Golder Associates Inc.

200 Unio n Boulevard, Suite 500 Lakewood, CO USA 80228 Telephon e (303] 980-0540 F ax (303) 985-2080

375793

GROUNDWATER BASELINE HUMAN HEALTH RISK ASSESSMENT

CALIFORNIA GULCH SITE LEADVILLE, COLORADO

Prepared For:

Asarco, Inc.

495 East 51st Avenue Denver, Colorado 80216-2098

Prepared By:

Golder Associates Inc.

200 Union Blvd., Suite 500 Lakewood, Colorado 80228

June 1996 943-2819

OFFICE S IN AUSTRALIA , CANADA , GERMANY , HUNGARY , ITALY , SWEDEN , UNITE D KINGDOM , UNITE D STATE S
June 1996 -i- 943-2819

TABLE OF CONTENTS

1 .0 INTRODUCTION 1

1.1 Objectives .........................................................................................1

1.2 Scope...............................................................................................2

2.0 EXPOSURE ASSESSMENT......................................................................2

2.1 Potential Receptor Populations ................................................................ 3

2.2 Conceptual Site Model.......................................................................... 6

2.3 Complete Exposure Pathways.................................................................. 7

2.4 Estimating Chemical Intakes and Exposure Point Concentrations....................... 7

2.5 Exposure Assumptions.......................................................................... 8

3 .0 RISK CHARACTERIZATION RESULTS......!..............................................9

4 .0 UNCERTAINTIES AND LIMITATIONS ................................................... 

5.0 CONCLUSIONS.................................................................................. 12

6.0 REFERENCES.................................................................................... 14

LIST OF TABLES

Table 1 Leadville Groundwater, Potentially Complete Exposure Pathways Quantitatively Evaluated Table 2 General Assumptions for Body Weight Table 3 Intake Assumptions for Groundwater Ingestion Table 4 Groundwater Carcinogenic Risks and Noncarcinogenic Hazard Index (H.I.) Table 5 Comparison of Exposure Point Concentrations (EPCs) with Maximum Contaminant Levels (MCLs) (mg/1) Table 6 Summary of Uncertainty Factors in the Groundwater Baseline Risk Assessment

LIST OF FIGURES

Figure 1 Conceptual Site Model , Groundwater, Leadville, Colorado Figure 2 Future Scenario, Exposure Point Location

LIST OF APPENDICES

Appendix A Human Health Risk Evaluation Methods

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1.0 INTRODUCTION

The followin g human health baseline risk assessment (RA) for groundwater has been

prepared as a supplement to the Hydrogeologic Remedial Investigation (RJ) Report (Asarco,

1996a) to evaluate potential health risks related to site-related metals in groundwater. All

potential exposures from multiple sources will be evaluated separately in a sitewide baseline

RA. This RA evaluates only the single source, contribution from groundwater. It is important

to note that the exposure parameters used in this RA may change in a sitewide baseline RA

for the California Gulch site.

During the course of conducting the RA evaluation, it was determined that the hlgestion of

fish was the only complete or significant exposure pathway for surface water at the site. The

results of the evaluation for human exposure to metals in fish fillet s indicate that the

noncarcinogenic Hazard Indexes (His) do not exceed the EPA level of concern of 1.0.

Estimated carcinogenic risks do not exceed the EPA acceptable risk level of 1 x 10^ for the

exposure pathway evaluated for any receptors. Additionally , potential total cancer risks from

birth to age 30 were 2.29E-06 (average scenario) and 3.13E-05 (RME scenario) and do not

exceed 1 x 10"4 for exposure by fish hlgestion. The RME scenario in this RA evaluation

used a combination of site-specific data and conservative assumptions that represent the

"high-end" exposure and more than likely this overestimates the actual total cancer risk given

the exposure and behavior patterns assumed for this assessment evaluation.

1.1 Objectives

The primary objective of this RA was to evaluate potential health risks due to exposure to

groundwater using recently collected groundwater data. Where possible, the RA uses sitespecific data. When site-specific data were lacking or incomplete, conservative assumptions

were used. Thi s approach is consistent with the guidance issued by the EPA Risk Assessment

Council stressing the use of site-specific data to evaluate potential health risks (EPA, 1992a,

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b). This section follows the Risk Assessment Council's guidance for risk characterization,

limiting discussion of information to risk assessment instead of including any risk

management discussions. The reasonable maximum exposure (RME) scenario is designed to

be a measure of "high-end" exposure and is used by risk managers in making remedial

decisions that are protective of human health. The average or central tendency exposure

scenario provides necessary information to make risk management decisions (EPA, 1992c).

Both the RME and average exposure scenarios have been included in this RA.

1.2 Scope

The scope of this RA is limited to the evaluation of potential health risks associated with

groundwater that has been affected by mining activities. The approach used is based on EPA

guidance for the evaluation of human health risks at Superfund sites. Specifically , this RA is

consistent with EPA guidance provided in the followin g resources: Exposure Factors

Handbook (EPA, 1989a), Risk Assessment Guidance for Superfund, Volume I: Human

Health Evaluation Manual (EPA, 1989b), and the Integrated Risk Information System (IRIS)

(EPA, 1992d), a computer database containing up-to-date health risk and EPA regulatory

information for numerous chemicals. EPA cautions that these sources are intended only to

provide guidance in conducting health risk assessments and that considerable professional

judgment must be used in their application (EPA, 1989b).

2 .0 EXPOSURE ASSESSMENT

The objective of the exposure assessment is to identify populations that may be exposed to

site-related metals in groundwater (potential receptors); the pathways by which exposures

may occur; the route of intake and intake parameter values for ingestion; and the frequency,

magnitude, and duration of these potential human exposures.

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2.1 Potential Receptor Populations

Populations in the Leadville area were evaluated to assess the likelihood and extent of

potential exposure to chemicals of concern (COCs) in groundwater.

During the Phase I RI studies, EPA identified 33 existing wells that were drilled in the

California Gulch alluvium. Many of these wells have since been abandoned due to poor

water quality (EPA, 1988). In 1986, EPA connected the one remaining household that used

the alluvial aquifer as a drinking water source to the public water system (EPA, 1988). According to information from the Parkville Water District, general areas served by a public

water supply include Leadville, Stringtown, Silverheels, and Matchless Estates (Parkville

Water District, 1993). Areas supplied by the Parkville Water District have water supplied

from the Big Evans Reservoirs and the Canterbury Tunnel (Parkville Water District, 1993).

Turquoise Lake Estates, Four Seasons Estates, and Lake Fork Trailer Park use private wells

or community drinking water wells. Turquoise Lake and Four Seasons Estates are located

upgradient from any source-related contamination. Groundwater at the Lake Fork Trailer

Park is not known to be affected by site-related metals. Therefore, these areas were not

quantitatively evaluated for potential risks due to groundwater ingestion because site-related

contaminants are not known to be present.

There are no known plans to use additional groundwater for a drinking water supply within

the Leadville area and there is no known current exposure. However, a future residential

groundwater user scenario was considered and the risks of consuming groundwater in the

Stringtown area were quantified. Even with this conservative approach, it is highly unlikely

that the water would be of potable quality considering the elevated levels of sulfate. Therefore, it is doubtful future residential receptors would consume this groundwater. This

aspect of groundwater quality is discussed further in the Hydrogeologic RI report (Asarco,

1996a).

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When identifyin g a location for a hypothetical well to use as a potential exposure location,

certain criteria must be considered. These include but are not limited to:

*• The hypothetical groundwater well should be located hi a position where it

is likely to be affected by upgradient contamination hi order to represent

the potential for risk associated with contaminated groundwater

consumption. In addition, appropriate upgradient groundwater chemical

data must be available to estimate concentrations. Risk-related

interpretation of upgradient data must agree with hydrogeological and

geochemical interpretations of the aquifer hi the area surrounding the

hypothetical well and actual monitoring locations.

*• The well should be screened hi the upper 10 to 15 feet of the alluvial

aquifer in order to assess risk from near-surface potential contamination

sources such as tailings piles and surface water. The potential of the

hypothetical receptors drinking from such a shallow well is questionable

because of lack of potable quality (e.g., high sulfate) and possible poor

long-term yield. Therefore, use of this groundwater as a source of

drinking water is a highly conservative assumption.

* Results from a previous investigation hi the area suggest that

concentrations of potential contaminants decrease with depth (EPA,

1987a). Recent investigations indicate that the alluvial aquifer may be

1,200 feet thick or more hi the areas.

The rationale for placing a hypothetical well in the Stringtown area to assess the risk of

consuming potentially contaminated groundwater include:

The hypothetical well would be located downgradient from several

potential sources of groundwater contamination, including Colorado Zinc- Lead, and Apache and Oregon Gulch tailings. In addition, the well would

be positioned near California Gulch, where the well could be affected by

surface water contributions to groundwater contamination.

Stringtown area residences are supplied with treated city water; however,

for the reasons presented above, a RA conducted for the Stringtown area

may best represent hypothetical future groundwater consumption from

private wells. The five existing private wells that may be used for

domestic purposes are also in the Stringtown area. Thus, a hypothetical

future exposure point in Stringtown will also provide an estimate of risk to

hypothetical current groundwater consumers.

