an d tailings in the Mill Area contained elevated concentrations of arsenic, lead, and mercury (Ref. 4, pp. 25-27 ).

### 4.0 S URFACE WATER MIGRATION PATHWAY

4.1 OVERLAND MIGRATION COMPONENT

Based on the 2014 SI sampling, t here are four wetlands with a documented observed release attributable to Argonaut Mine (Ref. 4, pp. 41, 46 -47 ; Ref. 38 ) . However, these wetlands are not considered to be

within the same watershed, as they are not connected by perennially

- flowing surface water, and average annual precipitation in the site vicinity exceeds 20 inches (Ref. 30, p. 2; Ref. 33; Ref. 38 ). Therefore, only the largest of these wetland s is scored, as scoring of the others does not affect the listing decision. The largest wetland is located on the surface of Source 1, above the EMAD (Ref. 38).

Photo 1: Source 1 Wetland, July 29, 2014

54 SWOF -Likelihood of ReleaseSWOF -Likelihood of Release 55 

### 4.1.1.1 Definition of Hazardous Substa nce Migration Path for Overland Component

Surface water from both the Mill Area and the Tailings Area of Argonaut Mine flows to North Fork Jackson Creek, then to Jackson Creek, then 7 miles westward to Lake Amador Reservoir. However, North Fork Jackson Creek is an intermittent stream, and average annual precipitation in the site vicinity exceeds 20 inches ( Ref. 3 ; Ref. 4, p. 45; Ref. 33 ). Therefore, this watershed is not scored.

The Source 1 wetland is located on the surface, and entirely within the boundary, of Source 1 . The

wetted perimeter of the wetl and, measuring 2,313 feet, or 0.44 mile, is in contact with Source 1. Therefore, the Probable Point of Entry is the interface between the wetland and Source 1 (Ref. 4, pp. 8

, 45, 65; Ref. 38 ). Using Attachment A

- 8, the wetted perimeter of the Source 1 wetland was measured based on the mapped boundary in the U.S. Fish and Wildlife Service Wetlands Inventory. The Wetlands Inventory classifies the Source 1 wetland as PEMAh, or Palustrine, Emergent, Water Regime, Diked/Impounded ( Ref. 38). This is an HRS

- eligib le wetland, in accordance with 40CFR Section 230.3 and Ref. 1, Table 4-24.

4.1.2.1 Likelihood of Release

4.1.2.1.1 Observed Release

Direct Observation

- Basis for Direct Observation:

The wetland above the EMAD is located on the surface, and entirely within the boundary, of Source 1,

the Tailings Area Tailings Impoundment . The approximate location of the Source 1 wetland is shown on

Attachment A -8 ( Ref. 38 ). The wetland is in direct contact with hazardous substances in Source 1, based

on concentrations of hazardous substances in sediments collected from the Source 1 wetland (Ref. 4, pp. 33, 41, 1724, 1750; see 2014 SI, Source Sediment Concentrations Table below ).

- Hazardous Substances in Release:

Weston Solutions, Inc. 2014 SI Sampling From July 28, 2014 through August 1, 2014, Weston Solutions, Inc. collected soil, sediment an d surface water samples as part of a SI of the Argonaut Mine. Samples were collected in accordance with a SAP approved by EPA on March 10, 2014. A total o f 90 soil samples were collected from the surface (0 to 6 inches) and shallow subsurface (up to 2 feet) at 47 sampling locations

. The subsurface samples were collected using either a track

- mounted direct push sampling rig and Macro

- core soil sampler lined with an acetate sleeve, or by hand auger. A total of 27 sediment samples were collected from 25 sampling locations (Ref. 4, p. 22).

S oil and sediment s amples were submitted to Bonner Analytical, located in Hattiesburg, Miss issippi,

under EPA Contract Laboratory Program for metal analysis by Inorganic Superfund Methods (ISM01.3)

and cyanide by EPA Method 9010/9012. The metal s analytical data were validated by EPA (Ref. 4, p. 22).56 SWOF -Likelihood of Release 

### Soil samples were collected from five locations w ithin Source 1 (Ref. 4, p . 27). Two sample locations (ATA

- 01 and ATA

- 02) were gray sands from the upper tailings dam. S ampling location ATA

- 03 was

near the Sierra View Estates residentia l properties off of Detert Lane. S ampling location ATA

- 04 was at

the northern end of the lower tailings dam; near Sierra View Estates . S ampling location ATA

- 05 was near residential properties off of Muldoon Place near Sierra View Estates (Ref. 4, pp. 27 -28 , 65 ). Sediment sample ATS

- 02 was collected from the Source 1 wetland (Ref. 4, p. 33). Soil and sediment sampling locations are presented in Attachment A -3.57 SWOF -Likelihood of Release 

### 2014 SI, Source 1 Sediment Concentrations

Sample ID Date Hazardous

Substance Hazardous

Substance

Concentration
(mg/kg) Sample Adjusted CRQL* (mg/kg) References

ATS

- 02 -0 (MY9F98) 7/29/14 Arsenic 204 1.3 Ref. 4, pp. 41, 65, 1812, 1815

- 1819,

1823 , 1942 ; Ref. 18, pp. 5-6 ; Ref. 23, pp. 11, 27 Lead 38.8 1.3

Mercury 1.5 0.13

mg/kg: milligrams analyte per kilogram sediment

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit *: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).



### Hazardous Substances Released

Arsenic , Lead, and Mercury

Surface Water Observed Release Factor Value: 55058 

### 4.1.2.2 D rinking Water Threat Waste Characteristics

There are no drinking water intakes in the Source 1 wetland. Therefore, the Drinking Water Threat is not

scored

.

4.1.3.2 Human Food Chain Threat Waste Characteristics

A fishery is not present in the Source 1 wetland. Therefore, the Human Food Chain Threat is not scored.

SWOF/HFC

- Targets

### 4.1.4.2 Environmental Threat Waste Characteristics

4.1.4.2.1 Ecosystem Toxicity/Persistence/Bioaccumulation

Hazardous

Substance Source No. Ecosystem Toxicity

Factor

Value Persistence

Factor

Value* Ecosystem

Bioaccumulation

Value** Ecosystem Toxicity/

Persistence/ Ecosystem

Bioaccumulation

Factor Value
(Ref. 1, Table 4

- 21) Reference

Arsenic 1 10 1 50

, 000 500,000 Ref. 2, p. 1

Lead 1 1, 000 1 50

, 000 50,000,000 Ref. 2, p p

. 7

- 8

Mercury 1 10

, 000 1 50

, 000 500,000,000 Ref. 2, p p. 9

- 10



### Notes:

* Persistence value for Lakes

** Bi oaccumulation factor value for Freshwater

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

4.1.4.2.2. Hazardous Waste Quantity

Source No. Source Type Source Hazardous Waste Quantity Source Hazardous Constituent Quantity Complete?

1 Pile 684,800 No



### Sum of Values: 684,800

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

59 SWOF/ENV

- Waste Characteristics60 SWOF/ENV

- Waste Characteristics 

### 4.1.4.2.3. Waste Characteristics Factor Category Value

Ecosystem Toxicity/Persistence Factor Value: 10,000 Hazardous Waste Quantity Factor Value: 10,000 Ecosystem Toxicity/Persistence Factor Value x Hazardous Waste Quantity Factor Value: 100,000,000

(Ecosystem Toxicity/Persistence Factor Value x Hazardous Waste Quantity Factor Value) x Environmental Bioaccumulation Factor Value: 5,000,000,000,000

Waste Characteristics Factor Category Value: 1,000 (Ref. 1, Table 2-7)61 

### 4.1.4.3 Environmental Threat Targets

Most Distant Level I Sample

Level I Concentrations are not established, as benchmarks are not available for sediment, and surface water was not sampled in the Source 1 wetland (Ref. 2, p. 14, 21-22).

Most Distant Level II Sample

Sample ID: ATS -02-0 Distance from the probable point of entry: 0 mile

Reference: Ref. 4, pp. 41, 65, 1812, 1823; Ref. 18, pp. 6

- 7; Ref. 23, pp. 11, 27; Ref. 38 ; see Attachments

A-3 and A-8

4.1.4.3.1 Sensitive Environments

4.1.4.3.1.1. Level I Concentrations

Level I Concentrations are not established, as benchmarks are not available for sediment, and surface water was not sampled in the Source 1 wetland (Ref. 1, Sections 4.1.2.3 and 4.1.4.3.1.1, Ref. 2, p. 14, 21-22). As an observed release by direct observation is scored, targets associated with this observed release by direct observation are evaluate d using Level II concentrations for that location. (Ref. 1, Sections 4.1.2.3, 4.4.3.1, 4.1.4.3.1.1, 4.1.4.3.1.2.)

4.1.4.3.1.2. Level II Concentrations

Level II Wetland Frontages The wetted perimeter of the Source 1 wetland measures approximately 2,313 feet, or 0.44 mile (Ref. 38). As the Source 1 wetland is in contact with Source 1 and the PPE to surface water is in the wetland, the perimeter of the wetland is evaluated as the length of wetlands subject to Level II concentrations (Section 4.1.2.1.1 of this HRS documentation record; Ref.1, Section 4.1.4.3.1.2). Using Attachment A -8, the wetted perimeter of the Source 1 wetland was measured based on the mapped boundary in the U.S. Fish and Wildlife Service Wetlands Inventory. The Wetlands Inventory classifies the Source 1 wetland as PEMAh, or Palustrine, Emergent, Water Regime, Diked/Impounded (Ref. 38) . This is an HRS

eligible wetland, in accordance with 40CFR Section 230.3 and Ref. 1, Table 4-24.

Wetland Wetland Frontage (miles) References

Source 1 wetland, classified as PEMAh, or Palustrine, Emergent, Water Regime, Diked/Impounded 0.44 Ref. 1 Section 4.1.4.3.1.2; Ref. 4, p. 45; Ref. 38

Sum of Level II Wetland Frontages: 0.44 mile

SWOF/ENV

- Targets62 SWOF/ENV

- Targets 

### Wetlands Value (Ref. 1, Table 4 -24): 25

Sum of Level II Sensitive Environments Value + Wetlands Value:

Level II Concentrations Factor Value: 25

### 5.0 SOIL EXPOSURE PATHWAY

The Argonaut Mining Company historically owned approximately 330 acres of land northwest of

downtown Jackson. The property was sold after the mine closed, and approximately 90 acres of the former property have been developed as residential nei ghborhoods (Ref. 4, pp. 7, 64 ). S ix areas of

observed contamination attributable to the Argonaut Mine site were ev aluated for scoring (see

Attachment A -2). Descriptions of the individual areas are provided in the sections below.

Area A is the Tail ings Area Tailings Impoundment

, a tailings pile containing approximately 1,712,000 tons of processed tailings. Areas B through E are areas of re sidential properties within the former

A rgonaut Mine property boundary that were built on imported fill placed over waste rock, tailings, and

soils contaminated by Argonaut Mine operations. Area F is the Jackson Junior High School athletic field, which was constructed on waste rock and tailings. Observed contamination of arsenic, lead, and/or

mercury is documented in Areas A through F.

Approximately 53 residents occupy residential properties within the areas of observed contamination. Currently, there are 406 students and 45 staff members at Jackson Junior High School (Ref. 13; see sections 5.1.3.2.1 and 5.1.3.2.2 of this HRS documentation record).

Argonaut Mine Areas of Contamination

Area Source Name Source Type

A Tailings Area Tailings Impoundment Pile

B Argonaut Estates Pile Pile

C Argonaut Heights – North Pile Pile

D Argonaut Heights – South Contaminated Soil Contaminated Soil

E Sierra View Estates Conta minated Soil Contaminated Soil

F Jackson Junior High School Tailings Pile Pile

63 SE

- GeneralArea Letter: A



### 5.0.1 GENERAL CONSIDERATIONS : Area A

, Tailings Area Tailings Impoundment

Letter by which this area is to be identified : A

Name of area : Tailings Area Tailings Impoundment

Source Type : Tailings Pile

Location and description of area ( see Attachment A -2 ): Area A correlates with Source 1, as identified in Section 2.2.1. Area A consists of a tailings pile covering approximately 48 acres const ructed in a drainage valley (Ref. 4, pp. 8, 13; Ref. 12, p. 9)

. In 1916, the EMAD was constructed in the ravine southeast of Argonaut Mine to impound tailings generated from Argonaut mining and milling operations (Ref. 6, p. 10; Ref. 12, pp. 9, 41). The EM AD is roughly 390 feet wide and 46 feet tall (Ref. 6, p. 10)

. The impoundment was expanded in 1931 and 1940 with two additional dams constructed of tailings (Ref. 12, pp. 41 -42; Ref. 41, pp. 9, 47 -48)

. Two wetlands are present on the surface of Source 1 (Ref. 4, pp. 8, 65; Ref. 38 ).

Sediment and tailings have filled the valley behind the EMAD to within a few feet of its top. Standing

water flows over the top of the dam during wet periods. Water also flows through cracks in the base of the dam, suggesting materials behind the dam are saturated (Ref. 6, p. 10).

Soils at the surface of Area A are predominantly gr ey tailings. In most areas , vegetation has been

re established and a thin layer of organic material is present, stabilizing the surface . However, la rge portions of Area A contain exposed gray tailings that are devoid of vegetation. These soils are easily eroded during large magnitude rain events and large gullies and sinkholes have formed. Some of the gullies exceed 20 feet in depth and top- width (Ref . 6, p. 9).

In February 1955, mining engineer and licensed surveyor C.E. Bronson estimated a total of 1,712,000 tons of tailings within Source 1 by comparing the existing tailings surface with an estimated contour of the original ground surface below (Ref . 12, pp. 43-45; Ref. 44 ).

Weston Solutions, Inc. 2014 Site Inspection Soil Sampling From July 28, 2014 through August 1, 2014, Weston Solutions, Inc. collected soil, sediment and surface water samples throughout the former Argonaut Mine property . Samples were collected in accordance

with a SAP approved by EPA on March 10, 2014

. Samples were submitted to Bonner Analytical, located in Hattiesburg, Miss issippi , under the EPA Contract Laboratory Program for metals analysis by Inorganic Superfund Methods (ISM01.3) and cyanide by EPA Method 9010/9012. The metals analytical data were validated by EPA (Ref. 4, p. 22).

- Background Concentrations: Background soil samples were collected from location AB

- 01 in pasture land located northwest of Area

A and location AB

- 02 in pasture land located southwest of Area A (Ref. 4, p. 24). Background sampling

locations are shown in Attachment A -3.

The Area A tailings pile was constructed in a ravine on farmland ( Ref. 6, p. 10; Ref. 12, pp. 28, 41 ; Ref.

50 ). Therefore, ba ckground samples were collected from nearby pasture lands to be representative of

64 SE

- GeneralArea Letter: A



### local conditions without the Argonaut Mine. Sample depths of the background and contaminated samples are all from the upper 2 feet, al though the background locations are nati ve soil while soils in Area A consist of tailings generated by Argonaut Mine operations.

