report on tailing bioaccessibility study results …

R E P O R T

REPORT ON TAILING BIOACCESSIBILITY STUDY RESULTS QUESTA MINE, NM

Prepared for Chevron Mining Inc. Questa, New Mexico

February 24, 2010

URS Corporation McDaniel Lambert Inc. 8181 E. Tufts Ave 1608 Pacific Ave. Suite 201 Denver, CO 80237 Venice, CA 90291 Project No. 22236243

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TABLE OF CONTENTS

Section 1 ONE Introduction..................................................................................................................... 1-1

Section 2 TWO Bioaccessibility Testing Procedure .............................................................................. 2-1

Section 3 THREE Sampling and Results .................................................................................................... 3-1

3.1 Sampling Locations and Analyses ........................................................... 3-1 3.2 In Vitro Bioaccessibility Test Results...................................................... 3-3

Section 4 FOUR Data Validation................................................................................................................ 4-1

Section 5 FIVE Conclusions .................................................................................................................... 5-1

5.1 Bioaccessibility ........................................................................................ 5-1 5.2 Mineral Species Present........................................................................... 5-2 5.3 Tailing Bioaccessibility and the Preliminary Remediation Goal............. 5-3

Section 6 SIX References ...................................................................................................................... 6-1

List of Tables Table 1 Tailing Sample Descriptions

Table 2 Tailing Phase In Vitro Bioaccessibility Test Results

Table 3 Relative Mass of Bioaccessible Molybdenum Minerals

List of Figures Figure 1 Questa Tailing Facility Tailing Bioaccessibility Sample Locations

Figure 2 Surface Tailing Pile near Dam No. 1

Figure 3 Tailing Pond behind (north) of Dam 4

Figure 4 Dam 1 Pond Sampling Location

Figure 5 Bioaccessible Molybdenum Concentrations in Tailing

Figure 6 Bioaccessible Molybdenum in Tailing and Spring Gulch Rock Pile

Figure 7 SEM/Microprobe Molybdenum Mineral Speciation

List of Appendices Appendix A Data Validation Report

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SECTIONONE Introduction

1. Section 1 ONE Introduction

A sampling program was undertaken at Chevron Mining Inc.’s (CMI) Questa Mine tailing facility (the Tailing Facility) to assess molybdenum bioaccessibility. This work comprises the third phase of bioaccessibility work and is comparable to similar work undertaken at the Questa mine proper in association with the Remedial Investigation/Feasibility Study in accordance with the Comprehensive Environmental Compliance and Liability Act. This phase of work was designed to evaluate what portion of the molybdenum present in the tailing impoundments is in a form that is available for potential exposure through the food chain to deer and elk.

Tailing samples from ongoing and past operational areas of the Tailing Facility were collected and evaluated for molybdenum bioaccessibility; the fraction of molybdenum ingested that becomes available for absorption in the body. In this report, the definitions of bioaccessibility and bioavailability put forward by Semple, Doick, Jones, Burauel and Craven (2004) will be used. They define a:

• “bioavailable compound as that which is freely available to cross an organism’s cellular membrane from the medium the organism inhabits at a given time;” and

• “bioaccessible compound as that which is available to cross an organism’s cellular membrane from the environment, if the organism has access to the chemical.”

• They summarize: “bioaccessibility encompasses what is actually bioavailable now plus what is potentially bioavailable.” They further clarify that “routine chemical techniques described in the literature, for example, actually estimate the bioaccessible rather than the bioavailable fraction.” This report focuses on bioaccessibility rather than bioavailablility.

This tailing bioaccessibility report complements the Spring Gulch Rock Pile Soil Molybdenum Toxicity Study, (GEI 2008) and the two previous phases of bioaccessibility work on Mine Site samples (URS 2008) by providing additional bioaccessibility data for tailing material from the Tailing Facility.

