Arlington, Washington:

Due diligence activities related to a potential real estate transaction identified substantial subsurface contamination beneath an operating retail gasoline station located in Arlington, Washington. SES conducted supplemental subsurface investigations to evaluate the lateral and vertical extent of the contamination and to install five monitoring wells – three of which would be converted to remediation wells. Following well installation activities, SES engineers conducted a pilot test on the property to evaluate the potential effectiveness of an air sparge/soil vapor extraction or recirculation well system. The pilot test results led SES engineers to recommend an alternative well remediation system (patented by an SES engineer) know as the PlumeEater Remediation System (PERS).

Mountlake Terrace, Washington:

SES engineers evaluated the design, condition, and performance of a 10-year old dual-phase extraction (DPE) system designed and installed by others at a former retail gasoline station in Mountlake Terrace, Washington. After approximately 10 years of operation, separate-phase petroleum hydrocarbons (SPH) and dissolved concentrations of gasoline had migrated beyond the radius of influence of the original remediation system. Pilot tests confirmed areas where no vacuum could be induced using the existing DPE blower. SES engineers recommended some system design improvements that will effectively address the present site conditions.

The conceptual site model generated in the SES remedial investigation indicated the presence of three separate water-bearing zones, including two zones of perched groundwater above a confined aquifer, and confirmed that contaminant migration was influenced by a dry well on the property where stormwater runoff was discharged. SES designed upgrades to the system that would extract SPH and lower the groundwater table independently from the DPE system, improving the radius of influence. The upgrades were designed on a modular basis that could be adapted to variable terms of off-property access, and included manifolds to control airflow.

Milton Freewater, Oregon:

SES engineers developed a plan that was approved by the Oregon Department of Environmental Quality (ODEQ) to justify the risk-based closure of a former retail gasoline station in Milton Freewater, Oregon. The results of soil vapor analysis demonstrated to the property owner and ODEQ that concentrations of benzene in soil vapor were disproportionately higher than expected and did not meet the regulatory criteria for risk-based closure. SES was able to demonstrate that groundwater was not impacted and that alternate exposure pathways were incomplete, leading to the selection of soil vapor extraction technology to close the “Soil Vapor Intrusion Into Buildings” exposure pathway. The results of remedial pilot testing indicated a radius of influence of 15 feet in windblown loess soils. SES designed a soil vapor extraction system adapted to the fine-grained soil conditions and equipped to capture benzene and other gasoline components in system emissions.