CJ
600R79103
5533
LAND TREATMENT OF WASTEWATER
SLOW RATE IRRIGATION METHODS
Prepared by
Daniel J. Hinrichs
Gordon L. Gulp
Culp/Wesner/Culp
El Dorado Hills, California
Prepared for
Environmental Research Information Center
Seminar
Land Treatment of Municipal Wastewater Effluents
June 1979
ENVIRONMENTAL RESEARCH INFORMATION CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
cu-
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CONTENTS
Slow Rate System Description 1
Introduction 1
Treatment Requirements 2
Objectives and Degree of Treatment 2
Crop Selection 3
Optimizing Crop Yields 4
Irrigation Methods 6
Silviculture 12
Application Rates 13
Costs 14
Design Examples I7
Arid Climate 17
Humid Climate 28
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FIGURES
Number Page
1 Various methods of applying irrigation water to
field crops 10
2 Irrigation area with buffer 23
3 Diagram for classification of irrigation waters 27
11
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TABLES
Number Paqe
1 Treatment Requirements for Land Application,
California Department of Health Services 3
2 Slow Rate System Treatment Results 4
3 Crop Comparisons for Use in Land Treatment Systems 5
4 Costs for Various Methods of Irrigation 15
5 Years of Use for Depreciation Purposes 16
6 Temperature and Precipitation Data 20
7 Monthly Consumptive Use, inches 21
8 Minimum Delivered to Irrigation System 21
9 Effluent Flow 22
10 Nozzle Discharge, gpm 25
11 Nitrogen Balance 26
12 Sprinkler Selection for Traveling Gun Sprinklers System . . 29
13 Rate of Travel for Traveling Big Guns for Different
Nozzle Sizes and Application Rates 31
14 Time Required to Irrigate One Lane 32
111
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INTRODUCTION
There are three classifications of land treatment systems commonly
used. They are slow rate systems, high rate systems (infiltration-
percolation) and overland flow systems. Slow rate systems are conven-
tional irrigation systems where a crop is grown. In most instances,
sale of this crop partially offsets treatment costs. Of the three
systems, slow rate systems are the most conducive to agricultural
production.
The potential advantages of this system are expansion of existing
agriculture, improved production of existing farmland, reduction in
fertilizer used by farmers, replacement of a water supply that can be
diverted to other uses, and excellent treatment of wastewater.
The disadvantages are primarily in administering the program. If
the authority chooses to operate its own system (e.g. Muskegon approach),
then a total farming operation must be provided. This includes hiring
an agronomist or agricultural engineer, farm equipment operators, and
irrigation operators. There is also a major investment in land and
eguipment. If the authority chooses to contract with a local farmer
or group of farmers, there are long term contracts to work out. These
disadvantages should rarely prevent project implementation.
Sources of information for the design of slow rate systems are avail-
able in almost every area of the country. Almost all local counties have
farm advisors and local offices of the U. S. Department of Agriculture
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Soil Conservation Service. Both sources have local crop information, soils
information, and irrigation usage and methodology data. Nearby University
or College extension offices usually have useful data on crops and irriga-
tion information.
TREATMENT REQUIREMENTS
Requirements for wastewater treatment prior to application to the land
by slow rate systems are variable depending on the local regulatory agency
requirements. Treatment requirements should be based primarily on the type
of crops grown. Crops grown for animal consumption require less treatment
than crops consumed by humans. If irrigation water does not contact, fruit
or vegetables, then treatment requirements are less stringent than systems
where water contacts the fruit or vegetables. For example, if an orchard
is spray irrigated the water may come into direct contact with the fruit.
If the orchard is irrigated by a surface flooding system, then irrigation
water will not come into contact with the fruit. Obviously, the latter
method of irrigation requires less stringent treatment standards than the
former. The State of California Department of Health Services has devel-
oped regulations that consider the use of the crop irrigated and the method
or irrigation used. Table 1 contains a summary of requirements taken from
these regulations.
OBJECTIVES AND DEGREE OF TREATMENT
Slow rate systems are capable of providing a very high degree of
treatment providing very high levels of removal of BOD, suspended solids,
and phosphorus under a wide range of soil and crop conditions. However,
the removal of nitrogen can vary significantly depending on crop manage-,
ment. Assuming runoff water is collected and recycled, the constituent
that is of concern is nitrate nitrogen. This is correct for domestic
wastewater or domestic combined with industrial wastewater assuming
industries have met EPA pretreatment standards. Systems with unusual chem-
ical or toxic elements must be evaluated on a case by case basis. The
concern for nitrate nitrogen is less of a problem with slow rate systems
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TABLE 1. TREATMENT REQUIREMENTS FOR LAND APPLICATION,
CALIFORNIA DEPARTMENT OF HEALTH SERVICES
Use
Irrigation methods
Requirement
Food crops
Food crops except
orchard & vineyards
Orchards & vineyards
Fodder, fiber and
seed
Pasture for milking
animals
Landscape irrigation
Spray
Surface
Surface
Surface or spray
Surface or spray
Surface or spray
Disinfected, Oxidized,
Coagulated, Clarified,
Filtered, Coliform
<_ 2.2/100ml
Disinfected, Oxidized
Coliform <_ 2.2/100ml
Primary Effluent
(assuming no contact
with fruit)
Primary Effluent
Disinfected, Oxidized
Coliform <_ 23/100ml
Disinfected, Oxidized
Coliform < 23/100ml
than high rate systems since crop harvesting provides a nitrogen removal
mechanism. Nitrate concentrations are a concern with systems where under-
lying groundwater systems are used for domestic water supply. Water applied
at agronomic rates will normally not be a hazard to groundwater. Water
applied at rates in excess of crop needs may cause an undesirable increase
in nitrate concentrations. The design example to be presented later will
show a nitrate balance computation. Typical treatment results are presented
in Table 2 for a system where the crop is managed for nitrogen removal.
