Testing of water delivered to Guerneville residents found no detectable levels of mercury, a California Water Service official said Wednesday.

Darin McCosker, local manager for the company known as Cal Water, said the tests were prompted by concerns by some customers following news reports that elevated levels of mercury from the abandoned Jackson Mercury Mine had entered the Russian River.

The Press Democrat reported two weeks ago that state water quality regulators were concerned that heavy winter rains may have allowed contaminants from large mining waste piles at the former mine site off Sweetwater Springs Road to enter a creek that flows into the river.

Cal Water routinely tests for mercury in compliance with state requirements, but took additional samples for testing in light of its customers’ concerns, McCosker said in a press release.

Water quality testing for mercury is required every three years, and Cal Water has consistently met the standards since it began operating the Guerneville area system in 2000.

The company’s water comes from two wells.