2014 SI, Area A Background Soil Concentrations

Sample ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration + ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

AB

- 01 -0
(MY9EX7) 0

- 0.5 7/31/14 Arsenic 8.9 1.0 Ref. 4, pp. 39

- 40, 66, 76, 1808, 1818

­ 1820, 1944; Ref. 18, p. 1 ; Ref. 23, pp. 7, 15 Lead 14.8 J (21.3) 1.0

Mercury 0.15 0.10

AB

- 01

- 1.5
(MY9EY0) 1.0

- 1.5 7/31/14 Arsenic 2 .0 J

- (3.5) 1.1 Ref. 4, pp. 39

- 40, 66, 76, 1808, 1830, 1832, 1834, 1944 ; Ref. 20, p. 1 ; Ref. 24, pp. 6, 10 Lead 9 .0 J (13.0) 1.1

Mercury <0.11 0.11

AB

- 02 -0
(MY9EY1) 0

- 0.5 7/28/14 Arsenic 3.1 J

- (5.4) 1.0 Ref. 4, pp. 39

- 40, 65, 1808, 1832, 1834, 1941; Ref. 20, p. 1 ; Ref. 24, pp. 6, 11 Lead 11.2 J (16.1) 1.0

Mercury <0.10 0.10

AB

- 02

- 1.5
(MY9EY2) 1.0

- 1.5 7/28/14 Arsenic 1.2 J

- (2.1) 1.1 Ref. 4, pp. 39

- 40, 65, 1808, 1830, 1832, 1834, 1941 ; Ref. 20, pp. 1 -2 ; Ref. 24, pp. 6, 12 Lead 7.1 J (10.2) 1.1

Mercury <0.11 0.11

3X Highest Background (to

establish concentrations significantly above background): Arsenic 26.7

Ref. 9 Lead 63.9* *

Mercury 0.45

mg/kg: milligrams analyte per kilogram soil

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit *: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

J: The result is an estimated quantity, with an unknown bias (Ref. 4, pp. 1818, 18 30

- 1832 , 1867 ). Therefore, the background value is multiplied by a factor of 1.74 for arsenic and 1.44 for lead. The adjusted value is included in parentheses (Ref. 9, pp. 8, 18)

. J- : The result is an estimated quantity, with a low bias (Ref. 4, pp. 1818, 1830

- 1832, 1867). <: The analyte was not detected.

** : Calculated with the adjusted value. +: Qualified data presented in this table reflect a positive identification of the substance, although the data may be qualif ied. ^: Page 1831of Reference 4 prese nt s a J qualifier for arsenic concentrations , and Reference 4 pages 1830 and 1834 indicate that the reported results may be biased low.



### - Contaminated Samples: Soil samples were collected from five locations within Source 1 (Ref. 4, p. 27). Two sample locations (ATA

- 01 and ATA

- 02) were gray sands from the upper tailings dam. S ampling location ATA

- 03 was

near the Sierra View Estates residentia l properties off of Detert Lane. S ampling location ATA

- 04 was at

the northern end of the lower tailings dam; near Sierra View Estates . S ampling location ATA

- 05 was near residential properties off of Muldoon Place near Sierra View Estates (Ref. 4, pp. 27 -28 , 65 ).

S ampling locations are presented in Attachment A -3.

65 SE

- GeneralArea Letter: A



### 2014 SI, Area A Tailings Concentrations Significantly Above Background

Sample ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration (mg/kg) Sample Adjusted CRQL* (mg/kg) References

ATA

- 01

- 0 (MY9F89) 0

- 0.5 7/29/14 Arsenic 54.8 1.0 Ref. 4, pp. 28, 39, 65, 1812, 1817, 1822; Ref. 18, p. 4; Ref. 23, pp. 11, 24

ATA

- 02

- 0 (MY9F90) 0

- 0.5 7/29/14 Arsenic 49.4 1.1 Ref. 4, pp. 28, 39, 65, 1812, 1817, 1822; Ref. 18, p. 5; Ref. 23, pp. 11, 25

ATA

- 03 -0 (MY9F91) 0

- 0.5 7/29/14 Arsenic 3,490 15.5 Ref. 4, pp. 28, 39, 65, 1812, 1892; Ref. 25, pp. 8, 25; Ref. 37, p. 6 Lead 193 1.0

Mercury 2.5 0.52

ATA

- 03

- 2 (MY9F92) 1.5 - 2 7/29/14 Arsenic 502 2.1 Ref. 4, pp. 28, 39, 65, 1812, 1892; Ref. 25, pp. 8, 26; Ref. 37, p. 6

ATA

- 04

- 0 (MY9F93) 0 - 0.5 7/29/14 Arsenic 362 1.0 Ref. 4, pp. 28, 39, 65, 1812, 1893; Ref. 25, pp. 8, 27; Ref. 37, p. 6

ATA

- 05

- 1.5 (MY9F96) 1

- 1.5 7/29/14 Arsenic 237 1.1 Ref. 4, pp. 28, 39, 65, 1812, 1893; Ref. 25, pp. 8, 30; Ref. 37, pp. 7-8 Mercury 0.52 0.11

mg/kg: milligrams analyte per kilogram tailings

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit *: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

66 SE

- GeneralArea Letter: A



### Area A Haza rdous Waste Quantity

Tier A: Hazardous Constituent Quantity The total Hazardous Constituent Quantity for Area A 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 ). 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 CERCLA

hazardous substances in the source and the associated re leases from the source. Therefore, there is insufficient information to calculate a total or partial Hazardous Constituent Quantity estimate for Area

A with reasonable confidence . Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

Tier B: Hazardous Wastestream Quantity The total Hazardous Wastestream Quantity for Area A 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 haza rdous 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

Area A with reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section 2.4.2.1.3).

Hazardous Wastestream Quantity Value: NE

Tier C: Volume Tier C, volume is not applicable to source type pile for the soil exposure pathway (Ref. 1, Section 5.1.2.2).

Volume Assigned Value: 0

Tier D: Area Area A consists of a tailings pile covering approximately 48 acres (Ref. 12, p. 9). In accordance with Ref. 1, Table 5-2:

48 acres = 2,090,880 square feet 2,090,880 / 34 = 61,496.5

Area Assigned Value: 61,496.5

Area Hazardous Waste Quantity Value: 61,496.5

67 SE

- GeneralArea Letter: B



### 5.0.1 GENERAL CONSIDERATIONS : Area B, Argonaut Estates Tailings Pile

Letter by which this area is to be identified : B

Name of area : Argonaut Estates

Source Type : Tailings Pile

Location and description of area ( see Attachment A -4 through A-6 ):

Area B correlates with Source 2 , the Argonaut Estates Tailings Pile. From 1989 through 2004, the Argonaut Estates, Jackson View Estates, Sierra View Estates, and Argonaut Heights residential developments were reportedly built on areas of known waste rock and mine tailings that were covered with imported fill prior to construction of the homes (see Attachment A -4) (Ref. 4, p p. 16, 40; Ref. 8, p.

1 ; Ref. 26, p. 2; Ref. 27, pp. 2 -3 ). A historical aerial photo review conducted by EPA showed that some residential properties in the Argonaut Estates development were built on the location of a waste rock pile associated with Argonaut operations ( Ref. 4, p . 28; Ref. 10, pp. 13, 28, 36 ). Sampling conducted at Argonaut Estates properties ARA

- 07 and ARA

- 08 on Spunn Road showed the presence of arsenic at concentrations significantly above background in soils from 0 to 2 feet bgs (Attachment A -5 ) (Ref. 4, pp. 28-29, 66; Ref. 15).

Attachment A -4 shows the locations of properties ARA

- 07 and ARA

- 08 overlaid on a 1944 aerial photo showing the waste rock pile (Ref. 10, pp. 29, 36). The total area of Area B is estimated to be approximately 79,500 square feet based on the footprint of the waste rock pile in the 1944 aerial photo, as well as the sampling locations on ARA

- 07 and ARA

- 08 showing elevated concentrations of arsenic (see Attachment A

- 6). This includ es the property between ARA

- 07 and ARA

- 08 (ARA

- 33) because the waste rock pile extended across this property as well. However, some of this area is covered by permanent or otherwise maintained, essentially impenetrable material. The average home is estimat ed to cover approximately 2,500 square feet, and an estimated 1,000 square feet of each property is paved (see

Attachment A

- 5 and A

- 6) ( Ref. 45). Therefore, the Area of Contamination for Area B is estimated to be approximately 69,000 square feet (i.e., 79,500 square feet – (3 properties * 3,500 covered square feet per property)).

In August 2015, EPA conducted removal actions at 11 residential properties built with in the former Argonaut Mine property ( Ref. 40, pp. 1 -2 , 7 ). However, this removal did not include any actions at the properties in Area B

.

Weston Solutions, Inc. 2014 SI Soil Sampling From July 28, 2014 through August 1, 2014, Weston Solutions, Inc. collected soil, sediment an d surface water samples as part of a SI of the Argonaut Mine. Samples were collected in accordance with a SAP approved by EPA on March 10, 2014

. Samples were submitted to Bonner Analytical, located in Hattiesburg, Miss issippi , under the EPA Contract Laboratory Program for metals analysis by Inorganic Superfund Methods (ISM01.3) and cyanide by EPA Method 9010/9012. The metals analytical data were validated by EPA (Ref. 4, p. 22).

68 SE

- GeneralArea Letter: B



### - Background Concentrations: Background soil samples were collected from location AB

- 01 in pasture land located northwest of the

Area A Tail ings Impoundment and location AB

- 02 in pasture land located southwest of the Area A Tailings Impoundment (Ref. 4, p. 24 ; See Attachment A -3 ). Background sampling locations are shown

in Attachment A -3.

Residential properties built within the former Argonau t Mine property boundary were built on imported fill placed over waste rock, tailings, and soils contaminated by Argonaut Mine operations (Ref. 4, pp. 16 , 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2

- 3). Prior to the construction of the Area A Tailings Impoundment and the AOC

- 2 Cyanide Plant, a part of the property was farmland (Ref. 12, p. 28 ; Ref.

50 ; see Attachment A -2 ). Therefore, background samples were collected from nearby pasture lands to be representative of local conditions without the Argonaut Mine. Sample depths of the background and release samples are all from the upper 2 feet, al though the background locations are native soil while soils from the residential properties include tailings and waste rock generated by mining activities, as well as imported fill.

2014 SI, Area B Background Soil Concentrations

Sample ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration + ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

AB

- 01 -0
(MY9EX7) 0

- 0.5 7/31/14 Arsenic 8.9 1.0 Ref. 4, pp. 25, 39

- 40, 66, 76, 1808,

1818

- 1820, 1944; Ref. 18, p. 1; Ref. 23, pp. 7, 15 Lead 14.8 J (21.3) 1.0

Mercury 0.15 0.10

AB

- 01

- 1.5
(MY9EY0) 1.0

- 1.5 7/31/14 Arsenic 2 .0 J

- (3.5) 1.1 Ref. 4, pp. 25, 39

- 40, 66, 76, 1808, 1830, 1832, 1834, 1944; Ref. 20, p. 1; Ref. 24, pp. 6, 10 Lead 9 .0 J (13.0) 1.1

Mercury <0.11 0.11

AB

- 02 -0
(MY9EY1) 0

- 0.5 7/28/14 Arsenic 3.1 J

- (5.4) 1.0 Ref. 4, pp. 25, 39

- 40, 65, 1808, 1832, 1834, 1941; Ref. 20, p. 1; Ref. 24, pp. 6, 11 Lead 11.2 J (16.1) 1.0

Mercury <0.10 0.10

AB

- 02

- 1.5
(MY9EY2) 1.0

- 1.5 7/28/14 Arsenic 1.2 J

- (2.1) 1.1 Ref. 4, pp. 25, 39

- 40, 65, 1808, 1830, 1832, 1834, 1941; Ref. 20, pp. 1

- 2; Ref. 24, pp. 6, 12 Lead 7.1 J (10.2) 1.1

Mercury <0.11 0.11

3X Highest Background (to

establish concentrations significantly above background): Arsenic 26.7

Ref. 9 Lead 63.9* *

Mercury 0.45

mg/kg: milligrams analyte per kilogram soil

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit *: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

J: The result is an estimated quantity, with an unknown bias (Ref. 4, pp. 1818, 1830

- 1832 , 1834

- 1839 , 1867 ). Therefore, the background val ue is multiplied by a factor of 1.74 for arsenic and 1.44 for lead. The adjusted value is included in parentheses (Ref. 9, pp. 8, 18).

J- : The result is an estimated quantity, with a low bias (Ref. 4, p. 1830). The adjusted value is included in parentheses (Ref. 9, pp. 8, 18). <: The analyte was not detected. **: Calculated with the adjusted value.

69 SE

- GeneralArea Letter: B



### 2014 SI, Area B Background Soil Concentrations

Sample ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration + ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

AB

- 01 -0
(MY9EX7) 0

- 0.5 7/31/14 Arsenic 8.9 1.0 Ref. 4, pp. 25, 39

- 40, 66, 76, 1808,

1818

- 1820, 1944; Ref. 18, p. 1; Ref. 23, pp. 7, 15 Lead 14.8 J (21.3) 1.0

Mercury 0.15 0.10

AB

- 01

- 1.5
(MY9EY0) 1.0

- 1.5 7/31/14 Arsenic 2 .0 J

- (3.5) 1.1 Ref. 4, pp. 25, 39

- 40, 66, 76, 1808, 1830, 1832, 1834, 1944; Ref. 20, p. 1; Ref. 24, pp. 6, 10 Lead 9 .0 J (13.0) 1.1

Mercury <0.11 0.11

AB

- 02 -0
(MY9EY1) 0

- 0.5 7/28/14 Arsenic 3.1 J

- (5.4) 1.0 Ref. 4, pp. 25, 39

- 40, 65, 1808, 1832, 1834, 1941; Ref. 20, p. 1; Ref. 24, pp. 6, 11 Lead 11.2 J (16.1) 1.0

Mercury <0.10 0.10

AB

- 02

- 1.5
(MY9EY2) 1.0

- 1.5 7/28/14 Arsenic 1.2 J

- (2.1) 1.1 Ref. 4, pp. 25, 39

- 40, 65, 1808, 1830, 1832, 1834, 1941; Ref. 20, pp. 1

- 2; Ref. 24, pp. 6, 12 Lead 7.1 J (10.2) 1.1

Mercury <0.11 0.11

3X Highest Background (to

establish concentrations significantly above background): Arsenic 26.7

Ref. 9 Lead 63.9* *

Mercury 0.45 +: Qualified data presented in this table reflect a positive identification of the substance, although the data may be qualif ied.

^: Page 1831of Reference 4 present s a J qualifier for arsenic, and Reference 4 pages 1830 and 1834 indicate that the reported results may be biased low.



### - Contaminated Samples: Surface soil and shallow subsurface soil samples were collected from 19 residential lots and from

Jacks on Junior High School to assess whether the properties were impacted by historical Argonaut Mine operations. Sampling locations ARA

- 07 and ARA -08 were collected from the Argonaut Estates neighborhood developed along the waste rock pile south of the Argonau t Mine Mill Area (Ref. 4, p. 28).

Sampling locations are presented in Attachment A -5. To preserve the privacy of local residents, soil samples are identified by address code only. A ddress codes are defined in a confidential reference (Ref.

15 ).

