AIR QUALITY

STANDARD OF REVIEW

According to the CBJ Mining Ordinance (49.65.135(a)), the CBJ shall require that:

Also, the Juneau Coastal Management Program (CBJ 49.70.955) incorporates the state air quality standards, as follows:

Thus, CBJ code does not provide specific air quality standards. Instead, the Mining Ordinance focuses on adverse health and environmental impacts, while relying on state air quality standards.

Air quality in Alaska is regulated by the Alaska Department of Environmental Conservation

(18 AAC 50) in accordance with standards and an implementation plan prepared by the state and approved by the U.S. Environmental Protection Agency (EPA). Air permits are issued by the Alaska Department of Environmental Conservation (ADEC).

This staff report analyzes the potential impacts that the Kensington Gold Project would have on air quality, proposed measures to control and to mitigate air impacts, and the extent to which air quality will be maintained in accordance with federal, state, and city and borough law. A separate staff report analyzes Dust Control.

BACKGROUND

Pollutant emissions are subject to two types of state regulatory controls. Air quality standards are established by regulation for conventional pollutants such as particulate matter and sulfur dioxide. These standards are limits on the total concentrations of pollutants in ambient air and are intended to protect public health and the environment. Air quality standards apply at the property boundary, and not within the confines of an industrial facility. Emissions limits are the maximum emissions allowed for a particular source. They are expressed as a weight per unit time ­ often tons per year ­ and apply at the source, such as a tailpipe.

Air emissions permit processing falls into one of two categories: Prevention of Significant Deterioration (or PSD), and non-PSD. The PSD process applies to "major sources," which are generally those that emit, or have the potential to emit, 250 tons per year or more of any single pollutant regulated by the Clean Air Act. The PSD permitting process requires extensive baseline monitoring, demonstrations of compliance with certain air quality limits and best available control technologies, and detailed analysis of expected impacts from the facility and associated growth. The non-PSD process is a less rigorous process demanding less in the way of baseline monitoring and applicant demonstrations, but still requires compliance with emissions and ambient air quality standards. As currently proposed, the Kensington Gold Project is not considered a major source of air emissions, and is subject to the non-PSD permitting process (ADEC, 1997a).

Permitting Status. The former Kensington Venture was first issued an Air Quality Control Permit to Operate by ADEC on July 1, 1991. That permit was succeeded by two other permits in 1992. Application for a modification of the last permit to reflect new operating plans ­ including dry tailings disposal and a change from propane-fired to diesel generators ­ was made in a document prepared by TRC Environmental Corporation for Coeur Alaska, Inc. dated Aug 7, 1996 (TRC, 1996). In responding to that application, ADEC issued a new permit on January 17, 1997 rescinding the old permit. The new permit authorizes air emissions from operations as currently proposed by Coeur.

ANALYSIS

Sources. The TRC application identifies ten types of emission sources, and a number of more specific sources within each type:

Mine Sources

Pollutants. The project includes stationary, mobile (vehicular) and fugitive (non-point) emission sources. Burning of fossil fuels, such as in diesel-fired generators or by trucks and other equipment, produces oxides of carbon, nitrogen, and sulfur; particulates; and a number of other combustion byproducts (Williamson, 1973). Oxides of nitrogen (NOX), primarily nitric oxide (NO) and nitrogen dioxide (NO2), can both contribute to the formation of photochemical smog. Nitrogen dioxide, however, is a toxic pollutant, and higher exposures can damage lung tissues. Sulfur dioxide (SO2) is also toxic and a pungent respiratory irritant. Carbon monoxide (CO), another toxic pollutant, is a result of incomplete combustion. Carbon dioxide is the gas released in the single greatest amount, and is thought to contribute (along with other gases) to the greenhouse effect.

Particulate emissions can result from both exhaust from fossil-fuel fired equipment, as well as dust from a number of proposed operations. Total particulate concentrations are often referred to as "total suspended particulates," or TSP. The fraction of smaller particulates -- those less than 10 microns in size -- are considered inhalable and have particular health significance. This smaller particulate fraction is often designated PM10. Particulates can have both health as well as visual impacts.

