DRAFT
RAPID INFILTRATION LAND TREATMENT:
A RECYCLE TECHNOLOGY
U.S. ENVIRONMENTAL PROTECTION AGENCY
WATER PROGRAM OPERATIONS
MUNICIPAL CONSTRUCTION DIVISION
E
Draft Copy - Photos Not Included
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025277
ACKNOWLEDGEMENTS
The direction and review comments of the
Environmental Protection Agency Project
Officer, Richard E. Thomas, are gratefully
acknowledged.
The report was written by Ronald W. Crites,
Project Manager and Elizabeth L. Meyer of
Metcalf & Eddy/ Inc., Sacramento, California.
Charles E. Pound and Franklin L. Burton,
Vice Presidents of Metcalf & Eddy, and
George Tchobanoglous, University of California
Davis, provided guidance and review comments.
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RAPID INFILTRATION LAND TREATMENT:
A RECYCLE TECHNOLOGY
The purpose of this bulletin is to introduce the concept and
discuss the applications of rapid infiltration land
treatment. To obtain an understanding of the process, it is
helpful to consider what rapid infiltration is, why it is
important, where it is being done, how it works, how much it
costs, and what can be accomplished with rapid infiltration
as an alternative to conventional wastewater treatment
methods.
WHAT IS IT?
Rapid infiltration land treatment is the application of
wastewater to very permeable soils, such as sands or loamy
sands, and in level, enclosed, shallow, earthen basins. The
wastewater is treated as it travels through the soil.
Vegetation is not usually a part of the treatment process,
although there are some exceptions.
[Photo of Ft. Devens, showing vegetation]
Land application of wastewater is normally preceded by some
form of preliminary treatment such as primary sedimentation,
as discussed later in this bulletin. The typical mode of
operation is to apply wastewater to a basin for a few days
and then to allow the basin to dry with no additional
application of wastewater for several days to a few weeks.
Drying is needed to reaerate the soil and restore the
initial infiltration rate (rate at which wastewater moves
into the soil), and will result in better overall treatment.
Together, an application (or loading) period and a drying
period are referred to as a hydraulic loading cycle.
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[Aerial view of Hollister, California]
At some rapid infiltration sites, to maintain infiltration
rates, to keep treated water from mixing with existing
ground water, or to recover the treated water for reuse, the
treated water is pumped or drained from the soil following
infiltration. Alternatively, renovated water can be allowed
to drain naturally from the soil into a nearby lake, river,
or stream. Cross-sections of typical rapid infiltration
systems are illustrated in Figure 1. These schematics
illustrate the basic hydraulic pathway as well as the
recovery and natural drainage pathways.
The principal objective of rapid infiltration systems is to
treat applied wastewater by natural processes as it seeps
through the soil. Other objectives have included (1) ground
water recharge to maintain or supplement irrigation water
supplies; (2) ground water recharge to prevent salinity
intrusion; (3) ground water recharge to reduce land
subsidence when fluids have been extracted; and
(4) temporary, subsurface storage of treated water for
planned withdrawal and reuse.
WHY IS IT IMPORTANT?
Frequently, communities must treat wastewater to a quality
equivalent to tertiary effluent. Treatment requirements
usually call for very low concentrations of biochemical
oxygen demand (BOD) and suspended solids (SS). Treatment
requirements may also include phosphorus or nitrogen removal
or both. Conventional advanced wastewater treatment (AWT)
systems capable of meeting these requirements are expensive
to build, even more expensive to operate, and consume large
quantities of energy and other resources. Rapid
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APPLIED
•ASTE1ATER
EVAPORATION
PERCOLATION
(a) HYDRAULIC MTNIAY
FLOODING MSINS
PCRCOLATItM
VNSATVRATED ZONE)
UNDERORAINS
WELLS
(b) RECOVERY FATHIAYS
FLOODING
(c) NATIRAL DRAINAGE INTO SURFACE IATERS
Figure 1. Typical rapid infiltration cross-section
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infiltration can often provide an effluent of comparable
quality to that obtained from AWT systems, and do it for
less cost in construction, operation, and maintenance, and
with less consumption of resources.
As shown in Table 1, a well designed and operated rapid
infiltration system provides better overall treatment than
conventional secondary treatment and the listed AWT
processes. Nitrogen is the only wastewater constituent of
interest that rapid infiltration does not remove as well as
some of the other treatment processes. Even so, nitrogen
removal at rapid infiltration sites is higher than at
conventional secondary treatment plants or AWT facilities
designed for phosphorus removal.
Table 1. EXPECTED EFFLUENT QUALITY3
mg/L
System
Rapid infiltration
AWT
Phosphorus removal
Nitrogen removal
Phosphorus and nitrogen removal
Secondary treatment
BOD
5
20
15
10
30
SS
2
20
16
5
30
Total
nitrogen
10
30
3
3
30
Total
phosphorus
0.5b
2
8
1
8
a. Adapted from reference [1].
b. For a travel distance of 15 ft or more through the soil.
In addition, AWT facilities must add chemicals to achieve
phosphorus removal. These chemicals react with phosphorus
to form a precipitate that settles out as sludge. Sludge
treatment and disposal are the most expensive parts of an
AWT system. Not only can rapid infiltration remove
phosphorus without the addition of chemicals, no sludge is
produced in the process. In summary, rapid infiltration can
METCALF
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provide better phosphorus treatment without consuming
chemicals, and without producing a phosphorus-containing
sludge.
Rapid infiltration is a low cost land treatment process.
This fact can be seen in Table 2, in which the total unit
cost and typical monthly user charges of a new 1 Mgal/d
treatment plant for various types of advanced wastewater
treatment and rapid infiltration are compared. These values
include both the cost of constructing new facilities and the
cost of operating and maintaining the facilities after
construction. Construction costs are spread out over a
20 year period. For a new 10 Mgal/d facility, total unit
costs are lower for all alternatives, but the relative order
of the unit costs is the same. In other words, user charges
for a new rapid infiltration system can be considerably
lower than user charges for a new AWT facility.
Table 2. TOTAL UNIT COST OF
NEW 1 Mgal/d TREATMENT PLANT: RAPID INFILTRATION
AND AWT ALTERNATIVES
Unit cost. Typical user charge/
Treatment level $/l,000 gal $/household/month
Rapid infiltrationb 0.78 7.00
AWT
Phosphorus removal 1.20 10.80
Nitrogen removal 2.10 18.90
Phosphorus and nitrogen removal 2.30 20.70
a. Adapted from reference [1]. •
b. Includes cost of land at $4,000/acre.
