PETITIONED PUBLIC HEALTH ASSESSMENT
CRIPPLE CREEK AND VICTOR GOLD MINING
CRIPPLE CREEK, TELLER COUNTY, COLORADO
The Agency for Toxic Substances and Disease Registry has concluded that the ambient air emissions associated with Cripple Creek and Victor Mining Company do not pose a threat to human health. The cancer incidence and birth defects in the Victor and Cripple Creek area are not elevated when compared to those in similar areas. The local drinking water has not been impacted by mining activities. The dust and metals levels in Victor and Cripple Creek do not a threat to public health. Current hydrogen cyanide levels on-site and in nearby residential areas are not at levels of health concern.
The Cripple Creek and Victor Gold Mining Company (CC&V) has conducted gold and silver mining in the Cripple Creek Mining District between Cripple Creek and Victor, Colorado since 1976. The Agency for Toxic Substances and Disease Registry (ATSDR) was petitioned by a local citizen's group to evaluate the potential public health impact of possible contaminants released from CC&V mining activities [1]. Some community members suspected that fugitive dust and hydrogen cyanide from current mining activities at the Cresson Mine, which is operated by CC&V, are associated with respiratory illnesses. These community members are also concerned that mining activities in general may be contributing to various cancers and birth defects in the area and impacting the drinking water quality. The purpose of this public health assessment is to identify potential human exposures related to CC&V mining activities by evaluating existing on- and off-site environmental data, health outcome data, and community health concerns, and to recommend appropriate public health follow-up activities.
The Cripple Creek mining district is on the western edge of Pikes Peak, about 100 miles south of Denver (Appendix A). Since gold was discovered in the district in 1890, this mining district has had over 500 mining and ore processing operations scattered over a 30 square mile area. Historically, the Cripple Creek mining district has produced more than 650 metric tons of gold, making it third largest gold producing district in the United States [2]. CC&V is currently the only mining operation in this district. The Cripple Creek mining district has been mined using underground mining techniques until the 1950s; mining activities in the district now use surface mining methods [2].
Mining Operations
By 1990, CC&V discovered a reserve of over 81 metric tons of contained
gold within the Cresson deposit. Gold has been produced from several mines within
the Cresson deposit since its discovery. The current mine producing gold from
the Cresson deposit is called the Cresson mine. Using surface mining methods,
rock is drilled and broken up using ammonium nitrate and fuel oil mixture as
an explosive. Drill hole samples are analyzed to distinguish the rock that contains
economically-recoverable gold (ore) from rock which is not (overburden). Ore
and overburden are loaded by front-end loaders or a diesel-hydraulic shovel
into 85-ton haul trucks. Ore is then hauled to a two-stage crushing system that
reduces the run-of-mine ore (pieces less than three feet) to a coarse gravel
measuring less than 1.5 inches wide at a rate up to 2,000 tons per hour (Appendix A) [2].
Overburden is placed in an area where no further mining is planned. The overburden storage areas are designed and constructed according to geotechnical stability, storm water runoff patterns, water quality assessments for infiltrating water, and specific plans for grading and reclamation through revegetation. CC&V reclaims and revegetates areas as soon as the mining activity has been completed. Mining operations are 24 hours a day, seven days a week, 365 days per year. Approximately 50,000 tons of ore and 85,000 tons of overburden are mined each day [2].
Gold is removed from the crushed ore by use of the same process used in the mining district since the 1890s. Water is added to sodium cyanide to form a solution that is used to dissolve metals that are exposed on the broken faces of crushed ore into a cyanide leach solution. This leaching of gold takes place outside in a "valley leach facility" (Appendix A) that has been constructed in a double- or triple-lined valley [2]. The crushed ore is placed in several 35 foot layers within the valley leach facility and the sodium cyanide solution is applied using agricultural drip irrigation tubes spread on top of the newly-placed ore [2]. The pH is elevated by applying lime to the crushed ore. The sodium cyanide solution moves through the ore toward the bottom of the valley leaching facility and dissolves gold and other metals to form their metal compounds in the solution. The solution is collected and pumped out of the valley leaching facility to the Adsorption Desorption Recovery (ADR) facility and is passed through activated carbon to remove the gold-cyanide compound. The cyanide leach solution is stripped of the dissolved gold and then sent back to the drip irrigators in the valley leach facility to start the whole process over. The dissolution of sodium cyanide forms a solution that contains hydrogen cyanide depending on the temperature and pH [3]. The solution is contained within the pore space of the ore until it is pumped into the ADR facility [2].
