Council directs staff to draft ordinance limiting architectural copper to protect stormwater

Carmel staff presented monitoring results and a draft policy on Nov. 4 recommending prohibition of architectural copper gutters and downspouts to reduce dissolved copper in stormwater entering the Monterey Bay National Marine Sanctuary. Staff cited multi-year monitoring and applied marine sciences reports that identified elevated dissolved-copper concentrations at monitored outfalls and discussed mitigation options such as biochar filters and stormwater diversion to the wastewater treatment plant.

Council members expressed support for a ban on new copper installations but requested a clear exemption for designated historic resources and asked staff to bring a codified ordinance to the planning commission for detailed treatment of exceptions (flashing, valleys, ornamental elements) and mitigation options for existing copper installations. Staff said codification would improve enforceability compared with the current design-review condition of approval and noted the longer-term cost and engineering implications of downstream stormwater-diversion options.

Why it matters: Dissolved copper is toxic to aquatic organisms at low concentrations. The city is an Area of Special Biological Significance under state water policy, and the council decision could alter future permitting and materials choices across rebuilds and reroofs.

Next steps: Council directed staff to prepare a codified ordinance, coordinate planning-commission review and include mitigation alternatives and carve-outs for designated historic resources. Staff will return with draft code language and options for implementation and enforcement.