EPA-R2-73-003
FEBRUARY 1973 Environmental Protection Technology
Wastewater Treatment
Studies in Aggregate and
Concrete Production
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
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EPA-R2-73-003
February 1973
WASTEWATER TREATMENT STUDIES
IN AGGREGATE AND CONCRETE PRODUCTION
By
Robert G. Monroe
Project 12080 HBM
(Project Officer
Edward G. Shdo
Environmental Protection Agency
1200 Sixth Avenue
Seattle, Washington 98101
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402
Price $1.2! domestic postpaid or $1 QFO Bookstore
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EPA Review Notice
This report has "been reviewed "by the
Environmental Protection Agency, and
approved for publication. Approval
does not signify that the contents
necessarily reflect the views and
policies of the Environmental Pro-
tection Agency, nor does mention of
trade names or commercial products
constitute endorsement or recommend-
ation for use.
ii
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ABSTRACT
This report contains discussions of various water clari-
fication systems used in the aggregate and ready-mixed
concrete industries. The overall problem of waste water
disposition in each type of plant is studied. An analysis
is made of the use of settling ponds', filter ponds and
coagulants. Recycling and use of recycled water is dis-
cussed with recommendations for further study of the
potential use of waste water from ready-mix plants for
concrete batch water. Since many aggregate and ready-
mix concrete plants now have effective clarification or
recycling systems the overall purpose of the study is to
make these systems known throughout the industry so proven
systems can be made available to all. The report is
based on a review of systems in reported 77 plants and
firms plus data obtained from a field trip inspection of
88 plants on the West Coast. The study contains ^5 charts
and photographs of clarification systems.
This report was submitted in fulfillment of Grant 12080
HBM under the sponsorship of the Office of Research and
Monitoring, Environmental Protection Agency.
iii
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CONTENTS
Section Page
I Conclusions and Recommendations for
Further Research 1
II Introduction 3
III Water Usage in United States 5
IV Aggregate Plant Waste Water Disposition 9
V Aggregate Plant Settling Ponds 13
VI Aggregate Plant Filter Ponds 33
VII Aggregate Plant Coagulation U7
VIII Ready-Mixed Concrete Waste Water Disposition 59
IX Ready-Mix Filter Ponds 63
X Ready-Mix Settling Basins 71
XI Ready-Mix Water Clarification Equipment 85
XII Ready-Mix Wash Water Used for Mix Water 91
XIII Cost of Clarification 93
XIV Acknowledgments 95
XV Reference Material 97
Appendix I—Available Chemicals For
Coagulation
/
Appendix II--Chemical Characteristics
Appendix III—Chemical Flow
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FIGURES
Page
1 SETTLEMENT RATES OF .01 INCH PARTICLES 15
2 SETTLEMENT RATES OF .005 INCH PARTICLES l6
3 SETTLEMENT RATES OF .001 INCH PARTICLES 17
U SETTLEMENT RATES OF .0005 INCH PARTICLES 18
5 SETTLEMENT RATES OF .0001 INCH PARTICLES 19
6 CROSS SECTIONAL AREA OF POND 20
7 VOLUME OF SEDIMENT BUILDUP IN SETTLING PONDS 21
8 WEIGHT OF DRIED SEDIMENT 22
9 POND HOLDING TIME 23
10 PLANT LAYOUT 27
11 SETTLING POND WEIR 28
12 SETTLING POND SHORT CIRCUIT 29
13 EFFECTIVE SETTLING POND 30
lU SETTLING POND LAND REHABILITATION 31
15 PLANT LAYOUT 3k
16 PLANT LAYOUT 35
17 PLANT LAYOUT 36
18 PLANT LAYOUT 38
19 PLANT LAYOUT 39
20 PLANT LAYOUT Ul
21 PLANT LAYOUT U2
22 FILTER PONDS WATER CONTROL U5
23 FILTER PONDS ARRANGEMENT U6
VI
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FIGURES CONT'D
Page
2k WEIR AND COAGULANT MIX POINT 1*9
25 PLANT LAYOUT 50
26 PLANT LAYOUT 53
27 CROSS SECTION—COAGULANT POND 5^
28 COAGULANT POND VOLUME 55
29 COAGULANT MIX POINT 57
30 COAGULANT BASIN 58
31 PLANT LAYOUT 6U
32 READY-MIX FILTER POND 67
33 READY-MIX FILTER POND ARRANGEMENT 68
3U READY-MIX FILTER POND ARRANGEMENT 69
35 PLANT LAYOUT 72
36 PLANT LAYOUT 7^
37 PLANT LAYOUT 76
38 PLANT LAYOUT 78
39 PLANT LAYOUT 80
40 PLANT LAYOUT , 83
Ul NEUTRALIZING READY-MIX WATER 84
U2 DRAG CHAIN WASHER 86
U3 SCREW WASHER 87
UU SCREW WASHER AND SCREEN 89
U5 WASHING SCREEN AND SAND SCREW 90
vii
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TABLES
No.
1 Percentage of Water Usage in United States 6
2 Approximate Filter Pond Size UU
3 Sedimentation Rates 66
viii
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SECTION I
CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER RESEARCH
The aggregate and ready-mixed concrete industries are
primarily smaller businesses producing a low cost product.
Probably for this reason, these industries have not had the
development in water clarification technology as in many
other industries. Thorough research needs to be made in
handling, clarifying and reuse or recycling of the waste
water.
The one area that became apparent first and which appears to
be one of the greatest importance is that of evaluating the
effects of using wash water as mix water in concrete. The
small amount of testing which has been done thus far,
points to encouraging results. It is expected that all the
wash water could be reused in this type of system and no
waste water would be discharged.
Research and experimentation should be made to design and
develop efficient methods of water clarification for the
various types of plants.
The aggregate industry uses much more water and has a some-
what more difficult problem than does the ready-mix concrete
industry. Additional study is needed to develop inexpensive
closed loop systems for the aggregate industry. The closed
loop system is desirable because the water does not need
to be completely clarified to be acceptable as wash water.
The natural or manmade filter ponds show a great deal of
promise, but current information is not complete enough
to be of measurable value to operators. Study in this area
would require construction of test models as well as design
research.
Plant operators are also in need of more knowledge regarding
the handling of waste water. The information needed includes
proper pump selection, required slope on pipe lines to
avoid settlement, proper methods for handling the very wet
sediment, as well as possible commercial uses for the wet
sediment.
Water clarification equipment is being developed very
rapidly at this time. The industry could benefit by having
each product explained, evaluated and tested so the plant
operators could choose the best equipment for their use.
Chemicals are being used to settle suspended particles out
of the water. The effects of these chemicals on the efflu-
ent water and on the product quality should be studied.
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Each of the above mentioned areas of needed study should
be extensive to develop the in-depth answers required.
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SECTION II
INTRODUCTION
This study was carried out through grant funds from The
Environmental Protection Agency and sponsorship of The
Oregon Concrete and Aggregate Producers Association, under
Grant No. 12080 HBM. The aggregate and ready-mixed concrete
industries use many gallons of water each year, some of
which adds to the national water pollution problem. The
basic purpose of the study is to provide a state-of-the-art
survey of aggregate and ready-mix production to determine
the kind and extent of present treatment methods for the
process water-
The study was conducted in four phases as follows:
Phase I--Surveyed the available literature pertaining to
water pollution caused by aggregate and ready-mix pro-
duction and the total national water pollution problem.
Phase II--The main purpose of this phase was to determine
the kind and extent of present treatment methods for
process water used in aggregate and ready-mix production.
The literature was reviewed. In addition, questionnaires
were submitted to principal aggregate and ready-mix
producers, and inspections were made in a selected number
of aggregate and ready-mix plants.
Phase Ill — Gaps in technology were identified during this
phase and recommendations for further research were
developed.
Phase IV--A11 the information developed in the first three
phases was assembled and the effective systems described
in this report.
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SECTION III
WATER USAGE IN UNITED STATES
Water in the United States is used primarily for irri-
gation, public water supply, domestic, industrial and
steam-electric power. Not all the water used in these
areas creates pollution. In general, one third of the
water returns to the waterway with the salt content approx-
imately doubled. One third is consumed in making products
or is lost in the atmosphere. One third "becomes contam-
inated with organic and inorganic solids originating in
the process water.
It is the latter one third of this water with which the
aggregate and ready-mixed concrete industries are con-
cerned. This report defines these industries to include
sand and gravel, crushed stone and ready-mixed concrete
plant s.
Before looking at the specific water pollution problems
and solutions it becomes necessary to compare overall
water consumption by the major classifications of users.
Sand and gravel production in the United States in 1969
totaled 937 million short tons valued at $1,070,000,000.
Crushed stone production in the United States in 19&9
totaled 86l million short tons valued at $1,326,0^7,000.
Many sand and gravel and crushed stone plants need no
washing in producing their finished product. Other plants
must use up to 800 gallons of water per ton of production.
Because many plants use no water, the average water demand
per plant is only 70 gallons per ton. About 126 billion
gallons of water is used per year in processing sand and
gravel and crushed stone.
The ready-mixed concrete industry takes this processed
material and adds cement, special additives and water. This
mixture becomes active'concrete which will begin to set
within a few hours, so trucks and other plant equipment
must be continually washed clean to prevent build-up of
concrete and the break down of machinery. There are
approximately 8,000 ready-mixed concrete plants in the
United States with a national production of 186,000,000
cubic yards per year. This mixed concrete is valued at
$2,930,000,000. Water used for making the product amounts
to six billion gallons per year. Since this vater is
totally consumed in the product it does add to the nation-
al water usage, but not to water pollution. The water
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TABLE 1
PERCENTAGE OF WATER USAGE IK UNITED STATES
Year Irrig Public Domestic Steam --Industry— Total
Water Electric Aggreg Total Gal/Year
Supply Power Trillion
I960 U3 7 2 25 .23 23 39-0
1965 Ul 7 2 26 .24 2h U5.0
1970 39 7 2 27 .25 25 50.5
1975 37 7 2 29 .25 25 56.6
i960 35 7 2 30 .26 26 66.2
1985 33 7 2 31 .27 27 75.0
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used to wash the trucks and equipment does become a
potential water pollutant.
The average ready-mix truck load is 6.8 cubic yards and
each truck averages U.2 trips per day. Each truck and its
portion of the plant equipment will use an average of 500
gallons of water per day.
The range of water use per truck per day varies widely
because some operators wash out trucks once a day, while
others wash out after each load. Availability of water
also affects usage. When water is abundant and low in cost,
operat-.ors use larger quantities. However, they wash off
about the same amount of solids in any case, so the
potential stream pollution load is not increased. Based on
500 gallons per day the annual water usage is as follows:
Annual wash water = 186,000,000 yards/year . 500 gal/day
6.8 yards/load.^.2loads/day
= k billion gallons/year.
The aggregate and ready-mixed concrete industries used
136 billion gallons of water in 19^9 and the rate is
increasing by four per cent per year. This figure agrees
closely with other surveys showing the stone and vitreous
products using two per cent of the total industrial water.
The aggregate and ready-mix concrete industries amount to
about one-half of the total stone and vitreous products.
This analysis gives a perspective of the volume of water
used by the aggregate and ready-mixed concrete industries
and the comparison to the total water use. The analysis
shows that although the aggregate and ready-mixed concrete
industries are heavy water users, they use only a small
percentage of the total water used in the United States.
Water is used by everyone as a carrier of product or waste,
for cooling, for washing, for irrigation, for addition to
products and many other uses. Most all of these uses
change the water characteristics if no clarification or
treatment is made. The change in the water quality varies
widely even within a specific industry. Effluent water
from food processing plants, sewage treatment plants and
other similar operations may produce harmful bacteria,
reduce dissolved oxygen and produce undesirable appear-
ances. Plastic, chemical and oil industries may discharge
oil or toxic substances, increase temperatures and produce
many other undesirable characteristics. Aggregate and
ready-mix plants may raise the pH factor, increase turbid-
ity and reduce the dissolved oxygen.
