v>EPA
United States
Environmental Protection
Agency
Office of Water
Washington, D.C.
EPA 932-F-99-067
September 1999
Waste water
Technology Fact Sheet
Intermittent Sand Filters
DESCRIPTION
Intermittent Sand Filters (ISFs) have 24-inch deep
filter beds of carefully graded media. Sand is a
commonly used medium, but anthracite, mineral
tailings, bottom ash, etc., have also been used. The
surface of the bed is intermittently dosed with
effluent that percolates in a single pass through the
sand to the bottom of the filter. After being collected
in the underdrain, the treated effluent is transported
to a line for further treatment or disposal. The two
basic components of an ISF system are a primary
treatment unit(s) (a septic tank or other
sedimentation system) and a sand filter. Figure 1
shows a schematic of a typical ISF.
05 to 0 75
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piping goes over—not through—the sand filter liner,
so the integrity of the liner is protected.
Bottomless ISFs
The bottomless ISF has no impermeable liner and
does not discharge to a drainfield, but rather directly
to the soil below the sand.
Table 1 shows the typical design values for ISFs.
These values are based on past experience and
current practices and are not necessarily optimum
values for a given application.
ADVANTAGES AND DISADVANTAGES
TABLE 1 TYPICAL DESIGN CRITERIA
FOR ISFs
Item
Design Criteria
Pretreatment
Filter medium
Material
Effective size
Uniformity coefficient
Depth
Underdrains
Type
Slope
Size
Hydraulic loading
Organic loading
Pressure distribution
Pipe size
Orifice size
Head on orifice
Lateral spacing
Orifice spacing
Dosing
Frequency
Volume/orifice
Dosing tank volume
Minimum level: septic
tank or equivalent
Washed durable granular
material
0.25-0.75 mm
<4.0
18-36 in
Slotted or perforated pipe
0-0.1%
3-4 in
2-5 gal/ft2/day
0.0005-0.002 Ib/ft2/day
1-2 in
1/8-1/4 in
3-6 ft
1-4 ft
1-4 ft
12-48 times/day
0.15-0.30 gal/orifice/dose
0.5-1.5 flow/day
Some advantages and disadvantages of ISFs are
listed below:
Advantages
ISFs produce a high quality effluent that
can be used for drip irrigation or can be
surface discharged after disinfection.
• Drainfields can be small and shallow.
• ISFs have low energy requirements.
ISFs are easily accessible for monitoring
and do not require skilled personnel to
operate.
No chemicals are required.
If sand is not feasible, other suitable media
can be substituted and may be found
locally.
Construction costs for ISFs are moderately
low, and the labor is mostly manual.
• The treatment capacity can be expanded
through modular design.
ISFs can be installed to blend into the
surrounding landscape.
Disadvantages
• The land area required may be a limiting
factor.
Regular (but minimal) maintenance is
required.
• Odor problems could result from open filter
configurations and may require buffer zones
from inhabited areas.
• If appropriate filter media are not available
locally, costs could be higher.
Clogging of the filter media is possible.
Source: Adapted from: U.S. EPA, 1980 and Crites and
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• ISFs could be sensitive to extremely cold
temperatures.
ISFs may require a National Pollutant
Discharge Elimination System (NPDES)
Permit when the effluent is surface
discharged.
PERFORMANCE
Sand filters produce a high quality effluent with
typical concentrations of 5 mg/L or less of
biochemical oxygen demand (BOD) and suspended
solids (SS), as well as nitrification of 80% or more
of the applied ammonia. Phosphorus removals are
limited, but significant fecal coliform bacteria
reductions can be achieved.
The performance of an ISF depends on the type and
biodegradability of the wastewater, the
environmental factors within the filter, and the
design characteristics of the filter. The most
important environmental factors that determine the
effectiveness of treatment are media reaeration and
temperature. Reaeration makes oxygen available for
the aerobic decomposition of the wastewater.