CROP SELECTION
The choice of crop depends on several factors related to the local
\
area. Generally, a review of existing agricultural operations will de-
termine which crops will be successful for the local climate, soils, and
t
jf
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TABLE 2. SLOW RATE SYSTEM TREATMENT RESULTS
Parameter Applied water Leachate at 5 feet1
below surface
BOD5, mg/1
Suspended Solids
Nitrogen, total,
Ammonia,
Nitrate,
Organic ,
, mg/1
mg/1 as
mg/1 as
mg/1 as
mg/1 as
N
N
N
N
35
50
30
8
17
5
<2
<1
<0.
3
0
5
Phosphorus, mg/1 13
U.S. E.P.A., Process Design Manual For Land Application of Wastewater.
market conditions. The first step in crop selection is determining whether
the crop yields are to be optimized to maximize revenues or if the crop is
to be harvested and disposed (e.g. grass clippings). If a cash crop is de-
sired, then the selection becomes a process of determining trade-offs between
high revenue producers (e.g. corn) or low revenue producers but high water
and nitrogen users (e.g. Reed Canary grass). Table 3 provides an indication
of these trade-offs. These are general rules and will vary depending on
local markets.
The field crops are highly variable as water and nitrogen users and are
generally marketable. The orchard crops are good water users and marketable
but are low nitrogen users. The forage crops exceed the others in water con-
sumption and nitrogen use but are highly variable as revenue producers. The
legumes are usually in high demand but some of the coarse grasses such as
Reed Canary grass and bromegrass are not palatable for ruminants.
OPTIMIZING CROP YIELDS
Optimization of crop yields can be a very complex process. For this
discussion, crop optimisation is considered in the context of designing a
system to maximize water disposal or to maximize crop revenues. Most crops
will be damaged or yields decreased by addition of excessive water. A system
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TABLE 3. CROP COMPARISONS FOR USE IN LAND TREATMENT SYSTEMS
Potential as
revenue producer-
Potential as
9
water user
Potential as
nitrogen user-^
Field Crops
Barley
Corn , grain
Corn, silage
Cotton (lint)
Grain , sorghum
Oats
Rice
Safflower
Soybeans
Wheat
Orchards
Almonds
Apples
Grapes
Oranges
Peaches
• Pears
Prunes
Forage Crops
Reed Canary grass
Alfalfa
Brome grass
Clover
Orchard grass
Sorghum-Sudan
Timothy
Vetch
Turf Crops
Bent grass
Bermuda grass
marginal
excellent
excellent
good
good
marginal
excellent
excellent
good
good
excellent
excellent
excellent
excellent
excellent
excellent
excellent
poor
excellent
poor
excellent
good
good
marginal
marginal
excellent
good
moderate
moderate
moderate
moderate
low
moderate
high
moderate
moderate
moderate
low
moderate
moderate-high
moderate
moderate
moderate
moderate
high
high
high
high
high
high
high
high
excellent
excellent
good
good
excellent
excellent
excellent
marginal
marginal
excellent
L
good-excellent
good
excellent
marginal
marginal
marginal
poor
poor
poor
excellent
good-excellent
good
good-excellent^
good-excellent^
excellent
good
excellent
excellent
excellent
Potential as revenue producers is a judgmental estimate based on nation-
wide demand. Local market differences may be substantial enough to
change a marginal revenue producer to a good or excellent revenue pro-
ducer and vice versa. Some of the forages are extremely difficult to
market due to their coarse nature and poor feed values.
?
"Water user definitions based on seasonal crop consumptive-use in relatior
to alfalfa.
High 0.8 to 1.0
Moderate 0.6 to 0.79
Low <0.6
Nitrogen user ratings -
Excellent >200 Ib N/ac
Good 150-200 Ib N/ac
Marginal 100-150 Ib N/ac
Poor <100 Ib N/ac
Source: Western Fertilizer Handbook
4
Depends on percentage of nitrogen that is fixed.
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may be operated such that, crop benefits are not sufficient enough to war-
rant close agricultural controls. In this case, the crop yields could
be sacrificed to maximize hydraulic loading and thus minimize land area
requirements. Crop removal would then be a means of nitrogen removal
only. A good example of this situation is growth of Reed Canary grass.
Reed Canary grass will tolerate extremely high amounts of water and will
remove approximately 325 Ib nitrogen/ac in a single growing season. How- "
ever, it is a very poor animal feed. Therefore, this system would be de-
signed as a water disposal system.
Conversely, corn yield will drop substantially if irrigation rates are
too high. Corn is a good revenue producer so excessive irrigation rates
should be avoided with systems designed and operated to prevent damage to
the crop.
IRRIGATION METHODS
The various irrigation methods can be classified as surface or spray.
