United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/116 May 1987
4>EPA Project Summary
Alternative Onsite Wastewater
Treatment and Disposal Systems
on Severely Limited Sites
Margaret M. Cashell, David D. Effert, and James M. Morand
Several research and evaluation
studies were performed on alternative
onsite wastewater treatment and dis-
posal systems at sites with severe
limitations for conventional systems.
The studies included systems that rely
on the soil for treatment and disposal
(including low-pressures pipe (LPP)
systems, alternating soil absorption field
systems, shallow conventional trenches,
gravelless trenches, and mound sys-
tems) and systems that discharge to
surface waters or to the atmosphere
(including intermittent sand filters, up-
flow gravel filters, subsurface gravel
beds, and evapotranspiration systems).
These studies were performed on full-
scale operating systems, scaled-down
field systems, or laboratory columns.
The soil properties, soil moisture
regime, and shallow groundwater table
at the research locations were char-
acterized to gain a better understanding
of the ability of the soils to treat and
dispose of wastewater. Several typical
site evaluation techniques were as-
sessed, and because of a seasonally
high groundwater table present in the
soils of this study, groundwater con-
tamination was investigated.
This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati, OH to announce
key findings of the research project that
is fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
Approximately 68 percent of the total
land area in the United States is un-
suitable for conventional onsite systems
that utilize the soil for final treatment and
disposal of wastewater. During the past
several decades many alternative systems
have been developed for use in these
areas. Many of the successful newly
developed alternative systems were
custom-designed for the soil and site
conditions at specific locations, and their
use in other soil and site conditions is
only slowly being evaluated. Many alter-
native systems have been demonstrated
only in localized areas, and officals else-
where are reluctant to approve their use
because the alternative systems are un-
proved and untested under the conditions
that pertain to their area.
The Cincinnati Center for Small Com-
munity Wastewater Systems Studies was
established in 1980, in conjunction with
the University of Cincinnati and the U.S.
Environmental Protection Agency, to
generate information relevant to onsite
wastewater disposal options for areas
with unfavorable soil and site conditions
such as those typically found in south-
western Ohio.
Several alternative systems that had
not been evaluated previously in south-
western Ohio were investigated by the
Center. In several studies, existing sys-
tems that had failed were replaced with
alternative systems. In other studies,
alternative systems that had already been
installed, but not yet proven as acceptable
alternatives in southwestern Ohio were
evaluated. Research was also performed
in situ on several scaled-down alternative
systems and in the laboratory on columns
simulating alternative systems. The al-
ternative systems studied included those
that rely on the soil for the treatment and
disposal of wastewater, and systems that
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do not rely on the soil for disposal, but
which discharge either to surface waters
or to the atmosphere.
Procedures
Study Site
The full-scale operating systems were
installed at individual homes in Hamilton.
and Clermont Counties in southwestern
Ohio, and the scaled-down field systems
were installed at a field research station
established in Clermont County, Ohio.
The major limitations for conventional
methods of onsite treatment and disposal
in this area include slow permeability, a
seasonally high water table, and limiting
soil horizons. The majority of soils in the
study areas formed in 40 to 100 cm of
Wisconsinan loess and in the underlying
weathered till of Illinoian age. The major
soil types at the field station were the
Avonburg silt loam (Aerie Fragiaqualf,
fine-silty, mixed, rnesic) and the Ross-
moyne silt loam (Aquic Fragiudalf, fine-
silty, mixed, mesic).
To describe the soil moisture regime of
a typical site in southwestern Ohio, the
groundwater table, soil moisture content,
and soil moisture potential were mea-
sured in areas of the research site not
affected by the addition of effluent. The
free water surface was within 15 to 60
cm of the soil surface during the late fall,
winter, and spring months, and receded
to greater than 1.5 m during the summer
months. The f ragipan that was present in
these soils did not greatly impede the
downward movement of water.
The soil moisture content remained
relatively constant during the late fall,
winter, and spring and decreased only in
the upper horizons of the soil profile
during the summer months. Below ap-
proximately 1 m, there was very little
change in the soil moisture content
throughout the study.