Temperature directly affects the rate of microbial
growth, chemical reactions, and other factors that
contribute to the stabilization of wastewater within
the ISF. Filter performance is typically higher in
areas where the climate is warmer compared to
areas that have colder climates.
Discussed below are several process design
parameters that affect the operation and
performance of ISFs.
The Degree of Pretreatment
An adequately sized, structurally sound, watertight
septic tank will ensure adequate pretreatment of
typical domestic wastewater.
Media Size
The effectiveness of the granular material as filter
media is dependent on the size, uniformity, and
composition of the grains. The size of the granular
media correlates with the surface area available to
support the microorganisms that treat the
wastewater. This consequently affects the quality
of the filtered effluent.
Media Depth
Adequate sand depth must be maintained in order
for the zone of capillarity to not infringe on the
upper zone required for treatment.
Hydraulic Loading Rate
In general, the higher the hydraulic load, the lower
the effluent quality for a given medium. High
hydraulic loading rates are typically used for filters
with a larger media size or systems that receive
higher quality wastewater.
Organic Loading Rate
The application of organic material in the filter bed
is a factor that affects the performance of ISFs.
Hydraulic loading rates should be set to
accommodate the varying organic load that can be
expected in the applied wastewater. As with
hydraulic loading, an increase in the organic loading
rate results in reduced effluent quality.
Dosing Techniques and Frequency
It is essential that a dosing system provide uniform
distribution (time and volume) of wastewater
across the filter. The system must also allow
sufficient time between doses for reaeration of the
pore space. Reliable dosing is achieved by
pressure-dosed manifold distribution systems.
OPERATION AND MAINTENANCE
The daily operation and maintenance (O&M) of
large filter systems is generally minimal when the
ISF is properly sized. Buried sand filters used for
residential application can perform for extended
periods of time.
Primary O&M tasks require minimal time and
include monitoring the influent and effluent,
inspecting the dosing equipment, maintaining the
filter surface, checking the discharge head on the
orifices, and flushing the distribution manifold
annually. In addition, the pumps should be installed
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with quick disconnect couplings for easy removal.
The septic tank should be checked for sludge and
scum buildup and pumped as needed. In extremely
cold temperatures, adequate precautions must be
taken to prevent freezing of the filter system by
using removable covers. Table 2 lists the typical
O&M tasks for ISFs.
TABLE 2 RECOMMENDED O&M FOR
ISFs
Item
O&M Requirement
Pretreatment
Dosing chamber
Pumps and controls
Timer sequence
Appurtenances
Filter media
Raking
Replacement
Other
Depends on process;
remove solids from septic
tank or other pretreatment
unit
Check every 3 months
Check and adjust every 3
months
Check every 3 months
As needed
Skim sand when heavy
incrustations occur;
replace sand to maintain
design depth
Weed as needed
Monitor/calibrate
distribution device as
needed
Prevent ice sheeting
APPLICABILITY
An assessment conducted in 1985 by the U.S.
Environmental Protection Agency of ISF systems
revealed that sand filters are a low-cost,
mechanically simple alternative. More recently, sand
filter systems have been serving subdivisions, mobile
home parks, rural schools, small communities, and
other generators of small wastewater flows.
Sand filters are a viable addition/alternative to
conventional methods when site conditions are not
conducive for proper treatment and disposal of
wastewater through percolative beds/trenches. Sand
filters can be used on sites that have shallow soil
cover, inadequate permeability, high groundwater,
and limited land area.
Placer County, California
Placer County, California, in the last 20 years has
had to develop their land with on-site systems due
to the popularity of their rural homes at elevations
of 100 to 4,000 feet. The county extends along the
western slope of the Sierra Nevada Mountains from
Lake Tahoe through the foothills and into the Great
Central Valley. Large areas of the county have
marginal soil quality, shallow soil depth, and
shallow perched groundwater levels.
In 1990, a program was initiated to permit the use
of the Oregon-type ISF system on an experimental
basis to evaluate their performance and other
related factors.
