Soil and perc tests in Whatcom County, Washington

What is a perc test and does Whatcom County require one?

Yes. Only a licensed engineer, a licensed designer, or the county may test the soil and the site.

A soil scientist may test only the soil, not the site.

Whatcom County Code § 24.05.180, Soil and Site Evaluation · checked 2026-09-23

How USDA rates the ground in Whatcom County

Very limited across most of the county — 99.2% of the rated acres. A rating describes the ground, not a parcel. The county's site evaluation decides each lot.

• Very limited — 941,932 acres — 99.2% of 949,429 rated acres.
• Somewhat limited — 7,497 acres — 0.8% of 949,429 rated acres.
• Not rated — 113,314 acres, excluded from the denominator — mostly urban land and water.

99.2% of 949,429 rated acres. 113,314 acres unrated. Spans 3 survey areas. The largest are WA673 (v25), WA774 (v13), WA749 (v26). Versions established 2025-08-28.

USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-13

What limits absorption here

The reasons USDA gives for the rating, by the acres they affect. A component can carry several, so the acres overlap.

• Slope — 776,051 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Seepage, bottom layer — 512,986 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Depth to bedrock — 346,790 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Slow water movement — 291,838 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Depth to saturated zone — 267,106 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Filtering capacity — 156,977 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Large stones — 95,514 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Flooding — 59,879 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Ponding — 28,786 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Subsidence — 13,408 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Depth to cemented pan — 3,150 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.

Ratings by soil map unit

The largest map units in the county, each with its rating. A soil survey names the ground. The county's evaluation of your lot is what a permit turns on.

• 9998 — Rock outcrop-Glaciers-Harlequin complex, 25 to 100 percent slopes — 88,190 acres in this county — rated Very limited. Dominant component: Rock outcrop (60% of the map unit).
• 9016 — Doubtful-Triumph-Perfect complex, 35 to 100 percent slopes — 44,578 acres in this county — rated Very limited. Dominant component: Doubtful (30% of the map unit).
• 9010 — Doubtful-Treen-Rock outcrop complex, 35 to 100 percent slopes — 42,831 acres in this county — rated Very limited. Dominant component: Doubtful (30% of the map unit).
• 9012 — Spickard-Tepeh-Maggib complex, 15 to 100 percent slopes — 38,895 acres in this county — rated Very limited. Dominant component: Spickard (40% of the map unit).
• 9008 — Mox-Doubtful-Perfect complex, 35 to 100 percent slopes — 38,131 acres in this county — rated Very limited. Dominant component: Mox (30% of the map unit).
• 9003 — Stetattle-Doubtful-Arriva complex, 15 to 100 percent slopes — 29,924 acres in this county — rated Very limited. Dominant component: Stetattle (30% of the map unit).
• 7015 — Thorton-Ragged-Benzarino complex, 35 to 100 percent slopes — 28,062 acres in this county — rated Very limited. Dominant component: Thorton (40% of the map unit).
• 710 — Typic Vitricryands-Andic Haplocryods complex, till substratum, 25 to 75 percent slopes — 27,607 acres in this county — rated Very limited. Dominant component: Typic Vitricryands (60% of the map unit).

USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-13

Sources

Each figure on this page has a government source and a checked-on date.

1. Whatcom County — On-Site Sewage · checked 2026-09-23
2. Whatcom County Health and Community Services — Septic Forms & Applications · checked 2026-09-23
3. Whatcom County — OSS Annual Fee · checked 2026-09-23
4. Whatcom County Code § 24.05.380, Licensing · checked 2026-09-23
5. Whatcom County Health and Community Services — On-Site Sewage System Permit Process · checked 2026-09-23
6. Washington Administrative Code § 246-272A-0232, Design Requirements — Septic Tank Sizing · checked 2026-09-23
7. Washington Administrative Code § 246-272A-0210, Location, Table IV · checked 2026-09-23
8. USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-13
9. Whatcom County — 2025-2026 Unified Fee Schedule · checked 2026-09-23

Related pages

• Septic rules and requirements in Whatcom County, Washington
• Septic permits and fees in Whatcom County, Washington
• Home-sale septic inspections in Whatcom County, Washington
• Septic rules and requirements in Washington
• Septic rules in Whatcom County