WATER POLLUTION CONTROL RESEARCH SERIES • DAST-9
Reduction of Infiltration
by Zone Pumping
IPARTMENT OF THE INTERIOR • FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Reports describe the results and
progress in the control and abatement of pollution of our Nation's Waters.
They provide a central source of information on the research, develop-
ment and demonstration activities of the Federal Water Pollution Control
Administration, Department of the Interior, through inhouse research and
grants and contracts with Federal, State, and local agencies, research
institutions, and industrial organizations.
Triplicate tear-out abstract cards are placed inside the back cover to
facilitate information retrieval Space is provided on the card for the
user's accession number and for additonal keywords. The abstracts
utilize the WRSIC system:
Water Pollution Control Research Reports will be distributed to requesters
as supplies permit. Requests should be sent to the Publications Office,
Department of the Interior, Federal Water Pollution Control Administration,
Washington, D.C. 202H2
Previously issued reports on the Storm and Combined Sewer Pollution Control
Program:
WP-20-11 Problems of Combined Sewer Facilities and Overflows-
1967.
WP-20-15 Water Pollution Aspects of Urban Runoff.
WP-20 16 Strainer/Filter Treatment of Combined Sewer Overflows.
WP-20-18 Improved Sealants for Infiltration Control.
WP-20-21 Selected Urban Storm Water Runoff Abstracts.
WP-20-22 Polymers for Sewer Flow Control.
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REDUCTION OF GROUND-WATER
INFILTRATION INTO SEWERS BY
ZONE PUMPING AT MERIDIAN, IDAHO
FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
GRANT 2 9-IDA-2
HOFFMANN & FISKE
CONSULTING ENGINEERS
2500 Kootenai, Boise, Idaho 83705
917 Eighth Ave., Lewiston, Idaho 83501
June, 1969
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FWPCA Review Notice
This report has been reviewed by the Federal
Water Pollution Control Administration and
approved for publication. Approval does not
signify that the contents necessarily reflect
the views and policies of the Federal Water
Pollution Control Administration.
ii
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ABSTRACT
The purpose of this study was to determine if the lowering of the high
water table by pumping in a given area of the City of Meridian would
eliminate infiltration of ground water to the municipal sewers . If the
infiltration could be eliminated, the large volume of sewage flow that
occurs during the irrigation season would be greatly reduced. Sewage
flows in excess of the capacity of the sewage treatment plant are now
bypassed to a small stream.
It was contemplated that the test results from this study could be
used to predict the lowering of water table in. ether areas in the City of
Meridian. The topography, geology, precipitation, as well as local
irrigation programs are so irregular in character that no definite criteria
could be set up to predict what would occur in other areas. It is concluded
that each area would have to be studied independently to decide the depth cf
well, pump capacity and local affecting conditions.
It is also concluded that the cost of capital investment, cost of
operation of these pumping projects in the entire Meridian area to lower the
water table would be too expensive to accomplish the purpose cf lowering
the water table below the sewers so as to materially decrease the flow of
infiltration water to the sewage treatment plant. It would be less expensive
to build holding lagoons or a separate lagoon system to treat the excess flow
to the sewage treatment plant during the irrigation period. This report
was submitted in fulfillment cf Grant 29-IDA-2 between the Federal Water
Pollution Control Administration and the City of Meridian, Idaho.
