CRH Canada Group Inc. operating as Ash Grove - Approval of a site-specific air standard

Public consultation by the ministry on the proposed site-specific standards was provided through an Environmental Registry of Ontario (ERO) posting for 45 days, from July 25, 2025 to September 8, 2025. As a result of this public consultation, the Director received 65 comment submissions and 40 email correspondences. All questions and comments submitted regarding this proposal were considered.

The following is an overview of 16 common themes that were raised and the ministry’s response to each.

Comment #1: Concerns were expressed that the technical information presented at the December 6, 2023 public meeting was overwhelming and did not provide details about Ash Grove's action plan to reduce emissions. It was challenging to read the poster boards especially with the large crowds. Several stakeholders requested additional information and follow-up meetings/discussions.

Response: In support of a transparent public consultation process, Ash Grove made their site-specific standard request documents publicly available via the company website, including access to key supporting documents containing the details of the proposed action plan. Ash Grove also reached out to stakeholders who requested additional information/meetings to clarify questions regarding the site-specific standard request.

Comment #2: Concerns with the site-specific standard process, providing exceptions to the air standards and allowing more time for Ash Grove to achieve compliance with the provincial air standards. Granting site-specific standards would put Mississauga and Ontario behind European cement producers that have stricter sulphur dioxide (SO₂) and nitrogen oxides (NO_x) limits.

Response: Ontario’s regulatory approach to improving local air quality starts with setting science-based standards. Under the Local Air Quality Regulation, we use air standards to assess the environmental performance of a regulated facility. Facilities that meet the air standards do not need to take any further action.

Since Ontario’s air standards are science-based and set without regard to the technical and economic feasibility of Ontario industries being able to comply with these standards, some facilities cannot meet an air standard due to unique technical or economic limitations. Under the Local Air Quality Regulation, facilities that do not meet the general air standard for a contaminant may request an alternative compliance approach, such as requesting and complying with a site-specific standard. Where a site-specific standard is set, it replaces the general air standard for the facility under the regulation; a facility that meets its site-specific standard is generally in compliance with the regulation. Site-specific standards are developed with full public transparency through public meetings and public comment periods.

Site-specific standards require emissions reductions by requiring the implementation of best available control technology or methodology to prevent, minimize or reduce emissions. The site-specific standard setting process includes technology benchmarking to determine what is feasible for a facility to achieve in terms of controlling emissions of a contaminant over a period of time (i.e., at least five years but not more than 10 years), and the site-specific standard is set at the minimum difference necessary from the general air standard. The ministry’s objectives for approving site-specific standards is to reduce air pollution levels as much as feasible with the goal of having the facility meet the general air standards over time.

The Ash Grove Mississauga Cement Plant is currently not able to comply with the one-hour sulphur dioxide and nitrogen oxides air standards. Ash Grove's site-specific standard request included technology benchmarking to assess best practices in other jurisdictions, including the European Union. The ministry’s review has confirmed that the control technologies described in Ash Grove’s site-specific standard request and the proposed action plan are consistent with best available techniques used in Europe and in the U.S. for the cement sector. The proposed action plan using a combination of add-on controls, stack improvements, process modification and material substitution is considered an appropriate path towards meeting the provincial air standards.

The site-specific standards for those contaminants will become more stringent over time to reflect the implementation of the action plan and will expire in 2031, at which point Ash Grove would be required to comply with the general air standards. The ministry will closely monitor Ash Grove’s progress to ensure the action plan is implemented and compliance with the general air standards is achieved by 2031.

Comment #3: Concerns that the requested 10-year site-specific standard approval is too long to achieve compliance with the provincial air standards. The ministry should consider a five-year site-specific standard approval to emphasize the urgency of reducing emissions considering the health impacts of SO₂ and NO_x emissions and to promote timely accountability by the facility.

Response: Ash Grove’s request included an action plan to significantly reduce the discharge of SO₂ and NO_x from the facility and achieve compliance with the provincial air standards at the completion of the 10-year period. The ministry has reviewed and decided to accept the steps set out in the Ash Grove action plan. However, the ministry is also of the opinion that the steps can be implemented before the ten years as initially proposed by Ash Grove.

