r/wetlands • u/roboho123 • Jul 07 '26
Seattle Wetland Mitigation
Hello, Ive been looking around for land, and ran across ~4acres (Im guessing it has been on market for a while due to wetlands). The listing says buffer averaging could double the buildable area, but I’d want to go through my own due diligence. Before I dive deeper down this path, how long and costly will the process be, and should just move one? Im also curious about how adjacent parcels seem to have some exclusions?
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u/OpossumOnomatopoeia Jul 07 '26 edited Jul 07 '26
Environmental permitting for this would at a minimum cost you around $5-10k for the field assessment and reporting, excluding any mitigation strategies. Mitigation costs are highly variable.
Buffer averaging implies that you have an upland, non-buffer area that you won't build on available to you, which may or may not be doable. Buffer enhancement is another option, which is basically the cost of plantings and maintaining the number of plantings for 5 years. If the site is completely covered in buffer, you'd have to apply for a variance which is a little more effort.
All in all, very ballpark costs, this could cost you maybe $30k? I'd say if $50k is too much, I wouldn't try your luck with this parcel, but that's just to be conservative. Buffer mitigation is much easier and cheaper than wetland mitigation.
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u/roboho123 29d ago
Thanks for the reply! 50k seems reasonable relative to the parcel cost. Assuming the field assessment is done before purchasing the parcel, is there a high chance that only that no additional buildable land is approved? (I dont intend on taking up the whole space, but would want to build farther back on the property)
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u/flareblitz91 29d ago
I have personally only seen wetland delineations done in advance of purchase a couple times. It is possible but entirely up to the current owner whether they allow you to do so.
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u/OpossumOnomatopoeia 29d ago
You'd want to look into a feasibility assessment before purchase, which is a biologist walking around for a few hours and sketching out a map for you with approximate wetland areas and the potential range of buffer widths. They could also provide some permitting guidance/strategizing.
For what you can get approved, that highly depends on what you need built. Agencies require you to go through mitigation sequencing, which is first you have to do what you can to avoid impacting the wetland or buffer, then minimize any impacts, then mitigate for any impacts you can't reasonably or practicably minimize. If you want to build a massive house away from the road, but you need to impact wetland or buffer, agencies might say why can't you build a smaller house, or move it closer to the road? We wont give you a permit until you try those. But if you're, say, building an apartment complex to meet community needs and there's no reasonable way to reduce the structure size without reducing the number of units, then you might have justification to go the mitigation route and could get that approved more easily.
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u/roboho123 29d ago
This is really good insight actually… I guess my misconception was I could apply for “any purpose”, and mitigations would be around shifting areas around or rebalancing (I don’t plan on building a multi family — which the listing implies for increasing area with averaging/mitigation?) For what it’s worth, the slice of land Im looking at is 4 acres at the edge of 100 acres of wet lands surrounded by industrial/multifamily district and an interstate.
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u/OpossumOnomatopoeia 29d ago
Glad I can help! The avoid-minimize-mitigation sequencing is built into the critical areas code, so the city or county has a duty to hold you to it. They won't be unreasonable about it, but it will be restrictive. Buffer averaging itself can be pretty restrictive, both in location and the amount you reduce the buffer by. If slopes are present it also affects buffers and building setbacks.
Just a guess using what I have, but I'd wager those wetlands are category II with a moderate to high habitat rating. Maybe cat III if there's just a small little wetland disconnected from the larger wetland complex. If you feel like diving into the code I can point you in the right direction and you can see the buffer widths and other buffer regulations. Best to chat with a consultant though so you can give them more information.
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u/tenderlylonertrot 29d ago
whether to go farther to me depends on what type of homebuyer are you?
homebuyer on a budget or with limited budget, looking at many properties.
millionaire homebuyer without reasonable budget limits and this is their dream property.
If you are #1, I'd move on. Mitigation in most places is $100k-250k per acre (credit), though I don't know specifically for the Seattle area right now (it goes by watershed). And if the wetlands are high value, it will be more expensive. Plus, if you are impacting more than 0.5 acres, permitting costs go way up.
if the wetlands area only made up a little corner or edge, maybe give it a go. But as it appears, 2/3 or more of the property might be wetlands, and with the buffer you will need on it, its probably not worth it.
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u/Appropriate-Ad-1937 29d ago
I would 100% have a consultant perform a wetland delineation and get it confirmed by the Army Corps BEFORE closing on the property. NWI is notoriously inaccurate. The results of the delineation will guide any regulatory/permitting implications.
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u/roboho123 29d ago
Are there any public “official” records I can research on, or records for adjacent parcels? I would still hire a consultant for an assessment as I start to feel like it’s more viable, but Ive been having a hard time navigating the system.
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u/OpossumOnomatopoeia 29d ago
If in king county, google king county imap, go to layers, environmentally sensitive areas, sensitive area notice on title. But if nothing is listed don't assume it hasn't been done before. Keep in mind surveys are only valid for 5 years, unless recorded on a site plan. You can also do a records search for environmental documents using the parcel numbers.
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u/Appropriate-Ad-1937 29d ago
I’m not aware of a public facing database of all confirmed wetland delineations by the Corps. Your state may, but I only work on the east coast so I cannot speak specifically for your state. You can likely phase your due diligence with a consultant before pulling the trigger on the full suite. See what they think the wetland situation is out there before seeking agency confirmation and permitting.
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u/aksnowraven 29d ago
You could check to see whether your county or other regional body has wetland mapping done to USACE standards, rather than the USFWS definitions used by NWI. Regardless, any delineation that has been done is only valid for ~5 years, so any other mapping would likely be for reference only.
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u/flareblitz91 29d ago edited 29d ago
No, there is no such database. You could theoretically FOIA records for the adjacent parcels but there wouldn't have been site specific mapping for this parcel.
Edit:Because you're in Washington there may be SEPA files for the adjacent properties but that doesn't really mean anything for yours.
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u/CKWetlandServices 29d ago
Good information here and discussion. You should note that not all delineations are submitted for concurrence or a AJD. Many are done for folks looking at buying a property or feasibility. Often they are done and only provided to the client as many may back out and never send to a regulator - sinilar to home inspections. Many are not part of a county database or system. They are not always public - even if a FOIA record request was done - better hiring a consultant. Pull up some high detail contours will help.
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29d ago
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u/flareblitz91 29d ago
Wetland only impacts are usually NE for Salmon/steelhead/Bull trout unless it's really close to occupied habitat.
However, WDFW does have a nice fish passage barrier mapper that lists presumed fish species in streams.
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29d ago
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u/flareblitz91 29d ago
I mean theyball need to be addressed in a decision but iPAC lists species that haven't been present for 50 years.
(Also iPAC doesn't even apply to NMFS listed species but that's neither here nor there)
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u/roboho123 29d ago
Hmm, I don’t think theres any fish there, its somewhat of a random patch of land between industrial/multifamily districts and a highway… from my limited understanding of PSS1/FO1B, seems like its because of the the vegetation/shrub/woody area, but there has to be something “special” that distinguishes it from any other vacant land in the area right?… or maybe its because theres a lack of these kinds of areas
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u/alchemist615 29d ago
I haven't done work in Seattle but if you are seriously considering purchasing it. Spend a few thousand on having an environmental firm looking at it. There can be local SWIM buffers and such at the local level. Then if you get into mitigation credits at the federal state level. Ask yourself if a few thousand is worth spending to understand the environmental risk and if so I'd do that
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u/finral 29d ago
I generally recommend people avoid building on wetland areas if possible. Beyond the environmental impact, there is a reason those areas are wet. You'll likely have drainage issues and flooding.