Systems Studied
Table 1 lists the various systems eval-
uated in this project, and the major objec-
tives for the individual studies. All systems .
utilizing the soil for disposal were moni-
tored with trench observation wells to
observe ponding depths. The soil absorp-
tion rates were determined by either
preset loading rates, or by mechanisms
in the trenches that controlled the amount
of wastewater applied to the trench based
on the amount of effluent the soil ab:
sorbed. The soil moisture regime sur-
rounding the trenches was monitored
with tehsiometers, depth moisture gauge
(neutron probe), and groundwater obser-
vation wells JThe groundwater surround-
ing several of the systems was analyzed
for contamination.
Influent ar^d effluent samples from the
systems that did not use the soil for
disposal were analyzed for common
wastewater parameters, including COD,
BODS, fecal coliforms, Total-P, nitrogen
species, and total suspended solids (TSS).
Site Suitability
Two comrrjon techniques to assess site
suitability foij onsite wastewater disposal,
the use of 2-chroma mottles to predict
the maximutn height of the fluctuating
high groundwater table, and the use of
percolation tests and hydraulic conduc-
tivity tests jto describe the hydraulic
capacity of a soil, were evaluated. Soil
colors described from core samples taken
in areas where soil-water monitoring
equipment was installed were compared
with the groundwater table data. In situ
hydraulic conductivity tests and percola-
tion tests were performed in triplicate at
four locations at the field research site
representing two soil types. All of the
tests were performed at a 50-cm depth to
correspond with the depth of the infiltra-
tive surface of a conventional soil absorp-
tion system! The values obtained were
then compared to actual absorption rates
obtained from two conventional trenches
installed in an Avonburg soil.
Results and Discussion
Alternating Soil Absorption
Field System
The installation of additional trench
capacity prevented surfacing of effluent
at a site vvith a failed soil absorption
system duri'ng the 3-year period of the
study. However, the alternating field
concept could not be evaluated because
the exisitinb, failed system had been
installed with only a few centimeters of
soil between the infiltrative surface of
the trench [and bedrock. Consequently,
when the grjoundwater table rose during
the late fall, jthe trenches were inundated
with groundwater. Therefore, during
these periods, even when effluent was
not being applied to the trenches, they
were filled with water/The trenches could
dry out during the summer months when
effluent was directed to the alternate
system, butihe longest continuous resting
period was only 90 days, and rejuvenation
was insufficient to allow the system to
dispose of ihe entire volume of waste-
water produced. The importance of main-
taining a suitable isolation distance
between the trench bottom and an im-
pervious horizon was clearly seen in this
study.
Low-Pressure Pipe System
The LPP system was installed on a 10
percent side slope in a Rossmoyne soil,
and consisted of 5 trenches that were
12.2 m long and spaced 1.5 m on centers.
The trenches were 20 cm wide and ap-
proximately 28 cm deep and were in-
stalled with a trenching machine. Septic
tank effluent was applied to the system
by pressure distribution.
Throughout the 2-year study, effluent
adsorption was variable and dependent
on climatic factors. The loading rates
ranged from 4 to 10 liters per day per
square meter (Lpd/m2) (based on the total
surface area that the system covered),
with the highest occurring during the
first summer of operation. After the first
year, the loading rate was kept constant
at approximately 4 Lpd/m2. However, oc-
casional periods of surface seepage oc-
curred at this loading rate. No freezing
was detected during the one winter that
the system was in continuous operation;
however, during a second winter when
system operation was interrupted for 4
weeks, the soil surrounding the trenches
froze.
Alternative Trench Design System
Two alternative trench designs and a
conventional trench were installed in
duplicate in a nearly level Avonburg soil.
The alternative designs included a gravel-
less trench that consisted of 25-cm
diameter corrugated plastic tubing
covered with a porous wrap and installed
at a depth of 50 cm, and a shallow trench
similar to a conventional trench except
that it was installed at a depth of 30 cm.
The trenches were 6 m long and were
installed 6 m apart. A constant ponding
depth of approximately 20 cm was
maintained.
The average absorption rates varied
greatly over the 2-year study. The shallow
trench design had a statistically signifi-
cant average absorption rate higher than
the other two trench designs. There was
no significant difference in the absorption
rates of the conventional and gravelless
trench designs throughout the study.
