Council approves $46,056 task order to study zinc discharge and revise NPDES permit calculations

The Mount Shasta City Council approved a $46,056 task order with engineering consultant Robertson Bridal to study dilution-credit adjustments and pursue revisions to the city's NPDES discharge permit.

Staff said earlier work, contracted in December 2025, found zinc levels in effluent increased since the new wastewater plant came online. Potential causes discussed included reduced inflow-and-infiltration dilution, new piping that could leach zinc, and recycled filtration material. Staff explained that initial dilution-credit calculations used limited monthly river-flow data and conservative low-flow assumptions; daily flow data from the dam are now available and could yield higher dilution credits.

Ken, the presenting staff member, said Robertson Bridal will re-run the complex calculations, meet with the state water board, and draft a proposed permit revision. "Robertson Bridal has very good relationship with the state water board at Sacramento level, and I think they'd be a great representative for us on this issue," he said. Council discussed funding: one council member noted the $46,056 would come from the sanitary sewer fund rather than the general fund. Staff warned that if a redesigned holding pond or pump system is required to provide buffering capacity, that construction would be an additional expense beyond the current task order. The motion to approve the task order passed with no recorded opposition.