Technical Bulletin 182
April 1967
Cost of Pumping
Irrigation Water
in Central Arizona
Arizona Agricultural Experiment Station
College of Agriculture
THE UNIVERSITY OF ARIZONA
Tucson, Arizona
CONTENTS
Page
Summary and Conclusions
5
Introduction
Objectives and Scope of Study
Source of Data
Description of Well and Pump Installations
Well and Casing
Column
Column Length Versus Well Depth
Lift
Lift Versus Column Length
8
Bowls
Electric Motors
Natural Gas Engines
Analysis of Operation
Gallons per Minute
Efficiency
Efficiency of Electric Wells
Efficiency of Gas Wells
Hours Operated and Water Pumped Annually
Fuel Consumption
Electric Energy Consumption
Natural Gas Wells
Capital Expenditures
Cost Analysis
Fixed Costs
Depreciation
Property Taxes
Interest on Investment
Total Fixed Costs of Electric Wells
Total Fixed Costs of Gas Wells
Added Capital Costs
Electric Wells
Natural Gas Wells
Variable Costs
Electric Wells
Natural Gas Wells
Total Costs
Estimating Costs of Pumping
Electric Wells, Variable Costs
Electric Wells, Annual Added Capital Costs
Electric Wells, Annual Fixed Costs
Gas Wells, Variable Costs
Gas Wells, Annual Added Capital Costs
Gas Wells, Annual Fixed Costs
Effects of Energy Rates on Costs
Effects of Efficiency on Costs
Repair Costs Versus Savings
COST OF PUMPING WATER
9
10
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13
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19
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32
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35
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37
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43
1
TABLES
Page
L Casing Diameter of District and Farm Survey Wells
2.
Depth Distribution of District and Farm Survey Wells
3. Age
4.
Distribution of District and Farm Survey Wells
Diameter of Column Pipe in District and Farm Survey Wells
12
12
13
14
5.
Length of Column in District and Farm Survey Wells
15
6.
Pumping Lift by District and Farm Survey Wells
15
7.
Depth of Water Over the Bowls, Number and Size of Bowls,
and Pumping Lift per Bowl Stage
16
8. Age of Bowls in
District
1
and Farm Survey Wells
17
Size Distribution of the Power Unit, District and Farm
Survey Wells
17
Rated Horsepower Related to Input Horsepower, Faitii
Survey Wells
18
11.
Speed of Electric Motors Related to Size, District Wells
19
12.
Age of Power Units Related to Rated Horsepower,
Farm Survey Wells
19
Discharge in Gallons per Minute, District and Farm
Survey Wells
20
Overall Plant Efficiency of Electrically Powered Wells,
District and Farm Survey Electric Wells
21
Overall Plant Efficiency on Natural Gas Powered Wells,
Farm Survey Gas Wells
22
Hours Operated, Acre-Feet of Water Pumped, and Fuel
Consumption Per Acre-Foot and Per Acre-Foot Per Foot of
T Aft, District and Farm Survey Wells, 1963
23
Itemized Capital Cost of Well, Pump, and Power Unit
Components, Including Installation Costs, 1963
28
Average Capital Investment Per Irrigation Well Assuming the
Wells and Appurtenant Equipment Were New at 1963
Price Level
30
9.
10.
13.
14.
15.
16.
17.
18.
2
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
TABLES (Continued)
Page
19.
Estimated Fixed, Added Capital and Variable Costs of
Pumping Irrigation Water Per Well, Per Acre-Foot, and Per
Acre-Foot Per Foot of Pumping Life
31
20. Estimated Added Capital Expenditures Related to Increased
21.
Pumping Lift
33
Farm Survey Wells: Energy Costs and Total Costs Per AcreFoot and Per Acre-Foot Per Foot of Lift, by Source of
Electricity and Natural Gas
38
22. Fuel Requirements and Costs Related to Overall Efficiency
23.
of the Pumping Plant
40
Costs Related to Gallons Per Minute, Farm Survey
Electric Wells
41
24. Acre-Feet of Pumpage Required for Electric Power Savings to
Equal Estimated Repair Costs to Raise Efficiency to 65 Percent
43
FIGURES
Page
1.
2.
Kilowatt Hours of Electricity Used Per Acre-Foot Per Foot
of Lift Related to Discharge for the Fifty Farm Survey Wells
25
Acre-Feet of Pumpage Required for Savings in Electric Power
Costs to Equal Estimated Repair Costs of Improving Pumping
Plant Efficiency
42
COST OF PUMPING WATER
3
Summary and Conclusions
This study was made to determine costs individual farmers
incur in pumping water for irrigation in Maricopa and Pinal Counties of central Arizona. Wells powered by electric motors, referred to as electric wells, and by natural gas engines, referred
to as gas wells, were included in the study. Fixed, added capital,
and variable costs are portrayed on an acre-foot, and acre-foot
per foot of lift basis. The capital investment in wells is shown in
conjunction with analysis of fixed costs. Physical data on the
wells, hours run, acre-feet of water pumped, power or fuel consumption and efficiency also are included.
Data for the study were obtained from a random sample of
wells of individual farmers, five major irrigation districts, two
large corporate farms ( included with irrigation districts in the
study), well drilling and pump companies, and power and natural
gas suppliers.
The approach followed was to develop costs and related data
for the farm survey electric wells, the farm survey gas wells, and
for the irrigation districts as separate groups. Since relatively
accurate data were available for large numbers of wells in the
irrigation districts ( all were electric wells ), the objective was to
use district well costs as a check on, or to substantiate, the farm
survey well costs. The farm survey well costs are believed to
represent more closely costs individual farmers will incur than
do irrigation district costs.
The typical well in the farm survey had a 20-inch casing
and was approximately 1,000 feet deep. Irrigation district wells
were slightly larger but averaged only 675 feet in depth. The
column pipe was typically 10 or 12 inches in diameter, the average for district and farm survey gas wells being about one inch
larger than the average for farm survey electric wells. Column
length averaged 415 feet for farm survey electric wells, about
480 feet for the gas wells, and about 300 feet for the district wells.
Pumping lift averaged about 380 feet for the farm survey electric
wells, 435 feet for the gas wells, and about 265 feet for the district
wells. Farm survey electric motors averaged about 210 horsepower compared with 190 horsepower for district wells. The
natural gas engines averaged about 365 horsepower.
During 1963, farm survey electric wells were operated an
average of 3,763 hours and farm survey gas wells an average of
3,717 hours. Irrigation district wells were operated an average
of 4,520 hours.
The quantity of water pumped per well averaged 870 acrefeet for farm survey electric wells, and 1,084 acre-feet for farm
COST OF PUMPING WATER
5
survey gas wells. Irrigation district wells averaged 1,558 acre feet per well. Discharge averaged about 1,255 gallons per minute
for farm survey electric wells and 1,585 gallons per minute for
the gas wells. Irrigation district wells averaged 1,810 gallons
per minute.
Overall efficiency of the pump and power unit averaged 52
percent for farm survey electric wells and 13 percent for the
natural gas wells. Compared with maximum efficiency attainable under ideal conditions -74 percent for electric wells and 18
percent for natural gas wells -the gas wells were operating at
approximately the same level of efficiency as the farm survey
electric wells. Overall efficiency of irrigation district wells averaged nearly 59 percent, materially higher than the farm survey
electric wells. The average replacement cost new of farm survey
electric wells was nearly S33,000, using 1963 costs. About 50
percent of the total investment was in the well and casing, 25
percent in the pump, and 25 percent in the power unit.
The average replacement cost new of farm survey gas wells
was a little over 349,000 per well, the higher replacement cost
relative to electric wells being due to the relatively higher price
of natural gas engines and the somewhat larger and deeper wells.
About 38 percent of the total investment was in the well and
casing, 22 percent in the pump, and about 40 percent in the power
unit.
Farm Survey
Cost per Acre- Foot -Foote
District
Farm Survey
(Cents) (Cents) (Cents)
Cost per Acre-Foots
District
Wells
Fixed Costs
Depreciation
Inter. on Invest. @ 6%
Property Taxes
Total
Added Capital Costs
Variable Costs
Fuel2
Repairs
Lubrication
Attendance
Total
Total Costs
Wells
Electric Gas
($)
($)
($)
.78
.57
.43
1.78
.13
1.48
1.13
.77
2.20
1.36
4.09
.663
4.75
6.66
-
3.38
.74
4.39
.42
.55
6.98
1.21
.13
.08
8.40
12.20
4.29
1.43
.38
.09
6.19
11.13
Wells
.29
.21
.16
.66
.05
Wells
Electric Gas
.40
.30
.20
.90
.11
1.53
2.253
1.85
.32
.03
.02
1.78
2.49
2.22
3.23
.53
.31
.17
1.01
.13
.99
.33
.08
.02
1.42
2.56
These costs relate to the cost of operating an established well. A charge is not
included for management required in arranging for drilling and equipping the well, or
in operating the well except as it may be included as a part of the "attendance" cost.
Moreover, a cost is not included for the land where the well is located, including land
required for access.
2 Electricity at nine mills per KWH and natural gas at 40 cents per MCF (thousand
cubic feet).
3Includes lubrication and attendance.
6
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
Estimated fixed, added capital, and variable costs per acrefoot and per acre -foot per foot of lift are as follows:
As indicated above, the costs for the farm survey wells are
believed to be fairly representative of costs typical farmers incur
in pumping water, assuming a nine -mill rate for electricity and
natural gas at 40 cents per thousand cubic feet.
Cost estimates for the farm survey electric and farm survey
gas wells given in the table are not entirely comparable due to
differences in lift, size of well, and quantity of water pumped.
Costs for district wells probably are lower than typical farmer
costs for a number of reasons: (1) Repairs, lubrication and
attendance are actual costs the districts incurred. These costs
may be low relative to individual farmer costs due to quantity
discounts on parts and since some of the districts do their own
repair work. ( 2) The efficiency of irrigation district wells averages higher than individual farmer wells. (3 ) The average
amount of water pumped annually by irrigation districts is substantially greater than the amount pumped by individual farmers.
Therefore, fixed costs per acre -foot and per acre-foot per foot of
lift are much lower for irrigation district wells than for individual
farmer wells. (4) The irrigation district costs per acre -foot are
relatively low due to the relatively lower pumping lift in the districts than in areas outside the districts.
The cost estimates given in the table represent the average
situation. Costs vary from area to area and from well to well for
a number of reasons. Equations given in the report facilitate
estimating costs per acre -foot and per acre -foot per foot of lift.
Electric power and natural gas rates have a significant influence on pumping costs. As indicated above, a rate of nine
mills per KWH was used in deriving fuel costs in the table.
