Land Treatment
of Municipal Wastewater
Effluents
Design Factors-1
EPA Technology Transfer Seminar Publication
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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 Charles E.
Pound, Ronald W. Crites, and Douglas A. Griffes, representing Metcalf and
Eddy Engineers, Palo Alto, California.
NOTICE
The mention of trade names or commercial products in this publication is for
illustration purposes, and does not constitute endorsement or recommendation for use
by the U.S. Environmental Protection Agency.
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CONTENTS
Page
Introduction 1
Chapter I. Objectives of Land Application Methods 3
Irrigation 3
Infiltration-Percolation 5
Overland Flow 5
Chapter II. Preapplication Treatment 7
Irrigation 7
Infiltration-Percolation 8
Overland Flow 8
Wastewater Quality 8
Chapter III. Land Suitability 11
Site Location 11
Compatibility With Overall Land Use Plan 11
Proximity to Surface Water 12
Number and Size of Available Land Parcels 12
Chapter IV. Selection of the Land Application Method 13
Site Evaluation 13
Treatment Efficiency 16
Land Area Required 17
Chapter V. Distribution Techniques 19
Irrigation 19
Infiltration-Percolation 22
Overland Flow 22
Chapter VI. Climatic Factors and Storage 23
Climatic Data 23
Storage Requirements 24
Water Balance 26
Computer Program 28
Chapter VII. Surface Runoff Control 31
Irrigation Systems 31
Overland Flow Systems 34
iii
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Page
Chapter VIII. Public Health Considerations 35
Pathogens 35
Effects on Workers 37
Groundwater Quality 38
Crop Quality 40
Insect Propagation 41
Chapter IX. Monitoring 43
Renovated Water 43
Vegetation 45
Soils 45
References 47
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INTRODUCTION
The land application of wastewater or treated effluent entails the use of plants, the soil
surface, and the soil matrix for removal of certain wastewater constituents. In addition to
treatment, land application systems may be used for a combination of water reuse and
disposal, with the renovated water either discharged to the groundwater or collected for
discharge to surface waters.
For most land application systems, a wide range of design possibilities is available to suit
specific site characteristics, climate, treatment requirements, and project objectives. The scope
of factors that are normally considered in the design process is shown in table 1. It should be
noted that the list is representative and not necessarily all-inclusive.
Table 1 .—General design considerations1
Wastewater
characteristics
Climate
Geology
Soils
Plant cover
Topography
Application
Flow volume
Precipitation
Groundwater
Type
Indigenous
Slope
Method
to region
Constituent
Evapotrans-
Seasonal
Gradation
Aspect of
Type of
load
piration
depth
Nutrient
slope
equipment
Infiltration/
removal
Temperature
Quality
permeability
capability
Erosion
Application
hazard
rate
Growing
Points of
Type and
Toxicity
season
discharge
quantity of
levels
Crop and
Types of
clay
farm
drainage
Occurrence
Bedrock
Moisture
management
and depth of
Cation exchange
and shade
frozen ground
Type
capacity
tolerance
Storage
Depth
Phosphorus ad-
Marketability
requirements
sorption potential
Permeability
Wind velocity
Heavy metal ad-
and direction
sorption potential
pH
Organic matter
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Because land application by nature must be site specific, and because a wide range of
design possibilities is available, it is not well-suited to standardized design guidelines. The few
guidelines that have been written are generally limited in scope, dealing mainly with spray
irrigation. In lieu of guidelines, the designer must rely on a comprehensive understanding of
the principles involved, site evaluation by specialists, and his own ingenuity. A multi-
disciplinary approach to planning land application systems is necessary, encompassing fields
such as
• Environmental engineering
• Hydrology
• Soil science
• Agriculture
• Geology
• Land use planning
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Chapter I
OBJECTIVES OF LAND APPLICATION METHODS
The three basic methods of land application are irrigation, infiltration-percolation, and
overland flow. Each method, shown schematically in figure 1-1, can produce renovated water
of different quality, can be adapted to different site conditions, and can satisfy different
overall objectives.
IRRIGATION
Irrigation, the predominant land application method in use today, involves the application
of effluent to the land for treatment and for meeting the growth needs of plants. The applied
effluent is treated by physical, chemical, and biological means as it seeps into the soil.
Effluent can be applied to crops or vegetation (including forestland) either by sprinkling or by
surface techniques, for purposes such as:
• Avoidance of surface discharge of nutrients
• Economic return from use of water and nutrients to produce marketable crops
• Water conservation by exchange when lawns, parks, or golf courses are irrigated
• Preservation and enlargement of greenbelts and open space
Where water for irrigation is valuable, crops can be irrigated at consumptive use rates (1
to 3 in./wk, depending on the crop), and the economic return from the sale of the crop can
be balanced against the increased cost of the land and distribution system. On the other hand,
where water for irrigation is of little value, hydraulic loadings can be maximized (provided
that renovated water quality criteria are met), thereby minimizing system costs. Crops grown
under high-rate irrigation (2.5 to 4 in./wk) are usually water-tolerant grasses with lower
potential for economic return but with high nutrient uptakes.
When requirements for surface discharge are very stringent with regard to nitrogen,
phosphorus, and BOD, irrigation can meet the objectives by avoiding a surface discharge,
provided that groundwater criteria can be met. If the renovated water quality must meet
Environmental Protection Agency drinking water standards, reduction in nitrogen below the 10
mg/1 standard for nitrate nitrogen is often the limiting criterion. In arid regions, however,
increases in chlorides and total dissolved salts in the groundwater may be limiting.
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EVAPOTRANSPI RATION
SPRAY OR
SURFACE
APPLICATION
ROOT ZONE
SUBSOIL
CROP
VARIABLE
SLOPE
DEEP
PERCOLATION
(A) IRRIGATION
EVAPORATION
1
SURFACE APPLICATION
1 • PERCOLATION THROUGH
INFILTRATION :
UNSATURATED ZONE
ZONE OF AERATION
AND TREATMENT
RECHARGE MOUND
¦ '• , ! J,['i l \ \ vjvP
/ //v \
n':W:0:S^ v^v-vA-*
OLD WATER TABLE
(B) INFILTRATION-PERCOLATION
SPRAY APPLICATION
SLOPE 2-4%
EVAPOTRANSPI RATION
GRASS AND VEGETATIVE LITTER
RUNOFF
COLLECTION
(C) OVERLAND FLOW
Figure 1-1. Methods of land application.
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INFILTRATION-PERCOLATION
In infiltration-percolation systems, effluent is applied to the soil at higher rates by
spreading in basins or by sprinkling. Treatment occurs as the water passes through the soil
matrix. System objectives can include:
• Groundwater recharge
• Natural treatment followed by pumped withdrawal or underdrains for recovery
• Natural treatment with renovated water moving vertically and laterally in the soil
and recharging a surface watercourse
Where groundwater quality is being degraded by salinity intrusion, groundwater recharge
can reverse the hydraulic gradient and protect the existing groundwater. Where existing
groundwater quality is not compatible with expected renovated quality, or where existing
water rights control the discharge location, a return of renovated water to surface water can
be designed, using pumped withdrawal, underdrains, or natural drainage. At Phoenix, Arizona,
for example, the native groundwater quality is poor, and the renovated water is to be
withdrawn by pumping, with discharge into an irrigation canal.
OVERLAND FLOW
Overland flow is essentially a biological treatment process in which wastewater is applied
over the upper reaches of sloped terraces and allowed to flow across the vegetated surface to
runoff collection ditches. Renovation is accomplished by physical, chemical, and biological
means as the wastewater flows in a thin sheet down the relatively impervious slope.
Overland flow can be used as a secondary treatment process where discharge of a
nitrified effluent low in BOD is acceptable or as an advanced wastewater treatment process.
The latter objective will allow higher rates of application (5 in./wk or more), depending on
the degree of advanced wastewater treatment required. Where a surface discharge is prohibited,
runoff can be recycled or applied to the land in irrigation or infiltration-percolation systems.
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Chapter II
PREAPPLICATION TREATMENT
Treatment of wastewater prior to land application may be necessary for a variety of
reasons, including:
• Maintaining a reliable distribution system
• Allowing storage of wastewater without nuisance conditions
• Maintaining high infiltration rates into the soil
• Allowing irrigation of crops that will be used for human consumption
In the following paragraphs, minimum preapplication treatment levels are described for
irrigation, infiltration-percolation, and overland flow, and wastewater quality is briefly
discussed.
IRRIGATION
Irrigation has been conducted successfully with food processing wastewater containing
BOD and suspended solids concentrations several times higher than those in municipal
wastewaters.2 Preapplication treatment for these industrial wastewaters often involves only
screening to keep the distribution system from clogging. Consequently, reduction of BOD and
suspended solids in municipal wastewaters is not generally necessary from the standpoint of
loadings on the soil. Reductions may be necessary, however, where clogging of the distribution
system may occur, where disinfection is required, or where considerable storage is required.
The bacteriological quality of municipal wastewater is usually limiting where food crops
or landscape areas (parks, golf courses, etc.) are to be irrigated or where aerosol generation by
sprinkling is anticipated (see Chapter VIII, Public Health Considerations). Pathogens should be
reduced to a level consistent with the protection of public health.
Generally, the state public health agencies place limitations on the quality of municipal
wastewater that can be used for irrigation. In California, for example, biological treatment
plus disinfection to a total of 23 coliform organisms per 100 milliliters is required for
irrigation of golf courses, parks, freeway landscapes, and pastures grazed by milking animals.