The gold compounds on the activated carbon are processed in a strip vessel to remove the gold using a hot alkaline (high pH) cyanide solution [2]. The gold-rich solution is piped to an electro-winning cell where strong direct current is used to attract metals from the solution to a steel wool cathode and forms a solid or "mud" [2]. The mud is sent to a refinery furnace where gold and silver are separated from the melted solid to produce a gold-silver amalgam called dore. The dore produced at this mine is shipped offsite for further refining. This entire process recovers about 70% of the gold in the ore.
Environmental Investigations
There are federal, state, and local regulations and ordinances that apply
to all CC&V mining operations such as blasting, noise levels, air emissions,
water quality impact, and solid wastes generated. Environmental monitoring is
required to obtain and keep these permits. The Colorado Department of Public
Health and Environment (CDPHE) regulate air emissions, storm water runoff, and
solid and hazardous waste generation and disposal. The Colorado Department of
Natural Resources regulates the construction, operation, and reclamation of
mining activities. Teller County regulates noise, wastewater 
disposal (i.e.,
septic tanks), and blasting. Although prolonged public access to the property
is controlled, the nearest house to CC&V property is about 3,100 feet. The
closest house to the valley leach facility is about 4,200 feet. Human exposure
to potential contaminants from mining activities is limited to fugitive air
emissions; primarily dust from excavation, ore hauling, and wind blowing against
the overburden storage piles and valley leach facility. The impact of air emissions
from mining activities to nearby residents is evaluated in the Discussion
section of this document.
Specific health concerns expressed by community members were about fugitive dust that comes from excavation, hauling, crushing, and overburden storage piles causing respiratory illnesses. Hydrogen cyanide levels coming from the heap leach pad are also thought to contribute to respiratory illnesses. Some community members are concerned that mining activities may impact their drinking water quality and increase cancer and birth defects in their community.
The noise from blasting was mentioned by several community members as a disturbance. Noise levels in the area around the mine are within the limits placed (and regulated) by Teller County and state government [4]. However, small communities, such as Victor, can appeal for more stringent local noise codes with public health and welfare as a means of noise control [5].
There are 626 people living within a one mile radius of CC&V (Appendix A) [6]. The population is 97% white, and 3% black, Hispanic, Asian or another race. Of the total population, 8% are under age 6 years and 11% are age 65 years and older. In 1990 there were 130 females of reproductive age (15-44 years) in the area.
The following sections contain an evaluation of the environmental data used for the CC&V assessment. ATSDR uses established methodologies for determining how people may be exposed to potential contamination related to CC&V and what harmful effects, if any, may result from such exposure. Chemical exposure pathways (or routes of physical contact with chemicals) that ATSDR evaluates are ingestion, inhalation, and skin contact. ATSDR uses comparison values (CVs), which are screening tools used to evaluate environmental data that are relevant to the exposure pathways. Comparison values are concentrations of contaminants that are considered safe levels of exposure. Chemicals detected below CVs are not likely to represent a health concern; chemicals that are detected above CVs require a more detailed evaluation of site specific exposure conditions. For a complete discussion of these criteria (quality assurance considerations, human exposure pathway analyses, ATSDR's health comparison values, and the methods of selecting contaminants above comparison values), refer to Appendix B.
An air quality permit has been issued to CC&V by Colorado Department of Public Health and Environment (CDPHE) in accordance with the Clean Air Act and state statutes. Fugitive dust generated from mining activities is primarily responsible for community concern. On-site particulate matter (dust) that is 10 micrometers or less (referred to as PM10) generated during excavation, blasting and hauling ore is required to be quantified and controlled to meet air quality standards off-site. The current emission control measures implemented by CC&V to reduce dust are:
Despite the dust control mechanisms, there are still complaints of dust from mining operations.