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Each year, from the aggregate produced, the aggregate
producing industry washes off many tons of fine sand, silts
and clays. Waste water from the ready-mix industry contains
fine sand, lime and cement. The uncontrolled and untreated
discharge from "both of these industries impairs the
aesthetic quality of our streams and may "be a hazard to
marine life.
With the increase in production of these industries, an
additional volume of water is required of approximately
four per cent per,year. The requirements for cleaner
products require more thorough washing and scrubbing which
in turn increases the amounts o.f suspended particles in
the waste water. This increase in volume and concentration
of suspended particles in the effluent water can only add
to the existing problem. The aggregate and ready-mixed
concrete industries, as well as all other water users ,
must have clarification systems in order to improve the
quality of water which they discharge into our streams and
rivers.
Many of these plants do have effective systems for clari-
fying the water or recycling it. It is the purpose of
this study to make these systems known to all the industry
so proven systems can be put into operation quickly.
8
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SECTION IV
AGGREGATE PLANT WASTE WATER DISPOSITION
Letters were written to 56 Ready-Mixed Concrete and
Aggregate Producers' state associations explaining this
study and asking for a list of their membership from whom
information could be sought. From 31 responses, 350
letters and questionnaires were sent to individual
companies. The summary present herewith is "based on
responses from 77 companies. To augment responses from
these questionnaires a field trip was made to 88 plants
on theAWest Coast.
A preliminary assumption could be made that only a few
plants are concerned about the waste water problem or
there would have been a greater response to the letters
and questionnaires. However, after reviewing the returned
questionnaires and visiting plant sites throughout the
area, impressive evidence was obtained that most plants
are more or less self-contained and have no actual figures
or data pertaining to the condition of their water or
amounts used. This is why they did not fill out and return
the form.
Most plants are located on the outskirts of towns and have
sites consisting of from several to many acres of ground
upon which they have been operating for many years. Most
of them have abandoned pits or low areas on their own
sites into which they discharge their waste water and waste
material. The plant is in this sense self-contained and
has at this time no water clarification problem. Many-
plants also have both aggregate and ready-mixed concrete
operations on the same site. There is no way to estimate
the proportion of these plants to the total number of
plants. Because of this it seems more logical and realistic
to analyze the methods of water clarification individually
rather than attempting to translate them into percentages
within the total industry.
The aggregate industry uses water primarily to wash out
the silts, clays and foreign materials from the raw material
and to separate out the excess fines in the classification
of the saleable product. The amount of water needed per ton
of material will vary with each site of operation as well as
within different areas and strata on the same site. It
is dependent upon the amount of contaminants that need to
be scrubbed off or washed from the product and the amount
of fines that may have to be separated out.
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Plant equipment needed for removing these foreign materials
and fines consists of washing screens, log washers, sand
screens and classifiers. The amounts and kinds of foreign
materials in the pit or quarry determine the kinds and
sizes of the equipment needed in the plant which in turn
determines the amount of water required. Sources of
aggregate may vary from relatively pure material requiring
little or no washing to material too contaminated to
process economically. However, in some parts of the
country, the lack of sufficient sources of sand and gravel
to meet the need for the product may require the use of
those pits or quarries whose material requires extensive
cleaning and separation of these foreign materials. Use of
water therefore varies from five to ten gallons per ton to
500 or more gallons per ton of material processed.
The water discharged from the plants varies from a light
to heavy concentration of suspended particles ranging from
fine sand to silts and clays to colored pigments. Methods
of clarifying this waste water vary from use of a simple
settling "basin to a complex combination of ponds and
flocculants. The location of the plant and the amount of
available space may also become factors in determining a
solution to the problem.
Information on water clarification systems used in sand
and gravel plants seemingly is very limited. Few plants
replied to the letters and questionnaires sent out. Of
those owners who did reply most indicated the use of low
ground or worked out pits on their own property as holding
or settling ponds. Most of the ponds or pits are large in
area and volume and have no overflow. A few overflow only
after heavy rains or during the spring run-off in which
case the turbidity of the water is mixed with run-off
water- Overflow from a few plants is discharged into
storm sewers.
Companies that had installed clarification systems used
parts of their excavated areas to form or build into
multiple basins. Plant waste water was treated with
coagulants and/or flocculants before discharging into the
first or primary basin. With the aid of the coagulant
and flocculants most of the suspended material settled
out in this first or primary basin. Water flowed over
weirs from one basin to the next. The weirs were made
relatively long to decrease the depth of water over the
weir and to serve as a skimmer- The clarified water in the
last basin was then recycled back as plant water. This
made a closed loop system and eliminated discharging
water from the plant site.
10
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Because the primary pond collects the major portion of the
sediment, it requires periodic cleaning or relocation.
Some companies use the primary pond as a means of restoring
its vorked out areas. The area is diked off and the waste
water is pumped to this pond. The overflow is piped to a
series of permanent basins separated by weirs and water
in the last basin is used as the source of plant water.
When sediment has built up in the primary pond to the
desired level, the pond is relocated over the next area
needing restoration.
Periodic cleaning is required in the permanent basins and
that sediment is also used as landfill.
One company has installed two separate primary holding
basins each having a capacity greater than a full day's
supply of discharged water. Each basin receives a day's
supply of water every other day, allowing one day for
settling time in each basin after which the water is
discharged into a third holding basin and pumped back to
the plant again. Periodically each of the primary settling
basins is cleaned and the sediment hauled off as waste
or used as'landfill material. This also becomes a closed
loop system with no water being discharged from the site.
One company that discharges all of its waste water into a
waterway has clarified its water from 7,000 mg/1 of suspended
particles to under 200 mg/1. This company uses three
ponds and a polymer treatment system. Waste water flows
into the first and largest pond where the coarser particles
settle out. The mixed and diluted polymer is mixed into
the waste water between the first and second ponds and
again between the second and third ponds. This company,
after experimentation, found this arrangement to be more
economical and satisfactory than introducing the polymer
in the flow into the first pond. Another company with a
similar chain of three ponds found it necessary to use
polymers and coagulants,at the inlets of all three ponds.
Inasmuch as each plant varies in size and orientation of
site as well as in the amount and kinds of suspended
material in the waste water, determining the kind and
arrangement of a water clarification system requires
careful study and planning. Samples of the waste water
should be analyzed both for its chemical content and for
the settling rate of the suspended particles. Areas to be
used for filtration ponds should be checked for absorption
rate. The size of the basins or ponds is dependent upon
the amount of water discharged and the settling rate of the
11
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suspended particles. The use of coagulants and flocculants
speeds up the settling rate of the suspended particles and
can help to decrease the size of the ponds or basins.
Samples of the waste water should "be tested with combinations
of these additives. The comparison of settling rates
with costs of the additives will determine which combination
should be used.
12
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SECTION V
AGGREGATE PLANT SETTLING PONDS
Settling ponds are generally used where there is sufficient
low ground or worked out areas available to form such ponds.
The sediment will fill the pond areas and restore the land.
Settling ponds are ponds that allow solids to settle and
the clarified water overflows. Those ponds that tfij.1
allow seepage are referred to as filter ponds and will be
discussed in the next section. Most settling ponds are
also filter ponds "but are separated in this report for
clarity.
Settling ponds have limited efficiency, especially in
deposits with clay or light fines that do not settle
quickly by the natural process. Yet, because this system
takes very little effort on the part of the operator and
because abandoned pits are frequently available, it is
widely used. Proper planning and sizing of ponds result
in an effecient and economical system. Water will rarely
clear up enough to be discharged into waterways, but it
normally will be clear enough for washing the aggregate
in a recycling operation.
Correspondence from many plant operators discussed
effectiveness of settling ponds. A number of plants were
visited during the course of the study. Figures 1, 2, 3,
U and 5 show settlement rates for various particle sizes
and specific gravities at maximum horizontal movement.
Often settlement rates are found to be much slower than
Stokes law would suggest, probably due to varying negative
charge of the suspended particles. The operator must decide
what size particles can be permitted in the recycled water
without damaging equipment and still achieve the necessary
washing effect. The specific gravity must also be known
and can be determined by using a hydrometer giving direct
specific gravity reading.
The specific gravity of a body is defined as the ratio
of its weight to an equal volume of water. The specific
gravity of effluent water from an aggregate plant runs
from 1.000 to 1.060. The weight of the dry sediment can
be determined by evaporating the water from a sample of
effluent and weighing the dry sample and measuring its
volume. (See Figure 8 and example later in report.)
Settling pond sizes can be determined from Figures 1
through 9.
13
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It has been found that ponds will short circuit, that is,
form a stream from inlet to outlet, causing great increases
in horizontal velocities and a reduction in settlement.
Turbulance, sediment and buildup variations in specific
gravity can greatly reduce the settling pond efficiency.
A second pond is required to skim off the cleanest vater
with a weir. The second pond is normally the same size
as the primary pond to allow for additional settling, thus
it can be used as a future primary pond. The water must
run from the pumping pond back to the plant. If clearer
water is desired, coagulants can be added just ahead of the
secondary ponds. (See section on coagulants for more
information.)
Several factors must be included in a well-designed
settling pond.
1. Water velocities must remain low, including inlet
and outlet.
2. Inlet water must be introduced into the pond across
the full width to avoid short circuiting and to get full
pond usage. This is accomplished by piping into the pond
in several places across the width.
3. Outlet water must flow out slowly to avoid scouring,
that is, picking up the particles that.are supposedly
being removed. This can be done by maintaining a minimum
outlet of one foot of width for every 25 GPM of water being
used. This has not been the practice in most plants, but
would be necessary to maintain pond efficiency. The depth
of outlet water can be controlled by the use of gates for
regulating the secondary pond level.
Before an operator makes a decision to adopt this system
a sample of water should be tested to determine the length
of time required to become sufficiently clear to p'ermit
recycling to the plant as wash water. If settling time
is too lengthy, a small amount of coagulant could :be used
to neutralize the particles and aid in settling. (See
section on coagulants.)
To explain the figures, a hypothetical plant will be used
as an example.
Known—plant water use—-2,500 GPM.
Known—jar test shows water would be clear enough for
rewashing after it has settled for a minimum of 1*8 hours.
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MAXIMUM HORIZONTAL
VELOCITY-4 FT/MIN
18
16
14
x
-12.
10
u
IT
w 4
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4
SPECIFIC GRAVITY
DEVELOPED FROM STOKE'S LAW AND FROM CHARTS IN THE NATIONAL READY
MIXED CONCRETE ASSN. PUBLICATION NUMBER 116.
FIGURE NO, 1 SETTLEMENT RATES
OF .01 INCH PARTICLES
15
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4,8
MAXIMUM HORIZONTAL
VELOCITY 2 FT/ MIN
4,2
3.6
3.0
2.4
o 1.8
o
1.2
<
o
u
.«
1.0 1.2 1,4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4
SPECIFIC GRAVITY
DEVELOPED FROM STOKE'5 LAW AND FROM CHARTS IN THE NATIONAL READY
MIXED CONCRETE ASSN. PUBLICATION NUMBER 116
FIGURE N0.2 SETTLEMENT RATES
OF,005 INCH PARTICLES
16
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.18
.16
.14
.12
.10
3
III
>
.06
.04
hi
.02
MAXIMUM HORIZONTAL
VELOCITY-,4 FT/MIN
1.0 1,2 1.4 1.6 | 1.8 2.0 2.2 2.4- 2.6 2.8 3.0 3.2 3.4
SPECIFIC GRAVITY
DEVELOPED FROM STOKE'S LAW AND FROM CHARTS IN THE NATIONAL READY
MIXED CONCRETE ASSN. PUBLICATION NUMBER 116
FIGURE N0.3 SETTLEMENT RATES
OF .001 INCH PARTICLES
IT
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MAXIMUM HORIZONTAL
VELOCITY- .2 FT/MIH
.050
.045
.040
.035
z
5
,030
H
O
Q
.025
.020
-I
P -018
oe
tu
.010
.005
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 32 3.4
SPECIFIC GRAVITY
DEVELOPED FROM STOKE'S LAW AND FROM CHARTS IN THE NATIONAL READY
MIXED CONCRETE ASSN. PUBLICATION NUMBER 116
FIGURE NOI4 SETTLEMENT RATES
OF ,0005 INCH PARTICLES
18
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MAXIMUM HORIZONTAL
VELOCITY-.04 FT/MIN
.0018
.OOI6
.0014
.0012
z
5
.**• .0010
Ik
£ ,O008
0
o
> .0006
_l
<
u
H .0004
oc
ui
>
.0002
0
/\
/
/
/
/
/
/
s
/
/
/
/
/
/
/
/
/
/
1.0 1.2 1.4 1.6 ) 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4
SPECIFIC GRAVITY
DEVELOPED FROM STOKE'S LAW AND FROM CHARTS IN THE NATIONAL READY
MIXED CONCRETE ASSN. PUBLICATION NUMBER 116
FIGURE N0.5 SETTLEMENT RATES
OF .0001 INCH PARTICLES
19
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u.