For direct irrigation of food crops, California requires oxidized, coagulated, filtered wastewater
disinfected to a total of 2.2 coliform organisms per 100 milliliters. Primary effluent is
acceptable for surface irrigation of orchards, vineyards, and fodder, fiber, and seed crops in
California.
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For many other states having guidelines, effluent of the quality produced by lagoons is
acceptable for irrigation. In Virginia, for example, lagoon effluent can be used to irrigate all
crops except those to be consumed raw (which cannot be irrigated with any effluent).
In Missouri, irrigation of forage crops and golf courses is permitted with effluent
disinfected to 200 fecal coliforms per 100 milliliters. Secondary treatment is required only to
provide effective disinfection.
INFILTRATION-PERCOLATION
Reduction of suspended solids is the most important preapplication treatment criterion
for infiltration-percolation systems, so that soil clogging and nuisance conditions from odors
are minimized. Biological treatment is often provided for this purpose. Disinfection is generally
not necessary, except possibly for sprinkling systems, as a number of studies have shown
infiltration-percolation to be quite effective in the reduction of pathogenic bacteria.2
OVERLAND FLOW
When overland flow is used as a secondary treatment process, the minimum
preapplication treatment is screening and possibly grit and grease removal to avoid clogging
the distribution system. No food crops are grown, and sprinkling systems can be designed to
minimize the generation of mists by using rotating-boom sprays or by sprinkling at low
pressures. In the pilot system at Ada, Oklahoma, raw comminuted wastewater, which was
settled for 10 minutes for grease and grit removal, was applied successfully using 30-foot
diameter rotating-boom sprays discharging slightly downward at 15 psi.3
When used as an advanced wastewater treatment process, lagoon or conventional
secondary effluent can be used. Nitrification prior to land application is not necessary for
nitrogen removal by denitrification; however, nitrified effluent can be treated successfully for
nitrogen removal. Disinfection prior to application may avoid post-disinfection and allow
sprinkling at higher pressures.
WASTEWATER QUALITY
The composition of most municipal wastewater effluent is acceptable for land application.
The effluent quality of 12 selected secondary treatment plants discharging to the land is
summarized in table II-1. Nitrogen, the constituent that will most often limit the liquid
loading rate, is discussed in Design Factors - II.
Suggested values for major inorganic constituents in water applied to the land are shown
in table II-2. In arid portions of the country, total dissolved solids may present a hazard in
irrigating certain crops. Crops vary in their tolerance to salinity and boron.8,9
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Table 11-1.—Quality of selected secondary effluents applied to the land
Constituent
Values, mg/l
(except as noted)
Range
Average
BOD
6-42
26
Suspended solids
12-88
48
TDSa
480-1,235
900
Total nitrogen
6.5-33.4
18.5
Total phosphorus
2.1-16.0
8.8
Sodium
40-260
160
SARb
1.3-7.4
4.I
Boron
0.4-1.0
0.7
aTDS total dissolved solids.
^SAR = sodium adsorption ratio.
Sources: Data for Abilene, Tex.; Conejo Valley Sanitary District, Calif.; Oak View Sanitary District, Calif.; Pomona,
Calif.4
Data for Moulton-Niguel Water District, Calif.; Phoenix, Ariz.; Lake George, N.Y.; Westby, Wis.; Woodland, Calif.3
Data for Muskegon, Mich.5
Data for Michigan State, Mich.4
Data for Pennsylvania State, Pa.7
Sodium can be toxic to crops; however, it usually affects permeability first. The sodium
adsorption ratio should be maintained below 9 to prevent deflocculation of the soil structure
or sealing of the soil.2 The sodium adsorption ratio is of special concern when the soil has a
high clay content. It can be reduced by increasing the wastewater concentrations of calcium
and magnesium through the addition of gypsum or other amendments.8 The effects of other
wastewater constituents, such as heavy metals, are addressed in Design Factors - II.
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Table 11-2.— Suggested values for major
inorganic constituents in water applied to the land1 0
Problem and related constituent
No problem
Increasing
problems
Severe
Salinity3
EC of irrigation water, in millimhos/cm
<0.75
0.75-3.0
>3.0
Permeability
EC of irrigation water, in mmho/cm
>0.5
<0.5
<0.2
SAR (Sodium adsorption ratio)b
<6.0
6.0-9.0
>9.0
Specific ion toxicity0
From root absorption
Sodium (evaluate by SAR)
<3
3.0-9.0
>9.0
Chloride, me/I
Chloride, mg/l
<4
<142
4.0-10
142-355
>10
>355
Boron, mg/l
<0.5
0.5-2.0
2.0-10.0
From foliar absorption^ (sprinklers)
Sodium, me/I
Sodium, mg/l
<3.0
<69
>3.0
>69
—
Chloride, me/I
Chloride, mg/l
<3.0
<106
>3.0
>106
—
Miscellaneous6
NO3 n} m9^' *or sens't've cr°Ps
<5
5-30
>30
HCO3, me/I ["only with over"!
HCO3, mg/l [head sprinklers]
<1.5
<90
1.5-8.5
90-520
>8.5
>520
pH Normal range = 6.5-8.4
aAssumes water for crop plus needed water for leaching requirement (LR) will be applied. Crops vary in tolerance to salinity.
Electrical conductivity (EC) mmho/cm x 640 = approximate total dissolved solids (TDS) in mg/l or ppm; mmho x 1,000 =
micromhos.
Na
bSAR = ^aTTfig" where Na = sodium, milliequivalents/l; Ca = calcium; Mg = magnesium.
sf 2
cMost tree crops and woody ornamentals are sensitive to sodium and chloride (use values shown). Most annual crops are not
sensitive.
dLeaf areas wet by sprinklers (rotating heads) may show a leaf burn due to sodium or chloride absorption under low-humidity,
high-evaporation conditions. (Evaporation increases ion concentration in water films on leaves between rotations of sprinkler heads.)
eExcess N may affect production or quality of certain crops, e.g., sugar beets, citrus, grapes, avocados, apricots, etc. (1 mg/l
N03-N = 2.72 lb N/acre-ft of applied water.) HC03 with overhead sprinkler irrigation may cause a white carbonate deposit to form
on fruit and leaves.
Note: Interpretations are based on possible effects of constituents on crops and/or soils. Suggested values are flexible and
should be modified when warranted by local experience or special conditions of crop, soil, and method of irrigation.
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Chapter III
LAND SUITABILITY
A checklist of characteristics to be evaluated for land suitability, included in Evaluation
of Land Application Systems,9 contains the following general items:
• Location with respect to point of wastewater collection/treatment facilities
• Compatibility of planned objectives with overall land use plan
• Proximity to surface waters
• Number and size of available land parcels
Important characteristics, such as climate, topography, vegetation, geology, and soils, are
discussed by type of land application method in the next chapter.
SITE LOCATION
A topographic map (for example, USGS 7.5- or 15-minute quadrangles) can be used for
initial site location. Distances and locations of potential transmission routes and elevation
differences can be determined. In many cases, a tradeoff can be made between increasing
costs for transmission and decreasing land values if the site is located in a sparsely developed
outlying area.
COMPATIBILITY WITH OVERALL LAND USE PLAN
Planning documents, such as basin plans, areawide wastewater management plans, or
regional management plans, should be consulted with regard to siting of wastewater treatment
facilities. Land use planning is usually conducted at either the regional or the county level,
and published plans should be investigated. Planning commissions and zoning authorities
should be contacted to determine:
• If land application can be planned in a specific area
• What future population densities are planned for the area
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• What the long-range planning objectives are for the area
• Which of these objectives can be integrated with land application
PROXIMITY TO SURFACE WATER
For overland flow systems and systems with underdrains or pumped withdrawal, discharge
of renovated water to surface waters should be considered. Distance from receiving surface
waters, as well as quality considerations, water rights, and the overall hydrology of the area, is
important. Flood plain mapping (U.S. Army Corps of Engineers) should be consulted to
determine if special protective provisions must be made in the design.
NUMBER AND SIZE OF AVAILABLE LAND PARCELS
The relative availablity of land at potential sites, together with the probable price per
acre, must be defined early in the evaluation. The number and size of available parcels will be
of significance, especially in relation to the complexity of land acquisition and control—a
subject that is discussed on pages 39 and 40 of Evaluation of Land Application Systems 9
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Chapter IV
SELECTION OF THE LAND APPLICATION METHOD
Selection of the appropriate land application method requires matching the management
objectives and wastewater characteristics to the characteristics of potential sites, expected
treatment efficiencies, and land requirements.
SITE EVALUATION
Criteria for climate, topography, soil, geology, hydrology, and vegetation vary with the
type of land application method. Climatic and topographic criteria are discussed in the
following paragraphs. Soil characteristics, groundwater conditions, and crop selection-
mentioned briefly here—are discussed in Design Factors — II.
Climate
For irrigation of annual crops, wastewater application is restricted to the growing season,
and storage may be required for a period ranging from 3 months in moderate climates to 7
months in cold northern states. Irrigation of perennial grasses or double cropping annual crops
can extend the period of application. Periods of snow cover, intense rainfall, and subfreezing
conditions may limit the application to perennial grasses and forestland. This depends on
water quality criteria for the percolating water because the treatment efficiency of soil
systems decreases under these conditions.
