LAND TREATMENT OF MUNICIPAL
WASTEWATER EFFLUENTS
DESIGN FACTORS - II
ENVIRONMENTAL PROTECTION AGENCY*Technology Transfer
JANUARY 1976
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ACKNOWLEDGMENTS
This seminar publication contains materials prepared for the U.S.
Environmental Protection Agency Technology Transfer Program and has
been presented at Technology Transfer design seminars throughout the
United States.
The information in this publication was prepared by G, Morgan
Powell, Ph.D., representing CH^M Hill, Denver, Colorado.
NOTICE
The mention of trade names or commercial products in this publication is for
illustration purposes, and docs not constitute endorsement or recommendation for use
by the U.S. Environmental Protection Agency.
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CONTENTS
Page
Introduction 1
Chapter I. Land Application Processes 3
Overland Flow 3
Irrigation 6
High-Rate Irrigation 6
Infiltration-Percolation .,,,,,.,, 7
Chapter II, Factors Affecting Site Selection 9
Soil 9
Geology and Groundwater 12
Land Use 12
Sensitive Environmental Areas 12
Water Rights 17
Land Application Process 18
Topography 18
Political Boundaries and Land Ownership 19
Chapter III. Identifying and Selecting Sites 21
Criteria for Potential Area Identification 21
Potential Sites 23
Site Evaluation and Selection 23
Chapter IV. Effluent Loading Characteristics 29
Infiltration 29
Permeabilities of Soil and Geologic Materials 31
Nitrogen Removal 40
Nitrogen Balance 46
Phosphorus 46
Suspended Solids 48
BOD and COD Oxidation 49
Inorganic Chemicals 49
Salts 52
Climate 53
Chapter V. Effluent Loading Design 55
Climate and Hydrology 55
Process Loading , 55
Rest Period 57
ill
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Page
Chapter VI. Components of Land Application Systems 59
System Components 59
Operation Components 63
Chapter VII. Alternative Evaluation 67
References 69
IV
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INTRODUCTION
This ' is the second of two papers prepared for the United States Environmental
Protection Agency Technology Transfer Program on Land Treatment of Municipal Wastewater
Effluents. Land treatment or land application is the treatment of wastewater by using plant
cover, soil surface, soil profile, and geologic materials to remove certain wastewater pollutants.
Figure 1 is a conceptual drawing of the relationship of land application to the entire water
cycle, from the water supply to the treatment and disposal of the used water.. Once applied
to the land, a portion of the water is lost to evaporation and transpiration, and the remainder
returns to the groundwater or surface water. Many pollutants are removed by the soil and
plants as the wastewater moves through the vegetation and soil profile.
The main concern about using land application for wastewater treatment is the possible
harmful effects of the pollutants on the vegetation, soil, and surface and groundwaters. To
SUBSURFACE
TILE DRAINAGE
EVAPORATION- /
TRANSPIRATION
TREATMENT
& STORAGE
LAGOONS
IMPERMEABLE
LAYER
GROUNDWATER
RECHARGE
Figure 1, Conceptual land application of wastewater effluents.1
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avoid adverse environmental impacts, many factors such as soil and crop characteristics and
wastewater makeup must be considered in designing a land application system. Consequently,
a land application method of treating municipal wastewater is specifically designed for a
selected site. The design for one site cannot normally be used at another location,
A main theme of many papers presented at the Second National Groundwater Quality
Symposium held in Denver in September 1974 was that wastes applied to land pollute the
groundwater. The only way to completely eliminate that pollution is to isolate the waste from
the environment. Isolation can be accomplished by surrounding the waste with a water
impermeable material. This is, of course, impossible to do with the wastewater volumes from
cities and furthermore would be a waste of the water as a valuable resource. The objective of
land application of wastewater should be to treat the water with due consideration to impacts
on the environment. This part discusses many design factors which are part of or which
impact the manmade and natural environments. The impacts can be minimized by giving
proper consideration to these factors.
A multidisciplinary approach to defining and evaluating land application alternatives is
usually required. Some of the technical areas involved in investigating land application include
hydrogeology, soil science, agronomy, and engineering. Other disciplines that may also be
relevant depending on the type and place of application are, toxicology, environmental
planning, regional planning, meteorology, hydrology, soil microbiology, soil physics, plant
pathology, irrigation engineering, farm management, and agricultural economics.
Design Factors — I discussed objectives of land application processes, preapplication
treatment, land suitability, selection of the land application process, distribution techniques,
climatic factors, storage, surface runoff control, public health considerations, and monitoring
requirements.
Design Factors — II begins with a review of land application processes and factors
influencing the identification and selection of land application sites. Effluent loading
constraints, effluent loading design, and alternative land application components and operations
are then discussed. Emphasis is given to the design of a suitable loading rate and to
requirements for drainage, field investigations, monitoring systems, crop selection, irrigation
schedules, and farm management.
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Chapter I
LAND APPLICATION PROCESSES
Four processes have been used successfully for land-based treatment of wastewater
effluents. These four processes are overland flow, irrigation, high-rate irrigation, and
infiltration-percolation. Except for overland flow, all processes have been used successfully in
this country for the treatment of municipal wastewater. In other countries, the overland flow
process has been used successfully for domestic wastewater treatment. All four processes have
been used for successful treatment of industrial wastewater, both in this country and
elsewhere.
A synopsis of the processes' characteristics and their requirements is given in table 1-1.
The objectives and other characteristics, as well as how the applied water is dispersed, are
distinctly different among the four processes. The quality of the water after treatment also
varies among the processes and is a function of soil characteristics, crop type, system
management, and especially loading rate. Loading rates and land area requirements overlap for
the different processes.
Factors such as wastewater quality, climate, soil, geology, topography, land availability,
and return flow quality requirements will determine which of the four processes would usually
be most suitable for a particular region. The following descriptions of these processes indicate
under what general conditions the processes would be feasible for municipal wastewater
treatment.
OVERLAND FLOW
With the overland flow process, the wastewater is filtered and oxidized as it passes over
the soil surface and through the grass cover. The land surface should have a uniform slope of
2 to 8 percent so that surface runoff will move downslope and uniformly spread over the soil
surface. A cover crop, usually grass, should be grown to protect the soil from erosion and to
maximize the wastewater treatment by providing surface area for biological treatment.
The overland flow process is used where soil permeability is slow and/or the groundwater
table is high so the water cannot move into the soil profile. The soil surface is carefully
shaped to produce the necessary uniform flow of water over the soil surface. Thus, in areas
with sandy soil, adverse topography, or very shallow soils, overland flow would be eliminated
from further considerations as a treatment alternative,
Because the applied water does not move through the soil profile, the overland flow
process does not have the benefit of the large buffering capacity and time lag of the soil
profile. This land application system is dependent on biological processes to treat the
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Table 1-1.—Four land application processes for treatment of municipal wastewater1
Overland flow
Irrigation
Annual
loading
acre
ft/ac/yr
5 to 25
1 to 5
Net irrigated
land area
requirement
for 1-mgd flow
45 to 225 ac
plus buffer
areas, etc.
225 to 1,100
ac plus buffer
areas, etc.
Objective
Maximizes water treat-
ment
Crop harvest is incidental.
May be used as secondary
treatment of raw waste-
water or advanced treat-
ment of secondary treated
waste water.
Maximizes agricultural
production by supplying
irrigation needs.
May be considered a
reuse option as well as
advanced treatment of
partially treated waste-
water.
Soils and
geologic
materials
Suitable for slow or very
slow permeable soils and/
or high water table
conditions.
Generally requires natural
or constructed slopes of
2 to 8 percent.
Suitable for most irrigable
agricultural soils.
Irrigation method will
depend on soil, topog-
raphy and crop.
Dispersal of
applied water
Most water to surface
runoff.
Some water to evapo-
transpiration and very
little water to percolation.
Most water to evapo-
transpi ration.
Some water to percola-
tion and leaching of
salts.
Tailwater runoff from
surface irrigation can be
controlled.
Impact on quality
of applied water
BOD and suspended
solids greatly reduced.
High nitrogen removal.
Some phosphorous
removal.
Reduction of some heavy
metals.
Little change in total
dissolved ionic solids
(TDIS).
BOD and suspended
solids almost completely
eliminated.
Nutrients removed by
crop and soil.
Heavy metals adsorbed
or precipitated.
TDIS concentration
greatly increased by
evapotranspi ration .
Little change in total
salts (applied — leached).
Increase in hardness of
percolate.
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Table \A.—Four land application processes for treatment of municipal wastewater1 (Continued)
High-rate
irrigation
Infiltration-
percolation
Annual
loading
acre
ft/ac/yr
1 to 10
1 1 to 500
Net irrigated
land area
requirement
for 1-mgd flow
110 to 1,100
ac plus buffer
areas, etc.
2 to 100 ac
plus buffer
areas, etc.
Objective
Maximizes wastewater
treatment by supplying
nutrients and water as
needed by crop.
Agricultural crops are a
side benefit. In case of
conflict, wastewater treat-
ment is higher priority
than crop production.
Maximizes water filtration
and percolation to ground-
water.
Crop production is not a
benefit. There may not
be a crop.
Soils and
geologic
materials
Suitable for more perme-
able irrigable agricultural
soils.
Irrigation method will
depend on soil, topog-
raphy, and crop.
Requires good natural or
constructed drainage.
Suitable for highly
permeable soils.
Requires very good
natural or constructed
drainage.
Dispersal of
applied water
Most water to percola-
tion and evapotranspiration.
Tailwater runoff from
surface irrigation can be
controlled.
May result in buildup of
groundwater mound.
Most water percolates to
groundwater.
Some water to evapo-
transpiration.
No runoff.
May result in buildup of
large groundwater
mound.
Impact on quality
of applied water
BOD and suspended
solids almost completely
eliminated.
Nutrients removed by
crop and/or soil.
TDIS concentration in-
creased by evapotrans-
piration.
Additional salts leached
out of soil by excess
applied water (salt
loading).
BOD and suspended solids
reduced.
Some nutrient removal by
soil and crop.
Additional salts leached
out of soil by excess
applied water (salt
loading).
Increase in hardness of
percolate.
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wastewater. Like all biological systems, overland flow is subject to temperature effects and
shock loads. With its sensitivity to temperatures below freezing, the overland flow process may
not be a feasible treatment alternative in areas with cold climate unless the wastewater can be
stored for application during warm weather. To be stored, the wastewater would have to be
biologically stabilized.
Because it provides only limited removal of phosphorus and heavy metals, overland flow
without chemical aids as a final treatment process may not be suitable if an ultra-high level of
treatment is required. Certain chemical additions such as lime or alum may improve the
removal of phorphorous and heavy metals.
IRRIGATION
The objective of the irrigation process is primarily to maximize crop production. Effluent
treatment and disposal are secondary benefits.
The irrigation process is a suitable treatment alternative in the rain fall-short western part
of the United States where irrigation is required for optimum crop production. In areas where
there is sufficient rainfall to grow crops, the irrigation treatment process could only be used
for supplemental watering or during sporadic dry periods and thus probably would not be
considered a viable wastewater treatment alternative.
Virtually all plant nutrients are found in municipal secondary effluent. Thus, irrigating
with wastewater rather than other water could have a greater agricultural value. In some cases,
the irrigation process may more appropriately be classified as a wastewater reuse alternative as
well as a treatment process.
The irrigation process has the highest potential of the four land application systems for
removal of most wastewater pollutants. Because of its lower loading rates, the irrigation
process involves the largest land area and widest dispersal of pollutants. As a result, adverse
•impacts'on "the soil and'vegetation are minimized. However, because of the high percentage of
water lost to evapotranspiration, the concentration of total dissolved ionic solids (salts—TDIS)
in percolate to the ground water may be undesirable.
HIGH-RATE IRRIGATION
Unlike the irrigation process described above, high-rate irrigation is primarily a method of
effluent treatment and has the side agricultural benefit of producing high-yield crops. Higher
loading rates are used than with the irrigation process, and much of the water percolates
below the root zone. For the best nutrient removal, crops that can remove nutrients to very
low concentrations should be grown. Much of the nitrogen not removed by the crop will be
leached to groundwater because of the high wastewater applications. It is necessary to select a
crop that will respond to the dilute nutrients in wastewater; otherwise, chemical fertilizer may
have to be added to produce the desired crop growth.
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High-rate irrigation is a feasible treatment method in almost all climates. Usually, a region
will have some area where land is available and where the soil, geological, and topographical
conditions are suitable for high-rate irrigation.
The high-rate irrigation process has the second highest potential for removal of
wastewater pollutants. Because its loading rates are considerably higher than for the irrigation
process, in a given area high-rate irrigation requires less land, but the pollutant load on the
land is more concentrated. Thus, the potential impact on soil and vegetation is greater than
for the irrigation process.
INFILTRATION-PERCOLATION
Infiltration-percolation treats the wastewater within a minimum land area and under some
conditions has the added benefit of recharging the groundwater. Wastewater is applied at high
rates for several days to weeks and then is removed during a rest period so the soil profile
can dry. The rest period restores the soil's infiltration and treatment capacity. A crop may be
grown to help maintain infiltration rates, but harvest usually would not be an objective.