As such, the ministry is issuing SO₂ and NO_x site-specific standards for Ash Grove for approximately six years (with expiry date of December 31, 2031). However, Ash Grove's final action step for implementing mitigation measures is anticipated to be completed in approximately five years (by June 30, 2031). The site-specific standards will also become more stringent over time to align with the facility’s action plan for the implementation of emissions control technology at the facility along specific timelines. The site-specific standards will expire in 2031, at which point the facility will be expected to have implemented sufficient emissions control technology and improvements and will be able and required to comply with the general air standards. This phased approach ensures that Ash Grove is reducing their emissions quickly with significant reductions to occur within the first two years. Further, as noted above, the site-specific standards are set at the minimum difference necessary from the general air standards for NO_x and SO₂.

Comment #4: Concerns related to why Ash Grove cannot meet the air standards for SO₂ and NO_x and how Ash Grove should have taken actions in 2018 when they were notified of the more stringent air standards for SO₂. 

Response: In 2018, industries were advised of changes to SO₂ air standards which would come into effect in 2023 (based on the ministry’s five-year service standard for notification). At that time, Ash Grove’s modelling for SO₂ indicated compliance with the SO₂ standard that was in effect.

Since 2021, Ash Grove has undertaken enhanced air dispersion modelling to assess the facility’s emissions and determine whether its location along the shoreline of Lake Ontario has any impacts on the dispersion of air emissions. This assessment, known as a shoreline fumigation analysis, indicated that emissions from the facility are subject to shoreline fumigation events under certain meteorological conditions. As a result, Ash Grove was required to use different air modelling software. The CALPUFF model was approved by the ministry for Ash Grove to use to conduct air dispersion modelling in October 2022. This new modelling demonstrated exceedances of both the existing and new 1-hour SO₂ air standards and the current 1-hour air standard for NO_x.

In October 2023, Ash Grove subsequently submitted an abatement plan indicating the facility would be requesting site-specific air standards for SO₂ and NO_x in accordance with the Local Air Quality Regulation.

Comment #5: Concerns related to the health impacts of sulphur dioxide and nitrogen oxides. Why is Ash Grove not being required to reduce production capacity instead of granting site-specific standards? Concerns that Ash Grove's exceedance level is above the air standard developed in 1970s for NO_x and the previous air standard for SO₂ that was also developed in 1970s. Concerns that the site-specific standards and interim limits are not health protective, that they exceed the Canadian Ambient Air Quality Standards (CAAQS) and World Health Organization (WHO) 2021 Air Quality Guidelines, which are substantially lower and designed to prevent asthma attacks, emergency room visits, and cardiovascular impacts.

Response: Provincial air standards are periodically reviewed and updated to reflect the most current scientific understanding of health and environmental effects. The current one-hour SO₂ standard of 100 micrograms per cubic metre (ug/m³) is a science-based standard that is more protective of human health than the previous standard it replaced.

Exceedance of an air standard does not mean that an adverse effect will occur, but rather that the risk of such effects increases with the concentration, frequency and duration of exposure. For this reason, while the ministry is issuing site-specific standards for NO_x and SO₂ that would provide Ash Grove with a compliance pathway for its emissions that exceed the general air standards for NO_x and SO₂, the site-specific standards are time limited and become more stringent over time to ensure that Ash Grove is implementing its proposed action plan as quickly as feasible to reduce emissions and air contaminant levels in the surrounding community.

In addition, Ash Grove has applied to consolidate and amend the current air environmental compliance approvals (ECA) for the facility. The amendments to the ECA will incorporate several protective measures. For example, Ash Grove will be required to predict off-site concentrations of SO₂ and NO_x and depending on the circumstances consider adjustments or other control measures, when elevated concentrations of SO₂ and NO_x are predicted (i.e. SO₂ concentrations above 320 ug/m³ and NO_x concentrations above 400 ug/m³, both over a one-hour averaging period). These actions are designed to protect individuals with asthma from the adverse effects of short-term exposure and to reduce the health risks associated with long-term exposure.