2014 Site Inspection, Area B Concentrations Significantly Above Background

Address

Code Sample

ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration + ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

ARA

- 07 ARA

07 -0

(MY9F5 6) 0

- 0.5 7/3 1 /14 Arsenic 68.5 J+ (39.4) 1.1 Ref. 4, pp. 29, 40

, 66, 1811, 1873, 1875, 1944; Ref. 16, p. 2; Ref. 21, pp. 7, 14

70 SE

- GeneralArea Letter: B



### 2014 Site Inspection, Area B Concentrations Significantly Above Background

Address

Code Sample

ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration + ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

ARA

07 -1
(MY9F 57) 1.5 - 2 7/3 1 /14 Arsenic 148 1.1 Ref. 4, pp. 29, 40

, 66, 1811, 1865, 1944; Ref. 17, p. 7; Ref. 22, pp. 10, 32

ARA

- 08 ARA

08 -0
(MY9F 58) 0

- 0.5 7/3 1 /14 Arsenic 68.3 J+ (39.2) 1.1 Ref. 4, pp. 29, 40, 66, 1811, 1873, 1876, 1944; Ref. 16, p. 2; Ref. 21, pp. 7, 15

mg/kg: milligrams analyte per kilogram soil
CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit
*: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

J+: The result is estimated and may be biased high (Ref. 4, p p

. 1867, 1873)

. Therefore, the value is divided by a facto r of 1.74. The adjusted value is included in parentheses (Ref. 9, pp. 8, 18).

+: Qualified data presented in this table reflect a positive identification of the substance, although the data may be quali fied.

^: Page 2 of Reference 16 presents a J

- qualifier for qualified arsenic samples, page s 1875 and 1876 of Reference 4 present arsenic concentrations without qualifiers, and Reference 4 page 1873 indicates that the qualified arsenic samples are biased high.

71 SE

- GeneralArea Letter: B



### Area B Hazardous Waste Quantity

Tier A: Hazardous Constituent Quantity The total Hazardous Constituent Quantity for Area B 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). 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 CERCLA hazardous substances in the source and the associated releases from the source. Therefore, there is insufficient information to calculate a total or partial Hazardous Constituent Quantity estimate for Area

B with reasonabl e confidence . Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

Tier B: Hazardous Wastestream Quantity The total Hazardous Wastestream Quantity for Area B 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 haza rdous 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

Area B with reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section 2.4.2.1.3).

Hazardous Wastestream Quantity Value: NE

Tier C: Volume: Tier C, volume is not applicable to source type pile for the soil exposure pathway (Ref. 1, Section 5.1.2.2).

Volume Assigned Value: 0

Tier D: Area:

The total area of Area B is estimated to be approximately 79,500 square feet based on the footprint of the waste rock pile in the 1944 aerial photo, as well as the sampling locations on ARA

- 07 and ARA -08 showing elevated concentrations of arsenic (see Attachment A -6). However, so me of this area is covered by permanent or otherwise maintained, essentially impenetrable material. The average home is estimated to cover approximately 2,500 square feet, and an estimated 1,000 square feet of each property is paved (see Attachment A -5 and A- 6) (Ref. 45). Therefore :

79,500 square feet – (3 properties * 3,500 covered square feet per property) = 69,000 square feet 69,000 / 34 = 2,029.4 (Ref. 1, Table 5-2)

72 SE

- GeneralSE

- General Area Letter: B



### Area Assigned Value: 2,029.4

Area Hazardous Waste Quantity Value : 2,029.4

73Area Letter: C



### 5.0.1 GENERAL CONSIDERATIONS Area C, Argonaut Heights – North Tailings Pile

Letter by which this area is to be identified : C

Name of area : Argonaut Heights

– North

Source Type : Tailings Pile

Location and description of area ( see Attachment A -4 through A-6 ): Area C correlates with Source 3, the Argonaut Heights

- North Tailings Pile. From 1989 through 2004, the Argonaut Estates, Jackson View Estates, Sierra View Estates, and Argonaut Heights residential developments were reportedly built on areas of known waste rock and mine tailings that were covered with imported fill prior to construction of the homes (see Attachment A -4) (Ref. 4, p p. 16, 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2 -3 ). A historical aerial photo review conducted by EPA showed trenches, pits, and berms for tailings disposal in the northern portion of the Argonaut Heights development near Pioneer Street and Argonaut Lane (Ref. 10 , pp. 29

- 30, 36; Ref. 42, p. 7 ). Sampling conducted at t hese properties showed the presence of elevated concentrations of arsenic, lead, and mercury in soils from 0 to 2 feet bgs (Attachment A -5 ) ( Ref. 4, pp. 28-29, 66; Ref. 15 ).

Attachment A -4 shows the locations of residential properties overlaid on a 1944 aerial photo of the Argonaut Mine property (Ref. 10, p. 36). In March 2015, EPA conducted a removal action of the vacant parcel located at the northeast corner of Pioneer Street and Argonaut Lane (EPA AOC

- 5) ( Attachment

A-1 ) (Ref. 42, p. 5). During the removal, mine tailings and wastes were observed to extend beyond the boundaries of AOC-5 into the neighboring residential properties of Area C (Ref. 42, pp. 10, 12, 45).

In August and Septembe r 2015, EPA conducted removal actions at 11 residential properties built within the former Argonaut Mine property, including four of the 12 residential properties in Area C ( Ref. 15; Ref. 40, pp. 1

- 2, 4 -5 , 7 ). Based on samples collected pre

- and post

- remov al, as well as samples collected during the 2014 SI, the total area of Area C is estimated to be approximately 97,350 square feet (see

Attachment A -6 ). However, some of this area is covered by permanent or otherwise maintained, essentially impenetrable mat erial. The average home is estimated to cover approximately 2,500 square feet, and an estimated 1,000 square feet of each property is paved (see Attachment A

- 5 and A

- 6) ( Ref.

45 ). Therefore, the Area of Contamination for Area C is estimated to be approxima tely 55,350 square feet (i.e., 97,350 square feet – (12 properties * 3,500 covered square feet per property)).

The August 2015 removal action did not change the calculated area of Area C, because soils exceeding 100 mg/kg arsenic were only removed to 12 inches bgs, and confirmation sampling showed that soils with elevated concentrations of arsenic were still present beneath the excavations (Ref. 39, pp. 7 -10; Ref. 40, pp. 2, 4).

During the August 2015 removal, the following actions were taken at each of t he residential properties within Area C ( Ref. 40, pp. 2, 4

- 5). Properties are identified by address code to preserve the privacy of the residents (Ref. 15).

74 SE

- GeneralArea Letter: C



### Address Code Action

ARA

- 09 No action.

ARA -10 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 1,223 square feet ( Ref. 39 , p. 8 ; Ref. 40, pp. 2, 5 ).

ARA -11 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 1,275 square feet ( Ref. 39 , p. 9 ; Ref. 40, pp. 2, 5 ).

ARA

- 12 No action.

ARA -13 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 2,846 square feet ( Ref. 39 , p. 7 ; Ref. 40, pp. 2, 5 ).

ARA

- 23 No action.

ARA

- 25 No action.

ARA

- 26 No action.

ARA

- 27 No action.

ARA -28 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 1,025 square feet ( Ref. 39 , p. 10 ; Ref. 40, pp. 2, 5 ).

ARA

- 31 No action.

ARA

- 32 No action.

Weston Solutions, Inc. 2014 SI Soil Sampling From July 28, 2014 through August 1, 2014, Weston Solutions, Inc. collected soil, sediment an d surface water samples as part of a SI of the Argonaut Mine. Samples were collected in accordance with a SAP approved by EPA on March 10, 2014

. Samples were submitted to Bonner Analytical, located in Hattiesburg, Miss issippi , under the EPA Contract Laboratory Program for metals analysis by Inorganic Superfund Methods (ISM01.3) and cyanide by EPA Method 9010/9012. The metals analytical data were validated by EPA (Re f. 4, p. 22).

- Background Concentrations: Background soil samples were collected from location AB

- 01 in pasture land located northwest of the Area A Tailings Impoundment and location AB

- 02 in pasture land located southwest of the Area A Tailings Impound ment (Ref. 4, p. 24). Background sampling locations are shown in Attachment A -3.

Residential properties built within the former Argonaut Mine property boundary were built on imported fill placed over waste rock, tailings, and soils contaminated by Argonau t Mine operations (Ref. 4, pp. 16 , 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2

- 3). Prior to the construction of the Area A Tailings Impoundment and the AOC

- 2 Cyanide Plant, the property was farmland (Ref. 12, p. 28; Ref. 50 ). Therefore, background samples were collected from nearby pasture lands to be representative of local conditions without the Argonaut Mine. Sample depths of the background and release samples are all from the upper 2 feet, though depths are not directly comparable as the background locations are native soil while soils from the residential properties include tailings and waste rock generated by mining activities, as well as imported fill.

75 SE

- GeneralArea Letter: C



### 2014 SI, Area C Background Soil Concentrations

Sample ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

AB

- 01 -0 0

- 0.5 7/31/14 Arsenic 8.9 1.0 Ref. 4, pp. 39

- 40, 66, 76, 1808, 1818

­ 1820, 1944; Ref. 18, p. 1; Ref. 23, pp. 7, 15 Lead 14.8 J (21.3) 1.0

Mercury 0.15 0.10

AB

- 01

- 1.5 1.0

- 1.5 7/31/14 Arsenic 2 .0 J

- (3.5) 1.1 Ref. 4, pp. 39

- 40, 66, 76, 1808, 1830, 1832, 1834, 1944; Ref. 20, p. 1; Ref. 24, pp. 6, 10 Lead 9 J (13.0) 1.1

Mercury <0.11 0.11

AB

- 02 -0 0

- 0.5 7/28/14 Arsenic 3.1 J

- (5.4) 1.0 Ref. 4, pp. 39

- 40, 65, 1808, 1832, 1834, 1941; Ref. 20, p. 1; Ref. 24, pp. 6, 11 Lead 11.2 J (16.1) 1.0

Mercury <0.10 0.10

AB

- 02

- 1.5 1.0

- 1.5 7/28/14 Arsenic 1.2 J

- (2.1) 1.1 Ref. 4, pp. 39

- 40, 65, 1808, 1830, 1832, 1834, 1941; Ref. 20, pp. 1

- 2; Ref. 24, pp. 6, 12 Lead 7.1 J (10.2) 1.1

Mercury <0.11 0.11

3X Highest Background (to

establish concentrations significantly above background): Arsenic 26.7

Ref. 9 Lead 63.9* *

Mercury 0.45
mg/kg: milligrams analyte per kilogram soil CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit *: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

J: The result is an estimated quantity, wit h an unknown bias (Ref. 4, pp. 1818, 1830

- 1832 , 186 7 ). Therefore, the background value is multiplied by a factor of 1.74 for arsenic and 1.44 for lead. The adjusted value is included in parentheses (Ref. 9, pp. 8, 18)

J- : The result is an estimated quantity, with a low bias (Ref. 4, p. 1830). The adjusted value is included in parentheses (Ref. 9, pp. 8, 18). <: The analyte was not detected.

* *: Calculated with the adjusted value. ^: Page 1831of Reference 4 present s a J qualifier for arsenic concentrations , and Reference 4 pages 1830 and 1834 indicate that the reported results may be biased low.



### - Contaminated Samples: Surface soil and shallow subsurface soil samples were collected from 19 residential lots and from Jackson Junior High School to assess whether the properties were impacted by historic al Argonaut Mine operations. Five sampling locations (ARA

- 09 through ARA

- 13) were collected from residential properties in Area C (Ref. 4, p. 28). Laboratory results are reported below. Analytical results from soils that were later removed during the August 2015 Removal Action are not reported.

Sampling locations are presented in Attachment A -5. To preserve the privacy of local residents, sample

locations are identified by address code only. A ddress codes are defined in a confidential reference (Ref.

15 ).

76 SE

- GeneralArea Letter: C



### 2014 Site Inspection, Area C Concentrations Significantly Above Background

Address

Code Sample

ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration +^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

ARA

- 09 ARA

09 -0
(MY9F 60) 0

- 0.5 7/31/14 Arsenic 1,380 J+ (793) 5.2 Ref. 4, pp. 40, 66

, 1811, 1873, 1876, 1945; Ref. 16, p. 3; Ref. 21, pp. 7, 17 Lead 226 1.0

Mercury 1.4 0.21

ARA

09 -2
(MY9F 61) 1.5 - 2 7/31/14 Arsenic 39,900 J+ (22,931) 123 Ref. 4, pp. 40, 66, 1811, 1873, 1876

, 1945; Ref. 16, p. 3; Ref. 21, pp. 7, 18 Lead 3,220 9.9

Mercury 193 24.6

ARA

- 10 ARA

10 -2
(MY9F 63) 1.5 - 2 7/31/14 Arsenic 655 J+ (376) 1.1 Ref. 4, pp. 40, 66, 1811, 1873, 1877

, 1944; Ref. 16, pp. 3

- 4; Ref. 21, pp. 7, 20

ARA

- 12 ARA

12 -2
(MY9F 67) 1.5 - 2 7/31/14 Arsenic 58.6 J+ (33.7) 1.1 Ref. 4, pp. 40

, 66, 1811, 1873, 1878, 1945; Ref. 16, p. 5; Ref. 21, pp. 7, 24

ARA

- 13 ARA

13 -1
(MY9F 69) 1.5 - 2 7/31/14 Arsenic 1,200 J+ (690) 4.4 Ref. 4, pp. 40, 66, 1811, 1873, 1878

, 1945; Ref. 16, pp. 5

- 6; Ref. 21, pp. 7, 26 Lead 225 1.1

Mercury 1.8 0.33

mg/kg: milligrams analyte per kilogram soil

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit
*: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

J+: The result is estimated and may be biased high (Ref. 4, p p

. 1867, 1873). Therefore, the arsenic value is divided by a factor of 1.74. The adjusted value is included in parentheses (Ref. 9, pp. 8, 18).

J: The result is estimated with an unknown bias (Ref. 4, p p

. 1867, 1873). Therefore, the arsenic value is divided by a factor of

1.74. The adjusted value is included in parentheses (Ref. 9, pp. 8, 18).

+: Qualified data presented in this table reflect a positive identification of the substa nce, although the data may be qualified.

^: Page s 3, 5 and 6 of Reference 16 present a J

- qualifier for qualified arsenic samples, pages 1876

- 1878 of Reference 4 present arsenic concentrations without qualifiers, and Reference 4 page 1873 indicates that the qualified arsenic samples are biased high

.



### March 2015 START Removal Assessment

In March 2015, START conducted a removal assessment of 20 residential properties in the Argonaut Heights and Sierra View Estates neighborhoods (Ref. 4, p. 14; Ref. 11, p. 2)

. The residential properties were divided into two to six DUs composed of roughly equal areas at a maximum of 1,250 square feet each to cover unpaved areas of the property. A 5

- point composite sample was collected from each DU at sampling intervals of 0 to 2 inches and 12 to 18 inches bgs using a trowel or hand auger and disposable scoops. Discrete samples were collected from some of the residences at the locations of play areas and gardens (Ref. 11, p. 2 ).

Samples were analyzed for lead and arsenic via XRF, with at least one sample from each property submitted to a laboratory for confirmation. Confirmation samples were submitted to the EPA Region 9

77 SE

- GeneralArea Letter: C



### Laboratory for analysis of arsenic and lead by EPA SW

- 846 Method 6010C (Ref. 11, pp. 3

- 4). Sampling locations are presented on Attachment A -5. Background sampling was not conducted during this sampling event; therefore, samples are compared to background concentrations from the 2014 SI sampling event.

