Ecological Research Series
ENVIRONMENTAL EFFECTS OF SEPTIC
TANK SYSTEMS
Robert S. Kerr Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Ada, Oklahoma 74820
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
cies, and materials. Problems are assessed for their long- and short-term influ-
ences. Investigations include formation, transport, and pathway studies to deter-
mine the fate of pollutants and their effects. This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/3-77-096
August 1977
ENVIRONMENTAL EFFECTS OF SEPTIC TANK SYSTEMS
Marion R. Scalf and William J. Dunlap
Ground Water Research Branch
Robert S. Kerr Environmental Research Laboratory
Ada, Oklahoma 74820
and
James F. Kreissl
Systems and Engineering Evaluation Branch
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
ROBERT S. KERR ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ADA, OKLAHOMA 74820
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DISCLAIMER
This report has been reviewed by the Robert S. Kerr Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publication.
Mention of trade names or commercial products does not constitute endorsement
or recommendation for use.
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FOREWORD
The Environmental Protection Agency was established to coordinate
administration of the major Federal programs designed to protect the
quality of our environment.
An important part of the Agency's effort involves the search for
information about environmental problems, management techniques, and new
technologies through which optimum use of the Nation's land and water
resources can be assured and the threat pollution poses to the welfare
of the American people can be minimized.
EPA's Office of Research and Development conducts this search through
a nationwide network of research facilities.
As one of these facilities, the Robert S. Kerr Environmental Research
Laboratory is responsible for the management of programs to: (a) investi-
gate the nature, transport, fate, and management of pollutants in ground
water; (b) develop and demonstrate methods for treating wastewaters with
soil and other natural systems; (c) develop and demonstrate pollution con-
trol technologies for irrigation return flows; (d) develop and demonstrate
pollution control technologies for animal production wastes; (e) develop
and demonstrate technologies to prevent, control or abate pollution from
the petroleum refining and petrochemical industries; and (f) develop and
demonstrate technologies to manage pollution resulting from combinations
of industrial wastewaters or industrial/municipal wastewaters.
This report contributes to that knowledge which is essential in order
for EPA to establish and enforce pollution control standards which are
reasonable, cost effective, and provide adequate environmental protection
for the American public.
William C. Galegar
Director
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ABSTRACT
Septic tank-soil absorption systems are the most widely-used method of
on-site domestic waste disposal. Almost one-third of the United States popu-
lation depends on such systems. Although the percentage of newly constructed
homes utilizing septic tanks is decreasing, the total number continues to
increase.
Properly designed, constructed and operated septic tank systems have
demonstrated an efficient and economical alternative to public sewer systems,
particularly in rural and sparsely developed suburban areas. However, because
of their widespread use in unsuitable situations, they have also demonstrated
the potential for contamination of ground and surface waters.
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CONTENTS
Foreword iii
Abstract iv
Figures vi
Tables vii
1. INTRODUCTION 1
2. CONCLUSIONS 2
3. RECOMMENDATIONS 3
4. SYSTEM DESIGN 4
5. PRESENT REGULATIONS 8
6. POLLUTION PROBLEMS 12
EFFECTS ON GROUND WATER 12
SEPTIC TANK SLUDGE DISPOSAL 20
7. CURRENT RESEARCH 23
MOVEMENT AND FATE OF LEACHATES 23
IMPROVEMENT OF CONVENTIONAL SYSTEMS 26
ALTERNATIVE ON-SITE DISPOSAL SYSTEMS 27
8. FUTURE TRENDS AND RECOMMENDATIONS 31
9. REFERENCES 33
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FIGURES
Number Page
1 Typical on-site system 5
2 Septic tank 6
3 Absorption trench and lateral 7
4 Effect of clogged absorption field on nearby well 13
5 Effect of a pumping well on contaminated water movement 15
6 Major aquifer types 16
7 Nitrogen reactions in soil 17
8 Density of housing units using on-site domestic waste
disposal systems (by county) 19
9 Evapotranspiration bed 29
10 Mound over creviced bedrock 29
11 Total annual costs of alternatives 30
VI
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TABLES
Number Page
1 ABSORPTION FIELD DESIGN 9
2 SEPTIC TANK DESIGN AND WATER DEPTH 10
3 SEPTAGE CHARACTERIZATION 20
4 SEPTAGE DISPOSAL ALTERNATIVES 22
vn
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SECTION 1
INTRODUCTION
Almost twenty million housing units, representing about twenty-nine percent
of the United States population, dispose of domestic waste through individual
on-site disposal units. About eighty-five percent of these units are septic
tanks and cesspools, which discharge approximately 3 billion cubic meters (800
billion gallons) of waste per year to the soil (1).
Septic tank systems were introduced into the United States almost one-
hundred years ago but the major growth in use of these systems took place after
World War II due to the combined effects of rural electrification and explosive
development of suburban areas around major cities. Although the relative percent
of newly constructed homes utilizing septic tanks is decreasing each year, the
total number is increasing at a rate of about one-half million per year (2).
The basic septic tank system consists of a buried tank where water-borne
wastes are collected, scum, grease and settleable solids are removed from the
liquid by gravity separation, and a subsurface drain system where clarified
effluent percolates into the soil. There have been few major design modifica-
tions in the past several decades and most systems are constructed and installed
today in much the same manner as before World War I (2).
Although the concept and design are relatively simple, the septic tank
system is a complex physical, chemical and biological system. Performance is
essentially a function of the design of the system components, construction
techniques employed, characteristics of the wastes, rate of hydraulic loading,
climate, area! geology and topography, physical and chemical composition of the
soil mantle, and care given to periodic maintenance (3).
Septic systems have performed a vital function of environmental sanitation,
particularly in rural and sparsely developed suburban areas. However, some esti-
mates indicate that less than one-half of all systems in use today perform satis-
factorily for the entire design life of fifteen to twenty years (2). Many public
health authorities feel that conventional septic systems are suitable only where
population density is strictly limited and soil conditions are suitable for
effective absorption. Otherwise, these systems may contaminate ground and surface
waters and result in sanitary nuisances and health hazards.
In spite of their limitations and potential for pollution, millions of con-
ventional septic tank systems will continue to be used throughout the United
States. Even in areas where housing density and pollution problems may justify
conversion to collecting sewers and treatment plants, several years are normally
required for public systems to become fully operational after the decision has
been made and funding has been secured.
1
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SECTION 2
CONCLUSIONS
1. Almost one-third of the homes in the United States dispose of domestic waste
through individual on-site disposal units.
2. Septic tank-soil absorption systems represent about eighty-five percent of
the individual disposal units.
3. Because of improper design, improper construction or improper maintenance
or a combination of these, a significant percentage of septic tank systems fail
within their design life.
4. Soils in many areas, perhaps in as much as one-half of the United States,
are not suitable for conventional septic tank-soil absorption systems.
5. Most of the numerical limits found in State and local codes governing septic
tank system design and construction are without a sound scientific basis.
6. Septic tank systems are common sources of surface water and especially ground
water contamination.
7- The most important factor influencing regional ground-water contamination by
septic tank systems is the density of these facilities in an area.