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After locating the exposure point, EPA guidance specifies that unflltered groundwater sample

data should be used (EPA, 1989b). Unflltered sample data were unavailable for the

groundwater monitoring wells upgradient of the hypothetical exposure point. However, data

from unflltered samples were available from four mini-piezometers and six springs in the

area. Furthermore:

Data from the four mini-piezometers and six springs probably provide a

realistic representation of metals concentrations that might migrate to a

downgradient well. Because the mini-piezometers and springs are spatially

distributed along California Gulch, concentrations measured at these

locations should represent the dilutional effect s of contaminant transport

from suspected source areas.

Groundwater analytical data for total metals are available from minipiezometers and springs located downgradient from potential

contamination sources and upgradient from the hypothetical receptor well. Groundwater chemistry results from the springs and mini-piezometers

were used to estimate groundwater chemistry as a basis for the RA (Asarco, 1996a).

For the initial comparison, concentrations of arsenic, cadmium, and zinc

were chosen because arsenic is the only COC with an oral slope factor and

cadmium and zinc had relatively high exposure point concentrations

(EPCs). [Selection of COC's and toxicity values are explained hi greater

detail in the Hydrologic RI Report (Asarco, 1996a)]. Because the

concentrations of these metals in mini-piezometers and springs appeared

similar (in terms of magnitude), these data were combined for statistical

evaluation for the risk assessment.

Arsenic, cadmium, and zinc levels in unflltered samples (total metals)

from the mini-piezometers and springs were compared with arsenic,

cadmium, and zinc levels in filtered samples (dissolved metals) from

monitoring wells downgradient of the Apache Tailings Impoundment. This comparison revealed higher concentrations in the mini-piezometers

and springs. Because EPA guidance recommends using total metal

concentrations when evaluating potential risks due to the ingestion of

groundwater (EPA, 1989b), and because higher metal concentrations were

found in unflltered samples, samples taken from the mini-piezometers and

springs were used in this RA as the more conservative choice.

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Populations within Leadville that may be particularly sensitive to chemical exposures from

the ingestion of groundwater could include infants and children, the elderly, pregnant and

nursing women, and those with chronic illnesses. Sensitive receptor locations may include

hospitals, convalescent homes, schools, and day-care centers that use groundwater as the

drinking water source. In order to evaluate sensitive receptor populations for potential risks

posed by groundwater consumption, the RA has identified both children and adults as the

sensitive population.

2.2 Conceptual Site Model

A Conceptual Site Model (CSM) shows all potentially complete exposure pathways for a

source (Figure 1). Those exposure pathways that are significant are represented with a solid

circle. EPA guidance defines an insignificant pathway as one that has an exposure estimated

to be two or more orders of magnitude less than by other pathways (to the same receptor), or

one with a very small likelihood of exposure (EPA, 1989b).

Exposure pathways associated with other media are labeled as "not evaluated" on the CSM as

these media, with the exception of garden vegetable ingestion, have been considered in other

risk assessments as part of separate remedial investigations. For example, affected

groundwater possibly discharging to surface water was not considered, but it was addressed

in the Surface Water RI Report (Asarco, 1996b). The ingestion of garden vegetables

potentially impacted by metals in groundwater will be considered in a sitewide baseline risk

assessment. Because metals are not absorbed well across the skin, dermal contact with

groundwater is not considered significant (EPA, 1991a).

Based on the evaluation of potentially complete pathways, the human receptors associated

with the exposure point selected are:

>• Future Adult Resident; and,

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+ Future Child Resident.

The Future Adult and Child Residents were selected to represent hypothetical receptors who

might routinely ingest groundwater after installing a water-supply well hi Stringtown. The

hypothetical exposure point is shown in Figure 2.

2.3 Complete Exposure Pathways

The final component of a complete exposure pathway is an intake route into the body. Table

1 summarizes the pathways that were evaluated in the RA. As shown hi the CSM (Figure 1),

the only complete exposure pathway considered quantitatively was the ingestion of

groundwater. This exposure was evaluated for both receptors.

2.4 Estimating Chemical Intakes and Exposure Point Concentrations

The next step hi the exposure assessment was to quantify the magnitude, frequency, and

duration of chemical intakes by receptor populations. This step was conducted in two stages:

1) estimation of EPCs, and 2) estimation of chemical intake for each exposure pathway under

consideration. Chemical intakes were calculated using guidance hi Risk Assessment

Guidance for Superfun d (EPA, 1989b) and Exposure Factors Handbook (EPA, 1989a), other

E PA documents, site-specific information, and professional judgment regarding likely

exposure conditions, as appropriate. Chemical intakes were estimated using average and

RME estimates of chemical concentrations in groundwater, and reasonable estimates of

exposure parameters such as body weight, ingestion rates, and other assumptions regarding

frequency and duration of exposure (Asarco, 1996a).

EPCs used to calculate potential risks from the ingestion of groundwater were obtained by

calculating the average and the 95 percent upper confidence limit on the arithmetic mean for

each chemical of concern using available analytical data from recent site investigations (EPA,

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1992e). Data collection and analysis are described in the Hydrogeologic RI Report (Asarco,

1996a).

2.5 Exposure Assumptions

The assumptions used to estimate potential intake received through the exposure pathway

were based on EPA guidance, site-specific information, and professional judgment. It is not

possible to estimate the exact level of exposure for specific individuals due to uncertainties in

behavior patterns and incomplete knowledge of exposure variable values. A primary

objective of this RA was to use site-specific data where possible.

Children were identified as a sensitive receptor population in Leadville. Therefore, exposure

variables were calculated that incorporated youth as a factor. Because body weights vary

over time, time-weighted average body weights were calculated for the Future Adult and

Child Resident to more accurately reflect the temporal nature of exposure and the doses

received by each receptor (Table 2).

The exposure frequencies used were 350 and 275 days per year for the RME and average

exposure scenarios respectively. While the former exposure frequency accounts for only two

weeks away from the hypothetical residence (for example, a vacation), the latter exposure

frequency accommodates for the hypothetical residents to be home 75 percent of the time (or

25 percent of the time spent away from home, i.e., 6 hours per day).

The groundwater ingestion rate for the Future Adult Residents was assumed to be 1.4 and

2.0 liters per day for the average and RME exposures, respectively (EPA, 1989b). These

figures are conservative because the assumption was made that the majority of fluids

consumed on a daily basis are from the ingestion of groundwater. Groundwater ingestion

rates for the Future Child Resident were assumed to be 0.5 and 0.6 liters per day for the

average and RME exposures, respectively. These figures represent the daily average intake

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of water (0.5 I/day) from ages one to seven. The RME of 0.6 represents the intake of a child

age six to seven. These intake amounts are presented in the EPA LEAD 0.5 IEUBK Model

(EPA, 1991a).

Because the RA considered children from birth to six years as a sensitive receptor, and

because the national median and upper bound estimates for residency are nine and thirty

years, respectively (EPA, 1989b), it was assumed that this receptor would be exposed for six

years for both the average and RME scenarios. In order to be most conservative, the

approach was taken to follow one person for the residency periods described above.

Therefore, it was also assumed that the Adult Resident would be exposed for 3 years (ages 7

through 9) and 24 years (ages 7 through 30) for the average and RME scenarios,

respectively. Addition of these exposure durations for the average scenario equals nine years

(6 years for children and 3 years for the adult) and for the RME scenario equals 30 years (6

years for children and 24 years for the adult). This receptor is referred to as a Future Typical

Resident who would be exposed for these timeframes. As such, the noncarcinogenic hazards

and carcinogenic risks for the Future Child and Adult Residents were summed to represent

these exposure durations.

The equation and specific variables used to estimate intake of chemicals via groundwater

ingestion are summarized in Table 3. Intake factor calculations are documented in Appendix

A.

3 .0 RISK CHARACTERIZATION RESULT S

The risk assessment is based on the folio whig risk characterization factors.

T he potential for adverse noncarcinogenic effect s resulting from exposure

to a chemical of concern is evaluated by comparing the average daily

intake of the chemical (expressed as mg/kg-day) to a reference dose

expressed as mg/kg-day). The resulting ratio is called a hazard quotient

(H.Q.) (EPA, 1989b).

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*• The potential for noncarcinogenic effect s is characterized by comparing

estimated chemical intakes with chemical-specific RfDs. This measure is

known as the hazard index (H.I.) for multiple chemicals.

A more detailed explanation of these factors is presented in Appendix A. Given the

conservative assumptions used in this RA, the combined H.I.s of the Future Adult and Child

Residents resulted in an H.I. greater than the EPA level of concern of one (1.0). This was

done by summing the chronic H.I.s across the ages of birth to 9 years and from birth to 30

years for average and RME scenarios, respectively, and represents the Typical Future Adult

Resident (Table 4). The results of the carcinogenic risks and noncarcinogenic hazards are

also shown in Table 4 for both the Future Adult and Child Residents. The average exposure

for the Typical Future Adult resulted in a chronic H.I. of 3.3 x 10

1

, and for RME

assumptions, the chronic H.I. was 4.6 x 10

1

. According to EPA guidance, a limitation of the

hazard index approach is the assumption of dose additivity. This assumption is most

properly applied to COC that induce the same effect by the same mechanism of action (EPA

1989b). The application of the hazard index equation to several COCs that have not

experimentally demonstrated the same critical effec t or mechanism of action could

overestimate the potential health effect s (EPA, 1989b).

