U.S. DEPARTMENT  OF HEALTH, EDUCATION, AND WELFARE
                   Public Health Service
     Consumer Protection and Environmental Health Service
             Environmental Control Administration

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                    Safety Considerations

  It is particularly important that proper safety  precautions be taken
when percolation holes or larger'excavations are dug to install septic
tanks or seepage pits. Means should be provided to prevent the side-
walls from  collapsing while workmen are in the  hole.  A common
method of affording proper protection to  the workmen is through the
use of sheeting formed by semicircular sections  of  corrugated  metal,
braced with semicircular compression rods which  are bolted  on the
inside with  expansion bolts. In another type of  seepage pit construc-
tion,  the walls are made of precast reinforced concrete sections with
slotted holes.  For  deep seepage pits, or where there  is any danger  of
caving, the sections are installed as the excavation progresses, and are
used  TLS  the necessary protective sheeting.  During  non-work  periods
holes should be covered with boards that  cannot  be easily  removed  or
the hole should  be surrounded with a  fence that  cannot  be easily
entered. Any open hole is dangerous and  should be filled in  when the
work is  completed.  Fatal  accidents have occurred  when  these basic
safety measures have not been  observed.

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  Manual  of
    SEPTIC - TANK
                  PRACTICE
 ^S   /  J  '  C    ' r    •//  //
<=~Lseveiepefi  m \^^&ope'cAlton with,  Ike

  l&int (^ontHtittee on  v^ata-l
  U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
         PUBLIC HEALTH SERVICE
         Consumer Protection and Environmental Health Service
         Environmental Control Administration
         Rockvifle, Maryland 20852

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              Public Health  Service Publication No. 526

                          First Printed  1957
                            Reprinted 1963
                             Revised 1967
                            Reprinted  1969
For sale by  the  Superintendent of Documents, U.S.  Government Printing Office
                     Washington, D.C. 20201 - 35 cents

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Foreword
  In  the preparation of this manual,  the  Public  Health Service was
fortunate in having the advisory assistance  of the Joint Committee on
Rural Sanitation. This committee  is composed of specialists from gov-
ernmental  and other agencies in  the field of rural sanitation. Their
comments  and suggestions based on the long experience of the mem-
bers were invaluable in the preparation of  the manual. The following
individuals and  organizations  constitute  the  current  Committee
membership:
U.S. DEPARTMENT OF AGRICULTURE:
    Agricultural Research Service
        Harry J. Eby, Agricultural Engineer, Agricultural Engineering
        Research  Branch.
    Farmers' Home Administration
        Earl R. Bell, Agricultural Engineer.
    Federal Extension Service
        W. T.  Cox, Agricultural  Engineer.
    Forest Service
        H. A. Smallwood, Division of Engineering, Consultation, and
        Standards.
    Soil Conservation  Service
        William G. Shannon,  Chief, Water Supply Forecasting Branch,
        Engineering Division.
AMERICAN  PUBLIC  HEALTH ASSOCIATION:
    Professor  John E.  Kiker, Jr., College of Engineering, University of
    Florida.
U.S. COAST GUARD:
    Captain James H. Le Van, Chief Sanitary Engineer Officer.
CONFERENCE OF MUNICIPAL PUBLIC HEALTH ENGINEERS:
    William H. Gary, Jr., Associate Director for Environmental Health,
    D.C. Department  of  Public Health.
FEDERAL HOUSING  ADMINISTRATION:
    William  K. Rodman, Special Assistant for  the Technical  Studies
     Program.
FEDERATION OF  SEWAGE AND  INDUSTRIAL WASTES ASSOCIATIONS:
     David B. Lee, Director, Bureau of Sanitary Engineering,  Florida
     State Board of Health.

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U.S. DEPARTMENT OF  HEALTH, EDUCATION, AND WELFARE:
    Office of Education
        John L. Cameron, Acting Director,  Division of Facilities De-
        velopment.
    Public Health Service
        Malcolm C. Hope, Sanitary Engineer Director.
        Joseph P. Schock, Public Health Engineer.
U.S. DEPARTMENT OF THE INTERIOR:
    U.S. Geological Survey
        Clyde S. Conover, District Chief, Water Resources Division.
TENNESSEE VALLEY AUTHORITY:
    F. E. Gartrell, Assistant Director of Health.
VETERANS HOUSING ADMINISTRATION:
    D. J.  Guthridge, Construction and Valuation  Specialist.
INDUSTRY ADVISORS:
    John  G. Hendrickson, Jr., Portland Cement Association.
    James J. Spear, Spear Water and Sewerage Supplies

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Preface
  Population movement within the United States continues to be from
rural to metropolitan areas. Because of the difficulty of providing ade-
quate sewerage systems for this new growth, individual septic tank - soil
absorption systems continue to be  an important method of sewage
disposal where they are acceptable. Accurate figures are not available,
but it is estimated that at  present 49 million persons are served  by  15
million individual sewage-disposal systems in the United States. Of even
more importance,  roughly  one-fourth of the new homes are being con-
structed with these systems.
  In  1946, the  Public Health  Service, in  cooperation with  Federal
agencies concerned with housing,  undertook a  5-year study on  septic
tank — soil absorption systems, seeking to develop a factual basis on which
they could be designed, installed and maintained. These  studies are
described  in  detail in three technical  reports:  Studies on  Household
Sewage Disposal Systems, Parts I, II, and III.
  Subsequent studies on septic tanks and soil absorption systems have
been conducted by the Public Health Service, Federal Housing Admin-
istration, Universities and  other organizations.
  This manual is a revision of PHS Publication No. 526,  Manual o/
Septic Tank Practice,  issued  in  1957, and reprinted  in  1963  with
Addendums on "Serial Distribution Systems" and "Seepage Beds." The
updating reflects changing  trends in  the problems of individual sewage
disposal systems and includes new information in this field.
  The decision  on the suitability of septic-tank installations must  be
based on  many factors outside  of those covered in the manual. It is
emphasized, however, that connection to an adequate public sewerage
system is  the most satisfactory method of disposing of sewage.  Every
effort  should be  made, therefore,  to  secure public-sewer extensions.
Where  connection to a public sewer is not feasible, and when a con-
siderable number of residences are  to  be served,  consideration should
be given next to the construction of a community sewerage system and
treatment plant. Specific information on this matter should be obtained
from the  local authority having jurisdiction.
  Individuals proposing to construct individual sewage-disposal systems
should consult the officials  having jurisdiction over such installations in
their area. A number of States and  localities have developed require-
ments which have been incorporated  in their official regulations, in
many cases soundly based on conditions peculiar to those areas and

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adequately representing good  practice there.  The recommendations
contained in this manual should be considered as supplemental to such
local  requirements.  Builders, homeowners, and others  interested in
septic-tank systems should seek advance guidance from the local authori-
ties prior to  land acquisition,  in  order to  have the benefits of their
experience as well as their approval of plans and construction.

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Contents
PART I. SEPTIC TANK - SOIL ABSORPTION SYSTEMS FOR PRIVATE RESIDENCES
                                                             Page
Introduction  	      1
Definitions 	      2
Suitability of Soil 	      3
Percolation Tests 	      4
    Procedure for Percolation Tests Developed at Robert A.
      Taft Sanitary Engineering Center 	      4
Soil Absorption System 	      8
    Absorption Trenches 	     10
        Construction Considerations	     12
    Seepage Beds 	     14
        Construction Considerations  	     15
    Distribution Boxes 	     16
    Serial Distribution 	     16
        Fields in Flat Areas 	     17
        Fields in Sloping Ground	     17
    Deep Absorption Trenches and Seepage Beds 	     20
    Seepage  Pits 	     20
        Sample Calculations 	     23
        Construction Considerations 	     26
Selection of a Septic Tank	    26
    Functions of Septic Tanks 	     26
        Removal of Solids 	    27
        Biological  Treatment	    27
         Sludge and Scum Storage  	    27
         Location 	    27
         Effluent 	    29
         Capacity	    29
     Specifications for Septic Tanks 	    29
         Materials  	    29
         General  	    30
         Inlet  	    30
         Outlet 	    30
         Tank Proportions	    32
         Storage Above Liquid  Level  	    33
         Use of Compartments 	    34

                                                                 vii

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    General Information on  Septic Tanks	    35
        Cleaning 	    35
        Grease Interceptors  	    38
        Chemicals	    38
        Miscellaneous 	    38
    Inspection 	    39
PART  II. SEPTIC TANK-SOIL  ABSORPTION SYSTEMS FOR  INSTITUTIONS,
RECREATIONAL AREAS, AND OTHER ESTABLISHMENTS
Introduction 	     41
Estimates of Sewage  Quantities 	     42
Estimates of Soil Absorption Areas 	     45
Building Sewers  	     48
Collection  Systems 	     49
Grease Traps 	     50
    Location  	     50
    Construction Details 	     51
    Capacity  	     52
    Operation 	     53
Septic Tanks for Institutional Systems 	     53
    Capacities 	     54
Dosing Tanks	     55
Sand-Filter  Trenches 	     56
    Construction Features 	     60
Subsurface Sand Filters 	     62
    Construction Features 	     62
Superficial Sand Filters 	     64
Chlorination 	     66
                            APPENDICES
Introduction to Appendices 	    71
A.   Soil Absorption Capacity 	    72
     Guide  for Estimating Soil  Absorption Potential 	    72
         Soil Maps 	    72
         Clues to Absorption  Capacity  	    72
         Texture 	    72
         Structure  	    73
         Color 	    73
         Depth or Thickness  of Permeable Strata 	    73
         Swelling Characteristics 	    73
     Evapotranspiration  	    74
     Curtain Drains for  Absorption Trench Systems 	    74

 viii

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    Percolation Test Holes  	    75
    Other Percolation Tests 	    75
B.  Suggested Ordinance  	    77
C.  Engineering Information Forms 	    81
D.  Drainage Fixture Unit Values 	    85
E.  Suggested Specifications  for Watertight Concrete 	    86
F.  Industrial Waste Treatment 	    88
BIBLIOGRAPHY  	    91
                                                                 ix

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                   Parti
                       Septic  Tank - Soil Absorption
                       Systems for Private Residences
            INTRODUCTION
  A  major factor influencing the health of individuals where  public
sewers are not available is the proper disposal of human excreta. Many
diseases,  such as dysentery,  infectious  hepatitis,  typhoid and para-
typhoid, and various types of diarrhea are transmitted from one person
to another through the fecal contamination of food and water,  largely
due  to the improper disposal of human wastes. For  this reason, every
effort should be made to prevent such  hazards and to dispose of all
human waste so that no opportunity will exist for  contamination  of
water or food.
  Safe disposal of all human and domestic wastes is necessary to protect
the health of the individual family and the community and to prevent
the occurrence of nuisances. To accomplish satisfactory results,  such
wastes must be disposed of so that:
  I.  They will not contaminate any drinking water supply.
  2.  They will not give rise to a public health hazard by being acces-
sible to insects, rodents, or other possible carriers which may come into
contact with food or drinking water.
  3.  They will not give rise to a public health hazard by being acces-
sible to children.
  4.  They will not violate laws or regulations  governing water pollu-
tion  or sewage disposal.
  5.  They will not pollute or contaminate the waters of any bathing
beach, shellfish breeding ground, or stream used for public or domestic
water supply purposes, or for recreational purposes.
  6.  They will not give  rise to a  nuisance  due to odor or  unsightly
appearance.
  These  criteria can best be met by the discharge of domestic sewage
to an adequate public or  community sewerage system. Where the instal-

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lation  of an  individual household sewage disposal system is necessary,
the basic  principles outlined  in  this manual on  design, construction,
installation, and maintenance should be followed. When these criteria
are met, and where soil and  site conditions  are  favorable, the  septic
tank system can be expected to give satisfactory service. Experience has
shown  that  adequate  supervision,  inspection and  maintenance  of
all features of the system are required to insure compliance in  this
respect. Underground portions of the system should be inspected before
being covered, so necessary  corrections can be made.

DEFINITIONS
   Absorption Trench—A trench not over 36" in width with a minimum
of 12" of  clean, coarse aggregate and a distribution pipe, and covered
with a minimum of 12" of  earth cover.
  Standard Absorption Trench—A  trench  12" to 36"  in width con-
taining 12" of clean, coarse aggregate and a distribution pipe, covered
with a minimum of 12" of  earth cover.
  Building Drain—That part  of the lowest piping of a drainage system
which  receives the discharge from soil, waste, and  other  drainage pipes
inside  the walls of the building and conveys it to the building sewer
beginning three feet outside the building wall.
   Building Sewer—That part of a drainage system which extends from
the end of the building drain  and conveys its discharge to a public
sewer,  private sewer, individual sewage disposal system  or other point
of disposal.
   Cesspool—A lined and covered excavation  in the ground which re-
ceives  the discharge of domestic sewage or other organic wastes from a
drainage system, so designed as to retain the organic matter and solids,
but permitting the liquids to seep  through the bottom  and sides.
   Drainage Fixture Unit Value—A common  measure of the probable
discharge  into a drainage system by  various types of plumbing fixtures.
This value for a particular fixture depends on its volume rate of  drain-
age discharge, on the time duration  of a single drainage  operation, and
on the average time between successive operations.
   Effective Size—That size of sand of which 10%  by weight is smaller.
   Individual Sewage Disposal System—A single system of sewage treat-
ment tanks and disposal facilities serving only a single lot.
   Sand Filter Trenches—A system of trenches, consisting of perforated
pipe or drain tile surrounded by clean, coarse aggregate containing an
intermediate layer of sand  as filtering material and provided with an
underdrain for carrying off the filtered sewage.
   Scum—A mass of sewage matter which floats on  the surface of sewage.
   Scum Clear Space—Distance  between the bottom of the scum  mat
and the bottom of the outlet  device.
   Seepage Bed—A trench or bed exceeding 36" in  width  containing 12"

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a minimum of clean, coarse aggregate and a system of distribution pip-
ing through which treated sewage may seep into the surrounding soil.
  Seepage Pit—A covered pit with lining designed  to permit treated
sewage to seep into the surrounding soil.
  Septic  Tank—A water-tight,  covered receptacle designed and con-
structed to receive  the discharge of sewage from a  building sewer, sep-
arate solids from the liquid, digest organic matter and store digested
solids through a period of detention, and allow the clarified liquids to
discharge for final  disposal.
  Serial Distribution—An arrangement of absorption trenches, seepage
pits, or seepage beds so that each  is forced to pond to utilize the total
effective  absorption  area  before  liquid  flows  into  the succeeding
component.
  Sewage—Any liquid waste containing animal or vegetable matter in
suspension or solution, and may include liquids containing chemicals
in solution.
  Sludge—The accumulated settled solids deposited from sewage and
containing more or less water to form a semi-liquid mass.
  Sludge Clear Space—The distance between the top of the sludge and
the bottom of the outlet device.
  Soil Absorption Field—A system of absorption trenches.
  Soil Absorption System—Any system that utilizes  the soil for subse-
quent absorption of the treated sewage; such as  an absorption  trench,
seepage bed, or a seepage  pit.
  Subsurface Sand Filters—A wide bed, consisting of a number of lines
of perforated pipe  or drain tile surrounded by clean coarse aggregate,
containing an  intermediate layer  of  sand as filtering material, and
provided with a system  of underdrains for  carrying  off the filtered
sewage.
  Subsurface Sewage Disposal System—A system for the treatment and
disposal of domestic sewage by means of a septic tank and a soil absorp-
tion system.
  Uniformity Coefficient—A coefficient obtained by  dividing that size
of sand of which 60% by weight is smaller,  by that  size of sand of
which 10% by weight is  smaller.

SUITABILITY OF SOIL
  The first step in the design of subsurface sewage disposal systems is
to determine whether the soil is suitable for the absorption of septic
tank effluent and, if so, how much area is required. The soil must have
an acceptable percolation rate, without interference from ground water
or impervious strata below the  level of the absorption system. In gen-
eral, two conditions must  be met:
  (1) The percolation time should be within  the range of those speci-
fied in Table 1, p.  8.

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  (2) The maximum seasonal  elevation  of  the ground water  table
should be at least  4-feet below the bottom of the trench or seepage
pit. Rock formulations or other impervious strata should be at a depth
greater than 4-feet below the bottom of trench or seepage pit.
  Unless these conditions can be  satisfied,  the site is unsuitable  for a
conventional subsurface  sewage  disposal system.
PERCOLATION TESTS
  Subsurface explorations are necessary to determine subsurface forma-
tions in a given area. An auger  with an extension handle, as shown in
Figure 1 (p.  5), is  often used  for making the  investigation. In  some
cases, an examination of road cuts, stream embankments, or building
excavations  will give useful  information. Wells  and well drillers' logs
can also be used to obtain information on ground water and subsurface
conditions. In some areas, subsoil  strata vary widely in short distances,
and  borings must be made at the site of the system. If the subsoil ap-
pears suitable, as judged by other characteristics described in Appen-
dix A, percolation tests should be made at points  and elevations selected
as typical of the area in which  the disposal field will be located.
  The percolation  tests  help to determine  the acceptability of the site
and  establish the design size of  the subsurface  disposal system.  The
length of time required for percolation tests will vary  in different types
of soil.  The  safest  method is to make  tests in holes which have been
kept  filled with water for at least 4 hours, preferably overnight. This
is particularly desirable if the tests are to be made by  an inexperienced
person, and in some soils it is necessary even if the individual has had
considerable  experience  (as in soils which swell upon wetting). Percola-
tion rates should be figured on the basis of the test data obtained after
the soil has  had opportunity to become wetted  or saturated  and has
had  opportunity to swell for at least 24 hours. Enough tests should be
made in separate holes to assure that  the results are valid.
  The percolation  test developed  at the Robert  A. Taft Sanitary Engi-
neering Center incorporates  these  principles.  Its use  is particularly
recommended when knowledge  of soil types and soil structure is lim-
ited.  When previous experience and information on soil characteristics
are available, some persons  prefer other percolation  test procedures,
such  as those developed by  Kiker and by  Ludwig which are cited in
Appendix A.
Procedure for Percolation Tests  Developed at Robert  A. Taft Sanitary
Engineering Center
  1.  Number and  location of tests.—Six or more tests shall be  made in
separate test holes spaced uniformly over the proposed absorption field
site.
  2. Type of test hole.—Dig or bore a hole, with horizontal dimensions
of from 4 to 12 inches and vertical sides to the  depth of the proposed
absorption trench.  In order  to  save time, labor, and volume of  water

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Figure  1.—Auger  and  extension  handle  for  making  test  borings.

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required per test, the holes can be bored with a 4 inch  auger. (See
Fig. 2, page 7.)
  3. Preparation  of  test  hole.—Carefully scratch the  bottom and sides
of the hole with a knife blade or sharp-pointed instrument, in order
to remove any smeared soil surfaces and to provide a  natural soil inter-
face into which water may  percolate. Remove all loose material  from
the hole.  Add  2 inches  of  coarse  sand  or fine  gravel to  protect the
bottom from scouring and sediment.
   4.  Saturation  and swelling of the soil,—It is important to distin-
guish between saturation and swelling. Saturation means that the void
spaces between  soil particles are full of water. This can be accomplished
in a short period of  time. Swelling is caused by intrusion of water into
the individual  soil particle.  This is a slow process, especially in clay-
type soil,  and is  the reason for requiring a prolonged  soaking  period.
  In  the conduct of the  test, carefully fill the hole with clear water to
a minimum depth of 12 inches over the gravel. In most  soils, it is neces-
sary to refill the hole by supplying a surplus reservoir of water, possibly
by means  of an automatic syphon, to keep water in the  hole for  at least
4 hours and preferably  overnight. Determine the  percolation  rate 24
hours after water is first  added to the hole.  This  procedure  is to insure
that the soil is given ample  opportunity to swell and to approach the
condition it will  be in during the wettest season  of the year. Thus, the
test will give comparable results in the  same soil, whether made in a
dry or in  a wet season. In sandy soils containing little or no clay, the
swelling procedure is  not essential, and the  test may  be made as de-
scribed under item 5C, after the water from one filling of the hole has
completely seeped away.
  5. Percolation-rate measurement.—With the exception of sandy soils,
percolation-rate measurements shall be made  on the  day following the
procedure described under item  4, above.
  A.  If water remains in the test hole after the  overnight swelling pe-
riod,  adjust the depth to approximately 6 inches over the gravel. From
a fixed reference point, measure the drop in water level over a  30 min-
ute period.  This drop is used  to calculate the percolation rate.
  B,  If no water remains in the hole after the overnight swelling pe-
riod,  add clear water to bring the depth of water in the hole to approxi-
mately 6 inches over the gravel. From a  fixed reference point, measure
the drop  in water level at  approximately 30 minute intervals  for 4
hours, refilling 6 inches  over  the  gravel as necessary.  The drop that
occurs during the final 30 minute period is used  to calculate the perco-
lation rate. The drops during prior periods provide  information for
possible modification of  the  procedure to suit local circumstances.
  C.  In sandy  soils  (or other soils in which the  first 6 inches of water
seeps away in less than 30 minutes, after  the overnight swelling period),
the time interval between measurements shall be taken as 10 minutes
and the test run for one hour. The drop that occurs during the final
10 minutes is used to calculate  the percolation  rate.

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                  WHEN MAKING PERCOLATION
                  TESTS MARK  LINES HERE AT
                  REGULAR TIME INTERVALS
WHEN MAKING PERCOLATION
TESTS  MARK LINES  HERE AT
REGULAR TIME INTERVALS
MEASURING STICK
                                                                           MEASURING STICK
                                                                          GUIDE LINE!

                                                                           BARER  BOARD
                                                                           OR OTHER FIXED
                                                                           REFERENCE POINT
           rx2"  BATTER BOARD
                             KEEP MEASURING
                             STICK WITHIN
                             GUIDE LINES ON
                             BATTER  BOARD
                             jWHEN EACH
                             [READING is
                             TAKEN
                   T*
            WATER SURFACE
    LEAVE BATTER BOARD IN PLACE
    BE CAREFUL NOT TO MOVE IT
    DURING TEST.
                     Figure 2.—Methods  of making  percolation tests.