8. Their success in some communities indicates that with proper design, con-
struction and maintenance, septic tank systems can provide satisfactory disposal
of wastewater.
9. There are several modifications available to conventional septic tank systems
which significantly expand their area of applicability.
10. Despite the potential for pollution and the unsatisfactory performance of
many systems, septic tank-soil absorption systems will continue to provide a
valuable domestic waste treatment alternative, especially where housing density
cannot economically justify sewers and treatment plants.
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SECTION 3
RECOMMENDATIONS
Zoning and land use planning in areas of considerable septic tank activity
should be based on a thorough understanding of soil variability, geology, topog-
raphy and aquifer characteristics.
Research should be continued into the basic questions of septic tank use.
What are the movement and fate characteristics in the subsurface environment of
pollutants from septic tanks, especially viruses and organics? What density of
septic tank systems can be tolerated in an area before pollution problems
necessitate sewers or septic system modifications?
Research should be continued into the development of septic system modifi-
cations and into alternative individual sewage disposal systems.
The social and economic consequences of converting from individual units
to sewered and central treatment facilities must be studied with consideration
of the resultant loss of ground-water recharge.
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SECTION 4
SYSTEM DESIGN
A typical septic tank-soil absorption system (ST-SAS), shown in Figure 1,
consists of a building sewer, laid to specified grade, which discharges to the
inlet of a septic tank. The septic tank effluent discharges to a series of
distribution pipes laid in trenches (absorption trenches) or to a single large
excavation (seepage bed). Since seepage beds are not generally satisfactory
in soils other than sands, only the absorption trenches are discussed herein.
A typical cross-section of a septic tank is shown in Figure 2. Raw waste-
water enters through an inlet structure which generally consists of either a
baffle or a tee to dissipate energy and help prevent short-circuiting of the
flow. In the main body of the tank, solids separation occurs with heavier
solids settling to the bottom where they become part of the sludge layer and
lighter solids (grease, wax, etc.) rising to the surface as part of the scum
layer. Particularly during warm periods, some amount of anaerobic digestion
can occur in these layers, reducing the overall volume of solids retained in
the tank. The liquid effluent is discharged through an outlet structure which
generally consists of either a baffle or a tee. The relative dimensions of the
tank, the type of control structures, etc. are dictated by the State or local
codes, as are the sizes and locations of the inspection parts and materials of
construction.
A typical cross-section of a soil absorption field (trench) is shown in
Figure 3. The intended purpose of the trench system is to distribute the septic
tank effluent over a large area for absorption into the ground. Specifications
for allowable width and depth of trenches; sizes, types, and depth of fill
materials; distances between trenches; minimum cover; and piping materials and
arrangements are dictated by local and State codes. More importantly, the over-
all size and horizontal and vertical distances from other physical and geological
features of the site are determined by these codes. Ancillary devices such as
dosing equipment and/or distribution boxes which are located between the septic
tank and the absorption field are generally specified in each code as*to their
desirability, physical design, and materials and methods of construction.
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NON PERFORATE
TILE
ABSORPTION
FIELD,
TILE
DRAINAGE
LINES
Figure 1. Typical on-site system.
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cr>
INSPECTION
PORTS
^g*?^?V**£^^
DIGEIG LDGE
Figure 2. Septic tank.
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pV\^. .0:« H?-^-"'H-o « ^ rft^y/^VJ: O'-?* o?-• • O
^fe^^^l^pvl^C-.^5^®?"^S?i?
2"MIN.
GRAVEL OR
BROKEN STONE
LONGITUDINAL
SECTION
OVERFILL TO ALLOW
_,_ /FOR SETTLEMENT
"
^£&•^£^:^r^S£^;^;
15: 9V-ttV^&^frr':v^••
''fS''» • *' 'r'-i 'ir!*i t7^- '^i'Q' f-rt' h'l
12" To 36"
CROSS SECTION
LATERAL OF
DRAIN TILE
(SHOWN) OPEN
JOINTED SEWER
PIPE OR
PERFORATED PIPE
Figure 3. Absorption trench and lateral.
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SECTION 5
PRESENT REGULATIONS
Present on-site system practice generally involves a design which must
meet some State or local code of requirements. However, these requirements
vary widely, as shown in Tables 1 and 2. Several States are not included, nor
are several national organization publications such as the USPHS Manual of
Septic Tank Practice and National Plumbing Code. However, the tables do illus-
trate not only the variability of criteria, but also some of the areas of con-
cern to public health officials. Some of these concerns include the movement
of pollutants from the absorption fields as indicated by setback distances and
minimum percolation restrictions; the flow net below absorption trenches as
indicated by the minimum spacings between trenches of varying widths; and
aeration, freezing and evapotranspiration phenomena as indicated by minimum
cover specifications.
Although not included in Table 1, each code considers the degree of puri-
fication imparted by the soil as indicated by minimum distances between trench
bottoms and maximum ground-water level, and impervious strata and the hydraulic
acceptance of the soil as indicated by flow per interfacial area of soil and
soil permeability specifications.
Due to the lack of scientific knowledge concerning what actually happens
in the ground, most of the numerical limits are without a sound basis. Between
1945 and 1965, significant data were produced by the U.S. Public Health Service
and the University of California but some of these data have been misapplied
into inflexible codes, thereby causing as many problems as they have solved.
Although some articles on the design and functioning of septic tank-soil
absorption fields appeared in the late 1960's, it was not until the advent of
the Small-Scale Waste Management Project at the University of Wisconsin that
a comprehensive study of on-site systems was attempted. Even though many of
the new results have not yet been organized and reduced to practice, several
States and local agencies have recognized the obvious lack of scientific back-
ground on which existing regulations are based. Some States, such as Maine,
have completely revised their codes in an attempt to find new answers directly
applicable to, their problems.
One of the primary shortcomings of existing codes relates to absorption
field sizing based on the percolation test. The percolation test is purported
to measure the rate of hydraulic acceptance of a given soil. Unfortunately,
the test is quite variable even in the hands of a competent, trained profes-
sional. To compound the problem, the test is rarely performed in the specified
manner, the manner specified is also questionable, the test has frequently been
faked, and the test can be quite costly (generally about $75 to $150).
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TABLE 1. ABSORPTION FIELD DESIGN (4)
j
State
Alabama
Alaska
Arizona
Arkansas
California
Coloi ado
Connecticut
Delaware
Florida
Georgia
Hawaii
Idano
Illinois
Indi ana
lOWc
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
South Dakota
Tennessee
Texau
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyorr.ii. g
.
Setbacks
Well
50-75
50-100
50-100
100
75
75-100
100
100
50-100
100-200
100
100-300
....
100
100
100
75
.
50
50-100
100
100
100
50
100
35-100
75-100
100
50-100
100
Surface
Water
50-100
100
50
50
50
50
100-300
50
25
50-100
100
50
100
75
50-100
50
50
100
50
100
50-100
100
100
50
50
Minimum Minimun Minimum Trench
Spacing Cover Percolation Widths
(Feet) (Inches) Restrictions (Inches) Sizing
6
6
6
6
6-9
6-8
10
6
6-7.5
7 .5
10
6
6
6
6-7.5
...
