APPENDIX M HUMAN HEALTH RISK ASSESSMENT

Transcription

1 APPENDIX M HUMAN HEALTH RISK ASSESSMENT

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3 Soledad Mountain Project Human Health Risk Assessment Golden Queen Mining Co., Inc. May 2008

4 Table of Contents Executive Summary List of Acronyms iv vi 1. Introduction Constituent Characterization Tailings Pile Data Soil Characterization Data Data Evaluation Particle Size Data Toxicity Assessment Non-carcinogenic Effects Carcinogenic Effects Dermal Toxicity Values and Dermal Absorption Lead Evaluation Exposure Assessment Exposure Point Concentration Exposure Scenario Exposure Assumptions Risk Characterization Non-carcinogenic Hazard Excess Lifetime Cancer Risk Site Worker Occupational Exposure Uncertainties in the Risk Assessment 6-1 Human Health Risk Assessment (5-2-08) Final.doc i

5 Table of Contents 7. Summary and Conclusions References 8-1 Tables 1) Analytical Data 2007 Tailings Pile Samples 2) Analytical Data Combined 2006 and 2007 Tailing and Soil Characterization Samples 3) Summary of Constituents Detected, 2007 Tailings Pile Samples 4) Summary of Constituents Detected, 2006 Soil Characterization Samples 5) Selection of Constituents of Potential Concern in 2007 Tailings Pile Samples 6) Selection of Constituents of Potential Concern in 2006 Soil Characterization Samples 7) Particle Size Distribution in 2007 Tailings Pile Samples 8) Noncarcinogenic Toxicity Values for Oral and Dermal Exposure 9) Noncarcinogenic Toxicity Values for Inhalation Exposure 10) Carcinogenic Toxicity Values for Oral and Dermal Exposure 11) Carcinogenic Toxicity Values for Inhalation Exposure 12) Dermal Absorption Parameters 13) Receptor-Specific Exposure Parameters 14) Risk and Hazard Equations for Exposure to Tailings and Soil 15) Calculation of Particulate Emission Factors for Tailings and Soil Exposure 16) Risk and Hazard Calculations for for Site Worker, 3-Month Exposure to Tailings, 2007 Tailings Pile Samples 17) Risk and Hazard Calculations for for Site Worker, 6-Month Exposure to Tailings, 2007 Tailings Pile Samples 18) Risk and Hazard Calculations for for Site Worker, 3-Month Exposure to 2006 Tailings and Soil Characterization Samples 19) Risk and Hazard Calculations for for Site Worker, 6-Month Exposure to 2006 Tailings and Soil Characterization Samples 20) Fugitive Dust Emission Calculations for Site Worker Exposure to Tailings 2007 Tailings Pile Samples Human Health Risk Assessment (5-2-08) Final.doc ii

6 Table of Contents 21) Fugitive Dust Emission Calculations for Site Worker Exposure to Tailings and Soil, 2006 Soil Characterization Samples Figures 1) Soil and Tailing Sample Locations 2) Wind Frequency Distribution Attachments 1 Soledad Mountain Project - Tailing Sampling Plan for Health Risk Assessment 2 Soledad Mountain Project Baseline Soil Sampling Plan (SAP) 3 Soledad Mountain Project Lead Evaluation Human Health Risk Assessment (5-2-08) Final.doc iii

7 Executive Summary Executive Summary ARCADIS U.S., Inc. (ARCADIS) was retained by Golden Queen Mining Co., Inc. (GQM) to conduct a human health risk assessment (HHRA) at their proposed Soledad Mountain Project Site (the Site), located near the community of Mojave, in Kern County, California. A baseline soil characterization program was previously conducted in late 2006 to comply with one condition in the Conditional Use Permits issued for the project by Kern County. The Baseline Soil Characterization Report (ARCADIS 2007a) noted elevated concentrations of metals in the soils on the Site, including arsenic, chromium, mercury, lead, and nickel. The Baseline Soil Characterization Report concluded that the highest levels of metals on Site were near the largest of the historical tailing piles and tailings was likely the source for the elevated metals concentrations in the soils. Based on the results of the soil characterization work, the program was expanded in 2007 by collecting samples directly from the historical tailings pile to gain a better understanding of the chemical and physical characteristics of the tailings and to assess the potential risk they pose to human health. The purpose of this HHRA is to evaluate potential risks and/or hazards to human health associated with the constituents detected in the tailings and soil samples. The 2006 baseline soil characterization program included collection of 38 soil samples from in and adjacent to the footprint of the proposed Heap Leach Facility and downwind of the largest and most recent of the historical tailings piles at the Site, the Gold Fields tailings deposit, present at the Site since the 1930s. As such, the Baseline Soil Characterization Report should be considered a companion report to this HHRA and reviewed in parallel to gain an understand the spatial distribution of metals across the Site, and the comparison of the metal concentrations on Site soils with background concentrations in Kern County and California. The supplemental sampling program performed for this HHRA included ten additional samples collected at five locations within the Gold Fields tailings pile. As part of the HHRA, the potential risk associated with chemical constituents in the tailings and soil was evaluated assuming worker exposure for both 3-month and a 6-month exposure periods during construction of the proposed heap leach facilities. The soil and tailings analytical results were used to evaluate exposure by selecting the 95 percent (%) upper confidence level (UCL) on the mean as exposure point concentrations for all samples. Risk characterization calculations were evaluated for site workers through a health-based comparison of constituent concentrations using both carcinogenic and non-carcinogenic toxicity Human Health Risk Assessment (5-2-08) Final.doc iv

8 Executive Summary values. The excess lifetime cancer risks (ELRCs) and hazard indices (HIs) were calculated assuming 3-month and 6-month exposure to constituents in soil and tailings. The calculated risks, using conservative exposure pathway assumptions for ingestion, skin contact and inhalation of dust from the Site, were slightly above, or less than, the California Environmental Protection Agency (CalEPA) benchmark of 1x10-5, and were all within the United States Environmental Protection Agency (USEPA) target risk range of 1x10-6 to 1x10-4. The HI s were all less than the CalEPA and USEPA benchmark of one. Arsenic is the risk driver for this evaluation, and the risk assessment incorporates a 50 percent bioavailability factor for arsenic based on scientific research which indicates that the predominant form of arsenic found in soils at mining sites is insoluble. Further research at Soledad Mountain is being conducted to determine the speciation of arsenic, which will further support the understanding of its bioavailability to humans. An evaluation for lead was conducted according to U.S. Department of Toxic Substances Control (DTSC) guidance and the results indicate that lead concentrations are low, and not a concern for potential receptors based on the assumed exposure parameters used in this assessment. The concentrations of mercury detected on the Site were also low such that the hazard quotients for all exposure scenarios were well below one. Fugitive dust emission concentrations were also calculated and compared with industrial standards to determine whether the concentration of each constituent potentially present in wind-blown tailings or soil generated under normal conditions at the Site represented an acceptable risk for site workers. The normal conditions are based on the diurnal and seasonal wind patterns and intensity as discussed in section 4 of this report. All of the calculated fugitive dust concentrations for both the tailings samples and the soil samples were below all of the threshold limit values (TLVs) and permissible exposure levels (PELs) for their respective constituents, indicating an acceptable level of risk for workers at the Site during construction. Furthermore, the particle sizes within the bulk tailings samples were measured to identify the percentage of particles that are of respirable size. The data indicate that approximately 25 percent of the particles are less than ten microns in size, which is the largest possible respirable size. The current USEPA compliance standard is 150 μg/m 3 averaged over 24 hours and 50 μg/m 3 averaged over one-year. Converting to units consistent with how the USEPA regulates for PM10, this is μg/m 3 silica that is are PM10 size or smaller. Thus, our estimated levels are much lower and show there is no hazard for the 3 and 6 month exposure periods used in this assessment. Human Health Risk Assessment (5-2-08) Final.doc v

9 List of Acronyms List of Acronyms ACGIH bgs CalEPA cm 2 COPC CSF CSF a CSF o DTSC ELCR EPC GQM HEAST HHRA HI HQ IRIS kg m³/day mg/cm²/day mg/day NOAEL OSHA PEF PEL PRG QA QC RfD RfD a RfD o SQL SSL TLV USEPA UCL American Council of Governmental Industrial Hygienists below ground surface California Environmental Protection Agency square centimeters constituent of potential concern cancer slope factor adjusted cancer slope factor oral cancer slope factor Department of Toxic Substances Control excess lifetime cancer risk exposure point concentration Golden Queen Mining Co., Inc. Health Effects Assessment Summary Tables human health risk assessment hazard index hazard quotient Integrated Risk Information System Kilogram cubic meters per day milligrams per square centimeter per day milligrams per day no observed adverse effect level Occupational Safety and Health Administration particulate emission factor permissible exposure limit preliminary remediation goal quality assurance quality control reference dose adjusted reference dose toxicity value oral reference dose toxicity value sample quantitation limit soil screening level threshold limit value United States Environmental Protection Agency upper confidence limit Human Health Risk Assessment (5-2-08) Final.doc vi

10 Soledad Mountain Project Human Health Risk Assessment 1. Introduction The Soledad Mountain Project (the Site) is located in Kern County, approximately five miles south of the town of Mojave, California. Gold mining in the area began in the early 1900s. Between 1935 and 1942, approximately 1,180,000 tons of ore was mined using underground mining methods. All mining activities ceased during the Second World War. Some remnants of the historical mine workings are still present at the Site, including the Gold Fields tailings deposit, which dates to the 1930s and is the largest and most recent of the historical tailings piles at the Site. The Site, situated in the western Mojave Desert, is typically very hot in the summer months, which extend from May to September, with maximum average daily temperatures commonly exceeding 100 degrees Fahrenheit. The Site is subject to very low humidity and dry winds from the west and southwest, characteristic of the interior California deserts. Typical winds at the Site are from the west, representing flow from the San Joaquin Valley. Wind rose data based on information gathered from a nearby meteorological station from October 2006 through March 2009 is presented at Figure 2. The average annual precipitation is approximately 5.5 inches. The estimated maximum and minimum monthly evaporation rates are inches occurring in July, and 1.26 inches occurring in December, respectively. The mean evaporation rate is 6.66 inches per month. There is no surface water on the Site and groundwater is approximately 180 to 260 feet below ground surface (bgs). The proposed project consists of open pit mining operations and cyanide heap leach and Merrill-Crowe processes to recover gold and silver from crushed and agglomerated ore. Most of the historical mine features at the Site will be removed or reclaimed by GQM during the construction of the planned mine and ore processing facilities. The currently proposed mine life includes approximately one year of construction, twelve years of mining (Phase 1 to Phase 5), fourteen years of heap leaching, including two years of rinsing and solution drain-down, two years of reclamation and a further three years of post-closure monitoring. During the presently planned mine life, 51 million tons of ore will be mined, crushed and leached; 108 million tons of waste rock will be produced, of which 19.0 million tons are expected to be sold as aggregate. Future potential mining could extend the life of the mine an additional four years. During construction of the heap leach pad, organic or unsuitable soils from the foundation area will be stripped and the Site graded for positive drainage. This step will Human Health Risk Assessment (5-2-08) Final.doc 1-1