Within the Maricopa -Pinal County farming area average rates
vary from .7506 cents to 1.0861 cents per KWH, with a result that
variable costs per acre-foot per foot of lift vary from 2.036 cents
to 2.786 cents. With a pumping lift of 400 feet this small difference amounts to $3.00 per acre-foot. Natural gas costs per acre foot per foot of lift vary from 0.929 cents to 1.152 cents due to
differences in rates charged per MCF. With a lift of 400 feet
this small difference amounts to about 90 cents per acre -foot
pumped.
Efficiency of the pump and power unit also has a significant
influence on pumping costs. Raising efficiency of electric wells
from 40 to 65 percent reduces power costs 40 percent. With a
378 -foot lift (the average for farm survey wells) this amounts
to about $3.35 per acre-foot. Savings in the power cost of pumping 685 acre -feet with a 420 -foot lift would equal the estimated
repair costs for raising efficiency from 40 to 65 percent.
COST OF PUMPING WATER
7
COST OF PUMPING
IRRIGATION WATER
IN CENTRAL ARIZONA
by
Aaron G. Nelson and Charles
D.
Busch'
introduction
This study pertains to the cost of pumping water for irrigation in
Maricopa and Pinal Counties of central Arizona. Primary consideration is
given to privately owned and operated irrigation wells, although the study
relates in part to wells of organized irrigation districts.
Water is a major cost factor in farm production in central Arizona.
The farmer will want to analyze the costs involved in pumping water to
determine whether or not it will pay him to pump water for crop production.
Three questions may be involved. The first pertains to the capital cost of
the well. If the farmer is considering buying a farm with an irrigation
well already installed, he will want to know the value of the well in determining how much he can afford to pay for the farm. If the farmer owns a
farm and is confronted with installing a replacement well, he will want to
analyze the costs involved to determine whether it likely will be a profitable venture. In these types of analyses all costs are pertinent -capital
expenditures and operating costs -in the comparison of costs and returns.
The analysis usually is made on the basis of average annual costs and
returns expected to prevail during the life of the well, with depreciation
of the well and appurtenant equipment being used to amortize the capital
expenditures involved.
The second question pertains to operating an established well from
Agricultural Economist and Associate Agricultural Engineer, respectively, Arizona
Agricultural Experiment Station.
A number of individuals and organizations contributed to making this study. The
field work was carried out by Alan P. Kleinman and Robert D. Lamoreaux, Research
Assistants, Agricultural Economics Department; C. Eugene Franzoy, Research Assistant,
Agricultural Engineering Department, and Marvin Nystrom, Bureau of Reclamation.
Master's theses prepared by Mr. Kleinman and Mr. Lamoreaux contributed to the study.
Dr. M. M. Kelso, Agricultural Economics Department, participated in the early planning
of this project and in review of the manuscript. Other Experiment Station and Extension
Service workers have provided counsel and advice.
The Bureau of Reclamation, U.S. Department of Interior, contributed to developing
initial plans for the study and provided financial support to help cover costs. A large
number of farmers cooperated by permitting measurements to be made on their wells
and by providing costs and related information. The Salt River Project, Roosevelt Water
Conservation District, Roosevelt Irrigation District, Buckeye Irrigation District, San
Carlos Irrigation District, and Boswell Farms and Goodyear Farms cooperated by making similar data available for their wells. Power and natural gas suppliers, well and
pump firms, and other businesses cooperated effectively in making needed information
available.
The authors express their appreciation to each of these individuals, organizations,
and businesses for their assistance.
8
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
a short-run point of view. The decision here is whether or not it will pay
to operate the well to provide water for a given crop. The capital expenditures involved in installing the equipped well are "fixed." There is nothing
the farmer can do about them. The pertinent costs are the additional costs
which will be incurred by operating the well compared with the additional
returns which will be produced with the water pumped. In economic terms
the additional costs are referred to as variable costs. If the returns produced
exceed variable costs, it will pay to operate the well.
In this regard, marginal returns versus marginal costs are pertinent.
How much water will it pay to apply? It will pay to apply additional
quantities of water to a given crop as long as the added ( marginal) returns
are greater than the added ( marginal) costs. However, it will not pay to
go beyond the point where the cost of the last unit of water applied to a
given crop ( say, one-half acre -foot) is just covered by the returns attributable to that water.
Water cost data are needed to facilitate profitable decisions when
planning a cropping system for a farm. As the groundwater level declines,
water costs will increase. This in turn may change the optimum cropping
system. The size of each crop enterprise should be adjusted so that the
last dollar spent on each enterprise will contribute an equal amount to
net income. Moreover, factors of production ( water, fertilizer, labor,
machine use, etc.) used in producing a given crop should be combined in
such quantities that the last dollar spent on each will contribute the
same amount to income.
The third question pertains to operating an established well from the
long -run point of view. Considerations involved are similar to those
outlined in discussion of the first question. The major difference is that
in the first case capital had not been expended-the farmer was still free
to decide whether or not to make the expenditure -while with this question the capital expenditure is fixed and the determination is whether the
returns produced by water pumped from the well are sufficient to cover
all costs involved, the fixed costs as well as the variable costs of operating
the well. If returns are not sufficient to cover all costs, capital will not
be available from earnings of the well to replace the well and appurtenant
equipment when it is worn out.
In considering questions pertaining to capital expenditures and variable
costs of pumping water, the farmer is concerned with economies which
may be realized. Information is needed on factors which influence the
cost of pumping water. The farmer may not be able to do anything about
some of these factors. However, some other factors may be amenable to
improvements which will significantly reduce costs.
Objectives and Scope of Study
The primary objective of this study was to determine the costs individual farmers incur in pumping water for irrigation. Since the well and
appurtenant equipment, depth to water, quantity of water pumped, and
source of power or fuel affect costs, these factors are described and analyzed to show their effect on costs. Other factors which influence costs
COST OF PUMPING WATER
9
also are examined with a view of determining where savings might be
realized.
Individual cost items involved in pumping water are grouped in three
categories: fixed, added capital, and variable. Fixed costs -those which
are not affected by the amount of water pumped from the well-include
depreciation, interest on capital invested in the well and equipment, and
property taxes. The capital investment in the well and appurtenant equipment provides a basis for deriving the fixed costs. In estimating the capital
investment, current costs new of the well and of each item of appurtenant
equipment are used to put all wells on an equal basis. Details of the
procedure followed are given in the section dealing with fixed costs.
Added capital costs are those incurred as a result of the declining
groundwater table; for example, costs of adding column pipe and pump
bowls, increasing the size and motor or engine, and the like. These items
basically are capital expenditures since, once installed, they form a part of
the capital invested in the equipped well. However, they are operating
costs involved in pumping water in the sense that they are essential to
continued operation of the well.
Variable costs -those which vary with the amount of water pumped
from the well-include energy, repairs, attendance, and lubrication.
Source of Data
Data for the study were obtained from farmers, pump companies, well
drillers, electric and natural gas suppliers, and irrigation districts.
Owners of a random sample of wells, stratified by geographic area,
were interviewed the summer of 1963 to obtain: (a) a description of the
physical features of the well and appurtenant equipment, including the
date the well was drilled and the equipment installed; (b) information
on added capital costs during the preceding 12 months; (e) information
on well performance and lift; and (d) repairs, lubrication and attendance
during the preceding 12 months. With the farmers' approval the following
measurements were made on each well at three different times during June,
July, and August 1963: lift (the distance the water was lifted), discharge
(gallons per minute pumped), and power input. Usable data were
obtained for 74 wells, 50 of which were powered by electric motors (referred
to as electric wells throughout this report) and 24 powered by natural gas
engines (referred to as gas wells) Thirty -four of the electric wells and
20 of the gas wells were in Pinal County and the remainder were in Mari copa County.
With the descriptive data for each of the wells obtained from the
farmer, well drillers and pump companies were contacted to obtain the
replacement cost new of each of the items; for example, the current cost
of drilling and equipping each well with items similar to those in use at
that time. This procedure was followed to provide a uniform and up -todate cost base for all of the wells in the sample.
The quantity and dollar value of electricity or gas used by each of
the wells, by months, were obtained from the suppliers.
During the summer of 1964 data similar to those outlined above were
obtained from the Salt River Project, Roosevelt Water Conservation District,
Roosevelt Irrigation District, Buckeye Irrigation District, San Carlos Irriga.
10
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
tion District, and Boswell Farms and Goodyear Farms in central Arizona.
These seven are referred to as "districts" or "irrigation districts" throughout
the report. The specific data assembled and their contribution to the study
will become evident as the analysis is presented.
Description of Well
and Pump Installations
The "Cable Tool" method of drilling wells is more common than the
"Rotary" method in central Arizona. With the "Cable Tool" method the
well is usually cased as the drilling progresses, depending on the nature
of the materials encountered. With a "Rotary" drilled well the bore hole is
larger than the casing. The well is cased after completion of the drilling
operation with the area outside the casing commonly being filled with
gravel. For either drilling method the casing may be perforated before
or after installation.
The vertical turbine pump and the discharge column pipe through
which water is lifted to the surface are Iowered in the well casing after
the well has been completed. The number and diameter of bowls that
make up the pump will depend on the discharge, lift, and motor speed.
In general, the pump bowls are four inches smaller in diameter than the
casing, and the column pipe diameter averages four inches less than that
of the bowls.
Power to the turbine pump is supplied by either an electric motor or
a natural gas engine. Within central Arizona the pump installations are
approximately three -fourths electric powered and one -fourth powered with
natural gas.2 The natural gas engines seemed to be favored in the localities with the greatest pumping lifts, and adjacent to the principal gas
transmission lines.
Well and Casing
The modal casing diameter of irrigation wells in central Arizona is
20 inches. The mean depth of the 613 wells included in the study was 713
feet. Farm survey wells, on the average, were deeper than district wells.
Electric survey wells average 949 feet, gas wells 1,080 feet, as compared
to the district average of 674 feet.
The mean age for all wells was 14.6 years. Farm survey wells were not
as old as the average of all wells, averaging 10.1 years for the electric and
8.6 years for the gas wells. The average age of district wells was 15.3
years. Further details on well size, depth and age are presented in Tables
1, 2, and 3, respectively.
2 From 1964 Survey by A. D.
Haldernian, Extension Agricultural Engineer (unpublished)
.
COST OF PUMPING WATER
11
Table 1. Casing Diameter o District and Farm Survey Wells
Diameter
Districts
Farm Survey
All
(inches)
(electric)
Electric
Gas
Wells
Number of Wells
12
14
16
18
-
3
-
20
22
24
22
10
9
7
5
1
1
11
416
42
17
475
2
100
613
1
1
100
539
Total
3
50
24
Mean Diameter and Standard Deviation (inches)
Mean
20.6
S'
19.4
1.4
1.8
S
X
X
n
=
=
=
19.2
20.4
1.8
1.8
()T-X)2, where
n -1
individual observation.
mean of the x's.
number of observations.
Table 2.