Infiltration-percolation can be used for wastewater treatment in most climates. Because
this process involves high loadings, soil and geologic conditions with rapid infiltration and
permeability are necessary. In areas where these conditions are not found, the
infiltration-percolation process can quickly be discarded from further consideration.
The infiltration-percolation process has the lowest potential for removal of pollutants
where the applied water moves through the soil-geologic profile. The capacity of soil and
crops to remove nutrients at high application rates is limited. Therefore, this process may not
be a feasible treatment method where there are strict limitations on discharge of nutrients
into groundwater. Infiltration-percolation has been successfully used in combination with wells
or other drainage to provide a good quality water for irrigation or industrial purposes.
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Chapter II
FACTORS AFFECTING SITE SELECTION
The following two basic approaches are used for identifying a site for land application:
» Select a site that best fits the requirements for treatment, the location conditions,
and the land application to be used.
Utilize a site already owned or readily available, select the appropriate process, and
design the system to fit the site conditions.
*
Normally municipalities will not already own uncommitted land where a land application
system may be implemented, but because they have power of eminent domain, the site
selection approach can be used. Conversely, industries do not have such power and are
restricted to using land that they already own or can acquire. This section will briefly discuss
some of the factors that should be considered when the site selection approach is used. Table
II-l outlines the information that may be needed and indicates possible sources for obtaining
the information.
SOIL
Soil properties of the root zone (top 5 feet or to the restrictive layer) determine the
suitable loading rate. The amount of land required and total project costs are inversely
proportional to the loading rates. The costs for site preparation, distribution system,
application system, and drainage, all costly items, are determined by the land requirements.
Thus, soil properties are an important factor in identifying and selecting sites that would
allow an economical land application system.
As mentioned previously, suitable soil properties differ for the land application processes.
Overland flow requires an impermeable soil, while the infiltration-percolation process requires a
highly permeable soil. Soils can be classified into suitability groups according to the soil
properties and the application process as shown in table 11-2,
Existing soil maps can often be used to evaluate and interpret the suitability of a soil for
a particular use. Detailed soil maps, if available, are the most useful and accurate references.
A few days of field checking by a qualified soil scientist can determine if the soil mapping is
sufficiently accurate for a preliminary study and if soil groupings made from available data
appear valid.
General soil association maps, particularly when they cover broad areas, should definitely
be field checked before sites are selected. A soil association comprises several soil series which
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Table 11-1.—Information needs and sources for land application of wastewater
INFORMATION SOURCE
INFORMATION NEEDS
Climatic data
Soil classification— mapping
Soil infiltration— permeability
Soil depth 0-5 feet
Soil drainage and water table <5 feet
Soil properties {chemical and physical)
Agricultural land use capability
Depth to bedrock
Unconsolidated materials
Bedrock type and structural characteristics
Jointing and permeability of rock
Rock outcrops
Surface slope, categories (ex. 0-3 pet)
Flood plain, flood hazard
Stream-flows
Groundwster yield
Groundwater alevation and contours
Groundwater aquifers
Irrigation methods
Crops
Interpretation of soil suitability
Interpretation of groundwater
Land use
Land values
Guidelines for land application
Sensitive environmental areas
Socioeeonomic factors
Institutions
*
* *
« •
•
*
• *
* * *
*
*
»
*
*
* •
» *
* *
* *
* « «
*
•
• •
*
•
•
ironmental Protection and/or Public Health
orical Society
e Geological Survey
e Div. or Dept. of Water Resources
e University Extension Specialists
e Planning Office
^ ^ co ra ro ro
UJ I ffs V> W U3
OT (- < (- IU
•
•
*
•
*
•
• *
*
*
*
• •
* *
* *
*
»
*
• •
•
*
• * *
»
• *
3s of Engineers
. Forest Service
. Geological Survey
3A, Agricultural Research Service
. Environmental Protection Agency
ining Agency (COG, River Basin Resource Management Districts)
3 w « o) w S
O D 13 ^ D £-
oc uii3 — Oz < _i
*
*
•
*
*
•
*
* •
* *
• *
*
• *
*
* *
*
•
*
*
* *
* *
*
*
*
10
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Table \\-2.-Examples of soil suitability for land application processes1
Soil
group
1
2
3
4
5
Minimum
depth
60 in.
40 to 60 in.
20 to 40 in.
Less than 20 in.
Less than 20 in.
Characteristics
Deep soil of moderate to rapid permeability
Moderately deep soils of moderate to rapid
permeability or deep soils with moderately
slow permeability
Moderately deep soils of slow to moderate
permeability or deep soils of slow
permeability
Shallow soils. Includes much of the alluvial
material adjacent to streams which has a
high water table.
Soils with slope greater than 20 percent
Irrigation
Very suitable
Very suitable
Suitable
Low suitability
Unsuitable
High-rate
irrigation
Maximum
High
Moderate
Low
Unsuitable
Infiltration-
percolation
Moderate
Moderate for rapid
permeability
Very low for slow
permeability
Maximum for rapid
permeability soil
Unsuitable
Note: Overland flow was unsuitable for local conditions and requirements in this example.
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are usually found in the same land area. Some small areas of other series with much different
properties may occur. Wide variation between soil properties obtained from a soil association
map and actual soil conditions in the field has been found. Figure II-1 is an example of a
general land classification map for a sample study area. To make the map, soil associations
with similar properties were grouped as shown in table II-2.
GEOLOGY AND GROUNDWATER
Geologic features below the root zone layer or restrictive layer are important for drainage
of water that is not lost to evapotranspiration. The depth to bedrock and the properties of
that rock should be known. For example, if the root zone is underlaid by unfractured shale
at shallow depths, drainage may be severely limited, and a reduced loading rate may be
necessary.
The availability of groundwater and water table depth within the area are general
indicators of properties of the geologic materials. Where groundwater yields are low,
permeabilities are usually restricted. Slow permeability of subsurface layers will restrict
drainage and may therefore restrict loading rates, thus increasing project costs by necessitating
artificial subsurface drainage. Figure II-2 is an example of a map of groundwater availability in
the sample study area which can be used in site identification and selection.
A more thorough process for site selection, based on a detailed inventory of
hydrogeologic conditions, was discussed in a paper by Bond, Williams, and Shadid (1972).2
When data on depth, permeability, and groundwater elevations are available, a hydrogeologist
can estimate the natural drainage capacity of an area, the groundwater movement, and the
need for artificial subsurface drainage. If the required data are not available from existing
information, a preliminary field investigation may be necessary to evaluate relative differences
for potential sites.
LAND USE
Land use information is usually available from local and regional planning agencies. Areas
committed for various uses should be identified and indicated on a map. The remaining areas
would be available for land application. Figure II-3 shows a land use map for the sample
study area which could be used for site identification purposes.
SENSITIVE ENVIRONMENTAL AREAS
Sensitive environmental areas should also be identified and plotted on a map. Examples
of environmentally sensitive areas are historical sites; unique environments for plants, animals,
or water species; and unique geologic features. Figure II-4 is a map of typical critical
environmental areas in the sample study area.
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GROUP
NOTE: SEE TABLE 3 FOR DESCRIPTION OF SOIL GROUPS.
3 2 l~~l 5 SOURCE. CH2M HILL, COMPARATIVE STUDY OF WASTEWATER TREATMENT,
3 3 CITY OF BOULDER.
Figure 11-1. General soil groups.1
13
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*>** u c ^ XXr
345 MILES •-%*!£}&*''
- I I ' * * 1 ^
STUDY AREA BOUNDARY
VERY LOW YIELD
MODERATE TO LOW YIELD
MODERATE TO HIGH YIELD
Figure 11-2. Groundwater availability.1
14
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LEGEND
URBAN AND SUBDIVISION
PROJECTED URBAN DEVELOPMENT FOR 1S90
(BOULDifi AREA GROWTH STUDY COMMISSION!
DRYLAND AQBICULTURE
• RANGE LAND
S3 RECREATION AND WOODLAND
^3 IRRIGATED AGRICULTURE
Figure 11-3. Land use.1
15
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2 Miles
Figure 11-4. Sensitive environmental areas.1
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WATER RIGHTS
In the United States, water laws governing the right to withdraw surface water fall into
three general classifications: 1) land ownership—common law or riparian rights, 2)
appropriative rights, and 3) a combination of the two. These distinct divisions in water law
have developed in relationship to the surplus and deficiency of water, as shown in figure II-5.
Water surplus areas are areas where the precipitation exceeds the evapotranspiration and results
in runoff and streamflow. Water deficient areas are areas where evapotranspiration exceeds
precipitation and little annual runoff occurs.
Simply stated, the land ownership or riparian doctrine says that the owner of land along
a stream is entitled to unreduced flow and undiminished quality. Thus, water may be taken
from the stream and used but must be returned. Since, in areas of surplus water, only a small
portion of wastewater would be lost to evapotranspiration by land application, there would
probably be no water rights problems associated with land application of effluents where
riparian rights are in force.
The appropriative doctrine dedicates the waters to the public. State laws differ, but in
general a right to the use of water is obtained by putting the water to use after or while
filing for the right. The first person who puts water to beneficial use receives senior rights.
Subsequent appropriators are called junior appropriators and must not damage senior rights in
APPROPRIATIVE AND
/7
LAND OWNERSHIP
RIGHTS
LAND OWNERSHIP
RIGHTS
AREAS OF WATER SURPLUS
AREAS OF WATIR DEFICIENCY
Figure 11-5, Dominant water rights doctrines.3
17
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times of short water supply. Thus, appropriated rights have a priority value based on the
principle of "first in time, first in right." Appropriated water rights are property and may be
bought, sold, exchanged, or transferred.
Where water use is highly developed in deficient areas, water rights would probably be
required for a land application wastewater treatment system. Land application on presently
unirrigated land would result in increased evapotranspiration (consumptive use), which would
decrease streamflows. Downstream water rights would be damaged by this action, and it might
be necessary to appropriate or purchase water rights to ensure a continued land application
system.
In water-deficient areas, the total loss of wastewater to evapotranspiration would be
inversely proportional to the loading rate. If the irrigation process is used to supply water
according to crop needs, losses to evapotranspiration would typically be greater than 50
percent of the wastewater. Evapotranspiration losses for the overland flow, high-rate irrigation,
and infiltration-percolation processes would probably be, respectively, 10 to 20 percent, 15 to
30 percent, and less than 10 percent of the applied water.
In some western streams, normal summer flows were fully appropriated by 1880, In
these cases, any right junior to that time can be called out so that senior rights can receive
their water. In those areas where unappropriated water does not exist in the stream, a water
right or replacement water would be necessary to ensure successful land treatment without
damage to senior rights. Where unappropriated water still exists in the stream, obtaining a
right for land application of effluent should be little problem.
The status of water rights in the local area should be investigated to avoid potentially
serious legal problems later. If water rights are required, the expense and quantity of the right
can be controlled to some extent in the process and site selection. For instance, if presently
irrigated land is selected as the application site, it would be possible to purchase the water
right with the land and make any necessary transfers. If a water right is necessary for only
the portion of water consumptively used, it may be desirable to select the process which
would minimize the evapotranspiration, A consultant familiar with water law and water
resources can determine the legal implication of land application and the extent of
replacement required.
LAND APPLICATION PROCESS
As noted above, certain soil and geologic characteristics are particularly suited for each of
the land application processes. Table II-2 shows that a soil group highly suited to one process
may be poorly suited to another process. Thus, it is necessary to eliminate those processes
which are not feasible for the local conditions and requirements. Then the areas with soil and
surface geology most suited to the remaining processes can be identified.
TOPOGRAPHY
Slopes up to 15 percent and 5 percent can usually be used, respectively, for sprinkler
and surface irrigation of cultivated crops. Slopes of up to 30 percent can often be adapted to
18
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sprinkler irrigation where noneultivated crops are grown. Increasing slopes reduce the
infiltration rates and place restrictions on surface and sprinkler irrigation. The overland flow
process on sod-covered ground requires slopes of 2 to 8 percent. In mountainous areas,
topographic restrictions are more of a problem. In general, topography may be a limiting
factor where low water infiltration into the soil can result in runoff and soil erosion.
Topographic maps, Field studies, and aerial photography of potential application sites would
identify areas with slopes suitable for each process and application method.
POLITICAL BOUNDARIES AND LAND OWNERSHIP
Political boundaries such as county or state lines may restrict site identification. Given
enough time and money, political boundaries may be crossed, but for expediency these
boundaries should be taken into consideration during site identification and selection.
Land ownership is another political boundary that must be recognized. Getting a right to
the use of public land from the Forest Service or Bureau of Land Management could involve
considerable time and negotiation. A land ownership map is very useful to locate properties to
be avoided or large areas of only a few ownerships. If land ownership is in small parcels, the
time and costs involved in acquiring the land are increased.
19
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Chapter 111
IDENTIFYING AND SELECTING SITES
The following steps can be used by municipalities to select land application sites for
detailed study:
• Establish criteria for identifying potential sites.
• Identify potential sites,
• Establish criteria for evaluating potential sites,
» Select sites for further study.
By following these steps, the municipality can narrow down the number of alternative sites
for more detailed investigation. The city must determine the relative weight of such
considerations as environmental impact, cost, and public acceptance.