11 Soledad Mountain Project Human Health Risk Assessment be followed by placement of a low permeability composite liner system. The bottom of the liner system will be a soil liner constructed of either the historical tailings, or native soils, amended with bentonite, or the tailings amended with native clayey soils. A baseline soil characterization program was conducted in late 2006 to comply with one of the conditions in the Conditional Use Permits issued by Kern County. The 2006 baseline soil characterization program consisted of 46 total samples, plus duplicates, 38 were included on a sample grid pattern spaced approximately 300 feet apart. Refer to Figure 1 for sample locations. Four of the samples were taken just north of Silver Queen Road and two at the closest residences. Thirty seven samples were included in this human health risk assessment because they were located in a downwind direction from the historical tailing pile and in an area where construction activities will occur. To characterize the baseline soil conditions at the Site, the analysis included Constituent of Potential Concern (COPC), including arsenic, chromium, mercury, lead, and nickel, as well as other elements expected to be present in the tailings and/or natural soil. The results of the soil characterization program indicated that the historical tailings on the Site had been eroded by both wind and water and mixed with the native soils. The analytical results demonstrated that the chemistry of the soil in the area downwind from the tailings pile has been altered by the erodedtailings. As a result, GQM expanded the soil characterization program to gain a better understanding of the physical and chemical characteristics of the tailings and any potential risk they may pose to future site construction workers and other receptors. A supplemental sampling program performed in 2007 included ten additional samples collected at five locations on the Gold Fields tailings pile. Samples were collected in accordance with the procedures documented in the Soledad Mountain Project Tailing Sampling Plan for Health Risk Assessment included as Attachment 1 and the Soledad Mountain Baseline and Background Soil Assessment Sampling and Analysis Plan (DeDycker & Associates, Inc. 2006) included as Attachment 2 to this report. This report presents the HHRA findings with respect to worker exposure to constituents detected in the historical tailings and soil at the Site. The purpose of this HHRA is to evaluate potential risks and/or hazards to human health associated with exposure to the chemical constituents in these materials that will be either moved or managed during the construction phase of the proposed Soledad Mountain Project. This report provides a brief description of the tailings and soil data used in the risk assessment, followed by the human health risk assessment. It is organized as follows: Constituent Characterization: summarizes the chemical constituents present in the tailings and soil and identifies COPCs for the health risk assessment. Human Health Risk Assessment (5-2-08) Final.doc 1-2

12 Soledad Mountain Project Human Health Risk Assessment Toxicity Assessment: identifies the general toxicological properties of the COPCs. Exposure Assessment: identifies the potential human exposure scenarios relevant to the risk assessment. Risk Characterization: presents the estimated human health risks associated with the identified COPCs and the relevant human exposure scenarios. Summary and Conclusions: summarizes the results of the human health risk assessment. Human Health Risk Assessment (5-2-08) Final.doc 1-3

13 Soledad Mountain Project Human Health Risk Assessment 2. Constituent Characterization This section discusses the soil and tailings data collected at the Site, the methodology used to evaluate the data, and the selection of COPCs. The analytical data for each data set are presented in Table 1 (2007 Tailings Pile Samples) and Table 2 (2006 Soil Characterization Samples). The approximate locations for each of the sampling points are shown on Figure 1. Tables 3 and 4 present a summary for each data set, including for each of the COPCs, the frequency of detection, range of detected concentrations, range of sample quantitation limits for non-detect results, and arithmetic mean concentration. These parameters are typically required as part of a health risk assessment Tailings Pile Data Ten samples were collected at five locations within the top two feet on the Gold Fields tailings pile in Six inorganic compounds (arsenic; chromium [total]; cyanide; lead; mercury; and silica) were detected in the samples. The analytical results are presented in Table 1. A summary of the COPCs is presented in Table 3. Hexavalent chromium was not detected in the samples Soil Characterization Data Prior to the sampling the Gold Fields tailings pile in 2007, 38 samples (BSK-5 to BSK- 38, BSK-20 Dup, BSK-35 Dup, BSK-B and BSK-C) were collected in 2006 from an area around the footprint of the proposed Merrill-Croweplant and downwind of the historical Gold Fields tailings pile 2006 as part of the Baseline Soil Characterization Report (ARCADIS 2007a). Soil samples were also taken at two of the nearest residences. Sample locations are shown on Figure 1. Twelve inorganic compounds (arsenic; barium; chromium [total]; cobalt; copper; cyanide; lead; mercury; silica; silver; vanadium; and zinc) were detected in the soil samples. A summary of the COPC is presented in Table 4. Hexavalent chromium was not detected in the samples. 2.3 Data Evaluation In Table 5 and Table 6, the maximum detected concentrations from each data set were compared to the available default health-based concentrations that the State of California and the USEPA have developed. The CalEPA, Department of Toxic Substances (DTSC), and the USEPA (Region IX) maintain lists of pre-calculated health-based soil concentrations that are termed Preliminary Remediation Goals (PRGs). The site data were compared to soil PRGs established for direct contact under residential land use, direct contact under industrial land use, and for protection of Human Health Risk Assessment (5-2-08) Final.doc 2-1

14 Soledad Mountain Project Human Health Risk Assessment underlying groundwater (i.e., migration from soil to groundwater) to provide a riskbased screening of the data. As shown in Table 5, three of the detected constituents from the tailings pile samples exceeded the CalEPA/DTSC and USEPA PRG for residential soil (arsenic, lead, and mercury) and two exceeded the PRG for industrial soil (arsenic and mercury). In addition, three constituents (arsenic, cyanide, and mercury) exceeded the USEPA Soil Screening Level (SSL) for protection of groundwater. Similarly, in Table 6 with the 2006 soil characterization data, four of the detected constituents exceeded the CalEPA/DTSC and USEPA PRG for residential soil (arsenic, lead, mercury, and vanadium) and two exceeded the PRG for industrial soil (arsenic and mercury). In addition, three constituents (arsenic, cyanide, and mercury) exceeded the USEPA SSL for protection of groundwater. Neither a residential nor an industrial PRG has been established for silica. Furthermore, SSLs were not available for cobalt, copper, lead or silica. In addition, cobalt, copper and vanadium were detected within the range of reference for California soils in all samples, and arsenic was detected within the range of reference for the 2006 Soil Characterization samples (Bradford et al., 1996). The primary aquifer in the area is the Quaternary age alluvium, which fills the basins and wide expanses of the Mojave Desert between isolated bedrock outcrops. Groundwater recharge in the alluvium is primarily from the Tehachapi Mountains and Sierra Nevada several miles west of the project. The primary flow direction in the alluvial aquifer in the Fremont valley is west to east, and then northeast toward Koehn Lake, a dry lake bed. The alluvium is divided into older alluvium and younger alluvium. The older alluvium is the principal aquifer in the area. On the flanks of Soledad Mountain, its thickness varies from zero to more than 250 feet thick. The physical properties of the older alluvium in the area of Soledad Mountain have not been determined by testing. At the Site, the older alluvium is comprised of silt, sand, gravel and boulders. Silt- and clayrich lake bed and playa deposits occur interbedded with the alluvial sands. These deposits have lower permeabilities, which restrict downward flow of water in the alluvium. The younger alluvium consists of lenses of fine to coarse-grained sand locally interbedded with low permeability silt and clay layers related to lacustrine or playa deposits. The low permeability layers restrict downward flow. Low permeability layers in both the older and younger alluvium likely contribute to groundwater recharge primarily occurring at the edge of the basin. Human Health Risk Assessment (5-2-08) Final.doc 2-2

15 Soledad Mountain Project Human Health Risk Assessment The combination of low precipitation (approximately six inches of annual precipitation), the relatively low permeability in the alluvium on the north flank of Soledad Mountain, and the depth to ground water from 180 to 260 feet bgs, makes it unlikely that leaching of the historical tailings could influence the groundwater quality in the area. While not all of the constituents detected in the soil or tailings were present at concentrations greater than the screening levels or reference, all of them were evaluated in this risk assessment as a conservative measure. 2.4 Particle Size Data During the 2007 sampling event, tailings samples were analyzed for their physical properties, including particle grain size distribution. The data, presented in Table 7, indicate that a substantial portion of the tailings particles are greater than 12 microns in diameter. Particulates that are 10 microns or smaller in size are considered to be respirable and are the primary concern in evaluating the inhalation exposure pathway and, consequently,the potential risk. Therefore, the data was reviewed to identify the percentage of particles that are respirable within the bulk tailings samples. As presented on Table 7, the data shows that approximately 28 percent of the particles are finer than 12 microns; Additionally, much of this fraction (approximately 22 percent) is finer than 9 microns. Overall, this indicates that roughly 25 percent of the total particles are of respirable size The particle size data are useful in that they aid in determining the respirable portion of the tailings and may be used as an estimate of the percentage of fugitive dust that is respirable. Human Health Risk Assessment (5-2-08) Final.doc 2-3

16 Soledad Mountain Project Human Health Risk Assessment 3. Toxicity Assessment This section discusses the two general categories of toxic effects (non-carcinogenic and carcinogenic) and constituent-specific toxicity values used to calculate potential risks for these two types of toxic effects. Toxicity values for potential non-carcinogenic and carcinogenic effects are determined from available databases. For this risk assessment, toxicity values were primarily obtained from the USEPA s Integrated Risk Information System (IRIS) (USEPA 2008), except when toxicity values were available from the CalEPA (2008). When toxicity values were unavailable from IRIS, the Health Effects Assessment Summary Tables (HEAST) (USEPA 1997b) were consulted. 3.1 Non-carcinogenic Effects For many non-carcinogenic effects, protective mechanisms must be overcome before an effect is manifested. Therefore, a finite dose (threshold), below which adverse effects will not occur, exists for non-carcinogens. Depending on the dose, a single compound might elicit several adverse effects based on the exposure route, the duration of exposure, and the susceptibility of the individual. Constituents may exhibit their toxic effects at the point of application or contact (local effect) or at other sites (systemic effects) after they have been distributed throughout the body. Most constituents can produce more than one type of toxic effect, depending on the dose and the susceptibility of the exposed individual or receptor. The goal of toxicity studies for application in risk assessment is to identify the constituent-specific toxicity values and the exposure levels that are expected to be safe. The potential for noncarcinogenic effects is estimated by comparing a calculated exposure dose with a reference dose (RfD) for each individual constituent. The RfD represents a daily exposure level that is designed to be protective of human health, even for sensitive individuals or subpopulations. For a given constituent, the dose or concentration that elicits no adverse effect when evaluating the most sensitive receptor s response is referred to as the no observed adverse effect level (NOAEL). The NOAEL is used to establish non-cancer toxicity values (called RfDs). The RfD represents a daily exposure level that is not expected to cause adverse non-carcinogenic health effects. Chronic RfDs are used to assess long-term exposures, ranging from 7 years to a lifetime. Subchronic RfDs are used to evaluate the potential for adverse health effects associated with exposure to constituents over a period of 2 weeks to 7 years. Human Health Risk Assessment (5-2-08) Final.doc 3-1

