Tectonic was retained to provide geotechnical and structural engineering and surveying services related to the deterioration of the Upper Candor Dam associated with Tropical Storm Lee in September of 2011. Tectonic evaluated the condition of the dam, determined required remediation and presented concept designs for repair options and cost estimates. Tectonic performed a field reconnaissance and a thorough inspection of the dam and provided an examination of the visible physical features of the dam and its appurtenant structures as an update to any past safety inspections performed for the dam.

Conditions encountered included evaluation of undermining and seepage associated with the dam’s pile supported embankment, as well as a structural evaluation of the concrete facing along the spillway and downstream face of the dam. Tectonic also performed a topographic survey of the dam and up and down stream portions of the river. The survey included the location and elevations of the dam, the rubble field downstream of the dam and hydraulic cross sections for modeling of flow.

Tectonic continued to support the Town in their efforts to advance the repairs with FEMA funding and NYSDEC Dam Safety consent. Through the Project Worksheet development and Appeals process, Tectonic was able to substantiate and secure over $740,000 in federal commitments. With the funding in place, Tectonic initiated detailed designs of the repairs by confirming the hazard classification of the dam. This work included a hydrologic analysis to determine the river’s 100-year peak flow rate at the dam, additional hydraulic survey of 4,000’ of river including the hydraulic opening of the Mill Street Bridge (County Route 17), a hydraulic model in HEC-RAS, mapping the resulting 100-year floodplain limits in the study area, and calculating the hydraulic effects of the dam breach scenarios to evaluate hazard classification considerations downstream. The analysis concluded the existing hazard classification (low-hazard) was appropriate. To decrease the seepage through the dam, Tectonic performed analyses and ultimately recommended a permanent sheet pile wall along the upstream side of the dam structure. As part of the design process, a geotechnical investigation and analysis of the subsurface conditions were performed to confirm the constructability of the sheet pile wall and obtain soil parameters required for design.

Upon securing of funding and completion of preliminary design, Tectonic performed final design, regulatory and permitting support (Army Corps, NYSDEC Article 15, Dam Safety, SEQRA, threatened & endangered species, invasive species management, and archaeological), construction document development, construction support, and resident inspection services.

The project was awarded in 2018 and completed on time and within budget. Challenges the project presented that were successfully overcome included:

• Design of detailed staging plans to allow for access to the site with minimal impact to the adjoining commercial properties.
• Design of staged cofferdams to allow for construction of sheet piling along the tall upstream side of the dam and construction of heavy stone scour protection along the full downstream side of the dam.

The environmental services performed for permitting included a formal freshwater wetlands delineation in accordance with Sections 404 and 401 of the Clean Water Act, and Articles 24 and 15 of the NYS Environmental Conservation Law (ECL) as well as a Threatened and Endangered (T&E) Species Survey in accordance with Section 7 of the Endangered Species Act (ESA), National Environmental Policy Act (NEPA), State Environmental Quality Review Act (SEQRA), Bald and Golden Eagle Protection Act (BGEPA), Migratory Bird Act (MBA) and Environmental Conservation Law Article 11 and 6 NYCRR Part 182 on parcels of land containing the Upper Candor Dam in Candor, Tioga County, New York. This potential habitat assessment and wetland investigation were performed in order to determine what, if any, regulated activities would occur. Upon completion of the freshwater wetlands field delineation and the T&E Species Survey, Tectonic prepared and submitted reports summarizing the results of the field assessments.

Finally, Federal emergency funding for dam reconstruction projects are infrequent and often substantial in magnitude. This investment brings an elevated level of documentation requirements and management to be coordinated with FEMA, NYS DHSES, and the community. Tectonic’s familiarity with FEMA’s Public Assistance program, the Federal/State documentation process, our own records management system, and our advocacy efforts for the municipality enabled: the successful documentation of the project, two successful Federal First Appeals, and a successful 2022 FEMA audit.