Infiltration-percolation is the method least affected by climate, particularly if flooded
basins are used. The system at Lake George, New York, is operated year-round, with the
relatively warm effluent being applied beneath a layer of ice during cold spells.2
Overland flow is similar to irrigation of perennial grasses in its response to climatic
factors. Because infiltration of the applied water is minimal and the systems are designed for
runoff, they may be operated during wetter weather than would be possible with irrigation
systems. Operation at temperatures of 25 degrees Fahrenheit has been practiced; however,
once operation ceases because of low temperatures, it is not started again until the
temperature reaches about 40 degrees Fahrenheit.
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Topography
Spray irrigation can generally be adapted to the existing wooded terrain if slopes are less
than approximately 30 percent and runoff and erosion are controlled. For cultivated
agriculture, the slopes should not exceed about 15 percent. For irrigation using standard
long-span center pivot sprinkling systems, the slopes are generally limited to 15 to 20 percent.
Relatively flat land is normally required for surface irrigation, although contour furrows
can be used with slopes as steep as 5 percent.
For infiltration-percolation systems, the primary concern with regard to topography is
that lateral movement of water be controlled so that percolation rates of lower basins are not
affected. At Westby, Wisconsin, basins have been terraced into a 5-percent sloping hillside, but
there are no underdrains and the lateral movement of water from the upper basins affects the
percolation rates in the lower basins.
For overland flow systems, the primary requirement is that the existing topography be
such that terrace slopes of 2 to 8 percent can be economically formed. The cost and impact
of the earthwork required would be the major constraints.
Geology and Soils
Although soil drainage cannot be predicted from soil type alone, a general indication of
soil type versus ranges of liquid loading rates is shown in figure IV-1. It should be noted that
the ranges in figure IV-1 denote typical practice and do not represent recommended loadings.
Loamy soils are preferred for irrigation systems; however, most soils from sandy to clay loams
are acceptable. Both the soil depth and minimum depth to groundwater should generally be at
least 5 feet to ensure proper renovation and root development. The depth to groundwater can
often be increased by underdrains or pumped withdrawal. Geologic discontinuities that may
cause short-circuiting of applied water to the groundwater should be avoided.
Infiltration-percolation systems require well-drained soils, such as sands, sandy loams,
loamy sands, and gravels. A depth of 10 to 15 feet to existing groundwater is preferred.2'
Lesser depths may be acceptable where underdrainage is provided.
Soils with limited drainability, such as clays and clay loams, are best suited for overland
flow systems. Soil depth should be sufficient to form the necessary slopes and maintain a
vegetative cover.
Vegetation
Existing vegetation can be analyzed to predict soil drainage and moisture-holding
capacity. It may also reflect sodic (high sodium), saline (high dissolved solids), or infertile soil
conditions.
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Figure IV-1. Soil type versus liquid loading rates for different land application approaches.2
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Forested sites can be irrigated provided the stand is not so thick as to prevent efficient
spray application. Clearing of sites is necessary for infiltration-percolation systems because the
high application rates will kill most native vegetation. For overland flow, clearing is necessary
to establish smooth slopes and to plant perennial, water-tolerant grasses.
TREATMENT EFFICIENCY
The expected treatment efficiencies of land treatment systems will vary with the
concentrations of constituents in the applied wastewater. The quality of the water after land
treatment, however, appears to be somewhat more consistent. Reed11 has shown that the
renovated water quality for BOD, nitrogen, and phosphorus is nearly the same whether
untreated, primary, or secondary effluent is applied. The values for renovated water quality
given in table IV-1 represent a typical range derived from Thomas,3 Reed,11 and other
references.2 '7'9
Table IV-1.—Expected quality of
renovated water from land treatment systems
Value, mg/l
Constituent
Irrigation
Infiltration-
percolation
Overland
flow
BOD
1-2
2-5
5-10
Suspended solids
1-2
1-2
8-10
Ammonia nitrogen as N
0.5-1
0.5-1
0.5-1
Total nitrogen as N
2-4
10-15
2-5
Phosphorus as P
0.1-0.5
1-3
3-5
LAND AREA REQUIRED
The total amount of land required for a land application system-though highly
variable-is primarily dependent on application rates. Other features that affect land
requirements include buffer zones, storage, access roads, dikes, flood control structures,
terraces, fencing, and an administration building. Because application rates vary significantly
for each land application method, the land area required for each one will be given as a
typical range.
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The total land required for a 1-mgd irrigation system can vary from 60 to 500 acres,
with 100 to 200 acres being the typical range. Buffer zones (unirrigated strips of land around
sites) are frequently required for sprinkling systems and can increase the total land
requirement significantly, particularly in cases where the land requirement is otherwise small.
Infiltration-percolation is the least land-intensive method of application. High-rate systems
may require as little as 3 to 6 acres per mgd, while low-rate systems may require 20 to 60
acres per mgd.
Land requirements for overland flow systems typically range from 25 to 110 acres per
mgd. As with spray irrigation, this range may be increased if buffer zones are required.
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Chapter V
DISTRIBUTION TECHNIQUES
As many as 20 distribution techniques for water are available for engineered wastewater
effluent applications. Many of the techniques developed in the irrigation industry have not
been applied to wastewater. Drip irrigation, for example, would require a filtered effluent for
crop irrigation and is therefore not an economical technique for wastewater. Other techniques
described by Pair12 may be applicable to wastewater application and should be investigated
with regard to economics, efficiency, operation and maintenance, and reliability.
IRRIGATION
Distribution techniques for irrigation can be classified into three main groups: fixed
sprinkling systems, moving sprinkling systems, and surface application systems. Detailed criteria
on these systems are available in Pair12 and other sources.13'14
Fixed Sprinkling Systems
Fixed sprinkling systems, often called solid set systems, may be either on the ground
surface or buried. Both types usually consist of impact sprinklers on risers that are spaced
along lateral pipelines, which are in turn connected to main pipelines. These systems are
adaptable to a wide variety of terrains and may be used for irrigation of either cultivated land
or woodlands.
Above-ground systems normally use portable aluminum pipe, which has the advantage of
a relatively low capital cost. Several serious disadvantages of surface aluminum pipe are:
• It is easily damaged.
• It has a short expected life due to corrosion.
• It must be moved during cultivation and harvesting operations.
Plastic or asbestos cement pipe is most often used for buried systems. Laterals may be
buried as deep as 1.5 feet, and main pipelines, 2.5 to 3 feet below the surface. Buried
systems generally have the greatest capital cost of any of the irrigation systems. On the other
hand, they are probably the most dependable, and they are well suited to automatic control.
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Sprinkler spacings, application rates, nozzle sizes and pressures, control systems, risers,
and drain valves are the major design parameters in fixed sprinkling systems. General practice
is as follows:
• Sprinkler spacing-May vary from 40 by 60 feet to 100 by 100 feet and may be
rectangular, square, or triangular. Typical spacings are 60 by 80 feet and 80 by 100
feet.
• Application rate-May range from 0.10 to 1 in./hr or more, with 0.16 to 0.25 in./hr
being typical. Application rate is calculated using equation (1):
Application rate, = 96.3Q (gpm per sprinkler) (1)
in./hr Area (sq ft covered)
Sample calculation: Determine the application rate for a spacing of 80 by 80
feet and a discharge per sprinkler head of 15 gpm.
96.3 (15)
Application rate - (80) (80) = in-/hr
• Nozzles-Generally vary in size of openings from 0.25 inch to 1 inch. The discharge
per nozzle can vary from 4 to 100 gpm, with a range from 8 to 25 gpm being
typical. Discharge pressures can vary from 30 to 100 psi, with 50 to 60 psi being
typical. Single-nozzle sprinklers are preferred because of lesser clogging tendencies
and larger spray diameters.
• Control systems—May be automatic, semiautomatic, or manual. Automatic systems
are the most popular for land application systems. Automatic valves may be either
hydraulically or electrically operated.
• Risers-May be galvanized pipe or PVC of sufficient height to clear the crop, usually
3 to 4 feet for grass. The riser should be adequately staked because impact
sprinklers cause vibrations that must be damped.
• Drain valves—Should be located at low points in lines, with gravel pits to allow
water to drain away and prevent in-line freezing.
Moving Sprinkling Systems
There are a number of different moving sprinkling systems, including center pivots, side
roll wheel move, rotating boom, and winch-propelled sprinkling machines. The center pivot
system is the most widely used for wastewater irrigation and is the only system discussed
here. General practice with respect to sizes, propulsion, pressures, and topography is as
follows:
• Sizes-Center pivot systems consist of a lateral that may be 600 to 1,400 feet long,
which is suspended by wheel supports and rotates about a point. Areas of 35 to
135 acres can be irrigated per unit.
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• Propulsion-By means of either hydraulic or electric drive. One rotation may take
from 8 hours to as much as 1 week.
• Pressures-Usually 50 to 60 psi at the nozzle, which may require 80 to 90 psi at
the pivot. Standard sprinkler nozzles or spray heads directed downward can be used.
• Topography-Can be adapted to rolling terrain up to 15 to 20 percent.
Surface Application Systems
The two main types of surface application systems are ridge and furrow, and border strip
flooding irrigation.
Ridge and furrow irrigation is accomplished by gravity flow of effluent through furrows
from which it seeps into the ground. General practice is as follows:
• Topography—Can be used on relatively flat land (less than 1 percent) with furrows
running down the slope, or on moderately sloped land with furrows running along
the contour.
