Current through August 31, 2023
Treatment facilities designed to include clarification for
processing surface water shall meet the following requirements:
(3-24-22)
01.
Two Units
Required. A minimum of two (2) units for redundancy shall be provided
for flocculation and sedimentation such that plant design capacity can be
maintained with any component out of service for maintenance or repairs.
(3-24-22)
02.
Parallel or
Serial Operation. The units shall be capable of being operated either in
series or parallel where softening is performed. (3-24-22)
03.
Independent Units. The units
shall be constructed in such a way that each can be taken out of service
without disrupting operation, and with drains or pumps sized to allow
dewatering in a reasonable period of time. (3-24-22)
04.
Manual Start-Up. The units
shall be started manually following shutdown. (3-24-22)
05.
Pre-Treatment. Waters
exhibiting high turbidity may require pretreatment, usually sedimentation with
or without the addition of coagulation chemicals. When presedimentation is
provided, the following requirements must be met: (3-24-22)
a. Incoming water shall be dispersed across
the full width of the line of travel as quickly as possible. Short circuiting
must be prevented. (3-24-22)
b.
Provisions for bypassing pre-sedimentation basins shall be included.
(3-24-22)
c. The need for redundant
pretreatment components shall be evaluated according to the type and necessity
of the pretreatment. (3-24-22)
06.
Rapid Mix. Unless otherwise
approved by the Department based on documentation provided by the design
engineer, a rapid mix device or chamber is required prior to flocculation,
clarification, sedimentation, and settler units. The need for redundant rapid
mix components shall be evaluated. Rapid mix shall mean the rapid dispersion of
chemicals throughout the water to be treated, usually by violent agitation. The
engineer shall submit the design basis for the velocity gradient (G value)
selected, considering the chemicals to be added and water temperature, color
and other related water quality parameters. Basins or mixing chambers shall be
equipped with devices capable of providing adequate mixing for all treatment
flow rates. (3-24-22)
07.
Flocculation. Flocculation shall mean the gathering together of
fine particles in water by gentle mixing after the addition of coagulant
chemicals to form larger particles. (3-24-22)
a. Basin inlet and outlet design shall
minimize short-circuiting and destruction of floc. A drain, pumps, or a
combination of both drain and pumps shall be provided to accomplish dewatering
and sludge removal. (3-24-22)
b.
The flow-through velocity shall not be less than one-half (0.5) nor greater
than one and one-half (1.5) feet per minute with a detention time for floc
formation of at least thirty (30) minutes unless otherwise approved by the
Department. (3-24-22)
c. Agitators
shall be driven by variable speed drives. (3-24-22)
d. Flocculation and sedimentation basins
shall be as close together as possible. The velocity of flocculated water
through pipes or conduits to settling basins shall be not less than one-half
(0.5) nor greater than one and one-half (1.5) feet per second. Allowances must
be made to minimize turbulence at bends and changes in direction.
(3-24-22)
08.
Small
Systems May Use Baffling. Baffling may be used to provide for
flocculation in small plants upon approval by the Department.
(3-24-22)
09.
Sedimentation
Units. The following criteria apply to conventional sedimentation units:
(3-24-22)
a. A minimum of two (2) hours of
settling time shall be provided following flocculation unless adequate settling
in less time can be demonstrated. (3-24-22)
b. Inlets shall be designed to distribute the
water equally and at uniform velocities. (3-24-22)
c. Outlet weirs or submerged orifices shall
maintain velocities suitable for settling in the basin and minimize
short-circuiting. Outlet weirs shall be designed so that the rate of flow over
the outlet weirs or through the submerged orifices shall not exceed
twenty-thousand (20,000) gallons per day per foot of the outlet launder. The
entrance velocity through the submerged orifices shall not exceed one-half
(0.5) feet per second. (3-24-22)
d.
The velocity through settling basins shall not exceed one-half (0.5) feet per
minute. The basins must be designed to minimize short-circuiting. Fixed or
adjustable baffles must be provided as necessary to achieve the maximum
potential for clarification. (3-24-22)
e. When an overflow weir or pipe is provided
the overflow shall discharge by gravity with a free fall at a location where
the discharge will be noted. (3-24-22)
f. Adequate sludge collection equipment that
ensures proper basin coverage shall be provided and basins must be provided
with a means for dewatering. (3-24-22)
g. Flushing lines or hydrants shall be
provided and must be equipped with backflow prevention devices acceptable to
the Department. (3-24-22)
h. Sludge
removal design shall provide that sludge pipes are not less than three (3)
inches in diameter and arranged so as to facilitate cleaning. Entrance to
sludge withdrawal piping shall be designed to prevent clogging. Provision shall
be made for the operator to observe and sample sludge being withdrawn from the
unit. (3-24-22)
i. Sludge shall be
disposed of in accordance with applicable regulations, as set forth in Section
540. (3-24-22)
10.
