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  • From: "Lawrence F. London, Jr." <lfl@intrex.net>
  • To: permaculture <permaculture@lists.ibiblio.org>
  • Subject: Re: [permaculture] greywater or graywater?
  • Date: Thu, 08 Dec 2005 01:07:42 -0500

Walt Dennig wrote:
There are also near-surface and surface systems for leach fields http://www.infiltratorsystems.com/ . There is a mound system that a friend of mine had approved in the coastal mountains of California.

If it is a LPP system here's more info. These are approved for use on tracts with very impermeble soils not allowing installation of a conventional septic tank and leach field. I found a link to a site recommending using a peristaltic hose pump to more sewage slurry from the tank to the leach field in a LPP system.

http://www.epa.gov/owm/mtb/finallpp.pdf

AND

http://www.nesc.wvu.edu/nsfc/pdf/eti/LPP_gen.pdf
-
A low-pressure pipe (LPP) system is a
shallow, pressure-dosed soil absorption
system with a network of small diameter
perforated pipes placed in narrow trenches.
Originating in North Carolina and Wisconsin,
LPP systems were developed as an alternative
to conventional soil absorption systems
to eliminate problems such as: clogging of
the soil from localized overloading, mechanical
sealing of the soil trench during construction,
anaerobic conditions due to continuous
saturation, and a high water table. The LPP
system has the following design features that
overcome these problems: 1) shallow
placement, 2) narrow trenches, 3) continuous
trenching, 4) pressure-dosed with uniform
distribution of the effluent, 5) design based
on areal loading, and 6) resting and
reaeration between doses.
The main components of an LPP system are:
• a septic tank or an aerobic unit;
• pumping (dosing) chamber (submersible
effluent pump, level controls, high water
alarm, and supply manifold); and
• small diameter distribution laterals with
small perforations (holes).
The septic tank is where settleable and
floatable solids are removed and primary
treatment occurs. Partially clarified effluent
then flows by gravity to a pumping chamber
where it is stored until it reaches the level of
the upper float control, which turns the
pump on. The level controls are set for a
specific pumping sequence of one to two
times daily, allowing breaks in between
doses for the soil to absorb the wastewater.
However, the dosing mechanisms and
frequency may vary for different systems.
The pump moves the effluent through
the supply line and manifold to the distribution
laterals under low pressure. The laterals
are a network of PVC pipes that have small,
drilled holes through which the wastewater
is distributed evenly. The laterals are
placed in narrow trenches that allow enough
storage volume so that the depth of the wastewater
does not exceed 2 or 3 inches of the total trench
depth during each dosing cycle.

What are the advantages and disadvantages of using LPPs?

Advantages

• Shallow placement of trenches in LPP
installations promotes evapotranspiration
and enhances growth of aerobic bacteria.
• Absorption fields can be located on
sloping ground or on uneven terrain that
would otherwise be unsuitable for gravity
flow systems.
• Improved distribution through pressurized
laterals disperses the effluent uniformly
throughout the entire drainfield area.
• Periodic dosing and resting cycles
enhance and encourage aerobic conditions
in the soil.
• Shallow, narrow trenches reduce site
disturbances and thereby minimize soil
compaction and loss of permeability.
• LPPs allow placement of the drainfield
area upslope of the home site.
• LPPs have reduced gravel requirements.
• There is a significant reduction in land area required for the
absorption system.
• Costs are comparable to other alternative distribution systems.
• LPPs overcome the problem of peak flows associated with
gravity-fed conventional septic systems.

Disadvantages

• In some cases, the suitability could be limited by soil, slope,
and space characteristics of the location.
• There is a potential for clogging of holes or laterals by solids
or roots.
• LPPs have limited storage capacity around their laterals.
• There is the possibility of wastewater accumulation in the
trenches or prolonged saturation of soil around orifices.
• LPPs could experience moderate to severe infiltration
problems.
• Regular monitoring and maintenance of the system is
required; lack of maintenance is a sure precursor to failure.
What determines the performance of an LPP
system?







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