• Dimensions—Furrow lengths usually range from 600 to 1,400 feet. Furrows are
usually spaced between 20 and 40 inches apart, depending on the crop.
• Application-Usually by gated aluminum pipe. Short runs of pipe (80 to 100 feet)
are preferred to minimize pipe diameter and headloss and to provide maximum
flexibility. Surface standpipes are used to provide the 3 to 4 feet of head necessary
for even distribution.
Border strip irrigation consists of low, parallel soil ridges constructed in the direction of
slope. The major design variables for surface flooding using border strips include strip
dimensions, method of distribution, and application rates. General practice is as follows:
• Strip dimensions-Vary with type of crop, type of soil, and slope. Border widths
may range from 20 to 100 feet; 40- to 60-foot widths are the most common.
Slopes may range from 0.2 to 0.4 percent. The steeper slopes are required for
relatively permeable soils. Strip length may vary from 600 to 1,400 feet.
• Method of distribution-Generally by means of either concrete-lined ditch with slide
gates at the head of each strip, underground pipe with risers and alfalfa valves, or
gated aluminum pipe.
• Application rates-At the head of each strip, will vary primarily with soil type and
may range from 10 to 20 gpm per foot width of strip for clay to 50 to 70 gpm
per foot width of strip for sand. The period of application for each strip will vary
with strip length and slope.
21
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INFILTRATION-PERCOLATION
Intermittent flooding in basins is the most common distribution method, although
high-rate spraying (more that 4 in./wk) may also be used. With flooding basins, the major
design variables include application rate, basin size, height of dikes, and maintenance of basin
surfaces. General practice is as follows:
• Application rates and cycles-Rates can vary from 4 to 120 in./wk, as discussed in
Design Factors - II. Loading cycles generally vary from 9 hours to 2 weeks of
wetting followed by 1 day to 3 weeks of drying.
• Basin size-Generally a function of design flow and relationship of wetting and
drying periods. Basins may range in size from less than 1 acre to 10 acres or more.
It is usually necessary to include at least two separate basins for even the smallest
systems.
• Height of dikes-Will vary with depths of water applied. For depths of 1 to 2 feet,
a height of approximately 4 feet is common.
• Maintenance of basin surface-Many systems require periodic tilling of the surface,
often annually, while some high-rate systems may require periodic replacement of
the sand or gravel.
OVERLAND FLOW
Sprinkling is the most common technique in the United States; however, surface flooding
may be practicable for effluents relatively low in suspended solids. General practice is as
follows:
• Sprinkler application-Either fixed sprinklers or rotating boom-type sprays may be
used. Moving or portable systems are not practicable as a smooth surface must be
maintained. Sprinklers are spaced from 60 to 80 feet apart on the laterals.
• Slopes-Slopes may range from 2 to 8 percent with 2 to 4 percent preferred for
adequate detention time. Lengths of slope may range from 150 to 300 feet, with
175 to 250 feet being typical.
• Application rates and cycles-Rates range from 2 to 10 in./wk, with 3.5 to 5.5
in./wk being typical. Common cycles are 6 to 8 hours of wetting and 16 to 18
hours drying to maintain the microorganisms on the soil surface active.
• Surface application-May be by flooding or by gated pipe. Most suited to wastewater
low in organic solids.
22
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Chapter VI
CLIMATIC FACTORS AND STORAGE
An evaluation of climatic factors, such as precipitation, evapotranspiration, and
temperature, is important primarily for the determination of the water balance, length of the
growing season, number of days when the system cannot be operated, and the storage
capacity requirement. Another important function of the climatic factors is stormwater runoff
control, which will be discussed in the next chapter. Climatic data, storage requirements, the
water balance, and a computer program to determine storage using climatic data are discussed
in this chapter.
CLIMATIC DATA
Sufficient climatic data are generally available for most locations in the country from
three publications of the National Oceanic and Atmospheric Administration (formerly the
Weather Bureau).
The Monthly Summary of Climatic Data provides basic data, such as total precipitation,
maximum and minimum temperatures, and relative humidity, for each day of the month for
every weather station in a given area. Evaporation data are also given where available.
The Climatic Summary of the United States provides 10-year summaries of data for the
same stations in the same given areas. This form of the data is convenient for use in most of
the evaluations that must be made, and includes:
• Total precipitation for each month of the 10-year period
• Total snowfall for each month of the period
• Mean number of days with precipitation exceeding 0.10 and 0.50 inch for each
month
• Mean temperature for each month of the period
• Mean daily maximum and minimum temperatures for each month
• Mean number of days per month with temperature less than or equal to 32 degrees
Fahrenheit, and greater than or equal to 90 degrees Fahrenheit
23
-------
Local Climatological Data, an annual summary with comparative data, is published for a
relatively small number of major weather stations. Among the more useful data contained in
the publication are the normals, means, and extremes which are based on all data for that
station, on record to date. To use such data, correlation may be required with a station
reasonably close to the site.
Data on evapotranspiration are often more difficult to obtain, particularly in the East.
When evaporation data are available, evapotranspiration can be predicted using empirical
equations. In other cases, values of net evapotranspiration obtained from the map shown in
figure VI-1 are often sufficient.
Figure VI-1. Potential evapotranspiration versus mean annual precipitation (inches).1 s
STORAGE REQUIREMENTS
Climate affects the operation of each land application method differently. Storage
requirements because of climate are discussed for each method.
24
-------
Irrigation
Storage requirements for systems that irrigate annual crops are primarily dependent on
the growing season of those crops, which in turn is dependent on the local climate. The
minimum storage requirement would then be equal to the flow over the remaining portion of
the year. In many areas with mild or moderate climates, two annual crops can be grown each
year, which of course will reduce the storage requirement.
The storage requirements for systems that irrigate perennials, including woodlands, are
normally related directly to climatic factors. Days on which application must be suspended
can be predicted from an evaluation of the number of days when:
• The temperature is below a certain level.
• Precipitation exceeds a certain amount.
• Snow cover exceeds a certain depth.
With regard to temperature, it has been shown that irrigation systems can usually operate
successfully below 32 degrees Fahrenheit. The most common lower limit is 25 degrees
Fahrenheit. At least two methods are available for predicting the number of days that are too
cold for operation. In the first method, it is assumed that application is suspended on all days
in which the mean temperature is below 32 degrees Fahrenheit. This method is probably
conservative, but it has the advantage of using readily accessible data. In the second method,
which has been used successfully for some spray systems, it is assumed that application is
suspended on days in which the minimum temperature is below 25 degrees Fahrenheit and is
not resumed until the maximum daily temperature exceeds 40 degrees Fahrenheit. Half-day
operation is assumed for days on which the minimum temperature is below 25 degrees
Fahrenheit and the maximum exceeds 40 degrees Fahrenheit.
The maximum precipitation allowed before application is stopped will depend primarily
on the maximum infiltration rates at the site and stormwater runoff considerations. At sites
with limited infiltration rates and where stormwater runoff is of concern, as little as 0.2 inch
of precipitation in a day may require suspension of application. In other cases, full-time
operation may be assumed during days with 1.0 inch or more of precipitation.
Irrigation of perennial grasses and woodlands can be conducted during snow cover
provided renovation is not critical under these conditions. When the built-up ice and snow
melt, the runoff must be contained. The persistence of snow on the field is important to
consider because snow that melts quickly is no more of a problem than rainfall.
Infiltration-Percolation
For high-rate spraying systems, the storage design factors are generally similar to those
for irrigation of perennial crops, except that storage is seldom required for days with high
amounts of precipitation.
Intermittent flooding systems using infiltration basins can often be operated continuously
and seldom require any significant storage, except possibly for system backup or extremely
severe climatic conditions.
25
-------
Overland Flow
The storage design factors for overland flow are similar to those for irrigation of
perennial crops, with one significant difference—that related to precipitation. This difference is
a result of the fact that applied water is collected after treatment. If runoff is to be strictly
controlled or disinfected after collection, maximum daily application rates allowable during
precipitation may be relatively small. On the other hand, if the wastewater is sufficiently
treated and disinfected prior to application, stormwater runoff might not be of special
concern, and storage requirements for periods of precipitation might be reduced.
WATER BALANCE
The water balance for land application systems is described by the equation:
Desipi + = Evapotranspiration + Percolation + Runoff (2)
precipitation applied
For most irrigation and infiltration-percolation systems, runoff will be zero. In high-rate
infiltration-percolation systems, precipitation and evapotranspiration will be of little sig-
nificance compared with effluent applied and percolation. In overland flow systems,
percolation will be minimal, and runoff may represent 40 to 80 percent of the effluent
applied.
If used on a monthly, weekly, or daily basis, the balance can be used to calculate
cumulated storage, with the maximum value over the year being the required capacity. In this
process, the term for effluent applied should reflect reduced operating time resulting from
adverse climatic conditions and increases during drawdown of storage. The method is
illustrated in Example 1.
Example 1. Determine the storage requirements from a monthly water balance for a
1-mgd irrigation system.
Assumptions
1. Design precipitation and evapotranspiration are for the wettest year in 25, with
average monthly distribution.
2. A perennial grass is grown and irrigated year-round.
^roJe" is and the area required as a result of the nitrogen balance is
120 field acres.