Solids Contact Clarifiers.
Solids contact clarifiers are generally acceptable for combined softening and
clarification where water characteristics, especially temperature, do not
fluctuate rapidly, flow rates are uniform and operation is continuous. A
minimum of two (2) units are required for surface water treatment as required
in Subsection 520.01.
(3-24-22)
a. Chemicals shall be applied at
such points and by such means as to ensure satisfactory mixing of the chemicals
with the water. (3-24-22)
b. Unless
otherwise approved by the Department based on documentation provided by the
design engineer, a rapid mix device or chamber ahead of the solids contact
clarifier is required to assure proper mixing of the chemicals applied. Mixing
devices employed shall be constructed so as to provide good mixing of the raw
water with previously formed sludge particles and prevent deposition of solids
in the mixing zone. (3-24-22)
c.
Flocculation equipment shall be adjustable as to speed, pitch, or a combination
of speed and pitch and must provide for coagulation in a separate chamber or
baffled zone within the unit. (3-24-22)
d. Sludge removal design shall provide that
sludge pipes are not less than three (3) inches in diameter and arranged so as
to facilitate cleaning. Entrance to sludge withdrawal piping shall be designed
to prevent clogging. Provision shall be made for the operator to observe and
sample sludge being withdrawn from the unit. (3-24-22)
e. Blow-off outlets and drains must terminate
and discharge at places acceptable to the Department in regard to control of
potential cross connections. Cross connection control must be included for the
potable water lines used to backflush sludge lines. (3-24-22)
f. The detention time shall be established on
the basis of the raw water characteristics and other local conditions that
affect the operation of the unit. The Department may request data to support
decisions made with respect to detention times. The Department may alter
detention time requirements. (3-24-22)
g. Controls for sludge withdrawal which
minimize water losses shall be provided. (3-24-22)
h. Unless otherwise approved by the
Department based on documentation provided by the design engineer, weirs shall
be adjustable and at least equivalent in length to the perimeter of the tank.
Weir loading shall not exceed ten (10) gallons per minute per foot of weir
length for units used as clarifiers or twenty (20) gallons per minute per foot
of weir length for units used for softening. Where orifices are used, the
loading rates per foot of launder rates shall be equivalent to weir loadings.
Either shall produce uniform rising rates over the entire area of the tank.
(3-24-22)
i. Upflow rates shall not
exceed one (1) gallon per minute per square foot of area at the sludge
separation line for units used as clarifiers or one and three-quarters (1.75)
gallons per minute per foot of area at the slurry separation line for units
used as softeners. The Department may consider higher rates if supporting data
is provided. (3-24-22)
11.
Settler Units. Settler units
consisting of variously shaped tubes or plates installed in multiple layers and
at an angle to the flow may be used for sedimentation following flocculation.
(3-24-22)
a. Inlets and outlets shall be
designed to maintain velocities suitable for settling in the basin and to
minimize short-circuiting. Plate units shall be designed to minimize unequal
distribution across the units. (3-24-22)
b. Drain piping from the settler units must
be sized to facilitate a quick flush of the settler units and to prevent
flooding other portions of the plant. (3-24-22)
c. Although most units will be located within
a plant, outdoor installations must provide sufficient freeboard above the top
of settlers to prevent freezing in the units. (3-24-22)
d. Water shall be applied to tube settlers at
a maximum rate of two (2) gallons per minute per square foot of cross-sectional
area for tube settlers, unless higher rates are justified through pilot plant
or in-plant demonstration studies. See Subsection
501.19 for general information
on conducting pilot studies. (3-24-22)
e. Water shall be applied to plate settlers
at a maximum plate loading rate of one-half (0.5) gallons per minute per square
foot, based on eighty (80) percent of the projected horizontal plate area.
(3-24-22)
f. Flushing lines shall
be provided to facilitate maintenance and must be properly protected against
backflow or back siphonage. (3-24-22)
12.
High Rate Clarification.
High rate clarification processes may be approved upon demonstrating
satisfactory performance under on-site pilot plant conditions or documentation
of full scale plant operation with similar raw water quality conditions.
Reductions in detention times and/or increases in weir loading rates shall be
justified. See Subsection
501.19 for general information
on conducting pilot studies. Examples of such processes include dissolved air
flotation, ballasted flocculation, contact flocculation/clarification, and
helical upflow. (3-24-22)
