Material topic

Energy and emissions

We continue to find new ways to use energy more efficiently in our operations, and are improving our measurement and reporting of energy efficiency. We aim over time to reduce our carbon footprint, in terms of carbon dioxide emissions per tonne of coal produced.

Energy use

This year energy consumption remained one of our largest operational inputs.

In efforts to reduce our consumption, we have been working with Mobil Oil New Zealand in assessing trials of Mobil Diesel Efficient in the performance of two CAT 777 dump trucks at Maramarua. It is expected that use of this new fuel will reduce consumption by up to 3 percent, with lower emissions of nitrogen oxides (up to 10 percent), particulate matter (22 percent), and carbon dioxide (2.8 percent). In addition, we have been supporting a project to assess the feasibility of a hydro scheme to generate 24 megawatts of power from the Stockton mine site water runoff, where over six metres of rain falls each year.

Total energy consumption for FY20 is reported in terms of energy consumed (fuel and electricity) by employees and contractors and amounted to 992,267 gigajoules (“GJ”) at our five operational sites, the Cascade mine rehabilitation project and corporate offices. This is approximately a 3 percent decrease on energy use reported in FY19. Overall total waste rock stripping which is the key determinant of our energy consumption decreased by 6 percent with 18.86 million banked cubic metres (M bcm) of waste rock stripped at the five sites in FY20, compared with 20.02 M bcm in FY19.

94 percent of the energy consumed at our sites includes fuel used for operations, and power for the Canterbury mine. The remaining 6 percent of energy consumed was purchased electricity.

When comparing energy consumption by operation, there are significant differences reflecting the scale of each operation and the mine life cycle stage. The Rotowaro mine was the largest consumer at 366,760 GJ, reflecting the movement of more than 8 M bcm of waste rock in FY20, due to increased stripping ratios at this mature site.

The Stockton mine was the second largest consumer of energy at 354,344 GJ. This is consistent with producing and washing the most coal of the five sites, and reflects the electricity used in the coal handling and preparation plant, and the Ngakawau coal loadout facility. To note, the Stockton mine did not operate during the COVID-19 lockdown period or it would have been the largest power consuming site.

Comparison of energy consumption by operation FY20

The above graph excludes Sullivan where consumption was zero.

Greenhouse gas emissions

We measure greenhouse gas emissions and participate in the New Zealand Emissions Trading Scheme (“ETS”) in which carbon pricing is passed on to our customers.

We assist our customers in relation to ETS in terms of the quality of energy supplied and efficiency in supply logistics. A key advantage of our Canterbury mine is that it is located within 20 km from its major customer in Darfield, significantly reducing transport emissions. This recognises that whilst we support a transition from coal to renewable energies, this will take time – so we will endeavour to provide coal in a responsible way as long as our energy customers require it.

If Canterbury’s existing customers were to source coal from elsewhere in New Zealand, this would require trucking the resource from either the West Coast (250 km away) or from Southland (610 km away), significantly increasing the transport carbon footprint. Alternatively, and as is the case for the Huntly power station, coal could be imported from overseas suppliers such as Indonesia, which also has a much higher transport carbon footprint.

Our mining operations use significant quantities of diesel fuel to extract coal and transport coal within the sites. Electricity is required for coal processing, water treatment plants and mine management systems. Our coal also releases its own greenhouse gases (“GHG”) to the atmosphere (fugitive emissions), accounted for in the FY20 production tonnages under the Scope 1 emissions category. We report our GHG emissions with reference to their source as follows:

GHG emissions intensity

Our reporting of Scope 1 and 2 emissions is consistent with GRI reporting guidelines. In accordance with GRI, we have reported carbon dioxide in our GHG emissions calculations as carbon dioxide equivalent (“CO2e”). This year we have also accounted for sulphur hexafluoride gas emissions from transformers, and emissions from the use of ammonium nitrate in blasting.

We work with blast consultants to ensure our blasting practices optimise the recovery of clean coal. This reduces our GHG emissions by reducing the tonnages of contaminated coal that needs to be processed in energy-intensive coal washeries.

