United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA-6007S2-84-157 Nov. 1984
Project Summary
Oregon Onsite Experimental
Systems Program
Mark P. Ronayne, Robert C. Paeth, and Steven A. Wilson
This study was initiated to develop
useful design end performance data on
onsfte wastewatar treatment and dis-
posal systems that would permit the
use of nonsewered technological solu-
tions to residents of rural and suburban
areas of the State of Oregon and the
rest of the United States.
To exclude the possibiHty of system
failure because of neglect or abuse, aH
•VAtAMftA U4^MM IMA^^MA^A ^6 46feA IfcJfeMKA-
•y iiwii* •• we msmieQ ai me noine
owner s expense* The systems were
chosen to suit the specific cUmate, soil
conditions, and topography of the she
from a variety of previously developed
and locally conceived systems modified
to suit the application. Among the
technologies evaluated were three
types of sand fitters, two types of
evapotransphration systems, mounds,
biological (composting) toilets, gray-
water systems, steep-slope systems,
pressure distribution, tile dewatering
systems, and various combination*
thereof.
The study resulted in several signifi-
cant findings. The sand filters consis-
tently (a) removed significant amounts
of nitrogen, (b) removed orgsntcs and
suspended solids to extremely low
levels, and (c) forestalled development
of ctoggin9 m«t* in subsequent dis-
posal trenches. Successful hand-dug
systems were installed on slopes of up
to 45% where soUs were deep (>150
cm). A successful demonstration was
given of the ability of pressure distribu-
tion to prevent groundwater contami-
nation where the unsaturated soil
depth exceeds 77 cm. Pure evapotrans-
piration systems in Oregon were
shown to be Impractical. And finally,
the substandard performance of some
commercial graywater treatment sys-
tems was demonstrated and compared
with that of conventional septic tanks
and subsurface disposal fields propor-
tioned to graywater flow only.
This Protect Summary was de-
veloped by EPA's Municipal Environ-
mental Research Laboratory, Cincin-
nati, OH, to announce toy findings of
the research pro/set Out is fuffy
documented1 in a separate report of the
seme title (see Project Report ordering
information at beck).
Introduction
Because of various site constraints,
many Oregon property owners and de-
velopers were not able to develop land
and build homes in the 1970's because
they could not obtain permits for onsite
subsurface sewage systems. This situa-
tion aggravated the housing shortage,
stimulated higher prices on existing
housing, and increased pressure to
develop prime agricultural land. These
trends conflicted with the stated land
use planning goals of Oregon to pro-
vide for the housing needs of the citi-
zens of the State and to preserve and
maintain agricultural lands. This con-
flict prompted the Oregon Department
of Environmental Quality (DEO) to
develop alternatives to the standard
septic tank and drainfield. In addition,
suitable alternatives were needed to re-
pair failing systems that were causing
public health and groundwater prob-
lems.
In 1975, the DEO initiated a program
to relate onsite sewage system perfor-
mance to soil, landscape, groundwater
depth, and other potentially important
site characteristics. A second facet of
this program was to install and test a
variety of experimental onsite systems
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designed to overcome site constraints
to conventional soil absorption sys-
tems. By 1977, the program was sup-
ported jointly by the Oregon Legislature
and the U.S. Environmental Protection
Agency (EPA). The intent of the pro-
gram was to develop alternatives to the
standard septic tank and drainfield
through controlled experimentation.
The DEQ identified problem soil areas,
either with a history of failing systems
or high denial rates, selected suitable
sites according to defined criteria, de-
signed alternatives to overcome site
limitations, supervised construction,
monitored system performance, eval-
uated data, and drafted rules to adopt
alternatives that would function satis-
factorily. The land owners installed sys-
tems according to plans and specifica-
tions and allowed the DEQ access to
monitor them. In addition, the owners
had to be willing to risk investing
money on experimental systems that
might fail.
As a result of this program, certain
technologies that proved successful
were adopted as alternative systems for
use where certain site constraints
existed that had heretofore prohibited
development of otherwise suitable
lands. These alternatives have raised
the site evaluation approval rate from
72 percent in 1978 to more than 95 per-
cent during the first half of 1981, thus
easing the demand for prime agricul-
tural land.
Results and Discussion
The most significant success has
been related to the sand filter systems.
The three basic designs evaluated were
recirculating, intermittent, and intermit-
tent-recirculating (I-R) filters. All three
reduced influent septic tank effluent
biochemical oxygen demand (BOD5) by
>95%, suspended solids (SS) by >93%,
and total nitrogen (TN) by >34%. Since
the septic tank effluent averaged 217
mg/L BOD5,146 mg/L SS, and 57.5 mg/L
TN, final concentrations were <4 mg/L,
<10 mg/L, and <35 mg/L, respectively.
Also, these effluents appeared to re-
duce the normal clogging usually en-
countered in the disposal trenches with
septic tank and aerobic unit effluents.