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          Table 1.—Absorption-area requirements for individual residences (a)

      [Provides for garbage grinder and  automatic clothes washing machines]
Percolation rate (time
required for water to
fall one inch,
in minutes)
1 or less
2
3
4
5 	

Required absorp-
tion area, in
sq. ft. per
bedroom (b),
standard trench
(c), seepage beds
(c), and seepage
pits (d)
70
85
100
115
125

Percolation rate (time
required for water to
fall one inch,
in minutes)
10
15
30 (e)
45 (e)
60 (e), (f) 	

Required absorp-
tion area in sq. ft.
per bedroom (b),
standard trench
(c), and seepage
beds (c), and
seepage pits (d)
165
190
250
300
330

  (a) It is desirable to provide sufficient land area for entire new absorption system
if needed in future.1
  (b) In every case sufficient land area should be provided  for the number of bed-
rooms  (minimum of 2)  that can be reasonably anticipated, including the unfinished
space available  for conversion as additional  bedrooms.
  (c) Absorption area is figured as  trench-bottom area and  includes a  statistical  al-
lowance  for vertical side wall area.
  (d) Absorption area  for seepage pits is figured as  effective side wall  area beneath
the inlet.
  (e) Unsuitable for seepage pits if over thirty.
  (f) Unsuitable for absorption systems if over sixty.
  1 Section 5.1(b) (2) (A) Page 20 of Recommended State Legislation and Regulations:
Urban Water Supply and Sewerage Systems Act and Regulations, Water Well Con-
struction and Pump Installation Act and Regulations, Individual Sewerage Disposal
Systems Act and Regulations.  U.S.D.H.E.W., Public Health  Service, July 1965.
SOIL ABSORPTION SYSTEM
   For areas  where  the percolation  rates and  soil  characteristics  are
good, the  next step after making the percolation tests  is to  determine
the  required  absorption area from Table  1  or Figure 3 (page 9), and
to select  the soil  absorption system that will be  satisfactory for  the
area in question.  As noted  in  Table 1, soil  in which  the percolation
rate is slower than 1 inch in 30 minutes is unsuitable for  seepage pits,
and that  slower than 1 inch in 60 minutes  is  unsuitable  for any type
of soil absorption system.

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   350
   300
    250
    200
    150
    100
     50
                  7
                            >r
                 10        20        30        40        50
                    PERCOLATION RATE IN MINUTES PER INCH
          Figure 3.—Absorption area requirements for private residences.
  When a soil absorption system is  determined  to  be useable,  three
types of design may be considered: Absorption  trenches, seepage beds.
and  seepage  pits. A modification of the standard absorption trench is
discussed on  page 20 giving credit for more than the standard 12 inches
of gravel depth in the trench.
  The selection  of the absorption  system  will be dependent to some
extent on the  location of the  system in the area  under consideration.
A safe distance should be maintained between the site and any source
of water supply. Since the distance that pollution will  travel under-
ground depends upon numerous factors, including the characteristics
of the subsoil  formations and  the  quantity of  sewage discharged,  no
specified distance would be absolutely safe in  all localities. Ordinarily,
of course, the  greater  the distance, the  greater will be the safety pro-
vided. In general, location of components  of sewage disposal  systems
should be as  shown in  the following table.

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     Table 2.—Minimum distance between components of sewage disposal system
Component
of
System
Building sewer 	
Septic tank 	
Disposal field and
Seepage Bed
Seepage Pit
Cesspool (b)

Horizontal Distance (feet)
Well or
suction
line
50
50
100
100
150
Water
supply
line
(pressure)
10 (a)
10
25
50
50
Stream
50
50
50
50
50
Dwelling
5
20
20
20
Property
line
10
5
10
15
  (a) Where the water  supply line must cross the sewer line, the bottom of the
water service within 10 feet of the point of  crossing, shall be at least  12 inches
above the top of the sewer line. The sewer line shall be of cast iron with  leaded or
mechanical joints at least 10 feet on either side of the crossing.
  (b) Not recommended as a substitute  for a septic  tank.  To be used only when
found necessary and approved by the health authority.

  Seepage pits should not be used  in areas where domestic water  sup-
plies  are obtained  from  shallow wells,  or  where  there are limestone
formations  and  sinkholes with  connection  to underground  channels
through which pollution  may travel to water sources.
    Details pertaining to local water wells, such as depth, type of  con-
struction,  vertical zone  of influence, etc., together  with data on  the
geological formations and porosity of  subsoil strata, should be consid-
ered in determining the safe allowable distance between wells  and  sub-
surface disposal  systems.

Absorption Trenches
  A soil absorption field consists of a field of 12 inch lengths of 4 inch
agricultural  drain tile, 2  to 3 foot  lengths of vitrified clay sewer pipe,
or perforated, nonmetallic pipe. In areas having unusual soil  or water
characteristics, local  experience should be  reviewed before  selecting
piping materials. The individual laterals preferably should not be  over
100 feet long, and the trench bottom and tile distribution lines should
be  level.  Use of  more and shorter  laterals is preferred because if some-
thing  should happen to disturb  one line, most of  the field will still be
serviceable.  From a theoretical  moisture flow viewpoint, a spacing of
twice the depth  of gravel would  prevent taxing the percolative capacity
of the adjacent  soil.
  Many different designs may be used in laying out subsurface disposal
fields. The choice may depend on the size and shape of the  available
 10

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disposal area, the capacity required, and the topography of the disposal
area.
  Typical layouts of absorption  trenches  are shown in  Figures  4,  6,
pages 11, and 17.
  To provide the minimum required gravel depth and earth cover, the
depth  of the absorption  trenches should be at  least 24  inches. Addi-
tional  depth may be needed for contour  adjustment, extra aggregate
under  the tile, or other design  purposes. The maintenance of a 4 feet
separation between  the bottom of the trench and the water table  is
required  to minimize ground water contamination. In considering the
depth of  the absorption field trenches, the  possibility of tile lines freez-
ing during prolonged cold period is raised. Freezing rarely occurs in a
carefully  constructed system  kept in continuous operation. It is impor-
tant during construction to assure that the tile lines are surrounded by
gravel.  Pipes under  driveways  or other  surfaces  which are  usually
cleared  of snow should  be insulated.


                •r-4" DRAIN TILE       / /


         ^^  mm^^^^^m ^^p^^^^^H •M^^^MMI r^^ffj •MBW ^•••••••B mm^mmm
       L	:7 r--i'	: _  -
            S                ' I                WATERTIGH-
                                                                  yr~
              DASHED LINES INDICATE EXTENT
              OF COARSE AGGREGATE
                                               WATERTIGHT JOINTS AT SEND

                                                DASHED LINES INDICATE EXTENT
                                                OF COARSE AGGREGATE
                              SECTION A-A

                 Figure 4.—Typical layout of absorption trench.
                                                                     11

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  The required absorption area is predicated on  the results of the soil
percolation test, and may  be obtained from column 2 or 4 of Table 1
(page 8),  or Figure  3  (page 9). Note especially that the area require-
ments are per bedroom. The area of the lot on which the house is  to
be built should be large enough to allow room for an additional system
if the first  one fails. Thus for a  3  bedroom house  on a lot where  the
minimum percolation rate  was  1  inch in  15  minutes,  the necessary
absorption  area will be 3  bedrooms X  190 sq. ft. per bedroom, or 570
sq. ft. For trenches 2 feet wide with 6 inches of gravel below the drain
pipe, the required total length of trench would be 570 + 2, or 285 feet.
If this were divided into 5 portions (i.e., 5 laterals), the length of each
line would be 285 •*- 5, or 57 feet. The spacing of trenches is generally
governed by  practical construction considerations   dependent on  the
type of equipment, safety, etc. For serial distribution on  sloping ground,
trenches  should be  separated by 6  feet  to prevent short circuiting.
Table 2,  page 10,  gives the various distances the system  has to be kept
away from  wells, dwellings, etc.
  In the  example  cited, trenches  are 2 feet wide X 5 trenches - 10 feet
plus  6 feet between trenches X 4 spaces — 24 feet. The total width of
34  feet x 57 feet in length =  1,938 square feet, plus  additional land
required  to keep the field  away  from wells, property lines, etc.
    •SUI1ABIE PERVIOUS BARRIER


         OPENINGS AT JOINTS
                    JOINT COVBtlNG
 IZ1


J
             LONGITUDINAL
             SECTION
                      GRAVEL OR
                      BROKEN 5IONE
      LATERAL OF
      DRAIN THE (SHOWN)
      OPfN JOINTED SEWER PIPE
      O« PERFOKAKO PIPE
       "iOtt Dt-W* Tin tAlB **"* JOINTS OKNcD
          fKJW I 8 TO I •« INGH. SPtC!»L COUAiS
          v*Y if IKED IF HSlttD.
                    Figure 5.—Absorption trench and lateral.

   Construction  Considerations.—Careful construction is important in
 obtaining a  satisfactory  soil absorption system. Attention should  be
 given to  the  protection of the natural absorption properties of the soil.
 Care must be  taken to prevent  sealing  of the  surface  on the bottom
 12

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 and sides of the trench. Trenches should not be excavated when the
 soil is wet enough to smear or compact easily.  Soil moisture is right
 for safe working  only when  a handful  will mold with  considerable
 pressure.  Open  trenches should be protected from  surface runoff  to
 prevent the entrance  of silt and debris. If it is necessary to walk in the
 trench, a  temporary board laid on the bottom will reduce the damage.
 Some smearing  and damage is  bound to occur. All smeared or com-
 pacted  surfaces should be raked to a depth of 1 inch,  and loose mate-
 rial removed, before  the gravel  is placed in the  trench.
  The  pipe, laid in a trench  of sufficient width and depth, should be
 surrounded by clean, graded gravel or rock, broken  hard burned clay
 brick, or similar aggregate.  The material may range in size  from i/2 inch
 to 2i/2 inches. Cinders, broken shell, and similar material are not rec-
 ommended, because they are usually too fine and may lead to prema-
 ture clogging. The material should extend from at least 2  inches above
 the top of the pipe to at least 6 inches below the bottom of the pipe.
 If tile is used, the upper half of the joint openings should be covered,
as shown in Figure 5, page 12. The top of the stone should be covered,
 with untreated building paper, a 2 inch layer of  hay or straw, or similar
pervious material  to  prevent the stone from becoming clogged  by the
 earth backfill. An impervious covering should not be used, as this inter-
feres with evaportranspiration  at the surface  (see Appendix A, page 74).
Although generally not figured in the calculations, evapotranspiration
is often an important factor in  the operation of horizontal absorption
systems.
  Drain tile connectors, collars, clips,  or  other spacers  with covers for
 the upper half of the joints are of value in obtaining uniform spacing,
proper  alignment, and protection of tile joints,  but  use  of such aides
is optional. They  have  been made  of  galvanized  iron,  copper, and
plastic.
  It has been found that root problems may be prevented best by using
a liberal amount of gravel  or stone around the tile. Clogging due  to
roots  has  occurred mostly  in  lines with  insufficient  gravel under the
tile. Furthermore, roots seek the location where moisture conditions are
most favorable for growth  and, in  the small percentage of cases where
they become troublesome in well designed installations, there is usually
some explanation  involving the moisture  conditions.  At  a  residence
which  is used only during the  summer,  for example,  roots  are most
likely to penetrate when the house is uninhabited,  or when moisture
immediately below or around  the gravel becomes less plentiful than
during the period  when the system is in  use. In  general,  trenches con-
structed with  10 feet  of large trees or dense shrubbery  should have
at least 12 inches of gravel or crushed stone beneath  the tile.
  "If trees are near  the sewage  disposal system, difficulty with roots
entering poorly  joined sewer lines can  be  anticipated.  Lead-caulked
cast iron pipe, a sulfur base or bituminous pipe joint  compound, me-

                                                                 13

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chanical clay pipe joints, copper rings over joints and lump copper
sulfate in pipe trenches have been found effective in resisting the en-
trance of roots into pipe joints. Roots will penetrate into the gravel in
tile field trenches rather  than  into the pipe. About 2  or 3  pounds of
copper sulfate crystals  flushed  down the toilet bowl once a year will
destroy roots the solution comes in contact with, but will not prevent
new roots from entering. The application of the chemical  should  be
done at a time, such as late in  the evening when the maximum contact
time  can be  obtained before  dilution.  Copper  sulfate will corrode
chrome,  iron and brass, hence  it should  not be allowed to  come into
contact with these metals. Cast iron is not affected  to any appreciable
extent. Some time must elapse before the roots are killed and broken
off. Copper  sulfate in the recommended dosage will not interfere with
operation of the septic tank." '
  The top  of a  new absorption trench should be  hand tamped and
should be overfilled with about 4 to  6 inches of earth. Unless this is
done, the top of the  trench may settle to a point lower than the sur-
face of  the  adjacent  ground. This will cause the collection of storm
water in the  trench,  which can lead to premature saturation of the
absorption  field  and  possibly   to complete  washout  of  the  trench.
Machine tamping or  hydraulic backfilling of the  trench should be
prohibited.
  Where sloping ground is used for the disposal  area, it  is  usually
necessary to construct a small  temporary dike or surface water diver-
sion ditch  above the  field,  to prevent  the disposal area from being
washed  out  by rain. The  dike should  be  maintained or the ditch kept
free of obstructions until the field becomes well covered with vegetation.
  A heavy vehicle would  readily crush the tile in a  shallow absorption
field. For this reason, heavy machinery should be excluded  from  the
disposal  area unless special provision is made to support the weight.
All machine grading should be completed before the field is  laid.
  The use of the field  area must be  restricted to activities which will
not contribute to the compaction of the soil with the consequent reduc-
tion in soil  aeration,

Seepage Beds
  Common  design practice for soil absorption systems for private resi-
dences provides for trench widths up  to 36 inches. Variations of design
utilizing increased width are being used in many areas.  Absorption sys-
tems having trenches wider than 3 feet are referred  to as seepage beds.
The design  of trenches is based on an empirical relationship between
the percolation test and the bottom area of the trenches. The use of seep-
age beds has been limited by the lack of experience with their perform-
ance and the absence of design  criteria comparable to that for trenches.
  Joseph A. Salvato, "Environmental Sanitation," page 214.

14

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  Studies sponsored by the Federal Housing Administration have dem-
onstrated that the seepage bed is a satisfactory device for disposing of
effluent in soils that  are acceptable  for soil  absorption systems.  The
studies have  further demonstrated  that the empirical relationship be-
tween  the percolation test and bottom  area  required for  trenches is
applicable for seepage beds.
  There are three main elements of a seepage bed: absorption surface,
rockfill  or packing material, and  the distribution  system. The design
of the seepage  bed should be such that  the total intended absorption
area is preserved, sufficient packing material is provided in the proper
place to allow for further treatment  and storage of excess liquid, and
a means for  distributing the effluent is protected  against siltation of
earth backfill and mechanical damage. Construction  details for a con-
ventional seepage bed are outlined in the following material in such a
way that these  principal design elements are incorporated. Tabulation
of construction details for the conventional seepage bed is not intended
to preclude other designs which may provide tne essential features in a
more economical or otherwise desirable manner. Specifically, there may
be equally acceptable or even superior methods  developed for distrib-
uting the liquid than  by tile or perforated pipe covered with gravel.
  The use of seepage beds results  in  the following  advantages:
  1. A wide bed makes more efficient use of land available for absorp-
tion systems  than a  series of long narrow  trenches  with wasted  land
between the trenches.
  2. Efficient use may be made of a variety of modern earth moving
equipment employed at housing projects  for other  purposes such as
basement excavation and landscaping, resulting in savings on the cost
of the system.

  Construction Considerations.—When seepage beds  are used, the fol-
lowing design and construction procedures providing for rockfill  or
packing material, an  adequate distribution system, and protection of
the absorption area, should be observed:
  1. The amount of bottom absorption area required shall be the same
as shown  in Table I, page 8.
  2. Percolation tests should be conducted in accordance with pages 4-8.
  3. The bed should  have a minimum depth  of  24 inches below natu-
ral ground level to provide a minimum earth backfill cover of 12 inches.
  4. The bed should have a minimum depth of 12  inches of rockfill or
packing material extending at least 2 inches above and 6 inches below
the distribution pipe.
  5. The bottom of the bed and distribution tile or perforated  pipe
should be level.
  6. Lines for distributing effluent shall be spaced not greater than 6
feet apart and  not greater than 3 feet from the  bed sidewall.

                                                                 15

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  7. When more than one bed is used: (a) there should be a minimum
of 6 feet of undisturbed earth between adjacent beds; and (b)  the beds
should be connected in series in accordance with the section concerning
serial distribution, below.
  8. Applicable construction  considerations for standard trenches on
pages 10 through 14 should also be followed.
Distribution Boxes
   The Final  Report  to the Federal  Housing  Administration on  the
study to: Determine if Distribution Boxes can  be Eliminated  Without
Inducing Increased  Failure of  Disposal  Fields by  the Public Health
Service reached the following conclusions:
  1. Distribution boxes can be eliminated from septic tank-soil absorp-
tion systems in favor of some  other  method  of  distribution without
inducing increased failure of disposal  fields. In fact,  evidence  indicates
that distribution boxes as presently used may be harmful to the system.
  2. Data indicates that on level ground, equal distribution is not nec-
essary if the system is  designed so that an overloaded trench can drain
back to the other trenches  before failure occurs.
  3. On  sloping ground a method of distribution is needed to prevent
excessive build-up of  head and  failure of any one  trench before  the
capacity of the entire system is utilized. It is doubtful that distribution
boxes as presently used give equal distribution. Rather, they probably
act as diversion devices sending most of the liquid to part of the system.
  For the above reasons it is recommended that distribution boxes  not
be used for individual sewage disposal systems.
Serial Distribution
  Serial  distribution is  achieved by arranging individual trenches of
the absorption system  so that each trench is forced to pond to the full
depth of the gravel  fill before liquid flows into the succeeding trench.
  Serial  distribution has the following advantages:
  1. Serial distribution minimizes the importance of variable absorption
rates by forcing each trench to absorb effluent until its ultimate capacity
is utilized. The variability of soils even  in  the small area of an indi-
vidual absorption field raises  doubt of the desirability of uniform  dis-
tribution. Any one or a combination of factors  may lead to nonuniform
absorptive capacity of  the several trenches in a system. Varying physical
and chemical characteristics of soil, construction damage such as  soil
interface smearing or excessive compaction, poor surface drainage, and
variation in depth of  trenches are some  of the factors involved.
  2.  Serial  distribution causes  successive trenches  in the absorption
system to be  used to full  capacity. Serial distribution has a distinct
advantage  on  sloping  terrain. With  imperfect division  of flow in a
parallel  system, one  trench could become overloaded, resulting in a
surcharged condition.  If the slope  of  the ground and elevation of the
distribution box were such that a surcharged trench continued to re-

16

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 ceive  more effluent than  it could absorb, local  failure would  occur
 before the  full capacity of the system was  utilized.
   3. The cost of the distribution  box is eliminated  in  serial  distribu-
 tion. Also,  long runs of closed pipe connecting the box  to each trench
 are unnecessary.

  Fields in  Flat Areas.—Where the slope of the ground surface  does not
 exceed six  inches  in any  direction  within the area utilized for the
 absorption  field, the septic tank effluent may be applied to the absorp-
 tion field through a system of interconnected tile lines and trenches in
 a continuous system. The following specific criteria should be followed:
  1. A minimum of 12 inches of earth cover is provided over the gravel
 fill  in  all trenches of the  system.
  2. The bottom of  the trenches and the distribution lines should be
level.
  3,  One type  of a  satisfactory absorption system layout for "level"
ground is shown in  Figure 6, below.
  4. Construction considerations for standard trenches, pages 10  through
14, should be followed.
  Fields in  Sloping Ground.—Serial  distribution may be used in all
                              EXTENT OF COARSE AGGREGATE
                                                         — B
                        ElEV.
                        100.4
                                               ..'• •';-
100.0
              A-A
                                                 B-B
              Figure 6.— Absorption-field system for level ground.

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 situations where a soil absorption system is permitted and and should
 be used where the fall of the ground surface exceeds approximately 6
 inches in any direction within the area utilized for the absorption field.
 The maximum  ground slope suitable  for serial  distribution  systems
 should be governed by local factors affecting the erosion of the ground
 used for the absorption field. Excessive  slopes which are not protected
 from surface water runoff or do not have adequate vegetation cover to
 prevent erosion  should  be avoided. Generally,  ground having  a  slope
 greater than one vertical to two horizontal should  be  investigated care-
 fully to determine if satisfactory from the erosion standpoint. Also,  the
 horizontal distance from side of the trench to the ground surface should
 be adequate to prevent lateral flow of effluent and breakout on surface
 and in  no case less than two feet.
   In serial  distribution, each adjacent  trench (or pair of trenches) is
 connected to the next by  a closed pipe line laid on an undisturbed
 section  of ground, as shown in Figure 7, page 19.  The arrangement is
 such that all effluent is discharged to the first trench until it is filled.
 Excess liquid is then carried by means of a closed  line to  the next suc-
 ceeding or lower trench. In that manner, each portion of the subsurface
 system  is used  in succession. When serial distribution  is used,  the
 following design and construction procedures should  be followed:
   1. The bottom of each  trench and  its distribution line should be
 level.
   2. There  should be a minimum of 12 inches of ground  cover over
 the gravel fill in the trenches.
   3. The absorption trenches should follow approximately the  ground
 surface contours  so that variations  in trench depth will be minimized.
   4. There  should be a minimum of 6 feet of  undisturbed earth  be-
 tween adjacent trenches and between the septic tank and the nearest
 trench.
   5. Adjacent trenches may be connected with the  relief line or a  drop
 box arrangement, Figure 7, page 19, in such a manner that each trench
 is  completely filled with septic tank effluent to  the full  depth of the
 gravel before effluent flows to succeeding trenches.  (The Figure shown
 does not  preclude the  use of other  arrangements to provide serial
distribution.)
      a. Trench connecting lines should be 4 inch,  tight-joint sewers
    with  direct  connections  to the  distribution lines  in adjacent
    trenches or  to a drop box arrangement.
      b. Care must be exercised in constructing relief lines to insure
    an  undisturbed block of earth  between trenches. The trench for
    the relief pipe, where  it  connects  with  the preceding absorption
    trench,  shall be dug no deeper than the top  of  the  gravel.  The
    relief line should rest on undisturbed earth and backfill should be
    carefully tamped.
      c. The relief lines connecting individual trenches should be as

18

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     far  from  each  other  as  practicable  in  order  to  prevent  short
     circuiting.
   6.  Invert of the overflow pipe in the first relief line must be  at least
4  inches lower than the  invert  of the septic tank  outlet, Figure  7.
                                        > FROM SEPTIC TANK

                                                                      L
                       • ALTERNATE DROP BOX METHOD AS SHOWN IN
                        SECTION BB MAY BE UStD.
                                       NOTE:
                                       INVERT OF THE OVERFLOW PIPE
                                       MUST BE AT LEAST 4" LOWER THAN
                                2J      INVERT OF THE SEPTIC TANK OUTLET
                             UNDISTURBED
                                EARTH
                                      •  •:
                            UNDISTURBED EARTH
         6' MINIMUM
      SECTION B-B
(ALTERNATE CONSTRUCTION)
              • DIFFERING GROUND SLOPES OVER SUBSURFACE DISPOSAL FIELD
               MAY REQUIRE USE OF VARIOUS COMBINATIONS OF FITTINGS.


