A leach field spreads septic tank effluent through shallow trenches, while a seepage pit is a drilled or dug hole that lets effluent soak into the soil. Both are dispersal systems that follow the septic tank, and Los Angeles County regulates both.
Los Angeles County's Local Agency Management Program (LAMP) defines a seepage pit as a drilled or dug excavation, three to six feet in diameter, either lined or gravel-filled, that receives effluent from a septic tank. EPA describes a conventional drain field as shallow underground trenches filled with stone or gravel, where effluent moves into the soil and microbes treat it.
The county describes the overall system the same way: a septic tank where solids settle, then effluent dispersed into a leach field or seepage pit. The method relies on gravity and on the soil's natural ability to filter contaminants as the effluent moves down.
The soil has to treat the water. The LAMP says that if soil absorbs effluent too fast, contaminated water can reach groundwater before it is filtered. In those cases the county may require a non-conventional system with extra treatment before dispersal. The LAMP gives test thresholds, such as 5.12 gallons per square foot per day for seepage pits and a drop faster than 5 minutes per inch for leach lines.
The LAMP also says the rules differ by which regional water board covers a parcel. For existing lots in the Antelope Valley under the Lahontan board, it keeps an older limit of one single-family residence per half acre. Ask the county which rules apply to your lot.
Start with records. EPA suggests asking the local health department for the system's as-built drawing. Los Angeles County's page says the Onsite Wastewater Treatment Program reviews designs and historical records, and it directs owners to the Public Health Custodian of Records to search public records for a property or septic system. An inspector can also tell you the type and condition.
If you have no records, the county has an Antelope Valley Environmental Health office in Lancaster for its septic program.
Riverside County lists signs of a malfunctioning absorption field: odors, persistent wet spots or lush green growth over the system, sluggish plumbing during heavy use or wet weather, and problems that persist after the tank is pumped. Those signs apply to any dispersal type. If drains stay slow right after a pump-out, ask the pro to check the leach field or pit.
Groundwater is also a local concern. The LAMP says Antelope Valley wells draw mainly from the principal aquifer, and parts of the basin have had nitrate above the 10 mg/L standard.
Call a licensed septic pro or the county's Antelope Valley Environmental Health office if you do not know what type of system you have.
No. The LAMP says a cesspool has no septic tank, while a seepage pit receives effluent from a septic tank. Cesspools are not authorized under the state OWTS Policy.
The county lists Lancaster and Palmdale among the cities with a Memorandum of Understanding that places septic review under its Public Health Department.
It depends on soil and lot space. The county says no permit is issued where lot area or soil is not adequate. Ask Public Health before you plan the change.
The LAMP says a minimum of 3 feet of undisturbed soil must be available under the dispersal system.
Antelope Valley Septic is a free referral service, not a contractor. Request a free quote from a local septic contractor.