Idaho Administrative Code
Title IDAPA 58 - Environmental Quality, Department of
Rule 58.01.08 - IDAHO RULES FOR PUBLIC DRINKING WATER SYSTEMS
Section 58.01.08.521 - FACILITY AND DESIGN STANDARDS: SURFACE WATER TREATMENT: FILTRATION USING RAPID RATE GRAVITY FILTERS
Universal Citation: ID Admin Code 58.01.08.521
Current through August 31, 2023
01. Pretreatment. The use of rapid rate gravity filters shall require pretreatment in the form of coagulation, flocculation, and sedimentation. (3-24-22)
02. Rate of Filtration. The filter rate must be proposed and justified by the design engineer to the satisfaction of the Department prior to the preparation of final plans and specifications. (3-24-22)
03. Number of Units. A minimum of two (2) units for redundancy shall be provided for filtration such that plant design capacity can be maintained with any component out of service for maintenance or repairs. Where declining rate filtration is provided, the variable aspect of filtration rates, and the number of filters must be considered when determining the design capacity for the filters. (3-24-22)
04. Structure and Hydraulics. The filter structure shall be designed to provide for: (3-24-22)
a. Vertical walls within the filter.
There shall be no protrusion of the filter walls into the filter media.
(3-24-22)
b. Cover by
superstructure with sufficient headroom to permit normal inspection and
operation. (3-24-22)
c. Minimum
depth of filter box of eight and one-half (8.5) feet. (3-24-22)
d. Minimum water depth over the surface of
the filter media of three (3) feet. (3-24-22)
e. Trapped effluent to prevent backflow of
air to the bottom of the filters. (3-24-22)
f. Prevention of floor drainage to the filter
with a minimum four (4) inch curb around the filters. (3-24-22)
g. Prevention of flooding by providing
overflow. (3-24-22)
h. Maximum
velocity of treated water entering the filters of two (2) feet per second.
(3-24-22)
i. Cleanouts and straight
alignment for influent pipes or conduits where solids loading is heavy, or
following lime-soda softening. (3-24-22)
j. Washwater drain capacity to carry maximum
flow. (3-24-22)
k. Walkways around
filters to be not less than twenty-four (24) inches wide and equipped with
safety handrails or walls. (3-24-22)
l. Construction so as to prevent cross
connections and common walls between potable water and non-potable fluids.
(3-24-22)
05. Washwater Troughs. Washwater troughs shall be constructed to have: (3-24-22)
a. The bottom elevation above the
maximum level of expanded media during washing. (3-24-22)
b. A two (2) inch freeboard at the maximum
rate of wash. (3-24-22)
c. The top
edge level and all at the same elevation. (3-24-22)
d. Spacing so that each trough serves the
same number of square feet of filter area. (3-24-22)
e. Maximum horizontal travel of suspended
particles to reach the trough not to exceed three (3) feet.
(3-24-22)
06. Filter Material. The media shall be clean silica sand or other natural or synthetic media free from detrimental chemical or bacterial contaminants, approved by the Department, and having the following characteristics: (3-24-22)
a. A total depth
of not less than twenty-four (24) inches and generally not more than thirty
(30) inches. (3-24-22)
b. An
effective size range of the smallest material no greater than forty-five
hundredths (0.45) of a millimeter to fifty-five hundredths (0.55) of a
millimeter. (3-24-22)
c. A
uniformity coefficient of the smallest material not greater than one and
sixty-five hundredths (1.65). (3-24-22)
d. A minimum of twelve (12) inches of media
with an effective size range no greater than forty-five hundredths (0.45) of a
millimeter to fifty-five hundredths (0.55) of a millimeter and a specific
gravity greater than other filtering materials within the filter.