Spray irrigation systems can be subdivided into mechanical move, hand move,
and solid set systems. Surface systems can be categorized as ridge and fur-
row, border check, contour check or ditch, and corrugation and basin flood-
ing. Each system is described below with advantages and disadvantages
discussed.
Mechanical move systems have become popular in recent years becciuse they
are a compromise between solid set systems and surface systems in terms of
labor and capital cost. The compromise is that surface systems require the
most labor of the three out require the least capital investment. Conversely,
^
solid set systems require the least labor but fire the highest in cost to con-
!'
struct. The mechanical nove systems are intermediate in terms of labor and
construction (purchase) cost. *
i
The most common mechanical move systems are:* '
• Center Pivot
• Moving Gun
*Descriptions from Irrigation Association "Wastewater Resource Manual".
6
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• Wheel Line
Center Pivot are systems in which the lateral is carried on self-
propelled towers and rotates about a permanent center anchor point at which
the water and power is introduced.
The lateral pipe is commonly 6, 6-5/8 or 8-in. diameter steel. Stand-
ard machines fitting in quarter sections are about 1,300 ft long and irri-
gate 130 acres. Towers are usually water or electrically powered. Water
powered systems are usually 13 tower with 96-ft cable-supported spans.
Electrically powered pivots are 8 to 10 towers with 126-ft standard spans
to 168-ft stretch spans. The most common structural arrangement is the bow
string truss with truss rods stabilized by "V" jacks. The main steel pipe
is the truss compression member.
A typical design with a system capacity of 1,000 gpm at a pivot pres-
sure of 75 psi would deposit 1.0 in. of water while making a revolution in
60 hrs. New systems have been developed utilizing lower pressures. This
results in decreased power needs and lower production of fine-spray aerosols.
Rotational speed can be varied to provide lighter or heavier applications.
Electrically driven machines can rotate faster than water-powered machines.
The bow string truss design will operate on more rugged terrain than the
cable-supported machines but results in a generally heavier machine which
may give trouble under soft field conditions.
Center pivots have enjoyed increasing popularity in recent years as an
economical way of achieving fully automatic irrigation. They were selected
for use on the pioneering Muskegon, Michigan wastewater project. In this
case, sprinklers were replaced by spray nozzles to reduce aerosol drift.
The major advantage of the center pivot system is that large volumes
of water can be applied to any crop. Labor requirements are lower than all
other 'systems. There are two disadvantages. Some soils cannot accept the
high application rates delivered by the center pivot machines. The other
disadvantage is the loss of area not covered by circles. This loss can be
eliminated by providing center pivots with cornering mechanisms which cover
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these lost areas. The additional cost for the cornering feature will often
be justified in terms of capital cost per acre irrigated but will be more
costly to operate and maintain. Exact costs are difficult to determine
since these systems are relatively new and little operating data are a\aila-
ble.
Moving Guns are designed to take advantage of a tough light-woiq^t h<_>;,L.
developement. The hose is available in 4 to 4-1/4-in. diameters and continu-
ous lengths of 660 ft. Other sizes and lengths are available but not com-
monly used. The hose will withstand system pressures over 100 psi and can
be pulled at full length and full of water. The traveler unit consists of
a trailer-mounted sprinkler and a water or gasoline engine-powered winch with
1,320 ft of cable.
The unit winches itself along a 1,300-ft roadway, pulling the hose be-
hind it. Sprinkler capacities vary from 300 to 650 gpm at operating pres-
sures of 70 to 100 psi. Spacing between lanes varies from 250 to 300 ft,
depending on sprinkler flow rate, wind, and uniformity considerations. Rate
of travel varies from about 1 to 4 ft per minute.
A typical system with lanes spaced 290 ft operating at 500 gpm and 2.0
ft per minute will cover 0.81 acres per hr and apply an average of 1.4 in.
Total area covered would be 8.8 acres in 11 hrs.
Moving guns are advantageous in rough terrain or in forested areas where
other mechanical move systems could not be used. The major disadvantages
are the high pressures required and the high production of aerosols. They
have been used by the Chicago Metropolitan Sanitary District to apply sludge
at Fulton County.
Vfoeel line or side wheel roll systems were developed primarily to re-
duce labor for hand-move systems (moving sprinklers is often an unpleasant
task, especially with effluent). Most wheel lines are propelled by a power
unit mounted on the sprinkler line. These systems do not move continuously
but intermittently; thus they are similar to a stationary system but are
moved mechanically between irrigation sets.
8
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There are two major advantages of wheel line systems. The first advan-
tage is that low applications can be developed for soils that are limited in
their water intake rate. Other mechanical move systems would apply water at
a rate which would result in runoff or ponding. The other advantage is that
the mechanism for moving does not require a power source other than water
pressure.
The main disadvantage is the limitation in application rates where high-
rate systems are desired. Wheel line systems also require more labor-than
the other mechanical move systems.
Permanent or solid set sprinklers, as previously mentioned, are extreme-
ly costly. The high capital cost is required for trenching and buried pipe-
line and the cost of providing more pipeline per acre than the movable systems.
For example, a hand move or wheel line system will require 1/7 to 1/10 as much
piping, depending on the irrigation interval chosen. Cost comparisons are
presented later in this report. They are advantageous in terms of saving
labor and can be used for systems where frost protection is desired.
