Carson City Sutro Regional Detention Basin Scoping

Terraphase was engaged to support the development of a Federal Emergency Management Agency (FEMA)-funded mitigation project in Carson City, Nevada for the Sutro Terrace Storm Drain system through a comprehensive set of technical studies and planning documents. The work aimed to refine prior analyses, assess environmental and cost feasibility, engage stakeholders, and develop a funding-ready project plan to reduce flood and debris flow risk in the area.

Scope of Services

Terraphase delivered a full suite of planning and analysis services, including refined hydrologic and hydraulic modeling using FLO-2D, environmental assessments, agency coordination, and cost-benefit evaluation. The team also led early-stage public outreach, developed preliminary designs and cost estimates, and compiled all project documentation into a Scoping Design Report (SDR). The SDR and supporting materials were presented to the Technical Advisory Committee (TAC) for review and finalized for future funding pursuits.

Notable Accomplishments

• Refined storm drain modeling using FLO-2D, including fire and debris flow scenarios
• Completed FEMA-compliant Benefit/Cost Analysis (BCA) using the BCA Toolkit
• Led proactive public engagement throughout project development
• Developed mitigation project scope, schedule, and budget to support future funding efforts

Woolsey Post-Fire Site Investigation and Risk Assessment

A total of 31 structures were destroyed in the Santa Monica Mountains National Recreation Area (SAMO) during the Woolsey Fire in California in November 2018. The structures were located in the nine areas within the SAMO (i.e., Paramount Ranch, Peter Strauss Ranch, Rocky Oaks, Cooper/Brown, Arroyo Sequit, Circle X Ranch, Morrison Ranch, Miller Property, and the Dragon Property). Terraphase was contracted to provide environmental consulting services and oversight of fire debris cleanup by Lead Builders, Inc. (LBI), working directly for the National Park Service (NPS).

Scope of Services

Terraphase prepared a Sampling and Analysis Plan (SAP) to characterize ash and soil following the Woolsey Fire in the Santa Monica Mountains and to implement a Time-Critical Removal Action (TCRA) to mitigate human and ecological exposure to burned building debris, ash, and impacted soil. To support decisions on removal of fire debris and impacted soil, Terraphase collected samples of ash and soil in nine burned areas. The Terraphase data visualization and management team supported the Woolsey Fire Time Critical Response Action with data management, ash and soil data tabulation and mapping, data screening, statistical analysis, and data validation.

Specific to the ash and soil characterization at the site, our team prepared site maps using Global Positioning System (GPS) data. We also prepared and managed a project-specific database to collect and analyze all ash and soil data, including preparation of data tables and data outputs to support data characterization and human and ecological risk assessment activities.

Based on the data collected, Terraphase developed risk-based human health and ecological remediation goals (RGs) for soil. The risk-based screening levels were used to select soil removal areas for the TCRA. Following implementation of the TCRA, Terraphase collected confirmation soil samples at the nine impacted areas to evaluate removal of soil above RGs. The RGs were used along with naturally occurring site-specific background concentrations to evaluate the results of post-cleanup confirmation soil samples following fire debris removal.

Notable Accomplishments

• Supported a TCRA over a large area to reduce human and ecological exposure to burned debris, ash, and impacted soil
• Created GPS-based site maps and managed a project-specific database for ash and soil data