Depth
(feet)
Depth Distribution of District and Farm Survey Wells
Districts
(electric)
Under 200
75
200 -399
400 -599
600 -799
800 -999
1,000 -1,199
1,200 -1,399
1,400 -1,599
1,600 -1,799
1,800 -1,999
89
101
139
97
22
6
4
4
2
Total
539
Mean
674
320
Farm Survey
Electric
Gas
Number of Wells
All
Wells
-
3
6
10
7
13
75
92
4
4
8
6
3
4
1
1
2
1
1
50
24
107
153
112
41
13
9
6
5
513
Mean Depth and Standard Deviation (feet)
S
12
949
427
1,080
386
713
332
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
Table 3. Age Distribution of District and Farm Survey Wells
Age
Districts
All
Farm Survey
(years)
(electric)
Electric
Wells
Gas
Number of Wells
Under 5
5 -9
10-14
15 -19
20 -24
25 -29
30-34
35-39
40-44
41
78
169
115
52
29
35
6
8
Total
533
Mean
15.3
8.7
9
15
15
8
-2
49
8
5
3
3
--2
21
58
98
187
126
54
29
35
8
8
603
Mean Age and Standard Deviation (years)
S
10.1
7.2
8.6
7.3
14.6
8.5
In a long -run situation a sample of irrigation wells would, on the
average, be half "worn out." In other words, the average age would reflect
half the life of a typical well. It is questionable that the average age
figures given above accurately reflect the half-life of irrigation wells in
central Arizona. The population of wells has not had adequate time to
"season "; that is, develop a normal age pattern.
Since an accurate approximation of average age is needed in arriving
at depreciation, a special analysis was made of the age of wells in the
Salt River Project. The first replacement well in the Project was drilled
in 1926. Wells in the Project at that time were, therefore, assumed to
constitute a population of wells. It was assumed, further, that all replacement wells since that time replaced a well drilled prior to 1926. (This
assumption may be unjustified since some replacement wells may have
replaced wells drilled since 1926, but data were not available to permit
"pairing" abandoned and replacement wells.) An average age was then
derived based upon the age of all wells drilled prior to 1926 which were
still in operation in 1964 (21 wells) plus the age of all replacement wells
(47 wells) in the Project. The average well age derived by this procedure
was 21.3 years, indicating an average well life of 42.6 years. This well -life
figure is consistent with the well life of 41.8 years indicated by the average
age of wells in the San Carlos District.
Column
The modal diameter of column in all wells in the study was 12 inches,
although there were nearly as many wells with 10 -inch as 12 -inch column.
Column in farm survey electric wells was slightly smaller on the average
than column in district wells. Column diameter of farm survey gas wells
average slightly smaller than district wells and larger than farm survey
electric wells.
The mean length of column of all wells in the study was 319 feet. The
length of column in farm survey wells was greater than in district wells,
COST OF PUMPING WATER
13
averaging 415 feet for the farm survey electric wells and 483 feet for the
farm survey gas wells compared with 303 feet for district wells. Tables
4 and 5 present column data in detail.
Column Length Versus Well Depth
The relationship of column length to well depth is important in areas
with declining groundwater levels since it indicates in part how much the
bowls may be lowered before the well must be deepened. Differences for
individual wells were not computed. However, comparison of average well
depth and average column length provides useful information. The data are
as follows:
District
Wells
Well Depth, ft.
Column Length, ft.
Difference, ft.
674
303
371
Farm Survey Wells
Electric
Gras
949
415
534
All
Wells
1,080
483
597
713
319
394
These figures indicate there is considerable opportunity for lowering
bowls as the groundwater level declines before it will be necessary to deepen
wells. It should be kept in mind, however, that these figures are averages
and do not reflect possible variation in the water -bearing strata. The
situation for individual wells may be markedly different.
Table 4. Diameter of Column Pipe in District and Farm Survey Wells
Diameter
Districts
Farm Survey
All
(inches)
(electric)
Electric
Gas
Wells
Number of Wells
6
8
10
12
14
Total
3
20
195
203
108
529
11
-
22
15
6
17
1
1
1
50
24
4
32
223
235
109
603
Mean Diameter and Standard Deviation (inches)
Mean
S
11.6
1.8
10.2
1.7
11.3
1.1
11.5
1.8
Lift
The mean pump lift of all wells in the study was 281 feet. Variation
in lift was great, ranging from less than 60 feet to nearly 600 feet. Details
are shown in Table 6.
Lift Versus Column Length
Wells in the study had an average of 38 feet of water above the bowls
( Table 7) . The district and farm survey electric figures were approximately
the same, averaging 36 and 37 feet, respectively. The farm survey gas wells
averaged 48 feet.
14
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
Table 5.
Length
(feet)
Length of Column in District and Farm Survey Wells
Under 100
100 -199
200 -299
300 -399
400-499
500 -599
600 -699
Total
Districts
(electric)
10
99
138
165
98
22
5
537
Farm Survey
Gas
Electric
Number of Wells
-
8
12
14
13
3
50
All
Wells
10
99
147
178
124
44
1
1
12
9
9
611
1
24
Mean Length and Standard Deviation (feet)
Mean
S
Table 6.
Lift
(feet)
Under 60
60 -119
120 -179
180-239
240 -299
300 -359
360 -419
420 -479
480 -539
540 -599
Total
303
120
415
115
483
75
319
118
Pumping Lift by District and Farm Survey Wells
Districts
(electric)
3
63
69
96
80
93
Farm Survey
Gas
Electric
Number of Wells
1
5
8
8
1
1
10
6
30
7
7
11
4
1
50
24
538
3
63
70
101
89
102
98
48
29
9
612
-
82
18
4
All
Wells
4
Mean Lift and Standard Deviation (feet)
Mean
S
267
115
378
112
281
113
435
68
Bowls
With a given revolution per minute ( RPM) of the motor, the lift and
discharge of the bowl assembly is determined largely by the number of stages
comprising the bowl assembly and the diameter of the bowl stages. Increased lift or discharge may be obtained either by adding stages or by
replacement of existing stages by larger diameter bowls. Bowl and impeller
selection are major factors in determining how efficiently the installed equipment is utilized.
Wells in the farm survey averaged 6.2 bowls per well. This number was
somewhat greater than the average of 5.1 for district wells (Table 7) The
difference was due, in part, to differences in lift.
.
COST OF PUMPING WATER
15
Data on diameter of bowls were not available from the farm survey.
Bowls in district wells averaged 15.2 inches in diameter.
Depth of Water Over the Bowls, Number and Size of Bowls,
and Pumping Lift Per Bowl Stage
District
Farm Survey
All
Item
(electric)
Electric
Gas
Wells
Table 7.
Column Length Versus Lift
Column Length-feet
Pumping Lift-feet
Length Minus Lift-feet
Bowls per
303
267
36
415
378
37
483
435
48
319
281
38
Number and Size of Bowls
Well-
number
Standard Deviation
Diameter of Bowlsinches
Standard Deviation
Bowl Diameter Divided
by Column Diameter
Standard Deviation
15.20
2.20
Lift per Bowl-feet
Standard Deviation
53.20
20.00
5.10
2.10
6.20
2.27
6.25
1.42
5.20
2.20
1.31
.14
Pumping Lift per Bowl Stage
61.00
69.60
54.40
The required size of the bowl assembly is largely a function of the
discharge of the well and the "head"-lift plus friction loss. Friction loss is
a function of column diameter and velocity of flow. Friction loss is inversely
related to column diameter and directly related to velocity. Thus, with
other things permitting and equal, discharge would be maximized and head
minimized by using a large column. However, considering costs involved
it may be more economical to use a smaller column even though the head
is slightly increased, the goal being to balance the added cost associated
with the increase in head with the reduction in cost realized by using smaller
column.
The study showed that the column was smaller on the average than the
bowls, thereby increasing the velocity which, in turn, slightly increased the
head. The district bowl diameter averaged 1.31 times the column diameter
(Table 7).
Lift per bowl averaged
61 feet for farm survey electric wells and 70
feet for farm survey gas wells. Lift per bowl averaged 53 feet for the
irrigation districts combined, the range by district being from 40 to 72 feet
( Table 7).
Data on age of bowls were available for the farm survey and one of the
districts. The average age of bowls in farm survey wells was about four
years while bowl age in the district wells averaged 2.3 years ( Table 8).
Bowls vary greatly in age, the range being from less than one year to 12
years.
16
ARIZONA ACRIC, EXPERIMENT STATION TECH. BULLETIN 182
Electric Motors
The rated horsepower of 588 electric motors in the study averaged 192
horsepower (Table 9). Farm survey motors averaged 208 horsepower
compared with an average for the districts of 190 horsepower. Variation
in horeepower was great, ranging from under 50 to over 500 horsepower.
The largest number of motors fell in the size group 200 -249 horsepower.
Table 8.
Age of Bowls in District 1 and Farm Survey Wells
Single
District
(electric)
Age
(years)
0-1
2-3
4 -5
Farm Survey
Gas
Electric
Number of Wells
Total
51
40
16
10
30
24
16
5
9
2
11
3
5
7
3
2
2
4
3
2
2
8
5
3
21
133
6 -7
8 -9
10-11
12
2
1
Total
63
49
Mean
2.3
3.0
-
Mean Age and Standard Deviation (years)
S
Table 9.
3.9
3.3
4.0
3.0
3.2
3.1
Size Distribution of the Power Unit, District and Farm
Survey Wells
Rated
HP
Under 50
Districts
(electric)
Farm
Survey
Total
Electric
All Electric
Number of Wells
8
1
9
50 -99
100-149
150-199
200-249
250-299
300 -349
350 -399
400 -449
450 -499
500 &Over
42
92
107
120
98
41
5
47
97
114
136
Total
538
Mean
190
86
14
7
1
8
5
7
16
6
6
2
-2
50
Farm Survey
S
COST OF PUMPING WATER
1
2
10
4
104
47
16
7
1
1
3
10
588
24
Mean Rated HP and. Standard Deviation
208
113
Gas
192
89
3
,
`364
84
17
Rated horsepower (symbol X16) and input horsepower (X15) for electric motors were highly correlated (Table 10) The majority of motors
were operating under nearly full load conditions. Of the 588 motors in the
irrigation districts, two -thirds operated at 1,800 RPM, 30 percent at 1,200
RPM, and three percent at 1,500 RPM ( Table 11). An inverse relationship
between horsepower and revolutions per minute of the motor may be
expected in the interest of minimizing vibration as motor size is increased.
Data on age of motors were available only for wells in the farm survey.
The mean age of this group of 50 motors was 6.1 years, with the range being
from 1 to 17 years ( Table 12) Smaller motors were older on the average
than larger motors
might be expected due to the declining groundwater table which necessitated installing larger motors.
Other information available indicates the average life of electric
motors is much longer than is indicated by the average age of motors in the
farm survey. Farmers interviewed in the survey felt electric motors would
last almost indefinitely provided they were rewound every 15 to 20 years.
