### HRS DOCUMENTATION RECORD COVER SHEET

Name of Site: New Idria Mercury Mine

EPA ID No. CA0001900463

Contact Persons

Site Investigation: Matt Mitguard, EPA Region 9

Documentation Record: Karen Jurist, EPA Region 9

Pathw ays, Components, or Threats Not Scored

Ground W ater Pathway

The ground water pathway was not scored because there are currently no known drinking water wells

within four miles of site sources.

Soil Exposure Pathway

The soil exposure pathway was not s cored because there are currently no known resident individuals, workers, sensitive environments, or resources on or within 200 feet of sources at the site.

Air Migration Pathway

The air pathway was not scored because there is no documented observed rele ase to the atmosphere, and scoring the potential to release to air would not likely contribute significantly to the overall listing decision

.1 

### HRS DOCUMENTATION RECORD

Name of Site: New Idria Mercury Mine

EPA Region: 9 Date Prepared: 3 /2011

Street Addre ss of Site: Township: 17S, Range: 12E

City, County, State , Zip Code : Idria, San Benito County, CA 95043

Latitude: 36.418 392 North Longitude: 120.672 511 West ( Ref. 18 ; Ref 21 )

Latitude/Longitude Reference Point: The latitude and longitude were measu red from the

centroid of Source 1 , the Calcine Tailings P iles ( Ref. 18 ; Ref. 21 ).

Scores

Air Pathway = not scored Ground Water Pathway = not scored Soil Exposure Pathway = not scored Surface Water Pathway = 63.33

HRS SITE SCORE = 31.66

*The street add ress, 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 su bstance has been "deposited, stored, placed, or 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

contamination has come to be located.

### 3/2011 2 

### HAZARD RANKING SYSTEM

SUMMARY SCORESHEETS

SITE NA ME: New Idria Mercury Mine

CITY/COUNTY/STATE: Idria

, San Benito County, California

EPA ID #: CA0001900463

EVALUATOR: Christina Marquis DA TE: March 2011

LATITUDE: 36.418 392 N orth LONGITUDE: 120.6725 11 W est

S S 2



### Ground Water Migration Pathway Score (S gw 

### ) Not scored Not scored Surface Water Migration Pathway Score (S

sw 

### ) 63.33 4,010.6 889 Soil Exposure Pa thway Score (S

s 

### ) Not scored Not scored Air Migration Pathway Score (S

a 

### ) Not scored Not scored

S gw 2 

### +S
sw 2 

### + S
s 2 

### + S
a 2 

### XXXXXXX 4,010.6 889 (S gw 2 

### +S
sw 2 

### + S
s 2 

### + S
a 2 

### ) / 4 XXXXXXX 1,002.6 722 SQRT ((S gw 2 

### +S
sw 2 

### + S
s 2 

### + S
a 2 

### ) / 4) XXXXXXX 31.6 6

### 3/2011 3 

### SURFACE WAT ER OVERLAND/FLOOD MIGRATION COMPONENT SCORESHEET

REF. 1, TABLE 4

- 1

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 Flo w:

2a. Containment 10 NS

2b. Runoff 25 NS

2c. Distance to Surface Water 25 NS

2d. Potential to Release by Overland Flow (lines 2a x [2b + 2c]) 500 NS

3. Potential to Release by Flood:

3a. Containment (Flood) 10 NS

3b. Flood Frequency 50 NS

3c. Potential to Release by Flood (lines 3a x 3b) 500 NS

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

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

Waste Characteristics:

6. Toxicity/Persistence a 10,000

7. Hazardous Waste Quantity a 10,000

8. Waste Characteristics 100 100

Targets:

9. Nearest Intake 50 0

10. Population:

10a. Level I Concentrations b 0

10b. Level II Concentrations b 0

10c. Potential Contamination b 0

10d. Population (lines 10a + 10b + 10c) b 0

11. Resources 5 5

12. Targets (lines 9 + 10d + 11) b 5

### 3/2011 4 Factor Categories and Factors Maximum Value Value Ass igned

DRINKING WATER THREAT (Concluded)

Drinking Water Threat Score:

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

100 3.33

HUMAN FOOD CHAIN THREAT

Likelihood of Release:

14. Likelihood of Re lease (same value as line 5) 550 550

Waste Characteristics:

15. Toxicity/Persistence/Bioaccumulation a 500,000,000

16. Hazardous Waste Quantity a 10,000

17. Waste Characteristics 1,000 1,000

Targets:

18. Food Chain Individ ual 50 0

19. Population:

19a. Level I Concentrations b 0

19b. Level II Concentrations b 0

19c. Potential Human Food Chain Contamination b 0

19d. Population (lines 19a + 19b + 19c) b 0

20. Targets (lines 18 + 19d) b 0

Human Food Chain Threat Score:

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

100 0

### 3/2011 5 Factor Categories and Factors Maximum Value Value Assigned

ENVIRONMENTAL THREAT

Likelihood of Re lease:

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. S ensitive Environments:

26a. Level I Concentrations b 0

26b. Level II Concentrations b 750

26c. Potential Contamination b 0

26d. Sensitive Environments (lines 26a + 26b + 26c) b 750

27. Targets (value from 26d) B 750

Environmental Threat Score:

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

60 60

SURFACE WATER OVERLAND/FLOOD MIGRATION COMPONENT SCORE FOR A WATERSHED

29. Watershed Score c (lines 13 + 21 + 28,

su bject to a maximum of 100) 100 63.33

SURFACE WATER OVERLAND/FLOOD MIGRATION COMPONENT SCORE

30. Component Score (S of ) c

, (highest score from line 29 for all watersheds evaluated, subject to a maximum of 100)

100 63.33

a 

### Maximum valu e applies to waste characteristics category.

b 

### Maximum value not applicable.

c 

### Do not round to nearest integer.

### 3/2011 6 

### REFERENCES

Reference

Number Description of the Reference

1 Hazard Ranking System; Final Rule, 14 Decembe r 1990, Vol. 55, No. 241, 138 pages. Available at: http://www.epa.gov/superfund/sites/npl/hrsres/index.htm#HRS%20Rule

.



### 2 U.S. Environmental Protection Agency (EPA), Superfund Chemical Data Matrix (SC DM) Methodology, January 2004, 15 pages. A complete copy of SCDM is available at http://www .epa.gov/superfund/sites/npl/hrsres/tools/scdm.htm.

3 Weston Solutions, Inc., New Idria Mercury Mine, Expanded Site Inspection, Idria, San Benito County, California, Sampling and Analysis Plan, April 2010, 48 pages.

4 Ecology & Environment, Inc., New Idr ia Mercury Mine, Preliminary Assessment/Site Inspection, March 31, 1998, 68 pages.

5 Dames & Moore, Application for Facility Permit/Waste Discharge, New Idria Mine, Idria, California 95021, April 21, 1989, 22 pages.

6 Weston Solutions, Inc., Expanded Sit e Inspection Report, New Idria Mercury Mine, San Benito County, California, October 2010, 1 20 0 pages.

7 Bureau of Land Management, Draft Clear Creek Management Area Resource Management Plan & Environmental Impact Statement, Hollister, California,

November 2009, 735 pages.

8 University of California Santa Cruz, Mercury Speciation in Acid Mine Drainage: New Idria Quicksilver Mine, California, September 1998, 41 pages.

9 California Regional Water Quality Control Board, Central Valley Region, New Idria

Mine , San Benito County

– Complaint Investigation, June 2, 1975, 4 pages.

10 California Regional Water Quality Control Board, Central Valley Region, Inspection of New Idria Mine, San Benito County, July 22, 1988, 6 pages.

11 California Regional Water Quality Control Board, Central Valley Region, New Idria Mine, San Benito County, March 7, 2003, 15 pages.

12 TechLaw, Inc., P otentially Responsible Party and Insurance Archeology Search Report, New Idria Mercury Mine Site, San Benito County, California, June 5, 2006, 205 pages.

13 U.S. Environmental Protection Agency, Region IX, Wetlands Regulatory Office (WTR

- 8)

, Summary of Site Inspection to Verify the Presence of Jurisdictional Wetlands for the New Idria Mercury Mine Site, including San Carlos and Silver

Cree ks, San Benito and Fresno Counties, California

, December 16 , 2010, 1 8 pages.

14 Weston Solutions, Inc., Expanded Site Inspection. Logbook, New Idria Mercury Mine, July 6, 2010 through July 23, 2010, 8 pages.

15 U.S. Bureau of Mines, Mercury Potential of the United States, Information Circular 8252, 1965 , 34 pages

.

16 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.

### 3/2011 7 

### 17 Count y of San Benito, Proposal by the County of San B enito before the Central Valley Regional Water Quality Control Board

– Request for Investigation, Enforcement, and Regional Planning necessary to clean up and abate the discharge of pollutants from

the New Id ria Mercury Mine in San Benito County, undated , 28 pages

. 18 U.S. Geological Survey, Idria , California 7.5 Minute quadrangle 1969

, 1 p age

.

19 National Operations Center, Sampling and Analysis Plan, Archer Mine, April 15, 2009, 12 pages.

20 Weston Soluti ons, Inc., Surface Water Pathway and Target Distance Limit Map, New

Idria Mercury Mine, December 13, 2010, 1 page.

21 Weston Solutions, Inc., Site Latitude and Longitude and Source Area, New Idria Mercury Mine, December 13, 2010, 1 page.

22 Meierer, Bob, CompuChem, Memorandum to Stan Kott, ESAT/ICF

- LDC, Case#: 40334, SDG#: MY71L3, October 5, 2010, 339 pages.

23 Meierer, Bob, CompuChem, Memorandum to Stan Kott, ESAT/ICF

- LDC, Case#: 40334, SDG#: MY71M9, October 11, 2010, 264 pages.

24 CompuChem, Memorandu m to Garrett Peterson, U.S. Environmental Protection Agency, Case# 40334, SDG#: MY71N3, undated, 271 pages.

25 CompuChem, Memorandum to Garrett Peterson, U.S. Environmental Protection Agency, Case# 40334, SDG#: MY71S3, undated, 341 pages.

26 CompuChem, M emorandum to Mary O’Donnell, U.S. Environmental Protection Agency, Case# 40334, SDG#: MY71S4, undated, 268 pages.

27 CompuChem, Memorandum to Mary O’Donnell, U.S. Environmental Protection Agency, Case# 40334, SDG#: MY71S5, undated, 510 pages.

28 CompuChe m, Memorandum to Mary O’Donnell, U.S. Environmental Protection Agency, Case# 40334, SDG#: MY71 S6, undated, 509 pages.

29 Reilly, Amanda K.C., Weston Solutions, Inc., Memorandum Re: Sample Quantitation Limits, January 6, 2011, 5 pages.

30 Susan Moore , U.S . Department of the Interior, Fish and Wildlife Service, letter addressed to Ms. Debbie Schechter, USEPA, Subject: United States Fish and Wildlife Service Review of Expanded Site Investigation Report on the New Idria Mercury Mine, San Benito County, Califo rnia, January 26, 2011, 9 p ages

.

31 Western Regional Climate Center, Period of Record Monthly Climate Summary,

Idria , California, www.wrcc.dri.edu , data extracted January 2 6 , 2011, 1 p ages

.

32 U.S. Fish and Wildlife Service, Species Report, Environmental Conservation Online System, Listed Animals, http://ecos.fws.gov/tess_public/pub/listedAnimals.jsp , data extracted January 26, 2011, 77 pages.

33 U.S. Fish and Wildlife Service, Species Report, Environmental Conservation Online System, Listed Plants, http ://ecos.fws.gov/tess_public/pub/listedPlants.jsp , data extracted January 26, 2011, 42 pages.

### 3/2011 8 

### ACRONYM LIST

AMD Acid Mine Drainage

BLM Bureau of Land Management

CERCL A Comprehensive Environmental Response, Compensation, and Liability Act

CLP Contract Laboratory Program

CLPAS Contract Laboratory Program Analytical Services

EPA U

. S

. Environmental Protection Agency

ESI Expanded Site Inspection

gpm gallons per minute

HRS Hazard Ranking System mg/kg milligrams per kilogram μg/l micrograms per lite r NIMM New Idria Mercury Mine

PPE Probable Point of Entry

ppm parts per million

SAP Sampling and Analysis Plan

USFW U.S. Fish and Wildlife Service

XRF X

- ray Fluorescence

### 3/2011 9 

### NOTES TO THE READER

1

. Attachment contains the following maps:

Figure 1: N ew Idria Mercury Mine Site Location Map

Figure 2: Sample Locations

– Map 1A

Figure 3: Historic Sample Locations

– Map 1B

Figure 4: Sample Locations

– Map 1C

Figure 5: Historic Sample Locations

– Map 1D

Figure 6: Sample Locations

– Map 2A

Figure 7: H istoric Sample Locations

– Map 2B

Figure 8: Sample Locations

– Map 3

Figure 9: Sample Locations

– Map 4A

Figure 10: Historic Sample Locations

– Map 4B

Figure 11: Sample Locations

– Map 5A

Figure 12: Historic Sample Locations

– Map 5B

### 3/2011 10 

### SITE DESCRIPT ION

The New Idria Mercury Mine (NIMM) is located at the abandoned town of Idria in San Benito County, California

, approximately 135 miles southeast of San Francisco within the New Idria Mining

District , Sections 28, 29, and 32, Township 17 South, Range 12 East of the Mount Diablo Meridian.

The facility property covers approximately 880 acres and is located 70 miles southeast of Hollister,

California ( Ref. 6, p. 7 ; Ref. 12, p. 2)

.

The New Idria Mercury Mine operated from approximately 1854 to 1972. Estima tes ranging from 0.5 to 2 million cubic yards of waste rock and calcines (processed mercury ore) cover 48.677 acres throughout the facility and along San Carlos Creek

. The abandoned Town of Idria is comprised of dozens of dilapidated buildings. A large f urnace and process area and other mine working features

remain at the property

. Acid mine drainage ( AMD ) discharges from the main adit at the facility

, known as the Level 10 Adit

. The AMD then enters an unnamed tributary that flows between and is

in dire ct contact with a waste rock pile and calcine tailings pile. It discharges to San Carlos Creek, approximately 2,000 feet away from the Level 10 adit. The AMD channel bypasses the former settling basin (AMD pond), located near the discharge point (Ref. 5, p. 7; Ref. 6, p. 7

- 8, Photo 23,

Photo 26 ; Ref. 7, p. 263; Ref. 12, pp. 2

- 3 ; Ref. 21 ).

The New Idria mining claim was declared in 1854 by prospectors and investors. In 1857 the first

brick furnace to roast cinnabar ore was built at the Facility . The mi ne operations expanded to include San Carlos, Aurora, and Molina mines and miles of tunnels, shafts and drifts were used to access the cinnabar. In the 1920s, the overburden was stripped down to form pits in order to access cinnabar. The mining continued nearly uninterrupted until the early 1970s with a few idle and low productivity periods due to economic lows in mercury values and land owner disputes. Several furnaces were built over the years including four large furnaces still located at the facility adjacent to the Level 10 adit. Mercury was extracted from the cinnabar ore by crushing the ore and roasting it to release elemental mercury vapor which was cooled and condensed for bottling. The roasting process

is called calcination and the roasted ore is known as calcines

, which still contain some soluble mercury. Some of the older tailings piles were reprocessed as mercury extraction methods improved.

The furnaces at the Facility were also used to process mercury ore from the San Carlos and Aurora

M ines which was transported by a 2

- mile aerial tram or through the Level 10 adit. Ore was also trucked in from the Alpine, Anita, North Star, and other mines to be processed at the New Idria furnace. The New Idria Mine was reported to be the second larges t mercury mine in the country and produced over 500,000 flasks (38,250,000 pounds) of mercury. One flask contains 76.5 pounds of

mercury (Ref. 6, p. 7; Ref. 12, pp. 2

- 3

, 20, 23

- 25, 28 ).

Over 30 miles of tunnels and 20 levels were constructed at the f acil ity . The Level 10 adit was used as the main haulage level and is connected to other levels by shafts and raises. The extensive mine levels have flooded with ground water, or possibly surface water, which reacts with the high iron and

sulfur content of th e bedrock to form an acidic solution. The ground water drains from the Level 10

A dit as AMD and flows into an unnamed tributary . The AMD and unnamed tributary are presently

not treated and flow through tailings piles and discharge to San Carlos Creek. S an Carlos Creek

### 3/2011 11 

### flows along the base of massive calcine tailings piles for a length of approximately 2,500 feet (Ref. 6, p. 8 ; Ref. 10, p. 1; Ref. 11, p. 6; Ref. 15, pp. 29

- 30 ).

Surface water from the s ite drains to San Carlos Creek which flows to Silver Creek and then to Panoche Creek. Panoche Creek flows to the Mendota Pool and San Joaquin River during periods of heavy precipitation and flood events. The Mendota Pool and San Joaquin River are recreational fisheries and are located approximately 45 rive r miles downstream from the Site. The San Joaquin River flows to the San Francisco Bay

, which is a commercial fishery. Sensitive habitats and wetlands are found along the surface water pathway between the Site and the San Joaquin River

. The entire lengt h s of San Carlos Creek and Silver Creek downstream of the site sources are documented wetlands (Ref. 6, p. 6 ; Ref. 13, p. 6 ).

Numerous complaints regarding degradation of San Carlos Creek by AMD have been made by property owners downstream of the New Idri a Mercury Mine (Ref. 6, p p

. 9

- 10 ; Ref. 9, pp. 1

- 4; Ref. 10, pp. 1

- 6; Ref. 11, p. 8). Previous investigations of surface water downstream of the site have demonstrated impacts to surface water bodies by mercury and other metals from site sources ( Ref. 4,

p

. 28 ; Ref. 6, p. 9; Ref. 8, p. 19; Ref. 9, pp. 1

- 4; Ref. 10, pp. 1

- 6; Ref. 11, p. 8 )

.