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Furthermore, the Clean Water Act of 1977 offers economic
incentives for the use of innovative or alternative
technologies, including rapid infiltration. Two of the more
important incentives are:
• A 15% advantage in the cost-effectiveness
analysis. (Life cycle costs may be 15% greater
than costs for conventional alternatives and still
be considered cost effective.)
• The potential for a 10% bonus on construction
grants (i.e., 85% versus 75%).
Advantages of the rapid infiltration treatment method
compared with conventional wastewater treatment methods may
be summarized as follows:
• Lower operating costs
• Higher quality effluent
• Lower energy requirements
• Limited use of chemicals
• Reduced sludge production
• Process stability and reliability
• Economic incentives in the Construction Grants
Program
WHERE IS IT BEING DONE?
In 1978, there were about 300 municipal rapid infiltration
systems operating or under construction in the United
States. A list of selected rapid infiltration systems is
presented by Environmental Protection Agency (EPA) region in
the DIGGING DEEPER section of this bulletin. These systems
are also shown by state in Figure 2.
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Figure 2. Locations of rapid infiltration systems.
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Five representative municipal rapid infiltration systems
selected to illustrate various aspects of rapid infiltration
technology—located at Boulder, Colorado; Calumet, Michigan;
Hollister, California; Lake George, New York; and Phoenix,
Arizona—are described briefly. General features of these
systems are compared in Table 3.
Table 3. COMPARISON OF REPRESENTATIVE
RAPID INFILTRATION SYSTEMS
Location
Boulder , Colorado
Calumet, Michigan
Hollister, California
Lake George, New York
Phoenix , Arizona
Avg flow
Mgal/d
0.
1.
1.
1.
14
22
6
3
1
, Area,
acres
2.5
15
39
6.4
40
Preapplication
treatment
Trickling
Untreated
Oxidation
Trickling
Activated
filters
ponds
filters
sludge
User charge,
$/household/yr
—
About
30
About
22
30
61
The systems at Calumet, Hollister, and Lake George have all
been operating successfully for many years. Data from these
systems provide a good indication of the long-term
capabilities of rapid infiltration systems. Although the
system at Phoenix has not existed as long, much important
research has been conducted at this site to determine how to
optimize treatment and infiltration rates. Also, recovery
and reuse of the renovated water has always been strongly
emphasized at this system. The Boulder system is relatively
new and is a pilot system. Because this system collects
renovated water in fairly shallow underdrains, data from the
Boulder system reflect the level of treatment afforded with
even minimal soil travel distance. In addition, the ability
of rapid infiltration systems to operate during cold weather
has been demonstrated at Boulder, Calumet, and Lake George.
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Boulder/ Colorado
Since the fall of 1976, the City of Boulder Wastewater
Utility Department has operated a pilot rapid infiltration
system. At Boulder, raw wastewater is treated prior to
rapid infiltration by means of a standard rate trickling
filter, as indicated in Figure 3. Then, unchlorinated
secondary effluent is conveyed to three infiltration basins,
shown in Figures 3 and 4. These basins vary in size from
0.60 acre to 0.87 acre [2]. Each basin is separated by a
berm and all three basins are surrounded by an impermeable
clay-core dike. In addition, underdrains have been
installed at a depth of 8 to 10 feet. Collected water flows
by gravity to a manhole at the end of each basin, then to a
central manhole for monitoring and sampling, and then into a
wet well for pumping to Boulder Creek.
Because this is a pilot-scale operation, various site
modifications and loading cycles have been used to determine
optimum operating parameters for the Boulder site. For
example, following 6 months of operation, the top loamy
layer of soil was removed from two of the basins to increase
the infiltration rates. A ridge and furrow system was also
constructed in one of the two basins to further improve
infiltration. Following removal of the topsoil from the two
basins, loading rates three to eight times the initial rates
were successfully used. The success of this operation
indicates that sites with relatively tight surface soils can
be modified to use rapid infiltration.
Initial studies at Boulder were conducted for about 2 years
with secondary effluent. After the initial studies, primary
effluent was applied to the basins from September 1978 to
September 1979. The use of primary effluent did not cause
MBTCALF » BOOV
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MEADIORKS
FLOW
DIVERSION PRIMARY
•OX CLARIFIERS
TRICRLINO
FILTERS
SECONDARY
CLARIFIERS
CHLORINATION
eiTi
COLLECTION
SYSTEM
\
\
•RIT TO
LAND DISPOSAL
SITE
TO LAND
DISPOSAL SITE
SLUDOE
NOLDINO
TANKS
VACUUM.
FILTERS
Figure 3. Schematic of Boulder wastewater treatment plant.
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CLAY DIKE
DISTRIBUTION BOX
INLINE FLOVHETER
CLARIFIER
BASIN 1 - 0.87 acre
CLAY DIKE
Figure 4. Rapid infiltration system layout.
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any operational or aesthetic problems, even at loading rates
of 144 and 120 ft/yr in the two modified basins. In fact/
loading the basins with raw wastewater, which was done for a
short period when the secondary treatment plant had an
upset, did not cause a reduction in effluent quality. In
summary, the rapid infiltration system proved to be very
flexible and reliable.
At Boulder, the infiltration basins are filled with
wastewater twice a week. Between applications, the
wastewater infiltrates into the soil, leaving a dry surface.
After 6 weeks on this application schedule, the basins are
allowed to dry thoroughly. Before being put back into
operation, the basins are scarified. This operation breaks
up the mat of solids that accumulates on the soil surface,
loosens up the soil, and restores the clean soil
infiltration rates.
During summer and autumn, basins are allowed approximately
1 week to thoroughly dry. Complete drying may take 2 weeks
or more during colder periods. Thus, a new application
schedule begins every 7 weeks during summer and autumn and
every 8 to 9 weeks during colder seasons.
Renovated water discharged to Boulder Creek must contain
only small concentrations of ammonia. For this reason, one
of the objectives of rapid infiltration at Boulder is to
convert wastewater ammonium to nitrate. This process,
called nitrification, occurs when short application
periods, followed by longer drying periods, are used (see
section entitled HOW DOES IT WORK?). The loading cycle used
at Boulder has been ideal for promoting nitrification.