Section 2 of this report describes the bioaccessibility test procedures; Section 3 presents the tailing sampling and results; Section 4 is a summary of the data validation results for both phases of work; Section 5 summarizes the conclusions of this bioaccessibility study; Section 6 contains the reference list; Appendix A contains the data validation findings.

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SECTIONTWO Bioaccessibility Testing Procedure

2. Section 2 TWO Bioaccessibility Testing Procedure

Tailing samples were analyzed for molybdenum bioaccessibility under the direction of Dr. John Drexler at the University of Colorado Laboratory for Environmental and Geological Studies. The in vitro bioaccessibility test that was used (Medlin and Drexler 1995) is designed to measure the fraction of a chemical that dissolves from a soil sample under simulated gastrointestinal conditions. In this test, the amount of an inorganic that is considered bioaccessible is what leaches into solution. The in vitro test procedure is conducted as follows:

• Sample preparation: the test material is air dried and fractionated using a 250 um sieve. The < 250 um soil fraction represents the fraction most likely to adhere to human hands and subsequently be ingested.

• Leachable molybdenum analysis: a known mass of the < 250 um test sample is added to an acidic aqueous extraction fluid, and adjusted to pH 1.5 using hydrochloric acid and a glycine buffer. The extraction proceeds at 37 °C (98.6 °F), with shaking, for one hour. Once this procedure is complete, the test solution (leachate) is analyzed for molybdenum.

• Digestible molybdenum analysis: the digestible molybdenum in a known mass of the < 250 um test fraction is extracted following EPA Method 3050 procedures using nitric acid, hydrochloric acid and hydrogen peroxide maintained at 95°C. Per Method 3050B, “this method is not a total digestion technique for most samples. It is a very strong acid digestion that will dissolve almost all elements that could become “environmentally available”. This procedure intentionally is not vigorous enough to dissolve elements bound in silicate structures because they are not usually mobile in the environment or in the digestive tract.

• Bioaccessibility calculation: the mass of molybdenum in the leachate is compared to the total mass of digestible molybdenum. The resultant fraction represents the portion of digestible molybdenum that is considered bioaccessible.

The test is generally accepted for risk assessment purposes by EPA and state agencies for inorganics for which there are accepted animal models demonstrating a strong correlation between in vitro and in vivo bioaccessibility and toxicity. Although additional in vivo work would be necessary to make the results directly applicable to risk assessment, the relative bioaccessibility of molybdenum provides insight into the relative solubilities and forms of molybdenum from various locations within the tailing deposited across time.


SECTIONTHREE Sampling and Results

3. Section 3 THREE Sampling and Results

3.1 SAMPLING LOCATIONS AND ANALYSES Tailing samples were collected from the Tailing Facility on January 26, 2010. Sample locations are shown on Figure 1. Tailing samples were collected from a zero to 12-inch depth range using a decontaminated hand-held bucket auger, pick axe or shovel. Surface soil was removed from above the tailing material where present. Only at the Dam 1 pond sampling location was a 1- to 4-inch thick layer of surface soil present on top of the tailing material. Surface debris (leaf litter, etc.), gravel-sized and larger rocks (visually determined), and snow were removed; the samples mixed in a stainless-steel bowl with a trowel and freshly gloved hands and placed into 1-gallon zip-loc bags for shipment under custody to the laboratory. Table 1 presents the bioaccessibility test material sample descriptions.

Table 1 – Tailing Sample Descriptions

Location Sample ID Soil

Description USCS Class Color Staining Odor Moist*

Surface tailing pile - south of Dam No. 1 Dam1-Pile-A-T01N-TLG Tailing - Light gray none none Dry

Surface Tailing Pile - south of Dam No. 1 Dam1-Pile-B-T01N-TLG Tailing - Light gray none none Dry

Surface Tailing Pile - south of Dam No. 1 Dam1-Pile-C-T01N-TLG Tailing - Light gray none none Dry

Tailing Pond behind Dam No. 4 - southwest corner of pond Dam4-SW-Pond-A-T01N-TLG Tailing - Light gray none none Dry