In July 2010, EPA tasked Weston Solutions, Inc. (WESTON) to conduct an Expanded Site Inspection ( ESI ) of the New Idria Mercury Mine facility , including the collection of environmental samples. The specific sampling objectives were to collect data that could be used to document whether a release of mercury or other metals had occurred to San Carlos and Silver Creeks that could

be attributed to the Site . An observed relea se of arsenic, cadmium, copper, lead, mercury, nickel, selenium, and zinc was documented by direct observation and by chemical analysis . These hazardous substances were documented in hazardous substance sources at the site, including the Calcine Tailings Piles and the Level 10 Adit AMD . The Calcine Tailings Piles and the Level 10 Adit AMD were observed to be in direct contact with San Carlos Creek. Mercury attributable to the

site was detected at concentrations significantly above background to a distanc e of 19.9 miles

downstream of the site sources (Ref. 6, p p. 5, 42

- 43 ).Source Characterization 12 

### 2.2 SOURCE CHARACTERIZATION

2.2.1 SOURCE IDENTIFICATION

Name of source: Calcine Tailings Pile s Number of source: 1

Source Type : Pile

Description and Location of Source ( see Reference 6, page 55 for map of Source 1 ):

Several furnaces were built over the years at the New Idria Mercury Mine facility, including four large furnaces still located at the facility adjacent to the Level 10 A dit. Mercury was extracted from

the ci nnabar ore by crushing the ore and roasting it in the furnaces to release elemental mercury vapor which was cooled and condensed for bottling. The roasting process is called calcination and the roasted ore is known as calcines, which still contain some so lub le mercury. Some of the older tailings piles were reprocessed as mercury extraction methods improved. Extensive waste rock and calcine tailings piles are still present and cover a large portion of the property. The Southern and Northern Calcine Tailing s Piles are estimated to cover 48.677 acres

. The calcine tailings area was calculated by creating a polygon of observable tailings from aerial images and filed o bservations and processing data (Ref. 6, p. 7 ; Ref. 12, p. 17; Ref. 21 )

.

The furnaces at th e f acility were also used to process mercury ore from the San Carlos and Aurora Mines which were transported by a 2

- mile aeria l tram or through the Level 10 A dit. Ore was also trucked in from the Alpine, Anita, North Star, and other mines to be processed at the New Idria

furnace. The New Idria Mine was reported to be the second most productive mercury mine in North America and produced over 500,000 flasks (38,250,000 pounds) of mercury. One flask contains 76.5 pounds of mercury (Ref. 6, p. 7; Ref. 12, p. 20

- 21, 23, 28 ).Source No: 1

Source Characterization 13 

### 2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

In July, 2010, EPA tasked WESTON to conduct an ESI of the New Idria Mercury Mine, including the collection of environmental samples. The specific sampling objectives were to coll ect data that could be used to document whether a release of mercury or other metals had occurred to San Carlos

and Silver Creeks that could be attributed to the Site. The field work was conducted in accordance with WESTON’s Sampling and Analysis Plan (SA P), approved by the EPA in April 2010 ( Ref. 3, p. 1; Ref. 6, p p. 15

- 16 ).

WESTON implemented the SAP during July 19

- 23, 2010. WESTON collected samples from the Calcine Tailings Piles. Background soil samples were collected from locations south of the Fac ility at areas upgradient from mercury mining activities. Samples were collected from 10 soil/tailing s locations. Samples were submitted to Liberty Analytical under the EPA Contract Laboratory Program (CLP) for metal analysis by EPA CLPAS ILM05.4. The a nalytical data were validated by

the EPA (Ref. 6, p. 16 ).

Calcine tailings samples were collected to document the presence of a hazardous substance source to
surface water. WESTON collected 10 soil samples to establish a source of metals at the Site. So il samples NIMM

- TL

- 3 through NIMM

- TL

- 5 were collected from the southern calcine tailings pile

, and soil sample s NIMM

- TL

- 6 through NIMM

- TL

- 10 were collected from the northern calcine tailings pile

. Soil samples NIMM

- SS

- 1 and NIMM

- SS

- 2 were collected from b ackground locations (Ref. 6, p. 19). Sample locations are shown on Figure 2 and Figure 4

.

Three samples were collected at each sampling location . Based on the BLM standard procedure for mercury mine sampling, the samples were sifted using a disposable s ieve to obtain a grain size of

less than 1.3 millimeters (Ref. 6, p. 19; Ref. 19, p. 10

- 11)

. The sieved samples were field screened

for mercury concentrations using an x

- ray florescence (XRF) metal analyzer

. The sieved sample exhibiting the highest mercu ry concentration was selected for laboratory analyses. The coarse fraction of the sample and the sieved portion of the sample were weighed to determine the percentage of fines in the matrix of each sample submitted to the laboratory. The XRF mercury

meas urements ranged from 35 to 785 parts per million (ppm) for the calcine tailings samples. Samples for laboratory analysis were contained in 4

- ounce glass containers and placed on ice for preservation ( Ref. 6 , p. 19 ; Ref. 14, p. 2 )

.

The weighted fractions of the sample used to determine the percentages of fines are presented in the

table below.Source No: 1

Source Characterization 14 

### Sample ID Total Weight (grams) Sieved Weight

- fines (grams) Remaining

-

coarse (grams) Percentage of fines (%) References

NIMM

- TL

- 3 (southern calcine

taili ngs pile) 348 199 149 57.18 Ref. 6, p. 885

NIMM

- TL

- 4 (southern calcine

tailings pile) 214 124 90 57.94 Ref. 6, p. 886

NIMM

- TL

- 5 (southern calcine

tailings pile) 265 79 186 29.81 Ref. 6, p. 887

NIMM

- TL

- 6 (southern calcine

tailings pile) 258 135 123 52 .33 Ref. 6, p. 888

NIMM

- TL

- 7 (northern calcine

tailings pile) 683 161 522 23.57 Ref. 6, p. 889

NIMM

- TL

- 8 (northern calcine

tailings pile) 367 75 292 20.44 Ref. 6, p. 890

NIMM

- TL

- 9 (northern calcine

tailings pile) 755 118 637 15.63 Ref. 6, p. 891

NIM M

- TL

- 10 (northern calcine

tailings pile) 848 197 651 23.23 Ref. 6, p. 892



### The tailings samples presented in the table below are representative of New Idria Mercury Mine calcine tailings pile materials. The source samples are not compared to background levels because the media sampled is waste tailings (Ref. 21)

.Source No: 1

Source Characterization 15 Sample ID Date Hazardous
Substance Hazardous Substance

Concentration (mg/kg fines ) SQL (mg/kg) References

NIMM

- TL

- 3 (southern calcine

tailings pile) 7/19/10 Arsenic 22.7 1.0 1 Ref. 6, pp. 2 0

- 21, 1133, 1135

- 1136, 1139; Ref. 14, p. 2 ; Ref. 16, p p . 8, 18 ; Ref. 22, p p . 2, 39, 67, 103, 104, 108,

115 ; Ref. 29 Cadmium 1.2 J 1 (0.85) 0.504

Copper 59.9 2.52

Lead 18.1 1.0 1 Mercury 191 2.016

Nickel 31.3 4.032

Zinc 56.2 6.048

NIM M

- TL

- 4 (southern calcine

tailings pile) 7/19/10 Arsenic 17.7 0.995 Ref. 6, pp. 20

- 21

, 1133, 1135

- 1136,

1139 ; Ref. 14, p. 2 ; Ref. 16, p p . 8, 18 ; Ref. 22, p p . 2, 40, 67, 103, 104, 108,

115 ; Ref. 29 Cadmium 0.51 J 1 (0.36) 0.497

Copper 39.2 2.49

Lea d 9.0 0.995 Mercury 134 5.03

Nickel 20.4 3.98

Zinc 39.3 5.97

NIMM

- TL

- 5 (southern calcine

tailings pile) 7/19/10 Arsenic 16.2 0.964 Ref. 6, pp. 20

- 21

, 1133, 1135

- 1136,

1139 ; Ref. 14, p. 2 ; Ref. 16, p p . 8, 18 ; Ref. 22, p p . 2, 41, 67, 103, 104, 108,

115 ; Ref. 29 Cadmium 1.3 J 1 (0.92) 0.482

Copper 48.5 2.41

Lead 49.5 0.964 Mercury 446 10.14

Nickel 67.7 3.86

Zinc 396 5.78

NIMM

- TL

- 6 (southern calcine

tailings pile) 7/19/10 Arsenic 17.2 0.965 Ref. 6, pp. 20

- 21

, 1133, 1135

- 113 6,

1139 ; Ref. 14, p. 2 ; Ref. 16, p p . 8, 18 ; Ref. 22, p p . 2, 42, 67, 103, 104, 108,

115 ; Ref. 29 Cadmium 0.99 J 1 (0.7) 0.483

Copper 47.1 2.41

Lead 61.5 0.965 Mercury 38.7 2.01

Nickel 159 3.86

Zinc 104 5.79Source No: 1

Source Characterization 16 Sample ID Date Hazard ous Substance Hazardous Substance

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

NIMM

- TL

- 7 (northern calcine

tailings pile) 7/19/10 Arsenic 23.6 0.978 Ref. 6, pp. 20

- 21

, 1133, 1135

- 1137

, 1139 ; Ref. 14, p. 2 ; Ref. 16, p p . 8, 18 ; Ref. 22, p p . 2, 43,
67, 103, 104, 108,

115 ; Ref. 29 Cadmium 1.5 J 1 (1.06) 0.489

Copper 69.0 2.45

Lead 23.5 0.978 Mercury 3.8 0.096

Nickel 66.1 3.91

Zinc 50.8 5.87

NIMM

- TL

- 8 (northern calcine

tailings pile) 7/19/10 Arsenic 18.8 0.99 Ref. 6, pp. 20

- 21

, 113 3, 1135

- 1137,

1139 ; Ref. 14, p. 2 ; Ref. 16, p p . 8, 18 ; Ref. 22, p p . 2, 45, 67, 103, 104, 108,

115 ; Ref. 29 Cadmium 1.3 J 1 (0.92) 0.495

Copper 60.3 2.48

Lead 18.2 0.99 Mercury 91.6 5.05

Nickel 99.8 3.96

Zinc 98.7 5.94

NIMM

- TL

- 9 (nor thern calcine

tailings pile) 7/19/10 Arsenic 27.7 1.01 Ref. 6, pp. 20

- 21

, 1133, 1135

- 1137,

1139 ; Ref. 14, p. 2 ; Ref. 16, p p . 8, 18 ; Ref. 22, p p . 2, 46, 67, 103, 105, 108,

115 ; Ref. 29 Cadmium 1.6 J 1 (1.13) 0.505

Copper 79.8 2.53

Lead 22.5 1.01 Mercury 72.3 2.01

Nickel 203 4.04

Zinc 71.3 6.06

NIMM

- TL

- 10 (northern calcine

tailings pile) 7/19/10 Arsenic 26.0 0.974 Ref. 6, pp. 20

- 21

, 1133, 1135

- 1137,

1139 ; Ref. 14, p. 2 ; Ref. 16, p p . 8, 18 ; Ref. 22, p p

. 3 , 47, 67, 103, 105, 108,

115 ; R ef. 29 Cadmium 1.8 J 1 (1.28) 0.487

Copper 73.7 2.44

Lead 26.2 0.974
Mercury 28.9 2.03

Nickel 228 3.90

Zinc 88 .4 5.84Source No: 1

Source Characterization 17 Sample ID Date Hazardous
Substance Hazardous Substance

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

NIM M

- TL

- 11 (duplicate of

NIMM

- TL

- 10) 7/19/10 Arsenic 26.7 1.0 Ref. 6, pp. 20

- 21

, 1133, 1135

- 1137,

1139 ; Ref. 14, p. 2 ; Ref. 16, p p . 8, 18 ; Ref. 22, p p . 2, 48, 67, 103, 105, 108,

115 ; Ref. 29 Cadmium 1.8 J 1 (1.28) 0.5

Copper 74.2 2.5

Lead 25.0 1.0 Mercury 31.5 2.02

Nickel 231 4.0

Zinc 90.3 6.0

mg/kg: milligrams analyte per kilogram tailings

J 1 : The analyte was positively identified ; however

, the reported value is an estimate due to ICP inter

- element interference problems. The

result was reported from undiluted analyses that contained iron concentrations above the level present in the interference check sam ple (ICS) solution, therefore the applied inter

- element correction (IEC) factors may not sufficiently compensate.

For cadmium the value reported may be biased high. However, the presence of the analyte in the sample is not in doubt. The adjusted value is presented in parentheses.

SQL: Sample Quantitation Limit. The S QL s provided in this table are CLP contract

- required detecti on limits (CRDLs) for that analyte with any dilution factors, volume adjustments, or percent solids for that analysis taken into account. SQLs were calculated as follows:

DF x kg 1 g 1000

x mL 1000 1L

x %S x wet wgt) (g weight sample (mL) volume final

x μg 1000 mg 1

x L μg CRDL dry wgt kg mg SQL ** **  ** **  ** ** 

**= **  ** **  ** **  ** **  ****

Where:

Final volume (mL) is the final extract volume fo llowing sample preparation Sample weight (g wet wgt) is the weight of the sample used for analysis

% S is % solids value divided by 100; % solids is determined as follows: (g dry weight of sample used for analysis )/(g wet weight of sample used for analys is ) x100%

DF is the dilution factor for the instrumental analysis



### List of Hazardous Substances Associated with Source

Arsenic, Cadmium, Copper, Lead, Mercury

, Nickel, ZincSource No: 1

Source Characterization 18 

### 2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY

Containment Description Containment

Factor Value Ref erence

Release via overland migration and/or flood: The Calcine Tailings

Piles are unlined and were observed to be in direct contact with San

Carlos Creek. In addition, there was no engineered cover or retaining wall suppor ting the waste rock from coming into contact with surface

water

. 10 Ref. 1, Table 4

- 2; Ref, 6, pp. 5 5

, Photos 7, 8, 26, 27, 28, 29, 30, 31, 32,

34.Source Characterization 19 

### 2.4.2 HAZARDOUS WASTE QUANTITY

2.4.2.1.1 Tier A: Hazardous Constituent Quantity

- Not Evaluated (NE)

The information available is not sufficient to meaningfully evaluate Tier A, hazardous constituent quantity; therefore it is not possible to adequately determine a hazardous constituent quantity for the Calcine Tailings Piles (Ref. 1, Section 2.4.2.1.1). Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

2.4.2.1.2 Tier B: Hazardous Wastestream Quantity

- NE

The information available is not sufficient to meaningfully evaluate Tier B, hazardous wastestream quantity; therefore, it is not possible to adequately determine a hazardous waste quantity for the Calcine Tailings Piles (Ref. 1, Section 2.4.2.1.2). 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

- NE

The information available is not sufficient to meaningfully evaluate Tier C

, volume ; therefore it is not possible to adequately determine a volume for the Calc ine Tailings Piles (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

The Southern and Northern Calcine Tailings Piles are estimated to cover 48.677 acres . The calcine tailings area was calculated by creating a polygon of observable tail ings from aerial images and fiel d observations and processing data using mapping tools (Ref. 21 )

. Therefore:

48.677 acres x 43

, 560 square feet = 2,120,370.12 square feet 2,120,370.12 / 13 = 163,105.3938 (Ref. 1, Table 2

- 5)

Area Assigned Value: 163,105.3938

2.4.2.1.5 Source Hazardous Waste Quantity Value

Highest assigned value assigned from Ref. 1, Table 2

- 5: 163,105.3938Source Characterization 20 

### 2.2.1 SOURCE IDENTIFICATION

Name of sourc e: Level 10 Adit AMD Number of source: 2

Source Type : Other

Description and Location of Source ( see Reference 6, page 55 for map of Source 2 ):

Over 30 miles of tunnels and 20 levels were constructed as part of mining operations at the New

Idria Mercu ry Mine

. The Level 10 A dit was used as the main haulage level and is connected to other levels by shafts and raises. The extensive mine levels have flooded with ground water , or possibly surface water, which reacts with the high iron and sulfur content o f the bedrock to form an acidic

solution. The ground water drains from the Level 10 A dit as AMD. Once the ground water discharges from the Level 10 Adit, it enters an unnamed tributary that bypasses the former settling pond (AMD pond) and runs between an d is in direct contact with a waste rock pile and the southern calcine tailings pile (Source 1). It discharges to San Carlos Creek, approximately 2,000 feet away

from the Level 10 adit

. The AMD is presently not treated prior to discharging (Ref. 6, p. 7

- 8 , Photo 23, Photo 26 ; Ref. 10, p. 1; Ref. 11, p. 6 ; Ref. 15, pp. 29

- 30 ).

In an attempt to control the flow of water from the mine, the Level 10 A dit was originally sealed

with a concrete bulkhead. However, as water backed up in the mine, it eventually b roke through the

bulkhead . Discharge to San Carlos Creek has been observed to be approximately 8 to 5 0 gallons per minute (gpm) ( Ref. 4, Photo 6; Ref. 5, p. 9; Ref. 10, p. 1; Ref. 11, p p . 6 , 12 ).Source No: 2

Source Characterization 21 

### 2.2.2 HAZARDOUS SUBSTANCES ASSOCIATED WITH THE SOURCE

In July 2010, EPA tasked WESTON to conduct an ESI of the New Idria Mercury Mine, including the collection of environmental samples. The specific sampling objectives were to collect data that could be used to document whether a release of mercury or other metals had occurred to San Carlos

and Silver Creeks that could be attributed to the Site. The field work was conducted in accordance with WESTON’s SAP, approved by the EPA in April 2010 ( Ref. 3, p. 7 ; Ref. 6, p p. 15

- 16 ).