            Figure 7.—A relief line arrangement  for  serial distribution.
                                                                              IS

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    7. All other construction features of the disposal field  are the same
 as recommended on  pages 10 to  14.
 Deep Absorption Trenches and Seepage Beds
   In cases where the  depth of filter material below the tile exceeds the
 standard six inch depth, credit may be given for the added absorption
 area provided in deeper trenches with  a resultant decrease in length of
 trench. Such  credit shall  be  given in  accordance with Table 5 which
 gives  the  percentage  of length of standard absorption  trench (as  com-
 puted  from Table 1), based on six inch increments of increase in depth
 of filter material.

                Table 3.—Percentage of length of standard trench 1
Depth of
Gravel Below
Pipe in Inches*
12
18
24
30
36
42

Trench
width
12"
75
60
50
43
37
33

Trench
width
18"
78
64
54
47
41
37

Trench
width
24"
80
66
57
50
44
40

Trench
width
36"
83
71
62
55
50
45

Trench
width
48"
86
75
66
60
54
50

Trench
width
60"
87
78
70
64
58
54

  1 The standard absorption trench is one in which the filter material extends two
inches above and six inches below the pipe.
  *For trenches or beds having width not shown in Table 3, the percent of length
of standard absorption trench may be computed as follows:
         Percent of length standard  trench =
                                              w
                                           w
1
                                                     2d
        X  100
               Where w = width of trench in feet
                     d = depth of gravel below pipe in feet

  To  use this table, consider the example on page 12. Using a trench 2 feet wide
with 6" of gravel  under tile, 285 feet  are required.  If the depth of gravel  is
increased to 18", keeping trench width at 2 feet, only 66% of 285 feet is required,
or 188 feet. If 4 laterals are used, the length would be 188 divided by 4 —  47 feet.
  The space between lines for serial distribution  on sloping ground is 6  feet  x
3 spaces =  18 feet, plus 4 lines x 2  feet = 8 feet. Total land required is 26 feet
in width x 47 feet in length = 1,222 square feet,  plus  additional area required to
keep the field away from  wells, property lines, etc.
Seepage Pits
   Seepage pits, as with all soil absorption systems, should never be used
where there is a likelihood of contaminating underground waters, nor
where adequate seepage beds or trenches can be provided. When seep-
age pits are to be used, the pit excavation should terminate 4 feet above
the ground water table.
   In some States, seepage pits are permitted  as  an  alternative when
20

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          PERVIOUS
          STRATA
                                         2" LAYER OF GRAVEL
                Figure 8.—Deep percolation test for seepage pit.

absorption fields are impracticable,  and where the top 3 or 4 feet of
soil is underlaid with  porous sand  or  fine gravel and the subsurface
conditions are otherwise  suitable  for pit installations. Where  circum-
stances permit, seepage pits may be  either supplemental or alternative
to the more shallow absorption fields. When seepage pits are  used in
combination with absorption  fields, the  absorption areas in each system
should be pro-rated, or based upon the weighted  average of the results
of the percolation tests.
  It is important that the capacity  of  a seepage pit be computed on
the basis of percolation tests made in each vertical stratum penetrated.
The weighted average  of  the results should be computed to obtain  a
design figure. Soil strata in which  the percolation rates are in excess of
30 minutes  per inch should not be included in computing the absorp-
tion area. As will be  apparent from Figure 8  (above), adequate tests

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                        DWELLING
                                         SEPTIC TANK
                                                    4" BELL AND SPIGOT PIPE
                                                    (TIGHT JOINTS)
D SHOULD  BE AT LEAST 3  TIMES DIAMETER OF SEEPAGE PIT

MINIMUM D AT LEAST 20 FT. FOR PITS OVER 20 FT. IN DEPTH

               Figure  9.—Disposal  system using two  seepage pits.

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for deep pits  are somewhat  difficult to make, time-consuming, and
expensive. Although few data have been collected comparing percola-
tion test results with deep pit performance,  nevertheless the results of
such percolation tests,  while of limited value,  combined with compe-
tent engineering judgment based on experience, are the best means of
arriving at  design data for seepage  pits.

               Table 4.—Vertical wall areas of circular seepage pits
                            [In Square Feet]
Diameter of
seepage pit
(feet)
3 	
4
5 	
6 	
7
8
'J
10
11 	
12 	

Effective strata depth below flow line (below inlet)
1 foot
9.4
12.6
15.7
18.8
22.0
25.1
28.3
31.4
34.6
37.7
2 feet
19
25
31
38
44
50
57
63
69
75
3 feet
28
38
47
57
66
75
85
94
104
113
4 feet
38
50
63
75
88
101
113
126
138
151
5 feet
47
63
79
94
110
126
141
157
173
188
6 feet
57
75
94
113
132
151
170
188
207
226
7 feet
66
88
110
132
154
176
198
220
242
264
8 feet
75
101
126
151
176
" 201
226
251
276
302
9 feet
85
113
141
170
198
226
254
283
311
339
10 feet
94
126
157
188
220
251
283
314
346
377
  Example: A pit of 5  foot diameter and 6 foot depth below  the inlet has  an
effective area  of 94 square feet. A pit of 5 foot diameter  and 16 foot depth has  an
area of 94 -f 157, or 251 square feet.

  Table 1  or Figure  3 (page 9) gives the absorption area requirements
per bedroom for  the percolation rate obtained.  The effective  area  of
the seepage pit is  the vertical wall area (based on dug diameter) of the
pervious strata below the inlet.  No allowance should be made for im-
pervious strata or bottom area. With this  in mind, Table 4 may  be
used for determining the effective side-wall area of circular or cylindri-
cal seepage pits.
  Sample Calculations.—Assume that a seepage pit absorption system is
to be designed for a 3  bedroom home on  a lot where the minimum
percolation rate of 1 inch in 15 minutes prevails.  According to Table I,
3  X  190 (or 570) square feet of absorption area would be needed.
Assume also that the water table does not rise above 27 feet below the
ground surface, that  seepage pits with effective depth of 20 feet can  be
provided, and that the house is  in a locality where it is common prac-
tice to install seepage pits of 5 feet diameter (i.e., 4 feet to the outside
walls, which  are surrounded by about 6 inches of gravel). Design  of
the system is  as follows:
                                                                   23

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  Let d  = depth  of pit in feet; D = pit diameter in feet:
                                 TrDd = 570 square feet.
                       3.14  X 5  X  d = 570 square feet
  Solving for  d        depth of pit = 36  feet (approx.)
  In other words, one 5 foot diameter pit 36 feet deep  would be needed,
but since the  maximum  effective depth  is  20  feet in this  particular
location, it will be  necessary to  increase  the diameter of the pit,  or
increase  the number of pits, or increase both  of  these. This is  illustrated
in  the example below:
  (a) Design for 2 pits  with a 10  foot diameter; d = depth of each pit.
                2 X  3.14 X 10  X  d = 570 square feet
                                     d = 9.1 feet deep

            NOTE: REMOVE PLUG FOR INSPECTION

       ' EARTH COVER
            FILL IN HOLE
VARIABLE      WITH MORTAR  .
        ENTRY PIPE	.  /   /     PRECAST REINFORCED CONCRETE
                           / SLAB NOT RESTING ON L
                                                    ^
                                                    t	I

                                                 SECOND LAVE* OF BRICK
              . DISTANCE TO GROUND WATER
               LEVEL A FT. MIN.
                                            .  NOTE  SECOND AND REMAINING
                                           /       LAYHS ARE LAID END TO END
                                                   AND AT RIGHT ANGLES WITH FIRST
                                                   LAYER  OF BRICK
        PLACE 6" COARSE AGGREGATE
        i'/j" TO I"! AROUND UNMORTARED
        MASONRY
                                                BRICKS OVERLAP ON EACH LAYER
                                      SSCONO LAYER
THIRD LAYER
FIRST LAYER
                                                     SECTION A-A
             FIRST LAYER OF BRICK
                SECTION B-B
                             Figure  10.—Seepage pit.
24

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  Use 2 pits 10 feet in diameter and 9.1  feet deep.
  (b) Design for 2 pits with a 5 foot diameter; d — depth of each pit.
                  2x 3.14 x 5 X d  = 570 square feet
                                 d  = 18 feet (approximately)
  Use 2 pits 5 feet in diameter and 18 feet deep.
  Experience has shown  that seepage pits should be separated  by a
distance equal to 3 times the diameter of the largest pit.  For pits over
20 feet in depth, the minimum space between pits should be  20 feet
(See  Fig. 9, page 22). The area of the lot on  which the house is to be
built should  be large  enough  to maintain this distance between the
pits  while still allowing room for additional pits  if the  first ones should
fail.  If this can be done,  such an absorption  system may  be  approved;
if not,  other suitable sewerage  facilities  should  be required.
   ROOf TERMINAL
                                                                     .
               FIXTURES TO BE
           'PERLY TRAP£
            VENTED
            V  CHOUSE SEWER (A]
                  TO IE LAID ON WELL-COMPACTED EARTH
                            SEPTIC TANK [81

                               COMPACT EARTH AROUND TANK
                  Figure 11 .—Septic-tank sewage-disposal system.

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  Construction Considerations.—Soil  is susceptible to damage during
excavation. Digging in wet soils should be avoided as much as possible.
Cutting teeth on  mechanical equipment should be kept sharp. Bucket
augered pits should  be reamed to a larger diameter  than the bucket.
All loose material should be removed  from the excavation.
  Pits should  be backfilled with clean gravel to a depth of  one  foot
above the pit bottom or one foot above the reamed ledge to  provide a
sound foundation for the lining. Preferred lining materials are clay or
concrete brick, block, or rings. Rings should have weep holes or notches
to provide for seepage. Brick and block should  be laid dry with stag-
gered joints. Standard brick should be laid flat to form a four inch wall.
The outside diameter of  the lining should be at least six inches less
than  the least excavation diameter. The annular space formed should
be filled with clean,  coarse gravel to the top  of the lining as shown in
Figure 10.
  Either brick dome  or flat concrete covers  are satisfactory. They
should be  based  on  undisturbed earth and  extend at least  12 inches
beyond the excavation and should not bear on the lining for  structural
support. Bricks should be either laid  in cement mortar or have a two
inch covering  of  concrete.  If flat covers are used, a prefabricated type
is  preferred, and they should be reinforced to be the  equivalent in
strength of an approved septic tank cover. A  nine inch capped opening
in the pit cover is convenient for pit inspection. All  concrete surfaces
should be located with a protective bitumastic or similar compound to
minimize corrosion.
  Connecting lines should be of a sound, durable material the same as
used  for the  house  to septic tank connection.  All  connecting lines
should be  laid on  a firm bed  of undisturbed  soil  throughout their
length. The grade of a connecting line should be at least two percent.
The pit inlet pipe should extend horizontally at least  one foot into the
pit with a  tee or ell to divert flow downward to prevent washing and
eroding of the sidewalls. If multiple pits are used,  or  in  the event
repair pits are added to an existing system,  they should  be connected
in series.
  Abandoned seepage pits should be filled with earth  or rock.
SELECTION OF A SEPTIC TANK
  Assuming that the lot will be large enough to accommodate one of
the types of absorption systems, and that  construction of the system is
permitted by local authority, the next step will be selection of a  suit-
able septic tank.
Functions of Septic Tanks
  Untreated liquid household wastes  (sewage) will quickly clog all but
the most porous gravel formations. The tank conditions sewage so that
it may be more readily percolated into the subsoil of the ground. Thus,
the most important  function of a septic tank is to provide protection

26

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for the absorption ability of the subsoil. Three functions  take  place
within the tank to provide this protection.
   1. Removal  of  Solids.—Clogging of soil with  tank effluent varies
directly with the amount of suspended solids in the liquid. As sewage
from a building sewer enters a septic tank, its  rate of flow is reduced
so that larger solids sink to the bottom  or rise to the surface. These
solids are retained in the tank,  and the clarified effluent is discharged.
   2. Biological  Treatment.—Solids and  liquid  in the tank  are  sub-
jected  to decomposition by  bacterial and natural processes.  Bacteria
present are of  a variety called  anaerobic  which thrive  in the  absence
of free oxygen. This decomposition or treatment of sewage under  anae-
robic conditions is termed "septic," hence the name of the tank. Sewage
which  has been subjected  to such treatment causes less clogging than
untreated sewage containing the same amount of suspended solids.
   3. Sludge and Scum Storage.—Sludge is an accumulation of solids at
the bottom of  the tank, while  scum is a partially submerged mat of
floating solids that may form at the surface of  the fluid in the  tank.
Sludge, and scum to a lesser degree, will be digested and  compacted
into a  smaller volume. However, no matter how efficient the process is
a residual of inert solid material will remain. Space must be provided
in the  tank to store this residue during the interval between cleanings;
otherwise, sludge and scum  will eventually be  scoured from the tank
and may clog the disposal  field.
   If adequately designed, constructed, maintained, and operated, septic
tanks are effective in accomplishing their purpose.
   The relative  position of  a  septic tank in a typical subsurface disposal
system  is illustrated in Figure 11 (page 25). The liquid contents of the
house sewer (A) are discharged first into the septic tank  (B), and finally
into the subsurface absorption field (C).
   The heavier sewage solids settle to the bottom of the tank, forming
a blanket of sludge. The lighter solids, including fats and greases, rise
to the  surface and form a layer of scum. A considerable portion of the
sludge  and scum  are liquefied through  decomposition or digestion.
During this process, gas is liberated from  the sludge, carrying a portion
of the  solids to the surface, where they accumulate with the scum.  Ordi-
narily, they undergo further digestion in  the scum layer, and a portion
settles  again to the sludge blanket on the  bottom. This action  is re-
tarded if there is  much grease  in the scum layer. The settling is also
retarded  because of  gasification in the sludge  blanket. Furthermore,
there are relatively wider  fluctuations  of  flow in  small tanks  than  in
the large units. This effect has been recognized in Table 5 (page 29),
which  shows the recommended minimum  liquid capacities of household
septic  tanks.
   Location.—Septic tanks  should be located where they cannot  cause
contamination  of  any well,  spring, or other source  of water supply.
Underground contamination may travel in  any  direction and for con-

                                                                  27

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siderable  distances,  unless  filtered effectively. Underground pollution
usually moves in the same general direction as  the normal movement
of the ground water in the locality. Ground water moves in the direc-
tion of the slope or gradient of the water table, i.e.,  from the area of
higher water table  to areas of lower water table. In general, the water
table follows the general contour of the ground surface. For this reason,
septic tanks should  be located downhill from wells or springs. Sewage
from disposal  systems  occasionally contaminate wells  having  higher
surface elevations.  Obviously,  the elevations of disposal systems are
almost always higher than the  level of water in such wells as may be
located nearby; hence, pollution from  a disposal system on a  lower
surface elevation may  still travel downward to the water bearing stra-
tum as shown  in  Figure 12,  below.  It is necessary, therefore, to  rely
       Figure 12.—Pollution  of well from sources with lower surface elevations.
upon  horizontal as  well  as vertical distances  for  protection. Tanks
should never be closer than 50 feet from any source of water supply:
and greater distances are preferred where  possible.
   The septic tank should  not be located within 5 feet of any building,
as structural  damage may result during  construction or seepage may
enter  the basement. The tank should not be located in swampy areas,
nor in areas subject to flooding. In  general, the  tank should be located
where  the largest possible area will  be available for the disposal field.
Consideration should also be given  to the location from the standpoint
of cleaning and maintenance. Where public sewers may be installed at
a future date, provision should be  made  in the household plumbing
system for connection  to such sewer.
 2B

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  Effluent.—Contrary to popular belief, septic tanks do not accomplish
a high degree of bacteria removal. Although  the sewage undergoes
treatment in passing  through the tank, this does not mean that infecti-
ous  agents  will be  removed; hence, septic  tank effluents cannot  be
considered safe. The  liquid that is discharged from a tank is, in some
respects, more objectionable  than that which goes in; it is septic and
malodorous. This,  however,  does not detract  from the  value  of  the
tank. As previously explained, its primary purpose is to condition  the
sewage so that it will cause less clogging of the disposal field.
  Further treatment  of the effluent, including  the removal  of patho-
gens, is  effected by  percolation through the soil. Disease producing
bacteria will,  in time, die out in the unfavorable environment afforded
by soil. In addition, bacteria are also removed by certain physical forces
during filtration. This  combination of factors results  in the  eventual
purification of the sewage effluent.
  Capacity.—Capacity is  one of the most important considerations in
septic tank design. Studies have proved that liberal tank capacity is  not
only important from  a functional standpoint, but is also good economy.
The liquid  capacities recommended in Table 5 allow for the use of all
household appliances, including garbage grinders.

                 Table 5.—liquid  capacity  of tank (gallons)
     [Provides  for use of garbage grinders,  automatic clothes washers,  and
                       other household appliances]
Number of bedrooms
2 or less
3 	
41 	

Recommended
minimum tank
capacity
750
900
1,000

Equivalent
capacity
per bedroom
375
300
250

  1 For each additional bedroom, add 250 gallons.

Specifications  for  Septic Tanks
  Materials.—Septic  tanks  should  be watertight  and  constructed  of
materials  not  subject to excessive corrosion or decay, such as concrete,
coated  metal,  vitrified  clay,  heavyweight concrete  blocks, or hard
burned  bricks. Properly cured precast and cast-in-place reinforced con-
crete tanks are believed to be acceptable everywhere. Steel tanks meet-
ing Commercial Standard 177-62 of the U. S. Department of Commerce
are generally acceptable. Special attention should be given to job built
tanks to insure water tightness. Heavyweight concrete block should  be
laid on a solid foundation and mortar joints should be well filled. The
interior of the tank should be surfaced with two 14 inch thick coats of
                                                                  29

-------
portland cement-sand plaster. Some typical septic tanks are illustrated
in Figure 13 (page 31). Suggested specifications for watertight concrete
are given in Appendix E.
  Precast tanks should have a  minimum  wall  thickness of 3 inches,
and should be adequately reinforced to facilitate handling. When pre-
cast slabs are used as covers, they should be watertight, have a thickness
of at least  3 inches, adequately reinforced. All concrete surfaces should
be coated with a bitumastic or similar compound to minimize corrosion.
  General.—Backfill around septic tanks should  be made in thin layers
thoroughly tamped in a manner that will not produce undue strain on
the tank. Settlement of backfill may be done with the use of  water,
provided the material is thoroughly wetted from the bottom  upwards
and the tank is first filled with water to prevent floating.
  Adequate access must be provided to each compartment of  the tank
for inspection and  cleaning.  Both the inlet and outlet devices should
be  accessible. Access should  be provided  to  each  compartment by
means of  either a removable  cover or a 20 inch  manhole in least
dimension. Where the top of the tank is located more  than 18  inches
below  the finished grade, manholes and inspection holes should extend
to approximately 8 inches  below  the finished  grade (see  Figure  14,
page 32), or can be extended  to finished  grade if a seal is provided
to keep odors from  escaping. In most instances, the  extension can be
made using clay or concrete pipe, but  proper attention must  be given
to the accident hazard involved when  manholes are extended close to
the ground surface. Typical single and double compartment tanks are
illustrated  in Figures 15 and 17, pages 33  and 35.
  Inlet.—The inlet invert should enter the tank at least 3 inches above
the liquid level  in  the tank, to allow for momentary rise in  liquid
level during discharges to the tank. This free drop prevents backwater
and stranding of solid material in the house sewer leading to the tank.
  A vented inlet tee or baffle should be provided to divert the incom-
ing sewage  downward. It should penetrate at least  6  inches below the
liquid level, but in no case should the penetration be  greater than
that allowed for the outlet  device. A number  of  arrangements com-
monly used for inlet  and  outlet devices are  shown  in  Figure 16
(page  34).
  Outlet.—It is  important  that the outlet  device penetrate just  far
enough below the liquid level  of the septic tank to provide a balance
between  sludge  and scum  storage volume; otherwise,  part of the
advantage of capacity is lost. A vertical section of a properly operating
tank would show it divided into three distinct layers; scum at the top,
a middle zone free of solids (called "clear space"), and  a  bottom layer
of sludge.  The outlet  device  retains  scum  in  the tank, but at the
same time,  it limits the amount of sludge that  can be accommodated
without  scouring, which results in sludge discharging  in the effluent
from the tank.  Observations of sludge accumulations in the field, as

30

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       .



