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 
-------
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

-------
•      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

-------
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

-------
     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.

-------
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.

-------
      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
                                                            IMTB
                                                           Excellence fh compliance through optimal techntal solutions
                                                           MUNICIPAL TECHNOLOGY BRANCH"

-------