17 Soledad Mountain Project Human Health Risk Assessment Table 8 presents the RfDs used to assess oral and dermal exposure, and Table 9 presents the RfDs used to assess inhalation exposure. Tables 8 and 9 also present the target sites associated with the non-carcinogenic toxicity values for each constituent, varying with the exposure route. USEPA confidence values and uncertainty factors associated with the RfDs also are listed (USEPA 2008). The uncertainty factor represents areas of uncertainty inherent in the extrapolation from the available data. The confidence levels (low, medium, high) assess the degree of confidence in the extrapolation of available data. 3.2 Carcinogenic Effects Cancer induced by chemicals in humans and animals proceeds through a complex series of reactions and processes. Carcinogenic constituents may produce tumors at the point of application or contact, or they may produce tumors in other tissues after they have been distributed throughout the body. Some constituents are associated only with one or two tumor types while others may cause tumors at many different sites. Constituents are classified as known, probable, or possible human carcinogens based on a USEPA weight-of-evidence scheme in which they are systematically evaluated for their ability to cause cancer in humans or laboratory animals. The USEPA classification scheme (USEPA 1989) contains five classes based on the weight of available evidence, as follows: A B B1 B2 C D E known human carcinogen; probable human carcinogen; probable human carcinogen limited evidence in humans; probable human carcinogen sufficient evidence in animals and inadequate data in humans; possible human carcinogen limited evidence in animals; inadequate evidence to classify; and evidence of non-carcinogenicity. Constituents in Classes A, B1, and B2 generally are evaluated as carcinogens in risk assessments; however, Class C carcinogens may be evaluated on a case-by-case basis (USEPA 1989). At the Site, one constituent was identified as a Class A constituent (arsenic), one constituent was identified as a Class B2 constituent (lead), Human Health Risk Assessment (5-2-08) Final.doc 3-2

18 Soledad Mountain Project Human Health Risk Assessment one constituent was identified as a Class C constituent (mercury), and five constituents were identified as Class D constituents (barium, copper, cobalt, silver, and zinc). Hexavalent chromium is a Class A carcinogen by the inhalation route; however, it was not detected in the samples collected at the Site. As a result, only trivalent chromium toxicity values are used in this assessment. For carcinogens, the current regulatory guidelines (USEPA 1989) are based on an extremely conservative approach in which it is assumed that any level of exposure could cause cancer. Based on this assumption, USEPA extrapolates from laboratory animal data using a mathematical model known as the linear multi-stage model. This model plots a line through the zero point and, based on the slope of this doseresponse line, assigns a risk level for increasingly smaller doses of a particular compound. The 95 percent upper confidence limit (UCL) for the slope of this line, called the cancer slope factor (CSF), is used to calculate the probability of an effect associated with a given dose. USEPA s slope factors thus are determined by a methodology that is likely to overestimate actual risk. An even greater problem may lie in the USEPA assumption of dose and response additivity for carcinogenic effects. Research by USEPA has suggested that summing upper-bound excess cancer risks from several carcinogens may greatly overestimate a true upper-bound risk for the mixture (Cogliano 1997). Table 10 and Table 11 present the carcinogenic toxicity values for oral and dermal exposure, and inhalation exposure (respectively) to the COPCs at the Site. The carcinogenic toxicity value used in the calculation of potential cancer risks is the CSF, which is derived from the conservative assumption that any dose level has a possibility of causing cancer. The cumulative dose, regardless of the particular exposure period, determines the risk; therefore, separate CSFs are not derived for sub-chronic and chronic exposure periods. 3.3 Dermal Toxicity Values and Dermal Absorption Whenever possible, route-specific toxicity values have been used in this HHRA; however, USEPA has not yet developed toxicity values for dermal exposures. For this reason, the oral toxicity values (oral reference dose toxicity value, RfD o, and oral cancer slope factor, CSF o ) and the oral absorption efficiency were used to derive adjusted toxicity values (adjusted reference dose toxicity value, RfD a, and adjusted cancer slope factor, CSF a ) (adjusted to the absorbed dose) for use in assessing dermal exposure (USEPA 1989): Human Health Risk Assessment (5-2-08) Final.doc 3-3

19 Soledad Mountain Project Human Health Risk Assessment RfD a = RfD o Oral Absorption Efficiency CSF a = CSF o / Oral Absorption Efficiency The adjusted toxicity values represent the theoretical toxicity of the orally absorbed dose of the constituent. The USEPA (2004d) guidance recommends that the oral toxicity values for organic constituents and many inorganic constituents should not be adjusted to assess dermal exposure (i.e., oral absorption efficiency = one) and presents recommended oral absorption efficiencies for a few inorganics. Table 8 presents the oral absorption efficiency values and the RfD a used to assess risk for the dermal exposure route. Table 10 presents the CSF a. Uncertainty is associated with the adjusted toxicity values and with the dermal risks derived using these values due to the uncertainty in the oral toxicity values, combined with the uncertainty in the oral absorption efficiency default and constituent-specific values. However, the calculated dermal risks are expected to be very conservative and, therefore, will overestimate human health risks. Table 12 presents the dermal absorption efficiencies for the detected constituents. The dermal absorption efficiency is used to estimate dermal uptake from a soil matrix. 3.4 Lead Evaluation The USEPA has determined that lead exposure can result in various health effects, depending on the level of exposure. Potential health effects differ, depending on whether an adult or a child is exposed. Also, lead exposure is typically evaluated in terms of blood-lead levels. For these reasons, a computer spreadsheet (LeadSpread v7) developed by the State of California (DTSC 2002) was used (Appendix 3), and the predicted blood-lead levels were compared to an action level of 10 micrograms per deciliter (µg/dl). The DTSC default values were maintained in LeadSpread v7 except for the soil EPCs, which were 100 and 74 mg/kg as shown in Table 3 and 4 for the 2007 and 2006 data, respectively. Human Health Risk Assessment (5-2-08) Final.doc 3-4

20 Soledad Mountain Project Human Health Risk Assessment 4. Exposure Assessment Exposure pathways were identified based on the site characterization information and the fate and transport properties of the COPCs to determine likely points where human receptors may come in contact with affected tailings or soil under current or potential future conditions at the Site. An exposure pathway is defined by the following four elements: a source and mechanism of constituent release to the environment, transport of a released constituent, a point of potential contact with a constituent (the exposure point), and exposure pathway. The purpose of the exposure assessment is to estimate the way(s) a population may potentially be exposed to constituents at a site. This typically involves projecting concentrations along potential pathways between sources and receptors. The projection usually is accomplished using site-specific data and, when necessary, mathematical modeling. Exposure can occur only when the potential exists for a receptor to contact released constituents directly, or when there is a mechanism for released constituents to be transported to a receptor. Without exposure there is no risk; therefore, the exposure assessment is a critical component of the risk assessment. The Site is an industrial area with a history of mining dating back to the early 1900s. Construction workers will be the primary receptors, with the greatest potential for exposure to the COPCs at the Site via the inhalation pathway. The local wind data (Figure 2) indicate that the predominant wind direction is from the southwest with an average wind speed of 5.1 m/s. The arsenic concentration in soil outside of the tailings pile peaks near the location of the proposed overflow pond at 70 mg/kg (ARCADIS 2007a). This is a downwind location approximately 1800 feet from the Gold Field tailings pile and within the footprint of the proposed Heap Leach Facility. There are six residences within a mile of the historical tailing piles. Soil samples secured during the 2006 baseline soil characterization study at the two nearest residences reflected that the arsenic concentrations in soil approximate the background concentration for Kern County (ARCADIS 2007a, Bradford et al, 1996). Human Health Risk Assessment (5-2-08) Final.doc 4-1

21 Soledad Mountain Project Human Health Risk Assessment 4.1 Exposure Point Concentration Exposure points are defined as areas where contact with COPCs occurs, generally with equal probability across the entire site. The exposure point concentration (EPC) is a representative constituent concentration that a receptor may contact at an exposure point over the exposure period (USEPA 1989). EPCs represent conservative estimates of the concentrations to which an individual may be exposed over the exposure period at the exposure point. According to USEPA (2004b; 2002b; 2000a; 1992) risk assessment guidance, the EPC is an estimate of the arithmetic average concentration for a constituent. Ideally, the EPC should be the true average concentration; however, because of the uncertainty associated with estimating the true average concentration based on a limited dataset, the estimated 95% (or higher, in some cases) UCL was used as the EPC. UCLs for the risk assessment EPCs were derived according to USEPA (2004b; 2002b, 2000a; 1992) guidance. The UCLs were calculated with the assumption that the sampling data are normally distributed. In calculating the means and UCLs, the detected concentrations were used at the reported values, and proxy concentrations were used to represent the non-detects (rather than ignoring those data points or substituting a zero). One-half of the sample quantitation limit (SQL) value was used as the proxy concentration for each non-detect. For duplicate samples, the result for each constituent was selected as follows: (1) if both samples reported positive detects, the higher measured analytical concentration was used; (2) if only one result was a positive detect, that concentration was used; (3) if both samples reported non-detects, one-half the lower SQL was used as the proxy concentration. For the case of two non-detects, the lower SQL was used because higher SQLs are frequently the result of dilution of the sample, and use of the higher SQL would introduce more uncertainty into the calculation. Additionally, it is not reasonable to use the higher SQL when the duplicate analysis for the sample indicated that the constituent was not present at the lower SQL. The UCL calculations were performed using the USEPA (2008) ProUCL Version 4.0 software. In each case, the EPC was selected as the lesser of the calculated UCL and the maximum detected concentration. Non-detect results were represented by onehalf the related SQL. The EPCs for each soil data set are presented in Table 3 (2007 Tailings Pile Samples) and Table 4 (2007 Tailings Pile Samples and 2006 Soil Characterization Samples). Human Health Risk Assessment (5-2-08) Final.doc 4-2

22 Soledad Mountain Project Human Health Risk Assessment 4.2 Exposure Scenario The exposure scenario considered in this assessment is the potential for site workers to be exposed to COPCs present in tailings and soil by oral, dermal and inhalation pathways. Default exposure assumptions were used for the potentially exposed populations at the Site and are presented on Table 13. The equations used to calculate potential exposures to constituents in tailings and soil are presented in Table 14, and provide the results of the intermediate calculations for tailings and soil exposure. 4.3 Exposure Assumptions A worker may be present at the Site to work on construction or excavation activities in the vicinity of the tailings pile; therefore, this exposure scenario was evaluated based on a hypothetical construction project. The construction project was assumed to take three months (60 working days) to six months (120 working days) to complete. The exposure assumptions for this potential receptor are included in Table 13 and are summarized as follows: Adult body weight of 70 kg (USEPA 1991; 1989); Exposure frequency of 60 days/year (5 workdays/week for 3 months) or 120 days/year (5 workdays/week for 6 months) (professional judgment); Exposure duration of 1 year for site workers (professional judgment). Incidental soil ingestion rate of 330 mg/day (USEPA 2002b); Exposed skin surface area of 3,300 square centimeters (cm²), which is the sum of the mean values for hands, forearms, and face for an adult (USEPA 2002b); Soil adherence rate of 0.3 mg/cm 2 /day (USEPA 2002b); and Inhalation rate of 20 m³/day (USEPA 1991; 1989). Human Health Risk Assessment (5-2-08) Final.doc 4-3

