Soil series profile

Elwell soil series

Elwell is a moderately well drained soil with a medial silt loam surface, mapped on 61,896 acres in 4 counties in WA. Hydrologic group C.

#5076 by mapped area medial Aquic Durudands (Andisols)

Drainage class: Moderately well drained
Hydrologic group: C
Typical topsoil pH: 4.6
Mapped area: 62k

Typical Elwell profile

Texture and pH by depth

Depth to scale. More strongly shaded layers hold more clay. Horizon names are the soil survey's (A = topsoil, B = subsoil, C = parent material).

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Typical Elwell horizons (representative values)
Depth	Texture	pH	Clay	Sand	Organic matter
0–2 in (H1)	Medial silt loam	4.6	15%	14%	12.5%
2–23 in (H2)	Medial silt loam	5.3	10%	21%	6%
23–27 in (H3)	Gravelly medial fine sandy loam	5.3	10%	64%	1.25%
27–60 in (H4)	Gravelly sandy loam	5.3	10%	64%	1.25%

Representative values from the most extensive Elwell map unit (Elwell-Olomount-Rock outcrop complex, 30 to 60 percent slopes, survey area WA661). Other map units of this series vary within the series range.

Stock photo for illustration, not a sample of this soil series. Credit on the Sources & method page.

What this means

What Elwell soil means for gardens, lawns and septic systems

For gardens

Typical topsoil in Elwell soils is very strongly acidic: pH 4.6 (most land between 4.6 and 5.3). Most vegetables and lawn grasses do best around 6.0 to 7.0, so lime is often needed; blueberries, azaleas and rhododendrons like it as it is.

Loamy topsoil (loam, silt loam and similar) covers >99% of mapped Elwell acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is medial silt loam (57% of mapped Elwell acres).

100% of mapped Elwell acres is moderately well to excessively drained, which suits most garden plants.

For lawns and yards

On >99% of mapped acres, rain soaks in slowly (hydrologic groups C and D, including dual groups that are D until drained). Expect runoff and puddles after heavy rain: core-aerate compacted lawns and keep ground sloping away from foundations.

For a septic system

For conventional septic absorption fields, NRCS rates >99% of the acres in mapped Elwell soils very limited, 0% somewhat limited and 0% not limited.

Where the soil is very limited (slow permeability, a high water table, flooding, shallow bedrock or steep slopes), alternative systems such as mound or sand-filter designs are common and cost more.

Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.

Generated from the mapped numbers above using fixed rules, not a site visit. See how these notes are written.

Where Elwell soil is found

Mapped acres

Elwell is mapped in Washington.

Counties with the most mapped Elwell soil
County	Acres	Share of county land
Snohomish County, WA	35,107	5.9%
Pierce County, WA	9,451	0.9%
King County, WA	9,223	0.8%
Skagit County, WA	8,115	1.0%

Septic absorption fields

NRCS rating, share of Elwell acres

Not limited 0%

Somewhat limited 0%

Very limited >99%

Not rated <1%

Septic tank absorption field rating across mapped Elwell acres. Scale 0 to 100% of mapped land.

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Septic tank absorption field rating across mapped Elwell acres.
Category	Share of acres
Not limited	0.0%
Somewhat limited	0.0%
Very limited	99.9%
Not rated	0.1%

Drainage, water table and flooding

Share of Elwell acres

Depth to seasonal high water table: About 2.2 feet (26 in) (median where reported).
Flooding: Not mapped as flooding on most acres.
Slope: Typically 17–48% (median 18%).
Topsoil organic matter: Median 12.5%.

Drainage class

Excessively drained 0%

Somewhat excessively drained 0%

Well drained 0%

Moderately well drained 100%

Somewhat poorly drained 0%

Poorly drained 0%

Very poorly drained 0%

Drainage class across mapped Elwell acres. Scale 0 to 100% of mapped land.

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Drainage class across mapped Elwell acres.
Category	Share of acres
Excessively drained	0.0%
Somewhat excessively drained	0.0%
Well drained	0.0%
Moderately well drained	100.0%
Somewhat poorly drained	0.0%
Poorly drained	0.0%
Very poorly drained	0.0%

Hydrologic soil group

A: fast infiltration (mostly sandy or gravelly) 0%

B: moderate infiltration 0%

C: slow infiltration >99%

D: very slow infiltration (clayey, shallow or wet) 0%

A/D: D as is, A if drained 0%

B/D: D as is, B if drained 0%

C/D: D as is, C if drained 0%

Not rated <1%

Hydrologic soil group across mapped Elwell acres. Scale 0 to 100% of mapped land.

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Hydrologic soil group across mapped Elwell acres.
Category	Share of acres
A: fast infiltration (mostly sandy or gravelly)	0.0%
B: moderate infiltration	0.0%
C: slow infiltration	99.9%
D: very slow infiltration (clayey, shallow or wet)	0.0%
A/D: D as is, A if drained	0.0%
B/D: D as is, B if drained	0.0%
C/D: D as is, C if drained	0.0%
Not rated	0.1%

Sources & data dates

Source: USDA NRCS Soil Survey Geographic Database (SSURGO), queried through Soil Data Access. Public domain.
Data date: SSURGO as published on November 3, 2026 (most recent survey area update October 26, 2026). NRCS refreshes SSURGO each October.
Scope: All map unit components named Elwell (component kind "Series") in SSURGO: 61,896 acres.
Method: Shares are by mapped acres of Elwell components. The profile comes from the single largest Elwell component. Full methodology.

Independent reference site. No government affiliation or endorsement.

Full narrative description: USDA Official Soil Series Description for Elwell.