Researchers at Purdue University have...
In 1997, EPA and Congress officially recognized onsite
wastewater treatment systems (commonly referred to as septic systems) as a
viable, long-term solution for treating wastewater. This was an important
designation since nearly 40 percent of new homes in the United States use this
type of system to treat household wastewater.
For more advanced wastewater management, there are dozens of
pretreatment technologies to choose from that use the standard septic system as
the core. The number of pretreatment installations is anticipated to grow over
the next ten years due to environmental issues and new regulations, but it is
predicted that the majority of systems installed in the future will still be
the standard septic type.
Why? The standard septic system provides effective
treatment, requires minimal maintenance, offers longevity and is a good
economical choice. This makes the standard septic system an effective solution for
the majority of onsite wastewater applications in the future.
Septic systems play a vital role in the protection of public
health and the environment. The goal of the septic system was once thought to
be a temporary one: provide a solution for wastewater disposal in
rural/suburban areas until sewer piping could be extended to those areas. A
significant shift away from this mindset occurred in 1997 when Congress
recognized the vitality and effectiveness of the tried and true standard septic
system, particularly for small communities. In its "Response to Congress
on the Use of Decentralized Wastewater Treatment Systems," the U.S.
Environmental Protection Agency (EPA) stated that onsite systems can and should
be considered as long-term solutions. For the professionals (contractors,
regulators, soil scientists, engineers and research professors) working with
onsite systems, this was not ground breaking information. However, obtaining
political acceptance from the EPA and Congress had been a long battle and
therefore made this conclusion a milestone.
Not all wastewater professionals agree on what specific
components make up the standard, every-day septic system. Scott Wallace, P.E.,
vice president of North American Wetland Engineering said, "For me, a
standard system is one that uses a septic tank and soil-based treatment and
disposal. What makes up a good standard system is combining the correct
application of soils evaluation, loading factors, topography and hydraulics to
develop a system layout that achieves high levels of treatment in a simple,
Bob Long, Chief of Special Programs for the Oakland (Mich.)
County Health Department said that to him, a standard system is one that meets
his local sanitary code related to the amount of trench per bedroom in optimum
or acceptable soil conditions.
"This can be a combination of conventional septic tank,
tile field, tile bed or drywell, however the system cannot be oversized from
what is prescribed in the sanitary code," Long said.
Although the characteristics of a standard system may vary
depending on to whom you speak, what people do agree on is that this method,
elegant in its simple utilization of a tank and a leachfield, does more than
meet the goal of disposal. In fact, the system far exceeds the original
expectations and provides highly effective wastewater treatment. Field and
laboratory research data available today draws the same conclusion.
What defines a standard onsite system depends on the
timeframe being considered. At one time, cesspools were standard systems. Then
came septic tanks with either seepage pits or seepage beds. Now the septic tank
and leachfield combination is generally considered the standard or standard system.
Today, more than 25 percent of homes and nearly 40 percent of new development
in the United States are served by onsite septic systems. Of this number,
approximately 70 percent are a combination of a septic tank and leachfield. Of
the remaining 30 percent, 25 percent incorporate pretreatment systems.
The perspective on what specific combination of tank and
leachfield makes up a standard system varies by region of the country. The tank
can have one or two compartments and it can be manufactured from a variety of
materials including concrete, plastic or fiberglass. Leachfields can be
constructed with plastic or concrete chambers, stone and pipe, or they can be
gravelless. Installation can be in beds, trenches or mounds, with sequential or
parallel distribution. The large majority of systems function by gravity, but
some may require pumping for mound applications or to overcome elevation
differences. In many areas with slowly permeable soils or seasonally saturated
soil conditions, mounds are the only soil treatment units that will function to
treat sewage. Therefore, mounds have today become standard in those areas such
as Wisconsin and Minnesota.
"I consider a standard system to have a septic tank or
tanks in a relatively shallow installation to allow access for cleaning and
service. My definition of a traditional system also includes a series of
drainfield trenches using drop boxes to provide sequential distribution,"
said Roger E. Machmeier, Ph.D., P.E.
How is this different than an advanced or pretreatment
Pretreatment systems were developed to handle wastewater in
extremely sensitive areas or to accommodate unusual applications such as
insufficient soil depth or difficult soil types. In some areas of the country,
regulation has begun to specify pretreatment as a safeguard for onsite system
performance whether it is necessary or not. This practice raises the cost of
wastewater treatment that is borne by homeowners and developers. While these
more complex systems are of tremendous value when enhanced treatment is
required to protect public health or the environment, they should not be
specified due to a lack of knowledge about the performance of standard systems.
Pretreatment systems come in a variety of shapes and sizes.
The majority fall under the heading of Advanced Treatment Units (ATUs) or
packed bed filters. A sand filter is a type of packed bed filter that has been
around for more than a century. Newer packed bed technologies consist of peat,
textile or foam media. The packed bed filters generally are very reliable and
provide good treatment.
