Cleanups like those at Willamette Cove have very strict sets of milestones that must be met before dirt starts to be excavated and hauled away. At the end of September, engineers and scientists at Metro and the Port of Portland, the two partners working to clean up the upland at Willamette Cove, reached one of those milestones when they submitted an important planning report to DEQ, the Oregon Department of Environmental Quality.
This latest document, called the basis of design report sets out how Metro and the Port will design the upland cleanup along the Willamette River in North Portland. The upland cleanup covers the land from the top of the riverbank and inland and is being done to make the site safe for people, plants and animals to use as a nature park. A separate cleanup is being planned from the top of the riverbank down into the river.
Let’s take a look at what milestones the project has already met and how the basis of design report is a step forward.
The in-water cleanup
The group designing the in-water cleanup at Willamette Cove also reached a major milestone recently. The teams designing both cleanups are working closely to find ways the two cleanup designs and the nature park design can complement each other.
Learn more about the in-water cleanup
What is in the basis of design report?
The basis of design report lays out an updated estimate of how much contaminated soil is going to be taken out of every square foot across the upland. It explains why, based on past studies, it is that much and then what needs to be done to cover the remaining soil. It also details how we’ll check our work to make sure we’ve met DEQ’s requirements and how we’ll design a long-term monitoring plan to make sure the cleanup stays cleaned.
Very importantly, the basis of design report reaffirms that there will not be a consolidated mound of excavated soil anywhere on the site.
Didn’t DEQ already say what needs to be done at Willamette Cove?
In 2021, DEQ selected the cleanup method for Willamette Cove in what’s called a record of decision. This document was based on work going back to 2000, including soil studies and assessments of three cleanups focused on the highest concentrations of contaminants. Public comments on a draft of the record of decision led DEQ to provide a cleanup option that took even more soil off the site, which Metro has chosen to follow.
- The record of decision laid out the requirements for what had to be done to clean up the soil at Willamette Cove from the top of the riverbank to the upland property line.
- All contamination that is a high risk to human health—called human health hot spots—must be hauled to a DEQ-approved landfill (human health hot spots were cleaned up in 2008 and 2015, and further studies have found no new human health hot spots).
- All contamination from metals that are a high risk to plants and animals—called ecological hot spots—must be hauled to a DEQ-approved landfill or covered with a protective barrier of clean soil.
- At least one foot of clean topsoil will be placed over the entire site as part of the final cap and to help re-establish native plants that will be planted across the site.
The next set of milestones figures out the specifics needed to make this happen.
Maps and diagrams
What is a cleanup design?
To implement the cleanup, we have to think about the end goal and work backwards. Metro and the Port have started the remedial design process to develop detailed plans for the construction of the cleanup. It’s a bit counterintuitive, but a cleanup is really a type of construction project, so let’s look at a more familiar type of construction project to understand the steps in the cleanup.
Let’s say you want to build a building at a specific spot. You start by looking at how much space you have, whether the ground is flat or steep, and what type of neighborhood it’s in. You think about what you want from the building: is it a home or an office or a water tower? Let’s say it’s a home. It could be super modern, a split-level ranch or a bungalow. You need to decide all of this first.
This is what the record of decision does. The basis of design report, for its part, is a fairly detailed sketch of the house and description of how you’ll make decisions while you build it. The basis of design report isn’t the blueprints, but it makes the process of drawing the blueprints much smoother. That step is about to start. Metro and the Port are scheduled to submit the next design document, called the remedial design work plan, to DEQ early next year.
How did you determine how much dirt needed to be excavated at any spot?
The most important data guiding the decisions about how much soil needs to go came from an extensive study in 2022 that looked at the top three feet of soil. The study divided the cove into 44 roughly half-acre sections and took 5,130 samples that showed the average amount of the contaminants in the first, second and third foot below ground level. This was a far more precise and extensive study than had been done before.
The basis of design report used that data to determine which of the contaminants was the biggest problem in any half-acre section and if any combination of chemicals added up to a health risk for people, plants and animals. The report then evaluated how deep down we need to excavate to remove the targeted contaminant or group of contaminants. Finally, it helped determine how thick the cap of clean soil needs to be to make that area safe.
What are these caps?
The caps keep people and animals from coming into contact with any contaminants left after the cleanup. They’re made of a foot of fresh topsoil over the top of, if needed, what’s called clean fill. The clean fill will vary depending on the location, but it will likely be other types of clean soil and may include sand, gravel or a layer of fabric marking the bottom of the cap.
Two areas may need a cap that’s more robust. The details on these caps and the clean fill will be nailed down in the next stages of design.
What is the plan for making sure the cleanup stays safe?
The basis of design report broadly describes four types of monitoring and maintenance that will ensure the site is safe. These plans will be detailed over the next year in future milestones.
The first is construction monitoring to make sure the construction workers on the site are safe and using best practices to make sure excavated dirt safely reaches its destination at disposal facilities.
The second is verification sampling. This is the step of checking our work to make sure we actually did reduce the amount of a contaminant to a safe level in any given area.
The third is long-term monitoring. This is the big one that makes sure we know the cleanup is staying cleaned up.
Finally, there will be a plan for maintenance if the monitoring ever finds a problem that needs to be fixed.
What’s the next milestone?
The next milestone is the blueprints we talked about earlier. The remedial design work plan will have engineering drawings and schematics that are the instructions the construction crews will use to know where and how deep they need to dig. The document will also lay out the schedule for the cleanup and the detailed steps for managing the day-to-day work.
There will be three to four more drafts after that. All of this is to make sure that when the work crews roll on site, they know exactly what they need to do to make the Willamette Cove uplands safe.