CEMEX Lyons Cement Plant and Dowe Flats Quarry

Recission of Notice to Terminate the Nonconforming Use at CEMEX, May 19, 2026

On May 19, 2026, Boulder County Community Planning and Permitting Director Dale Case sent a Rescission of Notice of Termination of Nonconforming Status letter to CEMEX, Inc., reinstating the company’s right to operate its cement plant near Lyons. View the Nonconforming Use Permitted to Continue at CEMEX Cement Plant in Lyons news release.

CEMEX submitted the following evidence to demonstrate that the determination was in error:

• May 9, 2024, Preliminary Response to Notice of Termination of Nonconforming Status
• Nov. 7, 2024, Supplemental Response to Notice of Termination of Nonconforming Status
• Nov. 7, 2024, CEMEX Access Analysis – Supplement Memo, Prepared by Stantec
• Nov. 5, 2024, CEMEX Lyons Plant Traffic Study, Prepared by Landis Evans + Partners
• Oct. 8, 2002, Letter from the Boulder County Land Use Department to Mr. John Lohr

Director Case received the following documents from Save Our Saint Vrain Valley in support of the Director’s determination regarding CEMEX’s nonconforming cement plant use:

• Dec. 20, 2024, Save Our Saint Vrain Valley Continued Support for Termination of CEMEX’s Nonconforming Use
• May 1993 Traffic Impact Analysis, Dowe Flats Project, Prepared by Felsburg Hold & Ullevig

Director Case also received the following information from Good Neighbors of Lyons:

• July 9, 2024, Good Neighbors of Lyons Support for Termination of CEMEX Nonconforming Use and Request for Final Determination on Remaining Outstanding Issues
• Dec. 1, 1994, Boulder County Health Department Air Pollution Control Field Inspection Worksheet
• Sept. 5, 1995 Boulder County Health Department Air Inspection Report
• Sundown News – Lyons Cement Plant (Date Unknown)
• Feb. 25, 2022, Weaver Limestone Quarry, Permit #658, 2021-2022 Annual Report

Because of the nature and complexity of the traffic studies provided, Director Case requested an independent analysis from Stolfus & Associates Inc., which Director Case received on Nov. 6, 2025:

• CEMEX Longmont Lyons Plant – Traffic Study Evaluation, Prepared by Stolfus & Associates Inc., Nov. 6, 2025

Note: Some documents contain material from external parties that may not be fully accessible. To request an Americans with Disability Act (ADA) accommodation, please email ada@bouldercounty.gov, or call 303-441-1386. View the county’s accessibility statement.

Background

On September 29, 2022, the Boulder County Commissioners voted 2-1 to deny Docket SU-22-0003, which would have allowed CEMEX to extend mining operations at the Dowe Flats quarry east of Lyons and north of State Highway 66, for an additional 15 years. The past mining operations permit, granted in 1994, expired on September 30, 2022.

Recent Code Enforcement Actions

Investigation opened on complaint ZON-23-0003 on January 23, 2023:

• View CPP Letter of Disclosure Request sent to CEMEX, Feb. 7, 2023
• View CPP Notice of Termination of Nonconforming Status Letter, April 10, 2024
• View Boulder County News Release, Notice of Termination Issued, April 10, 2024
• View CEMEX letter to Boulder County: Preliminary Response to Notice of Termination of Nonconforming Status, May 9, 2024
• View CEMEX letter to Boulder County, Nov. 7, 2024
  • Exhibit A – Cemex Preliminary Response
  • Exhibit B – Selected CORA Response Documents
  • Exhibit C – Stantec Supplemental Statement
  • Exhibit D – Landis Evans Cemex Lyons Plant Traffic Study
  • Exhibit E – Letter dated October 8, 2002, from the Boulder County Land Use Department

Past Land Use Review Dockets

Dowe Flats Quarry

• Docket SU-22-0003 CEMEX Dowe Flats Mining and Reclamation Extension: View the Planning Commission public meetings held on Aug. 17, 2022 and Sept. 1, 2022, or the Board of County Commissioners public meetings held on Sept. 14, 2022 and Sept. 29, 2022.
• Docket SU-93-14g: Dowe Flats 20 Year Interim Review
• Docket SU-93-14f: Dowe Flats 5 Year Interim Review
• Docket SU-93-14e: Dowe Flats 3 Year Interim Review
• Docket SU-93-14d: Amendment of the Dowe Flats specific site plan for the temporary / operations center
• Docket SU-93-14c: Dowe Flats 1 Year Interim Review
• Docket SU-93-14b: Specific site plan for the temporary Dowe Flats operations center
• Docket SU-93-14a: Special Use /Site Specific Development Plan. This is the original review and approval for the Dowe Flats quarry, limestone/shale open mining/quarrying.