About 98% of the nitrogen in the renovated water from one of
the basins is present as nitrate ion, although ammonium
12
METCALPA BOOV
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concentrations in the renovated water increased somewhat
during the coldest winter months. Solids and bacteria
removals also have been consistently greater than 96% and
99%, respectively. As part of the pilot operation, Boulder
plans to study methods for improving overall nitrogen
removal in the near future.
Although ice forms on the surface of the applied wastewater
in the cold winter months, the ice insulates the applied
wastewater during infiltration and eventually collapses.
The collapsed ice floats to the surface during the following
wastewater applications. Thus, icing does not cause
problems during wastewater loading.
Calumet, Michigan
Rapid infiltration has been used for municipal wastewater
treatment in Calumet since 1887 [3]. Initially, the system
was owned and operated by the Calumet and Hecla Consolidated
Copper Company. Following the decline of the local mining
industry, ownership passed to the Northern Michigan Water
Company (1961) and then to the neighboring village of
Laurium (1972). Ownership was transferred to Laurium so
federal funds could be used to improve the site. The system
continues to be operated by the Northern Michigan Water
Company under a contract with the village of Laurium.
Currently, the system is used by about 8,100 people who
contribute approximately 0.34 Mgal/d of wastewater. Large
quantities of infiltration/inflow also enter the collection
system, resulting in an average annual flowrate of
1.6 Mgal/d. Thus, although the wastewater is not treated
prior to application, it is quite dilute, resembling primary
effluent.
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[Photo of open channel inlet]
As shown in Figure 5, the system consists of 17 irregularly
shaped basins. Each of the basins is loaded at a rate of
approximately 116 ft/yrf but, because of the high
infiltration/inflow rate, day-to-day application rates are
quite variable. The system does not have any underdrains,
and two areas where water currently emerges from the ground
in springs have been observed. Furthermore, the area
receives an average of 180 in./yr of snow, which has caused
some basin overflows during spring melting. Plans are
underway to replace the ditch distribution system with
piping and to otherwise improve distribution and drainage.
Also, regular drying and scarification of the infiltration
basins is planned for future operations. With these
modifications, basin overflows should not occur.
[Photo of Calumet RI basin]
In spite of these existing deficiencies, analysis of samples
taken at interior and perimeter wells indicates that
phosphorus is being effectively adsorbed and that nitrogen
removal is substantial. As required by EPA guidance on
ground water protection, ground water at the system boundary
meets the EPA drinking water standards.
Hollister, California
The City of Hollister, located in the San Juan Valley
22 miles inland from Monterey Bay, first applied wastewater
to land in 1922 [4]. Controlled rapid infiltration was not
practiced until about 1946, when infiltration basins were
constructed.
14
MBTCALF
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LEGEND
™»«™i-««M^^—,
ROADWAY
— —— DISTRIBUTION DITCH
J r 1 l DIKES
• OBSERVATION WELLS
X*"7^ RAPID INFILTRATION BASINS
o
NOT TO SCALE
Figure 5. Rapid infiltration site at Calumet, Michigan.
15
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From 1946 to 1980, the city operated the facilities shown
schematically in Figure 6. In the mid 1970s, an earthen
reservoir was constructed and used to store and thereby
minimize wastewater flow peaks. In this way, flow leaving
the equalizing basin and traveling through the clarifier was
relatively constant. In this mode, the overall rapid
infiltration system was monitored extensively from 1976 to
1977 for long-term effects on soil and ground water.
In early 1980, the city upgraded and expanded their
facilities to meet the needs of a growing population.
Preapplication treatment now includes lagoons, as shown in
Figure 7. The new infiltration basins cover 39 acres of
land. Currently, the plant wastewater flow averages
1.3 Mgal/d. About 20% of this flow is contributed by a
paper recycler and a slaughterhouse. All other wastewater
originates from nonindustrial sources.
[Photo of Hollister RI basin, drying]
At present, the lagoons are still filling with wastewater
and the infiltration basins have not been used except during
construction of the preapplication treatment lagoon.
Eventually, the loading cycle should be similar to the cycle
maintained with the old facilities. Until construction of
the new facilities began, each infiltration basin was
flooded for 1 to 2 days every 14 to 21 days, depending on
basin size and season of the year. Using this cycle and
primary effluent in 1977, there were no indications that
trace elements or pathogenic bacteria were entering the
ground water from the applied wastewater.
16
METCAL' • EODV
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INFILTRATION '
BASINS
EQUALIZATION
RESERVOIR
0 90100 200 300 400 FEET
i 1 I I
100 200 METRE
Figure 6. Schematic of pre-1980 Hollister rapid
infiltration system.
17
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MCHAY
STRICTURE-
o
• IMl MTE
•(SECMOARY)
PtNO
(HOLDINS PONDS
NONITIRING WELL
RAPID INFILTRATION RASINS
FLOATING
AERATORS
FEET
Figure 7. Schematic of new Hollister rapid
infiltration system,
18
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Similarly, chemical oxygen demand (COD), BOD, and total
organic carbon (TOC) were being reduced to relatively minor
amounts after percolation through 22 feet of gravelly and
sandy loam. Almost complete nitrogen removal was being
achieved as wastewater passed from the soil surface to the
shallow ground water table. Thus, no detrimental effects
were observed as the shallow ground water moved laterally to
join the subflow of the San Benito River.
Lake George, New York
Because Lake George is a beautiful, clear lake and is used
as a drinking water supply, wastewater discharges into the
lake or into any waters discharging into the lake are
prohibited [5]. When the Lake George Village wastewater
treatment plant was constructed in 1936, this discharge
prohibition was interpreted to mean no surface discharge to
the lake or tributary streams. For this reason, a land
treatment system was selected. The Lake George rapid
infiltration system was put into operation in 1939 and has
operated continuously since that time.
[Photos of Lake George system]
At Lake George, wastewater flow ranges from a low of
0.4 Mgal/d in the winter to an average of approximately
1.1 Mgal/d during the summer months. Preapplication
treatment includes primary clarification, secondary
treatment with trickling filters, and secondary
sedimentation, as shown in Figure 8. A total of 21
infiltration basins are used; normally, 4 are dosed per day.
Lake George does not follow an established basin cleaning
schedule. Instead, beds are cleaned when they can be
spared, when it appears that cleaning is necessary, and when
plant personnel can take time to clean them.