6
10
6
6
6
6
6-7.5
6-9
6
6
10
6-7. 5
6
12
12
12
6
12
12
12
12
12
None
6-12
2-6
12
6
4-6
6
6
C
12
12
12
12
Hone
6
12
12
6-12
None
None
None
None
None
None
None
None
None
None
None
None
Yes
No
Yes
None
None
None
Yes
None
Yes
None
None
None
Yes
None
None
None
18-36
12-36
12-18
18-36
18-36
18-24
18-36
12-36
18-36
18
12-18
24
12-36
10-36
12-24
12-36
8-30
24
12-36
18
18-36
12-36
18-35
18-36
12-36
18-36
12-36
Perc
Perc & Soils
Perc
Perc
Perc
Perc s, Soils
Perc & Soils
Perc & Soils
Perc
Perc
Perc
Perc
Soils
Perc & Soils
Perc
Perc
Perc
Soils
Soils
Perc
Perc
Perc
Perc & Soils
Perc
Pore & Soils
Perc & Soils
Perc
Perc & Soils
Perc
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TABLE 2. SEPTIC TANK DESIGN AND WATER DEPTH (4)
States
Alabama
Alaska
Arizona
Colorado
Connecticut
Florida
Geor'jia
Idaho
Illinois
Indiana
Iowa
Kentucky
Louisi ana
Maine
Montana
Nebraska
Nevada
New Hampshire
ew e sey
North Carolina
Ohio
Oregon
Pennsylvania
Rhode Island
South Dakota
Tennessee
Utah
Virginia
Washington
West Virginia
Wisconsin
Wyoming
1
1000
750
960
750
1000
750
750
750
750
750
750
500
750
750
750
1000
750
750
1000
750
900
750
1000
750
750
30 hour
750
750
750
750
2
1000
750
960
750
1000
750
750
750
750
750
750
750
750
750
750
1000
750
750
1000
750
900
750
1000
750
750
Detention
750
750
750
750
Tank Size i
Number of
3
1000
900
960
900
1000
900
900
900
900
1000
900
900
900
900
900
1000
900
900
1500
900
900
900
1000
900
900
100 Gallons
900
900
975
900
n Gallons
Bedrooms
4
1200
1000
1200
1000
1250
1000
1000
1000
1100
1250
1000
1150
1000
1000
1000
1000
1000
1000
2000
1000
1000
1000
1250
1000
1000
Per Day
1000
1000
1200
1000
5
1400
1250
1500
1250
1500
1200
1250
1250
1250
1500
1250
1400
1250
1250
1250
1250
1250
1250
2000
1250
1100
1250
1500
1250
1250
1250
1250
1375
1250
Minimum
Water Depth
(Feet)
4
4
4
No Minimum
1.5
1.5
No Minimum
4
1.5A-
None
2
4
:*•
2A.
4A.
1.5*-
4
3
:*•
i
No Minimum
3A.
3-
4
Discharge
No
No
Yes
No
No
No
No
No
Yes
No
Yes
Yes
No
No
No
No
No
Yes
No
No
No
No
No
No
Yes
NO
No
No
Yes
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The tremendous difference in design requirements for absorption fields
indicates a wide disagreement on how far pollutants travel in the subsurface,
the importance of evapotranspiration assistance in the disposal of effluents,
the purification capacity of soils, the hydraulics of trench drainage, and
clogging mechanisms.
11
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SECTION 6
POLLUTION PROBLEMS
As noted earlier, some investigators estimate that as many as one-half of
all septic tank-soil absorption systems are not operating satisfactorily. It
is probably more than coincidence that another estimate classifies more than
half of the soil in the United States as unsuitable for septic systems with
respect to the percolation rate.
Also noted earlier, the acceptability of a site for a septic tank system is
commonly based upon the percolation rate or the ability of the local soil to ab-
sorb water at a fast enough rate to handle the anticipated volume of effluent.
It is assumed that if the percolation rate is acceptable and the tile field is
large enough, there will be removal of pollutants from the effluent by natural
adsorption and biological processes in the soil zone immediately adjacent to the
tile field.
Historically, system failure has meant that the capacity of the soil to
absorb effluent from the tank has been exceeded and that waste added to the sys-
tem moves to the soil surface above the lateral lines. This type failure results
from soil clogging and loss of infiltrative capacity and is caused by combined
physical, chemical, and biological factors.
Physical factors include compaction of the soils by excavating equipment
and the movement of fine soil particles into the voids at the trench-soil inter-
face. The most important chemical factor is the deflocculation of soils by high
sodium waters. Some high sodium wastewaters may preclude the use of septic tank
percolation systems, although insufficient data exists to confirm this theory.
Apparently, biological factors are the principal influences on soil clogging.
The deposition of suspended materials, bacterial buildup, and bacterial decomposi-
tion of organic material at the liquid-soil interface produces an organic mat of
only a few millimeters thickness that greatly reduces infiltrative capacity (3).
When system failure does occur from soil clogging and wastewaters do seep
to the surface, overland flow from rainfall may carry contaminants directly to
a stream or lake or into an inadequately sealed well, such as in Figure 4.
EFFECTS ON GROUND WATER
High absorptive capacity, however, does not necessarily correlate with the
capacity of soils to remove pollutants from infiltrating wastewater. Many soils,
of high hydraulic absorptive capacity (permeability) can be rapidly overloaded
12
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/ /PRECIPITATION
' / i i i
CONTAMINATED
WATER
GRAVEL PACK
TOO CLOSE
TO SURFACE
-WATER
AQUIFER
FRESH WATER
AQUICLUDE--
Figure 4. Effect of clogged absorption field on nearby well.
13
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with organic and inorganic chemicals and microorganisms permitting rapid move-
ment of contaminants from the lateral field to the ground-water zone, as in
Figure 5. This type of system failure has been largely ignored until recent
years.
Whether or not pollutants moving from the tile fields through the soil
reach the ground water and subsequently a water supply depends to a large ex-
tent on the type of subsurface material involved and the thickness. Figure 6
presents four common aquifer types which may transmit pollutants great distances.
Conventional septic tank systems should be avoided in any areas where fractured
or cavernous formations, such as the bottom three rock types, are less than a
few feet below the bottom of the absorption trench.
Such rock types provide a minimum of the three major processes necessary to
retard or control the movements of pollutants—filtration, adsorption, and micro-
bial degradation. Generally, the fissures and channels are too large to provide
significant filtration. The detention time and active surface areas available
are not great enough for appreciable adsorption or microbial degradation to occur.
The same may be true of gravel aquifers and, to a lesser extent, coarse sand
formations.
The type and thickness of soils overlying these rock types then becomes
critical. Various research efforts in the past have demonstrated that most of
the known contaminants in septic tank effluent—suspended solids, BOD, bacteria,
and viruses—can be removed by movement through a few feet of soil under proper
conditions. The amount of soil required is dependent on the particular contami-
nant; the pH, moisture, temperature, and oxidation-reduction potential of the
soil; the size, shape, and interstitial voids of the soil; and the velocity of
flow through the voids. Higher percentages of fine material such as clays in
the soil provide more surface area and generally result in reduced mobility of
pollutants. Viruses, for example, are known to be adsorbed more readily on
soils of high clay content and low pH at lower flow rates (4).
