Soil and perc tests in Ellis County, Texas

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

Yes. Texas requires a site evaluation before it issues a permit.

A site evaluator or an engineer checks the soil in two pits or borings. The evaluator also checks for shallow groundwater and reviews slope and flood risk. The county uses this report to set the system's size.

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

How USDA rates the ground in Ellis County

Very limited across most of the county — 97.3% of the rated acres. A rating describes the ground, not a parcel. The county's site evaluation decides each lot.

• Very limited — 509,249 acres — 97.3% of 523,502 rated acres.
• Somewhat limited — 14,253 acres — 2.7% of 523,502 rated acres.
• Not rated — 85,568 acres, excluded from the denominator — mostly urban land and water.

97.3% of 523,502 rated acres. 85,568 acres unrated. Survey area TX139 version 21, established 2025-09-04.

USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-24

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 — 443,619 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Depth to bedrock — 155,879 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Flooding — 87,088 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Slope — 34,336 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Depth to saturated zone — 21,860 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Seepage, bottom layer — 7,004 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Filtering capacity — 6,537 acres. Reasons overlap — a component can carry several — so these acres exceed rated acres.
• Ponding — 4,648 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.

• HaB — Houston Black clay, 1 to 3 percent slopes — 104,748 acres in this county — rated Very limited. Dominant component: Houston Black (80% of the map unit).
• Tc — Trinity clay, 0 to 1 percent slopes, frequently flooded — 46,514 acres in this county — rated Very limited. Dominant component: Trinity (85% of the map unit).
• AuB — Austin silty clay, 1 to 3 percent slopes — 42,644 acres in this county — rated Very limited. Dominant component: Austin (90% of the map unit).
• HcC2 — Heiden clay, 3 to 5 percent slopes, eroded — 34,740 acres in this county — rated Very limited. Dominant component: Heiden (85% of the map unit).
• EdD2 — Eddy soils, 3 to 8 percent slopes, eroded — 27,897 acres in this county — rated Very limited. Dominant component: Eddy (95% of the map unit).
• HbB — Branyon clay, 1 to 3 percent slopes — 20,865 acres in this county — rated Very limited. Dominant component: Branyon (85% of the map unit).
• HbA — Branyon clay, 0 to 1 percent slopes — 20,566 acres in this county — rated Very limited. Dominant component: Branyon (85% of the map unit).
• HaA — Houston Black clay, 0 to 1 percent slopes — 18,220 acres in this county — rated Very limited. Dominant component: Houston Black (85% of the map unit).

USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-24

Sources

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

1. Ellis County Department of Development · checked 2026-09-24
2. Ellis County Order Adopting Rules of Ellis County, Texas, for On-Site Sewage Facilities · checked 2026-09-24
3. Ellis County Quality Growth Initiatives, Volume I -- Subdivision and Development Standards · checked 2026-09-24
4. Ellis County Department of Development -- Master Development Fee Schedule, effective 09/01/2023 · checked 2026-09-24
5. Texas Administrative Code, Title 30, Chapter 285, Section 285.30, Site Evaluation · checked 2026-09-23
6. Ellis County Department of Development -- OSSF Permit Application (bilingual) · checked 2026-09-24
7. Collin County Development Services -- OSSF Aerobic Systems Information Sheet · checked 2026-09-23
8. USDA NRCS Soil Data Access (SSURGO) · checked 2026-09-24

Related pages

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