West Silver Valley Fine Particulate Matter Maintenance Plan
Background
The West Silver Valley in Idaho was designated nonattainment for the 2012 annual PM2.5 standards on January 15, 2015 and classified as Moderate (80 FR 2205). Nonattainment planning SIP revisions to address all applicable Moderate area requirements were due on October 15, 2016.
On April 6, 2018, EPA published a "finding of failure to submit" required SIP elements for the 2012 annual PM2.5 NAAQS for applicable nonattainment areas nationwide, including the West Silver Valley in Idaho (83 FR 14759).
EPA approved a 2013 base year inventory for the West Silver valley nonattainment area on September 11, 2018 (83 FR 45830). Later that year, on December 21, 2018, EPA determined that the West Silver Valley area has attained the 2012 annual PM2.5 NAAQS based on 2015-2017 ambient air quality monitoring data and made a "clean data determination" (83 FR 65535). The clean data determination suspended certain planning requirements for the area, including the requirement to submit an attainment demonstration and associated reasonably available control measures including reasonably available control technology, a plan for reasonable further progress, and contingency measures for failure to attain or meet reasonable further progress. These requirements are permanently discharged when the area is redesignated to attainment.
On June 2, 2020, Idaho submitted to EPA a redesignation request and maintenance plan that demonstrates the West Silver Valley area will maintain the 2012 annual PM2.5 standard through 2031. The EPA approved the maintenance plan and redesignated the West Silver Valley nonattainment area to attainment, effective December 16, 2021 (86 FR 63315).
Summary
The control strategy in the West Silver Valley maintenance plan focuses on reducing emissions from residential wood combustion, onroad, and nonroad sources. Control measures include Federal standards for wood heaters, a woodstove changeout program, Federal vehicle emissions standards, the Federal rule for heavy-duty engine and vehicle standards, and highway diesel fuel sulfur control requirements.
Contingency Plan
The West Silver Valley maintenance plan identifies actions Idaho will promptly take to prevent or correct a violation of the 2012 annual PM2.5 NAAQS. If the annual average PM2.5 concentration reaches 12.5 micrograms per cubic meter or greater in a single calendar year, Idaho will evaluate all appropriate data to determine the cause of the elevated levels and whether they are likely to continue. Idaho has identified the following potential contingency measures in the event the evaluation indicates additional control measures are necessary:
- Increases efforts to control mud and dirt track out from industrial, construction, and agricultural operations onto paved roads.
- Adopt local ordinances addressing nonresidential slash burning to require burn permits year-round.
- Adopt local ordinances addressing nonresidential slash burning to require burn permits year-round.
- Adopt local ordinances that reduce the residential open burning days.
- Adopt a local ordinance that prohibits installing uncertified wood stoves in residential and commercial buildings.
- Expand educational efforts to reduce PM2.5 from wood smoke.
- Pursue funds to continue offering wood stove changeouts and fireplace conversions within the West Silver Valley nonattainment area.
EPA Effective Date
December 16, 2021