Surface irrigation refers to a wide assortment of systems which depend
on gravity flow. There are minor exceptions to this requirement where high
volume low pressure pumps convey water to and through fields in concrete
pipe, gated aluminum pipe and thin walled large diameter plastic and rubber
hose. The final distribution to the crop would be through a flooded basin
or furrow so the system is still classified as surface irrigation. This is
contrasted to overhead irrigation where high pressure pumps supply water to
a wide range of irrigation systems which subsequently spray the water onto
the crop through rotating impact sprinklers or fixed nozzles. Surface irri-
gation methods are presently used on about 80% of the over 50 million irri-
gated areas in this country.
Figure 1 (Iraelsen & Hansen, 1962) serves to introduce the surface
irrigation methods to be discussed.
Usually, surface systems are not easily automated. As a result, they
are labor intensive. Recently, automated valves receiving signals from
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moisture sensors have been developed to reduce labor costs and provide
better control for reduction of runoff quantities.
Ridge and furrow Irrigation consists of constructing furrows on a grade
at lengths of from 100 to 1,500 ft. Depth and spacing depend on crop re-
quirements and the ability of the soil to distribute water laterally. Water
is introduced at the head end of the furrow and allowed to run until the
tail end of the furrow is adequately irrigated. This results in a non-
uniform application of water which can yield irrigation efficiencies as
poor as 25% in permeable soils. Furrow irrigation is well suited to row
crops, steeper terrain, and requires a minimum of land forming. Because of
the requirement of holding to grade, furrows network can get badly curved
and complicated on steeply breaking terrain. Gated pipe and ditches with
individual siphon tubes are commonly used to supply water to furrows.
Border Strip Irrigation consists of dividing fields into strips of
about 30 to 60 ft wide and lengths as dictated by the physical features
of the farm and soil conditions. The strips should be level across, sep-
arated by low levees and have a shallow slope downfield. Water is intro-
duced at the head of the border and advanced down the strip as a sheet.
Border irrigation requires fairly extensive land forming and is well suited
to alfalfa and small grains and other crops that do not lend themselves to
fun ow irrigation.
Contour check or contour ditches are almost identical but have differ-
ent applications. Contour check is used in areas where the crop or [ore-
pared soil is flooded for an extended period (e.g. rice). The water is
usually held to minimize currents and prevent erosion or damaqe to young
plants.
Contour ditches have the same appearance but are installed ir pasture
areas and represent a semi-controlled method of flood irrigation. With
this system, water advances as a sheet across the field as a reaction to
terrain.
Corrugations are essentially small furrows on grade with some flooding
between corrugations. It is well suited for close growing crops and'soils
11
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with low uptake rates.
Basins are essentially a variation of border irrigation with zero down-
field slope. It lends itself to flat fields and requires a substantial
amount of land forming. However, properly constructed and operated basins
can have good water application uniformity and efficiency. Relatively
large flows of water are introduced into the basins over a short period of
time to produce flooding to the desired depth.
In recent years a new type of irrigation system has been developed
which is drip irrigation. A modification of drip systems has also been de-
veloped which is trickle irrigation. These systems are popular in arid
areas because very high efficiencies can be attained. They are also advan-
tageous in terms of low energy consumption. These systems consist of
flexible plastic pipe with small nozzles (emitters). These systems are
usually not suitable for effluent irrigation because of the small openings
for the emitters and the resulting clogging problems. Theses systems even
require fine screening of fresh water.
SILVICULTURE
With silviculture, the growing of trees, annual removal (harvesting) of
organic material containing nitrogen and phosphorus is not accomplished.
These nutrients are stored in the tree and eventually will be removed.
The equivalent annual removal rate, however, is somewhat less than forage-
crops and most field crops. As pointed out in the EPA Manual, Land Treat-
ment of Municipal Wastewater, there are several advantages in using forests
for Land treatment. They are:
• Large forested areas exist near many sources of wastewater.
• Forest soils often exhibit better infiltration properties than
agricultural soils.
• Site acquisition costs for forestland are usually lower than site
acquisition costs for agricultural land because of lower land values
for forestlands.
• During cold weather, soil temperatures are often higher in forest-
lands than in comparable agricultural lands.
12
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There are several possible limitations. These may or may not be seri-
ous, depending on the forest type and soil conditions. Some trees, especi-
ally hardwoods, have a low water tolerance.
As mentioned earlier, nitrogen removals may be low. This problem can-
not be avoided other than by tree selection—in general, rapid growth trees
with an early maturity. An early maturity is 30-40 years, rather than 50-
60 years.
The other disadvantage is the limitation in selection of Irrigation
systems. Mechanical move systems and surface systems are not possible.
Solid set systems are required. Solid set systems are more costly to pur-
chase and install than the other systems, but do not require underground
piping for silviculture operation. This will greatly reduce the installa-
tion cost. By the time the forest has matured, the system will be worn out
and salvage unnecessary (disposal only).
APPLICATION RATES
Agricultural systems in the U.S. can be divided into two categories.
They are irrigated and non-irrigated agriculture. There are three
areas where: (1) irrigation is required for all agriculture, (2) re-
quired for some crops, and (3) not required for any crop. In determining
the application rate there is a variation in procedure depending en which
system is encountered. For most of the western U.S., irrigation is re-
quired to grow a crop during the summer months. Therefore, irrigation sys-
tem consumptive use determinations are used to calculate application rates.
In the midwest and eastern U.S., irrigation is not required (except south-
east and Gulf states). Determination of application rates is accomplished
by maximizing water application without flooding the crop being grown.