19
MCTCALP • BOOV
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/*
'{
FINAL SETTLING TANKS
LABORATORY BUILDING
% TANKS ^r-
-'--••Tgt?KA7!^
•;—• -ffi$/{>\%£—
•r4-
>r^ DIIU
SOUTH BEDS
1--T
"x,\^v
PUMP X
HOUSE
TRICKLING FILTERS
Figure 8. Plan of the Lake George Village
wastewater treatment plant.
20
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Within the first 10 feet of infiltration, BOD, COD, and
indicator bacteria are effectively removed; nitrification is
essentially completed; and orthophosphate concentrations are
greatly reduced. Enough nitrogen is removed so that the
concentration of nitrate-nitrogen meets drinking water
standards at a depth of 60 feet. In summary, the renovated
water quality is quite high.
It is ironic that the lake discharge prohibition that
produced the rapid infiltration system now threatens its
future. As a result of research studies conducted in the
1970s, the ground water flow that contains the treated water
was traced to a stream that flows into the lake. The same
research showed that no adverse effects were occurring as a
result of the discharge. At this time, however, a legal
remedy is required to allow the Lake George system to
continue to operate.
[Photo of West Brook with fisherman]
Phoenix, Arizona
During 1967, a research project on rapid infiltration was
constructed in the Salt River bed west of Phoenix, Arizona
[6]. The purpose of the project was to study the
feasibility of ground water recharge with secondary
effluent. It was hoped that rapid infiltration could be
used to provide water suitable for unrestricted irrigation,
recreation, and other purposes with either high economic or
social return. In this way, rapid infiltration would reduce
ground water overdraft and slow down the decline of the
ground water table, which had been as much as 10 ft/yr in
some areas.
21
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At the project, unchlorinated secondary effluent from an
activated sludge facility was applied to the infiltration
site. During the first 6 years of the research project, the
loading cycle was adjusted to maximize the hydraulic loading
rate. Maximum rates (300 to 400 ft/yr) were achieved by
alternating flooding periods of 2 to 3 weeks with drying
periods of 10 to 20 days. At these rates, however, nitrogen
removal averaged about 30%.
In 1973, the loading cycle and rate were varied to promote
nitrogen removal. Flooding periods were shortened, and the
loading rate was lowered. Nitrogen removal increased to
about 60% and remained fairly consistent during the
remainder of the project.
To monitor results, water was pumped from the ground at
depths of 20 to 100 feet immediately following treatment.
Water quality was found to be suitable for both unrestricted
irrigation and recreation.
Based on the results of the research project, a large-scale
(13 Mgal/d) rapid infiltration system to treat secondary
effluent was designed and constructed. Called the 23rd
Avenue Project, this system was completed in 1974. As shown
in Figure 9, this project uses secondary treatment
(activated sludge process) for preapplication treatment.
Unchlorinated secondary effluent is applied to four 10-acre
basins.
[Photo of inlet to Phoenix RI basin]
22
• ETCAI.F 4 C O OV
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PREAPPLICATION TREATMENT
20 Mgal/d SECONDARY
EFFLUENT FROM 23rd AVE
STP
ta
3
.111
8XI DAT I ON POND
OVERFLOW
INLET
STRUCTURE
MONITORING
WELL —v
b
1200 (t
BYPASS LEVEE
80 acre
OXIDATION'POND
t-r
Jt
INFILTRATION < t
n
,
BASIN OVERFLOW
/
jL
o
13 Hgal/d
BYPASSED TO RAPID
INFILTRATION BASINS
, 4-10 acre RAPID
/INFILTRATION BASINS
goo
ft
, MONITORING
WELL
3.000 ga /tain ~
RECOVERY WELLS AND
COLLECTION PI PINO
^-
PROPERTY LIMITS
Figure 9. Layout of the 23rd Avenue rapid
infiltration and recovery project.
23
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Monitoring data from 1979 indicate that the system removes
about 65% of the applied nitrogen and 75% of the applied
phosphorus, and reduces the average fecal coliform
concentration from 105-106 per 100 mL to 1.25-2.3 per
100 mL. In the near future, renovated water will be pumped
from depths of up to 100 to 200 feet and used for
unrestricted irrigation and recreation.
HOW DOES IT WORK?
Treatment Mechanisms
As wastewater travels through the soil, most of its
contaminants are treated or removed. These wastewater
constituents include organic matter, suspended solids,
nitrogen, phosphorus, heavy metals, microorganisms, and
trace organics. Many reactions and mechanisms are involved
in the treatment process. Several are discussed in the
following paragraphs.
Essentially all organic and other solids are removed by
filtration as the wastewater travels through the uppermost
soil layers. Soil bacteria consume both organic solids and
most of the dissolved organic molecules, using them for
growth and reproduction. As a result of the soil filtration
and bacterial growth, a mat of solids forms at the soil
surface. Drying the infiltration basins dries out this mat
and allows oxygen that is needed for bacterial growth to
enter the soil. Loosening the soil surface between
applications ensures that high application rates can be
maintained. Using these techniques, over 95% of the applied
organic material (measured as BOD) and 99% of the applied
suspended solids can be removed.
24
MCTCALP » EOOV
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Nitrogen is removed primarily through a two-step biological
mechanism known as nitrification-denitrification. In the
applied wastewater, most nitrogen is present as ammonium.
During the nitrification step, soil bacteria convert the
ammonium to nitrate. This process requires that there be
oxygen in the soil; thus, maximum nitrification occurs when
short application periods followed by longer drying periods
are used.
During the denitrification step, different types of bacteria
convert the nitrate to nitrogen gas. The gas moves up
through the soil and into the air. This step occurs only if
no oxygen is present. Also, some dissolved organic
molecules must be available to provide energy for the
denitrification step.
At operating rapid infiltration systems, ammonium nitrogen
removal is high, usually 95 to 99%. Total nitrogen removal
ranges from about 50% to over 90%. Nitrogen removal
improves as the lengths of the application and drying
periods are increased and as the ratio of BOD to nitrogen in
the applied wastewater is increased. Typically, a high BOD
to nitrogen ratio is obtained by providing primary rather
than secondary level treatment before land application of
the wastewater.
Phosphorus is removed primarily by two chemical processes
known as adsorption and precipitation. Adsorption is a
rapid mechanism and occurs first. During adsorption,
phosphorus adheres to soil particles and is not washed off
by additional wastewater applications. Although all soils
can adsorb phosphorus, soils with finer texture have more
sites where adsorption can occur. In other words, the
coarser the soil, the further the wastewater must travel
before all phosphorus is adsorbed.