Some other chemicals are not that easily removed. Chlorides and nitrates
are essentially unaffected by movement through most soils. However, nitrogen
requires special consideration. Most nitrogen from septic tank effluents occurs
in the organic and ammonia forms which are readily adsorbed to soil particles
within short distances. If anaerobic conditions are maintained in this soil,
there is little nitrogen movement. However, under favorable moisture, tempera-
ture, and oxygen conditions such as generally occur in well-drained soils, soil
bacteria will oxidize the nitrogen compounds to the more mobile nitrates, as
shown in Figure 7 (5).
Nitrates, primarily from septic tanks and fertilizers, have penetrated
hundreds of feet into an artesian aquifer underlying Nassau County, Long Island.
The combined discharge from septic tanks and cesspools from the adjoining counties
of Nassau and Suffolk is approximately 230,000 cubic meters per day (60 mgd or
about 50,000 gallons per day per square mile). A nitrate front is moving into
unaffected portions of the aquifer at a rate of 1.5-12.5 meters per year verti-
cally and about 40 meters per year horizontally. Sixteen public supply wells
serving thousands of residents in Nassau County now exceed EPA nitrate stand-
ards. Part of Nassau County was sewered between 1952 and 1964. In a 1970
14
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CONTAMINATED WATER,
LAND SURFACE
FRESH WATER
RECHARGE
j
AQUIFER
'f-'i'-'ii •'•"-'•'•'•'•'• :'-;--'-'-v''-:\~/r
Figure 5. Effect of a pumping well on contaminated water movement.
15
-------
ROCK TYPE
INTERSTICES
SAND AND GRAVEL
CONSOLIDATED ROCK:
IGNEOUS, METAMORPHIC,
SEDIMENTARY
PORE SPACES
FAULT
FRACTURES
CARBONATE ROCK:
LIMESTONE, DOLOMITE
SOLUTION CHANNELS
VOLCANIC ROCK:
LAVA FLOWS
SHRINKAGE CLACKS
INTRA-FORMATIONAL
CHANNELS
Figure 6. Major aquifer types (1).
16
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ORGANIC N
AMMONIFICATION
NITRIFICATION
This reaction occurs at temperatures above 60° F.
Nitrification occurs only under oxidizing conditions,
NITRATE
LOST Tp_AJ.R_
NITRITE
NITRIC OXIDES
ELEMENTAL
DENITRIFICATION
This reaction occurs only under conditions
of low oxygen tension.
Figure 7. Nitrogen reactions in soil (5).
-------
survey of streams in the area, ground-water fed streams averaged 11 mg/1 nitrates
(as NO3) in sewered areas and 25 mg/1 in unsewered areas (6). In terms of the
percolation test, Long Island would be considered acceptable by most public
health agencies for septic tank systems.
A study conducted by the Delaware Geological Survey in the early 1970's
demonstrates the dilemma of public health officials in properly locating septic
tanks. Two suburban areas were selected with homes situated on one-quarter to
one-half acre lots, each with its own septic tank and shallow well-water system.
One area was characterized by an extremely high water table and poorly-drained
soils. The other area was underlain by deep, well-drained soils on uplands.
In the first area of poorly-drained soils, soil clogging was a severe
problem and a number of wells were contaminated by coliform bacteria but nitrate
levels averaged only 6.9 to 11 mg/1 auring the period of sampling. In the second
area of well-drained soils, nitrate concentrations ranged from 22 to 136 mg/1 but
none of the wells were found to be contaminated with coliform bacteria (6).
Septic tank ground-water contamination problems may be individual, local,
or regional. A regional problem exists when many individual systems contaminate
extensive aquifers which supply water over a broad area, such as one or more
counties.
The most important parameter influencing regional contamination from septic
tank systems is the density of these facilities in an area, although geology,
depth to water table, and climate may affect the nature and degree of the prob-
lem. The potential for regional contamination in the United States may be indi-
cated by the relative density of systems in Figure 8. The three density ranges
indicated may be considered as low, intermediate, and relatively high. Adjoin-
ing counties falling into the same range form regions of varying regional ground-
water contamination potential. In addition, there are a few large counties which
have high densities in limited areas of the county which create potential regional
problems but do not appear in the relatively high range on Figure 8.
Obviously, there is one major region of high contamination potential along
the northeast coast and several other isolated regions are scattered over the
eastern third of the country. Because they are such large counties, Los Angeles,
San Bernardino, and Riverside are not shown as high density areas; however, they
should be considered as such because of the great number of systems concentrated
in urban areas of these large counties (1).
Although Figure 8 serves to indicate where to look for regional ground water
that may be contaminated, calculation of the volume of wastewater discharged in
any particular location cannot be used to determine the existence or magnitude
without consideration of other parameters such as hydrology, geology, soils, etc.
In a series of five regional studies sponsored by EPA since 1970, local,
State, and Federal officials, consultants, water well drillers, and other water
resource professionals in 35 States were interviewed concerning ground-water
pollution problems. Septic tanks and cesspools rank highest in total volume of
wastewater discharged directly to ground water and were the most frequently
reported sources of contamination (7). Contaminants identified included
bacteria, viruses, ammonia, nitrates, chlorides, phosphates, and sodium.
18
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UNITS/SQ. Ml
> 10
10-40
> 40
Figure 8. Density of housing units using on-site domestic waste
disposal systems (by county) (l).
-------
It may be significant that between 1946 and 1960, 61 percent of all water-
borne disease outbreaks in the United States were attributed to contaminated
ground water (8). It seems probable that septic tanks played a significant role
in these outbreaks. Contamination of water supplies by septic tanks has been
identified as causing diseases such as infectious hepatitis, typhoid fever,
dysentery, and various gastrointestinal illnesses. It is also quite probable
that contamination from septic tanks has been responsible for innumerable
subclinical cases of waterborne diseases that go unnoticed and unreported.
SEPTIC TANK SLUDGE DISPOSAL
Pollutants which are removed in septic tanks accumulate in the form of
scum and sludge. Since these accumulations occupy increasingly greater portions
of the total volume, they eventually reduce the tank's effectiveness by causing
an efflux of soil-clogging material to the soil absorption system. The amount
of "septage" which must be pumped out and handled each year in the United States
is estimated to be about 15 million cubic meters (4 billion gallons) (9).
Septage characterization data from EPA pilot plants at Lebanon, Ohio, and
Blue Plains in Washington, D.C. are shown in Table 3 (10). Septage contains
significantly lower concentrations of heavy metals than does municipal sludge
but heavy metal content of any concentrated residue (sludge or septage) is
obviously only one area of concern in the ultimate disposal of that residue to
the environment.