WESTON implemented the SAP during July 19

- 23, 2010. WESTON collected samples from the

C alcine T ailings Piles and AMD at the Site and stream samples (surface water and sediments) from the surface water pathway. Background soil and stream samples were collected from locations south

of the Site at areas upgradient from mercury mining activities. Samples were collected from 10 soil/tailing locations, 34 sediment locations, and 15 surface water locations. Samples were submitted to Liberty Analytical under the EPA CLP for metal analysis by E PA CLPAS ILM05.4. The analytical data w ere validated by EPA (Ref. 6, p. 16 ).

AMD samples were collected to document the presence of hazardous substance sources to surface

water. Filtered and un

- filtered surface water samples NIMM

- SW

- 4 we re collected fro m AMD

impacted surface water approximately 6 to 8 feet from the Level 10 A dit (Ref. 6, p. 22 , Photo 21 ). Sample locations are shown on Reference 6, page 5 5

.Source No: 2

Source Characterization 22 

### - Source Samples:

AMD Source Concentrations

– Total Metals ( μg/l )

Sample ID Date Hazardous
S ubstance Hazardous
Substance

Concentration SQL References

NIMM

- SW

- 4 (Level 10 Adit) 7/22/2010 Arsenic 72.4 1.0 Ref. 6, pp. 23, 1170, 1171, 1184

- 1187,

1190 ; Ref. 14, p. 6 ; Ref. 16, p p . 8, 18 ; Ref. 25, p. 2; Ref. 27, p p

. 34, 54, 70,

71 ; Ref. 29 Cadmium 1 .7 1.0

Selenium 11.2 J 1 ( 9.82) 5.0

Zinc 2,500 J 2 2.0

μg/l : micrograms analyte per liter water

J 1 : The analyte was positively identified ; however

, the reported value is an estimate due to matrix spike recovery results being outside method
quant itation control limits. The reported value may be bias high. However, the presence of the analyte in the sample is not in d oubt. The adjusted value is presented in parentheses.

J 2 : The analyte was positively identified ; however

, the reported value is a n estimate due to the serial dilution percent differences being outside the method quantitation control limits. The value reported may be biased low. However, the presence of the analyte in the s ample is not in

doubt.

SQL: Sample Quantitation Limit. Th e S QL s provided in this table are CLP contract

- required detection limits (CRDLs) for that analyte with any dilution factors, volume adjustments, or percent solids for that analysis taken into account. SQLs were calculated as follows:

**( )**  DF x (mL) volume initial (mL) volume final

x L μg CRDL / SQL ** **  ** **  ** ** 

**=** L μg

Where:

Final volume (mL) is the final extract volume following sample preparation Initial volume (mL) is the volume of sample used

DF is the dilution factorSource No: 2

Source Characterization 23 

### AMD Source Concentrations

– Dissolved Metals ( μg/l )

Sample ID Dat e Hazardous
Substance Hazardous
Substance

Concentration SQL References

Arsenic 66.1 1 .0

NIMM

- SW

- 4 (Level 10 Adit) 7/22/2010 Ref. 6, pp. 23, 1178, 1195, 1197

- 1198 ; Ref. 14, p. 6 ; Ref. 16, p p . 8,

18 ; Ref. 26, p. 2; Ref. 28, p p

. 34, 52, 68, 70 ; Ref. 2 9 Cadmium 1.4 1.0 Copper 3.2 2.0

Nickel 1,440 1.0

Selenium 10. 6 J 1 (9.3) 5.0

Zinc 2,350 2.0

μg/l : micrograms analyte per liter water

J 1 : The analyte was positively identified ; however

, the reported value is an estimate due to matrix spike recovery results being outside method quantitation control limits. The reported value may be bias high. However, the presence of the analyte in the sample is not in doubt. The adjusted value is presented in parentheses.

SQL: Sample Quantitation Limit. The S QL s provided in this table are CLP contract

- required detection limits (CRDLs) for that analyte with any dilution factors, volume adjustments, or percent solids for that analysis taken into account. SQLs were calculated as follows:

**( )**  DF x (mL) volume initial (mL) volume final

x L μg CRDL / SQL ** **  ** **  ** ** 

**=** L μg

Where:

Final volume (mL) is the final extract volume following sample preparation Initial volume (mL) is the volume of sample used

DF is the dilution factor



### List of Hazardous Substances Associated with Source

Arsenic, Cadmium, Co pper, Nickel, Selenium, ZincSource No: 2

Source Characterization 24 

### 2.2.3 HAZARDOUS SUBSTANCES AVAILABLE TO A PATHWAY

Containment Description Containment

Factor Value Reference

Release via overland migration and/or flood: The AMD was observed to be flowing directly into the unlined and unnamed tributary that flows into San Carlos Creek with no

containment. There was no engineered cover or retaining

wall to aid in the containment of the AMD. 10 Ref. 1, Table

4

- 2; Ref. 6,

pp. 6

- 8, 41

, 54, Photos 5, 6, 22, 24Source No: 2

Source Characterization 25 

### 2.4.2 HAZARDOUS WASTE QUAN TITY

2.4.2.1.1 Tier A: Hazardous Constitue nt Quantity

The information available is not sufficient to meaningfully evaluate Tier A, hazardous constituent quantity; therefore it is not possible to adequately determine a hazardous constituent quantity for the

Level 10 Adit AMD (Ref. 1, Section 2.4.2.1.1). Scoring proceeds to the evaluation of Tier B, hazardous wastestream quantity (Ref. 1, Section 2.4.2.1.2).

Hazardous Constituent Quantity Value: NE

2.4.2.1.2 Tier B: Hazardous Wastestream Quantity

T he rate of AMD discharging from the Level 10 adit has been measured over numerous years and investigations. In April 1988, the RWQCB conducted an inspection on the NIMM and observed the discharge from the Level 10 adit to be approximately 50 gpm (Ref. 10, p. 1). In 1989, the discharge was reported to have a range of 20 to 50 gpm, depending on year and season (Ref. 5, p. 9). In June 1997, the discharge from the Level 10 adit was observed to be 8 gpm (Ref. 4, Photo 6). In 2003, the RWQCB conducted Site In vestigation on the NIMM property the discharge rate was observed to be greater than 10 gpm (Ref. 11, p. 6). Using a conservative flow rate estimate

based on these measurements , the following hazardous wastestream quantity is calculated:

For one year of d ischarge:

8 gpm = 4,204

, 8 00 gallons per year 4,204,800 gallons = 42,048,000 pounds 42,048,000 pounds / 5,000 = 8,409.6 (Ref. 1, Table 2

- 5)

Hazardous Wastestream Quantity Value: 8,409.6

Tier C: Volume

The information available is not sufficient to me aningfully evaluate Tier C

, volume ; therefore it is not possible to adequately determine a volume for the Level 10 Adit AMD (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 : NESource No: 2

Source Characterization 26 

### Tier D: Area

The information available is not sufficient to meaningfully evaluate Tier D, area; therefore it is not possible to adequately determine an area for the Level 10 Adit AMD (Ref. 1, Section 2.4.2.1.4).

Area Assigned Value: NE

2.4. 2.1.5 Source Hazardous Waste Quantity Value

Highest assigned value assigned from Ref. 1, Table 2

- 5 (Ref. 1, Section 2.4.2.1.5) : 8,409.627 

### SUMMARY OF SOURCE DESCRIPTIONS

Source

No. Source

Hazardous

Waste Quantity

Value Source

Hazardous

Constituent

Quantity Complete? (Y/N) Containment Factor Value by Pathway

Ground

Water (GW) (Ref. 1,

Table 3

- 2) Surface Water (SW) Air

Overland/

flood (Ref. 1,

Table 4

- 2) G W to
SW (Ref. 1,

Table 3

- 2) Gas (Ref. 1,

Table 6

- 3) Particulate (Ref. 1,

Table 6

- 9)

1 1 63,105.3938 N NE 10 NE NE NE

2 8,409.6 N NE 10 NE NE NE

Total: 171,514.9938

NE: Not evaluated28 

### POSSIBLE SOURCES NOT SCORED

**•** AMD Pond . Historically, drainage from the Level 10 adit flowed through a shallow ponde d depression, referred to in previous reports as the “upper pond.” The water then flowed down the steep face of the dump into a channel incised in the calcines past a small holding pond (AMD Pond) , referred to in precious reports as the “lower pond.” Dur ing a 1989 investigation, the lower pond was breached and dry. However, the pond was historically used as a settling pond for drainage from the Level 10 adit (Ref. 4, Figure 2

- 4, Photo 2; Ref. 5, p. 9).

In 1997, a surface water sample and a tailings sam ple were collected adjacent to the AMD pond. The surface water sample, NIM

- 5 exhibited a mercury concentration of 0.4 ug/L, and the tailings sample, NIM

- 16, exhibited a mercury concentration of 42.2 mg/kg (Ref. 4, p. 21

- 22, Figure 2

- 4).

**•** Waste Rock Pile

. Immediately north of the Level 10 adit, is a graded pile of waste rock removed from the underground workings (Ref. 5, p. 8; Ref. 6, Fig. 4). The waste rock pile is a separate pile from the calcine tailings piles, which can distinctly be seen due to

the d ifferent colors of the piles (Ref. 6, Photo 27).

In 1997, a waste rock pile sample was collected and exhibited a mercury concentration of 27.1 mg/kg (Ref. 4, p. 22; Ref. 6, Figure 5).SWOF

- Likelihood of Release 29 

### 4.0 SURFACE WATER MIGRATION PATHWAY

4.1 OVERLAND/FLOOD MIGRATION COMPONENT

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

The HRS surface water pathway includes the unnamed tributary running through the NIMM property

to San Carlos Creek adjacent to site sources to Silver Creek and Silver Creek to Panoche Creek. The majority of San Carlos Creek is a perennial stream and becomes an intermittent stream before it

reaches the confluence of Larious Creek. Larious and Silver Creeks are also intermittent streams as
well as Panoche Cre ek at the Silver Creek Confluence. Although the streams are intermittent , they

are still evaluated under the HRS as an eligible surface water bodies as the drainage area receives

less than 20 inches of mean annual precipitation (Ref. 6, pp. 40 ; Ref. 12, p . 14 )

.

Ground water drains from the Level 10 A dit as AMD (Source 2)

. Once the ground water discharges from the Level 10 Adit, it enters an unnamed tributary that bypasses the former settling pond (AMD pond) and runs between and is in direct contact wit h a waste rock pile and the southern calcine tailings pile (Source 1). It discharges to San Carlos Creek, approximately 2,000 feet away from the Level 10 adit. (Ref. 6, p. 7

- 8, Photo 23, Photo 26; Ref. 10, p. 1; Ref. 11, p. 6; Ref. 15, pp. 29

- 30 ).

San Ca rlos Creek is mostly perennial, with only the lowermost reaches becoming intermittent by

mid

- summer. San Carlos Creek is bordered on both banks by wetlands along its entire length from

the New Idria Mercury Mine facility downstream to its confluence with Larious Creek (the beginning of Silver Creek) (Ref. 13, p. 4). Silver Creek is formed by the confluences of San Carlos and Larious creeks. Silver Creek is mostly intermittent, with seasonal flows typically forming a series of isolated bedrock pools inter rupted by long reaches of dry stream channel by mid

- summer. Silver Creek supports a mosaic riverine riparian, palustrine emergent, and palustrine shrub

- scrub wetlands that form a continuous border of varying widths on both banks for its entire length (Ref . 13, p. 5 ).

The remote Panoche

- Silver

- San Carlos Creek watershed is one of only a few large watersheds characterized by intermittent to perennial flow conditions flowing east to the San Joaquin Valley from the 200 mile long Diablo Range. San Carlos and Silver creeks are characterized by extensive wetlands in a predominantly arid, upland environment. These wetlands are continuous, running the entire length of both streams. As such, the aquatic and wetland habitats associated with San Carlos

and Silver c reeks, and their dependent animal species, are of regional ecological significance. The presence of the Pacific chorus frog and western pond turtle within this watershed is one measure of the importance of the aquatic and wetland features to regionally rar e aquatic species. In addition,

wetlands as sociated San Carlos and Silver C reeks perform other important ecological functions including surface and subsurface storage of water, energy dissipation, moderation of ground water flow or discharge, nutrient cyc ling, removal of imported elements and compounds, retention of particulates, organic carbon storage, the support of characteristic plant communities and detrital biomass, the maintenance of the spatial structure of animal habitat, the provision of habitatSWOF

- Likelihood of Release 30 

### interspersion and connectivity, and habitat support for the distribution and abundance of

invertebrates and vertebrates (Ref. 13, p. 6 )

.

The Level 10 A dit AMD (Source 2) flows overland through calcine and waste rock piles and discharges into San Carlos C reek south of the crossing of New Idria Road. The AMD

- impacted San

Carlos Creek flows northward along the base of the C alc ine Tailings P iles (Source 1) for a distance of approximately 2,500 feet resulting in additional mercury contamination. The AMD impa ct to San Carlos Creek is observed by the deposition of orange iron flocculants deposited on the stream bed and is apparent downstream to Silver Creek. San Carlos Creek becomes Silver Creek at the

confluence of Larious Creek

, approximately 4.7 miles downs tream of the site sources

. Silver Creek flows northward between the Griswold Hills and Tumey Hills and enters Panoche Creek approximately 19.5 river miles downstream from the Calc ine T aili ngs P iles (Ref. 6, p p

. 41 ; Ref. 20 )

.

Site sources are in direct co ntact with and are a continuous probable point of entry (PPE) in San Carlos Creek from approximately the location of samples NIMM

- SW

- 3 to NIMM

- SW

- 7. The furthest downstream PPE is at the location of sample NIMM

- SW

- 7 ( Ref. 6, p. 55

, Photo 23, Photo

26 ; Ref . 20 ). Sampling shows the presence of hazardous substances meeting the criteria for an

observed release attributable to the site to a distance of 19.9 miles downstream of the furthest

downstream PPE (Ref. 6, p. 29 ; Ref. 20 ). Although other mines existed in the vicinity of the site, the NIMM facility was the central processing area for the surrounding mines. The furnaces on the NIMM facility were used to process mercury ore from the San Carlos and Aurora mines which were transported by a 2

- mile aerial tra m and through the Level 10 adit (Source 2). In addition, ore was transported from the Alpine, Anita, North Star, and other mines to be processed at the NIMM furnace (Ref. 6, p p . 7 , 64 ; Ref. 12, p. 20, 23

- 25, 28 ). T he target distance limit for the New Idr ia Mercury Mine site is 19.9 miles (Ref. 20)

.SWOF

- Likelihood of Release 31 

### 4.1.2.1 Likelihood of Release

4.1.2.1.1 Observed Release

Direct Observation

- Basis for Direct Observation:

Both the Southern and Northern Calcine Tailings Piles (Source 1) were observed to be in direc t
contact with San Carlos Creek . San Carlos Creek flows along the base of the Northern and Southern Calcine Tailings Piles (Ref. 6, pp. Photo 26, Photo 34 ) . In addition, calcines attributable to the

NIMM site were observed in San Carlos Creek and Silver Creek to the target distance limit (Ref. 6, p. 36)

. The PPE for t he Level 10 A dit (Source 2) is the point at which the AMD leaves the mine. Once the ground water is discharged from the Level 10 adit, it was observed to be flowing

uncontrolled over wa ste rock and calcine tailings before enter ing San Carlos Creek ( Ref. 4, pp. 50 and 51; Ref. 6, pp. 6

- 8, 39 , 4 1

, 55

, 84

, 90 ).

- Hazardous Substances in Release:

Sample NIMM

- TL

- 4 was collected from the southern calcine tailings pile which was in direct

contac t with San Carlos Creek (Ref. 6, Photo 26).

Sample ID Date Hazardous
Substance Hazardous
Substance

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

NIMM

- TL

- 4 (southern calcine

tailings pile) 7/19/10 Arsenic 17.7 0.995 Ref. 6, pp. 20

- 21, 1133, 1135

- 113 6, 1139; Ref. 14, p. 4 ; Ref. 22,

p p . 2,40, 67, 103, 104, 108, 112, 115 ; Ref.

29 Cadmium 0.51J 1 (0.36) 0.497

Copper 39.2 2.49

Lead 9.0 0.995
Mercury 134 5.03

Nickel 20.4 3.98

Zinc 39.3 5.97

mg/kg: milligrams analyte per kilogram

J 1 : The analyte was positively identified ; however

, the reported value is an estimate due to ICP inter

- element interference problems. The result was reported from undiluted analyses that contained iron concentrations above the level present in the interferen ce check sample (ICS) solution, therefore the applied inter

- element correction (IEC) factors may not sufficiently compensate. For cadmium the value reported may be biased high. However, the presence of the analyte in the sample is not in doubt. The ad justed value is presented in parentheses.

SQL: Sample Quantitation Limit. The S QL s provided in this table are CLP contract

- required detection limits (CRDLs) for that analyte with any dilution factors, volume adjustments, or percent solids for that analys is taken into account. SQLs were calculated as follows:

DF x kg 1 g 1000

x mL 1000 1L

x %S x wet wgt) (g weight sample (mL) volume final

x μg 1000 mg 1

x L μg CRDL dry wgt kg mg SQL ** **  ** **  ** ** 

**= **  ** **  ** **  ** **  ****

Where:

Final volume (mL) is the final extract volume following sample preparationSWOF

- Likelihood of Release 32 Sample weight (g wet wgt) is the weight of the sample used for analysis

% S is % solid s value divided by 100; % solids is determined as follows: (g dry weight of sample used for analysis )/(g wet weight of sample used for analysis ) x100%

DF is the dilution factor for the instrumental analysis



### Sample NIMM

- SW

- 4 was collected from ground wate r discharging from the Level 10 adit, which was observed to be in direct contact with waste rock and calcine tailings piles prior to entering San Carlos Creek (Ref. 6, pp. 6

- 8, 39 , 4 1

, 55

, 84

, 90).