iii
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TABLE OF CONTENTS Page
ABSTRACT iii
I INTRODUCTION
1. Nature of Project 1
2. Findings 4
3. Conclusions 6
II DESCRIPTION OF PROTECT AREA
1. Location 7
2. Climate 7
3. Irrigation 7
4. Sewage Collection, Treatment and Disposal at Meridian. 8
5. Problems in Operating the Combined Sewer System. ... 8
III PROTECT CONSTRUCTION
1. Production Well. . . 9
2. Observation Wells 11
3. Flow Measuring S ystems 15
IV PROTECT OPERATION
1. Initial Pumping Period 16
2. Intermediate Pumping Period 16
3. Final Pumping Period 17
4. Presentation of Data 21
a. Observation Wells 21
b. Flow in Manhole No. 5 : 21
c . Flow in Five Mile Creek 21
d. Flow thru Sewage Treatment Plant 25
e. Domestic Water Pumps 25
f. Ground Water Pumped 25
g. Irrigation Season 25
h. Precipitation 25
IV
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V ANALYSIS OF DATA
1. Observation Wells 25
2. Flow in Manhole No. 5 26
3. Flow in Five Mile Creek. 27
4. Domestic Water Pumped 27
5. Irrigation Season 27
6. Daily Precipitation 28
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FIGURES
Page
1. Map of Meridian showing location of Sewage Treatment Plant, Five
Mile Creek, Meridian City and Project Area 2
2. Ground-Water Program Meridian Pump Project 3
3. Well Cross Section 10
4. Plan of Pump Pit 12
5. Section thru Pump Pit 13
6. Diagram typical Observation Well 14
7. Time-Draw Down Curve Pumping Rate 200 g. p.m. ... .... 18
8. Time-Draw Down Curve Pumping Rate 350 g.p.m 19
9. Time-Draw Down Curve Pumping Rate 570-618 g.p.m 20
10. Distance Draw Down Diagram Section l(Pumped Well O.W.
#6-O.W.#2) 22
11. Distance Draw-Down Diagram Section 2 (Pumped Well O.W.
#6-O.W. #3 23
12. Distance Draw Down Diagram Section 3 (Pumped Well O .W.
#6-0.W. #4) 24
13. Chart Showing Field Recordings & Data for City of Meridian
Drainage Project 29
vi
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REDUCTION OF GROUND-WATER
INFILTRATION INTO SEWERS BY
ZONE PUMPING AT MERIDIAN, IDAHO
1. INTRODUCTION
Nature of Project
The sewer systems in several of the south central cities of Idaho
have been troubled by the infiltration of irrigation water into the
sewers. As a result the sewage treatment facilities are overtaxed
during the irrigation season. The situation at Meridian, Idaho, is
unique in that the overtaxing of the sewage treatment plant comes
during the dry summer months from the infiltration of irrigation water
rather than in the winter during heavy rainfall period.
The City of Meridian Sewage System consists of several laterals
throughout the City which connect to a 21 inch trunk sewer that leads
to a secondary treatment plant Northwest of the City Center. The
effluent from the sewage plant flows into Five Mile Creek which runs
Northwesterly through the area. See Figure No. 1.
The Sewage Treatment Plant is designed for a flow of 1500
g.p.m. (2 ,160, 000 g.p.do). The plant takes care of the sewage
treatment during the winter months, but during the summer months
there are some flows over 2,160,000 gallons per day. The extra flow
is a result of infiltration of ground water during the irrigation season.
In some areas the ground water rises to within 18 inches cf the ground
surface. As a result of this heavy infiltration a great deal of untreat-
ed sewage bypasses the sewage treatment plant and flows into Five
Mile Creek. Five Mile Creek meanders westerly through a farming
area to the Boise River which eventually flows into the Snake River
near Parma, Idaho.
One of the areas of high water table is in the southwest portion
of the City. It is a residential area bounded on the north by Bower
Street; on the south by Cottonwood Avenue; on the west by Meridian
Street and on the east by East 3rd Street, See Figure 2. The ground
water in this area was only 18 inches below ground surface at this
point. This is probably the most critical area in the City of Meridian „
The basic idea of this project was to install a shallow well
pump in the center of the above area, which is the approximate low
point of the area,. and study the lowering of the water table to
determine the zone of influence of the well, If the pumping were
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able to keep the ground water level below the sewers, the irrigation
infiltration would be reduced and the flow to the sewage plant during
the irrigation period would be reduced. The study was to determine
if it would be economically feasible to install these pumps through-
out the City and thus eliminate the sewage bypassing the sewage
treatment plant during the summer months.
A 100 foot well was drilled as shown on Figure 2 at the alley
between Ada & King Avenues on East 2nd. This was completed on
December 21, 1967. A 500 g.p.m, pump was installed on June 23,
1968, and the City of Meridian construction crew completed construct-
ion of the 8 inch transite line to the Nine Mile Drain as shown on
Figure 2 at the same time. The pump was started on June 26, 1968,
at a capacity of 200 g.p.m. and pumped at this capacity until July 17,
1968. On July 17, 1968, the pumping capacity was changed to
350 g.p.m. and on August 7, 1968, the pump was opened to its full
capacity. Depending on the elevation of ground water this varied
from 570 to 660 g.p.m. The pump was left at its maximum pumping
capacity from August 7, 1968, until the wilting of this report and
will continue to operate at full capacity until ground-water conditions
warrant making a change.
2. Findings
The following are the findings of the study of the Meridian Drainage
Project, Meridian, Idaho:
a. The ground-water level in the Meridian area is a factor in
the infiltration of water into the sewer system. The water table
rises in the summer due tc irrigation water percolating into the
ground. In the winter excessive rainfall and snow melt also
percolate into the ground.
b. The flew in the sewer lines is affected by the ground-water
level. The higher the ground-water level, the greater the head
on the sewers and therefore the greater the rate of infiltration.
There is no doubt that the sewer lines constructed of vitrified
clay pipe during the 19305s have defective joints and broken
sections that contribute to this infiltration.
c. The flow through the sewage plant varys a great deal from
summer to winter months because of the infiltration of irrigation
water into thn sewers. The records shew some 1,150,000 gallons
per day byp?being the sewage in the peak summer flew. This is
untreated water and sewage that flows into Five Mile Creek.