2015 EPA Removal Assessment, Area C Concentrations Significantly Above Background

Address

Code Sample

ID Sample Depth (inches) Date Hazardous

Substance Hazardous

Substance

Concentration ( mg/kg ) QL (mg/kg) References

ARA

- 09 R- 12

- 03

­ C- 12 12 to 14 3/25/15 Arsenic 680 10 Ref. 11 , pp. 86, 91, 97; Ref. 15; Ref. 39, p p . 16 , 17 ; Ref. 47, pp. 4, 29, 32, 42 Lead 130 3

ARA

10 (1) R- 14

- 01

­ C- 12 12 to 14 3/25/15 Arsenic 220 2 Ref. 11 , pp. 86, 91, 97; Ref. 15; Ref. 39, p. 17; Ref. 47, pp. 4, 30, 33, 42

ARA

11 (1) R- 13

- 01

­ C- 12 12 to 14 3/25/15 Arsenic 590 10 Ref. 11 , pp. 86, 91, 97; Ref. 15; Ref. 39, p p . 16 , 17 ; Ref. 47, pp. 4, 29, 32, 42 Lead 120 3

ARA

- 12 R- 04

- 02

­ D-4 4 to 8 3/24 /15 Arsenic 430 2 Ref. 11 , pp. 84, 91, 96; Ref. 15; Ref. 39, p p . 14 , 15 ; Ref. 47, pp. 3, 28, 32, 41

ARA

13 (1) R- 10

- 06

­ C- 16 16 to 18 3/25/15 Arsenic 5,100 100 Ref. 11 , pp. 8 5 , 91, 97; Ref. 15; Ref. 39, p p

. 15, 16; Ref. 47, pp. 4, 29, 32, 41 Lead 1,900 3

ARA

- 23 R- 01

- 02

­ C- 12 12 to 14 3/23/15 Arsenic 140 2 Ref. 11 , pp. 8 4 , 91, 96; Ref. 15; Ref. 39, p p . 12 , 13 ; Ref. 47, pp. 3, 28, 32, 41

ARA

- 25 R- 03

- 02

­ C-0 0 to 2 3/23/15 Arsenic 270 2 Ref. 11 , pp. 84, 91, 96; Ref. 15; Ref. 39, p. 13; Ref. 47, pp. 3, 28, 32, 41

ARA

- 26 R- 05

- 02

­ C-0 0 to 2 3/24/15 Arsenic 40 2 Ref. 11 , pp. 86, 91, 96; Ref. 15; Ref. 39, p. 14; Ref. 47, pp. 3, 28, 32, 41 Lead 83 3

ARA

- 27 R- 06

- 03

­ D- 16 16 to 18 3/24/15 Arsenic 1,000 10 Ref. 11 , pp. 86, 91, 96; Ref. 15; Ref. 39, p. 14; Ref. 47, pp. 3, 28, 32, 41 Lead 110 3

ARA

28 (1) R- 07

- 01

­ C- 12 12 to 14 3/24/15 Arsenic 40 2 Ref. 11 , pp. 86, 91, 96; Ref. 15; Ref. 39, p p . 14 , 15 ; Ref. 47, pp. 3, 29, 32, 41

ARA

- 31 R- 18

- 01

­ C-0 0 to 2 3/2 5 /15 Arsenic 62 2 Ref. 11 , pp. 86, 91, 97; Ref. 15; Ref. 39, p. 18; Ref. 47, pp. 4, 30, 33, 42

mg/kg: milligrams analyte per kilogram soil

QL : Quantitation Limit . EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).

(1) : Although a removal was conducted on this property, soils were not excavated to this depth ( Ref. 15; Ref. 40, p. 2 ).

Ther efore, these soils are still present on the property.

78 SE

- GeneralArea Letter: C



### EPA August 2015 Removal Action In August 2015, EPA conducted removal actions at several residential properties built within the former Argonaut Mine property, including four of the residential properties in Area C (Ref. 15; Ref. 40 , pp. 1-2,

4- 5). Soils exceeding the action level of 100 mg/kg for arsenic were removed to 12 inches bgs and backfilled with clean topsoil ( Ref. 40, p. 2). Confirmation samples were collected from 12 to 14 inches bgs within the excavations (Ref. 39, p. 1). Samples were analyzed for lead and arsenic via XRF, wit h at least one sample from each property submitted to a laboratory for confirmation. Confirmation samples were submitted to the EPA Region 9 Laboratory for analysis of arsenic and lead by EPA SW -846 Method 6010C (Ref. 11 , pp 3-4, 120-121 ).

Sampling locat ions are presented on Attachment A -5. Background sampling was not conducted during this sampling event; therefore, samples are compared to background concentrations from the 2014 SI sampling event.

2015 EPA Removal Action

, Area C Concentrations Significan tly Above Background

Address

Code Sample ID Sample Depth (inches) Date Hazardous

Substance Hazardous

Substance

Concentration

( mg/kg ) QL (mg/kg) References

ARA

- 10 R- 14

- 01 -C12

- 082715 12 to 14 8/27/15 Arsenic 1,500 2 Ref. 11, p. 121; Ref. 39, pp. 1, 75; Ref. 49, pp. 4,

22

- 23, 27 Lead 320 3

ARA

- 13 R- 10

- 06 -C12

- 082115 12 to 14 8/21/15 Arsenic 5,300 4 Ref. 11, p p

. 90

- 92, 120; Ref. 39, p p . 1 , 77 ; Ref. 49, pp. 3, 22

- 23, 27 Lead 1,600 3

mg/kg: milligrams analyte per kilogram soil

QL : Quantitation Limit . EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).

79 SE

- GeneralArea Letter: C



### Area C Hazardous Waste Quantity

Tier A: Hazardous Constituent Quantity The total Hazardous Constituent Quantity for Area C 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 ). 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 CERCLA

hazardous substances in the source and the associated re leases from the source. Therefore, there is insufficient information to calculate a total or partial Hazardous Constituent Quantity estimate for Area

C with reasonable confidence. Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

Tier B: Hazardous Wastestream Quantity The total Hazardous Wastestream Quantity for Area C 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 historic al 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 associate d releases from the source. Therefore, there is insufficient information to adequately calculate or extrapolate a total or partial Hazardous Wastestream Quantity for

Area C with reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section 2.4.2.1.3).

Hazardous Wastestream Quantity Value: NE

Tier C: Volume: Tier C, volume is not applicable to source type pile for the soil exposure pathway (Ref. 1, Section 5.1.2.2).

Volume Assigned Value: 0

Tier D: Area: Based on pre

- and post

- removal samples collected in 2015, as well as samples collected during the 2014 SI, the total area of Area C is estimated to be approximately 97,350 square feet (see Attachment A -6 ). Any area where removal actions removed all hazardo us substances at observed contamination levels in the top two feet of soil and/or tailings were not included in this area estimate. However, some of this area is covered by permanent or otherwise maintained, essentially impenetrable material. The average

h ome is estimated to cover approximately 2,500 square feet, and an estimated 1,000 square feet of each property is paved (see Attachment A -5 and A- 6) ( Ref. 45 ). Therefore:

97,350 square feet – (12 properties * 3,500 covered square feet per property) = 55,350 square feet 55,350 / 34 = 1,627.9 (Ref. 1, Table 5-2)

80 SE

- GeneralSE

- General Area Letter: C



### Area Assigned Value: 1,627.9

Area Hazardous Waste Quantity Value : 1,627.9

81Area Letter: D



### 5.0.1 GENERAL CONSIDERATIONS : Area D , Argonaut Heights – South Contaminated Soil

Letter by which this area is to be identified : D

Name of area : Argonaut Heights - South

Source Type : Contaminated Soil

Location and description of area ( See Attachment A -4 through A-6 ): Area D correlates with Source 4, the Argonaut Heights

- South Conta minated Soil. From 1989 through 2004, the Argonaut Estates, Jackson View Estates, Sierra View Estates, and Argonaut Heights residential developments were reportedly built on areas of known waste rock and mine tailings that were covered with imported fill prior to construction of the homes (see Attachment A -4) (Ref. 4, p p. 16, 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2 -3 ). Elevated concentrations of arsenic, lead, and mercury have been detected in surface soils collected from 5 residential properties on Buena Vista Drive and Amador Street adjacent to the former cyanide plant located within EPA AOC

- 2 ( Ref. 4, pp. 28, 48, 66; Ref. 11,

p. 86; Ref. 15 ; Ref. 39, p. 1; see Attachment A -6 ). A historical aerial photo review conducted by EPA

showed that the cyanide plant was accessed by a dirt road and dirt trail through these residential properties. A former flume was also observed extending across all 5 properties (see Attachment A -4) (Ref. 10 , pp. 31, 36). During sampling conducted in 2014 and 201 5, distinct tailings or waste rock were not visually identified in Area D; therefore, the source type is evaluated as Contaminated Soil ( Ref. 46 ).

In August 2015, EPA conducted removal actions at 11 residential properties built within the former Argonaut Mine property, including four of the five properties in Area D ( Ref. 40, pp. 1

- 2, 4 -5 , 7 ). Based on samples collected pre

- and post

- removal, as well as samples collected during the 2014 SI, the total

area of Area D is estimated to be approximately 72,511 s quare feet (see Attachment A -6 ). However, some of this area is covered by permanent or otherwise maintained, essentially impenetrable material. The average home is estimated to cover approximately 2,500 square feet, and an estimated 1,000 square

feet of ea ch property is paved (see Attachment A

- 5 and A

- 6) (Ref. 45). Therefore, the Area of Contamination for Area D is estimated to be approximately 55,011 square feet (i.e., 72,411 square feet

– (5 properties * 3,500 covered square feet per property)).

The Augu st 2015 removal action did not change the calculated area of Area D, because soils exceeding 100 mg/kg arsenic were only removed to 12 inches bgs, and confirmation sampling showed that soils with elevated concentrations of arsenic were still present beneat h the excavations (Ref. 39, pp. 3

- 6; Ref. 40, pp. 2, 4).

During the August 2015 removal, the following actions were taken at each of the residential properties

within Area D ( Ref. 40, pp. 2, 4

- 5). Properties are identified by address code to preserve the privacy of the residents (Ref. 15).

82 SE

- GeneralArea Letter: D



### Address Code Action

ARA -15 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 2,846 square feet ( Ref. 39, p. 5; Ref. 40 , pp. 2, 4).

ARA -16 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 1,798 square feet ( Ref. 39, p. 6; Ref. 40 , pp. 2, 5).

ARA -17 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 1,275 square feet ( Ref. 39, p. 4; Ref. 40 , pp. 2, 4).

ARA

- 24 No action.

ARA -30 Soils exceeding 100 mg/kg arsenic were removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 7,297 square feet ( Ref. 39, p. 3; Ref. 40 , pp. 2, 4).

Weston Solutions, Inc. 2014 SI Soil Sampling From July 28, 2014 through August 1, 2014, Weston Solutions, Inc. collected soil, sediment an d surface water samples as part of a SI of the Argonaut Mine. Samples were collected in accordance with a SAP approved by EPA on March 10, 2014

. Samples were submitted to Bonner Analytical, located in Hattiesburg, Miss issippi , u nder the EPA Contract Laboratory Program for metals analysis by Inorganic Superfund Methods (ISM01.3) and cyanide by EPA Method 9010/9012. The metals analytical data were validated by EPA (Ref. 4, p. 22).

- Background Concentrations: Background soil sampl es were collected from location AB

- 01 in pasture land located northwest of the Source 1 Tailings Impoundment and location AB

- 02 in pasture land located southwest of the Area A Tailings Impoundment (Ref. 4, p. 24 ; see Attachment A -3 ). Background sampling lo cations are shown

in Attachment A -3.

Residential properties built within the former Argonaut Mine property boundary were built on imported fill placed over waste rock, tailings, and soils contaminated by Argonaut Mine operations (Ref. 4, pp. 16 , 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2

- 3). Prior to the construction of the Area A Tailings Impoundment and the AOC

- 2 Cyanide Plant, a portion of the property was farmland (Ref. 12, p. 28 ; Ref. 50). Therefore, background samples were collected f rom nearby pasture lands to be representative of local conditions without the Argonaut Mine. Sample depths of the background and release samples are all from the upper 2 feet, al though the background locations are native soil while soils from the

residenti al properties include tailings and waste rock generated by mining activities, as well as imported

fill.

83 SE

- GeneralArea Letter: D



### 2014 SI, Area D Background Soil Concentrations

Sample ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration + ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

AB

- 01 -0
(MY9EX7) 0

- 0.5 7/31/14 Arsenic 8.9 1.0 Ref. 4, pp. 25, 39

- 40, 66, 76, 1808,

1818

- 1820, 1944; Ref. 18, p. 1; Ref. 23, pp. 7, 15 Lead 14.8 J (21.3) 1.0

Mercury 0.15 0.10

AB

- 01

- 1.5
(MY9EY0) 1.0

- 1.5 7/31/14 Arsenic 2 .0 J

- (3.5) 1.1 Ref. 4, pp. 25, 39

- 40, 66, 76, 1808, 1830, 1832, 1834, 1944; Ref. 20, p. 1; Ref. 24, pp. 6, 10 Lead 9 J (13.0) 1.1

Mercury <0.11 0.11

AB

- 02 -0
(MY9EY1) 0

- 0.5 7/28/14 Arsenic 3.1 J

- (5.4) 1.0 Ref. 4, pp. 25, 39

- 40, 65, 1808, 1832, 1834, 1941; Ref. 20, p. 1; Ref. 24, pp. 6, 11 Lead 11.2 J (16.1) 1.0

Mercury <0.10 0.10

AB

- 02

- 1.5
(MY9EY2) 1.0

- 1.5 7/28/14 Arsenic 1.2 J

- (2.1) 1.1 Ref. 4, pp. 25, 39

- 40, 65, 1808, 1830, 1832, 1834, 1941; Ref. 20, pp. 1- 2; Ref. 24, pp. 6, 12 Lead 7.1 J (10.2) 1.1

Mercury <0.11 0.11

3X Highest Background (to

establish concentrations significantly above background): Arsenic 26.7

Ref. 9 Lead 63.9* *

Mercury 0.45
mg/kg: milligrams analyte per kilogram soil CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit *: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).).

J: The result is an estimated quantity, with an unknown bias (Ref. 4, pp. 1818, 1830

- 1832 , 1867 ). Therefore, the background value is multiplied by a factor of 1.74 for arsenic and 1.44 for lead. The adjusted value is included in parentheses (Ref. 9, pp. 8, 18)

. J- : The result is an estimated quantity, with a low bias (Ref. 4, pp. 1818, 1830

- 1832, 1867). <: The analyte was not detected.

* *: Calculated with the adjusted value. +: Qualified data presented in this table reflect a positive identification of the substance, although the data may be qualif ied.

^: Page 1831of Reference 4 present s a J qualifier for arsenic, and Reference 4 pages 1830 and 1834 indicate that the rep orted results may be biased low

.



### - Contaminated Samples: Surface soil and shallow subsurface soil samples were collected from 19 residential lots and from Jackson Junior High School to assess whether the properties were impacted by historical Argonaut Mine operations. Three sampling locations (ARA -15 through ARA -17 ) were collected from the Argonaut Heights neighborhood adjacent to the AOC

- 2 cya nide plant (Ref. 4, p. 28). Analytical results from soils that were later removed during the 2015 Removal Action are not reported.

Sampling locations are presented in Attachment A -5. To preserve the privacy of local residents, samples are identified by ad dress code only. Sample address codes are defined in a confidential reference (Ref.

15 ).