The amendments to the environmental compliance approval would require Ash Grove to immediately investigate the cause of any SO₂ discharge resulting in a measured or predicted off-property concentration above the upper risk threshold of 690 ug/m³. Following such an investigation, the facility would be required to implement corrective measures to mitigate the impact as soon as possible and prevent a similar occurrence in the future.

This framework establishes a robust system to manage emissions and protect public health while the facility implements the necessary measures to achieve compliance with the general air standards.

Comment #6: The ministry should evaluate emission loadings considering potential synergistic effects with other contaminants, such as fine particulate matter (PM2.5), dioxins and furans, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs) and other toxic chemicals, to ensure no new net contribution to existing pollutant loadings and to have quantifiable improvements of local air quality and no adverse effects on human health.

Response: The focus of the site-specific standards approval is to drive emissions reduction of SO₂ and NO_x from the Ash Grove Mississauga Cement Plant to improve local air quality and to better protect the local community. The site-specific standards will require Ash Grove to progressively reduce hourly off-site concentrations of SO₂ and NO_x from current levels over the duration of the site-specific standard approvals and after their expiry on December 31, 2031, Ash Grove will be required to comply with the general air standards for SO₂ and NO_x. This will be achieved primarily through the installation of best available controls, in combination with stack improvements, process modification and material substitution, with these actions being implemented in phases starting immediately and over for the next five to six years.

Ash Grove’s action plan measures to reduce SO₂ and NO_x emissions are not expected to result in new contributions of fine particulate matter, dioxins/furans, VOCs and PAHs emissions.

Comment #7: Nitrogen Oxides is defined by the Chemical Abstracts Service Registry Number (CAS RN) for NO₂ (10102-44-0). This is inconsistent. Compliance must be assessed against NO₂, the pollutant with established health standards, not total NO_x.

Response: Nitrogen oxides (NO_x) refer to the combined total of nitrogen dioxide (NO₂) and nitric oxide (NO). Nitric oxide rapidly oxidizes in ambient air to form NO₂. Consequently, the health effects of NO_x are evaluated based on NO₂, and the NO₂ CAS RN has been assigned to NO_x air standard. For details on how concentrations of NO₂ and NOx are considered and calculated, including for the purposes of assessing compliance, please refer to subsection 1(2.2) of O. Reg. 419/05, and to note 28 of the Air Contaminants Benchmarks (ACB) List.

Comment #8: Concerns related to the air quality in the local area resulting from cumulative impacts from Ash Grove and other major emitters in southern Mississauga. Concerns related to the impacts on populated residential areas and new housing development in the vicinity of Ash Grove.

Response: Ash Grove is requesting one-hour site-specific standards for SO₂ and NO_x. The ministry reviewed emissions from the largest emitters of SO₂ and NO_x near Ash Grove, and the ministry’s assessment and review of available data indicate that cumulative impact on the same receptors for these contaminants is not significant. The site-specific standards will require Ash Grove to significantly reduce emissions of SO₂ and NO_x and improve the local air quality in the surrounding community.

Under the amendments to the ECA, Ash Grove will be required to install ambient air monitors, and monitoring data are to be reported to the ministry and made available to the public to track and verify the contaminant concentrations in the community.

Comment #9: Concerns related to poor air quality in Clarkson area resulting from regional smog, truck traffic and wildfire smoke. Concerns related to smog and acid rain formation from SO₂ and NO_x emissions. Comments related to the site-specific standards approval that it should include requirements for a comprehensive community monitoring program that captures pollutants of greatest concern for human health and local air quality and that monitoring should include fine particulate matter (PM2.5), carbon monoxide (CO), total reduced sulfur (RS), ozone (O₃) and volatile organic compounds (VOCs) in addition to monitoring of SO₂ and NO_x.

Response: Ontario’s air quality has improved significantly over the last 10 years. The Ministry of the Environment, Conservation and Parks’ (ministry) 2022 Air Quality Report shows that Ontario’s air quality, including the Clarkson area, has improved over time.

