eck every 3 months

jeck and adjust every
13 months

leck every 3 months
p 3 inches deep when ponding

place top 1 to 4” of sand when
bonded more than 12" deep,
peptic tank fed filters are rested
proximately 6 to 9 mont

Recirculating

Same

Check every 3 months

Check and adjust every
3 months

Check every 3 months

To 3 inches deep when
ponding occurs

‘Skim sand if heavy
incrustations occur, add
new sand when bed
depth falls below 24”

While an altemate unit operates,
robic unit fed filters can
mediately be retumed to

bervice

Weed as required, maintain
distribution device, protect
filter against ice sheeting

bed as required, maintain
istribution device, protect filter
Igainst ice sheeting, check High
Vater alarm

Costs

The expenses incurred in constructing ISFs are a
function of local labor and material costs and are

greatly influenced by the land acquisition and filter
media costs. Approximate costs (1982 dollars) for
construction of three types of ISFs are as follows:

Buried: $2400 to $4500
Open: $3900 (average)
Recirculating: $3500 (average)

These examples assume a four bedroom house
having a 1,000-gallon septic tank and a design flo
of 600 gallons/day. The costs include $300 to $600
to reflect the costs of the septic tank. An aerobic
pretreatment unit will increase the system’s cost by
$600 to $3600. Annual O & M costs range from
$30 if pretreatment is a septic tank to $500 if



pretreatment is an aerobic system requiring
pumping plus a recirculating pump and final
disinfection.

Implementation

Several factors should be assessed prior to the
construction of an ISF system. Local jurisdictions
should be consulted to determine the acceptable
methods of effluent disposal. ISF effluent can be
discharged to surface waters, subsurface to ground
water, or to land. As with any wastewater treatment
system, it will be necessary to determine the need
for Federal or State discharge permits for the
specific application.

Careful planning may allow for the implementation
of ISF systems in situations where lot size and
topography may limit disposal by other processes.
A lot of .25 acres is usually large enough for
installation of an ISF. Topography is rarely
restrictive for ISF construction, but wastewater may
be conveyed to a nearby site where an ISF system
can be installed. However, where the topography of
individual lots is not amenable to standard
construction of an ISF, special designs such as
filter trenches often overcome the problem.

Prepared by Environmental Resources Management, Inc.

For additional information contact
Small flow coordinators:

EPA-OWPO(WH-595) EPA-MERL (489)
401 M Street, SW 26 West St. Clair Street
Washington, DC 2

(202)382-7263

EPA Region 1 EPA Region 6
John F, Kennedy Federal Building 4201 Eim Street
Boston, MA 02203

EPA Region 2 EPA Region 7
26 Federal Plaza 924 East 11th Street
New York, NY 10278 Kansas City, MO 64106

EPA Region 8
1860 Lincoln Street
Denver, CO 80203,

EPA Region 3
6th & Walnut Streets
Philadelphia, PA 19106

EPA Region 9
215 Fremont Strest
San Francisco, CA 94105

EPA Region 4
345 Courtland Street, NE
Allanta, GA 30308

EPA Region 10
4200 6th Avenue
Seattle, WA 98101

EPA Rogion 5
230 South Dearbome Street
Chicago, IL 60604

!
i
i
i
j



ftem Burled

Pretreatment
Septic Tank Inspect at 1 to 2 year
intervals, pump solids
if necessary (usually
‘once every 3 to 5

years)

Inspect at 4 to 6 month
intervals, pump solids
every 8 to 12 months

Aerobic Unit

Dosing Chamber

Pumps and Controls Check every year

Check and adjust every
6 months

Check every 6 months

Timer Sequence
Appurtenances
Filter Media
Raking None

Replacement None

Miscellaneous

jie 2 ISF Operation and Maintenance Activities

be performed by an informed homeowner. Service
of pumps, electrical equipment, and pretreatment
units should, however, be performed by
experienced maintenance personnel. Communities
may wish to consider establishing a community-run
or contract maintenance program, thereby relieving
the homeowner of direct involvement in
maintenance activities.

One of the most important O & M activities for an
ISF system is the periodic pumping of solids that
accumulate in the pretreatment unit. Properly
scheduled, pumping reduces the possibility that
materials such as oils, grease, and scum will
overflow and clog the filter surface. This is
especially critical for buried ISFs, since the filter
media is inaccessible for maintenance.



Recirculating: Recirculating filters are open filters
that treat a mixture of the pretreatment unit effluent
and recycled filter effluent. This filter depends on
biological activity for treatment, as do buried or open
filters. When the system is operating properly,

odors from the recirculation tank and open filter are
usually not objectionable since septic tank effluent

is mixed with aerobic effluent returning from the
filter.

Design

Treatment of domestic wastewater prior to filtration
is usually provided by a septic tank or aerobic unit.
Large wastewater volumes can be pretreated in
lagoons.

Filter media particle sizes can strongly influence
final effluent quality. Media that is too coarse allows
wastewater to pass rapidly through the filter which
results in insufficient detention time for biological
decomposition. Fine media limits the quantity of
wastewater filtered and may cause premature
clogging. The most effective filter media particle
size is different for each type of ISF.

