Environmental Investigations, Monitoring, and Remediation Services at King County Closed Landfills

Providing ongoing maintenance, and routine monitoring of groundwater, surface water, wastewater and landfill gas to satisfy post-closure requirements,  King County maintains custodial responsibilities for nine closed landfills (under WAC 173-304 and 173-351). At four of the closed landfills (Cedar Falls, Vashon Island, Enumclaw, and Duvall), Aspect provides hydrogeologic and engineering services to support the County in meeting reporting and compliance requirements of the Seattle-King County Department of Public Health, Ecology, and Puget Sound Clean Air Agency.  

We have helped develop landfill gas and groundwater monitoring networks; provided hydrogeologic characterization and site conceptual model development, monitoring, and aquifer testing; and contributed to engineering controls development.   Our hydrogeologic characterization has supported groundwater, gas, and surface water migration assessments; environmental assessments of groundwater, leachate and gas systems; and pre-design level assessments of environmental control systems. Engineering controls have included landfill gas system collection and treatment upgrades, design and monitoring of an evapotranspiration (Poplar) cover, and leachate collection improvements. 

Jefferson County Closed Landfill Groundwater Monitoring

To help Jefferson County streamline post-closure monitoring and reporting required by Jefferson County Public Health and Ecology (under WAC 173-304), Aspect developed a database to manage over 20 years of data to support statistical analyses on the groundwater quality data. The groundwater monitoring program includes groundwater sampling, water-level measurements, groundwater-flow direction and velocity, in addition to statistical data analysis. Our statistical analyses includes:  Time Series Plots, Sen’s Slope Estimator Plots and Mann-Kendall Tests, Box and Whisker Plots, and Mann-Whitney and Kruskal-Wallis Tests. The statistical methods efficiently evaluate if groundwater resources could be impacted by potential releases from the landfill.   

Port Angeles Landfill Engineering Services

Located on a steep bluff above the Strait of Juan de Fuca, Port Angeles’s 3-cell landfill was closed under three regulatory statutes (WAC 173-301, 173-304, and 173-351). Aspect  provides ongoing compliance and reporting to support all post-closure requirements. Analyzing geochemical data, we assess the groundwater and leachate monitoring program. We have addressed gas flare operations and maintenance, recommending strategies such as flow balancing and infrastructure improvements, and assisting with gas collection during relocation of a solid waste cell. We have also evaluated greenhouse gas emissions following EPA protocols. 

Georgetown Area RI/FS and Compliance Monitoring of Chlorinated Solvent Plume

A chlorinated solvent plume is impacting soil, groundwater, and soil vapor in Seattle’s Georgetown neighborhood. Aspect is working on behalf of Art Brass Plating to investigate and cleanup the plume. Our work includes completing the RI, initiating a source control air sparging/soil vapor extraction system, and leading public participation over an approximate six block area. We also monitor and mitigate against vapor intrusion potential in more than 20 neighboring buildings to protect against exposure while groundwater remediation progresses. We negotiated an Agreed Order with Ecology that enables facility-specific investigation and coordinated data sharing with the area potentially liable parties (PLPs). 

Gates Foundation Headquarters Redevelopment Integrated Remediation

In redeveloping a site adjacent to the Seattle Center grounds as the location of their new headquarters campus, the Bill and Melinda Gates Foundation negotiated a property transfer that obligated the Seattle Center to address groundwater remediation of the former vehicle maintenance site. Helping the Seattle Center meet the groundwater remediation obligations, Aspect led the groundwater assessment and remediation efforts with an emphasis on integrating cleanup into the redevelopment plans, designing a full-scale air sparging (AS) and soil vapor extraction (SVE) remediation system for phased installation. The first phase of AS/SVE was successfully installed in the pre-construction footprint and operated while the campus design and permitting process was completed. The second phase of the remedial system was installed within the active excavation footprint. By integrating the remediation system into the campus design, the second phase of the remedial action was designed to continue once the structure was completed.

Technical and Litigation Support for Closed Pasco Landfill

To protect human health and the environment, and to limit long-term financial liabilities, Aspect provides technical and litigation support to a select group of Potentially Liable Parties (PLPs) at the Pasco Landfill Site. The Site is on the National Priorities List and is regulated by Ecology under MTCA.  Our technical support includes optimizing a 24-well, landfill-gas collection system to prevent potential groundwater impacts, and maintaining flare operations to destroy hundreds of pounds of VOCs per day. Our litigation support includes forensic assessments in anticipation of cost recovery actions by other PLPs, and negotiation with Ecology to develop an effective Cleanup Action Plan.