I
o
o
u
o
IM
6PM CFM
5000 667
4000 539
30OO 400
2000 267
1000 133
500 67
O 200 400 600 600 1000 1200 1400 I60O I80O 2000
WIDTH X DEPTH = SO. FT.
DEVELOPED FROM* CU. FT. / WIN. = WIDTH X DEPTH X VELOCITY
FIGURE NO.6 CROSS SECTIONAL AREA OF POND
20
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5 OOP
4
12 CU.IN./ GAL.
14 CU. IN./ QAL.
16 CU.IN./ OAL.
18 CU.IN./ 6AL.
20 CU.IN./ OAU.
0 500 1000 1500 20OO 2500 3000 9500
SEDIMENT IN POND- CU. FT. / HR.
DEVELOPED FROM JAR TEST RATIO OF VOL. SEDIMENT / GAL. WATER X
TOTAL 6AL. OF WATER/ HR. = TOTAL VOL. SEDIMENT/ HR.
FIGURE N0.7 VOL. OF SEDIMENT BUILDUP
IN SETTLING PONDS
21
-------
1.000
1.010 1.020 1.030 1.040
SPECIFIC GRAVITY OF DISCHARGE WATER
1.050
DEVELOPED FROM > VOL. OF MIXTURE X S.G. OF MIXTURE =
VOL. OF SEDIMENT X S.G. OF SEDIMENT 4- (VOL. OF
MIXTURE -VOL. OF SEDIMENT) X S.G. OF WATER
FIGURE N0.8 WEIGHT OF DRIED SEDIMENT
22
-------
5000
5 10 IS 20 25 30
100
140
200
POND VOLUME - CUBIC FEET
VOLUME OF PONO
DEVELOPED FROM* HOLDING TIME >
VOLUME OF FLOW 7 HR.
FIGURE NO.9 POND HOLDING TIME
23
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Known--maximum particle size acceptable in recycle water--
0.0005 inch.
Determine discharge water specific gravity by using a
hydrometer--hydrometer reading—1.Ol8.
The specific gravity of the suspended solids can be deter-
mined by measuring one gallon of waste water and evaporating
the water. To speed this process it is possible to mix
some coagulants such as alum in the sample so the suspended
solids will settle out. The excess clear water can be
drained off and then the wet sediment placed in an oven
where the remaining moisture will evaporate off. The dry
sediment must be measured accurately in cubic inches.
Dried sediment volume = 10.2 cu in./gal.
With this information Figure 8 shows the specific gravity
and weight of the dried sediment for 10.2 cu in./gal. and
1.0l8 specific gravity.
Figure 8 dried sediment = l.Uo or 87.36 PCF.
Figure U shows the settling rates of .0005 inch particles
with a specific gravity of l.k and a horizontal velocity
of 0.2 feet per minute.
Figure h settling velocity = 0.008 ft/min.
Figure 6 gives the pond cross section or width times depth
for 2,500 GPM and 0.2 feet per minute horizontal velocity.
Figure 6 width x depth = 1,600 sq. ft or 200 ft wide and
8 ft deep.
When this much cross sectional area is needed, care must
be taken to avoid short circuiting. If the pond is to be
cleaned, it must be narrow enough for equipment to reach
half way across. Pond length can be determined by the
following formula:
Length = width + horizontal velocity x depth
vertical velocity
Length = 200 +
2 x 8 _
.008
feet
The water must flow over a long weir from the pond to the
pumping pond. The weir should be a minimum of one foot
wide for each 25 GPM. The pumping pond can be just large
enough for surge water or, if the land is being rehabilitated,
-------
it is "best to have the pumping pond the same size as the
primary pond. This will allow the pumping pond to become
the primary pond as soon as the existing primary pond is
filled. The holding time of the pond may be checked from
Figure 9- The ponds selected are two 200' x 8' x UOO'
ponds.
Volume = 2 x 200 x 8 x UOO = 1,280,000 cu ft.
Figure 9 holding time = 60 hours.
It was noted as known information from timing a jar sample
that U8 hours was required to get satisfactory clarification
This has been achieved by having pumping ponds the same size
as the primary pond.
Thus far the minimum pond depth has been discussed, but
provisions must be made for sediment. It was determined
earlier that there is a volume of 10.2 cubic inches per
gallon of dried sediment, which is above normal. The wet
sediment such as would be found in the pond bottom will
average about two times the bulk of the dry sample. Figure
7 shows the buildup in cubic feet.
Figure 7 sediment buildup = 1,800 CF/hr.
Almost all the sediment volume will settle in the primary
pond. One pond has a- bottom area of 200' x 1*00' = 80,000
square feet. The assumption is that the plant operates
200 hours per month.
Sediment buildup = 1,800 CF/hr x 200 hr/mo = 1^.5 ft/mo.
80,000 sq ft
The ponds could be two 200' x 25' x kOO1 and this would
allow approximately four months' filling time. As the
ponds filled, the additional ponds could be built. The
figures used in this ex'ample were taken from an operating
plant that has much higher than normal amount of suspended
solids.
It is important to make the jar test to determine the time
required to obtain adequate settling. In this example the
buildup of sediment becomes the main problem. The size of
the pond must be determined by available land. If land is
not available a much smaller pond can be used with almost
continual dredging and hauling away. The operator must now
decide which of his original decisions should be altered.
The most important considerations in settling pond design
are :
25
-------
1. Cross sectional area of pond must be large so horizontal
velocity is very slow.
2. Water must enter pond over most of the width to make
the entire pond effective.
3. Outlet must be wide to skim off top cleanest water
and to keep horizontal velocity low.
26
-------
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ZOO' X 400* X 25'
20O* X 4OO* X 25*
-------
£'•"••/
Notice narrow weir and large water drop causes
high horizontal velocities. Fines cannot
settle out.
FIGURE 11 SETTLING POND WEIR
28
-------
ines
Narrow fast-dropping stream does not allow f
to settle. This was the most frequently observe
problem. Water must have very low horizontal
velocities .
FIGURE 12 SETTLING POND SHORT CIRCUIT
29
-------
This pond is wide and deep allowing low horizontal
velocities and good settlement.
FIGURE 13 EFFECTIVE SETTLING POND
30
-------
' Qji
"1 •*••••-"
-
Combination settling ponds and land rehabili-
tation. Note land rehabilitation on right is
capable of growing good ground cover.
FIGURE Ik SETTLING POND LAND REHABILITATION
31
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SECTION VI
AGGREGATE PLANT FILTER PONDS
Filter ponds are those systems which allow the plant
discharge water to flow into a pond that has no outlet
or complete recirculation. The water seeps out the "bottom
and side of the pond and is clarified by this filtering
process. Many factors affect the success of such a system,
so they must be considered.
1. The water table must be low enough that the water will
filter out, not into, the pond at any time the plant is
running.
2. The walls and bottom of the pond must be porous
through which to allow the water to flow.
3- The pond must be large enough so it will not seal
too rapidly.
h. There must be enough water used so the suspended
particles will not seal the bottom and sides too quickly.
Most of the plants which use this system have used old
mined out pits or natural canyons for filter ponds. This
means the pond was not designed for minimum size, but
rather the land that was available was used. However, if
the size and depth of these ponds can be determined, the
bottom and side areas required to achieve equilibrium will
be known. Examples of typical plant layouts are cited
below.
The plant in Figure 15, discharging 200 GPM into a 50 feet
by 150 feet by U feet primary pond over a weir and into
a 80 feet by 1,800 feet by k feet filter pond, has operated
for seven years without, any signs of the pond sides or
bottom sealing. The soil has heavy vegetation and on first
appearance, woul'd not seem to be porous enough to allow
sufficient seepage. However, by inspecting the dredgings
from the primary pond, which must be cleaned every two
weeks, it was noted that the settled material is mostly
granular. Most of the fines in the natural deposit are
granular, thus porous. The filter pond wall and bottom
surface total about 150,000 square feet and provides an
area of 750 square feet for each gallon per minute of inflow,
The pond is at equilibrium at this point, giving an idea
of the area required for filtering in this type of soil.
33
-------
PLANT
200 GPM
ISO1
80'
o
o
FIGURE NO. 15 PLANT LAYOUT
-------
600'
29' DEEP
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,000 GPM
-»- PLANT
FIGURE NO, 16 PLANT LAYOUT
35
-------
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FIGURE NO, 17 PLANT LAYOUT
36
-------
The plant in Figure 16 discharges lU,000 GPM and recycles
1*,000 GPM, so 10,000 GPM filters out in a 1,600 feet "by
600 feet by 25 feet pond. Although the sediment will
gradually fill and seal part of the pond, there is ample
pond size to avoid sealing of the entire wall and bottom
surfaces of pond. The raw material has very little clay
and only 1% minus 50 mesh and only 0.2% minus 200 mesh.
The surface area of the bottom and walls is about one
million square feet or 100 square feet per GPM. It must
be kept in mind that this plant has little clay or fines,
resulting in ideal filtering with little or no sealing.
The plant in Figure 17 discharges 300 GPM and recycles
150 GPM, so 150 GPM filters out in a series of five
100 feet by 200 feet by U feet ponds. The first pond is
a primary settling pond, which becomes sealed, and the
remaining four are filter ponds. Approximate area of the
walls and bottoms of the four filter ponds is 80,000
square feet which provides 533 square feet of area per
GPM.
The plant in Figure 18 discharges 150 GPM with no recycle.
The pond is 60 feet by 120 feet by 5 feet. The material
making up the pond bottom is sand and silt and the wash
water is also sand and silt with very little clay. The
water table is well below the pond and an open pit exists
next to the pond, which may allov the water to seep away
more rapidly. This provides 67 square feet per GPM.
The plant in Figure 19 discharges 2,000 GPM with no recycle,
The entire amount flows into a 300 feet by 300 feet by 10
feet pond and filters into the ground. The ground water
is well below the pond bottom at all times of the year.
The pond bottom is sand and gravel and the discharge water
carries about 2% sand and very little clay. The pond is
seldom cleaned and has not sealed. It has a filter area
of 50 square feet per G'PM.
The plant in Figure 20 discharges 500 GPM with no
recirculation from the pond. However, the water washes
the aggregate five times during the process before being
discharged. The discharged water carries about 2% silt
and clay. The suspended solids and dissolved solids are
being used effectively for land rehabilitation. Discharge
runs through concrete pipe to a 200 feet by 500 feet area
to be built up. Water runs off this area into a UOO feet
by 500 feet pond. The overflow then goes into a UOO feet
by 200 feet pond. The water table varies due to irrigation
and precipitation. Sometimes the pond has water seeping
37
-------
PLANT
60'X 120' X 5'
<; <;
OPEN PIT
FIGURE NO. 18 PLANT LAYOUT
38
-------
PLANT 2000 6PM
300* X 300' X 10'
FIGURE NO. 19 PLANT LAYOUT
39
-------
in and other times the ponds dry up. During dry veather
"both ponds go dry- At that time the filtering takes place
in the 200 feet "by 500 feet buildup area, vhere 200 square
feet per GPM are required. During wet seasons and when
the irrigation canal is high there is an inflow of surface
water and canal water, and the ponds rise above the canal
and water table. The 200 square feet per GPM is still
approximately correct, but this does emphasize the necessity
of knowing ground water conditions for all times of the
year.