Tailing pond behind Dam No. 4 - southwest corner of pond Dam4-SW-Pond-B-T01N-TLG Tailing - Light gray none none Dry

Tailing pond behind Dam No. 4 - southwest corner of pond Dam4-SW-Pond-C-T01N-TLG Tailing - Light gray none none Dry

Dam 1 pond- north of Dam 1 and northwest of Change House Historic-Pond-A-T01N-TLG Tailing - Light brownish

gray none none Slight (frozen)

Dam 1 pond - north of Dam 1 and northwest of Change House

Historic-Pond-B-T01N-TLG Tailing - Light brownish gray none none Slight

(frozen)

Dam 1 pond - north of Dam 1 and northwest of Change House

Historic-Pond-C-T01N-TLG Tailing - Light brownish gray none none Slight

(frozen)

Note: Ambient air temperature during the sampling event was ~between 15 and 20° degrees Fahrenheit.

Three tailing samples were collected at each of three different areas in the Tailing Facility (Figure 1). Tailing samples were selected to represent three different types of physical conditions (surface, submerged, fresh) and lengths of time exposed to atmospheric conditions.


Inset 3

Inset 1

Inset 2

QuestaTailing Facility

RED RIVER

ChangeHouse

Questa

High

way 5

22

Dam No. 4

Dam No. 1

PROJECTNOTES:Aerial photograph provided byChevron Mining Inc. - Questa Mine (2007).

Scale 1:19200 or 1 in = 1600 ft

0 1,600

Feet

QUESTA TAILING FACILITYTAILING BIOACCESSABILITY

SAMPLE LOCATIONS

FIGURE 1LegendSample LocationProperty BoundaryTailing Pipeline

RiverCreekGulchCanyon

URS Center8181 East Tufts AvenueDenver, CO 80237-2637(303) 694-2770

TailingBioaccessibility Report

CHEVRON MINING INC. - QUESTA MINEArcGIS 9.3

Denver/GIS

APPLICATION

DRAWN BYfig1_tail_bioacc_loc.mxd

02/18/2010

FILENAME

DATE

REVISION DATE 22236247

Dam 1 Pond - CDam 1 Pond - B

Dam 1 Pond - A

Surface Tailing Pile - C Surface Tailing Pile - BSurface Tailing Pile - A

Tailing Pond Behind Dam No 4 - C

Tailing Pond Behind Dam No 4 - B

Tailing Pond Behind Dam No 4 - A

Inset 1

Inset 2

Inset 3

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• Tailing for the surface condition was sampled from the southeast portion of Dam No. 1. The sampling location was a deposit of tailing material that resulted from a pipeline break at the Tailing Facility. These materials have been exposed to the atmosphere for extended periods of time, existing in its current form for more than 20 years during which time oxidation of some of the molybdenum minerals could have occurred. Figure 2 provides pictures of the stockpiled material and the collection of these samples.

• Fresh tailing, recently impounded, from the current operations, which has had little chance for oxidation or alteration was also sampled. These samples were collect from the southwest portion of the Dam No. 4 impoundment in the southwest corner of the Tailing Facility. Tailing slurry is discharged into this pond through the tailing pipeline from the mill. The sampling location last received tailing slurry about six months ago. The pond in the sampling area had been allowed to dry. Pictures of these sampling locations are presented in Figure 3.

• Submerged tailing was sampled from the Dam 1 pond area northwest of the Change House and north of Dam No. 1. This impoundment last received tailing slurry in the 1980s. The pond, however, contained standing water up to last summer (2009) when the pond was drained. Figure 4 provides pictures of the sampling locations and the collection of these samples. These samples represent tailing that, over the majority of its impoundment life, were submerged under water and had relatively minor exposure to the atmosphere.

Figure 2 – Surface Tailing Pile near Dam No. 1

Figure 3 – Tailing Pond behind (north) of Dam 4



Figure 4 – Dam 1 Pond Sampling Location

3.2 IN VITRO BIOACCESSIBILITY TEST RESULTS The results of the tailing phase in vitro bioaccessibility analyses are summarized in Table 2 and Figure 5, and discussed in detail in subsequent sections.