The factors affecting site selection discussed in chapter II for which criteria are
established may be taken into consideration in several ways during site identification and
selection. One relatively unbiased approach is to prepare a series of transparent map overlays
showing areas of exclusion. These transparencies can then be placed over a base map of the
same scale. The areas of no exclusion or where exclusions are fewest are then selected as
potential sites. This process is time consuming and may not be justified. In addition, factors
.such as soil and geological conditions are often too varied and difficult to show only as areas
of exclusion.
Another approach is to identify three to five categories of land suitability as determined
from a general soil association map. Areas of exclusion because of committed land use,
sensitive environment, unsuitable topography, or political boundaries may be shown on the
same map. The result is a fairly quick and reasonably unbiased method of arriving at potential
areas. Figure III-l is a typical composite map made from combining the land suitability map
with the map of committed areas for the sample study area.
CRITERIA FOR POTENTIAL AREA IDENTIFICATION
To help eliminate the possibility of bias in selecting potential sites, criteria should be
established for the identification of suitable areas. Some possible criteria are as follows:
» Site should not conflict with present land use and should reinforce the adopted land
use plans.
21
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!*4 i 12#v.\T.t^ rfrflr
LEGEND
URBAN AND SUBDIVISION
RANGELAND
PROJECTED URBAN I 1 RECREATION
DEVELOPMENT FOR 1990 LJ AND WOODLAND
I." *| DRYLAND AGRICULTURE
[7*1
SOIL GROUP
MINIMUM MINIMUM
DEPTH DEPTH
60" [fjj 3 20" TO 40"
2 40" TO 60" j | 4 LESS THAN 20"
Figure 1II-1. Composite site selection map.
22
-------
* Site should not endanger sensitive environmental areas such as historical sites or rare
or endangered plant or animal species.
• Site should minimize adverse socioeconomic impacts. The density of dwellings, other
structures, and roads that would be affected must be considered.
» Preference should be given to the soil groups most suited for the process being
considered.
• Areas where geological conditions and groundwater availability would adversely affect
the process being considered should be avoided.
» Political or legal boundaries should be noted.
These criteria are only a few that may be used to identify areas potentially suited to a
land application process. Criteria appropriate to the particular area or municipality should be
used. Without some logical procedure to identify suitable areas, the city, EPA, or public may
object to the site selected and thus delay development of the land application project and/or
increase project costs.
POTENTIAL SITES
Once the criteria for identifying potential sites are established and maps have been
prepared showing the factors judged most critical, the identification of potential sites is a
simple process. Areas that meet all or most of the established criteria can be outlined on a
map as shown on figure III-2 for the sample study area. Sites A through J were identified for
the irrigation and high-rate irrigation processes. Sites HR-1 and HR-2 were identified for the
infiltration-percolation process. For the sample study area, overland flow was not suitable for
local conditions and requirements.
SITE EVALUATION AND SELECTION
Once the potential land application sites have been identified for a specific process, a
more in-depth comparison of the sites can be made. Section C of the new EPA report,
Evaluation of Land Application Systems (1975),4 discusses criteria which may be valuable for
evaluating potential sites, A few of the more important criteria follow:
• Location—Evaluate the site location with respect to the wastewater source, discharge
point, transport route, and length; the elevation difference between the site and the
water source; and the need for a storage area.
» Land availability and cost—Consider land ownership of the potential site, number of
owners, and associated land values.
« Environmental impact—Analyze the potential impact on both the natural and
socioeconomic environment.
23
-------
0 I
SCALE
2345 MILES
®te
Figure 111-2. Potential land application sites.
24
-------
• Loading capacity and area required—Evaluate the suitable loading rate and land area
requirement.
• Site treatment capacity and expansion—Define the total treatment capacity of the
proposed site and additional area for future expansion.
• Water rights^Identify possible alternatives for resolving potential water rights
problems.
» Water quality—Analyze the impact on receiving groundwater aquifers or streams by
land application on the proposed site.
If many sites are being compared, a table such as table II1-1 showing a comparison of
many of the criteria for the sample study area may be helpful, Ideally, a citizens group in the
local area should participate in the site selection. If representatives of the municipality and
local residents are involved in key parts of a wastewater treatment study such as site selection
and the treatment process, the site selected will be the most viable in respect to local
problems and priorities. By involving the public throughout the study, the need to make
changes after the study is completed can be minimized.
25
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Table 111-1.—Comparison of potential sites on figure ///-2l
Site
A
B
C
D
E
Approximate
cross area
(acres)
5,100
5,800
4,500
4,800
5,000
Estimated
treatment
capacity
(mgd)
11
20
19
17
Could be
enlarged
14
Area
of site
presently
irrigated
(percent)
5
90+
70
90
80
Distance
from
plant
(feet)
65,000
31,000
8,000
35,000
74,000
Elevation
difference
from plant
(feet)
1,080
280
105
-45
130
Homes
onsite
(no.)
5
81
133
53
196
Other
buildings
onsite
(no.)
14
126
127
55
104
Roads
onsite
(miles)
12.2
25.7
19.0
13.1
24.4
Comments— major problems or advantages
Outside of NCWCD boundary.
Little or no irrigation. Canals pass through
area.
Poor soil, low loading rates.
Outside of NCWCD boundary.
Possible storage in Baseline Reservoir or
Marshall Lake (15,700 ac ft).
Return flows return to Boulder Creek via
Coal Creek.
Most of site overlies abandoned coal mines.
Outside of NCWCD boundary.
Ditches flow through area. Requires sepa-
rate distribution system.
Possible storage in Valmont and Baseline
Reservoirs (11,300 ac ft).
Return flows return to Boulder Creek.
No good storage reservoir.
Transfer outside of watershed area.
Entirely within NCWCD boundary.
Ditches terminate within area.
Totally within NCWCD boundary.
Transfer outside of watershed area.
Supply ditch and rough and ready ditch
could benefit from a more firm water
supply.
Ditches do not terminate within this site.
to
CT\
-------
Table 111 -1.—Comparison of potential sites on figure ltl-21 (Continued}
Site
F
G
H
1
Approximate
cross area
(acres)
14,300
17,600
28,000
9,600
Estimated
treatment
capacity
(mgd)
50
61
61
20
Area
of site
presently
irrigated
(percent)
75
90
80
75
Distance
from
plant
(feet)
20,000
70,000
65,000
32,000
Elevation
difference
from plant
(feet)
-70
-245
-120
230
Homes
onsite
(no.)
215
254
341
245
Other
buildings
onsite
(no.)
170
306
362
46
Roads
onsite
(miles)
54.3
52.3
85.1
25.0
Comments— major problems or advantages
Panana No. 1 Reservoir is a good poten-
tial storage site (approx. 7,000 ac ft).
Part of return flows return to Boulder
Creek.
Ditches terminate within area.
Irrigation water supplied from Boulder
Creek and South Platte River.
Water rights exchanges may become
complex.
Ditches do not terminate within the site.
Numerous water supply canals flowing in
all directions.
Several lakes in area.
Transfer outside of watershed area.
Portion of site is city greenbelt.
Small portion of site outside of NCWCD
boundary.
Part of site outside of watershed area.
Part of site above Boulder water supply
reservoir.
No storage reservoir except Boulder
Reservoir.
to
-------
Table 111-1 .Comparison of potential sites on figure ///-21 (Continued)
Site
J
Approximate
cross area
(acres)
13,500
Estimated
treatment
capacity
(mgd)
39
Area
of site
presently
irrigated
(percent)
65
Distance
from
plant
(feet)
62,000
Elevation
difference
from plant
(feet)
-20
Homes
onsite
(no.)
154
Other
buildings
onsite
(no.)
37
Roads
onsite
(miles)
44.0
Comments— major problems or advantages
Majority of site outside of NCWCD
boundary.
Ditches do not terminate within the area.
Portion of site overlies abandoned coal
mines.
Portion of return flows return to Boulder
Creek.
Part of site outside of watershed area.
t-o
oo
-------
Chapter IV
EFFLUENT LOADING CHARACTERISTICS
Once suitable sites have been identified as described in chapter III, they can be compared
for selection of the best site for a chosen land application process. The comparison would
probably be made on the basis of costs and environmental impacts. Because the effluent
loading rate has a major influence on both cost and environmental impact, loading restrictions
must be considered.
For each of the previously described land application processes, the effluent loading rate
may be limited by any of several constraints. The process of water moving into and through
the soil depends on the soil's capacity for infiltration-percolation. Thus, these soil properties
can restrict loading rates. Limits placed on composition of deep percolation to ground water or
of return flow to surface streams may also result in a constraint on the loading rate or may
require higher levels of pretreatment. Another possible loading rate constraint is the finite
capacity of the soil-crop system to remove various pollutants. The following parameters may
be limiting for a given situation:
» Infiltration capacity of the soil
» Permeability of the root zone and underlying geologic materials
• Soil and plant capacity to remove major plant nutrients (nitrogen and phosphorus)
• Soil capacity to filter and assimilate suspended solids
• Soil capacity to remove and oxidize BOD and COD
* Soil capacity to remove and assimilate inorganic chemicals (heavy metals, specific
ions, salts, etc.)
* Discharge requirements to groundwater and surface water
• Climatic influences such as precipitation, evapotranspiration, and growing season
Several major effluent loading constraints are discussed in the following paragraphs.
INFILTRATION
Infiltration is the movement of water into the soil surface. The rate of infiltration is
dependent on soil properties, crop cover, and slope, as shown in figure IV-1. The higher the
29
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!C-1) COARSE SANDS AND LOAMY
SANDS-UNIFORM TO 6 FEET
(L-1) FINE SANDS TO FINE SANDY
LOAMS-UNIFORM TO 6 FEET
!M-1( SILT LOAMS-UNIFORM TO
6 FEET
(H-1) SI LTY CLAY LOAM TO CLAY
LOAMS-UNIFORM TO 6 FEET
(VH-1) HEAVY CLAY LOAMS TO VERY
HEAVY CLAYS-UNIFORM TO
6 FEET
EC
o
ac
\u
a.
LU
X
O
<
DC
UJ
s.
I
U
DC
U
tt
D
O
X
5S
IU
I
u
UJ
s.
BL
U.
4567
SLOPE-FEET PER 100 FT.
Figure 1V-1. Average seasonal intake rates by
furrows for various soil types, crop cover, and slope conditions,5
30
-------
initial soil moisture content, the lower the infiltration capacity, and infiltration rates decrease
over time as the water application continues. A rest period from application allows the soil to
dry and restores the soil's infiltration capacity. Also, infiltration may just be vertical
(downward), as with most irrigation designs, or it may be both vertical and lateral, as with a
furrow irrigation design.
Selection of land application processes will be influenced by the soil's infiltration
capacity. The infiltration capacity of the soil will also help determine the application rate,
distribution design, and operating schedule. However, except for the infiltration-percolation
process, constraints other than infiltration would limit the total seasonal application.
Steep slopes, previous erosion, and lack of dense vegetation will reduce the infiltration
capacity and necessitate a reduced design application rate. The application rate for sprinkler
irrigation must not exceed the infiltration rate under the most restrictive conditions or runoff
will result. General ranges of sprinkler application rates for various soil types and slopes are
given in table IV-1.
The infiltration rates shown in figure IV-1 for furrows and in table VI-1 for sprinklers
are usually adequate for preliminary planning in the absence of field measurements. However,
in unusual circumstances or more detailed planning, it may be necessary to obtain specific
field data on infiltration. When detailed information is required, cylinder, furrow, or sprinkler
infiltration tests can be made. Because of inherent differences between these test methods, it
is necessary to use the test appropriate to the irrigation method to be used. Prior to final
design, detailed field investigations, possibly including some pilot studies, should be made.
PERMEABILITIES OF SOIL AND GEOLOGIC MATERIALS
When water has infiltrated the soil, movement through the root zone to the groundwater
depends on vertical permeability, and the movement of groundwater depends on lateral
permeability. The permeability in these two directions may be quite different for some soils.
The permeability of the soil in a vertical direction will determine the total excess water
(precipitation plus effluent less evapotranspiration) that can percolate through the soil to the
groundwater. The permeability of the soil and surface geology in a horizontal direction will
determine the extent of the groundwater mound (which is discussed later) beneath a land
•application system.
Aeration of the root zone is important to most agricultural crops and thus is required in
a well-operated irrigation or high-rate irrigation process. Most agricultural crops show adverse
effects from inadequate oxygen at air contents less than 10 percent of soil volume. Virtually
no oxygen diffusion occurs during and following the water application until the soil has
drained. Drainage requires a few hours for coarse textured soil to several days for fine
textured soil. Oxygen diffusion rates increase approximately linearly as the water saturation
percentage decreases.6 An oxygen diffusion rate of 0.2 mg/cm2 /minute is considered a lower
limit for most crop growth.7 An example of the change in oxygen diffusion rate with time
and depth for one soil condition is shown in figure 1V-2.