AMD Source Concentrations

– Total Metals ( μg/l )

Sample ID Date Hazardous
Substance Hazardous
Substance

Concentration SQL References

NIMM

- SW

- 4 (Level 10 Adit) 7/22/2010 Arsenic 72.4 1.0 Ref. 6, pp. 23, 1170, 1171, 1184

- 1187,

1190 ; Ref. 14, p. 6 ; Ref. 16, p p . 8, 18 ; Ref. 25, p. 2; Ref. 27, p p

. 34, 54, 70,

71 ; R ef. 29 Cadmium 1.7 1.0

Selenium 11.2 J 1 ( 9.82) 5.0

Zinc 2,500 J 2 2.0

μg/l : micrograms analyte per liter water

J 1 : The analyte was positively identified ; however

, the reported value is an estimate due to matrix spike recovery results being o utside method quantitation control limits. The reported value may be bias high. However, the presence of the analyte in the sample is not in doubt. The adjusted value is presented in parentheses.

J 2 : The analyte was positively identified ; however

, the reported value is an estimate due to the serial dilution percent differences being outside the method quantitation control limits. The value reported may be biased low. However, the presence of the analyte in the s ample is not in

doubt.

SQL: Sample Quan titation Limit. The S QL s provided in this table are CLP contract

- required detection limits (CRDLs) for that analyte with any dilution factors, volume adjustments, or percent solids for that analysis taken into account. SQLs were calculated as follows:

**( )**  DF x (mL) volume initial (mL) volume final

x L μg CRDL / SQL ** **  ** **  ** ** 

**=** L μg

Where:

Final volume (mL) is the final extract volume following sample preparation Initial volume (mL) is the volume of sample used

DF is the dilution factorSWOF

- Likelihood of Release 33 

### AMD Source Concentrations

– Dissolved Metals ( μg/l )

Sample ID Date Hazardous
Substance Hazardous
Substance

Concentration SQL References

Arsenic 66.1 1 .0

NIMM

- SW

- 4 (Level 10 Adit) 7/22/2010 Ref. 6, pp. 23, 1178, 1195, 1197

- 1198 ; Ref. 14, p. 6 ; Ref. 16, p. 8,

18 ; Ref. 26, p. 2; Ref. 28, p p

. 34, 52, 68, 70 ; Ref. 29 Cadmium 1.4 1.0 Copper 3.2 2.0

Nickel 1,440 1.0

Selenium 10.6 J 1 (9.3) 5.0

Zinc 2,350 2.0

μg/l : micrograms analyte per liter water

J 1 : The analyte was positively identified ; however

, the reported value is an estimate due to matrix spike recovery results being outside method quantitation control limits. The reported value may be bias high. However, the presence of the analyte in the sample is not in doubt. The adjusted value is presented in parentheses.

SQL: Sample Quantitation Limit. The S QL s provided in this table are CLP contract

- required detection limits (CRDLs) for that analyte with any dilution factors, volume adjustments, or percent solids for that analysis taken into account. SQLs were calculated as follow s:

**( )**  DF x (mL) volume initial (mL) volume final

x L μg CRDL / SQL ** **  ** **  ** ** 

**=** L μg

Where:

Final volume (mL) is the final extract volume following sample preparation Initial volume (mL) is the volume of sample used

DF is the dilution factorSWOF

- Likelihood of Release 34 

### Chemical Analysis

Sediment Sampling

W ESTON collected a total of 34 sediment samples (NIMM

- SD

- 1 through NIMM

- SD

- 34) from the facility and from upstream and downstream locations of the Site to establish whether a release to

surface water has occurred. Background sediment sample NIMM

- SD

- 1 was collect ed from the headwaters of San Carlos Creek approximately 3.9 miles upstream from the AMD and calcine tailings piles

, and background sediment sample NIMM

- SD

- 11 was collected from a tributary leading to East Fork San Carlos Creek located approximately 2.7 mi les south

- southeast of the Site. Three sediment samples ( NIMM

- SD

- 3, NIMM

- SD

- 8 and NIMM

- SD

- 9) were collected from San Carlos

Creek adjacent to the Calcine Tailings P iles. F our sediment samples (NIMM

- SD

- 10, NIMM

- SD

- 12,

NIMM

- SD

- 13, and NIMM

- SD

- 15) were coll ected from San Carlos Creek from locations 0.6, 2.4, 4.1, and 4.7 miles, respectively, downstream from the C alcine Tailings P iles (Ref. 6, p. 24 )

.

One sediment sample (NIMM

- SD

- 14) was collected from Larious Creek, upstream from its

confluence with San C arlos and Silver Creeks, approximately 4.5 miles downstream from the calcine tailings piles, to assess attribution from mercury mines in the New Idria Mining District draining to Sampson and Larious Creeks. A total of 17 sediment samples (NIMM

- SD

- 16 throu gh NIMM

- SD

32) were collected at intervals of approximately one mile along Silver Creek to Panoche Creek. Two sediment samples (NIMM

- SD

- 33 and NIMM

- SD

- 34) were collected from Panoche Creek at locations upstream and downstream of Silver Creek

, respectively ( Ref. 6 , p. 24 )

. Sampling locations are shown on Reference 6, pages 53 , 5 5 , 5 7 , 5 9

- 60 , and 6 2

.

Three sediment sub

- samples were collected at each location and were sieved and field screened for mercury concentrations with the XRF. Samples for laboratory analysis were contained in 4

- ounce glass containers and placed on ice for preservation ( Ref. 6 , p. 24 ).

The weighted fractions of the sample used to determine the percentages of fines are presented in the

table below.SWOF

- Likelihood of Release 35 

### Sample ID Total Weight (grams) Sieved Weight

- fines (grams) Remaining

-

coarse (grams) Percentage of fines (%) References

NIMM

- SD

- 1 

### 343 262 81 76.38 Ref. 6, p. 893

NIMM

- SD

- 3 

### 407 80 327 19.66 Ref. 6, p. 899

NIMM

- SD

- 8 

### 445 111 334 24.94 Ref. 6, p. 904

NIMM

- SD

- 9 

### 707 437 270 61. 81 Ref. 6, p. 905

NIMM

- SD

- 10 

### 403 188 215 46.65 Ref. 6, p. 906

NIMM

- SD

- 11 

### 262 119 143 45.42 Ref. 6, p. 907

NIMM

- SD

- 12 

### 400 111 289 27.75 Ref. 6, p. 908

NIMM

- SD

- 13 

### 248 54 194 21.77 Ref. 6, p. 909

NIMM

- SD

- 14 

### 425 166 259 39.06 Ref. 6, p. 910

NIMM

- SD

- 15 

### 69 0 255 435 36.96 Ref. 6, p. 911

NIMM

- SD

- 16 

### 280 238 42 85.0 Ref. 6, p. 912

NIMM

- SD

- 17 

### 289 92 197 31.83 Ref. 6, p. 913

NIMM

- SD

- 18 

### 486 256 230 52.67 Ref. 6, p. 914

NIMM

- SD

- 20 

### 229 201 28 87.77 Ref. 6, p. 916

NIMM

- SD

- 21 

### 431 316 115 73.32 Ref. 6, p. 917

NIM M

- SD

- 22 

### 649 217 432 33.44 Ref. 6, p. 918

NIMM

- SD

- 23 

### 365 207 158 56.71 Ref. 6, p. 919

NIMM

- SD

- 24 

### Not noted Not noted Not noted Not noted Ref. 6, p. 920

NIMM

- SD

- 25 

### 556 435 121 78.24 Ref. 6, p. 921

NIMM

- SD

- 26 

### 792 647 145 81.69 Ref. 6, p. 922

NIMM

- SD

- 27 

### 2 62 144 118 54.96 Ref. 6, p. 923

NIMM

- SD

- 28 

### 295 261 34 88.47 Ref. 6, p. 924

NIMM

- SD

- 29 

### 269 100 169 37.17 Ref. 6, p. 925

NIMM

- SD

- 30 

### 344 286 58 83.14 Ref. 6, p. 926

NIMM

- SD

- 31 

### 261 61 200 23.37 Ref. 6, p. 927

NIMM

- SD

- 32 

### 532 234 298 43.98 Ref. 6, p. 928

N IMM

- SD

- 33 

### 376 285 91 75.80 Ref. 6, p. 929

NIMM

- SD

- 34 

### 213 142 71 66.67 Ref. 6, p. 930



### The tables presented below are sample description tables with the background samples corresponding with the downstream comparative contaminated samples. Background sa mples

NIMM

- SD

- 1 and NIMM

- SD

- 11 were collected upstream of all contaminated samples (Table A)

. Background sample NIMM

- SD

- 14 was collected in Larious Creek, upstream of contaminated samples NIMM

- SD

- 15 through NIMM

- SD

- 32 and contaminated sample NIMM

- SD

- 34 (Ta ble B) . Background samples NIMM

- SD

- 33 and NIMM

- SD

- 61 were collected in Panoche Creek,
upstream of sample NIMM

- SD

- 34 (Table C) (Figures 2, 4, 6, 8, 9, 11 of this HRS documentation

record ).SWOF

- Likelihood of Release 36 

### Table A

Sample ID Sample

Date Sample Depth (below surface) Sample Description References

Background Samples

NIMM

- SD

- 1 7/22/2010 2 inches Dark yellowish brown fine to course sand, no gravel Ref. 6, p. 893

NIMM

- SD

- 11 7/22/2010 2 inches Dark yellowish brown fine to medium sand, angular gravel Ref. 6, p. 907

Compara tive Contaminated Samples

NIMM

- SD

- 3 7/21/2010 Not noted Light olive brown, fine to course sand, fine to course rounded gravel Ref. 6, p. 899

NIMM

- SD

- 8 7/21/2010 2 inches Grayish brown fine to medium sand, fine to medium rounded and subrounded gravel Ref. 6, p. 904

NIMM

- SD

- 9 7/21/2010 2 inches Olive brown fine to medium sand, angular gravel Ref. 6, p. 905

NIMM

- SD

- 10 7/22/2010 2 inches Light olive brown fine to medium sand, fine to medium subrounded to angular gravel Ref. 6, p. 906

NIMM

- SD

- 12 7/22/2010 2 inches Light yellowish brown fine to course sand, fine to course rounded gravel Ref. 6, p. 908

NIMM

- SD

- 13 7/22/2010 2 inches Light yellowish brown very fine sand, fine gravel Ref. 6, p. 909

NIMM

- SD

- 15 7/22/2010 Not noted Light yellowish brown fine to me dium sand, very fine to medium angular gravel Ref. 6, p. 911



### Table B

Sample ID Sample

Date Sample Depth (below surface) Sample Description References

Background Sample

NIMM

- SD

- 14 7/21/2010 2 inches Olive brown very fine to medium sand, fine to

mediu m rounded gravel Ref. 6, p. 910

Comparative Contaminated Samples

NIMM

- SD

- 16 7/21/2010 2 inches Light olive brown fine to course sand, some fine gravel Ref. 6, p. 912

NIMM

- SD

- 17 7/22/2010 Not noted Light yellowish brown very fine sand, rounded

grav el Ref. 6, p. 913

NIMM

- SD

- 18 7/22/2010 Not noted Light olive brown fine to medium sand, fine to medium gravel Ref. 6, p. 914

NIMM

- SD

- 20 7/20/2010 2 inches Light olive brown fine to course sand, fine rounded gravel Ref. 6, p. 916

NIMM

- SD

- 21 7/20/2010 2 i nches Light olive brown very fine to medium sand, fine to medium rounded gravel Ref. 6, p. 917

NIMM

- SD

- 22 7/20/2010 2 inches Light yellowish brown very fine to medium sand, fine to course rounded gravel Ref. 6, p. 918

NIMM

- SD

- 23 7/20/2010 2 inches Grayis h brown fine to course sand, fine rounded gravel Ref. 6, p. 919SWOF

- Likelihood of Release 37 NIMM

- SD

- 24 7/20/2010 2 inches Light olive brown fine sand, no gravel Ref. 6, p. 920

NIMM

- SD

- 25 7/20/2010 2 inches Grayish brown fine to medium sand, fine to medium rounded gravel Ref. 6, p. 921

NIMM

- SD

- 26 7/20/2010 2 inches Light yellowish brown fine to medium sand Ref. 6, p. 922

NIMM

- SD

- 27 7/20/2010 2 inches Light brownish gray fine to course sand, rounded gravel Ref. 6, p. 923

NIMM

- SD

- 28 7/20/2010 2 inches Light brownish gray sand, some gravel Ref. 6, p. 924

NIMM

- SD

- 29 7/23/2010 2 inches Light brownish gray sand, rounded gravel Ref. 6, p. 925

NIMM

- SD

- 30 7/20/2010 2 inches Light brownish gray sand, rounded gravel Ref. 6, p. 926

NIMM

- SD

- 31 7/20/2010 2 inches Light brownish gray sand with rounded gravel Ref. 6, p. 927

NIMM

- SD

- 32 7/23/2010 2 inches Light brownish gray rounded gravel Ref. 6, p. 928



### Table C

Sample ID Sample

Date Sample Depth (below surface) Sample Description References

Background Samples

NIMM

- SD

- 33 7/23/2010 2 inches Light brownish gray fine to course sand, some gravel Ref. 6, p. 929

NIMM

- SD

- 61 (Duplicate of

NIMM

- SD

- 33) 7/23/2010 2 inches Light brownish gray fine to course sand, some gravel Ref. 6, p. 929

Comparative Contaminated Sample

NIMM

- SD

- 34 7/23/2010 2 inches Sandy Ref. 6, p. 930SWOF

- Likelihood of Release 38 

### - Background Concentrations: Total Metals in Sediments (mg/kg)

Sample ID Hazardous
Substance Hazardous
Substance

Concentration (mg/kg) SQL (mg/kg) Reference s

NIMM

- SD

- 1 ( San Carlos Creek , upstream of all contaminated samples) Arse nic 1.0 U 1.01 Ref. 6, pp. 26, 30, 1137, 1139 ; Ref. 14, p. 5 ; Ref. 22, p p . 3, 49, 67, 105, 108,

112 ; Ref. 29 Copper 6.2 2.53

Lead 3.9 1.01

Mercury 0.19 0.101

NIMM

- SD

- 11 ( Tributary to East Fork San

Carlos Creek

– upstream of all contaminated sampl es) Arsenic 1.1 U 1.05 Ref. 6, pp. 26, 30,

1154

- 1155, 1160,

1163 ; Ref. 14, p. 5 ; Ref. 24, p p . 2, 33, 60, 91, 92, 95 ; Ref.

29 Copper 8.6 2.63

Lead 4.1 1.05

NIMM

- SD

- 14 ( Larious Creek

– upstream of contaminated samples NIMM

SD

- 15 through

- 32,

- 34) Arse nic 6.6 1.06 Ref. 6, pp. 27, 30, 1155, 1160, 1163 ; Ref. 14, p. 4 ; Ref. 16, p p . 8, 18 ; Ref. 24, p p . 2, 36, 60, 91, 92, 95, 100 ; Ref. 29 Copper 19.4 2.65

Lead 7.3 1.06

Mercury 0.081 J 1 (0.15) 0.101

NIMM

- SD

- 33 ( Panoche Creek

– upstream of

contaminat ed sample NIMM

SD

- 34 ) Arsenic 3.9 0.975 Ref. 6, pp. 29

- 30, 1145, 1148, 1150 ; Ref. 14, p. 6 ; Ref. 23, p p . 4, 41, 58, 89, 90, 92, 98 ; Ref. 29 Copper 8.1 2.44

Lead 4.0 J 2 (5.76) 0.975

Mercury 0.10 U 0.1

NIMM

- SD

- 61 (duplicate of NIMM

- SD

- 33) Arsenic 3. 6 0.986 Ref. 6, pp. 29

- 30, 1145, 1149

- 1150 ; Ref. 14, p. 6 ; Ref. 23, p p . 4, 46, 58, 89, 90, 92, 98 ; Ref. 29 Copper 7.9 2.47

Lead 4.6 J 2 (6.6) 0.986

Mercury 0.050 J 3 0.101

mg/kg: milligrams analyte per kilogram sediment

J 1 : The analyte was positiv ely identified ; however

, the reported value is an estimate due to matrix spike recovery results being outside method quantitation control limits. The reported value may be bias low. However, the presence of the analyte in the sample is not in doubt. The adjusted value is presented in parentheses.

J 2 : The analyte was positively identified ; however

, the reported value is an estimate due to ICP serial dilution results being outside method quantitation control limits. The results may be bias l ow. However, the presence of the analyte in the sample is not in doubt. The adjusted value is presented in parentheses.

J 3 : Analyte detected at a level less than the CRQL

. U The analyte was analyzed for but was not detected above the level of he reported sample quantitation limit.

