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City'funded Monitoring Shows Occasional Hexavalent Chromium Exceedances but Not Sustained
Summary
Trinity Services updated the council on the city's hexavalent chromium monitoring program: sampling at several sites has recorded single-sample exceedances (1.2 ng and 1.64 ng) but not the consecutive three-sample threshold set by South Coast AQMD that would classify an exceedance of concern.
Trinity Services briefed the Paramount City Council on ongoing air monitoring for hexavalent chromium, describing the network of samplers at City Hall, two elementary schools and several pole-mounted locations and reporting occasional single-sample exceedances but no three-consecutive-sample exceedance during the monitoring period.
"Starting from the first sample on June 11, we had an invalid sample..." Randall Baxter said, describing network operations and the 1-in-6-day sampling cadence. He reported single-sample readings of 1.2 ng (July 25) and 1.64 ng (Nov. 26) at one location but noted that South Coast AQMD treats an exceedance as three consecutive samples above 1 ng.
Baxter described careful sample handling and quick lab turnarounds (filters moved to chilled conditions within 12'18 hours) and outlined the city's publicly available portal that posts results within about 24 hours of lab confirmation. He also described proposed South Coast AQMD Rule 1435 options under discussion (capture and HEPA filtration, demonstration of low emissions, or fence-line monitoring) that may affect local metal-heating operations.
Why it matters: Hexavalent chromium is a toxic metal with public-health implications; monitoring helps the city identify patterns and work with regulators and industry if sustained exceedances occur.
Next steps: Staff and Trinity will continue quarterly reports, maintain equipment and monitor proposed district rule changes. Council members asked follow-up questions about the monitoring schedule and the rule-drafting process.
Sources: Presentation by Randall Baxter (Trinity Services) at the Dec. 17 council meeting.