Soil permeability is the major factor determining the time required for the soil to
re-aerate after water is applied. Soil with slow permeability requires a much longer rest period
to allow aeration of the soil profile. The rest periods must be long enough to allow C02 to
31
-------
Table IV-1.—Typical ranges of infiltration rates and available soil moisture by soil f/pes'8>'
Very coarse textured sands
and fine sands
Coarse textured loamy
sands and loamy fine sands
Moderately coarse textured
sandy loams and fine sandy
loams
Medium textured very fine
sandy loams, loams, and
silt loams
Moderately fine textured
sandy clay loams and silty
clay loams
Fine textured sandy clays,
silty clays, and clays
Available soil moisture
storage3
Range
(in./ft)
0.50-1,00
0.75-1.25
1.25-1.75
1.50-2.30
1.75-2.50
1.60-2.50
Average
(in./ft)
0.75
1.00
1.50
2.00
2.20
2.30
Good condition base soil
basic infiltration rates'3
Slope
0-3 percent
linVhr)
1 +
0.7-1.5
0.5-1.0
0.3-0,7
0.2-0.4
0.1-0.2
3-9 percent
(in./hr)
0.7+
0.50-1.00
0.40-0.70
0.20-0.50
0.15-0.25
0.10-0.15
9+ percent
(in./hr)
0.5+
0.40-0". 70
0.30-0.50
0.15-0.30
0.10-0.15
<0.10
aStoraae between field capacity (1/10 to 1/3 ATMS and wilting point (15 ATM),
bFor good vegetath/e cover, these rates may increase by 25 to 50 percent. For poor surface soil conditions, these rates may
decrease by as much as 50 oercent.
32
-------
OXYGEN DIFFUSION RATIO lug cm"2 min"1)
.10
z
a.
* DAYS FOLLOWING
IRBJGATION
ADEQUATE FOR AGRICULTURAL CROPS
AGRICULTURAL CROPS
Figure IV-2, Oxygen diffusion rate (ODR) as a function
of soil depth on various days following irrigation in cotton fieid.10
escape and 02 to diffuse into the soil profile. The length of rest time necessary is also
dependent primarily on the soil profile, climate, crop growth, and biological activity.
For the irrigation and high-rate irrigation processes, at least 3 to 4 feet of aerated soil is
recommended to provide sufficient soil material to treat the applied effluent and allow crop
growth. The capillary fringe, the layer above the water table saturated by capillary actions,
also restricts aeration. Thus, the water table should be at least 5 feet below the soil surface.
The overland flow process, which utilizes a daily loading and soils of slow permeability,
will produce anaerobic soil conditions most of the time. The anaerobic soil will result in a
slower permeability and require selection of a plant tolerant to wet anaerobic soil conditions.
The infiltration-percolation process will develop an anaerobic condition a few days after
loading is started. This anaerobic condition will promote high rates of denitrification in the
soil. During the rest period, the soil will drain and aerobic conditions will be restored. If a
crop is grown, it should be tolerant to standing water and periodic anaerobic soil conditions.
A water table depth greater than 5 feet is often suggested for the infiltration-percolation
process.
Soil permeabilities are less for wastewater than for clear water. The average permeability
for Flushing Meadows has been about one-half that for clear water. Permeabilities for
wastewater under other conditions have been reported as low as 10 percent of the clear water
value. Effluent should be used for field measurements of permeability if at all possible. If
33
-------
effluent cannot be used, the design should be based on a reduction factor which would vary
with water quality and soil conditions. Once the permeability is known, the excess water and
effluent loading can be established.
Figure IV-3 shows maximum excess water loading rates for high-rate irrigation based on a
2-day load and removal of 30 percent of the available water holding capacity by
evapotranspiration between loadings for a 4-foot deep soil. Maximum excess water loading
rates for infiltration-percolation based on loading 50 percent of the time are also shown in
figure IV-3. As indicated in figure IV-3, these values are suggested maximums with uniform
deep soil conditions. The actual excess water should be reduced as temperature decreases and
soil profile conditions are less than ideal. Definition of the actual loading rate will be
discussed further in Chapter 5.
The natural drainage capacity of the underlying geologic material depends on the
permeability, the depth of wetted materials, and the hydraulic gradient.6.11 An analysis of
the groundwater drainage capacity and of the need for artificial drainage should be made for
evaluation of land application sites. Even though permeability may seem adequate, a site with
a low gradient and shallow wetted depth may still require artificial drainage. The extreme high
water table for a wet year would be expected to be maintained or exceeded if effluent is
applied.
Effluent loadings will increase excess water percolation to the groundwater and a
groundwater mound will develop, as figure IV-4 shows. Accurate prediction of groundwater
levels will usually require detailed information of permeabilities and depths of various strata.
To obtain details of the various strata as shown in figure IV-3, field investigations and input
from a hydrogeologist may be required. Selection of a wet year hydrology for design will
eliminate the possibility of requiring a reduction in effluent loading under this condition.
The buildup of the groundwater mound in relation to the soil surface should be known.
Figure IV-5 shows the rate of mound formation for the figure IV-4 site on dune sand. The
lag in years is the travel time as water moves from the surface to the groundwater.
For complex conditions, a groundwater model may be required for accurate prediction of
groundwater conditions. With maximum loading, drainage of the groundwater is critical if the
water is naturally shallow or if a groundwater mound will reach the surface. With artificial
drainage, the drains must be spaced and sized to remove the volume of water percolated so
the 5-foot aerated zone will not become waterlogged.
As indicated earlier, excess water is determined by subtracting evapotranspiration from
precipitation and adding wastewater loading. The precipitation and evapotranspiration (ET)
rates for the sample study area (figure III-2) are shown in figure IV-6. By subtracting
evapotranspiration from precipitation, a curve showing changes in soil moisture is obtained, as
shown in figure IV-7. Negative values are depletions in soil water storage. These depletions are
analogous to squeezing water out of a sponge, while positive values are like refilling the
sponge to the limit of its water-holding capacity. As excess water is available, it drains out of
the soil profile much as excess water would drain out of a sponge. Each month effluent is
applied, there is excess water available, as shown in figure IV-7. The objective is to have
approximately the same amount of excess water each month (8.5 inches/month for figure
IV-7).
Frequency of recurrence for evapotranspiration, design wastewater flows, and precipitation
should be considered when developing a design loading. Pilot work or field measurements may
be used to verify the assumptions about permeability and loadings. A detailed field
34
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LOADING LIMIT ASSUMPTIONS
GENERAL
MAXIMUM HATES FOB SUMMER MONTHS
SHOULD BE MADE AS TEMPERATURE OE
UNIFOBM SOL PROFILE WITHOUT BOCK
DEPTH - PROPORTIONATE SEDUCTIONS
MADE FOB PERCENTAGE HOCK AND HEI
PROFILE DEPTH.
PERMEABILITY OF THE MOST RESTRICT!
THE 5-FOOT PROFILE SHOULD BE USED.
CURVES ARE BASED ON PERMEABILITY
VALUES MEASURED WITH CLEAR WATER
INFILTRATION-PERCQLATION
REST PERIODS AHE SAME LENGTH AS A
(BIST PERIODS SHOULD BE INCREASED
TURES DECREASE TO ALLOW ADEQUATE
CURVE VALUES OF MAXIMUM LOADING
25% OF CLEAR WATER PERMEAilLITY.
HIGH RATE IRRIGATION
ACPLICAT ON FOR- Z DAYS.
REST PERIOD IS T ME REQUIRED TO RE
OF AVAILABLE WATER HOLDING CAPAC
4-FOOT PROFILE.
TIMING BETWEEN APPLICATIONS S 2 OA
REST PERIOD.
EXCESS WATER IS HATER DBA NINQ BE
ZONE (EQUALS 24 HH X CLEAR WATER
DIVIDED iY TIMING).
TOTAL LOADING EQUALS EXCESS MATE
(NET ET IS EVAPOTRANSP1RATION LESS
3
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SHOWN FOR CQMPARiSOW ONLY
MANUAL OF SEPTIC TANK PRACTICE, U.S. PUBLIC
HEALTH SERVICE, 1367
MONTANA STATE DEPARTMENT OF HEALTH, SEPTIC
TANK BULLETIN 332, APRIL 1963
..
NOTE: LEACH FIELD LOADING BASED ON PERCOLATION
TESTS. PERMEABILITY WOULD BE LESS THAN
PERCOLATION BY A FACTOR OF 3 TO 5.
i
90 2 3 456769
WATER HOLD1 KS CaPACIT?
0.0 3 4 5 S T 8 9
GENERALLY POOR WATER
HOLDIMB CAPACITY
ViHY RAP D
PERMEABILITY MEASURED WITH CLEAR WATER UN/HR)
Figure 1V-3. Suggested maximum loading rate versus
measured permeability for high-rate irrigation and infiltration-percolation.
35
-------
SHALLOW WELL PRODUCTION
FROM PERCHED WATER
TABLE
EAST
SURFACE EFFLUENT DISPOSAL
DEEP WELL PRODUCING
FROM 180 FOOT AND
400 FOOT AQUIFER
DOWN GRAVEL PACK
-100
SALINAS
RIVER CHANNEL
DEPOSITS
LEGEND
DUNE SAND
CLAY
SAND AND GRAVEL
MOUNDED PERCOLATE
PREDISPOSAL WATER TABLE
DIRECTION OF GROUNDS/VATER
MOVEMENT
UNSATURATED FLOW DIRECTION
OF EFFLUENT PERCOLATING BE-
LOW THE ROOT ZONE
Figure lV-4. Typical groundwater mound.12
36
-------
200
180
r- 160
-L
JJ
140
120
UJ
a.
Q
Z
3
O
O
Z
= 100
<
>
JJ
60
40
LEGEND
PREDICTED BY MODEL
_ PROJECTED ABOVE GROUND
SURFACE
L - TOTAL WASTEWATER APPLICATION
EW - EXCESS WATER
GROUND SURFACE ELEVATION
INITIAL GROUND WATER ELEV.
10 15
TIME SINCE LAND APPLICATION BEGAN (YEARS!
Figure IV-5. Relationship between height of groundwater
mound and time under various loading rates at application site on figure IV-4,12
37
-------
STUDY AREA
PRECIPITATION
0,0
APR, I MAY JUN. JUL. AUG.
MONTH
Figure IV-6. Precipitation and potential
evapotranspiration (ET) for sample study area on figure 1V-2.1
38
-------
X
O
i
LU
I
O
UJ
K
3
W
LU
O
N
s
O
E
O
H
O
H
D
m
e
H
Z
O
u
11.0
10,0
9,0
7.0
e.o
5.0
4,0
3,0
2.6
1.0
0.0
-1,0
-2,0
-3.0
-4.0
-5.0
-6.0
/ SEASONAL EFFLUENT //
AVERAGE MONTHLY DEPTH TRANSMITTED THROUGH
ROOT ZONE FOR SITE F ON FIGURE lil-2
77m. f////t ///// 7/77?,'///// '//// 77/7t
CHANGES IN SOIL MOISTURE
(MEAN PRECIPITATION LESS
EVAPOTRANSPI RATION)
a.
JAN. FEB. MAR. APR. MAY
JUN. JUL. AUG.
MONTH
SEP. OCT. NOV. DEC.
Figure IV-7, Changes in soil moisture and effluent application.1
39
-------
investigation, and possibly even a pilot study, may be required to determine the sustained
loading constraint over a long time period.
NITROGEN REMOVAL
Recent technical papers indicate many complex processes are involved in the removal of
the various nitrogen forms in a soil-plant system.13 >14''5 For a short period of time, ammonia
and organic forms of nitrogen are retained in the soil by adsorption and ion exchange until
mineralized, to the nitrate form. All nitrogen, regardless of form when applied, is eventually
mineralized to the nitrate form unless lost by volatilization.15 Nitrogen in the nitrate form is
very mobile and subject to movement with the water. Thus, nitrogen loading and leaching
below the root zone must be considered in the design to prevent excess nitrogen movement
to the groundwater.
Nitrogen removal from applied wastewater occurs through crop uptake, growth of
microbial cells, volatilization of ammonia, conversion to nonbiodegradable organic matter, and
denitrifieation. A conceptual drawing of the nitrogen removal processes is shown in figure
IV-8. The first few years after a land application system is initiated, the microbial population
may increase dramatically and result in increased nitrogen storage in the soil profile,
Nonbiodegradable organic matter containing nitrogen accumulates in a similar manner until a
new steady state condition is reached. The decay rate of the accumulated organic nitrogen
equals its production when a steady state condition is reached.
SECONDARY
SEWAGE
EFFLUENT
CHEMO-
DEN1TR1FICAT1ON
GROUNDWATER
Figure IV-8. Schematic drawing of nitrogen transformations.12
40
-------
The length of time needed to reach the steady state condition and the change of
nitrogen storage in the profile is not well understood. Data from the Melbourne and
Metropolitan Board of Works sewage farm at Werribee indicate that the storage process may
still be continuing at a relatively constant rate after several decades on pastures.16'17
However, a more typical situation for cultivated agricultural soils is an increase to a new
steady state level in 5 to 10 years. Thus, the accumulation of nitrogen in the soil profile may
not be important for a typical land application project life (20 years or more). Once a steady
state condition is reached, there will be no further nitrogen removal by the soil through
growth of aerobic microbes and conversion to nonbiodegradable organic matter.