VII
    Figure 13.—Typical septic-tank shapes.
              31

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                       MANHOLE COVER
                          BE EITHER
                       FLUSH WITH SURFACE
                       OR 8" BELOW SURFACE
\
G*S SEAL MADE SI FILLING TOP
Of MANHOLE WITH SAND OR BY PLASTERING
(I" MIN.I WITH STUCCO WIRE REINFORCED
OM TOP Of WOOD PLATFORM
               SECTION
        MANHOLE (WITHOUT GAS SEAL;
           SECTION
     MANHOLE (WITH GAS SEAL)
                                       NOTf: GAS SEAL iSANDI IS REMOVED TO
                                           GAIN ACCESS TO TANK. AND REPLACED
                                           TO REFORM SEAL
   MANHOLC COf£8
            PLAN

NOTt. USE STANDARD MANHOLE RING AND COVER
    FOR HEAVY TRAFFIC DUTY—LIGHT DUTY MANHOLE
    RING AND COVER FOR LIGHT TRAFFIC DUTY
      MANHOLE 'WITH TRAFFIC PROTECTION SLAB!
                        Figure 14.—Design of manholes.

reported in  Section B,  Part  III, of  "Studies on Household  Sewage
Disposal Systems" (bibliography reference, page  92), indicate that  the
outlet device should generally  extend  to  a distance  below  the  surface
equal to 40  percent of  the liquid  depth. For horizontal, cylindrical
tanks, this should be reduced to 35 percent. For example, in a horizon-
tal cylindrical  tank having a  liquid  depth  of  42 inches, the outlet
device should penetrate 42 X -35 = 14.7 inches below  the liquid level.
   The outlet device should extend  above the liquid line to approxi-
mately one inch  from  the  top of the tank. The space between  the  top
of the tank and  the baffle  allows gas to pass  off through the tank into
the house vent.
   Tank Proportions.—The available data indicate that,  for tanks of a
given capacity, shallow tanks function as well as deep ones.  Also, for
tanks of a given capacity  and depth,  the shape  of a  septic  tank is
unimportant. However,  it is  recommended that  the  smallest plan
dimension  be  at least 2  feet.  Liquid  depth may range  between  30
and 60 inches.
32

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   INLET
                             MAKE BAFFLES OF PRECAST REIN-
                             FORCED CONCRETE OR EQUIVALENT
                             MATERIAL I'/i" OR 2" THICK
[T
10"
J_
	 ' 1_ _
1 1
1 1
-i;--i



                                                                 • OUTLET
                                                  20"
                                  PLAN
                                                       SLOT IN WALL
      MANHOLE COVER
              •**•!*I ^^*^*  **^B*^ F"!"  T
4  MAXIMUM FOR MANHOLE COVfR AS SHOWN.
'  FOR GREATER DISTANCES BELOW GROUND
   PROVIDE EXTENSION COLLARS
                                             -A. —-
    »" TO 4"
INLET
                             0.2 D MIN.-(2O7, OF LIQUID DEPTH!  f
                                                                     OUTLET
  NOTE: MAKE INLET AT LEAST
      3" AJOVE OUTLET.
          PENETRATION OF OUTLET
          BAFFLE GENERALLY 40% OF LIQUID DEPTH
           FOR RECTANGULAR TANKS (SEE TEXT)
                              SECTION ON
                              CENTER LINE
                       Figure 15.—Household septic lank,
  Storage Above Liquid Level.—Capacity is required above the liquid
line to provide for  that  portion  of the scum  which  floats above the
liquid. Although some  variation  is to  be  expected,  on  the  average
about 30  percent of the  total scum  will accumulate above the liquid
line. In addition to the provision for scum  storage, one  inch is usually
provided at the top of the tank to permit  free passage  of gas back  to
the inlet and house vent  pipe.
  For tanks  having straight, vertical sides,  the distances between the
top of the tank and the liquid  line should be equal to approximately
20  percent of  the  liquid  depth. In  horizontal, cylindrical tanks, area
equal  to approximately 15  percent of the  total  circle should be pro-
vided  above the liquid level. This condition is  met if  the liquid depth
(distance from outlet invert to bottom of tank) is equal to 79 percent
of the diameter  of the tank.
                                                                        33

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                                                 TEE

                                       4" CAST IRON SOIL PIPE T BRANCH
                                       4" CAST IRON SANITARY T BRANCH
                                       4' VITRIFIED CLAY OR CONCRETE
                                       T BRANCHES

                                       PLACE INLET AND OUTLET TEE
                                       IN NOTCH AND FILL WITH MORTAR
                                                      PACK MORTAR
                                                      AROUND TEE
                                             STRAIGHT BAFFLE

                                        POURED IN PLACE OR PREFABRICATED
                                        AND DROPPED IN SIDES OF TANK
       Bfisam ft=B^^s3
                                           SEMI-CIRCULAR BAFFLE

                                        PREFABRICATED CONCRETE  CLAY
                                        TILE OR STEa
NOTE: 'A'  SHOULD BE NO LESS THAN 6'
     AND NO GREATER THAN B

      B  PENETRATION OF OUTLET DEVICE
     GENERALLY 40% OF LIQUID DEPTH FOR
     TANKS WITH VERTICAL SIDES & 35% FOR
     HORIZONTAL CYLINDERS TANKS.
                                 SECTION D-D
                  Figure 16.—Types of  inlet and outlet devices.
  Use of  Compartments.—Although  a number of  arrangements are
possible, compartments, as used here, refer  to  a number of units in
series. These can be either separate units  linked together,  or sections
enclosed in one continuous shell (as in Figure 17, page 35, with water-
tight partitions separating the individual  compartments.
  A single compartment tank will  give  acceptable performance. The
available research data indicate, however, that a two compartment  tank,
with the  first  compartment  equal  to  one-half to  two-thirds  of the
total volume, provides better suspended solids removal which may be
especially  valuable for protection  of the soil absorption  system. Tanks
with three  or  more equal compartments  give  at  least  as  good per-
formance  as single compartment tanks of  the same  total capacity.

-------
Each compartment should have a minimum plan dimension of 2 feet
with a liquid depth ranging from 30 to 60 inches.
  An access manhole should be provided to each compartment. Vent-
ing between compartments should be provided  to  allow free  passage
of gas. Inlet and outlet fittings in the compartmented tank should be
proportioned as for a single tank. (See  Figure  16, page 34). The same
allowance should be made for storage above  the  liquid line  as in a
single tank.


r ~ 11
i n
M
- •
4 	 •- !--,
I
: 	
- - — - —
	 ^


. •
-
_]]
1

                                                  H07C: ALL FITTINGS 4" V.C.
                                                      OUTLET FITTING SET 3"
                                                      BELOW INLET FITTING
                  PLAN
               -VENT
                                                            VENT

                                                        LIQUID CAPACiTI
                                                          750 GALS.
                  LONGITUDINAL
                  SECTION
                                                         SECTION A-A
                        Figure 17.—Precast septic tank.

 Genera/ Information on Septic Tanks
    Cleaning.—Septic tanks should be cleaned before too much sludge
 or scum is  allowed to  accumulate.  If  either the sludge or scum  ap-
 proaches too closely  to the  bottom of  the outlet device, particles will
 be scoured  into the disposal field and will clog the  system. Eventually,
 when  this  happens, liquid may break  through to the  ground  surface.
 and the sewage may  back up  in  the plumbing fixtures. When  a  dis-
 posal  field  is clogged  in this manner, it is not  only necessary to clean
 the tank, but it also may be necessary to construct a new disposal field.
    The tank capacities given in Table 5 on page 29 will give a reason-
                                                                    :s

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able period of good operation before cleaning becomes necessary. There
are wide differences in the rate that sludge and scum will accumulate
from one tank to the next. For  example, in one case out of 20, the tank
will reach the danger point, and should be cleaned, in less than 3 years.
Tanks should  be inspected at least once  a year and  cleaned when
necessary.
  Although it  is difficult for most  homeowners,  actual  inspection of
sludge and scum accumulations is the only way to determine definitely
when a given tank  needs to be pumped. When a tank is inspected, the
depth  of sludge and scum should be measured in the vicinity of the
outlet  baffle. The  tank should be cleaned if  either:  (a) The bottom
of the scum  mat is within  approximately 3 inches of the bottom of
the outlet  device; or (b)  sludge comes within the limits specified in
Table  6 (see  Figure 18, page 37).

                   Table 6.—Allowable sludge accirmu/ofion

Liquid capacity
of tank,
gallons *

750. .
900
1,000 	


2i/£ feet
Distance from 1
5
4
4

Liquk
3 feet
>ottom of outlet
6
4
4

I depth
4 feet
device to top c
10
7
6


5 feet
>f sludge, inches
13
10
8

  • Tanks smaller than the capacities listed will require more frequent cleaning.

  Scum can be measured with a stick to which  a  weighted flap  has
been  hinged,  or with any  device  that can be used  to  feel out  the
bottom of the scum  mat.  The stick is  forced  through the mat,  the
hinged flap falls into a horizontal position, and the stick is raised
until  resistance from the bottom of the scum is  felt. With the same
tool, the distance to the bottom of the outlet device can be found  (see
Figure 18, page 37).
  A long stick wrapped with rough, white toweling and lowered to the
bottom of the tank will show the depth of sludge and the liquid depth
of the tank. The stick should be lowered  behind the outlet device
to avoid scum particles. After  several minutes, if  the stick is carefully
removed, the sludge line can be distinguished by sludge particles cling-
ing to the toweling.
  In  most communities  where septic  tanks  are used, there are firms
which conduct a business  of cleaning septic tanks. The local health
department can  make suggestions on  how to  obtain  this  service.

-------
 Cleaning is usually accomplished by pumping the contents of the  tank
 into a  tank truck. Tanks should not  be washed or  disinfected after
 pumping.  A small residual  of sludge should be left  in the  tank for
 ceding purposes. The material removed may be buried in uninhabited
 places or,  with  permission  of the proper authority,  emptied into a
sanitary  sewer system. It should  never be emptied  into storm drains
or ducharged directly into any stream or watercourse.  Methods of dis-
posal should be approved by the health authorities.
  When a large  septic  tank is being cleaned,  care should  be  taken
    to enter  the tank until it has been  thoroughly  ventilated  and
 ;ases have  been removed to  prevent explosion hazards  or asphyxiation
   the workers. Anyone  entering  the  tank  should have  one  end  of a
 :out rope tied  around his waist, with the other end held  above ground
      MlEl
  -T
   6
                           SCUM CLEAR SPACE A

                               SLUDGE CLEAR SPACE B
                                                                 COVER
                                                                OUTLET
                       WHITE TOWELING WILL BE BLACKENED-
                       BY SLUDGE
         j- MEASURING
       /  DEVICES
           FOR SCUM-

                                             MEASURING STICK
                                             FOR SLUDGE -
                                             TURKISH TOWELING
                            WEIGHT

                         NOIE: MAKE MEASURING STICKS ABOUT 6 LONG
                          HINGE
   NOTE: CLEAN WHEN A IS 3" OR LESS, AND
       WHEN B IS WITHIN THE LIMITS SPECIFIED
       IN TABLE 6.
            Figure T8.-Devices for measuring sludge and
                                                 scum.

-------
by  another  person strong enough  to  pull  him out  if he  should be
overcome by any gas remaining in the tank.
  Grease Interceptors.—Grease interceptors (grease traps) are not ordi-
narily considered necessary on household sewage disposal systems. The
discharge from a garbage grinder should never be passed through them.
The septic tank capacities recommended in this manual are sufficient
to receive the grease normally discharged from a  home.
  Chemicals.—The functional operation of septic tanks is not improved
by the addition of disinfectants or other chemicals. In general, the addi-
tion of chemicals to a  septic tank is not recommended. Some proprie-
tary products which are claimed to "clean" septic tanks contain sodium
hydroxide or potassium hydroxide as the active  agent. Such compounds
may result in sludge bulking and  a large increase in  alkalinity, and
may interfere with  digestion. The resulting  effluent may severely dam-
age soil structure and cause accelerated  clogging, even though some tem-
porary relief may  be experienced immediately  after  application of
the  product.
  Frequently, however,  the harmful  effects  of ordinary  household
chemicals are overemphasized. Small  amounts of chlorine bleaches,
added ahead of  the tank, may be used for odor control and will have
no  adverse effects. Small quantities  of  lye or caustics normally used in
the  home, added to plumbing fixtures is not  objectionable as far as
operation of the tank  is concerned. If the septic tanks are  as large as
herein recommended, dilution of the  lye or caustics in the tank will
be enough to overcome any harmful effects that might otherwise occur.
  Some  1,200 products,  many containing enzymes, have been  placed
on  the  market  for use in septic tanks, and extravagant claims have
been made  for some of  them. As far  as is  known, however, none has
been proved of advantage in properly  controlled tests.
  Soaps, detergents, bleaches, drain cleaners, or other material, as nor-
mally used in the  household, will  have no appreciable adverse effect
on  the system. However, as both the soil and essential organisms might
be  susceptible to large doses of chemicals and disinfectants, moderation
should  be the rule. Advice of  responsible officials should be  sought
before chemicals arising  from a hobby or home industry are discharged
into the systems.
  Miscellaneous.—It is generally advisable  to  have all sanitary wastes
from a household discharge to a single septic tank and  disposal system.
For household installations, it is usually more economical to provide
a single  disposal system than two or more with the same total capacity.
Normal  household waste, including that from the laundry, bath, and
kitchen, should pass into a single system.
   Roof drains, foundation drains and  drainage from other sources pro-
ducing large intermittent or constant volumes of clear  water should
 not be piped into the septic tank or absorption  area. Such large volumes
 of  water will stir up  the  contents  of  the tank and carry some of the

 38

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solids into the outlet line; the disposal system following the  tank will
likewise become  flooded or clogged, and may fail. Drainage from garage
floors or other sources of oily waste should also  be excluded from the
tank.
  Toilet paper  substitutes should  not be flushed into a septic  tank.
Paper  towels, newspaper,  wrapping  paper,  rags, and  sticks  may not
decompose in the tank, and are likely to lead to clogging of the plumb-
ing and disposal system.
  Waste brines  from household water softener units have no adverse
effect on the action of the septic tank, but may cause a slight shorten-
ing of the life of a disposal field installed in  a structured clay type soil.
  Adequate venting is obtained through  the building plumbing if the
tank and the plumbing are designed and installed properly. A separate
vent on a septic tank is not necessary.
  A chart showing the location of  the septic tank and disposal system
should be placed at a suitable location in dwellings served by such a
system. Whether furnished by the builder, septic tank  installer, or the
local health  department, the charts  should  contain brief instructions
as to the inspection and maintenance required. The charts should assist
in acquainting homeowners of the  necessary maintenance which septic
tanks require, thus forestalling  failures by assuring satisfactory opera-
tion. The extension of the manholes  or  inspection holes of the septic
tank to within 8 inches of the ground surface will simplify maintenance
and cleaning.
  Abandoned septic tanks should be filled with earth or rock.
INSPECTION
  After a soil absorption system has been installed and  before it is used
the  entire system should be tested  and inspected. The septic  tank
should be filled with water  and allowed to stand  overnight to check
for leaks. If  leaks  occur, they should  be  repaired.  The soil absorption
system should be  promptly  inspected  before it  is covered to be sure
that the disposal system is installed properly. Prompt inspection before
backfilling should be  required by local regulations, even where approval
of plans for the subsurface sewage disposal system has been required
before issuance  of a  building permit. Backfill material should be free
of large stones and other deleterious  material and should be overfilled
a few inches to  allow for settling.
                                                                  39

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                   Part II
                        Septic  Tank - Soil Absorption
                        Systems for Institutions,
                        Recreational Areas, and
                        Other Establishments
             INTRODUCTION
  The septic tank system is utilized in providing sewage treatment and
disposal for many types of establishments, such as schools, small insti-
tutions, motels, rural hotels  and restaurants, trailer parks,  housing
projects,  large  private estates, and camps, where  larger quantities of
sewage are involved than are discharged from an individual home. In
general, the usefulness of the septic tank system decreases  as the size
of the establishment served increases.  Lack of competent sanitary engi-
neering advice  in  the development of such systems generally will lead
to failures, excessive costs, and a multitude of troubles.  The soundest
advice available to anyone contemplating such  a system is the early
retention  of competent sanitary engineering consultation, whose  first
determination should be the suitability of this method of sewage dis-
posal for the proposed establishment.
  Any institutional septic tank system must incorporate appurtenances
and  supplemental features of  design to meet the requirements  of the
establishment and varying site conditions. These can be  generally suc-
cessful when appropriate experience, study, and planning are employed
in the choice and development of such a system.  This manual cannot
present all of the results of experience gained in the design and opera-
tion  of such systems, but describes the most generally successful proce-
dures and practices as a guide  to engineers designing them.
  While many  effluents from institutional septic tanks are disposed of
by soil absorption methods, others are  discharged to available  water-
courses after suitable treatment. When soil absorption systems  are con-
templated, it is essential, as described  in Part I, to determine the char-
acteristics  and suitability of the soil as the first step toward  design. As
a matter of fact, the wise builder of an establishment will explore this
feature on a contemplated site before the site is purchased. After the

                                                                41

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percolation tests are completed,  the  quantity of sewage to be treated
must be estimated to determine  the size and capacities of  the disposal
units.

ESTIMATES OF SEWAGE QUANTITIES
  Where there are water meters in existing buildings, the quantity of
sewage may best be estimated from the recorded meter readings.
  In using water meter readings for estimating the quantity of sewage
to be contributed, some allowance should also be made for maximum
conditions  that may not be readily  apparent from the readings. For
example, water consumption by an ordinary family of four in an apart-
ment building may average 48 gallons of water per person per day over
a period of 5 months, but actually range from perhaps 30 gallons per
person on certain days to something in excess of 80 gallons per person
on days when water consumption  is  heaviest, as on washdays.  Besides
these peak loads, some allowance should be made for the  sewage con-
tributed by occasional guests. Therefore, when computing sewage flows
from average meter readings, a minimum factor of safety  gf about 25
percent should be allowed to cover the range of variations. Accordingly,
the design  of a  disposal  system  for the apartment house  referred  to,
where  the  average usage is 48 gallons per person per day, should be
based upon a computed maximum  usage of at  least  60  gallons per
person per day.
  Conversely, unusually high meter  readings may be caused by lawn
sprinkling or by leakage of water that does not enter the  disposal sys-
tem. Due allowances should be made for abnormalities of this kind.
  Where measurements of  water consumption  are  not  possible, as
where water meter records are not available, or where disposal facilities
are being planned for a new building, it is  necessary to use  other
methods of estimating the amount of sewage to be discharged. One way
is to base the estimated flow on the number of bedrooms, as in Part I.
Another way  is to compute  the  flow on the basis of the number and
kinds of plumbing fixtures. If the building is used as a restaurant, the
number of patrons or the number of meals served may be  the best cri-
terion. The competent designer will base his estimates upon a combina-
tion of the various influencing  factors. He will consider each case  on
its own merits, especially when disposal facilities are being designed for
a large institution where the cost of construction will  amount to a con-
siderable sum. If definite information and accurate water measurements
are not available, the quantity of sewage may be estimated from experi-
ences at establishments similar  to  that for which the new sewage dis-
posal facilities are intended. Table 7 (page 43) may be helpful  in such
cases.
  The quantities listed in the table are merely the best averages  avail-
able at this time,  and they  should be modified  in localities or  estab-
lishments where  experience indicates a need  for so doing.

42

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  It is sometimes  economical and advisable to construct separate dis-
posal systems for different types of wastes at a given establishment. The
decision  as  to the  number of disposal  systems may  be  influenced by
conditions of terrain,  topography, and locations of the buildings con-
tributing to  the wastes. At large camps, for example, and at some re-
sorts,  kitchens and central dining facilities  may  be  located at appre-
ciable distances from  the barracks or cottages and cabins.  Under such
circumstances,  the  kitchens  may be  provided with  separate  disposal
systems,  including  facilities  for the  removal  of  grease  ahead of  the
septic tank.


                      Table  7.—Quantities  of sewage flaws

Type of Establishment                               Gallons Per Person Per Day
  7r                                                (Unless Otherwise Noted)
Airports (per passenger)  	                     5
Apartments—multiple family (per resident)  	                    60
Bathhouses and swimming pools 	                    10
Camps:
  Campground with central  comfort stations  	                    35
  With flush toilets, no showers 	                    25
  Construction camps (semi-permanent)  	                    50
  Day camps (no meals served)  	                    15
  Resort camps (night and day) with limited plumbing                     50
  Luxury camps 	                    100
Cottages and small  dwellings with seasonal occupancy   ...                    50
Country clubs (per  resident member)  	                    100
Country clubs (per  non-resident member present)  	                    25
Dwellings:
  Boarding houses  	                    50
    additional for non-resident  boarders  	                    10
  Luxury  residences and estates 	                    150
  Multiple family dwellings (apartments)  	                     60
  Rooming houses  	                    40
  Single family  dwellings  	                    75
Factories (gallons per person, per shift, exclusive
  of industrial wastes) 	                     35
Hospitals (per bed  space)  	                    250+
Hotels with private baths (2 persons per room)  	                    60
Hotels without  private baths 	:	                    50
Institutions other than hospitals (per bed space) 	                    125
Laundries,  self-service (gallons  per wash, i.e., per
  customer)  	                    50
Mobile home parks (per space) 	                    250
Motels with bath,  toilet, and kitchen wastes
   (per bed  space)  	                    50
Motels (per bed space) 	                    40
Picnic Parks (toilet wastes only) (per picknicker)                             5
Picnic parks with bathhouses, showers, and flush toilets                       10
Restaurants (toilet  and kitchen wastes per patron) 	                     10

                                                                         43

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                              Table 7.—Continued
Type of Establishment
                      Gallons Per Person Per Day
                       (Unless Otherwise Noted)
Restaurants (kitchen wastes per meal served) 	
Restaurants additional for bars and cocktail lounges
Schools:
  Boarding  	
  Day, without gyms, cafeterias, or showers 	
  Day, with gyms, cafeteria, and showers  	
  Day, with cafeteria, but without gyms, or showers
Service stations  (per vehicle  served)  	
Swimming  pools and bathhouses	:	
Theaters:
  Movie (per auditorium seat) 	
  Drive-in  (per car space) ,	
Travel trailer  parks without individual water and
  sewer hook-ups (per  space)  	
Travel trailer  parks with individual  water  and
  sewer hook-ups (per  space)  	
Workers:
  Construction  (at semi-permanent camps)  	
  Day, at  schools and offices  (per  shift) 	
                                           3
                                           2

                                         100
                                          15
                                          25
                                          20
                                          10
                                          10

                                           5
                                           5

                                          50

                                         100

                                          50
                                          15
  Separate systems may also be used for community bathhouses. When
this is  done,  the total per capita flow must be  broken down into its
component parts, and some allowance  should  be made  for the amount
of sewage tributary to the different disposal systems. Table  8 (below)
illustrates how this may be done  where there are no definite data as to
the exact distribution of flow.

