Tac Sea Motel

The Tac Sea Motel Site is located in the City of SeaTac, King County, Washington near the north end of Sea-Tac International Airport. The former building was originally constructed as a strip mall in 1953. Two dry cleaners and a printer successively occupied one of the units, between approximately 1953 and the early 1980s, after which the building was converted to a motel. The property is currently being operated as a paid parking lot that opened in 1998.

In 2000, four major tasks were completed:

1. Excavation and offsite disposal of solvent and petroleum contaminated soils.
2. Construction and operation of a soil and groundwater treatment system to remove solvent (PCE) and petroleum contamination in soil and groundwater using Air-Sparging with Soil Vapor Extraction (AS/SVE). The AS/SVE system process did the following:

A.   Pumped clean air into the groundwater

B.   Vaporized the solvents 

C.   Vacuumed out the solvent vapors using pressure to withdraw and remove the solvents

D.   Passed the vapors through a scrubbing system

1. Construction of a surface cover using asphalt and concrete to minimize rain water and control stormwater runoff.
2. Groundwater compliance monitoring to evaluate the success and completion of the cleanup actions.  Four of the six groundwater compliance wells satisfied all the compliance requirements.  Two of the wells were approaching compliance. 

The AS/SVE remediation system operated at the Site between August 2000 and April 5, 2011. The system was turned off after it was determined that declining PCE concentrations in groundwater had reached asymptotic conditions. Ecology determined that the AS/SVE remediation system had achieved its maximum cleanup function, and that additional cleanup treatment would be cost disproportionate to the benefits. Ecology issued a memorandum on May 14, 2013 stating that Consent Decree cleanup requirements were met, thus leading to closing the Consent Decree with amendment and an environmental covenant that included periodic monitoring at the remaining two wells (MW-A and MW-C) that were out of compliance.  Ecology determined that an environmental covenant would protect human health and environment from the remaining low concentration of solvents at the two wells.

A periodic review is conducted every five years following a cleanup action when institutional controls are used as part of the remedy, as required by the Model Toxics Control Act (MTCA). The purpose of the periodic review is to evaluate current site conditions and to ensure continued protection of human health and the environment.

Tetrachloroethene (PCE) concentrations in groundwater remain asymptotic and have been less than 10 micrograms per liter (μg/L) for over 10 years. Occasionally, PCE concentrations dip below the MTCA Method A cleanup level of 5 μg/L. Ecology determined in 2013 that the AS/SVE remediation system achieved its maximum cleanup function, and that additional cleanup treatment would be cost disproportionate to the benefits.

The groundwater plume has not been delineated to the west of the property (down gradient). PCE in groundwater is likely in the right of way, but it is unknown whether it extends across the street to the west-adjoining property. It was reported to Ecology that the west-adjoining property owner did not grant access for sampling. PCE concentrations downgradient of the property are likely lower than in monitoring wells MWA and MWC, given the significant reduction in PCE as a result of the AS/SVE remediation system.

No drinking water wells are likely to be impacted. The cleanup actions completed at the Site appear to be protective of human health and the environment at this time. Groundwater monitoring should continue so that PCE concentrations continue to be evaluated over time. Additional details can be found in the 2020 Periodic Review report.

The Model Toxics Control Act (MTCA) is Washington’s environmental cleanup law.  It provides requirements for contaminated site cleanup and sets standards that protect human health and the environment.  Ecology enacts the MTCA and oversees cleanups.

​The MTCA site cleanup process is completed in steps over a variable timeline. 

Ecology determined that an environmental covenant would protect human health and environment from the remaining low concentration of solvents at the two wells.