The Clarkson Airshed Industrial Association, a non-profit organization monitored air quality in the Clarkson area of Mississauga for approximately 10 years (2010 - 2020) and demonstrated that fine particulate matter and nitrogen dioxide concentrations are typical for the Greater Toronto Area.

The ministry monitors ambient air quality at Air Quality Health Index (AQHI) monitoring stations across the province, including in Oakville and Mississauga. From 2013 to 2022, the ministry’s Mississauga and Oakville stations have shown a trend of decreasing concentrations of nitrogen dioxide (NO₂) and fine particulate matter (PM2.5).

The Air Quality Health Index air monitoring stations established in Oakville and Mississauga are considered representative of regional air quality for their communities and the ministry has no plans to expand the Air Quality Health Index air monitoring network at this time.

In 2022, Ontario reported air quality in the low-risk category 94% of the time, based on the AQHI. Mississauga and Oakville reported air quality in the low-risk category 95% and 92%, respectively.

The information collected by the ministry through its AQHI air monitoring network is reported 24 hours a day, seven days a week, through the ministry’s Air Quality Ontario website, and includes concentrations of common air pollutants and the AQHI.

The province continues to work with local industry, including Ash Grove, to drive strategies that improve air quality in the Clarkson area. The site-specific standards approval will require Ash Grove to comply with increasingly stringent standards for SO₂ and NO_x, which will involve taking short-term steps to reduce emissions before taking further action in order to comply with the general air standards for SO₂ and NO_x by 2031. The amendments to the environmental compliance approval will also require the installation and public sharing of data from additional ambient air monitoring equipment located near the facility. This will be used to track the reduction of emissions as Ash Grove implements their action plan over time.

Comment #10: Comments related to public transparency and accountability. To support transparency regarding air pollutant emissions and facility operations, it is recommended that the current Community Advisory Panel (CAP) undergo a review. We recommend that the CAP return to an Ash Grove funded but independently facilitated and chaired CAP. We also recommend revisiting the Terms of Reference with a focus on clearly defined roles and responsibilities for all participants. Meetings should be conducted with a formal agenda to which both community members and the facility can contribute. This approach fosters improved transparency, enhances trust between the facility and the community, and ensures that public health concerns are meaningfully addressed and addressed objectively. Minutes of meetings should be readily available to the community.

Response: The amendments to the environmental compliance approval will require Ash Grove to develop, in consultation with the ministry and the local community, a public engagement plan for the facility that includes local and Indigenous communities and public health representatives to establish a forum for sharing of information regarding the operation of the facility. The Terms of Reference from the Community Advisory Panel can be incorporated into the development of the public engagement plan. Ash Grove will be required to submit the public engagement plan to the ministry for acceptance.

Comment #11: To ensure transparency and public access to information, the established community liaison committee should be maintained to provide timely updates on operations and SO₂ and NO_x emissions. Additional information should also be shared, including regular action plan updates, data from continuous monitoring systems and community monitoring stations, details of proposed operational changes and upgrades, ministry reports related to ECAs and other relevant information that may impact local communities. Ambient monitoring data and continuous emissions monitoring data (on major stacks) should be published in real-time and alerts (of potentially dangerous levels of contaminants) on a public dashboard.

Response: Through the amendments to the environmental compliance approval, Ash Grove will be required to prepare quarterly and annual reports to be submitted to the ministry and make those reports available to the public. The information required to be included in the reports will include ambient monitoring data and emissions data from continuous monitoring systems to track the reduction of emissions over time, as well as site-specific standard action plan implementation updates. Any public notification made as a result of elevated concentrations of SO₂ and NO_x off property, either predicted or measured, would also be reported along with the corrective measures taken by Ash Grove.

Comment #12: Why is the ministry requiring Ash Grove that, at all times, any fuel oil burned in the cement kiln has a fuel sulphur content no greater than 0.5% by weight? If the primary source of SO₂ emissions is due to the presence of pyrite in the limestone, then the mining sequence and blending practices of the limestone should be optimized to a specific input level and every effort made to avoid spikes. Areas in the quarry where the pyrite is too high should be declared non-viable and bypassed. Has a mass balance on the sulphur inputs been reviewed and ideally correlated to the continuous emissions monitoring system SO₂ readings? If the fuel oil is still to be monitored then the coal and even the solvents that are also processed in the kiln should be similarly monitored. Continuous emissions monitoring requirements should include validation intervals to verify the emissions data.