TABLE 3. SEPTAGE CHARACTERIZATION
Concentration (mg/1)
Constituent
TS
TVS (%)
TSS
VSS (%)
BOD5
COD0
TOC
TKN
NH0-N
TP3
pH (units)
Grease
LAS
Fe
Zn
Mn
Cd
Ni
Hg
Se
Cr
As
Cu
Al
Pb
Arithmetic mean
38,800
65.1
13,014
67.0
5,000
42,850
9,930
677
157
253
-
9,090
157
205
49.0
5.02
0.71
<0.90
<0.28
0.076
1.07
0.16
6.4
48
8.4
Range
3,600
32
1,770
51
1,460
2,200
1,316
66
6
24
6.0
604
110
3
4.5
0.5
<0.05
0.2
<0.0005 -
<0.02
0.3
0.03
0.3
2
1.5
106,000
81
22,600
85
>18,600
190,000
18,400
1,560
385
460
8.8
23,468
200
750
153
32
10.8
3.7
4.00
0.3
2.2
0.5
34
200
31
20
-------
From an aesthetic standpoint, septage odors limit direct application to the
land except in isolated areas. The Wisconsin Department of Natural Resources has
reviewed the pathogenic aspects of sludge application and recommends that raw
sludge not be applied to agricultural land (11). Since septage is partially
digested domestic sludge, some intermediate processing may be required before
land disposal. Such intermediate processing could include anaerobic or aerobic
digestion, lime treatment, pasteurization or composting.
Alternative methods of septage treatment and disposal can be chiefly
categorized as:
1. Treatment at Sewage Treatment Plant (STP)
2. Treatment at a septage facility
3. Direct land application
Treatment of septage at an STP can involve direct addition of the septage
to the incoming municipal wastewater or addition of the septage to the sludge
processing system.
Since the choice of where to add septage to an STP would likely influence
effluent quality, as related to permit requirements, some emphasis on the sludge
processing mode is inevitable. If excess sludge processing capacity is available,
this choice becomes simpler. Since most smaller STP designs incorporate either
anaerobic or aerobic digestion followed by sand drying beds or vacuum filters,
the effects of septage addition on these processing steps should be determined.
Bench-scale studies have indicated that anaerobic digestion of pure septage at
loadings up to 1.3 kg VSS/m3/day (.08 Ib/ft3/day) was successful, but at 1.6 kg
VSS/m3/day (01 Ib/ftVday) was not. Continuous aerobic digestion at loadings
of 0.4 to 21 kg VSS/m3/day was quite effective in improving dewaterability, but
foaming problems were experienced (12). Pilot plant studies of anaerobic and
aerobic digestion of sludge-septage mixtures are now under way at the U.S. EPA
Lebanon, Ohio pilot plant.
Separate or regional septage treatment facilities are in a relatively
embryonic stage of development at this time, except for land disposal facilities.
Political forces are likely to cause these type of facilities to proliferate in
the future in areas where on-site wastewater treatment facilities alone are
feasible. Such forces, in the name of public health or environmental aesthetics,
may cause some conversion of direct land application sites to either modified
land disposal sites with pretreatment facilities or complete treatment facilities
with controlled effluent. The work presently under way to determine guidelines
for municipal sludge application to the land will strongly impact the former
possibility.
Table 4 contains a rough qualitative listing of the relative employment,
future employment, costs, limitations, and environmental impacts of several
classes of septage treatment and disposal methods currently used (10). It is
estimated that almost all of the septage generated each year is disposed of
either on the land or in existing sewage treatment plants (STP's). Based on
projected trends, land disposal methods will continue to predominate, despite
their potential environmental impacts.
21
-------
TABLE 4. SEPTAGE DISPOSAL ALTERNATIVES
ESTIMATED ESTIMA
METHOD USE COST
TED PHYSICAL ENVIRONMENTAL
S LIMITS IMPACTS
Untreated -* land application highest decreasinu
a. surface high low
b. soil infection high med
r. pits, holes, deep trenches low low
d. sanitary land fills (*) low iow
Minimal treatment -*• land disposal of effluent low increasing
a- anaerobic lagoons - sand recharge beds med. low
low yes yes high high med.
high poss . yes med. med. med.
low no yes high high /
low no yes high high high
low no yes high high med.
b. chemical treatment -+ sand recharge beds low high high no yes med. low med.
Condi t loning •+• dewatering -»- effluent treatment low increasing
a. aerobic digestion low high med. no no low low low
b. anaerobic digestion low high raed- no no low low low
d. chemical coagulation low raec
nigj] no nt» ±ow j.ow xow
high no no med. low low
F\> e . physical chemical oxidation low high high no no low low low
r\>
Sewage treatment plant addition (mainstream) high decreasing
a . activated s ludge (* ) low low
b. trickling filter (*) low low
Sewage treatment plant addition (sludge h ' dl ' g) low increasing
a. to conditioning step (*) low low
b. to separate cond. step •* dewatering (*) low med
Septage treatment plant > eff. to stream low no change
med . no no low low low
med . no no low low low
med . no no low low low
high no no low low low
a. anaerobic-aerobic treatmt . ->- tert . f i Iter high med. med. no no high high med.
b- AWT (chem, biol, tert) med. high high no no jOw low low
Composting
increasing med.
yes
yes
/ prohibitive
* assumes facility exists which can be used for this purpose with reasonable modification
-------
SECTION 7
CURRENT RESEARCH
MOVEMENT AND FATE OF LEACHATES
Satisfactory resolution of most of the questions regarding the effects of
septic tank systems on ground-water quality is ultimately dependent on the
development of a better understanding of the movement and fate in the subsur-
face of leachates generated by such systems. For example, definitive informa-
tion concerning the movement and fate of pollutants in both unsaturated and
saturated subsurface environments, were such information available, would
comprise the firm scientific basis needed for resolution of most of the dis-
agreements which underlie the wide variation in existing codes and regulations
presently governing the utilization and construction of septic tank systems.
Considerable research, therefore, has been and continues to be directed toward
the development of such information.
One aspect of current research on movement and fate of pollutants is con-
cerned with the development of guidelines for allowable densities of septic tank
systems for various geological and climatic conditions. Guidelines are urgently
needed in order that utilization of septic systems can be logically controlled
in situations where local or regional ground-water pollution problems may result
from their intensive use. Such work was instigated at the request of and par-
tially funded by the Office of Water and Hazardous Materials. It mainly entails
the development of definitive, quantitative information concerning the movement
in various soil types of chemicals and microorganisms, including various nitro-
gen forms, phosphate, sulfate, chloride, coliform organisms, viruses, and
organics known to be constituents of septic tank leachate. Although consider-
able information concerning the movement and fate of most of these pollutants
has been provided by many previous studies of septic tank systems, this informa-
tion has not been sufficiently definitive nor quantitative to provide a basis
for density criteria. This reflects inherent difficulties in conducting studies
of the movement and fate of pollutants in subsurface environments. Field investi-
gations have suffered because of sampling problems and difficulty in controlling
experimental conditions, while laboratory studies have usually utilized packed
columns of dried, sieved soils which bear little resemblance physically or
biologically to natural soil profiles. One investigation being conducted ,at
Texas A&M University seeks to obviate these difficulties by utilization of large
lysimeters constructed from 2.1 x 1.5 x 1.8 meter monoliths of soil which retain
the natural soil profile while permitting close control of experimental conditions
and calculation of water and pollutant balances.