Data available from one major irrigation district showing the number of
new motors purchased over a recent 10 -year period indicated an average
motor life of approximately 35 years. Other districts estimated a similar
life with the expectation that one rewind would be required on the average
during that period. On the basis of information obtained it was concluded
that electric motors would have an average life of 35 years with one rewind
at the end of 17 or 18 years.
.
-as
Table 10.
.
Rated Horsepower Related to Input Horsepower, Farm
Survey Wells
(X16 = bo ±b15 X15)1
Farm Survey
Item
Number of Wells
X162/
SX163/
X1521
SX153/
R4/
S16.155/
ba6/
b157/
Sb153/
Electric
50
208
113
216
136
.9428
38.20
38.38
.7823
.0399
Gas
24
364
84
1,261
326
.8982
37.93
70.36
.2326
.0243
= Input
horsepower; X16 = Rated horsepower.
Mean of specified variable.
3 SX = Standard deviation of specified mean.
4 Correlation coefficient.
Standard error of estimate.
6 Regression constant.
7 Regression coefficient of specified variable.
8 Standard
error of the regression coefficient.
1
2
18
X15
X=
ARIZONA AGRIC. EXPERIMENT STATION TECH, BULLETIN 182
Speed of Electric Motors Related to Size, District Wells
Revolutions per Minute
Table 11.
Rated
HP
1,200
28
26
17
29
41
22
14
5 -9
10 -14
15 -19
Total
Mean
S
9
8
All
8
9
19
62
47
97
114
136
104
47
16
89
107
63
25
2
7
-
1
Total
Percent
Under 5
-
1
50 -99
100-149
150 -199
200 -249
250 -299
300 -349
350 -399
400 -449
450 -499
500 & Over
179
30
Table 12.
1,800
Number of Wells
Under 50
Age
(years)
1,500
17
3
7
1
1
9
392
67
10
588
100
Age of Power Units Related to Rated Horsepower, Farrn
Survey Wells
Electric Motors, Rated HP
Natural Gas Engines, Rated HP
Under 200 200-349 350 & Over Total Under 300 300 -449 450 & Over Total
Number of Wells
6
8
2
13
8
3
1
19
26
-
7.3
2
2
4
-
--
21
18
6
4
-
4
49
3
1
1
1
-
-
15
3
21
1.7
4.0
12
2
1
3
16
3
1
1
Mean Age and Standard Deviation (years)
5.5
-
4.25
9.0
6.1
4.5
3.4
4.1
Natural Gas Engines
Manufacturer's continuous duty rated horsepower of the 24 natural
gas engines included in the farm survey averaged 364 horsepower, the range
being from 200 to 500 horsepower ( Table 9 ) Rated horsepower and input
horsepower were highly correlated, the coefficient being .898 ( Table 10)
The mean age of the gas engines in the study was 4.0 years ( Table 12)
As was the case with electric motors, smaller gas engines were considerably
older than the larger engines.
Indications are that the average life of engines is greater than the
eight years indicated by the 21 units for which data were available in the
farm survey. Information provided by several natural gas engine dealers
and service companies indicates a 15-year life, with a major overhaul at
the end of each five years of use. Therefore, a 15 -year life was used
subsequently in the analysis of fixed costs.
.
.
.
COST OF PUMPING WATER
19.
Analysis of Operations
In the preceding section a description has been given of the wells
and appurtenant equipment included in the study. An analysis now will
be made of various physical aspects related to operation of the wells.
Gallons per Minute
The average ( mean) discharge of farm survey electric wells was 1,256
gallons per minute and for gas wells 1,585 gallons per minute (Table 13)
.
Table 13.
Discharge
(gpìn)
Under 500
500 -999
1,000 -1,499
1,500 -1,999
2,000-2,499
2,500-2,999
3,000 -3,499
3,500 -3,999
4,000 -4,499
4,500 -4,999
Total
Discharge in Gallons Per Minute, District and Farm Survey
Wells
Districts
(electric)
7
66
139
140
90
57
15
17
6
Farm Survey
Electric
Gas
Number of Wells
10
7
15
10
5
2
All
Wells
-
17
4
10
4
77
159
160
99
1
60
5
16
17
1
6
1
1
538
50
24
612
Mean Discharge and Standard Deviation (gpm)
Mean
S
1,810
778
1,256
752
1,585
553
1,756
768
Production of district wells averaged somewhat higher, 1,810 gallons per
minute.
Discharge of farm survey electric wells varied widely, with 10 of the
50 producing less than 500 gpm. The farm survey gas wells showed a
greater concentration with 10 of the 24 wells producing 1,5004,999 gallons
per minute. The districts had relatively few low producing wells and some
high producers.
Efficiency
Efficiency of a pumping plant is equal to efficiency of the pump
multiplied by the efficiency of the motor. The equation may be written:
E = EP multiplied by Em
where E = Overall efficiency
Ea = Efficiency of the pump
Em = Efficiency of the motor
20
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
The analysis which follows will be in terms of overall efficiency
since data on the efficiency of the pump and motor are not available separately. Overall efficiency for electrically powered installations is not
directly comparable with natural gas overall plant efficiencies, however,
since the conversion from electrical to mechanical energy is more efficient
than conversion from chemical to mechanical energy. For this reason efficiency of electric wells is considered first followed by an analysis of gas
wells.
Table 14.
Efficiency
(percent)
Overall Plant Efficiency of Electrically Powered Wells,
District and Farm Survey Electric Wells
Farm
All
Electric
Districts
Survey
(electric)
20.0-29.9
30.0-39.9
40.0-49.9
50.0 -59.9
60.0-69.9
70.0 & Over
Electric
Number of Wells
8
15
61
185
210
59
538
Total
Wells
3
10
6
14
14
3
25
67
199
224
50
588
11
62
Mean Efficiency and Standard Deviation (percent)
Mean
58.7
10.2
S
51.7
13.9
58.1
10.6
-
Efficiency of Electric Wells
Overall efficiency is equal to water
horsepower divided by input horsepower as given by the equation,
Water horsepower
Overall efficiency
Input horsepower
Water horsepower is a function of gallons per minute and lift as given
by the equation,
( Lift, ft.)
( Discharge, gpm)
Water horsepower
-
-
3,960
Input horsepower for electrically powered installations is given by
the equation,
Input horsepower = Kw multiplied by 1.34,
where Kw is the kilowatt demand and 1.34 is the conversion constant. Efficiency, the ratio of power output to power input, may then be expressed
by the equation,
( Discharge, gpm)
( Lift, ft. )
Overall efficiency
3,960 (Kw) (1.34)
Efficiency of large electric motors such as those used on irrigation
wells varies only one or two percentage points with normal changes in
load. The efficiency change for 100 to 300 HP motors associated with
changing from one-half to full load is only two percentage points. Therefore, low overall efficiencies are directly attributable to the pump.
-
COST OF PUMPING WATER
21
Average overall efficiency of the farm survey electric wells was 51.7
percent (Table l4). The variation among pumping plants was great,
ranging from under 30 to over 70 percent.
The overall efficiency of district wells averaged 58.7 percent, 13.5
percent above the farm survey electric well average. The higher district
efficiencies stemmed primarily from a continuous testing and repair program for the correction of low efficiency wells
those below 40 percent
efficiency. Under ideal conditions, efficiency of an electric well could be
slightly above 74 percent.
-
Efficiency of Gas Wells
-
The initial equation for overall efficiency
However, the expression of input
horsepower varies to reflect the units used in measuring fuel input. Input
horsepower for natural gas engines is expressed by the equation,
Input horsepower -MCF per minute
is the same regardless of the fuel used.
0.000041
where MCF stands for thousand cubic feet and the denominator represents
conversion constant with an assumed thermal energy of 1,035 BTU for each
cubic foot of gas.
Overall efficiency for natural gas wells may now be expressed by the
equation,
(Discharge, gpm) (Lift, ft.) (0.000,041)
Overall efficiency
3,960 (MCF per minute)
Large natural gas engines such as those used to pump irrigation water
can show tremendous variation in the efficiency of converting fuel to power.
An electrical system in need of tune -up or poor carburetor adjustment can
markedly reduce overall efficiency. Therefore, an efficiency below that
considered to be optimum cannot be readily identified as a problem of the
pump or of the engine.
The average efficiency of the natural gas powered wells in the farm
survey was 13.2 percent (Table 15) The modal group -11 of the 24
wells -had 14 to 15.9 percent efficiency. Two wells had an efficiency of
-
.
Table 15.
Efficiency
(percent)
4.0 -5.9
6.0-7.9
8.0-9.9
10.0 -11.9
12.0 -13.9
14.0 -15.9
16.0
&
Total
Over
Overall Plant Efficiency on Natural Gas Powered Wells,
Farm Survey Gas Wells
Farm Survey
Gas
Number of Wells
2
1
6
2
11
2
24
Mean Efficiency and Standard Deviation (percent)
Mean
S
22
13.2
3.4
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
over 16 percent while, at the other extreme, two wells were only 4.0 to 5.9
percent efficient. Under ideal conditions gas wells could operate at an
efficiency level slightly above 18 percent, indicating that the farm survey
gas wells were operating at a relative level of efficiency approximately equal
to the farm survey electric wells.
Table 16. Hours Operated, Acre -Feet of Water Pumped, and Fuel
Consumption Per Acre -Foot and Per Acre -Foot Per Foot
of Lift, District and Farm Survey Wells, 1963
Item
Districts
Farm Survey
(electric)
Electric
Gas
Hours Operated
Mean
S
Acre -Feet Pumped
Mean
S
Fuel Consumption
Mean per AF
S
Mean per AFF
S
4,520
1,342
3,763
1,329
3,717
1,265
1,558
845
870
572
1,084
513
KWH
KWH
MCF'
477
818
371
2.22
.770
10.5
2.72
.0241
.0097
140
1.79
.385
Thousand cubic feet.
Hours Operated and Water Pumped Annually
The number of hours a well is operated annually will depend upon the
discharge and the water requirement. The water requirement, in turn,
depends upon the acres served, the cropping system, and irrigation practices. Wells in the farm survey served an average of 212 acres per well.
During the year 1963 farm survey electric wells were operated an average of 3,763 hours and farm survey gas wells an average of 3,717 hours
(Table 16) District wells were operated an average of 4,520 hours, substantially more than the farm survey wells.
A number of factors probably contribute to district wells being used
more hours than individually owned irrigation wells. Some of the irrigation districts through use of supplemental surface water during peak
demand periods are able to more fully utilize their wells over longer periods
than are individual farmers. Location of district wells may also facilitate
serving a larger acreage. Individual farmers may feel the need to maintain
a certain amount of "surplus" capacity for flexibility in scheduling and as
insurance against breakdowns in peak demand periods. Districts probably
can accomplish this objective with relatively less "surplus" capacity. The
cropping system in the districts showing the greatest number of hours run
makes use of the land a larger part of the year, thereby making a more
continuous demand for irrigation water.