T he three COCs responsible for driving the chronic H.I. above unity (1.0) were arsenic,

cadmium, and zinc for both average and RME scenarios. The critical effect s used to derive

oral RfDs for zinc, cadmium, and arsenic are dissimilar enough (differen t target organs and

endpoints) that the dose additivity assumption used in this RA overestimates noncarcinogenic

hazards. However, even when these COCs are used individually to estimate noncarcinogenic

hazards, the H.Q.s calculated for chronic exposure still exceed unity for both scenarios.

Carcinogenic risk estimates exceeded the EPA acceptable risk level of 1 x 10 for both

receptors with all of this risk contributed by arsenic (arsenic was the only COC with an oral

slope factor). Total carcinogenic risk estimated for the Typical Future Resident, adding

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across the ages from birth to 9 years of age (the average scenario), was 2.1 x 10^ and for

ages from birth to 30 years of age, 1.1 x 10"3 (the RME scenario).

To put these noncarcinogenic hazards and carcinogenic risks into perspective, EPCs for the

COCs evaluated were compared to MCLs or SMCLs (Table 5). Although arsenic

contributes significantly to the overall H.I.s and is solely responsible for the cancer risks,

EPCs for arsenic do not exceed the MCL (Table 5). Nickel and cadmium EPCs exceed their

respective MCLs and sulfate (not a COC) EPCs are above the SMCL.

4 .0 UNCERTAINTIES AND LIMITATIONS

The EPA guidance for risk assessment provides a systematic means for organizing,

analyzing, and presenting information on the nature and magnitude of potential risks to public

health and the environment posed by chemical exposures. Despite the advanced state of the

current methodology, uncertainties and limitations are inherent in the risk assessment

process. The quality of available data, incomplete information about existing conditions and

future circumstances, as well as other factors contribute to these uncertainties and limitations.

Discussed below is general information regarding uncertainties and limitations of the risk

assessment process. Specific uncertainties are summarized in Table 6.

Data used in the RA were collected using the Work Plan. The data collected during this

program are subject to uncertainty associated with sampling and analysis, and this may act to

over- or under-estimate the potential risks.

The exposure assessment was based on site-specific data and on a series of assumptions

concerning concentrations of chemicals to which humans may be exposed (EPCs) as well as

patterns of behavior leading to exposure or intake of chemicals (exposure scenarios). The

exposure assessment relied on assumptions for potential human exposure when site-specific

analytical data were incomplete or unavailable. Assumptions used were based upon:

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*• Site-specific information;

* EPA Human Health Evaluation Manual (EPA, 1989b) and the Exposure Factors Handbook (EPA, 1989a); and,

*• Professional judgment.

In general, the available scientific information is insufficient to provide a thorough

understanding of all the potential toxic properties of chemicals to which humans are

potentially exposed. Consequently, varying degrees of uncertainty surround the assessment of

adverse health effect s in exposed populations. In this case, several chemicals (aluminum,

copper, manganese, and titanium) were eliminated from consideration because toxicity values

were not available.

Due to uncertainties in each step of the RA process, uncertainties are often magnified in the

final risk characterization. The final quantitative estimates of risk may be one or several

orders of magnitude differen t from the potential risk associated with a given exposure. In an

attempt to minimize the consequences of uncertainty, EPA guidance typically relies on use of

conservative estimates of hazards in the absence of strong scientific data. The overall result

is that risk estimates presented in this report are much more likely to overestimate the

potential risk than to underestimate it.

The assessment has been prepared in a manner consistent with that generally used in the

consulting community and agency guidance at the time it was prepared.

5.0 CONCLUSIONS

Based on the current information and data used for this RA, the followin g conclusions can be

made:

There are no known current receptors for the exposure pathway

considered (groundwater ingestion). This is based on a recent

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demographics survey by Dr. Robert Bornschein of the University of Cincinnati' s Department of Environmental Health (Asarco, 1992) and an

EPA Record of Decision (ROD) (EPA, 1988). Additionally , the Parkville Water District, the municipal supplier of water, indicates that all residents

of the towns of Leadville and Stringtown are connected to their water

system (Parkville Water District, 1993).

K

 Hypothetical future receptors (adult and child residents) used in this RA

consumed groundwater with conservative EPCs. That is, the arithmetic

mean and 95th percent UCL on the arithmetic mean used in the average

and RME scenarios were calculated from data taken from minipiezometers and springs located in California Gulch. Data from unfiltered

samples (i.e., total metals) from mini-piezometers and springs were used

as a conservative substitute for groundwater monitoring wells because

unfiltered metals analyses for groundwater were unavailable. In addition,

the source area concentrations of metals probably would be unrealistically

high to expect at the hypothetical exposure point. The mini-piezometer

and spring concentration more realistically represent lower concentrations

that would result from advective and dispersive transport of the metals

from the suspected source areas.

*• Hypothetical future receptors used in this risk assessment had risks

estimated based on conservative exposure assumptions. Most assumptions

followed EPA default values that are used when site-specific data are

lacking (EPA, 1989b, 1991b). For the average exposure and RME

scenarios it was assumed that the receptors were ingesting 1.4 to 2.0 liters

of water per day, and that adult residents consumed 100 percent of their

daily fluid intake from the tap. This consumption rate was assumed to

occur over nine and thirty years for the average and RME scenarios,

respectively.

* Risks to hypothetical future receptors were estimated based on

conservative exposure assumptions. Site-specific data were used when

available; otherwise EPA default values were used (EPA, 1989c, 1991b). For example, the ingestion of 1.4 and 2.0 liters of water per day assumes

that the adult resident, for the average and RME exposure scenario,

consume 100 percent of their daily fluid intake from the tap. This

consumption rate was assumed to occur over nine and thirty years for the

average and RME scenarios, respectively.

*• Currently, there are no risks from the consumption of groundwater from

the alluvial aquifer in the California Gulch because no complete exposure

pathway exists. However, if groundwater was consumed, as assumed for

the hypothetical receptors in this RA, both cancer and non-cancer risks

would exceed regulatory levels.

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6.0 REFERENCES

ASARCO. 1992d. Metals Samplin g and Analysis Results and Demographics Results. Prepared by Woodward-Clyde Consultants. September 15.

ASARCO. 1996a. Hydrogeologic Remedial Investigation Report. California Gulch Site, Leadville, Colorado. Prepared by Colder Associates, Denver, for Asarco, Inc. May. ASARCO. 1996b. Surface Water Remedial Investigation Report. Prepared by Colder Associates, Denver, for Asarco, Inc. May.

Parkville Water District. 1993. Personal communication between Kirn Brogan (WCC) and Sandy Mason (PWD) on February 11.

U.S. Environmental Protection Agency (EPA). 1987a. Phase I Remedial Investigation Report, California Gulch, Leadville, Colorado. 53-8129.0/W63781.R1. Prepared by C H2

M Hill, Black & Veatch, ICF, PRC, and Ecology and Environment. May.

U.S. Environmental Protection Agency (EPA). 1988. Record of Decision (ROD), Yak Tunnel Operable Unit, California Gulch Site, Leadville, Colorado. March 29.

U.S. Environmental Protection Agency (EPA). 1989a. Exposure Factors Handbook.

Exposure Assessment Group Offic e of Health and Environmental Assessment. Washington, D.C. EPA/600/8-89/043.

U.S . Environmental Protection Agency (EPA). 1989b. Risk Assessment Guidance for Superfund. Volume I: Human Health Evaluation Manual. Interim final. Office of Emergency and Remedial Response. Washington, D.C. EPA/540/1-89/002.

U.S. Environmental Protection Agency (EPA). 1989c. Phase n Remedial Investigation Technical Memorandum, Draft, California Gulch, Leadville, Colorado. Vols. I-VI.

53-8129.0/DEN63786.R1. Prepared by CH2M Hill, Black & Veatch, ICF, PRC, and

Ecology and Environment. May.

U.S . Environmental Protection Agency (EPA). 1991a. Preliminary Human Health Baseline Risk Assessment for the California Gulch NPL Site, Leadville, Colorado. Prepared

f or the U.S. EPA Region VTfl, Denver, Colorado by Roy F. Weston, Inc., Lakewood, Colorado.

U.S. Environmental Protection Agency (EPA). 1991b. Human Health Evaluation Manual, Supplemental Guidance: "Standard Default Exposure Factors". OSWER Directive

9285.6-03. March 25.

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U.S. Environmental Protection Agency (EPA). 1992a. Guidelines for Exposure Assessment. 57 FR 22888-22938, May 29.

U.S. Environmental Protection Agency (EPA). 1992b. Memo from F. Henry Habicht, Deputy Administrator, EPA. Guidance on Risk Characterization for Risk Managers

and Risk Assessors. February 26.

U.S. Environmental Protection Agency (EPA). 1992c. Memo from Henry L. Longest, Director, Office of Emergency and Remedial Response. Implementing the Deputy Administrator' s Risk Characterization Memorandum. May 26.

U.S. Environmental Protection Agency (EPA). 1992d. Integrated Risk Information System

(IRIS). On-line database.

U.S . Environmental Protection Agency (EPA). 1992e. Office of Solid Waste and

Emergency Response. Memorandum "Supplemental Guidance to RAGS: Calculating

the concentration Term". June 22.

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TABLES

J MI

r

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I I

TABLE 1

LEADVILLE GROUNDWATER

POTENTIALLY COMPLETE EXPOSURE PATHWAYS QUANTITATIVELY EVALUATED

Potentially Exposed Receptor Scenario Potentially Complete Exposure Pathways

Child Resident Future2 Groundwater ingestion

Adult Resident Future3 Groundwater ingestion

This scenario is completely hypothetical.