23 Soledad Mountain Project Human Health Risk Assessment 5. Risk Characterization Potential risks and hazards to human health are evaluated quantitatively by combining calculated exposure levels and toxicity data. A distinction is made between noncarcinogenic and carcinogenic endpoints, and two general criteria are used to describe risk: HQ for non-carcinogenic effects, and ELCR for constituents evaluated as human carcinogens. 5.1 Non-carcinogenic Hazard Exposure doses are averaged over the expected exposure period to evaluate noncarcinogenic effects. The HQ is the ratio of the estimated exposure dose and the RfD. An HQ ratio greater than one indicates that the estimated exposure level for that constituent exceeds the RfD, but does not estimate the probability that an adverse effect will occur. An HQ of one indicates that health effects should not occur. An HQ that exceeds one does not imply that health effects will occur, but that health effects are possible. 5.2 Excess Lifetime Cancer Risk The ELCR is an estimate of the potential increased risk of cancer that may result from lifetime exposure, at specified average daily dosages, to constituents detected in media at a site. Estimated doses or intakes for each constituent are averaged over the hypothesized lifetime exposure of 70 years. It is assumed that a large dose received over a short period of time is equivalent to a smaller dose received over a longer period of time, as long as the total doses are equal. The ELCR is calculated as the product of the exposure dose and the CSF. The risk estimate is considered to be an upperbound estimate; therefore, it is likely that the true risk is far less than that predicted by the model. 5.3 Site Worker The assumptions used to evaluate site worker exposure to the constituents detected in tailings and soils are presented in Table 13. The equations used in the risk characterization calculations are presented in Table 14. Risk characterization calculations were prepared for workers exposed to the constituents in tailings and soil for both 3-month and 6-month exposure periods. These calculations present a health-based comparison of constituent concentrations, Human Health Risk Assessment (5-2-08) Final.doc 5-1

24 Soledad Mountain Project Human Health Risk Assessment using both carcinogenic and non-carcinogenic toxicity values. As shown in Table 16, the ELCR calculated using the EPC for a 3-month exposure to the 2007 tailings pile samples is , which is equal to the CalEPA target risk value of 1x10-5 for workers and is within the USEPA target risk range, and the HI is 0.3, which is below the HI target of one. Arsenic is the risk driver within this set of samples. As shown in Table 17, the ELCR calculated using the EPC for a 6-month exposure to the 2007 tailings pile samples is , which slightly exceeds the CalEPA target risk value and is within the USEPA target risk range, and the HI is one, which is equivalent to the HI target of one. As shown in Table 18, the ELCR calculated using the EPC for a 3-month exposure to the 2006 tailings and soil characterization samples is , which is below the Cal- EPA target risk value of 1x10-5 for workers and within the USEPA target risk range, and the HI is 0.1, which is below the HI target of one. As shown in Table 19, the ELCR calculated using the EPC for a 6-month exposure to the 2006 tailings and soil characterization samples is , which is below the CalEPA target risk value and is within the USEPA target risk range, and the HI is 0.2, which is below the HI target of one. Risks from exposures to lead were calculated directly using the LeadSpread v7 Spreadsheet model to estimate blood-lead levels (DTSC 2002). For lead, the 99 th percentile blood-lead concentration predicted for workers was predicted to be 3.7 and 3.6 μg/dl (refer to Attachment 2, Tables 1 and 2) for the 2007 tailings samples and 2006 soil characterization data, respectively. These levels are substantially below the 10 μg/dl, the blood-lead level of concern to DTSC and the USEPA. With respect to mercury, the concentrations were elevated above background, which is less than 1 mg/kg, but the risk estimates were very low. The mercury concentrations detected on the Site were low such that the HQs for all exposure scenarios were well below the target of one and the estimated fugitive dust concentrations were less than OSHA PELs based on normal site conditions. Therefore, mercury within the Site is not a health concern for workers. 5.4 Occupational Exposure The primary receptors for the Site COPCs are site construction workers. These individuals will be exposed to the constituents detected in soil and tailings as part of their normal work activities during the construction of the ore processing facilities. As such, while the evaluation performed above is appropriate for characterizing risk and hazards, the level of protection of the site worker is more stringent than that considered acceptable for work place exposures because the risk assessment considers Human Health Risk Assessment (5-2-08) Final.doc 5-2

25 Soledad Mountain Project Human Health Risk Assessment involuntary exposure such that the site workers would not be informed of the possible hazards associated with construction work at this site. Under the Occupational Safety and Health Act (OSHA) and the Mining Safety and Health Act (MSHA), the company is required to communicate the hazards and medically monitor their workers and, thus, the exposure scenarios are voluntary such that the workers are informed and remunerated based on their full willingness to work under these specific conditions. The occupational standards are higher than risk-based criteria derived in this report because they are based on the healthy worker effect, which incorporates epidemiological studies showing that workers are healthier than the sensitive human population that any risk assessment is meant to protect. Therefore, in order to provide context and meaning for this risk assessment, this evaluation compares the estimated dust data to occupational health standards. Based on the calculation presented in Table 15 and as shown in Tables 20 and Table 21, the fugitive dust emission concentrations were also calculated to discern the amount of each constituent present in the wind-blown dust generated under normal conditions at the Site. This fugitive dust emission concentration was calculated by dividing the EPC by the particulate emission factor (PEF). These individual constituent concentrations were then compared with the American Conference of Governmental Industrial Hygienists ([ACGIH] 2007) TLVs, the California Occupational Health and Safety Administration (OSHA) PELs, and the Federal OSHA PELs for each constituent. All of the calculated fugitive dust emission concentrations for the 2007 tailings pile samples (Table 20) and 2006 (Table 21) soil characterization samples were below all of the TLVs and PELs, indicating an acceptable level of risk to workers at the Site under normal site conditions. As shown on Table 20, the fugitive dust emissions from silica are 9.8x10-6 mg/m 3. Converting to units consistent with how USEPA regulates for PM10, this is μg/m 3 silica that is PM10 particle size. The current USEPA compliance standard is 150 μg/m 3 averaged over 24 hours and 50 μg/m 3 averaged over one-year. Thus, the estimated levels are much lower and show there is no hazard over the 3-month or 6- month exposure period used in this assessment. The National Institute for Occupational Safety and Health (NIOSH 2002) recommends 0.05 mg/m 3 for the timeweighted average (Table 20 includes the PEL, but not the TWA) and Table 20 shows no risk from silica as fugitive dust at that level. That said, the analysis was done for both 3-and 6-month exposure periods for the construction worker and was not done for a mine-worker working at the site for a considerably longer period. It is recommended that GQM monitor and account for possible long-term exposure issues from workers breathing dust containing silica during the life of mine. Human Health Risk Assessment (5-2-08) Final.doc 5-3

26 Soledad Mountain Project Human Health Risk Assessment 6. Uncertainties in the Risk Assessment The risk estimates presented herein are conservative estimates of potential risks associated with workers exposure to constituents detected in tailings and soil at the Site. Uncertainty is inherent in the risk assessment process, and a discussion of these uncertainties is presented in this section. Each of the three basic building blocks for risk assessment (monitoring data, exposure scenarios, and toxicity values) contributes uncertainties. Each of the uncertainties is accounted for by using conservative assumptions wherever specific data are unavailable. This risk assessment is based on the assumption that normal conditions prevail during construction of the mine and ore processing facilities.. The on-site air quality and climate montoring station was erected in late As shown on Figure 2, approximately 18 months of wind data has been compiled today and is available for evaluation and for development of construction plans. This data provides insight into the diurnal wind patterns and can be plotted as part of the project s fugitive dust suppression plan and, specifically, the timing of activities where dust suppression is critical. The optimal time for grading and excavation activities will be the calmest times of day for wind. This would also reduce the potential health risks associated with the historical tailing and downwind soils with elevated metal levels. The available data adequately describe the occurrence of constituents in tailings and soils at the Site. Environmental sampling itself introduces uncertainty. Environmental sampling at the Site was conducted using well-designed sampling plans, appropriate sampling techniques, and laboratory data validation and quality assurance / quality control (QA/QC) procedures, as detailed in sampling plans developed specifically for the each sampling event and included in Attachments 1 and 2 of this report. The data used in this report meet QA/QC requirements and are appropriate for use in an occupational health risk assessment. The assumption that the concentrations will remain constant throughout the exposure period is a conservative approach, since ongoing remediation and natural attenuation and degradation processes will likely reduce the concentrations over time. It is highly unlikely that receptors would be exposed to concentrations equal to the upper-bound estimates of the mean concentrations, particularly over an extended period of time. Exposure to the constituents detected in soil was based on the UCL. This provides a conservative yet realistic evaluation of exposure. Human Health Risk Assessment (5-2-08) Final.doc 6-1

27 Soledad Mountain Project Human Health Risk Assessment The toxicity values and other toxicological information used in this report are also associated with significant uncertainty. Many toxicity values are developed using results of studies in which laboratory animals are exposed to relatively high doses of particular constituents over an entire lifetime. As such, these studies do not represent realistic examples of environmental exposures. In addition, many animals used for laboratory studies are more sensitive than humans to specific compounds. The effects shown by the laboratory animals in the high dose studies are often very different than effects reported by humans in parallel epidemiological studies. This is because a particular compound may have a different mechanism of action in laboratory animals than it does in humans. Even epidemiological studies, which are generally preferable to animal toxicity studies, are characterized by several uncertainties, such as differential exposures and unknown (and uncontrolled) doses. The linear multi-stage model used to extrapolate from the results of laboratory studies to anticipated effects in humans is based on assumptions that may serve to overstate any actual risk. The first assumption is that any exposure to a carcinogenic constituent will cause cancer, regardless of the size of the dose. In addition, while constructing the model from the animal data, USEPA uses values that are based on a 95% UCL of the dose/response slope. Therefore, any risk estimates derived from the model are based on values higher than those reported in the underlying studies rather than the most likely estimates generated by applying the mathematical model to the actual study data. Also, recent research on the mechanisms of carcinogenesis suggests that the use of the linear multi-stage model may overestimate the cancer risks associated with exposure to low doses of constituents. It is theorized that the high dosage animal studies induce cell death on a large scale. To replace these cells, the laboratory animal stimulates cell production by rapid cell division, a type of division that is more subject to mutations than in non-dividing cells, thus increasing the potential for tumor formation. The administration of compounds at low doses doses more applicable to true environmental exposure likely would not increase the cell division rate and thus would not increase mutations; therefore, it is possible that the assumption that the risk of high dose exposure in animals can be extrapolated to estimate the risk of low dose environmental exposure is overly conservative. With respect to toxicity values, priority was given to the CalEPA toxicity values over USEPA values. The CalEPA cancer slope factor for arsenic is six times higher than the accepted USEPA value (i.e., 9.5 versus 1.5 (mg/kg/day) -1 ). In addition, a 50 percent bioavailability factor was incorporated into the oral exposure pathway evaluation for arsenic based on information available from the scientific literature. Human Health Risk Assessment (5-2-08) Final.doc 6-2

28 Soledad Mountain Project Human Health Risk Assessment GQM is currently conducting speciation work on arsenic, which may show that the bioavailability is lower than 50 percent. Uncertainty is also associated with constituent mixtures. Information on the toxicity of specific mixtures is rarely available. The procedure generally applied to a potential event of simultaneous exposure to multiple constituents from a variety of sources assumes dose additivity, although it is possible that the interaction of multiple constituents could be synergistic or antagonistic. Human Health Risk Assessment (5-2-08) Final.doc 6-3