The plant in Figure 21 discharges 2,500 GPM into a series
of three ponds. Seven hundred GPM overflow into a water-
way and the rest filters into the sides and bottom of the
filter ponds with 16 PPM suspended solids and Jackson
Turbidity unit readings of 13-36. Over two per cent of the
fines are smaller than 200 mesh with some silts and clays.
The series of three ponds total 650,000 square feet. This
plant has 360 square feet per GPM.
From these examples, areas to take into consideration in
designing filter ponds can be established.
1. Water table must be low enough all year to allow water
to flow out during operation and rains. Pond berms must
be high enough to guard against flood conditions carrying
out turbid water.
2. Pond walls and bottom areas must be inspected to
determine the porosity of the soil. The waste water solids
should also be evaluated as light or heavy concentration
of sand, silt or clay. The examples given show the wide
variation of results caused by porosity.
3. It is best to use two ponds. The primary pond is used
for heavy particle settlement, so the filter bed will not
fill with solids too fast. The weir from the primary pond
to the secondary pond should be as wide as possible to
reduce the velocity of water. This skims the cleanest water
off the top and minimizes short circuiting.
k. Filter pond walls are more efficient than the bottom,
so deep steep walled filter ponds are desirable. Ponds
will seal more slowly if they are kept full so all the
area of walls and bottom can be working.-. Allowing the
pond to rest every couple of months also improves its
filter life.
5. The use of flocculants will shorten the filter pond
life, therefore their use should be restricted to the primary
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pond; or three ponds could be used and flocculants added
in the secondary pond. Flocculants should not "be used in
the filter pond.
6. If the filter bed is above the water table, lowlands
or wells close by could be endangered by seepage from the
pond. This should be considered in the location and design
of the filter pond.
1*3
-------
TABLE 2
APPROXIMATE FILTER POND SIZE
Filter Pond
Area/GPM
50 sq. ft
100
150
200
250
300
350
TOO
750
800
Classification of Pond
Walls and Bottom
Coarse Aggregate
Aggregate and Sand
Aggregate, sand, silt
and clay
Sand, silt and clay
Wot recommended Clay
it
it
it
Classification
Plant Discharge Water
Sandy sediment
Sand and clay
Clay
Sandy sediment
Sand and clay
Clay
Sandy sediment
Sand and clay
Clay
Sandy sediment
Sand and clay
Clay
Sandy sediment
Sand and clay
Clay
Developed from information provided
"by field inspections of existing
filter ponds.
-------
Method of transporting water. Where no settling
is desired, water may be fast running in pipe or
narrow ditch. Note: Land where ditch is
located has been rehabilitated by allowing the
water to run slowly over entire area.
FIGURE 22 FILTER PONDS WATER CONTROL
-------
Combination filter pond and land rehabilitation.
Rehabilitated land on left. Filter pond in
background. Berm on right which allows water to
filter through to waterway.
FIGURE 23 FILTER PONDS ARRANGEMENT
1*6
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SECTION VII
AGGREGATE PLANT COAGULATION
Many aggregate plants are using coagulants as the answer
to their water clarification problem. Some of the reasons
for choosing coagulants are:
1. High concentration of solids that von't settle.
2. Water too dirty to reuse or discharge into water-
ways .
3. Limited land area for settling ponds.
k. The need to rehabilitate land quickly by settling all
the solids in very small ponding areas.
Water clarification for the aggregate industry is
primarily removing solids and reducing turbidity. The
reason for this clarification is often to meet water quality
standards set up by governmental bodies. However, clari-
fication is often justified to reduce amount of new water
needed and to reduce the wear on equipment caused by dirty
water.
Turbidity is the color or lack of clearness in water. The
turbidity is essentially a suspension of colloidal clay
particles which generally possess negative charges. The
negatively charged particles repel each other, hindering
agglomeration and settlement.
Coagulants are positively charged and when mixed with the
water, neutralize the negatively charged colloidal clay-
This process allows the particles to floe together, causing
the particles to have less surface exposed to the water,
allowing in turn, faster settlement. Often it is desirable
to use coagulant aids or another chemical to increase
settlement rates. The aid mechanically ties the floe
particles together, making bigger and heavier floes for
faster settlement.
Coagulants work better in warmer water- Settlement rate
is approximately doubled for every 18° F increase in
temperature.
Coagulants must be thoroughly mixed to be efficient. After
a thorough mixing, a period of slow mixing is desired, as
this causes the solids to pass close to other solids on
-------
which the floccing process depends. The water then must
move as slowly as possible to allow maximum settling rates.
The cost of water clarification varies widely with the
material and degree of clarification needed. In most
cases the cost of chemicals to clean the water sufficiently
for discharge into waterways would "be $0.03 to $0.06 per
ton of saleable aggregate. Normally, if the water is recycled
in the plant the cost is $0.02 to $0.0^ per ton.
There are a number of different arrangements which are used
for ponds, but the multi-pond concept seems to be the most
suitable.
The chemicals offering the best economy vary with the con-
dition of waste water. The most frequently used method of
determining which coagulant should be used is the jar test.
It consists of placing a measured amount of the waste water
in a jar, mixing in a specific amount of the coagulant, and
timing the rate of settlement. By using varying measured
amounts of the various coagulants and comparing the settle-
ment rates, the coagulants most applicable and the quanti-
ties per given volume of waste water can be determined.
Some of the coagulants frequently used are:
Aluminum sulphate
(AL2 (SOli)8l8H20) alum
Ferrous sulphate
(FeSOl|. 7H20) copperas
Calcium hydroxide
(Ca(OH)2) hydrated lime
Calcium oxide
(CaO) quicklime
Sodium aluminate
Sodium carbonate
soda ash
Ferric chloride
(FeCl3) ferrisul
Acid, so could be used on alkaline condition
(pH over 7)
Sodium silicate
Na20 + Si02)
Alkaline, so could be used on acid condition
(pH below 7)
U8
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COAGULANT
PIPE CUT IN HALF
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CORRUGATE PIPE
70' MINIMUM LENGTH
SECONDARY POND
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-------
Some of the chemicals which are available are listed in the
appendix.
There are a multitude of choices to be made in determining
which chemical should be used. An engineering firm familiar
with the available chemicals and plant problems can make
an unbiased evaluation. A chemical company with whom the
plant operator would like to do business can be of help.
The cost of clarifying the water can be very expensive so
it must be insisted that low-cost coagulants, such as alum
and lime be tried.
The ideal plant waste water system is one that is also
rehabilitating land. With this system, the primary pond
becomes the land that is being rehabilitated. If a high
percentage of solids is in the discharge and they settle
out quickly, no chemicals should be put into the discharge
water until it leaves the primary pond. The reason for
this is to avoid wasting chemicals on solids which will
settle out quickly by themselves. This places larger, more
stable material at the top of the rehabilitated land,
making a better fill. If very little settles out quickly,
the chemical can be introduced at the plant discharge and
a corrugated pipe used to create a mixing action before
reaching the pond. Most plant conditions will be such that
coagulants should be added between the first and second pond,
Providing adequate mixing economically becomes a problem.
The water should discharge from the primary pond over a
weir that is a minimum of one foot wide for every 25 GPM.
The chemical should be mixed with the water at the weir and
then allowed to travel a minimum of TO feet in a corru-
gated pipe that will cause mixing. The mixture of coagu-
lant and water will then flow into the secondary pond and
as it slows and spreads out, flocculation will begin.
Pond minimum sizes can be determined from Figures 27 and
28. The most desirable pond size should be determined
by available land and cost of developing pond. The
larger ponds will last longer, but land rehabilitation will
progress at a slower rate.
Frequently the plant operator does not have the need for
rehabilitating the land nor the room for large ponds. In
this case he must use the largest ponds his land will allow
and haul away the sediment as it builds up in the primary
pond. A second primary pond is required to be used while
the first pond is idle for the drying and removal of built
up sediment. Overflow from the primary ponds flows into a
pumping pond. With this system coagulants are usually
51
-------
mixed ahead of the two primary ponds. A typical plant lay-
out is shown in Figure 26.
The primary ponds can be sized as shown on Figures 27 and
28. The pumping pond should "be large enough to meet the
plant's water surge demands.
The primary pond cross section can "be sized "by limiting the
flow to a velocity of approximately one foot per minute and
making the pond twice as long as it is wide. If more
specific information is desired relative to anticipating the
sediment that will occur in the primary pond, refer to the
section on settling ponds. Larger ponds can "be used if
desired to increase pond life or increase sedimentation.
The ponds must also have sufficient holding time to "be
effective. From the jar tests an estimate can "be made for
the time needed for clarification and the pond can "be
sized accordingly. The available land may cause the
operator to use a different mixture of coagulants to fit
available pond size.
Example, Figure 25
Known, water use--2,500 GPM. The water specific gravity
is 1.010. It is known that the large particles will drop
out quickly.
The jar test shows 60 PPM alum and k PPM of commercial
polymer caused good clarification in three hours. Specific
gravity was down to 1.000 and water cloudy in one and a
half hours. By doubling the alum, clear water was obtained
in one and a half hours.
Minimum pond size from Figure 27-
Water flow is one foot per minute.
Figure 27 shows 3^0 square feet cross section or 50 feet
wide, 6.8 feet deep and 100 feet long.
Check holding time with Figure 28--one and a half hours
holding.
Figure 28 shows 60,000 cubic feet—70 feet wide, 6 feet
deep and 1^0 feet long. (Additional depth is required for
storage of sediment). The operator must decide whether
clear water is necessary or if cloudy water is acceptable.
If land is available, three hours of pond storage would
reduce coagulant requirements.
At this point it must be decided how the land will be
used. If this example is for an operation where land
can be rehabilitated, there would be a primary pond 70
feet by 6 feet by 1^0 feet. (The contour of the land would
determine the actual width and depth). The chemical would
52
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ADD COAGULANT
PRIMARY
POND
BEING
USED
PRIMARY
POND
DRYING
PUMPING
POND
PLANT RETURN
FIGURE N0.26 PLANT LAYOUT
53
-------
5000 667
4500
4000
3500
3000
2500
to
3
< 2000
e
1500
N
o
0.
1000
500
600
533
467
400
333
267
200
133
3 FT/ MIN 2 FT/MIN
ALSO
CHE :K FlU. 28
I FT/ MIN
.5 FT/ MIN
50 100 ISO 200 250 SOO 350 400 450 500 550
POND CROSS SECTION « WIDTH X DEPTH
(ADD FOR DESIRED SEDIMENT DEPTH )
DEVELOPED FROM* VELOCITY
VOL. OF FLOW
AREA OF CROSS SECTION
FIGURE N0.27 CROSS SECTION - COAGULANT POND
-------
5000
30 MIN. I HR
2HR
3 HR
POND VOLUME - WIDTH X DEPTH X LENGTH
( ADD FOR DESIRED SEDIMENT DEPTH )
POND ASSUMED 50% EFFICIENT
DEVELOPED FROM ' HOLDING TIME =
4 HR
5 HR
6 HR
8 HR
12 HR
HR.
FIGURE NO.28 COAGULANT POND VOLUME
55
-------
"be added between the primary and secondary ponds. The
secondary pond must also "be 70 feet by 6 feet "by 1^0 feet
to allow solids to settle. The pumping pond needs only to
"be large enough to have surge storage of water, but often
it is less expensive to make another 70 feet by 6 feet by
lUo feet pond, since it will be the next secondary pond.