23
-------
The density guidelines expected to result from the Texas A&M work should
be extremely useful, but it should be noted that they will be only first approxi-
mations based on best available information. Hence, they will undoubtedly be
revised and refined many times as new and improved information concerning the
subsurface movement and fate of various pollutants, particularly viruses and
potentially harmful organic compounds, is developed.
The movement and fate of viruses in the subsurface is of considerable
importance in regard to pollution of ground water by septic tank systems, as
well as other activities which involve introduction of wastes containing human
excretory matter into the earth's crust. Over 100 different types of human
enteric viruses have been identified, and some authorities feel that ingestion
of only one or two virus particles is sufficient to produce disease in a
suitable host (13).
Previous field and laboratory studies indicate that large numbers of
viruses may be removed from wastewaters, including septic tank effluents, by
percolation through soil. Removal is believed to result largely from adsorption
on soil particles. However, viruses are apparently not inactivated by adsorp-
tion, but may remain viable in the adsorbed state for long periods, possibly
to be released again when proper conditions for desorption develop. Research
currently under way seeks to answer important questions concerning the extent
of virus adsorption in different soils under various conditions, the longevity
of adsorbed viruses, and the conditions under which desorption occurs.
Investigations pertaining to viruses in wastewaters, including septic tank
effluent, are presently impeded by the absence of reliable, standardized analy-
tical methods for detecting and measuring low but significant levels of potentially
harmful viruses in water. Hence, several research groups are attempting to develop
methods for concentrating enteric viruses from large volumes of water in order to
significantly enhance the sensitivity of detection and quantisation of these
organisms.
The possibility that other constituents of wastewater may be utilized as
indicators for the presence of enteric viruses in subsurface waters and models
for the behavior of these organisms in subsurface environments is also receiving
attention, principally because of the difficulties inherent in handling and
analysis of the pathogenic enteric viruses themselves. The use of coliform
bacteria, which have traditionally been utilized as microbial indicators in
surface waters, appears questionable for this purpose in highly structured
subsurface environments where limited open space and sorptive forces are of
prime importance in governing pollutant behavior. Certainly, the coliforms
cannot be expected to behave analogously to the much smaller and biochemically
dissimilar enteric viruses in such environments. The most promising candidates
as indicators for enteric virus presence and behavior in subsurface work may be
bacterial viruses which commonly occur in wastewaters of domestic origin and
resemble enteric viruses in size and external chemical composition. A bacterial
virus, f2 coliphage, is being utilized as an indicator for virus movement in the
Texas A&M work mentioned above, while work being initiated in California will
examine in more detail the utility of coliphages as models for enteric virus
behavior in the subsurface.
24
-------
The movement and fate of organic pollutants in wastewaters, including septic
tank effluents, is also receiving increased attention in current research efforts.
Although previous studies have indicated that the major portion of organic matter
in septic tank effluent is readily removed by sorptive and degradative processes
as the effluent moves through soil under proper conditions, the potential pollu-
tion of ground water by these substances cannot be dismissed without further
study. There are two principal reasons for this concern. First, that small
portion of organic matter which is not readily removed during movement of the
effluent through the subsurface environment may be partly comprised of synthetic
organic chemicals which are relatively intractable to microbial degradation and
which may be hazardous to human health if ingested, even at low levels, over
long periods of time. Although synthetic organics are not usually considered
in regard to septic tank effluent, there are many household products, such as
Pharmaceuticals, disinfectants, deodorants, polishing agents, cleaning materials,
cosmetics, paint, and pesticide products, that contain such chemicals and may
be present in wastewater entering septic systems. Second, if those compounds
which are initially removed from the effluent by sorptive processes are rela-
tively intractable to degradation in the subsurface and are not irreversibly
adsorbed, they may eventually migrate chromatographically into and through an
underlying aquifer.
Research pertaining to the movement and fate of organic compounds in the
subsurface is difficult because of the large number of substances which must be
considered and the low levels which must be detected, identified, and measured
in the complex subsurface water-soil matrix. The Texas A&M project includes an
effort to identify individual organic pollutants which move through the soil in
septic system leachates and to develop information concerning their mobility and
longevity in the subsurface. Another current research effort seeks to develop
systematic and definitive information concerning the sorption of organic pollut-
ants on various soil types. Although this work is not concerned directly with
septic tank systems, it should yield information of value in assessing the
potential impact on ground water of organic pollutants from any source, including
septic systems. One goal is the development of methods for early detection of
organic pollution of ground water, using as indicators organic compounds that
are not appreciably sorbed by soils and subsoils.
Current research pertaining to the movement and fate of phosphorus in the
subsurface is also of interest in regard to the effects of septic systems on
ground water. Phosphorus in wastewaters entering the earth's crust is generally
not considered to be a potential water pollution problem because it is usually
rapidly sorbed by the soil, and, hence, exhibits essentially no mobility. How-
ever, there is evidence that phosphorus does move in the soil under some condi-
tions, and phosphorus from septic systems has been implicated in a few cases of
pollution of subsurface waters. Research currently under way is seeking to
better define the conditions under which phosphorus becomes mobilized in the
soil and to develop mathematical models describing its movement and fate in the
subsurface.
As previously noted, pollution of ground water by nitrate is a major problem
associated with septic tank systems. As shown in Figure 7, the reactions which
govern the form, and hence the mobility and ultimate fate, of nitrogen in the
soil are fairly well defined. Current research pertaining to the movement and
25
-------
fate in the subsurface of nitrogen from septic tank systems is primarily con-
cerned with manipulation of these reactions to minimize movement of nitrate into
ground water. In this connection, at least two research groups are investigating
the feasibility of achieving reduction of nitrate to elemental nitrogen in the
soil profile underneath septic tank lateral lines (14). Also under way are tests
to determine the feasibility of an ion exchanger to remove ammonia nitrogen from
septic tank effluent before it reaches the laterals. Other research efforts seek
to define the effect of soil type and environmental conditions on the fate of
nitrogen in soils receiving wastewater.
IMPROVEMENT OF CONVENTIONAL SYSTEMS
Surveys in various areas have found septic tank-soil absorption system half-
lives of 27 years in one Connecticut community and a 90 percent survival after
20 years of service in Fairfax County, Virginia (15, 16). Based on the concept
that properly designed, constructed and maintained systems operate satisfactorily
in many non-sewered areas of the country despite scientific gaps in knowledge,
there has been a resurgence of interest in recent years in a better understanding
of on-site wastewater disposal problems and in developing better design criteria.
The primary approach has concentrated on increasing understanding of the control-
ling parameters which govern the performance and effects of traditional septic
tank systems.
The reasons for system failure can be one or a combination of three factors--
improper design, improper construction, or improper maintenance. All three can be
significantly impacted through upgraded regulations for siting and design methods,
better inspection and construction (installation) procedures, and mandatory in-
spections and pumping policies. The relative value of these improved institutional
approaches is a function of the technical basis on which they are formulated and
the level of enforcement provided.