Response: The technology benchmarking report submitted by Ash Grove indicates that SO₂ emissions originate primarily from the pyrite sulphur in the limestone that is used in the cement making process. The site-specific standards request from Ash Grove included potential plans to no longer use bunker oil in the cement kiln and the ministry is requiring through amendments to the environmental compliance approval that any bunker oil or no. 2 fuel oil used in the cement kiln cannot have a sulphur content greater than 0.5% by weight.

The ministry’s review of the site-specific standards request from Ash Grove included considering the information provided on the SO₂ and NO_x emissions from all activities and all emission sources operated simultaneously at the facility, based on actual operating data obtained from the continuous monitoring system (CMS) for the previous five-year period (from 2018 to 2022, inclusive) and adjusted to the facility’s maximum production capacity. The ministry reviewed the raw data collection and analysis of the CMS database and concluded that the database is properly validated. Therefore, the ministry is satisfied that the emissions scenario provided by Ash Grove has accounted for the various operating conditions, including the variation of raw materials processed in the cement kiln and the use of coal and solvents in the kiln, and that the steps set out in the action plan considered mitigation measures to address the highest levels of hourly emissions from the facility. Regardless of the type of fuel or input materials being used, Ash Grove must ensure that any “spikes” in SO₂ emissions that may result from the use of particular materials do not cause exceedances of the applicable site-specific standard.

In accordance with the amendments to the environmental compliance approval, Ash Grove will be required to operate and maintain the CMS to continuously measure SO₂ and NO_x concentrations, and flowrates at various exhaust locations, as per the continuous monitoring plan to be accepted by the ministry and subsequent inspections by the ministry.

To provide further validation of the facility’s performance, the amendments to the environmental compliance approval will also require Ash Grove to install and operate air quality monitors in the local community. Data from these monitors will be made available to the public.

Comment #13: According to the National Pollutant Release Inventory (NPRI), Ash Grove released 132.55 tonnes of ammonia into the air in 2024 which puts them fourth in the province. How will the ministry ensure that the introduction of sorbents and ammonia at the stacks will not create new emissions issues? Can the ministry include additional sampling requirements during the introduction of these materials?

Response: The ministry acknowledges the comment regarding ammonia emissions and the introduction of sorbents, as identified in the facility’s Technology Benchmarking Report. The introduction of these reagents is part of a comprehensive strategy to implement Best Available Techniques (BAT) for the abatement of nitrogen oxides (NO_x) and sulphur dioxide (SO₂). The ammonia is used in a selective non-catalytic reduction system to convert NO_x into inert nitrogen gas and water. Similarly, the introduction of a dry sorbent, such as hydrated lime, is a proven add-on control that neutralizes gaseous SO₂ into a solid particulate. This resulting solid is then captured by the facility’s dust collection equipment and does not create a new gaseous emission issue.

The potential for unreacted ammonia to be emitted, a phenomenon known as “ammonia slip”, is a well-understood and manageable aspect of this control technology. To mitigate this, the amendments to the environmental compliance approval will require Ash Grove to prepare and implement operating procedures to minimize ammonia slip from the selective non-catalytic reduction system. For example, this may include automated feedback loops that continuously adjust the ammonia injection rate based on real-time monitoring of operational parameters to ensure a high reaction efficiency. The system is typically engineered to minimize ammonia slip by design, ensuring the reagent is used effectively for NO_x abatement rather than being released as a new emission source.

To ensure regulatory compliance and environmental protection, the facility’s environmental compliance approval includes specific conditions to govern the system’s operation and performance. These conditions will mandate Ash Grove to implement routine operating and maintenance procedures for the sorbent injection system and selective non-catalytic reduction system and also implement written procedures to monitor its performance.

