VACAVILLE, Calif. (AP) - An environmental group has sued the city of Vacaville over the amount of a naturally occurring carcinogen in groundwater.

The San Francisco Chronicle reports the federal lawsuit was filed Monday at the U.S. District Court in Sacramento.

California River Watch is demanding that the Solano County city purge its water of chromium-6, the naturally occurring carcinogen that famously sickened Southern California residents as depicted in the movie "Erin Brockovich."

The newspaper reported that the environmental advocacy group also wants Vacaville leaders to give residents more notice of potential health problems associated with the contaminant and provide bottled water or another clean source to seniors and children.

The suit comes as Vacaville is already taking steps to bring its drinking water into compliance with California health regulations by 2020.

City spokesman Mark Mazzaferro declined to comment on pending litigation.

What are chromium-6 standards in California?

Chromium-6 is found in groundwater but can also be produced by industrial processes, according to the U.S. Environmental Protection Agency (EPA). Chromium-6 can be released into the environment through improper disposal of industrial waste or through leakage.

In 2014, California adopted the country's first chromium-6 law requiring drinking water contain no more than 10 parts per billion of the contaminant, according to the State Water Resources Control Board.

The Chronicle compares this amount to the equivalent of 10 drops of water in an Olympic-size swimming pool.

However, state health officials say water should contain no more than 0.02 parts per billion.

If these recommendations are followed, the Association of California Water Agencies, who sponsored the state chromium-6 law, estimates that not more than one person in one million who consume half a gallon of water daily for 70 years would be expected to develop cancer as a result of exposure.

This means, a person ingesting a very low amount of chromium-6 consistently for most or all their life likely won't develop cancer. Currently, the recommendations are not law.

Vacaville's groundwater is testing at 24 parts per billion and well water makes up nearly 40 percent of the city's supply, according to the newspaper.

Before the 2014 law came into effect, California required the levels of all chromium measure 50 parts per billion, according to Water Resources.

Water Resources notes the national standard as 100 parts per billion.