Soil and perc tests in Oakland County, Michigan

USDA rates most of the soil in Oakland County Very limited for septic absorption fields — 89.4% of the rated acres. The county requires a soil check before it issues a permit. A backhoe digs test holes, and a Sanitarian must watch. USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-16

Very limited

USDA rating, 89.4% of rated acres

checked 2026-09-16

Slow water movement

Most common limiting reason

checked 2026-09-16

Yes

Site evaluation required

checked 2026-09-23

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

Yes. The county requires a soil check before it issues a permit. A backhoe digs test holes, and a Sanitarian must watch.

The county calls this visit a Perc soil evaluation test. The applicant arranges and pays for the backhoe.

Oakland County — Onsite Sewage Disposal System (Septic) · checked 2026-09-23

How USDA rates the ground in Oakland County

Very limited across most of the county — 89.4% of the rated acres. A rating describes the ground, not a parcel. The county's site evaluation decides each lot.

Very limited — 437,562 acres — 89.4% of 489,440 rated acres.
Somewhat limited — 43,904 acres — 9.0% of 489,440 rated acres.
Not limited — 7,974 acres — 1.6% of 489,440 rated acres.
Not rated — 91,283 acres, excluded from the denominator — mostly urban land and water.

89.4% of 489,440 rated acres. 91,283 acres unrated. Survey area MI125 version 24, established 2025-09-04.

USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-16

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.

Slow water movement — 266,886 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
Seepage, bottom layer — 262,314 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
Depth to saturated zone — 238,046 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
Slope — 128,970 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
Ponding — 108,553 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
Subsidence — 48,096 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
Filtering capacity — 43,047 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
Flooding — 7,665 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.

27 — Houghton and Adrian mucks — 47,800 acres in this county — rated Very limited. Dominant component: Houghton (55% of the map unit).
10B — Marlette sandy loam, 1 to 6 percent slopes — 40,920 acres in this county — rated Very limited. Dominant component: Marlette (90% of the map unit).
W — Water — 29,694 acres in this county — rated Not rated. Dominant component: Water (100% of the map unit).
10C — Marlette sandy loam, 6 to 12 percent slopes — 25,924 acres in this county — rated Very limited. Dominant component: Marlette (92% of the map unit).
15B — Spinks loamy sand, 0 to 6 percent slopes — 21,736 acres in this county — rated Very limited. Dominant component: Spinks (85% of the map unit).
13B — Oshtemo-Boyer loamy sands, 0 to 6 percent slopes — 21,314 acres in this county — rated Very limited. Dominant component: Oshtemo (55% of the map unit).
11B — Capac sandy loam, 0 to 4 percent slopes — 19,281 acres in this county — rated Very limited. Dominant component: Capac (92% of the map unit).
59 — Urban land — 18,700 acres in this county — rated Not rated. Dominant component: Urban land (100% of the map unit).

USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-16

Sources

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

Oakland County — Onsite Sewage Disposal System (Septic) · checked 2026-09-23
Oakland County Health Division — Contact Us · checked 2026-09-23
Oakland County Health Division Sanitary Code (January 2026), Article II § 2.2 · checked 2026-09-23
Oakland County Health Division — Environmental Health Fee Schedule, effective 10/01/2025 · checked 2026-09-23
USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-16

Verify before you act. Septic rules are set locally and they change. Check anything here before you spend money on it. Call the Oakland County Health Division, Environmental Health Services, on 248-858-1312.