25
MCTCALF * EDOV
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After a few days, the adsorbed phosphorus begins to
precipitate. During the precipitation process, phosphorus
combines with other elements, including iron, calcium, and
aluminum, to form molecules that do not dissolve in water.
This means that these molecules will not be dissolved by or
contaminate water percolating through the soil. As
phosphorus precipitates, it is released from the sites where
adsorption occurs. In this way, adsorption sites are freed
for adsorption of phosphorus from subsequent wastewater
applications. If adequate soil travel distance is allowed,
these two mechanisms can remove over 95% of the applied
phosphorus.
Three types of microorganisms must be removed during
wastewater treatment: bacteria, viruses, and parasitic
protozoa and helminths (worms). During rapid infiltration,
these microorganisms are removed by filtering, drying, solar
radiation, predation, and exposure to other adverse
conditions. Because of their large size, protozoa and
helminths are filtered out at the soil surface. Bacteria
are also removed by filtration at the soil surface, although
some bacteria are adsorbed in the same way that phosphorus
is adsorbed. Because they are so small, viruses are not
removed by filtration but travel into the soil profile,
where they are removed almost entirely by adsorption. If
the distance between a rapid infiltration site and drinking
water supplies or residential areas is adequate,
microorganisms are not a problem.
Trace element removal is a complex process. Mechanisms that
are involved include adsorption, precipitation, exchange of
metals for other charged particles in the soil, and
combination of metals with relatively large organic
molecules that are not soluble in water. At most rapid
26
MCTCALP A EOOV
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infiltration sites, heavy metal concentrations in untreated
wastewater are already lower than drinking or irrigation
limits. For this reason, metal removal has not been a
problem. If a community receives high concentrations of
heavy metals from local industries, industrial wastewater
pretreatment should be considered.
Trace organics can be adsorbed, or may evaporate from the
soil surface or degrade with time. Based on limited data,
trace organics concentrations in applied wastewater are low.
Thus, trace organics removal at operating systems has not
been a problem. If concentrations in the raw wastewater are
high, industrial pretreatment should be considered.
Elements of a Rapid Infiltration System
The major elements of a rapid infiltration system are:
• Preapplication treatment
• Transmission
• Flow equalization or storage
• Distribution
• Drainage
• Land
Preapplication Treatment. The degree of preapplication
treatment required depends on the relative isolation of the
site, the expected treatment in the soil, and final effluent
quality requirements. The EPA has recommended the following
levels of preapplication treatment [7]:
• Primary treatment, when the location is isolated
and public access is restricted
27
MCTCALP
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Biological treatment using lagoons or inplant
processes (trickling filter, activated sludge),
when the location is urban and public access is
controlled
Transmission. Often, wastewater must be transmitted to a
site where land is available and soils are suitable for
rapid infiltration. Pipeline transmission after
preapplication treatment is quite common when land treatment
is initiated after a conventional treatment plant has been
constructed and the treatment plant is used for
preapplication treatment.
Flow Equalization and Storage. A few days volume of
wastewater storage may be required for flow equalization or
for emergency backup in case of mechanical failures.
Storage for adverse weather conditions is usually not
necessary. If storage is necessary, the storage facilities
can be designed as stabilization ponds, and they can provide
both preapplication treatment and storage [8].
Distribution. For rapid infiltration, wastewater is
normally applied to land by surface spreading, although
sprinkling has been used. The distribution system should be
designed so wastewater can be applied at a rate that will
allow a constant basin water depth throughout the
application period [8]. Multiple basins are used to
maximize flexibility and allow variations in the application
cycle.
Drainage. If natural drainage is inadequate, drainage
facilities may be required to minimize ground water mounding
and to ensure that infiltration rates do not decrease.
Also, if renovated water is to be reused, some type of
drainage will be necessary to transport the renovated water
28
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from underneath the soil surface to the reuse location.
Three types of drainage are common:
1. Underdrains
2. Pumping
3. Natural flow to a surface water body (e.g., Lake
George)
If pumps are used to extract renovated water, as they are in
Phoenix, pumping costs may be a significant part of a
system's annual operation and maintenance costs.
Land. The primary factors and general criteria considered
in selecting a rapid infiltration site are listed in
Table 4.
Table 4. SITE SELECTION FACTORS
FOR RAPID INFILTRATION TREATMENT [8]
Factor Criteria
Soil Rapid permeability (such as sands and loamy sands).
Ground water Minimum depth to ground water of 10 ft is preferred;
lesser depths are acceptable if underdrainage is
provided.
Topography Slope is not critical but excessive slopes require
much earthwork.
Climate Although cold weather may require modified treatment
plant operations, climate should not restrict plant
siting.
Location For economic reasons, siting should minimize distance
and adverse grades between preapplication treatment
site and infiltration basins.
The amount of land required for a rapid infiltration system
depends on the loading rate, the loading cycle, and basin
management practices such as the frequency of basin cleaning
or soil turning. Land may also be required for wastewater
storage, buffer zones, buildings, preapplication treatment,
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MITCALP * EOOV
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roads, or ditches. In addition, the availability of land
for future expansions should be considered during site
selection and acquisition.
Design criteria for rapid infiltration systems are
summarized in Table 5. This table includes typical ranges
for each criterion as well as actual values used at the five
previously described rapid infiltration systems.
Table 5. DESIGN CRITERIA FOR
RAPID INFILTRATION SYSTEMS [2-6, 8]
Design feature
Annual
application
rate, ft
Field area
required,
acres/Mgal-d
Preapplication
treatment
Basin surface
cover
Hydraulic
loading cycle
On
Off
Typical
20-400
2-56
Primary or
secondary
Bare or
vegetated
1-14 days
4-14 davs
Boulder,
Colorado
100
11.2
Secondary
Bare (2 basins);
weeds (1 basin)
1 day
2-3 days
Calumet,
Michigan
120
10.0
Untreated
Bare
1-2 days
7-14 days
Hollister,
California
37
30
Oxidation
ponds
Bare
1-2 days
12-20 days
Lake George,
New York
140
5.8
Secondary
Bare
8-24 hours
4-5 days to
5-10 davs
Phoenix,
Arizona
250
4.5
Secondary
Bare
9 days
21 days
WHAT DOES IT COST?