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TABLE 2 GENERAL ASSUMPTIONS FOR BODY WEIGHT

Age Range

0-3

3-6

6-9

9-12

12-15

15-18

18-30

Years in Age Range

3

3

3

3

3

3

12

K ga

11.6

17.4

25.0

36.0

50.6

61.2

70

TIME WEIGHTED AVERAGE BODY WEIGHTS

Child (1-6

Adult (7-9

years)b

years and 7-30 years)0

Years in Age Range

6

3/24

Body Weight

16

25/57

Exposure Factors Handbook (EPA 1989e). RAGS (EPA, 1989f). Represents the 50th percentile body weights for children ages 1 to

6 years (not a true weighted average). Average scenario used 7 to 9 years of age and RME scenario used 7 to 30 years of age.

Colder Associates
TABLE 3 INTAKE ASSUMPTIONS FOR GROUNDWATERINGESTION

Intake Factor = IR x EF x ED x FI BWxA T

Parameter Average Reasonable Maximum

IR = Ingestion rate, L/da y Adult (>6) 1.4 2.0 Child (0-6 years)2

 0.5 0.6

EF = Exposure frequency, days/years2

Adult 275 350 Child 275 350

ED = Exposure duration, years

2

Future Adult Resident 3 24 Future Child Resident 6 6 Future Typical Resident 9 30

FI = Fraction ingested from

contaminated source

3

 1.0 1.0

BW = Body weight, kg4

Adul t (weighted average) 25 57 Child (weighted average) 16 16

AT = Averaging time, days5 Noncarcinogens Adult 1,095 (3 years) 8,760 (24 years) Child 2,190 (6 years) 2,190 (6 years) Carcinogens 25,550 (70 years) 25,550 (70 years)

1

 EPA, 1989f. (See text for further explanation, Section 6.2.5).

2

 See text , Section 6.2.5 for explanation. 3

 An FI of 1.0 represents a conservative assumption about the amount of groundwater that is consumed. The higher the FI, the greater amount of groundwater is consumed from the contaminated source. An FI

of one assumes all water is consumed from the contaminated source.

4

 EPA, 1989e. 5

 Nine years (6 years as a child and 3 years as an adult) and 30 years (6 years as a child and 24 years as an

adult) are years spent in one residence for the national median and upper bound estimates, respectively

(EPA, 1989f). Averaging tune is the product of these time periods and days per year.

Colder Associates
TABLE 4 GROUNDWATER CARCINOGENIC RISKS AND NONCARCINOGENIC HAZARD INDEX (H.I.)

Average Exposure Reasonable Maximum Exposure

Receptor/Pathway

Cancer Subchronic Chronic Risk H.I . H.I .

Cancer Subchronic Chronic Risk H.I . H.I .

Future Adult Resident

Ingestion of Groundwater l.OE-04 1.8E+01 2.1E+01

Future Child Resident

Ingestion of Groundwater 1. IE-04 9.9E+00 1.2E+01

Future Typical Adult Resident

Ingestion of Groundwater 2. IE-04 2.8E+01 3.3E+01

8.7E-04 1.8E+01 2.2E+01

2.3E-04 1.9E+01 2.4E+01

1.IE-03 4.6E+01 4.6E+01

Colder Associates
TABLES

COMPARISON OF EXPOSURE POINT CONCENTRATIONS (EPCs) WITH MAXIMUM CONTAMINANT LEVELS (MCLs)

(mg/1)

Chemical

Arsenic

Cadmium

Mercury Nickel

Silver

Sulfate

Zinc

Average13

3.17E-02

9.45E-02

7.70E-05

1.23E-01

1.34E-02

1.38E+03

6.00E+01

EPC

RMEb

4.3 IE-02

1.30E-02

1.44E-03

1.63E-01

1.58E-02

3.46E+03

7.38E+01

MCLa

5.00E-02

5.00E-03

2.00E-03

l.OOE-01

N AC

2.50E+02a d

N AC

a

 EPA 1992g. Office of Water. Drinking Water Regulations and Health Advisories. b

 Average = Average Exposure RME = Reasonable Maximum Exposure 0

 NA = Not Available d

 Secondary MCL; based on odor and aesthetics. BOLD Values represent those exceeding MCL.

Colder Associates
TABLE 6 SUMMARY OF UNCERTAINTY FACTORS IN THE GROUNDWATER BASELINE RISK ASSESSMENT

Uncertainty Factor Effec t of Uncertainty Comment

Use of cancer potency factors. May overestimate risks.

Critical toxicity values derived May over- or

primarily from animal studies. underestimate risks.

Critical toxicity values derived

primarily from high doses, most

exposures are at low doses.

Critical toxicity values.

May over- or

underestimate risks.

May over- or

underestimate risks.

Not all chemicals at the site have May underestimate

critical toxicity values. risks. Metals analysis for total metals May overestimate risks,

only.

Effec t of absorption. May over- or

underestimate risks.

Exposure assumptions regarding May overestimate risks,

the groundwater ingestion rate.

Exposures assumed constant over May over- or

time. underestimate risks.

Exposure point concentrations. May overestimate risks.

Exposure point concentrations. May overestimate risks.

Exposure point concentrations. May overestimate risks.

Contract required detection

limits.

Sampling.

May underestimate

risks. May overestimate risks.

Potencies are upper 95th percent confidence

limits derived from the linearized model. Considered unlikely to underestimate true risk.

Extrapolation from animal to humans may induce

error due to differences hi absorption,

pharmacokinetics, target organs, enzymes, and

population variability. Assumes linear at low doses. Tends to have

conservative exposure assumptions.

Not all values represent the same degree of

certainty. All are subject to change as new

evidence becomes available.

These chemical are not addressed quantitatively.

Did not distinguish between valence or

speciation. Assumed all metals were present as

total metals vs. dissolved metals.

The assumption that absorption is equivalent

across species is implicit hi the derivation of the

critical toxicity values. Absorption may actually

vary with species and age as well as other factors

such as nutritional status.

Groundwater intake does not account for time

spent away from the source or other fluids

ingested.

Does not account for environmental fate,

transport, or transfer which may alter alluvial

groundwater concentration of metals over tune.

Use of 95% UCL in calculating RME may not

accurately represent exposure levels.

Used the arithmetic mean concentration and 95% UCL to evaluate average and RME exposures. May not accurately represent exposure levels.

Use of unfiltered groundwater samples may not

accurately represent exposures as people may

never drink this quality of water.

For some chemicals, this detection limit is above

a concentration which might be of concern.

Samplin g biased toward areas of known or

suspected elevated metals concentrations.

Colder Associates
TABLE 6 (Concluded)

Uncertainty Factor Effec t of Uncertainty Comment

Exposure scenario. May overestimate risks. Very conservative approach by assuming that

hypothetical future exposure could occur.

Risks/doses within an exposure May over- or Does not account for synergism or antagonism.

route assumed to be additive. underestimate risks.

Risk characterization. May overestimate risks. Combining conservative assumptions at each step

of risk assessment may lead to highly

conservative risk estimates.

Colder Associates
FIGURES

Golder Associates
POTENTIA L HUMA N EXPOSUR E PATHWAY S

POTENTIA L HUMA N RECEPTOR

PRIMAR Y SOURC E T RELEASE MECHANIS M

r EXPOSURE MEDIU M

2* RELEASE MECHANIS M

2 EXPOSUR E MEDIU M EXPOSUR E ROUTE FUTUR E RESIDENT S ADULT | CHILD

SURFAC E WATE R RUN-OF F

INGESTIO N DERMAL I

I

I

I

•INGESTION , DERMA L

*H INGESTION [ NE [ NE

LEGEN D

• COMPLET E AN D SIGNIFICAN T PATHWA Y

I INCOMPLET E PATHWA Y

NE NOT EVALUATED

SOURCE : WOODWARD-CLYD E CONSULTANTS , DRAF T SURFAC E WATER R l

INFILTRATIO N ALLUVIA L GROUNDWATE R — ^-

COMMUNICATIO N WIT H SURFAC E WATER BODIES FIS H —————— — (fc. INGESTIONE N | N E

CLIENT/PROJEC T

ASARCO HYDROGEOLOGIC HUMAN HEALTH RISK ASSESSMENT Denver, Colorado

TITL E CONCEPTUAL SITE MODEL GROUNDWATER LEADVLLE, COLORADO

DRAWN RB CHECKE D AR REVIEWED BDP DATE JUN E 1996

SCAL E NO SCALE FIL E NO . 2819A060J OB NO. 943-2819

D WG NO./REV.NO.A060

FIG .
N 520,000

N 510,000

P-8

8PR-1

MINI-PIEZOMETE R

SPRIN G

MINI-PIEZOMETE R - DATA USED IN RA

EXPLANATION S

APPROXIMAT E LIMIT S OF TAILING S

LEADVILL E MUNICIPA L WAST E FACILIT Y

0 1000 2000 4000

TOPOGRAPHI C CONTOU R INTERVA L = 25

SURFAC E WATER DRAINAG E

- DOTTE D WHER E INTERMITTEN T

EXPOSUR E POIN T

-.—-,. AREA S IN WHICH BEDROCK ( • • ) FORMATIONS OUTCROP OR

Denver, Colorado

CLIENT/PROJEC T ASARCO HYDROGEOLOGIC HUMAN

TITll E FUTURE SCENARIO

EXPOSURE POINT LOCATION

DRAWN RB

 DATE

 JUNE 1996

CHECKE D SCALE -i»_ r =2.000*

J OB NO. 943-2819 DWG. NO./REV . NO.
APPENDIX A

RISKEVAL U

Golder Associal

METHODS
Appendix A

June 1996___________________A-l_________________943-2819

APPENDIX A - EXPLANATION OF RISK ASSESSMENT COMPUTER OUTPUT (ASSESS PROGRAM)

ASSESS is a computer program designed by Woodward-Clyde Consultants to calculate

noncarcinogenic hazards and carcinogenic risks. ASSESS considers all exposure pathways

evaluated at a site. All information needed to verify calculations is provided. Data are

organized and reported in categories listed below:

*• Chemical List

* Receptor/Pathway Summary

*• Pathway Summary

* Intake Factors

*• Media Concentrations

Numbers in ASSESS are written in scientific notation. The number followin g the E is a

power of 10; so 1.61E-02 is 0.0161.

