Tectonic provided engineering services across multiple contracts at Upper Minkel Dam, a Class C (High Hazard) dam also known as the Croton Dam and Dike. Tectonic’s services included the preparation of a Safety Inspection report, Engineering Assessment, Emergency Action Plan, Inundation Mapping, and a feasibility assessment of decommissioning.
Tectonic conducted a visual safety inspection of the dam site, spillway and appurtenant structures according to NYSDEC guidelines and provided recommendations relative to the dam safety and maintenance. The Engineering Assessment (EA), included a review of the available records, visual inspection, hazard classification evaluation, hydrologic analysis to evaluate the spillway capacity and stability/seepage analyses and preparation of a report presenting the results of the assessment and recommendations for remedial work needed to maintain compliance with the NYSDEC dam safety regulations. The Town has further contracted with Tectonic to perform enhanced monitoring and regular safety inspections through 2022.
As part of the ensuing feasibility study, two (2) alternatives; (a) dam decommissioning and (b) conversion to a highhazard dam were explored. Tectonic established hydraulic conditions to govern the alternative approaches, evaluated the environmental regulatory compliance considerations (wetlands & watercourses; threatened and endangered species; environmentally sensitive areas, habitats or communities; aquifers/local water wells; historic properties, archaeologically sensitive areas), performed a hydrogeological assessment of potential baseflow, planned wetland mitigation areas, sampled sediments for analytical testing, developed alternatives, estimated construction costs, provided renderings, and developed a restoration plan for the former waterbody. The recommendations were presented in multiple formats and venues to Town officials, the general public, adjoining property owners, and downstream municipalities.
A grant from the New York State Environmental Protection Fund through the Hudson River Estuary Program of the
NYSDEC partially funds the project.
As part of an interim step until the dam is decommissioned, an intensive visual inspection and monitoring program was required by the NYSDEC. Tectonic prepared an enhanced dam safety program for the dam, which included biweekly visual inspection and monitoring, and quarterly oversight reviews. The bi-weekly inspections were performed by Town of New Castle employees, and on a quarterly basis, Tectonic performed an inspection, reviewed the inspection reports, and prepared a submittal to the NYSDEC. The program will run until the dam is breached and decommissioned.
Tectonic has recently begun designing and permitting the decommissioning of the dam under a contract jointly funded between Westchester County and the Town of New Castle. Services include boundary and topographic surveys, biological inventories, sediment sampling and waste classification, schematic/design development/construction document phases, public interface, Federal/State/Local permitting, public procurement, construction inspection, certification, and mitigation monitoring. Mitigation design for the former impoundment restoration is being designed by Westchester County Planning Department staff as part of the municipal partnership.