Several design factors have been identified in recent years that can improve
system performance and reliability. Larger and multi-compartmented septic tanks
can improve effluent quality by increasing scum and sludge volume accumulations
per unit volume of wastewater treated. Equalizing distribution and dosing can
increase pollutant attenuation in some soils and increase life of absorption
fields before clogging occurs (17).
A more accurate soil test for sizing soil absorption fields has been
developed by the University of Wisconsin. Although too complicated /or general
use, it could be used by the Soil Conservation Service as part of its mapping
procedure to help simplify sizing problems and to reduce the cost of designing
systems which clearly lie inside mapping units (18).
Several investigations have shown that the greatest chance of system failure
occurs within the first three years of operation and that most of these failures
are due to faulty construction (and inspection) practices. Improper use of con-
struction equipment can compact the absorption area and reduce the soil's liquid
absorption capability. This situation is further compounded during periods of
excess soil moisture. Additional problems of smearing of soil absorption faces
have been noted when rainfall or excessive silt-laden wind occurred while trenches
were open during construction (19).
26
-------
Septic tanks should be inspected periodically to determine the need for pump-
ing tank contents in order to prevent wholesale unloading of accumulated sludge
and scum which will seriously degrade the performance of the soil absorption
system. Inspection and cleaning ports of adequate size and extended to or very
close to grade would make inspections more convenient and maintenance more
practical.
Since it is widely known that old clogged soil absorption fields can recover
their absorption capacity with sufficient resting, systems designed with dual
fields for alternate use can significantly increase capacity and provide a safety
factor where lot size permits.
A new method for restoration of clogged soil fields has also been developed.
This method involves pumping of the septic tank and soil absorption trenches,
followed by application of hydrogen peroxide to the trenches at appropriate
intervals (20).
ALTERNATIVE ON-SITE DISPOSAL SYSTEMS
Despite the many successful systems currently in operation and options noted
above to increase efficiency, there are widespread areas where conventional septic
tank-soil absorption systems cannot be properly employed. Conditions which require
alternatives include the following:
1. Thin soil over creviced bedrock
2. Highly impermeable soils
3. High ground-water conditions
4. Thin soil over impermeable strata on steep slopes
On-site alternatives may include modification at the household wastewater
generation fixtures or at the distribution system, or a combination of both.
Wastewater modifications may include reduced flow from all fixtures, elimination
of certain fixture contributions from wastewaters, and recycle systems. Although
such concepts have been strongly urged by environmentalists in recent years,
there are several gaps in our present understanding of the primary and secondary
aesthetic, health, and economic effects of such measures.
In recent years, individual home aeration units have been promoted for pre-
treatment of household wastewaters in place of the conventional septic tank.
These units are capable of improved reductions in organic matter (COD, BOD, etc.)
and detergents and, in certain cases, better suspended solids removal, when
compared to septic tanks. However, effluents remain unsuitable for direct
surface discharge and additional treatment, such as a sand filter, is necessary
(21).
Several claims have been made to the effect that aerobic unit effluents
result in fewer clogging problems than septic tank effluents. Studies at the
University of Wisconsin have found this true only in coarser soils where clog-
ging is not a significant problem anyway. However, one advantage for aerobic
units is that the required sand filter area is only about 50 percent of that
required for the analogous septic tank effluent to produce a high quality final
effluent (21).
27
-------
The relatively greater costs of aerobic units and greater routine mainte-
nance required apparently preclude their wide applicability.
The use of evapotranspiration (Figure 9) for disposal of septic tank effluent
has been employed for several years. In arid regions where the evapotranspiration
(ET) potential greatly exceeds rainfall, the concept is quite viable. Unfortu-
nately, although these regions account for almost one-third of the land area of
the 48 contiguous States, they include only about 10 percent of the unsewered
housing units in the United States. Some efforts are under way at the University
of Colorado to demonstrate the feasibility of mechanical evaporation units which
would potentially expand the areas of evaporative disposal applicability.
Mound systems, typified by Figure 10, have been successful for at least two
of the difficult soil conditions previously cited; i.e., thin soils over creviced
bedrock and high ground-water conditions. In the former case, the mound accom-
plishes most of the required treatment of the septic tank effluent prior to its
introduction to the natural soil, thereby protecting the ground water. In the
latter case, a similar treatment justification exists because of the known travel
of pollutants under saturated flow (ground water) conditions. In this circumstance,
the mound merely lifts the disposal system above the saturated zone during high
ground-water periods to insure the protection afforded by a sufficiently thick
zone of unsaturated flow. These mounds have also been applied with some success
over slowly permeable soils normally considered unsuitable for on-site soil
absorption systems.
Annual costs per household are compared in Figure 11 for several septic tank
system modifications and a conventional sewer system based on a population density
of five persons per acre (22, 23). Obviously, conventional sewer costs flucuate
greatly with population density while the other alternatives are relatively
unaffected.
28
-------
VEGETATION
Figure 9. Evapotranspiration bed.
EVAPOTR A NSPI RATION
TOPSOIL
Sxp:::!:^
;;p^ip^^
I
CREVICED BEDROCK
Figure 10. Mound over creviced bedrock.
29
-------
CONVENTIONAL
SEPTIC TANK
SOIL ABSORPTION
SYSTEM
ALTERNATING
LATERALS
MOUNDS SEPTIC TANK
EVAPOTRANSPIRATION
CONVENTIONAL
SEWERS
GO
O
0 ,0
o
ID
ID
CJ
01
*+.
O
or
u.
0
IT
0
O
a
•sj
o
0
o
*
cc
U-
o
o
o
a.
LJ
o:
? ^
CJ ^-
UJ U
3: <
^ X.
o z
1/1 OT
(T *"
D. UJ
a.
r>I "°
Figure 11. Total annual costs of alternatives.
-------
SECTION 8
FUTURE TRENDS AND RECOMMENDATIONS
Continued migration to suburban areas is expected to stress State, county,
and municipal governments in terms of regulations and providing those services
required by the people. These services include water supplies, schools, trans-
portation facilities, fire protection, and the collection and disposal of liquid
and solid wastes.
In many cases, it will not be immediately feasible to connect these suburban
developments to existing waste treatment facilities which were designed to serve
the central city. Considerable costs arise in expanding intercepter sewers ex-
tended distances. Unfavorable differences in elevation often accentuate the
complexities and costs of such extensions. Expanding existing treatment facilities
to meet these additional demands also contributes excessive costs.
This urban sprawl results in the extensive use of individual sewage treat-
ment units on relatively small lots which constitutes a high density and the
possibility of ground-water contamination. Even after this critical density is
reached, there is considerable resistance by residents to approve large expendi-
tures for conversion to central sewage collection and treatment.
The best approach to limiting future problems is better governmental control
and planning. Zoning and land use planning in areas where septic tanks will be
required should be based on a thorough understanding of soil variability, geol-
ogy, topography, aquifer characteristics, vegetation, and climate. This infor-
mation would serve to establish limitations on the construction of housing units
and the corresponding density of individual treatment facilities in areas which
have not yet reached critical densities. As areas reach critical septic tank
densities, further residential development would require the use of alternate
methods of sewage disposal. Areas which already exceed critical densities could
be individually evaluated to determine what corrective measures might be taken.
