Design & Engineering
Site evaluations, soil class, loading rates, setback distances, and when an engineer has to seal the plans.
State rules are the floor. Figures here are TCEQ minimums under 30 TAC Chapter 285. Your county can be stricter and around here most are — check your county before you rely on a number.
- What a site evaluation is and what the evaluator actually tests and documents.
- Soil profile analysis vs percolation test — which Texas requires, when each is allowed, how each is performed under 30 TAC 285.
- How design loading rate translates into drainfield square footage or spray-area size.Verify before relying on the figures
- When a Professional Engineer's seal is required on the design instead of a site evaluator's or installer's plan.
- Designing around hard site limits: shallow bedrock, high water table, steep slope, restrictive horizon, tight lot.
- Setback and separation distances under 30 TAC 285.91(10) — actual table numbers.Verify before relying on the figures
- Spray field layout — required coverage area, keeping spray within property, landscaping and planting restrictions over the field.
- Designing for future expansion — added bedrooms, guest house, ADU, barndominium, shop bathroom.
- Reserve/replacement area — whether Texas design rules require setting aside a second disposal area.
9 questions. Reviewed August 2026.