Soil and perc tests in Collin County, Texas

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

Yes. Texas requires a site evaluation before Collin County issues a permit.

Texas Administrative Code, Title 30, Chapter 285, Section 285.30, Site Evaluation · checked 2026-09-23

How USDA rates the ground in Collin County

Very limited across most of the county — 98.9% of the rated acres. A rating describes the ground, not a parcel. The county's site evaluation decides each lot.

• Very limited — 459,610 acres — 98.9% of 464,850 rated acres.
• Somewhat limited — 5,240 acres — 1.1% of 464,850 rated acres.
• Not rated — 102,292 acres, excluded from the denominator — mostly urban land and water.

98.9% of 464,850 rated acres. 102,292 acres unrated. Survey area TX085 version 21, established 2025-09-04.

USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-23

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 — 436,379 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Depth to bedrock — 121,764 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Flooding — 52,094 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Slope — 15,705 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Depth to saturated zone — 5,900 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.

• HoB — Houston Black clay, 1 to 3 percent slopes — 189,910 acres in this county — rated Very limited. Dominant component: Houston Black (80% of the map unit).
• HoA — Houston Black clay, 0 to 1 percent slopes — 42,206 acres in this county — rated Very limited. Dominant component: Houston Black (85% of the map unit).
• AuC2 — Austin silty clay, 2 to 5 percent slopes, moderately eroded — 32,005 acres in this county — rated Very limited. Dominant component: Austin (85% of the map unit).
• HcC2 — Heiden clay, 3 to 5 percent slopes, eroded — 28,534 acres in this county — rated Very limited. Dominant component: Heiden (85% of the map unit).
• AuB — Austin silty clay, 1 to 3 percent slopes — 25,525 acres in this county — rated Very limited. Dominant component: Austin (90% of the map unit).
• W — Water — 23,826 acres in this county — rated Not rated. Dominant component: Water (100% of the map unit).
• HoB2 — Houston Black clay, 2 to 4 percent slopes, eroded — 22,626 acres in this county — rated Very limited. Dominant component: Houston Black (100% of the map unit).
• Tf — Tinn clay, 0 to 1 percent slopes, frequently flooded — 22,086 acres in this county — rated Very limited. Dominant component: Tinn (85% of the map unit).

USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-23

Sources

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

1. Collin County Development Services -- OSSF Aerobic Systems Information Sheet · checked 2026-09-23
2. Collin County Development Services -- On-Site Sewage Facilities · checked 2026-09-23
3. Collin County Commissioners Court Order No. 2008-187-03-11 -- On-Site Sewage Facilities Rules and Regulations · checked 2026-09-23
4. Collin County Adopted Fee Schedule FY 2026 -- Development Services · checked 2026-09-23
5. Texas Administrative Code, Title 30, Chapter 285, Section 285.30, Site Evaluation · checked 2026-09-23
6. Collin County Development Services -- How to Apply for a Permit (CSS Portal) · checked 2026-09-23
7. USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-23

Related pages

• Septic rules and requirements in Collin County, Texas
• Septic permits and fees in Collin County, Texas
• Septic rules and requirements in Texas
• Septic rules in Collin County