Research is needed to develop the tools that can be used in decision making
related to septic tank feasibility and density. This includes studies concern-
ing the time of survival of microorganisms in soil and ground water and the
transport characteristics of organics in this media.
Additional work is required to develop more effective sewage disposal sys-
tems to replace septic tanks in rural and fringe urban areas. That research is
needed on sludge disposal from septic systems is evidenced by the lack of
information on the subject.
31
-------
The basic design and operation of individual treatment units requires addi-
tional study, particularly from the standpoint of avoiding failure. Improved
permeability tests, cleaning frequency, and dual lateral systems require
particular emphasis.
The social and economic consequences of converting from individual units to
sewered and central treatment facilities must be studied with consideration of
the resultant loss of ground-water recharge.
32
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SECTION 6
REFERENCES
1. U.S. Environmental Protection Agency. Waste Disposal Practices and
Their Effects on Ground Water. Report to Congress, December 1975.
525 pp.
2. Patterson, J. W., R. A. Minear, and T. K. Nedved. Septic Tanks and the
Environment. National Technical Information Service, Springfield, VA.
PB-204 519.
3. Cotteral, Joseph A., Jr., and Dan P. Norris. Septic Tank Systems.
J. Sanit. Eng. Div., ASCE, 95(SA4):715-746, 1969.
4. Plews, G. D. The Adequacy and Uniformity of Regulations for Onsite
Wastewater Disposal--A State Viewpoint. In: Proceedings of 2nd National
Conference on Individual Onsite Wastewater Systems, Ann Arbor, MI,
November 1975.
5. Miller, John C., Paul S. Hackenberry, and Frank A. DeLuca. Ground-Water
Pollution Problems in the Southeastern United States. EPA-600/3-77-012,
U.S. Environmental Protection Agency, Ada, Oklahoma, 1977. 379 pp.
6. Miller, David W., Frank A. DeLuca, and Thomas L. Tessier. Ground Water
Contamination in the Northeast States. EPA-660/2-74-056, U.S. Environ-
mental Protection Agency, Washington, D.C., 1974. 338 pp.
7. Miller, David W., and Marion R. Scalf. New Priorities for Ground-Water
Quality Protection. In: Proceedings of Second National Ground Water
Quality Symposium, Denver, CO, September 1974. pp. 7-19.
8. Gerba, Charles P., Craig Wallis, and Joseph L. Mclnick. Fate of Waste-
water Bacteria and Viruses in Soil. J. Irrig. & Drainage Div., ASCE,
101(IR3):157-174, 1975.
9. Kreissl, J. F. Rural Wastewater Research. In: Proceedings of 2nd
National Conference on Individual Onsite Wastewater Systems, Ann Arbor,
MI, November 1975.
10. Kreissl, J. F. Internal Memorandum on Septage Analysis. February 1976.
11. Keeney, D. R., K. W. Lee, and L. M. Walsh. Guidelines for the Applica-
tion of Wastewater Sludge to Agricultural Land in Wisconsin. Wisconsin
DNR, Technical Bulletin No. 88. 1975.
33
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12. Jewell, W. J., J. B. Howley, and D. R. Perrin. Design Guidelines for
Septic Tank Sludge Treatment and Disposal. 7th International Conference
on Water Pollution Research, Paris, France. September 1974.
13. Malina, Joseph F., Jr., and Bernard Phillip Sagik, Editors. Virus Survival
in Water and Wastewater Systems. Water Resources Symposium No. 7. The
University of Texas at Austin, 1974. 264 pp.
14. Andreoli, Aldo, Suffolk County Department of Health, New York. Private
communication. 1977.
15. Hill, D. E., and C. R. Frink. Longevity of Septic Systems in Connecticut
Soils. Connecticut Agricultural Experiment Station, Bulletin 747. June
1974.
16. Clayton, J. W. An Analysis of Septic Tank Survival Data in Fairfax County,
Virginia: 1952-1972. Ground Water, ll(3):29-32, May-June 1973.
17. Converse, J. C., J. L. Anderson, W. A. Ziebell, and J. Bouma. Pressure
Distribution to Improve Soil Absorption Systems. In: Proceedings of the
National Home Sewage Disposal Symposium, ASAE Publication No. PROC-175.
1975.
18. Bouma, J. Evaluation of the Field Percolation Test and an Alternative
Procedure to Test Soil Potential for Disposal of Septic Tank Effluent.
J. Soil Science Society of America Proceedings, 35:871, 1971.
19. Otis, R. J., and J. Bouma. Notes on Soil Absorption Field Construction
for Septic Tank Systems. University of Wisconsin Small Scale Waste
Management Project Technical Note. 1973.
20. Harkin, J. M., M. D. Jawson, and F- G. Baker. Causes and Remedy of Failure
of Septic Tank Seepage Systems. In: Proceedings of 2nd National Conference
on Individual Onsite Wastewater Systems, Ann Arbor, MI, November 1975.
21. Otis. R. J., W. C. Boyle, J. C. Converse, and E. J. Tyler. On-Site Disposal
of Small Wastewater Flows. Prepared for U.S. EPA, Technology Transfer
Seminars on Small Wastewater Treatment Systems. March 1977.
22. Kreissl, J. F. U.S. EPA Response to PL 92-500 Relating to Rural Waste-
water Problems. In: Individual Onsite Wastewater Systems, Ann Arbor
Science, Ann Arbor, MI, 1977.
23. Dearth, K., U.S. EPA, OWPO. Personal communication relating to analysis
of 258 facilities plans from 49 states. 1976.
34
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-77-Oq6
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
"ENVIRONMENTAL EFFECTS OF SEPTIC TANK SYSTEMS"
5. REPORT DATE
August 1977
issu ing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Marion R. Scalf and William J. Dunlap - RSKERL, Ada, OK
James F. Kreissl - MERL, Cincinnati, OH
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Robert S. Kerr Environmental Research Laboratory
Office of Research & Development
U.S. Environmental Protection Agency
Ada, Oklahoma 74820
10. PROGRAM ELEMENT NO.
1BA609
11. CONTRACT/GRANT NO.
N/A
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above.
13. TYPE OF REPORT AND PERIOD COVERED
In-House
1976-1977
14. SPONSORING AGENCY CODE
EPA/600/15
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Septic tank-soil absorption systems are the most widely-used method
of on-site domestic waste disposal. Almost one-third of the United States
population depends on such systems. Although the percentage of newly
constructed homes utilizing septic tanks is decreasing, the total number
continues to increase.
Properly designed, constructed, and operated septic tank systems
have demonstrated an efficient and economical alternative to public sewer
systems, particularly in rural and sparsely developed suburban areas.
However, because of their widespread use in unsuitable situations, they
have also demonstrated the potential for contamination of ground and
surface waters.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COS AT I Field/Group
Septic Tanks
Waste Disposal
Water Pollution
Substitutes
Soil Treatment
Septage Disposa'
Research Needs
13/B
13. DISTRIBUTION STATEMENT
Release to Public.
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
43
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
35
U S. GOVERNMENT PRINTING OFFICE 1977-757-056/6526 Region No. 5-1
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