All of the pollutants discussed so far are considered "conventional," even though some are known toxicants. Non-conventional pollutants are often categorically referred to as "toxics." Toxics of interest include metals contained in inhalable dust, and volatile organic compounds (VOCs) released in vapors from fuel storage and fueling operations as well as in diesel exhaust. Some of these toxics are known carcinogens, and all can cause acute or chronic toxic effects.

Control and Mitigation. This section summarizes the applicant's proposed equipment and measures to control air emissions at the site. The following section -- Predicted Emissions -- summarizes the amount of air pollution expected from the equipment and activities. The section after that -- Air Quality Impacts -- addresses whether predicted emissions levels will comply with applicable state and federal air quality law. It is important to note that emssions standards and compliance efforts are considered as a whole. Determination of whether emssions will comply with standards is based on the total of all emissions and the sum of control measures to deal with them.

Coeur proposes to use selective catalytic reduction (SCR) -- or similar -- technology to control emissions of NOX from the four large (3300 kw) diesel generators (Final SEIS, page 2-26). The ADEC-permitted emissions levels reflect the use of SCR technology. SCR technology involves injecting ammonia (NH3) into the exhaust gas and passing the mixture over a catalytic bed to promote reduction of NOX to elemental nitrogen and water. According to ADEC, the use of such sophisticated controls on equipment of the proposed scale is unusually advanced (Stone, 1997). An 80 percent reduction in NOX emissions is predicted.

The original air quality modeling assumed that fuel injection timing retard (FITR) technology would be used to control emissions from a smaller (365 kw) generator located near Comet Beach. The modeling assumed the FITR technology would result in a 20 percent reduction in NOX emissions (TRC, 1996). The final SEIS preferred alternative now calls for a 275 kw generator.

Emissions from the proposed refuse incinerator will be controlled primarily by optimizing combustion conditions and limiting feed rates. Emission limits specified in the Air Quality Control Permit to Operate correspond to an annual average feed rate of 500 lbs of material per day, with a maximum of 2000 lbs in any single day.

Water spray, where an area is blanketed with a fine mist, will be used to control particulate emissions from coarse ore storage and transfer (conveyor, transfer to and from coarse ore stockpile, and apron feeder), and transfer to the SAG mill. A 90 percent reduction in emissions is projected (TRC, 1996).

Road surface water application will be used to control fugitive dust emissions from the haul road on dry, above-freezing days. Percent control efficiencies of 50 to 85 percent are expected (TRC, 1996). Limited vehicle speeds will also help to control dust. See the staff report on Dust Control for further discussion of this topic.

Baghouse-type dust collectors will be used to control particulate emissions from the primary crusher (including associated ore transfer processes), laboratory crushers, and lime and cement loading silos. Baghouse collectors either suck or blow particulate-laden air through bag-like filter membranes where dust is removed. Percent reductions in particulate emissions are projected at 90 to 99 percent (TRC, 1996).

The applicant proposes to control wind erosion from the dry tailings facility (DTF) by limiting the size of active, exposed areas, and establishing or maintaining non-eroding cover over inactive areas in accordance with the DTF operating plans. Residual tailings moisture content will also help to reduce erosion. For modeling purposes, it was assumed that one-third of the total 115-acre facility (38 acres) is exposed to wind erosion -- while the other two thirds have not been constructed, or have been stabilized.

In some cases, incidental control is also provided by operating conditions, such as wet conditions within the mine, and enclosure afforded underground operations.