29 Soledad Mountain Project Human Health Risk Assessment 7. Summary and Conclusions Ten soil samples collected at five locations from the historical Gold Fields tailings pile in November 2007 and 38 soil samples from the 2006 baseline soil characterization program were evaluated as part of this HHRA to determine their physical and chemical properties and the potential risk to human health from exposure to COPCs in the tailings and mixtures of tailings and site soil. It was assumed that during construction, workers could be exposed to chemical constituents present in the tailings and soils for both 3-month and 6-month exposure periods. The sampling data were used to evaluate exposure selecting the 95% UCL on the mean as exposure point concentrations for all samples. Risk characterization results were evaluated for site workers, concluding in a healthbased comparison of constituent concentrations using both carcinogenic and noncarcinogenic toxicity values. The ELCR calculated using the EPC for a 3-month exposure period to the 2007 tailings pile samples is , which is equivalent to the CalEPA target risk value, and the HI is 0.3, which is below the HI target of one. The ELCR calculated using the EPC for a 6-month exposure period to the 2007 tailings pile samples is , which slightly exceeds the CalEPA target risk value, and the HI is one, equivalent to the HI target. The ELCR calculated using the EPC for a 3-month exposure to the 2006 soil characterization samples is , below the CalEPA target risk value, and the HI is 0.1. The ELCR calculated using the EPC for a 6-month exposure to the 2006 soil characterization samples is , which is below the CalEPA target risk value, and the HI is 0.2. Arsenic is the risk driver for this evaluation and the risk assessment incorporates a 50 percent bioavailability factor for arsenic based on scientific research which indicates that the predominant form of arsenic found in soils at mining sites is insoluble. Further research at Soledad Mountain is being conducted to determine the speciation of arsenic which will further support the understanding of its bioavailability to humans. An evaluation for lead was conducted according to DTSC guidance and the results indicate that lead concentrations are low and not a concern. The mercury concentrations detected on the Site were well below the target of one and the estimated fugitive dust concentrations were less than OSHA permissible exposure limits and, therefore, not a health risk concern. Fugitive dust emission concentrations were calculated and compared to industrial standards to determine whether the concentration of each constituent present in the wind-blown particulates generated under normal conditions at the Site was acceptable for site worker exposure. The onsite meteorological data collect since late 2006 indicate that the wind patterns and speeds vary considerably during the day, week and Human Health Risk Assessment (5-2-08) Final.doc 7-1

30 Soledad Mountain Project Human Health Risk Assessment time of year. The wind data can be plotted as histograms and should be an integral part of the fugitive dust control plans and, in particular, be considered for the timing of construction activities, especially in the area of the historical tailing and the downwind soils. Occupational health risk can be increased or reduced through planning and an understanding of planned activities and the Site conditions. All of the calculated fugitive particulate emission concentrations for both the tailings pile samples and the soil characterization samples were below all of the TLVs and PELs, indicating an acceptable level of risk for workers at the Site. From an occupational exposure consideration, there is no risk to site workers. Furthermore, the tailings particle sizes were measured to determine the percentage of particles within the bulk samples that are of respirable size. The data indicate that approximately 25 percent of the tailings particles are finer than ten microns, which is the largest possible respirable size. The fugitive dust levels estimated over the 3-month and 6-month exposure periods used in this assessment show there is no hazard to construction workers. It is recommended, however, that GQM monitor and account for possible long-term exposure issues from workers breathing dust containing silica during the life of mine. The results of the HHRA indicate that the potential levels of exposure of site workers to constituents in the historical tailings would not pose a risk based on either a 3 month or 6 month exposure period during construction of the heap leach facility. The calculated risks were below the CalEPA benchmark (except for one scenario) and within the USEPA target risk management range. Comparison of estimated dust concentrations to occupational exposure limits resulted in no significant risk. The calculated levels were all below the occupational exposure limits (e.g., TLVs or PELs). Finally, there are approximately six residences within a mile of the historical tailing piles. The soil samples secured during the 2006 baseline soil characterization study from the two nearest residences reflect that the COPCs concentrations in soil approximate the background concentration for Kern County (ARCADIS 2007a, Bradford et al., 1996). Human Health Risk Assessment (5-2-08) Final.doc 7-2

31 Soledad Mountain Project Human Health Risk Assessment 8. References Air Sciences Inc., Meteorological and Particulate Data Report, October 1, 2006 September 30, 2007, Soledad Project. Golden Queen Mining Co., October ARCADIS-US. Inc., 2007a. Baseline Soil Characterization Report, Soledad Mountain Project. Golden Queen Mining Co., April ARCADIS-US. Inc., 2007b. Tailing Sampling Plan for Human Health Risk Assessment, Soledad Mountain Project, Golden Queen Mining Co. Inc., August Bradford, G.R., A.C. Change, A.L. Page, D. Bakhtar, and J.A. Frampton, Background concentrations of trace and major elements in California Soils. Special Report of the Kearney Foundation. Kearney Foundation of Soil Science, Division of Agriculture and Natural Resources, University of California, March. California Environmental Protection Agency (CalEPA) Office of Environmental Health Hazard Assessment (OEHHA) Toxicity Criteria Database. 28 January. Internet access: Cogliano, V.J Plausible Upper Bounds: Are Their Sums Plausible? Risk Analysis, 17 (1): DeDycker & Associates, Inc Baseline and Background Soil Assessment Sampling and Analysis Plan. The National Institute for Occupational Safety and Health (NIOSH) Health Effects of Occupational Exposure to Respirable Crystalline Silica. U.S. Environmental Protection Agency (USEPA) Integrated Risk Information System (IRIS). Office of Research and Development, National Center for Environmental Assessment (NCEA). Internet access: [ USEPA ProUCL User s Guide, Version 4.0. April. USEPA. 2004a. Region IX Preliminary Remediation Goal Table. October. Internet access: [ Last update December 28, Human Health Risk Assessment (5-2-08) Final.doc 8-1

32 Soledad Mountain Project Human Health Risk Assessment USEPA. 2004b. EPI Suite software, Version Office of Pollution Prevention and Toxics, Washington DC. August 17. Available for free download at internet address: ( USEPA. 2004c. Superfund Chemical Database Matrix. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency. Washington, DC. January. USEPA. 2004d. Risk Assessment Guidance for Superfund, Volume 1: Human Health Evaluation Manual (Part E, Supplemental Guidance for Dermal Risk Assessment). Final. Office of Emergency and Remedial Response, Washington, DC. EPA/540/R/99/005. OSWER EP. PB July. USEPA. 2002a. Calculating Upper Confidence Limits for Exposure Point Concentrations at Hazardous Waste Sites. Office of Emergency and Remedial Response, Washington, DC. December. OSWER USEPA. 2002b. Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites. Office of Emergency and Remedial Response, Washington, DC. OSWER December. USEPA Health Effects Assessment Summary Tables (HEAST), FY-1997 Update. Office of Research and Development and Office of Emergency and Remedial Response, Washington, DC. EPA/540/R-97/036. OERR (97-1). NTIS No. PB July. USEPA Risk Assessment Guidance for Superfund, Volume I: Human Health Evaluation Manual. Supplemental Guidance, "Standard Default Exposure Factors." Interim Final. Office of Emergency and Remedial Response, Washington, DC. OSWER Directive March 25. USEPA Risk Assessment Guidance for Superfund, Human Health Evaluation Manual, Volume 1, Part A. Interim Final. Office of Emergency and Remedial Response, Washington, DC. EPA/540/1-89/002. December. Human Health Risk Assessment (5-2-08) Final.doc 8-2

33 Soledad Mountain Project Human Health Risk Assessment TABLES

34 Table 1. Analytical Data, 2007 Tailings Pile Samples,Soledad Mountain Project, Kern County, California. Sample: T-07-1C T-07-1C T-07-2C T-07-2C T-07-3C T-07-3C T-07-4C T-07-4C T-07-5C T-07-5C Analyte Depth (inches): Date: 10/4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/2007 Metals (mg/kg) Arsenic Chromium (total) Hexavalent Chromium <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Lead Mercury Silica Cyanide mg/kg - milligrams per kilogram. NA - Not available.

35 Table 2. Analytical Data Combined for 2006 and 2007 Tailing and Soil Samples, Soledad Mountain Project, Kern County, California Sample: T-07-1C T-07-1C T-07-2C T-07-2C T-07-3C T-07-3C T-07-4C T-07-4C T-07-5C T-07-5C BSK-5 BSK-6 Analyte Depth (inches): Date: 10/4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/2007 Other: Other01 Other02 Other03 Other04 Other05 Other06 Other07 Other08 Other09 Other10 Other10 Other10 Metals (mg/kg) Arsenic Chromium (total) <5 6 Hexavalent Chromium <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 NA NA Lead Mercury < Silica NA NA Cyanide NA NA Barium NA NA NA NA NA NA NA NA NA NA 35 NA Cobalt NA NA NA NA NA NA NA NA NA NA <5 NA Copper NA NA NA NA NA NA NA NA NA NA 5 NA Silver NA NA NA NA NA NA NA NA NA NA <2 NA Vanadium NA NA NA NA NA NA NA NA NA NA 11 NA Zinc NA NA NA NA NA NA NA NA NA NA 32 NA mg/kg - milligrams per kilogram. NA

36 Table 2 (continued). Analytical Data Combined for 2006 and 2007 Tailing and Soil Samples, Soledad Mountain Project, Kern County, California BSK-7 BSK-8 BSK-9 BSK-10 BSK-11 BSK-12 BSK-13 BSK-14 BSK-15 BSK-16 BSK-17 BSK-18 BSK-19 BSK-20 BSK-20 DUP DUPLICATES 10/4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/2007 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other * <5 6 <5 <5 5 <5 7 <5 11 <5 <5 <5 5 <5 <5* NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA * <0.1 <0.1 < <0.1* NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 20 NA NA NA NA 94 NA NA NA NA 44 36* NA NA NA <5 NA NA NA NA 7 NA NA NA NA <5 <5* NA NA NA 7 NA NA NA NA 17 NA NA NA NA 6 <5* NA NA NA 10 NA NA NA NA 10 NA NA NA NA 4 2* NA NA NA 4 NA NA NA NA 26 NA NA NA NA 10 8* NA NA NA 94 NA NA NA NA 100 NA NA NA NA 39 30*

37 Table 2 (continued). Analytical Data Combined for 2006 and 2007 Tailing and Soil Samples, Soledad Mountain Project, Kern County, California BSK-21 BSK-22 BSK-23 BSK-24 BSK-25 BSK-26 BSK-27 BSK-28 BSK-29 BSK-30 BSK-31 BSK-32 BSK-33 BSK-34 10/4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/2007 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other10 Other <5 <5 7 <5 7 <5 < < NA NA NA NA NA NA NA NA NA NA NA NA NA NA < <0.1 < < NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 90 NA NA NA NA 78 NA NA NA NA NA NA NA NA <5 NA NA NA NA <5 NA NA NA NA NA NA NA NA 29 NA NA NA NA 15 NA NA NA NA NA NA NA NA 7 NA NA NA NA 3 NA NA NA NA NA NA NA NA 15 NA NA NA NA 14 NA NA NA NA NA NA NA NA 100 NA NA NA NA 81 NA NA NA NA

38 Table 2 (continued). Analytical Data Combined for 2006 and 2007 Tailing and Soil Samples, BSK-35 BSK-35 DUP BSK-36 BSK-37 BSK-38 BSK-B BSK-C DUPLICATES 10/4/ /4/ /4/ /4/ /4/ /4/ /4/2007 Other10 Other10 Other10 Other10 Other10 Other10 Other * <5* 6 <5 <5 5 <5 NA NA NA NA NA NA NA 26 18* <0.1* 0.1 < NA NA NA NA NA NA NA NA NA NA NA NA NA NA 60 45* NA NA NA <5 <5* NA NA NA <5 <5 8 5* NA NA NA 7 <5 2 <2* NA NA NA 3 < * NA NA NA * NA NA NA 42 33

39 Table 3. Summary of Constituents Detected, 2007 Tailings Pile Samples, Soledad Mountain Project, Kern County, California. Range of SQLs Range of Detects Average Data Estimates of the Mean Frequency Percent Min Max Min Max Detect Distn (mg/kg) EPC Constituent Detects / Total Detects [a] (mg/kg) (mg/kg) (mg/kg) [b] Mean UCL [c] (mg/kg) Metals Arsenic 10 / % hi N t 220 Chromium (total) 10 / % hi N t 19 Cyanide 10 / % hi N t 32 Lead 10 / % hi N t 100 Mercury 10 / % hi N t 26 Silica 10 / % hi 1,990 2,500 2,200 N 2,200 2,300 t 2,300 [a] [b] [c] The percent detects in each data set is indicated as low "lo " (50 percent or less), medium "med " (between 50 and 85 percent), or high "hi " (85 percent or more). The UCLs were calculated with the assumption that the sampling data are normally distributed for all constituents. The UCLs were calculated using methods presented in USEPA (2007) guidance, indicated here as "t" (t-ucl). Not applicable. Data Distn Data distribution; "N" = normal. EPC Exposure point concentration; minimum of the maximum detectetd concentration (Max ) and the calculated UCL (rounded to two significant figures). mg/kg milligrams per kilogram. SQLs Practical sample quantitation limits for the non-detects. UCL The one-tailed upper confidence limit on the arithmetic mean (USEPA 2007, 2002a).