Therefore, the application rate is a function of the least permeable soil
layer. The EPA "Land Treatment of Municipal Wastewater Manual" contains an
example showing this approach.
In both instances, the procedure consists of determining the hydraulic
balance for the system and then calculating the nitrogen balance to be sure
13
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that nitrate concentrations in the leachate are not excessive (in most cases,
excessive rate is that rate which increases groundwater nitrate to a con-
centration >10 mg/1).
In arid regions, the application rate must be high enough to provide
flushing of salts through the soil mantle. Because this procedure is common
to most arid regions, local farm advisors can assist in determining the right
rate to prevent salt buildup.
Two design examples follow in a later section. These examples show
the step-by-step procedure for determination of application rates.
COSTS
Typical alternative slow rate system costs are shown on Table 4.
14
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TABLE 5. YEARS OF USE FOR DEPRECIATION PURPOSES
Pumps 20 years
Pipeline 20 years
Movable sprinklers 10 years
Permanent sprinklers 20 years
Hose drag 8 years
Aluminum tubing 10 years
Steel pipe, 14 gauge, dipped, buried . 8 years
Steel pipe, 12 gauge, dipped, buried . 15 years
Steel pipe, dipped, surface use .... 10 years
Steel pipe, galvanized, surface use . . 15 years
Asbestos-cement pipe 25 years
Plastic pipe 25+ years
Concrete pipe 20 years
Electric motors 15-20 years
Pumps (50,000 hours) 10-20 years
Sprinkler heads 7-8 years
Sprinkler pipe - permanent 10 years
- movable 5 years
16
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DESIGN EXAMPLE - ARID CLIMATE
A slow rate system generally involves growth and marketing of a crop. The
proceeds from the crop sale are then used to defray operation costs. The crop
grown must be adaptable to effluenc irrigation and be readily marketable if
revenue^ from crop sales are anticipated. The first step in designing a slow
rate irrigation system is to become familiar with area agricultural practices.
An effluent irrigation system can usually be patterned after existing agricul-
tural systems in the area (if any) with control modifications as required by
local Health Department Requirements. Existing agricultural system information
will include climatic, soil data, and crop requirements.
A good design allows for climate extremes and cropping variations. Extreme-
ly high rainfall years will require larger application areas (or greater off-
season storage capacity) due to lower allowable application rates and due to
higher flows from sewer system infiltration and inflow. Conversely, extremely
dry years may require higher irrigation flow to produce a good crop. Variation
in the crop grown will result in changes in water requirements and nutrient uti-
lization rates. The design should include an allowance for adjusting acreage to
accommodate different crops.
The following example problems are presented with the above considerations
in mind. The examples apply to the detailed design of a system for a specific
site. The process of selecting the specific site is an involved process in it-
self. Site selection procedures are described in Chapter 3 of the EPA Land
17
-------
Treatment Manual. The first example applies to an arid area where irrigation
is necessary to grow most crops.
DESIGN DATA
Location: Western U.S.
Existing Agricultural Practices: Field crops are grown including corn,
alfalfa, pasture, and barley.
Wastewater Characteristics:
Parameter
BOD , mg/1
Suspended solids, mg/1
Total dissolved solids, mg/1
Total nitrogen as N, mg/1
Ammonia as N, mg/1
Organic as N, mg/1
Nitrate as N, mg/1
Total phosphorus as P, mg/1
Chloride, mg/1
Raw
Wastewater
250
260
450
35
15
20
0
15
40
Effluent
To Be Applied To Land
35
50
440
30
8
5
17
13
37
Treatment by aerated lagoons, followed by storage ponds.
SITE DESCRIPTION
Most agricultural areas in the U.S. have been mapped by the U.S. Department
of Agriculture Soil Conservation Service. These mappings provide soil descrip-
tions pertinent to agricultural use. Typically, the SCS survey will provide in-
formation on soil characteristics such as: slope, color, thickness, absorption,
water capacity, permeability, suitability for roots, erosion potential, compati-
bility with various crops, pH, and soil boring data.
CLIMATE
This area experiences cold, damp winters and relatively warm, dry summers.
Low precipitation rates, extreme fluctuations in daily and seasonal temperatures
and occasional high winds are common. The average growing season is 150 days
18
-------
(May to September). Thus, storage is required for the flow anticipated during
the 215 days non-growing season. Because there will be years when the growing
season is less than average and the winter flows higher than average, it is
prudent to conservatively size the storage basin. Temperature and precipitation
data are shown on Table 6.
APPLICATION RATE
Consumptive use for the growing season months was obtained from the Soil
Conservation Service for corn, alfalfa, and pasture, and is shown on Table 7.
This shows the minimum water requirements to grow each of the four crops.
This requirement is accurate for a 100% water use efficiency. Generally, water
use efficiencies depend on the water delivery and irrigation method.
Water delivery or transport systems are usually pipeline, lined canal, or
unlined canal. Depending on which of these systems is used, losses could be
insignificant or substantial (20-25%). The irrigation efficiency is dependent
primarily on the method of irrigation. Table 8 shows the minimum water delivery
requirement. This table was developed assuming pipeline delivery. Because
there is typically no significant precipitation in the growing season, all of
the crop water needs are delivered by the irrigation system.