Total Scope 1 and 2 emissions for FY20 were 112,548 tonnes of CO2e, of which:

  • 40 percent related to fugitive emissions from coal production;
  • 1 percent related to electricity use; and
  • 59 percent related to fuel consumption and blast emissions.

The data for FY20 is approximately 7 percent less emissions than FY19. This is due to a 6 percent decrease in waste rock stripping (partially due to the COVID-19 lockdown at the Stockton mine), and reduced CO2e from fugitive emissions as 13.3 percent less saleable coal was produced in FY20 across the five sites compared with FY19.

In FY20, the highest GHG emissions intensity per tonne of coal produced was at the Canterbury and Rotowaro mines. Intensity is high at Canterbury because electricity is supplied from diesel generators in lieu of access to the national grid, and it has the lowest production rate of the five mines.

Rotowaro had a higher emission intensity this year because significant volumes of waste rock were stripped in the Waipuna West pit which is in the development stage. Also, saleable coal tonnages decreased due to a planned shift in supply to a key customer over a longer period.

Overall total GHG emissions intensity across all our operations were similar to FY19 at approximately 0.05 tonnes CO2e/tonne coal in both years.

Site FY20 Scope 1 emissions (t/C0₂e) FY19 Scope 1 emissions (t/C0₂e) FY20 Scope 2 emissions (t/C0₂e) FY19 Scope 2 emissions (t/C0₂e)
Stockton 43,545 47,525 1,084 1,093
Rotowaro 36,553 39,158 278 431
Maramarua 13,740 12,069 75 128
Canterbury 6,286 9,283 - -
Takitimu 10,626 10,786 29 30
Cascade 302 - - -
Corporate 15 15 15 8
Total 111,067 118,067 1,481 1,690

Scope 1 includes emissions from fuel and fugitive emissions from coal; Scope 2 are emissions related to electricity usage. The emissions are calculated following the procedures in the New Zealand Ministry for the Environment May 2019 report ME1414 titled “Measuring emissions: A guide for organisations – 2019 detailed guide”. Emissions for Escarpment and Sullivan were nil.

Material topic

Overburden management

Managing overburden materials to create stable landforms for rehabilitation is a key focus when developing our mine plans. This includes focus on implementing controls such as characterising mineral wastes and managing site storage to limit environmental effects and minimise closure costs.

The two mine sites that disturbed potentially acid forming (“PAF”) waste rock were Stockton and Canterbury.

PAF waste rock disturbed decreased by 2 percent compared with FY19, as overall waste rock disturbance reduced by 1.16 M bcm. The total amount of waste rock per tonne of saleable coal across all sites increased from 8.6 bcm/t in FY19 to 9.3 bcm/t, predominantly due to increased stripping ratios at Rotowaro and Stockton mines and the effects of the COVID-19 pandemic reducing coal output at Stockton.

Waste rock (bcm) disturbed in FY20

Following procedures in our Acid Mine Drainage management plan, in the Cypress pit at the Stockton mine we have been applying up to 16 kg of lime per tonne of PAF waste rock to minimise AMD production. At Stockton we have also constructed a second calcium oxide dosing plant to actively treat up to 3,000 tonnes of AMD per year in the St Patrick’s stream catchment. This plant started treating AMD in July 2020.

The Canterbury site actively manages PAF rock by selectively placing and compacting this material in areas of backfill where it can be safely covered by a minimum five-metre thickness of non-acid forming (“NAF”) rock. This minimises oxygen and water entry into PAF waste rock, ensuring minimal acidic water is produced from the backfill. Legacy AMD issues inherited from the mine’s previous owner have been managed by excavating an entire old overburden area that was the dominant origin of legacy high acidic seeps. This historic PAF material was placed into a new engineered landform and encapsulated, compacted and covered with a five-metre thick NAF cover.

Small historic acidic seeps from former underground mines in the Canterbury area are treated via two mussel shell bioreactors. The waste mussel shells neutralise acidic water and this is also a way of recycling the shells instead of disposal to landfill.

Material topic

Land use and biodiversity

We strive to avoid and minimise any significant impacts our operations may have on sensitive species, habitats and ecosystems. We integrate biodiversity into our business decision-making and management activities.

