Pay Online
Sign Up

Sulfur Dioxide (SO2) emissions at Intalco

Apr. 26, 2019

The Northwest Clean Air Agency is working with the Washington Department of Ecology, the U.S. Environmental Protection Agency’s Region 10 based in Seattle, and various stakeholders to bring sulfur dioxide (SO2) emissions from Alcoa’s Intalco aluminum smelter in Whatcom County in line with national air quality standards.

On Dec. 21, 2020, EPA designated a small portion of Whatcom County that includes the Intalco smelter as being in nonattainment of the federal standard.

The designated area is a 5.5-square-mile portion of the Cherry Point industrial area and the waters of the Strait of Georgia on the western shores of Whatcom County. The area encompasses the site of a now-defunct aluminum smelter, Intalco Aluminum LLC (Intalco). The Intalco smelter curtailed its operations in 2020 and permanently closed in 2023. Prior to that, SOemissions from the smelter’s processes caused the violation of the health-based national air quality standard.

Ecology is the environmental permitting agency for smelters in Washington. NWCAA is responsible for regulating other industrial sources of emissions located in Cherry Point. Now that the Intalco smelter has closed, NWCAA is the lead agency for the area and will lead the implementation of the maintenance plan and contingency measures.

UPDATE (April 30, 2024): The public comment period has been extended through May 17, 2024. An online public hearing will be held on May 14, 2024, at 6 p.m. Here is the online hearing registration (Zoom link.) For further information on how to submit comments or review documents, see the entry immediately below this.

UPDATE (March 26, 2024): A State Implementation Plan (SIP) revision is proposed for the Intalco-Ferndale SO2 Area. The proposed SIP Revision is a request to the EPA to recognize that the Intalco-Ferndale area has attained the federal air quality standard for sulfur dioxide (SO2) and that the improvements in air quality are due to permanent and enforceable changes. To support the redesignation request, we have developed a 10-year Maintenance Plan outlining:

  • Annual reviews of any changes to the SO2 emissions in the area.
  • An approved New Source Review (NSR) permitting program.
  • A requirement for air dispersion modeling for certain permits.
  • A commitment to conduct cumulative air dispersion modeling under certain conditions.
  • A commitment to install a monitoring site if the modeling shows levels of SO2 at or above 50 percent of the standard at any location within the area.

The proposed SIP Revision is available for public review through April 26, 2024, at the following locations:

This is a federally required revision to the Washington State Air Quality Implementation Plan (SIP). The SIP is a federal clean air tool that the EPA and the public may use for oversight and enforcement of certain state and local air quality rules and plans.

The proposed Maintenance Plan provides for annual area-wide evaluations and criteria for installation of a monitoring site should a new area be impacted by plumes from potential new facilities. If the EPA approves the proposed Maintenance Plan, the existing SOmonitoring sites operated by the Intalco facility and located in the areas previously affected by Intalco’s plume will be discontinued.

Comment period: March 27 – April 26, 2024

Please send us your written comments by April 26, 2024. If you would like to request a public hearing, please request by April 26, 2024. If requested, we will hold an online public hearing on May 14, 2024, at 6 p.m. and will extend the comment period through May 17, 2024. Find webinar link at: If no hearing is requested, we will post a cancellation to that webpage, or you may call Anya Caudill at 360-791-5499 to inquire about the status of the hearing and public comment period.

Comment or view comments online

Submit or view comments

Comment by mail

Anya Caudill, Air Quality Program, P.O. Box 47600, Olympia, WA 98504-7600

Mailed comments must be postmarked by April 26, 2024.

ADA accommodations

To request accommodations and services to support your participation in the document review and in the online hearing (if requested), contact Ecology at (360) 407-6831 or [email protected]. Persons with impaired hearing may call Washington Relay Service at 711. Persons with a speech disability may call TTY at 800-833-6384.

Past Material

UPDATE (Sept. 7, 2022): All areas in Washington state must meet national air quality standards for the six most common air pollutants. One of those pollutants is sulfur dioxide (SO2).

  • From 2017-2019, the Washington Department of Ecology and the Northwest Clean Air Agency worked together to evaluate air quality data from Whatcom County. Data from monitors near Intalco showed SO2 did not meet the national standard.
  • In December 2020, the U.S. Environmental Protection Agency (EPA) designated part of Whatcom County near the smelter to be in nonattainment for this standard. (EPA’s decision and response to comments.)