Volatilization of ammonia is only important in soils of high pH (alkaline) and where
ammonia does not come in contact with the soil or exceeds the adsorption capacity of the
profile. Many soils have a high capacity for ammonia adsorption, so what volatilization does
occur takes place before adsorption. Under most conditions, volatilization of ammonia will not
be a major removal mechanism.
Crop uptake and denitrification are considered the only two reliable long-term
mechanisms (steady state conditions) for removal of nitrogen.15'18 As with normal
agricultural activities, crop removal of nitrogen is dominant in irrigation and high-rate
irrigation processes with denitrification being much less important. Denitrification is dominant
and crop uptake negligible in the infiltration-percolation process under proper wet-dry cycles.
Both crop uptake and denitrification appear to be significant nitrogen removal mechanisms for
the overland flow process method.
Nitrogen removal by crops is dependent on the length of growing season and crop type
as well as nitrogen availability. Crop requirements for nitrogen during the growing season
approximately parallel the evapotranspiration demand. Thus, applications paralleling the
seasonal changes in evapotranspiration as shown in figure IV-6 may be more beneficial to the
crop than a constant application.
Crops normally used with land application can be divided into three broad groups and
removal rates. A forage crop will remove 150 to 600 Ib/acre or more, field crops will remove
75 to 150 Ib/acre, and forests will remove 20 to 100 Ib/acre, as shown in table IV-2. Wide
variation occurs within each group, and some crops do not fit this generalization.
Some crops show luxurious uptake of nutrients with total removal being as much as
twice the noted values. Nitrogen removal is generally dependent on the amount applied.
However, removal efficiency (nitrogen removed by crop divided by nitrogen applied times
100) decreases as the loading increases. A removal efficiency of 84 and 68 percent,
respectively, was reported for reed canary grass with 421 and 524 Ib/acre of total nitrogen
applied.18 Figures IV-9 and IV-10 show nitrogen removal and removal efficiency for corn
grain and com silage. Removal efficiency may be greater than 100 percent when loadings are
low becauses of the release of nitrogen stored in the soil.
Data from Kardos et al.19 also indicate that as nitrogen removal efficiency decreases,
nitrate-nitrogen concentrations in the percolate may increase significantly, as shown in figure
IV-11 for a corn crop. However, the increase in concentration will depend on the crop grown.
For example, the nitrate-nitrogen concentration in percolate at a 4-foot depth beneath reed
canary grass19 averaged 3.1 mg/1 for 4 years and showed no trend of increasing as the total
nitrogen applied increased. Crops vary widely in efficiency for nitrogen removal and total
amount removed depending on both the crop species and nitrogen loading. Where strict limits
are placed on the nitrogen concentration of percolate from land application, a crop with high
removal efficiency together with controlled loadings may be required.
41
-------
Table \\t-2.-Reported nutrient removal by
forage crops, field crops, and forest crops
Forage crops
Costal bermuda grass
Reed canary grass
Fescue
Alfalfa
Sweet clover
Red clover
Lespedeza hay
Field crops
Corn
Soy beans
Irish potatoes
Cotton
Milo maize
Wheat
Sweet potatoes
Sugar beets
Barley
Oats
Forest crops
Young deciduous (up to 5 years)
Young evergreen (up to 5 years)
Medium and mature deciduous
Medium and mature evergreen
Nitrogen uptake
(Ib/ac/yr)
480-600
226-359
275
155-2203
158a
77-1263
130
155
94-1t3a
108
66-100
81
50-76
75
73
63
53
100b
6Qb
3Q-5Qb
20-30b
aL*gurnes remove substantial nitrogen requirements from the air.
'•'Estimated,
Source: EPA (1975) Table 6; Driver et al. (1972); and Nations! Plant Food Institute.
Data from the University of California20 showed decreases in the efficiency of removing
applied fertilizer similar to those shown in figures IV-9 and IV-1Q. The data were obtained
from the application of fertilizer and irrigation water. The nitrate-nitrogen concentrations in
the unsaturated soil water below the root zone of agricultural sites were 6 to 491 (average
56) and 9 to 1,151 (average 86) mg/1 for coastal and inland counties, respectively.
Nitrate-nitrogen concentrations in groundwater beneath agricultural sites were substantially
lower, 1 to 244 (average 32) and 4 to 40 (average 16) mg/1 for the coastal and inland
counties, respectively. These data from agricultural sites indicate that it is difficult to control
nitrogen movement below agricultural crops.
42
-------
150
300
TOTAL NITROGEN REMOVED
NITROGEN REMOVAL EFFICIENCY
50 100 150
TOTAL NITROGEN APPLIED IN WASTEWATER EFFLUENT (Ibs/ac)
200
Figure IV-9. Total nitrogen removed and removal efficiency for grain corn.
19
ISO
•3
a
a.
a
o 100
2
Q
LU
o
\u
cc
z
Lu
(9
O
CC 50
I
TOTAL NITROGEN REMOVED
ONE CROP REMOVED IN 2
SEASONS OF OPERATION -
O AVERAGE OVER 2 YEARS
>
Spv
NITROGEN REMOVAL EFFICIENCY
50 100 150
TOTAL NITROGEN APPLIED IN WASTEWATER EFFLUENT (Ibs/ac)
200
Figure IV-10, Total nitrogen removed and removal efficiency for corn silage,15
300
200 O
LU
y
LL
O
LU
IX
100 Z
ID
43
-------
15
a.
Ul
a
S.
Ul
II
-i 5
5 ^
™ 1
1 o
10
i-
z
tu
U
z
o
U
z
Ul
<
a.
\-
z
Q
3
O
AVERAGE OF
5 YEARS OF DATA
100
TOTAL NITROGEN APPLIED (LBS/AC!
200
Figure IV-11. Nitrate-nitrogen concentration of percolate
beneath a corn crop versus total nitrogen applied in wastewater.19
44
-------
The University of California20 has reported progress in using computer modeling to
predict nitrogen concentrations and transport in cropped, irrigated lands. The main objective is
to predict nitrogen leaching losses from the root zone as a function of fertilizer application
rates and irrigation management. As a subproject, the application of sewage effluent on land
was modeled, and a paper covering the model was presented at the First Annual NSF Trace
Contaminants Conference at Oak Ridge National Laboratory in August 1973.
Denitrification, the conversion of nitrate-nitrogen to nitrogen gas by bacteria with a
carbon source and in the absence of oxygen, occurs naturally in all soil systems. The
denitrification rate is highest for stratified soils with 'saturated or near saturated conditions.
The lowest denitrification rates occur in uniform soils with moderate to rapid permeabilities.
Because the root zone must be aerated for most agricultural crops, significant anaerobic areas
will not persist and high rates of denitrification are not likely to occur within the active root
zone. Anaerobic conditions can develop toward the bottom of the root zone, and nitrates
moving below an active root zone would then be subject to denitrification. However, carbon
decreases with depth, and essentially no denitrification occurs below a 10-foot depth for most
soils.13
Denitrification has been shown to vary from 10 percent to more than 80 percent of the
nitrate-nitrogen moving below the root zone. Actual rates will be dependent on oxygen
diffusion rates and supply of a carbon source. Denitrification will be difficult to design for
and control under field conditions for irrigation and high-rate irrigation. An elaborate system
to create anaerobic conditions and to supply a carbon source for the denitrifying bacteria is
required to accomplish predictable high rates of denitrification in soil systems. Also, anaerobic
soil conditions tend to lower the soil pH and increase solubility of some pollutants which
may then leach to the groundwater.
High levels of nitrogen can interfere with productivity in some crops. Sugar beets, for
example, will not obtain high sugar levels if excess nitrogen is available late in the season.
Grape flavor, as well as the sugar content and pH, factors controlling wine quality, is
dependent in part on nitrogen availability.
There is little hazard of nitrogen toxicity of crops where typical municipal effluent is
applied to land. When loadings are low, the total quantities applied are usually comparable to
normal fertilizer applications. When loadings are high, the nitrogen is leached through the soil
profile and thus should be little problem to the plant.
A potential toxicity problem occurs when applications continue through the winter when
nitrogen is not nitrified. The organic nitrogen and ammonia-nitrogen are stored in the soil
during winter. When the weather warms, nitrification occurs over a short time and
concentrations may reach high levels. With excess nitrogen available, some crops, particularly
forages, can accumulate high levels of nitrate which may be toxic to livestock and people.
The potential nitrate toxicity , from crops would normally occur only during early spring,
probably before the first harvest. The potential hazard should not persist because leaching
through the soil should reduce soil nitrate levels. However, pollution of the groundwater may
then be a problem. Monitoring of vegetation can detect potential toxicity problems before
they cause damage.
45
-------
NITROGEN BALANCE
Under long-term operation (steady state conditions), the removal of nitrogen by the crop
and denitrification will control the nitrogen concentration in the percolate. Initially, higher
rates of removal may be obtained with an associated accumulation of organic nitrogen
(humus) in the soil, as discussed earlier. After a few years, the rate of accumulation will
decline and will reach a steady state condition with little or no additional accumulation.
Typical steady state nitrogen balance estimates for two effluent application rates and two
crop groups are shown in table IV-3 to illustrate a sample nitrogen budget. With steady state
conditions, the wastewater nitrogen additions of 1,300, 300, and 135 Ib/acre produce 10, 5,
and 5 mg/1 nitrogen concentrations in the percolate water as indicated. The balances in table
IV-3 are based on an assumed removal by crops and denitrification. Increasing the loadings
above those shown will probably increase the nitrogen concentration and the pounds of
nitrogen in the percolate unless the crop is changed. Requirements for a lower nitrogen
concentration in the percolate will necessitate reductions in the loading rate. Thus, nitrogen
limitations for discharge may control the loading rate.
Except for legume plants, nitrogen additions to the root zone from rainfall and fixation
(atmospheric nitrogen made available by bacteria living in the soil) are approximately equal to
the incidental losses from volatilization of ammonia and other removal mechanisms. Bacteria
living on the roots of legume plants fix (convert to an available form) large quantities of
nitrogen from the atmosphere. Indications are that with effluent application, where high
nitrogen loads are available, this fixation process is greatly reduced.
A soil scientist or agronomist can be helpful in determining estimated losses from
volatilization and denitrification. Such estimates may be used during preliminary planning.
Verification of the assumed losses will be necessary prior to final design if nitrogen removal is
a critical parameter (i.e., controls loading rate). Verification can be made by pilot studies with
measurement of losses. Unfortunately pilot projects typically take several years to become
steady state for nitrogen removal. It is especially important to determine nitrogen stored in
the soil during the pilot study and to subtract the storage from the budget to obtain a valid
steady state condition.
PHOSPHORUS
Phosphorus is removed by crops, precipitation, and adsorption by soil colloids. The
removal of phosphorus is, therefore, dependent on the soil texture, cation exchange capacity,
soil pH, presence of calcium, amount of iron and aluminum oxides present, and uptake of
phosphorus by the crop. Because of these removal mechanisms, there is a large capacity for
phosphorus removal, and little movement of phosphorus through the soil profile with the
drainage water can be expected. Phosphorus removal capacity is finite, and over a long time
period or with high loadings, the phosphorus additions may exceed the soil's capacity for
removal.
Phosphorus removal by adsorption can be estimated by the Langmuir adsorption
isotherm11 as follows:
_M_ _ J_ M
x/m kb b
46
-------
Table IV-3,— Approximate nitrogen balance for two land application processes
under steady state conditions (Ib/ac except as noted}1
Forage crop
Application
Effluent (ac ft/ac)
Nitrogen in effluent
Nitrogen added in precipitation and fixation less losses to
ammonia volatilization, etc.
Removed by crop
Leached below root zone
Lost to denitrification (35 and 25 percent)
Returned to groundwater
Treated effluent (ac ft/ac)
Nitrogen in treated effluent
Concentration in return flows (mg/l)
Cultivated field crop
Application
Effluent (ac ft/ac)
Nitrogen in effluent
Nitrogen added in precipitation and fixation less losses to
ammonia volatilization, etc.
Removed by crop
Leached below root zone
Lost to denitrification (25 percent)
Returned to groundwater
Treated effluent (ac ft/ac)
Nitrogen in treated effluent
Concentration in return flows (mg/l)
Infiltration-
percolation
24
1,300
0
300
1,000
350
24
650
10
High-rate
irrigation
6.9
300
0
200
100
25
5.6
75
5
3.1
135
0
100
35
9
1,8
26
5
47
-------
where M = the activity of the ion in moles per liter, x/m = meq of ion M adsorbed per 100
grams of adsorber, k = constant related to bonding energy, and b = the maximum amount of
ion M in meq/100 g that will be adsorbed by a given adsorber. The adsorption capacity has
been estimated for several soils with a range of 77 to over 900 Ib/acre-foot of soil profile.2'
At common loading rates of wastewater effluents, a soil with a storage capacity of only 77
Ib/acre-foot would be saturated in a few years.
Ellis indicates that the adsorption- capacity of the soil can be restored in a few months.
Apparently this saturation and restoration cycle can occur many times. Restoration occurs
when adsorbed phosphorus is precipitated or removed by crops. At a pH below 6, phosphate
is thought to precipitate with iron and aluminum.15 Thus, iron and aluminum contents of soil
will determine long-term storage of phosphorus for acid soils. For neutral or basic soils, the
primary precipitate is with calcium. Apparently precipitation occurs rapidly above a pH of 6.5
and where the ratio of calcium to phosphate concentration is at least 50:1 for the soil water
solution.
