Consultants present stormwater asset inventory, estimate $31.4 million replacement cost

Margaret Blank of Underwood Engineers presented the town’s draft stormwater asset management plan to the Town of Swanzey Select Board, saying the effort was funded by a $30,000 asset-management grant from the New Hampshire Department of Environmental Services and that the Southwest Regional Planning Commission completed field data collection.

Blank said field crews evaluated about 1,583 of the town’s roughly 1,685 stormwater assets and assigned condition scores; about 102 assets could not be located or were paved over. The inventory and supporting photographs and maps were uploaded to the town’s ArcGIS Online account and a local ArcGIS Pro project for staff use.

The report breaks assets into structures (manholes, catch basins, drop inlets), end treatments, and 35,834 linear feet of stormwater pipe. Blank said roughly 10% of the known assets were rated in “poor” condition and that those poor-condition items should be reviewed to determine whether problems are maintenance- or structure-related. "If it’s a maintenance issue you can clean it out; if it’s a structural issue you might need repair or replacement," Blank said.

The report includes a prioritization method that multiplies a probability-of-failure score by an impact-of-failure score to generate a risk ranking. Blank and Desmond Cager (Underwood) showed maps of trouble spots the town provided — Talbot Hill, California Brook, Winch Hill, Pebble Hill, Atkinson Hill, Dunhill, Cobble Hill and Swanzey Lake — and an example of the impact map that clusters higher‑risk locations in low-elevation, bowl-like areas.

Blank summarized costs broken down by asset type and unit cost and said the engineering team’s high-level estimate for replacing all stormwater assets is about $31,400,000. She emphasized that estimate is a systemwide, high-level calculation used for financial planning, not a construction bid, and said stormwater pipe accounted for the largest share of the cost.

Blank also described deliverables the consultant provided: the geospatial inventory, a story map (public-facing interactive map and narrative), Python tools saved to the town workstation to automate tasks, a financial-planning spreadsheet and a level-of-service matrix that captures the town’s SMARTER goals.

Board members asked about timing and next steps. Blank said the grant deadline was today, the draft report has been forwarded to the planning department, and the team will submit a final disbursement request; she also recommended beginning by cleaning assets known to be blocked to see whether service improves before pursuing larger structural work.

Several board members asked for access to photos and maps for the items currently rated poor; Blank said photos are labeled and available on the town workstation and online account and that staff would coordinate to make them viewable to board members and other stakeholders. The board noted some repairs already done over the last 18 months and asked staff to compare the 2023 inventory to work completed since then to update priorities.

The presentation also listed ongoing projects that incorporate stormwater work, including a North Winchester/California Street reconstruction described in the report as a $1.3 million project scheduled for completion in October 2025, and paving on Talbot Hill Road linked to flood remediation.

Blank recommended the town incorporate the asset management outputs into a broader stormwater planning study and use the inventory as the foundation for a multi-year maintenance and capital-replacement plan.

The board did not take formal action on the report during the meeting; members asked staff to circulate the full draft report, supporting photos, and timelines for the consultant’s recommended next steps.

Ending — The consultant team said final documentation would be completed under the DES grant and that town staff will have the maps, photos and spreadsheets to begin prioritizing maintenance work. The board directed staff to follow up with Underwood Engineers and the Southwest Regional Planning Commission to make visual materials available to members and to report back on items already repaired since the 2023 survey.