Acre -feet of water pumped is a function of discharge and hours run,
as indicated by the following equation,
GPM multiplied by Hours pumped
Acre-feet
.
-
5,431
A well produces approximately one acre -inch per hour for each 450 gallons
COST OF PUMPING WATER
23
pumped per minute. In other words,
One acre inch = 450 GPM for one hour.
In 1963, farm survey electric wells pumped an average of 870 acre feet and farm survey gas wells an average of 1,084 acre -feet (Table 16)
District wells averaged 1,558 acre -feet.
.
Fuel Consumption
Fuel consumption is a direct function of input over time. Input may
be expressed either as horsepower or in units of energy ( electrical or
chemical). In terms of horsepower the equation is as follows:
Water horsepower
Input horsepower =
Overall efficiency
in which water horsepower is the energy requirement based upon lift and
gallons per minute.
In terms of electrical energy the requirement to pump one acre -foot of
water is,
1.024 Lift (ft. )
KWH
Ee
when KWH stands for kilowatt hours and Ee stands for overall efficiency
of the electric motor and pump combined expressed as a decimal.
For natural gas powered wells the quantity of gas ( MCF) required to
pump one acre -foot of water is,
.00318 Lift (ft. )
MCF
Eg
where MCF stands for thousand cubic feet of natural gas and Eg stands for
the overall efficiency of the natural gas engine and pump combined expressed as a decimal.
As is indicated by each equation, fuel consumption is a direct function
of overall efficiency of the pumping plant.
-
Electric Energy Consumption-The farm survey electric wells used
an average of 818 KWH of electricity per acre -foot of water pumped ( Table
16) This amount was substantially greater than the average of 477 KWH
for the irrigation districts. Part of the difference in the electricity requirement per acre -foot is due to variations in pumping lift. With fuel consumption expressed on the basis of energy consumed per acre -foot per foot
of pumping lift, the average for the farm survey electric wells was 2.22 KWH
compared to 1.79 KWH for the districts.
The wide variation among survey wells in kilowatt hours of electricity
used per acre -foot per foot of lift is shown graphically in Figure 1. Wells
producing less than 1,000 gallons per minute generally were relatively inefficient in utilization of energy. Had the pumps in these wells been selected
for the lower production, their energy utilization would have compared
favorably with those of higher discharge. With energy comprising approximately 85 percent of the variable costs of pumping, and 57 percent of the
total costs of pumping, its inefficient use has a very important bearing on
pumping costs per acre -foot.
Examination of the individual records of the 12 lowest efficiency
electrically powered wells revealed that five of the 12 had bowls over five
years old, four of the 12 were pumping noticeable amounts of sand, and
two of the 12 were pumping air.
.
24
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
Bowls over five years in age, without benefit of overhaul, will have
experienced, on the average, an increased lift greater than 45 feet which,
combined with normal wear, causes a decrease in both efficiency and
discharge.
The abrasive action of sand causes rapid and excessive wear to the
impeller and pump bowl. Wear of the impeller makes it less effective,
and increased clearance from bowl wear allows leakage from the high to
4.5
4.0
J
o 3.5
v
óo
u_
a
á>
3.0
áo
-
u_
m
a
2.5
a
2.0
1.5
I.0
0
0.5
OUTPUT
10
15
20
2 5
30
3 5
(thousands of gallons per minute)
Figure__I- Kilowatt Hours of Electricity Used Per Acre -Foot Per
Foot of Lift Related to Discharge for the 50 Farm
Survey Wells (Each dot represents one well. The curve
was drawn free hand.)
COST OF PUMPING WATER
25
low pressure side of the bowl. The net result is a lowered discharge and
efficiency for the well. However, movement of sand into the well is reduced
by a decrease in discharge so that after the initial sand -induced wear the
rate of decrease is reduced until the pump is rebuilt to its former capacity.
Where a mixture of air and water is being pumped the volume of air
and its compressible characteristics reduce both discharge and efficiency.
By contrast, the 17 wells with efficiencies over 60 percent had no
noticeable sand or air pumping. Only one of the 17 had a bowl age greater
than five years and it was located in an area not affected by a rapidly
declining water table.
Natural as Wells-The farm survey natural gas wells used an average of 10.5 MCF ( thousand cubic feet) of gas per acre -foot of water pumped
(Table 16). Gas required per acre -foot per foot of lift was .0241 MCF.
Capital Expenditures
Capital expenditures associated with pumping irrigation water were
grouped in three categories: ( 1 ) well and casing, ( 2) pump components,
and ( 3) power unit. The well and casing includes drilling and casing of
the well, perforating the casing, and developing and testing the newly
drilled well. Pump components include the column assembly (column,
shaft, bearings, and oil tube, if any ), bowls, suction pipe, strainer (if any),
head, and discharge pipe. The power unit for electrically powered wells
includes the motor, starter, and electrical wiring. Transformers were not
included in this study since they were furnished by the power supplier for
a majority of electric wells in the farm survey. The power unit for natural
gas powered installations included the engine, drive line, gear head, and
water cooler.
In arriving at the capital expenditures the irrigation wells and appurtenant equipment were priced according to the schedule given in Table 17.
The prices, which include installation, represent 1963 costs of items similar
to those in wells included in the farm survey. Capital expenditures for the
wells are, therefore, on a current uniform cost basis regardless of their age
or cost at time of installation.
Using these prices the average replacement cost new of farm survey
electric wells was $32,841 (Table 18) About 50 percent of the investment
was in the well and casing, 25 percent in the pump, and 25 percent in the
power unit. Somewhat similar relationships prevailed for irrigation district
.
wells.
The investment in the power unit is relatively greater for gas than
for electric wells. Moreover, as indicated above, the farm survey gas wells
were somewhat larger and deeper on the average than the farm survey
electric wells. As a result the replacement cost new of farm survey gas
wells averaged $49,194 per well, substantially higher than for farm survey
electric wells. The power unit comprised about 40 percent of the total
investment, the pump about 22 percent, and the well and casing about
38 percent.
26
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
Cost Analysis
The cost analysis of pumping water was made in terms of fixed, added
capital and variable costs. Fixed costs include depreciation, property taxes
and interest on investment -costs which ordinarily do not vary with the
amount of water pumped. Added capital costs include those costs related
to the declining groundwater table; for example, adding column and bowls,
and increasing the size of the power unit to accommodate the greater lift,
together with installation costs. Variable costs include those costs related
directly to operation of the well: fuel, repair and maintenance, lubrication
and attendance.'
The approach followed in the study was to use the farm survey electric
and gas wells as the primary basis for deriving individual farm costs of
pumping irrigation water, and to use the district wells as a secondary basis
of costs to substantiate or support the farm survey cost estimates. As far
as possible the same procedures were followed in deriving costs for the
districts and the farm survey wells. The same unit prices were used in computing the replacement cost new of the wells and appurtenant equipment,
the same years of life were used in depreciation schedules, and comparable
values and rates were used in deriving property taxes and interest on invest-
ment.
Hours of operation and quantity of fuel used for the districts were
obtained from district records. Electric energy was priced at nine mills
per KWH to allow uniform comparison with farm survey wells. Repairs
and maintenance for the districts, which include the farm survey items of
"lubrication and "attendance," were obtained as a lump sum from each of
the districts. Compared with individual farmers, districts may realize
some savings from volume discounts and from using their own employees
rather than commercial repairmen. To the extent that such savings are
realized the district and farm survey figures may not be entirely comparable.
Fixed Costs
Fixed costs in this analysis relate directly to the capital investment in
the well and appurtenant equipment given earlier in the report.
Depreciation- Depreciation was calculated for the well, the pump,
and the power unit individually. The straight -line method was used, being
applied to the cost new of each item. Salvage value was considered negligible. Years of life were based upon the typical life of the component as
given above in the description of the well and pump installations.
The well and casing were depreciated over a 40-year life. Annual
depreciation, therefore, was equal to 2.5 percent of the cost new.
3
I should be noted that managementSince,
costs were not included in the study except
as will
as they may be reflected in attendance.
be shown, the attendance cost
item is relatively small, it appears unlikely that an adequate charge for management is
included. It may also be noted that well- deepening costs are not included in added
capital costs. As indicated earlier in the text, most of the wells are deep enough so it is
unlikely they will have to be deepened within the next decade. Thus, the "cost of
deepening" is included in the initial cost of the well and reflected in the fixed costs in this
analysis.
COST OF PUMPING WATER
27
Each Additional
Make B
ist Stage
Each Additional
Make C
1st Stage
Each Additional
Other Makes -- 1st Stage
Each Additional
-
-lst
Bowl Cost by Make, Dollars per Stage
Make A
Stage
Column Assembly, Dollars per Foot
Suction Pipe, Dollars per Foot
Discharge Pipe, Dollars per Foot
--
350
120
340
100
160
450
150
400
125
440
145
470
12
10
--
12.00
4.70
4.70
8
215.00
8.50
4.80
1.00
14.30
14
9.00
3.00
3.00
6
200.00
8.00
4.00
1.00
13.00
Column Assembly, Dollars per Foot
Drilling Well
Casing
Perforation
Total
Shoe, Dollars per Well
12
295.00
9.00
7.00
1.00
17.00
18
12
22.00
9.50
9.50
600
200
580
195
510
170
565
190
14
750
315
790
290
640
230
725
280
16
Outside Bowl Diameter (inches
16.00
6.50
6.50
10
Diameter ( inches)
242.00
9.00
5.60
1.00
15.60
16
Diameter of Casing (inches)
1,000
420
1,050
450
900
325
985
400
18
25.00
13.25
13.25
14
340.00
9.00
8.00
1.00
18.00
20
1,290
545
1,350
600
1,170
425
1,270
525
20
28.00
14.85
14.85
16
400.00
9.00
9.00
1.00
19.00
24
Itemized Capital Cost of Well, Pump, and Power Unit Components, Including Installation Costs, 1963
Item
Table 17.
Gas Engine, Dollars
Automatic Starter, Dollars
Head, Dollars
1,200 RPM
1,800 RPM
1,200 RPM
1,500 RPM
1,800 RPM
250
13,750
200
11,000
150
100
9,000
540
540
540
540
400
400
400
400
6,000
3,867
1,470
5,538
200
980
250
150
3,951
3,400
2,809
1,360
100
2,592
2,300
1,807
470
1,306
50
300
16,500
Horsepower
1,000
540
2,570
5,125
6,675
250
1,000
1,000
6,022
2,625
7,745
300
350
19,250
Horsepower
400
20,000
450
22,500
1,200
1,200
500
25,000
1,200
1,200
8,793
3,100
7,961
3,000
6,969
2,653
1,000
1,000
11,233
450
10,006
400
8,829
350
(Continued) Itemized Capital Cost of Well, Pump, and Power Unit Components, Including Installation Costs, 1963
Electric Motor, Dollars
Item
Table 17.