    Table ft.—Estimated distribution of sewage flows, in gallons per day per person
    Type of Waste
    Volume, gallons per day per person
  Total Flow (gallons)...
Kitchen wastes	
Toilet wastes	
Showers, washbasins, etc..
Laundry  wastes	
30
10
15
15
J0
40
 7
15
18
10
50
10
20
20
75
10
25
25
15
100
 15
 30
 35
 20
  1 No wastes from these uses.
Example: In a household contributing 75 gallons of sewage per day per person, as
shown  in column 4, an average breakdown  for each of the four types  of  wastes
listed might be about 10 gallons per day per person for kitchen wastes; 25 gallons

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per day per person for toilet wastes; 25 gallons per day per person for shower wastes,
bathtubs, and washbasins;  and about 15 gallons per day  per person  for laundry
wastes.

   For  certain types of new establishments, the designing engineer may
be unable  to obtain from  his clients accurate estimates as  to the num-
ber of  patrons to be served by the disposal facilities. This is particularly
true in the case of restaurants and at recreational places, such as picnic
areas, country clubs, and the like. In such cases, computations and esti-
mates  may best  be made  from  the number of plumbing fixtures  in-
stalled. Table 9 indicates average values  for quantities of  sanitary
wastes  per fixture at country clubs with modern plumbing.

                  Table 9.—Sewage flow from country dubs
Type of fixture
Showers
Baths ... 	
Lavatories 	

Gallons per
day per
fixture
500
300
100

Type of fixture
Toilets
Urinals 	
Sinks 	

Gallons per
day per
fixture
150
100
50

  Estimates of sewage quantities from golf clubs should be checked and
calculations based on the weekend population. Allowances of 10 gallons
per person for showers  and 7 gallons per person for toilet  and kitchen
wastes,  both for the average  weekend population, have  been found
reasonable.
  Table 10 shows one method used in estimating the amount of sewage
discharged hourly during the hours when public parks are open. Simi-
lar figures may be used  for fairgrounds, carnivals, ball parks, etc.

                   Table 10.—Sewage flow at public parks
                    [During hours when park  is open]

Type of fixture

Flush toilets
Urinals

Gallons per
hour per
fixture
36
10


Type of fixture

Showers
Faucets 	

Gallons per
hour per
fixture
100
15

ESTIMATES OF SOIL ABSORPTION AREAS
  With information from percolation tests and with due consideration
to the results of test borings or subsurface explorations, as explained in
                                                                  45

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 Part I and Appendix A, the rate at which sewage may be applied to a
 soil absorption system may be taken from Table 11 or from the corre-
 sponding curve in Figure  19 (see page 47).


      Table 11.—Allowable rate of cewage application to a toil absorption system


Percolation rate (time
in minutes for water
to fall 1 inch)


1 or less 	
2 	
5 	
4 	
5 	

Maximum rate of
sewage application
(gallons per square
foot per day)1 for
absorption
trenches,* seepage
beds, and seepage
pits 3
5.0
35
2.9
2-5
22



Percolation rate (time
in minutes for water
to fall 1 inch)


10
15
30*
45*
60**

Maximum rate of
sewage application
(gallons per square
foot per day)1 for
absorption
trenches,* seepage
beds, and seepage
pits3
16
1 3
09
08
06

   1 Not  including  effluents  from  septic  tanks that  receive wastes  from  garbage
 grinders and automatic washing machines.
   * Absorption area is figured as trench bottom area, and includes a statistical allow-
 ance for vertical sidewall area.
   'Absorption area for seepage pits is effective sidewall area.
   * Over 30 unsuitable for seepage  pits.
   s Over 60 unsuitable for absorption systems.
  Table 11 and the curves in Figure 19 do not allow for wastes from
garbage grinders and automatic washing machines. Discharge  from
these appliances to an institutional  septic tank system  calls for  extra
capacity of 20 and 40 percent, respectively, over the calculated absorp-
tion area values. If both of these appliances are installed, the absorption
area should be increased by about 60 percent over the calculated value.
Part I allowed for these types of waste in giving specifications for  small
household systems, but they may never  occur in institutional effluents,
such  as those from factories and offices. Other institutions, such as  a
country club  or drive-in theatre  with eating facilities, may contribute
wastes  from garbage grinders, but not from automatic washing ma-
chines. As  previously emphasized, all institutions should have  their
systems designed by an  engineer who  is competent to place proper
evaluations on the kind of wastes to be contributed.
  Use of Table 11  is demonstrated in the following examples, which
illustrates the design for the two types of soil absorption systems. For
each example assume: 5,000  gallons  of sewage per day to be disposed
of;  percolation  rate,  1 inch in 5 minutes.

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    2
    **•
                                 = 5
                               Q Yf'  F°r stondord trenches or seepage pits
          0         10        20        30         40        50       60
                      PERCOLATION RATE IN MINUTES PER INCH (t)

Figure 19.—Graph  showing relation  between percolation  rate and allowable  rate at
                            sewage  application.
Example I.—Absorption Trenches:
  Standard trench, 2 feet width.
  5,000 gal./ day -f- 2.2 gal./sq. ft./day — 2,270 square feet of absorp-
     tion  area required.
  2,270 -H 2 sq. ft/linear ft.  = 1,135  feet of trench required.
With garbage grinder only—1,135 -f- .20  (1,135) = 1,362 linear feet.
With automatic washing machine only—1,135  4- .40 (1,135)  —  1,589
  linear feet
With garbage  grinder and automatic washing machine—1,135 -\-  .60
  (1,135) = 1,816 linear feet.
Example II.—Seepage Pits:
  Seepage pit  10 foot diameter; depth of effective absorption area 25
feet; let d — effective depth of pit in feet; D equal pit diameter in feet.
Effective sidewall area equals total area needed.
7rD(d) = 2,270  sq. ft.
3.14 (10)  (d) - 2,270.
Solve for d, effective depth of pit — 72 ft.
Obviously, more than one pit is required.
Design for 3 pits, 10  ft.  in diameter.
  72 ~ 3 = 24 ft.
  Use 3  pits, 10 ft.  in diameter with an effective depth of 24 ft.
                                                                     47

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With garbage grinder only—3.14 (10) (d) = 2,270 + 2,270 (.20) = 2,724
  sq. ft.
Solve for d =  86.4 ft. Use  4  pits,  10 ft. in diameter with  an effective
  depth of 21.6 ft.
With automatic washing machine only—3.14 (10) (d) = 2,270 + 2,270
  (.40) = 3,178 sq. ft. Solve for d  = 101  ft. needed. Use 5 pits,  10 ft.
  in diameter with an effective depth of 20.2 ft.
With garbage grinder and automatic  washing machine—3.14 (10) (d) =
  2,270 +  2,270 (.60) = 3,632 sq. ft. required. Solve for d  = 115.7 ft.
  required. Use 5 pits, 10  ft.  in diameter with an effective  depth of
  23.1  ft.

BUILDING  SEWERS
  The building sewer or house sewer is the  pipeline carrying sewage
from the building or house  drain to a  private sewer, public  sewer,
septic tank, or  other point of  disposal. It usually extends from a  point
3 feet outside the building, where it is connected to the building drain.
  The building sewer should be constructed of cast iron, vitrified clay,
concrete, bituminized fiber,  asbestos cement, or other durable material.
AH joints in the sewer line should be watertight  and rootproof. The
grade of the building sewer should be at least 2 percent  (2 foot fall per
100 feet, or 14  inch per foot)  except for the 10 feet immediately pre-
ceding the  septic tank, where it should not exceed  2 percent.  Buildings
should be planned so that a proper slope  of the  building sewer can be
obtained. Where the terrain is extremely  flat, however, it  may be ad-
visable to allow a slope of only  6 inches  per 100 feet,  or  0.5 percent
(see Table  12, page 49).
  The size of the pipeline to a septic tank is generally dependent upon
its ability to allow objects  to  pass, and upon its  capacity to conduct
high flows  for short periods, rather than upon its capacity in relation
to the  average  flow. No building sewer serving water closets should be
less  than 4 inches in size. The relationship of minimum  sizes  to the
slopes  and to the number  of  fixture units is indicated in Table  12.
  Cleanouts should be provided  at the junction of the  building  drain
and  building sewer and at each change in direction of the  building
sewer greater than 45° They  should also  be provided  at  intervals of
not more than  100 feet. That  portion of the sewer line within 50 feet
of any well or suction  line  from a well, or within  10 feet of any
drinking water supply line under pressure  or  within  5 feet of any
basement foundation should be durable, corrosion  resistant, root proof,
and  so installed as to remain water tight. Cast  iron  or  other high
strength  pipe should be required wherever the line crosses under drive-
ways with  less  than 3 feet of  earth cover. While no general  statement
can  be made to cover all cases, Table 2 (page  10) should be followed
in locating components of the sewage  disposal system. Where  sewer
lines are in the vicinity  of trees  or dense shrubs,  and are not con-

45

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Table 12.—Maximum number of drainage  fixture  units1  served  by  building sewer  of
                          indicated size and  slope
Minimum pipe diameter,
inches
4 	
5
6 	
8 , ..
10
12 	


Me



1,400
2,500
3,900

Pipe slope i
ys
180
390
700
1,600
2,900
4,600

inch per foot)
y*
216
480
840
1,920
3,500
5,600


%
250
575
1,000
2,300
4,200
6,700

  1A  drainage fixture unit is a quantity  in  terms of which  the load producing
effects of different plumbing fixtures on the plumbing system are expressed on some
arbitrarily chosen scale. For example, a small lavatory is rated as 1 fixture unit; a
kitchen sink, 2; a bathtub, 2;  a tank operated water closet, 4; and a valve operated
water  closet, 6. A table of ratings from the United States of America Standards Insti-
tute National Plumbing Code  is given in Appendix  D, page 85.

structed  of cast iron as indicated above, the joint should be made of
special, root resistant construction.
   Bends ahead of  the  septic  tank should  be  limited to 45° or  less
wherever possible.  If 90° bends  cannot  be avoided,  they  should  be
made with  two 45°  ells, or a long sweep quarter curve or bends.

COLLECTION SYSTEMS
   At  institutions  where  there are a number of buildings,  it may  be
advisable to provide a system of  sewers for the collection,  transporta-
tion,  and possibly the pumping of sewage to the septic tank.  In general,
the collection system should be designed for a capacity expected to be
adequate for at least one decade, and preferably two. It  is usually ad-
visable to design the sewers with  capacities, when running full,  of not
less than 10 times the average estimated  flow of sewage.
   Institutional  sewers carrying raw or untreated  sewage should  be at
least  6 inches  in diameter and have slopes of at least ys inch  to the
foot (1.0 percent). In very small installations, 4 inch sewers  at 14  inch
per foot (2 percent)  may be used to carry raw sewage, and 4 inch sewers
with slopes of  y8 inch per foot are acceptable  for carrying settled sew-
age. All sewers should be  designed and  constructed with  hydraulic
slopes sufficient to give mean velocities, when  flowing full,  of not  less
than  2.0 feet per second, based on Kutter's or Manning's formula using
an "n" value of 0.013. Use of other practical  "n" values will be per-
mitted by the plan reviewing agency for longer pipe sections if deemed
justifiable on the basis of research or field data presented.
   Under exceptional conditions, if full and justifiable reasons are given,
                                                                    49

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and  if  special arrangements  are available  or will  be provided for
flushing, velocities as low as  1.6 feet per second may be permitted. In
general, the following minimum  grades should be provided:
                                                           Percent
    8 inch  sewers	 0.40
    10 inch  sewers	 058
    12 inch  sewers	 0.22
  The use of a larger sewer to take advantage of the lesser minimum
slope, when there is not enough sewage to fill the sewer nearly one-half
full, is generally not advisable. The  use of asbestos cement pipe or
enamel lined or cement lined cast iron pipe is suggested under such
conditions.
  Sewer  lines must be laid on straight alignment and uniform slope
between  manholes. Manholes should be placed on sewers at all points
of change of slope or alignment, at the upper ends of all sewer lines,
and otherwise at intervals not greater  than 400 feet. If the  topography
is very uneven and frequent changes in alignment and slope are neces-
sary, a limited number of lampholes may be substituted for manholes
at such  points of change.  Not more  than  one  lamphole should be
placed between two successive manholes.
  There must be  no physical connection- between a public or  private
potable water supply system and a sewer,  sewage disposal  system, or
appurtenances thereto, which would render possible the passage of any
sewage or polluted water into the potable water supply.

GREASE TRAPS
  Premature failures of septic tank systems are sometimes due to accu-
mulations of grease within the tanks.  Sewer lines frequently clog be-
cause of  grease collections. Where grease traps are  used, the grease must
be removed at frequent intervals. Grease traps may be used on kitchen
wastelines from institutions, hotels, restaurants,  schools  with lunch-
rooms, and other  places where the volume  of kitchen wastes is large.
After passing through the grease trap,  the kitchen wastes must  still be
treated in the septic tank before being discharged to the disposal area.
Wastes  from garbage grinders should not be discharged to a  grease
trap.  (Grease traps have been used with some degree of success for the
removal  of lints and fines from laundry wastes, but better results may
be  obtained by increasing  the size  of the septic  tanks receiving such
wastes, or by the use of rock filters to remove the lint.)

location
  Grease traps should be placed at a location that is  readily accessible
for cleaning, and  close to the fixture discharging  greasy wastes.

so

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Construction Details
  The most important considerations for design of grease traps are:
  1. Capacity of the trap.
  2. Facilities for insuring that both the inlet and  outlet are  properly
trapped.
  3. Ease  and  convenience with  which the traps can be cleaned and
the accumulated grease removed,
  4. Inaccessibility of  the  traps to insects and vermin.
  5. Distance between inlet  and  outlet,  which  should  be sufficient to
allow  gravity differential separation of the  grease,  so that  it  will  not
escape through the outlet.
  The principles are  illustrated in Figure  20.
INLET
                 PLAN
             (TOP REMOVED)     COVER OF REINFORCED
                            •CONCRETE, ALUMINUM
                             OR CAST IRON
                                    INLET
                               OUTLET
                   4
                   f
                SECTION
              CONCRETE BOX
                                                                 PLAN
                                                             (TOP REMOVED)
                                                                  OUTLET
                                                                 CLAY TILE
                                                                 PIPE
     ,
   /SEALED IN CONCRETE
  SECTION
CLAY TILE PIPE
         2" INLET FROM
         KITCHEN SINK
                                       ALUMINUM OR C.I. COVER

                                                   • CLEANOUT
                                                            4" OUTLET TO
                                                            MAIN SEWER
                      Figure 20.—Typical grease traps.

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  Flow control fittings should be installed on the inlet side of smaller
traps to protect against overloading or sudden surges from  the sink or
other fixtures.  Venting is not necessary  in the large, outdoor  traps,
where siphonage of the contents can be prevented by providing outlets
of liberal size. Where efficient removal of grease is very important, use
has been made of an improved 2 chamber trap which has a  primary
(or grease  separating) chamber and a secondary (or grease  storage)
chamber. By placing the trap as close as possible to the source of wastes,
where the wastes  are still hot, the separating grease at the surface may
be removed by means of an adjustable weir and  conveyed to  the  sep-
arate secondary chamber, where it accumulates,  cools, and solidifies.

Capacity

  Selection of size of traps should be based on verified efficiency ratings
and flow capacities. The required flow capacities should be  based upon
the number and  kind of sinks or fixtures discharging to the  trap. In
addition, a grease trap should be rated on its  accumulated grease ca-
pacity, which is the amount of grease (in  pounds) that the trap can
hold before its average efficiency drops below  90 percent.  It is com-
monly regarded that the grease retaining  capacity in pounds should
equal at least twice the flow rating in  gallons  per minute.  That is to
say, a trap rated at 20 g.p.m. should retain at  least 90 percent  of the
grease discharged to it until it holds at least 40 pounds of grease. Most
manufacturers  of  commercial traps rate  their  products in  accordance
with this procedure.
  Recommended minimum flow rate capacities of traps connected to
different types  of fixtures is given in Table 13.
           Table 13.—Recommended ratings for commerciaf grease traps

Type of fixture

Restaurant kitchen sink 	
Single compartment scullery sink ...
Double compartment scullery sink
2 single compartment sinks 	

2 double compartment sinks 	

Dishwashers for restaurants:
Up to 30 gal. water capacity 	
30 to 50 gal. water capacity 	
50 to 100 gal. water capacity 	

Rate of
flow, in
g.p.m.
15
20
25
25

35


15
25
40
Grease
retention
capacity
rating, in
pounds
30
40
50
50

70


30
50
80
Recommended
maximum
capacity of
fixture con-
nected to trap,
in gallons
37.5
50.0
62.5
62.5

87.5


37.5
62.5
100.0
52

-------
  A net capacity of 2.i/2 gallons per person has been found large enough
to hold the flow from  one meal  long enough  to  accomplish  proper
grease separation. The minimum allowable capacity should be about
125 gallons for small installations serving up to 50 people with propor-
tionately larger capacities for larger populations. As with septic tanks,
however, it is  generally good economy to build  grease  traps somewhat
oversize. For installations too small to justify a 125  gallon grease trap,
best results can usually be obtained by applying available funds to an
oversized and  properly fitted septic tank.
Operation
  In order to  be effective, grease traps must be  operated properly and
cleaned regularly to prevent the escape of appreciable quantities of
grease into the septic tank. The frequency of  cleaning at any given
installation can best be determined by experience based on observation
over selected typical periods of use. Generally,  cleaning should be done
when  75 percent of the grease retention capacity is filled with accumu-
lated grease.
  Grease traps must be  kept tightly covered to prevent odor nuisances
and to exclude insects and vermin. Grease removed from the traps is
disposed of by burial. (It may be used for making soap and glycerine,
and for other manufacturing purposes, when  economically feasible or
because of shortages of such materials during wartime.)
SEPTIC TANKS FOR INSTITUTIONAL SYSTEMS
  As explained in  Part I, septic  tanks of two compartments give better
results than single compartment tanks. Although single compartment
tanks  are  acceptable for small household installations,  tanks with two
or more compartments should be provided for the  larger institutional
systems.  Tanks  with  more than  two  compartments  are  installed
infrequently.
  The compartments should be  separated by walls containing ports or
ell fittings at proper elevations as discussed in  Part I, pages 30 and 32.
In the selection of these elevations, the same  general principles apply
as in the design of outlet fittings.  Vents for the passage of gases from
one compartment to another should  also be included.
  In a two compartment tank,  the compartment nearest the outlet is
used both as  a settling basin and as  an observation well. The relative
absence of solid material in  the  second compartment serves as an indi-
cation that the tank is functioning properly, although it may not serve
as an index of conditions within the  first compartment, and it is some-
times advisable to clean the  first compartment before accumulations in
the second become appreciable.  In a two compartment tank, the first
compartment should have a capacity of at least  two to three times the
capacity of the second compartment.
  Whatever the  number of  compartments, means should be provided
for gaining access to each compartment,  and for measuring the depths

                                                                53

-------
of sludge and  scum  at  the  outlet device as illustrated  in Figure  18
(page 37). Unless tops of septic tanks are near the surface of the ground,
as in  Figure 15 (page 33), manholes should be provided as required  to
facilitate ingress and egress. A  single manhole above  a  dividing  wall
may be used for gaining access to two compartments in a multicom-
partment tank. Manholes are also desirable over the inlet and outlet
devices.
  Alternate designs for manholes are shown in Figure 14 (page 32). The
design selected will depend  on whether or not the manhole cover must
be flush with  the  surface, and on  the anticipated traffic loadings  over
the area.
  The effect of a  multiple compartment tank can be accomplished  by-
using two  or three tanks in  series. A better construction  arrangement,
particularly for medium or large installations, is to connect special tank
sections together into a  unit having single end-walls and  two compart-
ments. A unit of four precast tank sections forming two  compartments
is shown in Figure 21.
                                                 7- DIA. IMi"KTlON HOU
      Figure 21.—Battery of four  precast reinforeed-concrete septic-tank sections.

 Capacities
   The net volume  or effective capacity below the  flowline of a septic
 tank, for flows up to 500  gallons per day, should be at least 750 gallons.
 For flows between  500 and 1,500 gallons per day,  the capacity  of the
 tank should  be equal to at least  H/2 days'  sewage flow. With flows
 greater than 1,500 gallons per day, the minimum effective tank capacity
 should equal 1,125  gallons plus 75  percent of the daily sewage flow; or
                         V  =  1,125 + 0.75Q
 where V is the net volume of the tank in  gallons and Q is the daily
 sewage flow in gallons. If garbage grinders are used, additional volume
 for extra sludge storage  may be desired to minimize the frequency of
 cleaning.

-------
  Recommended tank capacities for flows up to 14,500 gallons per day
may also be  obtained from  Figure 22  (below).  For higher  flows  of
up  to about 100,000  gallons per day,  Imhoff tanks may be more satis-
factory  than  septic  tanks for  primary  treatment.  For  flows  above
100,000 gallons, still  other types of sedimentation tanks may  be more
economical. These fall  within the category of  design  for  municipal
systems, and are beyond the scope of this manual.
DOSING TANKS
  When the quantity of sewage exceeds  the amount that can be dis-
posed of in about 500 lineal feet of tile, a dosing tank should be used
in conjunction with the septic tank, in order to obtain proper distribu-
1J.UUU


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          1000  2000 3000 4000  5000  6000 7000  8000  9000 10.00011,00012.00013.00014.000
                       SEWAGE FLOW, "Q". IN GALLONS PER DAY

   Figure 22.—Septic-tank capacities for sewage flows up to 14,500 gallons per day.
 tion of sewage throughout  the disposal area and give the absorption
 bed a chance  to rest or dry out  between dosings. Rest periods are always
 advantageous, especially  when the  soil  is  dense.  The  dosing  tank
 should be  equipped with an  automatic siphon which discharges the
 tank once every 3 or 4 hours.  The tank should have a capacity equal
 to  about 60  to  75  percent of  the interior  capacity of the tile to  be
 dosed  at  one  time.