(3-24-22)
e. Types of filter media
are as follows: (3-24-22)
i. Clean, crushed
anthracite or a combination of anthracite and other media may be considered on
the basis of experimental data specific to the project. The anthracite shall
have the following characteristics: (3-24-22)
(1) Effective size of forty-five hundredths
(0.45) of a millimeter to fifty-five hundredths (0.55) of a millimeter with
uniformity coefficient not greater than sixty-five hundredths (1.65) when used
alone. (3-24-22)
(2) Effective size
of eight tenths (0.8) of a millimeter to one and two-tenths (1.2) millimeters
with a uniformity coefficient not greater than one and eighty-five hundredths
(1.85) when used as a cap. (3-24-22)
(3) Effective size for anthracite used as a
single media on potable ground water for iron and manganese removal only shall
be a maximum of eight tenths (0.8) of a millimeter (effective sizes greater
than this may be approved based upon onsite pilot plant studies or other
demonstration acceptable to the Department). See Subsection
501.19 for general information
on conducting pilot studies. (3-24-22)
ii. Sand media shall have the following
characteristics: (3-24-22)
(1) Effective size
of forty-five hundredths (0.45) of a millimeter to fifty-five hundredths (0.55)
of a millimeter. (3-24-22)
(2)
Uniformity coefficient of not greater than one and sixty-five hundredths
(1.65). (3-24-22)
(3) Larger size
sand media may be allowed by the Department where full-scale tests have
demonstrated that treatment goals can be met under all conditions.
(3-24-22)
iii. Granular
activated carbon (GAC) as a single media may be considered for filtration only
after pilot or full-scale testing and with prior approval of the Department.
See Subsection 501.19 for
general information on conducting pilot studies. The design shall include the
following: (3-24-22)
(1) The media must meet
the basic specifications for filter media as given in Subsections
521.06.a. through d., except
that larger size media may be allowed where full scale tests have demonstrated
that treatment goals can be met under all conditions. (3-24-22)
(2) There must be a means for periodic
treatment of filter material for control of bacterial and other growth.
(3-24-22)
(3) Provisions must be
made for frequent replacement or regeneration. (3-24-22)
iv. Other media will be considered based on
experimental data and operating experience. (3-24-22)
v. A three (3) inch layer of torpedo sand
shall be used as a supporting media for filter sand where supporting gravel is
used, and shall have an effective size of eight-tenths (0.8) millimeters to two
(2.0) millimeters, and a uniformity coefficient not greater than one and
seven-tenths (1.7). (3-24-22)
vi.
Gravel, when used as the supporting media, shall consist of cleaned and washed,
hard, durable, rounded silica particles and shall not include flat or elongated
particles. The coarsest gravel shall be two and one-half (2.5) inches in size
when the gravel rests directly on a lateral system and must extend above the
top of the perforated laterals. Not less than four (4) layers of gravel shall
be provided in accordance with the size and depth distribution specified in the
table below. Reduction of gravel depths and other size gradations may be
considered upon justification to the reviewing authority for slow sand
filtration or when proprietary filter bottoms are specified.
|
Size of Gravel |
Depth |
|
2 ½ to 1 ½ inches |
5 to 8 inches |
|
1 ½ to % inches |
3 to 5 inches |
|
¾ to ½ inches |
3 to 5 inches |
|
½ to 3/16 inches |
2 to 3 inches |
|
3/16 to 3/32 inches |
2 to 3 inches |
(3-24-22)
07. Filter Bottoms and Strainer Systems. Departure from the standards set out in Subsection 521.07 may be acceptable for high rate filters and for proprietary bottoms. Porous plate bottoms shall not be used where iron or manganese may clog them or with waters softened by lime. The design of manifold-type collection systems shall: (3-24-22)
a. Minimize loss of head in the manifold and
laterals. (3-24-22)
b. Ensure even
distribution of wash water and even rate of filtration over the entire area of
the filter. (3-24-22)
c. Provide
the ratio of the area of the final openings of the strainer systems to the area
of the filter at about three-thousandths (0.003), (3-24-22)
d. Provide the total cross-sectional area of
the laterals at about twice the total area of the final openings.
(3-24-22)
e. Provide the
cross-sectional area of the manifold at one and one-half (1.5) to two (2) times
the total area of the laterals. (3-24-22)
f. Lateral perforations without strainers
shall be directed downward. (3-24-22)
08. Surface or Subsurface Wash. Surface or subsurface wash facilities are required except for filters used exclusively for iron or manganese removal, and may be accomplished by a system of fixed nozzles or a revolving-type apparatus. All devices shall be designed with: (3-24-22)
a. Provision for water
pressures of at least forty-five (45) pounds per square inch.