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d. The flow in Five Mile Creek varies from 10 c.f.s. in
winter to 45 c.f.s. in summer. There is contamination of Five
Mile Creek from the sewage which bypasses the sewage plant
during the summer months. Due to the greater flow of water in
summer months there is more oxygen available and a greater
flow for dilution of sewage.
e. The ground water pumped from the drainage well into the
Nampa Meridian Drainage Canal has low bacteria count and
B.O.D. demand indicating that the waters are not contaminated
and can be used for irrigation purposes .
f. The water levels in the different areas cf the project area
were not lowered uniformly with the pump operating 24 hrs. a
day. The ground-water levels fluctuate due to the impact of
local irrigation, rain and snow fall.
g. The total cost cf the construction project was as fellows:
Construction Costs
a. Contracts $11,745.67
b. Force Account 4,227.85
c. Engineering 6,265.00
d. Legal 100.00
e. Administration 450.00
f. O & M 1,711.48
Tctal Cost Project $24,500.00
h. The cost of operating the pump 24 hours a day at full
capacity is about $1.75 per day to pump an average 850,000
gallons of ground water.
i. Pumping the ground water lowered the water table below the
sewers for about a two block square area. This affected the
amount of flow into the sewers and thus the, flew through the
sewage treatment plant.
j. Pumping in the winter months lowered the water table as
it was affected by periodic rains ar^d snow melt.
k. The results of this study did net result in any empirical
formula to predict the results of drainage pumping in other
areas of City of Meridian. The subterranean geology as well
as the irrigaucr., topography and precipitation make this
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impossible.
1. A drainage pump will lower the water table below the sewers,
but each area will have to be studied independently to decide
the depth of well, pump capacity and waste way for pumped
water. This area was an ideal area as far as costs are concerned.
Elimination of waste water in other sections of City could present
a problem.
m. All construction should be in the winter months so that the
high water table will not present problems.
n. The City of Meridian consists of approximately 140 square
blocks in area which ne ans about 70 units . 70 units at an
average cost of $40,000. per unit would mean a capital outlay
of $2,800,000. This would mean a power bill of $122.50 a
day in addition.
There are other benefits derived from the pumping operations
besides the lowering of the infiltration into the sewer lines .
Several basements in the area have been dry as a result of the
drop in water table in the zone of influence of the pumping well.
Actually the water pumped into the Nine Mile Draw could be
used for irrigation and a benefit thus derived from the presently
wasted flow. Some people have shallow wells used for irrigat-
ing their own properties. Some of these have gone dry as a
result of lowering ground water. If the water table could be
lowered it would make all types of construction, particularly
utility construction, less expensive. At present utility
construction is limited to the winter months when the water
table is down.
3. Conclusions
a. There is no doubt that the drainage project accomplished
the purpose of lowering the water table below the sewers
within a two block area, but no definite criteria was established
by the project so that formula could be set up for future projects.
b. The cost for installing pumping stations throughout the
City of Meridian would be prohibitive in cost. It would be
cheaper to build a holding lagoon or separate lagoon system
to take care of the surplus irrigation water that infiltrates
into the sewer lines .
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II. DESCRIPTION OF PROJECT AREA
1. Location
The City of Meridian is located in Southwestern Idaho, 8 miles
West of Boise, Idaho. See Figure 1. It is the center of a farming
area and known as the "Heart of The Dairy-land" . Meridian has a
population of 2146 in accordance with the 1965 special census.
The topography of the area slopes to the northwest draining towards
the Boise River which is four miles north of Meridian. The ground
in the Boise Valley is somewhat uniform in its geological formation.
There are generally 3 to 4 feet of rich top soil, then 6 to 18 inches
of caliche hardpan; then gravel and sand strata to at least 50 feet.
The project area is in the southeastern part of Meridian. Bounded by
Bower Avenue on the north; Meridian Street on the west; Cottonwood
Avenue on the south; and East 3rd on the east. This area is 3 blocks
square. See Figure 2.
2. Climate
The climate in general may be described as dry and temperate,
with sufficient variation to be stimulating. Summer maximums
generally are reached in late afternoon followed by rapidly falling
temperatures after sunset.
The normal precipitation pattern in the Boise Area shows a winter
maximum and a very pronounced summer minimum. The greatest
24 hour precipitation was 2.24 inches on June 11-12, 1958. The
average annual rainfall is 12 inches . During the year June, 1967,
to June, 1968, the major periods of rainfall were 1.0 inch in June,
1967; 0.4 inch in October 1967; 4.0 inches snow and rainfall between Jan.
1, 1968, and April 1, 1968; and the balance of 2.1 inches fell at odd
times during the year for a total of 7 „ 5 inches.
