Quarries: climate change adaptation case study

Managing off-site dust impacts exacerbated by drought at quarries.

This future scenario outlines possible climate impacts, risks, adaptation measures and ongoing management measures at a hypothetical site in NSW.

Scenario

A quarry in the Hunter region of New South Wales (NSW) has been experiencing the impacts of drought with prolonged periods of extreme heat and little to no rainfall. During this drought, the quarry owner and operator identified that there has been excessive dust generation during operation leading to dust impacts off-site.

The quarry owner undertook preliminary investigations to better understand the site’s exposure to climate hazards. The Hunter region is projected to experience a 12.9% reduction in annual rainfall by 2050 and a reduction of 8.8% by 2090 under a high emissions scenario¹. The region is also projected to experience a 25-30% reduction in average winter rainfall and nearly four times the number of hot days (days over 35°C) per year under a high emissions scenario². It is projected that under a medium emissions scenario, drought events in the State (including the Hunter region) are likely to be 50-200 days longer in duration in the medium-term future (2050)³. Drought can be difficult to identify as it develops gradually, however, it is something that quarries owners/operators should consider and prepare for.

Climate impacts

Prolonged drought conditions in NSW will exacerbate dust generation from quarries by drying out exposed earth and reducing moisture levels, making it easier for fine particles to become airborne during excavation and transport. During the previous dry conditions, the quarry owner/operator identified a number of sources for excessive dust generation on site which led to unacceptable dust impacts off-site. These sources included:

• drier soil conditions leading to excessive dust generation from the movement of heavy vehicles on haul roads
• dust generation from material transfer locations and materials processing. Whilst these processes generate dust (regardless of climate change), the management of them is made more difficult due to water resource constraints.

The owner/operator noted that the existing processes and management mechanisms were designed using historical climate data and projected climate trends that may no longer be suitable. Without the adaptive capacity to manage projected drought conditions, excessive dust generation could become more commonplace.

Assessing climate risk

To understand climate change risks at the quarry, and to prioritise climate risk management, the owner/operator undertook a system wide climate change risk assessment using climate projection data for rainfall, temperature, bushfire, and storms and other relevant climate variables. While several climate hazards and potential climate related impacts related to the quarry were identified, this scenario focusses on drought conditions causing dust impacts off-site.

The assessment was undertaken across the remaining operational life of the quarry using projected climate change data for a medium and high emissions climate scenario. The site was found to be at high risk of causing dust impacts during drought conditions.

Identifying adaptation measures

With the key climate risks identified, the quarry owner and key stakeholders such as relevant site operations staff and sustainability managers, collaborated to identify potential adaptation measures that could be implemented to reduce the risk of dust impacts off-site.

The adaptation measures targeted different quarrying activities, infrastructure components, and vulnerabilities of the system, with each having different levels of feasibility and effectiveness in addressing off-site dust impacts. These included:

• Developing and/or updating site-specific management plans, manuals, and operating procedures including dust management plans and vegetation management plans to mitigate and manage dust impacts. They should include a list of management procedures such as those detailed below.
• Investigating the capture, treatment, storage of rainwater into aquifers (managed aquifer recharge). This can be drawn upon during periods of drought for dust suppression. This would require the acquisition of water sharing agreements (if available and appropriate for each site) as water harvesting can be an issue.
• Increasing the capacity of existing water treatment and storage infrastructure to process and retain increased volumes of water for beneficial reuse for dust suppression.
• Increasing the number of water carts on site and optimising the water droplet size used for dust suppression. Noting that given the drought conditions there will be reduced availability of water therefore the owner/operator should also consider investigating alterative dust suppression techniques such as using polymer-based sprays (prioritising biodegradable and non-toxic options).
• Optimising haulage distances which could be achieved through in-put crushing and conveying systems. By reducing distances travelled on haul roads there will be less dust generated.
• Optimising drop heights from which the overburden or quarried material is tipped. Reduced distances, again reduces the opportunity for airborne dust to be generated and can reduce the need for traditional water-based dust suppression methods.
• Monitoring and maintenance of haul roads to minimise dust generation. This may require regrading or leveling of the roads or implementation of automated water sprays.
• Optimisation of Run of Mine (ROM) bins through design and implementation of hoods, increasing the wall height around the ROM bins, or implementing automated dust suppression sprinklers to activate when hauls are being transferred.
• Enclosing all dust generating processes such as grinding/crushing plant and machinery, conveyors, chutes, or drills with dust collection systems or automated dust suppression systems.
• Implementing robust weather monitoring systems to predict wind conditions that could result in dust impacts off-site. This may indicate when additional control measures, such as modified operations, should be implemented.
• Progressive rehabilitation is already a requirement for quarries and mines. This reduces the area of exposed surfaces from which dust could generate, it can aid as a vegetation buffer for the open quarry and can aid in improving air quality.

Ongoing management of climate impacts

These adaptation measures to reduce off-site dust generation will be included in a climate adaptation plan for the quarry, along with measures to manage other climate risks. Trigger points for each of these adaptation measures will also be identified to guide when each of the measures should be implemented. For example, climate forecast data may indicate that increasing the existing on-site water treatment and storage infrastructure (a costly measure) may not be required until later in the future when average annual rainfall is projected to be lower, but the intensity will be higher. However, low-cost, no regret adaptation measures such as modifying operations based on forecast wind conditions to reduce dust generation and off-site dust impacts, may be readily implemented.

An adaptation pathway will then be developed to ensure that the adaptation measures are prioritised and implemented based on their trigger points. The adaptation pathway enables the quarry operator to address the high-risk, time critical climate change impacts now, while remaining open to future adjustments as the climate evolves.

Climate risk management is an iterative process and should be reviewed periodically to ensure the risk assessment and adaptation pathway remain effective and appropriate into the future. By planning ahead and building adaptability into administrative controls and infrastructure, the extractive industry can reduce its vulnerability, safeguard facilities, and protect and/or improve existing environmental conditions.