| (2) All plant piping shall be constructed so as to
be thoroughly tight against leakage. No cross-connection or interconnection
shall be permitted to exist in a filtration plant between a conduit
carrying filtered or post-chlorinated water and another conduit carrying
raw water or water in any prior stage of treatment.
(A) Vacuum breakers must be provided on each hose bibb
within the plant facility.
(B) No conduit or basin containing raw water or any
water in a prior stage of treatment shall be located directly above,
or be permitted to have a single common partition wall with another
conduit or basin containing finished water.
(C) Make-up water supply lines to chemical feeder solution
mixing chambers shall be provided with an air gap or other acceptable
backflow prevention device.
(D) Filters shall be located so that common walls will
not exist between them and aerators, mixing and sedimentation basins
or clearwells. This rule is not strictly applicable, however, to partitions
open to view and readily accessible for inspection and repair.
(E) Filter-to-waste connections, if included, shall
be provided with an air gap connection to waste.
(F) Air release devices on treated waterlines shall
be installed in such a manner as to preclude the possibility of submergence
or possible entrance of contaminants. In this respect, all openings
to the atmosphere shall be covered with 16-mesh or finer corrosion-resistant
screening material or an equivalent acceptable to the executive director.
(3) Return of the decanted water or solids to the treatment
process shall be adequately controlled so that there will be a minimum
of interference with the treatment process. Systems that do not comply
with the provisions of this paragraph commit a treatment technique
violation and must notify their customers in accordance with the requirements
of §290.122(b) of this title.
(A) Unless the executive director has approved an alternate
recycling location, spent backwash water and the liquids from sludge
settling lagoons, spent backwash water tanks, sludge thickeners, and
similar dewatering facilities shall be returned to the raw waterline
upstream of the raw water sample tap and coagulant feed point. The
blended recycled liquids shall pass through all of the major unit
processes at the plant.
(B) Recycle facilities shall be designed to minimize
the magnitude and impact of hydraulic surges that occur during the
recycling process.
(C) Solids produced by dewatering facilities such as
sludge lagoons, sludge thickeners, centrifuges, mechanical presses,
and similar devices shall not be returned to the treatment plant without
the prior approval of the executive director.
(4) Reservoirs for pretreatment or selective quality
control shall be provided where complete treatment facilities fail
to operate satisfactorily at times of maximum turbidities or other
abnormal raw water quality conditions exist. Recreational activities
at such reservoirs shall be prohibited.
(5) Flow-measuring devices shall be provided to measure
the raw water supplied to the plant, the recycled decant water, the
treated water used to backwash the filters, and the treated water
discharged from the plant. Additional metering devices shall be provided
as appropriate to monitor the flow rate through specific treatment
processes. Metering devices shall be located to facilitate use and
to assist in the determination of chemical dosages, the accumulation
of water production data, and the operation of plant facilities.
(6) Chemical storage facilities shall comply with applicable
requirements in subsection (f)(1) of this section.
(7) Chemical feed facilities shall comply with the
applicable requirements in subsection (f)(2) of this section.
(8) Flash mixing equipment shall be provided.
(A) Plants with a design capacity greater than 3.0
million gallons per day (MGD) must provide at least one hydraulic
mixing unit or at least two sets of mechanical flash mixing equipment
designed to operate in parallel. Public water systems with other surface
water treatment plants, interconnections with other systems, or wells
that can meet the system's average daily demand are exempt from the
requirement for redundant mechanical flash mixing equipment.
(B) Flash mixing equipment shall have sufficient flexibility
to ensure adequate dispersion and mixing of coagulants and other chemicals
under varying raw water characteristics and raw water flow rates.
(9) Flocculation equipment shall be provided.
(A) Plants with a design capacity greater than 3.0
MGD must provide at least two sets of flocculation equipment which
are designed to operate in parallel. Public water systems with other
surface water treatment plants, interconnections with other systems,
or wells that can meet the system's average daily demand are exempt
from the requirement for redundant flocculation equipment.
(B) Flocculation facilities shall be designed to provide
adequate time and mixing intensity to produce a settleable floc under
varying raw water characteristics and raw water flow rates.
(i) Flocculation facilities for straight-flow and up-flow
sedimentation basins shall provide a minimum theoretical detention
time of at least 20 minutes when operated at their design capacity.
Flocculation facilities constructed prior to October 1, 2000, are
exempt from this requirement if the settled water turbidity of each
sedimentation basin remains below 10.0 nephelometric turbidity units
and the treatment plant meets with turbidity requirements of §290.111
of this title.
(ii) The mixing intensity in multiple-stage flocculators
shall decrease as the coagulated water passes from one stage to the
next.
(C) Coagulated water or water from flocculators shall
flow to sedimentation basins in such a manner as to prevent destruction
of floc. Piping, flumes, and troughs shall be designed to provide
a flow velocity of 0.5 to 1.5 feet per second. Gates, ports, and valves
shall be designed at a maximum flow velocity of 4.0 feet per second
in the transfer of water between units.
(10) Clarification facilities shall be provided.
(A) Plants with a design capacity greater than 3.0
MGD must provide at least two sedimentation basins or clarification
units which are designed to operate in parallel. Public water systems
with other surface water treatment plants, interconnections with other
systems, or wells that can meet the system's average daily demand
are exempt from the requirement for redundant sedimentation basins
or clarification units.
(B) The inlet and outlet of clarification facilities
shall be designed to prevent short-circuiting of flow or the destruction
of floc.
(C) Clarification facilities shall be designed to remove
flocculated particles effectively.
(i) When operated at their design capacity, basins
for straight-flow or up-flow sedimentation of coagulated waters shall
provide either a theoretical detention time of at least six hours
in the flocculation and sedimentation chambers or a maximum surface
overflow rate of 0.6 gpm/sq ft of surface area in the sedimentation
chamber.
(ii) When operated at their design capacity, basins
for straight-flow or up-flow sedimentation of softened waters shall
provide either a theoretical detention time of at least 4.5 hours
in the flocculation and sedimentation chambers or a maximum surface
overflow rate of 1.0 gpm/sq ft of surface area in the sedimentation
chamber.
(iii) When operated at their design capacity, sludge-blanket
and solids-recirculation clarifiers shall provide either a theoretical
detention time of at least two hours in the flocculation and sedimentation
chambers or a maximum surface overflow rate of 1.0 gpm/sq ft in the
settling chamber.
(iv) A side wall water depth of at least 12 feet shall
be provided in clarification basins that are not equipped with mechanical
sludge removal facilities.
(v) The effective length of a straight-flow sedimentation
basin shall be at least twice its effective width.
(D) Clarification facilities shall be designed to prevent
the accumulation of settled solids.
(i) At treatment plants with a single clarification
basin, facilities shall be provided to drain the basin within six
hours. In the event that the plant site topography is such that gravity
draining cannot be realized, a permanently installed electric-powered
pump station shall be provided to dewater the basin. Public water
systems with other potable water sources that can meet the system's
average daily demand are exempt from this requirement.
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