Table 2 – Tailing Phase In Vitro Bioaccessibility Test Results

Location

Digestable Conc

(mg/kg-dry)

Mass MoDigested

(mg)Surface Tailing Pile A 0.66 0.07 126 0.13 53%Surface Tailing Pile B 0.69 0.07 168 0.17 41%Surface Tailing Pile C 0.82 0.08 176 0.18 47%

Average 47%Standard Deviation 6%

Tailing Pond Behind Dam No 4-A 0.04 0.00 290 0.29 1%Tailing Pond Behind Dam No 4-B 0.06 0.01 154 0.15 4%Tailing Pond Behind Dam No 4-C 0.04 0.00 101 0.10 4%


Dam 1 Pond-A 0.20 0.02 68 0.07 29%Dam 1 Pond-B 1.87 0.19 3592 3.59 5%Dam 1 Pond-C 0.57 0.06 289 0.29 20%


Leachable Conc (mg/L)

% Bioaccessible

Mass MoLeached

(mg)

The samples from the Dam 4 Pond area had the least bioaccessibility of all the tailing samples (1%, 4%, and 4%) with a mean of 3% and a relative standard deviation of 2%, as shown on Table 2 and Figure 5. The low bioaccessibility of molybdenum in this area is consistent with the



observation that the area is comprised of recently deposited tailing which is likely to contain predominantly molybdenum disulfide, a highly insoluble form of molybdenum. They are also consistent with the results from the tailing collected from the conveyor belt at the Mill (11%, 14%, and 11%) as reported in the Phase 2 Report (URS 2008).

Figure 5 – Bioaccessible Molybdenum Concentrations in Tailing

1% 4% 4% 5%

20%

29%

41%47%

53%

0%

10%

20%

30%

40%

50%

60%

FreshTailing

RecentlyExposed

OldTailing

Exposedfor

extendedPeriod

Bio

acce

ssib

ility

(%)

The samples from the surface tailing at the southeast end of Dam No. 1 had the highest observed bioaccessibilities (53%, 41% and 47%) with an average of 47% and a relative standard deviation of 6%. The tailing in these stockpiles has been exposed to the atmosphere for much longer than in the other two areas and the results suggest that the some of the molybdenum disulfide originally present as the predominant molybdenum mineral has been oxidized to a more soluble form such as molybdate. The bioaccessibility is consistent with that found in the Spring Gulch Rock Pile in areas where the near surface materials had been exposed to the atmosphere for extended periods of time (URS 2008).

The results from the Dam 1 pond location (29%, 5%, and 20% with an average of 18% and a relative standard deviation of 12%) indicate a more variable and somewhat lower bioaccessibility than the Dam No. 1 surface tailing samples but higher than the bioaccessibility in the “fresh” material.


SECTIONFOUR Data Validation

4. Section 4 FOUR Data Validation

All chemical data were validated in accordance with the provisions of Standard Operating Procedure No. 12-1 “Data Validation for RI/FS Data” from the RI/FS QAPP (URS 2007b). A summary of the conclusions from the data validation is provided below and the data validation report and qualified results summary forms are included as Appendix A.

All samples were analyzed within the specified holding time. No target analytes were detected in the method blanks. The accuracy and precision as measured by laboratory control sample and matrix spike recoveries and agreement between field duplicate, laboratory duplicate or spiked duplicate results was acceptable. All initial calibrations were verified, as applicable. All recoveries for the internal standards in field samples for ICP-MS metals were within acceptance limits. The conclusion of the data review was that the results may be used without qualification in meeting the project objectives of evaluating the portion of molybdenum present in the tailing impoundments that is potentially available through the food chain for exposure of deer and elk.