ATSDR was provided air monitoring results from four stations that were operating in 1999 on CC&V property. Three other air quality monitoring stations are located in a residential area near CC&V property and in the towns of Cripple Creek and Victor. PM10 has been monitored once every three days or once every six days from 1993 to 2000 [7] [8]. Some metals were also monitored on CC&V property from 1993 to 1996 [9]. The current air quality guideline for PM10 is the National Ambient Air Quality Standard (NAAQS) is 150 µg/m3 averaged over a 24 hour period and 50 µg/m3 as an annual average. Historical annual averages for on-site PM10 levels have remained below the NAAQS annual average standard (anywhere from 5-20 µg/m3). Air quality monitoring data on CC&V property show one exceedance of the NAAQS for PM10 in September 1999. The monitoring station in the town of Cripple Creek shows several PM10 concentrations that exceed the 24 hour NAAQS in December 1995 through February 1996. Theses monthly exceedances also factored into the 1995 annual average PM10 level of 51.5 µg/m3.
The PM10 concentrations that exceeded the 24 hour NAAQS are listed below:
| Date of PM10 Exceedance | Location | Maximum 24 hour Concentration (mg/m3) | Average Monthly Concentration (mg/m3) |
NAAQS 24 hour Standard (mg/m3) |
| December 1995 | Cripple Creek (Off-site) | 306 | 100 | 150 |
| January 1996 | Cripple Creek (Off-site) | 195 | 59 | 150 |
| February 1996 | Cripple Creek (Off-site) | 235 | 58 | 150 |
| September 1999 | Range View (On-site) | 183 | 34 | 150 |
The cause of particulate matter exceedances in the town of Cripple Creek in December 1995 through February 1996 was excess road sanding during these months to control ice [10]. The exceedances do not appear to be related to mining activities because the PM10 peaks detected in Cripple Creek occurred only during road sanding and the other monitoring stations located at the mine did not pick up high levels of PM10. The PM10 exceedance detected from on-site monitoring station (Range View) in September 1999 was from a motor vehicle hill climb race that occurred on Teller County Road 84 near this monitoring station [10]. This maximum on-site PM10 concentration was just above (183 µg/m3) the NAAQS PM10 standard, although the monthly average was considerably lower. Short-term exposures to levels of PM10 that occasionally exceed the NAAQS for PM10 (such as those described in this document) are unlikely to cause adverse health effects. However, exposure to dust in sensitive people, such as those with asthma or other pre-existing medical disease (for example, chronic pulmonary disease or emphysema) should be minimized [11]. Mining activities do not appear to have a significant impact on the PM10 levels in nearby communities. However, most roads in Cripple Creek and Victor are not paved; the unpaved roads are probably a major contributor to dust conditions in these towns.
CC&V monitored on-site levels of lead, cadmium, chromium, and arsenic in total suspended particulate matter from 1993 to 1996. The monitoring results showed that the levels of lead in the air were below the Colorado lead standard and the NAAQS of 1.5 µg/m3 [12]. Cadmium was detected one time in two years at a concentration of 0.0040 µg/m3 in January 1996. Background air levels of cadmium in the United States are usually around 0.001-0.003 µg/m3 [13]. On-site chromium concentrations ranged from non-detectable to 0.0086 µg/m3 during 1993-1996. The maximum chromium concentration detected was 0.0021 µg/m3; background air levels of total chromium in rural areas of the United States are typically 0.01 µg/m3 [14]. On-site arsenic levels ranged from non-detectable to 0.01 µg/m3. Background air levels of arsenic in rural areas of the United States are typically 0.003 µg/m3 [15]. The maximum levels of cadmium, chromium, and arsenic detected in on-site ambient air are all at least 1000 times below the lowest levels known to cause adverse health effects in humans [13] [14] [15]. Also, the concentrations of arsenic, cadmium, and chromium were not significantly different from concentrations from monitoring projects conducted by the state of Colorado or other operations that monitored metals in former mining or minerals processing areas [12]. CDPHE decided that the levels of metals monitored were not significantly different from expected background levels and further analysis for metals was not necessary [12]. CDPHE requires the mine to continue sampling for PM10 as a demonstration that levels of particulate matter meet national standards. Based on these air monitoring results, no adverse health effects are expected to occur to people living near these mining activities.