For many soils, the total removal capacity is large and would greatly exceed the planning
life of the land application project. For coarse textured soils with little calcium, iron, or
aluminum, the removal capacity may be limited. If phosphorus removal is critical for these
conditions, a soil chemist should be consulted regarding the storage capacity for phosphorus.
Phosphorus concentrations of the soil water at the 4-foot depth beneath crops generally
average less than 0.1 mg/1 with an upper limit of about 1.5 rng/1.19 A more detailed
discussion of phosphorus adsorption isotherms and methods for estimating the concentration
in percolate is given by Taylor and Kunishi.22
. . Phosphorus accumulating in soil over a long period of time may potentially interfere with
crop growth. This interference generally would occur as a nutrient imbalance in the plant,
that is, high phosphorus levels in the soil may reduce the availability of some crop
micronutrients. Thus, the plant may develop low levels of other required nutrients rather than
toxic levels of phosphorus. Precipitation of the phosphorus would be expected to minimize
any toxieiry problem; otherwise, corrective measures may be taken.
SUSPENDED SOLIDS
Suspended solids in typical secondary treated effluents are low enough that there
normally is no problem encountered with any of the land application processes. Food
processing wastes, having much higher concentrations, have been applied on land without
serious problems.
In all but coarse sands and gravel, the suspended solids are filtered out at or very close
to the soil surface. With high concentrations of some solids, the soil surface may be coated to
the extent that infiltration rates are reduced. If mineral solids are applied, periodic tilling of
the soil may be necessary. With coarse textured soils and high solid loading, it may be
necessary to apply a surface layer of a finer material or reduce solids loads in order to
prevent clogging pore spaces deeper in the soil. Solids more typically are organic, and a rest
period which allows the organic material to dry and oxidize may be sufficient to restore
infiltration rates.
High inorganic suspended solids loading rates could result in a long-term accumulation of
solids that would interfere with the application system's operation. Inorganic solids are not
48
-------
subject to the decay process which removes organic solids. If high inorganic suspended solids
are present, pilot studies of infiltration using the effluent may be desirable during planning
and design to evaluate the impacts.
BOD AND COD OXIDATION
BOD is often associated with the suspended solids, while COD is more often associated
with dissolved organic solids. Because the suspended material is filtered out near the surface,
the BOD load will normally not extend more than a few inches into the soil. At these
shallow depths, oxygen diffusion rates are high, and there should be ample opportunity for
reduction of BOD before percolation reaches the groundwater.
The soluble COD-causing material will be carried into the soil with the water. Organic
cations and basic compounds are removed by cation exchange. Polar molecules and some large
molecules are adsorbed. Organic anions are precipitated with iron and calcium. Large organic
cations are held tightly, while polar molecules are not. Some organics form films on soil
materials. Low soil moisture is a strong contributing factor to removal of many organic
compounds. Thus, COD removal is enhanced by low loadings and long rest periods. If the
COD-causing material is adsorbed, oxidation will be necessary to restore the soil's adsorption
capacity. All organics are subject to decomposition in soil, but a long time may be
required.15
Because of these factors, the removal capacity for COD-causing materials is expected to
be limited for high loading rates. Low COD levels found in domestic wastewater should pose
no problems in the soil. Removal and oxidation are dependent on many factors and are hard
to estimate. High levels of stable COD materials that have a long decay half-life may require
reduced loadings to permit oxidation if the COD must be removed.
The total oxygen demand of domestic wastewater applied to land is usually low in
comparison to the oxygen requirement for an actively growing crop as shown in table IV-4.
The additional oxygen requirement imposed by the wastewater application is not likely of
itself to significantly affect the soil or crop. Oxygen demand loadings by wastewater of 50 to
100 Ib/acre/day have been used successfully. The upper limit is dependent on the soil, system
management, and temperature.
INORGANIC CHEMICALS
Table IV-5 shows recommended concentration limits for specific elements for irrigation
water based on an application of 3 ft/year, a typical application rate of the irrigation process.
Estimated limits are also shown for loadings of 8 and 80 ft/year as might be used with
high-rate irrigation or infiltration-percolation. If these criteria are met, there should be little
concern about toxic effects on plants or excessive accumulation in soils. Many of the
elements are micronutrients or trace elements required by plants in small quantities.
Many of the specific elements shown in table IV-5 are also heavy metals and have
received a great deal of attention because of their impact on the environment. Most of the
heavy metals are effectively removed as water percolates through the soil. The mechanisms for
49
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Table \V-4.-Typicaf oxygen demands and loading rates for soil10
Fallow soil with no fresh- organ ics
Fallow soil following addition of organic residues
Soil with growing plants
Typical limits of BOD loading on land for
municipal wastewater8
Oxygen consumption
Ib/ac/hr
1-2
2-4
3-6
average
Ib/ac/day
36
72
108
100+
Reduction for low temperature may be necessary.
removal are adsorption on the exchange complex or with iron, aluminum, and other elements,
and precipitation in very insoluble forms. In general, the trace elements are most insoluble at
soil pH near 7.0,1S Thus, controlling the pH near neutral. 7.0, by addition of soil
amendments such as lime, is one method of maximizing the soil capacity for removing and
storing heavy metals.
Some precipitants such as iron and manganese become more soluble under anaerobic
conditions and are then subject to leaching and potential pollution of the groundwater.
Maintaining an aerobic soil may be important to effective removal of some heavy metals. In
soluble forms, the heavy metals are available to plants and subject to movement to the
groundwater. Management to maintain low solubility is a key to heavy metal removal. If good
management is practiced, water transmitted through the soil profile in the irrigation or
high-rate irrigation processes should be suitable for most uses. However, under some conditions
and for some uses, total salt concentrations may be higher than desirable because of salt
concentration by evapotranspiration.
For the overland flow process, water does not move through the soil, so there is little
chance for heavy metal removal in the soil matrix. For the irrigation and high-rate irrigation
processes, the soil will be very similar and heavy metal removal will be similar. Because of the
higher loadings for infiltration-percolation, the soil capacity for heavy metal removal will be
reached sooner. The limitation for heavy metals concentration should be a function of site life
and loading rate. The higher the loading rate and the longer the site life desired, the lower
the concentration limitation should be as shown in table IV-5. Estimated concentration
limitations for infiltration-percolation (80 feet per year application) are lower than for
high-rate irrigation (8 feet per year application). Removal of heavy metals by the soil profile
probably will decrease as the loading rate increases.
Trace elements, salt, or other pollutants toxic to plants may show toxic effects sooner
when high concentrations directly contact the vegetation than when the same concentrations are
applied to the soil. Plants may absorb some pollutants directly through contacted exposed parts.
Sprinkler and flood irrigation produce direct water contact on the plant. If high concentrations
of pollutants are of concern, furrow irrigation might be used to prevent foliage contact.
50
-------
Table \\J-b.-Recommended and estimated maximum concentrations
of specific ions in irrigation waters3 (mg/l)
Element
Aluminum
Arsenic
Beryllium
Boron
Cadmium
Chromium
Cobalt
Copper
Fluoride
Iron
Lead
Lithium
Manganese
Mercury
Molybdenum
Nickel
Selenium
Silver
Zinc
Removal
mechanism'3
PR, S
AD, S
PR
AD, W
AD, CE, S
AD, CE, S
AD, CE, S
AD, CE, S
AD, S
PR, CE, S
AD, CE, S
CE, W
PR, CE, S
AD, CE, S
AD, S
AD, CE, S
AE, W
AD, CE, S
AD, CE, S
For waters used
continuously on all soil
3 ft/yr application
recommended limitc
5.0
0.10
0.10
0.75
0.010
0.10
0.050
0.20
1.0
5.0
5.0
2.5d
0.20
—
0.010
0.20
0.020
—
2.0
For waters used up to 20 years on
fine textured soils of pH 6.0 to 8.5
3 ft/yr application
recommended limitc
20.0
2.0
0.50
2.0-10.0
0.050
1.0
5.0
5.0
15.0
20.0
10.0
2.5d
10.0
—
0.0506
2.0
0.020
—
10.0
8 ft/yr application
estimated limit
8.0
8.0
0.2
2.0
0.02
0.4
2.0
2.0
6.0
8.0
4.0
2.5
4.0
—
0.026
0.8
0.02
—
4.0
80 ft/yr application
estimated limit
0.8
0.08
0.02
2.0
0.002
0.04
0.2
0.2
0.6
0.8
0.4
2.5
0.4
—
0.0026
0.08
0.02
—
0.4
aThese levels will normally not adversely affect plants or soils. No data are available for mercury, silver, tin, titanium, or tungsten.
bAD = adsorption with iron or aluminum hydroxide, pH dependent; AE = anion exchange; CE = cation exchange; PR = precipitate, pH dependent—iron
and manganese are also subject to changes by oxidation reduction reaction; S = strong strength of removal; W = weak strength of removal.
CEPA Water Quality Criteria, 1972.
dRecommended maximum concentration for irrigating citrus is 0.075 mg/l.
eFor only acid fine textured soils or acid soils with relatively high iron oxide contents.
-------
SALTS
Salts are found in all natural waters from the weathering of soil and rocks into the basic
elements. Because irrigation water lost to evaporation and transpiration leaves salts behind,
water consumption increased above present levels by evapotranspiration will increase TDS
concentrations in the soil. The concentrating effect of evapotranspiration is directly
proportional to the water lost to evaporation and evapotranspiration. The concentrating effect
occurs with all irrigation systems, and additional water is applied as needed to leach the salts.
Conversely, the increase in weathering is less known and may be more important to land
application in water short areas.
Recent research, primarily at the Soil Salinity Laboratory at Riverside, California2 3 =2 4 -2 s
shows that the weathering rates of soil into salt are dependent on temperature, water quality,
and the quantity of water percolating through the soil. As more water of the same quality is
applied, higher weathering rates result. With little percolate water, less salt may be leached out
of the profile than applied, indicating salt precipitation in the profile. With large volumes of
percolate water, more salt may be leached out of the profile than applied, indicating
desolation of salts or weathering of the soil profile. A model has been developed and verified
which describes the above processes.
Apparently the acidifying reaction producing two hydrogen ions as each ammonium ion
is oxidized to nitrate as described by Broadbent3 3 is an important factor in the increased
leaching. The relative magnitude of the nitrification and denitrification processes will be a key
factor in the acidification reaction.
The effect of leaching by land application loading of 2.3, 6.0, and 29-0 feet per year for
the example study area is indicated in table IV-6. Table IV-6 shows that salt concentrations
would increase substantially for all three alternative loadings. More important than the
concentrations are the salt loading and the impact on the receiving stream.
A loading rate of 2.3 feet, which is consistent with normal irrigation practice, has little
impact on the total salt load of the stream. A loading rate of 6.0 feet, which might be used
for high-rate irrigation, has a rather significant impact with an increase of 19,8 percent on the
total salt load for the small stream system. This salt load is a result of desolution of calcium
carbonate from the highly calcareous soil profile. This desolution can continue indefinitely. A
loading of 29,0 feet as might be used for infiltration-percolation has the greatest impact on
the receiving stream with a 30.2 percent increase in the total salt load. Salt loads for this
alternative are from desolution of calcium carbonate and weathering of soil and gravel material
into basic elements. For the highest loading rate, the reported values represent a maximum;
actual values may be lower. Additional basic research must be conducted to determine the
validity of the salt loadings problem illustrated above.
In the water short west where consumptive use of water through irrigation produces high
salt concentrations, the impacts of an increased salt load as a result of increased leaching may
be significant. The impact on stream quality in the areas of excess water and little irrigation
will be minimal.
The effects of salts on soils and plants are dependent on chemical characteristics of the
wastewater and the physical and chemical properties of the soil. The higher levels of salts.
-------
Table IV-6,-Ss/f concentrations and salt loadings
for three land application rates3'1
IDS concentration (nng/i!
In applied water
Expected in percolate
Total salts
Applied (T/acre)
Drained (T/acre)
Salt load (T/acre)
Total salts added (T/year)
Percent change in total salts in stream*3
Loading
2.3 ft
370
2,000
1.13
1.20
0.07
1,000
2.3
6.0 ft
370
860
3.01
4,91
1.90
8,500
19.8
29.0 ft
370
770
15.08
28.45
13.36
13,000
30.2
aModeling contributed by USDA Soil Salinity Laboratory Staff, Riverside, California,
'-Total average salt load at the stream mouth = 43,000 T/year,
total dissolved ionic solids (TD1S), in wastewater lead to some potential problems. Generally,
the sodium adsorption ratio (SAR) given below and the TDIS are used to evaluate the quality
of irrigation water:
NA+
SAR =
Mg++)
Figure IV-12 shows the relationship between SAR and TDIS and the resultant hazard. The
main effect of excess sodium is a dispersion of the clay content of soil and consequent
reduction in permeability. Ellis21 discussed one case of 25-percent reduction of infiltration
rates resulting from 14 years of irrigation of agricultural crops by wastewater. Irrigation rates
recommended for the crops were used. Even though the SAR was low, the effect was
apparent. If loading rates higher than those required for irrigation had been used, the
reduction in infiltration rates might have occurred much more quickly.
