by Charles
Wardell
"Twenty years ago, if you were building on the beach, you put in a
leach field in the sand and got it permitted whether it worked or
not," recalls Larry Zucchino, a development planner for coastal
properties with J. Davis Architects in Raleigh, N.C. "Most
municipalities only worried about where the well was." No more. As
America has become more environmentally conscious, states and towns
have placed septic systems under closer scrutiny, especially in
sensitive coastal areas. And as communities look for ways to
grapple with burgeoning populations, wastewater regulations have
become a way to limit development.
To complicate things further, builders and developers working near
the shore often have to deal with small lots. And because septic
systems are land eaters, more developers and builders are turning
to a growing class of systems known as alternative treatment units,
or ATUs, that take up less space and have cleaner output than
conventional systems.
These systems have pros and cons for the builder. On the plus side,
an ATU might give a builder more choices in how to use a lot than a
conventional system would. On the other hand, the added expense can
tax the budget. "You have to understand the environmental and
wastewater issues before you can understand how to develop a
property and determine whether it's economically feasible," says
Zucchino. "You have to understand what the treatment options are in
your area."
CONVENTIONAL SEPTIC SYSTEMS
A standard septic tank (top) and leach field (bottom) rely on
lots of land and lots of aerated soil to adequately purify a home's
wastewater. Neither land nor such soil is available in many coastal
communities, which is driving more municipalities to alternative
systems.
CHEMISTRY PROJECTS
Think of a septic system as a small chemical plant. In it,
microorganisms slowly clean the water by eating the bad stuff.
Different sets of organisms take care of the solid waste and the
liquid effluent, and because each type thrives in a different
environment, a well-designed system will create optimal
environments for each.
Every system uses a combination of aerobic (oxygen-using) and
anaerobic (non-oxygen-using) organisms. Anaerobic bacteria grow in
the septic tank, where they eat up the feces, food particles, and
other organic matter. Their job is to decompose these solids, thus
constantly reducing the volume. Anaerobics are the reason the tank
doesn't fill up a lot faster than it does. "A septic tank is a big
settling basin," explains Craig Stead, president of Water
Engineering and Technology in Putney, Vt. "Solids drop to the
bottom, so what flows out is mostly soluble material."
While solids sink to the bottom of the tank, liquid wastewater, or
effluent, flows out of the top to the leaching field.
There, aerobic bacteria (as well as other microorganisms) feed on
it, cleaning it further. "In a leaching field, you get a slime
layer called a biomat," says Stead. "It's basically a
bunch of happy bugs that sit there and munch up the contaminants.
What comes out the bottom of the stone bed is pretty clear
water."
The strength of that effluent is expressed as biochemical
oxygen demand, or BOD. Technically, BOD refers to the oxygen
needed by the organisms in the system to break down the sewage. The
greater the oxygen demand, the stronger the sewage. The lower the
BOD number, the cleaner the effluent.
Another concern is the amount of nitrate put out by a conventional
system. Human waste contains organic nitrogen, which is converted
to ammonium by the anaerobics in the septic tank. This ammonium is
carried by the effluent to the leaching field. There, the aerobic
bacteria turn it into liquid nitrate, which is released to the
surrounding soil.
If ingested, liquid nitrate can make humans and animals very sick.
On the other hand, algae love the stuff, and if too much nitrate
enters a confined body of water, it will spawn algae blooms that
suck the oxygen out of the water, causing fish kills and dead
shellfish beds. While jurisdictions might not see a nitrate
increase as a concern on a beach, they are likely to if there's a
high water table, or if the home is on an estuary or wetland.
Regulations vary by location, but in general, more and more
communities are focusing on nitrogen removal, according Bob Smith,
an engineer with Orenco Systems, a company that sells ATUs across
the U.S.
ALTERNATIVE SYSTEMS
If the jurisdiction requires treatment to a higher standard than a
conventional system can provide, you'll need to use an ATU. These
miniaturized versions of wastewater treatment plants are designed
to reduce BOD in the effluent and, in some cases, to convert liquid
nitrate to nitrogen gas before the effluent flows to the leaching
field. While ATU technology is still in its infancy, there are
already a number of models on the market, and they're designed to
work in different environments and to clean different contaminants.
Some are installed between the tank and the field, while others
replace the tank but include separate compartments for decomposing
solids and cleaning the effluent (see "ATU Choices").
THE ATU
An alternative septic unit, such as the SeptiTech Model M400
residential system, can be used to reduce the size of the leach
field by treating the effluent first. Rather than just a settlement
tank and pumping station, a Fast system includes a media filter on
which microorganisms that digest the waste live.
If you're building near the beach, it's likely that ATUs will be in
your future, if they aren't already. Many of the new homes on Cape
Cod in Massachusetts, for example, are required to have alternative
systems, according to George Heufelder, health director for
Barnstable County, Mass., who also oversees the Massachusetts
Alternative Septic Systems Testing Center (www.buzzardsbay.org/etimain.htm). "There are 800 such
systems on the Cape, and we expect a lot more in the next few years
unless towns embrace comprehensive wastewater management."
The effluent coming out of an ATU is orders of magnitude cleaner
than that from a conventional system. Effluent from a conventional
system might include 200 to 250 parts per million (ppm) of BOD, 30
to 50 ppm of suspended solids, and 50 ppm of organic nitrogen. By
contrast, the SeptiTech system — one example of an ATU
— lowers BOD to 10 ppm, solids to 5 to 10 ppm, and organic
nitrogen to 2 to 5 ppm, says Dan Ostrye, SeptiTech's vice president
of product development. "In an alternative system, the leach field
is a way to get water back into the ground."