SECTIONFIVE Conclusions

5. Section 5 FIVE Conclusions

5.1 BIOACCESSIBILITY The bioaccessibility values for the tailing reported here are quite comparable to bioaccessibility measured during the first two phases of work on samples of potential cover material and other media located at the mine site. (URS 2008). Figure 6 shows the combined tailing and rock pile sample analysis results across the three phases of the work.

Figure 6 – Bioaccessible Molybdenum in Tailing and Spring Gulch Rock Pile

4% 4%1%

11%14%

11%

29%

20%

5%

51%

21% 21%27% 27%

53%

47%41%

36%

6%

58% 58%

0%

25%

50%

75%

100%

Dam-4-

SW-Pon

d-C

Dam-4-

SW-Pon

d-B

Dam-4-

SW-Pon

d-A

Millt

ail3-T

01N-TLG

Millt

ail2-T

01N-TLG

Millt

ail1-T

01N-TLG

Histori

c-Pon

d-A

Histori

c-Pon

d-C

Histori

c-Pon

d-B

Spri

ngGulc

h4-T

01N-S

OL

Spring

Gulch3

-T01

N-SOL

Spri

ngGulc

h3-T

01N-S

OL

Spring

Gulch2

-T01

N-SOL

Spri

ngGulc

h2-T01

N-SOL

Dam-1-

Pile A

Dam-1-

Pile C

Dam-1-

Pile B

Spri

ngGulc

h1-T

01N-S

OL

Spri

ngGulc

h7-T

01N-S

OL

Spri

ngGulc

h6-T

01N-S

OL

Spri

ngGulc

h5-T

01N-S

OL

Fresh Tailing Recently Exposed

Old Tailing

Spring Gulch Rockpile

Long Exposed

Tailing

PotentialSpring Gulch

Borrow

Figure 6 shows clearly the low bioaccessibility of molybdenum in fresh tailing, either in an impoundment or from the previous phase of work (URS 2008) for tailing collected off the conveyor belt at the Mill. This figure also presents the bioaccessibility results for the other tailing impoundment samples and the Phase 2 results for samples from the Spring Gulch Rockpile. Bioaccessibility for the tailing is variable, ranging from 1% to 53%. The Spring Gulch Rock Pile material has a similar variability ranging from 6% to 58%. The variability of results for the exposed tailing and Spring Gulch Rockpile surface samples is likely due to heterogeneity of the materials sampled. The two samples with lower bioavailability (Dam 1 Pond B and Spring Gulch 7) had bioaccessibilities of 5% and 6% respectively, indicative of the presence of molybdenum minerals with low bioaccessibility such as molybdenum disulfide. This is not surprising since the molybdenum minerals in the tailing are derived from the rocks



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being mined and the milling process increases the surface area of the material, which facilitates dissolution of soluble molybdenum forms leaving behind the less soluble molybdenum forms in the tailing.

5.2 MINERAL SPECIES PRESENT The Phase 2 SEM/microprobe studies (URS 2008) demonstrated that molybdenum disulfide, not the more soluble and bioaccessible molybdate salts, is generally the predominant molybdenum species in Mine Site soils and rock pile materials. SEM/microprobe analyses were also run on two of the tailing samples from this study, one with low bioaccessibility (Dam 1 Pond B with 5% bioaccessibility) and one with a high bioaccessibility (Surface Tailing Pile C with 47% bioaccessibility). The relative contributions for the molybdenum mineral phases identified are presented in Table 3 and Figure 7.

