CORRUGATED DRAIN PIPE IN WASTEWATER APPLICATION
Homes and businesses not connected to a sanitary sewer will be served by an on-site wastewater system. This discussion is limited to those types of
systems serving individual residences and businesses discharging small amounts of wastewater. The design and installation of these systems are
regulated by state and local health departments and may differ among states and sometimes even among counties within a state. However, the general
concept is the same throughout. Wastewater from the home or business drains to a septic tank where the solids settle to the bottom of the tank and
some biological decomposition can occur. Effluent exits the tank through the outlet and then drains into the leach field where it seeps into the
ground through perforated pipe.
Pipe used in conventional pipe-and-gravel leach fields may be either a HDPE
(smooth inside and out) or a HDPE
corrugated pipe (corrugated inside and out). The pipe,
usually 4-inch or 6-inch (100 or 150 mm), is laid in a gravel-filled trench either 2 ft (0.6 m) or 3 ft (1.0 m) wide. The pipe must be perforated so
that the effluent can drain out of the system. Perforations are larger than used for general drainage applications to prevent clogging.
An alternative to conventional pipe-and-gravel leach fields is a corrugated pipe wrapped with certain geotextile. These are known as gravelless
leach field because native soil, not gravel, is used around the pipe. An 8-inch (200 mm) geotextile-wrapped pipe replaces a 2 ft (0.6 m) wide
pipe-and-gravel system, and a 10-inch (250 mm) geotextile-wrapped pipe substitutes for a 3 ft (1.0 m) wide system. The pipe and geotextile
requirements are unique to leach field applications.
Benefits of HDPE pipe in on-site wastewater systems
- Easy installation
HDPE pipe is lightweight and even relatively long lengths can be easily handled by one
or two workers. HDPE pipe that is corrugated both inside and out can be curved to fit into the
- Variety of products available
Member companies produce a variety of pipe types, fittings, and accessories such as valves and distribution boxes to meet the
specifications of various agencies throughout the country. Pipe commonly used in this application are the following types:
- HDPE smoothwall pipe (smooth inside and out)It is available with or without perforations,
with different crush strengths, and in 4- and 6-inch (100 and 150 mm) diameters.
- HDPE corrugated pipe (corrugated inside and out)It is available with or without perforations
in 3-inch (75 mm) and larger diameters. Most producers provide a pipe with a slightly different corrugation pattern for leach field pipe than
for standard drainage pipe in order to accommodate the larger perforations.
- Gravelless pipe (corrugated inside and out and wrapped with certain geotextile)It is available perforated only and is available in 8- and 10-inch
(200 and 250 mm) diameters.
- Gravel is not required for some leach field products
Leach fields constructed with gravelless pipe do not require a gravel backfill. Aside from avoiding the expense, another benefit of
these systems is that no extra soil compaction occurs from equipment that would otherwise be used to place the gravel.
- Approved by most state and local health departments
Many styles of pipe, fittings, and accessories have been approved by health departments and are included in their local regulations.
Distributors generally stock what local requirements demand, however it is important for installers to carefully review these regulations
to ensure use of appropriate products and approval of the installed systems.
Corrugated HDPE - On The Job
In Bartow County, Georgia, there's a sanitary landfill under construction with a complex system of corrugated high density polyethylene pipe
underground. The county specifically chose HDPE
pipe over concrete pipe to do the job
and is already reaping the benefits of a less expensive, less time-consuming, service-oriented project.
As with many landfill projects, corrugated high density polyethylene pipe is used for leachate collection. But unique environmental concerns
surrounded the Bartow County landfill project calling for additional design considerations using HDPE
The site is in a valley, which means meeting Environmental Protection Agency (EPA) requirements can be more difficult. Design engineers had to come
up with a way to move storm water coming off the hills, keeping it from running over the garbage and contaminating the earth around the landfill.
Part of the system included pipe to be buried beneath the landfill to assist in water-flow divergence and resist any attack from chemicals
that might leak out of the landfill. The inert properties of corrugated HDPE
it to handle strong leachate solutions ranging in pH from 1.5 to 14. That and the rubber gasket joints attached to the pipe ensured the county
would not violate EPA regulations by contaminating groundwater. To design engineering firm Peoples and Quigley, Inc. the best solution was using