Danbury wastewater plant repairs planned after 2024 washout; commission tables Newtown Road permit

Dennis Diver of Wright Paris Engineers presented the commission with a redesigned restoration plan for the southerly drainage basin at the Danbury wastewater treatment plant on Newtown Road, explaining that the August 18, 2024 storm — which he characterized as a 200‑year event with roughly six inches of rain at about four inches per hour — washed out riprap, sent material into process tanks and plugged the originally installed trash rack.

Diver said the revised plan upsizes the 60‑inch and 48‑inch pipes, adds a third plunge pool for energy dissipation, installs gabion baskets to slow velocity and trap debris, and replaces the flat trash rack with a three‑sided rack so water can route around debris. He also described a proposed maintenance access road (gravel) so crews can remove logs, tires and other debris and perform regular cleaning. Diver said the plan would reuse much of the washed‑out riprap in gabion baskets and import larger‑diameter rock as needed; he did not provide a final truck‑count but offered to obtain quantity estimates for the commission.

Commissioners and staff focused on wetlands flags, discharge points downstream, the need for a temporary construction easement where plans appear to cross a property line, and responsibility for long‑term basin cleaning. Staff confirmed parts of the area had been previously flagged as wetlands — the presenter described the wetlands footprint as roughly "a tenth of an acre" in stream footage — which is why the permit is before the commission. One staff member told the commission they had walked the site with the city deputy director of utilities and the city engineer and recorded removal of about "10 to 12" small trees to create the access and staging areas.

Diver said Haley & Aldrich reviewed the geotechnical approach and recommended gabion baskets; he also described plans to place jersey barriers near aeration tanks to protect them from future riprap movement and to create an overflow weir and storm drain pipe to handle spillover if trash racks plug during a larger storm.

After questions about rock quantities and easements, a motion to table regular activity 1267538 (Newtown Road) was made, seconded and approved so staff can obtain additional quantities, confirm whether a temporary easement is required, and coordinate site visits.

The commission requested that the applicant provide truck‑load estimates for imported rock, a finalized staging plan showing any work across property lines, and the standard operating procedure for pre‑ and post‑storm inspection and maintenance of the trash rack and plunge pools.