4. Runoff is contained and reapplied.
5. The design year begins in October with the storage reservoir empty.
Solution
Computations and results are presented in table VI-1.
26
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Table VI-1.— Example of storage
determination from water balance for irrigation (inches)
Month
(1)
Evapo-
trans-
piration
(2)
Perco-
lation
(3)
Water
losses
(2) + (3) =
(4)
Precipi-
tation
(5)
Effluent
applied
(6)
Effluent
available
(7)
Total
water
available
(5) + (7) =
(8)
Change
in
storage,
(8) - (4) =
(9)
Total
storage
(10)
Oct
2.3
10.0
12,3
1.6
10.7
9.3
10.9
-1.4
0
No/
1.0
10.0
11.0
2.4
8.6
9.3
11.7
.7
.7
Dec
0.5
5.0
5.5
2.7
2.8
9.3
12.0
6.5
7.2
Jan
0.2
5.0
5.2
3.0
2.2
9.3
12.3
7.1
14.3
Feb
0.3
5.0
5.3
2.8
2.5
9.3
12.1
6.8
21.1
Mar
1.1
10.0
11.1
3.4
7.7
9.3
12.7
1.6
22.7
Apr
3.0
10.0
13.0
3.0
10.0
9.3
12.3
-.7
22.0
May
3.5
10.0
13.5
2.1
11.4
9.3
11.4
-2.1
19.9
Jun
4.8
10.0
14.8
1.0
13.8
9.3
10.3
-4.5
15.4
Jul
6.0
10.0
16.0
0.5
15.5
9.3
9.8
-6.2
9.2
Aug
5.7
10.0
15.7
1.1
14.6
9.3
10.4
-5.3
3.9
Sep
3.9
10.0
13.9
•2.0
11.9
9.3
11.3
-2.6
1.3
Total
annual
32.3
105.0
137.3
25.6
111.7
111.8
137.2
1. Precipitation and evapotranspiration data are entered into columns 5 and 2,
respectively.
2. On the basis of the nutrient balance, the design allowable percolation rate is 10
in./mo from March through November and 5 in./mo for the remaining months
(column 3).
3. The water losses (column 4) are found by summing evapotranspiration and
percolation.
4. The effluent applied (column 6) is the difference between the water losses and
the precipitation.
27
-------
5. The effluent available per month (column 7) is:
Effluent _ 1 mgd x 30.4 day/mo x 36.8 acre-in./mil gal.
available 120 acres
6. The total water available (column 8) is the sum of effluent available and
precipitation.
7. The monthly change in storage (column 9) is the difference between the total
water available (column 8) and the water losses (column 4).
8. The total accumulated storage (column 10) is computed by summing the
monthly change in storage.
9. The maximum storage is 22.7 inches occurring in March. This is equivalent to a
storage volume of:
Storage = (22.7 in ) (120 acre) = „ f,
volume 12 m./ft
10. The effluent applied is 111.7 inches (9.3 feet) on an annual basis with about
3.5 in./wk applied as the maximum rate in July.
Comments
1. The maximum storage volume of 227 acre-feet would be the equivalent of 74
days' flow at 1 mgd.
2. If a significant amount of storage remained at the end of the period (i.e., in
September), it could be reduced by increasing the field area to more than 120
acres, or increasing the design amount of percolation. However, increases in
design percolation rates would require reevaluation of nitrogen loading rates.
3. The accuracy of the water balance method can be improved if a time
increment smaller than a month (weekly or daily water balances) is used.
4. An alternative method for computing storage requirements from the water
balance is to calculate a series of water balances for each year of a period of
record (at least 10 to 20 years). The design storage requirements for the worst
year in 25 could then be determined by means of a frequency analysis of the
storage requirements for each year.
COMPUTER PROGRAM
A computer program, which relates many of the factors described previously in this
chapter, has recently become available through the National Climatic Center in Asheville,
North Carolina.16 It utilizes basic daily climatic data for a given weather station, for a given
period of years, and identifies which days are unfavorable for application. The total storage
capacity required each year can be calculated by adding one day's flow to storage each
unfavorable day. Storage is then reduced by some fraction of a day's flow (based on the
28
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actual drawdown rate) for each favorable day. The maximum storage capacity is then
identified for each year. A simplified example printout for a portion of a month is shown in
table VI-2.
Table VI-2.—Sample printout of climatic data program
Year
Month
Day
Temperature, deg F
Snow
depth,
in.
Precipi-
tation,
in.
Favorable
day
Unfavorable
day3
Storage,
days
Maxi-
mum
Mini-
mum
Mean
55
02
01
42
28
35
—
.01
X
55
02
02
34
17
26
3
.45
X
1
55
02
03
33
7
20
2
—
X
2
55
02
04
19
6
13
2
—
X
3
55
02
05
31
11
21
2
—
X
4
55
02
06
46
30
38
T
.95
X
5
55
02
07
48
32
40
—
.05
X
4.5b
55
02
08
49
19
34
—
—
X
4
55
02
09
20
9
15
—
—
X
5
55
02
10
44
28
36
—
—
X
4.5
aDefinition of unfavorable day:
Mean temperature <,32 deg F
Precipitation > 0.50 in.
^Drawdown^rate \rom storage on favorable days is 0.5 x daily flow; i.e., on favorable days the amount actually
applied to the field is the average daily flow plus an extra 50 percent from storage.
29
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Chapter VII
SURFACE RUNOFF CONTROL
Requirements for control of surface runoff resulting from both applied effluent and
stormwater depend mainly on the expected quality of the runoff—for which few data exist.
Considerations relating to surface runoff control are discussed here for both irrigation and
overland flow systems. Infiltration-percolation systems are not included in the discussion
because, in almost all cases, these systems are designed so that no runoff is allowed.
IRRIGATION SYSTEMS
Surface runoff control considerations for irrigation systems can be divided into tailwater
return, storm runoff, and system protection.
Tailwater Return
Surface runoff of applied effluent is usually designed into surface application systems,
such as ridge and furrow and border strip flooding, because it is difficult to maintain even
distribution across the field with these methods, and some excess water may accumulate at
the end of furrows or strips. Generally, this tailwater is returned by means of a series of
collection ditches, a small reservoir, a float-actuated pumping station, and a force main to the
main storage reservoir or distribution system.
The most common range of flows for tailwater is between 5 and 25 percent of applied
flows (depending on the management provided, the type of soil, and the rate of application).
In humid climates, the tailwater system design may be controlled by stormwater runoff flows.
A more detailed discussion of storm runoff follows in the next paragraph.
Storm Runoff
For high intensity rainfall events, some form of storm runoff control may be required
for irrigation systems, except those with well-drained soils, relatively flat sites, or where the
quality of the runoff is acceptable for discharge. Where runoff control is deemed necessary, it
generally consists of the collection and return of the runoff from a storm of specified
31
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intensity, with a provision for the overflow of a portion of all larger flows. Questions the
designer must answer include:
• How much precipitation will run off?
• What will the quality of the runoff be?
• How much runoff must be contained and reapplied?
The amount of runoff to be expected as a result of precipitation will depend on:
• Infiltration capability of the soil
• Antecedent moisture condition of the soil
• Slope
• Type of vegetation
• Temperature of both air and soil
The relationships between runoff and these factors are common to many other hydrologic
problems and are adequately covered by Viessman.17
Runoff quality during storms is essentially unknown for most parameters. To give some
perspective to the magnitude of nitrogen and phosphorus concentrations measured in runoff
from various rural areas, and until quantitative data from effluent-applied sites are available,
the average values given in table VII-1 may be useful.
It is important to note that the research work reported in table VII-1 was aimed
primarily at fertilizing practice and cultivation versus noncultivation as related to nutrient
losses. Other factors in sediment and nutrient loss include contour planting versus straight-row
planting and incorporation of plant residues to increase organic matter in the soil In each
research study, many additional factors that affect erosion losses were presented and the
interested reader should consult the literature. '
The question of how much runoff should be contained or reapplied is difficult to
answer. The answer depends on the quality of runoff, water quality of the stream during
storms and downstream uses of the water, as well as on rural runoff control objectives within
the hydrologic basin. Difficulties will remain until sufficient research has been completed to
define the problem Therefore, in the interim, some provision should be made for limited
storm runoff control from irrigation systems. This should consist of capturing and recycling
the first flush from the field as a minimum. It might range from capturing the fi»t 30
minutes to all of the flow resulting from a 2-year frequency storm event.
System Protection
An additional requirement for runoff control often results from the need for protection
from runoff caused by system failures. System failures may include ruptured sprinkler lines,
32
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Table VI1-1 -Average values of nitrogen and
phosphorus measured in rural storm water runoff studies
Total
Total
Location and
nitrogen,
phosphorus,
site description
Management practice
mg/l
mg/l
Reference
North Carolina
Heavily fertilized,
uncultivated
4.60
0.10
18
Lightly fertilized,
uncultivated
1.60
0.08
Cornell
Highly fertilized
6.17a
0.26b
(corn, beans, wheat)
19
Moderately fertilized
1.703
0.12
Ontario
Fertilized and cultivated
1,88c
0.67
(marsh)
20
Unfertilized and uncultivated
0.05c
0.17
Wisconsin
Fertilized, plowed surface
81.8d
(pilot plots, oat stubble)
1. In sediment
0.88
2. In water
2.8
0.49
84.6
1.37
21
Unfertilized plowed surface
1. In sediment
75.2
0.33
2. In water
0.7
0.10
75.9
0.43
aAmmonia plus nitrate nitrogen only.