Average Capital Investment Per Irrigation Well Assuming
the Wells and Appurtenant Equipment Were New at 1963
Price Level'
Table 18.
Districts
(electric)
(dollars)
Item
Well and Casing2
Pump'
Power Unit4
Total
Farm Survey
Electric
(dollars)
Gas
(dollars)
13,720
16,504
19,003
9,180
8,453
10,668
5,768
7,884
19,523
28,668
32,841
49,194
'Replacement cost new in 1963; that is, assumes the wells and appurtenant equipment were new in 1963 and that 1963 costs were used in deriving the capital investment,
based upon itemized costs given in Table 17.
2 Includes perforating the casing, developing and testing the newly drilled well.
3 Includes column assembly, bowls, suction pipe, strainer (if any), head, and
discharge pipe. Strainer costs per well for various districts were: Districts 1, 3, and 6,
$18; District 2, $20; and District 4, $44.
For gas wells,
4 For electric wells, includes motor, starter and electrical wiring.
includes natural gas engine, drive line, gear head, and water cooler.
The pump was depreciated over a 15 -year life, this life expectancy
being based upon the column assembly. Some of the items included in the
pump category typically will not last 15 years. Bowls, for example, may
wear out in a year of two. Such items would be replaced and the associated cost included as a part of repair and maintenance.
Electric motors were depreciated over a 35 -year life. One rewind
typically would be required during that period, the cost being a part of
repair and maintenance. Starters were depreciated over a life of 10 years.
Using these rates, annual depreciation amounted to $1.48 per acre foot for the farm survey electric wells and $0.78 per acre -foot for the districts
(Table 19). With lift considered, depreciation per acre -foot per foot of
lift averaged .39 cent for the farm survey electric wells and .29 cent for
the districts.
Natural gas engines typically have a life of 15 years. During this
expected life two major overhauls would be required, the cost being a part
of repair and maintenance. With this expected life annual depreciation
of natural gas engines was 6.7 percent of the replacement cost new. Using
this rate of depreciation on the engine, total annual depreciation for the
gas wells averaged $2.30 per acre -foot and .53 cent per acre -foot per foot
of lift.
It should be kept in mind that depreciation costs are directly related
to the period or years of life over which the item is depreciated. If years
of life are reduced, depreciation costs will increase, and vice versa. Thus,
individuals using these cost data should adjust the depreciation charges
according to the years of life of the well and appurtenant equipment with
which they are concerned.
30
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
GD
7,308
6,705
11,944
100
68
10,410 10,666
7,393
1,025
475
4,649
1,549
407
415
254
8.4011
12.2607
4.7455
6.6817
.6582
6.9798
1.2140
.1291
.0782
.4771
4.0873
.1628
3.3825
1.7734
4,764
6.1862
11.0195
4.288G
1.4293
.3759
.0924
.4386
4.3947
1.3616
.7380
2.2951
1.4845
1.1325
.7655
.4383
.6561
1.2007
.4743
.6477
.3625
.5682
.4271
.7781
.2200
.3927
.1654
1,476
800
2,488
475
711
1,302
6,072
1,056
112
2,943
2,763
6,368
985
666
1,292
564
315
413.
885
665
1,213
258
343
612
2.502
1.778
.247
1.531
.060
.664
.213
.160
.291
.082
.147
.062
3.244
2.228
1.847
.321
.034
.021
.126
.895
.300
.203
.392
.125
.171
.096
2.534
1.422
.986
.329
.086
.021
.101
1.011
.313
.170
.528
.101
.151
.276
I
These costs relate to the cost of operating an established well. A charge is not included for management required in
arranging for drilling
and equipping the well, or in operating the well except as it may be included as a part of the "attendance" cost. Moreover,
a cost is not
included for the land where the well is located, including land required for access.
2 Per
year.
3 At
9 mills per KWH, and $0.40 per MCF.
Repairs
Lubrication
Attendance
Total Variable Costs
Total Costs
Fuel3
Interest on Investment at 6%
Property Taxes
Total Fixed Costs
Added Capital Costs
Variable Costs
Cost per Acre -Foot
Cost /AF per Foot of Lift
Districts
Farm Survey Districts
Farm Survey
(electric) Electric Gas (electric) Electric Gas
(dollars) (dollars) (do liars) (dollars) (dollars) (dollars) (cents) (cents) (cents)
Cost per Welle
Districts
Farm Survey
Electric Gas
(electric)
Estimated Fixed, Added Capital and Variable Costs of Pumping Irrigation Water Per Well, Per
Acre -Foot, and Per Acre-Foot Per Foot of Pumping Lift'
Fixed Costs
Depreciation
Well and Casing
Pump
Power Unit
Total
Item
Table 19.
-In
Property Taxes
1963 irrigation wells typically were valued on the
basis of rated horsepower of the power unit for property tax purposes. The
rate was uniform at $40 per horsepower up to a maximum of 250 horsepower,
or $10,000 assessed value per well. Tax rates vary, of course, from one area
or school district to another. For purposes of this study a uniform rate of
$8.00 per hundred dollars of valuation was used, this amount being roughly
an average of rates in farming areas of Maricopa and Pinal Counties.
On this basis, property taxes on farm survey electric wells were 76 cents
per acre -foot and 43 cents per acre -foot for district wells ( Table 19 ) On a
per acre -foot per foot of lift basis property taxes on farm survey electric wells
were .20 cent compared with an average of .16 cent for irrigation district
wells. Property taxes on farm survey gas wells were 74 cents per acre -foot
and .17 cent per acre-foot per foot of lift.
.
Interest on Investment- Interest on the investment in the well and
appurtenant equipment was based upon one -half the replacement cost new,
it being assumed that the "average" well and equipment would be one -half
"worn out." Using a rate of six percent per annum, interest on investment
per acre-foot amounted to $1.13 for farm survey electric wells and 57 cents
for district wells (Table 19). On a per acre-foot per foot of lift basis interest
on investment average .30 cent for farm survey electric wells and .21 cent
for district wells. Interest on investment on natural gas wells averaged
$1.36 per acre -foot and .31 cent per acre -foot per foot of lift.
Total Fixed Costs of Electric Wells- Fixed costs for farm survey
electric wells totaled $3.38 per acre-foot, compared with $1.77 per acre-foot
for district wells ( Table 19) Part of this variation was due to differences
in acre -feet of water pumped per well. As indicated earlier in the report
(Table 16), farm survey electric wells pumped less water on the average
( 870 acre -feet) than district wells (1,558 acre-feet), thereby contributing
to higher fixed costs per acre -foot pumped.
Pumping lift is also an important factor. Fixed costs per acre-foot
per foot of lift show much less variation than fixed costs per acre -foot.
Fixed costs per acre -foot per foot of lift average .90 cent for the farm survey
electric wells and .66 cent for the districts.
With the rates used in the analysis, depreciation comprises 44 percent
of fixed costs for the electric wells. Interest on investment comprises about
one -third and property taxes just under one -fourth of fixed costs.
.
Total Fixed Costs of Gas Wells-Fixed costs for farm survey gas
wells totaled $4.40 per acre -foot and 1 cent per acre foot per foot of lift
With the rates used, depreciation accounts for a little over half
( Table 19)
(52 percent) of fixed costs of gas wells. Interest on investment comprises 31
percent and property taxes 17 percent of total fixed costs.
.
Added Capital Costs
As is well known, the groundwater level is gradually declining in most
parts of central Arizona. Data available indicate the average decline in
pump areas outside the irrigation districts is about nine feet per year. The
average decline within the seven irrigation districts included in this study
varied from 3.0 to 9.5 feet annually. These rates of decline were used in
estimating the cost of the additional column, bowls, and power unit capacity
required to lift water from greater depths.
32
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
cam,
375
450
250
300
350
480
540
600
660
720
780
2,098
2,146
3,073
2,146
3,414
2,050
4,264
1,954
2,978
1,858
3,746
1,762
43.39
45.53
51.82
40.30
49.90
2,848
2,146
5,212
2,050
4,656
1,954
4,560
1,858
3,854
1,762
41.62
60.52
55.08
53.48
46.80
Includes added cost of pump head.
Includes added cost of motor and automatic starter.
Variations are due to differences in cost of component parts required for different lifts.
7
8
One-half of cost, it being assumed the other half would be charged to repairs which usually are made at the same time added column or
bowls are installed.
6
5
3
Twelve -inch column pipe.
608
656
4
1,320
1,320
2,462
2,050
1,906
1,954
416
464
512
560
1,810
1,858
1,854
1,762
320
368
224
272
Normally aspirated natural gas engine loaded to 70 percent capacity for continuous use.
Fourteen -inch bowls of make C.
170
170
760
820
1,320
1,320
1,320
1,320
1,320
1,320
1,320
1,320
Assumes 1,800 RPM and 75 percent pump efficiency.
170
170
640
700
170
170
170
170
400
460
520
580
170
170
(dollars) (dollars) (dollars) (dollars) (dollars) (dollars) (dollars) (dollars)
280
340
2
12
13
10
11
8
9
6
7
5
4
Instal-Total
t
525
300
200
360
420
225
150
240
300
Lift
Table 20. Estimated Added Capital Expenditures Related to Increased Pumping Lift
Added Costs
Added Costs
Gas Wells
Added Capital Cost of Pump
Electric Wells
Physical Plant Required
Motor Engine
Bowl Column
Cost /Ft. Total Cost /Ft.
Bowls
Column
lation5
Total.'
Electric'
Declines
Gas
Declines
HP'
HP2
Feet4
Stages'
Since repairs frequently are made at the same time as added capital
items are installed, data obtained in the farm survey and from the districts
did not allow a precise distinction between added capital costs and repair
items. Therefore, using the unit price figures given in Table 17 a schedule
of added capital costs related to increased pumping lift was developed for
a typical well ( Table 20) Most wells in central Arizona are drilled to a
sufficient depth initially so that deepening appears to be unnecessary during the next decade as the groundwater level declines. Therefore, costs of
well deepening were not included in the schedule of added capital costs
related to increased lift.
Added capital costs thus derived were subtracted from the total of
added capital and repair costs, and the remainder was taken to represent
repair and maintenance costs.
Electric Wells -Added capital costs amount to 48 cents per acre -foot
for farm survey electric wells and to 16 cents per acre-foot for the districts
( Table 19 ). Comparable figures on an acre -foot per foot of lift basis are .13
cent and .06 cent. Differences in added capital costs for farm survey electric
and district wells are due in large measure to differences in the rate of decline in the groundwater level and to differences in the amount of water
pumped annually.
.
Natural Gas Wells-Added capital costs for farm survey natural gas
wells were 44 cents per acre -foot and .10 cent per acre -foot per foot of lift
(Table 19). Added capital costs per acre-foot and per acre -foot -foot for
natural gas wells were somewhat lower than for electric wells due to the
larger amount of water pumped. On a per well basis they were higher due
to the higher capital cost involved in increasing the size of the power unit.