3. Irrigation
The irrigation season in the Meridian Area starts in the middle
of April and runs to the middle of October. Generally the water is
distributed to the area in a main canal „ From the main canal
laterals lead out to the various areas, usually in the street right-
of-way or alleys. The property owners take their water out of the
laterals for their particular property. Generally it is done on a
local weekly distribution plan, depending on the property area. By
mutual agreement, days of the week may be exchanged or if it rains
for a few days seme people may not irrigate. Thus the surcharge of
ground water has no particular predictable pattern. This was in
evidence at the cbservation wells which would have the local water
table rise during the days of irrigation and then gradually subside
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until the next irrigation rotation.
4. Sewage Collection, Treatment and Disposal at Meridian
Most of the sewers in the residential areas were constructed
during the W.P.A. days and were not well constructed„ The sewers
are mainly vitrified clay tile. Over the years since 1930"s the
ground water has raised and lowered several times in the gravel
and sand formations, leaching out the fines from the gravel causing
voids; n the strata which resulted in unequal settlement of the pipe,
causing some of the joints to open. Whenever the water table rose,
the water infiltrated into the sewers.
The City of Meridian Sewage System consists cf several 8 inch lat-
erals feeding into 12 & 15 inch collector sewers, which eventually
empty ito a 21 inch trunk sewer that runs Northwest into a secondary
treatment plant Northwest of the City Center. The effluent from the
sewage plant flows into Five Mile Creek which runs northwesterly
thru the area to the Boise River. The Sewage Plant is designed for
a flow of 2,160,000 gallons per day. The treatment plant takes
care of the sewage treatment during the winter months, but during the
summer months there are some flows of 3,620,000 gallons per day.
The extra flow is a result of the infiltration of ground water during
the irrigation season. As a result cf this heavy infiltration, a
great deal of untreated sewage has to bypass the treatment plant
and flow into Five Mile Creek. Five Mile Creek meanders north-
westerly through farming area to the Boise River, which eventually
empties into the Snake River near Parma,- Idahc . On August 24,
1968, as much as 1,460,000 gallons per day bypassed the sewage
treatment plant.
5. Problems in Operating The Combined Sewer System
The sewage plant is designed for a-maximum flow of 1500
gallons per minute (2 ,160,000 gallons per da/), During the
irrigation period between April 15 and October 15 each year the
infiltration into sewer commences to build up until a peak of
almost 3,620,000 gallons per day flows to the plant. The
sewers are not designed as a combined sewer, but due to poor
original construction, there are open joints and poor house
connections, as well as, pieces of vitrified clay pipe broken out
of the pipe line. As the townspeople start their irrigation, the
arounr'-vater leva! builds up and is soon under a head which forces
the water into sewer pipes making a combined sewer cf the lines.
In some .. f the 8 inch lines that have a normal flow of 1 to 2 inches
during winter mortiis the pipe is entirely full in the middle of the
irrigation period.
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The sewage plant, of course, is not designed to take a flow cf
nearly 3,620,000 gallons per day; so the excess of 1,460,000
gallons is bypassed into Five Mile Creek which has a flow of
20-30 c.f.s. during the summer months. This stream flows north-
west to the Boise River and adds to its pollution.
It can readily be seen that if some method could be devised to
prevent the irrigation water from infiltrating into the sewers, the
load on the sewage plant would be substantially reduced. One
method would be to dig up the sewers and relay them or lay a
parallel line. This cost would be prohibitive in the paved streets.
Another method to reduce the infiltration would be to lower the
water table below the sewers by the operation of a pumped well.
III. PROJECT CONSTRUCTION
1. Production Well
Bids were advertised on the drilling of a 24-inch diameter well
to 100 feet as shown on Figure 3 and bids were open on October 26, 1967.
The Contract was awarded to Witt & Sons Drilling of Caldwell, Idaho. The
final well was 80 feet and cased 81.6 feet. The casing was perforated from
9 to 72 feet. The perforations were 1/4 x 5 inches spaced 9 inches
horizontally and 5 inches apart vertically. The well was developed and
gravel packed from November 30, 1967, until December 21, 1967. The
well was tested for a period of 16 hours. The first day the well was
tested at a flow of 300 g.p.mto 1,000 g.p.m. with an 8 inch turbine
pump with 60 feet of column. The static water level was 5 feet below
the top of casing. The pumping level was 31 to 34 feet below the top of
casing which corresponds to a draw down cf 26 to 29 feet. At the end
of the 16 hour test the pumping rate was 913 g.p.m. with a draw down
of 29 feet. The static water level was 6.5 feet below casing at termin-
ation of pumping. The log of the well is shown on Figure 3.
Bids were advertised and opened on April 9 , 1968 , for a vertical
turbine pump to pump 500 g.p.m. This was the type of pump and
the capacity specified after a study of the test well data.
