Pasco Sanitary Landfill | Region 10 | US EPA

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Pasco Sanitary Landfill

The Washington State Department of Ecology is the lead agency managing this site. For information on environmental or regulatory concerns on this site, please contact Chuck Gruenenfelder (chgr461@ecy.wa.gov), 509-329-3439.

Site Summary

The Pasco Sanitary Landfill (PSL) property is approximately 280 acres in size, located about 1.5 miles northeast of Pasco, Washington. PSL operated as an open burning dump from 1958 to 1971. Sanitary landfilling began in a 40-acre unlined area in 1972, operating until it was placed under interim cover in 1992.

Another portion of the property received hazardous wastes between 1972 and 1975; this portion now resides in five separate cells. Two of these cells collectively contained approximately 40,000 drums containing paints, resins, herbicide and pesticide manufacturing wastes, caustic chemicals, and other wastes. Three of these cells accepted bulk liquid waste and sludges in unlined lagoons, where the wastes were dried and later covered with a RCRA-compliant cover system.

Groundwater beneath and downgradient of the property is contaminated primarily with volatile organic compounds (VOCs). These include chlorinated solvents such as tetrachloroethene (Perc), trichloroethene (TCE), their degradation by-products, and other non-chlorinated organic compounds, such as Benzene, Toluene and Xylenes. Other organic compounds and inorganic constituents also have been detected. Groundwater within 3 miles of the site is used by over 1,000 people for drinking and irrigation of 10,000 acres of cropland. A groundwater protection area has been established by the City of Pasco to restrict groundwater usage within the area where landfill-related compounds may be present.

Groundwater Contamination

On-site and off-site groundwater contains detectable concentrations of volatile organic compounds (VOCs). Off-site contaminant concentrations have generally remained below Department of Ecology draft cleanup levels since remediation system upgrades were implemented in 2011/2012. People who ingest or come into direct contact with contaminated groundwater potentially could be at risk. However, based on current site monitoring and scientific information, the groundwater plume should not impact people’s health because:

If you have a well in this area and have questions or are concerned about where your drinking water comes from, please contact Jim Coleman of the Benton Franklin Health District at 509-460-4319.

Cleanup History

Preliminary interim actions to address source area soil and groundwater contamination by VOCs were initiated in 1996/1997. These actions included soil vapor extraction near one of the hazardous waste disposal cells along with an in-well air stripping technology [NoVOCs (tm)] for treating contaminated groundwater.

The Remedial Investigation and Feasibility Study (RI/FS) phase was completed in 1999. Based on the RI/FS findings, additional interim actions were initiated at both the industrial waste areas and the municipal solid waste (MSW) landfill. The PRPs conducted this work under agreed orders and unilateral orders with the state of Washington.

The Feasibility Study outcome recommended a 6-year performance monitoring period to evaluate the effectiveness of the interim cleanup remedy. Interim actions originally included: (1) expansion of the NoVOCs (tm) groundwater treatment system, (2) expansion of the soil vapor extraction system and thermal treatment of the captured vapors, (3) installation of final landfill covers over the former MSW landfill and four industrial waste disposal cells (4) capture and thermal treatment of landfill gas from the former MSW landfill, (5) removal of approximately 5,000 drums of herbicide manufacturing waste from one of the industrial waste disposal cells, and (6) institutional controls on groundwater withdrawal in the plume area. In addition, community water supplies were extended to selected residents whose groundwater had been or potentially could be affected by releases from the landfill.

In 2007, at the end of the 6-year Interim Action performance monitoring period, the state of Washington identified the need for additional site characterization, monitoring, and remedial system performance data to address critical data gaps. An initial phase of supplemental investigation and data collection was conducted in 2008. The initial phase of Additional Interim Action Work evaluated the performance of the existing soil vapor extraction system and the NoVOCs™ groundwater treatment system. Findings from this initial evaluation led to a discontinuation of NoVOCs™ system operations. Adjustments to the original SVE system also were made which helped improve operational performance.

In 2010/2011, the original SVE system was completely upgraded. Six new SVE wells consisting of two separate well clusters (shallow-intermediate-deep) were installed to improve contaminant capture beneath the largest drum disposal cell. Modifications to improve the collection and management of SVE-related condensate also were made, along with upgrades to the MSW flare unit where the SVE vapors were treated.

In 2013, a new RCRA-compliant cap was installed over the former herbicide waste disposal cell at the eastern edge of the site. The property line in this area was slightly modified to help accommodate the installation requirements of the new cap system. Other subsurface investigation and monitoring well installation work also was performed.

At the end of 2013, an underground landfill fire was detected in an area where baled MSW wastes had been disposed in the 1980’s and early 1990s. Efforts to extinguish the fire initially included a “smother and cover” approach, followed by subsurface injection of liquid carbon dioxide. These initial efforts helped to suppress, but not fully extinguish, the fire. In August and September 2015, a more aggressive excavation and slurry quench approach was used to fully extinguish the fire. The fire was fully contained within a slurry barrier wall, and all combusting waste materials were quenched and extinguished. As of October 2015, a separate slurry wall will be installed around portions of the primary drum disposal cell to help further isolate it from adjacent municipal solid wastes and buried tires.

In August 2015, a new regenerative thermal oxidation (RTO) unit was installed to treat the contaminated soil vapors generated by the SVE operations. This new RTO unit will eliminate the use of the MSW Landfill flare as the primary treatment unit for SVE vapors. From 1996 to September 2015, the interim soil vapor extraction system has removed nearly 1 million pounds of vapor-phase VOCs from beneath the primary drum disposal cell.

Current Actions

Current interim actions include soil vapor extraction and on-site thermal treatment of contaminated soil vapors. Landfill gas from the former MSW Landfill continues to be collected from the existing network of gas extraction wells and treated at the existing MSW flare unit. Routine groundwater monitoring and remedial system operations also are ongoing.

In September 2014, the PRPs prepared a draft focused feasibility study report. The focused feasibility study screens and evaluates potential cleanup remedies in advance of developing a draft cleanup action plan (DCAP) for the site. The state anticipates development of the DCAP by late 2016.


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