For the Todd Shipyard (Todd) Sediment Operable Unit of the Harbor Island Superfund Site, Floyd|Snider developed a Feasibility Study and design documents, led agency negotiations, and managed contractor procurement and construction for a complex $20 million remedy. The remedy included environmental dredging, under-pier capping and construction of nearshore aquatic habitat. Superfund Feasibility Study requirements were met through the development and formal evaluation of remedial alternatives within the Conceptual Design and Preliminary Design Report documents. Floyd|Snider's engineers developed and screened alternatives for dredging, capping and enhanced natural recovery, including evaluation of multiple technologies for placement of cover materials under pier structures. Floyd|Snider prepared detailed capital and operational cost estimates to support the selection of the preferred alternative. The Feasibility Study evaluation took into account the structural condition of existing bulkheads and pier structures, shipyard operational parameters, hydrodynamic forces and a range of potential future operation and maintenance scenarios. Floyd|Snider's work also included the maximization of nearshore aquatic habitat at the site to meet mitigation requirements, with supplemental habitat documented as credit towards a Natural Resource Damage (NRD) settlement. During preliminary design, Agency and Tribal stakeholders reviewed and approved the design, agreeing that the company had maximized aquatic benefit in the context of shipyard operations.
During remedial design for the Todd sediment cleanup, Floyd|Snider performed a source control evaluation addressing the sediment recontamination potential of both off-site and on-site sources. For off-site sources, contaminated sediment transport from upstream sites was evaluated based on review of area sediment data, West Waterway, and Elliott Bay transport mechanisms. Off-site storm drains and combined sewer overflows (CSOs) were also evaluated. This evaluation was used to determine that the remedial action should go forward as planned, although it documented that there was a risk that sediments could be recontaminated by off-site sources.
Floyd|Snider's on-site source control evaluation at Todd considered shipyard operational sources including dry dock activities such as grit blasting, grit storage and transport, and shipyard stormwater management. This work identified the need to revise facility-wide grit management procedures, and to collect and treat stormwater from the primary industrial areas of the yard. The project team then worked with shipyard employees to define and implement revised grit handling procedures and install additional structural Best Management Practices to prevent residual grit from entering the water. Floyd|Snider also managed the design and construction of a $3 million industrial stormwater collection and pretreatment system at the shipyard. We renegotiated National Pollutant Discharge Elimination System permit requirements for both dry docks and stormwater, and facilitated a unique sewer use agreement between Todd and the City of Seattle.
In addition to sediment-related activities, Floyd|Snider manages ongoing cleanup activities at the Todd Uplands Soil and Groundwater Operable Unit. This involves the recovery of a 7-acre pool of hydrocarbons (free product) floating atop groundwater at the facility within a tidally influenced aquifer at the edge of Elliott Bay. Floyd|Snider manages the operation of the free product recovery system using dual phase vacuum-enhancement and groundwater depression to recover free product. Over 300,000 gallons of product have been recovered. Floyd|Snider is responsible for a nearly two-fold increase in the rate of product recovery and the design and installation of additional recovery wells to accelerate recovery of remaining non-aqueous phase liquid (NAPL).