^Inorganic phosphorus only.
cNitrate plus nitrite nitrogen only. „ „
^Organic nitrogen from .oil sediment accounted for 90+% of all mtrogen. Runoff occurred from 1 hr of ram at 2.5
in./hr 24 hr after a similar rain event.
inadvertent overapplication, or soil sealing as a result of wastewater constituents or frost. The
requirements under this objective would probably be satisfied as part of the storm runoff
control system.
33
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OVERLAND FLOW SYSTEMS
Significantly, more extensive runoff control features are normally required for overland
flow than for irrigation systems, because overland flow systems are designed principally for
runoff of applied effluent rather than percolation. Typically, 40 to 80 percent of the applied
effluent runs off. The remainder is lost to percolation and evapotranspiration. In most cases,
the runoff is collected in ditches at the toe of each terrace and then conveyed by open
channel or gravity pipe to a discharge point, where it is monitored and, in some cases,
disinfected. Discharge may be to surface waters, to reuse facilities, or sometimes to additional
treatment facilities such as infiltration-percolation.
Storm runoff presents some special problems. Under conditions of light precipitation (on
the order of 0.05 to 0.10 in./hr), most overland flow systems can be operated as usual.
Although there is little documentation of the fact, the quality of runoff from greater amounts
of precipitation should improve as a result of dilution, provided erosion is not caused. For the
overland flow system at Paris, Texas, rainfall events of 0.1 to 2.0 inches increasingly reduced
from normal levels the effluent conductivity in the runoff.22 (Effluent conductivity was the
only constituent recorded under these conditions.) Pathogenic organisms in the runoff should
not generally cause serious problems if the effluent is disinfected before application, as they
do not normally regrow in the field.
34
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Chapter VIII
PUBLIC HEALTH CONSIDERATIONS
Public health aspects are related to the following:
• Pathogenic bacteria and viruses present in municipal wastewater and their possible
transmission to higher biological forms, including man
• Chemicals that may reach the groundwater and pose dangers to health if ingested
• Crop quality when irrigated with wastewater effluents
• Propagation of insects that could be vectors in disease transmission
PATHOGENS
The survival of pathogenic bacteria and viruses in sprayed aerosol droplets, on and in the
soil, and the effects on workers have received considerable attention. It is important to realize
that any connection between pathogens applied to land through wastewater and the
contraction of disease in animals or man would require a long and complex path of
epidemiological events. Nevertheless, questions have been raised, concern exists, and
precautions should be taken in dealing with possible disease transmission.
Aerosols
Effluents applied by sprinklers will produce a mist, often referred to as drift, that may
be transported by wind currents. Mist droplets that are extremely small in both dimension
and mass are referred to as aerosols. Aerosols are tiny airborne colloidal-like droplets of liquid
(0.01 to 50 microns in diameter). Aerosols generated in connection with inadequately
disinfected wastewater contain active bacteria and viruses. Sorber23 found that the median
size of viable particles collected downwind from effluent spray was 5 microns. This is
important because this size of particle is subject to inhalation by humans. He also reported
that aerosolization occurred for only about 0.3 percent of the wastewater being sprinkled, as
determined by fluorescein tracer tests.
Infectivity of a biological aerosol is dependent on the depth of respiratory tract
penetration. Particles of the 2- to 5-micron size range are primarily captured in the upper
respiratory tract and may ultimately pass to the digestive tract. Sizes in the 1- to 2-micron
35
-------
size may be inhaled into the lungs. Infectivity is most probable in the latter case. Therefore,
particle size distribution is an important factor in evaluating aerosol-borne pathogens.
The travel of aerosols and the effect of chlorination on bacterial levels in aerosols was
also studied by Sorber.23 Unchlorinated trickling filter effluent was discharged at 100 psi
through a 1/2-inch diameter Rainbird sprinkler. The study was performed in Arizona. With
wind velocities of 5.7 mph, viable coliforms were found at a distance of 500 feet. The effect
of wind is significant in aerosol production; however, Sorber found that the concentration of
coliforms in aerosols downwind from the sprinkler increased for lower wind velocities. In fact,
under stable atmospheric conditions (low wind velocities and night time), Sorber estimated
that a travel distance of over 1 mile would be necessary to reduce the concentration of viable
organisms to background levels. Sorber therefore concluded that relying on buffer zones alone
to reduce aerosol activity is impractical.
When the secondary effluent in this study was chlorinated, only one viable coliform per
cubic meter of air was found in the downwind samples. Chlorine contact time was longer
than normal (45 minutes), and the total chlorine residual was 0.8 mg/1. This disinfection
procedure resulted in a total concentration of 220 viable particles per milliliter in the
wastewater before sprinkling. Sorber concluded that the most important factors bearing on the
downwind aerosol concentrations observed are the concentration of organisms sprayed and the
atmospheric stability.2 3
In other studies on aerosol particles, it was found that as the relative humidity decreased
and air temperature increased, the death rate of bacteria increased.24 Sorber25 indicated that
a 50-micron water droplet will evaporate in 0.31 second in air, with 50-percent relative
humidity and a temperature of 22 degrees Centigrade. Thus, dessication is a major factor in
bacterial die-off. Dessication effects are limited by the number of aerosol-size particles in the
effluent before sprinkling.
Finally, although much remains to be determined in investigating aerosols and their
potential infectivity, some safeguards can be established. Among these are disinfection,
sprinklers that spray horizontally or downward with low nozzle pressure, and adequate buffer
zones. Although buffer zones may be relatively ineffective in reducing the strength of aerosols,
they are effective in containing the drift of spray mist which is aesthetically unpleasing!
Buffer zones that have been required by some states range from 50 feet to 1/4 mile around a
site.26 Low-trajectory nozzles and screens of trees and shrubs can be used to limit mist travel.
The travelling rig sprinklers designed for Muskegon, Michigan, have been modified to direct
the spray trajectory downward. Studies of aerosol drift are being planned for the Muskegon
operation.2 7
Survival in Soil and on Vegetation
The survival time of pathogenic organisms in the soil can vary from days to months,
depending on the soil moisture, soil temperature, and type of organism Sepp26 and Dunlop28
have prepared extensive tabulations of survival times of various organisms in soil, in water,
and on vegetation. A portion of these tabulations is shown in table VIII-1 It should hp noted
TOtel^er"'™1 UmeS reP°rted 8Ie "0t fr°m irriga,i0n SyStOTS applyins ,reated municipal
36
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Table V111 -1 —Survival times of organisms2 6 >2 8
Organism
Medium
Type of
application
Survival
time
Ascaris ova
Soil
Vegetables
Sewage
ACa
Up to 7 years
27-35 days
B. Typhosa
Soil
Vegetables
AC
AC
29-70 days
31 days
Cholera vibrios
Spinach, lettuce
Nonacid vegetables
AC
AC
22-29 days
2 days
Coliform
Grass
Tomatoes
Sewage
Sewage
14 days
35 days
Endamoeba histolytica
Vegetables
Soil
AC
AC
3 days
8 days
Hookworm larvae
Soil
Infected feces
6 weeks
Leptospira
Soil
AC
15-43 days
Polio virus
Polluted water
—
20 days
Salmonella typhi
Radishes
Soil
Infected feces
Infected feces
53 days
74 days
Shigella
Tomatoes
AC
2-7 days
Tubercle bacilli
Soil
AC
6 months
Typhoid bacilli
Soil
AC
7-40 days
aAC—Artificial contamination.
Survival time of organisms outside their natural habitat depends on the initial
concentration, humidity, amount of sunlight, type of soil, type of organism, and type of
medium. In relation to survival of coliform organisms, some bacteria do survive for a longer
time in soil. The survival of viruses in soil is essentially unexplored.2 7
EFFECTS ON WORKERS
The effects of working around and handling wastewater on land application sites are
ra. . , ®»ects 01 w
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histories with conclusions that, if handled with care, sewage effluent is not hazardous to the
personnel.
Work referenced in Sorber's paper25 indicates that spraying of chlorinated effluent for
landscape watering resulted in approximately 1.5 times the number of viable biological
aerosols emitted by a trickling filter. Napolitano et al.30 concluded that activated sludge
plants yield approximately 10 times as many coliform-bearing aerosol particles as do trickling
filter plants. In order to put numbers into perspective, a comparison was made between
results obtained by Sorber versus those obtained by Napolitano, insofar as the data can be
considered compatible. With the samplers located 150 feet from the source of aerosols, Sorber
reported a mean of 6 viable coliforms per cubic meter of air sampled from a chlorinated and
sprinkled trickling filter plant effluent, whereas Napolitano reported a range of 7 to 380
coliform colonies per cubic meter of air sampled downwind from an activated sludge aeration
tank. He also reported a range of 7 to 140 colonies per cubic meter of air sampled downwind
from a trickling filter plant. Of course, the relative humidity, wind velocity, and temperature
were different for the various tests. Both investigators reported that the median viable particle
size was about 5 microns; therefore, the particles are equally subject to inhalation by humans.
In short, no specific number can be given for quantifying health hazards at either land
application or conventional treatment plants. Dixon and McCabe31 cited several known cases
of illness associated with conventional wastewater treatment plant activities and found no
conclusive evidence that the overall health risks are higher for operators than for the public at
large.