Systems can be tweaked to provide different types of treatment,
whether it's removal of nitrogen or removal of phosphates.
(Phosphates are compounds used in detergents and other household
cleaning products. They are added to soften water and break apart
dirt in fabrics. They also promote plant growth, which is why they
are used in fertilizers, but in an effluent they can stimulate
algae blooms and are to be avoided near waterways.) "The most
powerful thing about the new technologies coming out now is the
fact that you can be flexible and use whatever works best for the
particular environment," notes Steve Barry, an ATU distributor in
Wilson, N.C. "It really helps for developer and builder to be able
to do with a parcel of property what they want to do." In fact,
because the effluent from these systems is so clean, builders may
be able to install a much smaller leach field. This gives more
flexibility in house placement, leaves room for a backup field, and
if the site has difficult soils, it can reduce the amount of soil
that needs to be trucked in. Or, at least, leach field reduction is
possible in theory. In reality, it varies by state. Heufelder
reports that, in Massachusetts, builders need to show that a
full-size system could have been installed. "You can't use these
systems to make an unbuildable lot buildable," he says. Other
states allow varying degrees of reduction, so it's important to
check the regulations.
FIXED-MEDIA SYSTEM
In a fixed-media system, liquid effluent, which has already
settled for a time in a processing tank, is pumped over a media
filter, and microorganisms digest the effluent as it trickles
through the filter. The key to the system is creating a home for
enough organisms to treat the effluent quickly and in a relatively
small space. One example — the AdvanTex system —
consists of a pumping station (below one of the fiberglass
cylinders, top left) and a fiberglass basin (center rectangular
box) filled with a porous textile filter (shown in the open basin,
top right). In the finished installation (bottom), the filter,
pump, and inspection covers sit flush to the ground, blending into
the landscaping.
ATU CONSIDERATIONS
Different ATUs are appropriate for different locations. Variables
include not just soil type but also temperature. "Just because a
system works in Florida doesn't mean it will work in New York or
New England," notes Heufelder. "All systems depend on bugs and all
bugs work by temperature. When temperatures fall below about
50°F, bugs go to sleep."
ATUs are also pricey. While a conventional septic system could cost
$3,000 to $8,000, an ATU will be at least $10,000 and likely closer
to $15,000 or more. Dennis Hallahan, P.E., technical director at
Infiltrator Systems in Old Saybrook, Conn., says he has seen costs
as high as $30,000 on difficult sites where fill needed to be
brought in because of the high water table.
All ATUs require electricity to run a pump. But that doesn't mean
you can't flush the toilet if there's a power outage. "If power
goes out, you have three to four days of storage time. "Mobile,
Alabama, has been hammered by hurricanes in recent years. Most
people in hurricane areas leave the area anyway when a hurricane
comes. And most people have a generator. You only need to run the
pump for a few hours every couple of days," says Barry.
ATUs also need more upkeep than conventional systems require. A
maintenance person typically has to come out twice a year to clean
the filter pump and, if necessary, spray off excess sludge
collected on the media. Most states require homes with these
systems to have a maintenance contract.
THE FUTURE
The future of ATUs lies in more efficient treatment and better
monitoring. Heufelder predicts that more and more systems will
include remote monitoring and control, allowing the maintenance
company to predict problems. "Say you have a pump that normally
pumps 330 gallons in 5 minutes. If it suddenly starts taking 10
minutes, you ask what's wrong. So you check the amperage and see
that it is now drawing 9 amps instead of 3. You know that something
is jamming the pump."
SUSPENDED-GROWTH SYSTEMS
These systems work by bubbling air into the effluent to
increase the oxygen available to the bacteria, which speeds up the
organisms' digestion. In the Fast system, for example, solids are
trapped in a concrete settlement tank, while effluent flows to a
second compartment (shown being lowered into place) with media
suspended in it. An air blower located above the tank forces air
into the central tube running through the media.
As coastal populations increase, systems will also have to get
better at nitrogen removal. The best systems remove 19 milligrams
(mg) of nitrogen per liter of water, but Heufelder predicts that
will eventually need to get down to 5 mg. No system is rated for
that yet.
Towns may also do more to encourage systems that serve clusters of
homes. "Towns like shared units because they're easier to keep
track of," notes Heufelder. Some homeowners like them because they
can pay a monthly fee and not worry about it, while others don't
want to be tied to their neighbors.
LEACHING CHAMBERS
While ATU systems don't always eliminate the leach field, they
can reduce its size, and can be made even more efficient with the
use of plastic chambers instead of stone. These Infiltrator
chambers protect the biomat, while putting the effluent in
immediate contact with the soil.
And look for more systems that use the cleaned effluent for
irrigation and other purposes. This is already happening on large
projects. In July, Zucchino got the site plan approved for Cannons
Gate, a coastal development in Moorhead City, N.C., which is on the
sound. Each of the development's 500 single-family homes will have
a septic tank for solid waste, along with a pump that sends the
effluent to a central treatment plant. This in itself may not be
unusual, but the way they're handling the end product is. "We
created a series of ponds," says Zucchino. "That's where the
treated water will go." What used to be a land eater has been
transformed into an amenity. ~
Charles Wardellwrites about building
science and technology from Vineyard Haven, Mass.