Soil series profile

Olympic soil series

Olympic is a well drained soil with a silt loam surface, mapped on 164,524 acres in 7 counties in WA. Hydrologic group C.

#2228 by mapped area clayey Xeric Palehumults (Ultisols)

Drainage class: Well drained
Hydrologic group: C
Typical topsoil pH: 5.6
Mapped area: 165k

Typical Olympic 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 Olympic horizons (representative values)
Depth	Texture	pH	Clay	Sand	Organic matter
0–4 in (H1)	Silt loam	6.1	21%	26%	5.5%
4–14 in (H2)	Silt loam	6.1	30%	20%	2%
14–38 in (H3)	Silty clay	5.3	48%	6%	0.5%
38–60 in (H4)	Silty clay	5.3	55%	3%	0.25%

Representative values from the most extensive Olympic map unit (Olympic silt loam, 8 to 20 percent slopes, survey area WA015). 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 Olympic soil means for gardens, lawns and septic systems

For gardens

Typical topsoil in Olympic soils is moderately acidic: pH 5.6 (most land between 5.5 and 6.1). Many vegetables grow well here, and some gardens benefit from a little lime. Test before adding any.

Loamy topsoil (loam, silt loam and similar) covers >99% of mapped Olympic acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silt loam (45% of mapped Olympic acres).

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

For lawns and yards

On 62% 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 79% of the acres in mapped Olympic soils very limited, 21% 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 Olympic soil is found

Mapped acres

Olympic is mapped in Washington.

Counties with the most mapped Olympic soil
County	Acres	Share of county land
Cowlitz County, WA	63,090	9.1%
Clark County, WA	59,780	14.9%
Lewis County, WA	18,791	1.6%
Grays Harbor County, WA	11,592	1.1%
Thurston County, WA	10,850	2.2%
Pacific County, WA	210	0.0%
Wahkiakum County, WA	210	0.1%

Septic absorption fields

NRCS rating, share of Olympic acres

Not limited 0%

Somewhat limited 21%

Very limited 79%

Not rated <1%

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

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Septic tank absorption field rating across mapped Olympic acres.
Category	Share of acres
Not limited	0.0%
Somewhat limited	20.9%
Very limited	78.7%
Not rated	0.3%

Drainage, water table and flooding

Share of Olympic acres

Depth to seasonal high water table: None reported within about 6.5 feet (median where reported).
Flooding: Not mapped as flooding on most acres.
Slope: Typically 12–45% (median 17%).
Topsoil organic matter: Median 5.5%.

Drainage class

Excessively drained 0%

Somewhat excessively drained 0%

Well drained 100%

Moderately well drained 0%

Somewhat poorly drained 0%

Poorly drained 0%

Very poorly drained 0%

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

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Drainage class across mapped Olympic acres.
Category	Share of acres
Excessively drained	0.0%
Somewhat excessively drained	0.0%
Well drained	100.0%
Moderately well drained	0.0%
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 38%

C: slow infiltration 62%

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 Olympic acres. Scale 0 to 100% of mapped land.

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Hydrologic soil group across mapped Olympic acres.
Category	Share of acres
A: fast infiltration (mostly sandy or gravelly)	0.0%
B: moderate infiltration	38.0%
C: slow infiltration	61.7%
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	0.3%

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 Olympic (component kind "Series") in SSURGO: 164,524 acres.
Method: Shares are by mapped acres of Olympic components. The profile comes from the single largest Olympic component. Full methodology.

Independent reference site. No government affiliation or endorsement.

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