PETITIONED PUBLIC HEALTH ASSESSMENT
CRIPPLE CREEK AND VICTOR GOLD MINING
CRIPPLE CREEK, TELLER COUNTY, COLORADO
APPENDIX B: QUALITY ASSURANCE AND ATSDR METHODOLOGY
Quality Assurance
In preparing this report, ATSDR relied on the information provided in the referenced documents and by contacts with the Colorado Department of Public Health and Environment, community members, and CC&V. ATSDR assumes that adequate quality assurance and control measures were taken during chain-of-custody, laboratory procedures, and data reporting. The validity of the analyses and conclusions drawn in this document are determined by the availability and reliability of the information.
Human Exposure Pathway Evaluation and the use of ATSDR Comparison Values
ATSDR assesses a site by evaluating the level of exposure in potential or completed exposure pathways. An exposure pathway is the way chemicals may enter a person's body to cause a health effect. It includes all the steps between the release of a chemical and the population exposed: (1) a chemical release source, (2) chemical movement, (3) a place where people can come into contact with the chemical, (4) a route of human exposure, and (5) a population that could be exposed. In this assessment, ATSDR evaluates chemicals in the air that people living in nearby residences may consume or come into contact with.
Data evaluators use comparison values (CVs), which are screening tools used to evaluate environmental data that is relevant to the exposure pathways. Comparison values are concentrations of contaminants that are considered to be safe levels of exposure. Comparison values used in this document include ATSDR's environmental media evaluation guide (EMEG) and cancer risk evaluation guide (CREG). Comparison values are derived from available health guidelines, such as ATSDR's minimal risk levels and EPA's cancer slope factor.
The derivation of a comparison value uses conservative exposure assumptions, resulting in values that are much lower than exposure concentrations observed to cause adverse health effects; thus, insuring the comparison values are protective of public health in essentially all exposure situations. That is, if the concentrations in the exposure medium are less than the CV, the exposures are not of health concern and no further analysis of the pathway is required. However, while concentrations below the comparison value are not expected to lead to any observable health effect, it should not be inferred that a concentration greater than the comparison value will necessarily lead to adverse effects. Depending on site-specific environmental exposure factors (for example, duration of exposure) and activities of people that result in exposure (time spent in area of contamination), exposure to levels above the comparison value may or may not lead to a health effect. Therefore, ATSDR's comparison values are not used to predict the occurrence of adverse health effects.
The comparison values used in this evaluation are defined as follows: The CREG is a concentration at which excess cancer risk is not likely to exceed one case of cancer in a million persons exposed over a lifetime. The CREG is a very conservative CV that is used to estimate cancer risk. Exposure to a concentration equal to or less than the CREG is defined as an insignificant risk and is an acceptable level of exposure over a lifetime. The risk from exposure is not considered as a significant risk unless the exposure concentration is approximately 10 times the CREG and exposure occurs over several years. The EMEG is a concentration at which daily exposure for a lifetime is unlikely to result in adverse noncancerous effects.
Selecting Contaminants of Concern
Contaminants of concern (COCs) are the site-specific chemical substances that the health assessor selects for further evaluation of potential health effects. Identifying contaminants of concern is a process that requires the assessor to examine contaminant concentrations at the site, the quality of environmental sampling data, and the potential for human exposure. A thorough review of each of these issues is required to accurately select COCs in the site-specific human exposure pathway. The following text describes the selection process.
In the first step of the COC selection process, the maximum contaminant concentrations are compared directly to health comparison values. ATSDR considers site-specific exposure factors to ensure selection of appropriate health comparison values. If the maximum concentration reported for a chemical was less than the health comparison value, ATSDR concluded that exposure to that chemical was not of public health concern; therefore, no further data review was required for that chemical. However, if the maximum concentration was greater than the health comparison value, the chemical was selected for additional data review. In addition, any chemicals detected that did not have relevant health comparison values were also selected for additional data review.
Comparison values have not been developed for some contaminants, and, based on new scientific information other comparison values may be determined to be inappropriate for the specific type of exposure. In those cases, the contaminants are included as contaminants of concern if current scientific information indicates exposure to those contaminants may be of public health concern.
The next step of the process requires a more in-depth review of data for each of the contaminants selected. Factors used in the selection of the COCs included the number of samples with detections above the minimum detection limit, the number of samples with detections above an acute or chronic health comparison value, and the potential for exposure at the monitoring location.
APPENDIX C: ATSDR HYDROGEN CYANIDE MODELING
ATSDR used the Industrial Source Complex, Version 3 Short Term Model (ISC3ST) to estimate the air transport of HCN from the heap leach areas to locations people may live or visit. The ISC3ST model was run via a commercial interface called BREEZE ISC SUITE (Version 3.2.2) made by Trinity Consultants, Inc.
ATSDR used 1993 meteorological data collected onsite by the CC&V; the Colorado Air Pollution Control Division concurs that 1993 data are representative of a dataset.
The emissions data are based on the HCN emission rates were collected by CC&V in 1999 (Reference to Schmidt 1999-Leach System Cyanide Emissions Quantification, CC&V, Victor Colorado, April 24, 1999). Twenty-three samples were collected at the Cresson Valley Leach Facility, one replicate sample was collected at an older and inactive pad where the gravel is approved for use in the mining operations ("Pad 4"), and two replicate samples were collected from another inactive pad from which the cyanide compounds had been removed using bacteria ("Victor Pad"). The data for the valley leach facility represent areas undergoing leaching and those that are not (not all of the area is leached at any one time).
The data from the samples were grouped into 5 classes based on leach activity and location. Each group was treated as area sources. ATSDR simplified the area sources into squares with the center of each square the approximate center of the Cresson Valley Leach Facility.
The areas and average emission rates for each class were obtained from Card (1999). The average emission rates and square dimensions are shown below. The arithmetic averages were used because the data from the active leach areas were better represented by a normal distribution as indicated by skewness and kurtosis.
1) Phase 1 Active Leach Area,
4.13e-7 µg/s/m2
366 meters by 366 meters
2) Phase 2 Active Leach Area,
4.13e-7 µg/s/m2
394 meters by 394
3) Cresson Valley Inactive Leach Areas,
8.18e-9 µg/s/m2
305 meters by 305
4) Pad 4, and
8.18e-9 µg/s/m2
236 meters by 236 meters
5) Process Tanks
5.28e-6 µg/s/m2
27 meters by 27 meters
Although the areas are represented in the model by square, the source are actually comprised of a patchwork quilt of dry (inactive) and wet (active) areas that are mixed differently as time changes). If adequate data were available to assign individual emission rates to areas undergoing leaching for different periods, as well as areas in which leaching had not taken place for various periods of time, the source term would be better represented.