The intermittent filters required no
maintenance, and the recirculating de-
signs and I-R systems required periodic
removal of fallen debris and weeds.
Also, the I-R systems were subject to
freezing and spray-nozzle clogging.
Though the results of these filter
studies were slightly better in terms of
removal efficiencies (particularly in re-
lation to nitrogen), the hydraulic load-
ing rates were lower and the media size
were smaller than other recent studies,
thus providing performance consis-
tency through variable adjustment.
Other onsite technologies studied in-
cluded graywater systems. The data
generated were similar to those from
other North American studies and
showed the similarity of composition to
combined household wastewaters and
the need for identical public health pre-
cautions in disposal. Evapotranspira-
tion-absorption (ETA) systems worked
well in areas where precipitation did not
exceed 63.5 cm/year, construction was
adequate, sufficient sizing was em-
ployed, and soils were adequately
drained. Most disposal was estimated
to have resulted from soil absorption.
Pressure distribution systems were
most useful in coarse- to medium-tex-
tured soils, where groundwater con-
tamination problems often associated
with gravity-dosed systems were
avoided. Hand-dug systems on steep
slopes of up to 45% performed well
where the soil was well-drained and the
unsaturated zone was a minimum of
150 cm deep. Most States have limited
the site slope to about 25% because of
the limitations of excavating equip-
ment. Drainage was successful in re-
ducing groundwater levels in a disposal
area of medium-textured soils with
otherwise intolerable water tables. Sev-
eral systems installed with this tile
drainage arrangement (1.2- to 1.8-m
deep) separated from pressure-distribu-
tion disposal trenches by at least 3 m
performed well and gave no indication
of deleterious effects on the ground-
water or drain water on sites with suffi-
cient relief to allow gravity drainage of
the perimeter drains.
Several other alternative onsite de-
signs were also installed and evaluated.
Some were never adopted as alterna-
tives by the State for various reasons.
For example, evapotranspiration sys-
tems were dropped because of their
cost even in arid regions of the State.
Also, mounds were dropped because of
their cost and lack of applicable sites in
Oregon. Some systems enjoyed a cer-
tain level of success, but they have not
yet been adopted for reasons varying
from insufficient data to inadequate
performance versus design parameter
evaluation.
Conclusions
Several alternative technologies are
arrayed against site constraints in Table
1, showing the technologies applicable
to a particular site condition. For exam-
ple, the table indicates that shallow
groundwater at a site should alert a de-
signer to choose among capping fills,
intermittent sand filters, tile dewater-
ing, pressure distribution, evapotrans-
piration systems, or mounds. Another
way of using the table is to determine
the applicability of a given alternative
technology. For example, pressurized
distribution has been determined to be
useful for very permeable, deep soils
with slopes of up to 30%. The table does
not include all of the site variables (such
as climate) or all of the technologies
studied during this project. But for ref-
erence it does include two previously
proven technologies—conventional on-
site and capping fill designs.
The main conclusion of the study is
that the conventional septic tank/soil
absorption system is the most cost-ef-
fective and trouble-free solution for on-
site wastewater disposal where suitable
site conditions exist, but that several al-
ternatives can be used to overcome one
or more site constraints.
The full report was submitted in ful-
fillment of Grant No. S 806349 by the
State of Oregon Department of Environ-
mental Quality under the sponsorship
of the U.S. Environmental Protection
Agency.
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Table 1. Oregon Onsite Subsurface Systems Versus Site Constraints
Site Constraints
System
Standard sub-
surface system
Camping fills
Evapotranspiration
absorption
Pressurized
distribution
Intermittent
sand filter
systems
Steep Slope
system
Tile dewatering
system
Split waste
system
Evapotranspiration
bed
Mounds
Soil Permeability
Rapid Moderate Slow
X*
X X
X
X X
XXX
X
X X
X
XXX
X X
Solid Bedrock
or Soil Pans
Shallow Deep
X
X X
X
X
X X
X
X
X
X X
X
Depth to Saprolite
or Fractured Bedrock Groundwater
Shallow Deep
X
X X
X
X
X X
X
X
X
X X
X
Shallow Deep
X
X X
X
X
X X
X
X
X
X X
X
Slope
0-12% 12-30% 30-45%
X X
X
X (15%)
X X
X
X
(3%)
X X
X
X
* X Means that system can function effectively with that constraint.
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Mark P. Ronayne, Robert C. Paeth, and Steven A. Wilson are with the State of
Oregon Department of Environmental Quality. Portland. OR 97207.
James F. Kreissl is the EPA Project Officer (see below).
The complete report, entitled "Oregon Onsite Experimental Systems Program."
(Order No. PB 85-107 126 Cost: $22.00, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
•fr U.S. GOVERNMENT PRINTING OFFICE; 1984 — 569-016/7848
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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