ATU - Advanced Treatment Unit.
Also known as STS or aerobic treatment unit. This is additional wastewater treatment after conventional septic treatment, and something now required by California law as part of many septic systems in our neighborhood. These units are large secondary tanks that require power and continuous monitoring. These units require maintenance on a regular schedule and have various parts (pumps, fans, etc) that will require replacement if they fail. There are other aerobic treatment methods which do not qualify as advanced treatment.
STS - Supplemental Treatment System. Often used interchangeably with ATU.
OWTS - Onsite Wastewater Treatment System. Official acronym referring to self-hosted methods of wastewater disposal, including both conventional septic systems and non-conventional systems (see NOWTS below) that include an ATU.
NOWTS - Non-conventional Onsite Wastewater Treatment System. Essentially a privately-owned sewage treatment plant. These include any system with an ATU, and require a yearly operating permit with SLO County as well as annual effluent testing, at your own cost.
LAMP - Local Area Management Plan. Developed by SLO county to manage septic systems and all types of wastwater within the county, as required by California law.
ADU - Accessory Dwelling Unit. a self-contained residential unit located on th same parcel as a single-family or multi-family hone, sometimes called in-law units, granny flats, backyard cottages.
Leach Field - (occasionally spelled “leech”) also known as leach pit, leach lines, leach system, dispersal system, drainfield, seepage pits, etc. This is how your septic system disposes of partially-treated wastewater, and where secondary treatment may occur. The septic tank captures wastewater as it exits your home, where the solids settle out and fats rise to the top. The middle section is where wastewater is partially treated by anaerobic bacteria, and is pushed out to the leach field by new water entering the other side of the tank. Conventional leach lines further treat the wastewater using aerobic bacteria found in the soil before it enters groundwater; leach pits (also known as vertical seepage pits) exist deep enough in the soil where aerobic bacteria mostly cannot treat the water any further.
Effluent - a term for the wastewater exiting a septic system destined for the leach field.
Failed (Septic context) - This means one or more components of your system has failed. The most common failure is the leach field, as this has an expected limited lifespan. When it fails, it means effluent is no longer being disposed at the expected rate to operate the system and needs to be replaced. Generally, leach fields cannot be repaired, and are not installed again in the same spot due to public health concerns.
Reserve area - this is a requirement by the LAMP that each leach field has a separate space of equal area reserved (not built on or hardscaped) for a replacement leach field when it fails, because every field is expected to fail. If your property has more than one OWTS, each will require a separate reserve area in addition to the leach field.