More frequently the ponds will be permanent and no land
rehabilitation is possible. (See Figure 26). A pond
70 feet by 6 feet by 1^0 feet would be used with some
depth added, perhaps four feet, for sediment. The water
in the pumping pond would go either back to the plant or
into a waterway. If it goes into the waterway, more
coagulant may be required to clear the water sufficiently.
If the pond is to be permanent, refer to section on
settling ponds for pond build-up rates. This will
determine how often the ponds must be cleaned so the ponds
can be sized more wisely.
-------
Most plants discharge the water at one location
Coagulants can easily be added and given good
mixing.
FIGURE 29 COAGULANT MIX POINT
57
-------
Although this system is too small, it can be
very effective with the use of coagulants and
frequent cleaning. Primary pond, secondary
pond and pumping pond. Water is recycled.
FIGURE 30 COAGULANT BASIN
-------
SECTION VIII
READY-MIXED CONCRETE WASTE WATER DISPOSITION
The ready-mixed concrete plant uses water primarily in the
batching of the concrete and for washing out and cleaning
the central mixer and/or mixing trucks.
The concrete "batch consists of a mixture of specific
proportions of sand, gravel, cement and water. These are
weighed or metered directly into the mixer truck or into
a central mixer which pre-mixes the material before dis-
charging into the trucks. Chemical additives may be
included in this mixture to increase the workability of
the concrete, to aid in the setting, to protect it from
frost or to color the concrete.
The general practice is to order slightly more concrete
than estimated to do the job to prevent running short. In
some cases the overage is dumped on the job site. In moct
cases, however, it returns to the plant in the truck to be
either incorporated in the following order or flushed out
as waste material. Disposition depends on the amount left
in the truck, the length of time since batching, the
consistency of the following order, and other factors. Most
trucks are washed out and cleaned only at the close of the
day's run or when discharging the waste material. The
amount of waste varies, but has been estimated at oOO
pounds.
The amount of water used in washing out and cleaning the
trucks varies from 50 gallons per truck to several hundred
gallons per truck, depending on the housekeeping practices
of the individual companies. Water discharged from the
washing operation contains sand and gravel and cement
slurry and contains a pH rating of between 11.0 and 12.0
on the average. Clarification of this waste water consists
primarily of lowering the pH factor and settling of the
sand, gravel and cement particles. The pH factor for
water being discharged into waterways is usually required
to fall below the 11.0 to 12.0 average. Lime causing the
high pH does actually act as a coagulant clearing the
water.
Of those plants in the ready-mixed concrete industry which
answered questionnaires, only a very small percentage had
installed clarification systems. As in the aggregate
industry, most of the plants use self-contained holding
or filtration ponds on their own sites into which they
discharge their waste water and material. The build-up
of this waste material is used either to fill the pond
59
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or pit or is periodically removed and hauled away as
landfill material.
Water clarification generally consists of first removing
the sand and gravel from the wash water and then removing
the suspended fines and cement particles. The wash water
also has a pH factor of around 10.0 to 12.0 and requires
an acid treatment to neutralize it. Chemicals may also ,
have to "be used to aid in settling out the cement particles.
Those companies having clarification systems use several
varying methods and arrangements. The general arrange-
ment consists of a truck washing facility, a primary "basin
or pad to settle out the coarse sand and gravel and
secondary basins or ponds to settle out the fines. Many
of them also recycle all of the wash water.
Recycled water may be used to wash out the mixer barrel,
but when used for washing the exterior may leave a white
film which may be undesirable. A supply line of clean
water may be installed in addition to the recycled line
for the final rinse to eliminate the film.
The truck washing facility is dependent upon the house-
keeping practice of the company, the amount of water
used per truck, the number of trucks, the arrangement of
the primary basin and many other factors. Trucks
generally discharge their waste load and water in one of
the following arrangements: (l) The truck discharges
onto a waste pile where the water runs off or drains
into the primary pond leaving the bulk of the coarse
material on the waste pile. The truck in this case receives
its water for rinsing from a separate source on the site;
(2) The truck may back up to the primary basin, fill
from a water source at that point and dump directly into
the primary basin; or (3) The truck may back into one of
several stalls located along a sloped paved apron which
extends the entire length or width of the primary basin;
after washing from water lines at each stall, the truck
may dump directly into the primary basin or onto a sloping
ramp which drains into the primary basin.
In some plants the trucks discharge their waste into a,
manufactured classifier or recovery unit with the over-
flow water running into the primary basin.
Primary basins seem to be generally of three styles. One
type has a bottom which starts at the level of the washing
pad and slopes away from the pad at about a 1:12 slope to
a depth of around four to five feet. The wall at the
deep end is slightly lower than the side walls and serves
60
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as a weir. The sloping bottom aids in retaining the solids
as they settle out and also enables clean-out with a front
end loader.
One other type of primary basin is constructed with a
flat bottom and a depth of five to ten feet or more. Some
use a poured slab for the bottom while others use a gravel
bottom. One side or part of a side is lower and serves as
a weir. In some cases where the bottom is omitted, the
basin also is used as a seepage pit.
The primary basin can also be in the form of a settling
pond or pit with the water flowing over a weir or channel
into the secondary basin or pond.
The main purpose of the primary basin is to settle out the
bulk of the waste material, which is the gravel and sand.
By so doing, the 'clean-out is confined primarily to this
basin and the treatment of the water in the secondary
basin becomes more efficient when coagulants are to be
used.
The secondary basin is used to settle out the super-fine
and cement particles. Again styles vary from a large
settling pond to a single basin holding a one day's
supply of wash water. The minimum basin seems to be one
which will hold all the wash water for a maximum day's
use. The water remains in the basin overnight and is
pumped from the top of the surface downward in the morning
until it starts to become cloudy. The water in this case
is generally pumped to a storage tank or basin and recycled
as wash water- The quality of this water in most cases
will not meet the requirements necessary for discharging
into a waterway.
Some plants use two secondary basins. Water from the
primary basin enters one or the other of the two basins on
alternate days. This arrangement allows the water to
rest a full day and night in each tank before it is pumped
out. Clarification of the water is greatly improved by
this arrangement. However, due to the fineness of the
cement particles and the high pH factor or alkaline content
of the water, chemical treatment is generally required
before the water will meet the standards required for
discharging into a stream or waterway.
Because of the difficulty in bringing the quality of the
discharged water within the required limits, most companies
which have been discharging waste water into a stream or
waterway are now discharging the water from the secondary
61
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"basin into a holding basin and recycling the water "back
as wash water, The secondary basins may be constructed
below ground level in the form of a filtration basin to
allow a percentage of the water to seep into the ground
and to prevent an accumulation of waste water. Fresh
water is used to augment the water from the basin.
When coagulants are used, it appears that they work most
economically and efficiently if they are introduced
into the flow of water from the primary to the secondary
basin. The chemicals are prepared in a mixing tank and are
metered into the flow of the waste water. Thorough mixing
of the chemical additive with the waste water is of
greatest importance in order to bring the chemical in
contact with the greatest number of suspended particles.
The designing of a clarification system will require the
consideration and analysis of all of the many variables.
The first consideration probably would be the feasibility
of eliminating the dischar/ge of waste water from the plant
site by installing a closed loop system. By recycling
all the water the problem would be isolated or restricted
to the plant area. Or perhaps by partial recycling, the
decreased amount of discharged waste water could be
treated to meet the required standards. Sizes and
arrangement of basins are dependent upon the amount of
water used, amount of ground available and the extent of
clarification required. The use and amount of chemicals
also is dependent on similar factors. Each plant needs
an independant study and analysis of these factors
to determine its own solution to the problem.
62
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SECTION IX
READY-MIX FILTER PONDS
One of the simplest clarification systems is a filter
"bed. The filter most often would be rock. (3/V to
6")
Figure 31 shows a rock filter that has worked very well.
This water clarification system was designed for four
wash stalls. The daily water usage is 20,000 gallons.
The trucks dump wash water and waste materials into a
ten foot wide basin. This basin is sloped so a front end
loader can get in to remove the material. Enough water
must be used to dilute the waste concrete that is dumped
into this basin so the loader can pick it up. This coarse
material basin needs to be cleaned about every two weeks.
The cleanout is done after a weekend so the water has had
time to settle out. A weir must be so designed as to
allow slow drainage of the surface water as the basin be-
comes full. This will require some effort on the part of
the operator to fill the entire length of the basin
uniformly. The loader can remove the aggregate without
running in water, which would damage brakes or bearings.
The filter pond is 60 feet by 60 feet by 16 feet,
excavated out of a natural gravel deposit. This gravel
provides an effective filter. Because cement does seal
the walls and bottom, this seal must be broken about
twice a year by excavating out the sediment and sealed
gravel.
The pumping pond is kO feet by UO feet by 20 feet and is
also in a gravel deposit. The water in the pond is clear
and suitable for washing both the drum and the outside
of the trucks.
The volume of wash water becomes important in the design of
this system. If too little water is used, the coarse
material will still retain cement and set up. This will
create a problem in cleanout. Using too much water will
increase the flow rate in the filter pond. Cement part-
icles will flow across the pond and will quickly seal the
wall next to the pumping pond. Settlement rates should
be checked in order to size the filter pond. Table 3
shows the settling rates of sand and cement.
Example, Figure 31.
To check this plant for correct size, it is assumed that
the .0001 inch and larger cement particles must settle out
63
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WASH WATER LINE
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40'
ELEVATION
-------
ahead of the rock filter and that the water volume is
20,000 gallons or 2,670 cubic feet/day.
Surge storage is dependent upon water table, surface
water, depth of pumping pond, etc. This system should
not be used where the water table is close to the surface.
The coarse aggregate basin has no surge storage because
it will be full of aggregate at times and should be
designed to allow the water to drain out of this basin.
In order to achieve this the water level in the filter
pond must not be higher than the bottom of the coarse
aggregate basin, except during the washout operation.
This allows a surge storage of 60' x 60' x k' = 1U,UOO cubic
feet. This is much more than the one day of surge
storage required.
Water volume
Horizontal velocity = Cross sectional area
= 2,670 cu ft . 1 day . 1 hr
12' x 60 ' . day . 2h hrs . 60 min
= .00257 ft/min
The horizontal velocity is well below the allowed .OU
feet/minute allowed on Table 3.
Vertical settling rate from Table 3 is .OOlU8 feet/minute.
Pond volume = 60' x 60' x 12' = U3,200 cubic feet.
Retention time = ' c^. = 16.2 days.
2,670 cu ft/day J
Time required for settling = - f „
„ ,
.001U8 ft/min
= 8,100 minutes or 5.6 days.
These ponds are usually only about 50 per cent efficient
due to the short circuiting of water, and also because of
the filter rock allowing water to filter out before it has
had time to settle.
Actual time required for settling = 5.6 days/50^ = 11.2 days
The pond is slightly oversized, but this is not a loss
in that this increases the pond life before sealing and
allows for some sediment build-up.
This cla~rif ication system could also be used liext to a
waterway with the water filtering into the waterway and
eliminating the pumping pond. However, some acid should
be added to decrease the pH factor.
65
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TABLE 3
SEDIMENTATION RATES
Diameter of
Particle
(Inches )
.01
.001
.0005
.0001
Description
Specific
Gravity
Fine Sand
Cement
Cement
Cement
2.65
3.15
3.15
3-15
Settling
Velocity
Ft/Min
11.U
.1U8
.0372
.001U8
Allowable
Maximum
Hori zontal
Velocity
Ft/Min
h.Q
.h
.2
.oU
Note: Actual tests indicate that cement settles somewhat
faster than indicated above until it is about five
d ay s old.
From National Ready-Mixed Concrete Association
Publication No. 116.
66
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Wash rack on left, primary cleanout trough at
center, and 60' x 60' x l6' settling pond at
right .
FIGURE 32 READY-MIX FILTER POND
67
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Wash rack in foreground, primary cleanout trough,
60' x 60' x l6' pond and recycle pumping pond
beyond fence.
