NSW government agencies have reiterated demands for more information from Santos about its plan to develop a $3 billion coal seam gas project in northern NSW, saying the company had failed to respond to their concerns.

A dozen agencies, including the Environment Protection Authority and the Rural Fire Service, have released their responses to Santos' answers to 23,000 submissions to its Narrabri environmental impact statement.

Unresolved issues include how Santos will dispose of salt generated from the 850 planned wells. Over 25 years, the gasfield is expect to produce more than 430,000 tonnes of the material.

The EPA had demanded Santos state where the waste would go, noting it had "the potential to create a large point of source of salt in the environment if not disposed of appropriately", and that the company's response "did not provide the details requested".

"The EPA expects that many, if not all, landfill facilities in the local government area will not have the capacity to receive the quantity of salt (and other waste) generated by the project," the agency said.