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Engineering firm outlines options to meet NPDES water‑quality rules; staff to propose UDO changes
Summary
Robinson Engineering presented post‑construction BMP options under the NPDES/IDEM permit, and town staff said PCBMP language will need to be integrated into the Unified Development Ordinance ahead of the next permit cycle.
Robinson Engineering presented an overview of post‑construction best management practices (PCBMPs) required under the National Pollutant Discharge Elimination System during the Town of St. John Plan Commission study session on July 1.
Susan Quasnney of Robinson Engineering explained that the 2021 permit update requires both volume control and water‑quality improvements for developments that disturb more than one acre; the town has discretion on how to implement water‑quality controls. She described structural options (settling basins, infiltration trenches, permeable pavement, hydrodynamic separators, underground detention) and nonstructural approaches (policy changes, increased open space, native plantings, design methods). Quasnney emphasized trade‑offs: some measures have higher developer costs and ongoing maintenance obligations, and municipal responsibilities include periodic inspections and oversight if maintenance is delegated to homeowners associations.
Town staff said the town recently completed a post‑construction audit and expects to integrate PCBMP requirements into the Unified Development Ordinance before the end of the year to align with the next storm‑water permit update. Staff asked the commission for direction on which practices the town should require for developments over one acre—options discussed included native plantings, bio‑swales, permeable pavements and under‑drain systems, or a mixed approach that combines policy and engineering elements.
Commissioners asked practical questions about definitions and costs; Quasnney said permeable pavement functions by allowing water to pass through a stone base and that green infrastructure can be inexpensive at small scales but more complicated (and costly) when combined with under‑drains in commercial settings. Staff will circulate the final presentation and links on green infrastructure for commission review, and the commission will revisit potential UDO amendments at a future study session.
Key quote: "This is the National Pollutant Discharge Elimination System Program," Quasnney said, describing why the town must now address water‑quality as well as volume control.
Next steps: staff will provide the audit report and draft language options so the commission can recommend specific PCBMP requirements for inclusion in the UDO; an ordinance amendment will return for formal consideration later this year.
