Technical guide
Diagrams and plain-language engineering for homeowners, builders and commercial owners in Texas.
01Overview
A septic system, called an on-site sewage facility (OSSF) in Texas, treats wastewater on your own property when no city sewer is available.
Solids settle out of the liquid in a tank.
Bacteria, oxygen and soil break down what is left in the water.
Treated water goes back to the ground through a drainfield, drip lines or spray heads.
TCEQ sets the rules (30 TAC Chapter 285) and counties enforce them locally.
02Conventional systems
The standard system, most common in older construction and typically used at single-family homes and small businesses.
A two-compartment tank separates solids. Bacteria begin digesting the organic matter.
Perforated pipe in gravel spreads liquid into the soil, where microorganisms treat it further.
Works when soil can absorb and treat the water and there is room for the field.
Poor soil, a high water table or a small lot often means an aerobic system instead.
Schematic, not to scale. Based on the description in Texas A&M AgriLife Extension publication L-5347.
Solids settle and are digested by bacteria. A baffle wall keeps solids in the first compartment, which holds about half to two-thirds of the tank length.
Risers bring access to the surface so tanks can be inspected and pumped without digging. Lids are kept at or near ground level.
Perforated pipe sits in gravel under geotextile fabric. Effluent trickles out along the pipe and spreads across the gravel.
Water moves down through the soil, where microorganisms consume contaminants. It then evaporates, is taken up by plants, or reaches groundwater.
03Aerobic treatment units
ATUs use the same processes as a municipal sewage plant, scaled down. Texas A&M AgriLife Extension reports they remove 85 to 98 percent of organic matter and solids.
Pretreatment tank, aeration chamber, settling chamber, and final treatment and dispersal.
Aerobic treatment greatly lowers BOD and suspended solids.
Certified units treat well enough to be used with spray distribution. TCEQ keeps the list.
Mechanical and electrical parts need regular service.
Schematic of the four components of the aerobic treatment process, per Texas A&M AgriLife Extension publication L-5302. Actual units vary by manufacturer.
Removes plastics and other solids that bacteria cannot break down, protecting the equipment downstream.
An air pump and diffuser supply oxygen. Aerobic microbes consume the waste, and rising bubbles keep the water mixed.
Microbes that have done their work settle out. The settled material is returned to the aeration chamber.
Treated water collects in a pump chamber and is sent to the drip or spray field. Spray systems add disinfection first.
04Drip distribution
Treated water is released through drip lines laid in the top 6 to 12 inches of soil, so no large soil mound is needed.
Treatment device, pump tank, filter and the drip distribution system.
About 1/2-inch tubing with an emitter in the wall, at roughly 15 to 20 psi inside and 0 psi at the emitter.
Works on many sites, including shallow and clay soils.
The return manifold connects back to the treatment unit so solids can be flushed out.
Schematic plan view of a subsurface drip system, per Texas A&M AgriLife Extension publication L-5237. Line spacing and layout are set by the engineered design.
Water is treated first (an aerobic unit is common), then stored in a pump tank until the field is ready for a dose.
A sand, disk or screen filter removes larger particles that could clog the emitters. Some systems use an automatic cleaning filter.
About 1/2-inch tubing with an emitter in the tube wall, run at roughly 15 to 20 psi inside the tube. Water leaves the emitter at 0 psi.
The return manifold connects back to the treatment unit so solids collecting in the tubing can be flushed out. A vacuum breaker protects the lines.
05Spray distribution
Spray systems work like a sprinkler system, irrigating the lawn with treated water.
Spray follows a certified Class I aerobic unit.
A chlorination unit kills microbes and bacteria before spraying.
There must be enough open grass for the spray heads.
A pump tank sends measured doses to the heads.
Schematic elevation, per Texas A&M AgriLife Extension publication L-5302. Spray area size and head layout are set by the engineered design.
Class I aerobic units treat wastewater well enough to be used with spray distribution.
A chlorinator kills disease-causing microorganisms before the water is sprayed.
Stores treated water and doses it out to the spray heads on a controlled schedule.
Heads spread the treated water across the lawn like a sprinkler system, where grass and soil use it.
06Siting and setbacks
Wells, water lines, property lines, buildings, surface water, slope, drainage and soil all limit the layout.
Set by state rules and your county. The design has to fit inside them.
We check the requirements for your property during the site evaluation, before any plan is drawn.
Illustrative layout. Required separation distances are set by state rules and your county, and we confirm them for your property during the site evaluation.
Septic components must stay a required distance from water wells and water supply lines to protect drinking water.
Tanks and fields need minimum clearances from property boundaries, so the layout has to fit inside the buildable area.
Streams, ponds and drainage paths need a protective buffer, and the field must not sit where water pools.
The layout also works around the house, driveway, trees, slope and where the soil is suitable.
07Design to inspection
Because one team handles design, permitting and installation, the system that gets approved is the system that gets built.
Compare systems
The right system depends on your soil, your lot and local rules. A site evaluation gives you the answer.
Septic tank + gravel drainfield
Aerobic unit + drip lines
Aerobic unit + spray heads
08Glossary
Sources: Texas A&M AgriLife Extension publications L-5347, L-5237 and L-5302, and TCEQ OSSF rules (30 TAC Chapter 285). Diagrams are schematic. Every system we design is engineered for its own site.
We evaluate your site and recommend the right system.
Free septic quote
Call 409-651-3045