FIGURE 33 READY-MIX FILTER POND ARRANGEMENT
68
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Recycle pumping pond behind camera, 60' x 60' x
l6' pond in foreground, primary cleanout trough
and wash rack in background.
FIGURE 3U READY-MIX FILTER POND ARRANGEMENT
69
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SECTION X
READY-MIX SETTLING BASINS
Much has "been done to develop workable settling basins
for ready-mix plants. The National Ready-Mixed Concrete
Association has surveyed some plants and printed the results,
Through this study additional plants have "been surveyed.
This research has pointed out that the basins are quite
similar, but each system seems to have some good and some
weak points. For this reason, the systems will not be
described exactly as they were put in, but rather they will
be grouped together as to the better ideas and an attempt
will be made to limit the weak points.
Example, Figure 35 •
The cost of operating the following described closed system
is about $50.00 per day. This plant operates with a very
small system and uses very little water--70 gallons per
day are used for drum washing and 20 gallons per day are
used for outside rinsing for each truck. A fleet of 35
trucks uses approximately 3,000 gallons of wash water per
day. Figure 35 shows arrangement of the water clarification
system. An aggregate reclaiming unit and a settling basin
are used to process mixer wash water and unused concrete.
The coarse aggregate tends to remain on the upper portion
of the slab while the cement, fine aggregate and water flow
toward the lower end where the fine solids partially settle
out. Cement-laden water flows around the end of the wall
at the lower end of the slab into settling basin (Bl),
which is ten feet by ten feet by four feet deep. Cement
settles in this basin leaving partially clarified water
to flow from the basin as more water enters. The clarified
water flows to a second basin (B2) and is allowed
additional settling time. Water then flows to (B3) and
is stored for reuse as wash water to be pumped out as
needed. \
Unused concrete in amounts over one-half cubic yard is
loaded into a reclaiming unit (C) which washes out and
separates the coarse and fine aggregate. The coarse
aggregate is collected in a dump truck and returned to
stock for reuse. The fine aggregate from the reclaimer
is dumped onto the inclined slab to drain; and the cement
and water flow to the settling basin. All the material
collected on the inclined slab is picked up each morning
with a front end loader and is either processed through
the reclaimer or hauled to the dump.
Also each morning, the clear water on top of the second
basin is pumped to the third basin. The sludge from the
71
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first and second "basins is pumped either into a tank truck
and hauled immediately to landfill or discharged to allow
drying just beyond the tank. Use of the tank truck
eliminates the necessity of drying this material before
hauling it away. In this case, one tank truck load per
day is sufficient to clean the basin.
The washing time is four hours per day, so the 3,000 gallons/
day flow is at the rate of 12.5 gallons per minute or 1.6?
cubic feet per minute.
_ Volume of water _
Horizontal velocity = Effective cross section of Bl
= 1.67 cu ft/min _
10' x U-
Table 3, ready-mix filter pond section shows .0001 inch
material will settle at . Ok feet per minute, so horizontal
velocity is acceptable.
Basin length = Horizontal velocity x depth
vertical velocity
Basins Bl and B2 act as settling ponds while B3 is a holding
basin. The combined length of basins Bl and B2 is 16 feet.
Sixteen feet is greater than the required 11.1* feet, so the
basins are adequate. Basin B3 must be large enough to hold
the surge which is a minimum of one day's water use. Most
plants use much more water per truck so they would require
much larger basins (Bl, B2 and B3 ) .
Example, Figure 36.
Many plants fill the truck drums full of water as a method
of cleaning. This system requires about 1,300 gallons to
fill an eight yard truck. Washing the outside of the
truck requires another UOO gallons of water. In some plants
these trucks will be washed out as often as twice a day.
A 30 truck fleet using water at this rate will use 78,000
gallons for drum washing and 2U,000 gallons for washing the
outside of the trucks per day. For this type of operation
using recycled water for drum washing and fresh water for
the outside, might be the best answer. For an example,
Figure 36 shows this type of plant arrangement with an eight
truck wash rack. Using the above mentioned washing
procedure and 30 trucks, the water volume per day is
78,000 + 2i*,000 gallons or 102,000 gallons. Assuming four
hours for washing time, the flow rate becomes k2k gallons
73
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FRESH WATER LINE
RECYCLED WATER
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per minute or 57 cubic feet per minute. The "basin is 120
feet vide, 16 feet long and 0 to 8 feet deep.
Horizontal velocity = - Volume of water/min -
in primary pond Effective cross section of basin
_ , , . , . _ Flov distance 16' _ , 3i. • _
Retention time = ^ - : - r - . ^n - -, — : — = —r-^ - 134 mm
Horiz rate of flow/mm .12
Table 3, Sedimentation Rates, shows that with a maximum
horizontal velocity of .12 feet per minute, cement part-
icles with a diameter of about .0003 or larger will settle
vertically at about .OlU feet per minute.
With a retention time of 13^- minutes, the particles larger
than .0003 inches in diameter will settle a vertical
distance of about two feet in the length of the pond.
Recycled and overflow water should contain suspended
particles smaller than .0003 inches in diameter. Due to
the abrasive action of the suspended particles a slurry
pump should be used to recycle the water. Should the
operator want to recycle water containing larger sized
particles, the size of the basin could be decreased.
From the total volume of 102,000 gallons per day, 78,000
gallons are recycled. The remaining 2^,000 gallons are
overflow and must be treated before the water can be
discharged from the plant. This contains the suspended
particles under .0003 inches in diameter and also has a
high pH factor. Chemicals must be added to aid in the
settling and to neutralize the alkaline condition. A
secondary basin must be used. Constructing the basin to
contain a full day's capacity would allow the treated
overflow water to be held overnight to clarify.
To contain the volume of 2U,000 gallons or 3,200 cubic
feet, the basin size could be 2k feet by 2k feet by 6
feet deep. Figure kl gives approximate acid required to
neutralize the water.
This water is now clear enough for discharging into the
waterways, or possibly this water could be used for mix
water, making it a closed system.
Example, Figure 37-
Some ready-rmixed concrete producers reuse clarified water
from their settling basins to conserve the limited water
supply- Wash water and unused concrete diluted with extra
75
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water are discharged at the top of a 100 feet square
inclined concrete slab which is divided into six "bays by
low concrete walls. (Figure 37) Openings in the walls
are staggered so that the wash water drains slowly toward
the lower end, depositing most of the solids on the way.
Gravel, graded No. h to one inch, is piled in the wall
openings and around the basin at the bottom of the slope
to filter out the fine solids. Most of the solid material
settles in the first two bays. It is pushed from the
slab with a front end loader and piled alongside to dry-
This material is hauled to a dump each week in dump trucks.
There is a settling basin, twelve feet by five feet by five
feet deep at the lower end of the slab where most of the
cement remaining in the water settles. The basin has valves
at three elevations so that clarified water may be pumped
from the top portion of the basin or sediment from the
bottom. The clarified water is reused in the plant as
mixing water.
Assume this plant to have 25 trucks using 500 gallons per
truck. Total water use per day = 12,500 gallons or
1,670 cubic feet/day. If the basin can hold in excess of
one day's water use, it will allow ample time for settling.
Basin volume = 100' x 1001 x 1 = 25,000.
Basin is large enough.
Example, Figure 38.
Figure 38 shows a smaller ready-mix water clarifier using
straw filter. This arrangement would be most suitable
for the operator willing to change the bales of straw more
often in order to reduce the original cost of installation
and reduce the amount of land used.
The first basin is designed to remove the coarse aggregate
just as was done with the rock filter design. The second
basin provides retention time for settling solids before
the water passes the straw filter-
In order to reduce the pond size, the pond should be
designed to settle .0005 inch cement particles before
passing the straw filter. The water volume is 8,000 gallons
or 1,070 cubic feet per day for a two stall wash rack with
a six truck fleet.
The surge storage = area x height of straw filter
= 30 x 20 x 2 = 1,200 cubic feet.
There is over one day's storage, so surge capacity is
77
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§2
3
O.
DRYING BED
+
STRAW BALES
SETTLING BASIN
COARSE AGGEGATE BASIN
_ 18' PER TRUCK
FIGURE N0.38 PLANT LAYOUT
78
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large enough. Washing to be spread over two hours each
day.
Horizontal velocity =
Volume of water
Effective cross section of basin
1,070 cu ft . Day . Hr
30
Day
2 hr . 60 min
Horizontal velocity is less than the allowable .2 feet
per minute shown in section on ready-mix filter ponds,
Table 3. The pumping pond must have a minimum of one
day's surge capacity.
The sediment can be drained off daily.
Example, Figure 39-
Here are a series of settling basins utilized in processing
the waste materials to obtain fairly clear water which is
discharged into a sewer- There is space for ten truck
mixers at the wash rack (Figure 39)- Wash water is
discharged onto an inclined slab (A), and most of the
coarser material accumulates there. The water and remaining
solids flow into the first settling basin (fi) through
two additional basins (C and D).
Since most of the solids are deposited on the inclined
slab (A), this area is cleaned weekly with a front end
loader and the material dumped on another slab (E) for
partial drying before being removed in dump trucks for
use as fill. The other basins (B, C and D), containing
fine sediment, are cleaned monthly using a front end loader
assisted by a portable pump. Screens (S) are located at
several points in the outfall to catch floating light-
weight aggregate particles. About 120 cubic yards of
material are hauled away weekly.
too high a flow rate, so
This system could easily have
it should be checked.
Assume a truck fleet of 25, each usin
day or 1,670 cubic feet/day. Wash ti
it amounts to 1^ cubic feet/minute.
using 500
time is
day
it amounts
Basin cross section = 30 x 5 + 0 = 75 sq. ft.
2
gallons per
two hours, so
Horizontal velocity = lk cu ft/min = .186 ft/min.
75 sq ft
79
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1 8 '
B
B AS!H
SOLIDS
DRYING
AREA
SECTION
FIGURE N0.39 PLANT LAYOUT
80
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Particles as large as .0005 inch would not settle and
in most cases would not "be allowed in a sewer system.
where
wash
Example, Figure bO .
Probably the most frequently used system is one whe
the waste ready-mix is dumped in a low area and the
water is allowed to run off into a nearby waterway.
Frequently this system is not adequate, but with some
modification it can be a very desirable one. The main
advantages are: low initial cost and land rehabilitation.
Figure hO shows a typical plant layout. The primary pond
should have one day's water storage plus the necessary
land rehabilitation capacity. This means the primary
pond should be quite large to avoid too rapid filling. The
rate of buildup will depend on the amount of waste concrete
discharged. The primary pond must have a minimum of one
day's storage before water is reused. If the water is to
be treated and discharged into waterways the secondary
pond should also have one day's holding capacity to allow
proper settling time.
The valves on the outflow pipes would be regulated to allow
a constant and uniform flow for a full 2h hours. The most
important design consideration is to provide enough cross
sectional area in the ponds to establish a horizontal rate
of flow Sufficiently slow to allow the fines to settle.
Assuming a ready-mix plant has 15 trucks using 1|0,000
gallons of water per day or 5,350 cubic feet per day.
Maximum horizontal velocity from Table 3, ready-mix filter
pond section is .OU feet per minute.
Water volume
Required cross section = Horizontal velocity
_ 5.350 cu ft/day . 1 day . 1 hr
.OV ft/min . 2k hrs . 60 min
! = 93 sq ft or U' x 25 '.
A pond k feet by 25 feet in cross section is adequate, but
because it would fill with sediment very quickly and because
the pond won't be 100$ efficient the actual size should be
much larger. This size would be determined by the land
conditions, but for this example use k feet by 80 feet by
160 feet.
There must be more than a day's surge from top of out-
let pipe to top of berm.
81
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Heiaht = 3,350 cu ft/day . 1 day surge
80' x 160'
Use 1 foot.
82
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POND
ADO CHEMICALS IF WATER
IS DISCHARGED TO WATERWAY
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pH FACTOR
11.8
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NOTE! A3 THE pH FACTOR GETS LOWER VERY LITTLE
ACID IS REQUIRED SO IT IS EASY TO OVERDOSE AND
CAUSE THE WATER TO BECOME ACID.