The specifications for the operating conditions of the well were
as follows:
1. Inside diameter of well - 24 inches .
2. Depth of Well - 80 feet.
3 . Static water level below topwell - 5 feet.
4. Pumping level below topwell - 40 feet.
5 . Pumping head above top of well - 10 feet.
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6. Total pump head - 50 feet.
7. Capacity of well - 500 g.p.m.
8. Power characteristics - 220 V., 3 phase, 60 cycles.
9. Normal rotative speed - 1760 R.P.M. maximum.
A venturi type, direct acting controller, water level indicator and
appurtenances were included in the bid. A recording meter to
indicate the depth of water in the well, with a shut off control at
40 feet was also specified. It was desired to control the flow from the
pump, if required, so that the water table would be kept just below the
level of the lowest sewer in the study area. Mayne Pump Co., of
Boise, Idaho, was awarded the Contract. See Figures 4 & 5.
The construction of 812 feet of 8 inch Transite pipe and a pump pit
were constructed by force account by the City of Meridian forces.
All construction work was completed on June 23rd, 1968.
The pump was started on June 26th, 1968, at 200 g.p.m.
2. Observation Wells
Four observation wells were constructed prior to the starting
of the pump on June 26, 1968 , as shown on Figure 6. These wells
were constructed by digging holes approximately 14 to 16 feet deep,
installing a 6 inch corrugated pipe and back filling with gravel. Except
for the top 2 to 3 feet, the 6 inch observation well pipes were in gravel.
The wells used finally are Nos. 2,3,4 and 6. Well No. 53s shown
on Figure 2 is a drainage well owned by the Nampa Meridian Irrigation
Company that is next to Nine Mile Draw and pumps directly into it.
It was mutually intended to use this well as an observation well, but
it was inconvenient to obtain access to measuring the water depth
because of the construction of the unit, thus this observation well was
abandoned. Wells Nos. 2, 3 and 4 were constructed Sept. 18, 1967.
Well No. 6 was constructed June 20, 1968. The depth of water in wells
Nos. 2,3 and 4 were measured by means of electrical resistance
measuring device. Depths to water were measured weekly prior to use
of recording meters . Recording meters were the Belfort Co. Catalogue
No. 5-FW-4*and were installed June 1, 1969.
The location of the observation wells from the pumped well is
as follows:
* Use of product and company names is for identification only and
does not constitute endorsement by the U.S. Department of the
Interior or the Federal Water Pollution Control Administration.
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Existing
Of PUMP PIT
FIGURE A
HOFFMANN- P/SKE CONSULTING ENGINEER
2SOO KOOTENAI STJfffT BOISE. IDAHO
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BZLFORT RECORDING METER
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See Figure 2.
Observation Well No. Distance From Pumped Well (feet)
2 688
3 630
4 769
6 98
Other data on the Observation Wells is as follows:
Elevation Water Level
6/28/68 and
Observation Elevation Zero Elevation
Well No. G D Elevation Bottom Well on Guage
2 2610.83 2598.08 2600.98
3 2605.59 2593.79 2600.09
4 2606.01 2596.16 2603.66
6 2601.96 2590.51 2598.76
All data is on U.S. Coast & Geodetic Control.
The level of water in each well was plotted weekly so that a study
could be made when the water table was below the grade of the
sewers in the vicinity of the wells.
3 . Flow-Measuring Systems
Several flow measurements were made in the study. A
Leopold-Stevens type "F" recorder * was installed at M.H. #5 to
indicate the depth of flow in this manhole which was indicative of
the flow of sewage in the area under study. Some troubles were
encountered in the function of the unit and as a result there were
some blank periods of recording.
The existing recording meter at the sewage plant was used to
record the amount of sewage flowing through the sewage plant.
Since the pumps to the primary clarifier could only handle 1500
g.p.m. (2,160,000 gallons per day) any flow in excess would
bypass the sewage plant and discharge into Five Mile Creek.
The flow on Five Mile Creek was measured by means of a staff
gage a hundred yards below the sewer out fall. The flow in the
* Use of product and company names is for indentification only and
does not constitute endorsement by the U.S. Department of the
Interior or the Federal Water Pollution Control Administration.
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creek was calibrated by a current meter and flow curve established.
The minimum measured flow was about 10 c.f.s. and the maximum
flow about 45 c.f.s. The B.O.D. was found to be about 55 p.p.m.
during the low winter flows and 200 p.p.m. in the high summer flows.
Suspended solids were 32 p.p.m.; total solids about 627 p.p.m.; and
the bacteria count was 20 m.p.n. in March, 1968. The floating
materials consist of grass , twigs , paper, and other debris . There
is a healthy growth of water crest, lillies and grass along Five Mile
Creek at waters edge.
