2.3.4.2 Water management for the coal resource developments

This section summarises the general characteristics of mine water management in the Namoi subregion in the context of the existing regulatory framework. Common elements important to informing the representation of mine impacts on water resources are identified.

Mine-specific data used in the groundwater and surface water modelling such as resource extraction start and end dates, mine footprints, flow rates, pumping depths, discharge rules and surface water extractions are provided in companion product 2.1-2.2 for the Namoi subregion (Aryal et al., 2018a).

During all life stages of a mine, from construction and production through to mine closure and rehabilitation, the water balance of the site and surrounding areas will change. Changes at the land surface through clearing of vegetation and disturbance of top soil during mine-site development, as well as changes in the fluxes of water between water stores during mine operations, have implications for water flow paths and water quality. For example, the disposal of lower quality groundwater from worked seams has the potential to degrade the quality of receiving waters if discharged to the stream network. Runoff from areas disturbed at the surface can often be sediment laden and carry other impurities. Minimising the discharge of low-quality water to the wider environment and ensuring the mine has sufficient water for on-site uses are key objectives of mine water management.

Since coal mining commenced in NSW, policies, legislation and practices have developed to manage the impacts of mining developments both on and off the mine site. Mine and CSG operators are required to prepare mine water management plans detailing how they will ensure their activities avoid or minimise any negative consequences on the environment from the extraction and use of water, both in terms of the quantity and quality of water. It is assumed that the plans are adhered to and that some generalisations about mine water management can be made that apply to all mines, whether a plan for a particular development has been drafted or not.

The key legislation and policies that govern the management of water in relation to mining in NSW are outlined in Table 13. They are listed in the order in which they came into effect, although they typically have had amendments since they were first enacted.

Table 13 NSW legislation and policies governing mine water management in the Namoi subregion

CSG = coal seam gas, DPI Water = Department of Primary Industries – Water, EPL = environment protection licence

Data: adapted from Water Regulations Overview (DPE, 2015)

NSW’s Mining Act 1992 makes provision for the protection of the environment in the course of mining. The definition of environment encompasses ecological and sociocultural assets, which are in or on the land over which authority or claim is sought (Part 11, section 237(1)). Under this Act, the NSW Government Minister may require environmental impact studies to be carried out.

Under NSW’s Environmental Planning and Assessment Act 1979, an environmental impact assessment (EIA) must be prepared for major developments, detailing the impacts to natural and human environments and the options to minimise damage for consideration by the regulatory authority in making a determination. Mining EIAs must assess the impacts to surface water and groundwater and include a mine water management plan and rehabilitation planning documents, which satisfy the NSW Government Minister that the impacts of the mine on water resources during and following mine closure are minimised. For underground operations, modern development consent requires the preparation of an extraction plan, which describes how impacts of subsidence will be managed to meet the requirements of the development consent. With respect to water resources, these extraction plans are particularly concerned with identifying and managing the risks to surface watercourses and alluvial aquifers, but may also consider impacts on drainage more generally through interception of rainfall and runoff in subsidence-induced depressions.

A typical mine water management plan provides details of expected pumping rates from the open-cut or underground workings, runoff diversions and on-site water storage, discharge locations to the river network, on-site water treatment, requirements for clean water, and post-mining hydrology following rehabilitation.

The following generalisations, which are reflected in site-scale mine water management plans as a consequence of the regulatory framework, are used to inform numerical modelling of the Namoi subregion:

The amount of runoff retained on site will vary significantly between open-cut and underground mine operations. Generally, a larger surface area is disturbed during open-cut mining than for underground mining, thus there will be bigger impacts on surface water hydrology from open-cut mines than on underground mines. However, underground mines can cause subsidence at the land surface and changes in the hydraulic properties of subsurface layers, leading to increased interception of runoff in the area of subsidence.

In NSW, surface water extracted from rivers and used on site has to be licensed under NSW’s Water Management Act 2000. The annual volumes of water licensed to be extracted from the stream network for uses on site, which are modelled in the Australian Water Resources Assessment river model (AWRA-R) and reported in companion product 2.6.1 for the Namoi subregion (Aryal et al., 2018b), are provided in companion product 2.1-2.2 for the Namoi subregion (Aryal et al., 2018a).

Similarly, the removal of groundwater from mine workings and extractions of groundwater from production bores have to be licensed under NSW’s Water Management Act 2000. The amount of groundwater extracted from mine workings can vary significantly between mines, depending on the hydrogeology of the worked area, including volumes of stored water and hydraulic conductivity and connectivity between the different stratigraphic layers. Modelling by the mining companies of groundwater impacts as part of their EIAs is used to estimate likely flow rates and requirements for water access licences. Flow rates (licensed volumes of water pumped from the mine workings) have been obtained from mine water management reports for each mine represented in the baseline and CRDP in the groundwater numerical model (see companion product 2.6.2 for the Namoi subregion (Janardhanan et al., 2018)) and are provided in companion product 2.1-2.2 for the Namoi subregion (Aryal et al., 2018a).

Groundwater pumped from the mine workings is often of lower quality than surface water. Discharges of low-quality water from mining operations need to be disposed of carefully. One of the objectives of NSW’s Protection of the Environment Operations Act 1997 (POEO Act) is to protect the quality of the environment in NSW from pollution. Mining, coal working and coking are scheduled activities under this Act and require an environmental protection licence (EPL) to discharge offsite. The Environment Protection Authority, who administers this Act, can stipulate the conditions relating to pollution prevention and monitoring on mine sites as part of their EPL, including:

To ensure that discharges to the river do not exceed specified thresholds, mines may have to treat low-quality water to the required standard prior to discharge. Not all mines will necessarily have an EPL to discharge water. Without a licence, discharges to the stream network are not permitted.