Variable Costs
Variable costs, as the term implies, include those costs which vary
directly with the amount of water pumped. In this respect they are the
converse of fixed and added capital costs which are not influenced by the
amount of water pumped from a well. Data obtained in the farm survey
permitted deriving the costs of power or fuel, repairs and maintenance,
lubrication and attendance for individual wells. Data obtained from the
districts showed the cost of power for individual wells and an aggregate
district figure for the other three items combined.
-In
Electric Wells
the initial tabulation of costs, energy was priced
at nine mills per kilowatt hour to provide a uniform base for comparisons.
The nine-mill figure is close to the average actual rate of 9.16 mills for the
50 farm survey electric wells. In the section "Effect of Energy Rates on
Costs" found later in the report, other rates typical of those charged by
the various electrical districts are used in the analysis.
With a rate of nine mills per kilowatt hour, power costs were $6.98 per
acre -foot for the farm survey electric wells and $4.09 for the districts
( Table 19)
Repair and maintenance costs, the second most important variable cost
item, amounted to $1.21 per acre -foot for farm survey electric wells. Lubrication costs were $.13 and attendance charges $.08, making a total for these
three items of $1.42 per acre -foot. The corresponding figure for the districts was $.66 (Table 19)
Total variable costs per acre -foot were $8.40 for the farm survey
electric and $4.75 for the districts. Differences in pumping lift, of course,
accounted for much of the variance in costs per acre -foot.
.
.
34
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
On the basis of cost per acre -foot per foot of lift power costs averaged
1.8 cents for farm survey electric wells and 1.5 for the districts (Table
19). Other variable costs (repairs and maintenance, lubrication and attendance) totaled to .38 of a cent per acre -foot per foot of lift for the farm survey
electric wells and .25 of a cent for the districts.
Total variable costs per acre -foot per foot of lift were 2.22 cents for the
farm survey electric wells and 1.778 cents for the irrigation districts. Variable costs per acre -foot per foot of lift are influenced by efficiency, primarily
as a result of savings in power costs.
Natural Gas Wells -With a rate of $0.40 per MCF ( thousand cubic
feet), fuel costs for farm survey gas wells was $4.29 per acre -foot (Table 19).
Repair and maintenance, lubrication and attendance totaled to $1.90 per
acre-foot, making a total variable cost of $6.19 per acre -foot.
When lift is considered, fuel costs for the farm survey gas wells
amounted to .99 of a cent per acre -foot per foot of lift. Repair and maintenance, lubrication and attendance combined amounted to .43 of a cent per
acre- foot -foot. Thus, total variable costs, for farm survey gas wells amounted
to 1.42 cents per acre -foot per foot of lift.
Total Costs
For electric wells fixed costs, added capital costs and variable costs
( with electricity at nine mills) totaled $12.26 per acre -foot for the farm
survey electric wells. The total for the districts was $6.68 per acre -foot
( Table 19)
With pumping lift considered, fixed costs, added capital costs, and
variable costs for farm survey electric wells totaled 3.24 cents per acre -foot
per foot of lift. The comparable figure for district wells was 2.50 cents per
acre -foot per foot of lift.
For natural gas wells fixed costs, added capital costs, and variable
costs ( with fuel at $0.40 per MCF) totaled $11.02 per acre -foot, and 2.53
cents per acre -foot per foot of lift ( Table 19)
.
.
Estimating Cost of Pumping
Using data for the farm survey wells given in preceding paragraphs,
equations were developed to facilitate estimating variable, added capital
and fixed costs under various conditions. The equations are given first
for electric wells and then for gas wells. Some of the costs calculated from
these equations with the farm survey means for lift and for efficiency vary
slightly from the values reported in Table 19. The difference reflects a
combination of rounding in calculation, measurement errors and the difference between the true mean and the averaged lift and efficiency data.
The equations are useful for estimating average costs. The degree of
error in any analysis will depend to a large extend on how the given well
being analyzed compares with the average of the wells in the farm survey.
Electric Wells, Variable Costs
(1.024) (Pe) ( Lift, ft. )
Variable costs per AF =
+ .00376 Lift
Variable costs per AFF =
1.024 Pe
.00376
+
Ee
Pe represents the price in dollars of electricity per KWH; Ee represents
COST OF PUMPING WATER
35
overall efficiency of the pumping plant; and .00376 represents the total
cost of repairs, lubrication and attendance.
Using a nine -mill energy rate (the same as was used above), and the
average lift (378 feet) and efficiency (51.7 percent) for the farm survey
electric wells, we have
(1.024) (378)
378 (.009)
+ (.00376) (378) = 8.1595
Variable costs per AF =
}
.517
Variable costs per AFF =
± .00376 = .02159
(1.024517.009)
Variable costs per acre -foot per foot of lift can also be obtained, of
course, by dividing variable costs per acre -foot by lift. The average lift of
the farm survey electric wells was 378 feet. Dividing 8.16 by 378 gives
.02159.
Electric Wells, Annual Added Capital Costs
(46.10) (Decline, ft.)
Added Capital Cost per AF
AF pumped per year
(46.10) (Decline, ft.)
Added Capital Cost per AFF ( Lift, ft.) (AF pumped per year)
Decline refers to the annual decline in the groundwater level;
i.e., the annual increase in pumping lift measured in feet.
The average annual decline in the groundwater level used in the above
analysis was nine feet, the average pumping lift for farm survey electric
wells was 378 feet, and the average quantity of water pumped by these
wells during the year was 870 acre -feet. Using these data in the above
equations, we have
(9)
(46.
.4769
Added Capital Cost per AF
0
©
Added Capital Cost per AFF
(46.10) (9)
(378) (870)
-
.001262
Electric Wells, Annual Fixed Costs
Fixed costs per AF
Fixed costs per AFF =
AF pumped per year
( 7.80) ( Lift, ft.)
7.80
AF pumped per year
Using the average lift (378 feet) and acre -feet of water pumped by the
farm survey electric wells (870), we have
378)
3.3889
Fixed costs per AF = (7'80870(
-
Fixed costs per AFF =
X70
-
.00896
Total costs per acre -foot and per acre -foot per foot of lift can be readily
determined by adding variable, added capital and fixed costs obtained by
using the above equations.
36
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
it should be kept in mind that the constants, 46..10 and 7.80, used in
these equations were based upon data in Table 19. Thus, they relate to the
average electric well in the farm survey described in the first part of the
report.
Equations for computing variable, added capital and fixed costs for
natural gas wells are given below. These equations are based upon the
data presented above for farm survey gas wells.
Gas Wells, Variable Costs
Variable costs per AF
(
.00318
)
(Pg))
(
Lift, ft.)
Eg
Variable costs per AFF
-
.00318 Pg
+
+ .00436 Lift
.00436
Eg
Pg represents the price of gas per MCF. Eg represents overall efficiency
of the pumping plant.
Using a rate of 40 cents per MCF ( the same as used above) and average
lift (435 feet) and efficiency (13.2 percent) of the farm survey gas wells,
we have
(.00318) (.40) (435)
Variable costs per AF
+ ( .00436) (435) = 6.0884
.132
Variable costs per AFF =
(.00318) (.40)
+
.132
.00436
=
.0140
Gas Wells, Annual Added Capital Costs
(52.80) ( Decline, ft.)
AF pumped per year
( 52.80 ) ( Decline, ft.)
Added Capital Cost per AFF =
( AF pumped per year) ( Lift, ft.)
Decline refers to the annual decline in the groundwater level; i.e., the annual
increase in the pumping lift.
Added Capital Cost per AF
-
Using a decline of nine feet, the average used in the above analysis, and
the average acre-feet pumped ( 1,084 ) and lift ( 435 feet) for the farm survey
gas wells, we have
Added Capital Cost per AF
Added Capital Cost per AFF
(52.80) (9)
1,084
( 5189
= (1,084)
(435)
)
(
9)
- .4384
- .00101
Gas Wells, Annual Fixed Costs
Fixed Costs per AF
Fixed Costs per AFF
COST OF PUMPING WATER
-
(11.00) ( Lift, ft.)
AF pumped per year
11.00
AF pumped per year
37
or)
co
.8015
.9614
1.0861
ED53
SRPD4
10.46
10.46
.0241
.0241
MCF/AFF
2.2164
2.2164
2.2164
2.2164
2.2164
2.2164
.0178
.0213
.0241
.0179
.0227
.0166
5.0020
4.0313
.01152
.00929
Fuel Cost
$/AF
$/AFF
6.5569
7.8650
8.8852
6.6207
8.3935
6.1405
6.8996
6.0289
7.9782
9.2863
10.3065
8.0420
9.8148
7.5618
.01588
.01365
.02156
.02506
.02786
.02166
.02646
.02036
11,8455
10.9748
11.7782
13.0863
14.1165
11.8420
13.6148
11.3618
.02726
.02503
.03161
.03511
.03791
.03171
.03651
.03041
Total Costs
$/AF
$/AFF
-
Average rate paid by farmers surveyed in each district or area adjusted to 1965 rates.
Pumping lift and all costs other than the rates paid for electricity and natural gas were held constant in order to show the effect of differences in rates charged for fuel on the cost of pumping water.
47.82
38.54
MCF/AF
818.08
818.08
818.08
818.08
818.08
818.08
Total Variable Cost
$/AF
$/AFF
6Southwest Gas.
5Arizona Public Service.
Salt River Power District.
3Electrical Districts in Pinal County
do not confuse with the seven districts referred to throughout the study, five of which were irrigation districts and two large corporate farms.
2
I
SWG6
APS5
Natural Gas
Supplier 0/MCF
APS5
.8093
1.0260
.7506
ED23
ED33
ED43
Power Cost
$/AF
$/AFF
Farm Survey Wells: Energy Costs and Total Costs Per Acre-Foot and Per Acre-Foot Per Foot of
Lift, by Source of Electricity and Natural Gas'
Electricity Rates'
Fuel Consumption
Supplier 0/KWH KWH/AF KWH/AFF
Table 21.
Using the average Iift (435 feet) and the average acre -feet pumped
per year (1,084) by the farm survey gas wells, we have
(435) _
Fixed Costs per AF = (11.00)
4.4142
1,084
Fixed Costs per AFF
-
11.00
1,084
-
.01015
As was the case with the electric wells, the added capital and fixed costs
for gas wells derived by use of the equations are nearly identical to those
given in Table 19. The differences are due to rounding in arriving at the
constants used in the equations.
Total costs per acre-foot and per acre -foot per foot of lift can be readily
computed by adding variable, added capital and fixed costs computed by
use of the equations.
The costs derived by using the above equations relate to gas wells of a
similar size and with similar equipment to the average of the farm survey
gas wells.
