Catherine Sullivan and Craig Day, of Bumbaldry, about 37km north-east of Grenfell, told the inquiry into the current and potential impacts of gold, silver, lead and zinc mining on human and environmental health they are "unable to farm" after agreeing to host a tailings dam on their property nearly two decades ago.

In 2005, they were approached by Resource Base, former owners of the Broula King goldmine to build a tailings storage facility on their property, covering four hectares to be built by 2012. The couple were offered $10,000 for the use of their land.

Tailings storage facilities hold the leftover materials from the mining process and can include waste rock, minerals and heavy metals including lead. Tailings dams create a slurry that can contaminate the surrounding environment and groundwater if not properly constructed and contained.

Sullivan told the inquiry the tailing storage dam on her property was promised to be a "nil-exit site", with no water leaving the dam. But with heavy rains, trickle pipes installed on neighbouring Broula sites began to spill on the farm, over historic tailings facilities and towards Tyagong Creek.

Day and Sullivan told the inquiry more than 80,000 litres were estimated to flow from trickle pipes each day during heavy rain, through their property and downstream into the Tyagong Creek.

"Craig was measuring what was coming out of there, it was a pH of 4.4," Sullivan said. A pH of 4.4 is comparable to acid rain and slightly more acidic than black coffee.

Daryl Young, director of BK Enterprises (BKE), the new owners of the Broula King mine, said low pH levels are comparable to the levels found in springs affected by historic mines.

"It needs to be put into perspective ... 30,000 tonnes of historic tailings were treated with mercury and amalgam. There's mercury and lead and cadmium leaching out of them downstream," he said. "There is evidence that they are polluting the downstream Tyagong creek."

Historic mine sites, built before 1992, and their rehabilitation are managed by the state resources regulator, as part of their legacy mines program. The program has strict guidelines for rehabilitation, limiting projects on private land and in areas where communities or companies could inherit the rehabilitation of a site.

BKE has conducted three water releases over the last two years to protect the tailings dam. Young said these were in line with EPA licensing regulations and were only from surrounding water holding facilities.

"We've been measuring [natural springs] at a number of sites and they have high metal content and have low pH's as well," Young said. "But by the time the water gets down to Tyagong Creek, it is registering a six plus pH level and lower metal contents."

Sullivan and Day measured the trickle pipe flow themselves, but are limited in what action they can take with the NSW EPA or the state's Resources Regulator.

After its purchase by BKE, Broula King is set to become a regional mine waste processing and recycling centre, extending the lifespan of the site.

"We thought the numerous checks and balances will ensure that this project would exhaust the gold reserve and allow us to get on with farming." Sullivan said. "Now we are unable to farm."

"We have dying vegetation in the Tyagong Creek ... We've publicly declared our land is contaminated and acknowledge that decades of rejuvenating our property have been thwarted by poor mining practice and regulation," she said.

"We are truly in an extreme position."

The inquiry concluded public hearings in Sydney last week, and is due to report its findings to parliament in December.