Conservation panel issues order of conditions for alum study to curb Artichoke reservoir blooms

Laura Diemer, a consultant working on the Artichoke reservoirs, presented the city's notice of intent for an alum (aluminum) treatment and told the Newburyport Conservation Commission the project is intended to reduce recurring cyanobacteria blooms that produced elevated saxitoxin last year. Diemer said the plan splits the reservoirs into five treatment zones (Zone 3 has subzones 3a and 3b) and aims to apply staged doses over roughly 10 treatment days in early May.

The treatment is intended to bind phosphorus in the water column and sediments to reduce nutrient availability that fuels cyanobacteria growth. ‘‘These treatments are designed to target the internal phosphorus load,’’ Diemer said, and she explained alum's mechanism and the importance of keeping pH between about 6 and 8 during applications so aluminum does not become toxic. Pete King, the city's water superintendent, described logistical steps: chemical tanks staged near the former Spring Bridge with secondary containment, application from barges, turbidity curtains near the intake, and a temporary shutdown of the treatment plant during active work in the lower reservoir.

The consultant contrasted alum with repeated copper-sulfate emergency treatments used in past seasons. ‘‘Copper is toxic to nontarget organisms, accumulates in sediments, and in 2025 we required six emergency copper treatments,’’ Diemer said, adding that repeated copper use can reduce effectiveness and increase ecological risk. She described the alum plan as a seasonally timed, monitored approach aimed at longer-term reduction of blooms while the city addresses watershed sources of nutrients.

The presentation included a watershed-load analysis: agriculture comprises about 9% of the watershed but was estimated to contribute roughly 36% of phosphorus load; developed areas (about 18% of the watershed) were estimated to contribute about 56% of the load. Diemer emphasized that alum addresses internal sediment phosphorus but that longer-term reductions will require watershed interventions and partnership with neighboring West Newbury, which contains a large share of the watershed.

Diemer outlined a comprehensive monitoring program: baseline sampling at monitoring stations before treatment; daily field monitoring of pH and turbidity during active treatment days; post-treatment laboratory analysis (including total aluminum) with the expectation that initial aluminum concentrations may spike but should return to EPA/MA criteria within 24 hours; and monthly sampling from June through October. She said visual assessments and biological sampling (phytoplankton and zooplankton) would be collected and that an on-site scientist would stop or adjust dosing immediately if distress to aquatic life was observed.

After questions about logistics, contingency plans, alternative treatments and dredging as a longer-term option, a commissioner made a motion to issue the order of conditions for the alum treatment study. The commission voted unanimously to issue the order of conditions, and the city will proceed to finalize contractor selection and follow the monitoring commitments described in the plan.

The project will proceed under the order of conditions with the monitoring and immediate reporting obligations described by the consultant; the commission will receive a final report summarizing all sampling and any incidents.