Effect of Energy Rates on Costs
As already indicated, the cost figures given above were based upon a
nine -mill rate for electricity and a rate of $0.40 per thousand cubic feet for
natural gas. Rates vary from these in the various electrical districts and in
areas served by other fuel suppliers. The average cost of electricity varied
from .7506 cent to 1.0861 cents per kilowatt hour ( Table 21) Charges for
natural gas were $0.3854 and $0.4782 per thousand cubic feet.
With fuel comprising a major part of the cost of pumping water, rates
charged naturally have a significant effect upon variable and total costs.
With all other costs being the same,4 variable costs for farm survey electric
wells varied from $7.56 to $10.31 per acre -foot, and from 2.036 cents to 2.786
cents per acre -foot per foot of lift, due to differences in charges for electricity ( Table 21 ) For farm survey gas wells the variation in variable costs is
from $6.03 to $6.90 per acre -foot, and from 1.365 cents to 1.588 cents per
acre -foot per foot of lift due to differences in gas rates. Similar differences
are reflected in total costs.
Effect of Efficiency on Costs
As was reported above, overall efficiency of farm survey electric wells
averaged 51.7 percent, with the variation being from less than 30 to more
than 70 percent. District wells averaged 58.7 percent efficient with over
10 percent having an efficiency rating of 70 percent or more.
In the discussion of fuel consumption it was pointed out that the electical energy required to pump one acre -foot of water is
1.024 Lift
KWH
Ee
where Ee stands for overall efficiency of the electric motor and pump.
Using this equation the power required per acre -foot per foot of lift was
computed for different levels of efficiency to show the effect on the annual
power bill and on power cost per acre -foot for a typical farm ( Table 22)
Lift and acre -feet pumped are averages for farm survey wells. The fuel
rates used are rounded averages from the farm survey.
.
.
-
.
4 Pumping lift and all costs other than the rates paid for electricity and natural gas
were held constant in order to show the effect of differences in rates charged for fuel
on the cost of pumping water.
COST OF PUMPING WATER
39
The level of efficiency has an important bearing on the cost of pumping
water. For electric wells similar to those in the farm survey, increasing
overall efficiency from 40 to 65 percent would reduce power costs 40 percent per acre -foot and save about $2,900 in the power bill for the year
Electric power costs for a well operating with 70 percent overall efficiency
are only half those for a similar well operating at 35 percent overall efficiency.
Table 22,
Fuel Requirements and Costs Related to Overall Efficiency
of the Pumping Plant
Overall Power per Rate per
Efficiency AFF'
KWH2
Acre -Ft.
Lifte Pumped2
(percent) (KWH) (cents)
(feet)
Electric Wells
30
35
40
45
50
55
60
65
70
378
378
378
378
378
378
378
378
378
3.4133
2.9257
2.5600
2.2756
2.0480
1.8618
1.7067
1.5754
1.4628
.9
.9
.9
.9
.9
.9
.9
.9
.9
870
870
870
870
870
870
870
870
870
Power Cost
per AF per AFF
Total
(dollars) (dollars) (cents)
10,102
8,659
7,577
6,735
6,061
5,512
5,051
4,663
4,328
11.61
9.95
8.71
7.74
6.97
6.34
5.80
5.36
4.97
3.071
2.632
2.304
2.048
1.844
1.677
1.534
1.418
1.315
Total
Fuel Cost
per AF
per AFF
6,000
5,000
4,285
3,750
5.54
4.61
3.95
3.46
1.274
1.060
.908
.795
Natural Gas Wells
Fuel per Rate per
10
12
14
16
1
MCF
AFF3
.03181
.40
.02651
.40
.40
.02272
.01988
KWH required per AFF
.40
=
Acre-Ft.
Lifte
435
435
435
435
Pumrped2
1,084
1,084
1,084
1,084
overall efficiency
Lift and acre -feet pumped are averages for farm survey wells.
are rounded averages from the farm survey.
.00318
3 MCF required per AFF
overall efficiency
2
Power and fuel rates
-
Data for the farm survey electric wells showed that when discharge
(gpm) was low overall efficiency usually was also low. Therefore, an analysis was made to show the relationship of discharge to variable and fixed
costs per acre -foot and per acre -foot per foot of lift (Table 23)
The 50 wells were divided into three groups on the basis of discharge,
and costs were summarized for each group. Since repair costs were based
on all 50 wells, it was not practical to obtain this cost item for each group.
Therefore, average repair costs per acre -foot per foot of lift were used for
each of the groups. Repair costs per acre -foot were computed by multiplying the cost per acre -foot per foot of lift by pumping lift.
It will be observed that average discharge for the three groups was
442, 1,183 and 2,044 gallons per minute. Variable costs per acre-foot and
.
40
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
per acre -foot per foot of lift are much lower for the higher output wells than
for the lowest output group. Power costs for the highest output group are
not much more than one -half power costs for the lowest output group.
Savings in fixed costs are even more marked. Fixed costs per acre -foot
and per acre -foot per foot of lift for the highest output group are less than
40 percent of those for the low output group.
The average efficiency for the three groups increases from 35.7 to 57.6
to 60.1 percent with increasing discharge. Although a small portion of this
change can be explained by increased efficiency with increased size, the
greater portion of the low efficiency and associated high power cost could
be overcome if the pumps were chosen according to the well capacity so as
to avoid movement of the fine sand, and to withstand a two to three year
decline in water table.
Table 23.
Costs Related to Gallons Per Minute, Farm Survey Electric
Wells
Gallons per Minute
1,500 & Over
Under 750
750 -1,499
16
364
442
35.7
16
18
392
1,183
57.6
378
2,044
60.1
Number of Wells
Average Lift-feet
Discharge-gpm
Efficiency
Costs per Acre -Foot, Dollars
Variable Costs
Power @ .9¢ per KWH 9.800
6.512
Repairs
1.168
1.258
Attendance
.234
.101
Lubrication
.354
.168
Total
11.556
8.039
Fixed Costs
Depreciation
3.033
1.388
Taxes
1.418
.675
Interest on Investment 2.468
1.139
Total
6.919
3.202
Costs per Acre -Foot per Foot of Lift,
Variable Costs
Power @ .9¢ per KWH 2.692
1.661
Repairs'
.321
.321
Attendance
.064
.026
Lubrication
.097
.043
Total
3.174
2.051
Fixed Costs
Depreciation
.824
.326
Taxes
.385
.158
Interest on Investment
.267
.671
Total
1.880
.751
1
5.618
1.213
.042
.075
6.948
1.138
.563
.910
2.611
Cents
1.487
.321
.011
.020
1.839
.313
.155
.251
.719
Based on average for all 50 wells.
COST OF PUMPING WATER
41
Similar savings can be realized by improving the operating efficiency
of natural gas wells (Table 22) Farm survey natural gas wells ranged in
overall efficiency from less than 10 percent to over 16 percent. The quantity of natural gas required to pump one acre -foot of water is approximated
.
by the equation
MCF
-
.00318 Lift
Eg
where Eg stands for overall efficiency of the natural gas engine and pump.
With a pumping lift and quantity of water pumped similar to that of the farm
survey wells the annual fuel bill could be reduced from $6,000 to $5,000 by
increasing efficiency from 10 to 12 percent. Further savings could be
realized by additional increases in efficiency.
1200
1000
800
600
400
200
30 to
65
40
to
65
50 to
65
INCREASE in EFFICIENCY (percent)
Figure 2 -Acre -Feet of Pumpage Required for Savings in Electric
Power Costs to Equal Estimated Repair Costs of
Improving Pumping Plant Efficiency.
42
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182
Table 24.
Acre-Feet of Pompage Required for Electric Power Savings to Equal Estimated Repair Costs to Raise Efficiency
to 65 Percent
Repair Cost to Increase Efficiency as Follows and AcreFeet of PumpageRequired for Savings to Equal Costs
Pump- BowlStages1 Incr. Eff. 30-65%
ing
Column R
Repair
s
Lift
No.
Length
Feet
(feet)
240
300
360
420
480
540
600
660
720
780
(dollars)
4
5
6
7
8
9
10
11
12
13
280
340
400
460
520
580
640
700
760
820
2,028
2,414
2,800
3,186
3,572
3,958
4,344
4,730
5,116
5,502
Incr. Eff. 40-65%
Repair
Cost
Feet
(dollars)
511
486
470
459
450
443
438
433
430
426
1,622
1,931
2,240
2,549
2,858
3,166
3,475
3,784
4,093
4,402
Incr. Eff. 50-65%
Repair
AcreCst
Feet
(dollars)
763
726
702
685
672
662
654
647
641
637
1,217
1,448
1,680
1,912
2,143
2,375
2,606
2,838
3,070
3,301
1,191
1,133
1,095
1,068
1,048
1,033
1,019
1,009
1,001
993
Fourteen inch make C bowls (See Table 17).
Repair costs Versus Savings
It should be recognized, of course, that increasing the level of efficiency costs money. Thus, it may not always pay to strive for maximum
efficiency. However, if the cost of repairs to improve efficiency is less than
the savings which will be realized in the fuel bill, it will pay to make the
repairs.
Information in Table 24 and in Figure 2 provides an indication of the
acre -feet which would need to be pumped from an electric well for the
savings in electric power costs to equal the cost of repairs necessary to
raise overall efficiency from 30, 40 and 50 percent to 65 percent, assuming
the higher level of efficiency continues. The estimated repairs are based
upon 14 -inch bowls and 12-inch column. While some wells may operate
more efficiently, it was estimated that in most cases repairs would not raise
overall efficiency above 65 percent. It was assumed that to raise efficiency
from 30 to 65 percent all new howls would be installed. Raising efficiency
from 40 to 65 percent would entail installing some new bowls and repairing
others. The increase in efficiency from 50 to 65 percent was assumed to
entail only repairs.
The smaller the lift, the greater the amount of water which must be
pumped for savings in power costs to equal repair costs (Figure 2 and
Table 24). With a 240 -foot lift, power cost savings in pumping 510 acre feet would approximately equal repair costs to increase efficiency from
30 to 65 percent. With a lift of 420 feet the acre -feet required would drop
to 460, and with a lift of 660 feet savings on power costs of pumping 430
acre -feet would approximately equal repair costs.
With less improvement in efficiency more water would have to be
pumped for power cost savings to equal repair costs. With a 420 -foot lift
savings in power costs of pumping 460 acre -feet would equal repair costs
COST OF PUMPING WATER
43
to increase efficiency from 30 to 65 percent. To cover costs of raising
efficiency from 40 to 65 percent would require pumpage of about 685 acre feet. Power cost savings in pumping about 1,050 acre -feet would approximately equal repair costs to raise efficiency from 50 to 65 percent.
For the average well from the farm survey with an efficiency below
( annual pumping 340 acre -feet; lift 363 feet) repair costs would
be approximately $2,800 and would be paid for by power savings on pumping about 470 acre -feet. In terms of time, the repair would be paid for in
less than one and a half years.
40 percent
tV.0
44
ARIZONA AGRIC. EXPERIMENT STATION TECH. BULLETIN 182