Save Our Coast has called on Environment Minister Matt Kean to further delay Centennial Coal's planned seismic survey in Lake Macquarie to allow for a thorough environmental assessment.
SOC founder Natasha Deen wrote in an email to Mr Kean this week that "Centennial Coal's documentation to the public that sound at this level does not have any impacts appears to be misleading and is in contradiction to the marine assessment and known scientific evidence".
The company has said it plans to use a spark-gap sounder to carry out sub-bottom profiling of the lake and the "strata above our mine workings" from next week.
A marine assessment prepared for Centennial last year by consultants GHD said the survey would involve firing pulses from a seismic "sparker" at up to 227 decibels.
The company said last week that the GHD report "unfortunately contains several inaccuracies" by referring to seismic air-gun technology, which Centennial had decided not to use.
Centennial published a question-and-answer sheet on its website saying the survey method was the "same" as that used regularly by NSW Maritime to gauge the depth of Swansea Channel and was a "standard" geotechnical survey technique used throughout the world.
In response to questions from the Newcastle Herald, Transport for NSW said NSW Maritime used an echo sounder, not a seismic sparker, to survey the channel and lake floor about twice a year.
It said it used bathymetric surveying to map the lake's depth, rather than sub-bottom profiling.
Centennial later corrected its Q&A sheet to say the technology the company planned to use was "similar" to that used by NSW Maritime.
Newcastle University's Dr Vincent Raoult told the Newcastle Herald this week that the sparker technology was less harmful than seismic air guns but the evidence did not support Centennial's view that it was harmless to marine animals.
Another scientist, Curtin University's Associate Professor Robert McCauley, congratulated the mine for using the less harmful method, which he said was unlikely to affect animals outside a range of "tens of metres".
Save Our Coast delivered a 60,000-strong petition to federal parliament this week calling for an end to seismic testing and drilling for oil or gas off Newcastle and the Central Coast.
Dr Deen, who made a submission to the Senate inquiry into seismic testing in December, remains unconvinced by Centennial's assurances that the lake survey will not affect marine life.
She called on the mine to produce a new marine assessment if it no longer planned to use the technology referred to in the GHD report.
"I urge you to please consider the need for a more thorough assessment of the use of seismic surveys or noise generating activities within the confines of Lake Macquarie, and in the meantime that this survey be postponed further," the Newcastle dentist wrote to Mr Kean.
Centennial agreed a week ago to delay the survey and a concurrent drilling program by seven days after an outcry from environmentalists, fishermen and politicians.
The survey, which is approved under the mine's 2013 lease, covers about four square kilometres of eastern Lake Macquarie from Swansea to Nords Wharf.
The sparker technology uses a high-voltage charge released in an arc across electrodes in the water. The underwater spark creates a high-pressure plasma or vapour bubble which expands then collapses, generating a low-frequency sound pulse.