STORAGE
With the data shown on Table 8 the reservoir storage requirements and land
area requirements can be computed. The reservoir storage must contain, at a mini-
mum, the flows in non-growing season which is about six months. However, if the
use rate is minimal during April and dry-down for harvesting corn is required
(Sept.-Oct.), then eight months storage may be required unless provisions are
made for alternate irrigation areas during these periods. For this example,
the monthly effluent flows are shown in Table 9.
Note that Table 9 shows the monthly flows in acre feet and as cumulative
flows. The cumulative flow shows the required storage. This is an especially
valuable method of presenting flows since seasonal variations are taken into
account. The minimum required storage is 611 ac ft. This is the flow that
19
-------
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20
-------
TABLE 7. MONTHLY CONSUMPTIVE USE, IN.
Month
Corn
Alfalfa
Pasture
Barley
April
May
June
July
August
September
Total
2
3
5
5
.80
.70
.48
.84
-
0.
3.
4.
6.
5.
3.
67
20
89
48
22
30
1
2
3
4
4
3
.31
.60
.92
.33
.45
.08
17.82
23.76
19.69
2.75
3.51
4.93
11.19
TABLE
MINIMUM DELIVERED TO IRRIGATION SYSTEM
Required delivered water (75% irrigation efficiency ) , in.
Month Corn Alfalfa Pasture Barley
Apri 1
May
June
July
August
September
Total
S.73
1.93
'.31
'.79
-
0.
4.
6.
8.
6.
4.
89
27
52
64
96
40
1
3
5
5
5
4
.75
.47
.23
.77
.93
.11
3.
4.
6.
-
-
67
68
57
23.76
31.68
26.26
14.92
Irrigation efficiency is defined as water delivered minns runoff and deep
percolation below root zone divided by water delivered. Spray irrigation
systems are capable of 75-85% efficiencies. 75% was chosen for this ex-
ample to maximize the application rate.
21
-------
has accumulated between the first of October and the end of April. From May
through September, more wc.ter is withdrawn than enters. The reservoir begins
refilling in October. This analysis would be varied with the climate. Some
areas may grow forage all year and provide storage only for rainy periods.
The storage reservoir sizing does not include winter rainfall, evapora-
tion or seepage losses. In most arid areas the evaporation exceeds preen pi~
tation. Winter precipitation can usually be contained within the reservoir
freeboard. For evaporation and seepage losses, provide a factor of safety
they are not considered in sizing the storage reservoir.
Note that the table begins with the month following the end of the grow-
ing season. For those crops where harvesting takes place prior to the end of
the growing season, the irrigation continues after harvest.
TABLE 9. EFFLUENT FLOW
Month
October
November
December
January
February
March
April
May
June
July
August
September
Total Annual
Avg. 0.94 mgd
Flow, mil gal
27
28
30
31
28
29
26
27
28
29
32
30
345 mil gal
Flow, ac ft
82. 9
86.0
92.1
95.2
86.0
89.0
79.8
82.9
86.0
89.0
98.2
92.1
1,059.2 ac ft
End of month
cumulative flow, ac ft
82.9
168 . 9
261. .8
356.2
442.2
531.2
611.0
643.9
779.9
868.9
967.1
1,059.2
ACREAGE
The next step is to determine the necessary acreage. The required acreage
depends on the percentage acreage planted with each crop. To simplify this ex-
ample, assume that the ertire parcel is planted in pasture. The water require-
ment is 26.26 in. per year (or 26.26 ac in. per acre). The required acreage is
computed as follows:
, ncn ... , -, -, . /f.
1,059 ac ft/year x 12 in. /ft =
26.26 in./yr
This acreage is the irrigated area. Additional area is required for access
roads and buffer areas. Access roads and buffer area sizing depends on local
22
-------
conditions, crops grown, and irrigation method used. For this example, assume
that 50 ft of buffer is required between the operation and adjoining property.
A 484-acre field in a square shape is 4,592 ft on a side. The buffer area is
[4,592(2) + 4,592(2)]50 T 43,560 = 21 acres. The total land area is 484 + 21
or 505 acres. (See Figure 2, below).
-Buffer
zone
Figure 2. Irrigation Area with Buffer
For this example, assume a wheel line system is used and no access roads
are required. Row crop-planting would require access roads, whereas vehicles
can be driven on the pasture as long as traffic is minimized.
IRRIGATION SYSTEM
Permeability for the site soils is rapid with a low available water capa-
city (AWC). Permeability is 6.0 in./hr and AWC is 1.4 in./ft. Assuming the
pasture grass has a 3.5 ft root depth, 75% allowable moisture depletion and a
peak daily evapotranspiration rate of 0.35 in./day, the irrigation interval is
computed as follows:
(1.4)(3.5)(.75)
.35
= 10.5 days, use 10 days
The rate of .35 in./day occurs for a short time only but the irrigation sys-
tem must be designed to meet this rate. At other times, the irrigation interval
23
-------
can be increased. The irrigation application is 3.5 inches per set. Using an
18-hour irrigation time, this is a .318 in./hr rate. Working with a 40 x 45
spacing or 1,800 sq ft per set of sprinklers this results in a flow rate of:
.318 in./hr x 1,800 sq ft _,_„
— * = 358 gph or 6 gpm
_L • t)
Using a 5-in. pipeline, sprinklers at 40-ft spacings, with trailing sprink-
lers at 45 ft and a lateral length of 1,320 ft, there are 34 sprinklers per
lateral. Total flow into the lateral is:
(34)(2) x 6 gpm/sprinkler = 408 gpm
The sprinkler size :.s taken from Table 10 and is 3/16 in. @ 40 psi. There
are other size/pressure combinations. Selection is specific to desired pressure
rating.
