A new Canadian sanitation system for single-family houses is being used in rural areas of Loudoun County that have no sewer lines.

"Aquarobic" units, made by a division of Waltec Enterprises in Ontario, have been functioning successfully for almost a year in two houses. One is being installed in a third house, and a unit has been programmed for a fourth residence.

Robert and Mary Gullo are having a unit installed in the three-story frame house they are remodeling in Ashburn. Several truckloads of crushed bluestone, about the size of coarse sand, are being used in a filter bed. All wastewater from the household of eight persons (the Gullos have six young children) will flow by gravity to a large underground tank made of fiberglass.

A 1/2-horsepower electric motor injects air into the liquid to break up solids and keep the process aerobic rather than septic (that is, to encourage the growth of air-loving bacteria). The liquid is then metered to a smaller tank, where any remaining solids settle out and are pumped back to the first tank for further treatment. From the settling tank the effluent flows by gravity to the filter bed.

The system can operate successfully where the soil is not permeable enough for use of a typical septic tank and drain field. (The red clay of the Gullos' lot did not look promising for a septic field; the 90-year-old house they are remodeling was served only by an outhouse.)

From the sand filter, about four feet deep, the effluent seeps into a level "contact area" of 3200 square feet, covered by 18 inches of crushed bluestone which is overlain by a layer of shredded topsoil.

Grass and shrubs on the surface will help to draw up some of the effluent and evaporate it; the remaining effluent will slowly seep through the crushed stone into the underlying soil.

An essential part of this novel sanitation system is a service contract. The manufacturer's representative inspects the system every 90 days and renews filters or other parts that need to be changed without further cost. Sludge is pumped out every five years. The contract costs $180 a year.

After each inspection a report is sent to county authorities. An alarm system in the house alerts the owners to malfunctions in the system. Service in the area is preformed by Aquarobic USA, headed by James F. Steffey and located in Fairfax.

James Forgie, general manaer of Aquarobic, said his company has installed about 1,700 units in Ontario. These are mainly at single-family houses, but several units can be hooked up for larger structures.

The installed cost of the Gullos' system is about $7,500 while installation of centralized sewer lines and treatment plants in rural communities typically costs $8,000 to $10,000 a house, or more, plus heavy annual maintenance fees. Where impermeable soil will not perk, local authorities will not approve installation of septic tanks.

Therefore the new aerobic tanks now coming on the market allow development to proceed where it could not otherwise take place.

Maufacturers of aerobic systems claim that their equipment is superior to traditional septic tanks. They maintain that:

The effluent is cleaner and has no odor.

There is less frequent need to pump out sludge.

Percolation is improved because the effluent contains dissolved oxygen that helps keep pores open in the soil.

Trees in the drainage "contact area" need not be removed, with consequent environmental improvement of the lot.