For this analysis, ATSDR assumed that Pad 4 was located at the Cresson Valley Leach Facility although it is located north of Victor. This assumption would produce slighter higher simulated ambient concentrations and is considered conservative for this screening analysis (i.e. produces a false positive).
For the ISC3ST model, we included complex terrain and a decay factor for HCN. The complex
terrain algorithms require United States Geological Survey (USGS) digital elevation models
(DEM). The DEM was obtained from the USGS website
(http://edcwww.cr.usgs.gov/glis/hyper/guide/usgs_dem#7m7) 
.
The decay factor, as measured by the half life, was obtained from ATSDR (Cyanide Toxicological Profile [Cyanide (Update) (PB/98/101207/AS) ]. The reported atmospheric half-life based on hydroxyl radical reactions for HCN range from 1.4 to 2.9 years. ATSDR used 1.4 years. Because of the relative size of the study area compared to the half life and area modeled, the decay of the HCN did not reduce the air concentrations. Although ATSDR used 1.4 years for modeling purposes, HCN breakdown may be greater due to processes other than hydroxyl radical reaction including (Smith et al 1991):
Removal by precipitation events
Since these process have not been quantified, ATSDR was not able to include greater degradation rates.
The model was run with the rural setting option.
References for Appendix C Hydrogen Cyanide Modeling
Rogers, Felix, J., George G. Killough, Shirley J. Thompson, Cheryl L. Addy, Robert E. McKeown, and David J. Cowen. Estimating environmental exposures to sulfur dioxide from multiple industrial sources for a case-control study, Journal of Exposure Analysis and Environmental Epidemiology, November-December 1999 (Volume 9, Number 6), 535-545.
Card 1999. Memorandum from Tom Card, Environmental Management Consulting to Mason Estes, Cripple Creek & Victor Gold Mining Company regarding Cyanide Emissions Assessment, April 25, 1999.
Card, Thomas R., and Charles E. Schmidt, 1999. Leach System Cyanide Emissions Quantification, Cripple Creek and Victor Gold Mining Company, Victor Colorado, April 24, 1999.
Machovec 1998. Memorandum from Chuck Machovec to Chip Hancock, Colorado Department of Public Health and Environment, Air Pollution Control Division regarding the Cripple Creek and Victor Cresson Mine - National Ambient Air Quality Standards Compliance Issues, November 16, 1998.
Smith, Adrian and Terry Mudder, 1991, The Chemistry and Treatment of Cyanidization Wastes, Mining Journal Books Limited.
Table 1. Completed Exposure Pathway
| Pathway Name | Source | Medium | Route of Exposure | Point of Exposure | Receptor Population | Time | Exposure Activities | Chemicals of Concern |
| Ambient Air | Unknown | Air | Inhalation | Off-site | Residents | Past, Current, Future | Normal Daily Activities | PM10 |
Table 2. Potential Exposure Pathway
| Pathway Name | Source | Medium | Route of Exposure | Point of Exposure | Receptor Population | Time | Exposure Activities | Chemicals of Concern |
| Ambient Air | Unknown | Air | Inhalation | On and off-site | Workers and Residents | Future | Working and Normal Daily Activities | Hydrogen Cyanide |
Response to Public Comments
ATSDR issued a draft for the public comment petitioned public health assessment on June 14, 2000 for the Cripple Creek and Victor Gold Mining site. Between June 14, 2000, and August 15, 2000, the public had the opportunity to provide comments on the draft public health assessment. During that time, ATSDR received written comments and questions from the Colorado Department of Public Health and Environment (CDPHE), Cripple Creek and Victor Gold Mining, and community members. These comments/questions are presented below. Each italicized comment is followed by a response from ATSDR.
Colorado Department of Public Health and Environment
Comment: The Air Pollution Control Division (APCD) generally agrees with the ATSDR's assessment of CC&V is an indeterminate public health hazard. Gaps in air monitoring data and modeling uncertainties require that additional study (ambient air monitoring) be conducted to provide a definitive answer to the human health hazard questions.
Response: ATSDR has responded to the specific comments presented below and has made changes to the public health assessment as appropriate in response to APCD.
Comment: A more thorough and careful discussion regarding hydrogen cyanide reference based concentrations and risk is needed for a final report. The June 14, 2000 public health assessment does not mention risk-based concentrations or any health guidelines for hydrogen cyanide exposures.
Response: ATSDR typically uses modeling results as predictors of environmental conditions, not predictors of public health impact. On page 7, public health guidelines are mentioned, but not detailed. To compare modeled data to health-based concentrations and exposure guidelines is misleading because of the potential inaccuracy of the modeling results. The ambient hydrogen cyanide (HCN) concentrations predicted by the ISC3ST model are below all state HCN regulations and guidelines (all states who have defined these). However, ATSDR cannot use these modeling data to evaluate potential human health problems. Once ambient air concentrations of HCN are collected and confirmed, ATSDR can evaluate if these levels are of health concern by considering site-specific exposure scenarios, health-based comparison values, epidemiological data, and health studies referenced in scientific literature.
Comment: ATSDR should ascertain that there are no decimal errors in the text, with respect to concentrations of HCN discussed on page 7 of the report, e.g., 0.015 mg/m3, 0.15 mg/m3, 1.5 mg/m3, and 15 mg/m3.
Response: There is a potential uncertainty level of two orders of magnitude when using the ISC3ST to predict ambient air concentrations of chemicals (as described on page 7). The two orders of magnitude refers to the entire range of values, not just the upper and lower end. All models used to predict environmental conditions have uncertainty factors. Accounting for this uncertainty factor, the predicted 24-hour maximum HCN concentrations could range 0.15 to 15 µg/m3. The predicted annual average HCN concentrations could range from 0.015 to 1.5 µg/m3. Several states use guidelines and regulations for 24-hour averages ranging from 40 to 250 µg/m3 [1]. Two states have guidelines for annual averages of 5 and 20 µg/m3 [1].