1 .0 CHEMICA L LIST

Thi s sheet lists the EPA toxicity values for each chemical. When available, values are listed

for both oral and inhalation exposure routes for either subchronic or chronic exposure

durations (reference doses or RfDs) or for carcinogenic risk (slope factors or SF). These

values are obtained using the hierarchy recommended by EPA's Risk Assessment Guidance

for Superfun d sites (EPA 1989b, 1991b). The first and second sources in this hierarchy are

( 1) IRIS (Integrated Risk Information System), an on-line computer database of chemical risk

information (EPA 1992d), and (2) HEAST (Health Effect s Assessment Summary Tables)

(EPA 1992e), EPA tables which are periodically up-dated. Toxicity values (RfDs and SFs)

do not yet exist for many chemicals. For risk assessment purposes, when this is true, a

Colder Associates
Appendix A June 1996___________________A-2__________________943-2819

chemical may be discussed qualitatively in the text of the report but will not be reported

quantitatively in ASSESS.

RfDs may be derived for either subchronic or chronic exposures and are used to calculate

subchronic or chronic hazard quotients, respectively. A subchronic RfD may not exist for a

particular chemical even though a chronic RfD exists.

2 .0 RECEPTOR/PATHWAY SUMMARY

The Receptor Summary sheet lists each receptor and the potential health risks associated with

chemical exposure from all pathways quantitated. The potential adverse health risks are

divided into two exposure scenarios: average exposure and reasonable maximum exposure

(RME). For each exposure scenario, potential health impacts are segregated into two

categories: cancer risk and a hazard index for both subchronic and chronic scenario. The

values shown on this sheet show the total carcinogenic risks and noncarcinogenic hazards

associated with average and RME scenario for each receptor listed.

RfDs are used with a level of exposure during a specific time period and expressed as a ratio

or hazard quotient. According to the EPA (EPA, 1989b, 1991b), generally, the greater the

value of the hazard quotient (or hazard index), the greater the level of concern for health

impacts. Another area of EPA guidance states that because H.I. is not a probability function,

an increased value does not indicate a degree of risk. The hazard index is the sum of a

number of hazard quotients for a particular pathway. A hazard index of one means the

estimated chemical intake equals the reference dose. When this occurs, a more detailed

evaluation of the site is indicated. When the H.I . is less than one, further evaluation is

generally not warranted, and the exposure is expected to be safe if the H.I. is equal to or less

than one.

Golder Associates
Appendix A June 1996__________________A-3_________________943-2819

A chemical' s slope factor is multiplied by the lifetime daily average intake of that chemical in

a certain medium to estimate the incremental probability (or risk) of an individual developing

cancer during a lifetime. When a receptor potentially is exposed to a variety of chemicals (in

a given medium) possessing slope factors, all of the products are summed to yield the total

cancer risk for those chemicals for that specific exposure pathway. This risk number is

acceptable if it is less than IE-4 or 10"4 or 1 in 10,000.

Receptor Detail Report

This report is included in the Receptor/Pathway Summary Sheet because it details the

carcinogenic risk and the noncarcinogenic hazard for each of the receptor's exposure

pathway(s) for both the average and RME exposure scenarios. Total carcinogenic risks and

noncarcinogenic hazards for each receptor are also given. Each receptor may have a number

of exposure pathways. An exposure pathway is a route that a chemical may take to reach a

population or receptor. Each pathway is categorized as one of the following:

*• Inhalation

*> Dermal contact with solids

*• Dermal contact with water

* Ingestion of solids

* Ingestion of water

3 .0 PATHWAY SUMMARY

Thi s sheet also provides the same basic information as the Receptor Detail Report described

above. The difference between the two is that the Receptor Detail Report includes all

receptors while the Pathway Summary Report is receptor-specific, providing information on

only one receptor per page.

Golder Associates
Appendix A June 1996___________________A-4__________________943-2819

Pathway Detail Report

These sheets comprise the majority of the ASSESS report. For both average and RME

exposure scenarios, carcinogenic risk and noncarcinogenic hazards are listed for each

receptor exposure route and chemical. Total carcinogenic risks and noncarcinogenic hazards

are also provided. This report is especially helpful in determining which chemical(s) is (are)

driving the overall risks or hazards for a particular exposure route. Other values provided in

this report include the concentration of each chemical in the medium, the intake factor for

that exposure route, and the daily intake of the chemical being evaluated. This daily intake

of an individual chemical is either multiplied by its slope factor or divided by its RfD for a

given exposure route (oral or inhalation). Until other information is available from EPA,

oral RfDs and SFs are used for assessing the potential health impacts of dermal exposure.

4 .0 INTAKE FACTORS

These sheets represent, in equation format, the method of calculating the intake factors that

appear in the pathway detail report explained above. Each of the parameters that goes into

an intake factor equation is defined for both the average and RME scenarios. These

parameters are more full y described in the Exposure Assessment section of this report.

5 .0 MEDIA CONCENTRATIONS

These sheets describe the chemical concentrations for the average and RME scenarios for a

given medium. In some cases, a higher concentration may be used to evaluate short-term

risks. For example, particulate concentrations in air may be higher during a short

construction project than the long-term (25 year) average might be. In most cases, the same

concentrations will be used for subchronic and chronic scenario. These figures are described

in the Data Summary and Selection of Chemicals of Concern section of this report.

Colder Associates
Chemical List: SURFACE WATER February 2, 19

• ' 18:

Inhalatio n ————————————— — ——— — Non-Inhalatio n Slop e Subchronic Chronic Slop e Subchronic Chronic Facto r RF D RF D Facto r ftF D RF O

Chemical (mg/kg/day)-1 mg/kg/da y mg/kg/da y (mg/kg/day)-1 mg/kg/da y mg/kg/da y

Arsenic - 1.50E+01 1.75E+00 3.00E-04 3.00E-CK

Cadmium (food ) 1.00E-03

Chromiun II I 2.00E-05 2.00E-06 1.00E+00 1.00E+00

Chromitm VI 4.10E+01 5.70E-06 5.70E-07 2.00E-02 5.00E-03

Copper 3.70E-02 3.70E-02

Mercury 8.60E-05 8.60E-05 3.00E-04 3.00E-04

Zin c 2.00E-01 3.00E-01
Receptor/Pathwa y Summary: SURFACE WATER Februar y 2, 199

18:1

Receptor / Pathway

ADUL T RECREATIONA L USE R

-- Inges t ion of Fis h

Average Exposure

Cancer Subchronic Chronic Risk H.I . H.I .

Reasonable Maximum Exposure

Cancer Subchronic Chronic Risk H.I . H.I .

1.92E-06 3.30E-01 3.58E-01 2.70E-05 5.S5E-01 5.98E-01

1.92E-06 3.30E-01 3.58E-01 2.70E-05 5.55E-01 5.98E-01

CHIL D RECREATIONA L USE R

-- Inges t io n of Fis h 3.74E-07 3.21E-02 3.48E-02 4.33E-06 3.56E-01 3.84E-01

3.74E-07 3.21E-02 3.48E-02 4.33E-06 •J.56E-01 3.8AE-01
ADUL T RECREATIONA L USE R Ingestio n of Fis h Average Exposure

1

| Carcinogenic Risk

i

Chemical

Arsenic

i

| Hazard Index -- Subchronic

i

Chemical

Arseni c

Chromium V I

Copper Mercury Zin c

i

| Hazard Index -- Chronic

r

Chemical

Arseni c

Chromiun V I

Copper Mercury Zin c

1

1

1

Chemical

Concentratio n

(ing/ kg)

3.00E-02

l

1

1

Chemical

Concentratio n

Cmg/kg )

3.00E-02

2.80E-01

3.80E-01

7.00E-02

5.62E+00

I

II

Chemical

Concentration

(mg/kg )

3.00E-02

2.80E-01

3.80E-01

7.00E-02

5.62E+00

Ingestio n Intak e Facto r C kg/ kg/ day)

3.66E-05

Ingestio n Intak e Facto r

(kg/kg/day )

8.55E-04

8.55E-04

8.55E-04

8.55E-04

8.55E-04

Ingestio n Intake Facto r

(kg/kg/day )

3.55E-04

8.55E-04

8.55E-04

8.55E-04

8.55E-04

Dail y Intak e

<mg/kg/day )

1.10E-06

Dail y Intak e

(mg/kg/day )

2.56E-05

2.39E-04

3.25E-04

5.98E-05

4.80E-03

Dail y Intake

<mg/kg/day )

2.56E-05

2.39E-04

3.25E-04

5.98E-05

4.80E-03

Slop e Facto r

(mg/kg/day)-1

1.75E+00

Subchronic R F O

(mg/kg/day )

3.00E-04

2.00E-02

3.70E-02

3.00E-04

2.00E-01

Chroni c R F D

<mg/kg/day )

3.00E-04

5.00E-03

3.70E-02

3.00E-04

3.00E-01

Carcinogenic Risk

1.92E-06

Hazard

Quotien t

8.55E-02

1.20E-02

8.78E-03

1.99E-01

2.40E-02

Hazard

Quotien t

S.55E-02

4.79E-02

8.78E-03

1.99E-01

1.60E-02

Tota l

Risk

1.92E-06

Hazard

Index

3.30E-01

Hazard

Index

3.58E-01
ADUL T RECREATIONA L USE R

Ingestio n o f Fis h Reasonable Maximum Exposure

J

| Carcinogenic Risk

i

Chemical

Arsenic

i

| Hazard Index -- Subchronic

!