The total cost of a rapid infiltration system may be
distributed among several major components:
• Preapplication treatment facilities
• Transmission facilities
• Storage facilities
• Land
• Distribution system
• Drainage
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MITCALF « BDOV
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Costs of new 1 Mgal/d and 10 Mgal/d rapid infiltration
systems are presented in Table 6. These costs are based on
hypothetical systems in which oxidation ponds are used for
preapplication treatment. For cost estimating purposes, it
was assumed that (1) 20 acres of land is needed for every
1 Mgal/d of wastewater treated, (2) land costs $4,000 per
acre, (3) six 40-ft deep monitoring wells are required for
every 100 acres of land, and (4) at least two monitoring
wells are necessary [1].
Table 6. ANNUAL COSTS OF NEW
RAPID INFILTRATION SYSTEM
(1.0 Mgal/d and 10 Mgal/d)
$/household
1.0 Mgal/d 10.0 Mgal/d
Capital 68 35
Operation and maintenance 17 9
Total 85 44
a. Adapted from reference [1].
As shown in Table 6, capital costs are nearly 80% of the
total annual cost. However, because federal grant funds are
available for capital expenditures but not for operation and
maintenance costs, this ratio is advantageous to the
operating agency. Rapid infiltration is considered
alternative technology and is eligible for up to 85% funding
of the capital cost under the Construction Grants Program.
The local share of the treatment cost is the portion of the
capital costs not paid by the federal government plus 100%
of the operation and maintenance costs. Therefore, if two
alternatives (e.g., rapid infiltration and a conventional
system) have the same total cost, the one with the larger
capital investment will have the smaller local share.
Furthermore, inflation and increasing energy and resources
31
MBTCAI.P
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costs cause operation and maintenance costs to increase each
year. The alternative that requires the least amount of
energy and resources probably would result in the greatest
user savings.
To illustrate these two points, compare the costs associated
with the rapid infiltration and conventional AWT
alternatives shown in Table 7. Expenses included under the
AWT alternative with phosphorus removal include primary
sedimentation, activated sludge secondary treatment,
chlorination, and ferric chloride addition. The AWT
alternative with both nitrogen and phosphorus removal
includes primary treatment, single-stage activated
sludge/nitrification, ferric chloride addition,
denitrification, filtration, and postaeration. As shown in
Table 7, the local cost of a rapid infiltration facility can
be much less than the local cost of an AWT plant.
Table 7. ANNUAL COSTS OP NEW 0.5 Mgal/d AND
50 Mgal/d SYSTEMS: RAPID INFILTRATION
AND CONVENTIONAL AWT ALTERNATIVES
f£/l,000 gallons
Costs
Capital
Operation and
maintenance
Total
Local shareb
Rapid
infiltration
80
20
100
32
0.5 Hgal/d
AWT with
phosphorus
removal
107
62
170
79
AWT with
phosphorus
and nitrogen
removal
228
112
340
146
Rapid
infiltration
22
6
28
9
SO Hgal/d
AWT with
phosohorus
removal
26
23
49
27
AWT with
phosphorus
and nit-rogen
removal
47
3J3
83
43
a. Adapted from reference [1].
b. Assuming that the local share is 15% of the capital costs plus 100% of the operation and
maintenance costs.
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HOW CAN IT WORK FOR YOU?
It is quite possible that rapid infiltration land treatment
can be used by your community. Although rapid infiltration
will not work everywhere, in many communities it can be used
as an environmentally sound and cost-effective solution to
wastewater management problems. In some communities,
innovative concepts can be used to tailor the process to the
community's special needs.
Opportunities
Rapid infiltration systems can be used effectively in the
following situations:
• Where there is a need for treatment without
surface water discharge. At Lake George, a direct
surface discharge prohibition has been met by
using rapid infiltration for both treatment and
disposal.
• Where there is a need for upgraded treatment. At
Hollister, rapid infiltration is provided to
improve the quality of the treated water so that
it will be compatible with existing ground water
quality.
• To reduce excessive operating costs for existing
or proposed AWT facilities. Where primary
treatment followed by rapid infiltration is
feasible, the operating costs for conventional
secondary treatment facilities can be avoided.
Innovative Concepts
Innovative modifications of the basic rapid infiltration
process can be used by many communities. Several are
noteworthy, for varying reasons.
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First, many communities may want to consider using rapid
infiltration together with another land treatment process,
such as overland flow or slow rate treatment. If nitrogen
concentrations in the renovated water must be very low,
overland flow can be used prior to rapid infiltration to
improve nitrogen removal efficiency. This technique has
been demonstrated successfully in Ada, Oklahoma. At Ada,
screened, raw wastewater was applied to an overland flow
site and the treated runoff was applied to the rapid
infiltration site. If crop irrigation (for slow rate
treatment) is planned and the selected crop requires very
high quality effluent, rapid infiltration can be used prior
to slow rate treatment. Using this combination, even the
most restrictive irrigation requirements can be met.
Second, renovated water from rapid infiltration systems can
be recovered and reused for unrestricted irrigation or
recreation. At Santee, California, rapid infiltration
removes nutrients and pathogens, enabling the community to
use the recovered water for recreational lakes. At Phoenix,
wells are used to recover renovated water. Renovated water
quality is suitable for either unrestricted irrigation or
recreational lakes. At one time, the City of Phoenix
considered using recovered water both for irrigation and for
a proposed aquatic park along the Salt River channel. At
present, the city is completing arrangements with a local
irrigation district for the use of all recovered water.
Third, rapid infiltration systems can be modified for year-
round operation in cold weather climates. Although many
systems—including those at Lake George; Boulder; Calumet;
Victor, Montana; and Fort Devens, Massachusetts—are able to
operate in cold weather without any modifications, some
communities use basin modifications to improve or ensure
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Because rapid infiltration uses high loading rates, soils
must be able to accept and pass on relatively large amounts
of water during short periods. Soils containing substantial
deposits of clay cannot do this. Where suitable soils
cannot be found, rapid infiltration land treatment may not
be practical.
Nitrification and oxidation of organic material require
aerobic soil conditions. However, soil reaeration during
resting periods cannot proceed if the soil is saturated with
water. Therefore, the ground water table must be deep
enough to allow drainage to occur and to keep infiltration
rates from decreasing. In addition, to maintain high levels
of treatment in the soil, the depth to the ground water
table should be adequate. Ground water can be pumped to
keep the table lower than it would be naturally, or
underdrains can be used to alleviate high ground water
problems.