40 Table 4. Summary of Constituents Detected, 2006 Soil Characterization Samples, Soledad Mountain Project, Kern County, California. Range of SQLs Range of Detects Average Data Estimates of the Mean Frequency Percent Min Max Min Max Detect Distn (mg/kg) EPC Constituent Detects / Total Detects [a] (mg/kg) (mg/kg) (mg/kg) [b] Mean UCL [c] (mg/kg) Metals Arsenic 46 / % hi N t 75 Barium 9 / % hi N t 91 Chromium (total) 27 / % med N t 8.2 Cobalt 1 / 9 11 % lo N t 3.9 Copper 8 / 9 89 % hi N t 16 Cyanide 10 / % hi N t 32 Lead 46 / % hi N t 74 Mercury 37 / % med N t 6.9 Silica 10 / % hi 1,990 2,500 2,200 N 2,200 2,300 t 2,300 Silver 7 / 9 78 % med N t Vanadium 9 / % hi N t 16 Zinc 9 / % hi N t 82 [a] [b] [c] The percent detects in each data set is indicated as low "lo " (50 percent or less), medium "med " (between 50 and 85 percent), or high "hi " (85 percent or more). The UCLs were calculated with the assumption that the sampling data are normally distributed for all constituents. The UCLs were calculated using methods presented in USEPA (2007) guidance, indicated here as "t" (t-ucl). Not applicable. Data Distn Data distribution; "N" = normal. EPC Exposure point concentration; minimum of the maximum detectetd concentration (Max ) and the calculated UCL (rounded to two significant figures). mg/kg milligrams per kilogram. SQLs Practical sample quantitation limits for the non-detects. UCL The one-tailed upper confidence limit on the arithmetic mean (USEPA 2007, 2002a).

41 Table 5. Selection of Constituents of Potential Concern, 2007 Tailings Pile Samples, Soledad Mountain Project, Kern County, California. Range of Detects Residential - Direct Contact Industrial - Direct Contact Protection of Groundwater Min Max Screening Value COPC? Screening Value COPC? Screening Value COPC? Constituent (mg/kg) (mg/kg) (YES/no) (mg/kg) (YES/no) (mg/kg) (YES/no) Arsenic [b] C YES 0.25 [b] C YES 29 YES Chromium (total) C no 450 C no 38 no Cyanide N no 1,200 N no 40 [c] YES Lead [b] YES 800 ** no NA YES Mercury N YES 31 N YES 2 [c] YES Silica 1,990 2,500 NA YES NA YES NA YES [a] California EPA and Department of Toxic Substances and the USEPA (2004a) Region IX Preliminary Remediation Goal for direct contact to residential surface soil and industrial soil, based on cancer risk (C) of 1E-06 or noncancer hazard (N) of 0.1; and for protection of groundwater, based on dilution attenuation factor (DAF) of 20 (i.e., migration from soil to groundwater). [b] California EPA modified value; screening value based on California toxicity values. [c] USEPA (2002b) Soil Screening Level, DAF = 20. USEPA Preliminary Remediation Goals [a] ** The screening level for lead is based on noncancer effects but uses a non-standard method and, therefore, is not adjusted by 0.1. COPC Constituent of potential concern; retained for the risk assessment calculations. mg/kg milligrams per kilogram. NA Not available.

42 Table 6. Selection of Constituents of Potential Concern, 2006 Soil Characterization Samples, Soledad Mountain Project, Kern County, California. USEPA Preliminary Remediation Goals [a] Range of Detects Residential - Direct Contact Industrial - Direct Contact Protection of Groundwater Min Max Screening Value COPC? Screening Value COPC? Screening Value COPC? Constituent (mg/kg) (mg/kg) (YES/no) (mg/kg) (YES/no) (mg/kg) (YES/no) Arsenic [b] C YES 0.25 [b] C YES 29 YES Barium N no 6,700 N no 1,600 no Chromium (total) C no 450 C no 38 no Cobalt N no 1,300 N no NA YES Copper N no 4,100 N no NA YES Cyanide N no 1,200 N no 40 [c] YES Lead [b] YES 800 ** no NA YES Mercury N YES 31 N YES 2 [c] YES Silica 1,990 2,500 NA YES NA YES NA YES Silver N no 510 N no 34 no Vanadium N YES 100 N no 6,000 no Zinc ,300 N no 100,000 M no 12,000 no [a] California EPA and Department of Toxic Substances and the USEPA (2004a) Region IX Preliminary Remediation Goal for direct contact to residential surface soil and industrial soil, based on cancer risk (C) of 1E-06 or noncancer hazard (N) of 0.1; and for protection of groundwater, based on dilution attenuation factor (DAF) of 20 (i.e., migration from soil to groundwater). [b] California EPA modified value; screening value based on California toxicity values. [c] USEPA (2002b) Soil Screening Level, DAF = 20. ** The screening level for lead is based on noncancer effects but uses a non-standard method and, therefore, is not adjusted by 0.1. COPC Constituent of potential concern; retained for the risk assessment calculations. mg/kg milligrams per kilogram. NA Not available.

43 Table 7. Particle Size Distribution, 2007 Tailings Pile Samples,Soledad Mountain Project, Kern County, California. Sample Point: T-07-1P T-07-1P T-07-2P T-07-2P T-07-3P T-07-3P T-07-4P T-07-4P T-07-5P T-07-5P Sample Depth (inches bgs): (3-7) (27-29) (4-8) (26-30) (2-4) (24-26) (2-4) (26-28) (8-12) (26-28) Sample Date: 10/4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/ /4/2007 Particle Size Lab ID: Hydrometer#1 (~31µm) Hydrometer#2 (~20µm) Hydrometer#3 (~12µm) Hydrometer#4 (~9µm) Hydrometer#5 (~6µm) Hydrometer#6 (~3µm) Hydrometer#7 (~1µm) ~ - Approximate. bgs - below ground surface. µm - micron

44 Table 8. Noncarcinogenic Toxicity Values for Oral and Dermal Exposure, Soledad Mountain Project, Kern County, California. Oral RfD (mg/kg/day) Adjustment Dermal RfD (mg/kg/day) Target Site/ Confidence Level/ Constituent Subchronic Chronic Factor [a] Subchronic Chronic Critical Effect Uncertainty Factor Metals Arsenic 3.0E-04 c 3.0E-04 I 1 3.0E E-04 skin, vascular medium/3 Barium 2.0E-01 c 2.0E-01 I E E-02 kidney medium/300 Chromium 1.0E+00 H 1.5E+00 I E E-02 NR low/100 Cobalt 2.0E-02 c 2.0E-02 N 1 2.0E E-02 skin NA Copper [b] 4.0E-02 c 4.0E-02 H 1 4.0E E-02 GI NA Cyanide 2.0E-02 H 2.0E-02 I 1 2.0E E-02 WB, thyroid, NS medium/100 Lead NA NA 1 NA NA CNS NA Mercury [c] 3.0E-03 cx 3.0E-04 Is E E-05 autoimmune effects high/1000 Silica NA NA 0 NA NA NA NA Silver 5.0E-03 H 5.0E-03 I E E-04 skin low/3 Vanadium 7.0E-03 H 1.0E-03 N E E-05 liver low/100 Zinc 3.0E-01 H 3.0E-01 I 1 3.0E E-01 blood medium/3 References: H USEPA (1997) (Health Effects Assessment Summary Tables [HEAST]). I USEPA (2008) Integrated Risk Information System (IRIS). N Provisional value from USEPA's National Center for Environmental Assessment (NCEA), obtained from USEPA (2004a) Region IX. [a] [b] [c] c CNS GI mg/kg/day NA NR NS RfD s WB x The oral-to-dermal adjustment factor (oral absorption efficiency) (USEPA 2004d) was used to calculate the dermal RfD values: RfD (dermal) = RfD (oral) Adjustment Factor (oral absorption efficiency). Based on current drinking-water standard. Oral RfD for mercury is based on mercuric chloride toxicity data. The chronic value is used if available. Central nervous system. Gastrointestinal tract. milligrams per kilogram per day. Not available. None reported. Nervous system. Reference dose. Value is based on use of a surrogate compound, as indicated. Whole body (includes increased mortality and changes to body weight). The uncertainty factor for subchronic to chronic extrapolation was removed.

45 Table 9. Noncarcinogenic Toxicity Values for Inhalation Exposure, Soledad Mountain Project, Kern County, California. Inhalation RfD (mg/kg/day) Target Site/ Confidence Level/ Constituent Subchronic Chronic Critical Effect Uncertainty Factor Metals Arsenic 8.6E-06 c 8.6E-06 CalEPA NA NA Barium 1.4E-03 H 1.4E-04 H fetus NA/1000 Chromium NA NA NA NA Cobalt 5.7E-06 c 5.7E-06 N NA NA Copper NA NA NA NA Cyanide NA NA NA NA Lead NA NA CNS NA Mercury [a] 2.6E-05 c 2.6E-05 CalEPA CNS medium/30 Silica NA NA NA NA Silver NA NA NA NA Vanadium NA NA NA NA Zinc NA NA NA NA References: CalEPA California Environmental Protection Agency (CalEPA) Toxicity Criteria Database (2008). H USEPA (1997) (Health Effects Assessment Summary Tables [HEAST]). I USEPA (2008) Integrated Risk Information System (IRIS). N Provisional value from USEPA's National Center for Environmental Assessment (NCEA), obtained from USEPA (2004a) Region IX. [a] c CNS mg/kg/day NA RfD s Inhalation toxicity value for mercury is based on data for elemental mercury. The chronic value is used if available. Central nervous system. milligrams per kilogram per day. Not available. Reference dose. Value is based on use of a surrogate compound, as indicated.