During the summer months, all of the
systems performed adequately. However,
during the late fall, winter, and spring,
absorption rates were much lower, and
there were periods of time lasting for up
to 5 months when no effluent was
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Table 1. Objectives of Individual Studies
System
(Size, Discharge, Installation)*
Objectives
Alternating SAS (FS,S,I)
Low Pressure Pipe (SD,S,I)
Alternative Trench (SD,S,I)
(Shallow, grave/less, conventional)
Mound (LC,S,Y)
Intermittent Sand Filter (FS.SW.I)
Intermittent Sand Filter (LC,SW,lj
Ftecirculating Sand Filter (LC,SW,I)
Aerobic Unit/Upflow
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units, but the effluent did not consistently
meet the State of Ohio standards for the
discharging of treated wastewater off of
private property for these parameters.
Fecal coliforms were reduced in numbers
through all of the units, but the mean
number exceeded the surface water
standard for recreational use. Total-N and
COD were inconsistently reduced through
the units, and little reduction of Total-P
occurred. The addition of the subsurface
gravel bed to the aerobic unit-upflow
gravel filter improved the quality of ef-
fluent, but the improvement was not
consistent.
Evapotranspiration-
Evapotranspiration/Absorption
Systems
The performance of 11 evapotranspira-
tion JET) and evapotranspiration/absorp-
tion (ETA) systems that had been installed
between 1978 and 1981 was evaluated
during the spring of 1982 and winter of
1985. Information about each system was
obtained through interviews with home-
owners, health department personnel,
plumbers, public water utilities, and onsite
inspections.
Only 5 of the 11 systems were con-
sidered to be functioning properly. Both
groups {failing and properly functioning)
contained ET and ETA systems, had low
and high flow rates, multiple and single
trench designs, various fill materials, and
were installed in suitable and unsuitable
soils. Also, it is possible that the ET
systems were actually operating as ETA
systems as the result of faulty installation,
and all modifications may not have been
reported. Therefore, it could not be deter-
mined why a system did or did not work.
Systems that rely solely on evapo-
transpiration for the disposal of effluent
should not be considered to be suitable
alternatives for year-round use in south-
western Ohio because precipitation ex-
ceeds potential evaporation 6 months of
the year. It is highly probable that the five
functioning systems were not true ET
systems and that other factors were in-
volved in their satisfactory performance.
Groundwater Contamination
Groundwater was sampled from ob-
servation wells over a 1-year period in
and around the LPP system, and from the
perimeter drains surrounding the alter-
native trench design system to determine
if groundwater contamination was oc-
curring as the result of the added effluent.
The concentration of chloride was
higher in th£ groundwater surrounding
the systems ^han in areas not influenced
by the addition of effluent. However, the
other parameters tested (NH3-N,
NO2-HMO3-N, TKN, Total-P, and fecal coli-
forms) showed little or no increase in
concentrations for the time period they
were monitpred.
Although [groundwater contamination
did not appear to be a problem for most of
the parameters measured during this
study, the systems should be monitored
for several years in soils with high water
tables, such ps those in this study, to fully
evaluate the potential for groundwater
contamination.
Soil Moisture Regime
Surrounding Trenches
The soil absorption rates of the systems
evaluated in this project suggest that the
soils were able to absorb an adequate
volume of wastewater during the summer
months but during the winter months the
absorption [capacity was greatly de-
creased. This decrease most likely re-
sulted from higher soil moisture contents,
lower evapotranspiration rates, and a high
groundwatejr table. Immediately sur-
rounding the systems, however, the soil
moisture regime remained relatively
constant Groundwater mounded below
the LPP anci alternative trench design
systems throughout the year. No measur-
able changeioccurred in the soil moisture
content below the elevation of the trench
bottom to a horizontal distance of 75 cm
between wifiter and summer, although
low soil moisture tensions were present
for a few weeks during the late summer.