Comment: The data validation draft of the public health assessment reviewed on May 25, 2000 indicates that EPA's risk-based concentration (RBC) for HCN is 3.1 mg/m3. Several of the projected levels cited are of concern. We note that a sizable portion of the uncertainty range for predicted HCN concentrations exceeds the EPA's RBC. It should also be noted that 1.5 mg/m3 -the projected 24-hour maximum at the western edge of Victor- is one half of the RBC. This is significant in view of the fact that CC&V operators have requested they be allowed to double the size of their operations. It is anticipated that the operators will double the size of the heap leach pit, using roughly twice the amount of HCN as is used today. This could cause ambient HCN concentrations to double- potentially hitting the 3.1 mg/m3 RBC level.
Response: EPA's RBC of 3.1 mg/m3 was not included in the public health assessment (public comment draft) because this concentration is considered acceptable based on a lifetime exposure (i.e., 70 years) to HCN. The models used for estimating HCN levels near CC&V generated a 24-hour maximum and an annual average. Comparing a long term (chronic) exposure level to estimated short term (acute) exposure levels is inappropriate. Also, relating modeling results to "risk levels" is inappropriate because of the uncertainty in the modeling results. RBC values are also derived by incorporating uncertainty factors (anywhere from a factor of 10 to 1000) into them based on data extrapolations from relevant human and animal toxicity studies. In the case of hydrogen cyanide, EPA applied a 1,000-fold uncertainty factor to worker-related cyanide exposure studies and derived a reference concentration (similar to the RBC) of 3 µg/m3 for chronic exposure to cyanide in air.
Upon receiving ambient air HCN results, ATSDR will evaluate appropriate health guidelines and toxicological and epidemiological studies to determine the possibility of adverse health effects occurring from HCN exposure.
Comment: In light of the operators' recent request to double the size of operations at CC&V Gold Mine, the APCD recommends continuous monitoring for hydrogen cyanide to begin as soon as feasible. Monitoring for HCN should continue through CC&V's expansion period, and beyond throughout its operating years.
Response: This is a direct recommendation from APCD to CC&V; ATSDR cannot comment on this recommendation until ambient HCN concentrations are quantified.
Comment: Within the town of Victor, CC&V has monitored with small-volume samples that are not EPA reference method samplers. Because this is where human exposures are likely to occur, the APCD recommends that in addition to conducting HCN ambient air sampling (ATSDR Recommendation No. 2, page 10), the agency monitor for PM-10 using EPA reference method samplers, sited per EPA guidance in the town.
Response: It should be noted that high volume samplers have been used since 1993 to measure PM10 levels on- and off-site. The mini-volume samplers are voluntarily used by CC&V as supplemental PM10 measurements.
ATSDR often uses mini- and medium-volume pumps to measure dust in residential areas to determine if a health threat exists. These samplers are quieter, portable, easier to move, and use less electricity (or can run on a battery pack) than the high-volume samplers. In some cases, they may be preferred over high-volume samplers to evaluate the public health impact because they can be operated easier in residential areas or inside homes. The method is recommended by the National Institute for Occupational Safety and Health (NIOSH) (#0600) for occupational monitoring but can be adjusted to measure a longer time period. To use this method for making a health determination, it is essential that sufficient volumes of air are collected so the detection levels are appropriate. CC&V added two mini volume samplers to measure PM10 in Victor and on-site (Bateman Creek). In the past, five on-site high-volume samplers were actively measuring PM10 levels. Currently one on-site high-volume sampler near Victor is active (Rigi). The results received from these pumps combined are adequate to evaluate if a potential health impact from dust exists.
Comment: The APCD believes that with filter pad analyses we could establish whether in-town PM is largely reintrained road dust (as we suspect, and as is the case in Cripple Creek), or whether it may consist of mined materials, e.g., if it had a larger metals component.
Response: Such correlations would only be possible if someone sieved the dust and soil samples to the same sized particles. If the metals and the dust are not a problem, no one is needed to sieve. It is expensive and the results would not produce any public health action.
Comment: The statement is made that, "PM10 has been monitored weekly from 1993 to 1999." This is technically incorrect. The CDPHE commenced sampling 1994 on an every-sixth-day frequency. In 1995 this was changed to every-day frequency.
Response: On April 7, 1999, CDPHE provided ATSDR with 1993 PM10 monitoring results (every-sixth-day) for the south monitoring site for the CC&V project. However, page 5 has been modified to reflect the correct monitoring regime.
Comment: In the same paragraph mention should be made of the annual PM10 NAAQS, which is an annual average standard of 50 mg/m3. The ATSDR should provide annual average concentration data to compare with this standard.
Response: ATSDR states the annual average NAAQS on page 5. Of the data that ATSDR have, the only monitoring station that slightly exceeded the NAAQS annual average was the 1995 Cripple Creek sampling location (Bennet Avenue and 2nd Street) at 51.5 µg/m3. This is because the PM10 concentration peaks detected in December of that year are believed to be from the road sanding. All other annual averages were below the NAAQS.
Comment: Regarding Page 6, the first paragraph uses forms of the word exceedance three times. To conform to EPA usage, the word should be spelled "exceedance."
Response: The document has been modified to conform with EPA usage.
Comment: On page 6, the statement "The cause(s) of particulate matter exceedances in the town of Cripple Creek in December 1995 through February 1996 are from excess road sanding... (and)... do not appear to be related to mining activities because of the distance between the mine and Cripple Creek (approximately 15 miles) (sic) and the monitoring locations located at the mine did not pick up high levels of PM10." The mining area is extensive. The closest edge of the mine is only about 1 mile from Cripple Creek. The nearest active mining areas are about 500 ft above town and hidden by steep, complex terrain. As part of the State permitting process, dispersion modeling has been done to estimate the mine's impact on the town of Cripple Creek. Modeling for a permit in 1998 suggests impacts from the mine range from about 5 to 13 mg/m3 in town on the worst day. Proposed modifications for a revised permit in May 2000 suggest impacts in town might increase from 5-13 mg/m3 to about 13-27 mg/m3 on the worst day. The maximum impacts from the mine will not necessarily occur on the same day as maximum local PM10 concentrations in Cripple Creek. The modeled impacts in Cripple Creek were estimated with a steady-ste Gaussian model (ISCST3). Thus, because of complex meteorology and terrain, the model estimates contain significant uncertainty at receptors in the town of Cripple Creek. The model probably tends to overestimate actual impacts in Cripple Creek.