46 Table 10. Carcinogenic Toxicity Values for Oral and Dermal Exposure, Soledad Mountain Project, Kern County, California. Oral CSF Adjustment Dermal CSF [a] Tumor Weight of Evidence Constituent (mg/kg/day) -1 Factor [a] (mg/kg/day) -1 Site Classification* Metals Arsenic 9.5E+00 CalEPA 1 9.5E+00 skin A Barium NC 0.07 NC D Chromium NC NC D Cobalt NC 1 NC NA Copper NC 1 NC D Cyanide NC 1 NC D Lead NA 1 NA NA B2 Mercury NA 0.07 NA C Silica NA NA NA NA Silver NC 0.04 NC D Vanadium NC NC NA Zinc NC 1 NC D References: CalEPA California Environmental Protection Agency (CalEPA) Toxicity Criteria Database (2008). I USEPA (2008) Integrated Risk Information System (IRIS). [a] The oral-to-dermal adjustment factor (oral absorption efficiency) (USEPA 2004d) was used to calculate the dermal CSF values: CSF (dermal) = CSF (oral) / Adjustment Factor (oral absorption efficiency). * Weight of Evidence Classification defined in text. Not applicable. CSF Cancer slope factor. (mg/kg/day) -1 Inverse milligrams per kilogram per day (risk per unit dose). NA Not available. NC Not evaluated as a carcinogen.

47 Table 11. Carcinogenic Toxicity Values for Inhalation Exposure, Soledad Mountain Project, Kern County, California. Inhalation CSF Weight of Evidence Constituent (mg/kg/day) -1 Tumor Site Classification* Metals Arsenic 1.2E+01 CalEPA lung A Barium NC D Chromium NC D Cobalt 9.8E+00 N lung NA Copper NC D Cyanide NC D Lead NA NA B2 Mercury NA C Silica NA NA NA Silver NC D Vanadium NC NA Zinc NC D References: CalEPA California Environmental Protection Agency (CalEPA) Toxicity Criteria Database (2008). I USEPA (2008) Integrated Risk Information System (IRIS). N Provisional value from USEPA's National Center for Environmental Assessment (NCEA), obtained from USEPA (2004a) Region IX. * Weight of Evidence Classification defined in text. Not applicable. CSF Cancer slope factor. (mg/kg/day) -1 Inverse milligrams per kilogram per day (risk per unit dose). NA Not available. NC Not evaluated as a carcinogen.

48 Table 12. Dermal Absorption Parameters, Soledad Mountain Project, Kern County, California. Constituent ABSd Kp [ DRA ] (cm/hour) Metals Arsenic E-03 W Barium 0 1.0E-03 W Chromium 0 1.0E-03 DRA Cobalt 0 1.0E-01 EPI Copper 0 1.0E-03 W Cyanide 0 1.0E-03 W Lead 0 1.0E-04 DRA Mercury 0 1.0E-03 DRA Silica 0 1.8E-02 EPI Silver 0 6.0E-04 DRA Vanadium 0 1.0E-03 W Zinc 0 6.0E-04 DRA References: DRA USEPA (2004d) (Dermal Risk Assessment). The B values are calculated but are consis EPI EPI Suite (USEPA 2004b). W Assumed to be equal to the value for water (USEPA 2004d). ABSd cm Kp Dermal absorption efficiency for dermal contact with constituents in soil. centimeter. Permeability coefficient for dermal contact with constituents in water.

49 Table 13. Receptor-Specific Exposure Parameters, Soledad Mountain Project, Kern County, California. Site Worker Site Worker Parameter Symbol units 3 Month Exposure 6 Month Exposure General Factors Averaging Time (cancer) ATc days 25,550 [a] 25,550 [a] Averaging Time (noncancer) ATnc days 365 [a] 365 [a] Body Weight BW kg 70 [b,c] 70 [b,c] Exposure Frequency EF days/year 60 PJ 120 PJ Exposure Duration ED years 1 PJ 1 PJ Soil - Ingestion (Oral) Incidental Soil Ingestion Rate IRs mg/day 330 [c] 330 [f] Fraction Ingested from Souce FI unitless 1 1 Soil - Dermal Contact Exposed Skin Surface Area SSAs cm² 3,300 [d] 3,300 [f] Soil-to-Skin Adherence Rate SAR mg/cm²/day 0.3 [d] 0.3 [f] Soil - Inhalation of Dust and Vapor Breathing Rate BRs m³/day 20 [b,c] 20 [b,c] [a] The averaging time for cancer risk is the expected lifespan of 70 years expressed in days. The averaging time for non-cancer hazard is the total exposure duration expressed in days. [b] USEPA (1989). [c] USEPA (1991). [d] USEPA (2002b) cm kg m mg centimeter. kilogram. meter. milligram.

50 Table 14. Risk and Hazard Equations for Exposure to Tailings and Soil, Soledad Mountain Project, Kern County, ROUTE-SPECIFIC RISK/HAZARD: Oral: ELCR o or HQ o = EPCs FI IRs EF ED (10 6 mg/kg) BW ( AT C or AT NC ) ( [1/CSF o ] or RfD o ) Dermal: ELCR d or HQ d = EPCs SSAs SAR ABSd EF ED (10 6 mg/kg) BW ( AT C or AT NC ) ( [1/CSF a ] or RfD a ) Inhalation: ELCR i or HQ i = EPCs BRs EF ED (PEF) BW ( AT C or AT NC ) ( [1/CSF i ] or RfD i ) PEF = Q/C wind (3,600 sec/hr) RPF (1-V) (Um/Ut)³ Fx used for non-vocs TOTAL CANCER RISK: TOTAL NON-CANCER HAZARD: ELCR = ELCR o + ELCR d + ELCR i HI = HQ o + HQ d + HQ i Variable Definitions: ABSd Dermal absorption efficiency (unitless) (Table 12). AT C Averaging time for cancer effects (days) (Table 13). AT NC Averaging time for noncancer effects (days) (Table 13). BRs Breathing rate for soil exposure (m³/day) (Table 13). BW Body weight (kg) (Table 13). CSF Cancer slope factor for oral (CSF o ), dermal (adjusted to an absorbed dose, CSF a ), or inhalation (CSF i ) exposure (kg-day/mg [inverse mg/kg/day]) (Tables 10 and 11). ED Exposure duration (years) (Table 13). EF Exposure frequency (days/year) (Table 13). ELCR Excess lifetime cancer risk (unitless). EPCs Exposure point concentration in soil (mg/kg) (Tables 1 and 2). EPC i Exposure point concentration relevant to inhalation (mg/kg) (minimum of EPCs and C sat ). FI Fraction ingested from area of concern (unitless) (Table 13). Fx Function of Ut/Um (unitless); Fx = 0.18 ( 8x³ + 12x ) exp[-(x²)], where x = (Ut/Um). HI Hazard index for non-cancer effects (unitless); sum of the HQs. HQ Hazard quotient for non-cancer effects (unitless). IRs Ingestion rate of soil (mg/day) (Table 13). PEF Particulate emission factor (m³/kg). Q/C wind Particulate emission flux per unit concentration [(g/m²/sec)/(kg/m³)]. RfD Reference dose for oral (RfD o ), dermal (adjusted to an absorbed dose, RfD a ), or inhalation (RfD i ) exposure (mg/kg/day) (Tables 8 and 9). RPF Respirable particle fraction (0.036 g/m²/hr). SAR Soil-to-skin adherence rate (mg/cm²/day) (Table 13). SSAs Exposed skin surface area for soil contact (cm²) (Table 13). T Exposure interval (sec). Um Ut V x VOCs Mean annual wind speed (m/sec). Equivalent threshold value of windspeed at 7 meters (11.32 m/sec). Fraction of vegetative cover (unitless). Intermediate value in the calculation of PEF; x = (Ut/Um). Volatile organic compounds.

51 Table 15. Calculation of Particulate Emission Factors for Tailings and Soil Exposure, Soledad Mountain Project, Kern County, California. Particulate Emission Factor: x = unitless Function of Ut/Um; x = (Ut/Um) Fx = unitless Function of x; Fx = 0.18 ( 8x³ + 12x ) exp(-x²) PEF = 2.36E+08 m³/kg Particulate emission factor (m³/kg) Model Input Parameters: Foc = unitless Fraction organic carbon (USEPA 2002b, default) ρ b = 1.5 g/cm³ Soil dry bulk density (USEPA 2002b, default) θ T = unitless Total soil porosity (USEPA 2002b, default) θ as = unitless Air-filled soil porosity [ = θ T - θ ws ] θ ws = 0.15 unitless Water-filled soil porosity (USEPA 2002b, default) Q/C wind = (g/m²/sec)/(kg/m³) Wind-related particulate emission flux per unit concentration (USEPA 2002b, calculated for Los Angeles,CA) RPF = g/m²/hour Respirable particle fraction (USEPA 2002b). T = 9.5E+08 sec Exposure interval (USEPA 2002b) Um = m/sec Mean annual wind speed site-specific specific (Air Sciences Inc., 2008) Ut = m/sec Equivalent threshold value of windspeed at 7 meters (USEPA 2002b) V = 0.5 unitless Fraction vegetative cover (USEPA 2002b, default) cm centimeter. m meter. g gram. sec second. kg kilogram

52 Table 16. Risk and Hazard Calculations for Site Worker 3 Month Exposure, 2007 Tailings Pile Samples, Soledad Mountain Project, Kern County, California. CANCER RISK Percent NON-CANCER HAZARD Percent EPCs PEF [a] Route-Specific Risk Calculated Total Route-Specific Hazard Calculated Total Constituent (mg/kg) (m³/kg) Oral Dermal Inhalation Risk ELCR Oral Dermal Inhalation Hazard HI (Table 15) ELCRo ELCRd ELCRi ELCR HQo HQd HQi HI Arsenic E+08 P 2.3E E E E % 5.7E E E E-01 99% Chromium E+08 P NC NC NC NC 1.5E E+00 NA 1.5E-05 0% Cyanide E+08 P NC NC NC NC 1.2E E+00 NA 1.2E-03 0% Lead E+08 P NA NA NA NA NA NA NA NA Mercury E+08 P NA NA NA NA 6.7E E E E-03 1% Silica 2, E+08 P NA NA NA NA NA NA NA NA Total ELCR 3E % Total HI % [a] Particulate emission factor (PEF), derived on Table 15. Not applicable. HQ Hazard quotient. NC Not evaluated as a carcinogen. ELCR Excess lifetime cancer risk. mg/kg milligrams per kilogram. PEF Particulate emission factor. EPCs Exposure point concentration in soil (mg/kg). m 3 /kg cubic meters per kilogram. HI Hazard index (sum of the HQs). NA Not available. Equations: (see Table 14) ELCRo = (EPCs CSFo) / (1,000, ,550) HQo = (EPCs ) / (1,000, RfDo) ELCRd = (EPCs 3, ABSd 60 1 CSFa) / (1,000, ,550) HQd = (EPCs 3, ABSd 60 1) / (1,000, RfDa) ELCRi = (EPCs CSFi ) / (PEF 70 25,550) HQi = (EPCs ) / (PEF RfDi)