IV. PROJECT OPERATION
1. Initial Pumping Period
The initial pumping started on June 26th, 1968, and the pump
was set at 200 g.p.m. and run until July 17, 1968. The water in
the well would drop until the people in the immediate area would
start irrigating. This flood irrigating would cause the level in the
wells to rise and then subside after irrigating. Actually there was
no true pattern as to how the neighborhood irrigation would affect
the water level in the wells. To try and use the formula developed
by Theis, Wenzel and Jacob produced such erratic results due to
the surcharging of ground water by surface irrigation, the idea was
abandoned. The curves indicating the lowering of water table
were plotted on logarithmic scale, but no data could be obtained
from them that was of any value except that over a long period
of time the ground water was dropping. The cost for pumping
200 g.p.m. was $1.33 per day of 24 hours. See Figure 7.
2. Intermediate Pumping Period
On July 17th, 1968, the pumping capacity was changed from
200 g.p.m. to 350 g.p.m. This was continued until August 7, 1968.
The same trouble was encountered at this pumping capacity because
the water in observation well would fluctuate, but at the end of the
period there was a definite decline in the water level. There really
was no definite period when the ground-water level would stabilize;
so it was decided on August 7th to increase the pumping capacity to
the maximum, which at the existing water table elevation was
665 gallons per minute. The cost for pumping 350 g.p.m. was
$ 1.54 per day of 24 hours. See Figure 8.
3. Final Pumping Period
On August 7th, 1968, the control valve was opened to maximum
capacity and was kept at this maximum until March 11, 1969, when
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it had to be turned off for a ten day period so the Nampa Meridian
Irrigation District could clean the Canal into which the pumped
ground water was discharged. During this pumping period the ground
water level varied due to irrigation, rain, and snow fall. Each of
these would recharge the ground water temporarily. After a few days
of pumping the ground water level would return to the level prior to
the temporary distrubance. The cost for pumping maximum capacity
570-660 g.p. m. was $1.75 per day of 24 hours. See Figure 9.
From the performance curve of the Johnson Pump * the following
is a table which shows the amount pumped and the level of water in
the well casing:
Pumping Capacity for Given Ground Water Depth Below Pump
GPM
Lift in Well Head Loss Above Ground Total Dynamic Head Pumping
50 10 60
40 10 50 570
39 10 49 580
38 10 48 585
37 10 47 590
36 10 46 600
35 10 45 605
34 10 44 610
33 10 43 615
32 10 42 620
31 10 41 625
30 10 40 630
29 10 39 635
28 10 38 640
27 10 37 645
26 10 36 650
25 10 35 655
24 10 34 660
23 10 33 665
Use of product and company names is for identification only and
does not constitute endorsement by the U.S. Department of the
Interior or the Federal Water Pollution Control Administration.
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1000
IQOOO
-------
(000
TIME SINCE
PUMP STARTED
10,000
IN MINUTE'S
FIGURE 8
-------
too
1000
-------
During the months of January, February and March the well
capacity was varying due to recharge from rain and snow fall.
At the date of shutting off the pump for ditch cleaning, the
water table was below each of the observation wells, just being
at the bottom of Well No. 4.
The following is a table showing the zone of influence of the
well in line with the observation wells . See Figures 10,11 & 12.
Line of Observation Well Distance From Well to Zero Influence (feet)
6-2 1000
6-3 3500
6-4 1500
4. Presentation of Data
Figure 13 indicates graphically the results of ail the field data
accumulated. Some area data is missing due to malfunction of the
recording device or recorder missed collecting data on schedule.
a. Observation Wells
The first series of 4 plottings indicates the rise and decline
of the water levels in each of the four observation wells over
the period of study from June 26, 1968, to March 11, 1969.
The vertical scale indicates the drop in feet from the water
level in each observation well from the initial pumping start
of June 26, 1968. The bottom of each well is plotted as the
lowest point in each well. It was calculated that when the
water table in the wells reached the bottom, the sewers in the
area would be above the water table. The horizontal ordinate
represents the date of the recording.
b. Flow in Manhole No. 1
This chart records the flow in Manhole #5 which is
indicative of the total flow in the sewers from the project area.