The majority of the hydrogen cyanide (HCN) produced within the valley leach facility stays in solution and does not leave the closed system [3]. The solution that is placed onto the ore is collected and sent to the processing plant. Once the precious metals are extracted, the solution is continuously recycled and placed back on the heap leach pad [3]. A small amount of HCN applied to the top of the ore in the valley leach facility vaporizes. The amount released to the air is approximately 7,000 pounds per year [3].
Modeling
ATSDR estimated HCN air concentrations nearby residents could be exposed
from the heap leach emissions at the Cresson Valley Leach Facility. Air concentrations
were estimated by using mathematical equations that simulate the transport of
contaminants in the environment. In this case, ATSDR looked at the transport
of HCN from heap piles through the air to people living in Victor, Colorado.
ATSDR used the Industrial Source Complex, Version 3 Short Term Model (ISC3ST) to estimate HCN air concentrations. ATSDR's use of this model and the results are explained in Appendix C. The model requires emission rates and meteorological data. ATSDR estimated air concentrations using sampled HCN emissions taken directly from the heap leach pads and 1993 meteorological data [16].
The ISC3ST model shows ambient air concentrations of approximately 1.5 ug/m3 for the 24-hour maximum and 0.15 ug/m3 for the annual average at the western edge of Victor.
The Colorado Department of Public Health and Environment, Air Pollution Control Division (APCD) has used the ISC3ST model in support of state air permits for particulate emissions from CC&V. The APCD has also compared ISCST3 results with air monitoring for PM10 at the mine and found in one case that the ISCT3 modeling system appears to have overpredicted PM10 concentrations by as much as a factor of three [17].
The level of uncertainty in using ISC3ST for complex terrain and long-term air releases has also been described as two orders of magnitude (referring to the entire range of values, not just the upper and lower end) [18]. With this uncertainty, the predicted concentrations of HCN in the air near Victor, could range from 0.15 to 15 ug/m3 using the ISC3ST model (including reported uncertainty) for the 24-hour maximum concentration. The average annual concentration with uncertainty could range from 0.015 to 1.5 ug/m3. These estimated HCN concentrations near Victor are within acceptable public health guidelines for annual averages and 24-hour exposure levels and do not pose a threat to human health [19]. However, ATSDR uses modeling results only as predictors of environmental conditions and generally does not base public health conclusions on such results because of the uncertainty factors in models. The main components of uncertainty in this case are the complex terrain and the use of only one year of onsite meteorological data. ATSDR's simplification of the dimensions of HCN source area may also introduce uncertainty. According to EPA's regulatory guidance, one year of onsite meteorological data is acceptable. However, multiple years of data are preferred.
The estimated modeling results of HCN ambient air levels near CC&V are not at levels of health concern; however, hydrogen cyanide ambient air sampling was conducted to confirm the modeling results.
Ambient Air Sampling
ATSDR monitored ambient air for HCN in October 2000 to assess whether residents
in the area are being exposed at levels of public health concern. Five ambient
air sampling locations were selected: two at residences and three on-site locations
at different distances from the Cresson Valley Leach Facility. The locations
of the monitoring stations are shown in Appendix F, Figure 1. The two private
residences were selected because they were among the homes in Victor that were
closest to the leach facility. HCN was not detected in any of the ambient air
samples collected at the two residential properties. HCN was detected intermittently
in on-site ambient air samples collected at monitoring stations 450 to1,400
feet from the leach facility. The on-site HCN concentrations ranged from non-detectable
to 1.86 ppb. Refer to Appendix F for complete details of the
HCN sampling results.