GROUNDWATER QUALITY
The proposed EPA regulations on interim primary drinking water standards are listed in
table VIII-2. Both nitrates and total dissolved solids can present health hazards if they are
present in high concentrations in groundwater that is used as a water supply. Because nitrate
has been demonstrated to be the causative agent of methemoglobinemia in children, its
concentration in drinking water is limited in the standards to 10 mg/1 as nitrate nitrogen. A
total dissolved solids limitation of 750 mg/1 in drinking water is recommended by Sorber
because high values of total dissolved solids can be harmful to people with cardiac, viral, or
circulatory diseases.27
Solids contained in wastewater effluents will be filtered from the water in the upper
layer of soil. Inorganic chemical constituents, such as trace metals, are usually removed from
the percolating water by adsorption or chemical precipitation within the first few feet of soil.
However, the concentrations of trace elements are usually below those limits set forth in the
drinking water standards before application. Trace organics are also usually below the
established limits before application. If there is any possibility that some particular constituent
is abnormally high, at least two analyses should be made before recommending the design
parameters. Bacterial removal from effluents passing through fine soils is quite complete.
However, this may not be true in coarse sandy or gravelly strata that are used for high-rate
infiltration systems. Fractured rock or limestone cavities may also provide a passage for
bacteria that can travel several hundred feet from the point of application. Both of these
latter cases deserve special consideration by the designer.
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Table VII1-2.-EPA proposed regulations on interim
primary drinking water standards, 197532
Constituent or characteristic
Value
Reason for standard
Physical
Turbidity, units
1a
Aesthetic
Chemical, mg/l
Arsenic
0.05
Toxic
Barium
1.0
Toxic
Cadmium
0.01
Toxic
Carbon chloroform extract
0.7
Toxic
Chromium, hexavalent
0.05
Toxic
Cyanide
0.2
Toxic
Fluoride
1.4-2.4&
Toxic
Lead
0.05
Toxic
Mercury
0.002
Toxic
Nitrates as N
10
Toxic
Selenium
0.01
Toxic
Silver
0.05
Cosmetic
Bacteriological
1
Total coliform, per 100 ml
Disease
Pesticides, mg/l
Chlordane
0.003
Toxic
Endrin
0.0002
Toxic
Heptachlor
0.0001
Toxic
Heptachlor epoxide
0.0001
Toxic
Lindane
0.004
Toxic
Methoxychlor
0.1
Toxic
Toxaphene
0.005
Toxic
2,4-D
0.1
Toxic
2,4,5-TP
0.01
Toxic
aFive mg/l may be substituted if it can be demonstrated that it does not interfere with disinfection.
^Dependent upon temperature; higher limits for lower temperatures.
In summary, the most common public health concerns for land treatment systems are
nitrogen and high total dissolved solids contamination of groundwater aquifers used for water
supply.
39
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CROP QUALITY
Few data exist on the quality of crops grown on wastewater effluents relative to those
obtaining water and nutrients from other sources. Data from crops grown on sludge are not
applicable because trace elements are several times higher in sludges than in effluents.
Data presented in table VII1-3 are for grasses at the land application site in Melbourne,
Australia.33 The authors collected green forage samples from grasses on nonirrigated (control)
areas and in areas irrigated for 60 years with sedimented wastewater. All constituents in the
plants, except nickel, are below the suggested tolerance limits proposed by Melsted.34 The
authors concluded that since nickel is poorly absorbed from ordinary diets and is relatively
nontoxic, it would not pose a health problem to animals.35
A second example is presented in table VIII-4 which presents tissue analysis from leaves
of corn grown on land that has been irrigated by effluent for 5 years. All values measured
were below suggested tolerance levels except for cadmium. The data indicate values below 5
but do not indicate how far below 5.
Table VI11-3.—Crop quality at Melbourne, Australia,
compared to suggested tolerance levels for heavy metals
Constituent
Grasses at Melbourne
Suggested
tolerance
levels,
ppm
Control
sample,
ppm
Wastewater
irrigated,
ppm
Cadmium
0.77
0.89
3
Cobalt
<0.64
0.64
5
Copper
6.5
12
150
Jron
970
361
75Q
Manganese
149
49
300
Nickel
2.7
4.9
3
Lead
<2.5
<2.5
10
Zinc
50
63
300
Sources: Melbourne samples;33 suggested tolerance levels by
Melsted.34
40
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Table VII1-4.—Accumulation of trace elements
in corn plants grown on soil irrigated for 5 years with effluent36
Sample
1
2
3
4
Suggested
tolerance
level3
Toxic
level*3
Barium
13
14
10
15
200
—
Boron
13
16
11
11
150
>75
Cadmium
<5
<5
<5
<5
3
—
Cobalt
<1
<1
<1
<1
5
—
Copper
4.5
4.6
4.5
4.0
150
>20
Chromium
<1
<1
<1
<1
2
-
Lead
<1
<1
<1
<1
10
—
Manganese
16
14
11
15
300
—
Molybdenum
2.1
1.8
1.9
1.7
3
—
Nickel
1.6
1.0
1.0
1.0
3
>50
Silver
0.30
0.26
0.28
0.24
-
—
Vanadium
<1
<1
<1
<1
2
>10
Zinc
33
00
CM
22
16
300
>200
Note: All values expressed in parts per million (ppml.
aSource: Soil-Plant Relationships, S. W. Melsted .34
bSource: Fate and Effects of Trace Elements in Sewage Sludge When Applied to Agricultural
Lands, A. L. Page37
INSECT PROPAGATION
Propagation of mosquitoes and flies poses a health hazard as well as a nuisance
condition. Mosquitoes are known vectors of several diseases.27 In the Pennsylvania State
study, mosquitoes increased in population mainly because of the wetter environment and the
availability of standing puddles for breeding.7
41
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At several California industrial land application sites, the major adverse environmental
effect has been the propagation of mosquitoes. At Hunt-Wesson in Davis, California, the
problem was anticipated, and mosquito fish or gambusia were planted in the runoff collection
sump. Where vegetation is grown, ample drying time should be scheduled in the operation to
prevent massive mosquito propagation.
42
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Chapter IX
MONITORING
As with any wastewater treatment facility, a comprehensive monitoring program will be
required to ensure that proper renovation of wastewater is occurring and that environmental
degradation is not occurring. Some monitoring requirements are similar to those required for
conventional systems. One example of this is the monitoring of water quality at various stages
in the process prior to application. Other monitoring requirements are generally unique to
land application systems, and these are the only ones discussed here. They are presented in
three categories:
• Renovated water
• Vegetation
• Soils
RENOVATED WATER
The monitoring of renovated water may be required for either groundwater or recovered
water or both. Recovered water may include runoff from overland flow or water from
recovery wells or underdrains.
Groundwater
Water quality parameters that should be analyzed in the groundwater include:
• Those normally required for drinking water supplies
• Those that may be required for state or local agencies
• Those necessary for system control
Generally, nitrate nitrogen is the parameter that must be most closely observed. To assess
the overall impact of the system, changes in groundwater quality can be compared with the
quality of background wells. An example of an operational and compliance monitoring
schedule for an irrigation system is given in table IX-1, showing the constituents to be
monitored and the frequency of sampling.
43
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Table IX-1 —Example of operational
and compliance monitoring schedule for an irrigation system
Sampling frequency at various points
Parameter3
Applied
effluent
Onsite
wells
(3 points)
Background
well
(1 point)
Perimeter
wells
(5 points)
Adjacent
lake
(1 point)
BOD
D
—
—
—
Q
CODb
Mc
Q
Q
Q
Q
Chlorine residual
2D
—
—
—
-
Coliform, fecal
M
Q
Q
Q
Q
Coliform, total
D
Q
Q
Q
Q
Flow
Cd
—
—
—
—
Nitrogene
Mc
Q
Q
Q
Q
pH
2Dd
Qd
Qd
Qd
Qd
Phosphorus
Mc
Q
Q
Q
Q
Suspended solids
D
—
—
—
—
Static water level
—
Md
Md
Md
—
Note: D = One sample or measurement per day
Q = One sample or measurement per quarter
M = One sample or measurement per month
2D= Two samples or measurements per day
C = Continuous measurement and recording
¦If filtered samples of raw wastewater demonstrate the concentration of a particular health-significant
parameter (not given abovel to be in excess of the permissible limit for drinking water sources that
parameter will be included in this schedule.
bMay also use TOC to establish a long-term correlation with BOD.
cDenotes samples to be 24-hour composites. All others are grab samples.
''Field measurement.
®Total nitrogen for effluent; nitrate-nitrogen for groundwater.
44
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In addition to changes in quality, changes in groundwater levels should also be
monitored. The effect of increased levels should be assessed with respect to changes in the
hydrogeologic conditions of the area. Changes in groundwater movement and the appearance
of seeps and perched water tables should be noted, and system modifications, such as
underdraining or reducing application rates in the area, should be undertaken.
Recovered Water
Monitoring requirements for recovered water will depend on the disposition of that
water. If the water is to be discharged, the parameters to be analyzed must include those
required by the NPDES permit. If the water is to be reused, analysis of additional parameters
may be required by cognizant public health agencies.
Monitoring of the flow rate of recovered water may be important for system control and
may also be required as a result of water rights considerations.
VEGETATION
When vegetation is grown as a part of the treatment system, monitoring may be required
to optimize growth and yield. Conventional farm management techniques would generally
apply; however, in many cases, special factors must be considered because of the normally
higher hydraulic loading rates.