The ISF system used in this study had the following
components: a conventional septic tank followed by
a separate pump vault; a plywood structure with a
30 mm PVC liner for the filter and appurtenances;
24 inches deep of carefully graded and clean sand;
a gravel over-layer and under-layer containing the
pressurized piping manifold to distribute the septic
tank effluent over the bed; and a collection
manifold to collect the wastewater. The
dimensions of the filter (for both three- and four-
bedroom homes) were 19 feet x 19 feet at a design
loading rate of 1.23 gal/ft2/day. Summarized below
in Table 3 are the results obtained from 30 ISF
systems serving single-family homes during warm
and cold weather.
The results of this study indicate that ISF systems
showed a marked improvement in their effluent
quality over septic tanks. Although the systems
performed well, nitrogen and bacteria were not
totally removed, which indicates that ISF systems
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TABLE 3 COMPARISON OF EFFLUENTS FROM SINGLE-FAMILY, RESIDENTIAL
SEPTIC TANKS AND ISFs FOR 30 SYSTEMS IN PLACER COUNTY
Effluent Characteristic
CBOD5
TSS
NO3-N
NH3-N
TKN
TN
TC
FC
Septic Tank Effluent
160.2(15)*
72.9(15)*
0.1 (15)*
47.8(15)*
61.8(15)*
61.8(15)*
6.82x105(13)*
1.14x105(13)*
ISF Effluent
2.17(44)*
16.2(44)*
31.1 (44)*
4.6 (44)*
5.9 (44)*
37.4 (44)*
7.30x102(45)*
1.11 x 102 (43)*
% Change
98
78
99
90
90
40
99 (3 logs)
99 (3 logs)
*Number of samples
CBOD5, TSS, and nitrogen expressed as mg/L; arithmetic mean. Fecal and total coliform expressed as geometric mean of
MPN/100 ml.
Source: Cagle and Johnson (1994), used with permission from the American Society of Agricultural Engineers.
should be used only where soil types and separations
from the groundwater are adequate. Other findings
show that early involvement of stakeholders is vital
to the program's success; effective system
maintenance is essential; and the local learning curve
allows errors that adversely affect system
performance.
Boone County, Missouri
A pressure-dosed ISF was installed and monitored
on the site of a three-bedroom single-family
residence in Boone County, Missouri. The sand
filter, followed by a shallow drainfield, replaced a
lagoon and was installed to serve as a demonstration
site for the county. The soil condition at this site is
normally acceptable for septic tank effluent, but the
top 30 to 35 cm had been removed to construct the
original sewage lagoon.
The existing septic tank was found to be acceptable
and was retrofitted with a pump vault and a
high-head submersible pump for pressure dosing the
sand filter. The sand filter effluent drained into the
pump vault in the center of the sand filter, which
then pressure dosed two shallow soil trenches
constructed with chambers. The system was installed
in October 1995, and the performance was
monitored for 15 months.
The sand filter used in this study consistently
produced a high quality effluent with low BOD, SS,
and ammonia nitrogen (NH4-N). Table 4 lists the
various parameters studied. The aerobic
environment in the sand filter is evident from the
conversion rate of NH4-N to nitrate nitrogen
(NO3-N) that also resulted in no odor problems.
The fecal coliform numbers were consistently
reduced by four log units.
The average electricity use by this system was 9.4
TABLE 4 EFFLUENT CHARACTERISTICS
OF THE ISF IN BOONE COUNTY, MO
Parameter
BOD (mg/L)
TSS (mg/L)
NH4-N (mg/L)
NO3-N (mg/L)
Fecal coliform
(#/100mL)
Septic
Tank
297
44
37
0.07
4.56E+05
Sand
Filter
3
3
0.48
27
7.28E+01
%
Change
99.0
93.2
98.7
384.71
99.9
Source: Sievers; used with permission from the American
Society of Agricultural Engineers, 1998.
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kWh/month, and the cost of operating two pumps in
the system has been less than 70 cents per month.
