Engineer A. I. Zhuravlev (Moscow)

On the Circumstances in Which Drainage Pipes May Be Used for Sewerage

The essential difference between stoneware (earthenware) pipes intended for sewerage and those intended for drainage is that sewer pipes must be coated inside and out with a salt glaze (hence their additional designation, “salt-glazed sewer pipes”), whereas pipes used for draining land are not glazed. The pores in the walls of sewer pipes are therefore completely sealed by the glaze, which allows no liquid to pass either outward or inward, while the pores of drainage pipes are open—

…open both to the exfiltration of liquids outward and to infiltration inward.

The sizes of the two types of pipe differ markedly: drainage pipes are manufactured in diameters of 75 and 100 mm, while sewer pipes are made in diameters of 125 and 150 mm and thereafter in increments of 50 mm, up to the maximum technically achieved for them—500 mm.

This description of their manufacture makes clear the question of whether drainage pipes may be used to convey wastewater.

From a sanitary standpoint, drainage pipes must not be used to convey the following liquids:

a) bacterially contaminated liquids (such as domestic sewage), since their exfiltration through the pores in the walls of drainage pipes will infect the soil in which the pipes are laid and, through the soil, the groundwater, which often serves as a source of drinking water;

b) liquids that are sufficiently heavily contaminated with chemicals, since the same exfiltration will introduce chemical compounds into the soil surrounding the pipes; these may include highly toxic substances soluble in groundwater, which may be used for drinking or domestic purposes.

As an exception to this rule, drainage pipes intended to convey such liquids may be laid:

a) in soils that are naturally completely impermeable to water;

b) in soils in which an impermeable layer has been artificially constructed around the pipes; and

c) where the porous walls of the pipes are coated with resinous or other waterproofing compounds.

As can be seen, the whole question comes down to reliable protection against the harm caused by contaminants passing through the pores of drainage pipes, or else to denaturalization of the pipes—sealing their pores with resin, etc.

From a hydraulic standpoint, it must be borne in mind that, other things being equal, drainage pipes, owing to their small diameter, have a considerably lower carrying capacity than sewer pipes.

From a technical standpoint, laying drainage pipes for sewerage—which are short (30 cm), have no socket ends, etc.—requires considerable effort to seal the large number of individual pipes, approximately three times as many as for sewer pipes, needed to form a continuous liquid-tight network from short pipes.

From an economic standpoint, denaturalizing drainage pipes, constructing watertight joints, or creating impermeable soil along the route of the pipes, etc., is costly work that is justified only in emergency situations when “no expense is spared.”

Clean and conditionally clean water may also be conveyed through drainage pipes, provided that each case is carefully and thoroughly examined by the supervisory authorities, both sanitary and technical, and that everything set out above is taken into account, including the degree of settlement in the area, its hydrogeology, and so forth.