For some systems, a more detailed vegetation monitoring program may be required in
which the uptake of certain elements is analyzed. Melsted34 suggests levels for micronutrients
in plants as well as methods of sampling. This analysis would generally be required only in
cases where potentially toxic constituents are present in the wastewater in abnormally high
concentrations.
SOILS
In almost all cases, the application of wastewater to the land will result in some changes
in the characteristics of the soil. Consequently, some sort of soil monitoring program will be
necessary for most systems, with at least annual sampling recommended. Characteristics that
are commonly of interest include:
• Salinity
• Levels of various elements
• pH
• Cation exchange capacity
45
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Salinity
The salinity of the soil, as measured by electrical conductivity, is of extreme concern in
many arid portions of the country. High levels of salinity are injurious to most plants in
various degrees.9 Remedial action, such as leaching or underdrainage, may be required.
Levels of Various Elements
One area of major concern in many cases is the sodium adsorption ratio. High values
may adversely affect the permeability of some soils, as discussed previously.8'9 Levels of
nitrogen, phosphorus, potassium, magnesium, and calcium are also important.
Levels of boron and a number of metals, such as cadmium, may also be of concern in
many cases because of their effects on crop growth and crop marketability, respectively. Many
such elements are micronutrients that are required for the proper growth of plants. At high
levels, however, they may be toxic to plants or animals in the food chain, as well as to
humans.
pH
The optimum soil pH range for retention of many wastewater constituents is the neutral
range (pH 6-7). Because wastewater usually has a neutral pH, fluctuations in soil pH are
uncommon but do sometimes occur. Should decreases in soil pH occur, they can be corrected
by the addition of lime.
Cation Exchange Capacity
The cation exchange capacity is an important parameter because of its role in the
chemical renovation of the water. The cation exchange sites may be occupied by ammonium,
calcium, magnesium, potassium, sodium, and hydrogen ions. Competition for the available sites
depends on the relative concentrations of these ions in the percolating water and in the soil,
and this competition is reflected in the quality of the renovated water. The change in percent
of available sites occupied by each cation is the important trend to monitor. If one cation,
such as sodium, builds up excessively, remedial measures, such as adding amendments, should
be considered.
46
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REFERENCES
1 R. D. Johnson, "Land Treatment of Wastewater," The Military Engineer 65 No 428
1973, pp. 375-378. '
2C. E. Pound and R. W. Crites, Wastewater Treatment and Reuse by Land Application,
Volumes I and II, Environmental Protection Agency, Office of Research and Development
EPA-660/2-73-006 a, b, August 1973.
3R. E. Thomas, et al., Feasibility of Overland Flow for Treatment of Raw Domestic
Wastewater, Environmental Protection Agency, Office of Research and Development
EPA-660/2-74-087, July 1974.
4C. E. Pound and R. W. Crites, "Characteristics of Municipal Effluents," Proceedings of
the Joint Conference on Recycling Municipal Sludges and Effluents on Land, Champaign,
University of Illinois, July 1973, pp. 49-62.
s W. A. Cowlishaw, "Update on Muskegon County, Michigan, Land Treatment System,"
ASCE Annual and National Environmental Engineering Convention, Kansas City, Missouri,
October 1974.
6T. G. Bahr, et al., Wastewater Use in the Production of Food and Fiber—Proceedings,
The Michigan State University Water Quality Management Program, EPA-660/2-74-041, June
1974.
7L. T. Kardos, et al., Renovation of Secondary Effluent for Reuse as a Water Resource,
Environmental Protection Agency, Office of Research and Development, EPA-660/2-74-016,
February 1974.
8 "Diagnosis and Improvement of Saline and Alkali Soils," Agriculture Handbook No. 60,
U.S. Department of Agriculture, U.S. Salinity Laboratory, 1954.
9 Evaluation of Land Application Systems, Environmental Protection Agency, Office of
Water Program Operations, EPA-430/9-75-001, March 1975.
10R. S. Ayers, "Water Quality Criteria for Agriculture," University of California-
Committee of Consultants, California Water Resources Control Board, April 1973.
11S. C. Reed, et al., "Pretreatment Requirements for Land Application of Wastewaters,"
presented at the Second ASCE National Conference on Environmental Research, Development,
and Design, University of Florida, July 20-23, 1975.
,2C. H. Pair (ed.), Sprinkler Irrigation, 3rd edition and supplement, Washington, D.C.,
Sprinkler Irrigation Association, 1969, 1973.
47
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13 "Sprinkler Irrigation," SCS National Engineering Handbook, Section 15, Chapter 11,
U.S. Department of Agriculture, Soil Conservation Service, July 1968.
14 "A Guide to Planning and Designing Effluent Irrigation Disposal Systems in Missouri,"
University of Missouri Extension Division, March 1973.
1SK. W. Flach, "Land Resources," Proceedings of the Joint Conference on Recycling
Municipal Sludges and Effluents on Land, Champaign, University of Illinois, July 1973, pp.
113-120.
16D. M. Whiting, Use of Climatic Data in Design of Soil Treatment Systems,
Environmental Protection Agency, Office of Research and Development, EPA-660/2-75-018,
July 1975.
17W. Viessman, Jr., T. E. Harbaugh, and J. W. Knapp, Introduction to Hydrology, Intext
Educational Publishers: New York, 1972.
18V. J. Kilmer, et al., "Nutrient Losses from Fertilized Grassed Watersheds in Western
North Carolina," Jour, of Environmental Quality, 3, No. 3, 1974, pp. 214-219.
19S. D. Klausner, et al., "Surface Runoff Losses of Soluble Nitrogen and Phosphorus
Under Two Systems of Soil Management," Jour, of Environmental Quality, 3, No. 1, 1974,
pp. 42-46.
20K. H. Nicholls and H. R. MacCrimmon, "Nutrients in Subsurface and Runoff Waters of
the Holland Marsh, Ontario," Jour of Environmental Quality, 3, No. 1, 1974, pp. 31-35.
21D. R. Timmons, R. E. Burwell, and R. F. Holt, "Nitrogen and Phosphorus Losses in
Surface Runoff from Agricultural Land as Influenced by Placement of Broadcast Fertilizer,"
Water Resources Research, Vol. 9, No. 3, June 1973, p. 658.
22 C. W. Thornthwaite Associates, "An Evaluation of Cannery Waste Disposal by Overland
Flow Spray Irrigation," Publications in Climatology, 22, No. 2, September 1969.
23C. A. Sorber, et al., "Bacterial Aerosols Created by Spray Irrigation of Wastewater,"
1975 Sprinkler Irrigation Association Technical Conference, Atlanta, Georgia, February 1975..
24C. P. C. Poon, "Viability of Long Storaged Airborne Bacterial Aerosols," ASCE San
Engr. Div., 94, No. SA 6, 1968, pp. 1136-1146.
25C. A. Sorber and K. J. Guter, "Health and Hygiene Aspects of Spray Irrigation,"
American Journal of Public Health, 65, No. 1, 1975, pp. 47-52.
26E. Sepp, "The Use of Sewage for Irrigation-A Literature Review," Bureau of Sanitary
Engineering, California State Department of Public Health, Berkeley, 1971.
27C. A. Sorber, "Protection of Public Health," Proceedings of the Conference on Land
Disposal of Municipal Effluents and Sludges, New Brunswick, Rutgers University, March 12-13
1973, pp. 201-209.
28S. G. Dunlop, "Survival of Pathogens and Related Disease Hazards," Proceedings of the
Symposium on Municipal Sewage Effluent for Irrigation, Louisiana Polytechnic Institution
July 30, 1968.
48
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29M. A. Benarde, "Land Disposal and Sewage Effluent: Appraisal of Health Effects of
Pathogenic Organisms," Jour. AWWA, 65, No. 6, 1973, pp. 432-440.
30P. J. Napolitano and D. R. Rowe, "Microbial Content of Air Near Sewage Treatment
Plants," Water and Sewage Works, December 1966, pp. 480-488.
31 Fritz R. Dixon and Leland J. McCable, "Health Aspects of Wastewater Treatment,"
JWPCF, Vol. 36, No. 8, August 1964, pp. 984-989.
3 2 "Proposed Environmental Protection Agency Regulations on Interim Primary Drinking
Water Standards," Environmental Protection Agency, 40 CFR 141, March 10, 1975.
33R. D. Johnson, et al., "Selected Chemical Characteristics of Soils, Forages, and
Drainage Water from the Sewage Farm Serving Melbourne, Australia," Prepared for the
Department of the Army, Corps of Engineers, January 1974.
34S. W. Melsted, "Soil-Plant Relationships (Some Practical Considerations in Waste
Management)," Proceedings of the Joint Conference on Recycling Municipal Sludges and
Effluents on Land, Champaign, University of Illinois, July 1973, pp. 121-128.
35E. J. Underwood, Trace Elements in Human and Animal Nutrition, Academic Press:
New York, 1971.
36L. M. Harwood and E. W. Holtz, "Progress Report of Reclamation of Waste Water
Forage Crop Trials," Sonoma County, Agricultural Extension, University of California, 1974.
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Agricultural Lands, Environmental Protection Agency, Office of Research and Development,
EPA-670/2-74-005, January 1974.
49
U. S. GOVERNMENT PUNTING OFFICE: 1977-757-056/6412 Region No. 5-11
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