Our objective is to rehabilitate mine sites to ensure self sustaining indigenous ecoystems are established or reestablished. Where the post mining land use preference is pasture by the landowner, we focus on enhancing the chemical, physical and biological aspects of the soil before carefully selecting climate adapted pasture species.

Currently we have several active biodiversity offset projects underway that involve thousands of hectares of pest control management (defined by consent conditions) on Department of Conservation administered land. We are also working with experts and stakeholders to deliver biodiversity outcomes in the context of current or future mine closures. That includes minimising our land disturbance footprint and progressively restoring disturbed land.

Soil is salvaged and where appropriate vegetation direct transfer (“VDT”) is undertaken to speed up and improve the quality of indigenous ecological restoration. VDT is a method in which the sods of intact plants and soils are moved intact from stripped areas, usually in six cubic metre chunks. This method avoids new plantings, boosts ecosystem recovery, maintains biological activity within the soil and enhances erosion control.

Overall net total land disturbance over all sites in FY20 increased by 18 hectares (“ha”). The Stockton mine accounts for 53 percent of the total disturbed area. Mining of the Millerton pit area at Stockton over the next few years will provide for a more established strip mining operation, in which progressive rehabilitation rates are projected to reach double the current Stockton mine rehabilitation rate of approximately 20 ha per year. Our budgeted rehabilitation area for FY21 is 72 ha across all sites. It is noted that Maramarua is in a development stage, so no areas will be available for rehabilitation during FY21.

Rehabilitation budget table

Site Rehabilitation budget FY21 (ha)
Stockton 19.3
Rotowaro 16
Maramarua 0
Canterbury 7.7
Takitimu 15
Escarpment-Cascade 11.7
Huntly West 2.3
Total 72

No rehabilitation was undertaken at the Escarpment or Sullivan mines in FY20 as these mines are in care and maintenance, and no rehabilitation was undertaken at Maramarua as it is in development mode.

Land disturbed and rehabilitated

A rehabilitation project commenced at Cascade mine this year, however as no final stage rehabilitation areas were completed by the 30 June there are no hectares shown in the graph above.

Material topic

Water management

We aim to manage our water inputs, use and outputs to inform our management of water-related risks, seeking to minimise the impact to other water users and the environment.

All our mine site discharges have specific conditions related to discharge consents to protect aquatic ecology. No downstream water sources have been adversely impacted by water use at our sites in FY20.

Overall water use this year was 927 million litres, a reduction of 8.2 percent in water use compared with that of FY19. A significant proportion of this reduction is due to approximately 200,000 less tonnes of coal being washed through the Stockton mine coal washery as the mine was not authorised to operate under the COVID-19 lockdown.

Success for freshwater ecology at the Takitimu mine has been confirmed by a fish survey undertaken in May 2020 in the diverted tributary stream of the Wairio stream, which reveals a healthy population (juvenile and adult size ranges) of 111 nationally vulnerable Gollum galaxias fish (rare whitebait species).

Consumptive water use

FY20 Consumptive water use (MI/yr) FY19 Consumptive water use (MI/yr)
Stockton 592 644
Rotowaro 195 209
Maramarua 49 46
Canterbury 54 56
Takitimu 35 53
Corporate 2 2
Total 927 1,010

Note that the Takitimu mine water usage was incorrectly reported in the FY19 annual report as 121 Ml/yr.

Water use intensity

Based on estimates of consumption, water use intensity (measured as litres of water used per tonne of coal produced) is shown below. This year sites used between 169 to 621 litres of water to produce a tonne of coal. Significant water use at sites with a large disturbed area or close proximity to residences is related to dust suppression using water carts and sprinklers.

The Canterbury mine had a particularly high water use intensity due to an unusual, very dry summer period.

Stockton has the highest intensity of water use, which reflects the intensive use of the coal handling and preparation plant, accounting for 86 percent of the site water usage. It is noted that the coal washery water is treated for acid and sediment load and is returned to the Mangatini Stream.

The Takitimu mine had a 34 percent reduction in water use due to significantly more rainfall during the summer months, requiring less water use for dust suppression.

Water use intensity at mine sites FY20