In Washington State, what you need before you buy or build on a piece of land depends entirely on your desired project outcome. That could mean anything from an environmental cleanup review to a site analysis for a public facility or an early learning center. Full stop, there is no single checklist that covers every property. There's a process for figuring out what you're actually allowed to do with the land you're buying, and most homeowners have never heard of it until they're standing in the middle of it.

Most homeowners aren't thinking about any of this when they picture their backyard ADU. Even when that backyard backs up to a creek. Here's what I would say about that to any buyer looking at land, a big lot, or an older home right now.

What a Feasibility Study Actually Means in Washington

I want to be precise here, because the phrase "feasibility study" gets used two different ways, and mixing them up leads people to the wrong expectations.

In the narrow, legal sense, a Feasibility Study is a specific, later-stage step under Washington's Model Toxics Control Act (MTCA). It only happens after a Remedial Investigation has already confirmed that a site is contaminated. At that point, the Department of Ecology and the responsible party evaluate a range of cleanup alternatives and pick the one that best balances cost against environmental benefit. That is not something most residential buyers will ever touch, and it's not what I'm talking a buyer through on a typical purchase.

What most buyers actually need is the broader, informal use of the term: a pre-purchase or pre-development review that answers the question, "what am I allowed to do here, and what's going to slow me down or cost me money?" That review can include a zoning and permitted-use check, a critical areas screening, and, when there's reason to suspect contamination, a Phase I Environmental Site Assessment, which can lead to a Phase II if the Phase I turns something up.

When Your Backyard Backs Up to a Creek

Want to buy that home with the large yard so you can build a shop, an ADU, or just have room to spread out? If there's a stream, wetland, or steep slope anywhere on or near the property, that's where I tell buyers to slow down and ask questions before writing an offer, not after.

Washington's Growth Management Act, under RCW 36.70A, requires every city and county in our service area to adopt critical areas ordinances that protect streams, wetlands, and their buffers. Every jurisdiction sets its own buffer distances and rules, so I'm not going to hand you a number here that might be wrong for your specific city. What I will tell you is that a buffer requirement can eat a meaningful chunk of a lot's usable building area, and that's information you want before closing, not during your permit application eighteen months later.

Running a Business Out of Your Land

Want to buy land for mixed use, a homestead and a shop side by side? Thinking about running a licensed childcare business out of a property with a large yard? Here's what I'd tell you to line up before you get attached to a specific address.

The One I Learned the Hard Way: Old Oil Tanks

There's one more instance that comes from my own personal experience, and it's the one I bring up most with buyers looking at older homes: oil-burning furnaces. Whether or not that furnace has been decommissioned and replaced, what may remain in the ground in the yard is a large underground oil tank. These can form leaks over time, or get overrun with water, and the oil starts to seep into the ground. The cleanup bill can get real expensive, real quick.

What Skipping This Can Actually Cost You

I want to be honest about scale here instead of throwing around a vague number. According to the Washington Department of Ecology, the state issued a combined total in environmental penalties of $1,000 or more statewide from January through June of 2026. Individual penalties in that release ranged from small reporting violations up to a six-figure case involving illegal wastewater disposal near the Chehalis River. Most of the individual penalties that hit homeowners and small property owners, rather than large commercial operators, tend to sit in the low thousands.

Figures per the Washington Department of Ecology's Sept. 3, 2026 release covering penalties issued January through June 2026. Confirm any property-specific environmental history through a site assessment, not through a blog post.

The point isn't to scare anyone off a piece of land. It's that the penalty range tells you something real: most of these situations are avoidable with basic homework, and the ones that turn expensive are almost always the ones where nobody asked the right question before closing.