84 SE

- GeneralArea Letter: D



### 2014 Site Inspection, Area D Concentrations Significantly Above Background

Address

Code Sample

ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration +^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

ARA

- 15 ARA

15 -1
(MY9F 73) 1.5 - 2 7/31/14 Arsenic 269 J+ (154) 1.1 Ref. 4, pp. 40, 1873, 1879

, 1944; Ref. 16, p. 7; Ref. 21, pp. 8, 30 Lead 286 1.1

Mercury 3.3 0.53

ARA

- 16 ARA

16 -1
(MY9F

75 ) 0.5 - 1 7/31/14 Arsenic 147 1.1 Ref. 4, pp. 40, 66

, 1889, 1944; Ref. 21, p. 8; Ref. 25, pp. 7, 12; Ref. 37, p. 1 Lead 121 1.1

Mercury 0.85 0.11

ARA

- 17 ARA

17 -2
(MY9F 77) 1.5 - 2 7/31/14 Arsenic 123 1.1 Ref. 4, pp. 40, 66

, 1812,

1888

- 1889, 1944; Ref. 21, p. 8; Ref. 25, pp. 7, 14; Ref. 37, p. 2

mg/kg: milligrams analyte per kilogram soil

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit
*: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).
J+: The result is an estimated quantity, but the result may be biased high (Ref. 4, p p

. 1867, 1873). Therefore, the value is divided by a factor of 1.74. The adjusted value is included in parentheses (Ref. 9, pp. 8, 18).

J: The result is an estimated quantity with an unknown bias (Ref. 4, pp. 1873) The adjusted value is included in parentheses (Ref. 9, pp. 8, 18).

+: Qualified data presented in this table reflect a positive identification of the subs tance, although the data may be qualified.

^: Page 7 of Reference 16 presents a J

- qualifier, p age 1944 of Reference 4 presents a J qualifier, and Reference 4 page 1879

indicates that the reported results may be bias ed high

.



### EPA March 2015 Removal Assessment

In March 2015, EPA conducted a removal assessment of 20 residential properties in the Argonaut Heights and Sierra View Estates neighborhoods (Ref. 4, p. 14; Ref. 11, p. 2)

. The residential properties were divided into two to six DUs composed of roughly equal areas at a maximum of 1,250 square feet each to cover unpaved areas of the property. A 5

- point composite sample was collected from each DU at sampling intervals of 0 to 2 inches and 12 to 18 inches bgs using a trowel or hand auger and disposable scoops. Discrete samples were collected from some of the residences at the locations of play areas and gardens (Ref. 11, p. 2 ). Samples were analyzed for lead and arsenic via XRF, with at least one sample from each property submitted to a laboratory for confirmation. Confirmation samples were submitted to the EPA Region 9 Laboratory for analysis of arsenic and lead by EPA SW

- 846 Method 6010C (Ref. 11, pp. 3-4).

Sampling locations are presented in Attachment A -5. Analytical results from soils that were later removed during the August 2015 EPA Removal Action are not reported. Background sampling was not conducted during this sampling event; therefore, samples are compared to background concentrations from the 2014 SI sampling event.

85 SE

- GeneralArea Letter: D



### 2015 EPA Removal Assessment, Area D Concentrations Significantly Above Background

Address

Code Sample

ID Sample Depth (inches) Date Hazardous

Substance Hazardous

Substance

Concentration ( mg/kg ) QL (mg/kg) References

ARA

15 (1) R- 08

- 04

­ C- 12 12 to 14 3/24/15 Arsenic 340 2 Ref. 11, pp. 85, 96 ; Ref. 39,

pp . 14, 15 ; Ref. 47, pp. 3, 29, 32, 41 Lead 280 3

ARA

16 (1) R- 09

- 03

­ C- 12 12 to 14 3/24/15 Arsenic 350 2 Ref. 11, pp. 85, 90

- 92, 96 ; Ref. 39, p p

. 15, 16; Ref. 47, pp. 3, 29, 32, 41 Lead 500 3

ARA

- 17 R- 19

- 02

­ C- 12 (1) 12 to 14 3/27/15 Arsenic 130 2 Ref. 11, pp. 87, 105 ; Ref. 39, p. 18; Ref. 47, pp. 9, 31, 33, 44

R- 19

- 04

­ C-0 (2) 0 to 2 6/23/15 Arsenic 92 2.1 Ref. 11, pp. 87, 115; Ref. 39, p. 4; Ref. 48, pp. 4, 25

­ 26, 30

ARA

- 24 R- 02

- 02

­ C-0 0 to 2 3/23/15 Arsenic 69 2 Ref. 11, pp. 8 4 , 96 ; Ref. 39, p. 13; Ref. 47, pp. 3, 28, 32,

41

mg/kg: milligrams analyte per kilogram soil

QL : Quantitation Limit. EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).

(1) : Although a removal was conducted on this property, soils were not excavated to this depth (Ref. 15; Ref. 41 , p. 2). Therefore, these soils are still present on the property.

(2) : Although a removal was conducted on this property, soils were not excavated at this location because the arsenic concentration was below the removal action level of 100 mg/kg (Ref. 39, p. 4; Ref. 40, p. 2).



### EPA August 2015 Removal Action In August 2015, EPA conducted removal actions at 11 residential properties built in the area of former Argonaut Mine operations, including four of the properties in Source 4 (Ref. 15; Ref. 40, pp. 1

- 2, 4

- 5). Soils exceeding the action level of 100 mg/kg for arsenic were removed to 12 inches bgs and backfilled with clean topsoil ( Ref. 40, p. 2). Confirmation samples were collected from 12 to 14 inches bgs within the excavations ( Ref. 39, p. 1). Samples were analyzed for lead and arsenic via XRF, with at least one sample fr om each property submitted to a laboratory for confirmation. Confirmation samples were submitted to the EPA Region 9 Laboratory for analysis of arsenic and lead by EPA SW

- 846 Method 6010C (Ref. 11, pp. 120-121 ).

Sampling locations are presented on Attach ment A -5. Background sampling was not conducted during this sampling event; therefore, samples are compared to background concentrations from the 2014 SI sampling event.

86 SE

- GeneralArea Letter: D



### 2015 EPA Removal Action

, Area D Concentrations Significantly Above Background

Address

Code Sample ID Sample Depth (inches) Date Hazardous

Substance Hazardous

Substance

Concentration
( mg/kg ) QL (mg/kg) References

ARA

- 16 R- 09

- 03 -C12

- 082415 12 to 14 8/24/15 Arsenic 580 2 Ref. 11, p. 120; Ref. 15; Ref. 39

, p p. 1 , 7 1 Lead 570 3

ARA

- 30 R- 17

- 02E -C12

- 081815 12 to 14 8/18/15 Arsenic 120 2 Ref. 11, p. 120; Ref. 15; Ref. 39, p. 1

mg/kg: milligrams analyte per kilogram soil
QL : Quantitation Limit. EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).

87 SE

- GeneralArea Letter: D



### Area D Hazardous Waste Quantity

Tier A: Hazardous Constituent Quantity The total Hazardous Constituent Quantity for Area D 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 ). 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 CERCLA

hazardous substances in the source and the associated re leases from the source. Therefore, there is insufficient information to calculate a total or partial Hazardous Constituent Quantity estimate for Area

D with reasonable confidence . Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

Tier B: Hazardous Wastestream Quantity The total Hazardous Wastestream Quantity for Area D 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 historic al 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 associate d releases from the source. Therefore, there is insufficient information to adequately calculate or extrapolate a total or partial Hazardous Wastestream Quantity for

Area D with reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section 2.4.2.1.3).

Hazardous Wastestream Quantity Value: NE

Tier C: Volume: Tier C, volume is not applicable to Contaminated Soil for the soil exposure pathway (Ref. 1, Section 5.1.2.2).

Volume Assigned Value: 0

88 SE

- GeneralArea Letter: D



### Tier D: Area:

Based on pre

- and post

- removal samples collected in 2015, as well as samples collected during the 2014 SI, the area of Area D is estimated to be approximately 72,511 square feet (see Attachment A -6 ). Any

area where removal actions removed all hazardous substances a t observed contamination levels in the top two feet of soil and/or tailings were not included in this area estimate. However, some of this area is covered by permanent or otherwise maintained, essentially impenetrable material. The average home is

estimate d to cover approximately 2,500 square feet, and an estimated 1,000 square feet of each property is paved (see Attachment A -5 and A- 6) (Ref. 45). Therefore :

72,511 square feet – (5 properties * 3,500 cov ered square feet per property) = 55,011 55,011 / 34,000 = 1.6 (Ref. 1, Table 5-2)

Area Assigned Value: 1.6

Area Hazardous Waste Quantity Value : 1.6

89 SE

- GeneralArea Letter: E



### 5.0.1 GENERAL CONSIDERATIONS ; Area E, Sierra View Estates Contaminated Soil

Letter by which this area is to be identified : E

Name of area : Sierra View Estates Contaminated Soil

Source Type : Contaminated Soil

Location and description of area ( See Attachment A -4 through A-6 ):

Area E correlates with Source 5 , the Sierra View Estates Contaminated Soil. From 1989 through 2004, the Argonaut Estates, Jackson View Estates, Sierra View Estates, and Argonaut Heights residential developments were reportedly built on areas of known waste rock and mine tailings that were covered with imported fill prior to construction of the homes (se e Attachment A -4) (Ref. 4, p p. 16, 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2 -3 ). Elevated concentrations of arsenic, lead, and mercury have been detected in surface soils collected from three residential properties on Detert Lane adjacent to the Sour ce 1 Tailings Impoundment (Ref. 4, pp. 23, 48, 66; Ref. 15 ; see Attachment A -6 ). A historical aerial photo review conducted by EPA showed a former flume across this area (see Attachment A -4) (Ref. 10 , pp. 23, 28, 32, 36). During sampling conducted in 2014 and 2015, distinct tailings or waste rock were not visually identified in Area E; therefore, the source type is evaluated as Contaminated Soil ( Ref. 46 ).

In August and September 2015, EPA conducted removal actions at 11 residential properties built within the former Argonaut Mine property, including two of the three properties in Area E ( Ref. 40 , pp. 1

- 2, 4

­ 5 , 7; Ref. 15; see Attachment A -6 ). Based on samples collected pre

- and post

- removal, as well as samples collected during the 2014 SI, the area of Area E is estimated to be approximately 40,341 square feet (see Attachment A -6 ). However, some of this area is covered by permanent or otherwise maintained, essentially impenetrable material. The average home is estimated to cover approximately 2,500 square feet, and an estimated 1,000 square feet of each property is paved (see Attachment A

- 5 and

A- 6) (Ref. 45). Therefore, the Area of Contamination for Area E is estimated to be approximately 29,841 square feet (i.e., 40,341 square feet – (3 properties * 3,500 covered square feet per property)).

The removal action did not change the calculated area of Area E, because soils with arsenic exceeding 100 mg/kg were only removed to 12 inches bgs, or were left in place and covered with wood chips and rock. Confirmation sampling showed that soils with elevated concentrations of arsenic were still present beneath the excavation (Ref. 39, p. 2; Ref. 40, pp. 2, 4).

During the August 2015 removal, the following actions were taken at each of the residential properties

within Area E ( Ref. 40 , pp. 2, 4

- 5). Properties are identified by address code to preserve the privacy of the residents (Ref. 15).

90 SE

- GeneralArea Letter: E



### Address Code Action

ARA -18 No soils were removed. An area of 5,324 square feet was covered with wood chips and rock ( Ref. 40

, pp. 2, 4).

ARA

- 19 No action.

ARA -29 Soil exceeding 100 mg/kg arsenic was removed to a depth of 12 inches and backfilled with clean topsoil. Removed soils covered an area of 1,275 square feet ( Ref. 39, p. 2; Ref. 40 , pp. 2, 4).

Weston Solutions, Inc. 2014 SI Soil Sampling From July 28, 2014 through August 1, 2014, Weston Solutions, Inc. collected soil, sediment an d surface water samples as part of a SI of the Argonaut Mine (Ref. 4, pp. 6, 22) . Samples were collected in

accordance with a SAP approved by EPA on March 10, 2014 (Ref. 4, p. 22)

. Samples were submitted to Bonner Analytical, located in Hattiesburg, Miss issippi , under the EPA Contract Laboratory Program for metals analysis by Inorganic Superfund Methods (ISM01.3) and cyanide by EPA Method 9010/9012 (Ref. 4, p. 22) . The metals analytical data were validated by EPA (Ref. 4, p. 22).

- Background Concentrations: Background soil samples were collected from location AB

- 01 in pasture land located northwest of the Tailings Area and location AB

- 02 in pasture land located southwest of the Tailings Area (Ref. 4, p. 24). Background sampling locations are shown in Attachme nt A-3.

Residential properties built within the former Argonaut Mine property boundary were built on imported fill placed over waste rock, tailings, and soils contaminated by Argonaut Mine operations (Ref. 4, pp. 16 , 40; Ref. 8, p. 1; Ref. 26, p. 2; Ref. 27, pp. 2

- 3). Prior to the construction of the Source 1 Tailings Impoundment and the AOC

- 2 Cyanide Plant, a part of the property was farmland (Ref. 12, p. 28 ; Ref.

50 ). Therefore, background samples were collected from nearby pasture lands to be representative of local conditions without the Argonaut Mine. Sample depths of the background and release samples are all from the upper 2 feet, al though the background locations are native soil while soils from the residential properties include tailings and waste rock generated by mining activities, as well as imported

fill (See 2014 SI, Area E Background Soil Concentrations and 2014 Site Inspection, Area E Soil Concentrations Significantly Above Background Tables below).

91 SE

- GeneralArea Letter: E



### 2014 SI, Area E Background Soil Concentrations

Sample ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration + ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

AB

- 01 -0
(MY9EX7) 0

- 0.5 7/31/14 Arsenic 8.9 1.0 Ref. 4, pp. 39

- 40, 66, 76, 1808, 1818

­ 1820, 1944; Ref. 18, p. 1; Ref. 23, pp. 7, 15 Lead 14.8 J (21.3) 1.0

Mercury 0.15 0.10

AB

- 01

- 1.5
(MY9EY0) 1.0

- 1.5 7/31/14 Arsenic 2 .0 J

- (3.5) 1.1 Ref. 4, pp. 39

- 40, 66, 76, 1808, 1830, 1832, 1834, 1944; Ref. 20, p. 1; Ref. 24, pp. 6, 10 Lead 9 J (13.0) 1.1

Mercury <0.11 0.11

AB

- 02 -0
(MY9EY1) 0

- 0.5 7/28/14 Arsenic 3.1 J

- (5.4) 1.0 Ref. 4, pp. 39

- 40, 65, 1808, 1832, 1834, 1941; Ref. 20, p. 1; Ref. 24, pp. 6, 11 Lead 11.2 J (16.1) 1.0

Mercury <0.10 0.10

AB

- 02

- 1.5
(MY9EY2) 1.0

- 1.5 7/28/14 Arsenic 1.2 J

- (2.1) 1.1 Ref. 4, pp. 39

- 40, 65, 1808, 1830, 1832, 1834, 1941; Ref. 20, pp. 1

- 2; Ref. 24, pp. 6, 12 Lead 7.1 J (10.2) 1.1

Mercury <0.11 0.11

3X Highest Background (to

establish concentrations significantly above background): Arsenic 26.7

Ref. 9 Lead 63.9* *

Mercury 0.45
mg/kg: milligrams analyte per kilogram soil CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit *: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

J: The result is an estimated quantity, with an unknown bias (Ref. 4, pp. 1818, 1830

- 1832). Therefore, the bac kground value is multiplied by a factor of 1.74 for arsenic and 1.44 for lead. The adjusted value is included in parentheses (Ref. 9, pp. 8, 1 8)

J- : The result is an estimated quantity, with a low bias (Ref. 4, pp. 1818, 1830

- 1832, 1867). <: The analyte was not detected.

** : Calculated with the adjusted value. +: Qualified data presented in this table reflect a positive identification of the substance, although the data may be quali fied.