There is no National Ambient Air Quality Standard for HCN in air. However, the U.S. Environmental Protection Agency has derived a Reference Concentration (RfC) for HCN of 3 µg/m3 (2.8 ppb). A RfC is protective of the general population, including sensitive subgroups, for chronic exposures. Chronic exposures refer to exposures that last for as long as a lifetime. HCN was not detected in air samples from residential properties and the on-site concentrations detected near the leach facility were below the RfC. Therefore, none of the HCN concentrations detected during this investigation posed a public health hazard. ATSDR concludes that current HCN emissions from the leach field do not pose a public health hazard under current operating conditions. If there are significant changes in the operation of the leach field, or if the size of the leach field is significantly increased, ATSDR recommends that additional air monitoring be conducted to ensure that hydrogen cyanide emissions do not pose a health hazard.
Municipal water is supplied to Victor from three watersheds: East Fork of West Beaver Creek, Bison Creek, and Boehmer Creek. Past and current water quality sampling data reveal no contaminants at levels of health concern [20]. Mining activities have not affected the local drinking water. There are no known private wells in the vicinity of CC&V that are being used for drinking water; therefore, no human exposure to groundwater. ATSDR concluded that no health effects are expected from using or drinking municipal water in Victor.
C. ATSDR Child Health Initiative
Children are at greater risk than adults from certain kinds of exposure to hazardous substances emitted from hazardous waste sites or industrial facilities. They are more likely to be exposed for several reasons; children play outside more often than adults, increasing the likelihood they will come into contact with chemicals in the environment. Since they are shorter than adults, they breathe more dust, soil, and heavy vapors close to the ground. Children are also smaller, resulting in higher doses of chemical exposure per body weight.
Many children live in the towns near CC&V. Even though children do not have prolonged access to the site, ATSDR closely reviewed possible exposure situations to children while evaluating this site. ATSDR did not identify any contaminants at levels of health concern to children.
Residents of Victor and surrounding communities expressed concern that potential exposures to emissions from CC&V mining activities are responsible for increased cancer incidence and birth defects prevalence in their communities. ATSDR reviewed available cancer and birth defects data that were obtained from the Colorado Central Cancer Registry and provided by CDPHE.
Cancer Data
Many state and local health agencies collect data on the number of people
who have been diagnosed with cancer each year and classify these cancer cases
into different categories such as lung, colon/rectum, breast, prostate, and
so forth, defined by the type of cell in the body that is affected. Depending
on the type of data available, the rate of specific cancers can be determined
for certain populations within a state, an entire state population, or the entire
United States population. The Colorado Central Cancer Registry has collected
information on all reported new cancer cases diagnosed in the state since 1985
[21]. Cancer "incidence" is the number of newly diagnosed cases of cancer during
a particular time period, usually in years. This number is compared to the number
of cases that occur in a larger, more stable population (in the case of this
study, the Denver Metro area was used) designated as "normal" or average. ATSDR
reviewed health statistics prepared by the Colorado Department of Public Health
and Environment [21]. ATSDR provides the following summary of the
data reviewed:
The CDPHE calculated the age adjusted cancer incidence rates for four major cancer types (lung, colon/rectum, breast, and prostate) by sex for the zip code 80860, which includes the city of Victor and surrounding communities [21]. In other words, the observed number of new cases of a particular type of cancer that was reported to have occurred from 1985-1997 was compared to the Denver Metro area incidence rate for the same time period. Denver Metro area cancer rates tend to be lower than national cancer rates. The CDPHE reported no significant increases for the rate of lung, colon/rectum, breast, or prostate cancer in the zip code 80860 when the rate was compared to rates for the Denver Metro area during the 13 year period studied [21].
Cancer is a complex disease (or group of diseases) that often involves multiple "risk" factors, such as environment, lifestyle (smoking, drinking, diet, etc.), and family history. The report defines their limitations and biases which did not account for any of these "risk" factors. Furthermore, apparent increases or decreases in cancer incidence over time may reflect changes in diagnostic methods or case reporting rather than true changes in cancer incidence. Analyzing cancer patterns by city or town may be arbitrary and an inexact way of assessing the relationship between geographic location and cancer. For example, the city or town recorded on the death certificate, or in the Colorado Central Cancer Registry, may not be where the person resided most of his or her life. However, cancer patterns in certain towns or cities may help in defining areas to target for further health care strategies. Since specific environmental exposures and other health risk factors are not known, ATSDR cannot conclude any association between contaminants from any source (including CC&V) and the incidence or mortality of cancer in Victor, Colorado.