Table 3 - Relative Mass of Bioaccessible Molybdenum Minerals Bioaccessible Molybdenum Mass

Sample

Mineral

Dam 1 Pond B(percent)

Surface Tailing Pile C (percent)

Iron Oxides 0.2 3.4

Lead Molybdate 1.2 81.8

Molybdenum Sulfate - 12.2

Clay - 0.01

Manganese Oxides 0.4 0.7

Molybdenum Disulfide 98.2 1.8

Figure 7 – SEM/Microprobe Molybdenum Mineral Speciation

Dam 1 Pond B

0 20 40 60 80 100 120

MoS2

MnOOH

PbMoO4

FeOOH

Frequency of Occurrence Bioaccessable Mo Mass Relative Mo Mass

Surface Tailing Pile C

0 20 40 60 80 10

FeOOH

PbMoO4

MoSO4

Clay

MnOOH

MoS2

0

Frequency of Occurrence Bioaccessable Mo Mass Relative Mo Mass

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The tailing material with the 5% bioaccessibility (Dam 1 Pond B) had 98% Molybdenum Disulfide (MoS2 or molybdenite) and only 2% of the soluble molybdenum species. In contrast, the tailing sample with higher bioaccessibility (Surface Tailing Pile C) that had been exposed to potentially oxidizing conditions for a long time was found to have only 2% of the non-oxidized molybdenum disulfide and 94% of the more soluble molybdenum minerals (82% lead molybdate {PbMoO4 or wulfenite} and 12 % molybdenum sulfate {MoSO4}). The observations that the predominant, identifiable molybdenum mineral in the low bioavailability sample was molybdenum sulfide and that those in the sample with higher bioaccessibility were oxidized forms of molybdenum such as lead molybdate, provide confidence in the interpretation presented in the Phase 2 report (URS 2008). There the data demonstrated that the molybdenum is essentially not available in the non-oxidized rock and tailing material and that, as the material is subjected to oxidation, the molybdenum is converted to the more soluble oxide forms, such as molybdates. These results suggest that the material in the tailing, the rock being mined and the unexposed material stored at the mine is predominantly molybdenum sulfide and has a very low bioaccessibility. As the material is subjected to normal atmospheric oxidizing conditions such as tailing at the Dam No 1 impoundment or at Spring Gulch Rockpile some of the molybdenum sulfide oxidizes to other mineral forms which in turn are more bioaccessible.

5.3 TAILING BIOACCESSIBILITY AND THE PRELIMINARY REMEDIATION GOAL EPA conducted a Baseline Ecological Risk Assessment for the CMI Questa Mine. In that assessment, a preliminary remediation goal (PRG) for terrestrial ecological receptors potentially exposed to molybdenum in Mine Site or Tailing Facility soils of 54 mg/kg was derived. This literature-based PRG relies on toxicity studies with western kingbirds in which a soluble form of molybdenum was used. This PRG assumes that molybdenum at the Tailing Facility is in a bioavailable, soluble form of molybdenum as well. However, because the most prevalent form of molybdenum in the Tailing Facility and rock piles is molybdenite (MoS2), it is likely that molybdenum in tailing and rock pile material is much less bioavailable than that used in the kingbird study. EPA has since released a Technical Memorandum setting a molybdenum PRG for large herbivores such as deer and elk at 41 mg/kg for tailing material at the Tailing Facility.

The results of this study on the bioaccessibility of molybdenum in tailing support the conclusion that molybdenum in the tailing is generally much less bioavailable and that the generic PRG of 41 mg/kg proposed by EPA for tailing is more conservative than warranted by the species of molybdenum found at the Tailing Facility.. The bioaccessibility studies demonstrate that the fraction of leachable molybdenum in tailing under simulated gastrointestinal conditions (the bioaccessible fraction) is at least two to five times less than the form of molybdenum used in developing the generic PRG. These data complement those from the Spring Gulch Rock Pile Soil Molybdenum Toxicity Testing Report (GEI 2008) (Appendix A in URS 2009) which concluded that, based on the 14-day and 28-day soil toxicity studies for earthworms, molybdenum levels of up to 756 mg/kg (molybdenite) and 712 mg/kg (sodium molybdate) have no measurable adverse effects on the survival or biomass. The rye grass 21-day soil toxicity test results indicated that concentrations up to 692 mg/kg molybdenite have no adverse effects on survival, mean shoot length, mean root length, and mean biomass. Safe levels (chronic values) for rye grass exposed to soil containing sodium molybdate (more soluble form) were 552 mg/kg for emergence and 413 mg/kg for all other endpoints.



