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Oro Valley presents ADEQ Small MS4 characterization monitoring results; mostly non-detects, traces linked to vehicles
Summary
Staff presented results of characterization monitoring required under the ADEQ small MS4 permit: Oro Valley sampled three outfalls and reported most constituents below lab detection levels, with recurring detections of barium and antimony linked to vehicular brake wear.
Scott Bennett, stormwater staff, presented the town’s characterization-monitoring work under the Arizona Department of Environmental Quality’s Small MS4 permit and described how the town met the monitoring requirement.
Bennett said the permit (issued in 2021) requires monitoring at three outfalls — industrial, commercial and residential — and that Oro Valley conducted sampling at three locations using available commercial and residential outfalls because the town lacks a clear industrial outfall. “We are doing two commercial and a residential, and it was one of them is really a combination,” Bennett said.
Bennett described the sampling method as grab samples collected during qualifying runoff events (the permit’s sampling trigger is 0.1 inch of rain or more) and said the town mailed samples to a laboratory; he noted some early sampling problems such as headspace in bottles and said lab technicians advised filling bottles completely in future events. He listed the constituents analyzed: pesticides, total metals, volatile organic compounds, cyanide and semi-volatile organic compounds.
On results, Bennett said most constituents were below the lab’s detectable limits. “The two that are popping in every report are really associated with cars parking lots, cars, brake pads, barium and antimony,” he said, adding the detected concentrations were not high. Bennett also recounted sampling locations used: a site near Home Depot, a water-utilities site sampled in December 2022 and a final sample at the Villages of La Cañada town golf course outfall.
At the end of the presentation Bennett told commissioners that the town had satisfied the permit’s monitoring requirements. Commissioners asked clarifying questions about sampling logistics and potential violations; staff said there were no major or minor permit violations based on the sampling.
