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.

Much of how the deep excavation is constrained traces to a single document: a March 28, 2019 SEPA comment letter from the Washington Department of Ecology on the “606 & 620 - 106th Ave NE Project” (Ecology SEPA #201901381). In it the state put the developer on notice that excavation for the underground garage “will most likely encounter the deeper Advance outwash aquifer, a regional water-bearing deposit,” and asked for a plan to dewater that more productive formation — a step beyond pumping the shallow perched water the checklist had described.

The letter tied the dewatering directly to the contamination: it said “management of dewatered contaminated ground water will be needed as well as measures to prevent vapor intrusion into the building,” warned a vapor-intrusion risk “may be present” if PCE-affected groundwater remained, and framed the endgame plainly — groundwater “is affected by an upgradient source” that “will need to be fully characterized and remediated” before Ecology could issue a No Further Action determination, with an environmental covenant possible if full removal proved infeasible. It was signed by SEPA Coordinator Tracy Nishikawa, directed technical questions to Heather Vick of the Toxics Cleanup Program, and was copied to Onni's Brandon Reeves.

Beneath the headline of “dig it out,” the selected remedy carries some specific machinery. Geopacific found the main groundwater table 65–87 feet down but also perched water within the glacial till and pre-glacial outwash, typically at 30–40 feet, plus discontinuous seepage zones. The groundwater piece is a segregated portion of the building's footing-drain system along the northern and western foundation that passively captures lingering PCE-impacted groundwater and discharges it to the sanitary sewer under a King County Industrial Wastewater (KCIW) authorization.

Treatment — granular activated carbon or air sparging — is held in reserve rather than built in: it would only be required if PCE in the drain water exceeded KCIW's 240 µg/L discharge limit, and with measured concentrations far below that (a peak of 21 µg/L shallow, 7.7 µg/L deep, against a 5.0 µg/L cleanup level), TRC considered treatment unlikely. The drain is expected to run for the life of the building, with the option to be re-routed to the storm system once the upgradient sources are cleaned up. Of three remedies studied, the chosen Alternative 2 was estimated at about $2,467,372 — below both pump-and-treat (~$2,823,000) and the in-situ-bioremediation option (~$2,897,882).

The cleanup has a precise file identity: Cleanup Site ID 14996 / Facility Site ID 73977, run by TRC Environmental under its project No. 462297 and Ecology's Expedited Voluntary Cleanup Program (E-VCP No. XN0011). TRC's quarterly reports are now prepared by Project Manager Laithan Briant and Senior Geologist Ruth Otteman (who replaced earlier staff in 2025), addressed to Ecology site contact Frank P. Winslow, LHG, with copies to Onni's Brendan Lawrence and Lorina Crain and outside counsel John Houlihan and JT Cooke of Houlihan Law P.C.

The most recent report on file, Quarterly Progress Report No. 19 (dated June 4, 2026 and posted that June 11), is the first to point at imminent field work: it lists “preparation for site redevelopment and site characterization activities planned for the end of June 2026.” Its tentative milestone schedule reads demolition in Q2 2026, additional contained-in characterization and Ecology approval in Q2–Q3 2026, remedial excavation in Q3–Q4 2026, an interim remedial action complete by Q4 2026–Q1 2027, and the final Remedial Action Report in Q2–Q3 2027 — still about four years later than the original 2022-era targets, expressly contingent on City of Bellevue permitting and market conditions, with long-term compliance monitoring listed as to-be-determined and the next report (No. 20) due September 10, 2026.

The lifecycle greenhouse-gas figure quoted across the environmental record — roughly 2,992,382 metric tons of CO₂-equivalent — comes from a King County Greenhouse Gas Emission Worksheet attached to the 2019 SEPA checklist, and the worksheet itemizes it by use. The residential program (1,289 multifamily units) is the largest share at about 1,489,690 MTCO₂e, followed by office (894,500 sf) at 1,206,989, lodging (259,200 sf of hotel) at 241,867, and retail (62,400 sf) at 53,836.

The split is a useful corrective to the intuition that the office tower would dominate: it is the homes, not the workplaces, that carry the heaviest modeled lifetime footprint. The figures are a gross 2019 estimate covering embodied, operational and transportation emissions before any sustainability measures, and the worksheet's office area of 894,500 sf runs slightly below the ~896,000 sf cited elsewhere in the same filing.