The Bremerton Gasworks is a former manufactured gas plant located along the Port Washington Narrows in Bremerton. The Gasworks produced fuel gas from about 1930 until 1963. Byproducts of the gas manufacturing process have contaminated soil, groundwater and sediment at the site. Aspect is performing investigation and cleanup activities for Cascade Natural Gas Corporation, who has entered into an Administrative Settlement Agreement and Order on Consent with the US Environmental Protection Agency for the performance of a remedial investigation and feasibility study under CERCLA.

Ameron Industrial Stormwater General Permit (ISGP) Support

Aspect is assisting a concrete pole manufacturer complete stormwater infrastructure improvements to comply with their ISGP. The facility is on a Port of Everett brownfield undergoing MTCA cleanup. We developed, coordinated, and implemented a strategy to fast-track remediation of overlying contaminated soils to facilitate replacement of their storm drainage pipes. Our approach resulted in faster removal of 2,000 cubic yards of contaminated soil, improved ISGP compliance, better site drainage, and lower construction cost by separating the work from the RI/FS process. Our involvement in both the remediation and stormwater work allows adaptation of the project to changing conditions.

Transfer Station Underground Injection Control (UIC) Design and Permitting, Pasco, WA

Aspect assisted in upgrading the stormwater management system for a municipal waste transfer station in Pasco. We authored a SWPPP, evaluated and designed upgrades to the stormwater treatment and disposal system to enhance protection of groundwater, and permitted the existing and new drywells under the Washington State’s UIC regulations.

Auto Recycler Stormwater Treatment System Design, Renton, WA

Aspect designed an innovative media-filtration treatment system to complete a Level 3 Corrective Action at a 5-acre auto-recycling facility as a component of settling a Clean Water Act citizen suit.  Our design was aimed at treating low to moderate levels of copper and turbidity. The media bed consisted of oyster shells over a bioretention soil mix. The system was constructed by the client at low cost. The client has not triggered a Level 2 or 3 Corrective Action since installation of the system.

Duwamish Marine Terminal Industrial Stormwater General Permit Support

After providing expert support during settlement of a Clean Water Act citizen suit, Aspect designed an above-ground media-filtration stormwater treatment system for a 5-acre marine terminal and barge loading facility on the Duwamish River.  Our design included an innovative collection and conveyance system to avoid soil disturbance along the shoreline and reduce local permitting requirements. The client has not triggered a Level 2 or 3 Corrective Action since installation of the system in 2011.

One Site. Four Sources. One System.

The groundwater beneath an eight-acre shopping center exhibited chlorinated solvent impacts from four different source areas of varying ages. 

To sort out the complexities of multiple sources with multiple responsible parties, Aspect hydrogeologists distinguished the relative solvent contribution from each historical source and developed a site conceptual model that was used to reach an equitable cost-sharing agreement. At the same time, our remediation engineers pilot tested an in situ chemical oxidation system for groundwater treatment without disruption to the active retail facility.

The final remediation system treats all source areas through one air sparge and soil vapor extraction (AS/SVE) system consisting of 16 soil-vapor extraction wells and 47 air-sparging wells spread over an acre of the property.

Olympic Sculpture Park Site Remediation

Seattle Art Museum (SAM) with the City of Seattle formed a public development authority to obtain remedial action grant funding for the cleanup and redevelopment of an 8-acre former fuel facility on the downtown Seattle waterfront for use as a park. As environmental lead, Aspect helped the development team incorporate the requirements of the Cleanup Action Plan (CAP) into the park design, integrating remedial elements into the infrastructure requirements. Many of the larger costs for park construction were covered as remediation expenses under remedial action match funding, providing substantial cost savings for the redevelopment project.

Metal Fabricator Industrial Stormwater General Permit Support, Seattle, WA

A metal fabricator and electrical supplier was sued under the Clean Water Act for elevated concentrations in stormwater zinc just weeks before of a Level 3 Corrective Action deadline. Aspect quickly determined roofing was the primary source and negotiated installation of a roof downspout filter—meeting the deadline and greatly aiding settlement. After settlement, we assisted the client in coating the roof to avoid ongoing maintenance costs. The site now routinely meets all benchmarks.

Log Yard Industrial Stormwater General Permit Support (ISGP), Hoquiam, WA

Aspect assisted a small, partially paved log yard respond to a Clean Water Act citizen’s suit. After investigating the fecal coliform monitoring requirement, we determined that Ecology erred in requiring additional monitoring and successfully worked with Ecology to eliminate the requirement. As a component of settling the lawsuit, Aspect updated the SWPPP, performed employee training, recommended operational and structural BMPs, and participated in Consent Decree negotiations.