Response: ATSDR inquired of the active surface mining area during the PM10 peaks December 1995 through February 1996 and verified it was approximately one mile from the Cripple Creek city limit. ATSDR appreciates APCD's correction and changed page 5 to note the correct distance. However, there is sufficient evidence that the peak PM10 levels are primarily attributed to sources other than surface mining. The prevailing wind direction is northwest from Cripple Creek toward the mine. No other PM10 peaks were detected other than during the road sanding events even though surface mining continued.
Comment: Regarding the statements, "The PM10 exceedance detected from the on-site monitoring station (Range View) in September 1999 was from a motor vehicle hill climb race.... This maximum onsite PM10 concentration was twice the NAAQS PM10 standard..."
The onsite exceedance level (183 mg/m3) is not twice the level of the PM10 standard. (In December 1995 there was an exceedance in the City of Cripple Creek that was twice the standard.) We note again that at its closest point, the City is only one mile from the mine. Depending on wind direction, the mine could affect the municipalities, just as reintrained road dust from Victor or Cripple Creek could affect PM10 levels at the mine site.
Response: This correction was applied to page 5.
Comment: ATSDR could clarify its discussion regarding metals by inserting a table that shows the background levels, levels on site, and human health guidelines.
Response: Since there are only three metals discussed in this section, describing the levels detected and the typical background levels in the text instead of a table provides sufficient technical information.
Comment: Regarding page 7. The statement, "The state has also compared ISCST3 results with air monitoring for particulates at the mine and found in one case (emphasis added), the model overpredicted the particulate concentrations by a factor of 3.7."
The statement that the model overpredicted by a factor of 3.7 implies too much certainty about the model evaluation method. The model evaluation method was casual and not statistically robust. It would be more accurate to say that "The state has also compared ISCST3 results with air monitoring for PM10 at the mine and found in one case that the ISCT3/AP-42 modeling system appears to have overpredicted PM10 concentrations by as much as a factor of three."
Response: ATSDR has changed the text as suggested.
Comment: Regarding page 9. The birth defects statistics seem high intuitively (18%). Additional discussion regarding birth defect types seen, rates elsewhere-both in similar and dissimilar areas, and any known contributing factors is needed here.
Response: Health outcome data were analyzed and provided to ATSDR by CDPHE under a cooperative agreement. There were 18% of the children born in this time frame were reported as having one or more eligible conditions (such as low birth weight, prematurity, young maternal age). There were actually about 10% of children diagnosed with major congenital anomalies (e.g., significant cardiac, cognitive or developmental effects). 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). These details have been added to the public health assessment. The health outcome data were reported on February 23, 2000 in a health consultation titled "Cancer Incidence and Birth Defects Prevalence, Victor, Teller County Colorado."
Cripple Creek & Victor Gold Mining Company
Comment: A Note of Explanation: This page appears to be boilerplate language to explain the health assessment process. One concern identified was usage of the phrase "potentially responsible parties," which is a term-of-art under the Comprehensive Environmental Response, Compensation, and Liability Act ("CERCLA"). 42 U.S.C. §§ 9601 et. seq. The primary focus for the Agency for Toxic Substances and Disease Registry ("ATSDR") is to perform health assessments for sites designated under CERCLA to the National Priorities List ("NPL"). See 42 U.S.C. § 9604(i)(6)(A). Beyond this primary focus, the ATSDR may perform health assessments as requested by individual persons or licensed physicians under certain circumstances. See 42 U.S.C. § 9604(i)(6)(B). The health assessment performed of the CC&V operations was not of a site on or nominated for inclusion on the NPL; rather, the assessment was performed at the request of an individual person or persons. As such, an uninformed reader could get the incorrect perception about CC&V's mining operation in light of the reference to "potentially responsible parties" and its relation to CERCLA. We request that ATSDR either delete reference to "potentially responsible parties" or provide clarification so that the public is not misinformed about the health assessment and realizes that CC&V's operation is neither on, being considered for inclusion, or nominated to the NPL.
Response: The standard language used in the section entitled, " The ATSDR Pubic Health Assessment: A Note of Explanation", is applicable to all public health assessments prepared by ATSDR, both NPL and non-NPL sites. The CERCLA legislation authorizing public health assessments does not restrict ATSDR public health assessments to NPL sites. Instead, the legislation clearly mandates ATSDR to respond to licensed physicians and individual persons concerned with human exposure to hazardous wastes from many types of sites which can include active mining operations not on the NPL. ATSDR does not believe a change is needed in the section.
Comment: Forward: This page appears to be boilerplate language to provide background on ATSDR. One concern identified was reference to "hazardous waste sites" in the first and second paragraphs. As noted above, ATSDR conducts health assessments in two instances: site on or being nominated to the NPL or site request by an individual person or licensed physician. A site on the NPL would be a "hazardous waste site." However, a site requested for consideration by an individual person or licensed physician is not automatically a "hazardous waste site" merely because ATSDR conducts a health assessment. Moreover, and most importantly in this instance, CC&V's operation is not a "hazardous waste site." We request that ATSDR either delete reference to "hazardous waste site" or provide clarification so that the public does not get the incorrect perception about CC&V's operation.
The second paragraph of the Forward again refers to the NPL. As indicated under the comments in the previous section, the health assessment performed of the CC&V operations was not of a site on or nominated for inclusion on the NPL; rather, the assessment was performed at the request of an individual person or persons. As such, an uninformed reader could get the incorrect perception about CC&V's mining operation in light of the reference to the EPA NPL. We request that ATSDR either delete reference to the NPL or provide clarification so that the public is not misinformed about the health assessment and realizes that CC&V's operation is neither on, being considered for inclusion, or nominated to the NPL.
Response: ATSDR has modified the Foreword.
Comment: Summary: It is noted on page 1 that "[t]he local drinking water supply does not appear to be impacted by mining activities" (underline added by us). We believe that the more correct statement is that the "local drinking water supply is not impacted by CC&V's mining activities." As correctly noted on page 8 of the document, the Victor municipal water supply originate from three watershed sources: East Fork of West Beaver Creek, Bison Creek, and Boehmer Creek. More specifically, the water supply is derived from two reservoirs that are up-gradient and quite some distance away from CC&V's mining operation. Water is conveyed from the reservoirs to Victor via a 12-inch diameter pipeline with no potential influence from the mining operations. As such, we request that ATSDR modify this sentence as suggested above so that the public is not inappropriately and incorrectly informed about this critical matter.