SQL: Sample Quantitation Limit. The S QL s provided in this table are CLP contract

- required detection limits (CRDLs) for that analyte with any dilution factors, volume adjustments, or percent solids for that analy sis taken into account. SQLs were calculated as follows:

DF x kg 1 g 1000

x mL 1000 1L

x %S x wet wgt) (g weight sample (mL) volume final

x μg 1000 mg 1

x L μg CRDL dry wgt kg mg SQL ** **  ** **  ** ** 

**= **  ** **  ** **  ** **  ****

Where: Final volume (mL) is the final extract volume following sample preparation Sample weight (g wet wgt) is the weight of the sample used for analysis

% S is % solid s value divided by 100; % solids is determined as follows: (g dry weight of sample used for analysis )/(g wet weight ofSWOF

- Likelihood of Release 39 sample used for analysis ) x100%

DF is the dilution factor for the instrumental analysis



### - Contaminated Samples:

Total Metals in Sedi ments Showing an Observed Release (mg/kg)

Sample ID Hazardous
Substance Hazardous
Substance

Concentration (mg/kg) SQL (mg/kg) Reference

NIMM

- SD

- 3 ( San Carlos Creek adjacent to southern calcine pile ) Arsenic 9.0 1.01 Ref. 6 , pp. 27, 30, 1138

- 1139 ; Ref. 14 , p. 4 ; Ref. 22, p p . 3, 51, 67, 103, 105, 109, 115 ; Ref. 29 Copper 44.6 2.53

Mercury 4.9 9.05

NIMM

- SD

- 8 ( San Carlos Creek adjacent

to southern calcine pile) Arsenic 10 1.02 Ref. 6 , pp. 27, 30, 1138

- 1139 ; Ref. 14, p. 4 ; Ref. 22, p p . 3, 55, 67, 103, 1 05, 109, 115 ; Ref. 29 Copper 40.3 2.55

Mercury 4.7 0.195

NIMM

- SD

- 9 ( San Carlos Creek adjacent

to northern calcine pile) Arsenic 14.1 1.03 Ref. 6 , pp. 27, 30, 1139 ; Ref. 14, p. 4 ; Ref. 22, p p . 4, 56, 67, 103, 105, 109, 115 ; Ref. 29 Copper 55.9 2.58

Lead 16.0 1.03 Mercury 4.9 0.196

NIMM

- SD

- 10 ( San Carlos Creek 0.6 mile from PPE) Arsenic 8.7 1.01 Ref. 6 , pp. 27, 30, 1156, 1160,

1163 ; Ref. 14, p. 5 ; Ref. 16, p. 8; Ref. 24, p p . 2, 32, 60, 91, 92, 95, 102 ; Ref. 29 Copper 30.7 2.54

Mercury 32 .6 J 1 2.03

NIMM

- SD

- 12 ( San Carlos Creek 2.4 miles from PPE) Arsenic 8.3 1.02 Ref. 6 , pp. 27, 30, 1156, 1160,

1163 ; Ref. 14, p. 5 ; Ref. 16, p. 8; Ref. 24, p p . 2, 34, 60, 91, 92, 95, 102 ; Ref. 29 Mercury 8.9 J 1 0.412

NIMM

- SD

- 13 ( San Carlos Creek 4.1 mi les from PPE) Arsenic 11.9 1.14 Ref. 6 , pp. 27, 30, 1156, 1160,

1163 ; Ref. 14, p. 5 ; Ref. 16, p. 8; Ref. 24, p p . 2, 35, 60, 91, 92, 95, 100 ; Ref. 29 Mercury 2.0 J 1 0.114

NIMM

- SD

- 15 ( San Carlos Creek 4.7 miles from PPE) Mercury 4.6 J 1 0.194 Ref. 6 , pp. 27, 30, 1156, 1160,

1163 ; Ref. 14, p. 5 ; Ref. 16, p. 8; Ref. 24, p p . 2, 37, 60, 92,

102 ; Ref. 29

NIMM

- SD

- 59 (duplicate of NIMM

- SD

15) Mercury 4.0 0.194 Ref. 6 , pp. 27, 30, 1149

- 1150 ; Ref. 14, p. 5 ; Ref. 23, p p . 4, 44, 58, 90, 100 ; Ref. 29

NIMM

- SD

- 15 (uns ieved sample) Mercury 4.4 0.194 Ref. 6 , pp. 27, 30, 1149

- 1150 ; Ref. 14, p. 5 ; Ref. 24, p p . 2, 37, 60, 92, 102 ; Ref. 29

NIMM

- SD

- 16 ( Silver Creek 5.4 miles Mercury 1.8 J 1 0.107 Ref. 6 , pp. 28, 30, 1156, 1161,

1163 ; Ref. 14, p. 4 ; Ref. 16, p.SWOF

- Likelihood of Release 40 

### Total Metals in Sedi ments Showing an Observed Release (mg/kg)

Sample ID Hazardous
Substance Hazardous
Substance

Concentration (mg/kg) SQL (mg/kg) Reference

from PPE) 8; Re f. 24, p p . 2, 38, 60, 92,

100 ; Ref. 29

NIMM

- SD

- 17 ( Silver Creek 6.4 miles from PPE) Mercury 3.9 J 1 0.204 Ref. 6 , pp. 28, 30, 1156, 1161,

1163 ; Ref. 14, p. 5 ; Ref. 16, p. 8; Ref. 24, p p . 2, 39, 60, 92,

102 ; Ref. 29

NIMM

- SD

- 18 ( Silver Creek 7.4 miles

from PPE) Mercury 2.7 J 1 0.101 Ref. 6 , pp. 28, 30, 1156, 1161, 1163; Ref. 14, p. 5; Ref. 16, p. 8; Ref. 24, p p . 2, 40, 60, 93,

100 ; Ref. 29

NIMM

- SD

- 20 ( Silver Creek 9.2 miles from PPE) Mercury 11.2 J 1 0.491 Ref. 6, pp. 28, 30, 1156, 1161,

1163 ; Ref. 14, p. 3 ; Ref. 16, p. 8; Ref. 24, p p . 3, 42, 60, 93,

102 ; Ref. 29

NIMM

- SD

- 21 ( Silver Creek 10.2 miles from PPE) Mercury 1.3 J 1 0.101 Ref. 6, pp. 28, 30, 1156, 1161,

1163 ; Ref. 14, p. 3 ; Ref. 24,

p p . 3, 43, 60, 93, 100 ; Ref. 29

NIMM

- SD

- 22 ( Silver Creek 11.2 miles

f rom PPE) Mercury 0.60 J 1 0.101 Ref. 6, pp. 28, 30, 1156, 1162

- 1163 ; Ref. 14, p. 3 ; Ref. 16, p. 8; Ref. 24, p p . 3, 44, 60, 93,

100 ; Ref. 29

NIMM

- SD

- 24 ( Silver Creek 13.0 miles from PPE) Mercury 4.2 J 1 0.206 Ref. 6, pp. 28, 30, 1156, 1162

- 1163 ; Ref. 14, p. 3 ; Ref. 16, p. 8; Ref. 24, p p . 3, 46, 60, 93,

102 ; Ref. 29

NIMM

- SD

- 25 ( Silver Creek 14.0 miles from PPE) Mercury 2.4 J 1 0.103 Ref. 6, pp. 28, 30, 1156, 1162

- 1163 ; Ref. 14, p. 3 ; Ref. 16, p. 8; Ref. 24, p p . 3, 47, 60, 93,

100 ; Ref. 29

NIMM

- SD

- 60 (duplicat e of NIMM

- SD

25) Mercury 1.4 0.098 Ref. 6, pp. 28, 30, 1146, 1149

- 1150 ; Ref. 14, p. 3 ; Ref. 23,

p p . 4, 45, 59, 90, 98 ; Ref. 29

NIMM

- SD

- 26 ( Silver Creek 15.0 miles from PPE) Mercury 1.7 J 1 0.101 Ref. 6, pp. 29, 30 1156, 1162

- 1163 ; Ref. 14, p. 3 ; Ref. 16, p

. 8; Ref. 24, p p . 3, 48, 60, 93,

99 ; Ref. 29

NIMM

- SD

- 27 ( Silver Creek 15.8 miles from PPE) Mercury 1.5 J 1 0.101 Ref. 6, pp. 29, 30 1156, 1162

- 1163 ; Ref. 14, p. 3 ; Ref. 16, p. 8; Ref. 24, p p . 3, 49, 60, 93,

100 ; Ref. 29

NIMM

- SD

- 28 ( Silver Creek 16.2 miles from PPE) Mercury 1.1 J 1 0.101 Ref. 6, pp. 29, 30 1156, 1163 ; Ref. 14, p. 3 ; Ref. 16, p. 8; Ref. 24, p p . 3, 50, 60, 93, 100 ; Ref. 29SWOF

- Likelihood of Release 41 

### Total Metals in Sedi ments Showing an Observed Release (mg/kg)

Sample ID Hazardous
Substance Hazardous
Substance

Concentration (mg/kg) SQL (mg/kg) Reference

NIMM

- SD

- 29 ( Silver Creek 16.9 miles from PPE) Mercury 2.3 J 1 0.101 Ref. 6, pp. 29, 30 1156, 1163 ; Ref. 14, p. 6 ; Ref. 16, p. 8; Ref. 24, p p . 3, 51, 60, 93, 100 ; Ref. 29

NIMM

- SD

- 30 ( Silver Creek 17.8 miles from PPE) Mercury 1.2 0.107 Ref. 6, pp. 29, 30 1148, 1150; Ref. 14, p. 3; Ref. 23, p p . 4, 38, 58, 90, 98 ; Ref. 29

NIMM

- SD

- 31 ( Silver Creek 18.7 miles from PPE) Mercury 1. 0 0.101 Ref. 6, pp. 29, 30 1148, 1150 ; Ref. 14, p. 3 ; Ref. 23, p p . 4, 39, 58, 90, 98 ; Ref. 29

NIMM

- SD

- 32 ( Silver Creek 19.5 miles from PPE) Mercury 1.0 0.096 Ref. 6, pp. 29, 30 1148, 1150 ; Ref. 14, p. 6 ; Ref. 23, p p . 4, 40, 58, 90, 98 ; Ref. 29

NIMM

- SD

- 34 ( Panoche Creek 19.9 miles from PPE) Mercury 1.1 0.103 Ref. 6, pp. 29, 30 1148, 1150 ; Ref. 14, p. 6 ; Ref. 23, p p . 4, 42, 58, 90, 98 ; Ref. 29

mg/kg: milligrams analyte per kilogram sediment

J 1 : The analyte was positively identified; however, the reporte d value is an estimate due to matrix spike recovery results being outside method quantitation control limits. The reported value may be bias low. However, the presence of the analyte in the sample is not in doubt.

SQL: Sample Quantitation Limit. The S QL s provided in this table are CLP contract

- required detection limits (CRDLs) for that analyte with any dilution factors, volume adjustments, or percent solids for that analysis taken into account. SQLs were calculated as follows:

DF x kg 1 g 1000

x mL 1000 1L

x %S x wet wgt) (g weight sample (mL) volume final

x μg 1000 mg 1

x L μg CRDL dry wgt kg mg SQL ** **  ** **  ** ** 

**= **  ** **  ** **  ** **  ****

Where: Final volume (mL) is the final extract volume following sample preparation Sample weight (g wet wgt) is the weight of the sample used for analysis

% S is % solids value divided by 100; % solids is determined as follows: (g dry weight of sample used for analysis )/(g wet weight of sample used for analysis ) x100%

DF is the dilution factor for the instrumental analysisSWOF

- Likelihood of Release 42 

### Surface Water Sampling

WESTON collected surface water samples from 15 upstream and downstream locations relative to

s ite sourc es to establish whether a release to surface water has occurred. Background sample

NIMM

- SW

- 1 was collected from the headwaters of San Carlos Creek approximately 3.5 m iles upstream from the AMD and C alcine T ailings P iles . B ackground sample NIMM

- SW

- 9 was

c ollected from a tributary leading to East Fork San Carlos Creek located approximately 2.7 miles

south

- southeast of the Site. Three surface water samples (BLM

- SW

- 1 through BLM

- SW

- 3) were collected from upper San Carlos Creek at locations upstream, adjacent , and downstream of the reclamated Aurora mercury mine, respectively. Three surface water samples ( NIMM

- SW

- 3, NIMM

SW

- 6 and NIMM

- S W

- 7) were collected from San Carlos Creek adjacent to the Calcine T ailings

P iles. Two surface water samples (NIMM

- SW

- 8 and N IMM

- SW

- 10) were collected from San

Carlos Creek from locations 0.6 and 2.4 miles downstream from t he C alcine Tailings P iles, respectively. One surface water sample (NIMM

- SW

- 12) was collected from Larious Creek, upstream from its confluence with San Carlos and Silver Creeks to assess attribution from mercury

mines in the New Idria Mining District draining to Larious Creek. Surface water sample NIMM

SW

- 14 was collected from a location in Silver Creek approximately 5.4 miles downstream from the

calcine taili ngs piles. At the time of sampling, water in Silver Creek was originating from Larious

Creek and San Carlos Creek was dry at the planned upstream surface water sample location NIMM

SW

- 11 ( Ref. 6 , p. 31 )

. Sampling locations are shown on Reference 6, pages 5 3 , 5 5 , and 5 7

.

Both filtered and un filtered water samples were collected at each sampling location by either submerging a clean one

- liter plastic bottle beneath the water surface or by using dedicated tubing and a peristaltic pump. The samples were pre served with nitric acid to a pH less than 2; the samples were placed on ice in preparation for shipping to a CLP laboratory for metals analysis by CLP

method ILM 5.2 ( Ref 6 , p. 3 1 ).

The tables presented below are sample description tables with the backgro und samples corresponding with the downstream comparative contaminated samples. Background samples

NIMM

- SW

- 1, NIMM

- SW

- 9, BLM

- SW

- 1, BLM

- SW

- 2, and BLM

- SW

- 3 were collected upstream of all contaminated samples (Table D) (Figures 2, 4, 6 of this HRS documentat ion

record ).SWOF

- Likelihood of Release 43 

### Table D

Sample ID Sample

Date Sample Description References

Background Samples

NIMM

- SW

- 1 7/22/2010 Some green algae, 2

- foot wide drainage with

low to moderate flow Ref. 6, p. 894

NIMM

- SW

- 9 7/22/2010 Small tributary, serpentine g ravel Ref. 6, p. 907

BLM

- SW

- 1 7/22/2010 Grassy banks, moderate flow Ref. 6, p. 895

BLM

- SW

- 2 7/22/2010 Sandy banks, 2.5

- foot wide drainage with low

to moderate flow Ref. 6, p. 896

BLM

- SW

- 3 7/22/2010 Grassy banks, 3

- foot wide drainage with low to

moderate flow Ref. 6, p. 897

Comparative Contaminated Samples

NIMM

- SW

- 3 7/21/2010 Not noted Ref. 6, p. 899

NIMM

- SW

- 6 7/21/2010 Grassy banks Ref. 6, p. 904

NIMM

- SW

- 7 7/21/2010 Grassy banks, brownish water Ref. 6, p. 905

NIMM

- SW

- 8 7/22/2010 Cloudy water with or ange

- rust colored

sediments Ref. 6, p. 906

NIMM

- SW

- 10 7/22/2010 Salt deposits on banks, orange

- rust colored

stream bed Ref. 6, p. 908



### - Background Concentrations:

Total Metals in Surface Water (μg/l)

Sample ID Hazardous
Substance Hazardous
Substan ce Concentration SQL References

NIMM

- SW

- 1 ( Upper San Carlos Creek

– upstream of all contaminated samples) Arsenic 1.0 U 1.0 Ref. 6 , pp. 34, 1166

- 1167,

1170

- 1171, 1182

- 1183, 1187,

1190 ; Ref. 14, p. 5 ; Ref. 16, pp. 8, 18; Ref. 25, p p . 2, 33, 62, 96, 104; Re f. 27, p p

. 31, 54, 70, 71 ; Ref. 29 Cadmium 1.0 U 1.0
Copper 2.0 U 2.0
Mercury 0.084 J 1 0.20

Zinc 1.4 J 1 ,2 (1.81) 2.0

NIMM

- SW

- 9 ( Tributary leading to East Fork

San Carlos Creek

– upstream of all contaminated samples) Arsenic 1.0 U 1.0 Ref. 6 , p p. 34, 1166, 1167,

1170

- 1171

, 1182, 1183, 1185, 1188, 1190 ; Ref. 14, p. 5 ; Ref. 16, pp. 8, 18; Ref. 25, p p . 3, 41, 62, 96, 104; Ref. 27, p p

. 39, 54, 70, 71 ; Ref. 29 Cadmium 1.0 U 1.0
Copper 4.0 2.0
Mercury 0.10 J 1 0.20

Zinc 9.5 J 2 (12.32) 2.0

BLM

- SW

- 1 Upper San Carlos Creek

, Aurora Mine background

– upstream of all contaminated samples ) Arsenic 1.0 U 1.0 Ref. 6 , pp. 34, 1171

, 1182, 1183, 1189

- 1190 ; Ref. 14, p. 6; Ref. 16, pp. 8, 18; Ref. 25,

p p . 4, 48, 62, 97, 104; Ref. 27,

p p

. 46, 54, 70, 72 ; Ref. 29 Cadmium 1.0 U 1.0

Copper 2.0 U 2.0

Mercury 0.20 U 0.20

Zinc 1.8 J 1 ,2 (2.32) 2.0SWOF

- Likelihood of Release 44 

### Total Metals in Surface Water (μg/l)

Sample ID Hazardous
Substance Hazardous
Substan ce Concentration SQL References

BLM

- SW

- 2 Upper San Carlos Creek adjacent to Aurora Mine

– upstream of all contaminated samples ) Arsenic 1.0 U 1.0 Ref. 6 , pp. 34, 1171, 1182, 1183, 1189

- 1 190 ; Ref. 14, p.

6 ; Ref. 16, pp. 8, 18; Ref. 25,

p p . 5, 49, 62, 97, 105; Ref. 27,

p p

. 47, 54, 70, 72 ; Ref. 29 Cadmium 1.0 U 1.0 Copper 2.0 U 2.0 Mercury 0.20 U 0.20

Zinc 1.4J J 1 ,2 (1.81) 2.0

BLM

- SW

- 3 ( Upper San Carlos Creek

downstream of Auror a Mine

– upstream of all contaminated samples) Arsenic 1.0 U 1.0 Ref. 6 , pp. 34, 1166, 1167, 1171, 1182, 1183, 1189

- 1190 ; Ref. 14, p. 6 ; Ref. 16, pp. 8, 18; Ref. 25, p p . 5, 50, 62, 97, 105; Ref. 27, p p

. 48, 70, 72 ; Ref. 29 Cadmium 1.0 U 1.0
Copper 2.0 U 2.0
Mercury 0.20 U 0.20

Zinc 1.3 J 1 ,2 (1.68) 2.0

μg/l : micrograms analyte per liter water CRQL: Contract Required Quantitation Limit

J 1 : Analyte detected at a level less than the CRQL.

