Fox Avenue Site (formerly Great Western Chemical)

A Floyd|Snider-led Team is remediating a significant release of chlorinated solvents from soil and groundwater related to prior storage, handling, and distribution of bulk chemicals associated with the defunct Great Western Chemical Company. The Fox Avenue Building Site is an active chemical distribution warehouse in the Duwamish industrial corridor of south Seattle. Floyd|Snider is assisted by CALIBRE Systems on the project, a specialist in in-situ bioremediation. Contamination is present at the site as dissolved phase in groundwater and dense non-aqueous phase liquid (DNAPL) stringers in soil to depths of 65 to 70 feet below ground. Remediation of the contaminant plume at this site is complicated as it extends beneath building foundations on the property, and off-site beneath adjacent downgradient properties. 

Floyd|Snider is implementing the 2008 Agreed Order for the site that calls for completion of pre-remediation initiatives that include a Data Gaps Investigation to identify source areas, and an immediate interim action to treat off-site groundwater using enhanced reductive dechlorination (ERD). ERD actions are being led by CALIBRE Systems and began in early 2009. Preliminary results indicate contaminant concentrations in the groundwater plume are degrading. As part of the Data Gaps Investigation, a Membrane Interface Probe (MIP) was used to collect continuous data from numerous locations. MIP data provides a snapshot of vertical distribution of contaminant concentration with depth. In addition, to satisfy requirements of the Agreed Order, the Team is conducting a vapor intrusion study at the Cascade Columbia warehouse including sub-slab soil vapor, indoor air, and ambient air sample collection. The study is being conducted to determine if a risk to human health exists from the soil gas vapor to indoor air pathway. Risks identified by the study will be addressed in the Feasibility Study. Floyd|Snider conducted an evaluation of the existing Soil Vapor Extraction (SVE) system installed in 2002 for remediation of site vadose soils. The Floyd|Snider evaluation determined the efficiency of the existing system to limit migration of soil vapor to indoor air, and also to remove measurable contaminant mass from the subsurface. 

Once these pre-remediation initiatives are complete, Floyd|Snider will develop a revised Feasibility Study report that evaluates remedial technologies and alternatives to control and/or treat site-wide source area groundwater and soil contamination.  Remedial technologies will likely include in-situ thermal destruction, excavation and off-site disposal, containment, and ERD. Discussion and evaluation of these technologies and development of remedial alternatives will be described in detail in the Feasibility Study and a preferred remedial alternative will be proposed for the site. The Feasibility Study was submitted to the Washington State Department of Ecology in 2009, and Floyd|Snider has assisted in development of the Cleanup Action Plan (CAP), which targets remediation of the site.


  • Remedial Investigation/Feasibility Study 
  • Data Gaps Investigation/Field Sampling
  • Vapor Intrusion Study
  • ERD Interim Action
  • Agency Coordination and Negotiation
  • Remedy Design and Remedial Cost Estimation

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