Above the elevation of the trench bottom,
90 cm from the trench, unsaturated
conditions existed during the summer,
but the tensions were much lower than
in areas not influenced by wastewater
addition. Also, after two years of opera-
tion, soil moisture potentials indicated
that saturated conditions were present
below the infiltrative surface of the
monitored trenches, and in the trench
sidewalls at the elevation of the trench
bottom. Unsaturated conditions existed
in the sidewall several centimeters above
the trench bottom.
Site Evaluation Procedures
Using thejpresence of soil mottles with
chromas of| two or less to predict the
depth to the [fluctuating high groundwater
table underestimated the height of the
high water table rise in this study.
Groundwater was observed for short
periods in horizons that did not contain
mottles with chromas of two or less, but
did contain 3-chroma mottles and man-
ganese nodules and cutans. Mottles with
chromas of two or less were found in
horizons that had extended periods of
saturation. Soil morphological features
such as 3-chroma mottles and manganese
and iron nodules and cutans should be
included in site evaluations on Avonburg
and Rossmoyne soils to accurately predict
the presence and duration of the high
water table.
Percolation rates and saturated hy-
draulic conductivity values obtained from
the auger-hole method and an in situ
falling-head test overestimated the ab-
sorption capacity of the Avonburg and
Rossmoyne soils in this study. No statis-
tically significant difference occurred
among the tests performed at four dif-
ferent locations. Percolation rates mathe-
matically converted to saturated hydraulic
conductivity values provided similar
values to the auger-hole method and the
in situ falling-head test in the soils in this
study.
The geometric mean of the saturated
hydraulic conductivity tests and the
percolation rates mathematically con-
verted to saturated hydraulic conductivity
values ranged from 4 to 158 cm/day.
Because no difference was found among
the soils and tests in this study, an
average saturated hydraulic conductivity
of 33 cm/day was assumed. The average
long-term acceptance rate for the con-
ventional trenches in this project was 2.2
cm/day under optimum climatic condi-
tions (i.e., summer). This loading rate
was approximately 7 percent of the
average saturated hydraulic conductivity
value. When a subsurface soil absorption
system is designed using a percolation
rate, the infiltrative surface is sized with
the use of empirically derived tables that
correlate application rate to the percola-
tion rate. Using standard tables, the
maximum allowable loading rate (based
on bottom area of trench) was 1.83
cm/day for the percolation rates in this
study, which is similar to 2.2 cm/day, the
long-term acceptance rate under optimum
climatic conditions. The loading rates
were much lower during the winter
months, however, and the percolation
rate greatly overestimated the absorption
capacity of the soil during these time
periods. Thus the percolation test ap-
proach for sizing appears to have serious
inadequacies for the soils in this study.
4
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Conclusions and
Recommendations
None of the systems studied that rely
on the soil for treatment and disposal of
wastewater functioned properly when the
groundwater table was high. The LPP
system and the shallow-conventional
trenches appeared to perform satisfac-
torily during most of the year, with only
occasional surface seepage of effluent.
Before they are recommended for use,
however, further studies should be per-
formed to determine if design modifica-
tions and reduced loadings could eliminate
the occasional surface seepage since this
is usually unacceptable for health and
nuisance reasons. Recommended design
modifications include increasing the
trench spacing to provide as large a
lateral absorption area as possible, and
installing the trenches as close to the soil
surface as possible to use the more
permeable topsoil horizons and to provide
the greatest possible spacing between
the high groundwater table and the in-
f iltrative surface. The potential for freezing
and methods of prevention in these
shallow systems should be further
investigated.
Because of the lack of centralized sewer
systems and suitable soils in many areas
of southwestern Ohio, the LPP and shal-
low trench systems are possible alter-
natives for wastewater disposal in areas
where soil absorption is the only option
available. Areas should be further
evaluated on a site-by-site basis to
determine what loading rates and design
modification are required to eliminate
seasonal failure.
The intermittent sand filters consis-
tently produced a high quality effluent
with respect to BOD5, COD, and TSS
when pretreatment was provided by
either a septic tank or an aerobic unit.
This process would be considered to be a
good alternative to subsurface disposal in
southwestern Ohio if an appropriate re-
ceiving water is available for surface dis-
charge, and if the regulatory agencies
permit such a discharge. The additional
expense of pretreating the wastewater
with an aerobic unit was not justified.