DEVELOPED FROM FIELD AND LAB. TESTS
FIGURE N0.4I NEUTRALIZING READY MIX WATER
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SECTION XI
READY-MIX WATER CLARIFICATION EQUIPMENT
Recently the manufacturers serving the ready-mix concrete
industry have developed wash out systems. Most of these
units are quite new and many need certain improvements.
The most popular type of clarifier is the drag chain type,
see Figure U2. The truck drum is washed and dumped into
the wash tank. The larger aggregates settle and are
carried away by the first drag chain and stacked at the
end of the washer. The finer aggregate and sand settle
more slowly, thus carrying them to the second drag chain.
The water is then recycled into the next ready-mix drum.
This water is not clear enough to discharge into rivers,
but will work well as a wash water for the insides of the
mixer drums. The outside of the truck must be washed down
with fresh water and some of this water can be collected
and used for the make-up water for the washer. In most
operations there will be an excess of water to clarify
and discharge or use as mix water-
Manufacturers can also furnish aggregate screws which will
separate the coarse aggregate and most of the sand, see
Figure ^3. The fine sand and cement particles will remain
in the water and can be recirculated into the ready-mix
truck drums or further clarified by weirs, settling basins,
coagulants or filters. This system might be used by some
operators because they may already have aggregate screws
on hand. A further refinement to the system is to discharge
the material from the screw onto a screen, see Figure hk.
This allows separation of waste aggregates so they can be
returned to the proper stockpile for reuse. If desired,
the ready-mix truck can discharge directly onto the screen
and the aggregate is separated, see Figure ^5- The sand
and water feed into a sand screw where the sand and water
are separated. The advantage of this arrangement is if the
plant has a sand screw on hand, but lacks an aggregate
screw, the existing equipment can be used. This system also
provides a larger capacity because only the sand goes
through the sand screw. One disadvantage is that spray
.bars will be needed on the screen requiring additional
water to be clarified. All these arrangements using screws
will require a surge tank with capacity for as many
trucks as will be washed at once. For example, if two
trucks were washed at a time, each using a maximum of 500
gallons, the tank must hold at least 1,000 gallons. These
washer units all salvage the aggregate for reuse. In the
case of the screen, the material is separated by size for
-------
II'-O
16'- 0
in
10
FIGURE N0.42 DRAG CHAIN WASHER
86
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VOLUME FOR NO. TRUCKS
WASHED AT SAME TIME
SLOPED FOR CLEAN OUT
RECLAIMED UNSIZED AGGREGATE
-------
future use in the mix. The drag chain system, on the
other hand, does not accurately grade the aggregate.
None of the units investigated clean the water sufficiently
for discharge into the waterways. The content of suspended
solids is too high as is the pH factor- Therefore, these
units must be used as closed systems.
The washing of the outside of the trucks must be a separate
system. The outsides of trucks will need less washing as
time goes on, due to increased demands for dust control
at plant sites. With less dust in the air, trucks will
require less frequent washing.
88
-------
pi
z
o
oo
vo
CO
o
3}
m
m
CO
o
30
m
m
WASHING SCREW
RECLAIMED 8 SIZED
AGGREGATE
-------
c
m
z
p
01
%
I
z
o
o
7)
m
m
SAND SCREW
RECLAIMED a SIZED
AGGREGATE
CA
O
m
-------
SECTION XII
READY-MIX WASH WATER USED FOR MIX WATER
Although few plants are using wash water for mix water,
this system should "be considered because of possible
economies and the fact that this system would eliminate
all discharge into the waterways.
The American Society for Testing and Materials C9U-6?
makes the following definition of acceptable mixing
water:
3.1.3 Water—The mixing water shall be clear and
apparently clean. If it contains quantities of
substances which discolor it or make it smell or
taste unusual pr objectionable or cause sus-
picion, it shall not be used unless service records
of concrete made with it or other information
indicates that it is not injurious to the quality
of the concrete.
Note 3--Information on the affects of questionable
mixing water may be secured by testing mortar made
with the water in question in comparison with
mortar mixed with potable water of known accept-
able- quality in accordance with ASTM Method C879
Test for Effect of Organic Impurities in Fine
Aggregate on Strength of Mortar.
Wash water from ready-mix operations, when allowed to
stand for short periods af time -will become clear and
apparently clean. There will be some cause for suspicion
and if so, tests or service records could be used which
should satisfy the user-
At least one plant has agitated the wash water to keep the
cement suspended and has reported good concrete quality;
however, clogged plumbing became a problem. Using slurries
in such concentration to cause clogging would also raise
a question as to the acceptance of the water as adequate
mixing water- At least at the present, it appears more
desirable to allow the aggregate, sand and cement to settle
and be hauled away. The water would still be unacceptable
for discharging into waterways, but should be very acceptable
wash water. .Extensive testing should^be done so operators
would be able to furnish this evidence in gaining approval
to use their wash water.
91
-------
SECTION XIII
COST OF CLARIFICATION
The cost of systems for clarifying water in the aggregate
and ready-mix industries varies widely. The plant owners
seem unable to establish realistic prices on their systems.
Some of the factors that must be considered in arriving at
the cost are:
1. Value of land used.
2. Cost of land development.
3. Cost of equipment.
k. Cost of operation.
5- Cost of maintenance.
6. Effect on plant production.
7- Change in water and sewer charges.
8. Cost of reporting to water control boards.
Many ready-mix plants located on expensive property in
or near cities have very limited space. To use any of this
land for a clarification system will make the production
facilities less efficient. For this type of operation
the only systems applicable and now developed are the
manufactured units similar to the drag chain washer. A
four-truck wash system of this kind, completely installed
with paved area, water piping, electrical, concrete slab,
pumps, etc., costs about $35,000.00.
Because most plants on high priced property are large
operations, one unit would not be adequate. A 30 truck
fleet should have two units in order to have a smooth
operation. The land required for equipment and truck
wash area would be 110 feet by 200 feet with allowance for
turning on one side, and a pond area for treating the
excess water before discharging into the stream. The
cost of operation includes repairs, power consumption,
removal of waste material by front end loader and trucks.
The operating costs could vary from $10.00 to $100.00
per day, depending on the ability to sell some of the
waste.
The ready-mix batch plant and component costs also can
vary widely from $50,000.00 to $250,000.00. The minimum
property size would be about 60,000 square feet. Property
value could vary from $30,000.00 per acre to $100,000.00
per acre. There can be a wide variation in the cost per
gallon of water to operate the plant inasmuch as the
volume of water to be clarified ranges from 150 to U,000
gallons of wash water per truck. It is apparent that the
93
-------
costs vary so widely that any averaging would only result
in creating false impressions. The cost of clarification
for some operators is a very small per cent of the total
cost of doing business, while for others the cost is very
high.
The aggregate plant clarification costs vary even more
than the ready-mix operation costs. Some reasons for
additional variations are:
Solids to "be settled vary widely in specific gravity,
negative charge and size.
Land availability varies more widely--some plants are
rehabilitating land with these solids and the clarification
can be profitable while others have little land and,must
pay to haul and dump the waste.
The natural deposits vary—some plants need no washing
at all while others use several million gallons of water
per day.
While an attempt was made in this survey to determine some
average cost of clarification, no representative figures
could be established. It appears that the price of the
finished product will be increased substantially to include
the cost of water clarification.
-------
SECTION XIV
ACKNOWLEDGMENTS
Much support vas given "by the National Sand and Gravel
Association, National Ready-Mixed Concrete Association
and many of the state concrete and aggregate producers'
associations. Many individual plant owners and operators
gave valuable assistance. Chemical companies and manu-
facturers making clarification equipment were of help.
The financial support and technical and administrative
guidance provided "by the Environmental Protection Agency,
Region X through the Project Officer, Mr. Edward G. Shdo
was very helpful in making the project a success.
95
-------
SECTION XV
REFERENCE MATERIAL
1. McClellon, Grant S., Protecting Our Environment.
2. Engineering Management of Water Quality (1968).
3. Stewart, George R., Not So Rich As You Think.
^. Water Supply Engineering, sixth edition (1962).
5. Eckenfelder, W. Wesley, Industrial Water Pollution.
6. Besselievre. Edmund B., Industrial Waste Treatment.
7- Rock Products , December, 1970.
8. Civil Engineering - ASCE, October, 1971.
9. Civil Engineering - ASCE, September, 1971-
10. National Ready-Mixed Concrete, Letter No. lU68,
June 1, 1971.
11. National Ready-Mixed Concrete, Letter No. 283,
June 9, 1971.
12. National Ready-Mixed Concrete, Paper by P. H. Smith,
p_U-e, November, 1967.
13. National Ready-Mixed Concrete, Letter by Stanley Ernst,
F-it-E, May 27, 1970.
lU. National Ready-Mixed Concrete, Technical Letter 276,
May 6, 1970.
I
15. National Ready-Mixed Concrete, Production and Value
Bulletin, 6.2M-12-69 (1968).
16. National Ready-Mixed Concrete, Production and Value
Bulletin, 6.2M-12-70 (1969).
17. National Ready-Mixed Concrete, Environmental Question-
naire, p-U-e, October 30, 1970.
18. National Ready-Mixed Concrete, Vacuum Filtration by
Fred Groom, February 2, 1972.
97
-------
REFERENCE MATERIAL CONT'D
19- National Ready-Mixed Concrete, Disposal of Truck
Mixer Wash Water and Unused Concrete, Bulletin 116,
December,196U.
20. National Ready-Mixed Concrete, Engineering Problems
of Sand and Gravel Production, Bulletin 88, May, 19&2.
21. National Ready-Mixed Concrete, Bulletin F-l*-e(2),
May 19, 1971-
22. National Ready-Mixed Concrete, Paper "by Raymond F.
Powell.
23- National Sand and Gravel Assn., Water Quality and the
Sand and Gravel Industry "by Joel Beeghly, November
18, 1971.
2U. National Sand and Gravel Assn., Closed Circuit
Treatment of Sand and Gravel "by Charles F. Myer, Jr. ,
February,1966.
25- National Sand and Gravel Assn., Pollution Control
Through Waste Fine Recovery by Charles A. Smith, Jr.,
Paper 110, March, 1971.
26. National Sand and Gravel Assn., The Contribution of
Aggregate Dredging to Sediment Pollution in the
Potomac River by David A. Parcher, January 27, 19&9.
27- American Institute of Mining, Metallurgical and Petroleum
Engineers, Inc., Environmental Factors in the Aggregate
Industry, EQC 68 (1971).
28. U. S. Dept. of the Interior—Federal Water Pollution
Control adm., Projects of the Industrial Pollution
Control Branch, DAS7-38, January, 1970.
29. United States Water Resources Council, The Nation's
Water Resources Summary Report (1968).
30. United States Dept. of Commerce, 1967 Census of
Manufacturers (1967).
31. Environmental Protection Agency, Flocculation and
Clarification of Mineral Suspensions., lUOlO DEB 05
(1971).
98
-------
REFERENCE MATERIAL CONT'D
32. Environmental Protection Agency, Process Design
Manual for Suspended Solids Removal, Program No.
17030 GNO, October, 1971.
33. Bureau of Mines, Review of Mining Technology,
Yearbook Reprint (1965).
3^. Bureau of Mines, Sand and Gravel , Yearbook Reprint
(1969).
35- Bureau of Mines, Stone , Yearbook Reprint (1970).
36. Bureau of Mines, Stone , Yearbook Reprint (1969)
^ •
37« Bureau of Mines, Sand and Gravel, Reprint Bulletin
650 (1970).
38. Bureau of Mines, Water Use in the Mineral Industry,
8285 (1966).
39. Columbia Basin Inter-Agency Committee, Alluvial
Mining in the Pacific Northwest, February, 1961.
UO. Geological Survey Research, Paper 550-D (1966).
Ul. Department of the Army Corps of Engineers, Permits
for Work and Structure in, and for Discharge or
Deposits into Navigable Waters.