Response: ATSDR has changed the text as suggested. Text in the Drinking Water section of this document has also been changed to the same affect.
Comment: Purpose and Health Issues: The forth sentence of the introductory paragraph starts with "Community members are concerned..." This statement is factually incorrect. We understand that the health assessment was requested by an individual person or, at most a couple of persons. The health assessment was not requested by the entire populous of the City of Victor or by its duly elected civil leaders. As such, we request ATSDR to revise this sentence by changing "community members" to "the petitioner" or "some community members" (as is factually correct) to avoid this factual inaccuracy. A similar request applies to the last sentence of the introductory paragraph. Please replace "community health concerns" with health concerns raised by the petitioner" in the last sentence.
Response: ATSDR concurs with CC&V's first recommendation and has changed the text accordingly. However, regarding the second recommendation, ATSDR believes that "community health concerns" is accurate when describing the health concerns voiced by several community members in a representative manner.
Comment: Site Background: The second sentence states: "This mining district contains over 500 mining and ore processing sites scattered over a 30 square mile area." Those readers unfamiliar with the Cripple Creek Mining District may not realize that CC&V's operations are the only active mining presently occurring in this District. As such, CC&V requests that the second sentence be revised as follows: "During the 110 year history of this district, over 500 different mining enterprises have existed, with the CC&V activities being the only active operation at the present time."
Response: ATSDR revised the text to reflect CC&V as the present sole mining operation.
Comment: Mining Operations (pages 2-3): The first full sentence at the top of page 3 should be revised for accuracy as follows: "Approximately 50,000 tons of ore and 85,000 tons of overburden are mined each day[2]."
Response: ATSDR changed the text as suggested.
Comment: Mining Operations (pages 2-3): The third sentence of the first full paragraph on page 3 should be revised for clarity as follows: "This leaching of gold takes place outside in a "valley leach facility" (Appendix A) that has been constructed in a valley that has been double- and triple-lined [2]." This change reflects addition of the word "double" and deletion of the word "bathtub".
Response: ATSDR changed most of the text as suggested. However, this sentence is further clarified by explaining that the valley leach facility is either double- "or" triple-lined (instead of "and") depending on its use.
Comment: Mining Operations (pages 2-3): The sixth sentence of the first full paragraph on page 3 should be revised for clarity as follows: "The dilute sodium cyanide solution moves through the ore toward the bottom of the lined facility and dissolves gold and other metals to form their metal compounds in solution." This change reflects insertion of the word dilute to properly qualify the solution being used by CC%V, replacement of the word "bathtub" with "lined facility", and substitution of "dissolves" for "exchanges sodium with".
Response: ATSDR modified the text to more accurately describe that water is added to a solid form of sodium cyanide to yield a solution. It is this sodium cyanide solution that is applied to the ore to leach (or dissolve) the metals out of the ore.
Comment: Mining Operations (pages 2-3): The tenth sentence of the first full paragraph on page 3 should be abbreviated as follows "The solution is contained within the pore space of the ore until it is pumped into the ADR facility [2]." This change reflects deletion of "There are no external ponds for the hydrogen cyanide leach solution," which is accurate with the deletion of the word "hydrogen," for the current operations but unnecessary in the context of this sentence and the report.
Response: ATSDR has changed the text as suggested.
Comment: Mining Operations (pages 2-3): The third sentence of the second full paragraph should be revised by replacing the word "solution" with "solid".
Response: ATSDR has changed the text as suggested.
Comment: Environmental Investigations (page 3): The fifth sentence of the last paragraph on page 3 notes that "Teller County and the city of Victor regulate noise, wastewater disposal (i.e., septic tanks), water supply, and blasting.: This sentence is factually incorrect as related to the City of Victor and CC&V's mining operation. CC&V's operation is wholly within unincorporated Teller County, and subject to applicable regulations related to land use activities as adopted by Teller County. CC&V has a contractual arrangement with the City of Victor to purchase water from the City; however, this contractual arrangement does not provide the City with any regulatory authority over CC&V's mining operation. Teller County regulates noise, wastewater disposal (i.e, septic tanks), and blasting, the latter only to the extent not already regulated by the State of Colorado. We request that ATSDR modify the specified sentence to delete reference to the City of Victor to avoid this factual inaccuracy.
Response: ATSDR has modified the text accordingly.
Comment: Environmental Investigations (page 3): The eighth sentence of the last paragraph on page 3 references "mine tailing pile" in relation to CC&V's mining operation. This is factually incorrect. "Tailing" is a term-of-art related to residual material from a mill. CC&V has never operated a mill from which tailing material would be produced. CC&V conducts surface mining activities with overburden placed in engineered overburden storage piles and ore transported to the lined Mining District at least 50 years ago, which significantly pre-dates CC&V's activities in the District. We request that ATSDR modify this sentence to delete reference to "mine tailing pile" to avoid this factual inaccuracy (and correct a similar statement on page 4 under "COMMUNITY HEALTH CONCERNS").
Response: ATSDR has modified the text as suggested.
Comment: Environmental Investigations (page 3): The eighth sentence of the last paragraph on page 3 references "mine tailing pile" in relation to CC&V's mining operation. This is factually incorrect. "Tailing" is a term-of-art related to residual material from a mill. CC&V has never operated a mill from which tailing material would be produced. CC&V conducts surface mining activities with overburden placed in engineered overburden storage piles and ore transported to the lined Mining District at least 50 years ago, which significantly pre-dates CC&V's activities in the District. We request that ATSDR modify this sentence to delete reference to "mine tailing pile" to avoid this factual inaccuracy (and correct a similar statement on page 4 under "COMMUNITY HEALTH CONCERNS").
Response: ATSDR has modified the text as suggested.
Comment: Community Health Concerns: The last sentence of the first full paragraph on page 4 references that the "community is concerned" about potential impacts of CC&V's mining operation to drinking water. This statement is factually incorrect. As previously noted above, we understand that the health assessment was requested by an individual, or at most, a couple of persons; the health assessment was not requested by the entire populous of the City of Victor or by its duly elected civic leaders. We request that ATSDR revise this sentence by deleting "community is" and inserting "a community member is" or "some community members are" (whichever is factually correct) to avoid this factual inaccuracy (and correct a similar statement in the second sentence of the carry-over paragraph at the top of page 5).
Response: ATSDR has modified the text on page 4. Within the context of page 5, "community concern" does not imply the entire community.
