The most common areas of non-compliance involve the discharge of saline water into local waterways and broken or faulty pollution monitoring equipment, a Newcastle Herald analysis of Hunter mines’ annual returns has discovered.

Although many of the instances are relatively minor in isolation, the compound effect is causing increasing concern among local communities.

The analysis of the returns of 15 of the region’s largest mines since 1999 showed the average rate of full compliance was 25per cent.

In one example from 2009-10, Wambo Coal reported that a pipeline leak had resulted in a discharge of saline water into North Wambo Creek. Steps were taken to contain the leaking water.

In another example from the same year, Coal & Allied reported that 16 dust samples were not collected at its Mount Thorley mine due to equipment failure and operator error.

Peabody Wambo Coal environment and community coordinator Troy Favell said instances of non-compliance needed to be viewed in context.

While there were the 13 reportable incidents at Wambo between October 2006 and October 2010, seven were technical non-compliances caused by factors such as broken glass sampling bottles and lack of access to private property for sampling purposes.

No penalty notices were issued because ‘‘the investigations and sustainable actions were found to be satisfactory,’’ he said.

A Coal & Allied spokesman said all instances of non-compliance were taken seriously.

‘‘We actively monitor our own performance and openly report any non-compliances as well as the actions we take to address them,’’ he said.

But community representative Carol Russell, from the Singleton Healthy Environment Group, said there was too much leniency given to the mines when it came to self-regulation.

The environmental protection licences also needed to be more strict.

‘‘The licences are inadequate because they don’t supply the mines with limits and the criteria they are expected to meet,’’ she said.

A NSW Minerals Council spokesman said reports of non-compliance may not provide a full picture of environmental performance.

Sometimes the breach ‘‘may simply have been the result of, for example, maintenance on equipment, which has led to gaps in reporting on air quality,’’ he said.

The Office of Environment and Heritage can respond in a number of ways to licence breaches, from warning letters and penalty notices to imposing pollution-reduction programs and prosecution.