J 2 : The analyte was positively identified; however, the r eported value is an estimate due to ICP serial dilution results being outside method quantitation control limits. The results may be bias low. However, the presence of the analyte in the sample is not in doub t. The adjusted value is presented in parenth eses. U: The analyte was analyzed for but was not detected above the level of the reported sample quantitation limit. SQL: Sample Quantitation Limit. The S QL s provided in this table are CLP contract

- required detection limits (CRDLs) for that a nalyte with any dilution factors, volume adjustments, or percent solids for that analysis taken into account. SSQLs were calculated as follows:

**( )**  DF x (mL) volume initial (mL) volume final

x L μg CRDL / SQL ** **  ** **  ** ** 

**=** L μg

Where:

Final volume (mL) is the final extract volume following sample preparation Initial volume (mL) is the volume of sample used

DF is the dilution factorSWOF

- Likelihood of Release 45 

### - Contaminated Samples:

Total Metals in Surface Water Showing an Observed Release (μg/l)

Sample ID Hazardous
Substance Hazardous
Substance

Concentration SQL Reference

NIMM

- SW

- 3 ( San Carlos Creek adjacent to southern calcine pile ) Mercury 0.28 0.20 Ref. 6 , pp. 35 , 1170

- 1171 ; Ref. 14, p. 4 ; Ref. 25, p p . 2, 35, 62, 96, 104; Ref. 27, p p . 54, 70,

71 ; Ref. 29

NIMM

- SW

- 6 ( San Carlos Creek adjacent to southern calcine pile) A rsenic 1.3 1.0 Ref. 6, pp. 35 , 1170

- 1171

, 1185, 1187, 1190 ; Ref. 14, p.

4 ; Ref. 16, p. 8 ; Ref. 25, p p . 3, 38, 62, 96, 104; Ref. 27, p p

. 36, 54, 70, 71 ; Ref. 29 Mercury 4.9 0.20

Zinc 396 J 1 2.0

NIMM

- SW

- 7 ( San Carlos Creek northern calcine pile) Arsen ic 1.9 1.0 Ref. 6, pp. 35 , 1170

- 1171, 1185, 1188, 1190; Ref. 14, p.

4 ; Ref. 16, p. 8 ; Ref. 25, p p . 3, 39, 62, 104; Ref. 27, p p . 54, 37, 70, 71 ; Ref. 29 Cadmium 1.2 1.0 Copper 17.2 2.0 Mercury 4.8 0.20

Zinc 1,150 J 1 2.0

NIMM

- SW

- 15 (duplicate of NIMM

- SW

- 7) Arsenic 1.3 1.0 Ref. 6, pp. 35 , 1171, 1185,

1189

- 1190 ; Ref. 14, p. 4 ; Ref. 16, p. 8 ; Ref. 25, p p . 4, 45, 62, 97, 104; Ref. 27, p p

. 43, 54, 70, 71 ; Ref. 29 Copper 18.0 2.0

Mercury 4.7 0.20

Zinc 1,270 J 1 2.0

NIMM

- SW

- 8 ( San Carlos Creek 0.6 miles from Site) Arsenic 1.8 1.0 Ref. 6 , pp. 35 , 1170

- 1171

, 1185, 1188, 1190 ; Ref. 14, p.

5 ; Ref. 16, p. 8 ; Ref. 25, p p . 3, 40, 62, 96, 104; Ref. 27, p p

. 38, 54, 70, 71 ; Ref. 29 Copper 13.6 2.0

Mercury 4.6 0.20

Zinc 987 J 1 2.0

NIMM

- SW

- 10 ( San Carlos Creek 2.4 miles from Site) Mercury 0.79 0.20 Ref. 6, pp. 35 , 1170

- 1171, 1185, 1188, 1190 ; Ref. 14, p.

5 ; Ref. 16, p. 8 ; Ref. 25, p p . 3, 42, 62, 96, 104; Ref. 27, p p

. 40, 54, 70, 71 ; Ref. 29 Zinc 176 J 1 2.0

μg/l : micrograms analyte per liter wa ter CRQL: Contract Required Quantitation Limit

J 1 : The analyte was positively identified ; however

, the reported value is an estimate due to ICP serial dilution results being outside method quantitation control limits. The results may be bias low. However , the presence of the analyte in the sample is not in doubt. SQL: Sample Quantitation Limit. The S QL s provided in this table are CLP contract

- required detection limits (CRDLs) for that analyte with any dilution factors, volume adjustments, or percent so lids for that analysis taken into account. SQLs were calculated as follows:

**( )**  DF x (mL) volume initial (mL) volume final

x L μg CRDL / SQL ** **  ** **  ** ** 

**=** L μg

Where:

Final volume (mL) is the final extract volume following sample preparation Initial volume (mL) is the volume of sample used

DF is the dilu tion factorSWOF

- Likelihood of Release 46 

### - Background Concentrations:

Dissolved Metals in Surface Water (μg/l)

Sample ID Hazardous
Substance Hazardous
Substance

Concentration SQL References

NIMM

- SW

- 1 (Upper San Carlos Creek

– upstream of all contaminated samples) Copper 0.4J 1 2.0 Ref. 6 , pp. 34, 1178

- 1179 ; Ref. 14, p. 5 ; Ref. 26, p p . 2, 32, 56, 82, 88; Ref. 28, p p

. 31, 52, 68,

70 ; Ref. 29 Mercury 0.20 U 0.20

Nickel 4.5 1.0

Selenium 5.0 U 5.0

Zinc 2.9 2.0

NIMM

- SW

- 9 (Tributary leading to East Fork

San Carlos Creek

– ups tream of all contaminated samples) Copper 2.0 U 2.0 Ref. 6 , pp. 34, 1178

- 1179 ; Ref. 14, p. 5 ; Ref. 26, p p . 3, 40, 56, 82, 88; Ref. 28, p p

. 39, 52, 68,

70 ; Ref. 29 Mercury 0.20 U 0.20

Nickel 5.1 1.0

Selenium 5.0 U 5.0

Zinc 2.4 2.0

BLM

- SW

- 1 ( Upp er San Carlos Creek, Aurora Mine background

– upstream of all contaminated samples) Copper 2.0 U 2.0 Ref. 6 , pp. 34, 1179; Ref. 14, p. 6 ; Ref. 16, p. 8, 18 ; Ref. 26, p p . 5, 45, 56, 82, 89; Ref. 28, p p

. 44, 52, 68, 71 ; Ref. 29 Mercury 0.20 U 0.20

Nick el 3.7 1.0

Selenium 5.0 U 5.0

Zinc 1. 5 J 1,2 ( 1.94 ) 2.0

BLM

- SW

- 2 Upper San Carlos Creek adjacent to Aurora Mine

– upstream of all contaminated samples) Copper 0.38 J 1 2.0 Ref. 6 , pp. 34, 1175,

1179 ; Ref. 14, p. 6 ; Ref. 26, p. 5; Ref. 28, p p

. 45, 52, 68, 71 ; Ref. 29 Nickel 3.5 1.0

Selenium 5.0 U 5.0

Zinc 2.3 2.0

μg/l : micrograms analyte per liter water CRQL: Contract Required Quantitation Limit

J 1 : Analyte detected at a level less than the CRQL.

J 2 : The analyte was positively identified ; however

, the reported value is an estimate due to ICP serial dilution results being outside method quantitation control limits. The results may be bias low. However, the presence of the analyte in the sample is not in doub t. The adjusted value is prese nted in parentheses.

J 3 : The analyte was positively identified ; however

, the reported value is an estimate due to matrix spike recovery results being outside method quantitation control limits. The reported value may be bias high. However, the presence of the analyte in the sample is not in

doubt.

U The analyte was analyzed for but was not detected above the level of the reported sample quantitation limit. SQL: Sample Quantitation Limit. The S QL s provided in this table are CLP contract

- required detec tion limits (CRDLs) for that analyte with any dilution factors, volume adjustments, or percent solids for that analysis taken into account. SQLs were calculated as follows:

**( )**  DF x (mL) volume initial (mL) volume final

x L μg CRDL / SQL ** **  ** **  ** ** 

**=** L μg

Where:

Final volume (mL) is the final extract volume following sample preparation Initial volume (mL) is the volume of sample used

DF is the dilution factorSWOF

- Likelihood of Release 47 

### - Contaminated Samples:

Dissolved Metals in Surface Water Showing an Observed Release (μg/l)

Sample ID Hazardous
Substance Hazardous
Substance

Con centration SQL Reference

NIMM

- SW

- 3 (San Carlos Creek adjacent to southern calcine pile ) Mercury 0. 30 0.20 Ref. 6, pp. 35 , 1178

- 1179 ; Ref. 14, p. 4 ; Ref. 26, p p . 2, 34, 56, 82, 88 ; Ref. 29

NIMM

- SW

- 6 (San Carlos Creek adjacent to southern calcine pile) Nic kel 231 1.0 Ref. 6, pp. 35 , 1178

- 1179, 1198, 1200 ; Ref. 14, p. 4 ; Ref. 26, p. 3; Ref. 28, p p

. 36, 52, 68,

70 ; Ref. 29 Zinc 61.6 2.0

NIMM

- SW

- 7 (San Carlos Creek northern calcine pile) Copper 3.2 2.0 Ref. 6, pp. 35 , 1178

- 1179, 1195, 1199

- 1200 ; Ref. 14, p . 4 : Ref. 16, p. 8, 18 ; Ref. 26, p. 3; Ref. 28, p p

. 37, 52, 68, 70 ; Ref. 29 Nickel 175 1.0

Selenium 6.6 J 1 ( 5.79 ) 5.0

Zinc 66.1 2.0

NIMM

- SW

- 15 (duplicate of NIMM

- SW

- 7) Nickel 172 1.0 Ref. 6, pp. 35 , 1179, 1195, 1200 ; Ref. 14, p. 4 ; Ref. 16, p. 8, 18 ; Ref. 26, p. 4; Ref. 28, p p

. 43, 52, 68, 70 ; Ref. 29 Selenium 6.3 J 1 ( 5.53 ) 5.0

Zinc 54.9 2.0

NIMM

- SW

- 8 (San Carlos Creek 0.6 miles from Site) Nickel 73.2 1.0 Ref. 6, pp. 35 , 1178

- 1179, 1199

- 1200 ; Ref. 14, p. 5 ; Ref. 26, p. 3; Ref. 28, p p

. 38, 5 2, 68,

70 ; Ref. 29 Zinc 13.5 2.0

NIMM

- SW

- 10 (San Carlos Creek 2.4 miles from Site) Copper 2.1 2.0 Ref. 6, pp. 35 , 1178

- 1179, 1199

- 1200 ; Ref. 14, p. 5 ; Ref. 26, p. 3; Ref. 28, p p

. 40, 52, 68,

70 ; Ref. 29 Nickel 33.5 1.0

Zinc 9.1 2.0

μg/l : microg rams analyte per liter water CRQL: Contract Required Quantitation Limit

J 1 : The analyte was positively identified ; however

, the reported value is an estimate due to matrix spike recovery results being outside method quantitation control limits. The rep orted value may be bias high. However, the presence of the analyte in the sample is not in

doubt. The adjusted value is presented in parentheses. SQL: Sample Quantitation Limit. The S QL s provided in this table are CLP contract

- required detection limits (CRDLs) for that analyte with any dilution factors, volume adjustments, or percent solids for that analysis taken into account. SQLs were calculated as follows:

**( )**  DF x (mL) volume initial (mL) volume final

x L μg CRDL / SQL ** **  ** **  ** ** 

**=** L μg

Where:

Final volume (mL) is the final extract volume following sa mple preparation Initial volume (mL) is the volume of sample used

DF is the dilution factorSWOF

- Likelihood of Release 48 

### ATTRIBUTION

During the 1998 PA/SI investigation conducted on the NIMM facility, observed releases of mercury,

nickel and zinc from the site to San Carlos Cre ek and Silver Creek were documented. Elevated downstream mercury concentrations in surface water ranged from 3.1 ug/l to 12.0 ug/l. Nickel had a maximum concentration of 471 ug/l in downstream surface water samples, and zinc had a maximum

concentration o f 1,920 ug/l (Ref. 4, Table 4

- 2).

An observed release was documented during the Jul y 2010 sampling investigation. H azardous substances arsenic, cadmium, copper, lead, mercury, nickel, selenium, and zinc were detected at concentrations significantly above background concentrations in onsite sources and downstream of

the New Idria Mercury Mine site (Ref. 6, pp. 26

- 29, 3 4

- 3 6 )

.

Background s ediment samples NIMM

- SD

- 1, NIMM

- SD

- 11 were collected upstream of site sources. Sediment samples NIMM

- SD

- 3, NIMM

- SD

- 8, NIMM

- SD

- 9, NIMM

- SD

- 10, NIMM

- SD

- 12, and

NIMM

- SD

- 13 were collected from San Carlos Creek adjacent to or downstream of site sources. Sample locations are presented in Figure 2, Figure 4 and Figure 6 of this HRS documentation record

. One or more of the abov e hazardous substances were detected in all of these samples at concentrations significantly above background ( Ref. 6, pp. 26

- 29 , Figures 2, 4, 6 ) . These hazardous substances have been detected in the Calcine Tailings Piles (Source 1) and/or the Level 10 Adit

AMD (Source 2) (Ref. 6, pp. 20

- 21 , 23 ). See tables in Observed Release section (Section 4.1.2.1.1).

Sediment sample NIMM

- SD

- 14 was collected from Larious Creek upstream of the confluence with San Carlos Creek to assess attribution from other mercury mines in the New Idria Mining District draining to Sampson and Larious Creeks. Sediment samples NIMM

- SD

- 15 through NIMM

- SD

- 32 were collected from Silver Creek downstream of the confluence with Larious Creek. Mercury was detected in all of these samples at concentrations significantly above all background samples including NIMM

- SD

- 14 ( Ref. 6, pp. 27

- 29 ). Sample location NIMM

- SD

- 14 and the surrounding creeks are presented in Figure 6 of this HRS documentation record

.

Sediment sample NIMM

- SD

- 33 and its du plicate NIMM

- SD

- 61 were collected from Panoche Creek upstream of the confluence with Silver Creek. Sediment sample NIMM

- SD

- 34 was collected from Panoche Creek immediately downstream of the confluence with Silver Creek. Mercury was detected

in NIMM

- SD

- 34 at a concentration significantly above all background samples, including NIMM

SD

- 33

. Sample locations are presented in Figure 11 of this HRS documentation record

. Sample

NIMM

- SD

- 34 is located 19.9 miles downstream of site sources (Ref. 6, p

. 29 ; Figure 1 1 ). Although other mines existed in the vicinity of the site, the NIMM facility was the central processing area for the surrounding mines. The furnaces on the NIMM facility were used to process mercury ore from

the San Carlos and Aurora mines which were transported by a 2

- mile aerial tram and through the Level 10 adit (Source 2). In addition, ore was transported from the Alpine, Anita, North Star, and other mines to be processed at the NIMM furnace (Ref. 6, p. 7 ; Ref. 12, p. 20, 23

- 25, 28 ). T he target

d istance limit for the New Idria Mercury Mine site is 19.9 miles (Ref. 20)

.SWOF

- Likelihood of Release 49 

### Surface water samples NIMM

- SW

- 1, NIMM

- SW

- 9, BLM

- SW

- 1, BLM

- SW

- 2, and BLM

- SW

- 3 were collected upstream of site sources (See Figure 2) . Surface water samples NIMM

- SW

- 3, NIMM

- SW

6, NI MM

- SW

- 7 (and its duplicate NIMM

- SW

- 15) , NIMM

- SW

- 8, and NIMM

- SW

- 10 were collected from San Carlos Creek adjacent to or downstream of site sources. One or more of the above hazardous substances were detected in all of these samples at concentrations signifi cantly above background (Ref. 6, pp. 3 4

- 3 6 ) . These hazardous substances have been detected in the Calcine Tailings Piles and/or the AMD (Ref. 6, pp. 20

- 21, 23 ).

In addition, the Calcine Tailings Piles (Source 1) and the Level 10 Adit AMD (Source 2) are

o bserved to be in direct contact with San Carlos Creek (Ref. 6, pp. 6

- 8, Photo 23, Photo 26 )

. A rsenic, cadmium, copper, lead, mercury, nickel, selenium, and zinc are present in one or both of these hazardous substance sources (Ref. 6, pp. 20

- 21, 23 ).SWOF

- Likelihood of Release 50 

### Haz ardous Substances Released

Arsenic, Cadmium, Copper, Lead, Mercury, Nickel, Selenium, Zinc

.

Surface Water Observed Release Factor Value: 550SWOF

- Likelihood of Release 51 

### 4.1.2.1.2 Potential to Release

Potential to Release was not scored, because an observed release was document ed.SWOF 

### / DW



### - Waste Characteristics 52 

### 4.1.2.2 Drinking Water Threat Waste Characteristics

4.1.2.2.1 Toxicity/Persistence

Hazardous
Substance Source

No. Toxicity

Factor

Value Persistence

Factor

Value * Toxicity/

Persistence

Factor Value (Ref. 1, Table 4

- 12) Reference

Arsenic 1,2 1 0,000 1 10,000 Ref. 2, p. 1

Cadmium 1,2 10,000 1 10,000 Ref. 2, p. 2

Copper 1,2 0 1 0 Ref. 2, p. 3

Lead 1 10,000 1 10,000 Ref. 2, p. 8 Mercury 1 10,000 1 10,000 Ref. 2, p. 8

Nickel 1,2 10,000 1 10,000 Ref. 2, p. 9

Selenium 2 100 1 100 Ref. 2, p. 10

Zinc 1,2 10 1 10 Ref. 2, p. 12



### Notes:

* The surface water category that includes rivers, oceans, coastal tidal waters, and great lakes was utilized to assign the hazardous substances persistence factor value (Ref. 1, Sect. 4.1.2.2.1.2). A persistence va lue of 1 was assigned according to the January 2004 Superfund Chemical Data Matrix (SCDM) table (Ref. 2, p p

. 1

- 3, 8

- 10, 12 ).