The wheel line is moved 90 ft each day and is 1,320 ft long. The irriga-
tion interval is 10 days, so the area covered per machine is 1,188,000 sq ft
or, 27.3 acres.
One side of the area is 4,592 ft, 4,592 v 1,320 = 3.48 or 4 rigs. Each rig
moves 900 ft, so 5.10 or 5 are required in this direction. The total number of
rigs required is 4 x 5 or 20.
NITROGEN BALANCE
The nitrogen balance is determined by subtracting the nitrogen usage by
each crop from the amou:it applied. This is a somewhat gross approximation
since there are several minor losses, such as volatilization of ammonia and
some residue left on ground which cycles nitrogen back into the plant-soil
system. If there is more nitrogen applied than consumed, then more detailed
analysis is necessary to control leaching of nitrates to groundwater sources.
I
Table 11 shows a nitrogen balance for each of the four crops. This balance was
determined based on 30 mg/1 nitrogen concentration in effluent applied and the
irrigation quantities as shown in Table 8. A 1-in. application or 1 ac in./ac
equals 27,154 gal/ac. The 30 mg/1 nitrogen concentration is equal to 2.50 x
—4
10 Ib/gal. This results in a nitrogen addition of 6.79 Ib N/ac per in. of
24
-------
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25
-------
application. The Table 11 data were developed using this approach.
TABLE 11. NITROGEN BALANCE
crop
Corn (grain)
Alfafa
Pasture
Barley
N applied,
Ib/ac
161
215
178
101
N requirement.. of crops,
Ib/ac
170
450
300
175
Applied-removed
Ib/ac
-9
-235
-122
-74
Source: Western Fertilizer Handbook.
2
Some nitrogen fixed from atmosphere.
All crops utilized more nitrogen than the quantity supplied. This means
that supplemental nitrogen is required or yields will decrease. One option
is to increase irrigation rates.
CHECK SODIUM ADSORPTION RATIO (SAR)
With certain effluents, sodium can damage soil structure and reduce water
infiltration rate. Determination of the potential for creating a problem is
made by solving the following equation:
SAR = Na+XAca"*"*" + Mg"*"V2
where the ionic concentrations are expressed in milliequivalents/liter.
The sodium hazard is then determined by Figure 3, The sodium or alkali
hazard is a function of the SAR and conductivity.
Assuming for this; example the ionic concentrations, the SAR is computed
below:
Na+ - 20 me/1
Ca++ - 10 me/1
Mg++ - 10 me/1
SAR = 20//UO+10) /2 = 6.32
From Figure 2, this has a low sodium hazard unless the conductivity ex-
ceeds 750 micromhos/cn.
26
-------
100
4 50C-J
100 2r'0 750 1HO
CONDUCTIVITY - MICROMHOS/CM ( EC x 1Q6) AT 25 C.
ME OIL/M
HIGH
VERY HIGH
JW'UNITY HAZARD
Figure 3, Diagram for the classification of irrigation waters.
Source: Agricultural Handbook 60, U.S. Dept. o f Agriculture
21
-------
DESIGN EXAMPLE - HUMID CLIMATE
The design example presented is ba.ced on t:i-_ (-xample uoqinning on P iqe
8-1'of the EPA Land Treatment Manual. The pzet.enr,cition parallels the writ t /•:>
text in Chapter 8. As will be apparent, the design of slow rate systems in
humid climates where the need for irrigation is marginal requires a more rven.-u -
tive analysis of many aspects than the arid climate example where virtually
no rainfall occurs during the growing season.
The EPA manual presents a design for a center pivot system. The follow-
ing alternative design illustrates the application of a different type irri-
gation system to the s.ame problem.
ALTERNATE DESIGN, TRAVELING GUN
The following design was developed from information in "Wastewater Re-
source Manual" by the Sprinkler Irrigation Association. The maximum applica-
tion for this example would be approximately 1 in./day. Using this value, a
1 in./pass is assumed for design. From Table 12 select a 1.93-in. nozzle size;
the following data are then set:
805 gpm
80 psi
27° trajectory
368 feet lane spacing
0.47 in./hour application rate
28
-------
TABLE 12. SPRINKLER SELECTION FOR TRAVELING GUN SPRINKLER SYSTEMS"
Source: Sprinkler Irrigation Association "Wastewater Resource Manual"
System Ring nozzle Nozzle Trajectory Max. lane Avg. application
capacity, size pressure, angle, spacing, rate
gal/min inches psi degrees feet inches/hour
110
143
182
245
295
355
415
515
590
675
805
900
.86"
.97"
1.08"
1.18"
1.26"
1.34"
1.56"
1.66"
1.74"
1.83"
1.93"
1.93"
(7/8")
(1")
(1-1/8")
(1-1/6")
(1-1/4")
(1-1/3")
(1-1/2")
(1-5/8")
(1-3/4")
(1-7/8")
(2")
(2")
60
60
60
70
70
70
70
80
80
80
80
100
24°
24°
o
24
24°
24°
24°
27°
27°
27°
27°
27°
27°
195'
210'
225'
248'
263'
274'
304'
330'
341'
353'
368'
390'
0.33
0.33
0.33
0.33
0.33
0.33
0.36
0.38
0.40
0.43
0.47
0.47
This is a short cut chart for selecting gun sprinklers for traveling gun
sprinkler systems.