CLIMATE
Climate is a constraint on the timing of effluent application on land. For the irrigation
and high-rate irrigation processes, effluent would not be applied during periods when the
ground is frozen because runoff directly to the surface waters could occur. Also, maximum
effluent loading will be limited to the active growing season. Plant and soil microorganism
activity is greater during this time, so treatment of the effluent will be most effective then.
Effluent applied during dormant crop and soil periods may not receive the desired levels of
53
-------
SODIUM HAZARD: SODIOM-ADSORPTION-RATIO (SARI
z
.4
<
LOW
SUITABLE FOR ALMOST
ALL SOILS
MEDIUM
APPRECIABLE
POTENTIAL
PROBLEM FOR FINE
TEXTURED SOILS*
HIGH
POTiVTIAL
PROBLEM
IN ALMOST
ALL SOILS*
VERY HIGH
GENERALLY
UNSATISFACTORY
FOR IRRIGATION
SUITABLE FOR MOST
CROPS AND SOILS
MEDIUM
REQUIRES
MODERATELY
TOLERANT CROPS
AND LEACHING
HIGH
REQUIRES ADEQUATE
DRAINAGE, TOLERANT
CROPS AND SPECIAL
MANAGEMENT
VERY HIGH
UNSUITABLE FOR
IRRIGATION UNDER
MOST CONDITIONS
250
750
100
4
5000
•MAY REQUIRE CHEMICAL AMENDMENTS SUCH AS (3YPSUM,
Figure IV-12. Sodium and salinity hazard.2'
treatment. Growing season and frozen soil conditions should be considered carefully where
high removal of pollutants is desired and where high reliability of treatment is a necessity.
For the infiltration-percolation process, the soil is much coarser to allow higher loadings.
Because of the coarse soil required, applications of warm effluent may keep the soil from
freezing under all but the most severe winter conditions. Surface irrigation is used successfully
through the winter in Idaho and Minnesota where winter temperatures are extreme.
Apparently the infiltration-percolation process can extend the application time appreciably;
however, operating experience from Flushing Meadows indicates loadings probably should be
reduced to about one-half of summer loadings to allow for slower drying and reduced rates of
biological activity.
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Chapter V
EFFLUENT LOADING DESIGN
FIELD INVESTIGATIONS
During the site selection process, some minimal field investigations by experienced soil
scientists and hydrogeologists should be done to establish the accuracy of the available data,
to evaluate differences between the sites, and to influence the site selection. Once the most
suitable site(s) has been identified for each process, then the general loading established for
site selection can be refined based on specific data for the selected site. If detailed
information on soils and hydrogeology is available, trained scientists can evaluate and interpret
the data to help establish a suitable loading based on the previously discussed constraints. If
detailed data are not available, a reconnaissance investigation in the field should be made to
collect the necessary data.
This chapter discusses the data and design factors that need to be considered to establish
loading rates and alternative components for a facilities plan. For predesign and final design,
much more detailed information is required. For example, loading and application rates must
be based on detailed field investigations. Pilot studies may be required under some conditions.
Normally soil scientists and hydrogeologists would make or would be heavily involved in these
investigations.
CLIMATE AND HYDROLOGY
Preliminary information on such climatic factors as growing season, freezing temperatures,
frozen soil, wind direction and velocity, precipitation, evaporation, and rainfall
depth-duration-frequency data will be beneficial or required to establish loadings and
operation. Since all of these factors are variable, a probability analysis may be helpful in
establishing suitable criteria.
PROCESS LOADING
The design loading will be controlled by the most restrictive constraint, as discussed in
the previous chapter. Once the climatic data are available, the evapotranspiration and irrigation
requirements for different crops can be estimated.
For the irrigation process, the loading will be the irrigation requirement, which is
evapotranspiration less effective precipitation plus the leaching requirement divided by the
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irrigation efficiency. The irrigation requirement varies by month but generally follows the crop
growth. Leaching requirements are high in low rainfall areas and are low in areas of higher
precipitation.
If precipitation (P), evapotranspiration (ET), and design excess water (EW) for percolation
are known, the maximum hydraulic loading rate (L) for high-rate irrigation or infiltration-
percolation can be established from the following equation:
L = EW + ET - P,
As discussed earlier, the monthly loading should vary with season and precipitation so
that the same amount of excess water percolates each month. Some evidence indicates that
the excess water should be reduced as soil temperature decreases because of increased
viscosity.27 A drop in temperature from 77 degrees Fahrenheit (25 degrees Centigrade) to 32
degrees Fahrenheit (0 degrees Centigrade) doubles the viscosity and thus would reduce the
excess water percolated by 50 percent.
Loadings of about 4 inches per week for overland flow28 have been successful in a mild
climate, using raw sewage with a settling of about 5 minutes before application. The effect of
precipitation and other climatic factors on this loading is not known, and very little
agricultural data are available on this process. Thus, at this time, design is more an art than a
science for the overland flow process.
The storage requirement can be determined once the effluent application and flow rates
are known. The monthly effluent loading may be calculated together with the monthly
waste water flows as a percent of the yearly total flow. Figure V-l is an example of how to
use these percentage figures to estimate, the required storage volume. The total storage volume
can easily be determined by adding up the percentages of waste water flows which are not
applied. Recurrence intervals for flows greater than average should be considered in sizing the
storage facility.
Strict limitation on removal of pollutants such as nitrogen, phosphorus, heavy metals, or
COD by the land application process as discussed earlier may place a greater constraint on
loading than that obtained by the hydraulic limitation. For example, Powell and Gulp2 9
indicated nitrogen requirements resulted in lower loading limits than the hydraulic limitation.
The paper prepared by Gulp for this seminar discusses this example in greater detail.
If the mechanisms for removal of the pollutant in question are understood, it is possible
to make estimates of the loading limitations to control concentrations. However, the removal
mechanisms are complex and interrelated with other soil chemistry processes and management
practices. Thus, complete understanding of these mechanisms is difficult to obtain. Methods
for estimating loading limits where strict nitrogen, phosphorus, heavy metals, or COD
constraints are imposed were discussed previously.
Field pilot work may be the only way of determining operational removals and
management requirements to ensure the removal of pollutants within the set limits. Field pilot
work is a long-term procedure. Thomas et al.28 indicated that the overland flow process may
not be stabilized after 18 months. Even longer times may be required to develop steady state
conditions for other land application processes.
For poor soil conditions, hydraulic limitation will usually be the determining loading
factor for high-rate irrigation and infiltration-percolation. For good soil conditions and strict
limitations on pollutants, the nutrient requirement for the crop will limit applications for
56
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Z
Z
o
H
LL
O
LU
O
<
z
UJ
u
tr
AVERAGE
WASTEWATER FLOW
/.WASTEWATER APPLICATION
JAN FEB I MAR APR MAY JUN JUL AUG SEP OCT MOV DEC
MONTH
Figure V-1. Wastewater application versus wastewater flow and resulting
storage requirements for data on figure IV-7,'
high-rate irrigation or infiltration-percolation. Loadings for the irrigation and overland flow
processes arc based on irrigation requirements and desired wastewater treatment, respectively.
REST PERIOD
The rest period is necessary to allow the soil to dry and re-aerate for restoration of the
infiltration rate and the removal capacities. The length of the rest period depends on the soil
properties, land application process, waste characteristics, climatic condition, crop, and time of
year. It may range from a day or less to several weeks. Evapotranspiration and precipitation
rates are very important in estimating the rest period. As a preliminary estimate, the removal
between applications of 30 percent of the available water storage of the 4-foot profile should
be adequate for the high-rate irrigation process. For infiltration-percolation, the rest period
should be at least 50 percent of the total time for year-round operations with a minimum of
several days between applications. For overland flow, the area is normally loaded on a daily
basis for a few hours with 1 or 2 days of rest per week. For irrigation, the rest period is
based on the evapotranspiration rate and the available water-holding capacity for the root
zone. As a preliminary estimate, 50 percent of the available soil moisture is extracted between
irrigations.
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Chapter VI
COMPONENTS OF LAND APPLICATION SYSTEMS
An alternative land application system is identified once a specific application process,
application site, irrigation method, and loading rate have been established. The next step is to
determine the conceptual design of the system's components and operation. Alternative land
application systems can only be evaluated once a conceptual layout of each system's
components has been made and an operation plan identified. In this chapter, the purpose,
function, and some suggested design criteria for system components are briefly discussed. The
development of a plan for operation of the components of an alternative will also be
mentioned, Chapter VII will outline a method for evaluating and comparing alternative
systems.
SYSTEM COMPONENTS
Transport
A transport system is necessary to transport the wastewater from the point of collection
to the application site. The delivery system must function year around and must be sized to
carry peak flows. The delivery system is normally a pipeline but may be an open channel
under some conditions.
Preapplieation Treatment
Preapplication treatment ensures reliable operation of the land' application process. Certain
minimal levels of treatment may be specified by the state and usually depend on the crop to
be grown, In the absence of state criteria, it may be necessary to establish criteria for the
project using available data on requirements for reliable operation for the process and
application method involved. The requirements for preapplication treatment for the various
processes have been discussed in Design Factors - I.
Storage
During the nonapplication periods, the effluent may have to be stored. The required
length of the storage period depends on the treatment process, site, and operation plan.
Storage may range from a few days for a small system in mild climates to many months in
cold climates. Storage is usually provided for all processes except overland flow.
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A storage facility may be a reservoir consisting of a dam and spillway or a lagoon with
constructed berrns surrounding it. The storage facility must be large enough to retain the
pretreated wastewater plus precipitation and any surface runoff into the facility. If the storage
facility is a reservoir, an effort should be made to minimize the area of the watershed that
would drain into the reservoir. A spillway will normally be required, with design criteria
established by the state. If state criteria do not exist, criteria of Federal agencies (Corps of
Engineers, Soil Conservation Service, or Bureau of Reclamation) may be used. Total storage
requirements are dependent on the wastewater flows, storage period, direct rainfall, and annual
watershed yield. Frequencies of recurrence for wastewater flows, watershed yield, and
stormwater runoff should be considered in determining the required storage capacity. A
hydrologist should make the analyses of the watershed and storm runoff.
Distribution
The distribution system should be sized for peak flow of the application schedule at
maximum operation time. Typically, irrigation systems operate 80 to 100 percent of the time
during the peak period. Less than 100-percent operation of the total system is generally used
to allow for downtime caused by adverse climatic conditions, such as wind or rain. Flexibility
in system operation will usually allow time for crop harvest, so no additional reduction in
percentage operation would be required for harvest. Sizing can be obtained by taking the
design peak application (20 percent for July on figure V-l) and dividing by the percentage
operation (say 80 percent) to obtain the system capacity (25 percent of the annual volume
during the peak month or three times the average annual flow rate).
Irrigation
The purpose of the irrigation system is to apply the effluent uniformly on the fields at
the desired rate, allowing for rest periods between applications. The irrigation system is
normally owned by the individual farmer. Irrigation systems may have a lot of hardware
consisting of sprinkler systems which automatically irrigate entire fields or may have a
minimum of equipment and high labor requirements for operation. The mechanized systems
provide the best irrigation uniformity and the best system control and therefore are
recommended for land application. Both sprinkler and surface irrigation may be appropriately
used under the proper conditions. Selection of the irrigation method is discussed in Design
Factors — I.
Surface Drainage
Surface drainage systems will collect natural surface runoff or runoff water from a
surface irrigation system. The runoff may be returned to the storage system or discharged if
the quality is suitable. Discharge requirements for coliform or fecal coliforms may make such
a system necessary. If a surface drainage system is required by the state to collect natural
runoff, it should be sized for storm runoff with recurrence intervals of 2 to 10 years unless
the state has specific requirements. The runoff collection system should be emptied within a
few days after the storm.
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Subsurface Drainage
A subsurface drainage system may be required to prevent a water table from rising into
the soil root zone. However, a groundwater table is necessary for a drainage system to work.
The system may consist of wells, buried drain line, or open drainage ditches. Buried drain
lines of concrete, tile, or plastic are usually most satisfactory. Inflow into the line occurs
between joints in the concrete or tile and through slits or holes in the plastic. Only rarely
will a drainage system recover all of the applied effluent. Usually flow will occur beneath the
drain lines around the site perimeter. A subsurface drainage system is often required where
applications are significantly above those required for irrigation.
A drainage system should be designed to drain the necessary quantity of applied effluent
and precipitation. The water table should be drawn down within a few days after an effluent
application or a major rainfall.
Spacing of the drainage system will be controlled by permeabilities and depth of wetted
materials. Standard procedures are available for designing drainage systems under nearly all
conditions. Where high loadings occur as in the infiltration-percolation process or where
permeabilities are low, drain spacing may be as close as 50 to 100 feet. Where higher
permeabilities occur and the loading is consistent as with the high-rate irrigation process,
drains may be spaced much further apart, up to 500 feet or more. Careful consideration of
the drainage for land application is a necessity, and normally some field investigation is
required to specify spacings and depth even in preliminary studies. Much more detailed
investigation is required before final design.