Chemical

Arsenic

Chromium V I

Copper Mercury Zin c

i

| Hazard Index -- Chronic

i

Chemical

Arseni c

Chromium V I

Copper Mercur y Zin c

1

1

1

Chemical

Concentratio n

(rog/kg )

4.00E-02

1

1I

Chemical

Concentratio n

(mg/kg )

4.00E-02

3.30E-01

4.20E-01

9.00E-02

6.42E+00

I

II

Chemical

Concentratio n

(mg/kg )

4.00E-02

3.30E-01

4.20E-01

9. 006-02

6.42E+00

Ingestio n Intak e Facto r

(kg/kg/day )

3.86E-04

Ingestio n Intak e Facto r C kg/kg/day )

1.12E-03

1.12E-03

1.12E-03

1.12E-03

1.12E-03

Ingestio n Intak e Facto r

(kg/kg/day )

1.12E-03

1.12E-03

1.12E-03

1.12E-03

1.12E-03

Dail y Intak e

(mg/kg/day )

1.54E-05

Dail y Intak e

(mg/kg/day )

4.50E-05

3.71E-04

4.72E-04

1.01E-04

7.22E-03

D ai l y Intak e

(mg/kg/day )

4.50E-05

3.71E-04

4.72E-04

1.01E-04

7.22E-03

Slop e Facto r

(mg/kg/day) - 1

1.75E+00

Subchronic R F D

(mg/kg/day )

3.00E-04

2.00E-02

3.70E-02

3.00E-04

2.00E-01

Chroni c R F O

(mg/kg/day )

3.00E-04

5.00E-03

3.70E-02

3.00E-04

3.00E-01

Carcinogenic Risk

2.70E-05

Hazard

Quot i ent

1.50E-01

1.86E-02

1.28E-02

3.37E-01

3.61E-02

Hazard

Quotien t

1.50E-01

7.42E-02

1.28E-02

3.37E-01

2.41E-02

Tota l

Risk

2.70E-05

Hazard

Index

5.55E-01

Hazard

Index

5.98E-01
CHIL D RECREATIONA L USE R

Ingestio n of Fis h

Average Exposure

1

| Carcinogenic Risk

i

Chemical

Arseni c

i

| Hazard Index -- Subchronic

i

Chemical

Arseni c

Chromium V I

Copper Mercur y Z i nc

i

| Hazard Index -- Chronic

i

Chemical

Arseni c

Chromium V I

Copper Mercury Zin c

1

1

1

Chemical

Concentratio n

(mg/kg )

3.00E-02

l

1

1

Chemical

Concentratio n

(mg/kg )

3.00E-02

2.80E-01

3.80E-01

7.00E-02

5.62E+00

l

Il

Chemical

Concentratio n

(mg/kg )

3.00E-02

2.806-01

3.80E-01

7.00E-02

5.62E+00

Ingestio n Intak e Facto r

(kg/kg/day )

7.13E-06

Ingestio n Intak e Facto r

(kg/kg/day )

8.32E-05

8.32E-05

8.32E-05

8.32E-05

8.32E-05

Ingestio n Intak e Facto r

(kg/kg/day )

8.32E-05

8.32E-U 5

8.32E-05

8.32E-05

8.32E-05

O ai ly Intak e

(mg/kg/day )

2.14E-07

Dail y Intak e

(mg/kg/day )

2.50E-0&

2.33E-05

3.16E-05

5.83E-J 6

4.68E-04

O ai l y Intak e

(mg/kg/day )

2.50E-06

2.33E-05

3.16E-05

5.83E-06

4.68E-04

Slop e Facto r

(mg/kg/day ) -1

1.75E+00

Subchronic R F D

(mg/kg/day )

3.00E-04

2.00E-02

3.70E-02

3.00E-04

2.00E-01

Chroni c R F D

(mg/kg/day )

3.00E-04

5.00E-03

3.70E-02

3.00E-04

3.00E-01

Carcinogenic Risk

3.74E-07

Hazard

Quotien t

8.32E-03

1.17E-03

8.55E-04

1.94E-02

2.34E-03

Hazard

Quotien t

8.32E-03

4.66E-03

8.55E-04

1.94E-02

1.56E-03

Tota l

Risk

3.74E-07

Hazard

Index

3.21E-02

Hazard

Index

3.48E-02
CHIL D RECREATIONA L USE R Ingestio n of Fish Reasonable Maximum Exposure

1

| Carcinogeni c Risk

i

Chemical

Arseni c

i

| Hazard Index -- Subchronic

i

Chemical

Arseni c

Chromium V!

Copper Mercury Zin c

i

| Hazard Index -- Chronic

i

Chemical

Arseni c

Chromium V I

Copper Mercur y Zin c

l

1

i

Chemical

Concentratio n

(ing/kg )

4.00E-02

1

1I

Chemical

Concentratio n

<mg/kg )

4.00E-02

3.30E-01

4.20E-01

9.00E-02

6.42E+00

l

I

i

Chemical

Concentratio n

(mg/kg )

4.00E-02

3.30E-01

4.20E-01

9.00E-02

6.42E+00

Ingestio n Intak e Facto r

(kg/kg/day )

6.18E-05

Ingestio n Intak e Facto r

{kg/kg/day )

7.21E-04

7.21E-04

7.21E-04

7.21E-04

7.21E-04

Ingestio n Intak e Facto r

(kg/kg/day )

7.21E-04

7.21E-04

7.21E-04

7.21E-04

7.21E-04

O ai ly Intak e

(mg/kg/day )

2.47E-06

Davlv

intan e

(mg/tcg/day )

2.88E-05

2.38E-04

3.03E-Q4

6.49E-05

4.63E-03

D ai l y Intak e

(mg/kg/day )

2.88E-05

2.38E-04

3.03E-04

6.49E-05

4.63E-03

Slop e Facto r

(mg/kg/day) - 1

T.75E+00

Subchronic R F D

(mg/kg/day )

3.00E-04

2.00E-02

3.70E-02

3.00E-04

2.00E-01

Chroni c R F D

(mg/kg/day )

3.00E-04

5.00E-03

3.70E-02

3.00E-04

3.00E-01

Carcinogeni c Risk

4.33E-06

Hazard

Quot i ent

9.62E-02

1.19E-02

8.19E-03

2.16E-01

2.32E-02

Hazard

Quotien t

9.62E-02

4.76E-02

8.19E-03

2.16E-01

1.54E-02

Tota l

Ris k

4.33E-06

Hazard

Index

3.S6E-01

Hazard

Index

3.84E-01
Intake Factor: SURFAC E WATE R

Description : Adul t Recreational User - Fis h Inges t io n Abbreviation : AUF G

Pathwa y Type: Ingestio n o f Soi l

Intak e Facto r =

Parameters:

( IR x EF x EO x ME X FI x CF x SS )

( BU x AT )

Carcinogeni c Abbreviatio n

I R

EF

ED

HE

F I

CF

S S

BW

A T

Descriptio n

Ingestio n Rate(mg/day }

Exposure Freq.(dys/yr )

Exposure Duration(yrs ) Matri x Effec t

Fractio n Contaminated

Conversion Facto r (kg/mg ) Site-specifi c Facto r Body Weight (kg ) Averagin g Tim e (dys )

A ve

150000

52

3

1

1

.000001

1

25

25550

R ME

150000

156

24

1

1

.000001

1

57

25550

Non - Carcinogenic A ve

150000

52

3

1

1

.000001

1

25

1095

R ME

150000

156

24

1

1

.000001

1

57

8760

Intak e Facto r Calculations :

Carcinogenic: Average Exposure

( 1.50E+05 x 5.20E+01 x 3.00E+00 x 1 x 1 x 1.00E-06 x 1

3.66E-05 =

( 2.50E+01 x 2.56E+04 >

Carcinogenic: Reasonable Maximum Exposure

( 1.50E+05 x 1.56E+02 x 2.40E+01 x 1 x 1 x 1.00E-06 x 1 )

3.86E-04 =

( 5.70E+01 x 2.56E+04 )

Non-Carcinogenic : Average Exposure

( 1.50E+05 x 5.20E+01 x 3.00E+00 x 1 x 1 x 1.00E-06 x 1 )

8.55E-04 =

( 2.50E+01 x 1.10E+03 )