The high quality effluent produced by the sand filter
also reduced the size of the absorption area.
The cost of an ISF system depends on the labor,
materials, site, capacity of the system, and
characteristics of the wastewater. The main factors
that determine construction costs are land and
media, which are very site-specific. Table 5 is an
example of a cost estimate for a single-family
residence.
Energy costs are mostly associated with the pumping
TABLE 5 COST ESTIMATES FOR SINGLE-
FAMILY RESIDENCE
REFERENCES
Item
Cost ($)
Capital Costs
Construction costs, 1,500-gallon 850
single compartment septic/pump
tank @ 57 cents/gallon
ISF complete equipment package 3,200
(includes dual simplex panel, pump
pkg., tank risers, lids, liner, lateral
kit, orifice shields, etc.)
Non-component costs 750
Engineering (includes soils 2,000
evaluation, siting, design submittal,
and construction inspections)
Contingencies (includes permit fees) 1,000
Land May vary
Total Capital Costs 10,800
Annual O&M Costs
Labor @ $65/hr. (2 hrs./yr.) 130/yr.
Power @10 cents/kWh May vary
Sludge disposal *25/yr.
*Septic tank pumping interval based on 7 years with five
occupants.
of wastewater onto the filter. The energy costs
typically range between 3 to 6 cents per day.
Consequently, the energy costs of sand filters are
lower than most small community wastewater
processes, except for lagoons.
7.
Anderson, D. L.; R. L. Siegrist; and R. J.
Otis. 1985. "Technology Assessment of
Intermittent Sand Filters." U.S.
Environmental Protection Agency (EPA).
Municipal Environmental Research
Laboratory. Cincinnati, Ohio.
Cagle, W. A. and L. A. Johnson. December
11-13, 1994. "Onsite Intermittent Sand
Filter Systems: A Regulatory/Scientific
Approach to Their Study in Placer County,
California." On-Site Wastewater Treatment:
Proceedings of the Seventh International
Symposium on Individual and Small
Community Sewage Systems. Atlanta,
Georgia.
Crites, R. and G. Tchobanoglous. 1998.
Small and Decentralized Wastewater
Management Systems. The McGraw-Hill
Companies. New York, New York.
Sievers, D. M. 1998. "Pressurized
Intermittent Sand Filter With Shallow
Disposal Field for a Single Residence in
Boone County, Missouri." On-Site
Wastewater Treatment: Proceedings of the
Eighth International Symposium on
Individual and Small Community Sewage
Systems. Orlando, Florida.
Tarquin, A.; R. Bustillos; and K.
Rutherford. 1993. "Evaluation of a Cluster
Wastewater Treatment System in an El Paso
Colonia." Texas On-Site Wastewater
Treatment and Research Council
Conference Proceedings.
U.S. Environmental Protection Agency.
1980. Design Manual: Onsite Wastewater
Treatment and Disposal Systems. EPA
Office of Water. EPA Office of Research &
Development. Cincinnati, Ohio. EPA
625/1-80-012.
. 1992. Manual: Wastewater
Treatment/Disposal for Small Communities.
EPA Office of Research & Development.
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EPA Office of Water. Washington, D.C.
EPA/625/R-92/005.
ADDITIONAL INFORMATION
Infiltrator Systems Inc.
Technical Sales and Services Department
P.O. box 768
Old Saybrook, CT 06475
Texas A&M University System
Agricultural Engineering Department
Dr. Bruce J. Lesikar, Associate Professor
201 ScoatesHall
College Station, TX 77843-2117
University of Texas at El Paso
Anthony Tarquin
Civil Engineering Department
El Paso, TX 79968
David Vehuizen, P.E.
5803 Gateshead Drive
Austin, TX 78745
The mention of trade names or commercial products
does not constitute endorsement or recommendation
for use by the U.S. Environmental Protection
Agency.
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
401 M St., S.W.
Washington, D.C., 20460
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