-------
  Where the total length of tile lateral exceeds 1,000 feet,  the dosing
tank should generally be provided with two siphons dosing  alternately
and each serving one-half of the tile field. The proper design of dosing
devices  involves hydraulic problems  and head  losses which  must be
carefully considered. Dosing siphons  require  operating heads ranging
from  about 5 feet down  to a minimum of 1 or 2 feet, and  repeated
studies of different layouts may be necessary  in order to arrive  at an
economical design in which available head is conserved and best  use is
made of existing conditions  of topography. Specal siphons  are manu-
factured for  low head losses. For  details  and capacities, the manufac-
turers' bulletins should be consulted.
  Special care must  be taken in the installation of siphons.  All dimen-
sions  and  elevations should be  carefully followed, and no changes
should be made without prior approval by the engineer or manufac-
turer. Tests should be made to determine that  there are no air  leaks,
either in the piping or bell casting, and if leaks  are found, they should
be repaired.  Leaks  may  be  detected by  filling the dosing tank with
water, to a  point where the bell  and piping connections are covered,
and observing the water surface for rising bubbles. New siphons should
be primed by filling with water when the system is first started anyway,
and  the  tests for leakage can be made at that time.
  When properly installed,  automatic dosing siphons will  give satis-
factory service. They contain no moving parts and are more  foolproof
than  any dosing device that depends upon moving parts for its  opera-
tion.  Figure 23  (page 57) shows a  septic tank and dosing compartment
with  alternating siphons, as illustrated in suggested plans and designs
developed  by a State health department.
  A typical layout plan or "general plan" of a system using alternating
siphons  is  illustrated in  Figure 24 (page 58).
  Separate siphon compartments  already equipped with siphons are
made by some manufacturers.  Duplex siphon compartments  equipped
with two siphons which operate alternately are  also prefabricated.
  If  the head  available is inadequate to permit  the use of  a siphon,
intermittent pump operation may be used  to obtain  proper dosing of
the field, as  shown  in Figure 25 (page 60). The pump discharge lines
may be inter-connected to obtain  flexibility and to facilitate operations
when one pump is down for repairs.

 SAND FILTER TRENCHES
   In permeable soil, absorption  trenches  of the  type  illustrated in
Figure 5 (page 12), seepage beds, or seepage pits as illustrated in  Figure
 10 (page 24),  provide  the best underground method of disposing of
 the effluent from a septic tank. The absorption  trench is preferred, and
 is required  in  some areas where seepage pits  are  prohibited.  In soil
 that  is relatively impermeable, however, neither  absorption trenches,
 seepage beds nor seepage pits are satisfactory.  They become more ex-

 56

-------

                  SEPTIC
                  TANK
                             l!  II
DOSING
CHAMBER
                                              ALTERNATING
                                              SIPHONS
                            PLAN
     GRADE
 INLET

                                                       OVERFLOW
                                                             DISCHARGE
                         SECTION (NOT TO SCALE)
         Figure 23.—Septic tank and dosing tank with  alternating siphons,
pensive as the soil permeability decreases, and may not be economically
feasible when the percolation time exceeds 30 or 40 minutes per  inch.
The exact point  at  which they  are no  longer  desirable will depend
largely  upon  the  relative costs  of labor and  material  in the locality
where  the disposal system is to  be constructed.  The  decision as to
whether to  use  absorption trenches, seepage beds  or seepage  pits may
also depend upon the area available. Where land is at a premium, ab-
sorption trenches  become less attractive.  They begin to  require exces-
sive areas when the percolation time exceeds 20  minutes per inch.
  When absorption trenches,  seepage beds, and seepage pits are imprac-
tical for institutional  or similar  use,  the possibility of treating the
tank effluent in subsurface sand filter trenches may be considered.
  The filter trenches are somewhat  similar to absorption trenches, the
major  difference being that  the  filter trenches are  deeper, generally
somewhat wider, contain an intermediate layer of  sand as filtering ma-
terial,  and are provided  with underdrains  for carrying off the  filtered
sewage. The tank effluent is  not absorbed, except to a  limited  extent.
It is simply filtered and must be disposed of when it  leaves the  trench.

-------
            WELL 6  DIA.-140  DEEP THROUGH SAND AND LIMESTONE
            NEAREST OTHER WELL 200 YDS. NORTH
153
                            HOTEL

                  26 RMS; 25 BATHS, 25 TOILETS

                     y/1  /— 6" PIPE
                     f
4" KITCHEN WASTE LINE
            \
  GREASE TRAP (150 GAL.)
               \
   GARBAGE GRINDER LINE
                                       SLOP! 1%

                                      MANHOLE
                                                    NEAREST ADJOINING WELL 375
                                                           "TEST HOLE"-(T.H.)
                                                           1" DROP IN 5%
                                                           MINUTES
                                        4050 GAL. OR
                                        LARGER SEPTIC TANK
                                         DOSING TANK
                                         PARTITION
                                                 80
                         ALTERNATING   "Sf   /
                             SIPHONS-—J/  y'
                 DIVERSION BOX	-
                                          V    ' I*-
                                                                                    150
       Figure  24.—Typical  layout plan  of  a subsurface sewage-disposal  system.

-------
         DESIGN  DATA FOR DISPOSAL ILLUSTRATED  IN FIGURE 24
      Hotel
  26 rooms total
  20 rooms with  private baths x 2 persons per room
      X 60 gal. per person per day                     = 2,400 gal.  per day
  6 rooms with connecting baths x 2  persons per room
      X 50 gal. per person per day                     =   600 gal.  per day
  5 daytime employees x 25 gal. per  person per day     r=   125 gal.  per day
  2 night employees x 25 gal. per person per day       —   50 gal.  per day
  Kitchen  wastes: 60 persons  x 3 meals per day
      X 4 gal. per meal                               =   720 gal.  per day
       Total daily sewage flow                        = 3,895 gal.  per day
       Required septic  tank capacity  (from Fig. 22)     = 4,046 gal.
  (In  this case, consideration should  be given to using a 5,000 gal.  capacity tank
  which will  require less frequent cleaning.)
  Required grease trap  capacity 60  persons x 2i/£ gal.   =   150 gal.
  Percolation  test:  6 min. per  inch drop.
  Allowable rate of  sewage application (from Fig. 19)      =  2.1 gal. per sq. ft.
                                                              per day
Trench area required for normal wastes                   = 	= 1,855 sq.  ft.
Plus 20% additional for wastes from garbage grinder          371 sq.  ft.
Total trench  area required                              = 2,226 sq.  ft.
Desired trench width                                   — 24 inches (2.0 ft.)
Total  trench length                                   = -?HH1 -  1,113 ft
    As stated in  the section on Dosing  Tanks,  where the  length of  trench1 exceeds
  1,000 feet a dosing tank should be used  with alternating  siphons,  each serving one
  half of  the  absorption field.
  Total trench length                                       111 s      ...   ,  r
	T	                  —     - — 557  Lineal  ft.
  Number of  separate absorption fields                       2          j trench
                                                                     per  field.
  80 ft. lengths can  best  be worked into  available disposal area with room for future
  additions if needed.
XK7
      —  7 lines of (4") laterals required for each field.
 80               \ /          i
  Preferred dosing tank  capacity =  75  percent of interior capacity of tile to be dosed
    at one time.
  4" tile = 3.14 x  22 X !2  = 151 cu. in. per ft.
151 cu. m./ft. x  0-75   _ 049  gai./ft.   required  dosing  tank  capacity  (say  0.5)
   231 cu. in./gal.
  Thus the capacity of  the dosing tank  should  be 0.5 gat./ft, x ~<  X  80 ft. — 280
    gallons.


    For  this  reason,  filter trenches  are  properly  regarded  as  a means  of
  sewage  treatment,  and not sewage  disposal.  They  accomplish  a  high
  degree of purification,  however, and the  sewage effluent coming from a
  filter trench  that is properly designed  can  sometimes be  disposed  of
  without further treatment, by  discharging into ditches,  small streams,
  or dry  streambeds.  If  the receiving stream contributes to  a source  of
  water supply, shellfish growing area, or recreational area,  chlorination
  should  be  required as  hereinafter explained. In   some  jurisdictions,
  chlorination is  required for all  effluents from sand filters.

                                                                            59

-------







1
-

t
II
1
-—, I'-ll
| seme TANK


1
li
: ij
1 '
'',1
1 1
                                HAN
                                   SECTION
                                 (NOT TO SCALE)
               Figure 25.—Septic tank and pump-dosing chamber.
  Approval should be obtained from the State or  local health depart-
ment before filter  trenches are installed. This method of sewage treat-
ment becomes less economical  and  less desirable  as the quantity  of
sewage and the required area increase.  Subsurface  sand filters may  be
needed for larger  installations.
Construction Features
  Typical details of an underdrained sand filter trench  are  shown  in
Figure 26 (page  61). For all year service, filter trenches should  be de-
signed for filtration rates as given in Table 14.

                 Table  14.—Loading rates  for subsurface fitters
Type of service
With(
With
With
With
>ut garbage grinder or automatic washer 	
garbage grinder
automatic washing machine
both garbage grinder and automatic washer
Area Requirements
Gallons
per acre
per day
50.000
41,500
50,000
41,500
Gallons per
square feet
per day
1.15
0.95
1.15
0.95
   The  filtering  material should  be clean,  coarse sand, all  passing a
screen having four rneshes to the inch.
   The  sand should have an effective size  between  0.25  and 0.6 mm
60

-------
                              FILL MATERIAL
                          UNTREATED BLDG. PAPER
                             "_2'/j" GRAVEL O«
                           CRUSHED STONE
                              FINE GRAVEL
                                                   4 PERFORATED P
                                                   OR DRAIN TILE
                                                   WITH OPEN JOINTS
4' PERFORATED PIPE
OR DRAIN THE
WITH OPEN JOINTS
                            UNDISTURBED EARTH
                             "-2'/>" GRAVEL OR
                           CRUSHED STONE
                             CROSS SECTION
                                                          SECTION B-B
             8' LENGTHS
                   PERFORATIONS
              CONNECTING TILE OF
              BELL AND SPIGOT PIPE-OPEN JOINTS
                          SECTION A-A
                  Figure 26.—Underdrained sand-filter trench.
and preferably 0.4  to 0.6  mm. The  uniformity coefficient should be
less than 4.0.
  Fine  sand will lead to premature clogging and  a need for replace-
ment. The sand should  be not less  than 2 feet  deep.
  The  distributors and underdrain should  be surrounded  by  coarse
screened gravel or crushed  stone. All of the gravel or stone should  pass
a 2y2  inch screen and should be retained on  a % inch screen. Fine
gravel,  down  to  14  inch,  may be  used above  and around the  coarse
material, both at the distributors and at the  underdrains.
  The  slope of  the  distributors should be  about 0.5 percent  where

                                                                      6'

-------
dosing tanks are not used, and the slope of the underdrains about 0.5
to  1.0 percent.  It is essential that the  sand be thoroughly  settled  by
flooding or other means before the distributors are placed at the final
grade. The distributor and underdrains may be of agricultural tile or,
bell and spigot pipe, or perforated pipe.
SUBSURFACE SAND FILTERS
  As indicated  previously, filter trenches are not economical for large
installations. Subsurface sand filters are cheaper. They require less area,
and will do the job just as  well as filter trenches.  They require more
care in design and construction, but this is more than  offset  by savings
in  cost. As a rough guide, filter trenches are impracticable  when the
amount of sewage (and consequently the filter area or the length of tile
distributors) is enough to require the use of dosing siphons. Subsurface
sand filters are generally indicated when dosing siphons are  needed in
conjunction with artificial filtration.
  The principles of design of subsurface sand filters are similar to the
fundamentals involved in the layout of filter  trenches. Both types of
installations have distributors  and underdrains, with  filter  sand  be-
tween. The essential difference in  the  two is  that filter trenches  are
smaller and the filter material is  laid in trenches, as implied in  the
name. When two or more  trenches are used, natural earth is  permitted
to remain between them. For subsurface sand filters, on the other hand,
the entire filtration  area is filled in artificially.  A typical plan and sec-
tion of  a subsurface sand filter are illustrated in Figure 27  (page 63).

Construct/on Features
  The sand in a subsurface filter should be of  a quality at least equal
to  that specified for a filter  trench, with  an effective size preferably
between 0.4 and 0.6  mm, and never less  than 0.25 mm, and with a uni-
formity coefficient less than 4.0. The gravel or crushed stone should
likewise be equal to the quality previously specified.  The  same depth
of sand is  used, and the required filter area is the same  as given  in
Table 14, with  one  exception: Where filters are constructed  solely for
seasonal use and have long rest periods over the greater  part of  the
year, they  may  be expected to work satisfactorily at rates as high  as
twice those given in Table 14, provided that the sand has an effective
size no smaller than 0.4 mm.
  Dosing tanks  should be  provided where  the total filter area exceeds
1,800 square feet and where the distributors exceed 300 lineal feet. The
size of the dose, or the net capacity of the dosing tank, should be 60 to
75 percent of the volume of the distributors dosed at one time. When
an  installation has over 1,000 feet of distributors, best results can be
obtained by constructing the  filter in two or more sections, dosed sep-
arately by alternating siphons.
  The distributors and underdrains may be of agricultural  tile, bell

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                DOSING TANK
                                   FROM SEPTIC TANK
                                             ALTERNATING SIPHON
TILE PIPE WITH TIGHT JOINTS i
(SLOPE TO FIELD, 0.5%) — X| \ DIVERSION
i - l - . •
18" TO 36"
t

i !
18" TO 36"



...1, .^ 	 BOXES 	 *..

I








































s


s"

                                                            MASONRY WALL
                                                            UNDERDRAIN PIPE
                                                            WITH OPEN JOINTS
       DISTRIBUTION PIPE ON 03% SLOPE
                                                           .CHLORINATE HERE
                                                            IF NECESSARY
     TO CHLORINE CONTACT TANK
UNDERDRAIN COLLECTOR
PIPE WITH BELL & SPIGOT JOINTS
                              PLAN
                        •6-
                                       OPEN JOINT OR
                       •,.TI   °"-      -./PE«FORA1»;PIPE
                       *•'"'. V
                 6'±
                                                            GRADED GRAVEL
                24 TO 30"
                    I
                                 CLEAN COARSE SAND
                                                            GRADED GRAVEL
                                ••4" FARMTILE OR VITRIFIEU PIPE
                                 WITH OPEN BELL * SPIGOT JOINTS
                         SECTIONAL ELEVATION
          Figure 27.—Typical  plan and section  of a subsurface  sand filter.
and spigot pipe; or perforated  pipe. Special joints of the precast, sleeve
coupling,  and taper  coupling  types are  available which  insure align-
ment of the pipe lengths. In any  event, the distributors should be laid
accurately  to  grade after the filter sand has been  thoroughly settled  by
flooding or other means. It may be necessary to surround  the  filter bed
with a masonry wall  to retain the filter bed.
  Where dosing tanks are used, the distributors  should be laid to 0.3
percent grade; otherwise,  they  are laid  to a grade of about 0.5 percent.
                                                                         63

-------
SUPERFICIAL SAND FILTERS
  In some areas, the ground water table is too near the surface to per-
mit construction or successful operation of any subsurface  method of
sewage disposal. The  construction of buildings and  sewage disposal
systems should generally be avoided  in such places.  Sometimes, how-
ever, the elevation of the water table may be found  to  fluctuate  over
a wide range unexpectedly. Through  floods or other hydrologic condi-
tions, areas  which, for decades, may have experienced  a water table
appreciably  below the ground surface may suddenly be faced with a
condition wherein the  ground water approaches  or even covers the sur-
face. Sometimes such occurrences are brought about  artificially, as by
the construction of dams or dikes, and the conditions may be likely to
remain relatively permanent.
  As previously explained,  impervious soil may also preclude subsurface
methods of  disposal, and the occurrence of solid rock at or just below
the surface  of the ground may make subsurface treatment methods
uneconomical.
  In these  events, it may  be necessary to forego completely the con-
struction or renovation of subsurface  methods of sewage  treatment and
disposal. The  circumstances may require treatment and disposal by
superficial  means  above the surface  of the ground.  This  frequently
necessitates  pumping, but can be accomplished in superficial  sand filters
constructed  as shown in Figure  28 (page 65), except that the ends and
sides must be surrounded by a masonry wall or earth dike for retaining
the filter bed. The filters may be completely above the ground or only
partly  above the surface, depending  primarily  upon  the depth  to
ground water or the depth to solid rock, as the case  may be.
  From the standpoint of operation, sewage filters do not  have to be
covered,  but in built-up areas a shallow earth cover of about 6 inches
is recommended, to prevent freezing in cold weather and  to prevent
emanation of odors and other nuisances from the septic sewage in warm
weather. While open  filters are  accessible  for  cleaning and can be
operated at higher rates than those covered with earth, they ordinarily
require daily attention, and are not usually advisable for private instal-
lations where septic  tanks are used. They are more suitable  for munici-
palities and large institutions where sewage plant  operators  are em-
ployed. In  such  cases,  the filters  generally follow a  conventional pri-
mary settling tank or secondary treatment and secondary settling tanks,
and the method of distributing sewage onto open filters  is different
from that indicated  for covered filters. Figure 28 (page 65)  illustrates a
typical installation of  open filter beds.
   Open filters are operated  intermittently  and, thus,  are known as
intermittent sand filters.  They should always be divided into two or
more units. Sand specifications  and depths are the same as for subsur-
face sand filters. Loading rates are influenced by temperature, effective
size and uniformity coefficient of the filtering medium, and the charac-

64

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             rTIGHT JOINTS
               3 CONTROL
               IN CI. PIPE LINE
FILTER SAND OR GRAVEL OR CRUSHED ROCKj
  	II
TILE LINES WITH
OPEN JOINTS
                TYPICAL SECTION AT A-A
                [NOT TO SCALE)
TIGHT JOINTS IN ALL TILE LINES OUTSIDE BED -r—
                                                     	—  TO DISPOSAL-
                                                            CONCRETE SPLASH
                                                            WITH ROUGH TOP
                                                            FINISH
                                        PLAN: TYPICAL FILTER BED WITH INFLUENT
                                            PIPE BELOW LEVEL OF FILTER SAND
                                            (NOT TO SCALE)
                                                           MASONRY RETAINING WALL
                                                           (ALL AROUND) WITH DIVIDING
                                                           WALL TO SEPARATE BEDS
                                             =i=. its*;.
                                            SLOPE BOTTOM OF CUT
                                            TOWARD DRAIN LINES AS SHOWN
                                                               TO DISPOSAL
   DRAIN LINES
WITH OPEN JOINTS
  CONCRETE SPLASH BLOCK
  WITH ROUGH
              3 CONTROL VALVES
              IN C.I. PIPE LINE
          *
        TOP FINISH^

        4Mt*&^
TYPICAL FILTER BED WITH INaUENT
PIPE ABOVE LEVEL OF RLTER SAND.
(NOT TO SCALE)
                                                         Cl. PIPS
          RLTER
          SAND
                                                                  CONCRETE
                                                                  SPLASH BLOCK
                                                                  AVERAGE SIZE
                                                                  «'0" i «'0" « 4" THICK
           IBELOW LEVEL OF FILTER SAND]       (ABOVE LEVEL OF FILTER SAND)

                  DETAIL— TYPICAL DISCHARGE FOR INFLUENT PIPE

                          Figure 28.— Open-filter-bed  layout.
teristics of the sewage  to be  treated. The  last depends largely upon  the
degree  of pretreatment received  by the influent to  the filter, but,  since
this  manual is concerned  only  with septic  tank  systems,  pretreatment
may be ruled  out  of consideration here.  Table 15 gives  recommended
maximum loading  rates for the  effluents from septic tanks which do
not  receive  wastes  from   garbage  grinders  or  automatic  washing
machines.
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Table 15.—Recommended loading rates of septic tank  effluents on open sand filters with
                    uniformity coefficients not over 4.0

                      [Gallons per acre per day l]
Region
Southern U. S....
Northern U. S....
Effective Size of Sand
05mm.
100,000
80,000
0.3 mm.
130,000
100,000
0.4 ram.
160,000
120,000
0.5 mm.
180,000
140,000
0.6 mm.
200,000
160,000
  1 Multiply rates by 0.83 if garbage grinders are used.

  In  addition  to  dosing by siphons or pumps, some open filters are
dosed by means of hand operated gates or valves. In some places, it has
been  customary to dose about once a day. Other plants operate with as
many as 4 doses per filter per day, but some dose at long and irregular
intervals of several days. With fine sands, filtration efficiencies  are in-
creased by loading twice daily.  With  coarse sand  (0.45 mm and up),
efficiencies are  increased by loading more frequently than  twice a day,
but multiple loadings present  a problem  in obtaining adequate cover-
age of the bed. Spray nozzles  and rotary distributors have been used
with  reasonable success  as  dosing devices  in some small installations,
but it has been found necessary to cover the surface of the sand with
several  inches  of  pea gravel in order  to  prevent disturbance  of the
surface sand.
  Dosing tanks should have capacities that will provide for flooding the
beds  to depths of  2 to 4  inches. Discharge from the dosing tanks should
at least equal the flow of the raw sewage.
  Since various States have different requirements or policies regarding
open filter installations, the State or  local health department  should
always be consulted before  filters of this type are designed.