Comment: Community Health Concerns: The last sentence of the second full paragraph on page 4 notes that communities, such as the City of Victor, "can choose more stringent local noise codes with public health and welfare as their basis for noise control." The sentence is factually incorrect as applied to CC&V's mining operation. CC&V's operation is wholly within unincorporated Teller County, and subject to applicable regulations related to land use activities as adopted by Teller County. Teller County regulates noise related to CC&V's mining operation; the City of Victor has no regulatory authority over CC&V's mining operation since it only can regulate those activities within its jurisdiction. We request ATSDR delete the last sentence of the second paragraph on page 4 to correct this factual inaccuracy.
Response: ATSDR modified this sentence in the Community Health Concerns section to refer citizens to Teller County for concerns regarding noise levels.
Comment: Air Discussion: The fourth sentence of the last full paragraph on page 5 states "[s]ome metals were also monitored on CC&V property from 1993 to 1996." The report notes on page 6 that such sampling occurred from 1994 through 1996. The metals sampling conducted by CC&V occurred from 1993 to 1996, and was discontinued upon approval by the Colorado Department of Public Health and Environment (CDPHE), Air Pollution Control Division (APCD) after this governing regulatory agency determined that low metals concentrations observed in collected samples did not warrant continuation of this monitoring program. We request that ATSDR revise the document so that metal sampling is noted as occurring from 1993 to 1996.
Response: ATSDR changed the text as suggested.
Comment: Air Discussion: The sixth sentence of the last full paragraph on page 5 notes an alleged exceedance of the PM10 standard in September 1999 and provides additional information on this matter in the first full paragraph on page 6 noting that the "PM10 exceedance detected from on-site monitoring station (Range View) in September 1999 was from a motor vehicle climb race that occurred on one of the roads at the mine near this monitoring station" (underline added by us). This discussion is factually incorrect. CC&V's Range View monitoring station recorded and apparent exceedance of the PM10 daily standard in September 1999. The apparent exceedance was caused by a road race that occurred on a Teller County dirt road adjacent to CC&V's mine site and near the monitoring station. The CDPHE investigated this matter and concurred that there was no exceedance of the PM10 daily standard due to CC&V's mining activities. The high reading was solely related to the vehicle race on the adjacent County road. We request that ATSDR correct this factual inaccuracy by replacing the clause underlined above with "...on Teller County Road 84"."
Response: ATSDR changed the text as suggested.
Comment: Air Discussion: In the forth sentence in the first paragraph on page 6 states: "This maximum on-site PM10 concentration was twice the NAAQS PM10 standard...". This statement is factually incorrect. The PM10 value recorded on the day of the vehicle race in September 1999 was 183 mg/m3. This value is about 22 percent higher than the applicable 150 mg/m3 24-hour NAAQS. As such, CC&V requests that the word "twice" be replaced with "...about 22 percent higher than..."
Response: ATSDR has modified this statement.
Comment: Air Discussion: The seventh sentence of the last full paragraph on page 5 notes that several high PM10 readings were recorded in the town of Cripple Creek and provides additional information on this matter in the first full paragraph on page 6 noting that the "cause(s) of particulate matter exceedances in the town of Cripple Creek in December 1995 through February 1996 are from excess road sanding during these months to control ice [10]. The exceedances do not appear to be related to mining activities because of the distance between the mine and Cripple Creek (approximately 15 miles) and the monitoring station located at the mine did not pick up high levels of PM10" (underline added by CC&V). This discussion is factually incorrect. CC&V's mining activities are not 15 miles from Cripple Creek. During the references period, CC&V's mining activities in the Main Cresson Mine and stored overburden material in the Arequa Gulch overburden storage area and Ironclad/Globe Hill surface mine areas as backfill. The distance between the Main Cresson Mine and Cripple Creek during this time period was approximately 1.7 miles, the distance between the overburden storage area in the Arequa Gulch and Cripple Creek was approximately 2.2 miles, and the distance between the Ironclad/Globe Hill backfill area and Cripple Creek was almost one mile. Moreover, the predominant air flow is from Cripple Creek towards CC&V's mining operation. Enclosed are wind direction frequency distributions indicating that the predominant air flow is from the north-northwest to south-southeast, that is, from Cripple Creek towards CC&V's mining operation. Also, CDPHE investigated the cause of PM10 exceedances in Cripple Creek and identified street sanding during winter months and unpaved roads during other months as causes for dust; CDPHE has not identified CC&V's mining operation as a contributing factor in light of the relevant facts. We request that ATSDR correct these factual inaccuracies and specify that the exceedances "are not related" to CC&V's mining activities.
Response: ATSDR has modified this statement.
Comment: Hydrogen Cyanide Discussion: The first sentence in the first paragraph on page 7 should have "... to determine if..." inserted between the words "concentrations" and "nearby".
Response: This is the sentence the previous comment addresses: "ATSDR estimated HCN air concentrations nearby residents could be exposed from the heap leach emissions at the Cresson Valley Leach Facility." ATSDR actually did estimate HCN concentrations in residential areas that residents could be exposed to as the current sentence implies.
Comment: Hydrogen Cyanide Discussion: The forth and fifth full paragraphs on page 7 discuss modeling using ISC3ST. The document notes that actual monitoring data collected by CC&V reveals that the ISC3ST "overpredicted particulate concentrations by a factor of 3.7." However, the document next notes uncertainty of ISC3ST, with a reference to an article addressing sulfur dioxide, as two orders of magnitude, and then adjusts hydrogen cyanide concentrations applicable to CC&V's mining operation in the remainder of the document based on this perceived two orders of magnitude uncertainty. We believe that actual, site-specific data from our particulate matter monitoring should be used as the basis of evaluation, rather than using a generic level of uncertainty. The site-specific monitoring of particulate matter strengthens the factual accuracy of the document. Thus, we request that subsequent discussions highlighting the range of emissions based on this perceived two orders of magnitude be deleted and replaced by highlighting the range of emissions based on the overprediction by a factor of 3.7.
Response: ATSDR rechecked the reference [18] that stated the uncertainty of the ISC3 model in complex terrain is two orders of magnitude. The two orders of magnitude refers to the entire range of values, not just the upper and lower end. So, the 24-hour maximum concentration of 1.5 µg/m3 could range from 0.15 to 15 µg/m3.