Each type of ISF requires a different method and
tate of wastewater application. Wastewater
characteristics also influence the loading rate. In
general, the higher the organic strength of the
waste, the lower will be the recommended loading
rate.

Typically recommended filter media particle sizes
and loading rates for the three different types of
ISFs are shown in Table 1.

A filter bed depth of 9 to 12 inches is sufficient to
treat most wastewaters. Additional depth of filter

media will not appreciably improve effluent quality
however, it is recommended that ISFs be supplie

Filter Media er
Particle Size c Mothod ot
(rnitimetors) Wastewater Application

4 times

t 7
more than 4 tes dally

Recirculating 1.0- 1.5 Dosed periodically

Table 1 Typical ISF Design Parameters

|
i



United States June
Environmental Protection 1984
Agency

SEPA An Emerging |
Technology

Intermittent
Sand
Filtration

A Process
Assessment



- A Process Assessmen

Raw wastewater first receives preliminary treatment
in a septic tank or aerobic unit. The effluent is then
periodically applied to a bed of granular material.
During its passage through the filter, the
wastewater is treated further by biological and
physical processes. Sand is the common choice as
filter media because of its tow cost and availability.

C. Recirculating ISF
Figure 2 Three Types of ISFs

Three types of ISFs are illustrated in Figure 2 and
described as follows:

Buried: Pretreated wastewater is distributed through
a network of pipes laid above the filter. Perforated
piping beneath the filter collects and conveys the
effluent for surface disposal. Buried ISFs are best
suited for single-family residences and small
commercial establishments.

Open: Wastewater from either aerobic treatment or
a septic tank is applied to the filter surface by a
distribution pipe. A buried concrete box structure is
often used to contain the filter media and can be
operated with or without a cover depending on the
climate. When septic tank treatment precedes an
open ISF, two independent filters may be required
to allow for recovery periods. Open filters,
sometimes referred to as “free access” ISFs, can
handle larger wastewater volumes than buried ISFs
and can also be used as small community, cluster,
and commercial systems.



Intermittent Sand Filtratia

Introduction

A goal of wastewater treatment processes is to
produce an environmentally acceptable effluent at
the lowest possible cost. The task of choosing a
process which fulfills this goal can be challenging
when the volume of wastewater is small. For
example, treatment of wastewater from a sparsely
populated community at a central facility may be
inappropriate due to the high cost of construction,
operation, and maintenance of long sewer lines,
numerous manholes, and lift-stations. Where only
small wastewater volumes are generated, on-site
treatment is a possible cost-effective solution. One
such system - capable of effective treatment of
wastewater from residences and small commercial
establishments at a reasonable cost - is the
Intermittent Sand Filter (ISF).

This brochure discusses the technology of the ISF
system and addresses design, performance,
operation and maintenance, and cost aspects of the
process.

In an ISF system, the effluent from a septic tank or
an aerobic unit receives additional treatment

* through periodic application to a filter. ISFs can be
used to upgrade: existing wastewater facilities such
as lagoons or replace failed soil absorption systems
(SAS). The ISF system can also be a low cost
alternative when site, soil, or other conditions
restrict the use of SASs.

Technology

The ISF relies primarily on biological and physical
processes to remove wastewater contaminants.
The effluent can then be discharged in an

environmentally sound manner. A simplified flow
schematic of the ISF process is shown in Figure 1.

Septic Tank or
Wastewater Aerobic Unit
Filter Media

Effiuent Disposal

Figure 1 ISF Process Flow Schematic



with 24 to 36 inches of media so that a “clogged”
top layer can be removed several times before total
bed replacement is necessary.

Compliance with local health regulations may
necessitate disinfection of the filter effluent prior to
discharge to surface water. Local codes may
stipulate the distance that an ISF must be
separated from potable water supplies (usually 100
feet).

Performance

Under normal operating conditions, ISFs will
produce high quality effluents with respect to BOD;
and suspended solids. The BODs concentration of
an ISF effluent is generally less than 10

except during filter startup and maturation. The
mean concentration of suspended solids in ISF
effluents is usually less than 15 mg/l. A

properly functioning ISF will have an organic mat
on the filter surface where microorganisms “treat”
the organics in the wastewater. As the age and
density of the mat increases, treatment improves
due to greater retention time. However, too thick a
mat results in filter clogging.

An ISF having clean sand can remove up to 50%
of a waste stream’s phosphorus. Phosphorus
removal by a mature fitter is low, and additional
treatment processes are necessary if discharge
permits require reduced phosphorus concentrations.
Removal of nitrogen is dependent on wastewater
type, filter loading rates, ambient temperature, and
other meteorological conditions.

ISFs can also significantly reduce the
concentrations of wastewater fecal and total
coliforms and fecal streptococci bacteria. ISF
performance will be a direct result of the system's
design, operation, and maintenance.

Operation and Maintenance

A properly designed ISF will require a minimum of
time spent on operation and maintenance (O & M).
Table 2 presents the major requirements and
suggested scheduling of O & M activities to obtain
optimum treatment efficiency. O & M requirements
for ISFs are not overly complicated, and many can