Comment #14: Comments related to the need for more robust ministry monitoring and enforcement to gain public confidence. The ministry should undertake compliance review at least on an annual basis and on key milestones dates, and review findings should be made public. The ministry should monitor the progress of Ash Grove's action plan and milestones. There should be automatic penalties for exceedance of site-specific standards and air standards, missed monitoring and missed action plan milestones.

Response: The quarterly and annual reporting requirements of the environmental compliance approval will assist the ministry in reviewing the progress in Ash Grove's emission reduction efforts and action plan implementation. In addition, Ash Grove will be required to prepare an Emission Summary Dispersion Modelling Report after the implementation of each milestone in the action plan. The facility will be required to demonstrate compliance with the relevant site-specific standard value or applicable air standard, by evaluating its emissions data from the continuous monitoring system and assessing the maximum off-property concentrations of SO₂ and NO_x, as the facility implements its action plan.

The ministry has a range of tools available to address non-compliance regarding site-specific standards, general air standards or terms and conditions of the environmental compliance approval. The ministry considers each situation on a case-by-case basis in accordance with Ontario’s Environmental Compliance Policy.

Comment #15: Where will the Ash Grove community monitors be located?

Response: The amendments to the environmental compliance approval will require Ash Grove to develop an ambient air monitoring plan, for approval by the ministry, for the continuous monitoring of concentrations of SO₂ and NO_x, as well as meteorological data. The ambient air monitoring plan is to include proposed locations of the community monitoring stations and a timeline for installation. The siting criteria for the ambient monitors is to be in accordance with the ministry’s technical guidance, “Operations Manual for Air Quality Monitoring in Ontario” and be located to measure impacts from Ash Grove operations. Ambient monitoring data will be reported to the ministry and made available to the public.

Comment #16: Comments related to the future use of alternative low carbon fuels (ALCF) in the cement kiln and how it may affect the site-specific standards for SO₂ and NO_x. With Ash Grove's historical failure to meet the provincial air standards for NO_x and SO₂, there should be a moratorium on approving projects that can increase these emissions, as may be the case for the ALCF project. 

Response: Under the O. Reg. 419/05 framework, a site-specific standard is not developed for a particular fuel used at a facility, but it is derived from a technical assessment of the facility’s ability to minimize emissions using best available control technologies and techniques. The site-specific standard is ultimately tied to the implementation of the facility’s action plan to reduce emissions and the off-site impacts of these emissions. Ash Grove’s site-specific standards request was established using the facility’s current operational scenario, which includes coal combustion. This scenario informs the required performance specifications for emission control technologies. The ministry’s review has confirmed that the abatement technologies contemplated to be implemented by Ash Grove to achieve compliance with the site-specific standards are equally applicable and effective for managing the contaminant emission profiles expected from the potential future transition to natural gas and alternative low carbon fuels. The site-specific standard is established based on the performance of the control technology, which remains consistent and necessary for both the existing and future operational scenarios. The standard ensures a required level of environmental performance, irrespective of the specific fuel being used as input.

In addition, Ash Grove has applied to consolidate and amend the current air environmental compliance approvals (ECA) for the facility. Under the amendments to the ECA Ash Grove will be required to operate and maintain the Continuous Monitoring System (CMS) to continuously measure SO₂ and NO_x concentrations, and flowrates at various exhaust locations, as per the continuous monitoring plan to be accepted by the ministry. In the case of any future changes in the materials processed in the cement kiln, the facility’s emissions will be measured by the CMS. Ash Grove will be required to provide regular (e.g. quarterly) and annual reports using CMS data along with ambient monitoring data to track their emission reduction efforts over time and verify the facility’s compliance with the relevant site-specific standard value or applicable air standard, regardless of the type of waste stream that is being used.

Ash Grove has also posted on their company website information related to their proposed use of ALCF in the cement kiln. According to Ash Grove's proposal, the use of ALCF is not expected to have an impact on the discharge of SO₂ emissions from the facility, because SO₂ emissions originate primarily from the pyrite sulphur in the limestone that is used in the cement making process. NO_x emissions are projected to decrease as the high moisture content in ALCF reduces the thermal NO_x emissions. Therefore, the ALCF project will not impact the facility's site-specific standard request and the proposed control methods in the submitted action plan.