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Council proposes a separate 'stormwater' matrix and guidance for wet/dry sampling
Summary
Staff proposed adding a distinct 'stormwater' matrix to separate MS4/permit-regulated effluent samples from ambient surface-water monitoring; participants urged recording wet vs. dry conditions and staff said SEEDin2 will add a wet/dry field and guidance will be added to sample comments.
At the December user-group meeting, staff proposed creating a separate "stormwater" matrix to distinguish permit-regulated point-source stormwater effluents (MS4, industrial, construction) from ambient surface-water samples used for integrated reporting.
"We're just calling the matrix name stormwater," database manager Tessa Foggitt said, explaining that the change will make it easier to exclude stormwater effluent from ambient water-quality assessments: "the description is effluent from point source discharges from MS4 boards, industrial facilities, and construction sites regulated under MPDS permits."
Participants raised the need to distinguish wet-weather (during or shortly after rainfall) from dry-weather runoff because the two can produce different water-quality results. "We sometimes sample dry weather runoff from stormwater drains," said Kelly, noting different objectives and analyses for dry versus wet samples. Keijin and Abigail emphasized the regulatory significance of recording wet/dry sampling conditions for the integrated report review process.
Foggitt said the matrix field itself is not ideal for marking wet/dry conditions, but SEEDin2 field forms will include a specific wet/dry indicator; she also agreed to add guidance suggesting users include wet or dry in the sample comment column of existing lookup lists to improve consistency until SEEDin2 is in place.
The runoff matrix for nonpoint-source surface runoff will remain separate. Foggitt said staff will test how much descriptive text can fit in the matrix description and expects to publish the new matrix and updated guidance through the usual review process (estimated availability in January).
