Scheme performance

The Hunter River Salinity Trading Scheme has proved tremendously successful and is widely supported by the community that contributed to its creation.

The EPA administers the scheme with guidance from an operations committee with representatives of the community, industry and the government.

The Hunter River Salinity Trading Scheme involves a finite system of salt credits that industries can buy and trade to discharge their salty water into the Hunter River. Discharges are only permitted when the river contains adequate fresh water to dilute the salt and maintain water quality. The Scheme therefore balances the amount of salt that industry can directly discharge, with the background level of salt in the river.

Overall, salinity is kept to an appropriate level by only allowing discharges during high flow or flood events and balancing the amount of salt that industry can discharge against the background salt levels in the river.

Salinity is measured by determining the electrical conductivity (EC) of water within the river. EC estimates the amount of total dissolved salts in the river and is measured in micro Siemens per centimetre (µS/cm). Spikes in EC may occur when river flows drop. There are multiple contributing factors including concentration of salt due to lower flows and potential inputs from surface water runoff and infiltration and saline groundwater inflows but also inflows from tributaries such as the Goulburn and Wybong rivers. These rivers have saline catchments that contribute water with high EC when flows in the Hunter River drop substantially.

Scheme performance in 2020–21

During the 2020-21 financial year, the Hunter River catchment received higher rainfall when compared to recent years, resulting in high flows and allowing the Scheme to safely discharge salty water into the Hunter River. The map below identifies the locations of each sector of the Hunter River referred to in the Scheme.

Hunter Valley map

Five discharge periods (known as blocks) were activated in 2020–21, providing 63 discharge opportunities for various industries, with 28 discharge opportunities for the Upper sector, 15 for the Middle sector, and 20 for the Lower sector.

In total, there were 98 individual discharge events of saline water from across 8 industry sources into the river in 2020-21, within the 63 discharge opportunities.

How did the Scheme perform during industry discharge events?

A total of 10,000 tonnes of salt were discharged to the Hunter River by Scheme participants during high flows, representing 7% of the Total Allowable Discharge (TAD) of salt per year, and 18% of the total salt load carried by the river past Singleton in 2020–21. Eight participants took advantage of discharge opportunities. The calculated TAD (i.e. without flood flows) was 151,900 tonnes. The average daily salinity in the river over the 2020–21 period was 650 µ/cm at Denman; 855 µS/cm at upstream Glennies Creek; and 742 µS/cm at Singleton.

Scheme performance reports

Each year the EPA assesses the performance of the scheme and produces a report.

Longer-term scheme performance

While the scheme operates to manage salinity levels in the river as a result of industry discharge, occasional exceedances still occur, caused by diffuse sources of saline runoff. New mines can readily be granted discharge licences, with significant economic and employment benefits for the valley.

However, since the scheme started, river salinity has more consistently been below the salinity target.

These improvements have occurred despite a drier-than-average weather pattern since the scheme began. The graph below shows that in previous dry spells (early 1980s and around the turn of the decade) salinity levels were very high. These have not been repeated during the time the scheme has been in operation (which has been similarly dry).

Hunter River Salinity Trading Scheme - electrical conductivity at Singleton

Electrical conductivity at Singleton 1980 to 2002

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