In urban areas, land may be expensive enough to limit the
use of rapid infiltration. Using March 1978 costs, the cost
of land at which AWT becomes less expensive than rapid
infiltration is $50,000/acre for a 10 Mgal/d facility. Even
if the cost of land is not unaffordably high, it may be
difficult to find an available site close to the urban area.
The reason most often cited for lack of public acceptance of
a rapid infiltration alternative is fear of public health
risks. Several health effects studies have been conducted
or are in progress to determine if any health problems are
caused by rapid infiltration land treatment. At Santee,
where renovated wastewater has been used to create five
recreational lakes, viral and bacteriological studies
conducted in 1965 indicated that rapid infiltration provides
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a safe water supply for the lakes [9], This assurance of
public health protection, along with an ongoing monitoring
program, has contributed to the public's enthusiastic
acceptance of the recreational lakes, including the swimming
area.
More recently, the Orange and Los Angeles Counties Water
Reuse Study has investigated the health impacts of
recharging ground water with renovated water. Ground water
recharge, using effluent from the Los Angeles County
Sanitation Districts' Whittier Narrows treatment facility,
has been practiced in this area since 1962 with no known
public health problems.
Factors contributing to public acceptance include improved
surface water quality, low cost, and simplicity of
operation. Compared with conventional treatment systems,
savings can be realized in lower capital and/or operation
and maintenance costs. These savings can mean lower user
charges. Using rapid infiltration, water can be reclaimed
and used for irrigation and/or recreation, instead of being
discharged to nonconsumptive or less beneficial uses.
Implementation
Many communities have successfully implemented rapid
infiltration systems. Here are a few examples of how this
has been accomplished.
In 1959, the community of Santee was required to either
upgrade or abandon their year-old treatment plant. If
additional treatment was to be the selected alternative, the
added cost would have to be justified by putting the water
to beneficial use. At first, the Santee County Water
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District proposed using stabilization ponds to reclaim water
for recreational use. When this idea was rejected by the
local health department, it was decided to treat about one-
third of the wastewater using rapid infiltration followed by
chlorination and recovery of the water for recreational
lakes [9].
Four of the Santee recreational lakes were completed in
1961; a fifth was opened in 1965. By 1965, an estimated
75,000 people used the facilities each year. Since the
lakes opened, the recreational program has expanded to
include picnicking, boating, fishing, and swimming.
In 1936, there was concern that Lake George was being
polluted by the increasing population of Lake George Village
at the southern end of the lake. A secondary treatment
plant, including trickling filters, was constructed to treat
wastewater from the Village. Due to the efforts of the Lake
George Association, organized in 1885, the lake was given an
11AA" classification by the State of New York. This
classification prohibits discharges into the lake or any
waters that discharge into the lake. Because all of the
surface waters in the area of Lake George Village discharge
to Lake George, land treatment was necessary. Natural delta
sand deposits were available, making Lake George Village an
ideal site for a rapid infiltration system. Thus, this
method of treatment was selected [5].
DIGGING DEEPER
The amount of reference material available on the research,
design, and operation of land treatment systems is
extensive, including: reports, design manuals, textbooks,
movies, and short courses complete with individual study
38
MCTCALP •
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modules and slides. Abstracts of the key reference
materials are followed by a listing of representative rapid
infiltration systems (by EPA region), contacts for selected
existing systems, and the references cited.
Process Design Manual for Land Treatment of Municipal
Wastewater. Environmental Protection Agency. EPA 625/1-77-
008. Center of Environmental Research Information,
Cincinnati, Ohio. October 1977
Planning and design procedures and criteria for all land
treatment systems are presented. Three case studies of
rapid infiltration systems are included and a design example
is provided. Treatment mechanisms for removal of nitrogen,
phosphorus, pathogens, and heavy metals are detailed.
Procedures for determining hydraulic capacity of sites are
also included. An updated manual is scheduled for release
in October 1981.
Proceedings of the International Symposium on Land Treatment
of Wastewater. Volumes 1 and 2. Cold Regions Research
Engineering Laboratory. Hanover, New Hampshire. August 20-
25, 1978
There are 101 research-oriented papers included on subjects
such as health considerations, public acceptability,
mathematical modeling, existing systems, agricultural and
forest use, and monitoring. This is one of the best of the
proceedings of land treatment conferences held in the 1970s.
Loehr, R.C. et al. Land Application of Wastes. Volumes I
and II.Van Nostrand Reinhold Co. New York. 1979
The text of this two-volume set represents the 21 self-study
modules on land treatment developed as an educational
package at Cornell University. In addition to the modules,
over 1,000 slides, 16 cassette tapes, and an Instructor's
39
IETCALP » BOOV
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Program are available at the EPA Training Center in
Cincinnati. These materials can be used in 2 to 5 day
workshops or in individual study. The modules are basic in
their coverage and are written for the uninitiated in land
treatment.
Reed, S.C. et al. Costs of Land Treatment Systems.
Environmental Protection Agency, Office of Water Program
Operations. Washington, D.C. EPA-430/9-75-003. 1980
This report updates the 1975 publication "Costs of
Wastewater Treatment by Land Application." The text is
shortened and reflects current EPA policy on land treatment.
Most of the original cost curves are retained along with the
1-page explanation of assumptions and items used in their
development. Cost curves for transport, storage,
preapplication treatment, distribution, underdrainage,
wells, and monitoring are included.
Where Rapid Infiltration Systems Can Be Found
REGION I
Massachusetts
Barnstable
Chatham
Concord
Edgartown
Fort Devens
Nantucket (2)
Wareham
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REGION II
New Jersey
Vineland
New York
Birchwood-North Shore (Holbrook)
Cedar Creek (Wantagh)
College Park (Farmingdale)
County Sewer District (Central Islip)
County Sewer District (Holbrook)
County Sewer District (Holtsville)
County Sewer District #5 (Huntington)
County Sewer District #11 (Ronkonkoma)
County Sewer District #12 (Holtsville)
Heatherwood (Calverton)
Huntington Sewer District
Lake George
Riverhead
Strathmore Ridge (Brookhaven)
REGION III
Maryland
Calhoun Marine Engineering School
Fort Smallwood
Jensen's Inc. - Hyde Park
Quality Inn of Pecomore, Inc.