ATSDR considered this comment taking into account site-specific factors and did not make any additional changes because:
The overprediction of the ISC3 model of 3.7 over that monitored is based on particulates while ATSDR's evaluation was studying gaseous HCN. The transport of particulates and gaseous pollutants are different because of particulate deposition. Hence a more generic uncertainty may be applicable.
The ISC3 model used for particulates was based on site specific emission factors. The uncertainty of the emission factors as applied to Cripple Creek is not known but contributes to the overall uncertainty. The uncertainty of the emission factors could offset uncertainty in the ISC3 model results. For example, a lower than actual emission factor could compensate for an overpredicting model. Therefore, the site-specific uncertainty factor may not be applicable to an application where emission factors are not applicable.
Comment: Drinking Water Quality: The third sentence of this section states that "Mining activities do not appear to have affected the local drinking water" (underline added by CC&V). As correctly noted in the first sentence, the Victor municipal water supply originates from three watershed resources: East Fork of West Beaver Creek, Bison Creek, and Boehmer Creek. More specifically, the water supply is derived from two reservoirs that are up-gradient and quite some distance away from CC&V's mining operation. Water is conveyed from the reservoirs to Victor via a 12-inch diameter pipeline with no potential influence from the mining operations. As such, we request ATSDR modify this sentence as by deleting the words "...do not appear to..." and adding the word "not" after the word "have" and before the word "affected".
Response: ATSDR has modified this statement.
Comment: ATSDR Child Health Initiative: The first sentence of the first paragraph refers to hazardous waste sites. As previously indicated, CC&V's operation is not a "hazardous waste site." We request that ATSDR either delete reference to "hazardous waste site" or provide clarification so that the public does not get the incorrect perception about CC&V's operation.
Response: ATSDR has modified this general sentence to include "industrial facilities".
Comment:Health Outcome Data: The first sentence of the first paragraph on page 8 states that "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". As written, this sentence implies that there is a more widespread concern than actually exists. We understand that the health assessment was requested by an individual person or, at most, a couple of persons. The health assessment was not requested by the entire populous of the City of Victor, or the surrounding communities, or by its duly elected civic leaders. As such, we request that ATSDR revise this sentence by adding the word "Some" before "residents" or replacing "Residents of Victor and surrounding communities …" to "The petitioner …".
Response: There are several residents with this common concern from Victor and other locations. ATSDR believes in this particular context, the sentence does not imply every resident in Victor and the surrounding communities.
Comment:Cancer Data: The last sentence of the first partial paragraph on the top of page 9 states: The CDPHE reported no significant increases for the rate of …" (underline added by CC&V). CC&V believes the word "differences" should be substituted for the word "increases" in this context, as occurs later on the same page.
Response: Health outcome data were prepared and analyzed by CDPHE. Observed versus expected statistical analysis of cancer incidence employed a two-tailed test. Therefore, it would be correct to say that "The CDPHE reported no significant differences for the rates...." The point of concern for communities, however, is whether rates are greater than expected, hence, "...significant increase for the rates..." Since a time-series analysis was not done, using the word "increase" does not in this context mean a rise in the rate. Although the use of the word may be considered "epi-jargon", for consistency and clarity, ATSDR used the word "increase" throughout the entire Health Outcome Data section.
Comment:Cancer Data: The last sentence of the first full paragraph on page 9 states: "Since specific environmental exposures and other health risk factors are not known, ATSDR …". CC&V believes the words "to exist" should be inserted after the word "known" and before "ATSDR".
Response: In the context of this sentence, all types of environmental exposures to chemical agents and environmental conditions are considered to be occurring or have occurred in the past to a certain degree (i.e., exposure to pesticides, cleaning agents, ultraviolet light, etc.). Individual health risks, such as poor diet, smoking, excessive alcohol consumption, and genetic probability to a certain disease, are also not known.
Comment: Conclusions: CC&V has been advised that the ATSDR is reluctant to base a health determination exclusively on air quality modeling information for hydrogen cyanide ("HCN"), hence the "Indeterminate Public Health Hazard" rating. However, when taken together, CC&V believes that the following factors should result in at least the "No Apparent Public Health Hazard" if not the "No Public Health Hazard" category being specified:
· the prevailing wind direction,
· the low level HCN emissions at the source,
· the low modeled HCN concentrations in Victor,
· the long distance to the nearest potential receptors,
· the tendency of the air quality dispersion models to over predict, and
· the known instability of HCN in the atmosphere.
CC&V understands that ATSDR is planning to conduct ambient air HCN sampling in the vicinity of Victor. Although direct measurements of targeted parameters in ambient air are typically preferred, CC&V is not aware of any reference method with detection limits sufficiently low to confirm the concentrations predicted in the dispersion modeling. As such, CC&V suggests that ATSDR use any sampling results in conjunction with the six factors itemized above in the final health determination.
Response: ATSDR will factor in all scientific and relevant information when making a final health conclusion regarding the CC&V site.
Comment:Public Health Action Plan:
Actions Completed - The term "gaseous" should be deleted under the second "bullet". The word "hot weather" should be replaced with "dry conditions"
Action Ongoing - The second word "are" should be replaced with "continues to" and "monitoring" changed to "monitor".
Response: ATSDR modified the text as requested.
Reference for Public Comment and Response Section
APPENDIX F: EXPOSURE INVESTIGATION: HYDROGEN CYANIDE SAMPLING
Background
On June 14, 2000, ATSDR released a petitioned Public Health Assessment (PHA) for the Cripple Creek and Victor Gold Mining Company in Victor, Colorado. The company mines and processes ore to extract gold and other precious metals. At the company's Cresson Valley Leach facility, a sodium cyanide solution is applied by drip irrigation tubes to piles of crushed ore to extract gold. If hydrogen cyanide gas (HCN) were released during this operation, it could migrate off site, and residents living in the area could be exposed to the chemical in ambient air. (The closest private residences are located about 3,500 feet from the edge of the leach field.) In the PHA, ATSDR noted that no ambient air monitoring data were available to assess the risk associated with potential exposures to hydrogen cyanide emissions from the facility. Therefore, the purpose of this Exposure Investigation (EI) was to collect ambient air monitoring data that could be used to assess whether residents in the area are being exposed to hydrogen cyanide at levels of public health concern.