U2. Cement * Lime and Gravel, Volume Uo (1965)-
1*3. Cement, Lime and Gravel--Some Experiments with
Flocculating Agents, May,
99
-------
APPENDIX I
Available Chemicals For Coagulation
Taken From
PEOCESS DESIGN MANUAL FOE SUSPENDED SOLIDS EEMOVAL
For
Environmental Protection Agency
By
Burns and Eoe, Inc.
101
-------
AVAILABLE CHEMICALS FOR COAGULATION
Poly electrolyte
Aquafloc U09
Aquafloc Ull
Aquafloc UlU
Aquafloc Ul8
Aquaria 1*9-702
Calgon G-2256
Calgon C-2260
Calgon C-2270
Calgon C-2300
Calgon C-2325
Calgon C-2350
Calgon C-2UOO
Calgon .C-2U25
Calgon WT-2600
Calgon WT-2630
dalgon WT-2666.
(ST-260)
Calgon WT-2690
Calgon WT-2700
Calgon WT-2900
Calgon WT^-3000
Hamaco 196
Hercofloc 810
Hercofloc 812
Hercofloc 8l8
lonac NA-710
Refer
App
II
AP
AP
NP
CP
CM
CP
CP
CP
NP
AP
AP
AP
AP
CP
CP
CP
NP
AP
AP
AP
S
CP
CP
AP
AP
Bulk Density
lb/cu ft
Loose Pack Work
25
U2
U8
33
30
2U
10
10
11
10
16
23
29
27
9
10
8
16
20
22
21
30
38
3U.
53
59
UU
U3
35
16
16
19
16
28
3U
U2
39
16
18
13
29
25
31
31
ho
kl
28
U5
61
36
3k
28
25
13
13
lU
13
22
27
33
31
12
lU
10
22
21
25
2k
33
Uo
Time to
disperse Percent
Refer into a max solution
App coll. solution concentration
III hour(s) pH recommended
CNKL
CNKL
CWKL
DPKL
E S
DLKP
DLKP
DLP
BLN
BLW
BLN
ALKM
BLKW
DKLP
DKLP
DKLP
ALM
DLP
AKLW
AKLW
DLP
EKLR
EKI,R
DKLN
CNL
1-2
1-2
1-2
1-2
1-2
1/2
1/2
1/2
3/U-l
3/U-l
3/U-l
3/U-l
3/U-l
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2-1
1-2
1-2
1-2
1/2-1
U-5
U-5
7
2.U
7-9
6.U
6.7
7.3
7
7
7
7
7
U
U
U
7
7.5
7-5
7-5
6-7
6-7
6-7
8-9
5-6
l
2
2
2
1.
1.
1.
0.
0.
0.
0.
0.
1.
1.
0.
0.
0.
0.
0.
2
0.
0.
0.
1
5
5
5
5
5
25
25
25
5
5
5
5
25
25
25
5
5
5
-------
AVAILABLE CHEMICALS FOR COAGULATION CONT'D
H
O
u>
Polyelectrolyt e
Jaguar Plus
Magnifloc 530C
Magnifloc 820A
Magnifloc 835A
Magnifloc 836A
Magnifloc 837A
MagnifJ.oc 865A
Magnifloc 8?OA
Magnifloc 8T5A
Magnifloc 880A
Magnifloc 900N
Magnifloc 901N
Magnifloc 902N
Magnifloc 905N
Nalcolyte „
Nalco 633-HD
Nalco 636-HD
Nalco 635
Nalco D-2339
Nalcolyte 675
Polymer F3
Polyfloc 1100
Polyfloc 1110
Polyfloc 1120
Polyfloc 1130
Polyfloc 1150
Refer
App
II
CG
CP
AD
-AD
AD
AD
AD
AD
AD
AD
ND
ND
ND
ND
P
CP
CP
AP
AP
AP
AG
AD
AD
AD
AD
AD
Bulk Density
lt/cu ft
Loose Pack Work
31
31*
30
27
28
1*0
32
27
26
1*2
^5
38
39
35
32
31*
36
36
35
33
1*0
1*0
1*2
35
36
U2
1*0
35
1*0
68
53
50
53
50
1*0
1*0
1*2
1*2
1*8
1*5
22
35
31*
29
30
50
28
28
26
33
29
31
52
1*7
1*1
1*3
Uo
31*
35
37
37
39
36
Refer
App
III
FLPR
CLP
DKP
CKP
DLP
CLN
CLN
CLN
DKLP
DJLN
DLN
DLN
DJIS
DLN
DLN
CKL
CKN
CKL
DKP
FJR
Time to
disperse Percent
into a max solution
coll. solution concentration
hour(s) pH recommended
1-2
1-2
1/2-1
1/2-1
1/2-
1 1/2-
1/1*
1/1*
1--2
1-2
1-2
1-2
1-2
1/2-
1/1*-1
lA-1
3/1*-
1/2-
1/2-3
1-2
1-2
1-2
1-2
1-2
1/2-
1
2
1
/2
/2
1
1
A
i
8-
1*.
9
2
6-7
6-
5
1*.
7.
7.
5.
1*.
U.
1*.
1*.
5-
3
8.
7.
8.
9.
8.
7.
8.
8.
7
1
5
5
5
7
7
7
7
1
5
0
5
5
5
5
8
8
6-7
1
0.
1
0.
0.
0.
1
1
1
1
1
1
1
1
1
2
1.
0.
0.
0.
1*
0.
0.
0.
0.
1
5
1
1
5
5
25
5
25
5
5
5
5
-------
AVAILABLE CHEMICALS FOR COAGULATION CONT'D
Polyelectrolyte
Polyfloc
Purifloc
Superf loc
Tychem
1160
A-23
128
Tychem 8013
Zeta Floe
Zeta Floe
Zeta Floe
Zeta Floe
Zeta Floe
Zeta Flox
C
0
K
S
WA
WN
Refer
App
II
CD
CD
ND
ND
ND
BC
BN
BC
BC
BA
BN
Bulk
Density
Ib/cu ft
Loose
31*
1*2
28
33
1*8
52
1*8
5 1*
5 1*
5 1*
Pack
1*0
53
33
1*3
68
7!*
68
78
78
78
Work
35
1*5
29
1*0
36
5!*
59
5l*
6l
61
6l
Refer
App
III
CJN
BKP
CLN
CLN
EKR
EJR
EKR
E S
E S
E S
Time to
di sper se
into a
coll
1
1
1
1
1
. . solution
hour ( s )
1/2-1
1-2
1-2
1-2
1-2
A-l/2
A-l/2
A-l/2
A-l/2
A-l/2
PH
5-6
10
6-7
5.5-6
6
8.2
8.2
8.5
lA-1/2
Percent
max solution
concentration
recommended
1
0.
1
1.
1
1
1
1
1
1
1
5
0
-------
APPENDIX II
Chemical Characteristics
105
-------
CHEMICAL CHARACTERISTICS
A -- Anionic
As-- Slightly Anionic
B -- Bentonite Clay or Clay, natural, colloidal-like type
b -- plus Bentonite
C -- Cationic
D -- Polyacrylamide, Synthetic, High M. W., Polyelectrolyte
Polymer
E -- Polyacrylonitrile, Synthetic Polyelectrolyte
F — Sulfonated Polymer
G- — Guar Gum, Polysaccharide , Natural Polymer
H -- High M. W., Organic Polymer
J — Alkyl Guanidineamine Complex
K -- Sodium Alginate or Algin Derivative, Natural Polymer
L -- Leguminous Seed Derivative, Natural Polymer
M -- Polyamine, Synthetic, High M. W., Polyelectrolyte
Polymer
N -- Nonionic
P — Synthetic High M. W., Polyelectrolyte Polymer
R -- Polyacrylamide and Carboxylic Group
S -- Starch, derivative, Modified, etc., Natural Polymer
T -- Synthetic Polymer and Caustic Soda
U -- Sodium Carboxymethylcellulose, Natural Polymer
X -- Ethylene Oxide Polymer
Y -- Carboxyl Polymer
2 -- Biocolloid + Inorganic Coagulant + Caustic Soda
3 -- Hydrophylic Colloid + Pregelatinized Starch in Alkalai
k — Aluminum Hydroxide + Complex Organic Polymer
5 — Alumina + Polymer + Caustic Soda
6 — Polyacrylic Acid or Polyacrylate of Sodium or Ammonium
7 — Aluminum Hydrate + Caustic Soda
8 — Alkalai Concentrate + Metallic Ions
9 -- Chemically Modified Natural Polymer
106
-------
APPENDIX III
Chemical Flow
107
-------
CHEMICAL FLOW
A. Soft flakes, may hang up if packed excessively in a
confining area, otherwise free flowing. Usually will
not need aid (vibration or agitation).
B. Powdered, soft flakes, hang up if packed excessively in
a confining area, may or may not need aid according to
rate of feed, etc.
C. Soft granules, sometimes fibrous or flattish, may hang
up if packed excessively in a confining area, otherwise
free flowing. Usually will not need aid.
D. Powdered, soft granules, sometimes fibrous or flattish,
hang up if packed excessively, may or may not need aid,
according to other factors.
E. Granular, fluid powder, will arch if packed and can be
fluidized or is floodable (to very floodable.) Needs
aid and may need rotor, according to rate, etc.
F. Granules and powder, will arch and can be fluidized.
Needs aid and could need rotor, etc.
G. Cohesive powder and granules, will arch, but will not
flood. Needs aid.
H. Cake up of room relative humidity.
J. Tendency to cake (or mass) at higher relative humidity.
K. Cake at higher relative humidity.
L. Moisture absorption, may lessen flowability.
M. Practically no dust.
N. Very little dust.
P. Some dust.
R. Dusty.
S. Very dusty.
108
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
1. Report No.
2.
3. Accession No.
w
4. Title
WASTEWATER TREATMENT STUDIES IN
AGGREGATE AND CONCRETE PRODUCTION,
7. Author(s)
Monroe, R. G.
9. Organization
Smith & Monroe & Gray Engineers , Incorporated
Lake Oswego, Oregon
5. Report Date
6.
8. Per/orming Organization
Report No.
10. Project No.
15. Supplementary Notes
12. Sponsoring Organization
Oregon Concrete and Aggregate
Producers Association, Incorporated
Environmental Protection Agency report
number, EPA-R2-73-003. February 1973
11. Contract/Grant No.
12080 HBM
13. Type of Report and
Period Covered
Section 5
Research Grant-
Class I
6/30/71--3/1/72
16. Abstract
This report contains discussions of various water clarification systems
used in the aggregate and ready-mixed concrete industries. The overall
problem of waste water disposition in each type of plant is studied. An
analysis is made of the use of settling ponds, filter ponds and coagu-
lants. Recycling and use of recycled water is discussed with recom-
mendations for further study of the potential use of waste water from
ready-mix plants for concrete batch water. Since many aggregate and
ready-mix concrete plants now have effective clarification or recycling
systems the overall purpose of the study is to make these systems known
throughout the industry so proven systems can be made available to all.
The report is based on a review of systems in reported 77 plants and
firms plus data obtained from a field trip inspection of 88 plants on the
West Coast. The study contains k5 charts and photographs of clarification
systems.
17a. Descriptors
*Aggregate Settling Ponds, *Filter Ponds, *Coagulation, *Ready-Mix
Settling Basins, Manufactured Equipment, Acid Treatment, Reuse in
Mix, Water Reuse,
17b. Identifiers
Aggregate Settling Ponds, Ready-Mix Settling Basins, Coagulation
17c. COWRR Field & Group
18. Availability
19. Security Class.
(Report)
20. Security Class.'
(Page)
21. No. of
Pages
22. Price
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
US DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C 20240
Abstractor
Robert G. Monroe
'?7 llOn WASHINGTON. D. C 20240
j institution gmith & Monroe & Gray Engineers, Inc
WRSIC 102 (REV. JUNE l»71)
------- |