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Why Snohomish and Marysville Homes Battle Drainage-Related Concrete Settling
Quick summary: Snohomish and Marysville sit on some of the most water-influenced ground in Snohomish County. Snohomish is tucked against the Snohomish River valley, a wide, flat floodplain with a long flooding history, and Marysville has grown fast across land shaped by creeks, ditches, wetlands, and the estuary around Ebey Slough and Quilceda Creek. Add glacial till soils that drain slowly and a wet season that can keep the ground saturated for months, and it’s no surprise we’re regularly called out for sinking driveways, walkways, patios, and garage floors in both cities. Drainage is a big factor, but it’s not the only one. Soil that was moved, filled, or backfilled during construction can also settle over time. This guide covers what’s going on underground in each area, what to check on your own property, and when slabjacking makes sense.
We’re a family owned company based in Lynnwood, which puts Snohomish and Marysville squarely in our backyard. We’ve spent over 20 years raising concrete across Western Washington, and when a call comes in from the Snohomish or Marysville area, we usually have a pretty good idea of the questions we’ll be asking before we ever pull into the driveway. Is the lot on low ground? Is the neighborhood new? Where does the water go when it rains? Those answers tell us a lot about why a slab has dropped.
Two cities, one common thread: water and the ground it moves through
On paper, Snohomish and Marysville look different. One is a historic river town and the other is one of the fastest growing cities in the county. Underground, they share a lot. Both sit on or beside low, water-influenced ground, both have soils that don’t always let water drain away quickly, and both get the same heavy winter rain as the rest of Puget Sound. Here’s how it plays out in each place.
Snohomish: living beside the valley
The town of Snohomish sits on a landform known as the Getchell Hill Plateau, flanked by the Snohomish Estuary, the Pilchuck outwash channel, and the Snohomish River Valley. That valley is wide and flat, carved by thousands of years of glacial meltwater, and it’s often described as a bathtub for good reason. The river here is lined with meander arms and oxbow lakes, which are reminders of how often it has flooded and changed course.
That history is not just trivia. In December 1975, the Snohomish River reached a record depth of 33.16 feet at Snohomish, and floodwater formed a lake roughly 50,000 acres in size between Everett and Monroe. Today the river is bordered almost entirely by levees, and Snohomish County notes that in parts of the lower delta, deep weak soils have led to levee subsidence. For homeowners, the practical takeaway is simple: in and near the valley, the ground can hold a lot of water for a long time, and soil conditions can change over short distances. A lot on the plateau and a lot down on the valley floor can behave very differently, even if they’re only a few minutes apart.
Marysville: fast growth on ground that was once much wetter
Marysville has grown dramatically. The city’s population was around 28,000 in 2004 and is now roughly 69,000, and its comprehensive plan targets nearly 88,000 residents by 2035. Areas like Smokey Point and Lakewood that were once more rural than urban now hold shopping centers, apartments, and new neighborhoods.
A lot of that growth happened across land that was shaped by water. Quilceda Creek drains a glacial plateau within and north of Marysville, and its headwaters include a large number of agricultural ditches that were once part of historical wetland complexes. Along the western edge of the city, the area around Ebey Slough is estuarine wetland and floodplain. The city’s own master drainage plans include channel realignments and conveyance projects on creeks like Hayho and Edgecomb, which tells you how much water management goes into keeping this part of the county developable.
None of that means a Marysville home is at special risk. It does mean that when a driveway or sidewalk settles here, water is one of the first things we look at.
The soil underneath: glacial till and a perched water table
Across much of Snohomish County, including areas in and around both cities, the soil survey maps a lot of Alderwood soil. It formed in glacial till and sits over a hardpan, a dense layer that water moves through very slowly. The survey notes that a seasonal perched water table can sit roughly 18 to 36 inches below the surface from January through March, and it specifically flags that drainage is needed where buildings with basements or crawl spaces are built.
In plain terms, rain soaks through the top layer and then has nowhere to go, so it sits and moves sideways along the hardpan. That’s the water that can find its way along a slab edge, under a walkway, or against a foundation. It’s also why the same neighborhood can have one house with a bone-dry yard and a neighbor with a soggy one. You can look up the soils mapped for your own address using the free USDA Web Soil Survey.
Newer neighborhoods have their own set of factors
Newer planned communities are built to modern stormwater standards, with retention ponds, catch basins, and lots graded to shed water. That’s a good thing. But new construction also means a lot of moved dirt: grading, utility trenches, fill, and backfill around foundations. Soil that’s been disturbed can continue to consolidate over the first several years, and when that happens right under a driveway apron, sidewalk, or patio, the concrete settles with it. That’s soil behavior, not a sign that anyone did anything wrong.
Water adds to it over time. A downspout that was draining fine in year one, can end up dumping beside a slab after a fence goes in, landscaping changes, or a side-yard swale gets blocked. If you live in a planned community, the catch basins, ponds, and drainage easements near your lot may also be maintained by an HOA or other shared owner, which is worth knowing when something isn’t draining right.
