SCAQMD Rule 1157 – Particulate Standards for Aggregate and Related Operations

South Coast Air Quality Management District (SCAQMD) of California adopted Rule 1157 in 2005 and amended it in 2008, with the purpose of reducing PM₁₀ emissions from aggregate and related operations. The rule defines “aggregate operations” as operations that produce sand, gravel, crushed stone, and quarried rocks.

Performance Standards

Rule 1157 establishes the following general performance standards for aggregate operations (Visible Emissions Performance Standards):

• Fugitive dust cannot exceed 20% opacity, averaged over 12 consecutive readings (SCAQMD Method 9B).
• Fugitive dust cannot exceed 50% opacity, averaged five consecutive readings (SCAQMD Method 9B).
• Visible dust plumes cannot extend more than 100 feet from the source.

In addition to the visible emissions limits stated above, SCAQMD sets dust-control rules for equipment, storage piles, and internal roads. Key requirements include:

• Spills: material spills must be moved away from internal roads with dust and operators must apply dust suppression and install gravel pads.
• Loading, Unloading, and Transferring: dust control methods shall be used when loading, unloading, and transferring materials
• Conveyors: dust suppressants or other dust control methods shall be used at the conveyor
• Crushing Equipment: crushing activities shall be controlled by baghouses, dust suppressants, or other dust control methods to achieve the Visible Emissions Performance Standards.
• Screening Equipment: outdoor screening activities shall use enclosed screening equipment that is equipped with a baghouse. Alternatively, dust suppressants or other dust control methods can be used to achieve the Visible Emissions Performance Standards.
• Storage Piles: the entire surface area of open storage piles shall be maintained in a stabilized condition. Alternatively, materials can be stored in a silo or bunker. Dust suppressants shall be reapplied after loading or unloading activities. If piles are located within 300 feet of off-site occupied buildings, they may not be higher than eight feet high.
• Internal Roads:
  • Unpaved Haul Roads: facilities must apply chemical stabilizers on unpaved haul roads and post signs at both ends of the unpaved haul roads stating that haul trucks shall use these roads unless they are traveling to the maintenance areas.
  • Unpaved Non-Haul Roads: facilities must apply chemical stabilizers or a gravel pad to unpaved non-haul roads and parking and staging areas.
  • Paved Roads:
    • Facilities with a minimum of 60 aggregate and/or mixer trucks exiting the facility each day shall sweep paved roads with a street sweeper by the end of each production work shift.
    • Facilities with less than 60 trucks exiting the facility each day shall sweep paved roads by the end of every other workday. Water shall be applied on days when the paved roads are not swept.
  • Track-Out: Unless exempt from the Rule, facilities shall install a rumble grate, wheel washer, or a truck washer.

Recordkeeping

The Rule requires that facilities keep certain records on-site for three years (non-Title V) or five years (Title V). Examples include records of watering and sweeping schedules for internal paved roads, aggregate and/or mixer trucks exiting the facility, and supporting documentation if the facility is seeking certain exemptions from the Rule.

Test Methods

To maintain compliance with requirements of the Rule, facilities must utilize SCAQMD Opacity Test Method No. 9B and The Stabilized Surface Test Method included in the SCAQMD Rule 403 Implementation Handbook.

Additional Requirements triggered by recurrent violation

Facilities located near communities face stricter requirements after repeated non-compliance with Rule 1157:

• If a facility is located within 500 meters of residencies or other sensitive receptors; and,
• The facility received three more validated Notices of Violation (NOV) within 12 months for causing or allowing fugitive dust emissions to exceed the Visible Emissions Performance Standards

The operations must submit an emissions reduction plan to the Executive Officer within 30 days of the third notice of violation. The plan must propose additional emissions control measures intended to remedy the cause of the recurring non-compliance for implementation as soon as practical. If a plan is disapproved, the facility shall submit a revised plan within 30 days notice of disapproval.

Exemptions

There are several activities and conditions that are exempt from certain requirements of the Rule. For example, during instances of high winds, facilities may be exempt from meeting the Performance Standards. Empty haul trucks traveling to and from maintenance areas are exempt from the requirement to use internal unpaved haul roads if they travel on internal unpaved non-haul roads. Truck trimming areas may be exempt from requirements to use a dust suppressant.

There are several types of facilities that do not need to install and operate a wheel washer (e.g., facilities that pave a minimum of ¼ mile from the rumble grate to the facility exit leading to a paved public road).

Alternative Control Options

Instead of using dust suppressants to comply with the Rule, a facility may request approval from the Executive Officer and the U.S. Environmental Protection Agency for a plan for achieving the Performance Standards through alternative control measures.

How ALL4 Can Help

As of September 2025, SCAQMD is amending Rule 1157. Stay tuned to ALL4’s 4 the Record series for updates on this Rule and other AQMD changes that could affect your facility.

Rule 1157 carries strict dust control requirements and violations can quickly turn into costly notices and mandatory corrective action plans. Don’t wait for enforcement to catch you off guard. Our Rancho Cucamonga team is ready to review your operations, spot compliance risks, and help you put practical solutions in place. Please reach out to Michael McHale (mmchale@all4inc.com) or Olivia Pehanick (opehanick@all4inc.com) today to talk about Rule 1157 and what it means for your facility.