^: Page 1 831 of Reference 4 present s a J qualifier for arsenic concentrations , and Reference 4 page s 1830 and 1834 indicate that the reported results may be biased low.



### - Contaminated Samples: Surface soil and shallow subsurface soil samples were collected from 19 residential lots and from Jackson Junior High Scho ol to assess whether the properties were impacted by historic al Argonaut Mine operations (Ref. 4, p. 28)

. Two sampling locations (ARA

- 18 and ARA -19 ) were collected from the

Sierra View Estates neighborhood adjacent to the Source 1 Tailings Impoundment (Ref . 4, p. 28). No soils were removed from these properties during the August 2015 Removal Action.

Sampling locations are presented in Attachment A -5. To preserve the privacy of local residents, sample

locations are identified by address code only. A ddress codes are defined in a confidential reference (Ref.

15 ).

92 SE

- GeneralArea Letter: E



### 2014 Site Inspection, Area E Concentrations Significantly Above Background

Address

Code Sample

ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration (mg/kg) Sample Adjusted CRQL* (mg/kg) References

ARA

- 18 ARA

18 -0
(MY9F 78) 0

- 0.5 7/31/14 Arsenic 310 1.0 Ref. 4, pp. 40, 66

, 1812, 1890, 1944; Ref. 25, pp. 7, 15; Ref. 37, p. 2 Mercury 0.63 0.10

ARA

18

- 1.5
(MY9D 79) 1

- 1.5 7/31/14 Arsenic 423 1.1 Ref. 4, pp. 40, 66

, 1812, 1890, 1944; Ref. 25, pp. 7, 16; Ref. 37, pp. 2 -3 Lead 115 1.1

Mercury 1.4 0.21

ARA

- 19 ARA

19 -0
(MY9F 81) 0

- 0.5 7/31/14 Arsenic 55.3 1.1 Ref. 4, pp. 40, 66

, 1812, 1888, 1890, 1944; Ref. 25, pp. 7, 17; Ref. 37, p. 3

ARA

19 -1
(MY9F 82) 1.5 - 2 7/31/14 Arsenic 122 1.1 Ref. 4, pp. 40, 66

, 1812, 1888, 1890, 1944; Ref. 25, pp. 7, 18; Ref. 37, p. 3

mg/kg: milligrams analyte per kilogram soil

CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit
*: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).



### EPA March 2015 Removal Assessment

In March 2015, EPA conducted a removal assessment of 20 residential properties in the Argonaut Heights and Sierra View Estates neighborhoods (Ref. 4, p. 14; Ref. 11, p p . 2, 6 ). The residential properties were divided into two to six DUs composed of roughly equal areas at a maximum of 1,250 square feet each to cover unpaved areas of the property (Ref. 11, p. 2) . A 5

- point composite sample was collected from each DU at sampling intervals of 0 to 2 inches and 12 to 18 inches bgs using a trowel or hand auger and disposable scoops (Ref. 11, p. 2) . Discrete samples were collected from some of the residences at the locations of play areas and gardens (Ref. 11, p. 2 ). Samples were analyzed for lead and arsenic via XRF, with at least one sample from each property submitted to a laboratory for confirmation. Confirmation samples were submitted t o the EPA Region 9 Laboratory for analysis of arsenic and lead by EPA SW -846 Method 6010C (Ref. 11, pp. 3-4).

Sampling locations are presented in Attachment A -5 . Background sampling was not conducted during this sampling event; therefore, samples are com pared to background concentrations from the 2014 SI sampling event.

93 SE

- GeneralArea Letter: E



### 2015 EPA Removal Assessment, Area E Concentrations Significantly Above Background

Address

Code Sample

ID Sample Depth (inches) Date Hazardous

Substance Hazardous

Substance

Concentration

mg/kg QL (mg/kg) References

ARA

18 (2) R- 16

- 01

­ C-0 0 to 2 3/26/15 Arsenic 210 2 Ref. 11 , pp. 86, 91, 97 ; Ref. 39, p. 18; Ref. 47, pp. 4, 30, 33, 39

R- 16

- 04

­ C-0 0 to 2 6/23/15 Arsenic 100 2 Ref. 11 , pp. 8 6 , 107, 115 ; Ref. 48, pp. 4, 24, 26, 30,

32

ARA

29 (1) R- 15

- 02

­ C- 12 12 to 14 3/26/15 Arsenic 910 10 Ref. 11 , pp. 86, 91, 97 ; Ref. 39, p. 1 7 ; Ref. 47, pp. 4, 30, 33, 39 Lead 66 3

mg/kg: milligrams analyte per kilogram soil

QL : Quantitation Limit. EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).

(1) : Although a removal was conducted on this property, soils were not excavated to this depth (Ref. 15; Ref. 41 , p. 2).

(2) : Although a removal was conducted on this property, no soi ls were excavated. Soils exceeding the action level were covered with wood chips and rock ( Ref. 40 , pp. 2, 4 ).

94 SE

- GeneralArea Letter: E



### Area E Hazardous Waste Quantity

Tier A: Hazardous Constituent Quantity The total Hazardous Constituent Quantity for Area E could not be adequ ately 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 ). Insuffici ent 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 CERCLA

hazardous substances in the source and the associated releases from the sou rce. Therefore, there is insufficient information to calculate a total or partial Hazardous Constituent Quantity estimate for Area

E with reasonable confidence. Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

Tier B: Hazardous Wastestream Quantity The total Hazardous Wastestream Quantity for Area E 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 haza rdous 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

Area E with reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section 2.4.2.1.3).

Hazardous Wastestream Quantity Value: NE

Tier C: Volume: Tier C, volume is not applicable to Contaminated Soil for the soil exposure pathway (Ref. 1, Section 5.1.2.2).

Volume Assigned Value: 0

95 SE

- GeneralArea Letter: E



### Tier D: Area: Based on pre

- and post

- removal samples collected in 2015, as well as samples collected during the 2014 SI, the area of Area E is estimated to be approximately 40,341 square feet (see Attachment A -6 ). Any

area where removal actions removed all hazardous substances at observed contamination levels in the top two feet of soil and/or tailings were not included in this area estimate. However, some of this area is covered by permanent or otherwise maintained, essentially impenetrable material. The average home is estimated to cover approximately 2,500 square feet, and an estimated 1,000 square feet of each property is paved (see Attachment A -5 and A- 6) (Ref. 45). Therefore :

40,341 square feet – (3 properties * 3,500 covered square feet per property) = 29,841 29,841 / 34,000 = 0.9 (Ref. 1, Table 5-2)

Area Assigned Value: 0.9

Area Hazardous Waste Quantity Value : 0.9

96 SE

- GeneralArea Letter: F



### 5.0.1 GENERAL CONSIDERATIONS : Ar ea F, Jackson Junior High School Tailings Pile

Letter by which this area is to be identified : F

Name of area : Jackson Junior High School Tailings Pile

Source Type : Tailings Pile

Location and description of area ( See Attachment A-7 ): Area F correlates with Source 6, the Jackson Junior High School Tailings Pile (See Attachment A -2) (Ref. 4, p. 26)

. Exposed fill material resembling processed tailings was observed in the east

- facing slope

of the athletic field embankment (Ref. 4, pp. 28, 77; Ref. 34 , p. 2, 609, 611 -612 ). The upper athletic field playing area may have been constructed using mine tailings imported from the Argonaut Mi ne (Ref. 10, p. 36; Ref. 34, pp. 2, 4, 609, 611 ). It appears the tailings were subsequently covered with impo rted s oil to establish a grass field. The extent of mine tailings and soil cover at the athletic field is

unknown. At several locations, a mound of black tailings was observed adjacent to a ground squirrel burrow, suggesting that ground squirrels are bring ing tailings to the surface of the playing field ( Ref. 34

, pp. 2, 3, 609, 610 ).

Elevated concentrations of arsenic, lead, and mercury were detected in samples collected from the athletic field embankment, as well as from the outdoor lunch area above the embankment (Ref. 4, pp. 28, 31; Ref. 11, pp. 5, 88, Ref. 34, pp. 2-3)

In July 2015, EPA conducted a removal action at Jackson Junior High School ( Ref. 34, p. 3 ). The eastern portion of the athletic field was divided into 10 DUs (see Attachment A -7) (Ref. 11, pp. 5, 10; Ref. 34, p. 13). DUs 1 through 5 were along the exposed eastern embankment of the athletic field. DUs 6 through 10 were from the outdoor lunch area above the embankment (Ref. 11, p. 5). DU 6 is located adjacent to the snack bar (Ref. 34, p. 612). DUs 1 through 5 were capped with shotcrete and fenced ( Ref.

34 , pp. 3 -5 , 13 ). Tailings

- impacted soils were excavated from DU

- 6 and the northern portion of DU

- 7 to a maximum depth of one foot bgs (Ref. 34 , p. 4). The excavations were backfilled with clean fill ( Ref. 34, p. 5).

Based on laboratory sampling results from DU

- 6, DU

- 7, and DU

- 9, elevated concentrations of arsenic are still present in these DUs within 2 feet of the surface (Ref. 11, p. 88, Ref. 34, pp. 17, 19, 612 ; see Attachment A -7 ). Laboratory samples were not collected from DUs 8 and 10 (Ref. 34, p. 17) . Therefore,

a minimum area of the Area F tailings pile is estimated based on the areas of DU -6, - 7, and

- 9. The area

of DU

- 6 is 1,513 square feet, the area of DU

- 7 is 2,002 square feet, and the area of DU

- 9 is 2,918 square feet (see Attachment A -7 ).

- Background Concentrations:

Weston Solutions, Inc. 2014 SI Soil Sampling From July 28, 2014 through August 1, 2014, Weston Solutions, Inc. collected soil, sediment an d surface

water s amples as part of a SI of the Argonaut Mine (Ref. 4, pp. 1, 22) . Samples were collected in

accordance with a SAP approved by EPA on March 10, 2014 (Ref. 4, pp. 1, 22)

. Samples were submitted to Bonner Analytical, located in Hattiesburg, Miss issippi , under the EPA Contract Laboratory

97 SE

- GeneralArea Letter: F



### Program for metals analysis by Inorganic Superfund Methods (ISM01.3) and cyanide by EPA Method 9010/9012 (Ref. 4, p. 22) . The metals analytical data were validated by EPA (Ref. 4, p. 22).

Background soil samples were c ollected from location AB

- 01 in pasture land located northwest of the Tailings Area and location AB

- 02 in pasture land located southwest of the Tailings Area (Ref. 4, p. 24). Background sampling locations are shown in Attachment A -3.

The Jackson Junior High School upper athletic field playing area appears to have been constructed of mine tailings covered with imported soil (Ref. 10, p. 36; Ref. 34 , pp. 2, 4 ). Prior to the construction of the Source 1 Tailings Impoundment and the AOC

- 2 Cyanide Plant, the pr operty was farmland (Ref. 12,

p. 28 ; Ref. 50). Therefore, background samples were collected from nearby pasture lands to be representative of local conditions without the Argonaut Mine. Sample depths of the background and release samples are all from the u pper 2 feet, al though the background locations are native soil while

soils from the Jackson Junior High School athletic field include tailings generated by mining activities, as well as imported fill (See 2014 SI, Area F Background Soil Concentrations and 2015 EPA Removal Assessment, Area F Concentrations Significantly Above Background Tables below)

.

2014 SI, Area F Background Soil Concentrations

Sample ID Sample Depth (feet) Date Hazardous

Substance Hazardous

Substance

Concentration + ^ (mg/kg) Sample Adjusted CRQL* (mg/kg) References

AB

- 01 -0
(MY9EX7) 0

- 0.5 7/31/14 Arsenic 8.9 1.0 Ref. 4, pp. 39

- 40, 66, 76, 1808, 1818

­ 1820, 1944; Ref. 18, p. 1; Ref. 23, pp. 7, 15 Lead 14.8 J (21.3) 1.0

Mercury 0.15 0.10

AB

- 01

- 1.5
(MY9EY0) 1.0

- 1.5 7/31/14 Arsenic 2 J

- (3.5) 1.1 Ref. 4, pp. 39

- 40, 66, 76, 1808, 1830, 1832, 1834, 1944; Ref. 20, p. 1; Ref. 24, pp. 6, 10 Lead 9 J (13.0) 1.1

Mercury <0.11 0.11

AB

- 02 -0
(MY9EY1) 0

- 0.5 7/28/14 Arsenic 3.1 J

- (5.4) 1.0 Ref. 4, pp. 39

- 40, 65, 1808, 1832, 1834, 1941; Ref. 20, p. 1; Ref. 24, pp. 6, 11 Lead 11.2 J (16.1) 1.0

Mercury <0.10 0.10

AB

- 02

- 1.5
(MY9EY2) 1.0

- 1.5 7/28/14 Arsenic 1.2 J

- (2.1) 1.1 Ref. 4, pp. 39

- 40, 65, 1808, 1830, 1832, 1834, 1941; Ref. 20, pp. 1

- 2; Ref. 24, pp. 6, 12 Lead 7.1 J (10.2) 1.1

Mercury <0.11 0.11

3X Highest Background (to

establish concentrations significantly above background): Arsenic 26.7

Ref. 9 Lead 63.9* *

Mercury 0.45

98 SE

- GeneralArea Letter: F

mg/kg: milligrams analyte per kilogram soil
CRQL: EPA Contract Laboratory Program Contract Required Quantitation Limit *: The Sample Adjusted CRQL is the CRQL adjusted for sample weight, volume, dilution, and percent solid ( Ref. 19 ).

J: The result is an estimated quantity, with an unknown bias (Ref. 4, pp. 1818, 18 30

- 1832). Therefore, the background value is multiplied by a factor of 1.74 for arsenic and 1.44 for lead. The adjusted value is included in parentheses (Ref. 9, pp. 8, 1 8)

J- : The result is an estimated quantity, with a low bias (Ref. 4, pp. 1818, 1830

- 1832, 1867). <: The analyte was not detected.

* *: Calculated with the adjusted value. +: Qualified data presented in this table reflect a positive identification of the substance, although the data may be quali fied. ^: Page 1831of Reference 4 pres ent s a J qualifier for arsenic concentration , and Reference 4 pages 1830 and 1834 indicate that the reported results may be biased low.

99 SE

- GeneralArea Letter: F



### - Contaminated Samples:

EPA June and July 2015 Removal Assessment

In June and July 2015, EPA conducted a removal assessment of Jackson Junior High School (Ref. 11, p. 2) . A total of 20 composite soil samples (10 surface and 10 subsurface) from 10 DUs were collected from the athletic field for metal analysis (Ref. 11, p. 2) . A 5

- point composite sample was collected fr om each DU at sampling intervals of 0 to 2 inches and 12 to 18 inches bgs using a trowel or hand auger and disposable scoops (Ref. 11, p. 2 ). Samples were analyzed for lead and arsenic via XRF (Ref. 11, p. 3)

. Laboratory samples were submitted to the EPA R egion 9 Laboratory for analysis of arsenic and lead by

EPA SW -846 Method 6010C (Ref. 11, pp. 3-4).

Sampling locations are shown on Attachment A -7. Analytical results from soils that were later removed or covered with shotcrete during the July 2015 EPA Removal Action are not reported below

. Background sampling was not conducted during this sampling event; therefore, samples are compared to background concentrations from the 2014 SI sampling event.