Non-Carcinogenic: Reasonable Maximum Exposure

( 1.50E+05 x 1.56E+02 x 2.40E+01 x 1 x 1 x 1.00E-06 x 1 )

1.12E-03 =

Februar y 2, 199

18:1

( 5.70E+01 x 8.76E+03 )
Intake Factor: SURFAC E WATE R

Description : Chil d Recreational User - Fish Ingestio n Abbreviation : CUF G Pathwa y Type: Ingestio n o f Soi l

Intak e Facto r =

( IR x EF x ED x ME x FI x CF x SS )

( BU x AT )

Februar y 2, 199

18:1

Parameters:

Carcinogenic Abbreviatio n

I R

EF

EO

ME

fl

CF

S S

BU

A T

Descriptio n

Ingestio n Rate(mg/day )

Exposure Freq.(dys/yr )

Exposure Duration(yrs ) Matri x Effec t

Fractio n Contaminated

Conversio n Facto r (kg/mg ) Site-specifi c Facto r Body Weigh t (kg ) Averagin g Tim e Cdys )

A ve

81000

6

6

1

1

.000001

1

16

25550

R ME

81000

52

6

1

1

.000001

1

16

25550

Non - Carcinogenic A ve

81000

6

6

1

T

.000001

\

16

2190

R ME

81000

52

6

1

1

.000001

1

16

2190

Intak e Facto r Calculations :

Carcinogenic: Average Exposure

( 8.10E+04 x 6.00E+00 x 6.00E+00 x 1 x 1 x 1.00E-06 x 1

7.13E-06 =

C 1.60E+01 x 2.56E+OA )

Carcinogenic: Reasonable Haxirtium Exposure

( 8.10E+04 K 5.20E+01 x 6.00E+00 x 1 x 1 x 1.006-06 x 1 )

6.18E-05 =

< 1.60E+01 x .2.56E+04 )

Non-Carcinogenic : Average Exposure

( 8.10E*04 x 6.00E+00 x 6.00E+00 x 1 x 1 x 1.00E-06 x 1 )

8.32E-05 =

( 1.60E+01 x 2.19E+03 )

Non-Carcinogenic: Reasonable Maximum Exposure

( 8.10E+04 x 5.20E+01 x 6.00E+00 x 1 x 1 x 1.00E-06 x 1 )

7.21E-04 =

( 1.60E+01 x 2.19E+03 >
Media Chemical Concentrations: SURFACE WATER February 2,

Medium: Fis h

Abbreviation : FIS H

Medium Type: Soi l

Subchronic Chronic/Carcinogeni c

Chemical Average

(mg/kg )

R.M.E .

(mg/kg ) Average R.M.E .(mg/kg ) (mci/kg )

Arsenic 3.00E-02 4.00E-02 3.00E-02 4.00E-02

Cadmium (food ) Chromium II I

Chromium VI 2.80E-01 3.30E-01 2.80E-Of

 :3.30E-01

Copper 3.80E-01 4.20E-01 3.80E-01 4.20E-01

Mercury 7.00E-02 9.00E-02 7.QOE-02 9.00E-02

Zin c 5.62E+00 6.42E+00 5,62E+00 6.42E+00
Appendix A June 1996__________________A-14________________943-2819

Data Analysis and Chemicals of Concern

An early step in the RA process was review of chemical data specific to groundwater at the

site. The objective of data analysis was to identify COCs related to groundwater. Data were

compiled and entered into a computer database.

The analytical data were obtained followin g the protocol, expressed in the Work Plan

(Asarco, 1991a), and were evaluated to identify COCs. The data were collected in 1991 and

1992. As described in Section 6.2-1, unfiltered metals samples collected from six springs

and four mini-piezometers were used to estimate EPCs.

COCs for groundwater were selected from springs and mini-piezometers located upgradient

of the hypothetical exposure point. Chemicals that were never detected in these samples

were eliminated and included antimony, beryllium, chromium, cyanide, and molybdenum.

EPA guidance recommends that a detection frequency of five percent or less be used in order

to exclude chemicals of potential concern (EPA, 1989f); barium was also excluded (four

percent detection frequency or one detect out of twenty-four records) on this basis. Iron was

excluded based on its classification as an essential nutrient (EPA, 1989c). Metals excluded

as COCs because of unavailable toxicity values were aluminum, copper, manganese, and

titanium.

Lead was not quantitatively evaluated in this medium-specific RA. The potential health

impacts from the exposure to lead will be quantitated in a sitewide, multi-media, baseline risk

assessment using the most current EPA Integrated Exposure Uptake-Biokinetic (IEUBK) lead

model available. The use of this model accounts for lead exposure from many sources and

predicts blood lead levels with the input of either EPA defaul t values, site-specific values, or

a combination of both.

Colder Associates
Appendix A June 1996___________________A-15__________________943-2819

T he followin g six metals were quantitatively evaluated for potential noncarcinogenic hazards

and carcinogenic risks:

*• Arsenic;

*• Cadmium;

* Mercury;

+ Nickel;

*• Silver; and,

+ Zinc.

The resulting analytical results for the COCs are provided in Table 6.3-1.

All data have been validated and only reliable data or data with a "J" qualifier were used hi

the quantitative evaluation of risks for the COCs. This qualifier refers to data that are

estimated values but are still appropriate to use in quantitative risk assessment (EPA, 1989f,

1990). Nondetect data were reported at the Contract Required Detection Limit (CRDL)

appropriately adjusted for any dilutions. In order to quantify analyte average and reasonable

maximum exposure (RME) concentrations, a value of one half the CRDL was used when the

analyte was reported as not being detected. The arithmetic mean analyte concentrations were

used to represent EPCs in the calculations of risk for average exposure and the 95 percent

upper confidence limit on the arithmetic mean analyte concentrations were used to represent

EPCs in the calculations of the RME scenario (EPA, 1992d).

Toxicity Assessment

The purpose of the toxicity assessment is to evaluate the toxicity of source-related COCs and

to estimate the dose-response relationship for each of these chemicals. The information

Colder Associates
Appendix A June 1996___________________A-16_________________943-2819

obtained in the toxicity assessment is combined with estimated contaminant intakes calculated

as part of the exposure assessment to estimate the potential excess lifetime cancer risks and

potential noncarcinogenic health hazards (EPA, 1989f).

The Reference Dose (RfD) and Slope Factor (SF) values used in this RA were obtained from

the followin g sources:

+ EPA's Integrated Risk Information System (IRIS) (EPA, 1992e) on-line

database system

> EPA' s Health Effect s Assessment Summary Tables (EPA, 1992f)

The EPA has developed various types of RfDs depending on the exposure route (ingestion or

inhalation), the critical effect , and the length of exposure being evaluated (chronic or

subchronic). The EPA bases the RfD on the most sensitive animal species tested (i.e., the

species that experiences adverse effect s at the lowest dose).

The EPA defines a chronic RfD as an estimate of a daily exposure level that is unlikely to

result in deleterious effect s during a lifetime for the human population (70 years, according to

EPA guidance). A chronic RfD is used to evaluate the potential noncarcinogenic hazards

associated with long-term contaminant exposures (7 years to a lifetime).

Subchronic RfDs have been developed to characterize potential noncarcinogenic hazards

associated with short-term contaminant exposures. The EPA defines subchronic exposure as

periods ranging from two weeks to seven years (EPA, 1989f). Subchronic RfDs generally

tend to be one order of magnitude higher than chronic RfDs because of the shorter exposure

duration.

Although not a COC, sulfate can contribute an offensive odor and taste to drinking water.

Despite sulfate currently not having an MCL, a secondary MCL based on odor and aesthetic

Colder Associates
Appendix A June 1996___________________A-17_________________943-2819

quality does exist. This secondary MCL (SMCL) is far exceeded by the EPCs (average and

RME) found in the mini-piezometers and the springs considered in the RA discussed in

Section 6.5.5.

Sulfate has been detected at elevated levels in the groundwater sampled from the springs and

mini-piezometers used in this RA (average concentration of 1,384 mg/1). The EPA has

established a SMCL for sulfate of 250 mg/1. Again, this SMCL is based on aesthetic effect s

(i.e., taste and odor) and is not health based (55 FR 143, July 25, 1992). No chronic health

effect s have been associated with long-term exposure to elevated levels of sulfate, however,

sulfate can have adverse acute effects .

Exposure to high levels of sulfate hi drinking water can lead to an osmotic diarrhea. Thi s

effec t eases and disappears as the person becomes acclimated to the high levels of sulfate. This effec t hi infants may lead to dehydration and is a potential concern. EPA has not

established any health-based maximum contaminant level MCL or RfDs for sulfate (57 FR

138, July 17, 1992). However, levels of sulfate as measured in the springs and minipiezometers used in the RA would more than likely be offensive. It is doubtful that

unfiltered groundwater of sulfurous odor and likely discoloration would be consumed.

Chemicals with high SFs and low RfDs exhibit higher toxicities. Table 6.4-1 summarizes

toxicity values used in the RA for the selected COCs.

Risk Characterization

Risk characterization is the final step of the RA process. In this step, the toxicity factors

(RfDs and SFs) for the COCs are applied in conjunction with estimated chemical intakes to

predict noncarcinogenic and carcinogenic health risks to exposed individuals.