Disinfection of the effluent should be
required before discharge.
An overview of project conclusions with
regard to the applicability of specific
technologies to soils with generally low
permeabilities, high groundwater tables,
and limiting soil horizons, such as those
present in southwestern Ohio, is pre-
sented in Table 2.
The full report was submitted in ful-
fillment of Cooperative Agreement No.
CR-808168 by the Cincinnati Center for
Small Community Wastewater Systems
Studies under the sponsorship of the
U.S. Environmental Protection Agency.
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Tab/o 2. Summary of Onsite Alternative Wastewater Treatment and Disposal Systems on Severely Limited Soils
Suitability for \
Technology Use in SW Ohio \ Remarks
Alternating
Soil
Absorption
System
(ASAS}
Low
Pressure
Pipe
Shallow
Trench
Grave/less
Trench
Conventional
Trench
Mound
Intermittent
Sand Filters
Aerobic
Unit/Upflow-
Gravel
Filters
Downflow
Gravel
Filters
Evapotrans-
pirotion
Beds(ET)
ET/Absorption
Beds (ETA}
Possibly
High
Potential
Limited
Potential
High
Potential
Limited
Potential
Low
Potential
Not Known
Very Suit-
able Where
Surface
Discharge
Allowed
Low
Potential
Limited
Potential
Not
Suitable
Low
Potential
This concept could not be evaluated because of high groundwater in the original trenches (built
prior to these studies directly on bedrock). However, if used with trenches which incorporated
sufficient volume to store flows during low absorption periods, this system might be successful.
Ponding in trenches was likely for long periods. Thus no advantage other than for summer homes
or where trenches are higher than septic tank. Freezing potential needs more evaluation.
Lower costs and increased absorption during low absorption periods of the year. Combined with
other concepts (e.g. ASAS), it represents part of the most potentially successful system designs.
Potential freezing problems/solutions and most cost-effective trenching methods need more
evaluation. [
Has no advantage over conventional trenches unless cost of gravel is high enough to justify
economics. Shadow installation and freezing problems/solutions need more evaluation.
I
Since shallow trench is superior in absorptive capacity, the only advantage could be greater
storage capacity ^during low absorption periods on small lots.
Not evaluated at full-scale, but inability of soils to absorb effluent even from shallow trenches for
long periods causes doubts about applicability. More frequent dosing improves nitrogen removal.
Superior performance over other surface discharge technologies. Pretreatment beyond septic
tank not justifiedr and post-disinfection is required to meet indicator organism limits. Very reliable
effluent quality and low maintenance features.
Unacceptable effluent quality with wide fluctuations; increased maintenance may improve some-
what. High annual costs.
Used to upgrade aerobic/upflow-gravel system to produce a better, but not fully acceptable,
effluent. Total capital costs high for complete package.
I
Non-discharging ET systems are not possible in SW Ohio because humidity and precipitation
outweigh evapotranspiration potential.
Because of the low ET potential in SW Ohio, the ETA systems that worked depended heavily on
absorption. (The shallow trench system is, in effect, an ETA system because it maximizes both soil
absorption and ET.J
Highest Potential
Subsurface System
Highest Potential
Surface Discharge System
A shallow trench system with sufficient volume to accommodate either a low
loading rate or storage capacity for low absorption periods. Although ASAS could not
be evaluated in tlyese studies, the use of shallow ASAS's could potentially be highly
successful.
Intermittent sand filters preceded by a septic tank and followed by disinfection, as
required.
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Margaret M. Cashell, David D. Effert, and James M. Morand are with the
University of Cincinnati, Cincinnati, OH 45221.
Margaret M. Cashell is the EPA Project Officer (see bellow).
The complete report, entitled "Alternative Onsite Wastewater Treatment and
Disposal Systems on Severely Limited Sites/' (Order No. PB 87-140 992/
AS; Cost: $24.95, 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: ;
Water Engineering Research Laboratory \
U.S. Environmental Protection Agency >
Cincinnati, OH 45268 I
United States
Environmental Protection
Agency
Center for Environmental, Research
Information i
Cincinnati OH 45268 [
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EPA/600/S2-86/116
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