Commission approves Mil Creek thin‑layer pilot to raise marsh elevation and study carbon/alkalinity effects

The commission voted Aug. 5 to approve an amended Order of Conditions for a thin‑layer pilot in Mil Creek, part of the Herring River Phase 1 restoration. Project proponents described a small, highly controlled experiment (about 1–1.5 acres of treatment within a ~3‑acre study area) that will place up to roughly 6 inches of material in three half‑acre cells, each receiving a different material treatment: Cape Cod sand (control), sand mixed with ground limestone, and sand mixed with ground olivine.

Presenters emphasized that this is a pilot and that the team will implement detailed baseline and post‑construction monitoring, turbidity controls, timing restrictions and a corrective‑action plan. Kevin, a project scientist, described the scientific rationale for adding alkaline minerals: accelerated mineral weathering in salt‑marsh soils can increase exported alkalinity (bicarbonate) that remains in the coastal ocean for long periods and thus represents a potential carbon‑removal pathway. "This is a natural process," he said, describing how alkalinity-producing minerals react with carbonic acid in water to form bicarbonate. The team also addressed ecological concerns: Grace Andrews cited a prior one‑year field trial in which oysters placed adjacent to olivine did not show statistically significant adverse impacts, and the team committed to comprehensive tissue and water testing and to predefined monitoring triggers and corrective measures if trace metals are detected.

Commissioners and shellfish stakeholders, including the Division of Marine Fisheries, asked for clarity on monitoring triggers and potential corrective steps (such as temporary flow controls and additional sand cover). Project engineers explained logistics — temporary access across the coastal bank using timber matting, reusing excavated channel material to build sparrow nesting islands, and contractor methods to place and grade material. The commission approved the amendment by recorded vote and asked the team to supply lab results for the olivine stockpile, the monitoring plan with explicit triggers, and continued coordination with fisheries and state reviewers.