ATUs can be further broken down into two groups: suspended
growth and attached growth. Suspended growth systems provide an environment for
organisms to thrive within the liquid. Attached growth systems rely on a media
as a surface for organisms to attach. Extended aeration is an example of a
suspended growth system, while a trickling filter is an example of an attached
The primary difference between a pretreatment system and a
standard system is not necessarily in treatment levels. It is in the increase
in cost and maintenance requirements of the pretreatment system. If a
pretreatment device is compared only to the septic tank in a standard system,
then yes, it provides an improvement in terms of treatment. When the treatment
provided by the soil is included in the equation, the difference is not so
Table 1 illustrates results from a study performed by the
Massachusetts Septic System Test Center. The highly controlled test compares new
technologies to the standard septic system. Each system receives the same
wastewater flow and each is designed for a three-bedroom home. They also each
receive the same wastewater strength, the sanitary sewer line is tapped, and
supplies flow to the test center. Each technology discharges to a soil
absorption system, and each has the same soil type and depth from which
effluent samples are taken.
As shown by the results, the standard system performs
similarly to the newer technologies in terms of treatment. The data suggests
that the term "Advanced" in Advanced Treatment Units (ATUs) may be
misleading. They may be advanced as compared to a septic tank alone, but not as
compared to the system of the tank and soil together. The noted exceptions are
nitrogen treatment, installation cost and O&M costs. The case where proper
treatment by standard onsite septic systems can be a potential concern is in
nutrient sensitive areas, waterfront areas or tight lots where the accumulation
of the nutrients is a concern.
At the National Onsite Wastewater Recycling Association
(NOWRA) 2000 Conference, E. Jerry Tyler presented a paper entitled, "What
happened to the passive onsite wastewater system?" At the presentation he
explained that the standard system uses the soil and the processes of nature to
treat wastewater. It is simple in design but effective, making it cost
efficient as well as environmentally responsible. It also is a passive system,
requiring no outside energy to operate. It is truly a wonder of nature. In our
highly technological world, the idea that something can function sufficiently
without constant attention is hard to accept.
Because of its simplicity, the standard system requires only
minimal maintenance. Tank pumping and overall inspection every three to five
years is typically required to ensure proper system function. Although improved
maintenance programs are needed and are on the horizon, this is mainly an
effort to ensure that the operator (homeowner) is actually contracting for the
basic maintenance required.
The standard septic system has an excellent track record
despite the bashing it often gets from advocates of sewering or more stringent regulation.
The low failure rates are the result of improved site evaluation and
installation by knowledgeable contractors. These contractors tailor the
installation and specific combination of products used to the available site
and usage information.
In Oregon, a recent study evaluating more than 400 systems
put the failure rate below two percent. The low failure rate was attributed to
a strong wastewater program operated by the Oregon Health Department. It also
was a result of modern site and soils evaluations, educated, trained site
evaluators and contractors that were certified and licensed.
The Massachusetts Septic System Test Center touches on
system longevity in its "Explanation of Facts" sheets. It states
"A conventional soil absorption system is expected to last a minimum of 30
years if properly designed." I would only add "…and
maintained," and I think most experts would agree.
It often has been said that in order for onsite septic systems
to play a major role in the future of wastewater treatment, the level of
standards and professionalism throughout the onsite wastewater industry must be
raised. While it may not be apparent to most users, the education, technology
and regulation related to onsite wastewater treatment has been the focus of
much attention for the last several years.
Contractors have an increased understanding of how systems
function due to the establishment of training centers and manufacturer
education initiatives. There are presently thirty onsite wastewater training
centers in the United States and Canada, and several states and provinces
require that installing contractors be licensed or certified.
The EPA manual and state regulatory codes have been revised
to incorporate the latest university research. State regulatory departments
also have increased their level of knowledge and professionalism. Many updated
codes require the site evaluation and/or the design of the system to be
conducted by professionals such as soil scientists or engineers.
Post-installation system management is being reviewed as a
key area needing further attention and regulation beyond the individual system
operator (the homeowner). The onsite industry is having growing pains regarding
system management, and many new management strategies currently are being
tested and discussed. These include fee-based utility oversight of individual
systems and mandatory pumping schedules with record keeping by the regulatory
Standard onsite wastewater treatment utilizing a septic tank
and a leachfield has accomplished the goals set out by EPA. The bad reputation
they sometimes receive due to poorly designed, installed or failing systems is
not generally deserved. They have been and will continue to be the workhorses
of the wastewater treatment industry, available to the public in areas where
there are no options and at a cost that no competitive technology can match.
These systems have protected community health for the last century. Due to
substantial improvements in the onsite wastewater industry from increased
science and understanding, higher standards for installers, updated codes, more
thorough site evaluations and inclusion of designers, there is no reason to
believe that the next century should be any different.
After reviewing the benefits and advantages of the standard
system as compared to new treatment technologies, ATUs or pretreatment systems,
it is clear that the standard septic system will remain the system of choice
for the majority of installations in the future.