Birth Defects
CDPHE monitors the prevalence of birth defects through a program established
in 1989 called Colorado Responds to Children with Special Needs (CRCSN) [21].
CRCSN receives diagnostic reports from a variety of sources on birth defects
as well as conditions believed to be related to developmental delay such as
low birth weight, prematurity, and young maternal age. As in the cancer incidence
study, the area used to investigate the prevalence of birth defects in Victor
and the surrounding communities was the 80860 zip code.
Using the residence zip code of the mother at the time of birth, CRCSN identified 71 live births in the 80860 zip code from 1989 through 1999. Of the 71 live births, 13 children were reported as having one or more eligible conditions [21]. Of these 13 children, 7 were identified as having been diagnosed with major congenital anomalies (e.g., significant cardiac, cognitive or developmental effects). Each birth defects case was examined more closely. That is, the diagnosis in the medical records of the child was examined to ensure that there was no pattern of similar conditions (birth defects) in the area. These data do not show a statistically significant difference between the major anomaly rate for this region and the Colorado state anomaly rate at an alpha level of 0.05. It is important to note that the statistical power of this test was somewhat limited due to the small sample size (number of live births) [21].
It is difficult to provide accurate information when the study population size is small, such as in this case. Residency information of the mother reflects her residence at the time of the birth, not during the entire pregnancy period. Determinations can not be made regarding case residence locations and possible exposures to environmental contamination [21].
ATSDR could not identify an elevated incidence of cancer or prevalence of birth defects in Victor, Colorado, and surrounding communities in the 80860 zip code.
Public access to the mine is controlled by fencing and signs. The mine operates 24 hours a day, seven days a week, and discourages unauthorized access. There have been no trespassers noted by CC&V personnel in active surface mining or processing areas of the site.
ATSDR determined that CC&V is a No Apparent Public Health Hazard based on the intermittent ambient air levels of hydrogen cyanide, dust, and metals detected. ATSDR uses one of five conclusion categories to summarize our findings of the site. These categories are: 1) Urgent Public Health Hazard, 2) Public Health Hazard, 3) Indeterminate Health Hazard, 4) No Apparent Public Health Hazard, and 5) No Public Health Hazard. A category is selected from site specific conditions such as the degree of public health hazard based on the presence and duration of human exposure, contaminant concentration, the nature of toxic effects associated with site related contaminants, presence of physical hazards, and community health concerns.
Based upon the conclusions and information reviewed, ATSDR makes the following recommendations:
The actions described in this section are designed to ensure that this public health assessment identifies public health hazards and provides a plan of action to mitigate and prevent adverse health effects resulting from exposure to hazardous substances in the environment.
Actions Completed:
Action Ongoing:
Actions Planned:
Kimberly K. Chapman, MSEH
Environmental Health Scientist
ATSDR/DHAC/EICB/PRS
Technical Assistance:
Brian Kaplan, MS
Environmental Health Scientist
ATSDR/DHAC/EICB/HC
Peter Kowalski, MS
Environmental Health Scientist
ATSDR/DHAC/EICB/HC
Ken Orloff, PhD
Toxicologist
ATSDR/DHAC/EICB/EI
Greg Zarus, MS
Atmospheric Scientist
ATSDR/DHAC/EICB/EI
Reviewers of Report:
Donald Joe, PE
Section Chief
ATSDR/DHAC/EICB/PRS
Maurice West, PE
Deputy Branch Chief
ATSDR/DHAC/EICB
Review and approval of this public health assessment for Cripple Creek and Victor
Gold Mining Company
Concurrence:
Environmental Health Scientist, PRS, EICB, DHAC
Section Chief, PRS, EICB, DHAC
Branch Chief, EICB, DHAC
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