Golder Associates
Appendix A

June 1996_____________________A-18___________________943-2819

The potential for noncarcinogenic effect s is characterized by comparing estimated chemical

intakes with chemical-specific RfDs. This measure is known as the hazard quotient (H.Q.)

for a single chemical or the hazard index (H.I.) for multiple chemicals. Potential

carcinogenic effect s are characterized in terms of the incremental or excess probability that

an individual will develop cancer in his or her lifetime due to the modeled exposure. Excess

cancer risk is estimated from the projected lifetime intakes and the cancer slope factor, which

represents an upper-bound estimate of the dose-response relationship.

In this RA, subchronic (2 weeks to 7 years) H.I. s are the appropriate indicator of potential

non-cancer adverse effect s for the average Child Resident exposure (6 years), the RME Child

Resident exposure (6 years), and the average Adult Resident (3 years). The chronic H.I . is

the appropriate indicator for the RME Adult Resident because the exposure duration is 24

years (which is greater than the 7-year cutof f between subchronic and chronic timespans). However, when the child and adult scenarios are summed to represent continuous exposure

of one individual over both age groups (e.g., birth through 9 years for average and birth

through 30 years for RME), the chronic H.I. s are summed as the appropriate indicators of

non-cancer risk for timespans exceeding 7 years.

Hazard Index for Noncarcinogenic Effect s

The potential for adverse noncarcinogenic effect s resulting from exposure to a chemical of

concern is evaluated by comparing the average daily intake of the chemical (expressed as

mg/kg-day) to a reference dose (expressed as mg/kg-day). The resulting ratio is called a

H.Q. (EPA 1989f). It is derived in the following manner:

xTNoncance „ . ~ .. . Chemical Intake (mg/ kg- day) r Hazard Quotient = —————————————— — RfD (mg/ kg- day) (6_1}

Colder Associates
Appendix A

June 1996 ___________________ A-19 _________________ 943-2819

Use of the RfD assumes a level of intake (the RfD) below which it is unlikely that even

sensitive individuals will experience adverse health effect s over a lifetime of exposure. If the

average daily intake exceeds the RfD (that is, if the H.Q. exceeds 1.0), there may be cause

for concern for potential noncancer effects . It should be noted, however, that the level of

concern does not increase linearly as the RfD is approached or exceeded. This is because all

RfDs are not equally accurate and are not based on the same severity of toxic effects . Thus,

the slopes of the dose-response curve in excess of the RfD can vary widely depending on the

substance. Furthermore, it must be emphasized that the H.Q. does not represent a statistical

probability of an effec t occurring (EPA, 1989f).

To assess the overall potential for adverse health effect s posed by exposure to multiple

chemicals, the H.Q. s for each chemical of concern associated with a given exposure pathway

are summed. The resulting sum is referred to by EPA as the H.I. The H.I. approach

assumes that multiple subthreshold exposures to several chemicals could result in an adverse

health effect . The H.I. is expressed as follows:

H.I. = Ej/RfD! + E2/RFD2 ... + Ej/RfDj (6

where:

Ej = Exposure level (or intake) for toxicant i

RfDj = Reference dose for toxicant i

Where a receptor may be subject to multiple exposure pathways (e.g., inhalation of

particulates and ingestion of soils), the individual H.I.s from all relevant pathways are

summed to obtain the total H.I. for that receptor. This RA has only one complete exposure

pathway: the ingestion of groundwater. For multiple chemical exposures, the total H.I.

might exceed 1.0, even if no single chemical intake exceeds its RfD. If the total H.I. is less

than 1 .0, cumulative exposures to the COCs at the site are judged unlikely to result in an

adverse effect . If the sum is greater than 1.0, a more detailed and critical evaluation of the

Colder Associates
Appendix A June 1996___________________A-20_________________943-2819

risks is required to ascertain if the cumulative exposure would in fact be likely to harm

exposed individuals (EPA 1989'f). The evaluation may include consideration of specific

target organs affected and mechanisms of toxic action of the COCs.

T he assumption of additive effect s reflected in the cumulative H.I. is most properly applied

to substances that induce the same effect by the same mechanism (EPA, 1989f).

Consequently, application of the equation to a mixture of substances that are not expected to

induce the same type of effect s could overestimate the potential for adverse health effects . The H.I. provides a rough measure of potential toxicity, but it is conservative and dependent

on the quality of the experimental evidence. Since the H.I. does not define dose-response

relationships, its numerical value cannot be construed as a direct estimate of risk (EPA,

1989f), but only as a level of concern.

Carcinogenic Risk

Carcinogenic risks are estimated as the incremental probability of an individual developing

cancer over a lifetime as a result of exposure to a potential carcinogen. The numerical

estimate of excess lifetime cancer risk is calculated by multiplying the chemical intake

averaged over a lifetime by the cancer slope factor (SF) as follows:

Risk = Chemical Intake (mg/kg-day) x SF (mg/kg-day)"1 (6-3

The EPA slope factors are 95th percent upper confidence limit of the probability of response

per unit intake of chemical over a lifetime. Slope factors are based on experimental animal

data and epidemiological studies when available. A linear nonthreshold mathematical model

for low-dose extrapolation, the linearized multistage model, is used to calculate a numerical

slope factor value. EPA states that carcinogenic risks estimated using this approach are

Colder Associates
Appendix A June 1996___________________A-21______________943-2819

upper-bound estimates. This means that the actual risk is likely to be less than the predicted

risk (EPA, 1989f).

EPA guidance to evaluate cancer risk from simultaneous exposure to several carcinogens

assumes that incremental cancer risks are additive. The concept that cancer risks are additive

is based on a number of assumptions. If these assumptions are incorrect, over- or underestimation of the actual risk could result (EPA, 1989f). The total cancer risk is estimated by

summing the risks estimated for each chemical of concern and for each pathway.

EPA policy must be considered in order to interpret the significance of the cancer risk

estimates. Current EPA guidance states that where the cumulative site risk to an individual

based on reasonable maximum exposure is less than 1 x 10"4, action is generally not

warranted (EPA, 1991b). A carcinogenic risk level of 1 x 10"4 was therefore used as the

appropriate risk level for evaluation of potential exposures in this RA.

Risk Quantification

The potential for noncarcinogenic health effect s due to a chemical of concern, expressed as a

H.Q. , is calculated using the followin g format:

[( Chemical Intake ) Daily ] RfD

Concentration X Factor = Intake X (mg/kg-day) = Hazard

(mg/y) (y/kg- (mg/kg- Quotient

day) day)

Where y = specific amount (weight or volume) of medium in which the chemical is

measured; the units of which are medium dependent. For example, a

chemical in soil may be reported in mg/kg and in water hi mg/liter.

Average or RME concentrations of each noncarcinogenic chemical of concern are multiplied

by the pathway-specific intake factors to yield an average or RME daily intake. The daily

Colder Associates
Appendix A June 1996___________________A-22__________________943-2819

intake is then divided by the RfD to obtain the H.Q. for average or reasonable maximum

exposures.

Individual H.Q.s are summed for all chemicals in an exposure pathway to provide a pathwayspecific H.I. Pathway-specific indexes are summed to obtain the total H.I. for all exposure

pathways applicable to a given receptor. For this RA, only the exposure pathway of

ingestion of groundwater was considered.

H.I.s for each receptor and pathway are summarized in Section 6.5.2. H.I.s are calculated

for chronic and subchronic exposures for all receptors at the exposure point selected. Risk

calculations are presented in Appendix H. The potential for carcinogenic effects , expressed as excess cancer risk, are calculated by:

[( Chemical Lifetime ) Lifetime ] Slope Factor Excess

Concentration X Intake = Daily X (mg/kg-day)"1 = Cancer

(mg/y) Factor Intake Risk

(y/kg-day) (mg/kgday)

Where y = specific amount (weight or volume) of a medium in which the chemical is

measured; the units of which are medium dependent.

Concentrations of each potential carcinogen are multiplied by pathway:specific intake factors

to yield a lifetime daily intake. The daily intake is then multiplied by the slope factor to

obtain a numerical estimate of excess cancer risk.

The cancer risks are then summed for all of the chemicals evaluated for each exposure

pathway. To determine the total carcinogenic risk to a given receptor, the cancer risks for

each exposure pathway are summed. However, only the exposure pathway of groundwater

ingestion was considered in this RA. Carcinogenic risks for average and RME conditions are

presented in Table 6.5-1. Cancer risk calculations are shown in Appendix H.

Colder Associates
ASARCO

GLOBE PLAN T

June 28, 1996

Ms. Rebecca Thomas Remedial Project Manager U.S . EPA Region VIII

999 18th Street, Suite 500 Denver, Colorado 80202-2405

R E: GROUNDWATER BASELINE HUMAN HEALTH RISK ASSESSMENT

Dear Rebecca:

Enclosed please find 4 copies of Asarco's Groundwater Baseline Human Health Risk Assessment for the California Gulch Superfun d Site, Leadville, Colorado. Please note that

this document was previously included as Section 6.0 of the Hydrogeologic Remedial Investigation (RI). In response to EPA comments, the groundwater risk assessment section

was removed from the Hydrogeologic RI and therefore is transmitted separately with this

letter.

Sincerely,

Margaret (Poppy) Staub Site Manager

4 copies sent

cc: Russ Alien, CDPHE Maureen Yaskanin, Golder Assoc. Scott Ronzio, Golder Assoc. Bob Comer, Asarco

19\2819swri.ltr

ASARCO Incorporated . 495 Eas t 51s t Avenue . Denver. Colorad o 80216 2098 Phon e (303 ) 296-5900 FAX (303 ) 296 0508