Chlorinated Solvent-Contaminated Groundwater Plume

(Snohomish County, WA) Since 2005, Landau Associates has provided environmental consulting services for remediation of a large chlorinated solvent groundwater plume at a commercial airplane manufacturing facility in Snohomish County, Washington. An historical release of trichloroethene (TCE) occurred to, or within the vicinity of, the facility’s stormwater detention pond. The plume extends approximately one-half mile from the detention pond and discharges to a creek. Landau Associates is conducting remedial investigation activities and source zone and downgradient plume interim remedial actions, and is preparing a Washington State Model Toxics Control Act (MTCA) Feasibility Study and Cleanup Action Plan (CAP) to address the plume. Work is being performed under an Agreed Order between the client and the Washington State Department of Ecology.

Prior to Landau Associates’ involvement in the project, the source of the contamination was unknown and the plume migration pathway was poorly understood. Landau Associates identified and characterized the source zone and downgradient plume within the first six months of taking over the project. Source zone characterization required dewatering the detention pond and conducting an expedited drilling program within the pond during a five-day dry period. Over the subsequent five-month period, Landau Associates completed the design and permitting necessary to construct a thermal remediation system interim action, referred to as electrical resistive heating (ERH), within the detention pond. Landau Associates assisted in negotiating an amendment to the agreed order to implement the interim action, managed construction and operation of the system, and conducted post-remediation monitoring following successful remediation of the TCE source zone. The system was successful in achieving treatment goals at 39 of the 40 monitoring wells located within the source zone. Following the ERH interim action, Landau Associates designed and implemented an enhanced bioremediation polishing step to address residual contamination in the source zone. The polishing step used an innovative electron donor delivery approach developed by Landau Associates to successfully distribute the donor material through the tight aquifer material.

Following source zone remediation, Landau Associates designed and managed construction of a $1M groundwater extraction and treatment system interim action to block further downgradient migration of the plume and discharge of the plume to the creek. The system successfully treated over 50 million gallons of groundwater in its first year of operation. Landau Associates is also currently conducting a MTCA feasibility study to address the remainder of the plume.