Cemex Lyons Cement Plant

• Docket MD-22-0029: Remove and replace telecom antenna and associated utilities
• Docket AP-22-0003: Appeal of the Land Use Director’s determination that the Special Use approved in Docket SU-96-18 has lapsed under Section 4-604 (C) of the Boulder County Land Use Code.
• Docket MD-20-0010: Modification of existing telecommunication facility
• Docket MD-19-0009: Minor Modification request to Sprint Facility
• Docket LU-17-0011: Limited Impact Special Review to perform flood-related restoration along 4 miles of St. Vrain Creek involving approximately 208,400 cubic yards of earthwork.
• Docket SU-06-0016: Special Use Review / Site Specific Development Plan for a telecommunications facility
• Docket SU-01-0008: Special Use Review / Site Specific Development Plan for a telecommunications facility
• Docket SPR-97-0160: Site Plan Review for the placement of a telecommunications antenna on existing silos
• Docket SU-96-0030: Special Use Review / Site Specific Development Plan for a Telecommunications Facility to place antennas on an existing cement silo (Note: This docket has not been digitized)
• Docket SU-96-0018: Amendment to existing Special Use for mining operations on an 881-acre parcel.
• Docket SU-88-0021: Special Use and Certificate of Designation for Solid Waste Disposal Site, use of tires as fuel for cement manufacture
• Docket Z-63-0360: Request for rezoning from Agricultural to General Industrial

Parks & Open Space’s Role

Boulder County Parks & Open Space does not have a decision-making role in determining whether CEMEX can continue its plant operations. The county’s regulatory role over mining lies with the Boulder County Community Planning & Permitting department in its administration of the Land Use Code, and the final decision-making authority lies with the Board of County Commissioners.

Reclamation Role

Authority over the final reclamation of the mine site north of State Highway 66 lies with the Colorado Division of Reclamation, Mining, and Safety (DRMS). Search DRMS Data And Documents

CEMEX must meet specified reclamation criteria, such as adequate vegetative cover, invasive weed control, and limiting erosion, before the State will release their bonds. Currently, the timeline is to have the final reclamation complete within three years of the cessation of mining which began as of October 2022. A minimum of two additional years, and potentially more, may be required to ensure successful establishment and growth of vegetation to meet the reclamation criteria. Any technical revisions to the current reclamation plan requires State approval. Parks & Open Space, as the future managing entity of the site, will continue to provide input at each stage of the process. The overall goal is to return the site to a native grassland as it existed prior to mining and past agricultural operations.

County’s Options to Acquire Dowe Flats for Open Space

Boulder County has an option to acquire land at Dowe Flats, which encompasses some of CEMEX’s land north of Highway 66. The option has two elements covering 766 acres. The 153-acre option for land southwest of the mine is exercisable 60 days after notice of reclamation completion. The 613-acre Dowe Flats mine option is exercisable between Dec. 31, 2024, and March 1, 2025, with closing to occur within 90 days of exercise. In the meantime, Boulder County holds term conservation easements over these parcels as a means of keeping the land from being sold for development until the options can be exercised.

Future Negotiations with CEMEX for Open Space

The county works only with willing landowners to acquire land for open space. CEMEX owns approximately 210 acres north of Highway 66 and its approximately 830-acre plant property south of Highway 66 that are not under a county option to become open space. If CEMEX becomes willing to sell any of its land that is not currently under county options to become open space, there would be a public process offering the public an opportunity to give input on the proposed deal. Negotiations with private landowners are confidential until a proposed deal has been reached, at which time Parks & Open Space would take the proposed deal to POSAC for consideration and a recommendation. Following the POSAC meeting, Parks & Open Space would ask the Board of County Commissioners (BOCC) for a decision at a public hearing. The public is welcome to provide comments for the POSAC meeting and the BOCC public hearing.

Boulder County Public Health

Boulder County Public Health (BCPH) is responsible for responding to outdoor air complaints and investigating complaints related to stationary sources of air pollution to determine compliance with applicable statutes, air quality regulations and permit conditions.

Cemex is a Major Source with a Title V Permit and so the Colorado Department of Public Health and Environment (CDPHE) performs the annual inspection of the facility to determine compliance with the permit conditions and the Environmental Protection Agency (EPA) New Source Performance Standards (NSPS) for Portland Cement plants.

BCPH staff is responsible for documenting outdoor air complaints in the CDPHE database, investigating complaints to determine any violations of air quality regulations, and reporting the violations to CDPHE, as well as recommending enforcement where warranted. CDPHE maintains the authority to issue any enforcement action.

Beyond the regulatory requirements, BCPH continues to work with Cemex staff to encourage them to make voluntary improvements to the plant and take additional preventative measure to minimize fugitive dust emissions from the operation. BCPH will continue to work with CDPHE to address the number of dust event and complaints concerning the plant.

BCPH will be commenting on the Cemex Title V Permit Renewal once it is available for public comment, and requesting that additional dust control measures be put in place.

View the Colorado Department of Public Health & Environment mapping tool and other resources or air emissions from business and industry information.

Colorado Division of Reclamation, Mining and Safety (DRMS)

Search Search Colorado Division Of Reclamation, Mining And Safety (DRMS) Data And Documents