2015 EPA Removal Assessment, Area F Concentrations Signifi cantly Above Background

DU Sample ID Sample Depth (inches) Date Hazardous

Substance Hazardous

Substance

Concentration
( mg/kg ) QL (mg/kg) References

DU

6 (1) JJHS -C- 02

­ 14

- 072715 12 to 14 7/27/15 Arsenic 290 2 Ref. 11 , p. 88, 120; Ref. 34, pp. 600

- 601; Ref. 39, pp. 20, 22; Ref. 49, pp. 3, 21, 23, 27

DU

7 (1) JJHS -C- 06

­ 14

- 072715 12 to 14 7/27/15 Arsenic 100 2 Ref. 11 , p. 88, 120; Ref. 34, pp. 600

- 601; Ref. 39, pp. 20, 22; Ref. 49, pp. 3, 21, 23, 27

DU -9 JJHS -C- 10

­ 2- 072715 0 to 2 7/27/15 Arsenic 62 2 Ref. 11 , p. 88, 120; Ref. 34, pp. 600

- 601; Ref. 39, pp.

21

- 22; Ref. 49, pp. 3, 21, 23, 27

mg/kg: milligrams analyte per kilogram soil
QL : Quantitation Limit. EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).

(1) : Although a removal was conducted in this DU , soils were not excavated to this depth ( Ref. 34 , p. 4).



### EPA July 2015 Removal Action In July 2015, EPA conducted a Removal Action at the Jackson Junior High School athletic field (Ref. 34, pp. 1, 4). Confirmation soil samples were collected from the excavations, and analyzed for lead and arsenic via XRF ( Ref. 34 , pp. 1, 6-7 ). Laboratory samples were submitted to the EPA Region 9 Laboratory for analysis of arsenic and lead by SW -84 6 Method 6010C (Ref. 34, p. 600). The sampling

location is shown on Attachment A -7 . Background sampling was not conducted during this sampling event; therefore, samples are compared to background concentrations from the 2014 SI sampling event.

100 SE

- GeneralArea Letter: F



### 2015 EPA Removal Action

, Area F Sampling Concentrations Significantly Above Background

DU Sample ID Sample Depth (inches) Date Hazardous

Substance Hazardous

Substance

Concentration
( mg/kg ) QL (mg/kg) References

DU -7 JJHS -C- 17

­ 12

- 080315 12 to 14 8/3/15 Arsenic 79 2 Ref. 34 , pp. 19, 600, Ref. 39, p. 34 ; Ref. 49, pp. 3, 22

- 23, 27

mg/kg: milligrams analyte per kilogram soil
QL : Quantitation Limit. EPA Region 9 Laboratory Quantitation Limits are equivalent to Sample Quantitation Limits (SQLs) (Ref. 43).

101 SE

- GeneralArea Letter: F



### Area F Hazardous Waste Quantity

Tier A: Hazardous Constituent Quantity The total Hazardous Constituent Quantity for Area F could not be adequately determined according to the HRS requirements; that is, the total mass of all CERCLA hazardous substances in the so urce and releases from the source is not known and cannot be estimated with reasonable confidence (Ref. 1, Section 2.4.2.1.1). Insufficient historical and current data (permits, waste concentration data, annual reports, etc.) are available to adequately ca lculate the total mass, or a partial estimate, of all CERCLA hazardous substances in the source and the associated releases from the source. Therefore, there is insufficient information to calculate a total or partial Hazardous Constituent Quantity estimat e for Area

F with reasonable confidence . Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

Tier B: Hazardous Wastestream Quantity

The total Hazardous Wast estream Quantity for Area F 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 Hazardou s Wastestream Quantity for

Area F with reasonable confidence. Scoring proceeds to the evaluation of Tier C, volume (Ref. 1, Section 2.4.2.1.3).

Hazardous Wastestream Quantity Value: NE

Tier C: Volume: Tier C, volume is not applicable to source type p ile for the soil exposure pathway (Ref. 1, Section 5.1.2.2).

Volume Assigned Value: 0

Tier D: Area: Based on samples collected pre

- and post

- removal, the area of Area F is estimated to be approximately 6,433 square feet (see Attachment A -7 ). Any area where removal actions removed all hazardous substances at observed contamination levels in the top two feet of soil and/or tailings were not included

in this area estimate. This area was calculated by adding the areas of DU -6, - 7, and -9. In accordance

wit h Ref. 1, Table 5-2:

6,433 / 34 = 189.2 Area Assigned Value: 189.2 Area Hazardous Waste Quantity Value : 189.2

102 SE

- General

### 5.1 RESIDENT POPULATION THREAT

5.1.1 LIKELIHOOD OF EXPOSURE

During the 2014 SI and the 2015 Removal Assessment, s oil samples collected f rom residences built within the former Argonaut Mine property contained arsenic, lead, and/or mercury at concentrations significantly above background (see Area s B through E for sampling results)

. Soil samples collected from Jackson Junior High School contained arsenic, lead, and/or mercury at concentrations significantly above background (see Area F for sampling results). These sampling locations are within an area of

observed contamination due to the release from the Ar gonaut Mine site . Arsenic was detected at concentrations exceeding the Cancer Risk Screening Concentration of 0. 71 mg/kg ( (Ref. 1, [Sections

2.5.1 and 5.3.1], pp. 51596, 51647; Ref. 2, p. 27). Therefore, Level I Actual Contamination is assigned.

The residential properties all measure less than 200 feet in length and width ; therefore, the observed

contamination sample from the same property is located within 200 feet of the residence on that property (see Attachment A -6 ). The observed contamination at Jackson Junior High School is located at the edge

of the athletic field in a regularly

- occupied lunch area adjacent to the snack bar (see Attachment A-7) (Ref. 34, pp. 2-3, 8, 13, 612-613 ).

Resident Population Threat Likelihood of Exposure Factor Category Value: 550

5.1.2 WASTE CHARACTERISTICS

5.1.2.1 Toxicity

Hazardous Substance Toxicity Factor Value References

Arsenic 10,000 Ref. 2, p. 1

Lead 10,000 Ref. 1, p. 51590; Ref. 2, p p . 7

- 8

Mercury 10,000 Ref. 2, p p

. 9

- 10

Toxicity Factor Value: 10,000

5.1.2.2 Hazardous Waste Quantity

Area Letter Source Type Area Hazardous Waste Quantity

A Pile 61,496.5

B Pile 2,029.4

C Pile 1

, 627.9

D Contaminated Soil 1.6

E Contaminated Soil 0.9

F Pile 189.2

Sum of Values: 66,889.6

103 SE

- Resident Population Threat

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

5.1.2.3 Calculation of Waste Characteristics Factor Category Value

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

Toxicity Factor Value x Hazardous Waste Quantity Factor Value: 100,000,000

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

104 SE

- Resident Population Threat

### 5.1.3 TARGETS

Level I Concentrations

Address

Code Sample ID Hazardous

Substance Hazardous

Substance

Concentration * mg/kg Benchmark

Concentration mg/kg Benchmark Reference

Argonaut Estates (Area B)

ARA

- 07 ARA

- 07

- 0 Arsenic 68.5 J+ (39.4) 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 07

- 1 Arsenic 148 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 08 ARA

- 08

- 0 Arsenic 68.3 J+ (39.2) 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

Argonaut Heights

– North (Area C)

ARA

- 09 ARA

- 09

- 0 Arsenic 1,380 J+ (793) 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 09 -2 Arsenic 39,900 J+ (22,931) 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

Mercury 193 10 Non

- Cancer Risk Screen

Conc. Ref. 2, p. 11

R

- 12

- 03

- C

- 12 Arsenic 680 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 10 ARA

- 10 -2 Arsenic 655 J+ (376) 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

R

- 14

- 01

- C

- 12 Arsenic 220 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

R- 14

- 01 -C- 12

­ 082715 Arsenic 1,500 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 11 R

- 13

- 01

- C

- 12 Arsenic 590 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 12 ARA

- 12

- 2 Arsenic 58.6 J+ (33.7) 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

R

- 04

- 02

- D

- 4 Arsenic 430 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 13 ARA

- 13

- 1 Arsenic 1,200 J+ (690) 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

R

- 10

- 06

- C

- 16 Arsenic 5,100 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

R- 10

- 06 -C- 12

­ 082115 Arsenic 5,300 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 23 R

- 01

- 02

- C

- 12 Arsenic 140 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 25 R

- 03

- 02

- C

- 0 Arsenic 270 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 26 R

- 05

- 02

- C

- 0 Arsenic 40 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 27 R

- 06

- 03

- D

- 16 Arsenic 1,000 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 28 R

- 07

- 01

- C

- 12 Arsenic 40 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 31 R

- 18

- 01

- C

- 0 Arsenic 62 0.71 Cancer Risk Screen Conc. Ref. 2, p. 27

Argonaut Heights

– South (Area D)

ARA

- 15 ARA

- 15

- 1 Arsenic 269 J+ (154) 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

R

- 08

- 04

- C

- 12 Arsenic 340 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 16 ARA

- 16

- 1 Arsenic 147 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

R

- 09

- 03

- C

- 12 Arsenic 350 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

R- 09

- 03 -C- 12

­ 082415 Arsenic 580 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

105 SE

- Resident Population Threat

### Level I Concentrations

Address

Code Sample ID Hazardous

Substance Hazardous

Substance

Concentration * mg/kg Benchmark

Concentration mg/kg Benchmark Reference

ARA

- 17 ARA

- 17

- 2 Arsenic 123 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

R

- 19

- 02

- C

- 12 Arsenic 130 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

R

- 19

- 04

- C

- 0 Arsenic 92 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 24 R

- 02

- 02

- C

- 0 Arsenic 69 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 30 R- 17

- 02E -C12

- 081815 Arsenic 120 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

Sierra View Estates (Area E)

ARA

- 18 ARA

- 18

- 0 Arsenic 310 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 18

- 1.5 Arsenic 423 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

R

- 16

- 01

- C

- 0 Arsenic 210 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

R

- 16

- 04

- C

- 0 Arsenic 100 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 19 ARA

- 19

- 0 Arsenic 55.3 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 19

- 1 Arsenic 122 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

ARA

- 29 R

- 15

- 02

- C

- 12 Arsenic 910 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

Jackson Junior High School (Area F)

DU -6 JJHS -C- 02

­ 14

- 072715 Arsenic 290 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

DU -7 JJHS -C- 06

­ 14

- 072715 Arsenic 100 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

JJHS -C- 17

­ 12

- 080315 Arsenic 79 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

DU -9 J JHS -C- 10 -2­

072715 Arsenic 62 0.71 Cancer Risk Screen Conc. Ref. 2, p. 2

J+: The result is estimated and may be biased high (Ref. 4, p p

. 1867, 1873)

. *: The possible impact of the po tential bias associated with the qualified contaminant concentrations was evaluated

consistent with the EPA factsheet

, Using Qualified Data to Document an Obser ved Release and Observed Contamination (Ref. 9) to ensure that the contaminant levels are above the applicable benchmark.

106 SE

- Resident Population Threat

### 5.1.3.1 Resident Individual

Area Letter : B through F

Level of Contamination : Level I

According to the HRS, hazardous constituents (as identified in the Superfund Chemical Data Matrix) that meet the criteria for an observed release (or observed contamination) and exceed media

- specific

benchmark values meet the criteria for Level I contamina tion (Ref. 1, Sect. 2.5). Based on results from

the 2014 Weston SI

, the 2015 EPA Removal Assessment, and the 2015 EPA Removal Action , Level I concentrations of arsenic and/or mercury have been established on residential properties and on a regularly occupi ed area of Jackson Junior High School (refer to HRS Documentation Record Section 5.0.1, Summary of S ite Contamination , above). A value of 50 is assigned to resident individual because there is at least one resident individual subject to Level I concentrati ons (Ref. 1, Sect. 5.1.3.1).

Resident Individual Factor Value: 50

107 SE

- Resident Population Threat

### 5.1.3.2 Resident Population

5.1.3.2.1 Level I Concentrations

Level I Resident Population Targets Observed contamination has been documented at residences in Areas B through E (see Section 5.0.1). Each residence is multiplied by the U.S. Census persons per household for Amador County to determine the resident population (Ref. 29).

Current e nrollment in Jackson Junior High School (Area F) is 406 students (Ref. 13). The observed contamination at Jackson Junior High School is located at the edge of the athletic field in a regularly

occupied lunch area adjacent to the snack bar (see Attachment A

- 7) (Ref. 34, pp. 2

- 3, 612 -613). Therefore, all students are likely to occupy the area of contamination at Jackson Junior High School.

Area

Letter Residences

with Observed

Contamination Number of

Residences County Multiplier Total No.

of Residents /

Students References

B ARA

- 07

ARA

- 08 2 2.32 4.64 Ref. 29

C ARA

- 09

ARA -10

ARA -11

ARA -12

ARA -13

ARA -23

ARA -25

ARA -26

ARA -27

ARA -28

ARA

- 31 11 2.32 25.52 Ref. 29

D ARA

- 15

ARA -16

ARA -17

ARA -24

ARA

- 30 5 2.32 11.6 Ref. 29

E ARA

- 18

ARA -19

ARA

- 29 3 2.32 6.96 Ref. 29

F Jackson Junior High School N/A N/A 406 students Ref. 13

Sum of individuals subject to Level I concentrations: 454.72 Sum of individuals subject to Level I concentrations x 10: 4,547.2

Level I Concentrations Factor Value : 4,547.2

108 SE

- Resident Population Threat

### 5.1.3.2.2 Level II Concentrations

Residential property ARA

- 32 is located in Argonaut Heights

– North (Area C) between ARA

- 26 and

ARA

- 28 ( see Attachment A -6 ). Though a composite laboratory sample collected on the property did not contain hazardous substances at concentrations significantly above background, XRF sampling showed the presence of elevated concentrations of arsenic and lead (Ref. 11, p. 86 ; Ref. 15 ). Therefore, Level II Actual Contamination is assigned to ARA -32.

Residential property ARA

- 33 is located in Argonaut Estates (Area B) between ARA

- 07 and ARA -08. Historical aerial photographs show that a waste rock pile beneath the neighborhood extends across all three properties (see Attachment A -6 ) ( Ref. 10, pp. 28, 36; Ref. 15 ). Therefore, Level II Actual

Contaminatio n is assigned to ARA-33.

Area

Letter Residences with

Observed

Contamination Number of

Residences County Multiplier Total No.

of Residents References

B ARA -33 1 2.32 2.32 Ref. 1, Section 5.1.3.2.2; Ref.

29

C ARA -32 1 2.32 2.32 Ref. 1, Section 5.1.3.2.2; Ref.

29

Sum of individuals subject to Level I I concentrations: 4.64

Level II Concentrations Factor Value : 4.64

5.1.3.3 Workers

Current s taff at Jackson Junior High School is 45 people (Ref. 13). The observed contamination at Jackson Junior High School is located at the edge of the athletic field in a regularly

- occupied lunch area adjacent to the snack bar (see Attachment A

- 7) (Ref. 34, pp. 2

- 3, 612

- 613). Therefore, all workers are likely to occupy the area of contamination at Jackson Junior High School.

Ar ea Letter Number of Workers References

F 45 Ref. 13

Total workers: 45

Workers Factor Value (Ref. 1, Table 5- 4): 5

109 SE

- Resident Population Threat

### 5.1.3.4 Resources

No known commercial agriculture, silviculture, or livestock production or grazing is known to be conducted within the area of observed contamination attributable to the Argonaut M ine site.

5.1.3.5 Terrestrial Sensitive Environments

There are no known terrestrial sensitive environments within the area of observed contamination attributable to the Argonaut Mine site.

