Virginia AOSS - What is it? and other definitions in Virginia wastewater
Michael Clayton
Are you wondering what exactly an AOSS is in Virginia onsite wastewater parlance? You are not alone.
In the last 12 months or so, AQWA has really started pressing into the Virginia commercial and community decentralized wastewater world. It is amazing how much wastewater lingo varies from state to state.
Some of the common words used in the Virginia on-site world aren’t found elsewhere. Words such as: Mass drainfield, AOSS, (have to be careful about auto-correct with that one), TL-3, TL-2, TL-1, groundwater dilution, etc etc.
Below are the definitions I found for a few of these items while searching through the Virginia Administrative Code. These definitions are relevant anytime you are considering the best approach to tackling an onsite wastewater treatment and dispersal system for more than one home or business.
"Alternative onsite sewage system," "AOSS," or "alternative onsite system" means a treatment works that is not a conventional onsite sewage system and does not result in a point source discharge.
"Large AOSS" means an AOSS that serves more than three attached or detached single-family residences with a combined average daily sewage flow greater than 1,000 GPD or a structure with an average daily sewage flow in excess of 1,000 GPD.
"Small AOSS" means an AOSS that serves no more than three attached or detached single-family residences with a combined average flow of less than or equal to 1,000 GPD, or a structure with an average daily sewage flow of less than or equal to 1,000 GPD.
"Dilution area" means the land immediately adjacent to and down gradient, in the direction of ground water flow, from a mass sewage disposal system, which is provided for the purpose of diluting nitrogen, or other nutrients occurring in wastewater, with ambient ground water, in order to assure compliance with nutrient standards contained in this chapter.
"Mass sewage disposal system" aka “Mass Drainfield” - means a sewage disposal system or systems which will discharge effluent to a single absorption area or multiple absorption areas with or without combined flows, such that the loading rate applied to any acre, as determined by the department, exceeds 1,200 gallons per day.
"Treatment level 2 effluent" or "TL-2 effluent" means secondary effluent as defined in 12VAC5-610-120 that has been treated to produce BOD5 and TSS concentrations equal to or less than 30 mg/l each.
"Treatment level 3 effluent" or "TL-3 effluent" means effluent that has been treated to produce BOD5 and TSS concentrations equal to or less than 10 mg/l each.
References if you want to read more:
Definitions - https://law.lis.virginia.gov/admincode/title12/agency5/chapter610/section120/
https://law.lis.virginia.gov/admincode/title12/agency5/chapter613/section90/