LOS ANGELES (CBSLA) — Protesters marked the anniversary of the largest methane leak in U.S. history at the Aliso Canyon natural gas storage facility near Porter Ranch in a demonstration Monday that ended in several arrests, police said.

Dozens of residents and members of the Save Porter Ranch community group were seen chanting slogans outside the facility, the site of the 2015-16 leak which several families claim is responsible for ongoing health issues.

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The rally marked the second anniversary of the massive methane leak, which was discovered in Oct. 2015 and continued until Feb. 11, 2016, when Southern California Gas Company officials announced the leak was capped.

An estimated 109,000 tons of methane was released in the leak and forced thousands of Porter Ranch residents to temporarily relocate.

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Demonstrators at Monday’s rally were almost hit by a passing big rig as they blocked an entry driveway to the Aliso Canyon site.

Police later declared an unlawful assembly and about a dozen people were led away in handcuffs.

Officials resumed limited operations the Aliso Canyon in late July with approval from state regulators even as Los Angeles County officials have failed in efforts to block resumed operations.

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