Due to malfunction of the recording equipment some data is
missing. The vertical scale represents flow in gallons per
minute . Horizontal scale shows date.
c. Flow in Five Mile Creek
A staff gauge was placed below the sewage plant to record
the depth of water in Five Mile Creek. The creek flow had
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10
DISTANCE FROM PUMPED
100
WELL IN FEET
1000
FIGURE fl
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-------
been calibrated for various depth by flow meter and curve plotted
for the station. The vertical scale indicates the flow in Five
Mile Creek in cubic feet per second and the horizontal scale the
date.
d. Flow thru Sewage Treatment Plant
This graph is a record of flow in sewage treatment plant from
June 1, 1967, to March 11, 1969. The vertical scale shows
flow in gallons per day. The maximum flow through the treatment
plant is 2,160,000 gallons per day and any flow larger than this
means the surplus has to be bypassed.
e. Domestic Water Pumped
This is a daily record of domestic water pumped from the
four wells. The vertical scale is in hundreds of thousands of
gallons per day. The horizontal scale represents the date.
f. Ground Water Pumped
This graph indicates the periods of pumping the drain well
pump for 200 g.p.m.; 350 g.p.m. and maximum capacity of pump.
g. Irrigation Season
This plot represents the irrigation period for the time of
the project study.
h. Precipitation
This graph represents the precipitation daily for the period
of the study. The vertical ordinate is inches of precipitation.
V. ANALYSIS OF DATA
1. Observation Wells
A general observation of each of the curves for the wells shows
that the water in each dropped from the initial day of start of the
pump June 26, 1968, until the date of ending the test March 11, 1969.
It can be readily seen that the local irrigation program effects the water
table to such an extent that no real correlation by formula (Theis,
Wenzel, Jacob) could be obtained from the available data, but all
cases the water table receded to the bottom of the observation wells.
Well No. 2 reached the bottom on August 25th, 1968; Well No. 3 on
June 4, 1969; Well No. 4 on Nov. 28, 1968; Well No. 6 as early as
August 13, 1968. Well No. 6 was affected by rainfall and snow
melting period in January and February 1969. Well No. 3 was affected
by the rainfall and snow in January and February. When the water level
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reached bottom of wells No. 2 and No. 4 there was a rise above the
bottom. It can be seen that the pumps must continue all winter to keep
the water table below the sewers or when they are shut off in winter the
water table would rise because of rainwater and snow melt penetrating the
gravel strata raising the water table.
The water table at any time is not the same on all observation
wells which indicates that due to the variable impervious hard pan
strata, probable clay barriers, the water table is not the same
throughout the project area. From this study it would not be possible
to predict what would happen in other areas of the City as there is no
correlation between the effects of pumping on each of the observation
wells, except that eventually if pumped long enough the water would
be lowered below the invert of sewers. The pumping capacity of the
well should be, ideally, that it could be set so that it would keep the
water table below the sewers in the area under study. I would
recommend a variable speed motor with controls to keep the water
table just below the deepest sewer. In our study a constant speed
Motor of 1750 R.P.M. was used to produce 500 g.p.m. under total
pump head of 50 feet. The pump was set wide open on August 7, 1968,
and was still pumping at full capacity on March 11, 1969. The flow varied
from 620 g.p.m. to 665 withatotal head varying from 43 feet to 33 feet.
The water was discharged into a drain ditch by agreement with
the Nampa Meridian Irrigation District. This water was put to
useful irrigation use as the bacteria count was low.
2. Flow in Manhole f 5
The records on flow in Manhole No. 5 were poor at certain times
during the test period. The recorder was found to be rubbing against
some supports; so that the recordings were not correct.
The maximum water table is generally reached during September each
year and remains practically static until through December when it
starts to recede.
The graph shows that the flow went from 200 g.p.m. in the
end of March, 1968, to a high of 790 g.p.m. in first of July, 1968.
After the pumping started on June 26, 1968, the flow in the sewer at
Manhole No. 5 receded to 400 g.p.m. in first part of September and
diminished to around 220 g.p.m. in October. Thus the pumping
did have some effect.
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During the winter months of December, 1968 - January, 1969,
the flow increased again, but this was affected by rainfall and
melted snow entering the gravel strata and infiltrating into the
sewers.
3. Flow in Five Mile Creek
The chart on flow in Five Mile Creek shows that during the
winter months and early spring the flow is down to 10 c . f .s . and
gradually rises as the area enters the irrigation season and
irrigation is started. It acts as a drain for the area and surplus
water flows into the Creek. It reached a high of 45 c.f.s. in
September and receded to 20 c.f.s. in December, 1968, rising
and falling during the winter from rain and snow melt. During
the summer months there is enough flow to dilute the treated sewage
and give some dilution to the 1,150,000 g.p. d. of untreated
sewage bypassed from June to September when this untreated
sewage is added to Five Mile Creek.
4. Domestic Water Pumped
The domestic water supply for Meridian varies from minimum
200,000 g.p.d. during the winter months to 700,000 maximum
g.p.d. during summer months. It can be noted during rainfall
period in the summer the water use drops on days of precipitation.
The amount of water entering sewers from domestic use rises during
summer months. Thus during summer months there are major
contributions to sewers from both irrigation and domestic water waste.
Records The area of influence is on an average about 1000 feet
from pump location. This would mean many wells in the entire City
area to lower the water table entirely below sewers. This area is about
3 city blocks square. The initial capital cost of the project was
about $15,000. The pumps should last 20 years before replacement
or this would be at a cost of $750. a year, per unit. The power
cost per day of $1.75 per day is negligible for benefit derived.