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Since the draft bioassay report was distributed, EPA has revisited the PRG for the mine site and determined that the PRG for the mine site should be increased to 300 mg/kg based on the sodium molybdate bioassay data. EPA also has released a Technical Memorandum setting a molybdenum PRG for large herbivores such as deer and elk at 41 mg/kg for tailing material at the Tailing Facility. The data in this report support the conclusion that a PRG of 41 mg/kg is also overly conservative. The bioaccessibility and SEM Microprobe data reported here demonstrate that the form of molybdenum at the Tailing Facility is no less than 50% low toxicity molybdenite (MoS2). Based on the results of the toxicity and bioaccessibility testing, the bioaccessibility of molybdenum in the tailing material should be considered in development of a PRG. The resultant calculated PRG would be no less than 82 mg/kg to reflect at least a factor of two increase due to the observation that tailing at the Tailing Facility is generally less than 50% bioaccessible.

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SECTIONSIX References

6. Section 6 SIX References

Basta, N. T., Ryan, J. A. and Chaney, R. L. 2005. Trace Element Chemistry in Residual-Treated Soil - Key Concepts and Metal Bioaccessibility. J. Environ. Qual. 34:49-63.

Semple, K.T., Doick, K.J, Jones, K.C., Burauel, Peter and Craven, Andrew (2004). Defining Bioavailability and Bioaccessibility of Contaminated Soil and Sediment is Complicated. Environ Sci & Tech June 15, 2004, pp 228a – 231a.

CMI. 2008. Personal communication with Bob Kilborn, Chevron Mining Inc., July 17, 2008.

Fox, Patricia M. and Doner, Harvey E. 2003. Accumulation, Release, and Solubility of Arsenic, Molybdenum, and Vanadium in Wetland Sediments. J. Environ. Qual. 32:2428-2435.

GEI Consultants, Inc. 2008. Spring Gulch Rock Pile Soil Toxicity Work Plan, prepared for Chevron Mining Inc.

Gupta, Umesh C ed. 1997. Molybdenum in Agriculture, Cambridge University Press, Cambridge MA.

Fairhall, L., et al. 1945. The Toxicity of Molybdenum. Public Health Bulletin No. 293, US Government, as cited in Vyskocil 1999.

Medlin, E., and Drexler, J.W. 1995. Development of an in vitro technique for the determination of bioaccessibility from metal-bearing solids. International Conference on the Biogeochemistry of Trace Elements, Paris, France.

Vyskocil, A. and Viau, C. 1999. Assessment of Molybdenum Toxicity in Humans. J. Appl. Toxicol. 19:185-192.


Appendix A

Data Validation Report

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Appendix A Data Validation Report

CHEVRON MINING, INC.

DATA REVIEW SUMMARY

Data Package Number: Sampling Event: Spring Gulch, Bioavailability

Sample-specific Parameter Review? Yes Laboratory Performance Parameters? Yes

Data Reviewer: Sheri O’Connor Date Completed: 2/9/2010

Peer Reviewer: Alan Roberts Date Completed: 2/9/2010

The table below summarizes the results presented in this data package.

Analyses

Field ID Sample Type Lab ID Matrix

Mol

ybde

num

(3

050

– D

iges

tion)

Mol

ybde

num

(I

nvitr

o)

DAM 1 PILE A T01D FD 401 Soil X X

DAM 1 PILE A T01N SA 402 Soil X X

DAM 1 PILE B SA 403 Soil X X

DAM 1 PILE C SA 404 Soil X X

DAM 4 PILE A SA 405 Soil X X

DAM 4 PILE B SA 406 Soil X X

DAM 4 PILE C SA 407 Soil X X

HIST POND A SA 408 Soil X X

HIST POND B SA 409 Soil X X

HIST POND C SA, MD 410 Soil Xm Xm

Matrix: QC Type: SA = Sample FD = Field Duplicate MD = Method duplicate

XM = matrix spike and/or matrix spike duplicate.