Arsenic, cadmium, lead, mercury and nickel had the highest toxicity/persistence value.

Toxicity/Persistence Factor Value: 10,00 0

4.1.2.2.2 Hazardous Waste Quantity

S o urce No. Source Type Source Hazardous Waste Quantity

1 Pile 163,105.3938

2 Other 8,409.6

Sum of Values: 171,514.9938 Hazardous Waste Quantity Factor Value : 10,000 (Ref. 1, Table 2

- 6)

4.1.2.2.3 Waste Cha racteristics Factor Category Value

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

Toxicity/Persistence Factor Value x Hazardous Waste Quantity Factor Value: 100,000,000 Subject to a maximum of 1 x 10 8 

### (Ref. 1, S ection 3.2.3)SWOF 

### / DW



### - Waste Characteristics 53 

### A hazardous waste quantity factor of 10,000 is assigned from Reference 1, Table 2

- 6 for a source hazardous waste quantity value of 171,514.9938. From Reference 2 and Table 4

- 12 of the HRS, arsenic, cadmium, lead, mercury and nickel have a t oxicity/persistence value of 10,000. The waste characteristics factor category value from Reference 1, Table 2

- 7 for a waste characteri stics product of 1 x 10 8 

### is 1 00.

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

- 7)SWOF / DW

- Targets 54 

### 4.1.2.3 Dri nking Water Threat Targets

4.1.2.3.1 Nearest Intake

There are no known drinking water intakes within the target distance limit.

Nearest Intake Factor Value: 0

4.1.2.3.2 Population

There are no known drinking water intakes within the target distance limit.

Population Factor Value: 0

4.1.2.3.3 Resources

Surface water is used for watering livestock within the target distance limit ( Ref. 9, p. 1; Ref. 11, p. 1; Ref. 17, pp. 8, 27)

.

Resources Factor Value: 5 (Ref. 1, Section 4.1.2.3.3 )SWOF/HFC

– Waste Characteristics 55 

### 4.1.3.2 Human Food Chain Threat Waste Characteristics

4.1.3.2.1 Toxicity/Persistence/Bioaccumulation

Hazardous
Substance Source

No. Toxicity

Factor

Value Persistence

Factor

Value* Bioaccumulation

Value** Toxicity/

Persistence/

Bioaccumulation

Factor Value (Ref . 1, Table 4

- 16) Reference

Arsenic 1,2 10,000 1 5 50,000 Ref. 2, p. 1

Cadmium 1,2 10,000 1 5,000 50,000,000 Ref. 2, p. 2

Copper 1,2 0 1 500 0 Ref. 2, p. 3

Lead 1 10,000 1 5 50,000 Ref. 2, p. 8
Mercury 1 10,000 1 50,000 500,000,000 Ref. 2, p. 8

Nickel 1,2 10,000 1 0.5 5,000 Ref. 2, p. 9

Selenium 2 100 1 50 5,000 Ref. 2, p. 10

Zinc 1,2 10 1 5 50 Ref. 2, p. 12



### Notes:

* 

### The surface water category that includes rivers, oceans, coastal tidal waters, and great lakes was utilized to assign the hazardous su bstances persistence factor value (Ref. 1, Sect. 4.1.2.2.1.2). A persistence value of 1 was assigned (Ref. 2, p p

. 1

- 3, 8

- 10, 12 ).

** 

### Bioaccumulation factor values are assigned from the SCDM (Ref. 2), for the type of water body "Fresh Water", in which the fisheries are located (Ref. 1, Sect. 4.1.3.2.1.3).

Mercury had the highest toxicity/persistence/bioaccumulation factor value.

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

– Waste Characteristics 56 

### 4.1.2.2.2 Hazardous Waste Quantity

Source No. Source Type Source Hazardous Waste Quantity

1 Pile 163,105.3938

2 Other 8409.6

Sum of Values: 171,514.9938

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

- 6)

4.1.2.2.3 Waste Characteristics Factor Category Value

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

(Toxicity/Persistence Factor Value) x (Hazardous Waste Quantity Factor Value) = 1 x 10 8


### Subject to a maximum of 1 x 10 8 

### (Ref. 1, Section 3. 2.3)

(Toxicity/Persistence Factor Value x Hazardous Waste Quantity Factor Value) x (Bioaccumulation Potential Factor Value) = 5 x 10 16



### A hazardous waste quantity factor of 10,000 is assigned from Reference 1, Table 2

- 6 for a source hazardous waste quanti ty value of 171,514.9938 . From Reference 2 and Table 4

- 12 of the HRS,

mercury has a toxicity/persistence value of 10,000 and a bioaccumulation potential factor of 50,000. The waste characteristics factor category value from Reference 1, Table 2

- 7 for a wa ste characteristics product of 5 x 10 1 6 

### (subject to a maximum product of 1 x 10 12 

### ) is 1,000.

Waste Characteristics Factor Category Value: 1,000 (Ref. 1, Table 2

- 7)SWOF/HFC

– Targets 57 

### 4.1.3.3 Human Food Chain Threat Targets

4.1.3.3.1 Food Chain Individual

T here are no known fisheries within the target distance limit.

Food Chain Individual Factor Value: 0

4.1.3.3.2 Population

There are no known fisheries within the target distance limit.

Human Food Chain Contamination Factor Value: 0SWOF/ENV

- Waste Characteristics 58 

### 4.1.4.2 Environmental T hreat Waste Characteristics

4.1.4.2.1 Ecosystem Toxicity/Persistence/Bioaccumulation

Hazardous
Substance Source

No. Ecosystem Toxicity Factor

Value Persistence

Factor

Value* Environmental

Bioaccumulation

Value** Ecosystem Toxicity/

Persistence/Env.

Bioa ccumulation

Factor Value (Ref. 1, Table 4

- 21) Reference

Arsenic 1, 2 10 1 5,000 50,000 Ref. 2, p. 1

Cadmium 1, 2 10,000 1 50,000 500,000,000 Ref. 2, p. 2

Copper 1, 2 1,000 1 5,000 5,000,000 Ref. 2, p. 3

Lead 1 1,000 1 50,000 50,000,000 Ref. 2, p. 8

Me rcury 1 10,000 1 50,000 500,000,000 Ref. 2, p. 8

Nickel 1, 2 100 1 500 50,000 Ref. 2, p. 9

Selenium 2 1,000 1 500 500,000 Ref. 2, p. 10

Zinc 1, 2 10 1 50,000 500,000 Ref. 2, p. 12



### Notes:

* 

### The surface water category that includes rivers, oceans, coast al tidal waters, and great lakes was utilized to assign the hazardous substances persistence factor value (Ref. 1, Sect. 4.1.2.2.1.2). A persistence value of 1 was assigned (Ref. 2, p p

. 1

- 3, 8

- 10, 12 ).

** 

### Bioaccumulation factor values are assigned for th e type of water body "Fresh Water", in which

the targets are located (Ref. 1, Sect. 4.1.3.2.1.3).

Cadmium and mercury had the highest ecosystem toxicity/persistence/environmental

bioaccumulation factor value.

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

- Waste Characteristics 59 

### 4.1.4.2.2. Hazardous Waste Quantity

Source No. Source Type Source Hazardous Waste Quantity

1 Pile 163,105.3938

2 Other 8,409.6

Sum of Values: 171,514.9938

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

- 6)

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 Subject to a maximum of 1 x 10 8 

### (Ref. 1, Section 3.2.3)

(Ecosystem Toxicity/Persistence Factor Value x Hazardous Waste Quantity Factor Value) x

Environmental Bioaccumulation Factor Value: 5 ,000,000,000,000

A hazardous waste qu antity factor of 10,000 is assigned from Reference 1, Table 2

- 6 for a source hazardous waste quantity value of 171,514.9938

. From Reference 2 and Table 4

- 12 of the HRS,

cadmium and mercury have a toxicity/persistence value of 10,000 and a n environmental

b ioaccumulation potential factor of 50,000. The waste characteristics factor category value from Reference 1, Table 2

- 7 for a waste characteristics product of 5 x 10 1 2 

### (subject to a maximum product of 1 x 10 12 

### ) is 1,000.

Waste Characteristics Factor Cat egory Value: 1,000 (Ref. 1, Table 2

- 7)SWOF / ENV

- Targets 60 

### 4.1.4.3 Environmental Threat Targets

Most Distant Level I Sample Samples have not been collected for documentation of Level I Actual Contamination.

Most Distant Level II Sample Sample ID: NIMM

- SD

- 34

Distance from the probable point of entry: 19.9 miles

Reference: Ref. 6, p. 29

4.1.4.3.1 Sensitive Environments

4.1.4.3.1.1. Level I Concentrations

Level I Actual Contamination is not documented

.

Sum of Level I Sensitive Environments Value: 0

4.1.4.3.1.2 Level II Concentrations

Level II Sensitive Environment Targets

The remote Panoche

- Silver

- San Carlos Creek watershed is one of only a few large watersheds characterized by intermittent to perennial flow conditions flowing east to the San Joaquin Valley

f rom the 200 mile long Diablo Range. San Carlos and Silver creeks are characterized by extensive wetlands in a predominantly arid, upland environment

. The average precipitation measured between 1918 and 1976 in the region is 15.17 inches annually (Ref. 13 , pp. 5

- 6 ; Ref. 31 )

. These wetlands are continuous, running the entire length of both streams. As such, the aquatic and wetland habitats and

associated with San Carlos and Silver C reeks, and their dependent animal species, are of regional ecological sign ificance. The presence of the Pacific chorus frog and western pond turtle within this watershed is one measure of the importance of the aquatic and wetland features to regionally rare aquatic species. In addition, wetlands associated San Carlos and Silver creeks perform other important ecological functions including surface and subsurface storage of water, energy dissipation,

moderation of ground water flow or discharge, nutrient cycling, removal of imported elements and compounds, retention of particulate s, organic carbon storage, the support of characteristic plant communities and detrital biomass, the maintenance of the spatial structure of animal habitat, the provision of habitat interspersion and connectivity, and habitat support for the distribution a nd

abundance of invertebrates and vertebrates (Ref. 13, pp. 5

- 6)

.

The U.S. Fish and Wildlife Service (USFW) reviewed a 4

- mile buffer zone area around the site and

the wetlands and intermittent pools up to 20 miles downstream of the NIMM site (analysis ar ea) that includes San Carlos, Silver, and Panoche Creeks. USFW stated that t he analysis area around the mine and areas of downstream water resources, including wetlands under public ownershipSWOF / ENV

- Targets 61 

### constitute very unique habitats to endemic threatened and endan gered species which use these

resources . The analysis area is comprised of unique biotic communities . In addition, it is in an area that is vitally important for the maintenance of an ecologically valuable biotic community. The

combination of a remnant ecosystem, an arid environment, seasonal and perennial wetlands in an important corridor, the northernmost populations of several threatened and endangered species, high biological diversity, and an internationally important area for migratory birds all co ntribute to the significant ecological uniqueness of the analysis area (Ref. 30, p. 1 , 2 )

.

The Pan oche Valley is one of only two valleys in California that support arid grassland as uncultivated grassland. This unconverted annual grassland support the endangered San Joaquin kit fox ( Vulpes macrotis mutica ), giant kangaroo rat ( Dipodomys ingens ), and blunt

- nosed leopard lizard ( Gambilia sila ) (Ref. 30, p. 3 ; Ref. 32, p. 22, 28, 31 ).

The unique soil types and geologic formations of the Idria, Sampson, and North Hill San Carlos peaks has lead to a unique assemblage of endemic plant species, which includes the threatened San Benito evening primrose ( Camissonia benitensis ) (Ref. 30, p. 4, 5 ; Ref. 33, p. 7)

.

Sensitive Environment Distance from

PPE to Neare st
Sensitive

Environment References Sensitive

Environment Value (Ref. 1,

Table 4

- 23) Particular areas, relatively small in size, important to maintenance of unique biotic

communities. 0 miles Ref. 13, pp. 5

- 6; Ref. 30, p. 1, 2 25

San Joaquin kit fox ( Vul pes macrotis mutica ) 0 miles Ref. 30, p. 2, 3 ; Ref. 32, p. 22 75

Giant kangaroo rat ( Dipodomys ingens ), 0 miles Ref. 30, p. 3 ; Ref. 32, p. 28 75

Blunt

- nosed leopard lizard ( Gambilia sila) 0 miles Ref. 30, p. 3 ; Ref. 32, p. 31 75

Sum of Level II Se nsitive Environments Value: 250

Level II Wetland FrontagesSWOF / ENV

- Targets 62 

### The EPA conducted a wetland survey of San Carlos Creek at the Site and downstream of the Site, the entire length of Silver Creek, and a portion of Panoche Creek at the confluence of Silver Creek.

Field identification of wetlands and other waters of the United States were conducted in accordance with the 1987 Corps of Engineers Wetlands Delineation Manual, National List of Vascular Plant Species that Occur in Wetlands: 1996 National Summar y; Arid West Regional Supplement to the Wetlands Delineation Manual; and the Corps Field Guide to the Identification of the Ordinary High Water Mark in the Arid West Region. The Corps’ 1987 Wetlands Delineation manual identifies key diagnostic criteria fo r determining the presence of wetlands. These include (1) wetland hydrology, (2) hydric soils, and (3) a predominance of wetland vegetation. Wetland sampling sites and boundaries were mapped using GPS. Wetland SAMPLE data sheets were filled out for

repr esentative wetland types and sites. The wetland delineation is consistent with guidance (Ref. 13, p. 2).

The wetland survey confirmed the presence of jurisdictional wetlands adjacent to both banks of San

Carlos Creek from the New Idria Mercury Mine facil ity downstream to its confluence with Larious Creek; and adjacent to both banks of Silver Creek from the confluences of San Carlos and Larious

creeks downstream to its confluence with Panoche Creek (Ref. 13, p. 6)

.

Distance from the furthest downstream PP E to the confluence of San Carlos Creek with Larious Creek is 4.7 miles. Distance from the confluence of San Carlos and Larious Creeks to the target distance limit (represented by sample NIMM

- SD

- 34) is 15.2 miles (Ref. 6, pp. 27, 29).

The wetland frontag e miles presented below include frontage from both banks of each creek. The length of the wetlands on San Carlos Creek and Silver Creek are presented in Figures 1 through 9 of Reference 13 (Ref. 13).

Wetland Wetland Frontage (miles) References

San Car los Creek 9.4 miles Ref. 6, p. 27 ; Ref. 13, pp. 4 , 6 , Figures

1

- 9 ; Ref. 20

Silver Creek 30.4 miles Ref. 6, p. 29 ; Ref. 13, pp. 5 , 6 , Figures

1

- 9 ; Ref. 20

Sum of Level II Wetland Frontages: 39.8 miles

Wetlands Value (Ref. 1, Table 4

- 24): 500

Sum of L evel II Sensitive Environments Value + Wetlands Value: 750 (Ref. 1, Section 4.1.4.3.1.2)

Level II Concentrations Factor Value: 75063 

# Attachments!)i!)i[i[i[i[i[i[i[i[i[i[i[i[i[i[i[i[i[i[i[i[i[i[i[i!)i[i[i[i!)i!)i!)i!)i[i[i[i[i[i!)i[i!)i[i[i!)i!)i!)i[i!)i[i!)i[i[i!)i[i[i[i!)i!)i!)i!)!)i!)i[i!)i!)i!)i!)i[i!)i[i[i!)i!)i!)i!)i!)i[i!)i[i!)i!)i[i!)i!)i!)i!)i!)i!)i!)i[i[i[i!)i!)i[i!)i[i!)i!)i!)i[i[i!!)i[i[i[i[i!)i!)i!)i!)i!)i!)i[i[i!)i[i!)i!)i[i[i[i!)i[i[i[i!)i[iihFigure10 5MilesSite Location MapNew Idria Mercury MineSan Benito County, CaliforniaMap 1Map 2Map 3Map 4Map 5MendotaPoolBelmont Avenue

P a n o c h e C r e e k

P a n o c h e C r e e k S i l v e r C r e e k

L a r i o u s

C r e ek S

a

n

C

a

r l

o

s

C

r ee

k



### S

i l

v

e

r

C

r

e

e k 

### Ea s t Fo r k S

a

n Ca r

l o s Cr e ekLegend[iMercury Mines!)iOther MinesSurface Water PathwayFlood Water PathwayStreams/drainagesSite Property BoundaryDetailed Maps

S u r f a ce W a t e r P a t h w a y F lo w D ir e ct io n

### ! .

! . ! .

! . ! . !

. ! .

! .

! . ! .

! . ! . ! .

! . ! .

! . ! . ! . ! . ! . ! . ! . ! . ! .



