Request for Qualifications - Conn Dam Stability Assessment, Spillway Improvements, and Feasibility Alternatives Study

1. Introduction

The City of Napa (“City”) requests qualifications (“Qualifications”) from qualified individuals or firms (individually, a “Respondent” and collectively, “Respondents”) for Request for Qualifications - Conn Dam Stability Assessment, Spillway Improvements, and Feasibility Alternatives Study (“Project”). The City is seeking highly qualified multidisciplinary engineering consulting firms specialized in dams to provide professional engineering, geotechnical, environmental, hydraulic, structural, dam safety, and economic evaluation services for the Conn Dam Stability Assessment, Spillway Improvements, and Long-Term Reservoir Expansion Feasibility Study.

The selected Consultant shall provide comprehensive engineering services to support regulatory compliance with the California Division of Safety of Dams (DSOD), assist the City in advancing federally authorized flood risk reduction studies through the U.S. Army Corps of Engineers (USACE), evaluate long-term improvements to increase water supply reliability, and prepare the technical basis for future environmental review, design, permitting, and construction.

The City intends to procure these services using a Qualifications-Based Selection (QBS) process consistent with applicable federal procurement requirements, including 2 CFR Part 200 and the principles of the Brooks Act, as it is anticipated federal funding will be a part of the design and construction funding.

The first phase of the project will generate a geotechnical data report that must be submitted to DSOD by December 31, 2028 followed by phase two with an assessment of the dam’s stability, including deformation estimates, under static and seismic conditions. Phase three will develop a feasibility alternatives analysis report addressing all identified deficiencies including the known spillway deficiencies. The City has been included by project name Conn Creek Dam, California in the 2022 Water Resources Development Act of 2022 (WRDA) and requested to be included in the USACE WRDA 2028 workplan with goal of completion of the alternative and design within 3 years inclusion in work plan.

2. Project Background

The City is a charter city located in Napa County, with an estimated population of 80,000. Additional information about the City is available online at www.cityofnapa.org .

Conn Dam is a critical component of the City of Napa's municipal water supply system and impounds Lake Hennessey, the City's primary local water storage reservoir.

Constructed in the mid-1940s, Conn Dam is an approximately 110-foot-high zoned earthen embankment dam with a crest length of approximately 700 feet. The embankment consists primarily of compacted impervious clay with upstream rock slope protection and impounds approximately 31,500 acre-feet of water.

Since its construction, multiple engineering evaluation and feasibility studies have been completed to assess the dam, spillway, intake facilities, and long-term water supply needs. Major milestones include:

The 2018 Spillway Re-evaluation Program, initiated following the Oroville Dam Spillway Incident, confirmed that the existing spillway no longer satisfies current Probable Maximum Flood (PMF) design criteria. Subsequent reviews by DSOD requested additional alternatives analyses to identify permanent improvements.

In June 2026, DSOD completed an independent review identifying additional concerns regarding the long-term geotechnical stability of the dam embankment and requested submission of a comprehensive geotechnical investigation report by December 31, 2028.

Separately, Congress reauthorized the Conn Dam Flood Risk Management Feasibility Study under the Water Resources Development Act of 2022 (WRDA 2022). The City continues to coordinate with the U.S. Army Corps of Engineers to secure General Investigation funding for the federally authorized feasibility study and is working to incorporate the full project in the 2028 workplan.

The City has also submitted an application under the Corps Water Infrastructure Financing Program (CWIFP) for future construction financing.