53 Table 17. Risk and Hazard Calculations for Site Worker 6 Month Exposure, 2007 Tailings Pile Samples, Soledad Mountain Project, Kern County, California. CANCER RISK Percent NON-CANCER HAZARD Percent EPCs PEF [a] Route-Specific Risk Calculated Total Route-Specific Hazard Calculated Total Constituent (mg/kg) (m³/kg) Oral Dermal Inhalation Risk ELCR Oral Dermal Inhalation Hazard HI (Table 15) ELCRo ELCRd ELCRi ELCR HQo HQd HQi HI Arsenic E+08 P 4.6E E E E % 1.1E E E E+00 99% Chromium E+08 P NC NC NC NC 2.9E E+00 NA 2.9E-05 0% Cyanide E+08 P NC NC NC NC 2.5E E+00 NA 2.5E-03 0% Lead E+08 P NA NA NA NA NA NA NA NA Mercury E+08 P NA NA NA NA 1.3E E E E-02 1% Silica 2, E+08 P NA NA NA NA NA NA NA NA Total ELCR 5E % Total HI 1 100% [a] Particulate emission factor (PEF), derived on Table 15. Not applicable. HQ Hazard quotient. NC Not evaluated as a carcinogen. ELCR Excess lifetime cancer risk. mg/kg milligrams per kilogram. PEF Particulate emission factor. EPCs Exposure point concentration in soil (mg/kg). m 3 /kg cubic meters per kilogram. HI Hazard index (sum of the HQs). NA Not available. Equations: (see Table 14) ELCRo = (EPCs CSFo) / (1,000, ,550) HQo = (EPCs ) / (1,000, RfDo) ELCRd = (EPCs 3, ABSd CSFa) / (1,000, ,550) HQd = (EPCs 3, ABSd 120 1) / (1,000, RfDa) ELCRi = (EPCs CSFi ) / (PEF 70 25,550) HQi = (EPCs ) / (PEF RfDi)

54 Table 18. Risk and Hazard Calculations for Site Worker 3 Month Exposure to Soil Characterization Samples, Soledad Mountain Project, Kern County, California. CANCER RISK Percent NON-CANCER HAZARD Percent EPCs PEF [a] Route-Specific Risk Calculated Total Route-Specific Hazard Calculated Total Constituent (mg/kg) (m³/kg) Oral Dermal Inhalation Risk ELCR Oral Dermal Inhalation Hazard HI (Table 15) ELCRo ELCRd ELCRi ELCR HQo HQd HQi HI Arsenic E+08 P 7.8E E E E % 1.9E E E E-01 97% Chromium E+08 P NC NC NC NC 6.4E E+00 NA 6.4E-06 0% Lead E+08 P NA NA NA NA NA NA NA NA Mercury E+08 P NA NA NA NA 1.8E E E E-03 1% Silica 2, E+08 P NA NA NA NA NA NA NA NA Cyanide E+08 P NC NC NC NC 1.2E E+00 NA 1.2E-03 1% Barium E+08 P NC NC NC NC 3.5E E E E-04 0% Cobalt E+08 P NC NC 1.1E E-10 0% 1.5E E E E-04 0% Copper E+08 P NC NC NC NC 3.1E E+00 NA 3.1E-04 0% Silver E+08 P NC NC NC NC 1.1E E+00 NA 1.1E-03 0% Vanadium E+08 P NC NC NC NC 1.8E E+00 NA 1.8E-03 1% Zinc E+08 P NC NC NC NC 2.1E E+00 NA 2.1E-04 0% Total ELCR 9E % Total HI % [a] Particulate emission factor (PEF), derived on Table 15. Not applicable. HQ Hazard quotient. NC Not evaluated as a carcinogen. ELCR Excess lifetime cancer risk. mg/kg milligrams per kilogram. PEF Particulate emission factor. EPCs Exposure point concentration in soil (mg/kg). m 3 /kg cubic meters per kilogram. HI Hazard index (sum of the HQs). NA Not available. Equations: (see Table 14) ELCRo = (EPCs CSFo) / (1,000, ,550) HQo = (EPCs ) / (1,000, RfDo) ELCRd = (EPCs 3, ABSd 60 1 CSFa) / (1,000, ,550) HQd = (EPCs 3, ABSd 60 1) / (1,000, RfDa) ELCRi = (EPCs CSFi ) / (PEF 70 25,550) HQi = (EPCs ) / (PEF RfDi)

55 Table 19. Risk and Hazard Calculations for Site Worker 6 Month Exposure to Soil Characterization Samples, Soledad Mountain Project, Kern County, California. CANCER RISK Percent NON-CANCER HAZARD Percent EPCs PEF [a] Route-Specific Risk Calculated Total Route-Specific Hazard Calculated Total Constituent (mg/kg) (m³/kg) Oral Dermal Inhalation Risk ELCR Oral Dermal Inhalation Hazard HI (Table 15) ELCRo ELCRd ELCRi ELCR HQo HQd HQi HI Arsenic E+08 P 1.6E E E E % 3.9E E E E-01 97% Chromium E+08 P NC NC NC NC 1.3E E+00 NA 1.3E-05 0% Lead E+08 P NA NA NA NA NA NA NA NA Mercury E+08 P NA NA NA NA 3.6E E E E-03 1% Silica 2, E+08 P NA NA NA NA NA NA NA NA Cyanide E+08 P NC NC NC NC 2.5E E+00 NA 2.5E-03 1% Barium E+08 P NC NC NC NC 7.1E E E E-04 0% Cobalt E+08 P NC NC 2.2E E-10 0% 3.0E E E E-04 0% Copper E+08 P NC NC NC NC 6.2E E+00 NA 6.2E-04 0% Silver E+08 P NC NC NC NC 2.1E E+00 NA 2.1E-03 0% Vanadium E+08 P NC NC NC NC 3.5E E+00 NA 3.5E-03 1% Zinc E+08 P NC NC NC NC 4.2E E+00 NA 4.2E-04 0% Total ELCR 2E % Total HI % [a] Particulate emission factor (PEF), derived on Table 15. Not applicable. HQ Hazard quotient. NC Not evaluated as a carcinogen. ELCR Excess lifetime cancer risk. mg/kg milligrams per kilogram. PEF Particulate emission factor. EPCs Exposure point concentration in soil (mg/kg). m 3 /kg cubic meters per kilogram. HI Hazard index (sum of the HQs). NA Not available. Equations: (see Table 14) ELCRo = (EPCs CSFo) / (1,000, ,550) HQo = (EPCs ) / (1,000, RfDo) ELCRd = (EPCs 3, ABSd CSFa) / (1,000, ,550) HQd = (EPCs 3, ABSd 120 1) / (1,000, RfDa) ELCRi = (EPCs CSFi ) / (PEF 70 25,550) HQi = (EPCs ) / (PEF RfDi)

56 Table 20. Fugitive Dust Emission Calculations for Site Worker Exposure, 2007 Tailings Pile Samples, Soledad Mountain Project, Kern County, California. Fugitive Dust Threshold Limit California OSHA OSHA EPCs PEF [a] Emission [b] Values [c] PEL [d] PEL [e] Constituent (mg/kg) (m³/kg) (mg/m 3 ) (mg/m 3 ) (mg/m 3 ) (mg/m 3 ) (Table 13) Arsenic E+08 P 9.3E E E E-02 Chromium E+08 P 8.1E E E E-01 Cyanide E+08 P 1.4E E E E+00 Lead E+08 P 4.2E E E E-02 Mercury E+08 P 1.1E E E E-02 Silica 2, E+08 P 9.8E E E E+01 [a] Particulate emission factor (PEF), derived on Table 15. [b] Fugitive Dust Emission = EPC / PEF. [c] Threshold Limit Values (2007), American Conference of Governmental Industrial Hygienists. [d] California OSHA Permissible Exposure Limit, Title 8 Table AC-1. [e] Federal OSHA Permissible Exposure Limit, 29 CFR EPCs Exposure point concentration in soil (mg/kg). OSHA Occupational Safety and Health Administration. m 3 /kg cubic meters per kilogram. PEF Particulate emission factor. mg/kg milligrams per kilogram. PEL Permissible Exposure Limit. mg/m 3 milligrams per cubic meter.

57 Table 21. Fugitive Dust Emission Calculations for Site Worker Exposure, 2006 Soil Characterization Samples, Soledad Mountain Project, Kern County, Fugitive Dust Threshold Limit California OSHA OSHA EPCs PEF [a] Emission [b] Values [c] PEL [d] PEL [e] Constituent (mg/kg) (m³/kg) (mg/m 3 ) (mg/m 3 ) (mg/m 3 ) (mg/m 3 ) (Table 13) Arsenic E+08 P 3.2E E E E-02 Barium E+08 P 3.9E E E E-01 Chromium E+08 P 3.5E E E E-01 Cobalt E+08 P 1.7E E E E-01 Copper E+08 P 6.8E E E E+00 Cyanide E+08 P 1.4E E E E+00 Lead E+08 P 3.1E E E E-02 Mercury E+08 P 2.9E E E E-02 Silica 2, E+08 P 9.8E E E E+01 Silver E+08 P 29E E 10E E 01 10E E 02 10E E 02 Vanadium E+08 P 6.8E E E E-01 Zinc E+08 P 3.5E E E E+01 [a] Particulate emission factor (PEF), derived on Table 15. [b] Fugitive Dust Emission = EPC / PEF. [c] Threshold Limit Values (2007), American Conference of Governmental Industrial Hygienists. [d] California OSHA Permissible Exposure Limit, Title 8 Table AC-1. [e] Federal OSHA Permissible Exposure Limit, 29 CFR EPCs Exposure point concentration in soil (mg/kg). OSHA Occupational Safety and Health Administratio m 3 /kg cubic meters per kilogram. PEF Particulate emission factor. mg/kg milligrams per kilogram. PEL Permissible Exposure Limit. mg/m 3 milligrams per cubic meter.

58 Soledad Mountain Project Human Health Risk Assessment FIGURES

59 California Map Area ") BSK-E BSK-A BSK-1 BSK-2 BSK-3 BSK-4 Silver Queen Road T-07-3 BSK-7 BSK-8 BSK-5 BSK-6 BSK-11 BSK-12 BSK-13 BSK-10 BSK-17 BSK-18 BSK-19 BSK-16 BSK-23 BSK-24 BSK-22 BSK-29 BSK-9 BSK-15 BSK-14 BSK-20 BSK-21 BSK-25 BSK-26 BSK-27 BSK-30 BSK-31 BSK-32 BSK-28 BSK-34 BSK-G BSK-36 T-07-5 T-07-4 T-07-1 T-07-2 BSK-C BSK-33 BSK-35 BSK-37 BSK-38 BSK-B BSK-I BSK-D ") Air Monitoring Station Legend!( Sampling Location 2006 #* Sample Location 2007 Silver Queen Road Proposed Plant Growth Media Proposed Merrill-Crowe Plant Proposed Parking Area Proposed Overflow Pond Proposed Heap Leach Facility Footprint ,000 Feet SOLEDAD MOUNTAIN FIGURE 1 SOIL AND TAILING SAMPLE LOCATIONS ANALYSIS AREA: KERN COUNTY, CALIFORNIA Date: 3/31/2008 File: I\AO000100\SoilTailing.mxd Prepared By: JG Layout: SoilTailing.pdf

60 2 SOLEDAD MOUNTAIN FIGURE 2 WIND FREQUENCY DISTRIBUTION OCTOBER 1, APRIL 30, 2008 Data provided by Air Sciences Inc. Golden, Colorado ANALYSIS AREA: SOUTHERN, CALIFORNIA Date: 5/19/2008 Prepared By: JG File: I\AO000100\WindRose.mxd Layout: WindRose.pdf