Comment period: Sept. 7 – Oct. 15, 2022

The Department of Ecology invites you to comment on the proposed plan to bring the area back into attainment.

The proposed plan describes actions the facility will have to take, including:

  • Installing and operating new SO2 controls
  • Merging and increasing the height of stacks
  • Limit facility-wide and unit-specific SO2 emissions
  • Different scenarios if the facility should restart before or after April 30, 2025

The Northwest Clean Air Agency, Intalco, and Blue Wolf Capital Partners (a private equity firm interested in purchasing and reopening the facility) have participated in the development of the proposed plan.

Submit comments

  • Using the online comment form
  • By mail to Kelsey Holbrook, Department of Ecology, Industrial Section, P.O. Box 47600, Olympia, WA 98504-7600
  • Orally at an online hearing, Oct. 11, 2022, starting at 6 p.m., register and attend

Next steps

EPA’s oversight of the plan is required under the federal Clean Air Act. When the comment period ends, Ecology will review comments received and make appropriate changes before submitting it to EPA. Once approved by EPA, the requirements of the attainment plan and Agreed Order become federally-enforceable.

Why this is important

Breathing elevated levels of SO2 causes inflammation and tightening of airways, and can trigger asthma symptoms. SO2 typically dissipates very quickly, but people living or working close to sources may be exposed to short-term levels that pose a risk to those with pre-existing breathing or health issues. SO2 pollution also decreases visibility in the form of haze and contributes to acid rain.

Join Ecology’s sulfur dioxide attainment email list to learn more about our efforts to monitor and evaluate SO2 levels in Washington.

UPDATE (early 2021): In early 2021, the Intalco nonattainment area was put on hold because of the recent change in the Federal Administration. Specifically, a hold was placed, pending review, on recent activities that occurred in the 90-day period prior to the change in administrations. That hold has now been lifted and the nonattainment area work is proceeding on its original schedule. Check Ecology’s Alcoa Intalco webpage for more information.

BACKGROUND: Two air quality monitors near the Intalco smelter have, at times, shown SO2 emissions above the National Ambient Air Quality Standard (NAAQS) of 75 parts per billion. Evidence suggests that the area where periodic exceedances occur is relatively small. But when this occurs a specified number of times within three consecutive years, EPA can designate the area as a nonattainment area, meaning it exceeds the federal standard.

Ecology and the Northwest Clean Air Agency prepared a technical report on their findings and submitted the report to EPA:

On Aug. 21, 2020, EPA proposed a nonattainment area that includes the Intalco facility.  EPA held a public comment period that ended Sept. 21, 2020. EPA had to finalize the designation by Dec. 31, 2020.

(Courtesy image.)

The federal Clean Air Act requires that a nonattainment area include not only the area that is violating the federal pollution standard but also nearby areas that contribute to the violation.

Criteria that factor into determining the boundaries for the nonattainment area include air quality data, emissions information, population density, traffic and commuting patterns, expected growth, weather, topography, jurisdictional boundaries, and control of emissions.

Ecology’s Industrial section has jurisdiction over the Intalco facility, including air emissions. But the proposed nonattainment area’s boundary also includes the Petrogas West facility and some private properties.

Intalco and Ecology (in coordination with other parties, including NWCAA) are required to put together a plan to bring the area back into attainment within a designated time period.

See Ecology’s web pages about SO2 air quality designations and SO2 in general for more information.

About Sulfur Dioxide (SO2) and health

Excess SO2 emissions are a concern because they can impact human health and the environment.

Short-term exposures to SO2 can harm the human respiratory system and make breathing difficult. Children, the elderly, and those who suffer from asthma are particularly sensitive to the effects of SO2.

SO2 and other sulfur oxides can react with other compounds in the atmosphere to form small particles, which may penetrate deeply into sensitive parts of the lungs and cause additional health problems.

SO2 and other sulfur oxides also could contribute to acid rain and to visibility-reducing haze on public lands like national parks and wilderness areas.

If you have questions about possible health impacts, call Whatcom County Health at 360-778-6000.