2
Ring nozzles were chosen because of their ease of interchangeability and good
droplet breakup.
These are suggested pressures to operate these gun sprinklers, to obtain a
reasonable degree of uniformity, and keeping in mind the extra costs associ-
ated with higher pressures. The sprinklers will operate as low as 50 psi.
A 23 -24 trajectory angle provides best average cover under moderate winds
and on sloping ground. For larger capacities, a 27 trajectory angle has a
lower application rate.
This maximum lane spacing is based on 75% of the manufacturer's published
wetted diameter. If wind speeds greater than 5 miles per hour are expected,
this should be decreased by 5 to 10%.
This is the average application rate under low wind conditions. Under windy
conditions, actual application rates can exceed two or three times this
amount. Select a sprinkler to match your soil conditions, with this in mind.
29
-------
From Table 12 the rate of travel is determined for a 1-inch application.
This rate is 42 inches/min. It takes approximately 6 hrs to travel 1320 ft.
(Table 13). Assuming the gun is moving 20 hrs per day, one gun covers the
following area:
Length of move: 42 in./min x 60 min/hr x 20 hr = 4,200 ft
12 in./ft
Area covered: 4,200 x 368 = 35.5 ac/gun/day
43,560
Ten-day rotation coverage per gun: 35.5 x 10 = 355 ac per gun
Therefore, to cover 1,150 ac, 3.2 or 4 guns are required.
The gun selection is a trial and error process to determine the best for
the local conditions.
30
-------
TABLE 13. RATE OF TRAVEL FOR TRAVELING BIG GUNS FOR DIFFERENT NOZZLE SIZES
AND APPLICATION RATES
Spacing Acres Acres
between irrigated irrigated
lanes per 1/4 mile 1000
Per minute in feet 'travel travel
100
200
300
400
500
600
700
800
900
1000
Note:
150'
ISO1
210'
180'
210'
240'
270'
210'
240'
270'
300'
240'
270'
300'
330'
270'
300'
330'
360"
300'
330'
360'
390'
300'
330'
360'
390'
330'
360'
390'
420'
330'
360'
390'
420'
360'
390'
420'
450'
4.6
5.5
6.4
5.5
6.4
7.3
8.3
6.4
7.3
8.3
9.1
7.3
8.3
9.1
10.0
8.2
9.1
10.0
10.9
9.1
10.0
10.9
11.8
9.1
10.0
10.9
11.8
10.0
10.9
11.8
12.7
10.0
10.9
11.8
12.7
3.5
4.2
4.8
4.2
4.8
5.5
6.3
4.8
5.5
6.3
6.9
5.5
6.3
6.9
7.6
6.3
6.9
7.6
8.3
6.9
7.6
8.3
8.9
6.9
7.6
8.3
8.9
7.6
8.3
8.9
9.6
7.6
8.3
8.9
9.6
10.9 8.3
11.8 8.9
12.7 9.6
13.6 10.3
Rate of travel
per minutes
in
to
inches
apply
1/2 111/2 2
inch inch inches inches
25.
21
19
42
37
32
28
55
48
43
38
64
57
51
47
71
64
58
53
77
70
64
59
90
83
75
69
94
85
80
74
96
89
82
98
92
86
4 13
11
9
21
19
16
14
27
24
22
19
32
29
26
23
36
32
29
27
38
35
32
30
45
41
37
35
47
42
40
37
52
48
44
41
53
49
46
43
8
7
• 6
14
12
11
5
18
16
14
13
21
19
17
16
24
21
19
18
26
23
21
20
30
27
25
23
31
28
27
25
35
32
30
27
36
33
31
29
The irrigated acreage per set can be increased by letting the
set at each end for an extra 1-2 hours. On medium and large
this can increase the irrigated acreage by the difference in
between the 1000 ' and 1320' run.
6
5
5
10
9
8
7
14
12
11
10
16
14
13
12
18
16
15
13
19
18
16
15
23
20
18
17
24
21
20
19
26
24
22
21
27
25
23
22
system
size guns,
acreage
Source: Sprinkler Irrigation Association "Wastewater Resource Manual",
31
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TABLE 14. TIME REQUIRED TO IRRIGATE ONE IANE
Rate of travel,
inches/ minute 105
Time required
to travel
1000 feet,
hours 1.9
Time required
to travel
1320 feet,
hours 2 1/2
Rate of travel
in. /minutes 19
Time required
to travel
1000 feet,
hours 10 . 6
Time required
to travel
1320 feet,
hours 14
87
2.3
3
17
11.4
15
66
3
4
16
1.2.1
16
52
3.8
5
15
13.6
18
44
4.5
6
13
15.2
20
37
5.3
*
7
11
18.2
24
33
6
8
10
19.7
26
29
6.8
9
9
22
29
26
7.6
10
8
25
33
24
8.3
11
7
28.8
38
22
9.1
12
6
33.3
44
20
9.8
13
5
39.4
52
Source: Sprinkler Irrigation Association "Wastewater Resource Manual".
32
U.S. GOVERNMENT PRINTING OFFICE: 1979— 657-O1 1/7O3 1
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