Predicted Emissions. Given the equipment and controls described in the previous section, mathematical models were used to predict emissions associated with the Final SEIS preferred alternative during both construction and production phases of the mine project. A number of models were used to predict emissions from each of the sources identified in the previous discussion. Total emissions from all sources associated with the final SEIS preferred alternative (Alternative D) during production are predicted (in tons per year) as follows:

Predicted Emissions in Tons per Year (Production Phase)

Type TSP2 PM103 NOX4 SO25 CO6 VOC7 Pb8
Point 30.6 29.8 244.8 156.1 37.0 29.5 3.0 x 10-6
Fugitive1 77.6 50.4 358.9 35.2 154.4 29.2 3.0 x 10-6
Total 108.2 80.2 603.7 191.3 191.5 58.7 6.0 x 10-6

1Fugitive emissions are non-point or are area wide

2Total suspended particulates

3Particulate matter less than 10 microns in size

4Oxides of nitrogen.

5Sulfur dioxide

6Carbon monoxide

7Volatile organic compounds

8Elemental lead

Emissions during the construction phase are predicted to be substantially less than during the production phase. For example, total particulates are not expected to exceed 9 tons per year.

Air Quality Impacts. TRC used mathematical models to calculate impacts of predicted emissions on ambient air quality at the periphery of the facility where air quality standards must be met. The following table (Final SEIS, page 4-13, table 4-13) compares the predicted concentrations associated with the applicant's original proposal with state air quality standards. Pollutant concentrations resulting from the FSEIS preferred alternative were not modeled, but would be less than those shown due to elimination of sources associated with trucking tailings from the mill to the dry tailings facility.

Predicted Pollutant Concentrations

Pollutant Averaging

Period

 Background

Concentration

(µg/m3)

 Max Periphery

Concentration

(µg/m3)

 Air Quality

Standard

(µg/m3)
Nitrogen dioxide annual 41 20.8 100
Carbon monoxide 1-hour n/a3 365.2 40,000
  8-hour n/a3 99.2 10,000
PM10 24-hour 401 65.8 150
  annual 221 25.4 50
Sulfur dioxide 3-hour 1722 325.8 1,300
  24-hour 732 115.2 365
  annual 0 4.9 80

1Assumed by TRC based on ADEC recommendations

2Based on concentrations measured in Juneau

3Not available

The concentrations of conventional pollutants predicted by the models and shown in the above table meet state standards at facility boundaries.

Modeling was also conducted to determine potential exposure to metals in particulates associated with the applicant's original proposal. The calculations are based on the conservative assumption that the metal mass fraction of all particulates was that of the highly mineralized ore. In fact, most dust will derive from sources that do not have the high metals content of the ore. Since Alaska has not adopted standards for metals, the calculated concentrations were compared with the most restrictive of standards adopted by other states. (See following table at the top of next page.)

Predicted Metals Concentrations (all units are µg/m3)

  24-hour Annual
  Predicted Standard Predicted Standard
Zinc 0.0037 12.0 0.00024 6.55
Nickel 0.00053 0.002 0.00003 0.002
Arsenic 0.00053 0.39 0.00003 0.0002
Antimony 0.00106 8.0 0.00007 1.19
Chromium 0.00739 0.068 0.00048 0.07
Cadmium 0.00106 0.0056 0.00007 0.000435
Selenium 0.00021 0.27 0.000014 0.26
Mercury 0.00002 0.08 0.0000014 0.01
Barium 0.00053 8.0 0.00003 11.9
Manganese 0.0844 17.0 0.00542 0.24

The TRC analysis suggests that metals concentrations averaged over 24-hour and annual periods would meet the most stringent of standards of those states with standards. (Remember that Alaska does not have air quality standards for metals.) Due to elimination of sources associated with trucking tailings from the mill to the DTF facility, metals levels associated with the final SEIS preferred alternative would be somewhat less than those shown above.

With prolonged exposure, four of the metals, Nickel, Cadmium, Chromium and Arsenic, are believed to cause cancer. Using standard risk factors and some very conservative assumptions, TRC calculated a cancer risk of six deaths per one million people for a 70-year exposure to maximum predicted particulate metal concentrations. The TRC analysis points out, however, that the predictions should be viewed as overly conservative for several reasons. For example, the metal mass fraction of all particulates was assumed to be that of the highly mineralized ore. In addition, a person would have to be physically located outdoors at the place of maximum metals concentrations for a period of 70 years ­ well in excess of the expected mine life. In fact, staff conclude that the actual cancer risk would be far less.