Materials and Methods
Air sampling was conducted from October 10 to October 12, 2000. ATSDR used a combination of NIOSH methods 7904 and 6010 to monitor for ambient air hydrogen cyanide. Air samples were collected for six consecutive 8-hour periods using a personal sampling pump operated at a flow rate of about 1 liter/minute. Hydrogen cyanide in the air samples was trapped in a bubbler apparatus containing 15 ml of 0.1 N potassium hydroxide (KOH) (NIOSH method 7904). Before and after each sampling event, the air flow rate through the collection apparatus was measured using a primary standard (Gilian Gilbrator).
At the end of the 8-hour sampling period, the KOH solution in the bubbler was transferred to a glass vial. The bubbler was rinsed with 2 ml of 0.1 N KOH, and the rinsate was added to the sample vial. At the end of the 48-hour monitoring period, the samples were sent by overnight mail to DataChem (Salt Lake City) for analysis. The samples were analyzed spectrophoto-metrically for HCN as described in NIOSH Method 6010.
ATSDR collected ambient air samples at five locations: (1) 450 feet northwest of the leach field [NW-01], (2) 600 feet southeast of the leach field [SE-01], (3) 1,400 feet southeast of the leach field [SE-02], and (4) at two residential properties on the west edge of Victor. These private residences were located about 3,500 feet southeast of the leach field. The locations of the sampling points are depicted on the map in Figure 1. The exact locations of the sampling points were determined using a Global Positioning System.
Samples were collected every 8-hours for a period of 48 hours, which yielded 6 samples per sampling location. Because of air pump failures, sampling was limited to four 8-hour samples at the two private residences. One KOH field blank was collected at each sampling location.
ATSDR obtained local meteorological data for the sample periods from the Bateman meteorological station, which is located 1,800 feet south of the leach field.
Informed Consent
Prior to testing, ATSDR obtained the written, informed consent of the owners of the properties where the air monitoring devices were located.
Results
Hydrogen cyanide was not detected in any of the ambient air samples collected at two residential properties. The detection level for hydrogen cyanide in these samples ranged from 0.1 to 0.2 parts per billion (ppb), depending on the volume of the air sample. The two private residences were selected because they were among the homes in Victor that were closest to the leach field. The locations of the monitoring stations are shown in Figure 1.
Two of the on-site sampling locations (SE-01 and SE-02) were chosen to be between the leach field and the town of Victor. Another on-site sampling station (NW-01) was located on the opposite side (northwest) of the leach field. Low concentrations of hydrogen cyanide were detected in 6 of the 18 on-site air samples. Hydrogen cyanide was not detected in the other 12 air samples at a detection level of 0.1 to 0.2 ppb. A summary of the on-site air sampling data is presented in Table 1. As indicated, the quantifiable air concentrations of hydrogen cyanide ranged from 0.26 to 0.63 ppb.
At sampling station SE-01, the pump stopped sometime during one of the sampling periods. The estimated hydrogen cyanide air concentration from this sample (1.86 ppb) is the minimum possible concentration assuming that the pump operated for 8-hours and pumped 500 liters of air. The actual air concentration cannot be determined because the sample volume is not known. However, the estimated concentration seems reasonable, since the ratio of the hydrogen cyanide concentrations at stations SE-01 and SE-02 for this sampling period (05) is similar to the ratio detected during an earlier sampling period (02).
Discussion
Low concentrations of hydrogen cyanide were detected in ambient air samples collected at monitoring stations located 450 to 1,400 feet from the cyanide leach field. However, hydrogen cyanide was not detected at the two stations at private residences. These findings are plausible, since the private residences were further away from the leach field, and cyanide concentrations in air would be diluted with increasing distance from the source.
There is no National Ambient Air Quality Standard for hydrogen cyanide in air. However, the U. S. Environmental Protection Agency has derived a Reference Concentration (RfC) for hydrogen cyanide 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. Hydrogen cyanide was not detected in air samples from residential properties. Furthermore, the hydrogen cyanide concentrations detected in on-site air samples collected near the leach field for 8-hour periods were below the RfC. Therefore, none of the hydrogen cyanide concentrations detected in this investigation posed a public health hazard.
This conclusion is based on ATSDR's sampling over a 2-day period. The cyanide leach field operates continuously for 24 hours/day and 365 days/year. Therefore, ATSDR does not expect that there would be large day-to-day variations in cyanide release from the leach field. However, on-site and off-site hydrogen cyanide air levels could be significantly affected by wind direction and speed, precipitation, temperature, and other meteorological conditions. During ATSDR's sampling, the weather was cool (40-58 F) and dry. Winds were variable (5-19 mph), but predominantly blew from the northwest and west, that is, across the leach field toward sampling stations SE-01, SE-02, and the residential stations. Therefore, if there were significant emissions from the leach field, they would have been detected during the two days of sampling. Since only low concentrations of hydrogen cyanide were intermittently detected, ATSDR concludes that hydrogen cyanide emissions from the leach field do not pose a public health hazard under current operating conditions.
Conclusions
ATSDR did not detect hydrogen cyanide in ambient air samples collected from on-site and off-site residential locations at concentrations of health concern.
Recommendations
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 for on-site workers or off-site residents.
Prepared by:
Kenneth G. Orloff, Ph.D., DABT
Exposure Investigations Section
Exposure Investigations and Consultations Branch
Division of Health Assessments and Consultation
Peter J. Kowalski, CIH
Health Consultations Section
Exposure Investigations and Consultations Branch
Division of Health Assessments and Consultation
Reviewed by:
John E. Abraham, PhD
Branch Chief
Exposure Investigation and Consultations Branch
Division of Health Assessments and Consultation
Susan Metcalf, MD
Section Chief, Exposure Investigation Section
Exposure Investigations and Consultations Branch
Division of Health Assessments and Consultations
Table 1. Hydrogen cyanide (ppb) in ambient air samples from on-site monitoring stations
|
Station Number
|
|||
|
NW-01
|
SE-01
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SE-02
|
|
|
Sampling Time Period
|
|||
|
01
|
ND
|
0.51
|
ND
|
|
02
|
0.26
|
0.63
|
0.26
|
|
03
|
ND
|
ND
|
ND
|
|
04
|
ND
|
ND
|
ND
|
|
05
|
ND
|
>1.86*
|
0.60
|
|
06
|
ND
|
ND
|
ND
|
ND - none detected
(*) estimated value based on an assumption that the pump operated for 8-hours and pumped an air volume of 500 liters
Cresson Project Crushing Circuit
Crossection of Cresson Leach Facility