Buffer Area
A buffer area around the application site may be provided for aesthetic, purposes or for
protection from pathogen transmissions if the effluent has not been disinfected. Some states
require buffer areas around the land application area. Other states have no requirement or
leave it up to the engineer. No set design criteria can apply to all situations. In the absence
of specific state requirements where biologically stabilized but nondisinfected wastewater is
applied, a buffer width of 400 feet (200 feet with shrubs or trees) appears adequate for most
sprinkler or spray systems. With adequate disinfection, the buffer may be reduced where there
are no specific state requirements. With surface irrigation, tailwater runoff control is required,
but no buffer zone is necessary,
The minimum travel distance of water droplets can be estimated from fall velocity, water
droplet particle size, and distribution and wind velocity. Prior to establishing buffer distances,
a detailed analysis of requirements should take into consideration wind velocity, wind
direction, downwind development, and the irrigation system to be used. For some irrigation
systems and sites it would be possible to incorporate operating options into the irrigation
system design so the downwind portion of the system could be shut off during moderate
wind conditions. If wind becomes high, it may be necessary to shut down the entire sprinkler
or spray system. A buffer area as a fixed condition or as an operational condition can be
effective in minimizing wind drift of water droplets from sprinkler irrigation systems. Surface
irrigation should not produce a wind drift condition.
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Monitoring System
The purpose of the monitoring system is to detect quality problems in the wastewater,
soils plants, percolate, and runoff and to provide a data base for future reference. The
monitoring system should give previous warning of a potential problem such as accumulation
of heavy metals approaching a limit, adverse changes in plant growth, or inadequate pollutant
removal. The type of tests and locations of the sampling points are critical to obtaining
meaningful results. Obtaining a statistical significance may require many samples. The design
of the monitoring system should consider the variability of the parameter being measured.
Location of the sampling points can determine whether or not a problem would ever be
detected. When a monitoring system is designed without proper consideration to water
movement through soil or porous media, it may not be properly located to detect pollution.
A detailed monitoring program should be developed for each system designed. The location of
sampling points should give proper consideration to water flow lines2 7 >3 ° and travel distances.
A hydrogeologic investigation may be required to determine the best monitoring locations.
Monitoring points for a hypothetical application site, are shown in figure VI-1. If samples
are taken at A and B, flow lines from the application area indicate no treated effluent would
reach these points. It may require several years for treated effluent to reach point C because
the flow lines are a long distance from the application surface. If samples were taken from
point D, mixing with water from sources other than effluent could make results invalid. If
samples are collected at point E in the groundwater and near point F in the soil, the samples
should show a quick response and should be representative of the system operation.
LEGEND
GROUNDWATERTABLE
I UNSATUBATED FLOW
SATURATED FLOW
B SAMPLE POINT
LAND APPLICATION
AREA
RIVER
CREEK
IMPERVIOUS
Figure VI-1, Typical land application site and possible monitoring points.
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The frequency and number of samples and parameters measured must also be determined
for each project. Because of the variability involved, it is more difficult to get representative
samples of plant vegetation than of soil or water. The same point on the plant must be
sampled at the same time each year in order to get an accurate indication of change. Some
elements are concentrated in one place in a plant and not in others. Where to sample for
what must be determined for the plant species involved, A peat deal of help can be obtained
from universities and various specialists about what to measure and where.27'30'31
OPERATION COMPONENTS
A land application system must be properly operated and managed or it may not meet
the treatment objectives and could be a public health nuisance. As indicated throughout this
report, many complex factors are involved in land application, making it very difficult to have
total control over the treatment process. The soil and plant system is adaptable to
considerable environmental stress and thus allows some variance in land application operations,
but the crop or pollutant parameters may show the results of this stress.
Crop
One of the most important aspects of managing a land application project is the crop
selection. For annual and perennial agricultural crops, it is easy to change the crop during the
project life. Factors which influence the crop selection are the crop's nutrient removal
efficiency; suitability to the climate, soil and water applications involved; and tolerance to
wastewater pollutants. If the crop is to be harvested, the local market for the crop must be
considered. In addition, the time and costs for planting, harvesting, and caring for the crop
compared to the expected return are also important in the crop selection.
If removal of nitrogen is a primary objective, a perennial forage grass appears to be the
best selection because it can remove nitrogen to low concentrations.32 Reed canary grass has
been shown to be effective in removing nitrogen; however, other grasses may be just as good
and may respond better under some circumstances. Climate, soil properties, and market for
the crop as well as nutrient removal will affect the crop selection.
The amount of nitrogen removed by selected crops was reported earlier in table IV-2.
However, very little information is available on the removal efficiencies at low element
concentrations. It may be possible to adapt data on fertilizer versus yield to get nitrogen
removal efficiency as follows:
Nr
E = —Lx 100,
N
a
where En = crop nitrogen removal efficiency, Nr - total nitrogen removed with the harvested
portion of crop, and Na = total nitrogen applied in wastewater. However, with fertilizer
experiments the purposes are different, and the depth of applied water may influence the
results dramatically.
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Forests are much less efficient than crops in nitrogen removal. Forests, particularly
deciduous trees, consume large amounts of nitrogen in annual leaf growth. This nitrogen is
then recycled when the leaves drop. With low effluent' applications of 1 inch/week, the
nitrogen at the 4-foot depth was found to increase considerably over the nitrogen level with
no application but was still below the nitrate-nitrogen limit of 10 mg/1 for drinking water
supplies.32 When applications of 2 inches/week were made, the nitrate-nitrogen generally
exceeded the concentration limit of 10 mg/1. Thus, to apply effluents to forests, the nitrogen
limitation will have to be lower than that for agricultural crops.
Crops vary greatly in tolerance to pollutants, such;-as boron, salts, and specific ions.
Consideration must be given to the wastewater quality in selection of the crop to be grown.
Effluents applied to corn and reed canary grass have been shown to have beneficial effects33
in the eastern United States. However, adverse plant responses to irrigating with wastewater
have also been noted,34 and the costs associated with quality changes when wastewater is
used for irrigation have been documented.35 Most of the adverse effects of using wastewater
for irription can be overcome with proper design and management. There may be a
difference in plant responses to wastewater between the eastern and western United States.
Because of the many different factors involved, the crop must be specifically selected for
each project. The agronomist or plant physiologist familiar with the local area should be
helpful in selecting a crop for a land application alternative. Consideration must be given to
the many factors mentioned above. In addition, changing crops is an option in management of
the wastewater treatment system. Such a change could greatly affect the nitrogen balance and
resulting nitrogen removal.
System Management
System management includes management of the crops, soil, irrigation, and monitoring as
well as mechanical equipment. A system evaluation and design cannot be complete without
'proper consideration of how the system will be operated as "a unit. Considerable planning
should go into development of a wastewater irrigation plan with enough flexibility to'allow
for adequate crop management including planting, tillage, and harvest. It has been stated that
good crops indicate good wastewater treatment: thus, adequate planning for good crops must
be done. Other system management factors include site ownership or lease, farm operation,
and monitoring.
The following three alternatives are available for acquiring rights to use a specific site for
wastewater treatment:3 6
* Obtaining the site in fee
* Obtaining a real property interest in the site other than fee (easement or lease)
* Contracting with the land owner or water user to take wastewater for irrigation (no
interest in real property is acquired)
Because of expensive site development and a need for long-term reliability of the treatment
process, the site is usually acquired in fee. This allows the greatest flexibility in land use, but
public ownership may remove the land from real property tax roles.
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The Corps of Engineers36 indicates that acquiring and maintaining interests by leasing
may in the long run equal or exceed the cost of acquiring the site in fee. However, the social
and political impacts of less-than-fee property interest may override the potentially higher cost
and reduced flexibility in land use.
Contractual agreements between the land owner and the agency with wastewater have
been developed for irrigation of agricultural crops.3 7 The application of the contractual
agreement is discussed further in the paper prepared by Gulp for this seminar.
Local practices for farm operations and leasing arrangements should be considered in
establishing the management and operation structure. The options for management and
operation are so diverse that they cannot adequately be covered in this discussion. The
overriding fact is that in most cases (except the irrigation process) the objective is to treat the
wastewater. The management and operation must provide treatment of the wastewater to the
required level prior to discharging it to surface or groundwaters. If management of the
treatment system conflicts with farm management, the farm management must be modified as
necessary.
The land application system which is controlled by the implementing entity (i.e., it has
property interest in the site) could be operated in the following ways:
» Managed and operated by the implementing agency
* Managed by the implementing agency and operated by a private party through
contract or crop sharing
* Managed and operated by contractual agreement with the same private party
« Managed by contractual agreement with a private party and operated by a
subcontractual agreement with another private party
Close cooperation between the treatment system management and the farm operation is
.required in all cases. Scheduling of irrigation with farm operations such as planting, tilling,
spraying, and harvesting is vital to successful management. If adequate consideration is not
given to the system operation, the design may be inappropriate. For instance, if crops are to
be harvested, flexibility is needed in the irrigation system for sufficient drying and harvesting
time. Farm management specialists can be helpful in setting up the management of the crops,
soil, and irrigation portions of the operation. These specialists should be consulted during the
planning stage.
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Chapter VI!
ALTERNATIVE EVALUATION
An evaluation for land application alternatives is based on economic, engineering, and
environmental considerations. The importance of these factors, especially the environmental
consideration, will vary with the local community, depending on its goals and objectives. The
importance or weighting which is given to each factor will vary greatly between individuals,
making an objective evaluation virtually impossible.
A recent paper by Davis38 discussed the impacts of land application on the metropolitan
environment. The areas discussed were:
» Shaping of metropolitan areas through massive land acquisition programs
• Regional organization structure necessary to execute a land application treatment
system
• An accelerated development backlash to control crowding in the surburban and
urban growth areas
Potential problems identified were land costs, difficulty of implementing regional projects,
need for sales effort, potential legal action, reduction of tax base, and time and expense for
human relocation. The land application option can be a new force in shaping urban sprawl
because it potentially involves the largest domestic land acquisition program for metropolitan
regions since the open space program.
Because land application alternatives can have major social ramifications, active public
involvement in their evaluation is nearly a requirement when options involve large or diverse
impacts. Consideration of potential impacts such as controlled land use and control of urban
sprawl cannot be measured as an engineer measures costs. Thus, most engineers find
themselves out of their field of expertise in projects involving major and diverse impacts.
Evaluation of alternative plans by the engineer alone is less common now than in times
past. Instead, planners and environmentalists are becoming involved as team members in land
application projects, and efforts are being directed at public information and involvement.
Printed matter summarizing the project and major effects is often prepared for distribution to
the public. Newspaper supplements are used a a means of "selling" the alternatives.
Thus, an engineer must depend more on input from many disciplines and may not make
the final recommendation. Instead, the final decision will be made by the local decision
makers (elected representatives). They may seek guidance and recommendations from citizens
groups and special committees. The engineer is the technical consultant to the decision makers
and to a limited extent to the advisory groups. Through team effort the engineer and planners
can bring together summaries of major features of the alternatives. The advantages,
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disadvantages, and major features of each alternative may be listed or a matrix table may
show the features and impacts for each alternative. The engineer's (project team's) challenge is
to put the summarized considerations before the decision makers and advisory groups and
possibly even the public in an unbiased manner. The decision makers must choose the
alternative which best accomplishes the treatment objective within the goals of the local area.
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71
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72
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BIBLIOGRAPHIC DATA
SHEET
1. Report No.
EPA/625/4r76/Q10~Vol
3, Recipient's Accession No,
Recipient $ Ace
PB-259 996
4. Title and Subtitle
Land Treatment of Municipal Wastewater Effluents,
Design Factors, Volume II
5. Report Date
Jan 76
6.
7. Author(s)
8. Performing Organization Rept,
No.
9. Performing Organization Name and Address
Environmental Protection Agency
Cincinnati, Ohio
Office of Technology Transfer
10. Project/Task/Work Unit No.
11. Contract/Grant No.
12. Sponsoring Organization Name and Address
13. Type of Report & Period
Coveted
14.
IS. Supplementary Notes
Also available in set of 3 reports as PB-259 994-SET, PC$12.00/MF$7.00.
The report is the second of two papers prepared for the United States Environmental
Protection Agency Technology Transfer Program on Land Treatment of Municipal Waste-
water Effluents. Land treatment or land application is the treatment of wastewater
by using plant cover, soil surface, soil profile, and geologic materials to remove
certain wastewater pollutants. The report discusses the objectives of land
application processes, preapplication treatment, land suitability, selection of the
land application process, distribution techniques, climatic factors, storage, surface
runoff control, public health considerations, and monitoring requirements.
17. Key Words and Document Analysis.
*Sewage treatment,
*Irrigation,
Municipalities,
Design criteria,
Percolation,
Topography,
Ground water,
Water rights,
Fluid filtration,
17b. Identifiers/Open-Ended Terms
*0verland flow,
*Sewage irrigation.
Land disposal.
I7a. Descriptors
Permeability,
Boundaries,
Nitrogen,
Phosphorus,
Hydrogeology,
Vegetation,
Evapotranspi ration,
Soil profiles,
Acceptability,
Systems engineering.
17e. COSATI Field/Group
13 B
18. Availability Statement
National Technical Information Service
Springfield, Virginia 22161
19..Security Class (This
Report)
[21.1
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