A plume the block didn't create.

The contamination under the block did not originate there. Tetrachloroethene (PCE), a dry-cleaning and degreasing solvent, migrated in as a dissolved groundwater plume from upgradient sources to the north — chiefly a former dry cleaner (Westco, operating roughly 1976–1986) within the site later known for the “Thinker Toys” computer store, across NE 8th Street, plus a former Unocal gas station on the adjacent corner.

Because the solvent merely drifted onto its land, Onni invoked Washington's Model Toxics Control Act “plume clause” and maintains it is not a potentially liable party — though the state still added the block to its contaminated-sites list in 2019 and required a cleanup.

At the source, PCE in groundwater exceeded 5,000 µg/L — roughly a thousand times the 5 µg/L drinking-water cleanup level. On Onni's own block it was far milder: the worst groundwater reading was 21 µg/L, and the single soil sample above the limit was 0.30 mg/kg, found about 65 feet down beneath the old Barnes & Noble.

A 2017 assessment flagged a second, home-grown concern: Belle Lanes ran an oil-burning furnace, and there is no record its underground heating-oil tank was ever removed. It may still be buried under the block, to be dealt with if crews encounter it during the dig.

The block's deeper past is agricultural. It was platted as “Cheriton Fruit Gardens” and used as orchards and gardens until commercial development began in the late 1950s — Bellevue itself had incorporated only in 1953 — and the site's legal description still reads “Cheriton Fruit Gardens Plat #1.” Early borings turned up the buildout's traces: iron pipe at 7.5 feet, with wood debris and glass in the fill.

The chosen remedy is, essentially, to dig the problem out. The plan removes roughly 17,500 tons of PCE-affected soil — about 2,500 cubic yards of shallow soil and 10,000 of deep — hauling it to a lined Subtitle D landfill under a state “contained-in determination,” which lets the lightly contaminated soil avoid being handled as dangerous waste. Because the towers require a lot-line-to-lot-line excavation roughly 80 feet deep for below-grade parking, that dig carries away essentially all the on-site contamination as a byproduct.

Of three studied remedies, Onni and Ecology selected the cheapest — a roughly $2.47 million option pairing the soil removal with a segregated footing-drain that routes captured groundwater to the sanitary sewer — over a pump-and-treat system and an in-situ bioremediation alternative.

Because some contaminated groundwater (and possibly soil below the dig) will remain, Ecology's “no further action likely” opinion is conditional. An environmental covenant recorded on the property title will permanently bar drilling water-supply wells, designate the parking-garage slab and walls as a protective “cap,” require up to ten years of groundwater monitoring, and warn any future crews who disturb the ground. If the building is ever removed, the contamination question must be reassessed.

A dedicated vapor barrier was studied and held in reserve: PCE came in just under the vapor-intrusion screening threshold, and the deep parking garage's ventilation provides a backstop.

The cleanup has a long paper trail and, for years, very little action. Onni first enrolled the block in Ecology's Voluntary Cleanup Program in August 2019, but the state terminated that enrollment in September 2020 after Onni indicated no cleanup was scheduled “in the foreseeable future.” Onni re-enrolled in the faster-track Expedited program in late 2021, and Ecology issued its “no further action likely” opinion that December.

From there the project stalled. Quarterly reports to Ecology recorded “no work performed at the Site” for roughly eighteen straight quarters, each blaming slow City of Bellevue permitting — and, from late 2024, “market conditions.” The planned demolition slipped from January 2022 to 2026, and the cleanup's closing report from late 2022 to 2027.

The first real field activity came in January 2026, when crews sampled groundwater for a “dewatering assessment” — the first sign of mobilization ahead of demolition and the deep dig.