Conn Creek Dam Phase II Spillway Assessment Technical Memorandum

This is a technical memorandum related to the City of Napa's Request for Qualifications for the Conn Dam Stability Assessment, Spillway Improvements, and Feasibility Alternatives Study. The document supports a Qualifications-Based Selection (QBS) procurement process consistent with federal requirements under 2 CFR Part 200 and the Brooks Act, anticipating federal funding participation. The project comprises three phases: Phase One focuses on generating a geotechnical data report to be submitted to the California Division of Safety of Dams (DSOD) by December 31, 2028; Phase Two involves comprehensive assessment of the dam's stability, including deformation estimates under static and seismic conditions; and Phase Three develops a feasibility alternatives analysis addressing identified deficiencies, including known spillway deficiencies. The selected consultant must be a highly qualified multidisciplinary engineering firm with specialization in dam engineering, capable of providing professional services in geotechnical, environmental, hydraulic, structural, dam safety, and economic evaluation disciplines.

The project supports regulatory compliance with DSOD, advancement of federally authorized flood risk reduction studies through the U.S. Army Corps of Engineers (USACE), and long-term improvements to increase water supply reliability. The Conn Creek Dam has been included by project name in the 2022 Water Resources Development Act (WRDA), positioning the project for federal funding support during design and construction phases. The technical assessment will provide the foundational basis for future environmental review, design, permitting, and construction activities, establishing critical engineering and feasibility documentation for this water infrastructure project.