# p o ! H 

# p o ! H



# p o ! H 

# p o ! H 

# p o ! H



# p o ! H



# p o p o p o p o p o ! H



# [ i [ i [ i [ i

[ i [ i [ i

[ i



# ! 

# ) i 

# [ i [ i

[ i

[ i [ i [ i [ i

[ i [ i [ i

[ i

Figure 

### 2 Sample Locations - Map 1A

New Idria Mercury Mine San Benito County, California 

# [ i Mercury Mines 

# ! 

# ) i Other Mines

Property Boundary

Site Boundary (Inset)

Surface Water Pathway

Streams

0 2

, 0 0 0 Feet



### Reservoir ppb = parts per billion ppm = parts per million ppt = parts per trillion Hg = mercury MMHg = methylmercury 

### Spanish

Mines

Aurora
Mine

North Star
Mine San Carlos
Mine Ranchito
Mine

Creek Pit Mine

Sulphur Spring
Mine New Idria
Mine

Molina Mine

NIMM-SW-9/SD-11 Hg in sediment: <0.11R ppm Hg in water: 0.10J ppb (total) Hg in water: <0.20 ppb (dissolved)

NIMM-SS-2 Hg in soil: <0.10 ppm

NIMM-SS-1 Hg in soil: 0.19 ppm NIMM-SD-1 Hg in sediment: 0.19 ppm NIMM-SW-1 Hg in water: 0.084J ppb (total) Hg in water: <0.20 ppb (dissolved) BLM-SW-1 Hg in water: <0.20 ppb (total) Hg in water: <0.20 ppb (dissolved) BLM-SW-2 Hg in water: <020 ppb (total) Hg in water: <0.20 ppb (dissolved) BLM-SW-3 Hg in water: <0.20 ppb (total) Hg in water: <0.20R ppb (dissolved) NIMM-SW-2/SD-2 (Reservoir Water Sample) Hg in sediment: 5.5 ppm Hg in water: <0.20 ppb (total) Hg in water: <0.20 ppb (dissolved) MMHg in water: 0.245 ppt (dissolved)

T ri b

u t a ry t o E

a s t F

o rk

S

a n C

a rl

o s C

re e k 

# p o Surface Water Sample 

# p o ! H 

### Sediment & Surface Water Samples 

### Legend

! . Soil/Sediment/Tailing Samples

### " / " /
" / " / " / " / " /

" / " / " / " / " / " / " / "

/ " /

" / " / " / # 0 # 0 # 0 # 0 # 0 # 0

# 0 # 0



### ! [ (

! [ ( ! [ ( ! [ (

! [ ( ! [ (

! [ ( ! [ ( ! [ ( ! [ (



# [ i [ i [ i [ i

[ i [ i [ i

[ i



# ! 

# ) i 

# [ i [ i

[ i

[ i [ i [ i [ i

[ i [ i [ i

[ i

Figure 

### 3 Historic Sample Locations - Map 1B New Idria Mercury Mine San Benito County, California 

### Legend

" / 1997 EPA Samples

! [ ( USGS Samples

# 0 

### RWQCB Samples



# [ i Mercury Mines 

# ! 

# ) i Other Mines

Property Boundary

Site Boundary (Inset)

Surface Water Pathway

Streams

0 2

, 0 0 0 Feet

1997 EPA Sample SW-1 Hg in sediment: 1.5 ppm Hg in water: 0.1 ppb 1999 USGS Sample 99AU-5 Hg in sediment: 2.13 ppm Hg in water: 0.0224 ppb 1997 EPA Sample SW-2 Hg in sediment: 1.6 ppm Hg in water: 0.1 ppb

1997 EPA Sample NIM-19 Hg in soil: 3.9 ppm 1999 USGS Sample 99AU-3 Hg in sediment: 0.83 ppm Hg in water: 0.00084 ppb

1999 USGS Sample 99AU-4 Hg in water: 0.876 ppb 1999 USGS Sample 99AU-1 Hg in sediment: 12.07 ppm Hg in water: 0.0364 ppb

1999 USGS Sample 99AU-2 Hg in sediment: >100 ppm Hg in water: 0.00826 ppb 1999 USGS Sample 99AU-6 Hg in sediment: 61.4 ppm Hg in water: 0.0215 ppb 1999 USGS Sample 99AU-7 Hg in sediment: 52.4 ppm Hg in water: 0.0139 ppb 1997 EPA Sample SW-3 Hg in sediment: 2.6 ppm Hg in water: 0.1 ppb 1997 EPA Sample NIM-18 Hg in soil: 1.4 ppm 1988 RWQCB Sample NIM6 Hg in water: ND <0.3 ppb 2003 RWQCB Sample 30115-5 Hg in water: ND <0.2 ppb



### Reservoir ppb = parts per billion ppm = parts per million Hg = mercury

T ri b

u t a ry t o E

a s t F

o rk

S

a n C

a rl

o s C

re e kV T 

### ! .

! . ! .

! . ! . ! . ! .

! . ! .

! .

! .

! . ! .

! .

! . 

# p o ! H



# p o ! H



# p o ! H 

# p o ! H



# p o ! H

Figure 

### 4 Sample Locations - Map-1C

New Idria Mercury Mine San Benito County, California N e w I d r i a R o a d

C l e a r C r e e k R o a d

Furnace S a n C a r l o s C r e e k
V T 

### Level 10 Adit

Site Boundary

Calcine Piles

Waste Rock Pile

Acid Mine Drainage

San Carlos Creek

0 4 0 0 Feet ppb = parts per billion ppm = parts per million ppt = parts per trillion Hg = mercury MMHg = Methyl mercury

School Parcel 

### Northern

Tailing

Piles

Southern Tailing

Piles

Waste
Rock
Pile

NIMM-SW-4/SD-4 Hg in sediment: 14.4 ppm Hg in water: <0.20 ppb (total) Hg in water: <0.20 ppb (dissolved) NIMM-SW-3/SD-3 Hg in sediment: 4.9 ppm Hg in water: 0.28 ppb (total) Hg in water: 0.30 ppb (dissolved) MMHg in water: 0.039J ppt (dissolved)

NIMM-SW-5/SD-7 Hg in sediment: 25.0 ppm Hg in water: 21.2 ppb (total) Hg in water: 11.2 ppb (dissolved) MMHg in water:2.30 ppt (dissolved) NIMM-SD-5 Hg in sediment: 12.1 ppm NIMM-SD-6 Hg in sediment: 41.3 ppm NIMM-SW-6/SD-8 Hg in sediment: 4.7 ppm Hg in water: 4.9 ppb (total) Hg in water: 0.16J ppb (dissolved)

NIMM-TL-5 Hg in tailings: 446 ppm NIMM-TL-4 Hg in tailings: 134 ppm

NIMM-TL-3 Hg in tailings: 191 ppm NIMM-TL-6 Hg in tailings: 38.7 ppm NIMM-TL-7 Hg in tailings: 3.8 ppm

NIMM-TL-8 Hg in tailings: 91.6 ppm

NIMM-TL-9 Hg in tailings: 72.3 ppm NIMM-TL-10 Hg in tailings: 31.5 ppm NIMM-SW-7/SD-9 Hg in sediment: 4.9 ppm Hg in water: 4.8 ppb (total) Hg in water: 0.14J ppb (dissolved) MMHg in water: 0.210 ppt (dissolved) 

### Legend

! . Soil/Sediment/Tailings 

# p o ! H 

### Sediment & Surface Samples

Water Samples Former Unpermitted
Landfill

Level 10 Adit" / " /

" / " / "

/

" / "

/ "

/ " / " /

" / " /

" /

" /

# 0

# 0 # 0

# 0

# 0 # 0

# 0

V T 

### ! [ ( ! [ ( ! [ (

Figure 

### 5 Historic Sample Locations - Map-1D New Idria Mercury Mine San Benito County, California Former Unpermitted
Landfill

N e w I d r i a R o a d

C l e a r C r e e k R o a d

Furnace S a n C a r l o s C r e e k " / 

### 1997 EPA Samples

! [ ( USGS Samples

# 0 

### RWQCB Samples V T 

### Level 10 Adit

Site Boundary

Calcine Piles

Waste Rock Pile

Acid Mine Drainage

San Carlos Creek

0 4 0 0 Feet

1975 RWQCB Sample #2 Hg in AMD: 2.3 ppb 1988 RWQCB Sample NIM1 Hg in AMD: ND <0.3 ppb 2003 RWQCB Sample 30115-7 Hg in AMD: <0.2 ppb 1997 EPA Sample NIM-1 Hg in AMD: 0.2 ppb 1997 EPA Sample NIM-7 Hg in sediment: 1.2 ppm 1997 EPA Sample SW-4 Hg in sediment: 19.7 ppm Hg in water: 0.54 ppb 1975 RWQCB Sample #1 Hg in water: 0.2 ppb

1988 RWQCB Sample NIM2 Hg in AMD: ND <0.3 ppb 1997 EPA Sample NIM-5 Hg in sediment: 0.4 ppb 1988 RWQCB Sample NIM4 Hg in water: 5.0 ppb 1997 EPA Sample SW-5 Hg in sediment: 8.4 ppm Hg in water: 5.0 ppb

1975 RWQCB Sample #4 Hg in water: 4 ppb 1988 RWQCB Sample NIM5 Hg in water: ND <0.3 ppm 1997 EPA Sample NIM-6 Hg in sediment 11.7 ppm 1997 EPA Sample NIM-17 Hg in sediment 43 ppm 1997 USGS Sample 97NI-5W Hg in water: 17.28 ppb 1997 USGS Sample 97NI-6W Hg in sediment: 0.0211 ppm Hg in water: 11.985 ppb

1975 RWQCB Sample #3 Hg in water: 2.7 ppb 1988 RWQCB Sample NIM3 Hg in water: 8.0 ppb 1997 USGS Sample 97NI-7W Hg in water: 4.471 ppb 1999 USGS Sample 99AU-8 Hg in water: 0.372 ppb 1997 EPA Sample NIM-13 Hg in tailings 40.7 ppm 1997 EPA Sample NIM-15 Hg in tailings 27.1 ppm 1997 EPA Sample NIM-14 Hg in tailings 74.6 ppm

1997 EPA Sample NIM-16 Hg in tailings 42.2 ppm

1997 EPA Samples Hg in Sediment NIM-8: 0.22 ppm NIM-9: 4.2 ppm NIM-10: 13.7 ppm NIM-11: 8.5 ppm NIM-12: 25.7 ppm Hg in AMD NIM-2: 0.2 ppb NIM-3: 0.6 ppb NIM-4: 16.5 ppb ppb = parts per billion ppm = parts per million Hg = mercury

School Parcel

2003 RWQCB Sample 30115-8 Hg in AMD: ND <0.2 ppb 

### Northern

Tailing

Piles

Southern Tailing

Piles

Waste
Rock
Pile 

### Legend

1997 EPA Samples Hg in Sediment NIM-8: 0.22 ppm NIM-9: 4.2 ppm NIM-10: 13.7 ppm NIM-11: 8.5 ppm NIM-12: 25.7 ppm Hg in AMD NIM-2: 0.2 ppb NIM-3: 0.6 ppb NIM-4: 16.5 ppb Level 10

Adit

# ! ! 

# ) ) i i 

# p o ! H



# p o ! H 

### ! .

! .



# p o ! H



# p o ! H NIMM-SW-8/SD-10 Hg in sediment: 32.6 ppm Hg in water: 4.6 ppb (total) Hg in water: 0.14J ppb (dissolved) NIMM-SW-10/SD-12 Hg in sediment: 8.9J ppm Hg in water: 0.79 ppb (total) Hg in water: <0.20 ppb (dissolved) NIMM-SD-13 Hg in sediment: 2.0J ppm NIMM-SW-12/SD-14 (attribution) Hg in sediment: 0.081J ppm Hg in water: <0.20 ppb (total) Hg in water: <0.20 ppb (dissolved) MMHg in water: 0.086 ppt (dissolved) NIMM-SW-14/SD-16 Hg in sediment: 1.8J ppm Hg in water: <0.20 ppb (total) Hg in water: <0.20 ppb (dissolved) MMHg in water: 0.072 ppt (dissolved)

NIMM-SD-15 Hg in sediment: 4.6J ppm

Figure 

### 6 Sample Locations - Map 2A

New Idria Mercury Mine San Benito County, California 

# [ i Mercury Mines 

# ! 

# ) i Other Mines

Surface Water Pathway

Streams

0 2

, 0 0 0 Feet

E

a

s t F o

r k S a

n C a

r

l o

s C r e

e

k ppb = parts per billion ppm = parts per million ppt = parts per trillion Hg = mercury MMHg = methyl mercury

L

a

ri

o

u

s C r e

e k



### Magnetite
Mine Gypsum
Mine Legend

! . Sediment Sample 

# p o ! H 

### Sediment & Surface Water Samples

# ! ! 

# ) ) i i

" / " / "

/ " / " / " / " / " / " /

# 0 # 0



### ! [ ( ! [ ( ! [ ( ! [ (

1997 EPA Sample SW-7 Hg in sediment: 1.5 ppm Hg in water: 0.1 ppb 1999 USGS Sample 99NI-3W Hg in sediment: 0.0278 ppm Hg in water: 13.55 ppb 1988 RWQCB Sample NIM7&8 Hg in sludge: 1.25 ppm Hg in water: <0.3 ppb 1975 RWQCB Sample #5 Hg in water: 7.8 ppb

1997 EPA Sample SW-6 Hg in sediment: 10 ppm Hg in water: 9.6 ppb 1997 EPA Sample SW-8 Hg in sediment: 1.6 ppm Hg in water: ND 1997 EPA Sample SW-9 Hg in sediment: 2.2 ppm Hg in water: 12 ppb 1999 USGS Sample 99NI-2W Hg in sediment: 0.0279 ppm Hg in water: 10.16 ppb 1997 EPA Sample SW-12 Hg in sediment: 13.4 ppm Hg in water: 11.4 ppb 1999 USGS Sample 99NI-1W Hg in sediment: 0.0275 ppm Hg in water: 19.6 ppb 1997 EPA Sample SW-13 Hg in sediment: 5.6 ppm Hg in water: 6.9 ppb

1997 EPA Sample SW-12 Hg in sediment: 0.11 ppm

1997 EPA Sample SW-10 Hg in sediment: 22.5 ppm Hg in water: 3.8 ppb 1997 EPA Sample SW-14 Hg in sediment: 9.7 ppm Hg in water: 0.47 ppb

Figure 

### 7 Historic Sample Locations - Map 2B New Idria Mercury Mine San Benito County, California



### Legend

" / 1997 EPA Samples

! [ ( USGS Samples

# 0 

### RWQCB Samples



# [ i Mercury Mines 

# ! 

# ) i Other Mines

Surface Water Pathway

Streams

0 2

, 0 0 0 Feet

E

a

s t F o

r k S a

n C a

r

l o

s C r e

e

k ppb = parts per billion ppm = parts per million Hg = mercury

L

a

ri

o

u

s C r e

e k



### Magnetite
Mine Gypsum
Mine

1997 USGS Sample 97NI-4W Hg in sediment: 0.0325 ppm Hg in water: 13.5 ppb

### ! . ! . ! .

! .

! .

!

.

Figure 

### 8 Sample Lcoations - Map 3

New Idria Mercury Mine San Benito County, California 

### Legend

! . Sediment Samples

Surface Water Pathway

Streams

0 2

, 0 0 0 Feet

NIMM-SD-17 Hg in sediment: 3.9J ppm ppb = parts per billion ppm = parts per million Hg = mercury

NIMM-SD-18 Hg in sediment: 2.7J ppm NIMM-SD-19 Hg in sediment: 0.070J ppm NIMM-SD-20 Hg in sediment: 11.2J ppm NIMM-SD-21 Hg in sediment: 1.3J ppm NIMM-SD-22 Hg in sediment: 0.60J ppm

S i l v e r C r e e k

### ! .

! . ! . ! . ! . ! . ! . ! .

Figure 

### 9 Sample Locations- Map 4A

New Idria Mercury Mine San Benito County, California 

### Legend

! . Sediment Samples

Surface Water Pathway

Streams

0 2

, 0 0 0 Feet ppm = parts per million Hg = mercury

NIMM-SD-23 Hg in sediment: 0.38J ppm NIMM-SD-24 Hg in sediment: 4.2J ppm NIMM-SD-25 Hg in sediment: 2.4J ppm NIMM-SD-26 Hg in sediment: 1.7J ppm NIMM-SD-27 Hg in sediment: 1.5J ppm NIMM-SD-28 Hg in sediment: 1.1J ppm NIMM-SD-29 Hg in sediment: 2.3J ppm NIMM-SD-30 Hg in sediment: 1.2 ppm

S

a

n

B

e

n

i t o

C

o

u

n t y F r e s

n o

C

o

u

n t y

### " /

Figure 

### 10 Historic Sample Locations- Map 4B New Idria Mercury Mine San Benito County, California 

### Legend

" / 1997 EPA Samples

Surface Water Pathway

Streams

0 2

, 0 0 0 Feet ppm = parts per million Hg = mercury

1997 EPA Sample SW-15 Hg in sediment: 1.5 ppm

S

a

n

B

e

n

i t o

C

o

u

n t y F r e s

n o

C

o

u

n t y

# ! 

# ) i

! . ! . ! . ! . P

Figure



### 11 Sample Locations - Map 5A

New Idria Mercury Mine San Benito County, California 

### Legend

! . Sediment Samples



# [ i Mercury Mines 

# ! 

# ) i Other Mines

Surface Water Pathway

Streams

0 2

, 0 0 0 Feet ppb = parts per billion ppm = parts per million Hg = mercury

NIMM-SD-31 Hg in sediment: 1.0 ppm NIMM-SD-33 Hg in sediment: 0.050J ppm

NIMM-SD-32 Hg in sediment: 1.0 ppm NIMM-SD-34 Hg in sediment: 1.1 ppm 

### Diatomite
Mine

S i l v e r C r e e k P a n o c h e C r e e k

# ! 

# ) i

" / " / " / P

Figure 

### 12 Historic Sample Locations - Map 5B New Idria Mercury Mine San Benito County, California 

### Legend

" / 1997 EPA Samples



# [ i Mercury Mines 

# ! 

# ) i Other Mines

Surface Water Pathway

Streams

0 2

, 0 0 0 Feet ppb = parts per billion ppm = parts per million Hg = mercury

1997 EPA Sample SW-17 Hg in sediment: 0.14 ppm Hg in water: 0.2 ppb 

### Diatomite
Mine

S i l v e r C r e e k P a n o c h e C r e e k

1997 EPA Sample SW-16 Hg in sediment: 1.5 ppm Hg in water: 0.2 ppb 1997 EPA Sample SW-18 Hg in sediment: 0.13 ppm