Around Snohomish and Marysville, we see a lot of different soil conditions, sometimes even within the same neighborhood,” says Israel Craig, Lead Field Advisor at 1-866-SLABJACK. “The first things we look at are where the water is going, whether the soil has been disturbed or backfilled, and what’s actually happening underneath the slab. A lot of times it’s a combination of those factors rather than just one thing
What Marysville property owners should know about stormwater responsibility
This is worth being aware of, though the details depend on your property. Marysville’s municipal code (chapter 14.17) places responsibility for maintaining private storm drainage systems on the property owner, including systems shared with other owners, and the city runs private stormwater facility inspections to check that those systems are working as designed. We’re not attorneys or stormwater engineers, and this isn’t legal advice, but if you’re not sure what applies to your property, the city’s surface water team is the right place to ask. Snohomish County also publishes a flood guide with information on drainage problems and who to contact.
A local checklist for Snohomish and Marysville homeowners
Walk your property after a good rain, ideally in the wetter months when problems show up fastest:
Check where every downspout discharges and confirm the water is being carried well away from the driveway, garage apron, and walkways.
Look for side-yard swales, ditches, or low spots that have been blocked by fences, sheds, mulch, or landscaping.
If there’s a catch basin, ditch, or retention pond near your lot, check whether it’s clogged with debris or holding water longer than it should.
Note any wet or muddy patches that show up between January and March, when seasonal groundwater is typically highest.
Look for gaps where your driveway meets the garage, lips or steps at sidewalk joints, and soil pulling away from the edge of a slab.
If you’re near the valley or a slough, check your concrete after any major rain or high water event, since it can be days or weeks before settling becomes visible.
For more detail on the most common causes, see our guide to the drainage mistakes that sink Puget Sound driveways.
Drainage fix, slabjacking, or both?
Here’s where we try to be straight with people. Fixing a drainage issue will protect your concrete going forward, but it won’t lift a slab that has already settled. And in some cases, lifting a settled slab is what restores proper slope and solves the water problem. We break down how to tell the difference in our post on drainage fixes vs. slabjacking, and we cover why the two are often separate jobs in why fixing your drainage won’t fix your sunken concrete.
When the concrete itself does need to be lifted, polyurethane slabjacking is well suited to this part of the county. The foam is lightweight, doesn’t absorb water, and cures within about 15 minutes, so it isn’t held up by saturated soil the way older water-based methods can be. Most driveways and walkways are back in use within a couple of hours. You can read more about the process on our poly slabjacking page, and about how the rainy season affects all of this in our post on why Western Washington’s wet season puts extra stress on sinking concrete. If your property went through extreme rainfall like the December 2025 atmospheric river, our article on how heavy winter storms undermine driveways and sidewalks explains what to watch for in the weeks and months afterward.
We also stand behind our work with a one year, no questions asked warranty that covers settling caused by soil compaction, which is the kind of settling that shows up shortly after a lift rather than years later.
Key Points
Snohomish sits beside a wide, flat river valley with a long flooding history, and Marysville has grown quickly across land shaped by creeks, ditches, wetlands, and estuary.
Glacial till soils with a hardpan layer can hold seasonal groundwater close to the surface from roughly January through March, which puts extra pressure on concrete.
Newer neighborhoods can see settling from disturbed or backfilled soil as well as from drainage, so the cause isn’t always water alone.
Marysville’s code places maintenance of private storm drainage systems on the property owner, so it’s worth knowing what’s on your lot or shared with neighbors.
Fixing drainage protects concrete going forward, but settled concrete still needs to be lifted separately, and sometimes lifting the slab is what fixes the drainage problem.
FAQ
Why is my driveway sinking in Snohomish?
There are several common reasons. Seasonal groundwater, a downspout draining near the slab, poor grading and soil that was disturbed during construction can all contribute. Homes near the Snohomish River valley can also see higher groundwater for longer periods. A free inspection can help sort out which factors apply to your property.
Is concrete settling common in Marysville’s newer neighborhoods?
We see it regularly, though it isn’t true of every home. Soil that was graded, filled, or backfilled during construction can continue to consolidate for several years, and changes to drainage over time, like new fences or landscaping, can send water toward a slab. It’s usually a matter of soil behavior, not a defect.
Who is responsible for stormwater drainage on my property in Marysville?
Under Marysville’s municipal code, property owners are generally responsible for maintaining private storm drainage systems on their property or shared with other owners, and the city inspects private facilities. Requirements depend on your property, so check with the city’s surface water team if you’re unsure.
Can concrete be lifted during the rainy season in Snohomish County?
Yes. Polyurethane foam is hydrophobic and cures within minutes, so wet or saturated soil doesn’t hold up the work the way it can with older water-based methods.
Does flooding in the Snohomish River valley affect concrete?
It can. Prolonged saturation and high groundwater can erode or shift the soil under slabs, and visible settling sometimes shows up weeks or months after a high water event rather than right away.
Do you serve Snohomish, Marysville, and Smokey Point?
Yes. We’re based in Lynnwood and serve Snohomish, Marysville, Smokey Point, Lakewood, and communities throughout Snohomish County and Western Washington. You can see our full service area here.
If you’re noticing a sunken driveway, a dipping walkway, or a garage apron that doesn’t sit flush anymore, schedule a free inspection and we’ll walk the property with you, look at the settling and the drainage together, and give you an honest read on what’s going on underneath.