South Dorchester K-8 Center
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REGION IV
Florida
Avon Park
Lehigh Acres
Sandlake (Orlando)
Tavares
Williston
Kentucky
Horse Cave
REGION V
Michigan
Bangor
Calumet
Decatur
Edmore
Gaastra
Cedar Springs (Grand Rapids)
Hopkins
Howard City
Leoni (Jackson)
Mackinaw
Marcellus
Marion
Olivet
Onekama
Ottawa County Road Commission
Pentwater
Shelby
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Wisconsin
Almond
Baldwin
Birchwood
Coloma
Deer Park
Fenwood
Fontana
Hammond
Lone Rock
Maribel
Milton
Roberts
Sextonville
Spring Green
Stone Lake
Unity
Wheeler
Wild Rose
Williams Bay
Winter
REGION VI
New Mexico
Hobbs
Springer
Vaughn
REGION VII
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REGION VIII
Colorado
Boulder (R&D)
Sterling
Montana
Bazin
Bozeman
Corvallis
Plains
Stevensville
Victor
North Dakota
Parshall
Reeder
South Dakota
Madison
Wyoming
Jackson
Laramie
REGION IX
Arizona
Arcosanti (Cordes Junction)
Duncan
Kingman Hilltop
Lo Lo Mai Springs
Mammoth
Miami
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MCTCALP • COOV
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Phoenix
Poston
Show Low
Snowflake
Thatcher
Marana (Tucson)
Ina Road (Tucson)
Green Valley (Tucson)
Avra Valley (Tucson)
Desert. Museum (Tucson)
Corona de Tucson (Tucson)
Sells (Tucson)
Wickenburg
Willcox
California
Bieber
Bishop
Blythe
Burney
Ceres
Corcoran
Delhi
El Monte (Los Angeles County, Whittier Narrows
treatment facility)
Escalon
Firebaugh
Fontana
Gilroy
Gridley
Hollister
Redlands
Ripon
Santee
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METCAL* * EOOV
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Tahoe-Truckee
Whittier (Los Angeles County, San Jose Creek treatment
facility
Yuba City
Hawaii
Kihei
Nevada
Beatty
Blue Diamond
Boulder City
Carlin
Eureka
Gabbs
Goldfield
Jackpot
McGill
Montello
Mountain City
Panaca
Paradise Spa
Paradise Valley
Tonopah
Wells
REGION X
Washington
Ritzville
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Contacts for Selected Existing Systems
Boulder, Colorado
Dr. K. Dan Linstedt
University of Colorado
Boulder, Colorado 80309
(303) 492-7315, X-7007
Calumet, Michigan
Dr. C. Robert Baillod
Department of Civil Engineering
Michigan Technological University
Houghton, Michigan 49931
(906) 487-2530
or
Dr. Neil J. Hutzler
Department of Civil Engineering
Michigan Technological University
Houghton, Michigan 49931
(906) 487-2194
Mr. Harry P. Bennetts, General Manager
Northern Michigan Water Company
311 Fifth Street
Calumet, Michigan 49913
(906) 337-3502
Hollister, California
Mr. Roger Grimsley, City Manager
375 Fifth Street
Hollister, California 95023
(408) 637-4491
Lake George, New York
Dr. Donald B. Aulenbach
Department of Environmental Engineering
Rensselaer Polytechnic Institute
Troy, New York 12181
(518) 270-6541
Mr. Harold Gordon, Plant Superintendent
Wastewater Treatment Plant
Lake George Village, New York
(518) 668-2188
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Phoenix, Arizona
Dr. Herman Bouwer
U.S. Water Conservation Laboratory
4331 East Broadway Road
Phoenix, Arizona 85040
(602) 261-4356
REFERENCES
1. Crites, R.W. , M.J. Dean, and H.L. Selznick. Land
Treatment vs. AWT - How Do Costs Compare? Water and
Wastes Engineering. August and September 1979.
2. Smith, D.G., K.D. Linstedt, and E.R. Bennett.
Treatment of Secondary Effluent by Infiltration -
Percolation. U.S. Environmental Protection Agency.
EPA-600/2-79-174. August 1979.
3. Baillod, C.R.f et al. Preliminary Evaluation of 88
Years Rapid Infiltration of Raw Municipal Sewage at
Calumet, Michigan. Proceedings of the Cornell
Agricultural Waste Management Conference: Land as a
Waste Management Alternative. R.C. Loehr, ed. Ithaca,
New York. 1976.
4. Pound, C.E., R.W. Crites, and J.V. Olson. Long-term
Effects of Land Application of Domestic Wastewater:
Hollister, California, Rapid Infiltration Site. U.S.
Environmental Protection Agency. EPA-600/2-78-084.
April 1978.
5. Aulenbach, D.B. Long Term Recharge of Trickling Filter
Effluent into Sand. U.S. Environmental Protection
Agency. EPA-600/2-79-068. March 1979.
6. Bouwer, H. , and R.C. Rice. The Flushing Meadows
Project. Proceedings of the International Symposium on
Land Treatment of Wastewater. Vol. 1. Hanover, New
Hampshire. August 20-25, 1978.
7. U.S. Environmental Protection Agency. Revision of
Agency Guidance for Evaluation of Land Treatment
Alternatives Employing Surface Application. PRM 73-9.
November 1978.
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8. Process Design Manual for Land Treatment of Municipal
Wastewater. U.S. Environmental Protection Agency.
EPA 625/1-77-008. October 1977.
9. Merrell, J.C., Jr., et al. The Santee Recreation
Project (Santee, California): Final Report. U.S.
Department of the Interior, Federal Water Pollution
Control Administration. Research Series Publication
No. WP-20-7. 1967.
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METRIC CONVERSIONS
acre
acre-ft
acre/Mgal
°F
gal/d
ft
in./wk
in./yr
lb/acre-yr
miles
Mgal/d
= 0.405 ha
= 1,233.5 m'
= '1.07 x 10
-7
ha/L
=' 0.555 (°F-32) °C
= 4.381 x 10~5 L/s
= 0.3043 m
= 2.54 cm/wk
= 2.54 cm/yr
= 1.12 kg/ha-yr
= 1.609 km
= 3,785 m3/d
ABBREVIATIONS
AWT Advanced wastewater treatment
BOD Biochemical oxygen demand
COD Chemical oxygen demand
EPA Environmental Protection Agency
SS Suspended solids
TOC Total organic carbon
50
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