Visual Impacts. The Final SEIS discusses visual impacts associated with predicted emissions. A screening model (VISCREEN) was used to predict visibility impacts due to particulates and nitrogen oxides. (A more thorough description of the overal Visual Management System used to predict and assess visual impacts from the overall mining operation is included in the staff report on Visual Resources.) Modeling from the standpoint of an observer aboard a cruise ship in the middle of Lynn Canal, and using worst-case meteorological conditions, showed "slight impact from some plume visibility." The Final SEIS concludes that impacts would be consistent with U.S. Forest Service visual quality objectives (VQOs). Staff has reviewed the methods used to evaluate visual impacts and finds the methods to be sound, and concurs with the SEIS conclusion that visual impacts from air emissions will be minimal.

Permit Conditions. Stipulations of the January 1997 Air Quality Control Permit to Operate issued by ADEC include:

a limit on the number and type of stationary sources to those identified by Coeur in the application and subsequent submittals;

overall compliance with state air quality standards and emissions limits;

limits on power production and exhaust conditions as derived using standard ADEC emission factors, or as set out in the application, whichever is most stringent;

a requirement that equipment be operated and maintained in accordance with manufacturer's suggested procedures;

a requirement that the permittee take "reasonable precautions" to control fugitive dust emissions from the ore dumping and crushing enclosure;

a requirement that a baghouse be operated to control emissions from the primary crusher during operation;

a requirement for annual inspection of the mill feed conveyor and water spray system with repair and replacement of components showing deterioration which may affect fugitive dust control efficiency;

a requirement for testing of one of the diesel generators within 180 days of start up to determine actual NOX and ammonia emissions;

requirements that the permittee control fugitive dust emissions;

requirements for monitoring and reporting of NOX (or surrogate) emissions, fuel consumption, power generation, equipment operating hours, ammonia concentrations in selective catalytic reduction exhaust, fuel sulfur content, water spray water consumption, pressure drop across the primary crusher baghouse, and quantities and types of incinerated wastes.

Discussion of Supplemental EIS Alternatives. Projected emissions from the Final SEIS preferred alternative (Alternative D) are less than those associated with the applicant's proposal (Alternative B) -- due to elimination of sources associated with trucking tailings from the mill to the dry tailings facility. Both the applicant's proposal and the SEIS preferred alternative result in greater emissions than the original wet tailings project configuration (SEIS Alternative A). Increases are due in large part to the proposed switch from gas turbine to diesel generators, as well as inclusion of new sources of particulate emissions, namely a generator at Comet Beach, the dry tailings facility, laboratory crushers, and the lime and cement silos.

Comparison of Projected Emissions (in tons per year)

Pollutant Projected Emissions

Alternative A

 Projected Emissions

Alternative B

 Projected Emissions

Alternative D
TSP1 33.3 159.0 108.2
PM102 23.6 103.1 80.2
NOX3 215.5 612.4 603.7
SO24 12.3 192.2 191.3
CO5 112.2 193.9 191.5
VOC6 14.0 59.1 58.7
Pb7 3.0 x 10-5 7.4 x 10-6 6.0 x 10-6

1Total suspended particulates

2Particulate matter less than 10 microns in size

3Oxides of nitrogen

4Sulfur dioxide

5Carbon monoxide

6Volatile organic compounds

7Elemental lead

STAFF FINDINGS

STAFF RECOMMENDATION

Staff recommends approval of this aspect of the project.

The applicant is advised that open burning during construction and operation shall be subject to the conditions of a CBJ Open Burn Permit, in accordance with CBJ 36.40.060.

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Last revised on 06/28/99 - bgb