The data review was conducted in accordance with SOP 12.0, Data Validation for Molycorp Permit Data.

General Overall Assessment:

X Data are usable without qualification.

Data are usable with qualification (noted below).

Some or all data are unusable for any purpose (detailed below).

Case Narrative Summary: Except as noted below, any of the issues noted in the laboratory case narrative potentially affecting data quality are addressed in the appropriate sections in the table below.

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Review Parameter

Criteria Met? Comments

Sample-specific Parameters Complete with “Yes”,

“No”, or “Not Applicable

(N/A)”.

For each “No” response, list what was out, associated acceptance limits, all qualified data, and bias direction or reference associated table with pertinent

details.

COC & Sample Receipt Yes Samples were received intact.

Holding Times Yes All samples were analyzed within the specified holding time. Further action was not necessary.

Method Blanks and CCBs No No target analytes were detected in the method blanks. After every ten samples two CCBs were analyzed. In some cases, the concentrations of the first CCB analyzed exceeded the instrument detection limit of 0.12 µg/l. With one exception, the second CCB was below the instrument detection limit. Data qualification was not necessary, as all molybdenum results were reported at concentrations greater than 5x the amount in the blanks.

Matrix QC

• MS

Yes The recoveries for the matrix spike (MS) analyses were within the laboratory-determined acceptance range.

• LD HIST POND C

Yes The agreement between parent sample results and the lab duplicate sample results was evaluated and the results met the evaluation criteria.

Method QC

• Serial Dilution NA

• Total vs. Partial Analyses NA

• Cation/Anion Balance NA

NA Only dissolved metal sample results were reported for these samples. An evaluation for total metal to dissolved metal sample results or anion/cation balance is not appropriate on said samples.

Field QC

• Rinsate Blank N/A

• Field Duplicate DAM 1 PILE A T01N /

DAM 1 PILE A T01D

• Field Blank N/A

Yes The comparison between results for the field duplicate pair met acceptance criteria. Therefore, data qualification was not necessary.

Elevated RLs without associated non-detect results

Yes

Package Completeness Yes The results may be used without qualification in meeting the project objectives.

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Review Parameter

Criteria Met? Comments

Laboratory Performance Review Initial Calibration Yes The relationship between instrument response and concentration was

established with a blank and at three standards. All initial calibrations were verified, as applicable. Data qualification on the basis of initial calibrations was not necessary.

Tuning (as applicable to the method)

Not provided The tuning data were not provided in the data package.

Initial/ Continuing Calibration Verification (ICV/CCV)

Yes All recoveries were within the acceptance limits. Therefore, data qualification was not necessary.

Internal Standard (ICP-MS) Yes All recoveries for the internal standards in field samples for ICP-MS metals were within acceptance limits. Therefore, data qualification based on ICP-MS internal standards was not necessary.

Laboratory Control Sample (LCS)

Yes All LCS recoveries and were within the applicable acceptance limits.

Interference Check Standard (ICS)

Yes The ICS AB solution percent recoveries were within the acceptance limits of 80-120%. Therefore, data qualification based was not considered necessary

Target Compound Identification

Yes The instrument printouts were reviewed. Results obtained for QC check samples (calibration standards and laboratory control samples) indicate that instrument signals reported were due to the target analytes. Reported signal intensities agreed with reported concentrations for all samples. No errors in compound identification were found and data qualification was not necessary.

Transcription Errors Yes The units listed on the summary form were found to be incorrect and were corrected by the data reviewer after verification by the laboratory.

Recalculation Yes No calculation or sample quantitation errors were found in this data package. The molybdenum result for sample Hist Pond B was slightly above the highest calibration point of 1000 micrograms per liter (µg/l) with a concentration of 1441 µg/l but within the linear range of the instrument. Therefore, data qualification was not necessary.

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report on tailing bioaccessibility study results …

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