110 SE

- Resident Population Threat

### 5.2 NEARBY POPULATION THREAT The Nearby Population Threat was not scored , a lthough the threat posed by the mining waste to nearby populations may be considered at a later point. However, as the Resident Population Threat is sufficient to identify that a threat to the residential population is present and significant, it is not necessary to score the Nearby Population Threat.

111 SE

- Resident Population Threat

### ATTACHMENT A DATA CITATIONS

Attachment A-1: Argonaut Mine Layout Argonaut Investigation Area

- Reference 4 Argonaut Historical Boundary

- Weston Solutions, Inc. (Weston) digitized from Reference 50.

Parcel

- GIS Division of the Amador County Information Technology Depart ment. Parcel boundaries from georeferenced scanned Assessor maps, May 2011

Wetland

- CONUS_wet_poly Classification of Wetlands and D eepwater Habitats of the United States. U.S. Department of the Interior, Fish and Wild life Service, Washington, DC. FWS/OBS-79/31, May 2009 (Reference 38).

Surface Water

- U.S. Geological Survey - Nationa l Hydrography Dataset, March 2012 Underground Culvert

- Weston digitized from U.S. Geological Surv ey - National Hydrogra phy Dataset, March 2012

Elevation Contour

- U.S. Geological Survey - The National Elevation Dataset Aerial Image

- ArcGIS Imagery from Microsoft, Resolution 0.03 meter, June 14, 2011

Attachment A-2: Argonaut Site Sources Argonaut Mine Sources

- Reference 4 Argonaut Historical Boundary

- Weston digitized from Reference 50

Residential Parcels

- References 4, 11, 15

- GIS Division of the Amador County Information Technology Depart ment. Parcel boundaries from georeferenced scanned Assessor maps, May 2011

Surface Water

- U.S. Geological Survey - Nationa l Hydrography Dataset, March 2012 Aerial Image

- ArcGIS Imagery from Microsoft, Resolution 0.03 meter, June 14, 2011

### Attachment A-3: Source 1 Sampling Locations Argonaut Investigation Area

- Reference 4 Argonaut Historical Boundary

- Weston digitized from Reference 50

Wetland

- CONUS_wet_poly Classification of Wetlands and D eepwater Habitats of the United States. U.S. Department of the Interior, Fish and Wild life Service, Washington, DC. FWS/OBS-79/31, May 2009 (Reference 38).

Surface Water

- U.S. Geological Survey - Nationa l Hydrography Dataset, March 2012 Aerial Image

- ArcGIS Imagery from Microsoft, Resolution 0.03 meter, June 14, 2011

Attachment A-4: Residential Parcels on the Historical Aerial

Residential Parcels

- References 4, 11, 15 Argonaut Historical Boundary

- Weston digitized from Reference 50 Aerial Image

- Weston Georeferenced - National Aerial Survey Ce nter Corp./Visual Image Presentations Silver Spring, Maryland, October 02, 1944. Scale: 1:20,000, Black & White Film, Mission I.D.: DDE

Frame Numbers 107 and 108.

Attachment A-5: Residential Soil Sampling Locations

Residential Parcels

- References 4, 11, 15 Argonaut Historical Boundary

- Weston digitized from Reference 50 Aerial Image

- ArcGIS Imagery from Microsoft, Resolution 0.03 meter, June 14, 2011

Attachment A-6: Observed Contamination Areas

Residential Parcels

- References 4, 11, 15 Argonaut Historical Boundary

- Weston digitized from Reference 50 Aerial Image

- ArcGIS Imagery from Microsoft, Resolution 0.03 meter, June 14, 2011

### Attachment A-7: Jackson Junior High School Sampling and Removal Locations

Residential Parcel

- Reference 34 Aerial Image

- ArcGIS Imagery from Microsoft, Resolution 0.03 meter, June 14, 2011

Attachment A-8: Source 1 Wetland Argonaut Investigation Area

- Reference 4

Wetland

- CONUS_wet_poly Classification of Wetlands and D eepwater Habitats of the United States. U.S. Department of the Interior, Fish and Wild life Service, Washington, DC. FWS/OBS-79/31, May 2009 (Reference 38). Aerial Image

- ArcGIS Imagery from Microsoft, Resolution 0.03 meter, June 14, 2011MAIN ARGONAUT STATE HIGHWAY 49

SPUNN EL DORADO

PIONEER BUENA VISTA ROSE RIDGECREST

AMADOR

1320 1340

1360 1380 1520

1500 1300

1400 1280

1480 1460 1440 1420 1260

1540 1560

1240 1580 1600

1220 1620

1640 1400

1320 1580 1420

1400

1260 1540 1300

1540 1340

1400 1260 1440 1420

1320 1400

1260 1580 

## Legend

Argonaut Investigation Area

Argonaut Historical Boundary

Parcels

Former Mill

Wetland

Surface Water

Underground Culvert

Elevation Contour Unnamed Intermittent Stream Waste

Rock Pile Cyanide Process Area (estimated location) Argonaut Mine 40-Stamp Mill (former)

Argonaut Mine 60-Stamp Mill (former) Argonaut Mill Buildings

North Fork Jackson Creek



### 0 1,000 Scale in Feet

PREPARED BY: Weston Solutions, Inc. 1340 Treat Blvd, Ste 210 Walnut Creek, CA 94597

PREPARED FOR: EPA Region 9
Pacific Southwest



## ATTACHMENT A-1

ARGONAUT MINE LAYOUT 

### Argonaut Mine Jackson, Amador County, California Argonaut

Mine Shaft

Processed Tailings (Gray Sands)

Waste Rock Pile

Unnamed Intermittent Stream Argonaut High School

Amador County Superior Court Cyanide

Plant Ore Storage

Area

Upper Tailings Impoundment (Gray Sands Area) Concrete Dam
Jackson Junior High

School Middle Tailings Impoundment Lower Tailings Impoundment Upper Earthen Tailings Dam Lower Earthen Tailings Dam AOC-5

AOC-1

AOC-2

AOC-3

AOC-4 Probable Amalgamation Building 

## S R Argonaut

Mine

Argonaut Mine

Mill Area

Argonaut Mine

Tailings Area JACKSON GATE
STATE HIGHWAY 88ARA-32 ARA-33

MAIN

HOFFMAN SUTTER ARGONAUT STATE HIGHWAY 49

VOGAN TOLL

CHURCH

VISTA

SU ARA-31

ARA-11

ARA-10 ARA-25

ARA-07 ARA-08

ARA-29 ARA-30

ARA-19 ARA-17 ARA-15

ARA-18 ARA-24

ARA-16 ARA-23

ARA-13 ARA-26

ARA-12 ARA-09 ARA-28

ARA-27

Unnamed Intermittent Stream North Fork Jackson Creek Argonaut High School

Amador County Superior Court Cyanide

Plant Ore Storage

Area

Upper Tailings Impoundment (Gray Sands Area) Concrete Dam

Jackson Junior High

School Middle Tailings Impoundment 

### 0 1,000 Scale in Feet

PREPARED BY: Weston Solutions, Inc. 1340 Treat Blvd, Ste 210 Walnut Creek, CA 94597

PREPARED FOR: EPA Region 9
Pacific Southwest



## ATTACHMENT A-2

ARGONAUT SITE SOURCES 

### Argonaut Mine Jackson, Amador County, California Lower Tailings Impoundment Upper Earthen Tailings Dam Lower Earthen Tailings Dam AOC-5

AOC-1

AOC-2

Source 1 (AOC-3) AOC-4 Probable Amalgamation Building 

## Legend

Argonaut Mine Sources

Argonaut Property Boundary

Residential Parcel

Surface Water

North Fork Jackson Creek Source 2

Source 3

Source 4

Source 5

Source 6 BUENA PIONEER

BLUE OAK MMIT MATTLEY ARGONAUT! . 

### " / ! .



### " / ! . ! . ! .

! . ! .

MAIN

HOFFMAN SUTTER STATE HIGHWAY 49

VOGAN TOLL

B AB-01

AB-02 ATA-05 ATA-03

ATA-01

ATA-02

ATS-01 ATA-04

ATS-02 Unnamed Intermittent Stream North Fork Jackson Creek Argonaut High School

Amador County Superior Court Cyanide

Plant Ore Storage

Area

Upper Tailings Impoundment (Gray Sands Area)
Concrete Dam

Jackson Junior High

School Middle Tailings Impoundment 

### 0 500 Scale in Feet

PREPARED BY: Weston Solutions, Inc. 1340 Treat Blvd, Ste 210 Walnut Creek, CA 94597

PREPARED FOR: EPA Region 9
Pacific Southwest



## ATTACHMENT A-3

SOURCE 1 SAMPLING LOCATIONS 

### Argonaut Mine Jackson, Amador County, California Lower Tailings Impoundment Upper Earthen Tailings Dam Lower Earthen Tailings Dam AOC-5

AOC-1

AOC-2

Source 1 (AOC-3) Probable Amalgamation Building 

## Legend

Argonaut Mine Sources

Argonaut Property Boundary

Wetland

Surface Water



## ! . Soil Sampling Location



### " / Sediment Sampling Location North Fork Jackson Creek

ARGONAUT

AMADOR CHURCH

LUE OAK SUMMIT MATTLEYARA-32 ARA-33

MAIN

HOFFMAN SUTTER STATE HIGHWAY 49

VOGAN TOLL

CHURCH

SU ARA-31

ARA-11

ARA-10 ARA-25 ARA-07 ARA-08

ARA-29 ARA-30

ARA-19 ARA-17 ARA-15

ARA-18 ARA-24

ARA-16 ARA-23

ARA-13 ARA-26

ARA-12 ARA-09 ARA-28

ARA-27

Unnamed Intermittent Stream Argonaut High School

Amador County Superior Court Cyanide

Plant Ore Storage

Area

Upper Tailings Impoundment (Gray Sands Area) Concrete Dam

Jackson Junior High

School Middle Tailings Impoundment 

### 0 500 Scale in Feet

PREPARED BY: Weston Solutions, Inc. 1340 Treat Blvd, Ste 210 Walnut Creek, CA 94597

PREPARED FOR: EPA Region 9
Pacific Southwest



## ATTACHMENT A-4

RESIDENTIAL PARCELS ON THE
HISTORICAL AERIAL 

### Argonaut Mine Jackson, Amador County, California Lower Tailings Impoundment Upper Earthen Tailings Dam Lower Earthen Tailings Dam AOC-5

AOC-1

AOC-2

Source 1 (AOC-3)

AOC-4 Probable Amalgamation Building 

## Legend

Argonaut Mine Tailings Area

Argonaut Property Boundary

Residential Parcel

Athletic Field

North Fork Jackson Creek Parcel boundaries from: Amador County Assessor Parcel Data, GIS Division of the Amador County Information Technology Department May 2011.

Background Aerial Photograph From 1944 Source 3 Source 2

Source 4

Source 5

Source 6

Athletic Field PIONEER

BLUE OAK MMIT MATTLEY ARGONAUT! . ! .

! .

! . ! . ! .

! . ! . ! . ! .

!

. ! . ARA-32 ARA-33

MAIN STATE HIGHWAY 49

VOGAN TOLL

CHUR ARA-31

ARA-11

ARA-10 ARA-25

ARA-07 ARA-08

ARA-29 ARA-30

ARA-19 ARA-17 ARA-15

ARA-18 ARA-24

ARA-16 ARA-23

ARA-13 ARA-26

ARA-12 ARA-09 ARA-28

ARA-27

Unnamed Intermittent Stream North Fork Jackson Creek Argonaut High School

Amador County Superior Court Cyanide

Plant Ore Storage

Area

Upper Tailings Impoundment (Gray Sands Area)

Concrete Dam

Jackson Junior High

School Middle Tailings Impoundment 

### 0 500 Scale in Feet

PREPARED BY: Weston Solutions, Inc. 1340 Treat Blvd, Ste 210 Walnut Creek, CA 94597

PREPARED FOR: EPA Region 9
Pacific Southwest



## ATTACHMENT A-5

RESIDENTIAL SOIL SAMPLING LOCATIONS 

### Argonaut Mine Jackson, Amador County, California Lower Tailings Impoundment Upper Earthen Tailings Dam Lower Earthen Tailings Dam AOC-5

AOC-1

AOC-2

Source 1 (AOC-3) AOC-4 Probable Amalgamation Building 

## Legend

Argonaut Property Boundary

Residential Parcel

Decision Unit Composite Sample

! . Discrete Sampling Location
North Fork Jackson Creek Only sampling locations with arsenic laboratory results above three times background concentrations are shown.

HOFFMAN SUTTER SPUNN CHARA-32 ARA-33

MAIN STATE HIGHWAY 49

VOGAN TOLL

CHUR ARA-31

ARA-11

ARA-10 ARA-25

ARA-07 ARA-08

ARA-29 ARA-30

ARA-19 ARA-17 ARA-15

ARA-18 ARA-24

ARA-16 ARA-23

ARA-13 ARA-26

ARA-12 ARA-09 ARA-28

ARA-27

Unnamed Intermittent Stream North Fork Jackson Creek Argonaut High School

Amador County Superior Court Cyanide

Plant Ore Storage

Area

Upper Tailings Impoundment (Gray Sands Area)

Concrete Dam

Jackson Junior High

School Middle Tailings Impoundment 

### 0 500 Scale in Feet

PREPARED BY: Weston Solutions, Inc. 1340 Treat Blvd, Ste 210 Walnut Creek, CA 94597

PREPARED FOR: EPA Region 9
Pacific Southwest



## ATTACHMENT A-6

OBSERVED CONTAMINATION AREAS 

### Argonaut Mine Jackson, Amador County, California Lower Tailings Impoundment Upper Earthen Tailings Dam Lower Earthen Tailings Dam AOC-5

AOC-1

AOC-2

Source 1 (AOC-3) AOC-4 Probable Amalgamation Building 

## Legend

Observed Contamination Area

Argonaut Property Boundary

Residential Parcel

North Fork Jackson Creek

Parcel boundaries from: Amador County Assessor Parcel Data, GIS Division of the Amador County Information Technology Department May 2011. Source 3 Source 2

Source 4

Source 5

Source 6

HOFFMAN SUTTER SPUNN CH0 40 Scale in Feet Legend

? ? Fence

óóóóóó Drainage Swale

Concrete Cover

Observed Contamination Area

Excavated and Backfilled Area

PREPARED BY: Weston Solutions, Inc. 1340 Treat Blvd, Ste 210 Walnut Creek, CA 94597 PREPARED FOR: EPA Region 9 Pacific Southwest 

## ATTACHMENT A-7

JACKSON JUNIOR HIGH SCHOOL SOURCE 

### Argonaut Mine Jackson, Amador County, California Hoffman Street Athletic Field

Gate Lunch

Area Canopy JJHS-C-02-14

JJHS-C-06-14

JJHS-C-10-2 DU-9 DU-7 DU-6

JJHS-C-17-12 (One Foot Depth)

## " / Lower Earthen Tailings Dam

Concrete Dam LEGEND

0 100 Scale in Feet 

## ! . Sediment Sampling Location

Property Boundary

Wetland

PREPARED BY: Weston Solutions, Inc. 1340 Treat Blvd, Ste 210 Walnut Creek, CA 94597 

## ATTACHMENT A-8

SOURCE 1 WETLAND 

### Argonaut Mine Jackson, Amador County, California Argonaut Drive

PREPARED FOR: EPA Region 9 Pacific Southwest U.S. Fish & Wildlife Service National Wetlands Inventory identifies the lower tailings impoundment wetland as a Palustrine Emergent, Temporary Flooded, Dikes/Impounded. Sediment Sample ATS-02 Arsenic: 240 mg/kg 1340

1420