(3-24-22)
b. A properly installed
vacuum breaker or other approved device to prevent back siphonage if connected
to the treated water system. (3-24-22)
c. Rate of flow of two (2.0) gallons per
minute per square foot of filter area with fixed nozzles or one-half (0.5)
gallon per minute per square foot with revolving arms. (3-24-22)
d. Air wash can be considered based on
experimental data and operating experiences. (3-24-22)
09. Air Scouring. Air scouring can be considered in place of surface wash provided the following conditions are met: (3-24-22)
a. Air flow for air
scouring the filter must be three (3) to five (5) standard cubic feet per
minute square foot of filter area when the air is introduced in the underdrain;
a lower air rate must be used when the air scour distribution system is placed
above the underdrains. (3-24-22)
b.
A method for avoiding excessive loss of the filter media during backwashing
must be provided. (3-24-22)
c. Air
scouring must be followed by a fluidization wash sufficient to restratify the
media. (3-24-22)
d. Air must be
free from contamination. (3-24-22)
e. Air scour distribution systems shall be
placed below the media and supporting bed interface with the following
exception: if placed at the interface the air scour nozzles shall be designed
to prevent media from clogging the nozzles or entering the air distribution
system. (3-24-22)
f. Piping for the
air distribution system shall not be flexible hose which will collapse when not
under air pressure and shall not be a relatively soft material which may erode
at the orifice opening with the passage of air at high velocity.
(3-24-22)
g. Air delivery piping
shall not pass down through the filter media nor shall there be any arrangement
in the filter design which would allow short circuiting between the applied
unfiltered water and the filtered water. (3-24-22)
h. The backwash water delivery system must be
capable of fifteen (15) gallons per minute per square foot of filter surface
area (37 m/hr); however, when air scour is provided the backwash water rate
must be variable and should not exceed eight (8) gallons per minute per square
foot (20 m/hr) unless operating experience shows that a higher rate is
necessary to remove scoured particles from filter media surfaces.
(3-24-22)
i. The filter underdrains
shall be designed to accommodate air scour piping when the piping is installed
in the underdrain. (3-24-22)
10. Filter Appurtenances. The following shall be provided for every filter: (3-24-22)
a. Influent and effluent sampling taps.
(3-24-22)
b. A gauge capable of
indicating loss of head. (3-24-22)
c. A meter indicating rate-of flow. A
modified rate controller which limits the rate of filtration to a maximum rate
may be used. However, equipment that simply maintains a constant water level on
the filters is not acceptable, unless the rate of flow onto the filter is
properly controlled. A pump or a flow meter in each filter effluent line may be
used as the limiting device for the rate of filtration only if approved by the
Department on a site-specific basis. (3-24-22)
11. Backwash. Provisions shall be made for washing filters as follows: (3-24-22)
a. A minimum backwash rate such that a fifty
(50) percent expansion of the filter bed is achieved. (3-24-22)
b. Filtered water provided at the required
rate by wash water tanks, a wash water pump, from the high service main, or a
combination of these. (3-24-22)
c.
Wash water pumps in duplicate unless an alternate means of obtaining wash water
is available. (3-24-22)
d. Not less
than fifteen (15) minutes wash of one filter at the design rate of wash.
(3-24-22)
e. A wash water regulator
or valve on the main wash water line to obtain the desired rate of filter wash
with the wash water valves on the individual filters open wide.
(3-24-22)
f. A rate-of-flow
indicator, preferably with a totalizer, on the main wash water line, located so
that it can be easily read by the operator during the washing process.
(3-24-22)
g. Design to prevent
rapid changes in backwash water flow. Backwash shall be operator initiated.
Automated systems shall be operator adjustable. (3-24-22)
12. Roof Drainage. Roof drains shall not discharge into the filters or basins and conduits preceding the filters. (3-24-22)
Disclaimer: These regulations may not be the most recent version. Idaho may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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