5. Irrigation Season
The irrigation season runs from April 15 to the first week in
October. The flow through the sewage plant shows the influence of
the irrigation water. A general schedule for each area is set up for
irrigation, but it is greatly affected by the whims of the users,
precipitation, and other factors. Due to these variable factors, the
actual surcharge of ground water is difficult to predict with so many
variables. Actually if the City of Meridian decides to install pumps
in the balance of the City to lower the water table I do not believe
that any data was obtained from this study to formulate a definite
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pattern of action in other areas. The zone of influence varied in
a line from the pump to each of the observation wells. The geology
of each area would have to be studied, as well as the irrigation
program, drain ditches in the area. There is no doubt that pumping
will lower the water table, but each area would have its own
peculiarities and I would recommend a study of each area with a
variable speed motor pump to determine what capacity pump would
best suit the local conditions.
6. Daily Precipitation
The daily precipitation chart indicates the rainfall for the full
period of the study. The records indicate that the year 1967 was
a dry year with 7.68 inches; the year 1968 was a relatively wet year
with 13.08 inches rainfall. Actually the month of August 1968 was a
wet month. Also there was quite a bit of precipitation during November
and December, 1968, and January and February, 1969, were real
wet months.
During the winter months of December, 1968, and January-
«. February, 1969, the heavy rainfall and snow melt affected the level
in the observation wells as well as the total daily flow through the
sewage plant. In addition to irrigation water, rain water and snow
melt penetrates the ground water strata.
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PAGE NOT
AVAILABLE
DIGITALLY
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I BIBLIOGRAPHIC: City of Meridian, Idaho
j Sewer Infiltration Reduction by Zone Pumping - Hoffmann anc
Fiske-FWPCA Publication DAST 9-1969. 1
ABSTRACT: The intent of this project was to demonstrate
| the reduction of ground-water infiltration into sanitary
sewers by pump down of the water table in the sewer area
| assuming the geology, precipitation and local irrigation
; practices were ameanable to rapid and wide zones of influ-
| ence. The water table was lowered below the sewer and re-
' duced the volume of flow to the treatment plant. The
| water table was not lowered uniformly. For 1^0 square
blocks 70 pump units would be required at an average cost
| of $UO,000 per unit with a total power bill of $122-50 per
; day. This is not economically favorable when compared
Jwith other corrective measures. This report was submitted
1 in fulfillment of Grant No. 29-3DA-2.
; KEBirrOCna^iircf~Crby~ol1~Meridian,"Idaho" " " ~ ~"
| Sewer Infiltration Reduction by Zone Pumping - Hoffmann and
', Fiske-FWPCA Publication DAST 9-1969.
ABSTRACT: The intent of this project was to demonstrate
|, the reduction of ground-water infiltration into sanitary
sewers by pump down of the water table in the sewer area
(.assuming the geology, precipitation and local irrigation
;practices were ameanable to rapid and wide zones of influ-
I ence. The water table was lowered below the sewer and re-
duced the volume of flow to the treatment plant. The
| water table was not lowered uniformly. For ikO square
blocks 70 pump units would be required at an average cost
| of $^0,000 per unit with a total power bill of $122.50 per
day This is not economically favorable when compared
|;with other corrective measures. This report was submitted
;in fulfillment of Grant No. 29-IDA-2
•BIBLfoGRAFHIC: -~Ci-ty~of"lferidlan7 Idaho
|,Sewer Infiltration Reduction by Zone Pumping - Hoffmann an<3
Fiske-FWPCA Publication DAST 9-1969.
I
ABSTRACT: The intent of this project was to demonstrate
| the reduction of ground-water infiltration into sanitary
sewers by pump down of the water table in the sewer area
| assuming the geology, precipitation and local irrigation
practices were ameanable to rapid and wide zones of influ-
|ence. The water table was lowered below the sewer and re-
duced the volume of flow to the treatment plant. The
(water table was not lowered uniformly. For lUo square
blocks 70 pump units would be required at an average cost
|of $UO,000 per unit with a total power bill of $122.50 per
day. This is not economically favorable when compared
(with other corrective measures. This report was submitted
in fulfillment of Grant No. 29-IDA-2.
"ACCESSION NO.'
KEY WORDS
I
Infiltra-
tion j
Volume Re- 1
duction
Surcharging
Zone-pump-
ing |
ACCESSION No.
i
KEY WORDS
Infiltra- :
tion I
Volume Re- I
duction
Surcharging
Zone-pump-
ing I
ACCESSION No.
KEY WORDS
Infiltra-
tion
Volume Re-
duction
Surcharging
Zone-pump-
ing
GPO 882-989
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