 CHLORINATION
  Filter trenches  and artificial sand filters that are properly designed
and operated will produce  an effluent that is clear and  sparkling, and
the filtration will remove a high percentage of the bacteria contained
in the sewage. Some of  the remaining bacteria may still be capable of
producing disease, however, and the sewage effluent must be disinfected
if it is discharged  to a ditch that is accessible to humans, or to a stream
that  contributes to a nearby source of water supply used for drinking,
growing of shellfish, or swimming.  Chlorine is  the  disinfectant most
commonly used.
  Present custom  is to apply chlorine in the amount necessary to obtain
a chlorine residual of  0.5  to  1.0  ppm after thorough mixing  and 15
 66

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minutes contact at peak flows. On an average, this requires a  chlorine
dosage in the neighborhood of 6 ppm for sand filter effluents. This is
equivalent to i/2 pound of available chlorine for every 10,000 gallons
of sewage, or less than 1 ounce per 1,000 gallons.  Most States require
a chlorine contact chamber large enough to retain the sewage  for at
least 15 minutes. A typical design is illustrated in Figure 29 (page 68).
  Chlorine may be obtained in steel cylinders in which the gas is com-
pressed to a  liquid state. It may also be obtained from sodium hypo-
chlorite or calcium hypochlorite.
  Sodium  hypochlorite is obtainable only as a solution. Upon drying,
it decomposes. Solutions of hypochlorite are  obtainable  in strengths
ranging from 1 percent to 15  percent of available chlorine. This mate-
rial is corrosive  to ordinary  metals and should be  handled  in  glass,
stoneware  crocks or plastic containers.
  Calcium hypochlorite is  obtainable  only in a dry form, of  which
there  are  two principal types. Hypochlorite  of lime (or "bleaching
powder") contains about 35 percent of available chlorine  when manu-
factured,  and  high-test hypochlorite contains  about 70 percent of
available  chlorine.
  The ordinary hypochlorite  of lime is really a mixture of compounds
which may be largely  a calcium oxychloride. It is not stable, and may
lose a large percentage of its chlorine content if stored for  long periods.
When made  into a water solution, it also has the undesirable character-
istic of forming a scale of calcium carbonate which tends to  clog the
feeding apparatus. It is cheaper than high-test hypochlorite, however,
and it can be used satisfactorily with  certain types  of feeding equip-
ment,  if large solution tanks are  employed and if proper precautions
are taken in  the preparation and utilization of the solution. The undis-
solved portion must be allowed to settle out of the solution, and only
the clear, supernatant liquid  fed through the feeding apparatus.
  High-test hypochlorite is a true calcium  hypochlorite. It  is  more
stable and more convenient  to handle  than ordinary hypochlorite of
lime.  It is available under several trade names,  familiar to sanitary
engineers and sanitarians. When made up  with soft water in solutions
containing 1 to 2 percent of available  chlorine, calcium  hypochlorite
does not give much trouble with  calcium carbonate deposits,  but pre-
caution should still be taken to feed only the clear,  supernatant por-
tion of the solution through the feeding equipment. When hard  water
is used to make up the solution, the addition of a small quantity of
sodium hexametaphosphate will help prevent deposits.
  The decision  between sodium hypochlorite  or calcium  hypochlorite
should depend upon the relative costs of the two materials in the local-
ity of the job. Information as to their costs can usually be  obtained
from  the  suppliers of the hypochlorinators.
  The decision  as to whether to  apply chlorine as a gas  or in  liquid
form  as a hypochlorite is sometimes dependent on the availability of

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                            ^— WOODEN IAFFUS -J
                                                    V
                                                       WIMfOdCtD CONCttlE
   - MOS€ «O* CHLOSINATOT
PCMNT Of *m.'CA-
1ION Of CHiOflINt
                    Figure 29.—Chlorine-contact chamber.
power. Most manufactured hypochlorinators require either electric cur-
rent or clean water under pressure for their operation. In some remote
places,  these are not  available.  In such cases, hypochlorinators using
chlorine in cylinders can be operated without any outside power source.
   Usually, however, power is available and the decision as to whether
to use hypochlorite or chlorine gas is dependent upon their relative cost.
Gas is the cheaper of the two, but equipment for controlling it is much
more expensive than simple hypochlorite feeders.
   In general, hypochlorite is  preferred when  the amount  of chlorine
required  is less than 2 or 3  pounds per day.  In other words,  hypochlo-
rite would normally be used for disinfecting the effluent  from a sand
sewage filter for sewage flows  up to about 50,000 gallons per day. For
chlorinating a  septic tank effluent, the sewage flow limit for hypochlori-
nators would be about 10,000 gallons per day.  Beyond these quantities,
savings in the  cost of  the  chlorine  gas will  usually offset  the  more
expensive original investment  in equipment.
   Several satisfactory types  of hypochlorinators  are available. Various
types of chlorinators are also made. Both kinds of apparatus are being
gradually improved. Both require  routine maintenance. Therefore,  in
choosing the make of apparatus  to  be purchased, the first consideration
should be that of service. It is practically always advisable to purchase
a chlorinator from a manufacturer who has a fulltime serviceman  trav-
eling through  the area where  it is  to be used.  Jobbers and agents han-
dling chlorinators are seldom qualified to furnish the best  technical
assistance, and are usually unable to render the prompt service that is
necessary when a chlorinator gets out of order.
 66

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  Wherever chlorination  is necessary, daily tests should be made  to
determine the amount of chlorine residual after the requisite  contact
period.  Many health  departments require monthly reports  giving the
results of the tests.
  The test is simple.  It is usually made  by adding a small  amount  of
standard orthotolidine solution  to a  sample of the  effluent and com-
paring the color developed with color standards which may be obtained
with the solution from most laboratory supply houses.  If the color  of
the sample changes to an orange-yellow hue, it indicates that chlorine
is being applied in a proper amount.
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                           Appendices

               Introduction To Appendices
  Since conditions vary in different parts of the country, practices that
are suitable in one section may not be acceptable in another.  Thus, it
would not be feasible to suggest one set  of standards that should be
followed in all circumstances. In a sense, this may be considered fortu-
nate,  as, to paraphrase Sedgwick,  "Standards are  devices to keep the
lazy mind from thinking." In public health work there can  be no sub-
stitute for the use of judgment or discretion, more aptly  termed by
Phelps as an exercise of "the principle of expediency."
  Just as no individual design of a sewage disposal system is applicable
for universal adoption because of  varying  local conditions,  so also no
single ordinance or code would be universally applicable. Though some
States  and many  local health  departments  have  laws or regulations
governing the installation of individual sewage disposal  systems,  there
is still a growing need for reasonable regulations which will protect the
public from unsound practices leading to health hazards.  The suggested
ordinance governing individual sewage disposal  systems presented  in
these  appendices may be useful as  a guide  in the development of new,
or the revision of  existing, regulations on this subject.
  The purpose of these appendices, therefore, is to discuss additional
practices which have been found successful in some parts of the coun-
try, although their application may be necessarily limited  in other parts,
and also to present  some additional information considered useful  to
workers in this field.
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                            Appendix A

                  Soil Absorption Capacity
        GUIDE  FOR ESTIMATING SOIL ABSORPTION POTENTIAL
   A percolation test is the only known means for obtaining a quantita-
 tive appraisal  of  soil absorption capacity. However, observation and
 evaluation of  soil characteristics provide useful clues  to  the  relative
 capacity of a soil to absorb liquid. Most suitable and unsuitable soils
 can be identified without  additional  testing.  When determined and
 evaluated by trained or experienced soil scientists or soil engineers, soil
 characteristics  may permit  further categorizing of suitable soils.  This
 has been done  for some areas of the country and described in the soils
 reports mentioned below.
   Soil Maps.—The capacity of a soil to absorb and transmit water is an
 important problem in agriculture, particularly in relation to irrigation,
 drainage, and  other land management practices. Through studies  in
 these fields,  a  variety of aids  have  been  developed for  judging the
 absorption of  water  transmission properties  of soils, which could be
 helpful in the sewage field. Considerable information  has been accu-
 mulated by agricultural authorities on the relative absorption capacities
 of specific  soils in many areas of the United States. Much of this infor-
 mation is included in Soil Survey Reports and Maps published by the
 United States Department of Agriculture in cooperation with the vari-
 ous State agricultural colleges.  The general suitability of specific soils
 for effluent disposal may often be interpreted  from these  reports and
 maps.
   Clues to Absorption Capacity.—Considerable information about rela-
 tive absorption capacities of soils may also be obtained by a close visual
 inspection  of the  soil. The  value of such an  inspection depends upon
 some knowledge of the pertinent soil properties. The main properties
 indicative of absorption capacity are soil texture, structure, color, depth
 or thickness of permeable strata, and swelling characteristics.
   Texture.—Soil texture,  the relative proportion of sand, silt, and clay,
 is the  most common clue to water absorption capacity. The size and
 distribution of  particles govern the size and distribution of pores which,
 in turn, govern the absorption capacity. The  larger the soil particles,
 the larger  are the pores and the faster is the rate of absorption.
  Texture can  best be judged  by the feel. The lighter or sandier soils

72

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have a gritty feel when rubbed between the thumb and forefinger; silty
type soils have a "floury"  feel and,  when  wetted have  no cohesion;
heavier, clay type soils are dense and hard when dry, and have a slick
greasy feel when wetted.
  The use of texture as  a  clue to  absorption  qualities has  its limita-
tions; it is primarily reliable in the sandier  soils. In the heavier type
soils,  including sandy soils containing appreciable amounts of silt or
clay,  one  must look for  additional clues, such  as structure and  soil
color, as indicators of absorption capacity.
  Structure.—Soil  structure  is characterized  by the  aggregation  or
grouping  together of textural particles, forming  secondary particles of
larger size. Such secondary particles then tend to govern the size  and
distribution of pores and, in  turn, the absorption properties. Structure
can easily be recognized by  the manner in which  a clod or lump breaks
apart. If a soil has structure, a clod  will break  with very little force,
along  well defined  cleavage  planes, into uniformly sized and  shaped
units. If a soil  has no structure, a clod will require more force to break
apart and will do so along irregular surfaces, with no uniformity in
size and shape of particles.
  In general, there are four fundamental structure types, named accord-
ing to the shape of the aggregate particles: platy, prism-like,  block-like,
and spheroidal. A  soil without structure is generally referred to as
massive. Spheroidal structure tends to provide the most favorable ab-
sorption properties, and  platy structure, the least. Although other fac-
tors, such as size and stability of aggregates to  water, also influence the
absorption capacity, recognition of the type of structure is probably
sufficient for a general appraisal.
  Color.—One of the  most important practical clues  to  water absorp-
tion is soil color. Most soils contain some iron compounds.  This iron,
like iron  in a  tool or piece of machinery, if alternately exposed to air
and to water,  oxidizes and takes on  a reddish-brown  to yellow color.
Thus, if a soil has  uniform reddish-brown to  yellow oxidized color, it
indicates  that there has been free alternate movement of air and water
in and through the soil.  Such a soil has desirable absorption character-
istics. At  the other extreme are soils of a dull gray or mottled coloring,
indicating lack of oxidizing conditions or very restricted movement of
air and water. These soils  have poor absorption characteristics.
  Depth or Thickness of  Permeable Strata.—The quantity of water that
may  be  absorbed  is proportional  to  the thickness or volume of the
absorbent stratum, when  all other conditions are alike.  In a soil having
a foot or more of permeable material above tight clay, absorption ca-
pacity is far greater than  that of the same kind of material lying within
3 inches  of tight clay. When examining soils  or studying soil descrip-
tions, the depth and thickness,  therefore,  are  important  criteria of
absorption capacity.
  Swelling  Characteristics.—Most,  but not  all,  clays  swell upon the

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addition of moisture. There are many clays (in the tropics, in particu-
lar) that do not  swell appreciably. There are also some soils in the
United States which do not swell noticeably. On the other hand, some
soils have a very  high percentage of  swelling, and these in particular
must be suspect. Relative swelling of different soils is indicated by rela-
tive shrinkage when dry, as shown by the numbers and sizes of cracks
that form. Those that shrink appreciably when dry are soils that may
give trouble in a  tile field  when  they are wet.
  Information obtained through  inspection or from soil maps and re-
ports can be of particular value in preliminary appraisal of soils for
sewage disposal. For instance, in many cases, unsuitable soils may be
immediately ruled out on the basis of such information; in other cases,
selection of the best of several sites may be  made  on  the basis  of the
inspection. Absorption capacity information obtained in this manner is
relative.  For quantitative  information upon which  to  base  specific
design, we still must depend on some direct measurement, such as a
water absorption  rate as measured by a percolation test.
                      EVAPOTRANSPI RATION
  In tight clay soils, where absorption is very limited, plant  transpira-
tion has been employed with some degree of success in aiding  in the
disposal of sewage effluent. By placing the tile lines near the top of the
trench, where they are not likely to become clogged with roots,  or by
laying the lines practically at ground surface and covering with suitable
fill material, use may be made of  the action of trees, shrubs, and grasses
in the absorption and subsequent release to the atmosphere of  appre-
ciable quantities of moisture,  through the process of evapotranspiration.
  Climate  is important,  Evapotranspiration increases wth  decreasng
humidity and increasing temperature and air turbulence. Length of day
and amount of sunshine are  further influencing factors. Consequently,
evapotranspiration should be of most benefit to soil absorption systems
in the southern portion of the country, where  the growing season is
longest. In the extreme North, where the growing season extends only
from  May to September,  evapotranspiration would  be of minimum
value, but may be useful in  summer resort  areas.
  Because of these variations, and equally great variations in the types
of plants grown in different parts of  the country,  as well as the differ-
ing transpiration  rates in  different plants, it would be hazardous  to
generalize in making specific suggestions on  design criteria for systems
dependent on evapotranspiration for  successful operation.
       CURTAIN  DRAINS FOR ABSORPTION TRENCH  SYSTEMS
  Even though proper precautions are taken to ascertain the maximum
ground  water table before the  absorption  trench method of sewage
effluent disposal  is approved  for a given area,  instances occur where
the height of a water table rises  above that indicated by past perform-
ances and observations. This  may lead to failure of the disposal system.

74

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  It is sometimes possible to rehabilitate such a system by constructing
around the disposal  area  a curtain drain  designed  to intercept  the
superficial ground water and carry it away from the area. If the absorp-
tion field is on sloping ground, a single drain at the upper end of the
area may be sufficient. Where open curtain drains are not feasible, rock-
filled trenches  above or around the disposal area may sometimes be
used. In either case,  it is  necessary to  have a suitable outlet for  the
ground water that is intercepted.
                     PERCOLATION TEST HOLES
  When making percolation tests  in  some  types  of soil, it  has been
found that the side  walls of test holes  have a tendency to cave in or
slough off, and settle to the bottom.  The condition  is most  likely to
occur where the earth is initially dry and overnight soaking is necessary.
The caving can be prevented, and more accurate results obtained, by
placing in  the test hole a wire cylinder surrounded  by gravel of  the
same size that is used in the tile field.
                     OTHER PERCOLATION TESTS
A  Soil  Percolation  Test  for Determining  the Capacity of   Soils  for
         Absorption  Sewage Effluents,  by John E. Kiker, Jr.1
  1. Dig a hole about 1 foot square to the depth at which it is  proposed
to lay the tile drain.
  2. Fill the hole  with water and allow the  water  to seep away. When
the water level falls  to within 6 or 8 inches  of the bottom of  the hole,
observe the  rate at which the water level drops.
  3. Continue these  observations  until  the  soil is saturated  and  the
water seeps  away at a constant rate. (Keep adding water until the rate
becomes constant.)
  4. Compute the time required for the water to drop 1 inch  after the
soil becomes saturated. This is  the standard percolation time, t.
A Percolation Test for Determining the Capacity  of  Soils for Absorp-
  tion Sewage Effluents, by Harvey  F. Ludwig, Gordon W. Ludwig, and
  John Stewart.
  While the previously cited percolation tests include procedures gen-
erally familiar to workers in  this field, the method  proposed by Ludwig
et al., includes an additional step.  The field data  are further  analyzed
graphically  to obtain  the percolation  rate under saturated soil condi-
tions. The mathematical evaluation is based on  the  premise  that  the
ratio, time in minutes for the water level to drop  1 inch, is constantly
increasing during the progress  of  the test,  but at a rate of  increase
which is constantly decreasing. This hyperbolic relationship is utilized
                                   minutes
to determine the maximum ratio	-.—;	which  is  the  saturated
                                     inch
  1 Reprinted from Subsurface Sewage Disposal, by John E, Kiker, Jr., Bulletin No.
23, Florida Engineering and Industrial Experiment Station, 1948.
                                                                  75

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condition under which  water  would seep away  at a constant rate. A
discussion of this method with illustrations and an example is found
in the following articles:  Improved Soil Percolation Test, Harvey F.
Ludwig and  Gordon W. Ludwig,  Water and Sewage Works Journal,
vol. 96, no. 5, May 1949, p. 192; Equilibrium Percolation Test for Esti-
mating Soil Leaching Capacity, Harvey F.  Ludwig and John Stewart,
Modern Sanitation, vol. 4, no. 10, Oct. 1952.
76

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                            Appendix B

                     Suggested  Ordinance
   The following is suggested for consideration in drafting an ordinance
for local  application to permit  the  exercise of appropriate legal con-
trols  over individual  sewage disposal systems.1  Persons  utilizing  this
draft as a guide are urged to familiarize themselves with the applicable
legal requirements governing  adoption of ordinances of this kind in
their locality.

AN ORDINANCE GOVERNING INDIVIDUAL SEWAGE DISPOSAL SYSTEMS
   An ordinance defining and  regulating individual  sewage  disposal
systems; requiring minimum standards governing the design, construc-
tion, and  installation of septic  tank-soil absorption systems, privies,  and
chemical-type toilets; authorizing the issuance of permits, and providing
for penalties for violations.

Section /—Definitions
   For the purposes of this ordinance, the following words and phrases
shall have the meanings ascribed to them in this section.
     1.1.1  Health officer shall  mean  the  legally designated health au-
          thority of the (name of political subdivision) or his authorized
          representative.
    1.1.2  Individual sewage disposal system shall  mean  a sewage  dis-
          posal system, other than a public or community system, which
          receives either human  excreta or liquid waste, or both, from
          one premises. Included within the scope of this definition are
          septic tank-soil absorption systems, privies, and chemical type
          toilets, and such other types as may  be prescribed in regu-
          lations by the health officer.
    1.1.3  Permit shall  mean a  written  permit  issued by  the health
          officer, permitting the construction of an individual sewage
          disposal system under  this  ordinance.
    1.1.4  Person shall mean any institution, public or  private corpo-
          ration, individual, partnership,  or other entity.
  1 Reference should also be made to Recommended State Legislation and Regula-
tions: Urban Water Supply and Sewerage Systems Act and Regulations, Water Well
Construction and Pump Installation Act and Regulations, Individual Sewerage Dis-
posal Systems Act and Regulations, U.S.D.H.E.W., Public Health Service, July 1965.
                                                                  77

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Section //—Requirements for Individual Sewage Disposal Systems
2.1  The health officer of (name of political subdivision),  in  order to
protect the health and safety of the people of (name of political sub-
division) and  of the  general public, is  authorized  and directed, after
public hearing, to promulgate and  amend, from time to  time, regula-
tions  establishing minimum standards governing the design, construc-
tion, installation, and operation of  individual sewage disposal systems.
Such  regulations shall establish such minimum standards as, in  the
judgment of the health officer, will insure that the wastes discharged
to various individual sewage disposal systems:
    1.  Do not contaminate any drinking water supply.
    2.  Are  not accessible to insects, rodents, or other possible carriers
        of disease which may come  into contact with food or drinking
        water.
    3.  Do not pollute or contaminate the waters of any bathing beach,
        shellfish breeding grounds,* or stream  used for public  or do-
        mestic water supply purposes or for recreational purposes.
    4.  Are  not a health hazard by  being accessible to children.
    5.  Do not give rise to a nuisance due to odor or unsightly appear-
        ance.
    6.  Will not violate any other laws or regulations governing water
        pollution or sewage disposal.
2.2  The health officer is authorized to promulgate such additional regu-
lations  as are  necessary in his judgment  to carry out the  provisions of
this ordinance.
Section ///—Permits
S.I  It shall  be unlawful for any person to construct,  alter, or extend
individual sewage disposal  systems  within  the  (name of political sub-
division) unless he holds a valid permit3  issued by the health  officer
in the name of such person for the specific construction, alteration, or
extension proposed.
3.2 All applications for permits shall be  made to the health officer, who
shall  issue a permit upon compliance by the applicant  with provisions
of this  ordinance and any regulations adopted hereunder.
3.3 The health officer may refuse to grant a permit for the  construction
of an individual sewage  disposal system where public or community
sewerage systems are  reasonably available.
3.4 Applications for permits shall be in  writing, shall be signed by the
applicant, and shall include the following:
    3.4.1 Name and  address of the applicant.
          Lot and  block number of property  on which  construction,
          alteration, or extension is proposed.

  •Optional with  locality.
  *The  permit issued by the Health Officer is  in addition  to the building permit
usually  required and should be obtained prior  to construction,  alteration, and
extension of the residence or facility to be served.

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     3.4.2 Complete  plan of the proposed disposal facility, with  sub-
          stantiating data, if necessary, attesting to its compliance with
          the minimum  standards of the health officer.
     3.4.3 Such further information as may be required by the health
          officer to substantiate that the proposed construction, altera-
          tion, or extension complies  with regulations  promulgated by
          the health officer.
3.5 A complete plan for  the purpose of obtaining a permit to be issued
by  the health officer shall include:
     3.5.1 The number,  location, and size of  all sewage disposal facili-
          ties to  be  constructed, altered, or extended.
     3.5.2 The location of water supplies, water supply piping, existing
          sewage disposal facilities, buildings or dwellings, and  adja-
          cent lot lines.
     3.5.3 Plans  of the proposed sewage disposal  facilities  to be  con-
          structed, altered, or extended.
3.6 Any person whose application for a permit under this ordinance
has  been denied may  request and shall be granted a hearing on the
matter  before the health officer within 30 days  after receipt of the
request.

Sect/on IV—Inspections
4.1  The health officer  is  hereby authorized and directed to make such
inspections as are necessary to determine  satisfactory compliance with
this ordinance and regulations promulgated hereunder.
4.2 It shall be the duty of the owner or occupant of a  property to give
the  health officer free access  to the property at reasonable times for
the  purpose  of making such inspections as are necessary  to determine
compliance  with the requirements  of this ordinance  and regulations
promulgated hereunder.

Section V—Penalties
5.1  Any person who violates  any provision of this ordinance, or any
provision of  any regulation adopted by the health officer pursuant  to
authority granted by this ordinance, shall, upon conviction, be punished
by a fine of  not less than	dollars nor more  than	
dollars, or by imprisonment for not less than	days nor more than
     Hays; and each day's failure to comply shall constitute a separate
violation.
Section W—Conflict of Ordinances, Effect  on  Partial Invalidity
6.1  In  any case where  a  provision of  this  ordinance is found to be in
conflict with a provision of any zoning,  building, fire, safety, or health
ordinance or code of  this (name  of political subdivision) existing on
the effective  date of this ordinance, the provision which,  in the judg-
ment of the health officer, establishes  the  higher standard for the  pro-
motion and  protection of the  health and safety  of the  people  shall
prevail. In any case where a provision of this ordinance is found to be

                                                                  79

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in conflict with  a  provision  of any other  ordinance or code  of  the
(name of political  subdivision) existing on the effective date of this
ordinance which establishes a lower standard for the promotion and
protection of the health and safety of the people, the provisions of this
ordinance shall be deemed to prevail, and such other ordinance  or
codes are hereby declared to  be repealed to the extent that they may
be found in conflict with  this ordinance.
6.2 If any section,  subsection, paragraphs, sentence,  clause,  or  phrase
of this ordinance should be declared invalid for any reason whatsoever,
such decision shall  not affect  the remaining portions of this ordinance,
which shall remain in  full force and effect; and, to this end, the pro-
visions of this ordinance are hereby declared to be severable.
Section VII-Effective Date
7.1  This ordinance shall be effective on and after the	day
of	,  19	

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                           Appendix C

              Engineering Information Forms
  The  pertinent information  needed on individual  sewage disposal
systems prior to approval by the health or other agency having juris-
diction is outlined in Appendix B. In those instances where subdivision
developments are involved,  considerably more data are needed  by the
health agency prior  to approval of water and sewage service facilities.
The possibility of providing connections to existing municipal systems
or the construction of community water and sewage systems should re-
ceive first consideration. In the  extreme situation  where this  is not
possible, and when subsoil conditions are favorable, information of the
type called for in the following "Statement of Information" has been
found satisfactory in one State. Unless real estate developments in non-
sewered  areas are properly planned and designed under  competent
sanitary  engineering supervision,  public health hazards  and nuisances
may result, with attendant economic loss to the community.
                  STATE DEPARTMENT OF HEALTH
                     Statement  of Information
   Regarding Water and Sewerage Service for Realty Subdivisions
To the State Commissioner Health	19	
Sir:
  As required by the provisions of section	of Article   	of the
Public Health Law, the following statement is made and submitted with
the plat of a proposed realty subdivision in	,	
                                                (State)
General Information
 I.  Name of subdivision	
 2.  Owner	,	
      (State name of person, company, corporation, or association owning
                           the subdivision)
 3.  Business address__	
 4.  Officers	
                   (If organized, give names of officers)
 5.  Location	
       (Give name of incorporated village or town in which subdivision
                              is located)
 6.  Area  of  subdivision	Number  of  lots	
                          (Total size in acres)
                                                                81

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      Families  accommodated.
 7.  Do you intend to build houses on this subdivision?_
    Do you intend to sell lots only?_
    Do you intend  to build  on  some  lots  and  sell others without
      buildings?	
 8.  Is this  subdivision or any part  thereof  located  in  an area under
      the control of local planning, zoning, or other officials?	
    If so, have these plans been submitted to such authorities?	
    Have these plans been approved or disapproved  by such  governing
      authority?	
 9.  Nature of soil	
                  (Describe to a depth of 10 feet if tile  fields are to  be  used

    for sewage disposal, or 20 feet if leaching pits are proposed, giving thickness

    of various strata,  such as top soil, clay, loam, sand, gravel, rock, etc.)
10.  Topography	
               (State whether ground is flat, rolling, steep, or gentle slope, etc.)
11.  Relative elevation of water table below ground surface	
                                                        (Give maximum

    and minimum,  if  there is any variation)

Water Service
12.  Proposed method of  supplying water_
                                         (Describe in detail, giving name of
    municipality, water district or company, if a public water supply is to be used.)
15. State approximate distance to nearest public water supply main of
       municipal  system	.	
    (Give name of municipality, water district, or company)

Sewerage Service
14. Proposed method of collection and disposal of sewage.
                                                           (Give name of
     municipality or sewer district, if public sewers are to be used)
15.  State approximate distance to nearest public sewer main of munici-
       pal system	
Storm Water Drainage
16.  State proposed method, if any, of disposing of surface water from
       streets, roofs, land, and other areas	.
82

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Subdivision Owners  Who Intend  to  Build Homes Must Submit the
Following Additional Information:
Additional Information:
17. Cellar drainage: Are cellar or footing drains LO be installed?	
    If so, how will drainage be disposed  of?	
18. Laundry wastes:  Are laundry tubs to be located in basement?	
    If so, how will wastes be disposed of?_
    It is hereby agreed that if the attached plans dated	
    or any amendment or revision thereof, are approved by the State
    Department of  Health,  installation  of  water supply and sewage
    disposal  facilities will  be made  in  accordance with the details
    thereof as shown on such approved plans. If the subdivided lands
    shown on such plans are sold before such installations are made, it
    is agreed that reference to said plans will be made in the deed or
    contract  of sale, and  a covenant inserted  therein requiring the
    purchaser  to  install such  facilities in accordance with such ap-
    proved plans.
                Signature	
                Official title__	
                This statement must be signed by the owner of the land platted
                for subdivision or the responsible official of the company or
                corporation offering the same for sale.
Important Note
  This form must be accompanied by:
(1)  One U. S. G. S.  topographic  map or other general map  showing
    exact location  and approximate boundaries  of subdivision.
(2)  A print on cloth for filing with the  State Department of Health,
    together with such other tracings and prints  (see below) as may be
    necessary for filing with the county  clerk and owner of  the sub-
    division, showing:
    (a)  subdivision layout, including streets, building lines, lot dimen-
        sions, and  other pertinent data;
    (b)  existing and  proposed water  mains, if  available.  If public
        water supply is available, show  existing and proposed water
        mains for all lots, and submit  a  copy of the contract  between
        the developer  and the waterworks  officials, or a letter from
        such officials stating that  an agreement has  been  reached
        regarding the supply of  such facilities.
    (c)  existing and proposed sewers;  if  already approved by Depart-
        ment give  date of approval; or,  if not approved, application
        must  be made  and detailed plans of sewer extensions sub-
        mitted by  officials in charge of  sewer systems,  in  accordance
        with section	of the Public Health Law.
    (d)  details of a typical lot arrangement showing general  location
        of well and septic  tank,  subsurface absorption devices,  etc.

                                                                 83

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         (where either or both public water and  sewerage service are
         inaccessible),  plus  the following:
         (1)  development of well (giving sufficient detail to show how
             the well will be developed and protected from pollution,
             its depth, and strata penetrated).
         (2)  cross section of soil showing depth of  various strata (unless
             explained in detail  under item 9).
         (3)  plan and section of all  parts  of sewage disposal  system,
             giving all dimensions and grades.
         (4)  actual field  results of soil tests to determine absorptive
             capacity of soil (may be submitted with correspondence).
Inasmuch as stamp  of approval  must be  placed  on face of plans,  a
space 3 by  6 inches should be reserved for this  purpose.  This space
must be blocked out in  white if  blueprints are submitted.
  Size of plans for filing with county clerk; 20 by 20 inches or 20 by 40
inches, tracing cloth or white prints on cloth.
84

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                                Appendix D

                Drainage Fixture  Unit  Values
Type of Fixture or Group of Fixtures         ____ Drainage Fixture Unit Value
Automatic clothes washer (2" standpipe) .........................                          3
Bathroom group consisting of a water closet, lavatory
  and bathtub or shower stall:
    Flushometer  valve closet ...............................................                          8
    Tank type  closet [[[                           6
Bathtub  (with or without overhead shower) ...................                          2
Combination sink and  tray with food disposal unit .....                          4
Combination sink and  tray with one li^" trap .............                          2 '
Combination sink and  tray with separate \i/z" traps ...                          3
Dental cup  or  cuspidor [[[                          1
Dental lavatory [[[                           1
Drinking  fountain [[[                          i/z
Dishwasher,  domestic (gravity drain) .................................                           2
Floor drains with 2" waste .................................................                           3
Kitchen sink, domestic, with one Ii/£" waste ...................                           2
Kitchen sink, domestic, with food waste  grinder ...........                           2
Lavatory with Ii4"  waste [[[                           1
Laundry  tray (1 or 2 compartments) ...............................                           2
Show stall,  domestic [[[                           2
Showers (group) per head [[[                           2
Sinks:
  Surgeon's [[[                           3
  Flushing rim (with valve) .................................................                           6
    Service  (trap standard) ..................................................                           3
    Service  (P  trap) [[[                           2
    Pot, scullery, etc [[[                           4
Urinal, pedestal,  syphon  jet blowout ...............................                           6
Urinal, wall lip [[[                           4
Urinal stall, washout [[[                           4
Urinal trough (each  6  ft. section) .....................................                           2
Wash sink (circular or multiple) each set of faucets .....                           2
Water closet, tank operated  ...............................................                           4

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                          Appendix E

   Suggested Specifications for  Watertight Concrete
1. Materials
  Portland cement  should  be free of hard lumps  caused by  moisture
during storage. Lumps from dry packing that are easily broken in  the
hand are not  objectionable.1
  Aggregates, such as sand and gravel, should be obtained from sources
known to make good concrete. They should be clean and hard. Particle
size of sand should range very fine to 14 inch. Gravel or crushed stone
should have particles from 14 inch to a maximum of \yz inches in size.
Water for mixing should be clean.
2. Proportioning
  Not more than 6 gallons of total water should be used for each bag
of cement. Since sand usually holds a considerable amount of water,
not more than 5 gallons of water per bag of cement should be added
at the mixer  when sand is of average dampness.  More mixing water
weakens the concrete and makes it less watertight. For average aggre-
gates, the mix proportions shown in  the  table below will give water-
tight concrete.


            Average  Proportions for  Watertight Concrete
Max. Size
Gravel (in.)
114 	
s/.

Cement
(volume)
1
1

Water »
(volume)
VA
/4

Sand
(volume)
O* y
o* /

Gravel
(volume)
3


  1 Assuming sand is of average dampness.

 3.  Mixing and  Placing
   All materials  should be mixed long enough so that the concrete has
 a uniform color. As  concrete is deposited in the forms, it should be
   1 Type V portland cement may be used when high sulfate resistance is required.

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tamped and spaded  to obtain a dense wall. The entire tank should be
cast  in  one continuous operation if possible, to prevent construction
joints.
4. Curing
  After it has set, new concrete should be kept moist for at least seven
days to  gain strength.

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                           Appendix F

               Industrial Waste Treatment
  Septic tank systems are not employed for the treatment of industrial
wastes from large manufacturing industries. In small industrial plants,
septic tank systems, assisted as needed by supplementary processes may
be used advantageously either for treating wastes to render them suit-
able for final disposal by one of the methods described in  Part  II, or
for conditioning wastes  to render them  acceptable for discharge to
sewer systems where they would  otherwise be objectionable.
  It is  important  to  note  that  the design of septic tank systems for
treatment and disposal of industrial wastes is not sufficiently simple to
permit formulation of specific criteria for design. This is because indus-
trial wastes vary widely in their composition; in fact, rarely do any two
plants produce  wastes of  the same character  and  composition.  The
design of an industrial waste treatment and disposal system is,  there-
fore, a problem  requiring specialized sanitary engineering consultation,
and this consultation usually includes special laboratory analyses and
studies  of the particular wastes under  consideration. With these pre-
cautions, however, it is possible, in many instances, to develop a  work-
able septic tank system which is  actually simple, effective, economical,
and within  the  means of the small industrial plant.
  The following is intended to indicate only qualitatively some of the
methods applicable to a few industrial wastes. The particular  design
for any given waste must be prepared by competent  sanitary engineers.
          LAUNDRY WASTES AND OTHER GREASY  WASTES
  Wastes derived from laundries and some other sources, which contain
soaps, oil, and greases in relatively low  concentrations, may be  success-
fully disposed of by one  of the methods previously described, provided
the greasy substances are first removed. If greasy substances, including
soaps and oils, are discharged into absorption systems, they accumulate
and soon cause clogging of the soil pores.
  The greasy substances contained in wastes are of  two types:  (1) the
floatable greases, which are nonemulsified and which, therefore, upon
quiescence or standing,  will separate and rise  to  the  surface  of the
liquid to form a surface layer;  and (2) the  emulsified  greases,  which
do  not separate upon standing.  Both  of these components may be
present in considerable  concentrations, and both  must be removed.

88

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 Properly  designed, conventional grease traps, such as  those  used for
 restaurant wastes,  will  remove  floatable grease,  but  not emulsified
 grease. Emulsified grease may be removed in a practical manner, how-
 ever, either (1) by passing the waste through a rock filter, or (2) by
 chemically flocculating the waste.
  Where  relatively low concentrations of emulsified grease are present,
 the  rock  filter process may be successfully used. The rock filter serves
 to deemulsify the grease, changing it  to floatable grease so that it may
 be subsequently removed by simple trapping. Septic tank units may be
 employed advantageously both for trapping the floatable  grease and
 to serve as the container for the rock filter. The servicing required for
 this  system includes  removal  of  the accumulated  floatable grease at
 regular intervals and occasional replacement of the filter rock.  The
 sizes of the trap and rock filter units will depend upon  the quantity of
 the  waste and its composition, as determined  by laboratory  analyses.
  Where  high concentrations of emulsified grease are present,  a chem-
 ical  flocculation process may be needed.  For all of these processes (trap-
 ping, flocculation, and settling), septic tanks  may be used as  the most
 economical means of obtaining the necessary capacities. Also required,
 as accessories  to  the  flocculation  process, are  a  suitable  electrically
 operated stirring device and a volumetric type chemical feeder. Mainte-
 nance of  the system includes keeping the chemical  feeder stocked with
 chemicals and periodic pumping of accumulated sludge  from the  set-
 tling basin. In  this process, the grease  particles are agglomerated by
 the  flocculating  action  into  large  particles  which settle out in  the
 settling basin. The sizes of the various tanks, the amounts of flocculat-
 ing  chemicals  needed, and  the frequency of pumping required will
 depend upon  the quantity of the waste and  its  composition,  as deter-
 mined by laboratory  analyses.

     SLAUGHTERHOUSE, DAIRY, AND OTHER ORGANIC  WASTES
  These wastes are generally characterized by very high concentrations
 of organic materials, up to (and even exceeding) 100 times the strength
 of ordinary sanitary  sewage.  Part  of the organic material is  in  true
solution,  and this may sometimes  be disposed of  by simple under-
ground absorption, provided there is adequate area and provided a suit-
able schedule  for resting the absorption areas is maintained. Much of
 the organic material,  including the emulsified greases, is in  colloidal
suspension. Colloidal  particles will clog underground  absorption  sys-
 tems. They do not settle out on quiescence and, therefore,  have to be
removed by some means,  such  as  by flocculation and sedimentation,
or by application to trickling filters followed by settling. As in the pre-
ceding example,  septic tanks may  advantageously be used  to  provide
 the  necessary  tank capacities for the trapping, flocculating,  and  set-
 tling processes.
                                                                  89

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                 MINERAL OR INORGANIC WASTES
  Mineral  and similar wastes  present special  problems generally re-
quiring chemical neutralization or  other  chemical treatment before
the wastes  may be filtered or absorbed into the ground. Important
factors are  the  metallic and nonmetallic ions present, their concentra-
tions, and,  for  underground absorption the nature  and importance of
the water basin lying  below the area  intended for absorption. Septic
tanks can sometimes be used  advantageously in the solution  of these
problems, as chemical  reaction chambers, settling tanks, etc.
90

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                               Bibliography

       Partial  List of References on  Septic  Tank-
                     Soil Absorption  Systems
Appendices to Study of Seepage Beds, James B. Coulter; Thomas \V. Bendixen; and
    Allen B. Edwards; Report to the Federal Housing Administration, December 15,
    1960.
A Basis for Classifying Soil Permeabilities, T. W. Bendixen; M. F. Hershberger; and
    C. S. Slater; Jour. Agric. Research, v. 77, no. 5; Sept. 1, 1948.
Causes  and Prevention of  Failure of  Septic  Tank  Percolation  Systems, P. H.
    McGauhey; and John H. Winneberger; Federal Housing Administration Report
    No. 533,  1964.
Degradation of ABS and Other Organics in Unsaturated Soils, G. G. Robeck; J. M.
    Cohen; W. J.  Sayers;  and  R.  L. Woodward;  Journal of the Water  Pollution
    Control Federation; v. 35;  no.  10; Oct. 1963.
Detergents and Septic  Tanks,  James E. Fuller; Sewage and  Ind.  \Vaste,  24, 844;
    July 1952.
The Effect of Automatic Sequence Clothes  Washing Machines  on  Individual Sewage
    Disposal Systems,  NAS  Publication 442,  Building  Research Institute, National
    Academy of Science, National Research Council, Washington,  D.C.
Effects of Food Waste  Grinders on Septic Tank Systems, T. W.  Bendixen;  A. A.
    McMahan; J. B. Coulter; and  R.  E. Thomas;  Report to the Federal  Housing
    Administration, Nov. 15, 1961.
Effects of  Ground  Garbage on Sewage Treatment Processes, William  Rudolfs;
    Sewage Works Journal, v. 18, no. 6, p.  1144; Nov. 1946.
Effectiveness of the Distribution Box, J. B. Coulter; and T. W.  Bendixen;  Report
    to the Federal  Housing Administration, Feb.  19,  1958.
Environmental Sanitation,  J. A. Salvato, Jr.; John Wiley &  Sons, Inc.  1958.
Estimating Soil Moisture  Conditions  and Time  for  Irrigation  with  the  Evapo-
    transpiration Method,  C. H. M. Van Bavel; U, S. Department of  Agriculture
    Publication ARS 41-11,  August 1956.
Factors Influencing the Design  and  Operation of Soil Systems for  Waste Treatment,
    G. G. Robeck;  T. W. Bendixen; W. A.  Schwartz, and R. L. Woodward; Journal
    of the Water Pollution  Control  Federation, v. 36, no. 8, Aug. 1964.
Field Investigation  of  Waste  Water Reclamation  in  Relation to Ground Water
    Pollution, State Water  Pollution Control  Board,  Publication No.  6,  State  of
    Calif.,  1953.
Final Report  on A Study of Preventing Failure of Septic Tank Percolation Systems,
    P. H. McGauhey; and  J. H. Winneberger; SERL  Report No. 65-17,  Sanitary
    Engineering Research  Laboratory,  University of California, Berkeley,  1965.
Improved Soil Percolation  Test, H. F.  Ludwig and  G. W. Ludwig,  Water and
    Sewage Works, v. 96, 5; May 1949.
Individual Sewage Disposal Systems,  Recommendations of Joint Committee  on Rural

                                                                          91

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     Sanitation;  Reprint  No.  2461  from Public  Health  Reports,  Public  Health
     Service  (revised  1947).
 Notes  on the Design  of  Sewage Disposal Works,  with Special  Reference  to Smalt
     Installations, Henry Ryon; Albany, N. Y.; 1928.
 Progress in  the Design of Rural Sewage  Disposal  Systems, Am. Jour.  Pub. Health,
     Year Book,  Part 2, 1952-53; May 1953.
 Septic  Tank Care, PHS Publication No. 73, U. S. Department of Health, Education,
     and Welfare, Public  Health Service, Washington,  D.C.
 Septic  Tank Drainage Systems, W. H. Sheldon;  Research Report No.  10, Michigan
     State University,  Agriculture Experiment Station,  East  Lansing.
 Septic   Tank  Soil Absorption  Systems  for Dwellings,  Construction  Aid  No.  5,
     Housing and Home Finance Agency, Division of Housing Research, Washington
     25, D. C.
 Soils Suitable  for Septic  Tank Filter Fields, W. H. Bender; U. S.  Department  of
     Agriculture, Agricultural Information  Bulletin  No. 243,  1961.
 Soil Survey  Manual, Agricultural  Handbook No.  18, U.S. Department of Agricul-
     ture, 1951.
 Some  Factors  Which  Modify the Rate  and  Total  Amount  of Infiltration  of Field
     Soils,  G.  W.  Musgrave; and G.  R.  Free;  Jour. Amer.  Soc.  Agron..  v.  28;
     727-739;  1936.
 Studies  on Household  Sewage Disposal Systems, Part I, S. R. Weibel; C. P. Straub;
     and J. R.  Thomas;  Federal  Security  Agency,  Public Health Service, Environ-
     mental Health Center,  1949.
 Studies on Household  Sewage Disposal Systems, Part II, T. W. Bendixen; M.  Berk;
     J.  P.  Sheehey; and  S.  R. Weibel;  Federal  Security Agency,  Public  Health
     Service, Environmental Health Center, 1950.
 Studies  on  Household  Sewage Disposal Systems,  Part III,  S. R. Weibel;  T.  W.
     Bendixen;  J.  B. Coulter; U. S. Dept, of Health, Education, and Welfare,  Public
     Health Service, Robert A. Taft Sanitary Engineering  Center, 1955.
 A Study of  Methods  of  Preventing Failure of  Septic  Tank Percolation  Systems,
     J.  H.  Winneberger and P. H. McGauhey, SERL  Report  No.  65-16,  Sanitary
     Engineering Research Laboratory,  University of California, Berkeley,  1965.
 Study of Seepage Beds, J.  B. Coulter; T. W.  Bendixen; and  A. B. Edwards;  Report
     to  the  Federal Housing Administration, Dec.   15, 1960.
 Study  of Seepage Pits, Thomas W.  Bendixen;  R.  E. Thomas; and  J.  B.  Coulter;
     Report to  the Federal Housing Administration, May 1,  1963.
 A Study of Serial Distribution for  Soil Absorption Systems,  G. M. Sullivan;  J. B.
     Coulter;  and  T.  W. Bendixen; Report to the Federal Housing Administration,
     April 8, 1959.
 Subsurface Sewage Disposal, J. E. Kiker, Jr.; Bull. No. 23, Florida Eng. Ind. Exper.
    Station, Univ. of  Florida, Dec. 1948.
 Transpiration and Total  Evaporation, Physics  of  the  Earth, IX, Charles  H. Lee,
    Hydrology;  McGraw-Hill Book  Co.,  Inc.;  1942.
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                                         •& US. GOVERNMENT PRINTING OFFICE: 1969—O-363-353
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